T.' >n,>n. ' J4- 
 
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 LIBI 
 
 1 UNIVERSITY 
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 LOAN STACK 
 
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ELEMENTS 
 
 OF 
 
 CHEMISTRY. 
 
 f contr HDttton. 
 
ELEMENTS OF CHEMISTRY, 
 
 THEORETICAL AND PRACTICAL, 
 
 INCLUDING 
 
 >. 
 
 THE MOST EECENT DISCOVERIES AND APPLICATIONS OF THE SCIENCE 
 TO MEDICINE AND PHARMACY, TO AGRICULTURE, 
 
 AND TO MANUFACTURES. 
 
 ILLUSTRATED BY 230 WOOD CUTS. 
 
 BY 
 
 SIR ROBERT KANE, MD., M.R.I.A. 
 
 PRESIDENT OF THE QUEEN'S COLLEGE, CORK; 
 
 DIRECTOR OP THB MUSEUM OP IRISH 1SDUSTRY, 
 
 MEMBER OF TBE SOCIETY OP PHARMACY 
 
 OP PARIS, ETC. ETC. ETC. 
 
 DUBLIN : 
 
 HODGES AND SMITH, GRAFTON-STREET, 
 
 Booksellers to tfje Jmi>crsftn. 
 
 LONDON : LONGMAN, BROWN, AND CO. 
 
 MDCCCXLIX. 
 
LOAN STACK 
 
 Goodwin, Son and Nethercott, Printers, 
 79, Marlborough-street. 
 
QD28 
 
 K25T 
 
 PREFACE 
 
 TO THE SECOND EDITION. 
 
 IN preparing for the press a Second Edition of the Elements of 
 Chemistry, I have endeavoured to render it deserving of a continuance 
 of the favour with which the first edition was received in Great Britain 
 and in America, as well as in this country. 
 
 For that purpose, the subject of every chapter has been carefully 
 reconsidered, and in many cases the matter almost entirely newly 
 written; so that the results of the numerous valuable researches in 
 organic and inorganic chemistry, and in chemical physics, which have 
 been added to science within the last few years, will be found intro- 
 duced in their proper places, with as much detail as was due to their 
 respective importance, or was consistent with the nature and objects of 
 an elementary work. I hope, therefore, to have succeeded in fairly 
 representing in the following pages the actual condition of the science. 
 
 a 
 
 87Q 
 
VI PREFACE. 
 
 As within the last few years the assistance afforded by chemical 
 knowledge in the prosecution of the most important branches of 
 industry, and especially of agriculture, has become much more popu- 
 larly recognized, I have made it specially my object, in preparing the 
 present edition, to refer to and describe therein, with suitable detail, all 
 the important applications of chemical science, by which, recent dis- 
 coveries have so remarkably enriched the various fields of industrial 
 and agricultural improvement. 
 
 I take this opportunity to express my acknowledgments to Professor 
 Draper of New York, for the exceeding care with which he prepared 
 for the press and edited the American edition of this work, the general 
 adoption of which, by the Chemical Students in the Colleges of the 
 United States, must be in great part attributed to his recommendation. 
 
PREFACE TO THE FIRST EDITION. 
 
 MY object in the following pages is to present to the student an 
 account of the general principles and facts of Chemistry, and of its 
 applications to pharmacy, to medicine, and to the useful arts. 
 
 In the arrangement of a work like the present, if the general 
 principles of the science are first described, it is impossible to avoid 
 the difficulty of introducing the names of many substances with whose 
 history the reader cannot be supposed conversant; and by entering 
 in the commencement on the description of individual substances, 
 reference to the principles of affinity and the laws of constitution is 
 continually necessary in order that the reactions of these bodies may 
 be understood. In both cases the student is liable to some embar- 
 rassment, but I believe it to be greater in the latter, and hence, I 
 have adopted the plan of fully describing all the general principles and 
 laws of chemical action, before entering on the description of the 
 chemical substances in detail. 
 
 Chemistry being itself but a department of natural philosophy, 
 
viii PREFACE. 
 
 although the most extensive in its objects and the most important in 
 its uses, it is connected so intimately with the other branches of 
 physics, that a knowledge of at least their general principles is neces- 
 sary for the proper understanding of the nature of chemical pheno- 
 mena. I have, consequently, embraced within the design of the 
 present work, a description of the physical properties of bodies, so 
 far as they serve to complete their chemical history, or influence their 
 chemical relations ; and thus, upon the one hand, supply characters by 
 which chemical substances may be recognized, and, upon the other, 
 modify the affinities by which the action of chemical substances upon 
 each other is determined. "With this two-fold object the chapters 
 on cohesion, light, heat, and electricity have been drawn up. 
 
 The portion of the work which treats of the general laws of chemical 
 combination, is followed by an account of the mode of preparation 
 and properties of all inorganic substances of interest to science, to 
 medicine, or to the arts. But, in this part, I will pass over very 
 briefly the history of numerous bodies which from their rarity are 
 objects only of scientific curiosity, referring those who would wish to 
 study their history more closely to the extended works of Thompson, 
 of Graham, of Dumas of Gmelin, of Liebig, or Berzelius. 
 
 In the department of organic chemistry my object will be fully to 
 discuss the history of all such bodies as are of importance, from their 
 bearing upon general principles or existing theories, from their use in 
 
PREFACE. ix 
 
 medicine or pharmacy, their employments in the arts or in ordinary 
 life. The numerous series of bodies which are every day discovered in 
 organic chemistry, but which do not come under any of the above 
 heads, shall be dismissed with only a notice of their existence. 
 
 The relations of chemical action to the functions of organized 
 matter, the application of chemistry to physiology and to pathology, 
 will be treated so far as our accurate knowledge extends, and, finally, 
 a succinct description of the mode of analysis of organic and inor- 
 ganic bodies will be given. 
 
 As this work is not intended to be a complete system of chemistry, 
 nor to satisfy the wants of those who wish to make chemistry their 
 special study, I have in almost all cases avoided references or quota- 
 tions, which would needlessly occupy much space ; for, in the larger 
 works already mentioned, the original authorities on all subjects will 
 be found. 
 
 The object of a work, like the present, being to represent faithfully 
 the general aspect and extent of science at the time of publication, 
 its details must be in great part founded on the results of others. 
 Hence, originality cannot in any great degree be either expected or 
 desired ; but I have not hesitated in many instances, where the best 
 consideration I could give the subject induced me to dissent from 
 views generally held, to make this work the vehicle, in a popular 
 form, of such suggestions as I thought deserved to be adopted. 
 
PREFACE. 
 
 The processes given for the preparation of the various substances 
 described, are, with very few exceptions, those followed either in my 
 private laboratory, or in the manufacturing laboratory of the Apothe- 
 caries' Hall of Ireland; and the apparatus figured in the wood-cuts 
 are generally similar to those which I employ in experiments of 
 research or at lecture. 
 
CONTENTS. 
 
 OBJECTS, UTILITY AND ORIGIN OF CHEMISTRY 
 
 PAGK. 
 1 
 
 CHAPTER I. 
 
 OF GRAVITY AND COHESIVE FORCES, AS CHARACTERIZING CHEMICAL 
 
 SUBSTANCES . . . .4 
 
 Determination of Specific Gravities 1 1 | Principles of Crystallography . 22 
 
 CHAPTER H. 
 
 OF THE PROPERTIES OF LIGHT, AS CHARACTERIZING CHEMICAL 
 
 SUBSTANCES 
 
 Nature of Light . 
 Polarization of Light . 
 
 39 I Magnetic Relations of Light 
 42 I 
 
 34 
 
 47 
 
 CHAPTER III. 
 
 OF HEAT, CONSIDERED AS CHARACTERIZING CHEMICAL SUBSTANCES 
 
 SECTION i. Elasticity of Vapours . 
 
 Latent Heats of Vapours 
 
 Expansion of Bodies by Heat 
 Instruments for Measuring Heat 
 Expansion of Liquids and Solids 
 
 SECTION II. 
 
 Of Specific Heat 
 
 Molecular Laws of Specific Heat 
 
 SECTION III. 
 
 Of Liquefaction 
 Theory of Latent Heat 
 
 SECTION IV. 
 
 j>4 OfHygrometry 
 73 
 
 80 
 84 
 
 91 
 
 SECTION V. 
 
 Of the Transmission of Heat 
 
 through Bodies 
 Conduction of Heat 
 Of Radiant Heat 
 Phenomena of Transcalescence 
 Relations of Heat to Light 
 
 SECTION VI. 
 
 Of Vaporization 
 
 Of the Cooling of Bodies , 
 96 ' Central Heat of the Earth 
 
 53 
 
 101 
 108 
 113 
 
 116 
 118 
 121 
 126 
 131 
 
 133 
 136 
 
Xll 
 
 CONTENTS. 
 
 CHAPTER IV. 
 
 OF ELECTRICITY CONSIDERED 
 SECTION I. 
 
 Of Statical Electricity 
 Laws of Electrical Attractions . 
 Electrical Machines 
 Electrical Induction 
 Electricity of Effluent Steam 
 
 SECTION II. 
 
 Of Dynamical Electricity . 
 
 AS CHARACTERIZING CHEMICAL . SUB- 
 STANCES 
 
 139 
 145 
 
 150 
 158 
 162 
 
 163 
 
 . 137 
 
 Simple Galvanic Batteries . 167 
 
 Complex Galvanic Batteries . 1 75 
 
 Thermo-electricity . . 182 
 Of Magnetism . . .185 
 
 Electro-magnetic Phenomena . 188 
 
 Construction of the Galvanometer 191 
 
 Phenomena of Diamagnetism . 192 
 
 CHAPTER V. 
 
 OF CHEMICAL NOMENCLATURE 
 
 Symbolical Nomenclature .... 
 
 194 
 203 
 
 CHAPTER VI. 
 
 OF CHEMICAL AFFINITY, 
 
 AND ITS RELATIONS TO 
 AND TO COHESION 
 
 SECTION I. 
 
 General Nature and Results of 
 
 Chemical Affinity . . 205 
 
 Nature of Double Decomposition 208 
 
 SECTION II. 
 
 Relation of the Molecular Forces to 
 
 Chemical Affinity . . 214 
 
 Influence of Cohesion . . 215 
 
 Influence of Elasticity . 218 
 
 HEAT, TO LIGHT, 
 
 SECTION III. 
 
 On the Influence of Light on Che- 
 mical Affinity . , 
 Chemical Rays of Light 
 Photography and Daguerreotype . 
 
 SECTION IV. 
 
 Of Catalysis or Action by Contact 
 
 Independent of Affinity 
 Theory of Catalytic Phenomena . 
 
 204 
 
 223 
 224 
 226 
 
 229 
 232 
 
 CHAPTER VII. 
 
 OF LIGHT AND HEAT DISENGAGED DURING CHEMICAL COMBINATION 
 
 Constitution of Flame . . 239 Theories of Combustion 
 
 Thermochemical Laws 
 
 245 
 
 235 
 
 249 
 
 CHAPTER VIII. 
 
 OF THE INFLUENCE OF ELECTRICITY ON CHEMICAL AFFINITY . 252 
 
 Electro-chemical Theories . . 256 I Relation of Electricity to Affinity' 270 
 
 Laws of Electrolysis . 263 
 
 CHAPTER IX. 
 
 OF THE LAWS OF COMBINATION 
 
 Of Chemical Equivalents . . 277 I Theory of Volumes 
 
 Law of Multiple Proportions . 280 
 
 274 
 
 289 
 
CONTENTS. 
 
 Xlll 
 
 CHAPTER X. 
 
 OF THE RELATIONS OF CHEMICAL CONSTITUTION TO THE MOLECULAR 
 
 STRUCTURE OF BODIES 
 SECTION I. 
 
 Of the Atomic Theory and the 
 
 Doctrine of Atomic Volume 
 Atomic Constitution of Matter 
 
 Table of Dimorphous Bodies . 
 Allotropic Conditions of Bodies 
 
 294 
 
 299 
 
 SECTION III. 
 
 SECTION II. 
 
 Of Isomorphism and Dimorphism 305 i Organic Tvpes 
 Isomorphous Groups . . 309 
 
 Of Isomerism and the Intimate 
 ! Structure of Chemical Groups 
 Theory of Compound Radicals and 
 
 293 
 
 315 
 
 318 
 
 319 
 325 
 
 CHAPTER XI. 
 
 ON THE CLASSIFICATION OF THE ELEMENTARY BODIES 
 
 . 327 
 
 CHAPTER XII. 
 
 OF THE SIMPLE NON-METALLIC BODIES AND OF THEIR COMPOUNDS WITH 
 
 EACH OTHER. 
 
 1. Of Oxygen. Its Preparation 331 
 
 2. Of Hydrogen. Its Preparation 338 
 Oxyhydrogen Blow Pipe . 344 
 Of Water. Oxide of Hydrogen 347 
 Various Functions of Water . 352 
 Of Oxygenated Water . 355 
 
 3. Of Nitrogen. Its Preparation. 357 
 Of the Atmospheric Air . 360 
 Analysis of Air . . 363 
 Pressure of the Air. Baro- 
 meter ... 368 
 
 Nitrous Oxide . . .373 
 
 Nitric Oxide . . 375 
 
 Hyponitrous Acid . . 377 
 
 Nitrous Acid . . x 378 
 
 Nitric Acid. Aquafortis . 379 
 
 4. Of Sulphur . . 386 
 Sulphurous Acid . . 390 
 Sulphuric Acid . 392 
 Manufacture of Oil of Vitriol. 395 
 Hyposulphurous Acid . 399 
 Group of Thionic Acids . 400 
 Constitution of the Compounds 
 
 of Sulphur and Oxygen . 402 
 
 Of Sulphuretted Hydrogen 404 
 
 Bisulphuretted Hydrogen . 406 
 
 5. Of Selenium and its Com- 
 
 pounds with Oxygen, Hydro- 
 gen, &c. . . . 407 
 
 6. Of Phosphorus . . 408 
 Oxide of Phosphorus. Hypo- 
 phosphorous Acid . .410 
 
 Phosphorous Acid . 411 
 Phosphoric Acid . .412 
 
 Phosphurets of Hydrogen . 415 
 
 7. Of Chlorine. Its Preparation 
 
 and Properties . . 418 
 
 Hypochlorous Acid . . 422 
 
 Chloric Acid. Chlorous Acids 423 
 Perchlorous and Perchloric 
 
 Acids ... 425 
 Chlorosochloric and Chloroso- 
 
 perchloric Acids . . 426 
 
 Chloride of Hydrogen . 427 
 
 Manufacture of Muriatic Acid 430 
 
 Nitro-muriatic Acid . 432 
 Chlorides of Sulphur and Phos- 
 phorus . . .433 
 
 8. Iodine. Its Preparation . 434 
 lodous Acid. lodic Acid . 437 
 Periodic Acid . . 438 
 Hydriodic Acid . . 439 
 lodo-phosphuret of Hydrogen 441 
 
 9. Of Bromine . . .442 
 Bromic Acid and Hydrobro- 
 
 mic Acid . . . 443 
 
 Other Compounds of Bromine 444 
 
 10. Of Fluorine . . 445 
 Hydrofluoric Acid . . 446 
 
 11. Of Silicon ... 447 
 Constitution of Silicic Acid . 449 
 Chloride of Silicon . 451 
 Fluoride of Silicon. Hydro - 
 
 fluosilicic Acid . . 452 
 
 12. Of Boron . . ,. . 454 
 Boracic Acid . . . 455 
 C hloride and Fluoride of Boron 456 
 
 13. Carbon referred to Organic 
 
 Chemistry . 457 
 
XIV 
 
 CONTENTS. 
 
 CHAPTER XIII. 
 
 OF THE GENERAL CHARACTERS OF THE METALS, AND OF THEIR COM- 
 POUNDS WITH THE NON-METALLIC BODIES 
 
 PAGE. 
 
 Classification of the Metals . 460 
 
 Separation of the Metals by their 
 
 Sulphurets . . .463 
 
 Metallurgy . . . 466 
 
 Electro-metallurgy . . 470 
 
 Of the Individual Metals, and of 
 their Compounds with the Non- 
 metallic Bodies . . 471 
 
 SECTION I. 
 
 Of Potassium . . .472 
 
 Oxides and Sulphurets . 475 
 
 Of Sodium and Soda . . 477 
 
 Of Lithium . . . 479 
 
 Of Barium and Barytes . . 480 
 
 Of Strontium and Strontia . 482 
 
 Of Calcium and Lime . . 483 
 
 Of Magnesium and Magnesia . 487 
 
 SECTION II. 
 
 Of Aluminum and Alumina . 489 
 
 Of Glucinum . . . 491 
 
 Of Yttrium, Terbium, Erbium, 
 
 Thorium and Zirconium . 492 
 
 Of Cerium, Lantanum and Didy- 
 
 mium . . . 493 
 
 Of Manganese and its Oxides . 494 
 
 Valuation of Oxide of Manganese 498 ! 
 
 Manganic and Permanganic Acids 500 
 
 SECTION III. 
 
 Of Iron . . .502 
 
 Commercial Varieties of Iron . 504 
 
 Oxides of Iron. Ferric Acid . 508 
 
 Sulphurets of Iron . . 510 
 
 Of Nickel and its Oxides . .512 
 
 Of Cobalt and its Oxides . 514 
 
 Of Zinc and its Oxides, &c. .516 
 
 Of Cadmium . . .518 
 
 Of Tin and its Oxides . .519 
 
 Sulphurets of Tin . . 522 
 
 457 
 
 523 
 525 
 526 
 
 Of Chrome and its Oxides 
 Chromic and Per-chromic Acids 
 Of Vanadium 
 
 SECTION IV. 
 
 Of Tungsten . . .527 
 
 Of Molybdenum. Its Oxides, &c. 528 
 
 Of Osmium. Its Oxides, &c. . 528 
 Of Tantalum, Niobium, Pelo- 
 
 pium and Ilrnenium . . 529 
 
 Of Titanium. Its Oxides, &c. . 531 
 
 Of Arsenic and its Oxides . 532 
 
 Arseniuret of Hydrogen . 535 
 
 Sulphurets of Arsenic . . 536 
 
 Modes of Detecting Arsenic . 538 
 
 Of Antimony and its Oxides . 543 
 
 Sulphurets of Antimony . 545 
 
 Antimoniuret of Hydrogen . 547 
 
 Of Tellurium and its Compounds 549 
 
 Of Uranium and Uranyle . . 550 
 
 SECTION v. 
 
 Of Copper .... 552 
 Oxides of Copper . . 554 
 
 Sulphurets of Copper . . 556 
 
 Of Lead . , .557 
 
 Oxides of Lead . . .558 
 
 Sulphurets of Lead . . 560 
 
 Of Bismuth and its Compounds . 561 
 
 SECTION VI. 
 
 Of Silver . . .564 
 Its Oxides and Sulphuret . . 566 
 Of Mercury or Quicksilver . 567 
 Oxides of Mercury . . 569 
 Sulphurets of Mercury . 570 
 Of Gold. Its Oxides, &c. . 571 
 Of Palladium . . .574 
 Of Platinum . . .575 
 Of Iridium, Rhodium and Ruthe- 
 nium . . . 577 
 
 CHAPTER XIV. 
 
 OF THE GENERAL PROPERTIES AND CONSTITUTION OF SALTS . 580 
 
 Constitution of Acids and Salts . 587 | Atomic Volumes of Salts .$( 593 
 
CONTENTS. 
 
 CHAPTER XV. 
 
 SPECIAL HISTORY OF THE MORE IMPORTANT SALTS OF THE 
 INORGANIC ACIDS AND BASES . 
 
 PAGE. 
 
 Salts of Potassium . 595 
 
 Iodide of Potassium. Chloride 
 
 and Bromide of Potassium . 596 
 
 Sulphate, Nitrate, Chlorate, lo- 
 date, &c., of Potash. Manufac- 
 ture of Gunpowder ; . 598 
 Valuation of Saltpetre 
 Salts of Sodium 
 
 Chloride of Sodium. Sulphate 
 and Phosphate of Soda. Ni- 
 trate, Hyposulphite, &c. . 603 
 Salts of Barium . '.-" 
 Chloride, Sulphate, Nitrate, &c. . 607 
 Salts of Strontium . . 608 
 Salts of Calcium . 
 Chloride, Sulphate, Nitrate, Phos- 
 phate. Manufacture of Chloride 
 of Lime . . .611 
 Processes of Chlorometry . 613 
 Salts of Magnesium. Epsom Salts 614 
 Salts of Aluminum. Manufac- 
 ture of Alum . . . 615 
 Constitution of Glass and Porce- 
 lain . 618 
 Manufacture of Glass . . 620 
 Manufacture of Earthenware . 624 
 Salts of Manganese . . 626 
 Salts of Iron. Chlorides and 
 
 Iodides . . 627 
 
 . 594 
 
 PAGE. 
 
 Sulphates of Iron. Copperas, 
 
 Nitrates, Phosphates, &c. . 629 
 
 Salts of Nickel and Cobalt . 631 
 
 Salts of Zinc and Cadmium . 632 
 
 Salts of Tin V V" 633 
 Salts of Chromium . .635 
 Manufacture of Chromate of 
 
 Potash . . . 637 
 Salts of Vanadium, Tungsten, 
 
 Molybdenum, Osmium and Co- 
 
 lumbium . . . 638 
 
 Salts of Arsenic . . 639 
 
 Salts of Antimony . . 641 
 Salts of Titanium, Tellurium and 
 
 Uranium . . . 643 
 Salts of Copper . . .644 
 
 Salts of Lead . . 646 
 Salts of Bismuth . . .648 
 
 Salts of Silver . . 649 
 Salts of Mercury . 
 
 Corrosive Sublimate and Calomel 651 
 
 Bromides and Iodides of Mercury 653 
 Sulphates, Nitrates and Chromates 
 
 of Mercury . . 655 
 Salts of Gold . . .656 
 
 Salts of Palladium . . 657 
 
 Salts of Platinum . . 658 
 Salts of Iridium. Rhodium and 
 
 Ruthenium . 659 
 
 CHAPTER XVI. 
 
 ON THE GENERAL PRINCIPLES OF THE CONSTITUTION OF ORGANIC 
 
 BODIES . . 660 
 
 Theory of the Compound Radicals 664 | Theory of Chemical Types . 668 
 
 CHAPTER XVII. 
 
 OF CARBON, AND ITS COMPOUNDS WITH OXYGEN, SULPHUR AND 
 
 CHLORINE 
 
 Forms of Carbon. Its Properties 673 
 General Principles of Organic 
 
 Analysis . .- . ,- . 678 
 
 Determination of Nitrogen . 683 
 Of Carbonic Acid . . .686 
 
 Carbonates of Potash and Soda 688 
 
 Manufacture of Soda-ash . . 690 
 
 Methods of Alcalimetry . 692 
 Carbonates of Magnesia, Lime, Ba- 
 rytes, Manganese, Iron, Zinc, 
 
 Lead, &c. 694 
 
 Carbonic Oxide 
 ! Oxalic Acid. Its Preparation 
 
 Oxalates of Potash, Soda, Lime, &c. 
 
 Compound of Carbonic Oxide and 
 Potassium, Rhodizonic Acid, 
 Croconic Acid, Mellitic Acid, 
 Paraban, EuchroicAcid 
 
 Of Sulphuret of Carbon . 
 
 Chlorides of Carbon 
 
 671 
 
 697 
 698 
 700 
 
 702 
 703 
 
 705 
 
XVI 
 
 CONTENTS. 
 
 CHAPTER XVIII. 
 
 OF THE COMPOUNDS OF NITROGEN AND HYDROGEN, AND THEIR 
 DERIVATIVES. 
 
 PAGE. 
 
 Of Ammonia . . . .706 
 
 Fulminating Compounds of Am- 
 monia . . . 710 
 Ammonia Chlorides of Sulphur and 
 
 Phosphorus . . .712 
 
 Ammonia Salts of Zinc and Copper 7 1 3 
 Ammonia Salts of Cobalt, Nickel 
 
 and Silver . . . 714 
 
 Ammonia Salts of Palladium . 715 
 Ammonia Chlorides of Mercury 716 
 
 Ammonia Sulphates and Nitrates 
 of Mercury . . 718 
 
 Ammonia Salts of Platinum . 719 
 
 Action of Ammonia on Anhydrous 
 Acids . . .721 
 
 Of the Common Ammoniacal Salts 722 
 
 Chloride, Iodide and Sulphuret of 
 Ammonium . . . 724 
 
 Sulphate, Nitrate, Phosphate, Car- 
 bonate and Oxalate of Ammonia 726 
 
 Oxamide and Oxamic Acid . 728 
 
 CHAPTER XIX. 
 
 OF CYANOGEN AND ITS COMPOUNDS, AND OF THE BODIES DERIVED 
 
 Of the Oxygen Compounds of Cya- 
 nogen 
 
 Of Cyanic Acid . .731 
 
 Of Urea and its Salts . 732 
 
 Of Fulminic Acid and the Ful- 
 minates of Silver and Mercury 734 
 Of Cyanuric Acid . . 736 
 
 Of Hydrocyanic Acid . 737 
 Modes of Valuing the Strength 
 
 of Prussic Acid 
 Chlorides and Iodides of Cya- 
 nogen 
 
 Of the Simple Metallic Cyanides 
 Cyanides of Potassium, Ba- 
 rium, &c. 
 
 FROM IT. . . . 729 
 
 I Cyanides of Mercury, Silver, 
 
 &c 742 
 
 Of the Complex Metallic Cyanides 
 Ferro-cyanide of Potassium, 
 
 &c. 743 
 
 Ferrid- Cyanides of Potassium, 
 
 &c 747 
 
 Platino- cyanides and Palladio- 
 
 cyanides . . 749 
 
 Cobalto-cyanides and Similar 
 
 Groups . . 750 
 
 Of Sulpho-cyanogen and the 
 
 Sulpho-cyanides . 751 
 
 Of Mellon and the Mellonides 752 
 Melam. Melamine. Ammeline 753 
 Glaucene. Ammelide , 754 
 
 739 
 740 
 
 741 
 
 CHAPTER XX. 
 
 OF STARCH, LIGNINE, GUM AND SUGAR, AND THE PRODUCTS OF THEIR 
 DECOMPOSITION. 
 
 Of Starch. Its Varieties, Inuline, N 
 
 Lichenine . . . 755 
 
 Of Lignine and Xyloidine 758 
 Gun Cotton. Its Nature and Mode 
 
 of Preparation . . . 759 
 
 Of the Different Varieties of Gum 760 
 
 Of Cane Sugar . . . 761 
 
 Sacchulmine. Saccharic Acid. 
 
 Caramel . . . .763 
 
 Of Grape Sugar. Glucose . 764 
 Of Starch and Dextrine Sugar . 765 
 Sugar of Milk. Glucic and Melas- 
 
 sic Acids . . . 766 
 
 Of Mucic Acid. Of Glycerrhizine. 
 
 Mannite and Fungus Sugar 767 
 Of the Lactic and Mucous Fermen- 
 tations. Of Lactic Acid and its 
 Salts .... 768 
 
CONTENTS. 
 
 XV11 
 
 CHAPTER XXI. 
 
 OF THE ALCOHOLIC AND ACETIC FERMENTATIONS. OF ALCOHOL, 
 ETHERS, ALDEHYD, ACETIC ACID, &C. . .* 
 
 Of Gluten, Albumen and Legumine, 
 and the Nature of the Alcoholic 
 Fermentation . . - 771 
 
 Vinic Alcohol, Rectified and Proof 
 
 Spirits . V .: 774 
 
 Preparation of Sulphuric Ether . 776 
 Theory of the Constitution of Ether 780 
 Of Sulphovinic Acid Ethionic and 
 Methionic Acids ; Althionic and 
 Isethionic Acids; Heavy and 
 Light Oils of Wine . . 782 
 
 Pbosphovinic and Arseniovinic 
 
 Acids . . .784 
 
 Muriatic, Hydrosulphuric, Nitrous, 
 Nitric, Hydrocyanic and other 
 Ethers . . . 7S6 
 
 Carbonic and Oxalic Ethers. Oxa- 
 
 methan . . . .788 
 
 OfOlefiantGas . . 790 
 
 Of Aldehyd; Its Preparation . 794 
 Aldehydic Acid ; Trigenic Acid 796 
 
 . 770 
 
 Of the Acetous Fermentation . 797 
 Of Acetic Acid, Of Vinegar . 798 
 Of the Acetates of Potash, Soda, 
 Lime, Iron, Copper, Mercury, 
 Lead, Silver, Ether, Ammonia, 
 
 &c 801 
 
 Of Acetone ; Mesitylene and the 
 
 Derived Bodies . . 805 
 
 Bodies of the Kacodyl Series ; Al- 
 karsin ; Alkargene ; Kacodylic 
 Acid . . . .806 
 
 Of Light Carburetted Hydrogen 807 
 Action of Chlorine on Alcohol; 
 
 Chloral and Chloro-acetic Acid 809 
 Series of Chlorine Ethers . 810 
 Of the Theoretic Constitution of 
 Alcohol, and of the Ethers de- 
 rived from it . .812 
 Secondary Products of the Alco- 
 holic Fermentation ; Oenanthic 
 Ether ; Corn Oil . . 814 
 Amylic Alcohol ; Valerianic Acid 815 
 
 CHAPTER XXII. 
 
 PRODUCTS OF THE DECOMPOSITION OF WOOD. 
 SECTION I. SECTION III. 
 
 Of the Slow Decomposition of 
 Wood ; Constitution of Ulmine 817 
 
 Formation and Composition of Turf 
 and Coal. . . 821 
 
 SECTION II. 
 
 Of Pyroxylic Spirit and its Deriva- 
 tives . . . 823 
 Methylic Ether and its Salts . 826 
 Ammonia Compounds of Methyl 829 
 Of Formic Acid and its Salts . 830 
 Of Chloroform and its Analogues 832 
 Products of the Distillation of Oil 
 
 and Resin . . - . 834 
 Of Wood Tar ; Kreasote and Simi- 
 lar Bodies . 835 
 
 Distillation of Coal ; Coal Gas 836 
 Of Napthaline ; Its Chlorine Com- 
 pounds . . . .837 
 Products of the Oxidation of Nap- 
 thaline . . . 839 
 Sulphuric Compounds of Naptha- 
 line . . , . 840 
 Anthracene; Chrysene, &c. . 841 
 Phenic or Benzid Series . . 842 
 Hydrate of Phenyl ; Carbolic 
 
 Acid ... 843 
 
 Picric and Oxypicric Acid . 844 
 
 Of Aniline ... 845 
 OfPiccoline, Leucoline . . 846 
 
 Distillation of Animal Bodies ; 
 Spirit of Hartshorn; Dippel's 
 Animal Oil. Petanine 847 
 
 CHAPTER XXHI. 
 
 OF THE ESSENTIAL OILS, CAMPHORS AND RESINS 
 
 Of Oils not pre-existing in the 
 Plant ; Oil of Bitter Almonds ; 
 Amygdaline ; Benzoic Acid ; 
 Compounds of Benzyl ; Stilbene 
 and its Derivatives . .851 
 
 Oil of Cinnamon and Cinnamic 
 Acid. Nature of the Balsams . 855 
 
 Oil of Cloves ; Eugenic Acid ; 
 Oil of Spirea ; Salicylic Acid . 857 
 
 . 848 
 Sulphur Essential Oils. Mustard 
 
 and Garlic . 859 
 Oils not forming Acids . .861 
 
 Isomeric Oils of Turpentine . 863 
 
 Of the Camphors of the Oils . 864 
 Of the Resins of Turpentine and 
 
 other Resins Y . . 866 
 
 Of Amber ; Succinic Acid. &c. 868 
 
 Caoutchouc ; Gutta Percha . 869 
 
XV111 
 
 CONTENTS. 
 
 CHAPTER XXIV. 
 
 Of Glycerine ; Acroleine ; Metace- 
 tonic Acid ; Acrylic Acid 
 
 Of Stearine and Stearic Acid . 
 
 Margarine and Margaric Acid 
 
 Oleine and Oleic Acid . 
 
 Sebacic ; Suberic ; Pelargonic ; 
 Adipic Acids, &c. . , 
 
 Elaidine ; Elaidic Acid 
 
 Action of Sulphuric Acid on Fats ; 
 Olein of the Drying Oils 
 
 PAGE. 
 
 THE SAPONIFIABLE OILS AND FATS . . 871 
 
 Cocoa-tallow and Palm Oil . 883 
 
 Of Nutmeg Butter . . 884 
 Of Common Butter, Butyric, Cap- 
 
 ric, Caproic and Vaccinic Acids 885 
 Of Fish Oils ; Castor Oil and Croton 
 
 Oil . -887 
 
 Manufacture of Soaps and Plasters 888 
 Of Spermaceti and Wax ; Cetylic 
 
 Acid and Ethal. Of Wax. 890 
 
 873 
 874 
 
 875 
 877 
 
 878 
 
 881 
 
 CHAPTER XXV. 
 
 OF THE ORGANIC ACIDS WHICH PRE-EXIST IN PLANTS. 
 
 Of Tartaric Acid; Tartrate of 
 Potash, Soda, Iron, Antimony, 
 Lime, &c. . . 892 
 
 Action of Heat on Tartaric Acid 896 
 Of Racemic Acid and its Salts . 898 
 Of Citric Acid and its Salts . 898 
 
 Aconitic, Itakonic and Citrakonic 
 
 Acids . . . .899 
 
 Of Malic Acid ; Its Salts ; the Ma- 
 leic and Fumaric Acids . 900 
 
 Of Meconic Acid ; Komenic Acid 902 
 
 Of Tannin or Tannic Acid . 903 
 
 Of Gallic Acid . . . 9U5 
 
 Pyrogallic and Ellagic Acids . 907 
 
 Of Catechine and Oxycatechine 908 
 Kinic Acid and Kinone . .911 
 Kinoic, Lactucic, Krameric, Ver- 
 
 dic, Chelidonic and other Acids 912 
 
 CHAPTER XXVI. 
 
 OF THE NEUTRAL ORGANIC SUBSTANCES. 
 
 Of Pectine and its Products . 914 
 
 Of Salicine and its Products . 916 
 
 Of Phloridzine and its Products . 917 
 
 Asparagine ; Aspartic Acid . 919 
 Caffeine or Theine ; Theobromine 920 
 
 Piperine; Anemonine . .921 
 
 Cetrarine ; Picrotoxine . 922 
 
 Columbine ; Cusparine ; Meconine 
 Elaterine; Esculine ; Populine 923 
 
 Quassine ; Santonine ; Saponine ; 
 Scillitine; Senegin; Smilacine, 
 &c. 925 
 
 Of Vegetable Extracts . 927 
 
 Aloetic, Chrysammic and Chryso- 
 lepicAcid . . .928 
 
 CHAPTER XXVII. 
 
 OF THE COLOURING MATTERS 
 
 Madder Colours ; Alcanna Red ; 
 Braziline ; Santaline ; Hema- 
 toxyline .... 930 
 
 Carthamine and Carmine ; Querci- 
 trine; Chrysorhamnine ; Luteoline; 
 Morin ; Orellin ; Curcumine 932 
 
 Of Indigo and Woad ; of the Sul- 
 phates of Indigo . . 934 
 
 Anilic Acid; Anthranilic Acid, 
 &c 937 
 
 Action of Chlorine on Indigo . 938 
 
 Of Indian Yellow and Purreic 
 Acid . 039 
 
 . 929 
 
 Of the Colouring Matters derived 
 from the Lichens ; Orcine and 
 Orceine . . . 940 
 
 Lecanoric and Erythric Acids . 941 
 Amarythrine ; Orsellic Acid ; Ro- 
 cellic Acid ; Evernesic Acid ; 
 Pseudorcine . . . 942 
 
 Nature of Archil and Litmus . 944 
 
 Erythrolein; Ery throlitmine ; Azo- 
 
 litmine .... 945 
 Colours of Leaves and Flowers . 946 
 General Nature of Colouring Mat- 
 ters, and of the Processes of 
 Dyeing and Bleaching . . 947 
 
CONTENTS. 
 
 xix 
 
 CHAPTER XXVIII. 
 
 OF THE VEGETABLE ALCALOIDS. 
 
 PAGB. 
 
 Of Quinine and its Salts . . 950 
 
 Cinchonine and Aricine . 952 
 
 Of Morphia and its Salts . . 9J3 
 Narcotine ; Narcogenine ; Cotar- 
 
 nine . . . .956 
 
 Codeine ; Thebaine, &c. . 957 
 
 Strychnine and its Salts . . 958 
 
 Brucine ; Curarine . '." 960 
 
 Delphinine ; Veratrine . . 961 
 Jervin ; Sabadilline, Colchicine, 
 
 Emetine, Solanine i..'. 962 
 
 Chelerythrine ; Chelidonine ; Aco- 
 nitine . A.'-, ; ; -,-^ . 964 
 
 Atropine; Belladonnine . 965 
 
 I Daturine; Hyoscyamine; Coneine; 
 
 Nicotine . ; - . r, ^ / 966 
 
 i Menispermine ; Glaucin ; Harma- 
 
 line; Cissampeline ; Digitaline 968 
 
 ; Of the Artificial Production of Or- 
 ganic Alcalies, and of the Con- 
 stitution of the Vegetable Alca- 
 loids . . . 969 
 
 Of Furfurol and Furf urine . 975 
 
 CHAPTER XXIX. 
 
 OF THE CHEMICAL PHENOMENA OF VEGETATION 
 
 Assimilation of Carbon by Plants 980 
 
 Assimilation of Nitrogen . 984 
 
 Assimilation of Hydrogen . 986 
 
 Inorganic Constituents of Plants . 987 
 
 Constitution of Soils and Manures 
 Economy of Residues of Crops 
 Objects of Drainage of Soils . 
 
 977 
 
 989 
 992 
 
 CHAPTER 
 
 OF ANIMAL CHEMISTRY 
 
 996 
 
 SECTION I. 
 
 997 
 
 1000 
 1003 
 1005 
 1006 
 1007 
 1008 
 1009 
 
 Of the Animal Tissues ; Of Fibrine 
 Of Albumen 
 
 Of Protein ; its Real Nature . 
 Of Gelatine and Chondrine 
 Of Glycocoll, Leucine, &c. . 
 Composition of the Brain 
 Nature of the Juice of Flesh . 
 Kreatine, Kreatinine 
 Sarcosine ; Inosinic Acid 
 Of the Composition of the Tissues, 
 of the Skin and Epidermis, Hair, 
 
 &c 1009 
 
 Cellular and Serous Tissues . 1010 
 Muscular and Nervous Tissues . 1011 
 Composition of the Bones and Teeth 1012 
 
 SECTION II. 
 
 Of the Composition of the Blood, 
 the Biliary Secretion, the Bone 
 and Lymph. 
 
 Nature and Properties of Blood 1013 
 Composition of Healthy Blood . 1014 
 Of Globuline and Hematosine . 1015 
 Alterations of the Blood in Disease 1017 
 
 Composition of the Bile . 1019 
 
 Cholic, Choleic and Choloidic Acids 1020 
 Cholalic Acid and Dy sly sin . 1021 
 
 Of Taurine and Carbothialdine 1022 
 Nature of Chyle and Lymph . 1023 
 
 SECTION III. 
 
 Chemical Phenomena of the Processes 
 of Respiration and Digestion. 
 
 Phenomena of Respiration . 1024 
 
 Theory of Arterialization . 1026 
 Sources of Animal Heat . . 1027 
 
 Chemical Phenomena of Digestion 1028 
 Of Pepsine and Chyme . 1029 
 
 SECTION IV. 
 
 Of the Composition of the Urine in 
 Health and Disease. 
 
 Nature of Healthy Urine . . 1030 
 
 Of Urea and Uric Acid . 1031 
 
 Products of the Oxidation of Uric 
 Acid; Allantoine . . 1032 
 
XX 
 
 CONTENTS. 
 
 Alloxan; Alloxanic Acid; Myco- 
 
 melinic Acid ; Parabanic Acid 1033 
 Oxaluric Acid; Thionuric Acid; 
 
 Uramil; Alloxantine i } 1034 
 
 Dialuric Acid ; Murexid . . 1035 
 
 Of the Urine of Herbivorous Ani- 
 mals. Hippuric Acid and Gly- 
 cocoll . . . .1036 
 
 Of Guano and its Uses ; Guanine 1037 
 Of the Urine in Diseases . 1038 
 
 Urinary Calculi; Uric Acid and 
 
 Phosphatic Calculi . . 1040 
 
 Cystic and Xanthic Oxides, Mul- 
 berry and Fibrous Calculi . 1041 
 
 SECTION v. 
 
 PAGE. 
 
 Of Milk and other Animal Secre- 
 tions and Products, Natural 
 and Morbid. 
 
 Composition of Milk . ; ... .1041 
 
 Of Caseine, Leucine, Tyrosine 1042 
 Constitution of Eggs . . 1043 
 
 Liquor of the Amnios ; Tissues of 
 
 the Eye; Ear Wax . .1044 
 
 Gall Stones ; Ambergris ; Pus . 1045 
 
 SECTION VI. 
 
 Of the Preservation and Putrefac- 
 tion of Animal Matters. 
 Of the Putrefactive Fermentation 1046 
 Of Contagious and Infectious 
 Miasms . . .1048 
 
ELEMENTS OF CHEMISTRY. 
 
 THE science of chemistry has its origiii in the principle, that the 
 bodies which constitute the external world are composed of a number 
 of different elements, united according to certain laws. If we could 
 conceive an universe consisting only of iron, or quicksilver, or sulphur, 
 the objects of the astronomer might still remain as extensive and as 
 sublime as they are in the actual state of things ; for in tracing the 
 constitution of planetary and satellitic systems, or reducing to precise 
 laws the forces by which the motions of the heavenly bodies might be 
 produced, all the resources of his science should still be brought into 
 play. In like manner the physical sciences could attain perfection, for 
 the relations of these bodies to heat, to light, to electricity, the various 
 problems and laws of statical and dynamical forces, could have been 
 known, and thus all that is essential to the science of natural philoso- 
 phy might be attained. But not even an idea of chemistry could have 
 been formed. The duty of chemistry is to discover the constituent 
 elementary substances, which by uniting form the various compound 
 bodies which we observe ; to ascertain the nature of the forces by which 
 they unite, and the laws by which their union or separation may be 
 regulated ; to trace the effects of their mutual action, in the properties 
 of the new substances formed by their combination, and in the pheno- 
 mena, independent of composition, which accompany the exertion of 
 chemical force. 
 
 This object of chemistry has been at all periods fully recognized; 
 for the earliest philosophers, even before the science had received a 
 name, considered its objects as well defined in the arrangement of the 
 elements of fire, air, earth, and water. When the methods of che- 
 mistry, and the reasonings to which they led, acquired a more exact 
 form, these elements, which had been assumed from speculations in 
 1 
 
2 Objects, Utility, and 
 
 natural history and metaphysics, gave way to others, as sulphur, spirit, 
 salt, oil, and earth, equally incorrect, but still, those, which, in the 
 rough trials of the period, were obtained by the decomposition of com- 
 pound bodies. As more accurate ideas and better processes were ac- 
 quired, these elementary principles again changed their character, 
 until finally the philosophical idea of chemistry was clearly stated and 
 established by Lavoisier; 1st, that we study to resolve the various 
 compound bodies found in nature into others which resist our power, 
 and which we term undecompounded or simple substances; without 
 pretending that they are elements ; for the advance of science enables 
 us to decompose, in each generation, bodies which to our own prede- 
 cessors had appeared simple ; 2nd, that we study to effect the recom- 
 bination of those simple bodies, either in the same proportions, and 
 thus regenerate the natural compound bodies, or in new proportions, 
 and thus add to the catalogue of bodies which may exist in nature. 
 
 Of these two operations, the first, or a separation x>f a compound 
 body into the simple substances which constitute it, is termed analysis. 
 The second, or combination of two or more simple bodies to form a 
 compound substance, is called synthesis. All chemical processes are 
 conducted upon the principle of one or other of these two, and occa- 
 sionally they are both, successively or synchronously, accomplished. 
 
 The objects of chemistry cannot, however, be considered as limited 
 to the mere abstract study of the laws of elementary composition ; to 
 it also belongs the improvement of processes in the useful arts by the 
 more accurate knowledge of their theory which chemistry confers, and 
 the invention of new processes or of new arts, by the application or 
 discovery of substances previously neglected or unknown ; the allevia- 
 tion of disease, by new remedies which may be placed at the command 
 of the physician, or by more correct ideas of the origin and results of 
 morbid action, to which the attentive study of the chemical processes 
 of the great laboratory of the human frame may ultimately lead, ranks 
 also among the most important of its applications ; and although even 
 an abstract science, which reveals some of the most beautiful of 
 nature's laws, should deserve our best attention; yet it becomes in- 
 vested with more general interest, and commands more universal 
 homage when, as with chemistry, it appears to be the basis of those 
 practical arts, on which so much of health, of national prosperity, and 
 of civilization may depend. 
 
 The origin or derivation of the word chemistry is unknown. It first 
 appeared as %^/X indicating the art of making gold and silver among 
 the Egyptians and Greeks of the empire, at the commencement of that 
 extraordinary perversion of the idea of elementary constitution which 
 
Origin of Chemistry. 3 
 
 fascinated mankind for nearly five hundred years. From the Greeks it 
 was naturally adopted, with the vain pursuit which it denoted, by 
 the Arabians, and passing with the Arabic prefix into the languages 
 of modern Europe, became alchemy. When the just objects and 
 powers of the science were finally recognized, it was termed chemia or 
 chemistry. 
 
 In studying those properties of the different kinds of matter by which 
 they are recognized to be distinct and independent chemical substances, 
 it is unavoidable to include those qualities which, although common to 
 all forms of matter, yet diner in degree among the different kinds, and 
 thus serve as distinguishing characteristics of them. The physical pro- 
 perties of various bodies are hence in common use among chemists as 
 serving to perfect their description, and indeed the limit between the 
 strictly physical and the strictly chemical properties of substances is not" 
 always capable of being distinctly drawn. It is consequently necessary 
 to preface the specially chemical history of those bodies by a general 
 account of the physical forces by whose action they are so much in- 
 fluenced. 
 
CHAPTER I. 
 
 OF GRAVITY AND COHESIVE FORCES AS CHARACTERIZING CHEMICAL 
 
 SUBSTANCES. 
 
 THE physical forces which are of most importance in determining the 
 characteristic properties of bodies are gravity and cohesion. These 
 differ, however, remarkably in principle from each other, and are ap- 
 plied to quite independent purposes. Gravity is common to all forms 
 of matter, and is totally independent of iis nature. It is exerted at 
 all, even the greatest conceivable, distances, and is the invisible yet 
 insuperable tie, which connecting together the satellites and planets of 
 our system with the central sun, assigns to each of the tenants of our 
 boundless skies its place and motions. Acting thus only on the mass, 
 gravity is a measure of the quantity of matter present in a body ; and 
 what we term weight is only the gravitating force exerted by the sub- 
 stance which we weigh. By no natural operation can the smallest 
 particle of matter be annihilated or destroyed; throughout the most 
 complicated processes the quantity of matter remains constant, and 
 hence we are enabled to verify the accuracy of our chemical opera- 
 tions, by proving the weight of the bodies ultimately formed, to be 
 equal to the weight of the substances by whose action they have been 
 produced. 
 
 Under the same volume different bodies have very different weights, 
 and hence contain different quantities of matter. Bodies are said to be 
 more or less dense according as in a given bulk they contain a greater 
 or less quantity of gravitating matter, and when a certain body is taken 
 as a standard, and their density reduced to numbers referred to that 
 standard, there is obtained the specific gravity of each body, or the 
 comparative quantity of matter it contains in a given bulk, which, 
 being almost always the same for the same body is an important element 
 in its history, and may often serve as a means of its recognition. The 
 processes by which the specific gravities of bodies are determined will 
 be described farther on. 
 
Divisibility of Matter. 5 
 
 The force of gravity is thus of importance in chemistry, by giving a 
 measure of the quantity of matter upon which we experiment, and by 
 affording characteristics of individual substances from the comparison of 
 the quantity of matter they contain in a standard volume. The force 
 of cohesion, although not so universally existant as that of gravity, is 
 of equal interest from the numerous peculiarities in its activity, which 
 almost every body is capable of presenting, and by which bodies are 
 remarkably distinguished from each other. To understand, however, 
 the nature of cohesive forces, and the causes of the variations of their 
 energy, it is necessary to notice those ideas of the peculiar consti- 
 tution of matter, on which philosophers have generally agreed, and 
 which result from, whilst they best serve to explain those remarkable 
 phenomena. 
 
 From the earliest period in science, discussions have arisen, as to 
 whether the masses of matter which we ordinarily employ, should be 
 considered as capable of infinite division, or whether, by continuing to 
 divide, a term should ultimately be found, at which no further sub- 
 division could be made ; that thus, the ultimate constituent and indivi- 
 sible particles, or atoms, which, by their aggregation, form sensible 
 masses, should be discovered. By no appeal to experiment can this 
 question be resolved ; when we call in the assistance of our most power- 
 ful means of mechanical division, we attain only to producing powders, 
 of which the finest particle is, in miniature, all that the mass from 
 which it had been formed was upon a larger scale, and capable evidently 
 of just as much subdivision, if our mechanical processes were perfect 
 enough to enable us to proceed. 
 
 That this divisibility may actually occur to an almost incredible de- 
 gree, may be easily demonstrated by experiment. In gilding silver wire a 
 grain of gold is spread over a surface of 1400 square inches ; and as, when 
 examined in a microscope, the gold upon the thousandth of a linear inch, 
 or one millionth of a square inch is distinctly visible, it is proved that 
 gold may be divided into particles of at least i-4oo-ooo-ooo f a square inch 
 in size, and yet possess the colour and all other characters of the 
 largest mass. If a grain of copper be dissolved in nitric acid, and then 
 in water of ammonia, it will give a decided violet colour to 39 cubic 
 inches of water. Even supposing, that each portion of the liquor of 
 the size of a grain of sand, and of which there are a million in a cubic 
 inch, contains only one particle of copper, the grain must have divided 
 itself into 392 million parts. A single drop of a strong solution of 
 indigo, wherein at least 500*000 distinctly visible portions can be 
 shown, colours 1000 cubic inches of water, and as this mass of water 
 contains certainly 500-000 times the bulk of the drop of indigo soliN 
 
G Ultimate Particles of Matter. 
 
 tion, the particles of the indigo must be smaller than 2500-000-000-000 the 
 twenty-five hundred millionth of a cubic inch. A rather more distinct 
 experiment is the following: if we dissolve a fragment of silver, of 
 O01 of a cubic line in size, in nitric acid, it will render distinctly 
 milky 500 cubic inches of a clear solution of common salt. Hence 
 the magnitude of each particle of silver cannot exceed, but must rather 
 fall far short of a billionth of a cubic line. To render the idea of 
 this degree of division more distinct than the mere mention of so im- 
 perfectly conceivable a number as a billion could effect, it may be 
 added, that a man, to reckon with a watch, counting day and night, a 
 single billion of seconds, should require 31 '6 7 5 years. 
 
 In the organized kingdoms of nature. even this excessive tenuity of 
 matter is far surpassed. Linen yarn has been spun of which a pound 
 was 1432 English miles in length, and of which, consequently, 171b. 
 13oz. would have girt the globe; a distinctly visible portion of such 
 thread could not have weighed more than 127-080-000 of a grain. Cotton 
 has been spun so that a pound of thread was 2 03 '000 yards in length, 
 and wool 168*000 yards. And yet, these, so far from being ultimate 
 particles of matter, must have contained more than one vegetable or 
 animal fibre ; that fibre being itself of complex organization, and built 
 up of an indefinitely great number of more simple forms of matter. 
 
 The microscope has, however, revealed to us still greater wonders, 
 as to the degree of minuteness, which even complex bodies are capable 
 of possessing. Each new improvement in our instruments, displays to 
 us new races of animals, too minute to be observed before, and of 
 which it would require the heaping together of millions upon millions 
 to be visible to the naked eye. And yet, these animals live and feed, 
 and have their organs for locomotion and prehension, their appetites to 
 gratify, their dangers to avoid. They possess circulating systems often 
 highly complex, and blood, with globules bearing to them, by analogy, 
 the same proportion, in size, that our blood globules do to us ; and 
 yet, these globules, themselves organized, possessed of definite struc- 
 ture, lead us, merely, to a point where all power of distinct conception 
 ceases ; where we discover that nothing is great or small, but by com- 
 parison, and that presented by Nature on the one hand with magnitudes 
 infinitely great, and on the other, with as inconceivable minuteness, it 
 only remains to bow down before the omnipotence of Nature's Lord, 
 and own our inability to understand Him. 
 
 These proofs of great divisibility, however, leave the question of in- 
 finite divisibility quite untouched. There are, however, many and 
 powerful reasons which have decided almost all modern philosophers to 
 consider the possible division as being finite. On the other view, in- 
 
Molecuhir Constitution. 7 
 
 deed,, the mind has no resting place, until, by the total disappearance 
 of material conceptions, the constitution of bodies resolves itself into a 
 collection of mathematical points, from which, as centres, certain forces 
 are exerted. With such abstract speculations, however, chemistry had 
 no connexion ; its fundamental condition, that there exist many kinds 
 of elementary matter, of which the quantity is measured by their 
 weight, being totally independent of any abstract idea of what matter 
 is, or how its properties may have their source. 
 
 In proof of the division of matter having a limit, experiments, made 
 principally by Faraday and Wollastou have been quoted. Thus, it 
 appears, as far as can be ascertained, that our atmosphere does not 
 extend into space, but is confined within comparatively a trifling dis- 
 tance from the earth, about 45 miles. Wollaston, considering the 
 particles of air as being balanced between their mutual repulsion, and 
 the general attraction towards the earth, suggested that if these parti- 
 cles could be divided to an infinite degree, there should be an infinite 
 source of repulsive power, and hence at a certain distance, tin's repul- 
 sion overcoming the gravitating force, the atmosphere should spread 
 into space, and being attracted to the other planets, in proportion to 
 their masses, should form round the larger, as Jupiter, and especially 
 the Sun, vast and dense atmospheres, the existence of which should 
 easily be recognized. No such atmospheres exist, and hence, as was 
 argued by Wollaston, the force of repulsion must have a finite limit ; 
 and the number of repelling particles cannot be infinite. In like 
 manner, Paraday found that bodies in evaporating, form atmospheres 
 of certain definite depths above the surface of the body, and drew from 
 hence the same conclusion. This argument cannot, however, be con- 
 sidered as decisive. It is not at all certain, that because the elasticity 
 of air is thus found to have a limit, that the number of particles of air, 
 in a given space, might not be infinite. 
 
 I shall consider the masses of matter, whose properties we purpose 
 to examine, as being made up of a great number of lesser masses, to 
 which the name of molecules or particles may be assigned. It is totally 
 indifferent, whether these molecules may be infinitely divisible or not ; 
 there is no fact in either chemistry or physics, which requires the posi- 
 tive adoption of either one side or the other. These molecules are 
 subjected to the influence of two forces, which oppose each other, and 
 by the relative balancing or preponderance of which, all the forms and 
 physical properties of ordinary substances are produced. One of these 
 forces is attractive ; it is the attraction of aggregation as it has been 
 termed, or cohesion. If it acted unimpeded, the molecules of every 
 portion of matter would cohere with insuperable power ; unconquerable 
 
8 States of Aggregation. 
 
 solidity, hardness and tenacity, should alone characterize external 
 nature. The other force is one of repulsion, which from a variety of 
 evidence is assumed as identical with the cause of heat. If it, alone, 
 prevailed, no other form of matter could exist but that of gas ; the solid 
 globe, the liquid waters, should change to atmospheres of vapours, and 
 the beneficient uses to which our earth is now adapted, could not exist. 
 
 Such is, perhaps, approximative^ what occurs in those extreme 
 members of our planetary system, Neptune and Mercury. The former 
 receiving from the Sun, but fgoo part of the heat which our earth derives, 
 must be reduced to the temperature of empty space; and with few 
 exceptions, the bodies which on this earth are gaseous or liquid, if they 
 exist there, are as rocky masses. The latter must at certain periods be 
 so hot, that quicksilver would naturally be a gas upon its surface, and 
 those metals which here constitute our examples of solidity, should 
 there form liquid oceans. On this earth, however, according as the 
 forces of heat and cohesion vary in different bodies, they pass through 
 different states of aggregation. Those bodies in which cohesion pre- 
 vails are solid, and by their tenacity and resistance to breakage or 
 change of form, display the force which binds their molecules together. 
 Where cohesion has been suppressed, and the repulsive agency of heat 
 acts uncontrolled, the body becomes gaseous, and its particles, devoid 
 of the least trace of cohesive power, repel each other. In intermediate 
 cases, where the. two forces appear balanced, the particles do not cohere, 
 and hence, may move upon and separate from each other without any 
 external force; but they do not repel, and thus remain in contact if no 
 external force tends to disturb them. This is the liquid condition; it 
 is that of water, of alcohol, of oil, whilst air and steam are gaseous, 
 and iron, wood, and stone are instances of the solid form. 
 
 The peculiar nature of each body determines whether, under common 
 circumstances, it shall have one or the other of these forms, but there 
 are few bodies which are not capable of assuming all the three. This 
 is artificially effected by diminishing or increasing the degree of heat, 
 and thus by cooling a liquid, it may, from the cohesion becoming greater, 
 be converted into a solid ; or by increasing the heat to which a solid is 
 subjected, it may be converted into a liquid, and from thence into a 
 gas. One liquid, pure alcohol, has not yet been frozen : some solids, 
 as charcoal, have not yet been melted : organized bodies are generally 
 decomposed too easily to allow of a change of state, but with these 
 exceptions, the principle of the change of form, artificially caused by 
 the increase or diminution of the quantity of heat, is universal. These 
 forms of matter, considered as effects of heat, will require and obtain 
 hereafter a more extended notice. 
 
Limits of Cohesion. 9 
 
 This force of molecular cohesion acts only at distances so minute 
 as to escape the most delicate examination. The fragments of a piece 
 of glass or metal which has been just broken, when laid ever so 
 closely together, have no tendency to unite again ; but, if the surfaces 
 be pressed together, union may take place, though only in a few points, 
 and imperfectly. Yet, when pieces of plate glass, laid flat on each 
 other, and subjected to considerable pressure, are allowed so to remain 
 for a certain time, they are found to grow together so completely, that 
 thick masses may often be ground, as if they had always formed a 
 single piece. If two surfaces of lead be cut quite clean and bright, 
 and forcibly pressed together, they unite also, and may require a force 
 of eighty or one hundred pounds to effect their separation. In liquids, 
 although the force of cohesion is very nearly absent, yet it is not 
 entirely so ; the viscidity of liquids depending upon the traces of it which 
 remain. The globular form of a rain drop, or of a drop of any liquid 
 allowed to fall from a point, arises also from the cohesive attraction of 
 its particles, and different liquids differ remarkably, in their relations to 
 heat, from the various degrees of force with which this residue of cohe- 
 sion is exerted. The particles of a liquid cohere not only to each other, 
 but, even more powerfully, to solid bodies in many cases. It is thus 
 that solid bodies are wetted by liquids. If the finger be dipped into 
 water, the particles of the water in contact with the finger adhere to it 
 more powerfully than they do to the other particles of the liquid, and 
 when the finger is removed, they accompany it, and thus it becomes 
 wet. Mercury does not wet the finger, for its particles cohere too 
 powerfully to each other ; but mercury adheres to, or wets a piece of 
 gold, as water wets the finger. Prom this cohesion of liquids to solids, 
 all the phenomena of capillary attraction result, as the filtering of 
 liquids in pharmacy and chemistry, to separate solids which had been 
 mixed with them ; the absorption of liquids by porous solid bodies, and 
 many others. 
 
 The existence of this form of cohesion may be very simply shown by 
 an experiment, such as is illustrated in the figure. A disk of any 
 
10 Force of Capillarity. 
 
 substance which may be wetted by water, is to be hung evenly from 
 the extremity of the beam of the balance, and brought exactly into 
 contact with the water in the cup below. It will be found necessary to 
 augment considerably the weights in the scale dish opposite, to separate 
 them ; and when the disk has been torn away from the surface of the 
 water, the force overcome will be found to have been, not that of the 
 solid to the liquid, which was still more intense, but the cohesion of 
 the liquid particles to each other ; for the solid is found to be wetted by 
 a layer of liquid particles which it had torn from the general mass of 
 liquid underneath. If the experiment be tried with a disk of polished 
 iron, and mercury as the fluid, there is no wetting, and the force 
 measured is really the cohesion of the solid to the fluid. 
 
 We shall now proceed to describe the methods adopted to determine 
 the specific gravities of bodies in their different states. 
 
 The determination of specific gravities is easily performed where the 
 volume of the substance can be exactly measured. Thus for liquids, as 
 water, oil of vitriol, or alcohol ; if a small bottle be taken containing an 
 ounce of water, or 480 grains, it will contain 343 grains of sulphuric 
 ether, or 885 grains of sulphuric acid. Now the densities will be 
 as these numbers ; or water being taken as the standard, and its specific 
 gravity being assumed at 1000, the specific gravities of the others 
 become proportional to it ; as : 
 
 Water, ... . - 480 : 1000 
 
 Ether, . .' '343 : 715 
 
 Sulphuric acid * sfci 885 : 1845 
 
 To save this little calculation the bottle in use is generally made to hold 
 1000 grains of pure water, and then filling it with the fluid to be tried, 
 the weight gives directly the specific gravity. 
 
 Where the substance exists naturally in the state of gas, a precisely 
 similar process may be had recourse to ; in place of a bottle with a 
 ground glass stopper, there is used a globe, g, with a stop cock, capable 
 
 of holding from twenty to thirty cubic 
 inches. A quantity of air having been 
 removed from the globe, the gas, which 
 must previously be either perfectly dried 
 or perfectly saturated with moisture, is 
 admitted to supply its place, and as the 
 volume of gas which passes in is exactly 
 equal to the volume of air which had 
 been taken out, the relative weights give 
 their densities, and hence the specific 
 
Specific Gravities. 11 
 
 gravity of the gas. For suppose that the globe full of air weighed 
 656 grains; that having been exhausted of air it weighed 647*5, 
 and then having received 28 cubic inches of carbonic acid gas 
 it weighed 660*3 grains. We thus know that the 28 cubic inches of 
 air had weighed 8*5 grains, and that 28 cubic inches of the gas had 
 weighed 12*8, hence the densities are as 8*5 to 12*8, and the specific 
 
 1 ft.Q 
 
 gravity of the gas, air being taken as 100, is-^xlOOO=l*506. 
 
 Tin's brief description being intended only to explain the principle 
 wliich the words " specific gravity" involve, it has been considered as 
 not liable to alteration ; but in reality the volumes of bodies, parti- 
 cularly of gases, are constantly in a state of change. According as the 
 air is warmer or colder ; according as the pressure to which it is sub- 
 jected, as indicated by the barometer, diminishes or augments, the 
 volume which a certain weight occupies, is altered, and the specific 
 gravity is changed. Hence, when we take air as a standard of specific 
 gravities for gases, we do so only with reference to a certain standard 
 of temperature and pressure ; thus at 32 on the scale of Fahrenheit's 
 thermometer, and at 30 inches of mercury in the barometer tube. It 
 is only by accident that an experiment might happen to be made at this 
 standard temperature and pressure, and hence it is necessary to reduce 
 the observed result to what the result should have been at the standard 
 points. If the gas be damp it is necessary also to correct for the 
 presence of the watery vapour, and hence the determination of the 
 specific gravity of a gas, although so simple in theory, is in practice a 
 most delicate operation. Under the proper heads of the constitution of 
 gases and vapours, with regard to heat and pressure, the mode of 
 making these corrections will be described. 
 
 The determination of the specific gravity of a solid body involves in 
 practice some principles in addition to those above stated. We cannot 
 regulate the bulk of a solid body as we wish, and hence the volume 
 must be determined indirectly. This is done by finding how much 
 water it displaces. Thus, if the solid be in many small fragments, 
 weighing altogether, for example, 357 grains, they may be introduced 
 into a specific gravity bottle containing 1000 grains of water. A 
 quantity of water overflows exactly equal in bulk to the solid which is 
 introduced. The bottle being full, the solid body and the remaining 
 water are then found to weigh 1285 grains. Now, if no water had 
 been expelled, the water and solid body should have weighed 1357 
 grains. The difference 72 is the weight of the water expelled, and 
 consequently the weights of equal volumes, or the densities of the 
 water and of the solid are as 72 and 357, or, the specific gravity of 
 the water being taken as 1000, that of the, solid is ^ X 100 or 4958. 
 
12 Modes of Determining 
 
 If the solid be unsuited for that method, its volume is next determined 
 by the principle that a solid body immersed in a liquid is partly supported 
 by the upward pressure of the liquid which it displaces. The solid, in 
 order to sink in the liquid, has to displace and push upwards a quantity 
 of it equal to its own bulk, and to resist its weight or tendency to sink 
 down again ; for this purpose a portion of the weight of the solid must 
 be employed, and it is only the overplus that is counterpoised by the 
 weights, when we proceed to weigh the solid body immersed in any 
 liquid. A solid weighs, therefore, less when immersed in a liquid than 
 when weighed in the ordinary manner, the difference being the portion 
 of the weight of the solid which is employed to sink it, or to resist the 
 force of the liquid which tends to float it up, and this is equal to the 
 weight of the liquid which the solid pushes out of its place, and which 
 is of the same volume as the solid. To effect this operation a balance, 
 
 as in the figure, is taken ; generally with one scale dish. The solid is 
 hung to the other extremity of the beam by a fine hair or thread of 
 cocoon-silk, b, and is thus weighed as usual; let us suppose that it 
 weighed 295 grains. A vessel of pure water is then so arranged that 
 the solid shall be immersed as nearly as possible in the centre of it, (as 
 a in figure,) and it, being then again weighed, is found to be lighter 
 than before ; let us suppose that it shall weigh 243 grains. Tin's is the 
 overplus of its weight after having neutralized the tendency of the 
 water to float it up. The difference of the two weighings 295 243=52 
 grains is therefore the amount of the upward pressure or the weight of 
 the water which the solid displaced. Equal volumes thus of the solid 
 and of the water are found to weigh respectively 295 and 52 grains, 
 and the comparison of these numbers, water being taken as 1000, gives 
 the specific gravity of the solid which is -52 xlOOO=5673. 
 
 A variety of other instruments are made use of for measuring the 
 specific gravities of solids and of liquids, as areometers, hydrome- 
 ters, &c. ; but as here it is rather the general principles, than the 
 practical details of such operations, that are of importance, I shall not 
 enter into their description. 
 
Specific Gravities. 13 
 
 The specific gravities of compound gases are found to have a highly 
 important relation to their ultimate constitution, and throw great light 
 upon some of the most general laws of chemistry ; and it has been the ob- 
 ject of some very interesting speculations, which I shall hereafter notice, 
 to trace a definite connexion between the chemical properties or com- 
 position of liquid or solid bodies and their specific gravities. The phy- 
 sical constitution of vapours and gases being, moreover, identical, those 
 bodies which, being volatile, are capable of assuming the form of vapour, 
 may render, by the examination of the specific gravities of their vapours, 
 most interesting indications of the manner in which their elements 
 are combined, and methods of performing this operation have been 
 contrived by some of the most illustrious chemists, as by Dumas and by 
 Gay Lussac. 
 
 The method of Gay Lussac is the simpler of the two, and, for sub- 
 stances which are volatilized at moderate temperatures, easily applied. 
 A basin, <?, is taken, which rests upon a little furnace, and 
 contains mercury. In this basin the graduated bell, #, is 
 inverted full of mercury. Let us suppose we wish to deter- 
 mine the specific gravity of vapour of water. One or two 
 little bulbs are taken, and filled with water as follows : the 
 bulb is warmed with a lamp, and allowed to cool with the 
 point dipped into the water. In this manner a little water 
 gets admission ; this is then boiled in the bulb until all air 
 has been expelled, and the bulb is filled with pure steam. 
 The point being then dipped under the surface of the water, 
 as the steam condenses, the water rushes up to supply its 
 place, and the whole becomes full. The point being then touched to 
 the flame of a lamp, it is melted, and the orifice is closed. A small 
 quantity, three or four grains, of water, being thus enclosed, the little 
 bulbs are passed under the edge of the jar, a, and rise to the top, 
 where they float upon the mercury ; a glass cylinder, b, open at both 
 ends, is now placed round the jar resting on and secured to the dish, 
 c, and into it is poured so much colourless oil as shall completely cover 
 the jar, a, but allow of the graduation being distinctly seen. The fur- 
 nace is then lighted, and as the temperature of the oil and mercury 
 rises, the water in the little bulbs form steam, which at last bursts the 
 bulbs, and the level of the quicksilver in the jar immediately falls, the 
 steam occupying the space above it. When the mercury ceases to de- 
 scend, it is known that all liquid has been converted into vapour ; the 
 temperature of the oil, which is necessarily the same as that of the va- 
 pour inside, is ascertained, and by the graduation on the jar the volume 
 occupied by the vapour is accurately read off ; the weight of the vapour 
 
14 Specific Gravities. 
 
 is known, for it is the weight of the water in the bulbs, and its volume 
 at this high temperature is thus found. Knowing then the volume of 
 a few grains of steam at 250, the volume at 32 may be calculated ; 
 and as the volume of so many grains of air at 32 is already known, 
 the specific gravity of the vapour of water is obtained. The tempera- 
 ture of the oil must be at least thirty or forty degrees above the boiling 
 point of the liquid ; and hence it is likely to become coloured, to fume, 
 or even to risk taking fire, unless great caution is employed. 
 
 The method invented by Dumas has the advantage of being applica- 
 ble to all temperatures below the melting point of glass ; and it is, 
 consequently, by its application, that the greatest benefit has been 
 conferred on science. It is, however, more complex in principle, 
 though less delicate in practice. A globe, holding from ten to fifteen 
 cubic inches, and drawn out at its beak to a capillary orifice, is care- 
 fully weighed, containing, as usual, atmospheric air. It is then warmed, 
 and its beak dipped into the liquid to be tried ; it is allowed to cool, 
 until by the contraction of the air a sufficient quantity of the liquid has 
 made its way in. The globe is then fitted in a sort of cage, by which 
 it is securely held in the centre of the liquid bath, by which the heat 
 is to be applied, and which may be water, or oil, a solution of chloride 
 of zinc, or best of all, the fusible alloy of bismuth, tin, and lead. 
 The capillary beak of the tube just projects over the surface of the 
 bath, as in the figure. When the globe becomes sufficiently heated, 
 
 the liquid boils, and its vapour, in passing away, carries off the air 
 which had previously filled the globe. The liquid should be present in 
 such quantity that its vapour, after carrying off all air, should occupy 
 the interior of the globe completely pure. The excess of vapour is 
 known to have passed away when there is no longer a jet proceeding 
 from the capillary beak, and then by means of a blowpipe the orifice 
 
Molecular Forces. 15 
 
 is closed, and the temperature of the bath being taken at the same 
 moment, the globe is removed from the bath, perfectly cleaned and 
 weighed. The liquid condensing as soon as the globe grows cold, 
 leaves its interior practically empty, and on breaking off the capillary 
 beak under the surface of quicksilver, this last enters into the vessel, 
 and if the operation had been well managed, fills it completely. The 
 globe, full of quicksilver, is then emptied into a graduated jar, by 
 which the quantity of the quicksilver being measured, the volume of 
 the globe is known ; when this has been done, all requisites for calcu- 
 lating the specific gravity of the vapour have been obtained. For, 
 knowing the volume of the globe, the weight of the air it contained is 
 known ; and subtracting that from the first weighing of the globe, the 
 weight of the globe when empty is obtained. Subtracting this from 
 the second weighing of the globe the weight of the vapour is obtained, 
 and as the air and vapour occupied the same volume, the densities 
 should be as these weights, if they had been at the same temperature ; 
 but, as this was not the case, a further calculation is required to reduce 
 them to the standard, and obtain the numerical specific gravities. 
 
 No process has been more fruitful in important results than this 
 mode of determining the specific gravity of vapours ; for it is only in 
 this way that such substances as sulphur, arsenic, phosphorus and 
 mercury, as well as numerous compound bodies with high boiling points, 
 could have been experimented on. 
 
 The particles of a body being held at certain distances from each 
 other by the balance of their attractions and repulsions, if by the appli- 
 cation of an external force, as pressure, they be brought nearer, so as 
 to occupy a smaller volume, the body is said to be compressible. If 
 when the external force is removed, the body, by the mutual repulsion 
 of its particles, regain its original volume, it is said to be elastic ; 
 if, on the contrary, it remains as when compressed, it is called inelastic. 
 In nature there are few bodies perfectly elastic, and none which can be 
 said to be perfectly inelastic. In solid bodies, when pressure produces 
 a change of volume, some traces of it are permanent ; but in liquids, 
 and gases, the restoration to the original bulk appears to be complete. 
 
 The amount to which solid and liquid bodies may be compressed is 
 very small, so much so, that very delicate methods are necessary to 
 determine it. Thus, it requires a pressure of about 4001bs. upon each 
 square inch of the surface of water to diminish its volume by the ^65 
 part. In gases, however, the repulsive force acting without interfer- 
 ence, and the particles being at much greater distances from one 
 another than in the liquid or solid form, the amount of compressibility 
 becomes very much increased, and the law by which it is regulated very 
 
16 Elasticity of Gases. 
 
 simple, being, that the volume of any gas varies inversely as the pres- 
 sure upon it ; that it is doubled if the pressure be diminished to one 
 half, and reduced to one half if the pressure upon its surface be 
 doubled. Thus, supposing a gas to measure 100 volumes under the 
 pressure of 201bs. 
 
 Then with pressures of 80 . 40 . 20 . 10 . 51bs. 
 The volume becomes 25 . 50 . 100 . 200 . 400. 
 
 The gases which are used in chemical operations are liable to con- 
 stant change of volume, from the alterations in the weight of the sur- 
 rounding atmosphere, by which they are always pressed ; and hence, 
 before we can tell how much of a gas we really have obtained by any 
 process, it is necessary to ascertain the amount of atmospheric pressure, 
 and to allow for it. The pressure which the air exercises is measured 
 by the barometer, in which a column of quicksilver balances the pres- 
 sure of the air, and varies in height according as this changes ; the 
 height of this mercurial column being accurately measured by a scale 
 applied to the tube of the barometer. In these countries, the height 
 of the barometric column fluctuates between 28 and 31 inches; but 
 the average height of a year is 29 '8 inches. Eor simplicity, a number 
 very near this, 30 inches, is taken as the standard pressure ; and when- 
 ever the specific gravity, or the volume of a gas is given, without par- 
 ticular remark, this standard height of he barometer is understood to 
 be the pressure. 
 
 If, therefore, we have a gas at a different pressure, it is usual, and 
 often necessary, to reduce its volume to what it should have been under 
 the standard pressure ; to do this we use the rule given above for the 
 change of volume with the pressure. Thus, if in an analysis of mor- 
 phia, we obtain 4- 54 cubic inches of nitrogen gas, when the barometer 
 is at 28*5 inches, we say, that expressing the volume at 30 inches by Y 
 Y : 28-5 ::4.54 : 30 or Y=^ X4'54=4'313. 
 
 Knowing, then, the weight of 100 cubic inches of nitrogen at 30 
 inches, the weight of 4*313 is easily obtained. 
 
 In this manner, the corrections for pressure, alluded to in the descrip- 
 tion of the modes of taking the specific gravities of gases and of va- 
 pours, are introduced. Thus, in taking the specific gravity of steam 
 by Gay Lussac's process, (page 13,) the vapour occupying but a portion 
 of the tube, there remains a column of mercury, suppose 5 inches 
 high : the pressure on the vapour is, therefore, only the difference be- 
 tween that and the external pressure, and if this be 30 inches, is 
 (30 5) =25. Then the measured volume of the steam is to what it 
 should be at the standard pressure, as 30 to 25. 
 
 In certain cases, of which atmospheric air may be taken as an 
 
Liquefaction of Gases. 
 
 17 
 
 example, this rule, of the volume being inversely as the pressure, holds 
 exactly ; but there are many other gases, in which, when the compres- 
 sion is very great, the particles appear to be brought within the sphere 
 of their respective cohesive forces, and the volume diminishes more 
 rapidly than it ought, by the rule. Thus, if a tube full of air, and a 
 tube full of sulphurous acid gas, be exposed to exactly the same pres- 
 sure, the volumes will not diminish in the same degree when the pres- 
 sure becomes high, but as follows : 
 
 The air as . . 1000 . 853 . 559 . 314. 
 
 Sulphurous acid as 1000 . 851 . 554 . 301. 
 In some other gases the same variation has been observed. 
 
 If such a gas be still more violently compressed, its particles may be 
 brought so completely within the sphere of cohesive action, that this 
 force comes into active play, and the body changes from the gaseous to 
 the liquid form ; and by the combined influences of intense cold and 
 great compression, many of the most active and characteristic gases 
 have been reduced even to the solid form. The pressures under which 
 the ordinary gases become liquid at the temperature of 32 Fahrenheit* 
 are as follows : 
 
 Name of Gas. 
 
 Atmospheres. 
 
 Pounds to the Inch. 
 
 Nitrous Oxide, 
 Carbonic Acid 
 Muriatic Acid 
 Sulphuretted Hydrogen, 
 Ammonia, . 
 Cyanogen, . 
 Sulphurous Acid, 
 
 44 
 36 
 24 
 15 
 5 
 3 
 2 
 
 660 
 540 
 360 
 225 
 75 
 45 
 30 
 
 and hydrobromic acid gas, sulphurous acid gas, sulphuretted hydrogen 
 gas, carbonic acid, cyanogen, and ammonia have been obtained as 
 crystalline solids. In tin's solid form these bodies manifest very anomal- 
 ous physical properties. Thus, the elastic force of the vapour of solid 
 carbonic acid is at 32 Fahrenheit, 38 atmospheres, and consequently, 
 according to our ordinary ideas, the boiling point of liquid carbonic 
 acid lies very far below its freezing point. The most intense cold that 
 is as yet known, is that from the evaporation of a mixture of solid 
 carbonic acid and sulphuric ether, by which a temperature of 166 
 Fahrenheit below the freezing point of water is produced. 
 
 Other gases, such as oxygen, hydrogen, and nitrogen, have been 
 
 subjected to a pressure of 800 atmospheres, not only without becoming 
 
 liquid, but without even deviating from the rule which implies perfect 
 
 elasticity, and hence, without even approximating to the term at which 
 
 2 
 
18 Solubility. 
 
 they should abandon the gaseous state. Notwithstanding this, we 
 cannot consider that there is any physical difference of constitution be- 
 tween those liquifiable and non-liquifiable gases ; and hence, the con- 
 clusion is, that, by a suitable increase of pressure, the molecules of 
 all gases might be so brought into coherent approximation, and con- 
 verted into liquids. 
 
 With regard to the means of applying such pressure, and actually 
 obtaining those gases in the liquid form, it is necessary to consider the 
 manner in which those gases are generated, and such methods will con- 
 sequently be described in the history of those bodies. 
 
 Cohesion is thus antagonistic to the force of heat, which tends to 
 render the molecules of a body repulsive to each other, and to separate 
 them to greater distances from each other than they had been before. 
 Cohesion is, therefore, diminished, and even annulled, by applying 
 heat, 
 
 "When the cohesion between the particles of a solid, and those of a 
 fluid, is more powerful than between the particles of the solid itself, 
 the latter is not merely moistened by the fluid, but it abandons altoge- 
 ther the solid form, and becoming liquid, mixes uniformly with the 
 fluid, and is said to have been dissolved by it. By this peculiarity of 
 cohesion, bodies are divided into the soluble and insoluble. Thus, 
 common salt and glauber's salt are soluble, whilst chalk and white lead 
 are insoluble, in water. These classes are, however, connected by a 
 series of intermediate degrees of sparingly soluble bodies, such as cream 
 of tartar, and plaster of paris. Bodies which are insoluble in water, 
 may be yet easily dissolved by other fluids ; thus, resinous bodies, 
 which do not dissolve in water, dissolve in alcohol. A great deal of 
 the success of vegetable proximate analysis, depends upon the skill, 
 with which the solvent powers of various fluids may be successfully 
 applied. 
 
 From the tendency of heat to diminish the force of cohesion, it na- 
 turally results, that the solubility of most bodies is increased by heat ; 
 thus, 100 parts of water, at 60 F. dissolve 11 of sulphate of potash, 
 and at 212 dissolve 25. At 60, 32 parts of dry sulphate of magnesia 
 are dissolved by 100 of water, but 74 at 212. This, however, is not 
 always the case. Some bodies, as common salt, are exactly equally 
 soluble in water at all temperatures, whilst in other cases the solubility 
 is greater at particular temperatures than either above or below them. 
 Of this peculiarity, the sulphate and nitrate of soda are examples. 
 Thus, 100 parts of water dissolve of dry sulphate of soda, at 32, 
 50-2; at 52, 10'22 ; at 76, 28; at 93, 53; at 122, 47; and at 
 212, 42. The solubility increasing up to 93, and from thence dimi- 
 
Phenomena of Solution. 
 
 19 
 
 nishing. 100 parts of water dissolve of nitrate of soda, at 21, 63 ; 
 at 32, 80 ; at 50, 23 ; at 60, 55 ; and at 246, 218 parts. Here 
 the peculiarity is of the opposite kind to what occurs with sulphate of 
 soda : the solubility diminishing up to 50, and from thence progres- 
 sively increasing. 
 
 52" 72 92 } 112' 132 152 172 
 
 The solubility of bodies in water may be strikingly represented to the 
 eye, by means of a kind of map, such as is given in the figure. The 
 horizontal lines represent the quantities of the salt dissolved by 100 
 parts of water, wliilst the vertical lines represent the temperatures. 
 Thus, the line of sulphate of soda commences at the temperature of 
 32 at the horizontal line 5, and rising rapidly, cuts the horizontal line 
 10 at 52, cuts the line of 40 at 88, and attains its highest point of 
 53 at 93 ; from thence it commences to redescend until at 232, there 
 are only 42 parts dissolved. The line of chloride of sodium is 
 horizontal, showing that it is equally soluble at all temperatures; 
 and in the other cases, the construction of the scale is easily seen on 
 inspection. 
 
 In general, when solid bodies dissolve in a liquid, there is cold pro- 
 duced, but occasionally the solution is accompanied with a remarkable 
 evolution of heat ; this last occurs when bodies which naturally contain 
 water, chemically combined, have been deprived of it by heat, and when thus 
 dried, are dissolved. In such cases, it is probable that the one portion of 
 water is taken by the salt into an intimate chemical combination, and 
 thus more heat produced than counteracts the cold which should arise 
 
20 Formation of Crystals, 
 
 from the mere solution of the hydrated salt thus formed. Such exam- 
 ples may be found in dry chloride of calcium, the dry sulphates of 
 copper, or of zinc or iron. 
 
 Solution is very much promoted by agitation, by the minute division 
 of the solid, and generally by all causes which tend to facilitate the 
 contact of the solid and liquid particles. When the liquid has dissolved 
 as much of the solid as possible, it is said to be saturated. The cohe- 
 sion of the liquid to the solid having been reduced to an equality 
 with that of the particles of the solid for each other, it can dissolve 
 no more. 
 
 If a saturated solution be so circumstanced as to diminish the cohe- 
 sion of the particles of the solid to that of the fluid, or to increase the 
 cohesion of the particles of the solid to each other, a portion of the 
 solid separates, the amount of which depends on the new conditions 
 under which the liquid is placed. Thus, if to a solution of nitre in 
 water, there be added spirits of wine, the water mixes with the spirits 
 of wine and abandons the nitre, which is precipitated. If strong mu- 
 riatic acid be added to a solution of chloride of barium in water, the 
 water is taken by the acid, and the salt falls down as a white powder. 
 But the most usual case, is, where the separation of the solid is 
 produced by the cohesion of its own particles, which, slowly 
 abandoning the liquid, dispose themselves according to certain laws, 
 and, assuming regular geometrical forms, are termed crystals. Solid 
 bodies, in separating slowly from liquids in which they had been dis- 
 solved, in general thus crystallize, and the figures of these crystals 
 being, to a great extent, characteristic of the bodies, deserve minute 
 attention. 
 
 To obtain substances regularly crystallized, several processes may be 
 followed, according to the nature of the body. Where the substance 
 is soluble, and more soluble in a hot than in a cold liquid, a saturated 
 boiling solution may be made and allowed to cool. The excess of the 
 solid body crystallizes out on cooling. Thus, if 151 parts of sulphate 
 of magnesia in crystals be dissolved in 100 parts of boiling water, and 
 allowed to cool to 60, a quantity of crystals will be obtained weighing 
 86 parts; for at 60 the 100 of water can only dissolve 65, and the 
 difference between that and the 151, which had been dissolved by the 
 boiling water must crystallize. If the body be, like common salt, 
 equally soluble in water at all temperatures, the above process cannot 
 be applied, and a quantity of the liquid must be removed by evapora- 
 tion ; the portion of salt corresponding to the quantity of water which 
 has passed away, is thus obtained solid. If the evaporation be slowly 
 carried on, so that the separation of the salt is not disturbed by 
 
By Fusion and Solution. 1 
 
 the boiling of the liquid, it forms regular crystals, which may attain to 
 considerable size. 
 
 In many cases the bodies which it is necessary to obtain crystallized 
 are not soluble, or it may be wished to obtain crystals otherwise than 
 by solution. By melting a solid substance, its particles are allowed 
 liberty of motion, and when it agaiii commences to solidify they may 
 arrange themselves regularly, and crystallize. Almost all bodies, when 
 melted, and then allowed to solidify, do thus crystallize; but the 
 spaces left between the crystals which first form, being completely filled 
 up by the portions which solidify afterwards, there remains only a 
 general crystalline structure, visible in the fracture of the body. Thus, 
 cast iron, sulphur, zinc, &c., have crystalline fractures. The beautiful 
 feathered appearance given to sheet tin, by washing with dilute acid, 
 and which was so popular some years ago under the name of moiree 
 metallique, was simply this crystalline structure, displayed by removing 
 the thin layer of metal on the outside, which had solidified too rapidly 
 to have acquired any trace of crystallization. To obtain, therefore, the 
 metals, crystallized by fusion, the excess of liquid metal must be re- 
 moved from around the crystals that are first formed. A quantity of 
 the metal or of sulphur, having been melted in a cup, is to be allowed 
 to cool until a solid crust has formed upon the surface and at the sides, 
 to a certain depth ; two apertures must be made in the upper crust, 
 and the fluid metal remaining, be poured out at the 
 one aperture, whils the air enters at the other, to 
 supply its place. On then breaking the vessel, the 
 interior of the solid layer of metal or sulphur is ge- 
 nerally found lined with well formed and character- 
 istic crystals, as represented in the figure. 
 Bodies may also be crystallized by sublimation. When a substance 
 has been converted into vapour, and that, in condensing, it assumes at 
 once the solid form, its particles arrange themselves so as to form crys- 
 tals. Thus are obtained in fine crystals, arsenic, arsenious acid, cor- 
 rosive sublimate, benzoic acid, &c. 
 
 It frequently happens that the same body may be obtained crystallized 
 by more than one of these processes. Thus, corrosive sublimate may 
 be crystallized by solution or by sublimation ; sulphur may be crystal- 
 lized either by fusion or by solution. It is remarkable that when this 
 occurs, the crystals obtained by the two processes are seldom of the 
 same shape ; they may not have even any simple relation of figure to one 
 another, but indicate a totally different mode of arrangement of par- 
 ticles, induced, probably, at least in part, by the different temperatures 
 at which the change of state of aggregation may have occurred. A 
 
22 Primary and Secondary 
 
 body which crystallizes thus in two forms is said to be dimorphous, and 
 this character will be found hereafter of the highest importance in the 
 theory of the atomic constitution of compound bodies. 
 
 The more slowly the change of state occurs, the more regular, and 
 the larger, are the crystals that are formed. Hence, in practice, 
 solutions are left to cool very slowly, or to evaporate spontaneously ; 
 and sublimation is effected by the most gentle heat that can be advan- 
 tageously applied. To favour the deposition of the particles, a variety 
 of artificial aids may be applied. Thus, crystallization takes place 
 better in a pan with some little roughness at the sides, than when it is 
 quite smooth, and threads are hung in sirup to promote the crystalliza- 
 tion of the sugar candy. A little crystal of the same kind of salt is 
 often introduced, to serve as a nucleus round which the new crystals 
 may gather; and, in a solution containing many salts, the nature of 
 the salt which shall crystallize may be determined by the nature of the 
 little crystal introduced. Thus, if equal parts of nitre and of glauber's 
 salt be mixed and dissolved in five parts of water, and the solution di- 
 vided between two similar dishes ; on a crystal of nitre being laid in 
 one dish, and a crystal of glauber's salt being laid in the other, a crys- 
 tallization of pure nitre will occur in the former, whilst nothing but 
 glauber's salt will crystallize in the latter dish. Salts which are mixed 
 together in solution may also be separated from one another by their 
 respective solubilities : thus, if sea water be evaporated, common salt 
 alone will be deposited according as the liquor boils away ; when it has 
 been removed from the fire no more common salt separates, but epsom 
 salt will crystallize, and after it has been removed the liquor will be 
 found to contain chloride and iodide of magnesium. The liquor from 
 which crystals have separated, is called the Mother liquor. 
 
 Crystals occasionally form in a body, although it may remain com- 
 pletely solid. Thus, the soft iron parts of machines which are kept in 
 rapid motion, assume a crystalline structure, and become dangerously 
 weak and brittle. When sugar is melted and allowed to cool, it 
 forms a perfectly transparent hard mass, destitute of any trace of crys- 
 talline arrangement, but after some months it becomes opake and 
 white, having changed into ordinary crystallized sugar. In cases, also, 
 where bodies are dimorphous, one form is generally instable, and the 
 body, when crystallized in it, changes after some time into the other 
 form. This takes place remarkably with sulphur, and will hereafter be 
 again referred to. 
 
 A solution of a salt, saturated at a high temperature, is found occa- 
 sionally to remain without crystallizing, although cooled to a very low 
 degree. In such case, on introducing a little crystal, or agitating the 
 
Forms vf Crystals. 23 
 
 liquor, it suddenly crystallizes, and frequently solidifies into one mass. 
 Sulphate of soda is remarkable for its tendency to manifest this in- 
 difference to crystallization. If two parts of crystallized sulphate of 
 soda be dissolved in one part of water, at 93, and the solution be laid 
 aside to cool, without being disturbed, it remains quite clear and liquid ; 
 but on producing crystallization by any of the means just stated, the 
 whole becomes solid. 
 
 In all cases of crystallization, there is heat evolved, consequent on 
 the general law, of heat being given out when a liquid or a vapour 
 becomes solid. There is sometimes a remarkable evolution of light, to 
 which I shall refer again. Indeed crystallization is sensibly affected by 
 the presence or absence of light. If a dish, half covered by paper, be 
 set aside with a solution, to crystallize, but few crystals will form in the 
 dark, although there may be an abundant crop on the illuminated por- 
 tion of the vessel. 
 
 It has been noticed, that when a body has been obtained, crystallized 
 at different temperatures, as by solution and fusion, the crystalline form 
 is generally different, and the body is said to be dimorphous. In this 
 case, the two forms are totally different in their geometrical character. 
 But independent of this, a body may, even simply by solution, be ob- 
 tained, crystallized in a great variety of forms. In a crop of crystals 
 of sulphate of iron, or of alum, obtained by cooling from a hot solu- 
 tion, a great many different figures may be observed, which, however, 
 are, on examination, all referable to one, more simple and fundamental, 
 form. Each substance has thus a characteristic form of crystal, which 
 is termed its primary form, and it may assume a great variety of figures, 
 produced by modifications of this form : these are termed secondary 
 forms. Thus, carbonate of lime has been found crystallized in more 
 than six hundred different secondary forms, all derivable, however, 
 from the one original primary figure, the rhombohedron. The growth 
 of a crystal, depending on the deposition of new layers of particles, 
 over its external surface, any change in the quantity deposited on each 
 side, will naturally produce a change of form. It is, therefore, neces- 
 sary when crystals are left long in a solution, to turn them, and change 
 their position frequently, as otherwise the growth would take place on 
 some sides rather than others, arid secondary forms should be pro- 
 duced, by which the characteristic figure of the crystal would be 
 injured. 
 
 The most ordinary source of change of figure consists in the replace- 
 ment of an edge, or of an angle by a plane. Thus one of the 
 simplest figures of crystals is the cube a ; it has eight edges and eight 
 solid angles. The effect of substituting plane surfaces for the edges 
 
Forms of Crystals. 
 
 is to produce the secondary form, b, and by replacing the solid angles, 
 
 by planes, the form c ; when these replacements occur together, Jhe 
 more complex figure d, is produced. If the edges of the cube be re- 
 placed, until all traces of the original planes disappear, the figure e, 
 
 the rhombic dodecahedron, is produced ; and if the replacement of the 
 solid angles, by planes, be carried on to the same extent, there is formed 
 a regular octohedron f. These last may be also simple and primary 
 forms, for by a similar mode of replacement, they may be reduced to 
 each other, or to the cube. 
 
 When a crystal augments in size by the deposition of layers of fresh 
 material upon its faces, the molecular cohesion in each new layer is 
 greater than its cohesion to the layer underneath, and hence, by skilful 
 splitting, a crystal may be separated into a number of plates, exhibiting 
 the order of its formation. The direction in which a crystal may be 
 split, is termed its cleavage, and it is of. great importance, in the deter- 
 mination of the primary form of the crystal, for it often occurs, that 
 the same secondary form may be produced by two different primary 
 forms, and in such case, the cleavage being simply related to the sur- 
 faces of the true primary form, determines which it is. 
 
Systems of Crystallization. 25 
 
 Notwithstanding the immense variety of forms of crystals which 
 exist, they may yet be reduced to a very few classes, by conceiving 
 them to be formed by their particles being built up around certain 
 straight lines as axes, which pass through the centre of the crystal. 
 These axes are usually three in number, representing the three dimen- 
 sions of space, and their relative position and magnitude determine the 
 manner in which the particles are arranged. 
 
 In this case there may be formed six systems of crystallization, cha- 
 racterized as follows : 
 
 1st System. The Regular System. The three axes are all equal in 
 length, and are at right angles to each other. 
 
 2nd System. The Rhombohedral System has three axes equal in 
 length, which are placed, however, at equal angles (60) with each 
 other, and are all in the same plane, whilst a fourth and unequal axis 
 is at right angles to that plane. 
 
 3rd System. The Square Prismatic System has the three axes at 
 right angles to each other, but there are only two of them equal, the 
 third is either longer or shorter than the other two. 
 
 4th System. The Right Prismatic System has the three axes at right 
 angles to each other, but there are no two of them of the same 
 length. 
 
 5th System. The Oblique Prismatic System has two of the axes 
 making an acute angle with each other, whilst the third is placed at 
 right angles to both. The three axes are all unequal in length. 
 
 6th System. The Doubly Oblique Prismatic System has all the axes 
 unequal in length, and making acute angles with one another. 
 
 The various actual forms of crystals, both primary and secondary, 
 are derivable from the manner in which the plane surfaces of the crys- 
 tals may be applied, around these axes. In order to conceive the 
 application of the planes, the axes shall be considered as placed, with 
 one in a vertical position, and it is called the principal axis. The 
 nature of the system determines which axis should be selected. 
 
 In the Regular System, the axes being all equal, it is a matter of 
 indifference which is chosen as the principal axis, and their perfect 
 symmetry is also a reason that the portions of the crystal around each 
 axis must be completely similar. The number of forms belonging to 
 this system is consequently not very large, and they are remarkable for 
 their simplicity. Thus, when each plane cuts the axes at equal dis- 
 tances from the centre, the form is the octohedron, and as the planes 
 must be equally inclined to all the axes, it is the regular octohedron 
 f, of which each plane is an equilateral triangle. "When each face of 
 the crystal cuts one axis at right angles, and is hence parallel to the 
 
26 
 
 Hemihedral Forms* 
 
 other two, the form is the cube a. When each face cuts two axes at 
 equal distances from the centre, and is parallel to the third, the figure 
 which results is the rhombic dodecahedron e. By the combined posi- 
 tions of sets of planes, other and more complicated (secondary) b. c. d. 
 forms are produced, arising from the partial coexistence of the condi- 
 tions of the formation of two simple forms. 
 
 The crystals belonging to this system are, generally, very well de- 
 fined, and easily recognized : a great number of important bodies crys- 
 tallize in the forms belonging to it : thus common salt, fluor spar, 
 galena, and iron pyrites, are found in cubes ; alum in octohedrons ; the 
 garnet is found in dodecahedrons. When pure metallic substances are' 
 found crystallized, it is usually in forms belonging to this system ; thus, 
 bismuth, copper, silver, gold, crystallize in cubes, and lead in octo- 
 hedrons. 
 
 A peculiarity of crystals, belonging, 
 particularly, to this system and to the 
 next, is, that every alternate face may 
 become developed to such a degree as to 
 obliterate the intervening planes, and thus 
 to generate a new form, having one half 
 of the number of planes. Thus a crystal 
 of alum is very seldom truly octohedral ; 
 it has usually the figure of g where four 
 of the sides of the octohedron have be- 
 come very large, whilst the other four 
 remain very small. When the obliteration 
 becomes complete, there is produced the 
 tetrahedron, or three-sided pyramid of fig. 
 h, which is hence properly called the hemioctohedron. Such crystals 
 are called hemihedral, from their containing half the proper number of 
 sides. Certain bodies have a natural tendency to hemihedral crystalli- 
 zation, and are but very rarely found with the proper number of planes. 
 The diamond is a remarkable instance of this. Its proper form is the 
 regular octohedron, but its crystals are universally hemihedral. 
 
 In the Rhomlohedral system the supplementary, or fourth axis, is 
 taken as the principal axis, and the crystals are formed by the planes 
 being applied to these axes, as in the former system. If the planes be 
 all inclined at the same angles to the three horizontal axes, and that 
 they cut the vertical axis, there is formed a double six-sided pyramid 
 (i} } and when the planes are perpendicular to the horizontal axes, and 
 parallel to the vertical axis, the six-sided prism (Jc) is produced. 
 
Rh&mbo&edrai System. 
 
 These forms generally coexist in quartz, as in the 
 figure, k. By the replacement of the edges in 
 these forms, there may be produced others, with 
 twelve sides in place of six ; as a twelve-sided 
 prism, and a twelve-sided pyramid, of which 
 quartz also affords examples. 
 
 This system is more remarkable for its modi- 
 fied forms, than for those simple figures above 
 described, although the six-sided prism, and six- 
 . sided pyramid, are characteristic of very many substances. If we sup- 
 pose in the terminal six-sided pyramid, every alternate side, above and 
 below, to grow at the expense of those next it at 
 each side, I will be formed. Ultimately the sides 
 of the prism shall disappear, and there will 
 remain a figure of six planes, of which all the 
 sides shall be equal and similar rhombs, the 
 rhombohedron m, which gives its name to this 
 system, although it be but a hemihedral modifi- 
 cation of the true typical form. The principal 
 axis of the rhombohedron is the vertical axis of 
 the pyramid, and the horizontal axes are found 
 by joining the solid angles to the centres of 
 the opposite faces, where originally the lateral angles of the pyramid 
 had been. 
 
 The carbonates of lime, of iron, and magnesia, are remarkable for 
 crystallizing with this hemihedral figure. Even in the six-sided prism 
 of carbonate of lime, the rhombohedral tendency is evident by the 
 crystal being terminated not by the six-sided prism as in quartz, but by 
 its three hemihedral replacing planes, as in figure I. 
 
28 Square) Right and Oblique Prismatic 
 
 3. The Square Prismatic System. The crystals of this class differ 
 
 from those of the regular system, in the vertical 
 axis not being necessarily equal to the other 
 two ; but on the contrary, being in almost all 
 cases, either longer or shorter. Where there 
 is formed an octohedron, n, it differs from the 
 regular octohedron, in the terminal angle of 
 each plane being not 60, but more or less. Its basis is, however, a 
 square, and to distinguish it from the octohedron of the following 
 system, it is termed the octohedron with the 
 square base. By the application of planes 
 perpendicular to the horizontal axes, a four- 
 sided pyramid with a square base is formed, o, 
 and by the replacement of the terminal edges 
 of this prism, four-sided pyramids may be 
 formed on its base and summit. By this* pro- 
 perty, the square prisms and octohedrons are 
 distinguished from all modifications of the 
 cube, and octohedron of the regular system. 
 When the edge of a cube is replaced, the plane substituted for it gains 
 equally on the two surfaces, and hence, when one is effaced, the other 
 must be so also. But in the square prisms, the replacement may efface 
 the terminal plane, giving a four-sided pyramid, and yet the lateral 
 planes be but little encroached upon. The sides of the crystal, in this 
 system, are thus independent of the top or bottom, and may be mo- 
 dified, whilst the top and bottom remain unaltered ; tins never takes 
 place in the regular system, where there being no one side particularly 
 upper or lower, all modifications must affect all sides alike. 
 
 4. The right Prismatic System. In this system the three axes being 
 all unequal, the length, breadth, and thickness of the crystal may be 
 
 different from each other. Thus, in the octohe- 
 dron, p, formed by the application of planes, each 
 connecting the extremities of the three axes, the 
 three dimensions of the crystal, as in the figure, 
 which is the primitive form of sulphur, are unequal ; 
 the octohedron has a rhombic base, and by planes 
 which are inclined to the horizontal axes, and pa- 
 rallel to the vertical axes, a prism, with a rhombic 
 base, may be produced. This also, by combina- 
 tion of the two forms, may obtain pyramidal ter- 
 minations, as in some forms of native sulphur. 
 
Systems of Crystallization . 
 
 29 
 
 An important character of this system, which arises from there being 
 no necessary connexion between the two horizontal 
 axes, is, that the lateral edges may be alternately 
 modified in a different manner, or in other words, 
 that looking at the crystal, its back and front may 
 be differently affected from its sides. Of this an 
 example may be found in a common modification 
 of the sulphur octohedron given in figure q. 
 
 5. The oblique Prismatic System. Prom the manner in which the 
 crystals, belonging to this system, form, one of the oblique axes is ge- 
 nerally by much the most developed, and is taken as the principal axis. 
 The remaining axes, which are at right angles to eacli other, are taken 
 as horizontal, the principal axis making with them the acute angle, 
 which belongs to the peculiar body. 
 
 By means of planes which are inclined to all the axes, there is formed 
 the oblique rhombic octohedron, such as cha- 
 racterizes gypsum, (sulphate of lime) as in 
 figure r, and by means of planes which are 
 inclined to two axes, but parallel to the third, 
 an oblique rhombic prism may be formed, s. A 
 remarkable character of these crystals is, that from 
 the crossing of the axes and their independence of 
 each other, the front and back of the crystal may 
 be quite different in relation to the sides. The 
 crystals of sulphate soda, of carbonate of soda, of 
 borax, of sulphate of iron, and of feldspar, may 
 be taken as examples of the numerous forms deri- 
 vable from this system. 
 
 6. The doubly oblique Prismatic System. The axes are all unequal, 
 
 and all form acute angles with each other, and 
 it is hence indifferent which is taken as the 
 principal axis of the crystal. The conse- 
 quence is complete absence of symmetry 
 between any two surfaces of the crystal, ex- 
 cept such as, being at the ends of the same axis, are parallel to each 
 other. The complexity of crystals of this system is hence usually very 
 great. The simplest forms are the oblique rhombic octohedron, t, and 
 the oblique rhombic prism, formed by planes, inclined to all the axes, 
 or to two, and parallel to the third, respectively. The soda-feldspar 
 (albit) and sulphate of copper are examples of this system ; the octo- 
 hedron of this system is figured in the margin. 
 
30 Pseudomorphism. 
 
 It might be at first supposed that the assumption of these axes, or 
 lines round which we have supposed the crystalline particles to be regu- 
 larly arranged, was merely a geometrical fiction, by which the form of 
 the crystal might be more easily represented to the mind ; but such is 
 not the case. Evidence derived from a variety of sources agrees in 
 demonstrating, that this diversity of crystalline systems arises from fun- 
 damental differences in the laws of molecular cohesion, by which the 
 formation of the crystal is regulated, and that these axes which have 
 been so much alluded to, are real centres, the proportion and position 
 of which determine all the physical properties of the body. It is pecu- 
 liarly from the action of crystallized bodies upon light, that accurate 
 and extraordinary information has been obtained of their internal struc- 
 ture, and the discoveries that have been made in this department, were 
 the means of advancing the physical theory of light to its present, 
 almost perfect, state. 
 
 Substances may assume crystalline forms, which do not properly 
 belong to them, in many ways. Thus, a group of crystals being im- 
 bedded in a rock, they may, by the filtration of the water of springs 
 across the rock, be dissolved out, leaving a hollow mould of their form ; 
 and, subsequently, substances of another kind may be introduced into 
 this cavity, and, solidifying there, may simulate the external form of the 
 original inhabitant. But these are no more real crystals than a mass of 
 plaster of Paris, which has solidified in a hollow mould, and comes out 
 as an Apollo or a Venus, can be said to have so crystallized. By 
 cleavage, and by the operation of polarized light, the unsuited internal 
 structure is recognized, and the crystal is stated to have been merely 
 pseudomorphous. Another mode in which a body may come to have a 
 form not its own, is by remaining behind after the decomposition of the 
 substance which had really crystallized. Thus, when hydrated chloride 
 of copper, which crystallizes in fine green prisms, is carefully heated, 
 the water is expelled, and the chloride of copper remains dry, and of a 
 fine yellowish brown colour, in the original crystalline form, and with 
 the surfaces quite bright. The red iodide of mercury combines with 
 ammonia to form a substance which crystallizes in long prisms of a 
 snow-white colour ; these, when exposed to the air, lose all ammonia, 
 and the iodide of mercury remains behind, pure, and of a brilliant red, 
 but with the perfect figure, and bright, smooth surfaces, and sharp 
 angles, of the body originally crystallized. 
 
 It has been thought that the presence of foreign bodies in a solution, 
 even where they did not enter into combination with the substances 
 which crystallized from it, might modify their form. Thus, when 
 common salt crystallizes in a solution of urea, it is deposited in octo- 
 
Modifications of Forms. 31 
 
 hedrons, and by dissolving alum in a solution of urea, it may be ob- 
 tained crystallized in cubes. But in this case, the substances which 
 crystallize are no longer common salt nor alum, but the one, a 
 combination of urea with common salt, and the other, a basic alum 
 produced by the mutual decomposition of the urea and the alum. The 
 presence of a trace of lead or tin, in a large quantity of iodide of po- 
 tassium, has been supposed to modify its form ; but it is more likely, 
 that the mechanical presence of an impurity of the kind may be sup- 
 posed to produce a tendency to macled crystals, and thus the external 
 form be somewhat altered, although the true constitution of the crystal 
 may remain the same. 
 
 Certain bodies, when they exist together in solution, may, however^ 
 remarkably modify each other's form, by crystallizing together so com- 
 pletely, that every individual crystal shall contain a quantity of each. 
 Yet those bodies will not have combined chemically with each other, for 
 the quantity of each present, in each crystal, is quite indefinite ; they 
 are mixed together mechanically in the crystals, and hence the form of 
 the actual crystal is intermediate between those, which the separate 
 bodies should have had, if they were pure. In order that bodies may 
 so crystallize together, it is not only necessary that they should be of 
 the same crystalline system, but the crystalline forms must resemble one 
 another very closely in all their angles and sides. Thus, not only will 
 iodide of potassium and sulphate of soda, which belong to different 
 systems of crystallization, not crystallize together ; but glauber salt and 
 carbonate of soda, which do belong to the same system, will not crys- 
 tallize together, because the relations of their angles and sides being 
 completely different, they cannot mix together so as to form an uniform 
 solid. But sulphate of zinc and sulphate of magnesia belong not 
 merely to the same crystalline system, but they are almost identical in 
 their figures ; the eye cannot make any distinction between their crys- 
 tals ; and hence when a crystal is being formed in a solution containing 
 these two bodies, the molecular and crystalline forces being the same 
 for both, they concur in the building of the crystal without interfering 
 with each other. Hence, as there is a very small difference between the 
 angles of the rhombic prisms of the two salts, the one being 90 30', 
 and the other 91 8', if they be mixed in equal proportions in the crys- 
 tal, its angle must be 90 49'. Carbonate of lime and carbonate of 
 magnesia are like the sulphates of zinc and magnesia, almost identical in 
 crystalline form, and they exist in nature mixed together, forming the 
 dolomite or magnesian limestone. The quantity of carbonate of lime 
 is to the quantity of carbonate of magnesia as 50 '6 to 42'8, and as the 
 angle of the rhomb of carbonate of lime is 105 4'; and that of car- 
 
32 Isomorphism. 
 
 bonate of magnesia is 107 40' ; the angle of the mixed crystal is found 
 by multiplying the angle of each constituent by its quantity, adding 
 these products together, and dividing by the quantity of the mixture, 
 and the result is 106 15', the angle of the rhombic crystal of mag- 
 nesian limestone. 
 
 The peculiarity of crystallization which such bodies possess may 
 be illustrated in another manner. Ordinary alum is a sulphate of 
 alumina and potash ; but there are a great variety of other double sul- 
 phates which crystallize in the same form, and which constitute a well 
 defined crystalline genus. If an octohedral crystal of common alum be 
 placed in a solution of the sulphate of alumina and ammonia, the crys- 
 tal augments in size by the addition of layers of that salt. If it be then 
 removed to a solution of sulphate of potash and peroxide of iron, it 
 acquires another layer; by a solution of sulphate of ammonia and 
 peroxide of iron, another still ; and by means of solution of the alums, 
 which consist of oxide of chrome united to potash or ammonia, with 
 sulphuric acid, the crystal may grow to a still greater size. The chemi- 
 cal constituents of the crystal may thus vary, but it retains its form ; 
 the number of equivalents of chemical substances contained in it remains 
 also the same, although they may not remain identical in nature. The 
 potash and the ammonia on the one hand, the oxide of iron, the 
 alumina, and the oxide of chrome upon the other, agree in producing 
 the same crystalline arrangement of particles ; in impressing upon their 
 compounds, with the same bodies, the same crystalline form. Bodies 
 so related are called isomorphous. Oxide of zinc and magnesia are iso- 
 morphous; barytes and oxide of lead are isomorphous; whilst lime is 
 a dimorphous body, being in one form isomorphous with magnesia, and 
 in the other with oxide of lead. Isomorphous bodies are remarkably 
 similar in their chemical properties ; they follow generally the same laws 
 of combination, and hence, as shall be further shown in the chapter on 
 chemical affinity, the principle of isomorphism has been of the highest 
 importance, in developing the true relations of chemical substances to 
 each other, and the intimate connexion of the forces which produce the 
 chemical combination, and those which direct the crystalline arrange- 
 ment of the particles of bodies. 
 
 It was, some time ago, considered an important question, whether 
 the ultimate particles of bodies had the same figure as their primary 
 crystalline form, whether they were globular or ellipsoidal. The law of 
 isomorphism was considered, at one time, to result from the ultimate 
 particles of those bodies, being themselves isomorphous, and hence, 
 when entering into similar combinations, giving to them also the same 
 form. It was at another time referred to the principle, that in any 
 
Goniometers. 33 
 
 chemical combination the crystalline 'form was determined by the number 
 of molecules or atoms present, and was independent of their nature. 
 Neither of these ideas has been found sufficient ; but the complete dis- 
 cussion of the relations of the isomorphous bodies will be found in a 
 future chapter. 
 
 The angular dimensions of crystals being thus the measures by which 
 they are recognized and compared with one another ; the instruments, 
 by means of which their measurement is effected, require a few words' 
 notice. They are called goniometers, (yovtoff an angle, psrgu I measure). 
 The simplest form consists of a semicircular scale of degrees attached 
 to a pair of blades, which, crossing each other at the centre, allow of 
 the crystal being adjusted exactly to their edges, and then show the 
 value of the angle, by the number of degrees intercepted on the scale, 
 between the blades. For all purposes requiring accuracy, the goniome- 
 ter of Wollaston must be applied. In it, the angle of the crystal is 
 determined, by measuring the number of degrees through which it is 
 necessary to turn the crystal, in order that two rays of light, reflected 
 successively from the two surfaces, including the angle, may be in ex- 
 actly the same direction. To the adoption of this principle of measure- 
 ment we owe almost all the great advance that has been lately made in 
 the relations of the crystalline forms of bodies to their chemical and 
 molecular constitution. 
 
 In all that has formed the subject of the chapter which has now 
 closed, the forces brought into play, and the effects which were pro- 
 duced by means of their action, were not such as to involve the princi- 
 ple upon which all purely chemical phenomena are based, the existence 
 of a variety of elements. The laws of cohesion, from its simplest 
 action in a liquid to its complex manifestation in a doubly oblique crys- 
 tal, might have existed in nature, and, being studied, make a part of 
 science, independent of any consideration of true chemical force, 
 although serving most usefully for the identification of chemical sub- 
 stances, and capable of modifying the circumstances of their mutual 
 action, in an eminent degree. 
 
CHAPTEE II. 
 
 OF THE PROPERTIES OF LIGHT AS CHARACTERIZING CHEMICAL 
 SUBSTANCES. 
 
 I SHALL not attempt to enter into the details of the history of the me- 
 chanical properties of light, as they constitute one of the most purely 
 mathematical of the physical sciences, and have but indirectly a relation 
 to chemical phenomena : a short notice of these properties is, however, 
 necessary, in order that the means of recognizing chemical substances 
 may be fully given. 
 
 Light, emanating from any luminous body, moves in straight lines ; 
 the smallest portion of it which can be admitted through an aperture 
 being termed a ray. When a ray of light falls upon the surface of a 
 body, it is either bent back again or it passes into the substance of the 
 body ; the bending back is termed reflection, and is regulated by the 
 law, that the angles of incidence upon the surface, and of reflection 
 from it, are always equal. It is thus that the images are formed in a 
 looking-glass ; for we see objects in the direction in which the ray of 
 light arrives at the eye, and hence we judge the image to be as much 
 behind the mirror, as the object is before it. 
 
 When the ray of light has passed into the substance of the body, it 
 may be absorbed, in which case the substance, not sending any light to 
 the eye, appears completely black, or is, rather, totally invisible, except 
 by contrast with some other body placed behind it ; or the light may be 
 transmitted, in which case the body is said to be transparent, as the 
 light may arrive at the eye, after passing through the substance. Bodies 
 which do not transmit light are said to be opaque ; but there are 
 two kinds of opacity, that of blackness, where the light which falls 
 upon the object is totally lost by being absorbed, and that of whiteness, 
 where the light is reflected, and, we can see the object itself, although 
 we cannot see anything through it. Where, in an opaque body, the 
 light is partly reflected to the eye, and partly absorbed, there arises the 
 diversity of colours which opaque bodies may possess. 
 
Nature and Properties of Light. 35 
 
 When the ray of light is neither totally reflected from the surface, 
 nor lost within the substance of the body, but passes through it, it is 
 refracted, that is, its direction is changed, and, if its path be repre- 
 sented by a line, it is broken at the surface of the medium, and hence 
 the name. It is thus, that an oar, partly immersed in water, appears 
 broken at the surface. Any substance, through which light is moving, 
 is termed a medium, and the refraction occurs at the limiting surface of 
 the two media, as air and water, air and glass, though not to the same 
 degree as if the light had passed, into the most refractive medium, 
 directly from an empty space. This refractive power is of importance, 
 as a characteristic property of bodies ; but to the chemist it is specially 
 of use in the study of crystallized bodies, and it is hence with reference 
 to the principles of the molecular structure of those substances, already 
 noticed, that the refraction of white light shall be examined. 
 
 This reflection, absorption, or refraction of the luminous rays which 
 fall upon the surface of a body is, however, in no case absolute and 
 simple. All bodies reflect some light, and there are none which allow 
 light to pass through them, without its undergoing some absorption. 
 In general, light incident upon a body is divided into three unequal 
 parts, of which one is reflected, another absorbed, and the third trans- 
 mitted, and the nature of the body determines which action shall be 
 most powerful. 
 
 In uncrystallized bodies a ray of light, in passing from a rarer to a 
 denser medium, is generally bent towards a line perpendicular to the 
 surface of the medium, and in passing from a denser to a rarer medium, 
 the refraction is from the perpendicular. In this case, the law of refrac- 
 tion is such that, the sines of the angles of incidence and refraction are 
 to each other, in a constant proportion, no matter how the direction of 
 the incident ray may change, and the number which expresses this ratio 
 is called the index of refraction. 
 
 The velocity with which light is transmitted, is exceedingly great ; 
 the light of the sun arrives at the earth in eight minutes, being at the 
 rate of 195,000 miles in a second. This, however, is but the mean 
 velocity of the coloured lights which a solar ray contains, for these differ 
 in velocity, those which are least refrangible being transmitted with the 
 greatest quickness. The velocity of light is changed when it passes 
 from one substance to another, and it is this sudden change which pro- 
 duces the refraction. In general, the denser the medium the more is 
 the velocity diminished ; and it was by the experimental proof of this, 
 that one of the most triumphant testimonies, in favour of the undula- 
 tory theory of light was found. 
 
 The refractive power of a body, is not connected with its chemical 
 
36 Simple and Double Refraction. 
 
 constitution, in any positive manner ; but inflammable substances are, 
 generally, possessed of high refractive powers. It was this fact which 
 led Newton to the celebrated prophecy, that the diamond should 
 be combustible, and that water should possess an inflammable 
 constituent ; but many bodies of high refracting powers are not at all 
 combustible. 
 
 The refracting power, as measured by the refractive index, is given 
 for some of the more remarkable bodies in the following table : 
 
 Realgar, 
 Octohedrite, 
 Diamond, . 
 Nitrate of lead, . 
 Phosphorus, 
 Sulphur, 
 Flint glass, from 
 to . . 
 
 2-549 
 2-500 
 2-439 
 2-322 
 2-224 
 2-148 
 2-028 
 1-830 
 
 Garnet, 
 Oil of cassia, 
 Plate glass, 
 Oil of turpentine, 
 Water, 
 Chlorine, . 
 Air, . 
 Vacuum, . 
 
 
 r 
 
 815 
 614 
 542 
 L-475 
 336 
 000772 
 000294 
 000000 
 
 In uncrystallized bodies, the molecular arrangement being irregular 
 and indefinite, the action upon light is the same in every direction, and 
 hence, a ray of light undergoes, when passing from air into water, or 
 glass, simple or ordinary refraction ; it is bent out of its path by an 
 angle which depends upon the angle of incidence, by the law of the 
 proportionality of their sines. In bodies which crystallize in the regu- 
 lar system, where there are three precisely similar axes, the molecular 
 constitution, although subjected to definite laws, must be the same in 
 every direction, and hence, a ray of light will be acted upon, in such a 
 crystal, in the same manner, no matter in what direction it may go. 
 Hence, in crystals of the regular system, there is only ordinary refrac- 
 tion and a single image. 
 
 When a ray of light passes, however, into a crystal of the rhombo- 
 hedral system, it is differently acted upon, according to the part of the 
 crystal it passes through. If it pass along the principal axis, it is 
 equally related on all sides to the crystalline forces, and hence, as in the 
 crystals of the regular system, there is only a single refracted ray. 
 But, if the light pass in any other direction, it is divided into two por- 
 tions, one of which is refracted according to the ordinary law of the 
 sines, whilst the other, following a totally new law, is termed the ex- 
 traordinary ray. The angle which these two rays make with each other, 
 increases according as the path of the incident ray is farther from the 
 principal axis, and when the light falls perpendicular to the sides of the 
 prism, and hence to the principal axis, the divergence of the two re- 
 fracted rays, is the greatest possible. In the square prismatic system, 
 the same peculiar action upon light exists ; when a ray of light passes 
 along the principal axis of the crystal, it undergoes simple refraction, 
 
Action of Crystals on Light. 37 
 
 according to the ordinary law, but in any other direction, the ray is 
 subdivided into two, of which one is refracted in the ordinary way, and 
 the other foUows a new and ]^culiar law. 
 
 The existence of double refraction, and the change in its amount, 
 according to the direction in which the light passes through the crystal, 
 may easily be observed. If a round dot be marked with ink, on a 
 sheet of paper, and a rhomb of calc-spar be laid upon it, the dot will 
 appear double, and on moving the crystal round, one image will be 
 seen to revolve round the other. By changing the position of the eye, 
 the distance between the two images of the dots will be found to 
 change ; it will be greatest when the eye is in a line connecting a solid 
 angle and the centre of the opposite plane, but to efface the double 
 image, and obtain single refraction, new surfaces would require to be 
 cut perpendicular to the principal axis. In a natural crystal, there are, 
 therefore, always two images of an object seen through it. 
 
 In the remaining three classes of crystals, where the rhombic octo- 
 hedron, whether right or oblique, gives the predominant character to 
 the forms, the existence of a molecular constitution, regulated by the 
 same cause as the external figure, is displayed in a peculiarly striking 
 manner. There is no longer a single line, in the crystal, in which ordi- 
 nary refraction alone occurs, but there are two such lines, or axes of 
 simple refraction. These axes, however, do not now coincide with the 
 principal crystalline axis, as was the case when there was only one, but 
 their position is so dependant on that of the crystalline axes, as to show 
 that they are the resultants of the forces which emanate from those, and 
 which govern ah 1 the molecular actions of the crystal. If the ray of 
 light does not pass exactly along one of these axes, but at some distance 
 from them, it is divided into two rays, and of these rays, both follow 
 new and peculiar laws of refraction, the proportionality of the sines 
 being totally abandoned. The real distinction of the crystalline systems 
 is thus completely proved, from the existence of these remarkable optical 
 properties, by which they are characterized, and so perfect is this dis- 
 tinction, that in cases where the external form and cleavage would lead 
 us totally astray, the optical properties of the body may show us its 
 true crystalline position. Thus the mineral boracite (borate of mag- 
 nesia) crystallizes in cubes, which were remarkable, however, for an 
 anomalous replacement of the opposite solid angles, by triangular 
 planes. When, however, boracite was optically examined, it was found 
 to possess double refraction, and to appear cubical, only from the 
 accidental circumstances of its rectangular axes being equal to each 
 other. 
 
38 
 
 Chromatic Analysis of Light. 
 
 Violet . 
 Indigo . 
 Blue . 
 Green . 
 Yellow 
 Orange 
 Red 
 
 When a ray of white light, s, P, admitted into a darkened room 
 through an aperture, H, passes into a refracting substance a, A, B, c, 
 whose surfaces are parallel, its path after refraction is parallel to its ori- 
 ginal course, and the ray continues white ; but if the surfaces of the 
 refracting medium be not parallel, if it be a prism, A, B, c, the ray 
 of white light is separated into a number of rays of light, of different 
 colours, and of different refrangibilities as at g, and if it had been de- 
 rived from the sun, in place of a round white image, P, there is formed 
 a series of solar images of different colours which, overlapping each 
 other, produce a long band, which is termed the prismatic spectrum or 
 image, of the sun. The order of colours is the same as that seen in the 
 rainbow, thus, commencing with the rays of greatest refrangibility ; 
 violet, indigo, blue, green, yellow, orange, and red ; the length of the 
 spectrum, and the space occupied by each colour, varying with the 
 nature of the refracting body, according to what is termed its dispersive 
 power. White light is, therefore, not a simple, but a highly complex, 
 phenomenon, consisting of impressions made simultaneously on the eye, 
 by the lights of these various colours. This may be verified by experi- 
 ments of very simple performance : if a circular disk be painted with 
 the colours of the spectrum, in segments proportional to the spaces 
 which each colour occupies, in the length of the spectrum, and then be 
 made to revolve rapidly on a central axis, the eye loses the sensation of 
 the individual colours, and an uniform greyish white tinge is produced : 
 if we had colours as perfect as those of pure solar light, their reunion 
 should form pure white, and this actually may be produced by receiving 
 the spectrum on a lens, by which all the coloured rays are brought to 
 bear upon a single point, the focus, where reproduction of the original 
 white light takes place. 
 
 Herschel has recently discovered, that there exists in the spectrum, 
 beyond the limits of the violet rays, other rays of a still higher refran- 
 gibility, and of a colour which he proposes to term, lavender. This 
 lavender light cannot merely be a weaker form of violet light, for on 
 
Composition of White Light. $9 
 
 concentrating it by means of a lens, it remains still unaltered, and 
 appears to have no tendency to assume a violet tinge when it becomes 
 more intense. If this proposal be adopted, there are then eight pris- 
 matic colours, and although some peculiarity of vision, with regard to 
 colours, may cause a difference of opinion, yet the evidence obtained 
 by Herschel, of the real existence of simple lavender coloured light, 
 appears to be satisfactory. 
 
 Of the seven prismatic colours, there are four which cannot be con- 
 sidered as simple lights, but as being formed by the mixing of rays of 
 two different colours, having the same refrangibility : these are orange, 
 green, indigo, and violet ; the first being the mixture of the superposing 
 extremes of the red and yellow, the second of the yellow and blue, and 
 the third and fourth of blue with red remaining in excess. There is, 
 in fact, blue, red, and yellow lights spread over every portion of the 
 spectrum, and, if they were so in equal quantities, the spectrum should 
 be white, and we could not have any decomposition of light by refrac- 
 tion ; but, although there are blue rays of every degree of refrangibility, 
 yet the larger proportion of them have a refrangibility greater than those 
 of any other colour, and they are hence collected nearer the upper ex- 
 tremity of the spectrum. A portion of red light is spread also over 
 the whole surface, but the majority of the red rays, having low refran- 
 gibility, are thrown to the opposite extremity, whilst the great propor- 
 tion of the yellow rays, having a mean refrangibility, occupy the centre. 
 In every portion of the spectrum there is, therefore, mixed blue, red, 
 yellow, and hence white light ; but where these simple lights prevail 
 the colours of the spectrum are produced, and where two are present in 
 excess, over the quantities which form white light, the secondary 
 colours, orange, green, indigo, and violet are formed. 
 The intensity of these spectra of simple light in 
 each portion of the prismatic spectrum is represented 
 in the figure by the distance of the curved lines, 
 R, Y, D, from the ground, M, N. Where the red 
 rises beyond the yellow and blue, the red space of 
 the spectrum is produced; where the curve of the 
 yellow light prevails, the space is coloured yellow, 
 and similarly in the blue ; at the point where the 
 curves of the red and yellow meet, the tint is orange ; 
 where the yellow and blue are equal, the colour pro- 
 duced is green ; and where the red and blue are both in excess over the 
 intermediate yellow, there is violet. 
 
 This idea of the constitution of the solar spectrum, leading to the 
 remarkable and unexpected consequence that there may be wliite light 
 
40 Colours of Chemical Bodies. 
 
 unalterable by the prism, its coloured rays having ah* the same degree 
 of refrangibility, was deduced by Brewster, from experiments on the 
 absorbing power of coloured bodies. If a ray of white light be incident 
 upon a glass coloured red by suboxide of copper, it is decomposed in 
 passing through it, the yellow and blue lights being intercepted or ab-. 
 sorbed, and the red rays alone being transmitted. A glass does not 
 possess this property of absorbing certain kinds of light, because it is 
 coloured, but it appears coloured to our vision because it acts so upon 
 white light. The colours so given to glass are of great importance from 
 the use which is made of them for ornamental purposes in the arts ; but 
 they afford also to the chemist one of the most delicate and most certain 
 means of detecting many metallic substances, thus : 
 
 Cobalt is known by colouring glass blue. 
 Nickel ,, ,, orange. 
 
 Chrome and vanadium 
 
 Copper 
 
 Iron ,, 
 
 Manganese 
 
 Silver , , 
 
 Gold 
 
 green. 
 
 green or red. 
 
 yellow or green. 
 
 purple. 
 
 yellow or orange. 
 
 crimson. 
 
 And these are not the only cases in which colours are produced. 
 
 The colours of chemical compounds are so varied, that there cannot 
 be laid down any principle by which they could be arranged : thus, lead 
 forms with other simple bodies compounds which are brown, or red, or 
 yellow, or white ; mercury has a still greater range. There are, how- 
 ever, certain general facts worth bearing in mind, in which classes of 
 bodies, to a certain extent, are characterized by colour : thus, the ordi- 
 nary compounds of copper are usually green or blue; those of nickel, 
 green ; those of cobalt, pink or blue ; those of chrome, green or 
 purple. A singular property of certain bodies consist in what is termed 
 dichroism, that is, when seen by light which has passed in different 
 directions, they appear of different colours ; which are often comple- 
 mentary, or such as, when mixed together, should form white light. 
 This dichroism occurs only in crystals which refract doubly, and in 
 which the absorption takes place unequally along the two refracted rays. 
 
 The colours of natural bodies, seen by transmitted light, depend 
 thus upon the analysis which they effect of the light incident upon them, 
 and of which they absorb one portion and transmit another. Where 
 the object is seen by reflected light, its colour is generally different 
 from that given by transmitted light, for it frequently reflects, in con- 
 siderable quantity, the light which it does not transmit. Thus, solution 
 of litmus, when seen by transmitted light, is of a rich reddish purple, 
 but, seen by reflected light, of a fine, pure blue. In general a portion 
 of the light is reflected from the second surface, tinged like the trans- 
 
Polarization of Light. 41 
 
 rnitted portion, which, mixing with that properly reflected at the first 
 surface, modifies its colour. The transmitted and reflected lights are 
 sometimes truly complementary ; thus, sea water, seen by reflection, is 
 of a fine green, but the light which it transmits is pink. 
 
 When a ray of light is reflected from any surface at a particular angle, 
 which is for glass 56 45', and for water 53 II 7 ; it acquires peculiar 
 properties which it had not previously possessed, and is said to be pola- 
 rized. If the ray be then made to fall upon a second reflecting surface, 
 the effect varies according to the position of the plane of the second 
 reflected ray. The reflection, if it be in the same plane as the first, is 
 complete, but if it be at right angles to the first there is no light re- 
 flected : in intermediate positions the quantity of light reflected varies 
 according to the angle which the second makes with the original plane. 
 Light is thus said to be polarized by reflection. In all cases of reflection 
 there is some of the light thus modified, for, although the angles above 
 mentioned are those at wliich alone the polarization is complete, at all 
 other angles the light reflected is partially polarized in a degree, accord- 
 ing to its deviation on either side from the proper angles. 
 
 Polarization may be effected by various other means, as by refraction 
 or absorption. Even in ordinary refraction some of the light trans- 
 mitted is polarized, but it is mixed with so much ordinary light that its 
 properties are obscured : however, if the same quantity of light be 
 refracted often it may be polarized completely : and hence transmitting 
 a ray of ordinary light, at a certain angle, through a pile of parallel 
 glass plates, is a usual mode of polarizing it. In double refraction, 
 the polarization of the refracted b'ght is perfect, and the two emergent 
 rays are found to be polarized in planes at right angles to each other. 
 If these proceed together to the eye, they mix again, and thus recom- 
 pose the orginal ray of common light ; but by contrivances, such as in 
 NichoFs prism, one may be turned aside or absorbed, and then the 
 other used. In polarizing light, by absorption, the mineral tourmaline 
 is generally used; this is a doubly refracting substance, of such a 
 nature that it absorbs completely one refracted ray and transmits the 
 other. It therefore gives only a single image of any object, but this 
 image is formed by light completely polarized. If two pieces of tour- 
 maline be laid together, and that the direction of their crystalline axes 
 be the same in both, they act similarly upon the light, and, the same pola- 
 rized ray being transmitted by both, the brightness of the image is almost 
 the same with the two as with only one ; but if they be placed with 
 their crystalline axes at right angles to each other, the ray that is trans- 
 mitted by the first is absorbed by the second, and no light can pass. If 
 a ray of light be polarized by reflection or refraction, it is known that 
 
42 Action of Crystallized Bodies. 
 
 the polarization has been complete when the ray is totally absorbed by a 
 tourmaline, the axis of which is perpendicular to the plane of polariza- 
 tion of the ray. 
 
 When a ray of light so polarized passes through a doubly refracting 
 substance, it undergoes double refraction like a beam of ordinary light, 
 being divided into two rays, polarized in two new planes at right angles 
 to each other ; and when these two rays are received upon another pola- 
 rizing instrument, they are each divided into two portions, again at 
 right angles, which unite, as the planes of polarization coincide two 
 and two, and by their union produce some of the most beautiful pheno- 
 mena in optics; for, as in the doubly refracting substance through 
 which the ray has passed, the two portions move with different velocities 
 according to the refractive indices of the body, one issues in advance of 
 the other by a certain distance, and according to this distance, which 
 depends on the difference between the two refractive indices of the 
 body, a series of colours is produced, the most gorgeous that can be 
 imagined ; for every little difference of thickness a different colour is 
 shown ; with the same thickness the colour passes through all the pris- 
 matic tints, according as the plane of polarization of the ray of light 
 is altered, and thus the action, exercised upon the ray by the doubly 
 refracting substance, shows itself in a manner equally beautiful and 
 strange. 
 
 The apparatus used, in so employing polarized light to exhibit these 
 properties of bodies, consists in, first, a means of polarizing the ray, 
 which may be any of those before described, but which is generally a 
 flat plate of obsidian or blackened glass, by which a polarized reflected 
 ray is given. The substance to be examined is supported upon a frame, 
 in a plane perpendicular to the direction of the ray, or, if it be liquid, a 
 glass tube is filled with it, and being closed by plates of glass with pa- 
 rallel surfaces, it is so placed that the ray shall pass along the axis of 
 the tube. The ray, after emergence, is examined in order to detect the 
 modifications which it has undergone, by an apparatus termed the ana- 
 lyzing piece, which may be, where two images are required, a doubly 
 refracting prism, or, where only one, the NichoFs prism, a doubly re- 
 fracting prism in which one image is destroyed ; a tourmaline might 
 also be used, but the brown or olive colour, which tourmalines possess, 
 would deprive the phenomenon to be observed of much of the interest 
 it derives from the beautiful display of colours. 
 
 In nothing is the action of polarized light so interesting as in the 
 evidence which it gives of the internal constitution of crystals of the 
 different systems that have been described; for the real difference of 
 molecular arrangement in crystals belonging to these various systems, is 
 
On Polarized Light. 
 
 43 
 
 rendered still more remarkably distinct by the action which they exercise 
 .upon light in this peculiar state of plane polarization. If a ray of 
 
 polarized light pass along the principal 
 axis of a crystal belonging to the rhom- 
 bohedral, or to the square prismatic 
 system, and on issuing be examined by 
 means of an analyzing plate, the axis of 
 the crystal is seen to be surrounded by 
 a series of beautiful rainbow-coloured 
 rings, the centre being occupied either 
 by a cross which is alternately black and 
 white, according as the analyzing plate 
 revolves, as with calc, spar, fig. a, or a circular space which is occupied 
 successively by a series of colours, similar to those which form the rings, 
 as in quartz. 
 
 If the crystal belong to any of the more complex systems, and that 
 its optical axes be not much inclined to one another, there will be seen, 
 
 on transmitting a ray of polarized light 
 along the crystalline axis intermediate to 
 the two, a double system of rings, which 
 uniting, form a very beautiful curved 
 figure, such as is represented in figure 
 b, which is the phenomenon as seen with 
 nitre. The curves are crossed by two 
 bands, black or white, according as the 
 analyzing plate revolves, but which, when 
 the crystal is turned round on its prin- 
 cipal axis, open out, revolving each on 
 its axis, A or B, and bend with the con- 
 vexity towards the centre of the figure. 
 In substances, as topaz and carbonate of 
 soda, where the axes make a large angle with each other, the complete 
 system of rings cannot be at once seen, and 
 only one-half, or the portion round one axis, 
 as in the case of topaz in figure c, is visible 
 in one direction. The angle of the axes in 
 topaz is 18 30', but in other cases, it may 
 be much greater ; thus, with green sulphate 
 of iron they are at right angles with each 
 other. 
 
 The physical production of these beautiful phenomena involves 
 optical principles too recondite to be here introduced. It is, for the 
 
44 Recognition of Molecular Structure. 
 
 purposes of the chemist, sufficient to say, that they arise from the 
 mutual action of the two rays, which are produced by the double 
 refraction of the crystal, and hence, if there be not double refraction, 
 there can be no colours produced. With crystals of the regular sys- 
 tem, there is consequently no such result, and hence, such crystals are 
 recognized by the complete absence of coloured rings. 
 
 The optical properties of the different systems of crystallization may 
 be thus summed up. 
 l._Kegular system. Single refraction. 
 
 Double refraction with one Simple system of rings 
 axis. by polarized light. 
 
 4 __ Right prismatic sys-"^ 
 
 C 
 
 tern 
 5._Oblique prismatic sys- [Double refraction with two ' Double system of rings 
 
 t em m . f axes. I by polarized light. 
 
 6 Doubly oblique pris- I 
 
 matic system J L 
 
 When crystals form in a crowded or confused manner, it frequently 
 happens, that not merely are their surfaces modified in a complicated 
 way, but that several crystals become soldered together so completely, 
 as to simulate a single form which does not belong to the substance of 
 which the crystal is composed. These crystals are called macles, or twin 
 or hemitrope crystals. Some bodies have a remarkable tendency to 
 crystallize in this way ; thus, sulphate of potash had been long consid- 
 ered as crystallizing in six-sided prisms, terminated by six-sided pyra- 
 mids, and such crystals of it occur with almost exactly the proportions 
 of the rhombohedral system ; but by optical examination, this figure 
 was found to be composed of three or six of the true crystals, which 
 are right rhombic prisms of the fourth system. These being laid 
 together, form, by their angles exactly joining, a six-sided prism, but 
 when tested by polarized light, they show, in place of the system of 
 rings, which a true crystal should produce, the tesselated structure of 
 the figure. In many cases, the agglutination 
 of the crystals is less complete, and irregular 
 figures, with the sides channelled by the imper- 
 fect joints, are found. A substance which illus- 
 trates remarkably this tendency to the macled 
 form, is the mineral analcime, which is termed 
 also cubizite, from its forms belonging most 
 perfectly, so far as external characters go, to the regular system. It 
 has, however, no distinct cleavage planes, and refracts doubly. When 
 examined by a ray of polarized light, the cube of analcime gives a most 
 
By means of Polarized Light. 45 
 
 beautiful appearance. The diagonals of each surface become occupied 
 by lines, which are alternately black and white, according as the analyser 
 is made to revolve, and in the intervening triangular spaces the richest 
 colours of the rainbow succeed one another, according to the optical 
 
 laws. This crystal is, therefore, made up 
 of a great number of other crystals be- 
 longing to some one of the more complex 
 systems, but its structure is so extraor- 
 dinary, that the determination of the form 
 of its real crystal has been as yet impossi- 
 ble. In this instance, and in that of 
 boracite, already noticed, the optical pro- 
 perties have been the means of showing 
 the true nature of bodies, which, from their external figure, should 
 otherwise have been ranked among those which crystallize in the forms 
 of the regular system. 
 
 It has been noticed as a general character of the crystals of the 
 rhombohedral and square prismatic systems, that by the analysis of a 
 beam of polarized light, transmitted along the principal axis, there is 
 seen a system of coloured rings, traversed by a cross, alternately black 
 and white, as the analysing plate revolves, but further, that in the case 
 of quartz, the cross is not produced, the central space being occupied 
 in succession by all the prismatic colours. Even in quartz, there have 
 been found two modifications of this property, with one the analysing 
 plate must be turned from right to left, to obtain the spectral colours, 
 from red to violet, but with the other, the rotation must be in the oppo- 
 site direction, to show them in the same order. The molecules of the 
 quartz cause these colours to appear along the axis, by turning the 
 plane of polarization of each colour round in a different degree, and 
 thus opening out, into a fan shape, those combined lights, w r hich had 
 previously affected the eye only as white or black. This faculty does 
 not depend upon the manner of arrangement of the particles of the 
 quartz ; it involves the chemical nature of the molecules, and, although 
 some observations appeared to connect it with the crystalline structure, 
 it is now fully established to be independent of it. In fact, this pro- 
 perty of circular polarization, as it is termed, belongs to certain bodies, 
 independent of their arrangement, and even in many cases accompanies 
 them when they enter into combination. It is even found in liquids, 
 particularly the volatile oils, and when oil of turpentine is converted in- 
 to vapour, its molecules preserve unaffected their rotative power. Its 
 existence is, however, subjected to remarkable anomalies ; thus, when 
 oil of turpentine combines with muriatic acid, and forms artificial cam- 
 
46 Circular Polarization of Light. 
 
 phor, it retains its power of rotation ; but when the artificial camphor 
 is decomposed, and the oil of turpentine got back again, its power of 
 changing the plane of polarization of the ray of light has totally disap- 
 peared. 
 
 In cases, therefore, where bodies exhibit this action upon light, 
 their power of rotation becomes an important numerical fact in their 
 descriptions, and it may be measured by the angle through which a 
 certain thickness of the body is capable of moving the plane of pola- 
 rization of a ray of homogeneous light, such as the pure red, given by 
 glass coloured by sub -oxide of copper. It may also be expressed, when 
 white light is used, by the angle at which the pure violet is produced, 
 and the direction of rotation is expressed by an arrow, turned either to 
 the right or left, according as it is necessary to make the analyzing 
 crystal revolve to the one or the other side. Thus, the rotative power 
 of oil of turpentine, contained in a tube six inches long, is for red light. 
 450^ ssand of oil of lemons, in the same length, 84ea >. The ro- 
 tative power of quartz is about 68.5 times greater than that of oil of 
 turpentine. This property is beautifully applied to trace the changes* 
 which occur during the saccharine fermentation : a solution of starch 
 possesses a highs**. power, but it gradually changes into the sugar of 
 
 grapes, the rotative power of which is* 3. Hence, the action of the 
 
 starch, when fermentation has commenced, rapidly diminishes, until 
 
 there is so much sugar formed, that the & *- and * exactly bal- 
 
 lance, and the solution is totally without action upon a polarized ray ; 
 after that time the quantity of sugar still increasing, the rotation be- 
 comes * aand increases until all the starch has been decomposed. 
 With such a solution, knowing the total quantity of starch originally 
 dissolved, the measure of its rotative power enables the quantity of 
 sugar present to be at once calculated. The juices of plants which 
 contain sugar, as the beet-root, the maple, the sugar cane, may be ex- 
 actly valued by a simple determination of their rotative power, com- 
 pared with their specific gravities. This property of the circular pola- 
 rization of a ray of light, which at the first aspect might appear so far 
 removed from proper chemical inquiry, or useful application, becomes 
 thus an instrument from which the distiller or sugar boiler may every 
 day derive advantage ; and when we come to discuss the means by 
 which we endeavour to learn the internal constitution of bodies, pro- 
 duced by the chemical affinity, we shall find that the light which ordi- 
 nary polarization throws upon the internal mechanical structure of the 
 crystal, is not more brilliant than that which we obtain of the arrange- 
 ment of the chemical constituents by their circular polarizing power. 
 
 Some specimens of quartz appear destitute of this rotative power : 
 
Magnetic Relations of Light. 47 
 
 the purple quartz, amethyst, is generally so, and gives with polarized 
 light, the ordinary black cross. But these peculiarities of quartz are 
 related to their crystalline arrangement. Thus, in those specimens 
 which possess rotative power, the solid angles of the pyramid (k, page 
 27,) are generally replaced by planes which are unequally inclined to 
 the axes, and where these planes are present, the direction of the rota- 
 tion can be foretold, it being to the right or to the left, according as 
 these unsymmetrical faces are inclined. Such crystals are called plagi- 
 Jiedral ; and in the cases where no such faces can be traced, the rotative 
 power is generally absent, which then arises, as is remarkably evident 
 in amethyst, from the crystal being formed of separate crystals rolled up 
 together, and as these may possess opposite rotations, and so neutralize 
 each other, the action on light should be like that of calcareous spar, 
 which has no rotative power. Such crystals are truly macles ; and 
 hence the circular polarization may show a still more intimate crystalline 
 arrangement than could be detected by light in its ordinary polarized 
 condition. 
 
 With such an example, it was not difficult to conclude, that the 
 power of rotation depended on the crystalline arrangement, particularly 
 as quartz, in all its uncrystallized conditions, is devoid of all rotative 
 power, and accordingly, until the discovery of the power of rotation 
 in liquids, and that this property was found to accompany the molecules 
 of the body through all stages of aggregation, it was considered to 
 have its origin in the mechanical structure of the body ; but we must 
 now invert the argument, and infer that the difference of rotative power 
 in right-handed and left-handed quartz, does not result from the differ- 
 ence of crystalline arrangement, but that this last is caused by actual 
 difference of properties in the molecules themselves, of which the most 
 remarkable is detected by the opposite actions upon light. 
 
 The very remarkable discovery has been recently made by Faraday, 
 that by the action of a magnet, or of a tranverse current of electricity, 
 the plane of polarization of a ray of light may be made to revolve as it 
 is by quartz or oil of turpentine. As this physical law will be described 
 more fully when speaking of magnetism, it will suffice here to state, 
 that the direction of rotation is always the same as that of the current 
 of electricity, in the direction of the magnetic curves emanating from 
 the north pole of the magnet, which passes round the ray, or which 
 may be considered to give power to the magnet which acts upon the 
 ray. This action is exerted specially on the molecules of the material 
 through which the ray passes ; but it is quite different from and inde- 
 pendant of ordinary rotating power. Thus, a tube full oil of turpen- 
 tine, enclosed in a coil carrying a galvanic current, has rotative force 
 
48 Wave Theory of Light. 
 
 generated by the magnetic action, but of a degree and direction de- 
 pending upon the electricity, and not upon its own power of acting 
 upon light. 
 
 The impression of light was at one time considered to be produced 
 by a series of exceedingly minute particles, of a peculiar substance, 
 emanating from the sun and from burning or luminous bodies, and 
 which strike upon the eye. This idea has been, however, now almost 
 totally abandoned, and all the phenomena are considered to arise from 
 the vibrations of an exceedingly attenuated medium, thrown into waves 
 by luminous bodies of every kind, and which, filling all space, and 
 being diffused through the substance of the most solid bodies, and 
 occupying the spaces between their more substantial molecules, trans- 
 mits and modifies these vibrations, and confers upon substances trans- 
 parency or opacity, colour, and all other properties of acting upon 
 light winch they may possess. 
 
 This medium, or luminiferous ether, as it is termed, is supposed ca- 
 pable of vibrating in waves of different lengths, and from this difference 
 in length of wave arises the difference in colour of the light produced. 
 The shortest wave produces violet, the most refrangible light ; the 
 longest wave, red, the least refrangible light : the length of the wave 
 being, in all cases, inversely proportional to the refrangibility of the 
 light. The impression of the different colours arises, therefore, pre- 
 cisely as the impression of different sounds is produced, by a difference 
 in the length of the waves in the vibrating air ; the shortest wave, in 
 sound, giving the highest note, and, in light, giving the violet colour. 
 The actual length of these waves of light is extremely small ; for violet 
 light there are 57,490 in an inch ; for red, 39,180 ; the average of the 
 different colours being 50,000, and hence in white light there acts upon 
 the eye in every second 610,000,000,000,000 luminiferous vibrations. 
 
 In the case of doubly refracting crystals with one axis, that is, those 
 belonging to the rhombohedral and the square prismatic system, the 
 elasticity of the ether is supposed to be so far modified by the arrange- 
 ment of the molecules of the body, that the velocity of propagation of 
 the waves is more rapid in one direction, than in another at right 
 angles to it, and hence there are two refracted rays. In the three sys- 
 tems, the crystals of which have double refraction with two axes, the 
 elasticity of the ether is supposed to be different in each of three per- 
 pendicular directions, and hence neither refracted ray can follow the 
 ordinary law. It is thus, as has been already stated, that the classifica- 
 tion of all crystallized bodies in these systems is shown not to be an 
 arbitrary assumption, but a principle based upon our most decisive evi- 
 dence of molecular arrangement. 
 
Wave Theory of Light. 49 
 
 The rays of light derive some of their most remarkable properties 
 from the principle, that the vibrations are accomplished iii a direction 
 perpendicular to the direction of the rays. Thus, if we conceive a ray 
 of light, moving from north to south, the little vibrations which con- 
 stitute it are effected in a direction east or west, and in every other di- 
 rection equally perpendicular to its path ; and ordinary light is charac- 
 terized by the fact, that its vibrations are accomplished in every ima- 
 ginable plane. If we reduce these vibratory movements to a single 
 plane, the light becomes polarized, and is, then, in the condition for 
 dissecting the interior of crystallized bodies, and exhibiting the beauti- 
 ful illustrations of their structure, that have been already noticed. But 
 it would lead us too far away from our proper subject, to enter into the 
 description of polarizing apparatus, or even of its principles, in detail, 
 as the indication just given of its nature is sufficient. 
 
 Perhaps the most remarkable and the most important principle of the 
 theory of waves is, that two portions of light may act on each other so 
 as to interfere and produce darkness, though at another point they may 
 form light of double brilliancy. To effect this, it is only necessary they 
 should be in opposite states of vibration, that is, whilst the waves of one 
 ray should be rising up, those of the other should be falling down : 
 these motions then compensate each other, and the result is the same as 
 if no vibratory motion had existed, that is, as if no light had arrived at 
 the points where the rays met. It is only, however, when one of the 
 simple coloured lights is employed that actual blackness occurs, by the 
 mutual destruction of the rays : if white light be used there is produced 
 a brilliant series of prismatic colours ; for at the moment when the red 
 light is destroyed, the remaining blue and yellow form a bright green ; 
 when the yellow is destroyed, the red and blue produce a purple. Cases 
 of this kind of interference are extremely common : it is thus that the 
 coloured rings of crystals, and the colours of the soap bubble or oil film 
 are produced. The brilliancy of the plumage of birds, the lustre of 
 many minerals, as of opal and labradorite, arise from the interference 
 of the portions of light which after reflection thus act on each other. 
 
 Under ordinary circumstances light is always associated with heat ; 
 the sun, the source of warmth to our globe, being also the natural ori- 
 gin of light : and in most cases where light is artificially produced, it is 
 associated with heat, which is also capable of being transmitted in a ra- 
 diant form. It was, indeed, once considered, that at certain tempera- 
 tures heat became converted into light, and that the colour of the light 
 depended on the degree of heat ; a body, when first rendered luminous 
 by being heated, emitting a dull red light, which gradually becomes 
 brighter as the temperature rises, until at the highest degree of heat the 
 
50 Phosphorescence. 
 
 light emitted is pure white, and similar in constitution to the solar ray. 
 The powers of emitting heat, and of emitting light, are, however, al- 
 though so frequently associated, quite independent and distinct ; and 
 the rays of heat and those of light may be perfectly separated from each 
 other. It would anticipate too much the account of radiant heat, to 
 describe the means of separating the heating from the luminous quali- 
 ties of ordinary light ; but elsewhere they will be described in full. A 
 body may become luminous when very moderately heated, as in the 
 case of minerals, as fluor spar. Light may be produced also by the 
 friction of bodies, as by rubbing two pieces of sugar briskly together, 
 or by striking together two pieces of quartz, and in these cases it is 
 difficult to assign its true origin, as, possibly, a minute trace of the sub- 
 stance may be very intensely heated. There are also many bodies, 
 which when exposed to the light of the sun, after having been made red 
 hot, appear to absorb a portion of it, and become capable of emitting it 
 slowly, giving a pale bluish light for some time afterwards in the dark. 
 This occurs, particularly with chloride of barium, native sulphate of 
 barytes, carbonate of lime, and a great number of other bodies. Such 
 substances are said to be phosphorescent '. Thus fluor spar is rendered 
 so by heat, sugar and quartz become so by friction, and the electric 
 spark is capable of conferring the phosphorescent property on a great 
 variety of bodies. 
 
 Organized substances become phosphorescent in the first stages of 
 their decay ; thus, rotten wood, and fish before actual putrefaction has 
 commenced. The light emitted is, in such cases, the result of an ex- 
 ceedingly slow, but distinct process of combustion ; it requires the pre- 
 sence of atmospheric air, of oxygen, although an exceedingly small 
 quantity may suffice, and it is extinguished and revived by all such means 
 as facilitate or retard the chemical action of the air upon organic bodies. 
 The light emitted by the glow-worm, and the fire-flies, as well as by 
 the great variety of marine zoophytes, appears also to be not merely an 
 evolution of light as a product of vital action, but to arise similarly 
 from the secretion of a substance, which slowly combining with the 
 oxygen of the atmosphere, produces the light as a consequence of com- 
 bustion. Animal phosphorescence is, therefore, to be ascribed to che- 
 mical action. 
 
 The white light, derived from different sources, does not always pos- 
 sess the same physical constitution. If the coloured spectrum produced 
 by the solar ray be closely examined, it will be found crossed by a mul- 
 titude of black lines, indicating the total absence in the sun's light of 
 rays of certain refrangibilities. That tins is inherent in the light is 
 shown by the fact, that when we change the nature of the prism, the 
 
Chemical Agencies of Light. 51 
 
 position of the space in which these black lines occur may alter, but 
 the lines preserve all their relative distances from each other totally un- 
 changed. Hence, in place of referring to the colours of the spectrum 
 in order to characterize its properties, those lines, of which the most 
 remarkable is a double line situated in the yellow space, are used as 
 marks. The light of the sun, of the moon, and planets, as well as the 
 white light produced by our processes of combustion, all consist of the 
 same elements of yellow, red, and blue, and all are distinguished by the 
 same set of lines. In the light of some of the fixed stars the same 
 lines are found, as is the case with Pollux ; but in the spectrum formed 
 by rays from Sirius or from Castor, this double line does not occur, but 
 is replaced by one broad line in the yellow space, and two remarkable 
 dark lines in the blue. It is very curious, that if we examine the spec- 
 trum through certain coloured media, as the vapours of iodine or bro- 
 mine, we find additional black lines, and by using gaseous nitrous acid 
 these become almost innumerable, and increase so much when the gas 
 is heated, that the spectrum is obliterated, and the gas becomes opaque. 
 It is possible that such may take place at the origin of the light of the 
 heavenly bodies ; and that the sun and the fixed stars are involved in 
 absorbing atmospheres, which allow only certain rays to pass, and that 
 hence there may exist in nature, kinds of light from which the eye of 
 man is screened for ever, by means of such an impervious veil. 
 
 Some classes of chemical substances are, to a certain extent, charac- 
 terized by the facility with which they are decomposed when under the 
 influence of light. The salts of silver, of gold, of platina, and, in 
 some instances, of mercury, are subject to this influence. A great va- 
 rietj of vegetable and animal bodies undergo important changes in their 
 constitution by the action of the solar rays, the development of certain 
 colours requiring the agency of light, and the majority of colours being 
 destroyed when its action is too great : hence the fading of dyes arises. 
 The power of light thus to modify the affinity by which chemical combi- 
 nation is produced, has been found to be exercised specially by the vio- 
 let or more refrangible extremity of the spectrum, and even with most 
 intensity by invisible rays quite outside of the luminous space, and ex- 
 tending beyond even the lavender-coloured prismatic space of Herschel. 
 It has been also considered, that the rays of the red extremity of the 
 spectrum possessed chemical properties of an inverse kind, and that the 
 decomposition produced by violet light might be counteracted, and the 
 elements brought to recombine by the red rays. This is not absolute. 
 All that has been established is, that there exists in solar light, and, 
 probably, in all light derived from sources of combustion, three distinct 
 sets of rays, the one of proper light, which produces only luminous 
 
52 Chemical Rays in the Spectrum 
 
 effects, the second of radiant heat, the nature of which shall be specially 
 examined in the following chapter, and the third, of rays which, thougla 
 neither luminous nor heating,, exercise an influence on chemical affinity, 
 and the nature of which shall be discussed with more detail when the 
 subject of chemical affinity and its relations to the other physical forces 
 has been described. To these chemically acting rays the name of Tithonic 
 Bays has been given by Dr. Draper, of New York, to whose researches 
 much of our knowledge of their peculiar properties is due ; and he pro- 
 poses to assume, as the basis of our theory of this department of science, 
 the existence of a force, to which he gives the name of Tithonictiy, 
 believing that it is capable of modifying the agencies of chemical affi- 
 nity in the like manner as electricity or heat. 
 
CHAPTEE HI. 
 
 OF HEAT CONSIDERED AS CHARACTERIZING CHEMICAL SUBSTANCES. 
 
 AT almost every step of chemical inquiry it is necessary to introduce 
 the action of heat, either as modifying the results of the chemical 
 action of bodies upon each other, or as affording characters by which 
 the substances we operate upon may be distinguished. The doctrine 
 of heat and the history of its effects have consequently at all periods 
 formed an important portion of the studies of the chemist, and it is, 
 indeed, only lately, since the brilliant course of discovery which was 
 opened, and so successfully prosecuted by Melloni, and by Eorbes, 
 has identified the theories of heat and light, that this subject has 
 been contemplated in its proper aspect, as a physical science, 
 and its application and influence in chemistry have ceased to be 
 considered as making up the science, properly so called, of heat 
 
 Of all the physical sciences, however, that of heat, or Thermotics, 
 as it is now termed, is the most important to the chemist, in guid- 
 ing him in his operations, and in the accurate description of their 
 results. On this account it will be necessary to describe the properties 
 of heat more in detail than those of any other of the physical agents, 
 and to illustrate these properties by more numerous references to cases 
 in which their utility in chemistry is apparent. 
 
 The effects of heat, by which, according to their degrees, bodies may 
 be characterized, are 
 
 1st. Change of volume for a given change of temperature. Ex- 
 pansion. 
 
 2nd. Quantity of heat required to produce a given change of tem- 
 perature. Specific heat. 
 
 3rd. Temperature necessary for liquefaction. Melting points. 
 
 4th. Temperature necessary for giving a certain elasticity to a vapour. 
 Soiling points. 
 
 5th. Quantity of heat required to produce a given change of aggre- 
 gation. Latent heat of liquids and vapours. 
 
54 Expansion ly Heat. 
 
 6th. Manner and rapidity of communicating or receiving heat. 
 Conduction and radiation of heat. 
 
 The subject of heat shall therefore be studied specially under these 
 heads and it will be necessary to introduce an account of our mode 
 of measuring heat and temperature, by the thermometer and pyrometer, 
 and to add some observations on the physical relations of heat and light, 
 and on the physical theory of heat. 
 
 SECTION I. 
 
 OP EXPANSION. 
 
 When describing the effects of cohesion, I have already noticed that 
 the molecular constitution of all bodies might be considered to depend 
 on the relative power of the attractive force of cohesion, and the repul- 
 sive force of heat, upon their particles. Thus where the attraction was 
 in excess, the molecules were knitted firmly together to form a solid 
 body, but that where repulsion was most powerful, all cohesion was lost, 
 and the body assumed the form of a vapour or a gas. In the inter- 
 mediate condition, where the forces appeared to be nearly in equili- 
 brium, there was produced the liquid state, wherein the molecules of 
 the body appeared still to unite, by a trace of remaining cohesion, but 
 they yet moved among one another with perfect ease, and the slightest 
 external force might disarrange them entirely. Now the change from 
 one to the other of any two of these conditions is not quite abrupt. 
 If a cold body be gradually heated until it shall begin to liquefy, its 
 particles do not remain in the same condition up to the moment when 
 they separate so far, as to change their state of aggregation ; on the 
 contrary, from the instant that the substance becomes warm, the change 
 begins ; the molecules of the body gradually separate, they occupy 
 more space than before, and from the very commencement of the in- 
 crease of heat, the body, though it may remain solid, yet expands. 
 In the same manner, if the liquid be heated, the change of aggrega- 
 tion does not commence until the increase of heat has reached a certain 
 degree ; but from the beginning a change of volume occurs, the in- 
 crease of which marks the gradual diminution of cohesion. In gases 
 there can take place no further change of form, and the only effect 
 which heat can produce on them is expansion. 
 
Repulsive power of Heat. 55 
 
 This power of repulsion which we suppose heat to exercise, in caus- 
 ing the transition from one state of aggregation to another, as well as 
 the expansion which occurs without change of form, may become 
 directly evident to the senses, at least in a partial way, in many cases. 
 Thus many powders, if sprinkled on a warm capsule, or still better, on 
 a silver plate, are thrown into violent motion, and dissipated by the 
 mutual repulsion of their particles, independent of any currents of air 
 which might affect them. "When liquids, particularly alcohol and the 
 oils, are brought to boil, the drops which are mechanically thrown up 
 out of the liquid, do not mix with it on falling back, but roll about on 
 the surface, and appear to repel each other, and to be repelled by the 
 hot glass of the vessel in a remarkable degree. If a brass poker, 
 strongly heated, be allowed to rest against a cold iron bar, or still 
 better, if a rounded bar of brass be made very hot and laid upon a flat 
 block of lead, the surface of the cold metal becoming heated, repels 
 the warmer brass, which instantly falls down again, by its weight over- 
 coming the repulsion, when the metal cools. When the brass again 
 touches the metal or lead, the latter is again heated at the point of 
 contact, and again there is repulsion succeeded by a new contact, and 
 these repeated motions throw the bar of brass into a slate of tremulous 
 agitation, which being conveyed to the ear by the intervening air, gives 
 a remarkably distinct and agreeable musical tone. The better conduc- 
 tor, the heated body, and the worse conductor, (of a metal,) the cold 
 body can be, the more successful is the result. 
 
 This force of repulsion is made still more distinct, and even measur- 
 able, by an experiment devised by Powell. When a flat and a convex 
 glass plate are strongly pressed together, they still do not touch, but 
 are separated by an exceedingly thin space, by the action of light in 
 which there are produced coloured rings, like those seen on the surface 
 of a soap bubble, or in a film of oil floating upon water. Each colour 
 belongs to a distinct and measurable thickness of this space, and when 
 such an apparatus is gradually heated, the rings close in towards the 
 centre, showing that the glass plates recede from one another, and the 
 degree of repulsion may be determined from the narrowing which occurs 
 in the breadth of any particular coloured ring, according as the tem- 
 perature rises. 
 
 In permanent gases the expanding force of heat is unaffected by any 
 disturbing cause ; there is no cohesion remaining to impede its opera- 
 tions ; hence a certain increase of heat affects all gases alike, and no 
 matter how hot or how cold a gas may be, a certain increase of heat 
 produces the same increase of volume in every case. In solids and in 
 liquids, however, it is different, the expansion which occurs is but the 
 
56 Influence of Cohesion on Expansion. 
 
 result of the opposing forces of cohesion and of heat, and hence the 
 amount of expansion depends not only on the quantity of heat which 
 is applied, but also on the power of cohesion by which it is resisted, 
 and which depends upon the nature of the body. Consequently every 
 liquid and every solid expands in a degree which is peculiar to it. There 
 is yet another consequence of the influence of cohesion upon the expan- 
 sion of solids and of liquids. Let us represent the cohesive force of a 
 certain substance, for example, copper, by 10, and let us suppose that 
 we apply to it a quantity of heat which will expand it through a space 
 which we will call 1, and will diminish its cohesion from 10 to 9. If, 
 then, we apply another quantity of heat, exactly equal to the former, 
 it will not have to contend against a cohesion of 10, but of 9, and will, 
 consequently, be able to produce an expansion of more than 1, say 1J, 
 and it will reduce the cohesion more than it did before, as from 9 to 7J. 
 If, then, another equal quantity of heat be added, it having still less 
 opposing force to overcome, will act still more powerfully, reducing, for 
 example, the cohesion from 7J to 5, and the increment of volume be- 
 coming, in place of 1 J, 2. In solids and liquids, the rate of expansion 
 increases thus, with the temperature, from the diminution of cohesion, 
 but in the permanent gases where the cohesion remains the same, or 
 rather is completely absent, the expansion is proportional to the addi- 
 tional quantity of heat, no matter how much may have been sensibly 
 present in the gas before. 
 
 I shall now proceed to consider in detail the rates of expansion of 
 various bodies, commencing with those of gases, for which the simplest 
 results have been obtained. Before doing so, however, it is necessary 
 to study the means by which we ascertain the quantities of heat whicto 
 we add or substract from bodies to effect their expansion or contraction ; 
 to investigate, in fact, the principle on which the thermometer and 
 pyrometer are founded, and such details of their construction as shall 
 hereafter be found necessary to be known. 
 
 Let a b be a glass bulb, with a long and narrow neck, which is 
 
 divided by a scale, as in the figure, of which each division is a certain 
 part, as 1^5 of the volume of the bulb. Let us suppose the bulb a 
 to be filled with pure dry air, at the same degree of heat as that at 
 which ice melts, and separated completely from the external air by 
 means of a globule of mercury, c, which is settled exactly at the com- 
 mencement of the scale. If now the instrument be warmed, the air in 
 
Nature of Temperature. 57 
 
 the bulb expands, and according as it increases in volume, pushes 
 before it, into the tube, the globule of mercury. This last serves, there- 
 fore, as an index of the increase of volume which the air gains as it is 
 heated, and by its position we can read off the exact proportion. If 
 the source of heat be water boiling, under ordinary circumstances, at 
 Dublin, at the level of the sea, as soon as the air has been heated to 
 exactly the same degree as the water, the globule will be found to have 
 arrived at the 366th division on the scale. Therefore, 1000 measures 
 of air, on being heated from the degree of melting ice, to that of boil- 
 ing water, become 1366. Now, as from the constitution of air and 
 gases, the effect of each increase of heat is the same, we may consider 
 the whole quantity of heat which is received from the boiling water, to 
 be divided into 366 parts or degrees, and one of these parts being 
 applied separately to the bulb, should have increased the volume of 
 air by T^Q P art > or should have converted the 1000 volumes into 1001. 
 There is thus obtained a scale of expansion, which is quite artificial 
 and arbitrary certainly, but which, having been once contrived, may be 
 with perfect accuracy applied to measure different quantities of heat. 
 Thus, if we warm water to blood heat, and immerse in it the air bulb 
 as described, the expansion of the air will move the globule of mercury 
 to the degree 122, which is thus exactly the one-third part of the 
 366, and hence the water in being heated from the degree of melting 
 ice to that of blood heat, received thereby exactly one-third of the 
 quantity of heat which should have made it boil, and its temperature is 
 increased one-third as much. 
 
 I have here spoken of measuring the successive quantities of heat 
 which the air received, and in this case the manner of expression is 
 sufficiently accurate, as well as the most simple. But it is necessary to 
 explain the true meaning of the words, quantity of heat, and tempera- 
 ture. The amount of expansion which a hot body is capable of pro- 
 ducing in the air or mercury of the thermometer, measures truly what 
 is called its temperature. The temperature has nothing whatsoever to 
 do with the quantity of heat which the body may contain; it refers 
 only to its expanding power. If a quantity of water, of oil, of ether, 
 of mercury, or of iron, produce all the same amount of expansion in 
 the air, or mercury, of the thermometer, we say they have the same 
 temperature, without pretending to know anything of the quantity of 
 heat which they may actually possess. The thermometer and pyrometer 
 are, therefore, instruments for measuring, not heat, but temperature, 
 and we denote by degrees of temperature the amount of expansion pro- 
 duced, marked off on an arbitrary scale winch we may think proper to 
 adopt. 
 
58 Construction and Use 
 
 Gases expanding more than any other bodies, the air thermometer is 
 the most sensible that can be made, and, in the form just described, it 
 is an exact measure of heat, subject only to one correction, which is, 
 that although the air, in being heated from the degree of melting ice, 
 to that of boiling water, actually expands iooo of its volume, yet that 
 expansion is not all visible, for the glass bulb expands also on being 
 heated, although in a very small proportion, and holds JQOO more than 
 it did when cold ; the visible expansion on the scale is, therefore, only 
 364 degrees, and this must be allowed for, to have complete accuracy. 
 The form of the air thermometer which has been just described, is, 
 however, quite unfit for ordinary use; the adjustment of the index 
 globule the necessity that the instrument should be perfectly horizon- 
 tal, which is quite impossible in the majority of practical cases ren- 
 ders this kind of an air thermometer too unmanageable, and since the 
 air changes its volume very much for every change of pressure and 
 our atmosphere varies in its weight almost every hour an air thermo- 
 meter left open, as at the orifice d, should change continually without 
 reference to the degrees of heat at all, and should thus give false 
 indications. The end of the tube must, therefore, be accurately 
 closed. 
 
 When, however, the air inside is thus confined, the simple rule of 
 the dilatation being proportioned to the increase of heat, ceases com- 
 pletely. For if the point b be closed, and that the bulb a be heated, 
 the globule of mercury, in moving along the scale, condenses the air 
 before it, and thus generates an elastic force, by which the expansion 
 is resisted and diminished in amount ; the degrees should, therefore, be 
 no longer equal, but rapidly diminish in size, so that on the upper 
 parts of the scale they could not be distinguished from one another, 
 and should hence be useless. But by having a second bulb, as in the 
 next figure, the elasticity of the air compressed in the cold bulb in- 
 creases much less rapidly, and the scale to be applied to the stem con- 
 necting the bulbs, is easily constructed. As the stems of these air 
 thermometers are generally upright, mercury would be too heavy a fluid 
 to introduce in a column, and the mere globule which we supposed, in 
 the example first taken, would not answer, from the facility with which 
 it might be broken or displaced : to any watery or spirituous liquid there 
 is also an objection, that the amount of expansion should be increased 
 in an uncertain degree, by the portion of fluid converted into vapour. 
 To avoid these errors, oil of vitriol may best be employed, and it is 
 generally coloured red, to render the motion of the fluid column more 
 easily visible. 
 
 An air thermometer, closed perfectly, indicates a change of tempera- 
 
Of Air Thermometers 
 
 59 
 
 ture only by the difference between the elas- 
 ticity of the air in the two bulbs. No matter 
 how high or how low the temperature may 
 be, if it affects both bulbs to the same degree, 
 the air in each bulb presses on the liquid 
 column with the same force, and exactly ba- 
 lances the other. The instrument indicates, 
 therefore, such temperatures only as affect 
 one bulb and not the other the difference, in 
 fact, between the temperatures of the two 
 bulbs, and hence is properly called the differ- 
 ential thermometer. In fig. a the one bulb is 
 much above the other. In fig. b the stem 
 which terminates above in a bulb is open be- 
 low, and plunges into the liquid which the 
 inferior bulb contains. Tins lower vessel is soldered or cemented at its 
 orifice round the tube, so as perfectly to prevent 
 the action of the air. Fig. c represents the most 
 ordinary form ; the bulbs are on a level, and are 
 connected by a U-shaped stem. 
 
 The air thermometer is thus, in all its forms, 
 liable to so many inconveniences from the limited 
 range of its scale, if it be open to the air, and 
 from the complex form which the scale assumes, 
 if the external air be prevented from communica- 
 tion, that it is never made use of in practice, 
 except in some particular cases, which shall here- 
 after be specially noticed. We are, therefore, 
 obliged to have recourse, for our accurate measures of temperature, to 
 other bodies, which, though not so sensitive as air, offer more practical 
 advantages. 
 
 The liquids which are generally used to measure, by their expansion, 
 changes of temperature, are alcohol and mercury. The former, in 
 being raised from the melting point of ice to that at which itself boils, 
 expands -& , whereas air, witldn the same limits, would have expanded 
 is,, being about three and a half times as much as alcohol : and mer- 
 cury, in having its temperature raised from the melting point of ice to 
 the boiling point of water, expands 1600, or about -0 of the quantity of 
 air. Hence these liquids are much less sensible, as thermometers, than 
 air ; but their other advantages are decidedly in their favour. Alcohol 
 is only employed where the object is to measure very great degrees of 
 
60 Mercurial Thermometer. 
 
 cold ; and for this purpose it is admirably fitted, as it is tlie only liquid 
 that has not yet been frozen. Mercury, on the other hand, may be 
 applied to an extensive range of temperatures, as it freezes only by the 
 application of an intense cold ; and it does not boil until it arrives 
 nearly at a red heat. It has the largest interval between its freezing 
 and boiling points of any liquid that is known. Mercury is also ad- 
 mirably suited to be a measure of heat, by the accidental circumstance 
 that its expansion, when contained in a glass bulb, is accurately pro- 
 portioned to the temperature, and its indications, therefore, absolutely 
 true. This is occasioned by the circumstance, that, as in all liquids 
 and solids, the expansion increases with the temperature, the rate of 
 increase of the capacity of the glass bulb exactly corresponds to the 
 increase of the rate of expansion of the mercury, and absorbs it ; so 
 that the visible expansion of the mercury is uniform, and a degree in 
 every part of the scale is of the same length. For instance, if mercury 
 and air be together heated from the freezing to the boiling point of 
 water, 1*000 measures of air become 1*366; and 10*000 measures of 
 mercury become 10*180. If, then, they be both heated as much more, 
 the air expanding at the same rate, becomes 1*732 ; but the mercury 
 expanding more rapidly, becomes 10*363 : and hence, if a scale were 
 so applied, there would be shown 180 degrees in the lower, and 183 
 degrees in the upper part of the scale, to the same quantity of heat. 
 This is corrected by the expansion of the glass bulb which holds the 
 mercury. At the temperature of melting ice, the bulb holds, for ex- 
 ample, 10*000 measures of mercury; but, on being heated to that of 
 boiling water, it holds 10*026. The mercury, however, having become 
 10*180, the difference, (10*180 10*026) == 154 measures, pass into 
 the stem, and makes the rise of temperature upon the scale. When 
 now the second portion of heat is applied, the mercury becomes 10*363 ; 
 and the glass bulb expanding at the same time, becomes able to hold 
 10*055 : and hence the difference (10*363 10*055) = 308 mea- 
 sures pass into the stem, and move along the scale. Thus, the visible 
 portion of the expansion is rendered exactly proportional to the increase 
 of heat ; and the mercurial thermometer becomes, not merely the most 
 convenient, but the most accurate measure of heat which we possess, 
 although, however, its indications become somewhat less exact as the 
 temperature approaches the boiling point of mercury. 
 
 The difference of composition of the various kinds of glass used in 
 the arts necessarily, however, produces slight differences of expansi- 
 sibility, which interfere with the exactness of the correction just de- 
 scribed ; and Eegnault has lately shown that this source of disagreement 
 amongst thermometers is much more important than had been supposed. 
 
Its Principle of Correction, 
 
 61 
 
 So that there cannot be any general rule given for connectiug the air 
 and the mercurial thermometers, but every thermometer will have its pe- 
 culiar correction depending upon the nature of its glass and even the 
 degree in which the glass has been worked in making the instrument. 
 The following table will however show the general range of differences 
 of the indications of mercurial thermometers made of different kinds of 
 glass compared with the standard scale of the thermometer. 
 
 Temperatures on 
 
 Temperature on the Mercurial Thermometer Centigrade Scale. 
 
 the air Thermo- 
 
 
 meter Centigrade 
 Scale. 
 
 Flint Glass. 
 
 Crown Glass. 
 
 Bottle Glass. 
 
 Swedish Glass. 
 
 Degrees. 
 
 Degrees. 
 
 Degrees. 
 
 Degrees. 
 
 Degrees. 
 
 100 
 
 100-00 
 
 100-00 
 
 100-00 
 
 100-00 
 
 120 
 
 120-12 
 
 119-95 
 
 120-08 
 
 120-04 
 
 140 
 
 140-29 
 
 139-85 
 
 140-21 140-11 
 
 160 
 
 160-52 
 
 159-74 
 
 160-40 160-20 
 
 180 
 
 180-80 
 
 179-63 
 
 180-60 180-33 
 
 200 
 
 201-25 
 
 199-70 
 
 200-80 200-50 
 
 220 
 
 221-82 
 
 219-80 
 
 221-20 
 
 220-75 
 
 250 
 
 253-00 
 
 250-05 
 
 251 -as 
 
 251-44 
 
 290 
 
 295-10 
 
 290-80 
 
 293-30 
 
 _____ 
 
 320 
 
 327-25 
 
 321-80 
 
 
 
 
 
 350 
 
 360-50 
 
 354-00 
 
 
 
 
 
 In constructing a thermometer the first requisite is, that the bore of 
 the tube shall be perfectly uniform, for otherwise the result above de- 
 scribed, which gives all its real value to the quicksilver thermometer, 
 would be completely inapplicable in practice. This is ascertained by 
 finding that a small quantity of mercury, moved up and down the tube, 
 occupies exactly the same length in every part. A proper tube having 
 been thus obtained, one extremity is closed, and a bulb is blown upon 
 it ; another is formed near the open end, leaving a space between the 
 two bulbs somewhat longer than the thermometer is intended to be. 
 The tube and bulbs having been heated, are allowed to cool, with the 
 open end immersed in pure and recently boiled mercury. By the con- 
 traction of the internal, and the pressure of the external air, a quantity 
 of mercury is forced into the first bulb, and ultimately the bulb at the 
 closed end is filled completely by a repetition of the process. When the 
 introduction of the mercury has been completed, the open end of the 
 tube is closed by a little sealing-wax, to prevent the admission of air or 
 dust, and the tube is allowed to cool with the terminal bulb down. 
 "When it has cooled completely, it is again heated to the highest degree 
 it is intended to indicate ; and the fine flame of a blow-pipe being di- 
 rected upon the point wlu'ch is to be the extremity of the tube, it is 
 melted, and the orifice completely closed. When the instrument then 
 
62 Determination of the 
 
 i 
 
 cools, there remains, over the mercury in the stem, a perfectly empty 
 space. 
 
 It remains then to attach the scale. When describing the general 
 principle of the thermometer, in the example of dry air, pushing, by its 
 expansion, an index globule of mercury along the stem, the scale which 
 included the interval from the freezing to the boiling points of water, 
 was supposed to be divided into 366 parts. This was, however, merely 
 because the 1,000 measures of air, in being heated through that inter- 
 val, expand in that proportion. The scales that are actually used, are 
 different, although quite as arbitrary. The simplest scale is that in 
 which the interval between the freezing and boiling points of water, 
 which is universally taken as the standard, is divided into 100 parts; it 
 is termed the centigrade scale, and is universally employed in France, 
 and generally in Germany and the north of Europe. In it ice is said to 
 melt at 0, and water to boil at 1 00 .On the scale generally used in this 
 country, and in Great Britain, the standard interval is divided into 180 
 degrees, but the melting point of ice is not taken as 0, but as 32, 
 from a very absurd idea of Fahrenheit's, who was the inventor of this 
 scale. He mixed together snow and salt, and having thus produced a 
 more intense cold than any body before him had done, he imagined that 
 he had attained a point at which the bodies had no heat at all ; that he 
 had arrived at what was afterwards called the absolute zero, and he 
 called that point ; the melting point of ice was then 32, and water 
 boiling at 180 higher, its temperature was marked 212. There is 
 another scale sometimes, Jbut not often used ; that of Eeaumur, in which 
 the melting point of ice is the commencement or 0, and the boiling 
 point of water is marked 80. The first step in the graduation is to 
 mark the extreme points of the standard interval : the melting point of 
 ice, and the boiling point of water. To do this correctly, some precau- 
 tions must be taken. I have frequently spoken of the melting point of 
 ice, and the freezing point of water as meaning the same temperature, 
 and under ordinary circumstances they do so; but they do not so 
 necessarily. The freezing of water is a crystallization, and, like all 
 other cases of crystallization, may take place with greater or less facility. 
 If water be agitated, or if it be contained in rough vessels, affording 
 prominences to which the crystals of ice may attach themselves, it 
 freezes exactly at 32 on Fahrenheit's scale, but if the water be kept 
 carefully at rest, and that it be contained in smooth glass vessels, free 
 from dust, it may be easily cooled to 25, and has been cooled even to 
 15, without becoming solid. Hence, if we wished to determine the 
 zero, by means of freezing water, an error might easily be committed. 
 Ice however, under all circumstances, melts at 32, and hence by 
 
Standard Interval. 63 
 
 plunging the bulb of the thermometer into a mixture of ice and water, 
 and marking on the stem the point at which the level of the mercury 
 settles, the first fixed point upon the scale is had. To determine the 
 second point, that at which water boils, it is necessary to attend to the 
 condition of the barometer. It will be hereafter described, how the 
 boiling point of every liquid varies with the atmospheric pressure ; it is 
 here enough to notice, that, either the boiling point must be determined 
 when the barometer stands at 29*8 inches, or a correction, which shall 
 be hereafter given, applied for any difference of height which may exist. 
 The water must boil also in a metallic vessel, for water in a glass, or 
 porcelain vessel, has its boiling point somewhat raised, and if the ther- 
 mometer is to be used for chemical purposes, the bulb and only a small 
 portion of the stem should be immersed in the boiling water. The two 
 fixed points having been thus obtained, the interval is to be divided into 
 180 equal parts or degrees, for the ordinary scale of Fahrenheit, and 
 then 32 of these degrees counted downwards from the point of melting 
 ice, to obtain the zero ; for the zero cannot be truly got in the manner 
 in which Fahrenheit is supposed originally to have invented it : a mixture 
 of snow and salt being found to produce always a cold of about 2 
 below zero, or 2. As our range of temperature passes far below the 
 zero of the scale, we count downward precisely as we count upwards, 
 only prefixing in the former case the minus sign, whereas in the de- 
 grees above zero, the + plus sign is usually omitted. Thus, -f 50, or 
 simply 50, is fifty degrees above zero, but 50, is the same number 
 below zero. To construct the centigrade scale, the method is precisely 
 the same, except that we make the point of melting ice, 0, and that of 
 boiling water, 100, and a degree being the 105- of the interval, we count 
 up and down from zero, precisely as in the other case. 
 
 It is, generally, proper to lay a thermometer aside for a few weeks 
 after having filled it, before proceeding to apply the scale. For it is 
 found that as there is a vacuum in the instrument above the mercury, 
 the external pressure acting on the thin glass of the bulb, gradually 
 changes its form a little, and would move up the fixed points, sometimes 
 through one or two degrees, if they had been marked before the change. 
 It is found that the same or even a much more considerable movement 
 of the zero point may be produced by exposing the thermometer for a 
 few hours to a temperature of about 400. 
 
 The centigrade scale is of such extensive use in the works of most 
 distinguished chemists, that it is well to show more closely its relation 
 to the ordinary scale of Fahrenheit, and the means of reducing one to 
 the other. The standard interval is divided into 180 Fahrenheit, and 
 into 100 centigrade degrees, and hence a degree of the former is equal 
 
64 Thermometrw Scales. 
 
 to fb or f th of a centigrade degree. To reduce any interval in centigrade 
 degrees to Fahrenheit's, it is, therefore, to be multiplied by 9, and di- 
 vided by 5 ; and for the reduction from Fahrenheit to centigrade, the 
 number is to be multiplied by 5, and divided by 9 : but, as the degrees 
 do not in number start from the same point, the Fahrenheit scale being 
 already 32, when the centigrade begins, it is necessary to add 32 to 
 the number of Fahrenheit degrees, which have been attained by calcu- 
 lation from the centigrade, and to subtract 32 from the number of de- 
 grees on Fahrenheit, which are to be converted into degrees upon the 
 other scale. 
 
 Thus, to reduce 167 of Fahrenheit, we proceed : 
 
 167 32 = 135 and 135 x | = 75 
 
 and find it to correspond to 75 centigrade. And to reduce 65 centi- 
 grade to Fahrenheit's scale, we say, 
 
 65 X |= 117 and 117 + 32 = 149 
 corresponding, therefore, to 149 of Fahrenheit. 
 
 Reaumur's scale being to the centigrade scale, as 4 to 5, similar re- 
 ductions are made to and from it, by using -| in place of |, as has been 
 employed in the example. 
 
 The range of temperatures observable with a mercurial thermometer, 
 on Fahrenheit's scale, is from 39 to + 630. The mercury freezes 
 a little below 40, and though it does not boil until it arrives at 660, 
 yet the quantity of vapour which it forms, when very near its boiling 
 point, prevents its indications from being exact between that point 
 and 630. 
 
 Our means of estimating temperatures above the boiling point of 
 mercury, are not at all so perfect as those that have been described for 
 the lower degrees of heat. Mercury when boiling, is not in the slightest 
 degree luminous, but the temperature at which a heated body becomes 
 visible in the dark, by emitting a dull red light, is not much higher. 
 Numerous instruments have been invented for the purpose of deter- 
 ming the higher temperatures, particularly of furnaces, and hence, they 
 have been called pyrometers. They are principally of two kinds. In 
 one class the temperatures are measured by the expansion of a solid 
 bar, the extremity of which gives motion to an index. Of these the 
 best is that of Daniell. In the other class, a small quantity of air en- 
 closed in an infusible bulb and tube expands, and produces indications 
 by raising or lowering the level of quicksilver contained in an attached 
 glass tube; of this kind, the most perfect is that constructed by 
 Pouillet. 
 
 In the Pyrometer of Daniell, the change of temperature is shown 
 by the excess of the expansion of an iron bar over the expansion of a 
 
Darnell's Pyrometer. 
 
 65 
 
 black lead case in which it is enclosed. The iron rod is somewhat 
 shorter than the black-lead-ware case and a plug of earthenware, 
 
 which fits tight in the case abuts against 
 the iron rod inside, and projects as in 
 the figure. Let us suppose the length of 
 the case to be 5 inches, that of the iron rod 
 4J inches, and that of the earthenware plug 
 to be 1 inch. If the whole be heated until 
 the case shall have expanded by 12 parts, 
 the iron rod will have increased in length 
 by 44, and the earthenware piece by 7, 
 which added to 44, makes 51. If the black 
 lead case did not increase in size, all these 
 51 parts should project, but as there is 
 additional room made for 1 2, the projecting 
 portion is only 39. If the parts of the ap- 
 paratus were all free to move, each contract- 
 ing again on cooling, the result should be that all should be restored to 
 their original position ; but this is not the case. The bar of iron, in ex- 
 panding, pushes out before it the plug of earthenware, which, however, is 
 held so tight in the case, that it cannot go back again, when the appa- 
 ratus has become cold. The protrusion of the earthenware plug, is 
 therefore, a permanent index of the greatest amount of expansion that 
 had been produced, whilst the instrument was exposed to heat. This 
 expansion is, however, very small. The three pieces being, as stated, 
 5, 4J and 1 inch, the expansion when heated from 32 to 212 is only 
 !ooo of an inch, and as this indicates 180 degrees, the expansion for a 
 degree is only about 4555 of an inch. It is, therefore, necessary to mag- 
 nify this expansion, in order that the indications may be read off, and 
 this is done by means of a graduated circular arc, with a move- 
 able index, kept by means of a spring constantly at when undis- 
 turbed. On fitting this scale to the pyrometric black lead case, after it 
 has been in the fire, the projection of the earthenware plug, catches 
 in the prolonged heel of the index, and moving it round, the point of 
 the index travels over a portion of the graduated scale, and indicates the 
 number of degrees through which the temperature had been raised. 
 This instrument is not always made of the same size, and hence the ab- 
 solute amount of expansion may vary, which however is reduced to the 
 same proportion on the scale, by which also the increase in the rate of 
 expansion of the metallic bar at very high temperatures must be allowed 
 for. By means of this very ingenious and useful instrument, Professor 
 Daniell has determined the melting point of most of the important 
 
 5 
 
66 Table of Temperatures. 
 
 metals, and also several other temperatures, at which remarkable phe- 
 nomena occur. 
 
 The pyrometer of Pouillet requires too many careful adaptations to 
 allow of it being employed except for special experiments of research, 
 and hence its detailed construction need not be described. A method 
 employed by Petersen however deserves notice. He takes a platinum 
 bulb like a small specific gravity bottle, which is closed by a cap that 
 screws on, but is not absolutely air tight. This bulb being full of 
 perfectly dry air is placed in the furnace, of which the heat is to be 
 measured, and when it has become fully heated, it is suddenly trans- 
 ferred to a vessel of cold water. A portion of air having escaped by 
 the expansion from the intense heat, -an equal bulk of water then enters 
 the platinum bulb through the minute interstices of the thread of the 
 screw, and on weighing the bulb the quantity of water so introduced is 
 ascertained, and being compared with the capacity of the bulb, indicates 
 the degree in which the air had been expanded by the heat, from which 
 the temperature of the furnace may be calculated. 
 
 The pyrometers of Wedgewood, of Guyton, and many others that 
 have been proposed, must be considered as now totally abandoned, and 
 do not require notice. 
 
 The most delicate, and perhaps the most important, indicator of heat 
 that has been contrived, is one totally independent of expansion, and 
 founded on the measurement of the electric current, which a change of 
 temperature produces under certain circumstances. It is the Thermo- 
 multiplier, invented by Nobili. The principles which the instrument in- 
 volves, in its construction and its form, will be described under the head 
 of electricity ; and the remarkable results obtained by means of it, and 
 which have completely remodelled our ideas of the physical constitution 
 of heat, will be noticed in another place : it does not however belong to 
 the present subject as its indications are incapable of being applied as an 
 exact measure of heat. 
 
 It may be of interest to subjoin the temperatures on Fahrenheit's 
 scale, at which some of the most remarkable effects of heat are pro- 
 duced : 
 
 166. The greatest cold that has been produced. 
 
 121. The solid compound of alcohol and carbonic acid melts. 
 
 91. Greatest cold by ordinary freezing mixtures. 
 
 58. Temperature of the planetary spaces. 
 
 60. Greatest cold observed in the arctic regions. 
 
 47. Sulphuric ether congeals. 
 
 45. Nitric acid congeals. 
 - 39. Mercury congeals. 
 
Expansion of Air. 
 
 67 
 
 1. 
 
 14. 
 
 20. 
 
 25. 
 
 32, 
 
 36. 
 
 98. 
 
 308, 
 
 174. 
 
 201. 
 
 211. 
 
 212. 
 
 218. 
 
 662. 
 
 810, 
 
 980. 
 
 1141, 
 
 1869. 
 
 1873. 
 
 1996 
 
 2200 
 
 2786 
 
 Oil of vitriol freezes. 
 
 Oil of turpentine freezes. 
 
 Wine freezes. 
 
 Blood freezes. 
 
 Ice melts. 
 
 Olive oil freezes. 
 
 Heat of human blood. 
 
 Phosphorus melts. 
 
 Alcohol boils. 
 
 Hose's metal melts. 
 
 Newton's metal melts. 
 
 Water boils. 
 
 Sulphur melts. 
 
 Mercury boils. 
 
 Antimony melts. 
 
 Dull red heat. 
 
 Heat of a common fire. 
 
 Brass melts. 
 
 Silver melts. 
 
 Copper melts. 
 
 Gold melts. 
 
 Cast iron melts. 
 
 The details which have been given, regarding the construction of tha 
 air thermometer, will show sufficiently the principle upon which the de- 
 termination of the rate of expansion of gaseous bodies has been effected. 
 The first experiments on the amount of the dilatation of gases were in- 
 stituted by Dalton and Gay Lussac, but the real laws of the expansion 
 of gaseous bodies have been determined only by the recent researches of 
 
 Rudberg, Magnus, and Eegnault. The apparatus here figured will in- 
 dicate the manner in which such experiments may be made. It consists 
 of a tin vessel, A, having five apertures. By means of the aperture in 
 
68 
 
 Determination of the Law of Expansion 
 
 the side, o, there is introduced the tube with the bulb, g g, containing 
 air dried by the tube h h, and arranged with the graduated scale and 
 index globule of mercury m, as described in page 56. By the opposite 
 orifice, o, is fixed a thermometer, I s, the bulb I of which is on the same 
 level as the bulb of the air tube. By means of the central orifice in 
 the top, a second thermometer v is introduced, the bulb of which is 
 situated exactly in the centre of the box. The other orifices in the top 
 are for the free escape of steam. The apparatus being so arranged, 
 water, rendered ice-cold by some snow or ice floating in it, is intro- 
 duced, until the thermometers and the air bulbs are covered to the 
 depth of a couple of inches ; and the index globule of mercury is thus 
 brought to the zero of the scale. The box is then placed on a furnace, 
 B, and gradually heated : the rise of temperature is indicated by the 
 thermometers, t, the expansion by the motion of the index globule, and 
 at each degree they may be compared together until the water is brought 
 to boil. 
 
 By substituting other substances for water, such as oil, or a bath of 
 fusible metal, the rate of expansion may be determined for still higher 
 temperatures, and has been thus ascertained up to the boiling point of 
 mercury. 
 
 From experiments with such apparatus conducted by Gay Lussac, and 
 Dulong, it resulted, that 1,000 volumes of air, when heated from 32 
 to 212, became 1,375, and that the change was in proportion for 
 higher or lower temperatures. The numbers actually obtained may be 
 stated as in the following table : 
 
 Temperature on a Mer- 
 curial Thermometer 
 by F. Scale. 
 
 10, 000 Volumes of Air 
 at 32o become 
 
 Expansion for one De- 
 gree on F. Scale in 
 Parts of the Volume 
 at 32 ... 
 
 33 
 + 32 
 212 
 300 
 387 
 473 
 559 
 660 
 
 8650 
 10000 
 13750 
 15576 
 17389 
 19189 
 20976 
 23125 
 
 20-77 
 
 20-83 
 20-70 
 20-82 
 20-84 
 20-83 
 20*90 
 
 The mean of the results gives the expansion for one degree at 20'81, 
 or almost exactly -5^ of the volume at 32, which result had been 
 adopted universally, without any suspicion of its being imperfect. Cir- 
 cumstances having, however, induced Eudberg to submit the subject to 
 an accurate reinvestigation, conducted with exceeding care and atten- 
 
Of Air and other Gases by Heat. 69 
 
 tion, particularly to the state of dryness of the air employed, he has 
 found that the amount of expansion assigned by Gay Lussac and 
 Dalton is decidedly too great, and that a volume of air, in being heated 
 from 32 to 212, expands from 1000 volumes to 1366. 
 
 The method which he employed was almost exactly the inverse of 
 that of Gay Lussac. Having dried with great care the air in a glass 
 bulb, the tube of which was drawn to a fine point, like that described, 
 page 10, for taking the specific gravity of vapours, he heated it for a 
 long time in a vessel of boiling water, taking care that all parts of the 
 bulb and tube were equally heated, and then, being completely certain 
 that all the air had attained the maximum temperature, he sealed, by 
 the blow-pipe, the minute orifice, and thus had the bulb containing air 
 in the expanded state. The vessel being then removed to a trough of 
 mercury, the orifice of the tube was placed deep below the surface, and 
 carefully opened ; a quantity of ice was then laid upon the globe, and 
 being supplied as fast as it melted, the whole was thus left for some 
 hours until the temperature was well established at 32, and that all 
 the mercury which should rise into the globe, by the contraction of the 
 air by cooling, had entered. The height of the mercury was then 
 noticed, and the height of the barometer and the corrections necessary 
 for its positive amount, or for any change which occurred during the 
 experiment, allowed for, as already described. The volume of the mer- 
 cury which had entered into the globe was then ascertained, and the 
 volume of the globe itself also determined, and by a comparison of 
 these, corrected for the expansion of the glass, and for any variation 
 in the boiling point from 212, the rate of expansion and its amount 
 were calculated. 
 
 From very numerous experiments, Rudberg and Magnus inferred, that 
 in being heated from 32 to 212 1000 volumes of air became between 
 1364 and 1366-4. These results have been fully confirmed by the more 
 recent investigations of Eegnault, and from their joint researches we 
 may consider it positive, that 1000 volumes of air in being heated from 
 32 to 212 become 1366 volumes, and that consequently for each 
 degree on Fahrenheit's scale, 1000 volumes expand ?|j or 2-033, being 
 the ^ part of the volume at 32. 
 
 I have mentioned that from the complete absence of cohesion, and 
 the identity of physical constitution in the gases, the rate of their ex- 
 pansion was the same, and such did appear to be the fact in all the 
 earlier investigations ; but the more exact methods of experiment now 
 adopted, especially in the very elaborate inquiries of Regnault has 
 brought to light differences amongst the gases themselves, as to their 
 expansion, which are of high importance. The gases which are truly 
 
70 Correction of Volumes for 
 
 permanent, and follow perfectly the law of elasticity described in page 
 3. 6, appear to have the same coefficient of expansion as air ; thus hydro- 
 gen, nitrogen, and carbonic oxide, when heated from 32 to 212, 
 increase in volume from 1000 to 1366. But those gases which have 
 been shown to be less perfectly elastic, are found to be more easily 
 expansible; thus by being heated from 32 to 212. 
 
 1000 Volumes of Carbonic acid become 1371 
 
 1000 " Nitrous oxide " 1372 
 
 1000 " Sulphurous acid " 1390 
 
 1000 " Cyanogen 1388 
 
 Another remarkable circumstance connected with the molecular 
 nature of gases, which has been found by Regnault, is that the rate of 
 expansion of a gas, even of air, is not the same when examined by 
 allowing the gas to expand under a constant pressure, or by maintain- 
 ing a constant volume, whilst the pressure varies. The difference is of 
 course but small, and practically unimportant; but it is highly interesting, 
 as teaching us that the molecules of a gas are by no means so indepen- 
 dent or repulsive of each other, as for popular explanation we usually 
 announce them to be. 
 
 In all operations upon gaseous mixtures the rate of expansion of 
 air comes into play, for as gases expand alike, and that the vapours, 
 even of these bodies which are least volatile, as camphor and corrosive 
 sublimate, expand, whilst in the elastic form, precisely as gases do, their 
 volumes are corrected for temperature and pressure in the same manner. 
 In determining the specific gravity of a vapour, it is also usual to reduce 
 it to the same standard as those of gases, that is, of air at 32, even where 
 the substance is of such a nature, as that at 32 it may not produce 
 any sensible vapour at all. In doing so it is assumed that the vapour 
 should, in cooling to 32, follow the same law as common air, and hence 
 an error, even though very slight, in the rate of expansion of air, might 
 lead to incorrect results in many cases. 
 
 The application of such corrections follow very simply from what has 
 been described. If there be a certain quantity, as 155 cubic inches of 
 hydrogen gas at 142 Fah., and that we wish to know what volume there 
 should be when cooled to 32, we say that, as 142 is 110 above 
 32 the 155 cubic inches are equal to the volume at 32, and in addi- 
 tion to 492 f it ; that being the quantity by which it is expanded from 
 32 to 142. Therefore denoting the volume at 32, by the letter Y, 
 there is the equation : 
 
 129-5 cubic inches are, therefore, the volume at 32. 
 
Change of Temperature. 71 
 
 If, on the other hand, we have a gas at a low temperature, and we 
 wish to ascertain what its volume should be at 32, it is evident that 
 the mode is the same, except that in place of subtracting the amount 
 of expansion we add it to the original volume. Thus, if the 155 cubic 
 inches of hydrogen had been at 6 Fahrenheit, then the equation should 
 have been, 32 6 being 26. 
 
 155 =V V ??- or V = 5X92 - = 163-7 cubic inches in exact 
 
 numbers. 
 
 It frequently happens that it is necessary to reduce a gas at one tem- 
 perature to its volume at another, neither of which being 32, it would 
 require two different sums to be worked, by the above process. But it 
 may be effected as follows, by a single calculation. 
 
 The volumes, at the two temperatures, are to one another in the 
 same proportion as the standard volume, 492, increased by the amount 
 of expansion proper to the temperatures. Thus, at the temperatures of 
 75 and 42, the standard volume, which is 492, at 32, becomes re- 
 spectively 535 and 502. Now any volume of gas, when heated from 
 42 to 75, or cooled from 75 to 42, changes its volume in these 
 proportions, and hence, if we have, for example, 127 cubic inches of a 
 gas at 75, and that we wish to calculate its volume when at the tem- 
 perature of 42, we say, calling the unknown volume V : 
 
 V : 127 : : 502 : 535 and V = 127 x = H9-2 
 
 The formulae for these corrections may be very simply written in a 
 general form ; thus, to reduce a volume to 32, denoting the tempera- 
 ture on Fahrenheit's scale by t ; by Y, the volume of gas which we 
 have measured at that temperature ; and by Yj, the volume at 32, the 
 formula is : 
 
 Vl= 
 
 492 ft 1 32) 
 
 And to reduce, without reference to 32 : denoting the known volume 
 by Y, and the unknown by Y 1 ; the temperature of Y by t, and that of 
 Y r , by t\, there is found : 
 
 Y _492==fl ! 32) d Vl = Y 492 ft 1 32) 
 
 V, 492==f* 32) 492== f* 32)' 
 
 Air which has been heated becomes, from its great increase in volume, 
 
 specifically much lighter than cold air, in which it, therefore, ascends 
 
 with a velocity due to the difference between their specific gravities. 
 
 It is thus that over every lamp, or candle, there may be felt a current 
 
 of heated air ascending from the flame ; that the heavy dark smoke 
 
72 Determination of the 
 
 rises in its heated form from the chimneys of our houses ; and that, in 
 crowded apartments or theatres, the upper portion of the space will be 
 occupied by oppressive hot air, whilst that near the floor will be quite 
 cool. By the ascent of the heated air, from our furnaces and fire- 
 places, there is generated the draught which gives the supply of air 
 necessary for continued burning ; and as the intensity of the combus- 
 tion and consequent heat produced, depends on the rapidity of draught, 
 the hot air is kept from being cooled by mixing with the cold external 
 air, by being collected in the chimney, where it obtains an ascensional 
 power corresponding to its height, and by which we are enabled to regu- 
 late with accuracy the temperature which shall be produced. On this 
 ascensional power of heated air, is founded also the construction of the 
 fire or Montgolfier balloon ; a bag of hot air, arising in the surrounding 
 colder atmosphere, precisely as a light flask, filled with oil or 
 alcohol, would ascend if let loose at the bottom of a vessel full of water. 
 
 It has been already noticed, that liquids do not, in expanding, follow 
 any simple proportion, such as that which exists for gaseous bodies, 
 but that each liquid has a peculiar dilatability of its own, and that the 
 rate of expansion varies with the temperature, being greater in the 
 higher portion of the thermometric scale than in the lower. Liquids 
 expand much less than gases, but much more than solids ; for, as is 
 particularly instanced in the thermometer, the visible expansion of a 
 fluid is, in most cases, only the excess of its expansion over the expan- 
 sion of the solid vessel in which it may be contained. 
 
 To measure the amount of expansion in liquids, they may be intro- 
 duced into graduated thermometer tubes ; and then, when exposed to 
 the same degree of heat, they will indicate temperatures proportional to 
 their expansibilities. Thus alcohol rising more into the stem than 
 water, and water more than mercury, will stand at different marks on 
 the stem, although the temperature be really the same. It may, how- 
 ever, be more easily and more accurately done by means of the apparatus 
 in the figure. A, B. is a glass tube, the neck of which is very narrow, 
 
 and bent as in the figure. This tube is to be filled completely, at 
 
Expansion of Liquids. 
 
 73 
 
 the lowest temperature, with the liquid, whose expansion is to be exam- 
 ined and then weighed, the weight of the tube itself being previously 
 known, and the quantity of liquid which it contains thus determined. 
 The tube is to be then arranged horizontally in a vessel of water or 
 oil C, to which heat may be applied by a furnace E, below ; and the liquid 
 expanding according as its temperature is raised, the excess of volume 
 flows out by the capillary beak A, and may be collected as in F, or let to 
 waste. When the apparatus has been brought to the highest temperature 
 required, as known by the thermometer Y. D. and that all further 
 expansion has ceased, as is known by no more liquid passing out 
 by A. the tube is to be removed from the bath, carefully cleaned, 
 and, when again cold, accurately weighed. The loss of weight 
 is the quantity of liquid that has been expelled, and this, compared 
 with the whole original quantity of liquid, gives the proportion of ex- 
 pansion. In this manner, however, the result appears to be less than it 
 really is, for the expansion of the glass tube itself diminishes the quan- 
 tity of liquid expelled. Such results require, therefore, to be corrected 
 for the expansion of the glass, which is, however, so small, that in the 
 more dilateable liquids it may be neglected. In mercury, however, it 
 affects the apparent expansion very much ; mercury expanding in glass 
 through 180 augments in volume only ^ whilst its real expansion is 
 
 The amount of expansion of different liquids, in passing through 180 
 degrees of Fahrenheit, is thus found to be : 
 
 Alcohol, . . .1 Oil of turpentine, . J 
 
 Nitric acid, . . i Sulphuric acid, . _i 
 
 Fixed oils, . . JL Water, i 
 
 Sulphuric ether, . i Mercury, . . i 
 
 The actual amount of expansion, independent of the expansion of 
 the containing vessel, is best observed by the apparatus used by Dulong 
 and Petit, and somewhat improved by Regnault. It consists of a glass 
 
 tube, a 6 c, bent in the form of an 
 U, of which the horizontal portion 
 c is narrow, but the vertical legs 
 pretty wide. WTien mercury is 
 poured into the tube, it stands at 
 the same height in both legs, if the 
 
 r ^^ temperature be the same ; but one 
 
 leg being immersed in a vessel of oil or water, I, by which heat can be 
 applied to it, and thereby the mercury in it caused to expand, the 
 height of the liquid column must increase in the proportion of the 
 augmented volume, in order to balance the colder column of mercury 
 The difference between the heights being read off, by means of an accu- 
 
74 
 
 Determination of the Law of Expansion. 
 
 rate scale, with a telescope, o, the amount of absolute expansion may 
 be easily calculated from it. 
 
 By means of such instruments those observers determined the rate 
 at which the expansion of mercury increases with the temperatu re, as 
 has been noticed generally in the description of the thermometer. Their 
 result was, that between 32 and 212, measured on the air thermo- 
 meter, the expansion is j^.j-. Prom 212 to 393 it is y^y. and from 
 
 392 to 572 it is 
 
 consequence is, that measured by its 
 
 own expansion, mercury boils at 680 Fahrenheit; but from the ex- 
 pansion of the glass of an ordinary thermometer bulb, it boils at 660 
 on the visible scale, which coincides almost exactly with 662, the 
 temperature given by the dilatation of air. The apparent expansion 
 of mercury in glass may, therefore, be taken as being uniform through 
 180 and as amounting to -^ T of its volume. 
 
 Considerable simplicity is given to the laws of dilatation of liquids, 
 by an observation of Gay Lussac, that, in order to obtain any common 
 rule for them, such as is found for gaseous bodies, we must examine 
 them when in the same molecular condition ; that is to say, the cohe- 
 sive powers of the liquids we employ must be brought into the same 
 state. This is most nearly done, by taking these liquids when heated 
 to their boiling points, for then the cohesion of each liquid is about to 
 cease ' altogether. Thus alcohol boils at 173, water at 212, sulphu- 
 ret of carbon at 134, and sulphuric ether at 96 '3 ; and, taking I'OOO 
 volumes of each at their boiling points, and allowing them to cool, they 
 contract as follows : 
 
 By cooling 
 through. 
 
 Water 
 contracts. 
 
 Alcohol 
 contracts. 
 
 Sulphuret 
 of Carbon 
 contracts. 
 
 Ether 
 contracts. 
 
 18 () 
 
 6-61 
 
 11-43 
 
 12-01 
 
 16-17 
 
 36" 
 
 13-15 
 
 24-34 
 
 23-80 
 
 31-83 
 
 54 
 
 18-85 
 
 34-74 
 
 35-06 ! 46-42 
 
 72 
 
 2410 
 
 45-68 
 
 45-77 
 
 58-77 
 
 90<> | 28 . 56 
 
 56-02 
 
 56-28 
 
 72-01 
 
 108 
 
 32-42 
 
 65-96 
 
 6621 
 
 
 
 We by this means find a very interesting relation between alcohol 
 and sulphuret of carbon, two fluids remarkably different in their speci- 
 fic gravities, and in their chemical constitution and properties. It ap- 
 pears that their molecular force must increase at the same rate, for in 
 cooling the same number of degrees below their boiling points, they 
 contract to exactly the same amount : and a still further connexion is 
 exhibited between their molecular conditions, by the remarkable fact, 
 
Maximum Density of Water. 75 
 
 that, in being converted into vapour, the augmentation of volume which 
 they undergo is the same. 
 
 Many liquids possess the property of contracting, by reduction of 
 temperature, only to a certain point ; below which, if the cooling be 
 continued, they expand. As the volume at this temperature is the least 
 possible, it is called the point of maximum density. This peculiarity 
 was first recognized in water; but it has since been found in many other 
 fluids, even in a still more remarkable degree. It is, however, in water 
 that the phenomenon is of most importance, in consequence of the ex- 
 tensive agency of that liquid in natural operations. The point of max- 
 imum density of water has been determined by the experiments of very 
 many persons to be 39'5 of Fahrenheit. When water below that tem- 
 perature is heated, it contracts; when heated above it, it expands: 
 when cooled from above it, it contracts ; when cooled below it, it ex- 
 pands : and when the experiment is made in glass vessels, the contrac- 
 tion of the glass has the effect of rendering the expansion of cooling 
 below, or of heating above, through the same number of degrees, exactly 
 equal. Thus, 100-000 volumes of water become 100'012 equally by 
 being cooled from 39.5 to 32 or heated to 46, and the specific 
 gravity of water at 46 and 32 is consequently the same. 
 
 A great deal of the permanence of the existing order of nature de- 
 pends upon this property of water : it is by means of it, that the 
 great mass of water, in our lakes and rivers, is preserved from being 
 converted into solid ice. When, by the cooling process of the winds, 
 the water has been all reduced to the temperature of 39.5, the water 
 at the surface acts as a screen to prevent the further loss of heat, and 
 thus retains the deeper portions at a temperature sufficiently high to 
 support the existence of its organized inhabitants ; for the superficial 
 water being cooled below 39.5, by the continued action of the cold 
 winds, it becomes lighter, and floats upon the heavier and warmer 
 water underneath ; and from the bad conducting power which water will 
 be hereafter demonstrated to possess, the loss of heat is effectually pre- 
 vented. If it were not for this property of water, all large collections 
 of it, in lakes and rivers, should, with few exceptions, be permanently 
 frozen. 
 
 The dilatation of solids is much inferior in amount to that of liquids, 
 and, as with these, the rate of dilatation is not uniform, but increases 
 with the temperature. The increase is, however, so exceedingly minute, 
 that in almost all cases it may be neglected, and hence need not occupy 
 much attention. The dilatation of solids, although so small, may yet 
 be demonstrated to be real, by many simple experiments. Thus, if an 
 iron rod be made to fit, when cold, in length and breadth, an exact scale, 
 
76 
 
 Determination of the 
 
 it will be found, when heated, to be too large to enter it. An iron ring 
 which is, when cold, too small to pass over a cylinder, becomes suffi- 
 ciently large on being heated, and if the cylinder could have passed 
 through when cold, its diameter becomes too great to allow its passage 
 when its temperature is raised. In the arts, the expansion of solids, 
 particularly of the metals, in this way, becomes the source of numerous 
 inconveniences, and of many useful applications, Thus, the iron rim 
 of a carriage wheel is secured by the power of its own contraction ; it 
 having been slipped upon the wooden frame, whilst in a hot and ex- 
 panded state. The force of contraction of iron bars in cooling, has 
 been applied successfully to restore to the proper position, buildings 
 which had been about to fall, and the rate of expansion has also, as in 
 the pyrometers of Daniell and others, served as an useful measure of 
 high temperatures ; on the other hand, by the alternate expansions and 
 contractions, under the successive influence of winters and summers, 
 of the metallic bars, which had imprudently been laid in the masonry 
 of some important public buildings, with the idea of giving additional 
 security, the courses of stone or brick have been loosened from one 
 another, and reconstruction rendered necessary, in order to prevent their 
 being gradually pulled to pieces. 
 
 In estimating the amount of expansion of a solid body, the great 
 difficulty is the accurate measurement of the small increase in length, 
 which takes place. For this purpose, a great variety of mechanical 
 arrangements have been constructed. As they all are in principle the 
 same, and the detailed description of any exact form would occupy too 
 much space, it will be sufficient to notice one, which, though not that 
 by which very accurate numbers may be obtained, is calculated to give 
 
 satisfactory idea of their general construction ; a b is the bar of which 
 
Expansibility of Solids. 77 
 
 the expansion is to be determined ; it is fastened securely at the extre- 
 mity a, and rests at b, in a groove along which it is free to move, as in 
 the figure. This end of the bar at b, presses against a rod, c, which is 
 a lever of the second order, very near the fulcrum, and this transfers its 
 motion to the end of the lever, increased in the proportion of the dis- 
 tance. This lever acts on another similar one d, the extremity of which 
 serves as an index on the graduated circular arc e t by which the amount 
 of expansion is read off. Thus, if the acting lengths of the arms of 
 the levers are respectively, 1 and 20, and that the end of the bar a at b, 
 moves, Y^ of an inch, the end of the index d will move on the scale 
 
 *1 A vv Of) 4- 
 
 e through TOOO~ = 10 ^ an " 1C ^ a s P ace ca P a ^ e f being divided by 
 a microscope and vernier into 200 measurable spaces, so that an ex- 
 pansion of the two hundred thousandth of an inch can be positively de- 
 termined. Tor a popular illustration, the source of heat may be lamps, 
 as in the figure, but for accurate experiments the bar is completely 
 immersed in a bath of oil or water, and the temperature ascertained by 
 a suitable arrangement of thermometers. 
 
 The most important results thus obtained are the following. The 
 temperature being raised from 32 to 212 ; the increase in length pro- 
 duced, is, with a bar of 
 
 ' SZTT 
 * TTBT 
 
 Flint Glass . 
 
 ' T5TG 
 
 Steel 
 
 Crown Glass . 
 
 ' 1087 
 
 Gold 
 
 Copper . 
 
 * JWS 
 
 Silver 
 
 Brass . . : 
 
 
 Lead. 
 
 
 J32 
 
 
 Soft Iron 
 
 
 Tin . 
 
 The increase in length is called the linear dilatation of a substance, 
 but its increase of volume is called the cubical dilatation, and is three 
 times the former. Thus, the cubical dilatation of glass is 15 5 1? or 
 yyg. Hence, a glass ball which holds 439 measures, at 32 becomes 
 capable of holding 440 at 212, or if it hold 10*000 at 32, it holds 
 10-028 at 212. In this manner the correction for the expansion of 
 glass is in all cases made. But it is necessary to apply the amount of 
 expansion belonging to the particular sort of glass ; thus, in the ac- 
 count of the thermometer, in page 60, the cubic dilatation of glass 
 was taken, not as 10'028, but 10'026. 
 
 Although it is abundantly proved that solid bodies expand more 
 rapidly, at high, than at low temperatures, yet, except in the case of 
 some particular substances, as glass, iron, and platinum, whose utility 
 as measures of heat rendered a knowledge of the law of their expansion 
 necessary, the subject has been little examined ; the degree to which 
 
78 
 
 Effects of the Expansion 
 
 the rate of expansion is affected by temperature will be sufficiently 
 shown in the table which follows. At the temperature of 212 Fah- 
 renheit, as given by an air thermometer, the dilatation for one degree 
 is thus, for 
 
 Glass. 
 
 Platinum. 
 
 Iron. 
 
 Copper. 
 
 1 
 
 1 
 
 1 
 
 1 
 
 69660 
 
 67860 
 
 50760 
 
 34120 
 
 whilst at 572 of Fahrenheit it becomes, for 
 
 Glass. 
 
 Platinum. 
 
 Iron. 
 
 Copper. 
 
 1 
 
 1 
 65340 
 
 ] 
 
 1 
 
 31860 
 
 59220 
 
 40678 
 
 and the temperatures deducible from the expansion of a thermometer, 
 made of each of these substances should be in passing from 212 to 
 572 as compared with air, 
 
 Air. 
 
 Glass. 
 
 Platinum. 
 
 Iron. 
 
 Copper. 
 
 572" 
 
 667 
 
 592 
 
 7020 
 
 623o 
 
 Platinum expands thus the most regularly of those bodies, and should, 
 therefore, be best fitted for a metallic thermometer. 
 
 It is remarkable that the rate of expansion is not increased by rise 
 of temperature, for all solid bodies, but, on the contrary, in some 
 cases there exists, for solids as for liquids, a point of maximum den- 
 sity, so that the body shall expand, whether it be cooled or heated from 
 that degree. This is peculiarly the case in Rose's fusible metal, which 
 has been so often mentioned as a means of applying a steady heat. 
 When heated from 32 to 111, this metallic alloy increases in volume, 
 from 100-000 to 100-830 parts ; but there the expansion stops, and 
 when further heated it contracts, until, when at 156, the volume is 
 only 99-291, being less than at 32. By a further rise of temperature 
 it again expands, and at 178 is at its original volume of 100.000, and 
 continues expanding until being 100*862 at 201, almost exactly what 
 it had been at 111, it begins to melt. It is curious that this substance 
 has no point of maximum density when in the liquid state. 
 
Of Compound Metallic Bars. 79 
 
 The different rates of expansion of different solid bodies are subser- 
 vient to some very important uses in the arts and in scientific research. 
 Thus, the difference between the expansibilities of platinum and brass, 
 or any other two metals which differ much, may be used as a very deli- 
 cate thermometric means. If we take a flat rule of platinum exactly 
 ten inches long, at 32, and lay it on a similar rule of brass, to which 
 it is firmly screwed at one extremity, and on which, at the free end, 
 there is engraved a scale of parts of an inch, for a small space, the 
 compound rule will serve as a thermometer. For the two rules being 
 exactly of the same length, at 32, if we place them, fastened together, 
 in boiling water, the brass rule will be elongated by 0'019, whilst the 
 platinum rule will expand only through 0*009, hence the end of the brass 
 rule will project beyond the platinum rule by 0*010 of an inch, and as 
 the expansion is uniform for these moderate temperatures, each degree 
 of Fahrenheit's scale will be indicated on the scale of the brass rule by 
 of an inch. In this form the spaces would be too mi- 
 
 nute to be easily determined ; but by modifying the form, and connecting 
 the rules through their whole length, the beautiful metallic thermometer 
 of Breguet has been invented. Its principle is as follows : if the two 
 rules be soldered completely together, as in a, in place of being con- 
 nected only at a single point, the result of the unequal expansion is to 
 bend the bar, as in b, until the most expansible metal being on the 
 
 outside, it forms an arch longer than that 
 
 a formed by the inside rule, by the difference 
 
 of their expansions. If the compound 
 bar be already bent into a circle, the ends 
 of which are not opposed, the effect of the 
 expansion is to make these edges project, and to diminish the diameter 
 of the circle ; by having a number of such circles, the expansion of all 
 being added together, a considerable circular motion is produced in the 
 extremity. In the thermometer of Breguet there is such a compound 
 spiral fastened at the upper end, and having attached to its lower 
 
 extremity an index, which moves round 
 a circular scale, c c, and indicates the 
 temperature of the instrument. On this 
 relative expansion is also founded the 
 construction of the compound pendulum. 
 A metallic bar, when used, as in an ordin- 
 ary clock, to measure time by its vibra- 
 tions, being constantly changing in length 
 according as the external temperature 
 varies, affects the rate of the clock, mak- 
 
80 Nature of Specific Heat. 
 
 ing it go too fast or too slow, by its shortening or elongation. This is 
 corrected by having two or more bars, by the expansion of one of which 
 the vibrating length of the pendulum is increased, whilst by the expan- 
 sion of the other it is just as much shortened ; the consequence of this 
 opposing action is, that the pendulum remains indifferent to all changes 
 of temperature, and the clock becomes an exact measure of time at all 
 seasons. 
 
 SECTION II. 
 
 OF SPECIFIC HEAT. 
 
 It is now necessary to examine into the quantity of heat which each 
 substance requires to raise its temperature a certain number of degrees, 
 for although it be quite impossible to assign the absolute proportion, 
 yet, by obtaining the relative proportions, we may arrive at results 
 which may serve to characterize those substances, and may, as shall be 
 hereafter shown, lead us to important views of the relations between 
 their physical and chemical constitution. The relative quantity of heat 
 necessary to raise the temperature of any body through a certain num- 
 ber of degrees, as ten, for example, is termed its specific keat. 
 
 If we take a pint of water at 150, and another pint of water at 50, 
 and that we mix them well in a very thin vessel, the temperature of the 
 mixture is found to be, if we allow for some sources of errors to which 
 this process is exposed, exactly 100. Thus the one part of water has 
 transferred to the other a quantity of heat sufficient to raise its tem- 
 perature 50, and whether this addition was from 50 to 100, or from 
 100 to 150, the result was the same. In water, therefore, the spe- 
 cific heat does not change within these limits ; but it will be found that 
 in high temperatures a trifling increase does occur ; for the present 
 purpose, however, it may be neglected. If, now, a pint of water be 
 taken at 150 as before, and a pint of mercury at 50, and that they 
 be well and rapidly mixed together, until both have attained the same 
 temperature, this will be found to be 118. The mercury here rises 
 from 50 to 118, through 68, whilst the water cools only through 
 32, or not quite half as much, so that the same quantity of heat can 
 raise the temperature of mercury through more than twice as many 
 degrees as that of water. 
 
 Taking thus equal volumes, the specific heats of water and mercury 
 are as 68 : 32 ; or water being adopted as the standard, for liquid and 
 solid bodies, and its specific heat taken as 1, the specific heat of mercury 
 
Method* by Mixtures and ly Cooling. 81 
 
 is 0-47, nearly. Such bodies are, however, generally taken not in 
 equal volumes, but in equal weights, and hence, it is necessary to divide 
 the 0'47 by 13*5 the specific gravity of mercury, and thus there is 
 obtained 0*035, its specific heat. 
 
 The process now given is known as the method of mixtures, and has 
 been selected for example, as that by which the meaning of the term 
 specific heat is best explained ; but it is not the only one, or even, 
 perhaps, the best by which specific heat may be determined. The 
 sources of error are, that a certain quantity of heat is absorbed by the 
 vessel in which the mixture is made, and that, as the mixture requires 
 some time to make, a certain loss occurs by the cooling power of the 
 air. But it is, however, in skilful hands, capable of exceeding accuracy ; 
 and, with the recent improvements that have been made in its details 
 by Regnault, it has yielded results of the highest value to science. The 
 various forms of apparatus used in such experiments need not be 
 described. For the use of the method of mixtures it is not necessary 
 that the two bodies should be liquid. Thus, if a pound of pure copper 
 in a bar be heated in an oil bath to 300, and then be immersed in a 
 pound of water at 50, the copper will give out its excess of heat to 
 the water, and both will arrive at a temperature of 72. The copper 
 has, therefore, lost 228, and the water has gained 22, and the specific 
 heats being inversely as these numbers, that of copper is found thus 
 to be 2 ^ = 0-096, water being I'OOO. 
 
 One process employed by Dulong and Petit consisted in heating to 
 the same degree the bodies to be tried, and allowing them to cool 
 under exactly the same circumstances. It is evident that "if we know 
 exactly the rate at which a body cools, and the time which it takes to 
 cool, we can calculate exactly how much heat it parts with. Thus, if 
 we have two bodies heated to 300, and that, when circumstanced in all 
 respects alike, one requires 15 minutes to cool to 50, and the other 
 25, the latter will have parted with more heat, in the proportion of 25 
 to 15, an4 the specific heat is expressed by the quantity of heat the 
 body gives out in cooling. Hence those substances which have high 
 specific heats require more time to heat or cool, through a certain 
 number of degrees, than those bodies whose specific heat is less. 
 
 It was by a process of this kind that the relative specific heats of 
 bodies was first discovered. Boerhaave having remarked, that when 
 two thin glass vessels, containing, one a pound of water and the other a 
 pound of mercury, were equally exposed to the heat at the front of a 
 strong fire, the temperature of the mercury rose much more rapidly than 
 that of the water, and that it attained its highest temperature in one-half 
 of the time which the water required ; and also, when both, equally hot; 
 6 
 
82 Determination of Specific Heats. 
 
 were removed from the fire, the mercury cooled twice as fast. Eor 
 accurate purposes, however, there are many precautions necessary in 
 order to place the substances under the same conditions, so as to render 
 the rapidity of cooling dependent only on their respective specific heats ; 
 thus, equal weights of the different bodies are placed in the same thin 
 polished silver vessel, so that their external surface may be the same in 
 extent and nature, and this vessel cools in an exhausted receiver in 
 order that there may be no loss of heat from contact with the external 
 air. The internal surface of the receiver must also be always in the 
 same molecular state, that the heat given out may pass off in all cases 
 with equal facility. 
 
 An extensive series of researches on the specific heats of bodies, 
 conducted by the illustrious associates Lavoisier and Laplace, have 
 been found on repetition to have been rendered useless by the imper- 
 fections of the apparatus they employed : it was termed the Calorimeter, 
 and consisted of a vessel containing ice, in the centre of which the 
 heated body was placed, and the quantity of heat this gave out in 
 cooling was measured by the quantity of ice which was melted into 
 water. Outside there was another case of ice to defend the instrument 
 from the action of the air. It was found in practice impossible to 
 collect all the water. A quantity remained infiltrated among the ice, 
 some solidified in one part of the vessel after having been melted in 
 another, and consequently, the numbers given by two of the greatest 
 men that have ever been attached to science, must be considered as 
 quite without authority. In cases, however, where the quantity of heat 
 was very large, as when the Calorimeter was employed to determine the 
 quantity of heat produced in combustion, these sources of error became 
 less influential, and such results will be utilized in a future chapter. 
 
 The specific heats of a number of the most important solid and liquid 
 bodies, determined by such methods, are given in the following Table : 
 
 Water . = 1-000 
 
 Iron . = 0-114 
 
 Ether . 
 Alcohol 
 
 
 = 0-520 
 = 0-660 
 
 sr. 
 
 
 = 0-095 
 = 0-031 
 
 Sulphuric A 
 
 id 
 
 = 0-333 
 
 Gold 
 
 
 = 0-032 
 
 Nitric Acid 
 
 
 = 0-442 
 
 Antimony 
 
 
 = 0-051 
 
 Sulphur 
 Carbon 
 
 
 = 0-202 
 = 0-241 
 
 Tin . 
 Iodine . 
 
 
 = 0-056 
 = 0-054 
 
 Mercury 
 
 
 = 0-035 
 
 Phosphorus 
 
 
 = 0-188 
 
 Arsenic 
 
 
 = 0-081 
 
 Glass . 
 
 
 = 0-177 
 
 Platinum 
 
 
 = 0-032 
 
 Calomel 
 
 
 = 0-041 
 
 Silver 
 
 
 = 0-057 
 
 Common Sa 
 
 t 
 
 = 0-225 
 
 Zinc . 
 
 
 = 0-095 
 
 Nitrate of So 
 
 da 
 
 = 0-240 
 
 Tellurium 
 
 
 = 0-051 
 
 Lime . 
 
 
 = 0-205 
 
 Nickel 
 
 
 = 0-109 
 
 Magnesia 
 
 
 = 0-276 
 
 Cobalt ; 
 
 
 = 0-107 
 
 
 The numbers given are generally those lately obtained by Regnault. 
 
Relation of Specific Heat to Atomic Weight. 
 
 83 
 
 The specific heats of bodies are not the same at all temperatures ; 
 thus Dulong and Petit have found that the specific heats, calculated 
 from the change of temperature from 32 to 212, and from 32 to 
 572, differ, as in the Mowing Table : - 
 
 Substance. 
 I 
 
 Sp. Heat from 
 32 to 212. 
 
 Sp. Heat from 
 32 to 572. 
 
 ; 
 Mercury 
 Zinc 
 Antimony 
 Silver . , .... 
 Copper . 
 Platinum 
 Glass . ' " ' 
 Iroti . * ; s 
 
 0-0330 
 0-0927 
 0-0507 
 0-0557 
 0-0949 
 0-0355 
 0-1770 
 0-1098 
 
 0-0350 
 0-1015 
 0-0549 
 0-0611 
 0-1013 
 0-0397 
 0-1900 
 0-1218 
 
 The specific heat increases, therefore, with the temperature, and 
 Nauman and Regnault have found that this holds, even with water, for 
 according to their experiments, the sp. heat of water at 32 being TOGO, 
 that of water at 212 is 1 "010, consequently the equal distribution of heat 
 between warm and cold water, which was described at the commence- 
 ment of this section, does not exactly hold; the temperature of the 
 mixture should be a very little above the mean. This was, however, 
 omitted, in order not to complicate the account of that manner of 
 finding the specific heats. 
 
 The specific heat of the same substance may vary very materially 
 according to its molecular condition ; thus carbon has been found to 
 possess the following different specific heats in its several forms : 
 
 Animal charcoal 
 Wood charcoal 
 Coak of coal 
 Coak of antracite 
 
 0.2608 
 0.2415 
 0.2031 
 0.2015 
 
 Graphite natural . 
 
 ,, of iron furnaces 
 ,, of gas retorts 
 
 Diamond 
 
 0.2019 
 0.1970 
 0.2036 
 0.1469 
 
 The specific heats of bodies are found to be connected very intimately 
 with their chemical and molecular constitution, although we are not able 
 at present to trace the exact cause of this connexion in all its forms. 
 The discovery of such connexion was the most remarkable result of the 
 experiments of Dulong and Petit, and it may be expressed as follows. 
 If we take the specific heats of any of the bodies given in the table, 
 and divide by each of them the number 3*1, we obtain a series of 
 numbers which are found to be either those which shall be hereafter 
 described as the chemical equivalents of the bodies, or to stand in some 
 remarkably simple relation to those equivalents, thus : 
 
84, 
 
 Molecular Laws of Specific Heat. 
 
 
 
 3*1 
 
 . 
 
 Substance. 
 
 
 Sp. Heat. 
 
 
 Sulphur 
 Iron 
 Nickel 
 Cobalt ' -. <v : 
 Copper 
 Zinc ... 
 Tin ~ . 
 Lead 
 Mercury ' . . 
 Platinum 
 
 0-202 
 0-114 
 0-109 
 0-107 
 0095 
 0-095 
 0-056 
 0-031 
 0-035 
 0-032 
 
 15-5 
 27-2 
 284 
 29-0 
 33-7 
 32-6 
 55-4 
 100-0 
 94-0 
 97' 
 
 16- 
 27-2 
 29-6 
 29-5 
 31-7 
 32-3 
 57'9 
 103*7 
 101-4 
 98-8 
 I 
 
 Bismuth . . . . 
 
 0-030 
 
 100-7 
 
 71 '0 
 
 Carbon . . 
 
 024 
 
 12-9 
 
 6-1 
 
 Iodine . . . 
 Phosphorus . ,-. 
 Silver 
 Gold . . ; - t 
 Arsenic . . .. 
 Antimony 
 
 0-054 
 0-188 
 0-057 
 0-032 
 0-081 
 0-051 
 
 57-4 
 16-5 
 54-5 
 97-0 
 38-3 
 61- 
 
 126-3 
 31-4 
 108- 
 199- 
 75-3 
 129-2 
 
 In the first division of this table, the quotient is so close to the true 
 equivalent, as sufficiently to show that, were it not for the unavoidable 
 errors of experiment, they should coincide. In bismuth the result is 
 1 J times the true equivalent. In carbon it is double the true equivalent. 
 In the bodies in the last division of the table, the numbers obtained are 
 evidently one-half those usually assumed as the chemical equivalents. 
 Each of these illustrations might be much extended, their numbers 
 being only intended as examples of the fact. 
 
 The above are all simple bodies ; but Nauman and Avogadro have 
 shown, that also in compound bodies this connexion between the equi- 
 valent number and the specific heat exists, although the connecting 
 dividend is no longer 3*1, but is a different number for each class of 
 bodies. 
 
 Thus, for the following carbonates, the specific heats being made the 
 divisors of the number 10 '4, there is 
 
 Substances. 
 
 Sp. Heat. 
 
 10-4 
 
 Sp. Heat. 
 
 True 
 Equivalent. 
 
 Carbonate of liine . 
 
 0-2044 
 
 50-9 
 
 50-6 
 
 Carbonate of iron . 
 
 0-1819 
 
 57-2 
 
 58-1 
 
 Carbonate of zinc . 
 
 0-1712 
 
 60-7 
 
 62-4 
 
 Magnesian limestone ! 0*2161 
 
 48-1 
 
 46-7 
 
ific Heats of Atoms. 
 For certain sulphates the number is 12'4. Thus : 
 
 85 
 
 Substances. 
 
 Sp. Heat. 
 
 12-4 
 Sp. Heat. 
 
 . 
 ; Equivalent. 
 
 Sulphate of barytes . 
 Sulphate of strontia . 
 Sulphate of lime 
 
 0-1068 
 0-1300 
 0.1854 
 
 116-1 
 95-4 
 66-8 
 
 116-1 
 91-9 
 68-6 
 
 For a number of metallic oxides, the constant appears to be 5 ' 
 Thus: 
 
 Substances. 
 
 Sp. Heat. 
 
 5-4 
 Sp. Heat. 
 
 Equivalent. 
 
 Magnesia - . ; 
 Red oxide of mercury 
 Oxide of zinc . 
 Oxide of Copper 
 
 0-276 
 0-049 
 0-132 
 0-137 
 
 19-6 
 110-2 
 40-9 
 39-4 
 
 20-7 
 109-4 
 40-3 
 39-6 
 
 j 
 
 These results have been completely confirmed by Begnault, and ex- 
 tended to other classes of bodies as chlorides and sulphurets, so that it 
 may be considered as a general principle, and one exercising remarkable 
 influence on our views of the internal constitution of bodies, that with 
 all substances of equal atomic constitution, and of similar chemical 
 composition, the specific heats vary in an inverse proportion to the 
 atomic weights. 
 
 It will be observed, however, that in very few instances does the calcu- 
 lated number exactly agree with the true equivalent. And, indeed, as 
 what is called specific heat involves portions of heat of other kinds in a 
 very distinct degree, an approximation only can be expected. The most 
 important source of discrepancy is, however, that the same body alters 
 its specific heat as its state of aggregation changes ; thus, liquid 
 mercury is not strictly comparable with those metals whose specific heat 
 were determined in the solid form ; and it is, hence, not surprising that 
 it deviates very materially from the rule. The same body, in all cases, 
 changes its specific heat when it has been strongly heated ; and the heat 
 that is given out on the sudden compression of a metal, as in stamping 
 a medal, or drawing a wire, is due to a diminution of specific heat. 
 Similarly the change of chemical properties which results from the 
 ignition of oxide of iron, or of chrome, or of peroxide of tin, is 
 accompanied with an important diminution of specific heat, which 
 enables us to account for the vivid ignition which often takes place at 
 the moment of the passing of such oxides from the soluble to the in- 
 soluble condition. 
 
6 Specific Heats of Atoms. 
 
 The relation between the specific heats of bodies, and their chemical 
 equivalents, is thus remarkably shown to extend not merely to the 
 simple substances, but even to saline bodies, and indicates a connexion 
 between the chemical equivalents and the molecules upon which the 
 heat exerts its action, of an intimate description. In fact, the specific 
 heat of a certain weight of any body is thus shown to be proportional 
 to the number of chemically equivalent masses contained in that weight ; 
 and the constant numbers, which were divided by the specific heats, are 
 the specific heats of the ultimate chemically equivalent particles. Thus, 
 the specific heat of the chemical molecules of zinc, of lead, and tin, is 
 3'1 ; that of the oxides of zinc, of copper, and of mercury, 5'4 ; the 
 specific heat of the chemical atom or ultimate particle of carbonate of 
 lime, or of zinc, 10*4 ; and that of the sulphates of barytes, strontia, 
 and lime, 12*4. Attempts have been made to connect these constants 
 together, but without good foundation; for 5*4 and 12*4, although 
 nearly the double and quadruple of 3'1, are yet too far removed to show 
 any necessary connexion, and 10.4 is completely out of the series of 
 3'1, though nearly the double of 5*4. 
 
 I shall have occasion to discuss this remarkable relation between the 
 physical and chemical characters of these bodies, when I come to 
 examine the subject of the laws of chemical combination in their full 
 extent. For the present, the details now given are sufficient. 
 
 It is not likely that any law, connecting the specific heats of different 
 bodies, can be obtained perfectly consistent, for the various bodies 
 necessary cannot be examined exactly in the same state. Eegnault has 
 well observed, that the quantity of heat which we measure as specific 
 heat, consists of several different portions : 1st, the true specific heat ; 
 2nd, the heat which produces dilatation; 3rd, the heat which causes 
 the rise of temperature ; and 4th, when a solid is near its fusing point, 
 the quantity employed in giving the softness and ductility, which most 
 bodies at certain temperatures acquire. These last three portions being 
 very small, do not conceal the law by which the true specific heat is 
 regulated ; but they influence it so far, as to prevent the law from being 
 verified in its numerical results with the accuracy which otherwise might 
 have been obtained. 
 
 When bodies combine chemically, there is generally found to be a 
 diminution of specific heat; and it has been attempted to account 
 thereby for the rise of temperature, by which combination is in most 
 cases accompanied. Thus, the specific heat of sulphuric acid is 0-33 ; 
 and when mixed with an equal weight of water, the specific heat of the 
 mixture should be, were there no action, --^=0,665 ; but the true 
 specific heat of the combined acid and water is found to be only 0*587. 
 
Specific Heats of Gases. 87 
 
 The excess therefore, O665 - 0*587=:0 1 078, becomes free, and shows 
 itself by raising the temperature of the mixture; and accordingly, on 
 mixing together sulphuric acid and water, it is well known that a 
 temperature higher than that of boiling water may be produced. It 
 was even supposed at one time, when heat was looked upon as being a 
 positive substance which combined with bodies in different proportions, 
 that the absolute quantity of heat which a Jaody contained might be 
 determined by such an experiment, thus : if the rise of temperature 
 produced by 0*078 of heat becoming free is expressed by 180 above 
 22, then the quantity of heat which stays behind must be greater than 
 that in the proportion of 587 to 78 ; and hence is equivalent to ^- 
 180=1335 : and thus, at the temperature of 1303 of Fahrenheit's 
 scale, a body should contain no heat at all ; it should be the absolute 
 zero. But no two such experiments, with different bodies, ever gave 
 the same result : and it is evident, from the fact of the specific heat 
 diminishing as the temperature sinks, that the term at which the two 
 quantities should vanish must be infinitely remote, and that there is no 
 such thing as an absolute zero at all. In fact, the physical existence of 
 an absolute zero is inconsistent with the more accurate ideas of the 
 nature of heat, which modern investigation has suggested. 
 
 The development of heat, in chemical combination, is also only in 
 some cases accompanied by a diminution of specific heat ; in at least as 
 many it is on the contrary remarkably augmented. 
 
 The specific heat of gases and vapours has obtained considerable 
 attention ; and yet, from the extreme delicacy of the processes necessary 
 and the small quantity of material which can be operated on, the results 
 hitherto obtained have not acquired that degree of positive accordance 
 which should render repetition unnecessary. The principal experi- 
 menters in this department have been Delaroche and Berard, Delarive 
 and Marcet, Haycraft, Dulong, and, latterly, Apjohn and Suerman. 
 
 The method adopted by Haycraft and, and by Delaroche, and Berard, 
 consisted in heating a quantity of gas to a certain temperature, and 
 then by passing it through a tube in a vessel of water, detetmining how 
 much it raised the temperature of the water in being cooled through a 
 certain number of degrees. In principle, this mode is perfect ; but the 
 extreme accuracy necessary in the management of the apparatus does 
 not appear to have been attained by Haycraft : and Delaroche and 
 Berard deprived their results of most of their value by the oversight of 
 using the gases in a damp state. The process of Delarive and Marcet 
 was not such as could lead to results worthy of much confidence. A 
 glass globe full of the gas, to which was attached a thermometer, with 
 the bulb exactly in the centre, was plunged into a vessel of hot water/ 
 
88 
 
 Specific Heats of Gases. 
 
 in the expectation that the time occupied by each gas, in having its tem- 
 perature raised a certain number of degrees, would be proportional to 
 the specific heat under a constant volume. But the communication of 
 the heat should be so much and so variously affected by currents, ac- 
 cording to the density of the gas, and the quantity of heat, absorbed by 
 the gas, so trifling in comparison to that which should be required to 
 heat the globe, that the amount of liability to error was very great. 
 
 The process employed by Dulong was very beautiful in principle, and 
 calculated to give experimental results of great accuracy. It consisted 
 in determining the velocity of sound in each gas, which was measured 
 by finding the musical note the same organ pipe gave with each : from 
 this, by very ingenious methods, which, however, need not here be 
 introduced, further than that the gases, with higher specific heats, give 
 more acute musical tones, he calculated the specific heats. The calcu- 
 lations were, however, based on certain other principles, which are not 
 necessarily true. 
 
 The method contrived by Apjohn is that which appears to be the 
 best calculated to give accurate results, and those which he obtained 
 have been verified by the experiments of Suerman. 
 
 Apjohn's method cannot be completely described, until we come to 
 speak of the latent heat of vapours and their relation to space ; but the 
 general principle of it is, that if several gases be employed to convert a 
 certain quantity of water into vapour, the gases will be cooled thereby 
 in inverse proportion to their specific heats. Thus, if one gas have 
 double the specific heat of another, it will saturate itself with vapour by 
 cooling through only half the number of degrees necessary for that with 
 the less specific heat ; and thus, by measuring simply the cooling power 
 of each gas, the specific heat may be calculated. 
 
 The numbers obtained by Delaroche and Berard, by Dulong and by 
 Apjohn, for the specific heats of the gases in equal volumes, are given 
 in the following table ; 
 
 Gases. 
 
 Apjohn. 
 
 Delaroche. 
 
 Dulong. 
 
 Air . 
 Nitrogen . 
 Oxygen . , .,, v ^ 
 Hydrogen . 
 Carbonic acid 
 Carbonic oxide 
 Nitrous oxide 
 
 1-000 
 1-048 
 808 
 1-459 
 1-195 
 993 
 1-193 
 
 1-000 
 1-006 
 976 
 900 
 1-258 
 1-034 
 1-350 
 
 1-000 
 1-000 
 1-000 
 1-300 
 1 -172 
 1-000 
 1-159 
 
 These numbers show the diversity which exists among even the best 
 experimenters ; and they also show that the different gases follow no 
 
Of Liquefaction. 89 
 
 simple law regarding their specific heats. The principle laid down by 
 the same specific heat, is thus shown by the combined evidence of all 
 the best results to be totally unfounded. 
 
 It is sometimes necessary to compare the specific heats of gases with 
 that of water ; this being 1*000, that of air is 0*267 for equal weights, 
 and so on for the other gases in proportion. 
 
 We do not know the specific heats of many bodies in the state of 
 vapour. For watery vapour, however, it is found to be 0*847, water 
 being 1*000, or 3*172, air being 1*000, for equal weights. Water is 
 thus the only substance of which we know the specific heat in the three 
 states of aggregation, that of ice being *513, water 1*000, and steam 
 847, for equal weights. 
 
 When the volume of a gas or of a vapour increases, its specific heat 
 increases also, and vice versa. Hence, when air is suddenly condensed, 
 so much heat is evolved that tinder may be lighted, and the barrel of a 
 condensing syringe may become too hot to hold ; thus, also, in some 
 kinds of machinery where air suddenly expands, so great a degree of 
 cold is produced that water may be frozen. 
 
 The exact degree of connexion between the amount of expansion of 
 the gas, and the increase, or of condensation, and the diminution of 
 specific heat, has not been ascertained. They are not proportional : that 
 is to say, when the volume of a gas is doubled, its specific heat is not 
 doubled, and vice versa ; and yet it would appear that it does not fall 
 much below that ratio. 
 
 SECTION III. 
 
 OF LIQUEFACTION. 
 
 It has already been frequently explained, that by the application of 
 heat to a solid body it commences, when its temperature has risen to a 
 certain degree, to become liquid, and that this point, the melting point 
 of such solid body, is one of the most determinate and characteristic of 
 its physical properties. Accordingly, the melting point is often used as 
 a means of distinguishing and recognizing substances otherwise very 
 similar in properties, as, for example, the numerous fatty acids can 
 scarcely be otherwise distinguished from each other, exclusive of analysis, 
 than by the temperatures at which they melt. There has been alreadv 
 
90 Absorption of Heat During Liquefaction. 
 
 given a list of the melting points of a number of solid bodies, and, in 
 the history of each individual substance, its fusibility will be described. 
 
 The change from the solid to the liquid state is accompanied, 
 however, by a phenomenon differing from any yet described, and 
 deserving of great attention from the important consequences which 
 flow from it. It is, that at the moment of liquefaction a very large 
 quantity of heat is absorbed, combining, as it were, with the solid to 
 form the liquid body, and after combination being insensible to the 
 thermometer, and having thence obtained the name of latent heat. A 
 pound of water at 32 and a pound of ice at 32 give on the ther- 
 mometer precisely the same degree ; and yet, independent of all consi- 
 derations of specific heat discussed in the last section, and which we 
 now lay aside, the water contains, in a state of intimate combination, a 
 great quantity of heat, by virtue of which it is liquid water, and by 
 losing which it should be reduced to the state of solid ice. In melting, 
 therefore, every body renders latent a quantity of heat. 
 
 This principle may be demonstrated by experiments of a very simple 
 kind. Thus, if a pound of ice be taken at 32, and added to a pound 
 of water at 174, the ice dissolves immediately, but the temperature of 
 the resulting two pounds of water is found to be 32. There has thus 
 disappeared a quantity of heat, which had previously raised the tem- 
 perature of the water to 174 or through 142. This heat has been 
 absorbed by the ice in becoming liquid, and rendered latent ; and it is 
 therefore said that the latent heat of liquid water is 142. If a vessel 
 of water, at the temperature of 103, be exposed freely to air below the 
 freezing point, it will rapidly cool, until it arrives at 32, but there the 
 lowering of the temperature ceases ; it begins to freeze, and, until the 
 entire mass is reduced to solid ice, no loss of heat, sensible to the 
 thermometer, is observed : yet it must still be giving out heat, precisely 
 as it was when it cooled from 103 to 32, this heat being, however, 
 that which gave to it the form of liquid water, and which had been 
 perfectly insensible, or latent, until the formation of ice commenced. If 
 the water had taken half-an-hour to cool from 103 to 32 ; it will be 
 found to require one hour more to become completely frozen; 
 and hence, as in the same time it loses the same quantity of heat, the 
 external air remaining equally cold, the latent heat is 71 X 2 = 142 
 as in the former experiment. Another mode of verifying the result 
 consists in exposing a pound of ice at 32, and a pound of water at the 
 same temperature, to the same source of heat, as on a steady fire, and it 
 will be found, that, by the time that the ice has completely melted, the 
 temperature of the water will have risen to 174. 
 
Heat Evolved in Solidifying. 91 
 
 Water is, of all liquids, that which contains the greatest quantity of 
 latent heat, and hence, that which changes from the liquid to the solid 
 state most slowly, and inversely, ice, is the solid which absorbs most 
 heat, and requires most time to liquefy. This property of water is of 
 the highest importance in the economy of nature, for, by means of it, 
 the change of seasons is rendered much less sudden than could other- 
 wise occur. If water passed from 32 to 31, and became solid, by 
 losing oidy the same quantity of heat that it gives out in cooling from 
 33 to 32, the change of seasons should be so rapid and so uncertain 
 as to interrupt almost entirely the proper cultivation of the soil, and, by 
 the vicissitudes of heat and cold, become injurious to the health. But 
 as these properties of water are now arranged, each particle, in freezing, 
 becomes a source of warmth to all around, and mitigates the severity of 
 the cold ; there can be but a comparatively small quantity of water 
 rendered solid ; and when, on the return of a warmer season, a sudden 
 liquefaction might prove equally injurious, the ice and snow, in melting, 
 absorb all excess of heat, and render the change gradual, and suitable 
 to the functions of those plants and animals to which a sudden transition 
 might prove fatal. 
 
 We do not know the latent heat of many liquid bodies, but those 
 given in the following table will suffice to show the remarkable pre- 
 eminence of water in that respect. The numbers are given in two 
 columns the first showing the interval through which the body itself, 
 in its liquid form, would be heated by the heat it absorbs in melting ; 
 and the second showing the interval through which that heat would 
 elevate the temperature of an equal weight of water. Thus : 
 
 Latent Heat of 
 Water . 
 Sulphur 
 Lead . 
 Zinc . 
 Bismuth 
 
 
 Mi 
 
 sasured by its 
 142 
 144 
 370 
 493 
 550 
 
 self. Measured by water. 
 . 142 
 . 27-14 
 . - . . 11-0 
 . 48-3 
 . 23-25 
 
 In every case a solid body begins to melt at the same temperature. 
 Thus, ice never begins to melt until it arrives at 32, and can never be 
 raised above 32 without melting; consequently, the fixed point is the 
 melting point of ice, and not the freezing point of water ; for if water 
 be cooled carefully without agitation, its temperature may be lowered 
 easily to 25, and has been reduced to 15 without solidifying. This 
 is a phenomenon like that which has been (page 23) noticed in the 
 crystallization of sulphate of soda, where the solution may remain 
 perfectly liquid until agitated, and then suddenly crystallizes with the 
 evolution of considerable heat. If water, so cooled below 32, be 
 
92 Heat Evoked in Crystallization. 
 
 agitated, it freezes suddenly, and the temperature rises to 32 ; the 
 latent heat, of that portion which freezes, becoming sensible, and thus 
 warming the entire mass. 
 
 Substances which crystallize easily generally expand in solidifying, 
 and in doing so exert great force. Thus, water is capable of bursting 
 the strongest vessels, if they be filled completely with it, and tightly 
 closed, so as to prevent expansion otherwise. It is by the agency of 
 this force that the gradual deterioration of the surface of rocks, and 
 the formation of the soil on the lower grounds, depends ; the rain water 
 being absorbed into the pores and small cavities, which even the hardest 
 rocks contain, and being there, in winter, frozen, breaks open the sub- 
 stance of the rock, and causes it gradually to fall to powder ; thus 
 generating the soft and porous soil fitted for the reception and susten- 
 ance of the seeds and roots of plants. It is also by the action of this 
 force of expansion, exerted by many bodies when they crystallize, that 
 we are enabled to take accurate copies of the moulds into which such 
 substances, in the liquid state, are poured. Cast iron, antimony, and 
 the alloy of antimony used for printers' types, the alloy used for stereo- 
 type plates, brass, bronze, and all such bodies, are capable of making 
 good castings by virtue of this expanding power ; whilst bodies, which 
 do not distinctly crystallize, as gold, silver, and copper, are not capable 
 of giving accurate castings, and hence the coinage of these metals is 
 made by stamping the necessary marks upon them by means of a violent 
 blow. 
 
 By the addition of small quantities of salts, or vegetable acids, the 
 freezing point of water may be considerably lowered : thus, sea-water 
 does not easily freeze. When such a solution is brought to solidify, it 
 is pure ice which first crystallizes out. Thus, from a strong solution of 
 potash, ice has been obtained in large six-sided prisms ; and the ice 
 mountains which form in the Polar seas are found to be almost com- 
 pletely fresh. This principle has been applied also to the concentra- 
 tion of vinegar and lemon juice, by freezing ; a large quantity of mere 
 ice being formed round the sides of the vessel, and a central cavity re- 
 maining filled with concentrated acid. 
 
 The principle of latent heat has been applied to the production of 
 artificial cold. For if a solid body suddenly liquefies, without the 
 application of external heat, it must abstract, from the surrounding 
 bodies, the heat necessary to its liquefaction, and thus reduce their 
 temperature and its own. Hence, when salts are dissolved in water, 
 without any chemical combination, there is cold produced. Thus, by 
 mixing nitrate of ammonia with an equal weight of water, the ther- 
 mometer sinks 46 degrees ; and carbonate and sulphate of soda, dis- 
 
Production of Cold ly Liquefaction. 93 
 
 solved in three times their weight of water, reduce the temperature, the 
 first 16 and the second 12. 
 
 In many cases where, by double decomposition, those soluble substances 
 may be formed, more powerful effects are produced by mixing two salts 
 together than by either separately. Thus neither nitre nor salammoniac 
 produce much cold, but, when mixed, they generate nitrate of ammonia, 
 which is very powerful, and hence cause a reduction of 40. In other 
 cases the cold results from a quantity of water of crystallization being 
 set free and suddenly liquefying. Thus when crystallized sulphate of 
 soda is dissolved in muriatic acid, there are formed bi-sulphate of soda 
 and chloride of sodium, with which but of the quantity of water re- 
 mains ; and the remaining being disengaged, and abstracting from 
 the surrounding bodies the heat necessary for their liquefaction, depress 
 the temperature through 50. 
 
 Another instance of this manner of producing cold involves a very 
 anomalous play of chemical affinities, thus on dissolving crystals of 
 sulphate of copper in strong muriatic acid a depression of temperature of 
 40 degrees may be obtained and from the liquor pure crystallized 
 chloride of copper separates whilst sulphuric acid is left diluted by 
 what had been the water of crystallization of the sulphate of copper. 
 
 By using snow or pounded ice, freezing mixtures of still greater 
 power may be produced. The cold is the greatest when a substance is 
 employed which contains itself a large quantity of water in a combined 
 form. Thus crystallized chloride of calcium contains half its weight of 
 water, and, when mixed with an equal weight of snow, the whole be- 
 comes liquid, and the quantity of heat absorbed is proportionally large. 
 By combining such freezing mixtures, intense degrees of cold have been 
 produced ; Mr. Walker, to whom the invention of most of them is due, 
 having obtained a depression of temperature to 91 of Fahrenheit. 
 For the experiments on the effects of intense cold, there is, however, now 
 generally employed the more powerful agency of the evaporation of the 
 mixture of solid carbonic acid, and sulphuric ether referred to in 
 page 17. 
 
 The following table contains the proportions for some of the most 
 useful freezing mixtures, and the degree of cold which can be obtained 
 by means of them. It is to be remarked, that in using freezing mix- 
 tures a great deal of the success depends on the rapidity with which the 
 liquefaction is produced, and that the thinnest possible vessels, and a 
 tolerably large quantity of materials should be employed. For producing 
 a great degree of cold it is also necessary to cool the materials previously 
 as much as possible ; thus to produce the intense cold of 91, Mr. 
 Walker had cooled the substance to be mixed down to 68, by means 
 of other freezing mixtures. 
 
Nature of Freezing Mixtures. 
 
 FRIGORIFIC MIXTURES WITHOUT ICE. 
 
 Mixtures. 
 
 Parts, 
 
 Thermometer sinks 
 
 Degree of Cold. 
 
 Nitrate of ammonia, 
 Water, 
 
 1 
 
 1 
 
 | from + 50 to + 4 
 
 46 
 
 Muriate of ammonia, . 
 Nitrate of potash, 
 Water, 
 
 5 
 5 
 16 
 
 i from + 50 to +10 
 
 40 U 
 
 " ' 1 
 
 Sulphate of soda, 
 Diluted nitric acid, 
 
 3 
 2 
 
 |from_f 50 to 3 
 
 53 
 
 Sulphate of soda, . 
 Muriate of ammonia, 
 Nitrate of potash, 
 Diluted nitric acid, . 
 
 6 
 4 
 2 
 
 4 
 
 1 
 
 [from -J-50 to 10 
 
 60 
 
 Sulphate of soda, 
 Nitrate of ammonia, 
 Diluted nitric acid, 
 
 6 
 5 
 4 
 
 1 from 50 to 14 
 
 64 
 
 Sulphate of soda, 
 Muriatic acid, 
 
 8 
 5 
 
 I from + 50 to 
 
 50" 
 
 Phosphate of soda, 
 Nitrate of ammonia, 
 Dilute nitric acid, ; i 1 - 
 
 5 
 3 
 4 
 
 C from to 34 
 
 34 
 
 FRIGORIFIC MIXTURES WITH ICE. 
 
 ! 
 
 Mixtures. 
 
 Parts. 
 
 
 Thermometer sinks 
 
 Degree of Cold. 
 
 Snow or pounded ice, 
 Common salt, ../; ., 
 
 2 
 
 1 
 
 a 
 
 to 5 
 
 * 
 
 Snow or pounded ice, . 
 Common salt, * .'' . 
 Salammoniac, . H 
 
 5 
 2 
 1 
 
 d 
 
 to 12 
 
 * 
 
 Snow or pounded ice, . 
 Common salt, 
 Salammoniac, ./ . 
 Nitrate of potash . -; 
 
 24 
 10 
 5 
 5 
 
 \ 
 
 to 18 
 
 * 
 
 Snow or pounded ice, . 
 Common salt, 
 Nitrate of ammonia, 
 
 12 
 5 
 5 
 
 & 
 
 to 25 
 , 
 
 * 
 
 Snow, .... 
 Dilute nitric acid 
 
 7 
 4 
 
 i 
 
 from -{- 32 to 30 
 
 60 
 
 Snow, .... 
 Crystal, muriate of lime, 
 
 2 
 3 
 
 I 
 
 from 4. 32 to 50 
 
 82^ 
 
 Snow, . . ; 
 
 Potash, ';;* -. . 
 
 3 
 4 
 
 ! 
 
 from -J- 32 to 51 
 
 83 
 
 Snow, .... 
 Diluted nitric acid 
 
 2 
 
 i 
 
 from 46 
 
 46 
 
 Snow, .... 
 Crystal, muriate of lime, 
 
 { 
 
 i 
 
 from 6ff 
 
 60 
 
 Snow, .... 
 Dilute sulphuric acid . 
 
 
 
 i 
 
 from 66 to 91 
 
 25 
 
Nature of Special Heat. 95 
 
 Li the ordinary experiment of freezing mercury by a mixture of snow 
 and crystallized chloride of calcium, success is seldom obtained unless 
 by having two portions of the mixture, and either cooling the materials 
 for the second by means of the first, or plunging the tube of mercury, 
 when it has exhausted the cooling powers of the first, into the second 
 and freshly mixed portion of materials. 
 
 There are many cases in which heat is evolved from solid bodies, 
 wthout our being able positively to ascertain its source, and where, 
 consequently, it may be considered as having previously been latent. 
 Thus, by the friction of two different bodies together, as when the 
 axle of a carriage becomes hot, or when, as among savage nations, fire 
 is obtained by rubbing two pieces of wood together. But it is rather 
 a misuse of words to say that the heat evolved had previously been 
 latent, for the latent heat of a body should properly be considered as 
 that by which the fluid condition is conferred upon it ; and hence a 
 solid body cannot be said to have such latent heat at all. It is most 
 likely that as a diminution of specific heat accompanies the increase of 
 density which occurs when oil of vitriol and water are mixed together, 
 so where, by compression, the density of a solid body is increased, its 
 specific heat may be diminished, and hence sensible heat evolved. Al- 
 though our knowledge of this subject is not at all as satisfactory as its 
 importance merits, it has been ascertained that when iron is violently 
 compressed, as in boring cannon, or by repeated hammering, its spe- 
 cific heat becomes much less, and the heat evolved is so considerable, 
 that the metal may easily be made red hot. It would be well to dis- 
 tinguish between heat, certainly before latent, which may thus be ren- 
 dered sensible, and the true latent heat which is absorbed during 
 liquefaction, and which can be only given out again by the reassump- 
 tion of the solid form, and this might be done, perhaps, and its con- 
 nexion with specific heat made evident, by adopting the word special 
 heat, or heat peculiar to the body. Thus, liquids and vapours only 
 can contain latent heat ; but every body contains a quantity of special 
 heal, equally insensible to the thermometer, but becoming manifest 
 when the specific heat is diminished. The special heat is thus the heat 
 which gives to the body the temperature which it possesses, and the 
 quantity of special heat necessary to produce a rise of temperature mea- 
 sures the specific heat. 
 
 Many bodies undergo, before liquefaction, remarkable changes in 
 their molecular constitution : thus, iron, wax, and glass, become soft 
 and pasty, so that different pieces may be perfectly united into one ; 
 and it is, indeed, on this property that the most useful applications of 
 glass and iron in ordinary life, depend. This has been referred to a 
 
96 Laws of Vaporization. 
 
 certain quantity of latent heat having already entered into the body, 
 and giving an intermediate condition, that of semifluidity. There is 
 no proof either for or against this view, as no exact experiments have 
 been made upon such bodies. In other cases, where semifluidity is 
 produced, as in lard, tallow, &c., it is plainly seen to arise from the 
 substance being a mixture of two bodies, of which one melts easily, and 
 being then liquid, forms with the other, which remains still solid, a 
 kind of pulp, which gradually becomes less thick, according as the 
 temperature rises, until all is liquefied. 
 
 SECTION IV. 
 
 OF VAPORIZATION. 
 
 By the application of a higher temperature than that which was 
 necessary for liquefaction, the generality of fusible bodies are capable 
 of being converted into vapour. In this form they resemble, in mole- 
 cular constitution, the most permanent of the gases, and are subjected 
 to precisely the same laws of change of volume, for any alteration of 
 temperature or pressure, as atmospheric air, as long as the elastic form 
 is preserved. This passage from the solid, or liquid, to the gaseous 
 state of aggregation, may occur either slowly and silently, or with 
 violence and rapidity ; the body may either evaporate or boil. The 
 evaporation may go on at any temperature, even at the lowest; but 
 boiling commences only at a certain temperature, which depends on the 
 nature of the body, and upon the pressure to which it is subjected. 
 Each of these modes of generating vapour will require to be specially 
 examined ; but it is necessary to attend, in the first place, to the phe- 
 nomenon which accompanies and may be supposed to produce the 
 change of form, the absorption of the heat of vaporization; for pre- 
 cisely as a solid absorbs heat in becoming liquid, so does a liquid in 
 assuming the vaporous condition, render heat latent, and even in still 
 greater quantity. 
 
 If we place upon a steady fire, or over a lamp, a cup of water, we 
 shall observe that its temperature rises until it begins to boil, but then 
 remains perfectly stationary rfntil the last drop of the water shall have 
 boiled away. If we remark the time, we shall find it to be in the fol- 
 lowing proportion. Let us suppose the temperature of the water to 
 have been originally 74, and that at the end of six minutes it began 
 to boil, having attained the temperature of 212. In each minute, 
 
Latent Heat of Vapours. 
 
 97 
 
 therefore, there entered into the water a quantity of heat sufficient to 
 raise its temperature 2J ^ = 23. Now, the source of heat remain- 
 ing perfectly steady, it -will be found necessary to apply it during 42 
 minutes to boil away all the water ; and, as in each minute there enters 
 heat enough to raise the temperature of the same weight of water 23, 
 the total quantity of heat absorbed by the water, in being converted 
 into steam, would have raised its temperature, had it remained liquid, 
 23 x 42 = 966, or just to redness. And yet this becomes perfectly 
 latent, the temperature of the vapour formed, that is, of the steam, 
 being exactly 212, that of the water it is formed from. 
 
 By the inverse process, a corresponding observation may be made. 
 Thus, water being boiled in a vessel, as in the figure, the steam may be 
 conducted by a tube into a glass containing a weighed quantity of cold 
 water, the temperature of which is accurately marked. The steam, by 
 condensing in the cold water, raises its temperature ; and, when a suffi- 
 cient rise has been produced, the steam may be shut off, and the glass 
 with the warm water weighed again. It is found to be heavier than 
 before, from the quantity of water added to it by the condensation of 
 the steam ; and the quantity of heat given out by the steam, in so con- 
 densing, may be easily calculated. Thus : let us suppose that there 
 were eight ounces of water, at 62, originally used, and that, at the ter- 
 mination of the experiment, there were nine ounces at the temperature 
 of 186. It is then evident, that one ounce of steam, in condensing, 
 had raised the temperature of the eight ounces 124. The temperature 
 of one ounce might have been, therefore, raised 124 X 8 = 992; but 
 this was not all latent heat, for the steam, by merely condensing, should 
 have formed liquid water at 212, whereas it cooled to 186. The dif- 
 ference, = 26, must be subtracted from the 992; and thus the latent 
 7 
 
98 
 
 Vaporization Accompanied 
 
 heat of steam is determined to be 966, as it had been found by the 
 previous process. 
 
 The great quantity of heat thus contained in an insensible form in 
 steam is very generally made use of for warming apartments, arid for 
 chemical operations, in which exposure to the direct action of a fire, or 
 even to a sand bath, might be injurious. By means of a series of pipes, 
 steam from a boiler, placed at a distance, is brought to circulate through 
 every part of the most extensive buildings, and condensing gradually, as 
 it passes along the cooling surfaces, the liquid water is conducted back 
 again to the boiler, there to be reconverted into steam. In large manu- 
 facturing laboratories, such as those of the Apothecaries' Halls of Dublin 
 and of London, there are steam ranges, or series of evaporating pans, 
 and stills, set in cast iron cases, within which steam is introduced, and 
 thus the most delicate vegetable preparations, such as extracts and inspis- 
 sated juices, are prepared at temperatures, which, being completely under 
 the control of the operator, allow all the freshness and active properties 
 of the plants to be perfectly preserved. 
 
 By means of apparatus similar in principle to that in the last figure, 
 the latent heats of the vapours of many fluids have been determined. 
 The most recent and accurate experiments are those by Brix and 
 Andrews of Belfast, by whom it has been found that the latent heat of 
 equal weights of the vapours of the following bodies would have raised 
 the temperature of an equal weight of water, in condensing : 
 
 Water 
 Alcohol 
 Ether 
 
 Oilofturpenl 
 Nitric acid. 
 
 The latent heats of bodies, such as vinegar and water of ammonia, which 
 have no definite chemical constitution, but contain mixed water, do not 
 possess any value or importance. In merely practical calculations the 
 latent heat of water is however usually taken for simplicity at 1000. 
 
 In changing from the liquid to the gaseous state, the volume is in- 
 creased in a very great degree ; the amount of increase, in some in- 
 stances, which may be taken as examples, is given in the following table. 
 
 966 
 376<> 
 163 
 138 
 335 
 
 Sulphuret of Carbon 
 Bromine -,.. 
 
 Hydriodic Ether 
 Acetic Ether . . 
 Oxalic Ether . 
 
 157 
 
 82" 
 85 
 15?' 
 
 Substance. 
 
 Spe. Gra. 
 Water = 
 1000. 
 
 Boiling 
 Point. 
 
 Volume 
 of Vapour 
 at boiling 
 Point. 
 
 Volume 
 of Vapour 
 at 212". 
 
 Specific 
 Gravity of 
 Vapour. 
 
 Water . *' *t 
 Alcohol 
 Ether 
 Oil of turpentine 
 Mercury . 
 
 1000 
 907 
 715 
 867 
 13500 
 
 212 
 172<> 
 97" 
 315 
 
 660 
 
 1696 
 488 
 240 
 221 
 3395 
 
 1696 
 . 519 
 289 
 192 
 1938 
 
 620 
 1601 
 2583 
 4763 
 6969 
 
By Great Increase of Volume. 99 
 
 In the first column are the names of the bodies ; in the second, their 
 specific gravities, water being 1000 ; in the third, their boiling points ; 
 in the fourth, the number of volumes of vapour furnished by one volume 
 of each fluid at its boiling point ; in the fifth, the number of volumes of 
 vapour, reduced to a standard temperature, 212, which one volume of 
 fluid may produce ; and in the sixth, the specific gravity of the vapour, 
 air being 1000. 
 
 It has been imagined that there should exist some physical connexion 
 between the increase of volume produced by the change from the liquid 
 to the gaseous state, and the quantity of heat rendered latent during the 
 change ; and it is in fact generally true, that those bodies which have 
 small latent heat, expand least, as oil of turpentine and ether. But, as 
 yet, from the few experiments that have been made upon latent heats, 
 with substances sufficiently pure to be taken as the basis of calculation, 
 nothing positive can be considered to be known. 
 
 The passage from the liquid condition to the state of vapour is distin- 
 guished from the change of a solid to a liquid, by the important fact, that 
 whilst liquefaction is definitely produced at one temperature, and at that 
 alone, vaporization occurs at all temperatures ; and it is only from the 
 influence of external circumstances that the change is accompanied, at a 
 particular temperature, by the phenomenon of boiling. The coldest 
 water is capable of forming vapour ; even ice evaporates, and in order 
 to do so, it is not necessary that it shall previously melt ; it is thus that 
 snow will gradually disappear from the ground, even when shaded from 
 the sun's rays, and though the air shall have continued below the melt- 
 ing point. Other solid bodies also evaporate without previous melting, 
 as camphor ; and arsenic cannot be melted, for when heated, it is con- 
 verted at once from the solid to the vapourous condition. The particles 
 of volatile bodies appear thus, at all temperatures, to repel each other to 
 a certain degree, and to spread abroad, in the form of vapour, until they 
 occupy completely the space in which the body is contained, and exer- 
 cise a pressure which is equal to the force of their mutual repulsion, and 
 which is termed the elasticity of the vapour. 
 
 The amount of elasticity, or as it is often called, the tension of a vapour, 
 is determined by very simple methods. Thus, for elasticities below that 
 of atmospheric air, a series of barometer tubes arranged in a stand, P P 
 a a, are to be carefully filled and inverted in a basin of mercury, c c, as 
 in the figure. One such tube, dd, is to be kept untouched, to measure 
 the elasticity of the external air. If a little water be allowed to pass 
 up into the next tube and there float upon the surface of the mercury, 
 it immediately forms vapour which spreads through all the empty space, 
 and pressing against the upper surface of the mercurial column, counter- 
 acts a portion of the pressure of the external air. The remaining 
 
100 
 
 Determination of th 
 
 pressure of the air is able to support, therefore, only a shorter column 
 of mercury, and the height of the mercury in the 
 tube diminishes. If into another tube some alcohol 
 be introduced, there is a similar, but still greater 
 depression of the mercurial column caused, and with 
 ether the height of the mercurial column is still more 
 diminished. The atmospheric pressure in these cases 
 balances the shortened column of mercury added to 
 the elasticity of the vapour, and this last is conse- 
 quently measured by the height of the column of 
 mercury which it is capable of replacing, that is, 
 by the space through which the mercury has been 
 depressed, which is read off by the rule and index, 
 r v r. Thus, if the barometer be at 30 inches and 
 temperature 80, the mercury will stand in the tube 
 with watery vapour at 29 inches, in that with alco- 
 hol at 28*1, and in that of ether at 10 inches. 
 The elasticities of these vapours are, therefore, at the 
 temperature of 80. 
 
 Vapour of water 
 ,, of alcohol 
 ,, of ether 
 
 1 -0 inch. 
 1-9 
 20-0 
 
 In order to ascertain how the elasticity of a vapour changes with the 
 temperature it is only necessary to enclose the upper part of the tube in 
 a cylindrical case, containing water or oil heated to the necessary degree. 
 As the heat increases the height of the mercurial column will diminish, 
 and at each temperature the elasticity is so determined. The apparatus 
 may be modified by bending the tube so as to immerse the bent portion 
 containing the vapour into a globule of water or oil to which heat may 
 applied, but the principle remains the same. In this way a table of the 
 elasticity of a vapour at all temperatures below their boiling points, may 
 be formed, and as there will be frequent reference hereafter to the 
 tension of the vapour of water, the following table is introduced for use 
 and as an example : 
 
 Temperature. 
 
 Elasticity. 
 
 Temperature. 
 
 Elasticity. 
 
 32 
 
 0-200 b 
 
 90 
 
 1-36 b 
 
 40 
 
 0-263 g 
 
 lOOo 
 
 1-86 
 
 5Qo 
 
 0-375 
 
 1-20" 
 
 3-33 o 
 
 55 
 
 0-443 
 
 140" 
 
 5-74 * 
 
 60 
 
 0-524 o 
 
 160 
 
 9-46 3 
 
 65" 
 
 0-616 * 
 
 180 
 
 15-15 8 
 
 70 
 
 0-721 | 
 
 200 
 
 23-64 | 
 
 80 
 
 1-000 -2 
 
 212 
 
 30-00 -S 
 
 
 .3 
 
 
 3 
 
Elasticity of Vapours. 
 
 101 
 
 When a liquid, in such an apparatus, is heated until the vapour 
 formed occupies all the tube, and expels the mercury, the elasticity of 
 the vapour is equal to that of the air, and the liquid exposed to the air 
 should boil ; the phenomenon of boiling arising simply from the fact, 
 that the elasticity of the vapour balances the pressure of the air, whilst 
 the bubble is passing through the fluid : thus, suppose a vessel of water 
 exposed to the air at 200, and a bubble of steam to form in it; the 
 pressure exercised by that bubble, being equal to its tension, should be 
 equivalent to a column of 23*64 inches of mercury, but the external 
 pressure being 30 inches, the bubble should be crushed in by a force 
 equal to the difference, (6 '36 inches of mercury,) and consequently, dis- 
 persed. If the water, however, be heated to 212, the elasticity be- 
 comes equal to 30 inches, and then the 
 external and internal pressures being 
 equal, the bubble rises in the liquid with- 
 out injury, and maintains itself at the 
 surface until its investing film of water is 
 ruptured by other causes, when the vapour 
 mixes uniformly with the air. 
 
 It is the bursting of the steam bubbles 
 that are first formed in this manner that 
 constitutes the simmering of a boiler OP 
 the singing of a kettle on the fire. The 
 bottom of the vessel heats more strongly 
 the layer of water in contact with it, so 
 that the steam has there a high degree of 
 elasticity, and forms a multitude of mi- 
 nute bubbles ; when these separate from 
 the hot metal, they are immediately burst 
 in by the greater external pressure, and 
 the mass of water is thus thrown into a 
 state of exceedingly rapid and uniform 
 vibrations, which fall upon the ear so re- 
 gularly, in many cases, as to produce a 
 musical and often agreeable tone, which 
 may become graver or more acute, ac- 
 cording as the bubbles burst more or less 
 rapidly after one another. 
 
 The elasticity increases very rapidly with the temperature, as is seen 
 in the table, where in rising from 180 to 212, the elasticity is doubled. 
 For high temperatures the rate of increase is still more rapid. To der 
 
102 
 
 Determination of the 
 
 termine the elasticity at temperatures above the ordinary boiling point, 
 an apparatus completely cut off from the external air is made use of. 
 In the figure there is a globular vessel of strong metal, into which is 
 introduced by the stopcock a, the fluid to be experimented on, as for 
 example, water. In the aperture b, is fitted a thermometer, the bulb of 
 which dips into the fluid near the centre and shows its temperature. 
 A quantity of mercury being in the bottom of the vessel, the tube c 
 dips under its surface, and rising to the necessary height has attached 
 to it the scale divided into inches and their parts. When the appara- 
 tus is heated, as the vapour produced cannot escape, all joinings being 
 perfectly steam-tight, the temperature rises continuously, in place of 
 stopping at the boiling point, and the vapour formed pressing on the 
 surface of the remaining liquid, and by it on the mercury underneath, 
 forces the mercury up the tube c until the mercurial column shall have 
 attained such a height as to counterbalance by its weight the elasticity 
 of the vapour. In these cases the elasticity is generally reckoned by 
 atmospheres, each atmosphere being equivalent to a mercurial column 
 thirty inches high. In this manner the vapour of water has been found 
 to exert a pressure of 
 
 1 atmosphere at 212o 
 
 2 250 
 
 16 atmospheres at 398 
 
 3 
 4 
 6 
 
 8 
 12 
 
 275 
 294 
 320 
 342 
 374 
 
 20 
 25 
 30 
 40 
 50 
 
 418 
 439 
 457 
 486 
 510 
 
 It is necessary, in order to understand such tables, to observe that 
 this great increase of the elasticity of steam, as the temperature rises, 
 results not from the expansion of steam already formed, but from the 
 constant addition of new quantities of steam for every variation of 
 temperature. If a globe full of steam at 212, but containing no li- 
 quid water, were heated to 294, it should tend to expand precisely as 
 air or any other gas, and the increase of elasticity should be only from 
 30 to 34 inches, or from one atmosphere to 1^ ; but if the globe con- 
 tain liquid water, there is such an additional quantity of vapour formed 
 and compressed into the same space, that the elasticity becomes equal 
 to four atmospheres, or to 120 inches of the mercurial column. Also, 
 when the pressure on a vapour is made to Vary, the result deviates from 
 the rule laid down in page 16, for the action of pressure upon gases; 
 as the elasticity of a vapour cannot be really increased by any increase 
 of pressure : it remains the same, but a quantity of the vapour becomes 
 
Properties of Vapours. 
 
 103 
 
 liquid, and there continues in the state of vapour only as much as oc- 
 cupies with the same elasticity the diminished volume which the column 
 of mercury leaves. Thus, let us consider the bent tube a b, of which 
 the extremity at a is closed, and the leg a, occupied 
 from the dotted line c d, by vapour of ether, at its 
 boiling point, and balancing in the leg b a column of 
 mercury c e thirty inches high. If now, without allow- 
 ing the temperature to change, mercury be poured in 
 at the orifice of b, until it shall rise in a up to the 
 line f g, and occupy exactly one-half of that leg, the 
 vapour will not be compressed into half its volume, 
 and, acquiring a double elasticity, support 60 inches of 
 mercury as a gas should do, but one-half of the ether 
 will assume the liquid form, and the remainder, occupying the remaining 
 half of the original volume, will balance thirty inches of mercury pre- 
 cisely as it did before, and the pressing column, counting from the line 
 fg, will terminate at h. 
 
 If, however, in place of attempting to increase the pressure on a va- 
 pour, we diminish it, then the vapour preserves its elastic form, and its 
 elasticity diminishes in all respects as if it were a gas. 
 
 The specific gravity of a vapour, formed at any certain temperature, 
 should be proportional simply to the elasticity, if the volume were 
 not altered by the change of temperature, and it should be inversely as 
 the volume, if it could all remain uncondensed ; but in reality, the re- 
 lation is more complex, and may be calculated upon the following prin- 
 ciples. Thus, if we wish to know the specific gravity of vapour of 
 water having an elasticity expressed by 7 '42 inches of mercury, and 
 the temperature 150, we proceed as follows : the specific gravity of 
 steam at 30 inches and 212 is 620*2; and hence if the volume 
 did not change, the specific gravity of the vapour at 150, should 
 be 620-2 X/o 4 o 2 o= 153 ' 39 J but cooling from 212 to 150, the por- 
 tion of steam which retains its elastic form is compressed within a 
 smaller volume, and hence has its specific gravity increased in propor- 
 tion to the change, and, therefore, the 153*39 obtained above must be 
 increased in the proportion of the volume at 150 to the volume at 
 212, or as 611:673, and thus becomes 169*24. The subjoined table 
 contains specific gravities for some temperatures calculated in that way, 
 and accompanied by the temperatures, the elasticities, and the weight 
 in grains of 100 cubic inches of the vapour. 
 
104 
 
 Properties of Compressed Vapours. 
 
 Temperature. 
 
 Elasticity in 
 Inches of Mer- 
 cury. 
 
 Specific Gravity. 
 Air =1000. 
 
 Weight of 100 
 cubic inches. 
 
 32o 
 
 50o 
 60 
 100 
 150 
 212 
 
 0-200 
 0-375 
 0-524 
 1-860 
 7'420 
 30-000 
 
 5-68 
 10-17 
 1406 
 46-36 
 169-24 
 620-20 
 
 0-1361 
 02474 
 0-3387 
 1-1028 
 4-0543 
 14-9600 
 
 There is some reason to suspect, however, that vapours do not follow 
 exactly the theoretic rules, upon which such tables are constructed, and 
 which in reality apply only to gaseous bodies. Thus, Despretz has 
 found the specific gravity of the vapour of water to be at 67, 7*72, 
 whilst by this calculation it should be 17'26, air at 212 being 1000; 
 his results cannot be considered as decisive, although they show the 
 necessity for an accurate reexamination of the subject. At very high 
 temperatures, the elasticity does certainly not increase with the specific 
 gravity, when the volume remains constant. Ether is found to become 
 gaseous, and to occupy only twice the volume it had when liquid, at the 
 temperature of 320, and its elasticity in that state equals 38 atmos- 
 pheres, whereas, by calculation, its elastic force should be 168 atmos- 
 pheres. Alcohol, inclosed in tubes hermetically sealed, is totally 
 converted into vapour, occupying only three times the volume of the 
 liquid at 404, and then exerts a pressure only of 129 atmospheres, 
 whilst by theory the pressure should equal 221. "Water, also, was 
 obtained by Cagniard de la Tour, gaseous in four times its liquid 
 volume, at 773, and should then by theory have an elasticity of 780 
 atmospheres, a force far above what the glass tube employed could 
 possibly have resisted. It would appear, therefore, that vapours, so far 
 as the relation between their specific gravity and their elasticity is 
 concerned, do not follow exactly the same law as gases, except within 
 certain limits, but that when the elasticity is much smaller or much 
 greater than the atmospheric pressure, variations which are very 
 remarkable, though as yet not well understood, present themselves. 
 
 When a vapour, as, for example, steam, which has been generated in 
 close vessels, and attained a great elasticity, is suddenly allowed to 
 escape into the air, its temperature is reduced in a remarkable degree, 
 even independently of condensation. If the steam had been formed 
 under a pressure of four atmospheres, its volume is but one-fourth of 
 what it should become when free, and hence, on escaping, it expands in 
 that proportion : under that pressure its temperature had been 294, 
 but by the increase of latent heat it falls immediately to 212 ; there, 
 
Measurement of Heights of Mountains. 105 
 
 however, the expansion does not stop ; the impulse of the particles of 
 vapour carries them much further, and as the specific heat increases, so 
 as nearly to be doubled when the volume becomes doubled, a consi- 
 derable reduction of the temperature below 212 occurs, which is still 
 further increased by admixture of cold air which presses into the rarefied 
 space left by the expansion of the steam. Hence it is that steam 
 escaping into the air from under considerable pressure possesses much 
 less heating power than steam arising from water boiling in an open 
 vessel : it is much less liable to scald. 
 
 The principle of the conversion of a solid or liquid body into a vapour, 
 at all ordinary temperatures, is true, even where the body may be very 
 slightly volatile. Thus the space over the mercury in the best barometers 
 is not truly empty, but contains a quantity of mercurial vapour, exer- 
 cising a certain elasticity, and, by depressing the liquid column, making 
 the pressure of the external air appear smaller than it really is. It 
 would appear, however, that there are, for some bodies at least, tem- 
 peratures below which evaporation does not go on ; thus no mercurial 
 vapour can be detected unless the temperature be above 40, and oil of 
 vitriol requires to be heated to 120 before any vapour forms from it : 
 it is probable, however, that even in these cases, the general principle 
 holds good, and that it is only from the minute quantity of vapour 
 eluding our means of research that the existence of a limit to evaporation 
 was believed to exist. 
 
 The boiling point of a liquid being that at which its vapour can 
 support the external pressure, it is liable to constant fluctuation as the 
 pressure changes, and hence the marking upon the thermometer the 
 temperature of boiling water requires the care and attention already 
 noticed. If the barometer stood at 23'64, water should boil at 200 in 
 place of 212 ; and so close is the connexion between the pressure and 
 boiling point, that the height of any place above- the level of the sea 
 may be determined by the temperature at which the water boils there. 
 Thus, if on heating some water on the summit of a mountain it be 
 found to boil at 203, we find by reference to a table that the elasticity 
 of its vapour is then 25'1 inches, and hence that in the same place, at 
 the same moment, the column of mercury in a barometer should have 
 been at that height. Then, by the ordinary calculation, the height of 
 the mountain may be found, with as much accuracy as if the barometer 
 itself had been carried up. The simple rule that the boiling point is lower- 
 ed one degree for every 550 feet of elevation comes very near the truth. 
 On the summit of Mont Blanc, the highest point of Europe, water has 
 been found to boil at 184. 
 
 By reducing, artificially, the amount of pressure upon a fluid, as by 
 
106 
 
 Alteration of the Boiling Point. 
 
 placing the vessel containing it under the receiver of an air pump, and 
 exhausting the air, the boiling point is lowered in a remarkable degree. 
 If the vacuum were perfect, a fluid should boil even at the lowest 
 possible temperature ; but this is not practicable, as the vapour formed 
 cannot be so perfectly removed but that it will exercise some pressure ; 
 but, with a good air pump, fluids may be got to boil 145 below their 
 ordinary boiling points ; thus water will boil at 67, alcohol at 32, 
 ether at a temperature at which quicksilver would freeze. If, at the 
 moment that such a fluid is in violent ebullition, the working of the 
 pump be stopped, the vapour accumulates, and, exercising on the surface 
 of the fluid an amount of pressure corresponding to its elasticity at the 
 existing temperature, raises the boiling point, and thus stops the ebul- 
 lition. This fact may be shown in a very simple and singular manner, 
 by half filling a flask B, with water, and boiling the water until all the 
 air in the flask shall have been expelled, and then carefully closing the 
 mouth of the flask b by an air tight cork. On removing the source of 
 heat, the upper part of the flask B, when inverted 
 as in the figure, remains full of vapour, which, 
 pressing upon the liquid water, arrests the ebul- 
 lition. If then a jet of cold water p be allowed 
 to play upon the flask, the vapour is condensed, 
 and, a partial vacuum being thus produced, the 
 water begins to boil ; if a jet of warm water be 
 employed, the vapour retains its elastic form, and 
 the ebullition ceases, so that in this apparatus the 
 application of cold may appear to cause, and that 
 of heat to prevent, the water's boiling. 
 
 The temperature at which a liquid boils is thus 
 entirely dependent on the amount of pressure to 
 which it is subjected. But the limits within which that pressure varies 
 near the level of the sea, in ordinary cases, are so small, that the boiling 
 point may be looked upon as one of the most important characteristic 
 properties of a volatile substance, and from the facility with which it 
 may be determined, it is almost universally capable of being applied. 
 Hence, in describing such bodies, the boiling point will be, in all 
 cases, given ; but, for illustrating the present subject, a table of the 
 boiling points of some of the most remarkable liquids is subjoined : 
 
 52 Water . : " ^ 212 
 
 96 Nitric acid 
 
 116 Oil of turpentine 
 
 Muriatic ether 
 Sulphuric ether 
 Sulphuret of carbon 
 Pyroacetic spirit 
 Water of ammonia 
 Pyroxylic spirit 
 Alcohol 
 
 132 
 140 
 151 
 173 
 
 Phosphorus 
 Sulphur . 
 Sulphuric acid 
 Mercury . 
 
 601 
 630 
 
Anomalous Property of Liquid*. 
 
 107 
 
 The boiling point is influenced by some other circumstances than the 
 atmospheric pressure ; the nature of the vessel may alter it several de- 
 grees. Thus, in a glass, or glazed porcelain vessel, water boils under 
 a pressure of 30 inches, not at 212 but 214 ; and in graduating a 
 thermometer it is hence necessary to use a metallic vessel. This latter 
 appears to favour ebullition by the minute irregularities on its surface, 
 affording a nucleus for the steam to form, as a crystal dropped into a 
 saline solution facilitates the crystallization ; and if the smooth surface 
 in the glass vessel be removed in a single point, by a scratch with a 
 diamond, the bubbles of steam will be seen to form there, before the 
 general mass of liquid comes to boil. The influence of roughened or 
 . angular surfaces in thus favouring the escape of steam may be shown 
 very well by heating water in a glass flask to boiling, and then allow- 
 ing it to cool a little, so that the boiling shall completely cease ; if then 
 a few filings of copper, or a platina wire be dipped into the liquid, if 
 the cooling had not gone too far, the boiling will immediately recom- 
 mence, the steam forming at the edges and angles of the rough sub- 
 stances introduced. 
 
 The temperature of the steam produced is not affected by the boiling 
 point of the liquid. Thus, although by dissolving salts, such as chlo- 
 ride of calcium, in water, its boiling point may be raised to 264, the 
 temperature of the vapour, immediately over the solution, is found to 
 be but 212, for though the temperature of a steam bubble which rises 
 up through such a solution must be 264, yet as its elasticity and latent 
 heat are proportioned to that temperature, it expands on mixing with 
 the less elastic atmospheric air, and is cooled down instantly to the 
 ordinary boiling point. The heat of a water bath may thus be in- 
 creased by the addition of saline bodies ; but the temperature of a steam 
 bath depends only on the elasticity of the steam. 
 
 A curious, though only apparent, anomaly in the relations of liquids 
 to their boiling points consists in the possibility of the vessel containing 
 the liquid being heated, even to redness, without the liquid boiling, 
 though exposed only to the ordinary pressure. This may easily be 
 shown by heating a platina crucible to redness, and dropping into it a 
 small quantity of water; the water remains on the red hot metal with- 
 out disturbance, and appears scarcely to evaporate. But if another 
 crucible be heated to 300, and the water be poured out of the first 
 into the second, it instantly boils, and is dissipated in a gush of vapour. 
 The reason is, that in the red hot crucible the water is not really in 
 contact with the metal, and hence the heat passes to it with extreme 
 slowness ; but the water wets the colder crucible, and absorbing from 
 it all the necessary heat, is instantly converted into steam. The cohe- 
 
108 Sum of Latent and Sensible Heat nearly Constant. 
 
 sive force of the metal to the water being diminished considerably, this 
 lies in a red hot crucible, as a clean steel needle floats on water, or a 
 globule of mercury moves upon glass, and is scarcely affected by the 
 heat until it wets the vessel, just as the needle does not sink in the 
 water until it is wetted by it. There occur, however, in a globule so 
 heated a very remarkable play of repulsive forces, by which a strong 
 movement of rotation may be observed to be produced in its interior ; 
 but so independent is the temperature of the water globule of the .heat 
 applied to the containing vessel, that if a jet of liquefied sulphurous 
 acid be made to strike the globule, the latter will be frozen by the cold 
 produced by the sudden gazification of the acid, and a mass of ice will 
 be produced in the bottom of the red hot crucible. At certain tem- 
 peratures all liquids manifest the same peculiarity. 
 
 When a liquid evaporates at a temperature below its boiling point, 
 it still absorbs and renders latent a great quantity of heat, and, indeed, 
 still more heat than it would render latent when converted into vapour 
 by ordinary boiling. It was found, by James Watt, in his experiments 
 with steam, and it was consequently supposed to be true, not merely 
 with water, but with liquids in general, that no matter at what tem- 
 perature a liquid vaporizes it absorbs the same total quantity of heat. 
 The more of this that becomes sensible the less is the portion which 
 remains latent ; the sum of the latent and sensible heats of the vapour 
 being at all temperatures the same. Thus, with water evaporating at 
 
 32 the latent heat is 1180 the sum being 1212 
 
 100 1112 1212 
 
 212 1000 1212 
 
 300o 912 1212 
 
 This has, however, been shown by the later more accurate researches 
 of Eegnault not to be accurately true, although it is so nearly correct 
 as to be an important rule in technical practice. Eegnault has deter- 
 mined that the total heat contained in vapour increases with the elas- 
 ticity, though very slowly. The following table exhibits the numbers 
 given in his experiments for the values of the total heat, latent and 
 sensible, and the latent heat at different temperatures and pressures. 
 
 Temperatures. 
 
 Pressures. 
 
 Total Heat. 
 
 Latent Heat. 
 
 32 
 
 0-006 
 
 1091 
 
 1059 
 
 122 
 
 0-121 
 
 1109 
 
 997 
 
 212 
 
 1-000 
 
 1147 967 
 
 302 
 
 4712 
 
 1174 872 
 
 392 
 
 15-380 
 
 1201 
 
 809 
 
 436 
 
 27-535 
 
 1218 
 
 782 
 
Artificial Cold Produced by Valorization. 109 
 
 There is, therefore, no economy in evaporating or distilling at one 
 temperature rather than another, as the same absolute quantity of heat 
 is necessary for the formation of the steam ; but, for other reasons, the 
 formation of vapours at low temperatures affords to the chemist pro- 
 cesses of the greatest value. Many vegetable substances undergo im- 
 portant alterations in their chemical constitution and medicinal proper- 
 ties, if they be exposed for a long time even to a heat of 212 ; and 
 hence, in the preparation of extracts and inspissated juices of plants, 
 in pharmacy, forms of apparatus are sometimes employed, in which the 
 evaporation is carried on in close vessels connected with an air pump, 
 and in which a partial vacuum, measured by a barometer guage, may 
 be established. In the manufacture of sugar, this principle of evapo- 
 ration at low temperatures, by removal of the atmospheric pressure, 
 was the source of great improvement, as the true crystallizable sugar 
 is converted into the uncrystallizable sugar (treacle) with great rapidity, 
 at the temperature of boiling syrup, and was hence, to a great extent, 
 lost to the manufacturer. By later improvements in the mode of ap- 
 plying heat, the necessity of evaporating the syrup in vacuo has been, 
 however, completely, obviated. 
 
 The absorption of heat in the conversion of a liquid into a vapour, 
 at ordinary temperatures, may become the source of considerable cold ; 
 and it is, indeed, in this way that the greatest cold yet generated has 
 been produced. The cold which is felt when a little ether or spirits of 
 wine is dropped upon the hand arises from this fact ; and by surrounding 
 the bulb of a mercurial thermometer with some loose cotton, and mois- 
 tening it with liquid sulphurous acid, the quicksilver in the bulb may 
 easily be frozen. By placing some ether in a shallow, thin, metallic 
 cup, which rests in a glass vessel, containing a small quantity of water, 
 and producing, by the air pump, the rapid vaporization of the ether, 
 the water may be so frozen, that the two cups shall be cemented firmly 
 together by the intervening sheet of ice. 
 
 Water may be even frozen by its own evaporation, as in the cryo- 
 phorus, which consists of a long tube, terminating in bulbs, which con- 
 tain some water, and from which the air had been carefully expelled by 
 boiling, before the apparatus was completely closed. The space above 
 
 the water remains then occupied 
 >\ only by watery vapour. If all 
 S^, the water be brought into one 
 bulb, and the other bulb be 
 immersed in a freezing mixture, 
 
 the vapour will condense there, and new vapour being formed, a distil- 
 lation will be produced from the one to the other bulb. The vapour 
 
110 Spontaneous Evaporation. 
 
 which forms in the warm bulb must derive its latent heat from the 
 water which remains behind, and this is gradually cooled to the freezing 
 point, and ultimately completely frozen; the latent heat, of about eight 
 parts of water, being given up to form the latent heat of one part of 
 vapour at 32. Even without the application of artificial cold, water 
 may be frozen by its own evaporation. Thus, if 
 under the receiver of an air pump we arrange two 
 flat dishes, the upper containing water, the lower 
 containing oil of vitriol, and then having removed 
 the air, we leave the apparatus for a short time to 
 act, we shall find the water in the upper vessel con- 
 verted into ice. Accordingly, as any portion of 
 vapour forms, it is immediately absorbed by the 
 sulphuric acid, which has a great affinity for water, 
 and the vapour being thus prevented from collect- 
 ing, the loss of heat by evaporation proceeds 
 without any cease, until so much heat has been removed, that the resi- 
 dual water is converted into ice. 
 
 In fluids more volatile than water, this synchronous freezing and eva- 
 poration may occur still more simply. Thus, if strong prussic acid be 
 allowed to form a pendent drop from a glass rod, the drop will become 
 solid by the evaporation of one portion of it, and the cooling of what 
 remains. The remarkable phenomenon of the solidification of carbonic 
 acid arises from the same principle. A jet of liquid carbonic acid 
 being allowed to escape into the air, one portion instantly flashes into 
 the state of gas, and absorbs so much heat, that the portion which 
 remains is converted into a compact solid mass, and if this solid car- 
 bonic acid be made into a pulp with sulphuric ether, the evaporation of 
 the mixture produces the degree of cold of 166 Fahrenheit, the most 
 intense as yet obtained. 
 
 In warm climates, the evaporation of water is commonly employed 
 to moderate the sultriness of the air, by the agreeable cold it produces. 
 The Spanish alcarrazas are earthen vessels, so porous, that any liquid 
 which is put into them gradually filters through, and, evaporating from 
 the outer surface, cools the interior mass. In chemical operations, the 
 same mode of refrigeration is in constant use, and when describing 
 these operations, the action of this principle, in the construction of the 
 apparatus used, will be referred to. 
 
 The conversion of a liquid into vapour, at ordinary temperatures, is 
 often called spontaneous evaporation ; and, in the case of water, from 
 the great extent to which it becomes subservient to the economy of 
 nature, this process is one of high importance. It was formerly sup- 
 
Diffusion of- Vapours and Gases. 
 
 Ill 
 
 posed that the atmosphere was necessary to evaporation ; and this idea 
 was strengthened by the fact, that by a current of air the evaporation 
 is much assisted ; but it is now established, that the pressure of air is 
 really an obstacle to evaporation, and that a current is useful, not by 
 supplying new quantities of air, but by removing the vapour according 
 as it is formed, and leaving fresh spaces into which the vapour may ex- 
 pand. When a liquid forms vapour, the quantity formed is determined 
 onlv by the space into which the vapour may spread, and by the 
 temperature. It is no matter whether the space be occupied before by 
 other vapours or by air, or whether it be a vacuum ; the quantity of 
 vapour which can form in it, is in all these cases the same. 
 
 Dalton was the first who clearly showed that different gases and 
 vapours offer no resistance to each other's elasticity : thus, that the par- 
 ticles of watery vapour in the air are not subjected to the pressure of 
 the atmosphere, but only influenced by the pressure of the particles of 
 the same kind ; and hence, that at 32, when the elasticity of vapour 
 is only 0*200 inch, it retains perfectly its elastic constitution, though 
 diffused through an atmosphere, the elasticity of which may equal 
 thirty inches. If we moisten the interior of a bell glass, filled by air, 
 with ether, alcohol, sulphuret of carbon, and water, all mixed together, 
 there will be formed in the bell as much of the vapour of each substance 
 as if the bell had been completely empty of the others ; each vapour 
 will exercise a pressure proportional to its elasticity, and by the sum of 
 all these pressures, the pressure of the external air will be equilibrated. 
 It is, consequently, possible to produce the rapid evaporation of one 
 fluid, whilst another beside it, or even mixed with it, shall not evaporate at 
 all; it being only necessary to remove the vapour of the one as rapidly 
 as it is formed, whilst the portion of the vapour of the second produced 
 in the first instant, shall remain, and prevent its further change. Thus, 
 by placing a shallow dish of dilute alcohol under the receiver of an air 
 pump, with a quantity of quicklime, the latter combines with and ab- 
 sorbs the watery vapour as fast as formed ; and there is, hence, a con- 
 tinual evaporation of the water, whilst the alcohol, after generating .as 
 much vapour as once fills the receiver, is pressed upon by it, and can- 
 not form any more. In this manner, alcohol, almost quite pure, though 
 much more volatile, in the ordinary sense, may be obtained by the 
 evaporation of its solution in water, as it were to dryness. 
 
 If the liquid be in excess, the vapour posseses the elasticity belong- 
 ing to its temperature ; but if there be not liquid enough to form so 
 much vapour, the vapour formed then expands, so as to occupy the en- 
 tire space, and its elasticity diminishes in proportion to the increase of 
 the volume; vapours being regulated by the same law of pressure 
 
112 Correction of Volumes of Gases for Moisture. 
 
 which holds with gases. If, thus, a bell glass of atmospheric air be con- 
 fined over water, at the temperature of 80, a quantity of vapour dif- 
 fuses itself through the air, and, as there is water in excess, the elasti- 
 city of that vapour will be I'OO inch. Now if we suppose the elasti- 
 city of the air to have been previously 30 inches it will become, by the 
 addition of the vapour, 29, for the vapour counteracts one inch of the 
 external atmospheric pressure ; the air in the bell glass will then expand, 
 in the proportion of 30 to 29; or, what is the same in practice, the 
 volume of the damp air is the same as the volume which the vapour 
 should occupy, if condensed in the proportion of its own elasticity to 
 the atmospheric pressure, added to the volume occupied by the air when 
 dry. It is thus that the volumes of gases, collected over water, are 
 corrected for the watery vapour that is mixed with them. Thus, in the 
 analysis of a substance containing nitrogen, let us suppose that 8'54 
 cubic inches of nitrogen have been collected over water, at the tem- 
 perature of 63, and the barometric pressure being 29*35 inches ; at 
 that temperature, the elasticity of vapour is 0'58, and hence that of the 
 dry air is 29'35 0'58=28'77. The volumes which they occupy 
 are as these numbers, and hence* the 8*54 of damp gas consists 
 of ^jX 8-54=017 of watery vapour, and |f;jf X 8-54=8-37 of 
 dry nitrogen. 
 
 This volume should still be corrected for temperature and pressure 
 before the quantity of nitrogen by weight could be inferred from it. 
 
 Where the air is not completely saturated with the watery vapour, it 
 is not so easy to determine the exact quantity of vapour which it con- 
 tains. One of the best methods consists in cooling it until its volume 
 is so much diminished that the quantity of vapour is sufficient to satu- 
 rate it, and from the temperature at which this occurs the quantity of 
 vapour may be calculated. This temperature is termed the dew point 
 of the air or gas, because if cooled in the least below that point a quan- 
 tity of water is deposited in the form of dew upon the neighbouring 
 cold bodies. This may be easily done by taking a tumbler of water, 
 somewhat too warm, and cooling it gradually by dissolving in it a little 
 mixed nitre and salammoniac, until a slight deposition of dew is per- 
 ceptible on the exterior of the glass ; the water is then at the tempera- 
 ture of the dew point. Another method consists in observing the ra- 
 pidity of evaporation from the surface of the bulb of a thermometer 
 which is covered with muslin kept wet by water. The thermometer so 
 arranged is always at a lower temperature than an ordinary thermome- 
 ter, from the quantity of heat carried away by evaporation, and the 
 temperature will be lower in proportion to the amount of evaporation, 
 in dry air, evaporation is quickest ; in air saturated with moisture eva- 
 
Nature and Use of Hygrometers. 118 
 
 poration ceases, and in all intermediate degrees there is a connexion 
 between the quantity of moisture already present in the air and the de- 
 pression of temperature, which accompanies the formation of as much 
 more as will saturate it. On this principle is founded the process 
 already described in page 88, as having been adopted by Apjohn for 
 ascertaining the specific heat of the gases, and it is easy now to under- 
 stand the general principle upon which his process was established. If 
 we consider a certain space which may be filled by the different gases 
 in succession, and that these gases being dry, they are made to saturate 
 themselves with watery vapour, for the formation of which they them- 
 selves supply the heat, it will be easily seen that as the quantity of heat 
 to be given out is the same for all, their temperatures will be reduced 
 in a degree, inverse to their specific heats. Hydrogen having a high 
 specific heat will only require to cool by about one-third the number of 
 degrees necessary for air or other gases. The numerical results obtained 
 by this process have been already given. 
 
 Instruments for the purpose of determining the quantity of watery 
 vapour which the atmosphere contains are termed hygrometers, and 
 that of Daniell is one of the most elegant and most useful. It is a 
 cryophorus a e b b t which in place of water 
 contains ether, and in one bulb, of which, 
 a i, is fixed a very delicate thermometer. 
 This bulb is made of blackened glass, and 
 the other bulb e o is covered with a little 
 bag of muslin. All the ether having been 
 made to pass into the black glass bulb, a 
 little ether is poured on the muslin envelope 
 of the other. This, by condensing the 
 vapour inside, causes the ether to distil from 
 the blackened bulb, and thus cools it and 
 the air in contact with it, until it arrives at the point of saturation, 
 when a dew of liquid water begins to be deposited, which is at once 
 observed upon the blackened glass. The internal thermometer shows 
 the temperature of the bulb, which is the dew point,and a thermometer 
 which is attached to the support of the instrument shows the tempera- 
 ture of the external air. A modification of this instrument lately pro- 
 posed by Regnault, enables the dew point to be determined with great 
 accuracy and facility, and is free from the inequalities of action to which 
 Darnell's hygrometer was subject, 
 
 When the dew point has been thus determined, the subsequent cal- 
 culation is very simple. Thus, if there be air at 72, of which the dew 
 point is 45 ; the barometric pressure being 30 inches : the elasticity of 
 8 
 
114 Speculation on the Boiling Points 
 
 of steam at 45 is 0-316, and as the elasticity diminishes according as 
 the volume increases from 45 to 7, the elasticity of the vapour in the 
 air at 7 is 0*30, and the atmospheric pressure of 30 inches is pro- 
 duced by the dry atmosphere, which balances 2 9' 70, and the watery vapour 
 which balances 0'30 ; and the respective volumes are as these pressures. 
 Gay Lussac has sought to establish a close relation between the 
 manner in which solid bodies dissolve in liquids, and that in which 
 vapours diffuse themselves through space. Thus, if a solid body dis- 
 solved only because the liquid diminished the cohesion of its particles, 
 the diminution of that cohesion in another way should increase the 
 solubility very much : this, however, does not occur. When paraffine 
 dissolves in alcohol, the solubility increases steadily with the temperature, 
 and does not change more rapidly at the temperature when the paraffine 
 melts than at any other. This is the case also with many other easily 
 fusible bodies. Hence he compares the diffusion of particles of the 
 solid through the liquid to the diffusion of particles of vapour of water 
 through the air, which is not affected by the solid or liquid form of 
 the water, but depends only on the temperature ; and certainly this 
 view, though not applicable to all, or even the majority of cases of 
 solution, is of much interest as pointing out a similarity between solu- 
 tion and vaporization previously unnoticed, and which may be applied 
 to the explanation of many anomalous facts. 
 
 The employment of steam as a moving power is of so much impor- 
 tance to science and to the arts, that it would be improper to terminate 
 a discussion of the properties of vapours, without some allusion to the 
 manner in which it is utilized. The little steam cylinder of Wollaston. 
 figured in the margin, contains all that is essential in principle, to the 
 application of steam, to produce motion. A glass tube, terminating 
 below in a bulb, is fitted with a little steam-tight piston, which slides 
 up and down, the rod passing through the brass 
 cap at top. If now a little water be placed in the 
 bulb and boiled, its steam pressing on the bottom 
 of the piston forces it up, and when at top, if 
 the bulb be dipped into cold water, the steam 
 condenses, and the pressure of the external air 
 forces the piston down again. This may be re- 
 peated any number of times, and is the essential 
 element of the atmospheric steam engine of 
 Newcomen. It was in this form when Watt 
 commenced Ms improvements on it, and by 
 applying all the resources of the exact knowledge 
 of the properties of heat then first obtained by 
 
Of the Condensed Gases. 115 
 
 himself and his illustrious associate Black, he converted it, though still 
 without changing its fundamental principle, from the machine of 
 Newcomen, which had been rejected from practice, for its inefficiency and 
 expense, into the instrument, which, after the art of printing, must be con- 
 sidered as the most powerful material agent of human improvement 
 and civilization of which mankind has ever obtained possession. 
 
 This similarity of constitution of gases and vapours has been already 
 pointed out on many occasions, and particularly in page 17, where the con- 
 version of gases into liquids by the application of great pressure, has been 
 detailed. A liquefied gas, so contained in a close vessel, is precisely in 
 the condition of water heated in a digester as in the apparatus figured 
 in page 101, far above its boiling point, and generating steam possessed 
 of considerable tension. On this analogy has been founded an inter- 
 esting speculation concerning the temperatures at which the gases 
 would, at ordinary pressures, assume their liquid form, that is to say, 
 their boiling points when liquid, thus : 
 
 At 44-5 the tension of liquid nitrous oxide is 50 atmospheres. 
 At 32-0 44 
 
 For 12-5 an increase of tension of . 6 atmospheres. 
 
 Steam exerts a pressure 
 
 of 50 atmospheres at . . . . 511 p 5o 
 and of 44 497*5 
 
 For 6 atmospheres the difference is . . 14*0 or just the same. 
 
 Liquid carbonic acid exerts a pressure 
 
 ^atmospheres at . . . . 3|>J ^^ ^ 
 
 The tension of steam is 
 
 25 atmospheres at 439-5) Diffe 2p 
 
 20 ,, ,,.... i *lo O 3 
 
 Muriatic acid exerts, when liquid, a tension 
 
 andofi atm 7 heres :! : : : : * 
 
 Steam balances 
 
 25 atmospheres at . . . . . 4jHM Difference, 21 
 
 Ammonia liquefies and exerts a pressure 
 
 of 6-5 atmospheres at .... 50) Differ 18 o 
 
 and of 5 ,, 32> 
 
 Steam exerts a pressure of 
 
 6-5 atmospheres at 326 > THflkiwinp ift^ 
 
 5-0 307.5"} -Uitterence, 18 5 
 
 It is hence evident that, in every case, the rate of increase of elasti- 
 city of these gases, with the temperature, follows the same law as that 
 of steam ; and there is, therefore, good reason to believe, that, if the 
 elasticity were diminished to one atmosphere, the reduction of tempera- 
 ture necessary to effect it should be regulated by the same law as that 
 of walery vapour ; the gases should then, under the ordinary pressure 
 
116 Transmission of Heat. 
 
 of 30 inches, become liquid, and, when liquid, their boiling points 
 should be : 
 
 Nitrous oxide "> *V . = 252*4 Fahrenheit. 
 
 Carbonic acid . . . = 230-8 
 
 Muriatic acid V-'V- . = 202-0 ,, 
 
 Ammonia 7- == 63*4 ,, 
 
 The great increase of elasticity, which these liquefied gases acquire 
 by a change of temperature, limited to a very few degrees, has led to 
 sanguine opinions of their advantages, as a source of power, in machines. 
 No experiments at all sufficiently satisfactory to be decisive upon the 
 question have as yet been made. 
 
 There are some other properties of gases, which, although closely 
 connected with the subject now discussed, I shall postpone, in order to 
 introduce them where they are found to be of the most practical impor- 
 tance. Thus, the manner in which gases spread through each other, 
 in virtue of their diffusive power, will be described under the head of 
 Atmospheric Air, to the proper constitution of which this law is indis- 
 pensable. The relation of gases to water, their solubility in that and 
 other liquids, and the various modes of depriving them of moisture, 
 for the purpose of chemical experiments, shall enter into the history of 
 the physical and chemical properties of water. 
 
 SECTION Y. 
 
 ON THE TRANSMISSION OF HEAT THROUGH BODIES. 
 
 It is a matter of every day experience, that heat may be propagated 
 from one part of a body to another, and also that this propagation takes 
 place in unequal degrees with different bodies. Thus, if one extremity 
 of a poker be heated to bright redness, the other will become so hot as 
 to be intolerable to the hand ; whilst, if a stick of the same length be 
 inserted in the fire, the heated extremity may be completely burned off, 
 without the farther extremity having its temperature raised in any re- 
 markable degree. The extremity of a glass rod may be melted by the 
 flame of a blow-pipe, though held in the fingers scarcely an inch from 
 the flame : but we shall find it difficult to melt the extremity of a silver 
 wire, from the heat spreading itself generally through its mass, and ele- 
 vating the temperature of its entire length to the same degree. Bodies 
 which act like silver are said to conduct heat well, and are termed con- 
 ductors. Bodies which intercept it, like wood or glass, are termed non- 
 
Conducting Power of Solids. 117 
 
 conductors. It is only a difference of degree, for there is no body 
 which prevents totally the passage of heat across its mass. 
 
 The propagation of heat through a body, in virtue of its conducting 
 power, is supposed to take place from particle to particle ; precisely as, 
 when we apply a heated to a cold ball of iron, the latter becomes heated 
 at its point of contact. If, in place of using balls of iron, cubical 
 masses were employed, touching by their surfaces, the communication 
 of heat would be much more rapid, from the greater number of points 
 at which transmission could take place. In the interior of a body we 
 should expect, therefore, to find the degree of approximation of the 
 particles to have some influence on the rapidity of transmission, that is, 
 on the conducting power, or, in other words, that the power of conduct- 
 ing heat should have some relation to the density and the cohesion of 
 each body. 
 
 Many series of experiments have been made to determine the con- 
 ducting power of different bodies. Such experiments may be arranged 
 in a variety of ways. Thus, if a number of similar rods, of different 
 substances, be coated to a certain distance from one extremity with wax, 
 and then heat be applied to the other extremity, the wax will melt ac- 
 cording as the temperature of each rod rises, from the transmission of 
 the heat along it ; and the length of the coating melted at the end of a 
 certain time will be a measure of its conducting power. Another mode 
 consists in forming the substances to be tried into disks, and, having 
 placed a small morsel of phosphorus upon each, warming all equally by 
 laying them on a heated surface. The phosphorus inflames first upon 
 the disk, which transmits most readily the heat ; and on the other disks 
 in the order of the conducting power of their substance. But such ex- 
 periments are only useful in giving the order of conducting power in a 
 general way, and are inapplicable to exact purposes. 
 
 The best results are those which have been obtained by Despretz, 
 whose method was the following. All the bars used in his experiments 
 were square prisms, and were all covered with the same black varnish, 
 in order that the loss of heat from their surface might be exactly simi- 
 lar. At every four inches of their length was a hole bored to half the 
 depth of the bar, which was filled with oil or mercury, into which the 
 bulb of a delicate thermometer dipped, so as at every instant to show 
 the temperature of the bar at this series of points. By means of a 
 lamp applied to one extremity of the bar, it was strongly heated, and 
 the steadiness of the heat secured by finding the temperature of the 
 thermometer nearest the lamp to be stationary for six hours, the usual 
 time for an experiment. The temperature of the air of the room, 
 
]1 8 Conduction of Heat. 
 
 which should scarcely at all vary during that time, is known by a ther* 
 mometer. 
 
 After the bar has been heated for two or three hours, each thermo- 
 meter arrives at a temperature which thenceforth continues the same, 
 as long as the source of heat is kept up. This temperature depends on 
 the difference between the quantity of heat that is propagated along the 
 bar from the lamp, and the quantity which is lost by cooling. The ex- 
 cess of the temperatures of the thermometers attached to the bar above 
 the temperature of the room, forms, therefore, a series, the ratio of 
 which depends upon the conducting power of the bar in a manner 
 which, though not simply proportional, is easily deduced from it by 
 calculation. By these principles, of which the theory was given by the 
 celebrated Fourier, Despretz has deduced, from his experiments, the 
 following conducting powers; gold being assumed as the standard of 
 comparison. 
 
 Gold . 
 
 Silver 
 
 Copper 
 
 Platii 
 
 Iron 
 
 Zinc 
 
 num 
 
 1000 Tin . 
 
 973 Lead . 
 
 898 Marble 
 
 381 Porcelain 
 
 374 Fireclay 
 
 304 
 
 180 
 23-6 
 12-2 
 11 -4 
 
 Although this series presents, when compared with the specific gravi- 
 ties, or other physical properties of these bodies, very great diversity, 
 yet it is remarkable that the more expansible and more fusible metals, 
 tin, lead, and zinc, are those which conduct heat worst. The position 
 of platinum is, however, quite anomalous, and must prevent any attempt 
 at generalization. 
 
 The difference of conducting power of solid bodies is of daily utility 
 in ordinary life, as well as in chemical operations. It is thus that sub- 
 stances of exactly the same temperature may produce quite opposite sen- 
 sations to the hand. If we grasp in one hand a piece of metal, and in 
 the other a piece of wood, both at 180, the hand will be reddened and 
 blistered by the metal, but the latter will feel only moderately warm. 
 If the metal and wood be both cooled at 32, the former will feel in- 
 tensely cold, but the latter scarcely at all so. In the first case, the 
 metal gives out its heat to the hand, and in the second, abstracts it 
 from the hand so rapidly, that the nerves and circulation become 
 acutely sensible of the change ; but with the wood, from its low con- 
 ducting power, the flow of heat takes place so gradually in each direc- 
 tion, as almost to escape notice. The brickwork of a fireplace, or of a 
 furnace, is for the purpose of keeping the heat, generated by combus- 
 tion, from spreading to the surrounding bodies, and so being lost. It 
 would be difficult to light a fire in a massive metallic grate, for the heat 
 
Conducting "Power of Liquids. 119 
 
 should be so rapidly carried off, by its conducting power, that the fuel, 
 if not well lighted before being introduced, would be cooled down and 
 extinguished. 
 
 Liquids conduct heat but very slowly; so slowly, that they were long 
 considered to be true non-conductors. It is now satisfactorily proved, 
 however, that they do conduct, and although no accurate numbers have 
 been obtained, their powers appears to be generally as their density ; 
 mercury being the best conductor, and alcohol and ether being the 
 worst. This low conducting power may easily be demonstrated by ex- 
 periment. Thus, if in a jar of water an air thermometer be inverted, 
 so that its bulb shall be very near the surface, and a cup. containing 
 ether, be laid floating on the water, as in the figure 
 the ether may be set on fire, and allowed to burn 
 for a considerable time, before any action on the 
 thermometer becomes sensible, and even then, the 
 heat appears to have travelled rather by the solid 
 material of the glass, than by the water. If a 
 little water be frozen in the bottom of a narrow 
 tube, and a solid adherent piece of ice being so ob- 
 tained, if more water be poured in, so as to cover the ice to the depth 
 of a few inches ; on inclining the tube, and applying the flame of a 
 lamp to the water near the surface, it may be kept boiling violently, and 
 for a long time, before the ice begins to liquefy, and then also it is by 
 the glass material of the tube that the heat shall be conveyed. 
 
 Notwithstanding such facts, it is still well known that heat may be 
 communicated through large quantities of fluid, so that the mass shall 
 be rapidly and uniformly heated. It occurs, then, not by conduction, 
 but by diffusion, and the source of heat cannot be applied indifferently 
 to any surface of the fluid, as it might be to a solid body, but must be 
 applied underneath. When any portion of a liquid is heated it expands, 
 and, becoming specifically lighter, ascends in the mass, and is replaced 
 by the colder and heavier portions, which, being in their turn heated, as- 
 cend also, and thus generate a circulating current of ascending warm, 
 and descending cold liquid, as in the figure, by which every particle of 
 the liquid is brought in succession into contact with the 
 source of heat, and the resulting temperature quickly and 
 uniformly gained. 
 
 In the case of water, and such liquids as have a point of 
 maximum density, this communication of heat, by ascend- 
 ing and descending currents, occurs in the inverse order be- 
 low that point. Thus to warm water which is below 
 39-5, the heat should be applied above, or to cool it fur- 
 
120 Theory of Cold and Warm Clothing. 
 
 ther the heat should be abstracted below. On this property depends 
 the preservation of the lakes and rivers of these countries from total and 
 eternal congelation. "When in winter the mass of water becomes cooled to 
 39-5, the superficial layer becoming lighter as it cools more, prevents, 
 by its non-conducting power, the further abstraction of heat from the 
 deeper portions, but when the warm air of spring plays on it, the heat 
 is rapidly diffused from above downwards, until the temperature of the 
 entire mass is raised to 39*5. 
 
 In their mode of communicating heat gases resemble liquids. Their 
 true conducting power is quite insensible, but by the currents 
 which are produced by the ascent of warm and the descent of 
 colder particles, they abstract and commum'cate heat with great rapi- 
 dity. The difference is easily felt by holding the hand first at the side 
 and then over the flame of a candle, the distance being the same. 
 In the latter case the great increase of heat arises from the ascend- 
 ing current of heated air which does not affect the hand when at the 
 side. 
 
 The non-conducting power of gases is practically of great importance. 
 The different kinds of clothing owe their warmth to the fact that they 
 prevent the heat of the body from escaping ; this they effect not so 
 much by the power of their proper solid substance, as that being of a 
 loose and spongy texture, they imprison in their pores a quantity of air, 
 which, not being able to form those continual currents, acts as a non- 
 conductor. The more loose and spongy, therefore, the tissue of a cloth 
 may be, the more air does it confine and the warmer it feels. This is fully 
 supported by the experiments of Eumford, who, having heated 
 to the same degree a thermometer, imbedded in the materials of 
 which clothing is generally made, found that it cooled through 135 
 when surrounded with 
 
 Air in 576" Raw silk in 1283" 
 
 Fine lint 1032" Beaver's fur 1296" 
 
 Cottonwool 1046" Eiderdown 1305" 
 
 Sheep's wool ,, 1118" Hare's fur ,, 1315" 
 
 When these bodies are tightly compressed, so as to diminish the 
 quantity of air confined within their tissue, the power of retaining 
 warmth diminishes in the same degree. 
 
 On standing before a fire, the influence of the heat is felt, even at 
 a considerable distance, although the air is, as has been just stated, so 
 bad a conductor that the warmth cannot be ascribed to direct transmis- 
 sion through its mass, and since, as a current of air is passing to the fire 
 in order to supply its combustion and produce the draught of the chim- 
 
Properties of Radiant Heat. 1 21 
 
 ney, no heat can arrive at the body by the current from the fire. Also, 
 if a heated iron ball be suspended in a room, it propagates heat in all 
 directions, although the current of air, which, so far as has been yet 
 described, alone can convey any great quantity of heat, is directed only 
 upwards. Heat is, therefore, propagated by a third mode, distinct from 
 diffusion and from conduction ; and the heated body being supposed 
 to emit actual quantities of heat in straight lines or rays from every 
 point of its surface, this mode is termed radiation. 
 
 Kadiation is remarkably distinct from conduction and diffusion in not 
 requiring for its existence any material medium. On the contrary, the 
 existence of any coherent substance in their path is an obstacle to the 
 transmission of the rays of heat, and hence in most solids and liquids 
 there is little heat transmitted by radiation, unless we look upon con- 
 duction as a kind of radiation from particle to particle in the interior 
 of the mass, and it is only with gases that radiation approaches to what 
 takes place in empty space. A heated body throws off rays of heat 
 precisely as a luminous body throws off rays of light, and in every 
 detail of physical constitution that has yet been discussed, there ex- 
 ists a perfect similarity between heat and light in these radiant 
 forms. 
 
 Different bodies radiate heat with different powers, which appear to 
 depend more upon the mechanical nature of the surface than upon the 
 internal constitution of the body. "When any substance is interposed 
 in the path of the rays of heat, these are either reflected, or are ab- 
 sorbed, or they pass through the body without loss. In general all 
 these effects are in part produced, that is to say, one portion of the in- 
 cident rays will be transmitted, another portion reflected, and a third 
 will disappear by being absorbed. There are thus in relation to radiant 
 heat four qualities, which various substances possess in different degrees, 
 the radiating, the absorbing, the reflecting, and the transmitting 
 power. 
 
 The rays of heat may, like those of light, be concentrated by reflec- 
 tion or refraction. By the former mode, that originally used by Pre- 
 vost and by Leslie, the properties of radiant heat may be demonstrated 
 in a simple manner. 
 
 The form of apparatus generally employed for demonstrative experi- 
 ments on radiant heat consists of reflecting mirrors of polished silvered 
 copper, of a paraboloid form M M' ; the property of this figure being 
 that rays emanating from the focus f of one mirror are reflected from 
 it in parallel directions, and falling thus parallel upon the other are 
 brought to convergence in its focus f. ' In this manner the heat 
 radiating from a body may be concentrated upon a single point, and all 
 
122 Radiation and Reflection of Heat. 
 
 its properties determined with great precision. Thus, a hot iron ball 
 may be placed at a distance of a few feet from a bit of phosphorus for 
 
 any length of time without affecting it ; but, if the hot ball be placed 
 in the focus of one mirror x, and the phosphorus in the focus of the 
 other x, this immediately begins to melt, and after a moment bursts 
 into flame. If the hand be held in the focus it feels hot, but on 
 moving it much nearer to the source of heat, the iron ball, it feels 
 cooled. It is thus not by the direct conduction of the air, or by 
 diffusion of warm currents, that the effects are caused, but from the 
 radiation of heat in a form which, like light, admits of being re- 
 flected from curved surfaces, and concentrated upon a focus, and 
 which shall be found to follow the analogy of light through all its 
 branches. 
 
 If a thermometer be placed in the focus of the mirror opposite the 
 heated ball, it immediately indicates the rise of temperature, and may 
 serve to measure it. But it is only the air thermometer which 
 is delicate enough for such experiments, and it is 
 specially for this use that the differential air ther- 
 mometer is constructed. One bulb being placed 
 in the focus, the difference of temperature between 
 the two bulbs is instantly shown, and it is thus 
 also proved that the rise of temperature is local, that 
 it is confined to the point where the rays of heat 
 are brought to meet, for the instrument is insensible 
 to every general change of temperature, no matter 
 how extensive. 
 
 By means of this apparatus the radiating and 
 absorbing, as well as the reflecting and transmitting 
 
Influence of lie Nature of Surface. 123 
 
 powers of bodies may be examined. The radiating power may be con- 
 veniently exhibited by filling a tin cube, c t, with boiling water, and 
 applying to the surfaces of the cube the bodies which are to be 
 examined. Thus, one side being left brightly polished, another dimmed 
 by being rubbed with sand paper, a third covered by paper, and the 
 fourth being blacked by the smoke from a candle, each side, on being 
 turned towards the mirror N, gives out a quantity of heat proportional 
 to its radiating power, and this being reflected and brought to bear 
 upon the thermometer in the focus e, is measured by its indication. 
 Leslie thus found the radiating power of the following surfaces to be 
 relatively. 
 
 Lampblack, . 100 Plumbago, . " . . 75 
 
 Writing paper .:. . . 98 Tarnished lead . . 45 
 
 Crown glass . ' 1 : - 90 Clean lead V . -^ * 19 
 
 Ice . friMUfi U 1 j 85 Polished iron . 15 
 
 Red lead ^--^ 'f~ n-J.. 80 Other bright metals 12 
 
 It is here evident that the radiating power is quite independent of 
 the colour of the body ; and that in all cases those bodies, with bright 
 metallic surfaces, radiate least; the radiating power of lead being 
 doubled by simply tarnishing its surface. It has been rendered pro- 
 bable, however, by recent observation, that it is not the degree of polishing 
 of the surface which influences the radiating power, so much as the 
 closeness and density of the exceedingly thin surface layer, on which 
 the quantity of radiant heat depends. In the process of polishing, the 
 surface of a metallic plate, particularly if it be rolled, is very much 
 compressed, and in this state radiates in the lowest possible degree ; 
 but if by rubbing with sand paper that dense film of compressed metal 
 be removed, the softer material underneath radiates with nearly double 
 the power. If a plate of silver be cast without being subjected to any 
 pressure, the surface, although perfectly bright, radiates with a power 
 of 22 ; but, if it be dimmed by rubbing with sand paper, the com- 
 pression, even so slight, diminishes the radiating power to 12. Sub- 
 stances which are highly elastic, as ivory, or very hard, as agate, radiate 
 in the same degree, no matter what be the rough or smooth condition 
 of the surface. 
 
 That the texture of the surface should influence the radiating power 
 is easily comprehended, when we know that it is not from the external 
 surface, but from a little depth below it, that radiation actually takes 
 place. If radiation were truly from the surface, every point of it 
 emitting rays equally intense in all directions, there should occur 
 inequalities in the temperatures of the surrounding bodies of the 
 
124 Of the Radiating, Absorbing, 
 
 most remarkable and intolerable kind. Thus, let us suppose two 
 surfaces at right angles, radiating heat, as, for instance, two sur- 
 faces of a red hot poker. A body A, at a certain distance from the 
 angle, should have its temperature raised much more than a body, B 
 or c, directly opposite either side, for it 
 should receive the rays A M, and A M', equally 
 intense ; while the bodies B and c should 
 receive from the same points only the rays 
 B M, or c M'. But the rays emanating not 
 1VJ from the surface at M or M', but from N' and 
 
 N, at some depth below, the oblique ray, N A, 
 
 has to pass through so much a thicker stratum of solid matter from 
 N to P than the direct ray from N to M ; that the conjoint action of the 
 two does no more than enable the surrounding bodies to attain an equa- 
 ble temperature. Bodies obliquely exposed to a flat radiating surface, 
 receive less heat, not that a smaller number of rays impinge upon 
 them, but that a greater portion of heat is lost in escaping from below 
 the surface of the body. 
 
 The radiating powers of bodies are the foundation of numerous ap- 
 plications in the arts. Those bodies which radiate least cool slowest ; 
 and hence if it be required to keep any material hot for a considerable 
 time, it should be enclosed in a vessel with a bright metallic surface, 
 that being the kind which retards most the escape of heat. If, on the 
 contrary, the object be to diffuse heat, the best radiating surface should 
 be made use of. It is thus that the tubes by which heated air or water 
 or steam, are supplied to buildings, for the purposes of warmth, should 
 be bright and polished until they arrive at the precise locality where 
 the heat is to be given out, but should there be painted with white- 
 lead or lampblack, the surfaces by which the heat is most rapidly given 
 out. 
 
 If two tin vessels, precisely similar in form, but one being painted 
 and the other polished, be filled with warm water, and placed in a cool 
 room, that which is painted will cool more rapidly than the other, in 
 consequence of its greater power of radiation. If the two vessels, 
 when cold, be placed opposite a steady fire, the temperature of the 
 water in that which is painted will be observed to rise more rapidly 
 than that of the other ; it will absorb the heat of the fire, precisely as 
 it had given out the heat of the water, with most rapidity. The bodies, 
 therefore, that radiate best, absorb heat, likewise, with greater power, 
 and those which, when hot, cool most slowly, are those also which have 
 least tendency to receive radiant heat. 
 
 The absorbing and radiating power may even be proved to be exactly 
 
And Reflecting Powers of Bodies. 125 
 
 proportional to one another by the following experiment. A large 
 differential thermometer is arranged, whose bulbs are chambers of con- 
 siderable size, presenting large and equal plane surfaces on the sides 
 that are towards each other other. Of these one is polished and the 
 other coated. Midway between them is placed a canister having equal 
 plane surfaces, facing each of the former respectively, and one polished, 
 the other coated with the same pigment as before. This canister is 
 filled with hot water, and is capable of turning on a vertical axis : thus 
 the coated surface of the canister can be turned to the coated bulb, or 
 to the polished ; in the former case, a great effect is produced upon the 
 coated bulb, and a very small effect upon the plain ; in the second case 
 the better radiating surface is directed to the worse absorbing one, and 
 the worse radiating to the best absorbing, and the liquid in the tube 
 remains perfectly stationary , establishing thereby the exact quality of 
 the absorbing and radiating powers. 
 
 Although colour is without influence on the radiating power, it yefc 
 appears to influence the absorbing power in a remarkable degree. If 
 pieces of cloth of various colours be laid upon snow, and exposed to 
 the direct solar rays, that which is black will, by absorbing more heat, 
 melt the snow away from under it, and sink deepest. White will sink 
 least, and the others in the order of their depth of colour. It is, 
 therefore, with reason that dark coloured cloths are preferred for winter 
 use, and light colours for summer. It is, however to be noticed, that 
 it is only upon the absorption of those rays of heat, which accompany 
 rays of light, that colour has this power. 
 
 The great difference of absorbing power of a blackened and of a 
 metallic surface may easily be shown, by coating one bulb of a differ- 
 ential thermometer with silver leaf and blackening the other. When, 
 with the same source of heat, the rays are received upon the silvered 
 bulb, scarcely any rise of temperature can be observed, but when the 
 blackened bulb is placed in the focus, the rise is much more than would 
 have occurred with the thermometer in its ordinary condition of the 
 bulb with a glass surface. 
 
 The mirrors which are used in those experiments do not become sen- 
 sibly heated until after a long time ; they absorb but very little heat : 
 but if the surface of the mirror be smeared with glue, it loses to a great 
 degree its power of reflecting, and having thus obtained an absorbing 
 and radiating power, it very soon becomes warm. If it be coated with 
 lampblack, its reflecting power vanishes, and its surface becomes highly 
 absorbent. The reflecting property is, therefore, possessed by the 
 surfaces of bodies in the inverse degree to the absorbing and ra- 
 diating powers, and hence the best absorbers are those which reflect least. 
 
126 
 
 Researches of Melloni and 
 
 The heat which is naturally associated with light in the sun's rays; 
 is capable of being so concentrated by reflection, that in the focus of 
 a burning mirror, results equal to those of the most intense artificial 
 heat may be produced. The heat of the sun's rays may also be con- 
 centrated by refraction; the heat accompanying the rays of light in 
 their passage across lenses ; hence the use of the burning glass. But 
 when we thus come to discuss the property possessed by bodies of trans- 
 mitting radiant heat through their substance it becomes necessary to look 
 further to the source and intimate structure of the heat. Eor the results 
 which have as yet been described, we are indebted almost exclusively to 
 Leslie, but the power of transmitting heat could only have led to the 
 important consequences deduced from it by Forbes and Melloni, more 
 recently when the progress of other sciences had placed at the disposal 
 of the experimenter measures of temperature infinitely more sensible 
 than any form of thermometer hitherto in use. 
 
 It is by means of the thermo-multiplier and galvanometer that the 
 effects of the transmission of heat require to be observed. 
 
 The apparatus employed by Melloni was, in its general arrangement, 
 such as is represented in the figure. 
 
 On a steady table there rests a frame M, M, along the middle of which 
 a slip, E, R, is cut, by which the various stands and supports may be 
 moved back and forwards, so as to vary their distances from each 
 other. On the stand s, is placed the source of heat ; in the figure it 
 is a coil of platina wire ignited by a spirit lamp, but the flame may be 
 
Forbes on Radiant Heat. 127 
 
 surrounded by a cylinder of blackened copper, or it may be a 
 vessel of boiling water, or an argand or Locatelli lamp. The rays 
 proceeding from it are received by the thermo-multiplier, B, from 
 which the wires F, F, convey the electricity generated to the galvano- 
 meter, G, which for steadiness is placed at a distance and on brackets 
 secured against a wall. These parts, p and G, will be represented in 
 full in the chapter on electricity. If it be required to study the action 
 of a plate of any substance upon the rays of heat, the screen E is inter- 
 posed, having an aperture o, somewhat smaller than the plate to be 
 employed. This last is then supported immediately behind the aper- 
 ture, by means of the little frame s, so that no heat can reach the 
 thermo-multiplier, unless after having passed through it. As it is of 
 great importance to have the end of p farthest from the lamp, unin-* 
 fluenced by any disturbing causes, the screen E" is placed immediately 
 behind it to protect it from irregular radiation and from currents ; 
 arid as the action of the heat upon the pile must be limited to the 
 actual time of the experiment, the double screen E' is interposed imme- 
 diately next the lamp, and being provided with a hinge, is raised or 
 lowered, at the moment when the rays of heat are to be allowed to pass, 
 or are to be intercepted. 
 
 The orifice of the thermo-multiplier was occasionally fitted with a 
 conical tube of plated brass, for the purpose of collecting the rays of 
 heat in greater number ; but that is not often wanted. 
 
 The reflecting power of bodies has been exactly determined by Buff 
 to be as follows. Of 100 rays incident at an angle of 60 from the 
 perpendicular, there are reflected, by 
 
 Polished gold . . ". " . 76 
 
 silver 62 
 
 brass . 62 
 
 Brass without polish 
 Polished brass varnished 
 Glass plate blackened on back 
 Looking glass 
 Metal plate blackened . 
 
 52 
 41 
 12 
 20 
 6 
 
 The power of a body to transmit heat is termed transcalescence, and 
 of intercepting heat intranscalescence. These properties are totally in- 
 dependent of the power of transmitting light, as will be at once seen 
 from the following table. It has been found by the experiments of 
 Nobili and Melloni, conducted with the apparatus just described, that 
 of 100 rays proceeding from the flame of an argand lamp, there are 
 transmitted by 
 
128 
 
 Permeability of Hodies to Heat. 
 
 Substance. 
 
 Colour. 
 
 No. 
 
 Substance. 
 
 Colour. 
 
 No. 
 
 Rock salt 
 
 colourless 
 
 92 
 
 Glass coloured 
 
 yellow 
 
 22 
 
 Calc spar 
 
 do. 
 
 62 
 
 Do. . . / ;. 
 
 blue 
 
 21 
 
 Smoke topaz 
 
 brown 
 
 57 
 
 Sulphuric ether 
 
 colourless 
 
 21 
 
 Plate glass 
 
 colourless 
 
 40 
 
 Gypsum . ...*_-; _ ^ 
 
 do. 
 
 20 
 
 White agate 
 
 do. 
 
 35 
 
 Tourmaline 
 
 green 
 
 18 
 
 Glass coloured 
 
 violet 
 
 34 
 
 Opaque quartz r *' 
 
 black 
 
 16 
 
 Do. . 
 
 red 
 
 33 
 
 Citric acid ; 
 
 colourless 
 
 15 
 
 Chromate of potash 
 
 orange 
 
 33 
 
 Alcohol . 
 
 do. 
 
 15 
 
 Borax . . ^ - 
 
 colourless 
 
 28 
 
 Alum 
 
 do. 
 
 12 
 
 Glass coloured 
 
 green 
 
 23 
 
 Water . 
 
 do. 
 
 11 
 
 Bock salt is thus the most transcalescent substance that has been 
 found. Glass arrests more than one-half of all the heat which it re- 
 ceives, whilst colourless and transparent alum, and the most limpid 
 water, arrest more of the heat which they receive than the deepest co- 
 loured glasses, or topaz, or quartz, so brown, as to be quite opaque. 
 
 But not merely do different bodies act differently on rays proceeding 
 from the same source, but the same body may allow the heat of one 
 source to pass freely through its substance, and intercept partially or 
 completely the heat radiating from another. Thus using, in his experi- 
 ments, the heat emanating from five kinds of source, first, the argand 
 lamp ; second, the lamp of Locatelli, which is remarkable for the stea- 
 diness of its flame ; third, a red-hot spiral of platina wire ; fourth, a 
 blackened copper plate, heated to 734 ; and fifth, a blackened copper 
 plate, heated to 212 by boiling water, Melloni found the heat arising 
 from these sources to be transmitted in the following proportion per 
 cent. ; the results with the argand lamp, having been given in the last 
 table, are here omitted. 
 
 Substance. 
 
 Locatelli 
 Lamp. 
 
 Ignited 
 Platina. 
 
 Copper at 
 734. 
 
 Copper at 
 212. 
 
 Free radiation 
 
 100 
 
 100 
 
 100 
 
 100 
 
 Rock salt 
 
 92 
 
 92 
 
 92 
 
 92 
 
 Fluor spar 
 
 78 
 
 69 
 
 42 
 
 33 
 
 Calc spar 
 
 39 
 
 28 
 
 6 
 
 
 
 Plate glass 
 
 39 
 
 24 
 
 6 
 
 
 
 Agate . 
 
 23 
 
 11 
 
 2 
 
 
 
 Gypsum . 
 
 14 
 
 5 
 
 
 
 
 
 Alum 
 
 9 
 
 2 
 
 
 
 
 
 Ice ' jj 
 
 6 
 
 
 
 
 
 
 
 Eock salt is thus not only the most transcalescent body, but it is that 
 which alone is equally transcalescent to heat of all temperatures. The 
 rays of heat evidently acquire a greater power of transmissibility as the 
 temperature of the source increases ; and hence glass arrests scarcely 
 
From Sources of Different Temperatures. 129 
 
 any portion of the direct solar heat ; whilst from the argand lamp, it 
 intercepts 47 ; from LocatelFs lamp, 61 ; from ignited platina, 72 j 
 from copper, at 734, 94; and from copper, at 212, 100 per cent. 
 The action of these media upon radiant heat consists not merely in 
 stopping a certain portion of it, but in separating it into portions, phy- 
 sically distinct, of which one is capable of transmission, whilst the other 
 is absorbed. Hence a second plate, of the same kind of substance, 
 exerts but a very slight action upon the heat which has already passed 
 through the first. Thus, though a plate of alum allows only 9 in 100 
 of the direct rays of the lamp to pass, yet it admits of the passage of 90 
 in 100 of rays which have already passed through a plate of the same 
 substance : and calc spar, which transmits only j?? of the direct heat, 
 transmits 91 of that which had passed through alum, and 89 of that 
 which had passed through gypsum. On the other hand, a green tour- 
 maline, which transmitted 18 out of 100 rays directly incident upon it, 
 intercepts ?| of those which had previously passed through alum, but 
 gives passage to $$ of radiant heat which had passed through black 
 glass. 
 
 The nature of the physical distinction between the intercepted and 
 the transmitted portions of the heat is to be found in the different re- 
 frangibility of the rays of heat emanating from sources of various tem- 
 peratures. If the rays of heat emanating from a lamp be incident upon 
 a rock salt prism, they will undergo refraction, subject to the same law 
 of the sines, as in the case of ordinary light, and there will be obtained 
 a band or spectrum of rays from the lamp ; the most refrangible will 
 coincide with about the middle of the luminous spectrum, whilst the 
 least refrangible will extend far beyond the limits of the least refrangible 
 rays of light. The mean refrangibility of heat is, therefore, less than 
 that of white light, and the length of its undulation, if the wave theory 
 be adopted, longer in proportion. 
 
 If now the heat spectrum, so obtained, be examined by means of the 
 media which have been already noticed, the explanation of the pecu- 
 liarities in their action will be at once observed. Eock salt allows the 
 rays of all degrees of refrangibility to permeate its mass ; it is to heat 
 what perfectly colourless glass is to white light, it acts equally on all 
 portions of it. Alum stops all but the very least refrangible rays ; it is 
 to heat what ruby-coloured glass is to light, which allows only the rays 
 of the least refrangible extremity of the spectrum to pass through. 
 Glass, gypsum, and such bodies as give passage to the rays of least and 
 of mean refrangibility, resemble those orange-coloured glasses which 
 exclude the blue and violet rays of light, but admit the others. 
 
 After long search, Melloni at last found that by coating with soot the 
 9 
 
130 Analogy of Heat to Coloured Light. 
 
 surface of a plate of rock salt, it became to heat what blue glass is to 
 light ; it excluded the rays of inferior refrangibility ; and when a plate 
 so prepared was combined with a plate of alum, all heat was intercepted, 
 precisely as when by laying a plate of blue and a plate of orange glass 
 together, perfect opacity is produced, the one absorbing the portion of 
 light which alone the other is capable of transmitting. 
 
 The rays of heat derived from sources of different temperatures are 
 thus analogous to the rays of light of different colours. The higher the 
 temperature of the source, the more does it resemble red light ; the 
 lower its temperature, the greater is its analogy with the violet rays. 
 Hence, alum absorbs all the heat from boiling water, but gives passage 
 to that from the argand lamp ; but alum is like a glass so deeply co- 
 loured red, that it is almost opaque, and transmits only a small portion 
 even of its own coloured light that may fall upon it. 
 
 When a ray of heat is incident upon a doubly refracting substance, it 
 follows precisely the same law as light, and is refracted doubly. In 
 this case, also, the rays after emergence are found to be polarized in 
 planes perpendicular to each other ; and all those consequences of the 
 mutual action of polarized rays, which give rise to such magnificent phe- 
 nomena of colours in the case of light, must occur with heat, and be 
 made sensible, if our organs, or our instruments, were of a construction 
 suitable for their appreciation. As yet, however, the fact which alone 
 remains wanted, towards a physical theory of heat, has not been ob- 
 served, that of interference ; up to the present time, the actual pro- 
 duction of cold by the combined action of two rays of heat has not been 
 seen ; but the closeness of the analogy, which in this case alone requires 
 additional observation, between light and heat, is so remarkable, that 
 we can have little hesitation in referring these agents, in their radiant 
 form, to the same kind of physical arrangement. 
 
 There is no difficulty in conceiving radiant heat to consist in vibra- 
 tions of the same ethereal medium which produces light, and in consi- 
 dering that the difference between heat and light should be in the mag- 
 nitude of the vibrations, and the consequent refrangibility of their rays. 
 On the contrary, it is not reasonable to suppose, that whilst we are con- 
 scious of the waves in air, although they may vary in length, from 32 
 feet to ^ of an inch, the limits of our sensibility to the ethereal waves 
 should be so narrow, that the shortest (violet) is to the longest (red) as 
 60 to 38 ; it is more consonant to our idea of the various and beautiful 
 uses to which every object of creation is made subservient, to believe, 
 that whilst the waves within these limits produce upon the eye the sen- 
 sation of coloured light, another range of lengths, greater than those of 
 light, should give to our organs the sensation of radiant heat ; and that 
 
Polarization of Heat. 131 
 
 a third order of vibration, still shorter, and more refrangible even than 
 violet light, is capable of acting npon the elementary constituents of 
 bodies, and constitute the chemical rays. The coexistence of these three 
 kinds of rays in solar light is an argument remarkably in favour of this 
 view, for we can well imagine, that by whatever means the sun commu- 
 nicates to the ethereal expanse the vibrations of various lengths which 
 constitute the rays of light, that vibrations of other magnitudes, greater 
 or less, should be at the same time produced, and thus the light, which 
 exhibits to us the beauty of the external world, be accompanied by the 
 heating power which animates all living nature, and without which the 
 universe should be a tenantless and barren void. 
 
 These arguments, however, natural, and in appearance sound, are met 
 by facts which, if not positive against light and heat differing only in 
 the length of the waves, by which they are produced, are, at least, of so 
 much importance as to deserve attentive study. If it were so, then the 
 heating rays of the spectrum should be thrown always below the co- 
 loured space, being less refrangible, and it is found that with a flint 
 glass prism the greatest heat is produced outside the visible confines of 
 the spectrum at the limit of the red light. This is, however, only acci- 
 dental from the nature of the prism ; for, if a prism of crown glass be 
 employed, the rays of heat are collected in the middle of the red space : 
 with a prism of sulphuric acid, in the orange, and by a prism of oil of 
 turpentine or water, they may be collected into the centre of the yellow 
 light. 
 
 The rays of heat, therefore, although generally less refrangible than 
 those of light, are still not necessarily or even always so. There is dis- 
 tributed, over the entire visible spectrum, a heating spectrum which has 
 its peculiar point of greatest energy, and which may be refracted more 
 or less, quite independently of the luminous space, and may be brought 
 to overlap it at either end, or to lie evenly upon it. The ethereal me- 
 dium, if it be the means of transmitting radiant heat, must be capable of 
 two distinct methods of vibration, by which rays of equal refrangibilities, 
 but totally different properties, may be produced. 
 
 The physical independence of solar light and heat was beautifully 
 shown by Melloni, who using quartz and black mica, perfectly opaque, 
 upon the one hand, and rock salt made perfectly opaque by soot upon 
 the other, obtained radiant heat of all refrangibilities, totally free from 
 light ; and on the other hand, by combining a plate of alum with a glass 
 coloured green by oxide of copper, he obtained a brilliant beam of light, 
 which, when concentrated by a lens upon the most delicate thermos cope 
 he could apply, exhibited no trace of any heating power whatsoever. 
 
 An interesting property of radiant heat, and one which shows the 
 
132 Constitution of Heat and Light. 
 
 remarkable distinction between it and light, in a very evident manner, is, 
 that the heat may change its degree of refrangibility, and hence if it be 
 vibrations, one wave may break up into several, or several smaller waves 
 may unite to form one. The light of the sun, deprived of all the more 
 refrangible rays, by passage through a plate of alum, may be received on 
 a blackened surface, the temperature of which will be thus elevated, and 
 which, in turn, will become a source of radiant heat. But the heat so 
 radiated, is found to have totally changed its properties; it can no longer 
 pass through alum ; it has passed from the state of heat of the lowest to 
 the state of heat of the highest refrangibility. In like manner, if the 
 most refrangible rays emanating from a source at 212, be concentrated 
 by a rock-salt lens, and brought to act on a small surface, they may raise 
 the temperature of this surface above 212, and radiate from thence in a 
 less refrangible condition than before. The parallel case to this has 
 never been found with light. Red light has never been changed into 
 blue, or violet into orange, and there must be in the physical theory of 
 radiant heat some general principle of so high an order, that the physical 
 optics of the present day is but a particular case of it. 
 
 This change of radiant heat from one degree of refrangibility to ano- 
 ther, occurs in nature very often, and is the source of some remarkable 
 phenomena. Thus the heat of the sun's rays, being of low refrangibility 
 from their intensely heated source, is transmitted easily by ice or snow ; 
 and hence a layer of snow upon a field, exposed even to the powerful 
 action of the sun, is but slowly melted : if, however, a dark-coloured 
 object, as a branch of a tree, be laid upon the surface, it absorbs the 
 solar heat, and becoming a source of radiation of heat of great refrangi- 
 bility, which the snow absorbs completely, this is melted under the wood* 
 which sinks and gradually disappears beneath the surface. The earlier 
 melting of snow upon the branches and round the stems of plants, which 
 was supposed to demonstrate a kind of natural warmth belonging to the 
 living vegetable, arises from this merely physical conversion. 
 
 Prom this results also the influence of colour on the power of bodies, 
 to absorb the heat of the sun or of a fire ; the strips of coloured cloth 
 (page 125) melted the snow beneath them, not merely because they 
 absorbed more heat in proportion to the depth of colour, but because, 
 they in that proportion possessed the property of changing the heat, 
 which should be transmitted, into the heat which would be absorbed, by 
 the snow on which they rested. 
 
 The construction of a theory of heat would be, even were an undula- 
 tory hypothesis adopted for its radiant form, involved in difficulties which 
 may require many years of research to render them even clearly under- 
 stood. The relation between radiation and conduction; the connexion 
 
Equilibrium of Temperature. 133 
 
 between specific and latent heat; the laws of cohesive force against which 
 heat acts in causing the expansion of a body, will all require to be com- 
 prehended within the folds of whatever principle shall hereafter be made 
 the basis of thermotics. But it is no disrespect to the illustrious names 
 that have been connected with speculations on this subject, to conclude, 
 that none of the views brought forward appear positive or clear enough 
 to be described in a work of an elementary nature like the present. 
 
 SECTION VI. 
 
 OF THE COOLING OF BODIES. 
 
 Bodies, at an elevated temperature, are capable of giving out the heat 
 which they contain, by every method by which, when cold, they become 
 heated at the expense of the surrounding warmer bodies. Cooling may 
 occur, therefore, by contact or by radiation. The rapidity of cooling by 
 the immediate contact of the hotter with the colder body depends on the 
 degree of intimacy of the contact, and the conducting powers of the 
 bodies. Thus solids, which merely touch at a few points, communicate 
 their relative temperatures but very slowly, whilst, with liquids or gases 
 which may mix completely with each other, the establishment of an 
 uniform temperature is almost instantaneous. The colder becomes heated 
 to the original temperature of the hotter, only when there is a continual 
 supply of heat to maintain that temperature, as in a furnace : in other 
 cases the hotter body cools in proportion as the colder becomes warm, 
 and the resulting temperature depends on the specific heat of each, as 
 has been described, page 81. In determining, therefore, the temperature 
 of a body by a thermometer, it must not be forgotten that the thermo- 
 meter, in becoming hot, cools the body, so that unless there be a conti- 
 nuous source of heat the true temperature of a body is never given by 
 the instrument. Where the substances, being solid, can only come into 
 external contact, the rapidity with which heat passes from one to the 
 other depends upon their conducting power ; thus, a cold brick may be 
 laid upon a heated brick for a considerable time without much heat 
 changing place, but a plate of red hot iron, laid upon a plate of cold 
 iron, abandons its excess of temperature so rapidly, that a mean temper- 
 ature is attained by both in a very short time. 
 
 The cooling of bodies by radiation is governed by the principle, that 
 all bodies in nature are in a continual state of interchange of heat ; no 
 
134 Equilibrium of Temperature. 
 
 matter how hot or how cold a body may be, it is constantly giving out 
 radiant heat to other bodies, and receiving in exchange, and absorbing 
 the heat which radiates from them. The quantity of heat, thus radi- 
 ated, depends on the temperature of the body ; the higher this is, the 
 greater quantity of heat is thrown off; the lower the temperature, the 
 less heat does a body radiate in a certain time. Hence, if we conceive 
 a ball heated to redness, and suspended in the centre of a number of 
 similar but colder balls, each will radiate and absorb, but the hotter 
 ball will give out more than it can gain in return, and will hence cool, 
 whilst the surrounding colder bodies, absorbing more of the radiant 
 heat than they return, will have their temperature raised. Every body 
 in nature, therefore, no matter how its temperature may, by peculiar 
 or local means, be elevated or depressed, tends, ultimately to an equili- 
 brium with all the neighbouring bodies, and hence the instant we re- 
 move a substance from our furnaces or freezing mixtures it begins to 
 cool or become less hot. This principle explains, in a very perfect 
 manner, a singular but instructive experiment which may be made with 
 the concave mirror apparatus described, page 122. In the ordinary 
 form, the thermometer and the heated ball tend, by radiation, to assume 
 a common temperature, and the thermometer, being the colder body, 
 becomes heated : but if, in place of the heated iron ball, a mass of ice 
 be substituted, the temperature of the thermometer in the focus of the 
 opposite mirror immediately sinks below that of the surrounding air. 
 The explanation consists simply in the fact, that the thermometer is now 
 the hotter body, and hence giving out to the ice more heat than the ice 
 gives back, has its temperature reduced. At first this effect appeared to 
 demonstrate the existence of rays of cold, which were reflected, radiated, 
 and absorbed like rays of heat. 
 
 In this principle of the uniformity of temperature being sustained by 
 the equivalent radiation and absorption of the bodies at the surface of 
 the earth, we find the solution of many interesting natural phenomena. 
 The production of dew and frost are to be thus accounted for. In the 
 absence of the sun, the surface of the earth losing, by radiation, a great 
 quantity of heat, should have its temperature considerably lowered, were 
 it not that the canopy of clouds which generally lie above it radiate in 
 return, and thus maintain the temperature almost the same. If then 
 the clouds be absent, all the heat radiated by the earth is lost in the 
 planetary spaces, and the temperature of its surface brought many de- 
 grees below that of the atmosphere. The stratum of air which lies in 
 contact with the surface of the ground is then cooled, by contact, and a 
 portion of the watery vapour, which it had possessed in its elastic form, 
 is deposited as liquid water. If the temperature of the air be itself low, 
 
Theory of Dew atid Frost. 135 
 
 and the night very clear, the cooling may proceed so far that the drops 
 of dew at the moment of their deposition shall be frozen, and thus 
 form frost. The truth of this explanation is demonstrated by the fact, 
 that it is only on the surfaces of good radiators, and during clear star- 
 lit nights, that the dew or frost is found. If a plate of polished metal 
 be laid on the centre of a rough board, and exposed to the air of a 
 frosty night, the rough surface will be found in the morning covered 
 with copious frost, but on the bright metal no trace will be deposited. 
 It is thus, that by lightly covering a thin layer of water with straw to 
 increase the radiating power, a sheet of ice may be obtained in a single 
 night between the tropics, where the actual temperature of the air may 
 have continued far above the freezing point. That the cooling effect is 
 produced by the loss of heat in its radiant form, and not by the contact 
 or diffusion of the particles of the air, may be proved by the interpo- 
 sition of a screen of any substance which intercepts the passage of ra- 
 diant heat, when the deposition of the dew or frost instantly ceases, 
 and the surface cools no more. Thus plants are protected by mats from 
 the frosts of spring and autumn, and thus the screen of snow, which 
 covers the surface in the depth of winter, prevents the loss of heat 
 from the soil below, and favours the vegetation of the seed. 
 
 The rapidity of cooling depends upon the difference of temperature 
 of the radiating bodies, but it is not proportional to this difference, ex- 
 cept within a very narrow range of temperature. Newton having ex- 
 perimented only within that limit, announced that law as general, but 
 the establishment of the true law is due to Petit and Dulong. It is 
 that the rapidity with which a body cools, for a constant excess of tem- 
 perature, increases in a geometrical proportion, of which the ratio is 
 1*161, when the temperatures increase in an arithmetical proportion. 
 Bodies at moderately high temperatures cool, therefore, much more ra- 
 pidly than they should do by Newton's law. 
 
 The heat, by means of which we produce a rise of temperature, or 
 any other of the effects which have been described, may be derived from 
 any one of a variety of sources. To the earth at large, the sun is the 
 source of warmth; and by his varying position in the heavens, by 
 which his rays strike upon the surface with different inclinations, and, 
 passing through the different thicknesses of atmosphere, undergo ab- 
 sorption, to a variable amount, the change of seasons as to tempera- 
 ture, is produced; and the alternation of vital activity and torpor 
 which characterizes the vegetable world, and a great portion of the ani- 
 mal creation, is occasioned. Although at the surface the temperature 
 of the earth is solely dependent upon the radiating power of the sun, 
 yet it is found that it contains within itself a source of heat, which, in 
 
136 Central Heat of the Earth. 
 
 ages excessively remote, must have retained the general mass of all the 
 constituents of the mineral globe in igneous liquefaction. In fact, if 
 we dig below the surface of the earth, we arrive, at a depth of about 
 forty feet, at a layer of which the temperature is in winter and in sum- 
 mer exactly the same. It is termed the stratum of invariable tempera- 
 ture, and is, in general, of the mean temperature of the place ; that is to 
 say, the temperature of the surface falls in winter as much below that of 
 the invariable stratum, as in summer it is raised above it by the excessive 
 action of the solar rays. The heat of the sun, falling upon the surface, 
 is transmitted inwards in virtue of the conducting power of the ground, 
 and thus each summer, a thin layer of elevated temperature moves in- 
 wards ; those of successive summers, being separated from each other by 
 the intervening colder shell, which marks the period of diminished heat 
 in winter, until they mix and confound themselves in the layer of 
 constant temperature, below which the influence of the sun is felt 
 no more. 
 
 But, on descending beyond this depth, it has been experimentally 
 proved that the temperature steadily increases, and although subject 
 to irregularities consequent on the different conducting powers of the 
 rocks of different formations, the augmentation is in general about 
 one degree for every forty-two feet, or about 120 for every mile. 
 At a depth of two miles, therefore, water could not exist as a liquid, 
 unless from the great pressure to which it should be subjected : at 
 four miles depth, tin and bismuth should naturally be liquid; and 
 at five miles, lead. At a depth of thirty miles the temperature should 
 be so high as to melt iron ; and still more easily, almost without 
 exception, the rocks, which constitute the solid earth that we 
 inhabit. The central heat, therefore, although insensible at the 
 surface, is still, there is every reason to believe, in violent activity at a 
 small depth below : we live upon a pellicle of solid crystalline rocks, 
 with which the melted mass has become skinned over, and which ex- 
 tends but to -%^-Q of the distance to the centre. Hence, we can well 
 imagine that in many places, where orifices or cracks in this solid crust 
 might form, violent manifestations of the internal fire should be pro- 
 duced, and the magnificent phenomena of volcanoes and earthquakes 
 should thus arise. 
 
 For artificial purposes, the source of heat is generally chemical com- 
 bination. The details of this mode of generating heat will require to 
 be carefully and minutely considered hereafter, under the heads of 
 Combustion and the relations of Heat to Chemical Affinity. By me- 
 chanical causes, as percussion and friction, heat may also be set free ; 
 but such cases arise from a change in the specific heat of the bodies 
 
Sources of Heat. 137 
 
 before and after the mechanical action : and hence, although once con- 
 sidered as influencing our ideas of the nature of heat, they do not now re- 
 quire special notice. A very interesting source of heat consists in the 
 respiration of certain kinds of animals, and constitutes an important 
 branch of chemical physiology, which shall be discussed in its proper 
 place : and, finally, one of the most remarkable sources of heat is to be 
 found in the properties of electricity, in its various forms ; and to the 
 description of this interesting and important agent we shall now pro- 
 ceed. 
 
 CHAPTER IV. 
 
 OF ELECTRICITY CONSIDERED AS CHARACTERIZING CHEMICAL SUBSTANCES. 
 
 AMONG the various forces which concur to the production of natural 
 phenomena, there are few whose agencies are more remarkable or more 
 general than those of electricity ; and so intimately does it appear to be 
 connected with chemical action, becoming sensible in all cases of union 
 or decomposition, and being even developed in a degree proportional to 
 their amount, that the most eminent philosophers have not hesitated to 
 consider electrical and chemical agencies as being, if not identical, at 
 least intimately connected with each other. 
 
 It is not the object of this work to enter into the minute description 
 of electrical phenomena, or to attempt the detailed discussion of their 
 causes ; as, for a complete examination of the subject, it must be consi- 
 dered as one, and certainly not one of the least extensive branches of 
 natural philosophy ; it is only with regard to the influence which elec- 
 tricity exercises in the operations and the theory of chemistry, and the 
 means which the electrical properties of bodies afford for their recogni- 
 tion, that it requires notice here : and hence, although it is necessary to 
 describe the peculiar origin and characters of each form which electri- 
 city assumes, yet that shall be accomplished within the shortest limits 
 that are consistent with the importance of this branch of science. In 
 the present chapter, the subject will be studied in its general history, 
 and considered as affording useful characteristics of substances, the pro- 
 perties of which we have to learn ; and in a future place, the influence 
 which it exercises upon chemical affinity, and the opinions which have 
 
138 Nature of Electricity. 
 
 been advanced concerning its relation to purely chemical forces, shall be 
 carefully discussed. 
 
 Of the true nature of electricity nothing is positively known ; whe- 
 ther it be a mere property of matter like attraction or cohesion, a mere 
 force acting independently of all interposed material, or whether, like 
 light, it consists in the undulations of an ethereal medium filling space, 
 cannot be determined. Indeed the ordinary views of its nature consist 
 in supposing the existence of one or two fluids of electricity, of exceed- 
 ing tenuity and of perfect elasticity; and that according as ordinary 
 bodies were supposed to contain more or less of these fluids of electri- 
 city, they acquired or lost the properties of electrical excitation. Of 
 these opinions it is exceedingly difficult to say which is the more rea- 
 sonable, or more consonant to experimental truth, so far as the expla- 
 nation of phenomena is concerned ; but no positive evidence has ever 
 been obtained of the existence of such an electric fluid : it has never 
 been found capable of being separated from the ordinary particles of 
 matter, of which it appears always as an additional property assumed 
 under peculiar circumstances, and not as a superadded constituent. I 
 consequently incline to the idea, that, in the phenomena of electricity, 
 we have exhibited only the results of new mechanical conditions of the 
 ordinary particles of matter, produced by the action of forces which may 
 be called into play in a variety of ways, and which may be either 
 totally new forces which are first generated at the time, or modifications 
 of the forces of gravity and cohesion which exist already. But, al- 
 though such may be the true condition of the electric properties of 
 bodies, yet such views are far too abstract and indefinite to be as yet 
 carried out into the detailed explanation of experiments ; and hence, 
 in the present chapter, I shall adopt the language of that view, which 
 has been so long in use as to have become incorporated with science, 
 and speak of an electric fluid uniting with or separating from ordinary 
 bodies, without being considered as at all believing in its actual exis- 
 tence. 
 
 This electric fluid, whether it be looked upon as of one or of two 
 kinds, may, like air or water, be examined in a state of rest or in mo- 
 tion ; and the science of electricity may be thus divided into electro- 
 dynamics and electro-statics. The electricity generated by friction, or 
 by change of state of aggregation, is ranked under the latter head ; 
 whilst the effects of electricity in motion are found to include the phe- 
 nomena of magnetism, of galvanism, and their relations to each other, 
 electro-magnetism and magneto-electricity, and also those of the elec- 
 tricity produced by a change of temperature in bodies. Under these 
 heads, therefore, the subject will be treated of at present. 
 
Statical and Dynamical Electricity. 139 
 
 SECTION I. 
 
 OF STATICAL ELECTRICITY. 
 
 Electricity, in its statical condition, may be evolved in various ways, 
 of which one of the most remarkable, and that most commonly em- 
 ployed, is friction. If a piece of silk, or a handkerchief, warm and 
 dry, be rubbed briskly against the surface of a dry glass rod, a peculiar 
 odour, that of ozone, will become manifest ; and in the dark, the sur- 
 face of the glass rod would appear covered with a peculiar phosphores- 
 cent glow. If the rod be brought near the cheek, a sensation as if a 
 spider's web had been drawn across the face will be felt ; and on ap- 
 proaching to the rod, as in the figure, any very 
 light bodies, as a silk thread, a feather, balls 
 of elder pith, or little bits of paper, they will 
 suddenly spring towards the rod, and become 
 attached to it for a moment ; after which, they 
 will spring from it, and fall away with equal 
 power, assuming the positions of the dotted 
 lines. The rod which has acquired these pro- 
 perties is said to have been electrified by fric- 
 tion with the silk handkerchief ; it has become 
 excited, and the phenomena produced are 
 
 known ; the phosphorescent appearance, as the electrical light : the 
 motion to and from the rod by the light bodies, as electrical attraction 
 and repulsion ; in which also, acting on the minute down of the cheek, 
 the sensation above described has its source. It is not alone by rubbing 
 together silk and glass that these phenomena may be produced ; two 
 pieces of silk, by their mutual friction, become electric also, particu- 
 larly if they be of different colours ; thus, on laying flat together slips 
 of black and of white ribbon, and drawing them smartly through the 
 fingers, each will attract the feathers or pith balls ; and being both light 
 bodies, they will also attract each other. A piece of sealing wax, or 
 any other resinous body, when rubbed with flannel or a woollen cloth, 
 becomes similarly excited. Sulphur and amber, in which last, indeed, 
 the property was first discovered, and from the Greek name of which, 
 TjXsxrgov, the science electricity has its name, assume this excited state 
 with remarkable facility and power. 
 
 It is still not every substance which may be thus electrified by fric- 
 tion, and even the same substance may often become incapable of being 
 
140 Conductors and Insulators. 
 
 excited ; thus, if the silk or flannel be not completely dry, or if the glass 
 rod be damp, no electric properties can be conferred upon them. But it 
 matters not how much care we use in drying a metallic substance which 
 rests upon the ground, or which we support by the hand, it cannot be 
 electrically excited by any amount of friction. Such a body is termed a 
 non-electric; dry glass, resin, sulphur, silk, &c., being called electrics. 
 Excitation may, therefore, be produced by rubbing together two electrics, 
 but by the friction of non-electrics no electrical effects can be observed. 
 
 This distinction is, however, not real ; it arises from the construction 
 of the apparatus, for if in place of resting the metallic rod or plate upon 
 the ground, or grasping it in the hand, we support it on a piece of seal- 
 ing wax, or hold it by a glass or resinous handle, it becomes, when 
 rubbed with the silk, as highly electrified as any of the electrics ; and 
 in this way, by suitable arrangement of supports, all bodies in nature 
 may be made to assume electric properties by friction. 
 
 To account for this diversity of character, bodies are supposed to 
 retain the electric fluid upon their surface with different degrees of 
 power, according to their nature. When by friction electricity has 
 been accumulated upon the surface of a glass rod, it being a highly 
 elastic fluid, its particles repel each other, and tend, consequently, to 
 escape from the limited space which it occupies, precisely as air tends 
 to escape from a vessel into which it has been powerfully condensed. 
 Glass, resin, sulphur, amber, silk, flannel, and such bodies, do not allow 
 of such escape of the electricity, and it is hence retained in its elastic 
 form upon their surface, and produces all the effects of excitation. 
 They are electrics because they are non-conductors of electricity. But 
 such is the molecular constitution of the metals, that they allow of the 
 escape of all that is set free upon their surface, unless its passage away 
 to other bodies is intercepted by the interposition of some non-conduct- 
 ing substance. A metal is thus a non-electric, because it is a conductor 
 of electricity ; and when, by supporting it upon a non-conductor, we 
 oblige it to retain its charge of electricity, it is said to be insulated. 
 Ice is a non-conductor of electricity, and by rubbing a stick of ice, it 
 becomes excited ; but it must not melt upon the surface, for liquid 
 water, although inferior to the metals in conducting power, is yet so 
 excellent a conductor, that it allows the electricity which we might de- 
 velope to pass totally away. Hence the necessity of drying carefully 
 the substances which are, by their friction, to produce the electricity, 
 and also the reason that insulating bodies must be kept free from damp, 
 for if the thinnest layer of moisture be deposited upon their surface, the 
 electricity will instantly escape by the path so opened for it. 
 
 The conducting powers of bodies have, as yet, been scarcely ascer^ 
 
Relative Conducting Powers. 141 
 
 tained with accuracy enough, to justify their being expressed in num- 
 bers, at least for the non-metallic bodies. The general order appears to 
 be commencing with the best insulators or worst conductors : 
 
 Dry air. Damp organic bodies. 
 
 Shell lac. Damp air. 
 
 Resins. Water. 
 
 Oil of turpentine. Strong acids. 
 
 Sulphur. Fused saline bodies. 
 
 Glass. Charcoal. 
 
 Spermaceti. Metals. 
 
 The worst metallic conductor is many thousand times better than 
 water, and by the following method, an idea of their relative power may 
 be formed. A wire, across which an electric discharge is passed, be- 
 comes heated in proportion to the resistance offered to the motion of 
 the electricity ; and, therefore, the rise of temperature is inversely pro- 
 portional to the conducting power. By such experiments, Harris found 
 that with 
 
 The heat evolved. The Conducting Power. 
 Silver .... 6 . 120 
 
 Copper . . . . 6 
 
 Gold 9 
 
 Zinc 18 
 
 Platinum .... 30 
 
 Iron 30 
 
 Tin 36 
 
 120 
 80 
 40 
 24 
 24 
 20 
 12 
 
 Lead 72 
 
 These numbers are merely comparative, and can only be looked upon 
 as approximations. 
 
 The difference of the conducting power explains the fact, that wlien 
 we excite by friction the surface of a glass plate or rod, it is only at the 
 points actually rubbed that electricity at first appears, and it requires 
 considerable time to creep over the other portions ; but on exciting an 
 insulated metallic rod or plate, no matter how extensive or how long, 
 the electricity, when evolved by friction at a single spot, appears 
 uniformly distributed over the entire. Hence, also, a spark may be 
 obtained by electricity passing instantly along a great extent of metal 
 surface, but is interrupted by a narrow interval filled by any non-con- 
 ducting matter. 
 
 The rapidity with which the electric impulse is propagated, has been 
 examined by Wheatstone in a very ingenious manner, the details of 
 wliich could not be well introduced here, but which enabled him to 
 determine an interval of the 1^^000 ^ a second ; he found that the 
 impulse of the shock of a Leyden jar is transmitted from each end of 
 an interposed wire, and arrives latest at the centre, so far appearing 
 favourable to the idea of the existence of two fluids rather than of only 
 one, and that the velocity of transmission of this impulse is greater than 
 
142 Velocity of the Motion of Electricity. 
 
 that with which light passes through the planetary space, that is, at the 
 rate of more than 195,000 miles in a second of time. 
 
 The electricity, when thus evolved, accumulates upon the surface of 
 the body, not penetrating to any appreciable depth, but forming a layer 
 of fluid, which, by its elasticity, and hence expansive power, tends con- 
 stantly to break away and pass to other bodies, which are not excited. 
 It thus passing through air produces the electric spark, and is accom- 
 panied by a snapping report. The tendency to' escape under the form 
 of the spark, depends upon the thickness of the layer of electricity, and 
 is accurately proportional to its square ; so that if we excite a brass ball, 
 with double or treble the quantity of electricity, the force of the elec- 
 tricity to pass away will be quadrupled or increased ninefold. Hence 
 it requires exceedingly good insulation to retain electricity of great 
 intensity. 
 
 These principles may be easily demonstrated, by means of the ap- 
 paratus in the figure. A, is a hollow sphere of some conducting sub- 
 stance, and B, B, are hemispheres of gilt paper, or thin metallic foil, 
 which when closed upon the globe cover its surface accurately. They 
 are provided with insulating handles c, c. The hemispheres being 
 placed on the globe, if the whole be excited by friction, or by a spark 
 from the machine, the electricity will be found uniformly diffused over 
 the whole external surface, and if the hemispheres be suddenly removed 
 by means of the handles, the globe A will remain totally deprived of its 
 electricity, which will be found all collected on the surfaces of B and B ; 
 but it will be no longer uniformly spread ; its intensity will be found 
 much greater on and near the edges of the hemispheres, and towards 
 the centres of the surfaces the signs of excitation will be extremely 
 feeble. 
 
 The form of a body has a remarkable influence upon the manner in 
 which the electricity is distributed upon its surface. In a sphere, the 
 layer is every where of equal thickness, but in an elongated body it 
 accumulates more at the extremities of the longest axis. Hence on a 
 wire or a needle, the electricity is accumulated almost exclusively on 
 the ends, and even though the total quantity of electricity may not be 
 large, it is there so thickly heaped, that it breaks off and rapidly escapes. 
 
Opposite Conditions of Excitation. 143 
 
 Hence electrical apparatus should be completely smooth, except where a 
 point or projection is intentionally attached, and many remarkable ex- 
 periments are founded upon the escape of electricity from points. 
 Electricity is not merely prevented from accumulating upon a pointed 
 body itself, but it cannot collect upon any surface near it ; the point 
 abstracting the electricity. Thus, a point held near to the excited 
 glass-tube used in the experiments first described, may prevent that 
 attraction of the light bodies, by which excitation is shown, by con- 
 centrating all the action upon itself. The detailed theory of this 
 power of points to dissipate their own electricity, and to absorb that 
 of other bodies, shall be hereafter fully noticed ; at present it is suffi- 
 cient to refer it to the thickness, and high elasticity of ths layer of 
 electric fluid, which forms upon them. 
 
 It has been already stated, that when two slips of silk ribbon are 
 excited by rubbing against each other, the electricity appeared to be 
 equally evolved upon each. This occurs in all cases of excitation by 
 friction. Thus, when the silk and glass are rubbed together, the silk 
 acquires as much electricity as the glass ; but the silk being held in the 
 hand, the fluid escapes by the dampness which is always present, and is 
 lost. If, however, the silk be insulated if a disk of dry wood, co- 
 vered with some folds of silk, be held upon an insulating handle, and 
 rubbed against a similar disk of glass then the same phenomena are 
 produced in an equal degree by both. The attraction and repulsion of 
 the lighter bodies, the odour and the phosphorescence belong to both, 
 and thus in every case where bodies are rubbed together, the excitation 
 is completely mutual. There is, however a profound and curious dif- 
 ference between the two conditions : separately they attract and repel 
 other bodies exactly in the same way ; together they produce neither 
 attraction nor repulsion : separately they may manifest the most re- 
 markable evidence of tension, giving sparks and shocks, but when com- 
 bined, all signs of free electricity are lost, and the body on which they 
 are collected appears as destitute of excitation as if the power had 
 never been in existence. The states of the two bodies are therefore so 
 far opposed, that they may interfere, and as from the action of two 
 lights there may be produced total darkness, so from the coalition of 
 the excitation of the two bodies which had been rubbed together, abso- 
 lute indifference may result. 
 
 This neutralizing power of the excitation of each body for that of 
 the other, may be shown by very simple means. If a feather be sus- 
 pended by a silken string, and upon the one side there be presented to 
 it the disk of glass, and upon the other the disk of silk, which had 
 been rubbed together, it may be brought to remain, by managing the 
 
144 Gold leaf Electroscope. 
 
 distance, perfectly at rest. If there be the glass alone, it instantly 
 attracts the feather, the silk alone acts in the same way ; but no matter 
 how strong the power of each may be, when at equal distances, the 
 feather remains indifferent to both. In order, however, to obtain 
 perfect demonstration of this principle, it is useful to examine it by 
 means of more exact instruments than the feather or other light bodies, 
 which hitherto had been found sufficient, and for this purpose the gold- 
 leaf electroscope is best adapted. Deferring the description of its principle 
 to another place, I shall here only notice its construction and the indi- 
 cations which it gives. A glass jar, A, is closed at the top by a metallic 
 (brass) plate, B, to which are attached below, by a 
 wire, two slips of gold leaf, lying, when unexcited, 
 flat on one another, and reaching below the middle 
 of the jar. The jar rests on a wooden or metal foot, 
 with which are connected two slips of tin-foil, applied 
 to the inside of the glass, and rising so far that the 
 gold leaves on opening out may come into contact 
 with them. When this occurs, there is evidently a 
 free conducting medium from the upper metallic 
 plate to the ground, but, except when the gold leaves touch the slips 
 of tin-foil, the cap and leaves are perfectly insulated, if the instrument 
 be kept dry. When this electroscope is brought near to an excited 
 body the gold leaves diverge, and remain so, as in the position of 
 the figure, as long as the excited body may be kept near it. But 
 if the instrument be not touched, the leaves collapse on its removal, 
 and all remains indifferent as it had been before. By the divergence 
 of the gold leaves, therefore, the existence of free electricity acting on 
 the electroscope is made known. 
 
 No matter what may be the nature of the excited body acting on 
 this instrument, it gives the same indication of its presence ; but when 
 exposed to the action of the two bodies which had been rubbed toge- 
 ther, the gold leaves remain quiescent. If they be made to separate 
 by the influence of the glass, and that the excited silk be then slowly 
 brought near, the divergence gradually diminishes, until at last the 
 leaves lie close together. If the silk be then brought still nearer, there 
 is a new divergence ; but it is due to the excess of power of the silk, 
 after the neutralization of the glass. On removing either of the excited 
 bodies, when the instrument is in the neutralized condition, the leaves 
 diverge, from that which remains being free to act. Not merely is the 
 excitation assumed by the two bodies immediately rubbed together, of 
 these opposite kinds, but it may be shown that this peculiar power may 
 exist in the conditions of two bodies, rubbed by a third, as when a glass 
 
Electrical Attractions and Repulsions. 145 
 
 is rubbed with silk, and an insulated metal rod is likewise excited by 
 rubbing with silk, the glass and metal rod assume electricities which 
 destroy each other, or the silk is related to the metal as the glass had 
 been to the silk. Bodies rubbed by different other substances are also 
 so circumstanced ; if a stick of sealing-wax be rubbed by flannel, it 
 win assume opposite excitation to that of glass when rubbed with silk, 
 and would counteract its influence, and consequently, the condition of 
 the flannel in the one case, and the silk in the other, would be opposite 
 also. This assumption of opposite states of excitation may be caused 
 by trifling mechanical conditions : thus, if smooth glass and muffed 
 glass be both rubbed with silk, they become oppositely electrified, and 
 two pieces x>f silk, which differ markedly in colour, neutralize each 
 other when electrified by their mutual friction. The peculiar characters 
 of these two forms of excitation extend, however, much further than 
 the principle of mutual destruction. If we hang by a dry silk thread, 
 varnished with shell-lac, in order to render it a better insulator, a little 
 cylinder of gilt paper, and that we bring near it an excited body, the 
 cylinder is attracted and moves towards the body until it touches, when 
 it is immediately and forcibly repelled. It has by contact participated 
 in the state of excitation of the body, and when that is so, they mu- 
 tually repel each other. In all cases, bodies which are in the same 
 electrical condition repel each other ; and it is thus that the gold leaves 
 of the electroscope become an index of any electricity which may be 
 present, for as both slips of leaf are necessarily excited in the same 
 way, they repel each other, and consequently they diverge. 
 
 If now the insulated gilt paper cylinder which has been, as above 
 described, repelled by the glass rod, after having shared its electricity, 
 be brought near the silk against which the glass rod had been rubbed, 
 or to any body which is in the same state of excitation as the silk, 
 attraction will ensue, and this will be found more powerful than if the 
 body had previously been neutral. If two such gilt paper cylinders be 
 touched, both with the glass rod, or both with the silken disk, they 
 will repel each other ; but if one be touched with the glass and the 
 other by the silk, they will attract each other, and move until they 
 touch, when the states of excitation neutralize each other, and they 
 become inactive. 
 
 When bodies are rubbed together, therefore, they become electric, 
 and with such properties, that whilst each when separate gives signs of 
 powerful excitation, together they destroy each other's power. Bodies 
 when thus oppositely electrified, attract each other ; bodies which are 
 excited in the same manner, repel each other ; and these attractions 
 and repulsions arise from the exertion of a force, which, like that of 
 10 
 
146 
 
 Law of Electrical Attractions. 
 
 CO 
 
 gravitation, diminishes in intensity, according as the square of the 
 distance between the bodies becomes greater. 
 
 This law, which is of the greatest importance, for the theory of 
 electricity, was discovered by Coulomb by means of the torsion electro- 
 meter. The gold-leaf apparatus, though exceedingly sensitive as a test 
 of the presence of free electricity, is yet not susceptible of being used 
 to measure its amount. It is an electroscope, but not an electrometer. 
 The torsion balance of Coulomb consists of a glass 
 drum, A, on the centre of which rises a glass tube, 
 B, to the height of one or two feet. Prom the top 
 of this tube is hung, by a fine thread of glass or of 
 cocoon silk, a very light wooden beam, to which is 
 attached at one end a ball of dry elder pith, and at 
 the other a piece of gilt paper, which serves as a coun- 
 terpoise, and by its extent of surface prevents irregular 
 motions of the beam. The pith ball is usually gilt, 
 to give it a more uniform surface. In the top of the 
 drum there is an aperture, by means of which a 
 second gilt pith ball, c, may be introduced, and made 
 to touch that of the balance ; and around the centre 
 of the drum is fixed a scale of degrees, by which the angular distance, 
 to which the balls separate after repulsion, may be measured. Now, 
 let us suppose that, by touching the second, or, as it is called, the 
 carrying ball, to an excited body, we charge it with electricity, and, 
 having inserted it in the aperture, it touches the ball of the balance, 
 which is immediately repelled : in moving away, this twists the thread 
 by which it is suspended, and the amount of the twisting which is 
 necessary, in the opposite direction, to bring it back again, and main- 
 tain it at a certain distance, measures the force of repulsion the balls 
 then exercise. This measurement is effected by the glass or silken 
 thread being attached, not to the tube, but to a stem, carrying an 
 index, which shows, on a graduated circle, the number of degrees 
 through which the thread is twisted ; and as the thread is exceedingly 
 long in proportion to its thickness, and its elasticity almost exact, the 
 force of torsion is taken as proportional to the angle through which the 
 index moves. 
 
 By this instrument, into the detail of experiments with which it 
 would be improper here to enter, Coulomb established the fundamental 
 law of electrical attraction and repulsion ; and it has been found, that 
 from this law all the results of the distribution of electricity on bodies, 
 its accumulation on and escape from points, that have been noticed, 
 might have been deduced. 
 
Theories of Electricity. 147 
 
 The fundamental principles of electrical excitation, the distribution of 
 electricity on bodies, and the manner in which the electric states of the 
 excited bodies are related to each other, having been thus described, I 
 shall pass to the explanation of the general principles under which those 
 phenomena and laws have been arranged, and a knowledge of which we 
 shall find necessary to our future progress. I shall lay aside all consi- 
 deration of the more abstract theories of electricity, which refer it to 
 mere molecular disturbance, or to vibrations, and consider only those 
 views which suppose the existence, in the one case, of two electric fluids, 
 the theory of Dufay, and, on the other, that of a single fluid, the theory 
 of Franklin. 
 
 Theory of two Fluids. It is assumed, that there exists in nature two 
 kinds of electricity, each a highly elastic fluid, whose particles repel each 
 other, according to the law of the inverse square, while they attract the 
 particles of matter, and also attract each other, according to the same 
 law : that every body in nature contains usually an exactly equal quantity 
 of each fluid ; that bodies then are in their ordinary state, and hence, 
 manifesting no unusual properties, we look upon them as being quiescent : 
 but, if a body contain more of one fluid than of another, it comes into 
 an extraordinary state, and acquiring new properties, we say that it has 
 become excited. 
 
 Upon this view, the phenomena of electricity are capable of very simple 
 explanation. When two bodies are rubbed together, the result is, that 
 one electric fluid accumulates in excess upon the one, and the other upon 
 the other body. They are thus brought into a state of excitation ; and 
 as the excess of the one fluid must be exactly equal to that of the other, 
 the excitation of both is equal, and, being opposite, must neutralize each 
 other when they are brought to reunite. Of these electricities, that 
 which passes to glass, when it is rubbed with silk, is termed, in the lan- 
 guage of Dufay, vitreous electricity; and that which accumulates on 
 resin, when rubbed with flannel, is called resinous. There are few bodies 
 which may not assume vitreous or resinous excitation, according to the 
 substance by which the friction is produced ; and, hence, these names 
 are liable to some objection, and are not much employed. 
 
 Since the electric fluids and matter attract each other, the bodies upon 
 which the electricities become free appear to attract or repel each other, 
 according as they are invested by the same or opposite fluids, in conse- 
 quence of the necessity of accompanying these fluids in their action on 
 each other. Hence, the electric attractions and repulsions which mani- 
 fest themselves in all cases of excitation, and hence the bodies return to 
 their indifferent condition as soon as the excess of electricity they contain 
 is neutralized. It was for a long time supposed, that the atmosphere, 
 
148 Hypotheses of One or I\vo Fluids. 
 
 by its mechanical pressure, assisted in retaining the free electricities upon 
 the surface of the excited bodies ; but this is not the case. The air acts 
 as an insulator of the excited body, without which no accumulation of 
 free electricity could occur ; but the mechanical pressure of the air may 
 be removed without affecting, the electrical conditions. 
 
 Theory of one Fluid. In the hypothesis of Franklin there is assumed 
 to exist but one electric fluid, of which, in its ordinary state, every sub- 
 stance contains a certain quantity. This fluid is considered to be highly 
 elastic, to repel its own particles with a force varying as the inverse square 
 of the distance, and to attract the particles of matter according to the 
 same law. A substance, with its proper share of electricity, is, therefore, 
 in its indifferent condition, possessing no properties beyond what we or- 
 dinarily attribute to it. But when two such bodies are rubbed together, 
 a quantity of electricity abandons one and collects upon the other ; and 
 thus both are brought into an abnormal state, and assume the unusual 
 properties which constitute excitation. The excitation is equal, for the 
 one has gained precisely what the other lost ; and by recombination they 
 destroy each other's action, for they are brought to their original ordinary 
 state. The excitation being produced, according to this view, by one 
 body having electricity in excess, whilst that of the other is deficient, one 
 is said to be plus and the other minus electrified ; or, more generally, 
 the one to be positively , the other negatively excited, and the signs + 
 and are often used as abbreviations for these words. 
 
 The particles of the electric fluid being mutually repulsive, and attract- 
 ing those of matter, it is natural that two bodies, having electricity in 
 excess, shall mutually repel ; and that a body, having an excess of elec- 
 tricity, shall attract one having an excess of matter. Bodies both + 
 therefore repel; a -f- and a body attract each other. But, to explain 
 the mutual repulsion of bodies, both in the negative condition, an assump- 
 tion is required, which, at first sight, appears to militate considerably 
 against our reason ; for, as it is matter which is in excess in that condi- 
 tion, we must consider that the particles of matter mutually repel each 
 other, according to precisely the same law, as it is demonstrated by the 
 whole construction of the universe, that the particles of matter mutually 
 attract each other. There is not, however, any real contradiction in 
 these principles ; the law of gravitation applies to matter in its ordinary 
 state, in which it contains its natural quantity of electricity ; and it affords 
 no grounds for supposing, that, if matter were deprived of that natural 
 electricity, it should continue to attract. There is, consequently, nothing 
 illegitimate in that assumption ; and the theory of a single fluid may be 
 as easily and successfully applied to the explanation of phenomena as 
 that of the two fluids before described. 
 
Theory and Construction of Electrical Machines. 149 
 
 Already, indeed, considerable progress has been made towards a 
 theory of electricity upon this idea. In order to account for the ordi- 
 nary molecular constitution of matter, it is necessary to suppose, that 
 the forces which act upon its particles may change from attractive to 
 repulsive, and again from repulsive to attractive, according as the dis- 
 tance between the particles is made to vary ; and Mosotti has shown, 
 that it is only necessary to assume that the mutual repulsion of matter, 
 when destitute of electricity, is inferior to its attraction for electricity, 
 and to the mutual repulsion of the electricity itself, and the law of 
 gravitation becomes a necessary consequence of the conditions under 
 which alone electrical equilibrium can be established. 
 
 Such are the theories of electricity that have hitherto met with most 
 general acceptation. In the succeeding portions of this work, I shall 
 adopt the language of the theory of the two fluids, except that I shall 
 use the Avords negative and positive fluids, in place of vitreous and resi- 
 nous ; but I do so merely from convenience, and seek not to connect 
 the idea of a fluid in any way more intimately with the true causes of 
 the electrical properties of bodies. 
 
 Before passing to the description of the phenomena, and the discus- 
 sion of the principles of electricity which yet remain to be examined, 
 it is necessary to notice the construction of some electrical apparatus, 
 which is employed in all cases where it is desirable to operate upon this 
 agent in a state of high intensity and power. Of these the most 
 important is the electrical machine. 
 
 The machine is in principle only a 
 modification of the glass tube which, 
 by friction with a piece of silk, evol- 
 ved the electricity in the first experi- 
 ments described. It consists of a 
 glass having such a form as to expose 
 a great extent of surface, and gene- 
 rally being used in the shape of a 
 cylinder A, or of a plate. To produce 
 the friction, , an elastic rubber B is 
 covered with silk, and made to press 
 against the surface of the glass ac- 
 cording as the plate or cylinder is 
 turned round by means of the handle. The rubber being generally in- 
 sulated, the electricity evolved upon it is at once collected, and may be 
 transferred along conductors, or drawn as sparks from the knob of brass 
 attached to it at the back. The electricity which is diffused upon the 
 glass, passes from itr surface to that of a brass cylinder, termed the 
 
150 Theory and Construction of Electrical Machines. 
 
 prime conductor c, being collected by 
 means of a series of pointed wires, 
 which graze the surface of the cylin- 
 der according as it is turned round. 
 The prune conductor is also insulated; 
 and in the case of a cylinder ma- 
 chine, the glass itself is often sup- 
 ported upon insulating pillars, by 
 which the loss of electricity is pre- 
 vented. To increase the energy of 
 the machine the silk of the rubber is 
 
 generally smeared over with a mixture of grease and an amalgam of 
 tin and zinc, and a silken apron extends from the rubber half over the 
 cylinder or plate to conduct the electricity to the points, and prevent 
 its being carried away by the air. 
 
 Although I shall have occasion, when we have examined the relative 
 action of excited bodies and conductors somewhat better, to notice the 
 true theory of the prime conductor, yet, for the present, it may be con- 
 sidered as simply, from its proximity collecting the free electricity on 
 its points from the surface of the glass cylinder or plate, and by thus 
 accumulating it upon a confined surface, enabling the experimenter to 
 apply it or carry it to other bodies at his pleasure. When the machine 
 is worked, the two portions of electricity become developed, as in the 
 rubbing of the tube and handkerchief, upon the silk and glass, and if 
 all be insulated, they attract each other so intensely, that they break 
 through the intervening air, and recombine across the surface of the 
 cylinder, or round the edges of the plate, presenting the appearance of 
 a brilliant spark, and accompanied by a snapping noise, and the peculiar 
 phosphorescent odour of ozone. To prevent this recombination, which 
 should of course render accumulation upon the prime conductor im- 
 possible, the rubber, when the machine is required for active work, must be 
 connected, with the ground by a wire or chain, through which the 
 electricity, which forms upon the silk, makes its escape, and as new 
 quantities are then liberated at each moment, those passing from the 
 glass to the prime conductor, by the projecting points with which it is 
 always furnished, collect upon it, and, acquiring a high degree of tension, 
 pass under the form of sparks to any conducting body which may be 
 brought near. 
 
 By means of a machine of such construction, the opposing proper- 
 ties of the electricities of the bodies rubbed together may be simply 
 and completely shown. 
 The degree of excitation of the prime conductor is "generally 
 
Effects of Electrical Machines. 151 
 
 though not very accurately, shown by means of the 
 quadrant electrometer. This consists of a stem of brass 
 which rests in a socket in the prime conductor, or when not 
 in use, in a wooden foot, To this is attached as in the figure, 
 an ivory semicircular scale of which a portion is graduated, 
 from whence the name ; on an axis at the centre of the ivgry 
 scale, there is hung, by a light arm of whalebone, a pith ball, 
 which, when the apparatus is unexcited, lies in contact with 
 the brass stem, and thus assumes the same electrical condition 
 with it, when the instrument is placed on the prime conductor. 
 The machine being worked, the stem and the pith ball repel each other, 
 and the ball being consequently set in motion by the united repulsion, 
 its radius moves through an angular space on the graduated scale, which 
 serves in rough experiments as an index of the intensity of the excita- 
 tion. Now, if when this instrument is fixed on the prime conductor, 
 the latter be connected with the insulated rubber by a chain or wire, no 
 matter how vigorously the machine may be worked, no signs of excita- 
 tion can be produced ; the electricity collected from the glass by the 
 prime conductor, passing along the chain or wire to unite with that 
 which is developed on the rubber, and the two being evolved in equal 
 quantities complete neutralization is produced. That bodies similarly 
 electrified repel each other, is shown by the principle of this instrument, 
 as its indications of free electricity depend upon the stem and ball 
 being both excited in the same way, and the repulsion being the same, 
 whether it be fixed upon the rubber or on the prime conductor. 
 
 To prove on a large scale, by means of the machine, that the oppo- 
 site electricities attract each other, it is only necessary to place in con- 
 nexion with the conductor on each side a metallic wire, to which is 
 hung, by a wetted thread, a ball of pith, or a cylinder of gilt paper. 
 When the machine is turned, the balls attract each other across the 
 cylinder, and touching, interchange the electricities by which they are 
 excited, and thus the fluids, separated by the friction, are continually 
 recomposed, being brought together by their mutual attractions. If to 
 each wire there be hung two such balls, those of each side will be seen 
 to repel each other, whilst they move towards those oppositely excited. 
 Numerous experiments of an amusing kind, which it would be foreign 
 to my purpose to introduce, are founded on these principles. 
 
 There have been now noticed four methods by which bodies may be 
 electrically excited. 1st, by friction, which is, indeed, the only true 
 excitation. 2nd, by contact; as when an insulated brass disk, excited 
 by friction, is touched by another, also insulated and neutral ; a spark 
 passes between them at the moment previous to actual contact, and the 
 
152 Laws of Electrica I Induction . 
 
 first is found to have divided its electricity with the second,, in propor- 
 tion to its surface. In this case the two bodies, after contact, are in 
 the same state of excitation. 3rd, as where the prime conductor, which 
 is neither itself rubbed, nor does it touch the cylinder of the machine, 
 yet gathers from it the electricity which is evolved thereon, and allows 
 it to be transferred, under the form of the spark, to other bodies ; and, 
 finally, all the attractions and repulsions which have been observed in- 
 dicate a power of action and excitation even at considerable distances, 
 and this mode, which results from the attraction and repulsion of the 
 electric fluids for each other, is, when examined, found really to com- 
 prehend the second and third modes of excitation, by contact and by 
 gathering with points. There are, therefore, truly, only two means of 
 excitation, this at a distance, which is termed induction, and that by 
 friction. 
 
 It is not difficult to understand how bodies come to be excited by 
 induction. Let us consider the insulated cylinders, B c, as being neu- 
 
 tral and having their natural electricities combined, and distributed uni- 
 formly over their surface. If a globe, A, excited, say with positive 
 electricity, to be brought near, it will attract the opposite electricity of 
 B to the end which is nearest it, and repel the electricity of the same 
 name to the farthest extremity ; both electricities of B will thus become 
 free, and B will be excited by the influence of the electricity of the 
 body, A, at a distance ; and the condition of B is characterized by its 
 two extremities being in opposite states, and hence at a certain point 
 between them, perfect neutrality remaining. This positively excited end 
 of B influencing c, in a corresponding way, brings it also into an ex- 
 cited state, and this communication of action would go on through any 
 number of bodies, the force set free being regulated by the law of the 
 inverse square of the distance from the original disturbing cause at A. 
 As long as A remains in its place, the state of electrical excitation is 
 kept up ; if A be totally removed the natural electricities of each body 
 recombine, and all become neutral ; if A be brought very close to B, or 
 B to c, the attractions, between the opposite electricities become so 
 great that they unite across the intervening space of air, and a spark 
 passes. The bodies are then found to be in the same state, and the 
 communication by contact, or the excitation which occurs, is shown to be 
 
Theory of the Prime Conductor. 153 
 
 only the termination of the inductive action. For suppose that A had 
 10 parts of + electricity, and that, by induction, it set free 5 of the 
 and 5 of the + fluid on the surface of the body B ; then, when the 
 spark had passed, the 5 destroying + 5 of the body A, the two 
 bodies should remain each with + 5, and thus the results of contact 
 already described should be produced. 
 
 The distance at which the combination of the electricities of the in- 
 ducing and induced body may occur, depends upon the intensity of the 
 fluids collected on the parts of the surface nearest to each other, and 
 hence, when there is on the body, a point on which the great propor- 
 tion of liberated fluid, as has been already described, becomes accumu- 
 lated, the fluid escapes from thence before it is in sufficient mass to 
 break its way under the form of a spark, and thus the permanent and 
 similar excitation of the body silently occurs. This is the true theory 
 of what has hitherto been described as the power of points to gather 
 and to disperse the electric fluid. If a pointed body be excited by 
 friction it induces an opposite state in the particles of air by which it is 
 is surrounded, and communicates to them with great rapidity the charge 
 wlu'ch it had received. The prime conductor of the machine, being in- 
 sulated, has its electricities separated by the inductive action of the ex- 
 cited glass cylinder or plate ; the negative electricity collected on the 
 points turned towards the glass, escapes from thence, and unites with 
 the positive fluid which had been set loose by friction, and proportional 
 quantities of the positive fluid of the prime conductor being left free 
 upon its surface, it serves the same purpose as a source of electricity as 
 if it had come directly from the glass. A point placed on the prime 
 conductor prevents the accumulation of the electricity, because it gives 
 the + to the air as fast as the other points give the to the glass; a 
 point held near the prime conductor also prevents its excitation, by 
 giving to it by induction electricity as fast as it obtains -f- electricity 
 from the glass of the machine. 
 
 In all these cases of induction, where the electricities attract and re- 
 pel each other, the bodies on which the electricities are collected will 
 accompany them in their motions, if they be not too heavy. Hence all 
 the singular motions of bodies, when excited, are explained upon this 
 principle. The variety of dancing figures, ringing bells, revolving 
 wheels, affrighted heads, and so on, that are exhibited in popular lec- 
 tures on tlu's aubject, will serve to practise the ingenuity of the student 
 in tracing out their theory in the detail, with which it would be quite 
 improper to occupy this work. 
 
 The theory of the Bennetts gold leaf electrometer, with which some 
 of the most important principles of statical electricity are demonstrated, 
 
154 Theory of the Electroscope. 
 
 must not, however, be omitted. When an excited rod is brought over 
 the electroscope, it separates the electricities of the metallic portions of 
 the instrument, attracting the opposite to the upper surface of the cap, 
 and repelling that of the same name into the gold leaves, which, being 
 thus excited with the same electricity, repel each other, and hence di- 
 verge. If the exciting body be + it is the + fluid by which the instru- 
 ment appears affected ; if it be the leaves diverge from the presence 
 of electricity. Hence if when under the influence of a glass rod 
 rubbed with silk, a stick of sealing wax which had been rubbed with 
 flannel be brought near, the divergence diminishes, until at last the 
 leaves collapse completely, the resin having driven down as much nega- 
 tive electricity as there had been positive brought into action by the 
 glass, and hence the gold leaves coming into their natural and indiffe- 
 rent condition. That it is by this inductive process that the gold leaves 
 act, may be thus shown. If the cap of the electroscope be rubbed 
 with a dry silk handkerchief it becomes excited, and the leaves diverge 
 with negative electricity ; if then an excited glass rod be brought near, 
 the divergence is neutralized, showing that positive electricity had been 
 sent down by the glass ; but if an excited resinous body be approached, 
 the divergence increases, indicating the superaddition of electricity of 
 the same name, from the inducing power of the resin. 
 
 If, as in the figure (page 153), the cylinder c be connected with the 
 ground by means of a wire or a wetted thread D, the positive electri- 
 city passes from that body through the wire into the earth, where, from 
 the enormous surface of the globe, it may be looked upon as lost, and 
 the surface of c is altogether in a state of negative excitation. If now 
 the exciting body A be taken away, the quantity of positive fluid re- 
 turns along the wire, and brings the body c into its neutral state ; but 
 if before the body A be taken away the conducting communication with 
 the ground be cut off by the removal of the wire or thread, the body c 
 cannot get its positive electricity back, and hence remains in a state of 
 negative excitement. In this manner a substance may, by induction, 
 be made to receive a permanent charge. This is often useful in experi- 
 ments with the electroscope, and the manipulation to charge it per- 
 manently is as follows : If it be desired to charge it positively, an ex- 
 cited stick of resin is held near, and the cap of the electroscope is 
 touched with the finger. The negative electricity then escapes by the 
 hand into the ground, and the positive electricity, accumulating over 
 the cap, and leaves, these last diverge. On then removing the finger, 
 the leaves are insulated ; and when the stick of resin is taken away, the 
 permanent charge remains. To charge with negative electricity, an 
 excited glass rod is to be used ; and it will be recollected, that where 
 
Construction of the Ley den Jar. 155 
 
 the charge of the leaves is temporary, its electricity is the same as that 
 of the exciting body ; but where the charge is permanent, the electri- 
 city is of an opposite kind. 
 
 After the exciting body, in the latter instance, has been withdrawn, 
 the divergence of the gold leaves becomes much greater than it had 
 been before. This arises from the charge being increased by its action 
 on the surrounding bodies, particularly on the glass by which the leaves 
 are enclosed. By taking advantage of the increase of change, by secon- 
 dary inductive action, various forms of the electroscope have been con- 
 trived for rendering it more sensible, and are described in special treatises 
 on electricity under the name of Doubters and Condensers. As they do 
 not add anything to our knowledge of principles, and have no peculiar 
 chemical relations, I shall not enter on their further consideration. 
 One of the most interesting instruments in statical electricity, founded 
 on the principle of induction, is the Leyden Jar ; so 
 called from the city where its construction was dis- 
 covered. It consists of a glass bottle, which is coated 
 inside and outside, to a small distance from the top, 
 with tin foil, and has fitted to the orifice a wooden or 
 qork stopper, through which passes a stout wire, touch- 
 ing at the bottom the internal coating, and terminated 
 outside by a metallic knob. When this jar is insulated, 
 and the knob is touched to the prime conductor of the machine, and 
 the handle turned, the positive electricity passes to the internal coating 
 of the jar, and excites it to an equally powerful degree. This, then, 
 reacting by induction upon the electricities of the external coating, 
 separates them, attracting the negative to the side next the glass, and re- 
 pelh'ng the positive to the outer side. The position becomes, there- 
 fore, -\ f- ; and, when the + fluid inside makes up by its greater 
 
 quantity for the thickness of the glass by which it is separated from 
 the fluid, no more can enter into the jar. In this case the inside of 
 the jar may be considered as being merely an extension of the prime 
 conductor ; and the electricities of the external coating, although sepa- 
 rated from each other, are only in the quantities which had been always 
 present. But if the external coating be connected with the ground, 
 the + fluid, being repelled by that inside, passes away, and another 
 quantity, entering from the prime conductor into the jar, decomposes a 
 new quantity of the natural fluids of the external coating, of which also 
 the positive escapes and the negative remains behind, held by the 
 attraction across the glass to the positive fluid inside. New quantities 
 of positive electricity, entering continually from the machine, the accu- 
 mulation of negative electricity on the outer coating proceeds, until the 
 
156 Theory of th e Ley den Jar. 
 
 tendency of the two to combine is so intense as to break their way across 
 the glass, cracking the jar ; or to creep over the mouth, from the edge 
 of one coating to that of the other, and thus the jar to discharge itself. 
 To discharge a jar, in which the electricities are so accumulated, it is 
 only necessary to connect by a wire the internal and external coatings ; 
 when the extremities of the wire, which are generally terminated by 
 brass balls, approach, a large brilliant spark passes, accompanied by a 
 loud report, and the jar returns to its original neutral state. 
 
 By thus collecting great intensities of electricity in large jars, or in 
 sets of jars (electrical batteries), the most beautiful and remarkable phe- 
 nomena of electrical force may be exhibited. 
 
 The principle of the construction of the Ley den jar may be experi- 
 mentally demonstrated, as follows. First, it has been already explained, 
 that the jar, when insulated, is incapable of receiving any other charge 
 from the machine, than what its internal coating obtains by forming 
 part of the surface of the prime conductor ; the principle of induction 
 requiring, in order that one electricity may accumulate upon its outer 
 surface, the other shall be dissipated in the ground. Second, a light 
 body placed between two balls, connected, one with the internal, and 
 one with the external coating, is alternately attracted and repelled by 
 each, and thus the accumulation on the two coatings is shown to be of 
 opposite kinds. Third, the quantity of electricity which passes from 
 the external coating may be shown to be equal to that which passes into 
 the internal coating from the machine, by insulating the jar, and ap- 
 plying the knob of a second jar which is not insulated to its outer sur- 
 face ; this second jar will be found charged to the same degree as the 
 first, and the inner and outer coatings will be respectively in the same 
 state. 
 
 Statical electricity, thus accumulated in the Leyden jar, is capable of 
 giving violent shocks to the animal frame, of evolving light and heat, 
 and producing also powerful mechanical effects. 
 
 An instrument founded on the principle of induction, and which is 
 of frequent use in chemical experiments, when an electric spark of 
 moderate power is required, is the eleclrophorus 
 of Volta. It consists of a flat cake of resin I, 
 which is generally spread on a circular board, of 
 eight or ten inches diameter. There is laid on 
 this another circular plate a, somewhat smaller, 
 and which may be either of brass or tinned iron, 
 with the edges turned up over a thick wire, so as to round it, or else a 
 board covered with tin foil. To this upper plate is attached an insulating 
 handle of glass c, and from its edge projects a wire, terminated by a 
 
Elect wphorvs of Volta. 157 
 
 knob. The resinous plate, being warmed, is to be strongly excited by 
 friction with a warm flannel cloth, or a cat's skin, and then the upper 
 plate is to be laid on it, and is touched with the finger. The nega- 
 tive electricity of this passes, then, into the ground, and* the positive 
 accumulates on the surface next the resin, of which it, by induction, in- 
 creases the negative charge. This new portion of negative fluid decom- 
 poses a new quantity of the electricities of the upper plate, which again 
 reacts, and thus the plates are mutually brought into a state of very 
 intense excitement. If, then, the finger be removed, the upper plate is 
 insulated, and its charge of positive electricity retained upon it ; and 
 on applying the knob of the wire to any conductor, or to the knuckle, 
 a strong spark may be obtained from it ; the instrument may be re- 
 peatedly charged and discharged in a few minutes, and retains its charge 
 better than the electrifying machine. 
 
 This inductive action of electricity would, at first, appear to be exer- 
 cised at a distance, altogether independent of the interposed substances, 
 and to produce the motions to which it gives rise, as gravity causes the 
 revolutions of the planets and their satellites, without the existence of 
 any interposed medium ; but a more exact examination shows that this 
 is not the case. The substances interposed in the path of the inductive 
 action are necessary to its transmission, and modify, by their nature, its 
 direction and amount ; and it is, indeed, only from molecule to molecule 
 of any substance gaseous or solid, that the decomposition of the natural 
 electricities can take place. 
 
 This may be beautifully shown, by plunging in a vessel of oil of tur- 
 pentine, which is an excellent fluid insulator, two brass balls, of which 
 one is in connexion with the electrical machine, and the other with the 
 ground. On turning the machine, the latter becomes excited by in- 
 duction. If now a number of short shreds of sewing silk be mixed with 
 the oil of turpentine, the mechanism of the inductive action is shown by 
 each little bit of silk acting like the bodies B and c in the figure, (p. 
 153), and attaching themselves mutually by their extremities, they 
 transmit the electricity of the machine, by a series of decompositions, to 
 the ball which is connected with the ground. If the excitation be very 
 violent, the attractions and repulsions become too strong to be regu- 
 larly transmitted ; and this induction is accompanied by a powerful cur- 
 rent of the particles of the oil from the first ball to the second. The 
 particles immediately in contact with the directly excited ball acquire 
 its state, and, being repelled, immediately pass off to that which has 
 obtained, by induction, the opposite condition, and there become neu- 
 tralized. Now what here occurs with the oil of turpentine, takes place 
 in ordinary induction with the air ; every molecule of it interposed be- 
 
158 
 
 Induction an Action of Contiguous Particles. 
 
 tween the solid bodies becomes itself subjected to the inductive action, 
 and forms a chain of alternate positive and negative poles, by which the 
 effect may be transmitted to any distance. If the excitation be very 
 great, the neutralization may occur with violence and rapidity, and ge- 
 nerate currents, as in the oil of turpentine. It is these currents which, 
 being produced by the repulsion of the particles of air from excited 
 points, are rendered sensible in the effect termed the electrical aura, 
 and are shown by the experiments of revolving flies. A still more 
 violent and rapid recomposition of the electricities of the air molecules, 
 which had been separated by induction, gives the electric spark in -its 
 various forms, such as the star, the brush, &c., according to the manner 
 in which it is received and generated. 
 
 That the excitation by induction of a body at a distance is effected in 
 in this manner, from particle to particle of the interposed substance, is 
 beautifully shown in the results obtained by Earaday, concerning the 
 influence of the nature of the medium on the 
 amount of inductive charge transmitted. The 
 instrument which he has termed an inducto- 
 meter, consists of a hollow sphere of brass, 
 a a b, and a sphere of smaller size, h, also of 
 brass, which is placed exactly concentric with 
 it. The interval between these, o o, may be 
 occupied by any substance, as air, or glass, or 
 sulphur, and then the central sphere being in- 
 sulated from the outer by the shell-lac column 
 b, and having been excited from the machine, 
 through the ball and wire B, the outer one is 
 insulated, and the whole becomes a Ley den jar, 
 in which the material may be varied at the 
 will of the experimenter. By means of the 
 tube and stopcock f d, the air in o o, may be 
 removed and any other gas substituted for it. 
 The outer sphere opens at b in two, so that 
 melted sulphur or shell-lac, may be poured in 
 to form the inductive medium. 
 When the internal sphere is excited always to the same degree, the 
 charge of the external coating should be the same, no matter what might 
 be the nature of the intervening substance, if the action took place 
 simply at a distance after the manner of gravitation. But this is not 
 the case. With the same internal charge, the excitation of the external 
 sphere was found to be, that with air being 100, with shell-lac, 150, with 
 flint-glass, 176, and with sulphur, 224. In these cases, therefore, the 
 
Specific Inductive Capacity. 159 
 
 molecular excitation was transmitted in proportion to these numbers, 
 which express, therefore, the degree of excitation, which a common 
 amount of inductive influence is able to produce in masses of these bodies. 
 All gases, no matter how different in chemical properties and constitu- 
 tion, even though the temperature and pressure do not remain the same, 
 possessed the same specific inductive capacity as air. 
 
 This principle is further shown in an interesting manner by the fact, 
 that the induction is not exercised only in the straight line connecting 
 the solid inducing and induced bodies, but that at every intervening 
 point there is a lateral action exercised by the interposed molecules of 
 air which may be themselves considered centres of inductive force. 
 Thus, if a cylinder a of shell-lac be excited by friction and a brass he- 
 misphere k, placed on the top of it, the intensity of the induced electri- 
 city will be found to depend not merely on the dis- 
 tance from the excited source and the nature of the 
 interposed material, but to be more energetic in cer- 
 v^ tain positions in the air, as when the carrier ball of 
 J Coulomb's torsion electrometer was placed at 0, than 
 when it was lower or higher at n or p. 
 
 Faraday has been led by his experiments to con- 
 clude, that the difference between conducting and 
 non-conducting bodies is, that the former assume 
 with exceeding rapidity, under an inductive influence, 
 this condition of molecular excitation, and hence ap- 
 pear to allow the electricity to pass, actually and 
 instantly, through their substance, whereas in reality 
 it is only that the separation and recomposition of 
 the electricities of the chain of molecules has been so accomplished. 
 They lose also this condition as soon as the exciting cause has been re- 
 moved, whereas, non-conductors, when their particles have acquired 
 electrical excitation, remain in that state of tension for a certain time. 
 Thus, if the internal and external coatings of a Leyden jar were con- 
 nected by a metallic wire, the inductive action should be propagated 
 immediately across it ; but the instant that the source of the excitation 
 was removed, the electricities of the two coatings should recombine, 
 from the facility with which the molecules of the wire could assume the 
 inverse condition. But with an interposed plate of glass the result is 
 different, the inductive action is propagated equally, but more slowly ; 
 and that it is the particles of the glass that really produce the charge 
 by their excitation, is demonstrated by the fact, that the metallic coat- 
 ings may be removed, and jet the accumulated electricities be not dis- 
 turbed; the tin-foil serving, only, to discharge at the same moment 
 
160 Lateral Inductive Action. 
 
 every particle of the glass, as if a wire had been individually applied to 
 each. That the induction has acted on the substance of the glass, ex- 
 plains also the peculiarity of what is called the secondary or residual 
 charge. When the particles at the surface have been discharged, they 
 are acted on by the deeper molecules which are still excited, and hence 
 acquire a second inductive charge, and with thick glass, and particularly 
 with bodies which do not insulate quite so well as glass, there may be 
 even a third or a fourth charge of this kind. 
 
 Conduction is therefore only the highest, most intense, and most 
 rapid form of induction ; and it appears from Faraday's investigations, 
 that the permanent excitation of an electrified body has its own origin 
 also in the inductive influence of the bodies that are around. 
 
 The source of the electricity evolved by the electrical machine, can- 
 not be considered as being positively known. Wollaston instituted a 
 series of experiments, by which it appeared to be demonstrated, that 
 there was no electricity evolved except where chemical combination took 
 place, and the superior power given to the machine by the amalgam of 
 tin and zinc being spread upon the rubber was supposed to verify this 
 idea. These experiments of Wollaston have been latterly repeated 
 with great care by Peltier, and with different results ; he found that 
 the electricity evolved was proportional only to the amount of friction, 
 and was the same under various circumstances of liability to the pre- 
 sence or absence of chemical action of the materials rubbed. It is 
 therefore likely that, at least, the electricity of the machine may be 
 generated by the simple molecular derangement and vibration which 
 friction necessary produces ; and this view is very much supported by 
 the undeniable fact, that by other agencies purely molecular, where no 
 trace of chemical action can be pretended, the same form of statical 
 electricity may be produced. 
 
 In almost all cases where the particles of bodies are suddenly and 
 violently disarranged, the separated surfaces are found to be electrically 
 excited ; for instance, if a piece of mica be torn into thin leaves, these 
 are powerfully electric. In many mineral substances, a change of tem- 
 perature causes a manifestation of electrical polarity in a very remark- 
 able degree ; thus, if a long prism of tourmaline be heated, one ex- 
 tremity becomes positive and the other negative ; when the temperature 
 attains its highest point and becomes stationary, all symptoms of elec- 
 tricity disappear, but on cooling they return; in the inverse order, 
 however, the end which had been positive becoming negative, and so 
 on. In this case it appears as if the particles, in the internal motion 
 which the expanding force of heat produces in them, acquired the same 
 condition of polarity, as they should have done by an external friction. 
 
Atmospheric Electricity. 161 
 
 If the expansive effect of heat and the consequent change of position 
 among the particles of the tourmaline had been the same throughout," 
 there would have been no reason for electrical disturbance, but this 
 mineral, and some others wlu'ch likewise become electric on being 
 heated, as boracite, are exceptions to the general law of crystalline sym- 
 metry, and in other respects, as with regard to light, indicate a kind of 
 structure, which is very complex and peculiar. In such cases, an in- 
 ternal friction, by the action of expansion on the unsymmetrically situ- 
 ated molecules of the crystal, is the origin of the electrical excitation. 
 
 The source of statical electricity, which is of the greatest importance 
 in nature, from the universality of its action, is that of change of state 
 of aggregation. When any body passes from the liquid to the solid, 
 or from the liquid to the vaporous condition, or in the reverse order, 
 from being solid or being gaseous becomes liquid, disturbance of the 
 previous electrical equilibrium results. Thus, if a little melted sul- 
 phur be poured into a glass, or if melted tallow or resin be poured out 
 on a metallic plate, the bodies after solidification will be found excited. 
 If a cup of water be placed on the plate of the electroscope, and a red 
 hot ball of metal, or even a red hot cinder be dropped into it, the gold 
 leaves immediately diverge by the influence of the negative excitement 
 which is assumed by the water which remains, and which communicates 
 itself to the metallic cup and to the instrument ; if the gush of vapour 
 had been allowed to impinge on the plate of another instrument, it 
 would have shown excitation by positive electricity. This last is one of 
 the most abundant sources of electricity ; for, as at all ordinary temper- 
 atures, evaporation takes place from the surface of all the water of the 
 globe, and the vapour produced, carrying with it the prodigious quan- 
 tity of positive electricity, which is thus set free, mixes with the air, 
 our atmosphere is almost continually in an electrical condition, gene- 
 rally positive, but at some times, from interfering causes, negative. 
 The great body of vapour, when condensed by the more elevated and 
 colder regions of the air, collects into the peculiar condition which con- 
 stitutes a mass of cloud ; and therein is thus concentrated all the elec- 
 tricity evolved by evaporation at the surface. The clouds are, there- 
 fore, intensely electric ; and when attracted by induction to each other, 
 or to some prominent object on the earth, as a mountain peak, or an 
 elevated building, the discharge and neutralization of the electricities 
 take place with the brilliancy and destructive agency of the lightning, 
 whilst the report, re-echoed from the surfaces of the remaining clouds, 
 or by the sides of the adjacent mountains, produces the effect upon the 
 ear of the continuous rattle of the thunder. 
 
 There is no doubt, however, but that in many cases of chemical com- 
 11 
 
- 162 Electricity of Effluent Steam. 
 
 bination and decomposition electricity in its statical form may be evolved ; 
 thus, Pouillet proved decisively, that, when charcoal is burned, the 
 carbonic acid which passes off is in a state of positive excitement, and 
 the residual mass of charcoal becomes negatively charged. When 
 hydrogen burns in air, the vapour of water carries off the positive elec- 
 tricity ; whilst the negative fluid distributes itself on the hydrogen 
 remaining, and the vessel from which it issues. There is thus, in the 
 combustion of our ordinary fuel, a vast source of the electricity of our 
 atmosphere, in addition to that evolved by water in evaporating ; and it 
 has been found that the evaporation of a saline solution, as sea water, 
 produces a much greater degree of excitement than when the water is 
 completely pure, owing, perhaps, to the destruction of the condition in 
 which the salt and water had been united. The evolution of statical 
 electricity occurs also when the chemical action is of a much more com- 
 plex and obscure kind : thus, in the growth of a seedling plant, the 
 carbonic acid which it evolves is in a positively excited state, and the 
 substance in which the seed is imbedded becomes negative. It would 
 appear, however, that, frequently, electricity that had been imagined to 
 arise from the chemical relations of the bodies brought into contact, 
 arose from their merely mechanical action on each other ; thus, are 
 produced the electricities evolved by sifting lime and oxalic acid 
 together on the plate of the electrometer. 
 
 The developement of electricity by the evaporation of water has 
 recently been submitted to more special examination, in consequence of 
 its having been found, that when the vapour so formed issues in a 
 strong stream from a narrow aperture, as from the escape pipe of a high 
 pressure steam boiler, the steam passes off intensely charged with posi- 
 tive electricity, and the boiler if insulated becomes so strongly excited 
 with the negative electricity, as to afford the most powerful source of 
 statical electric force that is now known. The phenomenon was first ob- 
 served on this great scale by Mr. Armstrong of Newcastle, but Faraday 
 has shown that the great developement of electricity does not arise from 
 the change in the state of aggregation of the water, but from the strong 
 friction of the issuing jet of steam against the pipe through which it 
 passes ; and the hydro-electric machine, as it has been termed, owes the 
 extraordinary power which has given it so much popular interest to the 
 practical construction of the nozzle of the escape pipe devised by him. 
 If the steam-pipe consist simply of metal, the contact of this with the 
 steam allows of the recombination of the + and electricities to a 
 degree which prevents any great accumulation, but by forming the ex- 
 tremity of the nozzle with an imperfect conductor, and interpositing in 
 the path of the escaping steam a disk against which it must forcibly rub, 
 
Dynamical Electricity. 163 
 
 the excitation is raised to its most intense form. This nozzle of the es- 
 cape pipe is represented in the figure about one-fourth of its proper size. 
 At the end of the steam tube a piece of brass is screwed on, 
 I having attached a wooden plug which forms the end of 
 the escape aperture. This longitudinally bored wooden 
 cylinder is secured to its place by a short brass cylinder 
 screwed into the first brass piece. A brass plate is so 
 placed before the opening of the bored cylinder that the 
 steam must pass along the winding course designated by the arrow, 
 before it can escape by the opening. To prevent the neutralizing action 
 of a positively charged atmosphere upon the electricity of the boiler, the 
 jet of steam is received upon a bundle of points of brass placed in con- 
 nection with the earth, so that the positive electricity may be dissipated 
 as fast as it is produced. 
 
 The mere contact of bodies has been supposed sufficient to evolve 
 electricity upon their surface. The trace of excitation in such experi- 
 ments is so small, and diminishes so much in proportion as care is taken 
 to avoid friction and other causes, that we may consider contact as being 
 in itself without power. 
 
 The remarkable characteristic of statical electricity, developed by any 
 of these methods, is the amazing energy of its action on bad conductors, 
 and on the best conductors, if their substance be not of sufficient mass 
 to give it free passage from one point to another ; whilst it is with diffi- 
 culty that we can obtain, by means of it, the slightest chemical decom- 
 position. In the language of the theory of electrical fluids, the electri- 
 city is developed in exceedingly small quantities by friction or change of 
 aggregation ; and hence can perform but feebly such offices, as chemical 
 decomposition, which depend on the quantity that passes in a given time: 
 but this small quantity is gifted with immense tension ; the few mole- 
 cules which become polarized are so to an intense degree, and the attract- 
 ive and repulsive forces which they exert are then sufficient to cause the 
 greatest mechanical effects. 
 
 SECTION II. 
 
 OF DYNAMICAL ELECTRICITY. 
 
 The sources from which electricity is derived in a continually circula- 
 ting form, so that its properties shall result from the uninterrupted 
 motion, must necessarily consist in arrangements from which all insula- 
 ting substances are to be carefully excluded. In statical electricity, the 
 connexion, by a conducting medium, of the opposite extremities of an 
 
164 Nature of Animal Electricity. 
 
 inductively excited body, caused all electrical indications instantly to dis- 
 appear ; whilst that kind of connexion is absolutely necessary to the con- 
 tinuous flowing of the electricity, which constitutes its dynamical condi- 
 tion, and when the conducting circle is broken by the intervention of 
 the smallest portion of insulating matter, either all electrical excitation 
 ceases, or at most a feeble trace of it remains, with the properties which 
 characterize its statical condition. 
 
 1st. Electricity thus circulating through conductors, is found naturally 
 existing in those substances which thereby possess magnetic properties. 
 There is every reason to believe that the native loadstone, as well as all 
 our artificial steel and iron magnets, are closed circles of dynamical 
 electricity, set in motion by forces which depend on the chemical and 
 mechanical constitution of these bodies. 2nd. When any closed con- 
 ducting circuit is at the same time unequal in mechanical constitution 
 and in temperature, so that the current may pass more easily through 
 one point than another, such a current is generated flowing from the 
 portion where the obstacle is greatest, to that part where it is least. 3rd. 
 When substances, capable of mutual chemical combination or decompo- 
 sition, act on one another, there is a current of electricity produced. In 
 the case of simple union, or double decomposition, the circle is internally 
 closed, like that of a steel magnet; but where there is simple decompo- 
 sition, or replacement, the current may be directed through any kind of 
 circuit ; and thus constituting the most important branch of dynamical 
 electricity, is called Galvanism or Yoltaism, from the names of its most 
 illustrious investigators. 
 
 4th. By means of organized structures, of which it is only lately, by 
 the researches of Matteucci, that the true nature and functions have 
 become known, certain fishes possess the power of transmitting a current 
 of electricity across even imperfect conductors, and employ, instinctively, 
 the effect of this current upon the living frame of smaller animals, in 
 order to obtain them for food. The identity of the electricity from this 
 animal origin, with the fluid of the other dynamic sources, has been com- 
 pletely proved, particularly by Faraday; and as the question of the ana- 
 tomical structure of the electric organ, and of the peculiar part of the 
 brain from which the electric nerves arise, interests the physiologist 
 rather than the chemist, I shall merely state, that the current so obtained 
 possesses all the properties that will be described as characterizing gal- 
 vanic electricity of very high tension, and allude no further to it. 
 
 To the chemist, the electricity of the Galvanic or Yoltaic battery is 
 the most interesting of all the forms which this agent may assume, from 
 the intimate relation which exists between it and the force by which the 
 elements of bodies are bound together in chemical combination. To it, 
 
Formation of a Galvanic Current. 165 
 
 therefore, I shall especially direct attention, and consider the remaining 
 sources only so far as the electricity which they yield may differ from it. 
 I shall endeavour, also, to consider it only as characterizing bodies by 
 their properties of exciting the current, or of conducting it when excited ; 
 deferring the important topic of the action of the current upon compound 
 bodies, until the nature of chemical affinities shall have been described. 
 Galvanic Electricity. The manner in which this form of excitation 
 occurs may be very simply shown. If a slip of perfectly pure zinc be 
 partly immersed in a cup of dilute muriatic acid, this last 
 remains totally without action on it, and there is no ap- 
 pearance of electrical disturbance ; but if a slip of copper 
 be introduced which touches the zinc at c, out of the 
 liquid, active decomposition of the muriatic acid begins, 
 the chlorine combining with, and dissolving the metallic zinc, and the 
 hydrogen making its appearance under the form of minute bubbles on 
 the surface of the copper. At the same moment a remarkable state of 
 electrical excitation is produced, in which the zinc resembles a body to 
 which negative electricity, in a state of exceedingly low tension, is unin- 
 terruptedly supplied, whilst an equal quantity of the positive fluid flows 
 along the copper, and these uniting at the point of contact, produce the 
 effects which are spoken of as those of the electric current, the passage 
 of ^yllich may be rendered evident in a great variety of ways. 
 
 The precise manner in which the electrical excitement is here produced, 
 may be explained sufficiently well without involving any consideration of 
 the theory of chemical decomposition, which, at the present moment, 
 would require a knowledge of principles that have not been as yet des- 
 cribed. We may suppose, simply, that the chemical relations of the 
 zinc and muriatic acid are such, that when placed in contact they mu- 
 tually induce on each other a developement of electricity : that part of 
 the zinc which is immersed becoming -f and that out of the acid , 
 whilst the molecules of the acid near the zinc become , and the general 
 mass of the fluid obtains -f- excitation ; the + electricity of the zinc 
 being, however, balanced between the fluids of its own mass and of the 
 acid, and the flnid of the acid being in equilibrium between the + 
 fluids of the zinc and of its own particles, it results that this condition of 
 induced excitation may remain for any length of time without increasing 
 or diminishing in intensity ; the apparatus being in the condition of a 
 very feebly charged Leyden jar : and on applying the slip of copper by 
 which the excited surfaces, the zinc and acid, are placed in communica- 
 tion, the negative electricity of the zinc unites with the positive of the 
 copper, whether by direct translation or by inductive action, and the 
 positive electricity of the liquid unites with the negative of the copper to 
 
166 
 
 Nature of a Galvanic Current. 
 
 produce neutralization ; at the same time the + of the zinc and the 
 of the acid combine. As, on the theory of Franklin, the single electric 
 fluid is supposed to pass from the body which is po- 
 sitively to the body which is negatively excited, it is 
 usual to imagine this exchange of electricities to take 
 place by a current, which in this case, as shown by the 
 arrows in the figure, is from the copper to the zinc, 
 at the superior junction, but from the zinc to the cop- 
 per in the acid underneath. At every moment, accord- 
 ing as the neutralization of the electricities is effected, 
 the system is competent to generate new quantities, and 
 hence the analogy of the weakly charged Ley den jar, noticed above, does 
 not completely hold, for to be accurate it would require the jar to possess 
 a power of charging itself as rapidly as it could be discharged. 
 
 The passage of the current is accompanied by the solution of the zinc, 
 and the liberation of the hydrogen. This hydrogen accompanies the 
 positively electrified molecules of the acid across the fluid, and is dis- 
 charged under the form of gas upon the surface of the copper plate. 
 
 The essential elements of an arrangement by which a current of elec- 
 tricity may be produced are, therefore ; first, two bodies, one simple 
 and one compound, which act chemically upon one another, in such a 
 way as that the simple element shall be substituted for a constituent of 
 the other, which shall be expelled ; and second, a conducting substance, 
 which is indifferent in a chemical point of view, and only furnishes a 
 route for the fluids of the actual elements to recombine continually with 
 each other. In the example given just now this con- 
 ductor was a slip of copper, but it may be of any form, 
 or almost any substance; thus as in the figure, a wire 
 may be soldered to the end of each slip, and, on 
 bringing these wires into contact, at x, the current 
 passes precisely as if the contact of z with c had 
 been direct. Such an arrangement is termed a simple 
 x circle. 
 
 It is not even necessary that the conductor should be solid or metallic, 
 it is, indeed, only for convenience that the ordinary conducting plates 
 and wires are metallic. Thus, in the figure, A z w, a plate 
 of zinc is in contact on the one side with muriatic acid, A, 
 and on the other with water, w, to which a better con- 
 ducting power has been given by dissolving in it a little 
 common salt. The current is then established, being from 
 the conductor to the zinc, and from the zinc to the acid, 
 precisely as in the former instances. 
 
Simple Galvanic Circles. 167 
 
 The passage of the current, under these various circumstances, may 
 be shown, and also that, for its origin and transfer, metallic communi- 
 cation between the plates, z and c, is not necessary, by a very simple 
 experiment. If the slip of zinc be bent, as in B, and a bit of paper 
 moistened with iodide of potassium be laid upon it, and the wire from 
 A be then brought to touch the upper surface of the mois- 
 tened paper, the current passes in the direction of the arrow, 
 and iodine is evolved at the point of contact of the wire. If 
 the surface of the paper next the zinc plate, B, be examined, 
 B it will be found to be alcaline, from free potash. Thus the 
 chemical action of the current, which will hereafter assume 
 so important a position, may here be simply used as a test 
 of its having passed. 
 The direction of the current depends upon the nature of the chemical 
 action which is produced at the period of its passage, and on this prin- 
 ciple is founded one of the most cogent and reasonable arguments in 
 favour of the idea that the current is produced by the chemical decom- 
 position, and not by the contact of the metals, as has been maintained. 
 Thus if a slip of iron and a plate of copper be immersed in muriatic acid, 
 the action is altogether on the iron, and the current passes from the 
 copper to the iron at the point of contact. But if the metals be im- 
 mersed in a strong solution of ammonia, which acts upon the copper, 
 but not upon the iron, the current is produced in the reverse direction. 
 If persulphuret of lime, dissolved in water, be used as the exciting fluid 
 with iron and copper, the current is from the copper to the iron through 
 the fluid ; but on using zinc and copper with the same fluid the direc- 
 tion of the current is reversed ; in the first case the copper, and in the 
 last the zinc is acted on : with acid solutions the copper would have 
 escaped action, and the current should be in both cases from the iron 
 or zinc, to it, through the liquid. 
 
 It thus appears that the relation between the current and the che- 
 mical action is of the most intimate nature possible : the one, as Para- 
 day and others have decisively shown, cannot exist in such arrange- 
 ments without the other, and the nature and tendencies of one deter- 
 mine the power and the direction of the other ; for the quantity of 
 electricity which is set in motion in such an arrangement depends strictly 
 on the amount of chemical decomposition which occurs in the liquid 
 element, and is simply proportional to it. 
 
 It is usual to arrange the various bodies in a list with relation to a 
 fluid, in which, if they be immersed and brought to touch outside, a 
 current is generated from that of the two metals which stands highest 
 in the scale to that which is below, the current through the fluid is, of 
 
168 
 
 Connexion of Galvanic and Chemical Action. 
 
 course, in the opposite direction. The metals arrange themselves, 
 however, very differently with different fluids, according to their liability 
 to chemical action from them, as may be seen in the following table : 
 
 Dilute Nitric 
 Acid. 
 
 Strong Nitric 
 Acid. 
 
 Muriatic 
 Acid. 
 
 Solution of 
 Caustic Potash 
 
 Yellow Hydrosul- 
 phuret of Potassium. 
 
 Platinum. 
 
 Platinum. 
 
 Platinum. 
 
 Platinum. 
 
 Platinum. 
 
 Silver. 
 
 Nickel. 
 
 Antimony. 
 
 Silver. 
 
 Iron. 
 
 Copper. 
 
 Silver. 
 
 Silver. 
 
 Nickel. 
 
 Nickel. 
 
 Antimony. 
 Bismuth. 
 
 Antimony. 
 Copper. 
 
 Nickel. 
 Bismuth. 
 
 Copper. 
 Iron. 
 
 Bismuth. 
 Antimony. 
 
 Nickel. 
 
 Bismuth. 
 
 Copper. 
 
 Bismuth. 
 
 Lead. 
 
 Iron. 
 
 Iron. 
 
 Iron. 
 
 Lead. 
 
 Silver. 
 
 Tin. 
 
 Tin. 
 
 Lead. 
 
 Antimony. 
 
 Tin. 
 
 Lead. 
 
 Lead. 
 
 Tin. 
 
 Cadmium. 
 
 Cadmium. 
 
 Cadmium. 
 
 Zinc. 
 
 Cadmium. 
 
 Tin. 
 
 Copper. 
 
 Zinc. 
 
 Cadmium. 
 
 Zinc. 
 
 Zinc. 
 
 Zinc. 
 
 At the head of each column is placed the name of the exciting fluid ; 
 on taking any two of the metals of the list beneath, and making them 
 the solid elements of the circle, the current is, at the point of contact, 
 from the npper to the lower, and is more powerful in proportion as the 
 metals are farther separated from one another in the list ; thus, with 
 dilute nitric acid and with solution of caustic potash, the most powerful 
 current is, after platinum, by silver and zinc ; with muriatic acid, by anti- 
 mony and zinc, and with persulphuret of potassium with iron and zinc. 
 
 If the metals in contact with the exciting liquid be such as that one 
 is totally without chemical action on it, it serves only as a means of me- 
 chanically transmitting the inductive force, and the current is simply 
 due and is proportional to the electricity evolved by the action of the 
 acid on the other. But if both metals be such that either would act 
 upon the acid, if by itself, and thus produce excitation, as when zinc 
 and copper are placed in dilute nitric acid, when the molecules of acid 
 are submitted to two polarizing forces in opposite directions, which, if 
 equal, would exactly neutralize ; but in practice they are not equal, and 
 a current is produced proportional to their difference. Hence, the 
 more nearly the metals resemble each other in their chemical relations 
 to a given liquid the weaker is the current they produce ; but, though 
 acting similarly to one liquid, they may be oppositely related to another, 
 with which, therefore, they become a source of powerful excitation. 
 Thus, copper and zinc being both acted on violently by sulphuret of 
 potassium, generate but a feeble current, whilst with dilute acid, which 
 acts very differently on each, the current is very powerful, and thus pla- 
 
Principle of Electrotype Copying. 169 
 
 tinum, which is inattackable by almost all liquids, forms the best pos- 
 sible element in every instance. 
 
 The metal which is used as the conducting medium, conducts by 
 having its natural polarity inverted ; and hence, in place of a disposi- 
 tion to combine with the oxygen or chlorine of the liquid/ it would, if 
 already combined, abandon it ; hence, this metal remains clean and 
 bright. On this principle was founded the mode of protecting the 
 copper sheathing of ships, by attaching small portions of iron, of 
 about 3^0 f the surface; the chlorine of the salt in the sea- water 
 being thus transferred to the iron, and the copper, in place of becom- 
 ing covered with the green rust of oxy-chloride of copper, remaining 
 completely bright. This process succeeded in practice somewhat too 
 well, for the negative elements of the sea water being transferred to the 
 iron, the positive bases present, liine and magnesia, were deposited upon 
 the copper, and thus affording points of adhesion for marine plants and 
 shell fish, caused the bottoms of the vessels to become so foul as mate- 
 rially to injure their sailing powers, and the substitution of a kind of 
 bronze or brass for copper, as in what is called Muntz's metal, has 
 been found more suitable. The process at present so extensively em- 
 ployed, of galvanizing iron, as it is termed, by fixing a layer of zinc upon 
 the iron surfaces, acts in protecting them from rust, in the same manner. 
 
 This transfer of the elements of the exciting liquids has become re- 
 cently, by the invention of Spencer, the basis of one of the most beautiful 
 and important of the applications of science to the arts. If one of the 
 exciting liquids be a solution of sulphate of copper, as in Daniell's bat- 
 tery, (page 177), the metallic copper which separates is deposited upon 
 the surface of the plate to which the current passes in the liquid, and 
 there is formed a layer of metal, which may be obtained, by slow and 
 long continued action, as dense and homogenous as the best hammered 
 copper. Any prominences or depressions, even a scratch of a pin, 
 drawn on the plate on which the deposit forms, are accurately repre- 
 sented on its internal surface ; and it is only necessary to use, as the 
 negative metallic element, a medal in relievo or intaglio, to reproduce, 
 with an accuracy equalling the powers of the most finished hand or ma- 
 chine, the finest works of art. This principle has been shown by Mr. 
 Spencer to be applicable to the copying of all varieties of designs, and 
 as perfected by Elkington and Napier, especially in the use of the metallic 
 cyanides in solution, may be looked upon as the most important means 
 of facilitating the possession of works of art, and thus elevating public 
 taste, that has been made since the discovery of the method of transferring 
 engravings to any number of steel plates. 
 
 The electricity which is evolved by the chemical action of such simple 
 
170 
 
 Formation of Compound Circles. 
 
 circles, is remarkably different in its characters from that form which has 
 been described as its statical condition. Although present in much 
 greater quantity than can be developed by friction, with the most pow- 
 erful machines, yet, from its state of continued recombination, it cannot 
 acquire intensity; it hence can pass only through good conductors; 
 pure water, which, from the facility with which it allows of the passage 
 of machine electricity, proves the great source of failure and uncertainty 
 in our experiments, intercepts almost completely the current from a 
 simple circle, and the wires which are used to effect communication may 
 be touched with the fingers, without any tendency to lateral shock be- 
 coming evident; and yet the disproportion in quantity between the 
 fluid, which bursts through the strongest insulating bonds of our appa- 
 ratus, or breaks from the clouds, devastating forests, as the lightning, 
 and that which passes silently across the wires of the voltaic circle, is 
 such, as almost to surpass belief. By actual experiment, it has been found, 
 that the immersion of two wires, one of platina, and the other of zinc, 
 each 0'06 inch in thickness, to a depth of five-eighths of an inch, in dilute 
 sulphuric acid, for three seconds, gave as much electricity as could be 
 generated by thirty turns of the most powerful machine of the Royal In- 
 stitution. Indeed, Faraday has rendered it probable, that in the current 
 which passes, during the decomposition of a grain of water, there is con- 
 tained more electricity than in the brightest flash of lightning. 
 
 If the metallic elements of a simple circle be connected, not directly 
 by metallic contact, or by a wire, but by means of one or more other 
 simple circles interposed in its path, the current of its electricity 
 is not at all interfered with, but the quantity of electricity which 
 circulates is precisely equal to what is generated by the chemical action 
 which takes place in each cell. For, considering the circle of four 
 cells represented in the figure, consisting of copper and zinc plates, 
 
 zl 
 
 c 
 
 f - 
 
 25 
 
 
 c 
 
 H 
 
 
 25 ] 
 
 c 
 
 f - 
 
 
 zT 
 
 Jcl 
 
 1 
 
 
 
 
 
 
 
 
 I 
 
 
 
 
 
 
 1 
 
 L- 
 
 
 + 
 
 
 ^ 
 
 
 
 u 
 
 
 
 
 
 -1- 
 
 1 
 
 d +. 
 
 acted upon by muriatic acid, the copper of each cell discharges its 
 positive electricity upon the negative fluid of the zinc in the adjoining 
 cell, and hence there is neutralization of effect at the points a, b, and c, 
 and it is only the amount of electricity liberated upon the copper and 
 zinc plates in the terminal cells, that passes along the wires, and re- 
 
Theory ofJhe Voltaic Battery. 171 
 
 combining at d, produces the phenomenon of the current ; Imt this is 
 the same quantity as should be evolved in any one of these simple cells 
 by itself, and hence the remarkable result, which has been fully demon- 
 strated by experiment, that no matter how we may increase the number 
 of the elements of a galvanic circle, the quantity of electricity passing 
 in the current is equal only to that evolved by a single cell. If the 
 chemical action be not of the same energy in all the cells, there passes 
 little more electricity than what is generated where the decomposition 
 is least active ; for, as the excess should have to penetrate through the 
 liquid conductor in all the cells, the obstacle afforded to its progress is 
 so great, that it is almost totally absorbed. 
 
 Although the increase in number of the elements of the galvanic 
 circuit is inefficient towards augmenting the quantity of electricity which 
 passes, yet it changes the character of the current in a very remarkable 
 degree, and confers upon the fluid an intensity which in a simple circle, 
 of no matter what magnitude, it never can possess. The ideas of phi- 
 losophers, however, regarding the real nature of what is called intensity 
 have been very vague, and no satisfactory explanation of its source and 
 measure has been given. I would suggest the following as at least 
 serving to indicate the kind of action in which intensity may consist. 
 It has been seen, that by the state of mutual excitation into which the 
 zinc and acid are thrown, before the circuit is completed, the intensity 
 of the evolved fluids is limited to that which will not suf- 
 fice to enable the excited particles of acid to discharge 
 themselves upon the oppositely excited particles of zinc, for 
 if this discharge occurred, all should be brought back to 
 the neutral condition. Now if there be added a second 
 cell, the equal and similar excitation of the electricities generated therein 
 will, by a mutual reaction analogous to that of two magnets placed near 
 each other, so increase by induction the amount of electricity developed 
 in the zinc upon the one hand, and in the acid on the other, that the 
 chemical decompositions will take place much more rapidly than before, 
 and there being in circulation at a given moment a much greater 
 amount of separated elements, the transferring, or what is the same 
 thing, the conducting power of the interposed liquid will be propor- 
 tionally increased, and the terminal wires being thrown by this increased 
 amount of electricity into the polarized condition which constitutes the 
 excitation or carrying of a current will communicate that state to any 
 suitable liquid conductor in which they may terminate. Decomposition 
 will, therefore, commence therein, and it will be rapid and intense in 
 proportion to the degree of excitation inductively produced in the cells 
 of the battery, and, therefore, proportional to the number of pairs of 
 
172 Nature and Source of Intensity. 
 
 plates combined together ; but as this induced excitement is only re- 
 peated from cell to cell by their mutual actions, and as the terminal 
 wire can only transfer to, and represent in, the decomposing vessel, or 
 on any body placed between the poles, the amount of action by which 
 their own excitement is produced, the decomposition which takes place 
 of any chemical substance between the poles can only be equal or equi- 
 valent to the amount of chemical decomposition which takes place in 
 any cell of the battery, and the quantity of electricity which passes in 
 the strongest battery is subjected to the law just stated, of being pro- 
 portional to the quantity of zinc dissolved in any one cell, but its in- 
 tensity being, according to the view which I now propose, proportional 
 to the quantity which passes in a given time, depends on the degree of 
 excitation inductively produced by the mutual action of the elements of 
 the battery, and is consequently proportional to the number of pairs of 
 plates, and to the energy of the chemical action of the solid and liquid 
 elements of the battery. The peculiar character of intensity has been 
 considered to arise, also, from the electricity generated by the outside 
 plates obtaining additional velocity, in passing across the intermediate 
 cells, in each of which it meets an equal quantity of fluid moving in 
 the same direction, and whose motion it absorbs, restoring them to rest, 
 and being thereby hurried itself onwards in proportion. 
 
 The intensity of the electricity which is thus excited is very slight, 
 even where the number of combinations is considerable ; thus, it re- 
 quires a series of at least 200 pairs of plates, four inches square, im- 
 mersed in dilute sulphuric acid, to cause a sensible divergence of the 
 gold leaves of the most delicate electroscope. It is only where the ar- 
 rangement involves some thousands of couples, that electricity is evol- 
 ved, of sufficient tension to produce a spark across a non-conductor, 
 such as that given by the electrical machine, or to cause any of those 
 attractive and repulsive motions by which the feeblest form of statical 
 electricity is recognized ; to obtain these effects also, the circuit must 
 be broken, for even with the most powerful combinations, the current 
 of electricity is without any action of intensity. Where, however, by 
 means of a sufficient number of elements, intensity has been given, the 
 quantity of electricity which accumulates, and the quantity of chemical 
 action from which it has its origin, is exceedingly minute. This is ex- 
 emplified in the dry piles of Zamboni, the form in which electricity may 
 be considered as connecting its purely dynamical and properly statical 
 conditions. The pile of Zamboni contains no apparent liquid element : 
 it consists of disks of gilt paper, and of exceedingly thin zinc foil, laid 
 alternately over one another, to the number of from five to twenty 
 thousand, care being taken to turn all the gilt surfaces the same way. 
 
Relation of Intensity to Quantity. 173 
 
 These are enclosed in a glass tube, and terminated at each end by a 
 brass cap, with a pressure screw. The paper containing in its pores, 
 when not artificially dried, a small quantity of water, this gradually acts 
 upon the zinc, and electricity is evolved, which, from the great obstacle 
 presented to its recombination, through the disks internally, and by the 
 atmospheric air outside, attains a degree of intensity so high, that it 
 
 acts decidedly upon the electro- 
 scope, as shown in the figure, 
 and is amusingly applied to pro- 
 duce various attractive and re- 
 pulsive motions, such as ringing 
 bells, &c., for there being a con- 
 tinual source of electricity in 
 the action of the moisture of the 
 paper on the zinc, these pheno- 
 mena may continue manifested 
 for years, without diminution. 
 
 Such a dry pile, when insulated, shows opposite electrical excitation 
 at the two extremities, these being, however, of equal force, and hence 
 producing neutrality when combined. If, therefore, the two ends of a 
 dry pile be connected by a wire, the electricities which had accumulated 
 recombine, and the pile becomes inert, and requires a certain time be- 
 fore it can recover a charge equal to that which it had lost. When the 
 pile is examined at a distance from its ends, the excitation is found to 
 be less powerful, until at the centre it is exactly neutral. This arises 
 from the action, at each point, being the resultant of the opposing 
 actions of the two extremities, and vanishing at the centre where these 
 last are equal, precisely as there exists a neutral place upon the surface 
 of any body inductively excited by ordinary electricity. If the pile be 
 held in the hand by one extremity, the electricity of that end is dissi- 
 pated, and the other end becomes capable of acting more powerfully 
 upon the electroscope, from the opposing influence being removed. 
 
 No principle has ever been discovered in science more rich in conse- 
 quences, than this of the increase of tension given to electricity in 
 motion, by the connexion of a number of simple galvanic circles. 
 Hence, deservedly, the instrument so formed has obtained the name of 
 the Yoltaic pile. It has enriched chemistry with a crowd of important 
 substances discovered by its means, and has led, by its results, to the 
 suggestion of the most plausible theory of chemical combination that has 
 been as yet proposed. In physical science it became the origin of all sub- 
 sequent improvements in the domain of electricity, for without its agency 
 it is hard to see how the steps which followed could have been made. 
 
174 Theory of the Action of the Battery. 
 
 The form in which the Yoltaic pile was first constructed, was similar 
 to that of the dry pile noticed above. The disks were of zinc, and sil- 
 ver, or copper. The fluid conductor which was rendered more capable 
 of acting on the zinc, by the addition to it of some acid or of common 
 salt, was imbibed in disks of woollen cloth, which were interposed be- 
 tween every pair of metallic disks. There were thus, copper-zinc, acid, 
 copper-zinc, acid, copper-zinc, and so on to an indefinite extent. It is 
 a peculiarity of this instrument, which as it extends to many forms of it 
 even now in use, and affects our chemical nomenclature remarkably, it 
 is necessary to notice, that the current in the connecting wires appears 
 to be in a direction opposite to that described in the battery of cells of 
 page 171, for the outer copper plate at the one end and the outer zinc 
 plate at the other, having no communication with the exciting acid, 
 transmit the current merely as portions of the attached wires ; and 
 hence, the direction of the current is in appearance from the zinc to the 
 copper end, whilst it is properly the copper from which the positive 
 fluid emanates, and it is the negative which arises from the zinc. This 
 diversity had its origin in the circumstance, that the theory of the pile 
 maintained by Yolta, and even at the present moment supported by 
 some illustrious men, ascribed the origin of the electricity not to the 
 action of the acid upon the zinc, but to the contact of the zinc with the 
 copper ; the point where the metals touched being supposed to be a 
 continual source of positive electricity to the zinc, and of negative elec- 
 tricity to the copper. It was even attempted to prove this by sold- 
 ering together plates of zinc and copper, and testing their electrical 
 condition by the gold-leaf condenser, which was supposed to indicate a 
 permanent state of excitation, independent of all fluid or chemically acting 
 media. It has been fully proved, however, that according as such con- 
 tact experiments are made with increased care, the results become less 
 evident in favour of that theory. Such trials tend to show the evolution 
 of minute traces of statical electricity, whereas the simple galvanic circle 
 is characterized by the great quantity of electricity it may yield, and by 
 its total want of statical intensity. Even, therefore, if it were proved, 
 which it is not, that the mere contact of bodies, evolved electricity affect- 
 ing the gold-leaf electroscope, it would be as far from accounting for the 
 totally different kind of electrical excitement by which the galvanic bat- 
 tery is created, as it would be from giving a true or satisfactory theory 
 of the cause of magnetism. 
 
 But the pretended excitation by contact, or the electromotor force, as 
 it was termed by Yolta, must be carefully distinguished from the capa- 
 bility of inductive excitement, which bodies capable of chemical action, 
 as a slip of zinc and muriatic acid, mutually confer upon each other. 
 
Construction of Galvanic Batteries. 
 
 175 
 
 This last arises from the possible substitution of the zinc for the hy- 
 drogen of the acid, which does occur as soon as the interchange of the 
 electricities allows of the transfer of elements ; for on the first immersion 
 of the zinc, the equilibrium of the chlorine and hydrogen, which had 
 previously been totally engaged with each other is interrupted, and 
 that of the particles of the zinc, which had before been all circumstanced 
 alike, is disturbed by some of them being nearer the acting muriatic acid 
 than the others, and thus the induced condition of both arises. On this 
 positive and necessary principle, the theory of the simple and compound 
 circles already described has been given, and although it will require to 
 be again noticed in describing the phenomena of decomposition which 
 accompany the passage of the current, yet for the only purpose which 
 we here require of studying the manner in which the current of elec- 
 tricity of the battery has its origin, the peculiar and important influence 
 exercised by the chemical reaction amongst the elements of which it 
 consists, has been sufficiently described. 
 
 It is now necessary to notice more in detail the construction of some 
 of the more usual forms of the Voltaic or Galvanic battery. The first 
 improvement on the pile of Yolta consisted in placing it horizontally 
 
 in a wooden trough, and replacing by 
 cells containing dilute acid, the moist- 
 ened disks of cloth employed by the 
 original inventor. It being difficult 
 to cleanse the surfaces of the plates, 
 which in this form were permanently cemented into the trough, this 
 
 was next made of delftware divided into 
 cells, and the plates being soldered 
 together by projecting bands at the 
 top, were hung upon a rod, as in the 
 figure, so that when wanted, they might 
 be immersed with great rapidity, and 
 withdrawn as easily from the liquid 
 when the battery was not wanted. The 
 power of such troughs is increased by 
 one-half when the copper slip is doubled over, so as to oppose both 
 surfaces of the zinc. Batteries intended rather for intensity than for 
 quantity, and which consequently consist of a great number of plates 
 of moderate dimensions, were generally employed on this last construc- 
 tion : each delftware trough holding ten pairs of plates, and any num- 
 ber of troughs that may be required, being rapidly and easily arranged 
 together. When a current of electricity of great quantity, but not of 
 intensity, is required, it is usual to employ a few or even only one pair 
 
176 Interfering Action of Common Zinc. 
 
 of plates of considerable size. Thus, a sheet of copper and a sheet of 
 zinc, each of from 80 to 120 square feet of surface, being kept sepa- 
 rated by ropes of horse hair, have been rolled up together and immersed 
 into a large tub of acid, forming thus a simple circle, giving a current 
 so feeble in intensity as to pass with difficulty through a short column 
 of distilled water, and to be quite insensible to the feeling, but which 
 fused down into globules the most refractory metals, and gave with 
 charcoal points a light of brilliancy insupportable to the eye. The 
 copper plate may be very conveniently made to act as the cell contain- 
 ing the acid : cylindrical batteries of moderate size are very frequently 
 so constructed. 
 
 I have supposed, in the description of the nature of simple and com- 
 pound Yoltaic circles, that the zinc employed was completely pure, in 
 which state, when first immersed in the acid, there is no chemical 
 action, but only the preparatory inductive state produced, the decom- 
 position of the acid by the zinc commencing only when the circuit is 
 completed. But such pure zinc is too expensive for ordinary use, and 
 the commercial zinc contains always traces of impurities, particularly 
 iron, from which it acquires a power of generating a multitude of little 
 secondary currents across the fluid, and thus preventing to a great ex- 
 tent the formation of the proper current. For suppose that there is on 
 the centre of zinc a little piece of iron or of copper, this serves to re- 
 turn to the zinc from the acid, the positive electricity, which passed 
 away from it, precisely as if it had been a copper wire, which touched 
 the acid with the one end, and the zinc with the other. Such a plate 
 is, therefore, occupied almost solely with its own self- continued cur- 
 rents, and scarcely assists in generating the electricity which is brought 
 into play in the battery at large. To this cause must be assigned the 
 property which ordinary zinc possesses of dissolving readily in an acid, 
 and of evolving hydrogen upon its own surface. It evolves the hydro- 
 gen upon those points of its surface on which foreign metals being de- 
 posited serve to complete its circuits. This injurious property of ordi- 
 nary zinc is remedied by coating the surface of the plate with mercury 
 or, as it is termed, amalgamating it. By this means the whole surface 
 of the metal is brought into the same state, and must hence act in the 
 same manner on the acid. Any secondary current which might arise 
 could, therefore, find no means of discharge, and such zinc is not act- 
 ed on, until the circuit is completed, and then all hydrogen is carried 
 by the excited molecules of acid to the copper plate, and there evolved 
 as gas. 
 
 To amalgamate the zinc plates of a battery, a quantity of mercury 
 is to be laid in a flat dish, sufficient to cover the bottom ; moderately 
 
Forms of ^Constant batteries. 177 
 
 dilute nitric acid, to which a small quantity of nitrate of mercury had 
 been added, is to be then poured on the mercury, so deep that the zinc 
 plate, when floating on the mercury, shall be covered by the acid. Be- 
 fore immersing the zinc plate, it should be, if not new, cleaned as well 
 as possible, with sand paper, from adhering dirt, and then it combines 
 with the mercury very rapidly, so as to form a surface, which, by rub- 
 bing with a little flannel, may be rendered completely uniform. The 
 zinc should not be too highly mercurialized, for then it becomes ex- 
 tremely brittle, and requires considerable care in using it. The power 
 of a battery may often be quadrupled by this method, A source of 
 great inconvenience in the ordinary batteries, arises from the hydrogen 
 acting on the oxide of zinc which is dissolved, and reducing it to the 
 metallic state, when it is carried, with the remaining hydrogen, to the 
 copper plate, and deposited upon it. In this way, there is gradually 
 formed a second zinc surface, opposite to the proper zinc plate, and 
 which, tending to transmit a current in the reversed direction, neutra- 
 lizes a certain proportion of the power of the circle, and may even de- 
 stroy it altogether. Hence, an ordinary battery is most active when 
 first brought into play, and diminishes very rapidly in power, until, 
 after the lapse of some hours, even though the acid be not saturated, 
 its action ceases. 
 
 This disadvantage has been beautifully removed, by the principle of 
 absorbing the hydrogen, by means of a solution of sulphate of copper, 
 which it decomposes, and precipitates upon the surface of the copper plate 
 a layer of clean, new, metallic copper, in the best possible condition, for 
 supporting the action of the battery. The simplest arrangement of this 
 kind is that proposed by Becquerel and Mullins; the mechanical construc- 
 tion is most perfect in DanielFs constant battery. Mullins' battery consists 
 of a delft ware trough, D, in which the cylindrical zinc 
 plate, B, of nearly the same diameter, is placed, and 
 inside of which, again, is the copper cylinder, A, 
 which is close, and acts only by its external surface ; 
 round the upper edge of the copper cylinder, c, is 
 tied a bladder, into which fluid may be introduced, 
 by means of a row of apertures in the rim to which 
 the bladder is attached. A solution of sulphate of 
 copper is poured into the bladder, and its state of 
 concentration is kept up by heaping some coarsely pounded crystals on 
 the top of the copper cylinder. Into the trough, in contact with the 
 zinc, is then poured dilute sulphuric acid. When the action commen- 
 ces, the hydrogen is transferred through the membrane, and, meeting 
 there the solution of sulphate of copper, is absorbed in the production 
 12 
 
178 Batteries of Mullens, Daniell, and Smee. 
 
 of metallic copper. The copper cylinder never wears nor dirties. The 
 metal is all recovered from the sulphate of copper, and the only thing 
 necessary is, that the plates of zinc shall be renewed from time to time. 
 DanielFs battery has the advantage that the copper is outside, and hence, 
 is capable, with exposure of the same surface of 
 zinc, of producing a much more powerful current* 
 c HlHIHI The cell consists of a copper cylinder c, c, near the 
 top of which is attached a perforated plate, r, on 
 which, when the cell has been filled with the solu- 
 tion of sulphate of copper, a quantity of crystals 
 are laid, to be dissolved according as they are re- 
 quired. A solid zinc rod z, supported at the top 
 of the copper cylinder by a wooden cross piece, is 
 contained in a membranous bag, formed of the gul- 
 let of an ox, t, t, and into this is poured the dilute acid, which consists 
 of one part of oil of vitriol and eight parts of water. Any number of 
 these cells may be arranged together, so as to give a battery, which, if 
 all the coppers be connected upon the one hand, and all the zinc rods 
 upon the other, will evolve large quantities of electricity of low tension, 
 but when the copper and zinc elements are alternately connected with 
 each other, the tension of the electricity evolved is much increased, 
 though at the expense of the quantity generated. 
 
 The great advantage of such batteries, is the perfect uniformity of 
 their action, by which they deserve fully the name applied by Daniell to 
 his construction, of the constant battery ; with such an instrument, the 
 conditions of the current may remain for days perfectly unaltered ; and 
 thus the laws of action of the current have been determined, particu- 
 larly in its chemical relations, with complete success, and views of the 
 analogies between affinity and electricity, equally novel and important, 
 which shall be discussed in another place, have been arrived at by its 
 means. 
 
 Latterly the membranous bags, originally used by Daniell and others, 
 as the diaphragm between the acid solution and that of the sulphate of 
 copper, have been with great advantage replaced by porous cells of bis- 
 cuit ware, such as is represented in the figure by t, t. 
 
 Some forms of battery have recently been proposed, in which, under 
 a small compass, very great power is obtained, by, 1st, bringing the 
 plates very near each other ; 2nd, selecting solid elements, which differ 
 as much as possible in their chemical relations ; and, 3rd, using as the 
 exciting fluids those of the most intense action, and of the highest 
 conducting power. In this way are formed the most powerful Voltaic 
 combinations that have been yet made. In that of Mr. Groves, plates 
 
Batteries of Groves, Bnnsen, and Callan. 179 
 
 of zinc and platina are separated by diaphragms of porous earthenware, 
 the zinc being acted upon by dilute sulphuric acid, mixed with some 
 nitric acid, and the platina being in contact with tolerably strong nitric 
 acid. The hydrogen evolved by the zinc is completely absorbed by the 
 nitric acid on which it acts, forming nitrous acid which remains disol- 
 ved ; and the metals being those most opposite in their electrical rela- 
 tions, give the most powerful current possible. 
 
 To save the cost of platinum it has been proposed to employ silver plates 
 on which a surface of platinum has been deposited, as in Smee's battery, 
 or lead plates similarly platinized, as in one form of Gallants battery. 
 Bunsen has suggested to make cylinders of coke, by compressing finely 
 powdered coal with a small admixture of sugar into an iron mould, which 
 is to be strongly ignited. "When well prepared, these coke cylinders are 
 excellent conductors, and form negative elements of batteries scarcely in- 
 ferior in power to Groves' s combinations. Another very interesting modi- 
 fication of the principle of Groves' s battery, is that invented by Rev. Pro- 
 fessor Callan of Maynooth College. Taking advantage of the remarkable 
 passitivity of cast iron, in relation to a mixture of strong nitric and sul- 
 phuric acids, he constructs his battery of cast iron cells, in which a porous 
 porcelain cell with a zinc plate is inserted. The porous cell contains 
 dilute sulphuric acid. The cast-iron cell contains a mixture of strong 
 nitric acid and sulphuric acids. The electro-motive force here brought 
 into play, appears to be even greater than in the case of platina and zinc, 
 and the original cost is very small. A battery of 800 four-inch square 
 plates, made upon this principle for the Maynooth College, produces 
 most brilliant results, and is probably the most powerful galvanic appa- 
 ratus now existing. 
 
 The same metal when placed in different molecular states, may become 
 the negative or the positive elements of a battery, thus : iron which 
 might replace zinc in contact with dilute sulphuric acid, replaces plati- 
 num in contact with strong nitric acid in Callan' s battery. In platinum 
 itself the difference of molecular condition appears to be produced accord- 
 ing as it is in contact with hydrogen or oxygen, and the latter may be 
 replaced by sulphur or chlorine. In this manner is constructed the gas 
 battery, recently invented by Mr. Groves. Two glass tubes are filled, 
 one with oxygen, and one with hydrogen gas. Each glass tube contains 
 a platinum plate attached to a wire which is passed into the top of the 
 tube, and by its external extremity is placed in connection with other 
 tubes, or with any other apparatus to which the current generated is to 
 be transmitted. The tubes so filled, are placed standing in a vessel con- 
 taining dilute acid, as a conducting medium. On connecting the wires 
 of the tubes, a current is established. The platinum in contact with the 
 
180 Relative Conducting Powers. 
 
 oxygen acting as the negative, and that in contact with the hydrogen 
 as a positive element ; and the water of the intervening conductor is de- 
 composed, its elements gradually uniting with those contained in the 
 tubes, and reconstituting the equivalent of that electrolysed. 
 
 The conducting powers of various bodies, for this form of electricity 
 has been determined with great care by Pouillet, whose results are, that 
 the relative conducting powers of the various metals are expressed by the 
 following numbers : 
 
 Palladium . , . 5791 Brass from ... 900 
 
 Silver . . .. 5152 to ... 200 
 
 Gold . . . 3975 Cast Steel from . . 800 
 
 Copper : . . 3838 to , : . . 500 
 
 Platina ... 855 Iron ... 600 
 
 Bismuth ... 384 Mercury ... 100 
 
 He ascertained, also, the relative conducting powers of the saline so- 
 lutions usually contained in the cells of the Galvanic battery ; and it 
 appears that the conducting power of platina is two millions and a half 
 times that of a saturated solution of sulphate of copper, and hence that 
 of copper is sixteen millions times as great. The conducting power of 
 the saturated solution of the sulphate of copper being taken as 10 '000, 
 he found that of 
 
 a saturated solution of sulphate of zinc to be 4' 170 
 distilled water, ...... 0-025 
 
 distilled water with ---- of nitric acid, . 0-150 
 
 The great retardation which occurs when the current has to pass through 
 any considerable length of liquid, will now be easily understood. Pure 
 water may be considered, with feeble circles, as an absolute non-con- 
 ductor ; and, even with the most powerful combinations that have been 
 yet made, the current is unable to force its way through the smallest 
 measurable interval of air. It was, not long ago, believed, that even 
 with simple circles, a spark indicating the passage of a current was seen 
 on making contact, and hence that the electricity had passed before the 
 metals had touched, and, consequently, that the chemical action should 
 be alone considered as the source of the electricity. It is, however, now 
 acknowledged, that no spark can pass until the wires have touched and 
 are again separated, and the passage of the electricity is then accomplished, 
 not by the action of the excited molecules of air, as occurs with the 
 machine, but by the violent inductive polarization of the particles of the 
 terminal conductors, which are torn off and pass from one pole to the 
 other. 
 
 When the current of electricity is retarded by means of an insufficient 
 
First Discovery of Galvanism. 181 
 
 conducting medium, the centre of the conductor becomes hot, and thus 
 the most brilliant effects of heat and light may be produced ; even the 
 most refractory metals, as gold and platina, being, when in thin foil or 
 wire, dissipated actually in smoke. By terminal points of well burned 
 charcoal this phenomenon is beautifully produced, the ignition being 
 totally independent of combustion, for it takes place in vacuo, or in car- 
 bonic acid gas, and when the points are separated from one another to a 
 certain distance, the interval becomes occupied by a splendid arch of 
 light formed by the inductively excited particles of charcoal, which, in a 
 state of intense ignition, abandon the positive, to attach themselves to 
 the negative extremity of the conductor. 
 
 The action of galvanic electricity upon the animal frame does not pro- 
 perly fall within the scope of the present work, but, in terminating the 
 subject, the mode in which the first view of this important science was 
 obtained may, with propriety, be noticed. Galvani was Professor of 
 Anatomy at Bologna, and, whilst preparing frogs for some physiological 
 experiments, he happened to touch, by one extremity of a metallic wire, 
 the lumbar nerves which still remained attached to the spine, whilst the 
 other extremity of the wire was in contact with the muscles of the leg ; 
 
 these last were instantly thrown into strong 
 convulsions. To perform this experiment 
 w ith success, the legs of the frog are to be 
 left attached to the spine by the crural nerves 
 alone, and then a copper wire and a zinc 
 wire, being either twisted or soldered toge- 
 ther at one end, the nerves are to be touched 
 with one wire, whilst the other is to be ap- 
 plied to the muscles of the leg. 
 
 Galvani erred in the explanation of this remarkable effect ; he looked 
 upon the body as being in the state of a charged Leyden jar, of which 
 the nerves and muscles were the external and internal coatings, and that 
 on connecting these by the conducting wire, the electricities recombined., 
 and their passage renewed for the instant the phenomena of life. Yolta 
 pointed out, however, that in order to produce full effect, the presence 
 of two metals in the conductor was required, and he ascribed the origin 
 of the electricity not to the body, but to the contact of the two metals, 
 and supposed the convulsive motions to be merely the indication of the 
 passage of the current across the body of the frog. This view has also 
 been since modified by ascribing the electricity to minute traces of che- 
 mical action on the wires ; but it was so fruitful in results, of which the 
 construction of the Yoltaic pile is the most remarkable, that Volta is, 
 with justice, looked upon as the true originator of this branch of electri- 
 
182 Thermo-Electric Currents. 
 
 city, as a science, although it was Galvani who observed the first fact 
 belonging to it. 
 
 The frog so prepared is a most delicate test of the passage of a Gal- 
 vanic current, it is truly a galvanoscope, corresponding to the gold-leaf 
 electroscope for ordinary electricity ; but it does not measure the quan- 
 tity or intensity of the electricity which passes. As yet we have no exact 
 measure of the intensity of Galvanic electricity ; but that its quantity 
 may be exactly determined, two of its properties may be applied ; the 
 first consists in determining the quantity of a given chemical substance, 
 as water, which the current can decompose in a certain time, for the 
 quantity decomposed is proportional to the quantity of electricity which 
 passes ; the second consists in observing the degree to which the current 
 is able to deflect the magnetic needle from its natural position of north 
 and south, for the angle of deflection is connected with the quantity of 
 of electricity in the current by a very simple law ; we are not yet in a 
 position to understand fully the theory either of the chemical or the 
 magnetic galvanometer, and hence I merely indicate, for the present, 
 their existence and their names. 
 
 Thermo-electricity. If heat be applied to a wire, uniform in texture 
 and thickness, and bent into a ring, there is no disturbance of elec- 
 trical equilibrium ; but if any obstacle to the transmission of the heat, 
 such as a knot or a coil on the wire, exist, a current will be established, 
 of which the direction shall be from the point of the current to which 
 the heat is applied towards the point where the retarding cause exists. 
 If in place of merely causing an artificial obstacle on an uniform wire, 
 two metals, a I, be selected, which differ in conducting power, and 
 that the point at which they touch one another, c, be kept at a different 
 temperature from the rest, a current is also produced from the latter 
 point towards the metal which is the worst conductor. The more 
 unlike the metals are in molecular constitution, and the greater the 
 difference between their conducting powers, the more energetic is the 
 current. The best combinations are, therefore, of a crystalline and a 
 non-crystalline metal, or of two metals which crystallize in different 
 systems. Bismuth and antimony, which are the worst 
 conductors of the metals, are also among the most 
 crystalline ; and whilst bismuth crystallizes in cubes, 
 the form of antimony is a rhombohedron. These 
 metals, therefore, combine all the essential qualities 
 for generating a current when unequally heated, and 
 they are, consequently, the most powerful sources of 
 thermo-electricity that have been found. The results obtained with 
 other metals will be understood by writing them down in the following 
 
Production of Cold by Electricity. 183 
 
 order, any two of them being capable of forming a current when their 
 junctions are unequally heated ; the current being from the metal highest 
 to that which is lowest in the list, and the power of the current being 
 greater in proportion to the distance between the metals in the follow- 
 ing order : bismuth, platinum, lead, tin, copper or silver, zinc, iron, 
 antimony. The molecular texture would appear from this list to have 
 more influence on the production of the current than the mere difference 
 of conducting power. ^ 
 
 The intensity of the thermo-electric current so excited is exceedingly 
 small ; it is only capable of passing through very good conductors, and 
 it requires the combination of a number of exciting couples to give 
 sufficient tension to enable it to produce a spark, or to show any signs 
 of chemical influence. It then, however, agrees in all respects with 
 the electricity of the Galvanic battery when in an excessively feeble 
 state of tension, and it resembles remarkably the hydro-electric current 
 in being able to reproduce at a distance the circumstances in which it 
 originates ; for precisely as a current passes through a combination of 
 antimony and bismuth, when its junctions are at unequal temperatures, 
 so when a similar current from any other source is passed through the 
 metallic couple, a change of temperature is produced at a place where 
 the two unite. If the current pass from the bismuth to the antimony 
 the junction becomes heated, but if the electricity pass in the opposite 
 direction, the junction is cooled to a remarkable degree ; so that if a 
 little hole be bored where the metals touch, and a drop of water be 
 laid therein, it is frozen after a few moments. This result, which was 
 first obtained by Peltier, and has been confirmed by Bottger, is one of 
 the most remarkable proofs of connexion between the physical sources 
 of temperature and electrical equilibrium that has been as yet discovered, 
 and may influence our theories of the nature of heat in no inconsiderable 
 degree. 
 
 The principle of strengthening the thermo-electric current, by com- 
 bining together the action of a number of metallic couples, is due to 
 Nobili. If we consider a number of bars of antimony and bismuth, 
 
 a &, soldered together alternately at 
 their ends, so that every alternate 
 soldering shall be in the same plane, 
 and that the extremities of the ter- 
 minal bars be connected by a wire ; 
 on applying heat to the alternate sol- 
 derings currents are generated at each, 
 which, being all in the same direction, travel together through the 
 system, and thus increase its energy in proportion to the number of 
 
184 Construction of the Thermoscope. 
 
 combinations, The important distinction between this and the com- 
 bination of elements in the Yoltaic pile, is, that in the latter the 
 increase of number affects only the tension of the current, but leaves 
 the quantity the same as the single couple ; but, in the thermo-electric 
 pile, although the intensity is increased, yet the quantity which passes 
 in the current is augmented also. 
 
 It is this principle which has been applied by Nobili to the construc- 
 tion of the thermo-multiplier, or thermo-electroscope, used by Melloni 
 and Forbes, in their researches on radiant heat, of which a sketch has 
 been given in the last chapter. The thermoscope consists of fifty small 
 bars of bismuth and antimony, placed parallel beside one another, and 
 forming a single prismatic bundle, F, E', about \\ inch long and } inch 
 
 square in section. The two terminal faces are blackened. The bars of 
 bismuth, which are arranged alternately with those of antimony, are 
 soldered at their extremities, and are separated all through their length by 
 an insulating substance. To the first and last bars are attached copper 
 wires, which terminate in the pins c c, of the same metal, passing 
 across a piece of ivory fixed on the ring A A. The space between the 
 interior of this ring and the elements of the pile is filled by insulating 
 material. The free extremities of the two wires are put in communi- 
 cation with the terminal wires of a magnetic galvanometer, the needle 
 of which indicates, by its motions, when the temperature of the anterior 
 surface of the thermo-electric pile is raised or lowered, in comparison 
 to that of the posterior surface. See p. in figure, page 126. 
 
 By means of a jointed support, the axis of the pile may be turned 
 in any direction that may be wished ; and to protect its surface from 
 lateral radiation, the metallic tubes, B B, brilliant externally and black- 
 ened on the inside, are attached to the extremities of the ring A A. 
 
 If by changing through one degree the temperature of a single sol- 
 dering, a current of a certain power be obtained, there should be with 
 fifty solderings a current fifty times as strong ; or an equal current 
 when the temperature of the solderings varied through one-fiftieth of a 
 degree. It has been ascertained, that instruments of this kind may 
 be made to indicate a variation of temperature of y^ff f a degree on 
 Fahrenheit's scale. 
 
 The electricity which is thus evolved by change of temperature in 
 
Magnetism a "Form of Electricity. 185 
 
 conducting bodies, although so feeble in quantity and intensity as to be 
 utterly devoid of those brilliant qualities which attach so much popularity 
 to the phenomena of Galvanism and of friction electricity, has thus 
 been found the means of assigning the true laws of some of the most 
 interesting and important branches of the physical sciences ; and it will 
 be hereafter seen that thermo-electric currents excited in the superficial 
 stratum of the globe, by the inequality of temperature which arises 
 from the action of the sun, may generate not only the magnetic pro- 
 perties, on which are founded the commercial intercourse of civilized 
 nations, but by influencing the amnitary powers of the elementary con- 
 stituents of our planet, may have been the agent in silently, but effec- 
 tively, regulating the constitution of inorganic nature. 
 
 Magnetic Electricity. The properties which are now known as mag- 
 netic, were first recognized in a peculiar ore of iron, found in the 
 vicinity of the town Magnesia, in Asia Minor, from which the names 
 of the substance and of the science have been derived. The native 
 magnetic ore or loadstone consists of iron and oxygen. This mineral, 
 although quite inert with regard to all other bodies, attracts iron and 
 steel with great power ; and the pieces of iron and steel, whilst in con- 
 tact with the loadstone, participate in its powers, and are capable of 
 attracting other pieces to themselves. Iron and steel, though both 
 attracted by the magnet, differ remarkably in the fact, that iron, al- 
 though magnetic whilst in contact with the loadstone, loses all its pro- 
 perties when it is removed ; whilst steel, which is at first attracted with 
 inferior power, when it has become magnetic by contact with the mine- 
 ral, retains that condition after separation, and thus becomes a perma- 
 nent artificial magnet. A steel magnet thus formed, may in its turn be 
 used in place of a loadstone to form others ; and almost all the mag- 
 nets we employ in experiments have thus obtained their power, as native 
 loadstone is not found in sufficient quantity, or sufficiently intense in 
 action, for our purposes. The steel bars which are magnetized are 
 generally straight, but often also bent in the centre, so that the halves 
 are nearly parallel, and are then called horse-shoe magnets. 
 
 When a magnetic bar is dusted over with iron filings, it will be found 
 that the filings attach themselves to the extremities of the bar, and 
 
 scarcely at all to the centre ; the magnetic 
 power is thus seen to exist only near the 
 ends of the bar. Each filing being itself 
 for the time a magnet, attracts others, so that they form strings, which 
 arrange themselves according to definite laws in a form which is termed 
 that of the magnetic curves ; and from the disposition of these curves, 
 it is evident that the action of the magnet emanates from a single 
 
186 
 
 Magnetic Properties of Iron and Steel. 
 
 point, p, near each extremity : these points being the centres of 
 
 action of the magnet are termed 
 its poles. Thus, in the figure 
 the bar being a magnet, the 
 points P and p are the poles, 
 and the directions of attractive 
 force are indicated by the di- 
 verging lines, which, uniting on 
 the other side, form the mag- 
 netic curves. 
 
 The utility of the magnet in navigation is well known; it arises 
 from the poles of the magnet being attracted by the earth in such a 
 way, that when free to move, the magnet rests in a direction nearly 
 north and south : the pole of the magnet which is turned to the north, 
 is termed the north pole, the other, the south pole. If two magnets be 
 brought into the neighbourhood of one another, they do not attract in- 
 differently, as either would attract a mass of iron ; but the north pole 
 of one magnet attracts the south pole of the other, and is attracted by 
 it, whilst the north poles of the two, or the south poles, if brought near 
 each other, repel as powerfully. In magnets, therefore, poles of the 
 same name repel, and poles of opposite names attract, a condition pre- 
 cisely similar to that which holds between the electricities evolved by 
 friction. In magnetism also the attractions and repulsions follow the 
 law of the inverse square of the distance, and thus complete the super- 
 ficial analogy which led astray for so many years the investigators of this 
 branch of science. 
 
 The action of the earth upon magnets at its surface, can only be ex- 
 plained by supposing the earth itself to possess magnetic properties. 
 The northern portions of the earth attract the north pole of a magnet, 
 and must, therefore, possess southern polarity ; the southern portions 
 of the earth attracting the south pole of the magnet must possess 
 northern polarity. The action of the earth cannot be explained, how- 
 ever, by supposing it to be a simple magnet with a pole at each extre- 
 mity. It possesses two centres of force, or poles, in the north, one in 
 Siberia and one in North America, whilst the distribution of magnetic 
 force in the southern hemisphere has been found by Eoss most probably 
 due to the action of one pole. These centres themselves are, however, 
 not fixed ; the needle is continually changing in direction ; at present it 
 points to 24 west of north ; but in the year 1664, it pointed to the 
 north, and it had previously pointed in an easterly direction, towards 
 which it is now returning. 
 
 Prior to the discovery, by Ampere, of the true nature of magnetic 
 
Intimate Structure of Magnets. 187 
 
 phenomena, a theory similar for the most part to that of the two elec- 
 trical fluids was maintained, two magnetisms were supposed to exist, 
 the particles of the same fluid repelling each other, but the particles of 
 one fluid attracting those of the other. The assumption of magnetic 
 properties by a piece of iron or steel in contact with a magnet, became 
 therefore, a phenomenon of induction similar to that described under 
 the head of statical electricity, the constitution of iron being such that 
 the fluids recombined on the disturbing cause being removed ; the con- 
 stitution of steel, on the contrary, preventing their reunion. There ex- 
 isted, however, one great difference between a magnetic bar and a body 
 excited by induction with machine electricity. If the bar A, c, B, ex- 
 A c B cited by induction, and of which the portion 
 
 ( [ ~) A is positive, and B negative, the middle c being 
 
 /\ ^ J\^ neutral, be cut in two at c, the portions A and 
 A B B retain their peculiar states, one positive and 
 
 the other negative. But if the magnetic bar, 
 A, c, B, be broken across at the neutral portion 
 c, then each half becomes a perfect magnet of 
 |^ half the strength of the entire ; the points c', 
 and c", which had been neutral, acquire mag- 
 netic power; and if these portions be again 
 broken, each fragment is still a perfect magnet. 
 Magnetism belongs, in this way, to the inmost particles of the body, and 
 in the general mass each magnetic molecule is still active and indepen- 
 dent; a magnet resembles, therefore, an exceedingly bad conductor, 
 which has been inductively excited by common electricity, and the par- 
 ticles of which retain for an indefinite length of time their state of polar 
 excitation. 
 
 In order to understand the real nature of magnetic action, we must 
 free ourselves, however, from all these analogies to machine electricity, 
 no matter how well grounded they may appear to be, when superficially 
 examined. The electricity of the magnet is constantly circulating, and 
 it possesses so little tension, that it never leaves the magnetic element, 
 or molecule of iron or steel, in which it has its origin ; in fact, every 
 current of electricity possesses magnetic properties, and simulates the 
 action of a magnet situated transversely to it. Thus, if a needle be 
 held transversely on a wire carrying an electric current, it becomes mag- 
 netic, precisely as if it had been laid parallel to a magnet ; and by bend- 
 ing the wire round, so as to form a coil, the magnetism which it con- 
 fers being increased in proportion to the number of turns, may be ren- 
 dered so intense, as to surpass that of the most powerful steel magnets 
 that are made. In fig. 1, a small coil is represented, by which mag- 
 
188 
 
 Magnetic Properties of a Galvanic Current. 
 
 Fig. 1. 
 
 netisin is conferred upon the bar of steel inside. And in fig. 2, a 
 
 large horseshoe, of soft iron, by 
 being covered by a helix of many 
 hundred turns, may become able 
 to raise a weight of some hun- 
 dreds of pounds, by the magnetism 
 it acquires. 
 
 The coil of wire carrying the current may be shown, also, to possess 
 magnetic properties, by its attractive and repulsive action on a magnet. 
 A coil, as in fig. 3, suspended so as to be able to move freely, is attracted 
 and repelled by the poles of a magnet, precisely as if it also had a mag- 
 netic pole at each end. A flat coil, as fig. 4, is also found to be mag- 
 netic, the poles being indefinitely near each other at the centre of the 
 coil. A beautiful form of the experiment consists in a long wire, which 
 is made into a close coil, and connected at the ends with a pair of 
 
 Fig. 2. 
 
 Fig. 3. 
 
 Fig. 4. 
 
 little plates of zinc and copper, as in Tig. 5. On placing this system, 
 buoyed by a piece of cork, in a dish of acidulated water, it settles itself 
 at right angles to the direction of the magnetic needle, and behaves in 
 all respects like a magnet situated in the centre of the coil, and perpen- 
 dicular to its plane. 
 
 It is now necessary to examine into the relation which the direction 
 of the current bears to the poles of the magnets which it forms, or which 
 it might represent in action. If A, B, be a wire, in which a cur- 
 rent is descending, as marked by the arrow, and that a needle, 
 i | i N s, is placed transverse to it, the right-hand end of the needle, 
 s I N becomes the north, and left-hand end of the needle, the south 
 B pole ; if the direction of the current be reversed, the north pole 
 is formed at the left. In a circular current, the position of the pole 
 may be, consequently, easily seen ; the current A B, which descends in 
 
Attraction and Repulsion of Currents. 189 
 
 front of, and ascends behind the needle, produces in the bar, 
 N s, a northern polarity to the right, and a southern to the 
 s \J, ** left ; the action of magnetic currents upon each other, sup- 
 plies the explanation of these phenomena. If two wires, 
 carrying Galvanic currents, be brought near each other, there is attrac- 
 tion or repulsion, according to the direction of the currents ; if two cur- 
 rents be in the same direction, the wires attract ; if in opposite direc- 
 | | tions, the wires repel each other. The cause is evident, on 
 r-j-i rfe inspecting the figure : the upper arrows being wires which 
 8 t t * carry currents in the same direction, they act on each other, 
 as should a pair of magnets, placed transverse to their direc- 
 tion ; the ends of the magnets which are juxtaposed, have 
 5 opposite polarities, and attract ; whilst in the lower arrows, 
 where the currents are in opposite directions, the effect is the 
 same as should result from the magnets of which the contiguous poles 
 are of the same name, and hence repulsion. 
 
 A wire carrying an electric current being thus a magnet, it acts upon 
 permanent magnets, attracting or repelling, according to its position, 
 and generally, from the combination of the two forces, generating very 
 complex and singular motions. These actions have been so minutely 
 and so extensively studied, as to constitute a distinct branch of this de- 
 partment of science termed electro-magnetism j but being unimportant 
 in detail, except in physical relations, I shall only notice the experiments 
 by which CEersted first created this branch of science, and which have 
 ultimately led to one of the best measures of electricity, the multiplying 
 galvanometer. 
 
 If a Galvanic current be passed over a magnet in the direction of 
 the arrow in the figure, and that the needle be moveable on its centre, 
 
 it endeavours to assume a position such 
 as will bring it parallel, and with opposite 
 poles presented to the magnet which the 
 wire represents ; and hence in the figure 
 the motion should be to bring the south 
 pole above the plane of the paper, and to 
 depress the north pole below it, until the needle had assumed a position 
 perpendicular to the conducting wire. If the current had been in the 
 opposite direction, the action should have been reversed, and the north 
 pole should have been turned up from the paper, but if the current be 
 reversed at the same time that it is brought under the needle as in the 
 figure, it causes a deflection similar to that of the superior portion, and 
 hence the angle through which the needle moves is much increased. If 
 the needle were affected only by the current passing over or under it, its 
 
190 Action of a Galvanic Current on a Magnet. 
 
 ultimate position should be, in all cases, at right angles to the current, 
 but as the magnetic action of the earth tends constantly to bring it back 
 to its direction of north and south, the position which it ultimately as- 
 sumes is the resultant of the two forces. 
 
 The deflection of the needle being thus an indication of the passage 
 of an electric current through the wire, it is desirable in practice to give 
 the power of the current as much effect as possible, and at the same 
 time to diminish as much as can be done the action of the terrestrial 
 magnetism. The first is effected easily by increasing to the desired de- 
 gree the number of turns which the wire makes round the needle, for 
 the total effect, as will easily be understood from the description of the 
 figure above, is proportional to the number of coils ; but the diminution 
 of the effect of the earth upon the needle requires some more care. If 
 the needle be made but feebly magnetic, the power of the current to 
 turn it diminishes just as much as the power of the earth to prevent its 
 turning, and there is hence nothing gained, but the object is effected by 
 using a combination of two, three, or four powerful needles so arranged, 
 that with regard to the earth they are made to represent one very feeble 
 needle. Thus, in the figure, the three magnets N and s, being suspended 
 with their opposite poles next one another, act 
 on each other so powerfully, that the remote 
 and weaker opposing action of the earth be- 
 comes almost insensible. A current passing 
 in the direction of the arrows c, E, D, will tend 
 to depress the north poles of the upper and 
 lower, and the south pole of the middle needle below the plane of the 
 paper, and when it passes under the middle needle, its action upon it 
 will be the same, since its direction is reversed. The amount of deflec- 
 tion of such a system of needles will still be regulated by residual ter- 
 restrial influence, but as this may be rendered as small as may be wished, 
 the delicacy of the apparatus may be increased without limit. It is not 
 desirable that the system of needles should be completely astatic, that is, 
 indifferent to the earth, for then the degree of deflection by a given 
 current should be affected by trivial and accidental causes; but by 
 leaving a small residue of terrestrial magnetic effect, the current acts 
 against this, and thus produces a deflection subject to an assignable law, 
 by which the strength of the current may be determined. Within a 
 certain limit, about 30, the angle of deflection is proportional to the 
 quantity of electricity flowing along the wire, but beyond that it follows 
 a more complicated law, which, as involving mathematical relations, I 
 shall not admit here. To obtain a greater degree of delicacy and uni- 
 formity of action, the system of needles is in all good instruments hung 
 
Construction of the Galvanometer. 
 
 191 
 
 by a thread of glass or of silk, like the beam of Coulomb's balance (page 
 147). The deflecting force then acts against the force of torsion, and 
 the resistance to be overcome is reduced to its simplest possible con- 
 ditions. 
 
 M 
 
 The galvanometer, such as with the thermo-pile, constitutes the 
 thermo-multiplier, is represented in section and in perspective, in the 
 above figures ; the same letters apply to both. A, B, c, is the frame 
 around which the copper wire is coiled, the ends T of which terminate 
 in the metallic tubes F, F'. This frame is fixed on a horizontal plate D, 
 E, which can turn in its own plane around its centre, by means of a 
 toothed- wheel and endless screw, which is put in motion by the button 
 G. Q, M, N, is the support of the astatic system of two magnetic needles, 
 suspended to a thread of cocoon-silk, v, L. R s is the glass cylinder* 
 secured by brass rings P, s, y, z, which covers the apparatus, and rests 
 on the base K, I. A graduated semicircle, accurately divided, is drawn 
 upon the card, and by means of the supporting screws, and the move- 
 ment of the frame A, B, c, the upper needle is brought to be exactly 
 parallel to the coils, and to point to the commencement of the scale, 
 being regulated in its height by means of the screw x, with which the 
 silk thread is in connexion. 
 
 Where the current to be measured by the Galvanometer is derived 
 from a thermo-electric combination, it is necessary that the wire should 
 be much thicker than for a similar current from a hydro-electric source, 
 as the low intensity of the fluid thrown into motion by heat might cause 
 
192 Diamagnetism of Bodies. 
 
 false indications of its quantity, unless an ample path were opened 
 through the best conductors for it ; the number of coils for a thermo- 
 electric galvanometer should also, for the same reason, be few as possible. 
 It is, therefore, not usual to employ the same instrument for these two 
 kinds of researches. The position of the galvanometer in employing the 
 thermo-electric pile in the researches on radiant heat, has been described, 
 page 126, and its use in measuring the quantity of electricity flowing 
 from galvanic sources, which has been already partly noticed, will be 
 further described in a future place. 
 
 The passage of an electric current in the vicinity of any substance 
 capable of assuming magnetic properties is thus, by what has been said, 
 shown to be sufficient for their excitation, and conversely if a magnet, 
 whether permanent or temporarily produced, be brought near a substance 
 through which an electric current may circulate, a current is immediately 
 formed, the direction of which is always the same as that of a pre-exist- 
 ing current which would have conferred on the magnet the properties 
 which it actually has. In like manner one current may generate another 
 in a closed conductor near it, precisely as one magnet may produce ano- 
 ther, or that a body statically excited may induce the electric condition 
 on the bodies in its neighbourhood ; but such peculiar influences are too 
 far removed from the proper domain of chemistry to justify any detailed 
 description of them here. 
 
 The recent investigations of Faraday have proved that the magnetic 
 force, although most remarkably shown in its relations to iron and some 
 other metals, does really exert a much more general influence, and that 
 whilst a limited class of bodies are magnetic, a much larger class, and, 
 indeed, probably all bodies, are what he terms diamagnetic. It would 
 appear that most solid and liquid bodies are repelled by the poles of a 
 magnet, and tend to settle themselves with their longest dimensions trans- 
 verse to the line joining the poles, and hence, that in reference to the 
 earth's magnetism, that all liquid and solid bodies would tend naturally 
 to settle themselves east and west, as a magnetic needle settles itself in 
 a north and south direction. 
 
 In air and gases the diamagnetic properties appear much less deve- 
 loped, possibly owing to their want of mass ; but certainly it is shown 
 that the magnetic action is not limited to the small number of metals, 
 of which iron is the most important, but that it manifests itself, al- 
 though in an opposite manner, on every kind of substance, especially 
 those having the liquid or solid form. 
 
 In concluding this section of the subject of electricity, it is, however, 
 important to prevent its being supposed, that, by the omission of the 
 considerations of its purely physical influences which lie apart from the 
 
Rotation of the Earth a source of Currents. 193 
 
 proper chemical subjects of this work, they are to be considered as of 
 inferior interest in the phenomena of nature. It is so much the re- 
 verse, that, perhaps, one of the most active sources of the electricity 
 which we shall find to play a most important part in chemical com- 
 bination, is derived from the induction of the magnetic influence of the 
 earth itself; for the earth being rendered magnetic, by means of the 
 thermo-electric currents which circulate around it, spirally from the 
 equator to the poles, it is sufficient to bend a bit of copper wire into a 
 ring and whirl it round the finger, in the plane of the magnetic equator, 
 to obtain a current through the wire. A disk of copper revolving in 
 this plane is a source of electricity derived from the inductive influence 
 of the earth, differing, indeed, amazingly from the brilliant excitation of 
 the thunder cloud, but far surpassing it in real power of effect, and in 
 the quantity of the electric fluid actually brought into play. We arrive 
 here, indeed, at the extreme modification of this active and omnipresent 
 force : we found it in the commencement, though existing in exceed- 
 ingly small quantity, preservable only by the very best insulating means, 
 and manifesting its tendency to escape, by the attractions, the flashes, 
 the mechanical violence which characterize machine electricity ; whilst 
 in the form of magnetism, or of a magneto-electric current, though 
 present in a quantity many millions of times greater, it flows uniformly, 
 and almost insensibly along the perfect conductors through which alone 
 it is competent to pass, and it requires particular care to succeed in 
 demonstrating its heating, its luminous, or its mechanical effects ; but 
 we recognise in it, nevertheless, the untiring agent by which the inor- 
 ganic superstructure of the habitable globe has been produced, by which 
 the depositories of the most important metals in the clefts of rocks have 
 been accumulated, and which being thus the safeguard of navigation, 
 the source of all metallurgic industry becomes not less important to the 
 civilization of mankind at large, than it is found, from its paramount 
 influence on chemical affinity, its power to separate those elements most 
 intimately joined, and to effect the union of those which appear most 
 adverse to mutual combination, as well as the facility with which its 
 principles may be applied to the explanation of the laws of chemical 
 phenomena, to be available in the hands of the philosopher for the ad- 
 vancement of science. 
 
 The physical influences of electricity, however, do not even limit 
 themselves to the production of heat, of chemical decomposition and of 
 magnetism, but we are enabled to induce such molecular actions in 
 transparent bodies, as confer upon them totally new optical properties. 
 These have been partly noticed, page (47). If a ray of polarized light 
 pass through a piece of glass, placed between the poles of a magnet, or 
 13 
 
194 Principles of Nomenclature. 
 
 round which a current of electricity is made to pass, the glass acquires 
 the power of causing the plane of polarization of the ray to revolve 
 through an angle which is proportional to the intensity of the current, 
 and is towards the direction in which the current moves. By this re- 
 sult it is fully shown that the molecules of any substance carrying a 
 galvanic current tend to assume a form of molecular arrangement due to 
 the action of the current, and this molecular arrangement even extends 
 to the non-conducting substances in whose vicinity the current passes. 
 To the chemist, therefore, the most useful property of electricity is 
 the power which it possesses of modifying, annulling, or superseding 
 chemical affinity. I have hitherto avoided as much as possible in- 
 volving any idea of chemical decomposition in the account of electricity 
 just given, restricting myself to narrate such circumstances as might 
 serve for the recognition of bodies by means of their electrical pro- 
 perties, independent of their chemical construction. But the question 
 of whether electrical influence and affinity are identical, or what are 
 their exact relations, and the discussion of the theory of electro-che- 
 mical combination, still remain, and will be examined when, first, the 
 nature of affinity and the distinction between it and the action of co- 
 hesive force has been described, and the general system of nomenclature 
 according to which chemical substances are designated shall have been 
 briefly noticed. 
 
 CHAPTER V. 
 
 OF CHEMICAL NOMENCLATURE. 
 
 THE general properties and laws of the physical agents, cohesion, light, 
 heat, and electricity, have been now described so far as was necessary, 
 that we may avail ourselves of those properties in characterizing the 
 substances, elementary or compound, whose more peculiarly chemical 
 relations we shall now proceed to study ; it is necessary to prefix to the 
 description of the forces by which chemical union is effected, and of the 
 laws by which it is controlled, a short statement of the principles upon 
 which the names of the substances to which there will be frequent oc- 
 casion to refer, have been constructed. 
 
General Rules of the Lavoisierian Nomenclature. 
 
 195 
 
 There are at present known sixty-two substances, which the chemist 
 has not been as yet able to separate into other elements. These are 
 distinguished by the following names : 
 
 Oxygen, 
 
 
 
 Lithium, 
 
 Li 
 
 Tungsten, 
 
 W 
 
 Hydrogen, 
 
 H 
 
 Barium, 
 
 Ba 
 
 Molybdenum, 
 
 Mo 
 
 Nitrogen, 
 
 N 
 
 Strontium,. 
 
 Sr 
 
 Tantalum, 
 
 Ta 
 
 Carbon, 
 
 C 
 
 Calcium, 
 
 Ca 
 
 Terbium, 
 
 Te 
 
 Boron, 
 
 B 
 
 Magnesium, 
 
 Mg 
 
 Erbium, 
 
 Er 
 
 Silicon, 
 
 Si 
 
 Aluminum, 
 
 Al 
 
 Chromium, 
 
 Cr 
 
 Sulphur, 
 
 S 
 
 Glucinum, 
 
 G 
 
 Vanadium, 
 
 V 
 
 Selenium, 
 
 Se 
 
 Zirconium, 
 
 Zr 
 
 Uranium, 
 
 U 
 
 Phosphorus, 
 
 P 
 
 Thorium, 
 
 Th 
 
 Gold, 
 
 Au 
 
 Chlorine, 
 
 Cl 
 
 Yttrium, 
 
 -VT 
 
 Iridium, 
 
 Ir 
 
 Iodine, 
 Bromine, 
 
 I 
 Br 
 
 Didymium, 
 Cerium, 
 
 D 
 Ce 
 
 Osmium, 
 Platinum, 
 
 Os 
 PI 
 
 Fluorine, 
 
 F 
 
 Niobium, 
 
 Nb 
 
 Tin, 
 
 Sn 
 
 Tellurium, 
 
 Te 
 
 Pelopium, 
 
 Pe 
 
 Lead, 
 
 Pb 
 
 Mercury, 
 
 Hg 
 
 Lanthanum, 
 
 Ln 
 
 Bismuth, 
 
 Bi 
 
 Zinc, 
 
 Zn 
 
 Manganese, 
 
 Mn 
 
 Silver, 
 
 Ag 
 
 Cadmium, 
 
 Cd 
 
 Iron, 
 
 Fe 
 
 Palladium, 
 
 Pd 
 
 Cobalt, 
 
 Co 
 
 Copper, 
 
 Cu 
 
 Rhodium, 
 
 R 
 
 Nickel, 
 
 Ni 
 
 Titanium, 
 
 Ti 
 
 Ruthenium, 
 
 Ru 
 
 Potassium, 
 
 K 
 
 Arsenic, 
 
 As 
 
 Ilmenium, 
 
 11 
 
 Sodium, 
 
 Na 
 
 Antimony, 
 
 Sb 
 
 
 
 By the combination of these bodies amongst each other, the various 
 substances which exist in nature are produced. 
 
 These simple bodies have been divided, from the earliest days of 
 accurate chemistry, into two classes, the metallic and the non-metallic 
 elements. The first thirteen in the list are non-metallic ; the remaining 
 bodies are metallic. It is found, however, that this division is only 
 popularly correct ; no matter how we may define a metal, we cannot 
 avoid breaking through connexions of the most intimate and important 
 kind, if we endeavour to retain the class of metals as one founded on 
 really existing chemical principles. Thus, in density of lustre, arsenic 
 and tellurium are indubitably metals, and yet if we class these bodies 
 with copper or lead, we break through all laws of chemical analogy, for, 
 in their combinations, they assimilate themselves most perfectly, one to 
 sulphur, and one to phosphorus. In selenium, also, the metallic cha- 
 racters are so feebly marked, that even did we not know that by its 
 properties it should be classed with sulphur, we could not place it as a 
 metal without great doubt. 
 
 In describing the simple bodies, I shall retain as a division the che- 
 mistry of the metals, for the classification, like all those which have 
 been long in extensive use, has in some respects much utility and truth, 
 but in cases where the study of certain bodies will be facilitated by de- 
 parting from it, I shall not hesitate to do so. In order to avoid con- 
 
196 Construction of the Names of 
 
 fusion subsequently, I shall here describe as succinctly as possible the 
 nomenclature which has been adopted in chemistry; for, in a science 
 where the multiplicity of objects to be noticed is so great, it is of the 
 highest importance that the principles upon which the names of these 
 objects are founded, should clearly be understood. 
 
 In all conditions of science, the nomenclature has been regulated by 
 the prevalent theoretical ideas of the time, and it is probably vain to 
 look for a system of names which shall tell what the bodies really are, 
 and not pretend to tell more ; for that would suppose that we knew 
 what the bodies are, whereas, in the most perfect state of science, we 
 only know what we believe them to be. Thus, when, by a mal-ap- 
 plication to chemistry of the idea of the relation of the human body 
 to its soul, all bodies were looked upon as having a volatile and a fixed, 
 an active and an inert element, the names of spirit of wine, spirit of 
 hartshorn, and spirit of salt, were invented ; at a later period, when the 
 theory of phlogiston prevailed in the minds of chemists, the spirit of 
 salt became dephlogisticated marine acid ; when the important functions 
 of oxygen were pointed out by Lavoisier, the name was in his theory 
 changed to oxymuriatic acid ; and, finally, when the present view was 
 introduced by Davy, the name hydrochloric acid became the most 
 correct. The cause of this is, that in a good system of chemical 
 nomenclature, we require two conditions which it is very difficult to 
 successfully combine ; that the name shall not only tell us that the sub- 
 stance is an independent substance, but that it shall give to us an idea 
 of its most important chemical character, its composition; thus, the 
 name prussic acid is less strictly scientific than that of hydrocyanic acid, 
 which shows that its elements are hydrogen and cyanogen ; and iron 
 pyrites gives a less perfect picture of the body it describes than the 
 words bisulphuret of iron. The necessity for indicating by the chemical 
 name of a body its chemical composition, is thus what renders chemical 
 nomenclature at once so variable and so complex, but it is also that 
 which alone enables us to connect distinct ideas with our words. 
 
 The benefit conferred upon chemistry by the nomenclature intro- 
 duced by Lavoisier and Guyton, was scarcely inferior in its importance 
 to the accurate ideas of combination in which it had its origin. The 
 removal of the unconnected and unfounded names, which had been in- 
 vented by the older chemists, and the invention of the idea that every 
 name of a compound body should express its composition, involved the 
 increase of accuracy in the minds of those chemists by whom science 
 was subsequently to be prosecuted, which may be looked upon as the 
 most fertile source of the discoveries made up to the present day. 
 
 The names most employed in chemistry, are add, base, and salt. 
 
Simple Bodies and of Primary Compounds 197 
 
 The word acid signifying originally sour, was applied to all bodies which 
 tasted like vinegar. The word base signifies any substance which, unit- 
 ing with an acid, forms a compound, of which it is the basis or founda- 
 tion, and the compound formed by their union, being generally similar 
 to common salt in superficial characters, is termed a salt. Thus oil of 
 vitriol tasting, when mixed with water, sour, is an acid ; soda is a base, 
 and when combined they form the well known salt called after Glauber, 
 who discovered it. Such are the names of those classes of bodies, the 
 discovery of which dates from a remote period. 
 
 Acting on the principle, that in naming a simple substance, the 
 name should be derived from its most characteristic property, Lavoisier 
 formed the word " oxygen" from ou& acid, and yswaw, I generate, to 
 signify the important substance, the functions of which he was the first 
 to show, and which he imagined to have the peculiar property of form- 
 ing acids. In like manner, he constructed the word "hydrogen," 
 from u5, water, and yewau, to express its most important property, of 
 being an element of water. This principle can, however, seldom be 
 rigidly acted on ; for example, oxygen is as much a water former as 
 hydrogen, and the name of oxygen itself is not without objection, as 
 the pre-eminence as acid former, which Lavoisier imagined it to possess, 
 has been latterly overthrown. In the case of simple bodies, names 
 derived from quite arbitrary sources, as tellurium, from tellus, the 
 earth ; selenium, from ffrt^vr,, the moon ; vanadium and thorium, from 
 Yanadis and Thor, deities of Scandinavian mythology ; chlorine, from 
 -X\UPOZ, yellowish green (its colour) ; and similarly iodine, from lueidys, 
 (like a violet), have a great superiority over those, which, by attempting 
 to teach more when first invented, have the disadvantage of teaching 
 falsely at a future period. 
 
 The simple bodies, combining with each other, form compound 
 bodies of the first order, or binary compounds. The names of those 
 binary compounds which contain oxygen are of two kinds, according 
 as the compound possesses acid properties or not ; if it be an acid, the 
 word acid is added to that of the other body to which the termination 
 ic is joined. Thus, the acid compound of sulphur and oxygen is sul- 
 phuric acid; the acid compound of phosphorus and oxygen is phos- 
 phoric acid. It frequently happens that the same body forms with 
 oxygen two acids, in which case, that containing most oxygen retains 
 the terminal ic, whilst that in which there is least oxygen ends in ous. 
 Thus, there is sulphurous acid, and phosphorous acid, consisting of 
 sulphur united with less oxygen than could form the sulphuric or the 
 phosphoric acids. Many bodies form, however, with oxygen more than 
 two acids, and in this case a new principle of nomenclature has been 
 
198 Construction of the Names of 
 
 introduced. The words, wo, hypo, and **& hyper, under and over, 
 are prefixed to the degrees terminating as before stated. Thus, there 
 is an acid of sulphur, containing less oxygen than the sulphurous acid, 
 and it is called hypo-sulphurous acid ; and also an acid containing more 
 oxygen than the sulphurous, but less than the sulphuric acid, this 
 might be called either hyper-sulphurous, or hypo-sulphuric add ; the 
 latter name has been universally adopted. Chlorine forms, with oxygen, 
 four acids, which are the hypo-chlorous acid, chlorous acid, chloric acid, 
 and hyper-chloric acid, or, as it is often called, substituting the shorter 
 Latin per for the Greek wg, perchloric acid. 
 
 In cases where the compound formed with oxygen is not an acid, it 
 is termed an oxide of the substance with which the oxygen is united. 
 Thus, oxide of lead, oxide of iron, oxide of copper, are respectively 
 the compounds of oxygen with lead, with iron, and with copper. In 
 many cases, where oxygen unites with bodies in more than one propor- 
 tion, one compound may be an acid and the other not. Thus, man- 
 ganese uniting with oxygen gives manganic acid and permanganic acid, 
 but in a lower degree of oxidation it forms several oxides of manganese. 
 For as a substance uniting with oxygen may form many acids, so may 
 it form many oxides also ; and in such cases, it becomes necessary to 
 distinguish them from one another. This is done by the adoption of 
 the Greek words, irgoros, dwrsgog, rgirog, (first, second, third,) prefixed 
 to the word oxide. Thus, we say, protoxide of lead, deutoxide of lead, 
 tritoxide of iron. The oxide which contains most oxygen is often called 
 the peroxide, and that which contains least the suboxide, as peroxide of 
 manganese, suboxide of copper. The word sesqui (one and a half,) is 
 also used for oxides intermediate between protoxides and deutoxides, 
 but the nomenclature then involves numerical proportions, which will 
 require to be described hereafter. 
 
 Some other simple non-metallic bodies, in combining with the metals, 
 form compounds, of which the names are constructed on the same plan 
 as those of the metallic oxides. Thus, 
 
 Chlorine forms Chlorides, 
 Iodine ,, Iodides, 
 Bromine ,, Bromides, 
 Fluorine ,, Fluorides. 
 
 The compounds of "sulphur with the metals having been popularly 
 named before Lavoisier's time, and it being desirable to retain, as much 
 as possible, the names already in common use, a different form of ter- 
 mination is adopted for that body and some others. Thus, 
 
 Sulphur gives Sulphurets, 
 Selenium ,, Seleniurets, 
 
Various Classes of Primary Compounds. 199 
 
 Tellurium Tellurets, 
 
 Carbon Carburets, 
 
 Nitrogen ,, Nitrurets, 
 
 Phosphorus Phosphurets, 
 
 Arsenic Arseniurets. 
 
 To distinguish between the different sulphurets or chlorides, &c., of 
 the same metal, the Greek prefixes are adopted as in the case of oxides. 
 We have thus, proto-chloride and deuto-chloride of manganese ; also, 
 perchlorides and subclilorides. The Latin bis is often substituted for 
 the Greek deuto, as the bichloride of tin in place of the deuto-chloride. 
 Among continental chemists, names which should be translated chlo- 
 ruret in place of chloride, and sulphide in place of sulphuret, are fre- 
 quently employed; but as these are founded on certain theoretical 
 ideas that have not been yet discussed, the propriety of adopting 
 such additional terminations cannot be considered until we have pro- 
 ceeded farther. 
 
 "Where two non-metallic bodies are united, it is a question how the 
 name of the compound should be formed. Thus, in a compound of 
 chlorine and phosphorus, should it be called chloride of phosphorus or 
 phosphuret of chlorine ? This is decided by referring to the classifica- 
 tion of the simple bodies which will be hereafter given, and which is 
 founded on a view of all their chemical properties taken together. 
 "Whichever element stands highest in the scale, gives the characteristic 
 name to the compound body. Thus, chlorine is above phosphorus, and 
 we say chloride of phosphorus. Iodine is also above phosphorus, and 
 we say iodide of phosphorus ; but iodine is below chlorine, and we hence 
 call the compound which they form, chloride of iodine. 
 
 The combination of the metals with each other, except in some pecu- 
 liar instances, are termed alloys. Thus we say brass is an alloy of 
 copper and zinc ; fusible metal is an alloy of bismuth, tin, and lead. 
 "Where one metal is mercury, the alloy is termed an amalgam of the 
 other metal ; thus, an amalgam of silver is an alloy of mercury and 
 silver ; an amalgam of tin is an alloy of mercury and tin. Arsenic 
 and tellurium are so far removed from the metals by their chemical 
 characters, that their compounds with the proper metals have the pecu- 
 liar termination of uret. 
 
 By the union of two primary compounds, there is formed a secondary 
 compound. These secondary compounds are generally termed salts. 
 The word salt is, however, applied to numerous classes of primary 
 compounds. Thus, the metallic iodides, chlorides, bromides, and fluo- 
 rides are recognized as salts. It is now also a debated question whether 
 the bodies formed by the direct union of an acid and an oxide are really 
 
00 Names of Secondary, Ternary. 
 
 primary or secondary compounds ; but I shall now describe only the 
 ordinary nomenclature of those bodies, postponing the discussion of 
 their intimate constitution to another place. When an acid and a 
 metallic oxide, both primary compounds, combine to form a secondary 
 compound or a salt, the specific name of the salt is that of the base, 
 without any change ; we thus say a salt of soda, a salt of oxide of 
 copper j the generic name is taken from the acid, the word acid being 
 omitted, and the final ic being changed into ate j or the final ous into 
 ite. There is thus formed from sulphuric acid and soda sulphate of 
 soda. Erom nitric acid and oxide of lead, nitrate of oxide of lead. 
 From sulphurous acid and potash, sulphite of potash. Erom hypochlo- 
 rous acid and lime, hypochlorite of lime. Where the salt contains an 
 oxide of one of the common metals, it is usual to suppress the words 
 of oxide in its name, and thus to say, sulphate of copper, in place of 
 sulphate of oxide of copper ; nitrate of lead, in place of nitrate of 
 oxide of lead. The strict correctness of language is thus sacrificed; 
 but, if the idea of the composition of the salt be held clearly in the 
 mind, the abbreviation is not injurious, and this mode of naming salts is 
 so universal, that breaking in on it might be productive of more injury 
 than allowing it to remain. I shall therefore say, for example, nitrate 
 of lead, understanding however, that the nitric acid is combined not 
 with lead, but with oxide of lead. 
 
 It frequently happens that a metal forming with oxygen two oxides, 
 will form with acids a class of salts for each oxide. In this case the 
 words proto, deuto, sesqui, or per, by which the oxides are distinguished 
 from each other, are prefixed to the generic name of the salt. We thus say, 
 protosulphate of iron ; persulphate of iron ; indicating that there is in 
 the one salt the protoxide, and in the other the peroxide of iron. We 
 have sesqui-sulphate of manganese, and deuto-sulphate of platinum. 
 The relative quantity of acid and base being liable to variation, there 
 are acid salts with an excess of acid, and basic salts with an excess of 
 base. In such case, the proportion of acid is marked by the Latin bi, 
 ter, &c., as bisulphate of potash, and the proportion of base where it is 
 in excess by the Greek &$, rp$, &c., as di-sulphate of zinc, tri-sulphate 
 of mercury ; or still better by the words bi-basic, tri-basic, &c., to in- 
 dicate the quantity of base ; there is thus tribasic-sulphate of mercury, 
 quadribasic-sulphate of copper, and so on. 
 
 There are many other kinds of secondary compounds than the salts 
 just noticed. Thus, water enters into numerous compounds which are 
 called hydrates. This water may act in very different capacities, and 
 its nomenclature must be varied accordingly, as shall be seen under its 
 proper head j but where we wish to indicate that a body contains water, 
 
And Quaternary Compounds. 201 
 
 without determining more nearly the specific function of the water, we 
 describe the body as being hydrated. 
 
 Oxides and chlorides combine together to form secondary compounds, 
 which are called oxychlorides, as the oxychlorides of mercury, the oxy- 
 chloride of lead. Oxides and sulphurets combining form oxy sulphurets, 
 as oxy sulphuret of antimony. Chlorides and sulphurets form by their 
 union chloro-sulphurets, as chloro-sulphuret of mercury. 
 
 "When two chlorides combine, the compound is termed a double 
 chloride, or a chloride of the metals ; as the chloride of gold and so- 
 dium, the chloride of copper and potassium. In the same way there 
 are double iodides and double bromides. But where two sulphurets 
 unite, the nomenclature has received an important change. 
 
 Berzelius has proved that in very numerous cases where a body forms 
 an acid with oxygen, which acid uniting with a metallic oxide forms a 
 salt ; that body uniting also with sulphur, gives a sulphur acid, which may 
 combine with a sulphuret of a basic metal, (a sulphur base,) to form what 
 he terms a sulphur salt. Thus double sulphurets are salts, consisting of a 
 sulphur acid united to a sulphur base. Hence, as arsenic combining 
 with oxygen forms arsenious acid, so uniting with sulphur it produces 
 sulpho-arsenious acid, which uniting with sulphuret of lead, forms 
 sulpharsenite of lead, precisely as the oxygen acid, uniting with oxide 
 of lead, produces what should be called oxyarsenite of lead. The pre- 
 fix oxy, is, however, not used; the ordinary salts are supposed to con- 
 tain the oxygen acid, and it is only where a salt does not contain an 
 oxygen acid, that an additional word is necessary to point out what sort 
 of acid it does contain. Tellurium and selenium act like sulphur ; 
 there are tellurium acids and tellurium bases, selenium acids aud sele- 
 nium bases, and hence in place of caning the compound of seleniuret 
 of antimony, and seleniuret of sodium, a double seleniuret, it is called 
 the selenio-stibiate of sodium. 
 
 An attempt was made to assimilate the nomenclature of chlorine and 
 iodine bodies to that of the oxygen and sulphur compounds ; thus, to 
 call chloride of mercury a chlorine acid, and chloride of sodium a 
 chlorine base, and the compound which they form, a chlorine salt, 
 chlorohydrar gyrate of sodium. This idea, however, has not been re- 
 ceived into science, for, indeed, the precisely contrary ideas are now 
 most popular among chemists, and in place of assimilating the double 
 chlorides to ordinary oxygen salts, there is a general tendency to class 
 the ordinary salts along with the simple chlorides. 
 
 Ternary compounds are formed by the union of two secondary com- 
 pounds. Thus, dry alum is a compound of sulphate of potash and sul- 
 phate of alumina. Compounds of this order seldom exist in more 
 
202 Names of Organic Bodies. 
 
 than one proportion. Alum combining with water to produce the 
 crystallized alum, generates a quaternary compound, and even more 
 complicated stages may be attain ed, but they are so rare, and of so 
 little scientific importance, that they do not require notice here. 
 
 In organic chemistry, the principles of the nomenclature employed have 
 been, for the most part, identical with those now stated ; but it is only 
 to those simpler organic compounds, which resemble in constitution 
 mineral bodies, that this nomenclature can be applied. 
 
 In fact, the great variety and complexity of the chemical substances 
 which the progress of organic chemistry has recently made known, and 
 the peculiarity of the laws of organic combination and decomposition, 
 have rendered it necessary, for the further advance of science, that 
 some new system of nomenclature should be adopted by chemists. In 
 organic substances there does not at all prevail the simple system of 
 binary union, by which most of the relations of mineral substances, can 
 be explained. The facts of Isomerism, and of typic substitutions, can- 
 not be comprised in the forms of expression which the nomenclature of 
 Guyton employs, or in the principle on which it is founded, nor can our 
 ideas of the nature of the forces which produce chemical action be ac- 
 curately described upon the now antiquated system. 
 
 Hence, many chemists have proposed novel plans of nomenclature, 
 but those only which deserve mention are that by Laurent, and the gene- 
 ralization of it lately proposed and employed by Leopold Gmelin. 
 
 Laurent's nomenclature was invented for the purpose of indicating 
 the nature of the numerous organic bodies derived by the action of 
 chlorine from napthene. He proposed to indicate those derived bodies 
 as a class, by altering the terminal ne, which marks a carbo-hydrogen, 
 into se, and to indicate the degree of replacement of hydrogen by an- 
 other body, by the vowel which precedes the se in the word. Thus 
 napthene, being C 20 H 8 , there is produced by the agency of chlorine, 
 
 Chlor-napthose, Cao H 4 CU 
 Chlor-napthuse, Cao Ha Cls 
 Chlor-napthalase, C2o H<> Cl6 
 
 Chlor-napthase, Cao H 7 Cl 
 Chlor-napthese, Cao He Cla 
 Chlor-napthise, Cao H 5 Cla 
 
 It will be seen, that when the five vowels are exhausted, the series 
 recommences with the syllable al before the vowel. In this manner an 
 indefinitely great number of modifications can be made. 
 
 GmehVs proposed nomenclature, which embraces Laurent's plan of 
 vowels, would extend, however, to the entire of chemistry, and conse- 
 quently displace altogether that which has been so long employed, and 
 been found of such utility in mineral chemistry. He proposes totally 
 new names for all the simple bodies, and new modes of uniting them. 
 
Symbolical Nomenclature. 203 
 
 Thus, sulphate of barytes should be baran-afin, nitrate of silver should 
 be targan-atan. These barbarous expressions have no likelihood of being 
 used in any ordinary chemical descriptions, and I consequently do not 
 think it necessary to describe his nomenclature more fully in this ele- 
 mentary work. 
 
 Under these circumstances it has become most useful in practice to 
 employ rather a symbolical than a verbal nomenclature, and certainly 
 there has been no step recently made that conferred more definiteness 
 and clearness of expression on the language of science than the system 
 of chemical symbols proposed by Berzelius, and now universally em- 
 ployed. By it, in place of using an arbitrary and probably unmeaning 
 word, we write the symbols of its constituents, which of themselves, 
 in most cases, exhibit important facts in its history and properties. 
 
 In the list of the simple bodies in page 195, the name of each sub- 
 stance is accompanied by its symbol, which is generally the initial letter 
 of its Latin name ; and in cases where the name of more than one 
 body begins with the same letter, they are distinguished by adding to 
 the symbols, of all the bodies but one, a second letter in smaller type, 
 which may be the second letter of the word, or whatever letter will 
 best serve to characterize the name. 
 
 If there be but one non-metallic substance in the group, it is gene- 
 rally selected to be denoted by the single letter, as, C. and P. for car- 
 bon and phosphorus, whilst the metals, whose symbols have the same 
 letter, are denoted by Ca. Co. Cd. Ce. and PI. Pb. Pd. Where there 
 are more than one non-metallic body commencing with the same letter, 
 it is a matter of indifference which is designated by the one or by the 
 two, but the single letter is generally attached to the body which is of 
 most importance in chemical phenomena. Thus, S. is sulphur, whilst 
 Si. and Se. denote silicon and selenium respectively. 
 
 The symbols of compound bodies are constructed by grouping to- 
 gether the symbols of their constituents ; thus, Pb.O. represents a com- 
 pound of oxygen and lead ; C.H. N.O. a compound of carbon, hydro- 
 gen, nitrogen, and oxygen. The algebraic sign of addition is frequently 
 used to connect symbols, as, Cl + S chloride of sulphur, I +K iodide 
 of potassium. But I shall use that sign only where I wish to express 
 that the bodies so connected are united by an inferior degree of affinity ; 
 thus, Cl.Ca. is chloride of calcium dry, but when crystallized, it becomes 
 Cl.Ca. -f- 6H.O. in which the + sign is used to show that the water is 
 united with the Ca. Cl. by a power distinct from, and inferior to, that 
 which retains Ca. and Cl. in combination. Water thus combined is 
 often represented by the symbol Aq. : for water is capable of acting in a 
 variety of ways in combination, and, as will be shown when we come to 
 
204 Nature of Chemical Affinity. 
 
 speak of the chemical relations of water, it requires to be expressed 
 sometimes as H.O. and sometimes as Aq. 
 
 But that which requires special notice, in speaking of symbolical 
 nomenclature, is, that it involves essentially the idea of numerical re- 
 lations. Thus, the symbols Pb. or Cu. do not call up to the mind of 
 the chemist the simple ideas of lead or copper, but of a quantity of 
 lead, and of a quantity of copper, in the proportion of 103'6 and 31*7 
 which is termed an equivalent of each. Thus, also, the Symbol PbO. 
 signifies not merely a compound of lead and oxygen, but specially a 
 compound of an equivalent of lead, and an equivalent of oxygen, in 
 the proportion by weight of 103*6 of lead and 8'0 of oxygen. It is 
 thus that the symbol PbO 2 , or Pb + 20, which represents also a com- 
 pound of lead with oxygen, shows to the chemist that this second body 
 contains to the same 103'6, of lead, twice as much, or 16*0 of oxygen, 
 as had existed in the former. PbO is, therefore, protoxide, and PbO 2 is 
 the deutoxide of lead. 
 
 The details of the application of those symbols involve thus the nu- 
 merical laws of constitution, which have yet to be described ; and hence 
 it is unnecessary to develope their arrangement further at present. It 
 Avas necessary to allude so far to them when speaking of nomenclature, 
 as I may have occasion to introduce some of them in a general way in 
 the next chapter. 
 
 CHAPTEE VI. 
 
 OF CHEMICAL AFFINITY, AND ITS RELATIONS TO HEAT, TO LIGHT, AND 
 
 TO COHESION. 
 
 SECTION I. 
 
 GENERAL NATURE AND RESULTS OF THE ACTION OF AFFINITY. 
 
 THE peculiar power by which we suppose chemical phenomena to be 
 produced, is specially distinguished from cohesion, and from all other 
 forces in nature, by exerting in the different kinds of elementary or 
 compound substances various degrees of energy ; and by its capability 
 of acting upon certain bodies exclusively, and in preference to acting 
 upon others, which, so far as physical circumstances go, appear equally 
 exposed to its effects. Thus, if to some liquid muriatic acid there be 
 added a mixture of lime and alumina, the lime will all dissolve in the 
 
Principles of Elective Decomposition. 205 
 
 acid, before any trace of the alumina will be taken up. If a slip of 
 iron be placed in a cup of nitric acid, a large quantity of deep red fumes 
 are immediately expelled from the acid, with an appearance of boiling or 
 effervescence ; and the iron disappears, being taken up by the liquid in 
 place of the substances which had been expelled. If a slip of copper be 
 dipped in the acid, the same effect is produced : but, if the iron and 
 copper be left together in the acid, no action takes place upon the 
 copper until the iron shall have been totally dissolved. The muriatic 
 acid, therefore, presented equally to lime and alumina, combines with 
 the lime in preference, and the nitric acid takes up copper, giving off, 
 to make room for it, a quantity of gaseous elements (nitrous acid fumes) 
 it had previously contained; but it will take iron in preference to 
 copper, if the two be presented to it at the same time. Chemical affinity 
 is, therefore, elective ; it chooses among a variety of bodies which it will 
 act upon, and is thus different from cohesion or gravity, which will act 
 upon all bodies equally exposed to their influence at the same time. 
 
 In the example of the metal and nitric acid, there is involved a second 
 phenomenon, which, equally with elective affinity, is characteristic of 
 chemical force. It is decomposition. The copper cannot dissolve in 
 the nitric acid without the expulsion of another substance. By a 
 simpler example, the decomposition may be rendered more evident. 
 Sulphuret of hydrogen, consists of sulphur and hydrogen; if it be 
 brought into contact with iodine, the iodine expels the sulphur, and 
 takes the hydrogen ; the sulphuret of hydrogen is decomposed, and a 
 new body, iodide of hydrogen, is formed. Here the hydrogen chose 
 between iodine and sulphur, and preferred the former : the greater affi- 
 nity for the iodine caused the decomposition. Hydrogen has, however, 
 a still more decided tendency to combine with chlorine ; and, if chlorine 
 be brought into contact with iodide of hydrogen, the iodine is in its 
 turn expelled, and chloride of hydrogen formed. Here is a series of 
 decompositions depending on the relative power of the affinities of 
 chlorine, iodine, and sulphur for the one body, hydrogen. Thus, by 
 the elective affinity of an uncombined body, choosing among a variety 
 of other bodies all equally uncombined, there is produced a new com- 
 bination, containing that for which its affinity was strongest. But when 
 an uncombined body is put in contact with two substances already united, 
 it tends to separate them, to combine with one and to set the other free. 
 
 If we could combine any one body, as hydrogen, for example, with 
 every other of the simple substances, we might, by such experiments as 
 those described with the sulphuret of hydrogen, iodine, and chlorine, 
 obtain an idea of the exact order of intensity of the affinity of each of 
 them for hydrogen, and could easily represent, under a tabular form, 
 
206 . Nature of Chemical Affinity. 
 
 such an idea. This has accordingly been tried, and was, indeed, the 
 result of the first sound ideas of the nature of chemical affinity 
 which were obtained. It was not done completely in any case, for even 
 at present our knowledge is not sufficient to enable us to form a series, 
 including all the simple bodies. It was particularly in the chemistry of 
 the salts that the benefit of this principle was found ; and it was to 
 explain and predict the result of the decomposition of salts that tables 
 of elective affinity were constructed. 
 
 It will be found that if lime and magnesia be placed together in 
 contact with muriatic acid, the acid will act upon the lime before it 
 acts upon the magnesia ; the affinity of lime for muriatic acid is there- 
 fore greater than that of magnesia for the same acid, and hence, if to a 
 solution of magnesia there be lime added, the magnesia will be expelled 
 and the lime will take its place. If to the solution of lime, soda be 
 added, the lime will separate, and the soda may be in turn expelled by pot- 
 ash. On the other hand, there are many metallic oxides which exert a 
 still more feeble affinity than magnesia ; thus, if to a solution containing 
 oxide of iron, magnesia be added, the oxide of iron is thrown down and 
 the magnesia taken in its place. In this manner may be arranged a 
 series of compounds, consisting of different bases, in union with the 
 same acid ; and by observing the order of decomposition by each other, 
 a view of the relative affinities which they exercise may be formed. 
 If also a series of acids be combined with the same base, a similar view 
 of their relative affinities may be drawn up. Thus, when a solution of 
 potash is exposed to the air, it absorbs carbonic acid, for which, there- 
 fore, the potash has an affinity of a certain energy ; on adding acetic 
 acid, the carbonic acid is expelled, and acetate of potash formed ; on 
 adding nitric acid, the acetic acid is expelled from it, and nitrate of pot- 
 ash formed ; and from this, by means of sulphuric acid, the nitric acid 
 may be recovered, the potash remaining in the state of sulphate. 
 
 The results so described may be exhibited as follows : by writing in a 
 column the names of the different acids, in the order of their affinities 
 for a certain base, (soda) which is placed at top. Similarly in a column, 
 at the top of which is placed the name of a given acid, the various bases 
 in the order of their affinities may be written. Thus, 
 
 Soda. Muriatic Acid. 
 Sulphuric acid. Potash. 
 
 Nitric acid. Soda. 
 
 Muriatic acid. Lime. 
 
 Acetic acid. Magnesia. 
 
 Carbonic acid. Oxide of Iron. 
 
 Eor the simple bodies similar lists might be constructed : thus, in 
 the same way as the series of affinities for hydrogen already noticed, a 
 
Order of Elective Decomposition. 207 
 
 table of affinities of the different metals for oxygen may be drawn up 
 from observation. If to a solution of nitrate of silver, in which the 
 silver is combined with oxygen, a globule of mercury be placed, |it dis- 
 solves, and the silver is set free. By dipping into the solution of nitrate 
 of mercury a slip of copper, the mercury is thrown down, and the cop- 
 per takes its place. From the nitrate of copper the metal may be thrown 
 down by lead, and the lead again precipitated by a plate of zinc. The 
 affinities of the simple bodies for each other may be therefore expres- 
 sed, taking hydrogen and oxygen as illustrations, by the following 
 columns : 
 
 Hydrogen . Oxygen . 
 
 Chlorine, Zinc, 
 
 Iodine, Lead, 
 
 Sulphur, Copper, 
 
 Mercury, 
 Silver, 
 
 in which any body in the list may expel all below it from combination, 
 and will itself be expelled by every body below which it stands. 
 
 Such is simple elective affinity ; but it often manifests itself in a 
 more complex form, as when it acts among a greater number of bodies 
 than three, and by the mutual action of two compound bodies, two 
 new ones may be formed. Thus, when nitrate of lime is decomposed 
 by potash, there is simple decomposition, and the lime is set free ; but 
 if in place of pure potash, we employ carbonate of potash, the result 
 is, the formation of carbonate of lime : for when the potash leaves the 
 carbonic acid, to go to the nitric acid, and the nitric acid leaves the 
 lime, to go to the potash, the carbonic acid and the lime, finding 
 themselves in presence of one another, unite and precipitate as car- 
 bonate of lime. The nature of the decomposition may be more clearly 
 shown from the figure : 
 
 C Nitric Acid, Potash, > 
 
 Lime, Carbonic Acid, J 
 
 The bodies existing before mixture being composed of those written 
 above one another, and those formed by decomposition consisting of 
 those which are in the same horizontal line. 
 
 This action is termed double decomposition. In the example just 
 stated, the difference between it and simple decomposition may appear 
 to have been accidental, the potash acting precisely as if it had been 
 free, and the lime and carbonic acid uniting, only because they came 
 into contact, without any other ties, and hence combined together ; but 
 the peculiarity of double decomposition is, that by means of it, reac- 
 tions may occur which could not have been produced by simple affinity, 
 and which, on the contrary, appear to have been produced in opposition 
 
208 Nature of Double Decomposition. 
 
 to it. Thus, ammonia cannot decompose nitrate of lime; on the con- 
 trary, lime will take nitric acid from ammonia ; and yet if we mix a so- 
 lution of nitrate of lime and carbonate of ammonia, they decompose 
 each other, and by double elective affinity, there are formed nitrate of 
 ammonia and carbonate of lime. As in the former diagram, the several 
 compounds, before and after mixture, are found arranged in the hori- 
 zontal and vertical lines of the diagram : 
 
 Nitrate of Ammonia. 
 
 Nitrate of Lime. { ""^ <&+*. } Carbonate f An o " i! <- 
 
 Carbonate of Lime. 
 
 In fact, in order to understand the cause of such double decomposi- 
 tion, we must take into account not merely the affinity of the ammonia 
 for the nitric acid, but that of the lime for the carbonic acid. Thus, 
 if the affinity of lime for nitric acid be represented by 80, and that of 
 ammonia for nitric acid be represented by 70, the lime will be the 
 stronger, and can, when by itself, expel ammonia ; but if the carbonic 
 acid intervene, and the affinity of lime for carbonic acid be 50, and of 
 ammonia for the same acid be 30, then decomposition must occur; for 
 the forces preventing decomposition are the affinities of nitric acid for 
 lime, and of carbonic acid for ammonia, that is, 80 + 30=: 110; 
 whilst those tending to cause decomposition are the affinities of nitric 
 acid for ammonia, and of carbonic acid for lime, =70 + 50 = 120; 
 the latter are the more powerful, and the constituents, of the two salts 
 consequently exchange places. The former affinities are termed the 
 quiescent, the latter the divellent affinities, and whenever the sum of 
 the divellent is greater than that of the quiescent affinities, decompo- 
 sition must occur. 
 
 Thus, the simple affinity of hydrogen for sulphur is much greater 
 than that of mercury for sulphur, and the affinity of mercury for chlo- 
 rine is much greater than its affinity for sulphur ; and yet, on bringing 
 chloride of mercury into contact with sulphuret of hydrogen, complete 
 decomposition ensues, chloride of hydrogen and sulphuret of mercury 
 being produced. In this case the affinity of mercury for chlorine being 
 20, and for sulphur being 10 ; the affinity of hydrogen being for sul- 
 phur 15, and for chlorine 30, the result may be shown as follows : 
 
 Chloride of Hydrogen. 
 30 
 
 Chloride of Mercury. 20 j jjjJSJ^ idtfST' } 15 Sulphuret of Hydrogen. 
 
 10 
 
 Sulphuret of Mercury. 
 
Order of Affinity not Constant. 209 
 
 the forces producing decomposition being, 30 -f 10 = 40, and greater 
 than those, 20 + 15=: 3 5, which tend to keep the elements as they 
 were. 
 
 Such are the results of chemical affinity manifesting itself in its 
 simple, and in its more complex forms ; hence there would appear to be 
 nothing more easy than to determine the scale of affinities, and to 
 construct a series of tables in which all existing substances should find 
 their place, and all possible cases of chemical decomposition might be 
 foretold with the same accuracy, as the law of gravitation allows the 
 disturbing effects of a new planet to be calculated ; but unfortunately 
 for the simplicity of expression which the laws of chemical affinity 
 should thus assume, new and unexpected complications arise and em- 
 barrass all our explanations ; thus, if we take muriatic acid and form 
 a table of the affinities of bases for it, we shall find that it is as given 
 in No. 1, and constructing for sulphuric acid an independent column, 
 we shall find it to be as in No. 2. 
 
 No. 1. Muriatic Acid. No. 2 Sulphuric Acid. 
 
 Oxide of silver. Barytes. 
 
 Potash. Strontia, 
 
 Soda. Potash. 
 
 Barytes. Soda. 
 
 Strontia. Lime. 
 
 Lime. Magnesia. 
 
 Magnesia. Oxide of silver. 
 
 Here the order is quite reversed, for oxide of silver, the strongest 
 base in one column, is the weakest in the other; and barytes and 
 strontia, which manifest the most intense affinity for sulphuric acid, are 
 found but mid-way among the bases arranged in order of strength for 
 muriatic acid. Which column must be taken as representing the true 
 order of aifinities ? What principle is there by which these conflicting 
 testimonies of experiments may be brought to correspond ? The 
 answer is, that neither table is exclusively correct; that these lists, 
 although showing the order of decomposition, and thus exhibiting to 
 the eye most usefully, the result of a great number of experiments, must 
 not be supposed as strictly showing to us the order of the affinities of 
 these bodies, unless we apply thereto a variety of corrections, arising 
 from those numerous and important causes which influence and disturb 
 the simple action of affinity, and frequently invert altogether the results, 
 which, if unimpeded, it would have produced. 
 
 For the chemical action of two bodies does not arise simply from 
 their chemical affinities, but results from the combined influences of 
 heat, electricity, cohesion, and other physical agencies, which frequently 
 14 
 
210 The Power of Affinity Influenced 
 
 modify the chemical forces to a remarkable extent. By a change of 
 temperature, an affinity originally weak may be made to preponderate 
 over one, previously much stronger; by electrical conditions, the 
 strongest and most direct chemical affinities may be overcome ; accord- 
 ing as the cohesion of the acting bodies may prevail, decompositions, 
 simple or compound, may be produced in opposite ways ; and thus a 
 chemical result is not the simple consequence of affinity, directly acting, 
 but is the resultant of a number of forces acting in different directions, 
 and with variable intensities, of which affinity is but one, although that 
 one which, for our object, is the most important. 
 
 It is indeed fortunate for the intellectual progress of mankind that it 
 is so ; for, on the variability of the intensity with which chemical affinity 
 may be exerted, depends the existence of the infinite variety of organ- 
 ized and inorganic beings which people and beautify this earth. Had 
 mere affinity been omnipotent ; had those bodies which attract each 
 other most powerfully, been in all cases able to combine, and that there 
 had been no means of dissolving their connexion when once formed : im- 
 mediately on the origin of our globe, those bodies which have the most 
 powerful affinities would have satisfied them by entering into eternal 
 union ; those next in power would subsequently have satisfied their ten- 
 dency to combine, and long since all nature should have been arranged 
 into some few chemical combinations, the breaking up of which could 
 not be accomplished by any existing force. The complex changes of 
 animal and vegetable digestion and respiration could not go on, the 
 working of the metals, the chemical arts of civilized life could not have 
 been invented, and the planet which we inhabit should have revolved in 
 space a barren and uninhabitable ball. 
 
 The action of these modifying causes may be easily exhibited by one 
 or two examples. It has been already described how a solution of mu- 
 riate of lime is decomposed by carbonate of ammonia ; carbonate of lime 
 being precipitated, and muriate of ammonia remaining in the liquor ; 
 but if, in place of bringing these substances into contact in solution, 
 they be brought to act on each other at a high temperature, the result 
 Is exactly the reverse. If muriate of ammonia and carbonate of lime be 
 heated together without water, carbonate of ammonia is found to be 
 sublimed, and muriate of lime remains behind. If watery vapour be 
 brought into contact with metallic iron heated to bright redness, it is 
 decomposed, one of its constituents, oxygen, combining with the iron, 
 the other, hydrogen, being set free ; here evidently the affinity of iron 
 for oxygen is greater than that of hydrogen. But if oxide of iron be 
 heated to redness also, and hydrogen gas be passed over it, the oxygen 
 is totally removed by the hydrogen in the state of water, and metallic 
 
By External^ Modifying Causes. 211 
 
 iron is set free ; here the order of affinity is exactly the reverse ; and we 
 shall soon discover the cause to which it must be attributed. 
 
 The philosopher who first declared that the order of decomposition 
 was not the order of affinity, and pointed out the importance of attend- 
 ing to the other forces that modify it, was led by his observations to 
 assert that the power to which we have attached so much importance, 
 elective affinity, had no real existence ; he said, that chemical union dif- 
 fered from mechanical cohesion only in being exerted between the par- 
 ticles of different substances, and that in all cases where certain bodies 
 combined in preference to others, the source was to be found in the ac- 
 cidental and external circumstances. On his ideas, the force by which 
 the particles of a fragment of sulphate of soda are united, differs from 
 the force by which the sulphuric acid is united to the soda, only in the 
 fact that the cohesion unites particles of the same kind, whilst affinity 
 unites particles of different kinds. A salt dissolved in water should 
 thus be held in solution by chemical attraction. Two pieces of lead 
 which adhere together are retained by mechanical cohesion, but if a 
 piece of lead adhere to a piece of tin, or a drop of water to a surface of 
 glass or metal, the union should be attributed to chemical affinity. It 
 will be seen hereafter, that a great deal of this peculiarity of view arose 
 from the principle of indefinite chemical combination, which although 
 supported by the amazing talents of Berthollet, has been finally and 
 totally given up. We do not now consider such phenomena as solution 
 to be produced by chemical affinity, for we require that a chemical com- 
 pound should have parted with the properties of its constituents, and 
 acquired peculiar properties of its own, in order to prove its title to the 
 name. 
 
 But it is still by no means easy to fix upon the limits, beyond which 
 the change of properties must pass. A change of state of aggregation 
 is one of the most common evidences of chemical combination, as where 
 muriatic acid and ammonia, both gases, become solid; oxygen and 
 hydrogen, both gases become liquid ; water and bichloride of tin, both 
 liquid, become solid, and innumerable other cases. The production of 
 heat, and often light, is one of the most universal attributes of chemical 
 action ; and hence for many ages the explanation of the phenomena of 
 combustion included all that was of importance in the philosophy of 
 chemistry. A change of volume is also very frequent, though not so 
 universal, and consequent on this change of volume a change, generally 
 an increase, of specific gravity of the body from the mean specific 
 gravity of its constituents; thus, when oxygen and nitrogen unite to 
 form nitrous oxide, the volume of the compound is but f of that of the 
 mixed constituents; when nitrogen and hydrogen unite to form ammonia, 
 
212 Characteristic Distinctions Between Affinity and Cohesion. 
 
 the resulting volume is but J of that of the gases mixed before combin- 
 ing; if 100 volumes of alcohol be mixed with 100 volumes of water, 
 the mixture will occupy but 196 volumes, and on mixing similar quan- 
 tities of water and oil of vitriol the resulting volume is but 185. Change 
 of colour also frequently occurs, but in all these cases, although such 
 marked results indicate an intimacy of union that can scarcely be ex- 
 plained by mere cohesion, yet other physical forces may intervene, and 
 in addition to the evidence of chemical action already stated, the most 
 important and necessary still remains, change of chemical properties. 
 
 I have, on several occasions, mentioned change of properties as cha- 
 racteristic of chemical combination, but it may be proper here to enter 
 into a few detailed examples of its nature and its source. Chemical 
 affinity is not a single force, giving to all bodies within its influence the 
 same properties, though it may be in different degrees. On the con- 
 trary, the power which confers upon bodies their chemical properties is 
 of two kinds, antagonistic to each other, and such that, by acting with 
 equal energies, their effects are mutually destroyed. Gravity, in acting 
 upon bodies, acts upon all bodies in the same manner ; the molecular 
 forces, which determine the hardness, the ductility, the solid, or liquid 
 condition of bodies, may make one body more or less hard or ductile 
 than another, or they may render one body solid and another gaseous ; 
 but it is not in the nature of cohesive forces to render the hardness of 
 one body opposite to the hardness of another, so that together they 
 may produce soft. Yet such is the nature of the sources of chemical 
 activity ; thus sulphuric acid and soda are actuated by affinities for each 
 other ; the same force which gives to them their tendency to combine, 
 gives to one the properties of an intense acid, and to the other the cha- 
 racter of a powerful alcali ; yet these forces are so peculiarly related to 
 each other, that, when the bodies have combined, the acid and the alca- 
 line properties disappear, and there results a substance, formed by their 
 union, (Glauber's salt,) innocent, inactive, with little tendency to com- 
 bine, destitute of chemical affinity for other bodies, yet containing in 
 itself constituents which may be again set free, and exhibited with all 
 their active properties. 
 
 The force of chemical affinity is, therefore, exerted only between 
 bodies possessing opposite qualities, and, by their union, a substance 
 is produced possessing qualities which are not the mixed qualities of its 
 components. The forces which produce cohesion and solution are 
 found most active where the resemblance between the bodies is most 
 complete. Thus, metals adhere most powerfully to other metals, and 
 for their solution, mercury, a liquid metal, can alone be used ; salts dis- 
 solve in water always most easily when they show their resemblance to 
 
Diversity of 'Chemical Properties. 213 
 
 it by already containing water of crystallization in their mass ; inflam- 
 mable bodies, as sulphur and phosphorus, do not dissolve in water, nor 
 in acids, but in liquids, themselves inflammable, as ether, sulphuret of 
 carbon, and the oils; camphor, the resins, the fatty matters, require 
 also, for their solution, fluid menstrua of analogous, oily, and spirituous 
 natures. It is the contrary with chemical combination ; the more com- 
 plete the opposition of properties may be, the more intense is the affinity 
 by virtue of which combination is effected : a metal combines with 
 oxygen or chlorine : ether, or a metallic oxide combines with the acids 
 to form salts. In all these cases the opposition of properties is the 
 cause of the chemical affinity, and the neutralization or change of pro- 
 perties is its effect. Thus, the gases, ammonia, and muriatic acid, a 
 caustic alcali, and an intense acid, form the solid sal-ammoniac, a neutral 
 salt, destitute of the active properties of its constituents : thus carbon, 
 hydrogen, and nitrogen, elements of our daily food, combine to generate 
 the most active poison that has been found, the prussic acid, and this 
 prussic acid by further combination with oxide of iron, and with potash, 
 shall generate a yellow salt, which is perfectly without action on the 
 living body, and which, under the name of ferro-prussiate of potash, is 
 of daily extensive employment in the arts. 
 
 The elements which, mixed together, constitute our atmospheric air, 
 combined in one proportion, form a gas, which, when breathed, pro- 
 duces agreeable intoxication, (nitrous oxide ;) in other proportions, a deep 
 orange-coloured gas, (nitrous acid,) which, by intense cold, may be ob- 
 tained liquid ; and in an intermediate form, a gas colourless and trans- 
 parent, (nitric oxide,) which when mixed with air, produces, by combin- 
 ing with its oxygen, the nitrous acid. In all these cases new properties 
 are assumed ; the characters of the constituent elements furnishing no 
 means of predicting the properties of the compound. 
 
 This clear distinction between chemical affinity and cohesion was not 
 perceived by Berthollet ; and hence, misled by the supposed existence 
 of compounds, which connected together the extremes of chemical and 
 mechanical force, he advanced the principle, that the differences ob- 
 served between them arose solely from external circumstaces. This 
 principle has been rejected ; but the discussion to which it was sub- 
 jected showed the importance of attending to the influence which ex- 
 ternal circumstances really do exercise, and which is frequently in prac- 
 tice more powerful than the force of affinity itself. It is, therefore, 
 necessary to study in detail the influence of the external physical agents 
 upon chemical affinity. 
 
21 4 Influence of Cohesion on the 
 
 SECTION II. 
 
 RELATION OF THE MOLECULAR FORCES TO CHEMICAL AFFINITY. 
 
 1st. Influence of Cohesion. A diminution of cohesive power among 
 the particles of one body, allows those of another to come into closer 
 approximation to them, and favours the chemical action of the two 
 bodies. Thus, the ancient chemists, expressed the influence of cohe- 
 sion by the Latin proverb : Corpora non agunt nisi sint soluta ; bodies 
 do not act unless they be dissolved. And of all forms of matter, liqui- 
 dity is that in which chemical action is most rapid and most energetic. 
 
 There are many instances of bodies acting on each other, although in 
 the solid form. Thus, when chlorate of potash and sulphur, or chlorate 
 of potash and sulphuret of antimony, are rubbed together, the mixture 
 explodes from the rapid decomposition which ensues. When fulminate 
 of silver, or iodide of amidogen, are even slightly touched, detonation 
 follows. In these cases, the original arrangement of particles must 
 have been so instable, that the imperfect approach produced by me- 
 chanical mixture, or the slight change of position arising from a sudden 
 shock, was sufficient to cause a new mode of combination. But, if such 
 cases as these be considered as exceptions, we may look upon solid 
 bodies in general as being without chemical action on one another. 
 
 In the gaseous form of matter, chemical affinity appears to be con- 
 trolled and weakened by the mutual mechanical repulsion of the gaseous 
 particles. Thus, oxygen and hydrogen, bodies whose affinities are so 
 strong, may remain in contact as gases for an indefinite period. Nitro- 
 gen and hydrogen have no apparent tendency to unite when mixed. 
 Hydrogen, in the form of gas, is without action on carbon, or arsenic 
 or phosphorus; although under other circumstances it unites with 
 them, forming characteristic bodies. In order to obtain the full che- 
 mical action of gaseous bodies, they must be brought into play at the 
 moment of their being set free, or formed ; in their nascent state, as it 
 is termed. It may well be, that, when water is decomposed, and that 
 hydrogen is liberated, there is a moment before the hydrogen actually 
 assumes the permanently elastic form, being then perhaps liquid, and 
 in a highly concentrated condition, its affinities are manifested with 
 extraordinary force. It is the same with other gases ; they act always 
 with their full power only in their nascent state. 
 
 The influence of cohesion, in determining chemical action, is, how- 
 ever, of much greater importance in another way, as serving, upon the 
 
Order of Chemical Decomposition. 215 
 
 principles of Berthollet, to explain the anomalous discordance between 
 those experiments upon which the tables of the affinities of bodies for 
 each other had been constructed. Thus, it has been shown, that in a 
 table of affinities of the bases, oxide of silver would appear to be the 
 strongest base, if we used muriatic acid : barytes should be looked 
 upon as the most powerful, if sulphuric acid had been employed; 
 whilst, if the relation of the base to nitric acid were taken as the 
 standard, potash would be found to excel the others. In such cases, 
 the diversity is to be ascribed to the influence of cohesion ; and in all 
 cases of the mutual action of various bodies in solution, the result is 
 found to be, the formation of such compounds as are least soluble. 
 
 Let us imagine a quantity of sulphate of soda and nitrate of potash 
 to be dissolved in water. Each acid is attracted at the same moment 
 by both bases, and each base by both acids, so that there occurs a 
 division of each acid between the two bases, and of each base between 
 the two acids. There are thus in solution sulphate of soda and sulphate 
 of potash, nitrate of soda and nitrate of potash ; and whilst the solu- 
 tion is dilute all remains so, but if the liquor be very much concen- 
 trated, the sulphate of potash, being a sparingly soluble salt, is . depo- 
 sited in crystals, and a new distribution . takes place in the mother 
 liquor. Supposing all sulphate of potash removed, and that there 
 remain sulphate of soda, nitrate of soda, and nitrate of potash, the 
 remaining potash divides itself again between the acids, and a new 
 portion of sulphate of potash is formed, which, by a new crystallization, 
 may be separated. In this way, according as the evaporation is con- 
 tinued, new quantities of sulphate of potash are consecutively formed, 
 until there remains in solution neither potash nor sulphuric acid, but 
 only soda in combination with nitric acid. Here, then, supposing the 
 chemical affinities of potash and soda, of sulphuric and of nitric acids, 
 to be exactly equal, the decomposition which actually occurs, and the 
 manner in which it really takes place, are explained perfectly by the 
 greater cohesion of the sulphate of potash and its consequent sparing 
 solubility. 
 
 In like manner, ordinary hard water contains soda, muriatic acid, 
 lime, and sulphuric acid. The soda is certainly the stronger base, and 
 the sulphuric the stronger acid; and yet, on evaporating such water, 
 the salt which first crystallizes is sulphate of lime, and on continuing 
 the evaporation all sulphuric acid may be removed in combination with 
 the lime. For the acids and bases being divided among one another in 
 solution, there coexist sulphate of lime, sulphate of soda, muriate of 
 lime, and muriate of soda. But when the liquor is concentrated, the 
 sulphate of lime is first deposited, and a new quantity being formed, 
 
216 Mode of Arrangement of Acids 
 
 all its constituents are eliminated in combination, precisely as the sul- 
 phate of potash was separated in the former case. 
 
 In these instances the separation of the least soluble ingredients took 
 place by degrees, and, as it were, artificially ; but if any one of the 
 substances produced be perfectly insoluble, it is at once and in full 
 quantity expelled. Thus, when we mix together solutions of nitrate of 
 barytes and sulphate of soda, there is instant formation of sulphate of 
 barytes, and the solution contains only nitrate of soda. But even 
 here, although the formation of the sulphate of barytes appears instant- 
 aneous to the senses, it yet may, in point of fact, be just as gradual as 
 in other cases. Thus, there may have been a moment after mixing the 
 solutions, when there were present dissolved together, nitrate of barytes, 
 nitrate of soda, sulphate of soda, and sulphate of barytes ; in the next 
 moment the latter precipitates, and the barytes in solution, still dividing 
 itself between the two acids, another quantity is formed. This then 
 precipitates, and thus, in a space of time that is too small to be de- 
 tected, the quantity of barytes in the solution is reduced to the mere 
 trace of sulphate which the quantity of water can dissolve, and which 
 is too small to be detected by our ordinary tests. 
 
 The nature of double decomposition depends thus on the relative 
 solubility of the compounds formed. In whatever way the most inso- 
 luble bodies may be generated, the decomposition occurs. It is thus 
 that, on mixing solutions of carbonate of ammonia and of nitrate of 
 lime, there are formed carbonate of lime and nitrate of ammonia ; not 
 merely that the divellent affinities were more powerful than the quiescent 
 forces, but that the insolubility of the carbonate of lime produced its 
 separation from the liquid, and hence the union of the substances which 
 compose it. 
 
 The inversion of affinity, which is produced by the influence of cohe- 
 sion, is not limited to cases of double decomposition. There is no 
 doubt but that acetic acid is a stronger acid than carbonic acid, and on 
 adding acetic acid to a solution of carbonate of potash in water, the 
 carbonic acid is expelled, and acetate of potash formed. Yet, if a 
 stream of carbonic acid gas be passed into a solution of acetate of pot- 
 ash in alcohol, the salt is decomposed, acetic acid being set free, and 
 carbonate of potash formed. The cause of this is the insolubility of 
 the carbonate of potash in alcohol ; for, on the first action of the car- 
 bonic acid, the potash divides itself between the two acids, and there 
 is formed some carbonate, which is thrown down ; then another quan- 
 tity, which also separates, until ultimately all is precipitated, and thus 
 one of the feeblest acids may overcome the affinities of another which 
 is much stronger. 
 
And Bases whitft Co-exist in Solution. 217 
 
 By this principle of distribution of acids and bases, we are thus 
 enabled to account for a variety of facts which appear totally opposed 
 to affinity, if it were not subject to such modifications ; but, although 
 it is so convenient for explanation, it should not be admitted as a prin- 
 ciple in science, if there could not be adduced evidence of its actual 
 and independent truth. That it does occur in many cases, cannot well 
 be doubted ; thus, the solution of sulphate of copper in water is of a 
 rich blue colour, and that of muriate (chloride) of copper, of an eme- 
 rald green. Now, on mixing muriatic acid with a solution of sulphate 
 of copper, the blue solution is immediately changed to green, showing 
 that the weaker acid has divided the oxide of copper with the stronger, 
 although, so far from precipitation occurring, the new compound is the 
 more soluble of the two. Also on mixing a solution of sulphate of 
 iron with sulphocyauic acid, the liquor becomes intensely blood-red 
 coloured, showing that a quantity of sulpho-cyanide of iron has been 
 formed, although the sulpho-cyanic acid is much weaker than the sul- 
 phuric, and no precipitation occurs to favour its production. 
 
 These, and many other such examples which might be brought for- 
 ward, show that the opinion of Berthollet, that the acids and bases, 
 when mixed together in solution, arrange themselves so as that each 
 base shall be divided among all the acids, and each acid among all the 
 bases, is in a great many cases true, and that it is one of the most 
 fruitful sources of the decompositions which occur in our experiments ; 
 but it remains to be decided whether it is universally true, and whether 
 if all acids and bases act thus equally on one another, we should aban- 
 don the idea of chemical affinity being elective. 
 
 The answer to this question has been long since received in science. 
 The principle of Berthollet does not hold always, for numerous instances 
 may be produced where this partition of acids or of bases does *not 
 take place. Thus, boracic acid and sulphuric acid both redden litmus, 
 but the former colours it of a port wine colour, whilst the latter tinges 
 it of the red of an onion skin. If a quantity of borax (borate of soda) 
 be dissolved in water, coloured blue by litmus, and some sulphuric acid 
 be added thereto, the liquor becomes coloured wine-red from free boracic 
 acid ; but although the slightest trace of sulphuric acid in excess would 
 show itself by changing the red to that of the onion skin, no sign of 
 it is found until all the boracic acid has been expelled. Here, there- 
 fore, there is no partition of the base between two acids ; all the sul- 
 phuric acid which is added unites with the soda, and all the boracic 
 acid is expelled. If a solution of carbonate of soda be coloured blue 
 by litmus, and sulphuric acid added, it may also be shown by the ab- 
 sence of the peculiar red which free sulphuric acid gives, that there is 
 
218 Distribution not Invariable. 
 
 no division of base between the two. The carbonic acid is totally ex- 
 pelled, and the sulphuric acid combines exclusively with the soda. If 
 the solution be dilute, the carbonic acid remains dissolved in the liquor ; 
 if it be concentrated, it is evolved in the gaseous form ; that makes no 
 difference. 
 
 Affinities are not, therefore, as Berthollet considered, all the same 
 in power. The framers of the tables of affinity were right as to the 
 general principle, that different bodies have different degrees of affinity 
 for each other ; but they erred in supposing that they could construct 
 a table of the absolute order of affinities. 
 
 To sum up the details that have been given of the influence of cohe- 
 sion on the affinities of bodies acting on each other in solution, it may 
 be said, 1st, In almost all cases of precipitation, the nature of the double 
 decomposition is determined much more by the fact of one of the bodies 
 formed being insoluble, than by the resultant of the united affinities of 
 the bodies which are engaged. 2nd, That where there is no separation 
 of an insoluble or of a sparingly soluble compound, the acids and bases, 
 if they differ very much in energy, are exclusively united, the strongest 
 acid with the strongest base, and the weakest acid with the weakest base, 
 and if there be not base sufficient to neutralize all of the acids, a corres- 
 ponding quantity of the weakest acid being left out of combination alto- 
 gether ; but, 3rd, That if the acids and bases be not very different in 
 energy of affinity, they arrange themselves in such a manner that each 
 base shall be divided between all the acids, and each acid divided between 
 all the bases, in proportions which depend upon the quantities of each 
 acid and of each base that may be present, and on its affinitary force. 
 Thus, if there be two acids and two bases present, there will be four 
 salts ; if three acids and three bases, nine different salts ; and generally, 
 that the number of compounds in solution will be equal to the whole 
 number of acids multiplied by the whole number of bases present. 
 
 2nd. The Influence of Elasticity. The absence of cohesion, or still 
 more, the substitution for cohesion of its antagonist power repulsion, as 
 shown by the property of elasticity in the form of gas or vapour, modifies 
 chemical affinity in a perfectly analogous manner to that which has been 
 already described ; for, precisely as the formation of an insoluble sub- 
 stance in a liquid will enable lower degrees of affinity to preponderate by 
 removing the body which is formed by its insolubility, so will repulsion 
 or elasticity determine the production of such substances as, by their 
 volatility, may be driven off, even though the affinities of their elements 
 may be much feebler than those of other bodies. In all such cases the 
 same principle of distribution, so fully described already, may be supposed 
 to hold ; thus, a solution of sulphate of magnesia is perfectly decomposed 
 
Change m the Order of Decomposition produced by Elasticity. 219 
 
 by ammonia, the magnesia being precipitated ; but on mixing sulphate 
 of ammonia with dry magnesia, and applying heat, the ammonia is ex- 
 pelled, and the sulphuric acid remains, united exclusively with the mag- 
 nesia. Supposing that there is little difference between the affinities of 
 these two bases for sulphuric acid, the acid in the mixture may be 
 divided between the two ; in each case there is free magnesia and free 
 ammonia, for the acid is only able to saturate a part of each. In the 
 solution the excess of magnesia is insoluble, and it is expelled ; in the 
 dry way the excess of ammonia is gaseous, and it is driven off, and thus^ 
 with the same substances and the same affinities, precisely opposite de- 
 compositions are produced by the influence of cohesion and elasticity. 
 The decomposition of muriate of lime by carbonate of ammonia in solu- 
 tion has been already noticed, where carbonate of lime is formed in con- 
 sequence of its insolubility. If the carbonate of lime and the muriate of 
 ammonia so produced be dried and heated, the precisely reversed decom- 
 position will take place ; there are at first produced muriate and carbonate 
 of lime, muriate and carbonate of ammonia, and this latter being volatile 
 at the high temperature which is used, is driven off, and new portions 
 formed until the interchange of elements is complete. 
 
 The boracic acid has been already noticed, as being one so feeble in its 
 affinities, that the law of division of acids and bases does not hold with 
 it, and that sulphuric acid can deprive it of every particle of base. This 
 is quite true, as long as these acids are in the liquid form ; but, at a high 
 temperature, the reaction is reversed. If a mixture of sulphate of soda 
 and boracic acid be heated to redness in a crucible, the sulphuric acid will 
 be driven off in consequence of its volatility, whilst the fixed boracic acid 
 will remain combined with the whole quantity of base. The white, inert, 
 earthy substance, silica (powdered flints,) the acid properties of winch 
 are so feeble, that it is only from analogy that it is recognized by chemists 
 to be an acid, may, at a high temperature, expel the most powerful acids 
 from their combinations ; thus, the commonest sort of pottery is glazed 
 by throwing over it, when at a bright red heat, handfuls of common salt; 
 this is instantly decomposed ; the silica of the earthy material of the 
 vessels combines with the soda of the common salt, and the muriatic acid 
 is driven off in white clouds of elastic vapour. Here the acid, which is 
 the feeblest when dissolved in water, may expel the strongest when the 
 temperature is raised ; and admitting that in the commencement a parti- 
 tion of the base between the two took place, even to a very small extent, 
 the final and complete expulsion of the more volatile must result. 
 
 Erom the great variety of compounds into which water enters, it is 
 easily expelled, not that it is inferior in affinity to most other bodies, but 
 from its greater volatility. We shall hereafter see reason for looking 
 
220 Change in the Order of Decomposition 
 
 upon water as being a base of considerable force, and entering into com- 
 bination in forms which should possess considerable stability ; but when 
 a compound of water is subjected to heat, the elasticity of the water 
 diminishes its affinity so far that it may easily be expelled. 
 
 The elasticity which certain elements possess, when free, may be a 
 cause why the compounds which they form are easily decomposed by heat> 
 if their actual affinity to one another be not considerable. Thus, the 
 nitrate of barytes, which contains nitrogen and oxygen in combination 
 with barytes, gives, when heated, a mixture of nitrogen and oxygen 
 gases : nitrate of lead gives, when heated, pure oxygen and nitrous acid 
 fumes. Chlorate of potash, by a high temperature, abandons all its 
 oxygen gas, and the remaining elements, having a powerful affinity for 
 each other, resist the increase of heat, and remain as chloride of potassium. 
 
 When the decomposition of a body, by heat, is thus determined by 
 the elasticity of one of its constituents, it is necessary, for the success of 
 the process, that this constituent should be allowed freely to escape. If 
 it be forced to remain enveloping the residual substance, the decomposi- 
 tion ceases. Thus, by heating carbonate of lime to redness, it is resolved 
 into lime and carbonic acid ; but, if the carbonic acid be not removed, 
 the decomposition would immediately cease, and the carbonate of lime 
 might be melted without being decomposed. The removal of the car- 
 bonic acid is accomplished, in burning lime on the large scale, by the 
 limestone being heated in a kiln, through which there is a continuous 
 draught, by which the carbonic acid is carried off according as it is 
 formed. The necessity for the removal of the carbonic acid may be 
 shown by placing bits of white marble in a porcelain tube, heated to red- 
 ness in a furnace, connected with a pneumatic trough, and fitted to a 
 retort at the other end, by which steam may be passed into the tube ; at 
 first, scarcely any carbonic acid is set free, but, by keeping up a supply 
 of steam, the gas is rapidly produced, and the lime becomes very soon 
 completely caustic. 
 
 It is in this way, also, that we may explain the contrary order of de- 
 composition that may be produced by oxygen, hydrogen, and iron. If 
 metallic iron be in the tube, and the latter be kept full of steam, every 
 particle of hydrogen which is formed is carried off : and there being then 
 a space provided, into which the hydrogen can easily spread itself, the 
 steam will be decomposed, and the iron converted into oxide. If, on 
 the contrary, the tube contain oxide of iron, and be filled by a current 
 of hydrogen gas, there is presented to every molecule of steam produced, 
 room for its escape, and the formation of steam being thus favoured by 
 its elasticity being allowed full play, the reduction of the metal is com- 
 pleted. 
 
Produced by Various Modifying Causes. 221 
 
 Independent of its influence on cohesion, a change of temperature is 
 capable of modifying the affinities of bodies in a remarkable degree- 
 Thus, charcoal is not capable of being melted or vaporized, and yet 
 although at ordinary temperatures quite inert, few bodies can resist its 
 deoxidizing action at a red heat. Bodies which take fire when heated, 
 do so in consequence of their affinity for oxygen being augmented by 
 the increase of temperature. The action of the electric spark, in pro- 
 ducing the explosion of gaseous mixtures, depends on its heating very 
 much the few particles of gas which lie immediately in its path, and the 
 combustion being communicated by them to the general mass. The 
 affinities of bodies for each other appear to be thus exalted by the 
 agency of heat in many cases, but the exaltation does not appear to be 
 the same for all. Heat appears often to diminish the affinity of bodies ; 
 thus the explosion of detonating compounds was so explained ; but this 
 appears to arise from the heat really exalting the affinity of the more 
 powerful constituents, so that new and more permanent bodies may be 
 formed : thus fulminating silver explodes, not that its elements may 
 separate, but that bodies of a more permanent constitution may be formed. 
 The iodide and chloride of azote were looked upon as being examples of 
 mere separation of elements on the application of heat, but Marchand 
 and I have found that these bodies contain hydrogen, and that they are 
 decomposed in consequence of the formation of hydrochloric or hydriodic 
 acid. To produce many bodies of instable nature it is necessary to avoid 
 the use of heat, not that heat diminishes the affinities of their elements 
 in general, but that the heat enables those elements to satisfy their affi- 
 nities better, by combining in a more stable form. 
 
 In many cases, however, heat does appear directly to nullify the affi- 
 nity of bodies, and produce decomposition. Thus, ammonia is resolved 
 into nitrogen and hydrogen by passing through a red-hot tube, and 
 Groves has recently shewn that by exposing steam to an intense heat it 
 is resolved into its elementary gases. 
 
 It has been mentioned that Berthollet considered affinity as being 
 not elective, but that the combination of one body to another was de- 
 termined by the circumstances under which they were placed ; and that 
 in cases where many bodies of equal solubilities existed together, they 
 were divided among one another in proportion to their masses ; but he, 
 in this case, introduces a term which has caused great difficulty in the 
 discussion of the doctrines which he advanced. He says, that the 
 bodies mixed together combine, not only in proportion to their masses, 
 but of their affinities, and hence might appear to admit that bodies had 
 different degrees of affinity, and that this might, therefore, be elect- 
 ive ; but, if I conceive his opinions rightly, the affinity of which he 
 
222 Relation of Affinity to Neutralizing Power. 
 
 spoke was not the force to which we assign the power of choice of one 
 body over another, but that he carried on the analogy to cohesion, and 
 considered, that the affinity of one body, A, to another, B, might be 
 greater than to a third, c, not so as to make A unite with B, in 
 preference to c, but that when it had been united with B it would 
 hold it more firmly than it could retain c. This is like what is 
 found with cohesion; if several bodies be placed beside each other 
 they show no power of elective cohesion, but if they be brought into 
 actual close contact, the degree of cohesion may be different for each. 
 It is in this way that Berthollet recognizes a difference of affinity, and 
 hence the obscurity that is often ascribed to his statement of his views, 
 from the sense which he attached to the word affinity being mistaken. 
 We owe to this philosopher an attempt at measuring this power of 
 affinity, which, though incorrect, yet, as being one of the first steps 
 made towards numerical laws in chemistry, deserves notice. He looked 
 upon the neutralizing power of a body as being the measure of its affi- 
 nity for another, and considered that the deviations from this rule arose 
 from the influence of cohesion or elasticity : thus, the same quantity of 
 potash is saturated by 
 
 Sulphuric acid, 40 parts. Muriatic acid, 36 '5 parts. 
 
 Nitric acid, . 54 Acetic acid, 51 
 
 Carbonic acid, 22 ,, Oxalic acid, 36 ,, 
 
 Hence, if mere affinity were allowed to act, carbonic acid should be the 
 strongest, and nitric acid the weakest in the list ; in like manner, the 
 same quantity of sulphuric acid neutralizes 
 
 Potash, . 48 parts. Lime, . 28 parts. 
 Soda, V; 32 ,, Barytes, . 76 ,, 
 
 Ammonia, 17 ,, Magnesia, 18 ,, 
 
 and ammonia and magnesia should be the strongest of all bases, were 
 it not for the insolubility of the one and the volatility of the other 
 body. 
 
 These numbers which are now known as expressing the quantities of 
 substances that are equivalent to each other in combination, are fully 
 recognized as totally independent of the force of affinity exercised by 
 each body. As yet we have no other measure of affinity than the or- 
 der of decomposition, controlled by the estimate of the influence which 
 cohesion and elasticity may exercise. From the electrical relations of 
 bodies, attempts have been made to estimate the relative affinities of 
 chemical substances, the results of which will be described in their 
 proper place. 
 
Influence of Light on Chemical Affinity. 223 
 
 SECTION III. 
 
 ON THE INFLUENCE OF LIGHT ON CHEMICAL AFFINITY. 
 
 Although attention has latterly been very much directed to the influ- 
 ence of light on chemical affinity, from the accidental observation of some 
 very remarkable circumstances connected with it, yet there have not 
 been discovered as yet any general principles to which those results can 
 be reduced ; and the greater number of the investigations that have 
 been made are occupied by experiments of detail, which from their 
 want of connexion and their multiplicity, cannot be successfully con- 
 templated from any general point of view at the present moment. So 
 far, however, as positive facts have been discovered, and as even plau- 
 sible explanations of those facts have been suggested, I shall endeavour 
 to represent briefly, the actual condition of our knowledge of this de- 
 partment. 
 
 In many cases, bodies which in obscurity remain totally without 
 action on one another, are brought into combination by exposure to 
 light, and the rapidity of their reaction is proportional to the brilliancy 
 of the light. Thus, chlorine and hydrogen mixed, remain unaltered for 
 any period in the dark ; if exposed to the diffuse day light, they silently 
 combine : but explode suddenly if a direct ray of sunshine fall upon the 
 mixture. Chlorine dissolved in water, if kept in the dark, remains a 
 long time unaltered, but if exposed to sunshine, is rapidly converted in- 
 to chloride of hydrogen, water being decomposed, and oxygen elimi- 
 nated in a gaseous form. Chlorine unites with carbonic oxide only 
 under the influence of light, whence the name Phosgene, a light formed 
 gas, was given to the compound by its discoverer, Dr. Davy. Chlorine 
 and sulphurous acid unite also, only when exposed to brilliant sunshine ; 
 so much so, that but few days in summer are found bright enough to 
 form the compound. The decomposing action of chlorine, iodine, and 
 bromine upon organic bodies, which consists in the separation of hy- 
 drogen, and the assumption generally of a corresponding quantity of 
 chlorine, &c., in its place, is regulated also in a remarkable degree, by 
 the brilliancy of the light under which this operation is carried on. 
 Thus, even in summer, in Dublin, I never could deprive acetone of more 
 than one-third of its hydrogen forming from C 5 H 3 O, the body 
 C 5 H 2 Cl O; but in Paris, in summer, the chlorine removes another 
 equivalent of hydrogen, and Dumas and I succceeded in obtaining the 
 body C 3 H Clg O. In like manner, in bright sunshine, the action of 
 
224 Influence of Light on Affinity. 
 
 chlorine on pyroxylic spirit is so violent, that unless the vessel be care- 
 fully shaded, the decomposition proceeds by a series of explosions, 
 whilst I have found it exceedingly difficult in gloomy weather to produce 
 any action whatsoever. Instances of this kind might be very much multi- 
 plied, but those described are sufficient to point out the general manner 
 in which light is found to act. It is still more remarkable, that chlo- 
 rine gas exposed to sunshine, acquires the property of afterwards com- 
 bining with hydrogen in the dark : it becomes tithonized, according to 
 Dr. Draper, or more probably it is put into an isomeric condition, in 
 which its electro-negative character is exalted. This power may be re- 
 moved, and the gas detithonized by the inverse action of red light ac- 
 cording to the observations of Dr. Draper. 
 
 The action of light appears occasionally limited to the simple sepa- 
 ration of bodies previously combined. Thus, colourless nitric acid, 
 when exposed to sunshine, evolves oxygen gas, and becomes coloured 
 yellow from nitrous acid which remains. The fading of Prussian blue 
 patterns on cotton, which Chevreul found to depend on the escape of 
 cyanogen, and the conversion of the blue into a white compound, con- 
 taining less cyanogen, is also an example of this principle. 
 
 Setting aside, for the present, the influence of light on the produc- 
 tion of colouring matters in organic bodies, which shall be described as 
 a portion of the chemical history of the individual substances, I shall 
 now only advert to the action of light upon the compounds of the 
 easily reducible metals, particularly silver, by the study of which sucli 
 remarkable results have latterly been obtained. 
 
 Scanlan first showed that when nitrate of silver blackens under the 
 influence of light, its decomposition is produced by organic matter, 
 as by contact with paper, or by the organic substance, which even dis- 
 tilled water contains in small quantity. Chloride of silver also is affec- 
 ted by light only when in contact with organic matter or with water, 
 and in the latter case, also, most probably from acting on the organic 
 matter which the water held in solution. When oil of vitriol is poured 
 over chloride of silver, this is not altered by the light, the sulphuric 
 acid combining with the water and probably destroying the organic 
 matter therein dissolved. I apprehend that in most, if not in all cases of 
 decomposition of a metallic salt and the reduction of the metal under 
 the influence of light, a substance containing hydrogen, exclusive of 
 the water of solution, must come into play. 
 
 The decomposition of the salts of silver in contact with paper under 
 the influence of light, has become of interest to the arts as a process for 
 obtaining accurate copies, and is called photography, or photographic 
 drawing. If a sheet of paper be washed with a very dilute solution of 
 
Photographic Drawing. 225 
 
 chloride, iodide, or better, bromide of potassium, and then with a 
 solution of nitrate of silver, there is formed in the substance of the 
 paper, chloride iodide, or bromide of silver, which being in contact 
 with abundance of organic matter, is blackened by a very short expo- 
 sure even to moderate light. If an opaque body be laid between a 
 sheet of such paper and the light, the portions to which the light ar- 
 rives become dark, whilst those under the object remain white, and thus 
 the most delicate and complicated outlines of foliage or fibres may, by 
 a few minutes' exposure to the solar rays, be fixed upon the paper with 
 a degree of accuracy inimitable by the hand. To render such a drawing 
 permanent, it is necessary to remove the silver compound under the 
 pattern, for if it remained the blackness would gradually become uni- 
 form over the entire surface, and the picture should become effaced. 
 This is effected by washing the paper after the image has been com- 
 pletely formed, by a solution of some substance capable of dissolving 
 out all of the undecomposed salt of silver ; for this purpose, ammonia, 
 hypo-sulphite of soda, or strong solution of common salt are those 
 generally employed. 
 
 The picture so produced is said to be negative, as it is formed by 
 lights upon a dark ground ; but it may be converted into a positive 
 picture, shaded in the ordinary manner by processes which will be 
 found described in any special work on photography. Preparations of 
 gold, of chrome, of iron, and of copper, have been also made the 
 bases of photographic processes ; and, in fact, any metallic salt which 
 decomposes, and deposits its oxide or metal under the influence of light 
 in contact with organic matter, may be used for the purpose. 
 
 The most remarkable features connected with the chemical agencies 
 of light result from the recent experiments of Herschel. He has shown, 
 as was slightly noticed when describing the general characters of light, 
 that the chemical effects are not regulated by, nor limited to the luminous 
 spectrum ; but by totally distinct rays, which, according to the sub- 
 stance employed to show their decomposing action, may extend far 
 beyond the visible limits on either side, or may stop short in the middle 
 of the coloured space, and that the greatest effect, which generally occurs 
 at the violet extremity of the spectrum, may be produced at other and 
 widely distant points. 
 
 A singular, and at present unaccountable, consequence of the action 
 of the prismatic spectrum on paper impregnated with chloride of silver, 
 is, that the spaces on which the coloured rays fall become coloured, 
 acquiring a tint corresponding to that of the light incident upon them, 
 so that the spectrum fixes its own image on the paper. Thus, the 
 colours impressed were in one experiment : 
 15 
 
226 
 
 Colouring Effects of the Chemical Rays. 
 
 Spectrum Colours. 
 
 Colours formed on the Paper. 
 
 Extreme red. 
 
 Mean red. 
 
 Orange yellow. 
 
 Yellow. 
 
 Yellow green. 
 
 Green. 
 
 Blue green. 
 
 Blue. 
 
 Violet. 
 
 Beyond the violet. 
 
 None. 
 
 None. 
 
 Faint brick red. 
 
 Brick rfed, pretty strong. 
 
 Red, passing into green. 
 
 Dull bottle green. 
 
 Very sombre blue. 
 
 Black, passing into metallic yellow. 
 
 Do. Do. 
 
 Violet, or purplish black. 
 
 It is in the lavender coloured space that the chemical effects are ge- 
 nerally most intense ; when the light of it had been concentrated by a 
 lens, and received on a piece of prepared paper, the blackening was 
 instantaneous ; precisely as if a red-hot body had been applied behind, 
 or a smoky flame directed on the paper over all the space illuminated, 
 and accurately making its outline. 
 
 In the table of impressed colours just given, the red rays appear to 
 have produced no effect ; but they are by no means destitute of action. 
 When a quantity of diffused light is allowed to fall upon the paper, in 
 addition to the more brilliant spectral colours, the chemical image is 
 found to acquire a pure white prolongation beyond the red space, in 
 which the darkening action of the diffuse light appears to have been 
 suspended. The opposite extremities of the spectrum appear, there- 
 fore, to have different powers, the darkening quality of white light 
 being due to the difference between the two in favour of the violet end ; 
 and it is probable that by a balance of action, a sensitive paper might 
 be exposed to the action of united beams of brilliant violet and red 
 light, and remain perfectly unaltered in its colour. Herschel did not, 
 however, succeed so far. Paper blackened by violet light has that 
 blackness removed by the action of red light upon it ; but it was found 
 impossible to catch the point where the paper should be white, for, 
 according as the black of the violet end passed off, the red impression 
 was substituted for it. When, however, the different coloured rays 
 were made to fall simultaneously on the paper, the neutralizing power 
 of the opposite ends of the spectrum was beautifully shown. The 
 blackening power of the more refrangible rays was suspended over all 
 the space upon which the less refrangible rays fell, and the shades of 
 green and sombre blue, which the latter would have impressed upon a 
 white paper, were produced on that portion, which, but for their action, 
 would have been merely blackened. 
 
Formation of Daguerreotype Images. 227 
 
 The paper with which those results were obtained, derived its sensi- 
 bility to light from chloride of silver ; but the action of other salts of 
 silver give such anomalous and variable effects, that no general principle 
 whatsoever can be deduced from them ; thus, with bromide of silver, 
 the blackening proceeds uniformly over the whole of the visible spec- 
 trum, and the whitening effect is produced beyond it to a considerable 
 distance. The subject has been shown by Herschel to be one of con- 
 siderable importance and great extent ; and for the popular interest it 
 excites, some clue to more general knowledge of its principles will pro- 
 bably be soon obtained. 
 
 The process lately discovered by Daguerre, of fixing the images of 
 external objects upon a prepared metallic plate, is one which also de- 
 serves attention, as being founded upon the chemical agencies of light, 
 although hitherto there has been but little success in the attempts made 
 to assign a theory of it. It is not complicated in detail. A plate of 
 silvered copper is cleaned with dilute nitric acid, so that the surface of 
 silver shall be absolutely pure, and is then exposed to the vapour of 
 iodine, or better, chloride of iodine or of bromine, until a gold-co- 
 loured pellicle of excessive tenuity is deposited upon it. In this state 
 it is very sensitive to light. The plate so prepared is placed in a camera 
 obscura, and the image of the object required is allowed to remain on 
 it for a space of time, which varies with the brightness of the light. 
 When it has been sufficiently exposed, it is removed, and submitted to 
 the action of the vapour of mercury, by which the picture is rendered 
 visible. As there still remains, however, a general sensibility to the 
 further influence of light, this is removed by dissolving away all the 
 excess of the chloride of iodine, or of bromine, and of the salt of silver 
 formed, by a solution of hypo-sulphite of soda. The shadows remain 
 then marked by smooth amalgamated surfaces, and the lights, by the 
 corresponding portions being of a dull grey colour, possessing only a 
 power of diffuse reflection. 
 
 The theory of the production of photographic images cannot be con- 
 sidered as being yet perfectly established, notwithstanding that the 
 processes of the art have been so extensively practised, and so variously 
 modified. The views which I originally put forward as to their cause 
 still appear to me the most satisfactory, and have been since then sup- 
 ported by additional evidence. It is certain that we must recognize 
 two perfectly different sources of photographic impressions. The one 
 where a metallic salt is decomposed by an organic substance, under the 
 influence of light ; and the second where there is no organic substance, 
 and, as I conceive, the. action is purely molecular. The first class give 
 the results of common photography, chromotype, calotype, &c. ; the 
 
228 Formation of Daguerreotype Images. 
 
 second class of actions is that of the daguerreotype, and the actions 
 discovered by Moser, and ascribed by him to latent light* 
 
 It has been the popular idea, that under the influence of light the 
 iodide of silver on the daguerreotype plate was decomposed, and iodine 
 set free, whilst the reduced silver so presented afforded a surface on 
 which the mercurial vapour deposited itself. But there is no evidence 
 whatsoever of iodine so becoming free, and the recent researches of 
 M. Claudet, the eminent daguerreotypist, have quite excluded the idea 
 of any such chemical decomposition. Mr. Claudet, verifying HerscheFs 
 discovery, that the red rays had the power of reversing the action of 
 the blue light, found that an iodized plate that had been fully acted on 
 by blue or white light, might be brought back to its sensitive state, the 
 picture obliterated, and it made ready for a new picture, by a suitable 
 exposure to red or yellow light, and this for several successive times. 
 Hence there could be no chemical elements disengaged, for if so, there 
 was no way for them to get back ; but each ray had the power of pro- 
 ducing a molecular action which was opposite for the blue and the red 
 rays. By this molecular action of the light, the iodide of silver on the 
 plate obtains a surface of such structure, that the mercurial vapour de- 
 posits on it more or less according as the light has been stronger and 
 the structure more developed. Thus the picture is formed, precisely as 
 the radiation of the bodies, even in the dark, by rays which do not 
 affect the eye, which have shorter waves than even the lavender light, 
 and which probably approximate to the condition of low temperature 
 heat waves, has the power so affecting the molecular condition of sur- 
 faces as that when breathed upon, complete pictures of the most minute 
 details of the radiating surface are produced. 
 
 The influence of colour on the production of pictures, by Daguerre's 
 process, is very marked ; the images of green objects are scarcely at all 
 defined ; so that the method is scarcely applicable to taking landscapes. 
 Bed and orange are also very feeble in their effect * but blue even so in- 
 tense as to be not at all bright, is more powerful than a brilliant white 
 light. In order, therefore, to produce good effects, objects should be 
 selected either white, or of colours from which red and orange should be 
 absent. The fixation of colours in a manner similar to that discovered 
 by Herschel, and already noticed, has been remarked in Daguerre's pro- 
 cess, although so irregularly that no advantage has as yet been taken of 
 it for technical uses ; but I have myself seen on more than one occasion^ 
 where a deep blue sky was interspersed by patches of bright white clouds, 
 a perfect picture of the sky in its natural colours to be formed upon the 
 plate. Time-worn stains, and marks upon the surface of stone buildings, 
 are also occasionally represented in their natural colours. In the majority 
 
Of Catalysis or Actions by Contact. 229 
 
 of cases, however, where colours are produced upon the plate, they do 
 not correspond in position or tint to those of the natural objects whose 
 image had been obtained. 
 
 From the assemblage of facts which have been now referred to, it is 
 evident that the solar light contains some power immediately distinct 
 from its heating or illuminating qualities, which influences the force and 
 nature of chemical action in a very remarkable degree, as well as shows 
 itself capable of profoundly affecting the molecular structure of bodies. 
 Our ideas as to the nature of the force will, of course, depend on our 
 conceptions of the nature of light and heat. Dr. Draper of New York, 
 who has studied the subject with great care, proposes to give to this 
 force the name, Tithonicity, and to term those actions Tithonic. Sir J. 
 Herschel, to whose researches this branch of science is equally indebted, 
 suggests the words actinism and actinic forces. I shall not attempt to 
 decide which should be employed, as both possess the important character 
 of good names that of being independent of any hypothesis of the cause 
 of those phenomena ; and the essential requisite of good nomenclature, 
 that of not involving any questionable theoretical ideas. 
 
 SECTION IV. 
 
 OF CATALYSIS, OR ACTIONS BY CONTACT INDEPENDENT OF AFFINITY. 
 
 The decomposition of compound bodies is frequently effected by the 
 intervention of causes, which cannot be referred to ordinary affinity ; 
 and in many cases, bodies which have but little tendency to unite, enter 
 into combination when brought into contact with a substance for which 
 neither has affinity, and which remains, after the action is completed, 
 perfectly unaltered. Thus, when hydrogen and oxygen mixed together, 
 in a gaseous form, are brought into contact with a clean slip of pla- 
 tinum, they gradually unite ; and so much heat may be evolved by their 
 rapid combination, as to ignite the platinum, and explode the remainder 
 of the gas. In this case, we seek to explain the phenomenon, by sup- 
 posing that the platinum condenses powerfully on its surface a layer of 
 mixed gaseous particles, and thus brings them within the sphere of their 
 mutual attraction. But this explanation does not apply to other cases. 
 If we boil starch (C, 2 H 10 O JO ) with diluted sulphuric acid, it is converted 
 successively into dextrine, gum, starch-sugar, and finally crystallizable 
 grape sugar, (C, 2 H 12 O|2) having associated to itself the constituents of 
 two equivalents of water. At the termination of the process, the sul- 
 phuric acid is found unaltered in properties and in quantity; so that 
 
Of Catalysis and Analysis. 
 
 the smallest portion of sulphuric! acid is sufficient to convert into sugar, 
 an indefinitely great quantity of starch. If oxamide (C 2 O 2 NH 2 ) be dif- 
 fused through water, Jin contact with the smallest possible quantity of 
 oxalic acid, it gradually disappears, and appropriating to itself the ele- 
 ments of an equivalent of water, is converted into neutral oxalate of 
 ammonia, (C 2 3 + NH 3 ) : the small quantity of oxalic acid originally 
 added remaining unaltered and in excess. 
 
 Among the instances of decomposition by forces of this kind, the 
 oxygenated water (H0 2 ) may be taken as an example. This substance, 
 when pure, separates spontaneously, after some time, into water and 
 oxygen gas, but its decomposition may be rendered violent and instan- 
 taneous, by putting it into contact with finely divided metallic platinum, 
 or metallic silver, or black oxide of manganese, or fibrine, or a variety 
 of other bodies. In all these cases the body added remains quite un- 
 altered ; no affinity can be traced between it and the oxygenated water, 
 the mere presence of the foreign body appearing to cause the decom- 
 position. 
 
 Berzelius, who first directed general attention to these phenomena, 
 proposed to attribute them to a peculiar force, differing from ordinary 
 affinity. When one body is decomposed by another, in virtue of a 
 superior affinitary power, the decomposing body combines with one 
 element of the body which is decomposed, and the other is then ex- 
 pelled. It is in this way that we obtain the constituents of bodies by 
 ordinary analysis, and for distinction, he proposes to term such decom- 
 positions as those just described, operations of catalysis, and to name 
 the power which these bodies have of acting by mere contact, a catalytic 
 force. 
 
 It is evident, certainly, that by giving a name to this class of phe- 
 nomena, we are enabled usefully to contemplate them as a group, and 
 to examine, more easily, their relations to each other and to ordinary 
 action; yet the word catalysis really teaches us nothing of the phe- 
 nomena, and it is indeed very improbable, that such varied cases of 
 union and separation should be derivable from one single force. It is 
 hence necessary, before concluding on the nature of this action, to trace 
 it through a greater variety of cases, and to revert briefly to the con- 
 ditions of affinity by which the elements of compound bodies are held 
 together. 
 
 The elements of a compound substance are retained together in a 
 certain molecular arrangement, because the affinities are then satisfied ; 
 but it is natural to suppose, that whilst the elements remain the same, 
 their affinities for each other might be just as completely satisfied by a 
 different molecular arrangement. The original body might therefore be 
 
Catalytic Effects of Heat. 231 
 
 changed into another, by a change in the action of its own particles, 
 independent of any substance acting chemically on it from without; 
 and hence the principle of catalytic decomposition resolves itself into a 
 means of disturbing the molecular equilibrium of a compound body, so 
 that it can only be restored when the particles are differently arranged. 
 Catalysis may, therefore, be produced not merely by the presence of 
 various bodies, but still more remarkably by the action of physical 
 agents, amongst which, heat is the most powerful ; thus, when acetate of 
 lime (C 4 H 3 O 4 Ca) is strongly heated, the equilibrium of its molecular 
 group is overturned, and when the affinities again satisfy themselves, 
 two new bodies result, acetone and carbonate of lime (C 3 H 3 and 
 CO 3 Ca.) Destructive distillation is therefore a catalytic process, and 
 the origin of all pyrogenic products is to be traced to the new conditions 
 under which the affinities are satisfied, which had originally united the 
 elements of the body exposed to heat. The sudden decomposition of 
 explosive bodies by an elevation of temperature, or by a slight blow, is 
 traceable to the same disturbance of the old equilibrium, and establish- 
 ment of the new. A most important means of thus setting into motion 
 the particles of bodies, and enabling them to re-arrange themselves under 
 new forms, consists in bringing them into contact with a substance 
 already in a state of decomposition ; thus if oxygenated water be brought 
 into contact with oxide of silver, the decomposition is propagated to 
 the latter, which is completely resolved into oxygen and metallic silver ; 
 if peroxide of lead be used, it is converted into protoxide by the escape 
 of half its oxygen, and even the black oxide of manganese may be re- 
 duced to the state of protoxide, if the solution contain an acid ; in all 
 these cases, the decomposition, which commenced with the oxygenated 
 water, extends to the metallic oxide, in virtue of the motion communi- 
 cated to their particles, enabling the new arrangement to be effected. 
 In some instances, in organic chemistry, this principle is still more 
 beautifully shown. If a solution of sugar (CjaHnOn), be brought into 
 contact with a little decomposing gluten or yeast, it unites with the 
 elements of an equivalent of water, and divides itself into two equiva- 
 lents of alcohol, 2 (C 4 H 6 02), and four of carbonic acid, 4 (C0 2 ). If a 
 solution of urea (CONH 2 ) be put in contact with yeast, it unites also 
 with an atom of water, and is then decomposed into ammonia (NH 3 ) 
 and carbonic acid. The conversion of starch into sugar in the pro- 
 cesses of germination and of malting is effected by a substance which 
 accompanies the starch in the grain. This substance is called diastase, 
 and is analogous in most of its properties to vegetable gluten. The 
 slow decomposition of the diastase communicates to the molecules of 
 many thousand times its weight of starch, the degree of motion neces- 
 
232 Catalytic Effects ascribable to 
 
 sary for their rearrangement, and the appropriation of the elements of 
 water requisite for the formation of starch sugar. 
 
 If platinum, which is by itself totally unacted on by nitric acid, be 
 alloyed with silver, the alloy dissolves in dilute nitric acid without leav- 
 ing any residue. Pure copper is not acted upon by dilute sulphuric 
 acid ; but when it is alloyed with nickel and zinc, as in the argentine 
 or German silver of commerce, it dissolves completely. In these cases 
 the molecular action which produces the combination with the acid, 
 was not possessed by the platina, or copper, when alone, but is acquired 
 by them ; being transmitted by the other metals with which they are 
 aUoyed. 
 
 It may not be easy to reduce to the action of this principle all phe- 
 nomena of catalysis ; for in the imperfect light by which we contemplate 
 them, it is possible that we may rank together circumstances whose real 
 nature is very different ; but, at all events, we must recognize in this 
 principle, the definite introduction of which into science is due to Lie- 
 big, a cause of chemical decomposition peculiarly important in explain- 
 ing the complex reactions of organic bodies. It is remarkable, also, 
 that this law, of which the simplest expression is, that where two che- 
 mical substances are in contact, any motion occurring amongst the par- 
 ticles of the one may be communicated to the particles of the other, is 
 of a more purely mechanical nature than any other principle as yet 
 received in chemistry; and when more definitely established by suc- 
 ceeding research, it may be the basis of a dynamical theory in chemistry, 
 as the law of equivalents and of multiple combination expresses the 
 statical condition of bodies which unite by chemical force. 
 
 These peculiar catalytic actions may, however, be also looked upon as 
 differing from ordinary afnnitary decompositions only in the primary dis- 
 tributing force being so feeble or so disguised as to escape direct observ- 
 ation, and revealing itself only in the more intense secondary consequences 
 of its agency. Playfair has recently drawn attention to the clearness 
 and simplicity with which many apparently catalytic decompositions may 
 be explained upon this view : thus, dilute nitric acid has no action on 
 oxalic acid, but if a small quantity of a protosalt of manganese be added, 
 violent action commences, and the oxalic and nitric acids are resolved 
 into carbonic acid and nitrous fumes : C 2 O 5 and N0 5 giving C 2 O 4 and 
 NO 4 . Yet the salt of manganese added may not undergo any change. 
 In this case we may suppose that the protoxide of manganese tends to 
 become peroxide in contact with the nitric acid, but the peroxide imme- 
 diately converts the oxalic acid into carbonic acid, and thus although we 
 could not show the existence at any moment of any quantity of peroxide 
 of manganese, its potential or transient formation may cause the action. 
 
the Communication of Motion 233 
 
 Similarly, dilute nitric acid has no action on indigo, but if some oxide, 
 as alumina, or peroxide of tin be placed in it with, a cloth dyed blue by 
 indigo, the presence of the metallic oxide, which has some affinity for 
 more oxygen, will so disturb the equilibrium of the fifth atom of the 
 oxygen of the nitric acid, that it will separate itself and fasten not on 
 the oxide however, but on the indigo, and will bleach the latter with 
 evolution of nitrous fumes. This loose condition of the fifth atom of 
 oxygen is in fact shown in the relation of most nitrates to heat. It is 
 not nitric acid that is expelled, but a mixture of nitrous acid and oxygen 
 gas, NO 4 and O. 
 
 The instability of the union of the elements of nitrous acid itself, ren- 
 ders it like yeast (as noticed, page 231,) a source of many catalytic 
 actions; thus, urea unites readily with nitric acid, and produces a pure 
 white salt, nitrate of urea. But if nitrous acid be put in contact with 
 urea, there is immediate absorption of water and formation of carbonate 
 of ammonia, CO 2 +NH 3 from CO NH 2 and HO. Similarly, though 
 uric acid is converted simply into alloxan by pure nitric acid, it is 
 totally broken up into oxalic acid and ammonia, if the nitric acid contain 
 even a trace of nitrous fumes. 
 
 It is quite reasonable to suppose, as Playfair suggests, that prior to 
 decomposition taking place in any ordinary reaction, the atoms engaged 
 must be brought into a condition in which the bond that had previously 
 united them is loosened, if not dissolved, and yet before they actually 
 pass into the new permanent condition. Now, affinities may be easily 
 conceived so far to act as to produce the former condition of instability, 
 and yet not fully determine the final action, and in such case if any new 
 element be introduced, though seemingly inactive, and having no special 
 affinitary powers, yet the slight addition of disturbance which it causes, 
 may just turn the groups of molecules over the point of tottering equili- 
 brium, and cause the sudden manifestation of powerful affinity to take 
 place. 
 
 When protoxide of manganese is added to a solution of chloride of 
 lime, peroxide of manganese is formed and chloride of calcium, Mn O 
 and Cl. O. Ca giving Mn O.^ and Ca Cl. This is evidently by the play 
 of common affinity, but if we add peroxide of manganese to a warm 
 solution of chloride of lime, we have oxygen gas copiously evolved, and 
 chloride of calcium formed whilst the peroxide remains unaltered. Here 
 would appear Catalysis, but in reality the peroxide of manganese tends 
 to form manganic acid, and to cause the decomposition of Mn O 2 and 
 Ca Cl O into Mn O and Ca Cl, but its affinity is not strong enough for 
 that. The atom of oxygen becomes loose between Mn 2 and CaCl, and 
 not being strongly fixed by either escapes as gas. Its elasticity, as des- 
 
234 Relation of Catalysis to Affinity. 
 
 cribed page 220, overcoming the slight affinity which should attach it to 
 either. Further, when chlorate of potash has been melted but not suffi- 
 ciently heated to decompose, if some powdered peroxide of manganese 
 be thrown upon it, oxygen gas is immediately given off in abundance. 
 Here the tendency of the manganese is to form manganic acid, but the 
 manganic acid cannot exist free at that temperature ; it cannot retain 
 the oxygen it has taken, nor can the chloride of potassium formed take 
 it back ; and, accordingly, the oxygen is evolved as gas, the chlorate is 
 converted into chloride of potassium, and the peroxide of manganese 
 remains apparently unchanged. 
 
 Those examples will serve to illustrate how influential in producing 
 decompositions may become, slight secondary affinities, to which we 
 should be disposed in our ordinary mode of view to attach little jimport- 
 ance. There is, at least, as much probability in the view that the catalytic 
 force is merely a modified form of chemical affinity exerted under peculiar 
 conditions, as there is in ascribing it to an unknown power, or to the 
 communication of an intestine motion to the atoms of a complex molecule. 
 A catalytic body is considered by Playfair as one which acts by adding 
 its own affinity to that of another body, or by exerting an attraction 
 sufficient to effect decomposition under certain circumstances without 
 being powerful enough to overcome new conditions, such as elasticity 
 and cohesion, which occasionally intervene and alter the expected result. 
 
 Such are the views now held by chemists regarding those interesting 
 classes of phenomena. We shall find occasion in a future chapter to 
 connect them with important discussions as to the molecular structure 
 and chemical constitution of the more complex bodies, and shall probably 
 therein obtain additional light for illustrating the real nature of the force 
 to which, as affinity, chemical action has been so far referred. 
 
235 
 
 CHAPTER VII. 
 
 OF THE LIGHT AND HEAT DISENGAGED DURING CHEMICAL 
 COMBINATION. 
 
 IT has been already noticed that the union of substances, having che- 
 mical affinity for each other, is accompanied by increase of temperature; 
 and in cases where the affinity is powerful, the effect may be so great 
 that the bodies shall become luminous : in such instances the chemical 
 action is said to be accompanied by combustion. In considering the re- 
 lations of this phenomenon to affinity, it will be necessary to notice, 
 first, the general circumstances of combustion ; secondly, the relation 
 between the amount of affinity and the quantity of heat evolved ; and, 
 finally, the explanations that have been offered of the origin of the light 
 and heat. 
 
 In ordinary language, a body is said to burn when its elements unite 
 with the oxygen of the air, and form new products. The accompany- 
 ing phenomena are in general those on which popular attention becomes 
 fixed, and for which the process is generally carried on ; and hence, to 
 the world at large, combustion is of importance only as a source of heat 
 and light. One of the bodies, as hydrogen or sulphur, is termed the 
 burning or combustible body, and the oxygen is said to be the supporter 
 of combustion ; but this language, although convenient for common 
 use, is incorrect as a scientific expression, for oxygen may be burned in 
 a vessel of hydrogen, as well as hydrogen may be burned in a vessel of 
 oxygen gas ; the one and the other being equally active in the process, 
 and being related to each other in every way alike. In combustion, as 
 indeed in all cases of combination, no particle of matter becomes lost 
 or annihilated ; it assumes new forms, in general gaseous and invisible 
 to the eye of popular observation, but easily collected, weighed, and 
 analysed by the means that chemistry possesses. The solid coal or wood 
 which burns to ashes, changes but its external aspect ; mixing with the 
 general mass of air under the form of carbonic acid gas and watery 
 vapour, its elements become the food of living plants, which, in their 
 
236 Products of Slow Combustion. 
 
 turn, cut down or fossilized, form to succeeding ages the stores of light 
 and warmth such as we now enjoy. 
 
 There are but few bodies endowed with so great an affinity for oxy- 
 gen as to enter into combustion at ordinary temperatures by contact 
 with it. If they do combine at ordinary temperatures with oxygen, the 
 products are not those which combustion would tend to generate, but a 
 distinct class of substances containing a smaller proportion of oxygen 
 combined. Thus, nitric oxide gas, combines with oxygen, even when 
 quite cold, forming red fumes of nitrous acid gas, which is an inferior 
 degree of oxidation. Phosphorus, wlien burning at common tempera- 
 tures, emits but little light, and forms phosphorous acid ; if it be heated, 
 it bursts into brilliant flame, and forms phosphoric acid, which contains 
 Jth more oxygen. Potassium combines at common temperatures with oxy- 
 gen, forming potash ; but when heated, it burns with flame, and com- 
 bines with three times as much oxygen. In the complete combustion 
 of organic matters the products are always water and carbonic acid. 
 Thus, woody fibre, which is C.HO. combines with 20 to form C0 2 and 
 HO. ; and alcohol, which is C 2 H 3 0, combines with 60 to form 2(C0 2 ) 
 and 3 (HO). But at common temperatures the slow oxidizement of 
 woody fibre produces the black vegetable mould, a form of ulmine, the 
 CHO taking O. to form CH0 2 . At common temperatures alcohol be- 
 comes acetic acid, the C 2 H 3 O combining with 2O to form C 2 H 2 O a and 
 HO. The pyroxylic spirit at common temperatures becomes, by slow 
 combustion, formic acid, C 2 H 4 O 2 taking 4 to form C 2 H 2 4 and 2 
 (HO). 
 
 This slow combustion produces heat, although so much less than is 
 evolved by the more rapid process, that it may easily be overlooked. 
 But if a number of sticks of phosphorus be laid together, and allowed 
 to oxidize, they will warm each other so much as to melt and burst in- 
 to vivid flame. The oils and tallow, if there be a large surface exposed 
 to the air, as when cotton or linen rags imbibed in oil, lie in a heap, 
 combine so rapidly with oxygen to form a sort of resin, that by the heat 
 evolved the mass will be set on fire, and hence the origin of those spon- 
 taneous fires, so called, which consumed the naval arsenal at St. Peters- 
 burgh, and, in many cases, cotton mills in England. To this cause also 
 may be ascribed the light which issues from points in the surface of a 
 marsh or bog, and the luminous appearance which fish assumes when 
 decomposition has just commenced. The energy of this slow combus- 
 tion may be much increased by heat applied below the point which 
 produces rapid action : thus tallow, when heated below redness, burns 
 with a pale lambent flame, invisible in daylight, but still so marked, 
 that if it be plunged into a vessel of oxygen the whole mass bursts into 
 
Products of Slow Combustion. 237 
 
 brilliant combustion, forming then the ultimate products, water and 
 carbonic acid. 
 
 On tliis fact of the increased energy in the process of slow combus- 
 tion produced by a heat below that at which the body is inflamed, is 
 founded the construction of the lamp without flame, or the aphlogistic 
 lamp. If a tall narrow wine glass be moistened inside with strong al- 
 cohol, or ether, and then a coil of fine platina wire, or a ball of spongy 
 platina heated to redness, be suspended in the middle of the glass, it will 
 remain red until all the alcohol or ether has been exhausted. The 
 glass becomes filled with a mixture of air and inflammable vapour, 
 which, by the influence of the heated platina, is enabled to combine and 
 form acetic and formic acids. By this combination heat is evolved, 
 which prevents the cooling of the wire or ball, and thus, as long as any 
 combustible material remains, the platina is kept ignited. The platina 
 ball or wire may also be (and in practice generally is) fixed over the 
 wick of a spirit lamp, and the lamp having been ignited, is blown out 
 as soon as the platina has become red, which then continues to glow 
 until the lamp has been emptied of the spirit ; the latter ascending 
 through the capillary wick, and forming over its top a little explosive 
 atmosphere in which the ball of platina is immersed and works. 
 
 This property of platina appears to depend on the power which it 
 possesses of attracting to its surface in a condensed form a layer of par- 
 ticles of whatsoever gaseous mixture it may be immersed in. Hence, if 
 its surface be in the slightest degree soiled it ceases to exert this action, 
 and by increasing the surface its energy may be augmented in a remark- 
 able degree. The form in which it is most powerful is that of the 
 slightly coherent spongy mass, obtained by reducing at a full red heat 
 the ammonia-chloride of platinum ; if a ball of the metal so prepared 
 be plunged into a vessel of oxygen and hydrogen, mixed in suitable 
 proportions, to form water, the gases instantly explode ; for the oxygen 
 and hydrogen, being absorbed by the spongy platina, are brought into 
 intimate contact upon its surface, and unite, thereby evolving so much 
 heat, as to raise the temperature of the platina ball to redness, and 
 thereby inflame the remaining gas. The action of the spongy platina 
 may be weakened by mixing it with some pipeclay, or using, as in the 
 aphlogistic lamp, the platina in the form of plate or wire. In this way 
 all combustible gases may be caused to combine gradually with oxygen, 
 but they require different temperatures, and the action is modified by 
 the presence of other gases, in a manner which is often taken advantage 
 of in gaseous analysis. 
 
 The most remarkable application of this property is to procure in- 
 stantaneous light by means of the hydrogen gas lamp. A vessel f t 
 
238 
 
 Action of Spongy Platina on Gaseous Mixtures. 
 
 contains dilute sulphuric acid, into which the tube of 
 the vessel gh dips nearly to the bottom, having at- 
 tached a piece of ordinary zinc e. The vessels being 
 ground air-tight where they fit to one another; when 
 the stop-cock b is closed, and that the acid acts on the 
 zinc, the hydrogen evolved cannot escape, and, press- 
 ing on the liquid in f, forces it up into h, until the 
 acid falling below the level of the zinc, the action 
 ceases. To the stop-cock I is attached a jet c, in 
 front of which is fixed a ball of spongy platina a, 
 which, being in the air, has always condensed in its pores a quantity of 
 oxygen gas ; on opening the stop-cock, the hydrogen, issuing from the 
 jet, strikes upon the platinum, and combining with the oxygen, heats 
 the ball so highly, that it inflames the jet of gas, and thus affords a 
 flame, at which any other substance may be lighted. This lamp has 
 assumed a variety of forms, of which the above is that which best shows 
 its principle. All bodies possess this property to a slight extent, par- 
 ticularly when hot ; but in none is it active enough to be usefully ap- 
 plied, except in platinum. 
 
 The temperatures at which bodies enter into rapid combustion are 
 very various ; thus, phosphorus inflames at a temperature of 1 20 P., 
 and sulphur at 300 E. Phosphuretted hydrogen gas inflames at all 
 ordinary temperatures, whilst hydrogen requires a dull red, and carbu- 
 retted hydrogen a bright red heat, before they will take fire. The in- 
 flammability of phosphorus has been shown by Graham to be affected 
 by the presence of small quantities of various substances, in a very 
 curious manner ; thus, phosphorus may be sublimed in air saturated 
 with vapour of oil of turpentine, without any tendency to combustion, 
 or combination with oxygen, being evinced. 
 
 Combustion occurs only at the point where the two substances which 
 enter into union are in contact. Thus in an ordinary flame 
 the true combustion is limited to a thin sheet, inside of which 
 is totally dark, and occupied by the combustible material of 
 the burning body in a state of gas. This is easily shown by 
 holding over the flame of a candle or a spirit lamp, a piece of 
 wire gauze, the burning sheet is marked by a ring of light, 
 but the interior is dark, although full of inflammable vapour, 
 which passes through uninflamed, and may be ignited on 
 the opposite side of the gauze. In the flame of an ordinary 
 candle a four distinct portions may be observed, having totally distinct 
 constitutions ; at the base of the flame ii a pale, blue coloured light 
 is emitted, for there the air is in excess, and the combustion is at once 
 
Constitution of Flame. 239 
 
 complete ; higher up from i i to c the combustible material is in excess, 
 and the most brilliant light is produced by the active combination ; this 
 portion is surrounded by a sheet of much paler and yellower light, e e, 
 which is observable particularly at the sides of the flame, whilst the 
 inside of the flame b remains completely black, and is occupied only 
 by vapour incapable of burning from having no access to the ex- 
 ternal air. The light emitted arises also from the circumstances of 
 the combination; the temperature of flame is, in all cases, exceed- 
 ingly high, although often but little luminous, for it is found, that 
 a current of air, hot enough to brilliantly ignite a solid body, is itself 
 not at all incandescent. Hence, in all cases where bright light is pro- 
 duced in combustion, one of the bodies engaged must be solid, and the 
 light is really derived from its becoming ignited. Thus hydrogen and 
 sulphur give, in burning, very little light, because the one is a gas, and 
 the other, when burning, is in the state of vapour, and the products of 
 combustion are, when formed, in both cases, gaseous. Phosphorus 
 when it, in burning, forms a volatile body, gives but little light, but 
 when it forms a fixed product, is one of the most brilliant instances of 
 combustion. Iron and zinc, which form solid oxides, burn with great 
 light, and carbon, although forming a gas, being itself solid, produces 
 light also. In the case of a candle, the source of light is to be found 
 in the decomposition which the inflammable vapour inside of the flame 
 undergoes from the high temperature to which it is subjected ; one half 
 of its carbon is deposited in the solid form, forming smoke, and it is 
 this smoke, which becoming ignited, constitutes the great source of 
 light. A body which could not form smoke, could not give out much 
 light in burning. The separation of this carbon (soot) in the flame may 
 easily be shown by placing over the flame of the candle a sheet of wire 
 gauze ; below the middle of the luminous space, the flame becomes dull, 
 and the carbon, which in burning should have rendered it brilliant, 
 passes, as smoke, through the gauze, and may be inflamed above ; when 
 the supply of air is insufficient, this smoke is not completely burned, and 
 a corresponding quantity of heating and lighting material is lost, and, as 
 it carries off with it a great quantity of the heat already formed, it actu- 
 ally cools the flame. When, therefore, a high temperature, or a clear 
 flame, without smoke, is required, all carbon must be consumed. This 
 is effected by a variety of contrivances : in the burner of the Argand 
 lamp, or gas jet, a current of air is established through the centre of the 
 flame, and thus the combustion of the inflammable vapour much acce- 
 lerated ; in the flame of the blow-pipe the same effect is produced, by 
 the current of air from the bellows or the mouth ; and on a large scale 
 by the numerous ways of burning smoke, so necessary in factories 
 
240 Constitution of Flame. 
 
 situated in large cities. In the employment of the blow-pipe, the con- 
 stitution of the flame is of great importance, for according as the body 
 to be heated is placed at b, where the oxygen of 
 the air preponderates, or between a and b, where 
 it is immersed in an atmosphere of inflammable 
 material., the most opposite effects of violent oxi- 
 dation, and of reduction from the state of oxide, 
 may be produced. Thus a glass of copper be- 
 comes green at b } and red from a to b ; a glass of manganese is ren- 
 dered purple at b, but colourless from a to b ; there being few bodies 
 whose relations to the blow-pipe can be completely known without a 
 comparison of the effect of the oxidizing and reducing flames. 
 
 The intimate nature of flame has been recently studied by Professor 
 Draper. It appears from his researches, that the light evolved by flame 
 contains, in every case, all the prismatic colours, and that the peculiar 
 tint of any one flame depends only on the dominance of some one 
 coloured ray. The different coloured lights are not, however, uniformly 
 mixed in flame, but, as Dr. Draper has beautifully shown, disposed in 
 a series of concentric shells, superposed, so that their intersection would 
 form a spectrum more or less perfectly prismatic according to the 
 nature of the burning body. The less refrangible, or red tints, form 
 the internal, and the more refrangible, or violet tints, the external 
 shells ; and, in fact, it is a general result of Dr. Draper's investigation, 
 that the colour of the light produced in combustion depends on the heat 
 evolved, the rays becoming more refrangible according as the tempera- 
 ture of the burning body rises, and less refrangible as the heat becomes 
 less intense. Thus the flame of a smoking candle, changes from reddish 
 white to blue when it becomes intensely hot from the blow-pipe. 
 
 During combustion the heat evolved is at first absorbed by the body 
 which is then produced ; but it is afterwards distributed through the 
 mass of all neighbouring bodies in proportion to their conducting 
 powers. It is easy to calculate the temperature to which the product 
 of the combustion is in the first place raised. Thus eight parts of 
 oxygen unite with one part of hydrogen by weight to form nine of 
 water. If watery vapour had the same capacity for heat as water, the 
 temperature of the vapour produced should be, since one part of oxygen 
 heats twenty-nine of water, 180 degrees, = f (29 x 180) = 4640 
 above the freezing point ; but the capacity of watery vapour in equal 
 weight is only 0*847, and therefore it is more easily heated in that pro- 
 portion than liquid water ; hence the temperature really produced is = 
 4640 x 0*847, or 5478 above the freezing point of water. If, how- 
 ever, instead of pure oxygen, atmospheric air had been made use of, 
 
Cooling Effect of Apertures. 241 
 
 then 23'1 parts of oxygen are mixed therein with 7 6 '9 parts of nitro- 
 gen, which must be heated to the same temperature with the watery 
 vapour, and of course at its expense. The capacity of nitrogen gas for 
 heat is 0*2865, one-third that of watery vapour ; but in the air which 
 is necessary to form nine parts of water, there are 26- 8, or almost ex- 
 actly three times as much nitrogen, so that precisely one-half of the 
 quantity of heat produced is absorbed by the nitrogen, and the tem- 
 perature of the mixture rises only to 2739 above the freezing point. 
 
 Such being the temperatures produced by hydrogen gas in burning in 
 oxygen and in atmospheric air, it is easy to understand why we can by 
 its power fuse those substances which resist almost every other means. 
 The melting point of cast iron is 2786, that is almost exactly the same 
 as that produced by hydrogen burning in the open air, but the temper- 
 ature of 5478, given by hydrogen burning in oxygen, is very nearly 
 double that, and passes, therefore, far beyond the melting point of pla- 
 tinum, and exceeds the heat of all our other artificial fires ; it is only in 
 the discharge of the Galvanic battery, or in the solar rays concentrated 
 by a lens, that the heating effects of burning hydrogen and oxygen can 
 be equalled. If the nitrogen had been present in a quantity ten times 
 as great, it would have absorbed | of the amount of heat evolved, and 
 hence the resulting temperature should be only about 500. Such a 
 mixture, therefore, could not explode at all, for the first little portion 
 which might be burned could not produce the necessary temperature for 
 communicating the combustion to the mass. In this manner the com- 
 bustibility of gaseous mixtures may be destroyed by mixing them with 
 other gases, in such quantities as may cool them below the temperatures 
 at which explosion can take place. One volume of a mixture of oxygen 
 and hydrogen is prevented from exploding by the presence of nine 
 volumes of hydrogen, six volumes of nitrogen, one of olefiant gas, two 
 of ammonia, three of carbonic acid ; but with eight volumes of hydro- 
 gen, or five volumes of nitrogen, explosion may occur. 
 
 The greater density of solid bodies, and the greater rapidity with 
 which they are capable of conducting away the heat 
 which they receive, enables them in a still more re- 
 markable degree to reduce the temperature of flame, 
 and consequently to extinguish it. Thus, if a piece 
 of metallic gauze be held over a jet of ignited coal 
 gas, the flame will be arrested at the lower surface 
 of the gauze ; and, although the gas and air may 
 pass through, forming an explosive mixture, yet no 
 inflammation can be propagated : and, if the mix- 
 ture of air and gas be allowed to pass through the 
 
Construction of the Safety Lamp. 
 
 metallic gauze, and then be ignited at its upper surface, it will burn there ; 
 but although the space between the jet and gauze be occupied by in- 
 flammable material, the flame cannot pass down; the metallic tissue 
 conducting away the heat so rapidly as to prevent the temperature from 
 rising to the necessary degree. Another and a very striking form of 
 this experiment is, to lay on the metallic gauze a piece of camphor, and 
 to hold it over a lamp ; the camphor will melt, and vaporize, but, as it 
 melts, it will in part filter through the gauze : this portion takes fire, 
 and a sheet of smoky flame covers the lower surface ; but above, the 
 camphor in vapour mixes with the air without inflaming. 
 
 The application of this principle to the construction of the safety 
 lamp for mines, constitutes one of the most beautiful instances of the 
 advantages which may practically flow from what, superficially con- 
 sidered, might appear a mere abstract principle in science. The fire 
 damp, or light carburetted hydrogen, which, issuing from the minute 
 fissures in the excavations of a coal mine, is diffused through the air 
 introduced for the purposes of ventilation, often forms an explosive 
 mixture, which being set on fire by accident or negligence, detonates 
 with awful violence, and destroys all living beings which may at the 
 time be in the mine. This gas is one of the least easily inflammable, 
 and hence, most fortunately for humanity, one to which the principle 
 
 of cooling orifices may be most success- 
 fully applied. The candle or lamp, 6, by 
 which light is to be obtained for working 
 in the mine, is surrounded by a cylinder 
 of wire gauze, of about 1500 orifices in 
 the square inch. Inside of this the in- 
 flammable mixture may explode, but the 
 flame cannot pass out. The combustion 
 cannot be communicated to the general 
 mass of external air, and thus the miner, 
 guided by the never-failing indications 
 of his safety lamp, passes along through 
 galleries under ground, where the emis- 
 sion of a spark would cause destruction, 
 and measures, by the appearance of the 
 lamp, the actual condition of the air he 
 breathes ; the phenomena of the flame 
 indicating also its fitness for respiration. If the air be pure, the lamp 
 burns clear, as in the upper air ; if some fire damp be present, the 
 lamp shows much less light, the flame becomes red and smoky ; if the 
 noxious impregnation be still increased, the flame of the lamp itself 
 
Quantity of Heat Evolved in Perfect Combustion. 243 
 
 becomes extinguished, and the cylinder of metallic gauze is filled by a 
 sheet of lurid flame ; the miner being then enveloped by an atmosphere 
 fully explosive, and even fatal to life, if it be long respired. If he 
 proceed still further, all flame is lost, for, as the fire damp then pre- 
 dominates, there is produced, from deficiency of oxygen, only a slow 
 invisible combustion ; but even this is made, by the sublime genius of 
 its inventor, Davy, to give the miner the last warning to return to safer 
 regions : a sheet of thin platina being coiled up, and hung over the 
 wick of the lamp, becomes ignited, as in the aphlogistic lamp, and 
 continues to emit a faint, but most useful beacon glow, until an atmos- 
 phere is obtained, where there is oxygen enough to support rapid com- 
 bustion, or until a place is reached, so destitute of oxygen, that no 
 combustion whatsoever can take place. 
 
 The determination of the quantity of heat produced during the com- 
 bustion of a given quantity of combustible substance, is a problem of 
 great importance in the arts, as on it depends the economic value of 
 all varieties of fuel. The plan generally followed has been to burn the 
 substance by means of the smallest quantity of air which is sufficient, 
 in a vessel surrounded, as far as possible, with water. If it be found 
 that the burning of a pound of wood heats 38 pounds of water from 
 32 to 212, no idea can be thereby formed of the quantity of heat 
 evolved; but if, in another trial, it be found that the burning of a 
 pound of charcoal raises the temperature of 76 pounds of water through 
 the same range, it follows that the charcoal had double the calorific 
 power of the wood. True relative numbers can thus be obtained, 
 although they have independently no positive signification. The results 
 obtained in this manner have been exceedingly discordant. By the 
 researches of Despretz, Dulong, and of Bull, an idea, first suggested 
 by Welther, appeared to be sustained, viz : that in all cases of combus- 
 tion the quantity of heat evolved is proportional to the quantity of 
 oxygen which enters into combination. Thus, Despretz found 
 
 1 lb. of oxygen, uniting with hydrogen, heats from 32 to 212, 29 Ibs. of water. 
 ,, ,, charcoal, ,, ,, 29 
 
 ,, alcohol, ,, 28 
 
 ether, 28* 
 
 This rule, however, must be liable to some very curious changes, for 
 one pound of oxygen, in combining with iron, could heat, by Despretz's 
 experiments, 53 pounds of water, or almost exactly twice as much as 
 in the former list, and with tin and zinc the same double proportion 
 held. With phosphorus a singular peculiarity was observed, which, 
 when the subject comes to be more fully studied, may throw some 
 
244 Theories of Combustion. 
 
 
 
 light upon the former differences. When phosphorus burns slowly, so 
 as to form phosphorous acid, it heats in combining with a pound of 
 oxygen, 28 pounds of water ; but when it burns brilliantly, and forms 
 phosphoric acid, the heat evolved is doubled, and becomes the same as 
 that produced with iron, tin, or zinc. As a suggestion, I would re- 
 mark, that, in the cases where the smaller proportion of heat is evolved, 
 the products of combustion are all volatile, and where the larger pro- 
 portion is produced, the products are fixed and solid : even in the case 
 of phosphorus, when it combines, producing least heat, it forms a vola- 
 tile product ; but one which resists a full red heat, in the case where 
 the combination has been complete. 
 
 Another peculiar anomaly is the relative amounts of heat given out 
 in the combustion of carbon and of carbonic oxide. By burning 1 
 pound of charcoal, 76 pounds of water are heated from 32 to 212; 
 but if that 1 pound of charcoal be converted into carbonic oxide, of 
 which it forms 2*33 pounds, the burning of this gas will produce heat 
 enough to raise 62 pounds of water through the same temperature. 
 Here the final product of combustion is the same in both cases, being 
 3'66 pounds of carbonic acid ; but the heat evolved is not at all pro- 
 portional to the quantities of oxygen absorbed. The 1 pound of char- 
 coal takes double the oxygen that the 2*33 pounds of carbonic oxide 
 takes; but the heat evolved is greater only in the proportion of 76 
 to 62. 
 
 The accuracy of Welther's rule has been, however, altogether put in 
 doubt by Grassi, who has made a very full examination of the quantities 
 of heat evolved in combustion, and his researches appear to have been 
 very carefully conducted. Taking the unit of heat to be 1 pound of 
 water heated from 32 to 212, he found that, 
 
 1 lb. hydrogen, evolved 347 unities. 1 lb. carbonic oxide, evolved 19 units. 
 
 1 lb. charcoal 79 ,, 1 lb. olefiant gas ,, 91 ,, 
 
 lib. alcohol 65 1 lb. marsh gas 125 
 
 1 lb. oil of turpentine 105 ,, 1 lb. pyroxylic spirit ,, 58 ,, 
 
 These results are not at all proportional to the quantities of oxygen 
 absorbed, but would rather favour an idea suggested by Hess, that a 
 compound body, in burning, always emits less heat than its elements, if 
 burning separately, should give. Thus, 1 pound of marsh gas gives out 
 125 units of heat; but the carbon of it, J pound, should give 57 
 units, and its hydrogen, \ pound, 89 units together, 146. There 
 had been, therefore, 21 units of heat lost by the elements being pre- 
 viously combined. Similarly, f pounds carbon and -f pounds hydrogen, 
 would have evolved 116 units of heat; that is 25 more than the 1 
 pound of olefiant gas which they form had been able to give out. 
 
Theories-of Combustion. 245 
 
 This subject has been further examined, and, indeed, Welther's prin- 
 ciple finally negatived by the investigations of Faber, Silbennan, and 
 Andrews. Those chemists having determined the heat evolved by the 
 combustion of a great variety of ethers and carbo-hydrogens, found by 
 their results, that on subtracting the oxygen, together with the hydrogen 
 necessary to convert it into water, the remaining elements do not de- 
 velope as much heat as they should in a free state. They also examined 
 sulphur in its different forms, and found that it evolved 23 units of heat. 
 In its combination of sulphuret of carbon, which yields 34 units, the 
 elements if free would have given 31 \ : that is, when combined they 
 yield 2J more than when free. This result is opposite in direction to 
 those previously quoted, and shews how much still remains before any 
 general principle can be announced as positively true, either in the form 
 proposed by Hess or "Welther. 
 
 Hess has lately pointed out a relation between the amount of chemical 
 action and the quantity of heat evolved, which may, when examined in 
 a greater number of cases, lead to very important conclusions. He has 
 found that sulphuric acid, in combining with any base, generates, in all 
 cases, the same quantity of heat ; the rise of temperature is, of course, 
 greatest when the acid and base are both in an uncombined condition, 
 as where vapour of anhydrous sulphuric acid produces, by contact with 
 dry barytes, brilliant ignition ; but although the barytes generates, by 
 contact with dilute sulphuric acid, much less heat, yet, if the two quan- 
 tities evolved, first by mixing the strong acid with water, and then the 
 dilute acid with the base, be added together, the sum appears, from a 
 great number of experiments, to be constant ; thus diluting oil of vitriol 
 with water, and neutralizing it, so diluted, with ammonia, Hess found 
 the heat in each case to be 
 
 With Ammonia. With Water. Sum. 
 
 OH of vitriol . . 595-8 . .. ./ ...... 595-8 
 
 First dilution . . 518-9 . . . 77'8 . 596'7 
 
 Second dilution V: 480-5 ... . 1167 . . 597'2 
 
 Connecting these results with those of Despretz just given for the 
 bodies which unite with oxygen, it would appear likely that the quantity 
 of heat evolved in chemical combination, may be connected with the 
 equivalent number and the electrical condition of the substances, by a 
 definite law which further investigation may disclose. 
 
 M. Hess has endeavoured to extend this principle to the union of 
 other acids with water and with bases ; thus, on uniting the three mineral 
 acids with the more important bases, he found the quantities of heat 
 evolved to be as follows : 
 
246 Thermo-Chemical Equivalents. 
 
 Sulphuric acid. Nitric acid. Muriatic acid. 
 Potash . . 601 409 361 
 
 Soda ; j r , 605 410 368 
 
 Ammonia . '. 598 404 368 
 
 Lime .* .642 451 436 
 
 In this table it is shown that by the neutralization of sulphuric acid, 
 by an aqueous solution of potash, 601 units of heat are evolved : the 
 same acid combining with ammonia evolves 598, and with soda, 605. 
 These numbers agree so well that Hess proposes to deduce the general 
 principle, that the quantity of heat which a given acid evolves in union 
 with different bases is the same in all cases, and to determine for each 
 acid thus a number which should be its tkermo-chemical equivalent. 
 From this principle follows also the condition of thermo-neutrality; thus, 
 if we take two solutions of neutral salts, which have the same temperature, 
 and produce by double decomposition two new salts, the temperature is 
 not altered, provided the salts before and after the experiment are in the 
 same condition of hydration. This phenomenon is perfectly explained 
 by the numbers given above in the table of Hess' results ; thus, the 
 therm o-chemical equivalents are- 
 Before the mixture. After the mixture. 
 CaO, NO 5 -f* Aq. .451 Ca O SO 3 + Aq. . 642 
 KO, 80s . . 601 KO, NO 5 ... 409 
 
 Sum . 1052 Sum . 1051 
 
 This subject has been also investigated by Professor Andrews of Bel- 
 fast, whose results differ materially from those of Hess ; indeed, in some 
 important respects, directly contradict them. From a very extensive 
 series of experiments on the heat evolved by the union of acids and bases, 
 it appeared that the quantity of heat was determined by the nature of 
 the base, and not at all by the nature of the acid, which might be varied 
 almost indefinitely without altering the result. The experiments were 
 all performed with very dilute solutions to avoid the corrections for the 
 heat produced when strong solutions of acids or alcalies are diluted. The 
 method of operating was as follows : In separate glass vessels solutions 
 of determinate weights were prepared, one containing the quantity of 
 alcali whose power of generating heat was sought, and the other a little 
 more than the equivalent of acid required for its neutralization. After 
 the liquids had. acquired the same temperature, they were mixed together 
 in the jar containing the alcali, and the increase of heat carefully observed 
 by a delicate thermometer. This process was adopted from the facility 
 of its execution and the uniformity of its results. It was, however, ne- 
 cessary to allow for the large quantity of heat absorbed by the glass 
 
Laws of Tliermic Substitution*. 247 
 
 vessels ; and the necessary corrections for this object and, also for the 
 specific heat of the liquids were determined by preliminary experiments. 
 The result of these experiments may be expressed in the following 
 table. An equivalent of each of the following bases evolve when neutral- 
 ized by an acid the following quantities of heat ; thus, 
 
 Magnesia . . 8*24 Ammonia . . . 5*52 
 
 Lime . . 7'10 Oxide of zinc . . 4-91 
 
 Barytes . . 675 Oxide of lead . . 3'98 
 
 Potash . . 6-52 Oxide of silver . . 3'23 
 
 Soda . . . 6-48 Oxide of copper . . 3-08 
 
 From these numbers Professor Andrews has inferred the following 
 general principles : 
 
 1st. That the heat developed during the union of acids and bases is 
 determined by the base and not by the acid : the same base producing 
 when combined with an equivalent of different acids nearly the same 
 quantity of heat, but different bases, a different quantity. 
 
 2nd. When a neutral is converted into an acid salt, by combining 
 with one or more atoms of acid, no increase of temperature occurs. 
 
 3rd. When a neutral is converted into a basic salt, by combining with 
 an additional proportion of base, the combination is accompanied with 
 the evolution of heat. 
 
 Looking to the constitution of all ordinary acids as salts of water, it 
 is evident that the neutralization of that acid is in fact the replacement 
 of the water by another base ; and hence the principle announced above 
 may be better stated, that when the same base displaces water from any 
 of its acid combinations, the same quantity of heat is evolved, and hence 
 the law has been shown by Andrews to be susceptible of a much more 
 general form of expression as follows. When any one base displaces 
 another from any of its neutral combinations t the heat evolved is always 
 the same, whatever the acid element may be, provided the bases are the 
 same. By the series of experiments made for the purpose of verifying 
 this general principle, Andrews found that the heat* evolved when the 
 several bases were expelled from their neutral salts by potash, were as 
 follows : 
 
 Lime . . 0-36 Protoxide of iron . . I '74 
 
 Barytes . . O'OO Oxide of mercury . 1 '86 
 
 Strontia . . 0-00 Oxide of lead . . 2 -82 
 
 Soda . . 0*08 Oxide of copper . . 3'00 
 
 Ammonia . . 0'74 Oxide of silver . . 3'93 
 
 Oxide of manganese . 1 '07 Peroxide of iron . . 4*09 
 
 The thermic conditions of the precipitation of one metal by another 
 
248 
 
 Thermo-Chemical Laws, 
 
 from a solution of one of its salts, have also been examined by Andrews, 
 who has announced the following expression of his results. When an 
 equivalent of one and the same metal replaces another in a solution of 
 any of its salts of the same order, the heat evolved is always the same, 
 but a change in either of the metals produces a different developement 
 of heat. By the expression, solution of a salt of the same order, is un- 
 derstood a solution in which a similar precipitate is produced by the 
 addition of alcali, or on one view of the composition of such salts in 
 which the metal exists in the same state of oxidation. Thus equivalent 
 solutions of the sulphate, chloride, acetate, and formiate of copper, gave 
 respectively, 868, 860, 877, and 869 units of heat, when precipitated 
 by zinc ; numbers which may be considered identical. The following 
 table embraces the general results. The numbers expressing the cen- 
 tigrade degrees through which a grain of water would be raised by the 
 heat developed by the precipitation of a grain of metal are, 
 
 Salt of Copper, precipitated by zinc 
 
 Copper by iron 
 
 Copper by lead 
 
 Silver by zinc 
 
 Silver by copper 
 
 Lead by zinc 
 
 Mercury by zinc 
 
 Platinum by zinc 
 
 592 
 268 
 426 
 161 
 182 
 333 
 
 It also appears that if three or more metals, A, B, and c, be so related 
 that A is capable of displacing both B and c from their combinations, 
 and that B is also capable of displacing c, then the heat evolved in the 
 substitution of A for c, will be equal to that developed in the substi- 
 tution of A for B, added to that evolved in the substitution of B for c. 
 By applying this principle, the amount of heat evolved in other cases of 
 metallic decomposition may be calculated. 
 
 An extensive series of experiments by Graham, on the change of tem- 
 perature which accompanies the solution of salts in water, and the union 
 of acids and bases, appear decidedly to support the general accuracy of 
 Andrew's views ; and although the differences between his results and 
 those of Hess, as to the heat of combination, will require further ex- 
 planation, it must be recognised that we are indebted to the Professor 
 in Belfast College, for the philosophical announcement of the numerical 
 laws of thermo-chemical action. 
 
 An interesting comparison has been made by Apjohn of the heat 
 evolved by the combination of ammonia and of muriatic acid with water, 
 and with each other, of which the following are the results. He found 
 the quantities of heat evolved by 
 
Theories of Combustion. 249 
 
 Would raise the temperature of 
 
 an equal weight of an atom 
 
 water. of water. 
 
 Ammoniacal gas passed into water . . 940 940 
 
 Muriatic acid gas passed into water . . 885o 1900 
 
 And that the heat evolved by passing ammonia 
 
 gas into muriatic acid 2523 
 
 Muriatic acid gas into liquid ammonia 1527 
 
 It is evident that these numbers are complicated by the simultaneous 
 developement of the heat of condensation and of the heat of neutraliza- 
 tion of the alcali and acid ; and the discrepancies have led Dr. Apjohn 
 to conclude, that although gaseous ammonia, when uniting with water, 
 gives out its heat of elasticity, yet that if liquefied ammoniacal gas were 
 brought into contact with water the production of a very intense degree 
 of cold should be the result. 
 
 At all periods in the history of chemistry, the explanation of the phe- 
 nomena of combustion was that for which the general theory of the 
 science was constructed ; and accordingly we find that every period of 
 its progress has been marked by the views adopted to account for the 
 heat and light so evolved. The coarse and unphilosophical ideas of the 
 existence of a peculiar principle of inflammability, which prevailed be- 
 fore Lavoisier's time, do not require notice ; but the theory which he 
 proposed, although not now received, is yet like all his works, of so 
 much interest and importance, that it would be improper to pass it over. 
 
 When Lavoisier lived, the minds of philosophers were fixed in the 
 opinion, that heat and light were positively existing substances, which 
 might enter into combination, or be disengaged from combinations in 
 which they had previously been engaged, just as lead or oxygen, or any 
 other of the ordinary bodies we operate upon in our experiments. 
 Gases were believed to be compounds of the true solid body with light 
 and heat ; and, hence, when oxygen gas, combined with iron or with 
 phosphorus, and assumed the solid form, the light and heat with which 
 the real oxygen had previously been united, were set free. Hydrogen 
 and oxygen gases, in combining to form liquid water, underwent the 
 greatest condensation, and by their union, therefore, the greatest heat 
 was evolved ; and in all such cases, where a gas became a liquid or a 
 solid, this theory was fully competent to explain the facts. However, in 
 very many cases it failed completely ; thus, by the union of carbon with 
 oxygen, so far from a gas becoming solid, and so evolving heat, a solid 
 becomes a gas, and should produce an equivalent degree of cold. La- 
 voisier here brought to his aid the relative specific heats of the gases 
 before and after union ; thus, if the carbonic acid, formed by burning 
 carbon in oxygen gas, had a much less specific heat than oxygen, there 
 
250 Heat of Combination derived from the 
 
 might be evolved a quantity of heat in the same way as it occurs with 
 water and sulphuric acid ; but this is not the fact : on the contrary, the 
 carbonic acid has a specific heat greater than that of the oxygen gas it 
 was formed from, in the proportion of 1195 to 808: and hence, on 
 Lavoisier's views, an intense degree of cold should be produced in the 
 combustion of charcoal, as well by the latent heat, which the solid 
 should absorb in becoming gaseous, as by the increased specific heat of 
 the gas so formed. This example is sufficient to show the way in which 
 Lavoisier's theory became inapplicable to the wants of science, 
 
 Dr. Thompson has recently endeavoured to account for the heat 
 evolved in chemical combination, by an application of the law of Dulong, 
 regarding specific heats (described page 83). Every molecule of a 
 simple body being supposed provided with the same quantity of heat, 
 he suggests, that when a number of them combine together, the heat of 
 one or more is expelled, and thus produces the rise of temperature. 
 Thus considering oil of vitriol to contain seven combining equivalents, 
 two of hydrogen, four of oxygen, and one of sulphur, and that the spe- 
 cific heat of all of these is the same, 3*1, as results from Dulong's law 
 if it be supposed rigidly exact, the specific heat of oil of vitriol should be 
 
 3*1 x 7 
 
 =0*442, 49*1 being the equivalent number of oil of vitriol; 
 
 4y * JL 
 
 but the specific heat found by experiment is only 0.352 ; so that ex- 
 actly one-fifth of the total quantity of heat has been lost by the act of 
 combination, and may hence be supposed to have caused the phenomena 
 of combustion. 
 
 In the extension of this principle a little further than Dr. Thompson 
 appears to have contemplated its application, some coincidences, with 
 results already known, are found, which give it an aspect of consider- 
 able theoretic interest. Thus, we may consider certain metallic oxides 
 as consisting of an equivalent of each constituent, and that hence their 
 proper specific heat should be, if none were lost by combination, 
 3*1x2=6-2; but the specific heat of the compound molecule is ex- 
 perimentally found to be 5*4, and thus that 0*8 of heat had been lost, 
 producing the phenomena of combustion in combination. In this man- 
 ner we can understand why Despretz found that a certain quantity of 
 oxygen evolves the same quantity of heat in combining with very many 
 bodies. If we examine the sulphates noticed, p. 85, in relation to 
 the same principle, we find that as there are in each, six molecules, the 
 specific heat should be 18*6=3'1 X6, but it is found to be but two 
 thirds of that, 12*4. Now, if here, as in the oxides, the combustible 
 material retains its heat, and that it be from the oxygen that the por- 
 tion set free is taken, the experimental result arises from the heat of 
 
Change of Specific heat in Combustion. 
 
 251 
 
 each oxygen molecule being reduced by 1*6, and hence, that when oxy- 
 gen forms a salt with sulphur and a metal, the heat evolved is double 
 that produced in simple oxidation. The fact of the same quantity of 
 oxygen giving double the amount of heat when it converts phosphorous 
 into phosphoric acid, than when it forms only phosphorous acid, may 
 have its origin in an analogous condition. 
 
 In the case of the carbonates, another form of the principle becomes 
 manifest ; but on this view, it is necessary to consider carbonic acid as 
 containing five molecules, one of carbon and four of oxygen, and as 
 uniting with two molecules of a metallic oxide. The carbon and metal 
 burn each in half of the quantity of oxygen with which they ultimately 
 unite, and, like phosphorus, separate from that oxygen only the smaller 
 quantity which it can lose when entering into combination ; the car- 
 bonic oxide and suboxide then unite with the residue of oxygen, and 
 from it separate the larger portion of heat, as occurs when phosphoric 
 acid is produced. The resulting specific heat for a carbonate is, there- 
 fore, 9 t 3 + 6'9 + 4*5= 20*7, or reduced to the equivalent number used 
 in p. 84, it is 10*35, the experimental number being 10*4. 
 
 The results in these three cases may be shown in the form of the 
 following table, in which the first column contains the equivalent mole- 
 cule of the body, M denoting the equivalent of a metal ; the second 
 column contains the specific heats calculated on the supposition that 
 there is none lost in combining ; the third, the calculation by which the 
 fourth column of true calculated specific heats is obtained ; and the 
 fifth, the specific heats that have been found by experiment. 
 
 1. 
 
 2 
 
 3. 
 
 4. 
 
 5. 
 
 MO 
 
 6-2 
 
 3-1 _|_ 2-3 
 
 5-4 
 
 5-4 
 
 MOS 
 
 186 
 
 (2X3-1) + (4X1-5.) 
 
 122 
 
 12-4 
 
 M*OC 
 
 27.0 
 
 (3 X 31) + (3 X 2-3) + (3 X 1'5) 
 
 207 
 
 20-8 
 
 The coincidences refer only to the bodies already selected, pp. 83, 
 85, as examples of simplicity in the relation of their specific heats, 
 and certainly do not exist in a great number of other cases in which I 
 have sought for them ; they may, therefore, be accidental, but there is 
 yet so much likelihood of some physical law of the kind being to be 
 discovered, that every thing that may assist in its detection is of im- 
 portance. Laying aside altogether the attempt at deducing the pheno- 
 mena of combustion from any change in the amount of latent or spe- 
 cific heat in the bodies which enter into combination, it remains only to 
 be admitted as a general and independent principle, that chemical com- 
 
352 Electro- Chemical Decomposition . 
 
 bination is a source of heat and light. It is, however, impossible to 
 arrest inquiry at that point, and accordingly the speculations of philo- 
 sophers have been directed to seeking a cause for the phenomena of 
 combustion, to the disengagement of electricity, which accompanies all 
 manifestations of chemical action, and have endeavoured to identify the 
 light and heat emanating from a burning body with that which is pro- 
 duced by the separation or combination of the electric fluids. The 
 evidence in favour of this view will be best described among the rela- 
 tions of electricity to affinity. 
 
 CHAPTER VIII. 
 
 OF THE INFLUENCE OF ELECTRICITY ON CHEMICAL AFFINITY. 
 
 IT has been already shown that in the production of Galvanic or hydro- 
 electric currents, there always occurs between the liquid and solid ele- 
 ments of the circle a degree of chemical action to which the quantity 
 of electricity generated is exactly proportional in amount, and that no 
 current, such as was there described, can be generated without that, by 
 the chemical action of the more oxidizable metal, the zinc, the liquid be 
 decomposed, and some one element of it be expelled, in place of which 
 a corresponding quantity of zinc may be substituted. I did not then 
 attempt to discuss the question of whether the chemical action in the 
 battery be the cause or the effect of the current which arises, as that can 
 be best done when the action of the current, no matter from what 
 source it may have been derived, upon chemical substances, similar to 
 those that are used as exciting liquids in the galvanic battery, has been 
 described. 
 
 If the wires belonging to the plates z c, of the 
 simple circuit in the figure, be brought into commu- 
 nication by means of a cup of water, the current 
 passes, and it is found that at the terminations of the 
 wires, bubbles of gas form in considerable number, 
 which when collected, are found to be, from the wire 
 in connexion with the copper plate, oxygen gas, and 
 hydrogen gas, from the wire which is attached to the 
 plate of zinc. If the conducting liquid had been muriatic acid, hydro- 
 
Influence of Electricity on Affinity. 253 
 
 gen would have been evolved as gas at the zinc extremity, and chlorine 
 liberated upon the wire of the copper plate, though from its solubility 
 in the liquid, it would not be disengaged as gas. 
 
 If a solution of iodide of potassium had been employed, iodine would 
 appear upon the copper side, and potassium should be set free upon the 
 zinc-wire ; but by the action of the water, the metal should be instantly 
 converted into potash, and hydrogen set free. 
 
 It is not necessary that such bodies should be in solution, for this 
 only serves to give to their particles the freedom of motion, which may 
 allow their elements to separate. If chloride of lead melted in a cup, 
 be used to complete the voltaic circuit, chlorine is evolved upon 
 the + and lead upon the wire ; with oxide of lead (litharge) the 
 evolution of lead at the , and of oxygen upon the + extremity of 
 the wires, occurs similarly ; proto-chloride of tin, iodide of lead, chloride 
 of silver, all act in the same way. 
 
 In place of bodies consisting of two elements, such as those above 
 described, we may employ in solution, or in a fused state, secondary 
 compounds, consisting of an acid and a base. If the current of electri- 
 city pass through a solution of sulphate of soda, the sulphuric acid 
 appears upon the + and the alcali upon the wire. With sulphate 
 of magnesia, the earth passes to the negative, and the acid to the positive 
 extremity of the liquid circuit ; in these cases water is also decomposed, 
 of which the hydrogen accompanies the base, and the oxygen the acid ; 
 but, on using a salt of lead, of silver, or of copper, the metallic oxide is 
 reduced by the action of the nascent hydrogen, or at least it may be so 
 expressed, and the metal is deposited in crystals upon the wire, whilst 
 the acid and the oxygen are evolved together, upon the extremity of the 
 positive conductor. 
 
 The affinity which held together these bodies in combination, is super- 
 seded during the passage of the electric current. The elements pre- 
 viously united appear to repel each other, and to be at the same time 
 attracted by the excited terminations of the metallic wires, by which 
 the battery is placed in connexion with the substance to be decom- 
 posed. 
 
 The simplest mode of accounting for these phenomena, is to say that 
 water is decomposed, because the oxygen is attracted more powerfully 
 by the positive pole of the Galvanic battery than by the hydrogen, with 
 which it had previously been associated, whilst this last is more power- 
 fully attracted by the negative pole than by the oxygen. The elemen- 
 tary bodies separate, therefore, from each other, but not being capable 
 of entering into combination with the substance of the poles, they are 
 evolved as gas. This explanation may be applied to all such cases, 
 
254 
 
 Electro- Chemical Classification. 
 
 Oxygen, chlorine, iodine, sulphur, as well as the various acids, are at- 
 tracted by the positively electric pole, whilst the hydrogen, potassium, 
 sodium, copper, silver, lead, and the various bases are attracted to the 
 negative side of the battery. But one force cannot completely super- 
 sede another, as electricity here supersedes affinity, unless it be of the 
 same kind, or at least closely resembling it in nature. What then is 
 the relation between the chemical force which had kept the elements 
 united, and the electrical force which makes them separate ? The cause 
 was easily found : they are identical. The oxygen and hydrogen united 
 originally from being in opposite electrical states, and they are found to 
 separate, from being subjected to the action of still more powerful at- 
 tractions ; the decomposition of water by the voltaic current becoming 
 thus a case of double decomposition in which the original electricities 
 of the two simple bodies were the quiescent, and the excitation of the 
 opposite poles of the battery were the divellent forces. 
 
 Chemical substances were thus considered to have affinities for each 
 other, from being in opposite electric states, and the peculiar play of 
 affinity of each body depends on which electricity it was naturally ex- 
 cited by, when in combination ; those bodies which are attracted by the 
 positive pole of the battery being necessarily in the negative condition, 
 and vice versa. Thus, all substances may be divided into two classes ; 
 those being termed electro-negative which are evolved at the copper 
 pole of a simple, or at the zinc pole of a compound circle, and those 
 which appear at the opposite pole being termed electro-positive. The 
 simple bodies thus classified are ranged as in the following list :- 
 
 Electro-negative. 
 
 
 Electro-positive. 
 
 Oxygen. 
 
 , r ' 
 
 Mercury. 
 
 Palladium. 
 
 Potassium. 
 
 * Fluorine. 
 
 Chrome. 
 
 1 Silver. 
 
 ! Sodium. 
 
 j Chlorine. 
 
 s Vanadium. 
 
 1 Copper. 
 
 Lithium. 
 
 1 Bromine. 
 
 T Iridium. 'y 
 
 | Lead 
 
 Barium. 
 
 i Iodine. 
 
 Rhodium. 
 
 Tin. 
 
 Strontium. 
 
 Sulphur. 
 
 I Uranium. 
 
 Bismuth. 
 
 Calcium. 
 
 * Selenium. 
 
 Osmium. 
 
 Cobalt. 
 
 Magnesium. 
 
 T Tellurium. 
 
 i Platinum. 
 
 Nickel. 
 
 Glucinum. 
 
 1 Nitrogen. 
 
 Titanium. 
 
 I Iron. 
 
 ! Yttrium. 
 
 i Phosphorus. 
 Arsenic. 
 
 Gold. 
 Molybdenum. 
 
 Manganese. 
 Cadmium, 
 
 Thorium 4 
 Aluminum. 
 
 Antimony. 
 
 Tungsten. j Zinc. 
 
 Zirconium. 
 
 Silicon. 
 
 Columbium. 
 
 Hydrogen. 
 
 Lanthanum. 
 
 Boron. 
 
 . j 
 
 Carbon. 
 
 Cerium. 
 
 1 
 
 
 The most powerfully negative bodies are placed in the first, and those 
 most powerfully positive in the fourth column, these being connected by 
 the intermediate columns, in the order marked by the brackets and 
 
Theories of Chemical Combination. 255 
 
 arrows. Any substance in the list is positive with regard to any other 
 towards which the arrow points, and negative in relation to any from 
 which the arrow is directed. Thus, hydrogen is negative to all in the 
 fourth, but positive to all in the three preceding columns, and so on. 
 These positions should also indicate the relative affinities of the simple 
 bodies towards each other, but in interpreting such arrangements, it 
 must be recollected that the order of affinities may be totally changed 
 by heat or by cohesion, and that the electrical order may be completely 
 different according to the nature of the exciting liquid, as in the table, 
 p. 168. 
 
 Two bodies in combination are, therefore, like two pith balls which 
 mutually adhere, but of which the attraction is permanent from their 
 electricities not being discharged. How do these bodies acquire those 
 oppositely excited states ? and why, if their condition resembles that of 
 ordinary electricity, do they remain combined when their opposite fluids 
 might unite, and neutralization being produced, all combination cease ? 
 
 These two questions have not yet been answered. Several times 
 their explanation has been attempted ; and thus the electro-chemical 
 theories of Davy, Ampere, and Berzelius, have been proposed. I shall 
 briefly notice the leading features of these before proceeding to discuss 
 the remarkable advances recently made in our ideas of the electro-che- 
 mical relation of bodies by Faraday and Graham. 
 
 The theory of Davy was based upon the principle, that bodies in their 
 ordinary uncombined condition do not contain free electricity, but that by 
 contact they become excited. Thus, a disk of sulphur touched to a disk 
 of copper becomes negative and the copper positive ; its charge increases 
 in intensity on applying heat, until, at a certain temperature, the tension 
 of the electricities becomes so great that they suddenly recombine, car- 
 rying with them the molecules of the sulphur and copper which thus 
 enter into union, and producing the evolution of light and heat by which 
 the chemical action is accompanied. The sulphuret of copper, when 
 formed, is no longer electric ; it remains permanent in virtue of a force 
 which Davy does not strictly define, but which he appears to have con- 
 sidered an intimate cohesion between the particles which had been closely 
 approximated by their electrical attractions ; and when by an electric 
 current the molecules of copper and sulphur are brought into the reverse 
 state to that which favoured their combination, they separate. This view 
 supposes, therefore, the electrical excitation to be only momentary, during 
 the act of combination, and during the moment of disunion ; before and 
 after, all is neutral. To all phenomena of decomposition this theory 
 suffices, but it is vitally deficient in the principle upon which it is based. 
 It has been since completely proved, that it is not the contact which 
 
256 Electro-Chemical Theories. 
 
 evolves electricity, but the chemical action ; and also, on Davy's viewer, 
 the electrical disturbance only suffices to account for the secondary phe- 
 nomena of union, the light and heat, leaving the act of combination to 
 be ascribed to a different and independent force of affinity or cohesion. 
 
 A more complete theory was proposed by Ampere, whose philosophical 
 views in magnetism and other sciences have been found so singularly in 
 accordance with experiment. He proposed to consider, that each sub- 
 stance in nature is endowed with a definite amount of one or of the other 
 electricity, and is thus naturally and invariably electro-positive or electro- 
 negative, and stands higher or lower in the list of bodies, according to 
 the intensity of the charge. Such an excited body he considered to 
 attract round its mass an atmosphere of electricity of the opposite kind, 
 and corresponding in intensity. Now, on bringing into contact an 
 electro-positive and an electro-negative body, their atmospheres unite, 
 and produce the heat and light resulting from their chemical action on 
 each other ; but the bodies themselves must remain permanently com- 
 bined, as each retains its own excitement, and they hence attract without 
 cessation. When one body is exactly as negative as the other is positive, 
 the resulting compound cannot manifest any signs of electro-chemical 
 activity ; but if the charge of the negative body be more powerful than 
 that of the positive element, the resulting compound will be negatively 
 excited to the amount of the difference between the two ; if the propor- 
 tions be reversed, the new body formed will be positive in the same 
 degree ; and such compound electro-negative and electro-positive bodies, 
 being acids and bases, attract each other, and unite to form neutral salts. 
 
 All that was difficult to comprehend upon the theory of Davy is here 
 beautifully explained. The light and heat of combination is produced 
 by the atmospheres of electricity ; the permanence of combination, by 
 the invariable excitation of the molecules. The gradually diminishing 
 intensity of charge, according as the bodies formed become more complex, 
 necessarily follows : but the assumption, that any one body is naturally 
 and invariably positive or negative, is contradicted by the history of 
 almost all the simple substances. 
 
 Thus, if sulphur or arsenic be heated in oxygen gas, they burn, and 
 the combination is effected with all the phenomena of intense action, the 
 resulting compounds being acid and electro -negative. The sulphur and 
 arsenic are thus shown to have been feebly positive bodies. But if sul- 
 phur or arsenic be heated with potassium, there is similarly combustion, 
 shewing that chemical combination has taken place, and as potassium is 
 the most positive body in the series, the sulphur and arsenic must be the 
 negative elements of the compounds. Sulphur and arsenic are therefore 
 at one time positive and at another negative. There is indeed no sub- 
 
Electro -Chemical Theory of Ampere. 257 
 
 stance known which can be said to be invariably negative or positive. 
 Nor can the amount of negative or positive excitement be in any case 
 looked upon as constant, for oxygen is often found to be less negative 
 than chlorine, and potassium to be less positive than iron, or than 
 carbon ; and hence if electrical forces be considered as representing 
 affinitary power, they must be capable of the same fluctuations in 
 intensity. 
 
 It was for the purpose of bringing Ampere's theory into harmony 
 with the changes of chemical decomposition, that Berzelius proposed 
 the modification of it, which now remains to be described. He sug- 
 gested, that each body should be looked upon as containing the two 
 electricities, but that the one might be more powerfully developed than 
 the other, as in a magnet one pole may be stronger than the other ; 
 also, from the analogy of certain bodies, which were supposed to admit 
 the passage of one electricity rather than the other, he imagined that a 
 body thus excited with the two fluids might discharge the one, and yet 
 retain the other. Thus, oxygen possesses high negative and feeble 
 positive excitation ; hydrogen, an intense positive, but a feeble negative 
 charge. When these bodies combine, the phenomena of combustion 
 follow from the union of the positive fluid of the oxygen with the ne- 
 gative of the hydrogen, and the more intense and more permanent 
 charges retain the bodies in combination. To account in this way for 
 certain bodies being at one time electro-negative, and at another electro- 
 positive, Berzelius considers, that when potassium is brought into con- 
 tact with sulphur, the naturally feeble negativity of the latter is height- 
 ened by induction ; whilst, if the sulphur be acted on by oxygen, it is 
 its positive charge that is increased : and thus any substance, near the 
 middle of the electro-chemical series, may become positive or negative, 
 according as it combines with a body situated nearer to the negative 
 or positive extremity. 
 
 This view might explain most chemical phenomena ; but it is, like 
 Davy's theory, founded on physical principles which cannot be considered 
 sound. Thus, although the effect of one pole of a magnet may be 
 weaker than another, that only happens where the action is complicated 
 by the existence of more poles than two ; and in ah 1 cases, the amount 
 of north and south magnetism present is exactly equal. Also, the fact 
 of the existence of bodies, which conduct the one better than the 
 other electricity, is now abandoned by all sound reasoners, and cannot 
 be looked upon as even in any degree probable in theory. Indeed, all 
 views like those of Berzelius and Ampere, which are founded on the 
 existence of different degrees of electrical excitement, which represent 
 the different powers of affinity by which chemical substances combine 
 17 
 
258 Elements Evolved not on Attracting Poles, lut 
 
 must be now abandoned ; for it has been proved by Faraday, that a 
 molecule of oxygen, in uniting with hydrogen to form water, or with 
 zinc to form its oxide, a molecule of iodine or chlorine, uniting with 
 lead, with tin, with silver, or potassium, bodies so far separated in the 
 electro-chemical scale founded on their re-actions, evolve, in uniting, 
 the same quantity of electricity, and require for their separation, 
 when combined, the same amount of current derived from another 
 source. 
 
 Before more definite and correct ideas of the electrical relations of 
 chemical substances can be obtained, it is necessary to study somewhat 
 more in detail the chemical phenomena which occur in the Galvanic 
 battery, which for simplicity shall be considered as a simple circle ; and 
 in the liquid through which the circuit is completed ; the former is 
 generally termed the generating; and the latter the decomposing cell. 
 
 The decompositions hitherto described, have been considered as re- 
 sulting from the attractive and repulsive forces of the extremities of the 
 wires on which the charge of the battery was supposed to be collected. 
 But, when the circuit is completed, no such accumulation can exist ; 
 once the current passes, it is everywhere present in equal quantity and 
 of uniform tension : and such forces of attraction and repulsion, acting 
 upon molecules already electrically excited, were only imagined for the 
 foundation of the imperfect theories already noticed, and, when impar- 
 tially examined, are found to have no real existence. It is also fatal 
 to the idea of attractive forces exercised by the poles, that the sub- 
 stances evolved upon their surface do not necessarily combine with 
 them ; thus, if one platina pole have such attraction for oxygen as to 
 separate it from the hydrogen it had been united with, it is unreasonable 
 that it should lose, suddenly and completely, this power, and allow 
 the oxygen totally to escape ; the other platina pole behaving similarly 
 to the hydrogen. 
 
 Faraday has definitely shown, that the disengagement of the sub- 
 stances, which are separated from each other by the 
 current, take place in all cases at the bounding sur- 
 faces of the body decomposed ; and that where they 
 are evolved on the metallic conducting wires, it is 
 only because those are the limits of the decomposing 
 fluid. The proofs of this principle are numerous 
 and simple : thus, in a glass basin, a partition of 
 mica, a, is cemented so as to be completely water 
 tight, and extending half way to the bottom ; a 
 strong solution of sulphate of magnesia is poured in 
 until it rises a little above the edge of the partition ; 
 
>i 
 
 on the Limiting Surfaces of the Liquid. 259 
 
 and then distilled water poured in on the side c, d, with such precaution 
 that it shall not mix with the saline solution, but shall float on it, the 
 surface separating the two liquids remaining perfect at c. The solution 
 of sulphate of magnesia is now to be connected with the negative pole 
 .of a battery by means of the platina plate, b, and the water with the 
 other pole of the battery by the plate c, which dips slightly inclined 
 below the surface. When the circuit is completed, the sulphate of 
 magnesia and the water are simultaneously decomposed, the oxygen 
 appears upon the plate 6, the hydrogen gas upon the plate e ; but 
 although the sulphuric acid is liberated freely upon the plate b, no mag- 
 nesia travels further than the limiting surface of the saline liquor, c. 
 Here the metal e serves as a pole to the hydrogen, but not to the mag- 
 nesia ; and the water on which the magnesia is evolved has no power 
 to prevent the further passage of the hydrogen. 
 
 If A, c, B, be filled with solution of sulphate of soda, and that by 
 means of the plates p and N, a current from a 
 battery be passed through it, the acid will 
 collect upon the one and the alkali upon the 
 other plate : but, if by means of pieces of 
 bladder, a and 6, the vessel be divided into 
 three compartments, A, c, and B, and that the 
 central one being filled with a solution of sulphate of soda, whilst dilute 
 nitric acid is poured into those at the sides in order to afford a conducting 
 medium, no acid or alkali appears at the metallic poles when the current 
 passes, but are evolved upon the inner surfaces of the partitions a and 
 b : it is only when, by mechanical filtration, some of the liquor of c 
 passes into A and B, that the slightest trace of sulphuric acid or of 
 soda can be found upon the metallic plates. 
 
 By the electricity of the machine the same principle can be demon- 
 strated ; if a slip of paper, moistened with solution of iodide of pot- 
 assium, be held near the insulated prime conductor, of the electrical 
 maclnne, whilst in action, and that the rubber be connected with the 
 ground, so as to ensure a continuous discharge of positive electricity 
 into the air, iodine will be evolved in quantity upon the point of the 
 paper nearest the prime conductor, whilst hydrogen and potash may be 
 traced as far as any liquid conductor, admitting of their passage, goes. 
 Here there is nothing that can be termed a pole, the iodine is dis- 
 charged upon the limiting surface, which is here that of the atmospheric 
 air. 
 
 Hence the idea of poles which produce attractions and repulsions in 
 a closed circuit must be abandoned, and some other way of explaining 
 the decomposition of the liquid elements of the circuit must be obtained. 
 
260 Internal Molecular Mechanism 
 
 The word poles must first be laid aside, and the expressions proposed 
 by Faraday in their place, deserve universal adoption. The surfaces, 
 whether of metal, of water, of acid, or of air, by which the current 
 passes from one kind of conductor to another, he terms electrodes 
 (TjXsxrgov, odo$) y they being the routes through which the electricity makes. 
 its way. I shall, therefore, in future speak of the positive and nega- 
 tive electrodes, in relation to the surfaces, generally of metal, by which 
 the battery is brought to act upon the substance which is to be de- 
 composed. 
 
 Since there are thus no attractive forces by which the chemical affi- 
 nities of the substances in the decomposing cell can be overcome ; to 
 what mechanism can we attribute the separation of elements which 
 occurs ? Concerning this as yet there is only speculation to be pre- 
 sented. The decomposition is certainly propagated from particle to 
 particle, that is to say, at the moment that the molecule of water loses 
 oxygen, at the positive electrode, a different molecule gives off its hydro- 
 gen upon the negative electrode ; neither the hydrogen of the former 
 nor the oxygen of the latter become free, but the decomposition is 
 transferred from one particle to another along the line, all particles of 
 oxygen advancing a step against the current, and the molecules of 
 hydrogen moving in a corresponding manner in the direction of it. 
 Thus, if a line of particles of water in a decomposing cell, be repre- 
 sented before the current passes, the electrodes being represented by 
 
 & ^ the plus and minus signs ; on the current passing, 
 
 -f. OH. OH. OH a molecule of oxygen will be evolved upon the 
 
 63 positive, and one of hydrogen upon the negative 
 
 TT O O ^ side, as in the second line, and as this motion is 
 
 H H participated in by every molecule of oxygen and 
 
 s * hydrogen in the circuit, they will come into the 
 
 + OH. OH fi na l position of the third line. The current still 
 
 & * passing, another molecule of each will be evolved 
 
 H * TT + as in the fourth, and ultimately all the intervening 
 
 water may be decomposed. The separation of 
 
 /^QT/ * ne elements being thus accompanied by a continual 
 
 rotation on each other of the intermediate mo- 
 lecules, each molecule of oxygen being successively united with every 
 molecule of hydrogen in the series, and each molecule of hydrogen 
 combining in turn with every particle of oxygen as it passes along. In 
 Paraday's words, the current is an axis of power, equal, and exerted in 
 opposite directions, by which, in every case of a binary compound, the 
 molecules of one element are carried in one direction, whilst those of 
 the other constituent move in the reverse course. 
 
of Electro- Chemical Decomposition. 261 
 
 From this idea, the evolution of the iodine, the soda, or the magnesia 
 on surfaces of air, of bladder, or of water, is easily understood. The 
 sulphates of magnesia and soda are decomposed, because there exists in 
 the solution a chain of particles of sulphuric acid capable of conveying 
 their bases along, and these are evolved where that chain of acid par- 
 ticles is broken, although there may. be other conductors to complete 
 the circuit. The iodine is evolved where the air touches the surface of 
 the paper, because the air has no potassium by which it could be car- 
 ried further. The decomposition appears thus to be effected, not by 
 annulling chemical affinity, but with its assistance, for it is exactly with 
 those conducting bodies, whose elements have the strongest affinities 
 for each other, that decomposition is most easily effected. Thus iodide 
 of potassium is decomposed much more easily than iodide of lead, yet 
 the affinity of potassium for iodine is certainly greater than that of lead 
 for the same element. 
 
 It is in this manner that arise the remarkable phenomena of transfer 
 observed first by Humphrey Davy. 
 
 If a solution of sulphate of soda be 
 placed in the glass a, dilute sulphuric 
 acid in the glass o, and water in the 
 glass c, and that they may be connected 
 together with slips of amianthus, moist- 
 ened to allow the passage of the cur- 
 rent, and that the positive electrode of a battery be immersed in a, and 
 the negative in c, the sulphate of soda will be decomposed, and its al- 
 cali will appear in <?, although the acid in I, through which it must 
 have passed, retains all its power. Here then was the affinity of the 
 acid in b for soda completely annulled by the superior attraction of the 
 negatively electric pole in c } and this was considered to be further 
 proved by the acid preventing the passage of barytes, for which its affi- 
 nity was so much stronger ; when a contained nitrate of barytes, the 
 earth, on entering into d, combined with the sulphuric acid, and went 
 no further. But in these experiments, considered at the time so deci- 
 dedly in favour of Davy's theory, that which was believed to be the 
 obstacle to the passage of the soda, is in reality the cause of it. Had 
 there been no acid in #, no alcali could have passed across it, and the 
 barytes remained combined only because, becoming insoluble, it no 
 longer formed any portion of the liquid conducting medium. 
 
 It has been, indeed, found, that although a feeble current may be 
 transmitted through liquid conductors, without any sign of decom- 
 position, that yet, in general, the passage of a more powerful current 
 can only be accomplished by means of bodies which are at the same 
 
262 Of Electrolysis and Electrolytes. 
 
 time decomposed by its influence. Faraday proposes to term the de- 
 composition by the current electrolysis [jjXexrgov, Xu] and such bodies 
 as undergo electrolysis electrolytes. It is, therefore, only electrolytes 
 that are capable of conducting, and they do so by the opposite direc- 
 tions in which the chains of liberated particles move. That electroly- 
 sis may occur, it is necessary that the substance be in the liquid state, 
 and hence all conducting power is lost when the body becomes solid ; 
 ice is a nonconductor, and it is only by being melted that the chlorides 
 and iodides of lead and silver, and such bodies, become capable of con- 
 duction, and of being hence decomposed. But there are many bodies 
 which insulate when cold, and yet when heated, allow the current to 
 to pass even before they fuse, its passage being unattended by any elec- 
 trolysis, even though the current be very powerful. Sulphuret of sil- 
 ver, iodide and chloride of mercury, and fluoride of lead are remarkable 
 examples of this anomaly. 
 
 Faraday, considering that such words as electro-positive, and electro- 
 negative, involve too much those ideas of attractive and repulsive forces 
 emanating from the poles, which have been proved to be incorrect, pro- 
 posed some changes of nomenclature, which if not adopted, deserve to 
 be at least described. If we consider a voltaic battery lying on the 
 ground, with the positive end to the east, and the wire connecting the 
 ends bent into an arch, similar to that which the sun describes in his 
 daily rotation, the current will flow up from the point of the sun's 
 rising, and pass down into the battery opposite the point at which he 
 sets. If the wire be now interrupted by a decomposing cell, the sur- 
 face at which the current enters the liquid may be termed the anode 
 (ava upwards) and the other the cathode (nark, downwards) ; oxygen 
 chlorine, and such bodies, are evolved upon the surface of the anode, 
 whilst from the cathode hydrogen and the metals are liberated. The 
 elements which, by their combination, form electrolytes, Faraday pro- 
 poses to term ions ('V',) and to distinguish them into anions which pass 
 to the anode, and cations which pass to the cathode. Electro-negative 
 bodies are, therefore, anions, and electro -positive substances are cations 
 in Faraday's nomenclature. These names are shorter and involve less 
 theory than the older terms, and hence deserve adoption. 
 
 The most important principle that has been as yet discovered, con- 
 necting the agencies of electricity and affinity, is the law of definite 
 electro-chemical decomposition. If the same current of electricity pass 
 through a series of electrolytes, it will decompose a quantity of each, 
 which is proportional to its chemical equivalent. Thus, at the same 
 time, and by the same force there are obtained, 
 
Electro- Chemical Equivalents. 263 
 
 8 grains Oxygen, and 1 Hydrogen, from 9 parts of water. 
 35-4 Chlorine, and I Hydrogen, 36-4 muriatic acid. 
 35-4 Chlorine, and 108 Silver, 143*4 ,, chloride of silver. 
 
 126-3 Iodine, and 103*6 Lead, 229'9 ,, iodide of lead. 
 
 The principle of definite electro -chemical action may be applied to 
 measure the quantity of electricity which is circulating in the current, 
 for by collecting the substances evolved in the decomposing cell, we 
 may obtain a standard to which all other effects may be reduced. In 
 such case the decomposing cell becomes a voltameter, or measurer of 
 voltaic electricity. One of its most convenient forms consists in a 
 
 conical vessel, A, terminated by a tube, 
 B, in the neck of which are soldered 
 the platina electrodes in connexion 
 with the battery, the vessel and tube 
 being filled with water, which is ren- 
 dered easily decomposed by the addi- 
 tion of sulphuric acid ; when the circuit 
 is completed, a quantity of oxygen and 
 hydrogen, proportional to the amount of electricity which passes, is 
 evolved, and issuing from the aperture at c, may be collected in an 
 inverted glass and measured. A variety of other forms, not differing 
 in principle, have been proposed and are in use. 
 
 If the absolute identity of electrical and chemical agency be insisted 
 on, then, in all electrolytes, the elements must be held together by the 
 same force, since they require the same amount of electricity to procure 
 decomposition ; and we should return nearly to the principles of Ber- 
 thollet, that chemical affinity was equally powerful for all bodies, and 
 merely appeared to vary from external influences ; but this would be a 
 rash and unphilosophical conclusion ; those electrolytes are but one class 
 of chemical bodies, those which are primary compounds, of an equivalent 
 of each element ; the current does not act upon deuxtoxides or bichlor- 
 ides, and on double salts its agency is exceedingly complicated. All 
 that can be inferred from this very beautiful result is, that the elements 
 of bodies in separating from each other under the influence of a current, 
 combine all with the same quantity of electricity, and that, as the spe- 
 cific heats of the ultimate particles of bodies have been already found to 
 bear a simple relation to each other, the specific electricities may follow 
 an equally, or still more, simple law. 
 
 Having thus examined the important phenomena produced in the 
 decomposing cell, the current being considered as originating in any 
 sufficient source, we shall pass to the discussion of what occurs in the 
 generating cell, where the current, which passes through the other, is 
 
A 
 
 264 The Chemical Voltameter. 
 
 evolved by the mutual action of the liquid and solid elements of the 
 Voltaic battery. 
 
 For the generation of the current, it has been already shown to be 
 necessary, that the liquid excitant should be an electrolyte, and that the 
 solid elements should occupy positions in the electro-chemical scale, as 
 remote as possible from each other in relation to the liquid which is 
 employed. That the solid elements also should be conductors ; by which 
 the selection is limited to the metals and to some forms of carbon. Now 
 when a slip of zinc is immersed in an electrolyte, which we shall, for 
 simplicity, consider for the future to be muriatic acid, the particles of 
 the acid are brought into a state of excitation, the molecules 
 of hydrogen becoming positively excited, and those of chlo- 
 rine becoming negative. This condition was already de- 
 scribed (page 178) as being that of the acid particles; but 
 it is now necessary to indicate more nearly the immediate 
 manner in which it is produced. The mass -of zinc itself, which we before 
 considered as having, like a magnet, its positive excitation referrible to 
 one, and its negative to the other extremity, must also, like the magnet, 
 be looked upon as consisting of a great number of excited elements, 
 each of which has its positive and negative extremities ; or, for greater 
 definiteness, they may be considered as grouped in pairs, of which one 
 molecule is positively and the other negatively excited. The condition 
 of the slip of zinc of last figure may, therefore, be represented as in the 
 figure at the side ; the particles of zinc being contained in the shaded 
 A bar, and those of the liquid, consisting 
 
 r -T+T T+lf-YV) f-Y?) ^ cn l r i ne an d hydrogen, represented 
 d *^-^^ ^- /v outside of it. The terminal particle of 
 Zn Zn Zn Zn Cl H Cl H . , . ... -, ,f 
 
 zinc becoming positive, and the nearest 
 
 particle of chlorine becoming negative, there would result immediate 
 union if no other action interfered, but the chlorine is held back by the 
 positive molecule of hydrogen with which it is united, and so the action 
 continues balanced, no matter how far the series may extend on either 
 side. If now the plate of copper be introduced so as to complete the 
 circuit, and to allow the passage of the Galvanic 
 current, it is easy to see how the decomposition of the 
 exciting fluid follows. Tor, although in the arrange, 
 ment above described the inductive excitement is 
 most active at A, and diminishes from thence as it ex- 
 tends along the zinc upon the one hand, and through 
 the fluid upon the other, yet, when, as in the figure, 
 the circuit is completed, the action becomes equally 
 powerful all through ; the particles of copper assume 
 
Arrangement of the Elements of the Generating Cell. 265 
 
 a condition similar to those of the zinc, but in the reverse order, the 
 molecule next the acid being negative, and that becoming positive 
 which is in contact with the zinc, and hence a complete chain of induc- 
 tively polarized particles being established, precisely such as are repre- 
 sented by the cuttings of silk thread which convey a current from an elec- 
 tric machine through oil of turpentine ; the 
 molecular arrangement being represented 
 in the adjoining figure. Such being the 
 k Cu position of the mutually excited mole- 
 cules, the electricities of the particles of 
 zmc an ^ chlorine nearest to each other 
 combine, and their neutralization is fol- 
 Acid. lowed by that of the entire chain; the ad- 
 
 jacent particles of zinc and chlorine then unite, and the hydrogen, dis- 
 engaged, is thrown upon the second particle 
 of chlorine, its hydrogen upon the third chlo- 
 rine molecule, by which the hydrogen it had 
 V r k een previously united with, being thrown 
 off, is emitted under the form of gas. 
 
 The three distinct stages in this reaction 
 are, therefore, 1st, The mutual excitation by 
 inductive polarization of the zinc and muriatic 
 acid. This is the fundamental fact due to the chemical relations of these 
 bodies. 2nd, The completion of the chain of inductively polarized par- 
 ticles by the intervention of the copper plate and connecting wire. 3rd, 
 The passage of the current and the consequent decomposition of the 
 liquid electrolyte in the cell, the chlorine being evolved upon the zinc 
 with which it enters into combination, and the hydrogen being eliminated 
 upon the surface of the copper plate. 
 
 The source of the current is, therefore, not to be found in the decom- 
 position of the acid, for it precedes it ; but the quantity of chemical 
 action in the generating cell is proportional to the quantity of electricity 
 which passes, for it is produced entirely by its agency. There is, there- 
 fore, no difference in reality between the generating and the decomposing 
 cell ; the action in each is equally produced by the passage of the electric 
 current ; but in the generating cell one element at least, the chlorine, is 
 absorbed by the electrode (the zinc) on which it is evolved, and the 
 amount of obstacle presented to the passage of the current is proportion- 
 ally less. 
 
 Such is the theory of Galvanism, which I believe to be most consistent 
 with all the results hitherto obtained. The current cannot have its 
 origin in the contact of solid bodies, for it remains the same, no matter 
 
66 Molecular Origin of the Current. 
 
 how much the circumstances of contact may be changed ; and by every 
 alteration of the conditions of chemical action, it varies in direction and 
 in power, although the relations of the solid bodies which are in contact 
 are not affected. Neither does the current arise from the transfer of 
 elements which occurs in the generating cell, for on the contrary, the 
 transfer of elements results from the passage of the current, indicating 
 its direction and measuring its amount ; but the current arises from the 
 continuous restoration through the copper, or positive element, of the 
 excitation produced by the tendency of the zinc to combine with the 
 chlorine of the muriatic acid. In fact, although I have hitherto con- 
 sidered the zinc as only influencing the acid by means of a disposition 
 to unite with one of its constituents, yet, such expressions being rather 
 abstract and indefinite, may in the present case be laid aside. The zinc 
 does, on immersion, decompose a certain quantity of acid, of which the 
 hydrogen is evolved in the form of gas, constituting upon the surface of 
 the zinc an exceedingly thin layer. The chlorine is then in a state of 
 combination, which is not without analogy in other cases, that is, in pre- 
 sence of two substances for which its affinity is equally intense, it is dis- 
 posed to unite with either according as external forces intervene, and is 
 determined to the zinc by the establishment of the current. 
 
 The proofs that hydrogen must be thus nascently liberated upon the 
 surface of the zinc, are to be found in a phenomenon already noticed 
 under the head of affinity ; the precipitation of one metal from its salts, 
 by means of another, having a greater affinity for oxygen than it. If 
 we immerse in a solution of sulphate of copper, a slip of pure zinc, there 
 is instantly a deposition of copper, which we must ascribe to the superior 
 affinity of zinc for oxygen and sulphuric acid ; but when the zinc has 
 become thus sheathed in metallic copper, the decomposition should 
 cease, by the access of the acid being prevented, were it not that the 
 copper deposited acts as the copper element of a Galvanic circuit, and 
 the subsequent decomposition proceeds, each new portion of copper 
 being deposited on the outside, farthest from the zinc, the action of 
 which becomes thus at every moment more intense. If hydrogen had 
 a physical constitution, such as would enable it to act as the positive 
 element of a simple Galvanic circle, then, no doubt, the purest zinc 
 would decompose the muriatic acid, the circuit being completed by the 
 hydrogen evolved, but such is not the case owing to its gaseous form ; 
 but it being that alone which is the obstacle, the previous step, which 
 depends simply on the chemical affinity of hydrogen and chlorine, may 
 reasonably be considered to have occurred. 
 
 The action of electricity in separating the elements of bodies is 
 scarcely of greater interest or importance from the ideas it suggests of 
 
Compound Bodies formed fy the Current. 267 
 
 the nature of chemical affinity, that it becomes as a means of presenting 
 to each other, under the most favourable circumstances for union, the 
 different elements of the Yoltaic circuit, and thus causing the formation 
 of bodies for whose construction the ordinary processes of the laboratory 
 are much too violent and abrupt. In this way some of the most re- 
 markable substances of the mineral kingdom may be artificially pro- 
 duced, the secretion of the metalliferous ores into the veins and cavities 
 of rocks accurately represented, and bodies, whose affinities for each 
 other rank as the most intense, completely, though silently and gra- 
 dually, separated from each other. It is to Becquerel that we owe 
 almost all our knowledge of this important function of electricity ; from 
 him we have also received the important lession, that it is not in the 
 brilliant effects of the great batteries of Davy or of Callan that we must 
 seek a clue to the history of the electrical processes of chemical affinity, 
 but in the slow but unintermitting action of currents of such low in- 
 tensity that a drop of pure water would be an insuperable obstacle in 
 their path. The electricity to be employed in the artificial formation of 
 compound bodies must be such as is generated by a single pair, and 
 these generally of metals whose similarity prevents that current from 
 being of great amount. 
 
 These phenomena, into the examination of which I cannot enter with 
 much detail, are best observed by means of a tube bent into a U shape, 
 and at the bottom of which is interposed a porous par- 
 tition of clay or plaster of Paris ; the liquids, whose 
 mutual reaction is to generate the new substance, are 
 placed in the legs of the tube, one at each side of the 
 partition, through the pores of which they gradually 
 mix with each other. The Voltaic current is then 
 supplied either by connecting the liquids with the 
 poles of a feeble battery, or by immersing in one leg a zinc, and in the 
 other a copper or platina plate, connected by a wire with each other. 
 If a solution of carbonate of soda and of sulphate of copper be thus 
 brought to act on one another, a double carbonate of copper and soda 
 crystallizes on the plate immersed in the copper liquor ; and if then the 
 solution of soda be replaced by ordinary water, a new current is gene- 
 rated which decomposes the first product, and forms a new crystalliza- 
 tion of carbonate of copper. If the zinc leg be filled with a solution of 
 oxide of zinc in potash water, and a solution of nitrate of copper be 
 placed on the copper side, a crystallization of oxide of zinc is produced 
 upon the zinc plate, and a deposition of crystallized copper upon the 
 metallic surface in the other leg of the tube. 
 
 By using two liquids which have unequal chemical actions on a strip 
 
268 
 
 Formation of New Compounds ly the Current. 
 
 of metal, this may be made to precipitate itself, being reduced at one 
 extremity according as it is dissolved at the other. 
 Thus, if the glass, A, be filled with solution of ni- 
 trate of copper to a, and then water, rendered 
 slightly acid by nitric acid, be gently added, up to 
 the level of B ; a slip of copper, introduced so as to 
 present equal surfaces to the two liquids, generates 
 a current which passes up through its mass, and 
 down from the lighter to the denser fluid ; the cop- 
 per dissolves, therefore, above, and the salt formed 
 being electrolyzed by the current, its metal is de- 
 posited on the lowest surface, under the form of crystals, and this is 
 continued until the free acid, and hence the electro-motive force in the 
 liquid, becomes equal, when, of course, no current passes. 
 
 Dr. Bird, who has extended considerably the results obtained by 
 Becquerel, has constructed an apparatus for such reactions, with which 
 he has obtained, in an isolated form, those simple bodies, as boron, 
 silicon, potassium, &c. whose compounds resist ordinary means most 
 
 obstinately. It consists of a gene- 
 rating and of a decomposing cell. 
 This last is a glass cylinder #, with- 
 in another glass cylinder b. The 
 inner one a is four inches long, and 
 an inch and a half in diameter, and 
 is closed at the lower end by a plug 
 of plaster of Paris, 0* 7-inch in 
 thickness. The cylinder is sup- 
 ported within the other 1), which is 
 an ordinary jar, about eight inches deep and two inches diameter, by 
 means of wedges of cork. A piece of sheet copper c, four inches long 
 and three inches wide, having a copper conducting wire soldered to it, 
 is loosely coiled up and placed in the inner cylinder, whilst a piece of 
 sheet zinc, of equal size, is also coiled up, and laid on the bottom of the 
 outer cylinder, it being also furnished with a conducting wire. The 
 outer cylinder is then to be nearly filled with a weak brine, and the 
 smaller with a saturated solution of sulphate of copper : the two fluids 
 being prevented from mixing by the plaster of Paris diaphragm. After 
 it has been in action for some weeks, chloride of zinc is found in the 
 external cylinder, and beautiful crystals of metallic copper, frequently 
 mixed with the ruby protoxide, (closely resembling the native ruby 
 copper ore,) and large crystals of sulphate of soda, are found adhering 
 to the copper plate in the smaller cylinder, especially on that part where 
 
Synthetic Action of Electricity. 269 
 
 it touches the plaster diaphragm. The apparatus is completed by the 
 decomposing cell which is, in fact a counterpart of the battery itself, 
 consisting like it, of two glass cylinders, one within the other, the 
 smaller one having a bottom or floor of plaster of Paris fixed into it ; 
 this smaller tube may be about half an inch wide and three inches in 
 length, and is intended to hold the metallic solution submitted to expe- 
 riment, the external tube, b, into which it is immersed being filled with 
 a weak solution of common salt. Into the latter solution, a slip of 
 amalgamated zinc, (for the positive electrode,) soldered to the wire 
 coming from the copper plate of the battery, is immersed ; whilst, for 
 the negative electrode, a slip of platina foil, fixed to the wire from the 
 zinc plate of the battery, passes through a cork, c, fixed in the mouth 
 of the smaller tube, and dips into the metallic solution it contains. 
 
 The influence which electricity thus exercises upon affinity, and the 
 modifications in its results, producible by its means, although proving a 
 most intimate connexion, do not go, as I believe, so far as to demonstrate 
 a complete identity of cause. It is possible that, hereafter, some sublime 
 generalization may embrace the phenomena of heat, of light, and of 
 electricity, of cohesion, and gravity, as well as of chemical affinity within 
 one law, and indicate how, by varied manifestations of a single agent, 
 their separate peculiarities may arise ; but though we may look forward 
 to such a state of science, we dare not rashly seek to anticipate its ap- 
 proach, and I look upon electricity as producing, and being produced by 
 chemical phenomena, precisely as we find heat to influence as well as to 
 be evolved by chemical combination. 
 
 \There electricity is brought into play so powerfully by the action of 
 a simple body upon a compound fluid, it is, I consider, unreasonable to 
 imagine, that in the combination of simple bodies, or of compound 
 bodies, with each other, no electricity should be set free ; particularly 
 when it is proved, that in such cases some electricity does appear, al- 
 though in quantity, bearing no proportion to that of the feeblest Gal- 
 vanic battery. If I were to suggest an electro-chemical theory, such as 
 might agree with the facts that have hitherto been discovered, I would 
 consider that bodies in their free state, are perfectly destitute of excita- 
 tion ; but that chemical union, or the degree of intimate approximation 
 which precedes union, may be a source of electrical disturbance, and is 
 that which, in all ordinary cases, gives origin to the electricity employed 
 in our experiments. When united, bo.dies are likewise destitute of 
 electrical properties ; in iodide of potassium, the bond is the affinity of 
 iodine and potassium for each other, and not that the iodine is in a 
 permanent state of negative excitation whilst the potassium remains 
 positive. 
 
270 Theory of the Relations 
 
 If hydrogen gas be burned in oxygen, there is evolution of electricity, 
 of which only a trace escapes immediate recombination under the form 
 of light and heat, but the existence of which, in a highly intense form, 
 has been demonstrated by Pouillet. The oxygen and the vapour of 
 water produced, assume the positive condition ; the residual hydrogen 
 becomes negative. If carbon be burned in oxygen, there is likewise 
 combustion and evolution of electricity, of which the positive passes off 
 with the carbonic acid, aud the negative rests upon the carbon. The 
 evolution of heat may be in these cases an independent effect of combi- 
 nation, but I would look upon it as being more probably the result of 
 the union of the electricities evolved. If the bodies which act upon 
 each other, are dissolved in water, there is no combustion, but heat is 
 still evolved, and the electricities unite with one another, without the 
 necessity for any intermediate circuit. It is only where the replacement 
 of one body by another occurs, that the establishment of the chain of 
 inductively polarized molecules becomes necessary ; for the particles of 
 zinc and hydrogen, which become oppositely excited, have no power to 
 combine, and hence cannot be restored to neutrality unless by the 
 medium of a third body, to which both may impart their excitations. 
 That the zinc and hydrogen upon the one hand, and the copper and 
 hydrogen upon the other, do not unite, is, as I conceive, fatal to those 
 views which assume the identity of chemical and electrical, or, as they 
 call it, current or inductive affinity ; for if a molecule of copper in the 
 acid stood in the place of, and acted as a molecule of chlorine, it should 
 unite with the hydrogen in place of allowing it to pass off free. 
 
 The act of chemical union being such as to produce electrical excita- 
 tion and discharge, before it is completed, and the permanent combina- 
 tion of the elements being the result of the return to the neutral state, 
 it is easy to understand that, when these conditions are reversed, the 
 chemical affinity should be superseded, and the bodies brought into the 
 state in which they had been at the moment of excitation, and whilst 
 their elements, oppositely excited, were yet separate from each other. 
 A compound body is, therefore, as I apprehend, decomposed by the 
 battery, from having this electrical state given to it by the current, and 
 the transfer of its elements across the liquid is accomplished by a series 
 of neutralizations and excitations, accompanying the unions and decom- 
 positions by which they pass to the electrodes, where they yield up their 
 ultimate excitation, and appear isolated and completely neutral. The 
 quantity of electricity necessary to decompose a body is, therefore, the 
 same as it had evolved when its elements entered into union ; and it 
 should hence follow, that the current of electricity evolved in the union 
 of chemical equivalents of the simple bodies with each other, should be 
 
of Electricity and Affinity. 271 
 
 the same. That this actually occurs, would follow from the laws of 
 heat; if an equivalent of oxygen, in combining with various metals, 
 evolves the same quantity of heat, and if the heat be a consequence of 
 the neutralization of electricity, the quantity of this evolved should be 
 the same also. It appears likewise that an equivalent of any base 
 in combining with different acids, evolves the same quantity of heat, and 
 to decompose the various salts thus formed, the same quantity of elec- 
 tricity should be required ; and hence, that the two actions, so com- 
 pletely equivalent to each other, may satisfactorily be referred to the 
 same source. 
 
 Such is the interpretation I put upon the phenomena of electro-che- 
 mical decomposition, and the relations of electrical forces to affinity. 
 In the molecular condition of polar excitation, which accompanies the 
 passage of a current, I adopt fully the peculiarly explicit mode of repre- 
 senting the actions of the bodies on each other, proposed by Graham, 
 but I consider it too hypothetical to assume that such molecular state 
 naturally exists in bodies ; it may or it may not ; but in the absence of 
 evidence that it does, I am not inclined to presuppose it unnecessarily. 
 I look upon the current as being produced by the union of opposite po- 
 larities, which are themselves not the cause but the consequence, of the 
 chemical affinities of bodies. Graham is not disposed to admit that the 
 union of simple bodies, may be accompanied by any electrical pheno- 
 mena, and to exclude also from the application of an electro-chemical 
 theory the combination of acids and of bases with each other, as not 
 capable of generating currents ; but the reason of this is, as I imagine, 
 that the currents so generated are necessarily closed. 
 
 In concluding the admirable Treatise on Electricity, with which he 
 has enriched scientific literature, M. Becquerel details the views which 
 he has adopted regarding the electro-chemical relations of bodies ; and 
 although they are not expressed with the definiteness which might be 
 wished from so distinguished a philosopher, I shall endeavour, in conclud- 
 ing this section, to give a short description of them. In the main, 
 they do not differ much from the principles of electro-chemical combi- 
 nation which I have long since adopted, and which have been already 
 noticed. 
 
 M. Becquerel considers that in all bodies there is distributed a quan- 
 tity of electricity indefinitely great, which is so intimately connected 
 with their molecular constitution, that it is disturbed and excitation 
 produced in all cases where molecular disarrangement is produced, 
 hence pressure, friction, an unequal distribution of heat, &c., are sources 
 of electricity. 
 
 Chemical affinity is also a source of electrical disturbance. When an 
 
272 -Electro-Chemical Theory of Becquerel. 
 
 acid combines with an alcali, the first sets free positive electricity, and 
 the second an equal quantity of negative electricity ; these two combine 
 immediately in the liquor forming neutral fluid, and produce as many 
 currents as there had been particles in action ; now this multitude of 
 little currents ought to determine the production of a quantity of heat, 
 depending on the energy with whicli the affinity was manifested and the 
 conducting power of the liquid. In decompositions, the electrical effects 
 are inverse, that is, the acid takes the negative, and the alcali the positive 
 electricity ; hence, it may be concluded, as M. Becquerel had already 
 stated with regard to aggregation, that if electricity does not constitute 
 affinity, it is at least indispensable to its manifestation, since it is always 
 subjected to the same laws every time that simple or compound atoms 
 unite or separate. From all considerations it appears, that the electricity 
 produced by chemical action is only an effect resulting from the action 
 of the affinities brought into play, and this effect being brought into in- 
 verse action in decomposition announces at the same time a molecular 
 electric state, indispensable to the permanent union of the elements of 
 compound bodies. 
 
 To explain decomposition by a current of electricity, M. Becquerel 
 adopts Ampere's idea of electrical atmospheres, although he denies that 
 any bodies are naturally or permanently in a positive or negative con- 
 dition ; but he supposes that the neutral condition of a body consists in 
 the molecule being either positive or negative, and being surrounded 
 by an atmosphere in an opposite state. When bodies unite, the union of 
 their atmospheres produces light and heat, and the molecules remain ex- 
 cited whilst in union ; although the union is the cause of the electrical 
 disturbance, and not its effect. Now, when zinc is put in contact with 
 water, this last is decomposed, and there is hence a disturbance of elec- 
 tricity, the particle of zinc abandons its negative atmosphere, and unites 
 in a positive condition with the negative and nascent oxygen ; the hydro- 
 gen is liberated nascent also, and highly positive ; in this state the oxy- 
 gen would be balanced between the two equally positive particles of zinc 
 and hydrogen, and the decomposition could not proceed ; but if a slip of 
 copper be introduced, this supplies a negative atmosphere to the positive 
 hydrogen, which becoming neutral, is evolved as gas, and, transferring its 
 positive electricity to the point of contact with the zinc, neutralizes its 
 excess of negative excitement, and generates the current. M. Becquerel 
 refers the chemical action of the current, in the decomposing cell, to each 
 electricity setting the same electricity of the compound in motion in the 
 same direction with which the particles are transferred by a series of 
 combinations and decompositions, as has been already described, until 
 the limits of the substance are attained, and then the elements are evolved 
 in the neutral state. 
 
Of the Measure of Affinity. 273 
 
 M. Becquerel has endeavoured to apply the agency of electricity to 
 determine the relative affinities which bodies have for each other. His 
 principle is as follows : if nitrate of copper and nitrate of silver be dis- 
 solved together in equal quantities, and decomposed by a Galvanic cur- 
 rent, the nitrate of silver alone is at first affected, because the affinity of 
 the silver for the oxygen and acid is so much less than that of the cop- 
 per for the same. But, when the quantity of nitrate of copper is gra- 
 dually increased, a term is arrived at when the electric current is ex- 
 actly equally divided between the two metals ; the greater quantity of 
 copper making up for the greater resistance it offers to the decomposing 
 power. His results are, that when the solution contains twenty parts 
 of copper to one of silver, the current acts equally on both ; when the 
 copper is 25 to 1, the current acts as if it divided itself | to the cop- 
 per, and to the silver ; and when the quantity of copper is thirty 
 times that of the silver, there are three equivalents of the copper salt 
 decomposed for one of the salt of silver. M.E. Becquerel has essayed 
 the same important problem in a different way, by testing the power of 
 solutions of chlorine, iodine, and bromine, to absorb nascent hydrogen 
 and nascent oxygen, evolved in their mass by means of a Galvaniq cur- 
 rent. His results appear to show, that the affinities are expressed by 
 the numbers : for 
 
 Hydrogen. Oxygen. 
 
 For Chlorine 1"! . .^h * 922 For Chlorine ?. ' i ?K> ? 169 
 
 Bromine Y^T-.;csOiIo '. 712 Bromine T 'io v:-r;;^ 3 80 
 
 Iodine , ,':. f 212 Iodine . .. - . .469 
 
 These two series are, however, independent of each other, and afford 
 no mutual term of comparison whatsoever. 
 
 It is to be trusted that such investigations, conducted with the inge- 
 nuity and accuracy which the Becquerels can so well apply, may lead to 
 results of the highest interest to science. The reduction to numerical 
 laws of the influence of quantity on affinity, and the determination in 
 numbers of the tendencies of the simple bodies to unite, would certainly 
 advance the condition of chemistry, as an exact science, in a remarkable 
 degree. 
 
 18 
 
274 
 
 CHAPTEE IX. 
 
 ON THE LAWS OF COMBINATION. 
 
 THE general nature of affinity and the modifications which it undergoes 
 from the influence of the physical agents, having been now stated, I 
 shall proceed to discuss the numerical laws to which its results are sub- 
 jected, the discovery of which was the first step in conferring upon 
 chemistry the character of an exact science. 
 
 It is characteristic of chemical affinity, that the proportions, in which 
 bodies are brought to unite by its agency, are limited upon both sides, 
 whereas in those cases where molecular forces alone prevail, the pro- 
 portions, although perhaps limited in one direction, are indefinite in the 
 other. Thus, a saturated solution of chloride of sodium cannot take 
 up any more salt, but it may be mixed with any quantity of water, 
 whereas the chlorine and the sodium, which constitute the salt, form it 
 only in certain proportions which are invariable, 100 parts containing 
 always 39-66 of sodium and 60*34 of chlorine. If it were not for 
 this constancy of proportion, the science of chemistry could never have 
 advanced beyond its merest elements ; for had chlorine and sodium 
 been capable of combining in all indeterminate proportions, or had the 
 properties which we recognise in chloride of sodium been ascribed to 
 compounds of those elements in every possible proportion, no accurate 
 ideas regarding the constitution or properties of bodies could have been 
 acquired, and none of the benefits derivable from experience or experi- 
 ment could have been attained. The first law of constitution is, there- 
 fore, that the composition and properties of any given substance are 
 always the same. 
 
 When by the intervention of superior affinities or by double decom- 
 position, a compound body is decomposed and a new compound formed, 
 the proportions, by weight, of the various substances brought into 
 action, have a constant relation to one another, and as they represent 
 the quantities of the bodies which exercise equal, or at least equivalent 
 combining powers, they are termed, when reduced to numbers, the 
 combining proportions or equivalents of these bodies. Thus, if 100 
 parts of oxide of copper be heated in a current of hydrogen gas, it is 
 reduced, and the hydrogen, uniting with the oxygen which it contained, 
 
Numerical Determination of Chemical Equivalents. 275 
 
 forms water. In the 100 of oxide, there were 79-83 of metallic cop- 
 per and 20*17 of oxygen, which last taking 2' 5 2 of hydrogen forms 
 22-69 of water. Now, in this case the 2*52 of hydrogen produce the 
 same result of satisfying the combining power of the 20*17 of oxygen 
 as the 79*83 of copper; and hence these quantities of hydrogen and 
 copper are equivalent to each other. This example may be, however, 
 brought much farther. If, in place of treating the oxide of copper by 
 hydrogen gas, it had been acted on by chloride of hydrogen, the oxy- 
 gen should have been carried off by the hydrogen, which would aban- 
 don its chlorine for that purpose ; but the chlorine should not be set 
 free ; it, on the contrary, would unite with the copper from which the 
 oxygen had been taken, and the reaction would be so proportioned that 
 the quantity of copper reduced by the hydrogen of the chloride of hy- 
 drogen would be exactly sufficient to unite with all Jthe chlorine which 
 was therein contained, and form with it chloride of copper. In this 
 case the 100 parts of oxide of copper would require for its decompo- 
 sition 91-73 of chloride of hydrogen, and there would be formed 169*04 
 of chloride of copper and 22.69 of water. Here, as before, the 20*17 
 of oxygen uniting with 79*83 of copper and 2*52 of hydrogen, show 
 their equivalency ; but we learn in addition, that 79*83 of copper and 
 2*52 of hydrogen unite equally with 89*21 of chlorine, and hence, 
 that that quantity of chlorine corresponds, and is equivalent in combi- 
 nation, to 20*17 of oxygen. 
 
 Starting from tin's point, we may proceed to a still more extended 
 range of instances. If we treat sulphuretted hydrogen gas with iodine, 
 we find that it is totally decomposed, sulphur being precipitated, and 
 iodide of hydrogen being formed. Now, taking the quantity of the 
 sulphuret of hydrogen, containing the weight obtained in the former 
 example, 2*52 of hydrogen, we find it to be 43*09, and hence to con- 
 tain 40*57 of sulphur, which separates by the action of the iodine, of 
 which 318*27 parts, uniting with the 2*52 of hydrogen, form 320*79 
 of iodide of hydrogen. If this iodide of hydrogen be next treated 
 with chlorine, it abandons its iodine, and forms 91*73 of chloride of 
 hydrogen. 
 
 Setting out, therefore, from 100 parts of oxide of copper, and 
 tracing its elements through a variety of decompositions, in all of which, 
 the quantities engaged effect the same purpose of satisfying the ten- 
 dency to combine, we found for the numbers which express the equi- 
 valent quantities of the simple bodies employed, the following : 
 
 Copper . . . 79-83 Chlorine . . . 89-21 
 Hydrogen . . . 2-52 Sulphur . . . 40-57 
 Oxygen '* l I . 20-17 Iodine ,<- ,': .318-27 
 
276 Law of Equivalent Constitution. 
 
 and as the compound bodies formed are also equivalent, from their 
 being produced by the same, or equivalent combining actions, we may 
 express also in numbers their combining proportions, thus \r 
 
 Oxide of copper . . 100-00 Sulphuret of hydrogen . 43-09 
 Oxide of hydrogen . 22-69 Iodide of hydrogen . 320-79 
 Chloride of hydrogen . 91'73 Chloride of copper . 169*04 
 
 It is evident that if, in place of oxide of copper, any other metallic 
 oxide, reducible by hydrogen, had been employed, its equivalent; 
 should have been obtained, and in this way the equivalents of the ma- 
 jority of the metals have been determined. 
 
 These numbers are quite arbitrary ; and any other body in the list 
 might as well have been taken for the origin as oxide of copper. In 
 practice such numbers are reduced to a standard, which is taken as 1, 
 or 100, and, for this purpose, either oxygen or hydrogen, the most im- 
 portant bodies, are usually selected. 
 
 Any number experimentally obtained, as the above, may be reduced 
 to the standard scale by the rule of simple proportions : thus, the equi- 
 valent of copper being 79*83, oxygen being 20*17, and hydrogen 
 2-52, it is 
 
 20-17 : 79*83 : : 100 = 3957 Oxygen = 100 
 and 2-52 : 79'83 : : 1 = 31 71 Hydrogen = 1 
 
 It is difficult to decide which of the two scales, thus formed, deserves 
 preference : the hydrogen scale has been, by the authority of Davy, so 
 long prevalent in these countries, that it is difficult to supersede it ; and 
 it possesses the advantage that hydrogen has the smallest equivalent of 
 all bodies. The standard of oxygen is, however, for use, the more con- 
 venient, as, in consequence of the great preponderance of bodies in 
 which oxygen exists, the calculations are much simplified by its num- 
 ber being 100 ; and there are but two bodies which, on that scale, re- 
 quire to be expressed in a fractional form. 
 
 When the study of these equivalent proportions first occupied the 
 minds of chemists, Drs. Prout and Thompson were led, from specula- 
 tions regarding the physical constitution of gaseous bodies, to suggest 
 that the equivalent numbers of all substances should be simple multiples 
 of that of hydrogen ; and as, representing hydrogen by 1, the other 
 numbers should be all whole numbers, the scale acquired thereby consi- 
 derable simplicity. The researches of Berzelius appeared, however, to 
 controvert that hypothesis ; and in his numbers, which are for the most 
 part those given in the following list, no trace of such a law can be de- 
 tected. The progress of organic chemistry having, however, fixed the 
 attention of the most exact chemists on the precise value of the equivalent 
 number for carbon, it was found by Dumas that Berzelius's number 76 
 
Scales of Chemical Equivalents. 
 
 277 
 
 was certainly too high, and it appeared that 75 on the oxygen, or 6 on 
 the hydrogen scale ought to be adopted ; as this coincided with the 
 original view of Prout, it led to a general re-opening of the discussion 
 of the equivalent numbers, which has resulted in the correction of many 
 of Berzelius's numbers : several have been found to be exact multiples 
 of the number for hydrogen, and amongst them some of the most im- 
 portant bodies, as carbon, sulphur, nitrogen, oxygen ; still taking into 
 account the inevitable range of limits of experimental error, it does not 
 appear that a greater proportion of the numbers are exact multiples of 
 that for hydrogen, than should happen amongst so many others from 
 the calculation of probabilities, and therefore the occurrence of those 
 simple multiples do not at all form any proof of the truth of Thompson 
 and Front's idea of the existence of a general law. The chemists who 
 have most contributed to establish those more correct numbers are 
 Dumas, Liebig, Marignac, Pelouze, and Erdman, and on their results 
 the following table has been drawn up. 
 
 In the following table the equivalents of all the simple bodies are 
 expressed both on the oxygen and on the hydrogen scales ; and through- 
 out this work the two equivalent numbers will be given for each compound 
 body, except where it is otherwise remarked. 
 
 Names of Elements. 
 
 Equivalents. 
 
 Names of Substances 
 
 Equivalents. 
 
 O=100 
 
 H = l 
 
 0=100 
 
 H=l 
 
 Aluminum 
 
 171-2 
 
 137 
 
 Mercury . ; 7 ^ 
 
 1250-8 
 
 100-00 
 
 Antimony [.""'"*' 
 
 1612-9 
 
 129-2 
 
 Molybdenum . v 
 
 598-5 
 
 4796 
 
 Arsenic . ' ~~ v ; 
 
 937-5 
 
 75- 
 
 Nickel - - 
 
 369-7 
 
 29-62 
 
 Barium :? 
 
 858-0 
 
 68-66 
 
 Nitrogen 
 
 175-0 
 
 14-00 
 
 Bismuth r 
 
 886-9 
 
 7MO 
 
 Osmium 
 
 1244-5 
 
 9972 
 
 Boron 
 
 136-2 
 
 10-91 
 
 Oxygen 
 
 100-0 
 
 8-00 
 
 Bromine , 
 
 978-3 
 
 78-26 
 
 Palladium 
 
 665-9 
 
 53-36 
 
 Cadmium .-,. * \ 
 
 696-8 
 
 55-74 
 
 Phosphorus 
 
 400-3 
 
 32-00 
 
 Calcium % t ' ? 
 
 250-0 
 
 20-00 
 
 Platinum 
 
 1233-5 
 
 98-84 
 
 Carbon 
 
 75-0 
 
 6-00 
 
 Potassium 
 
 487-5 
 
 39- 
 
 Cerium 
 
 574-7 
 
 46-05 
 
 Rhodium 
 
 651-4 
 
 52-2 
 
 Chlorine . 
 
 4437 
 
 35-47 
 
 Ruthenium 
 
 651-4 
 
 52-1 
 
 Chromium 
 
 351-8 
 
 2819 
 
 Selenium 
 
 494-6 
 
 39-63 
 
 Cobalt 
 
 369-0 
 
 29-57 
 
 Silicon 
 
 266-8 
 
 21-35 
 
 Columbium 
 
 2307-4 
 
 184-90 
 
 Silver 
 
 1350-0 
 
 108- 
 
 Copper 
 
 395-7 
 
 31-70 
 
 Sodium ! \ - 
 
 287-2 
 
 22-97 
 
 Fluorine 
 
 233-8 
 
 18-74 
 
 Strontium 
 
 547-3 
 
 43-85 
 
 Glucinum 
 
 331-3 
 
 26-54 
 
 Sulphur 
 
 200-0 
 
 16-00 
 
 Gold 
 
 1229-0 
 
 98-33 
 
 Tellurium' ' v 
 
 801-7 
 
 64-25 
 
 Hydrogen 
 
 12-5 
 
 1-00 
 
 Thorium 
 
 744-9 
 
 59-83 
 
 Iodine 
 
 1579-5 
 
 126-4 
 
 Tin tl. 
 
 735-2 
 
 58-92 
 
 Iridium 
 
 1233-5 
 
 98-84 
 
 Titanium 
 
 303-6 
 
 24-33 
 
 Iron 
 
 350-0 
 
 28-00 
 
 Tungsten * 
 
 1183-0 
 
 94-80 
 
 Lanthanum 
 
 600-0 
 
 48-0 
 
 Vanadium ' 
 
 856-9 
 
 68-66 
 
 Lead 
 
 1294-5 
 
 103-73 
 
 Uranium 
 
 750-0 
 
 60-0 
 
 Lithium 
 
 80-3 
 
 6-44 
 
 Yttrium 402-5 
 
 32-25 
 
 Magnesium V 
 
 158-3 
 
 12-69 
 
 Zinc . 
 
 406-6 
 
 32-51 
 
 Manganese 
 
 345-9 
 
 27-72 
 
 Zirconium ' 
 
 420-2 
 
 33-07 
 
278 
 
 Double Decomposition necessarily 
 
 The determination of the equivalents of compound bodies is an equally 
 remarkable application of the principles that have been laid down. The 
 equivalent number of a compound is the sum of the equivalent numbers 
 of its constituents, as has been already seen in the numbers obtained for 
 the oxides and chlorides of copper and of hydrogen. In this way may 
 be constructed lists of the equivalents of compound bodies ; thus reducing 
 the substances, already noticed, to the scales, there are : 
 
 Substances. 
 
 Equivalents. 
 
 Substances. 
 
 Equivalents. 
 
 0=100 
 
 H-l 
 
 O = 100 
 
 H = l 
 
 Oxide of copper .. . 
 Oxide of hydrogen . 
 Chloride of hydro- 
 gen ... 
 
 4957 
 112-5 
 
 445-1 
 
 39-72 
 9-00 
 
 36-47 
 
 Chloride of copper 
 Iodide of hydrogen 
 Sulphuret of hydro- 
 gen 
 
 838-3 
 1592-0 
 
 213-7 
 
 67-18 
 127-57 
 
 17- 
 
 It is in relation, however, to the mutual decomposition of saline bodies 
 that the principle of equivalent proportion becomes of most interest and 
 by which it is best illustrated. If to a solution of nitrate of barytes we 
 add a solution of sulphate of soda, there is immediate decomposition, by 
 the mutual interchange of acids and bases, and the neutrality of the 
 solution remains completely undisturbed ; the salts which exist after 
 mixture are equally neutral with those which had existed previously, and 
 the quantities of acids and bases which are involved in the decomposition 
 are hence equivalent to each other. Thus, if we take 130*7 parts of 
 nitrate of barytes, we find that they require for their decomposition ex- 
 actly 71*3 parts of dry sulphate of soda, and that there are formed 11 6 '7 
 parts of sulphate of barytes, and 85'3 parts of nitrate of soda. The 
 composition of these four salts is : 
 
 Sulphate of Barytes. 
 Sulphuric acid . 40 
 Barytes . . 767 
 
 1167 
 
 Nitrate of Soda. 
 Nitric acid . 55 
 Soda . . 31-3 
 
 85-3 
 
 Nitrate of Barytes. 
 Nitric acid . 54 
 
 Barytes . . 767 
 
 1307 
 
 Sulphate of Soda. 
 Sulphuric acid 40 
 Soda . . 31-3 
 
 71-3 
 
 All four are neutral ; the acids and bases are in all equally neutralized, 
 and hence, the 40 of sulphuric acid and 54 of nitric acid, being capable 
 of saturating the same quantity of base, whether it be soda or barytes, 
 
occurs in Equivalent Proportions. 
 
 279 
 
 are equivalent quantities and represent the combining proportions of 
 these acids; and the 76*7 of barytes, and the 31*3 of soda, being like- 
 wise shown to possess equal powers of neutralizing the acid, whether 
 nitric or sulphuric, are the numerical equivalents of those bases. If 
 there had been a larger quantity of either salt present, it would have 
 remained unaffected, the interchange of elements taking place only in 
 equivalent proportions. Had nitrate of lead been employed, in place of 
 nitrate of barytes, the proportion necessary should have been different, 
 and a different quantity of sulphate of lead would have been produced 
 from the same sulphate of soda. Thus, to the 71 '3 of sulphate of soda, 
 there should be added, 
 
 Nitric acid . 54-0 producing Sulphuric acid . 40 '0 
 Oxide of lead 1117 Oxide of lead . 1117 
 
 Nitrate of lead 1637 
 
 Sulphate of lead . 1517 
 
 If, in place of sulphate of soda, we take oxalate of soda, we will find 
 that 67'3 of it will exactly fulfil the functions of 71 '3 of sulphate of 
 soda, and these consisting of 31*3 of soda and 36*0 of oxalic acid, will, 
 by decomposing 130 '7 of nitrate of barytes, or 165*7 of nitrate of lead, 
 produce 147*7 of oxalate of lead, or 112'7 of oxalate of barytes. 36 of 
 oxalic acid are, therefore, equivalent to 40'0 of sulphuric acid, and 54*0 
 of nitric acid. 
 
 A table of equivalents of acids and bases might thus be drawn up : 
 there should be, 
 
 Substances. 
 
 Equivalents. 
 
 Substances. 
 
 Equivalents. 
 
 0=100 
 
 H = l 
 
 0=100 
 
 H=l 
 
 Nitric acid 
 Sulphuric acid 
 Oxalic acid . ^ i. 
 
 677'0 
 501-0 
 450-0 
 
 54-0 
 40-0 
 36-0 
 
 Soda . 
 Barytes . , f . 
 Oxide of lead 
 
 390-1 
 956-9 
 1394-5 
 
 31-3 
 76-7 
 1117 
 
 It was in this form that the equivalency of different quantities of 
 chemical substances was first recognised, and numbers assigned with 
 extraordinary skill, by Wenzel, whose labours, although overlooked at 
 the time, must be considered as the first and greatest step towards assign- 
 ing the numerical conditions of chemical action. 
 
 The mode of determining the equivalent number of a new substance 
 can now be easily understood. If it be an acid, it is to be combined 
 with some base of which the equivalent is known ; if it be a base it must 
 be united with an acid, If it be a metal, it may be united with chlorine 
 
280 Equivalents of Compound Bodies. 
 
 or oxygen. If it be a simple non-metallic body, it may be united with 
 a metal. In any case, a well defined compound of the new body with 
 one whose equivalent number is already known must be obtained and 
 accurately analyzed. The equivalent numbers of the two bodies are 
 proportional to the quantities in which they were combined, provided we 
 have reason to consider that the compound examined, contained an 
 equivalent of each. Thus, if the new body form with sulphuric acid, a 
 perfectly neutral and soluble salt, and, on analysis, this yields 37 '3 of 
 sulphuric acid and 62*7 of the new base in 100, the equivalent is found 
 by the proportion, as37-3:62-7::40'0:x=67-4, which is the equi- 
 valent of the body, 40 '0 being that of sulphuric acid, and hydrogen 
 being = 1. 
 
 A calculation of this kind requires, however, to be checked by a know- 
 ledge of the next law of combination, that of multiple proportions ; for, 
 as has been stated, in the example, we presume the salt analysed to be 
 composed of an equivalent of each constituent. It may be, however, 
 that it contained two equivalents of acid to one of base, in which case 
 the number for the latter should become 134*8; or two equivalents of 
 base to one of acid, which would make the number 33*7. The propor- 
 tions might be even still more complex ; and hence, before attempting 
 to decide on the equivalent number of a body, its general history must 
 be studied. 
 
 The third law of combination is, that where one body unites with 
 another in more proportions than one, there exists a simple relation 
 between the quantities of the second, which, in the different compounds, 
 unite with the same quantity of the first. Thus, taking manganese and 
 nitrogen, which are remarkable for the number of compounds which they 
 form with oxygen, we find that 
 
 345-9 of manganese unite with 100 of oxygen, forming protoxide. 
 
 345*9 ,, 150 ,, sesquioxide. 
 
 345-9 :i lo-..200 peroxide. 
 
 345 9 ,, 300 ,, manganic acid. 
 
 345-9 ,, 350 ,, permanganic acid. 
 
 and with nitrogen, 
 
 175 of nitrogen unite with 100 of oxygen, forming nitrous oxide. 
 
 175 ,, 200 nitric oxide. 
 
 175 ,, 300 ,, hyponitrous acid. 
 
 175 ,, 400 ,, nitrous acid. 
 
 175 ,, 500 ,, nitric acid. 
 
 Here the successive quantities of oxygen taken by the mangajiese 
 
 are as the numbers 2, 3, 4, 6, 7, and those which combine with the 
 
Law of Multiple Proportions. 281 
 
 nitrogen are as 1, 2, 3, 4, 5. In the last case they are all simple mul- 
 tiples of the first proportion, but in the case of manganese they are 
 multiples of one-half of the quantity contained in the protoxide. The 
 analogy of some other similar bodies, however, renders it extremely 
 probable, that although it has not been yet discovered, there exists a 
 compound of 345 '9 of manganese with 50 of oxygen, and this should 
 then be the first term of the series. 
 
 This law of multiple proportions holds not only with regard to the 
 simple bodies already stated, but also with compound bodies of every 
 class. Thus, chromic acid combines with potash in three different pro- 
 portions, forming by 
 
 52 -2 chromic acid _[- 47 3 potash, neutral chromate of potash. 
 104*4 ,, -f-47-3 ,, bichromate of potash. 
 156-6 -j-47'3 terchromate of potash. 
 
 Sulphuric acid combines with potash in two proportions, 
 
 40-0 sulphuric acid-f-47'3 potash, neutral sulphate. 
 80-0 L -|- 47 ' 3 " ^sulphate. 
 
 It was indeed by the verification of it, in the case of the carbonates and 
 oxalates of potash, by Wollaston, that this law obtained in the first 
 instance general acceptation. 
 
 22 of carbonic acid + 47'3 potash, form carbonate of potash. 
 44 ,, +47'3 ,, bicarbonate of potash. 
 
 36 of oxalic acid -f- 47 ' 3 potash, form oxalate of potash. 
 72 <$ -i- 4 7'3 binoxalate of potash. 
 
 144 - -j~ 47 ' 3 ,, quadroxalate of potash. 
 
 In salts, with excess of base, the same principle holds. Thus, in the 
 sulphates of copper I have shown that, 
 
 397 oxide of copper -f-40'0 sulphuric acid, form neutral sulphate. 
 
 79'4 ,, -f-40'0 ,, bibasic sulphate. 
 
 158-8 -j-40-0 ,, quadribasic sulphate. 
 
 317-6 ,, +40-0 octobasic sulphate. 
 
 In other cases the series, although not so complete, evidently follows 
 the same law. 
 
 The great use of the symbolical nomenclature, noticed already in 
 page 203, consists in its supplying an exact expression of multiple 
 proportions. The ordinary symbol of a simple body indicating an 
 equivalent of it, the number by which that symbol is multiplied, in the 
 formula of each compound body, represents the number of equivalents 
 
282 Law of Multiple Proportions. 
 
 therein contained. Thus, for manganese and nitrogen, already used as 
 instances, the symbolical expression of the law is given in 
 
 NO Nitrous oxide. MnO Protoxide of manganese. 
 
 NO 2 Nitric oxide. Mn. 2 O 3 Sesquioxide. 
 
 NO 3 Hyponitrous acid. MnOa Peroxide. 
 
 NO 4 Nitrous acid. MnO 3 Manganic acid. 
 
 NOs Nitric acid, Mn 2 O 7 Permanganic acid. 
 
 The numerical coefficient is sometimes placed, as here, below and to 
 the right of the letter symbol ; by other chemists it is placed to the 
 left and on the same line, as Pb + 2O. Cr+30., and sometimes to the 
 right and above the letter, as PbO 2 . CrO 3 . This makes no difference 
 in chemistry ; but the student must be very careful not to confound 
 chemical with mathematical symbols, in which the position of the num- 
 ber might alter its power and meaning altogether. It must be no- 
 ticed, however, that numbers written as the above affect only the 
 immediate symbol to which they are attached ; but sometimes a number 
 affects a group of symbols : thus, 3MnO is three equivalents of pro- 
 toxide of manganese = Mn 3 3 : thus, also, S0 3 KO. + A1 2 3 . 3S0 3 , 
 the formula of dry alum, contains four figures of 3, of which the first, 
 second, and fourth only affect the O to which they are subjoined ; but 
 the tliird affects the S0 3 , to which it is prefixed. A little practice will 
 enable the student to become quite familiar with the arrangement of 
 the symbols, or formulae, as they are termed, of bodies, even of the 
 most complicated nature. 
 
 This is the principle of multiple proportions, that the successive quan- 
 tities in which one body may unite with another are multiples of the 
 first, by a whole number ; and the cause of this is at once seen, and a 
 simple and positive meaning given to this law, by saying, that the first 
 body contains an equivalent of each element ; the second, one equiva- 
 lent of one and two equivalents of the other, and so on ; the succes- 
 sive steps being formed by the number of combining proportions of the 
 second body which unite with one combining proportion of the first. 
 
 This principle, which establishes a remarkable distinction between 
 the action of chemical affinity and of cohesion, was, at the moment of 
 its first being traced, attacked by Berthollet, to whose exclusive doc- 
 trines it was quite fatal. Berthollet, in fact, considered that the affinity 
 of bodies should make them unite in all possible proportions, and that 
 it was only by the influence of cohesion and elasticity that the forma- 
 tion of the bodies, actually produced, resulted. Thus he asserted, that 
 sulphuric acid and barytes actually unite in all proportions, but those 
 of 40 -0 of acid to 76*7 of base forming the body of the least solubility, 
 the whole quantity of acid is determined to unite with the barytes in 
 
Researches of Proust mi the Definiteness of Composition. 283 
 
 those proportions, and in none others. Thus he imagined also, that mer- 
 cury and oxygen should unite in all proportions, and that it was only 
 by the intervention of external causes that their union was determined 
 in preference to occur in the proportions of 100 of mercury to 4 of 
 oxygen, and 100 of metal to 8 of oxygen. We owe to Proust the 
 complete refutation of Berthollet' s views in this respect; he cleared 
 away a heap of incorrect ideas which had prevailed regarding compound 
 bodies, showing that numerous degrees of oxidation, which had been 
 looked upon as intermediate, and connecting the extreme limits, as 
 Berthollet thought they ought to be connected, were impure and badly 
 prepared mixtures of the true compounds, and that when pure, the 
 transition from one state to the other is sudden and definite, as has 
 been shown to be the consequence of the law of multiple proportion. 
 It is interesting to notice, however, as an example of how easily a great 
 discovery in science may be lost, that, although Proust had in his hand 
 all materials necessary for establishing the laws of combination, such as 
 they have been described, they escaped his notice, from his having 
 contemplated his results only in one point of view ; thus he found that 
 in 100 parts, 
 
 1st Oxide of copper contained, 2nd Oxide of copper contained, 
 Oxygen, . .11-22 Oxygen, . 20-17 
 
 Copper, . . 8878 Copper, . 79-83 
 
 1st Oxide of mercury, 2nd Oxide of mercury, 
 
 Oxygen, . . 3'80 Oxygen, . 7'32 
 
 Mercury, . . 96-20 Mercury, . 92.68 
 
 1st Sulphuret of iron, 2nd Sulphuret of iron, 
 Sulphur, . . 37'23 Sulphur, . 54-26 
 
 Iron, . . 62-77 Iron, . . 43-74 
 
 He proved that no indefinite intermediate degree of combination could 
 be traced, and that the influence of cohesion could not be supposed to 
 be the only cause of the definiteness of constitution ; but had he made 
 a trifling change in his way of calculation had he taken a certain 
 weight of one element as the standard, and not 1 00 parts of the com- 
 pound body his numbers should have become, 
 
 1st Oxide of copper, 2nd Oxide of copper, 
 
 Oxygen, . . 100-0 Oxygen, . 200'0 
 
 Copper, . . 791-4 Copper, . 791*4 
 
 1st Oxide of mercury, 2nd Oxide of mercury, 
 
 Oxygen, . . lOO'O Oxygen, , 200-0 
 
 Mercury, . . 2531-6 Mercury, . 2531-6 
 
 1st Sulphuret of iron, 2nd Sulphuret of iron, 
 
 Sulphur, . . 200-0 Sulphur, . 400-0 
 
 Iron . . 339-2 Iron, . . 339'2 
 
 And thus, the fact of the quantity of oxygen or sulphur, in the second 
 
284< Methods of determining the 
 
 range of compounds, being exactly double that in each of the first, 
 would have been evident, and the law of multiple proportions been 
 discovered twenty years before its existence was suspected. 
 
 We are now in a condition to examine more in detail the method of 
 determining the equivalent number of a body, which, as was before 
 noticed, is rendered difficult, sometimes, when the substances in question 
 unite in more proportions than one. Thus, it is evident that the man- 
 ganese series might be represented as 
 
 100 of oxygen + 345*9 of manganese, forming protoxide. 
 
 100 230-5 ,, ,, sesquioxide. 
 
 100 ,, 172-9 ,, ,, peroxide. 
 
 100 ,, 115'3 ,, ,, manganic acid. 
 
 100 ,, 98 '8 ,, ,, permanganic acid. 
 
 And the metallic oxides and sulphurets above described might be 
 written, and express still the law of multiple proportion ; as, 
 
 1st Oxide of copper, 2nd Oxide of copper, 
 
 Oxygen, . . 100*0 Oxygen, . 100 -0 
 
 Copper, . . 791-4 Copper, . 3957 
 
 1st Oxide of mercury, 2nd Oxide of mercury. 
 
 Oxygen, . . lOO'O Oxygen, . 100-0 
 
 Mercury, . . 2531-16 Mercury, . 1265-8 
 
 1st Sulphuret of iron, 2nd Sulphuret of iron, 
 
 Sulphur, ^ ." . 200-0 Sulphur, . 200-0 
 
 Iron, . 339-2 Iron, . . 169'6 
 
 There might thus be deduced from each kind of compound a different 
 equivalent for each simple body, and it is, therefore, necessary to lay 
 down some general principles by which one must be guided in their 
 choice. 
 
 First. Whenever there exists but one proportion in which two bodies 
 are capable of combining, it may be concluded, unless there is good 
 reason to the contrary, derived from other sources, that the proportion 
 is one equivalent of each element. Thus, lime and magnesia are the 
 only compounds formed by the metals calcium and magnesium, uniting 
 with oxygen, and are hence looked upon as protoxides. 
 
 Second. Whenever one body combines with another in two propor- 
 tions, as a metal with oxygen, and that the quantities of oxygen are as 
 2 : 1, it may be concluded, unless there are other reasons for an opposite 
 decision, that the bodies consist either of one equivalent of metal united 
 respectively with one and two of oxygen, or of one equivalent of oxygen 
 united respectively with one and two of metal. To decide between 
 these views, it must be considered, that as the tendency of the metal 
 
Equivalent Constitution of Bodies. 285 
 
 and of oxygen to unite, is pretty well satisfied by the combination of an 
 equivalent of each, if the protoxide so formed unite with another equi- 
 valent of either metal or of oxygen, this will be retained with inferior 
 power, and when the substance so produced is exposed to decomposing 
 agencies, it may be resolved into protoxide and metal in the one case, 
 and protoxide and free oxygen in the other. Thus, copper, lead, and 
 mercury unite each with oxygen in two proportions, and if black oxide 
 of mercury be heated, it resolves itself easily into metallic mercury and 
 red oxide, whilst the red oxide undergoes no change except total decom- 
 position into mercury and free oxygen. Bed oxide of copper decom- 
 poses itself easily into metallic copper, and black oxide of copper ; but 
 this last does not admit of any decomposition which is not total. If 
 we take yellow oxide of lead, we cannot change it by the application of 
 heat ; but if we heat brown oxide of lead, it gives off one-half of its 
 oxygen, and yellow oxide remains ; similarly when peroxide of manga- 
 nese is heated by deoxidizing agents, it abandons one -half of its oxygen, 
 but the oxide so formed cannot be further reduced. In this way, there- 
 fore, we conclude that 
 
 Red oxide of copper is suboxide. Cu^O. 
 Black oxide of copper is protoxide. CuO. 
 Black oxide of mercury is suboxide. Hg 2 O. 
 Red oxide of mercury is protoxide. HgO. 
 Yellow oxide of lead is protoxide. PbO. 
 Brown oxide of lead is deutoxide. PbO. 
 Olive oxide of manganese is protoxide. MnO. 
 Black oxide of manganese is deutoxide. MnO 2 . 
 
 Thus, also, hydrogen and oxygen unite in two proportions, to form, in 
 one, water, a body remarkably ; neutral in properties and permanent in 
 constitution, and in the other oxygenated water, of which half of the 
 oxygen is so loosely combined that its decomposition is provoked by 
 the slightest causes, and is explosively violent. It is hence concluded 
 that, 
 
 Water is protoxide of hydrogen. HO. 
 Oxygenated water is deutoxide. HO 2 . 
 
 If there be still more degrees of combination of the two bodies, these 
 principles apply still more determinately to their characteristic pro- 
 perties. 
 
 Third. The constitution of an acid may be frequently determined by 
 the consideration, that an equivalent of it is the quantity which neu- 
 tralizes an equivalent of a well characterised base. Thus the equivalent 
 number of potash on the hydrogen scale is 4 7 '4, and this combining 
 with 40'0 of sulphuric acid to form neutral sulphate of potash, this 
 
286: Methods of determining the 
 
 number is determined to be the equivalent of the acid, and as it is 
 made up 16'0 of sulphur and 24 of oxygen, the acid is considered to be 
 composed of one equivalent of sulphur 16*0, and three equivalents of 
 oxygen 8 X 3 = 24. Its formula is, therefore, S0 3 . In the same 
 way, on analysing hyposulphate of potash, it is found to consist of 47 '3 
 of potash, united to 72*0 of the x acid, which is, therefore, its equivalent 
 number. But this number is made up of 32'0, or two equivalents of 
 sulphur, and 40, or five equivalents of oxygen, and the formula express- 
 ing its constitution is S^O.,. 
 
 When an acid forms several classes of salts, it is difficult to determine 
 which is that containing an equivalent of each element, and hence this 
 mode of ascertaining the constitution of the acid may be occasionally at 
 fault. This happens particularly with the acids of phosphorus and ar- 
 senic ; and in these cases it is necessary to recur to considerations re- 
 garding the constitution of their salts, which will be described when we 
 come to speak of salts in general. 
 
 Fourth. In cases where the ratio between the quantities in wliich the 
 bodies combine does not follow the simple proportions of 1:2:3, &c., 
 but assumes the more complex forms of 2 : 3, or 3 : 4, or 3 : 5 : 7, it is 
 necessary to seek for analogies between the members of the series and 
 certain other bodies with regard to which there is not the same uncer- 
 tainty. Thus, there are two oxides of iron which may be looked upon 
 as consisting, either 
 
 .,/.;> the 1st of 28 of iron _|. 8 oxygen. 
 
 the 2nd 28 ,, -{- 12 
 
 or the 2nd 18-6 ,, -j- 8 ,, 
 
 the 1st 28 4- 8 " 
 
 In the first mode of view the oxygen varies as 2 : 3, but in the second 
 it is the metal which changes in proportion. Here we obtain a guide 
 in the study of the salts formed by these bodies. It is found that the 
 oxide which contains 28 of iron to 8 of oxygen, agrees in its laws 
 and properties with magnesia, with black oxide of copper, and with 
 olive oxide of manganese, which are all protoxides, and that it differs 
 totally in its relations from such bodies as are very fully known to be 
 suboxides. This oxide of iron contains, therefore, an equivalent of each 
 element, and its formula is FeO. The peroxide of iron then becomes 
 Fe.O^, but as the equivalent of oxygen cannot be considered to be 
 divided, we look upon it as being rather Pe 2 O 3 , and having its equiva- 
 lent number twice as large. This view is confirmed by finding that 
 when sulphate of peroxide of iron unites with sulphate of potash to 
 form iron alum, it does so in the proportion of Fe 2 O 3 , dry iron alum 
 
Equivalent Constitution of Bodies. 87 
 
 being SO 3 . KO. 4. FeA. 3SO 3 , and as this is the only proportion in 
 which these two salts unite, it is reasonable to suppose that it contains 
 an atom of each element. 
 
 This mode of controlling the equivalent numbers is beautifully shown 
 in the instance of the compounds of chrome with oxygen. There are 
 two; the 
 
 Green oxide of chrome consists of 1 879 chrome -j_ 8 oxygen. 
 Chromic acid 1879 -j- 16 
 
 Here the quantity of oxygen is doubled in the second compound ; and 
 as this yields half of its oxygen readily, either by heat, or to any sub- 
 stance having an affinity for it, it would appear highly probable that the 
 18*79 is the equivalent of chrome, and that the oxide of chrome should 
 be looked upon as a protoxide : but such is not the case. Sulphate of 
 chrome combines with sulphate of potash to form a chrome alum, re- 
 sembling in all characters and constitution the iron alum already noticed, 
 and hence oxide of chrome corresponds to peroxide of iron, and its for- 
 mula is Cr 2 3 . This is further proved by the relations of chromic acid 
 to bases. The chromates resemble perfectly the sulphates with which 
 they are isomorphous, and to saturate 47*3 of potash 52'2 of chromic 
 acid are required, consisting of 28*2 of chrome and 24 of oxygen, and 
 hence the formula of chromic acid is CrO 3 , resembling that of sulphuric 
 acid SO 3 . 
 
 Fifth. In cases where there is only one compound of a body with 
 oxygen, we may be induced, from analogical grounds such as those now 
 described, to consider it not to be composed of an equivalent of each 
 element. Thus aluminum and oxygen form only one compound, alu- 
 mina ; but this resembles in all its laws of combination and crystalline 
 form oxide of chrome and peroxide of iron, and hence it is considered 
 to be a compound of two equivalents of metal and three of oxygen, and 
 its formula to be A1 2 .O 3 . 
 
 Sixth. When bodies are found combined in proportions expressed by 
 high numbers, they are generally looked upon as secondary compounds, 
 formed by the reunion of others the ratio of whose elements are more 
 simple. Thus lead forms with oxygen compounds intermediate to the 
 true oxides already described, the one containing three equivalents of 
 lead and four of oxygen, the other, four of lead and five of oxygen; these 
 consist really of the protoxide and peroxide united in the proportions 
 shown by the equations : 
 
 Pb 4 O 5 = 3 PbO -f_ PbOs and PbaO = 2 PbO -f. PbO 2 . 
 In like manner, between the two proper oxides of iron there intervene 
 
288 Law of Multiple Proportions. 
 
 the two magnetic oxides, the formulse of which are Fe 4 5 and Fe 3 4 : 
 being compounds of protoxide and peroxide, as, 
 
 . Fe 4 5 = 2 FeO + Fe 2 O 3 and Fe 3 O 4 = FeO -f FeaOa. 
 
 By this means the constitution of an extensive class of complex bodies 
 is reduced to very simple forms. 
 
 The relative combining equivalents of bodies which unite in several 
 proportions, may however be considered under another point of view, 
 which although not employed as the basis of popular chemical explana- 
 tions, requires notice in a philosophical point of view. In a series of 
 oxides for example, we may consider not that an equivalent of metal com- 
 bines with successively added equivalents of oxygen, but that an equiva- 
 lent of oxygen combines with different quantities of the metals. That 
 in fact, the same metal should have different equivalent numbers, and in 
 combining in such would generate different oxides and different salts. 
 Thus, protoxide of iron consists of 28 iron and eight oxygen. Peroxide 
 of iron 28 metal and 12 oxygen. But peroxide may also be considered 
 as composed of 18' 7 iron and eight oxygen, and that the sulphate of the 
 peroxide consists of an equivalent of acid and an equivalent of base 
 SO 3 -f- Eef .0. This view obtains considerable support from the fact, 
 that under the influence of oxygen, chlorine, or bromine, it is always the 
 percompound that iron forms, and not the protocompound, which is 
 only secondarily generated by the action of the percompound on the 
 excess of iron then present. So that Fe 2 O 3 is not formed by the addi- 
 tion of to Ee 2 O 2 , but Ee O is formed by the union of Ee to F 2 O 3 . 
 This principle has, it is seen, already been used in order to explain the 
 formation of suboxides ; thus, mercury acts either with the equivalent 
 100 or 200. Copper either with the equivalents 31*7 or 63'4. Sulphur 
 certainly may form compounds, having any of at least four different 
 equivalents. This topic connects itself however so immediately with the 
 theory of atomic constitution, that its further discussion will fall better 
 under that head. 
 
 If we take oxygen, hydrogen, chlorine, and nitrogen in the proportions 
 by weight which correspond to their equivalent numbers, and measure 
 the volumes which, as gases, they occupy, an exceedingly striking rela- 
 tion will be found between them : the volume of oxygen being exactly 
 one-half that of each of the other gases. If, also, we heat iodine and 
 bromine in quantities proportional to their equivalents by weight, we 
 shall find, that when converted into vapour, they occupy precisely the 
 same volume as the equivalent of hydrogen gas at the same temperature 
 and pressure. On 'converting into vapour equivalent weights of arsenic 
 and phosphorus, they occupy precisely the same volume, which is equal to 
 
Theory^ of Tolumes. 
 
 289 
 
 that of the equivalent of oxygen gas; and by similarly treating an 
 equivalent of sulphur, its volume becomes one-third that of the oxygen. 
 Finally, when a quantity of mercury, representing its equivalent num- 
 ber, is converted into vapour, its volume, reduced to the same standard 
 of temperature and pressure, is four times that of oxygen and double 
 that of hydrogen or chlorine gases. It hence results, that, although 
 the equivalent weights of the simple bodies may be totally unconnected, 
 and may range within very extensive limits, yet the volumes which 
 these equivalent quantities occupy, when in the state of gas or vapour, 
 have a very simple relation to one another ; thus, taking the equivalent 
 weight of oxygen as 100, and its equivalent volume as 1, the propor- 
 tions of the other bodies mentioned are : 
 
 Name of Substance. 
 
 Equivalent Weight. 
 
 Equivalent 
 Volume. 
 
 Sp. gr. of Vapour 
 air =1000. 
 
 Oxygen , 
 
 100-0 
 
 1 
 
 1105-6 
 
 Hydrogen . 
 
 12-5 
 
 2 
 
 69-3 
 
 Chlorine 
 
 443-6 
 
 2 
 
 2470-0 
 
 Iodine 
 
 1579-5 
 
 2 
 
 8701-0 
 
 Bromine 
 
 978-3 
 
 2 
 
 5393-0 
 
 Nitrogen 
 
 175-0 
 
 2 
 
 976-0 
 
 Sulphur 
 
 200-2 
 
 | 
 
 6648-0 
 
 Phosphorus 
 
 400-3 
 
 J 
 
 4327-0 
 
 Arsenic 
 
 937-5 
 
 1 
 
 10362-0 
 
 Mercury 
 
 1250-8 
 
 4 
 
 6969-0 
 
 Not merely does this simple proportion of equivalent volumes hold 
 among the simple bodies, but it determines in the compounds, which 
 they form, an equally regular constitution. 
 
 The volumes of the gases which unite are necessarily in simple equi- 
 valent proportion to each other, and when the same gases unite in more 
 than one proportion, the second is a multiple of the first. In all cases 
 also where, after union, a condensation of volume occurs, the resulting 
 volume is simply related to the volumes which the constituents had 
 occupied before combination. Thus, in the formation of water, one 
 volume of oxygen unites with exactly two of hydrogen, and the volume 
 of watery vapour which is formed is equal to that of the hydrogen em- 
 ployed. To form ammonia one volume of nitrogen unites with three 
 of hydrogen, and the four volumes are condensed into two by the com- 
 bination. There may, therefore, be arranged for the various bodies 
 which assume the gaseous form, a series of equivalents in volume, 
 which will not be totally unconnected numbers, like those of the equi- 
 valents by weight, but are found to be, as the weights should become, 
 if the suggestion of Prout were verified, simple multiples of the equi- 
 19 
 
290 
 
 Equivalent Volumes of Compound Gases. 
 
 valent of some standard body which may .be selected, as oxygen in the 
 table. 
 
 i ^'' 
 
 
 
 
 
 .0 
 
 
 1 
 
 -|j 
 
 |*S | 
 
 "S'g'o 
 
 ^ i 
 
 Name of the Compound 
 
 
 'ri-S 
 
 1 1 
 
 f So 
 
 fcC eS ^ 
 
 Vapour. 
 
 H 
 
 *S '53 
 
 S JS'S 
 
 4 P * 
 
 .> || 
 
 
 & 
 
 1* 
 
 H g 
 
 III 
 
 |A 
 
 Water 
 
 HO 
 
 112-5 
 
 3 
 
 2 
 
 6220 
 
 Nitrous oxide :.>; ., v 
 
 NO 
 
 275-0 
 
 3 
 
 2 
 
 1527-3 
 
 Nitric oxide " ' ' ' 
 
 NO* 
 
 375-0 
 
 4 
 
 4 
 
 1039-3 
 
 Sulphurous acid 
 
 SO 2 
 
 400-0 
 
 7 
 
 6 
 
 2210-6 
 
 Sulphuric acid 
 
 S0 3 
 
 500-0 
 
 10 
 
 6 
 
 2761 -9 
 
 Sulphuretted hydrogen 
 
 SH 
 
 212-5 
 
 7 
 
 6 
 
 1177-0 
 
 Muriatic acid 
 
 C1H 
 
 456-1 
 
 4 
 
 4 
 
 1269-5 
 
 Hydriodic acid 
 
 IH 
 
 1592-0 
 
 4 
 
 4 
 
 4385-0 
 
 Hydrobromic acid 
 
 BrH 
 
 990-8 
 
 4 
 
 4 
 
 2731-0 
 
 Ammonia . . f^j 
 
 NH 3 
 
 214-5 
 
 4 
 
 4 
 
 591-5 
 
 Arseniuretted hydrogen 
 
 AsH 3 
 
 952-6 
 
 7 
 
 4 
 
 2694-0 
 
 Terchloride of arsenic 
 
 AsCl 3 
 
 2268-0 
 
 7 
 
 4 
 
 6295-0 
 
 Calomel 
 
 Hg 2 Cl 
 
 2974-3 
 
 6 
 
 4 
 
 8204-0 
 
 Corrosive sublimate 
 
 HgCl 
 
 1708-5 
 
 8 
 
 4 
 
 94390 
 
 Arsenious acid i ^ 
 
 As0 3 
 
 1240-1 
 
 4 
 
 1 
 
 13670 
 
 Sulphuret of mercury 
 
 HgS 
 
 1467-0 
 
 7 
 
 9 
 
 5384-0 
 
 Chloride of sulphur 
 
 S Cl 
 
 845-0 
 
 4 
 
 3 
 
 4686-0 
 
 Protochloride of phosphorus 
 
 PC1 3 
 
 1720-1 
 
 7 
 
 4 
 
 4741 -1 
 
 Perchloride of phosphorus 
 
 PClo 
 
 2505-3 
 
 11 
 
 6 
 
 4788-1 
 
 The simplicity thus shown to exist between the volumes of the con- 
 stituent and compound vapours enables us very often to calculate before- 
 hand what the specific gravity of a vapour should be, and thus to 
 ascertain how closely the numbers found experimentally by the methods 
 described in the first chapter may approach to absolute correctness. 
 Thus, to calculate the specific gravity of ammonia ; it is formed by the 
 union of three volumes of hydrogen and one of nitrogen, and the 
 weights of these volumes being as their specific gravities, the weight of 
 the ammonia formed should be 976 + (3 X 69) = 1183. if the four 
 volumes of constituents were condensed into one ; but as the condensa- 
 tion is into two, the specific gravity of the ammonia is 1183 -=- 2 = 
 5 91 '5 as given in the table. Sulphur and hydrogen unite in the pro- 
 portion of one volume of sulphur to six of hydrogen, and hence if 
 there were but one volume of resulting gas, the specific gravity should 
 be 6648 -f (6 X 69) = 7062, but as there are six volumes of gas 
 formed, the true specific gravity of sulphuretted hydrogen is 7062 -=- 
 6 1177. The general rule being to multiply the specific gravities 
 of the simple gases or vapours respectively by the volumes in which 
 they combine, to add those products together, and then to divide the 
 sum by the number of volumes of the compound gas produced. 
 
Theoretic density of Carbon Vapour. 291 
 
 By the application of this principle, we may often decide with great 
 probability on the specific gravity which certain bodies should have in 
 the state of vapour, although it has not been as yet possible to weigh 
 their vapours experimentally. Thus, the temperature at which anti- 
 mony is volatile is so high that the specific gravity of its vapour may 
 possibly never be determined by experiment ; but the chloride of anti- 
 mony resembles, in all its chemical relations, chloride of arsenic, and 
 there is the greatest probability that the constitution of the two are 
 alike in the state of vapour. Now, we know that chloride of arsenic 
 consists of six volumes of chlorine and one volume of arsenic vapour 
 condensed into four volumes ; and hence, if we multiply the specific 
 gravity of the vapour of chloride of antimony, which is 8106*5, by 
 four, we obtain 32426-0, and subtracting from it the weight of six 
 volumes of chlorine = 14820, there remains 17606, which, if the 
 analogy between arsenic and antimony be correct, must be the specific 
 gravity of the vapour of antimony reduced to the standard of air 
 = 1000. 
 
 Similar principles have been applied to the determination of the spe- 
 cific gravity which carbon should possess if it were converted into 
 vapour. This number would be of great importance in all calculations 
 of the specific gravities of the vapours of organic bodies, most of which 
 contain carbon as an element ; but unfortunately there is no volatile 
 body so similar to carbon, as that its analogies can be taken as a guide, 
 and hence the bases of the calculated density of gaseous carbon are 
 purely hypothetical. Indeed chemists are not agreed upon the precise 
 number, some making it the double of what it is estimated at by others. 
 If we look upon carbonic acid as consisting of equal volumes of va- 
 pour of carbon and oxygen, the two condensed into one, the specific 
 gravity of carbon is 1524'! 1102'6 = 421'5, but if the carbonic 
 acid consist of two volumes of oxygen and one of carbon, the three 
 volumes condensed into two, the calculated specific gravity of the 
 latter vapour is 3048-2 2205-2 = 843'0. On the first idea, the 
 carbonic oxide consists of two volumes of carbon vapour, and one of 
 oxygen, the three condensed to two (2 X 421*5 -f 1102-6) ~- 2 = 
 972*8, and on the latter, of equal volumes united without condensation 
 (843-0 -f 1102-6) -- 2 = 972-8. It is this latter which I adopt, and 
 in any calculations that may occur hereafter, I shall consider the specific 
 gravity of gaseous carbon as 843. It does not at all necessarily follow 
 that the true specific gravity is either of these numbers ; as it may be 
 that the relations by volume of carbonic acid and carbonic oxide are 
 much more complex. Before the specific gravity of the vapour of sul- 
 phur had been experimentally determined, it was considered from 
 
292 . Theory of Volumes. 
 
 similar theoretic grounds to be 2216, but it is actually three times as 
 great, 6648, and we must hence not reckon too implicitly on the 
 relations by volume at present given, for the gaseous compounds of 
 carbon. 
 
 The relation between the volume actually occupied by the quantity of 
 vapour corresponding to an equivalent of a body and the density calcu- 
 lated from its composition, has been found, however, in some instances 
 to be subjected to curious anomalies from sudden and great alterations 
 which take place in the density of some vapours, for even slight altera- 
 tions of temperature near their boiling points. Thus, the vapour of 
 acetic acid has a density of 3200 at 257, and of 2080 at 482, which 
 last corresponds to the theoretical density, and is retained at ah 1 higher 
 temperatures. Butyric and formic acid vapours show similar discre- 
 pancies. The vapour of oil of vitriol, which is 2500 at 630, becomes 
 1680 at 928, the calculated density being 1640. Some oils are found 
 also anomalous ; but with these comparatively few exceptions, the den- 
 sities of the vapours of compound bodies, found by experiment, agree 
 with those obtained by calculation from the densities of their consti- 
 tuents, and the equivalent is represented in almost all cases by two or 
 four volumes of the vapour. 
 
 In the combination by volume, the same laws of multiple proportion 
 hold as in combination by equivalents ; thus, the compounds of chlo- 
 rine and oxygen which are, by weight, Cl.O. C1.O 4 . C1.0 5 . and C1.0 7 , 
 are by volume two of chlorine, to one, to four, to five, and to seven 
 volumes of oxygen respectively, and so in all other instances, and, 
 consequently, all remarks that have been made regarding the law of 
 multiple proportions in equivalents by weight, apply to combinations of 
 equivalents by volume also. 
 
< 293 
 
 CHAPTER X. 
 
 OF THE RELATIONS OF CHEMICAL CONSTITUTION TO THE MOLECULAR 
 STRUCTURE OF BODIES. 
 
 IT has been abundantly shown, throughout the preceding portions of 
 this work, that even the most purely physical properties of a body are 
 closely connected with its chemical constitution ; and thus the density, 
 the crystalline structure, or the electrical relations of a substance, or the 
 manner in which it is acted on by heat, may, by affording distinctive 
 characters, or by influencing its affinities, become necessary to its chemical 
 history. The numerical laws of constitution last described, yield addi- 
 tional evidence of the intimate relation of chemical to molecular consti- 
 tution ; and in the present chapter I purpose to conclude the description 
 of the general history of chemical action, by an account of such principles 
 as have been advanced, and such facts as have been discovered illustra- 
 tive of this connexion. They are as follows : 
 
 1st. The connexion between molecular constitution and the equivalent 
 numbers of bodies. The atomic theory and the speculations on atomic 
 volume. 
 
 2nd. The connexion between the crystalline form and the chemical 
 equivalency of bodies. The laws of isomorphism and phenomena of di- 
 morphism. 
 
 3rd. The connexion between constitution and composition, as affecting 
 specific individuality of chemical bodies. Doctrines of allotropy and 
 isomerism. Of the theories of types and of compound radicals. 
 
294 Atomic Theory of Dalton. 
 
 SECTION I. 
 
 OF THE ATOMIC THEOEY AND THE DOCTRINE OF ATOMIC VOLUME. 
 
 IT was natural that as soon as the remarkable laws of combination, dis- 
 cussed in the last chapter, had been discovered, philosophers should be 
 anxious to ascend to the causes in which they had their rise, and to trace, 
 in the operation of some one general principle, the three determinate 
 numerical conditions to which experiment has proved chemical action to 
 be subjected; accordingly, such theoretical views were promulgated, 
 even before the laws of combination were fully understood ; and it has 
 been since one of the most difficult tasks of the philosophic chemist, to 
 disentangle the real and practical, from the merely speculative portions, 
 of atomic chemistry. 
 
 For Dalton, in promulgating the law of multiple combination, the 
 most beautiful, as well as the most extensive principle that has been 
 conferred on chemistry since the epoch of Lavoisier, announced it as the 
 result of speculations, which, though, in their general nature, true, and 
 constituting still the essential basis of all theories of chemical action, 
 were yet overlaid by a tissue of hypotheses so irregular, and so unneces- 
 sary, th&t for a long time the real dignity and excellence of the experi- 
 mental laws was underrated and misunderstood. These accessory specu- 
 lations have now, however, passed away, and the theory of combination 
 laid down by Dalton may, in all its essential conditions, be very briefly 
 expressed as follows. 
 
 All substances are supposed to be constituted of particles perfectly 
 indivisible, and hence truly atoms. In different kinds of matter these 
 atoms are of different weights, and probably of different magnitudes ; 
 but this latter quality is of no material interest. When bodies combine 
 chemically, their combination must be so effected that one atom of one 
 unites with one atom of another ; or one of the first with two, or three, 
 or four of the second ; or two of the first with three, or five, or seven of 
 the second ; but no intermediate degrees can possibly occur, for the atom 
 being absolutely indivisible, no intermediate degree of union can take 
 place. The relative weights of these atoms are the equivalent numbers 
 of the bodies combined ; eight parts of oxygen unite with one part of 
 hydrogen, by weight, to form water, because the simplest proportions in 
 which they can unite are one atom of each, and the atom of oxygen is 
 eight times as heavy as the atom of hydrogen ; eight parts of oxygen 
 are equivalent to 35*4 parts of chlorine, because when an atom of hydro- 
 gen leaves the atom of oxygen, it combines with an atom of chlorine in 
 its place, which is weightier than that of oxygen in the proportion of 
 3 5 -4 to 8 ; and the quantity must be consequently so determined. When 
 
Laws of Atomic Combination. 295 
 
 a second atom of oxygen combines with hydrogen, it being equally heavy 
 with the first, doubles the quantity of oxygen which the equivalent of 
 hydrogen has taken up, and as might be illustrated by any series of 
 examples, introduces as a necessary consequence the law of multiple 
 combination. 
 
 Such is the atomic theory of Dalton. It expresses faithfully the laws 
 of combination ; 1st, the law of definite constitution ; 2nd, the principle 
 of equivalent proportion ; and 3rd, the law of multiple combination. It 
 is therefore, even in this form, the most embracing and perfect general- 
 ization that has ever been proposed in chemistry ; but before committing 
 ourselves implicitly to its adoption, it is necessary to examine into its 
 basis with some detail. 
 
 Dalton assumes that matter is constituted of indefinitely small particles, 
 atoms, but he advances no proof that it is so ; he adopts unreservedly 
 that side of the discussion, which, from the earliest ages has divided the 
 opinions of philosophers, and shows that on that hypothesis all the most 
 remarkable phenomena of chemistry can be explained. But I have already, 
 in the first chapter of this work, pointed out, that the question of the 
 ultimate constitution of matter is now no nearer its solution than it was 
 twenty centuries ago ; and I will now proceed to show, that for the ex- 
 planation of the laws of combination, the atomic theory of Dalton is 
 unnecessary, or at least that it becomes only one out of a variety of 
 molecular conditions, which matter may assume. In the first place it is 
 necessary to ascertain in what matter the relative weights of the atoms 
 of bodies, if they really exist, are to be determined. 
 
 I pointed out in the last chapter the number of circumstances which 
 should be taken into account for the determination of the equivalent 
 number of a body ; it is by such considerations that in similar cases the 
 atomic weight of a body is determined, and where the idea of the exist- 
 ence of such ultimate combining molecules is adopted, the atom is the 
 equivalent, and the number is its weight. If therefore, the theory of 
 molecular constitution involved chemical results alone, no difficulty would 
 occur ; but when we consider these atoms as building up the mass, and 
 conferring upon it its physical properties, at the same time that they 
 produce its chemical constitution, inconsistencies are found, which must 
 prevent our coming too hastily to a conclusion. 
 
 AYhen Gay-Lussac first determined the existence of those simple rela- 
 tions which have been described as existing between the volumes of gases 
 which combine together, it was considered certain, that all gases con- 
 tained in the same volume the same number of atoms. The gases are 
 remarkable for all possessing the same physical constitution. Their 
 relations to pressure and to heat are governed by the same law in all 
 
296 Atomic Constitution of Gases. 
 
 cases, which can be best explained by supposing that in the same space 
 they contain the same number of ponderable atoms, set at equal distances 
 from each other, and whose material repulsion is expressed by the same 
 law. Hence, when one volume of chlorine unites with one of hydrogen, 
 an equal number of atoms of each element come into play, and an atom 
 of the compound consists of an atom of each constituent. But here a 
 difficulty occurs ; the chloride of hydrogen, which results, occupies two 
 volumes, and yet it is in physical properties identical with the hydrogen 
 or chlorine ; all physical evidence would lead us to believe, that muriatic 
 acid contained in the same volume the same number of atoms as its con- 
 stituents, but the most positive chemical evidence shows that it contains 
 but half so many. In like manner, on physical grounds, there should 
 be the same number of atoms in the same volume of oxygen and hydro- 
 gen, and as water is formed by the union of one volume of oxygen, with 
 two of hydrogen, it should consist of one atom of oxygen and two atoms 
 of hydrogen ; but the most perfect chemical evidence we possess proves 
 that water is composed of an equivalent of each element. The number 
 of chemical molecules in gases is different therefore for each gas ; it is 
 the combining or equivalent volume which contains equal numbers of 
 chemically equivalent molecules or atoms, and as has been shown in the 
 tables in last chapter, those volumes differ remarkably from one gas to 
 another. 
 
 Another physical condition, which is intimately connected with the 
 molecular constitution and the chemical relations of bodies, is their 
 specific heats, on the remarkable law of which, regarding the simple 
 bodies, as discovered by Dulong and Petit, and extended to many com- 
 pound bodies by Nauman, Eegnault, and Avogadro, I have already 
 fixed attention (page 84.) If we look upon the specific heats of all 
 the ultimate particles of simple bodies as being the same, we should 
 at once have a mode of determining their atomic weights, and these should 
 coincide with the equivalents deduced from chemical considerations. 
 
 In the great majority of cases the atomic weights of the solid simple 
 bodies, deduced from their specific heats, coincide with those adopted 
 from chemical considerations, and in some of the exceptional instances, 
 as bismuth and silver, there is some doubt as to the true number, which 
 may be fairly interpreted as so far remaining neutral. But in other 
 cases we find that it completely fails ; thus, the atomic weight of iodine 
 deduced from its specific heat is 63'3, whilst there is no doubt but that 
 its chemical equivalent is 126*3, twice as much. Also, the history of 
 arsenic and phosphorus is so complete, that there is no doubt that 
 their equivalents are 75*4 and 32*0, but when we calculate the atomic 
 weights from Iheir specific heats, we find as the result for arsenie 37*7, 
 
Physical and CJiemical Atoms. 297 
 
 and for phosphorus 16*0, that is, in each case but the half of the real 
 number. In the gases, also, there is complete discordance between the 
 specific heats and the chemical equivalents, no matter whether we con- 
 sider their purely molecular constitution, by which they should have an 
 equal number of atoms and equal specific heats in equal volumes, or 
 whether we compare their combining volumes with their specific heats. 
 The specific heats of volumes (p. 88) of oxygen and of hydrogen, have 
 been proved by Apjohn to be as 808 to 1459, whilst, on chemical 
 grounds, that of oxygen should be double, and on molecular considera- 
 tions the same as, that of the hydrogen. 
 
 It follows from what has been said, that it is totally impossible to 
 adopt completely the opinion of Dalton, that bodies are composed of 
 ultimate and indivisible particles, which, aggregating together, give 
 origin to sensible masses of the same nature, when similar particles unite, 
 and to the phenomena of chemical combination when the union is be- 
 tween particles of different kinds ; I adopt fully the idea of Dumas, that 
 it is possible, and, indeed, more consonant to experiment, to explain all 
 the laws of chemical combination, quite independent of any consideration 
 as to whether the masses which combine are indivisible or the reverse. 
 The word atom, if interpreted in this strict and proper sense, is unne- 
 cessary, and may be injurious if employed with any vague or undefined 
 meaning. 
 
 I consider, as I have already stated, (page 7,) that sensible masses 
 of matter are constituted of a number of lesser masses, which again may 
 be made up of similar constituent groups, proceeding downwards to any 
 extent, but still without involving the question of a limit to the degree 
 of possible division. One class of these groups of particles I consider 
 to be represented by the equivalent numbers ; and it is possible that 
 these numbers may indicate the manner in which the chemically com- 
 bining groups may be disposed to subdivide themselves, in order to ge- 
 nerate a set of groups of an inferior class. The specific heats of bodies 
 may be considered to have reference to an order of groups of particles 
 often, but not necessarily, coincident with those which combine to pro- 
 duce chemical compounds ; and the third, probably the most remote, 
 engaged in the ordinary properties of matter, may be such as being 
 uniformly distributed in the gaseous form, confers upon those bodies 
 the properties which characterize mechanically that condition, and are 
 independent alike of the chemical properties and specific heats which 
 appertain to, and are exhibited by, groups of a more complex structure 
 and superior order. 
 
 From this point of view I contemplate the atomic theory ; for these 
 groups, engaged in chemical combination, and indivisible by chemical 
 
298 Various Orders of Molecular Groups. 
 
 means, are, in all chemical relations, atoms. Their relative weights are 
 our equivalent numbers. Prom their union the laws of definite and 
 multiple combination directly follow. But, when we remove them from 
 their proper sphere, when we subject them to physical forces, we may 
 dissect them, and separate them into other groups ; or we may unite 
 many of them together, to form a larger group, characterized by the re- 
 lations to heat and to pressure that have been already stated, but no 
 longer the group or atom engaged in chemical operations. Thus, the 
 group which is acted on by the heat when a gas expands, occupies only 
 half the space in muriatic acid that the chemical group takes up ; but 
 in gaseous sulphur, it occupies three times the space of the chemical 
 atom. In gaseous oxygen, arsenic, and phosphorus, the mechanical 
 atom is of the same volume, but the chemical atom only of half the vo- 
 lume, that they respectively occupy in hydrogen, chlorine, and iodine. 
 In most of the simple bodies the same groups produce chemical combi- 
 nation, and determine the specific heat ; but in iodine, in arsenic, and 
 in phosphorus, the group which enters into chemical combination con- 
 tains two of the groups which are pointed out from the specific heats of 
 these bodies. 
 
 I shall frequently employ the word atom in the course of the follow- 
 lowing pages; 'but I do so only as an abbreviation for the terms equiva- 
 lent quantity, or combining masses. Of the ultimate particles of matter, 
 or true atoms, we know nothing ; and all the discussions that have taken 
 place, from the earliest and vaguest speculations of Democritus or Leu- 
 cippus, to the modern experiments of Wollaston and Earaday, must be 
 considered as absolutely without influence on the positive decision of 
 the question. 
 
 Indeed the last named eminent philosopher has been induced by the 
 consideration of the phenomena of electrical conduction, to propose for 
 its explanation a point of view which negatives all definitive idea 
 of molecular or atomic consitution of matter, and would lead to the 
 resolution of its properties into mere actions of force emanating from 
 mathematical points in space ; in fact to the adoption of what has been 
 termed the dynamical theory of the constitution of matter. His line 
 of argument is as follows : If we adopt an atomic theory, we shall 
 find from considerations of atomic volume which shall be described just 
 now, that different bodies contain, under the same bulk, different num- 
 bers of atoms, and that those atoms must be believed to be separated 
 from each other by spaces many times larger than they themselves 
 occupied. Thus if we convert a cubic inch of potassium into hydrate 
 of potash, not merely will the bulk of potassium be not increased by 
 absorbing so much oxygen and water, but the volume will diminish so 
 
Atomic Constitution of Matter. 299 
 
 that the bulk of the hydrate of potash will be only 0'97 cubic inch, whilst 
 it contains four times as many atoms as the potassium. But if there 
 be this great empty space in matter, how can conduction take place ? 
 All Farada/s previous researches tend to prove that electric force can 
 only be transmitted by means of matter, and he asks How can the 
 space which separates the particles of sulphur refuse to allow the trans- 
 mission of heat or electricity, whilst the space which separates the parti- 
 cles of copper or of silver allow its passage ? He suggests, therefore, 
 that there is no empty space, but that the particles of matter materially 
 penetrate, and that each one exists in every point of the space which 
 the entire mass occupies. It is evident, however, that if we abandon 
 the idea of the impenetrability of matter, we give up the basis of 
 our fundamental conception of its existence and we resolve its proper- 
 ties into mere manifestations of abstract force, emanating from mathe- 
 matical points as centres. This dynamical conception of physical and 
 chemical action is adopted by many as being more in harmony with 
 present philosophical theory than the crude and gross ideas of solid 
 atoms proposed by Dalton ; but I would remark, that as we regard the 
 transparency or opacity of a body to be the result at once of the 
 arrangement of its molecules and the distribution of the luminiferous 
 ether within its mass, so the conducting or insulating property of a 
 body may find its explanation in a similar way by the undulatory theory 
 of electricity, and the vacuum which Faraday, like nature in the middle 
 ages, so much abhors, may be removed, not by the omnipresence and 
 mutual penetration of the physical or chemical molecules of every body 
 but by the existence and conditions of movement of a medium, bearing 
 to electrical theory the relation which the medium of light waves has 
 to the explanation of optical facts. 
 
 A full inquiry into the atomic constitution of bodies requires us^ 
 however, to examine not only those laws which govern and those effects 
 which follow from the agency of their mass, but also those consequences 
 which result from the influence of their volume and of their method of 
 arrangement. For if there exist atoms at all, if we have an atomic 
 theory, those atoms must have definite magnitude and form as well as 
 weight, and the physical and chemical properties of bodies must be 
 influenced in a very important degree by the diversities manifested in 
 this way by their constituents. There is little doubt but that the laws 
 of crystallization of bodies are influenced mainly by the volumes and 
 arrangement of the physical molecules of which crystals are built up, 
 and it is consequently the special study of the crystalline relations of 
 chemical bodies that have led chemists to examine their atomic volumes. 
 This subject had been first opened by Polydore Boullay, and then 
 
300 Doctrine of Atomic Volumes. 
 
 examined by Dumas,, but it is most especially by Kopp and Schrceder in 
 Germany, and by Playfair and Joule in England, that it has been 
 followed out. I do not consider that the results obtained have been 
 .very satisfactory as an addition to onr knowledge, but it is necessary to 
 describe what has been done in order to correct some inconsequences 
 into which even estimable chemists have fallen. 
 
 The idea of a volume of an atom arises from the consideration that 
 in a given weight of a body the number of atoms must be inversely as the 
 weight of each atom. Thus, as we assume the atom of sulphur to weigh 
 16, and the atom of lead to weigh 104, the number of atoms in an 
 ounce of sulphur will be greater than the number in an ounce of lead 
 in the proportion of 104 to 16, but the ounce of sulphur occupies 0.95 
 cubic inch, and the bulk of the ounce of lead is 0'17 cubic inch; and 
 hence the bulk of an atom of sulphur is in proportion to the bulk of an 
 atom of lead as 16xO'95tol04xO'17. But the comparison above 
 made of the bulk and the weight of the cubic inch of each body leads to 
 the inverse of the specific gravity, and hence we can similarly and more 
 simply indeed obtain the atomic volume by dividing the atomic weight 
 by the specific gravity. Thus for sulphur j- = 8, and for lead -J-^ = 9*1. 
 In this manner tables of atomic volumes of bodies have been con- 
 structed of which however it is unnecessary to give details. 
 
 It is evident that the idea of atomic volume thus obtained is purely 
 speculative, and indeed involves the idea of the interior of the mass of 
 every body being absolutely occupied by matter. For if we admit the 
 possibility of the particles being not in contact, their bulk becomes quite 
 indeterminate. But this hypothesis is highly questionable, and as I 
 shall hereafter show, would lead, if carried out, to the purely dynamical 
 idea of the non-existence of solid matter. There is this great difference, 
 therefore, between the determination of atomic weights and atomic 
 volumes. We know by the laws of combination that if bodies unite by 
 atoms, those atoms must have certain relative weights, which are posi- 
 tively determined by experiment; but it is quite possible that there may 
 be atomic volumes, and yet those volumes not be ascertainable from the 
 impossibility of knowing how much of the bulk of each body is really 
 solid and how much is not so. This total uncertainty is shown by the 
 great diversities of density which take place even in the same body in 
 the same state of aggregation. Thus for water not merely is the specific 
 gravity diminished and the atomic volume consequently increased 1700 
 times on changing from the liquid to the vapour state, but the density 
 of platinum may vary from 17 '76 to 21-21; and that of silver may 
 vary from 10.50 to 10*62 that of gold may pass from 18 '02 to 
 20'69, according as these bodies are prepared in different ways, and yet 
 
Volumes of Isomorphous Bodies. 
 
 301 
 
 we cannot admit that the absolute atom is swelled out or squeezed in, 
 or thus changes its volume within such wide limits. It is evident that 
 if we admit an atomic constitution of matter at all, we must allow that 
 those little particles are arranged in masses according to their attractions, 
 but separated by interspaces of which we cannot tell the precise 
 dimensions, but which must allow of being increased or diminished by 
 heat or cold, of the transudation of liquids, as of mercury through lead ; 
 of the transmission of light and heat rays. The relation of the atomic 
 weight to the density cannot be admitted, in my opinion, to measure 
 the real bulk of the physical or chemical molecule, and consequently I 
 believe the introduction of the term atomic volume not to be any real 
 addition to science, but it may serve as a useful numerical point of com- 
 parison among bodies, and in this respect the calculations made by Kopp 
 and others deserve attention. 
 
 It is found that bodies of the same chemical group, or closely re- 
 sembling in their chemical habitudes, have nearly, or even exactly, the 
 same atomic volume. Thus in the following table some of the simple 
 bodies are arranged with their atomic weights, their specific gravities, 
 and the quotients of these, the atomic volume : 
 
 Substances. 
 
 Atomic 
 Weight. 
 
 Specific 
 Gravity. 
 
 Atomic 
 Volume. 
 
 Bromine 
 Chlorine liquid 
 Cyanogen liquid 
 Iodine 
 
 78-2 
 35-5 
 26-0 
 126-3 
 
 2-99 
 1-35 
 98 
 4-95 
 
 26-2 
 26-4 
 26-5 
 25-5 
 
 Cobalt 
 Copper ./v* ._; v 
 Iron , '. .^ , * 
 Manganese . *^*T** 
 
 29-5 
 317 
 28-0 
 
 277 
 
 8-49 
 8-96 
 779 
 8-01 
 
 3-47 
 3-54 
 3-59 
 3-46 
 
 In other cases of similarly allied bodies, the atomic volumes, though 
 not the same, are very simply related, as doubles or halves. 
 
 If we proceed to calculate the atomic volumes of the oxides of the 
 above metals, we shall see that there does not exist at all a similarly 
 simple relation. I shall associate them to the two earths which are 
 admitted to belong to the same chemical group. 
 
 Substances. 
 
 Atomic 
 Weight. 
 
 Specific 
 Gravity. 
 
 Atomic 
 Volume. 
 
 Lime * i 
 
 28- 
 
 3-17 
 
 8-83 
 
 Magnesia . 
 
 207 
 
 3-20 
 
 6-47 
 
 Oxide of copper 
 Oxide of manganese 
 
 397 
 357 
 
 6-43 
 473 
 
 6-17 
 7-55 
 
 Oxide of zinc . . , 
 
 40-5 
 
 573 
 
 7-07 - 
 
302 
 
 Doctrine of Atomic Volumes. 
 
 In the case of salts, some remarkably simple relations occur, and, 
 indeed, as employed by Kopp, to explain the phenomena of isomorphism, 
 have mainly tended to attract attention to the subject ; thus, for car- 
 bonates and sulphates 
 
 Substances. 
 
 Atomic 
 Weight. 
 
 Specific 
 Gravity. 
 
 Atomic 
 Volume. 
 
 Carbonate of lime, calc. spar, 
 magnesia 
 zinc 
 iron . . 
 manganese 
 lime, arragonite 
 
 50 
 427 
 62-5 
 58-0 
 57-7 
 50-0 
 
 2-72 
 2-88 
 4-44 
 3-83 
 3-55 
 3-00 
 
 18-4 
 14-8 
 14-1 
 15-1 
 16-2 
 16-7 
 
 Sulphate of zinc 
 Sulphate of magnesia 
 
 80-6 
 60-8 
 
 3-40 
 2-61 
 
 23-7 
 23-3 
 
 It is here seen that the sulphates of zinc and magnesia, which, when 
 crystallized, are isomorphous, have the same atomic volume, and that 
 the volumes of the above carbonates differ but little. Kopp has very 
 well shown that even this difference was just proportional to the actual 
 difference of their crystalline forms, which are only nearly, not abso- 
 lutely the same, and has hence advanced as a law, that isomorphism is 
 caused by bodies having the same atomic volume. But on referring to 
 the above table, it will be seen that the atomic form of the prismatic 
 carbonate of lime (arragonite), differs less from the atomic volumes of 
 any of the rhomboidal carbonates than does that of the rhomb oidal 
 carbonate of lime (calc spar), with which they are all isomorphous. So 
 that bodies may have the same atomic volume and yet not have any 
 isomorphic crystalline relation of structure whatsoever. This topic, 
 however, will be more fully discussed in the next section. 
 
 A peculiar value which has been supposed to be attached to the idea 
 of atomic volume, is that by supplying a general rule for the volumes of 
 combinations in the solid or liquid form, somewhat analogous to that 
 which has been described in page 290 for gaseous combinations, it 
 might enable us to calculate the specific gravity of a solid compound 
 from the specific gravity of its constituents, and perhaps arrive at other 
 expressions for molecular laws tending to throw light upon the intimate 
 structure of bodies. Thus, if we subtract from the atomic volumes of 
 the oxides above enumerated, the atomic volumes of their metals, we 
 obtain the bulk occupied by the oxygen : this will be found not to 
 be the same in all, but to be almost exactly some multiple of 1'3 by a 
 whole number. Assuming, therefore, that the atomic volume of oxygen 
 is 1*3, or some multiple of it, the atomic volumes of oxides and their 
 
Calculation of Physical Properties. 
 
 303 
 
 specific gravities may be calculated as follows, for the specific gravity is 
 the quotient of the atomic weight by the atomic volume. 
 
 Substances. 
 Oxide of 
 
 Atomic 
 Weight. 
 
 Calculated 
 Atomic Volume. 
 
 Calculated Experimental 
 Specific Specific 
 Gravity. Gravity. 
 
 Antimony 
 
 129 + 24 
 
 19-2 + 7-8 
 
 5-67 5-57 
 
 Chrome 
 
 56-2 + 24 
 
 11-0 + 3-9 
 
 5-38 5-21 
 
 Tin 
 
 58-8+16 
 
 8-1 + 2-6 
 
 7-00 6-95 
 
 Lead 
 
 103-5+ 8 
 
 9-1 + 2-6 | 9-53 9-50 
 
 Mercury red . 
 
 100-1+ 8 
 
 7-4 + 2-6 
 
 10-81 11-00 
 
 Titanium 
 
 24-3+16 
 
 4-5 + 5-2 
 
 4-16 4-18 
 
 Silver 
 
 108+ 8 
 
 10-4+3-9 
 
 7-44 7-25 
 
 Mercury black 
 
 200-2 -|_ 8 
 
 H-9 + 5'2 
 
 10-35 10-69 
 
 I 
 
 It is here seen that by assuming the volume occupied in the com- 
 pound atom to be a simple multiple of 1*3, the specific gravity may be 
 calulated with very great accuracy; and Kopp and Boullay have ob- 
 tained equally close approximations to the truth in the case of chlorides, 
 sulphates, and other bodies. But still the whole system is essentially 
 arbitrary and inconsistent ; thus, in oxide of lead and red oxide of mer- 
 cury, one atom of oxygen is represented by the volume 2*6. But in 
 peroxide of tin 2*6 represents two atoms of oxygen : whilst one atom of 
 oxygen is represented in oxide of silver by 3 '9, and in black oxide of 
 mercury by 5*2 ; farther, three atoms of oxygen are represented in oxide 
 of antimony by 7 '8, and in oxide of chrome by 3 '9. Similar gratuitous 
 suppositions are made in order to extend this principle of atomic 
 volumes to the various classes of bodies by Kopp and Schroeder, but 
 what has been described will abundantly serve to show, that although 
 considerable interest belongs to such arithmetical researches, they can- 
 not be considered as at all occupying any positive relation to the science 
 of the atomic constitution of the molecular structure of bodies. The 
 very idea of a definite atomic volume is practically abandoned by its 
 authors when they assume that the volume of the atom uncombined and 
 combined is different, and that in different classes of combinations the 
 volume of the atom is different. These expansions and contractions 
 cannot take place with a solid ultimate molecule ; and if atoms be not 
 so, if they be mutually penetrative and of indefinite volume and figure, 
 then all our conceptions of an atomic theory, and, indeed of the exis- 
 tence of matter according to our popular conception of its nature must 
 be abandoned. 
 
 The researches of Playfair and Joule, although most worthy of praise 
 for their experimental accuracy, appear equally without result as to any 
 satisfactory determination of a law. They have deduced the following 
 conclusions : 
 
304 
 
 Atomic Volumes and Densities of Bodies. 
 
 1st. That the atomic volumes of solid bodies bear a simple relation 
 to each other, being multiples of a submultiple of the volume of ice 
 which, for convenience, is adopted as a standard. 
 
 2nd. That deviations from the natural volume are produced by cohe- 
 sion, and by allotropic condition, and that these deviations are expressed 
 by a submultiple of the volume of ice. 
 
 But as the volume of ice is 9*8, and the submultiple of this taken 
 as the standard unit is J, or 1*225, whilst the numbers to be deter- 
 mined are usually twenty or even forty times the unit, it is quite evi- 
 dent that the limits of error or deviation, from extraneous causes, are 
 far too wide, in comparison with the unit, to allow of the coincidences 
 which they have observed being taken as evidence of a natural law. 
 The determinations of specific gravity by those experimentalists have, 
 however, very great value, from the care with which they were con- 
 ducted. 
 
 The connection which may be presumed to exist between the che- 
 mical constitution and physical structure of bodies, has induced many 
 chemists, as Persoz and Einbrodt, to occupy themselves with specula- 
 tions analogous to those described already, but extending more to the 
 atomic weights, specific gravities, and boiling points of organic sub- 
 stances. Such hypotheses have led but to little practical result, and, 
 in fact, merely embrace in some kind of empirical rule the general 
 principle that bodies of analogous composition, or belonging to the 
 same chemical group, have their densities generally greater, and the 
 temperatures at which they assume the gaseous form higher, as their 
 atomic weight is larger. 
 
 Thus in the series of alcohols, all of which have the ultimate formula 
 CvH x +2HO, the molecular cohesion, the density of vapour, and the 
 boiling point all increase with the atomic weight as folloAvs : 
 
 Substance. 
 
 Formula, 
 
 Equiva- 
 lent. 
 
 State. 
 
 Sp. gr. of 
 Gas. 
 
 Boils at. 
 
 Sp. gr. of 
 Liquid. 
 
 Methylic alcohol - 
 Common alcohol - 
 Amylic alcohol - 
 Cetylic alcohol - 
 
 C 2 H4O 2 
 C 4 H 6 2 
 
 C10H12O2 
 C32H3402 
 
 32 
 46 
 88 
 242 
 
 Liquid 
 Liquid 
 Liquid 
 Solid 
 
 1105 
 1601 
 3147 
 M( 
 
 150 
 
 168 
 270 
 >lts at 116 
 
 798 
 795 
 813 
 . 
 
 But although an augmentation of molecular cohesion is evident, as 
 the magnitude and mass of the chemical atom augments, yet there is 
 no law or principle as yet made out by which the nature or precise 
 amount of connection between those characters can be calculated or 
 explained. 
 
Relation of Constitution to Form. 305 
 
 SECTION II. 
 
 OP ISOMORPHISM, DIMORPHISM, AND ALLOTROPY. 
 
 THE general principles of the isomorphism of crystallized substances 
 have been already noticed, with relation to the fact of their substitution 
 for each other, (page 32,) and of the advantage with which this property 
 may be applied to determine equivalent numbers (page 287) ; it now 
 remains to study this character, as indicative of the molecular constitu- 
 tion of the body. 
 
 It must, in the first place, be carefully observed, that identity of crys- 
 talline form does not simply imply similar chemical constitution, unless 
 under limiting circumstances, which require to be studied with great care. 
 The principle upon which all subsequent reasoning must rest is, that in 
 proportion as the structure of the crystal becomes more complex, and the 
 conditions necessary for its formation, consequently, more varied, the 
 greater probability is there, that two bodies shall not assume exactly the 
 same form, unless their chemical constitution and the molecular arrange- 
 ment belonging to it, be the same, or at least similar, in both. Hence 
 in the regular system, there can be no inference whatsoever drawn with 
 regard to constitution, from the crystalline form alone. Bodies, the 
 most contrasted possible in their properties and composition, have iden- 
 tical external figures, as fluor spar, bismuth, alum, sulphuret of lead, 
 common salt. The conditions of molecular arrangement, for the forms 
 belonging to this system, being the easiest possible to fulfil, the greatest 
 variety, in the number and grouping of the chemical constituents, is 
 allowable. 
 
 In the other systems of crystallization, where the double refraction 
 and the rings produced by polarized light transmitted along their prin- 
 cipal axis, indicate a much greater complexity of structure, it becomes 
 highly improbable, that the molecules of two bodies shall be so similar 
 to each other, as to produce identity of crystalline form, unless there 
 is, if the body be compound, a similarity of composition, or if the 
 body be simple, such similarity of properties as brings the two into the 
 same group, in a natural classification. This probability increases with 
 the complexity of molecular structure of the crystals. 
 
 The isomorphism of compound bodies has been explained upon the 
 supposition, that, in such cases, the replacing elements were, themselves, 
 isomorphous, and hence might change places without disturbing the 
 mechanical arrangement of the other components of the crystal. Thus, 
 that in the sulphuric, chromic, selenic, telluric, and manganic acids, 
 which contain each three equivalents of oxygen, the molecules of sulphur, 
 20 
 
306 Various Hypotheses on which the Isomorphism 
 
 chrome, tellurium, selenium, and manganese had all the same form. 
 The perfect determination of whether those elements are really thus 
 isomorphous, is very difficult, from the fact of comparatively very few 
 being crystallizable. Thus tellurium and sulphur are those of which, 
 alone, we know the crystalline form, for the only crystals of selenium 
 that have been observed are microscopic and imperfect, and neither 
 chrome nor manganese can be had crystallized at all. We must, there- 
 fore, be guided by analogy in such cases, and if we examine another 
 group of compounds into which chrome and manganese enter, we find, 
 that Cr 2 3 and Mn 2 Oa, are isomorphous with ^6263, and that MnO and 
 EeO are isomorphous with CuO. Now, we here arrive, by a chain of 
 isomorphous conditions, at a metal which may be obtained crystallized, 
 but the crystalline form of copper is always one of the regular system, 
 as the cube, octohedron, rhomboidal dodecahedron, &c., whilst sulphur, 
 with which it should be isomorphous, if this principle were absolutely 
 true, crystallizes in two forms, of which one belongs to the oblique 
 prismatic, and the other to the right prismatic system ; whilst tellurium 
 belongs to the rhombohedral system, affecting a totally different form 
 altogether. Numerous other instances might be taken; thus the 
 periodic, perchloric, and permanganic acids are isomorphous, (I0 7 , CIO 7 
 and Mn 2 07) , whilst the elements themselves are certainly not necessarily 
 isomorphous, as iodine belongs to the right prismatic system. Also the 
 isomorphism of the phosphoric and arsenic acids (PO 5 and As0 5 ) is 
 one of the best examples that has been found; but phosphorus and 
 arsenic are so far from being isomorphous, that phosphorus crystallizes 
 in the regular, and arsenic in the rhombohedral system. The principle, 
 that compound bodies are isomorphous, because their replacing elements 
 have, necessarily the same figure, is, therefore, one which cannot be 
 received in science. 
 
 Another idea suggested for the explanation of the phenomena of iso- 
 morphism is, that the crystalline form of a body is completely indepen- 
 dent of its chemical composition, and is produced only by the number 
 of ultimate particles or atoms by which it is made up. Thus alum has 
 the same form, whether it contains aluminum or iron, or manganese or 
 chrome, not because their particles have the same figure, but because, 
 in all these cases, the molecule of alum is made up of the same number 
 (71) of simple atoms. This idea is, however, even less tenable than the 
 former, for it supposes, that we have arrived at the ultimately simple 
 bodies, the true elements, which is a very unphilosophical assumption, 
 and according to it, bodies could replace each other only when they 
 were all simple or all of the same degree of composition, which is not 
 the case, and that also among the simple bodies, that the replacement 
 
of Compound Bodies has leen Explained. 307 
 
 should be always by an equal number of ultimate molecules, which is 
 also negatived by experiment. Thus we find, that an equivalent of a 
 simple body, K, is replaced by a group of five equivalents, NIL, and 
 that the simple atom, Cl, is replaced by the two atoms Mn 2 . This sug- 
 gestion cannot, therefore, be considered as satisfactory, and we must 
 examine further into the conditions of isomorphous replacement, before 
 we attempt the further discussion of the source from whence it has its 
 rise. 
 
 It is necessary first to study the crystalline relations of the undecom- 
 posed bodies, both so far as they have been really observed, and as they 
 generate similar compounds which are isomorphous. The simple bodies 
 which are known to crystallize are : 
 
 Regular System. Rhombohedral. 
 
 Carbon. Platinum. Carbon. Arsenic. 
 
 Phosphorus. Mercury. Tellurium. Antimony. 
 
 Selenium. Bismuth. Right Prismatic. 
 
 Copper. Titanium. Sulphur. Iodine. 
 
 Silver. Lead. Oblique Prismatic. 
 Gold. Sulphur. 
 
 It is thus seen that, of the simple bodies, which may be obtained 
 crystallized, two-thirds crystallize in the regular system, which, as 
 already noticed, prevents our resting upon their forms any chemical 
 reasoning ; and the bodies whose isomorphous equivalency is best 
 established, are not found to belong even to the same system. Carbon 
 and sulphur are known also to have each two forms of different systems, 
 and to be thus dimorphous. It must be observed, however, that the 
 assumption of the forms of the regular system, by so many of the 
 simple bodies, particularly among the metals, may arise from circum- 
 stances such as confer the external cubical figure on analcime or boracite, 
 and that their internal structure may be, in reality, more complex, and 
 their arrangement different ; for the metals do not reflect light as other 
 bodies of the regular system do ; they change it into the state of ellip- 
 tical polarization, and in the only case where light can be examined, 
 after having been refracted through a metal, that of gold-leaf, it is found 
 to be elliptically polarized also. The diamond resembles the metals in 
 this property, and is found sometimes to possess double refraction, which 
 should belong also to the metals, probably, if their nature allowed it to 
 be tried. The cubic crystals of gold, copper, and bismuth, the octo- 
 hedrons of lead, silver, and zinc, may, therefore, belong to the square 
 or right prismatic system, the three axes being equal amongst each 
 other, and hence the isomorphism of the simple bodies be rendered still 
 less probable. 
 
308 Isomorpkous Groups. 
 
 The examples of isomorphism in compound bodies, which are most 
 deserving of attention, are the following : 
 
 GROUP I. 
 
 Sulphuric acid 
 Telluric acid 
 Selenic acid 
 Chromic acid 
 Manganic acid 
 
 SO 3 n These acids, the composition of which 
 Te 3 is similar in all, form salts which, when 
 
 con ^ am the same base, and the 
 
 MnOa J same proportion of base and of water 
 of crystallization, have the same crystalline form. 
 
 GROUP II. 
 
 These protoxides combine with acids, 
 
 Magnesia ". . . MgO - 
 Protoxide of iron . . FeO 
 
 Protoxide of manganese . MnO 
 Oxide of copper . . CuO 
 
 and form salts, which, when in the 
 same degree of saturation with base 
 
 Protoxide of cobalt . CoO [" an( j wa t er o f crystallization, have the 
 
 Protoxide of nickel . MO f The ^ h fc f th 
 
 Oxide of zinc. .. , , ZnO \ 
 
 Oxide of cadmium . CdO J oxides combine with sulphate ot potash 
 
 to form isomorphous double salts. 
 
 GKOUP III. 
 
 Sesqui-oxide of iron . Fe 2 O 3 -j These sesqui-oxides, combined with 
 Sesqui-oxide of manganese MnaOa 11- i -11 i i j /> 
 
 Oxide of chrome . . Cr 2 O 3 j" sulphuric acid, with sulphate of potash, 
 
 Alumina . . . A1 2 3 J and with water, form the different spe- 
 cies of alum, which have all the octohedral form. They are themselves 
 also isomorphous. 
 
 GROUP IV. 
 
 Potash fcjtf ?1 These fixed alkalies may be substi- 
 
 Hytarted ammonia '. NH 3 ILO \ tufced for each other in the different 
 Hydrate of lime . CaO.HO J species of alum. The hydrated ammo- 
 nia, HO.NH 3 (often called oxide of ammonium, NH 4 .O,) is truly 
 isomorphous with potash in all its compounds ; but it is only rarely 
 that the compounds containing soda appear to have the same form. 
 In minerals, and in some forms of alums, potash is replaced by an atom 
 of any oxide in group n., united with an atom of water, as hydrate of 
 lime, or by two atoms of such compound without water. 
 
 GROUP v. 
 
 Phosphoric acid . . POs ) These acids combine with bases in 
 Arsenic acid , . . AsOs 5 different proportions, to form various 
 classes of salts, between which respectively the isomorphism is complete. 
 It was by the study of the forms of the corresponding arseniates and 
 phosphates that Mitscherlich first established the principle of isomorph- 
 
Principle of Plesiotnarphism. 309 
 
 ism, although the true laws of their constitution escaped his notice, and 
 were only brought into view by the later excellent researches of Graham. 
 Even still there is no example of isomorphism, between two complete 
 series of compounds, so well established as that of the arseniates and 
 phosphates. 
 
 GROUP VI. 
 
 SEi: i-SSl U corresponding salts of these 
 Periodic acid . . IO 7 J acids are truly isomorphous, and this 
 group affords an example of a form of substitution to which I shall 
 again refer, that of one equivalent of one body being replaced by 
 two of another, as Cl by Mn2. 
 
 GROUP VII. 
 
 S2C 5 a a r : 52 ) These bodies, which are found crys- 
 
 Sulphuret of bismuth . Bi 2 S3 J tallized in nature, have the same form. 
 The oxide of antimony and the arsenious acid, SbO 3 and AsO 3 , though 
 they are not found crystallized in the same form, appear to replace each 
 other in some salts, without changing the figure, and may, therefore, be 
 sometimes isomorphous. 
 
 GROUP VIII. 
 
 Stannic acid , . SnO 2 I These are found native crystallized 
 
 Titanic acid . . . TiO* * in the same form. 
 
 There are many other cases, in which similarity of crystalline form 
 has been observed between bodies of more or less analogous consti- 
 tution ; but as, here, I wish to bring forward only a sufficient number 
 of the most remarkable examples of the principle, I shall postpone for 
 the present the consideration of the remainder. 
 
 The principle of isomorphism, as thus described, has been supposed 
 to require, that the angles of the crystals of the isomorphous bodies 
 should be truly equal, which they are not found really to be, for even in 
 the best examples taken, slight differences appear. Thus in the carbo- 
 nates of lime and magnesia the angles of the rhombs differ by 2 3 6 ; in 
 in the sulphates of zinc and magnesia they differ by 38' ; in the sulphates 
 of barytes and strontia the difference is, 2 48'. To express this, the 
 word plesioi/iorphism, indicating, that such crystals are not exactly, but 
 nearly, of the same form, has been proposed, but it is totally useless, as 
 absolutely isomorphous forms would then be extremely rare. It is easy 
 to understand, that slight changes in external circumstances might pre- 
 vent the absolute isomorphism of two bodies, particularly as it is found, 
 that the value of the angles in different specimens of even the same 
 
310 Connexion between the Crystalline form 
 
 substances, is liable to fluctuate even to nearly a degree. I apprehend, 
 that we must seek the cause of these plesioraorphic differences in the 
 peculiar circumstances under which the body forms, particularly with 
 regard to temperature ; for when a crystallized body, not of the regular 
 system, is heated or cooled, it expands in different degrees according to 
 the direction of its axis, and may even contract in one direction, whilst 
 it is expanding in another ; thus when carbonate of lime is heated from 
 32 to 212, the linear expansion in the direction of the principal axis is, 
 0' 00 1961, whilst in the direction of each horizontal axis, a contraction 
 of 0-00056 occurs; in consequence of this, the obtuse angle of the 
 rhomb, which at 40 Fall, is equal to 105 4', becomes more acute by 
 8J', and the acute angles which are 74 54' 15" become more obtuse in 
 a corresponding degree. Hence, if we heated or cooled, through a 
 certain range of temperature, the various crystallized bodies of that 
 group, they might be brought to coincide absolutely in form, and 
 possibly when at first generated, they had done so ; but by change of 
 figure, when brought to ordinary temperatures, the small plesiomorphic 
 differences may have occurred. 
 
 The laws of isomorphism have lattely been announced by Kopp and 
 Schroeder to be intimately connected with, and indeed to flow from the 
 considerations of atomic volume, which have been so fully discussed in 
 the preceding section ; and it has been advanced as a general fact, that 
 bodies which are isomorphous have equal atomic volumes, and, vice 
 versa, that bodies of equal atomic volumes are isomorphous. As this 
 principle appears to be received favourably by many chemists, it will 
 be necessary to examine the facts regarding it a little in detail. 
 
 The principal evidence in favour of this view is derived from the fact 
 that the rhomboidal carbonates of the group of magnesian metals, lime, 
 magnesia, iron, and zinc, which are isomorphous, have atomic vo- 
 lumes nearly the same, ranging only from 18 '4 for carbonate of lime 
 to 14'1 for carbonate of zinc, and that these small differences of vo- 
 lume are accompanied by similar small differences in the angles of the 
 crystals, which may be supposed to arise therefrom, though referred 
 to a different origin in last page ; also, as noticed in page 302, the 
 isomorphous sulphates of magnesia and zinc have the same atomic 
 volume. The isomorphous sulphates of lead, of barytes and of strontia, 
 and the chromate of lead, have all nearly the same atomic volume, as 
 also the isomorphous carbonates of lead and strontia. The isomorphous 
 sesqui-oxides, alumina, peroxide of iron, and oxide of chrome have 
 nearly the same atomic volume. Many other instances might be given 
 iti which certainly the specific gravity of isomorphous bodies appears to 
 be proportional to their atomic weight, and, consequently, their atomic 
 
and the Atontic Volumes of Bodies. 311 
 
 volumes to be the same ; but the coincidence is seldom perfect, and those 
 now described will suffice to illustrate the nature of the evidence on 
 which Kopp advocates his doctrine. 
 
 It is evident, however, that really isomorphous bodies are substances 
 in which the chemical structure and the molecular structure are either 
 identical, or at least remarkably similar ; and hence the atomic volume 
 being the same, is not necessarily the cause, but only one of the con- 
 sequences of their general molecular resemblance. If the identity of 
 atomic volume caused the isomorphism, then there should be no iso- 
 morphism unless the atomic volume were the same ; and all bodies 
 with the same atomic volume should be isomorphous. But it is easy to 
 show that neither of these positions can be maintained. 
 
 Carbonate of lime, as calc spar, with an atomic volume of 18*4 crys- 
 tallizes in a rhomboid of 105. 4', and carbonate of iron crystallizes in 
 a rhomboid of 107, having an atomic volume of 15*1. Now, when 
 carbonate of lime crystallizes as arragonite, its density is 3'00, and its 
 atomic volume 16*7, just half way between calc spar and carbonate of 
 iron, and it consequently should have a rhomboidal crystal, with an 
 angle intermediate to theirs. But, on the contrary, it abandons alto- 
 gether the rhomboidal system of crystallization, and forms right rhombic 
 prisms. Here it is shown fully that a molecular change, far more pro- 
 found than alteration of atomic volume, has brought totally new crys- 
 talline forces into play. 
 
 It will only require a few casually selected instances to show that 
 bodies may have the same atomic volume, and yet be in no way con- 
 nected in form. Thus, carbonate of iron, oxide of silver, sulphuret 
 of cadmium, and peroxide of iron, none of which bodies have any 
 isomorphous connexion, have yet the same atomic volume, 15; and 
 sulphate of barytes, which crystallizes in rhombic prisms, and chloride 
 of silver, which crystallizes in cubes, have the same atomic volume, 26. 
 In like manner it may be shown, that the most perfect isomorphism 
 may exist without identity of atomic volume, just as it may exist between 
 bodies destitute of any true chemical relationship. Thus, in the fol- 
 lowing table of pairs of isomorphous bodies the atomic volumes will be 
 seen to be totally different. 
 
 Substances. 
 
 Atomic 
 Volume. 
 
 Substances. 
 
 Atomic 
 Volume. 
 
 Calc spar 
 Nitrate of soda 
 
 18-5 
 38-2 
 
 Chloride of potassium 
 Chloride of silver 
 
 38-9 
 '26-1 
 
 Sulphur 
 Bi Sulphate of potash 
 
 8-0 
 63-3 
 
 Arragonite 
 Nitrate of potash . 
 
 16-8 
 497 
 
312 Similarity of Chemical Constitution not 
 
 It is thus abundantly evident, that in no way can the proposition 
 put forward by Kopp and Schrceder, of the law of isomorphism result- 
 ing from the atomic volumes of isomorphous bodies being equal, be 
 admitted as sustained by facts, and I shall pass altogether from its 
 consideration. 
 
 Isomorphism, considered as thus sketched, affords to the chemist 
 the most valuable criterion at present at his disposal, for determining 
 those substances which replace each other, most truly, in combination ; 
 and where a number of bodies are so connected by external form, very 
 important conclusions may be obtained, as to the internal arrangement 
 of their constituents. In this manner it has been satisfactorily estab- 
 lished, that bodies may replace each other in proportions quite different 
 from those of their ordinary equivalents, and thus pass, as it were, 
 by a doubling or a trebling of their atomic weights, into a different 
 natural group, and that even two bodies, combined in an equivalent of 
 each, may form a complex group, capable of being substituted for one 
 of simpler structure. Thus an equivalent of chlorine is replaced by 
 two equivalents of manganese, an equivalent of silver is replaced by 
 two equivalents of copper, an equivalent of soda or of potash is re- 
 placed by two equivalents of lime, or of one of lime and one of water, 
 or by one of lime and one of oxide of manganese or of iron, or by 
 ammonia and water united to each other, or to an equivalent of a pro- 
 toxide of the magnesian group. By such observations, we obtain the 
 foundations of a philosophical classification of bodies, with which the 
 analogies drawn from purely chemical characters are found remarkably 
 to correspond. 
 
 But it is important to ascertain, whether the isomorphism of various 
 bodies establishes necessarily, or even probably, in the absence of other 
 reasons, grounds for assimilating the formulae of the bodies, or imagin- 
 ing, that their chemical constituents are equivalent and are arranged in 
 the same way. This is a point which has been, as I consider, much 
 misunderstood, and has led to some error and confusion. Thus anhy- 
 drous sulphate of soda crystallizes in the same form as perchlorate of 
 barytes and permanganate of barytes, and if it be necessary, as a con- 
 sequence of isomorphism, that these bodies should have similar consti- 
 tutions, we must change the formula, S0 3 .NaO into S 2 7 . Na 2 0, in 
 order to make it resemble Mn 2 O 7 . BaO. This requires us to compare 
 the sulphates whose elements are most powerfully united, with some of 
 the most easily decomposed salts that we know ; it requires us to con- 
 sider the alcalies as being sub-oxides, which is opposed to every cir- 
 cumstance in their history ; and it requires us to consider two equiva- 
 lents of sodium, as being equivalent to one of barium, for which no 
 
the Cause of homorpJwus replacement. 313 
 
 other evidence can be had from other examples. But again, the anhy- 
 drous sulphate of soda is isomorphons with sulphate of silver, and 
 hence the formula of this should be, S 2 O 7 . Ag 2 O, which is so totally un- 
 supported by other evidence, that it has been proposed to subdivide the 
 atomic weight of silver and sodium, for the purpose of explaining the 
 isomorphism of Cu 2 and Ag. These examples are sufficient to show, 
 how unphilosophical is the attempt at rashly inverting the principle of 
 isomorphism, and seeking to deduce, as a necessary consequence of the 
 mere similarity of form, similarity of chemical constitution. Bodies of 
 similar chemical constitution affect the same crystalline form, but bodies 
 of the most diverse natures may have the same crystalline form also. 
 Even without speaking of the regular system, where fluor spar and 
 alum, CaF and KO. SO 3 + A1 2 3 . 3SO 3 + 24HO, have the same form, 
 we find numerous examples of this fact ; nitrate of soda and carbonate 
 of lime are isomorphous in the rhombohedral system, and nitrate of 
 potash and carbonate of lead in the right prismatic system ; the che- 
 mical constitution giving the formulae NO 5 . XaO and CO 2 . CaO, and 
 that of the formulae, NO 5 . KO and CO 2 . PbO are widely different, but 
 the forces, by which the assumption of crystalline form is governed, are 
 alike. Even in these instances, the attempts at generalizing the che- 
 mical formula have been tried, and the nitrates of soda and potash have 
 been written NO 6 . K and NO*;. Na, with which the formula of the car- 
 bonates, when doubled, C 2 6 Ca2 and C 2 O 6 Ba2, have been compared. In 
 this way one equivalent of soda is made isomorphous with two of barytes, 
 whilst by a former and similar reasoning, one of barytes was made iso- 
 morphous with two of soda. Bisulphate of potash, KO . SOa + HO . 
 SO 3 crystallizes in two forms, one of which is that of sulphur, a simple 
 body, and the other of which is that of feldspar, KO . SiOa-fAlaOs^Sig. 
 Here, in neither case, is there the slightest similarity of constitution. 
 
 The circumstances of isomorphous replacement may be reduced to 
 the following simple propositions, with which I shall terminate the 
 subject : 
 
 1st. Similarity of crystalline form requires that the molecular struc- 
 ture of the bodies shall be alike, but has no necessary reference to the 
 chemical nature, or composition of these molecules. Examples. Ni- 
 trate of soda and carbonate of lime, sulphate of soda and perchlorate of 
 barytes, bisulphate of potash and sulphur. 
 
 2nd. When the physical molecules consist of chemical elements 
 which follow the same law of combination, and which belong to the same 
 chemical family, the similarity of molecular structure is most completely 
 and most easily produced, and such crystals are isomorphous. Exam- 
 
314 Of Dimorphism and Allotropy. 
 
 pies. Sulphate of zinc and sulphate of magnesia, carbonate of lime and 
 carbonate of zinc, sulphate of barytes and sulphate of strontia. 
 
 3rd. But identity of molecular structure may result from the aggre- 
 gation of substances the most different in their chemical relations ; and 
 hence isomorphous bodies are not necessarily of similar chemical consti- 
 tutions. 
 
 4th. As the influence of the chemical constitution does not extend 
 to the absolute determination of the molecular structure, a body, che- 
 mically the same, may assume incompatible crystalline forms, and so 
 become dimorphous ; but as the chemical structure influences the 
 molecular arrangement in some degree, dimorphous bodies, which are 
 isomorphous in one form, are generally so in the other ; they are isodi- 
 morphous. Examples. Sulphur, and bisulphate of potash ; nitrate of 
 potash and carbonate of lime; garnet and idocrase, arsenious acid and 
 oxide of antimony. 
 
 5th. We cannot assert that the similarity of form of truly isomor- 
 phous bodies results from the isomorphism of their elements, for, so far 
 as our observation goes, their simple constituents, are not necessarily 
 or even usually isomorphous. Examples. Arseniates and phosphates, 
 sulphates and seleniates. 
 
 6th. We cannot assert that isomorphism results from the aggrega- 
 tion of the same number of simple molecules ; for we do not know what 
 bodies are truly simple, nor do we know, without doubt, that we can 
 value the relative number of atoms present ; but, even in the existing 
 state of our knowledge, we have numerous examples of bodies truly 
 isomorphous, which* contain an unlike number of atoms according to 
 our present ideas. Examples. Potash and ammonia, natrolite and 
 mesotype, sulphur, feldspar and bisulphate of potash. 
 
 7th. We cannot admit that isomorphism results from equality of the 
 atomic volumes of bodies, as we have found that, although many iso- 
 morphous bodies have the atomic volumes the same, many others have 
 quite different atomic volumes, and bodies have the same atomic volumes, 
 which are not at all isomorphous. 
 
 Finally. Isomorphism does result from the aggregation, according to 
 the same laws, of similar molecular groups, which are most generally 
 formed by the reunion of similar chemical substances, in the same state 
 of combination. 
 
 The fact of the same body being capable of crystallizing in forms 
 belonging to two different systems, has been already frequently referred 
 to ; but, for convenience of reference, a more detailed list of such cases 
 of dimorphous bodies is here inserted, taken from Professor Johnston's 
 excellent report on the subject, made to the British Association. 
 
List of Dimorphous Bodies. 315 
 
 
 Symbol or Form. 
 
 Crystalline Form. 
 
 1. Elementary bodies : 
 Sulphur, - - - A 
 
 Carbon, - - - A 7 
 -- B( 
 
 S 
 C 
 
 Cu 2 
 
 CuS or Cu 2 S 
 
 AgS or Ag 2 S 
 MnS 
 Fe S 2 
 HgI 2 
 HgCl 2 
 As 2 Os 
 Sb 2 0s 
 
 CaO_[-CO 2 
 
 FeO-f-CO 2 
 PbO-f C0 2 
 KO-f-N0 5 
 PbO + CrOa 
 
 NiO + SO 3 +7HO 
 ZnO + Se0 3 + 7HO 
 
 ( Rt. Rh Pr. M on M 101-59 Haid. 
 I Oblique Rh. Pr. of 90 32' M. 
 C Reg. Octohedron. 
 I Rhombohedral. 
 
 f Cube. 
 1 Rh. of 99 15', 6-sid. Pr. Rhomb. 
 C cleav. Sk. 
 ( Do primary a rhomb. P. on F' 
 j = 71 30' 
 (Reg. octohedrons. 
 / Cube in Silver glance. 
 1 Rhomboid. 
 /Cubes. 
 (.Rhomboid. 
 /Cubes. 
 IRt. Rh. R., M on M' 106 2'. 
 /Octohed. with square base. 
 \Rt. Rh. Pr. MM= 114. 
 ( Rt. Rh. Pr. MM = 71 '55. 
 1 Octohed. with rect. base. 
 /Reg. octohedrons. 
 \Rt. Rh. Pr. 
 /Do. MonM'136 58'. 
 (^Reg. octohedrons. 
 
 /Rhomb, of 105<> 4' M. 
 IRt. Rh. Pr. of 116 16' Ku. 
 /Rhomb, of 106 15'. 
 IRt. Rh. Pr. 
 /Rhomb, of 107'0. 
 IRt. Rh. Pr. 10826', 118 0'? 
 rRhomboid 104 53 J'? 
 JRt. Rh. Pr. of 117o 14', Ku. 
 c K t. Rh. Pr. M on M' = 1 1 8" 52' Lv. 
 \ Rhomboid of 106'36, Fm. 
 (Ob. Rh. Pr. 
 ( Square prism. 
 
 rRt. Rh. Pr. M on M' 91 10' Bk. 
 \ Square prism, 
 j Rt. Rh. Pr. 
 \ Square prism. 
 ( Rhombic octohed. (form of sul- 
 < phur) M. 
 C Ob. Rh. Pr. (form of Felspar) M. 
 f Rt. Rh. Pr. of M on M' 93 54'. 
 
 ( Do. of 78 30'. 
 C Reg. dodecahedron. 
 
 Square prism. 
 f Oblique Rh. prism. 
 -J Right Rh. prism, (form of arrago- 
 ( nite.) 
 /Acute rhomboid of 72 30'. 
 iRt. rhombic prism* M on M = 120. 
 
 II. Bi -elementary Compounds : 
 Dioxide of Copper, - A } 
 P > 
 
 Disulphuret of Copper, - AS 
 B) 
 
 Sulphuret of Silver, - A 7 
 B \ 
 
 Sulphuret of Manganese, A 7 
 
 Bisulphuret of Iron, - A 7 
 B\ 
 
 Biniodide of Mercury, - A 7 
 B \ 
 
 Bichloride of mercury, - A 7 
 B\ 
 
 Arsenious acid, - - A 7 
 B \ 
 
 Oxide of Antimony, - A 7 
 B \ 
 
 [II. Compounds of 3 Elements : 
 Carbonate of Lime - A 
 
 Carbonate of Magnesia, A 7 
 
 Carbonate of Iron - A 7 
 
 Carbonate of Lead - A 
 
 Nitrate of Potash, - A 
 B 
 
 Chromate of Lead - A 
 
 IV. Compounds of 4 or more 
 Elements : 
 Sulphate of Nickel, - A 7 
 
 Seleniate of Zinc,' - A 7 
 
 Bisulpliate of Potash, - A ^ 
 
 K0+S0 3 +H0+S0 3 
 
 Biphosphate of Soda, - A 1 
 
 n \ 
 
 NaO -|- P 2 Os -|- 4HO 
 or NaH 2 P_|_2H 
 
 Ca07^ Co Ba07 ^ 
 PbS+3PbC 
 
 Garnet - - - Al 
 
 Idocrase - - B j 
 Baryto-Calcite, - - A) 
 
 R f 
 
 J 
 
 Sulphate -Tricarbonate of 7 
 Lead, J 
 
 Ilaidinger says an oblique rhombic prism, which, according to the subsequent measure- 
 ment of Brooke, is incorrect. Bk., Brooke ; Ku., Kuffcr; Lv., Levey ; M,, Mitscherlich ; S.,Sukow. 
 
316 Difference in Structure of Dimorphous Bodies. 
 
 The molecular arrangements which produce this diversity of form are 
 not in general of equal stability, on the contrary, one figure appears to 
 be, in general, forced upon the body, and is abandoned by it upon very 
 slight disturbance. Thus when a prism of arragonite is heated in the 
 flame of a spirit lamp, it breaks up into a congeries of little rhombs of 
 common calc spar, at a temperature far below that at which the carbon- 
 ate of lime commences to be decomposed ; but no alteration of tempe- 
 rature can convert calc spar back again into arragonite. Indeed arra- 
 gonite appears to be formed only between very narrow limits of tempe- 
 rature. When chalk is melted, it forms, on cooling, marble, whose 
 fracture shews it to have the rhombohedral structure, and when carbo- 
 nate of lime is precipitated at ordinary temperatures, the microscopic 
 crystals produced are rhombohedrons ; but when it is precipitated from 
 a boiling solution, it deposits minute crystals of arragonite, which a 
 higher or a lower temperature should have prevented. 
 
 When sulphur has been crystallized by fusion in oblique rhombic 
 prisms, these lose their transparency after a day or two, and change into 
 a mass of very minute right rhombic octohedrons. When the arsenious 
 acid is crystallized in rhombic prisms, it alters slowly, and eventually 
 becomes a dull white mass, which is a congeries of regular octohedrons, 
 but if the rhombic form of the acid be dissolved in muriatic acid, and 
 the solution set to crystallize, it is deposited in the octohedral form, and 
 the formation of each crystal is accompanied by a brilliant flash of light, 
 indicating probably the moment of the change of molecular condition. 
 One form is, therefore, the stable condition of arrangement ; the other 
 being produced by the sudden fixation of the molecules, in a form, 
 which is naturally only transitive, and from which they free themselves, 
 as soon as the external circumstances admit of their suitable motion 
 amongst each other. 
 
 Independent of the change in external figure, dimorphous bodies 
 present remarkable differences in physical properties ; thus the density 
 is generally different ; in one form the substance is more soluble than 
 in the other ; they differ also in hardness, and generally speaking, in all 
 characters derived from the physical arrangement of molecules. 
 
 The changes in density which thus usually accompany the total alter- 
 ation of molecular structure that must occur where bodies pass into 
 dimorphous states, would, of course, make it quite possible to assert that 
 the same body in its different conditions had different atomic volumes ; 
 this substitution of effect for cause would be very unphilosophical, and 
 besides, the differences of atomic volumes among dimorphous bodies, are 
 in no case so great as have been already shown to commonly exist among 
 bodies truly isomorphous. In regard to dimorphism therefore, as in 
 
Allot ropic Characters indicate an approach to Dimorphism. 317 
 
 regard to isomorphism, I regard the doctrine of atomic volume as not 
 establishing any new principle in science. 
 
 A body, in its dimorphous conditions, presents frequently a differ- 
 ence of chemical properties deserving of particular notice. The bisul- 
 phuret of iron, in its cubical form, is remarkably permanent, not being 
 acted on either by air or water ; but in its right rhombic form, when 
 exposed to moist air, it absorbs oxygen with avidity, and is converted 
 intea crystalline mass of copperas. On this principle depends, most 
 probably, the change of molecular condition which takes place in oxide 
 of chrome, peroxide of tin, zirconia, and alumina, when exposed to a 
 temperature just below redness. These substances, which had been 
 easily soluble in acids, become almost totally insoluble, except in boil- 
 ing oil of vitriol, and this change is generally accompanied by the spon- 
 taneous ignition of the body, which the temperature applied would be 
 quite insufficient to produce. 
 
 Independent of crystalline form, we must refer to circumstances simi- 
 lar to those which produce dimorphism, a variety of differences in phy- 
 sical constitution, observable in certain bodies, and which have been 
 grouped together recently by Berzelius under the name of allotropic 
 modifications. Thus, melted sulphur is, at 230 F., perfectly liquid ; 
 on being heated to 430 it becomes thick, and so tenacious that the 
 vessel containing it may be inverted, without it running out ; when 
 heated further to 480, it becomes again liquid, and continues so until 
 it begins to boil. When the red oxide of mercury is heated nearly to 
 redness, it becomes almost quite black. 
 
 When metallic mercury is rubbed in a mortar with sulphur, or a 
 solution of corrosive sublimate is precipitated by hydro-sulphuric gas, the 
 sulphuret of mercury is formed as a black powder ; but if that powder 
 be sublimed, or if mercury be agitated with a solution of persulphuret of 
 potassium, there is generated vermilion, which merely differs in colour 
 from the black sulphuret, and may be reconverted into it by being heated 
 until it just begins to give off sulphur, and then suddenly cooled. The 
 sulphuret of antimony may be had either as the brown kermes mineral 
 of medicine, or as the steel grey crystallized mineral. Oxide of zinc 
 when very hot is of a bright lemon yellow, but when cool perfectly 
 white. 
 
 If the red iodide of mercury, formed by precipitation, be sublimed, it 
 becomes yellow ; but if the sublimed mass be scratched with a pin, the 
 edges of the scratch turn red, and the redness spreads from thence, until 
 the whole mass is converted into its original condition. Even in liquids 
 and gases, this difference in molecular condition, whether produced by 
 temperature or by other causes, appears frequently to occur. Thus, the 
 
318 Allotropic Conditions of Bodies. 
 
 liquid hyponitrous acid (NO 8 ) is deep green at 60, but at 4 it is quite 
 colourless ; and the deep red gas of nitrous acid (NO 4 ) becomes, when 
 heated to 212, absolutely black and opaque. The compound of starch 
 and iodine, so beautifully blue-coloured at ordinary temperatures, be- 
 comes colourless when heated to 200, but acquires its original tint in 
 proportion as it again cools. In all such cases, there is scarcely room 
 to doubt but that if we had as perfect methods of determining the mo- 
 lecular structure, as is afforded by the measure of the angles and the 
 optical properties of the bodies, when crystallized, we should find these 
 phenomena to depend upon causes of the same kind. 
 
 In solid bodies, a difference of molecular structure, fully equivalent 
 to that to which dimorphism may be referred, is capable of being pro- 
 duced by very simple means. Thus, when a plate of glass is compressed 
 by means of a screw it assumes a doubly refracting structure, and gives 
 with polarized light, a cross and rings, variously disposed according to 
 the direction of the pressure. In this case, the change of structure 
 arises necessarily from an increase of density in the compressed portions ; 
 but the same effect may be produced by the converse process ; a plate of 
 glass which has been suddenly cooled from having been red hot, assumes 
 a similar doubly refracting and polarizing structure, although here the 
 density is diminished in place of being increased. I have found the sp. 
 gr. of glass, suddenly chilled, to be about T n less than that of glass of 
 the same kind, which had cooled slowly, indicating, that the volume was 
 the same that it had occupied at a dull red heat, and that hence the 
 internal molecules were arranged so as to occupy a greater space than in 
 the usual condition. 
 
 The tendency of glass to assume allotropic conditions is further shown 
 by the separation of its constituent silicates when it is allowed to cool very 
 slowly ; it becomes devitrified and milk white, being changed into what 
 is called Reaumur's Porcelain. Glass is, in fact, but a mixture of silicates 
 of potash, soda, lime, lead, &c., according to the kind of glass ; and all 
 these silicates may exist either as really crystallized bodies or as the 
 plastic, uncrystalline material of glass. The tendency to assume the 
 latter condition is singularly promoted by their being mixed together, 
 and hence even the simplest kind of glass is a mixture of at least two 
 silicates. 
 
 These allotropic modifications of bodies are, however, found to involve 
 other phenomena than those of molecular form, or change of aggregation 
 or of colour, and indeed, are probably but the external indication of a 
 far more profound alteration in the physical and chemical nature of the 
 body. Its relations to heat are altered. The assumption of the new 
 condition is often accompanied by vivid spontaneous ignition, as in the 
 
Relation of Allot ropy to Isoinerlsm. 319 
 
 case of oxide of chrome, and their tendency to combine with other bodies 
 may be totally changed. There is involved then the question of the 
 chemical individuality of the body, and the allotropy may connect itself 
 with isomerism. 
 
 SECTION III. 
 
 OF ISOMERISM, AND THE INTIMATE STRUCTURE OP CHEMICAL GROUPS 
 
 THEORY OP COMPOUND RADICALS THEORY OF TYPES CONSTITUTION 
 
 OF SALTS. 
 
 BERZELTUS first fixed the attention of chemists upon the fact that the 
 allotropy, which as described above, exists among many simple bodies, 
 might be supposed to continue even when those simple bodies entered 
 into combination, and might give rise to the allotropy of those com- 
 pound bodies, or to other differences of molecular characters as dimor- 
 phism, which have been found to exist. Thus, silicon may be obtained 
 in two quite different allotropic states, in one of which it is combustible 
 and dissolves in hydrofluoric acid with evolution of hydrogen gas, whilst 
 in the other it is totally incombustible and inattackable by hydrofluoric 
 acid. These two states of silicon correspond precisely to two conditions 
 of silicic acid, which in one is soluble in water, and separated from its 
 salts by even the feeblest acids, but in the other is insoluble in water, 
 and its salts cannot be decomposed even by strong acids. The metal 
 chrome may be prepared either unalterable by heat or acids, or easily 
 oxidized by either, and its oxide may assume either a form inattackable 
 by acids, or it may be easily dissolved and form salts. Of these salts 
 there are again evidently two conditions, the one green and the other 
 red, so that this difference of molecular state in the metal is continued 
 throughout its chemical combinations, and generates a difference of pro- 
 perties which might belong to a totally different substance. We might 
 in fact say that there are two chromes, chrome A and chrome B, and 
 that chrome A forms a totally different class of compounds from chrome 
 B. There is then really nothing to reduce them to the same chemical 
 element, but that we can change one into the other. 
 
 It appears to me indeed, that in order to fully explain the relations 
 which the allotropic conditions of bodies bear to their chemical habi- 
 tudes, we must admit that the same elementary body may in forming 
 different classes of compounds, abandon that absolute simplicity and act 
 in as totally different capacity as if those series arose from different 
 elementary bases. Thus, the manganese which forms a powerfully basic 
 
320 Allot ro^^y and Isomerism. 
 
 protoxide, may be a different body from the manganese, which forms with 
 oxygen a powerful acid, and that it may have a different atomic weight. 
 I therefore believe that permanganic acid is not formed of two atoms of 
 manganese, a strongly electro-positive metal, and seven of oxygen, but of 
 an atom of manganese with the equivalent 56, which is a powerfully 
 electro-negative metal, like gold or platinum, and this allotropic con- 
 dition of manganese is perfectly illustrated in the passive condition " 
 produced, in its analogous metal iron, by strong nitric acid : a state in 
 which iron is inattackable by oxidizing means, and in which, being sub- 
 stituted for platinum, it forms the electro-negative element of the 
 powerful batteries invented by Professor Callan. Manganese and iron 
 therefore, as I believe, may exist in different allotropic states in which 
 they have different atomic weights, and totally different chemical pro- 
 perties states in which, in fact, they are different metals, but that we 
 know how to transmute them into their ordinary conditions. 
 
 In this manner we can perfectly conceive a metal belonging to quite 
 different natural groups, and manifesting a totally different kind of che- 
 mical properties according as it acts with one or the other atomic weight. 
 Copper, when it unites with the equivalent 31 '7, forms a soluble chlo- 
 ride and sulphate. Its salts are blue or green. It ranges in the class 
 of iron, nickel and cobalt. But when copper combines in the equivalent 
 63'4, which is usually called two atoms of copper, then it forms an in- 
 soluble chloride and a very sparingly soluble sulphate, and its salts are 
 white. It belongs then to the family of silver and lead. Similarly, 
 mercury according as has the atomic weight 100 or 200 approaches to 
 the copper or silver group respectively. But in these cases, except that 
 when we actually break up the compounds and extract the metal, it is 
 the same, Cu 2 differs far more from Cu, as a chemical substance, and 
 Hg 2 from Hg. than Cu 2 does from Ag. or Pb. or Hg 2 . from Cu 2 . We, 
 therefore, arrive at the principle, very important for the philosophical 
 theory of combination, that the degrees of combination of a metal may 
 really have totally different radicals and be as perfectly independent and 
 unconnected as are the compounds of quite different metals, the only tie 
 embracing them being, that by certain processes we are enabled to ex- 
 tract the same metal from both. But that each allotropic state of the 
 metal which gives it its different atomic weight, and its different chemical 
 properties, really constitutes it for the time a different metal, and thus a 
 transmutation, although in a different point of view from that of the 
 alchemists, takes place as one of the most common facts of chemistry. 
 
 The differences of chemical properties may, however, proceed much 
 further, so that in place of considering that there is one chemical sub- 
 stance which may exist in two molecular conditions, we are obliged to 
 
Principle of Isomerism. 321 
 
 consider, that the individuality of the body is lost, and that in its two 
 forms it constitutes two distinct and independent chemical substances. 
 Thus, by the action of sulphuric acid on alcohol, we obtain a gas con- 
 sisting of carbon and hydrogen, in the proportion of an equivalent of 
 each. In the destructive distillation of wood, a solid substance is ob- 
 tained, fusible like wax, and volatile only at a high temperature ; this 
 consists also of carbon and hydrogen, and in the same proportions. 
 These elements, so combined, present, therefore, a difference in mole- 
 cular arrangement, still greater than those which have been observed 
 amongst merely allotropic bodies; and when we examine their che- 
 mical relations, the diversity becomes still more marked. The gas 
 (olefiant gas) is remarkable for the number of compounds to which it 
 gives rise, and has been, from the variety of its re-actions, of great 
 influence on the existing theories of organic chemistry. The solid is 
 inattackable even by the strongest agents, and from its total indifference 
 to combination, has been called paraffine, (parum affinis.) In this case, 
 the difference of properties indicates a difference of structure, much 
 more profound than that by which change of density, colour, or even 
 crystalline arrangement could have its source ; it is not merely that the 
 molecules are differently placed, but that the molecules are different. 
 The carbon and hydrogen which unite to constitute the chemical equi- 
 valent of the body are themselves differently arranged, and thus give 
 rise to difference of properties ; and the physical molecules formed by 
 their reunion being again grouped according to dissimilar laws, produce 
 the diversity of physical properties and states of aggregation. The 
 bodies being thus in every property unlike, are to be looked upon as 
 independent substances ; they are said to be isomeric (from rfo$ [J<t%s), 
 because they have the same ultimate composition, but in all their che- 
 mical relations they may differ as widely as bodies which have no element 
 in common. 
 
 When, therefore, the groups of chemical molecules are differently 
 arranged, the various differences in colour, density, solubility, and 
 figure, which belong to allotropic and dimorphous bodies are produced ; 
 but when the difference of arrangement extends to the chemical consti- 
 tuents of these molecular groups, independent, but isomeric, bodies 
 are generated. 
 
 It is generally found, that this difference in the constitution of the 
 chemical molecule has the effect of changing, in a simple manner, the 
 equivalent number of the body. Thus, oil of turpentine, and oil of 
 citron, are isomeric, each having the composition C 5 H 4 , but when we 
 combine these oils with muriatic acid, we find that the equivalent group 
 of oil of turpentine contains C 20 H J6 , whilst that of oil of citron is only 
 21 
 
322 Principle of Isomerism. 
 
 Ci H 8 ; it is remarkable, that although the chemical group of oil of 
 citron is only one-half the weight of that of oil of turpentine, it exer- 
 cises the same power of circular polarization, but in the opposite direc- 
 tion. Another example of this simplicity of proportion in weight 
 between the equivalents of isomeric bodies, is met with in common 
 alcohol and methylic ether; that of the former being C 4 H 6 2 , that of 
 the latter being C2H3O. 
 
 The difference of the chemical constitution in isomeric bodies is not 
 limited to magnitude, as determined by the weight of their equivalent, 
 but extends to internal structure. Thus, alcohol is composed of ether 
 and water, C 4 H 5 O -f HO, whilst methylic ether cannot be resolved into 
 those substances. Pormiate of methylene, and glacial acetic acid, are 
 each C 4 H 4 O 4 , not differing even in the weight of their equivalent, but 
 all the properties of these bodies show that glacial acetic acid is 
 C 4 H 3 3 + HO, whilst formiate of methylene is C 2 H0 3 + C 2 H 3 O. 
 Instances of this kind might be multipled to any extent, but these will 
 be sufficient to illustrate the principle. 
 
 It is necessary, however, in studying such cases of isomorphism, to 
 bear in mind what has been so beautifully shown by Graham, that the 
 presence of foreign bodies, in quantities so small as to be totally unap- 
 preciable, except in the most rigidly accurate analysis, may change so 
 completely the properties of bodies, that they shall simulate isomerism. 
 Thus, phosphuretted hydrogen may exist in two conditions, in one of 
 which it is spontaneously inflammable, and in the other not. They 
 both give, on analysis, the same formula, PH 3 , but the first may be 
 changed into the second, by mere admixture with a very small quantity 
 of the vapour of ether ; and the second may be converted into the first 
 by the most minute bubble of nitrous acid gas. Such bodies, there- 
 fore, which owe their diversity of properties to accidental circumstances, 
 are not isomeric, and must be carefully distinguished from those before 
 described. 
 
 As we have thus traced a gradual transition from the feeblest indica- 
 tions of dimorphism to the complete difference of structure and pro- 
 perties constituting isomerism, it becomes an interesting question, 
 whether we may not have occasion to retrace our steps, and to seek in 
 those bodies which we have hitherto considered as only differing in 
 physical properties, for evidences of difference in chemical arrangement. 
 May not, as already suggested, a simple substance, as sulphur or anti- 
 mony, enter into combination with equivalents of different weights, and 
 so resemble oil of turpentine and oil of citron ; and may not this dif- 
 ference in equivalents be the source of diversity in form ? When sul- 
 phur crystallizes in the form of bisulphate of potash, may we not 
 
Connexion of Dimorphism and Isomerism. 
 
 323 
 
 reasonably suppose that its molecules are grouped iuto a complex figure, 
 like that of the compound salt, and that its equivalent is, in proportion, 
 greater than when it crystallizes as a simple body ? We say that two 
 ordinary equivalents of manganese replace one of chlorine ; but is it 
 not really that when manganese replaces chlorine, its equivalent is 
 double what it is when it replaces hydrogen or copper, and it is no 
 longer common manganese ? Manganese replacing chlorine, is to man- 
 ganese replacing copper, what oil of turpentine is to oil of citron ; and 
 hence, it may be isomeric with itself, for the functions it performs in 
 its two modes of combination are the most widely different possible. 
 The bisulphuret of iron, in its cubical form, is FeS 2 , and like Mn0 2 , 
 is decomposed only by a red heat, when it parts with one-third of its 
 volatile constituent ; but in its rhombic form, may not its equivalent 
 be Ee 2 S 4 , resembling C10 and like it, be decomposed by the slightest 
 causes ? 
 
 The circumstance that isomeric bodies are almost universally con- 
 nected by simple relations between their atomic weights, coupled with 
 the idea, that even amongst the simple bodies, a kind of isomerism 
 may be the cause of their dimorphous conditions, acquires remarkable 
 interest from the fact, that the equivalent numbers of many of the 
 simple bodies are closely related to one another, as is shown in the 
 following table. 
 
 1 equivalent of bismuth = 106*65 
 
 2 palladium . . 10672 
 
 rhodium . . 52-11 
 
 ruthenium . . 52- 11 
 
 equivalent of osmium . . 199'72 
 
 gold . . . 199-21 
 
 equivalent of platina . . 98'84 
 
 ,, iridium . . 98*84 
 
 equivalent of molybdenum . 47 "96 
 
 ,, tungsten . . 47 '40 
 
 equivalent of zinc . . 32-31 
 
 yttrium . . 32 25 
 
 \ antimony . . 32-40 
 
 i ,, tellurium . . 32-13 
 
 2 sulphur . . 32-24 
 
 1 equivalent of cobalt . . . 29 57 
 
 1 , nickel . . . 29'62 
 
 * tin 29.46 
 
 May it not be possible that science shall hereafter find the metals so 
 connected, to be truly isomeric ? In no case are their properties more 
 different ; and we find, in the racemic and tartaric acids, an example of 
 the general similarity of the properties in the compounds of isomeric 
 
324 Possible Isomerism of the Metals. 
 
 bodies, which is so remarkable in the combinations of sulphur and tellu- 
 rium, or of cobalt and nickel, amongst the simple substances. 
 
 Considerable probability is given to the idea of the compound nature 
 of bodies, at present considered simple, by the existence of certain com- 
 pound bodies, which simulate the properties of, and enter into combina- 
 tion subject to the same laws as the undecompounded substances. Thus, 
 carbon and hydrogen unite to form a gas, cyanogen, which combines 
 with the metals, with oxygen, with hydrogen, &c., precisely as chlorine 
 does ; it is the origin or root of a series of very important bodies, named 
 cyanides, of which cyanide of hydrogen, prussic acid, and cyanide of 
 iron or Prussian blue may serve as examples, as chlorine is of a series 
 of chlorides, and it is hence called a compound radical. The discovery 
 of this principle by Gay-Lussac, was the foundation of all that is exact 
 and philosophical in our views of organic chemistry. Bodies which 
 contain the same ultimate elements, may be different, because they con- 
 tain different radicals, precisely as the salts of nickel and cobalt may be 
 hereafter shown to be isomeric bodies. 
 
 Of electro -negative compound radicals, the cyanogen just noticed is 
 the most remarkable example, and the type of electro-positive or basic 
 radicals is to be found in the Kacodyle, or basis of the fuming liquor of 
 Cadet, lately examined with so much success by Bunsen. This body is 
 composed of carbon, hydrogen, and arsenic. It combines with oxygen, 
 chlorine, iodine, sulphur, &c. Its oxide unites with acids to form well 
 denned salts. Its salts unite with other salts to form double salts. Its 
 oxide unites with a further proportion of oxygen and produces an acid 
 which forms with metallic oxides perfect salts. Further, not merely is 
 the oxide separated from its solutions by stronger bases, but the radical, 
 the kakodyle is separated by the addition of a more oxidizable metal, and 
 the only point in which its history would differ from that of zinc or 
 copper is, that when it separates it appears not as a metal but as a heavy 
 oily liquid, and that by certain processes we can resolve it into its con- 
 stituent elements. We know its composition, but we do not know the 
 composition of the simple metallic bases. This is the only philo- 
 sophical distinction between the simple and the compound radicals. 
 
 The theory of compound radicals has received a very remarkable exten- 
 sion by the general reception among chemists of the theory which looks 
 upon all salts as combinations not of acids and of bases, but of metals with 
 an electro-negative compound radical ; thus bringing all salts into the 
 same category, and making the common sea salt the type of the whole 
 class. Tor example, that glauber salt is not sulphate of soda, that it 
 contains neither sulphuric acid nor soda, although we may extract these 
 bodies from it by decomposition ; but that its elements are arranged not 
 
Nature of Compound Radicals. 325 
 
 as NaO -j- S0 3 , but as Na -f- SO^ analogous to common salt, Na-fCl. 
 The sodium, Na, being present as an unoxidized metal in both, and the 
 SO 4 of the common salt being a hypothetic compound radical, acting 
 like chlorine. This view, however, will be discussed in detail when we 
 come to study the special history of the salts. 
 
 Tnis principle of compound radicals is so beautiful, and so easily 
 applied, that its use has been, as I conceive, somewhat too extensively 
 adopted ; and hence, wherever simplicity of expression was sought for, 
 or a difference of properties was to be explained, the formulae of organic 
 bodies were, perhaps, too hastily grouped, by the hypothetic assumption 
 of the existence of a radical, of which the different bodies of the series 
 were supposed to be combinations. It is certain that, in many cases, 
 tin's plan has been of great use to science, as in the benzyle theory of 
 Liebig, and in the ether and ammonia theories proposed by Berzelius 
 and myself ; but I consider the degree to which it has latterly been ex- 
 tended, by which the existence of a great variety of bodies has been 
 assumed, for which there is scarcely any reason, except some additional 
 simplicity of formulae which often served to conceal the truth, to have 
 been productive of much disadvantage to true science and a misdirection 
 of thought, which we should seek as much as possible to avoid. 
 
 In all that has been described of the arrangement of the elements 
 of compound bodies, their chemical union has been considered as 
 resulting from their antagonistic and mutually neutralizing properties, 
 and that the successive stages of composition were effected in binary 
 groups : thus, crystallized alum is a compound of water and dry alum ; 
 this last, a compound of sulphate of potash and sulphate of alumina ; 
 these respectively compounds of sulphuric acid and a base which con- 
 sists of oxygen united to a metal ; the sulphuric acid itself being formed 
 by the union of oxygen and sulphur. This view results necessarily 
 from what has been said of the nature of chemical affinity, and ex- 
 presses faithfully the principle upon which the electro-chemical theory 
 has been formed ; there is no doubt but that the constitution of inor- 
 ganic bodies is regulated in this way, but we meet with considerable 
 difficulty in applying its principles to organic chemistry. Thus, I myself 
 suggested a few years ago, that the formic and acetic acids should be 
 looked upon as oxides of compound radicals, formyle and acetyle, 
 C 2 HO 3 = FoO 3 and C 4 H 3 O 3 = AcO 3 by which means a variety of 
 substances of analogous constitution were simply connected toge- 
 ther, as the formyle or acetyle, which combine with oxygen to form 
 those vegetable acids, combine with iodine, chlorine, sulphur, and cya- 
 nogen, to form binary compounds, precisely as manganese (a simple 
 radical) combines with oxygen to form manganic acid, and with 
 
326 Theory of Organic Types. 
 
 chlorine, &c., to form an analogous series of bodies. I am far from 
 abandoning this view : the question of its full applicability will be dis- 
 cussed amongst the general laws of organic chemistry, but at present 
 we will attend only to one circumstance connected with it. Hydrated 
 acetic acid is formed from alcohol, by the latter losing two equivalents 
 of hydrogen, and gaining two of oxygen in their place, and in like 
 manner, hydrated formic acid is produced from pyroxylic spirit, by losing 
 H 2 and gaining 2 , thus : 
 
 Alcohol, . . C 4 H6O 2 Pyroxylic spirit, C 2 H 4 O 2 
 
 gives by, H 2 +O 2 gives by, H 2 +O 2 
 
 Hydrated acetic acid, C 4 H 4 O4. Hydrated formic acid, C 2 H 2 4 . 
 
 Now, if acetic acid contains acetyle, does it exist in alcohol ; or must 
 we consider, that by the gradual process of oxidation, the molecular 
 structure of the alcohol is totally broken up, and that the acetic acid 
 formed has no natural or necessary connexion with it. 
 
 We owe to Dumas the introduction of a principle into organic 
 chemistry, which applied to changes such as those described above, 
 promises to shed considerable light upon the reactions and constitution 
 of organic bodies ; but it yet involves conditions so opposed to our 
 present ideas of chemical affinity, that we can only look on it as a pro- 
 position which merits profound attention. He considers that the ele- 
 ments of organic bodies are not united by affinity arising from opposition 
 of properties, but that they represent a group of molecules connected 
 by a single force, precisely as the planetary masses are by gravitation, 
 and just as any of the planets might be replaced in the solar system by 
 a ball of matter of totally different chemical properties, provided 'its 
 gravitating mass remained the same, without disturbing in the least the 
 conditions of mechanical equilibrium; so, in an organic substance ele- 
 ments of the most diverse characters may be substituted for each other, 
 and yet the molecular group remain unaltered in structure and physical 
 constitution. Thus, the molecular group of alcohol (C 4 H 6 O 2 ) contains 
 twelve chemical atoms. When it is changed into acetic acid (C 4 H 4 4 ) 
 the number of chemical atoms is the same; the mechanical type of the 
 body is unaltered, although its chemical properties are completely 
 changed and a new substance formed. Bodies, therefore, are classified 
 by Dumas according to certain types or models. When the number of 
 molecules in the equivalents of the bodies remains the same whilst the 
 nature of the elements changes, the bodies have the same mechanical 
 type ; but if the substitution of elements is accompanied by a change 
 of properties, the chemical type of the original body is destroyed. 
 Thus, alcohol and acetic acid have not the same chemical type. 
 
Classification of Bodies. 327 
 
 When acetic acid is treated with chlorine, it loses three equivalents of 
 hydrogen and gains three of chlorine, (C 4 H 4 O 4 H 3 + C1 3 = C-iClaHO^) 
 forming chloro-acetic acid. The sum of the molecules is here twelve, 
 and this substance has the same mechanical type as alcohol and com- 
 mon acetic acid ; but in changing to this body, common acetic acid 
 scarcely changes its properties, and hence is said to retain its chemi- 
 cal type. When ether (C 4 H 5 O) is treated with chlorine, its hydrogen is 
 totally replaced by chlorine and the body C 4 C1 5 O, chlor-ether, is pro- 
 duced. The number of molecules being the same the mechanical type 
 is preserved, but more, the chlorine ether combines with acids forming 
 salts like those of common ether, which it resembles in all essential 
 chemical characters ; and hence in this case the chemical type also is 
 undisturbed, notwithstanding the total substitution of chlorine for hy- 
 drogen, a body differing from it so much in general characters in its 
 ordinary form. 
 
 The CRiestion how far this theory of types should be adopted, and how 
 far the law of substitution on which it rests is verified by experiment, 
 will be hereafter examined. The theory is here only noticed as involving 
 important relations between the mechanical structure and the chemical 
 constitution of organic bodies. 
 
 CHAPTER XI. 
 
 ON THE CLASSIFICATION OF THE ELEMENTAEY BODIES. 
 
 THE principal classifications of the simple bodies that have been proposed 
 are those of Berzelius, founded on their electro-chemical relations, and 
 of Thompson, who divided them into supporters and non-supporters of 
 combustion. It has, however, being fully shown, that, in combustion, 
 each body is mutually a supporter and a combustible : oxygen burns in 
 hydrogen or in the vapour of sulphur, just as much as hydrogen or sul- 
 phur burn in oxygen; Thompson's principle is, therefore, radically 
 defective ; and the electro-chemical theory, although far superior as a 
 principle, is liable to weighty objections of a somewhat similar kind. 
 These have been already, however, so far noticed, and the arrangement 
 
328 Classification of Bodies. 
 
 of the simple bodies in that series so fully given, p. 254, that it is unne- 
 cessary to recur further to the subject. 
 
 The kind of classification that is suited to the present wants of chem- 
 istry, must be founded upon the general analogy of properties, between 
 substances belonging to the same class, and on their isomorphous replace- 
 ment of one another. This last character is not absolute ; for, from the 
 dimorphism of many of the simple bodies, it is often difficult to assign 
 their true crystalline relations to each other, and in many cases we do 
 not possess any positive information of their forms. 
 
 Graham has recently proposed a classification which expresses, more 
 completely than any other, the natural relations of -the simple bodies. 
 The first class consists of oxygen, sulphur, selenium, and tellurium. 
 The parallelism in properties of the three last is complete, and their 
 compounds are strictly isomorphous ; their similarity to oxygen is not 
 so perfect, but they resemble it in their method of combination and in 
 the characters of the substances which they form in uniting with hydrogen 
 and the metals. 
 
 The second class comprises magnesium, calcium, manganese, iron, 
 cobalt, nickel, zinc, cadmium, copper, hydrogen, bismuth, chromium, 
 aluminum, glucinum, vanadium, zirconium, yttrium, thorium. The 
 similar salts of the protoxides of this class are isomorphous ; and, as has 
 been already shown under the head of Isomorphism, two equivalents of 
 a protoxide of this class replace one equivalent of an alcali. Chromium, 
 aluminum, glucinum, vanadium, and zirconium, do not form protoxides 
 but sesquioxides, the salts of which are isomorphous with those of the 
 sesquioxides of iron and manganese. A remarkable connexion is esta- 
 blished between this class and the preceding by the isomorphism of the 
 manganic acid (MnO 3 ), and the chromic acid (Cr0 3 ), with sulphuric 
 acid (S0 3 ), indicating that under certain circumstances these metals may 
 change from one natural family to another. 
 
 The third class contains barium, strontium, and lead. Their salts are 
 strictly isomorphous, and they are connected together by great similarity 
 of chemical properties. Thus, the sulphates of the metals of the second 
 class are all easily soluble in water, whilst the sulphates of this class are 
 almost insoluble. Calcium approximates to this condition by the sparing 
 solubility of sulphate of lime ; and the connexion between the two families 
 is still more fully shown by the dimorphism of carbonate of lime, it 
 having in one form the figure of the carbonates of magnesia and of iron, 
 and in the other that of the carbonates of barytes and of lead. 
 
 The fourth class consists of potassium, sodium, and silver. The 
 similarity of chemical properties of potassium and sodium is sufficiently 
 evident ; and although their compounds are not frequently isomorphous, 
 
Natural Groups of Elements. 329 
 
 yet there is good reason for attributing that to the dimorphism of each. 
 Silver differs remarkably in its chemical relations from potassium and 
 sodium,, and the only grounds for inserting it in this class is the isomor- 
 phism of sulphate of silver with anhydrous sulphate of soda. 
 
 The salts of potash are perfectly isomorphous with the salts of ammo- 
 nia which contain an atom of water ; and hence, if the base of the 
 ammoniacal salts (NH 3 -f-HO) be written NH 4 .O, it may be considered 
 as an oxide of a compound radical which is isomorphous with potassium, 
 and would rank, did we not know its composition, in the present group. 
 This view of the composition of the ammoniacal salts was suggested by 
 Berzelius, who gave to that compound radical the name ammonium ; 
 but I have since shown that the replacement is really by two equivalents 
 of a hydrogen compound, as already noticed in speaking of the second 
 class. 
 
 Fifth class, chlorine, iodine, bromine, and fluorine. This group is 
 best characterized by similarity of chemical properties ; and, so far as 
 observation extends, their isomorphism appears to be complete. It is 
 connected with the first and second classes by means of manganese, of 
 which two equivalents replace, in truly isomorphous componnds, one of 
 chlorine. 
 
 Sixth class, nitrogen, phosphorus, arsenic, and antimony. In their 
 chemical history these compounds exhibit considerable, though not com- 
 plete, similarity. The corresponding compounds of arsenic, antimony, 
 and phosphorus, are generally isomorphous, but in no case has isomor- 
 phism been observed between their compounds and those of nitrogen. 
 A certain analogy appears to exist between nitrogen and the substances 
 of the fifth class, as the nitric acid corresponds remarkably in properties 
 to the chloric and iodic acids, with which, however, it is not isomorphous. 
 Nitrogen appears also to replace oxygen in many cases in the proportion 
 of one-third of its equivalent weight. 
 
 Seventh class, tin and titanium, connected by the isomorphism of 
 titanic acid and peroxide of tin. 
 
 Eighth class, silver and gold, from their isomorphism in the metallic 
 state. 
 
 Ninth class, platinum, palladium, iridium, and osmium, from the 
 isomorphism of their double chlorides, by which also Graham considers 
 this class to be connected with the seventh. 
 
 Tenth class, tungsten and molybdenum ; the tungstates and molyb- 
 dates being isomorphous. These metals will probably be found to be of 
 the same family with chrome, as chromate of lead has been found crys- 
 tallized in the same form as the molybdate. 
 
 Eleventh class, carbon, boron, and silicon ; of these substances, no 
 
330 Classification of Elements. 
 
 -9 
 
 isomorphous relations are known ; they are brought together by a general, 
 though imperfect analogy of properties. 
 
 Graham, makes no attempt at classifying mercury, cerium, columbium, 
 lithium, rhodium, or uranium. 
 
 I agree completely with the general principles of this classification, 
 but, in a few cases, researches made since it was drawn up by Graham 
 render some alterations necessary ; thus the similarity of constitution 
 between the compounds of bismuth and copper, which had induced him 
 to insert bismuth in the second class, has no real existence, and I would 
 transfer it to the same class with antimony ; their sulphurets being 
 isomorphous, and their chemical properties being, generally speaking, 
 very similar. Indeed it is almost certain, that the oxide of bismuth is 
 not a protoxide, but a sesquioxide, and hence corresponds to the oxide 
 of antimony. 
 
 I do not consider the isomorphism of sulphate of soda, and sulphate 
 of silver, as being sufficient grounds for ranking the latter metal in the 
 fourth class. We have already seen numerous examples of isomorphism 
 amongst substances of totally different chemical constitution, and the 
 properties of the compounds of silver resemble so completely those of 
 lead, as to demonstrate positively, that it belongs to the same natural 
 group. When copper enters into combination with a double equivalent 
 Cu 2 , it becomes likewise a member of the lead and barytes group, as is 
 shewn by the sparing solubility of its sulphate and chloride, and being 
 isomorphous with silver, furnishes additional evidence of its true position. 
 
 Silver and gold being isomorphous only in the regular system, and 
 their compounds being totally dissimilar in constitution, I do not retain 
 the eighth class of Graham. 
 
 I have satisfied myself of the perfect analogy of palladium with cop- 
 per, it therefore must be separated from platinum and removed to the 
 second class. When mercury enters into combination with the equi- 
 valent, lOO'l (Hg,) it coincides in the nature of its compounds, with 
 palladium and copper, and attaches itself to the second class ; but when 
 its equivalent is 00'2 (Hg 2 ,) its compounds resembles those of lead 
 and silver, and like copper, it then becomes a member of the third class. 
 
 A classification such as this, although necessary for the philosophical 
 study of the relations of the simple bodies, could not, without consider- 
 able inconvenience, be strictly adhered to in an elementary work like 
 this ; I shall, therefore, having thus laid down those general principles, 
 place it for a time aside, and commence the study of the non-metallic 
 bodies, and their compounds with each other, without reference to any 
 arrangement, except that of treating first those subjects, which may be 
 useful towards understanding or illustrating those that follow. 
 
331 
 
 CHAPTER XII. 
 
 OF THE SIMPLE NON-METALLIC BODIES, AND THEIR COMPOUNDS WITH 
 
 EACH OTHER. 
 
 OF OXYGEN. 
 
 FROM the great quantity in which it exists in nature, the numerous pro- 
 cesses into which it enters as an agent, and the influence which its dis- 
 covery exercised upon the progress of chemical theory, oxygen may be 
 looked upon as the most important of the simple bodies. It constitutes 
 more than a fifth of the atmosphere by which our planet is invested, 
 eight-ninths of the whole quantity of water which exists upon its surface, 
 and besides being found in great quantity in most animal and vegetable 
 bodies, it forms, at least, a third of the total weight of the mineral 
 crust of the globe. On it the processes of combination and of respira- 
 tion are dependant, and the functions of organized existence, in both its 
 forms, are essentially connected and sustained through its agency. 
 
 Oxygen exists only under the form of gas ; it is colourless and trans- 
 parent; its specific gravity is 1105*6; 100 cubic inches of it weigh 
 34*2 grains ; its refractive index is 0*8616, that of air being 1*0000. 
 It is very sparingly dissolved by water, 100 cubic inches of water taking 
 up only between 3 and 4 of the gas. It is, consequently, in most 
 cases, collected over water, by forms of apparatus which shall be now 
 described. 
 
 For the collection and preservation of gases, such as oxygen, the in- 
 struments generally employed are the pneumatic trough and the gaso- 
 
332 Pneumatic Trough and Gasometers. 
 
 meter. The former is any vessel g containing water, for such gases as 
 are not absorbed by it, in which is inverted a glass vessel full of water, 
 which is sustained in it by the pressure of the external air, as is the 
 mercury in the tube of the barometer. The orifice of the tube c, from 
 which the gas issues, being brought under the edge of the jar, which is 
 generally supported upon a shelf, the water descends as the bubbles of 
 gas ascend, and when the water in the jar has been all replaced by the 
 gas, the jar may be removed on a tray, containing as much water as 
 serves to prevent all communication from the interior, with the external 
 air. 
 
 The gasometer, or gas-holder, consists of a 
 cylindrical copper vessel, on which another is 
 secured by five props of copper, of which two are 
 hollow tubes, in connexion with the cylinder be- 
 low. The tube m passes down nearly to the bot- 
 tom of the cylinder, but the other, n, only extends 
 to the upper surface : both are provided with stop- 
 cocks, so that the communication between the 
 cylinder and the upper vessel may be opened or 
 cut off at pleasure. At I there is also a small 
 tube, with a stop-cock, and below there is a large 
 orifice at i, which can be tightly closed, by means 
 of a screw-plug. 
 
 To fill the cylinder with water, the orifice i is to be closed, and all 
 the stop-cocks, m, n, I, left open. Water being then poured into the 
 upper vessel, it flows in through the tubes m and n } whilst the air 
 issues at I. When the water begins to flow out at I, that stop-cock is 
 to be closed, and the air, which still remains, escapes by the tube n, 
 bubbling through the water in the upper vessel. When this also 
 ceases, the stop-cocks m and n are to be closed, and the orifice i being 
 then opened, the cylinder remains full of water, by the external pressure. 
 The tube from which the gas issues is inserted at i, and a quantity of 
 water escapes by that aperture, equal in volume to the gas which 
 
 passes in. 
 
 A great variety of processes may be put in practice for the purpose 
 of obtaining oxygen gas ; one which is very simple in theory, and of 
 great interest in history, from being that by which the important 
 agencies of oxygen, in chemistry, were first recognised, although it is not 
 at present practically useful, is the following. 
 
 Some red oxide of mercury (HgO) is to be introduced into a retort a 
 of hard glass, to which is then attached a receiver 6, with a tube c, 
 passing to the pneumatic trough. On applying the heat of the argand 
 
Preparation of Oxygen. 33*3 
 
 spirit lamp to the oxide of mercury, it is decomposed : the oxygen is 
 given off in the state of gas, and may be collected in the bell glass e, 
 and the mercury distils over, and condensing in the neck of the retort, 
 
 collects in drops which flow into the receiver. The substance used is 
 thus resolved into mercury and oxygen ; from 108 grains, there would 
 have been obtained 100 grains of metallic mercury, and 8 grains of 
 oxygen gas, occupying at the standard temperature and pressure 23*4 
 cubic inches. It was by an experiment of this kind, that Layoisier 
 demonstrated the true constitution of the metallic oxides. 
 
 Although there are few metallic oxides, which, as that of mercury, 
 admit of being resolved by heat completely into free metal and oxygen, 
 yet, many, when heated, give off a portion of their oxygen, the metal 
 remaining in a lower degree of oxidation. Of this kind, are the perox- 
 ides of lead, and of manganese, and it is generally from the latter, that 
 oxygen is obtained for experimental purposes, when it is not required to 
 be absolutely pure. The peroxide of manganese, (Mn02.) abandons, 
 when at a red heat, one-third of its oxygen, and a complex oxide, 
 Mn 3 O 4 remains, analogous to the black magnetic oxide of iron, and 
 formed by the union of equivalents of protoxide and of sesquioxide 
 (MnO -}- Mn 2 3 ). For this purpose the manganese is introduced into 
 
 an iron bottle #, to the neck of which is attached a piece of gun barrel, 
 b, and this connected by a cork c, with a smaller tube d. For sake of 
 freedom of motion, the tube^ which passes to the pneumatic trough or 
 the gasometer, is attached to d by a caoutchouc connector e. The 
 bottle having been filled about two-thirds with oxide of manganese, may 
 be placed either in a common fire, or in a furnace, its parts being all 
 arranged as in the figure. When first heated, some water passes off, 
 
334 
 
 Oxygen Gas from Oxide of Manganese. 
 
 and frequently, from the occurrence of carbonate of lime and of ammo- 
 nia in the substance, the first portions of gas are mixed with carbonic 
 
 R.JCNC3SC 
 
 acid or with nitrogen ; these should be allowed to pass away, and the 
 oxygen collected only when a small tube full of it is capable of relight- 
 ing a taper four or five times. The pure dry oxide of manganese con- 
 sists of 27*7 of manganese, united to sixteen of oxygen, of which 5*3 
 are given off, and hence lib. Troy of it is capable of furnishing about 
 700 grains, or nearly 2000 cubic inches, equal to seven imperial gallons 
 of gas. The oxide of manganese found in commerce is, however, not 
 pure ; in general it does not contain more than 65 per cent, of pure 
 oxide, and hence the quantity of oxygen furnished by a pound of it is 
 about two-thirds only of that just stated. 
 
 Peroxide of manganese yields more of its oxygen when treated with 
 oil of vitriol, than when simply ignited ; one-half becoming free, whilst 
 the manganese, with the remainder, forms protoxide, which combines 
 with the sulphuric acid thus: HO.SO 3 . + MnO 2 . = HO . SO 3 . 
 MnO + O. 
 
 This operation is conducted by placing the manganese in a flask, a, 
 
Oxygen Gas from Chlorate of Potash. 335 
 
 supported in a little cup of sand, b, over a lamp, and mixing it with 
 twice its weight of oil of vitriol ; a tube <?, bent, as in the figure, passes 
 to the pneumatic trough, and dips under the edge of the jar in which 
 the gas is to be collected. AVhen the flask is heated, oxygen gas is ra- 
 pidly disengaged, but care must ' be taken, that towards the close, the 
 water of the trough may not pass back into the flask, where mixing 
 with the hot oil of vitriol, it might produce an unpleasant explosion. 
 
 The decomposition which here occurs has been supposed to consist 
 simply in the expulsion of the second atom of oxygen by the sulphuric 
 acid, which takes its place. This, however, is not the case. By a very 
 gentle heat the sulphuric acid decomposes the peroxide, MnO 2 , into 
 protoxide, MnO, and permanganic acid, Mu 2 O 7 . (5MnO 2 = 3MnO -f 
 Mn 2 O 7 ). This last is decomposed, when the temperature rises, into 2 
 (MnO 3 ) manganic acid, giving out one equivalent of oxygen ; but the 
 temperature must be raised very much to complete the separation of the 
 MnO 3 into O 2 and MnO. Hence, in this process, as ordinarily con- 
 ducted, the residue in the flask is found to be green, from manganic 
 acid ; and, although in theory a more abundant source of oxygen than 
 that by simple ignition, in the proportion of 3 to 2, it is not so useful 
 in practice. 
 
 When oxygen is required completely pure, it is generally prepared 
 by heating in a glass tube, or flask, to which a bent tube is attached, as in 
 the figure, a small quantity of chlorate of potash. 
 This salt consists of chloric acid united to pot- 
 ash C1O 5 -f- KO, and when heated somewhat 
 above its melting point, it is decomposed, all 
 the oxygen it contains being evolved in the state 
 of gas, and the other elements remaining com- 
 bined as chloride of potassium. The constitu- 
 ents of this salt are by weight 3 5 '4 chlorine, 
 39-7 potassium, and 48 of oxygen. Hence, 
 100 parts of it gives 39 of oxygen by weight, or 
 an ounce troy, 187 grains, or 543 cubic inches. 
 An ounce of it is, therefore equivalent in effect to six ounces of ordinary 
 peroxide of manganese. 
 
 It is not easy to complete the decomposition of the chlorate of potash 
 in a glass vessel without finally applying a heat so high as to soften the 
 glass, for the reaction is not simply the resolution of KO. C1O 5 into 
 KC1 and 60., but there are produced in the first instance from two 
 equivalents of chlorate of potash, one of chloride of potassium, four of 
 oxygen gas, and one of a new salt, perchlorate of potash. Thus 2. KO. 
 C10 5 giving 40 and K. Cl and KO. Cl. 7 . The perchlorate is itself de- 
 
336 Oxygen Gas from Chr ornate of Potash. 
 
 composed by a higher temperature, until finally all oxygen is given out 
 as gas, and only chloride of potassium now remains. The decom- 
 position may be, however, much facilitated by mixing the chlorate of 
 potash with any inorganic powders, such as peroxide of manganese or 
 black oxide of copper, or even spongy platinum, on which it does not 
 act, but which appears to favour the formation of gas bubbles in the 
 melted mass, as they would favour the formation of steam bubbles in 
 boiling water. By using a mixture of two parts chlorate of potash, and 
 one of black oxide of manganese, the decomposition can be completed 
 with great facility in a Florence flask. 
 
 Another mode of preparing oxygen, which is very convenient in prac- 
 tice, is by the action of oil of vitriol on the bichromate of potash. When 
 this salt, which consists of two atoms of chromic acid and one of potash, 
 KO-f-2 CrO 3 , is put in contact with strong sulphuric acid, it is decom- 
 posed and the chromic acid separates, and may be obtained crystallized 
 in brilliant crimson needles. If, however, the mixture be heated the 
 chromic acid is decomposed ; giving out one-half of its oxygen as gas, 
 it is converted into chromic oxide, which combines with sulphuric acid 
 and the sulphate of potash to form chrome-alum. The reactions are 
 therefore : from 
 
 4. HO. SOs or 196 parts of Oil of Vitriol. 
 
 and KO-f2 Cr.Oa or 151 " Bichromate of Potash 
 
 347 
 
 There are produced 
 
 3 O. or 24 parts of Oxygen Gas. 
 KO.SO 3 -fCr2O3.3SO 3 or 187 " Chrome Alum. 
 
 4 HO or 36 Water. 
 
 347 
 
 The decomposition is effected in a Florence flask and bent glass tube, or 
 in a retort, as with black oxide of manganese, but is much more manage- 
 able and more productive. 
 
 The most remarkable property of oxygen is the energy with which 
 it supports combustion. If a lighted taper be blown out, so that a 
 point of the wick shall continue red, it will be brilliantly relighted on 
 being plunged into a vessel of oxygen gas, and this may be repeated 
 several times in succession. A bit of charcoal, heated to redness at a 
 single point, burns, when immersed in oxygen with rapid scintilla- 
 tions of exceeding brilliancy, and when phosphorus is inflamed in oxy- 
 gen gas the splendour of the combustion is insupportable to the eye. 
 
Oxygen necessary to Combustion and Respiration. 337 
 
 Even bodies which are not combustible under ordinary circumstances, 
 may be made to burn in oxygen. Thus, if an iron wire be tipped 
 at its extremity with sulphur, or have attached to it a small bit of 
 waxed cotton wick, on lighting this, and plunging the whole into the 
 gas, the combustion extends from the sulphur or wick to the iron, 
 which is converted into oxide, with the disengagement of most brilliant 
 light. The heat evolved by the combination of the oxygen and iron 
 is so great, that the oxide formed is melted, and flows down from 
 the extremity of the burning wire, in drops which, even after having 
 passed through a layer of water, fuse themselves into the substance 
 of the earthenware plate, upon which the gas jar generally stands. If, 
 at the moment when a drop of oxide is about to fall, it be projected 
 by a little jerk against the side of the glass, it will melt its way into its 
 substance, or even, if it be not thick, pass completely through. 
 
 The heat evolved when the body burns in pure oxygen, may be readily 
 shown by simple methods. If a jet u, be 
 attached to the lateral stopcock I, of the 
 gasometer, and the flame of a spirit lamp h 
 be urged by the issuing stream of gas, as 
 by a blow-pipe, the most refractory sub- 
 stances may be fused by it. If the tube be 
 curved downwards, the jet may be brought 
 to bear on a little cup of red hot charcoal, 
 in which the body to be fused may be laid, 
 and thus, upon a small scale, the construc- 
 tion and effect of the most powerful wind 
 furnaces may be imitated. 
 
 Oxygen gas is necessary to the support of animal life. It is the 
 oxygen which exists in the atmospheric air, that fits it for its uses in the 
 economy of nature. The blood which returns dark and venous into 
 the lungs, is there changed into the bright arterial state, by absorbing 
 oxygen, and evolving carbonic acid, in a manner of which the exact 
 details shall be hereafter studied. This change occurs even with blood 
 which has been removed from the body. If a quantity of dark blood, 
 drawn from a vein, be agitated in a vessel of oxygen gas, it is imme- 
 diately changed into the vermilion-coloured arterial blood. An animal 
 can live longer in a vessel of pure oxygen than in the same volume of 
 atmospheric air ; but still, pure oxygen is not fitted for the support of 
 life. It is too stimulating ; the animal lives too fast, and ultimately 
 dies with symptoms of general inflammatory fever, even though there 
 may remain still a quantity of oxygen gas, capable of supporting the life 
 of another animal for a considerable time. 
 22 
 
338 Nature and Properties of Ozone. 
 
 The equivalent number of oxygen is 100 or 8, according as itself or 
 hydrogen is taken as the standard of the scale. 
 
 The name of oxygen was given to this body from the idea of its 
 peculiar power of conferring acid properties on its compounds ; and, in 
 reality, most of the bodies recognized by chemists amongst the class of 
 acids contain oxygen. But this is not invariable ; other simple bodies 
 possess the same power, as has been already noticed on more than one 
 occasion, and I shall have opportunities of recurring to it when describing 
 the properties of those bodies. 
 
 Ozone. It has been mentioned in page 139, that the passage of the 
 electric spark through air, or even the excitation of less intense elec- 
 tricity, was accompanied with a peculiar odour like that of phosphorus. 
 This effect is found to depend upon a change which takes place in the 
 air itself, under a variety of circumstances, and Professor Schrenbein 
 attributes it to the production of a peculiar substance, which he terms 
 ozone. The precise nature of this ozone is still uncertain ; but the 
 properties which the air or oxygen assumes are very remarkable. The 
 oxygen evolved by the decomposition of water by the voltaic current 
 possesses the odour in a very high degreee. If phosphorus be allowed 
 to burn slowly in air at ordinary temperatures, the air becomes very 
 strongly impregnated with ozone ; and this is the most convenient mode 
 of obtaining the substance for experimental purposes. 
 
 Air containing ozone acts in many ways as if a very small quantity of 
 chlorine was diffused through it. It liberates iodine from iodide of 
 potassium ; it separates peroxide of manganese from salts of the protox- 
 ide ; it converts yellow prussiate of potash into red prussiate ; it is re- 
 moved or decomposed by contact with most organic matters. All these 
 characters indicate either the presence of oxygen in a more active form 
 than that in which it exists in ordinary air, or the existence of some 
 powerfully oxidizing body. The opinions put forward by chemists are 
 different. Eerzelius supposes that traces of oxygen are put into an allo- 
 tropic or isoineric condition, in which its electro-negative character is 
 heightened. Schoenbein considers the ozone to be a volatile binoxide 
 of hydrogen. Other still less probable suppositions have been made, 
 but the substance never having been isolated, our knowledge of its 
 properties is exceedingly imperfect, and no positive opinion can be 
 at present substantiated. 
 
 OF HYDROGEN. H. 
 Eq. = L or 12-5. 
 
 Hydrogen exists abundantly in nature, as a constituent of animal 
 and vegetable substances, and is particularly of importance by being a 
 
Preparation of Hydrogen Gas. 339 
 
 constituent of water. From this fact it derives its name, vb 
 
 (I form water,) and it is by the decomposition of water that hydrogen 
 
 is almost always obtained for experimental purposes. 
 
 If a small quantity of the metal potassium be placed in contact with 
 water, it immediately abstracts the oxygen, forming potash, which is an 
 oxide of potassium. The hydrogen is set free, and appears as a gas. 
 If the experiment be performed under a bell glass, inverted in a basin 
 of mercury or water, the gas may be collected ; but if the decomposition 
 takes place in contact with the atmospheric air, so much heat is evolved 
 by the rapidity and intensity of the action, that the hydrogen takes 
 fire, and burns according as it is produced. This is the simplest form 
 under which the decomposition of water can be exhibited, the reaction 
 being K + H'O = KO + H. 
 
 If the circuit of the electrical current from a voltaic battery be com- 
 pleted through water, which has been rendered a good conductor by 
 the addition of sulphuric acid or common or Glauber's salt, the two con- 
 stituents of the water are evolved at the opposite electrodes, or ter- 
 minating surfaces of the liquid, and the two gases may be collected 
 either separately or mixed together, and will be then found to have 
 been evolved in such proportions that the hydrogen will be double the 
 volume of the oxygen. The theory of this mode of obtaining hydrogen 
 has been described, so far as we are competent to explain it, in a former 
 chapter. 
 
 These methods, although the simplest, are yet not applicable to or- 
 dinary purposes, from their expense ; those usually employed are the 
 following. There are many metals which, although having a powerful 
 affinity for oxygen, are yet not able to abstract it from hydrogen, and 
 so to decompose water at ordinary temperatures ; but at a red heat, the 
 decomposition rapidly takes place. For this purpose, iron is generally 
 employed. A gun barrel, or an iron tube, cc, is taken, and the 
 interior having been loosely filled by iron turnings or coils of iron wire, 
 it is placed horizontally in a furnace, by means of which it can be 
 brought to a full red heat. To one extremity of the tube is connected 
 a small glass retort, a, containing water ; to the other, a flexible metal 
 tube^ which passes under the shelf of the pneumatic trough. The 
 iron tube being made red hot, the water in the retort is made to boil ; the 
 vapour passes into the tube, and comes into contact with the red hot 
 iron ; decomposition immediately occurs, and the iron is oxidized, 
 whilst the hydrogen gas is disengaged in large quantity. The state of 
 combination into which the iron is found to have passed, is that of 
 the black oxide, such as the scales that are formed at the smith's forge, 
 by the action of the atmospheric air on iron, and which is also formed 
 
340 Preparation of Hydrogen Gas ly 
 
 when iron is burned in oxygen gas. The action may, however, be 
 simply represented as follows : 
 
 Fe .f. H.O = H -|_ Fe . O Protoxide of iron. 
 2Fe -f. 3H.O =3H -j_ Fe 2 O 3 Peroxide of iron. 
 
 3Fe _}- 4H.O = 4H J. Fe 3 O 4 Black oxide of iron. 
 
 The action of the iron in thus decomposing water, might appear 
 paradoxical, as it will be seen hereafter that by means of a current of 
 hydrogen gas, acting at a red heat, oxide of iron may be decomposed, 
 the iron separating in the metallic state, and water being produced ; and 
 thus, at the same temperature, two decompositions, precisely the reverse of 
 each other, may go on. It would appear that this is one of those cases 
 in which affinities, nearly equal otherwise, are directed to one or the 
 other object according as one or the other substance is in excess. When 
 the iron is kept in a stream of watery vapour, this latter is decomposed, 
 and the hydrogen being carried away, according as it is formed, by the 
 current, it cannot interfere by its presence in any opposing manner. 
 On the other hand, when oxide of iron is heated in a stream of hydro- 
 gen gas, it is decomposed, and the water being removed as rapidly as 
 it is produced, the tendency to reaction is prevented. 
 
 By the agency of a dilute acid we may also increase the tendency of 
 a metal to combine with water, so that the decomposition of water can 
 be effected rapidly even at common temperatures. If a few slips of 
 zinc or iron be placed in a flask to which a bent tube, f 9 is adapted, as 
 in the apparatus represented in the figure, and then oil of vitriol diluted 
 with eight times its weight of water be poured upon it, through the 
 funnel, an abundant effervescence occurs, arising from the escape of 
 
the Decomposition of Water. 341 
 
 hydrogen gas, and the zinc or iron rapidly dissolves. The action con- 
 tinues until the acid has been all neutralized by the zinc, or the zinc 
 all dissolved by the acid ; or finally, until so much of the compound 
 formed during the reaction has been produced, that the water present 
 
 cannot dissolve any more. This compound consists of oxide of zinc 
 or of iron united to the sulphuric acid, the oxygen of the decomposed 
 water uniting with the metal whilst the hydrogen is set free. The pro- 
 cess may be thus represented, zinc being used, Zn -f- SO 3 + HO = H 
 + (SO 3 + ZnO.) 
 
 To account for the circumstances of this reaction, a peculiar power 
 was at one time supposed to exist, termed disposing affinity ; and it was 
 said that the presence of the sulphuric acid disposed the zinc to decom- 
 pose the water, because the oxide of zinc, when formed by the decom- 
 position, might unite with the acid. This theory is quite futile. There 
 can be no oxide of zinc to influence the acid, until the water has been 
 decomposed, and the effect, the source of which was to be sought for, 
 had consequently been produced. It appears to me that the explanation 
 is of much simpler form. Zinc and iron decompose water at ordinary 
 temperatures, even without the presence of any acid, but with excessive 
 slowness, so that the effect is almost imperceptible. In fact, the first 
 minute trace of oxide which is formed, being insoluble in water, coats 
 over the metallic surface with a varnish impermeable to the fluid, and 
 thus prevents its further action. This coating of metallic oxide is 
 soluble in acids ; and thus, by the presence of an acid, a fresh surface 
 of bright metal is kept constantly exposed, and the decomposing action 
 is allowed to proceed without hindrance. It is possible, however, that 
 this simple view may require some alteration, and that this mode of ob- 
 taining hydrogen gas may be found to involve voltaic conditions which 
 at present are not well understood. Pure zinc is but very feebly acted 
 on even by a diluted acid ; and the rapid action which occurs with com- 
 mercial zinc or iron, may be referred to decomposition by the electric 
 currents which circulate from one portion of the impure metal to the 
 other, through the liquid. See page 176. 
 
342 Properties of Hydrogen Gas. 
 
 Hydrogen gas, when it has been prepared by any of these processes, 
 is seldom pure. The iron and zinc of commerce contain generally 
 traces of carbon, of sulphur, and sometimes of arsenic, which com- 
 bining with some hydrogen, form gaseous or volatile products, which 
 give to the hydrogen a peculiar disagreeable odour, and colour its flame. 
 Occasionally, also, traces of potassium and zinc in very minute division, 
 are carried up with the hydrogen by the mechanical force of the effer- 
 vescence, but by repose these latter impurities are found completely to 
 separate. To get rid of the former class of impurities, the gas may be 
 made to bubble very slowly through solutions of potash and corrosive 
 sublimate, by which the arsenic and sulphur would be absorbed, and 
 through alcohol, which would for the most part dissolve the carburetted 
 hydrogen. It is, however, better, when pure hydrogen is required, to 
 prepare it by acting upon water with metallic sodium mixed with quick- 
 silver, so as to moderate the rapidity of the decomposition. Zinc, which 
 has been refined by distillation, gives also, with sulphuric acid and water, 
 a gas almost completely pure. 
 
 When free from foreign matters, hydrogen gas burns with a very pale 
 white flame, almost invisible in bright day. In burning, it combines 
 with the oxygen of the air and forms water. If a jar of hydrogen gas 
 be suddenly turned with the orifice upwards, and inflamed, the whole 
 mass of gas rushes out, and gives a sheet of pale white, or yellowish 
 flame. If it be mixed with air previous to being set on fire, the com- 
 bustion of the mixture is instantaneous, and accompanied with an ex- 
 plosive report. The proper proportions are two volumes of hydrogen 
 gas, to five of air. If a lighted taper be plunged into a jar of hydrogen, 
 it is immediately extinguished, the gas not being able to support com- 
 bustion. 
 
 Hydrogen gas is colourless and transparent, it is absorbed by water 
 in very small quantity, and hence, for ordinary purposes, is always col- 
 lected over that liquid. It refracts light strongly, its refractive index 
 being 6*61, air being 1*00. In its capacity for heat, it exceeds all other 
 gases, being 21'9 by Apjohn's experiments, air being I'OO, for equal 
 weights, or 1*46 for equal volumes. It is the lightest substance known, 
 being only one-fifteenth of the specific gravity of air; or more accu- 
 rately, its specific gravity is 69*3 : that of air being 1000' 0. It is hence 
 used for filling balloons ; as the balloon full of hydrogen weighs less 
 than the same volume of air, it ascends with a force equal to the difference 
 of weight. For the purpose of illustrating this property of hydrogen, 
 a small balloon made of gold-beater's skin, or of the serous membrane 
 of the turkey's craw, may be made use of. On this minute scale, 
 however, the gas should be used dry, as when prepared and collected 
 
Composition of Water. 343 
 
 over water, its specific gravity may be so much increased by the watery 
 vapour it may contain, that although good enough for a large balloon, 
 yet it could not carry up a small one, the small balloon being really 
 much heavier in proportion to the quantity of gas it can contain ; con- 
 sequently the hydrogen should be dried, which may be effected by caus- 
 ing it to stream from the gasometer through a tube filled with fragments 
 of fused chloride of calcium, which absorbs water with great avidity ; 
 and from thence to enter the balloon. At present, hydrogen gas is but 
 seldom employed, it being found cheaper to make the balloon very large, 
 and to use coal gas, which, although much heavier than hydrogen, is 
 still considerably lighter than atmospheric air, under the same volume. 
 
 By one kind of experiment, the three most remarkable properties of 
 hydrogen may be exhibited in an interesting form. If a jar of hydro- 
 gen be held vertically, with the orifice downwards and open, it will 
 remain filled by the hydrogen for a certain time, as the air, being so 
 much heavier, mixes itself but very slowly with the lighter gas. If a 
 lighted taper be now applied, the gas will inflame at the surface where 
 it is in contact with the atmosphere, but on plunging the taper upwards 
 into the pure gas, it will be extinguished ; being then lowered, it can be 
 relighted at the sheet of flame which marks the surface of contact of 
 the gas and the atmosphere, and when again raised into the pure gas, it 
 will again be extinguished ; this can be repeated very often : the hori- 
 zontal sheet of flame having been gradually rising into the jar according 
 as the hydrogen consumed, if then the jar be suddenly turned with the 
 orifice directed upwards, the residual gas will at once rush out, and 
 mixing with the air, will bum explosively with a single flash. 
 
 The same experiments on the combustion of hydrogen, may be made 
 with pure oxygen gas in place of atmospheric air, and then the results 
 are at least five times more brilliant. The proportions for burning 
 hydrogen with oxygen gas, are two volumes of hydrogen, and one of 
 oxygen j then if the gases were pure, nothing but pure water should 
 remain. 
 
 If a bladder be filled with the two gases mixed in these proportions, 
 and being punctured, the flame of a taper be applied to the orifice, the 
 whole explodes with a flash of brilliant light and a deafening explosion ; 
 the strongest bladder being torn to shreds by the expansive force of the 
 ignited gases. In this experiment, the bladder must, of course, be 
 secured, which is easily done by tying the stopcock by which the gas 
 has been passed into the bladder, between two nails, with some stout 
 cord or copper wire. 
 
 A mixture of hydrogen and oxygen may also be exploded by means 
 of the electric spark ; for this purpose, a strong tube closed at the top, 
 
344 Spongy Platinum Eudiometer. 
 
 and graduated into parts of a cubic inch, is taken, and two brass or 
 platina wires are inserted through the opposite sides near the top, their 
 extremities being kept about one-eighth of an inch asunder. This tube 
 
 is termed an eudiometer, as it is frequently 
 usec * to measure the quantity of oxygen in 
 tne atmosphere, and generally for the ana- 
 lysis of gaseous mixtures. The oxygen and 
 hydrogen gases being confined in this tube 
 over water or mercury, an electric spark is 
 passed through the mixture by means of the 
 wires ; the gases explode, and if the propor- 
 tions had been accurately observed, no resi- 
 due is found. If one of the gases had been 
 in excess,, the excess remains behind; one- 
 third of the volume which disappears being 
 oxygen, and the other two-thirds being hy- 
 drogen. In order to explode a bladder full 
 of the mixed gases by means of electricity, 
 
 a very simple plan is, to fasten the bladder upon a large cork having 
 in the centre an opening, into which a stopcock is screwed for the 
 passage of the gas, and, through which, near the edges, pass two 
 stout brass wires, terminating inside the bladder in small knobs ; these 
 ends being brought near each other, and the external ends being con- 
 nected by long wires with the coatings of a charged Leyden jar, the 
 spark passes between the terminal knobs in the bladder, and the explo- 
 sion immediately occurs. 
 
 Hydrogen and oxygen are capable of entering into combination, and 
 forming water without any explosion or visible combustion. If the 
 mixed gases be transmitted through a tube heated to scarcely visible 
 redness, they quietly combine, and this effect occurs at a still lower 
 temperature, if the tube contains coarsely powdered glass or sand. 
 Slips of gold and silver are still more favourable, but the most rapid 
 union is effected, even at ordinary temperatures, by platinum. This 
 effect appears to be due to the metallic surface retaining a thin layer of 
 gas by so strong a force as by condensation to bring the molecules within 
 the sphere of their mutual chemical attraction : they, combining, form 
 water, and a new quantity of the gaseous mixture comes in contact with 
 the platinum and follows the same course. If the platinum be in the 
 form of sponge, in which the acting surfaces are very great, the union 
 takes place so rapidly, that the heat evolved raises the temperature of 
 the platinum ball to bright redness, and then the remaining gas explodes. 
 Platinum in form of sponge, always contains a quantity of air, in this 
 
Use of the Ox-yliydrogen Blowpipe. 345 
 
 condensed condition, and hence, when a jet of hydrogen gas is let to 
 play upon a morsel of spongy platina, it is absorbed, and water being 
 formed, the ball of platinum becomes red hot and inflames the jet of 
 gas. This constitutes a sort of lamp for instantaneous light, equally 
 pretty and ingenious ; the jet of hydrogen in its turn being contrived to 
 fall upon, and light a little lamp ; see pp. 238 and 229. 
 
 Spongy platinum introduced into a mixture of oxygen and hydrogen, 
 explodes them instantly, but it can be usefully diluted, as it were, by 
 being made into balls, with a little pipe -clay, and then it can only pro- 
 duce their union in the slow and silent way. This mode is accordingly 
 often used in the analysis of mixtures of gases, and the energy of the 
 platinum balls can be graduated by the proportions of metal and of pipe- 
 clay which are employed. Hydrogen and oxygen, however, are not the 
 only gases which can be made to unite by the agency of platinum sur- 
 faces, as will be elsewhere shown. 
 
 The heat produced by the combustion of oxygen and hydrogen gases, 
 is the most intense that can be obtained by any artificial means. It is 
 hence, at present, much used in an instrument termed the hydro-oxygen 
 blowpipe. The apparatus employed must be of such a nature, as to 
 prevent any risk of injury from explosion, which, with any large quantity 
 of the gases might produce serious accidents. The safest form for 
 experiment on a large scale, consists in having the gases separate in two 
 gasometers connected by tubes, and of such a size and pressure, as that 
 in the same time there shall be delivered two volumes of hydrogen to one 
 of oxygen gas ; the hydrogen gas tube terminates in a hollow cylindrical 
 jet, inside of which passes the jet of oxygen gas. The flame thus pro- 
 duced, resembled that of a candle, into the interior of which is injected 
 a stream of air, by the blowpipe in common use. Another form con- 
 sists of a metallic box, made so exceedingly strong, that even were the 
 gases to explode within it, there could be no danger of its being burst. 
 The gases, previously mixed in a bladder, are forced by means of a con- 
 densing syringe into the box, and a sufficient quantity having been 
 introduced, the condensing syringe is removed, and a stopcock connected 
 with a jet opened. The pressure of the condensed gas inside forces out 
 a stream, which is ignited, and if the flame be not allowed to burn too 
 long, the rapidity of the current is sufficient to prevent the passage back- 
 wards of the flame. This form is now, however, almost totally super- 
 seded by the very ingenious safety cylinder and jet of Mr. Hemming. 
 It consists of a brass cylinder of about five or six inches long, by three- 
 fourths of an inch in diameter, which is filled as closely as possible by a 
 bundle of fine brass wires, into the centre of which, a wedge-shaped 
 brass rod is introduced and driven very hard, so as to pack the wires 
 
346 Hydroxygen Blowpipe. 
 
 closely. The interstices between the wires form thus a collection of 
 exceedingly minute tubes, through which the gas must pass. To one 
 end of this cylinder, is connected a bladder containing the mixed gases, 
 the other end terminates in a jet from which the gas issues ; the flame, 
 in passing backwards from the jet, must, in its way to the bladder, stream 
 through the metallic cylinder, and then comes into contact with so great 
 a surface, and so large a mass of material which conducts heat rapidly, 
 that the gases are cooled far below the temperature at which their union 
 can occur, and their further combustion is, of course, prevented. 
 
 For experiments upon a small scale, this little apparatus combines 
 the highest qualifications of convenience, security, and simplicity. 
 
 In the flame of the hydroxygen blowpipe, the most infusible substances 
 are melted ; flint, pipeclay, the most refractory metals, as platinum, not 
 merely fuse, but even appear to evaporate : a rod of iron takes fire, and 
 burns with a brilliancy surpassing that of its combustion in oxygen gas. 
 Some of the earths alone, are capable of resisting its highest power. 
 These, as lime and magnesia, particularly the former, become in the 
 flame of the mixed gases, so brightly luminous, as to rival in intensity 
 the noonday sun, and hence furnish one of the most important uses of 
 the blowpipe, by serving for optical purposes, as a substitute for the 
 solar ray, which, in our climate, is so uncertain in its supply. The solar 
 microscope fitted up with a ball of lime, ignited by a jet of the mixed 
 gases in place of the solar rays, constitutes the hydro-oxygen microscope, 
 now a common exhibition in our large towns, and the same light has 
 been proposed for use in light-houses, and has been actually employed 
 for signals in connecting the trigonometrical surveys of the British 
 islands. In one case the light emitted by the ball of lime was distinctly 
 visible at a distance of seventy miles. 
 
 A singular phenomenon, which is best produced by the flame of hy- 
 drogen, although not peculiar to it, is the production of musical sounds, 
 if an open tube be held over the flame. The flame, in fact, although 
 uniform to the eye, consists of a succession of little explosions of mixed 
 air and gas, which recur too rapidly to be individually distinguishable. 
 If the tube be now held over the flame, it will be seen to flicker, and 
 after a few irregular, interrupted, explosive sounds, a distinct musical 
 note is heard. The explosions set the air in the tube to vibrate, at first 
 irregularly, but at last with such a velocity of vibration, as corresponds 
 to the length of the tube, and to the rapidity with which the explosive 
 mixtures of air and gas can be formed ; and thus, by any of the known 
 methods of determining the number of vibrations corresponding to a 
 given note, the frequency of the little explosions may be found. Occa- 
 sionally, also, a distinct beat, or alternations of sound and silence, may 
 
Hydrogen Harmonicon. 347 
 
 be heard, as in two organ pipes,which being nearly but not completely in 
 unison, sound together ; this arises from a current of hot air ascending 
 in the centre of the tube, whilst a current of cold air is formed next the 
 side. These, do not, for a time, vibrate completely as one mass ; and 
 hence, at certain periods, alternately redouble and destroy the sounds 
 which they produce. 
 
 In its relation to other bodies, hydrogen plays a very remarkable and 
 peculiar part. It was at one time supposed that it shared with oxygen 
 the power of generating acids, and as sulphur, chlorine, cyanogen, 
 iodine, &c., form one class of acids, by combining with oxygen, so they 
 formed a second class, called hydracids, by entering into union with 
 hydrogen, and hydrogen was believed to be related to hydrochloric acid, 
 as oxygen was to the sulphuric or the phosphoric acids. I have, how- 
 ever, long since proved this view to be totally incorrect, and that all the 
 properties of the compounds of hydrogen combined to show, that it 
 was eminently an electro-positive body ; that it took a place along with 
 iron, manganese, and zinc, and that the compounds of hydrogen with 
 chlorine, oxygen, iodine, and sulphur, were almost universally electro- 
 positive in combination, and possessed basic characters derived from the 
 pre-eminent positive energies of the hydrogen itself. These views have, 
 since that period, been still further corroborated by the researches of 
 Graham, and by additional investigations of my own ; and although the 
 old and familiar nomenclature will still retain its place to a great extent, 
 yet there rests now no doubt upon the minds of philosophical chemists, 
 that hydrogen is most closely allied to the metals, particularly to zinc 
 and copper; that the chlorides, iodides, and fluorides of hydrogen, 
 although they simulate some of the characters which we assign to acids, 
 resemble, in all important points, the chlorides, iodides, &c. of the 
 metals above mentioned ; that, in fact, hydrogen is a metal, enormously 
 volatile, standing probably in the same relation to mercury that mercury 
 does to platinum in that respect, but still possessed of all truly chemical 
 peculiarities of the metallic state, and no more deprived of the common- 
 place qualities of lustre, hardness, or brilliancy, than is the mercurial at- 
 mosphere which fills the apparently empty top of the tube of a baro- 
 meter, or the salivating atmosphere of a quicksilver mine, or of a gilder's 
 workshop. 
 
 Of Water Oxide of Hydrogen. H.O. 
 Eq. = 9 or 112'5. 
 
 It has been already shown that water consists of hydrogen and oxygen 
 combined, in the proportions of two volumes of the former gas to one 
 
348 Analysis and Synthesis of Water. 
 
 volume of the latter, and by weight of one part of hydrogen united to 
 eight of oxygen, or of 11 ! hydrogen and 88*9 of oxygen, in 100 parts. 
 The exact determination of the composition of water is one of the 
 most important investigations in the domain of chemistry, as from the 
 great range of affinities which oxygen and hydrogen exercise, and the 
 variety of compounds into which they respectively enter, the numbers 
 adopted for the combining proportions of almost all other bodies hinge 
 upon those which are employed for the constituents of water. It has, 
 consequently, attracted the attention of many distinguished chemists. 
 But although the determination of the respective volumes in which the 
 oxygen and hydrogen unite, as determined by Gay-Lussac, gave a very 
 accurate result, yet the most positive determination was obtained by 
 Berzelius, with the method now to be described, and with the apparatus 
 of which the general arrangement is illustrated by the figure. 
 
 A known weight of black oxide of copper is introduced into a glass 
 tube, on which a bulb is blown, and to the extremity of which a flask, 
 containing the materials for generating pure hydrogen gas, is connected. 
 As, however, the hydrogen passes off in a damp condition, and thus in- 
 troducing water might falsify the result, there is interposed a bottle con- 
 taining a quantity of very strong oil of vitriol, by which from its great 
 affinity for moisture, the hydrogen gas is completely dried, before it 
 comes into contact with the oxide of copper. When the apparatus has 
 been filled with pure dry hydrogen, heat is applied to the bulb, contain- 
 
Atomic Constitution of Water. 349 
 
 ing the black oxide of copper, and as soon as its temperature has been 
 raised to dull redness, decomposition commences. The oxide of copper 
 becomes glowing red, and then, even if the heat of the lamp be much 
 reduced, the reaction still goes on ; the glowing gradually pervades the 
 whole mass, water is formed and condensed on the colder parts of the 
 tube in considerable quantity, and when the reaction is completed, there 
 remains in the bulb a porous mass of pure metallic copper. It is ne- 
 cessary, however, to determine exactly the quantity of water formed : 
 for this purpose, a small tube filled with fragments of fused chloride of 
 calcium, is attached to the bulb tube by means of a caoutchouc connecter, 
 and the stream of hydrogen gas is allowed to continue through the ap- 
 paratus, until the residual copper has become quite cold, and all traces of 
 water have been carried into the chloride of calcium tube, where it is 
 completely absorbed and retained. The oxide of copper tube having 
 been weighed before and after the experiment, the loss found is the oxy- 
 gen which has been carried off : the chloride of calcium tube having 
 been also weighed before and after, the gain gives the weight of water 
 formed, and hence, the composition of water may easily be calculated, 
 thus : 
 
 100 parts of black oxide of copper give 
 79 '85 of metallic copper, and lose 
 20-15 of oxygen, which form 
 22 -67 of water; 
 
 consequently, 22-67 of water consist of 
 20- 15 of oxygen, 
 
 2-52 of hydrogen ; 
 or in 100 parts, 
 
 88-9 of oxygen, 
 ll'I of hydrogen. 
 
 To determine the combining equivalents of these substances, or, in 
 theoretical language, their atomic weights, it is first necessary to ascer- 
 tain what grounds there are for deciding on the atomic constitution of 
 water. 
 
 It has been already mentioned that at one time equal volumes of all 
 gases were considered to contain the same number of atoms ; and hence, 
 as water is formed by the union of one volume of oxygen and two of 
 hydrogen, it was considered by some chemists to consist of one atom of 
 oxygen united to two of hydrogen ; therefore, if we take oxygen as the 
 standard of atomic weights, and call its equivalent number 100, the 
 result would be that 88'9:11-1::100:12'50 = weight of two atoms of 
 hydrogen; and hence the atomic weight of hydrogen should be 6*25. 
 To the adoption of this number there are very many objections ; 1st, 
 The ground upon which it was first adopted has been proved to be 
 
350 Chemical Constitution of Water. 
 
 false, as the same volumes of all gases certainly do not contain the same 
 number of chemical atoms ; and although hydrogen enters so often into 
 combination, it is but very rarely that it does so in the proportion of 
 6 -25. Likewise water, in all the modes in which it is capable of com- 
 bining, does so in a quantity containing 12*50, and not 6 '25 ; and, 
 finally, water in combination allies itself to a variety of metallic oxides, 
 all of which there is the strongest reason for supposing to be composed 
 of one equivalent or atom of the metal united with one of oxygen. 
 
 Water is, therefore, assumed to be composed of an equivalent of 
 each of its constituents, and according as the standard of oxygen or of 
 hydrogen is taken, its atomic weight is 
 
 One atom of oxygen, . . lOO'O 8 
 
 One atom of hydrogen, . . 12*5 1 
 
 forming one atom of water 1 12-5 9 
 
 Water is colourless, transparent, destitute of taste and smell. If 
 agitated, it solidifies at a temperature of 32 ~F. (0. Centigrade), but if 
 preserved quiescent, it may be cooled much lower without freezing ; if 
 it be then touched or shaken, a portion is immediately converted into 
 ice, and the temperature of the whole is raised to 32. In freezing, 
 water expands very much, and exerts therein so great a force as to burst 
 the strongest vessels in which it is contained. It is thus that the sur- 
 faces of the hardest rocks are gradually crumbled into soil fit for the 
 support of vegetable life ; the water percolating into minute crevices 
 and fissures during the warmer months, and when frozen in winter, 
 breaking down by repeated and increasing expansive efforts during suc- 
 cessive years, the substance of masses, which should appear from com- 
 pactness and hardness fitted to withstand the severest effects of time 
 and climate. 
 
 The specific gravity of steam, such as it would be at the standard 
 temperature and pressure, is found to be 622'1, atmospheric air being 
 lOOO'O. Two volumes of steam contain two of hydrogen and one of 
 oxygen ; here there is a condensation of three volumes to two produced 
 by the union of the gases. The calculated result is thus found : 
 
 Two volumes of hydrogen, 69-3 X 2 = 138-6. 
 One volume of oxygen, . . = 1 105-6. 
 
 give two volumes of vapour of water, = 1244'2. 
 hence one volume of vapour of water, r= 622' 1. 
 In forming the steam at 212, and a pressure of 30 inches mercury, 
 
Solubility of Gases in Water. 351 
 
 water expands to 1696 times its volume, according to the determination 
 of Gay-Lussac, which gives almost exactly the proportion of a cubic 
 inch of water forming a cubic foot of steam, which contains 1728 cubic 
 inches. 
 
 The solution of gases in water appears to be governed by principles 
 similar to those which regulate the solvent action of water upon solid 
 bodies. In some instances there certainly takes place chemical union, as 
 in the case of muriatic acid gas and of ammonia ; and in these cases the 
 condensation of the gases by the water is accompanied by the evolution 
 of considerable heat. But in other cases, particularly where the quan- 
 tity of gas is small, the result appears to be merely a mechanical distri- 
 bution of the molecules of the gas throughout the mass of the liquid. 
 The following is a table of the quantity of those gases absorbed by 
 water without combination. 
 
 100 volumes of water at 60 Far. and 30 inches Bar. absorb of 
 
 Sulphuretted hydrogen, ' . . . 253vol. 
 
 Sulphurous acid, .... 438 
 
 Chlorine, 206 
 
 Carbonic acid, 100 
 
 Nitrous oxide, 76 
 
 Olefiant gas, 12'5 
 
 Oxygen, 3'7 
 
 Nitrogen, ~) 
 
 1-6 
 
 Hydrogen, } 
 
 The mixture of nitrogen and oxygen, which constitutes the air we 
 breathe, is absorbed by water, and it is to the air thus dissolved, that 
 water in great part owes its refreshing taste. If water be boiled, this 
 air is expelled, and this should be done, if it be wished to saturate the 
 water with any other gas, as the power of water to absorb any other gas 
 is remarkably diminished by the presence of even a small quantity of 
 air. If water already saturated with one gas, be exposed to the action 
 of a second, it lets a portion of the first escape, and absorbs a corres- 
 ponding quantity of the second. In this way, a very small quantity of 
 a sparingly soluble gas may expel a large quantity of one much more 
 soluble. A familiar example of this fact consists in taking a glass half 
 full of champagne, and having formed the palm of the hand into a hol- 
 low cup, to strike the top of the glass, closing the glass and flattening 
 the hand at the same time ; the air above the wine is thus forcibly com- 
 pressed, and a portion is then absorbed, under pressure, by the liquid, 
 from which a quantity of carbonic acid is expelled, greater than that of 
 air absorbed, in the proportion of 1060 to 16, and thus the effervescent 
 character of the wine restored. 
 
352 Various Functions of Water. 
 
 Notwithstanding this character of neutrality, which renders water so 
 useful as a vehicle or solvent for more energetic bodies, water is actively- 
 engaged in a great variety of chemical reactions, in which its elements 
 separating from one another, appear in an isolated state, or by combining 
 with other substances which may be present, generate new compounds. 
 Even, however independent of decomposition, water plays a most im- 
 portant part in chemical theory, from the numerous classes of compounds 
 of which it forms a constituent. The generality of saline bodies, in 
 crystallizing, retain a quantity of water, often more than one-half their 
 weight ; this is termed water of crystallization. On the application of 
 a moderate heat, this water separates, and frequently the salt dissolves 
 in its own water of crystallization, on being heated, undergoing what is 
 termed watery fusion. 
 
 Salts containing water of crystallization, often attract still more if 
 surrounded by damp air, and fall into a liquid state ; such are termed 
 deliquescent salts ; others on the contrary, give off their water of crystal- 
 lization even at ordinary temperatures, if the air be moderately dry ; 
 some, such as the carbonate and sulphate of soda, losing all, others, as 
 the phosphate of soda, only a portion of that constituent ; these are 
 termed efflorescent salts ; when the efflorescence is complete, they lose 
 their crystalline arrangement and fall to powder. 
 
 Graham has shewn, that in many classes of salts, particularly the 
 sulphates, one portion of the water is much more intimately united 
 than the remainder ; that, in fact, in addition to the mere water of 
 crystallization, which may be removed without injury, there is water 
 essential to the constitution of the salt, and replaced by other bodies 
 when the salt enters into combination. Thus, in the common crystal- 
 lized sulphate of copper, there are five atoms of water, of which four 
 are removable by a temperature of 150, but the fifth withstands a 
 temperature of 300. The formula of this salt is, therefore, not CuO. 
 S0 3 + 5HO. but CuO. SO 3 . HO + 4HO. the four atoms being water 
 of crystallization. Now, if this salt be combined with sulphate of 
 potash, this fifth atom of water disappears, and the double salt is (CuO. 
 S0 3 ) (KO. SO 3 ) + 4HO ; the KO. SO 3 having entered into the place 
 of the water which had been expelled. Water thus circumstanced is 
 termed constitutional water, as being necessary to the complete consti- 
 tution of the substance. 
 
 Water, in combination with the stronger acids, is capable of acting 
 as a base, and, indeed, we know of the existence of many acids only in 
 the form of their compounds with water. Thus, the nitric, the chloric, 
 the oxalic, the acetic acids, have never been obtained in a separate 
 form ; what we generally term those acids being, in reality, compounds 
 
Acid, Basic and Saline Water. 353 
 
 of these acids with water ; salts of water. Oil of vitriol is a compound 
 of sulphuric acid and water, sulphate of water, and it combines with 
 more water, producing great heat, to form a sulphate of water, with 
 excess of base, precisely as the sulphate of copper combines with more 
 oxide of copper to produce a corresponding basic salt. The salts of 
 water possess the most complete similarity with those of zinc and copper, 
 and it is from their comparative study, that the evidence in favour of 
 the view inculcated already, of hydrogen being a volatile metal, has 
 been in greatest part derived. 
 
 T\ ater combines also with bases : the majority of metallic oxides 
 combine with water, often with the evolution of considerable heat. 
 The slaking of lime, which is the act of combination of dry lime with 
 water, produces so much heat as to ignite gunpowder, and, when in 
 large quantity, to become red hot. Ships laden with lime have often 
 been burned at sea, from water getting into the hold among the lime, 
 and so much heat being evolved as to set the ship on fire. Barytes and 
 strontia produce, in slaking, still more heat. Potash retains water so 
 strongly that it can only be obtained free from it by the direct com- 
 bustion of the metal, potassium, in dry oxygen gas or air. In relation 
 to these powerful bases water appears, therefore to act the part of a 
 feeble acid. 
 
 The compounds of water have been generally termed by chemists 
 hydrates; thus, hydrate of lime, hydrated oxide of copper, hydrated 
 sulphuric acid, hydrated sulphate of zinc. The very different functions 
 performed by water, in the various modes of combination it affects, 
 render it necessary to adopt a definite principle of nomenclature in this 
 respect. In the subsequent pages I shall employ the word hydrate only 
 where the water is combined with a base, such as a metallic oxide ; thus, 
 hydrate of lime, hydrate of potash, hydrated oxide of lead. AVhere 
 the water is united to an acid, I shall, in all cases in which the true 
 chemical nature of the compound comes into play, term it a salt ; as 
 sulphate of water, oxalate of water, &c. : but where no strict theoretical 
 explanation is involved, I shall continue to use the common name, as- 
 oil of vitriol, strong sulphuric acid, oxalic acid, aquafortis, c. There 
 is no name peculiarly applicable to the class of compounds which con- 
 tain constitutional water, but it will serve as well to characterize the 
 absence or deprivation of this water, by the word anhydrous ; the ordi- 
 nary name of the substance being supposed to include the combined 
 water; thus, common sulphate of zinc, freed from water of crystal- 
 lization, is ZnO. S0 3 HO ; anhydrous sulphate of zinc is ZnO. SO J4 
 
 TUiere there exists water of crystallization in a salt, it is of course 
 included when the salt is spoken of as crystallized. In formulae, for the- 
 23 
 
354 Mineral Waters. 
 
 purpose of distinguishing between water of crystallization and water 
 more closely united, the latter will always be marked by the symbols of 
 its constituents,, the former by the two initial letters of the Latin word, 
 aqua, aq. ; thus the crystallized oxalic acid is C 2 3 . HO + 2 Aq. The 
 phosphate of soda is P 2 5 + 2NaO.HO -f 24 Aq. 
 
 Water does not exist in nature in a perfectly pure condition. It 
 contains dissolved a small portion of atmospheric air and of carbonic 
 acid, and also certain quantities of solid impurities, of which common 
 salt, sulphates and carbonates of lime, and chloride of magnesium, are 
 the most important. In particular localities, the water issuing from the 
 earth contains iron, and often sulphuretted hydrogen ; also traces of 
 iodine and bromine ; and occasionally the quantity of these foreign 
 matters present is so great as to confer upon the water medicinal pro- 
 perties, and to make such springs under the name of mineral springs, 
 spas, be resorted to for the purpose of preserving or recovering health. 
 These impurities arise from the water, in percolating through the porous 
 rocky strata, of which the mountains and general crust of the earth 
 are constituted, dissolving in small quantity almost all the substances 
 it meets. Hence, rain water or snow water, collected at a distance 
 from houses, is the purest water which can be obtained in nature. It 
 contains only some carbonic acid and air dissolved. The sea being the 
 general reservoir into which all the rivers of the earth discharge their 
 waters, contains in a concentrated form all the materials which the 
 river waters had carried down. Although not of absolutely the same 
 constitution all over the globe, yet it varies so little that the deviation 
 may be explained by local circumstances. It is in many countries the 
 source from which common salt and sulphate of magnesia are derived. 
 When sea water freezes, the ice contains scarcely a trace of saline 
 matter; so that when melted, it forms a sweet drinkable water. Hence, 
 in voyages in the Northern Seas supplies of fresh water are obtained by 
 chopping blocks of ice from the frozen surface of the ocean. To obtain 
 water pure for chemical purposes, it is necessary to distil it. The saline 
 and fixed impurities remain behind, the pure water passes over. Its 
 purity may be ascertained by means of the reagents fitted to detect the 
 most important impurities. Thus, if free from common salt, it will give 
 no precipitate with a solution of nitrate of silver ; if free from lime, it 
 will not be affected by oxalate of ammonia ; and if it be not rendered 
 turbid by nitrate of barytes, it cannot contain sulphuric acid. 
 
 These impurities frequently exist to such extent that it is often 
 necessary to purify the water before it can be employed for domestic 
 purposes or for many manufacturing uses. This is generally done by 
 filtration through layers of such substances as by their chemical or other 
 
Peroxide of Hydrogen. 355 
 
 properties may remove the impurities. The most active purifying sub- 
 stance is charcoal, by which all decomposing organic matter may be 
 taken up, and also a certain quantity of carbonate of lime : and by the 
 addition of a carefully adjusted quantity of quicklime, the carbonic acid, 
 wliich holds the calcareous impurities of the water dissolved, may be 
 removed, all the lime precipitated as carbonate, and the hardest waters 
 thus rendered perfectly soft. 
 
 From the inactivity of water, and the facility with which it may be 
 obtained pure, as well as the important part which it plays in the eco- 
 nomy of nature, it is taken as the standard with which the properties of 
 other bodies, when numerically determined, are compared. Thus, the 
 specific heats of solids and liquids are reduced to a scale, water being 
 taken as 1*000. The specific gravities of liquids and solids are also 
 taken in numbers, that of water being the standard. If, however, the 
 specific gravities and heats of gases and vapours were reduced to the 
 standard of water, the fractions by which they should be expressed 
 would be inconveniently small ; and hence, for this class of bodies, a 
 better suited standard substance is found in atmospheric air. 
 
 Of Oxygenated Water* Peroxide of Hydrogen. 
 HO + O or HO 2 . Eq. 17 or 212-5. 
 
 This singular substance was first discovered by Thenard ; its prepa- 
 ration is somewhat circuitous and indirect ; oxygen and hydrogen not 
 combining with each other directly in any other proportions, but those 
 which form water. 
 
 For its preparation, peroxide of barium must be first procured ; this 
 is prepared by placing pure barytes (oxide of barium) in a porcelain 
 tube, which is heated to redness in a charcoal furnace, and then a stream 
 of pure oxygen gas passed over it as long as it is absorbed ; the barytes 
 absorbs as much more oxygen as it already contained, and from BaO 
 becomes BaO. 2 . 
 
 This substance may be still more easily prepared, by mixing pure 
 barytes with its weight of chlorate of potash and heating it nearly to 
 redness ; when the disengagement of oxygen from the chlorate of potash 
 has set in, the mass becomes glowing red at one point, and this appear- 
 ance spreads over the whole mass like tinder. The barytes burns as it 
 were in the atmosphere of oxygen, and forms the deutoxide of barium. 
 If, then, the residual mass be washed with water, the chloride of po- 
 tassium, which remains from the chlorate of potash, is dissolved, and 
 the deutoxide of barium, combining with an equivalent of water to form 
 a bulky, white, insoluble hydrate, remains behind, and may be collected 
 on a filter. 
 
355 Preparation and Properties 
 
 The best mode of obtaining peroxide of hydrogen from this substance 
 is that proposed by Pelouze. To dilute hydrofluoric acid, (fluoride of 
 hydrogen,) the peroxide of barium is added, until the acidity of the 
 liquor is completely neutralized. The reaction is very simple; the 
 fluorine combines with the barium, whilst all the oxygen is transferred 
 to the hydrogen, which the fluoric acid abandons ; thus, H.F 4~ BaO 2 = 
 BaJF + H0 2 . 
 
 The fluoride of barium is insoluble, and may be collected on a filter 
 along with the excess of peroxide of barium ; the liquor contains only 
 pure oxygenated water. Muosilieic acid, which is cheaper, and more 
 convenient than the fluoric acid, may also be used in this decomposition. 
 The fluosilicate of barium separates as an insoluble white powder, and 
 the peroxide of hydrogen remains dissolved. 
 
 Theuard's plan consisted in dissolving the peroxide of barium in 
 dilute muriatic acid, and then precipitating the barytes by sulphuric 
 acid. The muriatic acid which became free, was then neutralized by 
 another portion of peroxide of barium, and this again precipitated by 
 sulphuric acid. When the liquor had become strong enough, the free 
 muriatic acid was removed by the cautious addition of sulphate of silver, 
 and the sulphuric acid then evolved was precipitated by the addition of 
 pure barytes, carefully avoiding an excess. 
 
 The weak solution of peroxide of hydrogen thus obtained, must be 
 placed along with a capsule of sulphuric acid, under the exhausted 
 receiver of the air pump. The water being more volatile, evaporates 
 first, and the liquor gradually becomes more concentrated, until, finally, 
 the peroxide of hydrogen remains pure behind. If left too long in the 
 exhausted vessel, it evaporates itself without alteration. 
 
 Peroxide of hydrogen is a thick, colourless liquid. Its specific 
 gravity is 1*452. It has a nauseous taste, and irritates the skin. It 
 bleaches and destroys all vegetable colours. Its reactions are generally 
 so violent that it must be diluted with many times its volume of water 
 before they can be accurately observed. 
 
 Its most curious property is, that by being put in contact with any 
 one of a great number of solid substances, it is decomposed with great 
 rapidity, being resolved into oxygen and water. Black oxide of manga- 
 nese is one of the most active. If a little of this substance, in powder, 
 be introduced into strong peroxide of hydrogen, in a graduated tube, 
 over mercury, the latter is decomposed almost explosively, disengaging 
 475 times its volume of oxygen ; the oxide of manganese remaining 
 perfectly unaltered. Platinum, gold, silver, quicksilver, particularly if 
 the metal be in the form of leaf, or sponge, produce the same effect; 
 and if the peroxide of hydrogen be put into contact with an oxide of 
 
of Peroxide of Hydrogen. 357 
 
 these metals, as oxide of silver, it is not merely decomposed itself, but 
 the oxide is also decomposed, the oxygen and metal both becoming 
 free. In the dark, and with strong peroxide of hydrogen, a flash of 
 light is seen to accompany its decomposition, and the tube becomes red 
 hot. The decomposition of the oxide of silver cannot, however, be re- 
 ferred to the great heat produced, as even if the peroxide of hydrogen 
 be diluted with fifty times its volume of water, oxide of silver produces 
 complete decomposition, evolution of oxygen, and separation of metallic 
 silver, yet the effervescence is not very energetic, and the liquor does 
 not become sensibly warm to the hand. 
 
 With other metals, the oxygen, in place of becoming free, enters into 
 combination, forming an oxide of a higher degree ; thus, with the oxides 
 of lead and bismuth, there are formed peroxides of those metals, with 
 arsenic there is formed arsenic acid. The animal substances fibrine and 
 albumen, which are so similar in most respects, are distinguished from 
 each other by their action on this body, fibrine decomposing it with 
 rapidity, whilst albumen is without effect. It is highly probable, that 
 in the decomposition of water by the voltaic pile, some of this com- 
 pound may be formed, as the quantity of oxygen collected is frequently 
 smaller than it should be ; and a portion of the process of bleaching, 
 by exposing the wetted cloth to the action of light and air, may possibly 
 be carried on by the formation and subsequent decomposition of this 
 substance. 
 
 Peroxide of hydrogen, when kept for any length of time, even in a 
 dilute condition, gradually decomposes, oxygen being given off, and 
 water remaining behind. The presence of an acid in the liquor retards 
 this action very much, whilst the presence of an alkali accelerates it. 
 It was in great part from the remarkable characters of this body, that 
 Berzelius derived his evidence in favour of the existence of a catalytic 
 force, influencing chemical action, which has been described already. 
 
 OF NITROGEN. 
 Symbol. N. Eq. 14 or 175. 
 
 It has been already noticed, that the substance by which the oxygen 
 is diluted in atmospheric air, so as to render it suitable to the respi- 
 ration of animals, is called nitrogen, from its being the basis of nitric 
 acid and nitre, (the nitre former.) It is also called by some chemists 
 azote, from its incapability of supporting life; but as a great number of 
 gases resemble it in that respect, the former name is the more charac- 
 teristic, and it alone shall be hereafter used. 
 
 As nitrogen exists in great quantity in the air we breathe, it is most 
 
358 Different processes for the 
 
 easily obtained by acting upon a confined portion of the air so as to 1 
 abstract the oxygen, when the residual gas is 
 found to be nitrogen almost completely pure. 
 Thus, if a small piece of phosphorus, laid 
 in a cup d floating in water, be set on fire, and 
 a bell glass a be inverted over it, the phos- 
 phorus, in burning, unites with the oxygen of 
 the air, and forms white fumes of phosphoric 
 acid. At first, from the great expansion of 
 the air caused by the high temperature of the 
 flame, some bubbles escape from under the edge of the glass, but soon, 
 even before the phosphorus has ceased to burn, the water begins to rise 
 in the bell, and finally, the clouds of phosphoric acid gradually dis- 
 solving in the water, the residual gas will be found to occupy about 
 four-fifths of the original volume of the air, and to be colourless as the 
 air had been before. Any other burning body would answer the same 
 purpose, although not so perfectly as the phosphorus. Thus, if spirit 
 of wine, or pyroxylic spirit, or ether, which burn without smoke, be 
 placed in the little cup, and set on fire under the bell glass, as in the 
 former instance, the inflammable constituents, carbon and hydrogen, 
 combine with the oxygen of the air, forming carbonic acid and water ; 
 the nitrogen remaining behind. The gas thus obtained must be washed 
 well with water, or better, a little solution of potash, to remove the 
 carbonic acid, and even then the nitrogen contains some oxygen uncon- 
 sumed ; for in every case where carbonic acid is formed by a burning 
 body, the combustion ceases before all the oxygen present has been 
 consumed, the carbonic acid exercising on combustion a positively im- 
 peding power, similar to that which it has on respiration. The purest 
 nitrogen is consequently obtained by means of phosphorus. 
 
 Independent of this source of nitrogen in atmospheric air, it may be 
 obtained indirectly from a great number of substances. Thus, most 
 animal substances contain nitrogen, in large quantity, united to carbon, 
 hydrogen, and oxygen. If, therefore, some pieces of muscle, or albumen, 
 or gelatine, be boiled in a retort with some nitric acid, the oxygen of 
 the nitric acid combines with the carbon and hydrogen of the animal 
 substance, forming different compounds according to the temperature 
 and the proportions, whilst the nitrogen of both is disengaged. 
 
 If a gas, termed nitrous oxide, which will be described in a subsequent 
 section, be put into contact with a slip of metallic zinc, at the moment 
 of its formation the zinc deprives it of its oxygen, forming oxide of zinc, 
 and the nitrogen is set free. The apparatus used for this purpose con- 
 sists of a tubulated retort, into which is introduced the salt (nitrate of 
 
Preparation of Nitrogen, Gas. 359 
 
 ammonia), which, when heated, yields nitrous oxide. Into the tubulure 
 is fitted a cork, through which passes a copper wire, to the end of which 
 a slip of zinc is fastened. To the neck of the retort a bent tube is 
 adapted, passing to the pneumatic trough. Heat being applied to the 
 retort by means of a lamp, the salt melts, and then begins to emit gas. 
 At this moment the copper wire is depressed, so that the slip of zinc 
 may touch the surface of the melted mass. The effervescence imme- 
 diately becomes much more violent, white clouds of oxide of zinc are 
 formed, and the gas, which passes over, is nitrogen quite pure. The 
 theory of the formation of the nitrous oxide will be noticed under the 
 proper head. Its decomposition by the zinc is simple : nitrous oxide is 
 XO, and acted on by Zn their products are N and ZnO. 
 
 If ammonia dissolved in water be exposed to the action of a current 
 of chlorine, it is decomposed, salammoniac is formed, and nitrogen gas 
 is disengaged. The solution of ammonia may be contained in a bottle 
 with a wide neck, g, to which a cork is fitted, perforated to admit two 
 tubes, the one,/) conveying the chlorine from the vessel a, in which it 
 
 it disengaged, and opening under the 
 surface of the liquid near the bottom, the 
 other projecting but little under the cork, 
 and leading to the pneumatic trough. 
 The action of the chlorine upon the am- 
 monia is accompanied by the formation 
 of white fumes and the evolution of much 
 heat. If the solution be strong, a flash 
 of light is seen at the entrance of each 
 bubble of chlorine gas; but these are 
 
 not attended with any danger. The ammonia, however, must, all 
 through the process, be kept in excess, as, were the chlorine in excess, 
 it might produce a body, chloride of amidogene, possessed of the most 
 eminently dangerous explosive properties. 
 
 The reaction which here takes place may be simply shown. Ammo- 
 nia consists of one equivalent of nitrogen and three of hydrogen ; by the 
 action of three equivalents of chlorine there are formed three of chloride 
 of hydrogen, (muriatic acid), which unite then with three equivalents of 
 ammonia to form three of salammoniac (muriate of ammonia). Thus, 
 (N+3H) and 3C1 give N and (3C1H), which combine with 3NH 3 to 
 form 3 (C1H.NH 3 ), one equivalent of nitrogen becoming free. 
 
 Nitrogen, when obtained by any of these processes, is a permanent 
 gas, colourless and transparent ; it is absorbed by water only in very 
 small quantity. It is lighter than atmospheric air, its specific gravity 
 being 976, air being 1000. It is characterized by the complete absence 
 
360 Nature of Atmospheric Air. 
 
 of the positive properties which distinguish other gases. Thus, it does 
 not support combustion or respiration ; it extinguishes a taper, and ani- 
 mals are suffocated in it ; but these effects appear to be due only to the 
 absence of oxygen. 
 
 Although nitrogen is thus incapable of combining directly with oxy- 
 gen, yet by indirect methods, they may be made to unite, and the com- 
 pounds formed of these elements are surpassed in number and import- 
 ance by few series of binary combinations. When oxygen and nitrogen 
 combine, their result is almost universally that which contains most 
 oxygen, nitric acid ; their union may be effected by the electric spark, 
 provided water, or a solution of an alcali be present ; hence rain water 
 often contains traces of nitric acid, particularly if its deposition has been 
 preceded by discharges of lightning between the clouds ; and lime or 
 potash contained in old walls are found, after a certain time, to be neu- 
 tralized by nitric acid. A mixture of ammonia and oxygen may be 
 converted into nitric acid and water, likewise, by spongy platinum at a 
 temperature of 572. 
 
 The combining proportion of nitrogen is, on the hydrogen scale, 14'0, 
 and on the oxygen scale, 175. In a great number of instances, how- 
 ever, it appears to enter into combination with one-third of its ordinary 
 equivalent, and I have found this peculiarity to extend to arsenic and 
 phosphorus, which are so closely assimilated to it throughout their che- 
 mical relations. 
 
 Before entering upon the history of the compounds of nitrogen with 
 oxygen, I shall describe more particularly the properties and composition 
 of atmospheric air, which, being of so much importance in the majority 
 of chemical reactions which occur on a large scale, and being assumed 
 as the standard of properties "for gaseous and vaporous bodies, deserves 
 minute attention. 
 
 OF THE ATMOSPHERE. 
 
 The analysis of atmospheric air was the first important problem, in 
 the chemistry of gaseous bodies, with which chemists occupied them- 
 selves, and hence the names of instruments originally devised for examin- 
 ing atmospheric air, became generally used to indicate those employed 
 in the analysis of gaseous mixtures or compounds of any kind. The 
 word eudiometer signifies a measurer of the goodness of the air, and 
 from the interest which the problem presented, numerous methods were 
 early invented, although it is only recently that very great precision in 
 the results has been obtained. It was at first believed, that the relative 
 salubrity of districts, and even of different localities in the same neigh- 
 
Chemical Analysis of Air. 361 
 
 bourhood, could be determined by the proportions of oxygen and 
 nitrogen, which the air of these places might contain ; and that the 
 admixture of pernicious substances, exhaling from a marsh, or generated 
 within the ill-ventilated apartments of an hospital or jail, might be 
 recognized, and means discovered of removing them, or of destroying 
 their activity, when their nature had become determined by the analysis 
 of the air in which they had been contained. The differences between 
 the results of various chemists, on which these expectations had been 
 founded, have gradually disappeared by the use of better methods, and 
 the constitution of atmospheric air is now recognized as being almost 
 absolutely the same throughout its entire mass ; but from other sources, 
 the very results which had been originally sought after, now appear to 
 form a legitimate and promising subject of inquiry. 
 
 In addition to oxygen and nitrogen, its principal constituents, atmos- 
 pheric air contains some carbonic acid and watery vapour ; the quantity 
 of the latter is determined by methods almost entirely physical, and 
 forms a practical department in the theory of vapours, termed hygro- 
 metry. I shall, therefore, not touch upon it here, referring to what has 
 been already noticed of it, in the sections upon water, and upon heat. 
 
 The determination of the quantity of carbonic acid present in atmos- 
 pheric air, has been made accurately by Saussure, who found that in 
 general, 10,000 volumes of air, contain 4* 15 of carbonic acid; the max- 
 imum of carbonic acid he found to be 5'74, and the minimum 3*15. 
 Over the surface of lakes, as that of Geneva, the quantity of carbonic 
 acid is smaller, but in cities greater, amounting to 4'46 in the average : 
 the quantity is somewhat greater by night than by day, and in the higher 
 regions of the air, than on the surface or low ground ; it is diminished also 
 during, and for some time after rain. To determine the quantity of the 
 carbonic acid, a large globe or bottle containing air is taken, and a 
 solution of barytes is introduced, until after having been well agitated 
 with the air, it is found, by browning turmeric paper, to be present in 
 excess. The carbonic acid combines with barytes to form a white 
 powder, carbonate of barytes, which being collected on a filter, and 
 weighed, gives, by a simple calculation, the volume of the carbonic acid 
 in the air. 
 
 The decomposition of animal and vegetable matter, which is con- 
 tinually taking place over the surface of the globe, throws into the 
 atmosphere quantities of ammonia, which have been satisfactorily traced 
 by analysis, and will be shown to play an important part in the general 
 economy of nature ; for although the quantity is relatively so small as 
 not to be reckoned in any ordinary estimate of the constituents of the 
 air, it yet forms the source from whence a great deal of the nitrogen of 
 
362 Composition of the Atmosphere. 
 
 plants is derived, the ammonia being absorbed by the foliage of the liv- 
 ing vegetables, and its constituents assimilated to their tissues. 
 
 The experiments of Saussure, and of Boussingault, have made it pro- 
 bable, that carbon combined with hydrogen (probably as the gas of 
 marshes) exists in very small quantity in atmospheric air. Thus, when 
 Saussure after having removed all carbonic acid by barytes, detonated 
 the residual air with pure hydrogen, he obtained a quantity of carbonic 
 acid, equal to nearly one part in 2000 of the air employed; and 
 although employing other methods, the results of Boussingault strongly 
 corroborate the same idea ; he found sulphuric acid to be blackened 
 when exposed to air, although all access of dust or accidental impurities 
 was removed, and that when air, previously freed from carbonic acid, 
 was passed over red hot oxide of copper, a perceptible quantity of water 
 and of carbonic acid was produced. 
 
 But the most important portion of the analysis of atmospheric air is, 
 to ascertain the proportions of the oxygen and nitrogen. To effect this, 
 any one of a great variety of bodies which are capable of uniting with 
 oxygen may be used ; thus, if a solution of sulphuret of potassium be 
 exposed to air, it absorbs oxygen, and gradually passes to the state of 
 hyposulphite of potash, and by the amount of absorption the quantity 
 of oxygen may be ascertained. This is the method of Scheele. One 
 proposed by Sir Humphrey Davy consisted in agitating the deep olive 
 liquor, formed by passing nitric oxide gas into a solution of green sul- 
 phate of iron, with a measured quantity of atmospheric air ; but it is 
 now abandoned. An excellent mode of using these bodies as eudiome- 
 ters, is to fill, with the liquid, a small caoutchouc bottle, holding about 
 two fluid ounces, and then tie it securely on the tube of air which 
 passes pretty closely in at the neck ; the mass of air and fluid can thus 
 be brought extensively into contact, and the absorption is shown by the 
 gradual rise of the liquid in the tube, the soft parietes of the bottle 
 yielding to the pressure of the external air. 
 
 Nitric oxide gas possesses the property of combining with the 
 oxygen of the air, and forming deep red fumes of nitrous acid, which 
 dissolve in water. By this means, using an excess of the nitric oxide, 
 all oxygen may easily be removed from atmospheric air, but the com- 
 position of the nitrous acid fumes is not always the same, and hence the 
 quantity of oxygen which the air contained, is liable to be mistaken. 
 This mode, therefore, from the great precaution necessary in its use, has 
 been quite laid aside. 
 
 The use of the hydrogen gas eudiometer, whether the combination of 
 that substance with the oxygen be accomplished by the agency of the 
 electric spark, or by means of spongy platina, has been already noticed. 
 
Different modes of Analysing Air. 363 
 
 It is one of the most accurate and easy methods that can be used, and 
 hence has been most generally employed. The risk of accident from 
 the violence of the explosion by the electric spark is much diminished, 
 by using the form proposed by Ure. The tube, which need not be at 
 all so stont as in the common form, is taken about twice as long, and 
 bent in the form of an IT. Having been filled with mercury, the mix- 
 ture of the air and hydrogen is transferred to the sealed leg, and then, 
 the open leg being about half occupied by air, it is to be firmly closed 
 by the thumb or by a cock. When the explosion follows, the air in 
 the open leg yields to the pressure and graduates the shock ; no portion 
 of the exploded mixture can be projected. 
 
 Slips of copper foir", moistened with muriatic acid, absorb oxygen 
 with great avidity, and have been proposed by Gay-Lussac for the ana- 
 lysis of atmospheric air. Saussure has used in his accurate researches 
 thin filings or turnings of lead, which combine with oxygen very rapidly, 
 and remove it totally from the air. 
 
 Phosphorus, which burns in oxygen and in air so brightly, may also 
 be employed to form an eudiometer ; it may be used either by slow or 
 by rapid combustion. In the former mode, a stick of moistened phos- 
 phorus placed in a graduated tube of air, deprives it completely of its 
 oxygen in about twenty hours ; the residue is nitrogen, which has the 
 smell of phosphorus, and requires a correction for a small quantity of 
 vapour of that substance which is diffused through it. The rapid com- 
 bustion of phosphorus is too violent, and exposes the vessels to too 
 much risk of breaking, to be made use of for accurate experiment. 
 
 All of these methods are, however, liable to error to the amount of 
 nearly 1 per cent., which is to be in great part attributed to the small 
 quantity of air which the apparatus allows to be experimented on. This 
 disadvantage has been obviated by the mode proposed by Branner, and 
 used by him in some determinations lately made, in which the Uability 
 to error has been reduced to 0*20 per cent. In the figure, a, I, c, is 
 a tube consisting of a wide portion, 6, and a narrow, 
 c ; the wider part being drawn, in a, to a capillary 
 opening. Into it is introduced a quantity of loose 
 cotton and some bits of phosphorus, and being then 
 warmed, the melted phosphoruses allowed to spread 
 over the fibres of the cotton so as to expose a very 
 great surface. The tube at c fits air-tight to the 
 orifice of the vessel, d, which is graduated and filled 
 with mercury ; a cock at e allows the mercury to flow 
 out on occasion. To use this apparatus the tube a, d, <?, 
 is weighed and then attached to the vessel d ; the 
 
364 Atmospheric Air a Mixture, 
 
 cock e is tlien slightly opened; the mercury issues out in a pro- 
 perly graduated stream, and its place is supplied by air, which en- 
 tering at the capillary orifice, a, streams over the surface of the phos- 
 phorus, by which all its oxygen is removed, and the residual nitrogen 
 passing into the graduated vessel, its volume can be easily read off ; or 
 the mercury which flows off being caught in a graduated glass, its vo- 
 lume is equal to that of the nitrogen which has passed in. Besides 
 extending the surface of the phosphorus, and thus quickening the ab- 
 sorption of the oxygen, the mass of cotton serves as a filter to collect 
 the white fumes or flakes of phosphorous acid formed. When a suffi- 
 cient quantity of air has passed through the apparatus, the tube a, b, c, is 
 to be weighed again ; the increase of weight is the quantity of oxygen 
 absorbed, from which the volume may be known, and the mercury 
 measured is the volume of the nitrogen ; from whence its weight may 
 be calculated. The air must be of course dry. This is effected by se- 
 curing to the tube a, I, c, by means of a caoutchouc connecter, a small 
 tube containing fragments of fused chloride of calcium, through which 
 the air streaming deposits the moisture it may contain. 
 
 The most perfect mode of analysis of air is, however, that lately 
 employed by Dumas. He allows air to stream over ignited metallic 
 copper in the pulverulent form, in which it is obtained by reducing the 
 oxide with hydrogen gas. The absorption of the oxygen of the air is 
 complete, and the air having been previously dried, and deprived of 
 carbonic acid, by passing through tubes containing caustic potash and 
 oil of vitriol respectively, the increase of weight of the metallic copper 
 gives the quantity of oxygen, and the increase of weight of the globe 
 into which the air is drawn, gives the nitrogen ; so that the relative 
 numbers are determined with remarkable precision. 
 
 The result of all these methods indicates that atmospheric air con- 
 tains 20' 7 9 to 21 '08 of oxygen gas in 100 volumes; and from expe- 
 riments of Gay-Lussac on air brought down by him from a height of 
 21,735 feet, to which he had ascended in a balloon, and those of Brunner, 
 for the air on the summit of the Faulhorn, 8,020 feet above the level 
 of the sea, the constitution appears to be identical at all heights. By 
 weight the constituents of the atmospheric air, in 100 parts, are, omit- 
 ting carbonic acid and water, 
 
 Oxygen gas, .&*: . . = 23-08 
 Nitrogen gas, * . . = 76 -92 
 
 100-00 
 
 This permanency of constitution of atmospheric air, together with 
 many other circumstances which I shall briefly notice, led to the opi- 
 
mid not a CJiemical Compound. 365 
 
 ttion, amongst many chemists, of its being a compound, and not a 
 mere mixture of its constituents. The analysis not being then so accu- 
 rately made, it was supposed to consist of one volume of oxygen united 
 to four volumes of nitrogen, a simplicity of proportion which charac- 
 terizes chemical union among gases. It was also remarked, that if the 
 nitrogen and oxygen were merely mixed, their different densities should 
 cause them to separate ; the heavier oxygen accumulating near the earth/ 
 whilst the lighter nitrogen should occupy the higher regions of the air. 
 The former ground has been completely disproved by later research, and 
 the elements of air are separated from one another by such feeble 
 means, thus, by nitric oxide, by metallic lead, by agitation with water, 
 &c., as would be unexampled in chemistry amongst substances of a 
 constitution such as it, if a true compound, should be supposed to 
 have. Besides, its density, its refractive power, its specific heat, are 
 the rnean qualities of the oxygen and nitrogen which form it, circum- 
 stances which necessarily occur if it be a mixture, but which do not 
 take place in any case of chemical combination. An artificial mixture, 
 also, of oxygen and nitrogen possesses all the properties of atmospheric 
 air. 
 
 It is also not the fact, that gases of different densities tend, when 
 mixed together, to separate, and form different layers, in accordance 
 with their specific gravities. On the contrary, if two bottles containing, 
 the one a a lighter, and the other e a heavier gas, be connected by stop- 
 cocks, I, c, d, and allowed to stand for a few hours, the 
 bottle containing the heavy gas being lowest, they will be 
 found to mix, the lighter gas finding its way to the lower 
 bottle, and the heavy gas ascending to the bottle which is 
 above. In this process, the gases evince a positively -active 
 power of penetrating into the spaces occupied by each 
 other; and this occurs even when they are separated by 
 membranes, or by masses of porous, earthy substances. 
 This peculiar property of gases was first recognized by 
 Dobereiner, and then studied by Mitchel, but finally exa- 
 mined, and its laws accurately assigned by Graham. 
 When gases of unequal densities are placed in contact with each other, 
 they tend to mix ultimately in an uniform manner ; but the rapidity 
 with which they penetrate each other's volume, or, as it is termed by 
 Graham, the velocity of diffusion of the gases, is unequal, and depends 
 upon their densities ; the lighter gases diffusing themselves most rapidly, 
 the heavier more slowly. Thus, if a tube be closed at the top by a 
 plug of plaster of paris, which when dry is very porous, and filled with 
 hydrogen gas, the plug being kept dry, the hydrogen and the external 
 
366 
 
 Constitution of the Atmosphere. 
 
 air tend to mix across the porous plug, but the hydrogen comes out 
 more rapidly than the air gets in, and hence the water rises considerably 
 in the tube. In a similar way, if a glass be filled with hydrogen gas, 
 and, the top being closed by a sheet of Indian rubber, a bell glass of 
 air be inverted over it, the hydrogen passing out of the glass more 
 rapidly than air enters to supply its place, the sheet of Indian rubber is 
 gradually bent in the glass, and ultimately burst by the external pres- 
 sure. On the contrary, if the small glass contain air, and the bell glass 
 hydrogen, the membranous cover is gradually forced outward by means 
 of the excess of hydrogen which passes in, and which finally breaks 
 through it, by the elasticity thus produced inside. 
 
 The exact law of the diffusion of gases is, that the velocity of diffu- 
 sion is inversely proportional to the square roots of the specific gravities 
 of the gases. This is exhibited in the following table. 
 
 
 Specific 
 Gravities. 
 
 Square Roots 
 of S. G. 
 
 Diffusion 
 Volumes. 
 
 Hydrogen, . 
 Ammonia, . 
 Air, . 
 Carbonic acid, ';".: 
 Chlorine, ... ;. 
 
 0-0693 
 0-5898 
 1-0000 
 1-5239 
 2-4700 
 
 0-2633 
 0-7681 
 1-0000 
 1-2345 
 1-5716 
 
 457 
 130 
 100 
 81 
 64 
 
 By this table it will be seen that in the same time in which 100 
 volumes of atmospheric air escape from a vessel, through a membranous 
 or porous plug, 457 volumes of hydrogen pass in, and if the vessel 
 were previously full of hydrogen, 457 volumes will escape from it during 
 the entrance of 100 volumes of atmospheric air. If the vessel contained 
 carbonic acid, the result would be the passage of 81 volumes in the 
 same time, and so of the other gases. 
 
 This law of the passage of gases through each other is the same as 
 that for the passage of a gas into a perfectly empty space. If the dif- 
 ferent gases be allowed to strain through a porous plug, into a vessel 
 from which the air has been removed by the air pump, they will enter 
 with different velocities, regulated by their specific gravities, precisely as 
 in the former instance ; and hence it is experimentally demonstrated 
 that different gases are ultimately permeable to each other, precisely as 
 the spaces they occupy would be, if entirely empty ; that the gases, in 
 fact, form vacua to each other, but that so far as the law of mixture and 
 the final effect are concerned, the mixture taking place more slowly, in 
 consequence of the mechanical obstruction. 
 
 This general principle had, however, been laid hold of by the keen 
 intellect of Dalton, and announced long before its truth had been accu- 
 
Law of Diffusion of Gases. 367 
 
 rately proved in the manner that has been now described ; to him we 
 are indebted for the first philosophical view of the molecular constitution 
 of the atmosphere ; he proposed to consider the different gases which 
 exist in the atmosphere, as being in all points independent of each other, 
 mixed uniformly in virtue of the diffusive power which he had been the 
 first to recognize, and exercising pressures upon the surface of the 
 earth, proportional to their quantities. Thus, if we suppose 100 parts 
 of atmospheric air to consist by weight of : 
 
 Nitrogen gas, . . . 75'88 
 
 Oxygen gas, . . . 2304 
 
 Watery vapour, . 
 Carbonic acid, 
 
 *1 
 
 04! 
 
 03 r 
 
 OoJ 
 
 The pressure of air being taken at thirty inches of mercury, the respec- 
 tive pressures of the independent atmospheres will be as follows : 
 
 Pressure of the nitrogen gas, 22764 inches. 
 ,, oxygen gas, 6-912 
 
 ,, watery vapour, 0'309 ,, 
 
 ,, carbonic acid gas, 0*015 ,, 
 
 30-000 
 
 The different constituents of air are thus in the state best suited to 
 the purposes for which the atmosphere is destined ; no one gas can 
 interfere with, or retard the others'' action; there are no affinities to be 
 overcome, or existing combinations to be broken up before the agency 
 of watery vapour, of carbonic acid, and of oxygen, can be brought 
 into the extended alternations on which the continued and happy exist- 
 ence of animal and vegetable life depends, from which arises the diver- 
 sity of aspect of our ever varying sky, and the gradual detrition of the 
 solid rocky materials of the earth's surface giving a fruitful soil. 
 
 By the processes of combustion and of respiration, which are in action 
 on the surface of the earth, the oxygen of the atmosphere is continually 
 removed, and an equal volume of carbonic acid generally substituted for 
 it. This carbonic acid is absolutely a narcotic poison, and the air 
 becomes unfitted for the support of life, before one-half of the quantity 
 of oxygen it contains has been consumed. A healthy man spoils in 
 twenty-four hours, by respiration, 726 cubic feet of atmospheric air, 
 that is, a mass of air eleven feet square and six feet thick. The burn- 
 ing of three ounces of charcoal produces the same effect. In many 
 factories, there are burned daily, ten tons of coal, which deteriorate at 
 least as much air as the same weight of charcoal, and hence each day, 
 by such a factory, there is rendered unfit for respiration, 3,185,760 
 
36S Permanency of Constitution of the Atmosphere. 
 
 cubic yards of air, which would cover to the depth of six feet, a space* 
 quarter of a mile in square. Nevertheless, it has been already 
 mentioned, that even in cities, the relative proportions of oxygen, nitro- 
 gen, and carbonic acid in the air, are but little altered, and it becomes 
 an object of great interest to ascertain, in what manner that perma- 
 nency, on which the stability, in truth, of all organized nature seems 
 ultimately to depend, has been secured. 
 
 In the first place, from the frequent occurrences of storms and violent 
 currents which agitate vast tracts of air, the accumulation of noxious gases, 
 or corrupted portions, cannot take place except in some rare and limited 
 localities, which do not affect the condition of the atmosphere even near 
 at hand ; and although the numbers which have been shown as indi- 
 cating the amount of air destroyed, become enormous when multiplied 
 by the number of breathing beings and the quantity of fuel burned on 
 the earth's surface, they yet bear but a trifling proportion to the im- 
 mensity of the aerial ocean in which we live. The atmosphere may be 
 considered as being, if brought, throughout, to its usual density at the 
 surface of the earth, about five miles deep ; and Prevost has calculated 
 that the loss of all the oxygen employed in respiration and combustion 
 for 100 years could not diminish its quantity by 7200 part, a quantity 
 quite too trifling to be detected by our methods, even had the exact 
 sciences flourished for such a period as to allow a comparison to be 
 made. 
 
 But, independent of this negative proof of permanence of compo- 
 sition, science has pointed out, in the peculiar relations of the functions 
 of vegetable and animal beings, a provision of adaptation to each other's 
 wants, which retains the atmosphere in a condition practically of eternal 
 identity of constitution. A healthy growing plant, exposed to sun light, 
 is found to absorb carbonic acid, and to emit oxygen from the surfaces 
 of its green leaves. In the dark, an inverse effect takes place; oxygen 
 being absorbed, and carbonic acid formed. The coloured parts of plants, 
 as flowers and fruits, absorb likewise oxygen, and emit carbonic acid, 
 but as the green surfaces preponderate so much, throughout the vege- 
 table world, and that the stimulus of light is active throughout the 
 greater portion of the twenty-four hours, the ultimate effect is, that an 
 action, the opposite of that which animals exercise upon the atmosphere, 
 is constantly going on. That which the plant rejects, is to the animal 
 the source of energy and of all vital powers, whilst the same substance 
 which the plant absorbs, and from which it forms its issues, has been 
 thrown out as useless by the animal, and would, if not removed, accu- 
 mulate in the end, and destroy all animal existence. 
 
 The most accurate experiments have determined, that 100 cubic 
 
Atmospheric Pressure. Barometer. 369 
 
 inches of atmospheric air, freed from moisture and carbonic acid, weigh 
 31-0117 grains; the barometer being at 30 inches, and the thermometer 
 at 60. Its specific gravity is taken as the standard for gases and 
 vapours, and is hence 1000. It is about 780 times lighter than water 
 as 40 '5 Fahrenheit, when water is at its greatest density, and is then 
 also 10,600 times lighter than quicksilver. 
 
 The weight of the atmosphere pressing upon the surface of the 
 earth, is equivalent to about fifteen pounds on each square inch of sur- 
 face. The existence of this pressure may be shewn in many ways : a 
 bladder or a thin plate of glass may be burst, if the pressure of the 
 air be removed from one side by the air pump, while it is allowed to 
 act against the other ; a pair of brass hemispheres which are easily 
 separated, whilst filled by air, are pressed very firmly together if the 
 air be removed from their interior. This pressure is equivalent to that 
 exercised by a column of mercury in a tube about thirty inches high, 
 and accordingly an instrument, the common barometer or pressure 
 measurer, is thus constructed, to register, at every moment, the pres- 
 sure which the atmosphere exercises. A tube closed at one end, and 
 about thirty-two inches long, is to be carefully filled with pure mer- 
 cury ; it is then inverted in a basin of mercury, and being placed in a 
 vertical position, the column of mercury sinks to a certain height in 
 the tube, generally between twenty-nine and thirty inches, leaving 
 about it, a space which is, at low temperatures, the most perfectly 
 empty that can be experimentally procured, and which, from the name of 
 the inventor of the instrument, is called the Torricellian vacuum. If the 
 external pressure varies, the height of the column of mercury alters 
 likewise, rising when the pressure increases, descending when it is 
 diminished; and as considerable changes in the amount of pressure 
 generally depend on violent motions in the air, which produce changes 
 in the weather also, the barometer is popularly regarded as a weather 
 glass, although no accurate indications of approaching changes can be 
 at all reckoned on from its use. 
 
 If the atmosphere preserved throughout its entire mass the same 
 density and elasticity which it possesses at the surface of the earth, its 
 height should be about five miles. But such is not the case; the 
 lower portions of the air which press upon the earth, are pressed upon 
 by the portions next over them, these again by those still higher up, so 
 that the amount of pressure, and consequently, the density of the air, 
 decreases continually, as we ascend through its mass. The rate of 
 diminution is even very rapid, forming a geometrical proportion when 
 the heights are taken in an arithmetic series ; and on this principle is 
 founded one of the most accurate modes of estimating heights that has 
 24 
 
370 Extent of the Atmosphere. 
 
 been yet discovered. If a barometer be carried to the summit of a 
 mountain, the column of quicksilver will be observed to be shorter 
 than it had been upon the plain, and the difference being marked, the 
 height corresponding to it is determined from a knowledge of the law 
 just stated. In practice there are corrections depending on tempera- 
 ture and other causes, to which it is not necessary to allude. So rapid 
 is this diminution of density, that one-half of the whole mass of the 
 atmosphere lies within three miles of the surface of the earth, and 
 four-fifths of it within eight miles. Hence, in those elevated regions, 
 the lungs receive, even in a deep inspiration, but little oxygen, and the 
 blood not being well arterialized, causes the headaches, lassitude, and 
 faintness, which those who ascend high mountains, or in balloons, feel so 
 severely. The lakes in the mountainous valleys of Switzerland and the 
 Andes are, for the like reason, destitute of fish ; the water holds no 
 air dissolved, to fit it for their respiration ; precisely as one may kill a 
 fish in water, by placing it under the receiver of the air-pump, and 
 abstracting the atmospheric air. 
 
 The question of how far the atmosphere really extends in space, 
 possesses, in relation to the views of the ultimate constitution of matter, 
 already noticed, considerable interest. If the particles of atmospheric 
 air were capable of division to an infinite degree, then the attenuation 
 which occurs in the higher regions of the air should have no limit, and 
 we should look upon all space as occupied by the elements which form 
 our atmosphere, rarefied to an inconceivably great degree, and that our 
 earth had provided itself, in its course through space, with as much of 
 this circumambient matter as, from its attractive power, it was able to 
 keep round it. If, on the other hand, the oxygen and nitrogen of the 
 air consist of molecules of definite form and size, these, being in the 
 gaseous form, are subjected to the simultaneous action of two forces, 
 one, the mutual repulsion which characterizes the gaseous condition, 
 and which causes their elasticity, but which, diminishing with this 
 elasticity, must become very small in the upper strata of our atmos- 
 phere ; the other, the general attraction of the earth, which, though 
 much inferior at the surface, must, since it diminishes but very little 
 in ascending so far, at a certain point become equal to the former, and 
 then all further expanding tendency being overcome, the atmosphere 
 should be terminated by a definite surface, similar in form to that of 
 the solid earth, having its tides and currents like those of our great 
 oceans, and from these various fluctuations in its depth, producing the 
 regular variations in the height of the barometer, the laws of which, 
 though complicated and obscured by the irregular motions of much 
 larger amount, have been detected. 
 
Poisson's Atmospheric Theory. 871 
 
 The amount of refraction proves that the sensible atmosphere does 
 not extend beyond 45 miles, at least, if it exist higher up, it must be 
 so rare as to have no effect in deflecting a ray of light. But other 
 considerations prove that the air does not extend through space. If 
 we had obtained our atmosphere by gathering up, in virtue of our 
 attracting force, the thin air which pervades all space, the other bodies 
 of our system should also possess atmospheres, whose densities should 
 represent the masses of the bodies they include. However, exact ob- 
 servation has shewn that even the largest bodies of our system possess 
 no atmospheres. A ray of light suffers no bending in its course, 
 although it passes by the edge of Jupiter, yet, from the immense size 
 of that planet, it should have collected round it an atmosphere so 
 dense, that by its refraction, a star should become visible to us upon 
 one side of it, before it had disappeared at the other. The sun, like- 
 wise, the gravitating centre of our system, does not possess a trace of 
 atmosphere sufficient to cause a sensible refraction. 
 
 Poisson has recently suggested a view of the constitution of our 
 atmosphere, upon grounds, however, so little connected with experi- 
 ment, that it would not be a subject for notice here, had it not been 
 introduced to the notice of chemists under the sanction of Dumas' 
 eloquent discourses. I will, therefore, briefly describe the theory he 
 has put forward. 
 
 The atmosphere, as we ascend, grows colder. The source from 
 which the atmosphere derives its heat is not the sun, but the solid 
 earth ; the solar rays passing tlirough the air, as they pass through 
 glass and all transparent bodies, without communicating much of their 
 heat. These heating rays are absorbed by the dark and rugged surface 
 of the earth. From this the layer of air next to it derives its warmth, 
 and hence, the farther from the earth the air is taken, the colder it is 
 found to be. Hence, even under the glare of a tropical sun, there 
 exists an elevation where the temperature never rises above 32, the 
 melting point of ice ; above that height all is eternal snow. Highest 
 above the level of the sea at the equator, being there 1 5,000 feet, this line 
 of perpetual congelation gradually descends, until, at the poles, it sinks 
 below the surface of the earth. In these countries we have no moun- 
 tains high enough to be capped with perpetual snow, the line of con- 
 gelation being 6,000 feet above the sea-level. 
 
 From this source, also, are derived the various phenomena of fog 
 and cloud, the production of snow, of hail and rain. The vapour 
 forming at the surface of a pond, is generated with an elasticity pro- 
 portional to its temperature, and when the air, thus mixed with vapour, 
 rises to a higher and colder stratum, the elasticity of the vapour is 
 
372 Production of Clouds, Dew, etc. 
 
 diminished, and a portion separates either as cloud or rain. Thus, if 
 air becomes loaded with vapour at the surface, having a temperature of 
 60, and that ascending, it becomes cooled to 40, the quantity of 
 water separated is thus found. 
 
 The elasticity at 60 is 0'524 inch of mercury. 
 40 is 0-263 
 
 the difference is 0'261 
 
 But 524:261::100:49'8 or nearly 50, and hence almost exactly, 
 one-half of the quantity of vapour carried up is deposited under the 
 form of cloud ; in addition to this, another portion of vapour that is 
 equal to about four per cent., is deposited, as liquid water, from the 
 circumstance of the diminution in volume of the mixture of gas and 
 vapour produced by the lowering of its temperature, so that there re- 
 mains as invisible vapour, only about forty-six, whilst fifty-four per 
 cent, are engaged in the production of the cloudy masses. The further 
 properties of clouds, the circumstances which determine the production 
 of rain, of snow, or hail, are of so little reference to chemistry, that I 
 shall pass from them without remark. 
 
 Reasoning from the principle that all gases may, by suitable reduc- 
 tion of their temperature, be reduced to the solid form, Poisson pro- 
 poses, to consider the atmosphere as being extended above the earth, 
 gradually becoming more attenuated and more cold, until it arrives at a 
 point at which its gases freeze ; there then should be a shell of transparent 
 colourless air-ice, lined on its concave surface with a sea of liquid 
 oxygen and nitrogen mixed or combined together. Erom such assump- 
 tion, Poisson proposes to render the theory of astronomical refractions 
 more definite and exact than it had before been, but those grounds can 
 scarcely be deemed sufficient to justify the adoption of that idea as a 
 physical reality. So far, in fact, as collateral evidence can be found, 
 the fundamental idea of Poisson's theory is disproved, for it results 
 from Fourier's researches on the distribution of Heat, that the temper- 
 ature of the planetary spaces cannot be below 57 of Fahrenheit, a 
 degree of cold which is met with in Melville Island during winter, and 
 which has been far exceeded by artificial means. At this temperature, 
 air shows no sign of even becoming liquid, far less solid ; and hence 
 the supposition of such a hollow sphere of frozen air cannot be granted. 
 
Nitrous Oxide. 
 
 373 
 
 OF THE COMPOUNDS OF NITROGEN AND OXYGEN. 
 
 Nitrous oxide . . N = 14'0 + O= 8 = NO =22-0 
 
 Nitric oxide . . N = 1 4-0 -j- 2O = 16 = NO* = 30 
 
 Hypo-nitrous acid . N = 14'0 -j- 3O = 24 = NOa = 38-0 
 
 Nitrous acid . . N = 14-0-J-4O = 32 = NO 4 = 46'0 
 
 Nitric acid . . N = 14-0+5O = 40 = NO 5 = 54'0 
 
 Nitrous Oxide. Protoxide of Nitrogen. NO. Eq. 22 or 275. 
 
 This substance, which exists, under ordinary pressure, in the gaseous 
 form, is best and most easily prepared by heating to about 350 Fah., 
 the crystallized nitrate of ammonia. This salt melts at 300 Fah., 
 into a colourless liquid, without being at all decomposed or losing 
 water, but when the temperature is raised to 350, a lively efferves- 
 cence occurs, and the salt is totally resolved into vapour of water and 
 nitrous oxide gas ; an equivalent of nitrate of ammonia producing two 
 equivalents of the gas, and four of water, thus : 
 
 N0 5 + NH 4 = 2(NO) +4 (HO). 
 
 The nitrate of ammonia mav 
 be placed in the flask a, im- 
 bedded in the little cup of sand. 
 A bent tube conducts the' gas 
 evolved to the pneumatic trough, 
 as in the figure, or to the gas- 
 ometer, if the quantity be 
 large. In this process the tem- 
 perature should not be allowed 
 to rise beyond the point at 
 which the effervescence is mode- 
 rately brisk ; for when the salt 
 becomes much hotter, the decomposition is tumultuously rapid, and the 
 gas obtained may not be at all pure. 
 
 The nitrous oxide gas so obtained is perfectly colourless and trans- 
 parent ; it is absorbed by water in moderate quantity, and hence the 
 water over which it is collected should always be heated to about 90 in 
 order to diminish the loss of gas thus suffered. It is heavier than air, 
 its specific gravity being T527. 
 
 A lighted taper burns with increased brilliancy in this gas, and if 
 blown out may be relighted, provided a pretty large portion of the wick 
 remains bright red. If the gas be mixed with its own volume of hydro- 
 gen, it may be inflamed by a taper or by an electric spark, and then 
 
374 Properties and Composition of Nitrous Oxide. 
 
 burns with a loud explosion. If phosphorus be heated in this gas, 
 it inflames and burns with almost as much brilliancy as in pure 
 oxygen. 
 
 In none of these instances does the nitrous oxide enter into combin- 
 ation. It is decomposed by the high temperature of the burning body 
 and the affinity of this last for oxygen, and the combustion is main- 
 tained by means of the oxygen which is thus disengaged. After the 
 process is completed, the nitrogen of the nitrous oxide remains free. 
 
 In this manner nitrous oxide may be analysed. If a little bit of 
 potassium or of phosphorus be heated in a measured quantity of the 
 gas until the decomposition is complete, and then the apparatus cool to 
 its original temperature ; it will be found that a quantity of nitrogen 
 remains exactly equal in volume to the nitrous oxide used, and the 
 quantity of oxygen absorbed is such, that in its gaseous form, it had 
 exactly half that volume. The nitrous oxide consists, therefore, of two 
 volumes of nitrogen and one of oxygen condensed to two volumes ; 
 and hence its specific gravity may be calculated, thus : 
 
 Two volumes of nitrogen, 976 X 2 = 1952-0 
 One volume of oxygen, . . 1105*6 
 
 give two volumes of nitrous oxide, . 3057'6 
 
 and one volume weighs, therefore, . 1 528 '8 
 
 By weight the composition of nitrous oxide and its equivalent num- 
 ber on each scale is expressed as follows : 
 
 Nitrogen, 63-9 One equivalent, 1 4'0 or 175 
 
 Oxygen, 36'1 8-0 100 
 
 100-0 22-0 275 
 
 and its formula is NO. 
 
 The most singular property of this gas is, that when breathed pure 
 for a few minutes it produces a lively and agreeable intoxication, which 
 does not leave any lassitude or disagreeable sensation when it goes off. 
 To prepare the gas for being breathed, it is necessary to attend to the 
 purity of the nitrate of ammonia used, as very frequently the salt 
 found in commerce contains muriate of ammonia, in which case the gas 
 obtained may be contaminated by nitrous acid and chlorine, and prove 
 very irritating to the lungs. To obtain the full effects of the gas upon 
 the system, four or five quarts must be introduced into an air-tight bag 
 or bladder, and inspired through a pretty wide glass tube. About two 
 ounces of nitrate of ammonia yield sufficient gas to intoxicate one 
 person. 
 
Preparation and Properties of Nitric Oxide. 375 
 
 Nitric Oxide. Leutoxide of Nitrogen. N0 2 . Eq. 30 or 375. 
 
 This substance exists naturally under the form of a gas which che- 
 mists have not as yet been able to reduce to the liquid form. It is very 
 easily prepared, being almost always the principal product of the decom- 
 position of nitric acid by any metal. 
 
 If a small quantity of quicksilver, or of copper cut into small bits, be 
 placed in the gas bottle, as in the figure, and diluted nitric acid, prepared 
 by mixing equal volumes of the aquafortis of commerce and of water, 
 be poured in by the funnel a, effervescence is immediately produced, 
 
 even without the application of heat, and the metal dissolves in the acid, 
 which becomes pale green coloured, if quicksilver had been employed, 
 but of a rich blue if copper had been used. Prom greater economy, 
 the latter metal is almost always that employed. Tor some time after 
 the action commences, the space in the bottle, over the liquid, is occu- 
 pied by reddish fumes, but these gradually pass away, and the gas may 
 be collected when the upper part of the generating flask being occupied 
 by it has become completely colourless. 
 
 The theory of this process is very simple ; a quantity of nitric acid 
 gives off three-fifths of its oxygen to the copper, and the nitrogen is 
 evolved in combination with the remaining two-fifths, forming nitric 
 oxide. The copper being thus oxidised combines with another portion 
 of nitric acid to form a fine blue salt, nitrate of copper, which exists in 
 the blue liquor, and may be obtained crystallized. Eor complete decom- 
 position four equivalents of nitric acid and three of copper are required, 
 and the action may be then expressed as follows : 4NO 5 and 3Cu give 
 3(N0 5 . CuO) and (NO 2 ). 
 
 By the action of organic substances, such as starch or sugar, upon 
 nitric acid, nitric oxide may also be formed in abundance, but it is not, 
 then, so uniformly pure, as when obtained by means of mercury or 
 copper. 
 
 This gas is colourless and transparent ; it is scarcely absorbed by 
 
376 Properties of Nitric Oxide. 
 
 water, and may hence be, on all occasions, collected over it. It is a 
 little heavier than air, its sp. gr. being 1041 ; its refractive index is 
 0*8761. A lighted taper plunged into this gas is extinguished, and a 
 red hot wire may be applied to phosphorus in it without inflaming it, 
 but if the phosphorus be already set on fire, it not only continues to 
 burn when plunged into the nitric oxide gas, but the combustion is 
 almost as brilliant as in pure oxygen. In this case, it is indeed in oxy- 
 gen and not in nitric oxide that the combustion actually occurs, for the 
 gas is decomposed by the high temperature of the burning phosphorus, 
 and being resolved into its constituents, the oxygen is the body with 
 which the phosphorus combines, and the nitrogen remains untouched. 
 
 In this way nitric oxide may be analysed, and is found to consist of 
 equal volumes of nitrogen and oxygen united without any condensation. 
 From this its specific gravity may be calculated : 
 
 One volume of nitrogen, = 976'0 
 One volume of oxygen, =1105-6 
 
 gives two volumes of nitric oxide, 2081'6 
 
 of which one is found to weigh, . 1040'8 
 
 Its equivalent volume is therefore 4, and its composition by weight 
 and its equivalent number on each scale is as follows : 
 
 Nitrogen, 46*95 One equivalent, = 175 or 14-0 
 Oxygen, 53-05 Two equivalents, = 200 or 16-0 
 
 100-00 375 30-0 
 
 and its formula is NO 2 . 
 
 Nitric oxide may be deprived of one-half of its oxygen, and so be re- 
 duced to the state of nitrous oxide, by remaining in contact for some 
 days with moist iron or zinc filings ; in this case its volume is reduced 
 to one-half. 
 
 The most remarkable property of nitric oxide is its tendency to unite 
 with oxygen, when this last is uncombined. Nitric oxide cannot take 
 oxygen from any other substance ; but when it is mixed with air, or 
 with any mixture of gases, of which oxygen is one, it unites with this, 
 forming deep red fumes. It is this which causes the red fumes in the 
 flask in which the nitric oxide is generated. The oxygen, in combining 
 with the nitric oxide, may form either hyponitrous acid (NOs) or 
 nitrous acid (N0 4 ), and they are both generally formed in uncertain 
 proportions. Hence, we cannot exactly calculate the quantity of oxy- 
 gen that liad been present ; and this process does not answer well for 
 gaseous analysis, but it is useful for removing oxygen from a gaseous 
 
Preparation of Hypo nitrous Acid. 377 
 
 mixture, which it effects completely if the nitric oxide be added 
 in excess. The red fumes so formed are soluble in water, and by 
 washing the mixed gases with water may, therefore, be completely 
 removed. 
 
 Xitric oxide combines with a great number of salts and with some 
 acids, to form compounds, which, in some respects, possess considera- 
 ble interest : these shall be noticed under those heads to which their 
 history more particularly belongs. 
 
 Hyponitrous Acid. NO 3 . Eq. 38 or 475. 
 
 The red fumes which are formed when nitric oxide is mixed with 
 atmospheric air or oxygen, consist in great part of hyponitrous acid, 
 particularly when the nitric oxide is in excess. To obtain it pure, four 
 volumes of nitric oxide should be mixed with one volume of oxygen, and 
 the vessel containing the hyponitrous acid vapour formed, exposed to a 
 cold of about 40 degrees below the freezing point of water. The acid 
 then condenses into a deep green- coloured liquid, which is excessively 
 volatile. When hyponitrous acid, either in the state of liquid or of 
 vapour, is brought into contact with water, it is in great part decom- 
 posed, being resolved into nitric oxide and nitric acid. Three equiva- 
 lents of hyponitrous acid 3(NO 3 ) giving 2(NO 2 ) and NO 5 . The same 
 occurs when it is acted on by bases dissolved in water, and hence, the 
 salts of this acid can only be prepared by indirect means. 
 
 When nitre has been kept melted for some time, so as to have parted 
 with a portion of its oxygen, it is reduced to the state of hyponitrite of 
 potash; KO 5 .KO, giving off 2O, and leaving M) 3 KO. This is known 
 by the hyponitrite being decomposed by acetic acid, and giving off 
 copious red fumes, whilst the nitrate of potash is unalterable by acetic 
 acid. The hyponitrite of potash cannot be crystallized, so as to free it 
 from the excess of unaltered nitre, but it may be converted into sparingly 
 soluble salts, as those of silver and of lead, and so pure salts of hyponi- 
 trous acid formed. 
 
 The specific gravity of the vapour of this acid has not been experi- 
 mentally determined. It consists of two volumes of nitrogen, united to 
 three of oxygen, but of their condensation we know nothing. Its com- 
 position by weight, and its equivalent constitution, are 
 
 Nitrogen, 37-11 One equivalent, = 175 or 14 '0 
 Oxygen, 62-89 Three equivalents, = 300 or 24'0 
 
 100-00 475 38-0 
 
378 Properties and Composition of Nitrous Acid. 
 
 Nitrous Acid. NO 4 . Eq. 46 or 575. 
 
 This substance presents itself, like the last, under the form of deep 
 red fumes, and is produced by an admixture of oxygen in excess with 
 nitric oxide. By a cold of about on Fahrenheit's scale, it .may 
 be rendered liquid. To form it directly, four volumes of nitric oxide 
 are to be mixed with two volumes of oxygen, and the mixture exposed 
 to a great cold ; but it is more conveniently prepared by means of the 
 decomposition of nitrate of lead by heat. 
 
 A quantity of finely-powdered and dry nitrate of lead is to be placed 
 in an earthenware or hard glass retort, and heated to full redness. The 
 red vapours that are produced are to be conducted into a receiver, care- 
 fully cooled by a mixture of snow and salt. They then condense into a 
 liquid, whilst a quantity of oxygen gas escapes, and oxide of lead 
 remains behind in the retort. The nitric acid of the nitrate of lead is 
 decomposed into nitrous acid and oxygen, as follows : N0 5 .PbO gives 
 PbO, N0 4 and free 0. 
 
 The liquid nitrous acid is nearly colourless at zero ; at 60 it is orange 
 yellow, and at 40 it solidifies into a white crystalline mass. It boils 
 at 82, and its vapour, which is ruddy red at that temperature, is almost 
 perfectly black at 212. In these variously coloured states, it exercises 
 remarkable absorbing power on light. The specific gravity of the liquid 
 acid is 1451. 
 
 Nitrous acid is the most stable compound of nitrogen and oxygen ; 
 it is not decomposed by a red heat ; it is decomposed in great part by 
 water, nitric acid being formed, and nitric oxide being given off as gas. 
 Thus, 3(NO 4 ) give NO 2 and 2(N0 5 )*. The nitric acid formed always 
 protects a portion of the nitrous acid from this reaction. 
 
 When the nitrous acid is formed by the direct union of nitric oxide 
 and oxygen, it is found that the six volumes of gas are condensed by 
 combination into two ; hence, the specific gravity of nitrous acid vapour 
 should be 3187'2; thus, 
 
 One volume of nitrogen, . . . 976*0 
 Two volumes of oxygen, . . . 2211-2 
 
 One volume of nitrous acid, . . . 3 187 '2 
 
 Its composition by weight, and the constitution of its equivalent, are 
 as follows : 
 
 Nitrogen, = 30-33 One equivalent, = 175 or 14-0 
 Oxygen, = 69'67 Four equivalents, = 400 or 32-0 
 
 575 46-0 
 
Preparation of Nitric Acid. 379 
 
 Considerable doubt has been tlirown upon the nature of this sub- 
 stance, for many chemists regard it as incapable of uniting with bases, 
 and hence, look upon it as a kind of acid salt, consisting of nitric and 
 hyponitrous acids combined together ; 2(NO 4 ) = NO 5 + NO 3 . But 
 late researches have shown that it does produce true salts, and that even 
 many saline compounds which had been supposed to be salts of hyponi- 
 trous acid, really contain this substance ; thus, the yellow basic salt, 
 formed by boiling a solution of nitrate of lead on metallic lead is a true 
 nitrite. I retain, therefore, for this body the old name of nitrous acid, 
 the more as that of peroxide of nitrogen, proposed for it by Graham, is 
 frequently applied to nitric oxide. 
 
 Nitric Acid. 
 NO 5 . Eq. 54 or 675. 
 
 It is found that when nitric oxide is brought into contact with a great 
 excess of oxygen over water, they combine in the proportion of four 
 volumes of the first to three of the second ; and when the red fumes 
 which are produced have dissolved in the water, this is found to be a 
 solution of pure nitric acid. Looking to the composition of nitric 
 oxide, we find in this manner that the nitric acid consists of two volumes 
 of nitrogen gas, united with five volumes of oxygen. 
 
 Although nitrogen and oxygen do not unite at once when directly 
 brought into contact with each other, yet they are capable of combining 
 under certain circumstances, and there is no doubt, but that a great, 
 although not the only source of nitric acid in nature, is the union of the 
 nitrogen and oxygen of the atmosphere. Although nitrogen is not strictly 
 inflammable, yet if some of it be mixed with hydrogen, and this mixture 
 be set on fire, the flame is coloured green, and the water formed is found 
 to contain nitric acid ; if a series of electric sparks be passed through a 
 quantity of air confined over a strong solution of potash, this gradually 
 loses its alcaline reaction, and after a time, crystals of saltpetre, (nitrate 
 of potash,) form in it. This may be shewn also, by simply moistening 
 some litmus paper with a solution of an alkali, and taking by means of 
 it, a succession of sparks from a strong electrical machine ; at the point 
 where the spark passes, the paper becomes reddened, and that nitric acid 
 has been formed, is shewn by its burning like touch paper, when dried 
 and set on fire. Rain water, particularly that which falls after a thunder 
 storm, contains a certain quantity of nitrate of ammonia ; the lightning 
 forming, as the electric spark does, nitric acid, in passing through the 
 air, and this then uniting with the ammonia which is always present in 
 our atmosphere from decomposing organic remains. 
 
380 
 
 Natural Sources of Nitric Acid. 
 
 In warm climates, where the abundance of organic matter and its 
 rapid decomposition, pour into the atmosphere a copious supply of 
 ammonia, the formation of nitric acid proceeds with extraordinary 
 energy, whether from the nitrogen of the air or the slow combustion 
 of the elements of the ammonia and the nitrate of ammonia so formed 
 being washed down by the rains, into the porous limestone soils, 
 the ammonia is again given off, whilst the ground becomes coated 
 with an efflorescence of earthy nitrates, when it dries on the cessation 
 of the rain ; a small quantity of nitrate of potash is also thus formed, 
 but the nitrate of lime, of which the crude produce of nitre principally 
 consists, is converted into saltpetre by means of carbonate of potash. 
 In this way there is formed in the East Indies, a quantity of nitrate 
 of potash sufficient to supply the wants of Europe. On the con- 
 tinent, this process is imitated in artificial nitre-beds, and large quantities 
 of home-made saltpetre are used in Prance and Germany for the manu- 
 facture of gunpowder. In South America, particularly in Chili and 
 Peru, there are found immense deposits of nitrate of soda, upon the sur- 
 face of the soil, and it is now extensively imported into these countries ; 
 the source of the nitric acid is, in this case also, from the elements of the 
 atmosphere, and of ammonia ; the alcali being probably derived from 
 the sea-salt, which the soils of the coast usually contain. 
 
 It is from the nitrates of soda or potash so produced, that the nitric 
 acid is always obtained. True nitric acid has never been isolated ; that 
 substance which is generally spoken of, as nitric acid, and which I shall, 
 unless especially remarked otherwise, be understood to mean in the fol- 
 owing account of its properties and preparation, is a compound of it 
 with water, it is a nitrate of water, or as it is popularly termed, liquid 
 nitric acid, or aquafortis. 
 
 To prepare liquid nitric acid from nitrate of potash, equal weights of 
 this salt and of oil of vitriol are mixed in a glass retort A, which is 
 
 placed in a furnace, supported 
 in a sand bath, as in the figure. 
 The oil of vitriol consists of 
 sulphuric acid and water, and 
 by the reaction which ensues, 
 the sulphuric acid combines 
 v with the potash of the nitre, 
 whilst the water of the oil of 
 vitriol uniting with the nitric 
 acid, forms the liquid nitric 
 acid, which distils over, and is condensed in the receiver, B. To render 
 the condensation more complete, this is surrounded by a net, and 
 
Preparation of Nitric Acid. 381 
 
 placed in a trough c c ; a stream of cold water flows continually on it 
 from the pipe i, and being distributed evenly over the surface by the 
 net work, flows out by the exit pipe of the trough I, and escapes into 
 d e. Using the proportions just noticed, (equal weights,) the quantity 
 of sulphuric acid present is double that necessary to neutralize the pot- 
 ash of the nitre, and to completely expel the nitric acid, for 
 
 The nitre consists of Oil of vitriol consists of 
 
 One atom nitric acid 54*0 One atom sulph. acid, 40*0 
 
 One atom potash, 47 3 One atom water, 9'0 
 
 101-3 49-0 
 
 These reacting upon each other, should produce, 
 
 Sulphate of potash consisting of Liquid nitric acid formed of 
 One atom sulph. acid, 40*0 One atom nitric acid, 54 '0 
 
 One atom potash, . 47'3 One atom water, . 9'0 
 
 873 63-0 
 
 And hence nitre might be decomposed by half its weight of oil of vitriol, 
 but the following reasons prevent those proportions being employed in 
 practice. 
 
 When oil of vitriol acts upon nitre, there is at first but one-half of 
 the sulphuric acid taken by the potash, and the sulphate of potash so 
 produced, unites with the remaining oil of vitriol, (sulphate of water,) 
 to form bisulphate of potash, thus, 2(S0 3 .HO) andKO.M) 5 give 
 
 (SO,. HO + KO.S0 3 ) and HO. N0 5 
 
 If there be oil of vitriol enough, the nitre is thus perfectly decom- 
 posed at a temperature not exceeding 260 F., and the bisulphate of 
 potash which remains, is very easily soluble and fusible, and may 
 hence be removed from the retort without inconvenience. But if the 
 nitre and oil of vitriol be used in the proportion of an equivalent of 
 each, or by weight in round numbers, of two parts of nitre to one of 
 oil of vitriol, then, one-half of the nitre remains at first totally unacted 
 on, and the retort contains, when the process is half finished, a pasty 
 mass of bisulphate of potash and of nitre, which do not fully act on 
 each other until the temperature rises to 400. The nitre is then de- 
 composed ; the nitric acid distils over, and there remains in the retort a 
 mass of neutral sulphate of potash, which can seldom be removed from 
 glass vessels with success. The high temperature necessary also in- 
 creases very much the risk of the apparatus breaking. 
 
 The scientific chemist or the apothecary, however, do not prepare 
 nitric acid ; it is made on the large scale for the purposes of the arts, 
 
382 
 
 Commercial Production of Nitric Acid. 
 
 and the processes of purifying the acid of commerce are so simple, that 
 no other source is required. On the great scale the nitric acid is pre- 
 
 pared, not in glass retorts, but in iron cylinders, connected with con- 
 densers, as represented in the figures, one being a section perpendicular 
 to the axes of the cylinders, and the other, a section parallel to the axes : 
 the same letters apply to both. 
 
 a is the grate, and d the ashpit of the furnace b. In each furnace 
 two cast iron cylinders, <?, c, are set, of such capacity that about 1J 
 cwt. of the nitrate used may be decomposed at once. The ends of the 
 cylinders are closed by covers, e, e, in one of which is fixed a tube f, 
 for introducing the oil of vitriol, and to the other is adapted a tube of 
 glazed earthenware, g, h, by which the vapours of the nitric acid are con- 
 ducted to the range of condensing jars of earthenware, fitted with safety 
 tubes, of which the first is seen in the figure, as k, I, k. The flues, 
 m, m, m, pass from the furnaces to the chimney, n. As in this appa- 
 ratus the temperature can be raised to dull redness without injury, and 
 that the residuum can be removed in the solid form, a smaller quantity 
 of oil of vitriol may suffice, and is generally used. 
 
 Since the introduction of nitrate of soda into commerce, it has almost 
 completely superseded nitrate of potash for making nitric acid. It is 
 much cheaper, and it yields a larger product. It does not require, 
 either, so much sulphuric acid, nor so high a temperature. The nitrate 
 of soda consists of 
 
 One equivalent of nitric acid, 
 One equivalent of soda, 
 
 54-0 
 31-3 
 
 85-3 
 
 and hence, 100 parts of it yield about 74 parts of liquid nitric acid, 
 whilst 100 parts of nitrate of potash yield 62. 
 
 In making nitric acid, there always occurs at the commencement of 
 the process, a disengagement of red fumes, which dissolve in the liquid 
 acid which comes next, and tinge it yellow. This arises from the oil of 
 vitriol in excess, abstracting the water from some of the nitric acid, 
 which then is decomposed into nitrous acid, and some oxygen becomes 
 
Preparation of Nitric Acid. 383 
 
 free. At the termination of the process, if the temperature pass much 
 beyond 300, there is a new evolution of red fumes, for the nitric acid 
 is then similarly decomposed into NO 4 and O. 
 
 The strongest nitric acid that can be thus made is of specific gravity 
 1-521, and consists of NO 5 + HO. 
 
 One equivalent of nitric acid, 54-0 or per cent, 85*71 
 One equivalent of water, . 9'0 14-29 
 
 63-0 100-00 
 
 It boils at 187 F., but cannot be distilled without partial decompo- 
 sition. The acid is very seldom obtained of this strength. In general 
 the specific gravity of the strong liquid acid is 1*500, and it consists of 
 2NO 5 + 3HO. 
 
 Two equivalents of nitric acid, 108'0 or per cent., 80*00 
 Three equivalents of water, . 27'0 20'00 
 
 135-0 100-00 
 
 When the nitric acid is gradually mixed with water, the boiling 
 point rises until when the specific gravity is T420, it boils at 248. 
 If it be further diluted, the boiling point is again lowered. At this 
 point, the acid has a definite chemical constitution; it consists of 
 N0 5 + 4HO. 
 
 One equivalent of nitric acid, 54-0 or per cent., 60'22 
 Four equivalents of water, . 36'0 39'78 
 
 90-0 100-00 
 
 The liquid nitric acid is, when pure, completely colourless, it fumes 
 when exposed to the air, and if exposed to the direct solar light, very 
 soon becomes deep yellow, whilst oxygen gas is disengaged ; the same 
 decomposition into nitrous acid and oxygen gas, may be instantly effec- 
 ted by passing the vapours of the acid through a red hot porcelain 
 tube. In a great variety of processes, where substances are to be 
 oxidized, nitric acid is employed. It acts with remarkable rapidity on 
 the generality of the metals and of organic bodies, supplying oxygen 
 for the constitution of a variety of new compounds, and being itself 
 reduced to the state of nitric or nitrous oxide, or even pure nitrogen. 
 
 If the organic body do not contain nitrogen, it is generally ultimately 
 converted into the oxalic and carbonic acids ; with animal substances, 
 new bodies are formed of a deep yellow colour, and hence the stains 
 produced upon the nails and fingers, where nitric acid touches, and it 
 is hence used for stamping the yellow patterns on woollen table covers. 
 
384 Purification of Nitric Acid. 
 
 The decomposition of the acid is generally accompanied by the produc- 
 tion of red fumes. 
 
 In its action on the metals, nitric acid presents some remarkable 
 anomalies; when of the specific gravity of 1*48, it may be put into 
 contact with tin or iron, without acting on those metals, although if a 
 little stronger or weaker, its action is very great, and this inactive acid 
 may be brought into activity by various means, as by touching the im- 
 mersed metal with another different one. These phenomena appear to 
 involve conditions probably electrical, which have been referred to in 
 describing the molecular relations of bodies. 
 
 The nitric acid prepared by decomposing nitre by half its weight of 
 oil of vitriol, is always of a deep red or orange colour, owing to a 
 quantity of the acid having been decomposed into nitrous acid, which 
 remains dissolved. This deep coloured acid is frequently useful, as it 
 gives off oxygen still more easily than the pure acid, and is hence some- 
 times applicable as an oxidizing agent where the colourless acid fails. A 
 deep red fuming acid may be prepared by passing a stream of nitric 
 oxide gas through the colourless acid ; it is absorbed in great quantity, 
 and the liquor assumes successively various shades of yellow, green, 
 and red colours, according to its state of dilution. The nitric oxide (N0 2 ) 
 decomposes the nitric acid (N0 5 ) and forms nitrous acid (NO 4 ) which 
 dissolves in the excess of liquid acid. This strong deep-coloured acid 
 is often termed nitroso-nitric acid. If it be required to obtain a 
 colourless acid, it is sufficient that the coloured acid should be boiled 
 for a few minutes ; all the nitrous acid fumes pass off, and the nitric 
 acid remains colourless, though somewhat weaker. 
 
 I have mentioned, that the nitric acid is not prepared on the small 
 scale, as the commercial aquafortis is easily purified. The impurities 
 of it are, generally, clilorine, arising from the nitre employed having 
 contained common salt, sulphuric acid, from some having been distilled 
 over by too great heat, and some iron arising from the cylinders or 
 stone ware bottles in which the acid is preserved. These may be easily 
 detected ; on mixing a few drops of the commercial acid with half an 
 ounce of distilled water, a drop of solution of nitrate of barytes will 
 give a precipitate, if sulphuric acid be present ; nitrate of silver will 
 indicate, by a precipitate, the presence of clilorine; whilst a little 
 solution of yellow prussiate of potash will form Prussian blue, if the 
 acid contain any iron. Prom these impurities, the acid may be freed 
 by being redistilled ; the chlorine passes off along with the portions 
 which first come over, and by thus testing from time to time the acid 
 which is obtained, it will be found no longer to precipitate the nitrate 
 of silver, and may then be considered pure ; the iron and sulphuric acid 
 
Detection !>/ Nitric Acid. 385 
 
 remain behind in the retort, provided the distillation be not pushed too 
 far. I have found, that from twelve pounds of commercial aquafortis, 
 there can be obtained eight quite pure, three being allowed to come 
 over first, to carry off the chlorine, and one being left in the retort with 
 the fixed impurities. This mode of purifying nitric acid is, however, 
 unsuited to any but laboratories, where other uses are found for that 
 portion in which the chlorine is concentrated. Another, and probably 
 the best, is to add to the commercial acid a strong solution of nitrate of 
 silver as long as the peculiar curdy precipitate of chloride of silver is 
 formed. When it is found that the silver has been added a little in 
 excess, the clear acid is to be poured off the precipitate and distilled : it 
 comes over quite pure : This mode is not costly, as all the silver is re- 
 covered from the chloride and may be reconverted into nitrate by 
 simple means, and thus the same quantity may be always used for this 
 process. 
 
 The detection of nitric acid is not difficult ; it cannot be recognized 
 by forming precipitates, as all its neutral salts are soluble, but its proper- 
 ties are, notwithstanding, very marked. 1st, The production of red fumes 
 by nitric oxide when it is brought into contact with a metal, is charac- 
 teristic of it. 2nd, When a drop of nitric acid is added to water tinged 
 blue by sulphate of indigo, and the mixture boiled, it is bleached by the 
 oxidizement of the indigo by the acid. 3rd, When a small crystal of 
 protosulphate of iron is placed in contact with water containing nitric 
 acid, a ring of deep olive coloured liquid forms round it, according as 
 it dissolves ; from one portion of the protosulphate reducing the acid 
 to the state of nitric oxide, which then combines with the remaining 
 protosulphate. 4th, Nitric acid confers upon muriatic acid the power 
 of dissolving gold leaf, but this test is not of such ^distinctness as the 
 others, from the same effect being produced by the chloric and some 
 other acids. 5th, Nitric acid may also be distinguished by the deep 
 red colour it produces with a crystal of morphia. 
 
 For the detection of a small quantity of nitric acid, the best plan is 
 to neutralize the liquor, if it be acid, by a solution of potash, and to 
 evaporate to dryness. The salt so obtained crystallizes irf sharp needles, 
 and deflagrates when placed on ignited charcoal ; heated with a little 
 bisulphate of potash and some copper filings it evolves copious red 
 fumes, and with a drop of sulphuric acid and a crystal o protosulphate 
 of iron produces the olive-coloured liquor already noticed. All solid 
 compounds of nitric acid, such as the basic nitrates, may be recognized 
 in this way. 
 
 The nitric acid, not being isolable, we do not know the state of con- 
 densation of its elements, which are united in the proportion of two 
 25 
 
386 Composition of Nitric Acid. 
 
 volumes of nitrogen to five of oxygen. Its composition by weight and 
 its equivalent numbers are as follows : 
 
 Nitrogen, 26' 15 One equivalent, == 175 or 14'0 
 Oxygen, 73-85 Five equivalents, = 500 or 40'0 
 
 100-00 :;: .. 675 54-0 
 
 The specific gravity of the vapour of the liquid nitric acid, HO.N0 5 , 
 is not known ; but Bineau has found the sp. gr, of the vapour of the 
 liquid acid which boils at 248, HO.M) 5 +3HO, to be 1243, which 
 might result from, 
 
 Two volumes of nitrogen, - ; v 976 X 2 = 1952-0 
 
 Five volumes of oxygen, . . 1 1 05 6 X 5 = 5528 -0 
 Eight volumes of watery vapour, . 622-1 X 8 = 4976 -8 
 
 condensed into ten volumes, 12456-8 
 
 of which one, therefore, should weigh, ... , ^,., . 1245-6 
 This result requires confirmation. 
 
 SULPHUR. 
 
 Symbol. S. Eq. 16 or 200. 
 
 This substance exists in large quantity in nature in combination. 
 The most important ores of copper, lead, silver, mercury, antimony, 
 and many other metals are their sulphurets ; and a great quantity of 
 the sulphur at present used in commerce is derived from the iron 
 pyrites, bisulphuret of iron. Sulphur is exhaled in large quantity also 
 from volcanoes, partly uncombined, partly in the state of sulphuret of 
 hydrogen, arising probably from the decomposition of metallic sulphu- 
 rets by the high temperature in the interior of the earth. The native 
 sulphur so produced condensing in fissures constitutes the great deposits 
 of volcanic sulphur of Sicily and other places, which supply a large 
 proportion of that employed in commerce. It exists also native, com- 
 bined with oxygen and various metallic oxides, forming native sulphates, 
 of which those of lime and of barytes are the most abundant. In 
 many organic bodies also sulphur exists as a constituent, as in the 
 white, and particularly the yolk of egg, the hair, the horns, and hoofs 
 of animals, and in the black mustard seed it exists in considerable 
 quantity. 
 
 The specific gravity and appearance of sulphur differs in its various 
 allotropic conditions (page 316) ; but at ordinary temperatures it exists 
 generally as an opaque solid, sp. gr. 1*98. When heated, it melts at 
 226 into an amber coloured thin liquid ; if the temperature be then 
 
Source and Properties of Sulphur. 
 
 387 
 
 raised to about 400 it becomes dark brown, opaque, and so thick that 
 the vessel containing it may be inverted without its pouring out, but 
 when heated further it becomes thinner, until at 601 its boiling point, 
 it is as thin and limpid as when first it began to melt. If the 
 sulphur, when just melted, be allowed to cool slowly, and the internal 
 .liquid be poured out when the outer crust 
 has solidified, the interior will be found lined 
 with crystals, as in the figure, which have 
 the form of the oblique rhombic prism, of 
 which a common modification with secon- 
 dary faces, and the surfaces of the octohe- 
 dron which determines the height of the 
 principal axis of the crystal is given. These 
 crystals, when first obtained, are transparent 
 and amber-coloured, but after a few days 
 they become opaque, sulphur yellow, and 
 friable, being then changed into the dimor- 
 phous state. 
 
 If the thick tenacious sulphur at 400 be suddenly cooled by immer- 
 sion in a large quantity of water, it forms a soft and transparent mass 
 of considerable elasticity, and may be drawn out into long threads 
 like Indian rubber; after some time, however, it changes into the 
 ordinary state. 
 
 Sulphur is used in pharmacy under two forms, that of roll and 
 ilowers ; the former is made by melting the rough native sulphur, and 
 pouring it into slightly conical moulds, in which it solidifies. The 
 flowers of sulphur are formed by the condensation of the vapour of 
 sulphur so rapidly that the molecules have not time to form crystals of 
 any perceptible size, so that the condensed sulphur, although really 
 crystalline, appears to the sight and touch as an impalpable soft powder. 
 
 Eor the manufacture of flowers of sulphur, the apparatus is arranged 
 as in the annexed figures, in which A is a vertical and B a horizontal 
 section, to which the same letters refer. In an apartment and shed, 
 
388 AUotropic Properties of Sulphur. 
 
 M, M, a chamber, A, is constructed, which must have at least 4 2000 
 cubic feet capacity. Outside of this chamber is an iron pan, c, in 
 which by a fire at o } the sulphur is kept gently boiling. The boiler 
 and fire-place must be completely surrounded by brick work, so that as 
 little heat as possible may be communicated to the vaulted chamber, A ; 
 the draught from the fire passes to the chimney, g ; the pan is sup- 
 plied with sulphur by the door, n } which can be closed air-tight; "the 
 vapour of sulphur mixes with the air in the wide space, d, over the 
 boiler, and, passing through the aperture, b, rises into the chamber, 
 where, mixing with the large mass of cold air, the sulphur is condensed, 
 and falls like a fine snow shower upon the floor underneath. When a 
 sufficient quantity of the flowers of sulphur have been thus formed, 
 they are removed by the door at jp. If, at the commencement of the 
 process, the mixture of sulphur-vapour and air should inflame, the ex- 
 plosion opens the valve at e, the gases escape at t, and all danger is avoided. 
 The form of crystal of sublimed sulphur is the right rhombic octo- 
 hedron, of which a common modification is represented 
 in the margin. Sulphur is found crystallized in this 
 form on the edges of the craters of most volcanoes, the 
 crystals being transparent, and sometimes of considera- 
 ble size. When sulphur is deposited from its solution 
 in chloride of sulphur or in sulphuret of carbon, it 
 is in this form also that its particles arrange them- 
 selves. 
 
 Sulphur may be obtained, however, in a state of much more minute 
 division, and destitute of all crystalline structure, by precipitation from 
 solution. Thus, if the persulphuret of potassium, K.S 5 , be decom- 
 posed by muriatic acid, sulphuretted hydrogen is evolved, and four 
 equivalents of sulphur are set free, which separate as a milk-white 
 powder, constituting the Sulp/mr Precipitatum of pharmacy. In 
 this form the sulphur retains a trace of sulphuret of hydrogen from 
 which it can be freed only by fusion, and the pure white colour may be 
 partly owing thereto, as when sulphur is precipitated by the action of 
 sulphurous acid on a persulphuret, the powder which separates is of 
 the proper sulphur yellow colour. 
 
 In these different allotropic states, sulphur is found to differ mate- 
 rially in its density as in its other physical characters. Thus the brown 
 transparent prisms formed by fusion have a Sp. Gr. 1*982. The 
 yellow crystals deposited from solution in sulphuret of carbon have 
 Sp. Gr. 2*0454. When the brown transparent prisms become yellow 
 and opaque, they become warm and their specific heat is lessened in the 
 proportion of {$. They contract in volume by 1*35 per cent, by 
 
Relations of Oxygen to SulpJiur. 389 
 
 the change into octohedrons. The natural crystals of sulphur have 
 Sp. Gr. 2-066. The soft sulphur, to which form every kind of preci- 
 pitated sulphur at first belongs, has a Sp. Gr. of 1/957 ; but it rises 
 to 2-0454 on becoming hard and opaque, assuming the condition of 
 the mass of octohedrons which appear to be the natural and stable con- 
 dition of this simple substance. 
 
 Sulphur is not soluble in water or in alcohol ; it dissolves in the oils; 
 still more in those liquids mentioned above. It dissolves in alkaline 
 solutions, or in milk of lime ; but there then occur complex reactions 
 which shall be studied hereafter. 
 
 When sulphur is boiled it forms a deep yellow vapour, the specific 
 gravity of which is 6648. Sulphur evaporates, however, very rapidly 
 long before it boils, and even forms some vapour below its melting 
 point. At a temperature of about 300 it takes fire, burning with a 
 bluish violet flame, and forming sulphurous acid (S0 2 .) 
 
 The resemblance of sulphur to oxygen in its chemical relations, is 
 very striking ; by combining with the same bodies, according to the 
 same proportions, they generate completely parallel classes of acids, 
 bases, and salts. Thus with carbon and potassium there are formed 
 
 C.O2 Carbonic acid, 
 K.O Oxide of potassium. 
 
 KO.CO 2 Carbonate of potassium, 
 and with arsenic and potassium. 
 
 AsO 5 Arsenic acid. 
 
 KO Oxide of potassium. 
 
 KO.AsO 5 Arseniate of potassium. 
 
 CS-2 Sulpho-carbonic acid. 
 KS Sulphuret of potassium. 
 
 KS.CS 2 Sulpho -carbonate of potassium. 
 
 AsSs Sulpharsenic acid. 
 
 KS Sulphuret of potassium. 
 
 KS. AsSo Sulpharseniate of potassium. 
 
 In like manner, the similar compounds 3?e 3 O 4 and Fe 3 S 4 are not 
 altered by heat, but are magnetic, whilst EeSa and MnO 2 give out 
 oxygen and sulphur, and are reduced to Fe 3 S 4 and Mn 3 O 4 . I shall 
 have frequent occasion to revert to these considerations, which have 
 already been noticed under a different point of view, (p. 328.) 
 
 The equivalent number of sulphur is 16'0 or 200-, and its com- 
 bining volume one-third that of oxygen. 
 
 The compounds of sulphur are very numerous and important, thus 
 it combines with oxygen in several proportions, forming 
 
 Sulphurous acid, . . . SOz. 
 Sulphuric acid, . . . SO 3 , or SO 2 .O. 
 
 Hyposulphurous acid ,. . SaO^, or SOjS. 
 
390 Preparation and Properties 
 
 There is further a group of acids, all of which agree in containing 
 in their equivalent, five atoms of oxygen, but differ in the quantity of 
 sulphur which is at least two atoms. The nomenclature of this group 
 is usually very complex, but I shall endeavour to simplify it by calling 
 them generically the T/donic acids, to distinguish them from the sul- 
 pJiuric acids, in which the quantity of oxygen is three atoms, and then 
 the proportion of sulphur may be indicated by the prefix of a Greek 
 numeral. Thus the first of the series being what has been usually 
 termed the Hyposulphuric acid, = S 2 O 5 , it becomes 
 
 Deutothionic acid = 8265 and there are 
 
 Trithionic acid = SsOa acid of Langlois. 
 
 Tetrathionic acid = 8405 acid of Fordos. 
 
 Pentathionic acid = SsOs acid of Wackenroeder. 
 
 There are also described two acids having the formulae S 8 O, and 
 S 5 6 . But the information regarding them is very imperfect. 
 
 We shall proceed now to the study of those acids of sulphur in 
 detail. 
 
 Sulphuro^ls acid. S0 2 Eq. 32 or 400. 
 
 Sulphurous acid exists at ordinary temperatures and pressures in the 
 gaseous form ; it is one, however, of the most easily liquefied gases. 
 It is produced always when sulphur burns either in air or in pure 
 oxygen, sulphur not being capable of passing directly to a higher 
 degree of oxidation. In the burning of sulphur, the volume of 
 sulphurous acid gas formed is exactly equal to that of the oxygen con- 
 sumed. 
 
 When required pure, it is prepared generally by decomposing sul- 
 phuric acid, by means of a metal not very easily oxidized, as mercury 
 or copper. The metal combines with one atom of the oxygen of the 
 sulphuric acid, and the sulphur, with the remaining two atoms of 
 oxygen, pass off as sulphurous acid gas ; the oxide formed unites with 
 the remaining sulphuric acid to form a salt. Thus, if mercury be used, 
 S0 3 and Hg give SO 2 and HgO, and HgO unites with SO 3 to form 
 sulphate of mercury. If the heat be not raised beyond 200 in this 
 process, it is black oxide of mercury which is produced, (Hg 2 O) but 
 above that degree the red oxide (HgO) alone is formed. 
 
 Sulphurous acid gas may also be very simply prepared by heating 
 three parts of flowers of sulphur with four of peroxide of manganese. 
 The reaction is very simple, one part of the sulphur uniting with the 
 metal, and another with the oxygen, form sulphuret of manganese and 
 sulphurous acid ; thus, Mn02 and 2S give MnS and SO 2 . The appa- 
 
of Sulphurous Acid. 391 
 
 ratus used in these processes may be those figured under the heads of 
 oxygen (p. 334) or nitrous oxide (p. 373.) 
 
 Sulphurous acid gas is absorbed by water ; and hence, in order to 
 examine its properties in that state, it must be collected over mercury. 
 It is colourless and transparent, possessing an odour peculiarly irritating, 
 (the smell of burning sulphur,) and cannot be breathed. It is not com- 
 bustible, nor does it support combustion. It bleaches a variety of 
 vegetable and animal bodies, and is hence used in the arts to whiten 
 straw bonnets, corn, silk, sponges, and other substances. The bleaching 
 is produced by the sulphurous acid combining with the coloured sub- 
 stance, and forming a white compound, from which the gas gradually 
 escapes on exposure to air, and hence, such bleaching is not permanent. 
 The sulphurous acid may be expelled, also, from this kind of compound 
 by a stronger acid, and the colour generally restored ; thus, if a red rose 
 be exposed to the fumes of burning sulphur, it becomes completely 
 white, but if washed in dilute sulphuric acid, its red colour is perfectly 
 renewed. 
 
 The specific gravity of sulphurous acid gas is, 2213*6, and it is 
 formed by 
 
 One volume of sulphur- vapour, . . 6648-0 
 Six volumes of oxygen, . . . 6633*6 
 
 The seven volumes condensed to six, give . 13281-6 
 
 Weight of one volume of SO 2 . . 2213-6 
 
 When this gas is exposed to a cold of 0F, it condenses into a liquid 
 heavier than watS 1 , which boils at 14, and produces by its evaporation, 
 a very intense cold ; it is easily obtained in the liquid form, by putting 
 a quantity of mercury and oil of vitriol into a tube, and sealing up the 
 
 ends, as in the figure ; on applying 
 heat to the extremity a, containing 
 those materials, and cooling the 
 other end by means of ether, the 
 gas evolved is liquefied by its own pressure, and collects in quantity 
 at I. 
 
 When a large quantity of sulphurous acid is required dissolved in 
 water, or that it is to be employed to form compounds with bases, it may 
 be produced in a much cheaper way than those described above. Into 
 a matras a, placed in a furnace, is introduced a quantity of well burned 
 charcoal, in bits about the size of a hazel nut, and by means of the safety 
 funnel I, as much oil of vitriol is poured in, as that the mixture shall 
 
392 
 
 Composition of Sulphurous Acid. 
 
 about half fill the vessel; a tube passes to a bottle i, containing 
 
 some water to wash the gas 
 from any adhering sulphuric 
 acid, and it is then conducted 
 by the tube^ which passes to 
 the bottom of the vessel k, 
 containing the liquor in which 
 the gas is to be dissolved. 
 On applying heat, the carbon 
 of the charcoal abstracts from 
 the sulphuric acid one-third 
 of its oxygen, so that with 
 C and 2SO 3 there are formed 
 C0 2 and 2SO 2 ; there is pro- 
 duced a mixture of two vo- 
 lumes of sulphurous acid and one of carbonic acid, which last cannot 
 enter into combination, and passes off from the apparatus without 
 change. 
 
 Water dissolves about thirty-seven times its volume of sulphurous 
 acid ; the solution possesses the properties of the gas in a very high 
 degree, and bleaches vegetable colours with great power ; when kept for 
 some time, it gradually absorbs oxygen, and the sulphurous becomes 
 changed into sulphuric acid. 
 
 The sulphurous acid is one of the feeblest acids, and is expelled from 
 its combinations, by almost all but the carbonic acid. Of its salts, those 
 which are soluble, all possess alcaline reaction. 
 
 The sulphurous acid passes into the state of sulphu^c acid, by absorb- 
 ing oxygen ^from many bodies, thus when it is heated with a solution of 
 gold or silver, or of mercury, these metals are reduced to the metallic 
 state ; others yield but a part of their oxygen ; thus, the peroxide of 
 iron abandons a third, and the black oxide of copper one-half of that 
 constituent. 
 
 The salts of sulphurous acid possess the same deoxidizing power. 
 The composition and equivalent of sulphurous acid is as follows : 
 
 Sulphur, 50-00 One equivalent, == 200'0 or 16'0 
 Oxygen, 50'00 Two equivalents, = 200-0 or 16-0 
 
 32-0 
 
 100-00 400-0 
 
 Sulphuric Acid. 
 S0 3 . Eq. 40 or 500. 
 
 Sulphuric acid, one of the most important compound bodies, from 
 the energy of its action, and the variety of combinations which it forms, 
 
Preparation of SulpJiuric Acid. 
 
 393 
 
 is not produced by the direct union of oxygen and sulphur, in any case, 
 but arises from the combination of sulphurous acid with another quantity 
 of oxygen. Thus, by the action of sulphurous acid on the easily redu- 
 cible metallic oxides, sulphuric acid is produced. This principle is 
 beautifully shewn, by passing a mixture of sulphurous acid gas and air, 
 through a tube filled with spongy platinum, and heated to dull redness, 
 when there issues from the extremity, a mixture of vapour of sulphuric 
 acid, mixed with the residual nitrogen of the air ; by such processes, 
 however, it could not be formed in quantities suited to the purposes of 
 commerce. 
 
 The preparation of sulphuric acid is effected upon the large scale, by 
 bringing sulphurous acid, produced by the burning of sulphur, into 
 contact with watery vapour and nitrous acid fumes. In this case the 
 necessary quantity of oxygen is transferred from the nitrous fumes to the 
 sulphurous acid, sulphuric acid being formed, which combining with the 
 water present, produces oil of vitriol, and nitric oxide is disengaged. 
 This, however, as there is an excess of air present, immediately taking 
 oxygen, forms a new quantity of nitrous or hyponitrous acid which 
 oxidizes a new quantity of sulphurous acid gas, and thus a very small 
 quantity of nitrous fumes will serve by a succession of changes to con- 
 vert a large quantity of sulphur into oil of vitriol. It is most probable 
 that on the great scale the reaction does take place in this simple man- 
 ner, but the remarkable affinity which sulphuric acid exercises for the 
 oxide of nitrogen, gives rise to the appearance of some peculiar bodies 
 which must be noticed. 
 
 Sulphuric acid, whether dry or as oil of vitriol, combines with nitric 
 oxide to form a crystallizable solid of remarkably definite composition 
 and properties, which may be termed nitro-sulphuric acid. Its formula, 
 when thus prepared, is NO 2 +S0 3 . It is white ; when heated it distils 
 unchanged. It is decomposed by water into oil of vitriol and nitric 
 oxide. This body always forms in some quantity in the manufacture of 
 nitric oxide, and owing to it the theory of its formation has been sup- 
 posed to be much more complex. 
 In fact when we bring together moist 
 sulphurous acid and nitrous acid 
 gases, these unite to form a white 
 crystalline solid, which appears to be 
 a compound of sulphuric and hypo- 
 nitrous acid (SO 3 -f-N0 3 ) mixed with 
 a quantity of sulphuric acid and 
 water which is not constant. The 
 formation of this substance may be 
 
394 Formation of Sulphuric Acid. 
 
 shown by the arrangement in the figure. The central vessel, the inner 
 surface of which is slightly moistened, contains atmospheric air; by 
 means of the tubes, sulphurous acid gas generated in the flask, a, and 
 nitric oxide formed in b, are introduced, to the latter of which the oxy- 
 gen is supplied by the air to form nitrous acid fumes ; the interior of 
 the vessel becomes gradually covered with a deposit like hoar frost, con- 
 sisting of this substance, and in order that its production may proceed 
 without interrupption, the vessel may be filled with fresh atmospheric 
 air, by blowing through one of the tubes c, d, whilst the residual gases 
 are expelled through the other. 
 
 This crystalline substance is decomposed by a larger quantity of 
 water ; hence if the bottom of the central vessel be covered by a layer 
 of water, the crystalline substance falling into it, according as it is gene- 
 rated, separates into oil of vitriol and hyponitrous acids ; thus, SO 3 + 
 NO 3 , gives S0 3 , + HO, and, N0 3 , which last is decomposed by the ex- 
 cess of water into nitric acid and nitric oxide, 3N0 3 giving N0 5 , and 
 2 NO 2 ; the nitric acid remains combined with the water along with 
 the sulphuric acid, whilst the nitric oxide escaping with effervescence, 
 generates, on arriving at the air, a new quantity of red fumes, and oxi- 
 dizes a new quantity of sulphurous acid. 
 
 It was supposed, that a certain quantity of water was necessary to the 
 existence of this solid body, although a larger quantity decomposed it, 
 but it has been found, that a similar substance may be formed which 
 contaics no water. Sulphurous and nitrous acids do not act on each 
 other when in the gaseous form, unless water be present, but they com- 
 bine if placed in contact under considerable pressure, and liquid, even 
 when completely dry. A portion of the nitrous acid converts an equi- 
 valent of the sulphurous acid into sulphuric acid, it being itself reduced 
 to the state of hyponitrous acid ; whilst another quantity of nitrous and 
 sulphurous acid unites directly ; there are thus formed from 2S0 2 and 
 2NO 4 a white crystalline solid SO 2 . NO 4 with S0 3 and a quantity of N0 3 , 
 which is given off, on the tube, in which the combination is produced, 
 being opened. 
 
 It may be questioned, however, whether this substance interferes in 
 the formation of sulphuric acid on the large scale, where the nitrous and 
 sulphurous acids act on one another in the gaseous forms in presence of 
 a large excess of air and water, and I agree with Berzelius in consider- 
 ing the .phenomena sufficiently explained by the more simple theory 
 previously given. 
 
 In the manufacture of sulphuric acid, the apparatus consists of a long 
 leaden chamber, constructed in two portons ; the lower, a tray of about 
 ] \ feet deep, the other, a quadrangular bell, which being suspended on 
 
Manufacture of Oil of Vitriol. 
 
 395 
 
 wooden frame work, b, I, rests with its edges immersed in the liquid, 
 with which the tray is filled, like the cylinder of a bell gasometer. The 
 bottom of the chamber, which is supported at a certain distance from 
 
 ; 
 
 the ground on pillars, 0, a, a, slants from before, so that the liquid 
 which occupies it increases in depth towards the end. Under the front 
 is placed a furnace, d, on the floor of which, e, the sulphur is burned, 
 and the sulphurous acid passes into the chamber by the chimney/; the 
 heat necessary is supplied by the fire-place under e ; the nitrous acid is 
 obtained by placing over the burning sulphur in e a pan, containing a 
 quantity of nitrate of soda and oil of vitriol, the nitric acid evolved 
 from which directly oxidizes a portion of sulphurous acid, and then 
 being brought to the state of NO 4 acts on the mass of sulphurous acid, 
 as has been just described : g is a boiler, by which steam is driven into 
 the chamber at h, and thus, in the interior, are provided the conditions 
 for the reunion of steam, sulphurous acid gas and nitrous acid fumes, 
 which may produce, as in the apparatus figured already, the white crystal- 
 line solid, by which, when decomposed by the water at the bottom of the 
 chamber, the sulphuric acid is produced, and nitric oxide gas evolved. 
 This nitric oxide, mixing with the atmospheric air, which is always 
 present in large excess in the interior of the chamber, is reconverted 
 into nitrous acid, which combines with a new quantity of sulphurous 
 acid generating another proportion of the solid body, from whose de- 
 composition by the water the nitric oxide is again evolved with little 
 
396 Manufacture of Oil of Vitriol. 
 
 loss; and thus the oxygen of the air is gradually transferred to the 
 sulphurous acid by the intermediate agency of the nitrous acid fumes. 
 Were there no nitric acid formed, the same quantity of nitric oxide 
 might convert an infinite quantity of sulphurous acid into sulphuric 
 acid ; but as the oil of vitriol produced always retains a certain portion 
 of the nitric acid, it is necessary to supply its loss, and to send into 
 the chamber a continued current of nitrous acid fumes. This is secured 
 by the construction already described; about one part of nitrate of 
 soda being decomposed for every eight or nine parts of sulphur burned 
 in the furnace, d } e. The draught is regulated by the chimney, <?, which 
 is fitted with a valve, by the position of which a current of air is 
 established through the chamber sufficient to bring the gases into com- 
 plete mixture inside, and in due proportions, but which does not carry 
 them away until their action is complete. 
 
 The inclination given to the bottom of the chamber is for the purpose 
 that the water, which having dissolved most of the sulphuric acid, be- 
 comes heaviest, shall flow down to the farthest end, antl thus there shall 
 be, on the surface next the front, a layer of the weakest acid, ready to 
 absorb and decompose the great quantity of the crystalline body formed 
 when the mixed sulphurous and nitrous acid gases meet the damp atmo- 
 sphere of the chamber. 
 
 The water in the chamber is allowed to remain unchanged until it 
 has attained a specific gravity of about 1*600; it is then removed by 
 leaden pipes, and concentrated by evaporation in leaden cisterns, until 
 its specific gravity is increased to about 1'76. When so strong, it 
 begins to act on the lead, and must be transferred to vessels of glass, or 
 still better, of platinum, in which the concentration may be finished. 
 In the strongest form in which it can be so obtained, its specific gra- 
 vity is 1'847, and it contains 8T64 of real acid in 100. 
 
 It is found that the white crystalline body already described as en- 
 gaged in the conversion of sulphurous into sulphuric acid, dissolves in 
 some proportion in the oil of vitriol produced and becomes, under cer- 
 tain circumstances, a very disadvantageous impurity. Thus it corrodes 
 the leaden or even platinum vessels in which the acid is concentrated, 
 and it injures the colour of indigo when dissolved in the oil of vitriol. 
 It is best removed by the addition of a small quantity of sulphate of 
 ammonia, which it decomposes, and the nitrogen of both bodies is given 
 off as gas. SOa + N0 3 and S0 3 + NH 3 giving 2S0 3 . 3HO and 2N. 
 This compound of hyponitrous acid, and sulphuric acid, may also be 
 separated by distillation. The pure oil of vitriol passing over first, and 
 the residue may be so concentrated as that the nitro-sulphuric acid shall 
 crystallize out on cooling. 
 
Fuming Sulphuric Acid. 397 
 
 Thus is the oil of vitriol of commerce manufactured. Latterly, a 
 modification of the process has been introduced, in consequence of the 
 extensive use of the iron pyrites (bisulphuret of iron, FeS 2 ), in place of 
 sulphur, as the source of the sulphurous acid. Instead of the furnace, 
 e,f, there is built, in front of the chamber, a kiln, somewhat like a 
 limekiln, except that it is narrowed at top into a chimney passing into 
 the chamber. At the bottom of the kiln is placed a^layer of coal or 
 wood ; on it the pyrites in small pieces. The fire is lighted, and the 
 ignition being communicated to the pyrites, the sulphur burns, forming 
 sulphuric acid, which is conducted into the chamber, whilst the iron 
 remains behind as the peroxide. The pan with nitre and oil of vitriol 
 is supported in the kiln at such a height above the mass of burning 
 pyrites, as that the temperature may not be too great. According as 
 the combustion proceeds, new quantities of pyrites are introduced by 
 apertures high up in the kiln, whilst the residue of adherent rock and 
 oxide of iron is raked out from the ashpits at the bottom. The iron 
 pyrites being, however, always intermixed with the arseniuret of iron, 
 the oil of vitriol so manufactured contains often a large quantity of 
 arsenic, which unfits it for all medical uses and for many uses of the 
 arts. It can scarcely be purified. 
 
 Fnming Sulplmric Acid. A form of sulphuric acid is prepared upon 
 the Continent, and known as German oil of vitriol, or fuming sulphuric 
 acid, which is much stronger than can be made by the combustion of 
 sulphur, as has been described. It is obtained by exposing sulphate of 
 iron to a red heat, in earthen retorts. If the sulphate of iron, perfectly 
 dry, be strongly heated, the sulphuric acid is driven off, and oxide of 
 iron remains behind, but the acid is mostly resolved into sulphurous 
 acid and oxygen, and consequently lost. But if the sulphate of iron be 
 not completely dried, the sulphuric acid combines with the water, and 
 distilling over in combination with it, forms a dark coloured liquid, of a 
 thick, oily consistence, specific gravity about 1*9, and consisting gene- 
 rally of about 90 of real acid and 10 of water, in 100, approaching 
 closely to the formula 2S0 3 + HO. At the same time, a quantity 
 (one-half) of the acid is decomposed, the iron becomg peroxidized, and 
 sulphurous acid gas being evolved. Thus 4(SO 3 -f- FeO) and HO give 
 2SO 3 + HO and 280^ leaving behind 2Fe 2 O 3 , known in commerce as 
 colcothar of vitriol. 
 
 This process is carried on in a long furnace, in wliich are ranged 
 
 about 120 earthen retorts, as i, in rows 
 of 20, containing the partially dried sul- 
 phate of iron. They are gradually heated, 
 until the fumes of sulphuric acid begin to appear, and the receiver, A, 
 
398 Anhydrous Sulphuric Add. 
 
 is then attached, in which the acid is condensed by means of cold applied 
 externally. 
 
 When this fuming sulphuric acid is heated, it is resolved into ordi- 
 nary oil of vitriol and real sulphuric acid. This last being very volatile, 
 distills over in colourless vapours, which, on coming into contact with 
 moist air, forms dense white fumes of liquid acid. If the colourless 
 vapour be received in a dry vessel, cooled by a freezing mixture, it con- 
 denses in beautiful white satiny fibres, constituting the dry sulphuric 
 acid. This acid melts at 77, and very little above that temperature it 
 boils. The specific gravity of its vapour is 2766, formed by 
 
 One volume of vapour of sulphur, . . = 6648*0 
 Nine volumes of oxygen, . 11056x9= 9950-4 
 
 The ten volumes forming six, . = 16598 '4 
 
 Of which one weighs, therefore, . . . 2766 '4 
 
 When this dry sulphuric acid in vapour is brought into contact with 
 dry barytes, lime, or magnesia, they combine with brilliant combustion, 
 forming sulphates of those earths. When a mass of the crystals is 
 thrown into water, it hisses as on the immersion of red hot iron, and 
 ordinary liquid sulphuric acid is produced. 
 
 There exist several definite compounds of sulphuric acid with water, 
 of which the most remarkable are two ; the first is the strongest oil of 
 vitriol made in this country, and contains an equivalent of acid united 
 to one of water ; its formula is S0 3 + HO ; its most important proper- 
 ties have been already described. The other contains twice as much 
 water; its formula being S0 3 -f- 2HO; its specific gravity is 1780. 
 When exposed to the temperature of melting ice, this acid forms large 
 and regular crystals, whilst the stronger or weaker acids require very 
 intense cold to solidify them. When oil of vitriol is mixed with water, 
 the great heat which is produced results from the formation of definite 
 compounds ; and it has been already shewn, (page 245,) that no matter 
 what combination a certain quantity of sulphuric acid forms, it evolves 
 the same quantity of heat on entering into union. 
 
 Sulphuric acid, formed by the combustion of sulphur, as described, 
 in leaden chambers, is liable to be contaminated by the presence of some 
 nitric acid and of lead ; from these it may be freed by redistillation, 
 which should, however, be conducted with great care, as the vapour of 
 the acid forms interruptedly and by sudden bursts, which might 
 endanger the apparatus. On diluting common oil of vitriol, a white 
 powder is generally seen to form, which is sulphate of lead, that had 
 been held in solution by the strong acid, but which the diluted acid lets 
 
Hyposidphurous Acid. 399 
 
 precipitate. The acid now formed from the iron pyrites is found to 
 contain frequently arsenic and selenium; the presence of the former 
 may become of great importance in medico-legal investigations, and the 
 detection of it will be fully described in its proper place. 
 
 Sulphuric acid is very easily detected by means of a solution of 
 nitrate of barytes or of nitrate of lead. If the smallest quantity of sul- 
 phuric acid be present, a white precipitate is formed, which is insoluble 
 in dilute muriatic acid, even when boiled. 
 
 Sulphuric acid appears to dissolve certain bodies in small quantity, 
 which are not soluble without alteration in any other medium. These 
 are sulphur, carbon, tellurium, and selenium. These solutions are not, 
 however, of any independent interest. 
 
 Hyposulphurous Add. 
 
 nyposuipnurous Acid. 
 S 2 O 2 or SO 2 + S. Eq. 48 or 600. 
 
 i r\T cntlWnvWATta nsvirl *~ro /Gil \ ic< i~*ooi 
 
 When a stream of sulphurous acid gas (S0 2 ) is passed into a solution 
 of sulphuret of calcium, it is absorbed, a quantity of sulphur is pre- 
 cipitated, and the liquor, when filtered, is found to be a solution of 
 hyposulphite of lime. The reaction which occurs is simple. Half of 
 the oxygen of the sulphurous acid passes to the calcium, to form lime, 
 reducing the sulphurous to the state of hyposulphurous acid, and, at 
 the same time, the sulphur which has been combined with the calcium 
 is set free. 2CaS and 2SO 2 giving 2CaO + S 2 O 2 , whilst 2S is 
 precipitated. 
 
 This acid is also formed when sulphur is boiled with an alkaline 
 liquor, or with milk of lime. Thus, when soda and sulphur are boiled 
 in water, the liquor contains hyposulphite of soda and sulphuret of 
 sodium, produced by 3NaO and 4S giving NaO + S 2 O 2 and 2Na.S. 
 
 This acid itself is very easily decomposed; it may, however, be ob- 
 tained, at least for a time, in a free state, by adding to any of its salts 
 a stronger acid ; or better, by bringing sulphurous acid and sulphuretted 
 hydrogen gas to meet in water; the reaction which occurs is that 
 4S0 2 and 2SH give 3S 2 O 2 and 2 O.H. The water gradually becomes 
 intensely sour, but after some time, this acid resolves itself into sulphur 
 and sulphurous acid. 
 
 The most remarkable character which the compounds of hyposul- 
 phurous acid possesses,. is, that they dissolve those compounds of silver 
 which are insoluble in water, as the chloride and iodide, and form a solu- 
 tion possessing an intensely sweet taste ; upon this property is founded 
 their use in daguerreotype and photogenic drawing. This acid is also 
 
400 Real Constitution of the 
 
 recognized by its silver salt being decomposed, when boiled, into black 
 sulphuret of silver and free sulphuric acid. S 2 2 + AgO giving SO : , 
 and AgS. It is an important fact, also, in the history of the hyposul- 
 phurous acid, that its salts do not always contain metallic oxides, but 
 that it may form salts with metallic sulphurets ; thus, there are two 
 hyposulphites of sodium, of which, one contains oxide of sodium, 
 (soda,) the other sulphuret of sodium. Their formulae are S. 2 2 + NaO 
 and S 2 0. 2 + NaS. Each of these, in crystallizing, combines with ten 
 atoms of water, like common sulphate of soda ; they possess like it a 
 point of maximum solubility, and the crystals of all three appear to be 
 isomorphous. There are, therefore, three salts, 
 
 SO2.S-|-NaO-|-10.HO, 
 
 the similar constitution of which evidences the relation of sulphur and 
 oxygen in a remarkable degree, and will furnish the ground of specu- 
 lations of great interest, to which I shall just now recur. 
 
 Hyposulphuric Acid, or Deutothionic Acid. 
 S 2 5 or S 2 4 + O. Eq. 900 or 72. 
 
 When sulphurous acid gas is passed through water in which pure 
 peroxide of manganese is diffused, this dissolves, and the solution con- 
 tains neutral hyposulphate of manganese. The reaction by which it is 
 produced is simply that the second atom of oxygen of the peroxide of 
 manganese converts two equivalents of sulphurous acid into hyposul- 
 phuric acid, which is exactly neutralized by the protoxide of manganese 
 that is evolved. 2S0 2 and MnO 2 giving MnO + S 2 O 5 . 
 
 When a salt of hyposulphuric acid is heated, it is resolved into sul- 
 phurous acid, which passes off as gas, and a neutral sulphate which 
 remains behind. S 2 O 5 -f EO giving S0 2 and S0 3 + RO. The acid 
 may be obtained free by decomposing its barytes salt by sulphuric acid, 
 but it cannot be kept long. When heated, it gives off sulphurous acid, 
 and sulphuric acid remains ; and even when cold it gradually forms sul- 
 phuric acid, by absorbing oxygen. 
 
 Trithionic Acid. S 3 5 . Eq. 83 or 1100. 
 
 This and the succeeding acids were first discovered in consequence 
 of the numerous processes tried to prepare hyposulphite of soda for 
 
Compounds of Sulphur and Oxygen. 401 
 
 daguerreotype processes. This one was discovered by Lauglois, and 
 obtained by boiling sulphur with a solution of bisulphite of potash. The 
 trithionate of potash crystallizes easily. When heated it is resolved 
 into sulphur, sulphurous acid and sulphate of potash. This kind of 
 reaction is, in fact, common to this class of acids ; the only difference 
 being in the proportion of sulphur set free. The quantity of oxygen 
 and of base in their salts being in every case such as to produce an 
 equivalent of sulphurous acid and an equivalent of a neutral sulphate. 
 Another and better mode of preparing this acid consists in digesting 
 dithionate (Hyposulphate) of potash with sulphur for some hours ; the 
 reaction which requires days, by Langlois' process, is completed, and 
 the salt is ready to crystallize. The facility of this method may be an 
 indication of the real constitution of this family of acids. 
 
 Tetralhionic acid. S 4 O 5 . Eq. 104 or 1300. 
 Pentathionic acid. S 5 O 5 . Eq. 120 or 1500. 
 
 The former acid was obtained by Pordos and Gelis, by decomposing 
 hyposulphite of soda with iodine. There are formed iodide of sodium 
 and tetrathionate of soda. 2(S 2 O 2 + NaO) and I. producing Nal and 
 S 4 5 . NaO. The acid may be obtained isolated from the barytes salt, 
 which is prepared by digesting hyposulphite of barytes in water with 
 iodine. A solution is produced from which the tetrathionate of barytes 
 separates as a crystalline powder, which may be rendered quite pure by 
 washing with alcohol, to remove the iodide of barium. This crystal- 
 line powder, when decomposed by dilute sulphuric acid, gives sulphate 
 of barytes and a solution of tetrathionic acid. This liquor reacts sour, 
 forms well-defined salts, and is decomposed by heat. 
 
 The pentathionic acid is generated when sulphurous acid and sulphu- 
 retted hydrogen are brought into contact. By this reaction, which shall 
 be again referred to, sulphur is deposited, and the water formed be- 
 comes strongly acid. This acid forms well-defined salts ; an important 
 property of it is, that by boiling, sulphur is deposited, and dithionic 
 acid formed ; it being only subsequently, and by further heat, that it 
 is resolved into sulphurous and sulphuric acids. 
 
 By acting on the chloride and the dichloride of sulphur with sul- 
 phurous acid and water, Plessy has obtained two acids which form crys- 
 tallizable salts, and to which he assigns the formulae of S 4 O 5 and S 5 O 6 . 
 respectively. His account of their properties is, however, too imper- 
 fect to admit of any detailed description here, and they are evidently 
 either the same as those already described, or they are additional mem- 
 bers of the same series. 
 26 
 
40 Real Constitution of the 
 
 Remarks on the Constitution of the Compounds of Oxygen and 
 
 Sulphur. 
 
 The progress of science has gradually brought into view a number of 
 facts, by which it is now very nearly fully established, that of the bodies 
 just now described, we must look upon the sulphurous acid as the only 
 direct compound of sulphur and oxygen, and that in the others, sulphu- 
 rous acid, or some modification of it, must be considered as pre-existing. 
 The reasons for this are very numerous. By the direct union of 
 sulphur and oxygen we never can obtain any other compound 
 than sulphurous acid ; the others being always formed by its means ; 
 it being prepared either perfectly distinctly, or at the moment of 
 the reaction, and then presented to other elements with which it may 
 unite. 
 
 On this view the rationale of the indirect process of manufacture of 
 sulphuric acid becomes evident. The sulphur, when it forms sulphu- 
 ric acid, is really saturated with oxygen, and cannot combine with any 
 more ; but the sulphurous acid (S0 2 ) acts as a compound radical, like 
 cyanogen, as described in p. 324, and may unite with any of the simple 
 or compound bodies. It does not unite directly with oxygen, but it 
 does so with nitrous acid, and the body so formed is decomposed by 
 water, producing sulphuric acid, as has been fully described. In like 
 manner, to form hyposulphurous acid, the radical, sulphurous acid, may 
 be considered to combine with sulphur ; the compound being a sulphur 
 acid, S0 2 + S, which combines with sulphur bases to form a distinct 
 class of salts. The hyposulphuric acid may contain also sulphurous 
 acid as its basis ; but there are two equivalents of the radical to one of 
 oxygen : it is 2S0 2 -f O. This hypothesis is rendered still stronger 
 by the fact, that sulphurous acid combines with chlorine and with 
 iodine to form, the chloro -sulphurous acid, S0 2 -f- 01; and the iodo- 
 sulphurous acid, S0 2 -f I. It combines also with nitric oxide to form 
 the nitro-sulphurous acid, S0 2 + N0 2 . The chloro-sulphurous acid is 
 produced by the direct combination of chlorine and sulphurous acid, 
 when exposed to sun-light. The iodo-sulphurous acid is formed by 
 passing sulphurous acid gas through a solution of iodine in pyroxylic 
 spirit, and the nitro-sulphurous acid, which exists only combined with 
 bases, by placing a solution of sulphite of potash in contact with 
 nitric oxide, which it gradually absorbs. The sulphurous acid forms, 
 therefore an extensive range of combinations, in which it serves as a 
 a compound radical, and of which the formulae may be written as 
 follows : 
 
Compounds of Sulphur and Oxygen. 403 
 
 Sulphuric acid, . . . SO 2 + O 
 
 Hypo-sulphuric acid, . . 2SO 2 + O 
 
 Hypo-sulphurous acid, . . SO-2 + S 
 
 Chloro-sulphurous acid, . SO2 -f- Cl 
 
 lodo-sulphurous acid, . . SO 2 + 1 
 
 Mtro-sulphurous acid, . . SO 2 -{- NO 2 
 
 The ordinary salts of sulphurous acid, the Sulphites, scarcely appear 
 to belong properly to that class, and would rather rank along with the 
 compounds of chlorine with the metallic oxides, and with peroxide 
 of hydrogen, which bodies they resemble also in their bleaching powers. 
 
 The discovery of the complex group of compounds of sulphur with 
 oxygen to which I have given the name of the Thionic acids, renders it 
 necessary to extend our inquiry into their rational constitution even 
 beyond that point. The study of the allotropic conditions of sulphur 
 furnishes us, however, with a clue to what is probably their true con- 
 stitution. It is evident that they all stand apart from sulphuric acid, 
 which appears in their history only as the final product of their destruc- 
 tion by heat. It is evident that they have all the hyposulphuric acid 
 as their type. The acid of Langlois is best formed from it. The 
 Pentathionic acid breaks up into it and sulphur, and they all differ 
 from it only in the quantity of sulphur they contain. But if we con- 
 sider that as explained in page 320, the same simple compounds may 
 act in various combining proportions, forming classes of compounds 
 essentially distinct, we may well consider that, the prismatic sulphur, 
 the octohedral sulphur, and the soft sulphur may have really different 
 equivalent numbers, as they have different densities and different forms. 
 One may be S a with the equivalent 16, another S b with the equivalent 
 32, another S c with the equivalent 48. We might, therefore, have 
 several kinds of sulphurous acids : not isomeric but allotropic as re- 
 gards the sulphur ; of totally different numerical composition, but of 
 the same type : thus S a O 2 would be common SO 2 : but S b O 2 would be 
 S 2 O 2 which is hyposulphurous acid, and S C O 2 would be S 3 O 2 . In each 
 case one equivalent of sulphur and two of oxygen, but in each case 
 the equivalent of the sulphur would have a different number. 
 
 Applying these principles to the composition of the group of thionic 
 acids we shall find that, 
 
 Hyposulphuric acid or dithionic acid may be supposed to contain 
 ordinary sulphurous acid, and its formula to be 
 
 2 (S a Cg + 0=2 (S0 2 ) + 0=S 2 5 . 
 
 Trithionic acid probably contains partly a and partly b sulphur, and 
 hence its formula is 
 
 ,) +0 = (SO,+S 2 O a J +0 = 8A- 
 
404 Preparation and Properties 
 
 Tetrathionic acid contains on the same view all I sulphur, or possibly 
 partly c and partly a, as there may be 
 
 2 (S b 2 ) + O = 2 (S 2 2 ) + O or else 
 (S a 2 +S c 2 ) +0 = (S0 2 +S 3 2 ) + = S 4 5 . 
 
 Pentathionic acid similarly may be looked upon as containing sulphur 
 in the b and the c state thus 
 
 (S b 2 +S c 2 ) + = (S 2 2 +S 3 2 ) + = S 5 5 . 
 
 On this view the hyposulphurous acid might be considered as sul- 
 phurous acid with the b sulphur ; but the isomorphism of the hyposul- 
 phites and sulphate of soda mentioned in page 400 negative that idea. 
 The greatest importance of the theory I propose, consists in shewing 
 that, assuming the different allotropic conditions which we know sulphur 
 to admit, to be accompanied by different combining proportions, we 
 can reduce all those complex acids to the type of the hyposulphuric or 
 dithionic acid. 
 
 Berzelius suggests that these acids may be all considered to contain 
 hydrogen, and to be compounds of hyposulphuric acid with different 
 sulphurets of hydrogen. This view is founded on some indications of 
 sulphuretted hydrogen found in the analyses of the pentathionic and of 
 Plessy's acids. The weight of evidence is, however, totally against the 
 existence of sulphuretted hydrogen in the acids that have been best 
 examined, and Berzelius does not himself abide by that view. 
 
 Compounds of Sulphur and Hydrogen. 
 
 Sulphur unites with hydrogen in two proportions, forming a gas, 
 Sulphuretted Hydrogen, by an equivalent of each element, and a heavy 
 liquid, when in the proportion of one equivalent of hydrogen to two of 
 sulphur. 
 
 To prepare sulphuretted hydrogen, the proto-sulphuret of iron (FeS) 
 is acted on by dilute sulphuric acid, in the apparatus figured in p. 375. 
 A lively effervescence occurs from the escape of sulphuretted hydrogen 
 gas, and the solution contains sulphate of protoxide of iron ; a gentle 
 heat may be applied to favour the reaction of the materials. In this 
 process water is decomposed, its oxygen being transferred to the iron 
 and its hydrogen to the sulphur ; the result may be expressed as fol- 
 lows : FeS and S0 3 + HO give HS and 80s + FeO. This gas may 
 also be obtained by acting on sulphuret of potassium by dilute sul- 
 phuric or muriatic acid, in which case the theory is similar to that 
 already given. Sulphuret of antimony and liquid muriatic acid pro- 
 duce, when heated, very pure sulphuretted hydrogen, the reaction .being 
 that Sb 2 S 3 and 3(HC1) give Sb 2 Cl 3 and 3(HS). 
 
of Sulphuretted Hydrogen. 405 
 
 The sulphuretted hydrogen gas, being absorbed by water, cannot be 
 well collected over it, except it be saturated with common salt, or be 
 heated to above 90, in which case its solvent power is very much 
 diminished. It cannot be kept long over the mercurial pneumatic 
 trough, for the lead and tin always present in the mercury of commerce 
 gradually decompose it, combining with the sulphur, and leaving the 
 hydrogen free ; the volume of the gas remains the same during this 
 decomposition. 
 
 This gas is colourless and transparent : it is characterized by its fetid 
 odour, that of rotten eggs, which indeed owe their peculiar odour to 
 the formation of this gas during their putrefaction. Its specific gravity 
 is 1177. It consists, therefore, of 
 
 One volume of vapour of sulphur, . . . 6648*0 
 Six volumes of hydrogen, . . 69'3 x 6 = 415'8 
 
 the seven volumes are condensed to six, . . 7063 '8 
 
 of which one weighs, therefore, . . . . 1177'3 
 
 The sulphuretted hydrogen gas dissolves in water, forming a solution 
 which is extensively used as a reagent for the metals, from the solutions 
 of most of which it precipitates metallic sulphurets of various colours, 
 by which many metals may be recognized. Thus, antimony gives an 
 orange, manganese a flesh red, arsenic and cadmium a canary yellow, 
 and several, as lead, mercury, and bismuth, black or brown precipitates. 
 
 When a solution of sulphuretted hydrogen in water has access to the 
 air, oxygen is absorbed, and combining with the hydrogen sets the 
 sulphur free as a milky precipitate. The nascent sulphur, however, in 
 part also absorbs oxygen, and there is formed some sulphuric acid 
 whereby the presence of this acid, free, in volcanic springs, occurs as in 
 the Rio Yinaigre in New Spain. If a solution of sulphurous acid be 
 mixed with sulphuretted hydrogen, half of the whole quantity of sulphur 
 is precipitated and the remainder is converted into pentathionic acid ; 
 5SO 2 and 5SH producing 5S and 5HO with S 5 O 5 . 
 
 Sulphuretted hydrogen is highly inflammable ; if burned in a limited 
 quantity of air, the hydrogen is consumed, whilst most of the sulphur 
 is deposited. By means of nitric acid or chlorine it may be completely 
 decomposed; hence, chlorine acts as a disinfectant and purifier of 
 sewers or rooms impregnated with the odour of sulphuretted hydrogen. 
 This gas is very poisonous ; air being capable of producing death to 
 large animals, if respired, though it may not contain more than ^fa of 
 this gas. Many of the metals decompose sulphuretted hydrogen, par- 
 ticularly when heated in this gas, combining with the sulphur, and 
 
406 Sulphur ets of Hydrogen. 
 
 setting the hydrogen free. This occurs slowly, even at common tempe- 
 ratures ; and hence metals, as gold and silver, which are not oxidized 
 by the air, are gradually tarnished by the sulphuretted hydrogen, which 
 exhaled from decomposing animal matter, is always present in the 
 atmosphere. This gas, evolved probably by the action of water on the 
 native sulphurets of iron, at high temperatures, is a frequent constituent 
 of mineral springs, and forms the class of spas termed sulphureous, 
 such as those of Harrowgate, Lucan, and Golden-bridge. They are 
 easily recognized by the fetid odour, by blackening a silver spoon, or 
 by giving a black or brown precipitate with a solution of acetate of 
 lead. 
 
 In its chemical relations, sulphuretted hydrogen assimilates itself 
 closely to water ; its composition and equivalent numbers are as follows : 
 
 Sulphur, 94-18 One equivalent = 200-0 or 16-0 
 Hydrogen, 5'82 One equivalent = 12-5 or PO 
 
 100-00 212-5 17-0 
 
 Bi-Sulpkuret of Hydrogen. To prepare this substance, bi-sulphuret 
 of potassium is to be dissolved in water, and the solution gently poured 
 into dilute muriatic acid; the potassium combines with the chlorine, 
 and the hydrogen unites with the sulphur ; KS2 and H Cl giving KC1 
 and HS 2 ; the latter sinks to the bottom of the vessel as a heavy yellow 
 liquid, insoluble in water, but decomposed rapidly by contact with it, 
 unless free acid be present. It is not easily obtained pure, as the sul- 
 phuret of potassium, formed by melting salt of tartar and sulphur 
 together, or by dissolving sulphur in a solution of caustic potash, 
 always contains an excess of sulphur, beyond two atoms, which precipi- 
 tating along with the true compound, dissolves in it and modifies its 
 properties and composition. 
 
 This oily liquid is characterized by separating, with great ease, into 
 sulphuretted hydrogen gas and solid sulphur; indeed the best way of 
 obtaining sulphuretted hydrogen condensed into a liquid, is to seal up, 
 in a strong tube, a quantity of this bisulphuretted hydrogen, which, 
 after a short time, is decomposed ; the gas not being able to escape, is 
 liquefied by the pressure it exercises, whilst the sulphur separates in octo- 
 hedral crystals. 
 
 This body is decomposed by all substances which decompose deutoxide 
 of hydrogen. Black oxide of manganese, or oxide of silver put in con- 
 tact with it, evolve sulphuretted hydrogen gas, and often with the 
 appearance of light and heat ; it corrodes the skin, and appears to pos- 
 sess bleaching properties. 
 
Selenium, and its Compounds, fyc. 407 
 
 Sulphurets of nitrogen have been discovered and described ; they are 
 solid and crystallizable, but are of no importance. 
 
 OF SELENIUM. 
 Symbol. Se. Eq. 39'6 or 494r6. 
 
 Selenium was discovered by Berzelius, and accompanies, although in 
 exceedingly small quantity, the native metallic sulphurets, existing as 
 seleniurets of the same metals. It remains even still a very rare sub- 
 stance : it has not been introduced into the arts or into medicine, and 
 it will hence be necessary to touch upon its history but very slightly. 
 
 When extracted from its native combinations, selenium is a solid, of 
 a dark brown colour, and when smooth, with metallic lustre. Its den- 
 sity is 4*32 ; its fracture is crystalline ; it melts a little above the boiling 
 point of water, and boils at 650; its vapour is of a deep yellow 
 colour, like that of sulphur. In its manner of combination it resembles, 
 almost completely sulphur. 
 
 In one respect, however, they differ ; when selenium is burned in air, 
 it combines with but one equivalent of oxygen, forming oxide of selenium 
 (SeO.), a colourless gas, which is remarkable for its pungent odour of 
 horse-radish. By this means selenium may be recognized, even when 
 present in exceedingly small quantity. Sulphur does not appear to form 
 a similar compound. 
 
 When selenium is boiled with nitric acid, it unites with two equiva- 
 lents of oxygen, and forms selenious acid, Se0 2 . This may be also 
 produced by burning selenium in oxygen gas at a high temperature. It 
 is solid, white, volatile, and may be obtained crystallized by subli- 
 mation, or from its watery solution. Selenious acid may be deprived of 
 its oxygen by contact with zinc or iron filings, or by sulphurous acid : 
 selenium is set free as a fine crimson precipitate. When selenite of 
 ammonia is heated, it gives water, nitrogen, and free selenium. 
 
 If a current of chlorine gas be passed through a solution of selenious 
 acid, or if selenium be melted with nitre, selenic acid is formed (SeO 3 ), 
 which has the most remarkable analogy with sulphuric acid. All their 
 similar salts are isomorphous, and almost identical in properties. In- 
 deed, to distinguish them, it is necessary to boil the salt with muriatic 
 acid, which has no action on the sulphate, but gives with the seleniate, 
 chlorine, and selenious acid. 
 
 Seleniuretted Hydrogen is formed by the action of acids upon metallic 
 seleniurets, in precisely the same manner as that described under the 
 head of sulphuretted hydrogen. It is a colourless gas, of an extremely 
 fetid odour, irrespirable, soluble in water, and precipitating, from the 
 
408 
 
 Preparation and Properties 
 
 solutions of many of the metals, metallic seleniurets ; these are gene- 
 rally black or brown, but the seleniuret of manganese is, like the sul- 
 phuret, flesh-red, and that of zinc is white. 
 
 When sulphuret of hydrogen is passed into a solution of selenious 
 acid, water is formed, and a sulphuret of selenium is produced, analo- 
 gous to selenious acid, its formula being Se + S 2 . It is a canary yel- 
 low powder, insoluble in water. 
 
 OF PHOSPHORUS. 
 
 P. Eq. = 32 or 400. 
 
 Phosphorus exists in nature, principally in the animal kingdom, in 
 the bones of the vertebrated animals, in the fluids of the body, and also 
 in the pulpy material of the brain and nerves. It is found in small 
 quantity in many vegetables, and is a constituent of some minerals. It 
 is prepared as an article of manufacture in large quantity in London 
 and Paris. In the latter city it is computed that about 200,0001bs. of 
 phosphorus are annually obtained. 
 
 The principal source of phosphorus is the earthy material of bones 
 (phosphate of lime.) The bones are first burned until they become 
 completely white, and are then ground to powder. To three parts of this 
 powder are added thirty parts of water and two of oil of vitriol. The 
 sulphuric acid unites with a portion of the lime of the bone ashes, whilst 
 the remainder forms with the whole of the phosphoric acid a soluble 
 salt which is obtained in the liquor, when the insoluble sulphate of lime 
 is separated by straining through a cloth. The liquor is evaporated to 
 the consistence of a sirup, and gradually mixed with a quantity of pow- 
 dered charcoal, about one-fourth the weight of the bones that had been 
 used, and the whole completely dried at a temperature just below red- 
 ness. This mass is introduced, in powder, into an earthen retort a, 
 
 which is placed in a furnace, as in the 
 figure. To the neck of the retort is 
 adapted a copper tube, b, the other ex- 
 tremity of which dips a little into the 
 water in the bottle which serves as a 
 receiver. The retort being gradually 
 heated, the excess of the phosphoric acid 
 is decomposed by the charcoal, the car- 
 bon of which combines with the oxygen 
 to form carbonic acid, whilst the phos- 
 phorus becomes free; this being vola- 
 tilized by the high temperature, passes 
 in the state of vapour into the copper 
 
of Phosphorus. 409 
 
 tube, where it is condensed, and flowing down in the liquid form into 
 the bottle, collects under the surface of the water. The copper tube 
 must dip so little under the water, that by no condensation could this 
 be forced back into the retort. 
 
 The phosphorus so obtained is again melted under the surface of the 
 water, and poured into glass tubes, where it is allowed to solidify. It 
 thus gets the cylindrical form in which it is found in commerce. 
 
 Phosphorus, when pure, is transparent and colourless, but, as gene- 
 rally found, it is of a pale yellow, or even of a reddish colour. At or- 
 dinary temperatures it is soft, so that it may be bent, or cut with a knife ; 
 but at 32 it becomes quite brittle and crystalline in its fracture. It 
 is insoluble in water, but it dissolves in the volatile oils, in ether, and 
 in sulphuret of carbon, from which last it may be obtained in crys- 
 tals of considerable size, which are regular dodecahedrons, as in the 
 figure. It has also been obtained crystallized by 
 fusion, under the form of octohedrons. At 108 
 phosphorus melts into a colourless liquid, and at 
 550 it boils, forming a colourless vapour, the sp. 
 gr. of which is 4327. Phosphorus appears to as- 
 sume allotropic conditions like those of sulphur ; 
 when strongly heated and suddenly cooled, it be- 
 comes jet black and opaque, but gradually returns 
 to its ordinary aspect. 
 
 Phosphorus is exceedingly inflammable. Even at ordinary tempera- 
 tures, when exposed to the air, it burns slowly, forming phosphorous 
 acid, and emitting light visible in the dark, from whence its name 
 (<pug pegu, I bring light.) It, at the same time, emits a remarkable and 
 penetrating garlic smell. It is hence that phosphorus is used to ana- 
 lyze atmospheric air, and that it must always be preserved under water. 
 "When heated to 130 phosphorus bursts into brilliant flame, and unites 
 with oxygen to form phosphoric acid. The combustibility of phos- 
 phorus is influenced by the presence of various gaseous bodies in a very 
 remarkable degree. Thus, in pure oxygen phosphorus does not bum, 
 or give any light, until the temperature is raised to 80 ; and if the 
 oxygen or air be mixed with small quantities of olefiant gas, or the 
 vapours of ether or of oil of turpentine, its slow combustion may be 
 totally prevented. The influence even extends, under some circum- 
 stances, to much higher temperatures. 
 
 The atomic weight of phosphorus had been formerly taken as 16 
 (H = 1) in consequence of some views of the constitution of its com- 
 pounds, which are now generally abandoned, and I consider, the true 
 equivalent number to be 32' 0, double the former. 
 
410 Properties of Phosphorus. 
 
 Phosphorus combines with oxygen in four proportions forming an 
 oxide, and three acid compounds, the constitution of which follows : 
 
 Oxide of phosphorus, . = 2P+O = 64+ 8'0 = 72 
 
 Hypophosphorous acid, . = P+O = 32+ 8'0 = 40 
 
 Phosphorous acid, . = P+O 3 = 32+24-0 = 56 
 
 Phosphoric acid, . = P+O 5 = 32 + 40-0 = 72 
 
 Oxide of Phosphorus. When phosphorus is exposed to light, in 
 water containing air dissolved, it gradually becomes covered with a 
 white powder, which is a compound of phosphorus with water, but 
 there forms at the same time a reddish substance, which is oxide of 
 phosphorus. It is generated also whenever phosphorus is incompletely 
 burned, and may be formed in large quantity by melting phosphorus 
 under water, and bringing a stream of oxygen gas to act upon it by 
 means of a tube passing to the bottom of the vessel ; the phosphorus 
 burns brilliantly, but being present in great excess, it passes principally 
 only to the lowest degree of combination that it can form. It may be 
 obtained purer by other processes, which are, however, too complicated 
 to be introduced in this place. 
 
 The oxide of phosphorus so formed, is a red or yellow powder inso- 
 luble in water ; it is exceedingly inflammable in some forms, but in 
 others does not take fire until heated to near the boiling point of mer- 
 cury. It is not probable that the red and yellow substances, which are 
 called oxide of phosphorus, are really identical, as they differ in their 
 most striking characters, besides in colour. The formula P 2 O, is that 
 obtained from the yellow matter ; Pelouze considers the reddish matter 
 to be expressed by P 3 O 2 . 
 
 Hypophosphorous Acid. This acid is very little known ; it is formed 
 when phosphorus is heated in a solution of an alcali or earth ; water is 
 decomposed, one portion of the phosphorus combining with the hydro- 
 gen, and another with the oxygen, produces phosphuretted hydrogen 
 gas, which passes off, and hypophosphorous acid which remains com- 
 bined with the alcali or earth employed ; the reaction may be shewn 
 thus, with phosphorus and solution of barytes, 4P, 3HO and 3BaO give 
 3(PO + BaO) and PH 3 . 
 
 The hypophosphite of barytes, so obtained, may be decomposed by 
 sulphuric acid, and the sulphate of barytes being removed by nitration, 
 the hypophosphorous acid remains uncombined; its solution may be 
 evaporated to the consistence of a sirup, but it cannot be obtained 
 solid ; it is decomposed, by continuing the heat, into phosphuretted 
 hydrogen, phosphoric acid, and some phosphorus is set free. The 
 circumstance that neither the phosphorous acid, nor any of its salts, 
 
Compounds of Phosphorus and Oxygen. 411 
 
 can be obtained anhydrous, but are decomposed when heated, and 
 phosphuretted hydrogen given off, have made some chemists to propose 
 that its real formula is P.H 2 O 3 . ; its radical being not phosphorus, but 
 the body PH 2 , to which I shall refer again. 
 
 Its salts are all soluble in water, and most of them crystallize. 
 "When heated strongly, they give phosphuretted hydrogen, and a phos- 
 phate of the base ; a reaction very consonant to the view just explained, 
 as the acid should contain the elements of two atoms of water, 
 PH 2 O 3 being equal to PO -f- 2HO. 
 
 Phosphorous Acid. This acid is the principal product of the slow 
 combustion of phosphorus, but to obtain it pure it is necessary to avoid 
 carefully an excess of oxygen ; for this purpose a glass tube of ten 
 inches long, and half an inch bore, is drawn out, at one end, to a 
 point with an aperture large enough to admit a pin, and bent at an ob- 
 tuse angle about two inches from the point ; at the bend is laid a piece 
 of phosphorus, which is heated until it takes fire, but the temperature 
 must not rise so high as to sublime any of it. As there is a great ex- 
 cess of phosphorus present, the principal product of the combustion is 
 phosphorous acid, which being formed in exceedingly light flakes, is 
 carried by the current of air to the upper part of the tube, where it is 
 deposited. These flakes are volatile, and may be sublimed from one 
 part of the tube to another ; they attract water so powerfully, that the 
 heat evolved is sometimes great enough to inflame the phosphorous 
 acid, which then combines with more oxygen, and forms phosphoric acid. 
 
 Phosphorous acid is more easily prepared in the liquid form ; for this 
 purpose, a quantity of phosphorus is placed in a thin glass vessel, co- 
 vered with water, to the depth of some inches ; a current of chlorine 
 is then conducted by a tube to the phosphorus, which inflames, and 
 forms proto-chloride of phosphorus ; this substance is immediately de- 
 composed by the water, phosphorous acid and muriatic acid being pro- 
 duced : theP.CL, and 3HO, giving PO 3 and 3H.C1; both acids dis- 
 solve in water, but by evaporating the solution to the consistence of a 
 sirup, the muriatic acid passes off as gas, and the hydrate of phospho- 
 rous acid, PO 3 + 3HO, remains behind. This hydrated acid cannot 
 be freed from water by further heat, it being then decomposed into 
 phosphoric acid, and the variety of phosphuretted hydrogen which is 
 not spontaneously inflammable. Thus, 4(PO 3 + 3HO) give 3(P0 5 + 
 3HO) and PH 3 . 
 
 The solution of phosphorous acid absorbs oxygen rapidly from the 
 air, and with the assistance of heat, reduces to the metallic state the 
 salts of mercury, silver, gold, and platina. It is hence occasionally 
 used as a de-oxidizing agent. 
 
412 Phosphoric Acid. 
 
 Phosphoric Acid. P0 5 . Eq. 72 or 900. 
 
 When this acid is required in large quantity, it is generally prepared 
 from the earth of bones, which are acted on by sulphuric acid, as was 
 described for the preparation of phosphorus. The acid solution of 
 superphosphate of lime is decomposed by carbonate of ammonia, by 
 which the lime is thrown down in combination with carbonic acid, and 
 the phosphoric acid remains in solution as phosphate of ammonia. This 
 salt may be crystallized, but it is generally evaporated to dryness, and 
 ignited ; the ammonia passes off, and the phosphoric acid remains be- 
 hind melted, and solidifies on cooling into a colourless glass, the glacial 
 phosphoric acid. 
 
 This process has been lately improved and simplified by Liebig and 
 Gregory, in the following manner : The solution of superphosphate 
 of lime, obtained by the action of sulphuric acid on the bone earth, is 
 to be concentrated to a sirupy consistence, and then more strong sul- 
 phuric acid to be gradually added as long as sulphate of lime is pro- 
 duced. By a little attention the who]e quantity of lime can be thus 
 precipitated. The solution of phosphoric acid is then to be separated 
 from the sulphate of lime, by draining and careful washing. The 
 liquor contains then as impurities oidy the small quantity of magnesia 
 and of soda which existed in the bones. This solution of phosphoric 
 acid is to be evaporated to the density of sirup, and kept at a tempera- 
 ture of 600 Fahrenheit ; after some time a precipitate forms, which is 
 an insoluble phosphate of magnesia and soda. The acid liquor being 
 decanted, is now to be dried down and ignited, to expel any traces of 
 sulphuric acid that might remain. The phosphoric acid is then obtained 
 quite pure. 
 
 It may also be obtained by acting on phosphorus with dilute nitric 
 acid. This supplies oxygen to the phosphorus, and nitric oxide is 
 evolved. When the action has terminated, the solution is to be evapo- 
 rated to dryness, and the residual phosphoric acid ignited, to expel all 
 traces of nitric acid. This process is somewhat dangerous, as some- 
 times fragments of phosphorus are projected, by the effervescence, out of 
 the liquid, and burning in the nitric oxide gas, may burst the retort, 
 and also that during the concentration further reaction takes place by 
 which phosphuretted hydrogen gas is given out and sometimes burns 
 violently. The phosphoric acid may also be prepared very simply, and 
 in a pure and dry state, by setting fire to some phosphorus in a little 
 cup, and covering it with a large bell glass. The oxygen of the con- 
 tained air forms phosphoric acid, which is deposited in white flakes on 
 the inside of the glass, and on the supporting plate, and by continuing 
 
Phosphates of Water. 413 
 
 a supply of pure oxygen from a gasometer, and adding from time to 
 time additional bits of phosphorus, a very large quantity of acid may be 
 readily and economically prepared. In all these cases, the acid so ob- 
 tained is destitute of water ; it is anhydrous. 
 
 The phosphoric acid has a great affinity for water, combining with it 
 almost explosively. It may form three distinct compounds, which have 
 been obtained crystallized, phosphates of water, the constitution of which 
 is as follows : 
 
 Monobasic phosphate of water, . POs+ HO. 
 Bibasic phosphate of water, . . PO5-J-2HO. 
 Tribasic phosphate of water, . . POs-fSHO. 
 
 This relation was first established by the researches of Graham, whose 
 admirable memoir on the arseniates and phosphates formed an impor- 
 tant epoch in science. The phosphoric acid combines not only with 
 water in these three proportions, but each of them is a type of a series 
 of salts, which the phosphoric acid is capable of forming. Thus, there 
 is a class of monobasic phosphates y another class of dibasic phosphates, 
 and a third, which is the most common, of tribasic phosphates ; the 
 water contained in the phosphates of water being replaced to a greater 
 or less extent, by means of equivalent proportions of ammonia or metal- 
 lic oxides. 
 
 A solution of phosphoric acid in water may contain any one of the 
 three phosphates of water that have been described, and when neutral- 
 ized by bases, may hence produce totally different salts. The properties 
 of a solution of phosphoric acid may, therefore, be totally different ac- 
 cording to the manner in which it had been prepared, and hence this 
 acid was at one time ranked as a remarkable instance of isomerism ; but 
 Graham has beautifully shewn, that the difference of properties is only 
 the result of the existence of the different states of combination in which 
 the phosphoric acid actually exists. It will consequently be necessary 
 to study separately the properties of the three compounds of phosphoric 
 acid with water. 
 
 Monobasic Phosphate of Water. A solution of this body reacts pow- 
 erfully acid, it precipitates albumen (white of egg) in white curds ; when 
 neutralized by a base, it gives salts which contain but one atom of base, 
 their formula being P0 5 + EO, and a soluble salt of it produces, in so- 
 lutions of silver, a white, soft, precipitate, PO 5 + AgO. This is the 
 least stable of the phosphates of water, it gradually passes into the other 
 forms, particularly when its solution is boiled. 
 
 Bibasic Phosphate of Water. This form of the acid may be prepared 
 by decomposing bibasic phosphate of lead by sulphuretted hydrogen. 
 
414 Salts of Phosphoric Acid. 
 
 It is characterized by combining always with two equivalents of base, 
 forming salts, whose formula is P0 5 + 2RO ; its salts give, with nitrate 
 of silver, a white precipitate PO 5 -f- 2AgO, which is not pasty like the 
 monobasic phosphate. The salts of this acid may contain only one 
 equivalent of fixed base, the other being water, and hence, at first sight, 
 appear to be constituted like the monobasic salts ; the basic water is, 
 however, easily known to be present, by its not being expelled by a mo- 
 derate heat, with the water of crystallization, but requiring a tempera- 
 ture approaching to ignition for its expulsion. 
 
 Tribasic Phosphate of Water. This is the form of phosphoric acid 
 which represents the class of salts most generally known ; it is character- 
 ized by not precipitating albumen, and by combining with three equiva- 
 lents of base when fully neutralized. In the majority of cases, of the three 
 equivalents of base, one is water, thus the common phosphate of soda 
 is a tribasic phosphate, its formula being (PO 5 + 2NaO.HO) -J- 24Aq ; 
 when moderately heated, or even by long exposure to dry air, it loses 
 the 24Aq, but it requires to be melted at a red heat, in order to drive 
 off the twenty-fifth atom of water, and if this be done, on redissolving 
 the fused mass in water, it crystallizes in a totally different form, and is 
 found to have been changed into bibasic phosphate of soda, the formula 
 of which is (PO 5 + 2NaO) + 10 Aq. The difference is remarkably shewn 
 by the action of these salts on solution of silver ; common phosphate of 
 soda precipitates nitrate of silver of a canary yellow, and the solution 
 becomes acid ; one equivalent of tribasic phosphate of soda, decomposing 
 three equivalents of nitrate of silver, producing one equivalent of tribasic 
 phosphate of silver, two of nitrate of soda, and one of nitrate of water ; 
 this last being liquid nitric acid, of course renders the liquor acid. The 
 reaction may be simply expressed 
 
 PO 5 -}-2]SraO.HO and 8(NO 8 + AgO) 
 give PO 5 +3AgO with 2(NO 5 +FaO) and M) 5 -f HO. 
 If on the other hand bibasic phosphate of soda be used, the liquor re- 
 mains neutral, for P0 5 +2NaO and 2(NO B +AgO) giveP0 6 +2AgO 
 and 2(N0 5 +NaO). 
 
 In the tribasic phosphates, it frequently occurs, that there shall be 
 but one equivalent of fixed base, the other two being water ; such salts 
 have frequently an acid reaction, and were formerly termed biphosphates. 
 Thus one tribasic phosphate of soda is PO 5 +NaO.2HO; the biphos- 
 phate of ammonia is tribasic, its formula being P0 5 + NH 4 O.2HO. 
 
 These salts of phosphoric acid were originally designated by Graham, 
 metaphosphates, pyrophosphates, and common phosphates, but the sys- 
 tematic names which have been since proposed should be universally 
 adopted. 
 
Phosphuretted Hydrogen. 415 
 
 This peculiarity in phosphoric acid, which will be hereafter found to 
 be but an example of the laws which govern the constitution of a large 
 class of acids, appears to stand in close relation to the theories of the 
 nature of salts referred to in page 324. Thus, on the older idea, there is 
 no reason given why phosphoric acid should form in one state monobasic, 
 in another bibasic, and in a third tribasic salts, except by assuming the 
 existence of isomeric states, for which there is, in fact, no other grounds, 
 and which is but an admission of ignorance. But on the salt radical 
 theory, the existence of the different classes of salts follows from the 
 different states of hydration of the free acids ; the radical of each class 
 of salts being, in fact, quite different. Thus, M being the symbol for 
 an atom of any metal, 
 
 POs + HO becomes POe-j-H and forms POe+M. Monbasic. 
 P05 + 2HO P0 7 +H 2 P0 7 + M 2 \ Bibasic 
 
 or PO H.M. j 
 
 2 M.l 
 - M2 > 
 
 or POs-fH.M2 V Tribasic. 
 or POs-j-Ma J 
 
 There should be therefore, three phosphoric salt radicals, PO 6 , PO 7 , and 
 P0 8 . These combine respectively with one, two, and three atoms of 
 hydrogen, and the replacement of these several atoms of hydrogen by 
 equivalents of metals, produces the classes of monobasic, bibasic, and 
 tribasic salts. 
 
 In the general remarks on the constitution of salts, and on some 
 other subjects, I shall have further occasions to return to the consider- 
 ation of this subject. 
 
 Compounds of Phosphorus and Hydrogen. 
 
 It is probable that there exist at least three compounds of phosphorus 
 and hydrogen, and I shall describe first that which is gaseous (PH 3 ), as 
 of it we possess more accurate knowledge. 
 
 The modes of preparing this gas have been already noticed. It may 
 be formed, 1st, when phosphorus is heated in a solution of potash or 
 barytes, or with milk of lime ; the water being decomposed, gives its 
 oxygen to one portion of the phosphorus to form hypophosphorous acid, 
 and its hydrogen to another, forming phosphuretted hydrogen gas : 
 2nd, when the hydrated phosphorous acid is heated, the water is decom- 
 posed, and phosphoric acid and phosphuretted hydrogen are produced. 
 The gas, prepared in these ways, possesses very different properties ; I 
 shall term that obtained by the first process, the A, and that by the 
 
416 
 
 Preparation and Properties of 
 
 second, the B variety. If the A gas, evolved from the retort a, be 
 allowed to bubble through the water of the pneumatic trough, each 
 bubble of gas, as it bursts in the air, takes fire spontaneously, and burn- 
 ing with a beautiful white flame, forms a ring of phosphoric acid smoke, 
 which, widening as it rises, may ascend to a considerable height, if the 
 air of the apartment be still, without its form being broken up. The 
 
 structure of this ring is exceedingly curious and pretty ; it consists of 
 an amazing number of small rings, which revolve with great rapidity on 
 their axis, and whose plane is perpendicular to that of the general ring 
 which they produce. This is spontaneously inflammable phosphuretted 
 hydrogen : if the gas bubbles be received in a jar of pure oxygen, the 
 combustion is excessively brilliant and explosive. The B variety of the 
 gas is not spontaneously inflammable, but if set on fire it burns with the 
 same appearance as the other. 
 
 On analysis, the two varieties give exactly the same result : they are 
 colourless and transparent, and of a very disagreeable garlic smell ; but 
 slightly absorbed by water, arid precipitating the generality of metallic 
 salts, giving insoluble phosphurets. The specific gravity is the same 
 for both, being 1185, which arises from 
 
 One volume of phosphorus-vapour, 
 and six volumes of hydrogen, 
 
 . = 4327-0 
 69-3 x 6 = 415-8 
 
 being condensed to four, \..\ ', . .*, .'".'".' . 4742-8 
 
 of which one weighs, therefore, .... 11857 
 
 Their constituents by weight, and equivalent numbers, are as follows : 
 
 Phosphorus, = 91-29 
 Hydrogen, . 8'71 
 
 1000-00 
 
 One equivalent, = 400-0 or 32-0 
 Three equivalents, = 37*5 or 3-0 
 
 437-5 32-0 
 
 These two varieties were naturally looked upon as isomeric, but 
 Graham has shown that the difference of properties may arise from the 
 
The PJiosphnrets of Hydrogen. 417 
 
 presence of a small quantity of foreign substance, as such may change 
 the one variety into the other. Thus, a very small quantity of the vapour 
 of ether removes altogether the power of spontaneous inflammability 
 from the A variety ; the vapour of the essential oils, and even carbon, 
 phosphoric acid, and potassium, produce the same effect. On the other 
 hand, an exceedingly small quantity of vapour of nitrous acid, or nitric 
 oxide, converts the variety B into A, and makes it spontaneously inflam- 
 mable. Graham considers, that in obtaining the gas from phosphorus 
 and milk of lime, &c., it is accompanied by a very minute trace of some 
 compound of phosphorus and oxygen, probably the same as is formed 
 by nitrous acid with the B variety, which is really spontaneously inflam- 
 mable, and acting as a match, inflames the general mass of gas. 
 
 The cause of the difference in the two varieties of phosphuretted 
 hydrogen has been finally cleared up by the researches of Thenard, who 
 has discovered it to be the presence of the vapour of the really inflam- 
 mable phosphuret of hydrogen, PH 2 . a highly volatile liquid. "When 
 the spontaneously inflammable gas is passed through a narrow tube, 
 cooled to 40 Eah. a colourless liquid condenses from the gas, and the 
 latter is found to have totally lost its spontaneous inflammability. This 
 liquid is pellucid and colourless, excessively volatile ; at ordinary tem- 
 perature a gas : On contact with air it immediately inflames. A small 
 portion of its vapour confers the same property on phosphuretted hydro- 
 gen gas, and even on common hydrogen gas. Exposed to the light, it 
 is decomposed into a solid red powder, hydruret of phosphorus PH. 
 and phosphuretted hydrogen gas PH 3 , which is not spontaneously in- 
 flammable. These important results modify the views of Graham above 
 given, but prove their general accuracy in attributing the difference of 
 properties of the phosphuretted hydrogen gases to the presence of a 
 foreign body. 
 
 Phosphuretted hydrogen gas has, in some respects, strong analogies 
 to ammonia. It unites with hydriodic acid to form a kind of salt. It 
 combines with metallic chlorides, and in these reactions appears to be 
 frequently changed from the inflammable to the non-inflammable state, 
 and vice versa, by some reaction which has not been satisfactorily traced. 
 Its properties in this respect render it very probable that the combining 
 equivalent of phosphuretted hydrogen is not as stated above PH> but 
 that the phosphorus acts with one-third of its ordinary equivalent = 
 10*67, and that the formula of phosphuretted hydrogen gas is .H. 
 That it resembles, therefore, sulphuretted hydrogen, as containing one 
 equivalent only of hydrogen in its combining proportion, and that phos- 
 phorus when acting with the equivalent 10-67 and the symbol J, allies itself 
 to sulphur and tellurium. This point of view shall be again considered 
 27 
 
418 Preparation of Chlorine. 
 
 Phosphuret of Nitrogen. This compound has been discovered and 
 described by Bose, but possesses no important properties. 
 
 The Sulphurets of Phosphorus are formed by melting together sulphur 
 and phosphorus in equivalent weights. These elements unite in several 
 proportions. The compounds are much more inflammable than phos- 
 phorus, and form the material used in the phosphorus match-boxes. 
 Some of them are spontaneously inflammable, and Berzelius refers the 
 difference of properties to the allotropic condition of the phosphorus 
 which they contain. 
 
 OF CHLORINE. 
 Symbol. Cl. Eq. 35'47 or 443*7. 
 
 Chlorine exists in large quantity in nature, principally combined with 
 sodium, forming immense deposits of rock salt (chloride of sodium) in 
 England, in Poland, and elsewhere ; and in the same state it commu- 
 nicates the saltness, and constitutes the chief ingredient of sea water. 
 It is found also combined with calcium, mercury, lead, silver, and some 
 other metals ; but these compounds are rare, and exist only in small 
 quantity. The only source of chlorine, practically useful in chemistry 
 and in the arts, is from common salt. 
 
 To obtain chlorine in large quantity, the common salt is mixed with 
 peroxide of manganese, and then decomposed by sulphuric acid ; the 
 half of the oxygen of the peroxide of manganese passes to the so- 
 dium, the chlorine being expelled, and the soda and protoxide of man- 
 ganese both unite with the sulphuric acid. Thus, Mn0 2 and NaCl, 
 treated with 2S0 3 produce S0 3 . NaO -J- S0 3 . MnO, and Cl is evolved. 
 By weight, about six parts of oxide of manganese and eight of chloride 
 of sodium are employed with thirteen of oil of vitriol ; and as the manu- 
 facturers of chloride of lime are generally makers of oil of vitriol also, a 
 proportionate quantity of acid of 1.600 from the chamber (p. 396) is ge- 
 nerally used in place of strong oil of vitriol ; the expense of concen- 
 tration being thus saved. Into a leaden still, h, h, such as is repre- 
 sented in the figure, the mixed salt and man- 
 ganese are introduced at the aperture, i, which 
 is then tightly closed; the sulphuric acid 
 enters by the bent funnel, #, and these mate- 
 rials are well mixed by means of the agitator 
 turned by the cross handle, n ; the gas evolved 
 escapes by the tube, a, which conducts it to 
 its destination. At first the operation does 
 not require heat, but the still sits in an iron 
 jacket, <?, e, into which steam is conducted by 
 
Processes for obtaining Chlorine Gas. 
 
 419 
 
 the tube, /, and thus the heat necessary for the decomposition is kept 
 up ; a waste pipe, g, serves for running out the residue of one process 
 in order to clear the still for another. 
 
 Chlorine may be, however, more conveniently prepared from the 
 muriatic acid of commerce, which is a solution of chloride of hydrogen 
 gas in water. This is completely decomposed by peroxide of manga- 
 nese at very moderate temperatures, the hydrogen of the muriatic acid 
 combining with the oxygen of the peroxide of manganese, to form a 
 deuto-chloride of manganese, which is completely resolved by a very 
 moderate heat into proto-chloride and free chlorine. Thus, at first, 
 MnO 2 and 2.C1.H. give MnCl 2 and 2HO., and then MnCl 2 separates 
 into MnCl and Cl, which is evolved as gas. 
 
 This process also is employed, and indeed now more frequently on 
 the great scale, and also very often a mixture of muriatic and sulphuric 
 acids is employed in the proportions of an equivalent of each ; so that 
 the residue in the still is sulphate of the protoxide of manganese, 
 MnO 2 with HC1 and SO 3 producing MnO. S0 3 . HO and Cl. The still 
 is now also frequently constructed, not of lead but of slabs of sand- 
 stone cemented, the bottom being of iron, which, as it is gradually 
 worn away by the acid, may be easily replaced. 
 
 AYlien it is wished to prepare chlorine on the small scale, for laboratory 
 purposes, in the state of gas, it is only necessary to introduce about 
 one part of peroxide of manganese and three of muriatic acid into an ap- 
 paratus, such as those already often figured, and the gas may be obtained. 
 The collection of the chlorine requires some remark. It is absorbed ra- 
 pidly in cold water, and it cannot be collected over mercury, as it com- 
 bines rapidly with it, forming calomel; water, heated to above 90, 
 should therefore be used, but it is still better to take advantage of the 
 great density of chlorine for its collection. 
 
 If the tube conducting the chlorine from the flask a, in which it is 
 
 generated, be brought to the 
 bottom of a dry glass, c, the 
 chlorine issues there, and being 
 much heavier than the air, 
 pushes the air up out of its 
 way, and gradually fills the jar 
 completely, precisely as by con- 
 ducting a stream of water to 
 the bottom of a vessel contain- 
 ing oil, this might be perfectly 
 expelled, and the vessel filled 
 with water. The colour of the 
 
420 Properties and Preparation of Chlorine. 
 
 chlorine allows the gradual filling of the bottle to be seen, and by 
 stopping its aperture with a greased stopple, the gas may be preserved 
 unaltered for a long time. 
 
 A very convenient mode of preparing chlorine, without heat, is by 
 the action of muriatic acid on chlorate of potash. The large quantity 
 of oxygen which this salt contains, uniting with the hydrogen of the 
 muriatic acid, forms water, whilst chlorine is set free. Thus, KO. 
 C10 5 and 6HC1 produce KC1. 6HO and 6.C1. ; it is only necessary to 
 drop to the bottom of a glass or bottle the chlorate of potash in crys- 
 tals, and pour on the liquid muriatic acid ; the salt dissolves with 
 effervescence, and the heavy chlorine gas rapidly fills the vessel, and is 
 recognized by its peculiar colour. 
 
 The chlorine, when thus prepared, is a greenish yellow gas, whence 
 its name, (%^o$) of an extremely suffocating odour, irritating the air 
 passages when respired, even though very much diluted, in an intolerable 
 degree; its specific gravity is 2470. On plunging a lighted taper into 
 chlorine, it burns for a moment with a red smoky flame, but is soon 
 extinguished. Many bodies burn, however, more readily in chlorine 
 than in air, or even in oxygen gas. If some powdered antimony or 
 arsenic be thrown into a bottle of chlorine, they take fire, with bright 
 scintillations. Tin or brass foil burns spontaneously, as also phospho- 
 rus, although with little light. A paper dipped in oil of turpentine 
 takes fire spontaneously, the hydrogen burning, and the carbon being 
 deposited as a thick black smoke. The affinity of chlorine for hydrogen 
 is very great : when mixed, these gases gradually unite, even at com- 
 mon temperatures, and suddenly with explosion, if set on fire by a 
 taper, or by the electric spark. The remarkable action of light in con- 
 fering upon chlorine the property of afterwards uniting with hydrogen 
 in the dark has been described in page 234. In consequence of this 
 affinity for hydrogen, chlorine decomposes most organic substances, 
 one-half of the chlorine removing an equivalent quantity of hydrogen, 
 and the other half going in its place ; thus, ether and chlorine give 
 chloride of hydrogen and chlorine ether; C 4 H 5 and 10C1 giving C 4 C1 5 O 
 and 5HC1. Very often, however, the action of chlorine is much more 
 complex. 
 
 Perhaps the most important character of chlorine, and certainly that 
 upon which its value in the arts depends, is its power of removing the 
 colour of organic substances; its bleaching properties. Formerly it 
 was considered that water was necessary for this bleaching, and that 
 the chlorine combined with the hydrogen, whilst the oxygen of the 
 water being thus thrown upon the organic substance, oxidized it, and 
 formed a new body, which was colourless. I have shown, however, 
 
Bleaching Power of Chlorine. 421 
 
 that this is not the case, but that the chlorine enters into the constitu- 
 tion of the new substance formed, sometimes replacing hydrogen, at 
 others simply combining with the coloured body, and in some, the 
 reaction being so complex, that its immediate stages cannot be com- 
 pletely traced. I shaU notice this agency of chlorine again, when de- 
 scribing the chloride of lime, and also when discussing its relations to 
 organic chemistry. 
 
 Prom this action on organic bodies, chlorine is extensively employed 
 as a disinfectant, to remove the miasmata and infectious impurities by 
 which the atmosphere of an hospital may be contaminated. Eor this 
 purpose, it is desirable to evolve the gas slowly, but continuously ; in 
 order to do so, some chloride of lime, diffused through water, may be 
 placed in a capsule or teacup, and by a funnel, the throat of which is 
 partly stopped, dilute sulphuric acid be allowed to drop down on it. 
 The acid takes the lime, and the chlorine is set free. 
 
 When chlorine is brought into contact with water at 32, they com- 
 bine, forming a hydrate which crystallizes in plates, and which, when 
 heated to about 45, is decomposed. If a quantity of these crystals 
 be sealed up in a strong glass tube, the chlorine, when liberated, exer- 
 cises so much pressure, as to condense itself into a liquid. This was 
 the first instance in which the liquefaction of the gases was successful. 
 Water holding chlorine in solution possesses the colour, odour, taste, 
 and bleaching properties of the gas itself, and may hence be used for 
 the purposes of the arts, although not so manageable or convenient as 
 many other forms. When chlorine water is exposed to the light, it is 
 gradually decomposed, chloride of hydrogen being formed, and oxygen 
 set free ; the solution becomes colourless, loses its bleaching powers, 
 and acquires an acid reaction. In contact with other bodies, chlorine 
 may decompose water much more rapidly; and is hence frequently em- 
 ployed as an oxidizing agent, substances being frequently oxidized by 
 chlorine to a higher degree than by nitric acid. This results, probably, 
 from the chlorine first combining with the body, and the compound 
 then decomposing water ; thus, when chlorine converts selenious acid 
 into selenic acid, it is probable that it is not that the chlorine decom- 
 poses water, but that it unites with the selenious acid, forming chloro- 
 selenious acid, Se0 2 .Cl, which, in contact with water, is resolved into 
 SeO 2 .O and C1H. Very frequently chlorine oxidizes a metal to a higher 
 degree by combining with one portion of it, and hence throwing all of 
 the oxygen upon the remainder ; thus, protoxide of iron is converted 
 into peroxide, by chlorine, because 6FeO, acted on by 3C1/ produce 
 Ee 2 Cl 3 and 2FeaO 3 . The direct decomposition of water by chlorine, I 
 consider to occur very seldom. 
 
Oxidizing Power of Chlorine. 
 
 The combinations of chlorine form, perhaps, next to those of oxygen, 
 the most complete series which exists in chemistry. Its affinities are so 
 varied that it unites with almost all the simple bodies, metallic and non- 
 metallic, and in most cases it forms more than one compound with the 
 other body. Its metallic compounds are generally constituted like the 
 oxides of the same metals, but in its union with the non-metallic bodies, 
 it does not appear to follow so closely the analogies of oxygen. 
 
 Chlorine has been supposed to possess also the property of combining 
 with metallic oxides without decomposition, in many cases, and of form- 
 ing compounds resembling peroxides, in which a portion of the oxygen 
 is replaced by chlorine. Thus, with lime it appears to form CaO . Cl . 
 with protoxide of lead PbO.Cl. with barytes BaO.Cl. which correspond 
 probably to Pb.O 2 and Ba.O 2 . In the hydrate of chlorine, which is 
 Cl -f 10HO, it is likely that a compound corresponding to peroxide of 
 hydrogen may exist, and that the constitution of the crystals may be 
 HO.C1 -|- 9HO, and that bleaching compounds in general may have 
 that type. The theory of those compounds is, however, very doubtful, 
 and they will require to be discussed specially, as containing oxygen 
 compounds of chlorine. 
 
 Chlorine is easily recognised, when free, by its peculiar odour, by its 
 bleaching powers, and by producing with a solution of nitrate of silver 
 a white curdy precipitate, which is insoluble in acids but soluble in water 
 of ammonia, and is rapidly blackened by exposure to the sun's rays. 
 When in combination with a metal, its solution gives the same kind of 
 precipitate of chloride of silver, but the bleaching properties and smell 
 are absent, 
 
 Compounds of Chlorine with Oxygen. 
 
 These are seven, constituted as follows : 
 
 Hypochlorous acid, . Cl + O = 35-47 + 8 = 43-47 
 
 Chlorous acid, . . . = Cl -j- 3O = 35 ' 47 + 24 = 59 - 47 
 
 Perchlorous acid, . . = Cl -f- 40 = 35-47 + 32 =67 -47 
 
 Chloric acid, , . . = Cl -f 5O = 35 "47 -f- 40 = 75 -47 
 
 Perchloric acid, . . = Cl -f- 7O = 35-47 -f- 56 = 91 -47 
 
 Chloroso-Chloric acid, = Cb -J- 13O == 106-4 -}- 104 = 210-4 
 
 Chloroso-Perchloric acid, = C1 3 4. 17O = 106-4 -f. 136 = 242-4 
 
 Hypochlorous Acid. 
 
 If red oxide of mercury, diffused through a small quantity of water, 
 be introduced into bottles containing chlorine, and the whole be agi- 
 tated, the gas is rapidly absorbed, and combining with both constituents 
 
Hypochlorous Acid. 423 
 
 of the oxide, forms chloride of mercury and hypochlorous acid. Thus, 
 Hg. O and 2C1 give Hg. Cl and Cl. O. As there is always an excess of 
 oxide of mercury employed, the chloride of mercury combines with it, 
 forming the insoluble brown oxychloride of mercury Hg.Cl + 3Hg. O 
 which separates, and the hypochlorous acid remains nearly pure in solu- 
 tion in the water. By a very moderate heat it may be distilled in a 
 dilute form, and so obtained quite free from mercury; but at 212 
 the acid is rapidly decomposed into chlorine and oxygen. 
 
 A solution of hypochlorous acid is yellow ; its odour is like that of 
 chlorine ; it bleaches powerfully ; it decomposes spontaneously even 
 in the cold, forming chlorine and chloric acid ; it oxidizes most bodies 
 with extreme energy. To obtain it in the gaseous form, it is sufficient 
 to introduce a small quantity of the solution into a tube over mercury, 
 and to add pieces of dry nitrate of lime, the water is absorbed by this 
 deliquescent salt, and the acid remains as a reddish yellow gas, nearly 
 similar to chlorine in all respects ; water absorbs 200 volumes of it ; by 
 raising its temperature even slightly, it explodes, and its volume is in- 
 creased by one-half : 100 volumes of it produce 100 of chlorine, and 
 50 of oxygen. Its specific gravity is by theory, 3021*3, and its equiva- 
 lent numbers 542*6 or 43*4: its formula is Cl.O. 
 
 The gas may also be obtained by slowly conducting a stream of dry 
 clilorine through a tube containing red oxide of mercury in fine powder. 
 Perfect reaction takes place, and hypochlorous acid gas issues from the 
 other extremity of the tube, and may be collected like chlorine in dry 
 bottles. By intense cold or pressure this gas may be condensed into a 
 bright red liquid. 
 
 The hypochlorous acid combines with bases to form salts, hypochlo- 
 rites, which possesses the bleaching properties of the acid in a great 
 degree ; but their nature is involved so much in the general history of 
 the bleaching compounds of chlorine, that I shall not enter upon any 
 notice of them here. 
 
 Chloric Acid, 
 
 Chloric acid is only formed by the decomposition of the lower oxides 
 of chlorine, which are produced when chlorine is brought into contact 
 with an alkaline solution ; the gas being absorbed with great avidity, 
 and the liquor acquiring powerful bleaching properties. As to the 
 nature of the reaction, it may be supposed, on the one hand, that the 
 chlorine unites directly with the alcali, forming simply, if potash be 
 employed, chloride of potassa, KO.C1. : on the other hand, it is possible 
 that a quantity of alcali may be decomposed, and that chloride of potas- 
 sium and hypochlorite of potash may coexist in the liquor ; thus, that 2KO 
 
4*24} Preparation of Chloric Acid. 
 
 and 2C1 should produce KC1 and Cl. + KO. The majority of chemists 
 incline to the latter view, but the subject will hereafter receive detailed 
 consideration. In any case this bleaching alcaline liquor becomes com- 
 pletely decomposed by boiling, particularly if it be very concentrated. 
 Oxygen gas is then evolved in considerable quantity, whilst chloride of 
 potassium and chlorate of potash are produced, thus 9(K.O + Cl.O) 
 evolve 12O and form 8KC1 and KO + C1O 5 . It is in this way that the 
 chlorate of potash of commerce is obtained, and from it the chemist pre- 
 pares chloric acid. 
 
 A solution of this acid is readily prepared, by decomposing a solution 
 of chlorate of barytes by sulphuric acid. It cannot be obtained solid, 
 as when a concentrated solution of it is heated, it is resolved into chlo- 
 rine, oxygen, and perchloric acid. It does not bleach ; it does not 
 precipitate a solution of nitrate of silver : when in its strongest form, that 
 of a thick oily consistence, it sets fire to many organic bodies and is a 
 powerful oxidizing agent. 
 
 The compounds of chloric acid are easily recognized, by yielding, 
 when heated, oxygen and a metallic chloride ; thus the chlorate of pot- 
 ash is used in the preparation of oxygen, (p. 338) C10 5 + KO, giving 
 C1K and 6.O. When mixed with sulphur, and rubbed in a warm mor- 
 tar, they explode, and if thrown upon an ignited coal, they deflagate 
 with violence. 
 
 The chlorate of potash is of very great commercial importance, from 
 its utility in making matches, and is the source from whence the che- 
 mist obtains the remaining compounds of chlorine and oxygen. 
 
 The constitution and equivalent numbers of chloric acid are as fol- 
 lows by weight, 
 
 Chlorine, 46'95 One equivalent = 4437 or 35'47 
 Oxygen, 53-05 Five equivalents = 500-0 or 40'0 
 
 100-00 943-7 75-47 
 
 Its formula is C10 5 and like the nitric acid which it resembles in so 
 many other properties, it consists of five volumes of oxygen united to 
 two of the other element. 
 
 Perchlorous Acid. When chlorate of potash in fine powder is de- 
 composed by moderately strong sulphuric acid, the chloric acid, at the 
 moment of being set free, breaks up into two other compounds, one 
 containing more, and the other less oxygen, the former being the perchlo- 
 rous, and the latter the perchloric acid; 3. C10 5 giving 2(C10 4 ) and 
 C1O 7 . This process must be conducted very cautiously, and the retort 
 warmed very gently in a water bath. The perchlorous acid may be col- 
 
Perchlorous and Chlorous Acids. 425 
 
 lected over mercury, or from its great density, like chlorine, in a dry 
 jar ; there remains in the retort, a mixture of bisulphate and of per- 
 chlorate of potash. 
 
 This acid gas is of a rich yellowish green colour, and an aromatic 
 odour ; it is rapidly absorbed by water ; by pressure it is condensed 
 into a deep red-coloured liquid ; it bleaches strongly, and is a powerful 
 oxidizing agent, its elements separating from the slightest causes. If it 
 be heated above 212 it explodes with a flash of light ; phosphorus im- 
 mersed in it takes fire spontaneously, and burns brilliantly in the mix- 
 ture of chlorine and oxygen which results from its decomposition. This 
 may be very well shewn by placing some crystals of chlorate of potash 
 and some phosphorus, together, at the bottom of a tall glass filled with 
 water, and conducting to the mixture, by means of a long glass funnel, 
 some oil of vitriol, the phosphorus burns in each bubble of perchlorous 
 acid gas which forms, and a brilliant combustion under water results. 
 
 When this gas is decomposed, 100 volumes produce 150, of which 
 50 are chlorine and 100 oxygen; its specific gravity may therefore be 
 calculated to be 2337*5. 
 
 The perchlorous acid combines with bases to form salts, perchlorites, 
 which possess bleaching properties, but are not of much importance, 
 as they do not enter into practical use. 
 
 The true chlorom acid, which had been suspected to exist in the 
 bleaching liquids of the arts, has lately been isolated aud its existence 
 proved by Millon, its formula is C1O 3 . It is prepared by acting on an 
 equivalent of chloric acid by an equivalent of arsenious acid. A simple 
 reaction occurs, C10 5 and AsO 3 producing As0 5 and C10 3 . By gently 
 heating the liquor the chlorous acid is expelled as gas, whilst the arsenic 
 acid remains dissolved. The gaseous chlorous acid may also be prepared 
 by acting on a mixture of arsenious acid and chlorate of potash with 
 nitric acid. A very gentle heat must be applied, as otherwise the gas 
 might be decomposed with a violent explosion. 
 
 This gas is of a green yellow colour. Its general properties are 
 similar to those of hypochlorous and perchlorous acids. It is decom- 
 posed by light. It does not act on the metals when dry, but rapidly 
 oxidizes them if water be present. It has no action on arsenious acid, 
 which therefore cannot be used to measure its bleaching property. It 
 consists of two volumes of chlorine and three of oxygen, and its equiva- 
 lent is 59-47 or 743-7. 
 
 Perchloric Acid. This acid is formed in the process for obtaining per- 
 chlorous acid, as already described, and is obtained by washing the saline 
 residue with cold water. The bisulphate of potash readily dissolves, 
 leaving behind the perchlorate of potash, which is but sparingly soluble 
 
426 Preparation of Perchloric Acid. 
 
 therein ; this may then be dissolved in boiling water, from which it 
 crystallizes as the solution cools. When the object is only the prepa- 
 ration of perchloric acid, and not of chlorous acid, the process becomes 
 easier by heating chlorate of potash with dilute nitric acid ; the ele- 
 ments of the chlorous acid are then separated, merely mixed together, 
 and the explosions and sputtering which occur with sulphuric acid are 
 avoided. 
 
 In the process of obtaining oxygen from chlorate of potash, there 
 occurs a period at which it is necessary to elevate the temperature very 
 much in order to keep up the evolution of gas ; this arises from the 
 salt being at first decomposed into oxygen, chloride of potassium, and 
 perchlorate of potash, 3(KO. C1O 5 ) giving 2(C1K) and KO.C10 7 whilst 
 100 are evolved as gas. This is five-ninths of the oxygen which the 
 salt contains. If the saline mass then remaining be washed with a 
 small quantity of water, the chloride of potassium dissolves, and the 
 perchlorate of potash remains behind. 
 
 Perchloric acid may be prepared from this potash salt by mixing it, 
 in a retort, with half its weight of oil of vitriol, and as much water. 
 If it be distilled with an excess of oil of vitriol, it may be obtained free 
 from water, and is then a white crystalline mass, very deliquescent, and 
 evolving great heat when mixed with water. In this process, however, 
 a great part of the acid is decomposed. 
 
 The perchloric acid is the most stable compound of chlorine and 
 oxygen. It is not decomposed by muriatic acid, by which the chloric 
 acid is immediately decomposed, a mixture of chlorous acids and chlorine 
 being evolved. By this means the salts of perchloric and of chloric acid 
 may be distinguished. It is not decomposed by alcohol, nor has it any 
 spontaneous action on organic bodies. It is well characterized by the 
 very sparingly solubility of its potash salt, whence it has been employed 
 as a reagent to detect that alcali. 
 
 The constitution and equivalent numbers of perchloric acid are as 
 follows : 
 
 Chlorine, 3874 One equivalent, = 442-6 or 35-4 
 Oxygen, 61-26 Seven equivalents, = 700-0 or 56-0 
 
 100-00 1142-6 91-4 
 
 Millon has recently demonstrated the existence of two more com- 
 pounds of chlorine and oxygen of a very complex nature. 
 
 Chloroso-chloric Acid.C\f) ls . or C10 3 + 2C1O 5 . When chlorate 
 of potash is acted on by muriatic acid, a green yellow gas is produced 
 which was named by Humphrey Davy euchlorwe> and was described by 
 him as a protoxide of chlorine ; but this gas was found to be a mere 
 
Chloride of Hydrogen. 427 
 
 mixture of chlorine, and as it was thought perchlorous acid. * Millon, 
 however, on cooling the gas found that the liquid which condenses is 
 not perchlorons acid, but a new body, which is decomposed by bases 
 into one equivalent of chlorous and two of chloric acid. It is not 
 otherwise important. 
 
 Chloroso-perchlaric Acid.C[ 3 O l7 or C10 3 + 2C1O 7 . When perchlo- 
 rous acid gas is exposed to bright light it separates perfectly into chlorine 
 gas and perchloric acid, which deposits in crystals on the side of the jar, 
 but if the light be feeble a deep red liquid condenses on the inside of 
 the vessel and runs down in drops. This liquid fumes strongly in damp 
 air. It is decomposed by heat without explosion : by bases it is de- 
 composed into chlorous and perchloric acids, and it gradually undergoes 
 a spontaneous decomposition of the same nature. 
 
 Compound of Chlorine with Hydrogen. Muriatic Add or 
 
 Hydrochloric Acid. 
 Symbol. HC1. Eq. 36*47 or 469'2. 
 
 This compound exists naturally as a gas, of which a solution in water 
 has been known since a very early period in chemistry under the names 
 of spirit of salt, marine acid, muriatic acid, hydrochloric acid, and, 
 more properly, chloride of hydrogen. In speaking of it under ordinary 
 circumstances, I shall use the common names of liquid or gaseous 
 muriatic acid, according as it is free or combined with water ; but in 
 cases where its functions in combination are discussed, I shall term it 
 chloride of hydrogen. 
 
 To prepare the gaseous muriatic acid, a small quantity of the com- 
 mercial spirit of salt may be placed in a flask or retort, connected with 
 the mercurial pneumatic trough, and the gas, which passes off on the 
 application of heat, collected. It may also be prepared by the action 
 of oil of vitriol on common salt ; water being decomposed, its oxygen 
 unites with the sodium, forming soda, which combines with the sul- 
 phuric acid, whilst its hydrogen, uniting with the chlorine, produces the 
 chloride of hydrogen, which is given off as a gas ; the reaction may be 
 thus expressed SO 3 .HO and NaCl give SO 3 .NaO and H.C1. 
 
 This gas may also be formed by putting together chlorine and hydro- 
 gen, in equal volumes. Even in diffuse light, they combine completely 
 in some hours, but, in the direct sunshine, the union is instant and ex- 
 plosive. The mixture may also be fired by the taper or by the electric 
 spark ; the colour of the chlorine disappears, and the resulting muriatic 
 acid gas occupies the same volume as its ingredients. In almost all 
 
428 Composition of Chloride of Hydrogen. 
 
 cases of the action of chlorine on organic matters, this substance is also 
 formed : indeed, the agency of chlorine in bleaching, and in decom- 
 posing organic compounds, appears generally to result from its dispo- 
 sition to unite with hydrogen. ^ ^ 
 
 The chloride of hydrogen is a colourless and invisible gas. When 
 completely dry it has no action on vegetable colours, but if a trace of 
 moisture be present it reddens litmus paper, and restores the colour of 
 turmeric paper that had been browned by an alkali ; hence, it is gene- 
 rally looked upon as a powerful acid. When mixed with damp air, it 
 forms heavy white fumes, by uniting with the watery vapour, and con- 
 densing in minute drops of liquid acid. It may be liquefied by great 
 pressure. It cannot be breathed, but does not produce anything like 
 the suffocating effects of chlorine. 
 
 When muriatic acid gas is put in contact with a metallic oxide, both 
 are decomposed, a metallic chloride and water being produced ; thus, 
 Cu.O and H.C1 give Cu.Cl and H.O. If any of the more oxidable 
 metals, as iron, zinc, or potassium be heated in a current of the gas, it 
 is decomposed, a metallic chloride being formed, and hydrogen gas 
 evolved. This occurs, also, when these metals are immersed in the 
 liquid acid ; a copious effervescence is produced by the escape of hydro- 
 gen, and the water holds a chloride of the metal in solution. In this 
 way muriatic acid may be proved to consist of equal volumes of hydro- 
 gen and chlorine united without condensation. Its specific gravity is, 
 by theory, 
 
 One volume of chlorine, . . . = 2470-0 
 One volume of hydrogen, . . . == 69-3 
 
 give two volumes of muriatic acid, = 2539 -3 
 
 of which one weighs, therefore, . 1269-9 
 its constitution and equivalent numbers are, therefore, 
 
 Chlorine, 97'26 One equivalent = 443*7 or 35*47 
 Hydrogen, 2'74 One equivalent = 12-5 or 1-00 
 
 100.00 456-2 36.47 
 
 This gas is distinguished by its great affinity for water. If a jar of it 
 be opened under water, this fluid rushes in, as if it were into a vacuum. 
 If a fragment of ice be introduced into a bell glass of the gas, over 
 mercury, the ice instantly melts, and the mercury rises in the tube, the 
 gas being totally absorbed. The solution of the gas in water is one of 
 the most valuable agents in chemical research. To prepare liquid muri- 
 atic acid in the laboratory, chloride of sodium is to be introduced into 
 
Preparation of Muriatic Acid. 429 
 
 a glass globe, placed in a sand bath on the furnace, as in the figure, 
 
 and then an equal weight of sulphuric acid and the same of water, 
 mixed together, are to be introduced by the funnel : the decomposition 
 proceeds as already explained, and the gas evolved passes by the tube 
 into the first of a range of three-necked bottles, as in the figure. 
 Each bottle is about half full of water. When that in the first has 
 become completely saturated with the gas, this passes into the second, 
 and when it has been saturated, into the third. The vertical tube 
 in the central neck of each bottle is a safety tube, the action of 
 which is as follows : If a sudden condensation occurred in the first 
 bottle, the acid in the second might, by the greater pressure on its 
 surface, be forced back into it ; but before it can rise so high as to pass 
 through the connecting tube, the external air enters by the safety tube, 
 being driven in by the difference of pressure inside and outside, and 
 thus restores the equilibrium. Pure muriatic acid may be much more 
 conveniently prepared for laboratory use by rectifying the spirits of salts 
 of commerce. When this is placed in a distilh'Dg apparatus, arranged 
 as that figured in p. 380, and that about one-fourth as much water is 
 introduced into the receiver, to condense the quantity of gas which is 
 first expelled, the distillation may be carried on until the retort shall be 
 nearly empty, and an acid so obtained completely pure, and of a very 
 convenient strength for the general range of applications. 
 
 As the muriatic acid of commerce is now frequently contaminated by 
 the presence of arsenic, derived from the oil of vitriol used in its manu- 
 facture, having been made with iron pyrites, (see page 400,) and that 
 the purification of it would be troublesome, it is better to make it 
 directly from oil of vitriol and common salt, and the process above given 
 may be usefully modified as proposed by Gregory, as follows : 
 
430 . Preparation of Muriatic Acid. 
 
 Six parts by weight of pure salt, are introduced into a flask containing 
 a mixture of ten parts by weight of oil of vitriol and four of water, pre- 
 viously cooled. A long tube bent twice at right angles being adjusted 
 to the flask, its extremity is made just to touch the surface of a quantity 
 of distilled water of the same weight as the salt, and contained in a 
 bottle immersed in ice or cold water. A gentle heat is now applied to 
 the flask, which is placed in a sand bath, and continued as long as gas 
 comes over. About two-thirds of the acid gas comes over dry, but the 
 last third is mixed with steam, and the receiver should then be changed, 
 when a second portion of acid may be obtained, though not so strong 
 as the first, which has usually a sp. gr. of 1'140. By using a second 
 charge of salt and oil of vitriol with the same receiver, the muriatic 
 acid may be obtained in its most concentrated form with a sp. gr. of 
 1-210. 
 
 In this process, there being two atoms of sulphuric acid used to one 
 of salt, the latter is decomposed at a low temperature, and as the oil of 
 vitriol is diluted, chloride of arsenic is not formed, and no arsenious 
 acid can be distilled over. 
 
 The manufacture of this acid is carried on, on a very large scale, more 
 generally with a view to the extraction of the alcali from the residual 
 sulphate of soda, than for sake of the muriatic acid. The great diffi- 
 culty in a soda factory being, how to get rid of the muriatic acid which 
 is produced. When the object is, however, to prepare the liquid acid, 
 precisely the same apparatus is employed as for the manufacture of nitric 
 acid, which has been already figured and described, (p. 382,) the cylin- 
 ders being somewhat larger, as from four to five cwts. of common salt 
 are generally decomposed in each cylinder at a charge ; the upper part 
 of the cylinder is generally, both in this operation and in the making of 
 nitric acid, protected from the too corrosive action of the acid vapours, 
 by being lined internally with thin fire tiles, and the heads ee in the 
 figure are very frequently constructed, not of metal, but of freestone or 
 of granite. In the decomposition of the salt upon this large scale, the 
 oil of vitriol is employed of the strength to which it is brought in the 
 chambers, without concentration, and in such quantity, that for each 
 equivalent of chloride of sodium, an equivalent of real sulphuric acid is 
 employed. The strongest liquid muriatic acid, thus prepared, possesses 
 a specific gravity of 1*211. In order to obtain water fully saturated 
 with the gas, it must be kept near the freezing point by artificial cold, 
 it then absorbs 480 times its volume, and increases in bulk, by about 
 one-fifth. Its constitution is quite definite, for in this state it consists 
 of HC1+6HO or in numbers, 
 
Liquid Muriatic Acid. 431 
 
 Muriatic acid, 40-27 One equivalent = 456-2 or 36-47 
 Water, . .59'73 Six equivalents = 675-0 or 54-0 
 
 100-00 1131-2 90-47 
 
 When this concentrated acid is heated, it evolves a large quantity of 
 gas, and the boiling point gradually rises to 230, at which temperature 
 the residual acid distils over unchanged ; it then has a specific gravity 
 of 1'094, and consists of HC1+16HO or in numbers, 
 
 Muriatic acid, 20' 13 One equivalent, = 456-2 or 36-47 
 Water, 79'87 Sixteen equivalents, = 1800-0 or 144-0 
 
 100-00 2256-2 180-47 
 
 Graham has found, that the strong acid, when evaporated in the 
 open air, abandons a quantity of gas, whilst the remaining liquid becomes 
 HC1+12HO. 
 
 The metallic character of hydrogen, and the analogy of its combina- 
 tions with those of zinc, is completely shewn by comparing the formulae 
 of the compounds of oxide and chloride of hydrogen with the compounds 
 of oxide and chloride of zinc, and their combinations with water. 
 Thus I have shewn, that the hydrates of oxychloride of zinc are as 
 follows : 
 
 ZnCl -f 6ZnO 
 
 ZnCl + 6ZnO -f 6 Aq. 
 
 ZnCl -f 6ZnO -f- 10 A <1- 
 
 and the definite states of liquid muriatic acid are 
 
 HC1 + 6HO. 
 
 HC1 + 6HO + 6 Aq. 
 
 HC1 + 6HO + 10 Aq. 
 
 As we proceed, other similar proofs of the electro-positive and 
 metallic character of hydrogen will be found. 
 
 The other degrees of strength of the liquid muriatic acid are solu- 
 tions in water of one or other of these definite compounds ; a table of 
 them will be found in the appendix. 
 
 The muriatic acid of commerce frequently contains sulphuric acid, 
 and always a trace of iron, derived from the metal cylinders in which 
 it is fabricated. Occasionally, sulphuric acid is formed in it in small 
 quantity. These impurities are detected thus : by diluting the muri- 
 atic acid with water, and adding nitrate of barytes, a white precipitate 
 is formed, if sulphuric acid be present ; yellow ferroprussiate of potash 
 indicates the existence of iron ; whilst solution of protochloride of tin 
 produces a brown precipitate of sulphuret of tin, if sulphurous acid 
 
Nitro-Muriatic Acid. 
 
 had been present. The bichloride of hydrogen, described by Millon, 
 has not been found to have any real existence. 
 
 Muriatic acid is easily recognized, as a gas, by its action on moist 
 litmus paper, its fuming in the air, its forming with ammonia dense 
 white clouds of salammoniac, and in solution, by giving with nitrate of 
 silver a curdy white precipitate, which blackens on exposure to light, 
 is totally insoluble in nitric acid, but dissolves easily in water of 
 ammonia. 
 
 Niiro-muriatic Acid. Aqua Eegia. When nitric and muriatic 
 acids, both colourless, are mixed together, the mixture becomes deep 
 yellow, and exhales a strong smell of chlorine and of nitrous acid, 
 H.C1 and N0 5 giving Cl and N0 4 , with formation of H.O. This 
 decomposition, however, proceeds only so far as to saturate the liquid 
 with chlorine ; but if a metal be placed in the liquid, it unites with 
 the chlorine, and new quantities of the acid are decomposed. Thus 
 the nitro-muriatic acid is a source of chlorine in a very concentrated 
 state, and is hence employed to dissolve gold and platina, which are 
 not soluble in nitric acid, and to oxidize some bodies (metallic sul- 
 phurets,) which resist the action of nitric acid. The name aqua regia 
 was given to it from its power of dissolving gold, the ancient rex 
 metallorum. It has been supposed by Baudrimont, and by Ed. Davy, 
 that in the action of nitric acid on muriatic acid, or on chlorides, there 
 is generated a peculiar acid, liquifiable gas, termed chloronitrous gas, 
 or chloronitric acid, and the formula NC1 2 O 3 has been proposed for its 
 composition. The product is however proved to be only a mixture of 
 hyponitrous acid and chlorine. 
 
 Chloride of Sulphur. In order to obtain this body, a quantity of 
 sulphur is placed in a tubulated retort, into which a current of chlorine 
 
 gas is conducted, by means 
 of the bent tube e, in the 
 figure. The chlorine and 
 sulphur unite to form a 
 volatile reddish yellow li- 
 quid, which distils over, 
 and condenses in the re- 
 ceiver/J which must be 
 kept very cool; any un- 
 
 condensed gas is conducted away by the tube L The chloride of sul- 
 phur, thus obtained, has always an excess of sulphur dissolved in it, 
 from which it may be freed by a second distillation. Its specific 
 gravity is 1-687. When exposed to the air, it gives off very acrid 
 fumes ; it boils at 280 ; the specific gravity of its vapour is 4686. 
 
Chlorides of Sulphur and Phosphorus. 
 
 433 
 
 It consists of one equivalent of chlorine united to two of sulphur, 
 S^Cl, and in contact with water, muriatic acid, sulphur, and hyposul- 
 phurous acid are formed by mutual decomposition. 
 
 It is probable that there is another chloride of sulphur consisting of 
 one equivalent of each. S.C1. 
 
 Chlorides of Phosphorus. Chlorine unites with phosphorus in two 
 proportions, forming a liquid proto-chloride, P.C1 3 , and a solid perchlo- 
 ride, P.C1 5 . These may be prepared in a simple apparatus like that 
 used for chloride of sulphur ; but as a more complex arrangement is 
 
 necessary for examining the action of chlorine upon many substances 
 that shall be described hereafter, I will introduce the description of it 
 here. The chlorine is generated by liquid muriatic acid and peroxide 
 of manganese, in the flask a, supported on a sand bath over the lamp ; 
 from it a bent tube passes to the receiver, 6, in which a quantity of 
 watery vapour is condensed, and serves to absorb any muriatic gas that 
 might escape decomposition. The pure chlorine passes then through 
 the tube c, which is filled with fragments of fused chloride of calcium, 
 which, from its great affinity for water, dries the gas completely. In 
 the bulb e is contained the substance to be acted on by the chlorine, 
 and the product of the reaction, if volatile, distils over into the receiver 
 k } in which it condenses ; the excess of chlorine escapes by the tube I, 
 and a stream of water from the reservoir i, h, retains the receiver k at 
 the temperature proper for condensation. 
 
 The phosphorus being placed in the bulb e, takes fire on the arrival 
 of the chlorine gas, and continues burning until it is all converted into 
 the liquid chloride which collects in k. Whilst there is an excess of 
 phosphorus, the proto-chloride is principally formed ; but after all the 
 phosphorus has been consumed, if the current of chlorine be continued, 
 it is absorbed by the liquid in k, which changes into the solid per- 
 chloride. 
 
 28 
 
434 Chlorides of Phosphorus. 
 
 The Protochloride of Phosphorus is obtained pure by stopping the 
 process before all the phosphorus has been consumed, and rectifying the 
 colourless liquid by distilling it in a retort containing some bits of 
 phosphorus, which bring back any perchloride it might contain dissolved, 
 to the state of proto-chloride. This body is heavier than water, by 
 which it is completely decomposed, P.C1 3 and 3.H.O giving P.0 3 and 
 3.HC1. It is thus that the liquid phosphorous acid is obtained, as 
 described in p. 411. 
 
 The Perchloride of Phosphorus is a white solid, volatile under 212, 
 and condensing in a crystalline form. In contact with water it is de- 
 composed with the evolution of great heat, producing phosphoric acid 
 and muriatic acid, P.C1 5 and 5.H.O. giving P.O 5 and 5.HO; the sp. 
 gr. of its vapour is 4788, consisting of ten volumes of chlorine and one 
 of vapour of phosphorus, the eleven being condensed to six. 
 
 There is a Chloride of Selenium analogous in general properties to 
 the chloride of sulphur, 
 
 IODINE. 
 Symbol. I. Eq. 126-4 or 1579-5. 
 
 Iodine is found, principally, in sea water, associated with chlorine, and 
 combined with sodium and magnesium. It has been also discovered in 
 the mineral kingdom, united with silver. For the purposes of com- 
 merce it is always extracted from kelp, which is a semifused mass of 
 saline ashes remaining after the burning of various species of fuci (sea 
 weed). 
 
 Tor this purpose, the powdered kelp is lixiviated in water, to which 
 it yields about half its weight of salts. The solution is evaporated 
 down in an open pan, and when concentrated to a certain point, begins 
 to deposit its soda-salts, namely, common salt, carbonate and sulphate 
 of soda, which are removed from the boiling liquor by means of a shovel 
 pierced with holes like a colander. The liquid is afterwards run into a 
 shallow pan to cool, in which it deposits a crop of crystals of chloride 
 of potassium ; the same operations are repeated on the mother-ley of 
 these crystals until it is exhausted. A dense, dark-coloured liquid re- 
 mains, which contains the iodine, in the form, it is believed, of iodide of 
 sodium, but mixed with a large quantity of other salts, and this is called 
 the iodine ley. 
 
 To this ley, the sulphuric acid is gradually added in such quantity as 
 to leave the liquid very sour, which causes an evolution of carbonic 
 acid, sulphuretted hydrogen, and sulphurous acid gases, with a consider- 
 
Manufacture of Iodine. 
 
 435 
 
 able deposition of sulphur. After standing for a day or two, the ley so 
 prepared is heated with peroxide of manganese, to separate the iodine. 
 
 This operation is conducted 
 in a leaden retort, a, (see 
 figure,) of a cylindrical 
 form, supported in a sand- 
 bath, which is heated by a 
 small fire below. The re- 
 tort has a large opening, 
 to which a capital, b, c, 
 resembling the head of an 
 alembic, is adapted, and 
 luted with pipeclay. In 
 the capital itself there are 
 two openings, a larger and 
 a smaller, at b and c, closed 
 by leaden stoppers. A 
 series of bottles d, having each two openings, connected together, as 
 represented in the figure, and with their joinings luted, are used as 
 condensers. The prepared ley being heated to about 140 in the re- 
 tort, the manganese is then introduced, and b c luted to a. Iodine 
 immediately begins to come off, and proceeds on to the condensers, in 
 which it is collected ; the progress of its evolution is watched by occa- 
 sionally removing the stopper at c ; and additions of sulphuric acid, or 
 manganese, are made by b, if deemed necessary. This description of 
 the manufacture of iodine upon the large scale at Glasgow is due to 
 Professor Graham. 
 
 In this operation, the peroxide of manganese will be in contact at 
 once with hydriodic, hydrochloric, and sulphuric acids ; but for success, 
 the quantity of sulphuric acid must be sufficient only to decompose the 
 iodides but not the chlorides. If both were decomposed, the chlorine 
 and iodine simultaneously evolved should unite to form chloride of 
 iodine, by which the iodine would be lost ; but as the chlorine remains 
 combined, the action becomes simply, that the metal of the iodide pre- 
 sent is oxidized by the oxide of manganese, and the iodine set free ; 
 thus, employing iodide of sodium, SO 3 with MnO 2 and Nal, give 
 Mn.O.SO 3 . NaO and I. 
 
 Another mode of preparing iodine consists in adding to the solution 
 containing iodide of sodium, a solution of sulphate of copper, in which 
 the copper is reduced to the state of sub-oxide (Cu 2 0) by means of 
 protosulphate of iron dissolved along with it. By the interchange of 
 elements, sulphate of soda is formed, and a sub-iodide of copper of a 
 
436 Preparation and Properties of Iodine. 
 
 very pale yellow colour/ and "quite insoluble in" water, is produced, 
 SO 3 +Cu 2 O and Nal giving SO 3 +NaO and Cu 2 I. This last is then 
 decomposed by peroxide of manganese and sulphuric acid, as in the 
 former process : in this way the various crystallizations described above 
 may be avoided. 
 
 Iodine exists generally in crystalline scales of a blueish black colour 
 and metallic lustre. It may also be obtained from solution, in the form 
 of oblique octohedrons with a rhomboidal base, as in the figure, or in 
 prisms. The density of iodine is 4*948 ; it fuses at 225, 
 and boils at 347 ; but it evaporates at the usual temper- 
 ature, and more rapidly when damp than when dry, diffu- 
 sing an odour having considerable resemblance to chlorine, 
 but easily distinguished from it. Iodine stains the skin of 
 a yellow colour, which, however, disappears in a few hours. 
 Its vapour is of a splendid violet colour, which is seen to 
 great advantage when a scruple or two of iodine is thrown 
 at once upon a hot brick. Hence- its name, from Iwg/6^, 
 like a violet. The vapour of iodine is the heaviest of gaseous 
 bodies, its density being 8701*0, according to calculation from its 
 atomic weight. 
 
 Pure water dissolves about 1-7 00 Oth of its weight of iodine, and 
 acquires a brown colour. In general, iodine comports itself like chlo- 
 rine, but its affinities are much less powerful. Iodine is soluble in 
 alcohol and ether, with which it forms dark reddish brown liquors ; 
 solutions of iodides, too, all dissolve much iodine. 
 
 A solution of starch forms an insoluble compound with iodine, of a 
 deep blue colour, the production of which is an exceedingly delicate test 
 of iodine. If the iodine be free, starch produces at once the blue pre- 
 cipitate, but if it be in combination as a soluble iodide, no change takes 
 place, till chlorine or nitric or sulphuric acids is added to liberate the 
 iodine. If more chlorine, however, be added than is necessary for that 
 purpose, the iodine is withdrawn from the starch, chloride of iodine 
 formed, and the blue compound destroyed. The iodide of starch, in 
 water, becomes colourless when heated to 200, but recovers its blue 
 colour if immediately cooled. The soluble iodides give, with nitrate of 
 silver an iodide of silver, of a pale yellow colour, insoluble in acids and 
 in ammonia ; with salts of lead, an iodide of a rich yellow colour, and 
 with corrosive sublimate, a fine scarlet iodide of mercury. 
 
 Iodine combines with most of the non-metallic bodies, and with all 
 the metals, forming compounds which possess the closest similarity to the 
 analogous compounds of chlorine. It is employed in the laboratory for 
 many chemical preparations, and as a test of starch, and for several metals. 
 
Preparation of Iodic Acid. 437 
 
 Compounds of Iodine and Oxygen. 
 
 lodousacid IO4. Eq. 126-4 +32= 158-4 
 
 lodoso-iodic acid I 5 O 19 Eq. 632- + 15 ' 2 = 784- 
 
 lodicacid ...IO 5 126-4 +40 = 166-4 
 
 Periodic acid I0 7 126-4 + 55 = 1S2-4 
 
 The two first named bodies are but of inferior importance, they are 
 prepared by the action of the nitric and sulphuric acids on iodine, and 
 on the iodic acid. If very strong nitric acid be digested on finely divided 
 iodine without heat, the latter is converted into a yellow powder, which 
 is a compound of nitric acid with iodous acid. 
 
 lodous acid. The latter is obtained free and pure by circuitous 
 processes, which need not be described here. When iodic acid is 
 boiled in oil of vitriol some oxygen is given off and a compound of 
 sulphuric acid and iodoso-iodic acid precipitates. This last is of very 
 complex composition, and most probably a compound of iodic acid with 
 a hypo-iodic acid not yet isolated, IO ; being similar to the complex 
 oxacids of chlorine, described page 422. 
 
 Iodic Acid. This acid may be very easily prepared by boiling iodine 
 in fuming nitric acid, until it is all dissolved, and then distilling off the 
 excess of acid ; the iodic acid remains as a white crystalline mass, which 
 deliquesces in the air. If the quantity of iodine be large, this process 
 would occupy a very long time ; and a much shorter, though more 
 complex method is the following : The iodine being diffused through 
 water, a current of chlorine is passed through it until all iodine is dis- 
 solved ; the acid liquor so obtained is to be neutralized by carbonate of 
 soda, by which a quantity of iodine is precipitated ; the chlorine is then 
 passed through until this iodine disappears, and then more carbonate of 
 soda added; and this alternation continued until 'the addition of the 
 carbonate of soda produces no deposit of iodine ; the solution contains 
 then iodate of soda and chloride of sodium, generated by the decompo- 
 sition of the soda by the chloride of iodine first formed. Thus, 5C1 
 and I produce IC1 5 , which, with 6NaO give 5.NaCl and NaO + IO 5 . 
 This solution is then mixed with a solution of a salt of barytes and 
 iodate of barytes precipitates, which may be decomposed by boiling it 
 for some time with one-fourth of its weight of oil of vitriol and 1 \ times 
 its weight of water; the sulphate of barytes may be then separated 
 by the filter, and the solution of iodic acid evaporated gently to dryness. 
 
 The process recommended by Millon is as follows : 80 parts of 
 iodine, 75 parts of chlorate of potash, 1 part of nitric acid, and 400 
 parts of water are to be digested in a flask and finally boiled for some 
 
438 lodons and lodic Acids. 
 
 time. The iodine totally disappears, and the liquor contains chloride of 
 potassium and iodic acid. On adding a solution of chloride of barium, 
 iodate of barytes is precipitated ; this being washed is decomposed 
 by the equivalent quantity of sulphuric acid ; the sulphate of barytes is 
 separated by filtration, and the iodic acid crystallized from the solution. 
 
 Iodic acid is very soluble in water ; from a strong solution it crystal- 
 lizes in rhombic plates, which contain an atom of water, or in anhydrous 
 octohedrons. When heated strongly it separates into iodine and oxygen. 
 It first reddens, and then bleaches litmus paper. It acts as powerfully 
 as nitric acid in oxidizing the metals. When mixed with solution of 
 sulphurous acid, water and sulphuric acid are formed, and iodine is set 
 free ; with sulphuretted hydrogen it gives water, sulphur, and iodine 
 intermixed : with an excess of this agent the iodine is finally converted 
 into iodide of hydrogen. By these means the iodic acid may be recog- 
 nized, and also by its peculiar action upon morphia, which it decom- 
 poses, iodine being set free. This is more valuable as a character of 
 morphia than of iodic acid. 
 
 The salts of iodic acid resemble the chlorates in most respects, and, 
 like them, when heated, separate into oxygen and a metallic iodide. 
 One mode of preparing the iodide of potassium of commerce is founded 
 on this property. Iodine is dissolved in a solution of potash, and, 
 when dried down, gives a mixture of 5.KI and I0 5 .KO. When this 
 mass is fused, oxygen is given off in abundance, and ultimately pure 
 KI remains. The commercial salt prepared in this way has been shewn 
 by Mr. Scanlan frequently to contain iodate of potash, either fraudu- 
 lently or accidentally, left undecomposed. 
 
 The composition and equivalent numbers of the iodic acid are as 
 follows, its formula being I0 5 : 
 
 Iodine, = 75 -96 One equivalent, = 1579 '5 or 126-4 
 Oxygen, = 24-04 Five equivalents, = 500-0 or 40-0 
 
 100-00 2079-5 166-4 
 
 Its elements are united in the proportion, by volume, of two volumes 
 of vapour of iodine to five volumes of oxygen. 
 
 Per-iodic Acid, IO 7 . If a solution of iodate of soda be mixed with 
 a great excess of caustic soda, and acted upon by a current of chlorine, 
 a quantity of the soda is decomposed ; its sodium combining with the 
 chlorine, whilst its oxygen, being added to the iodic acid, converts it 
 into the periodic acid, which combines with two equivalents of soda. 
 Thus, 2C1 acting on SNaOand I0 5 + NaO, produce 2NaCl and IO 7 + 
 2NaO. On adding to the solution of this salt nitrate of silver, a basic 
 
Periodic Acid Hydriodic Acid. 439 
 
 periodate of silver is produced, which being dissolved in nitric acid, gives 
 yellow crystals of neutral periodate of silver. When put in contact 
 with water these crystals are decomposed, half of the periodic acid pre- 
 cipitating with the whole of the oxide of silver as the insoluble salt, 
 I0 7 -f- 2AgO, whilst the other half of the acid remains in solution 
 quite pure, and by evaporation may be obtained as a white crystallized 
 mass. 
 
 This acid is more stable than the iodic acid ; it resists a higher tem- 
 perature without decomposition. All its important characters may be 
 inferred from the method of preparation. 
 
 Its composition and equivalent numbers are, 
 
 Iodine, 69-31 One equivalent, . = 1579'5 or 126-4 
 Oxygen, 30*69 Seven equivalents, = 700-0 or 56*0 
 
 100-00 2279-5 182-4 
 
 Com/pound of Iodine and Hydrogen. Hydriodic Acid. 
 Symbol. HI. Eq. 1592-0 or 127'4. 
 
 There is but one compound of iodine with hydrogen : this exists 
 under ordinary temperatures and pressures as a colourless gas, which 
 may be best generated in the following manner : Some iodine and 
 small fragments of phosphorus are to be put together at the bottom of 
 a glass tube, then covered with pounded glass, and gently heated, so as 
 to produce combination. Iodide of phosphorus is thus formed. If a 
 little water be now poured on the pounded glass, it filters through to 
 the bottom, and there, acting violently on the iodide of phosphorus, is 
 decomposed ; from P.I and H.O there are pro- 
 duced P.O and H.I. To the mouth of the tube 
 may be adapted, by a cork, a smaller tube, bent 
 as in the figure, and the hydriodic acid gas 
 issuing from it may be collected. This gas is 
 obtained by the method of displacement, as has 
 been described for chlorine (p. 420) ; and as 
 it fumes like muriatic acid when in contact with 
 the air, it can easily be recognized when the 
 bottle is full. 
 The specific gravity of this gas is 4385, produced by 
 
 One volume of vapour of iodine, . . = 8701 -0 
 One volume of hydrogen, = 69'3 
 
 united without condensation, .... 8770*3 
 
 and one volume weighing, therefore, . . . 4385-1 
 
440 "Preparation of Hydriodic Acid. 
 
 . To obtain hydriodic acid dissolved in water, the simplest process is 
 to act on iodine, diffused through water, by sulphuretted hydrogen gas. 
 The iodine combines with the hydrogen, and the sulphur is set free. 
 When the iodine has all disappeared, the liquor should be well boiled 
 to drive off the excess of sulphuretted hydrogen, and then filtered ; the 
 liquid hydriodic acid may be evaporated to a sp. gr. of 1*700 : it is then 
 in its strongest form, and may be distilled unaltered. Liquid hydriodic 
 acid reddens litmus paper strongly ; it dissolves iodine in large quantity ; 
 it is decomposed by all the oxidable metals, and even by mercury ; and 
 hence, the gaseous acid cannot be collected over mercury. Exposed to 
 the air, it rapidly absorbs oxygen, water being formed, and iodine being 
 set free. It is decomposed by sulphuric acid, sulphurous acid and 
 iodine being produced, also by nitric acid and by chlorine. 
 
 Hydriodic acid may also be obtained by acting on iodide of barium 
 with dilute sulphuric acid. 
 
 Its composition and equivalent numbers are as follows : 
 
 Iodine, = 99'22 One equivalent = 1579'5 or 126-4 
 
 Hydrogen, = 078 One equivalent = 12-5 or 1 -0 
 
 100-00 1592-0 127-4 
 
 A solution of hydriodic acid, or of a metal, produces with nitrate of 
 silver, a curdy yellow precipitate, which is insoluble in acids and in 
 water of ammonia ; by this character, the iodides are distinguished from 
 the chlorides, even without the action of starch upon the iodine when 
 set free, 
 
 Iodine and sulphur may be melted together in equivalent proportions, 
 and on cooling form a steel-gray crystalline mass, iodide of sulphur ; 
 which is decomposed gradually by exposure to the air, and appears to 
 be rather a mixture, than a true compound of its elements. 
 
 When iodine and phosphorus are warmed together very gently, they 
 combine, evolving considerable heat, and forming iodides of phospho- 
 rus, the constitution of which depends on the proportions used ; there 
 appears to be at least three : the first fuses at 212, is orange-coloured, 
 and gives, when decomposed by water, hydriodic and hypophosphorous 
 acids, its composition is, therefore, P.I ; the second is grey, it fuses at 
 84, and gives with water, hydriodic and phosphorous acids ; its for- 
 mula is hence, P.I 3 . The third, which produces, when decomposed by 
 water, hydriodic acid and phosphoric acid, consists of P.I 5 , is black, 
 and melts at 114. 
 
 Hydriodic acid combines with phosphuretted hydrogen, forming a 
 white solid compound, the constitution of which is of considerable in- 
 
lodo-phosphuret of Hydrogen. 441 
 
 terest. It cannot be prepared directly, as the gases are without action 
 on each other, except when in their nascent form. It is best prepared 
 by introducing eight -parts of iodine, two of phosphorus, and one of 
 water, into a retort, mixed with some coarsely powdered glass ; to the 
 neck of the retort is adapted a wide glass tube with a cork, through 
 which a small tube passes and dips into some water. On applying 
 heat, the phosphorus and iodine unite, and the iodide of phosphorus, 
 being instantly decomposed by the water, hydriodic acid and hypophos- 
 phorous acid are produced, which last is resolved by contact with the 
 water at that temperature into phosphorous acid and phosphuretted hy- 
 drogen. This last immediately unites with the hydriodic acid, and the 
 compound formed condenses in the neck of the retort in well shaped 
 crystals, which, by a proper management of the heat, may be driven 
 into the wide glass tube to be preserved. The excess of hydriodic acid 
 gas is conducted off by the small tube and condensed in the water. 
 
 This body was supposed to crystallize in cubes, and to be isomorphous 
 with hydriodate of ammonia, to which this formula in one way might 
 assimilate it, HI -f PH 3 corresponding to HI + NH 3 ; the difference 
 being only, that phosphorus replaced nitrogen. It will, however, be 
 shown fully in the division on organic chemistry, that ammonia is not 
 mere nitruret of hydrogen NHg, but that it contains amidogene (NH 2 ) 
 being amidide of hydrogen, Ad. H. It has been also shown, that the 
 crystals of the body HI + PH 3 are not cubes but belongs to a rhombic 
 system. When I come to describe the compounds of mercury, I shall 
 show that there exist similar bodies containing phosphuret of mercury, 
 and nitruret of mercury, and that the constitution of phosphuretted hy- 
 drogen, may with great reason, be supposed, to be, not PH 3 , but that a 
 quantity of phosphorus equal to one-third of its ordinary atomic weight 
 unites with an equivalent of hydrogen, its formula being J.H. and the 
 commonly received equivalent of phosphuretted hydrogen being in rea- 
 lity three equivalents = 3. J.H. I therefore consider the compound, 
 which I have just described, as having for its true constitution, H.I-f- 
 3.J.H as there will be hereafter described, the bodies HgCi-f-S.f.Hg 
 and 2HgCl-f-3.^.Hg: the equivalent of nitrogen being capable of the 
 same subdivision into three. See page 417. 
 
 This hydriodate of phosphuretted hydrogen is decomposed by water, 
 hydriodic acid and phosphuretted hydrogen being given off; the last in 
 the B variety. But if a little oxide of silver be sprinkled on the salt; 
 the gas is evolved in its spontaneously inflammable condition. It burns 
 when heated in air, but in a dry tube containing no oxygen, it may be 
 sublimed from place to place unaltered. 
 
 Chlorides of Iodine. -I have shewn, that chlorine and iodine unite 
 
442 Preparation of Bromine. 
 
 in three proportions forming bodies having the formulae I 4- Cl ; I 4- 
 3C1 and I -f 5C1. By much water the first and second are decom- 
 posed, producing muriatic and iodic acids, and iodine becoming free. 
 The third, which was long ago discovered by Humphrey Davy, gives 
 muriatic and iodic acids without separation of iodine. These bodies 
 are interesting only as being employed to obtain the iodic and periodic 
 acids, as already noticed. 
 
 OF BROMINE. 
 . Br. Eq. 78-26 or 978'3. 
 
 This substance, which is intermediate in almost all chemical proper- 
 ties to chlorine and iodine, exists associated with those bodies in sea 
 water, in many varieties of sea weeds, and in some of the brine springs 
 belonging to the deposits of rock salt in the earth. In these cases it is 
 generally combined with sodium or with magnesium, forming very 
 soluble salts which remain behind when the common salt crystallizes 
 out by evaporation from sea water. When a current of chlorine gas is 
 passed through the mother liquor so obtained, which is called bittern, 
 the bromine is set free and tinges the solution yellow. On agitating 
 this liquor with some ether, the bromine is completely taken up by it, 
 and an ethereal solution of bromine of a fine hyacinth red colour is pro- 
 duced ; when this is acted on by potash, there is found a mixture of 
 bromide of potassium and bromate of potash, which by fusion gives off 
 oxygen, and pure bromide of potassium remains ; this is mixed with 
 peroxide of manganese and sulphuric acid, -and precisely as in the pre- 
 paration of chlorine or of iodine, the bromine is set free and may be 
 distilled over. It is necessary to condense the bromine with great care, 
 and to receive it in water, to the bottom of which it sinks ; the reaction 
 that occurs is, that 2S0 3 , with Mn0 2 and K.Br produce (S0 3 .MnO+KO. 
 SO 3 ) and Br. 
 
 Bromine is a liquid at ordinary temperatures, but at 4 it solidifies ; 
 it is deep red by transmitted, but black by reflected light ; it is much 
 heavier than water, its specific gravity being 2' 9 7 ; its odour is like that 
 of chlorine, but much more disagreeable, whence its name (from Bgw//,og.) 
 It is very volatile, boiling at 116 ; but even at common temperatures it 
 forms copious fumes which have the same orange red colour as those of 
 nitrous acid; the specific gravity of its vapour is 5 '393; it does not 
 conduct electricity ; it must be preserved under water, as otherwise the 
 quantity of vapour it would form might burst the vessel containing it. 
 It dissolves sparingly in water, but copiously in alcohol and ether. A 
 
Properties of Bromine and Bromic Acid. 443 
 
 taper is extinguished by its vapour, but not immediately, burning for a 
 moment with a green flame and much smoke. Some of the metals in 
 fine powder or leaf burn spontaneously in its vapour, as in chlorine ; a 
 drop of liquid bromine put in contact with a globule of potassium unites 
 with it explosively and with brilliant ignition. It bleaches vegetable 
 colours, but leaves itself a yellowish stain, less intense than that of 
 iodine : it is poisonous. 
 
 Bromine unites with water, forming a crystalline hydrate like that of 
 chlorine. 
 
 "\Vith starch, bromine produces a fine yellow colour, which is not 
 intense, if the solution be very much diluted. 
 
 Bromine is easily recognised by the peculiar colour and odour of its 
 vapour, which can only be confounded with that of nitrous and hyponi- 
 trous acid, from which its other characters completely separate it. A 
 solution containing bromine or a metallic bromide, gives, with nitrate of 
 silver, a white, curdy precipitate, insoluble in nitric acid, but dissolved 
 by ammonia. This precipitate is distinguished from the chloride of 
 silver, by giving vapours of bromine when heated with a little chlo- 
 rine water. 
 
 The equivalent numbers of bromine are 978*2, on the oxygen scale, 
 and 78'4, hydrogen being unity. 
 
 Bromic Acid. There is known only one compound of bromine and 
 oxygen, the bromic acid, the history of which is still very imperfect. 
 When bromine is dissolved in a solution of potash, bromide of potas- 
 sium and bromate of potash are formed, 6Br and 6.KO giving 5KBr 
 and BrO 5 + KO. On adding a solution of a salt of barytes to the 
 liquor so obtained, bromate of barytes is precipitated, and this may be 
 decomposed by sulphuric acid, which forms sulphate of barytes, leaving 
 the bromic acid in solution. 
 
 The bromic acid has not been obtained solid ; it is still more easily 
 decomposed by deoxidizing agents than the chloric acid ; thus the sul- 
 phurous acid and the phosphorous acid liberate bromine. The same 
 effect is produced by sulphuretted hydrogen. Its salts have not been 
 much examined, but appear to resemble the chlorates and iodates. 
 
 Its formula is BrO,,, its composition by weight, and equivalent num- 
 bers being 
 
 Bromine, 66-18 One equivalent = 978-3 or 78-26 
 Oxygen, 33-82 Five equivalents = 500-0 or 40-00 
 
 100-00 1478-3 118-26 
 
 These elements are united by volume in the ratio of two volumes of 
 bromine-vapour to five volumes of oxygen. 
 
444 Hydrobromic Acid. 
 
 Hydrobromic Acid. The processes for obtaining the bromide of hy- 
 drogen are precisely the same as those described for preparing hydriodic 
 acid in the liquid or in the gaseous form, to which I shall therefore 
 refer (p. 439) ; bromine being substituted for iodine in every case. 
 This gas is colourless ; it is rapidly absorbed by water, the solution 
 reacting acid : it is not decomposed by oxygen, nor does bromine de- 
 compose water, so that it stands between iodine and chlorine in that 
 respect. It resembles muriatic acid in almost all its reactions, but is 
 at once distinguished from it, by evolving bromine on contact with 
 chlorine or nitric acid. If bromide of potassium be acted on by oil of 
 vitriol, the result is partly as occurs with a chloride, water being de- 
 composed and hydrobromic acid evolved, and partly as occurs with an 
 iodide, bromine and sulphurous acid being evolved together ; hence 
 hydrobromic acid cannot be prepared pure in that way. 
 
 The sp. gr. of hydrobromic acid gas is 2731, being produced by 
 
 One volume of bromine vapour, . . 5393'0 
 
 One volume of hydrogen, 
 
 united without condensation, . . . 5462-3 
 
 and hence one volume weighs, . , . 2731 ] 
 
 The Bromide of Sulphur is a heavy, reddish, liquid, like chloride of 
 sulphur, probably S 2 Br. 
 
 There are two Bromides of Phosphorus, one liquid, P.Br 3 , and the 
 other solid, P.Brs, which present complete analogy with the chlorides 
 of phosphorus. None of these bodies present particular interest. 
 
 The bromide of hydrogen unites with phosphuretted hydrogen, 
 forming a compound similar to that already noticed, containing hy- 
 driodic acid. It is sufficient to mix the two gases together over mer- 
 cury j a dense white cloud forms, which condenses on the sides of the 
 glass in small crystals, which appear to be cubes, but are not so really. 
 This substance can also be formed in the indirect manner described for 
 the iodine compound. It consists of an equivalent of each element, its 
 formula being HBr + PH 3 , or as I prefer to write it, for the reasons 
 already stated, HBr -f- 3.|.H. 
 
 This body is volatile, and may be sublimed, provided neither oxygen 
 nor water be present ; heated in oxygen it takes fire, and with water it 
 is instantly decomposed. 
 
 The Chloride of Bromine and the Bromides of Iodine resemble in 
 general characters the compounds of chlorine and iodine. The first, 
 when decomposed by water, produces hydrochloric and bromic acids ; 
 the latter, on the contrary, gves hydrobromic and iodic acids. These 
 bodies are not otherwise of interest. 
 
Of Fluorine. 445 
 
 OF FLUORINE. 
 Symbol. F. Eq. = 18'74 or 233'8. 
 
 Although the existence of this body is rendered exceedingly probable 
 by analogical reasoning, and that recent experiments have gone very 
 far in establishing its distinctive characters, yet it cannot be prepared 
 in an isolated form, or exhibited like all of the simple bodies as yet 
 described ; for such is the intensity and variety of its affinities, that no 
 sooner is it liberated from combination with one substance than it en- 
 ters into union with some other, attacking the materials of which the 
 apparatus used may be constructed. The most successful experiments 
 made for examining it in its isolated form are due to two talented Irish 
 chemists, the Messrs. Knox. 
 
 The only substance on which fluorine is incapable of acting, being 
 such as already are fully saturated with it, Messrs. Knox had con- 
 structed vessels of fluor spar, (fluoride of calcium,) which were filled 
 with pure dry chlorine gas. Into these vessels was then introduced 
 fluoride of mercury, and the whole carefully warmed. The chlorine 
 decomposed the fluoride of mercury, forming chloride of mercury, and 
 the fluorine was disengaged ; Hg.F and Cl giving HgCl and F. There 
 was in this way obtained a colourless gas which acted with violence on 
 the fragments of metallic foils, that by means of a very ingenious ar- 
 rangement were submitted to its action. The small quantity of material 
 on which the experiments were conducted did not allow of the metallic 
 compounds so formed being analyzed ; and the only doubt that can 
 exist of the isolation of fluorine in this process, is that, according as it 
 was liberated, it may have combined with the excess of chlorine pre- 
 sent, and that the colourless gas may have been chloride of fluorine, 
 and not the mere fluorine itself. 
 
 The specific gravity of gaseous fluorine, calculated from the analogy 
 of its compounds to those of chlorine, is 1289; its equivalent number 
 is 233.8, or 1S'7. 
 
 Fluorine does not combine with oxygen. 
 
 The most important compound of fluorine that is known is the 
 Fluoride of Hydrogen or Hydrofluoric Acid. To prepare it, pure fluor 
 spar, which consists of fluorine and calcium, is reduced to powder, and 
 distilled in a leaden retort with twice its weight of the strongest oil of 
 vitriol. The receiver must also be of lead, and be kept cod by ice. 
 An acid liquor distils over, of an excessively suffocating odour, and so 
 intensely corrosive, that a drop let fall upon the hand produces a sore 
 
446 Hydrofluoric Acid. 
 
 very difficult to heal. This liquid is hydrofluoric acid, the reaction 
 being, that HO.SO 3 and CaF give CaO.S0 3 and HE. Sulphate of lime 
 remains in the retort. 
 
 The hydrofluoric acid, which is thus obtained in an anhydrous form, 
 is very volatile, boiling at 60. It is heavier than water, and becomes 
 still more so when diluted to a certain degree. It dissolves the more 
 oxidable metals rapidly with the escape of hydrogen gas, and the for- 
 mation of a metallic fluoride. The only metals which it does not act 
 upon are gold, platina, silver, and lead. There must be no solder 
 about the leaden vessels in which the acid is kept, as it is acted on very 
 violently. It is dangerous to have much to do with the anhydrous acid 
 from its corrosive power, and as a dilute acid answers for all practical 
 purposes, a quantity of water is generally put into the receiver, into 
 which the acid is distilled. 
 
 The most remarkable property of hydrofluoric acid is its action upon 
 glass, which it corrodes and dissolves. The glass contains silica, which the 
 hydrofluoric acid decomposes, SiO 3 and 3.HF producing 3HO and SiP 3 . 
 This fluoride of silicon is a gas decomposed by water in a way that shall 
 be soon described. Patterns or designs may, therefore, be etched upon 
 glass by means of this hydrofluoric acid. There are two modes in 
 which this operation may be conducted : 1st, by the liquid acid ; 2nd, 
 by the acid in vapour. For the first, the glass plate being covered 
 with an uniform covering of wax, the design is traced on it with the 
 point of a needle or graving tool, taking care that the surface of the 
 glass shall be laid bare throughout the whole extent of each line ; a 
 rim of wax being then formed round the edge of the plate, the liquid 
 acid, the strength of which must be regulated by the depth of the 
 engraving required, is poured on the plate to the depth of two or 
 three lines, and left to act for so long a time as the operator wishes. 
 When it has remained long enough, the remaining acid is poured off 
 and the wax cleared away. The etched portions of the glass are equally 
 transparent with the others, and the design is therefore indistinct, 
 except in certain incidences of the light. A glass plate so prepared 
 may be used like a copper plate to print from, but the risk of breaking 
 is too great to allow of its introduction into practice. 
 
 To etch by the second mode, the plate of glass . is prepared exactly 
 as described for the first, except that there need not be any raised 
 edge. A flat leaden basin, of the size of the plate, is used to hold the 
 mixture of powdered fluor spar and oil of vitriol, and the glass plate is 
 laid upon it, with the waxed side down ; the basin is then heated so 
 gently as not to melt the wax or injure the accuracy of the design ; the 
 hydrofluoric acid, which rises in vapour, acts upon the surface of glass 
 
Preparation of Silicon. 447 
 
 exposed, and decomposes the silica, forming fluoride of silicon ; but a 
 sufficient quantity of watery vapour rises to decompose this substance, 
 and a quantity of silica is regenerated and deposited upon the corroded 
 surface, giving it a rough and white appearance, so as to be easily 
 visible in every direction. When the action has continued long enough, 
 the plate is removed from the basin, and the wax cleared off by means 
 of some spirits of turpentine. Other uses of the hydrofluoric acid, 
 such as in mineral analysis, shall be described hereafter. 
 
 The composition and equivalent numbers of the hydrofluoric acid are 
 as follows : 
 
 Fluorine. 94'93 One equivalent, = 233-88 or 187 
 Hydrogen, 5-07 One equivalent, = 12-5 or TO 
 
 100-00 246-38 197 
 
 There are no other combinations known of fluorine with any of the 
 simple bodies as yet described, except sulphur and phosphorus : these 
 are dense volatile liquids. The Fluoride of Phosphorus, when decom- 
 posed by water, produces hydrofluoric acid and phosphorous acid : it is, 
 therefore, P.F 3 . When heated in the air it burns, but the product of 
 the combustion has not been examined. 
 
 OF SILICON. 
 
 Symbol. = Eq. 266'8 or 21-35 if Silica be SiOs 
 
 Si. 177-9 or 14-23 SiO 2 
 
 88-9 or 7-12 SiO 
 
 This substance is one of the most extensively distributed of the un- 
 decomposed bodies, constituting, probably, a sixth of the total weight 
 of the mineral crust of the globe. It never exists free, but always in 
 nature combined with oxygen, forming silicic acid, or as it is termed in 
 popular language, the earth silica. Quartz, in the state of rock, and 
 crystallized, flints, agate, sand, and many other mineral substances, are 
 silica completely or nearly pure, and when combined with various me- 
 tallic oxides, it forms the great family of silicates, which includes the 
 majority of earthy minerals. 
 
 It is exceedingly difficult to deprive silicic acid of its oxygen ; even 
 by ignition with potassium, it is but imperfectly decomposed. To pre- 
 pare silicon, therefore, a somewhat complex body is selected to be acted 
 on, the double fluoride of silicon and potassium, which is a white 
 powder like starch, very sparingly soluble in water ; a quantity of this 
 substance is to be mixed with nearly its own weight of potassium, cut 
 
448 Properties of Silicon. 
 
 into little bits and placed in an iron cylinder, or in a tube of hard glass, 
 which may be held, as in the figure, over the 
 flame of a spirit lamp. As soon as the bottom 
 of the tube has been heated to redness, vivid 
 ignition occurs by the decomposition, which 
 spreads, with little need of external heat, 
 throughout the entire mass ; the potassium 
 taking fluorine from the fluoride of silicon, 
 whilst the silicon is set free as a brown powder. 
 The fluoride of potassium formed mixing with that pre-existent in the 
 compound. When the apparatus has become cold, the residual brown 
 matter is to be washed carefully with water : fluoride of potassium dis- 
 solves, and the silicon remains behind. To have the silicon quite pure, 
 numerous precautions are necessary which need not be detailed here. 
 
 The silicon so obtained, is a dull brown powder, which, when heated 
 in the air or oxygen, takes fire and burns, forming silicic acid. If it be 
 ignited in a closely covered vessel it shrinks in volume, increases very 
 much in density, and becomes insoluble in acids or alcalies, which, in 
 its original form, it would dissolve in, with evolution of hydrogen gas ; 
 it then also cannot be made to burn in oxygen gas ; it burns in the 
 vapour of sulphur and in chlorine, combining with these bodies. 
 The silicon according to the temperature to which it has been exposed, 
 presents thus the different allotropic states referred to in page 319, 
 and these may be indicated by the Greek letters, a, C. the combustible 
 silicon being Si.a, and the less combustible being Si.C. When ignited 
 with carbonate of potash, the silicon burns brilliantly, setting carbon 
 free, and forming with the oxygen of the carbonic acid, silicic acid, 
 which combines with the potash. 
 
 The determination of the equivalent number of silicon is involved in 
 much difficulty from the different views which may be taken of the con- 
 stitution of its most important compounds. Berzelius in classifying the 
 mineral species as salts of silicic acid, was led to compare silicic acid with 
 sulphuric acid, and to assign for it the formula Si0 3 ; and on his authority 
 that formula has been since almost universally adopted. Mineralogists 
 have, however, found that the relations of the mineral species are much 
 more simply expressed by considering the silicic acid to contain but two 
 atoms of oxygen, and to have the formula Si0 2 , and this view derives 
 very great support from the resemblance which silicic acid bears to 
 titanic acid and to stannic acid, and the close analogy of the chlorides 
 of tin, titanium and silicon. Further, the composition of the fluorine 
 compounds of silicon are more simply explained on this idea. Finally, 
 the researches of Ebelmen on the ethers formed by silicic acid, excluded 
 
Constitution of Silica. 
 
 449 
 
 the formula Si0 3 , as the three ethers contained, united with one atom 
 ether, quantities of silicic acid, the oxygen of which is one atom, or two 
 atoms, or four atoms, but which are inconsistent with the existence of 
 three atoms of oxygen in the equivalent of silica. Ebelmen proposes 
 to adopt the formula SiO, which was already long before suggested by 
 Dumas. But on a review of the whole evidence I propose to assume, 
 in considering the history of those compounds, the formula for silicic acid 
 to be SiOa, and consequently to take the equivalent number of silicon 
 as ]4'45 on the hydrogen and 377*8 on the oxygen scale. It will be 
 hereafter seen that similar considerations influence the determination of 
 the atomic weight of boron. 
 
 It is very possible, however, that the remarkable different allotropic 
 states in which silicon presents itself, as described above and in page 
 319, and which are followed by similar conditions in the silicic acid 
 itself, may be connected with the assumption of really different atomic 
 weights and combining powers. Thus, that silicic acid might be in one 
 class of minerals a very feeble acid, like carbonic acid or titanic acid, 
 and have the formula Si a O 2 , whilst in a different class of minerals it 
 might be a powerful acid, like sulphuric acid, and have the formula 
 Si b O 3 . These views, however, are but points of philosophical specu- 
 lation, and need not be detailed farther. 
 
 Silicic Acid. Silica. This, the only compound of silicon and oxygen, 
 exists in nature completely pure, in masses constituting quartz rock, and 
 in crystals which belong to the rhombohedral system ; their ordinary 
 form is represented in the margin. It is exceedingly hard, and in order 
 to be reduced to powder, requires to be heated first 
 to redness and then thrown into a large mass of cold 
 water. The piece of quartz cracks in every direc- 
 tion, by being so suddenly cooled, and is then easily 
 reduced to powder in an agate mortar. It may be 
 obtained in a state of much more minute division, 
 by melting, in a platinum crucible, a mixture of 
 equal weights of carbonate of potash and of carbon- 
 ate of soda, and adding thereto powdered flint, by 
 small quantities at a time ; the silica dissolves in 
 the melted alcali, whilst carbonic acid gas is given 
 off ; when the alcaline silicates, so formed, are dis- 
 solved in water, and a stronger acid added, the silicic acid is precipitated 
 as a gelatinous hydrate, which, when completely dried, forms a white 
 powder, still somewhat gritty to the feel. When the gaseous fluoride 
 of silicon comes into contact with water, a portion of it is decomposed, 
 fluoride of hydrogen and silicic acid being produced, this last separates 
 29 
 
450 Properties of Silicic Acid. 
 
 in the gelatinous form, but on drying, becomes an exceedingly fine light 
 powder. 
 
 Silica, even when prepared by precipitation, feels gritty between the 
 teeth ; when in mass, it is exceedingly hard, scratching glass and the 
 generality of minerals. Its specific gravity is 2*66 ; it is fusible only 
 by the oxy-hydrogen blowpipe, in the flame of which it melts into a 
 colourless glass which is remarkably plastic and ductile, and may be 
 drawn into capillary threads which possess a very high degree of elas- 
 ticity : when once dried, it is totally insoluble in water, but in its gela- 
 tinous form, it is soluble to a small extent ; hence many mineral wa- 
 ters contain silica, which being gradually precipitated in the substance 
 of decomposed organic matter, produces the silicious petrefactions, in 
 which the most delicate vegetable tissues are so beautifully preserved. 
 The differences between silica in its dry and in its hydrated condition are 
 so great, that we can scarcely suppose them to be satisfactorily accounted 
 for by the presence of a substance for which the silica appears to have so 
 little affinity as water. When a dilute alcaline solution of silica is 
 decomposed by an acid there is no precipitation, the silica remaining 
 dissolved ; but on evaporating the liquor to dryness, the silica assumes 
 the insoluble condition, and remains behind when the saline constituent 
 is dissolved. On the other hand, by the presence of an alcali, the in- 
 soluble silica is made to assume the soluble state. These allotropic 
 states may, like the similar conditions of the silicon itself, be marked 
 by the Greek letters, the insoluble silica being Si a O 2 and the soluble, 
 the silica Si O 2 . 
 
 There is some difference of opinion as to whether the compounds of 
 silica and water are truly definite, but I look upon the existence of at 
 least two as being certain; I have found the light spongy masses 
 of silica deposited from volcanic springs, and on the edges of volcanic 
 craters from Iceland and Teneriffe, to have accurately the constitution 
 of the formula 3Si0 2 + HO, and Ebelmen has found the silicic acid 
 deposited from silicic ether to be a hydrate with the composition of 
 Si0 2 + HO. 
 
 It is probable that a great deal of the silica which exists in nature 
 had been originally deposited in the soluble condition. The structure 
 of the agates, chalcedony, and many other minerals, proves that they 
 were formed by a solution of silica, having penetrated into a cavity in 
 the surrounding rock, and having then gradually dried down or crystal- 
 lized. It is even pretty certain, that the crystallized quartz is also of 
 this aqueous origin. 
 
 In the arts, silica is of exceeding importance, being an essential con- 
 stituent of glass, porcelain, and every kind of delft and earthenware. 
 
Chloride of Silicon. 451 
 
 For purely chemical purposes, it is only of interest from the compound 
 which silicon forms with fluorine ; the hydrofluoric acid being the only 
 acid capable of dissolving silica. 
 
 The composition of silica and its equivalent numbers are now inferred, 
 from the considerations already described, to be as follows, its formula 
 being SiO 3 : 
 
 Silicon, 47-45 One equivalent = 177'8 or 14-45 
 Oxygen, 52-55 Two equivalents == 200-0 or 16-00 
 
 100-00 377-8 30-45 
 
 Silicon does not combine with hydrogen, nor with nitrogen : there 
 exists a sulphuret of silicon which is probably SiS 2 , as when acted on 
 by water it produces soluble silica and sulphuretted hydrogen. 
 
 Chloride of Silicon. This substance, although not itself important, 
 is yet interesting from the fact, that the method of preparing it is one 
 by which a number of remarkable compounds of chlorine have been 
 discovered, and hence it deserves to be described. Chlorine has no 
 action on silica at any temperature ; but if finely divided silica be mixed 
 with powdered charcoal and heated to redness in a porcelain tube, a, c, 
 
 inserted in the furnace, as in the figure, and by means of a glass tube, 
 attached at I, a current of dry chlorine be made to stream over the 
 ignited mixture, decomposition ensues, the oxygen of the silica com- 
 bining with the carbon to form carbonic oxide gas, whilst the chlorine 
 and silicon unite, producing the chloride of silicon, which, being a 
 very volatile liquid, requires to be carefully condensed ; for this purpose 
 the tube c f, is wrapped up in a cloth, or in paper kept constantly 
 wetted by a stream of water from the reservoir, e, and the liquid pro- 
 duced then collects in the bottle, f t whilst the oxide of carbon and the 
 excess of chlorine pass off by the tube m. In this process the reaction 
 is such, that 2C1 acting on Si0 2 and 2C give rise to 2 'CO and SiCl 2 . 
 
452 
 
 Fluoride of Silicon. 
 
 The stream of dry chlorine may be very conveniently obtained by the 
 apparatus here figured. The muriatic acid and peroxide of manganese 
 
 are placed in the flask 
 a, and the gas evolved, 
 depositing the accom- 
 panying liquid in the 
 receiver , passes through 
 the tube c, which being 
 filled with fragments of 
 recently fused chloride 
 of calcium, absorbs all 
 the watery vapour. The 
 gas issues dry from the 
 extremity, where it is 
 
 connected with the end, #, of the porcelain tube in the preceding 
 figure. 
 
 The chloride of silicon is a colourless liquid, denser than water ; it 
 boils at 124; in contact with water, it is resolved into silica and hy- 
 drochloric acid, from whence its formula must be SiCl 2 . 
 
 Fluoride of Silicon. This is the most remarkable compound of sili- 
 con, after silicic acid ; it is a gas colourless and transparent : to prepare 
 it, fluor spar and sand, or glass in powder, are mixed together and 
 heated in -contact with oil of vitriol, the mass swells up very much, so 
 that a large vessel must be employed. In this reaction we may look 
 upon water as being decomposed or not, as the results may be explained 
 in either way. Thus, the oxygen of the silica may combine with the 
 calcium, forming lime, and this with the sulphuric acid, whilst the 
 silicon unites with the fluorine of the fluor spar. Or, water being de- 
 composed, hydrofluoric acid and lime may be first produced, and the 
 former reacting on the silica may reproduce water, and form fluoride 
 of silicon. I prefer to omit here, as I did when describing the forma- 
 tion of chlorine, all the unnecessary theoretic agency of the water, and 
 to express the decomposition as 2(S0 3 .HO) with SiO 2 and 2(CaP.) 
 give 2(SO 3 .CaO.HO) and SiF 2 . 
 
 This gas must be collected over mercury, and in vessels dried with 
 the greatest care. When it mixes with air, it forms dense white fumes, 
 which arise from the formation of silica by the watery vapour present 
 being decomposed. 
 
 It is colourless and transparent ; its specific gravity is 3600. Its 
 composition and equivalent numbers are as follows, its formula being 
 
llydrofluomlicic Acid. 
 
 Silicon, 28-32 One equivalent = 177'8 or 14-45 
 Fluorine, 71-68 Two equivalents = 467 '6 or 37'40 
 
 100-00 645-4 51-85 
 
 The hydrofluosilicic acid, or the double fluoride of hydrogen and 
 silicon, cannot be obtained free from water, but its solution is of con- 
 siderable importance as a chemical re-agent, and hence its preparation 
 requires to be described. 
 
 The mixture of powdered fluor spar and sand is introduced into the 
 matrass, a, which is imbedded in a sand 
 bath, as in the figure. By means of the 
 syphon funnel, I, the oil of vitriol is then 
 poured in, and the gas evolved is con- 
 ducted by the tube to the water in the 
 vessel, d, e. If the tube opened into the 
 water directly, so much silica would be 
 deposited at its orifice as to stop it up 
 every moment ; and hence, a quantity of 
 mercury, e, is placed at the bottom, and 
 the end of the tube dips into it. The gas 
 bubble, therefore, does not touch the water 
 until completely separated from the tube : 
 it escapes from the surface of the mercury, and then it becomes in- 
 vested with a coating of silica, like a bag of tissue paper, of which 
 many preserve their form for a certain time. The passage of the gas 
 is to be continued until the water becomes thick from the quantity of 
 silica separated ; it is then to be poured on a fine linen cloth, and the 
 silica removed by straining and pressure. In this process, one-third of 
 the fluoride of silicon is decomposed by the water forming silica and 
 hydrofluoric acid, which last unites with the remaining fluoride of sili- 
 con, to form the hydrofluosilicic acid, the formula of which is SiF 2 
 + HF. 
 
 "When a solution of this acid is heated, fluoride of silicon is given 
 off and hydrofluoric acid remains. Hence, although the hydrofluosilicic 
 acid is without action upon glass, glass vessels in which it is evaporated 
 are corroded. 
 
 The property of this acid which is of most interest to the chemist 
 is, that it forms, by acting on the salts of potassium and barium, com- 
 pounds, fluosilicates, or double fluorides of those metals, which are 
 very sparingly soluble in water ; and hence, it is used to detect the 
 presence of these substances in solution. The precipitate so obtained 
 is remarkable for being at first so gelatinous and transparent, that it 
 
454 Ilydrofluosilicic Acid. 
 
 can be recognized in the liquor only by the play of colours in the light 
 reflected from its upper surface. When collected on a filter and dried, 
 these compounds appear like powdered starch. The constitution of the 
 salts of the hydrofluosilicic acid resembles that of the acid itself, the 
 hydrogen being replaced by a metal; thus, the fluosilicate of potassium, 
 already described as used for preparing silicon, is expressed by the for- 
 mula SiF 2 +KF. 
 
 The composition of hydrofluosilicic acid is easily known from that of 
 the hydrofluoric acid and fluoride of silicon. Its equivalent number is 
 891-7 or 71-55. 
 
 OF BORON. 
 Symbol. B. Eq. 90'8 or 7'26. 
 
 The history of this substance presents a very close analogy with that 
 of silicon. It was first obtained by decomposing boracic acid by gal- 
 vanism, but is best prepared by acting on the fluoborate of potash by 
 metallic potassium, exactly as has been described under the head of 
 silicon. That salt consists of fluoride of boron united to fluoride of 
 potassium ; by the reaction, all the fluorine passes to the potassium 
 and the boron is set free. 
 
 Boron is a dark olive substance, which does not conduct electricity. 
 It is insoluble in water and all other neutral fluids. When heated to 
 600 in air or oxygen it takes fire, and burning, forms boracic acid; the 
 same effect is produced by boiling with nitric acid, or by ignition with 
 nitrate or with carbonate of potash. 
 
 This element is not extensively distributed in nature, and only found 
 combined with oxygen, forming boracic acid. This exists in certain 
 springs in India, combined with soda, and being crystallized in an im- 
 perfect way, was brought into commerce under the name of tinkal, or 
 crude borax. The boracic acid is also found, and in much larger quan- 
 tity, free, or combined only with a small quantity of ammonia, in the 
 small volcanic lakes or lagoons of Tuscany. It accompanies the watery 
 vapour which gushes out of fissures in the earth, and which contains 
 also muriatic acid. The water of those lakes is evaporated, and the 
 boracic acid being crystallized, is imported into these countries for the 
 manufacture of borax (borate of soda) and other salts. 
 
 The equivalent number of boron has been usually taken as 136'2 on 
 the oxygen, or 10'9 on the hydrogen scale, from the supposition that 
 the boracic acid contained three atoms of oxygen, and had the formula 
 BOs. This supposition was principally grounded on the analogy of 
 
Properties of Boracic Acid. 455 
 
 silicic acid, and consequently, for the reasons given in the preceding 
 section, it will be now most reasonable to assume the boracic acid to 
 contain two atoms of oxygen, and the equivalent number of boron to be 
 on the oxygen scale 90 '8, and on the hydrogen scale 7 "26. The boracic 
 ethers, as well of the methylic and amylic as of the common alcohol, 
 would decidedly support Ebelmen's view of the boracic acid having the 
 formula BO. as the ether and acid contain the same quantity of oxygen ; 
 but with boron, as with silicon, I consider the history of the chlorine 
 and fluorine compounds to be best satisfied by the assumption of the 
 atomic weight above mentioned, and of its combination with two atoms 
 of the more electro-negative body to form the acid. 
 
 Boracic Acid. B.O 2 . 
 Eq. 290-8 or 23'26. 
 
 The boracic acid is the only compound of boron and oxygen ; it may 
 be obtained quite pure, from the native acid, by boiling this with eight 
 parts of water, and a little white of egg, and filtering the solution. On 
 cooling slowly, the boracic acid crystallizes in large brilliant plates, soft 
 and unctuous to the feel, and of an irregular crystalline form. It may 
 be also produced from borax, by dissolving it in four times its weight of 
 boiling water, and adding sulphuric acid until the liquor becomes sour 
 to the taste. On cooling, the boracic acid crystallizes ; but as it retains 
 a little sulphuric acid and sulphate of soda, a second solution and crys- 
 tallization is necessary to have them pure. 
 
 The crystals of boracic acid, so prepared, contained water, the oxy- 
 gen of which is equal to the oxygen of the acid ; when heated, this 
 water passes off and the acid melts ; on cooling, it forms a colourless 
 glass ; when completely dry it is fixed, but in the presence of water it 
 is carried off by the vapour in great quantity. The glacial acid, when 
 exposed to the air, absorbs water, swells, and becomes opaque. The 
 boracic acid is much more soluble in hot than in cold water, the crystals 
 requiring twenty-six parts of water at 60, and only three at 21 2 for 
 their solution. Alcohol dissolves boracic acid copiously ; and the solu- 
 tion, when set on fire, burns with a beautiful green flame, by which this 
 body may easily be recognised. The boracic acid possesses but very 
 feeble acid properties, many of its soluble salts possess alcaline reaction, 
 and all are decomposed by the weakest acids. It does not redden lit- 
 mus, but it gives it a port wine colour, and a strong solution of it 
 browns turmeric paper like an alcali. At high temperatures, however, 
 boracic acid may decompose the salts of the nitric or even of the sul- 
 
456 CJdoride of Boron. 
 
 phuric acids, from the principles that have been already explained in the 
 chapter on Affinity (p. 219.) 
 
 The composition and equivalent numbers of boracic acid are as fol- 
 lows, its formula being B.O 2 : 
 
 Boron, 31 '22 One equivalent . = 90'8 or 7'26 
 Oxygen, 68'78 Two equivalents, = 200-0 or IG'OO 
 
 100-00 290-8 23-26 
 
 Boron does not combine with hydrogen or nitrogen ; its compounds 
 with sulphur and selenium are not important. 
 
 Chloride of Boron Boron bums spontaneously in chlorine gas, but 
 the best way to prepare the compound of chlorine and boron is to pro- 
 ceed as described for making chloride of silicon, substituting boracic 
 acid for the silica. The product is a gas colourless and transparent, 
 but producing dense white fumes in contact with damp air, owing to 
 its decomposition and the formation of boracic and hydrochloric acids. 
 The presence of this last in the volcanic lagoons would render it probable 
 that by some subterraneous action chloride of boron is generated, and 
 is decomposed when mixed with the watery vapour simultaneously ex- 
 haled. The chloride of boron is rapidly absorbed and decomposed by 
 water; its specific gravity is 4079 ; it contains 1J times its volume of 
 chlorine ; its formula is B.C1 2 . 
 
 Fluoride of Boron. This substance is prepared in exactly the same 
 way as fluoride of silicon, substituting the boracic acid for the silicic 
 acid. It is a gas, rapidly absorbed and decomposed by water, and ge- 
 nerating hydrofluoboric acid, which is perfectly analogous to the hydro- 
 fluosilicic acid. It hence forms dense white fumes when mixed with 
 damp air. Its sp. gr. is 2362. 
 
 The hydrofluoboric acid is obtained by precisely the same plan as that 
 described for the hydrofluosilicic acid. The boracic acid is deposited 
 in crystals according as the gas is absorbed. If the liquor be evapo- 
 rated without the acid deposited being removed, it is all again taken up 
 and carried off as gaseous fluoride of boron. The liquid hydrofluoboric 
 acid resembles, in the combinations that it forms, the hydrofluosilicic 
 acid, and is similar to it also in constitution, its formula being 
 + HE. 
 
 No other compound of boron of any interest is known, 
 
 The history of carbon involves so many considerations regarding the 
 constitution and properties of organic substances, that I shall postpone 
 
General Characters of the Metals. 457 
 
 entering upon it until after the description of the metals and their salts, 
 and other compounds "with the non-metallic bodies. I shall then com- 
 mence the study of the chemistry of organic substances with that of 
 their most constant ingredient, carbon. 
 
 The compound of nitrogen with hydrogen (ammonia,) has not been 
 introduced amongst those of the non-metallic bodies with each other, 
 because all the details of its history attach it to organic chemistry, 
 under which head it shall consequently be found. The hypothetical 
 compounds of nitrogen and hydrogen (amidogene and ammonium) will 
 be associated with it. 
 
 The substances hitherto described as chloride and iodide of nitrogen, 
 having been derived from ammonia, and ranging themselves in an 
 important series of organic combinations, have not been noticed in 
 the chapter now closed, but will be found in their true position here- 
 after. 
 
 CHAPTER XII. 
 
 OF THE GENERAL CHARACTERS OF THE METALS AND OF THEIR 
 COMPOUNDS WITH THE NON-METALLIC BODIES. 
 
 ALTHOUGH, as has been already noticed, the metals cannot be considered 
 as forming a class of bodies, united by such analogies of chemical pro- 
 perties and laws of combination, as would constitute a natural family, 
 yet in their physical characters, and the most prominent facts of their 
 technical history, they have so much in common, as to render a notice 
 of the conditions in which they exist in nature, the methods by which 
 they are extracted upon the large scale, and the physical and chemical 
 properties by which they are distinguished as a great division of the 
 elementary bodies, necessary, before proceeding to the detailed history 
 of the individual metals. 
 
458 Malleability and Ductility. 
 
 The metals are forty-two in number ; their names have been already 
 given in more than one place (pp. 195 and 277.) They reflect light 
 powerfully, and hence possess what is termed metallic lustre. If the 
 incident light be plane polarized, it undergoes a remarkable change pro- 
 duced only by the metals and by diamond, becoming elliptically polar- 
 .ized on reflection. The metals are characterized very completely by 
 their power of conducting heat and electricity, in which, although they 
 differ amongst each other, yet the worst excels all non-metallic bodies. 
 Lists of their relative conducting powers in those respects have been 
 already given (pp. 118, 141, and 180.). By the combination of those 
 characters, the lustre and conducting power, the metallic or non-metallic 
 nature of a body is always determined. 
 
 In the other properties of the metals, there is found remarkable di- 
 versity ; thus, in colour, although silver is purely white, the majority of 
 the metals are of various shades of bluish-white, or grey, whilst copper 
 and titanium are reddish coloured, and gold is yellow. In specific gra- 
 vity, the metals include some of the lightest along with the heaviest 
 solids that we know; the density of platinum being 21 times, of gold 
 19 times, and that of potassium only -f^ that of water. 
 
 Some of the most important applications of the metals in the arts, 
 depend on their malleability and ductility. Those metals are mallea- 
 ble which admit of being rolled or beaten out into thin leaves ; those 
 being ductile which can be drawn into wire, pold is the most mallea- 
 ble of metals ; gold leaf may be obtained of 212020 of an inch in thick- 
 ness, and is hence the only metal in which any trace of transparency 
 has been found ; silver, copper, tin, rank next in malleability. The 
 most malleable metals are not at all the most ductile ; platinum, and 
 even iron can be obtained in finer wire than gold ; platinum wire was 
 made by "Wollaston of 3 000 6 inch diameter ; but a metal which is not 
 malleable cannot be ductile, and, vice versa, thus antimony, arsenic, 
 and bismuth, the brittle metals, may be powdered in a mortar, but give 
 neither leaves nor wire. The texture of the metals which produces the 
 malleable and ductile conditions, depends closely upon temperature. 
 Thus zinc is malleable and ductile at 300 ; it loses this power, but 
 remains tough, at 60, while at 600 it becomes so brittle, that it 
 powders as easily as bismuth. In the drawing of a lead pipe, and in 
 making most of the metallic wires, there is a peculiar temperature re- 
 quired for the most perfect execution, by which is regulated the rapidity 
 with which the process is carried on. 
 
 In strength and tenacity, the metals differ also ; iron is the strongest 
 inetal, an iron wire of a given thickness will support a greater weight 
 than a similar wire of any other metal ; copper is next to iron, but only 
 
Classification of the Metals. 459 
 
 about one-half so strong ; then platinum, silver, and gold ; tin and lead 
 are the weakest of the metals. The tenacity depends also on the mole 
 cular structure ; if the wires had been annealed, so as to allow of an 
 approach to internal crystallization, the tenacity is often found to be 
 reduced to one-half. 
 
 In their relations to heat, the metals exhibit remarkable variety. But 
 one metal is liquid at ordinary temperatures. All of the metals are 
 fusible, but they require for their liquefaction, the greatest range of 
 temperature which can be produced ; thus mercury melts at 39, 
 potassium and sodium below the heat of boiling water ; tin, lead, zinc, 
 antimony, and tellurium, below a red heat, and many metals, as platinum, 
 are infusible in the most intense heat of a blast furnace, and yield only 
 to the flame of the oxy-hydrogen blow-pipe. In the history of each 
 individual metal, its point of fusion will be given so far as it is known. 
 
 The majority of the metals are fixed at the greatest heat of our fur- 
 naces, but mercury, zinc, cadmium, arsenic, tellurium, potassium, and 
 sodium, may be volatilized. 
 
 The generality of metals, when exposed to the air, particularly when 
 damp, absorb oxygen and form oxides ; some becoming merely tarnished 
 upon the surface ; others becoming thoroughly oxidized. Some metals, 
 however, as gold, silver, platinum, palladium, and mercury, are not liable 
 to this action. Those metals which oxidize when exposed to air, unite 
 with oxygen at a higher .temperature, with great rapidity, many with 
 actual combustion. Thus zinc, when heated to full redness, takes fire 
 and burns brilliantly with a white flame, and the combustion of iron 
 wire in oxygen is one of the prettiest lecture experiments. Mercury 
 also, which does not tarnish when exposed to oxygen at common tem- 
 peratures, becomes oxidized when heated to near its boiling point, but 
 the oxide is resolved again at a red heat into oxygen and metallic 
 mercury. 
 
 It is owing to their affinity for oxygen, that many of the metals de- 
 compose water, and one of the most convenient classifications that have 
 been proposed for ordinary use, is founded on the fact of the different 
 degrees of facility with which this decomposition proceeds. Thus, 
 
 Potassium, 
 
 Sodium, 
 
 Lithium, 
 
 Barium, 
 
 Strontium, 
 
 Calcium, 
 
 Magnesium, 
 
 The first class consists of metals which decompose 
 water with lively effervescence even at 32. 
 
460 
 
 Classification of the Metals. 
 
 Aluminum, 
 
 Glucinum, 
 
 Thorium, 
 
 Yttrium, 
 
 Zirconium, 
 
 Lanthanum, 
 
 Cerium, 
 
 Manganese, 
 
 Iron, 
 
 Nickel, 
 
 Cobalt, 
 
 Zinc, 
 
 Cadmium, 
 
 Tin, 
 
 Chromium, 
 
 Yanadium, 
 
 Tungsten, 
 
 Molybdenum, 
 
 Osmium, 
 
 Columbium, 
 
 Titanium, 
 
 Arsenic, 
 
 Antimony, 
 
 Tellurium, 
 
 Uranium, 
 
 Copper, 
 
 Lead, 
 
 Bismuth, 
 
 Silver, 
 
 Mercury, 
 
 Gold, 
 
 Palladium, 
 
 Platinum, 
 
 Ehodium, 
 
 Iridium, 
 
 The second class consists of metals which do not 
 decompose water with lively effervescence, except at 
 about 212, but very far below a red heat. 
 
 The third class consists of metals which do not 
 decompose water except at a red heat, or at common 
 temperatures in contact with strong acids. 
 
 The fourth class consists of metals which decom- 
 pose vapour of water energetically at a red heat, but 
 which do not decompose it at common temperatures, 
 even in contact with strong acids. 
 
 The fifth class consists of metals which decompose 
 water, at a red heat, but very feebly ; but whose ox- 
 ides are not reducible to the metallic state by heat 
 alone. 
 
 The sixth class consists of metals whose oxides are 
 decomposed alone at a high temperature, and which 
 do not decompose water under any circumstances. 
 
 This kind of classification was first proposed by Thenard, and has 
 been adopted by Graham in a form differing very slightly from that now 
 given. 
 
 The following classification, although old and founded solely on 
 
Degrees of Oxidation. 461 
 
 popular considerations, is yet so far consonant with the simplest char- 
 acters of the metals, as to be frequently referred to, and hence to be 
 worthy of notice. 
 
 Those metals which do not tarnish on exposure to the air, and the 
 oxides of which are reduced by heat alone, were termed the viable or 
 perfect metals ; at the head of this list stood gold, and at the bottom 
 mercury. 
 
 All the other metals known to the older chemists, were termed 
 ordinary or imperfect metals. Of the metals of the first and second 
 class, none had been then discovered, and of their oxides, only potash, 
 soda, barytes, lime, magnesia, and alumina were known. Prom the old 
 name of potash, Kali, with the Arabic prefix al, potash and soda, at 
 one time confounded together, were termed alcalies, and ammonia re- 
 sembling them very much, when dissolved in water or combined with 
 acids, was also called an alcali ; it was the volatile alcali, potash and 
 soda being fixed alcalies ; it was also termed the animal alcali, whilst 
 soda was the mineral alcali, being derived from rock salt or from the 
 ocean ; and potash received the name of the vegetable alcali, from its 
 source being the ashes of plants growing upon land. The alcalies are 
 characterized by being very soluble in water, and by neutralizing the 
 strongest acids. They hence restore the blue colour of reddened litmus 
 paper, and change the vegetable colours in general; the yellows to 
 brown, the reds and blues to green. 
 
 Paper tinged yellow by turmeric, is a delicate test of the presence of 
 an alcali, by which it is browned. 
 
 Magnesia and alumina were termed earths, and silica was classed 
 with them; these bodies, the earths proper, are insoluble in water, and 
 have no action on turmeric paper. 
 
 Barytes, lime, and strontia, were termed alcaline earths, they are 
 soluble in water, but much less so than the alcalies, these solutions 
 brown turmeric paper, and neutralize acids ; but they are completely 
 distinguished from the alcalies by their combinations with carbonic 
 acid, which are insoluble in water, whilst the alcaline carbonates are 
 very soluble in that liquid. These phrases of alcalies and earths, are 
 of constant recurrence in descriptions of chemical processes and results, 
 and are thus seen to be founded on and expressive of some of the most 
 important characters in those bodies. 
 
 Most of the metals combine with oxygen in more than one propor- 
 tion, and the characters of the oxides are found to be regulated in a 
 great degree by their composition. All protoxides (E.G.) (E. repre- 
 senting an equivalent of any metal) appear capable of combining with 
 acids to form neutral salts, they constitute, properly, the metallic bases, 
 
46 Relations of the Metals to Chlorine. 
 
 but in many cases suboxides, (E 2 O) such as those of copper and mer- 
 cury, form well characterized salts, and sesqui-oxides (E 2 O 3 ) as those of 
 iron, manganese, aluminum, and chrome, produce well denned classes 
 of salts also, which, however, in solution always possess an acid reac- 
 tion. Peroxides, (E0 2 ) as those of manganese, tin, titanium, and lead, 
 are either indifferent, or feebly acid, and the higher degrees of oxidation 
 lose all basic character, and become true acids, as the manganic acid, 
 MnOg, and the chromic acid (Cr0 3 .) 
 
 The different oxides of the same metal frequently unite with each 
 other, producing compounds which have great similarity to salts. 
 Examples of this will be found under the heads of manganese, of iron, 
 and of lead. 
 
 The affinity of the metals for chlorine is, in many cases, even more 
 remarkable than that which they manifest for oxygen ; thus gold and 
 platinum, which resist even nitric acid, at once combine with chlorine ; 
 and tin, copper, mercury, antimony, arsenic, and bismuth, which re- 
 quire a high temperature to effect their rapid combination with oxygen, 
 burn spontaneously when introduced into chlorine gas in a state of 
 minute division. Most metallic oxides are decomposed by chlorine also 
 at a high temperature ; thus if a stream of chlorine gas be passed over 
 lime heated to redness in a porcelain tube, oxygen gas is expelled, and 
 the calcium remains combined with chlorine. On this account, the 
 chlorides are generally, after the oxides, the most important metallic 
 compounds. Towards iodine, bromine, and fluorine, the metals are 
 related nearly as to chlorine, the affinities being, however, much weaker 
 towards bromine, and still more so towards iodine ; of fluorine we do 
 not as yet possess much positive knowledge, but its affinities appear to 
 be at least as intense as those of chlorine. 
 
 The compounds of sulphur with the metals constitute a very exten- 
 sive and important series, which, as has been more fully noticed in p. 
 389, resembles in a very striking manner, the series of oxides of the 
 same metal. Many metals, at a high temperature, combine with sul- 
 phur with brilliant combustion ; and even at common temperatures, if 
 iron filings and sulphur be mixed together with a little water, they will, 
 in uniting, produce so much heat as to burst into flame, if the mass be 
 moderately large. The metallic sulphurets, like the metallic oxides, are 
 some acids and some bases, and these, by uniting, form the extensive 
 classes of sulphur-salts. The metals combine with selenium and with 
 phosphorus, subject to nearly the same conditions as in forming sulphu- 
 rets, but the history of those compounds is not nearly so complete. 
 As yet but very little has been done towards the history of the com- 
 pounds of the metals with silicium, or boron. 
 
Classification of Ike Metals by their Sulphurets. 463 
 
 The metals appear to form with nitrogen compounds, usually termed 
 nUrurets or azoturets, which derive interest from the relation they bear 
 to the compounds of ammonia. They are mostly obtained by the 
 decomposition by heat of the compounds of ammonia with the oxides 
 or the chlorides of the metals. 
 
 Some of the metals, as tellurium., arsenic, and antimony, combine with 
 hydrogen, forming gaseous compounds, which resemble very closely the 
 sulphurets and phosphurets of hydrogen in properties and constitution. 
 In these bodies the hydrogen is the positive element, the metal playing 
 the part of the sulphur or of oxygen. 
 
 The relations of the metals to sulphur form so important and so 
 characteristic a portion of their history, that the sulphuret of hydrogen 
 and the hydrosulphuret of ammonia are adopted in the laboratory as 
 the most ordinary and useful agents for detecting the metals, and for 
 separating them when mixed. A very useful practical classification of 
 the metals may be formed in this way. Thus there is first the binary 
 classification 
 
 Metals precipitated by Metals not precipitated 
 
 Sulphuretted Hydrogen. by Sulphuretted Hydrogen. 
 
 Tin. Cadmium. Potassium. Sodium. 
 
 Chromium. Vanadium. Lithium. Barium. 
 
 Tungsten. Molybdenum. Strontium. Calcium. 
 
 Osmium. Columbium. Magnesium. Aluminum. 
 
 Titanium. Arsenic. Glucinum. Thorium. 
 
 Antimony. Tellurium. Yttrium. Zirconium. 
 
 Uranium. Copper. Lanthanum. Cerium. 
 
 Lead. Bismuth. Manganese. Iron. 
 
 Silver. Mercury. Nickel. Cobalt. 
 
 Gold. Palladium. * Zinc. 
 
 Platinum. Rhodium. 
 
 Iridium . Ruthenium . 
 
 Each of these groups may be subdivided by the agency of hydrosul- 
 phuret of ammonium, upon the following principles 
 
 The metallic sulphurets which possess electro -negative or acid charac- 
 ters unite with hydrosulphuret of ammonia to form sulphur salts, and 
 the precipitated sulphuret is consequently redissolved by the addition of 
 an excess of that reagent, whilst the sulphurets of the electro-positive 
 or basic metals are not redissolved because they do not unite with the 
 re-agent. Hence 
 
 Precipitated Sulphurets Precipitated Sulphurets 
 
 re-dissolved by Hydro-Sulphuret not re-dissolved by Hydro-Sul- 
 
 of Ammonia. phuret of Ammonia. 
 
 Tin. Chromium. Cadmium. Copper. 
 
 Vanadium. Tungsten. Lead. Bismuth. 
 
464 Analytical Classification of the Metals. 
 
 Molybdenum. Osmium. Silver. Mercury. 
 
 Columbium. Titanium. Palladium. Rhodium. 
 
 Arsenic. Antimony, Ruthenium. 
 
 Tellurium. Uranium. 
 
 Gold. Platinum. 
 Iridium. 
 
 The metals not precipitated by sulphuret of hydrogen are also sepa- 
 ted into two groups by hydro-sulphuret of ammonia; thus, in one 
 group, the metallic sulphuret is insoluble in water, and its precipitation 
 is only prevented by the presence of free acid, which being neutralized 
 by hydrosulphuret of ammonia, the sulphuret of the metal separates ; 
 in the other group, the metallic sulphuret is really soluble in water, 
 and hence cannot be precipitated at all. There is consequently of the 
 metals not precipitated by sulphuretted hydrogen 
 
 Metals precipitated by Metals not precipitated by 
 
 Hydro- Sulphuret of Ammonia. Hydro-Sulphuret of Ammonia. 
 Cerium. Lanthanum. Potassium. Sodium. 
 
 Manganese. Iron. Lithium. Barium. 
 
 Nickel. Cobalt. Strontium. Calcium. 
 
 Zinc. Magnesium. Aluminum. 
 
 Aluminum and some of its allied earthy matters are given as not 
 precipitated by hydrosulphuret of ammonia, although their solutions do 
 in reality afford precipitates with that re-agent, but that precipitate is 
 not a metallic sulphuret ; it is the pure earth, the same as it should 
 have been precipitated by the ammonia alone ; whilst the sulphuretted 
 hydrogen become free in the liquor. This fact, although not at all 
 influencing the classification, requires to be carefully considered in 
 practical analysis. 
 
 This last group may be still further subdivided by means of the rela- 
 tive solubility of the carbonates of their oxides ; thus, the carbonates of 
 the alcaline metals potassium, sodium, and lithium, are soluble, but the 
 carbonates of the earthy metals are insoluble in water. Hence, on 
 adding a solution of carbonate of soda to solutions of the metals not 
 precipitated by hydro-sulphuret of ammonia, we at once distinguish the 
 solutions of alcalies from the solutions of what are properly termed 
 earths. 
 
 By taking advantage of these properties of the metallic sulphurets, 
 the analytical chemist can thus determine the special and comparatively 
 small group to which any metal he may have under examination must 
 belong, and then by a few of the more characteristic properties of its 
 other compounds as to solubility, or colour, or volatility, the individual 
 character of the metal is determined and its identity, if already known, 
 or its distinctiveness, if new to science, may be satisfactorily proved. 
 
Redaction of the Metals. 465 
 
 The circumstances tinder which the metals are found in nature are 
 exceedingly diverse. Some are found native, or only alloyed with other 
 metals, as gold, silver, tellurium, bismuth, and some others. Many ex- 
 ist combined with arsenic, the sources of cobalt and nickel being almost 
 exclusively their native arseniurets. Some metallic chlorides and iodides 
 exist also native, but the most abundant forms in which the metals are 
 to be found, are combinations with oxygen and sulphur. There are few 
 of the metals that do not exist naturally in the state of oxides, which 
 are either free or else combined with acids, forming salts. Thus, lead, 
 copper, iron, zinc, tin, manganese, antimony are all found in abun- 
 dance as native oxides, or as native sulphates, carbonates, arseniates, 
 phosphates, silicates, &c. The majority of the metals exist also in 
 nature combined with sulphur. The sulphurets of lead, of zinc, and of 
 copper are the sources from whence the supplies of those metals are 
 obtained; and the sulphuret of iron exists in great abundance, and 
 although not used for the extraction of the metal, is of great impor- 
 tance in the manufacture of green vitriol, of alum, and of sulphuric 
 acid. These native compounds of the metals are termed ores ; and 
 the metal is said to mineralized by the substance with which it is 
 united. 
 
 The process followed in the extraction of the metals must be, of 
 course, regulated by the composition of the ores in which it is contained; 
 and as it will save the necessity of frequent repetition hereafter, I shall 
 describe the general manner of treating each kind of ore, so far as may 
 serve the purpose of an elementary work like the present, in which the 
 introduction of minute and technical details would be useless and im- 
 proper. In cases where the plan followed for any particular metal, 
 deviates essentially from that now about to be described, I shall notice 
 the circumstance in its special history. 
 
 There are two objects to be effected in the extraction of a metal from 
 its ores. First, to set free the metal from whatsoever bodies it had 
 been united with, which is done by adding some body having a stronger 
 affinity for the mineralizing substance : the second, to give to the mate- 
 rials such liquidity or fusibility as that the particles of metal when set 
 free may be able to unite so as to form a mass. This is done by the 
 addition of fluxes, as lime, fluor spar, and on the small scale, alcalies, 
 which combining with the earthy and silicious matters of the ore, form 
 fusible glasses or slags, which float on the reduced and melted metal. 
 
 Where the metal exists in a simply oxidized condition, it is only 
 necessary to heat the ore strongly in contact with the fuel, by which 
 carbon is supplied in abundance for its reduction. The carbon com- 
 bines witli the oxygen, and the metal is set free. It is not often that 
 30 
 
466 General Principles of the 
 
 the ores have this simple constitution, but in many cases the metal exists 
 as a carbonate, and then the carbonic acid being expelled by the first 
 application of the heat, the oxide which remains is reduced by the de- 
 oxidizing action of the ignited fuel. Thus, the native carbonates of 
 lead, of copper, of zinc, and specially of iron, are simply reduced in this 
 way : the last mentioned is the ore which constitutes the great iron 
 deposit of several coal districts. 
 
 If the mineralizing substance, however, be any other than oxygen, 
 carbon, no matter how intensely heated, cannot produce any effect upon 
 the ore. Thus, the native sulphurets and arseiiiurets are not acted upon 
 by carbon. Nor can the metals be obtained in a pure form from any of 
 their salts except the carbonates, by means of carbon, for the oxygen of 
 the acid and base being simultaneously removed by its agency, the 
 radical of the acid remains united with the metal, which is thus only 
 changed into a new kind of ore. Thus, if sulphate of lead be heated 
 with any of the forms of carbon, it is converted into sulphuret of lead, 
 S0 3 +PbO and 40 giving S + Pb and 4CO. And if arseniate of 
 iron be ignited with carbon, all the oxygen is removed, and the arsenic 
 and iron remain in combination. In such cases, it is necessary to adopt 
 somewhat more circuitous methods, suited to the constitution of the 
 individual ores. 
 
 In the case of certain metallic sulphurets, the metal may be very 
 simply separated by melting the ore with a proportional quantity of a 
 metal having a greater affinity for sulphur. Thus, metallic antimony is 
 very generally obtained by the fusion of the native sulphuret with iron ; 
 SbS 3 and 3Fe giving S.Fe.S and Sb. On the large scale, however, 
 this method would not be economically available. In order to extract 
 the metal from its sulphuret, as in the generality of the ores of lead, of 
 copper, and of zinc, the ore, first reduced to fine powder, is heated to 
 redness in a current of air, by the oxygen of which the sulphur is con- 
 verted into sulphurous and sulphuric acid, whilst the metal is oxidized. 
 This process is termed calcination. A great part of the sulphuric acid 
 formed is carried off with the current of air, and the remaining product 
 is a sulphate of the metal, with excess of base. When the salt so 
 formed is deoxidized by contact with the ignited fuel, the excess of 
 oxide abandoning its oxygen, yields an equivalent quantity of metal, 
 which, however, would be impure and of inferior quality, by having 
 dissolved a portion of the sulphuret reproduced by the reduction of the 
 sulphur from the sulphuric acid. It is, therefore, necessary to get rid 
 of that residual portion of the sulphuric acid before the deoxidizing 
 process commences, and this is effected by mixing up a proper quantity 
 of lime with the calcined mass. The lime decomposes the metallic sul- 
 
Reduction of the Metals. 
 
 467 
 
 phate, combines with the sulphuric acid, and sets the oxide free ; and 
 when the deoxidizing flames of the furnace pass over the calcined mass, 
 the metallic oxide being reduced, yields a pure metal, whilst the sul- 
 phate of lime, though, by losing its oxygen, it is brought to the state of 
 sulphuret of calcium, remains as a scoria upon the surface without 
 doing injury. This kind of operation is generally carried on in a sort of 
 furnace termed reverberatary, from its office of beating down the flames 
 from the fire-place upon the materials strewed upon the hearth. The 
 adjoining figures will give an idea of its construction. The upper is a 
 
 vertical, and the lower a horizontal 
 section, to which the same letters ap- 
 ply, a is the fire-place, and 6 the 
 ash-pit ; at c a low wall is raised, 
 termed the bridge, and the" flames 
 and heated air ascending from the 
 fire are reflected downwards by the 
 low, vaulted roof, and impinging 
 upon the hearth or sole of the fur- 
 nace, d, produce the greatest heat- 
 ing effect upon the materials laid 
 thereon. The openings, i and g, 
 serve for the introduction of the 
 materials, and for giving them the 
 
 arrangement, agitation, and mixture most conducive to the success of 
 the operation. The damper, p, in the flue, regulates the draught, and 
 hence the intensity of the fire. 
 
 In this furnace the calcining, or oxidizing, and the reducing, or 
 deoxidizing effect is produced, according as the supply of fuel and of 
 air is regulated ; and thus the two stages just described, in the extrac- 
 tion of a metal from its native sulphuret, are carried on. The hearth, 
 d } is generally dished or concave towards the centre, so that the reduced 
 metal, in its melted condition, may flow there, and be run out by an 
 aperture in the side of the furnace, when the operation is concluded. 
 
 In the case of sulphuret of lead, a very simple and beautiful process 
 of reduction consists in roasting the ore at a moderate temperature, so 
 that about one-half of it shall be converted into sulphate of lead by 
 oxidizement, without any of the sulphuric acid being driven off; and 
 then, having mixed this up well with the unaltered portion of the ore, 
 increasing the temperature very rapidly, so that the two shall be fluxed 
 together. The result is the complete conversion of the mixture into 
 sulphurous acid gas, which passes off, and pure metallic lead which 
 remains ; the sulphur of the unaltered ore combining with the sulphur 
 
468 General principles of the 
 
 and oxygen of that portion which had been oxidized. Thus SO 3 -f PbO 
 and S + Pb produce exactly 2'SO2 and 2Pb. 
 
 One of the most interesting processes of reduction is that by which 
 iron is obtained from its most abundant ore, the clay iron stone. This 
 substance consists of oxide of iron combined with carbonic acid and 
 mixed with a quantity of clay. If the ore were simply strongly heated 
 the carbonic acid being driven off, the oxide of iron would unite the 
 alumina and silica of the clay to form a kind of iron glass, or slag, on 
 which the fuel would then have no action, as carbon cannot decompose 
 any silicate. It is necessary, therefore, to prevent the formation of the 
 silicate of iron from the materials of the ore, and this is effected by 
 means of lime. The coal or coke and the ore are introduced into the 
 furnace, mixed with a proportion of limestone, which being calcined by 
 the heat, yields lime, which seizes upon the silicic acid, and the oxide 
 of iron being left free, is immediately reduced by the carbon of the 
 fuel with which it is in contact, and produces metallic iron. The lime, 
 the silica, and the alumina, when melted together, form a substance, 
 a complex silicate, of a nature somewhat between glass and porcelain, 
 which floats upon the mass of melted metal, and constitutes the 
 slags or scoriae of the iron furnaces. The remarkable loss of heat 
 by the dissipation of carbon as carbonic oxide which takes place 
 in that process, will be noticed in detail in the description of that gas, 
 and of carbonic acid. 
 
 In the case of ores containing arsenic, of which only the arseniurets 
 of cobalt and nickel are of technical importance, the method followed 
 is to roast the ore in a furnace, so constructed, as that a powerful oxi- 
 dizing action shall be produced by a current of air streaming over the 
 ignited ore ; both metals being thus oxidized, arsenious acid, and oxide 
 of cobalt, or of nickel are produced; the greater part of the arsenious acid 
 is expelled by the heat, and being carried off by the draught, is conducted 
 into large chambers, where it is gradually deposited under the form of 
 a fine white powder upon the walls and floor. The metal with which 
 the arsenic had been combined remains in the state of oxide, united with 
 a little arsenious acid, and is subsequently extracted or employed in 
 other processes. 
 
 The reduction of a metal from the state of sulphuret is frequently 
 effected upon the small scale by fusion with a mixture of lime and 
 charcoal, or of carbonate of potash and charcoal, which last is fami- 
 liarly termed black flux. The theory of this process is very simple. 
 Thus, if sulphuret of antimony, lime, and charcoal be melted together, 
 the sulphur combines with the calcium of the lime, the oxygen of which 
 unites with the antimony, SbSs and 3.CaO giving 3.CaS and Sb.O 3 . 
 
Reduction of the Metals. 469 
 
 This last is then decomposed by the charcoal, the oxygen combining 
 with the carbon, and the metallic antimony separates. 
 
 The black flux used in such operations is prepared by deflagrating 
 together equal parts of nitre and cream of tartar ; the nitrogen and 
 oxygen of the former unite with the carbon and hydrogen of the latter, 
 forming carbonic acid, nitrogen, and water : the potash of both remain 
 behind as carbonate, mixed with the excess of carbon which had 
 escaped combustion. If two parts of nitre be used with one of cream 
 of tartar, there remains after deflagration a white mass of carbonate of 
 potash, which is known as white flux, and is used in processes where the 
 deoxidizing effect of the carbon is not required. Thus, for the reduc- 
 tion of chloride of silver, it is sufficient to fuse it with half its weight 
 of white flux; the chlorine combines with the potassium, and the silver, 
 which at a lower temperature would have united with the oxygen and 
 carbonic acid, is separated, those two bodies escaping in the gaseous 
 form. The formula of the reaction being that KO.C0 2 and Cl. Ag give 
 K.C1 and free Ag, whilst O and CO 2 are driven off. 
 
 Hydrogen, although inapplicable to the reduction of the metals upon 
 the large scale, and for the purposes of the arts, is yet to the chemist a 
 most valuable agent for this office, as it acts upon all varieties of 
 metallic combinations, whether oxides, chlorides, or sulphurets ; and 
 that the results it gives are so accurate, as to serve as basis for some 
 of the most fundamental propositions of the science. Thus, we have 
 already seen that the composition of water is best determined by the 
 action of hydrogen gas upon oxide of copper, and in analytical inves- 
 tigations, the isolation of a metal, by decomposing its chloride or sul- 
 phuret, in a stream of hydrogen gas, is frequently employed. The 
 deoxidizing action of hydrogen is occasionally used in an indirect man- 
 ner. Thus, a very convenient mode of obtaining silver from the 
 chloride, consists in fusing it with some common resin : this consists of 
 carbon, hydrogen, and oxygen, of which only the hydrogen is active ; 
 it combining with the chlorine carries it off as muriatic acid gas, whilst 
 the metallic silver is separated. If the chloride of silver be diffused 
 through water rendered slightly acid, and a slip of zinc be introduced, 
 an evolution of hydrogen commences, and the silver separates as a fine 
 metallic powder, according as the zinc dissolves. But the action is 
 here more properly galvanic ; an equivalent (32*3) of zinc combining 
 with the chlorine, in place of each equivalent (108) of silver, which is 
 set free. The precipitation of copper, from the water of copper mines, 
 which hold sulphate of copper dissolved, by dipping therein pieces of 
 iron, and indeed all cases of the precipitation of one metal by another, 
 are referable to the same source. 
 
470 Electro-Metallurgy. 
 
 The physical agent, electricity, which has been already found to influ- 
 ence chemical action in so remarkable a degree, has been employed with 
 considerable success in the reduction of certain metals. It was first 
 applied by Davy, who thereby made his admirable discoveries of the 
 composition of the alcalies and earths. It has been totally superseded 
 in that point of view by simpler processes, but has recently been applied 
 by Becquerel, upon the large scale, to the extraction of the precious 
 metals from their ores, and has been made the basis of several improved 
 processes for extracting copper from the native sulphurets, the practical 
 value of which cannot be considered as yet decided, but of which the 
 general features are as follows : 
 
 The ores, namely, copper-pyrites, the double sulphuret of copper 
 and iron, JFe 2 S 3 -f Cu 2 S mixed usually with iron pyrites, is fully roasted so 
 as to convert the sulphurets into sulphates. The roasted product 
 being lixiviated with water, a solution is obtained from which the cop- 
 per is precipitated, by the immersion of plates of iron, which form the 
 positive element of a simple voltaic circle, of which the negative ele- 
 ment is formed by a sheet of copper. The sheet of copper is immersed in 
 the copper liquor from the ore, and the sheet of iron in a strong solution 
 of sulphate of iron which serves as the excitant, and the two cells 
 communicate by a diaphragm or partition so porous as to admit of the 
 current being established. The copper precipitates at first quite pure, 
 but as the liquor from the roasted ores always contains a great deal of 
 iron, the portions of copper last deposited are contaminated by admix- 
 ture with that metal. The processes of this class are in principle 
 identical with the deposition of copper for electrotyping purposes 
 described in page 267, and differ only in the source of the copper 
 liquor, and in the scale on which the operation is carried on. 
 
 There are many other methods of reduction, which, however, being 
 limited in their application to individual metals, will form more properly 
 a part of their special history. 
 
471 
 
 CHAPTEE XIII. 
 
 OF THE INDIVIDUAL METALS, AND OF THEIR COMPOUNDS WITH 
 OXYGEN, SULPHUR, SELENIUM, AND PHOSPHORUS. 
 
 SECTION I. 
 
 METALS OF THE FIRST CLASS. 
 POTASSIUM. 
 
 Symbol. K. Eq. 39 or 487'5. 
 
 POTASSIUM is the metallic basis of the alcali potash. It was originally 
 discovered by Sir Humphrey Davy, who obtained it by submitting a 
 stick of caustic potash, slightly moistened, so as to be a conductor of 
 electricity, to the action of a powerful galvanic battery ; the water and 
 the potash were simultaneously decomposed ; oxygen being evolved at 
 the positive electrode, whilst hydrogen and potassium were separated at 
 the negative wire. Erom the heat generated by the intense power used, 
 the metallic globules generally burned, as soon as they came into con- 
 tact with the air, and it was with difficulty that a quantity was obtained 
 sufficient for the important researches in which it was employed by its 
 illustrious discoverer. By using mercury as the negative electrode, the 
 decomposition can be effected by a much weaker force, and even with 
 a single pair of plates, as in the arrangement of Dr. Bird, described in 
 page 268. 
 
 The decomposition of potash, by truly chemical means, is due to 
 Gay-Lussac, but it is by the process of Brunner, that the metal is now 
 universally obtained. As it is carried on only, however, in the most 
 extensive and best appointed laboratories, a very short sketch of it will 
 suffice here. 
 
 Cream of tartar, which consists of tartaric acid united to potash, is 
 to be ignited in a covered crucible, until there remains a mass of car- 
 bonate of potash mixed with carbon in a state of very minute division, 
 and this mass is to be intimately mixed whilst still hot, with a quantity 
 of coarsely powdered wood charcoal, which serves to render the whole 
 
472 Preparation and Properties of Potassium. 
 
 porous, so as to allow of the escape of the gases generated in its interior 
 without its swelling up. The material so prepared, is introduced into 
 an iron bottle, such as those in which quicksilver is imported ; to the 
 mouth of the bottle, which is laid horizontally in a wind furnace, is 
 adapted a short iron tube, passing to a copper condenser partly filled 
 with rectified naptha, and so constructed with partitions, as to exclude 
 the air, whilst there passes through it a stout iron wire, terminated by a 
 screw, with which the iron tube can be cleared of any solid material 
 that might be deposited in it. The apparatus being so arranged, and 
 the receiver surrounded by ice, a fire is lighted in the furnace, and when 
 the iron bottle has become white hot, the decomposition of the potash 
 begins, the metal distils over, and condenses in the receiver in globules, 
 which are protected by the naptha, in which they sink, whilst the oxygen 
 of the potash and of the carbonic acid combines with carbon, forming 
 carbonic oxide, which escaping under the partitions in the receiver, passes 
 away; KO + C0 2 and 2C producing K and 3'CO. The great diffi- 
 culty and loss in this process arises, however, from a cause, which is not 
 at first apparent ; it is, that carbonic oxide and potassium unite, to form 
 a dark grey mass, which sublimes, and condensing in the short iron 
 tube, renders the screw necessary to keep the passage clear, and fre- 
 quently causes the failure of the process. Even in the most successful 
 result, one-half of the metal actually reduced, is lost by combining with 
 the carbonic oxide. 
 
 The potassium thus obtained is very impure, containing much carbon, 
 and a quantity of that compound of carbonic oxide, which passes over 
 into the receiver. To purify it, it is redistilled in cast iron retorts, from 
 which the air has been previously excluded by vapour of naptha, and it 
 is thus obtained in globules like peas, in which state it may be preserved 
 under naptha perfectly free from oxygen. 
 
 At common temperatures, potassium is soft, and may be moulded in 
 the fingers like wax. At 32, it is quite brittle and crystallizes in 
 cubes ; at 70 it is pasty, and at 150, perfectly liquid. At a dull red 
 heat it boils, forming a green vapour, and may, as described above, be 
 easily distilled. It is specifically lighter than water, its specific gravity 
 being 0'865. 
 
 The colour of potassium is of a bluish white, but its surface instantly 
 becomes grey when exposed to the air, owing to the absorption of oxygen 
 and the formation of a crust of potash. If it be heated, it burns with 
 a vivid violet flame. So great is its affinity for oxygen, that it decom- 
 poses water, and even ice, with great violence, so much heat being 
 evolved, that if the experiment be made in the air, the hydrogen gas 
 evolved and the metal both inflame and burn with a fine violet colour. 
 
Compounds of Potassium and Oxygen. 473 
 
 When the metal has been all consumed, a globule of fused dry potash 
 remains, which, when it has cooled to a certain degree, combines with 
 water with a loud explosion, and instantly then dissolves. 
 
 Potassium is remarkably characterized by its great affinity for oxygen, 
 which it abstracts from almost all bodies ; thus its use in the prepa- 
 ration of boron and silicon has been already noticed ; and although at 
 very high temperatures iron and carbon take oxygen from potassium, 
 yet at a lower degree of heat, oxide of iron and carbonic acid are both 
 decomposed by potassium, carbon being deposited from the one, and 
 metallic iron separated from the other. 
 
 The symbol of potassium is K, the initial of the word Kalium, by 
 which the metal is designated by most of the Continental chemists ; the 
 old name kali being still retained in preference to the word potash, 
 which has been adopted only in Great Britain and in Trance. The 
 equivalent is 48 7 '5 or 39, according to the scale. 
 
 Oxides of Potassium. Potassium combines with oxygen in two pro- 
 portions, forming a protoxide KO, and a peroxide KOa. 
 
 The protoxide of potassium constitutes the important alcali potash ; 
 it can only be obtained free from water, by exposing potassium to the 
 action of dry air, when it is converted into a white powder, which is 
 fusible at a red, and volatile at a white heat ; if this substance be once 
 united with water, it cannot be separated from it, except by combination 
 with an acid. The potash of commerce, and that used in the laboratory, 
 is, therefore, always hydrate of potash ; the dry potash, in uniting with 
 water, becomes ignited. Before the discovery of carbonic acid, the 
 alcalies and their carbonates were distinguished from each other, by the 
 epithets of mild and caustic, and hence for medicinal purposes, and 
 in some pharmacopoeias, the hydrate of potash is still termed caustic 
 potash. 
 
 To prepare a solution of potash, the carbonate of potash of com- 
 merce, derived from the sources to be detailed in its description, is to 
 be dissolved in ten parts of water, and the solution being made to boil 
 smartly, is to be decomposed by one part of slaked lime in fine powder, 
 which is to be gradually added, the boiling being briskly kept up ; the 
 lime abstracts the carbonic acid from the potash, and carbonate of lime 
 is formed, which at that temperature, constituting minute crystals of 
 arragonite, is rapidly and completely deposited. The clear liquor is 
 to be tested occasionally by adding to a small quantity of it an excess 
 of muriatic acid ; as soon as the absence of effervescence shews that all 
 the alcaline carbonate has been decomposed, the pan is to be removed, 
 and being laid aside, carefully covered until the carbonate of lime has 
 been well settled, the clear liquor may be siphoned off. The decom- 
 
474 Preparation of Potash. 
 
 position of the carbonate of potash by the lime would take place also 
 at ordinary temperatures, but the precipitate would be in the rhombo- 
 hedral form, and being specifically lighter and more finely divided, 
 should occupy much more room, and could not separate so well. If 
 the carbonate of potash be dissolved in less than six parts of water, it 
 is not decomposed by lime ; on the contrary, when a strong solution of 
 caustic potash is boiled with carbonate of lime, carbonate of potash is 
 produced, and lime set free. 
 
 When the solution of caustic potash is evaporated in a basin of iron 
 or silver, or platina, there remains a liquid which solidifies on cooling, 
 into the hydrate of potash, KO.HO. This viscid liquid is generally 
 run into cylindrical moulds, in which form the caustic potash or fused 
 potash of the shops is generally found. In this state it is, however, 
 impure, and it requires to be freed from the admixed sulphate and car- 
 bonate of potash, chloride and peroxide of potassium, and oxide of 
 iron, which it generally contains, by being dissolved in absolute al- 
 cohol, the solution evaporated to dryness, and the remaining potash 
 fused a second time. 
 
 Hydrate of potash is a pure white solid, of a crystalline fracture ; it 
 fuses below redness. In the fingers, it has a peculiar soapy feel, owing 
 to its dissolving the cuticle, with which it forms a kind of soap ; it acts 
 powerfully on all organic tissues, dissolving and decomposing them, 
 and hence its use in surgery, and its name of caustic potash. It dis- 
 solves in water, with the evolution of considerable heat ; a concentrated 
 solution of it crystallizes when exposed to cold, in rhombic octohed- 
 rons, whose composition is KO+5HO. 
 
 The solution of potash is pre-eminently alcaline ; it neutralizes the 
 strongest acids, browns turmeric paper, and restores the blue colour of 
 litmus paper reddened by an acid. It absorbs carbonic acid rapidly 
 from the air, and must hence be preserved in close vessels. It acts 
 rapidly on glass containing much alcali or lead, and hence should be 
 preserved in bottles of common green glass. 
 
 The uses of potash in chemistry are too numerous to mention ; it 
 being the strongest base, is employed in almost ah 1 cases of saline de- 
 composition, and its various compounds are of great importance in the 
 chemical arts, of which many will be noticed hereafter in detail. 
 
 Potash is distinguished, when free, first by its general alcaline cha- 
 racters, and by its not being precipitated by carbonate of soda, which 
 separates it from everything but soda and ammonia. Prom the latter 
 it is known by the brown stain produced on turmeric paper being per- 
 manent, whereas the brown colour produced by ammonia disappears 
 when the paper is warmed ; and from soda it is known by giving with 
 
Sutpkurefo of Potassium. 475 
 
 an excess of the perchloric, tartaric and hydrofluosilicic acids, sparingly 
 soluble salts, whereas the soda salts of these acids are all easily soluble. 
 A solution of potash, if neutralized by muriatic acid, gives, on the 
 addition of chloride of platinum, a fine yellow precipitate, whereas 
 with a solution of soda no precipitation occurs. 
 
 The salts of potash act in all respects similarly, except that as there 
 is no alcali in excess, the action on vegetable colours is not that of an 
 alcali. The salts of ammonia resemble precisely the salts of potash in 
 their action on those precipitants described above, but they are at once 
 distinguished by the application of heat. The salts of ammonia are all 
 volatilized, either with or without decomposition, by a red heat, whilst 
 those of potash are fixed, and give to the flame of the blowpipe a dis- 
 tinct and characteristic violet tinge. 
 
 Potash consisting of an equivalent of each element, its formula is 
 K.O, and its composition 
 
 Potassium, 83-05 One equivalent = 487'5 or 39'0 
 Oxygen, 16-95 One equivalent = 100 or 8-0 
 
 100.00 587.5 47-0 
 
 Peroxide of Potassium, KO 3 . This substance, which is of very little 
 importance, is formed by burning potassium in an excess of oxygen 
 gas ; it is a yellow powder, decomposed by water, potash dissolving, 
 and oxygen being given off. When hydrate of potash is heated to 
 redness in the air, some peroxide is always formed, and hence the fused 
 potash of the shops generally gives off minute bubbles of oxygen gas 
 when dissolved in water. 
 
 Sulpkurets of Potassium. When potassium is gently heated in con- 
 tact with sulphur, they unite with brilliant combustion, and, according 
 to the proportions in which they were employed, form the sulphurets of 
 potassium, of which there are altogether four. These bodies are, how- 
 ever, always prepared in practice by more economical processes. 
 
 If sulphate of potash be ignited in a glass tube, and a current of 
 dry hydrogen gas be passed over it, all the oxygen both of acid and 
 base is removed in the state of water, and protosulphuret of potassium 
 remains. Thus, KO.SO 3 and 4H produce 4.HO and K.S. The same 
 result follows from igniting strongly, in a crucible, a mixture of char- 
 coal and sulphate of potash, all the oxygen is removed, as carbonic 
 oxide, and the sulphur and the potassium remain in combination. KO. 
 S0 3 and 4C giving 4.CO and K.S. 
 
 This protosulphuret is of a brown colour, fusible below a red heat ; 
 it is easily soluble in water ; its solution is yellow, and reacts highly 
 
476 Sulphurets of Potassium. 
 
 alcaline and caustic. When exposed to the air it absorbs oxygen ra- 
 pidly ; and in preparing it from sulphate of potash, by carbon, if 
 lampblack be used, so that the product shall be in a state of very mi- 
 nute division, it takes fire spontaneously on coming into contact with 
 the air, constituting a pyropkorw. If the protosulphuret of potassium 
 be acted upon by acids, water is decomposed, K.S and H.O giving 
 K.O and H.S ; the potash remains united with the acid, and the sul- 
 phuret of hydrogen is given off. No solid sulphur is deposited, and 
 the liquor remains clear. 
 
 A solution of the protosulphuret dissolves sulphur in large quantity, 
 the higher sulphurets being formed. It absorbs sulphuretted hydrogen 
 in such proportion that a compound is produced, K.S + H.S, exactly 
 similar to the hydrate of potash, K.O + H.O. 
 
 The tersulphuret of potassium corresponds to the peroxide, its for- 
 mula being K.S 3 . It constitutes the mass of the kepar sulphuris, liver 
 of sulphur, of the pharmacopeias. It may be prepared by fusing at a 
 moderate heat, one part of sulphur and two of carbonate of potash ; the 
 mass being kept liquid as long as it effervesces from carbonic acid gas 
 being evolved. In this reaction, a quantity of oxygen from the potash 
 combines with one portion of the sulphur, forming an acid of sulphur 
 differing in its composition, according to the temperature, whilst the 
 remainder of the sulphur combines with the potassium, producing a 
 sulphuret, the composition of which is determined by the quantity of 
 sulphur present. With the above proportions the final reaction may be 
 considered to be 4(KO + C0 2 ) and 10S give 3.KS 3 and KO.SO 3 , which 
 constitutes the fused mass, whilst 4C0 2 is driven off with effervescence. 
 If, however, equal weights of carbonate of potash and of sulphur had 
 been employed, the sulphuret formed contains five equivalents of sul- 
 phur ; it is the pentasulpkuret. The reaction commences even at the 
 temperature at which sulphur fuses, and all carbonic acid is given off 
 before a red heat ; hyposulphite and sulphite of potash only being 
 formed. The action of a higher temperature decomposes the salt first 
 formed and produces sulphate of potash. 
 
 These sulphurets resemble each other completely in external appear- 
 ance ; they are liver brown, they deliquesce in the air, and absorb oxy- 
 gen rapidly. Their solutions, which are at first deep yellow, become 
 colourless by uniting with oxygen, hyposulphite of potash being formed, 
 and sulphur precipitated. If a solution of the tersulphuret or penta- 
 sulphuret be treated with an acid, water is decomposed, and potash 
 being formed, sulphuret of hydrogen is produced ; the remaining sul- 
 phur then separates in a state of very minute division, and of a milk 
 white colour, constituting the lac sulphuris or the sulphur precipi- 
 
Sodium and Soda. 477 
 
 tatum of pharmacy. If the acid employed be strong and in great ex- 
 cess, a quantity of bisulphuret of hydrogen is formed, as explained in 
 page 406. 
 
 Rose is of opinion that the whiteness of precipitated sulphur depends 
 not merely upon its minute division, but that it is owing to the pre- 
 sence of a trace of bisulphuret of hydrogen. When the Jiepar sul- 
 phurls is decomposed by an acid, it is not merely that the excess of 
 sulphur is set free, but in addition, as there is always hyposulphurous 
 acid present, this, when evolved, acts on the sulphuretted hydrogen, 
 and the sulphur of both is precipitated, water being formed. S0 2 and 
 2HS giving 2. HO and 2S : see page 401. 
 
 The pentasutphuret of potassium is prepared perfectly pure by de- 
 composing sulphate of potash by sulphuret of hydrogen, at a red heat. 
 Thus, KO.S0 3 and 4HS give KS 5 and 4HO. This reaction supports 
 very much the view that this pentasulphuret is really sulphate of potash, 
 in which the oxygen, both of acid and base, is replaced by sulphur, for 
 K.S 5 may be constituted of KS and S.S 8 . 
 
 The seleniurets of potassium are similar in constitution to the sul- 
 phurets. They evolve seleniuret of hydrogen when treated by acids, 
 with precipitation of selenium when it is present in greater proportion 
 than one equivalent. 
 
 OF SODIUM. 
 Symbol. Na. Eq. 23 or 287'5. 
 
 Sodium exists in great quantities in the mineral kingdom, especially 
 combined with chlorine, as common salt, of which enormous deposits 
 are found in England, Poland, and elsewhere, besides forming the 
 leading saline ingredient of the waters of salt lakes and of the ocean. 
 It is found in many minerals, and is remarkably prevalent in the animal 
 fluids, all of which contain common salt. It is, indeed, from the chlo- 
 ride of sodium that we derive, whether directly or indirectly, all the 
 supplies of the various compounds of this metal. 
 
 The discovery of sodium was made in the same manner and imme- 
 diately subsequent to that of potassium, by Humphrey Davy, and it is 
 now prepared in exactly the same manner as that metal. It is, how- 
 ever, much more easily prepared, its reduction does not require so high 
 a temperature, and it does not unite with carbonic oxide, so that the 
 formation of the black sublimate, which is the principal source of loss 
 and failure in preparing potassium, does not occur. 
 
 Sodium is lighter than water, its sp. gr. being 0'972; it conse- 
 quently floats upon that liquid ; and when a globule of the metal is 
 
478 Sodium and Soda. 
 
 thrown into a basin of water, this is decomposed with great rapidity, 
 hydrogen being evolved; but the action is not so energetic as with 
 potassium ; the gas does not take fire spontaneously, but if the glo- 
 bule be prevented from moving about, the water becomes heated, and 
 the action increases to such a degree as to set fire to the gas -, this 
 occurs when there is so little water that the globule does not swim, or 
 when it is fastened to the edge of the vessel, or if the water be thick- 
 ened by gum or starch. If some oil of vitriol be added to the water, 
 the action is so much more active, that combustion occurs even when 
 the metallic globule moves rapidly about. 
 
 The symbol of sodium is Na. derived from the word Natrium, as 
 soda still retains in many countries, the name Natron. Its equivalent 
 numbers are 287 '5 or 23'0. 
 
 Sodium unites with oxygen in two proportions, forming the protoxide 
 of soda, NaO, and the peroxide, of which the constitution is not ex- 
 actly known. This last is prepared just as the peroxide of potassium, 
 which it resembles completely in its properties. The former only re- 
 quires detailed notice. 
 
 The preparation of dry soda is effected like that of potash, by heating 
 the metal in dry air or oxygen. It is greyish white, and absorbs water 
 with excessive power. Erom the hydrate of soda the water can be ex- 
 pelled only by an acid. The caustic soda is, therefore, always, like 
 caustic potash, a hydrate of the alcali. For the preparation of caustic 
 soda the same process is to be followed as for that of potash. The 
 carbonate of -soda of commerce, dissolved in boiling water, is decomposed 
 by slaked lime, it being necessary, however, to use one-third more lime, 
 from the smaller equivalent number of soda. The solution of caustic 
 soda resembles that of caustic potash in all its alcaline characters, but 
 that its action is not so intense. It is a weaker alcali ; its salts being 
 decomposed in most cases by potash. 
 
 The soda consists of an equivalent of each element ; its formula is 
 Na.O, and its composition 
 
 Sodium, 74-42 One equivalent = 287*5 or 23*0 
 Oxygen, 25*58 One equivalent = lOO'O or 8'0 
 
 100-00 387-5 ln/0 
 
 The detection of soda is very simple. On adding to a solution of 
 the substance to be examined a solution of carbonate of soda, if there 
 be no precipitate produced, the base of the salt present must be an 
 alcali. On then applying the various tests for potash and for ammonia 
 detailed in the last section, if no evidence of their presence be obtained, 
 the alcali must be soda ; and even where potash also is present, a small 
 
Lithium and Lithia. 479 
 
 quantity of soda may be recognized, by its tinging the flame of the 
 blowpipe of a fine yellow colour. 
 
 The salts of soda are usually very soluble, but it forms with antimonic 
 acid a very sparingly soluble salt, and may be precipitated from its solu- 
 tions by the addition of antimoniate of potash, which is very soluble. 
 
 The compounds of soda are very numerous and important, and will 
 be described in their proper place, among the salts. 
 
 The sulphurets of sodium resemble so completely the sulphurets of 
 potassium, as not to require more than a reference to their description. 
 To the seleniurets of sodium the same remark applies. 
 
 LITHIUM. 
 
 This metal is found only in a few minerals., of which one of the most 
 common, spodumene, occurs at Killiney, near Dublin. This mineral is 
 a double silicate of the alcali lithia (oxide of lithium) and alumina. 
 The metal has been obtained by voltaic decomposition, but only in very 
 small quantity. It is white, like sodium, and becomes oxidized imme- 
 diately on exposure to the air. Its symbol is L, and its equivalent 
 number 80'3 or 6'4. 
 
 To obtain lithia, the simplest process is to mix the mineral containing 
 it, (generally lepidolite or spodurnene) previously reduced to very fine 
 powder, with fluor spar, and to digest the mass with oil of vitriol, until it 
 is completely decomposed ; the silica is carried off by the hydrofluoric 
 acid, (see page 446,) and the lime, the alumina, and the lithia remain 
 combined with the sulphuric acid. By the action of a small quantity of 
 water, the sulphates of lithia and alumina are dissolved out, and the last 
 then precipitated by ammonia. The sulphates of lithia and ammonia 
 being then ignited, the sulphate of ammonia is decomposed, and the 
 sulphate of lithia obtained pure. This is but a general outline of the 
 process, which requires many additional operations for a fully successful 
 result. 
 
 Lithia is distinguished from the other alcalies by the sparing solubility 
 of its carbonate, in which character it approximates to the property of 
 the earths, thus connecting the two classes of metals. Being so rarely 
 found, and of no application in the arts, its history is not of much 
 importance. 
 
 Lithia is recognized by the sparing solubility of its carbonate, and by 
 tinging the flame of the blowpipe of a brilliant red colour. This last 
 character easily distinguishes it from soda; but as strontia possesses the 
 same property, a mode of distinguishing strontia from lithia will be 
 given in the history of that earth. Lithia is a protoxide, its formula 
 being L.O. ; its equivalents ISO'S or 14'4. 
 
480 Properties of Barium. 
 
 The sulplmrets and seleniurets of lithium do not possess any interest. 
 
 The alcali ammonia might, on one hypothesis of its nature, be de- 
 scribed here. When combined with hydrogen it is considered by Ber- 
 zelius and many other chemists to form a remarkable compound metal, 
 ammonium, NH 4 , whose relations to potassium are of an exceedingly 
 intimate kind ; and the salts of ammonia, which contain ammonia and 
 water, NH 3 -|-HO, are looked upon as consisting of an oxide of that 
 metal, NH 4 .O in combination with an acid. I prefer, however, to study 
 the history of ammonia, and all the classes of compounds into which it 
 enters, among the bodies of organic origin. 
 
 BARIUM. 
 
 Symbol. Ba. Eq. 68'7 or 858. 
 
 Barium is found exclusively in the mineral kingdom, where its oxide, 
 barytes, is the basis of several minerals, as the sulphate and carbonate, 
 which are the usual sources from which it is obtained for use. 
 
 The metal barium was discovered by Sir Humphrey Davy, immediately 
 after the discovery of the bases of the alcalies. It may be prepared by 
 voltaic action, as described under the head of potassium, or much better, 
 by passing the vapour of potassium over barytes heated to redness ; the 
 potassium takes the oxygen of the barytes and the barium is set free. 
 By washing the residue with mercury, the metallic barium is dissolved 
 out, and the mercury being then distilled off in a retort of hard glass, 
 the barium remains behind ; it is a white metal like silver ; it fuses 
 below a red heat ; it is denser than oil of vitriol : it decomposes water 
 with great rapidity, evolving hydrogen gas and forming barytes, (oxide 
 of barium.) 
 
 The name barium is derived from /3gu?, heavy ; the native sulphate 
 of barytes having been called formerly terra ponderosa or heavy spar. 
 Its symbol is Ba; its equivalent numbers 858 or 68*7. 
 
 Barium combines with oxygen in two proportions, forming a protox- 
 ide which is the earth barytes, Ba.O and a deutoxide, BaO 2 . The pre- 
 paration of this last has been described so fully when explaining its only 
 important use, the formation of deutoxide of hydrogen, (p. 355,) that it 
 need not be further noticed here. The protoxide, barytes, is, however, 
 one of the most important earths. 
 
 To procure pure barytes, the nitrate of barytes is to be gently heated 
 to redness in a porcelain crucible. It fuses at a dull red heat, and boils 
 briskly from the rapid escape of oxygen ; when this has terminated, 
 there remains a grey loosely coherent powder, which is barytes. The 
 melted salt in this process is very apt to froth up, so much as to over- 
 
Preparation of Barytes. 481 
 
 flow, unless the vessel be of considerable size; this is very simply 
 avoided by mixing the nitrate of barytes, beforehand, with twice its 
 weight of sulphate of barytes in fine powder. When the nitrate melts, 
 the sulphate gives the mass a degree of consistence which prevents its 
 frothing up, and on boiling the residual mass with water, all the pure 
 barytes dissolves, the sulphate remaining totally unacted on. 
 
 If the native carbonate of barytes, BaO.C0 2 , be strongly heated with 
 carbon, the carbonic acid is converted into carbonic oxide, which passes 
 off, and pure barytes remains behind ; BaO.CO 2 and C giving BaO, 
 and 2. CO; the former process is, however, so much easier, that it alone 
 is now usually employed. Graham has suggested the employment of 
 iodate of barytes as a substitute for the nitrate. 
 
 Another process consists in the decomposition of sulphuret of barium by 
 water. A saturated boiling solution of sulphuret of barium, deposits on 
 cooling a large mass of crystals of hydrate of barytes whilst the remaining 
 undecomposed portion of the sulphuret remains in solution united with 
 sulphuretted hydrogen. On separating the crystals from the mother 
 liquor, they only require to be redissolved and crystallized from pure 
 water twice or thrice to be perfectly pure. The mother liquor when 
 concentrated by boiling gives off sulphuretted hydrogen, and will, on 
 cooling, deposit more crystals, so that finally there takes place a 
 decomposition of the total quantity of sulphuret of barium with 
 the elements of water into sulphuretted hydrogen and barytes, which 
 latter may thus be easily obtained pure. The sulphuret of barium 
 may also be decomposed by metallic oxides, as shall be hereafter 
 described. 
 
 Pure barytes is a heavy grey powder ; when exposed to the air, it ab- 
 sorbs water rapidly, giving out much heat and falling into a fine white 
 powder, hydrate of larytes, BaO -f- HO. Another hydrate may be 
 obtained crystallized, by dissolving barytes in three parts of boiling 
 water, and allowing the solution to cool slowly ; it contains nine equi- 
 valents of water. The solution of barytes is very caustic and alcaline ; 
 exposed to the air, it absorbs carbonic acid, and a white precipitate of 
 carbonate of barytes is formed; it is hence used to determine the 
 quantity of carbonic acid present in the air, (page 361,) and in some 
 other cases. 
 
 The detection of barytes is very simple ; its soluble compounds give 
 white precipitates with carbonate of soda, with sulphuric acid, and with 
 hydrofluosilicic acid, and none of these are affected by a solution of sul- 
 phuretted hydrogen gas in water. The sulphate of barytes is not 
 merely insoluble in water, but also in nitric and muriatic acids, which is 
 a further characteristic of this earth. 
 31 
 
482 Sulphuret of Barium. 
 
 The formula of barytes is Ba.O, and its composition 
 
 Barium, 89'55 One equivalent = 858-0 or 68'7 
 Oxygen, 10'45 One equivalent = 100-0 or 8-0 
 
 100 00 958-0 767 
 
 The soluble compounds of barytes are all poisonous, and the car- 
 bonate, although insoluble in water, is yet dissolved by the free acids 
 of the stomach and becomes poisonous. The antidote to all barytic 
 preparations is sulphate of soda, or sulphate of magnesia, administered 
 in excess ; the sulphate of barytes then produced is absolutely inert. 
 
 Sulphuret of Barium. Ba.S. This body is of considerable interest, 
 as the source of barytes and of most of its ordinary compounds ; to pre- 
 pare it, sulphate of barytes in fine powder is to be mixed with one- 
 fourth of its weight of lampblack, and exposed to a very strong heat 
 for two hours ; the carbon removes all the oxygen from the salt ; car- 
 bonic oxide is evolved, and sulphuret of barium remains ; BaO.SO 3 and 
 4C, giving 4.CO and Ba.S. The mass thus obtained forms an olive 
 powder. It dissolves readily in water, forming a deep yellow solution, but 
 is partly decomposed, barytes and sulphuretted hydrogen being formed, 
 which latter unites with the undecomposed sulphuret of barium to pro- 
 duce the body BaS + HS corresponding to hydrate of barytes BaO. + 
 HO. The sulphuret of barium is decomposed by acids, sulphuret of 
 hydrogen being evolved, and a salt of barytes formed : it is thus that 
 the salts of barytes are obtained for laboratory use. 
 
 A simple mode of obtaining caustic barytes directly from the sul- 
 phuret of barium has been recently given by Mohr. It consists, in 
 adding to a boiling solution of the sulphuret, black oxide of copper 
 until the whole of the sulphuret of barium is decomposed, as is easily 
 ascertained, by adding a drop of the solution to a solution of acetate of 
 lead ; the copper combines with the sulphur, whilst the barium and the 
 oxygen unite, Ba.S and Cu.O producing Ba.O and Cu.S. This is 
 probably the simplest and cheapest means of obtaining pure barytes. 
 Other metallic oxides may be used for the same purpose, but they gene- 
 rally produce some hyposulphite or hyposulphate of barytes which oxide 
 of copper does not. 
 
 OF STRONTIUM. 
 Symbol. Sr. Eq. 43'85 or 547 '3. 
 
 This metal is the basis of the earth strontia, protoxide of strontium, 
 which exists native, combined with sulphuric and carbonic acids. The 
 native carbonate of strontia was first found at Strontian in Scotland, 
 
Strontium and Strontia. 483 
 
 and proved to contain an earth different from barytes, by Dr. Hope. 
 The similarity of these two earths is very great, so that the general out- 
 line of the history of strontia is the same as that of barytes. 
 
 The metal strontium is obtained precisely as barium, with which it 
 perfectly agrees in character so far as its properties have been ascer- 
 tained. Its symbol is Sr, and its equivalent number 547 '3 or 43*8. 
 To obtain strontia the same processes may be employed which were 
 described for the preparation of barytes, substituting the native car- 
 bonate or sulphate of strontia for the compounds of barytes. The 
 strontia is grey, slakes on exposure to the air, forming a hydrate, SrO. 
 HO, and by crystallization from its watery solution, another hydrate 
 SrO -j- 9. HO. Strontia is less soluble than barytes, its taste is not so 
 caustic ; nor is it so poisonous. 
 
 Strontia is distinguished from barytes by tinging the flame of the 
 blowpipe a rich crimson. The red lights used in fireworks owe their 
 colour to nitrate of strontia which is used in their preparation. But the 
 red colour from strontia is destroyed and changed to yellow by the 
 addition of a little barytes, whilst the presence of barytes does not 
 at all interfere with the red flame from lithia. By this means strontia 
 and lithia are distinguished. Like barytes, the soluble salts of strontia 
 are precipitated by sulphuric acid, but the sulphate of strontia is 
 not so very insoluble as sulphate of barytes; a solution of strontia 
 is also precipitated by carbonate of soda. The hydrofluosilicic and the 
 hyposulphurous acids which precipitate barytes, do not precipitate 
 strontia, and thus these earths may be distinguished and separated from 
 each other ; the chromic acid acts in a similar manner. 
 
 The sulphuret and seleniuret of strontium resemble perfectly those 
 of barium, and are prepared in the same way. 
 
 OF CALCIUM. 
 Symbol. Ca. Eq. 20 or 250. 
 
 The existence of this metal was first recognized by Sir Humphrey 
 Davy, it being obtained from lime, by the same method as that described 
 under the head of barium ; it is white like silver ; it sinks in water, 
 which it decomposes rapidly, evolving hydrogen and uniting with 
 oxygen, to form lime (protoxide of calcium.) The symbol of calcium is 
 Ca, and its equivalent number 250 or 20. 
 
 Calcium combines with oxygen only in one proportion, forming lime, 
 the most important of the earths. It is found very extensively distri- 
 buted in the mineral kingdom, principally combined with sulphuric and 
 carbonic acids, forming sulphate of lime (gypsum, plaster of Paris) and 
 
484 Sources of Lime in Nature. 
 
 carbonate of lime (marble, limestone, chalk.) These substances exist 
 as rocks or crystallized, the last constituting the mineral species, arra- 
 gonite and calc spar, often referred to under the heads of crystalline 
 systems, isomorphism, and dimorphism. Lime is found also combined 
 with phosphoric and arsenic acids, in several minerals, and the native 
 fluoride of calcium is the fluor spar, used for the preparation of the 
 hydrofluoric acid and other compounds of fluorine. 
 
 Notwithstanding the immense quantities of carbonate of lime which 
 are found constituting a great proportion of the surface of the globe, 
 as for instance, the whole centre of Ireland is one vast plain of lime- 
 stone, and in that as well as other forms, chalk, marble, &c. it is equally 
 extensive in most other countries, it is questionable whether lime should 
 not be looked upon as rather a characteristic of the animal than of the 
 mineral kingdom of nature. The bony or testaceous skeleton, by 
 which the softer portions of the animal frame are attached, is always 
 found to consist of lime united either with carbonic or phosphoric 
 acids, and the diversity of chemical composition in this respect is found 
 to coincide in a remarkable degree with the most natural physiological 
 classification. The skeletons of the vertebrated animals consist prin- 
 cipally of phosphate of lime, whilst in the shells of the invertebrate 
 animals, the carbonate of lime is the prevalent component. The teeth 
 also consist of phosphate of lime ; in all these cases, the phosphate of 
 lime is associated with fluoride of calcium, just as occurs in the native 
 phosphate, the mineral apatite. 
 
 Now it is remarkable, that all the great geological formations which 
 contain carbonate of lime are found to consist of the aggregated skele- 
 tons (shells) of myriads of the tribes of invertebrated animals, which 
 had existed in some former period of the world's history. Prom the 
 densest and hardest limestone, to the softest chalk, the entire mass re- 
 solves itself ultimately into a congeries of animal remains, and hence the 
 great supply of lime in the mineral state arises from the destruction of 
 its animal sources. Even those crystalline marbles in which no organic 
 remains can be traced, appear destitute of them only from having been 
 subjected, by volcanic heat or otherwise, to the influence of causes 
 which have gradually rendered the texture of the mass completely uni- 
 form. The lime which exists in nature must, therefore, be looked upon 
 as being continually in a state of passage between the organized and the 
 inorganic kingdoms. The plants which grow upon the soil take up, by 
 dissolution in their juices, salts of lime, which pass into the substance 
 of the animal which feeds upon them, and accumulating in its system, 
 afford materials for the proper development of the skeleton. When the 
 animal dies, the materials of its tissues either serve for the nutrition of 
 
Properties of Lime. 485 
 
 some other animal, or being totally decomposed, its elements return to 
 the mineral kingdom, to be, in after ages, the subject of similar alterna- 
 tions. 
 
 Lime is always obtained for the purposes of chemistry and of the arts, 
 by the decomposition of the native carbonate. To obtain lime perfectly 
 pure, crystals of calc spar or pieces of Carrara marble should be strongly 
 heated in a crucible loosely covered, so that the carbonic acid can 
 readily escape. In the presence of carbonic acid, carbonate of lime is 
 not decomposed by heat, as was explained already in p. 220. On the 
 large scale, lime is obtained by burning the ordinary limestone in kilns. 
 At the bottom is a grate on which fuel is laid, and the kiln then filled 
 with limestone and fuel, (culm or small coal) mixed in suitable propor- 
 tions; when the fire is lighted on the grate, the combustion extends 
 throughout the mass, and as the perfectly burned lime is extracted at 
 the bottom by the orifice of the grate, new quantities of fuel and lime- 
 stone are introduced above, so that the combustion is continuous \ the 
 carbonic acid evolved is completely removed by the rapid draught 
 through the fire. 
 
 Lime is a pure white earth. When exposed to the air, it rapidly ab- 
 sorbs water, and falls into a white powder, (slaked lime,) which is a 
 hydrate CaO. HO. If a little water be poured on a piece of well burned 
 lime it is absorbed instantly, and the lime appears quite dry, but after a 
 few moments it cracks, and falls into a powder of hydrate, evolving 
 so much heat as to char wood, and inflame gunpowder, when in large 
 quantities. It is thus that vessels laden with lime have been burned at 
 sea, by water penetrating to the hold. Lime is soluble in water, though 
 but sparingly, and still less soluble in boiling than in cold water ; one 
 part of lime requiring 778 of water at 60 and 1270 at 212 for its so- 
 lution ; hence when lime water is boiled it becomes turbid. The solu- 
 tion of lime has an acrid, slightly caustic taste ; it reacts alcaline ; ex- 
 posed to the air it absorbs carbonic acid, becoming covered with a crys- 
 talline pellicle of carbonate of lime. On breathing into lime water 
 through a glass tube, it is immediately rendered turbid by the carbon- 
 ate of lime produced by respiration ; an excess of the carbonic acid, 
 however, dissolves the precipitate. It is in this way that carbonate of 
 lime is held dissolved in almost all ordinary spring and river waters. If 
 lime be perfectly dry, it has little or no tendency to absorb carbonic 
 acid ; it requires to be first slaked and then the hydrate is decomposed, 
 the water being expelled by the carbonic acid ; the absorption is very 
 rapid until the lime becomes one-half saturated, a compound of CaO. 
 CO2 + CaO. HO being probably formed, but after that point the ab, 
 sorption advances but very slowly. 
 
486 Oxides and Sulphurets of Calcium. 
 
 Lime being a protoxide, its formula is Ca.O and its composition and 
 equivalent numbers are as follows : 
 
 Calcium, 71 '91 One equivalent = 250'0 or 20-0 
 Oxygen, 28-09 One equivalent = lOO'O or 8-0 
 
 100-00 350-0 28-0 
 
 Lime is easily distinguished by its dilute solutions not being precipi- 
 tated by sulphuric acid or sulphate of soda, but giving a white precipi- 
 tate of oxalate of lime on the addition of a solution of oxalic acid ; an 
 excess of oxalic acid does not redissolve this precipitate. The nitrate of 
 lime is deliquescent and soluble in alcohol, by which it also differs from 
 the preceding earths. The compounds of lime, when ignited before the 
 blowpipe, tinge the flame of a brick-red colour. 
 
 Lime is of great importance in the arts, from its use in making mor- 
 tar, and in agriculture from its application as a manure. The lime in 
 mortar is not as carbonate, and its coherent property appears to depend 
 only on the gradual drying of the hydrate by which the stones are re- 
 tained together, as boards are by the drying of the glue between their 
 surfaces. The use of lime as a manure, arises from its decomposing the 
 insoluble organic matters of the soil, woody fibres, ulmine, &c., and 
 producing other products more readily taken up by the sensitive radicles 
 of the growing plants. It is hence on such soils as possess a large 
 quantity of organic matter, but are still barren from its not being in 
 the suitable condition, that the beneficial effects of lime are peculiarly 
 marked. 
 
 There is a deutoxide of calcium CaO 2 prepared by adding a solution 
 of deutoxide of hydrogen to lime water ; it resembles deutoxide of ba- 
 rium, but is of no importance. 
 
 There are three compounds of sulphur and calcium known ; the first, 
 or protosulpJmret of calcium, CaS, may be prepared by heating sulphate 
 of lime to redness in a stream of hydrogen gas, or more simply by ig- 
 niting sulphate of lime with one-third of its weight of lampblack ; all 
 the oxygen of the salt is carried off as water, in the one, or as carbonic 
 oxide, in the other case, and the sulphur and calcium remain united. 
 It is a white powder, but very sparingly soluble in water. By boiling 
 in water it is decomposed similarly to sulphuret of barium, hydrosul- 
 phuretted sulphuret of calcium dissolving, and hydrate of lime being 
 deposited. It plays an important part in the manufacture of carbonate 
 of soda, as shall be hereafter explained. 
 
 When flowers of sulphur and slaked lime are boiled together in water, 
 a deep yellow solution is obtained, which is said to be a sulphuret of 
 lime, but which really consists of a mixture of hyposulphite of lime and 
 
Of Magnesium and Magn esia . 487 
 
 lisulphnret of calcium, 6.S and 3.CaO producing 8262 -f CaO and 2. 
 CaS 2 . If the solution be concentrated, this last separates in yellow, 
 prisms with water of crystallization. It is from this yellow liquor, that 
 the precipitated sulphur is prepared, for on adding to it an acid, sul- 
 phuret of hydrogen is evolved from the sulphuret of calcium in such 
 proportion as to decompose the hyposulphurous acid, and all the sulphur 
 is precipitated, whilst the lime remains in combination with the acid 
 which is employed. If the sulphur be in great excess in proportion to 
 the lime, a pentasulpJiuret of calcium may be formed. 
 
 The seleniuret of calcium is not important. If phosphorus in vapour be 
 passed through a red hot tube loosely filled with lime, a brown substance 
 is produced, popularly termed phosphuret of lime but which is a mixture 
 of phosphate of lime and phosphuret of calcium ; the temperature must 
 not be raised too high or else the phosphorus may be expelled again. 
 When this phosphuret of calcium is brought into contact with water, 
 it is decomposed, phosphite of lime, and phosphuretted hydrogen being 
 produced ; this last being evolved in its spontaneously inflammable con- 
 dition, it is an interesting experiment to throw a fragment of the brown 
 substance into a glass of water, numerous gas bubbles are immediately 
 formed, which explode when they reach the air as described in p. 416. 
 When phosphuret of calcium is decomposed by muriatic acid, the phos- 
 phuret of hydrogen evolved is not spontaneously inflammable. 
 
 OF MAGNESIUM. 
 Symbol. Mg. Eq. 127 or 158'3. 
 
 This metal, like the bases of the other earths, was first recognised by 
 Humphrey Davy, but the process by which it is best prepared, is that 
 given by Bussy. A few pieces of potassium are to be placed at the 
 bottom of a tube of hard glass, and then a quantity of anhydrous chlo- 
 ride of magnesium in small fragments is to be laid upon them ; the part 
 of the tube containing the earthy chloride is to be heated to near its 
 point of fusion, and then the metal converted into vapour by the appli- 
 cation of the lamp, as in the figure, p. 448 ; as soon as the vapour of 
 the potassium comes into contact with the heated salt vivid ignition en- 
 sues, and chloride of potassium being formed, the magnesium is libe- 
 rated in the metallic state. Mg. Cl and K giving K. Cl and Mg. 
 When the action has ceased, and the tube is completely cool, the mass 
 is to be washed with water, the chloride of potassium dissolves and 
 leaves the magnesium, with perfect metallic properties, behind. It is 
 white like silver, malleable and fusible at a red heat ; it is not changed 
 by dry air, and but slowly oxidized by damp air ; it may be boiled in 
 
488 Magnesia an Antidote to Arsenic. 
 
 water without this being decomposed. If magnesium be heated to red- 
 ness in air or oxygen, it burns with brilliancy, forming magnesia, and 
 it inflames spontaneously in chlorine ; it dissolves in dilute acids with 
 the evolution of hydrogen gas, and the formation of a salt of magnesia. 
 The symbol of magnesium is Mg. and its equivalent number is 158'3 
 or 12*7 according to the standard. 
 
 Magnesia, the only known compound of magnesium and oxygen, is a 
 protoxide. It exists in considerable quantity in nature, being a consti- 
 tuent of a great variety of minerals ; it is found as hydrate, as carbon- 
 ate, sulphate, and silicate, but its most abundant source is the magne- 
 sian limestone, common both in Ireland and England, which consists of 
 an equivalent of each carbonate, its formula being CaO. CO 2 -f MgO. 
 C0 2 . The pure magnesia is always prepared by exposing the carbonate 
 of magnesia of commerce, the preparation of which will be described 
 among the salts, to a full red heat ; the carbonic acid is expelled, and 
 the earth remains pure. Magnesia is a very light white powder, with- 
 out taste or smell ; it is almost perfectly infusible ; but it and lime are 
 remarkable for becoming beautifully phosphorescent when strongly 
 heated, and it is hence that lime is used as a source of the most brilliant 
 light when it is heated in the jet of the oxyhydrogen blowpipe. It is 
 very sparingly soluble in water, and still less so in hot than in cold 
 water ; its solution browns turmeric paper very slightly. It is remark- 
 ably inferior to lime in basic power, but still neutralizes the strongest 
 acids perfectly, forming excellently characterized classes of salts. 
 
 Magnesia forms with arsenious acid a very insoluble salt, and has on 
 that account been recommended as a remedy to poisoning by arsenic. 
 It acts only however when in the form of a gelatinous hydrate, and 
 should therefore be administered as freshly precipitated by potash from 
 a solution of epsom salts, or as prepared anhydrous by the decompo- 
 sition of the carbonate at a temperature just below ignition. In this 
 state the magnesia when put into contact with water combines with it, 
 forming a bulky gelatinous hydrate, which diffused through water forms 
 the antidote. 
 
 The formula of magnesia is Mg.O, and its composition and equivalent 
 numbers are, 
 
 Magnesium, 61-29 One equivalent = 158-3 or 12.7 
 Oxygen, 3871 One equivalent = 100-0 or 8-0 
 
 100-00 258-3 20-7 
 
 Magnesia is recognized by its sulphate being very soluble in water, 
 and a solution containing it being precipitated by the alcalies and their 
 
Preparation of Aliuitimcm. 489 
 
 carbonates. The precipitate so obtained is redissolved on adding to the 
 liquor a strong solution of sal-ammoniac. The most delicate test for 
 magnesia consists in rendering the liquor suspected to contain it alcaline 
 by ammonia, and then adding a solution of phosphate of soda ; after a 
 short time the phosphate of ammonia and magnesia crystallizes on the 
 side of the glass, particularly if it be scratched by a glass rod : this 
 double salt is almost completely insoluble in an alcaline liquor. A solid 
 substance containing magnesia possesses the property, that if it be 
 moistened by a very small quantity of nitrate of cobalt and ignited 
 strongly by the blowpipe, it becomes a fine pink or rose colour ; the 
 presence of other bodies may, however, interfere with this result. 
 
 The sulphurets and seleniurets of magnesium are of no importance ; 
 they resemble, almost perfectly, those of calcium already noticed. 
 
 SECTION II. 
 
 METALS OP THE SECOND CLASS. 
 
 OF ALUMINUM. 
 Symbol. Al. Eq. 13*7 or 171-2. 
 
 This metal is prepared by the action of potassium upon its chloride, 
 exactly as described for magnesium in the last division, but the opera- 
 tion must be performed in vessels of platinum or porcelain, as the heat 
 spontaneously evolved during the reaction is so intense, as to fuse the 
 most refractory glass; the quantity operated on should likewise be 
 small. A grey melted mass of chloride of potassium and metallic alu- 
 minum remains, which is to be washed with cold water, and the metal 
 is thus obtained in minute but brilliant scales. 
 
 Aluminum does not decompose water at ordinary temperatures, and 
 only slowly even at a boiling heat, but it dissolves rapidly in dilute 
 acids, and also in solutions of the caustic alcalies, with the evolution of 
 hydrogen gas, from the water being decomposed. The symbol of alu- 
 minum is Al. and its equivalent numbers 171*2 or 13' 7, according to 
 the sale. 
 
 There is but one compound known of aluminum and oxygen ; it is 
 alumina. This earth exists in very large quantity in nature, being even 
 still more abundant than lime ; it is a principal ingredient of almost all 
 rocks, except the purest kind of limestone; it constitutes the great 
 mass of the ordinary clays and soils, these deposits being produced by 
 the gradual decomposition and detrition of various kinds of rocks. In 
 
490 Condition of Alumina in Nature. 
 
 all these forms the alumina is generally combined with silica, and some- 
 times with sulphuric or phosphoric acids ; it is also met with pure, or at 
 least contaminated by the presence of only a trace of foreign matter ; 
 thus the ruby and the sapphire, two of the most highly prized precious 
 stones, are alumina, combined with small quantities of colouring 
 matter. The importance of alumina in the arts is very great ; it is a 
 necessary ingredient in the formation of all kinds of earthenware, from 
 tiles or bricks to the finest kind of porcelain, and is extensively used 
 as the basis or mordant for some of the most brilliant and durable co- 
 lours that can be fixed upon cotton or woollen cloth. The alumina 
 derives its name from the salt which it forms with potash and sulphuric 
 acid, the alum of commerce, from which it is always prepared for the 
 purposes of the chemist. 
 
 To prepare pure alumina, a solution of alum is to be decomposed by 
 carbonate of potash, and the precipitate separated by the filter. This 
 precipitate is alumina, the sulphuric acid being taken by the potash, 
 and the carbonic acid, which cannot combine with the alumina, being 
 evolved as gas. The alumina thus produced is, however, not quite 
 pure, it always carries down with it a little sulphate of potash, from 
 which it must be separated by being dissolved in dilute muriatic acid, 
 and again precipitated by carbonate of ammonia ; being then well 
 washed, until the water passes from the filter completely free from sal- 
 ammoniac, it may be looked upon as pure. The alumina so obtained, 
 when dried at common temperatures, constitutes a bulky gummy mass, 
 which is a hydrate, the earth and water containing equal quantities of 
 oxygen. To expel this water completely, it must be exposed to a white 
 heat ; in drying it contracts very much. It was on the measurement 
 of this contraction that Wedgewood founded his pyrometer, now gone 
 out of use, and to allow for it, all vessels of earthenware and china are 
 made much larger than they are intended to be, when completely 
 baked. 
 
 In consequence of the great power with which alumina absorbs and 
 retains moisture, it adheres strongly to the tongue, producing a very 
 peculiar sensation when applied to it. The more or less retentive qua- 
 lity of soils results from the same property, and is generally proportional 
 to the quantity of pure clay which they contain. 
 
 Alumina is white ; if dried at moderate temperatures, it dissolves freely 
 in acids, and in solutions of the fixed caustic alcalies, but if it be very 
 strongly heated, particularly if fused by the oxy-hydrogen blowpipe, it 
 dissolves much more slowly. It is particularly remarkable for its ten- 
 dency to unite with organic matters. If a cotton cloth be immersed 
 in a solution of acetate of alumina, the earth will deposit itself com- 
 
Glucinum and Glucina. 491 
 
 pletely in the fibres of the cotton and leave the acetic acid free. 
 The most important processes in calico printing repose upon this 
 principle. 
 
 Although alumina is the only compound of aluminum and oxygen, 
 it is yet not to be considered as a protoxide. I have already described, 
 (pages 287 and 308) the isomorphous and other relations which estab- 
 lish its constitution to be similar to that of peroxide of iron. It is 
 hence a sesquioxide, and its formula is A1 2 O 3 . Its composition and 
 equivalent numbers are 
 
 Alumina, 53'3 Two equivalents, = 342*4 or 27'4 
 Oxygen, 467 Three equivalents, = 300-0 or 24-0 
 
 lOO'O 642.4 51-4 
 
 Alumina is easily recognized. Its solution is precipitated by the al- 
 caline carbonates, and the precipitate is dissolved by the caustic fixed 
 alcalies, but not by ammonia. It is also precipitated white by hydro- 
 sulphuret of ammonia. A very minute trace of alumina may be redissolved 
 by ammonia, and is 'then best detected by adding phosphoric acid ; a 
 precipitate of phosphate of alumina forms, which is perfectly insoluble 
 in water of ammonia and in acetic acid, but dissolves in caustic potash. 
 If a solid substance containing alumina be moistened with a trace of 
 nitrate of cobalt, and ignited by the blowpipe, it becomes of a beau- 
 tiful blue colour. 
 
 If aluminum be heated in the vapour of sulphur, it takes fire, and 
 forms a grey mass of sulphuret of aluminum. This is decomposed by 
 water, producing alumina and sulphuretted hydrogen, shewing that its 
 formula was A1 2 .S 3 , which with 3.HO give A1 2 O 3 and 3.HS. This sul- 
 phuret, therefore, cannot be formed in solution ; and when a solution 
 of alumina is precipitated by hydrosulphuret of ammonia, as already 
 noticed, the precipitate is pure alumina, and the liquor contains sul- 
 phuret of hydrogen. 
 
 The seleniuret and phosphuret of aluminum are known, but of no 
 importance. 
 
 OF GLUCINUM. 
 
 The earth of which this metal is the basis has been found but in a few 
 rare minerals, and as it exercises no influence on science, from the nature 
 of its compounds, and is of no application in medicine or in the arts, a 
 very brief notice of it will suffice. It exists in the emerald, beryl, and 
 euclase. To obtain it from beryl, the mineral is fused with carbonate 
 of potash, the mass treated with dilute muriatic acid, and evaporated to 
 
492 Yttrium, Terbium, Erbium. 
 
 dryness to separate the silica. The portion which dissolves then in 
 water is to be decomposed by ammonia, which precipitates the alumina 
 and glucina together, and the moist precipitate digested in a strong cold 
 solution of carbonate of ammonia, in which the glucina dissolves. On 
 boiling the filtered liquor so obtained the glucina separates in combi- 
 nation with carbonic acid, from which it is freed by ignition, and so ob- 
 tained pure. 
 
 This earth is tasteless and inodorous ; it is insoluble in water, and 
 has no action on vegetable colours. Its salts taste remarkably sweet, 
 whence its name (yXuxug.) It is easily recognized by its relation to 
 pure and carbonated ammonia, described in the details of its prepa- 
 ration. The metal glucmum is prepared from its chloride precisely as 
 aluminum and magnesium, which it resembles very closely in all its 
 properties. Its symbol is Or, and its equivalent numbers 331*4 or 
 26-5. 
 
 Glucina is considered to be, like alumina, a sesquioxide, and its 
 formula being G 2 O 3 , its composition and equivalents may easily be 
 calculated. 
 
 OF YTTEIUM, TERBIUM, ERBIUM, THORIUM, AND ZIRCONIUM. 
 
 These metals are the bases of earths, concerning which, from the 
 rarity of the sources from which they have hitherto been derived, but 
 little is known, and from their being destitute of scientific importance 
 as well as of practical application, a short notice of their characters only 
 need be given. 
 
 Yttrium, Erbium, and Terbium. The earth yttria, oxide of yttrium, 
 exists in some rare Swedish minerals, which were its only sources until 
 the remarkable announcement, by Apjohn, of its presence in the ordi- 
 nary Bohemian garnet, or pyrope. The method of its extraction is too 
 complicated for description here. It is insoluble in the fixed caustic 
 alcalies, and is precipitated by the yellow prussiate of potash, by which 
 it is completely distinguished from the other earths. It is a protoxide. 
 Its formula is hence Y.O. 
 
 The characters of true yttria have, however, recently been rendered 
 very doubtful by the discovery by Mosander of the substance usually 
 termed yttria, containing, besides the true earth, at least two other new 
 metallic oxides, which are separated as yet but imperfectly from it and 
 from each other. To the new metals the presumed bases of those new 
 earthy oxides, the names erbium and terbium have been given. Their 
 characteristic properties will be sufficiently evident from the following 
 modes of preparation: 
 
 On precipitating a solution of yttria with an alcali, gradually added, 
 
Of Thorium, Zirconium, Cerium. 493 
 
 and separately collecting the precipitates which form after each addition, 
 they are found to assume different colours when dried and ignited. The 
 portions first precipitated becoming orange, the last becoming only very 
 pale yellow or remaining white. The last appears to be pure yttria, so 
 far as it is known. The first portion (orange,) appears to be oxide of 
 erbium, whilst in the intermediate stages oxide of terbium principally 
 exists. The oxide of erbium appear to be orange coloured and to form 
 red salts. The oxide of terbium appears to be white but to form pale red 
 salts. The pure yttria is white and forms colourless salts. Of the 
 equivalent numbers of these bodies, and indeed of their detailed history 
 we are as yet quite ignorant. 
 
 Thorium. The earth Thoria. Oxide of Thorium, Th.O, has been 
 found but in two excessively rare minerals. It is the heaviest of all the 
 earths, its sp. gr. being 9*4. It resembles yttria closely in its proper- 
 ties, especially in being precipitated by ferro-prussiate of potash, but its 
 sulphate forms double salts which differ from those of sulphate of yttria. 
 It is, however, evident that as the history of yttria is now so doubtful, 
 its relations to the still less known thoria cannot be positively described. 
 
 Zirconium. The earth Zirconia. Sesquioxide of Zirconium, Zr 2 Os, 
 is found in two rare minerals, the hyacinth and zircon. It resembles 
 alumina very closely in all its properties, and in some respects assimi- 
 lates itself to silica, and appears to form the link by which the metallic 
 and non-metallic bodies are connected in this direction. Thus, the 
 double fluoride of zirconium and potassium is a sparingly soluble salt, 
 like the fluoride of silicon and potassium, and it is from this double 
 fluoride that zirconium is obtained, by a process identical with that 
 which is described in page 448, for the preparation of silicon. 
 
 CERIUM. LANTHANUM. DIDYMIUM. 
 
 These metals are found in a few rather rare minerals, and have been 
 but very recently distinguished from one another. They are always 
 associated together in nature. Their history does not possess any par- 
 ticular interest, and need hence be noticed but very briefly. 
 
 The metallic cerium is obtained by igniting the protochloride of 
 cerium with potassium, as has been already described for other metals. 
 It is a slightly coherent brown powder, which decomposes water slowly, 
 evolving hydrogen, particularly if the water be hot, and forming oxide 
 cerium. It combines with oxygen in two proportions, forming a pro- 
 toxide and a sesquioxide, CeO and Ce 2 0a. But all the results obtained 
 with it now require revision, as the discovery of lanthanum has thrown 
 much doubt on the purity of the substances that have been hitherto 
 
494 Cerium, Lanthanum, Didymium. 
 
 analysed as compounds of cerium,, and on its received atomic weight. 
 The protoxide of cerium is of a whitish colour. If it be heated in the 
 open air, it absorbs oxygen, and changes into the peroxide (which when 
 pure is white,) ; and if this be reduced by hydrogen gas, at a red 
 heat, it forms a pale yellow complex oxide, probably Ce 3 O 4 . 
 
 Lanthanum. It was found by Mosander, that by calcining protoxide 
 of cerium, so as to convert it into peroxide, only a portion of it became 
 insoluble in dilute nitric acid, and that which dissolved was found, on 
 accurate examination, to be really an oxide of a new metal, which, not 
 forming an insoluble peroxide, may be thus separated from oxide of 
 cerium. From its having been so long hidden in the oxide of cerium 
 usually made, he named it lanthanum (Xavdavu.) Its protoxide is a 
 white powder ; it reacts slightly alcaline ; its colour is not changed by 
 ignition; it forms colourless salts, which yield white precipitates with 
 caustic and carbonated alcalies. It is not precipitated by sulphuretted 
 hydrogen. Its compounds are as yet so little known that its equivalent 
 number cannot be stated. 
 
 Didymium. The oxides of cerium as usually prepared become brown 
 when calcined, and the peroxide of cerium was formerly described to be 
 a brown powder, but this colour is really due to peroxide of didymium, 
 which is a metal apparently similar to manganese, and associated with 
 cerium and lanthanum. By violent ignition, oxide of didymium loses 
 its brown colour and becomes grey. The salts of didymium are rose 
 red or amethyst coloured. The equivalent number is not known. 
 
 OF MANGANESE. 
 Symbol. Mn. Eq. 27'72 or 345'9. 
 
 This metal exists very extensively diffused through nature, although 
 not in very great quantity. Traces of it are found in the animal and 
 vegetable kingdoms, but its great sources are the numerous combinations 
 which it forms with oxygen, and which are employed for the purposes 
 of the arts and of research. Its name is a modification of magnesia, for 
 the native peroxide of manganese was once termed magnesia nigra, 
 but when the peculiar metal which it contained was recognized, the pre- 
 sent appellation was given to it. 
 
 Manganese is one of the metals most difficult to reduce, from its 
 great affinity for oxygen, and the high temperature necessary for its 
 fusion. To obtain it, the oxide must be taken in a state of very fine 
 division, and for that object it is best to use an oxide artificially prepared, 
 as described farther on. This is to be mixed with an equal weight of 
 
Preparation of Manganese. 495 
 
 lamp-black, and made into a dough with oil, and this mass fixed into a 
 crucible, previously coated with a mixture of clay and charcoal powder. 
 The crucible, so filled, being covered, is to be exposed to the most 
 violent heat of a smith's forge for a couple of hours. On then examining 
 it, a button of metallic manganese will be found occupying its lowest 
 portion. 
 
 The metallic manganese is greyish white, granular and brittle ; its sp. 
 gr. 8'013. It is exceedingly infusible. It very soon tarnishes in the 
 air, absorbing oxygen, and falling into a black powder after some time. 
 It decomposes pure water, but very slowly ; but rapidly dissolves in 
 dilute sulphuric acid with the evolution of hydrogen gas : sulphate of 
 the protoxide of manganese being formed. 
 
 The symbol of manganese is Mn, and its atomic weight is 346 or 
 27 '7, according to the standard. 
 
 It is remarkable for the number of compounds which it forms with 
 oxygen, which are as follows : 
 
 Protoxide of manganese, . . . . MnO 
 
 Sesqnioxide of manganese, . . . Mn 2 Os 
 
 Peroxide of manganese, . . . MnO 2 
 
 Manganic acid, MnOs 
 
 Permanganic acid, MnaO? 
 
 In addition there are two complex oxides, 
 
 The red oxide, Mn 3 O 4 or MnO -f- Mn 2 O3 
 
 Varvicite Mn 4 O 7 or Mn 2 O 3 -f 2MnO 2 
 
 The metallic manganese being of such difficult preparation, the 
 various compounds of it are usually obtained from its most abundant 
 source, the native peroxide, which is sent into commerce in large quan- 
 tities to be employed in the arts for the fabrication of chlorine, and in 
 chemistry to prepare oxygen, and many other purposes. The simplest 
 way of preparing the salts of manganese from this native peroxide, 
 which is usually associated with a large quantity of oxide of iron, con- 
 sists in dissolving it in an excess of muriatic acid, and evaporating the 
 liquor so obtained to dryness. The resulting mass consists of chloride 
 of manganese mixed with perchloride of iron. When this mass is 
 heated to redness, the perchloride of iron is partly decomposed, and 
 partly volatilized, and on digesting the residual mass in water, oxide of 
 iron remains undissolved, and a colourless or faintly amethystine solu- 
 tion of protochloride of manganese is obtained. Prom this the various 
 other preparations may be easily formed. 
 
 Protoxide of Manganese. MnO. Equivalent 446, or 35" 7. May 
 be prepared in many ways. If to a solution of protochloride of man- 
 
496 Oxides of Manganese. 
 
 ganese an excess of a caustic alcali be added, a bulky white precipitate 
 is produced, which is hydrated protoxide of manganese. In this state 
 it rapidly absorbs oxygen from the air, becoming reddish brown, being 
 converted into red oxide, which is the most permanent of the oxygen 
 compounds of manganese. If any of the higher oxides of manganese, 
 in a state of fine division, such as the red oxide or peroxide artificially 
 prepared, be heated to redness in a tube of hard glass, in a stream of 
 hydrogen gas, oxygen is removed in such proportion as to leave pro- 
 toxide of manganese behind. The oxide so obtained is of a greenish 
 grey colour ; it does not absorb oxygen at all so rapidly as the hydrated 
 oxide ; but if it be exposed to the air whilst hot it rapidly becomes 
 brown, or even burns. But it is best obtained by mixing together 
 chloride of manganese, carbonate of soda, and sal-ammoniac, and 
 exposing them in a platinum crucible to a full red heat. The chloride 
 of manganese is decomposed by the carbonate of soda, chloride of 
 sodium and carbonate of manganese being formed. MnCl and 
 NaO.C0 2 giving NaCl and MnO.C0 2 . The carbonic acid is, however, 
 driven off by the high temperature, and the protoxide of manganese 
 set free, being evolved in presence of the sal-ammoniac, which readily 
 yields hydrogen, is prevented from passing to a higher degree of oxida- 
 tion. The oxide obtained at this high temperature has no tendency to 
 combine further with oxygen under ordinary circumstances, and may 
 hence be easily preserved. 
 
 The oxide is of various shades of greyish green, according to the 
 method of preparation. It is without action on vegetable colours, but 
 it combines with all the acids, evolving in some cases, as with oil of 
 vitriol, intense heat, and forms salts, remarkable for their definiteness 
 and neutrality. These salts are generally colourless, but often of a 
 peculiar rose colour, which is not due to the presence of any higher 
 degree of oxidation, but either to a peculiar (isomeric) condition of the 
 salt itself, or to the presence of a minute trace of cobalt derived from 
 the manganese ore. 
 
 Sesquioxide of Manganese. Mn 2 O 3 . Equivalent 992, or 79*4. 
 This oxide is found in nature in considerable quantity, either pure, as 
 in the mineral braunite, or combined with water, as in the mineral 
 manganite. It may be prepared artificially by exposing the peroxide 
 for a short time to a dull red heat, but it is difficult to manage the 
 decomposition of that substance so that it should not proceed too far. 
 The sesquioxide is of a dark brown colour ; exposed to a strong heat it 
 is partly decomposed, evolving oxygen and being reduced to the state 
 of red oxide. It combines with acids forming salts which are of a 
 deep red colour, and which are isomorphous with those of alumina. 
 
Technical uses of Manganese. 497 
 
 Its salts are immediately decolorized by sulphurous acid and by sul- 
 phuretted hydrogen. This oxide possesses the property of staining 
 glass purple or violet, and by this character an exceedingly small trace 
 of manganese can be detected by fusing the substance with borax in 
 the oxidating flame of the blowpipe. 
 
 Peroxide of Manganese, or Black Oxide. Mn0 2 . Equivalent 546, 
 or 43*4. This substance, which is the most abundant source of man- 
 ganese, and that from which all its technical applications are derived, 
 exists in nature in a variety of forms. Crystallized and pure it forms 
 the mineral pyrolusite ; combined with water, 2 MnO 2 + HO, it consti- 
 tutes the mineral Wadd, which in an impure form, contaminated with 
 variable quantities of peroxide of iron, carbonate of lime and carbonate 
 of barytes forms the earthy varieties, which are those usually found in 
 commerce. This oxide may be prepared artificially by decomposing the 
 protochloride of manganese by a solution of chloride of lime. Mn.Cl 
 and 2CaO + Cl producing 2.CaCl and MnO 2 . It is also produced when 
 permanganate of potash is decomposed by any organic substance. In 
 these cases it is precipitated in combination with one equivalent of water 
 Mn0 2 + H0, from which it may be freed by a temperature below 
 redness. 
 
 This peroxide of manganese is black ; exposed to heat it abandons 
 oxygen, being reduced first to the state of sesquioxide, and finally to 
 that of red oxide. It does not unite with either acids or alcalies ; but 
 when heated with strong sulphuric acid, it is decomposed in the manner 
 fully described under the head of oxygen, in page 334. Its use in the 
 preparation of chlorine has been also noticed, page 418. An important 
 object to which it is applied is to peroxidize the iron contained in the 
 ordinary materials used in the manufacture of glass. If the iron were 
 as protoxide it would colour the glass green, but the red oxide produces 
 only a very faint yellowish tinge, and as the protoxide of manganese is 
 itself destitute of colouring power, by the action of Mn0 2 on 2FeO 
 there are formed MnO and FeaOg, two substances which have no injurious 
 effect upon the glass ; if, however, the peroxide of manganese be added 
 in excess, a purple colour is produced. 
 
 Of the complex oxides, the red oxide is alone of interest. It is the 
 most stable of the compounds of manganese ; and whenever the quantity 
 of this metal present in a substance is to be determined by analysis, it 
 is always as the red oxide that it is obtained. A solution of any salt of 
 manganese, being precipitated by an excess of a caustic alcali, the pre- 
 cipitate, cautiously washed and ignited in an open crucible, gives the 
 quantity of red oxide corresponding to the quantity of manganese pre- 
 sent. The varvacite,, the other complex oxide, is a mineral of rare 
 32 
 
498- Determination of the real value 
 
 occurrence, and only of interest, as it may be mistaken for the peroxide, 
 to which it is inferior in technical value. 
 
 The peroxide of manganese found in commerce is never quite pure ; 
 and, as its use in the arts, and consequently its price, is, generally 
 speaking, due exclusively to the quantity of oxygen it is capable of 
 yielding, a ready mode of effecting its analysis becomes of great import- 
 ance. There are two modes in which this may be accomplished upon 
 very simple principles, and in a short time, with sufficient accuracy for 
 all practical purposes. The first consists in converting oxalic acid into 
 carbonic acid by means of the second atom of oxygen which the peroxide 
 of manganese contains. For Mn0 2 and C 2 3 produce MnO and 2.C0 2 . 
 For this purpose 100 grains of the manganese are to be introduced into 
 a weighed flask, and 150 grains of oxalic acid dissolved in 500 grains 
 of water are to be then poured upon it ; to these 350 grains of oil of 
 vitriol are to be added, and the orifice of the flask closed by a cork, 
 through which passes a tube containing fragments of recently fused 
 chloride of calcium. The weight of this cork and tube are to be in- 
 cluded in the tare of the flask. On the addition of the oil of vitriol a 
 brisk effervescence takes place, owing to the escape of carbonic acid gas, 
 which, passing over the fragments of chloride of calcium in the tube, 
 are dried, so that the gas alone passes off. When the action slackens, 
 a gentle heat may be applied until all the oxide of manganese has dis- 
 solved ; a small quantity of a light brownish sediment, which generally 
 forms, is easily distinguished from the particles of black oxide : as soon 
 as the action is quite over, the flask is let to cool, and as it contains 
 still a quantity of carbonic acid gas, this is removed, by taking out the 
 cork, and blowing air into the flask gently by a glass tube ; the cork is 
 then to be replaced, and the flask with its contents weighed. It is 
 found to be lighter than it and the materials together had been, and the 
 loss is the carbonic acid. The quantity of carbonic acid formed is thus 
 found, and the quantity of oxygen it contained calculated ; one-fourth 
 of this had been derived from the peroxide of manganese by its conver- 
 sion into protoxide, which remains combined with sulphuric acid in the 
 liquor, and the quantity of peroxide in the 100 grains of the ore are 
 thus directly found. Thus, taking as example an actual determination 
 made a few weeks ago, the flask and materials weighed altogether 1876 
 grains; after the action had terminated it weighed 1816*5 grains; the 
 loss was, therefore, 59'5. This consisted of 16-3 of carbon and 43*2 
 of oxygen. The oxygen derived from the mineral was, therefore, 
 ^ = 10'8, which represent 59 grains of pure peroxide of manganese in 
 the 100 of the substance used. In round numbers the carbonic acid 
 produced is equal in weight to the pure peroxide present. 
 
Of Commercial Peroxide of Manganese. 49 & 
 
 The second mode of analysis consists in treating a certain quantity 
 of the native oxide with an excess of muriatic acid, and passing the 
 chlorine so evolved through water in which lime is diffused ; chloride 
 of lime is formed. A certain quantity of protosulphate of iron (green 
 copperas) is to be dissolved in water, and the solution of chloride of 
 lime added thereto, until the iron liquor ceases to strike a blue colour 
 with a drop of solution of red prussiate of potash ; then comparing the 
 quantity of the solution of chloride of lime required with the quantity 
 that was produced, the total quantity of chlorine generated, and hence 
 the total quantity of oxygen available in the mineral, is known. The 
 theory of the process may be still more simply expressed by the formulae 
 of the bodies engaged, as follows : MnO 2 and 2. HC1 acting together 
 produce MnCl and 2.HO, whilst Cl is given off as gas; this combines 
 with CaO. When the compound CaO.Cl is brought into contact with 
 2.(FeO.SO 3 ), the oxygen passing from the lime to the iron, we have 
 Ca.Cl and Fe 2 O 3 .2SO 3 produced. As long as any protosulphate of iron 
 exists, the solution gives prussian blue with the red prussiate of potash, 
 but when all the iron is changed to peroxide the blue colour is no 
 longer produced. The following example of an actual operation will 
 complete this explanation. 100 grains of commercial oxide of manga- 
 nese were placed in a flask with about one ounce of strong spirits of 
 salts, and the chlorine evolved was conducted by a bent tube to the 
 bottom of a deep jar containing 1600 grains of water with 100 grains 
 of slaked lime; when the oxide of manganese had been completely 
 decomposed by the muriatic acid, and all evolution of chlorine had 
 ceased, a quantity of the solution of chloride of lime was filtered for 
 use; this being very strong, 500 grs. of it were diluted with 1000 of 
 water. On the other hand, 100 of crystallized protosulphate of iron 
 were dissolved in 1000 grains of water, and the dilute solution of 
 chloride of liine added thereto by drops from an accurately graduated 
 tube, until by the test of red prussiate of potash all the iron was 
 peroxidized. It required 1300 grains of the dilute solution, and 
 hence, 433 of the strong solution. Now, as 100 grains of the mineral 
 had given 1600 grains of this strong solution, the 433 grains corres- 
 ponded to 27 grains; the available oxygen of which was exactly 
 equivalent to transfer the iron of the protosulphate to the state of 
 peroxide. Now, the 100 grains contain 45 '6 of water, 28'9 of acid, 
 and 25 '5 of protoxide of iron, consisting of 19' 7 of iron and 5'8 of 
 oxygen, and it requires one-half more, that is 2*9, to form peroxide. 
 The result is, that in the 27 grains of commercial oxide of manganese 
 the available oxygen is 2' 9, and the quantity of pure peroxide con- 
 sequently 15*8 grains, or 58*7 per cent. This whole process, although 
 
500 Manganic and Permanganic Acids. 
 
 when thus described in detail it may appear complex, is exceedingly 
 simple in execution, and does not occupy much time. In accuracy, 
 the two methods are about equal, giving results which may be depended 
 on to one per cent. 
 
 A mode has been recommended which consists in simply adding the 
 green sulphate of iron directly to the muriatic acid and oxide of manga- 
 nese in the flask, until the salt is found to be slightly in excess by the 
 filtered liquor giving prussian blue with red prussiate of potash ; the 
 quantity of green copperas added is known by having previously 
 weighed out a quantity, and then weighing what may remain after the 
 process has been completed. If no chlorine could escape the action of 
 the iron salt, this method would be much the shortest and simplest that 
 could be employed ; but it is exceedingly difficult so to manage the 
 decomposition as to avoid its partial loss. On this account I look 
 upon this method as inferior in accuracy, and really not much simpler 
 of execution than those previously described. 
 
 The composition of the commercial oxide is very variable, but the 
 general limits may be considered as being between 60 and 70 of pure 
 peroxide in 100 parts. Frequently, the commercial substance con- 
 tains sesquioxide, or one of the complex oxides ; but in all these cases 
 the methods given, as they determine the quantity of available oxygen, 
 shew the true value of the specimen, no matter what the state of com- 
 bination of the metal may be. 
 
 Manganic Acid. MnO 3 . Equivalent, 646 or 51*7. If peroxide of 
 manganese be mixed with caustic potash or carbonate or nitrate of 
 potash in a crucible, and ignited moderately, a green fused mass is 
 obtained, which dissolves in a small quantity of water with a fine grass- 
 green colour. After some time, particularly if the solution be diluted, 
 it gradually changes colour, a brown powder separates, and the liquor 
 becomes of a splendid red colour. This substance first got the name 
 of mineral chameleon from these changes, but their production is now 
 known to depend on the formation of two distinct acids of manganese. 
 The peroxide of manganese in these cases combines with another atom 
 of oxygen to form manganic acid, which unites with the potash. If 
 potash, caustic or carbonated, be used, the oxygen is derived from the 
 air ; if nitre, it supplies oxygen ; but the best source consists in mixing 
 four parts of peroxide of manganese in fine powder with 3J parts of 
 chlorate of potash, and adding thereto five parts of caustic potash 
 dissolved in a small quantity of water. This mixture is to be evaporated 
 to dryness, powdered, and afterwards ignited in a platinum crucible, at 
 a low red heat insufficient for fusion. By digestion of this mass in 
 cold water a deep green solution is obtained, from which, by evapora- 
 
Detection of Manganese. 501 
 
 tion in vacuo, the manganate of potash is obtained in crystals. The 
 salts of this acid are isomorphous with those of the sulphuric and 
 chromic acids. They are decomposed very easily, particularly if organic 
 matter be present, and the acid itself is hence incapable of being exhi- 
 bited in an isolated form. 
 
 Permanganic Acid. Mn 2 O 7 . Equivalent, 1392 or 11 1.4 When a 
 solution of manganate of potash is diluted with boiling water, a copious 
 precipitate of hydrated peroxide of manganese forms, and a fine crim- 
 son solution of permanganate of potash is obtained. 3.Mn0 3 produces 
 MnO 2 and Mn 2 O 7 . By rapidly evaporating this solution until a pellicle 
 forms, an abundant crop of crystals of permanganate of potash is ob- 
 tained on cooling : these are isomorphous with the perchlorate of pot- 
 ash, and are almost completely black, but with a very peculiar bronze 
 lustre. The salts of this acid are very stable, and by treating the per- 
 manganate of barytes with a proper quantity of dilute sulphuric acid, a 
 deep crimson solution of permanganic acid is obtained. This acid can- 
 not be had solid, according to Mitscherlich ; its solution when heated 
 to 100 F. being decomposed into peroxide of manganese and oxygen 
 gas. It is very probable, that the solid substance, described as dry 
 permanganic acid by some chemists, contained some other matter COHN 
 bined with it. 
 
 The formation of these acids by the action of sulphuric acid on pe- 
 roxide of manganese, has been already noticed, and the most delicate 
 test of the presence of manganese in minerals consists in fusing a frag- 
 ment of the substance with a little carbonate of soda on a slip of 
 platina foil, by means of the oxidizing flame of the blowpipe. The mass, 
 on cooling becomes apple-green, from the formation of manganate of 
 soda, if there be the smallest trace of manganese in the substance used. 
 
 There is but one sulphuret of manganese. It is found as a mineral, 
 and formed also by heating oxide of manganese and sulphur, (page 
 390). It is precipitated in a hydrated state, when a solution of man- 
 ganese is decomposed by hydrosulphuret of ammonia. Its colour is then 
 flesh red. Its formula is Mn.S. 
 
 The detection of manganese is very simple. When in a solid form 
 its compounds are recognized by giving before the blowpipe a purple 
 glass with borax, and a green bead with carbonate of soda. In solution, 
 if the manganese be as protoxide, the solution is colourless, and yields 
 with the caustic alcalies a white precipitate, (MnO,) rapidly becoming 
 brown, (Mn 3 4 ) : with the alcaliue carbonates a white precipitate, 
 MnO.CQ;,, and with hydrosulphuret of ammonia, a flesh red hydrated 
 sulphuret. The yellow prussiate of potash precipitates the salts of man- 
 ganese pure white, if there be no trace of iron present. When the 
 
502 State of Iron in Nature. 
 
 manganese is not in the state of protoxide, the solution is always 
 coloured red or green. These solutions are decolorized by sulphurous 
 acid, and by sulphuretted hydrogen, which absorbs oxygen from all the 
 higher degrees of oxidation, and a colourless solution of protoxide is 
 then obtained, which gives the reactions already described. Another 
 very sensitive re-agent for manganese is, to mix some peroxide of lead 
 with nitric acid and then add the liquor to be examined. If the man- 
 ganese be present, the purple colour of permanganic acid will be de- 
 veloped after a few minutes. 
 
 SECTION III. 
 
 METALS OF THE THIRD CLASS. 
 OF IRON. 
 
 Symbol. Fe. Eq. 28 or 350. 
 
 This is the most extensively distributed, and also the most important 
 of the metals ; it may, indeed, be considered as being after those ele- 
 ments necessary to the functions of animal existence, that which is most 
 indispensable to man for the wants of ordinary life. On its employ- 
 ment and applications, is founded every important step which marks the 
 gradual progress of the human race from barbarism to civilization. The 
 difficulties which its reduction from the state of ore present, the variety 
 of conditions necessary for its being successfully wrought into useful 
 forms, and the pre-eminent advantage it possesses over every other 
 metal for the construction equally of the simplest tool and the most 
 complex machine, for the implements of war as well as peace ; all com- 
 bine to excite the energies of a people to its acquisition, whether by 
 their own labour or by commerce ; and thus impel them to mental 
 activity and civilization, either of native and independent growth, or 
 borrowed from more advanced neighbours. As gold and jewels hence 
 become the type of ignorant and barbaric pomp, so iron may be regarded 
 as the greatest material source of national intelligence and industry. 
 
 Iron exists in nature under a variety of forms ; it is found native, 
 for in addition to loose blocks of metallic iron found on the surface in 
 various countries, and to which a different nature may be assigned, it is 
 found in veins, in mines, in Eussia and America. Its most abundant 
 form is that of oxide, either pure, forming the various black and mag- 
 netic oxides, the hsematite, or red oxide, &c., or combined with carbonic 
 acid, constituting the clay iron stone from which the iron of commerce 
 is principally extracted. Its sulphurets are also found in abundance, and 
 iiative arseniates, phosphates, sulphates, and other salts have been found. 
 
S/neUing of Iron Ores. 503 
 
 A most remarkable source of iron is one not truly terrestrial, but 
 that occasionally masses appear in our atmosphere at great heights 
 above the surface, and presenting all the appearances of vivid ignition 
 and combustion ; they move generally with great velocity obliquely 
 towards the ground, and generally, before touching, or at the moment 
 of contact with the surface, burst with an explosion, scattering their 
 fragments to considerable distances. These masses are termed aerolithes ; 
 they consist, in general, of an alloy of iron, with some nickel and 
 chrome, with traces of other metals, and are generally invested with a 
 vitreous glaze of earthy matter, which is constituted of minerals (olivine 
 and pyroxene) found native in volcanic rocks. The only theory which 
 can explain the origin of these meteors is, that they are expelled vio- 
 lently from the active volcanoes, which telescopic research has proved 
 to exist in great numbers on the surface of the moon, and that passing 
 beyond the limits of the attraction of our satellite, they come under the 
 influence of this earth and fall towards its surface. No such substances 
 are ever found projected from terrestrial volcanoes. 
 
 The general principles of the smelting of the clay iron stone, have 
 been already noticed, (p. 468,) both considering it as a mere carbonate 
 of iron, and where it contains clay, silica and alumina, so as to render 
 lime necessary as a flux. It is, however, a remarkable property of iron, 
 one on which rests, perhaps, its most useful applications, that the metal 
 so obtained is not pure. The iron, when reduced, combines with a 
 quantity of carbon, generally about five per cent., approximating to the 
 formula, C+ 4. Fe, and forming cast iron, which is easily fusible, whilst 
 the pure metal is almost quite infusible. The cast iron, is, however, not 
 by any means a pure carburet of iron, it contains small quantities of 
 silicon and phosphorus, according to the proportions of which it varies 
 in properties, so as to constitute a number of varieties, known in the 
 arts by their colour and texture, but of which it would be superfluous 
 to speak here. When cast iron remains under water for a considerable 
 time, it becomes gradually oxidized, magnetic oxide of iron being formed, 
 and dissolved out, whilst the carbon remains under the form of a spongy 
 mass, preserving, even in minute details, the figure of the original mass. 
 
 Cast iron has a great tendency to crystallize in becoming solid, and 
 then expands powerfully; hence its property of filling up the most 
 minute crevices of moulds into which it is poured in the liquid state, 
 and its multifarious uses, for making castings, from whence it derives 
 its name. 
 
 Pure or malleable iron, is made from cast irun by taking advantage 
 of the fact, that though iron and carbon are both combustible, yet carbon 
 is the more so of the two. Hence if cast iron be melted in a reverbe- 
 
504 Preparation of Malleable Iron. 
 
 ratory furnace, (see p. 46 7 ,) and exposed to a current of air, the carbon 
 is gradually burned out ; the metal becomes less and less fusible, and 
 ultimately breaks up into an incoherent granular mass like sand ; by 
 then increasing the heat, these grains agglutinate, and are worked up 
 into a ball about the size of a large loaf, which is taken out of the fur- 
 nace on a shovel, and subjected to great pressure by machinery. The 
 soft pasty particles of malleable iron are thus welded to each other, and 
 any portions of liquid, unaltered cast iron that might remain, are 
 squirted out, as water should be by pressure from the pores of a sponge ; 
 this lump of malleable iron is then passed through a succession of rollers, 
 turned by powerful steam engines ; each pair of rollers having a smaller 
 interval than the preceding, the mass is gradually elongated into a bar, 
 and finally is delivered, at the end farthest from the furnace, in the 
 form of the soft bar iron of commerce. The heat evolved by the enor- 
 mous pressure, to which the metal is subjected in this process, is so 
 great, that the bar remains soft enough to be moulded by the rollers all 
 through its passage. 
 
 This process by the reverberatory furnace is termed puclling, and has 
 been very much improved lately by burning out the carbon by means of 
 a certain quantity of oxide of iron or oxide of manganese. Thus, by 
 heating together two parts of cast iron and one of scales of black oxide 
 of iron from a forge, all the carbon and oxygen pass off as carbonic acid, 
 and the iron of both remains pure. Fe 3 4 and Fe 8 Qj produce Fe,, and 
 
 The bar iron thus obtained differs remarkably from the cast iron in 
 all characters : it is soft, flexible, ductile, and malleable, none of which 
 properties cast iron possesses. It fuses only at the very highest temper- 
 ature, and then becomes only semifluid. It is, consequently, quite 
 impossible to run it into moulds. It possesses, however, the important 
 character of welding at a white heat ; that is to say, it assumes a doughy 
 consistence, so that several pieces of it laid together may be kneaded 
 into one by blows of a hammer or by pressure between rollers, so as to 
 form a single mass, the points of junction being totally undistinguish- 
 able. It is thus that soft iron is always worked at a white heat. Its 
 strength is much increased by several pieces being thus welded together, 
 and hence all parts which require to possess peculiar tenacity, such as 
 anchors, &c., are always made, not in single piece, but by thus welding 
 together a bundle of small bars. 
 
 A third and equally important form in which iron exists in the arts, 
 is that of steel. Steel is intermediate to cast iron and bar iron, in con- 
 stitution, containing generally about 1*5 per cent, of carbon. Steel 
 may be formed directly from the ore or from cast iron, by proportioning 
 
Different varieties of Iron. 
 
 505 
 
 the action of the fuel and of the air in the furnaces, so as to leave com- 
 bined with the iron as much carbon as constitutes steel. But the most 
 important and curious mode of making steel is by what is termed 
 cementation. Bars of iron are laid in boxes, imbedded in powdered 
 charcoal, and exposed for some hours to a full red heat ; the carbon 
 gradually penetrates through the whole substance of the iron, changing 
 it into a bar of steel of pretty uniform structure. The bar becomes, 
 frequently, blistered, from gas bubbles forming in its substance. This 
 process can be effected even though the carbon may not directly touch 
 the iron, provided oxygen be present ; carbonic oxide being formed, 
 which is decomposed by the iron, half the carbon being absorbed and 
 carbonic acid given off. It is the escape of this last gas under the form 
 of bubbles that produces the blistering of steel. The decomposition of 
 the carbonic oxide takes place at the surface of the bar in great part, 
 but the carbon is transferred from particle to particle of the iron until 
 the entire mass assumes the same constitution. Steel is harder and 
 more fusible than pure iron, but its peculiar hardness is given to it only 
 when it has been heated to redness and suddenly cooled, it is then ex- 
 ceedingly brittle, hard, and elastic, and is thus fitted for its extensive 
 use in cutting instruments, pivots, files, &c. The steel when it has 
 cooled slowly, is so soft that it is easily engraved upon, cut, and may be 
 welded with soft iron ; the instrument being so constructed, it is heated 
 to redness and suddenly cooled ; it is thus hardened, but is still unfit 
 for being employed until it is tempered to the particular use for which 
 it is destined by being heated in oil to a certain degree and then allowed 
 to cool slowly. By this means the excess of hardness is got rid of, and 
 the steel remains of the quality required. 
 
 Notwithstanding that iron is at once the most common and the most 
 useful of the metals, it can scarcely be considered as having been yet 
 obtained pure. For even in its purest form of soft malleable iron, it 
 is not absolutely free from carbon, and the other conditions of cast 
 iron and steel which the metal may assume, are due to the presence of 
 foreign materials. The proportions and nature of these bodies present 
 in the different kinds of iron, are shewn in the following table. 
 
 100,000 parts of iron in its different states, contain usually about 
 
 
 Carbon. 
 
 Phosphorus. 
 
 Silicon. 
 
 Manganese. 
 
 Sulphur. 
 
 Cold Blast Cast Iron 
 
 4-770 
 
 1-230 
 
 710 
 
 a trace 
 
 trace 
 
 Hot Blast Cast Iron 
 
 3-430 
 
 370 
 
 1-750 
 
 1-20 
 
 120 
 
 Best Swedish Iron . 
 
 293 
 
 077 
 
 traces 
 
 traces 
 
 none 
 
 English Bar Iron 
 
 285 
 
 180 
 
 230 
 
 traces 
 
 trace 
 
 Best Scrap Iron 
 
 245 
 
 160 
 
 210 
 
 traces 
 
 none 
 
506 Relations of Iron to Oxygen. 
 
 Sometimes the quantity of manganese is larger, amounting to three 
 or four per cent, from the iron ore having contained carbonate of 
 manganese : but such irons are always of inferior quality. 
 
 Steel being made from the best iron or purest ores, the other admix- 
 tures, except carbon, are of course nearly in the same proportion as in 
 bar iron ; but the quantity of carbon is much greater : thus in bar steel, 
 usually one per cent. : in cast steel, from one to one and a-half per cent. 
 or sometimes so high as two per cent. Its precise mode of combination 
 is not certainly known. 
 
 The peculiar property of iron aud steel of becoming magnetic, have 
 been described in page 185. Not only is iron in the pure state, and 
 when combined with carbon, attracted by the magnet, but several of 
 its oxides and sulphurets possess the same character ; of these, one con- 
 stitutes, indeed, the natural magnet, the native loadstone. 
 
 Pure iron is bluish-white, exceedingly brilliant, very malleable and 
 ductile; it is the strongest of all the metals. Its sp. gr. is 7*8. It 
 becomes pasty when intensely heated, whence its remarkable power of 
 welding, which belongs besides only to platinum and sodium. 
 
 When iron in mass is exposed to dry air, it does not become oxidized ; 
 but if it be in a state of very minute division, it takes fire when gently 
 warmed, and burns, forming peroxide of iron ; when strongly heated in 
 oxygen gas, as by attaching a little sulphur or a bit of taper wick to a 
 wire, and plunging it into a vessel of oxygen, it burns with exceeding 
 brilliancy, and forms globules of black oxide of iron, Pe 3 4 . The true 
 product of the combustion is peroxide, Fe 2 O 3 ; this loses one-ninth of its 
 oxygen by the intense temperature, and forms the black magnetic oxide. 
 It is hence, that when iron is burned in oxygen gas, the oxide which 
 is thrown off in minute grains, collects on the inside of the jar as per- 
 oxide, but the larger globules which are intensely heated for some time 
 before they melt off the wire, are reduced to the state of black oxide. 
 It is not quite certain whether iron decomposes water in the absence of 
 an acid, but the presence of a small quantity even of carbonic acid 
 produces decided action, and hence the rapid corrosion of iron in damp 
 air, forming carbonate of iron (rust). In dilute sulphuric acid iron 
 dissolves with great rapidity, evolving hydrogen, which, however, is 
 very impure, for even the softest iron contains traces of carbon which 
 combines with some of the hydrogen, forming compounds, which give 
 the gas a peculiar odour, and colour its flame yellow. At a red heat 
 water is decomposed rapidly by iron, as fully described in p. 340. If 
 iron be immersed in water holding potash, lime, or soda in solution, or 
 if the iron be covered up in quick lime, all rusting is prevented, pro- 
 bably from any carbonic acid present being totally taken up by the base. 
 
Passive Condition of Iron. 507 
 
 A remarkable property of iron, though not absolutely peculiar to it 
 alone, is, that when placed in contact with the hydrated nitric acid, 
 sp. gr. 1'35, it may remain unacted on, becoming passive ; although, 
 under ordinary circumstances, it is rapidly dissolved by that acid with 
 evolution of nitric oxide. This passive condition may be produced in 
 many ways. 1st. If one end of a long iron wire be ignited, and then, 
 when cool, the wire be immersed in the acid, the ignited end being 
 dipped first, it remains unaltered. 2nd. If a piece of platina wire be 
 fastened to a piece of iron wire, and then immersed in the acid, the 
 platina first. 3rd. By placing a platina wire in the acid, then immers- 
 ing an iron wire in contact with it, the platiua wire may be withdrawn, 
 and the iron wire remain passive. 4th. By making the iron wire the 
 positive pole of a galvanic battery. 5th. By contact with a wire already 
 passive ; thus, an iron wire being immersed in the acid, as in No. 3, 
 another wire may be put in contact with it, and the first then with- 
 drawn, and so on for an unlimited succession of wires. These are not 
 the only methods, but merely the most remarkable. 
 
 The properties of iron thus rendered passive are curious. It appears 
 to have lost all tendency to unite with oxygen ; it does not rust ; it 
 does not dissolve in acids ; it does not precipitate copper from its solu- 
 tion ; and when used as a positive electrode of a voltaic battery, oxygen 
 is evolved from it precisely as if the electrode had been platinum. We 
 do not as yet know the true theory of these effects. The most available 
 explanation is, that the iron, by an alteration of molecular structure, 
 assumes a condition by which it becomes similar in its electrical rela- 
 tions to the noble metals. It is possible, that this property may be 
 connected with the equivalency of two equivalents of the iron and man- 
 ganese group of metals to one of chlorine, and that when by a change 
 of molecular arrangement, like isomerism, the particle becomes Pe 2 in 
 place of Fe, it is incapable of acting as the positive element in galvanic 
 or chemical combinations. It has, however, been latterly proposed to 
 attribute the passitivity of the iron to the presence of a thin layer of 
 peroxide of iron insoluble in nitric acid. 
 
 The equivalent of iron is not so accurately known as those of metals 
 much less important and less common. The best determinations make 
 it about 350 upon the oxygen, and 28 upon the hydrogen scale. Its 
 symbol is Fe, from its Latin name. 
 
 Oxides of Iron. Iron combines with oxygen in two proportions, 
 forming a protoxide and a sesquioxide, and these again unite to form 
 complex oxides, the black or magnetic oxides of iron. It has also been 
 asserted that iron, when burned by the hydrogen gas blowpipe, forms a 
 suboxide Fe 4 0. but it is most probably a fused mixture of black oxide 
 and metallic iron. 
 
508 Various Oxides of Iron. 
 
 Protoxide of Iron.FeO. Equivalent 4-50 or 36. This oxide 
 cannot be obtained pure in a dry state, from the rapidity with which it 
 absorbs oxygen. It exists as the basis of a very extensive class of salts, 
 the green or proto-salts of iron. From their solutions, it is precipitated 
 by an alcali, as a white hydrate, which rapidly becomes green, and 
 finally brown-red, from absorption of oxygen. If we attempt to form 
 the protoxide by processes similar to those described for obtaining 
 the protoxide of manganese, the iron is reduced either to black oxide or 
 to the metallic state. This oxide exists native, combined with carbonic 
 acid, in the common carbonate of iron, and is the form in which the 
 metal exists, dissolved in all chalybeate springs. 
 
 Peroxide of Iron. ~Fe 2 O 3 . Equivalent 1000 or 80. This substance 
 exists in very great abundance in nature, crystallized in rhombohedrons, 
 being isomorphous with the crystallized alumina, corundum. This, the 
 ologist iron, constitutes the celebrated Elba iron ore. It forms, in a more 
 or less hydrated condition, the hematite, of various shades of red and 
 brown, from which a great deal of the best iron and steel is made. It 
 exists in a variety of minerals, and forms the red or yellow colouring 
 matter of clay and of the different kinds of ochres. I have noticed 
 that when iron is burned in a full supply of oxygen, this red oxide is 
 formed, and it is produced also when iron rusts, for the protocarbonate 
 which first forms is gradually decomposed, abandoning its acid, and ab- 
 sorbing oxygen. It is thus that the margins of chalybeate springs 
 become coated with an ochrey deposit ; the carbonate of iron originally 
 dissolved being gradually converted into red oxide, whilst the carbonic 
 acid passes off as gas. 
 
 The peroxide of iron may be artificially prepared, by precipitating 
 a solution of any of its salts with an alcali caustic or carbonated. In 
 the latter case, the carbonic acid is given off, as the peroxide of iron 
 does not combine with it. The hydrated peroxide, which is precipitated, 
 is of a light reddish brown colour, but when dried it becomes dark 
 brown. Strongly ignited, it becomes nearly black ; and indeed, by an 
 intense heat it loses some of its oxygen, 3 (Ee 2 O 3 ) giving 2 (Pe 3 4 ) and 
 escaping, being decomposed just as the sesquioxide of manganese, 
 but requiring much greater heat. The peroxide of iron combines with 
 acids to form salts, which are all acid, and easily decomposed. They 
 will be described hereafter. Its chemical combinations resemble those of 
 alumina and sesquioxide of manganese, with which they are isomorphous. 
 
 The hydrated peroxide may be very conveniently prepared in a state 
 fit for its use as an antidote to arsenic, by dissolving together one part 
 of chlorate of potash, fourteen parts of crystallized protosulphate of 
 iron, and sixteen parts of crystallized carbonate of soda. The preci- 
 pitate must be well washed. 
 
Preparation and Properties of Ferric Acid. 509 
 
 When a solution of a protosalt of iron is exposed to the air, it gra- 
 dually absorbs oxygen, until two-thirds of the iron becomes perox- 
 idized, and then the decomposition ceases. The liquor then contains 
 a compound oxide, FeO + Fe 2 O 3 , and on the addition of a caustic 
 alcali, this is precipitated as a black powder, which when dry is power- 
 fully attracted by the magnet. This is the artificial magnetic oxide of 
 iron. It may be prepared at will, by taking three equal portions of 
 protosulphate of iron, and peroxidizing two of them by means of a 
 little boiling nitric acid, then mixing the solutions, and precipitating 
 the whole by water of caustic ammonia. The precipitate is a hydrate, 
 but may be deprived of the water without alteration. 
 
 This magnetic oxide of iron exists native in great abundance ; it 
 constitutes the common loadstone, and is that produced when iron is 
 oxidized at high temperatures. It thus constitutes the scales of iron 
 which form in smythies and forges, during the successive heatings and 
 hammerings to which the metal is subjected. These scales of iron are, 
 however, not uniform in constitution, and are hence inferior as a steady 
 medicinal agent to the oxide artificially prepared by precipitation. 
 
 Ferric Acid. FeO 3 = 52 or 650. It had been long known that, 
 under certain circumstances, the caustic alcalies dissolved peroxide of 
 iron, but the subject has been only lately accurately examined, when 
 it was found by Fremy that by processes similar to those of forming mi- 
 neral chameleon with manganese, iron absorbs so much oxygen as to 
 form a true Ferric acid. The results have been extended and confirmed 
 by other chemists. If a mixture of iron filings and nitrate of potash 
 be deflagrated, and the residual mass be dissolved in water, a deep 
 purple liquor is obtained, which contains ferrate of potash. A similar 
 liquor is obtained by diffusing hydrated peroxide of iron through a 
 strong solution of potash, and passing a stream of chlorine gas into 
 the liquor. Ferrate of barytes may be precipitated by decomposing 
 ferrate of potash with chloride of barium ; it is a purple black powder. 
 The ferric acid is decomposed very easily contact with organic bodies, 
 or with salts of suboxides, or even the dilution of its solution by a 
 large quantity of water, or the boiling of its solution, all resolve it 
 into peroxide of iron and oxygen. In this manner it has been analyzed 
 and found to have a constitution similar to manganic acid, as stated 
 above. 
 
 Sulpkurets of Iron. Sulphur combines with iron in three propor- 
 tions, forming the protosulphuret, the sesquisulphuret, and the bisul- 
 phuret. These again combine, so as to produce complex (magnetic) 
 sulphurets. Other degrees (subsulphurets) are problematical. 
 
 Protosulpkuret of Iron. Fe.S. Equivalent 550 or 44. The af- 
 
510 Sulphur ets of Iron. 
 
 finity of iron for sulphur is very remarkable. If a rod of iron be 
 heated to whiteness, and then touched to a stick of sulphur, they com- 
 bine with energy, and the sulphuret of iron flows down in copious 
 drops. If vapour of sulphur be made to gush from a jet, and an iron 
 wire, heated to bright redness, be placed in it, it takes fire and burns 
 with scintillations as brilliantly as if it had been immersed in oxygen 
 gas. In these cases, where the iron is in excess, the protosulphuret is 
 formed. It is most conveniently prepared by heating together to bright 
 redness, in a crucible, three parts of iron filings, or turnings, and two 
 of sulphur ; at a high temperature the resulting mass may be fused. 
 This compound is black, its fracture yellowish. It dissolves in dilute 
 acids, evolving sulphuret of hydrogen, and forming a salt of protoxide 
 of iron. This is almost its only use in the laboratory. The manner 
 of obtaining sulphuret of hydrogen from it has been described in page 
 404. This protosulphuret of iron exists sometimes, though rarely, in 
 nature, and is dangerous, particularly in coal mines, from the avidity 
 with which, when moist, it absorbs oxygen, forming protosulphate of 
 iron, Fe.S and 4O, giving FeO.S0 3 ; during which process it occa- 
 sionally becomes so heated, as to set fire to the beds of coal near it, and 
 thus to cause considerable loss. 
 
 This sulphuret may be prepared in the moist way by adding hydro- 
 sulphuret of ammonia to a protosalt of iron ; thus, Ee.Cl and SH -{- 
 NH 3 produce Ee.S and C1H + NH 3 . It is a jet black powder, which 
 dissolves readily in acids, and when exposed moist to the air, rapidly 
 absorbs oxygen, forming green copperas. 
 
 Sesquisulphuret of Iron. Fe 2 S 3 . Equivalent 1300 or 104'0. This 
 compound, which corresponds to the peroxide, is very instable in con- 
 stitution. It may be prepared in the moist way by adding to a persalt 
 of iron in solution, hydrosulphuret of ammonia. A black precipitate 
 forms, which may be dried in vacuo. It may be also produced by 
 heating peroxide of iron in a current of sulphuretted hydrogen gas, 
 water being formed. It is not attracted by the magnet. It dissolves 
 in acids, but one-third of the sulphur is precipitated, two-thirds only 
 combining with hydrogen, and the iron existing in solution as a proto- 
 salt. Thus, Pe 2 S 3 and 2HC1 give 2(Pe. Cl) and 2.HS with deposition 
 of S. This arises from the circumstance that peroxide of iron is re- 
 duced by sulphuretted hydrogen to protoxide, water being formed, and 
 sulphur set free. 
 
 Bisulphuret of Iron. EeS 2 . Equivalent 750, or 60. This sub- 
 stance is met with in very large quantity in nature, constituting the 
 iron pyrites, used in the manufacture of sulphuric acid and of copperas. 
 It is dimorphous, (pages 317-323,) and in its two forms possesses very 
 
Detection of Iron. 511 
 
 different properties. It may be prepared artificially by heating together 
 the protosulphuret in a state of minute division, with half its weight of 
 sulphur. When the excess of sulphur has been distilled off, there re- 
 mains a voluminous yellow powder, not acted on by the magnet and 
 insoluble in acids, which is the bisulphuret of iron. This bisulphuret 
 of iron is found in a variety of forms, which belong properly to the 
 different kinds of native oxides of iron, which being probably acted on 
 by vapour of sulphur from volcanic sources, have lost their oxygen, and, 
 without being melted, have changed into bisulphuret. It is also found 
 simulating the figures of a variety of organic remains, as nautili, &c., 
 where, probably, the animal having perished in water holding traces of 
 sulphate of iron in solution, the hydrogen compounds evolved by its 
 decomposition have reacted on the sulphate of iron, abstracting its 
 oxygen and producing a deposit of pyrites. 
 
 Magnetic Sulphureis of Iron. Of these the most remarkable is that 
 which corresponds to the magnetic oxide, having the formula Fe 3 O 4 = 
 FeS + r& 2 S 3 . It is found native at Bareges, and may be formed by ex- 
 posing to a red heat in close vessels the bisulphuret or sesquisulphuret. 
 The pyrites, 3 (FeSJ, producing Fe 3 S 4 and S 2 precisely as peroxide of 
 manganese 3.(Mn0 2 ) produces O-2 and Mn 3 O4. If, however, the heat 
 be raised too high, more sulphur is expelled and another kind of mag- 
 netic sulphuret Fe 7 S 8 = 5FeS -f- Fe 2 S 3 formed, which is also found 
 native, and which corresponds to the black scales of oxides of iron 
 which are 5FeO + Fe 2 3 . This compound is always formed in making 
 the protosulphuret, if there be an excess of sulphur, above the proper 
 proportion, used. 
 
 The seleniuret and phosphurets of iron resemble very closely the sul- 
 phurets. Phosphuret of iron exists generally in cast iron in small quantity. 
 
 The detection of iron is very simple. It may exist in solution, in the 
 state either of protoxide, black oxide, or peroxide, and as the appli- 
 cation of reagents becomes much simpler in the last case, it is best, 
 when the object is only to ascertain the presence or absence of iron, to 
 boil the solution with a few drops of nitric acid by which any iron that 
 may be present is peroxidized. 
 
 A solution containing peroxide of iron, produces with water of 
 ammonia a reddish-brown precipitate of hydrated peroxide ; with yellow 
 prussiate of potash a fine prussian blue ; with sulphocyanide of potassium 
 a deep blood-red colour, but no precipitate; with a solution of tannin 
 or tincture of galls, a deep violet or black. With sulphuret of hydro- 
 gen there is no effect except the separation of a deposit of pure sulphur, 
 but with hydrosulphuret of ammonia a black precipitate of sesquisul- 
 phuret of iron is formed. 
 
512 Preparation of Nickel. 
 
 If the solution contain the iron only as protoxide, ammonia produces 
 a precipitate, at first whitish but rapidly becoming bluish-green. The 
 yellow prussiate of potash, gives a precipitate, at first white, but rapidly 
 becoming blue. The sulphocyanide of potassium, the tannin and the sul- 
 phuret of hydrogen are without effect, but the hydrosulphuret of am- 
 monia forms the black protosulphuret. The most characteristic re-agent 
 for protoxide of iron is the red prussiate of potash, which gives prussian 
 blue, but does not act upon the solution of peroxide. 
 
 If a solution contain at the same time both oxides, the precipitate 
 by ammonia is, from the commencement, green or black, and all the 
 other reagents concur in the demonstration of the presence of the two- 
 states of oxidation of the metal. 
 
 OF NICKEL. 
 Symbol. Ni. Eq. 29'62 or 369'7. 
 
 An ore which, from its external characters, was supposed by the 
 German miners to contain copper, but resisted all endeavours to extract 
 that metal from it, received the name of kupfer-nickel, or deceitful 
 copper. Subsequently it was found to consist of a peculiar metal united 
 to arsenic, and this metal retained the name nickel, its meaning being 
 forgotton or lost sight of. A substance found in commerce, termed 
 speis-Sj a residue from the manufacture of smalts, is also an arseniuret 
 of nickel, and from either of these sources the metal is generally ex- 
 tracted. 
 
 The mass containing nickel and arsenic is dissolved by a mixture of 
 nitric acid and sulphuric acid, diluted with water. By this means the 
 nickel is converted into sulphate of its oxide, and the arsenic into 
 arsenious acid. On concentrating the liquor, most of the latter is got 
 rid of by crystallization. Carbonate of potash is then to be added to 
 the liquor, until the green precipitate which first forms ceases to be re- 
 dissolved. On then evaporating and cooling, a double sulphate of 
 nickel and potash is obtained, which, by two -or three recrystallizations, 
 is freed from all traces of arsenic. This double salt may, however, be 
 contaminated by iron and copper ; from the first it is separated by sul- 
 phuretted hydrogen, and from the last by the solubility of the oxide of 
 nickel in water of ammonia. From the ammoniacal solution, the oxide 
 of nickel may be precipitated by oxalic acid, as an insoluble oxalate, 
 which, when dried and heated, gives off carbonic acid, and leaves me- 
 tallic nickel, Ni.O 4- C 2 3 , producing 2.C0 2 and Ni. The metallic 
 nickel is then in the form of a very light sponge. It is somewhat more 
 
Alloys and Compounds of Nickel. 513 
 
 fusible than cast iron ; of a silvery white colour. It does not rust 
 when exposed even to damp air. Its sp. gr. is about 8'5. It is nearly 
 as magnetic as iron, and retains its magnetism, resembling in that 
 respect steel rather than pure iron. In its permanency of lustre, nickel 
 resembles the precious metals, and its alloys are of singular brilliancy 
 and whiteness. 
 
 This character has long led to the employment of nickel for giving a 
 silvery appearance to the alloys of copper, such as brass. The metal of 
 gongs, known as packfong in China, is thus made. Latterly, under the 
 names of German silver, argentane, nickel silver, British plate, this 
 alloy has been extensively manufactured in these countries. Usually 
 brass is first made by fusing together eight parts of copper and two 
 one-half parts of zinc, of which latter about one-half is burned out in 
 the process. Then by the addition of two parts of nickel, an alloy is 
 produced of a somewhat yellowish white, and which is an inferior and 
 cheap article. With three parts of nickel a very good alloy is formed. 
 With four parts of nickel the alloy is equal in whiteness and lustre to 
 standard silver. With six parts of nickel the alloy is perfectly undis- 
 tinguishable in appearance from fine silver, and even takes the same 
 blue lustre by polishing. But with this large proportion of nickel the 
 substance becomes too costly, and unless the nickel were completely 
 free from arsenic, which it is very difficult to effect, the alloy is hard, 
 and liable to get flaws in working. 
 
 The symbol of nickel is M; its equivalent 369'7 or 29*6, 
 
 Oxides of Nickel. This metal combines with oxygen in two propor- 
 tions, forming a protoxide and a sesquioxide. The protoxide NiO, is 
 prepared by precipitating a salt of nickel by caustic potash; a grass- 
 green hydrated oxide of nickel separates, NiO -f HO, which when dry 
 gives the pure ash-grey oxide. This is the only oxide of nickel which forms 
 salts. It is not, by itself, soluble in water of ammonia ; but if a salt of 
 nickel be decomposed by ammonia, the precipitate which first forms is 
 re-dissolved on adding an excess of the alcali, forming a blue solution, in 
 a great degree characteristic of this metal. This oxide has been found 
 as a product of the roasting of copper ores in Germany, of a ruby red 
 colour and in octohedrons, closely resembling native suboxide of copper. 
 
 The Peroxide of Nickel, Ni 2 Os, is a black powder, prepared by boiling 
 the protoxide in a solution of chloride of lime ; the oxygen of the lime 
 changes the protoxide into peroxide, 2. NiO and CaO.Cl producing 
 Ni 2 .O 3 and CaCl. When ignited, this oxide gives oxygen and pro- 
 toxide ; with muriatic acid it forms protochloride and chlorine. It does 
 not form any true salts. 
 
 Nickel is easily recognized by its solutions giving with ammonia a 
 oo 
 
514 Properties of Nickel and its Oxides. 
 
 green precipitate, which dissolves in an excess, forming a blue solution, 
 and by giving with yellow prussiate of potash, a white precipitate. 
 The solutions of nickel are not precipitated by sulphuretted hydrogen, 
 but give a black sulphuret of nickel with hydrosulphuret of ammonia. 
 Its separation from the following metal, cobalt, with which it is almost 
 always associated in nature, is of peculiar interest, and shall be fully 
 described under the next head. 
 
 The sulphuret, seleniuret, and phosphuret of nickel do not present 
 any point of interest. 
 
 OF COBALT. 
 Symbol. Co. Eq. 29'57 or 369. 
 
 The name of this metal had its origin in a still more singular cir- 
 cumstance than that of the preceding; from the bright metallic ap- 
 pearance of its ores, the miners of the middle ages were led to expect 
 an abundant produce, but the modes of reduction then in use were 
 employed without avail ; it was hence imagined, that these ores were 
 specially protected by the guardian spirits of the mines, or Kobolds, 
 and these minerals were termed Die Kobold's erze, the Kolold's ores. 
 At a later period, a peculiar metal was extracted from them, and as the 
 older name had been corrupted into kobalt ore, the metal was called 
 cobalt. 
 
 Cobalt exists in nature, combined with arsenic and with sulphur, it 
 is universally associated with nickel, which it resembles so closely in its 
 properties, that the perfect separation of these two metals is one of the 
 most difficult operations in analysis. To obtain the cobalt, the native 
 arseniuret is roasted in a current of air, so as to oxidize both metals, as 
 described, p. 468. The residual impure oxide of cobalt is sold in 
 commerce under the name of Zaffre. This zaffre is dissolved in muri- 
 atic acid, and treated with sulphuretted hydrogen, by which the copper 
 and arsenic are separated. From the filtered liquor, the cobalt is thrown 
 down by carbonate of potash, and then, to free it from oxide of iron, 
 it is digested with oxalic acid which dissolves the peroxide of iron, 
 and leaves an insoluble oxalate of cobalt ; this may still be contaminated 
 with nickel, but for the details of the separation of these metals, I 
 must refer to subsequent remarks. 
 
 The oxalate of cobalt, when ignited, yields carbonic acid and metallic 
 cobalt in a spongy form ; it melts into a button more easily than cast 
 iron; it is reddish-grey; specific gravity 8*5; when perfectly pure, it 
 is not susceptible of becoming magnetic. It acts upon water aud acids 
 
Properties of Cobalt and its Oxides. 515 
 
 more rapidly than nickel, but much less actively than iron or zinc. 
 The symbol of cobalt is Co, and its equivalent 369, or 29*6. 
 
 Oxides of Cobalt. Cobalt combines with oxygen to form two well 
 denned oxides ; a protoxide and sesquioxide ; there are also two com- 
 plex oxides, and a compound of which the constitution is not well 
 known, but which is probably a deutoxide. 
 
 Protoxide of Cobalt, CoO, is prepared by adding caustic potash in 
 excess to a solution of a salt of cobalt, a fine blue powder falls, which 
 is a hydrate, CoO.HO ; when deprived of its water, it becomes ash- 
 grey ; it is the only oxide of cobalt which forms salts with acids. 
 
 Sesquioxide of Cobalt, Co 2 3 , is prepared as the sesquioxide of nickel ; 
 it is a black powder, which is decomposed by a red heat, and with 
 hydrochloric acid gives chlorine and protochloride ; it does not form 
 salts. 
 
 The first complex oxide, Co 3 O 4 = CoO + Co 2 O 3 , is produced by 
 heating the sesquioxide to redness as long as it gives out oxygen gas : 
 it is similar to the magnetic oxide of iron and red oxide of manganese. 
 
 The second complex oxide Co 6 O 7 or 4CoO + Co 2 3 is formed by 
 calcining the protoxide in the air as long as it increases in weight by 
 absorbing oxygen. It is probably the best form in which to estimate 
 cobalt. 
 
 Cobalt is recognized in solution, by producing with water of ammonia, 
 a blue precipitate, which redissolves in an excess of the alcali, forming 
 a liquor which is of a fine rose colour, if the cobalt be pure, but 
 brownish red if nickel be present ; it is not precipitated by sulphu- 
 retted hydrogen, but is thrown down black by hydrosulphuret of am- 
 monia. The most remarkable test for cobalt, is its power of colouring 
 glass blue. The most minute trace of this metal may be thus recog- 
 nized before the blowpipe. It is, indeed, on this character that is 
 founded the most important uses of cobalt in the arts ; glass coloured 
 deep blue by cobalt, and ground to an impalpable powder, constitutes 
 the smalts used to give to writing paper and to linen a delicate shade 
 of blue. The blue colours upon porcelain and delft, are also produced 
 by cobalt ; when speaking of magnesia (p. 488) and alumina, (p. 491,) 
 I have noticed the assistance given by cobalt in the detection of these 
 earths before the blowpipe ; alumina, coloured strongly blue by cobalt, 
 is used in commerce as a pigment, cobalt blue, in place of ultramarine. 
 
 The most important analytical relation of cobalt is its separation from 
 its most closely allied metal, nickel, which may be done by either of the 
 following processes : 1st. If a current of chlorine gas be passed 
 through the muriatic solution of the two metals, the cobalt becomes 
 converted into perchloride, whilst the nickel undergoes no change. 
 
516 Uses of Cobalt in the Arts. 
 
 On the adding carbonate of barytes, peroxide of cobalt precipitates, and 
 pure protochloride of nickel remains in solution. The barytes being 
 then removed by sulphuric acid, the nickel may be precipitated by pot- 
 ash in the usual way. This mode is recommended by Henry Eose. 
 
 A mode proposed by Liebig is to convert the mixed metallic com- 
 pounds into cyanides by boiling with cyanide of potassium in excess. 
 On then digesting with moist hydrated oxide of mercury, nickelo-cpnide 
 of mercury precipitates, and on being collected and ignited, leaves pure 
 oxide of nickel, the cyanogen and mercury being expelled. The filtered 
 liquor contains cobalto-cyanide of potassium, and on adding sulphate of 
 copper, cobalto-cyanide of copper precipitates, which is to be collected, 
 dissolved by muriatic acid, and decomposed by sulphuretted hydrogen, 
 which removes the copper as sulphuret. The filtered liquor contains 
 chloride of cobalt, and on boiling with an excess of potash, deposits the 
 oxide of cobalt pure. 
 
 The blue colours of cobalt are spoiled if brought into contact with 
 chlorine or oxygen, the black sesquioxide of cobalt being formed. If 
 paper be blued by smalts without the bleaching liquor having been 
 well washed out of the pulp, it is injured by acquiring a brown tinge, 
 and by melting together cobalt-glass, and black oxide of manganese, a 
 deep black glass is formed, 2 (CoO) and MnO 2 giving Co 2 3 and 
 MnO. 
 
 The sulphuret as well as the seleniuret of cobalt consists of an equi- 
 valent of each element, but does not require notice. 
 
 OF ZINC. 
 Symbol. Zn. Eq. 32'51 or 406'6. 
 
 This metal is found in nature in considerable quantity, combined 
 with sulphur, forming sulphuret of zinc, zinc blende ; also as oxide of 
 zinc, which united with carbonic acid, or with silicic acid, forms the 
 two varieties of calamine. The reduction of the metal is effected from 
 these ores respectively on the principles already described in Chapter 
 XII., but from the volatility of the metallic zinc, the process is carried 
 on in crucibles, or large earthen retorts, in place of the open reverbe- 
 ratory furnaces In England, the crucibles are closed above, but per- 
 forated at the bottom, so as to admit an iron tube to be fitted in, the 
 top of which rises a little above the surface of the materials, and the 
 bottom of which, passing through the floor of the furnace, opens just 
 over the surface of a reservoir of water. The zinc, when reduced, is 
 converted into vapour, which escapes through the tube, condensing 
 when it gets below the fire into a liquid metal, which dropping into 
 
Preparation and Properties of Zinc. 517 
 
 the water, solidifies. In Silesia, very large earthen retorts are employed, 
 not unlike those figured in page 397, for the preparation of German 
 oil of vitriol. 
 
 The zinc of commerce, as thus obtained, is impure ; it contains traces 
 of carbon, iron, cadmium, and often arsenic. It may be freed from the 
 fixed impurities by redistillation in an iron retort, and by rejecting the 
 portions which distil over first, and which contain the cadmium and 
 arsenic, it may be obtained quite pure. It is owing to the presence of 
 these foreign bodies that ordinary zinc dissolves so rapidly in dilute sul- 
 phuric acid, as explained in page 176. It is a brilliant bluish-white 
 metal, of a very crystalKne texture ; its singular variations of tenacity 
 are described in page 458. At 773 it melts, and at a full red heat is 
 volatilized ; its vapour burning in air with a splendid white flame, and 
 forming clouds of oxide of zinc, so light as to have been called by the 
 older chemists lana philosophica and nihil album. When exposed to 
 the air, even in presence of water, zinc is not continuously oxidized. 
 It becomes covered with a varnish of a grey substance, probably a defi- 
 nite suboxide, which is not further altered by exposure, and hence, this 
 metal is admirably fitted for the various purposes of domestic and tech- 
 nical use to which it has recently been applied. In a galvanic circuit 
 of two metals, zinc is almost always positive, and hence it preserves the 
 other metal, even if it be iron, from oxidation. The actual corrosion is, 
 however, in this case, not diminished, but rather augmented in amount ; 
 but being concentrated solely upon the zinc, it is easy to arrange it so 
 as to prevent injury. If zinc be quite pure, it is little acted upon by 
 acid ; all that is known of its relations in this respect has been already 
 described in pages 266 and 341. 
 
 The symbol for zinc is Zn. Its equivalent number 406-6 or 32'5. 
 
 Oxide of Zinc.- -Zn.0 Equivalent 506-6 or 40*5. Although there 
 is some reason to suppose the existence of other oxides of zinc, yet at 
 present we possess accurate knowledge only of the protoxide. This 
 is formed when the metal is burned in air or oxygen. It is produced 
 also when the zinc is oxidized by the decomposition of water, either at 
 a red heat or assisted by an acid. To form the oxide by combustion, it 
 it is sufficient to project a small fragment of zinc into a crucible heated 
 to bright redness, and slightly inclined, so that- a current of air may 
 pass through it. When the metal takes fire, another crucible is to be 
 placed inverted over the first, but still allowing a certain access of air. 
 The oxide of zinc being not really volatile, but only mechanically carried 
 up the current of air, is deposited on the inside of the upper crucible, 
 as a loose cottony mass, which whilst very hot is of a fine canary colour, 
 but becomes pure white when completely cold. 
 
518 Of the Oxides and Sulphur ets of Zinc and Cadmium. 
 
 In zinc works the oxide is sometimes fonnd crystallized on the fur- 
 naces in six-sided prisms, and sometimes in bipyrainidal dodecahedrons 
 like quartz. 
 
 Such is the tendency of oxide of ziuc to enter into combination, that 
 the precipitates given by the caustic alcalies in a solution of a salt of 
 zinc, are merely basic salts, and not the pure oxide. To prepare the 
 oxide, a solution of sulphate of zinc is to be decomposed by carbonate 
 of soda ; the precipitate is carbonate of zinc, and by heating this to 
 redness in a crucible, the carbonic acid passes off and the oxide of zinc 
 remains pure. This oxide is a powerful base ; it neutralizes the strong- 
 est acids, and its salts are some of the most definite and characteristic 
 that exist ; they are easily recognized. In their solutions, the caustic 
 alcalies all produce voluminous white precipitates, which are redissolved 
 by an excess of the alcali, with which oxide of zinc unites, forming de- 
 finite compounds, in some cases crystallizable. An alcaline carbonate 
 gives a similar precipitate, which, however, is not redissolved by an ex- 
 cess, except it be carbonate of ammonia. Hydrosulphuret of ammonia, 
 produces a white precipitate of hydrated sulphuret of zinc, if the solu- 
 tion be not be very acid. Sulphuretted hydrogen does so only if the 
 solution be completely neutral. A solution of zinc with much free acid, 
 is not affected by sulphuretted hydrogen either free or combined. 
 
 The native sulphuret of zinc, ZnS., is found in crystals of a variety of 
 colours ; it is a protosulphuret, and may be artificially formed by melt- 
 ing zinc and sulphur together. It is decomposed by acids, sulphuretted 
 hydrogen being given off and a salt of zinc produced. Its crystalline 
 form is the same as that of the crystallized oxide, and also that of an 
 oxysulphuret which is found occasionally as a product of the smelting of 
 zinc ores. 
 
 OF CADMIUM. 
 Symbol. Cd. Eq. 55'74 or 697. 
 
 This metal exists but in small quantities in nature ; the only ore of 
 it is its sulphuret, a mineral but lately found and still very rare ; it ac- 
 companies almost universally, though in small quantities only, the ores 
 of zinc, and is obtained in the working of zinc ores, by taking advantage 
 of its greater volatility. The details of its purification need not be in- 
 serted. It is white like tin ; it is more fusible and more volatile than 
 zinc; its specific gravity is 8 '69; it dissolves very slowly in dilute sul- 
 phuric acid but rapidly in dilute nitric acid ; it combines with oxygen 
 only in one proportion. Its symbol is Cd. and its equivalent 697 
 or 55-8. 
 
Extraction and Properties of Tin. 519 
 
 The oxide of cadmium, Cd.O. equivalent 797 or 63'8, is obtained 
 by processes exactly such as described for oxide of zinc. When anhy- 
 drous, it is an orange powder ; its salts which are very stable, resemble 
 closely those of zinc, from which they are distinguished by giving with 
 sulphuretted hydrogen, a fine yellow precipitate, and with carbonate of 
 ammonia a white precipitate, soluble in an excess ; its salts, like those 
 of zinc, are all colourless. 
 
 Sulpkuret of cadmium, Cd. S., is found native near Greenock ; it is 
 yellow like orpiment, but is not volatile ; it does not dissolve in water 
 of ammonia, nor of potash. 
 
 OF TIN. 
 Symbol. Sn. Eq. 58'92 or 735'2. 
 
 This metal, from the ease with which it is extracted from its ores, 
 has been known from the earliest ages, and in all countries, both of the 
 east and west. Before the working of iron was discovered, cutting in- 
 struments of all kinds were made of an alloy of tin and copper (bronze), 
 which in hardness was little inferior to steel ; but from its incapability 
 of being tempered with the same exactness, was only an imperfect sub- 
 stitute for it. It was from the tin mines of Cornwall that England first 
 became known to the then more civilized nation of Phoenicia. A great 
 quantity of the tin of commerce is still obtained from that country ; but, 
 in addition, it is imported from Mexico and the East Indies. The tin 
 ore has been found in Ireland, (county Wicklow), but not as yet sought 
 for with a view of extracting metal from it. 
 
 The usual ore of tin is the native peroxide, which is found in veins 
 and also in fragments in the soil formed by the disintegration of the 
 rocks. The process of reduction is the simplest possible, the ore being 
 smelted with the fuel, as described, p. 465. The metal thus obtained is 
 still further purified from any admixture of foreign metals by the pro- 
 cess of liquation, which is founded on the easy fusibility of pure tin. The 
 ingots, or pigs of tin, are gently heated, until they begin to melt, and 
 then the heat being prevented from rising higher, the pure metal melts 
 completely out, leaving behind the impurities combined with a propor- 
 tion of tin, forming a mass of less commercial value. The tin thus 
 purified is termed grain tin ; the residual mass is called block tin. The 
 former is known by presenting the appearance of a mass of irregular 
 columns, like those formed by starch, or by basalt, as in the Giant's 
 Gauseway, and emitting when bent a peculiar creaking sound. The 
 block tin possesses these characters in a very small degree, or not at all. 
 
520 Allotropic forms of Protoxide of Tin. 
 
 Tin when pure is white like silver, brilliant, and after gold, silver, 
 and copper, the most malleable of the metals. It is very soft, may be 
 bent easily, and has but little tenacity. It may be obtained in regular 
 crystals belonging to the pyramidal system. Its sp. gr. is 7*3. It is 
 one of the most fusible of the metals, melting at 442 Fah. Tin oxi- 
 dizes but very slowly in contact with air and water, and is hence used 
 to protect the surface of the more easily oxidable metals, particularly 
 copper, in household use. It dissolves but slowly in dilute muriatic 
 acid, but rapidly, if the acid be strong and boiling. Nitric acid acts 
 with great energy on it when concentrated, forming the peroxide. 
 
 The symbol of tin is Sn, derived from its Latin name stannum. Its 
 equivalent numbers are 735*3 or 58*9 
 
 There are three oxides of tin, of which the first acts as a base, the 
 second appears indifferent, and the third possesses acid properties. 
 
 Protoxide of Tin. SnO. Equivalent 835'3, or 66'9. On adding 
 water of ammonia to a solution of protochloride of tin a copious white 
 precipitate is obtained, which does not contain ammonia, but is the hy- 
 drated oxide, SnO.HO. The same precipitate is produced by an alca- 
 line carbonate, the carbonic acid becoming free. When this white hydrate 
 is heated in a retort filled with carbonic acid gas, it gives off its water, 
 and the true protoxide of tin remains as a dense black powder If the 
 hydrate be heated in the open air it absorbs oxygen, and becomes per- 
 oxide ; and if the black protoxide be touched when cold with a red hot 
 coal or wire, it flames and burns like tinder, forming peroxide. This 
 black protoxide may also be formed by boiling the white hydrated 
 oxide with a little strong solution of caustic potash ; but the protoxide 
 of tin is obtained in a different allotropic condition by precipitating pro- 
 tochloride of tin by caustic ammonia. It then forms an olive powder, 
 into which the black crystalline powder is also resolved by a tempera- 
 ture of about 400 in close vessels. 
 
 A third allotropic state of protoxide of tin is formed by boiling the 
 white hydrated protoxide with a solution of sal-ammoniac until the 
 latter begins to be deposited. The oxide is changed into a bright red- 
 coloured powder, which, however, gradually passes by heat or friction 
 back to the ordinary olive-coloured state. 
 
 The salts of tin may be formed by digesting the hydrated oxide in 
 acids. It also dissolves in solutions of the caustic fixed alcalies, but 
 after some time metallic tin is deposited, and a compound of the alcali 
 with peroxide of tin remains dissolved, 2SnO, producing Sn and SnO 2 . 
 This protoxide of tin is remarkable for its tendency to unite with more 
 oxygen. Hence, by a solution of a protosalt of tin, the less oxidable 
 metals are reduced from their solutions. In this way mercury, silver, 
 
Isomeric Forms of Stannic Acid. 521 
 
 gold, platina, may be thrown down in the metallic state, and iron and 
 copper reduced from the higher to the lower degrees of oxidation. 
 
 The Sesquioxide of Tin, Sn 2 O 3 , is prepared by boiling peroxide of 
 iron in a neutral solution of protochloride of tin. The sesquioxide of 
 tin precipitates, and protochloride of iron dissolves ; 2.Sn.Cl and Fe 2 O 
 producing Sn 2 O 3 and 2.FeCl. It is a grey powder ; it absorbs oxygen 
 readily, and appears to form salts which have been as yet little ex- 
 amined. 
 
 Peroxide of Tin. Stannic Acid. SnO.J. Equivalent 935'3, or 74'9. 
 This substance is produced in all cases where tin is allowed to combine 
 with oxygen freely. It exists in nature constituting the common ore of 
 tin (tin stone). It is most readily prepared artificially by pouring the 
 liquid nitric acid, sp. gr. 1*42, on metallic tin, in foil or powder; the 
 action is very violent, and the metal is totally converted into a white 
 powder, which is the hydrated peroxide. By ignition the water is 
 given off, and the anhydrous oxide remains of a pale yellow colour. 
 
 If the perchloride of tin be decomposed by an alcali, a white preci- 
 pitate of hydrated oxide is obtained, in appearance identical with that 
 prepared by nitric acid, but so different in properties, that Berzelius, 
 and after him many chemists, look upon them as isomeric bodies. He 
 calls that by nitric acid, peroxide, and that from the perchloride, (3 
 peroxide, and their properties may be contrasted as follows : 
 
 The modification is totally insoluble in nitric acid and in sulphuric 
 acid, whether strong or dilute. It is insoluble in muriatic acid, but is 
 changed by it into an insoluble basic salt. 
 
 The /3 modification dissolves whilst yet moist in dilute nitric and 
 sulphuric acids very copiously, and the solution is permanent if some 
 salt of ammonia be added to it. In muriatic acid it dissolves rapidly 
 and copiously. 
 
 The two modifications of oxide of tin dissolve in solution of caustic 
 potash, and when again precipitated from it by an acid retain their ori- 
 ginal properties. These modifications are also capable of being trans- 
 formed into each other ; the a into /3 by distillation with strong muriatic 
 acid, and the /3 into by boiling with nitric acid. 
 
 The hydrated peroxide of tin reddens litmus and combines with alca- 
 lies to form salts, but not with acids, except in the /3 form. It is used 
 in the arts as a polishing material under the name of putty, and in 
 glass and enamelling, in order to give the milk whiteness used for dials 
 of watches and other purposes. 
 
 Fremy has recently studied the compounds of the peroxide of tin 
 with alcalies, and has arrived at the conclusion, that the real equivalent 
 of that compound, as well of the as of the P variety, contains three 
 
522 Preparation of Mosaic Gold. 
 
 atoms of tin aiid six of oxygen, = Sn 3 O 6 = 3Sn0 2 , and that in com- 
 bining with bases the allotropic modifications resemble the different 
 forms of the phosphoric acid, the , Sn 3 O 6 being a tribasic, and the j3 
 Sn 3 6 being a monobasic acid. The evidence, however, is not fully 
 conclusive on the subject. 
 
 There are three sulphurets of tin corresponding to the oxides. The 
 protosulpJiuret, Sn.S, is precipitated as a brown powder from a solution 
 of protochloride of tin on the addition of sulphuret of hydrogen. It 
 thus serves for the detection of tin in that condition. The sesquisul- 
 pliuretj Sn 2 S 3 , is of no importance. 
 
 The Bisufykuret of Tin.SnS 2 . Equivalent 1137'6 or 91-1. May 
 be prepared by decomposing a solution of perchloride of tin by sulphu- 
 retted hydrogen, which it precipitates of a golden yellow colour. This 
 is a strong sulphur acid ; it dissolves readily in solutions of the sulphu- 
 rets of the alcaline metals forming sulphur salts. If it be strongly 
 heated, it abandons an atom of sulphur and is converted into the proto- 
 sulphuret. It may be also prepared in the dry way, and then possesses 
 considerable interest as being one of those substances, which although 
 obtained from the common metals yet simulate the appearance and some 
 of the properties of gold, and led the ancient alchemists to the belief 
 of probable success in their attempts at transmutation. The bisulphuret 
 of tin may be prepared in the dry way, according to several processes, 
 but to give it the peculiar lustre which obtained for it the name of mosaic 
 gold, the following is the best though not the most simple : twelve 
 parts of pure tin are to be melted with six parts of mercury, and rubbed 
 up in a glass mortar with seven of flowers of sulphur and six of sal- 
 ammoniac. This mixture is to be placed in a glass flask and heated in 
 a sand bath until no more fetid white vapours are given off. The heat 
 is to be then raised to dull redness, sulphuret of mercury and chloride 
 of tin sublime, and the mosaic gold remains in the bottom of the vessel 
 in metallic looking scales of a brilliant gold colour. The use of the 
 mercury in this process is to facilitate the combination of the tin and 
 sulphur, and the sal-ammoniac seems by its evaporation to prevent the 
 temperature becoming so high as to decompose the bisulphuret. 
 
 The seleniurets and phosphurets of tin are not known. 
 
 Tin is easily recognized in solution by the action of hydrosulphuret 
 of ammonia, which produces, with solutions of the peroxide, a golden 
 yellow, and in solutions of the protoxide a brown precipitate. These 
 both dissolve in an an excess of the precipitant. The protoxide of tin 
 is also known by its power of reducing the salts of gold, silver, and 
 mercury to the metallic state. 
 
Of Chrome and its Compounds. 523 
 
 OF CHROMIUM, OR CHROME. 
 Symbol. Or. Eq. 334*9 or 27-8. 
 
 This metal derives its name from the variety and brilliancy of the 
 colours of its compounds (Xgw/o,o.) It exists as chromic acid combined 
 with lead or with copper, in some rare minerals, but abundantly as 
 chromic oxide, in the chrome-iron ore. (FeO + Cr 2 O 3 .) It is from 
 this source that all the preparations of chrome are obtained indirectly, 
 but that ore being treated upon the large scale for the manufacture of 
 chromate of potash, it is this salt, as found in commerce, that may be 
 looked upon as the source of chrome for all other purposes. The metal 
 is obtained by mixing the oxide with lampblack and oil, and exposing it 
 to an intense heat in a crucible lined with charcoal. It is a greyish- 
 white metal, very infusible, brittle, not magnetic, and sp. gr. 5*9 or 
 6*0. It is not attacked by dilute sulphuric or muriatic acids, but dis- 
 solves in hydrofluoric acid with evolution of hydrogen gas. 
 
 Chrome combines with oxygen in four proportions, forming two 
 oxides and two acids. Its symbol is Cr : its equivalent numbers were 
 given by Berzelius as 351*8 or 28*39, but the recent investigations of 
 Peligot and Moberg have led to the adoption of 334*9 or 27*8. 
 
 The series of oxygen compounds of chrome nearly resembles that of 
 manganese, there being 
 
 Protoxide of chrome CrO. Eq. 35-3. or 434 9. 
 
 Sesqui-oxide Cr 2 0a. 79'6. ... 969-8. 
 
 Chromic acid CrOa. 51-8. ... 634-9. 
 
 Perchromic acid Cr2O7. 111-6. ... 1369-8. 
 
 Protoxide of Chrome. This body whose properties are .as yet but im- 
 perfectly known, is formed from the protochloride by the action of 
 potash. A yellow precipitate forms which is the hydrated protoxide. 
 It must be washed with water quite free from air, and must be dried in 
 an atmosphere of hydrogen. When dry it is brown. Its formula is 
 CrO + HO. It combines with acids to form salts. When heated it 
 decomposes its constituent water ; hydrogen being evolved and sesqui- 
 oxide of chrome formed. The protochloride of chrome is obtained by 
 igniting the sesquichloride in a current of hydrogen gas by which one 
 third of the chlorine is removed as muriatic acid. 
 
 Sesqui-oxide of Chrome. Cr 2 3 . Equivalent 969*8 or 79*6 May 
 be obtained by a great variety of processes. Thus if chromate of 
 mercury be heated to redness, the oxide of mercury and half the oxygen 
 of the chromic acid are expelled, and the chromic oxide remains of a 
 
524 Preparation and Properties of Oxide of Chrome. 
 
 beautiful green colour. If bichromate of potash be mixed with sal- 
 ammoniac and heated to redness, chloride of potassium, water, nitrogen, 
 and oxide of chrome result, and the latter is obtained pure by washing 
 the residual mass with boiling water. In this process 2Cr0 3 + KG 
 and C1.NH 4 produce KC1, N, 4HO and Cr 2 3 . The oxide so obtained 
 is pulverulent, but it may be obtained crystallized as follows : the vapour 
 of a compound which will be hereafter described, chloro-chromic acid, 
 is to be passed through a tube of hard glass kept at a full red heat, 
 oxygen and chlorine gases are given off, and oxide of chrome is deposited 
 on the inside of the tube ill rhombic octohedrons, isomorphous with 
 those of alumina (corundum) and peroxide of iron found native. The 
 chloro-chromic acid 2(Cr0 2 Cl) giving off 2C1 and O and Cr 2 3 re- 
 maining. 
 
 Another cheap and ready process consists in igniting bichromate of 
 potash with one fourth its weight of starch, and lixiviating the product 
 to dissolve out the carbonate of potash formed. The oxide remains, 
 when washed and dried, quite pure and fit for all chemical and technical 
 uses. 
 
 This sesqui-oxide of chrome is the basis of an extensive class of salts, 
 and it may also be obtained by precipitation from any solution contain- 
 ing it. Its salts are generally made from the bichromate of potash of 
 commerce, by the addition of some deoxidating agent and the necessary 
 acid. Thus, to form sulphate of chrome, a solution of bichromate of 
 potash is warmed, and treated successively with sulphuric acid and 
 alcohol, until its orange colour is changed into deep green. The liquor 
 then contains the double sulphate of chrome and potash, (chrome alum) 
 and from it the oxide may be precipitated on the addition of an alcali, 
 as a pale green hydrate. In this condition, the oxide of chrome dis- 
 solves readily in acids, and also in solutions of the fixed caustic alcalies, 
 but scarcely in ammonia, resembling very closely in all these characters, 
 alumina. Its solutions are either green or purple, and it is probable 
 that this difference is due to allotropic conditions rather than to a mere 
 difference in the degree of concentration. When the hydrated oxide is 
 heated nearly to redness, it suddenly begins to glow like tinder, giving 
 off its water, and losing its solubility in acids, except they be hot and 
 concentrated. It is remarkable, that sulphate of chrome, made from 
 the ignited oxide, will not combine with sulphate of potash to form a 
 chrome alum. 
 
 Chromic Acid. Cr0 3 . Equivalent 634.^ or 5T8. To prepare this 
 acid, a solution of bichromate of potash is to be treated by hydrofluo- 
 silicic acid gas, until the potash has been precipitated completely. The 
 resulting liquor is to be cautiously evaporated to dryness, and then re- 
 
Chromic and Perchromic Adda. 525 
 
 dissolved in a small quantity of water. The solution is of a dark 
 brownish-red, and when evaporated again gives the dry chromic acid. 
 It may be obtained in a beautiful form, though not in quantity, by 
 decomposing the vapour of the perfluoride of chrome by a moistened 
 slip of paper. Cr.F 3 and 3HO produce 3.HF and CrO 3 , which last is 
 deposited on the surface of the paper in crimson scales and needles of 
 great brilh'ancy. This acid when heated strongly, gives up half its 
 oxygen, being reduced to the state of oxide. It oxidizes organic bodies 
 very powerfully, and is employed for that purpose in organic analysis. 
 If added to alcohol or ether it sets those bodies on fire and often with 
 explosion, the solid product being green oxide of chrome. On this 
 oxidizing power is also founded its employment as a bleaching agent 
 which is now very extensive. It combines with bases, forming several 
 important classes of salts, in which it is isomorphous with the sul- 
 phuric and manganic acids. Its salts are all coloured, generally yellow, 
 orange, or red. They will be described in another chapter. 
 
 The chromic acid may be very beautifully and abundantly prepared 
 crystallized by decomposing bichromate of potash with strong oil of 
 vitriol. By mixing two volumes of a cold saturated solution of bichro- 
 mate of potash with three volumes of oil of vitriol, and allowing the 
 mixture to cool, the chromic acid separates in long needles of a mag- 
 nificent crimson colour. The acid solution of bisulphate of potash may 
 be drained off, and the crystals dried on a porous tile. By using less 
 oil of vitriol, the chromic acid remains dissolved, and the bisulphate of 
 potash may be first crystallized out ; the liquors being then concen- 
 trated by evaporation, the chromic acid may be separated by the addi- 
 tion of more oil of vitriol, and is purer than when prepared by the first 
 process. 
 
 The sulphuric liquors must not be heated, for, as shown in page 336, 
 the chromic acid is totally decomposed, by even a moderate heat, in 
 contact with sulphuric acid, into oxide of chrome and free oxygen 
 gas. 
 
 Perchromic Add. Cr 2 O 7 . When chromic acid is treated with per- 
 oxide of hydrogen, it dissolves, producing an acid liquor of a deep blue 
 colour, which, however, spontaneously evolves oxygen gas, and leaves 
 chromic acid again. The precise history of this presumed perchromic 
 acid has not been established. 
 
 Chromium is characterized by the remarkable colours of its com- 
 pounds when dissolved, and by giving, when in the state of sesqui- 
 oxide, a green precipitate with the alcalies. In the state of chromic 
 acid, it is known by producing, with the salts of lead, a yellow, and 
 with the salts of black oxide of mercury, an orange precipitate. It is 
 
526 Vanadium, its Oxides and Acids. 
 
 at once recognized by the beautiful green colour, which it communicates 
 to glass. It is on this account extensively used in staining glass and 
 painting on porcelain, and a number of its salts are employed as pig- 
 ments and as dyes. 
 
 By the action of deoxidizing agents, as sulphurous acid or sugar, 
 upon bichromate of potash, a brown substance is generated, concerning 
 the nature of which opinion is very much unsettled. There is reason 
 to suspect the existence of a peroxide of chrome, CrCh, which this mat- 
 ter may possibly be. When it is washed with much water, or digested 
 in alcaline liquors, chromic acid is dissolved out and oxide of chrome 
 remains, Cr 2 O 3 -f- CrOa = 3.Cr0 2 . Its history is, however, very 
 uncertain. 
 
 The sulphurets, seleniurets, and phosphurets of chrome are not 
 important. 
 
 OF VANADIUM. 
 
 This metal, of recent discovery, derives its name from Vanadis, a 
 deity of Scandinavian mythology. It is found native as vanadic acid, in 
 a very rare mineral, vanadiate of lead, but is of so little importance 
 that a slight notice of it will suffice, although it forms a great variety of 
 combinations which resemble, very remarkably, those of manganese and 
 chrome. The metal itself has been obtained, but of its properties 
 nothing positive is known. Its symbol is V ; its equivalent numbers 
 856-9 or 68.7. 
 
 The Protoxide of Vanadium, YO, is a black powder formed by act- 
 ing on vanadic acid at a red heat with hydrogen gas. It combines with 
 acids forming salts which resemble probably those of the protoxide of 
 manganese. When heated in the air it absorbs oxygen and becomes 
 vanadic oxide, YO 2 , which is a base combining with acids and forming 
 salts which are generally blue. It acts also as an acid, forming crystal- 
 tallizable salts with the fixed alcalies. 
 
 The Vanadic Acid, Y0 3 , resembles very much the chromic and man- 
 ganic acids. It is a red powder that may be melted at a red heat with- 
 out losing oxygen. It is very slightly soluble in water. It forms 
 various classes of salts, of which some are white, some yellow, and others 
 orange red. In these characters it resembles the chromic acid, but it is 
 distinguished from chrome by producing, when deoxidized, a blue solu- 
 tion, whilst that from chrome is green. 
 
Tungsten and its Oxides. 527 
 
 SECTION IV. 
 
 METALS OF THE FOURTH CLASS. 
 TUNGSTEN AND MOLYBDENUM. 
 
 Tungsten. This metal exists combined with oxygen as tungstic acid, 
 in the native tungstates of lime and iron ; by boiling the tungstate of 
 linie in strong muriatic acid, the lime is dissolved out and tungstic acid 
 remains as a yellow powder, which may be further purified by solution 
 in water of ammonia and igniting the dried tungstate of ammonia. It 
 is a deep yellow powder which forms well denned crystallizable salts with 
 the alcalies. The symbol of tungsten is "W, from its German name 
 Wolfram, and its equivalent 1183 or 94' 8. The tungstic acid resem- 
 bles the chromic acid, being WO 3 . When this acid is exposed to a 
 current of hydrogen gas at a temperature about dull redness, it loses 
 one-third of its oxygen and forms tungstic oxide, WO 2 , of a copper-red 
 colour. This may be also formed by diffusing tungstic acid through 
 dilute muriatic acid in which a slip of zinc is immersed, the nascent 
 hydrogen then effects the deoxidation. At a full red heat, hydrogen 
 reduces tungsten to the metallic state, removing all the oxygen. The 
 metal is like iron in appearance, and very heavy, its sp. gr. being 
 about 17 '5. 
 
 The most curious fact in the history of tungsten is its producing a 
 substance having an extraordinary similarity to gold. It is prepared by 
 adding to fused tungstate of soda as much tungstic acid as it will dis- 
 solve, and exposing the product at a full red heat, to a current of hydro- 
 gen gas ; the residual tungstate of soda is then to be dissolved out. 
 The new compound, which consists of tungstic oxide united to soda, 
 ]Xf aO -f- 2 WO 2 , remains in scales and cubes of a splendid gold colour. 
 It resists the action of acids and alcalies, even of aqua regia, in which 
 gold dissolves, and only yields to strong hydrofluoric acid. Had it been 
 discovered at an earlier period in science, it might have lent exceedingly 
 plausible support to the belief in transmutation. It is the more 
 curious as it cannot be formed by directly combining soda with tungstic 
 oxide, which, indeed, appears unable to unite either with alcalies or 
 acids. 
 
 There exist two sulphurets of tungsten, W.S* and W.S 3 of which the 
 latter is the most interesting. It is formed by dissolving tungstic acid 
 in hydrosulphuret of ammonia and precipitating by an acid. It is a 
 blackish-brown powder, and one of the strongest sulphur acids. Many 
 
528 Molybdenum and its Compounds. 
 
 of its compounds with the sulphurets of the alcaline metals may be 
 crystallized. 
 
 Molybdenum. This metal exists combined with sulphur, and also 
 with oxygen, as molybdic acid, in some minerals. It is not of any con- 
 siderable interest. When obtained in the metallic state it is white : sp. 
 gr. 8'6 : it is acted on only by concentrated nitric and sulphuric acids, 
 and by aqua regia. Its symbol is Mo. Its equivalent 598*5 or 47 '9. 
 It combines with oxygen in three proportions. 
 
 Molybdic Acid. MoOa. Is easily prepared by roasting the native 
 sulphuret of molybdenum ; the sulphur burns out as sulphurous acid gas 
 and the molybdenum absorbing oxygen remains as molybdic acid. This 
 may be purified as described for tungstic acid. Molybdic acid prepared 
 at a low temperature is white, but becomes yellow when fused at a red 
 heat. It is sparingly soluble in water. It dissolves in alcaline liquors 
 forming salts which are neutral and cry stalliz able. 
 
 Molyldic Oxide. Mo0 2 . Is best prepared by mixing together 
 molybdate of soda and sal-ammoniac in a crucible, and igniting the mass 
 rapidly. When the product is washed with water a dark brown powder 
 is obtained, which is molybdic oxide. This oxide appears to form salts 
 with both acids or alcalies, of which some may be crystallized. A mo- 
 lybdate of molybdenum, or rather a complex oxide, also exists, MoO 2 
 + 2Mo.0 3 =Mo 3 8 . It is a blue powder, and has latterly been employed 
 in calico printing. 
 
 When a solution of a molybdate is decomposed by as much muriatic 
 acid as redissolves the molybdic acid, which is at first thrown down, and 
 a slip of zinc is immersed in the liquor, the hydrogen evolved deoxidizes 
 the molybdic acid, and a precipitate is formed upon the zinc, at first 
 blue, then brown, and finally black ; thus passing through all the inter- 
 mediate degrees to the last, the molyldous oxide, MoO. This is a very 
 feeble base, forming with acids, salts which do not crystallize. 
 
 Sulphur combines with molybdenum in three proportions, forming 
 Mo.S 2 , Mo.S 3 , and Mo.S 4 . Of these the bisulphuret, Mo.S 2 , is impor- 
 tant as being the native ore from which the metal and its compounds are 
 generally prepared. It is a soft grey substance, so like black lead as to 
 have been mistaken for it until its nature was pointed out by Scheele. 
 All these sulphurets are sulphur acids, and form salts. 
 
 OF OSMIUM. 
 
 This metal exists in nature alloyed with iridium, and accompanies 
 the ores of platinum. The methods of its extraction from these ores 
 are so complex and circuitous that I shall not introduce them here. 
 
Osmium and its Compounds. 529 
 
 In the systematic works a complete account of the processes pursued 
 will be found. 
 
 The most interesting property of osmium is its forming a highly 
 volatile oxide of an exceedingly penetrating odour, whence the name 
 (off/^Tj.) When this is dissolved in muriatic acid, and placed in contact 
 with mercury, the osmium is reduced, and by distilling off the mercury 
 it is obtained as a black powder ; but by heat and compression it may 
 be rendered coherent, and of a brilliant white colour. In the state of 
 powder, osmium burns Avhen heated to redness in the air, and is oxi- 
 dized by nitric acid, but loses both these characters when ignited. The 
 symbol of osmium is Os. Its equivalent is 1244*5 or 99'7. It com- 
 bines with oxygen in three proportions. 
 
 The Osmic Add, or Peroxide of Osmium. Os.0 4 . is always formed 
 when osmium is burned in air or in oxygen gas. It is volatile and con- 
 denses in long white needles. Its odour is remarkably acid and pungent. 
 It melts at 2 12, and boils at a heat little higher. It is soluble in water. 
 The solution has no action on vegetable colours, but it combines with 
 the alcalies forming osmiates. 
 
 The Osmic Oxide, Deutoxide of Osmium.' Os. O 3 . Is produced by 
 the decomposition of a solution of osmiate of ammonia, by a tempera- 
 ture of 150, nitrogen gas is given off and a brown powder is deposited. 
 
 The Protoxide of Osmium is produced by decomposing a solution of 
 protochloride of osmium by potash, a deep green, almost black, pow- 
 der is thrown down, in which the oxide is combined with water and 
 traces of the alcali. 
 
 The sulphurets of osmium are not known. 
 
 TANTALUM, NIOBIUM, PELOPIUM, AND ILMENTUM. 
 
 Tantalum. This metal was discovered in some very rare Swedish 
 minerals, and from the difficulty of its extraction the name tantalum was 
 given to it, whence its symbol is Ta. Its discovery was simultaneously 
 made in England in an American mineral, and the name Columbium 
 proposed for it, but the word Tantalum having been generally adopted 
 in Europe I shall employ it here. The process required to prepare it 
 need not be described, as it is similar to that for obtaining silicon. 
 
 Metallic Columbium, or Tantalum, is a black powder, which, when 
 burnished, appears iron grey. No acid but the hydrofluoric appears 
 to have any action on it. It takes fire when heated in the air and 
 burns vividly. Its equivalent numbers are 2 30 '7 or 185. It com- 
 bines with oxygen in two proportions. 
 
 34 
 
530 Tantalum, Pelopium, and Niobium. 
 
 Tantalic, or Columbia Acid. Ta. 3 . Exists native in all the mi- 
 nerals containing the metal. To procure it, the mineral is fused with 
 carbonate of potash, and the tantalate of potash, which is soluble, is 
 to be decomposed by muriatic acid. The tantalic acid precipitates as a 
 white powder which contains water, and reddens litmus paper. "When 
 tantalic acid is heated strongly in a crucible with charcoal, but a slight 
 film of it is reduced to the metallic state, the great mass being brought 
 only to the state of tantalic oxide, TaO 2 . This substance is grey. It 
 is insoluble in all acids. 
 
 The similarity of tantalum to silicon is very great ; it resembles it 
 in forming with fluorine and potassium a double fluoride from which 
 the metal is obtained. 
 
 Some slight differences of character had been always remarked between 
 the tantalic acid extracted from the American and from some of the 
 European tantalites, and recent researches by Henry Rose have shewn 
 those differences to arise from the presence of some new bodies, acids 
 analogous to the tantalic and having metallic bases. To these metals, 
 as belonging to the tantalic family, the names niobium and pelopium 
 have been given. Their history is as yet not complete. 
 
 Niobium. The niobic acid is prepared from the American or Bava- 
 rian tantalites, as the tantalic acid is prepared from the Swedish minerals, 
 It is a white powder. Its characteristic distinctions from the true tan- 
 talic acid is that the niobate of soda is a soluble salt. Tincture of galls 
 give with tantalic acid liquors a clear yellow, and with niobic acid an 
 orange red colour. By yellow prussiate of potash tantalum is precipi- 
 tated yellow and niobium red. Tantalum gives with red prussiate of 
 potash a white, whilst niobium gives a dark yellow precipitate. 
 
 If a salt of tantalic acid be rendered acid by some muriatic acid, and 
 a slip of zinc be introduced, there is no change of colour, but tantalate 
 of zinc gradually deposits as a white powder. With a salt of niobic 
 acid similarly treated a fine blue colour is produced, which finally 
 becomes brown, and a brown precipitate falls. 
 
 Pelopium. The oxygen compound of this metal, pelopic acid, exists 
 with the niobic acid. The separation is effected by mixing the acid 
 with charcoal powder and passing chlorine over the mixture at a red 
 heat, with the apparatus figured in page 451, for the preparation of 
 chloride of silicon. Chlorides of niobium and pelopium are produced, 
 but the latter being much the more volatile it sublimes into the more 
 distant and colder part of the tube, and can be obtained there pure. 
 
 This chloride of pelopium is yellow ; it absorbs ammoniacal gas: when 
 the compound is ignited, water and muriatic acid gas are evolved and 
 metallic pelopium remains. The chloride is decomposed by water, mu- 
 
Titanic Acid and Titanic Oxide. 531 
 
 riatic acid and pelopic acid being produced. If the pelopate of soda 
 be heated with sulphuret of hydrogen, the pelopic acid is converted 
 into sulphuret of pelopium. Niobate of soda acts similarly,, but if the 
 tantalate of soda be used, the soda only is converted into sulphuret, the 
 tantalic acid remaining unaltered. 
 
 Ilmenium. In analysing another new mineral of the group of tanta- 
 lites, Hermann considered that he had discovered another new metallic 
 acid to which he gave the name ilmenic acid, and to its metallic basis 
 the name ilmenium. But Rose asserts that the ilmenic acid is only 
 niobic acid contaminated by the presence of tungstic acid. The evidence 
 of the real distinctiveness of this body must therefore be left to addi- 
 tional researches to decide. 
 
 The pelopic acid is replaced in this new mineral (Samarskite) by oxide 
 of uranium, and as the tantalic, niobic, and pelopic acids all replace each 
 other, it is probable that they have all analogous formulae to that of 
 oxide of uranium, the complex nature of which has been shown by the 
 recent researches of Peligot. See page 551. 
 
 TITANIUM. 
 Symbol. Ti. Eq. 24'3 or 303'7. 
 
 This metal, although not met with in large quantities, is yet found in 
 a gpeat variety of minerals. It has not been found native in a metallic 
 state but combined with oxygen, forming titanic acid. To obtain me- 
 tallic titanium, the volatile perchloride is employed. This body absorbs 
 ammonia, forming a white substance, Ti.Cl 2 -f 2.NHa, which when heated 
 to redness gives metallic titanium, with sal-ammoniac and nitrogen, the 
 hydrogen carrying off the chlorine. The metal is of a bright copper colour, 
 almost perfectly infusible. Titanium exists in most of the clay iron 
 stone, and hence being reduced during the smelting of the iron, is found 
 in the slags, crystallized in cubes of excessive hardness and brilliancy, 
 sp. gr. 5*3. This metal is not acted upon by any acid except a mixture 
 of nitric acid with hydrofluoric acid, and is oxidized, but very slowly, 
 by melted nitre. It is perfectly unalterable in the air. Its symbol 
 is Ti. Its equivalent numbers 303*7 or 24*3, and it combines with 
 oxygen in two proportions. 
 
 Titanic Acid. TiO 2 . Exists native, constituting the mineral rutile, 
 isomorphous with tin stone (SnO 2 ), and also in the mineral anatase. 
 More abundantly it is found in the titanic iron, ilmenite, the formula of 
 which is FeO.Ti0 2 , and which is very remarkable, from having the same 
 crystalline form as peroxide of iron Fe 2 O 3 , so that the titanium would 
 appear to replace the second atom of iron, and the formula to be 
 
532 Properties of Arsenic. 
 
 Fe.Ti -f-O 3 . This is merely speculative, however, as iron is never isomor- 
 phous with tin, and in no case with titanium, and I hence consider 
 this instance as one of the coincidences of form described in pages 360 
 and 367. 
 
 Titanic acid is artificially prepared from the titanate of iron by igniting 
 it with sulphur. The oxide of iron and sulphur form sulphurous acid 
 and sulphuret of iron, and when this last is dissolved out by muriatic 
 acid, the titanic acid remains behind. It requires other processes to 
 render it absolutely pure which need not be described here. It is a 
 pure white powder, resembling silica very remarkably in its properties, 
 and like it having a soluble and insoluble modification. It is remark- 
 ably characterized by its solution in muriatic acid, giving with tincture 
 of galls an orange precipitate, and by the immersion of a slip of zinc a 
 fine purple powder which is oxide of titanium, Ti.O ; the second atom 
 of oxygen being removed from the acid by the nascent hydrogen. This 
 oxide of titanium may also be procured by igniting titanic acid with 
 charcoal ; it is then a black powder insoluble in all acids. 
 
 The Bisulphuret of Titanium. Ti.S 2 . Is a strong sulphur acid, but 
 not otherwise important. 
 
 OF ARSENIC. 
 Symbol, As. Eq. 75*34 or 940-1. 
 
 This metal exists in nature in a great variety of forms, and in con- 
 siderable quantity. It is found native, but more generally combined 
 with other metals, as nickel, cobalt, iron ; being considered, like oxy- 
 gen and sulphur, as a mineralizer of other metals. Combined with 
 sulphur it constitutes the native orpiinent and realgar ; and with oxygen, 
 as arsenic acid, it is united with metallic oxides in the native arseniates 
 of lime, of iron, of lead, &c. The great proportion of the arsenic of 
 commerce is obtained in the roasting of the cobalt and nickel ores, as 
 described in p. 468. The current of hot air which has passed over the 
 ignited ore carries with it, into a series of large chambers, the volatile 
 arsenious acid, which is deposited under the form of a fine greyish 
 powder on the walls and floor. This is discoloured by some of the 
 oxide of the fixed metals, which is carried over mechanically by the 
 draught, and it is, therefore, resublimed in iron vessels, the covers of 
 which are allowed to become so hot that the arsenious acid, in con- 
 densing, shall aggregate itself into a vitreous mass, in which state it is 
 sent into commerce. 
 
 The metallic arsenic may be prepared from the arsenious acid in many 
 
Arsenious Add. 533 
 
 ways, but best by mixture with three times its weight of black flux 
 (p. 469) in a crucible, or earthenware retort, which is then to be heated 
 to redness. If a crucible be used, another cold crucible, somewhat 
 larger, must be inverted over it, on the inside of which the metal con- 
 denses, but with a retort it is deposited in the neck as an irregular mass 
 of rhombohedrons, variously modified. It is very brittle ; its sp. gr. 
 5'96. It sublimes at 356 P. without previously melting. The sp. 
 gr. of its vapour is 10362. Its vapour, if in contact with the air, has 
 a very characteristic garlic odour ; which, however, belongs not to the 
 pure metal, but to an oxide produced by a low degree of combustion 
 which occurs. In the air it gradually absorbs oxygen, and falls into a 
 grey powder (suboxide, fy powder). By nitric acid it is rapidly oxi- 
 dized, and deflagrates violently in melted nitre. In fine powder it 
 burns spontaneously in chlorine gas, with a brilliant white flame, and 
 burns similarly when heated in oxygen gas. The symbol of arsenic is 
 As, and its equivalent numbers 940*1, or 75*34. 
 
 Arsenic combines with oxygen in three proportions, forming a sub- 
 oxide, of which the composition is not known. Many chemists look 
 upon it as a mere mixture of metal and arsenious acid, for when it is 
 heated it separates into these bodies. The other degrees of oxidation, 
 the arsenious acid and arsenic acid, are of great importance. 
 
 Arsenious Acid. White Arsenic. Oxide of Arsenic. As.0 3 . 
 Equivalent 1240*1 or 99*34. Is found in commerce in masses, which, 
 if recently sublimed, are perfectly colourless and transparent, but 
 gradually become milk white and opaque. In general, the outer por- 
 tions of the commercial masses have thus changed whilst the interior 
 retains its original transparency. This alteration is probably connected 
 with the dimorphism of arsenious acid, (p. 3 15,) for the acid in these 
 conditions differs in density and in solubility. The transparent acid has 
 sp. gr. 3*74, and 100 parts of boiling water dissolve 9*68 parts of it; but 
 the opaque acid is of sp. gr. 3*69, and 11*47 of it are soluble in 100 
 parts of boiling water. A solution of the vitreous acid reddens litmus 
 paper, but that of the opaque acid restores, though feebly, the blue 
 colour of litmus paper already reddened by an acid. The taste of arsen- 
 ious acid is not marked, but rather slightly sweet : it leaves upon the 
 palate, however, an acrid sensation. 
 
 The arsenious acid sublimes at 380 P. without previously melting. 
 Its vapour is of sp. gr. 13670, being produced by 
 
 One volume of vapour of arsenic, = 10362-0 
 Three volumes of oxygen, . = 3307'8 
 
 the four volumes forming one, . = 13669'8 
 
534 Arsenious and Arsenic Acids. 
 
 If it be very slowly sublimed, it condenses in regular octohedrons of 
 exceeding brilliancy. It is, however, sometimes found, in the roasting 
 of its ores, in crystals belonging to a different system (the rhombohe- 
 dral). Arsenious acid is dissolved by liquid muriatic acid in large 
 quantity, but crystallizes from that solution in octohedrons. If the 
 opaque acid had been employed, the crystallization is not peculiar ; but 
 if it had been the transparent variety, the deposition of every crystal 
 is accompanied by a sudden flash of light, very brilliant in the dark. 
 The crystals so produced belong to the opaque kind, so that it would 
 appear as if at the moment of deposition the particles changed their 
 mode of arrangement, so as to pass from the transparent to the 
 opaque dimorphous form, and that the alteration in molecular con- 
 stitution occasioned the evolution of light, and probably of heat and 
 electricity. 
 
 The arsenious acid combines with bases to form salts, which are, 
 however, of such unstable constitution that they are but little known. 
 It is particularly of importance from its highly poisonous properties, 
 and from its being, more frequently than any other substance, adminis- 
 tered to produce death. Its recognition is, therefore, to the medical 
 chemist, one of the most important problems in analysis, and will 
 be fully discussed when the other combinations of arsenic have been 
 described. 
 
 Arsenic Acid. As0 5 . Equivalent 1440*1, or 115-34. To obtain this 
 acid, eight parts of arsenious acid are to be placed in a retort with two 
 parts of strong muriatic acid, and boiled, whilst twenty-four parts of 
 dilute nitric acid of sp. gr. 1*25 are to be added in small quantities at 
 a time. The mixture is to be distilled in a retort to the consistence of 
 a syrup, and then transferred to a platina dish, in which it is to be 
 evaporated to perfect dryness, and heated until all traces of nitric acid 
 are expelled. The residual mass is milk white, but anhydrous, arsenic 
 acid. The heat should not be raised to near redness, for then the 
 arsenic acid is decomposed into arsenious acid and free oxygen. The 
 mass thus obtained dissolves but slowly in water, but ultimately the 
 solution is complete ; the arsenic acid has even so much affinity for 
 water as to deliquesce rapidly in vessels which are not kept carefully 
 closed. 
 
 The arsenic acid reddens litmus paper strongly, and forms with the 
 alcalies perfectly neutral salts. At a high temperature it is capable of 
 expelling all the volatile acids, even the sulphuric acid, from their com- 
 binations. In its compounds it resembles very closely the phosphoric 
 acid ; but it appears capable of forming only one of the three classes of 
 salts which phosphoric acid produces. The arseniates are all tribasic, 
 
Arseniuret of Hydrogen* 535 
 
 but as the quantity of fixed base varies, there are some neutral and 
 others acid arseniates; the latter were formerly called binarseniates. 
 Thus there are, 
 
 3NaO -f- AsOa -{- 24 aq. called subarseniate of soda, 
 
 2NaO. HO. -f- AsOo -|- 14 aq. neutral arseniate of soda, 
 NaO. 2HO -f, AsOj -f 2aq, binarseniate of soda ; 
 
 but the quantity of base is really constant, being in each three atoms, 
 made up partly of water and partly of soda. 
 
 The arsenic acid is recognized by being precipitated golden yellow by 
 sulphuretted hydrogen. The precipitate dissolves instantly in ammonia, 
 and even in an excess of sulphuret of hydrogen ; so that it may not be 
 visibly produced, if the quantity of arsenic be small, until the liquid 
 shall have been well boiled, A solution of any arseniate gives with 
 nitrate of silver a brick-red powder, arseniate of silver, 3AgO-f AsO 5 , 
 the formation of which is easily explained. An insoluble arseniate 
 heated in a glass tube with charcoal powder gives a sublimate of 
 metallic arsenic. 
 
 Arseniuret of Hydrogen. It has been supposed, that when metallic 
 arsenic is used as the negative electrode of a voltaic battery, the 
 hydrogen evolved combines with it, and forms a brown powder, 
 hydruret of arsenic. The same body was supposed to be generated 
 in other ways ; but it is most usually believed that this substance is 
 only metallic arsenic finely divided, and that there is but one com- 
 pound of arsenic and hydrogen, the gaseous arseniuret of hydrogen, AsH 3 . 
 
 This compound is easily obtained whenever nascent hydrogen comes 
 into contact with metallic arsenic ; thus when an alloy of equal parts of 
 zinc and arsenic is dissolved in dilute sulphuric acid, the hydrogen 
 evolved combines with the arsenic, 3(S0 3 + HO) and Zn 3 As, produc- 
 ing 3(S0 3 + ZnO) and H 3 As. It is still more easily prepared, by add- 
 ing muriatic acid to a solution of arsenious acid in water, and immers- 
 ing therein a piece of zinc; the hydrogen first evolved reduces the 
 arsenious acid, and the metal is then separated as a fine brown powder, 
 with which the hydrogen next evolved combines. This gas is generally 
 stated to have a very disagreeable odour, which, however, I have not 
 found it to possess. It is exceedingly poisonous ; it burns with a bril- 
 liant white flame, water being formed, and arsenious acid or metallic 
 arsenic being deposited according to the supply of oxygen to the gas ; 
 it is not absorbed by water; its specific gravity is 2694, formed by 
 
 One volume of arsenic vapour = 10362*0 
 
 Six volumes of hydrogen 69 3 X 6, = 415-8 
 
 The seven being condensed to four 
 Of which one weighs, 
 
536 Arseniuret of Hydrogen. 
 
 Arseniuret of hydrogen decomposes most metallic solutions, preci- 
 pitating metallic arseniurets of corresponding constitution (R 3 .As). If 
 a current of it be passed over chloride of copper, heated to about 400, 
 it is decomposed, H 3 As and S.CuCl giving Cu 3 As and 3.HC1. This gas 
 is absorbed by dry sulphate of copper, which it decomposes, water being 
 evolved, and a blackish compound of sulphuric acid and arseniuret of 
 copper being produced. This property is made available in the medico- 
 legal examination of substances containing arsenic. If a fragment of 
 chloride of mercury be heated in this gas, it is rapidly decomposed, 
 muriatic acid gas and arseniuret of mercury being formed. At a full 
 red heat, the gas is decomposed completely by itself, so that if a single 
 point of a tube, through which it streams, be ignited, all the arsenic is 
 deposited beyond that point, in the metallic state, and only pure hydro- 
 gen passes on. 
 
 Sulphur and arsenic combine in several proportions ; the lisulphuret 
 of arsenic AsS 2 , exists native, forming the mineral realgar. It may be pre- 
 pared by fusing the following sulphuret with metallic arsenic, and sub- 
 liming the product. It is a ruby-red crystalline mass; when it is 
 digested in solution of caustic potash, a blackish powder remains, which 
 may be looked upon as subsulphuret ; its definite nature is problema- 
 tical. The tersulplmret of arsenic AsS 3 yellow arsenic, orpiment, is 
 found native, and may be easily prepared by decomposing a solution of 
 arsenious acid with sulphuret of hydrogen, As.O 3 and 3.HS. giving 
 As.S 3 and 3. HO. It is a rich yellow powder; when heated it melts, 
 and in close vessels sublimes unaltered, but otherwise it burns, partly 
 forming arsenious and sulphurous acids ; it is not quite insoluble in 
 water. It is insoluble in acids, and best precipitated from an acid 
 liquor. It is a strong sulphur acid, combining with the sulphur bases 
 to form salts, sulpJw-arsenites. It hence dissolves readily in hydrosul- 
 phuret of ammonia, and also in the caustic alcalies. In the last case, 
 there exists in solution, an ordinary arsenite, besides the sulphur salt ; 
 for, using potash, 2.AsS 3 and 6.KO. produce (AsS 3 -f 3.KS) and 
 (As0 3 -{- 3KO). When sulphuret of arsenic is ignited with black flux, 
 metallic arsenic sublimes, and the separation of the metal is still more 
 elegantly effected by heating the sulphuret mixed with carbonate of 
 potash in a current of dry hydrogen gas. 
 
 The persulphuret of arsenic, As.S 5 . corresponds to the arsenic acid, 
 and is prepared by decomposing a solution of it, or of any of its salts, 
 by sulphuretted hydrogen. It is yellow, paler than orpiment ; sublimes 
 without alteration in close vessels ; is a strong sulphur acid, and hence 
 dissolves in solutions of the alcaline hydrosulphurets, forming sulplio- 
 arseniates ; the metal may be eliminated from it by the same means as 
 those described for orpiment. 
 
Sulphur els of Arsenic. 537 
 
 A substance sold in this country for killing flies, under the name of 
 king's yellow , is, or ought to be, orpiment. The best sort is made by 
 boiling together lime, sulphur, and white arsenic ; but much of it con- 
 sists merely of white arsenic coloured by some sulphur mixed with it. 
 Erom the facility with which it may be obtained, and the manner in 
 which it is left exposed, it is very frequently the source of fatal accidents. 
 
 Notwithstanding the scientific importance which arsenic possesses 
 from the number and variety of its compounds, it is of much higher 
 interest in consequence of the frequent necessity for the detection of 
 excessively minute traces of it in cases of suspected poisoning, where a 
 responsibility, involving the life of a fellow-creature, rests on the skill 
 and accuracy of the medical chemist. The detection of arsenic under all 
 possible circumstances, is an object, therefore, to which all the powers 
 of analysis should be brought to bear, and the methods at our disposal 
 appear, if properly applied, to be satisfactory and complete. In a ques- 
 tion so grave as this, no colours of precipitates, however so marked, 
 no arrangement of mere results by test, no matter how corroborative, 
 should be considered as by themselves decisive ; the object of the 
 chemist should be, the isolation and production of the metallic arsenic, 
 and where this has not been done, it is certain that either there is no 
 arsenic present, or that the skill of the operator cannot be absolutely 
 relied on. 
 
 In poisoning by arsenic, the substance used is almost universally 
 arsenious acid. To this, therefore, I shall confine my remarks at 
 present ; I shall afterwards notice the peculiarities of its other pre- 
 parations. 
 
 The arsenious acid being a very heavy powder, and but sparingly 
 soluble, it is very rapidly deposited from any liquid through which it 
 might have been diffused, and hence, the vessels, in which food had 
 been contained, should be carefully examined for any traces of it which 
 might remain. This should not be omitted, even though they might 
 appear to have been subsequently rinsed. Any substances vomited by 
 the person suspected to be poisoned, should be carefully examined for 
 the same object ; and in case of death, the materials in the stomach and 
 its mucous surfaces must be similarly searched. The little grains of 
 arsenious acid adherent to the surface of the stomach are frequently 
 tinged yellow at the surface by sulphuretted hydrogen, if the exami- 
 nation be deferred until some time after death. 
 
 In case of such traces of white powder being found, the examination 
 is very simple. If it be arsenious acid, the properties are : 
 
 1st. Heated alone in a glass tube, the powder sublimes and condenses 
 in minute brilliant octohedrons. 
 
538 Detection of Arsenic. 
 
 2nd. Mixed, in a tube closed at one end, with a little black flux, 
 and ignited, metallic arsenic sublimes, forming a steel-grey crust, 
 brilliant on the side next the tube, but dull and crystalline on the inside. 
 On applying the nose to the open end of the tube and inspiring, a garlic 
 odour is perceived. 
 
 3rd. On cutting off the sealed end of the tube;, and then heating 
 the part containing the metallic crust, the tube being slightly inclined, 
 the metal disappears, and a crust of white arsenic condenses a little 
 higher up. A current of air passes through the tube, with the oxygen 
 of which the metal combines. In this process, the garlic smell becomes 
 more marked than in No. . 
 
 4th. The white powder dissolves in boiling water. It yields pre- 
 cipitates with the following reagents : 
 
 A. Sulphuretted Hydrogen. A rich yellow : soluble in ammonia, 
 and precipitated on the addition of an acid. This precipitate is 
 
 B. Ammonia-nitrate of Silver. A canary yellow : arsenite of silver. 
 This reagent is very delicate, but the precipitate is soluble both in acids 
 and ammonia, so that an excess of either must be avoided. 
 
 C. Ammonia-sulphate of Copper. A fine apple-green. This is re- 
 dissolved also by an excess of acid or of ammonia. 
 
 Each of these liquid re-agents is liable to fallacy ; which must be 
 guarded against. 
 
 A. Sulphuretted Hydrogen gives precipitates more or less resembling 
 that from arsenic with the following metals : 
 
 Cadmium. Antimony. 
 
 Tin (persalts.) Iron (persalts.) 
 
 The precipitate from cadmium is not soluble in water of ammonia. 
 
 The precipitate from tin, when dried and ignited with black flux, 
 gives no sublimate of metal. 
 
 The precipitate of antimony acts in the same way as tin, but also it 
 dissolves in strong muriatic acid, and the solution, diluted with much 
 water, gives a white precipitate. The sulphuret of antimony is much 
 more orange-coloured than that of arsenic. 
 
 The precipitate from a persalt of iron is pure sulphur ; heated, it 
 melts and burns completely away, without forming any solid product. 
 
 B. Ammonia-nitrate of Silver. Phosphate of soda produces a yellow 
 precipitate of tribasic phosphate of silver, exactly resembling the 
 arsenite. It is, however, much more soluble in ammonia. They are at 
 once distinguished by being collected and ignited. The arsenite gives 
 
Liquid Tests for Arsenic. 539 
 
 off oxygen and arsenious acid, whilst metallic silver remains, but the 
 phosphate gives no volatile product. 
 
 C. The ammonia sulphate of copper is uncertain, unless it be dried 
 and reduced, for there are numerous basic compounds of copper, which 
 resemble it very much in colour. 
 
 None of these liquid re-agents are, therefore, in themselves positive, 
 unless by extraction of the metal ; and this is the more important when 
 the operator has to work, not with the clear solutions prepared inten- 
 tionally for illustration, but with the complex and discoloured liquids 
 obtained from the stomach and intestines. 
 
 The process to be then followed may be either of two kinds; the first 
 consists in converting the arsenic into sulphuret, the second into arse- 
 niuret of hydrogen. I shall describe each in their turn. 
 
 The contents of the stomach and small intestines, or the matter 
 ejected by vomiting during life, are to be boiled in distilled water for 
 half an hour, and then the liquor strained through a linen cloth. If it 
 be too thick or coloured, to allow of a small quantity of precipitate 
 being observed and separated, a current of chlorine gas is to be passed 
 through it, by which most of the animal matter dissolved is coagulated, 
 and a more convenient solution obtained. This being strained or 
 filtered, is to be well boiled to expel the excess of chlorine, and then 
 submitted to the action of a current of sulphuretted hydrogen gas. The 
 animal matters may also be removed from the solution, by rendering it 
 acid by nitric acid, and then adding an excess of nitrate of silver. 
 When the precipitate which forms has been separated, the excess of 
 silver is to be thrown down by some common salt, and the liquor being 
 then filtered, is fit for the action of the sulphuretted hydrogen. 
 
 When the liquor smells strongly of this gas, there has been enough 
 passed through, and it is then to be boiled briskly for a few minutes to 
 expel the excess, and favour the deposition of the precipitate produced. 
 This is to be then collected on a filter, washed carefully with water aci- 
 dulated by muriatic acid, and then dried at a moderate heat. 
 
 When completely dry, it is to be mixed with about twice its bulk of 
 black flux, and ignited in a small tube of hard glass closed at one end. 
 In introducing the materials, care must be taken not to soil the side of 
 the tube ; metallic arsenic sublimes, which is recognized by the characters 
 given already in pages 533, 537. 
 
 The process by arseniuretted hydrogen was first proposed by Mr. 
 Marsh, and has been found of surprising delicacy and exactness ; the 
 liquid having been freed from animal matters and obtained as thin a 
 fluid as possible by either of the processes, by chlorine or nitrate of 
 silver, already described ; it is rendered moderately acid by muriatic or 
 
540 Arseniuretted Hydrogen. 
 
 sulphuric acid, and introduced into a flask or bottle, to the neck of 
 which is adapted a narrow tube of hard glass, which after passing hori- 
 zontally for a few inches, turns up and forms a jet ; a piece of zinc 
 being introduced into the acid liquor, hydrogen is evolved, which com- 
 bines with any arsenic that may be present, and forming the gaseous 
 arseniuret of hydrogen passes off. "When the gas issuing from the jet 
 is set on fire, if the hydrogen be pure, no other product is generated 
 but water ; but if a slight trace of arsenic be present, the flame is 
 whitish, and holding over the jet a fragment of glass or porcelain, or a 
 film of mica, a deposit is produced, which may be white from the arseni- 
 ous acid, or brown from metallic arsenic, according to the height at 
 which the plate is held, and the consequent completeness of the com- 
 bustion, or the reverse. If the quantity of arsenic be too small to pro- 
 duce this effect in a certain time, it may be better detected by igniting 
 a portion of the horizontal arm of the tube. All the arseniuretted 
 hydrogen, in passing that point, deposits its arsenic, which is carried a 
 little beyond the heated portion by the current, and condenses there as 
 a distinct metallic film ; as the tube may be kept thus red hot for some 
 hours, the smallest trace of arsenic may be thus concentrated on a 
 single point, and its properties accurately verified. 
 
 "Where the liquor is still thickish from dissolved organic matter the 
 gas bubbles would not break rapidly, but form a froth, which passing 
 into the tube, would prevent altogether the successful employment of 
 the methods just described. In this case the liquid should be made so 
 slightly acid as that the gas shall be generated but very slowly, and that 
 there shall be but little hydrogen in excess. The tube, in place of ter- 
 minating in a jet, is to be bent down so that it shall pass under the 
 edge of a jar in the pneumatic trough, and, the apparatus being so left 
 for any length of time, the gas evolved may be collected and subse- 
 quently examined ; or, what is perhaps still better, the tube may dip 
 under the surface of a dilute solution of nitrate of silver or of sulphate 
 of copper, and all the arseniuretted hydrogen being then absorbed and 
 decomposed, metallic arseniurets are produced, which easily yield the 
 arsenic in the metallic form by the application of heat. 
 
 The removal of organic matter, which is almost indispensable for the 
 management of the regular disengagement of gas, may best be effected 
 by combining the agencies of chlorine and of sulphuric acid, as already 
 referred to. In destroying organic acid by oil of vitriol alone, it being- 
 necessary to evaporate to dryness for perfect carbonization, there might 
 be danger of some arsenic being lost, and, on the other hand, the pro- 
 ducts of the action of chlorine on animal substances impart themselves 
 frequently a disagreeable viscidity to the liquor. The mass should, 
 
Sources of Fallacy in detecting Arsenic. 541 
 
 therefore, be first disorganized by oil of vitriol, and evaporated to the 
 consistence of paste; then diluted with water, and subjected to the 
 action of a current of chlorine for some time. On being filtered, the 
 liquor will be found clear and limpid, and in the best circumstances for 
 the satisfactory employment of Marsh's test. 
 
 In this mode of detecting the presence of arsenic, it is necessary to 
 avoid some sources of error into which, without previous knowledge of 
 their existence, an operator might easily fall. If the effervescence be 
 rapid, it frequently happens that very minute portions of zinc, or of 
 the salt of zinc generated, may be carried up by the stream of gas, and, 
 being deposited upon the plate, form a crust, which might lead to sus- 
 picion, or perhaps to wrong conclusions. This may be avoided by 
 either moderating the effervescence, or by passing the gas before using 
 it through a tube filled loosely with cotton, by which it is filtered, as it 
 were, and all mechanically diffused particles separated. Much more 
 important sources of error arise, however, from the existence of arsenic 
 in most of the zinc and some of the sulphuric acid of commerce. The 
 ores of zinc occasionally contain orpiment, which being reduced along 
 with the other sulphuret, it is necessary to distil the zinc in order to 
 have it pure, and to reject it as long as it contains arsenic. The iron 
 pyrites also occasionally contains traces of orpiment, and this passes 
 into the oil of vitriol. In employing this method it is necessary, there- 
 fore, to test the purity of the zinc and sulphuric acid by the method 
 itself. A jet of the hydrogen, evolved from the zinc and dilute sul- 
 phuric acid simply, should be burned, or the gas passed through a 
 solution of ammonia-nitrate of silver for a quarter of an hour. If no 
 trace of deposition of arsenic occur, the materials may be considered as 
 pure, and the suspected liquor may then be employed with confidence 
 in the result. 
 
 A more remarkable source of error arises from the fact, that the 
 compounds of antimony yield, under similar circumstances, a precisely 
 similar gas, antimoniuret of hydrogen. It would anticipate too much 
 the history of that metal to enter into the details of the means of dis- 
 tinguishing that gas from the arseniuretted hydrogen, but they will be 
 fully described in their proper place. 
 
 Arsenious acid possesses the power of preventing the putrefaction of 
 animal substances, and hence the bodies of persons that have been 
 poisoned by it, do not readily putrefy. The arsenious acid combines 
 with the fatty and albuminous tissues to form solid compounds which 
 are not susceptible of alteration under ordinary circumstances. It hence 
 has frequently occurred, that the bodies of persons poisoned by arsenic 
 have been found, long after death, scarcely at all decomposed, and even 
 
542 Action of Arsenic on the Body. 
 
 where the general mass of the body had completely disappeared, the 
 stomach and intestines had remained preserved by the arsenious acid 
 which had combined with them, and by its detection the crimes com- 
 mitted many years before were brought to light and punished. In the 
 cases where the whole body has been found fresh, it resulted from the 
 person having survived for a length of time sufficient for the complete 
 permeation of the tissues by the absorption of the poison ; in the others 
 death has occurred whilst it was yet only in the intestinal tube. The 
 absorption of the arsenious acid in cases where death has not been rapid, 
 renders its detection possible in all the various organs, particularly where 
 the poisoning has been produced, not by the administration of a single 
 dose, but by frequently repeated doses, each insufficient to produce 
 rapid poisoning. The decision in such cases is rendered, however, ex- 
 tremely difficult by the disco very, recently announced, that the resemblance 
 of function, so often alluded to, between arsenic and phosphorus, is such, 
 that the latter element, which characterizes the animal tissues by its 
 almost constant presence, may be replaced as a constituent of our organs 
 by arsenic. Thus, that the bones may contain traces of arseniate of lime, 
 as a substitute for some of their proper phosphate of lime, and that in 
 the phosphoric salts, which are found in the blood, a similar replace- 
 ment may occur. It is certain that the quantity of arsenic thus found 
 naturally replacing phosphorus in the body is very small, but there is no 
 necessary limit to its extent, and although in cases of suspected chronic 
 poisoning, the analysis of the organs might lead to useful evidence, yet 
 the discovery of arsenic out of the alimentary organs should, as I con- 
 ceive, not without great caution, be considered as necessarily involving 
 its having been administered. 
 
 The sulphuret of arsenic of commerce, fang's yellow, when taken as 
 a poison, is recognized by its solubility in ammonia, from which it is 
 again thrown down by an excess of any acid. Its reduction to the me- 
 tallic state has been already fully described. 
 
 An antidote has been recently discovered to the poisonous effects of 
 arsenious acid, which is founded on a very remarkable reaction. "When 
 hydrated peroxide of iron is made into a thin paste with solution of ar- 
 senious acid, this disappears, being changed into arsenic acid and the 
 iron protoxide, 2.T?e 2 O 3 and AsO 3 producing 4.EeO -f. AsO 5 . This ar- 
 seniate of iron has no action on the system ; and hence, in cases of 
 poisoning by arsenic, this hydrate of peroxide should be administered 
 as largely and as rapidly as possible. It may be made in a few mo- 
 ments by adding carbonate of soda to any salt of red oxide of iron 
 (permuriate, muriate, or acetate tincture.) It need not be washed, as 
 the liquor contains only a salt of soda, which would be, if not beneficial, 
 certainly not injurious. 
 
Antidotes to Arsenious Aid. 543 
 
 Another antidote recently proposed for arsenic is the hydrate of mag- 
 nesia, described in page 488. The experimental evidence of its utility 
 has been brought forward by Bussy, and appears to be of a very satis- 
 factory nature. 
 
 The preparations of arsenic are of very extensive use in the arts. 
 The metal is used to alloy the lead of which shot is made. White 
 arsenic is employed in glass-making to prevent the deoxidation of the 
 oxide of lead, and the orpiment is employed to render indigo soluble in 
 some processes of dying. It has many other less extensive uses. 
 
 OF ANTIMONY. 
 Symbol. Sb. Eq. 129*2 or 1613. 
 
 This metal was first discovered, and its preparations introduced into 
 medicine by Basil Yalentine, from the unpleasant results of whose expe- 
 riments upon his fellow monks, it got the name anti-moine ; its proper 
 Latin name is stibium, and hence its symbol, Sb. Antimony exists in 
 nature, principally as sulphuret, sometimes as oxide, and also, these two 
 combined, forming the oxysulphuret, red antimonial ore. It is from 
 the native sulphuret that the metal is prepared. The process for ob- 
 taining it by means of iron, is noticed p. 466, but it is had purer by 
 fusing the sulphuret at a bright red heat with black flux. Sulphuret of 
 potassium and oxide of antimony are first formed, and this last being 
 decomposed by the carbon, carbonic oxide is evolved and metallic anti- 
 mony separates ; this process is further detailed in p. 469. 
 
 The antimony thus obtained is a brilliant white metal, of a highly 
 crystalline fracture, and may be obtained crystallized in rhombohedrons 
 like those of arsenic, by fusion, as described in p. 21 ; its specific gra- 
 vity is 6*8 ; it melts at about 800, just below redness, and may he 
 volatized by a white heat. If heated violently in contact with air it 
 takes fire, burning with a brilliant white flame, and forming antimonious 
 acid, which, though not volatile, is carried up by the current of air, and 
 is deposited on the neighbouring bodies as a white powder, flowers of 
 antimony. Antimony in powder takes fire spontaneously in chlorine, 
 burning with a yellowish flame ; the antimony is not oxidized by ex- 
 posure to the air nor by water ; it is not acted on by sulphuric nor mu- 
 riatic acids, but is rapidly oxidized by nitric acid. The symbol of anti- 
 mony is Sb. Its equivalent numbers 1613 or 129*2 ; it combines with 
 oxygen in three proportions. 
 
 * Oxide of Antimony. SbO 3 . Equivalent 1913 or 153*2, may be 
 prepared by adding, to an acid and boiling solution of chloride of anti- 
 mony in water, carbonate of soda in excess. The carbonic acid does 
 
544 Antimony and its Oxides. 
 
 not combine with oxide of antimony, which, therefore, precipitates 
 pure ; it is a white powder, not quite insoluble in water, and becomes 
 yellowish when heated. If metallic antimony be burned in a limited 
 supply of air, this oxide forms, and has been obtained crystallized both 
 in the prismatic and octohedral forms of arsenious acid, with whicjj it 
 is, therefore, isodimorphous ; both the metal and this oxide, when ig- 
 nited in a full supply of air, produce antimonious acid. 
 
 This oxide of antimony combines with acids to form salts of very 
 little stability, but it produces with the acid potash salts of the ve- 
 getable acids, double salts of remarkable constitution ; of these the pot- 
 ash tartrate of antimony (tartar emetic) is the most important ; it also 
 may act as a feeble acid ; thus, if in its preparation, caustic potash be 
 used to decompose the chloride, a granular white powder is obtained, in 
 which the oxide of antimony is combined with potash ; it is on this ac- 
 count called, hypo-antimonious acid by many chemists. 
 
 When a strong solution of tartar emetic is decomposed by a galvanic 
 battery, a black powder is deposited on the positive pole, which appears 
 perfectly homogeneous. It is resolved by acids or by heat into oxide of 
 antimony and metallic antimony. It is stated by Marchand to be a 
 suboxide of antimony with the formula Sb 3 O 4 . 
 
 Oxysulpkuret of Antimony. Sb.O 3 -f- 2Sb.S 3 . This substance con- 
 stitutes the red ore of antimony, and may be artificially produced by 
 roasting the native sulphuret in contact with the air, the sulphur burns 
 out as sulphurous acid, and the antimony becomes oxidized ; the product 
 generally contains an excess of oxide which may be dissolved out by 
 tartaric acid, and it is thus that the basis for tartar emetic is sometimes 
 prepared; by continued roasting, the whole of the sulphur may be 
 expelled and an impure oxide of antimony produced ; this, when melted, 
 constitutes the glass of antimony, and the oxy-sulphuret is the crocus 
 of antimony of the older pharmacopoeias. 
 
 Antimonious Acid, Peroxide of Antimony. Sb04. equivalent 2013 
 161*2 ; this is the most stable compound of oxygen and antimony; it 
 is formed when antimony is oxidized freely, either by combustion or by 
 the action of nitric acid, and igniting the resulting powder. It is a 
 white powder insoluble in water ; it is not volatile ; it combines with 
 alcalies forming salts, insoluble in water, and from which, by a stronger 
 acid, it is separated as a hydrate, Sb.0 4 + HO. This hydrate dissolves 
 in strong muriatic acid. 
 
 Antimonic Acid. Sb0 5 , equivalent 2113 or 169'2. This substance 
 is first formed when metallic antimony is oxidized by an excess of nitric 
 acid, and remains as a pale yellow powder, which, when exposed to a 
 dull red heat, abandons one atom of oxygen, leaving antimonious acid, 
 
Sulphurets of Antimony. 545 
 
 as just described ; it is, however, more stable in combination, and may 
 hence be prepared by deflagrating antimony with nitre; when the 
 resulting mass is digested in cold water, nitrate and nitrite of potash 
 dissolve out, and leave the antimoniate of potash as a white powder ; 
 this is decomposed by boiling water which dissolves a basic salt, and 
 leaves one with an excess of acid behind. In its hydrated condition, 
 this acid dissolves in hydrochloric acid. 
 
 The antimonic acid is remarkable for producing with soda, the only 
 insoluble salt of that alcali. The use of antimonic acid as a test for 
 soda has been described in page 479. 
 
 Antimony and sulphur combine in three proportions, forming sul- 
 phurets, which resemble completely, in constitution, the oxygen com- 
 pounds, they are sulphur acids, dissolving in a solution of the alcaline 
 sulphurets, and forming sulphur salts. 
 
 Sulphuret of Antimony. Sb.S 3 , equivalent 2216*6 or 177*5. This 
 substance constitutes the common grey ore of antimony, and crystallizes 
 in the same form as orpiment, with which it is frequently contaminated; 
 in its native state it is dark gray with highly metallic lustre, crystalline 
 in structure, and very easily reduced to powder ; it may be prepared 
 also by precipitation from a solution of any salt of oxide of antimony, 
 as the chloride, or tartar emetic, by sulphuretted hydrogen ; it is then 
 an orange powder, which becomes darker on being dried, and has the 
 same composition as the native sulphuret, with which it becomes iden- 
 tical in appearance by fusion. This sulphuret dissolves in alcaline solu- 
 tions, on which circumstance are founded the various pharmacopceial 
 processes for its formation. It has been used in medicine every since 
 the first discovery of antimony, and in all countries ; the methods of 
 preparation, and the purity of the products obtainable, are, therefore, 
 exceedingly variable. 
 
 "When finely powdered sulphuret of antimony is boiled in a strong 
 solution of caustic potash, it dissolves, and the liquor contains two salts 
 perfectly similar to one another, but containing, the one sulphur and 
 the other oxygen, united to antimony and potassium : one-half of each 
 substance being decomposed, the oxygen passing to the antimony, and 
 the sulphur to the potassium, so that oxide of antimony, and sulphuret 
 of potassium result, and these respectively combine with the quantities 
 of potash and sulphuret of antimony that had not been altered ; so 
 that in this way, 
 
 rSb.S 3 3.KO} rSb.Sa 4. 3.KS ) 
 
 and > produce < and 
 
 ( Sb.Ss 3.KO ) ( Sb.Oa + 3.KO ) 
 
 85 
 
54G Preparation of Kermes Mineral. 
 
 When the solution cools, both compounds are partly decomposed, so 
 that a quantity of sulphuret and of oxide of antimony precipitate 
 mixed together ; and hence, an opinion has generally prevailed, and, 
 indeed, been supported by the high authorities of Liebig and Gay- 
 Lussac, that these bodies are chemically united in the precipitate so 
 obtained, and that it is an oxy-sulphuret, identical in constitution with 
 that already described. It is, however, quite established, particularly 
 by the experiments of Berzelius and H. Rose, that the oxide and the 
 sulphuret are but mechanically mixed ; under the microscope, the for- 
 mer is seen as brilliant white crystals, mixed with the fine amorphous 
 brown powder of the latter ; and, besides, the quantity of oxide is com- 
 .pletely variable, and in no case so great as the composition of the true 
 oxy-sulphuret should require. 
 
 The precipitate thus obtained by cooling, is generally of a fine orange- 
 brown colour, the exact shade of which varies very much with the tem- 
 perature, and the degree of concentration of the liquor. It is termed 
 in pharmacy Jcermes mineral, from a very remote analogy of its colour 
 to that afforded by the insect kernes, (coccus ilicis,) which is used as a 
 cheap substitute for cochineal. 
 
 After the separation of the kermes, the liquor, containing still the 
 sulphur and oxygen salts above described, but with a greater propor- 
 tion of base, is precipitated by adding an acid in excess. The sulphuret 
 of potassium is decomposed, and the sulphuret of antimony, with 
 . which it had been combined, separates ; at the same time the sulphu- 
 retted hydrogen, evolved from the sulphuret of potassium, reacts on the 
 oxide of antimony, converting it into sulphuret. This precipitate is 
 much lighter-coloured generally than the kermes, and is sometimes 
 called the golden sulphuret of antimony, although the name properly 
 belongs to a different substance to be described farther on. In many 
 cases, in place of collecting the kermes and the portion precipitated by 
 the acid separately as now described, the hot filtered liquor is added to 
 the acid before the kermes has had time to separate, and the whole 
 being then mixed assumes an intermediate shade of colour, and consti- 
 tutes the brown sulphuret, or orange sulphuret of antimony of the British 
 pharmacopoeias. 
 
 In place of caustic potash, the native sulphuret of antimony is fre- 
 . quently boiled with carbonate of soda. In this case the whole of the 
 carbonic acid unites with one-half of the soda, forming bicarbonate, 
 and the other half of the soda acts with the sulphuret of antimony pre- 
 cisely as if it had been used in the caustic state. 
 
 An important mode of preparing these pharmaceutical substances 
 consists in fusing the materials together instead of boiling their solu- 
 
Forms of Sulphur et of Antimony. 547 
 
 tions. Thus, an excellent kermes is prepared by fusing together three 
 parts of native sulphuret and one of carbonate of potash. The general 
 reaction is the same as described when the materials were dissolved ; 
 the melted mass is boiled in water, and the solution so obtained treated 
 as already noticed. Rose has, however, directed attention to a circum- 
 stance which, though occurring in all cases, is more marked in this pro- 
 cess than the others. It is, that some antimony separates in the me- 
 tallic state, whilst another portion is changed into persulphuret, thus, 
 5.SbS 3 produces 3'SbS 5 , and 2Sb is set free. The solution contains, 
 therefore, not only the ordinary sulphuret, but some persulphuret of 
 antimony, the colour of which is much brighter than that of the other, 
 and it hence modifies the tint of the preparation in a variable manner. 
 The persulphuret carries down with it also some sulphuret of potassium, 
 and hence the ordinary kermes mineral appears always to contain traces 
 of potash. The quantity of persulphuret of antimony present seldom 
 exceeds two or three per cent. 
 
 Sulpho-antimonious Acid.Sb.S 4 . This substance is produced as a 
 yellow powder when the solution of antimonious acid is decomposed by 
 sulphuretted hydrogen. 
 
 Sulpho-antimonic Acid, Persulphuret of Antimony. Sb.S 5 , is ob- 
 tained when a solution of antimonic acid in muriatic acid is treated with 
 sulphuretted hydrogen. It is of a fine golden orange colour. Its for- 
 mation in the process for kermes mineral has been already explained. 
 This is the true golden sulphuret. To obtain it in large quantity, as is 
 given in many pharmacopoeias, three parts of sulphuret of antimony 
 and one of carbonate of potash are to be fused with one-half part 
 of sulphur; this last converts the antimony into the persulphuret. 
 The fused mass is to be dissolved in water and decomposed by muriatic 
 acid. 
 
 Antimoniuret of Hydrogen. Sb.H 3 . When hydrogen is evolved in 
 contact with antimony in a nascent or finely divided state, they combine 
 and form a gas which, in properties and constitution, has a remarka- 
 ble similarity to arseniuret of hydrogen. The easiest mode of effect- 
 ing this is, to dissolve zinc in dilute sulphuric acid to which tartar 
 emetic has been added. The gas so evolved is colourless, insoluble in 
 water, has neither acid nor alcaline reaction. It precipitates the salts 
 of mercury and most metals, but not copper, by which it is distin- 
 guished from the arseniuret of hydrogen. Its specific gravity has not 
 been experimentally determined, but if it be composed, like arseniuret- 
 ted hydrogen, of one volume of metallic vapour and six of hydrogen, 
 condensed to four, it should be 4504'7. When this gas burns, water 
 is formed, and antimony deposited, either as metal or as oxide, accord- 
 
548 Antimoniuret of Hydrogen. 
 
 ing to the supply of oxygen. It hence superficially resembles in its 
 combustion the gas containing arsenic, but it is distinguished readily by 
 the following characters : 
 
 1st. The antimoniuret of hydrogen, when it is decomposed by heat- 
 ing a point of the tube, through which it passes, to redness, deposits 
 the metal at the heated part, whilst arsenic settles at a certain distance 
 beyond, only where the tube is colder. 
 
 2nd. The metallic crust is not volatilized at any temperature which 
 can be applied to glass. 
 
 3rd. If the metallic scale be deposited on a porcelain plate and oxi- 
 dized by the outer flame of the blow-pipe, it forms a powder yellow 
 whilst hot, but white when cold ; which is not volatilized by any further 
 application of the flame. Arsenic, on the contrary, becomes oxidized 
 only in the act of being vaporized. 
 
 In certain cases of compound poisoning, and where tartar emetic has 
 been given, as an emetic, in cases of poisoning by arsenic, it is possible 
 that the two metals may coexist in solution. In these cases, they may be 
 separated, either, by converting both into the hydrogen compounds, and 
 decomposing the mixed gases by igniting the tube through which they 
 pass : the antimony is deposited close to the heated part, and the 
 arsenic at a little distance ; or if the two metals be precipitated by sul- 
 phuretted hydrogen from their solution, and the mixed sulphurets be 
 dried and heated in a current of muriatic acid gas : the sulphuret 
 of antimony is decomposed, and the chloride of antimony passes off 
 and may be collected, whilst the sulphuret of arsenic remains un- 
 changed. 
 
 Erom the formation of spontaneously inflammable bubbles of gas in 
 a solution of an antimonial salt by the galvanic battery, Moreand an- 
 nounces that the antimoniuret of hydrogen, like the phosphuret, may 
 exist in different allotropic states, or may have several stages of com- 
 bination. 
 
 The detection of antimony is generally simple; in all its combi- 
 nations it is immediately recognized by the formation of its compound 
 with hydrogen just described. In solution, in the state of oxide, it 
 gives with sulphuretted hydrogen, the orange precipitate of sulphuret. 
 In the other states of oxidation the precipitates by sulphuret of hydro- 
 gen are more yellow, but are all easily distinguished from orpiment by 
 not being volatile, and from the bisulphuret of tin by yielding the anti- 
 moniuret of hydrogen. From the sulphuret of cadmium they are 
 known by their solubility in hydrosulphuret of ammonia. 
 
Tellurium and its compounds. 549 
 
 OF TELLURIUM. 
 Symbol. Te. Eq. 64'2 or 801-8. 
 
 This is one of the rarest of the metals, and although classified with 
 them from its lustre and power of conducting electricity and heat, in 
 which it is, however, far inferior to the others, it ranks naturally with 
 sulphur and selenium, to which last it assimilates completely in its pro- 
 perties. It exists in nature, native, and combined with a variety of 
 metals, gold, silver, antimony, lead, &c., forming ores of very indefinite 
 constitution. Its extraction, which is still further complicated by the 
 presence of sulphur and selenium, would require too detailed des- 
 cription, and is too seldom an object with chemists to require des- 
 cription here. Its properties and principal compounds alone deserve 
 attention. 
 
 Pare tellurium is silver white and very brilliant. It crystallizes easily 
 in rhombohedrons. It is brittle and easily powdered. Its sp. gr. is 
 6*14. It is about as fusible as antimony, and at a very high tempera- 
 ture may be volatilized. Its vapour smells like selenium ; when heated 
 in the air it burns with a bluish flame, forming tellurous acid. It is 
 rapidly oxidized by nitric acid. 
 
 The analogy of tellurium to sulphur is very close. "When tellurium 
 is boiled in a strong solution of potash, there is formed tellurite of 
 potash and telluret of potassium ; but if this solution be diluted, the 
 potassium reduces the tellurous acid and the metal is precipitated, potash 
 being regenerated. The symbol of tellurium is Te. Its equivalent 
 numbers are 801' 8 and 64- 2. 
 
 Tellurium combines with oxygen in two proportions, forming tellurous 
 and telluric acids. The former, tellurous acid, TeO 2 , is prepared by de- 
 composing the bichloride of tellurium by water, TeCl 2 and 2 HO produc- 
 ing 2.HC1 and Te0. 2 . This last precipitates as a bulky white powder 
 containing combined water. In this state it is sensibly soluble in water 
 and reddens litmus. It dissolves readily both in acid and alcaline solu- 
 tions, forming compounds of a very instable character. When its 
 solution in water is heated to about 110, it deposits the tellurous acid 
 in an anhydrous form. The water is also expelled, by a moderate heat, 
 from the hydrated acid in powder. The anhydrous acid thus obtained 
 differs essentially from the hydrated form. It is insoluble in water, in 
 acids, and in alcalies, and has no acid reaction whatsoever. No salts 
 of it can be formed in the humid way ; but if it be fused at a red heat 
 with carbonate of potash, the carbonic acid is expelled and tellurite of 
 potash formed, which dissolves in water ; from this solution the hydrated 
 tellurous acid is thrown down on the addition of an acid. 
 
550 Compounds of Tellurium. 
 
 Berzelius considers these remarkable differences of properties as indi- 
 cating an isomeric distinction between the two acids. In a subsequent 
 chapter I shall point out the manner in which I believe such compounds 
 should be viewed. 
 
 Telluric Acid. Te0 3 . Is prepared by deflagrating tellurous acid 
 with nitre ; a soluble tellurate of potash is thus obtained, which, when 
 mixed with nitrate of barytes, gives an insoluble tellurate of barytes, 
 and this, acted on by sulphuric acid, yields sulphate of barytes, and in 
 solution telluric acid, which crystallizes in large prisms, containing 
 three atoms of water. Of these, two are given off at 212 F. It does 
 not taste acid, but reddens litmus slightly. It combines readily with 
 bases, forming classes of salts containing one, two, and four equivalents 
 of acid. When the crystallized telluric acid is heated to redness, all its 
 water passes off; it becomes orange, and undergoes a change of pro- 
 perties like stannic acid. It becomes insoluble in water, in acids and 
 alcaline solutions ; when very strongly heated, it gives off oxygen and 
 tellurous acid remains : but if this anhydrous acid be fused with potash, 
 the tellurate of potash which dissolves, contains the acid in its hydrated 
 state. These forms are considered as being isomeric, and not identical 
 bodies ; their real nature will be noticed hereafter. 
 
 Tellurium and hydrogen combine to form a gas, telluret of hydrogen, 
 H.Te, which resemble in its characters, sulphuret of hydrogen, parti- 
 cularly in its odour ; it reddens litmus, is soluble in water, decomposes 
 the alcalies and earths, forming soluble tellurets, and precipitates inso- 
 luble tellurets from solutions of the other metals. 
 
 Tellurium combines with sulphur in two proportions, forming sul- 
 phurets which do not require detailed notice ; its compounds with the 
 metals resemble so completely the metallic sulphurets as to render a 
 separate account unnecessary. Thus, in every case where a metallic 
 sulphuret evolves sulphuretted hydrogen gas with an acid, the telluret 
 of the metal produces telluretted hydrogen, and the metallic tellurets 
 are soluble or insoluble in water, precisely as the sulphurets of the 
 same metals are. 
 
 OF URANIUM AND URANYLE. 
 
 This metal exists in some rather rare minerals, particularly m^pec/i- 
 llende, combined with oxygen ; the processes for its extraction are ren- 
 dered very complex by the presence of a great number of other metals, 
 and I shall refer, therefore, to the systematic works for the details of 
 its extraction. 
 
Uranium and its Compounds. 551 
 
 The substance which had been long looked upon by chemists as 
 metallic uranium, has been shown by Peligot to be really a protoxide, 
 and that the real metal is to be prepared only by the decomposition of 
 its proto-chloride by potassium; this proto-chloride being produced by 
 passing chlorine over a mixture of protoxide of uranium and charcoal, 
 strongly ignited. 
 
 True metallic uranium has a metallic lustre, like silver. It is malle- 
 able; it is very combustible, and in contact with acids decomposes 
 water, evolving hydrogen and forming the ordinary uranium salts. 
 The atomic weight of uranium is 105, and its symbol U. With chlo- 
 rine it forms a green chloride, UC1, and with oxygen the true protoxide, 
 1 T 0, which body, formerly called metallic uranium, does not appear 
 really to act as an oxide or base, but with a double atomic weight as a 
 compound radical, U 2 O 2 . Peligot considers that all the ordinary ura- 
 nium salts contain not the real metal, but tin's oxide as their radical, 
 and gives to it the name uranyle. Eor this view very strong reasons 
 have been urged. 
 
 The oxide, U 2 O 2 , may be easily prepared by the action of hydrogen 
 on any of the higher oxides at a red heat. It is a dark grey powder, 
 infusible ; it does not unite with acids : it is scarcely acted on by chlo- 
 rine or sulphur. When heated, or treated with nitric acid, it forms 
 the next oxide, formerly called protoxide of uranium, but recently 
 shewn to be a sesquioxide of the metal, although a protoxide of the 
 compound radical. 
 
 Sesqidoxide of Uranium. U 2 O 3 is obtained by decomposing any salt 
 of uranium by a caustic alcali ; it precipitates as a greenish hydrate 
 which rapidly becomes yellow, from forming the peroxide by absorbing 
 oxygen : this sesquioxide of uranium is dissolved by an excess of am- 
 monia. Its salts are very definite, and in constitution resemble salts 
 of protoxides, thus giving support to Peligot' s view of its being a 
 protoxide of the compound radical uranyle, U^O 2 -f O. Peroxide of 
 Uranium, U 2 5 is formed when the protoxide is heated in air; it 
 is yellow, and possesses some of the characters of an acid, and is 
 more properly termed uranic acid ; it reddens litmus ; it enters into 
 combination as well with alcalies as with acids ; the alcaline and earthy 
 uranates are insoluble, yellow or orange coloured. This oxide is used 
 to colour glass of a fine lemon yellow. 
 
 The sulphurets, &c., of uranium are unimportant. 
 

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 lit 
 
 IWU.PI M. 
 
 T. : 
 
 if OS.! 
 
Properties of Copper. 553 
 
 oxidizing action of the fuel be not applied long enough, some suboxide 
 remains undecomposed, which dissolves in the metallic copper. In both 
 these cases the metal is brittle, and of a bad grain, so as to be unfit for 
 many of its uses. 
 
 Copper is obtained also in the metallic state, by precipitation from the 
 water which collects in the galleries and shafts of the copper mines, and 
 which, from the oxidation of the sulphuret of copper, contains sulphate 
 of copper dissolved. Fragments of old iron are thrown into the reser- 
 voirs, in which the drainage water of the mine is collected, and by elec- 
 tro-chemical action, as described, pp. 176, 268, the iron is dissolved 
 and the copper precipitated in irregularly crystallized masses. This 
 process, by cementation as it has been termed, has been recently more 
 specially employed and conducted with arrangements for powerful gal- 
 vanic action, as described, p. 470. 
 
 Pure copper is of a peculiar well known reddish colour. It is very 
 malleable and ductile ; after iron it is the strongest of the metals. It crys- 
 tallizes by fusion in a form which is not the same as that found native, 
 or produced when the metal is precipitated from its solutions. Its sp. 
 gr. is 8'9. It is fusible at 1996. It is not volatile. In dry air it 
 is not tarnished, but in damp air it gradually becomes covered with a 
 greenish coating of basic carbonate of copper. When heated in contact 
 with air, copper combines rapidly with oxygen, and passes through a 
 variety of rainbow colours, but is at last converted into black oxide, 
 which forms as scales upon its surface. The series of colours arises 
 first from the action of light upon the thin coating of oxide, as also 
 happens in the oxidation of iron. The generality of acids do not act on 
 copper, at ordinary temperatures, unless in contact with air, for the 
 copper is incapable of decomposing water ; but at the point of contact 
 with air, oxygen is directly absorbed, and the acid combines with the 
 oxide so generated. In this way, the feeblest acids may act upon cop- 
 per, as the acetic acid and the acids contained in the various fatty bodies, 
 and the metal be thus introduced into culinary preparations, and so 
 produce poisonous effects. The acids which give off oxygen directly 
 dissolve copper, as nitric acid, with evolution of nitric oxide. Strong 
 oil of vitriol, also, when boiled on copper, gives sulphate of copper and 
 sulphurous acid gas. 
 
 The symbol of copper is Cu, from its Latin name ; its equivalent 
 395-7, or 31'7. 
 
 Copper combines with oxygen in three proportions, forming a subox- 
 ide, protoxide, and a peroxide, which last appears to have acid proper- 
 ties, but is little known. 
 
 Protoxide of Copper. CuO. Equivalent 495'7, or 397. This 
 
554 Oxides of Copper. 
 
 oxide is formed by exposing copper, at a red heat, to a current of air. 
 It may also be obtained by igniting the nitrate of copper. It is a dull 
 black powder, which, by a very high temperature, may be melted, and 
 crystallizes on cooling. It dissolves but slowly in acids, forming the 
 ordinary blue or green salts of copper. When heated, even below red- 
 ness, in a stream of hydrogen gas it is perfectly reduced, water being 
 formed. It is thus that, as described in p. 348, the composition of 
 water is best determined. At a dull red heat this oxide is reduced com- 
 pletely by carbon and all its compounds, carbonic acid being produced. 
 For this reason it is extensively employed in the ultimate analysis of 
 organic substances, of which it converts the carbon into carbonic acid, 
 and the hydrogen into water. The metallic copper thus obtained, by 
 the reduction from the oxide, is a fine pinkish red powder, which has a 
 remarkable affinity for oxygen, and is hence used in the analysis of 
 organic substances containing nitrogen, to prevent the formation of 
 nitrous or nitric oxides, and in analysing air. 
 
 When a solution of caustic potash is added in excess to a solution of 
 a salt of copper, the protoxide is thrown down as a hydrate, CuO.HO. 
 It is a fine blue powder which is decomposed by a very gentle heat, so 
 that if a liquor containing it be boiled, it becomes brown and anhydrous, 
 even though in the midst of water. It is hence, that if the solution 
 of copper be added to a boiling solution of potash, the precipitate 
 is the dark brown anhydrous oxide which, however, obstinately retains 
 a little potash. 
 
 If the protoxide of copper be exposed to a very strong red heat, it 
 partially melts and gives off oxygen gas, producing a brownish black 
 complex oxide having the formula Cu 5 O 3; or 2Cu 2 O-f-CuO. 
 
 Suboxide of Copper. Cu 2 0. Equivalent 891*4, or 71*4. This body 
 exists native, constituting the ruby copper ore, and may be prepared 
 artificially by igniting a mixture of five parts of black oxide of copper 
 and four of copper filings ; half of the oxygen of the former passes to 
 the latter, and the whole becomes suboxide. It is likewise made by 
 fusing together three parts of subchloride of copper and two of dry car- 
 bonate of soda; chloride of sodium and suboxide of copper result, 
 Cu 2 .Cl and NaO giving Cu 9 and JSTaCl, whilst the carbonic acid is 
 given off. This suboxide of copper is a reddish-brown powder, which 
 is much less acted on by moist air than pure copper ; and hence, under 
 ordinary circumstances, when copper becomes brown by being coated 
 with this oxide, the action ceases. Articles of copper are thus coated 
 intentionally, for the purpose of preserving their surface, by covering 
 them with a paste of red oxide of iron, which, when heated, is thus 
 reduced to the state of protoxide 2Cu and Fe 2 3 giving Cu^O and 
 
Siilpliurets of Copper. 555 
 
 2.FeO ; this last is then removed by digestion in a boiling solution of 
 acetate of copper. 
 
 The generality of acids decompose the suboxide of copper into me- 
 tallic copper and the black oxide, with which the acid combines, but 
 besides the subchloride of copper, several of its salts may be formed by 
 the action of deoxidizing agents on the salts of the black oxide ; thus 
 sulphurous acid converts the hydrate of the black oxide into sulphate 
 of the suboxide, SO. 2 and 2CuO producing SO 3 + Cu 2 .O. From the 
 . solution of this salt, a fine orange hydrate of the red oxide is thrown 
 down by the caustic alcalies. Protochloride of tin and protosulphate 
 of iron, also reduce the salts of copper to this state of oxidation. 
 
 Grape and milk sugar have so remarkably the power of reducing 
 copper to the state of suboxide as to be most readily detected thereby. 
 The suboxide is also by this means easily prepared. If one part of 
 sulphate of copper, and one part of milk sugar, be dissolved in 10 
 parts of water, and treated with solution of caustic potash, until the 
 whole has produced a blue liquid, then, on boiling, suboxide of copper, 
 precipitates, at first brown, but it becomes rapidly rich crimson coloured. 
 It can then be filtered and dried. If it be boiled too long it loses its 
 rich colour, and becomes crystalline and brown. 
 
 Peroxide of Copper. Ciipric Acid. If hypochlorite of lime be 
 mixed up with water and a solution of nitrate of copper be added 
 thereto, a greenish precipitate at first forms, which gradually becomes 
 dark, and finally crimson red. This precipitate is cuprate of lime. It 
 cannot be collected or dried. It gives off oxygen gas and resolves 
 itself into lime and protoxide of copper. With hypochlorite of barytes, 
 cuprate of barytes can be formed, and with hypochlorite of soda or 
 potash, cuprates of those alcalies. The solutions of the alcaline cu- 
 prates are claret red, but lose their colour gradually, whilst oxygen gas 
 goes off, and oxide of copper separates. A solution of cuprate of 
 potash may be also prepared by deflagrating nitre with a mixture of 
 zinc and copper filings, and washing the mass with cold water. The 
 formula of this cv.pric acid or peroxide of copper is not known. 
 
 Sulphur combines with copper in two proportions, forming sulphurets 
 equivalent to the oxides just described ; they are both found native, and 
 constitute, particularly the sulphuret, important ores of copper. They 
 may be prepared artificially, by fusing together sulphur and metallic 
 copper; the union takes place with brilliant combustion. If some 
 sulphur be placed in a flask and heat be applied so as to fill the flask 
 with the vapour of sulphur, a thin copper wire dipped in it burns, as 
 iron does in oxygen, forming the subsulphuret ; these bodies are not 
 of importance, except as the great sources of metallic copper. 
 
556 Detection of Copper. 
 
 The sulphurets of copper may also be formed by precipitating the 
 salts of copper with sulphuretted hydrogen, a deep brown powder is 
 produced, which is Cu 2 S or CuS according as the solution contained the 
 suboxide or the protoxide of the metal. 
 
 The detection of copper in solution is very simple ; the salts of the 
 black oxide are generally green or blue ; on the addition of ammonia, 
 a precipitate is produced, bluish or green, according to the acid with 
 which the oxide had been combined, but in all cases producing with an 
 excess of the ammonia, a deep violet coloured solution. The only 
 metal which resembles copper in this respect, is nickel, and from it, it 
 is distinguished by all its other properties, particularly by the yellow 
 prussiate of potash, which produces a fine chocolate brown precipitate of 
 ferrocyanide of copper. With sulphuret of hydrogen, the salts of 
 copper give a dark brown sulphuret, insoluble in hydrosulphuret of 
 ammonia ; and when a slip of clean iron or zinc is introduced into a 
 liquor containing copper, this is reduced and deposited upon the surface 
 of the zinc or iron, as a bright coating of metallic copper. 
 
 When the copper exists as suboxide, its reactions are very different, 
 it gives, with ammonia, a white precipitate which redissolves in an excess, 
 forming a colourless liquor ; if there be no excess of acid, chloride of 
 sodium gives a white precipitate of subchloride of copper. But in 
 practice it is never necessary to look for copper by these reactions, the 
 salts of the suboxide absorbing oxygen with such avidity, that by a few 
 minutes' exposure to the air, their constitution changes. The colourless 
 solution of suboxide of copper in ammonia becomes violet blue in the 
 act of pouring it from one bottle to another ; and hence for the mere 
 detection of copper, the properties of the protoxide alone need be taken 
 into accouqt. 
 
 Like the oxides of cobalt and nickel, the oxides of copper are not by 
 themselves soluble in water of ammonia. The solutions of these me- 
 tallic compounds in water of ammonia, are basic salts, to the constitu- 
 tion of which the acid, with which the metallic oxide had been origi- 
 nally combined, is necessary. The detailed nature of these bodies will 
 be noticed among the compounds of ammonia. 
 
 The detection of copper by the blowpipe is very simple and distinct. 
 Eused with borax, a substance containing the most minute trace of 
 copper gives a glass, which when heated in the oxidizing flame, becomes 
 green, being coloured by the protoxide, but when ignited in the reduc- 
 ing flame, and suddenly cooled, is deep ruby-red, generally opaque. 
 This change of colour arises from the copper being reduced to the state 
 of suboxide. The colour given to glass by this suboxide is a pure pris- 
 matic red, so homogeneous that red light may be obtained for optical 
 
State of Lead in Nature. 557 
 
 experiments, by transmitting white light through this coloured glass, 
 and the tint is so fine that this ruby glass is the most valuable that can 
 be used for ornamental purposes. 
 
 The salts of copper generally tinge the flame of the blowpipe blue or 
 green, according to the other bodies that may be present. 
 
 Independent of the direct employment of copper in the arts, for 
 which its properties eminently qualify it, it enters into the composition 
 of a great number of alloys of great importance. Thus bronze, formerly 
 used as a substitute for steel, and still employed in the casting of statues 
 and monuments, from the accuracy with which it adapts itself to the 
 mould, and its durability, consists of ninety parts of copper and ten of 
 tin in 100. It is curious, that from the very earliest ages, this which 
 is still the best proportion, should have been employed ; the bronze 
 swords from ancient Egypt, from Scandinavia, and those found in Ire- 
 land, having all this constitution. Gun metal, or that of which can- 
 nons are cast, is an inferior kind of bronze, containing somewhat 
 less tin. 
 
 The elasticity and sonorousness of these alloys is very remarkable. 
 That used for bells, lell metal, consists of 80 parts of copper and 20 of 
 tin. The Indian gongs have this composition, but common bells con- 
 tain less tin, and in place of it some lead and zinc. In the proportion 
 of two parts of copper to one of tin, or, more accurately, of four atoms 
 of copper to one of tin, 127 to 59, an alloy is formed, of exceeding 
 brittleness and hardness, and so brilliant, when truly polished, as to be 
 used for the mirror surface in reflecting telescopes ; it is here called 
 speculum metal. The quality of this alloy is remarkably deteriorated by 
 a slight deviation to either side of the true atomic proportions. 
 
 The alloys of zinc and copper are very numerous and important, con- 
 stituting the different varieties of brass. The best brass consists of 
 four atoms of copper to one of zinc; but by changing the proportions 
 of the metals, a variety of shades of gold lustre, used in counterfeit 
 jewellery, are obtained. In the proportion of equal parts of copper and 
 zinc, hard solder is produced ; this is used in soldering together sur- 
 faces of brass and copper. The nature of the alloy of brass and nickel 
 termed German silver has been already described in page 513. 
 
 OF LEAD. 
 Symbol. Pb. Eq. 103-7 or 1294 5. 
 
 This metal exists in nature, very extensively diffused and in a great 
 variety of forms. The sulphate, phosphate, arseniate, carbonate, and 
 
558 Properties and Combinations of Lead. 
 
 chloride of lead are found native ; but it is exclusively from the sul- 
 phuret of lead, galena, that the metal is extracted for the purposes of 
 commerce. The methods used in its reduction have been very fully 
 described in the preceding chapter, page 467. 
 
 Lead is one of the softest and least tenacious of the metals; it is 
 bluish white, and very brilliant, but rapidly tarnishes in the air, becom- 
 ing covered with a greyish coating, beyond which the action does not 
 appear to extend; its specific gravity is 11*44; it inelts at 612, and 
 in solidifying, diminishes in volume so that it is unfit for accurate cast- 
 ings ; it may, however, be obtained, by fusion, crystallized in octo- 
 hedrons ; it is not volatile ; it is not sensibly acted on by muriatic nor 
 sulphuric acids, except at very high temperatures, but by nitric acid it 
 is rapidly oxidized and dissolved. 
 
 When lead is exposed at the same time to air and moisture, its oxi- 
 dation proceeds with great rapidity, so as to be used to analyse atmos- 
 pheric air (p. 363.) The oxide so formed is not quite insoluble, so 
 that when pure water, rain, or even common soft water, is preserved in 
 leaden cisterns, an impregnation with lead may occur in such amount 
 as to produce dangerous consequences, if employed habitually as a 
 drink. Fortunately this is obviated, in general, by the small quantities 
 of saline matters, particularly sulphates, which all ordinary spring and 
 river waters contain. These react on the oxide of lead, and forming 
 compounds totally insoluble in water, remove thus all traces of it from 
 solution. A whitish crust gradually forms on the interior of the cistern, 
 and assists, subsequently, in protecting it from the oxidizing action of 
 the air ; no danger is, therefore, to be apprehended from the supply of 
 water to a city being conveyed through leaden pipes, and preserved in 
 leaden cisterns, for all water, of mineral origin, dissolves, in filtering 
 through the layers of rocks in its passage to the surface, a sufficiency of 
 saline matters to serve for its protection. 
 
 The symbol of lead is Pb, from its Latin name ; its equivalent is 
 1294*5 or 103*7. It combines with oxygen in two proportions forming 
 oxides, which again uniting form an intermediate complex oxide, and 
 there is reason also to admit the existence of a suboxide of lead. 
 
 Protoxide of Lead. Pb.O. Equivalent 1394*5 or 111*7. This may 
 be prepared by exposing metallic lead at a red heat to a current of air, 
 the lead rapidly combines with oxygen, and the oxide so produced 
 fuses. It forms on cooling crystalline masses of a greenish yellow 
 colour ; this constitutes the litharge of commerce, which is generally 
 obtained in the cupellation of lead for the purpose of extracting from it 
 the small quantity of silver which its ores generally contain. When the 
 litharge is kept for some time, the masses of it break up into a brick- 
 
Protoxide an $ Peroxide of Lead. 559 
 
 red crystalline powder, evolving heat. This change is technically 
 termed slaking, but it is not due, like the slaking of lime, to combina- 
 tion with water, but to a change of the crystalline form of the litharge. 
 The yellow form appears to be more permanent if the lead be oxidized 
 at a lower temperature, and when powdered was once used as a yellow 
 pigment under the name of massicot. This may be produced of the 
 richest colour by decomposing the sub-nitrate of lead at a temperature 
 insufficient for the fusion of the oxide. 
 
 This oxide may also be prepared by decomposing a soluble salt of lead 
 by caustic potash, a white precipitate is produced, which is a hydrate of 
 the oxide, 2PbO + HO. By a great excess of caustic potash the precipi- 
 tate may be redissolved ; the oxide of lead appearing to have the power of 
 uniting with most of the alcalies and earths to form compounds more or 
 less soluble. A body of this kind formed by boiling lime and litharge 
 together is capable of crystallizing, and is used to dye the hair black, 
 The hair contains sulphur, and a black sulphuret of lead forms in its 
 substance, and is not liable to change. The protoxide of lead requires 
 12,000 parts of water to dissolve it; the solution reacts feebly alca- 
 line ; it is a strong base, and the only oxide of lead which combines 
 with acids. 
 
 Peroxide of Lead. Pb0 2 . Is obtained by digesting the protoxide 
 in chlorine water, or in a solution of chloride of lime. In the first case 
 2.PbO and Cl produce Pb0 2 and PbCl ; in the second case, PbO and 
 CaO.Cl produce PbO 2 and CaCl. Another simple plan consists in heat- 
 ing red lead, which is a compound of the protoxide and the peroxide, 
 with dilute nitric acid, until all the protoxide is dissolved out, washing 
 the residue well and drying it at a moderate heat. The peroxide so ob- 
 tained is of a dull, dark brown colour, when heated it gives off half its 
 oxygen, leaving litharge. With muriatic acid it produces chlorine and 
 protochloride of lead, and with sulphurous acid, which it rapidly ab- 
 sorbs, neutral white sulphate of lead, Pb0 2 and SO 2 producing PbO-f 
 S0 3 . This oxide of lead does not form salts. 
 
 The Red Lead, or Minium, Pb 3 O 4 =2.PbO + Pb0 2 , is produced when 
 lead is oxidized, so that the oxide formed shall not be fused, and when 
 the metal is all converted into the yellow powder, increasing the heat 
 to incipient redness. Oxygen continues to be absorbed until one-third 
 of the metal is converted into peroxide, giving the constitution above 
 expressed. This is the pure red lead, the colour of which is exceedingly 
 brilliant ; but the generality of red lead found in commerce contains an 
 excess of protoxide, which may be removed by boiling in a solution of 
 neutral acetate of lead. 
 
 When red lead is ignited it gives off oxygen and becomes protoxide ; 
 
560 SulpJiuret of Lead. 
 
 with muriatic acid it forms protocliloride and chlorine. It does not 
 form any proper salts, but it dissolves in acetic acid, completely, giving 
 a colourless liquor, from which, after a little time, peroxide of lead 
 separates. 
 
 When oxalate of lead is very cautiously decomposed by heat, there 
 remains a true suboxide of lead. Pb 2 0. It is a velvety black powder. 
 By acids it is converted into protoxide and metallic lead.- Strong alca- 
 lies produce a similar result. Heated in the air it burns like tinder 
 and forms protoxide. If wet it absorbs oxygen rapidly at the ordinary 
 temperature, and produces white hydrated protoxide of lead. It does 
 not form salts. The grey coating which forms on lead exposed to the 
 air, is looked upon by many chemists as also a suboxide. In general 
 these bodies have been considered as mixtures of the metal in powder 
 with the real protoxide, but I think the evidence of their definite con- 
 stitution very strong. 
 
 From the similarity of the formula of red lead, PbsC)4, to those of the 
 black oxide of iron, Fe 3 O 4 , and of the red oxide of manganese, Mn 3 O4, 
 it has been suggested that it may contain sesquioxide of lead Pb 2 3 , si- 
 milar to Fe 2 O 3 , and Mn 2 3 . The formula of red lead should then be 
 PbO-fPb 2 O 3 ; but this idea, though interesting, is only hypothetical. 
 
 Sulpkuret of Lead. There is but one compound of sulphur and 
 lead, the protosulphuret Pb.S. It constitutes the abundant lead ore, 
 galena, and may be formed artificially, either by fusing together lead 
 and sulphur, or by decomposing a solution of a salt of lead by sulphur- 
 etted hydrogen gas or hydrosulphuret of ammonia. It is then a black 
 powder, insoluble in water, and in alcalies, and dilute acids. It is ra- 
 pidly oxidized by nitric acid, being converted into sulphate of lead. 
 From the perfect insolubility and marked colour of this sulphuret, a 
 salt of lead and sulphuretted hydrogen are respectively the most delicate 
 re-agents for each other. 
 
 There are some indications of the existence of other sulphurets of 
 lead, which, however, do not require special notice. If a salt of lead be 
 decomposed by bisulphuret of calcium, a red precipitate appears, possibly 
 a bisulpkuret of lead, analogous to the deutoxide, and galena may be 
 fused with metallic lead, forming a homogeneous mass in which, pro- 
 bably, subsulphurets are contained. 
 
 The detection of lead is simplified very much by its forming but one 
 series of salts, those of the protoxide. Its solutions are recognized by 
 giving, with caustic potash, a white precipitate soluble in excess ; with 
 carbonate of potash, one also white, but insoluble in excess ; with sul- 
 phuretted hydrogen, one dark brown or black, whose characters are 
 described above ; with a solution of bichromate of potash, the salts of 
 
State of Bismuth in Nature. 561 
 
 lead produce a fine yellow precipitate, chrome yelloiv ; and with iodide 
 of potassium, the iodide of lead, in brilliant yellow scales, like fragments 
 of gold leaf. Yellow prussiate of potash gives a white precipitate, and 
 sulphate of soda a white sulphate of lead, insoluble in water, but not 
 insoluble in strong acids. If the solution contain much lead, any soluble 
 chloride throws down sparingly soluble chloride of lead, which, how- 
 ever, remains dissolved, if the solution be dilute. 
 
 Lead and its preparations are of the most extensive use in the arts. 
 In making pipes and cisterns, sulphuric acid chambers, bullets, and for 
 a variety of other purposes, the metal is employed unaltered ; and its 
 alloys are also of important application. Thus, the metal of which 
 printing types are made consists of three parts of lead to one of anti- 
 mony. The inferior sorts of pewter are alloys of lead and tin, but the 
 fine kinds should be tin with very little lead, and some antimony and 
 bismuth. The solder used for soldering surfaces of lead, or of tinned 
 iron, to each other, consists of lead and tin, the proportions of which 
 vary from two parts of tin and one of lead to three parts of lead and one 
 of tin, according to the object. The more tin the alloy contains, the 
 more fusible the alloy is. Fine solder fuses at 360, coarse solder at 
 500. 
 
 OF BISMUTH. 
 Symbol. Bi. Eq. 213'3 or 2660*7. 
 
 Bismuth is not a common metal; it is found but in a few places, and 
 only in the metallic state in quantity, for the sulphuret of bismuth is 
 too rare to be of technical interest. It is extracted from the rocks 
 through which it is disseminated, by reducing it to coarse powder, and 
 igniting this in a kind of kiln ; the bismuth being very fusible, melts 
 out, and collects at the bottom, in a trough placed to receive it. 
 
 It is a white metal, with a peculiar reddish shade, and remarkably 
 crystalline structure. It may be obtained in separate crystals of con- 
 siderable size, which are cubes, generally hollow at the sides. To 
 obtain good crystals, the metal should be perfectly pure ; this is 
 effected by deflagrating some nitre on the surface of the melted metal, 
 the impurities are more easily oxidized than the bismuth, and hence, 
 pass into the scorise which form on the surface. The crystals so ob- 
 tained have frequently beautiful rainbow tints on their surface, from an 
 exceedingly thin layer of oxide of bismuth, by which they become 
 coated. 
 
 Bismuth is very brittle, and easily oxidized. It is scarcely acted on 
 by sulphuric or muriatic acid, but it decomposes nitric acid violently, 
 
 36 
 
562 Atomic Weight of Bismuth. 
 
 evolving nitric oxide, and forming oxide of bismuth, with which the 
 nitric acid combines. It fuses at 497, is volatile at a white heat, and 
 then burns with a bluish-white flame. Its sp. gr. is 9*9. 
 
 The symbol of bismuth is Bi. Concerning its equivalent there is 
 some doubt at present, as to whether it should be 886*9, or three times 
 so much, 2660 '7, on the oxygen scale, and hence, 71 "1 or 213*3 on 
 the hydrogen scale. The first number assumed would make the oxide 
 of bismuth a protoxide, BiO, the last, a teroxide, Bi0 3 . The ground 
 upon which the former view stands is the supposed similarity of some 
 salts of bismuth to those of magnesia and the protoxide of copper ; 
 but recent examination has gone to shew that this analogy is not at all 
 so strong as had been supposed, and that their difference is more re- 
 markable than their resemblance. On the other hand, the sulphuret 
 of bismuth is isomorphous with the sulphurets of antimony and arsenic, 
 and the equivalent deduced from the specific heat of bismuth agrees 
 with those for arsenic and antimony, and assigns the same constitution 
 to the compounds of the three. The salts of the oxide of bismuth are 
 exceedingly instable, and like those of antimony, are decomposed by 
 water, so that whilst it allies itself to that metal in every important 
 point of physical and chemical characters, it recedes in all the impor- 
 tant facts of its history from copper, iron, zinc, and the other metals 
 of the magnesia class. I, therefore, think there are sufficient grounds 
 for abandoning the numbers 886'9 and 71*1, given in the table, p. 277, 
 and to assume 2660*7 and 213*3, as the equivalents of bismuth on the 
 oxygen and hydrogen scales respectively. 
 
 Oxide of Bismuth, Bi0 3 , equivalent 2960' 7, or 237*3, may be pre- 
 pared either by the combustion of bismuth at a high temperature, or 
 by the ignition of the subnitrate of bismuth. It is a buff-coloured 
 powder, which may be melted. It combines with acids to form well 
 characterized salts. 
 
 This oxide may also be obtained hydrated by dropping a solution of 
 nitrate of bismuth into a solution of caustic potash ; a white precipitate 
 falls, which is HO. Bi0 3 . On ignition it leaves the anhydrous oxide. 
 
 Peroxide of Bismuth. Bi0 4 . When oxide of bismuth is diffused 
 through a dilute solution of caustic potash, and a current of chlorine 
 gas passed through the liquor, the oxide is converted into peroxide, 
 which combines with some potash. This can be removed by dilute 
 acetic acid, and the peroxide obtained pure. It is a dark yellow pow- 
 der. ' It reacts slightly acid, and corresponds to antimonious acid. If 
 the solution of potash had been strong, the oxide absorbs more oxygen 
 and passes into the following body. 
 
 The Superoxide of Bismuth, or Bismuthic Acid, BiO 5 , is prepared by 
 
Compounds of Bismuth. 563 
 
 boiling finely levigated oxide of bismuth in a strong solution of chloride 
 of soda. A fine brown powder is produced, which is freed with great 
 difficulty from admixed unaltered oxide. When heated to dull redness 
 it is decomposed into oxygen and oxide of bismuth ; with muriatic acid 
 it gives chlorine and ordinary chloride of bismuth. Its composition 
 was supposed to corroborate the idea, that the yellow oxide was a pro- 
 toxide, for on that idea this might be a sesquioxide, Bi 2 O 3 , like the 
 sesquioxides of cobalt and nickel, which it resembles so much in pro- 
 perties ; but the discovery of the body last described, and more accu- 
 rate analysis, have shown its true formula to be Bi O 5 , and it is now 
 looked upon as corresponding to antimonic acid. There appear to 
 exist yellow and brown, allotropic, conditions of both peroxide of bis- 
 muth and of bismuthic acid, but the study of these bodies has been 
 not yet completed. 
 
 Sulphuret of Bismuth, BiS 3 , exists native, in crystals isomorphous 
 with the sulphurets of antimony and arsenic. It may be prepared by 
 fusing bismuth and sulphur together, or by adding sulphuretted 
 hydrogen to a solution of a salt of bismuth : it then precipitates as 
 a brown powder. It is insoluble in water, and in hydrosulphuret of 
 ammonia. 
 
 Bismuth is easily known by its solutions being precipitated brown by 
 sulphuretted hydrogen and by iodide of potassium, and yellow by 
 chromate of potash. The caustic and carbonated alcalies produce a 
 white precipitate of hydrated oxide of bismuth which is insoluble in 
 excess. A strong solution of a salt of bismuth is decomposed by the 
 addition of water, whereby a white basic salt is precipitated, and the 
 liquor contains free acid. 
 
 Bismuth is extensively employed for some purposes in the arts. The 
 alloy used for casting stereotype plates consists of tin, lead, and bis- 
 muth ; and by increasing the quantity of bismuth, the fusibility of this 
 alloy becomes so great that a compound of two parts of bismuth, one 
 of tin, and one of lead, fuses at 201. This is the fusible metal used 
 for the bath in taking the specific gravities of vapours, as described, p. 
 14, and for supplying a steady source of heat for other purposes. 
 
564 State of Silver in Nature. 
 
 SECTION VI. 
 
 METALS OF THE SIXTH CLASS. 
 OF SILVER. 
 
 Symbol. Aq. Eq. 108 or 1350. 
 
 This metal exists native, and in the state of sulphuret, in a great 
 variety of places, and from the facility with which it may be extracted 
 and the permanence of its lustre it became known at a very early 
 period. The principal sources of silver are the mines of South 
 America; in Europe, those of Saxony are the most remarkable. A 
 great deal of silver is also obtained from the ores of lead, the sulphuret 
 of lead being generally accompanied by the sulphuret of silver in small 
 quantity. 
 
 The native silver of America exists, generally speaking, too finely 
 disseminated to be simply melted out. It is washed out by mercury, 
 this fluid metal dissolving the silver, and being then distilled off, leaves 
 the precious metal behind. A very remarkable process is used to ex- 
 tract the silver from the sulphuret. This ore is roasted in a reverbera- 
 tory furnace with chloride of sodium, by which chloride of silver and 
 sulphuret of sodium are formed, Ag.S and NaCl giving AgCl and NaS. 
 This last is washed out, and then the chloride of silver being put into 
 barrels with some water, pieces of iron, and mercury, the iron decom- 
 poses the chloride of silver, forming chloride of iron and setting the 
 silver free, which dissolves in the mercury forming a fluid amalgam ; 
 this is strained through leather bags, by which a great part of the mer- 
 cury passes off, and a pulpy mass of amalgam of silver is obtained, 
 which is then submitted to distillation, by which the mercury is sepa- 
 rated and the silver remains pure. 
 
 The method of extraction of the silver which accompanies the lead, 
 in galena, is founded on the greater rapidity with which lead combines 
 with oxygen. In the smelting of the ore the silver is reduced with the 
 lead, and the resulting impure metal is melted in a shallow porous dish 
 made of bone ashes, and when at a full red heat a current of air is 
 urged across it from powerful bellows, The lead becomes converted 
 into litharge, as described in p. 558, and new coatings of oxide of lead 
 succeed one another upon the surface, until the whole quantity of that 
 metal has been removed. When the silver remains pure, the surface 
 becomes suddenly brilliant, and the completion of the work is known 
 
Extraction of Silver from its Ores. 565 
 
 bj the metal thus flashing or tightening, as it is technically termed. 
 This is the process of cupellation. The porous bone earth capsule, or 
 cupel, absorbs a great deal of the litharge, and the rest is blown away 
 from the surface, as it forms, by the blast of air, and is collected in the 
 front of the furnace. 
 
 This process has been - remarkably shortened by the discovery that 
 the quantity of silver may be concentrated, in a comparatively small 
 quantity of lead, by crystallization. The silver is not diffused uniformly 
 through all the lead, but combined in atomic proportions with a certain 
 quantity of it, forming an alloy which is then mixed with the excess of 
 lead. This alloy is more fusible than lead, so that when a large basin 
 of lead, containing a small quantity of silver, is melted and allowed to 
 cool very slowly, so as to crystallize, the portions which first solidify are 
 pure lead, and these being removed with iron colanders, all the silver 
 remains in the mother liquor. The process must be stopped, however, 
 before this begins to congeal. By a succession of crystallization of this 
 sort the great excess of lead is gradually got rid of, and the quantity to 
 be oxidized at the cupel diminished in a corresponding degree. 
 
 The silver of commerce is never pure, and, hence, for chemical pur- 
 poses must be freed from the metals, generally copper, associated with 
 it. For this purpose it is dissolved in nitric acid, and its solution pre- 
 cipitated by common salt. Chloride of silver separates, which is then 
 reduced by any of the methods described in p. 469. Another very 
 convenient mode of reducing silver from the chloride is to boil it with 
 solution of sugar and caustic potash. The silver separates as a powder ; 
 chloride of potassium being formed. The method of assaying may 
 also be used to obtain pure silver. The impure silver is melted with 
 from four to eight times its weight of lead, and this alloy cupelled as 
 already detailed ; the lead is not only itself oxidized, but the other 
 metals present, which would not otherwise separate, are converted into 
 oxides, which pass off with the oxide of lead. It is in this way that 
 the standard alloys of silver, for coinage and plate, are verified at the 
 mint and other offices. 
 
 Silver, when completely pure, is very brilliant, it is the whitest of 
 the metals and takes a fine polish. It is very ductile and malleable. Its 
 sp. gr. is 10'5, it fuses at 1873. It is not altered by air or water, but 
 when kept melted for a considerable time, it absorbs oxygen, which it 
 appears to hold rather dissolved than combined, for, on solidifying, it 
 discharges this oxygen, by which the surface is thrown into irregular 
 granulations. The quantity of oxygen may be so great as twenty times 
 the volume of the metal. 
 
 Silver is very soft. It is hence necessary, in coin, and in articles for 
 
566 Properties of Silver. 
 
 domestic use, to add a certain quantity of copper, to render it less liable 
 to deterioration from use or in being cleaned. 
 
 When silver is exposed to the air it gradually tarnishes, which is due 
 not to the formation of oxide but of sulphuret, the air always containing 
 traces of sulphuretted hydrogen, derived from organic bodies. It is not 
 acted on by sulphuric or muriatic acid, but is rapidly dissolved by nitric 
 acid, with evolution of nitric oxide gas. 
 
 Silver combines with oxygen in three proportions, forming oxides, of 
 which only one, the protoxide, is well known. The equivalent of silver 
 is 1350 or 108, and its symbol is Ag, from the Latin name. 
 
 Protoxide of Silver. AgO. Equivalent 1450 or 116. May be 
 prepared by adding caustic potash, or lime water, to a solution of 
 nitrate of silver. A brown powder is thrown down, which may be dried 
 at a gentle heat without alteration. It then becomes very dark. When 
 heated strongly, it is decomposed into oxygen and metallic silver, and 
 this takes place at ordinary temperatures, if it be in contact with 
 organic matter. The oxide of silver may be prepared in a very dense 
 form as a black powder, by boiling recently precipitated and moist 
 chloride of silver with a very strong solution of caustic potash. The 
 oxide of silver neutralizes the strongest acids, as the sulphuric and 
 nitric, and forms well characterized salts. It is not acted on by the 
 fixed alcalies, but with ammonia it gives fulminating silver, one of a 
 series of bodies to be hereafter examined. When citrate of silver is 
 heated to 212, in a current of hydrogen gas, the metal is not reduced, 
 as should have occurred with the pure oxide, but one-half of the oxy- 
 gen is removed, and the citric acid remains combined with the suloxide 
 of silver, Ag 2 O. This salt dissolves in water, the solution being brown, 
 and giving a brown precipitate of suboxide and potash. When the 
 solution of this salt is heated, it becomes colourless, contains a salt of 
 the protoxide, and metallic silver separates. Some other silver salts of 
 organic acids give the same result with hydrogen gas. When a solution 
 of nitrate of silver is decomposed by the battery, a substance is depo- 
 sited upon the positive electrode in needles, sometimes half an inch 
 long. These are resolved by sulphuric acid into protoxide of silver and 
 oxygen, and give, with muriatic acid, chloride of silver and free chlo- 
 rine. They are, therefore, crystals of the peroxide of silver, probably 
 Ag0 2 . 
 
 Although silver does not combine with oxygen directly, yet when it 
 is heated in contact with glass it stains this of a deep yellow orange 
 colour, being converted into oxide. 
 
 Sulphuret of Silver. Equivalent 1550 or 124*0, exists native pure, 
 and also in combination with other metallic sulplmrets, particularly 
 
Detection of Silver. 567 
 
 those of lead, antimony, copper, and arsenic, forming a variety of mine- 
 rals. It is the most common ore of silver. It may be formed artifi- 
 cially by fusing together sulphur and silver, the excess of sulphur being 
 expelled by the heat. Silver has, indeed, a remarkable affinity for sul- 
 phur, so that it even decomposes sulphuretted hydrogen, and hence 
 arises the tarnishing of silver when exposed to the atmosphere. An 
 exceedingly delicate test for silver in a solid body consists in igniting a 
 minute fragment of it on charcoal, in the reducing flame of the blow- 
 pipe ; the fused globule is to be then laid on a bright surface of silver, 
 as on a clean shilling, and moistened ; if there be a trace of sulphur in 
 the substance, a black or olive spot will form on the silver where it is 
 moistened 
 
 The sulphuret of silver may be formed also in the wet way, by adding 
 sulphuretted hydrogen, or hydrosulphuret of ammonia to a solution of 
 a salt of silver. It forms as a black powder, which is not soluble in an 
 excess of the precipitant. This sulphuret is a powerful sulphur base, and in 
 its native forms, is generally combined with negative metallic sulphurets. 
 
 The detection of silver is very easy ; from the facility with which its 
 oxide is reduced to the metallic state, its solutions are precipitated by 
 the sulphites, by protosulphate of iron, and by protochloride of tin, the 
 silver being reduced. A solution of common salt, or muriatic acid, 
 gives a white curdy precipitate of chloride of silver, which is insoluble 
 in water and in acids, but dissolves in water of ammonia ; when exposed 
 to light in contact with organic matter, the chloride of silver becomes 
 tinged violet or black, owing to the formation of a subchloride ; on this 
 is founded its application in photography, described p. 224. The solu- 
 tions of silver give, with iodide of potassium, a canary-yellow precipitate 
 insoluble in ammonia, and with sulphuretted hydrogen, a deep brown 
 sulphuret of silver. 
 
 The uses of silver are well known ; its advantages as a medium of 
 exchange depend on the steadiness of the quantity of it brought into 
 commerce, which prevents great changes in its value, and on its not being 
 corroded or worn down by ordinary agents. In a pure state, it would, 
 however, be too soft to be used as coin, and is hence hardened by being 
 alloyed, in the proportions of 222 parts to 18 of copper; this is the 
 standard silver of the mint ; the silver used for the purposes of luxury, 
 contain a greater, but a variable quantity of copper. 
 
 OF MEECURY, OR QUICKSILVER. 
 Symbol. Hg. Eq. 100 or 1250. 
 
 From the remarkable properties of this metal, and its occurring in the 
 metallic state in nature, it has attracted much attention, from the 
 
568 State of Mercury in Nature. 
 
 earliest ages, and formed the object of the most elaborate inquiries of 
 the older chemists. Its volatility and the variety of its compounds, 
 made it enter into the theories of that period as an important element, 
 and hence there is perhaps no metal concerning which so much valua- 
 ble knowledge was obtained in the infancy of chemistry. 
 
 Mercury is found native, and also combined with gold and silver, 
 but its most abundant ore is the native sulphuret, cinnabar ; from this 
 it is extracted by one or other of* two processes. The first consists in 
 distilling the ore with lime, or with iron in small pieces ; in the first 
 case, Hg.S and CaO produce Ca.S, whilst Hg. and pass off, the tem- 
 perature being too high to allow of the formation of oxide of mercury ; 
 in the second case Hg.S and Fe produce Fe.S and Hg ; this process is 
 carried on in long furnaces, wherein are arranged numbers of earthen 
 or iron retorts having adapted to them receivers, in which the mercurial 
 vapours condense. The other plan, which is that now adopted in the 
 best arranged works, consist of a kiln, like that in which the pyrites is 
 roasted for the manufacture of oil of vitriol ; below, there is a grate on 
 which is lighted a fire of brushwood, over this is a light arch of fire- 
 brick, with numerous perforations, and on this is arranged the cinnabar, 
 the poorest kinds being placed below, until the kiln is filled nearly to 
 the orifice of the chimney which passes off at the side ; the fire commu- 
 nicating to the ore, the sulphur contained in it burns, and the mercury 
 is set free ; HgS and 20 producing S0 2 and Hg. The kiln is so hot, 
 that the metal is completely volatilized, and the mixed vapour of mercury 
 and sulphurous acid gas are carried by the draughts into the chimney, 
 which leads into a wide chamber of brick-work, the sides of which are 
 hung with leather ; on these the mercury condenses in drops which 
 gradually flow down and collect on the floor, whilst the sulphurous acid 
 gas passes away by a small chimney at the farther end, by means of 
 which the continuous combustion of the ore is sustained ; at certain 
 periods, an aperture in the side of this chamber is opened, and the mer- 
 cury which had collected is withdrawn. 
 
 The mercury is sent into commerce in iron bottles, but generally in a 
 very impure state; it being intentionally adulterated with the alloy of 
 tin, lead, and bismuth, already noticed, page 563, of which it can dis- 
 solve large quantities. It may be purified by distillation, or by being left 
 for some time in contact with dilute nitric acid. The mercury having 
 less affinity for oxygen than any of the other metals present, is the last 
 to dissolve, and as soon as the liquor is found to contain mercury, the 
 metal remaining may be looked upon as pure. 
 
 A mode of purification which has been found very useful consists in 
 digesting the impure mercury with an acid solution of perchloride of 
 
Properties of Mercury. 569 
 
 iron. The more easily oxidized metals are converted into chlorides, 
 and a small part of the quicksilver into calomel : the perchloride of iron 
 being reduced to the state of protochloride. On washing and straining 
 the mass previously warmed the mercury is obtained quite pure. 
 
 Mercury is distinguished by being liquid at ordinary temperatures ; 
 this, together with its resemblance to silver in brilliancy, is the origin 
 of its various names, hydrargyrum, (vduo aeyvpsov,) quicksilver, argentum 
 vivum. If pure it is not tarnished by exposure to the air, but in damp 
 air its impurities become oxidized very rapidly, in consequence of a 
 complete galvanic circuit being formed with the mercury and other 
 metals present. At 39 it becomes solid, and crystallizes in octohe- 
 drons ; it then contracts very much ; its sp. gr. being 13'5 when liquid, 
 and 14'0 when solid. At 662 it boils and forms a colourless vapour, 
 the sp. gr. of which is 6978. At and just below its boiling point, it 
 absorbs oxygen from the air, forming oxide, which at a red heat is 
 again decomposed. 
 
 Mercury is not acted on at common temperatures by sulphuric or 
 muriatic acid ; nitric acid oxidizes it rapidly, the nature of the product 
 varying with the circumstances. Boiling oil of vitriol is decomposed 
 by mercury, sulphurous acid being evolved and oxide of mercury pro- 
 duced. There are two oxides of mercury, a suboxide and a protoxide. 
 The symbol of mercury is Hg, from its Latin name, and its equivalent 
 is 1250 or 100. 
 
 Suboxide of Mercury. Hg 2 O. Equivalent 2600 or 208. This 
 oxide is the basis of many important preparations, and is best prepared 
 by decomposing calomel (subchloride of mercury) by a solution of 
 potash. The calomel being insoluble, the action must be favoured by 
 mixing the two together well by agitation in a mortar ; a black powder 
 is produced, which must be dried in the dark, and by a very gentle 
 heat. In this process, Hg 2 Cl and KO, produce K.C1 and Hg 2 0. Lime 
 water may be used in place of potash. When this suboxide, or as it 
 is often called, black oxide of mercury, is heated, it is resolved into 
 metallic mercury, and the protoxide, and this change occurs slowly at 
 ordinary temperatures, if it be exposed to the light. This oxide com- 
 bines with acids and forms well characterized salts. 
 
 Protoxide of Mercury. HgO. Equivalent 1350 or 108. May 
 be prepared in a variety of ways : 1st, By exposing mercury for a long 
 time to the action of the air, at a temperature just below its boiling 
 point, it is gradually converted into small deep red crystals of this 
 oxide ; in this state it was the red precipitate per se of the older 
 chemists. 2nd. By heating crystals of nitrate of mercury until all 
 the water and nitric acid have been expelled, the oxide remaining, is 
 
570 Siilphurets of Mercury. 
 
 a crystalline powder of an orange-red colour, the red precipitate by 
 nitric acid. 3rd. When a solution of chloride of mercury (corrosive 
 sublimate) is decomposed by caustic potash or lime water, HgCl and 
 KO produce KC1 and HgO. It is thus obtained as a canary -yellow 
 powder, which, however, when heated, becomes deeper coloured. 
 The red precipitate also when finely divided assumes the same yellow 
 tint. 
 
 This oxide of mercury is slightly soluble in water. The solution 
 browns turmeric paper slightly, and restores the blue colour of reddened 
 litmus. It combines with acids, forming a numerous and important 
 class of salts. At a full red heat it is totally redissolved into mercury 
 and oxygen, as described fully in page 333. It changes its colour 
 remarkably with the temperature, becoming nearly black when very 
 hot. 
 
 The differences between the yellow and the red forms of the oxide 
 of mercury, obtained by precipitation or by heating the nitrate, extend 
 beyond the mere colour or aggregation, and indicate specific allotropic 
 states. Thus, the yellow form at once combines with oxalic acid, form- 
 ing a colourless salt : a solution of chloride of mercury in alcohol 
 changes the yellow oxide into black oxy chloride, but does not alter the 
 red oxide. By heat, however, the yellow passes into the red condition. 
 
 SubsulpJmret of Mercury, Hg 2 S, may be prepared by decomposing 
 any salt of the suboxide by hydrosulphuret of ammonia. It is a black 
 powder, which, on the application of heat, is decomposed into the pro- 
 tosulphuret and metallic mercury. 
 
 Protosulphuret of Mercury, HgS. Equivalent 1450 or 116, consti- 
 tutes the native cinnabar, the usual ore of quicksilver. It may be pre- 
 pared artificially by fusing sulphur in a crucible, and adding thereto six 
 times its weight of mercury ; they combine with the evolution of consi- 
 derable heat. The mass must be stirred frequently to favour their 
 union, and covered in order to prevent the sulphur from burning away. 
 In this state it is black, but when sublimed at a red heat in glass ves- 
 sels, it becomes deep red, constituting factitious cinnabar, and this, 
 when levigated, and exposed to strong light, in flat dishes covered with 
 a thin layer of water, gradually assumes a very brilliant colour, and 
 forms the pigment vermilion. This sulphuret may also be prepared by 
 adding to a solution of corrosive sublimate an excess of hydrosulphuret 
 of ammonia, or sulphuret of hydrogen ; it is a dense black powder. It 
 may, however, be obtained red, but not so bright as vermilion, in the 
 wet way, by digesting white precipitate (chloramide of mercury) with 
 hydrosulphuret of ammonia, to which an excess of sulphur has been 
 added. The sulphuret of mercury forms at first black, but after some 
 
Detection of Mercury. 571 
 
 time becomes red, which colour may be brightened by the action of a 
 warm solution of caustic potash. 
 
 The phosphurets and seleniurets of mercury are of no importance. 
 
 The presence of mercury in solution is very easily ascertained. By 
 the immersion of a clean slip of copper, the mercury is precipitated in 
 the metallic state, as a grey powder on the surface of the copper. With 
 a magnifying glass, this is found to consist of minute but brilliant glo- 
 bules, and the surface becomes brilliant when rubbed. Protochloride 
 of tin and phosphorous acid also precipitate the mercury in the metallic 
 state, which by boiling aggregates into larger globules, easily collected 
 and recognized. Any solid body containing mercury gives, when 
 ignited in a tube of hard glass, particularly on the addition of a little 
 carbonate of potash, a sublimate of metallic mercury, which, if in very 
 small quantity, appears only as a ring of grey powder, but is found to 
 consist of brilliant globules, when inspected with a lens. 
 
 The two classes of salts which quicksilver forms are very distinctly 
 characterized by their behaviour to re-agents. The salts of the suboxide 
 give with the caustic alcalies black or grey precipitates. Sulphuretted 
 hydrogen produces the black sulphuret. Solution of chloride of sodium 
 gives a white precipitate, which is calomel, and the bichromate of potash 
 produces an orange chromate of the suboxide. 
 
 The salts of the red oxide are precipitated, yellowish by an excess of 
 caustic potash, and white by ammonia ; with sulphuretted hydrogen in 
 excess, a black precipitate of protosulphuret ; and with iodide of potas- 
 sium, a red precipitate, which is redissolved in an excess. 
 
 In many cases, the appearance of these precipitates varies with the 
 nature of the acid with which the oxide of mercury had been combined, 
 but in all cases ammonia gives a black precipitate with the salts of the 
 suboxide, and a white precipitate with those of the red oxide, in the 
 cold. 
 
 There is a class of pharmaceutical preparations obtained by triturating 
 mercury with other inactive substances. In these the mercury is only 
 reduced to a state of very minute division ; it is not oxidized. By tri- 
 turating mercury with sulphur, however, a certain quantity of sulphuret 
 is formed, although the great mass of the metal, and of the sulphur, re- 
 mains uncombined. 
 
 OF GOLD. 
 Symbol. Au. Eq. 196'6 or 2458. 
 
 This valuable metal is found only in the metallic state, either pure or 
 alloyed with other metals, particularly silver, tellurium, and mercury ; 
 
572 Extraction and Properties of Gold. 
 
 the rocks in which it is found distributed are generally those of igneous 
 origin, but the greater part of the gold of commerce is obtained by 
 washing the sands of the rivers which have their source in such moun- 
 tains, the particles of metal being carried down with the detritus of the 
 rock, and, from their greater density, being deposited first when the 
 sand is washed ; any fragments large enough to be visible are separated 
 by the hand, but the remainder is dissolved out by a process of amalga- 
 mation, similar to that described, p. 564, for the extraction of native 
 silver. When the gold is alloyed with silver they are separated by 
 means of nitric acid, which dissolves the latter metal, but if the quantity 
 present be small, the gold protects it from the action of the acid, and a 
 process termed quartation is employed ; this consists in alloying the 
 gold with three times its weight of silver, and then acting on the mass 
 with nitric acid ; when the solution of the silver has once commenced 
 it does not cease until the entire quantity present has been removed. 
 
 Pure gold is yellow, very malleable and ductile, and nearly as soft as 
 lead ; hence for the purposes of commerce and of the coinage, it is 
 alloyed with a quantity of copper, amounting to 83 in 1000. Instances 
 of the exceeding degree of division to which this metal may be reduced, 
 have been given, p. 5. Gold has no tendency to combine with oxygen 
 or sulphur, and hence retains its brilliancy in the open air for any 
 length of time. It melts at 2016 ; its density is 19 '5 ; it is not acted 
 on by any single acid, but is dissolved by nitro-muriatic acid, and by a 
 mixture of nitric and hydrofluoric acids. 
 
 The symbol of gold is Au, from its Latin name, and its equivalent 
 numbers 2458 or 196-6 
 
 There are two oxides of gold obtained by the decomposition of the 
 corresponding chlorides, which will be hereafter described. The pro- 
 toxide of gold, AuO, is a powder of a violet colour, so dark that it 
 appears quite black : it does not combine with acids, but dissolves in 
 solution of caustic potash and soon separates into the higher oxide and 
 metallic gold. The peroxide of gold, auric acid, Au0 2 , is easily pre- 
 pared by decomposing perchloride of gold by an excess of magnesia ; 
 chloride of magnesium dissolves, and an insoluble aurate of magnesia 
 remains ; this is to be then digested in cold dilute nitric acid which 
 dissolves out the magnesia with a little auric acid, but leaves the greater 
 part of this last behind as a reddish hydrate, which, when dried in the 
 air, becomes brown, and at 212 gives off water and remains black. 
 This substance does not combine with any acid ; by muriatic acid it is 
 decomposed, perchloride of gold being formed ; it combines with alca- 
 lies strongly, so that the precipitate given by a solution of gold, with a 
 caustic alcali, is always a compound of auric acid with the base ; there 
 
Properties and detection of Gold. 573 
 
 are soluble and insoluble aurates, but their atomic constitution has not 
 been studied. Solutions of auric acid, and even that body in powder, 
 are decomposed rapidly on exposure to the light ; metallic gold being 
 separated. 
 
 Owing to the extensive employment of an alcaline solution of this 
 oxide of gold or auric acid, instead of cyanide of gold, for the processes 
 ot electro-gilding, its preparation has become of importance, and the 
 following process is much more advantageous than the older one above 
 given. One part of gold is to be dissolved in four of nitro-muriatic 
 acid, the liquor evaporated to dryness, and then redissolved in water, 
 which leaves behind a little metallic gold and some protochloride. The 
 solution thus obtained is to be mixed with pure potash until it has a 
 strongly alcaline reaction ; it becomes turbid and is then to be gradually 
 mixed with solution of chloride of barium : a canary yellow precipitate 
 of aurate of barytes is immediately formed. By some care the whole 
 of the gold can be precipitated and the solution left colourless, but an 
 excess of barytes should be avoided. The aurate of barytes is to be 
 very well washed with water, and is to be then decomposed by boiling 
 with dilute nitric acid which sets the auric acid free, and takes the 
 barytes. The auric acid thus obtained must be dried with extreme care, 
 as even the temperature of a water bath decomposes some of it reducing 
 the gold : it is best dried in vacuo over sulphuric acid. The wash 
 liquors of the precipitates always contain some gold which may be re- 
 covered by appropriate means. 
 
 Gold is deposited from its solutions, by means of any of the deoxi- 
 dizing agents, noticed under silver and mercury. Protosulphate of iron 
 gives a brown powder, which, under the burnisher, assumes the colour 
 and brilliancy of the metal ; protochloride of tin produces a fine purple 
 precipitate, the purple of Cassius, which is not metallic gold, but it 
 appears to be a compound of oxide of tin and protoxide of gold, for it 
 is perfectly soluble in water of ammonia, and mercury digested on it 
 does not dissolve out any metallic gold. It is hydrated. It is disputed 
 whether it contains the sesquioxide or the peroxide of tin only. The 
 formula AuO + 3Sn0 2 + 4HO. has been given for it, but Berzelius 
 prefers AuO. SnO 2 + Sn 2 O 3 + 4HO. Various processes are given 
 for preparing this substance, which it is not easy to obtain of the pro- 
 per depth and purity of colour ; when exposed to a red heat, it is 
 changed into a mixture of peroxide of tin and metallic gold, but its 
 purple colour remains ; it is hence employed for painting on glass and 
 porcelain. "When metallic gold is heated on the surface of glass, it 
 appears to become oxidized, and in that state to combine with the glass, 
 staining it a rich purple colour. This colour is due apparently to the 
 
574 Properties of Palladium. 
 
 protoxide which exists in the purple of cassius. Por if the glass be 
 melted with full access of air it becomes colourless, whilst the colour is 
 also removed by deoxidizing agents. The gold appears, therefore, to 
 produce colour only in the intermediate state of prot oxidation. 
 
 Sulphur and gold combine to form sulphurets similar in constitution 
 to the oxides ; they are produced by decomposing the corresponding 
 chlorides by sulphuretted hydrogen ; they are brown powders, which 
 are strong sulphur acids, and dissolve in hydrosulphuret of ammonia. 
 
 The uses of gold are well known. The commercial value of its alloys 
 is ascertained, either by cupellation, p. 564, by quartation, p. 572, or 
 by the touchstone, which is a variety of flinty slate (lydian stone), or 
 basalt, of an uniform black colour. A streak is drawn on the surface 
 of the stone with the piece of gold to be tried, and this is compared 
 with those given by a series of alloys, the composition of which is 
 known, until one is found identical in aspect with it, which must result 
 from the two being of the same degree of purity. In these trials it is 
 necessary, however, to know beforehand whether the alloy is silver or 
 copper, or whether, as frequently occurs, both be present. 
 
 OF PALLADIUM. 
 
 This metal is found associated with platinum, but seldom constitutes 
 more than one per cent, of the ore. After the platinum has been pre- 
 cipitated from the solution in aqua-regia, by means of sal-ammoniac, 
 cyanide of mercury is added by which all the palladium is thrown down 
 as cyanide; this, when ignited, is totally decomposed and metallic 
 palladium remains. 
 
 The general characters of palladium are very similar to those of 
 platinum ; it is white, almost infusible, but admits of being welded ; it 
 is malleable and ductile ; specific gravity, 11'5. When heated below 
 ignition, its surface becomes blue and green from the formation of a 
 thin layer of sub-oxide, but by a stronger heat this is reduced and the 
 metal becomes bright. Palladium is not sensibly acted on by muriatic 
 or sulphuric acid, but it dissolves in nitric acid with facility. The 
 symbol of palladium is Pd, and its atomic weight 665'9 or 53'4. 
 
 There are three oxides of palladium, of which only one, the protoxide 
 PdO, equivalent 7 65 -9 or 61 -4, has been as yet studied with much 
 care ; this oxide is formed when palladium dissolves in nitric acid, and 
 is obtained as a black powder when the nitrate is decomposed at a 
 temperature below redness ; by the addition of potash to a salt of pal- 
 ladium, this oxide is thrown down, hydrated, as a brown powder. If 
 the protoxide of palladium be exposed to a dull red heat, it parts with 
 
State of Platinum in Nature. 575 
 
 half its oxygen, and a suboxide Pd 2 O is produced, which gives a series 
 of salts, resembling in general characters those of the suboxide of 
 copper. 
 
 By decomposing the bichloride of palladium with carbonate of pot- 
 ash, the deutoxide Pd0 2 is obtained as a yellowish brown powder ; it 
 appears to combine both with acids and alcalies, but of its properties 
 very little is known. 
 
 There are sulphurets of palladium, which correspond to the oxides, 
 but further than that they are brown powders, generated by the action 
 of sulphuret of hydrogen on the respective chlorides, they have not been 
 much examined. 
 
 Palladium in solution, is at once recognized by giving with ammonia 
 a flesh-red precipitate, which dissolves in an excess, giving a colourless 
 solution ; with cyanide of mercury it produces a whitish precipitate, and 
 with iodide of potassium, a black powder. 
 
 OF PLATINUM. 
 
 Platinum was originally discovered in the sands of some South Ame- 
 rican rivers, and from its similarity to silver (plata) obtained the name 
 of platina (little silver.) It has since been found more abundantly in 
 the mountains of the Oural, which separate European from Asiatic 
 Russia. The supply of platinum has increased so much lately, that a 
 coinage of it, issued some years ago by the Eussian government, was 
 obliged to be recalled, from the rapid diminution in value which it 
 underwent. 
 
 The platinum exists native, but is associated with a great number of 
 metals, particularly five, remarkable for not being found except along 
 with it. The grains of metal are disseminated in rocks of igneous 
 origin, (granite, syenite) and in the sands of rivers which flow over 
 them. The processes for the extraction of platinum from the crude ore 
 are very complex, and the working of it has become a branch of manu- 
 facture, the chemist always obtaining the pure metal in commerce, and 
 its details need not be inserted. 
 
 Pure platinum is white like silver, but not so brilliant. It is the 
 densest of all bodies, its sp. gr. being 21*5. It is very malleable and 
 ductile. It is infusible except by the hydroxygen blow-pipe, but at a 
 high temperature may be welded like iron, and thus worked into the 
 various forms in which it is employed in the chemical arts. Platinum 
 may also exist in a state of minute division, and thereby becomes useful 
 in many operations, particularly those of slow combustion, as noticed 
 in pp. 229, 237, 344. The finely divided platinum is of two kinds, 
 
576 Different forms of Platinum. 
 
 spongy platinum and platinum-black. The former is prepared by dis- 
 solving chloride of platinum and sal-ammoniac separately in alcohol, 
 and mixing the solutions; the double chloride of platinum and ammon- 
 ium is thus produced, as a fine yellow powder, which, whilst yet moist, 
 is to be made into balls like peas, and heated to full redness. The 
 chlorine is all carried off by the hydrogen of the ammonia, and the 
 platinum remains as a light grey sponge, in the form of the little balls ; 
 it is this kind of platinum that is used in the aphlogistic lamp, in the 
 eudiometer, and for other purposes already noticed. The platinum- 
 black may be obtained either by precipitating a solution of bichloride 
 of platinum with zinc, and boiling the precipitate in muriatic acid for 
 a few minutes ; or better, by dissolving protochloride of platinum in 
 a boiling solution of potash, and of adding thereto alcohol, in small 
 quantities at a time, until all effervescence ceases ; a jet black precipi- 
 tate is produced, which is to be boiled successively with alcohol, mu- 
 riatic acid, and potash, and, finally, four or five times in water. The 
 substance thus obtained is pure metallic platinum, but it is a dull black 
 power. It absorbs oxygen in considerable quantity, and hence when 
 brought into an atmosphere of any inflammable vapour it facilitates the 
 combination of the two with remarkable energy. Doebereiner terms it 
 an oxyphorus from this property. Many interesting reactions in organic 
 chemistry succeed only by the aid of this platinum-black. 
 
 Platinum has no tendency to combine with the oxygen of the air, 
 but it is oxidized slightly when nitre or even potash is fused in contact 
 with it. It resists the action of all acids except the nitro-muriatic acid 
 and the nitro-hydrofluoric acids, and in these it dissolves more slowly 
 than gold. 
 
 The symbol of platinum is PL Its equivalent is 1233'5 or 98*8. 
 By the decomposition of the chlorides of platinum, two oxides of it are 
 obtained. 
 
 Protoxide of Platinum. PtO. Equivalent 1333-5 or 106'8. Is 
 produced by digesting the protochloride with as much potash as exactly 
 suffices it for its decomposition. An excess of potash dissolves it, 
 forming a dark olive liquor. When pure it is a black powder, easily 
 decomposed by heat into platinum and oxygen. It combines with acids 
 forming salts, which have been as yet but little studied. 
 
 Deutoxide of Platinum. Pt0 2 . Equivalent 1433*5 or 114'8. This 
 substance has a remarkable tendency to combine with bases, and hence 
 cannot be obtained pure by the direct decomposition of the chloride, as 
 it carries down with it, always, a quantity of the alcali employed, if 
 this be in excess, and if it be not, then only a basic chloride is obtained. 
 The nitrate of platinum, however, when decomposed by soda, yields 
 
Detection of Platinum. 577 
 
 one-half of the oxide of platinum, pure, but hydrated, forming a brown 
 powder like the peroxide of iron ; when anhydrous it is black ; by heat 
 it is resolved into oxygen and platinum. This oxide appears to form 
 two kinds of salts, one with acids, in which it is the base, and the 
 other with alcalies and earths, in which it is the acid. In another place 
 I shall notice them further. 
 
 There are two sulphurets of platinum corresponding to the two 
 oxides. The first Pt.S. is produced by digesting the protochloride with 
 sulphuret of hydrogen. It is a deep brown powder, decomposed by a 
 red heat, but not otherwise interesting. The bisulphuret, PtS 2 , is pro- 
 duced in a similar way by adding sulphuret of hydrogen to a solution 
 of bichloride of platinum. It is a brown powder, which absorbs oxygen 
 rapidly even in drying, and becomes acid. By nitric acid it is converted 
 with intense action into sulphate of platinum. 
 
 Phosphurets and seleniurets of platinum have been, formed, but they 
 are not important. 
 
 The detection of platinum is effected easily by precipitating its solu- 
 tion by a slip of zinc, when a black powder separates, soluble only in 
 aqua regia, and then giving with re-agents the following results. A 
 solution of sal-ammoniac in alcohol gives a fine yellow crystalline pre- 
 cipitate ; a solution of iodide of potassium a black precipitate, which 
 dissolves in an excess producing a rich crimson solution ; with sulphuret 
 of hydrogen the brown bisulphuret of platinum, and with proto- 
 chloride of tin, a chocolate precipitate or a deep reddish solution, accord- 
 ing to the quantity present. 
 
 The action of this last re-agent is founded on the reduction of the 
 bichloride of platinum to the state of protochloride by the first portion 
 of protochloride of tin employed. This test acts, therefore, also with 
 solutions of the protoxide of platinum, and the metal may be also 
 known to be in the state of protoxide, when, on the application of 
 iodide of potassium in excess, the liquor is not coloured red, but be- 
 comes so on the addition of a drop of nitric acid or chlorine water. 
 
 The great use of platinum is for the manufacture of the large boilers 
 used in the concentration of oil of vitriol ; it is also universally em- 
 ployed as the material for the crucibles used in the more delicate opera- 
 tions of mineral analysis. Indeed the accuracy now attained in that 
 department of research, is in a great part due to the introduction of 
 platinum vessels into the laboratory ; it is also occasionally used in 
 enamelling on glass and porcelain. 
 
 OF IKIDIUM, RHODIUM AND RUTHENIUM. 
 
 These metals are, like palladium and osmium, found only associated 
 37 
 
578 Iridium and its Compounds. 
 
 with platinum, and are extracted from the crude ore already noticed ; 
 the iridium and osmium are, however, united, forming an alloy, the 
 crystalline grains of which are merely mixed with the particles of the 
 platinum ore in which the rhodium and palladium are contained ; when 
 the platinum ore is dissolved in aqua regia, the iridium and osmium ore 
 remains undissolved, and requires to be treated by fusion with caustic 
 potash, the iridium then becomes oxidized and combines with the alcali. 
 
 The processes of purification need not be inserted. 
 
 Metallic iridium resembles platinum, but is still more infusible ; when 
 fused by the voltaic battery, it is white and very brilliant ; specific gra- 
 vity 18-68 ; after being strongly heated, it is insoluble in acids, but 
 when obtained in the spongy form by the reduction of its oxides by 
 hydrogen at a red heat, it becomes slightly oxidized and is soluble in 
 aqua-regia. 
 
 Iridium combines with oxygen in four proportions, its symbol is Ir, 
 and its equivalent 1233 5 or 98*8, the same as that of platinum. 
 
 Protoxide of Iridium. IrO, is obtained by decomposing the proto- 
 chloride by carbonate of potash ; it appears as a greenish-grey hydrate. 
 This oxide combines with acids. The sesquioxide, Ir 2 3 , is that formed 
 when the metal is ignited with potash ; it is a bluish-black powder, and 
 is the most permanent of the oxides ; it is not decomposed except at a 
 heat above the melting point of silver, whereas the higher and lower 
 degrees pass into it on the application of heat. This oxide unites with 
 acids, giving dark blood-red coloured salts. The deutoxide of iridium, 
 IrO-2, exists combined with acids, but has not been isolated. Thej^er- 
 oxide, Ir0 3 , is formed in small quantity when iridium is ignited with 
 nitre, but is best prepared by the decomposition of the perchloride. 
 Solutions containing salts of the protoxide and of the peroxide toge- 
 ther, present a great variety of shades of purple and blue, and hence 
 gave origin to the name of the metal (Iris). 
 
 Rhodium. This metal remains dissolved in the nitro-muriatic solu- 
 tion of the platinum ore after the platinum and palladium have been 
 separated from it ; for the mode of eliminating it from the many metals 
 which still remain, I refer to the systematic works. 
 
 Metallic rhodium is obtained by the decomposition of its chloride at 
 a red heat by hydrogen gas ; when rendered coherent by pressure it is 
 white, but very brittle and hard ; sp. gr. about 11*0. If completely 
 pure, it is not acted on even by aqua-regia, but it illustrates remarkably 
 the principle of communicated affinity described, p. 232, for when 
 alloyed with copper, lead, or platina, it dissolves along with the other 
 metal in aqua-regia. Rhodium derives its name from the beautiful rose 
 (godog) colour of its solutions ; it combines with oxygen in two propor- 
 tions; its symbol is R, and its equivalent 661'4 or 52'2. 
 
Rhodium and Ruthenium. 579 
 
 Of ike protoxide of rhodium, it is only known that it exists in cer- 
 tain salts that have been but little examined ; the sesquioxide, R 2 O 3 , is 
 the basis of the most important compounds of this metal. It is pre- 
 pared by igniting metallic rhodium with a mixture of caustic potash 
 and nitre ; a brown mass is formed, which, when decomposed by mu- 
 riatic acid, yields the oxide as a grey hydrate, insoluble in acids. 
 Berzelius is of opinion, that there are two isomeric forms of this oxide, 
 the salts of one being yellow in solution, and those of the other being 
 rose-coloured. There are supposed to exist also, complex oxides of 
 rhodium, resembling, probably, the complex oxides of iron and man- 
 ganese, The equivalent of rhodium is so nearly equal to that of palla- 
 dium, that some relations might be expected in the constitution of their 
 combinations, which as yet does not appear to have been experimentally 
 investigated. 
 
 Ruthenium. This is a metal recently discovered by Glaus among the 
 residues of the treatment of platinum ores, combined with osmium and 
 iridium. The material is mixed with common salt, and treated by a 
 current of chlorine ; the product dissolved in water and precipitated by 
 ammonia. On distilling this precipitate with nitric acid, osmic acid is 
 given off, and the residue in the retort is to be mixed with nitre and 
 caustic potash and fused in a silver crucible. The fused mass is dis- 
 solved in cold water and left to clear ; a beautiful orange-coloured solu- 
 tion of rutheniate of potash is produced, which, when neutralized by 
 nitric acid, is decomposed, sets free oxygen, and deposits a velvety- 
 black precipitate of- sesquioxide of ruthenium, from which the metal is 
 reduced by the action of a current of hydrogen gas at a red heat. 
 
 In the metallic state, ruthenium closely resembles iridium ; its sp. 
 gr. is 8*6. With oxygen it combines in four proportions. The pro- 
 toxide, Eu.O. is obtained by igniting protochloride of ruthenium with 
 carbonate of soda in a current of carbonic acid gas; it is a black 
 powder. When heated in contact with air it absorbs oxygen. The 
 sesquioxide may be obtained anhydrous by calcining the metal or the 
 protoxide, or hydrated by decomposing the sesquichloride by alcalies ; 
 in both states it is a black powder, which is insoluble in alcalies. It is 
 formed by the decomposition of ruthenic acid in the mode of extracting 
 the metal described above. 
 
 Peroxide of Ruthenium. RuO 2 , is produced by roasting the persul- 
 phuret, KuS 2 , in a current of air ; it is a blackish-blue powder. It is 
 precipitated as a hydrate by evaporating together solutions of carbonate 
 of soda and of the double bichloride of ruthenium and potassium. In 
 this state, however, it retains alcali combined. 
 
 Ruthenic Acid. Ru0 3 . Has not been isolated, but is formed by 
 
580 General Characters of Salts. 
 
 igniting the oxides with nitre and potash. Riitheniate of potash is 
 formed, which dissolves in water with a rich orange colour. If set free 
 by an acid, it rapidly decomposes into sesquioxide of ruthenium and 
 free oxygen. 
 
 The Sulphurets of Ruthenium are of no importance ; its salts, except 
 the chlorides, have not yet been much studied. Its characteristic re- 
 actions are evident from what has been above described. 
 
 CHAPTER XIY. 
 
 ON THE GENERAL PROPERTIES AND CONSTITUTION OF SALTS. 
 
 THE bodies included under the name of salts, may be arranged in two 
 classes, characterized by a remarkable difference of chemical constitu- 
 tion ; the first comprehends such as are formed "by the union of a 
 simple body of the chlorine family, with a metal, thus chloride of so- 
 dium, iodide of potassium, bromide of iron, fluoride of calcium, are of 
 this kind. The salts of the second class, on the contrary, are formed 
 by the union of substances already compound, and possessed of those 
 opposite properties, by which one is determined to be an acid and the 
 other a base. The general characters of acids and bases, and of the 
 salts formed by their union, have been sufficiently described in many 
 places already, (pp. 199, 207, 353,) and need not be here repeated. 
 In general, the acids and basis so engaged contain oxygen as their 
 electro -negative ingredient, but there are classes of salts formed by the 
 union of sulphur acids and sulphur bases, and as noticed in pp. 328 and 
 389, selenium and tellurium resemble oxygen and sulphur in this re- 
 spect. The history of the metallic compounds in the last chapter 
 affords many cases of the existence of such salts, arid, in the detailed 
 history of the more important salts which will follow, others shall be 
 described ; but there are some points of more general interest touching 
 the salts as a class, the laws of formation to which they are subjected, 
 
General Characters of Salts. 581 
 
 and the relations between their several subdivisions, which I shall now 
 proceed to notice, as briefly as the subject will admit. 
 
 I have frequently adverted to the circumstance that the bodies termed 
 hydracids, were in reality not acids but compounds of hydrogen, in 
 which that element acted as a positive metallic constituent, and that 
 when they act on a metallic oxide, double decomposition generally 
 occurs, precisely as when a chloride, or iodide of zinc, or copper, is de- 
 composed by potash or by soda. Thus, Cl.H and K.O produce Cl.K 
 and H.O ; precisely as when Cl.Cu and KO produce C1K and CuO. The 
 chlorides and iodides of hydrogen, although popularly called acids 
 (muriatic and hydriodic acids) are, thus, really salts, and in all their 
 reactions display that constitution. Also when a hydracid is put in 
 contact with a metal, the solution of it is determined altogether by its 
 power of expelling the hydrogen, and of taking its place. Erom C1H 
 and Zn there are produced ClZn, and H becomes free, precisely as 
 chloride of copper, CuCl, is decomposed by zinc, copper being preci- 
 pitated. The hydracids, therefore, do not unite with metallic oxides to 
 form salts, but they decompose them, water being evolved. 
 
 The hydracids are capable of forming what are termed acid-salts, thus 
 the fluoride of potassium combines with hydrofluoric acid to form an 
 acid compound ; the chloride of hydrogen combines with chloride of 
 gold; but these bodies are really double salts. The compounds of 
 hydrogen, in such combinations, resembling the corresponding com- 
 pounds of zinc, copper, &c., which, under the same circumstances, all 
 form corresponding double salts. 
 
 I have already described the functions of water, in the hydrates of the 
 ordinary oxygen acids, showing that these are salts of water, subject to the 
 same rules of composition as the ordinary salts of the same acid. When 
 such an acid, as for example, oil of vitriol, S0 3 + HO, acts upon a 
 metallic oxide, the water is displaced, and a salt of the metallic oxide 
 formed. When such a hydrated acid acts on a metal, this may be dis- 
 solved either by substitution for, and displacement of, the hydrogen, as 
 in the ordinary cases of obtaining that gas, or by the direct decom- 
 position of a part of the acid, as in the processes for obtaining sul- 
 phurous acid and nitric oxide, (pp. 341, 375, 390.) 
 
 Salts may be either neutral, acid, or basic. A salt is neutral wlu'ch 
 does not manifest, in its action on vegetable colours, acid or alcaline 
 properties, and consists generally of one equivalent of acid united to 
 one equivalent of base, this last containing one equivalent of oxygen. 
 The true neutral salts have, therefore, for bases, either suboxides or 
 protoxides. The salts of sesquioxides and deutoxides generally react 
 like acids, except where there is an excess of base. The quantity of 
 
582 General Characters of Salts. 
 
 acid with which metallic oxides are disposed to unite, in their most 
 neutral salts, is subject to a remarkable proportion, being one equiva- 
 lent for each atom of oxygen which the base contains. Thus, a pro- 
 toxide or suboxide combines with one equivalent of acid. The sulphate 
 of zinc is ZnO.SO 3 ; sulphate of copper CuO.SO 3 ; the subnitrate of 
 mercury Hg 2 O.NO 5 . A sesquioxide unites with three equivalents of 
 acid, as sulphate of alumina, A1 2 O 3 + 3S0 3 . Salts in which this law 
 is observed to hold are generally described as neutral, even though their 
 action on vegetable colours may indicate a preponderance of acid ; and 
 understanding by the word, not the absence or presence of the property 
 of changing turmeric or litmus, but the state in which the characteristic 
 properties of acid and base are most neutralized, the definition of a neu- 
 tral salt may best be, that in which the number of atoms of acid is equal 
 to the number of atoms of oxygen in the base. 
 
 There are two kinds of add salts ; 1st, those in which the excess of 
 acid is present in its hydrated form ; and 2nd, those in which the dry 
 acid is in excess. These differ remarkably in nature, those of the first 
 class being not really acid salts, but double salts, of which one base is 
 water. Thus, the common bisulphate of potash, of which the formula 
 is KO.S0 3 + HO.S0 3 , is one of a family of double salts, in which 
 sulphate of potash is united to a sulphate of protoxide, as sulphate of 
 copper, of zinc, of iron, or of magnesia. There is thus really no excess 
 of acid. In like manner, the bicarbonate of potash is a double car- 
 bonate of potash and water, KO.C0 2 + HO.C0 2 , to which similar 
 analogies exist. These salts resemble completely the acid salts of the 
 hydracids, described in the beginning of this chapter; KO.S0 3 -f- 
 HO.SO 3 corresponding exactly to K.F. + H.F. 
 
 It is only the salts which do not contain water, that can be looked 
 upon as having a true excess of acid. Of these, the chromates of 
 potash afford the best examples, in which an atom of potash is com- 
 bined with one, two, or three equivalents of acid, forming KO -f Cr0 3 , 
 KO -f- 2Cr0 3 , and KO + SCrOa. There exists a similar compound of 
 sulphuric acid and potash, which is easily decomposed by water, being 
 changed into the ordinary bisulphate. 
 
 Basic salts are those in which there is present more than one equi- 
 valent of base for each equivalent of acid ; thus in turbeth mineral there 
 is 3HgO + S0 3 . In basic nitrate of copper, 3CuO + N0 5 .HO ; in 
 basic sulphate of copper, 4CuO + S0 3 + 4HO. It has been thought, 
 that the proportion of base in basic salts bore a simple relation to the 
 quantity of oxygen in the acid, being generally equal to it. This idea 
 was founded on the circumstance, that the early analyses of many basic 
 sulphates gave the proportion of three atoms of base to one of acid ; 
 
Acid and Basic Salts. 583 
 
 but the basic sulphate of mercury is the only example I have found 
 really to exist of that constitution ; the other sulphates containing 
 always a quantity of metallic oxide, amounting to two, or four, or six 
 equivalents. 
 
 The first and most remarkable insight into the constitution of basic 
 salts which we obtained, was the principle laid down by Graham, that 
 all salts are really neutral in constitution. The analogies of hydrogen 
 to the magnesian family of metals, and hence of water to the oxides of 
 that class, suggested the idea, that the excess of base should not be 
 considered as actually combined with the acid, but that it replaced the 
 water of crystallization which the neutral salt contains. This view was 
 remarkably supported by the evidence of the basic nitrates, adduced by 
 Graham, and has been extended to the chlorides and sulphates by my 
 own investigations. Thus, nitrate of copper, in its crystallized and 
 neutral condition, is CuO.NO 5 -f- 3HO, and the basic nitrate is 
 formed by HO.NO 5 -f- 3CuO. Comparing these two with the hydrated 
 nitric acid, sp. gr. 1*42, the formulae 
 
 Nitrate of water, = HO.NO 5 + 3HO. 
 
 Nitrate of copper, = CuO.NOs + 3HO. 
 
 Basic nitrate of copper, = HO.NO 5 + 3 CuO. 
 
 evidently correspond, the only difference being, that in place of oxide 
 of hydrogen, there is oxide of copper substituted, in a proportion con- 
 tinually increasing. Prom these conditions it follows, that with the 
 same acid and base, there may be formed a great variety of basic salts ; 
 for the neutral salt may crystallize with many different proportions of 
 water, and from each there may be one or more basic salts derived, by 
 substitution of metallic oxide. Thus, the sulphate of zinc generally 
 contains eight atoms of base to one of acid, and in its common crys- 
 tallized form these consist of one of oxide of zinc and seven of water ; 
 but in becoming basic, the quantity of oxide of zinc gradually increases, 
 and a series of basic salts is formed, as 
 
 SO 3 + ZnO 4. 7HO, SO 3 -f- 6ZnO 4. 2HO, 
 
 SOa-f 4ZnO + 4HO, SO 3 + 8Zn - 
 
 The salts, consisting of a simple body of the chlorine family, united 
 with a metal, as chloride of sodium, iodide of potassium, &c., and 
 which, from the analogy of common salt, are termed haloid salts, (dx$ 
 and sido$), combine frequently with the oxide of the metal which they 
 contain, and form basic haloid salts. Thus, we have Cu Cl -f 3 Cu O, 
 basic chloride of copper ; HgCl + 3 HgO, basic chloride of mercury ; 
 PbI+2PbO, basic iodide of lead. Such compounds are, however, 
 
584 Constitution of Basic Salts. 
 
 generally termed oxy chlorides, oxyiodides, fyc. ; they are subjected to 
 precisely the same laws of derivation and constitution as the basic salts 
 of the same metals with ordinary acids. 
 
 Prom what has been said above, it might be concluded that a neutral 
 salt consisted in all cases of one equivalent of base, united to one of 
 acid, and that wherever the base was present in larger quantity, the salt 
 should necessarily be termed basic ; but an important distinction re- 
 quires to be here laid down. There are three phosphates of silver, 
 which contain respectively one, two, and three atoms of oxide of silver 
 united to one atom of acid ; but we do not consider the first as being 
 neutral, and the others as containing an excess of base, for we find 
 them to arise from the state of the phosphoric acid, which, according as 
 it had been combined with more or less basic water, gives origin to 
 classes of salts, containing one, two, or three equivalents of oxide. The 
 peculiar relations of the phosphoric acid, and of arsenic acid also, to 
 water, and the effect of it on the composition of these salts, have been 
 noticed already in pp. 413 and 535. In addition, therefore, to ordi- 
 nary neutral salts, which are monobasic, or contain an equivalent of base 
 and one of acid ; there are bibasic and tribasic salts, containing respec- 
 tively two and three equivalents of base to one of acid, and yet being 
 neutral ; by which is meant, not that they are without action on test 
 paper, since one tribasic salt may redden litmus, whilst another may 
 brown turmeric paper ; but they are derived from a definite combination 
 of the acid with basic water, and not by the replacement of the water of 
 crystallization by metallic oxide, as in the case of real basic salts. 
 
 A simple distinction between bibasic and tribasic salts on the one 
 hand, and ordinary basic salts on the other, is, that in the former the 
 different atoms of base may be of different kinds, whilst, in the latter, 
 the metallic oxide replacing the water is all of the same sort. Thus, 
 there is basic sulphate of zinc and basic sulphate of copper, but there 
 could not be a basic sulphate partly of zinc and partly of copper : the 
 sulphuric acid being monobasic. But there is a tribasic phosphate of 
 soda, ammonia, and water ; another of magnesia, ammonia, and water ; 
 others of potash and water. The presence of two or more bases of dif- 
 ferent kinds, thus distinguishing completely the salts of the bibasic and 
 tribasic acids from the ordinary basic salts. 
 
 These principles, which are now of the highest importance in philo- 
 sophical chemistry, were first applied by Graham to the salts of the 
 phosphoric and arsenic acids, but they have been found to throw light 
 upon some of the most difficult questions in the history of the organic 
 acids, of which a great number have been shown by Liebig to be simi- 
 larly circumstanced. 
 
Of Loulle Salts. 585 
 
 Double salts are formed by the union of two simple salts. In general 
 both salts contain the same acid, but different bases, and the two bases 
 belong to different natural groups ; as when sulphate of potash com- 
 bines with the sulphates of the protoxides of the metals of the second 
 isomorphous group, replacing therein the atom of constitutional water 
 which they all contain. Thus, ordinary sulphate of zinc, ZnO.SO 3 .HO 
 + 6aq. gives with KO.S0 3 the double salt (ZnO.SO 3 +KO.S0 3 ) +6aq ; 
 and sulphate of copper, CuO.S0 3 .HO + 4aq. gives (CuO.SO 3 +KO.SO 3 ) 
 + 4aq. The sulphate of potash combines also with the sesquioxides of 
 the third isomorphous group, such as alumina, and gives origin to the 
 various kinds of alums. Similar classes of salts are formed by the 
 union of the other alcaline sulphates with the sulphates of the second 
 and third isomorphous groups. The salts of isomorphous bases with 
 the same acid do not appear capable of combining, so as to produce 
 salts; but in crystallizing are mechanically mixed (p. 31). This rule, 
 however, is not without exception, as the constant composition of the 
 magnesian limestone CaO.CO^j+MgO.COg, indicates that its elements 
 are chemically united. 
 
 Salts of different acids, with the same base, may combine to form 
 double salts, as the oxalate and nitrate of lead ; and there are examples, 
 though few, of a double salt containing two acids and bases. 
 
 The relations of salts to water have been fully discussed, under the 
 heads of solution and crystallization (p. 20, et seq.), and of the chemi- 
 cal properties of water (p. 352), to which it is sufficient to refer. 
 
 The haloid salts combine together to form double salts, as the double 
 chloride of gold and sodium, the double chloride of copper and potas- 
 sium, and conform therein to the same general principles that have been 
 just described for the oxygen salts. 
 
 It has been always mentioned, that when muriatic acid acts on a 
 metallic oxide, water is formed, and a chloride of the metal produced. 
 The question of whether this always occurs is not without interest, and 
 has been often agitated. There is no doubt but that it is the general 
 rule ; but I am inclined to think it may be not without exception. The 
 difference of properties of the chlorides of magnesium and of alu- 
 minum in the anhydrous state, and when crystallized with water, is so 
 great, as to give reason to suppose that these chlorides decompose water, 
 and that the crystallized hydrated salts are not A1 2 C1 3 4. 3. HO, and 
 Mg Cl + HO, but A1 2 O 3 -f 3.H Cl, and Mg O + H Cl. Hence, it 
 is probable that magnesia and alumina combine with hydracids without 
 decomposition. 
 
 The sulphur salts consists of a sulphur acid, which is generally a 
 sulphuret of an electro-negative metal or of carbon, combined with a 
 
586 Nature of Sulphur Salts. 
 
 sulphur base, which is a sulphuret of an electro-positive metal. In 
 their constitution they resemble the analogous oxygen salts. Many of 
 their characters have been described already page 389. 
 
 The positive metallic sulphurets combine frequently with the haloid, 
 or oxygen salts of the same metal, to form basic salts ; this is the case 
 particularly with mercury. Thus there is HgO. S0 3 -f 2 Hg S, similar 
 to HgO.S0 3 -f- 2 HgO, ordinary turbeth mineral. 
 
 It had been long remarked as curious, that bodies so totally different 
 in composition as the compound of chlorine with a metal on the one 
 hand, and of an oxygen acid with the oxide of the metal on the other, 
 should be so similar in properties, that both must be classed together as 
 salts, and should give origin to series of basic and acid compounds for 
 the most part completely parallel. This difficulty has been so much felt 
 by the most enlightened chemists, that doubts have been raised as to 
 whether the acid and base, which are placed in contact to form by their 
 union an oxygen salt, really exist in it when formed ; and it has been 
 suggested, that at the moment of union a new arrangement of elements 
 takes place, by which the structure of the resulting salt is assimilated to 
 that of a compound of chlorine or of iodine with a metal. This view, 
 at first sight so far fetched, which considers that in glauber's salt there 
 is neither sulphuric acid, nor soda, -but sulphur, oxygen, and sodium, in 
 some other and simpler mode of combination, is now very extensively 
 received by chemists ; and I shall proceed, therefore, to describe with 
 some detail the form which it has assumed, and the evidence by which 
 it is supported. 
 
 The greater number of those bodies which are termed oxygen acids, 
 have not been in reality insulated, and what are popularly so called are 
 merely supposed to contain the dry acid combined with water. Thus 
 the nearest approach we can make to nitric acid, is the liquid N0 6 H ; 
 to acetic acid, the crystalline body C 4 H 4 4 ; and to oxalic acid, the sub- 
 limed crystals C 2 4 H ; we look upon these bodies as being combinations 
 of the dry acid with water, and we write their formulae JST0 5 + HO, 
 and C 4 H 3 3 + HO and C 2 3 + HO, but that these dry acids exist at 
 all is a mere assumption. Hence with regard to such instances, and 
 they embrace the majority of all known acids, the idea that the acid and 
 base really exist in the salt formed by the action of hydrated acids on a 
 base, is purely theoretical. 
 
 When we compare the constitution of a neutral salt with that of the 
 hydrated acid by which it is formed, we find the positive result to be 
 the substitution of a metal for the hydrogen of the latter, thus, S0 3 4. 
 HO gives with zinc, S0 3 -f- ZnO ; and where a metal is acted on by an 
 hydrated acid the hydrogen is thus evolved either directly as gas, or it 
 
Constitution of Acids and Salts. 587 
 
 reacts on the elements of the acid and gives rise to secondary products 
 which are evolved, such as sulphurous acid, nitric oxide, &c. In all 
 cases we may consider the action of a metal on a hydrated acid to be 
 primarily, the elimination of hydrogen and the formation of a neutral 
 salt. But in this respect the action becomes completely analogous to 
 that of the metal on a hydracid, except that in the latter case a haloid 
 salt is formed, and hence we assimilate the two classes in constitution by 
 a very simple arrangement of their formulae. 
 
 There are, however, a number of acids which may be obtained in a 
 dry and isolated form, as the sulphuric, the silicic, the telluric, the stan- 
 nic, the arsenic, the phosphoric, &c., and when they combine with bases, 
 it is most natural to consider the union as being direct, and that the 
 salt contains acid and base really as such. This is accordingly the 
 strongest point of the ordinary theory. But other and important cir- 
 cumstances intervene. These acids, although they may be obtained free 
 from water, yet in that state they combine with bases but very feebly, 
 and require a high temperature in order to bring their affinities into 
 play. On the other hand, in all cases where these bodies manifest their 
 acid characters in the highest degree, they are combined with water, as 
 in oil of vitriol, and phosphoric acid, and when expelled from combi- 
 nation with a base, they immediately enter into combination with water 
 in an equivalent proportion. Thus where phosphate of lime is decom- 
 posed by oil of vitriol, it is not phosphoric acid (P0 5 ), which is found 
 in the liquor, but its terhydrate (P0 5 + 3 HO), as is shown by its 
 forming with oxide of silver the yellow phosphate P0 5 + 3AgO. In 
 the case of telluric acid, its hydrate (TeO 3 + 3 HO) is very soluble in 
 water, it crystallizes in large prisms ; by 212, two atoms of water are 
 given off, but its nature is not changed, the body which remains (TeO 3 + 
 HO) is still acid and soluble in water, perfectly neutralizing the alcalies ; 
 but by a red heat this last atom of water is driven off, and then the 
 whole nature of the body changes, it is insoluble in water, and even in 
 the strongest alcaline solutions, and can only be brought back to its 
 former state by being fused with potash at a red heat. Here it is evi- 
 dent that the acid properties and the water go together ; and we may 
 conclude, that in order to manifest strong acid properties, the acid must 
 be in its hydrated form. But in that hydrated form if the water acted 
 as a base, simply, the tendency of the acid to combine with other bases 
 should be inferior to that of the dry acid ; for if we place oil of vitriol 
 and barytes together, the water must be first expelled, before the barytes 
 and sulphuric acid can unite, and hence, an impediment would exist to 
 their union which should not occur with cold barytes and dry sulphuric 
 acid in vapour, and yet cold barytes and oil of vitriol will combine with 
 
588 Theories Respecting the Intimate 
 
 such intensity as to produce ignition, whilst the barytes must be heated 
 before it begins to combine with the dry sulphuric acid. The water 
 therefore, is essential to the manifestation of strong acid properties, and 
 it does not exist in combination with the acid merely as a base. What 
 then is the constitution of a hydrated oxygen acid ? 
 
 When muriatic acid (H.C1.) acts on zinc, the metal is taken up, 
 forming ZnCl, and hydrogen is expelled, and if, in place of zinc, oxide of 
 zinc be taken, the effect is the same, except that the hydrogen combin- 
 ing with the oxygen of the oxide forms water ; HC1 and ZnO, giving 
 ZnCl and HO. Now we have in oil of vitriol the elements S0 4 H, com- 
 bined together; when put in contact with zinc, H is expelled, and 
 S0 4 Zn is formed, and with ZnO. and SO 4 H, there are produced S0 4 Zn, 
 and HO is set free. In both cases, of which the former may be taken 
 as the type of all the haloid salts and the latter of all salts formed by 
 oxygen acids, there is H as the element which is removable by a metal, 
 precisely as one metal is replaceable by another, as indeed from the real 
 metallic character of hydrogen may be considered to occur in this case. 
 Every acid may, therefore, be considered to consist of hydrogen com- 
 bined with an electro-negative element ; which may be simple, as chlo- 
 rine, iodine, fluorine ; or may be compound, as cyanogen, NC 2 , and yet 
 capable of being isolated ; or as occurs in the great majority of cases, 
 its elements may be such as can only remain together when in combina- 
 tion. Thus oil of vitriol does not contain, SO 3 and HO, but consists 
 of hydrogen united to a compound radical S0 4 . Liquid nitric acid 
 does not contain NO 5 and HO, but consists of hydrogen united to a 
 compound radical N0 6 , and the acetic acid is written C 4 H 3 4 + H, the 
 oxalic acid C 2 4 + H, and so on. 
 
 The elegance and simplicity with which the laws of saline combina- 
 tion may be deduced from these principles is really remarkable. Thus, 
 it has been remarked as a fact substantiated by experiment, that in 
 neutral salts the number of equivalents of acid were proportional to the 
 number of equivalents of oxygen in the base, but the ordinary theory 
 gave no indication of why this should occur. It follows necessarily 
 from the principles of the newer theory. Thus, if a protoxide be acted 
 on by an acid, M denoting the metal of the oxide, and E the radical of 
 the acid, the resulting action is 
 
 M .j- and H -}- E, produce H -J- O and M _|_ K, 
 
 and in the neutral salt, there is an equivalent of each. Now in the 
 case of a sesquioxide, in order that water shah 1 be formed, and so neither 
 acid nor base be in excess, the reaction is that 
 
 M* + Oj and 3 (H + R), produce 3 (H+ 0) and M 2 4_K 3 , 
 
Constitution of Acids and Salts. 589 
 
 a sesqui-compound being formed perfectly analogous to a sesqui-oxide, 
 and the number of atoms of acid, 3 (H + B), is equal to the number 
 of atoms of oxygen in the base (M 2 3 ) because that number of atoms 
 of hydrogen are required for the decomposition of the base. In like 
 manner for a deutoxide, there is 
 
 M 4. Os and 2 (H + R), producing 2 (HO) and M -j- E 2 . 
 
 The power of salts to replace water in the magnesian sulphates, so as 
 to form double salts, becomes much more intelligible when we compare 
 H-f- with K -f SO 4 , than where H.O was contrasted with the complex 
 formula KO -f- S0 3 . 
 
 The circumstance that on the new theory (or as it is now often called 
 the Binary theory of salts), it is necessary to admit the existence 
 of a great number of bodies (these salt radicals) which have never 
 been isolated, and in favour of whose existence there is no other proof 
 than their utility in supporting this view, becomes more powerful as an 
 objection, when we proceed to apply its principles to the salts of phos- 
 phoric acid. For it has been already described, that this acid forms 
 three distinct classes of salts, all neutral, and which have their origin in 
 the three hydrated states of the phosphoric acid. These states are 
 written on the two views as follows : 
 
 Old Theory. New Theory. 
 
 Monobasic acid, PO 5 + HO . . . PO 6 -f H 
 
 Bibasic acid, POa -j- 2HO . . . PO 7 -J- H 2 
 
 Tribasic acid, PO 5 + 3HO . . . POs -}- Hs 
 
 Now, it appears very useless, when the older view accounts so simply 
 for the properties and constitution of these salts, to adopt so violent an 
 idea, as that there are three distinct compounds of phosphorus and 
 oxygen, which no chemist has ever been able to detect. But, here 
 again, other circumstances must be studied; first, the difference 
 of properties of phosphoric acid, in its three states, is totally inexpli- 
 cable, on the idea of there being merely three degrees of hydration. 
 Nitric acid forms three hydrates, but when neutralized by potash, it 
 always gives the same saltpetre ; sulphuric acid forms two perfectly 
 definite hydrates, but with soda forms always the same glauber's salt ; 
 whilst phosphoric acid, when neutralized by soda, gives a different kind 
 of salt according to the state it may be in. Also, the permanence of 
 these conditions of phosphoric acid as a different hydracid in each of its 
 three conditions, on the other hand, not merely explains the fact of 
 these differences of properties, but it renders the formation of bibasic 
 and tribasic salts, which is such an anomaly on the old theory, a neces- 
 
590 Binary Theory of Salts. 
 
 sary consequence of the new, for the phosphoric salt radicals, P0 6 ,PO 7 
 and P0 8 , differ not merely in the quantity of oxygen they contain, but 
 are combined with different quantities of hydrogen, and hence in acting 
 on metallic oxides, (bases), there is a different number of atoms re- 
 quired for each to replace the hydrogen and form water. Thus 
 
 POe.H and NaO give HO and POg.Na. monobasic phosphate of soda, 
 PO 7 .H 2 and 2NaO give 2HO and PO?.Na 2 . bibasic phosphate of soda, 
 and 3NaO give 3HO and PO 8 .Na 3 , tribasic phosphate of soda. 
 
 A circumstance which gives additional reason to infer, that the water is 
 not merely as base in the phosphoric acid, is the following ; if it were 
 so, then it should be most completely expelled by the strongest bases, 
 and the bibasic and tribasic phosphates of the alcalies, should be those 
 least likely to retain any portion of the basic water ; but the reverse is 
 the fact ; whilst oxide of silver, a very weak base, is that which most 
 easily and totally displaces the water. On the idea, however, of hydra- 
 cids, this is easily understood, for the oxide of silver is one most easily 
 reduced by hydrogen, and consequently one on which the action of a 
 hydrogen acid, as P0 8 + H 3 , or PO 7 -f- H 2 , would be most completely 
 exercised. See page 413. 
 
 A remarkable verification of this theory has been recently found in 
 the decomposition of solutions of the oxysalts in water, by voltaic 
 electricity. It has been already explained, (pp. 262 et seq.) that it 
 requires the same quantity of electricity to decompose an equivalent of 
 any binary compound, such as iodide of lead, chloride of silver, muri- 
 atic acid or water. Now, if we dissolve sulphate of soda in water, and 
 pass a current of voltaic electricity through that solution, we have 
 water decomposed, and also the glauber's salt; oxygen, and sulphuric 
 acid being evolved at one pole, and soda and hydrogen at the other. 
 Here, on the old view, the electricity performs two decomposing actions 
 at the same time, and, as it thus divides itself, its action on each must 
 be lessened, and the quantity of each decomposed be diminished, so 
 that the sum should represent the proper energy of the current. On 
 measuring these quantities, however, the result is totally different, the 
 quantity of sulphate of soda decomposed is found to be equal to the 
 full duty of the current, and an equivalent of water appears to be de- 
 composed in addition. It is quite unphilosophic to imagine, that the 
 strength of a current should be thus suddenly doubled, and a simple 
 and sufficient explanation of it is found in the new theory of salts. 
 The sulphate of soda in solution having the formula NaSO 4 is resolved 
 by the current into its elements, Na and SO 4 , as chloride of sodium 
 should also be; the sodium, on emerging on the negative electrode, 
 
Electrical decomposition of Salts. 591 
 
 from the influence of the current, instantly decomposes water, and 
 soda, and hydrogen, of each an equivalent, are evolved ; at the positive 
 electrode, the compound radical SO 4 also decomposes water, and pro- 
 duces H.SO 4 and O. The appearance of the oxygen and hydrogen is 
 thus but secondary, and the body really decomposed by the current is 
 only NaS0 4 . 
 
 In the case of the salts of such metals as do not decompose water, 
 the phenomena are much more simple. Thus, a solution of sulphate 
 of copper, when decomposed by the battery, yields metallic copper at 
 the negative and sulphuric acid and oxygen at the positive electrode, 
 and the quantity of copper separated represents exactly the energy of 
 the current which has passed, for the salt being Cu.SO 4 is simply 
 resolved into its elements, but S0 4 reacting on the water, produces 
 H.SO 4 , and O at the positive electrode. On the old view it was sup- 
 posed, that water and sulphate of copper were both decomposed, oxygen 
 and acid being evolved at one side, and oxide of copper and hydrogen 
 being separated at the other ; which reacting, produced water and the 
 metal. Such an explanation, however, is directly opposed to the law of 
 the definite action of electricity, and cannot be received. 
 
 In the case of solutions of chlorides or iodides, where there can be 
 no doubt of the relations of the elements, the results of voltaic decom- 
 position are precisely similar. Chloride of copper gives simply chlorine 
 and copper, no water being decomposed. Chloride of sodium or iodide 
 of potassium give chlorine or iodine at one electrode, and alcali and 
 hydrogen at the other ; the evolution of these last being caused by the 
 action of the metallic basis on the water of the solution. 
 
 Professor Daniell, to whom these important electro -chemical re- 
 searches are due, considered the truth of the binary theory of salts to 
 be fully established by them. 
 
 If this theory be adopted, a profound change in our nomenclature of 
 salts will become necessary. Graham has proposed, that the name of 
 the salt-radical should be formed by prefixing to the word oxygen, the 
 first word of the ordinary name of the class of salts, and that the salts 
 be termed by changing oxygen into oxides. Thus, S0 4 . sutphat 'oxygen 
 gives sulphatoxides ; the sulphates. NOe nitratoxygen, gives nitratox- 
 ides, the nitrates, and so on ; but I consider that the form of nomen- 
 clature proposed by Daniell deserves the preference. It has been de- 
 scribed, (p. 262), that Faraday proposed to term the elements which 
 pass to the electrodes of the battery, ions ; acting on this, Daniell pro- 
 poses to term the electro-negative element of the sulphates, oxysulphion, 
 that of the nitrates, oxynitrion, and so on, and the salts may be termed 
 oxysulphion of copper, oxynitrion of sodium, &c. It would be desira- 
 
592 Nature of Doulle Haloid Salts. 
 
 ble, however, for a long time, to introduce these names only where 
 theoretical considerations rendered their employment decidedly useful, 
 and hence, in all future description of the salts, I shall make use of the 
 language of our ordinary views, and treat of their preparation and com- 
 position without any reference to the discussion in which we have been 
 now engaged. 
 
 The general adoption of the binary theory of salts has deprived of 
 much of its interest and importance a question, which some years since 
 was very ingeniously discussed, viz., whether, in the formation of double 
 salts, the salts which unite had the same relation to each other that acid 
 and base were then thought to have. Thus, it was supposed that the 
 electro-negative qualities of sulphuric acid being less controlled by oxide 
 of copper than by potash, the alcaline sulphate acted as a base to the 
 sulphate of copper, when these two salts combined to form the double 
 sulphate of potash and copper, and so on in other instances ; but, in 
 addition to the circumstance, that all we have said as to the constitution 
 of the salts militates against this view, we have the positive evidence, 
 that first, these double salts are formed not by combination merely, but 
 by replacement of the constitutional water of the sulphates of the copper 
 or magnesia class, which water has never been supposed to act in them 
 as a base ; and second, that when a solution of such a double salt is 
 decomposed by the battery, the two salts are not separated as if they 
 were acid and base, but are decomposed independently in the propor- 
 tions of an equivalent of each, making together the sum of the chemical 
 energy of the current. 
 
 A similar idea was advocated by Bonsdorff regarding the double 
 chlorides, iodides, &c. He proposed to consider the chlorides of gold, 
 platina, mercury, &c., as chlorine acids, and those of potassium, &c., 
 as chlorine bases, and so with the iodides. This view, however, although 
 at first very extensively adopted, has given way to the gradual growth 
 of knowledge. There is no analogy between a dry oxygen acid and a 
 chloride ; but the chlorides are in perfect analogy with the neutral salts. 
 Thus, CuCl does not resemble S0 3 , but Cu.SO 4 and CuCl + KC1 is 
 analogous not to S0 3 .KO, but to the double salt, Cu.SO 4 + K.S0 4 . 
 Bonsdorff's idea was exactly counter to the direction of truth; he 
 sought to bring all salts under the one head, by extending to all the 
 constitution of oxygen acids and oxygen bases, whilst the progress of 
 science has led us to the opposite generalization of reducing all salts to 
 simple haloid type. 
 
 The doctrines of atomic volume already fully described, pages 300 
 and 310, have been applied by Schroeder and Kopp in favour of the 
 salt radical theory. Thus : the atomic volume of many protoxides is the 
 
Atomic Volumes of Salts. 593 
 
 sum of the atomic volume of the metal, and the number 2 '6, as Pb.O. 
 or Hg.O. The atomic volumes of other protoxides is the sum of the 
 atomic volume of the metal, and the number 5*2, as Ag.O. All these 
 kinds of oxides are upon the older theory constituents of the same 
 kinds of salts, as PbO. NO 5 and Hg 2 O.lS T O 5 and AgO. NO 5 . ; but on 
 the theory of salt radicals, it is not these oxides but the metals which 
 exist in the salt. 
 
 The atomic volume of lead is 9;1; that of nitrate of lead is 37*8; 
 and if we subtract the former we have for the salt radical NO 6 contained 
 in the salt Pb. NO 6 . the atomic volume 28*7. Now if we calculate 
 the specific gravities of the other nitrates of the dense metals by this 
 rule that the atomic volume of the salt is the sum of the atomic volume 
 of the metal, and of that of the salt radical N0 6 =r 28*7 we find the 
 results remarkably exact. The atomic volume of silver is 10 '4, and that 
 of nitrate of silver consequently 39*1, which divided into the atomic 
 weight 170 gives the specific gravity = 4*35, agreeing perfectly with 
 experiment. 
 
 If on the other hand, nitrate of silver be written AgO. N0 3 . and 
 that its atomic volume be supposed the sum of the volumes of the 
 base 15 '6 and of the acid, the volume of the latter is =39*1 15*6 
 = 23" 5. But the atomic volume of oxide of lead is 11 '7 which sub- 
 tracted from 37 '8, that of nitrate of lead leaves 26*1 for the atomic 
 volume of nitric acid, N0 5 . Hence on the old salt theory the atomic 
 volume appears to be different in the different salts, but on the salt 
 radical theory the atomic volumes of the salts is simply the sum of the 
 atomic volume of the metal and that of the salt radical. The newer 
 point of view has therefore the advantage of simplicity, but in this case 
 as in the other examples already given of the application of the doctrine 
 of atomic volumes, the induction employed is quite too narrow to justify 
 any general or positive conclusion. (In page 303 where the atomic 
 volume of oxide of silver is given it should have been stated 15 '6 = 
 10-4 -f 5-2 in place of 14'3 = 10'4 + 3'9) 
 
 Some time ago, when discussing the evidence regarding the theories 
 of the ammonia combinations, I had occasion to point out that if we 
 adopted Graham's extension of Berzelius' theory and supposed that 
 compound metallic radicals, as ammonium, might exist, containing more 
 or less of the hydrogen replaced by metals as cuprammonium NH 3 Cu, 
 or Hydrargammonium NH 2 Hg 2 ; it became impossible to avoid the still 
 further extension of the radical character to those groups containing 
 oxygen or sulphur, and that the basic salts should be looked upon as 
 salts of compound radicals. Thus, that from 
 
 38 
 
594 Constitution of Basic Salts. 
 
 Sal-ammoniac Cl -f- NH4. 
 
 passing to Sal cuprammoniac Cl -j- NHaCu. 
 
 White precipitate Cl _|- NH2Hg2. 
 
 Yellow precipitate Cl _|- NH2Hg 4 O 2 . 
 
 Oxychloride of mercury Cl ^_ Hg 4 O3. 
 
 Chlorosulpliuret of mercury Cl J. HgsS2. 
 
 there is no point at which the line of demarcation could be posi- 
 tively drawn, and hence I thought myself justified in rejecting Graham's 
 proposal to extend Berzelius' theory, and defended the theory of the am- 
 monia compounds, winch I had proposed, and which shall be described 
 further on. Millon has, however, recently taken up the idea of basic 
 salts being salts of compound radicals, which I had suggested only 
 to show its inadmissibility, and has endeavoured to explain the con- 
 stitution of hydrated acids and salts thereon. The evidence he brings 
 forward, however, possesses no additional weight, and the proposition 
 cannot, as I believe, be admitted into science. 
 
 CHAPTER XV. 
 
 SPECIAL HISTORY OF THE MOST IMPORTANT SALTS OF THE 
 INORGANIC ACIDS AND BASES. 
 
 THE multitude of salts known to chemists is so very great, that it is 
 only possible to detail the history of the most important of each class. 
 They are arranged according to their bases, except in some few cases 
 where a metal is also the radical of their acid element. In that case, 
 the salts of the acids of the metal are described after those formed by 
 its oxides with other acids. This plan has been adopted in order to 
 give as much unity as possible to the history of each metal, and influ- 
 ences only the compounds of chrome and arsenic to any degree. 
 
 OF THE SALTS OF POTASH. 
 
 Chloride of Potaarium.-'KGL. Eq. 931% or 74-47. This salt may 
 be artificially produced, by neutralizing potash with hydrochloric acid. 
 It exists abundantly in the water of many brine springs, and in the 
 
Iodide of Potassium. 595 
 
 ashes of plants. It is very soluble in water, producing so much cold, 
 as to be employed as a freezing mixture ; it crystallizes in cubes, which 
 are anhydrous ; its principal use is in the manufacture of alum. 
 
 Iodide of Potassium. KI. Eq. 2067'4 or 165*4; a variety of pro- 
 cesses may be employed to prepare this salt. One of the simplest, 
 consists in dissolving iodine in solution of potash until this is com- 
 pletely neutralized. The potash being decomposed, there is formed 
 from 6-1 and 6'KO, 5KI and KOIO 5 . The solution is evaporated to 
 dryness, and the mass being heated to redness, is kept fused as long as 
 bubbles of oxygen gas are given off : the residual salt, which is pure 
 iodide of potassium, is, when cold, to be dissolved in its weight of 
 boiling water, and allowed to crystallize very slowly. A certain loss 
 may occur in this process, if the heat applied be too high, and if the 
 temperature be not high enough, iodate of potash may remain unde- 
 composed ; this last effect being advantageous to the manufacturer by 
 increasing the quantity of product, is more liable to occur, and may 
 be detected by means of tartaric acid, as very ingeniously proposed by 
 Mr. Maurice Scanlan. This acid is without action on pure iodide of 
 potassium, further than to liberate hydriodic acid, which remains for a 
 certain time unaltered, but if a trace of iodate of potash be present, 
 the iodic acid which is set free immediately reacts on the hydriodic acid, 
 water being formed and iodine liberated, which may be recognized by 
 means of starch. 
 
 Another process, adopted by the London and Edinburgh Pharmaco- 
 peias, consists in putting together iodine, metallic iron, and carbonate 
 of potash : the iron and iodine unite directly to form a soluble iodide 
 of iron, which is decomposed as rapidly as formed, by the carbonate of 
 potash. Iodide of potassium is produced, with oxide of iron and car- 
 bonic acid ; but as described page 288, the iron being first as periodide, 
 peroxide is produced, and this not combining with carbonic acid, the 
 latter is mostly given off as gas. The reaction consists in Fe 2 .I 3 and 
 3.KO.C0 2 giving rise to 3.K.I and Fe 2 O 3 . with 3.CO 2 . The liquor 
 being filtered and evaporated to a pellicle, the iodide of potassium is 
 obtained crystallized. This salt crystallizes in cubes; sometimes in 
 square prisms, which are macles. It is not deliquescent when pure, and 
 is without action on turmeric paper ; by tin's means it is known to be 
 free from carbonate of potash. It is sometimes adulterated by chloride 
 of potassium, which may be detected by decomposing its solution by ni- 
 trate of silver, washing the precipitate with water, digesting it in strong 
 water of ammonia, and filtering ; if the solution, when rendered slightly 
 acid with nitric acid, give a white precipitate of chloride of silver, chlo- 
 ride of potassium was present, and its amount may be thus determined. 
 
596 Commercial Valuation of Iodide of Potassium. 
 
 The iodide of potassium is extensively used in medicine, by the 
 chemist as a re-agent, and for the preparation of other metallic iodides. 
 
 A solution of iodide of potassium dissolves iodine in large quantity, 
 forming a brown liquor used in medicine. It is not certain, however, 
 that in this case any definite compound (as a biniodide) is formed. 
 
 It has been recently proposed to test the purity of the commercial 
 iodide of potassium by adding to a certain weight of it, a standard 
 solution of iodate of potash, to which as much dilute sulphuric acid 
 has been added as will render the liquors slightly acid. By the reaction 
 of the iodic acid on the iodide of potassium, there is iodine set free, 
 and potash formed which combines with the sulphuric acid. The preci- 
 pitated iodine at first dissolves in the iodide of potassium remaining, 
 but as the decomposition advances, it separates as a brown powder, 
 which on boiling the liquor, passes away in violet fumes leaving the 
 liquor clear and colourless. One equivalent, or 213 parts of iodate of 
 potash, and 6 equivalents, or 294 parts of oil of vitriol, decompose 
 five equivalents or 825 parts of iodide of potassium, thus 
 
 I0 5 + KO with 6.HO.S0 3 and 5.KI. 
 produce 
 
 6.1. and 6.KO.SO 3 with 6.HO. 
 
 Hence let 100 grains of iodide of potassium be dissolved in an ounce 
 of water, and a standard liquor be prepared by dissolving 26 grains of 
 iodate of potash in water, and adding 36 grains of the strongest oil of 
 vitriol, and so much water as will bring the liquor to a volume of 1000 
 grains measure. Then on bringing the solution of iodide of potassium 
 to boil in a flask, and adding gradually by drops the test solution as 
 long as iodine separates, and violet fumes are given off, the quantity 
 required will indicate the purity of the iodide of potassium. If it 
 were quite pure the whole thousand grains of volume of the test liquor 
 should be needed. If 800 grains measure be required, it indicates 80 
 per cent, of pure iodide, and 20 per cent, of impurities : each ten 
 grains measure of test liquor corresponding to one grain of pure iodide 
 of potassium. 
 
 Neither chlorides, sulphates nor nitrates interfere with this test ; nor 
 do bromides as it is easy by ordinary attention to distinguish accurately 
 when the evolution of iodine ceases, and the formation of the yellow 
 orange vapour of bromine may commence, if that body be present. 
 
 Bromide of Potassium. K.Br. Eq. 1465-8 orll7'3. This salt may 
 be prepared exactly as the iodide of potassium, which it resembles in 
 most of its physical characters. It is recognized by giving, with oil of 
 vitriol, orange red fumes of bromine. The commercial article is fre- 
 
Bromide of Potassium Sulphate of Potash. 597 
 
 quently adulterated with chloride of potassium, the presence of which 
 may be detected as follows : dissolve 100 grains of the salt in four 
 ounces of water, and decompose it by an excess of nitrate of silver ; 
 collect the precipitate, wash it carefully, and dry it in a capsule till it 
 ceases to lose weight ; then weigh it. If it were perfectly pure, the 
 bromide of silver should weigh 158*8 grains, but the presence of chlo- 
 ride of potassium would have the effect (from the smaller equivalent of 
 chlorine) of increasing the weight ; therefore, if the precipitate, when 
 when quite dry, weighs more than 158*8 grains, the sample is impure, 
 and the quantity of chlorine present may be calculated from the over- 
 plus weight; for 100 grains of pure chloride of potassium should give 
 192-6 grains of precipitate. Thus, if there were 10 per cent, of im- 
 purity, the precipitate would weigh 162 grains; if 20 per cent, it would 
 weigh 165*4. Thus, the precipitate increases in weight about 3*3 for 
 each 10 per cent, of chloride of potassium present. 
 
 The properties of the Fluoride, and of the Silico-fiuoride of Potas- 
 sium, are not of importance beyond what has been already said in pp. 
 446 and 453. 
 
 Sulphate of Potash. KO.SO 3 . Eq. 1087*5 or 87. This salt is pro- 
 duced upon the large scale in the manufacture of the sulphuric and 
 nitric acids, where nitrate of potash is employed. It may be prepared 
 by the direct union of its constituents, and being but sparingly soluble, 
 it precipitates as a fine crystalline powder, when oil of vitriol is mixed 
 with a strong solution of potash. It is more soluble in boiling water, 
 and crystallizes on cooling in right rhombic prisms, or in six-sided 
 prisms, terminated by pyramids, which are macles, being formed by 
 the union of three simple crystals, as described in p. 44. In the figures, 
 A represents the manner in which the three rhombic prisms 
 adhere together, the letters marking the corresponding 
 planes in each original, and B the form which results 
 when all traces of the junctions have disappeared. This 
 salt does not contain water; its crystals decrepitate violently when 
 B heated, but are not decomposed. 100 parts of water 
 
 dissolve 8*3 of the salt at 32, and 25 parts at 212. 
 This salt combines with dry sulphuric acid to form a 
 bisulphate of potash, KO + 2SO 3 , which may be pre- 
 pared by exposing the neutral salt to the vapour of 
 dry sulphuric acid, or by dissolving it with 1J equiva- 
 lents of oil of vitriol in the smallest possible quantity 
 of distilled water. This bisulphate of potash crystal- 
 lizes in small prisms, which are gradually decomposed by water, the 
 following salt being formed. 
 
593 Nitrate of Potash Nitre. 
 
 Common Bisulphate of Potash Double Sulphate of Water and Pot- 
 ash. KO.S0 3 + HO.SO 3 . Eq. 1700-0 or 136. This salt is produced 
 when nitrate of potash is decomposed by two atoms of oil of vitriol, 
 and is formed when neutral sulphate of potash is gently heated with \ 
 its weight of oil of vitriol to just below redness. It may be obtained 
 crystallized from a strong solution in right rhombic prisms. It is de- 
 composed into neutral sulphate and oil of vitriol by a large quantity of 
 water. When heated to full redness it fuses, and may be obtained on 
 cooling in oblique rhombic crystals; it is thus dimorphous (see p. 315); 
 at a higher temperature it abandons its excess of acid, and neutral sul- 
 phate remains. 
 
 There exists also a Jiydrated sesquisulphate of potash, 2(KO.SO 3 ) -f- 
 HO.S0 3 , which crystallizes in fine needles. Similar compounds of sul- 
 phate of potash with hydrated nitric and phosphoric acids have also been 
 described. 
 
 Nitrate of Potash Saltpetre. Nitre. KO.N0 5 . Eq. 1262-5 or 
 101. The general principles of the formation of nitric acid by the 
 conjoined action of decomposing animal matter and of earthy bases on 
 atmospheric air, have been described already. By lixiviating the ma- 
 terials thus obtained, whether naturally or from artificial nitre beds, 
 with water, a solution is obtained, containing, among other saline 
 matters, a considerable quantity of nitrate of lime ; this is then decom- 
 posed by an impure carbonate of potash, and carbonate of lime being 
 precipitated, a solution of nitrate of potash is obtained, from which 
 the salt is procured by evaporation and crystallization. Its form is that 
 of a six-sided prism with dihedral summits, derived from the right 
 rhombic system. It is anhydrous; 100 parts of water dissolve 13'3 
 parts at 32, and 240 parts at 212. When heated to redness it melts 
 and evolves oxygen, at first pure, but subsequently mixed with nitrogen 
 gas. 
 
 As nitrate of potash contains oxygen in large quantity, and gives it 
 out readily to combustible bodies, it is much employed for the prepara- 
 tion of fireworks, and especially of gunpowder. The action of gun- 
 powder depends upon its generating, when decomposed, a large quantity 
 of gases, which occupy more than 1000 times its volume. If this took 
 place instantaneously, all bodies near, which could not resist this force, 
 should be burst or broken, as takes place with chloride of azote, which, 
 if placed in a gun, would burst it, but has no power to propel a ball : 
 the decomposition of gunpowder, however, occupying a certain time, 
 the disengagement of gas is progressive, and the ball is forced through 
 the barrel with the velocity due to the ultimate effect of the whole 
 quantity of gas produced. When gunpowder is completely decomposed, 
 
Manufacture of Gunpowder. 599 
 
 the products are found to be sulphuret of potassium, nitrogen, and 
 carbonic acid gas ; and from these the proportions by weight of its con- 
 stituents may be calculated, for S, KO.N0 5 and 30, produce K.S, N 
 and 3C0 2 . The parts by weight are, therefore, 
 
 Theory. French. English. Prussian. 
 
 S = 16-1 11-8 12 5 10-0 11-5 
 
 3C = 18-3 13-5 12-5 15'0 13-5 
 
 = 101 -074-7 75'0 75-0 75'0 
 
 135-4 100-0 100-0 100-0 lOO'O 
 
 The proportions employed in the government factories of the most im- 
 portant countries are given also above. The Prussian mixture agrees 
 best with theory. Eor the coarse blasting powder, there are employed 
 sixty-five parts of saltpetre, twenty of sulphur, and fifteen of charcoal. 
 The excess of sulphur renders the explosion more intense, but would 
 corrode firearms too much. A mixture of three parts of saltpetre, four 
 of carbonate of potash, and one of sulphur is decomposed instantaneously 
 when fused, and with an explosion so violent, that if it be placed on a 
 thin iron plate, this may be perforated. If three parts of nitre be 
 mixed with one of finely powdered charcoal, a mass is obtained which, 
 when touched with an ignited coal, burns nearly as fast as loose gun- 
 powder, but totally without explosion. It is, therefore, the sulphur 
 which determines the violence and rapidity of the deflagration of gun- 
 powder, whilst the charcoal produces the great volume of gas on which 
 its mechanical effect depends. 
 
 The preparation of the materials for making gunpowder requires 
 great care. Most of the success depends on the preparation of the 
 charcoal. This should be made from a light wood containing little 
 ashes, such as birch, and carbonized in cylinders, very slowly, and at 
 the lowest possible heat. When reduced to impalpable powder, this 
 charcoal is so inflammable as sometimes to take fire at ordinary tem- 
 peratures. The purification of the saltpetre is performed by successive 
 recrystallizations, and by washing the crystals with water already satu- 
 rated with saltpetre, which dissolves out any common salt that may be 
 present, but does not act on the crystals of saltpetre. The description 
 of the mechanical operations of the manufacture would be out of place 
 here. 
 
 The extensive use of nitrate of potash in the arts render the determi- 
 nation of the true value of the commercial samples of it a matter of 
 very great practical importance. There are two methods capable of 
 giving accurate results. The, first by Pelouze, consists in determining 
 
600 Practical Valuation of Saltpetre. 
 
 the quantity of iron which the nitric acid contained in the saltpetre can 
 peroxidize. It is thus carried out 83 parts of pure iron wire are to 
 be dissolved in pure dilute muriatic acid, and 100 grains of the nitre 
 to be tested are to be weighed out and very gradually added to the 
 solution of protochloride of iron so formed, which is to be rendered 
 strongly acid by more muriatic acid if necessary; the whole being 
 boiled until all evolution of nitric oxide gas ceases, and the iron shall 
 have become perfectly peroxidized, which is most conveniently known 
 by the addition from time to time of a drop of a solution of chameleon 
 mineral (see p. 500), the rich pink colour of which is destroyed as 
 long as any protochloride of iron remains. If the nitre had been per- 
 fectly pure, fifty grains should peroxide all the iron, but more will 
 always be required. The quantity used will indicate therefore the pre- 
 sence of fifty grains, and the difference will be of course the impurities : 
 thus, if sixty grains were used, there were therein ten grains of impu- 
 rities, or sixteen two-third per cent., if seventy-five were used the 
 sample consisted of sixty- seven per cent, of pure nitre, and thirty- three 
 per cent, of impurities. 
 
 The second mode is that which I have myself usually employed for 
 assaying saltpetre and nitrate of soda. It consists in weighing out 100 
 grains of the sample, and deflagrating it very gently in a deep narrow 
 iron crucible loosely covered, with an excess of dense wood charcoal in 
 coarse powder. It is easily managed so that none shall be lost, and the 
 heat shall not be so high as to allow of the charcoal acting on any of 
 the residual product. On dissolving the saline mass so obtained in 
 water, an alcaline solution is obtained, the contents of which in caustic 
 alcali, potash, or soda, can be determined by the alcalimetrical process 
 to be described hereafter under the head of carbonate of soda. Each 
 grain per cent, of potash corresponds to 2.13 of pure nitre, and each 
 grain of soda corresponds to 2.74 of nitrate of soda. Neither chlorides 
 nor sulphates interfere with this test, and as alcalimetrical determina- 
 tions are made every day in most chemical factories, the assays of nitre 
 come in with them thus in a very convenient manner. This process is 
 fully accurate to one part in one hundred. 
 
 Hypochlorite of Potash. When gaseous chlorine is passed into a 
 solution of carbonate of potash, it is abundantly absorbed ; but no car- 
 bonic acid is disengaged until the liquor contains an atom of chlorine 
 for every two atoms of alcaline carbonate. On examination it is then 
 found to contain, hypochlorite of potash, chloride of potassium, and 
 bicarbonate of potash, which are mixed in solution, and may be partially 
 separated by crystallization. The reaction has been such that 2C1 and 
 4 KO.CO 2 give KC1, KO.C1O and 2 (KO -f CO 2 + HO.CO 2 ). If the 
 
Hypochlorite and Chlorate of Potash. 601 
 
 stream of chlorine be continued carbonic acid is copiously evolved, and 
 as much more chlorine is absorbed, giving ultimately a mixture of KC1 
 and KO.C1O. The liquor becomes deep yellow, owing to the liberation 
 of a quantity of hypochlorous acid by the free carbonic acid, and hence 
 the quantity of chlorine absorbed amounts to much more than the exact 
 atomic proportion. 
 
 Further details of the theory of these bleaching compounds are given 
 under the head of chloride of lime. 
 
 Chlorate of Potash. KO.C1O 5 . Eq. 1531'2 or 122'47. When 
 chlorine gas is passed into a strong solution of potash it is absorbed 
 rapidly until the alkali is completely neutralized, and chloride of potas- 
 sium and hypochlorite of potash are formed ; 2KO and 2C1 giving KC1 
 and KO.C1O. If, then, this liquor be boiled for some time, oxygen gas 
 is given off, the hypochlorite being decomposed, and chloride of potas- 
 sium and chlorate of potash being formed; 9(KO.C1O) producing 
 12. with 8.KC1 and KO.ClOs. If carbonate of potash has been em- 
 ployed, the absorption of chlorine is rapid until half of the salt had 
 been decomposed, and the remainder converted into bicarbonate, from 
 combining with the evolved carbonic acid, as described under the pre- 
 ceding head : but a high temperature and a great excess of chlorine 
 being necessary to complete the reaction, rendered the operations tedious 
 and very troublesome ; and as owing to the large quantity of oxygen 
 evolved, there was but one equivalent of chlorate of potash obtained by 
 the action of eighteen equivalents of chlorine on eighteen of potash, the 
 process was one of considerable expense. 
 
 We owe to Graham a method which is free from these disadvantages. 
 If an equivalent of carbonate of potash be mixed with one of hydrate 
 of lime, (by weight about 2 of KO.C0 2 to 1 of CaO.HO) and exposed 
 to a current of chlorine, the gas is absorbed with avidity, and the solid 
 mass becomes very hot, whilst water is given off abundantly. When 
 saturated, it may be gently heated to complete the decomposition. No 
 oxygen is given off, the reaction being that 6(KO.C0 2 ) and 6 (CaO.HO) 
 acted on by 6C1, produce 5.KC1, 6.CaO.CO 2 and KO.C1O 5 , whilst 6HO 
 are evolved. By digesting the mass in water, the potash salts are dis- 
 solved out, carbonate of lime remaining, and the chlorate of potash 
 may be separated from the chloride of potassium by crystallization. By 
 this means three times as much product may be obtained from the same 
 materials, as by the older process. 
 
 This salt crystallizes in rhomboidal tables of a pearly lustre : it is 
 anhydrous : 100 parts of water dissolve but 3 '5 parts at 32, and 60 
 parts at 219. It tastes sharp and cooling, like nitre; when heated, it 
 melts and evolves oxygen gas, being decomposed into chloride of potas- 
 
602 Perchlorate and lodaie of Potash. 
 
 sium and hyperchlorate of potash ; on increasing the heat this also is 
 decomposed, and chloride of potassium remains pure. Its uses in pre- 
 paring oxygen, and the compounds of chlorine and oxygen, have been 
 already noticed. Prom its supplying oxygen still more readily than 
 nitre, it is the basis of a variety of deflagrating mixtures. "When rub- 
 bed in a mortar with sulphur, or with sulphuret of antimony, it explodes 
 violently. Placed in contact with a minute bit of phosphorus on an 
 anvil, and struck by a hammer, it gives a dangerous detonation. The 
 ordinary lucifer matches are formed by mixtures of chlorate of potash 
 with sulphur and charcoal, or sulphuret of antimony, or of cinnabar, 
 made into a paste with gum arabic, and applied to the extremity of a 
 bit of stick, previously smeared with sulphur. Students should be 
 very cautious how they employ this salt in such experiments as those 
 now noticed. 
 
 Perchlorate of potash, KO.C1O 7 . Eq. 1731-2 or 138*47, is of im- 
 portance only from being one of the least soluble salts of potash, and, 
 consequently, that the perchloric acid may be used as a test for the 
 presence of potash in solution, it giving a granular crystalline precipi- 
 tate if that alkali be present. Its preparation is sufficiently noticed in 
 page 426. 
 
 The silicate of potash is of considerable importance as a constituent 
 of glass, and will be noticed as such hereafter. 
 
 lodate of potash, KQ.IO 5 . This salt, which is but sparingly soluble 
 in water, may be obtained by neutralizing the perchloride of iodine 
 with caustic potash; IC1 5 and 6KO, produce 5KC1 and KO.I0 5 . This 
 last separates in crystalline grains. It may also be obtained by adding 
 iodide of potassium to fused chlorate of potash, the mass froths up, the 
 oxygen passing to the iodine, and there is obtained a mixture of chloride 
 of potassium and iodate of potash, which may be separated by crystal- 
 lization. This salt has a remarkable tendency to form acid and double 
 salts, of which, however, none are specially interesting. See page 596. 
 
 SALTS OF SODIUM. 
 
 Chloride of Sodium. Common Salt. Sea Salt. NaCl. Eq. 730-9 
 or 58-5, exists in great abundance in nature ; solid, as rock salt, and in 
 solution in the water of the ocean, and in many inland seas and lakes. 
 The deposits of rock salt occur only among the more recent (secondary) 
 geological formations, lying above the coal, and in connexion with the 
 new red sandstone, as in Cheshire. The beds of salt are sometimes of 
 great magnitude ; thus at Norwich, the bed now worked is supposed to 
 be not less than 60 feet thick, a mile and a half long, and 1300 yards 
 wide, and the deposits at Wieliczka, in Poland, appear to be still larger. 
 
Manufacture of Common Salt. 603 
 
 The origin of these deposits of salt is probably to be found in the 
 gradual drying up, by evaporation, of salt lakes, to which fresh quan- 
 tities of salt were continually supplied by the surrounding springs. 
 Owing to the admixture of earthy matters, the rock salt, as quarried, is 
 generally brownish-coloured, and hence requires to be dissolved in water 
 and crystallized for use. The expense of extracting the salt may be in 
 many cases lessened, by simply boring down to the bed with a pipe a 
 few inches in diameter, and letting thereby water run in upon the salt ; 
 a strong solution of salt is thus produced, which is pumped up and 
 evaporated. The expense of sinking a shaft and quarrying out the solid 
 salt is thus avoided. 
 
 In warm countries, as on the coasts of Portugal and of the South of 
 Trance, salt is obtained by the spontaneous evaporation of sea water, 
 which is allowed, on the rise of the tide, to flow into shallow basins, 
 being passed from one to another, according as it becomes more con- 
 centrated, and, finally, the evaporation being finished by means of arti- 
 ficial heat. The sea water is not evaporated to dryness, as its other 
 saline ingredients would, in that case, be mixed with the common salt. 
 The sea water is generally composed of 
 
 Chloride of sodium, 2-50 
 
 Chloride of magnesium, 0*35 
 
 Sulphate of magnesia, 0*58 
 
 Carbonate of lime and 
 
 0-02 
 
 100-00 
 
 Carbonate of magnesia, 
 
 Sulphate of lime, 0-01 
 
 Water, 96'54 
 
 With generally some traces of iodide and bromide of magnesium. 
 According as the evaporation proceeds, the common salt is deposited in 
 crystals, and the mother liquor, or bittern, being rich in salts of mag- 
 nesia, is preserved for the manufacture of Epsom salts. 
 
 In addition to these sources, chloride of sodium may be obtained 
 by the direct combination of its elements, or by decomposing carbonate 
 of soda by muriatic acid. In practice, however, this is never done. 
 
 Chloride of sodium crystallizes in cubes. Its taste is purely saline. 
 It is equally soluble in water at all temperatures, 100 of water dissol- 
 ving 36-5 ; by a very strong heat it may be volatilized. Its crystals are 
 anhydrous, but are generally fissured, containing water, which, when 
 heated, bursts the crystal, producing loud decrepitation. A strong solu- 
 tion of salt does not freeze at 0, but deposits crystals in rhombic plates, 
 which are a hydrated chloride of sodium. If these crystals be heated 
 beyond 15 they give out water, and are changed into minute cubes. 
 
 The uses of chloride of sodium are very numerous and important. 
 Besides being employed in seasoning food, it is now universally the 
 
604 Manufacture of Sulphate of Soda. 
 
 source from whence the other compounds of sodium, such as the car- 
 bonate and sulphate, are obtained. It is employed also in the manu- 
 facture of glass and of porcelain and as a manure. 
 
 The bromide and iodide of sodium resemble, in properties and mode 
 of preparation, the corresponding compounds of potassium, and do not 
 require special notice. 
 
 Sulphate of Soda. Glauber's Salt.NaO.S0 3 + 10 Aq. Eq. 
 887-2 + 1125 or 71 -f~ 90. So named after its discoverer, exists 
 in some mineral waters, and may be prepared by neutralizing carbonate 
 of soda by dilute sulphuric acid. For the purposes of commerce, it is 
 manufactured in great quantities from common salt, as described under 
 the head of muriatic acid, (p. 427). 
 
 "When it is not the object of the process to economize the muriatic acid' 
 gas, the decomposition is carried on in a reverberatory furnace similar 
 to that figured in p. 467. Three or four hundred weight of salt being 
 spread over the floor of the furnace, forming a layer three or four 
 inches deep, the equivalent quantity (an equal weight), of sulphuric 
 acid, of the strength 1'600, as taken from the chambers, is poured 
 in through an aperture in the dome, and a moderate fire kept up until 
 the materials begin to dry ; the fire is then increased gradually until all 
 the muriatic acid gas has been expelled, and the residual sulphate of 
 soda begins to fuse. The acid gas passes up the chimney, and is either 
 allowed to pass away into the air, or is condensed by meeting with a 
 stream of water, and the weak liquid acid thus formed is let to run to 
 waste. The greater part of the sulphate of soda thus produced is 
 immediately used to make carbonate of soda ; but to form Glauber's 
 salt, it is only necessary to dissolve it in warm water and let it crystal- 
 lize by cooling. 
 
 The sulphate of soda crystallizes in six-sided 
 prisms, as in the figure, very much channelled at 
 the sides. It is easily soluble in water, having a 
 point of maximum solubility at 93, as figured in 
 page 19. Its ordinary crystals contain 56 per 
 cent, of water ; by exposure to the air it loses all 
 its water by efflorescence, and falls into a white 
 powder; from a hot saturated solution opaque rhombic octohedral 
 crystals are deposited, which are anhydrous. The isomorphism of 
 these crystals with permanganate of barytes, and the speculations 
 founded on it have been noticed, p. 312. A UsulpJiate and a sesgui- 
 sulphate of soda may be formed by adding oil of vitriol to a solution 
 of the neutral salt, and crystallizing by evaporation. They are much 
 less determinate than the acid sulphates of potash. 
 
Nitrate, Hypochlorite and Hyposulphite of Soda. 605 
 
 Nitrate of Soda. Cubic Nitre. NaO.NO 5 . Eq. 1062'2 or 85. 
 The spontaneous formation of this salt by the atmospheric influence, 
 probably on a soil containing chloride of sodium, has been noticed, p. 
 380. It may also be obtained by means of nitric acid and carbonate 
 of soda. It crystallizes in rhombs, isomorphous with calc spar, (p. 
 312). It is very soluble in water, and is slightly deliquescent; hence 
 it cannot be employed in the manufacture of gunpowder. It is used 
 for the manufacture of nitric and sulphuric acids, and as a manure. 
 Tor the modes of estimating the purity of the commercial nitrate of 
 soda, see page 600. 
 
 Hyposulphite of Soda. NaO.S 2 2 +10 Aq. This salt, which has 
 become of some practical interest, from its use in dissolving off the 
 sensitive silver compounds in making photogenic drawings, may be 
 made by boiling together three parts of dry carbonate of soda with one 
 of sulphur until this last is dissolved, and then passing a stream of 
 sulphurous acid gas through the liquor until it smells strongly of it. 
 NaO.CO 2 , with S and S0 2 produce NaO.SA whilst CO 2 is evolved. 
 If the three parts of carbonate of soda be boiled with two of sulphur, 
 and the deep yellow liquor be exposed to the air, until it yields a colour- 
 less liquor on filtration, the salt is more simply produced ; the necessary 
 quantity of oxygen being absorbed from the air. The hyposulphite of 
 soda thus formed is easily soluble in water. Its resemblance to 
 Glauber's salt in form, and its other properties are noticed in p. 400. 
 The mode of preparing the soda salts of the different species of thionic 
 acids have been sufficiently noticed in p. 401, et seq. 
 
 Hypochlorite of Soda. Chloride of Soda. Disinfecting Liquor of 
 Labaraque. Is produced by treating a solution of carbonate of soda 
 with chlorine, as long as this is absorbed, but no carbonic acid evolved. 
 For further observations, see the hypochlorites of potash, and of lime. 
 A. Tribasic Phosphate of Soda. The common phosphate of soda of 
 the shops is a tribasic salt, containing (P0 5 + 2NaO + HO) + 24 
 Aq. It is prepared by decomposing the solution of acid tribasic phos- 
 phate of lime obtained from bones, (as described p. 412), by means of 
 carbonate of soda. Carbonate of lime is thrown down, and phosphate 
 of soda formed. It is easily soluble in water, and crystallizes in ob- 
 lique rhombic prisms, as in the figure, which react 
 alkaline. When exposed to the air, it loses some of its 
 water by efflorescence, (ten atoms ?) but the crystals 
 retain their form. If this salt be mixed with an excess 
 of caustic soda, the atom of basic water is displaced, 
 and the sub-phosphate of soda (P0 5 -f 3NaO + 24Aq), 
 crystallizes in long prisms ; and by the addition of hy- 
 
606 Phosphates of SodaBorate of Soda. 
 
 drated phosphoric acid to its solution, and cautious evaporation, the 
 acid tribasic phosphate (PO 5 -f NaO -f- 2HO) -f. 2Aq. which crystal- 
 lizes in oblique rhombic prisms is formed; it is dimorphous. 
 
 The characteristic of these three salts is to give with nitrate of silver 
 a yellow precipitate of tribasic phosphate of silver. 
 
 B. Bibasic Phosphate of Soda. Of these salts that termed the 
 pyrophosphate of soda (PO 5 -f- 2NaO) + lOAq. is of interest, as its 
 discovery led the way to the true history of these bodies. It is formed by 
 fusing the common phosphate of soda (PO 5 -f 2NaO + HO) -f 24Aq. 
 at a red heat. All the water of crystallization is given off at a very 
 moderate heat ; but by a red heat the twenty-fifth or basic atom is ex- 
 pelled, and when the salt is then redissolved, the phosphoric acid does 
 not recombine with basic water, but remains united only with the soda. 
 It is recognized by giving a white precipitate with nitrate of silver. 
 
 C. The Monobasic Phosphate of Soda. P0 5 + JSFaO. is obtained by 
 heating the acid tribasic or bibasic phosphates of soda to redness. All 
 the volatile base being thus expelled, the phosphoric acid remains com- 
 bined with one equivalent of soda. This salt fuses into a transparent 
 glass ; is deliquescent ; its solution does not crystallize. It is easily 
 recognized by throwing down from solutions of lead and silver, pre- 
 cipitates, which are not powders but soft tenacious pastes. 
 
 Borates of Soda. Boracic acid combines with soda in many propor- 
 tions, forming salts, of which the most important is the triborate, the 
 borax of commerce (NaO -f 3.B0 2 ) -f 10 Aq. It exists in the water 
 of several lakes in Thibet and China, also in Hungary, and was im- 
 ported thence in small crystals, smeared with a fatty matter, under the 
 name of tinkal. The borax of commerce is now obtained by treating 
 the native boracic acid obtained from Tuscany, p. 455, by carbonate of 
 soda. On the application of heat, the acid dissolves with the evolution 
 of carbonic acid and ammonia : the liquor is run into large vats lined 
 with lead, where- it cools very slowly, and the borax gradually crystal- 
 lizes in oblique rhombic prisms, as i, u, m, in the figure. If a strong 
 solution of borax be kept at 33, the salt crystallizes in 
 regular octohedrons with only five atoms water. Although 
 this salt contains three equivalents of acid it has an alka- 
 line reaction : when heated, it frothes up very much, 
 abandoning the water. The dry salt melts at a red heat 
 
 into a colourless glass, which dissolves most metallic oxides very readily, 
 and hence is serviceable in experiments with the blowpipe, as enabling 
 the metals to produce the colourless glasses by which they are recog- 
 nized ; under the head of glass and porcelain, its use in these branches 
 of art will be again noticed. 
 
Chloride of Barium Sulphate of Barytes. 607 
 
 The remaining compounds of boracic acid with soda, as the neutral 
 borate, NaO.B0 2 + 8Aq. and acid salts as NaO + 6BO 2 and NaO + 
 9B0 2 are not important. 
 
 Silicate of Soda will be described under the head of glass. 
 
 Salts of Lithium. From the rarity of this body, its salts require no 
 further notice, than that its carbonate is but very sparingly soluble in 
 water, yet its solution possesses an alkaline reaction. It thus serves to 
 connect the alkaline with the earthly bases. 
 
 SALTS OF BARIUM. 
 
 Chloride of Barium. Bad + 2Aq. Eq. 1301'7 + 225, or 104'] 
 + 18. This salt may be prepared by decomposing the native carbo- 
 nate of barytes with dilute muriatic acid, or, more especially, by decom- 
 posing the sulphuret of barium, the preparation of which is described 
 in p. 482, by dilute muriatic acid. In the former case carbonic acid, 
 in the latter, sulphuretted hydrogen, is given off. The chloride of 
 barium crystallizes from a hot solution in rhomboidal tables which con- 
 tain 14' 7 of water. 
 
 Sulphate of Barytes.- BaO.S0 3 . Eq. 1458, or 116-7. This salt 
 exists native, in great abundance, being the most common source of 
 barytes. It is very generally associated with sulphuret of lead, and 
 serves as an indication of the probable proximity of that ore. It is 
 totally insoluble in water. Its crystalline form is an oblique rhombic 
 prism, generally very flat, as in the figure ; 
 derived from an octohedron of which * and e 
 are planes ; the secondary planes, p and u be- 
 long to the prism. It is one of the heaviest of 
 saline bodies, its specific gravity being 4*3, 
 hence its name of heavy spar and terra ponderosa. When ground to 
 fine powder, it is used as a cheap substitute for white lead in painting, 
 for which large quantities of it are employed, but its crystalline texture 
 prevents its having the opacity, or body, necessary in a good pigment. 
 It may be prepared artificially, by adding sulphuric acid to any solu- 
 tion containing barytes ; it falls as a heavy white crystalline powder. 
 Its total insolubility renders its constituents excellent re-agents for each 
 other. 
 
 Nitrate of Barytes. BaO + 1\ T 5 . Eq. 1633, or 130, may be pro- 
 duced by acting on carbonate of barytes with dilute nitric acid, or more 
 cheaply by mixing strong hot solutions of sulphuret of barium and 
 nitrate of soda. The sparingly soluble nitrate of barytes crystallizes as 
 the mixed liquors cool, but the sulphuret of sodium remains dissolved 
 
608 Nitrate of Barytes Salts of Strontium. 
 
 In this process from Ba.S and NaO.N0 5 we obtain BaO.N0 5 and Na.S. 
 This salt requires twelve parts of cold water for solution, but dissolves 
 in four of boiling water, from which it crystallizes on cooling in octo- 
 hedrons. These crystals are anhydrous. "When heated they yield pure 
 barytes. 
 
 The other salts of barytes do not require notice. 
 
 SALTS OF STRONTIUM. 
 
 Chloride of Strontium. Sr.CL + 6Aq. Eq. 989'9 or 79'32. This 
 salt is obtained from the native carbonate or sulphate of strontia, exactly 
 as chloride of barium is obtained from the native salts of barytes. 
 It crystallizes in long needles which deliquesce. It is very soluble in 
 water. 
 
 Sulphate of Strontia. SrO. SO 3 . Eq. 1148-4 or 91-9. This, the 
 most abundant source of strontia, is found native crystallized, isomorph- 
 ous with sulphate of barytes. It may be produced artificially, as a 
 white powder, by adding sulphuric acid to any solution containing 
 strontia. It is dissolved by 3600 parts of boiling water, and remains 
 dissolved after cooling. It is fused by a strong heat ; with charcoal it 
 gives sulphuret of strontium. 
 
 Nitrate of Strontia. SrO.N0 5 . Crystallizes in octohedrons, which 
 dissolve in five parts of cold, and one-half part of boiling water. Mr. 
 Scanlan has observed, that during the crystallization of this salt 
 bright flashes of light are emitted. It is anhydrous, but decrepitates 
 when heated, owing to mechanically included water. On the applica- 
 tion of heat, these crystals evolve oxygen and nitrogen, and leave pure 
 strontia. 
 
 SALTS OF CALCIUM. 
 
 Chloride of Calcium. -CaCl + 6Aq. Eq. 693-7 + 675 or 55'47 
 4. 54, is obtained by decomposing carbonate of lime with muriatic acid. 
 In the laboratory it is abundantly procured as the residue of the pre- 
 paration of carbonic acid, ammonia, &c. It is very soluble in water ; 
 its solution, evaporated to the consistence of syrup, gives, by cooling, 
 long striated rhombic prisms, which deliquesce with great rapidity, and 
 when heated undergo watery fusion ; soon after which it abandons two- 
 thirds of its water of crystallization, and a powder is obtained, CaCl 
 + 2Aq. in which form it is best adapted for freezing mixtures. Heated 
 still further, it becomes anhydrous, and at a red heat fuses. In this 
 state it is phosphorescent in the dark, forming Homberg's pyrophorus. 
 
Chloride and Fluoride of Calcium. 60 9 
 
 It has a very great affinity for water, combining with two atoms of it 
 with the evolution of much heat, and is hence employed to dry gases 
 for experimental purposes, and to remove water from liquids, as in the 
 rectification of alcohol. 
 
 This salt combines with lime, forming an oxy-chloride of calcium, 
 CaCl + 3CaO. which is obtained by boiling a solution of it with an 
 excess of lime and filtering. The new substance crystallizes, on cooling, 
 in small flat rhombs, which contain forty-nine per cent, or fifteen atoms 
 of water. 
 
 The bromide, or iodide of calcium do not present any interest. 
 
 Fluoride of Calcium. Oa.F. is an abundant mineral known as fluor 
 spar, found crystallized in cubes and octohedrons, but principally mas- 
 sive. When first extracted from the earth it is moderately tough and 
 soft, and is cut into ornaments which present a beautiful variety of 
 colours. Its crystals become strongly phosphorescent by heat, or by 
 electricity ; it is insoluble in water : from it all the other preparations 
 of fluorine are derived, as noticed in pp. 445, and 452. It is quite 
 insoluble in water, and appears as a gelatinous precipitate when 
 hydrofluoric acid is added to any soluble salt of lime. When heated 
 in contact with siticious or aluminous minerals, it forms easily fusible 
 compounds, and being thus of use as a. flux in the smelting of metallic 
 ores, its name of fluor spar was thence derived. 
 
 Sulphate o/Lime.VaQ. S0 3 + 2Aq. Eq. 850'0 -f 225 or 68 + 
 18. May be prepared artificially, by mixing a solution of any soluble 
 salt of lime with sulphuric acid. It forms a crystalline powder, nearly 
 equally soluble in hot and cold water, requiring 461 times its weight 
 for its solution. It occurs in nature abundantly, and in various forms : 
 1st, in distinct, colourless crystals ; 2nd, in semi-transparent masses 
 of crystalline structure, constituting alabaster, and in amorphous masses 
 forming extensive rocky strata, in many places, in which state it is 
 called common gypsum. Prom this plaster of paris is obtained, by 
 calcining the gypsum, broken into small pieces, in ovens at a tempera- 
 ture below 300, until its water of crystallization is expelled. In this 
 operation it falls to powder, and is to be put up in tight vessels, so as 
 to exclude the air. When mixed with water it rapidly recombines with 
 the two atoms, evolving heat and expanding in becoming solid, so as 
 to fill up all interstices of the mould into which it may be poured. On 
 this property is founded the art of casting in plaster and the formation 
 of the various kinds of stucco, or artificial stone, in which a solution 
 of glue, or of various earthy salts, may be substituted for pure water. 
 If the gypsum had been heated, in baking, above 300, it is changed 
 in nature, and no longer combines with water, so as to set ; it is then 
 39 
 
610 Sulphate and Phosphate of Lime. 
 
 converted into a form which exists in nature crystallized,, and which is 
 termed anhydrite. 
 
 A double salt of sulphate of lime and sulphate of soda is found 
 native, and termed Glauberite. It is insoluble in water, by which it is 
 also decomposed. It cannot be formed artificially. 
 
 The Hyposulphite of Lime is a soluble salt, the mode of preparing 
 which is described p. 399. 
 
 The Nitrate of Lime is very deliquescent, and is decomposed by a 
 moderate heat. 
 
 Phosphoric acid combines with lime in several proportions, of which 
 the most important is the Basic tribasic phosphate of lime, or Earth of 
 bones. This salt, which constitutes the inorganic portion of the skele- 
 ton of the mammalia, mixed only with small quantities of carbonate 
 and sulphate of lime, and of fluoride of calcium, has the formula 
 8CaO + 3PO 5 . It may be obtained precipitated, by dissolving bone 
 earth in muriatic acid, and exactly neutralizing the solution by caustic 
 ammonia. It falls as a gelatinous powder containing four atoms of 
 water. As the phosphoric acid of bones is in its tribasic condition, 
 Graham considers it to be a combination of two phosphates, thus, 
 2(3CaO.PO 5 + Aq.) + (HO.2CaO.POs 4. Aq.) Each of these tribasic 
 phosphates of lime may be obtained separate, by decomposing solutions 
 of chloride of calcium by solutions of the ordinary phosphate, or of the 
 subphosphate of soda. 
 
 Hypochlorite of Lime. Chloride of Lime. Bleaching Salt. When 
 speaking of the oxygen compounds of chlorine, and of the chlorate and 
 hypochlorate of potash, I have had occasion to notice the diversity of 
 opinion regarding the nature of the bleaching substances formed by the 
 action of chlorine on the alkalies, and on lime. Of these the chloride 
 of lime is by far the most important in the arts. It is prepared by 
 generating chlorine in a large still, a, b, h, f, as described p. 418, the 
 materials being kept constantly mixed, by means of an agitator moved 
 round by the handle d. The gas is conducted by the tube e e to the 
 upper part of a wooden reservoir, or apartment, as in the figure, (next 
 page), made very tight, i, i, on the floor of which, pure hydrate of lime 
 is exposed to the action of the gas. The lime is introduced by the 
 door k, h, and the surface is changed occasionally by stirring with rakes 
 by means of the apertures I, I, I': the absorption should take place so 
 slowly as not to evolve any sensible heat. In this way 100 parts of 
 slaked lime combine generally with from fifty to sixty of chlorine. If 
 the process be carried on too rapidly, a quantity of lime is decomposed, 
 chlorate of lime and chloride of calcium being formed, which may be 
 recognized by the product getting damp when exposed to the air. 
 
Manufacture of Chloride of Lime. 
 
 Gil 
 
 The best bleaching powder thus prepared by the dry way, does not 
 contain more than forty per cent, of chlorine ; this does not correspond 
 
 to any exact atomic constitution ; but if lime be diffused through water 
 so as to form a thin cream, it then absorbs more than its own weight of 
 gas, and is totally dissolved. It is probably the mechanical disadvan- 
 tages of the dry powder, which prevents the absorption of the gas reach- 
 ing this limit, and the best bleaching powder may be looked on as a 
 mixture of true chloride of lime, with about eighteen per cent, of hy- 
 drate of lime in excess. Accordingly, w^hen ordinary bleaching powder 
 is treated with water, the true atomic compound is dissolved out and 
 the excess of lime remains. The composition of the theoretical and the 
 best practical substances may, therefore, be expressed as follows : 
 
 Theoretical. 
 
 1 atom chlorine, 35'47 48'93 
 
 1 lime, 28-00 38'64 
 
 1 water, 9 -00 12-43 
 
 72-47 100-00 
 
 Best practical 
 
 Chlorine, 40'32 
 
 Lime, 45-40 
 
 Water, 14'28 
 
 100-00 
 
 But the generality of good samples in commerce will be found not to 
 exceed thirty per cent, of chlorine. 
 
 The solution of this chloride of lime has a marked alkaline reaction; 
 it is without any bleaching power, except an acid be present, which libe- 
 rates chlorine and enables it to destroy the colouring matter. It is 
 thus that the colour can be removed from certain points without injur- 
 ing others, which is of very great importance in calico printing ; thus a 
 piece of cloth being dyed uniformly with madder, (as Turkey red), the 
 pattern is printed on with tartaric acid thickened with gum, and the 
 whole being immersed in a bath of chloride of lime, the chlorine is 
 liberated by the acid at every point of the pattern, and the cloth is 
 there bleached, giving a white ground, on which other colours may be 
 
612 Process of Chlorometry. 
 
 be applied, whilst the general surface remains deep red. A solution of 
 bleaching powder in water exhales a sensible odour of chlorine, owing 
 to the absorption of carbonic acid from the air, and obtains thereby 
 weak bleaching properties. 
 
 As the technical value of bleaching powder depends on the total 
 quantity of chlorine which it contains, this may be determined without 
 reference to its theoretical constitution. For this purpose a variety of 
 methods have been proposed, and the process is termed Chlorometry. 
 The earliest method employed, consisted in preparing a standard solution 
 of sulphate of indigo, which, being of a deep blue colour, was bleached 
 by the chlorine expelled from the lime by the sulphuric acid, and evi- 
 dently, the richer the bleaching powder was in chlorine, the more solu- 
 tion of indigo a certain weight of it could bleach. The action of 
 chlorine on indigo is, however, so complex, that this method was found 
 exposed to numerous fallacies, and may be considered as now obsolete. 
 Latterly Gay Lussac has proposed to substitute for this, the more 
 definite action of chlorine in acidifying arsenic. He prepares a solution 
 of arsenious acid in muriatic acid, and dilutes this with water. On 
 adding thereto a solution of chloride of lime, the muriatic acid takes 
 the lime, and the chlorine, decomposing water, converts the arsenious 
 acid into arsenic acid, and itself forms hydrochloric acid ; AsO 3 with 
 2C1 and 2. HO producing AsO 5 and 2.HC1. The proportions which I 
 employ in this reaction are as follows : 100 grains of arsenious acid are 
 to be dissolved in 2000 grains of strong spirits of salt, and this liquor 
 diluted with distilled water, till it occupies the volume of 7000 grains 
 of water. This is the standard test liquor ; to employ it, 100 grains of 
 bleaching powder to be tested are to be diffused through 1000 grains of 
 water and the test liquor to be gently poured from a graduated glass on 
 it, in a deep jar, continually stirring the mixture. A drop of weak 
 solution of sulphate of indigo is to be occasionally applied by means of 
 a glass rod to the surface of the liquor ; as long as any chlorine remains 
 unaltered, the blue colour of the drop is instantly destroyed, and the 
 addition of the arsenic liquor is to be continued until the blue drop re- 
 mains unaltered. Then the quantity of chlorine present in the 100 
 grains of bleaching powder, is represented by lioth of the quantity of 
 the test liquor employed ; thus if there were 2565 grains of the test 
 liquor necessary to destroy the bleaching powder of the 100 grains of 
 chloride of lime, the quantity of chlorine would be 25'65. This is not 
 absolutely correct, for in theory, the true quantity of chlorine indicated 
 would be 26*08, but as a few drops of the solution are always em- 
 ployed, more than what should by theory be necessary, the practical 
 proportion of T ^ comes excessively close to the truth. Even one- 
 
Practical value of the Bleaching Powder. 613 
 
 half per cent., which is the limit of error, is quite unimportant in 
 practice. 
 
 Another method, which is simple and rapid in execution, is nearly 
 the same as that described in p. 499, for determining the technical 
 value of black oxide of manganese by means of copperas, (green sul- 
 phate of iron). The proportion and method of testing which I employ 
 are as follows : 390 grains of clean and dry crystals of green sulphate 
 of iron are to be dissolved in as much water as will bring the solution 
 to the volume of 5000 grains of water. On the other hand, 100 grains 
 of the chloride of lime is to be diffused through 1000 grains of water, 
 and the solution of copperas is to be added thereto, until the presence 
 of a trace of the protosulphate of iron in excess is indicated, by the 
 mixed liquor striking a full blue colour when a drop of it is placed on 
 a slip of paper, imbibed with red prussiate of potash. The quantity of 
 chlorine present in the 100 grains of the bleaching powder, is -j-J^ of 
 the quantity of the standard copperas liquor employed; thus, if 2783 
 grains measure of the volume of the solution be found necessary, the 
 sample contains 27*83 of chlorine per cent. For the 27'83 of liquor 
 contains 217 grains of sulphate of iron which is peroxidized by the 
 action of 27 '6 grains of chlorine; here also the limit of error need not 
 exceed one-half per cent. Other processes have been proposed, founded, 
 some on the change of yellow 7 prussiate into red prussiate of potash, by 
 means of the chlorine of the bleaching powder ; and others, by decom- 
 posing the bleaching powder by means of an excess of water of ammonia, 
 and measuring the nitrogen gas evolved, but these are more trouble- 
 some and less exact than the processes already detailed, which are those 
 most worthy of confidence from the manufacturer. 
 
 As to the theoretical nature of bleaching powder, chemists are not as 
 yet able to decide positively. The original and simple idea of a direct 
 combination between the chlorine and the lime, has been revived by 
 Millon, who advanced, that by decomposing the salts of lead, iron, and 
 copper, by solution of chloride of lime, precipitates were obtained, 
 which were compounds of the protoxide of the metal united with as 
 much chlorine as was equivalent to the oxygen necessary to form perox- 
 ide. Thus, that with lead, a chloroxide Pb.O.Cl ; that with iron, a 
 chloroxide Fe 2 .Q2.Cl. The chloride of lime CaO.Cl. should thus be 
 equivalent to deutoxide of calcium, Ca.O.O, It has been found, how- 
 ever, that the evidence, is not yet satisfactory. The peroxide of potas- 
 sium is KOs, whilst chloride of potash is not K.O.C1 2 but KO.C1. The 
 composition of all these bleaching compounds, appears to be an atom 
 of chlorine united to an atom of a protoxide, and this may be explained, 
 by supposing a hypochlorite and a metallic chloride to be formed ; thus 
 
614 Salts of Magnesium. 
 
 2CaO and 2C1 may give CaO + CIO and CaCl. But if this happens, 
 the chloride of calcium certainly remains combined, forming a double 
 salt ; for the bleaching powder, if properly prepared, has no tendency 
 to deliquesce, and only becomes damp when long kept, and then chlo- 
 rate of lime, and free chloride of calcium are formed, and all its bleach- 
 ing qualities are lost. There are thus two views equally tenable ; first, 
 that the bleaching compounds are chlorides of oxides, corresponding to 
 peroxides ; and second, that they are double salts of a hypochlorite^ 
 with a chloride, but there is no reason to consider, that the chlorous 
 acid C1O 4 comes into play in their manufacture, although the salts of 
 that acid when otherwise prepared, do possess bleaching properties. 
 
 SALTS OF MAGNESIUM. 
 
 Chloride of Magnesium. MgCl. Eq. 60O9, or 48*16, may be ob- 
 tained in solution by acting on the carbonate of magnesia with muriatic 
 acid ; by evaporation, it may be obtained in prisms with 6 Aq. which 
 are very deliquescent. These crystals cannot be deprived of water, 
 without total decomposition, the chlorine passing off as muriatic acid, 
 and magnesia remaining behind. The chloride may, however, be ob- 
 tained anhydrous, by previously mixing its solution with sal-ammoniac, 
 with which it forms an anhydrous double salt, which, when heated to 
 redness, gives off sal-ammoniac, and the pure chloride of magnesium 
 remains melted, and forms a clear crystalline mass when cold. The 
 chloride of magnesium exists in sea water. 
 
 Sulphate of Magnesia. MgO.SO 3 . Eq. 759'4 or 60'8. This salt 
 exists abundantly in saline mineral springs, as those of Seidlitz, Selters, 
 and Epsom, from whence it derives its common name of epsom salt. 
 It is extracted principally from the magnesian limestone, which is cal- 
 cined, and the mixed lime and magnesia treated with dilute sulphuric 
 acid ; the sulphate of lime being very sparingly soluble, is easily sepa- 
 rated from the sulphate of magnesia by washing with water, the latter 
 is dissolved out and the liquor evaporated and crys- 
 tallized. A great deal is also made from the 
 mother liquor of sea water, or littern, (p. 603). 
 This is decomposed by sulphuric acid and the 
 salt formed separated by crystallization. 
 
 The sulphate of magnesia crystallizes in oblique 
 rhombic prisms, as in the figure, containing seven 
 atoms of water, of which one is constitutional, and 
 the other six crystalline ; its formula is therefore 
 MgO,SO 3 . HO -f- 6 Aq; when heated to 212, it easily abandons the 
 
Manufacture of Epsom Salts. 615 
 
 6 Aq. but retains the seventh atom of water even at 4 CO . It com- 
 bines with the sulphate of potash, to form a double salt, (MgO' 
 SO 3 -f KO.SOJ -f 6 Aq ; the atom of constitutional water being re- 
 placed by the alkaline sulphate. The sulphates of soda and of ammonia 
 act in the same way. 
 
 Nitrate of Magnesia. MgO.N0 5 is very soluble and deliquescent. 
 It cannot be obtained dry, as it crystallizes with six equivalents of 
 water, of which five are expelled by a moderate heat, and by a higher 
 temperature, the nitric acid itself passes off and magnesia remains be- 
 hind ; MgO.NO 5 .HO producing MgO and HO.NO 5 . 
 
 The Borate of Magnesia constitutes the mineral boracite, whose elec- 
 trical and crystalline properties have been already noticed. 
 
 There exists a great number of combinations of silicic acid with 
 magnesia, constituting the steatite, or soapstone; the meerschaum, of 
 which pipe bowls are cut ; olivine, and the serpentine which exists abun- 
 dantly in the green marble of Galway ; these are simple silicates of 
 magnesia ; others, as amphibole and pyroxene, are double silicates of 
 magnesia and lime, more or less replaced by protoxide of iron. 
 
 SALTS OF ALUMINUM. 
 
 Chloride of Aluminum. A1 2 C1 3 . Eq. 1 670*3, or 133'84. In a 
 hydrated form this salt may be prepared by dissolving alumina in 
 muriatic acid, a solution being obtained, which, when evaporated, yields 
 very deliquescent crystals, containing twelve atoms of water. On ap- 
 plying heat to this, the salt itself is decomposed, muriatic acid is given 
 off, and pure alumina remains. The dry chloride of aluminum is 
 formed only by a process analogous to that described for chloride of 
 silicon, p. 451. Pure alumina is mixed with lampblack and ignited in 
 a porcelain tube, whilst a stream of dry chlorine is passed over it ; the 
 oxygen of the alumina combines with the carbon and forms carbonic 
 oxide, and the chlorine combines with the aluminum. The resulting 
 chloride, being volatile, sublimes, and is condensed in the cool portion 
 of the tube, which is allowed to project some distance beyond the 
 furnace for that purpose, or a wide glass tube is adapted to receive 
 the salt. 
 
 The chloride of aluminum thus formed is a pale-green crystalline 
 mass. Exposed to the air, it fumes and deliquesces. Once combined 
 with water, it cannot be freed from it. It is used to obtain metallic 
 aluminum, as described p. 490. 
 
 The Fluoride of Aluminum is found in the mineral kingdom. The 
 beautiful gem, the topaz, is a double fluoride and silicate of alumina. 
 
616 Salts of Aluminum. 
 
 Sulphate of Alumina (A1 2 O 3 + 3SO 3 ) + 18 Aq. This salt is ob- 
 tained by dissolving alumina in dilute sulphuric acid, it has a sweetish 
 styptic taste, is very soluble in water, and crystallizes in thin flexible 
 plates; when heated, it abandons its water, and at a red heat, its sulphuric 
 acid, alumina remaining pure. The sulphuric acid unites with alumina 
 in many other proportions, of which that constituting the mineral alu- 
 minite is the most important ; its formula is A1 2 3 -f- S0 3 -\- 3 Aq. ; 
 the base, acid and water, each containing the same quantity of oxygen. 
 This salt is produced also, by adding an excess of caustic ammonia to a 
 solution of alum ; hence caustic ammonia cannot be used to prepare 
 pure alumina (p. 490). 
 
 The sulphate of alumina combines with the alkaline sulphates to form 
 the remarkable double salts, the common alums. The most ordinary 
 kind is the double sulphate of alumina and potash } the formula of which 
 is (KO.S0 3 + A1 2 O 3 -|- 3S0 3 ) + 24 Aq. Erom the large quantities of 
 this salt employed in the processes of dying, its manufacture is conducted 
 upon the great scale. In the coal districts, and interstratified with the 
 beds of good coal, strata of clay-slate are generally found, containing a 
 certain quantity of coaly material, and through which abundance of 
 bisulphuret of iron is disseminated in the instable rhombic form, (see 
 pp. 315 and 510.) When this alum slate is exposed to the air, the 
 sulphuret of iron rapidly absorbs oxygen and forms copperas, with an 
 excess of sulphuric acid, which reacts on the clays, with the alumina 
 of which it combines. This effect is accelerated by the application of 
 heat, which is applied by building up the mineral into pyramidal heaps, 
 with some fuel underneath, and channels through the interior, by which 
 a draught may be established ; the fuel below being set on fire, the 
 slate contains coal enough to maintain its own combustion, and the 
 mass changes in colour as it burns, becoming brick red ; according as 
 the process is carried through, successive quantities of mineral are added 
 to the burning heap, until it often acquires a height of sixty or eighty 
 feet. When the mass thus calcined has become quite cold, it is pow- 
 dered and lixiviated with water ; a large quantity of sulphate of alumina 
 and sulphate of iron dissolve out, and the liquor is brought by evapora- 
 tion to a certain degree of strength. A solution of some salt of potash 
 is then added, generally the waste chloride of potassium from soap 
 boilers, and the sulphate of iron being decomposed, forms sulphate of 
 potash, which unites with the sulphate of alumina, and crystallizes out 
 as alum, whilst the iron remains as chloride in the liquor. 
 
 In some volcanic countries, as Italy, a mineral is found already con- 
 taining potash and sulphuric acid unites to alumina, from which is ob- 
 tained a very pure alum, rock-alum, which is valued very much by dyers, 
 
Manufacture of Alum. 617 
 
 on account of its total freedom from sulphate of iron, of which Eng- 
 lish alum generally contains a small trace, which injures the colours 
 of the dyes. 
 
 Alum crystallizes in regular octohedrons, the solid angles being often 
 replaced by the surfaces of a cube. When heated, the water is first 
 expelled, and at a red heat, it parts with most of its sulphuric acid, 
 sulphate of potash and pure alumina remaining. The taste of alum is 
 sweet and astringent, it reacts acid, and is soluble in 18*4 parts of cold, 
 and in 0'75 parts of boiling water. A remarkable pyrophorus, that of 
 Homberg, is prepared from alum ; three parts of dried alum and one of 
 lampblack well mixed, are to be placed in a stout glass bottle, and being 
 bedded with sand in a crucible, are to be carefully heated to redness, 
 until a blue flame appears at the mouth of the bottle ; when this has 
 lasted a few minutes, the bottle is to be stoppered with a bit of chalk, 
 and the whole cautiously cooled. The bottle contains a black powder, 
 a mixture of lampblack, alumina, and sulphuret of potassium, which 
 last being in a state of exceedingly minute division, takes fire when a 
 little of the product is shaken out of the bottle, and emits considerable 
 light. 
 
 Basic Alum. Cubical Alum.M> z . 2SO 3 . + KO.SO 3 . This sub- 
 stance, which is preferred to ordinary alum as a mordant, is prepared by 
 adding carbonate of potash to a solution of alum, as long as the pre- 
 cipitate which first forms is redissolved by agitation. It crystallizes in 
 cubes which have no acid reaction. 
 
 The sulphate of soda combining with sulphate of alumina, forms the 
 soda alum, which is not much used. The ammonia alum will be here- 
 after noticed. 
 
 The Phosphate of Alumina constitutes a remarkable mineral found in 
 Cork and Tipperary, the wavellite. 
 
 The simple and double silicates of alumina constitute probably the 
 majority of all known minerals ; such of them as possess technical or 
 pharinaceutic value are noticed under the heads of the uses to which 
 they are applied. Tor a description of the others, I refer to the ordi- 
 nary works on mineralogy. 
 
 One substance, however, of which the constitution is very curious, 
 may, from its technical importance, be here noticed, the lapis lazuli, or 
 ultramarine. It is found in veins in igneous rocks in Siberia, but par- 
 ticularly in China. It is of a rich blue colour, not crystalline, and 
 being powdered, serves in painting as the richest and most permanent 
 blue ; its composition has been found to be in 100 parts, silica, 35*8; 
 alumina 34 8 ; soda, 2 3' 2 ; sulphur, 3'1 ; carbonate of lime, 3*1 ; it 
 is difficult to deduce a formula from these numbers, and the state of 
 
618 Nature of Glass and Porcelain. 
 
 combination of the sulphur is not well understood. Attempts at imi- 
 tating the composition of this body have been partially successful, and 
 a large quantity of artificial ultramarine is now made for painters' use 
 by the following process ; freshly precipitated silicic acid, and alumina, 
 are mixed with sulphur in a solution of caustic soda, all in the propor- 
 tions above given, and the mixture dried down ; the resulting mass is 
 placed in a covered crucible and exposed to a white heat, it gives a dark 
 and pure blue mass, to which, for the perfect bringing out of the colour, 
 the air must have had partial access during its ignition. The product 
 is reduced to impalpable powder by the same process adopted for the 
 native substance. 
 
 Constitution of Glass and Porcelain. 
 
 I deferred the description of the silicates of potash, soda, and lime, 
 because they stand so closely allied with the silicate of alumina, in rela- 
 tion to the important manufactures of glass and earthenware, that their 
 properties could only be well understood when studied in connexion 
 with it. 
 
 Silicic acid combines with the alkalies in many proportions, of which 
 those that contain a considerable excess of base are soluble in water. 
 
 Thus is prepared the liquor of flints, by melting together one part of 
 powdered quartz, and two of carbonate of potash ; the carbonic acid is 
 expelled and a glassy mass is obtained, which deliquesces in the air, and 
 is very soluble in water. It reacts strongly alkaline, and gives, with 
 acids, a precipitate of silica in its soluble form, as described p. 450. 
 In this preparation, soda may be constituted for potash in a proportion 
 one-third less, and a mixture of seventy parts carbonate of potash, fifty- 
 four dry carbonate of soda, and 152 of fine quartz sand, gives a still 
 more fusible and soluble product. This substance, under the name of 
 soluble glass, has been employed to render wood incombustible ; several 
 coats of a strong solution of it being applied under the paint. 
 
 "When the quantity of silicic acid is greater, the resulting alkaline 
 silicate is insoluble in water, and possesses the qualities which give to 
 glass its peculiar value. These are, first, to solidify, after being melted, 
 very gradually, and to pass through a condition of pastiness, which ad- 
 mits of its being blown out, cut, and fashioned in every way ; and 
 second, to remain, when solid, quite transparent and destitute of any 
 tendency to crystalline structure. Its composition should also be such 
 as to resist completely the action of air and water. 
 
 The materials used in the manufacture of glass are, 1st, quartz sand, 
 as free as possible from iron ; 2nd, lirnc used sometimes pure, some- 
 times slaked ; occasionally chalk is employed in place of lime ; 3rd, 
 
Composition of Glass. 
 
 619 
 
 carbonate of potash,, (pearl ashes of commerce) ; 4th, carbonate of soda, 
 or a salt of soda, as Glauber's salt, or common salt ; 5th, old broken 
 glass, technically termed cullet ; 6th, red lead, which must be extremely 
 pure ; and for corrective purposes, arsenious acid sometimes, but more 
 frequently black oxide of manganese. These materials are by no 
 means all employed together; the composition of various kinds of 
 glass differing very much, as is shown in the following table of the 
 best analyses of glass. 
 
 Constituents. 
 
 Hard white 
 
 
 
 3 
 
 Crown 
 
 Glass. 
 
 Bottle 
 
 Glass. 
 
 'eS 
 
 I 
 
 Flint 
 
 Glass. 
 
 
 No.l 
 
 No.2 
 
 No. 3. 
 
 No. 4. 
 
 No. 5. 
 
 No. 6. 
 
 No. 7. 
 
 No. 8. 
 
 No. 9. 
 
 Silicic Acid 
 Potash . . . 
 Soda 
 
 71-7 
 12-7 
 ' 2-5 
 
 69-2 
 15-8 
 3-0 
 
 62-8 
 22-1 
 
 69-2 
 8-0 
 3-0 
 
 604 
 3-2 
 
 53-5 
 5-5 
 
 592 
 9-0 
 
 51-9 
 13-8 
 
 42-5 
 117 
 
 Lime 
 Alumina 
 Magnesia 
 
 10-3 
 0-4 
 
 7-6 
 1-2 
 2-0 
 
 12-5 
 
 I 2-6 
 
 13-0 
 3-6 
 0-6 
 
 20-7 
 10-4 
 0-6 
 
 29-2 
 6-0 
 
 ... 
 
 ... 
 
 0-5 
 
 1-8 
 
 Oxide of Iron 
 Oxide of Manganese 
 
 0-3 
 0-9 
 
 0-5 
 
 i 
 
 1-6 
 
 3-8 
 
 5-8 
 
 6 V 4 
 1-0 
 
 ... 
 
 ... 
 
 Oxide of Lead 
 
 
 
 
 
 
 
 28-2 
 
 33-3 
 
 43-5 
 
 
 
 
 
 
 
 
 
 
 
 
 98-1 
 
 99-3 
 
 100-0 
 
 99-0 
 
 99-1 
 
 100-0 
 
 97'8 
 
 99-0 
 
 100-0 
 
 Although in some of these analyses a slight loss occurred, yet they 
 are sufficiently accurate for all purposes. No 1 is the hard Bohemian 
 glass so valuable to the chemist, from the high temperature it bears 
 without softening. No. 2, also a Bohemian glass, is much more fusi- 
 ble, and is that in ordinary use. No. 3 is English plate, and No. 
 4, German plate glass. Nos. 5 and 6 are both Trench. Nos. 7 and 
 
 8 are English glass for the table use and chemical apparatus ; and No. 
 
 9 is the glass so celebrated for optical purposes, made by Guinaud. 
 
 It is difficult to trace any definite relation between the acid and bases 
 in these glasses; indeed we cannot look upon the different silicates as 
 being really combined with each other : they are rather in a state of 
 intimate mechanical mixture. Hence, if the glass be kept soft, but 
 not liquid, for a considerable time, the silicates gradually separate ; the 
 less fusible crystallizing, and rendering the glass opaque white. This 
 takes place most easily with such glass as contains much silicate of lime 
 or alumina. In tins form, the mass is so hard, as to strike fire with 
 steel, and becomes almost infusible. From the name of its discoverer, 
 it is termed Reaumur's porcelain. 
 
 The arrangement of the furnaces for the manufacture of glass varies 
 
620 Manufacture of Glass. 
 
 according the materials and the kind of product. The materials, re- 
 duced to the state of very fine powder, are intimately mixed, and fused 
 in crucibles of very refractory clay. The silica decomposes the carbo- 
 nates of lime and potash or soda, and expelling the carbonic acid, com- 
 bines with the alkali and earth. If sulphate of soda had been used, a 
 certain quantity of carbon is added, by which the sulphuric acid is de- 
 composed, sulphurous and carbonic acids being evolved (p. 391) ; 
 otherwise the silica could not completely expel the sulphuric acid. 
 From the presence of minute quantities of protoxide of iron in the 
 materials, the glass has, at first, a pale-greenish tint, which is coun- 
 teracted by the addition of a little nitre or arsenious acid, these agents 
 giving oxygen to the iron, which does not colour when peroxidized ; 
 with the latter body the metallic arsenic is evolved in vapour, the bad 
 effects of which should prevent its employment. More generally per- 
 oxide of manganese is used, which, acting on protoxide of iron, pro- 
 duces peroxide of iron and protoxide of manganese, neither of which 
 bodies give any sensible tint to glass. If there be too much manga- 
 nese employed, the glass acquires a violet tint. There is reason to 
 suspect that soda glass is greenish even when absolutely free from 
 iron. 
 
 The general arrangement of a glass furnace may be illustrated by 
 reference to the figures, which represent the essential parts of one of 
 the most perfect forms employed in the manufacture of the fine crown 
 glass of Germany. In the oval furnace A, which is covered by a dome, 
 
 the crucibles are arranged in two rows, of which one is represented in 
 the sectional figure. These crucibles are left open, but if employed for 
 a glass containing lead, they should be covered with a hood presenting 
 only an aperture external to the furnace, for the workman ; as the glass 
 would require to be thus protected from the smoke and combustible 
 
Manufacture of Glass. 621 
 
 gases of the furnace which would reduce the lead to the metallic state. 
 Between the banks is a rectangular space for the fire, resting on the 
 gratings Ib, which are separated by the partition wall F, and have aper- 
 
 tures at the sides for the introduction of the fuel. By means of the 
 passage D, there is access beneath the grate for the purpose of clearing 
 it, and the draught is regulated by the opening or closing of the doors 
 ee. The flame of the fuel, which should be either wood or a very bitu- 
 minous coal, issues partly through the apertures in front of the cruci- 
 bles 00) and partly passes by g, into the wings and chimney ; by means 
 of the wings, a great quantity of the heat is economized for prepara- 
 tory operations. Next the furnace are placed the fresh crucibles ee, 
 which being always made in the glass-house, are there dried, baked, 
 and ultimately brought to a full red heat, so as to be fit for introduction 
 into the furnace with a charge of glass. The draught passing in the 
 direction of the arrows, over the low partition, the flame and hot air 
 acts on the space k, on the floor of which are spread the materials for 
 the next charge of glass, well mixed, and introduced by the apertures 
 II; these being brought to a dull red heat, undergo a commencement 
 of vitrefaction, and are thus fritted or prepared for the perfect com- 
 bination by fusion in the crucibles. This operation of fritting was for- 
 merly performed in a separate reverberatory furnace. The draught 
 escapes partly from the small chimney x, but a portion of the hot air 
 having passed over the partition m, is conducted into the chamber w, 
 which is filled with wood supported on the grating ; the hot air, in 
 passing off, carries away the moisture of the wood, which is thus brought 
 to a state of perfect desiccation, so as to give the greatest possible effect 
 in the furnace. 
 
 For the perfect combination of the materials and obtaining a mass 
 free from streaks and air bubbles, it is essential that the glass should 
 be brought into a state of perfect liquidity, so as to allow the gases to 
 
622 Useful Properties of Glass. 
 
 pass off freely ; and then be let to cool until it acquires the pasty con- 
 sistence which fits it for being worked into the necessary forms. In 
 thus cooling down, however, those glasses which contain oxide of lead 
 frequently separate into two or more layers of glass of different densi- 
 ties, which, when stirred up by the tools of the workman, give by their 
 imperfect mixture a clouded and streaked appearance to the articles 
 made from such glass. This imperfection is peculiarly fatal to glass for 
 optical purposes, as each layer may have a different refractive power, 
 and thus give distorted images. 
 
 The great use of glass in the arts and in ordinary life, depends upon 
 its plasticity at a red heat, which renders it capable of being moulded 
 into every form ; its insolubility in water ; its resisting the action of 
 acids and the generality of chemical re-agents under all ordinary circum- 
 stances ; its transparency and lustre, and the relations to heat, to light, 
 and to electricity, which have been already fully noticed. From the 
 low conducting power of glass for heat, thick portions of it are liable 
 to break when suddenly warmed, the part to which the heat is directly 
 applied expanding and thereby separating from that which remains 
 cold. When a lump of glass is suddenly cooled, as by being laid 
 while soft on a plate of cold iron, or being dropped into water, the 
 internal portions being prevented from contracting, remain in a state 
 of instable arrangement, on which depends its doubly refracting and 
 polarizing properties, (p. 318.) When the molecules of such a piece 
 of chilled glass are made to vibrate, by being scratched, or a little 
 fragment being broken off, they change totally their disposition, and 
 flying asunder, the mass crumbles into powder with an explosion. 
 Prince Rupert's drops, with which this property of glass may be 
 exemplified, are prepared by taking up on an irod rod a little melted 
 glass, and allowing the drops of it to fall into a vessel of cold water ; 
 when one is held in the hand, and the long projecting tail broken off, 
 a smart blow is felt with a dull noise, and the drop is found to be 
 reduced to fine powder. As this excessive frangibility would render 
 glass unfit for most household and chemical purposes, it is necessary 
 to lessen it as much as possible, which is done by allowing it to cool 
 very slowly. Tor this purpose, the vessels when formed are placed in 
 the annealing furnace, or leer, which is a long gallery containing a 
 number of iron trays moveable along it by means of an endless chain ; 
 the hot glass articles are placed in the trays at one end, where a strong- 
 fire is made, the flame of which sweeps to a certain distance into the 
 gallery. According as new trays come up, those already full are drawn 
 down into the cooler part of the gallery by the chain, and finally issue 
 at the other end quite cold. The passage down occupying from 
 
Annealing of Glass Stained Glass. 02-3 
 
 twenty-four to forty-eight hours, the particles of the glass, in cooling, 
 have time to assume their most stable arrangement, and may then be 
 exposed, if not very thick, to changes of temperature, provided they be 
 not very sudden. 
 
 The specific gravity of glass varies with its composition from 2 '4 to 
 3'6, the latter being that of flint glass containing 40 per cent, of oxide 
 of lead. The lighter glasses are generally those which are hardest, and 
 resist the action of water and of re-agents the best. The oxide of lead 
 H in flint glass is acted on by a variety of chemical substances, which 
 unfits it for many laboratory uses. Where alkali predominates, the 
 glass is rapidly acted on by the air, attracting moisture, and thus fre- 
 quently embarrassing electrical experiments. Bottle glass which contains 
 too much lime, is so rapidly corroded by the cream of tartar in wine, as 
 sometimes to become opaque, and spoil the wine in the course of a few 
 days. 
 
 I have had frequent occasion to notice the various coloured glasses 
 produced by the addition of metallic oxides ; (see p. 40) ; on this 
 principle is founded the art of painting on, or staining glass, and also 
 the manufacture of artificial gems. These arts I will have to notice 
 farther on, and any detail of their methods would be foreign to a work 
 like the present. 
 
 The manufacture of porcelain and earthenware depends on two prin- 
 ciples, first, that of the plasticity and infusibility of clay, and secondly, 
 the fusibility of a glass by which the substance of the porous clay may 
 be imbibed, and thus rendered water tight. Clay, when perfectly pure, 
 appears to be silicate of alumina, 2 A1 2 O 3 4. 3 SiO 3 ; but as the great de- 
 posits of clay used for the purposes of the arts are produced by the 
 weathering (decomposition) of a variety of rocks, a number of foreign 
 ingredients are intermixed in small quantity, and produce varieties 
 which influence very much the proportions used in the manufacture. 
 The purest porcelain clay is formed by the decomposition of the feld- 
 spar contained in granitic and syanitic rocks. The feldspar has the 
 formula KO.SiO 3 + (A1 2 O 3 + 3 SiO 3 ) : by the action of water the 
 silicate of potash is dissolved out as soluble glass (p. 618), and the sili- 
 cate of alumina remains as a fine powder, perfectly white, impalpable, 
 forming with water a paste capable of being moulded into any form, 
 and when heated abandoning the water, and contracting in volume, but 
 retaining the form which had been given to it. The pure porcelain 
 clay is seldom found, and hence is used only for the finest objects ; 
 other clays of greater or less purity are therefore used either alone or 
 mixed with porcelain clay, for such objects as stone-china and delft ; 
 and clays in which a quantity of alumina is replaced by iron, and which, 
 
624 
 
 Manufacture of Earthenware. 
 
 consequently, when burned, assume a red or yellow colour, are employed 
 for common earthenware. In the clays which contain very little iron, 
 and hence bum white, there are present almost universally certain quan- 
 tities of alkali remaining from the decomposed feldspar, this is gene- 
 rally potash, but may be soda when the clay is formed from albite, 
 (NaO.Si0 3 + 3A1 2 3 + 3SiO 3 ), and when the source of the clay is not 
 a pure granitic rock, the associated minerals generally yield a certain 
 quantity of lime which mixes with it. Hence, the composition of the 
 following clays from various countries used in the manufacture of por- 
 celain, can easily be accounted for : 
 
 Clay from 
 
 Mori. 
 
 Schneeberg. 
 
 Limoges. 
 
 Cornwall. 
 
 Silica 
 Alumina 
 L/ime 
 
 71-42 
 26-07 
 0-13 
 
 43-6 
 377 
 
 468 
 37-3 
 
 49-60 
 37-40 
 
 > A 
 
 Potash % 
 Water 
 
 0-45 
 
 12-6 
 
 2-5 
 
 13-0 
 
 > traces 
 11-20 
 
 Oxide of Iron 
 
 1-93 
 
 1-5 
 
 
 
 
 
 
 
 
 If clay alone were used in the fabrication of earthenware, although 
 from its plasticity it should assume perfectly the required form, yet 
 from its infusibility it would, when baked, have so little coherence, and, 
 from its contraction, be so liable to crack, that in practice it could not 
 be beneficially employed. The paste of which the china and delft 
 articles are made consists therefore of clay, to which is added, silica, 
 lime, and potash, in other words, the constituents of crown glass, 
 which, being fusible at a high temperature, cement together the parti- 
 cles of clay, and enable the different portions of the vessel to hold 
 together during the bakings. Thus, to form the body of ironstone 
 chinaware, forty parts of Devonshire clay are mixed with from forty to 
 sixty of feldspar, and generally about five parts of flint glass, and ten 
 of quartz. 
 
 It would not be within the object of the present work to detail the 
 mechanical process of fashioning articles of earthenware. When 
 formed, they are first dried in the air, and then heated moderately, to 
 expel as much water as will fit them for the reception of the glaze. 
 This consists in covering them perfectly with a sheet of easily-fusible 
 glass, which, by entering into all their pores, and varnishing their sur- 
 face, renders the vessels impervious to water ; the glassy constituents 
 of the paste having, in quantity and fusibility, only sufficient power to 
 cement the particles of the clay together, without depriving the mass in- 
 ternally of its porosity. The composition of the glaze may vary much in 
 
Baking of Earthemcare. 
 
 625 
 
 different establishments ; an ordinary one, for ironstone china, consists 
 of feldspar 36, quartz 20, white lead 40, flint-glass 8. These materials 
 are fritted together, and then being reduced to impalpable powder, are 
 diffused through water, into which the vessel to be glazed is dipped and 
 is then taken out again. The clayey substance of the vessel rapidly 
 imbibes the water, and the fine powder of the glaze remains uniformly 
 spread upon the surface. The articles so prepared are arranged in 
 capsules of a very refractory ware, and placed in the kiln or furnace to 
 be baked. The construction of the porcelain kiln is represented in the 
 figure. It is a vaulted building, generally of three stories, provided 
 with five fireplaces, from which the flames pass into the kiln by the 
 
 passages, b, m, a, p, marked with the arrows ; from the third story the 
 chimney issues. The highest floor is reserved for drying the capsules 
 in which the articles to be baked are arranged ; on the floor of the 
 second, the articles are dried to the degree which fits them for the 
 reception of the glaze ; and, in the lowest chamber, by the full action 
 of the fire, the final baking is performed. The operation commences 
 first with a moderate fire, the fuel being introduced into the cavity h, 
 and supplied with air by the apertures e, s ; the heat being allowed to 
 rise gradually for six or eight hours, the space Ji becomes full of ignited 
 fuel, and a strong draught is established. The apertures are then 
 closed, fuel (and for this, as for glass making, wood answers best) is 
 heaped on the rest b, and the air admitted to the kiln only after having 
 passed through h. The temperature is thus kept uniformly intense 
 40 
 
626 Glazing of Earthenware. 
 
 for seventeen or eighteen hours, and then, the kiln being allowed to 
 cool slowly for three or four days, the articles are extracted in their 
 finished state. 
 
 The glaze on earthenware being a transparent glass, it may be 
 coloured by various metallic oxides, and thus the patterns produced, 
 which give to the finer kinds of ware so much popularity. The 
 coloured glass being reduced to fine powder, is mixed up with oil of 
 spike, and either laid on with a brush, as in ordinary painting, or 
 printed, in a very ingenious manner, by having the pattern engraved 
 on copper, and printing it with the glaze made with oil into a very 
 thin ink on damp tissue paper. The paper with the figure thus formed 
 is laid evenly on the vessel, which, from its porosity, immediately 
 absorbs the liquid materials of the ink, and leaves the powder of the 
 glaze on the surface in all the fine tracings of the design. The paper 
 is then cautiously rubbed off by the finger, in a vessel of cold water, 
 and the uniform glazing applied over all, as before described. The 
 blue patterns are produced by cobalt ; the black by a mixture of oxides 
 of iron and manganese ; the crimson by gold ; and gold and platiiia 
 are applied also, in their metallic state, by dissolving their chlorides in 
 oil of turpentine, and applying this varnish with a pencil, then burning, 
 and burnishing the metallic surface. 
 
 A coarse kind of glazing, given to the common articles of earthen- 
 ware, is produced by throwing into the kiln, when intensely hot, a few 
 handfuls of common salt ; by means of the watery vapour produced by 
 the combustion of the fuel, the silicic acid on the surface of the earthen- 
 ware decomposes the common salt, which is converted into vapour by 
 the heat; Si.O 2 with Na.Cl and HO, producing NaO.Si0 2 , which 
 forms a transparent glassy varnish on their surface, whilst HC1 
 passes off with the excess of watery vapour, forming copious white 
 fumes. 
 
 The general characters of the salts of gludnum, thorium, yttrium, 
 zirconium, lanthanum, and cerium have been noticed under the heads 
 of these respective metals (p. 573 et seq.) and do not require further 
 detail. 
 
 SALTS OF MANGANESE. 
 
 Manganese may give origin to four classes of salts, in two of which 
 it constitutes the base, and in the others forms an element of the acid ; 
 these last, the manganates and permanganates, have been sufficiently 
 noticed in pp. 500, and it remains only to describe the former. 
 
 Protochloride of Manganese. MnCl + 4Aq. Eq. 7 88 '5 + 450, or 
 63*19 -f- 36. This salt may be obtained by digesting the commercial 
 
Salts of Manganese. 
 
 black oxide in muriatic acid, until all the excess of chlorine has been 
 expelled, then evaporating to dryness, and fusing the mass, at a bright 
 red heat, in a crucible. The chloride of iron, which is formed by the 
 impurities of the ore, is decomposed by the last portions of water, and 
 muriatic acid being given off, oxide of iron remains. Hence, on digest- 
 ing the melted mass in water, protochloride of manganese dissolves, 
 and all the iron remains insoluble. The solution, which is of a pale 
 pinkish tint, is to be evaporated, and the salt crystallized. The crystals 
 are rhombic tables, rose coloured ; by heat they lose their water of 
 crystallization, but are not otherwise altered. It is known to be free 
 from iron when its solution gives, with yellow prussiate of potash, a 
 pure white precipitate. 
 
 Perchloride of Manganese. MnCl 2 . appears to be formed when 
 strong muriatic acid is digested on peroxide of manganese without heat. 
 A gentle heat resolves it into protochloride and free chlorine. 
 
 Protosulphate of Manganese. MnO.SO 3 + 7Aq. This salt may be 
 obtained pure from the commercial oxide by mixing this into a thick 
 cream, with oil of vitriol, and heating it in a shallow dish, until it 
 becomes quite dry ; oxygen being given off. The dry mass which con- 
 tains the mixed sulphates of iron and manganese is to be then placed 
 in a crucible, and heated to bright redness ; the sulphate of iron is 
 decomposed, its sulphuric acid being expelled by the heat ; but the 
 sulphate of manganese is not altered, and on digesting the resulting 
 mass in water, it dissolves, and is obtained crystallized, by evaporation 
 and cooling. This salt crystallizes in oblique rhombic prisms, with 
 7 aq., but is also found with 5 aq., and with 4 aq., its form changing 
 in each case. In all, one equivalent of water is constitutional, and 
 may be replaced by an alkaline sulphate, with which the sulphate of 
 manganese forms double salts, like those of sulphate of magnesia. 
 
 Sesquisulphate of Manganese, Mn 2 O 3 + 3S0 3 . may be obtained by 
 dissolving the sesquioxide in sulphuric acid. The solution is of a rich 
 crimson colour : when heated, it becomes colourless, giving off oxygen, 
 and it is instantly bleached by sulphurous acid, or any deoxidizing 
 agent. Its most important property is that of forming with the 
 sulphate of potash, or of ammonia, double salts crystallizing in octo- 
 hedrons, which are manganese alums, similar in constitution to the 
 ordinary alum, but with A1 2 3 , replaced by Mn 2 O 3 . 
 
 No other salt of manganese requires special notice. 
 
 SALTS OF IRON. 
 
 There are two series of iron salts corresponding to the two oxides, 
 proto-salts and sesyui-salts. 
 
628 Salts of Iron. 
 
 Protochloride of Iron. EeCl -\- 4HO. This salt is formed when 
 metallic iron is dissolved in muriatic acid, hydrogen being evolved ; 
 the solution, which is of a pale bluish-green colour, yields, on evapora- 
 tion, rhombic crystals of the hydrated chloride, which are slightly 
 deliquescent. This solution absorbs oxygen from the air with great 
 avidity, and becomes dark-green coloured. When these crystals are 
 heated they lose water, and, if the air have not access, a white mass of 
 dry protochloride of iron is obtained, but otherwise perchloride is 
 formed and the whole decomposed. The anhydrous protochloride is 
 very elegantly prepared by passing a stream of dry chloride of hy- 
 drogen over fine iron wire, coiled up in a tube of hard Bohemian glass, 
 and heated to bright redness : hydrogen gas is evolved, and proto- 
 chloride of iron formed, which sublimes into the cold part of the tube 
 as brilliant white spangles. By the action of the air it is rapidly 
 decomposed. 
 
 Sesquichloride of Iron. Fe 2 Cl 3 . This salt is formed when iron is 
 dissolved in aqua regia; a deep brown solution is obtained, which, 
 when evaporated to the consistence of a syrup, gives large red crystals 
 of hydrated chloride, which are very deliquescent. On the application 
 of heat, this salt is totally decomposed ; muriatic acid is given off, and 
 red oxide of iron remains behind, with some unaltered chloride, as a 
 basic salt. To obtain the anhydrous sesquichloride, a stream of dry 
 chlorine gas is to be passed over iron wire heated to redness in a tube 
 of Bohemian glass. The iron burns in the chlorine, and the salt 
 sublimes into the cool portion of the tube, where it forms a dark olive 
 crystalline mass, which rapidly attracts moisture from, the air. This 
 salt is very soluble in alcohol. 
 
 The sesquichloride of iron, when dissolved along with sal-ammoniac, 
 may form a true double salt, containing an equivalent of each salt ; 
 but the crystals which are generally thus obtained, although deeply- 
 coloured red, contain but two or three per cent, of the chloride of iron. 
 
 Proto-iodide of Iron. Pe.I. Is formed by digesting iodine in 
 water, on an excess of iron filings. Considerable heat is evolved, and 
 there is at first formed a reddish-brown solution of periodide, which, 
 however, gradually takes up more iron, forming protoiodide, and a 
 colourless solution is obtained, which when evaporated yields a crystal- 
 line mass, containing water of crystallization, and which is decomposed 
 by a further action of the heat, iodine being evolved. It absorbs 
 oxygen very rapidly. A solution of proto-iodide of iron dissolves 
 iodine abundantly, becoming brown, and possibly containing the sesqui- 
 iodide Fe 2 l3, but it is more likely that the iodine is not combined, as it 
 is sensible to the test of starch. 
 
Manvf act ure of Copperas. 629 
 
 The bromides of Iron resemble perfectly the iodides. 
 Protosulphate of Iron Green Copperas. FeO.SO 3 -f 7 Aq. The 
 manufacture of this salt is conducted on the large scale for the pur- 
 poses of the arts, by exposing to the action of air and moisture, the 
 nodules of bisulphuret of iron, which are found abundantly in the 
 strata of alum-slate-clay (p. 617). Oxygen is rapidly absorbed both 
 by the iron and the sulphur, sulphuric 'acid and oxide of iron being 
 formed, and the liquor which, holding these in solution, drains from 
 the beds of decomposing pyrites, is run into tanks, where it is put in 
 contact with pieces of old iron, which serve to neutralize the excess of 
 acid, produced from the pyrites, being a bisulphuret, and also, by 
 means of the hydrogen evolved, to retain all the iron in the state of 
 protoxide; after proper evaporation, the salt is obtained crystallized 
 from these solutions. On the small scale, it may be prepared by dis- 
 solving iron wire in dilute sulphuric acid, as in the process for preparing 
 hydrogen gas, (p. 341). The protosulphate of iron generally crystal- 
 lizes with seven atoms of water, of which one is constitutional, and 
 may be replaced by an alcaline sulphate, forming double salts. The 
 form of its crystal is a short oblique rhombic prism, i, u, u, with nu- 
 merous secondary faces, as /3, c, in the fig. Its taste is styptic and 
 metallic; it dissolves in 1'64 parts of water at 50, and 
 in 0'30 parts at 212. Like the other protosalts of iron, 
 it is but very sparingly soluble in alcohol. When heated, 
 it abandons first its water, and at full red heat its sulphuric 
 acid, of which a portion is decomposed into sulphurous 
 acid and oxygen, by which the iron becomes peroxidized. 
 The peroxide of iron thus formed is much used in the arts under the 
 names of rouge and colcothar, as a polishing material. On these pro- 
 perties is founded the manufacture of fuming oil of vitriol, described 
 in p. 397. The protosulphate of iron absorbs oxygen rapidly, even 
 when dry, and becomes covered with a reddish crust of basic persul- 
 phate, whence its commercial name. In solution, the absorption of 
 oxygen proceeds quickly, until f of the iron is peroxidized and a 
 reddish solution obtained, from which alcalies throw down the black 
 magnetic oxide, (see p. 509). This solution does not crystallize. 
 
 Sesquisulpkate of mm. Fe 2 O 3 + 3S0 3 . Eq. 2481'9 or 188'9. 
 This salt is found native in large quantities in Chili, combined with 
 9Aq. It may be prepared artificially, by pouring oil of vitriol on red 
 oxide of iron, stirring the mass well and applying a moderate heat to 
 expel the excess of acid. The salt may then be dissolved in water, 
 forming a red solution, and giving, when evaporated, a deliquescent 
 mass scarcely crystallized. In this way it retains an excess of acid, 
 
630 Salts of Iron. 
 
 which may be driven off by a heat just below redness. The persulphate 
 then appears as a white powder, which dissolves but very slowly in 
 water. By a strong heat, this salt is totally decomposed. The proto- 
 sulphate may be converted into persulphate, by adding to a boiling 
 solution, nitric acid in small quantities, as long as any nitric oxide gas 
 is given off. There are several basic persulphates of iron, of which 
 the most important is the rust-coloured powder, which precipitates 
 from a solution of protosulphate of iron when oxidized by exposure to 
 the air; its formula is 2Ee 2 3 -f S0 3 + 3Aq. 
 
 The persulphate of iron combines with the alcaline sulphates to form 
 a class of alums, which contain Fe 2 O 3 in place of A1 2 O 3 . These iron 
 alums are generally pale red in colour, but have the form, solubility, 
 and nearly the taste of common alum. 
 
 Protonitrate of iron may be formed by dissolving sulphuret of iron 
 in cold dilute nitric acicd ; it crystallizes in pale green rhombs, which, 
 when heated, evolve nitric oxide gas, and form a basic nitrate of the 
 peroxide. Metallic iron dissolves in dilute nitric acid, without the 
 evolution of any gas ; water and nitric acid being simultaneously de- 
 composed, and oxide of iron and ammonia produced. Thus, N0 5 with 
 3HO and 8Ee, give 8'FeO and NH 3 . 
 
 Pernitrate of Iron is produced when iron is dissolved in hot nitric 
 acid ; the solution is reddish brown, and gives, by drying, a deliques- 
 cent mass easily decomposed by heat. When a solution of this salt is 
 decomposed by carbonate of potash added in excess, the oxide of iron, 
 which first precipitates, is redissolved, and a deep red liquor obtained, 
 which is sometimes used in medicine under the name of StaMs alkaline 
 tincture of iron. 
 
 Protophosphate of IronTribasic. HO.SEeO + PO 5 . May be 
 formed by decomposing a solution of protosulphate of iron with 
 tribasic phosphate of soda. It is a white powder, which rapidly be- 
 comes blue by exposure to the air, a portion of the iron becoming 
 peroxidized. This blue phosphate of iron is a double salt, which 
 exists in nature, forming the bog iron ore, arid may be produced 
 artificially by adding solution of phosphate of soda to the solution of 
 mixed sulphate of iron, from which alkalies precipitate the black oxide, 
 (page 509). The precipitate which forms is of a rich blue colour, and 
 is not changed by exposure to the air. Its formula is (HO.2FeO -f- 
 P0 5 ) -f 2(Fe 2 3 .ro 5 ). It is used in medicine. 
 
 Sesquiphospkate of iron. 2.Fe 2 O 3 + POs. Is obtained by decom- 
 posing solution of sesquisulphate of iron by phosphate of soda. It is 
 a white powder, insoluble in water. It is used in medicine. 
 
 The salts of the protoxide of iron are remarkable for absorbing nitric 
 
Salts of Nickel and Cobalt. 631 
 
 oxide in considerable quantity, and forming therewith a deep olive- 
 coloured liquor, which rapidly attracts oxygen from the air. The 
 quantity of gas absorbed is one atom for two atoms of salt, and the 
 nitric oxide may be considered as replacing the third atom of oxygen, 
 which forms the sesquioxide. Thus, the protochloride give Fe. 2 -f da- 
 NO 2 , and the protosulphate (Ee 2 4- O 2 .M) 2 ) 2S0 3 , analogous to Fe 2 + 
 C1 3 and (Pe 2 -f- O 3 ) -f- 2SO 3 . The utility of this olive liquor, as a 
 test for nitric acid and in eudiometry, has been noticed in pp. 385 
 and 362. 
 
 SALTS OF NICKEL AND COBALT. 
 
 Chloride of Nickel. N1.C1. May be obtained by dissolving ox- 
 ide of nickel in dilute muriatic acid, or by acting on the metal with 
 the hot concentrated acid. It crystallizes in emerald green rhombs. 
 When heated, it loses its water of crystallization, and gives a yellow 
 powder, which by a red heat sublimes in crystals, resembling Mosaic gold. 
 
 Sulphate of Nickel. NiO.SO 3 . This salt is obtained by dissolving 
 the oxide in dilute sulphuric acid, or by acting on the metal with a 
 mixture of nitric and sulphuric acids diluted with water ; the nitric 
 acid then supplies oxygen. This solution gives fine emerald green 
 crystals, which vary in form according to the quantity of water they 
 contain. When they form below 60, they are long rhombic prisms, 
 containing 7 Aq. and isomorphous with the sulphates of zinc and mag- 
 nesia ; but when formed at any temperature above 60, the quantity of 
 water is six atoms, and the form is an octohedron with a square base. 
 If a prismatic crystal be exposed to a moderate heat, or to sunshine, 
 it gives off an atom of water and becomes opaque, by breaking up into 
 a number of very minute crystals of the octohedral form. In sulphate 
 of nickel, one atom of water being constitutional may be replaced by 
 the alkaline sulphates, and double salts formed, of which some are very 
 beautiful. 
 
 Chloride of Cobalt. Co.Cl. Is formed by dissolving oxide of co- 
 balt, or the zaffre of commerce in muriatic acid. The solution is 
 pinkish, and gives, on evaporation, rose-red crystals of hydrated 
 chloride ; if the evaporation be pushed very far, the liquor becomes 
 blue, and dark-blue crystals of anhydrous chloride are deposited. If 
 the solution contains nickel, which is always the case when prepared 
 from zaffre, the colour becomes green, and it is thus that sympathetic 
 inks of cobalt are produced, and summer and winter scenes in land- 
 scapes alternated ; the surface of a drawing washed with a very dilute 
 solution of chloride of cobalt being white until dried before the fire, 
 but then becoming grass-green. 
 
632 Salts of Zinc. 
 
 Sulphate of Cobalt. Co.O + S0 3 is obtained by treating zaffre 
 with sulphuric acid. In its general characters, it resembles the 
 chloride ; when heated strongly, it gives off sulphuric acid and oxide 
 of cobalt remains ; it contains six atoms of water of crystallization, 
 and gives a double salt with sulphate of potash. 
 
 Phosphate of Cobalt. H0.2CoO + P0 5 . Is precipitated in dark 
 violet flocks when solution of sulphate of cobalt and phosphate of soda 
 are mixed together. This substance is the basis of a very beautiful 
 pigment, Thenard's Hue, which is prepared by mixing intimately, one 
 part of phosphate of cobalt with two or three of alumina, and exposing 
 the mixture to an intense white heat in a wind furnace. The blue 
 tint thus given to alumina, serves as a test for that earth, particularly 
 to distinguish it from magnesia by the blowpipe. (See pp. 488 and 491). 
 
 Silicate of Cobalt constitutes the blue smalts employed to tinge paper 
 and to colour glass ; the finest kind is known in commerce as azure. 
 Its manufacture is conducted on the great scale in Saxony and Sweden, 
 and is the process in which most of the arsenic of commerce is obtained; 
 that being expelled in the roasting of the cobalt ores, (pp. 468, 512), 
 Prom the zaffre, a sulphate of cobalt is prepared, and on the other hand, 
 a silicate of potash, by melting together fine sand and carbonate of 
 potash; these solutions being mixed, silicate of cobalt is precipitated, 
 whilst sulphate of potash remains dissolved. This precipitate is the 
 material for colouring porcelain and glass, but the ordinary smalts are 
 formed by melting impure carbonate of cobalt with potash and quartz 
 into a blue glass, which is then reduced to impalpable powder, and 
 sorted according to the quality, for commerce. 
 
 SALTS OF ZINC AND CADMIUM. 
 
 Chloride ofZmc.7x\. Eq. S50'3 or 68. May be prepared by 
 burning metallic zinc in chlorine, or by dissolving the metal in muriatic 
 acid. The solution is colourless ; when evaporated, it yields rhombic 
 crystals, which contain water and deliquesce with extreme rapidity. The 
 dry salt is white, and melts a little above 212, so that a solution, when 
 evaporated, never becomes solid. It is hence sometimes applied as a 
 bath, in place of oil or fusible metal, in taking the specific gravity of 
 vapours (p. 14). Erom its fusibility and softness, it had formerly the 
 name of butter of zinc. Prom its affinity for water, it acts powerfully 
 as a caustic on the living tissues, and is employed in medicine as such. 
 
 Chloride of zinc combines with oxide of zinc in many proportions 
 forming oxychlorides, of which there are three worthy of notice : the 
 first, which is long known, is formed by decomposing chloride of zinc 
 by a small quantity of ammonia ; its formula is, ZnCl + 3ZnO + 4Aq. 
 
Salts of Cadmium. 633 
 
 The second results from the action of water on the aminoniacal chloride 
 of zinc, its formula is ZnCl -f- 6ZnO -f lOAq. and is that whose 
 analogies to the liquid muriatic acid have been pointed out in p. 431. 
 The third is formed by acting on chloride of zinc with an excess of 
 potash, its formula is ZnCl + 9ZnO + 14Aq. 
 
 The bromide and iodide of zinc resemble completely the chloride in 
 general characters ; a solution of iodide of zinc is capable of dissolving 
 a large quantity of iodine. 
 
 Sulphate of zinc. ZnO.S0 3 -f 7Aq. may be produced by dissolving 
 the metal in dilute sulphuric acid. For the purposes of the arts, it is 
 made upon the great scale by roasting, in a current of hot air in a 
 reverberatory furnace, the native sulphuret of zinc, blende. The metal 
 and sulphur both combining with oxygen, a neutral sulphate of the 
 oxide is formed, which being then dissolved out by water, the solution 
 is evaporated to a pellicle and allowed to crystallize. Sometimes the 
 blende, in place of being roasted, is exposed on sloping beds, to the 
 action of the air and moisture, when it gradually attracts oxygen, and 
 is treated as has been described under the head of sulphate of iron. 
 The crystals which first form, are heated until they undergo watery 
 fusion, and are then poured into conical moulds, where they solidify, 
 and the salt is thus sent into commerce in masses like 
 sugar loaves : its commercial name is white vitriol. 
 The crystals of sulphate of zinc are oblique rhombic 
 prisms, as in the figure ; containing 43*9 per cent of 
 water, and are soluble in two-and-a-half times their 
 weight of cold water. It is permanent in the air. 
 It combines with the alkaline sulphates, which re- 
 place its constitutional water forming double salts, 
 and with oxide of zinc to form basic salts, of which several are known, 
 and which agree in constitution with the oxychlorides of zinc. Their 
 composition has been already noticed in p. 583. 
 
 Nitrate of Zinc. ZnO.N0 5 . Obtained by dissolving the metal in 
 dilute nitric acid ; it crystallizes in flat four-sided prisms. It is deli- 
 quescent, and soluble in alcohol. 
 
 No other salt of zinc is of importance. 
 
 Chloride of Cadmium. Cd.Cl. Crystallizes in large four-sided 
 prisms ; it is not deliquescent. The other salts of cadmium resemble 
 completely the corresponding salts of zinc, and do not require notice. 
 
 SALTS OF TIN. 
 
 Protochloride of Tin. SnCl + 3 Aq. Eq. 117S'9 -f 337'5 or 
 94-29 + 37. This salt is obtained anhydrous by heating tin in a 
 
634 Salts of Tin. 
 
 current of muriatic acid gas, hydrogen being evolved ; or by distilling 
 a mixture of equal parts of tin and corrosive sublimate in a glass retort, 
 the metallic mercury first passes over, and finally the protochloride of 
 tin sublimes at a strong red heat. It forms a grey glassy mass. In 
 combination with water, it may be obtained by dissolving tin in strong 
 muriatic acid, until it is saturated, and on evaporation, the salt crys- 
 tallizes in long prisms, which contain three atoms of water. "When 
 these crystals are heated, they first lose water, but afterwards muriatic 
 acid passes off, and a basic salt remains. This crytallized protochloride, 
 under the name of salt of tin, is used extensively in dyeing, as a mor- 
 dant ; in its preparation on a large scale, copper vessels may be em- 
 ployed ; because as long as any metallic tin is present, the copper is 
 electrically protected by it, and is not acted on by the acid. This salt 
 is very soluble in water, but is decomposed by a large quantity, a basic 
 salt SnCl -f SnO being thrown down ; hence, in order to have a dilute 
 solution clear, it requires the addition of a few drops of muriatic acid. 
 Protochloride of tin is remarkable for its affinity for oxygen and for 
 chlorine, it reduces the salts of silver, quicksilver, and gold to the metallic 
 state, and the salts of copper, iron and manganese to the lowest state of 
 oxidation. It acts similarly on many organic substances, as indigo, 
 litmine, orcein; forming colourless compounds, which have some im- 
 portant applications in the art of dyeing. 
 
 The protochloride of tin combines with chloride of potassium and 
 with sal-ammoniac, to form double salts, which crystallize and are fre- 
 quently employed in the process of dyeing. 
 
 Perckloride of Tin. SnCl 2 . Is prepared anhydrous by distilling a 
 mixture of four parts of corrosive sublimate and one of metallic tin ; at 
 a very moderate heat, a colourless liquid distils over, which forms dense 
 white fumes where it comes into contact with the air : this is the bichlo- 
 ride of tin, the fuming liquor of Libavius. Metallic mercury remains 
 in the retort. This singular compound boils at 248 Fah., the specific 
 gravity of its vapour is 9'12. When mixed with ^ its weight of water 
 it solidifies into a crystalline mass, and it is hence that it forms such 
 dense fumes by exposure to damp air. It may be prepared in this 
 crystallized form, by dissolving tin in nitromuriatic acid and evaporating 
 the solution ; or by passing chlorine into a solution of protochloride as 
 long as it is absorbed. If the crystals be heated, they are decomposed, 
 muriatic acid being given off and peroxide of tin remaining. 
 
 Protoiodide of Tin. SnI. May be formed by heating together tin 
 and iodine, or by mixing solutions of iodide of potassium with a slight 
 excess of protochloride of tin. It is a brownish red mass, soluble in 
 water, and crystallizing from the solution in long prisms of a bright 
 
Salts of Chrome and Vanadium. 635 
 
 orange colour. It is decomposed by a large quantity of water. It 
 combines with the iodide of potassium to form a soluble double iodide. 
 The biniodide of tin crystallizes in yellow needles, which are decom- 
 posed by much water. 
 
 The bromides of tin are not important. 
 
 Protosulphate of Tin. SnO.SO 3 . Is formed when tin is dissolved 
 in strong sulphuric acid. A saline mass is obtained, which dissolves 
 in water, giving a brown solution, from which the salt crystallizes in 
 small neeoies. Bancrofts mordant, for dyers, is prepared by digesting 
 two parts of tin with three of strong muriatic acid for an hour, and 
 then adding one and a-half parts of oil of vitriol very cautiously. The 
 mass becomes hot and the tin is rapidly dissolved. The heat is to be 
 kept up on the sand-bath as long as hydrogen is evolved. The solu- 
 tion, on cooling, forms a crystalline mass, which is to be dissolved in 
 water, so that eight parts of the solution shall contain one of tin. 
 
 The sulphuric and nitric acids may be neutralized by freshly pre- 
 cipitated peroxide of tin : but these salts possess very little stability, 
 and are of no technical or scientific interest. The peroxide of tin 
 itself acts as an acid, and its relations to the alkalies have been des- 
 cribed in p. 521. 
 
 The sulphurets of tin act as sulphur acids, combining with the sul- 
 phurets of the alkaline metals. The bisulphuret forms with sulphuret 
 of sodium, a crystallizable salt, 2 Na.S + Sn.S 2 + 12Aq. sulphostan- 
 nate of sodium. 
 
 SALTS OF CHROMIUM AND VANADIUM. 
 
 There are two kinds of salts of chrome, one in which the oxides of 
 chrome act as base, and the other in which the chromic acid is com- 
 bined with bases. 
 
 A. Salts of sesqui-oxide of chrome. 
 
 Sesqui-chloride of Chrome. r. 2 Cl 3 . Eq. 2031'6 or 162'8. When 
 sesqui-oxide of chrome is mixed with lampblack, and treated by a cur- 
 rent of dry chlorine at a red heat, as described for the preparation of 
 the chlorides of silicon and aluminum, the chloride is obtained sublimed 
 in the cold part of the tube in peach blossom coloured scales of exceed- 
 ing beauty, which when pure are nearly insoluble in water, but become 
 easily soluble if there be a small quantity of the protochloride present. 
 It may also be obtained by dissolving oxide of chrome in muriatic 
 acid, and evaporating the solution; it remains as a green mass, in 
 which it is combined with 3HO. When heated to 450, it froths up 
 very much, gives off that water, and forms a rose coloured mass not so 
 beautiful as that obtained by the process first described. 
 
636 Sulphates of Chrome. 
 
 Protochloride of Chrome. When hydrogen gas is passed over the 
 sesqui-chloride of chrome at a dull red heat in a tube of hard glass, 
 muriatic acid gas is given off and the protochloride, CrCl, sublimes as 
 a network of fine acicular crystals. These are easily soluble in water, 
 and possess the property of conferring solubility on the otherwise in- 
 soluble sesqui-chloride. Prom the protochloride is obtained the pro- 
 toxide of chrome recently discovered and described, p. 523. 
 
 Chlorochromic Acid. CrCl 3 + 2Cr0 3 . This singular compound is 
 obtained by melting together in a crucible ten parts of common salt 
 and seventeen of bichromate of potash ; the melted mass is poured out 
 on a slab, and broken into small pieces, with which a tubulated retort 
 may be filled, and after a receiver and condensing apparatus have been 
 attached, forty parts of oil of vitriol are to be poured on the mass. 
 The decomposition occurs so violently, that in a few minutes all the 
 product distils over without the application of external heat. This 
 substance is a thin blood-red liquid, appearing black by reflected light ; 
 it fumes much by exposure to the air ; its vapour is red like nitrous 
 acid. "When its vapour is heated to redness it is decomposed, as de- 
 scribed in p. 524. It is decomposed by water. Alcohol placed in 
 contact with it takes fire, burning with a bright flame ; phosphorus acts 
 in the same way. This substance may either be looked upon as a 
 compound of perchloride of chrome with chromic acid, CrCl 3 + 2Cr 
 O 3 , or as a compound of chlorine with a deutoxide of chrome; 
 Cr0 2 Cl. The analogy of the sulphuric to the chromic acid is sup- 
 posed to favour this latter view, as also the sp. gr. of its vapour, which 
 is 5-9. 
 
 Sulphate of Chrome. Cr 2 3 + 3S0 3 . May be formed by dissolving 
 oxide of chrome in dilute sulphuric acid, but does not crystallize. Its 
 only important character is, that it combines with the sulphates of 
 potash or of ammonia to form double salts, the chrome alums, which 
 crystallize in dark purple octohedrons, and which contain the same pro- 
 portion of acid, alkali and water, as common alum, but oxide of chrome 
 in place of alumina. The solution of chrome alum - in cold water is 
 purple, but when heated becomes green, and the elements of the salt 
 are then found to be no longer chemically united, as by evaporation they 
 may be separated, and the alcaline sulphate crystallized out. It would 
 appear, indeed, that almost every salt of chrome may exist in either a 
 green or a red condition, and that in the former they do not crystallize. 
 The chrome alum is obtained abundantly, by setting aside for a few 
 days the residue of the process for making aldehyd as described farther 
 on. 
 
 The Perfluoride of Chrome, Cr.F 3; is formed by acting with oil of 
 
Manufacture of Chromate of Potash. 637 
 
 vitriol on a mixture of powdered fluor spar and bichromate of potash, 
 in a platinum retort. It is a gas of a rich crimson colour, which can 
 only be collected in a platinum crucible inverted in the quicksilver 
 trough. Its decomposition by water, and the consequent formation of 
 chromic acid has been already noticed, p. 525. 
 
 B. Salts of Chromic Acid. 
 
 Chromates of Potash. The manufacture of the bichromate of potash, 
 KO + 2CrOa is carried on extensively, as it is from that salt that all 
 the compounds of the metal used in chemistry or in the arts are pre- 
 pared. It is made from the only abundant ore of chrome, the chrome- 
 iron, FeO + Cr 2 3 , by the following process : Two parts of the ore, 
 ground to a fine powder are intimately mixed with one part of saltpetre, 
 or four parts of ore are used with two parts of pearl ashes and one of 
 saltpetre, and the mixture exposed for several hours on the floor of a 
 reverberatory furnace to a violent heat. Under the influence of the 
 potash, the oxide of chrome absorbs the oxygen from the air and forms 
 chromic acid. The calcined mass is lixiviated with water and a deep 
 yellow liquor is produced, which contains neutral chromate of potash, 
 which may be obtained, crystallized, by evaporation ; but as this salt is 
 not well suited for the purposes of commerce, it is generally changed 
 into the bichromate by adding to the liquor a quantity of sulphuric 
 acid, which takes one-half of the potash, and the bichromate is then 
 obtained by crystallization in tanks lined with lead. The process for 
 the manufacture of chromate of potash has lately been rendered more 
 economical by the substitution of lime for the potash in the preliminary 
 calcination. A mixture of the chrome-iron ore and lime, or chalk, in 
 very fine powder, being calcined, oxygen is absorbed by the chrome and 
 a chromate of lime formed which is extracted from the mass by water. 
 The solutions are then decomposed by means of any potash salt, and 
 the chromate or bichromate of potash separated from the lime salt pro- 
 duced by crystallization in the usual way. 
 
 Bichromate of Potash crystallizes in large four-sided prisms and 
 square tables of a rich orange-red colour; it melts easily, and, in 
 cooling, crystallizes in another form. It is soluble in ten parts of cold 
 water. It is not decomposed except by a white heat, which expels 
 oxygen, and leaves a mixture of oxide of chrome, and neutral chro- 
 mate of potash. The uses of this salt for the preparation of oxygen 
 gas, and of chromic acid, have been already described. 
 
 The neutral Chromate of Potash, KO.Cr0 3 , may be prepared by 
 adding to a solution of bichromate of potash as much more alkali as it 
 
638 Sails of Osmium, Tungsten, fyc. 
 
 already contained. It is soluble in twice its weight of 
 cold water. Its solution is intense golden yellow ; it crys- 
 tallizes in rhombic prisms, isomorphous with those of sul- 
 phate of potash, as in the figure, of which n f n, and u, u, 
 are primary, and i, m, are secondary planes. 
 If bichromate of potash be dissolved in hot dilute nitric acid, a 
 terckromate of potash, KO. + 3CrO 3 , crystallizes when the solution 
 cools. 
 
 When bichromate of potash is dissolved in rather more than its own 
 weight of strong muriatic acid, with a very gentle heat, so that no 
 chlorine shall be evolved, and that the liquor shall retain its clear 
 orange colour, a salt crystallizes on cooling in fine four-sided prisms, 
 which is very remarkable in constitution, consisting of an equivalent 
 of chloride of potassium united to two of chromic acid, KC1 -f- 2Cr0 3 . 
 
 None other of the chromates of the metals that have been as yet 
 described possess interest. 
 
 Vanadium is the basis of several classes of salts, which, however, 
 from the exceeding rarity of the metal, have been but little studied. 
 The salts containing the vanadic oxide are generally splendid blue ; 
 those containing the vanadic acid as basis, are red or yellow, whilst 
 those which contain vanadic acid as acid, are colourless, or coloured 
 according to the nature of the base with which it may be combined. 
 
 SALTS OF TUNGSTEN, MOLYBDENUM, OSMIUM AND 
 COLUMBIUM. 
 
 Tungsten combines directly with chlorine in two proportions, forming 
 the bichloride and perchloride, according as the metal or the gas is in 
 excess. Both are volatile and condense in red needles. They are de- 
 composed by water, giving muriatic acid, and tungstic oxide, W0 2 , or 
 tungstic acid, W0 3 . A chlorotungstic acid exists, WO 2 C1, analogous 
 to the chlorochromic acid. 
 
 None of the compounds of tungsten with oxygen act as bases. The 
 nature of the salts of tungstic acid has been sufficiently explained al- 
 ready in p. 527. 
 
 Molybdenum takes fire when heated in a stream of chlorine gas, and 
 forms the terchloride, Mo.Cl 3 , which crystallizes in the cold part of the 
 tube in brilliant black scales, like iodine : its vapour is dark red. Two 
 other chlorides of this metal, Mod and MoCl 2 , are known to exist. 
 
 The protoxide of molybdenum forms salts with the oxygen acids, 
 which are purple or black coloured, and are very easily decomposed by 
 
Salts of Arsenic. 639 
 
 heat. Thus, the sulphate is resolved into sulphurous acid gas and 
 molybdic oxide. The molybdic oxide also forms a series of salts, ge- 
 nerally red coloured, which do not possess any special interest. The 
 molybdic acid forms two series of salts, in one of which it acts as base 
 and in the other as an acid. 
 
 Osmium is the basis of several classes of salts which are as yet very 
 little known. When metallic osmium is heated in a stream of dry 
 chlorine, in a long glass tube, a volatile mixture of protochloride and 
 perchloride of osmium is produced. The former, which is the less 
 volatile, condenses near the heat in long needles of a fine green colour ; 
 whilst the latter, being carried much further by the current of gas, is 
 deposited as a red powder destitute of any crystalline texture. Both 
 these salts combine with the alkaline chlorides forming double salts. 
 All three oxides of osmium combine with the oxygen acids to form 
 salts which do not crystallize, and have been very little studied. 
 
 Columlium forms a volatile chloride. Its oxide, TaO 2 , does not 
 combine with acids, and the columbic acid forms salts which are not 
 of practical importance. 
 
 SALTS OF ARSENIC. 
 
 Chloride of Arsenic. As C1 3 . Eq. 2271'9 or 181-54. Is formed 
 when the metal burns spontaneously in chlorine; it is a volatile liquid 
 which forms dense white fumes on exposure to the air. It may be ob- 
 tained also by mixing intimately one part of arsenious acid and three 
 of common salt ; putting them into a retort to which a condenser is 
 attached, and adding four parts of oil of vitriol. By a moderate heat 
 the chloride of arsenic distils over as a dense liquid. By much water it 
 is resolved into arsenious and muriatic acids. The sp. gr. of its vapour 
 is 6295. 
 
 Iodide of Arsenic. As.I 3 . Is best prepared by digesting one part 
 of arsenic with five of iodine and fifty of water, until the iodine dis- 
 appears ; on cooling, the iodide separates in orange-red crystals. It is 
 decomposed by water into hydriodic and arsenious acids. The bromide 
 of arsenic may be similarly formed. 
 
 Arsenic does not form any compound with chlorine, bromine, or 
 iodine analogous to arsenic acid. 
 
 Neither compound of arsenic with oxygen is capable of acting as a 
 base, and hence the only classes of salts of arsenious or arsenic acids 
 are those in which they constitute the electro-negative element. 
 
 Arsenious Acid is dissolved in large quantities by the caustic and 
 
640 Salts of Arsenic Acid. 
 
 carbonated alkalies, but the salts thus formed cannot be obtained crys- 
 tallized, and appear to be very indefinite in constitution. The combi- 
 nations of arsenious acid with the earths are white powders, of which 
 the only one of interest is arsenite of lime, HO.2CaO + AsO 3 , which 
 precipitates when arsenious acid is mixed with lime water, or arsenite 
 of potash with a salt of lime. It is redissolved by an excess of any 
 acid. The arsenite of magnesia has been noticed, pages 488 and 543. 
 
 Arsenious acid is decomposed by peroxide of iron, an arseniate of 
 the protoxide being produced ; on this is founded the efficacy of the 
 peroxide of iron as an antidote to the poisonous effects of arsenious 
 acid, (see p. 542.) 
 
 The arsenite of cobalt is found native, as a rose-red powder, and the 
 arsenite of nickel exists as a mineral of a pale green colour ; both con- 
 tain combined water. The arsenites of copper and silver will be de- 
 scribed under the heads of those metals, and have been already noticed 
 in pp. 538, et seq. 
 
 The constitution of the salts of arsenic acid has been already men- 
 tioned in p. 534. They are all tribasic, and are isomorphous with the 
 corresponding tribasic phosphates. Some of them are of technical and 
 medicinal importance. The neutral arseniate of potash, H0.2KO + 
 AsO 5 forms a deliquescent saline mass. The binarseniate of potash, 
 2HO.KO + As0 5 , is formed by adding to the former as much arseni- 
 ous acid as it already contained, or by igniting in a crucible equal 
 weights of arsenious acid and nitrate of potash ; red fumes are given 
 off, and on dissolving the residual mass in boiling water, the salt is 
 obtained in large crystals, which are modifications of the square octo- 
 hedron. 
 
 There are three arseniates of soda which resemble the three tribasic 
 phosphates of soda. The first (3NaO + As0 5 ) + 24Aq. is obtained 
 by igniting arsenic acid with an excess of carbonate of soda. When 
 a solution of arsenic acid is neutralized by carbonate of soda, the salt 
 H0.2NaO -f- As0 5 is obtained, which may be had either with 24 Aq. 
 or 14 Aq., according to the temperature at which it crystallizes. 
 The binarseniate of soda, 2HO.NaO + As0 5 , resembles the corres- 
 ponding salt of phosphoric acid. 
 
 The arseniates of the earths are white powders insoluble in water, 
 but soluble in an excess of any acid. 
 
 Arseniates of Iron. That of the protoxide, H0.2FeO + AsO 5 , is a 
 white powder, which, by exposure to the air, gradually becomes green 
 by absorbing oxygen, thereby approaching to the constitution of the 
 native arseniate of iron in which the iron is in the state of black mag- 
 netic oxide. This salt corresponds to the blue phosphate of iron ; its 
 formula being (2FeO.HO + As0 5 ) + 2Fe 2 O 3 .As0 5 + 12Aq. 
 
Chloride of Antimony. 641 
 
 The perarseniate of iron is a white powder, which, when heated, 
 gives off 12 Aq. and becomes red ; it has the singular property of dis- 
 solving totally in water of ammonia. 
 
 Arseniate of nickel is a pale green powder. Arseniate of cobalt is a 
 rose-red powder, and may be used in place of phosphate of cobalt in 
 preparing Thenard's blue (which see). It is prepared on the large 
 scale by roasting the native arseniuret of cobalt, Co 3 As. 
 
 The sulphur salts of arsenic are some of the best characterized among 
 that class (p. 536). There are three sulphoarseniates of potassium 
 having respectively the formulae, (3.KS -f AsS 5 ), (2.KS + AsS 5 ), and 
 (KS -f- AsS 5 ) They are all deliquescent, and crystallize with water. 
 It would be very interesting to find whether the second and third salts 
 contain basic water, such as would keep up the tribasic character of 
 the first. The sulphoarseniates of sodium resemble those of potassium. 
 The basic salt (3NaS + AsS 5 +15 Aq. crystallizes in large colourless 
 rhomboidal tables. When orpiment is dissolved in solution of sul- 
 phuret of potassium, sulphoarsenite of potassium is obtained, KS + 
 AsS 3 , which, when evaporated, is decomposed, and deposits a brown 
 powder, which consists of K.As.S 3 and appears to contain a bisulphuret 
 of arsenic AsS 2 combined with K.S, which is decomposed when sepa- 
 rated from the state of combination. 
 
 SALTS OF ANTIMONY. 
 
 Sesquichloride of Antimony. SbCl 3 . Eq. 2944'5 or 235-4. To ob- 
 tain this salt completely pure, sulphuret of antimony in fine powder is 
 to be mixed with its own weight of corrosive sublimate, and distilled 
 in a hard glass retort. The chloride of antimony distils over with a 
 gentle heat, as an oily liquid, which gradually solidifies into a white 
 crystalline mass. It is very deliquescent, and becomes soft on expo- 
 sure to the air, whence its old name of butter of antimony ; it may be 
 obtained more cheaply for surgical use, but not quite dry, by mixing 
 together two parts of fine common salt, and one of crocus of antimony, 
 (oxysulphuret, see p. 544), and distilling them in a retort with one 
 part of strong oil of vitriol. Chloride of antimony distils over, and 
 there remains behind, sulphate of soda mixed with sulphuret of anti- 
 mony. In this operation, the crocus antimonii being 2SbS 3 + SbO 3 , 
 the former remains passive, but the latter acting on 3NaCl and 3SO 3 , 
 produces SbCl 3 and 3.NaO.S0 3 , As there is, however, some water 
 supplied by the oil of vitrio], the product is not solid ; it is, however, 
 quite strong enough for its successful application as a caustic. 
 41 
 
6-12 Iodide, fyc., of 
 
 When chloride of antimony is put in contact with much water, both 
 are decomposed, and a white oxychloride is precipitated, called powder 
 of Algarotti, from the name of its discoverer. If the water be hot, the 
 precipitate is distinctly crystallized. In it one-fourth of the metal is 
 combined with chlorine, and three-fourths with oxygen, it contains also 
 water, its formula being, according to Berzelius, SbCla + 3.SbO 3 -f- 
 3Aq. The formula given by Malaguti and Johnstone, is 2'SbCl 3 -f- 
 9.Sb0 3 and it is possible that there are two oxychlorides which may be 
 produced separately, or mixed, according to the circumstances of the 
 precipitation. This oxychloride is employed to furnish oxide of anti- 
 mony in the preparation of tartar emetic, and of some other salts of 
 antimony. 
 
 The terchloride of antimony combines with the chlorides of the 
 alkaline metals forming double salts, consisting of an equivalent of each 
 constitution. 
 
 Perckloride of Antimony. SbCl 5 is formed when metallic antimony 
 is burned in chlorine gas. It is a heavy liquid which fumes in the air, 
 and has a very bad smell ; with a small quantity of water, it forms 
 crystals (hydrate) ; with a large quantity of water, it gives antimonic 
 and muriatic acids : it is formed also, by heating sulphuret of antimony 
 in chlorine gas. 
 
 The bromide and iodide of antimony are prepared by the direct com- 
 bination of their elements ; the operation does not require external heat ; 
 the former is colourless ; the latter orange-red. They are both easily 
 fusible, volatile, and decomposed by water. 
 
 The sulphurets of antimony act as sulphur acids, (pp. 544, 547) 
 combining with the sulphurets of the alkaline metals to form double 
 salts, of which several may be crystallized in large rhomboidal tables, 
 perfectly colourless. The basic Jiyposulplioantimonite of potassium 
 which remains in solution after the precipitation of Kermes by cooling, 
 crystallizes on evaporation, in colourless deliquescent plates. 
 
 The sesquioxide of antimony combines with oxygen acids to form 
 salts, which possess but little interest. Metallic antimony decom- 
 poses hot oil of vitriol, evolving sulphurous acid gas, and forming 
 the sulphate of antimony, a white salt which is decomposed by water. 
 
 Antimonial Powder, James 3 Powder. This preparation, to which at 
 one time the highest medicinal virtues were attached, is prepared by 
 mixing together equal parts of sulphuret of antimony and hartshorn 
 shavings, and calcining them in an iron pot at a dull red-heat, until the 
 mass becomes ash-gray ; this is to be then placed in a loosely covered 
 crucible, and exposed to a white heat for two hours, or until the mass 
 becomes quite white ; it is then to be reduced to a fine powder. In 
 
Nature of James's Powder. 643 
 
 this process the sulphur, and the carbon and hydrogen of the hartshorn 
 are burned away, and the antimony is converted into antimonious acid, 
 of which a small quantity unites with the lime that had been as car- 
 bonate in the bone ; the rest of the lime remains as phosphate mixed 
 with the antimonite of lime and the antimonious acid. Its composition 
 varies very much ; it seldom contains more than one per cent, of anti- 
 monite of lime, which is its only soluble and active principle, and where 
 it has been washed, as is sometimes done, even this is removed. It is 
 also a mere mechanical mixture of its ingredients. 
 
 Tartar emetic will be described under the head of tartaric acid and 
 its salts. 
 
 SALTS OF TITANIUM, TELLURIUM AND URANIUM. 
 
 Chloride of Titanium. TiCl 2 . Is best prepared by treating a mix- 
 ture of titanic acid and lamblack by chlorine, as for the preparation of 
 chloride of silicon. It is a colourless liquid, very volatile, fuming in 
 the air, resembling closely bichloride of tin ; it combines with water 
 so violently as to produce explosion, and is decomposed by a large 
 quantity. 
 
 There are no oxygen salts of titanium of any interest. 
 
 Bichloride of Tellurium. TeCl 2 . Is produced by heating tellurium 
 in a current of dry chlorine ; a thick liquid is produced, at first dark- 
 red, but becoming yellow as it cools, and at last solidifying into a snow- 
 white crystalline mass. This salt is decomposed by water, into tellu- 
 rous and muriatic acids, and combines with the alkaline chlorides to 
 form double salts. The protochloride is prepared by melting together, 
 equal weights of the bichloride and of tellurium and distilling ; it con- 
 denses as a deep yellow liquid which solidifies, but does not appear crys- 
 talline. It forms double salts. 
 
 The tellurous acid appears to possess feeble basic properties, as it 
 unites with the strong acids to form compounds, which are not impor- 
 tant. The relations of tellurous and telluric acids to bases have been 
 already noticed at sufficient length (p. 549). 
 
 The Chlorides of Uranium, U.C1. and U 2 Cl3, give yellowish-green 
 solutions, but do not crystallize. With the alkaline chlorides they unite, 
 forming crystallizable double salts. 
 
 Protosulphate of Uranium crystallizes in green prisms. 
 
 Sesquisulphate of Uranium, U 2 O 3 + 3.SO 3 , is not itself crystalliza- 
 ble, but combines with sulphate of potash in several proportions, to 
 form double salts of very complex constitution. 
 
 The Sesquinitrate of Uranium, U 2 0s + 3,N0 5 , crystallizes in large 
 
64.4 Salts of Copper. 
 
 tabular crystals of a bright yellow colour. This salt is remarkable as 
 the most definite nitrate of a sesquioxide that is known to chemists. 
 
 All these salts are prepared by dissolving the oxides of uranium in 
 the dilute acids. 
 
 SALTS OF COPPER. 
 
 Copper forms two series of salts, one corresponding to the suboxide, 
 and the other to the black oxide. The former are generally white, and 
 the latter blue or green. 
 
 Chloride of Copper, CuCl. is produced by dissolving copper in aqua 
 regia, or oxide of copper in muriatic acid. Its solution is green, and 
 it gives, on evaporation, the hydrated salt in long slender green prisms, 
 CuCl + 2Aq., which are slightly deliquescent, and are soluble in 
 alcohol. When heated they give off water, and the dry chloride re- 
 mains as a brown powder, which recombines with water, with the evo- 
 lution of much heat. Strongly heated, it fuses, gives off half its 
 chlorine, and the subchloride remains, melted into a brown resinous- 
 looking mass, whence its name of resina cupri. By the action of an 
 alkali on a solution of chloride of copper, an oxychloride may be formed, 
 which precipitates as a fine green powder, having the formula CuCl -f- 
 3CuO + Aq., and which is used as a pigment by the name of 
 Brunswick green. There exist two other oxychlorides of copper 
 which have the formulae CuCl + 2CuO + 3Aq., and CuCl + 4CuO+ 
 6HO, prepared by the decomposition of the ammoniacal chlorides of 
 copper. 
 
 The Subchloride of Copper, Cu 2 Cl, may be prepared either by heating 
 the chloride, as above, or by digesting the clippings of thin copper in a 
 strong solution of chloride of copper, to which some muriatic acid had 
 been added. The liquor gradually acquires an olive colour, and the 
 subchloride is deposited in the form of a white powder. In this case, 
 the CuCl combines with a second equivalent of copper, forming Cu 2 Cl. 
 It also precipitates when chloride of copper is acted on by protochloride 
 of tin, 2.CuCl and SnCl producing Cu 2 Cl and SnCl 2 . This subchloride 
 is insoluble in water ; it dissolves in muriatic acid, which lets it fall 
 by dilution with water. It absorbs oxygen rapidly from the air, and 
 becomes green. It forms with water of ammonia a colourless solution, 
 which rapidly becomes blue on exposure to the air. 
 
 Both chlorides of copper combine with the chlorides of the alkaline 
 metals, to form double salts. 
 
 The Bromide and Subbromide of Copper, CuBr, and Cu 2 Br, resemble 
 in every respect the chlorides just described. 
 
Manufacture of Blue Vitriol. 645 
 
 The Iodide of Copper Cul, does not appear to exist except in combi- 
 nation. If solutions of iodide of potassium and chloride of copper be 
 mixed, the subiodide is precipitated whilst half the iodine is set free, 
 2.Cu.Cl and 2.K.I, producing 2.K.C1 and Cu 2 T, with free I. But if an 
 excess of iodide of potassium be added, these elements recombine, and 
 a double salt, Cul + KI may be obtained. The preparation of the 
 subiodide of copper, just given, involves the loss of an atom of iodine, 
 which is avoided by previously mixing the liquor with an excess of 
 solution of protosulphate of iron, by which the copper salt is reduced 
 to the state of suboxide, and all the iodine then precipitated as sub- 
 iodide. Thus made, it is a pale yellow powder, unaltered by the air. 
 
 Sulphate of Copper. CuO.SO 3 HO -f 4Aq. Eq. 996'9 + 562'5, or 
 79*9^4* 45. Eor the purposes of the arts, in which this salt is ex- 
 tensively employed, it is prepared by treating the native sulphuret of 
 copper, in the manner described under the head of the sulphates of iron 
 and zinc. It may also be obtained by boiling oil of vitriol on metallic 
 copper, when sulphurous acid gas is given off, or by acting on the metal 
 with dilute sulphuric acid to which some nitric acid had been added. 
 It crystallizes in large doubly oblique rhombs, of a fine blue colour, 
 whence its name, blue vitriol. In the figure the primary rhomb, and 
 the most usual secondary form are given, i, u, v, 
 marking the primary planes in each. These 
 crystals dissolve in four parts of cold and two of 
 boiling water. Of the five atoms of water which 
 it contains, one is constitutional, and may be 
 replaced by the alkaline sulphates, to form a 
 class of double salts of great beauty. By the 
 action of a small quantity of ammonia, a basic sulphate is obtained, 
 of which the formula is CuO.SOa + 3CuO + 4Aq. and another 
 containing CuO.SOa + 7CuO + 12 Aq. is occasionally observed to 
 form. 
 
 Nitrate of Copper. CuO.NCk + 3Aq. This salt is obtained when 
 copper is dissolved in dilute nitric acid ; it crystallizes in oblique rhombs 
 of a rich blue colour, and sometimes in paler rhomboidal plates, which 
 contain 6 Aq. This salt deflagrates violently when thrown on burning 
 coals, or when struck on an anvil with a little phosphorus. If some of 
 it be wrapped up tight in tinfoil, it becomes very hot, swells up, fumes, 
 and oxidizes the tin so rapidly, that in some points brilliant sparks are 
 thrown out. When heated above 200, it loses acid, and a basic nitrate 
 remains, which may also be formed, by adding a small quantity of am- 
 monia to a solution of the neutral salt. The formula of the basic salt 
 is HO.m + 3CuO. 
 
646 Scheele's Green, Emerald, Green. 
 
 Phosphate of Copper, H0.2CuO 4- P0 5 , and the arseniate of cop- 
 per H0.2CuO + AsO 5 are pale green powders, obtained by double 
 decomposition. 
 
 Arsenite of Copper. H0.2QuO 4- AsOs. Is obtained by the de- 
 composition of arsenite of potash and sulphate of copper ; it is a fine 
 apple-green powder, the importance of which, as a test for arsenic, has 
 been already discussed, (p. 625). It is employed in the arts under the 
 name of Scheele's green, as a pigment, and is prepared on the large 
 scale, by dissolving two pounds of pure sulphate of copper in twelve 
 quarts of water, previously heated in a copper pan. In another pan, 
 two pounds of pure calcined pearlash are dissolved, with eleven ounces 
 of arsenious acid, in four quarts of pure water. Both liquors are 
 strained through linen, and then the arsenical solution is gradually 
 added to the solution of copper. The precipitate is collected on a cloth, 
 and carefully dried. The produce should be lib. 6| oz. A still more 
 beautiful pigment, which may be best described here, is prepared under 
 the name of Schweinfurt green or Emerald greeny it is a compound of 
 acetate of copper, and arsenite of copper, CuO. A + 3(HO.2CuO + 
 AsO 3 ). It is prepared by mixing up ten parts of pure verdigris with 
 as much hot water as will make it into a thin pulp, and straining it 
 through a sieve, to separate the impurities ; nine or ten parts of arseni- 
 ous acid are to be then dissolved in 100 parts of boiling water, and 
 whilst boiling, the verdigris pulp is to be gradually added thereto, 
 continually stirring. At first, a mere arsenite of copper falls, and all the 
 acetic acid remains in the liquor ; it being only after much agitation that 
 the double salt is produced, which is known by the light flocculent pre- 
 cipitate changing into a heavy granular powder of a brilliant green colour. 
 
 The history of the salts of the suboxide of copper with the oxygen 
 acids possesses no practical interest. 
 
 SALTS OF LEAD. 
 
 Chloride of Lead. Pb.Cl. May be produced by boiling lead in 
 strong muriatic acid, or by acting on oxide of lead with the same acid ; 
 but more simply, by adding to any soluble salt of lead a solution of 
 chloride of sodium. A curdy white precipitate falls, which dissolves in 
 boiling water, and on cooling, crystallizes in opaque plates, of a pearly 
 lustre, which do not contain water. This salt requires 135 parts of 
 cold water to dissolve it, but is much more soluble in boiling water. It 
 is easily fused, and, on cooling, forms a semitransparent mass, like horn, 
 whence the old waaeplimfam corneum, By the action of ammonia on 
 
Salts of Lead. 647 
 
 chloride of lead, several oxycJdorides may be formed, of which none are 
 now of interest. 
 
 Bromide of lead resembles perfectly the chloride. 
 Iodide of Lead. Pb.I. Is formed by adding iodide of potassium, to 
 a solution of nitrate of lead ; a bright lemon-yellow precipitate falls, 
 which requires 1235 parts of cold, and but 194 of boiling water to dis- 
 solve it. The solution is colourless, and on cooling deposits the iodide 
 of lead in splendid gold-coloured six-sided plates, which maintain their 
 metallic lustre perfectly in drying. The iodide of lead forms double 
 salts with the alkaline iodides, and gives with ammonia oxyiodides when 
 the alkali is not in excess. 
 
 Sulphate of Lead. PbO.SO 3 . This salt is found in the mineral 
 kingdom, in large transparent rhombs, isomorphous with sulphate of 
 barytes, and of which the octohedron , y, in the figure is the primary 
 form. It may be also formed by adding to any solution 
 containing lead, sulphuric acid, or a sulphate. It falls 
 down as a white powder, which, from its insolubility, 
 furnishes a good test for lead. When strongly ignited, 
 it melts without decomposition, but with charcoal it is 
 reduced to sulphuret of lead. The sulphate of lead is soluble in strong 
 acids, and hence the oil of vitriol, manufactured in leaden chambers, 
 generally contains a small quantity of it dissolved, which is precipitated 
 on the addition of water. 
 
 Nitrate of Lead. PbO.NOs. Is obtained by dissolving lead in di- 
 lute nitric acid and evaporating. It crystallizes in regular octohedrons, 
 often modified, which are generally opaque ; it is soluble in seven and 
 a-half parts of cold, and much less of boiling water. It is not solu- 
 ble in nitric acid. When heated, it gives out a mixture of oxygen and 
 nitrous acid gases, (p. 448), and leaves melted protoxide of lead. 
 By the action of ammonia, a series of basic salts are obtained, which 
 contain two, three, and six atoms of oxide of lead united to one of 
 nitric acid. 
 
 When a solution of nitrate of lead is boiled on finely divided metallic 
 lead, this dissolves, and on cooling, brilliant yellow plates are deposited, 
 which are basic nitrate of lead. 2PbO -f N0 4 . By adding sulphuric 
 acid to a solution of this salt, a neutral nitrite is obtained, PbO.NO 4 
 + HO., which crystallizes in yellow octohedrons. If an excess of lead 
 be used in the preparation of the nitrate, the acid is still further deoxi- 
 dized, and a Jiyponitrite of lead y 3PbO + NO 3 -f- 3Aq. is produced, 
 which crystallizes in rose-red scales. These salts are of interest, as it 
 was doubted whether the nitrous acid (N0 4 ) could combine with bases, 
 and it is only in these cases that we have obtained positive evidence of 
 its doing so, which we owe to Peligot. 
 
648 Salts of Bismuth. 
 
 Phosphate of Lead. H0.2PbO + P0 5 . Is formed by the action 
 of common tribasic phosphate of soda on a solution of nitrate of lead ; 
 it is a white powder, which is changed by ammonia into 3PbO + PO 5 . 
 
 Silicate of Lead has been noticed in relation to crystal and to flint 
 
 Chromate of Lead. PbO.Cr0 3 . Chrome-yellow, is formed by mix- 
 ing together solutions of nitrate of lead and bichromate of potash. It 
 precipitates as a fine lemon yellow powder, insoluble in water. It 
 occurs native in ruby-red crystals, constituting the real lead ore. This 
 salt is manufactured largely for a pigment, which is found of various 
 shades of yellow and orange in the market, being mixtures of the true 
 metallic chromate, prepared as above, with the basic chromate of lead 
 2PbO + CrO 3 , which is of a bright vermilion colour, and is termed 
 Chrome red. This may be prepared by adding potash to a solution of 
 chromate of potash until this reacts strongly alkaline, and then mixing 
 it with nitrate of lead ; or by digesting the neutral chromate of lead 
 in a warm solution of potash, which removes half the acid. These 
 give products, however, inferior in brilliancy of tint to the following. 
 Saltpetre is to be melted in a crucible at a dull red heat, and chrome 
 yellow gradually added thereto, as long as effervescence with escape of 
 red fumes occurs. The potash abandons the nitric acid and takes half 
 the chromic acid, and basic, chromate of lead is formed. The mass 
 becomes black and is then to be allowed to settle, and the melted salt 
 poured off from the heavy powder at the bottom ; this, when cold, be- 
 comes of a splendid vermilion red, and is to be taken out and washed 
 with the smallest possible quantity of water. 
 
 * ' & 
 
 SALTS OF BISMUTH. 
 
 Chloride of Bismuth. BiCl 3 . Is formed by dissolving bismuth in 
 hot strong muriatic acid ; by evaporation it forms a crystalline mass 
 which is very deliquescent, volatile, and fusible. By water it is de- 
 composed, giving the oxychloride of bismuth, a white powder, having 
 the composition BiCl 3 + 2Bi0 3 + 3HO. In the arts this powder is 
 sometimes employed under the name of Spanish white or pearl white. 
 
 The chloride of bismuth combines with the chlorides of the alkaline 
 metals, forming double salts, in which the chlorine combined with the 
 bismuth is to that combined with the other metal, as three to two. In 
 the double salts formed by protochlorides, this relation is never ob- 
 served, and hence it furnishes additional proof that the chloride of 
 bismuth is a ter-chloride, on which idea the formulae become 2KC1 
 + BiCl 3 + 2Aq, and 2NaCl -f- BiCl 3 -f 3Aq. 
 
Salts of Silver. 649 
 
 Sulphate of Bismuth. BiO 3 -f 3.S0 3 . Is formed by dissolving bis- 
 muth in hot sulphuric acid. It forms a deliquescent mass of acicular 
 crystals, which are decomposed by water, giving a white powder, the 
 basic sulphate of bismuth BiO 3 -f- SO 3 . 
 
 The Nitrate of ismutLBi0 3 + 31S T O 5 + 9Aq. Is formed by 
 dissolving the metal in dilute nitric acid ; by evaporation and cooling 
 rhomboidal crystals are obtained, which easily deliquesce ; when heated, 
 they lose water and nitric acid, and form a basic salt, and finally oxide 
 of bismuth remains behind. Like the other salts of bismuth, this is 
 decomposed by water, and may produce one or other of two basic salts, 
 according to circumstances. When the crystals, without any excess of 
 acid, are decomposed by water, the precipitate has the composition, 
 4Bi0 3 -f- 3N0 5 -f 9HO ; whilst, if an acid liquor be decomposed by 
 water, the precipitate has the formula BiO 3 + NO 5 . Both of these 
 salts yield very nearly the same quantity of oxide of bismuth on ana- 
 lysis, and were hence long confounded together. The several reasons 
 for considering the oxide of bismuth to be a teroxide have been given 
 (p. 562). These subnitrates of bismuth are used indiscriminately in 
 medicine, but the latter form is more generally found in the shops. 
 The name pearl-white, &c., are also applied to these bodies. 
 
 SALTS OF SILVER. 
 
 Chloride of Silver. AgCl. Eq. 1794'3 or 143'8. Exists native as 
 an ore of silver, horn silver, and may be formed by mixing a solution 
 of common salt with a soluble salt of silver. It forms a curdy white 
 precipitate, perfectly insoluble in water and in acids, but easily soluble 
 in water of ammonia. When heated, it fuses below redness, and, on 
 cooling, congeals into a semitransparent mass, of a horny aspect, 
 whence its old name. When freshly precipitated, it is exceedingly 
 sensible to the action of light, becoming pink, violet, and ultimately 
 black, by exposure to the sun's rays ; but for this reaction, it is neces- 
 sary that organic matter or water should be present, with the hydrogen 
 of which the chlorine may combine, and that thus a thin layer of sub- 
 chloride or of metal may be produced. The relations of chloride of 
 silver to light are of the highest importance in photography, and in 
 examining the structure of the solar rays, as noticed in pp. 224, et 
 seq. The processes for the reduction of chloride of silver to the metallic 
 state have been described in p. 469. 
 
 Iodide of Silver. Agl. Is obtained by decomposing a soluble salt 
 of silver by iodide of potassium ; a primrose-yellow precipitate falls, 
 which is insoluble in water and in ammonia, at least it requires 2500 
 
650 Nitrate of Silver. 
 
 parts of strong water of ammonia to dissolve one of iodide of silver. 
 It is easily fusible, and becomes opaque on cooling. In certain forms 
 it is still more sensible to light than the chloride, and is hence the basis 
 of the impression in the photographic process of Daguerre (see p. 227). 
 It is reduced to the metallic state by the same means as the chloride. 
 
 Bromide of Silver. AgBr. Resembles the chloride in every parti- 
 cular respect. 
 
 Sulphate of Silver. AgO.S0 3 . Is formed by boiling metallic silver 
 in oil of vitriol ; sulphurous gas is given off, and a white saline mass 
 formed, which, when more strongly heated, is totally decomposed, leav- 
 ing metallic silver. This salt dissolves in eighty-eight parts of boiling 
 water, and crystallizes on cooling, in small needles. 
 
 Hyposulphite of Silver. 2AgO + S 2 2 . The relations of hypo- 
 sulphurous acid to oxide of silver, are very curious. On adding a 
 neutral solution of nitrate of silver to a solution of hyposulphite of 
 soda, a white precipitate appears, which at first redissolves, but subse- 
 quently becomes permanent. It soon loses its pure colour, especially 
 if heated, and at last becomes black from sulphuret of silver, whilst 
 the liquor contains sulphate of silver; thus, 2AgO + S 2 2 produce 
 AgS and AgO.SO 3 . The solution of this salt is extremely sweet. So 
 great is the affinity of hyposulphurous acid to oxide of silver, that a 
 solution of it dissolves chloride of silver, forming an intensely sweet 
 liquor ; and the solutions of the alkaline and earthy hyposulphites dis- 
 solve all the salts of silver insoluble in water, except the arseniate and 
 the iodide, and form double salts of exceedingly sweet taste. The 
 double hyposulphites contain generally one equivalent of hyposulphite 
 of silver to two of the other salt, but our knowledge of these salts is 
 not as yet by any means complete. 
 
 Nitrate of Silver.- AgO.N0 5 . Eq. 2128'5 or 170-57. This is the 
 most important salt of silver ; it is manufactured on a very large scale 
 in the Apothecaries' Hall of Ireland, for medicinal use. 
 
 It is prepared by dissolving granulated silver in dilute nitric acid, 
 which at first occurs without the disengagement of any gas, as the nitric 
 acid dissolves the nitric oxide formed, but towards the end copious red 
 fumes are evolved. By evaporation and cooling, the salt is obtained in 
 
 colourless rhomboidal plates, as in the figure, 
 often four inches across, which are anhy- 
 drous. It is soluble in its own weight of 
 cold water. When heated to about 430, 
 it melts into a colourless liquid which is 
 poured into cylindrical silver moulds, and 
 congealing, forms the sticks of lunar caustic 
 
Salts of Mercury. 651 
 
 used in surgery. This fused salt should be snow white; it is not 
 affected by light unless organic matter be present, as has been fully 
 shown by Scanlan ; but with organic matter it soon becomes quite 
 black, silver being reduced. It is hence used as marking ink, and for 
 staining hair black. When strongly heated, nitrate of silver is totally 
 decomposed. It yields its oxygen readily to combustible bodies ; thus 
 if a few grains of it be laid on an anvil with a little bit of phosphorus, 
 and struck with a hammer, it explodes violently. Its solution is re- 
 duced to the metallic state by all deoxidating agents. 
 
 Hyponitrite of Silver. AgO.N0 3 . It is obtained in granular crys- 
 tals, by adding the soda salt prepared by melting nitrate of soda (p. 
 377), to a boiling solution of nitrate of silver, and filtering whilst 
 very hot. 
 
 Tribasic Phosphate of Silver. 3AgO -f- PO 5 . Is the canary-yellow 
 precipitate produced by adding a tribasic phosphate of soda to a solu- 
 tion of nitrate of silver. Its relations to the other phosphates of silver 
 and to the silver test for arsenic, have been noticed in pp. 413 and 
 538. 
 
 Arseniate of Silver. -^^ AgO + AsG 5 . Is precipitated as a reddish- 
 brown powder, on adding any solution of an arseniate to a solution of 
 nitrate of silver. Its formation is one of the most characteristic pro- 
 perties of arsenic acid. 
 
 Arsenite of Silver. HO. 2 AgO -f- As0 3 . Is produced as has been 
 noted in p. 538, by adding a solution of arsenious acid to the ammo- 
 niacal nitrate of silver. It is a canary-yellow powder ; soluble in am- 
 monia and in nitric acid. When heated, it first yields water and 
 becomes brown ; then it gives oxygen, arsenious acid, and leaves me- 
 tallic silver. 
 
 SALTS OF MERCURY. 
 
 Chloride of Mercury Corrosive Sublimate. HgCl. Eq. 1693*7 or 
 135*4. May be prepared by dissolving red oxide of mercury in mu- 
 riatic acid, and evaporating. It crystallizes in long right-rhombic 
 prisms, generally opaque. It may also be very economically prepared 
 by dissolving the basic sulphate (turpeth mineral) in strong muriatic 
 acid, and crystallizing ; the sulphate of mercury remains in the mother 
 liquor and may be again converted into basic sulphate by the action of 
 water. The corrosive sublimate is, however, generally prepared, for 
 pharmaceutic purposes, by the dry way, as follows : sulphate of mer- 
 cury, HgO.SO 3 , is to be well mixed with its own weight of common 
 salt, INaCl, and the mixture introduced into a wide necked glass retort, 
 
652 Corrosive Sublimate. 
 
 or, on the large scale, into a stone-ware pot, to which a globular glass 
 head is attached. The retort or pot being bedded in sand, is gradually 
 heated to redness, decomposition occurs, the chlorine of the common 
 salt combining with the mercury, whilst the sodium takes the oxygen 
 and acid ; we have therefore formed, HgCl, which sublimes into the 
 head, forming a mass of prismatic crystals, which being partly fused 
 by the heat cohere strongly together, and sulphate of soda which re- 
 mains behind; HgO.S0 3 , and Nad, giving HgCl and NaO.S0 3 . 
 
 The sublimed chloride of mercury crystallizes in a right rhombic 
 prism, as represented in the figure. Its specific gravity is 5*4 ; it 
 melts at 590, and boils at 563. The specific gra- 
 vity of its vapour is 9420. It dissolves in two parts 
 of boiling and twenty of cold water ; the hot solution 
 crystallizes, on cooling, in prisms of a different form 
 from that of the sublimed salt ; it is therefore di- 
 morphous ; it is soluble in 2 J parts of cold alcohol, 
 and in three parts of cold ether ; it dissolves much 
 more readily in muriatic acid, and in solutions of the alkaline chlorides, 
 than in pure water, as it forms with these bodies double salts, which 
 are very soluble ; of these the double chloride of mercury and ammonium 
 sal alemlrotk, is employed in pharmacy. It will be specially described 
 hereafter. A solution of corrosive sublimate yields all the reactions of 
 a salt of the red oxide of mercury, as described previously. When a 
 small quantity of potash is added to a solution of sublimate a brown 
 precipitate falls, which by boiling becomes black and crystalline ; the 
 same substance may be formed by boiling red oxide of mercury in a 
 solution of sublimate ; it is an oxyckloride of mercury, whose formula 
 is HgCl + 3HgO. 
 
 If a solutiflfti of sublimate be treated by a small quantity of sulphuret 
 of hydrogen, a precipitate forms, at first brownish, but which ulti- 
 mately becomes quite white, provided there be sublimate in excess ; it 
 is a cklorosulpkuret, of which the formula is, HgCl + 2HgS. 
 
 Subchloride of Mercury Calomel. Hg 2 CL Eq. 2943'7 or 235'4. 
 This important medicinal agent may be prepared either by precipitation 
 or by sublimation. For the former object, nine parts of mercury are 
 to be digested in eight parts of nitric acid, sp. gr. T25, without heat, 
 until no more mercury appears to dissolve, and the liquor begins to 
 assume a yellow colour ; eight parts of common salt are next to be 
 dissolved in 250 parts of boiling water, to which a little muriatic acid 
 may be added : these solutions being mixed, the calomel immediately 
 precipitates, and thus prepared, it is absolutely pure. The mercury 
 dissolving in the nitric acid, forms nitrate of the suboxide, and by the 
 
Calomel Bromides of Mercury. 653 
 
 chloride of sodium, nitrate of soda, and subchloride of mercury are 
 formed ; Hg 2 O.NO 5 and NaCl, giving Hg 2 Cl and NaO.NO 5 . 
 
 To obtain calomel by sublimation, four parts of corrosive sublimate 
 may be rubbed up with three 'parts of mercury, so intimately that no 
 trace of metal shall be visible, and the mixture being introduced into 
 an earthen pot to which a glass head is fitted, heat is to be gradually 
 applied, until the materials have all sublimed. In this operation, HgCl, 
 combining directly with Hg, gives Hg 2 Cl. The union is never per- 
 fected by the first sublimation, and the product is to be again powdered, 
 well mixed, and again sublimed. The process followed by the British 
 pharmacopoeias is different, and is best carried on in the following pro- 
 portions. Thirty-one parts of dry sulphate of the red oxide of mer- 
 cury (persulphate) is to be intimately mixed with twenty and one-third 
 parts of metallic mercury, and twenty parts of fused common salt, 
 and the whole rubbed together until the mercurial globules totally dis- 
 appear. This method is the same as the former in principle, except 
 that the corrosive sublimate is generated only when required to com- 
 bine with the additional quantity of mercury, to form calomel. The 
 sublimation is carried on as described above. The sublimed mass is 
 always contaminated with some undecomposed sublimate. Hence it 
 must be carefully levigated, and washed with boiling water, as long as 
 the washings give any milkiness on the addition of a few drops of water 
 of ammonia. 
 
 The precipitated calomel is a pure white powder. "When sublimed 
 it forms a crystalline mass whose primitive form as in the figure, is a 
 square prism. It is insoluble in water, and the 
 minute division of the sublimed calomel may be 
 elegantly secured by conducting its vapour into a 
 vessel containing boiling water, by the vapour of 
 which it is suddenly condensed, and falls as an ex- 
 cessively fine powder. Its sp. gr. is 6 -5. The 
 presence of sublimate in the calomel of the shops is 
 detected by boiling for a few minutes in alcohol, and 
 adding to the alcoholic liquor some water of am- 
 monia, which gives a white precipitate if corrosive 
 sublimate be present. By boiling with muriatic 
 acid, or with solution of common salt, or sal-ammoniac, calomel is 
 gradually decomposed into sublimate, which dissolves, and metallic 
 mercury, which remains behind. 
 
 The Bromide and Sulbromide of Mercury. Hg.Br. and Hg 2 Br. 
 may be prepared ; the first by acting directly on mercury with bromine, 
 when a colourless solution is obtained, which gives prismatic crystals 
 
654 Iodides of Mercury. 
 
 by evaporation ; the second by decomposing nitrate of the suboxide by 
 bromide of potassium. These bodies resemble completely sublimate 
 and calomel in their properties. 
 
 Iodide of Mercury. Red Iodide. Hgl. Eq. 2845'0 or 228'0. 
 May be formed by the direct combination of its elements, even without 
 heat, by trituration together with a few drops of alcohol. It is then 
 dark red, but may be obtained of a brilliant red colour by precipitating 
 a solution of corrosive sublimate with an equivalent of iodide of potas- 
 sium. An excess of the latter redissolves the precipitate, as it forms a 
 double salt, (KI + Hgl), soluble in water, and crystallizable in octo- 
 hedrons. The iodide of mercury is insoluble in water ; when heated it 
 fuses and sublimes, condensing in a yellow crystalline mass, formed of 
 rhomboidal plates, which, when broken or scratched, gradually become 
 red, breaking up into a number of minute crystals of a different form. 
 It is somewhat soluble in alcohol, and abundantly in aqueous hydriodic 
 acid. A hot solution of iodide of potassium dissolves much more than 
 the atomic proportion of it ; the excess crystallizes in long, red, square 
 prisms, according as the solution cools. It dissolves also in a strong 
 solution of corrosive sublimate with which it combines in two propor- 
 tions. It forms a class of double salts, equally extensive with that 
 produced by corrosive sublimate. 
 
 Subiodide of Mercury. Hg 2 I. May be formed by triturating 
 iodine with mercury, or by precipitating a solution of iodide of potas- 
 sium by a slight excess of nitrate of the suboxide of mercury. It 
 is an olive-green powder, which is resolved by heat into metallic 
 mercury and iodide, and is similarly decomposed by a solution of 
 iodide of potassium, with which the iodide of mercury formed com- 
 bines. 
 
 Sesquiodide of Mercury, or Yellow Iodide. Hg 4 I 3 , or + 2HgI + 
 Hg 2 I. To obtain this substance, a solution of iodide of potassium, to 
 which half as much iodine as it already contained has been added, is to 
 be decomposed by a slight excess of a solution of the subnitrate of 
 mercury. The bright yellow powder which precipitates must be dried 
 cautiously with little exposure to light. By means of a solution of 
 iodide of potassium, it is resolved into red iodide and metallic mercury. 
 The reaction by which it is formed is that, of the subiodide first pro- 
 duced, by the KI. and Hg 2 O.NO 5 , one-half is converted into red iodide 
 by the additional atom of iodine which is supplied. 2(KI) + I, and 
 2 (Hg 2 O.NO 5 ), giving 2 (KON0 5 ) and Hg 2 I -f 2.HgI. This prepa- 
 ration is employed in pharmacy. 
 
 A preparation which has been proposed by Donovan, under the 
 name of lodo-hydraryyrate of Arsenic, is prepared by rubbing together 
 
Oxygeii Salts of Mercury. 655 
 
 6 '08 grs. arsenic, 15 '3 8 grs. of mercury, and 50 grs. iodine, with a 
 few drops of alcohol until they combine, and then adding eight ounces 
 of water with a few drops of hydriodic acid ; a solution is obtained at 
 first colourless, but soon becoming yellowish-brown by light, from 
 iodine being set free. This preparation is not a chemical compound, 
 but the iodide of arsenic being decomposed by the water, the iodide of 
 mercury is dissolved by the hydriodic acid formed, whilst arsenious 
 acid exists free in the solution. 
 
 Sulphate of Mercury. HgO.SOs. Eq. 1850 or 148'0, is produced 
 by boiling oil of vitriol on mercury, until it is converted into a white 
 saline mass, which requires to be finally heated nearly to redness to 
 expel the excess of acid. Sulphurous acid is evolved, Hg and 2SO 3 , 
 giving HgO.S0 3 and SO; but this may be avoided by adding from 
 time to time a small quantity of nitric acid, by which oxygen will be 
 supplied. This salt forms a white powder, not crystalline ; at a full 
 red heat it is resolved into mercury, sulphurous acid, and oxygen. Its 
 use is extensive in preparing calomel and sublimate. By a large quan- 
 tity of water it is decomposed into free acid and basic sulphate, turpeth 
 mineral, 3HgO -f SO 3 , which is a bright yellow powder, which, when 
 heated with muriatic acid gives neutral sulphate and corrosive sublimate, 
 2-HCland (3HgO + 80s), producing 2'HgCl and IIgOS0 3 ; water 
 being formed, (see p. 651). 
 
 Subsulpkate of Mercury. ~ Hg20.S0 3 . Sulphate of the UacJc oxide 
 may be formed by heating metallic mercury with oil of vitriol, provided 
 the heat do not pass beyond 212 ; or by mixing strong solutions of 
 nitrate of the black oxide and of sulphate of soda. It is a white pow- 
 der, very sparingly soluble in water, by which it is not decomposed, 
 and is thereby distinguished from the preceding salt. 
 
 Nitrate of Mercury. Nitrate of the red Oxide. 2HgO.N0 5 + 2 
 Aq. This salt is formed when mercury is dissolved in an excess of 
 nitric acid with heat. It crystallizes in rhomboidal plates, which are 
 deliquescent, and soluble in a small quantity of water. Its solution is 
 decomposed when diluted, a basic nitrate of the red oxide being preci- 
 pitated of a bright canary colour, and having the formula HO.NO + 
 3HgO. If this powder be boiled with much water, a still more basic 
 salt is formed, which has the formula, NO 5 + 6HgO. Both this salt 
 and the sulphate, when heated by sulphuretted hydrogen not in excess, 
 give white basic compounds, like the chlorosulphuret (p. 652), having 
 the formulas, HgO.im -f- 2HgS and HgO.SO 3 -f- 2HgS. 
 
 Subnitrate of Mercury. Nitrate of the Black Oxide. When mer- 
 cury is dissolved in dilute nitric acid, without any heat, or with only as 
 much as sustains a very moderate action, the black oxide forms and may 
 
656 Salts of Gold. 
 
 unite with the nitric acid in various proportions. 1st. If there be 
 nitric acid in excess, the solution gives by cautious evaporation clear 
 transparent rhombs of neutral sufinitrate, having the formula, Hg20. 
 N0 5 -|- 2HO. 2nd. If there be an excess of mercury, large opaque 
 white rhombic prisms sometimes form, which have the composition, 
 (3Hg 2 O + 2N0 5 + 3HO). 3rd. By letting this solution stand, 
 these crystals gradually disappear, and very small canary-yellow crystals, 
 nearly spherical, with numerous brilliant facets are produced ; this is a 
 basic salt, the formula being HO.NOs + 2.Hg 2 O. This salt may also 
 be formed by the action of water on either the first or second ; both 
 being decomposed into free acid, and the basic salt, which is no further 
 altered even by boiling water. The second salt may be looked upon as 
 a compound of the first and third, since (3Hg 2 O + 2N0 5 + 3HO) = 
 (Hg 2 O.N0 5 + 2HO.) + (HO.N0 5 + 2Hg 2 0). 
 
 Subchromate of Mercury. Hg 2 O + CrOa. Produced by mixing 
 solutions of chromate of potash and subnitrate of mercury, is a bright 
 orange powder insoluble in water ; when heated to redness, it gives off 
 mercury and oxygen, and chromic oxide of a fine green colour remains, 
 p. 523. 
 
 Eed nitrate of mercury combines with iodide of mercury to form a 
 double salt, which is formed by half precipitating a solution of the mer- 
 curic salt by iodide of potassium, and boiling until the precipitate redis- 
 solves ; on cooling, the new salt is deposited in brilliant red crystalline 
 scales, which are decomposed by much water. 
 
 m. 
 
 SALTS OF GOLD. 
 
 Per chloride of Gold. AuCl 3 . When gold is dissolved in nitro- 
 muriatic acid, and the solution evaporated very cautiously to dryness, 
 this salt remains as a ruby red crystalline mass, which dissolves with a 
 yellowish-red colour in water. Its solution is acid, and is decomposed 
 by the light, and by all deoxidizing agents. It combines with muriatic 
 acid, and forms a deep yellow liquor, from which the acid chloride of 
 gold crystallizes in long yellow needles. It is soluble in alcohol and in 
 ether, from which last solution it is deposited in the metallic state on 
 evaporation, the chlorine combining with the ether. In this way some 
 forms of gilding are effected, as on steel. The chloride of gold com- 
 bines with many other chlorides, forming double salts. The chloride of 
 gold and potassium, AuCl 3 + KC1 + 5Aq., crystallizes in orange-red 
 striated rectangular prisms. It effloresces in the air, and may be ob- 
 tained anhydrous ; it is then ruby red. Chloride of gold and sodium 
 (NaCl + AuCla + 4Aq), forms crystals of the same form and colour, 
 
Salts of Palladium and Platinum. 657 
 
 bufc which do not effloresce : when heated, they fuse in their water of 
 crystallization. 
 
 Subchloride of Gold. AuCl. Is produced by heating the chloride to 
 about 450 in a porcelain dish, stirring it very carefully until no more 
 chlorine is given off. It is a yellowish-white mass, insoluble in water, 
 by which it is gradually decomposed into chloride and metallic gold. 
 It is in this way only that a solution of chloride of gold perfectly free 
 from an excess of acid can be obtained. 
 
 Iodides of Gold. When solutions of chloride of gold and iodide of 
 potassium are mixed, a greenish precipitate occurs of sub-iodide of gold, 
 AuL, whilst two-thirds of the iodine become free. If the iodide of 
 potassium be in great excess, however, the iodine and subiodide are both 
 redissolved and a double salt obtained, which crystallizes, and which 
 contains pcriodide of gold, its formula is KI + AuI 3 : by the cautious 
 addition of chloride of gold to a solution of this salt, a greenish preci- 
 pitate may be obtained without any liberation of iodine, and which hence 
 must be the iodide. 
 
 The oxides of gold do not act as bases, and the general nature of the 
 salts which they form, as acids, has been noticed in p. 573. 
 
 SALTS OF PALLADIUM. 
 
 Chloride of Palladium. PdCl. Is formed by dissolving palladium 
 in nitro-muriatic acid. Its solution is deep brown, and it forms by 
 evaporation, a crystalline mass ; by the action of a small quantity of a 
 caustic alkali, a basic salt, or oxy chloride of palladium, PdCl + 3PdO 
 + 4Aq., is produced, it is a brown powder, insoluble in water. The 
 chloride of palladium combines with other chlorides to form double 
 salts : when heated to about 600, it abandons half its chlorine, and 
 subcliloride of palladium remains, an olive brown powder insoluble in 
 water. By a strong red heat this is totally decomposed. 
 
 Deutochloride of Palladium. PdCl 2 . Is formed when the chloride 
 of palladium is gently heated with aqua regia ; it forms a dark brown 
 liquor, which gives, with a solution of chloride of potassium, a 
 sparingly soluble double salt, KC1 + PdCl 2 . This deutochloride 
 cannot be obtained solid, its solution giving off chlorine, and chloride 
 remaining. 
 
 Iodide of Palladium. Pdl. Is a black powder obtained by double 
 decomposition. It forms double salts with other iodides. By heat it 
 is decomposed, without forming any subiodide. 
 
 Sulphate of Palladium. PdO.S0 3 . Is produced by dissolving the 
 metal in a mixture of nitric and sulphuric acids. By evaporation, a 
 saline mass is obtained, which is decomposed by water. 
 42 
 
C58 Salts of Platinum and Indium. 
 
 Nitrate of Palladium. PdO.N0 5 . Is obtained by acting on the 
 metal with nitric acid. At first it dissolves without any evolution of 
 gas, forming a deep olive liquor ; but when heated, it gives off, N0 2 , 
 and becomes brown. The nitrate of palladium is decomposed by water, 
 giving basic salts. 
 
 SALTS OF PLATINUM. 
 
 Protockloride of Platinum. Pt.Cl. Is formed by exposing the bi- 
 chloride in fine powder, to a temperature of about 500 in a porcelain 
 dish, and frequently stirring ; one-half of the chlorine being evolved, a 
 greenish olive powder is produced, which is the proto chloride. It is 
 insoluble in water ; by a red heat it is redissolved into chlorine and 
 metallic platinum. If the bichloride be exposed only to a temperature 
 of about 400, water dissolves from out of the resulting mass, a sub- 
 stance which colours it intensely brown, and which is, probably, a ses- 
 quichloride, Pt 2 Cl 3 . 
 
 Bichloride of Platinum. PtCl 2 . This salt is produced by dissolv- 
 ing platinum in nitro-muriatic acid. The solution, when free from ex- 
 cess of acid, is intensely yellow ; on evaporation, it gives a crystalline 
 deliquescent mass. This salt is very soluble in alcohol, and is so used 
 for the detection of potash (p. 474). It combines with other chlorides, 
 forming double salts, of which some possess considerable interest. 
 Those with chloride of potassium, KC1 + PtCl 2 , and with sal-ammoniac, 
 NH 4 C1 + PtCl 2 , are precipitated as yellow powders, from strong solu- 
 tions, or as minute octohedral orange-red crystals, from dilute solutions 
 of those alkalies, and are hence used for their detection. These salts 
 are insoluble in alcohol. The sodium double salt (NaCl + PtCl 2 ) is, on 
 the contrary, easily soluble both in alcohol and water. 
 
 The Iodides of Platinum are black powders, insoluble in water, 
 formed by the double decomposition of iodide of potassium with the 
 respective chlorides. The biniodide combines with iodide of potassium 
 to form a double salt, KI -f PtI 2 , which dissolves in water, giving a 
 solution so deeply claret-coloured that it may serve to detect a very 
 minute trace of platinum in solution. 
 
 Although many oxygen salts of platinum are described in the syste- 
 matic books (sulphate, nitrate, &c.,) I consider that we possess no accu- 
 rate knowledge whatsoever of that class of combinations. 
 
 SALTS OF IRIDIUM AND RHODIUM. 
 
 There are four chlorides of iridium. The protochloride, IrCl, is 
 prepared by heating metallic iridium to redness in chlorine; it is an 
 
Salts of Ruthenium and Rhodium. 659 
 
 olive-green body, which is insoluble in water, but combines with other 
 chlorides to form double salts. The sesqui-chloride, Ir 2 Q 3 , is formed 
 by dissolving the sesquioxide in muriatic acid. It is a brown crystal- 
 line substance, volatile, and forming double salts. The bichloride, 
 IrCk, is produced when a concentrated solution of the former is treated 
 with aqua regia. It forms a dark brown solution, giving, when dried, 
 a black mass. It gives with chloride of potassium a sparingly soluble 
 double salt in black octohedral crystals. The perchloride, IC1 3 , is not 
 known, except in the state of a double salt, KC1 + IC1 3 , which is 
 produced by processes, for which I refer to the larger systematic 
 works. 
 
 The protoxide, sesquioxide, and deutoxide of indium form salts, with 
 the oxygen acids ; the solutions of the first class being green or purple, 
 those of the second class blood-red, and those of the third orange, 
 produce the variety of tints which gives the name of iridium to the 
 metal ; they are not otherwise important. 
 
 Sesqui- Chloride of Rhodium. EaCla. Is prepared by decomposing 
 the double chloride of rhodium and potassium by hydrofluosilicic acid. 
 The filtered liquor gives, when evaporated, a brown-red mass, destitute 
 of crystalline structure ; by heat it is completely decomposed. It com- 
 bines with other chlorides to form well-defined double salts, such as 
 that, 2KC1 -f- E 2 C1 3 + 2Aq. formed by acting on metallic rhodium and 
 chloride of potassium by aqua regia. When metallic rhodium alone is 
 treated by chlorine, a rose-red powder is obtained insoluble in water 
 and acids, which is a similar compound of protochloride and sesqui- 
 chloride of rhodium, E 4 C1 5 = 2-BC1 + R1 3 . 
 
 By igniting metallic rhodium with bisulphate of potash a double salt 
 is obtained, which does not crystallize. The nitrate of rhodium is a 
 dark red deliquescent salt, which gives with nitrate of soda a double 
 salt in dark red crystals. 
 
 The characters of the salts of Ruthenium, so far as they are as yet 
 known, have been sufficiently described in the history of that metal 
 already given. 
 
660 
 
 CHAPTER XVI. 
 
 ON THE GENERAL PRINCIPLES OF THE CONSTITUTION OF 
 ORGANIC BODIES. 
 
 ORGANIC bodies are distinguished generally by a much greater com- 
 plexity of composition than occurs in substances of mineral origin. 
 Thus, so far as the principles described in the chapter on the Atomic 
 Theory allow of our concluding as to the absolute molecular constitu- 
 tion, it would appear that, except in the case of carbonic oxide, there is 
 no example of an atom of an organic compound containing but two simple 
 atoms ; and carbonic acid and cyanogen are the only examples of an 
 organic atom being formed by three elementary atoms. On the contrary, 
 the number of simple atoms entering into the composition of an organic 
 body is .sometimes very great : thus, an equivalent of oleic acid con- 
 tains 270 simple atoms ; an atom of albumen is formed of 883 simple 
 atoms ; an atom of spermaceti includes 468 simple atoms ; numbers 
 to which we find no form of combination approaching in inorganic 
 compounds. 
 
 Besides this greater complexity of constitution, organic bodies are 
 distinguished by the nature of their elements. I have had occasion 
 already to describe, as inorganic, sixty-one undecompounded bodies, 
 which, by their reunion in various proportions, generate the compound 
 substances, which constitute the mineral crust of the globe; but 
 amongst organic bodies we meet with few of these. Although equalling 
 in number and surpassing in variety of properties the mineral species, 
 the products of the animal and vegetable kingdom may be looked upon 
 as consisting almost exclusively of six elements, of which two, sulphur 
 and phosphorus, are met with but seldom ; nitrogen is much more ex- 
 tensively found, especially in animal substances ; oxygen and hydrogen 
 exist in almost all, but the element which is peculiarly organic, and 
 which, with the one exception of ammonia, exists in all bodies derived 
 from an animal or vegetable source is Carbon. It is hence that I have 
 deferred the description of carbon and its compounds, until I could 
 pass directly from it to the great variety of organic bodies of which it 
 
Elements of Organic Bodies. 661 
 
 is the basis. With the constituents of inorganic bodies it has but an 
 accidental connexion, for as I shall hereafter show, there is no form of 
 carbon which has not at some time made part of an organized being. 
 Besides these six elements of organic bodies, there are many which 
 enter into the structure of animals and plants, and are subservient in 
 an important degree to the proper performance of their functions, 
 without being really constituents of their organic tissues, or secretory 
 products. Thus iodine and bromine exist in many marine plants and 
 sponges; common salt and oxygen-salts of potash, soda, lime, and 
 magnesia exist in most animal and vegetable juices; phosphate of lime 
 constitutes the bony skeleton of one, and carbonate of lime the tes- 
 taceous covering of another tribe of animals, whilst silica forms the 
 solid basis of some of the lower tribes of zoophytes. In the red colour- 
 ing matter of the blood, iron is an essential element, and the same 
 metal has been found in minute quantity in other parts of animals ; 
 indications of fluorine and of silica have been found in the bones and 
 teeth; but in all these instances, except perhaps the one fact of the iron 
 element of red blood, we find these saline substances to be contained in 
 fluids in a condition of merely physical solution, or to be deposited as 
 solids in the bones or teeth in a purely inorganic form, clearly to be dis- 
 tinguished from the proper state of organic combination, in which the 
 carbon, hydrogen, oxygen, and nitrogen of the tissues and secretory pro- 
 ducts are united. 
 
 Amongst organic bodies, it is necessary to distinguish three classes, 
 which differ no less in complexity of composition than in the circum- 
 stances under which they are formed, and their relation to organic 
 life. These are, first, those bodies which are directly elements of an 
 organized and living being, and which, while in connexion with it, ap- 
 pear to possess the power of elaborating, from certain nutritious juices, 
 additional material similar to themselves. Such are the organic con- 
 stituents of the animal and vegetable tissues of the blood, which, while 
 in connexion with, and forming portions of the animal or plant, partici- 
 pate to a certain degree in its vitality, and do not obey the laws of ordi- 
 nary affinity, unless by being, in the first instance, killed ; these bodies 
 should be more properly called organized, than merely organic ; their 
 chemical relations commence only when they have been deprived of 
 their most essential character, life. They are organs ; their constitu- 
 tion cannot be expressed by formulse, nor their properties accounted 
 for by analysis, and the attempts which have been recently made by 
 some eminent chemists to embrace^ the constitution and relations of 
 those living organizations within the forms of expression of merely 
 chemical compounds, have led but to throw into confusion the most 
 
663 Organized and Organic Bodies. 
 
 interesting questions of physiology, and animal chemistry. After their 
 death we may obtain from them, by chemical treatment, a variety of 
 organic bodies ; but that they were composed of these bodies, and that 
 their properties resulted from the combination of such elements as we 
 extract from them, it would be false philosophy to imagine. The fibrine 
 and albumen of the blood, the muscles, and the cellular tissues, the 
 fatty matter of the brain, perform their functions in virtue of vital 
 power, and not of any chemical properties they possess. The albumen 
 of the egg is not a chemical substance, but a delicately constructed 
 mass, destined to be transmuted into the organs of the chick, and by 
 participating in its life, protected from putrefaction. But when albu- 
 men is precipitated by corrosive sublimate it is killed, and the product 
 of its decomposition combines with the oxide of mercury. 
 
 This class of bodies have their origin, therefore, in actions purely 
 vital. They have a structure organic-molecular, totally different from 
 crystallization, and for the most part consisting of minute cells. When 
 dead, these tissues undergo spontaneous decomposition, with more or 
 less rapidity, according as their composition is more complex ; but for 
 this, water must be present. Some forms of animal tissue, which 
 appear to lose the organized structure and vitality with which they were 
 at first formed, are capable still of remaining in connexion with the 
 living system, and, although dead, have no tendency to putrify ; 
 probably from not being in any degree soluble in water. The formation 
 and growth of nails and hoofs, hair and horns, are examples of the im- 
 portant uses of this property. 
 
 It is by virtue of the vital forces of the bodies of this first class, not 
 individually, but united together so as to constitute the tissues, 'glands, 
 &c., of plants and animals, that the organic bodies of the second class 
 have their origin. These are substances produced (secreted) from the 
 elements by which organized bodies are nourished, probably by the 
 union, under peculiar conditions, of such portions of the constituents 
 of the food as were not proper to be assimilated to the organized 
 tissues of the living being itself, or have already served their turn. 
 It is thus, that by a plant which uses water, carbonic acid, and atmo- 
 spheric air as nutriment, after the assimilation of a certain quantity of 
 their constituents to its proper tissues, sugar, starch, and albumen, adapted 
 for the nutrition of its young, may be formed as secreted products; and 
 oils, resins, colouring matters, &c., rejected as useless or worn out. 
 
 The third class of organic bodies contains those which are evolved 
 by the chemical decompositions, Blether spontaneous or artificial, to 
 which substances of the first and second class are subjected. Thus, 
 sugar by fermentation, yields alcohol and carbonic acid ; alcohol, by 
 
Possible Synthesis of Organic Bodies. 663 
 
 oxidation, yields acetic acid, or aldehyd ; acetic acid, variously treated, 
 produces acetone, or alkarsin ; whilst ligneous fibre gives origin, when 
 heated, to a crowd of organic products, of which pyroxylic spirit is an 
 example. 
 
 It is very interesting to contrast these classes of bodies with each 
 other, in relation to the forces by which their constitution is regulated, 
 as compared with the simple forms of affinity by which the actions of 
 inorganic elements are controlled. In the first, there is found nothing 
 referable to chemical attraction ; all affinity is annulled by the supre- 
 macy of life and organization. Hence, it is only when dead, that such 
 bodies can be analysed, and by treatment with re-agents a crowd of pro- 
 ducts belonging to the third class be obtained from the more or less 
 evident decomposition. No matter, therefore, how perfect our mediate 
 or immediate analyses of such substances may be, the synthesis of such 
 bodies, or their production by the union of their elements, is strictly 
 impossible to the chemist. The formation of a molecule of albumen 
 would not be a case of chemical combination, but of the formation of 
 a portion of an organized cell, it would require not merely the combi- 
 nation of its elements, but also that the compound should have life 
 imparted to it. 
 
 In relation, however, to the second and third classes, the circum- 
 stances are quite different ; although we cannot trace, precisely, the 
 force by which the organized tissues act in eliminating from a liquid of 
 uniform composition, such as the blood or sap, the various secretions 
 which constitute the second class ; yet the circumstances of their for- 
 mation admit of being examined, and already some insight has been 
 obtained, as to the way in which organic bodies may separate, or be 
 converted into others, without reference to the mere affinities of their 
 elements, by means of the influence that has been already described as 
 catalytic (p. 229, et seq.) ; in this way, the functions of organized 
 tissues may be imitated, and a true synthesis of organic bodies of the 
 second class may be effected. With the bodies of the third class we 
 find, also, that the circumstances of their formation are either purely 
 artificial, or capable of being easily imitated, and the reactions by which 
 they are evolved, although often catalytic, fall, in the majority of cases, 
 under the rules of ordinary affinity. In structure also, the bodies of 
 the second and third class range themselves with inorganic compounds ; 
 those which are solid may, for the most part, be obtained crystal- 
 lized, and the liquid substances possesses definite freezing and boiling 
 points. 
 
 Between such organic bodies and mineral substances, we find the 
 greatest similarity, not merely in their physical relations, but in chemical 
 
664 Theory of Compound 'Radicals. 
 
 properties also. The great classes of acids and bases exist, well marked, 
 among organic bodies, and in their combinations with each other, the 
 same principles of multiple, and equivalent combination are followed, 
 as hold for inorganic compounds. So perfect is the analogy of general 
 characters, that it has long been an object with chemists to unite, under 
 one principle, the laws of composition of organic and inorganic bodies, 
 and as the characteristic distinction of mineral substances is to consist 
 of a series of elements which are respectively combined, two and two, 
 in virtue of their opposite affinities, attempts have been made to reduce 
 the complex constitution of organic bodies to the same principle of 
 binary union, by supposing that certain of the elements are, in the 
 first instance, grouped together, so as to form a single molecule, and 
 that this acting as a simple body, combines with the element which re- 
 mains. It is from the discovery of Cyanogen, and the discussions as to 
 the nature of the ethers, and of the ammoniacal salts, that we must date 
 the positive introduction of this theory of compound radicals into 
 chemistry. Its utility has not been limited to the explanation of the 
 constitution of organic bodies ; on the contrary, it has been applied 
 successfully to explain the phenomena presented by numerous classes of 
 inorganic compounds, such as the compounds of sulphur and oxygen, 
 noticed p. 402, and especially to the foundation of the binary theory of 
 salts, as described in the fifteenth chapter. 
 
 Were we, however, to apply the theory of compound radicals indis- 
 criminately to explain the constitution of organic bodies, we should be 
 liable to fall into continual error. The criterion which I would assume 
 as decisive of the constitution of an organic body, is, whether certain 
 of its elements may be exchanged for others, in accordance with the 
 ordinary laws of substitution of inorganic bodies ; and thus a series of 
 compounds be produced, through which some elements of the original 
 substance shall have passed untouched, and from which again, by suit- 
 able reactions, the original substance can be obtained unaltered. In 
 such cases I would consider those elements which remain unaffected as 
 being strictly united with each other, and constituting a compound 
 radical, which, combining with other bodies, gives origin to a series of 
 compounds more or less extensive. Thus, if we treat oil of bitter 
 almonds, Ci 4 H 6 O 2 , by chlorine, we obtain a compound, C 14 H 5 O 2 C1, 
 which gives, with iodide, or sulphuret, of potassium, bodies whose for- 
 mulae are respectively C 14 H 5 O 2 I and C M H 5 O 2 S. Again acted on by 
 oxygen, it gives crystallized benzoic acid, Ci 4 H 6 O 4 ., or rather, C 14 H 5 O 3 
 -j- Aq. Now, it will be seen that throughout this whole series the 
 element, C 14 H 5 2 , has remained unaltered. In the oil it was combined 
 with hydrogen : in benzoic acid it unites with oxygen ; in the other 
 
Limits of Us Application. 665 
 
 bodies it is united with chlorine, iodine, &c., and from these the oil 
 may be recovered by processes by no means indirect. Now when we 
 state, that in these compounds the elements, C 14 H 5 O 2 , are united, first 
 with each other, by an affinity which ordinary reagents cannot over- 
 come, and that this compound group unites with the simple bodies, 
 hydrogen, oxygen, &c., by an affinity so much weaker, that they can 
 be readily substituted for each other, we state only an established fact, 
 and in denominating the group, C 14 H 5 O 2 , the root or radical of the 
 series of bodies thus produced, we involve no hypothetical idea. For 
 brevity, we express that compound radical by the symbol Bz, and we 
 term it Benzyle ; we write the formulae of its combinations respectively, 
 BzH, Bz.Cl, Bz.I, and BzO + Aq. 
 
 But we must not be induced by the brilliancy shed on certain branches 
 of organic chemistry, through the application of this principle, to 
 transgress the boundaries of sound induction. There are numerous 
 organic compounds in which I believe that no binary structure exists, 
 and consequently to which the theory of organic radicals should not be 
 applied. It is the class of bodies characterized by a remarkable indif- 
 ference to combination, and which, when decomposed by the influence 
 of re-agents, lose not merely one constituent, and gain another in its 
 place, but are totally transformed into new compounds, into which all 
 of their original components enter, and towards which the re-agent that 
 had been applied frequently appears indifferent,,, so that the action ap- 
 pears to have more the character of catalysis than of true chemical 
 affinity. Such bodies are gum, sugar, starch, some of the oily and 
 colouring matters, urea and many others ; treat these bodies as you 
 will, there are no phenomena of true replacement ; they may be decom- 
 posed, but bodies of a totally different type are formed, and the original 
 substances cannot be regenerated. 
 
 The organic radical which is thus assumed as the basis of a series of 
 compounds, acts as a simple body, but it does so only in relation to 
 the nature and intensity of the forces that act upon it ; it may be de- 
 composed, and frequently it cannot be separated from combination 
 without total decomposition ; hence few compound radicals can be iso- 
 lated. But they can be decomposed even whilst still in combination, 
 by the intervention of powerful affinities ; and this decomposition may 
 be either total, so as to leave no trace of the original constitution of the 
 substance, or by giving origin to another series of combinations, may 
 indicate a still more intimate constitution, and unveil an organic radical 
 of a simpler structure acting as the basis of the first. 
 
 Thus we have seen what positive grounds there are for admitting 
 benzyle, C I4 H 5 O2, to be the radical of the oil of bitter almonds and of 
 
666 Theory of Organic Adds. 
 
 benzole acid; but if we digest oil of bitter almonds with ammonia, all 
 oxygen is removed, and we obtain a compound of nitrogen with the 
 body, Ci 4 H 5 , which may also be obtained in other forms of combination. 
 Now this organic substance C 14 H 5 acts as the basis of benzyle, for the 
 oil of bitter almonds can be reproduced from it, and we thus obtain 
 evidence of three stages of constitution in benzoic acid, whose formula 
 should be written therefore as (C 14 .H 5 , + O 2 ) + O. The considerations 
 described in p. 402 point out a perfect analogy to this in the constitu- 
 tion of sulphuric acid. Reduced to its ultimate elements, its formula 
 is S0 3 , but powerful evidence shows, that its real basis is sulphurous 
 acid, and not sulphur ; its rational formula being S0 2 + 0. Now, 
 here the primary radical, C ]4 H 5 , corresponds to sulphur, and benzyle 
 to sulphurous acid. The total quantity of oxygen in such acids being 
 divided into two portions, differing in order and intensity of combina- 
 tion with the ultimate radical. If we add to these considerations, the 
 view of salt-radicals, and consider the salts of benzoic acid as expressed 
 by the formula Bz0 2 -f- M, as that of the sulphates has been shown to 
 be S0 2 .0 2 -f M, we observe even a fourth degree to which the mole- 
 cular structure of the complex organic radical may be traced. 
 
 It is indeed when applied to explain the constitution of the organic 
 acids, that the theory of compound radicals, as employed in the new 
 views of the constitution of oxygen salts, appears most interesting, as 
 the anomalies of properties and composition presented by the salts of 
 the organic acids, were more numerous and more extraordinary than 
 any which the mineral acids presented, and were indeed totally unin- 
 telligible until illustrated by the conjoined investigations of Dumas and 
 of Liebig. An example of this may easily be selected. Of the organic 
 acids, the majority are monobasic, but there are also many bibasic and 
 tribasic ; thus the citric acid, whose formula isCi 2 H 5 O H , combines with 
 three atoms of base ; the meconic acid, C J4 HO n , is also tribasic ; the 
 tartaric acid, C 8 H 4 O ]0 , and the mucic acid, C 12 H 8 O 14 , are bibasic. 
 In these instances, the quality of combining with many atoms of base, 
 which is so anomalous in the older view, necessarily follows from the 
 formula? of the hydrated acids, which become respectively, for citric 
 acid C 12 H 5 Oj 4 + H 3 , for meconic acid C 14 H0 14 + H 3 , for tartaric acid 
 C 8 H 4 12 + H 2 , and for mucic acid C 12 H 8 16 -f H 2 . By its means, 
 many other singular properties of organic acids are explained : thus 
 there appear to exist three acids, having absolutely the same composi- 
 tion of C 2 NO, viz., the cyanic, the fulminic, and the cyanuric acids ; 
 they are isomeric, they possess excessively different properties. Whence 
 has that difference its rise ? if we say that the cyanic acid contains 
 cyanogen ready formed, and that the others do not, it still remains to 
 
Constitution of Organic Radicals. 667 
 
 explain the isomerism of the others ; and we find that the cyanic and 
 cyanuric acids are transformed into each other by the slightest causes. 
 We obtain,, however, at once the key to this isomerism, when we study 
 the salts formed by these acids. The cyanic acid is monobasic, its 
 hydrate is C 2 NO + HO ; the fulminic acid is bibasic, its hydrate is 
 C 4 N 2 2 + 2 HO ; the cyanuric acid is tribasic, its formula is C 6 N 3 O 3 
 + 3HO. These acids are thus found to have different atomic weights ; 
 their molecular groups are ascertained to contain different numbers of 
 molecules, and hence to admit of totally distinct internal structure. 
 When expressed in formulse on the binary theory, we have C 2 ]SiO 2 +H, 
 for the cyanic, C 4 N 2 O 4 + H 2 for the fulminic, and 6 N 3 6 + H 3 , for 
 the cyanuric acid, and not merely the difference in nature of the acids, 
 but also the distinctive characters of their salts necessarily result. 
 
 Although chemists are unanimous in regarding the principle of com- 
 pound radicals as the basis of the philosophy of organic chemistry, yet 
 science has not yet arrived at the point when the principle is adopted 
 by all in the same form of detailed application. On the contrary, there 
 are few specific examples of that principle that are not still open to 
 discussion. The views of Berzelius on this subject are specially of im- 
 portance. He considers that the compound radicals of organic bodies 
 consist only of carbon and hydrogen, or of carbon and nitrogen : that 
 they never contain oxygen. Hence he does not admit the existence of 
 benzyle, in benzoic acid, or in oil of bitter almonds ; he considers the 
 only radical to be the carbo-hydrogen, C 14 H 5 , and benzoic acid to be 
 directly, C 14 H 5 + O 3 . He looks upon the oil of bitter almonds as con- 
 taining ready formed benzoic acid, combined with the true hydruret of 
 the radical, as 3 (C 14 H 6 O 2 ) = 2 (C 14 H 5 + O 3 ) + (C 14 H 5 + H 3 ). The 
 chloride of benzyle he looks upon as an oxychloride, 3 (C 14 H 5 2 C1) 
 being equal to 2 (G 14 H 5 + 3 ) + (C 14 H 5 + C1 3 ). This is evidently the 
 same difference of view that exists as to the nature of the sulphurous 
 acid compounds, which Berzelius also regards as more complex. Thus 
 the chlorosulphurous acid is, according to him, a compound of sul- 
 phuric acid with a terchloride of sulphur, 3 (SO 2 .C1) = 2.SO 3 + SC1 3 ; 
 and so in all other bodies similarly circumstanced. 
 
 The opinions of a man to whose extraordinary industry and genius 
 we owe some of the most important additions both theoretical and prac- 
 tical that science has received since the epoch of Lavoisier, should not 
 be rejected without much consideration ; but on applying these ideas 
 to express the constitution of the crowd of bodies, containing four or 
 five elements, which have recently been discovered, we are led to sup- 
 positions destitute of experimental proof, and yet which, assuming the 
 existence of numerous hypothetical bodies of anomalous constitution, 
 
668 Theory of Chemical Types. 
 
 and combined in very unusual ways, would require for their legitimate 
 admission into science, a very strong body of experimental evidence. 
 It would be impossible here to discuss the principles of his opinion in 
 detail ; I am led to conclude, from the consideration of the whole body 
 of facts which bear upon it, that it is inferior in power and simplicity 
 of explanation of known facts, and as an instrument of discovery, to 
 the simpler view of the constitution of organic bodies which has been 
 described ; and being thus deficient in all the important duties of a 
 sound theory, I do not hesitate to reject it. 
 
 The proposition of the theory of types, by Dumas (see p. 326), will 
 probably constitute an epoch in science, by fixing attention on the 
 permanent equivalency of an organic atom, notwithstanding complete 
 alteration in the nature of its elements. This did not follow necessarily 
 from the theory of compound radicals, nor does the conservation of 
 the type require that the radical be preserved unaltered, but only the 
 type of the radical. Thus, when aldehyd is changed into chloral, 
 (C 4 H 4 2 into C 4 HC1 3 2 ), the type is preserved, since the hydrogen is 
 replaced by an equivalent of chlorine ; the radical is altered, since 
 acetyl, C 4 H 3 , is changed into C 4 C1 3 , but the new radical is still con- 
 structed on the type of the original. The theory of types, so far from 
 being inconsistent with the theory of compound radicals, is in perfect 
 harmony with it, at least as I understand it, and as I believe it to have 
 been proposed by Dumas. The basis upon which it rests may be an- 
 nounced as follows. 
 
 1st. That the hydrogen of a compound radical may be replaced by 
 chlorine, or by oxygen, &c. equivalent for equivalent, and a new radical 
 thus produced, which being constructed on the same type as the original, 
 will have the same general laws of combination, and will hence form 
 compounds of the same type as those containing the original radical. 
 Thus, from C 4 H 3 may be formed C 4 C1 3 , and these, combining with oxy- 
 gen and water, form C 4 H 3 O. + Aq. or C 4 H 3 .03 + Aq. and C 4 Cl3. -f Aq. 
 or C 4 C1 3 .0 3 + Aq : also by uniting with chlorine they produce C 4 H3C1 
 and C 4 C1 3 .CL 
 
 2nd. That when bodies of the same type, and containing radicals of 
 the same type, are subjected to the action of strong affinities by which 
 their constitution is broken up, the resulting products are constituted 
 also upon the same plan, although differing in composition ; thus 
 C 4 H 4 4 , when heated with potash gives 2.C0 2 and C 2 H 4 ; and C 4 HC1 3 
 O 4 similarly treated gives 2.C0 2 and C 2 H.C1 3 . The types of C 2 H.H 3 and 
 C 2 H.C1 3 , being the same, and containing equivalent radicals. 
 
 3rd. When bodies of the same chemical, though of different me- 
 chanical types, or, as I would term them, bodies of the same natural 
 
General principles of Replacement of Elements. 669 
 
 families, as the alcohols, are submitted to the action of affinities of 
 equal power ; the bodies generated have the same relation to one another, 
 as the original bodies had ; and the radicals are either unchanged, or 
 all changed in a similar degree. Thus from wine-alcohol, (C^sCfe) ; 
 methylic alcohol (C 2 H 4 2 ) ; essential oil of potato spirit, C 10 H 12 O 2 , and 
 ethal, C 32 H 34 O 2 , there are produced by the action of potash, a series of 
 acids, each having the same type and containing the same radical as its 
 alcohol ; thus the acetic acid (C 4 H 4 4 ), the formic acid (C 2 H 2 4 ), the 
 valerianic acid (C 10 Hi 4 ), and the ethalic acid C 32 H 32 04. 
 
 Considering in this way, the theory of types is an important addition 
 to our ideas on the constitution of organic bodies. It serves to attach, 
 under a few very simple principles, numerous classes of compounds, 
 whose composition would otherwise appear very complex and anoma- 
 lous, and will probably, when applied to the study of such bodies as, 
 not containing compound radicals, give only their molecular group, as a 
 mass, to our examination, become a source of still more important ad- 
 ditions to our knowledge. 
 
 Although each organic substance gives, when acted on by reagents, 
 products which are characteristic of, and often peculiar to itself, yet 
 there are some general rules which being now noticed, will obviate the 
 necessity of much detail hereafter. 
 
 When an organic substance is treated with dry chlorine, it either com- 
 bines directly with the gas, or, as more frequently happens, hydrogen is 
 removed to an amount equivalent to that of the chlorine absorbed. 
 Even in the first case, the direct union is often but apparent, and arises 
 from the muriatic acid formed, combining with the true product. Thus 
 olefiant gas, C 4 H 4 , gives the oily liquid, C 4 H 4 C1 2 , but this, in place of 
 being a direct combination, consists of C 4 H 3 .C1, which is the true pro- 
 duct formed by substitution of Cl for H, but is united with the H.C1 
 thus generated. 
 
 If water be present, it influences the reaction very much, being gene- 
 rally decomposed. In some cases, all the chlorine unites with its hydro- 
 gen, whilst the oxygen combines with the organic substance; but, 
 generally, the chlorine unites with both elements of the water, forming 
 muriatic acids, which remains free, and hypochlorous or chlorous acids 
 which enter into the composition of the organic product. In other 
 cases, again, the presence of water does not appear to exercise any 
 influence. 
 
 When an organic substance is treated with nitric acid, it is always 
 raised to a higher degree of oxidation. Very rarely does the action 
 stop there. Hydrogen is usually separated, and oxygen put in its 
 place; whilst the new products formed contain usually a smaller 
 
670 Action of He-agents on Organic Compounds. 
 
 number of molecules than the original substance. Thus gum (Ci 2 H 10 
 O 10 ), when acted on by nitric acid, gives, first by simple oxidation, 
 mucic acid (C 12 H 10 Oi 6 ) : but, if the action of the acid be more violent, 
 all hydrogen is removed, and two atoms of oxygen substituted, thus 
 producing C 12 O 18 , the elements of six atoms of oxalic acid. 
 
 In many cases the action of nitric acid is not limited to the oxida- 
 tion, whether direct or indirect, of the organic substances, but, by the 
 removal of some hydrogen from it, in combination with some of the 
 oxygen of the nitric acid, water is formed, and the nitrogen, or nitric 
 oxide, or nitrous acid, combines with the remaining organic elements, 
 and forms new products. Thus, from napthaline and benzine, nume- 
 rous substances containing nitrogen are derived. This fixation of 
 nitrogen may occur even with .bodies which already contain it, thus, 
 indigo treated with nitric acid produces bodies, the indigotic and the 
 picric acids, which contain a larger proportion of nitrogen than the 
 indigo itself. 
 
 The peroxides of manganese and lead often serve to oxidize organic 
 bodies in a more regulated manner than nitric acid ; the new substance 
 combining with the protoxide of the metal ; thus, by PbO i? uric acid is 
 decomposed into allantoin, urea, and oxalic acid. 
 
 By fusion with hydrate of potash, the oxidizement of organic sub- 
 stances is very powerfully effected ; water being decomposed, its hydro- 
 gen evolved, and the oxygen uniting with the organic body to form an 
 acid, which remains combined with the potash. Thus, alcohol 
 C 4 H 6 2 and 2HO, produce acetic acid, C 4 H 4 4 , and H 4 becomes free. 
 Often the organic substance is merely broken up into other bodies of 
 simpler constitution, as when tartaric acid, C 8 H 4 10 , by fusion with 
 potash, is decomposed into acetic acid, C 4 H 4 O 4 , and oxalic acid, 
 2(C 2 3 ). In every case, if the temperature be much raised, carbonic 
 acid is one of the products ; thus acetic acid (C 4 H 4 O 4 ) separates into 
 C 4 H 4 and 2.C0 2 . 
 
 The action of sulphuric acid upon organic bodies may be very diffe- 
 rent, according to circumstances ; thus, from starch we may obtain, by 
 a merely catalytic influence, gum, grape-sugar, and ultimately sacchul- 
 mine. In these cases, the sulphuric acid remains totally unchanged 
 and free, but generally it enters into combination with the organic 
 body ; either without decomposition, as in the sulphovinic and sulpho- 
 methylic acids ; or else water is formed by its reaction on the organic 
 body, which, thus deprived of an atom of hydrogen, combines with 
 hyposulphuric acid, S 2 O 5 . It is thus that the sulphurous element exists 
 in the sulphobenzoic acid, the isethionic acids, &c. 
 
 If an organic substance containing nitrogen be acted on by these 
 
Organic Origin of Carbon. 671 
 
 re-agents, at a high temperature, this is generally separated under the 
 form of ammonia; water being decomposed, and its hydrogen so 
 applied, whilst its oxygen forms the ordinary oxidized organic pro- 
 ducts. If potash be the re-agent, the ammonia is expelled, and a salt of 
 potash with the new organic acid remains ; if sulphuric acid be the 
 re-agent, the organic acid is set free, and a sulphate of ammonia 
 remains. 
 
 By the action of heat upon fixed organic compounds, a variety of 
 products are formed, which may generally be described as formed by the 
 abstraction of a portion of carbon and oxygen, as carbonic acid, and of 
 hydrogen and oxygen as water. Hence such pyrogenic products are 
 always richer in hydrogen and carbon than the bodies they are formed 
 from, and of less acid characters. This kind of decomposition will, 
 however, require to be described in a distinct chapter. 
 
 CHAPTEE XYIL 
 
 OF CARBON AND ITS COMPOUNDS WITH OXYGEN, SULPHITE, AND 
 
 CHLORINE. 
 
 CARBON exists in large quantities and is very extensively distributed in 
 nature, as a constituent of all vegetable and animal bodies. It is found 
 also in the mineral kingdom, under forms, however, which may be 
 shown to have originally been derived from organic bodies. Thus, the 
 different varieties of coal have been produced by the aggregation of 
 great quantities of wood, the materials of primeval forests, which being 
 submerged in water, and covered by the gradually deposited layers of 
 sand and mud, have been elevated, in connexion with the strata of 
 clay and sandstone so produced, to their present situations. The wood 
 thus circumstanced has undergone a kind of decomposition, which shall 
 be hereafter fully noticed, and the mixture of fixed and volatile organic 
 products which constitute our coal has thus its origin. This formation 
 
672 Nature of Limestone Eoch. 
 
 of coal, as well as the formation of peat and turf at the present day, 
 almost at the surface, is accompanied by a disengagement of carbonic 
 acid in large quantity, and hence the probable source, in the air and in 
 mineral waters of that substance, of which also much may be derived 
 from the respiration of animals. 
 
 A more strictly mineral form of carbon is that of carbonic acid united 
 to lime, and to other metallic oxides, forming the numerous class of 
 native carbonates. Of these the most abundant is the carbonate of 
 lime, which, under the form of chalk, oolite, coral, mountain lime- 
 stone, &c., constitutes a large proportion of the geological formations 
 of our globe. In all these cases, the rock is formed of shells of ani- 
 mals, aggregated together in great masses ; these geological formations, 
 resulting from the collection, at the bottom of a sea or lake, of the 
 spoils of myriads of generations of those animals, which, by superin- 
 cumbent pressure, may be more or less densely aggregated; or by 
 proximity of igneous rocks, may be partially or completely fused, and 
 their organic characters obliterated to a greater or less degree. In this 
 way the crystalline marbles are formed, in which few or no traces of 
 organic origin remain. The comparatively small quantity of carbonate 
 of lime, which is found separately or distinctly crystalline, either as 
 arragonite or calc spar, may be traced to the solvent action of water 
 impregnated with carbonic acid, filtering through strata containing 
 shells, and then gradually depositing, in favourable situations, the 
 matter it had thus taken up, in crystals, the form of which depends 
 upon the temperature at which they are produced (p. 316). The other 
 native carbonates, of which the quantity is very small in comparison 
 with that of the carbonate of lime, may have been produced by double 
 decomposition. Thus, a water, holding carbonate of lime in solution, 
 filtering across a stratum containing oxidized iron or copper pyrites, 
 would give origin on the spot to a crystalline deposit of sulphate of 
 lime, and, at a certain distance, carbonate of iron or of copper* would 
 be separated. Those instances suffice to point out the reasons for con- 
 sidering carbon as truly the organic element, and that its appearance in 
 a mineralized condition arises from secondary actions. 
 
 Carbon presents itself in a great variety of forms. Absolutely 
 pure, it constitutes the diamond, which, from its exceeding hardness, 
 brilliancy, and rarity, ranks as the first of gems. It is found disse- 
 minated in alluvial strata in Golconda, Brazil, &c., and is separated 
 from the sand and mud by processes of washing. No deposition of 
 diamond in rocks has ever yet been found. It crystallizes in forms of the 
 regular system, generally having a great number of sides, bounded by 
 curved edges, in virtue of which it splits glass like a wedge, in place of 
 
Nature and Origin of Diamond and Plumbago. 673 
 
 scratching it as a file. Its crystals are generally hemihedral, and fre- 
 quently rough and discoloured at the surface. These crystals all cleave 
 parallel to the faces of a regular octohedron (fig. f, p. 24), but the 
 properties of the diamond separate it completely from the proper mineral 
 crystals of the regular system. Thus, it possesses double refraction in 
 some cases ; it polarizes light elliptically ; its structure has been found 
 by Brewster to consist in layers, sometimes containing cavities, indi- 
 cating that the crystal had been originally soft, and only concreted by 
 degrees ; and in the recent researches of Dumas, on the atomic weight 
 of carbon, it was found that when burned, diamonds generally leave 
 behind a minute skeleton of inorganic matter. These considerations 
 fully show, that the diamond derives its origin from the decomposition 
 of organic matter. The diamond is the hardest body known; it cuts 
 every other, and can be ground only by means of its own powder. It 
 is usually colourless, but sometimes brown, or rose-coloured ; its re- 
 fractive power is very great (2 '43 9), whence its great brilliancy. It 
 conducts heat and electricity very badly ; it resists most chemical agents, 
 but burns in melted nitre brilliantly, forming carbonate of potash; it 
 burns also when heated to redness in oxygen gas, and evolves sufficient 
 heat to maintain the continuance of the combustion ; its specific gravity 
 is about 3'5. 
 
 Another very remarkable form of carbon is that of plumbago, or 
 graphite. This is found in many localities, but sufficiently pure for the 
 purposes of the arts, only in Borrowdale in Cumberland. It is perfectly 
 opaque ; crystallized in rhombohedrons, or six-sided tables ; but its 
 usual appearance is in brilliant leaves or spangles. As a mass it is soft 
 and unctuous to the touch, and gives, on paper, a continuous grey 
 streak, whence its name of blacklead, and its use in making pencils. 
 Its formation appears to be connected with the action of iron, and 
 with a high temperature : it is found only in igneous rocks, as granite, 
 and mica slate, and contains almost always a large quantity of iron 
 intermixed in the metallic state, so that it was once supposed to be a 
 carbonate of iron. Graphite may be formed artificially, by adding 
 charcoal to melted cast iron ; the charcoal dissolves largely, but on 
 cooling, is found to separate in brilliant flexible plates, more or less 
 regularly six-sided. Graphite is lighter than diamond ; its specific gra- 
 vity being 2'5, and it conducts heat and electricity much better. It is 
 very hard to set on fire, and does not continue to burn unless heat be 
 applied from without. 
 
 Carbon, in a form more or less mixed with foreign matters, is ob- 
 tained by the application of a very high temperature to animal or vege- 
 table substances, in close vessels. The kinds of carbon thus produced 
 43 
 
Manufacture of Coke and Charcoal. 
 
 still differ very much. Thus coke is obtained by heating coal in iron 
 retorts, until all the volatile products are driven off, and the excess of 
 carbon remains mixed with the earthy matter which all coal contains. 
 The properties of coke approximate more or less to those of graphite, 
 according to the temperature at which it has been produced, but its 
 particles are frequently found so hard, and in structure so closely resem- 
 bling the diamond, as to be capable of not merely scratching glass, but 
 of being used in splitting and cutting glass, in place of the diamond 
 alone hitherto employed. By, the proximity of igneous rocks to coal, 
 under the earth, a similar expulsion of its volatile matters may be effec- 
 ted, and a form of carbon nearly pure, antfiracite, results. These fuels 
 are difficult to light, but when once ignited, give out an intense heat by 
 their combustion. 
 
 If an organic substance, which contains hydrogen and carbon, be set 
 on fire, and that there be a copious supply of air, it is totally converted 
 into water and carbonic acid ; but if the supply of air be limited, the 
 affinity of the hydrogen for the oxygen preponderates, and no carbon is 
 consumed until all hydrogen is converted into water. By this method 
 of imperfect combustion, several forms of carbon are prepared, such as 
 wood-charcoal and lampblack. If we take a splinter of wood and set 
 it on fire, we observe that at first only the volatile products of the wood 
 burn with flame, and that a mass of charcoal forms inside, and remains 
 unaltered as long as, being surrounded by flame, it is protected from 
 the air ; but when the end projects beyond the flame, it ignites, and 
 burns away, leaving only a trifling ash. If, however, a tube be taken, 
 and as in the figure, as the combustion, advances along the stick b, 
 the burned portion a be gradually plunged into a narrow tube, 
 this becomes filled with carbonic acid, which does not support 
 combustion, and the cylinder of the charcoal formed may thus 
 be permanently preserved ; on this principle wood-charcoal is 
 prepared. Billets of wood are heaped together regularly, so 
 as to form a hemispherical mass of about forty feet diameter ; 
 in the centre a hole reaches from the top to the bottom, form- 
 ing a chimney. The outside is then coated with sods, so as to 
 render it impervious to air, except at the bottom, where some 
 apertures are left. Burning charcoal is then thrown into the chimney, 
 and the fire communicating to the billets, these burn with a supply of 
 air so limited, that the charcoal remains unconsumed ; the combustion 
 commencing at the top and proceeding down. The outside of the heap 
 is then covered with denser sods, so as to cut off the supply of air as 
 the combustion proceeds. When the carbonization has been completed, 
 the whole mass is covered up and allowed to cool perfectly before being 
 
Manufacture of Lampblack. 675 
 
 opened. In this co urn try, most of the charcoal used is obtained in the 
 preparation of vinegar by the destructive distillation of wood, as will 
 be hereafter noticed. The quantity of charcoal produced from wood 
 varies very much with the rapidity of the process ; the generality of 
 fresh woods yielding but thirteen or fourteen per cent, by a rapid de- 
 composition, whilst when slowly charred they may yield twenty-five or 
 twenty-six. The mode of conducting the process, therefore, must be 
 changed according as the residual charcoal, or the volatile materials, are 
 the most valuable products. The charcoal preserves, in a remarkable 
 manner, the structure of the wood from which it is produced, so that 
 by the microscope some of the most delicate forms of vegetable organi- 
 zation may be traced in charcoal that had been slowly prepared. 
 
 Lampblack is formed by a still more direct application of the princi- 
 ple of imperfect combustion. In the apparatus represented in the 
 figure, a is a pot placed in a furnace which is 
 vaulted over, so that all vapour from it may pass 
 into the chamber, b, c, whilst by some apertures 
 a small quantity of air is allowed to sweep over 
 its surface ; the sides of the round chamber are 
 lined with leather, and, above, is a conical cover 
 of coarse linen, d, through which the draught 
 from the furnace passses, and which may be 
 lowered or raised by the cord and pulley. A 
 quantity of pitch or tar is placed in the pot and 
 made to boil ; it takes fire, and as the quantity of air which has access 
 to it is very small, the hydrogen alone burns, and the carbon being 
 carried up by the current in a very finely divided state, is deposited on 
 the sides and cover as an impalpable powder. 
 
 Animal charcoal is produced by the decomposition of animal matters 
 in close vessels. From its properties, which I shall just now notice, it 
 is manufactured in large quantities for the arts, especially from bones, 
 and is hence called, ivory -black or lone-black. The bones are placed in 
 iron cylinders, which are arranged, vertically or horizontally in a fur- 
 nace, in connexion with a series of condensing vessels containing water 
 the volatile constituents of the animal matter being expelled principally 
 as carbonate of ammonia, of which a large quantity is thus made, the 
 excess of carbon remains in a state of very minute division mixed with 
 the earth of bones (phosphate of lime). 
 
 Some of the most important uses of carbon are founded on proper- 
 ties, which the various forms of it possess in different degrees. Its 
 inflammability varies with its density and closeness of aggregation 
 being least in graphite, and becoming so great when wood charcoal, 
 
676 
 
 Combination of Charcoal with Colouring Matters. 
 
 prepared at a low temperature, has been reduced to powder for the pre- 
 paration of gunpowder, as to inflame sometimes spontaneously and give 
 rise to destructive accidents. Carbon possesses a remarkable tendency 
 to unite with colouring and odorous substances. This property is 
 specially possessed by ivory black, in consequence of the extreme degree 
 of division of its particles. When a purely organic body yields carbon, 
 the molecules of the latter aggregate themselves to a degree which de- 
 pends on the temperature, and if, as in wood, there be a fusible ash 
 present, this acts as a cement, and diminishes the porosity very much. 
 If the organic substance be fusible, as starch or sugar, the closeness of 
 texture of the charcoal becomes still greater, and its utility less ; but in 
 bones, the molecules of organic matter are separated by an infusible 
 earthy salt, and when carbonized, the charcoal is obtained in the 
 greatest possible state of comminution. A still more efficient charcoal 
 is formed by calcining dried blood, hoofs, or horns, with carbonate of 
 potash, which prevents the aggregation of the particles of carbon, 
 which, the alkaline salt being washed out with water, is left in the most 
 active condition possible. In the arts this property is applied to the 
 purification of sugar ; to clearing solutions of many organic substances ; 
 and barrels, in which water is to be kept, are charred on the insides in 
 order to remove any organic matter dissolved in the water, which might 
 be liable to putrefy. 
 
 The following table contains some numerical results of the relative 
 decolorizing power of equal quantities of carbon in various forms ; the 
 first column containing the number expressing the power of removing 
 the colour of a solution of indigo, and the second column that of a 
 solution of coarse sugar. The power of ivory black is taken as the 
 standard : 
 
 Kinds of Charcoal. 
 
 Indigo. 
 
 Sugar. 
 
 Common ivory black 
 
 1 
 
 1 
 
 Well ignited lampblack 
 
 4 
 
 
 Lampblack ignited with potashes . / 
 
 17 
 
 10 
 
 Charcoal from the decomposition of acetate of lead 
 
 5-6 
 
 4.4 
 
 Starch ignited with potashes 
 Blood ignited with phosphate of lime 
 
 11-9 
 11-9 
 
 8-9 
 10 
 
 Ivory black digested in muriatic acid 
 
 1-9 
 
 1-7 
 
 Ivory black digested in muriatic acid, and afterwards 
 
 
 
 ignited with potashes 
 
 45-3 
 
 20 
 
 Blood ignited with potashes 
 
 50 
 
 20 
 
 The decolorizing power is thus not the same for all bodies. If char- 
 coal that had once been used be again ignited, it does not recover its 
 
Absorption of Gases by Charcoal. 677 
 
 activity, as the colouring matter fuses before charring and thereby 
 lessens its porosity. Charcoal possesses also a remarkable power of 
 absorbing gases. If a fragment of wood charcoal, which had been 
 strongly heated, and allowed to cool without access of air, be intro- 
 duced into a tube containing ammonical gas, in the mercurial pneu- 
 matic trough, an immediate absorption occurs, to the amount of ninety 
 times the volume of the charcoal. In other cases the absorption is 
 not so great, a cubic inch of boxwood charcoal, which is the most 
 active, absorbing 
 
 90 cubic inches of ammonia. 
 85 muriatic acid. 
 
 65 ,, sulphurous acid. 
 
 55 ,, sulphuretted hy- 
 
 drogen. 
 35 ,, olefiant gas. 
 
 40 cubic inches of nitrous oxide. 
 35 ,, carbonic acid. 
 
 9-25 ,, oxygen. 
 
 7*5 nitrogen. 
 
 1'75 hydrogen. 
 
 These gases in this absorption undergo no chemical change, but ap- 
 pear to be retained on the surface of the pores of the charcoal by 
 powerful cohesion, and probably in the liquid form, as it is such gases 
 as may be rendered liquid by pressure that are absorbed in larger 
 quantity. 
 
 The number expressing the atomic weight of carbon is only lately 
 exactly fixed. By Drs. Prout and Thompson it was fixed at seventy-five 
 upon the oxygen, and six upon the hydrogen scale ; but the investi- 
 gation of Berzelius andDulong induced the majority of chemists to assume 
 a higher number, 76*4, or 6' L3. The latest experiments of Dumas and 
 Stass directed to the determination of this point, induced those eminent 
 chemists to recur to the original number 75 ; whilst Liebig and Eed- 
 tenbacher have deduced from their researches, the number 75 '8. Dr. 
 Clarke, from a re-examination of Berzelius' results, finds that they give, 
 when corrected for some minute sources of error, 7 5 '6, but the very 
 careful researches by Marchand and Erdman have fully verified the 
 results obtained by Dumas, and therefore I shall assume as the number 
 expressing the equivalent of carbon, 75 upon the oxygen, and 6'0 upon 
 the hydrogen scale. 
 
 If we admitted the truth of Dulong and Petit's law, (pp. 83, 296), 
 connecting the specific heats with the atomic weights of bodies, we 
 should consider the equivalent of carbon to be double that above given, 
 as Eegnault has found the specific heat to be 0'241. This idea 
 appears favoured by the fact, that it is doubtful whether there really 
 exists a combination of carbon, containing an odd number of equiva- 
 lents, taking the number as 6-0. But the force of this result is totally 
 
678 Method of Organic Analysis. 
 
 obviated by the fact, that the specific heat of carbon varies with its 
 state of aggregation so much, that for poplar charcoal it is 0'296, and 
 for diamond but 0'147 ; hence we cannot connect these numbers with 
 the chemical equivalent of the body. 
 
 Notwithstanding that carbon is absolutely infusible and fixed, yet 
 from the variety of gaseous and volatile compounds into which it enters, 
 and whose constitution is remarkably illustrated by the application of 
 the theory of volumes, carbon vapour is frequently spoken of by che- 
 mists, although its existence is purely hypothetical. I have mentioned 
 (p. 291) the difference of opinion as to its sp. gr. which I assume at 
 843. The new results would appear to show, that it is really but 836' 8 
 upon the one, or 418*4 upon the other view. 
 
 GENERAL PRINCIPLES OF ORGANIC ANALYSIS. 
 
 Substances which contain much carbon are, in general, easily recog- 
 nized, by their being more or less combustible and forming carbonic 
 acid when burned, besides often leaving a carbonaceous residue. 
 Even where the bodies are not inflammable, simply, they deflagrate 
 more or less violently when heated with nitre, and form carbonate of 
 potash. 
 
 Although it is not within the scope of the present work to embrace 
 the details of chemical analysis, it would yet be improper to omit a 
 general description of the methods adopted for the determination of 
 the quantities of carbon, hydrogen and nitrogen, which enter into the 
 constitution of organic bodies. The general principle upon which this 
 process is carried out, consists in supplying oxygen so abundantly to 
 the organic substance, as that all its carbon shall be converted into 
 carbonic acid, and all its hydrogen into water, and yet the supply of 
 oxygen shall be so graduated, and the decomposition so regularly pro- 
 gressive, as to admit of the products being collected with accuracy. 
 The nitrogen is always determined by an independent operation, in 
 which the other elements are neglected : and although processes have 
 been proposed, which provided for a direct valuation of the oxygen, it 
 is found in practice better to obtain its value, by subtracting the weight 
 of all the other constituents from that of the substance employed. Tor 
 the analysis of an organic substance, there are therefore two processes ; 
 the first to determine the carbon and hydrogen, and the second to 
 determine the amount of nitrogen. 
 
 The substance generally used to supply oxygen is the black oxide of 
 copper, prepared by gently igniting the nitrate. Sometimes chromate 
 
Analysis of Organic Bodies. 679 
 
 of lead is employed, particularly for bodies rich in chlorine. Where 
 the substance to be analyzed burns with difficulty, it is often neces- 
 sary, in order to be certain of the complete combustion of the car- 
 bon, to pass a stream of oxygen gas over it at the termination of the 
 process. 
 
 A straight tube of hard Bohemian glass of about sixteen inches 
 long, and from \ to \ inch diameter, is to be drawn out at one end to 
 a point, which is to be sealed and turned up, as in the figure. Some 
 
 oxide of copper (or chromate of lead, as the case may be) is to be then 
 poured in so as to occupy about two inches of the tube next the 
 bottom. As much oxide of copper as will occupy about six inches of 
 the tube is to be then intimately mixed with the substance to be ana- 
 lyzed, if it be solid, by rubbing in a mortar, and this mixture then intro- 
 duced. The mortar is next to be rinsed out with as much oxide of 
 copper as will fill two or three inches, and, finally, pure oxide of copper 
 is to be placed for about three inches in front of all. The whole mate- 
 rials thus introduced will occupy about fourteen inches of the tube, 
 when it is shaken down by tapping it, nearly horizontally on the edge 
 of a table, so as to leave, as in the figure, where the dotted lines mark 
 the spaces of the several portions, a free passage above the materials 
 from end to end of the tube. In these operations the greatest care 
 must be taken to avoid all access of moisture ; the tube, the mortar, 
 and the substance, must be made absolutely dry, and the oxide of 
 copper, being powerfully hygroscopic, should be ignited before each 
 operation, and allowed to cool, under a bell glass with a capsule of oil 
 of vitriol, or by being placed whilst very hot in a long dry tube, which 
 is then to be corked completely tight. After the substance and oxide 
 of copper have been placed in the tube, it is generally necessary to 
 remove even the traces of damp which might have been absorbed, by 
 exposure to the air, during the mixing in the mortar. This is done by 
 means of a small exhausting syringe, which is attached to the combus- 
 tion tube by a cork, a tube containing fused chloride of calcium being 
 interposed. The combustion tube is bedded in warm sand, and by 
 means of the syringe, the damp air it contains is withdrawn, and re- 
 placed by air which passing over the chloride of calcium becomes com- 
 pletely dry. After a few repetitions of this process all moisture is re- 
 moved, and the combustion tube is ready to be attached to the other 
 parts of the apparatus. 
 
680 Processes of Organic Analysis. 
 
 These are, 1st, a tube of the form represented in the figure, into 
 
 which a little cotton wool is dropped at a, and it is then filled with 
 recently fused chloride of calcium in fragments of the size of a split 
 pea. At b a little cotton wool is also placed, and a small tube is con- 
 nected with it by a cork. To its smaller end, a cork is adapted, which 
 accurately fits the end of the combustion tube, and which has been 
 carefully dried. This apparatus (but without the last cork) is carefully 
 weighed before the operation. 
 
 The 2nd apparatus is the potash bulb-tube, the inven- 
 tion of which by Liebig was the great cause of the rapid 
 progress of organic chemistry within the last few years, as 
 it facilitated the analysis of organic bodies in a remarkable 
 degree. It consists of a tube on which are blown five 
 bulbs ; the three interior communicating by pretty wide openings, but 
 each outer bulb separated from the others by a couple of inches of 
 tube. The relative proportions of the respective bulbs may be col- 
 lected from the figure, which represents also the form into which the 
 tube is bent. The three central bulbs are to be nearly filled with a 
 strong solution of caustic potash (sp. gr. 1'27), and the apparatus 
 attached to the small tube I, of the water tube by a caoutchouc con- 
 nector tied very carefully on. It is to be allowed to incline, at the 
 angle represented in the next figure, so that the carbonic acid gas, when 
 passing through it, shall bubble from bulb to bulb, without any danger 
 of expelling any portion of the liquor. 
 
 The combustion tube is to be placed in a sheet iron furnace, the 
 form and size of which may be collected from the figure, its open end 
 
 so far projecting (1J inch) as that the cork by which the water tube is 
 attached shall not be in any danger of being charred, but yet shall be 
 so hot, that no water can condense upon it. The joinings being found 
 to be completely tight, and the water tube and potash bulbs being 
 attached, and arranged as in the figure, the analysis may be proceeded 
 
Collection of the Water and Carbonic Acid. 681 
 
 with. Some ignited charcoal is to be placed round the first three 
 inches of the tube, and when the pure oxide of copper is completely 
 red-hot, the next portion, which, having rinsed out the mortar, con- 
 tains some traces of the organic substance, is to be similarly ignited. 
 The hydrogen of the substance reduces the oxide of copper, and forms 
 water, which is collected by the chloride of calcium in the water tube, 
 and the carbon also reducing the oxide of copper is converted into 
 carbonic acid, which being dried in passing over the chloride of calcium 
 is totally absorbed by the potash in the bulbs. By the addition of 
 burning charcoal, the combustion of the organic matter is made to 
 progress down the tube, the operator being directed in his proceedings 
 by the rate at which the evolution of carbonic acid, and its absorption, 
 proceed, until he arrives within two inches of the end of the tube. 
 He then stops until he has made the point and the pure oxide of copper 
 near it red hot, and then closes in the charcoal on the remaining space. 
 
 The combustion being thus completed, the tube remains, however, 
 occupied by a mixture of watery vapour and carbonic acid, which must 
 not be lost ; for this the point of the tube serves. It is broken with a 
 nippers, and then a current of air is gently sucked, by means of a tube 
 fitted to the potash bulb-tube, through the whole apparatus ; this car- 
 ries the water vapour to the water tube, and the carbonic acid to the 
 potash, so that all the products of the combustion are obtained. The 
 apparatus is then taken asunder, and the potash tube and water tube 
 weighed, the increase of weight gives of course the quantities of car- 
 bonic acid and of water collected, and hence, by simple calculation, the 
 proportions of carbon and hydrogen, contained in the quantity of sub- 
 stance that had been operated on. 
 
 If the substance had been one very difficult to burn, and hence re- 
 quiring oxygen to finish its combustion, the tube is not drawn out at 
 the end, but widened a little so as to form a small bulb in which some 
 chlorate of potash is placed. At the end of the process, this being 
 heated evolves oxygen, which not only burns any traces of carbon that 
 might remain, but serves also to carry the carbonic acid and vapour 
 fully into the water tube and bulbs. 
 
 There are a variety of circumstances to be attended to in this opera- 
 tion, in order to obtain the high degree of accuracy which alone confers 
 value on numerical results. These can be learned only in the laboratory, 
 and not even from the most detailed description. My object is merely 
 to afford an idea of the general principles of the method. 
 
 If the substance to be analysed be liquid 
 and volatile, it is introduced into small bulbs 
 of the size of the figure, by the method given 
 
 o 
 
682 Analysis of Volatile Liquids. 
 
 in page 14. There are generally two of these bulbs, one placed about 
 two and the other about six inches from the sealed end of the tube, as 
 
 
 shown in the figure ; the little stem is broken across in the act of 
 introducing them, so that the liquid may easily flow out, when, by the 
 approach of a piece of red hot charcoal, it is gently heated so as to 
 form vapour. The peculiar precautions necessary in the management 
 of the analysis of such bodies, and the methods adopted for non- 
 volatile liquids, and other bodies of peculiar properties, can only bo 
 learned by experience, and do not fall within my purpose to describe. 
 
 For the determination of the nitrogen of an organic substance, 
 several processes have been proposed, of which the most advantageous 
 are those invented by Dumas and by Will. According to the former, 
 a long combustion tube is taken (2 or 2*5 feet), sealed at one end, but 
 not drawn out, as in the figure. Next the sealed end is placed carbo- 
 
 ;/ 1 I L_1J 
 
 nate of copper, for a space of six or eight inches, and then the pure 
 oxide of copper, the mixture, the rinsing of the mortar, and again, 
 pure oxide, occupying fourteen or fifteen inches, exactly as in the 
 former case ; in front of all five or six inches are occupied by clean 
 metallic copper, in a finely divided state, either as reduced by hydrogen 
 from the oxide, or as very thin turnings. These divisions and the 
 general form of the tube are given by the figure. To the combustion 
 tube there is fitted by a tight cork, a quill tube, which is in connexion 
 on the one hand with an exhausting syringe, and then, by a vertical 
 tube more than thirty inches long, passes to the mercurial pneumatic 
 trough. All the joinings being found tight, and the combustion tube 
 arranged in the furnace, red hot charcoal is applied to the closed end 
 of the tube, where it disengages carbonic acid from the carbonate of 
 copper, which sweeping through the apparatus expels the atmospheric 
 air. To render this the more effectual, the whole apparatus is exhausted 
 by the syringe, and again filled with carbonic acid, and this is continued 
 until the bubbles of gas which come over are perfectly absorbed by 
 solution of potash. In this expulsion of the air of the apparatus, not 
 more than one-half of the carbonate of copper should have been used. 
 The fire is now to be withdrawn from the closed end of the tube, 
 and applied to the part occupied by the metallic copper. When this 
 is red hot, the combustion is carried backwards, just as in the former 
 
Determination of Nitrogen. 683 
 
 example, and when all the substance has been burned the coals are 
 applied to the remaining carbonate of copper, which, evolving carbonic 
 acid, clears out all the nitrogen of the apparatus, just as it had in the 
 commencement cleared out all the atmospheric air. The mixed gases 
 that are produced in this operation are received in a bell glass which 
 contains some strong solution of potash, by which the carbonic acid is 
 absorbed, and the nitrogen remaining may then be measured. The 
 volume of gas is next to be corrected for temperature, moisture, and pres- 
 sure, as directed in pp. 17, 70, and 112, audits weight then calculated. 
 
 The use of the metallic copper in the front of the mixture requires 
 notice ; when nitrogen passes over red hot oxide of copper, there is 
 always some nitric oxide formed, which would falsify the result, as its 
 volume is double that of the nitrogen it contains ; but nitric oxide is 
 completely decomposed by red-hot metallic copper, pure nitrogen being 
 evolved, and hence the purity of the resulting gas is secured by this 
 arrangement. Indeed, in all combustions of an azotized body, the 
 mixture should have some bright metallic copper in front of it. 
 
 The direct valuation of nitrogen by this process is thus a very deli- 
 cate operation, and occupies several hours. If the substance contain a 
 large quantity of nitrogen, its amount may be indirectly ascertained in 
 a much simpler way. The quantity of carbon in the substance is first 
 learned by an ordinary analysis, then another combustion tube is 
 arranged, with very clean copper in front ; but in place of adapting the 
 water-tube and bulbs, the water is taken no count of, and the gases 
 evolved are collected in narrow graduated tubes, over mercury. In 
 order to clear out the air from the tube, some of the mixture next the 
 sealed end is first ignited, and the gas allowed to escape : the tubes 
 being filled from the products of the subsequent periods of combus- 
 tion. In this case, no weights need be attended to, as it is only the 
 analysis of the gas in the tubes that is required for the result. The 
 volume of gas in a tube being marked, some solution of potash is 
 introduced, and agitated in it. The carbonic acid is absorbed, and the 
 nitrogen remains, the volume of which is read off, taking care that the 
 level of the mercury is the same inside and outside the tube. The 
 relative volumes of the carbonic acid and nitrogen gases are thus 
 found; and as an equal volume represents an atom, for each, the 
 relative number of atoms of carbon and nitrogen is thus determined ; 
 and as the total quantity of carbon is known by a previous experiment, 
 the total quantity of nitrogen may be calculated. When the relation 
 of the number of atoms of carbon to those of nitrogen is simple, as 
 occurs in cyanogen and oxamide, 2C to N, mellon, 3C to 2N, caffein 
 and taurine 4C to N, this method gives very accurate results. 
 
684 Absolute and Relative Methods 
 
 A mode of determining the quantity of nitrogen, more simple and 
 more rapid in execution than that just described, consists in converting 
 it into ammonia, and estimating* '\e quantity of that alcali in the form 
 of its double chloride with pM,^ -n. This process was first proposed 
 by Will and Yarrentrapp, and its e. actitude has been verified by most 
 chemists, so that it is now most generally employed. It has been al- 
 ready described in p. 670, that when an organic substance is strongly 
 heated in contact with an excess of caustic potash, or soda, water is 
 decomposed, the oxygen uniting with the elements of the organic sub- 
 stance, and hydrogen gas being set free ; so that when a great excess 
 of caustic alcali, and a dull red heat applied, the oxidation may become 
 so complete, as that the final products shall be solely water, carbonic 
 acid, and free hydrogen gas. Now if the organic substance contained 
 nitrogen, this unites with the nascent hydrogen, and forms ammonia, 
 which is given off as gas, and this takes place so exactly, that it may 
 be used as a test for the presence of nitrogen, even in the most minute 
 quantity, in an organic body. 
 
 To carry on the process, a mixture of two parts of fused hydrate of 
 caustic soda with one part of hydrate of lime in fine powder is em- 
 ployed, and the organic substance mixed with it in a combustion tube, 
 precisely as it should be mixed with oxide of copper for a carbon 
 determination as described in p. 679. To the cork of the combustion 
 tube is to be fitted a stout quill tube, about three or four inches long, 
 to which is attached by means of a caoutchouc connector, either a 
 Liebig's potash apparatus, as figured in p. 680, or, still better, the 
 form of bulb apparatus represented in the annexed figure. This appa- 
 ratus is to be half filled with moder- 
 ately strong muriatic acid ; the quan- 
 tity being such, that if by a rush of 
 uncondensed gas the acid be propelled 
 into the bulb, 3, it may be there 
 safely contained, and the uncondensed 
 gas escape by the vertical tube, whilst 
 should the gas be absorbed too ra- 
 pidly, and that the acid rises into the 
 
 bulb, #, there shall be no danger of its rising so high as to flow back 
 into the combustion tube. The interposition of the small bulb, c, 
 serves to give surface, and to mark by the bubbling of the gas, the 
 rapidity with which the process proceeds. 
 
 The last portions of the ammonia are carried out of the tube into 
 the muriatic acid, by the watery vapour from the pure hydrate of lime, 
 with which the combustion tube should be occupied, for some three 
 
of Determining Nitrogen. 685 
 
 inches next its closed end. The acid liquor is to be carefully drained 
 and washed out of the bulb apparatus into a small porcelain dish, and 
 mixed with solution of bichloride of platinum. A double chloride of 
 ammonium and platinum is thus produced, but as it is not insoluble in 
 water, the liquor is to be evaporated in a water bath very nearly to 
 dryness, and then mixed with alcohol, to which some ether has been 
 added. The excess of bichloride of platinum is thereby re-dissolved, 
 as well as any traces of oily organic matter that had come over. There 
 remains undissolved the platinum-ammonia chloride, which is to be 
 collected on a filter, well washed with alcohol, and then dried and ig- 
 nited ; all the chlorine and ammonia being expelled by the heat, there 
 remains pure metallic platinum, and as the formula of the salt is 
 NH 4 C1 + PtCl. 2 , there is found for every 14 parts of nitrogen which 
 the organic substance employed had contained, 98 '8 parts of platinum. 
 The determination of the nitrogen is thus rendered like that of the 
 carbon, a process of weighing, always far more capable of certainty 
 than that of measuring the volume of a gas, and any error of weight 
 on the platinum obtained, influences, but by one-seventh of its amount, 
 the quantity of nitrogen calculated from it. 
 
 Caustic potash is not used in this process, as should any minute 
 trace of it be carried by the current of gas into the muriatic acid bulb 
 apparatus, it would be very difficult to prevent its falsifying the esti- 
 mate of the ammonia, whereas, even should any traces of soda be 
 driven over, they would not interfere, as the double chlorides of plati- 
 num and sodium or calcium are abundantly soluble as well in alcohol 
 as in water. 
 
 Where the organic substance contains chlorine, sulphur, arsenic, &c. 
 it is to be destroyed by nitric acid, or by ignition with potash or lime, 
 and the inorganic constituents then determined in the ordinary way. 
 In some instances the sulphur of organic bodies can only be perfectly 
 oxidized by ignition with a mixture of nitrate and chlorate of potash. 
 The quantity of sulphuric acid produced is then determined. It is thus 
 that the presence of sulphur in taurine and in choleic acid may be found. 
 In organic salts, the metallic basis is determined by igniting the sub- 
 stance, burning away the organic element, ^and determining the quantity 
 of inorganic base, by whatever method is best suited to its individual 
 nature. 
 
 Carbon combines with oxygen in several proportions, of which three, 
 those in which it forms the carbonic oxide, and the carbonic and oxalic 
 acids, are the most important, and deserve a more detailed description 
 than is necessary for the others. 
 
686 Properties of Carbonic AciJ. 
 
 OF CARBONIC ACID. 
 Eq. 275, or 22. 
 
 Carbonic acid exists in the atmosphere, as a product of combustion, 
 and of the respiration of animals. Combined with metallic oxides, 
 it forms the numerous class of native earthy and metallic carbonates, 
 of which the carbonate of lime is much the most important. It is a 
 result, also, of the slow decomposition of most vegetable substances, 
 and is evolved in great quantity from the ground in volcanic countries. 
 In the fermentation of sugar, it is produced in abundance along with 
 alcohol. Eor the purposes of the chemist, it is generally prepared by 
 decomposing marble, or calc-spar, by means of any stronger acid ; from 
 its cheapness, and the solubility of the residual salt, muriatic is generally 
 employed. Some fragments of white marble being placed in a wide- 
 necked bottle, the acid diluted with its own volume of water is poured 
 
 in by a funnel tube, as in the 
 figure, and the gas which is 
 evolved is conducted by the 
 tubej^ <?, to be made use of as 
 required. The reaction con- 
 sists in HC1 and CaO.CO 2 , 
 I producing HO and Ca.Cl, 
 [which remains in the bottle, 
 1 whist C0 2 is driven off. Car- 
 bonic acid being dissolved by water, and it being generally required in 
 larger quantity than it is convenient to collect over mercury, we may 
 take advantage of the density of the gas, to collect it in dry jars, as 
 described and figured for chlorine in p. 419. The jar is known to be full 
 when a lighted taper, applied near the mouth, is instantly extinguished. 
 The properties of carbonic acid are very remarkable ; it is perfectly 
 colourless, and invisible ; it is irrespirable, producing, when an attempt 
 is made to breathe it, violent spasms of the glottis. If it be inspired, 
 mixed with air, even in the proportion of 1 to 10, it gradually produces 
 stupor and death, acting as a narcotic poison. Its specific gravity is 
 1*511. It hence, when disengaged in large quantities, whether by 
 natural operations, or in process of manufacture, accumulates in all 
 cavities within its reach, and may cause fatal accidents to animals who 
 enter unadvisedly. Thus, workmen engaged in cleaning out dry wells 
 or vaults, or the large vats from which fermenting liquors have been 
 run off, should carefully observe, whether a candle can remain for some 
 time burning brightly at the bottom. In volcanic countries, caverns 
 are frequently occupied, to the level of their surface, by this gas, exhaled 
 
Liquid and Solid Carbonic Acid. 687 
 
 from tlie ground ; and an experiment often tried, to amuse the traveller, 
 consists in walking into such a cavern with a dog, which, holding the 
 head near the floor, is almost instantly asphixated by the layer of car- 
 bonic acid, whilst men whose heads are above its level, breathe pure 
 air ; the dog on being thrown immediately into a neighbouring pond, 
 recovers from his stupor. Carbonic acid does not support combustion. 
 A taper plunged into a jar full of gas is instantly extinguished, and the 
 high specific gravity of the gas may be well shown by placing a lighted 
 taper at the bottom of a jar containing air, and taking in the hand 
 another jar containing carbonic acid, on inclining this jar the heavy 
 gas pours over the edge, nearly as water would do, into that in which 
 the taper is placed, and falling to the bottom, extinguishes it. 
 
 Water dissolves its own volume of carbonic acid gas, forming a so- 
 lution of an agreeably acidulous taste, which sparkles when agitated ; 
 it colours blue litmus paper of a wine red, which disappears on ex- 
 posure to the air, or by heat. By means of pressure, water can be 
 made to absorb a large quantity of carbonic acid, which escapes with 
 effervescence when the pressure is removed, and is thus the basis of a 
 variety of agreeable effervescing beverages. Solution of carbonic acid 
 in water precipitates solutions of lime and barytes white, forming car- 
 bonates, which redissolve in an excess of the carbonic acid. 
 
 Under a pressure of thirty-six atmospheres, carbonic acid may be 
 liquefied. It then forms a colourless, exceedingly mobile liquid, of 
 specific gravity, 0*83 at 32, which is remarkable for its excessive ex- 
 pansibility by heat, it having four times that of air, or nearly one per 
 cent, for each degree of Fahrenheit. When the pressure is suddenly 
 removed from this liquid acid, it gasefies with such rapidity, that, one 
 portion absorbing heat from the other, this latter is rendered solid (see 
 page 115.) Solid carbonic acid can thus be obtained in large quantity 
 by the apparatus contrived by Thilorier. It is a white body in filamen- 
 tous masses, like asbestus ; it evaporates but slowly ; it is very soluble 
 in alcohol and ether ; the ethereal solution produces by its evaporation 
 the most intense cold known, estimated at 166 degrees of Fahrenheit. 
 The composition of carbonic acid may be determined by very simple 
 experiments. If, into a bottle of pure oxygen gas, we insert 
 a little bit of charcoal, ignited at one point, at the end of the 
 wire a, as in the figure, it burns with vivid scintillations, and 
 the oxygen is all converted into carbonic acid. The stopper 
 of the bottle, through which the wire passes, being perfectly 
 tight, it will be found that the volume of the gas, when cold, 
 has not sensibly altered, and thus, that carbonic acid con- 
 tains its own volume of oxygen. It consists therefore of 
 
688 Composition of Carbonic Acid. 
 
 Two volumes of oxygen, 1105-6 X 2 = 2211-2 
 One vol. of carbon vapour, 836*8 
 
 Forming two volumes of carbonic acid, 2 -f- 3048*0 
 Of which one volume weighs, therefore, = 1524* 
 
 The corrected specific gravity of carbonic acid, 1*521, thus indicates 
 that the theoretical density of carbon vapour is more correctly taken as 
 836, than 843. 
 
 To demonstrate the existence of carbon in carbonic acid gas, it is 
 sufficient to heat to dull redness, in a current of the gas, a small glo- 
 bule of potassium. The metal takes fire, burning with a brilliant 
 violent flame, and forms potash, whilst carbon is abundantly deposited 
 as a brilliant jet black film on the interior of the tube. 
 
 Carbonic acid combines with the bases, forming a very important 
 class of salts, the carbonates. It forms neutral, basic, and acid salts, 
 which last are really double salts, containing carbonate of water, which, 
 however, exists only in combination, as the carbonic acid does not com- 
 bine with water directly in definite proportions. All salts of carbonic 
 acid are known, by yielding, when acted on by muriatic acid in the 
 cold, the gas possessing the properties just now described. 
 
 Carbonate of Potash. KO.CO 2 . Eq. 862*5, or 9'. This salt, 
 which is the great source of all other combinations of this alkali, is 
 obtained for the purposes of commerce from the ashes of plants, grow- 
 ing at a distance from the sea. The vegetable juices contain potash, 
 combined with various acids, as the nitric, oxalic, acetic, malic, &c., 
 which, by the burning of the wood, are converted into carbonates. 
 The produce differs according to the kind of wood, and with the season. 
 The softer and more juicy the plants are, the more potash they yield. 
 Plants of the natural families composite and cruciferse, are the richest : 
 the grasses rank next ; and amongst the woods, the leaves yield more 
 than the small branches, and these again more than the stems. In 
 countries where there are large forests, as America and Russia, the 
 small wood is burned, and the ashes collected ; these are boiled with 
 water in large iron pans or pots, from whence the name pot-ask is de- 
 rived. By this means, a large quantity of insoluble salts is separated, 
 and the carbonate of potash, which dissolves, is obtained in a purer 
 form by evaporation to dryness. It then constitutes the pearlashes, or 
 refined potashes, of commerce. Even these still retain much silica, 
 sulphate of potash, and chloride of potassium, so that the best Ame- 
 rican pearlashes seldom contain more than eighty-five per cent., and 
 Eusian potash often not sixty per cent., of true carbonate of potash. 
 
Manufacture of Potashes. 689 
 
 The purification of pearl ashes being difficult, carbonate of potash is 
 best prepared for chemical purposes by calcining cream of tartar ; the 
 tartaric acid which it contains is decomposed, and carbonic acid 
 formed, which combines with the potash ; the mass is digested with 
 water, filtered to separate the excess of charcoal, and evaporated to 
 dryness in a clean iron vessel. A white granular mass is 
 obtained, the salt of tartar of the older pharmacopoeias. 
 It is very deliquescent, soluble in half its weight of water, 
 and crystallizes with two atoms of water in oblique rhom- 
 bic octohedrons, a, a', a", a'", as in the figure, (KOC0 2 + 
 2Aq.) It reacts strongly alcaline. It is almost in- 
 soluble in alcohol, and when added to weak spirit, 
 combines with the excess of water, forming a heavy 
 fluid, which remains separated from the lighter and 
 stronger alcohol above. 
 
 As it is only the carbonate of potash that constitutes the value of 
 pearlashes in the manufacture to which it is applied, it is important to 
 be able to determine by a single and simple operation, the relative 
 worth of commercial samples. This process is termed alcalimetry. 
 The best method of performing it will be described under the head of 
 "Carbonate of Soda/' 
 
 Bicarbonate of Potash. KO.CO..J +HO.CO 2 . Is formed by passing 
 a current of carbonic acid gas through a saturated 
 solution of the neutral carbonate, the temperature 
 of which should not be above 100. In cooling, it 
 crystallizes in right rhombic prisms of eight sides, 
 as in the figure. It dissolves in four parts of cold 
 water, and in much less when hot. If its solution 
 be boiled, it abandons its second atom of carbonic 
 acid and becomes neutral carbonate, Its reaction 
 on vegetable colours is feebly alcaline. 
 
 Carbonate of Soda. NaO.C0 2 + lOAq. Eq. 662'5 + 1125, or 
 53* + 90. Is manufactured upon a very large scale, for the purposes 
 of commerce, from common salt, which must first be converted into 
 sulphate of soda in the manner described in page 604. 
 
 The dry sulphate of soda is to be mixed with its own weight of lime- 
 stone or chalk, and half its weight of small coal, and the mixture 
 being reduced to fine powder, is introduced into a reverberatory fur- 
 nace, such as in the figure, in charges about four cwt. each. After 
 being exposed to a full red heat for about three hours, carefully spread 
 out upon the floor of the furnace, the mass fuses, and being then well 
 44 
 
690 
 
 Manufacture of Soda-ask. 
 
 stirred for another hour, it is raked 
 off through the opening in the side 
 and received in metal boxes. It 
 forms a black mass, which is known 
 in commerce as UacJc-ask or British 
 barilla. The theory of this process 
 is very remarkable ; the sulphate of 
 soda being melted in contact with the 
 coaly matter, is deoxidized, its oxy- 
 gen being carried off by the carbon, 
 and sulphuret of sodium remaining. 
 This is immediately decomposed by 
 the carbonate of lime; an insoluble 
 oxy-sulphuret of calcium (Ca S -f- 
 
 2 Ca 0) and carbonate of soda being produced. SO 3 .NaO and 2C, 
 form 2.CO and NaS. which with CaO.CO,, gives CaS. and NaO.C0 2 . 
 As, however, much of the carbonic acid of the chalk is expelled by 
 the heat, a certain quantity of the soda remains caustic in the produce, 
 and also some sulphuret of sodium undecomposed. This Hack-ash 
 generally contains about 22 per cent, of real alcali. To obtain the 
 soda under a purer form, the masses of black-ash are broken up and 
 digested in cold water, until all soluble matter is extracted. The resi- 
 due consists of oxy-sulphuret of calcium and the excess of coaly matter. 
 The liquor is then evaporated to dryness, and the saline mass obtained 
 is calcined in the reverberatory furnace, with one-fourth of its weight of 
 sawdust, in order to convert all of the alcali into carbonate, and to 
 burn out some traces of sulphur which still remain ; on being then re- 
 dissolved in water, and the clear solution dried down, it constitutes 
 white-ash, or soda-ash of the best quality, containing from 45 to 52 
 per cent, of real alcali. 
 
 For the preparation of the crystallized carbonate, the soda-ash is 
 dissolved in boiling water, and the solution, being evaporated to a 
 pellicle, is left to crystallize for some days. The mother liquor, when 
 drained off the crystals, yields, when dried down, an inferior soda-ash, 
 which is, however, applied to many manufacturing uses. The large 
 quantity of soda which, however, exists in soda ash in the caustic state, 
 impedes very much the crystallization of the carbonate, and various 
 methods are had recourse to, to carbonate the ash prior to crystallization. 
 Thus it is again calcined with sawdust; but the best consists in spreading 
 the soda ash in coarse powder, slightly wetted, on the floor of a 
 chamber, into which carbonic acid produced by a charcoal stove is 
 introduced. The carbonic acid is very rapidly absorbed, and after 
 
Methods of Alcalimetry. 691 
 
 some hours the soda ash is found to be mostly converted into the bi- 
 carbonate of soda. On dissolving this then in a solution of more soda 
 ash, the whole is made into neutral carbonate, and the liquors are then 
 found to crystallize readily, and to deliver their whole content in car- 
 bonate of soda in a very pure form. It is found that about one part 
 of soda ash, when bicarbonated, can convert four parts of raw soda 
 ash into the neutral carbonate. 
 
 The pure carbonate of soda crystallizes in flat, oblique rhomboidal 
 prisms, as in the figure, which contain ten atoms of water, Na.CO 2 + 
 
 lOAq. In a dry atmosphere, they lose 
 by efflorescence all their water, and fall 
 into a white powder. It dissolves in 
 five parts of cold, and in less than one 
 of boiling water. By a gentle heat, the salt undergoes aqueous fusion, 
 and when dried, gives a white powder, soda siccata. By a strong heat, 
 the carbonate of soda melts, but is not otherwise affected. 
 
 Prior to the invention, by Leblanc, of the soda process described above, 
 the carbonate of soda was obtained from the ashes of marine plants, 
 as the salsola, and various fuci, which were burned in large quantities 
 on the west coast of Ireland, in the Orkneys, and on the coasts of 
 France and Spain. The saline products thus obtained were known in 
 commerce, as kelp, barilla, varec ; but these sources of alcali may now 
 be considered as extinct. Graham states, on the authority of Mr. 
 Muspratt, that, annually, there are manufactured, from common salt, 
 above 50,000 tons of soda-ash, and 20,000 tons of crystallized car- 
 bonate, and the manufacture is continually on the increase. 
 
 To the practical chemist and the manufacturer, it is important to be 
 able to determine by a rapid and easily executed process, the real quan- 
 tity of alcali present in any sample of pearl-ashes or soda-ash that may 
 be in the market. All such processes depend on measuring the quan- 
 tity of sulphuric acid necessary to produce a neutral salt with a certain 
 weight of the sample ; but in the management of the details considera- 
 ble difference may exist. A mode which I have found to be very ac- 
 curate, and easily executed even by ordinary persons, consists in pre- 
 paring beforehand a stock of a dilute sulphuric acid of sp. gr. 1*068 at 
 a temperature of 60. This acid may be formed by mixing one ounce 
 of the strongest oil of vitriol with nine ounces of water, but its sp. gr. 
 should be verified by trial before being used. 
 
 One hundred grains of the sample to be tried is then to be powdered 
 and stirred up in a capsule with an ounce of water. A glass jar about 
 a foot high and an inch wide, provided with a lip to pour from and a 
 steady foot, and graduated into 400 parts, of which each part indicates 
 
692 Carbonates of Potash and Soda. 
 
 five grains of the standard acid, is to be filled with the acid up to the 
 400th mark, and then by pouring very cautiously from the lip, a few 
 drops at a time, the alcaline liquor in the capsule is to be exactly neu- 
 tralized. A little bit of litmus paper may be left in it, and stirred 
 about well after each addition of a few drops of acid. A drop of acid 
 in excess reddens the litmus paper permanently, and as this does not 
 injure the result sensibly, it may be done in order to secure complete 
 neutralization. The graduations of the glass being numbered from 
 above downwards, simple inspection shows how much acid has been 
 employed, and it is only necessary to multiply the number of divisions 
 by thirty-one, if the alcali be soda, or forty -seven, if the alcali be 
 potash, and divide in each case by 100, to obtain the quantity of real 
 alcali present in the 100 grains examined. 
 
 The principle of this method is, that 100 grains of the standard 
 acid contain eight grains of dry sulphuric acid, and hence 100 mea- 
 sures contain forty grains, which number being that of the equivalent 
 of the acid, neutralizes almost exactly thirty-one grains of soda, or 
 forty-seven grains of potash, which are the equivalent weights also. 
 To find, therefore, the quantity of either alcali in a sample neutralized 
 by, for example, 137 measures of acid, we say, 
 
 For potash, . 100 : 47 : : 137 : x = iJ X 47 = 64'4 
 And for soda, 100 : 31 : : 137 : x = L X 31 = 42'5 
 
 A table may easily be constructed beforehand on those principles, so 
 as to save this little calculation. The greatest amount of error at all 
 likely to occur in this process is one division of acid in excess. The 
 difference made by this, however, does not influence the result for com- 
 mercial purposes ; thus, in the examples above taken, if the quantity 
 of acid had been measured wrongly at 138, the indications should be, 
 for potash 64'9, and for soda 42'8 ; the error in no case exceeding 
 half a part per cent, and being counterbalanced by assuming the 
 equivalents of the respective alcalies as whole numbers. 
 
 The above method is liable to some small sources of error arising 
 from the portions of alcali present in the sample as silicate or sulphuret, 
 or hypo-sulphite, being indicated by the test acid as if they had been 
 caustic or carbonated, and these quantities are often such as to influ- 
 ence the commercial value of the samples. Hence an improved method 
 of alcalimetry has been proposed by Will and Fresenius, and as it is 
 available also for other important technical determinations, I shall de- 
 scribe it somewhat in full. The new process is effected by means of 
 the apparatus represented in the following figure. 
 
Methods of Akalirnetry. 693 
 
 A and B are two small bottles or mat- 
 trasses with necks so wide as to admit each 
 f of a cork perforated for two tubes. Of 
 a III! Ill) these tubes one is bent and connects the 
 
 two bottles. The other tubes are straight. 
 The bottle A may be somewhat larger than 
 B. The former may hold from two to three 
 ounces of water, the latter from \\ to 2 
 ounces. The straight tube b, a, reaches 
 down to the bottom of the bottle A, and 
 is a little widened at the top, so that it 
 may be closed with a bit of wax or a cork. The syphon-bent tube c 
 terminates in A close under the cork. In the bottle A is placed a known 
 weight of the sample to be examined, and the bottle is then one third 
 filled with water. The bottle B is to be half filled with oil of vitriol, 
 the cork then tightly fitted in and the whole apparatus exactly weighed. 
 The opening of the tube a b is now to be closed, and a little air 
 sucked out by the tube d, so that it shall also bubble out from the 
 bottle A into B. On the restoration of the pressure some oil of vitriol 
 is forced from B into A, where it acts on the alcaline solution and ex- 
 pels the carbonic acid with effervescence. The gas, however, can escape 
 only by bubbling through the oil of vitriol in B, by which all moisture 
 is absorbed, so that only dry gas escapes. This operation is repeated, 
 introducing only a little sulphuric acid at a time, until the alcali is 
 totally decomposed and the acid is in excess in the bottle A. By the 
 oil of vitriol and water mixing so much heat is evolved that the liquor 
 does not retain any gas dissolved. Finally, when no more effervescence 
 occurs, the carbonic acid is removed from the apparatus by taking 
 away the stopper from the end of the tube b a, and sucking air through 
 the apparatus by means of the tube d, as long as the taste of carbonic 
 acid is sensible. When the apparatus is cold it is to be weighed, and 
 the weight lost is the carbonic acid, from which the content in alcali of 
 the sample can be calculated. 
 
 If the sample contains a sulphite or an hypo-sulphite, its interference 
 is prevented by adding to the liquor in A a small quantity of neutral 
 chromate of potash, by which those acids are converted into sulphuric 
 acid which does not interfere with the reaction. 
 
 As in most commercial samples of soda-ash a certain quantity of 
 alcali is present in the caustic state, it is necessary to convert it into 
 carbonate, which is done by moistening the weighed sample with a 
 strong solution of carbonate of ammonia and gently igniting. All soda 
 present becomes then fully combined with carbonic acid, and the process 
 may be carried on with full accuracy. 
 
694 
 
 Alcalimetri/ and Acidimetry. 
 / i/ 
 
 It is evident that this little apparatus may be also used for the pur- 
 poses of acidimetry, to measure the real strength of sulphuric, acetic, 
 or other similar acids. The acid is to be placed in the bottle A, and 
 a solution of bi-carbonate of soda, containing somewhat more soda 
 than the sample of acid can neutralize, is to be put into a small test 
 tube which is to be placed in the bottle A, and so hung by means of a 
 silk thread, that, until after the apparatus is weighed, its orifice is 
 quite above the level of the acid liquor. When the weighing is accom- 
 plished, the test tube is allowed to drop into the acid, and the cork of 
 it instantly tightened. The carbonic acid expelled passes through the 
 oil of vitriol in B, and is thereby dried. The remaining carbonic acid 
 is sucked out as already described, and the apparatus being again 
 weighed, the loss gives the carbonic acid, of which two atoms corres- 
 pond to one atom of acid in the sample. 
 
 Eor measuring the value of commercial peroxide of manganese, this 
 apparatus is also usefully employed in the process described in page 498. 
 Por this purpose, the sample of manganese and the oxalic acid is put 
 into the bottle A, the oil of vitriol is then passed to it from the bottle 
 B, and the evolution of the carbonic acid conducted just as in the ex- 
 amination of an alcaline carbonate. 
 
 The manipulation of this process becomes easier by using the form 
 of apparatus now figured. In it the bottle A is fitted with a chloride 
 
 of calcium drying tube, and the 
 carbonic acid gas is allowed to es- 
 cape at once through it. The acid 
 is put into the two-necked bottle 
 B, and the tube b, connecting the 
 two bottles, has its longer leg 
 passing to the bottom of B, whilst 
 its shorter leg opens immediately 
 under the cork of the smaller neck 
 of A. To use this apparatus the 
 sample is put into A, and the 
 strong acid into B, and the tubes 
 adjusted. Then on blowing gently 
 into the tube a, a small quantity 
 of acid is blown over into A across the tube d. When this has acted, 
 another small quantity may be blown over, and so on until the addition 
 of more acid produces no more action. Then the carbonic acid gas of 
 the apparatus is extracted by sucking gently at the end of the tube a, 
 so that a current of air passes from A to B, as long as it tastes of gas. 
 The apparatus is then weighed, and the calculation effected as already 
 described. 
 
Carbonates of Lime, Barytes, Magnesia, fyc. 695 
 
 This apparatus is found to be more under the exact controul of the 
 operator than that first figured, and deserves therefore to be employed 
 in preference. 
 
 Bicarbonate of Soda. HO.CO 2 + NaO.CO 2 , is formed by passing 
 a current of carbonic acid gas through a cold solution of carbonate, 
 the new salt precipitates in small opaque crystals, having the appear- 
 ance of starch. It requires fifteen parts of cold water for its solution ; 
 it has an alcaline reaction, but is not disagreeable to the taste. 
 
 Sesquicarbonate of Soda occurs native on the banks of certain lakes 
 in Mexico and in Africa, whence it is exported under the name of trona. 
 Its formula is 2NaO + 3C0 2 + 4HO. It cannot be formed at will. 
 
 Carbonate of Barytes. BaO.CO 2 . This salt exists native, crystal- 
 lized in oblique rhombic prisms ; it is insoluble in pure water, but dis- 
 solves in water containing carbonic acid. It is very poisonous. It 
 may be prepared artificially by mixing solutions of chloride of barium 
 and carbonate of ammonia ; a white precipitate falls, which, being well 
 washed and dried, is pure carbonate of barytes. It is used in the ana- 
 lysis of minerals containing alcali, and for the preparation of various 
 salts of barytes. It lias been used in the manufacture of glass. 
 
 Carbonate of Strontia resembles perfectly the former. 
 
 Carbonate of Lime.Ga.O.CO z . Eq. 632'5 or 50'7. The circum- 
 stances and forms under which this salt exists in nature have been so 
 frequently noticed, (pp. 484, 670, 787), and the molecular constitution 
 and peculiar relations to light of its crystals so fully described, that it 
 is not necessary to enter upon its history here further. It may be pre- 
 pared pure by decomposing chloride of calcium by means of carbonate 
 of ammonia ; it forms then a white powder insoluble in pure water, 
 but dissolving in water containing carbonic acid. This is not due to 
 the formation of a bicarbonate of lime, but owing to a specific solvent 
 power which a solution of carbonic acid in water has on many bodies, 
 as silica, phosphate of lime, &c. which are insoluble in pure water. It 
 is thus that carbonate of lime is held dissolved in most waters, and is 
 deposited as a crust on the interior of any vessels in which such water 
 may be boiled. By the gradual dissipation of the carbonic acid on ex- 
 posure to the air, the carbonate of lime may be slowly deposited and 
 then crystallizes ; thus are formed the remarkable stalactites, &c. of 
 limestone caverns. 
 
 Carbonate of Magnesia. MgO.CO 2 . This salt exists anhydrous in 
 nature, crystallized in rhombohedrons like calcspar. By dissolving 
 magnesia in water by a stream of carbonic acid, it may be formed, and 
 is gradually deposited in rhomboidal prisms, of six or eight sides, as 
 w, v } a, in figure, which contain three atoms of water. It is this salt, 
 
.. j 
 
 696 Carbonates of Magnesia, Iron, Copper, fyc. 
 
 MgO.C0 2 -f 3 Ag. which exists in Murray's solution of magnesia. 
 When acted on by pure hot water this salt is decomposed, 
 carbonic acid escaping, and basic carbonate of magnesia 
 being produced. It is this basic carbonate which consti- 
 tutes the magnesia alba, or common carbonate of magnesia 
 of the shops. It is prepared by mixing boiling solutions 
 of sulphate of magnesia and carbonate of soda, leaving 
 the former slightly in excess. The precipitate is very light 
 and bulky, and almost totally insoluble in water. One-fourth of the 
 carbonic acid is given off in this reaction, and the precipitate is found 
 to be a compound of carbonate and of hydrate of magnesia, MgO.HO 
 + 3 (MgO.C0 2 HO), or 4MgO + 3C0 2 + 4 Aq. 
 
 The nature of dolomite or magnesian limestone has been already 
 sufficiently noticed, (p. 488). 
 
 Carbonate of Manganese. MnO.C0 2 . It is a white powder formed 
 by double decomposition, and decomposed by a red heat. It is found 
 also native, and occurs largely as a kind of marl in the West of Ire- 
 land. 
 
 Proto-carbonate of Iron. FeO.CXK Exists native in rhombs iso- 
 morphous with calc-spar. It may be prepared by decomposing proto- 
 sulphate of iron by carbonate of soda ; it forms a white precipitate, 
 which, by exposure to the air, rapidly absorbs oxygen and gives out 
 carbonic acid, becoming green, and ultimately red, being then mere 
 peroxide of iron. The carbonate of iron can therefore scarcely be ob- 
 tained pure, but by mixing the fresh precipitate with sugar, and evapo- 
 rating to dryness with constant agitation, a quantity of the carbonate 
 remains undecomposed, being protected from the air by a varnish of 
 sugar on its particles, and thus constitutes the carbonas ferri cum 
 saccharo of pharmacy. The carbonate of iron is soluble in water 
 containing acid, and exists thus dissolved in chalybeate spas. 
 
 When solutions of sulphate of zinc and carbonate of soda are mixed 
 together, a basic carbonate of zinc is formed, consisting of 2(ZnO.CO 2 ) 
 + 3.ZnO.HO if the solutions were warm, but of ZnO.C0. 2 -f- S.ZnO.HO 
 if cold ; carbonic acid gas is given off in both cases. 
 
 There are two carbonates of copper, both basic ; the green carbonate 
 exist native, (malachite) and is used as a pigment. It may be formed by 
 mixing solutions of a salt of copper and an alcaline carbonate; the 
 precipitate is at first flocculent, and of a fine pale blue, but when boiled 
 it becomes dense, granular, and bright green : its formula- is 2 CuO + 
 CO 2 + HO. The blue carbonate, exists also native (copper-azure), 
 but cannot be prepared artificially so as to be permanent, its formula is 
 3CuO -f 2C0 2 + HO. 
 
Preparation of Carbonic Oxide, fyc. 697 
 
 Carbonate of Lead. PbO.C0 2 . Exists native crystallized in forms 
 isomorphous with those of the carbonate of barytes, and may be formed 
 as a finely crystalline powder, by decomposing solution of nitrate of 
 lead by carbonate of soda. There are several basic carbonates of lead, 
 which, in a greater or less degree of mixture, constitute the white lead, 
 or ceruse of commerce, so much used in painting. The composition of 
 white lead generally falls between those given by the formulas 3PbO 
 + 2C0 2 + HO, and 4PbO + 3C0 2 + HO. 
 
 For the manufacture of white lead, very thin sheets of the metal are 
 exposed to the fumes arising from vessels containing weak vinegar, 
 which are kept moderately warm by being imbedded in fermenting tan ; 
 the lead, absorbing oxygen from the air, combines with the acetic acid, 
 forming a basic acetate of lead, which is decomposed by the carbonic 
 acid of the surrounding air, basic carbonate of lead being produced, 
 and neutral acetate of lead remaining; this, under the action of the 
 air, takes up a new quantity of lead, and the same decomposition is 
 renewed ; a minute quantity of acetic acid thus serving to produce a 
 very large quantity of ceruse. This process has lately been much im- 
 proved by exposing litharge, finely ground and with one per cent, of 
 acetate of lead, to a stream of carbonic acid, generally derived from the 
 fermenting vats of a brewery ; the one portion of neutral acetate suc- 
 cessively unites with all the litharge to form basic acetate, the successive 
 portions of which are decomposed by the carbonic acid, white lead 
 being formed, and the original quantity of neutral acetate remaining 
 uncombined at the end. 
 
 The carbonates of the other metals are unimportant. 
 
 Carbon combines with the metals to form carburets, of which the 
 best known are those of iron and silver; the former has been fully 
 noticed in the description of cast iron and steel (p. 503), and the 
 carburet of silver is a grey powder, which remains when certain silver 
 salts of organic acids, as the citrate and tartrate, are imperfectly burned 
 away. 
 
 CARBONIC OXIDE. 
 CO, Atomic Weight, 175 or 14. 
 
 If carbonic acid gas be passed through a tube containing red-hot 
 charcoal, it takes up as much more carbon as it already contained, and 
 forms carbonic oxide ; its volume being thereby doubled. The gas may 
 also be prepared by heating to redness, in an iron retort, a mixture of 
 charcoal and chalk, when the carbonic acid evolved from the latter 
 combines with the excess of carbon and forms carbonic oxide ; in place 
 
698 Preparation of Carbonic Oxide. 
 
 of charcoal, iron filings or zinc may be used ; the metal in this case 
 takes half of the oxygen from the carbonic acid, C0 2 and Zn giving 
 ZnO and CO. 
 
 A very simple and elegant way of obtaining this gas consists in 
 warming strong oil of vitriol with crystals of oxalic acid, in a flask a b 
 from which a tube/ 1 passes to a bottle containing solution of caustic 
 potash a, as in the figure ; from this another tube conducts to the 
 
 pneumatic trough. The oxalic acid, 
 C 2 3 + HO yields up its basic water 
 to the sulphuric acid, and as the oxalic 
 acid cannot exist except in combination 
 with some base, it is resolved in carbonic 
 oxide and carbonic acid, (C 2 O 3 = CO 
 -{- C0 2 ) which are evolved as gases, 
 mixed in equal volumes; in bubbling 
 through the bottle containing potash, 
 the carbonic acid is completely absorbed, 
 and the pure carbonic oxide may be collected over water. 
 
 It is a colourless, inodorous gas, and has no action on vegetable 
 colours; it extinguishes a taper, but it is combustible, and burning 
 with a pale blue flame, forms carbonic acid. It is this gas which pro- 
 duces, on the top of a clear coke fire, a blue flame, which appears 
 purple when seen with the red back-ground of the glowing cinders. 
 In the smelting of iron in the high furnaces, the carbonic acid, first 
 produced by the combustion, passing through the column of ignited fuel 
 is mostly converted into carbonic oxide, which escaping at the top, pro- 
 duced a loss of more than one-third of the whole heat, until the process 
 was invented of conveying this gas by tubes to the refining fur- 
 naces, and effecting the subsequent operations by the heat of its flame. 
 The carbonic oxide contains half its volume of oxygen ; its specific 
 gravity is 972*8, Carbonic oxide appears to enter into union with a 
 great variety of bodies, and to act in such compounds as a compound 
 radical. Thus, if potassium be heated in carbonic oxide gas, it com- 
 bines therewith, and forms a grey body, which acted on by water, gives 
 off carburetted hydrogen, and produces croconate of potash. It is this 
 reaction which causes the great loss of potassium in preparing that 
 metal, see p. 472. 
 
 Oxalic Acid, C 2 3 or 2(00) -f- 0. Eq. 451 or 36. 
 Oxalic acid is one of the most important organic bodies. It is found 
 combined with potash, forming the salt of sorrel, in several plants of 
 the genera oxalis and rumex, and combined with lime in the roots of 
 
Manufacture and Properties of Oxalic Acid. 699 
 
 rhubarb, and in a variety of lichens. It was formerly extracted prin- 
 cipally from the oxalis acetosella, from whence its name is derived, but 
 is now manufactured in larger quantities, artificially. It is generally 
 a product of the oxidation of vegetable substances by nitric acid, on 
 which fact its mode of preparation is founded. The substances em- 
 ployed are usually starch or sugar, a quantity of which is placed in an 
 earthen pipkin, of which a great number are arranged in a shallow 
 vessel containing warm water ; about four parts of nitric acid, specific 
 gravity 1*42, are poured into each pipkin. The starch is rapidly oxi- 
 dized, and nitrous fumes given off abundantly ; when the action has 
 become slow, one part more of acid is to be added, and the heat in- 
 creased. The liquors, so obtained, are mixed, evaporated to a pellicle, 
 and set aside to crystallize, and the crystals are purified by re-solution 
 and crystallization. Prom the mother liquors new quantities of oxalic 
 acid may be obtained by heating with more nitric acid. 
 
 If we consider the sugar, in its dryest form, as being C, 2 H 9 9 , the 
 action of the nitric acid should consist in first removing the nine equi- 
 valents of hydrogen, and substituting for them nine equivalents of 
 oxygen, thus C 12 H 9 O 9 and 6XO 5 should give 6(C 2 3 ) with 9HO and 
 6N0. 2 . But the action is not so simple ; as other products, especially 
 the saccharic add, are at the same time formed. By means of per- 
 manganate of potash, however, the carbon of sugar may be very 
 elegantly and directly changed into oxalic acid, C 12 H 9 O 9 and 6(Mn 2 O 7 
 + KO), producing 12(Mn0 2 ) with 9HO and 6(C 2 O 3 + KO). The 
 oxalic acid formed exactly neutralizing the potash of the manganic salt 
 employed. The oxalic acid is also a product of the action of caustic 
 alcalies at a high temperature on organic bodies. Thus, if starch or 
 sawdust, or any similar organic body, be heated to 600 Fahrenheit in 
 a crucible with caustic potash or soda, hydrogen gas is given off, and 
 a salt of oxalic acid formed ; by a still higher heat this is again decom- 
 posed, and, finally the alcali remains as neutral carbonate. 
 
 The oxalic acid crystallizes from its solution, in oblique rhombic 
 prisms, of which those planes marked i c are primary, and af second- 
 
 A i ,..-"\ ary : the summit is often dihedral, in which case the 
 \ \ plane a, and that vertically opposite to it are absent. 
 
 \Jj These crystals contain three atoms of water, of which 
 
 ^ f V one is basic : C 2 O 3 + HO + 2Aq. When warmed, 
 they give off 2Aq., and the hydrate of oxalic acid re- 
 mains as a white powder, which melts at 350, and when heated further 
 sublimes, a portion being however decomposed; the products of the 
 reaction of oil of vitriol on oxalic acid have been already noticed (p. 
 698). Oxalic acid is converted -in carbonic acid by contact with many 
 
700 Oxalates of Potash. 
 
 peroxides, as the peroxide of manganese, by which means the technical 
 value of manganese ores may be determined, see p. 499 and 694. By 
 contact with a great excess of hot nitric acid, or of chlorine, it is also 
 converted into carbonic acid. 
 
 The acidity of oxalic acid is very great ; a grain of it dissolved in 
 30,000 grains of water will still affect litmus paper. It neutralizes 
 the alcalies perfectly, and forms with them two series of acid salts. 
 In the neutral oxalates, the oxygen of the acid to that of the base is 
 3:1. By heat, those of the metals proper are generally converted into 
 carbonic acid and metal, C 2 O 3 -f MO. giving C 2 4 and M. Those of 
 the earth and alcalies evolve carbonic oxide, and produce a carbonate, 
 QOa -f MO giving CO and C0 2 + MO. The former action is use- 
 fully employed to obtain cobalt and nickel in the metallic state. 
 
 Oxalic acid is detected easily by its strong acidity, and its not leaving 
 a carbonaceous residue when heated. Its solution gives, with lime 
 water, a precipitate which is insoluble in an excess of oxalic acid, or of 
 any organic acid. It precipitates, also, the solutions of barytes and 
 lead. It acts violently on animals, as a poison ; for an antidote, mag- 
 nesia is the best, but chalk or whiting is the most readily procured. 
 
 Several of the oxalates deserve special notice. There are three 
 oxalates of potash, remarkable as being the bodies by which Wollaston 
 satisfied himself of the truth of the law of multiple combination, p. 
 281 j their proportions of acid being as 1 : 2 : 4. 
 : The neutral Oxalate of Potash. KO.C0 2 + Aq. May be formed, 
 by acting on sugar by permanganate of potash ; or by heating any 
 fixed organic matter, as sawdust, or paper, with an excess of potash, 
 below redness. It is more simply produced by neutralizing oxalic 
 acid, or the following salt, with carbonate of potash ; it crystallizes in 
 rhombic prisms, of a bitter taste, which dissolve in three parts of water, 
 and are insoluble in alcohol. 
 
 Binoxalate . of Potash. KO.C 2 O 3 + HO.C 2 3 + 2 Aq. Exists 
 naturally in the various kinds of sorrel, from whence it was originally 
 extracted, under the name of salt of sorrel, but is now artificially made. 
 One part of oxalic acid is exactly neutralized by potash, and then 
 exactly as much more oxalic acid is added to the solution, from which, 
 by evaporation and cooling, the salt crystallizes in oblique rhombic 
 prisms, which are soluble in forty parts of cold, and in six parts of 
 boiling water. Its taste is strongly acid and saline, and it is poisonous, 
 though less so than the acid uncombined. When heated, the salt is 
 decomposed, evolving carbonic acid and carbonic oxide, and leaving a 
 residue of carbonate of potash, which should be scarcely coloured if 
 the salt were pure. 
 
Single and Double Oxalates. 701 
 
 Quadroxalate of Potash. KO.C 2 O 3 + 3 HOC 2 O 3 + 4 Aq. Is 
 formed by neutralizing one part of oxalic acid by potash, and adding to 
 the solution three times as much oxalic acid more. It may also be pre- 
 pared by dissolving the binoxalate in muriatic acid, which takes half of 
 the alcali ana the quadroxalate crystallizes out. This, and the last 
 salt, are indiscriminately sold in commerce as salt of sorrel, and, also, 
 often as salt of lemons, for removing iron moulds and stains of ink, 
 which they do by forming, with the peroxide of iron, a soluble double 
 salt. 
 
 There are similar oxalates of soda, which are not important. 
 
 Oxalate of Lime. CaO.C 2 O 3 + 2Aq. Exists abundantly in nature, 
 forming the hard earthy basis of many lichens, and may be prepared 
 by mixing solutions of oxalate of ammonia and of any soluble salt of 
 lime. It forms a white flocculent precipitate, which, by boiling, be- 
 comes heavy and granular. It is totally insoluble in water, and is 
 hence used as a means of removing lime from solutions, and deter- 
 mining its quantity. It dissolves in the mineral acids, but is insoluble 
 in all organic acids, even the acetic. When heated, it leaves a per- 
 fectly white residue of carbonate of lime. 
 
 The remaining simple oxalates are not important, except the oxalate 
 of silver, which is a white powder, prepared by double decomposition, 
 and remarkable for being decomposed by a moderate heat, with a slight 
 explosion, into carbonic acid and metallic silver. 
 
 There are several double oxalates possessing interest. 
 
 Oxalate of 'Potash and Peroxide of 'Iron. (Fe 2 O 3 + 3C 2 3 ) + 3.KO. 
 C 2 O 3 + 6Aq. Is prepared by dissolving peroxide of iron in solution 
 of binoxalate of potash ; it crystallizes in fine grass-green tables, which 
 are permanent in the air. There exists a similar salt containing soda. 
 
 Oxalate of Potash and Chrome. (,T) Z + 3C 2 3 ) 4. 3KO.C 2 3 + 
 6Aq. Is prepared by dissolving together in hot water one part of bi- 
 chromate of potash, two of crystallized oxalic acid, and two of binox- 
 alate of potash. A copious evolution of carbonic acid occurs, the 
 chromic acid being deprived of half its oxygen by a part of the oxalic 
 acid, with the remainder of which the oxide of chrome unites. The 
 liquor assumes a fine purple colour, and, on cooling, yields prisms of 
 a splendid blue colour, .so deep, as to be perfectly opaque, unless the 
 crystals be very thin. 
 
 Oxalate of Copper and Potash. KO. C 2 O 3 + CuO. C 2 O 3 -f 2Aq. 
 Is formed by digesting a solution of binoxalate of potash on oxide of 
 copper. It crystallizes in fine blue prisms. It may also be obtained 
 with 4 Aq. 
 
 Chloro-carbonic Acid.QQ + Cl. Eq. 619'1 or 49'5. When 
 
702 CMoro-carlonic Acid. 
 
 equal volumes of carbonic oxide and chlorine are exposed for some 
 hours to the light, they gradually combine, forming a colourless gas, 
 which was termed by J. Davy, its discoverer, phosgene gas. Its odour 
 is very irritating ; the volume being diminished to one-half, its density 
 is 3412. It is decomposed by water, carbonic and muriatic acids being 
 formed. It is decomposed by most metals, which unite with the 
 chlorine and liberate carbonic acid. Its action on ammonia and on 
 alcohol will be hereafter noticed. 
 
 COMBINATION OF CARBONIC OXIDE AND POTASSIUM, AND THE 
 PRODUCTS OF ITS DECOMPOSITION. 
 
 If potassium be heated in a current of carbonic oxide, the gas is 
 rapidly absorbed, but no charcoal is separated, as occurs with carbonic 
 acid gas. The metal is converted into a blackish-green porous mass. 
 If the air be admitted to this while hot, it inflames ; when brought 
 into contact with water it is immediately decomposed, a peculiar gas 
 being given off, and a rhodizonate of potash formed. This oxicarburet 
 of potassium is obtained in quantity in the process by which potassium 
 is procured, and constitutes the great obstacle in obtaining that metal, 
 as described in p. 472. It is also formed, but very impure, by merely 
 brightly igniting cream of tartar in a covered crucible for an hour. 
 The composition of this body is not yet known, and hence the mode of 
 its decomposition cannot be expressed in formulae. The gas, which it 
 evolves by solution in water, has been examined by Mr. Davy. It is 
 colourless and inflammable, and burns more brightly than olefiant gas. 
 Its characteristic property is to detonate with a brilliant flash, and de- 
 posit charcoal, when mixed with chlorine, even in the dark. He 
 assigns to it the formula, C 2 H. 
 
 Rhodizonic Acid. This is formed when the oxicarburet of potassium 
 is dissolved in cold water. It is, when dry, isomeric with carbonic 
 oxide, C 7 O 7 , but it appears to be a tribasic hydracid, and its formula 
 C 7 O 10 + H 3 . Its salts are of a fine scarlet red colour, whence its name. 
 
 Croconic Acid. C 5 O 4 . Is formed when a solution of rhodizonate of 
 potash is boiled ; an atom of potash becomes free, and croconate and 
 oxalate of potash are produced ; C 7 7 + 3KO, giving KO and C 2 O 3 + 
 KO, with C 5 O 4 + KO. The salts of croconic acid are bright yellow 
 coloured, but do not require other notice. 
 
 Mettitic Acid. C 4 O 3 , when dry. Is found only native, combined 
 with alumina, in a very rare mineral, mellite or honeystone. It crys- 
 tallizes with water, C 4 O 3 + HO, and from its characters, especially the 
 properties of the mellate of silver, it appears to be properly a hydro- 
 
Isomeric Oxides of Carbon. 
 
 703 
 
 gen acid, having carbonic oxide as its radical, and its formula to be 
 C 4 O 4 + H. When its ammonia salt is decomposed by heat, it is re- 
 solved into two very singular bodies, paraban and euchroic acid, whose 
 history, however, is not important here. 
 
 In concluding this account of the oxygen compounds of carbon, it 
 is proper to notice the peculiar function which the carbonic oxide ap- 
 pears to play. From the composition of its chlorine compound, it is 
 certain that the equivalent of the gas is CO, and combining with oxy- 
 gen it forms carbonic acid, C0 2 . But I consider, that we cannot look 
 upon oxalic acid as being a lower degree of oxidation of the same 
 radical as carbonic acid. On the contrary, the body C 2 O 2 , which is 
 the basis of it, enters into a completely distinct series of compounds, 
 such as oxamide, and is probably merely isomeric with carbonic oxide, 
 into which it may be changed by a variety of reactions. Still less is 
 carbonic oxide the basis of the rhodizonates, C 7 O 7 , or of the croconates 
 or meUates ; but the gas is changed into these more complex bodies by 
 an isomeric action, which appears to occur at the moment that it com- 
 bines with the potassium. I look upon the carbonic oxide gas, there- 
 fore, as being the basis only of carbonic acid and phosgene gas, and 
 that the radicals of the oxalic acid and the bodies of its series, as well 
 as of the rhodizonic and other acids, are compounds of carbon and 
 oxygen, isomeric with carbonic oxide, but not yet isolated. 
 
 The mesoxalic acid will be described hereafter with uric acid. 
 
 OF SULPHURET OF CAKBON. 
 CS 2 . Eq. 475 or 38. 
 
 This remarkable substance is formed whenever sulphur comes into 
 contact with red-hot charcoal. It may be easily prepared by means of 
 the apparatus, represented in the figure. The tube a, c, being filled 
 
 with pieces of charcoal, about the size of almonds, is to be strongly 
 
704 Sulphur et of Carbon. 
 
 ignited in the furnace, arid bits of sulphur introduced from time to 
 time, at h, which is to be then tightly closed with a cork. The sulphur 
 fuses, and the tube being a little inclined, runs down upon the ignited 
 charcoal, combines with it, and the product passing as vapour into the 
 long glass tube, e, f, is condensed and collected as a liquid in the 
 bottle. 
 
 In large quantity, it is more .conveniently prepared by fixing, air 
 tight, into an iron cylinder about a foot high, (such as a quicksilver 
 bottle), two iron tubes, one long, ~b, reaching nearly to the bottom, 
 and projecting a foot above the top, and the other short, c 9 and bent at 
 
 a right angle, serving to convey the product to the condensing appara- 
 tus. By means of the tube c, the bottle may be filled with small frag- 
 ments of charcoal, and then placed in a furnace, the wide glass tube e, 
 and the narrower f t are to be attached by corks. Prom the cock d, a 
 stream of water flows, which, guided by the tin-plate gutter o, cools the 
 tube f, and is conducted by the thread h to the basin x. When the 
 bottle is bright red, small pieces of sulphur are to be dropped in by 
 the long tube, the end of which is to be then carefully closed up by a 
 cork. The sulphur, being vaporized, acts on the charcoal, and the 
 sulphuret of carbon formed, being condensed in the narrow tube e,f, 
 collects in the bottle n, which is half filled with ice, in order more per- 
 fectly to preserve it. Any incondensible gases that may be formed 
 escape by the tube m. The process might be continued until all the 
 charcoal in the bottle had been converted into sulphuret ; but if sul- 
 phur were allowed to be present in excess, it would melt the bottom of 
 the bottle. The process, therefore, should not be pushed so far. 
 
 The sulphuret of carbon, thus obtained, contains an excess of sul- 
 phur dissolved in it, and must be purified by re-distillation, at a very 
 
Chlorides of Carlon. 705 
 
 moderate heat, (in a water bath) ; when about nine-tenths have distilled 
 over, by allowing the residue to evaporate spontaneously in a capsule, 
 very fine right rhombic crystals of sulphur may be obtained (p. 388). 
 
 The sulphuret of carbon is a colourless liquid, of a very disagreeable 
 garlic smell. It does not mix with water, but dissolves in alcohol and 
 ether. It dissolves sulphur and phosphorus in large quantity. Its 
 specific gravity is 1 '2 7 2. It boils at 108 Tali., and forms a colourless 
 vapour, whose specific gravity is 2*621 . .Erom its volatility, it obtained 
 the name of alcohol of sulphur . In evaporating- it produces great cold; 
 mercury may be frozen by suspending, under a bell glass, a thermometer 
 the bulb of which is surrounded by cotton moistened with this fluid, and 
 rapidly exhausting the air. It is very inflammable, burning with a blue 
 flame, and producing carbonic and sulphurous acids. If a few drops 
 of it be let fall into a strong bottle containing oxygen, so much of it 
 evaporates as to form an explosive mixture with the gas, which then 
 detonates when touched with a lighted taper, like a mixture of oxygen 
 and hydrogen. When the sulphuret of carbon is heated in contact 
 with a metal, carbon is separated and a metallic sulphuret produced. 
 It is thus found to consist of one atom of carbon united to two of 
 sulphur, and its formula to be CS 2 . 
 
 It is a powerful sulphur acid, combining with the sulphurets of the 
 alcaline metals and forming sulphur-salts, which are cry stalliz able ; with 
 the sulphurets of lead, silver, copper, &c., it forms insoluble compounds, 
 which correspond closely in composition to the ordinary carbonates. 
 This substance is in fact exactly equivalent to carbonic acid, C0 2 , the 
 sulphur being replaced by oxygen, with which its analogies have been 
 already noticed in p. 389. The sulphuret of carbon is hence often 
 called sulpliocarlonic acid. 
 
 Moist chlorine converts this body into a crystalline substance like 
 camphor ; but this as well as the products of the action of nitric acid 
 and of strong alcalies have not yet been accurately examined. 
 
 CHLORIDES OF CARBON. 
 
 Sulchloride of Carbon. C 2 C1. Is formed by passing the vapour of 
 the protochloride many times through an ignited glass tube ; chlorine 
 is given off, and the subchloride deposited in silky crystals, which are 
 fusible, and sublime at about 303 unchanged. 
 
 Protochloride of Carlon. C 2 C1 2 . Is also formed from the sesqui- 
 
 chloride of carbon by heating its vapour to redness, when chlorine is 
 
 given off; or better by distilling the sesquichloride with an alcoholic 
 
 solution of sulphuret of potassium, which removes one-third of the 
 
 45 
 
706 Ammonia, its Compounds and Derivatives. 
 
 chlorine. It is a limpid fluid, boiling at 160 ; the sp. gr. of its 
 vapour is 2862. By a strong heat it gives subchloride and free chlorine. 
 
 Sesquichloride of Carbon. C 2 C1 3 . Is produced by the action of a 
 great excess of chlorine in bright sunshine on olefiant gas, or on mu- 
 riatic ether ; all the hydrogen of these bodies is removed, and the car- 
 bon remains united with chlorine. It forms a white crystalline mass 
 like camphor, which is insoluble in water, but soluble in alcohol and 
 ether. It melts at 320, and sublimes at 360 unchanged ; at a red- 
 heat it abandons chlorine and forms the bodies last described. 
 
 Bichloride of Carbon. C 2 C1 4 . Is formed by exposing a body termed 
 chloroform, whose formula is C 2 HC1 3 , or marsh gas C 2 H 4 to an excess 
 of chlorine in bright sunlight. The hydrogen is gradually removed and 
 replaced by chlorine. It is liquid; its sp. gr. is 1*6 ; it boils at 192. 
 The sp. gr. of its vapour is 5302. 
 
 CHAPTER XVIII. 
 
 OF THE COMPOUNDS OF NITROGEN AND HYDROGEN. 
 AMMONIA, ITS DERIVATIVES AND COMPOUNDS. 
 
 ALTHOUGH there is very perfect evidence that hydrogen and nitrogen 
 unite in two, perhaps in three proportions, we as yet know but one of 
 these in an isolated form, which is the volatile alcali, ammonia. This 
 was known to the earliest chemists, but the importance of its history 
 to the progress of chemical philosophy has been but lately felt to its 
 just extent. 
 
 Ammonia is produced in almost all reactions where nitrogen and 
 hydrogen are brought together, one or both being nascent. Thus when 
 an electric spark is passed through damp air, nitric acid and ammonia 
 are both formed, and hence the rain which falls after thunder-storms 
 contains nitrate of ammonia. It is evolved in large quantities in the 
 putrefaction of organic substances containing nitrogen, and is formed 
 also by their distillation at high temperatures, whence the greater supply 
 of ammonia used in the arts is derived. When any oxide of nitrogen 
 
Preparation of Ammoniacal Gas. 
 
 707 
 
 is mixed with hydrogen, and passed through a tube containing red hot 
 spongy platinum, ammonia is formed ; and lastly it is produced abun- 
 dantly when iron or tin is oxidized violently by nitric acid, the oxygen 
 being taken both from the acid and water, the nascent hydrogen and 
 nitrogen unite. Ammonia is also a product of organization, being 
 contained in the sweat of animals, and being exhaled by the flowers of 
 many plants, and by the leaves also of the cruciferse. 
 
 For the purposes of the chemist, ammonia is obtained from the mu- 
 riate of ammonia, or sal-ammoniac, which is manufactured in large 
 quantities for commerce, by processes to be hereafter described. Equal 
 parts of the sal-ammoniac, in powder, and slaked lime are to be inti- 
 mately mixed and heated in a flask a, from which a bent tube passes ; 
 the gas which issues is to be conducted through a tube c, as in the 
 
 figure, containing dry 
 lime, or fused potash, 
 by which adhering mois- 
 ture is removed, and it 
 may then be collected 
 
 over mercury, a 
 
 vessel 
 
 b being interposed to 
 collect most of the water 
 by condensing the watery 
 
 / ^ /"'I l**\ vapour as it passes over. 
 
 liiHiiiiiiiiiiiiiiiiSr ^~ ' tin ."M.J Gaseous ammonia is co- 
 
 lourless and transparent. Its odour is strong, pungent and irritating, 
 well known as the smell of hartshorn. When perfectly dry, it has no 
 action on vegetable colours, but if damp, it reacts powerfully alcaline. 
 The brown colour which it produces on turmeric disappears when heat 
 is applied, by which it is distinguished from the browning by the fixed 
 alcalies, or earths. By a pressure of 6 J atmospheres, or at a tempe- 
 rature of 61 gaseous ammonia is liquefied. When inspired pure, it 
 proves excessively caustic and poisonous. 
 
 Ammonia is slightly combustible. It does not support combustion. 
 "When a series of electric sparks are passed through a quantity of the 
 gas confined over mercury, its volume enlarges, and ultimately becomes 
 double. It is then totally decomposed, and the resulting gas consists 
 of three volumes of hydrogen and one of nitrogen : the specific gravity 
 of ammonia is therefore, 591 '5, as deduced in p. 289 and its formula 
 NH 3 . If a current of ammoniacal gas be passed through a red-hot 
 tube filled with iron wire, it is decomposed in the same way as by elec- 
 tricity. If the tube contain red-hot charcoal, carbon is taken up, and 
 prussiate of ammonia and carburet of hydrogen produced. 
 
708 Water of Ammonia. 
 
 Ammoniacal gas is rapidly absorbed by water, which takes up 780 
 times its volume at 32 Great heat is thereby evolved, and the solu- 
 tion, which augments two-thirds in volume, has a specific gravity of 
 0-872, and boils at 120. It contains then about 32 per cent, of am- 
 monia, and approximates to the formula NH 3 -f- 4Aq. This solution 
 is termed water of ammonia, or improperly liquid ammonia. To pre- 
 pare it upon a larger scale, the matrass and series of three-necked 
 bottles, represented in this figure, may be employed. 
 
 Pive parts of lime, slaked, and mixed with as much water as will con- 
 vert it into a thin paste, are to be introduced with 4 parts of powdered 
 sal-ammoniac, into the matrass, which is then to be placed upon the 
 sand bath, and connected with the range of bottles. The first bottle 
 should be left empty, in order to catch any water, or mixture, that 
 may be carried over, and it should be allowed to grow warm, in order 
 that it may retain no gas ; in the other bottles water is placed, by which 
 the gas is absorbed, and they are kept cool by damp cloths applied to 
 their surface. For ordinary purposes, water of ammonia need not con- 
 tain more than 18 per cent, of gas ; it then has a specific gravity of 
 0-930. 
 
 The watery solution of ammonia possesses all the characters of the 
 gas in a strong degree. It neutralizes the strongest acids, and acts in 
 all respects as a strong base, ranking next to lime. It forms many 
 classes of combinations, in some of which it exists unaltered, but in 
 others, it first undergoes peculiar decomposition. Its action on chlo- 
 rine is very violent and accompanied by flame ; sal-ammoniac is formed 
 and nitrogen set free, as described in p. 359. 
 
 Ammonia is very easily recognized; its odour, the brown colour 
 
Constitution of Ammonia and Amidogene. 709 
 
 given to turmeric paper, which is removed by a gentle heat, and its 
 forming dense white fumes on the approach of a glass rod moistened 
 with strong muriatic acid, characterize it when free; all substances 
 which contain ammonia are either volatilized by heat, or decomposed, 
 the ammonia being generally liberated ; in all cases, by heating the 
 body with moist caustic potash, ammonia is evolved as gas, and may 
 be known by the properties now described. 
 
 The real nature of ammonia has recently been the subject of much 
 inquiry ; its equivalent is satisfactorily determined to be 17, and hence 
 its formula is NH 3 and its equivalent volume 4. It may enter into 
 combination directly with dry oxygen acids, but it does not then form 
 the proper ammoniacal salts, which all contain an atom of water 
 essential to their constitution. It combines with a great number of 
 saline bodies, and then resembles, in its functions, their water of 
 crystallization. Its most remarkable property, however, is, that in 
 acting on metallic compounds, and on certain organic acids, it aban- 
 dons an atom of hydrogen, and the remaining NH 2 combines with the 
 metal, or with the radical of the acid. Thus with HgCl, and NH 3 
 there result Hg.NH 2 and H.C1; with PtCl 2 and 2.NH 3 there are 
 formed Pt + 2.NH 2 and 2.H.C1. Of organic bodies, oxalate of am- 
 monia gives, when heated, C 2 O 2 -f j^H 2 and benzoate of ammonia 
 produces similarly C 14 H 5 O 2 + NH 2 It is hence evident that the third 
 atom of ammonia is not so intimately combined with the nitrogen as 
 the remaining two ; it may be eliminated by the simplest reactions, but 
 the N and H 2 remain much more firmly united, and separate only when 
 the constitution of the ammonia is totally broken up. I hence con- 
 cluded, that the ]^H 2 should be considered as the radical of ammonia, 
 and proposed to term it amidogene, and its symbol Ad. The ammonia 
 is then amidide of hydrogen, and its rational formula NH 2 .H or Ad.H. 
 Ammonia is thus assimilated to water, and to chloride of hydrogen, in 
 constitution, the radical amidogene having the closest analogy to 
 oxygen and chlorine. These conclusions have been almost unanimously 
 adopted by chemists. 
 
 These views are remarkably illustrated by the action of ammonia on 
 potassium; when this metal is heated in the dry gas, hydrogen is 
 disengaged, and a fusible olive green substance is obtained. The 
 quantity of hydrogen evolved is the same as that which the metal 
 should evolve from water, that is one atom, and the olive body con- 
 sists of K.NH 2 . It is amidide of potassium. When put into water, 
 potash and ammonia are produced, K.Ad and HO, giving KO, and 
 H.Ad. When this olive substance is heated nearly to redness, am- 
 monia is expelled and nitmret of potassium remains, 3K.NH 2 giving 
 
710 Compounds of Amidogene. 
 
 21STH 3 and K 3 N. The phenomena are exactly the same with sodium, 
 an amidide and a nitruret of sodium being thus formed. 
 
 In describing the compounds of ammonia, it is unnecessary to dis- 
 tinguish those in which ammonia acts .simply as amidide of hydrogen, 
 resembling in its functions, the oxide or chloride of hydrogen, from 
 the class of bodies in which the ammonia is associated with water, the 
 proper salts of ammonia, which, as already noticed, are isomorphous 
 with those of potash. I shall have occasion to discuss the theory of 
 these bodies further, but shall first describe the most important mem- 
 bers of the former class. 
 
 Ammonia and Chlorine. If a bottle full of chlorine gas be inverted 
 in a cup containing a solution of the sulphate or muriate of ammonia, 
 it is gradually absorbed, and a yellow heavy liquid collects in globules 
 in the bottom of the cup. This substance must be treated with the 
 utmost caution ; if strongly rubbed or struck, or if it be touched with 
 any greasy body, or with phosphorus, it explodes with intense violence; 
 a globule as large as a pin-head, on being exploded in a teacup, shat- 
 ters it to pieces. Almost every chemist who has examined it, has been 
 severely hurt, and hence its composition is not yet well known. Sir 
 Humphrey Davy found, that when decomposed over mercury, it gives 
 nitrogen and chlorine in the proportions by volume of 1 : 3, and hence 
 it was concluded to be chloride of azote N.C1 3 under which name it is 
 described in most books. It has been observed, however, that traces 
 of sal-ammoniac are formed when it is decomposed ; it consequently 
 must contain hydrogen, and it may possibly be bichloride of amidogene, 
 AdCl 2 , which, when decomposed, should produce, N and C1 3 besides 
 AdH.HCl. 
 
 Iodine and Ammonia. When the semi-fluid compound of iodine 
 and ammonia is put into water, it is decomposed into hydriodate of 
 ammonia, and a brown powder which is usually described as iodide of 
 azote, N.I 3 . This substance may also be prepared, by digesting iodine 
 in water of ammonia ; the iodine gradually changing into the brown 
 substance, and the solution containing hydriodate of ammonia : this 
 body must be collected on filters in very small quantity, and dried 
 merely by exposure to the air ; if it be rubbed, even under water, it 
 explodes with a violent detonation, though not so powerfully as the 
 previous body, The cloud of hydriodate of ammonia, formed by its 
 decomposition, is very evident ; it therefore contains hydrogen, and it 
 may be looked upon as a liniodide of amidogene, Ad.Iu- 
 
 A corresponding compound containing bromine has been formed. 
 
 By the action of ammonia on metallic oxides, a numerous class of 
 bodies may be formed, which all possess more or less violent detonating 
 
Fulminating Compounds of Ammonia. 711 
 
 properties ; they all contain combined water. It is impossible to say, 
 positively, whether the ammonia exists undecomposed in these bodies ; 
 I rather think it does, and I shall hence term them ammoniurets. 
 
 Ammoniuret of Silver. This is the most violent of all these com- 
 pounds; it may be formed by digesting recently prepared oxide of 
 silver in water of ammonia, and precipitating the solution by caustic 
 potash. It is a brown powder, which detonates violently by the slightest 
 shock or friction; when exploded, it is said to produce water, azote and 
 metallic silver, which should give for its formula, NHa + 3.AgO -f- Aq. 
 But the facility of its decomposition, which has been the cause of many 
 serious accidents, has prevented it being accurately analyzed. 
 
 Ammoniuret of Gold. AuO 3 -f 2AdH, is produced by the action 
 or water of ammonia on peroxide of gold. It is a brown powder, 
 nearly as explosive as the former body, but it has been accurately ana- 
 lysed by Dumas. These bodies are known as fulminating gold or silver. 
 
 The ammoniuret of platinum is formed by digesting hydrated oxide 
 of platinum in water of ammonia. It is a light brown powder, not yet 
 analysed, and quite different from the impure substance described in 
 books, as Davy's fulminating platinum. 
 
 I have examined the ammoniurets of copper and mercury, formed by 
 digesting the oxides of these metals in water of ammonia, the first is 
 blue, the second yellow; their formulae are 3CuO -f 2.AdH -f 6Aq., 
 and 3.HgO + AdH + 2.Aq. They detonate feebly when heated. 
 There exist, also, compounds of ammonia with the oxides of uranium, 
 of iron, and of osmium, which have not been accurately examined. 
 
 By the action of heat on some metallic compounds of ammonia, 
 true nitrurets of the metals have been obtained, of which the most 
 remarkable are those of copper and mercury. The nitruret of copper 
 was formed by passing ammonia over anhydrous oxide of copper, at a 
 temperature of 480 Pah. ; water is evolved, and the nitrogen and 
 copper unite, forming a black powder, which, at the temperature of 
 540, is decomposed, with the evolution of a red light, into its ele- 
 ments. Its formula appears to be Cu 6 N which corresponds to the sub- 
 
 M 
 
 oxide Cu 2 O, as when replacing oxygen - is equivalent to O (see p. 441)> 
 and Cu 6 N = 3(Cu 2 + -). Schrseter, to whom the discovery of the 
 above compound is due, formed also a nitruret of chrame, whose for- 
 mula is not quite ascertained. When the chloro-amidide of mercury 
 is heated cautiously, the chlorine, hydrogen and some nitrogen are 
 given off, and the nitruret of mercury remains, as a red brown powder, 
 which is eminently explosive. Other less important metallic nitrurets 
 have also been formed. 
 
7 1 2 Nitrurets of Sulphur and Phosphorus. 
 
 Ammonia is absorbed in large quantities by the chlorides of phos- 
 phorus and of sulphur, and substances produced, which possess singular 
 properties. 
 
 Ammoniacal Pro tochloride of Phosphorus. PC1 3 + 5Ad.H. Is ob- 
 tained by exposing the liquid chloride of phosphorus to a current of 
 dry ammonia. It forms a white powder, which, when put in contact 
 with water, produces sal-ammoniac, and an insoluble white substance 
 that has not been analysed ; the reaction is probably that 3(ClH.AdH) 
 and PN 2 H 3 result. ' If the ammoniacal protochloride of phosphorus be 
 calcined without access of air, a very remarkable body, phosphuret of 
 azote, the formula of which is P.N 2 , is produced, whilst phosphorus, 
 hydrogen, ammonia, and sal-ammoniac are expelled. The phosphuret 
 of azote is insoluble in water, and resists the action of the most power- 
 ful acids and alcalies. The composition of the ammoniacal perchlorides 
 of phosphorus is not quite certain, as these bodies appear to decompose 
 each other. The formula given is PC1 5 + 2Ad.H. When calcined they 
 yield phosphuret of azote. Late researches have, however, rendered it 
 very doubtful, if these bodies have really the compositions here given 
 from the analyses of Henry Rose, and their history requires complete 
 re-examination. 
 
 Gaseous ammonia and chloride of sulphur combine in two propor- 
 tions, according as each ingredient is in excess. The formulae of these 
 bodies are SCI -f- AdH and SCI + 2AdH. The former is a brown 
 powder soluble in alcohol and ether ; the latter is a citron-yellow pow- 
 der. They are remarkable for delivering as a product of their decom- 
 position by water or by heat, the sulphuret of azote (S 3 N.) which is 
 a volatile yellow powder, decomposed by the prolonged action of water 
 into ammonia and hyposulphurous acid, 2 (S 3 N) and 6HO. giving 
 3.S 2 O 2 and 2AdH. 
 
 When chloride of sulphur is digested with water of ammonia, a 
 brown substance is formed whose composition is C1S 4 N 3 H 6 . It is pro- 
 bably formed of chloride and amidide of sulphur, SCI + 3 (S.Ad). 
 
 Ammoniacal gas is absorbed in great quantity by the volatile chlor- 
 ides of boron, arsenic, tin, and titanium. The compounds formed are 
 white and crystalline ; they are decomposed by water, and the solution 
 contains sal-ammoniac, and the metal, or the boron, in combination with 
 oxygen. 
 
 There are few metallic salts which do not absorb ammonia, when ex- 
 posed to a current of the dry gas ; but certain metals are specially dis- 
 tinguished by the character that ammonia added to their solutions pro- 
 duces precipitates, which either contain ammonia or amidogene, as is 
 the case with mercury, palladium, and platinum, or by an excess of the 
 
Ammonia- Salts of Zinc and Copper. 713 
 
 ammonia the precipitate is redissolved, and soluble compounds contain- 
 ing ammonia are produced, as occurs with zinc, copper, nickel, cobalt, 
 and also palladium and platinum. The number of combinations thus 
 formed is so very great that it would be tedious to describe all, and 
 
 1 shall hence notice only such as possess scientific or pharmaceutical 
 importance. 
 
 1. AMMONIA-SALTS OF ZINC. 
 
 Dry sulphate of zinc exposed to a current of dry ammonia absorbs 
 it, producing a white powder, 2 (XnO.SO 3 ) + 5 AdH, which dissolves 
 perfectly in water. 
 
 If water of ammonia be added to a solution of chloride of zinc, a 
 basic chloride is precipitated, which being redissolved by an excess of 
 the ammonia, a colourless solution is obtained which crystallizes on 
 cooling. According to the proportion of ammonia in excess, I have 
 found that one or other of two compounds may be formed, one in long 
 and brilliant prisms, the other in fine pearly tables. The latter salt 
 consists of Zn.Cl. -f- 2AdH -f- HO. The former of 2 (Zn.Cl) 4- 
 
 2 AdH + HO. In these salts, as in all such as are produced by the 
 action of an excess of ammonia on a solution of a metallic salt, I consider 
 that the acid exists combined with ammonia, and not with the metallic 
 oxide, in which they differ essentially from those produced by the direct 
 absorption of ammonia by an anhydrous salt, in which I conceive the 
 union of the acid and oxide not to be disturbed. Hence I write the 
 formula of the tabular ammonia-chloride of zinc, as AdH.HCl + 
 AdH.ZnO. When heated it gives oif ammonia and water and a 
 white powder, AdH.ZnCl remains. 
 
 By the action of an excess of ammonia on a solution of sulphate of 
 zinc, the ammonia-sulphate of zinc is formed ; its formula is AdH. HO. 
 S0 3 + AdH.ZnO. It crystallizes in short prisms; when heated it 
 evolves AdH. HO, and a white powder, AdH.ZnO.SOs remains. In 
 crystals it contains 3.Aq. of which it loses two by efflorescence, and the 
 third by a moderate heat. 
 
 2. AMMONIA-SALTS OF COPPEK. 
 
 Chloride of copper absorbs dry ammonia, forming a blue compound, 
 CuCl -f S.AdH, soluble in water. 
 
 When ammonia is added to a strong and hot solution of chloride of 
 copper, until the precipitate which first forms is perfectly redissolved, 
 a deep purple liquor is produced from which octohedral crystals are 
 deposited on cooling. Their formula is AdH.HCl + AdH.CuO. 
 When heated, these crystals evolve ammonia and water, and a blue 
 
714 Ammonia-Salts of Copper, Nickel and Cobalt. 
 
 powder, AdH.CuCl remains, which is totally decomposed by a strong 
 heat. 
 
 Dry sulphate of copper exposed to a current of dry ammonia forms 
 a fine purple powder, whose formula is 2 (CuO.SO 3 ) + 5.AdH. 
 
 An excess of ammonia gives with a strong solution of sulphate of 
 copper a rich purple liquor, from which the ammoniacal sulphate of 
 copper crystallizes on cooling, in large right rhombic prisms, u, u', with 
 dihedral summits, i, i, as in the figure, m being a secon- 
 dary plane. I consider these crystals, however, to be 
 macles. The formula of this salt is AdH.HO.SO 3 + 
 AdH.CuO. When heated, it gives off ammonia and water 
 and a green powder, AdH.CuO. SO 3 remains. 
 Under the name of cuprum ammoniatum, the ammoniacal sulphate of 
 copper is employed in medicine. It is then prepared, by rubbing 
 together sulphate of copper and carbonate of ammonia in a mortar. 
 The mass becomes pasty, owing to the water of crystallization of the 
 sulphate of copper becoming free, aad carbonic acid is given off. The 
 purple mass which results is soluble in water, and generally contains 
 carbonate of ammonia in excess. When a hot and strong solution of 
 nitrate of copper is decomposed by an excess of ammonia, and allowed 
 to cool, the ammoniacal nitrate of copper crystallizes in rhombic octo- 
 hedrons, of a fine purple colour ; its formula is AdH.HO.NOs + Cu.Ad. 
 In this body there is no doubt of the metal being combined with 
 amidogene, and not the oxide with ammonia ; hence, probably, arises 
 its remarkable character of deflagrating violently, when heated until it 
 begins to melt. 
 
 The iodide and fluoride of copper produce compounds resembling 
 those of the chloride. 
 
 3. AMMONIA-SALTS OF NICKEL AND OF COBALT. 
 
 These resemble the correponding salts of copper so perfectly, that it 
 is sufficient to refer to the foregoing for their properties ; and their 
 composition is obtained by substituting Ni or Co for Cu in the 
 formulae. 
 
 4. AMMONIA-SALTS OF SILVER. 
 
 The chloride of silver is soluble in water of ammonia. The solution 
 gives opaque white rhombic crystals, which exhale ammonia when ex- 
 posed to the air, and leave chloride of silver. 
 
 When the sulphate, or the nitrate of silver is treated with an excess 
 of water of ammonia, colourless solutions are obtained, which yield by 
 
Ammonia-Salts of Palladium and Silver. 715 
 
 evaporation double salts, in rhombic prisms having the formulae, AdH. 
 HO.SO 3 + AgAd and AdH.HO.NOg + AgAd. In both salts the 
 silver is combined with amidogene. Chromate of silver and ammonia 
 gives a similar salt. The ammonia-nitrate of silver is employed in 
 testing for arsenic, and in preparing fulminating silver. A remarkable 
 property of it is, that when fused it evolves ammonia and nitrogen, and 
 metallic silver remains mixed with ordinary nitrate of ammonia, and 
 coats the sides of the glass containing it with a brilliant mirror surface. 
 By a higher temperature the nitrate of ammonia is decomposed, and 
 nitrous oxide evolved. 
 
 5. AMMONIA-SALTS OF PALLADIUM. 
 
 This metal is remarkable for giving with ammonia, two series of 
 salts, of which one is soluble, and the other insoluble in water. 
 
 When ammonia is added to a solution of protochloride of palladium, 
 a flesh-coloured precipitate is produced, having the formula, PdCl.AdH. 
 When more ammonia is added, it dissolves, and from the solution, the 
 second salt crystallizes in long rectangular prisms, having the formula 
 AdH.HCl -f- Pd.O.HAd. By a gentle heat, an atom of water is given 
 off, and the metal exists then in the salt as amidide. If, in a solution 
 of this salt, the excess of ammonia be neutralized by muriatic acid, a 
 yellow crystalline precipitate forms, which has the same formula as the 
 first salt, PdCl + HAd. 
 
 With solution of sulphate of palladium and water of ammonia, a pre- 
 cisely similar series of salts is formed ; the first being flesh-red, PdO. 
 S0 3 -f- HAd ; the second salt in colourless prisms, AdH.OH.S0 3 -f- 
 PdO.HAd, and, when dried, the last member becoming PdAd ; and by 
 a small quantity of an acid, a crystalline precipitate, which consists also 
 of Pd.O.S0 3 + HAd. 
 
 The iodide of palladium gives similar salts. With the nitrate no 
 other than the colourless crystalline salt can be obtained, whose form is 
 thin rhombic plates, AdH.HO.N0 5 + Pd.Ad. When heated, it defla- 
 grates like loose gunpowder, and leaves behind metallic palladium, as a 
 black powder. 
 
 In the red and yellow insoluble ammonia-salts of palladium, although 
 the experimental composition is the same, I consider that an important 
 difference of constitution exists. The red salts are formed by adding 
 ammonia to a simple salt of the metal ; direct union then occurs, and 
 we have, for example, PdCl + HAd. But when we form the yellow 
 salt by adding an acid to a solution of the soluble ammonia-salt, I 
 conceive that the acid unites directly with the amidide of the metal, 
 
716 White Precipitate of Mercury. 
 
 and thus forms, for example, PdAd 4- HC1. The yellow ammonia- 
 iodide, PdAd -|- H.I, gradually changes itself back into the red sub- 
 stance, Pdl -f HAd. 
 
 6. AMMONIA-SALTS OF MERCURY. 
 
 From the great influence these bodies have had on the theory of 
 ammonia, and their importance in pharmacy, the mercurial compounds 
 containing ammonia deserve more detailed notice those of any other 
 metal. 
 
 A. Action of Ammonia on the Haloid Salts of Mercury. 
 
 When corrosive sublimate is heated in a current of dry ammoniacal 
 gas, it unites therewith, forming a white compound, fusible and volatile, 
 having the composition 2. HgCl. -f- HAd. By contact with water, this 
 body is decomposed into sal-alembroth and white precipitate; the 
 former, a compound of sublimate and sal-ammoniac, dissolving, and 
 the latter, whose composition will be next studied, separating as a white 
 powder. 
 
 If we add to a cold solution of corrosive sublimate, a very slight 
 excess of ammonia, a copious white precipitate is produced, and the 
 liquor is found to contain exactly half the chlorine of the sublimate 
 combined with hydrogen and ammonia, as sal-ammoniac ; the white 
 powder, which had been known to the early chemists as white precipi- 
 tate of mercury, contains all the mercury and the remaining half of the 
 chlorine of the sublimate. It was supposed to contain also, ammonia 
 and oxygen, but I have proved that it contains only the elements of 
 amidogene, and no oxygen; that its formula is HgCl -f- HgAd; it 
 being a true chloro-amidide of mercury. The theory of its formation 
 is very simple ; 2. HgCl, and 2. HAd, producing, by interchange of the 
 elements of one equivalent of each body, HgCl -f- HgAd, which pre- 
 cipitates, and HC1 + HAd which remains dissolved. This was the 
 first instance in which amidogene was discovered to be combined with 
 a metal, and from its establishment, the true constitution of ammonia 
 was first recognized. 
 
 White precipitate is insoluble in cold water. It is decomposed by 
 boiling water ; two atoms of which, reacting on two of white precipi- 
 tate, produce sal-ammoniac, which dissolves, and a heavy yellow pow- 
 der which is insoluble in water, and has the formula HgCl -f- 2.HgO 
 + HgAd. This body is completely analogous to the oxy chloride of 
 mercury, HgCl + 3.HgO, from which it may be prepared by the action 
 
Ammonia-Haloid Salts of Mercury. 717 
 
 of ammoniacal gas, the third atom of HgO and H.Ad, giving HgAd, 
 and HO which is expelled. When white precipitate is heated suddenly, 
 it is totally converted into calomel, nitrogen and ammonia, but by 
 careful management of the heat, sublimate and ammonia are given off, 
 and a red powder remains, which is a compound of chloride and ni- 
 truret of mercury, HgCl -f- S.HgJ, exactly analogous to the oxy chlo- 
 ride ; by careful management all the sublimate may be expelled and the 
 azoturet of mercury HgJ is obtained as a brown powder, which deto- 
 nates with great violence when struck. 
 
 The white precipitate which has been now described, must be dis- 
 tinguished from another body, which has been confounded with it in 
 the pharmacopoeias, until the difference was shown by Woehler's ob- 
 servations and my analysis. This second or beta- white precipitate is 
 prepared by adding caustic potash to a cold solution of the double salt 
 formed by corrosive sublimate and sal-ammoniac. It may also be 
 formed by boiling alpha- white precipitate in a solution of sal-ammoniac. 
 It has a crystalline aspect, and is not decomposed by boiling water ; 
 when heated it fuses and gives off ammonia and azote, whilst a mixture 
 of calomel, sublimate, and sal-ammoniac sublimes. Its formula is very 
 simple, HgCl -f HAd ; but it may also be looked upon as a compound 
 of alpha-white precipitate and sal-ammoniac, (HgCl 4" HgAd) + 
 (HC1 + HAd) = 2(HgCl + HAd). 
 
 When calomel absorbs dry ammonia, it forms a dark grey powder, 
 which is 2Hg 2 Cl + HAd; by a gentle heat all ammonia may be ex- 
 pelled and the calomel remains quite white. 
 
 If the calomel be, however, digested in water of ammonia, one-half 
 of its chlorine is converted into sal-ammoniac, and a dark grey powder 
 results, which is a compound of subchloride and subamidide of mer- 
 cury ; Hg 2 Cl + Hg 2 Ad. This body which I have termed black pre- 
 cipitate, is formed by a similar reaction to that by which alpha- white 
 precipitate is produced, 2.Hg 2 Cl and 2. HAd. giving Hg 2 Cl -f Hg 2 Ad 
 and HC1 + HAd. By several chemists, the action of water of am- 
 monia on calomel is given as a means of preparing black oxide of mer- 
 cury, which is quite incorrect. The compound formed contains no 
 oxygen. 
 
 The action of the bromides of mercury with ammonia, has not been 
 so minutely studied as that of the chlorides ; it is known, however, that 
 bromide of mercury gives with water of ammonia, a white precipitate, 
 consisting of bromide and amidide, HgBr + HgAd, and analogous to 
 the alpha-white precipitate. The subbromide of mercury produces with 
 water of ammonia, a black powder consisting of Hg 2 Br + Hg 2 Ad. 
 
 Iodide of mercury dissolves plentifully in hot water of ammonia, and 
 
718 Ammonia-Salts of Mercury. 
 
 the solution deposits, on cooling, long prisms of a snow- white colour, 
 which, however, rapidly exhale ammonia when exposed to the air, and 
 leave red iodide of mercury in pseudomorphous crystals. This white 
 body has the formula 2.HgI + HAd. 
 
 There is no iodine compound analogous to alpha- white precipitate, 
 but when that substance is warmed in a solution of iodide of potas- 
 sium, ammonia is evolved and a brown powder is formed, having the 
 formula Hgl + S.HgO + HgAd. 
 
 B. Action of Ammonia on the Oxygen Salts of Mercury. 
 
 When sulphate of mercury is digested in water of ammonia, it is 
 converted into a white substance, to which I have given the name of 
 ammonia-lurpeth. It is not acted on by water nor by alcalies. Its 
 formula is S.HgO -f- SO 3 + HgAd. It is therefore ordinary turpeth 
 mineral combined with amidide of mercury. 
 
 When water of ammonia is added to a solution of nitrate of mer- 
 cury, being cold and not in excess, a white precipitate is formed, a 
 basic ammonia-nitrate, which is found to consist of HAd.N0 5 + 3HgO. 
 It is therefore a basic nitrate of mercury analogous to the ordinary 
 basic nitrate, HO.NO 5 + S.HgO, except that ammonia (amidide of 
 hydrogen) is substituted for water (oxide of hydrogen). If an excess 
 of ammonia be added, and the mixture boiled, the white precipitate 
 becomes heavier and granular, and is then found to consist of HgAd. 
 N0 5 + S.HgO. This substance, the j8 basic ammonia-nitrate, is evi- 
 dently analogous to the former, the hydrogen being replaced by mer- 
 cury, and it corresponds accurately in constitution also to the ammonia- 
 turpeth. 
 
 If either of these basic ammonia-nitrates be boiled in water contain- 
 ing much nitrate of ammonia, they dissolve and form double salts ; 
 that usually formed is in short opaque white prisms, having the very 
 simple composition 4HgO -f- 3(HAd.HO.N05) ; but as it is decom- 
 posed by water into the /3 basic ammonia-nitrate, its formula must be 
 (HgAd.N0 5 + S.HgO) + 2(HAd.N0 5 + SHO). The double salt 
 whicli forms less frequently, is in yellow plates, and has the formula 
 (HgAd.NOs + SHgO) + (HAd.]\ T 5 .HO). 
 
 These double salts may also be generated by boiling oxide of mer- 
 cury in solution of nitrate of ammonia. If the common basic nitrate 
 of mercury be boiled in a solution of nitrate of ammonia, this is decom- 
 posed ; the ammonia being employed in forming amidide of mercury, 
 and the nitric acid being set free, as may be recognised by litmus. 
 
 The subsulphate of mercury, Hg 2 O.S0 3 acted on by water of am- 
 
Ammonmcal Salts of Platinum. 719 
 
 monia, produces a black powder, the formula of which is, Hg 2 O.S0 3 + 
 Hg 2 Ad ; it is easily decomposed. 
 
 By acting on a solution of subnitrate of mercury in water, with 
 ammonia, added dilute, and in such quantities as to leave a portion of 
 the mercurial salt undecornposed, a fine velvety black precipitate is 
 obtained, known in pharmacy as Hahnemann's soluble mercury. It is 
 very easily decomposed by heat or by an excess of ammonia. In order 
 to obtain it pure, the solution should be quite free from red oxide, and 
 not more than three-fourths of the whole quantity should be precipi- 
 tated. When quite pure, I have found its formula to be HAd.NOs + 
 2.Hg2O ; it being perfectly analogous to the common basic subnitrate 
 HO.NO 5 + 2.Hg 2 O. The oxide of hydrogen being replaced by the 
 amidide. 
 
 The results with the other salts, both of the red and black oxide of 
 mercury, are similar to those above described ; but as none of them are 
 specially important, I shall not occupy space with their description. 
 
 7. AMMONIA-SALTS OF PLATINUM. 
 
 When protochloride of platinum is dissolved in muriatic acid and 
 an excess of ammonia, a green precipitate is produced, composed of 
 PtCl + HAd. It may be prepared in larger quantity by passing a 
 current of sulphurous acid gas through a solution of bichloride of 
 platinum until it assumes a deep brown colour, and then adding am- 
 monia. By boiling this green substance in strong water of ammonia, 
 it forms a white powder, the formula of which is PtCl -f 2. HAd. 
 
 The relations of the ammonia compounds of platinum have become 
 even more remarkable than those just described for the ammonia com- 
 pounds of mercury, and there is no doubt but that platina with ami- 
 dogene and chlorine, or oxygen, is capable of generating a number of 
 compound radicals, or quasi-metallic bases, which form full classes of 
 salts of very definite and marked character, and which serve thus to 
 connect the more simple relations of the metallic salts of inorganic 
 chemistry with the history of the organic compounds. 
 
 The green body just noticed appears to be simply a compound of 
 protochloride of platina with ammonia, its formula to be PtCl -f- NH 3 . 
 But when it is dissolved in water of ammonia, so as to form the white 
 body, its nature appears totally changed. This white substance is 
 apparently a chloride of a compound radical PtAd 2 H 2 + Cl. By de- 
 composition with an alcali the oxide of the radical is obtained hydrated 
 PtAd 2 H 2 -f -f Aq.j with oxygen acids, as the nitric, it forms a class 
 of crystallizable salts, of which the formula is (PtAd2H 2 ) O + X. 
 
720 Ammonia-Salts of Platinum. 
 
 When any of these bodies is carefully heated, it is partly decomposed, 
 an atom of ammonia being given off, and there remains a corresponding 
 compound of another compound radical, of which the formula should 
 be PtAdH. Thus by heating the chloride, PtAd 2 H 2 + Cl, there is 
 obtained by loss of NH 3 the new chloride PtAdH + Cl. This is isomeric 
 with the green ammonia protochloride of platina, but it is totally dif- 
 ferent from it in properties. It is evident that the relation between 
 these two classes of bodies might be also explained, by the simple 
 presence in one class of an atom of ammonia, absent in the other, as 
 the chloride, PtAdH -f Cl, might unite with an atom of ammonia, just 
 as chloride of copper or of mercury may. But it is adverse to this 
 view that the alcaline salts to which these salts of compound radicals 
 ally themselves, do not absorb ammonia, which is taken up usually by 
 the salts of the magnesian and copper class, to form more complex 
 saline combinations. Moreover, solutions of the oxides of these platina 
 compound radicals are strongly alcaline and caustic; they absorb car- 
 bonic acid from the air, and they perfectly neutralize the strongest 
 acids, so that certainly their analogue and type is the ammonium NH 4 , 
 of which class of radicals they serve as still more complex instances. 
 
 There is even a third radical derived from the green ammonia proto- 
 chloride of platinum. On dissolving it in nitric acid, boiling, but not 
 in great excess, there is formed a salt which is the nitrate of a com- 
 pound radical, containing the elements PtClAd 2 H 2 . Erom this nitrate 
 may be prepared the oxide, chloride, and all other salts of this radical, 
 whose combinations are crystallizable, or sparingly soluble, so that they 
 are easily obtained pure. Still more if the green salt be dissolved in a 
 larger excess of strong nitric acid, salts are obtained, which appear to 
 contain still other radicals. Thus the complex nitrates 
 
 Pt 2 Cl O 5 N 4 Hi 2 + 2NO 5 and 
 Pt 2 C1 2 4 N 4 Hi 2 + 2NO 5 
 
 As there are no simple nitrates known containing two atoms of nitric 
 acid, these are, evidently, either double salts of two distinct radicals, or 
 mixtures of the two crystallized together. Those radicals should be 
 PtC10Ad 2 H 2 , and PtO 2 Ad 2 H 2 . Thus being formed by the addition of 
 oxygen to the radical No. 3 in the first instance, and by the substitu- 
 tion, completely, of oxygen for chlorine in the latter case. 
 
 There thus appears to be no less than five compound radicals de- 
 rivable from the green ammonia-protochloride of platinum, or Magnus' 
 Salt as it is usually termed. These radicals are all analogous to alca- 
 line metallic bases, like ammonium. Their oxides are soluble, brown 
 turmeric, taste caustic, and perfectly neutralize even strong acids. 
 
Compound Platinum-lases. 721 
 
 They may be characterized from the names of the Chemists who have 
 most studied them, thus 
 
 A. Pt. AdH. Eadical of Keiset. 
 
 B. Pt. Ad 2 H 2 . -- Peyronne. 
 
 C. Pt.Cl. Ad 2 H 2 . -- Gros. 
 
 ' ' 2 ' \ Radicals presumed to exist in Rawsky's nitrates. 
 
 Mi. Jrt.U 2 Aa 2 .H 2 . 3 
 
 When the bichloride of platina is acted on by ammonia, a very com- 
 plex series of re-actions takes place, which I have described in detail 
 elsewhere, and which terminate in the production of a colourless solu- 
 tion containing an ammoniacal base, which has considerable relation to 
 those just noticed in Raewsky's nitrates. The removal of the chlorine 
 from the bichloride of platinum takes place by so many stages, that it 
 is excessively difficult to obtain any one condition perfectly separate. 
 There may be fully traced, however, the formation first of a chloride 
 analogous to that of Gros' Radical, and then a chloride analogous to 
 that of the radical PtC10.Ad 2 H 2 , and finally the chloride of the radical 
 PtO 2 Ad 2 H 2 is obtained ; but whether these are identical or isomeric 
 with the radicals of Gros' and Raewsk/s salts, I do not consider to 
 have been perfectly established. 
 
 I have shown that by acting on the biniodide of platinum with water 
 of ammonia, there is produced a biniodo-amidide of platinum quite 
 analogous to the white precipitate of mercury, but which, however, re- 
 tains water, its formula when most dry being PtI 2 -f PtAd 2 H- 4Aq. 
 It does not appear to act as a compound radical. 
 
 By the action of ammonia on perchloride of gold, an olive-brown 
 powder is produced, which fulminates when rubbed. It is decomposed 
 by water, and its real formula has not yet been established. 
 
 PRODUCTS OF THE ACTION OF AMMONIA ON THE ANHYDROUS 
 
 ACIDS. 
 
 "When chloro-sulphurous acid, S0 2 C1, is exposed to dry ammonia, it 
 is converted into a white saline mass, which is a mixture of sal- 
 ammoniac and sulph-amide ; S0 2 .C1 and 2AdH, giving SO 2 .Ad. and 
 HC1 -f HAd. The former, which consists of amidogene united to 
 sulphurous acid, is soluble in water, and may be obtained crystallized ; 
 but, when boiled with water, it is changed into common sulphate of 
 ammonia, 2HO and SO 2 .Ad, giving SO 3 + AdH.HO. 
 
 When dry sulphurous acid and ammonia gases are mixed, they com- 
 bine to form a reddish substance, which is decomposed by water ; there 
 appears to be two proportions possible, giving the bodies, SO 2 .HAd, and 
 2SO 2 . HAd. 
 46 
 
722 Ordinary Salts of Ammonia. 
 
 Dry sulphuric acid unites with dry ammonia in two proportions, 
 forming S0 3 .HAd, and 2SO 3 .HAd. I consider these compounds as 
 corresponding to the English and German hydrates of sulphuric acid ; 
 the ammonia playing the part of water. A solution of these bodies is 
 not at first precipitated by barytes, but gradually becomes changed into 
 ordinary sulphate of ammonia. 
 
 It was supposed that the chloro-carbonic acid CO.C1, combined di- 
 rectly with ammonia, but Regnault has found that decomposition occurs, 
 and that sal-ammoniac and amidide of carbonic oxide result. This 
 body, which he terms carbamide, CO.Ad, is white, soluble in water, 
 is not deliquescent, and resists the action of alcalies and acids, unless 
 they be very concentrated. 
 
 OF THE COMMON AMMONIACAL SALTS. 
 
 Prom the great number of classes of compounds, described in the 
 preceding sections, it is evident that ammonia enters into combination 
 with acids and with bases, with haloid and with oxygen salts, in such 
 manner as assimilates it fully to the oxide and chloride of hydrogen in 
 its action, but removes it totally from all analogy with the alcalies, to 
 which it, in other points of view, strictly belongs. For the ordinary 
 salts of ammonia, of which the description now comes, are isomorphous 
 with the corresponding salts of potash, and the strong basic characters 
 of the solution of ammonia had given to it, from the earliest times, the 
 name of the volatile, or animal alcali. The characteristic distinction is, 
 that in all cases where it acts as an alcali, ammonia is associated with 
 water, it is not AdH, which is the alcali, but AdH + HO, or rather 
 NH 4 O. The element which replaces potassium in the isomorphous 
 salts being subamidide of hydrogen, AdH 2 , or NH 4 . 
 
 At the time when Mitscherlich showed the isomorphism of the potash 
 and ammonia salts, nothing was known of the true constitution of am- 
 monia, or of amidogene, and in order to explain the necessity of the 
 presence of water, a very ingenious theory was proposed by Berzelius 
 arid Ampere. It was, to consider that these ammoniacal salts do not 
 contain ammonia at all, but another compound of nitrogen and hydro- 
 gen, NH 4 , which is metallic, and resembles potassium in all general 
 characters, and for which the name ammonium was proposed. This 
 view squared accurately with experiment, as in every oxygen salt of 
 ammonia there is just so much water as may form, with the ammonia, 
 oxide of ammonium, NH 4 .0, and in every haloid salt, the electro-ne- 
 gative body is combined with as much hydrogen as may convert the 
 ammonia into the compound metal ; thus, NH 3 .HO -f- S0 3 , and NH 3 
 -f- HC1, would give NH 4 .O -f SO 3 and NH 4 .C1. Not merely was 
 
Ammoniacal Amalgam. 723 
 
 this theory consonant to numbers, but experiment gave very good reason 
 to believe in the real existence of this compound metal, by the remark- 
 able properties of the ammoniacal amalgam. 
 
 When a globule of mercury, immersed in water of ammonia, is made 
 the negative pole of a galvanic battery, it increases fifty-times in vo- 
 lume, becomes semifluid and covered with warty excrescences, and 
 finally becomes so light as to float on water. No hydrogen is evolved 
 from its surface, but oxygen is copiously given off 1 from the positive 
 electrode. If the current be interrupted, a copious disengagement of 
 hydrogen occurs from this metallic sponge, which also gives off am- 
 monia, and it soon falls back to its original appearance. By cold this 
 decomposition may be retarded ; the pasty mass may be removed from 
 the liquor, and is found to crystallize in cubes at a cold of 0, and if 
 decomposed when dry, over mercury, it evolves ammonia and hydrogen 
 by volume in the proportion of 2 : 1. This indicates that the mercury 
 is therein combined with a body which consists of NH 4 , and as the 
 mercury retains its lustre, the compound formed is properly an alloy, 
 and the body NH 4 , is of a metallic nature. It may be the metal am- 
 monium, almost perfectly isolated. All these phenomena may be ob- 
 served by dissolving one grain of potassium in 100 grains of mercury, 
 and dropping the globule into a glass containing strong solution of sal- 
 ammoniac. By the action of K.Hg on NH 4 .C1, there are produced 
 K.C1 and Hg.NH 4 ; the globule of mercury swells up rapidly, and the 
 amalgam is sufficiently permanent to be easily examined. 
 
 I have no doubt, there is thus obtained a substance possessing some 
 metallic characters, and consisting of ammonia and hydrogen, in fact, 
 subamidide of hydrogen, Ad.H 2 ; but whether the water which is found 
 in the common ammoniacal salts exist therein as such, or whether these 
 salts contain true oxide of ammonium, is not thus decided. In fact, 
 among the metallic compounds of ammonia already examined, we have 
 found bodies every way similar to the ordinary salts of ammonia, except 
 that a part of the hydrogen is replaced by a metal. Thus, if we com- 
 pare sal-ammoniac with other similar bodies, as in the following for- 
 mulae : 
 
 1. C1NH4. 5. CINHaNi. 
 
 2. Cl N H 3 Cu. 6. Cl N H 3 Hg. 
 
 3. ClNH 3 Zn. 7. Cl N H 2 Hg2. 
 
 4. Cl N H3 Pd. 8. CL N H 2 Pt 2 . 
 
 and that we find them all produced by the action of ammonia on a 
 chloride of a metal, just as sal-ammoniac is formed by the action of 
 ammonia on chloride of hydrogen, we must admit their similarity of 
 constitution; and if we say that in No. 1, NH 4 forms a compound 
 metal, we must consider all the others as chlorides of compound radi- 
 
724 Theory of Ammonium. 
 
 cals also. Still more, the connexion is so perfect from these bodies to 
 such as resemble the yellow powder, HgCl -f 2HgO 4- HgAd, and 
 from that to the oxychloride, HgCl + 3HgO, that if we insist on as- 
 suming the compound metal ammonium to exist ready formed in the 
 salts of ammonia, we must lay down as a general principle that all basic 
 salts are salts of compound metals, a proposition which, as already ex- 
 plained in pages 593, 594, cannot be at present admitted in chemical 
 philosophy. At the same time, therefore, that I consider the ammo- 
 niacal amalgam to contain ammonium, I believe it to be formed only 
 at the time, and that the ordinary salts of ammonia contain ammonia 
 and water, the latter being united as the constitutional water is in the 
 magnesian sulphates, but more intimately. Thus, sulphate of ammo- 
 nia, S0 8 -f- AdH.HO, I consider to resemble the bihydrated sulphuric 
 acid, SO 3 + HO. HO. In both cases an atom of water may be re- 
 placed by an oxide of the magnesian class. 
 
 It will be necessary only to notice the more important of the ordi- 
 nary salts of ammonia. 
 
 Muriate of Ammonia Sal-ammoniac. C1.H 2 Ad. Eq. 666*8 or 53*5. 
 This salt, formerly derived from Africa, is now manufactured on the 
 large scale from the ammoniacal liquor obtained in the destructive dis- 
 tillation of horns, bones, coals, and such other organic matters as con- 
 tain nitrogen. Those liquors, which contain ammonia, combined prin- 
 cipally with carbonic acid and sulphuretted hydrogen, are decomposed 
 by means of muriatic acid added in slight excess. By evaporation to 
 a pellicle and cooling, the sal-ammoniac is obtained in small crystals, 
 deeply coloured with tarry matter. They are purified by re-crystalliza- 
 tion, and finally placed in cast iron pots, set in a furnace, lined with 
 fire-tiles, and fitted with leaden heads, into which the sal-ammoniac is 
 sublimed. The temperature is so managed that the sublimed salt forms 
 a coherent, hemispherical mass, often weighing lOOlbs., and when pure 
 should be perfectly free from yellow stains, and nearly transparent. If 
 muriatic acid be dear, the ammoniacal liquor may be neutralized by 
 sulphuric acid ; sulphate of ammonia is formed, which is decomposed 
 by the addition of common salt, and the sulphate of soda and sal-ain- 
 moniac separated by crystallization. 
 
 Sal-ammoniac is very soluble in water ; it crystallizes both by sub- 
 limation and solution, in cubes and octohedrons ; it is slightly deli- 
 quescent and is soluble in alcohol; it volatilizes below a red heat. 
 "When heated with lime or potash it yields ammonia, as described in p. 
 708. It consists of an equivalent of each element, its formula being 
 HCl.HAd. It may be formed by their direct combination. When 
 equal volumes of dry muriatic acid gas and ammonia are mixed toge- 
 
Preparation of Sal-ammoniac. 725 
 
 ther, the two gases disappear, and a snow-white powder of sal-ammo- 
 niac results. Hence arise the white fumes when a rod dipped in water 
 of ammonia is brought where chlorine or muriatic acid gas is evolved, 
 or when a rod dipped in muriatic acid is brought to where ammonia is 
 escaping. It thus renders these bodies the means of detecting each 
 other. 
 
 Sal-ammoniac is remarkable for the number of double salts which it 
 produces, and of which some deserve notice. 
 
 With chloride of magnesium, it forms the anhydrous salt Adfl^Cl 
 + MgCl, which is used in preparing metallic magnesium. 
 
 With perchloride of iron, it crystallizes in fine red octohedrons, 
 Ee 2 Cl 3 + 3(AdH 2 Cl). When these are heated, sal-ammoniac sublimes, 
 coloured by some chloride of iron, and forms thus ike fares martiales. 
 
 The double salts formed with the chlorides of copper, zinc and nickel, 
 crystallize in cubes. They are all composed like that of copper, which 
 is CuCl + AdH 2 Cl + 2Aq. 
 
 Corrosive sublimate unites in two proportions with sal-ammoniac. 
 The first salt, of which the formula is HgCl -f AdH 2 Cl + Aq. is very 
 soluble in water, and crystallizes in flat rhomboidal tables, which efflo- 
 resce when exposed to the air. This is the sal-alembroth of the older 
 chemists. The second salt crystallizes in rhomboidal prisms, which 
 sublime unchanged, and have the formula, 2HgCl + AdH 2 Cl. It is 
 by the formation of these salts that corrosive sublimate becomes so 
 easily soluble in a solution of sal-ammoniac. 
 
 Sal-ammoniac and bichloride of platinum form a double salt, whose 
 formula is PtCl 2 -f- AdH 2 Cl. It precipitates as a bright yellow powder, 
 when solutions of its constituents are mixed, and especially if alcohol 
 be added, in which it is very insoluble. It is but very sparingly so- 
 luble in water, but more so in boiling water, from which it crystallizes 
 in orange- red octohedrons. When ignited, it leaves behind metallic 
 platinum in the form of a light sponge. It is of use in preparing 
 spongy platina, and in the detection of ammonia. 
 
 With chloride of gold, sal-ammoniac forms a double salt, which 
 crystallizes in orange-red cubes, having the formula AuCl 3 + AdH 2 Cl 
 
 The hydrobromate and hydriodate of ammonia do not require special 
 notice ; they resemble the sal-ammoniac in all important characters, 
 and combine with the metallic bromides and iodides to form similar 
 double salts. 
 
 HyclrosulpJiuret of Ammonia. When sulphuretted hydrogen and 
 ammonia gases are mixed in equal volumes, in a vessel cooled by ice, 
 they combine, forming colourless needles, which evaporate at ordinary 
 
726 Sulphate and Nitrate of Ammonia. 
 
 temperatures. The formula of this compound is SH-f-HAd, or S.NH 4 
 analogous to protosulphuret of potassium S.K. Like that it combines 
 with as much more sulphuret of hydrogen, forming a volatile crystal- 
 line compound, AdH 2 ,S + SH. This Uhydrosulphuret of ammonia is 
 formed also when sulphuretted hydrogen is passed into water of am- 
 monia, as long as it is absorbed. Por each atom of ammonia present, 
 two atoms of sulphuretted hydrogen are taken up. By exposure to the 
 air, this solution becomes yellow, owing to the absorption of oxygen 
 and the liberation of sulphur. It is capable of dissolving a large quan- 
 tity of sulphur, forming compounds analogous to the higher sulphurets 
 of potassium. This hydrosulphuret of ammonia is of great importance 
 in the detection of the metals, from the formation of metallic sulphur- 
 ets. It is a sulphur base, and forms salts with the sulphur acids, 
 analogous to those formed by sulphuret of potassium 
 
 Sulphate of Ammoniac AdH 2 .O.S0 3 -f Aq. This salt is formed on 
 the large scale in the manufacture of sal-ammoniac ; it may be prepared 
 pure by neutralizing water of ammonia by sulphuric acid ; it crystallizes 
 in flat rhomboidal prisms, as in fig. or in macles, isomor- 
 phous with the crystals of sulphate of potash. It is very 
 soluble in water, but insoluble in alcohol ; when heated, it 
 gives off water, ammonia and azote, and sulphite of am- 
 monia sublimes. It combines with the sulphates of copper, 
 zinc, iron, alumina, &c., forming double salts exactly analogous to 
 those formed by sulphate of potash. With oil of vitriol it unites to 
 form Usulphate of ammonia, which is deliquescent and soluble in al- 
 cohol. 
 
 Nitrate of Ammonia. AdH 2 O.N0 3 . Is formed by neutralizing nitric 
 acid by ammonia. It crystallizes in striated hexagonal prisms, isomor- 
 phous with nitre, of a bitter saline taste ; they are deliquescent and 
 very soluble in water. When heated, thev fuse at 230, and at about 
 460 are rapidly decomposed into nitrous oxide and water, as described 
 p. 373. By the presence of a large excess of sulphuric acid, this 
 action takes place at much lower temperatures. When heated with 
 combustible bodies, it deflagrates with extreme violence. 
 
 Phosphates of Ammonia. The tribasic phosphoric acid forms, with 
 ammonia, two salts ; the first, whose formula is (P0 5 -j- AdH 2 -f 
 2 HO) -f Aq., is prepared by adding the acid in excess to water of am- 
 monia; it crystallizes in rhombic prisms, which are very soluble in 
 water. Their reaction to test paper is strongly acid. If the ammonia 
 be added in excess, a salt crystallizes, possessing nearly the same cha- 
 racters, except that its reaction is alcaline, and its formula P0 5 + 
 2(AdH 2 O) -f. HO. Both of these salts yield, by ignition, phosphoric 
 acid. 
 
Phosphates and Carbonates of Ammonia. 727 
 
 Ammoniaco-Maffnesian Phosphate. When a solution of a salt of 
 magnesia is added to any soluble phosphate, and the liquor rendered 
 alcaline by ammonia, a crystalline precipitate is formed, which is so- 
 luble in acids, sparingly soluble in water, but insoluble in alcaline 
 liquors. Its formula is PO 5 -f (AdH 2 O -f 2MgO) -f 12Aq. Its for- 
 mation is often of use for the detection of magnesia, and it is occasion- 
 ally generated in urine by the action of ammonia, produced by the 
 spontaneous decomposition of urea, upon the soluble phosphates of 
 magnesia, which it contains. It then constitutes a common variety of 
 calculus. 
 
 Phosphate of Ammonia and Soda. This salt, of which the formula 
 is PO 5 + (AdH 2 O -f NaO -f- HO) + 8 Aq., is easily produced by mix- 
 ing together, in solution, six parts of common phosphate of soda and 
 one of sal-ammoniac. On cooling, it crystallizes in large prisms, 
 which effloresce in the air. When heated, it gives monobasic phos- 
 phate of soda and free phosphoric acid, as a source of which it is much 
 used in blowpipe experiments, under the name of microcosmic salt. It 
 is found in all the animal fluids. 
 
 Carbonates of Ammonia. The salt which under this name is used 
 for medicinal purposes, is prepared by mixing together one part of sal- 
 ammoniac with two of powdered chalk, and exposing the mixture in 
 an earthen pot to a heat below redness. These bodies reacting, pro- 
 duce chloride of calcium and carbonate of ammonia, which sublimes 
 and is condensed as a crystalline semi-transparent mass, in a dome- 
 shaped receiver, which is fastened on the subliming pot. By right this 
 should be a neutral salt, AdH 2 .Cl. and CaO.CO 2 , giving CaCl and 
 AdH 2 O.CO 2 ; but a quantity of ammonia and water is given off", and 
 the sublimed salt was considered to be a sesquicarbonate, consisting of 
 2 (AdH 2 O) + S.COg, until Scanlan showed that it was a mixture of 
 two different salts, which may be separated by water. Rose has re- 
 cently thoroughly examined the carbonates of ammonia, of which there 
 are a great number, but only four sufficiently important to be noticed 
 here. 
 
 The proper neutral carbonate of ammonia, AdHaO.COg, does not 
 exist, except in combination, but its compounds are very numerous ; it 
 forms, 
 
 1st. With carbonate of water, the ordinary bicarbonate of ammonia, 
 AdH 2 O.CO + HO.CO 2 . This is prepared by washing the commercial 
 sesquicarbonate with cold water or alcohol, when it remains behind as a 
 skeleton of crystalline grains, which are isomorphous with bicarbonate 
 of potash. It evaporates spontaneously, with a weak odour of ammonia. 
 Its solution reacts feebly alcaline. By pouring on the commercial 
 
728 Carbonates and Oxalates of Ammonia. 
 
 sesquicarbonate as much boiling water as dissolves it, and letting the 
 solution cool in a close bottle, so that no carbonic acid can escape, this 
 salt may be obtained in large rhomboidal crystals, which contain one 
 and a-half atoms of water. 
 
 2nd. The substance which is dissolved out of the sublimed mass of 
 sesquicarbonate, by alcohol, is identical with that formed by the union 
 of dry carbonic acid and ammonia. Its formula is therefore .AdH.CO 2 , 
 and the ordinary sesquicarbonate is a mechanical mixture of it with the 
 bicarbonate. 
 
 When the sublimed sesquicarbonate is distilled at a moderate heat in 
 a retort, it abandons carbonic acid, and two salts, differing in volatility, 
 are condensed in the neck. The more volatile consists of AdH 2 O.CO 2 + 
 HAd.C0 2 ; being a compound of neutral carbonate with dry carbonate, 
 or a bicarbonate in which the basic oxide of hydrogen is replaced by 
 amidide of hydrogen ; the two double salts, 
 
 AdH-2O.CO 2 -f- HO.CO2, water-bicarbonate of ammonia. 
 AdH 2 O.CO2 + HAd.CO2, ammonia-bicarbonate of ammonia. 
 
 being precisely equivalent in composition. The less volatile product is 
 of very complex composition ; its formula is 4(AdH 2 0) + 5C0 2 , or it 
 consists of an atom of neutral carbonate united to an atom of each of 
 the different bicarbonates, thus : 
 
 AdH 2 O.CO 2 ) 
 
 AdH 2 O.C0 2 + HO.C0 2 \ = 4(AdH 2 0) 4- 5CO 2 
 
 AdH 2 O.CO 2 + HAd.CO 2 ) 
 
 Oxalate of Ammonia. AdH 2 O.C 2 O 3 . May be prepared by neu- 
 tralizing oxalic acid by water of ammonia; it crystallizes in right 
 rhombic prisms, as in the figure, where p, u, u, are 
 primary, and i, t, secondary planes. These crystals con- 
 tain an atom of water, which they lose by efflorescence in 
 dry air. When heated, it is completely decomposed, water 
 being evolved, and oxamide subliming, Ad.H 2 .O.C 2 O 3 , 
 producing 2. HO and Ad.C 2 2 . This neutral oxalate of ammonia com- 
 bines with oxalic acid, forming a binoxalate and a quadroxalate like 
 those of potash. 
 
 The oxamide may also be prepared by acting on oxalic ether with 
 water of ammonia, or by dissolving oxalic acid in a mixture of equal 
 volumes of oil of vitriol and alcohol, and adding ammonia in excess. 
 It is a light white powder, tasteless and insoluble in water ; it is de- 
 composed by acids and by strong bases, in contact with water, oxalic 
 acid and ammonia being regenerated. Its discovery by Duinas laid 
 the foundation of our present knowledge of the nature of ammonia, 
 by leading him to the idea of the probable existence of arnidogene, as 
 
Oxamide and Oxamic Acid. 729 
 
 its composition was so simply explained by considering the oxalic acid 
 and ammonia to have lost simply the element of an atom of water. It 
 might also be looked upon as a hydrate of cyanogen, C 2 N -f- 2 HO. 
 
 The oxamide is not the only product of the decomposition of oxalate 
 of ammonia ; at a lower temperature, there is found in the retort, a 
 yellow mass which possesses acid properties, and has been termed the 
 oxamic add. This acid is moderately soluble in water, and forms 
 crystallizable salts. Its formula is C 4 1X T H 2 O 5 , that is C 2 O 3 -f- C 2 O 2 1S T H 2 , 
 so that it may be considered as a compound of oxalic acid and oxamide. 
 The stages in the decomposition of oxalate of ammonia may thus be 
 now understood 
 
 Two atoms of the salt, C^e^He + 4Aq. 
 
 give off N Ha and HO with 4Aq. 
 
 and leave oxamic acid, 
 which more strongly heated, give off CO and CO2 C 2 Os elements of oxalic acid, 
 
 and leave oxamide, C2O2NH2 
 
 This again by a still stronger heat is resolved into carbonic acid, 
 prussic acid, and ammonia, 2(C 2 2 NH 2 ), producing C 2 O 4 with C 2 NH 
 and 
 
 CHAPTER XIX. 
 
 OF CYANOGEN AND ITS COMPOUNDS, AND OF THE BODIES 
 DERIVED FROM IT. 
 
 THERE is no class of organic bodies of which our knowledge is more 
 extensive and exact, than those which have cyanogen as their basis. 
 The powerful affinities which this radical exerts, the simplicity of its 
 constitution, and above aD, our being able to prepare it in an isolated 
 form, and to generate its compounds directly from it, as we could those 
 of a truly simple body, render its history the most advanced portion of 
 organic chemistry, and that to which the analogy of mineral bodies 
 
730 Preparation of Cyanogen. 
 
 and the theory of compound organic radicals, is most undeniably appli- 
 cable. 
 
 Cyanogen does not exist in nature ready formed ; the kernels of 
 peaches, plums, bitter almonds, &c. and the leaves of the cherry-laurel, 
 yield, by simple distillation, abundance of prussic acid, (cyanide of 
 hydrogen), but this is only then produced by the decomposition of 
 other substances containing nitrogen. 
 
 Cyanogen may, however, be formed abundantly, and in a simple 
 manner, by bringing its elements together at a high temperature, in 
 contact with substances with which it may unite. Thus when any or- 
 ganic substance containing nitrogen is calcined with potash, the nascent 
 carbon and hydrogen unite, and cyanide of potassium is formed ; even 
 with pure charcoal this occurs, nitrogen being derived from the air ; 
 and Mr. Eownes has shown, that when a mixture of pure charcoal and 
 potash are ignited in a tube, and a current of pure nitrogen passed 
 through it, this is absorbed and carbonic oxide gas being given off, 
 cyanide of potassium is produced, 3C with KO and N, giving CO and 
 C 2 N.K. This mode of forming cyanogen has even been made the basis 
 of manufacturing processes on the great scale, and at present much 
 ferroprussiate of potash so formed is sent into commerce. By the 
 action of ammonia also, on ignited charcoal, cyanogen is formed in 
 abundance ; it combines with hydrogen and the excess of ammonia, 
 and produces prussiate of ammonia. In this case 2C and 2NH 3 pro- 
 duce C 2 N 4- NH 4 and H 2 become free. It is by virtue of these pro- 
 cesses, that cyanogen is produced for its various applications in the 
 arts, but as I shall return to them in detail, I shall now only consider 
 further the mode of obtaining it free and pure. 
 
 Cyanide of silver, or cyanide of mercury, of which the preparation 
 will be described hereafter, is to be introduced into a small glass retort, 
 and heated to just below redness ; a gas is given off which must be 
 collected over the mercurial trough; the cyanide of silver separates 
 simply into metal and cyanogen ; but when cyanide of mercury is used, 
 a brown powder appears, the quantity of which is less as the tempera- 
 ture of decomposition has been lower. The gas which comes over is, 
 however, cyanogen completely pure. If a large supply of cyanogen 
 be required, but not of absolute purity, it may be prepared by mixing 
 boiling solutions of two parts of corrosive sublimate and three parts of 
 yellow prussiate of potash, and drying down the liquor : the dry mass 
 which is a mixture of cyanide of mercury, of chloride of potassium, 
 and cyanide of iron, gives out on the application of heat a very large 
 quantity of cyanogen gas nearly pure. 
 
 The properties of cyanogen are very marked. It is colourless, of a 
 
Properties of Cyanogen . 731 
 
 sharp smell, which irritates the eyes. Its sp. gr. is 1819. If a quan- 
 tity of cyanide of silver be sealed up in a strong tube, bent as in the 
 figure, and then heated at one end a, the cyanogen is condensed by a 
 
 pressure of about four atmospheres, 
 and collects at the other end b as a 
 colourless liquid. It is combustible, 
 burning with a beautiful rose-coloured 
 flame, and producing two volumes of carbonic acid and one of nitro- 
 gen. It is constituted, therefore, of equal volumes of carbon vapour, 
 and nitrogen ; the two volumes being condensed to one ; hence 836 4* 
 976 = 1812 is its sp. gr. It dissolves abundantly in alcohol and water, 
 but these solutions soon undergo very complex decompositions ; the 
 liquor being found to contain carbonic acid, prussic acid, ammonia, 
 urea, and oxalic acid, besides a brown insoluble matter. A similar de- 
 composition is produced much more rapidly by contact with water of am- 
 monia. The composition of this brown matter appears to be C 4 N2HO. 
 It dissolves in alkalies, and gives precipitates with the metallic salts ; 
 it has been termed hence azulmic acid. When heated it gives off 
 water, and leaves a deep brown powder, of the same composition as 
 cyanogen, and which has been termed paracyanogen. This may be 
 also formed by heating cyanide of mercury very strongly. It dissolves 
 in hot nitric acid, and the solution gives, with water, a yellow preci- 
 pitate, which combines with bases, and has been termed paracyanic 
 acid. By strong ignition, paracyanogen evolves nitrogen, and a very 
 dense carbon remains. 
 
 Cyanogen combines directly with hydrogen and with the metals, but 
 its oxygen combinations require to be indirectly formed ; there are three 
 compounds of cyanogen and oxygen, which are all acids, and are poly- 
 meric bodies. It unites also with sulphur, and its compounds have a 
 remarkable tendency to form double and triple combinations. 
 
 The formula of cyanogen is indifferently written C 2 N or Cy. Its 
 equivalent number is 325, or 26- 
 
 NON-METALLIC COMPOUNDS OF CYANOGEN. 
 Cyanic Acid.Cj.O. Eq. 425 or 34' 
 
 Is very easily obtained in combination, by calcining the cyanide of 
 potassium in contact with the air, at a temperature below redness, in 
 which case oxygen is directly absorbed ; or by heating the cyanide with 
 nitre, or with peroxide of manganese, which yield the oxygen required. 
 For this purpose the yellow prussiate of potash of commerce may be 
 employed, as the cyanide of iron which it contains is totally decom- 
 
732 Preparation of Cyanic Acid. 
 
 posed, and the cyanide of potassium then acts as if it were completely 
 pure. It is very easily obtained pure by fusing cyanide of potassium 
 with litharge, (protoxide of lead.) Cyanate of potash and metallic 
 lead being formed. The cyanic acid cannot, however, be isolated from 
 these salts by a stronger acid, as it then rapidly changes into bicarbo- 
 nate of ammonia, uniting with the elements of three atoms of water, 
 thus C 2 NO and 3.HO produce NH 3 and 2.C0 2 . 
 
 The cyanic acid can be obtained free, only by distilling the cyanuric 
 acid, Cy 3 O 3 -f- 3. HO, which then transforms itself into the hydrated 
 cyanic acid CyO -f- HO, and is to be collected in a receiver surrounded 
 with snow. It is a colourless liquid, of a very pungent odour ; cau- 
 terizes the skin, and when mixed wtth water is decomposed as above 
 stated. When preserved in its most concentrated form, it soon trans- 
 forms itself into a white mass, like porcelain, of the same composition 
 C 2 NHO 2 which has been termed cyanamelide. This body is insoluble 
 in water, but by heat is transformed back again into hydrated cyanic 
 acid, and by strong acids is resolved into carbonate of ammonia. 
 
 Cyanic acid does not exist in the anhydrous state. 
 
 The cyanic acid forms but one series of salts, being monobasic; 
 those of the alcalies are soluble ; the others are white insoluble pow- 
 ders. 
 
 Cyanate of Potash. CyO.KO. The yellow prussiate of potash of 
 commerce being roasted in an earthen dish absorbs oxygen, and the 
 cyanide of potassium is converted into cyanate of potash. When the 
 mass becomes adhesive from the fusion of the product, it is to be di- 
 gested with alcohol, from which the pure cyanate crystallizes on cooling, 
 in rhombic tables like chlorate of potash. In contact with hot water, 
 this salt is rapidly decomposed, ammonia being evolved, and carbonate 
 of potash formed. If dry cyanate of potash and dry crystals of oxalic 
 acid be rubbed together in a mortar, oxalate of potash is formed, and 
 the cyanic acid changes into cyanamelide. 
 
 Cyanic Acid and Ammonia Urea. 
 
 If hydrated cyanic acid be placed in contact with dry ammonia, they 
 combine and form a white woolly mass, which dissolves in water, and 
 acts as an ordinary cyanate. It appears to contain CyO -f HO -f- 
 2.NH 3 . If it be gently heated it gives off ammonia, and is trans- 
 formed into an important substance, urea, which though thus capable 
 of being artificially produced, will be again noticed as an important 
 product of the organization, in another chapter. Whenever we at- 
 tempt to form the neutral cyanate of ammonia, CyO.NH 3 .HO, urea is 
 
Preparation of Urea. 733 
 
 produced ; thus by acting on cyanate of silver with inuriate of ammo- 
 nia, or by mixing solutions of sulphate of ammonia and cyanate of 
 potash. But still we cannot consider urea to be merely cyanate of am- 
 monia, to which it bears the same relation that cyanamelide does to 
 hydrated cyanic acid. 
 
 Its characters and modes of decomposition are however so much 
 connected with the general history of the cyanogen series of bodies, 
 that the practical modes of its preparation, and its more important 
 properties, are better studied here. 
 
 If fresh urine be evaporated to the consistence of a syrup, and be 
 mixed with its own volume of strong but colourless nitric acid, the 
 whole will soon form a nearly solid mass of pearly crystalline plates of 
 nitrate of urea. If the nitric acid were quite colourless, it will be 
 quite without any decomposing action on the urea, but will destroy the 
 colouring matters of the urine, so that the crystals of nitrate of urea 
 will be obtained nearly white ; but if the acid contained any nitrous 
 acid, or if the urine had not been sufficiently concentrated, so that fur- 
 ther evaporation be necessary after adding the nitric acid, then a large 
 quantity of the urea is destroyed, red fumes given off, and the product 
 diminished in purity as well as in amount. The nitrate of urea so ob- 
 tained is to be digested in water with carbonate of barytes, the filtered 
 liquor on evaporation gives first nitrate of barytes, and then urea in 
 long needly prisms. These crystals are to be dissolved in boiling al- 
 cohol, which separates the last traces of nitrate of barytes, and on 
 cooling the urea crystallizes pure. 
 
 The concentrated urine may also be decomposed by the addition of 
 an excess of oxalic acid which precipitates the sparingly soluble oxalate 
 of urea in granular crystals. These being collected on a filter and 
 washed with very cold water, are decomposed by digestion with car- 
 bonate of lime, oxalate of lime is produced and urea. By cautious 
 evaporation and cooling of the liquor the latter is obtained crystallized, 
 and may be further purified by crystallization from an alcoholic solution 
 as already described. 
 
 A coloured solution of urine may be decoloured by animal charcoal, 
 or by the very cautious addition of a solution of permanganate of pot- 
 ash, as recommended by Professor Gregory. 
 
 It is much simpler however in practice to form urea artificially by 
 the following process, recommended by Liebig. 28 parts of dry fer- 
 roprussiate of potash and 14 parts of peroxide of manganese are to be 
 mixed in powder, and calcined at a very low red heat. The mass soon 
 glows. When this is past, the product is to be allowed to cool and 
 then washed with cold water which dissolves out cyanate of potash. 
 
734 Oxalate and Nitrate of Urea. 
 
 The washing being repeated two or three times, the filtered liquors are 
 to be mixed with a solution of 20J parts of sulphate of ammonia. 
 Some sulphate of potash is at once deposited, but the liquor is to be 
 very cautiously evaporated to dryness, during which process the trans- 
 formation of the cyanate of potash into urea becomes complete. The 
 mass is to be then boiled in alcohol, which dissolves the urea and 
 deposits it, on cooling, pure. 
 
 Urea crystallizes in colourless four-sided prisms. It is very soluble 
 in water, and somewhat less so in alcohol. Its taste is cooling like 
 nitre. If pure it is very permanent, but if contaminated by adhering 
 animal matter, it decomposes rapidly, with a kind of putrefaction, into 
 carbonate of ammonia. It melts at 250 ; by a strong heat it is re- 
 solved into ammonia, and cyanic and cyanuric acids. The formula of 
 urea is C 2 N 2 H4O 2 . It is therefore equivalent to cyanate of ammonia, 
 C 2 NO + NH 4 O, or to amidide of carbonic oxide 2(NH 2 + CO). 
 Although the reaction of urea is neutral, it acts as a base, combining 
 with acids, and forming well defined neutral salts. In its salts, with 
 oxygen acids, there is present, besides the urea, an atom of water, 
 but it combines directly with the hydracids; herein it agrees with 
 ammonia, and with the true organic alcaloids. Some of the salts of 
 urea deserve specific mention. 
 
 Nitrate of Urea. (Urea + HO -f- N0 5 ). Crystallizes in large bril- 
 liant plates by the cooling of its solution. It is pleasantly acid, and 
 is soluble in alcohol, but much more in water. If rapidly heated it 
 explodes. It is but sparingly soluble in nitric acid, whence the ad- 
 dition of a great excess of nitric acid serves as a test for the presence 
 of urea; the salt being precipitated in pearly scales. 
 
 Oxalate of Urea. (Urea + HO -f- C 2 O 3 ). Crystallizes in long rhom- 
 boidal tables. It tastes acid. It is copiously soluble in boiling water, 
 but crystallizes almost completely out on cooling, as 100 parts of cold 
 water retain but four of the salt. It is still less soluble in alcohol. 
 
 The relations of urea to the processes of animal life will be described 
 in another place. 
 
 Fulminic Acid.Cyf) 2 -f 2.HO. 
 
 This acid, which has attracted much attention from the detonating 
 properties of its salts, is prepared by the action of nitric acid on al- 
 cohol, in presence of oxide of mercury or silver. The reaction is very 
 complex ; a crowd of products of the oxidation of the alcohol being 
 evolved, as aldehyd, formic, acetic, and oxalic acid, &c. If the action 
 were limited to the essential conditions it would probably consist in 
 
Fulminates of Silver and Mercury. 7-35 
 
 two equivalents of alcohol and two of nitric acid, producing one of 
 acetic acid, one of fulrainic acid, and eight of water, thus 2.NO 5 and 
 2(C 4 H 6 O 2 ), give C 4 H 4 O 4 and C 4 NA, besides 8.HO. 
 
 The fulminic acid cannot be obtained in an isolated form ; when we 
 attempt to separate it from bases, it is instantly decomposed. Thus, if 
 fulminate of silver be acted on by dilute muriatic acid, chloride of 
 silver, and a peculiar acid containing chlorine and cyanogen, are pro- 
 duced. The fulminic acid is bibasic, and forms two series of salts, of 
 which the neutral contain two equivalents of fixed base ; the acid salts 
 containing one of fixed base and one of water. 
 
 Fulminate of Silver Cy 2 O 2 -f- 2.AgO. It is prepared by dis- 
 solving silver in ten parts of nitric acid, sp. gr. T35, and pouring the 
 solution, when cold, into twenty parts of rectified spirits of wine. 
 The mixture is to be gently heated till it begins to boil, and then left 
 to cool slowly. The fulminate of silver is deposited in fine silky crys- 
 tals, snow-white, and equal in weight to the silver employed. It is 
 very sparingly soluble in cold water. It detonates with the slightest 
 shock, or by contact with sulphuric acid. When acted on by a caustic 
 alcali, as potash, half of the silver separates as oxide, and a salt is 
 formed, Cy 2 O 2 + KO.AgO. If it be dissolved in warm dilute nitric 
 acid, half of the silver is also removed and replaced by water, and on 
 cooling, the acid fulminate of silver, Cy 2 O 2 4- HO.AgO, crystallizes 
 out. This explodes more readily than the first salt, by friction and by 
 contact with oil of vitriol or chlorine gas. 
 
 By digesting these fulminates of silver with metallic zinc, or copper, 
 fulminates of these metals with two atoms of oxide are obtained, and 
 by acting on these salts with an alcali, or barytes, salts with two dif- 
 ferent bases may be formed. In no case, however, can a fulminate 
 containing two atoms of an alcaline base be produced. All these salts 
 possess detonating properties more or less violent. 
 
 Fulminate of the Suboxide of Mercury. Cy 2 O 2 + 2Hg a O. This, 
 the most important salt of fulminic acid, is prepared by dissolving 
 mercury in nitric acid, and treating it by alcohol, as in preparing ful- 
 minate of silver. As the solution cools, some metallic mercury preci- 
 pitates, and the fulminate of the suboxide is deposited in hard opaque 
 white crystals, generally very minute. It is to be washed and redis- 
 solved in boiling water, and crystallizes then in fine silky needles. 
 This salt detonates violently when struck between two hard bodies. It 
 is extensively used in the manufacture of the percussion caps used with 
 fire-arms. As a great quantity of alcohol is wasted in this process, it 
 was proposed to carry on the action in close vessels, and condense the 
 spirit, which, however, was found to be unfit for any but the same use, 
 
736 Cyanuric Acid. 
 
 from containing a large quantity of prussic acid. When solution of 
 fulminate of silver is decomposed by muriatic acid, the acid itself is 
 decomposed, and a new acid, a Jiydrochlorocyanic acid is produced. 
 Its formula has been given as C 2 NC1 5 -|- H 2 , but it still requires exam- 
 ination. 
 
 Cyanuric Acid. Cy 3 O 3 -f- 3 HO. 
 
 This acid is produced under a variety of circumstances where the 
 elements of cyanic acid become free. Thus, if the solid chloride of 
 cyanogen be treated with water, CyCl and H.O produce H.C1 and CyO, 
 but this transforms itself immediately into cyanuric acid. It is formed 
 abundantly, as a white sublimate, in the dry distillation of uric acid, 
 and may be very simply produced by heating urea a little above its 
 point of fusion, in a glass retort ; ammonia is given off, and the urea 
 changes into a dry grey mass, which is to be dissolved in strong sul- 
 phuric acid, and treated with nitric acid, added in small quantities, 
 until it becomes quite colourless. Being then diluted with its own 
 weight of water, the liquor yields crystals of cyanuric acid on cooling. 
 It is evident that three atoms of urea, 3(C 2 H 4 N 2 O 2 ) contain the ele- 
 ments of three atoms of ammonia, and one of cyanuric acid, C 6 N 3 O 3 -f 
 3HO. 
 
 By means of substances which will be hereafter noticed, termed 
 melam and ammelide, cyanuric acid may be formed simply and in quan- 
 tity. 
 
 Melam consists of C 12 N n H 9 . When it is dissolved in dilute sul- 
 phuric acid, it takes 6 equivalents of water, and resolves itself into two 
 equivalents of cyanuric acid, and five of ammonia. Thus C 12 N U H9 -{- 
 6 H 6 = 2(C 6 Ts[ 3 C 3 ) and 5.NH 3 . The latter unites with the sulphuric 
 acid, and the cyanuric acid crystallizes out. Similarly, the ammelide 
 which is, Ci 2 H 9 N 9 O 6 , produces with sulphuric acid, two atoms of cyan- 
 uric acid, C 12 N 6 O 6 , and three atoms of ammonia, =N 3 H 9 . 
 
 Cyanuric acid is colourless, and nearly tasteless, possessing a very 
 slight acid reaction. It crystallizes in oblique rhombic prisms, which 
 have the formula Cy 3 O 3 -j- 3HO + 4Aq. By a moderate heat, the 
 4Aq. are expelled, and when more strongly heated, the dry acid 
 changes into hydrated cyanic acid. This acid, being tribasic, forms 
 three distinct classes of salts, which differ as the quantity of fixed base 
 is one, or two, or three atoms. If any of these salts be acted on by a 
 stronger acid, the cyanuric acid is completely liberated. 
 
Preparation of Prussia Acid. 737 
 
 Cyanide of Hydrogen. Hydrocyanic Add. Prmsic Acid. 
 C 2 NH. or CyH. Eq. = 337-5 or 27. 
 
 This remarkable substance may be formed by the direct combination 
 of hydrogen and cyanogen. It exists in the water distilled from bitter 
 almonds, or from the leaves of the cherry-laurel, being produced by the 
 decomposition of a peculiar substance, amygdaline, which those plants 
 contain. For the purposes of medicine and chemistry, it is prepared 
 by indirect processes of many kinds. Thus, if formiate of ammonia 
 (C 2 HO 3 + ]\ T H 4 O) be passed in vapour through a red-hot porcelain tube, 
 it is totally converted into prussic acid and water ; C 2 N.H and 4HO. 
 Also by passing ammonia over red-hot charcoal, hydrocyanate of am- 
 monia is formed in such quantity that prussic acid may be economically 
 prepared from it. If cyanide of silver be decomposed by muriatic acid, 
 chloride of silver and cyanide of hydrogen are produced, (Ag.Cy and 
 H.C1, giving Ag.Cl and H.Cy) ; and by sulphuret of hydrogen, cyanide 
 of mercury gives sulphuret of mercury and prussic acid. Tor its pre- 
 paration on the large scale, however, the substance used is the yellow 
 prussiate of potash of commerce. 
 
 This salt, the preparation of which will be hereafter described, con- 
 sists of cyanide of iron united to cyanide of potassium ; by the action 
 of sulphuric acid, three-fourths of the latter are decomposed, bisul- 
 phate of potash being formed, and prussic acid liberated ; (2SO 3 + 
 HO) and CyK giving (KO.S0 3 + HO.SO 3 ) and CyH.) The cyanide 
 of iron remains still combined with the other fourth of the cyanide of 
 potassium, forming a compound first described by Mr. Everitt. The 
 prussic acid thus produced contains, therefore, one-half of the cyano- 
 gen, which existed in the salt employed. The precise decomposition 
 is, that two equivalents of the yellow ferroprussiate of potash, 2(EeCy 
 + 2.KCy), acted on by six atoms of oil of vitriol, 6(SO 3 -f HO) pro- 
 duce three atoms of bisulphate of potash, 3(HO.S0 3 + KOS 3 O), and 
 three atoms of prussic acid, 3.HCy; there remains then an atom of 
 Everitt's salt (2.EeCy + K.Cy), which, when first formed, is yellow, 
 but by rapidly absorbing oxygen it becomes greenish, and abandoning 
 its cyanide of potassium, is finally converted into basic Prussian blue. 
 
 The mode of conducting the process depends on the degree of 
 strength at which the prussic acid is required. To obtain the anhydrous 
 acid, three parts of yellow prussiate of potash, in fine powder, are to 
 be decomposed by a mixture of two parts of oil of vitriol and two of 
 water, in a small retort, at a very gentle heat, and the product collected 
 in a receiver, surrounded by ice, and containing some fragments of 
 47 
 
738 Preparation and Properties of Prussic Acid. 
 
 recently fused chloride of calcium, by which any traces of water which 
 come over are absorbed. The process originally employed by Gay- 
 Lussac, consists in decomposing cyanide of mercury by strong muriatic 
 acid, and passing the vapour through a long tube, of which the half 
 next the retort contains small fragments of marble, and the other half 
 fragments of recently fused chloride of calcium ; any muriatic acid 
 vapour is arrested by the former, and the prussic acid is rendered an- 
 hydrous by the latter ; the vapour is then condensed in a receiver, sur- 
 rounded by ice. 
 
 Pure prussic acid is a colourless liquid; its specific gravity at 67 is 
 0'6969; at 5 Eah. it congeals into a mass of fibrous crystals, (which 
 however appear to be due to traces of water, as the perfectly anhydrous 
 acid remains liquid even at 64). When heated to 80 it boils. In 
 consequence of this great volatility, if a drop of it be suspended from a 
 glass rod, one part of it will be solidified by the cold, produced by the 
 rapid evaporation of another portion. The density of its vapour is 
 944*1, consisting of equal volumes of cyanogen and hydrogen, united 
 without condensation, as (1819'0 + 69'3) -r- 2 = 944.1. It reddens 
 litmus paper feebly, and the tint disappears by heat. Its odour is ex- 
 tremely suffocating and pungent, and resembles that of bitter almonds. 
 Its taste is bitter and acrid. It is combustible, burning with a bright 
 white flame. Being a poison of intense activity, the greatest care 
 should be used in manipulating with it, in this concentrated form. 
 
 Anhydrous prussic acid decomposes rapidly, especially if exposed to 
 light. It forms ammonia, and a brown substance, probably the same 
 as that produced from a solution of cyanogen in water, and termed 
 azulmic acid, as noticed, p. 731, but of which the composition is not 
 well known. By contact with a strong acid, prussic acid assimilates 
 the elements of three atoms of water, and produces formic acid and ' 
 ammonia ; (C 2 NH and 3. HO giving C HO 3 and NHs). Hence, in the 
 preparation of prussic acid, an excess of any mineral acid should be 
 avoided. With chlorine, prussic acid forms muriatic acid and chloride 
 of cyanogen, and with iodine it acts similarly. 
 
 Eor medicinal use, the prussic acid is prepared in a very dilute "con- 
 dition. The directions sometimes given in pharmacopoeias to distil 
 over an acid of a specific strength, are, in practice, very difficult to 
 execute, and might give rise to serious errors. The proper method is, 
 to prepare an acid stronger than that required ; then to ascertain by 
 accurate analysis its strength, and dilute it with distilled water until it 
 be brought exactly to the degree required. This process is carried on 
 in the manufacturing laboratory of the Apothecaries' Hall of Ireland, 
 as follows : lib. of crystallized yellow prussiate of potash, in fine pow- 
 
Estimate of the Strength of Prussic Acid. 739 
 
 der, is placed in a capacious retort, and 2lbs. of water poured on it ; 
 to this is added a mixture of 12 ozs. of oil of vitriol and 2 Ibs. of 
 water, previously suffered to cool. These materials are well agitated, 
 and allowed to digest for three or four hours, and then between 2 and 
 3 Ibs. of dilute acid are distilled over into a receiver containing already 
 lib. of distilled water ; there are obtained thus, 3 or 41bs. of an acid 
 containing from 6 to 8 per cent, of real acid. 200 grs. of this are 
 weighed and decomposed by an excess of nitrate of silver ; the cyanide 
 of silver precipitated is carefully collected, washed, and dried. Being 
 then weighed, the exact per centage of acid present is found by calcu- 
 lation, and the necessary quantity of water is added, so as to bring it 
 to the standard strength of the Dublin pharmacopeia, which is that of 
 1/6 per cent, of real acid, and specific gravity of 0'998. 
 
 As an example of this process, let us suppose that the 200 grs. of 
 distilled acid gave, with nitrate of silver, 74 grs. of cyanide ; as this 
 contains 14'95 of cyanogen, the 200 grs. contained 15'53 of real acid, 
 or 7 '76 percent.; now to reduce this to the Dublin standard, divide 
 7'76 by 1-6, which gives 4*85; indicating that by adding 3'851bs. of 
 distilled water to each Ib. of acid, the mixture will have accurately the 
 strength directed by the pharmacopoeia. Some of this calculation may 
 be spared by considering the cyanide of silver to be equivalent to ^th 
 of its weight of real prussic acid ; the quantity per cent, in the sup- 
 posed example should then be j^th of the weight of cyanide of silver 
 obtained from the 200 grs. ; that is 7 '4 per cent.; and the water ne- 
 cessary to bring it to the Dublin standard should be 3*63 times its 
 weight. The error introduced by this simplification is not sensible, 
 being but 0'002 per cent. 
 
 The strength of the prussic acid directed by the British Pharmaco- 
 poeias differs very much ; that prescribed by the London College con- 
 tains about 2 per cent, of real acid ; that of the Edinburgh College 
 contains about 3*3 per cent. ; whilst the Dublin strength is but 1'5 or 
 1*6 of real acid per cent. This should be carefully attended to in 
 practice. 
 
 A method has been proposed for determining the value of prussic 
 acid, by digesting it on a known quantity of red oxide of mercury ; 
 when the prussic acid has saturated itself with the oxide, what remains 
 is to be washed, dried, and weighed. Now as 116- of oxide of mer- 
 cury is converted into cyanide by 27* of prussic acid, which propor- 
 tion is nearly 4 to 1, the quantity of prussic acid is pretty correctly 
 one-fourth of the weight of the oxide of mercury dissolved. But as 
 cyanide of mercury may combine with an excess of oxide, and as the 
 quantity thus liable to be taken up is not constant, it is dangerous to 
 rely on this method for medicinal or analytical purposes. 
 
740 Method of detecting Prussic Acid. 
 
 The detection of prussic acid is very simple. 1st. Its solution gives, 
 with nitrate of silver, a white precipitate, cyanide of silver, insoluble 
 in strong nitric acid, when cold, but dissolved by boiling ; it is soluble 
 in ammonia. If a liquor, containing even a very small trace of prussic 
 acid be boiled, the vapour produces a white cloud on a piece of glass 
 moistened with solution of nitrate of silver. 2nd. If a solution of 
 sulphate of iron be added to prussic acid, there is no change, but on 
 adding some potash liquor, a dirty greenish precipitate is produced, 
 from which muriatic acid dissolves out the excess of oxide of iron, and 
 leaves Prussian blue (cyanide of iron) of a very rich colour : it is es- 
 sential to the proper action of this test, that both protoxide and per- 
 oxide of iron be present in the solution. 3rd. If a solution of sul- 
 phate of copper be added to the liquor containing prussic acid, and 
 then treated successively with potash and muriatic acid, as above, a 
 white precipitate remains undissolved, which is cyanide of copper. 
 The theory of these last actions is, that the prussic acid is too weak to 
 decompose, by itself, either metallic sulphates, but on the addition of 
 potash, double decomposition occurs, sulphate of potash, and a metallic 
 cyanide being formed. As the potash is always added in excess, a 
 quantity of metallic oxide is at the same time precipitated, which masks 
 the colour of the result, but is removed by the addition of the muriatic 
 acid. 4th. These insoluble cyanides may be recognized very elegantly 
 by heating them with a little potash and sulphur, and dissolving the 
 fused mass in water. The solution gives, with a persalt of iron, a fine 
 blood-red colour. 5th. The cyanide of silver, also, is known by giving 
 off cyanogen when heated. 
 
 Chlorides and Iodides of Cyanogen. 
 
 There are two chlorides of cyanogen of the same composition, and 
 bearing to each other the same relation as the cyanic and cyanuric acids. 
 One is gaseous, the other solid ; the first is prepared by acting on 
 moist cyanide of mercury by chlorine, or by passing chlorine into weak 
 prussic acid, and warming the mixture in which the chloride of cyan- 
 ogen dissolves. This gas. which is very irritating and poisonous, may 
 be obtained crystallized in needles by exposure to a very low tempera- 
 ture. It combines with ammonia, forming a crystalline substance. 
 
 The solid chloride may be prepared by acting on anhydrous prussic 
 acid with chlorine, or by heating sulphocyanide of potassium in a cur- 
 rent of chlorine. It sublimes in white transparent needles. It dis- 
 solves unaltered in alcohol and ether, and is decomposed by hot water 
 into hydrochloric and cyanuric acids. 
 
Chlorides of Cyanogen Cy ankle of Potassium. 741 
 
 Iodide of cyanogen is prepared by distilling, in a retort, a mixture 
 of iodine, cyanide of mercury and water. At a moderate heat, the 
 iodide of cyanogen passes over and condenses in the neck of the retort, 
 as a flocculent mass of snow-white needles. These crystals irritate the 
 eyes ; they dissolve in water unaltered, and volatilize at 113. 
 
 OF THE SIMPLE METALLIC CYANIDES. 
 
 Cyanide of Potassium. K.Cy. May be formed by the direct union 
 of its elements, or by adding an excess of prussic acid to a solution of 
 potash, and evaporating rapidly without the access of air. It is pro- 
 duced also whenever carbonaceous matter is calcined in contact with 
 potash, provided nitrogen be present. The best mode of obtaining it, 
 however, is to expose the yellow prussiate of potash to a full red heat 
 in a close iron crucible. The cyanide of iron is decomposed, nitrogen 
 being given off, and carburet of iron remaining with the unaltered, 
 cyanide of potassium. The half-melted mass is to be coarsely pow- 
 dered, and digested in boiling weak spirit of wine, from which the salt 
 crystallizes in cubes on cooling. Spirit of sp. gr. 0*900 at 60, is re- 
 markable for dissolving a large quantity of cyanide of potassium when 
 boiling, but depositing it nearly totally when it cools. 
 
 This salt in solution reacts alcaline, and smeUs of bitter almonds, 
 and hence probably decomposes water when dissolved. Its crystals de- 
 liquesce and are decomposed, even in close vessels, after a short time, 
 by contact with water, into ammonia and formiate of potash. 
 
 The cyanide of potassium possesses very remarkable reducing pro- 
 perties when fused with metallic compounds. It deoxidizes and desul- 
 phurates as well by means of its potassium as by its carbon, and hence 
 has become a highly valuable agent in metallurgic and assay analyses ; 
 its great fusibility enabling it to act most beneficially as a flux. In 
 solution also it serves as an agent as well of qualitative as of quanti- 
 tative research, and has now become an indispensable material in the 
 laboratory. For these purposes it need not however be absolutely pure, 
 and the following process affords it in a state fit for use. Eight parts 
 of dry ferroprussiate of potassium and three of pure carbonate of pot- 
 ash are to be fused together in an iron crucible, until the iron of the 
 salt has perfectly separated as a grey spongy mass, and the fused salt 
 appears perfectly colourless on cooling. It is to be then poured out on 
 a flag, and preserved in close vessels for use. In this process the 
 action is, that the cyanide of iron of the ferro-cyanide of potassium 
 is decomposed, and produces with the carbonate of potash, metallic 
 iron, and a mixture of cyanide of potassium and cyanate of potash, 
 whilst carbonic acid is given off. From two equivalents of ferroprussiate 
 
742 Cyanides of Zinc, Mercury, Copper, fyc. 
 
 of potash and one of carbonate of potash, result two of metallic iron, 
 five equivalents of cyanide of potassium, and one equivalent of cyanate 
 of potash. 
 
 The properties of the cyanide of sodium and of the hydro-cyanate 
 of ammonia are quite similar. 
 
 The Cyanides of Barium, strontium, calcium, and magnesium are 
 soluble in water and crystallizable. 
 
 Cyanide of Zinc is prepared by adding prussic acid to a solution of 
 acetate of zinc, when it precipitates as a white powder. Chloride of 
 zinc is not decomposed by prussic acid. With cyanide of potassium it 
 forms a double salt. 
 
 Cyanide of Copper is formed as a whitish precipitate when prussic 
 acid and potash are added to a solution of sulphate of copper. When 
 boiled it becomes yellow, and combines with the oxide of copper to 
 form an oxy cyanide of a lively green colour. It forms double salts with 
 the alcaline cyanides. 
 
 Cyanide of Mercury. Hg.Cy. Eq. ]575 or 126*. May be pre- 
 pared by boiling two parts of prussian blue with one of red oxide of 
 mercury and eight of water, until the residue becomes red-brown. The 
 filtered liquor yields cyanide of mercury in crystals, which, however, 
 are not quite free from iron, and require to be digested with a little 
 more oxide of mercury and then recrystallized. The best mode of 
 preparing it is to distil fifteen parts of yellow prussiate of potash with 
 thirteen of oil of vitriol and 100 of water, nearly to dryness, and to 
 digest the prussic acid so obtained with twelve parts of finely powdered 
 oxide of mercury, until this is completely dissolved. The solution 
 yields by evaporation, and cooling, fourteen parts of pure crystallized 
 cyanide of mercury. By washing out the residue in the retort with 
 water, five parts of pure Prussian blue may be obtained. 
 
 Cyanide of mercury crystallizes in colourless rectangular prisms, as 
 qq in the figure, terminated by numerous secondary faces, 
 as, ee. These crystals are anhydrous and occasionally 
 opaque. When heated it is resolved into mercury and 
 cyanogen, of which a portion is transformed into the brown 
 powder (paracyanogen). It is sparingly soluble in alcohol. 
 It tastes as the other mercurial salts. So great is the affinity of mer- 
 cury to cyanogen, that cyanide of potassium, when boiled with oxide 
 of mercury, is decomposed, and caustic potash liberated. In a solu- 
 tion of cyanide of mercury, no test indicates the presence of the metal 
 except sulphuretted hydrogen. It is not decomposed by oxygen acids, 
 but muriatic acid forms prussic acid and chloride of mercury. 
 
 Cyanide of mercury, when digested with an excess of oxide of mer- 
 
Simple and Complex Metallic Cyanides. 743 
 
 cury, combines with it in two proportions, forming the oxy-cyanides of 
 mercury, HgCy -f HgO, and HgCy + 3HgO. These bodies are so- 
 luble in water, and crystallize in prismatic needles. 
 
 With iodide of potassium, cyanide of mercury combines, forming a 
 substance, 2 HgCy -f- K.I, which is very soluble in boiling water, and 
 crystallizes in brilliant white micaceous plates, on cooling. This salt 
 is instantly reddened by any mineral acid, which liberates iodide of 
 mercury. With sulphocyanide of potassium a similar compound is 
 formed, 2 HgCy + K.CyS 2 . 
 
 Cyanide of mercury combines with the alcaline cyanides, and with 
 the alcaline chlorides, and bromides, forming double salts, possessing 
 no special interest. It combines with many oxygen-salts also, as the 
 chromate and formiate of potash. 
 
 As prussic acid is now no longer prepared from cyanide of mercury, 
 this body is not so important as formerly. It is poisonous and is occa- 
 sionally employed in medicine. 
 
 Cyanide of Silver. AgCy, Is a white powder insoluble in water, 
 which combines with other cyanides to form double salts. It is soluble 
 in water of ammonia, but insoluble in nitric acid, except it be strong 
 and boiling. Heated it gives cyanogen and metallic silver. 
 
 Cyanide of Palladium. In its affinity for cyanogen, palladium re- 
 sembles mercury. Every soluble salt of palladium is decomposed by 
 prussic acid, a pale yellow precipitate being formed. This cyanide of 
 palladium is insoluble in water, but soluble in acids, and in ammonia. 
 Heated it gives cyanogen and leaves the metal. It forms a very ex- 
 tensive class of double salts. 
 
 Cyanide of Gold. AuCy 3 . Is a pale yellow powder, forming double 
 salts with the alcaline cyanides. 
 
 Protocyanide of Iron. PeCy. Is not known in an isolated form, 
 but it enters into combination with the other metallic cyanides, forming 
 double salts, which are some of the most interesting of the cyanogen 
 compounds. The iron in these salts cannot be separated by an alcali, 
 and hence may be looked upon as an element of the negative consti- 
 tuent ; they are hence often termed ferrocyanides, or ferroprussiates of 
 whatever other metal they may contain. 
 
 COMPLEX METALLIC CYANIDES. 
 
 It is found that the property just referred to in the case of cyanide 
 of iron, presents itself also in the case of other cyanides, in which also 
 the peculiar reactions of the contained metal are no longer observable, 
 but it appears to form with cyanogen a species of compound radical, 
 
744 Ferrocyanides and Ferridcyanides. 
 
 ranking with cyanogen itself, and generating with the several metals, 
 salts, equally remarkable and definite with the simple cyanides. Of the 
 bodies that possess this singular character, the cyanides of iron are the 
 most remarkable; the cyanides of platinum, and of palladium, of 
 nickel, and of cobalt, affect the same law, and require some notice. 
 The theoretical views put forward in relation to this class of bodies will 
 be best described after having noticed the properties of the most im- 
 portant, ferrocyanides. 
 
 Ferrocyanides and Ferridcyanides. 
 
 Ferrocyanide of Hydrogen. Ferrocyanic Acid. PeCy + 8.HCy. 
 When the ferrocyanide of lead is decomposed by sulphuret of hydro- 
 gen, a solution is obtained, which yields, on evaporation in vacuo, 
 small granular crystals, which have a well marked acid reaction, and 
 produce, by acting on metallic oxides, all the ordinary ferrocyanides. 
 If the solution be boiled, it is resolved into prussic acid and a white 
 precipitate which becomes blue in the air. The crystals undergo the 
 same change spontaneously after some time. 
 
 The ferrocyanide of hydrogen may be more easily prepared by mix- 
 ing a cold saturated solution of ferrocyanide of potassium with its own 
 volume of strong muriatic acid, and agitating the mixture with ether, 
 which separates the ferrocyanic acid in whitish scales. These may 
 easily be removed with the ether, which floats on the dense solution of 
 chloride of potassium, and on being very cautiously dried they may be 
 purified by solution in alcohol, from which they can be crystallized by 
 spontaneous evaporation. Unless access of air be prevented they will 
 be totally decomposed, water and prussian blue being formed. 
 
 Ferrocyanide af Potassium.FeCy + 2.KCy + 3Aq. Eq. 2637'5, 
 or 211*0. This compound, of which I have often spoken as yellow 
 prussiate of potash, is prepared on the large scale for the purposes of 
 the arts, and of pharmacy, by calcining together some animal matters, 
 as blood, hoofs, horns, &c. with pearlashes, and iron filings. It may 
 be formed even if the organic matter do not contain nitrogen, as that 
 element may be supplied from the air. The operation is conducted in 
 large iron pots arranged in a furnace, so that the mass can be heated 
 to dull redness and continually agitated as it forms a tenacious paste, 
 the calcining of which is continued as long as it burns with a white 
 flame ; it is then taken out of the pot, and when cold, boiled in water, 
 which, by evaporation, yields the salt in crystals. If it has not dis- 
 solved iron enough, some copperas is added as long as the Prussian 
 blue, which at first forms, is found to redissolve. After what has been 
 
Manufacture of Ferrocyanide of Potassium. 745 
 
 said of the formation of cyanogen (p. 730), the general theory of this 
 process may easily be understood. 
 
 The process for preparing this salt has recently been accurately 
 studied by Liebig whose observations have explained satisfactorily the 
 conditions necessary for practical success. He has shown that the mass 
 formed by the fusion of the alcali with the organic matter does not 
 contain any iron in combination. There is no ferrocyanide formed at 
 that stage, in fact we know that it could not exist at that high tem- 
 perature. On washing such a saline mass with cold water, only cyanide 
 of potassium is dissolved, but if that mass, which always contains a 
 quantity of iron either metallic or as sulphuret, derived from the pots, 
 or from the materials employed, be digested with hot water, the solution 
 becomes yellow, iron is dissolved, and ferrocyanide of potassium is 
 produced. If air be excluded, the iron dissolves in the solution of 
 cyanide of potassium with the evolution of hydrogen gas, but if air be 
 present oxygen is absorbed. In both cases potash is produced. If the 
 iron were a sulphuret, sulphuret of potassium is formed. The fused 
 mass contains an excess of potash, which, when boiled with the cyanide 
 of potassium tends to break up the latter into formiate of potash and 
 ammonia, C 2 N + K with 4HO, giving C 2 HO + KO and NH 3 . It- is 
 therefore recommended in the process of manufacture not to heat the 
 liquors from the fused mass to boiling, until, by dissolving the proper 
 quantity of iron, the cyanide has been totally converted into ferrocyan- 
 ide of potassium. It is also of importance to exclude any excess of 
 air from the furnace in which the fusion of the alcali and ammoniacal 
 matter is conducted as the formation of cyanate of potash, which 
 should afterwards be decomposed by the water into bicarbonate of am- 
 monia, might entail considerable loss. 
 
 The ferrocyanide of potassium crystallizes in truncated octohedrons 
 with a rectangular base e e e, as in the figure, of which A represents the 
 
 usual simple, and B a more complicated 
 form ; the secondary plane p often being 
 so large as to render the crystal merely 
 tabular. Its colour is fine citron-yellow, but when dried it becomes 
 white. By a further heat, in close vessels, it fuses, and when ignited 
 gives off nitrogen, and leaves cyanide of potassium and carburet of 
 iron. Heated in open vessels, it absorbs oxygen, and forms cyanate 
 of potash. Its use in the preparation of these bodies and of prussic 
 acid has been already detailed. If it be digested with oxide of mer- 
 cury, cyanide of mercury is formed, and oxide of iron and caustic 
 potash set free. 
 
 If ferrocyanide of potassium be boiled in water, with sulphate of 
 
746 Prussian Blue Red Prussiate of Potash. 
 
 mercury it gives sulphate of potash, cyanide of mercury, and Everitt's 
 yellow salt. This process was recommended as a mode of obtaining 
 cyanide of mercury, but it is rendered difficult in practice, because that 
 with cyanide of mercury, ferrocyanide of potassium forms a double 
 salt, whose formula I found to be 3HgCy + (FeCy + 2KCy) + 4Aq. 
 It crystallizes in pale yellow rhombic tables. 
 
 In the arts, the ferrocyanide of potassium is of importance for dye- 
 ing various shades of blue ; to the chemist it is specially of interest, 
 as from it all the cyanogen compounds are most economically formed, 
 and that from the peculiar precipitates it gives with solutions of most 
 metals, it is of eminent service in their detection. Thus, with solutions 
 of silver, mercury, bismuth, tin, lead, nickel, zinc, manganese and 
 cerium, it gives white precipitates ; that with mercury gradually be- 
 comes blueish, and that of manganese reddish. With copper, the pre- 
 cipitate is of a rich chocolate colour ; with cobalt, greenish, changing 
 to red ; with uranium and molybdenum, brown, and with chrome, grey- 
 ish-green. All these precipitates contain cyanide of iron, united to 
 two atoms of cyanide of the other metal ; being ims/errocyanides. 
 
 It is on solutions of iron that the action of this re-agent is the most 
 remarkable. With solution of protosulphate of iron, a whitish pre- 
 cipitate is obtained, which consists of the cyanides of iron and potas- 
 sium, united in proportions, which are not well known. Exposed to 
 the air this body absorbs oxygen and becomes blue. With a solution 
 of sulphate of iron pure Prussian blue is precipitated. This substance 
 is insoluble in water and in muriatic acid, and gives with caustic alca- 
 lies, oxide of iron, and ferrocyanide of potassium; its formula is 
 Ee 7 Cy 9 , or it consists of S.FeCy + 2.Ee 2 Cy 3 . Its formation involves 
 3(FeCy + 2.KCy) and 2(Pe 2 O 3 + 3.S0 3 ), and there remain dissolved 
 six atoms of sulphate of potash. Por the manufacture of Prussian 
 blue, for the purposes of the arts, the impure liquor obtained by di- 
 gesting in water the calcined mass of animal matter, potash and iron, 
 described (p. 744), is decomposed by an excess of sulphate of iron, 
 and the resulting precipitate digested in muriatic acid, and exposed to 
 the air, until it assumes its proper colour. It is then dried carefully 
 at a moderate heat. 
 
 Another kind of Prussian blue is produced, when Everitt's salt, or 
 the white precipitate produced by protosulphate of iron with yellow 
 pmssiate of potash, is exposed moist to the air. It is termed basic 
 Prussian blue. As Everitt's salt consists of 2FeCy + KCy, and that 
 this last dissolves out, there is the same number of atoms of cyanogen 
 and iron, and the excess of iron above that necessary to form true 
 Prussian blue, combines with the oxygen of the air; the oxide so 
 
Ferrid-cyatiides of Hydrogen, fyc. 747 
 
 formed remaining united with the Prussian blue. Prom 9FeCy and 
 3O, there is thus formed (3FeCy + 2.Fe 2 Cy 3 + Fe 2 3 ) the basic com- 
 pound. Its formula may also be writtten as Fe 3 Cy 3 O or Fe 2 Cy 3 + FeO. 
 being analogous to magnetic oxide of iron in constitution. 
 
 Theferrocyanides of sodium, barium, &c., possess all the essential 
 characters of the potassium salt, and need not be further noticed. 
 
 The ferrocyauides in many cases combine with each other, forming 
 salts, which contain three different metals combined with cyanogen. 
 
 Sesquicyanide of Iron. Fe 2 Cy 3 . Is not known in an isolated form, 
 but like the protocyanide, enters into a number of combinations with 
 the other metallic cyanides, which may be called either perferrocyanides 
 Q? ferridcyanides as proposed by Liebig. 
 
 Ferridcyanide of Potassium. Red Prussiate of Potash. Fe2Cy 3 + 
 3.KCy. Is formed by passing chlorine through a solution of yellow 
 prussiate of potash, until it ceases to give Prussian blue with solution 
 of persulphate of iron. The liquor becomes of a deep-green colour, 
 but on evaporation yields anhydrous fine ruby-red prismatic crystals, 
 which are generally macles. The products of its decomposition by 
 heat are the same as those of the yellow salt. It dissolves in thirty- 
 eight parts of cold water ; its solution, if pure, is yellow, but more 
 commonly is green. 
 
 This salt rivals that already described in its utility as a re-agent for 
 the proper metals. The precipitates it gives with their solutions are, 
 tin, white ; mercury, silver and zinc, yellow ; titanium, nickel, copper 
 and bismuth, yellowish brown ; and cobalt, uranium and manganese, 
 brown. It is, however, with the salts of iron that its reaction is most 
 remarkable. With a persalt of iron it merely colours the liquor green, 
 but with a solution of a protosalt it gives a blue precipitate, even richer 
 in colour than the proper Prussian blue, and consisting of Fe 5 Cy 6 , or 
 of Fe 2 Cy 3 + 3.FeCy ; thus, containing the same protocyanide with half 
 as much sesquicyanide as exists in common Prussian blue. This Fer- 
 ridcyanide of iron is made for commerce, and sold as Turnbull's Prus- 
 sian blue. It is used extensively in calico printing. 
 
 Ferridcyanide of Hydrogen. If we digest ferridcyanide of lead with 
 dilute sulphuric acid, a red liquor is obtained, which yields on evapora- 
 tion a mass of minute brownish-yellow needles, the formula of which 
 is Fe 2 Cy 3 + 8CyH. This body reddens litmus, and has a sour astrin- 
 gent taste ; upon another theory it is considered to be a compound of 
 hydrogen with a compound radical, (~Fe 2 Cy 6 ), and is termed ferridcyanic 
 acid. 
 
 In the history of these complex cyanides we meet three facts, on 
 which the theories of their constitution must be founded, 1st. The 
 
748 Constitution of the Complex Cyanides. 
 
 extraordinary tendency to double combination, which no other body 
 possesses in the same degree. 2nd. That in almost all cases the cyan- 
 ogen enters into the compound, in the proportion of three, six or nine 
 atoms. And 3rd. That one metallic element, as iron, in each com- 
 pound, is retained with extraordinary force, not being detected therein 
 by its ordinary re-agents. The original view proposed by Berzelius, of 
 considering these compounds as mere double salts, and upon which the 
 formulae given hitherto have been constructed, does not account 
 sufficiently for these facts, and I hence consider it as less applicable to 
 them than the theories suggested by Graham and by Liebig. 
 
 The latter chemist founds his view upon the third fact, and supposes 
 that there exists a series of compound radicals, consisting of cyanogen 
 united with a metal. Thus, ferrocyanogen (PeCy 3 ) or Cfy, svAferricl- 
 cyanogen (Pe 2 Cy 6 ) or Cfy 2 , these two being isomeric ; colaltocyanogen 
 (Co 2 Cy 6 ) or Cky, and many others ; and these radicals combine with 
 hydrogen to form polybasic hydracids, from which, the hydrogen being 
 replaced by a metal, result the ordinary complex cyanides. Thus, the 
 ferrocyanogen being bibasic, its acid is Cfy + 2H ; its potash salt Cfy 
 + 2K ; its copper salt Cfy + 2Cu ; and if each atom of hydrogen be 
 replaced by a different metal, then the triple salt, formed by Mosander, 
 are produced : thus, the salt written on Berzelius' view, as (FeCy + 
 2KCy) -f- (PeCy + 2CaCy) becomes Cfy + Ca.K. and similarly there 
 is Cfy + Ba.K. &c. 
 
 The red prussiate of potash, Liebig supposes to contain a radical 
 (Fe 2 Cy 6 ) or Cfy 2 isomeric with, but of double the atomic weight of 
 ferrocyanogen ; timsferridcyanogen forms with hydrogen a tribasic acid, 
 Cfy 2 + H 3 , by replacement of the hydrogen, in which, by three atoms 
 of the same or of different metals, the various ferridcyanides are pro- 
 duced, as Cfy 2 + K 3 , Cfy 2 + 3Cu, &c. 
 
 The prussian blues, on this theory, are considered to be compounds 
 of ferrocyanide with ferridcyanide of iron ; thus, 
 
 3. Cfy. Fe 2 + Cfy2- ^ e s expresses common Prussian blue. 
 Cfy 2 . Fe 3 ,, Turnbull's Prussian blue. 
 
 S.Cfy.Fe + Cfy 2 .Fe 3 + Fe 2 O 3 ,, basic Prussian blue. 
 
 This theory accounts very strictly for the first and third of the fund- 
 amental facts which I described, as characterizing the cyanogen com- 
 pounds. The theory of Graham is specially based upon the tendency 
 of three atoms of cyanogen to enter together into combination with 
 other bodies, as is shown not only in its relation to metals, but to 
 oxygen, as in cyanuric acid, and hence we may assume that cyanogen, 
 as Cy 3 , with three times its ordinary atomic weight, forms a distinct 
 radical (paracyan ?) which forms with oxygen and with hydrogen 
 
Complex Metallic Cyanides. 
 
 tribasic acids, Cy 3 .0 3 and Cy 3 .H 3 . From the replacement of more or 
 less of this hydrogen, in the latter, by equivalents of one or more 
 metal, the various cyanides may be formed. Thus, for example : 
 
 Cya -|- Fe.2K . . . yellow prussiate of potash. 
 
 Cya -{- Fe.K.Ca . . ferroprussiate of lime and potash. 
 
 Cya ~}~ Fe.2H . . . ferroprussic acid. 
 
 The basic of the red prussiate of potash should be then another 
 polymeric cyanogen, Cye, which would form, with hydrogen, a penta- 
 basic acid Cy 6 + H 5 , in which, more or less of replacement by metals 
 should give the various ferridcyanides. Thus, ferridprussic acid should 
 be Cy 6 4- Fe 2 .Ha, and red prussiate of potash Cy 6 + Fe 2 .K 3 . and so 
 on ; TurnbulTs Prussian blue becomes, on this theory, simply Cy 6 -f- 
 Fe 5 ; the common Prussian blue is (Cy 3 -f Ee 2 ) + Cy 6 .Fe 5 . ; and by 
 the addition of Fe 2 O 3 to that the basic Prussian blue is formed. 
 
 I am rather inclined to adopt Graham's view, although in the present 
 state of our knowledge, we have not grounds for positive decision. 
 He proposes to term the radical, Cy^ prussine, but has not given any 
 name to that whose formula is Cy 6 . 
 
 Platinocyanides and Palladiocyanides. 
 
 If finely divided platinum, either spongy platinum or platinum black, 
 be cautiously heated with ferrocyanide of potassium until the mass fuses, 
 a dark mass is formed, which on boiling with water, gives a solution of 
 platino-cyanide of potassium, from which on cooling, the salt crystal- 
 lizes in long prisms. The formula of this salt is PtCy -f KCy. and if 
 we assume a radical, platino-cyanogen, Cpty. = PtC) T 2. the salt is 
 K.Cpty. It is therefore monobasic. This salt is dichroic, being yellow 
 by transmitted, and blue by reflected light. 
 
 There also exists another more complex platinocyanide of potassium, 
 having the formula 5PtCy 4. 6. KCy. 
 
 By decomposing the soluble salts of mercury or lead, by platino- 
 cyanide of potassium, insoluble compounds are obtained, from which 
 when decomposed by sulphuretted hydrogen water, the hydroplatino- 
 cyanic acid is set free. PtCy + HCy. This acid crystallizes in copper- 
 red scales. Another kind of salt may be formed by acting on a solution 
 of platinocyanide of potassium with chlorine. Its formula is Pt 2 Cy 3 -f- 
 2.K Cy + 5Aq. and is related to the former as the red is to the yellow 
 prussiate of potash. 
 
 The Palladia-cyanides are perfectly analogous in their history to the 
 platino-cyanides, as are also the Iridio-cyanides, except that the latter 
 are apparently bibasic, the salt being constituted like the ferrocyanides. 
 
750 Compounds of Sulphocyanogen. 
 
 Cobalto- Cyanides. 
 
 On decomposing a salt of cobalt with an excess of cyanide of potas- 
 sium, the precipitate first formed redissolves, and forms a colourless 
 solution, from which the col) alto -cyanide of potassium crystallizes, by 
 evaporation and cooling, in pale yellow oblique rhombic prisms. In 
 this salt the cobalt exists as sesqui-cyanide, and as the metal cannot be 
 recognized by ordinary tests, a cobalto-cyanogen is assumed, which is 
 tribasic, and has hence the formula Co 2 Cy 6 or Cky. The potash salt 
 is consequently Co 2 Cy3 -f- 3KCy or K 3 .Cky. The cobalto-cyanic acid 
 is best prepared from the cobalto-cyanide of lead, which is a white 
 powder insoluble in water, and easily prepared by mixing solutions of 
 cobalto-cyanide of potassium and acetate of lead. On diffusing the 
 lead compound through water, and subjecting it to the action of a 
 current of sulphuretted hydrogen, sulphuret of lead is formed, and 
 cobalto-cyanic acid set free in solution ; from which by evaporation and 
 cooling it may be obtained crystallized in needles. It tastes acid, 
 and neutralizes bases, and is decomposed by a strong heat ; its formula 
 is Co 2 Cy 3 + 3HCy or H 3 Cky. 
 
 The use of these compounds in separating nickel and cobalt has been 
 described in page 516. 
 
 The Mangano-cyanides, Chromo -cyanides, and NicJcelo -cyanides are 
 perfectly similar to the cobalto-cyanides in general properties, and 
 appear to have the same tribasic character of their saline combinations. 
 Therein resembling the ferrid-cyanides and the cyanogen being equally 
 divided between the two metals. 
 
 OF SULPHOCYANOGEN AND THE PRODUCTS OF ITS 
 DECOMPOSITION. 
 
 If yellow prussiate of potash, well dried, and mixed carefully with 
 half its weight of sulphur, in fine powder, be heated in an iron vessel, 
 to perfect fusion, which takes place at a dull red heat, the sulphur 
 combines with all the cyanogen, forming sulpho-cyanogen, which unites 
 with the potassium, whilst the iron is converted into sulphuret. By 
 digesting the fused mass in water, the former dissolves, and is obtained, 
 by evaporation and cooling, in long striated prisms similar to those of 
 nitre. The composition of this salt is expressed by the formula CyS 
 4- KS or CyS 2 + K. It is termed sulpho-cyanide of potassium. If 
 the temperature be not raised too high, the iron forms also sulpho- 
 cyanide, which dissolves, and may be decomposed by the addition of a 
 slight excess of carbonate of potash; by this means, one-half more 
 
Sulphocyanide of Potassium. 751 
 
 product may be obtained than is yielded if the sulpho-cyanide of iron 
 be too violently heated, and thereby converted into sulphuret. 
 
 On passing a current of chlorine gas into a solution of the salt thus 
 formed, or by heating it in dilute nitric acid, chloride, or nitrate of 
 potassium is formed, and a deep yellow precipitate produced, which 
 contains all the sulphur and cyanogen of the salt ; this body had been 
 considered to be the sulphocyanogen, but its composition is complex, 
 being a mixture of several different bodies. It is very light and 
 insoluble in water. It combines with all of the metals, and with hy- 
 drogen, forming well-defined salts. 
 
 Hydro-sulphocyanic Acid. Cy.S 2 + H. Is formed by decomposing 
 sulpho-cyanide of lead by dilute sulphuric acid, or by sulphuret of 
 hydrogen. It is a colourless liquid, which reacts, and tastes acid. By 
 distillation it is decomposed. 
 
 Sulpho-cyanide of Potassium. Cy.S 2 + K. This salt, of which 
 the mode of preparation has been just described, forms anhydrous 
 prisms, cool and pungent in taste ; it is abundantly soluble in water 
 and alcohol, and slightly deliquescent. It is employed in the laboratory 
 as a test for peroxide of iron. 
 
 Sulpho-cyarMe of lead is a crystalline powder, prepared by mixing 
 solutions of a salt of lead and of sulpho-cyanide of potassium. 
 
 Of the sulpJio-cyanides of iron, the proto-salt, Pe -f- CyS 2 forms a 
 colourless solution, which becomes red on exposure to the air. The 
 sesqui-salt, Ee 2 + 3.CyS 2 , forms a deep blood-red liquor, when a solu- 
 ble sulpho-cyanide is mixed with any salt of the peroxide of iron. It 
 serves thus as a very delicate test of the presence of iron, and also for 
 that of cyanogen ; it is so applied to the detection of prussic acid, as 
 noticed p. 740. 
 
 These sulpho-cyanides may be considered either as double sulphurets 
 of cyanogen and of a metal, as Cy.S + S.K, &c., or as salts of the 
 compound radical sulpho-cyanogen, CyS 2 + K. &c. The latter view 
 has been almost universally adopted by chemists. Berzelius has pro- 
 posed to term this hypothetic radical, Rhodan, and its salts rJiodanides, 
 for the radical is certainly not mere sulphuret of cyanogen, nor can a 
 pure sulphuret of cyanogen be prepared from any of those salts. 
 
 It appears, however, from the researches of Parnell, Yoelkel and 
 Jameson, that although sulpho-cyanogen really exists in these salts, 
 yet that the yellow substance extracted from them by chlorine, or by 
 nitric acid, as described just now under that name, is only a product of 
 the decomposition of the true radical rliodan, which has not been as yet 
 isolated. The formula of the yellow powder is found to be S 4 C 4 N 2 H 2 O. 
 When acted on by alcalies, or by nitric acid, it produces an acid which 
 
752 Xanthan Mellon. 
 
 Parnell had termed the tkiocyanic, which is polybasic. It is a pale 
 yellow powder, sparingly soluble in water, more so in alcohol. Its 
 formula is Si 2 C 10 N 5 H 6 2 . Its compounds with the oxides of lead, 
 silver, mercury, &c., are insoluble. This new acid is but one of the 
 bodies produced in this reaction. 
 
 Jameson considers this yellow body C 4 S 4 N 2 H 2 O, to be really a com- 
 pound of the true sulphocyanic radical, with hydro-sulphocyanic acid 
 and water, C 4 S 4 N 2 H 2 O, being equal to S 2 Cy -f S 2 Cy.H + HO. When 
 dissolved in hydrosulphuret of potassium, sulphuretted hydrogen is 
 given off, and if the liquor be neutralized by an acid, a white precipitate 
 forms, consisting of S 4 C 6 N 4 H 4 . This body acts as an electro-negative 
 radical, and forms salts, which being colourless or white, Berzelius 
 proposes to call acJiromanides ; but Jameson terms this body sulpJio- 
 mellon, as it is decomposed by heat into sulphuret of hydrogen, and 
 mellon, S4H 4 and C 6 N 4 . 
 
 Persulpliocyanogen. If sulphocyanide of potassium be heated strongly 
 in a current of dry muriatic gas it is decomposed, bisulphuret of carbon 
 and prussic acid being set free, and a yellow powder produced, which 
 is volatile, insoluble in water, but soluble in alcohol, from which it 
 crystallizes. Its composition is CyS 3 + H or CyS 2 + HS. It there- 
 fore is a hydracid, containing more sulphur than sulphocyanic acid. 
 It forms salts, generally of a yellow colour, whence Berzelius proposes 
 to term the radical of its salts Xantkan. 
 
 Mellon. "When the yellow powder obtained from sulphocyanide of 
 potassium by means of chlorine or nitric acid, is. heated, it is decom- 
 posed, yielding sulphur, sulphuret of carbon, and a yellow powder 
 which remains as fixed residue, and to which Liebig has given the name 
 of mellon. This material is not constant in composition, being a mix- 
 ture of a substance termed glaucene with the true mellon which is ana- 
 logous to cyanogen in its characters. It is insoluble in water, alcohol, 
 or dilute acids. Its formula is C 6 N 4 or Ml, and when strongly ignited 
 it is decomposed into three volumes of cyanogen and one of nitrogen. 
 Heated with potassium, they unite with combustion, and if it be fused 
 with the iodide, or bromide of potassium, iodine or bromine is expelled, 
 and mellonide of potassium formed. 
 
 Hydro-mellonic Acid. H.M1. Is formed by dissolving mellonide of 
 potassium in boiling water and adding a strong acid. A gelatinous 
 white precipitate forms, which dries into a yellowish powder, HM1. 
 4- Aq. 
 
 Mellonide of Potassium. K.M1. Is produced by adding mellon to 
 sulpho-cyanide of potassium, fused in a porcelain capsule ; sulphur and 
 sulphuret of carbon are evolved. On dissolving the brown mass thus 
 
Melam. Melamine. Ammeline. 753 
 
 formed, in boiling water, the mellonide of potassium crystallizes, on 
 cooling, in fine colourless needles. 
 
 If we take the formula of sulphocyanogen at C 2 NS 3 , the formation 
 of mellon consists in 4(C 2 NS 2 ), producing 2(CS 2 ) with 4S, and leaving 
 C 6 N 4 ; but on Mr. ParnelTs view the decomposition is by no means so 
 simple, and the subsequent discovery of glaucen by Voelckel has 
 rendered Liebig's explanation insufficient. 
 
 When mellon is boiled with strong nitric acid it dissolves, and on 
 cooling, the liquor yields octohedral crystals of cyanilic add. This 
 substance has the same formula as cyanuric acid, Cy 3 3 -f 3Aq ; but 
 its relations to bases are not well understood. Nitrate of ammonia is 
 formed ; mellon, CeN^ and three atoms of water, giving C 6 N 3 O 3 and 
 NHX 
 
 Melam. C 12 H 9 N H . Sulphocyanide of ammonium, on being heated, 
 is decomposed into ammonia, sulphuret of carbon, and sulphuret of 
 hydrogen which pass off, whilst a greyish-white powder remains, 
 which is melam. The same result is obtained, by heating to fusion a 
 mixture of sulphocyanide of potassium and sal-ammoniac ; in this case, 
 chloride of potassium also remains behind, but may be removed by 
 washing. Melam is insoluble in water, and alcohol. It is dissolved 
 and decomposed by boiling acids and alcaline solutions, giving origin 
 to a series of remarkable bodies. 
 
 Melamine. C 6 H 6 N 6 . Is prepared by boiling melam with a dilute 
 solution of caustic potash, until the liquor becomes quite clear ; it is 
 then to be evaporated until it begins to deposit small crystalline plates, 
 and being then allowed to cool, the melamine crystallizes out in colour- 
 less octohedrons, scarcely soluble in cold water. It has no action on 
 vegetable colours, but it combines with dilute acids, acting as a base, 
 and forming well defined salts, which have an acid reaction, and may be 
 obtained crystallized. 
 
 Ammeline. C 6 N 6 H 5 O 2 . After the alcaline solution has deposited 
 the melamine by cooling, it contains ammeline, which precipitates when 
 acetic acid is added. This is to be purified by solution in dilute nitric 
 acid, and precipitation by carbonate of ammonia. It then forms fine 
 silky needles, insoluble in water and alcohol. It combines with the 
 dilute acids, forming crystallizable salts. 
 
 The origin of these bodies consists in the melam decomposing two 
 atoms of water, and then CjaHnNnOg, producing C 6 H 6 N 6 , and C 6 N 5 H 5 
 O 2 . By boiling melam in dilute muriatic acid, the same decomposition 
 occurs, and the muriates of melamine and ammeline crystallize together 
 on cooling. 
 
 If any of the above three bodies be dissolved in strong sulphuric 
 48 
 
754 Glaucene. Ammelide. 
 
 acid, and the solution be precipitated by alcohol, a white powder is 
 obtained, insoluble in water and alcohol, but soluble in strong acids and 
 alcalies. It is nearly indifferently acid or base, as it combines with 
 nitric acid, and also with oxide of silver. It is termed ammelide. Its 
 formula is C^H^NgC^ + 2Aq. When this body is boiled for a long 
 time with dilute sulphuric or nitric acid, it is resolved into ammonia 
 and cyanuric add, which last is the ultimate product of the similar 
 treatment of all the bodies of this series. 
 
 Voelckel has shown, that in the action of heat upon sulphocyanide 
 of ammonia and on sulphocyanogen, there are produced a great number 
 of other bodies than those described by Liebig, and also has rendered 
 it probable that some of those analysed by Liebig were mixtures. Thus 
 it appears tolerably certain that the mellon of Liebig only exists pure 
 in combination ; the powder obtained as mellon by Liebig' s process 
 always containing hydrogen. When melamine is strongly heated it gives 
 off ammonia, and leaves a grey-white powder which is termed glaucene 
 2.C 6 N 6 H 6 , losing 3NH 3 and leaving C^Ha or 2.C 6 N 4 + NH 3 . There 
 is therefore the simple relation between 
 
 Mellon, radical. C^N 4 = Ml. 
 Glaucene. base Ci 2 N 9 H 3 = 2M1 + NH 3 . 
 Melamine. base C 6 N 6 H 6 = Ml + 2.NH 3 . 
 
 The theoretical constitution of these bodies remains exceedingly ob- 
 scure. The bases, melamine and ammeline, are of great importance, 
 from their close analogy to the alcaloids, which are found naturally in 
 many plants ; but still we have no idea of the mode of arrangement of 
 their elements. 
 
 Some other sulphur compounds of cyanogen are known, but do not 
 require much notice. Cyanogen and sulphuretted hydrogen combining, 
 form orange crystals, insoluble in water. 
 
Structure of Starch. 755 
 
 CHAPTER XX. 
 
 OP STARCH, LIGNINE, GUM AND SUGAR, WITH THE PRODUCTS OF 
 THEIR DECOMPOSITION BY ACIDS AND ALCALIES. 
 
 THE substances now to be described form a very remarkable class of 
 organic bodies. They are found abundantly in most plants, but vary- 
 ing somewhat in characters, according to their immediate source, and 
 are subservient to the most important offices of the vegetable organ- 
 ization, being the materials from whence the tissues and secretions of 
 the plant are elaborated. In a chemical point of view, they are 
 distinguished by a remarkable similarity of composition, all containing 
 the same quantity of carbon (twelve atoms) in the equivalent, united 
 to oxygen and hydrogen, which are always present in the proportions 
 to form water. In this may be found the cause of the extraordinary 
 transmutations of these bodies, from one to another, by the mere 
 fixation of the elements of water, effected by the influence of re-agents, 
 or by the organic power of the plant. In these bodies also we find 
 an example of the difficulty of distinguishing between a constitution 
 derived from physical, and that resulting from vital force. In the 
 different kinds of sugar, the crystalline condition, solubility, &c. 
 indicate that the elements are combined by forces merely chemical; 
 but in the different varieties of starch, and especially in lignirie, traces 
 of organized structure are found, and properties manifested, which 
 attach their history as closely to the physiology as to the chemistry of 
 plants. Under this point of view they shall be hereafter reconsidered. 
 
 OF STARCH ITS VARIETIES AND PRODUCTS. 
 
 The most important variety of this principle is that known as 
 common starch. It exists in most plants and in all parts of them. It 
 is extracted from the seeds of wheat and barley ; from the tubers of 
 the potato ; from the root of the jatropha manihot, as tapioca or 
 cassava, and of the maranta arundinacea, as arrow root ; and from the 
 stems of palms, as the sagus rumphii, which furnishes the sago of 
 commerce. The starch is imbedded in the cellular tissue of the plant 
 as small white grains, totally destitute of any crystalline structure. 
 They differ in size in almost every plant. Those of the potato, which 
 are the largest, do not exceed in diameter ^- of an inch ; those of 
 
756 Properties of Starch. 
 
 arrow root, which are some of the smallest, do not exceed E ^. In 
 form, these grains vary also, some being globular, others ovoidal, and 
 often, even in the same plant, irregular. Each grain is formed by a 
 number of concentric layers which increase in density and consistence 
 from the centre ; the most external being so hard as to resemble a 
 membranous envelope, filled by a softer material. 
 
 The grains of starch are quite insoluble in cold water ; in boiling 
 water they dissolve, except the outer layers, which, floating in the 
 liquor, give it a peculiar opalescent aspect. On cooling, the solution 
 gelatinizes. If the solution of starch be dried at a gentle heat, and 
 then digested with cold water, the outer layers of the grains may be 
 separated by filtration, and a colourless transparent solution of starch 
 thus obtained. 
 
 The preparation of starch rests on its insolubility in cold water. 
 The texture of the plant is first broken up by rasping, or coarse grind- 
 ing, and being then mashed up with water, the starch grains fall out 
 from the ruptured cells, and are carried off by the current, from which 
 they deposit themselves, when the liquors are left at rest. In obtaining 
 starch from wheat, this liquor is allowed to ferment and become sour, 
 by which a quantity of gluten that would otherwise attach itself to the 
 starch is removed. If the moist starch grains be dried at a tempera- 
 ture of about ] 40, they gelatinize to a semitransparent mass, which 
 remains so when dried, and is not granular or mealy. It is thus that 
 .the peculiar aspect of tapioca and sago is produced. 
 
 By the vital action of the seed in germination, the transformation of 
 starch into sugar is effected, and constitutes the saccharine fermentation. 
 It is artificially induced by malting the grain, for the preparation of 
 alcoholic liquors by brewers and distillers. The circumstances of this 
 change will be specially noticed when describing the mode of nutrition 
 and of the growth of plants. 
 
 If starch be heated beyond 240, it softens and becomes brown. 
 If the heat be increased until the mass smokes, it is found to be 
 changed into a substance totally soluble in cold water, and known as 
 
 The action of re-agents on starch is very remarkable. By boiling 
 with nitric acid, it gives saccharic and oxalic acids. These reactions 
 will be hereafter studied in detail. A solution of it is precipitated by 
 basic acetate of lead and by infusion of galls. With bromine it gives 
 a yellow precipitate, which is decomposed by heat, the bromine being 
 expelled. With iodine it produces a compound of an intense blue 
 colour, which is its most remarkable property. 
 
 Iodide of Starch is produced when a solution of free iodine is added 
 
Inuline Lichenine . 757' 
 
 to a solution of starch. Its colour is violet-blue or nearly black, 
 according to the proportion of starch. It is very soluble in water, but 
 insoluble in alcohol, and may be obtained solid by adding alcohol to a 
 very strong aqueous solution, and collecting the precipitate on a filter. 
 It is decomposed by alcalies and by chlorine ; indeed by all bodies 
 which combine with iodine ; and its formation serves, therefore, as a 
 test only for free iodine, as described in p. 436. When a solution of 
 iodide of starch is heated, it becomes quite colourless below 200, and, 
 if it be not boiled, regains its colour perfectly as it cools. When the 
 liquor remains colourless after cooling, the blue may be restored by 
 oxalic acid or by chlorine, which expels the iodine from the com- 
 bination it had formed. 
 
 The composition of starch, no matter what plant it may be derived 
 from, is C 12 H 9 O 9 -f 2. HO, as confirmed by a variety of reactions. At 
 212 it loses an atom of water, and becomes a transparent mass, 
 Ci2H 9 O 9 + HO. Its combination with oxide of lead, amylate of lead, 
 is C 12 H 9 O 9 + 2PbO. 
 
 Inulin. This kind of starch is found in the roots of the iiiula, 
 dahlia, angelica, leontodon, and many other plants. It may be pre- 
 pared in the same way as common starch. It is a white and very fine 
 powder, almost insoluble in cold water, but easily dissolved by boiling 
 water; forming a liquor which becomes thick, but not gelatinous, when 
 it cools, and deposits the greater part of the inulin unchanged. It is 
 transformed by acids, like common starch, but more easily. It is 
 precipitated like it, by solutions of borax and subacetate of lead, and 
 by infusion of galls. It is peculiarly distinguished from it by not 
 giving with iodine any blue colour, being merely tinged yellow. The 
 structure of the grains of inulin has not been accurately examined. 
 Its formula, when dry, is Ci 2 HioO 10 , like that of common starch, and 
 in combining with oxide of lead it also appears to lose one atom of 
 water and to become C 12 H 9 9 , as remarked by Parnell. 
 
 Licheuine. This variety of starch, which is found in many lichens, 
 especially the icelaud moss, and the carrigeen, (spho3rococcus crispus) 
 is not contained in the plant in grains, but in a soluble condition. To 
 obtain it, the lichen is first digested in a cold dilute solution of car- 
 bonate of soda, to dissolve the bitter resinous principle, and this being 
 completely washed away, the lichen is boiled for a long time in water ; 
 a liquor is obtained from which, on cooling, the lichenine separates as 
 an opaque grey jelly, which, when dried, is black, hard, and glassy. 
 Its properties are very similar to those of inuline. It gives with iodine 
 a greenish-brown colour. Its composition is expressed by the same 
 formula as the others, C 12 H 10 Oi Q . 
 
758 Lignine. Xyloidine. Gun Cotton. 
 
 Of Lignine. Xyloidine. Gun Cotton. 
 
 When any kind of wood is treated successively, and repeatedly, by 
 dilute acids and alcalies, by water and by alcohol, so that every soluble 
 material is removed from it, we find that the substance which remains 
 is of very constant composition, being expressed by the formula C 12 H 8 
 O 8 . According to the recent experiments of Payen, the true tissue of 
 wood, cellulose, has the same composition as starch, C 12 H 10 O 10 , but the 
 true lignine which is secreted into the cells and fills them, has the for- 
 mula C 38 H 2 40 2 o. Of this substance, lignine, the proper wood of the 
 plant is constituted ; its molecules being arranged so as to form the 
 tubes and cells of the vegetable tissues, and cohering so firmly as to 
 produce the fibres of flax, cotton, and hemp, which constitute the 
 materials of our most important woven textures, of paper, &c. Although 
 the lignine is thus rather the remains of an organized body than a mere 
 chemical substance, it forms some combinations which are of great 
 importance in the arts. Thus if linen or cotton cloth be dipped in 
 dilute solution of acetate of alumina, the earth abandons the acid to 
 combine with the lignine, and thus serves as the means of fixing on the 
 cloth the various colouring matters used in the processes of dyeing. 
 The same occurs with oxide of iron ; and other metallic oxides have a 
 similar though weaker affinity for lignine, and thus serve as mordants 
 for various colours. The observations of Crum, would however show, 
 that the mordant is only deposited in the interior of the cells or tubes 
 of the ligneous fibre where it had been mechanically absorbed, and 
 not held by any chemical affinity. 
 
 Lignine when quite pure is white ; the bleaching of linen, cotton, 
 paper, &c., being effected by destroying, by means of the air, or of 
 chlorine, the resinous and other matters which are associated with the 
 lignine in the fibres or cells of the plants ; the lignine itself resists these 
 agents unless applied in a very concentrated form. With cold nitric 
 acid, lignine combines directly, forming a very remarkable substance, 
 xylo'idine, which may be produced by immersing for a moment a piece 
 of paper in strong nitric acid, and then washing it well in pure water. 
 It assumes the feel and toughness of parchment, and is so combustible, 
 as to serve for tinder. 
 
 The composition of xyloidine is remarkable, being expressed by 
 Ci 2 lSr 2 H 8 O 18 . It may therefore be regarded as lignine, in which two 
 atoms of hydrogen are replaced by two of nitrous acid. This material 
 may be also formed by digesting starch in cold strong nitric acid in 
 which it dissolves, and by the addition of water, pure xyloidine is pre- 
 cipitated. 
 
 The digestion of fine ligneous fibre in nitric acid produces a body of 
 
Xyloidine Gun Cotton. 751) 
 
 still more combustible nature than xylo'idine, and as cotton has been 
 found to be the best material for the purpose, the body has been named 
 gun cotton, as it explodes when heated with a force even superior to 
 that of ordinary gunpowder. Gun cotton is best prepared by digesting 
 for a few minutes cotton wool, in as much as will cover it and com- 
 pletely moisten it, of a mixture of equal volumes of the strongest oil of 
 vitriol and nitric acid. The cotton when taken out is to be freed by 
 pressure from the great excess of acid, and then washed with cold 
 water until it becomes perfectly tasteless ; it must be then dried very 
 cautiously, as when well prepared it often will explode when drying in 
 a water bath, below 212. The gun cotton has precisely the appearance 
 of ordinary cotton, but it contains a large quantity of nitric acid 100 
 parts of cotton yielding 170 of gun cotton. 
 
 The gun cotton appears to be a direct compound of anhydrous lignine 
 with nitric acid C 12 H 8 O 8 -f 2N0 5 . The two atoms of nitric acid re- 
 placing the two atoms of water which ordinary lignine C 12 H 10 Oi = 
 Oj 2 H 8 O 8 -f- 2Aq. contain. It has also been proposed, however, to con- 
 sider the lignine as oxidized and combined with four equivalent of 
 hyponitrous acid, thus C 12 H 8 O 16 -f- 4NO 3 . In this view the oxide of 
 lignine, C 12 H 8 O 16 is regarded as a powerful base, and as certainly no 
 simple salt can be assumed to contain four atoms of acid, the formula 
 should be subdivided and become C 3 H 2 O 4 -f- NO 3 . Those questions, 
 however, cannot be considered to be as yet decided. 
 
 It is evident that gun cotton, Ci 2 N 4 H 8 O 28 contains in itself the 
 elements of 
 
 Eight atoms of water . . H 8 . O 8 
 
 Eight " carbonic acid Cs. . . Oie 
 
 Four " carbonic oxide C4 . . 04 
 
 Four " nitrogen . N~4. 
 
 Ci2. N 4 . H 8 . O 2 8. 
 
 It is consequently resolved by heat altogether into gases with ex- 
 plosion ; it leaves no residue, and requires no access of oxygen, although 
 when burned in the open air, the carbonic oxide is converted into 
 carbonic acid. There appear to be found in its explosion very decided 
 quantities of nitrous acid and of prussic acid. The former corrodes 
 fire arms, and the latter vitiates the surrounding air if in a mine. 
 These circumstances coupled with the inconstancy of its preparation 
 and of its strength, will probably restrict its use within much narrower 
 limits than was at one time supposed, from the immense explosive 
 power which it possesses, which is four or five times that of an equal 
 weight of gunpowder. 
 
 If sawdust be heated with a warm solution of potash for some hours, 
 
760 Araline^Tragacanthine. Dextrine. 
 
 the liquor will be found to contain a considerable quantity of common 
 starch, capable of striking a blue colour with iodine ; but by this means, 
 the ligneous fibre is dissected, and not. decomposed. The starch may 
 be extracted also by mechanical means, and pure lignine does not yield 
 any. If lignine be strongly heated with, hydrate of potash) hydrogen 
 is evolved and a mixture of acetate and oxalate. of potash 'results; 
 C I2 H 8 O 8 and 4 HO, giving 6. H, with 2(C 2 3 ) and 2(G 4 H 3 O 3 ). Hot 
 nitric acid converts lignine into oxalic acid ; with sulphuric acid it is 
 changed into gum, and ultimately into sugar, as will be detailed further 
 on. At the same time a portion of organic matter unites with sul- 
 phuric acid, forming ligno-sulpJmric acid, which forms soluble salts with 
 barytes and with oxide of lead ; its precise composition is not known. 
 In dry air, or immersed under water free from air, lignine remains 
 for an indefinite length of time unaltered ; but if both air and water 
 have access, oxygen is absorbed and carbonic acid and water given out, 
 and a series of products of decomposition result, which form the basis 
 of vegetable soil, and thus serve as the materials for a new generation 
 of plants. By the conjoint action of heat and water, lignine produces 
 another class of products, and a third series arises from the destructive 
 distillation of dry wood. These subjects will be examined specially in 
 their proper place. 
 
 Of t7ie different Varieties of Gum. 
 
 It is necessary to distinguish three varieties of gum, to which the 
 names of arabine, cerasine, and dextrine may be given. The two first 
 are natural, the last is a product of the transmutation of starch. 
 
 Arabine is found in the juices of many species of acacia and prunus; 
 it exudes from crevices in the bark and forms lumps, in which state it 
 is found in commerce (gum arable and gum Senegal). The roots of 
 mallow, comfrey, and many other plants contain a great deal of ara- 
 bine. It is never crystalline, and is colourless and transparent, with a 
 vitreous fracture. It is dissolved by water in all proportions, forming 
 a thick "adhesive liquid (mucilage). It is not dissolved by alcohol, 
 which precipitates its watery solution. It combines with bases forming 
 well defined insoluble compounds, and is not in any way acted on by 
 iodine. A solution of arabine exercises sinistral rotatory power on a 
 ray of polarized light (p. 46). By contact with sulphuric acid, arabine 
 is gradually converted into dextrine, and if the digestion be continued, 
 this then changes into sugar. "With nitric acid arabine gives mucic 
 acid, and afterwards oxalic acid ; another characteristic property of it 
 is, that of giving a precipitate with solution of silicate of potash 
 (soluble glass, p. 618). Its composition is expressed by the formula 
 
Varieties of Sugar. 761 
 
 TragacantJdne or Vegetable ffiww, exists in cherry-tree gum, mixed 
 with arabine, but is purer in gum tragacanth, in flax-seed, and in 
 quinceseed. It is extracted by digestion in water, when it gradually 
 swells up and appears rather to imbibe the water than to dissolve ; a 
 thick tenacious liquor is obtained, which is precipitated by alcohol and 
 by solution of basic acetate of lead, but not by silicate of potash. 
 With sulphuric and nitric acid, the same products are formed as from 
 arabine. 
 
 The Salep of commerce is the tragacanthine extracted from the roots 
 of various species of orchis, and dried. 
 
 Dextrine. This variety of gum is formed from the starch of the 
 seed, in germination, and may be obtained by digesting starch in dilute 
 sulphuric acid. If five parts of starch, with one of oil of vitriol and 
 fifteen of water, be kept at 200 for some time, the starch completely 
 disappears, the solution loses its power of gelatinizing ; it acquires the 
 characteristic rotatory power of dextrine, and colours iodine of a port 
 wine red, without any tinge of blue, If the liquor be neutralized by 
 carbonate of barytes, the whole quantity of sulphuric acid separates, 
 and by evaporation, the dextrine is obtained as a pale yellow mass of a 
 vitreous fracture; it is not adhesive like common gum, nor does it yield 
 any mucic acid when acted on by nitric acid. 
 
 Dextrine precipitates a solution of basic acetate of lead, but is not 
 affected by silicate of potash. If dextrine be boiled too long with the 
 sulphuric acid, it passes into a substance, more analogous to tragacan- 
 thine, which is also formed when arabine or lignine is so treated. In 
 this state its rotatory power is feeble, and it is not at all coloured by 
 iodine. In both these forms the composition of dextrine is C 12 H 10 Oi . 
 
 OF THE DIFFERENT VARIETIES OF SUGAR. 
 
 The species of sugar are much better distinguished from each other, 
 both by properties and composition, than the various kinds of starch, 
 or of gum, have been found to be. They are all characterized by being 
 capable of undergoing the alcoholic fermentation. 
 
 Cane-sugar. 
 
 Formula C 12 H 9 9 + 2Aq. when crystallized. This species of sugar 
 is found abundantly in the juices of many plants. It is extracted for 
 use, from the sugar-cane, the maple, and the beet-root. The juice, 
 when fresh, runs into fermentation with great quickness, and is there- 
 fore clarified by being warmed to 150, with a little lime, by which the 
 vegetable albumen is coagulated, and the fermentation checked. The 
 juice is then evaporated with as little heat as possible, and allowed to 
 
762 Compounds of Cane Sugar. Sacchulmine. 
 
 cool in vessels, at the bottom of which a number of small apertures, 
 stopped with plugs, are situated. The sirup congeals into a granular 
 mass, and when it is quite cold, the apertures below are opened, and 
 the liquid portion allowed to run out. The sugar thus obtained in fine 
 crystalline grains, is brownish-coloured, and is termed muscovado or 
 raw sugar. The liquid uncrystallizable portion constitutes molasses or 
 treacle. To obtain the sugar pure it is redissolved, and the liquor 
 having been cautiously evaporated (in some establishments, in vacua, 
 see p. 109) to the necessary degree, is poured into cones of unglazed 
 earthenware, which are placed on their summits, the orifice in which is 
 stopped by a plug. When by cooling, the sirup has crystallized, 
 during which the mass is continually stirred about to render the crys- 
 tals very minute and close, the plug below is removed, and the coloured 
 liquor drains out ; the last portions of it being removed by laying a 
 sponge, moistened with some spirit, or with a clear sirup, on the sugar 
 at the base of the cone, and allowing the pure liquid to filter through. 
 Thus is obtained refined or loaf-sugar. If a strong sirup be laid aside 
 in a warm place, it crystallizes in very beautiful oblique rhombs, which 
 constitute the sugar-candy of commerce. 
 
 Cane-sugar is perfectly colourless. Its sp. gr. is 1'6 ; when heated, 
 it fuses at 350 into a clear yellow liquid, and congeals, on cooling, 
 into a hard brittle mass (barley-sugar), which, after some weeks, be- 
 comes opaque, white, and crystalline. If the temperature rises to 
 630, water is given off, and the sugar becomes dark brown, being 
 changed into caramel; more strongly heated, it is totally decomposed. 
 Sugar dissolves in one-third of its weight of cold, and in all propor- 
 tions in boiling water. A saturated solution becomes quite solid when 
 it cools. If a strong solution of sugar be kept for some time near its 
 boiling point, it is gradually changed into uncrystallizable sugar; hence 
 arises the most important source of loss in the manufacture and 
 refining of sugar. It is sparingly soluble in absolute alcohol, and but 
 moderately in weak spirit. 
 
 Sugar combines with some bases and salts, acting as a feeble acid ; 
 the compound with oxide of lead is insoluble, and has the formula 
 Ci 2 H 9 9 + 2PbO; that with barytes is crystalline, its formula is 
 C 12 H 10 O 10 + BaO. With common salt sugar combines, forming 
 crystals, easily soluble in water, and consisting of 2.C 12 H 10 10 -f Na.Cl. 
 
 The action of acids on cane-sugar is very remarkable. When 
 digested with very dilute sulphuric or muriatic acid, it is converted 
 into grape sugar; but with stronger acids, it is changed into two 
 brown substances, insoluble in water, one of them soluble, the other 
 insoluble in alcaline liquors. The former is termed sacckulmine, the 
 
Saccharic Add. Caramel. 763 
 
 latter, saccJmlmic acid. These bodies are formed even with very dilute 
 acids, if the digestion be continued for a long- time. According as the 
 reaction proceeds, the sacchulmine separates in minute brilliant brown 
 crystalline plates, mixed with a dull brown powder, which is sacchulmic 
 acid. They are separated by water of ammonia, which dissolves the 
 latter. The composition of these bodies is not quite definitely estab- 
 lished, as it appears to be influenced by the strength of the acid used 
 and other circumstances. The best grounded idea is that they have 
 both the same composition, C^H^O^; being isorneric with ulmhie. 
 If in this reaction the atmospheric air have access, oxygen is absorbed, 
 and a large quantity of formic acid generated. 
 
 Saccharic Acid. The preparation of oxalic acid by means of nitric 
 acid and sugar, has been already described (p. 699) ; but if in that 
 process a dilute acid be used, so that the oxidation may not be forced 
 so far, a liquor is obtained which gives with carbonate of lime a neutral 
 solution. When this is decomposed by acetate of lead, a white pre- 
 cipitate is thrown down, which being acted on by sulphuretted hydrogen, 
 the acid is set free, and may be obtained crystallized by evaporating 
 and cooling its solution. This is termed the saccharic acid. It gives 
 an extensive series of salts, being a pentabasic acid. Its formula is 
 C 12 H 5 On -f- 5. HO, when crystallized. Its potash salt is C 12 H 5 On + 
 K0.4HO. Its lead salt C 12 H 5 O n + 5PbO. The saccharate of lime 
 is sparingly soluble in water, but dissolves in a very slight excess of 
 acid, which distinguishes it from an oxalate. An ammoniacal solution 
 of saccharate of silver is decomposed by heat ; metallic silver being 
 deposited and forming a mirror-surface on the interior of the vessel. 
 
 Cane-sugar dissolves several of the salts of copper insoluble in water, 
 as the carbonate ; and if solutions of salts of copper or of peroxide of 
 iron be mixed with much sugar, they are no longer precipitated by 
 alcalies. Hydrated oxide of copper dissolves in a solution of potash 
 if sugar be added, and forms a violet solution from which, by boiling, 
 metallic copper or suboxide of copper is deposited according to the 
 quantity of sugar present. In this reaction much formic acid is pro- 
 duced. 
 
 The caramel formed by heating sugar to 650, appears as a porous, 
 shining, jet black mass. It is completely soluble in water, and free 
 from any empyreumatic taste. It is insoluble in alcohol ; it combines 
 with bases ; its formula is Ci 2 H 9 O 9 . The sugar in forming it, there- 
 fore, loses the elements of an atom of water, besides its water of crys- 
 tallization. By heating sugar with lime, a volatile liquid is obtained, 
 which has the formula C 6 H 5 0, and is termed metacetone. It shall be 
 specially noticed in another place in conjunction with acetone. 
 
764 Saccharine Fermentation. Grape Sugar. 
 
 Grape Sugar. Glucose. 
 
 Formula. C^H^On -f- 3Aq, when crystallized. This kind of sugar 
 is still more extensively distributed in nature than the former. It gives 
 the sweet taste to fruits, and forms the solid part of honey. It is 
 produced in the animal body in certain forms of disease, as diabetes, 
 and by the transformation of starch in germination, and by artificial 
 processes. In consequence of this variety of sources, it is better to 
 term it glucose, as suggested by Dumas, than to use a name indicating 
 any one special origin. 
 
 Glucose may be obtained from raisins, or honey, by digestion first 
 with cold strong alcohol, to remove the uncrystallizable sugar, and then 
 expressing the residue, which is to be dissolved in water, and neutralized 
 by chalk. The liquor so obtained may be clarified by white of egg, 
 and evaporated to crystallization. 
 
 From starch, gum, or cane-sugar, it may be prepared by the action 
 of sulphuric acid, as follows : one part of potato-starch is to be boiled 
 with four parts of water, and -fa of oil of vitriol, during 36 or 40 
 hours; the water which evaporates being replaced. The jelly does 
 not assume any consistence ; the liquor remains clear, and the material 
 used is found completely converted into sugar. By means of chalk, 
 the acid is removed, and the solution being evaporated, the sugar 
 crystallizes. 
 
 If starch paste be moistened with an infusion of pale malt, it is 
 rapidly converted into dextrine, and thence into grape sugar. This 
 occurs from the catalytic influence of a principle termed diastase, which 
 exists in the malt, and the formation of which shall be detailed under 
 the head of germination. 
 
 To convert lignine into sugar, bits of paper or linen are to be im- 
 bibed with their own weight of oil of vitriol, until they are converted 
 into an uniform viscid mass, taking care that it shall not become hot ; 
 this is then to be diluted, and the liquor boiled for some time. The 
 acid being then removed by chalk, the sugar is obtained pure, by 
 crystallization, as in the former case. 
 
 Sugar of grapes crystallizes in hard colourless tables, or in hemi- 
 spherical grains, consisting of minute needles closely aggregated together; 
 its specific gravity is 1'38; it is much sweeter than cane sugar, and 
 less soluble in water. When heated to 212, it gives off two atoms of 
 water, which it recovers when redissolved ; but by a stronger heat it is 
 changed into caramel. It is soluble in twenty parts of boiling absolute 
 alcohol, and separates almost totally on cooling, in granular crystals, 
 which contain alcohol combined. It combines with bases, forming 
 compounds analogous to those given by cane sugar. 
 
Transformation of Starch into Sugar. 765 
 
 The composition of crystallized grape sugar is C 12 H 14 14 , or C^HnOn 
 -f 3Aq. When fused at 212, it becomes C 12 H, 2 O 12 , or C^HnOn -f 
 Aq. Its compound with chloride of sodium, which crystallizes in fine 
 double six-sided pyramids, consist of 2(C 12 Hi 2 O 12 ) + NaCl + 2Aq. 
 With a solution of basic acetate of lead it gives a white precipitate, 
 the formula of which is Ci 2 HnOn + 3PbO, corresponding to the crys- 
 tallized sugar. The dry grape sugar has evidently the same composition 
 as the crystallized cane sugar. 
 
 The kinds of sugar (glucose) derived from these different sources are 
 not so really identical as has been generally supposed, since they are 
 found to act differently upon polarized light. Grape sugar, as con- 
 tained in the grape juice, or in the juice of the flowering grasses, ro- 
 tates the plane of polarization to the left, but if the juice be evaporated, 
 and the sugar crystallized, its molecular constitution is so totally altered, 
 as that when redissolved it gives a rotation to the right. The starch 
 sugar, as well as cane sugar, rotates also to the right, but in a much 
 inferior degree to the starch gum, which, as already mentioned, re- 
 ceives its name of dextrine from that quality. 
 
 As lignine, starch, gum, and cane sugar, all contain the same quan- 
 tity of carbon (C J2 ), their transformation into grape sugar consists 
 evidently in the fixation of the elements of water; thus lignine, 
 C 12 H 8 O 8 takes 4HO, and 100 parts of sawdust have been found to give 
 115 of sugar; starch (C 12 H 10 O 10 ) takes 2HO, and 100 parts of it 
 usually yield 106. It has been remarked, that a certain quantity of 
 mannite is at the same time produced, besides sacchulmine. 
 
 Grape sugar yields, when treated with dilute sulphuric acid, the 
 same brown substances as cane sugar; but if the sulphuric acid be 
 concentrated, it forms with the elements of the sugar a peculiar acid 
 termed the sulpho-saccharic. Sugar of starch or grapes is to be fused 
 at a low heat, and 1 J parts of oil of vitriol then well mixed with it. 
 If the sugar be pure and the temperature be kept low, the product is 
 not coloured. Its constitution is not rigidly determined, but its lead 
 salt consists of 2(C 12 H 11 O 11 ) + S0 3 + 4PbO. 
 
 In acting on grape sugar, nitric acid gives rise to the same products, 
 oxalic and saccharic acids, as cane sugar; indeed it appears probable, 
 that like the other strong acids this also first changes the cane sugar 
 into glucose, and that the saccharic acid is really derived from the 
 latter. On this view its formation is more easily explained, for as the 
 dry glucose is C 12 H u On and the saccharic acid is C J2 H 5 Oji, the oxygen 
 of the nitric acid simply removes six atoms of the hydrogen of the 
 grape sugar and the elements of the acid remain. 
 
766 Lactine Mucic Acid. 
 
 Glucic and Melassic Acids. 
 
 By contact, even with the strongest bases, cane sugar is but slowly 
 altered, and hence lime may be employed to clarify the vegetable juices 
 which contain it; but under the same circumstances grape sugar is 
 rapidly decomposed and an acid formed, which is termed gludc acid. 
 It is very soluble in water and does not crystallize ; with lime, barytes, 
 and lead, it forms neutral soluble salts, but it precipitates a solution of 
 basic acetate of lead. Its taste is purely acid, and it reddens litmus. 
 Its composition is C 12 H 8 8 , and it is isomeric, therefore, in its dry 
 state, with lignine. When a strong solution of caustic potash is added 
 to fused grape sugar and boiled, the glucic acid, which at first forms, 
 is decomposed. The liquor become deep brown, and yields, on the 
 addition of muriatic acid, a black flocculent precipitate of melassic acid. 
 The formula C 2 4H 12 Oi has been assigned to it, but its nature is not 
 well known. 
 
 Lactine, or Sugar of milk. 
 
 This remarkable substance, which is found only in the milk of the 
 mammalia, is obtained by evaporating whey to a pellicle and setting it 
 aside to cool, when the sugar crystallizes in small square prisms, white, 
 semitransparent, hard and gritty under the teeth. The taste of the 
 crystals is but slightly sweet, but that of a strong solution is much 
 more so. It dissolves very slowly in water and is insoluble in alcohol. 
 
 When the crystals of lactine are gradually heated to 290, they give 
 off two atoms of water; at about 300 they fuse and give off three 
 atoms of water more. The composition of the dry sugar thus obtained 
 is C 24 H 19 O 19 , and of the crystals C24Hi 9 O 19 + 5Aq. By mixing solu- 
 tions of sugar of milk, and of basic acetate of lead, a white precipi- 
 tate is produced, the formula of which is C 2 4H 19 19 + 5PbO. 
 
 By digestion with dilute sulphuric acid, sugar of milk is changed 
 into grape sugar, and then produces the other reactions already de- 
 scribed. With alcalies the decomposition is also the same as that of 
 glucose, but the action of nitric acid on lactine differs from that on any 
 other sugar, as the acid formed is not the saccharic, but that already 
 noticed as obtained from native gum, the mucic acid. 
 
 To obtain mucic acid, one part of gum or lactine is to be dissolved 
 in four parts of nitric acid, specific gravity 1*42, mixed with one part 
 of water. Heat is to be applied until all effervescence has ceased, and 
 the mucic acid is deposited on cooling. It is a crystalline powder, 
 gritty under the teeth and feebly acid. It dissolves in six parts of 
 
Glycyrrhizine. Mannite. 767 
 
 boiling water, but is insoluble in alcohol. Its crystals have the for- 
 mula, C 12 H 10 O 16 , being formed from gum by the simple addition of 
 six equivalents of oxygen. This formula contains, however, 2Aq. as 
 it is a bibasic acid, and its salts consist of C 12 H 8 O 14 + 2. MO. The 
 alcaline mucates are soluble, the earthy and metallic salts are insoluble 
 in water. 
 
 When mucic acid is long boiled with water, its acid properties become 
 much stronger, and it becomes more soluble in water and soluble in 
 alcohol ; it gradually returns from this state to its ordinary condition, 
 even when combined with bases. If mucic acid be distilled at a high 
 temperature, water and carbonic acid are evolved, and a sublimate forms 
 in brilliant white plates, which are soluble in alcohol and water; 
 C 12 H 10 16 give 2C0 2 and 6HO, besides C 10 H 4 6 , which is the formula 
 of the hydrated pyromucic acid. This substance fuses at 270, and is 
 volatile at 290 without decomposition. Its salts contain one equiv- 
 alent of base ; those of lead, barytes, and silver are insoluble ; those 
 of the alcalies are very soluble in water. 
 
 With this acid a certain quantity of chlorine may be combined, 
 forming ckloropyromucic acid, C 10 H 3 C1 4 O 5 , which is prepared by acting 
 with chlorine on pyromucic ether. 
 
 Fungus Sugar. Is deposited in rhombic prisms from the watery 
 solution of the alcoholic extract of ergot of rye. They are insoluble 
 in ether ; they give oxalic acid by nitric acid, and undergo the alcoholic 
 fermentation. Their composition was found to give the formula 
 Ci 2 H 13 O i3 , but little is known accurately of this variety of sugar. 
 
 Of Gfycyrrhizzine and Mannile. 
 
 These bodies are connected so closely with the true sugars, that, 
 although wanting in the characteristic of forming alcohol by fermenta- 
 tion, they may be best described here. 
 
 Glycyrrhyzine. This substance, which is found in the liquorice 
 root, and in some other sweet woods, is obtained by boiling the root 
 of liquorice in water, and after concentrating the liquor adding thereto 
 sulphuric acid. A white precipitate containing the glycyrrhyzine com- 
 bined with sulphuric acid and albumen is formed. This is to be washed 
 with acid water, and then with pure water, and to be dissolved in al- 
 cohol, which leaves the albumen. The alcoholic solution is to be de- 
 composed by carbonate of potash, which throws down the sulphuric 
 acid, and by evaporating the filtered liquor, the sweet principle remains 
 pure, as a yellow transparent mass. 
 
 Its most remarkable property is that of combining very definitely 
 
768 Mucous and Lactic Fermentations. 
 
 with acids and bases, and with several neutral sails. Almost every 
 acid precipitates a compound from a solution of glycyrrhyzine. It 
 expels the carbonic acid from the carbonates of potash, soda, and 
 barytes, combining with the base, and it precipitates the solutions of 
 most of the ordinary metallic salts. Neither the pure substance, nor 
 any of its compounds, have been accurately analyzed. 
 
 Mannite C 6 H 7 6 . Is found in manna, of which it constitutes 
 the sweet principle. It exudes also from the bark of other trees, and 
 exists in most mushrooms. It is produced by the decomposition of 
 cane sugar in certain cases. To obtain it, manna is digested in boiling 
 alcohol, and the liquor filtered whilst very hot; on cooling, the mannite 
 is deposited almost totally, and may be purified by repeated crystalliza- 
 tions. Its taste is slightly sweet; it is very soluble in water, and 
 crystallizes in brilliant white prisms of silky lustre. When heated 
 gently, it fuses without losing weight. With nitric acid it gives oxalic 
 and saccharic acids. It does not appear to combine with bases. 
 
 If the unclarified juice of the beet or carrot root be kept at a tem- 
 perature of 100 for some time, a tumultuous decomposition sets in, 
 which is termed the mucous fermentation. All the sugar disappears, 
 and the liquor is found to contain a large quantity of gum and of 
 mannite, with a peculiar acid, which exists naturally in all the animal 
 fluids, but especially in milk, and is termed the lactic acid. At the 
 same time carbonic acid gas is evolved and the liquor contains ammonia. 
 This action is too complex to be expressed in formulae, but it may be 
 noticed that one equivalent of dry cane sugar contains the elements of 
 two equivalents of lactic acid; whilst by abstracting two atoms of 
 oxygen from an equivalent of crystallized grape sugar, the constituents 
 of two atoms of mannite remain. 
 
 Lactic Acid and the Lactates. 
 
 Lactic acid may be prepared by means of this mucous fermentation, 
 or also abundantly from sour whey or from the sour waters obtained in 
 the manufacture of wheaten starch ; but it is best obtained in quantity 
 by the conversion of sugar in a peculiar species of catalysis, which 
 may be termed lactic fermentation. If a solution of one part of sugar 
 in five parts of water be made to ferment at a temperature of 90 or 
 100, by the addition of a small quantity of cheese or an animal mem- 
 brane, and that prepared chalk be added from time to time to neutralize 
 the acid which is generated, after some time the liquor becomes nearly 
 solid from the deposition of crystalline grains of lactate of lime which 
 may be purified by solution in boiling water and recrystallization. In 
 
Lactic Acid. Lactates. 769 
 
 this action, if well carried on, the sole product is lactic acid. Traces 
 of mannite sometimes appear, but only from the liquor having acciden- 
 tally passed into the mucous fermentation. The conversion of the 
 sugar is purely catalytic, two equivalents of hydrated lactic acid, 
 2(C 6 H 6 O 6 ) being equal to one equivalent of grape sugar, or one of cane 
 sugar -f- one of water. 
 
 To obtain the acid pure, advantage is taken of the facility of crys- 
 tallizing the lactate of zinc. The lactate of lime may be decomposed 
 by sulphate of zinc, and the sulphate of lime being removed by the 
 filter, the liquor is to be evaporated, and on cooling the lactate of zinc 
 may be obtained in large crystals, easily rendered quite pure by re- 
 solution and crystallization. A solution of pure lactate of zinc being 
 decomposed by water of barytes, lactate of barytes is obtained, which, 
 with sulphuric acid, gives sulphate of barytes, and the pure lactic acid 
 dissolves. The solution is to be placed in vacuo over sulphuric acid ; 
 it gives a sirup-thick liquor which has the formula C 6 H 6 O 6 , or C 6 H 5 O 5 
 + Aq., as it contains an atom of basic water ; it tastes strongly acid. 
 When heated to 480, it gives off water and a white sublimate forms 
 in brilliant white rhomboidal plates, which is paralactic add. It is 
 purified by solution in boiling alcohol, from which it crystallizes. The 
 composition of this body is C 6 H 4 O 4 ; it fuses at 225, and sublimes at 
 450 ; it tastes very slightly acid, and dissolves but very slowly in 
 water ; the solution gives, when evaporated, only the sirupy liquid of 
 the hydrated acid, and does not crystallize. 
 
 The lactic acid coagulates albumen ; it mixes with milk when cold, 
 but coagulates it when boiled. It forms monobasic salts, in which its 
 formula is C 6 H 5 5 . They are all soluble in water, and crystallize but 
 imperfectly, except that of zinc, which forms brilliant white four-sided 
 prisms, containing three atoms of crystal water. The protolactate of 
 iron, C 6 H05 -j- FeO + 3Aq. may be obtained crystallized in small 
 prisms of a greenish-yellow colour. The perlactate of iron dries into 
 a reddish transparent mass like shell -lac. These last are used in me- 
 dicine. 
 
 The lactic acid will be again noticed as a constituent of the animal 
 system where it exists in the blood and flesh, perhaps also in urine, but 
 this latter is questionable after Liebig's experiments. 
 
 49 
 
770 
 
 CHAPTEE XXI. 
 
 OF THE ALCOHOLIC AND ACETIC FERMENTATIONS OF ALCOHOL, THE 
 ETHERS, ALDEHYD, ACETIC ACID, AND OTHER BODIES DERIVED 
 FROM IT. 
 
 AN aqueous solution of pure sugar may remain perfectly unaltered for 
 any length of time, if carefully excluded from the air. If the air have 
 access, it is gradually decomposed, becoming brown and sour, but no 
 alcohol is generated. If, however, the solution of sugar be brought 
 into contact with any organic substance which is itself in the act of slow 
 decomposition, then the particles of sugar participate in the change 
 which is going forward, and carbonic acid and alcohol result. 
 
 The substance which is specially active in inducing this kind of fer- 
 mentation, is an azotized body termed yeast ; but a number of animal 
 and vegetable substances can also effect it. Blood, white of egg, glue, 
 flesh, if they have begun to putrefy, are capable of exciting it ; but 
 the bodies of most practical importance in that respect are, vegetable 
 albumen and gluten. These bodies exist in all fruits and seeds, in 
 greater or less proportion, but they differ in character, according to the 
 plants they are derived from, nearly in the same way as the varieties of 
 starch. I shall here only notice them as derived from wheat and from 
 beans, as I shall have occasion to describe some other forms hereafter. 
 If wheaten flour be washed with water, in a linen bag, the starch 
 passes oft', and a tenacious paste remains, which consists of albumen 
 and gluten mixed. They may be separated by boiling in alcohol, which 
 dissolves the latter, and leaves the former behind. On mixing the 
 alcoholic liquor with water, the gluten is precipitated, and may be col- 
 lected and dried. 
 
 Vegetable Gluten so obtained is pale yellow, and forms, when soft, 
 an adhesive mass, very extensile and elastic. Its solution in alcohol 
 is thick-fluid when concentrated; insoluble in ether, it dissolves in 
 acetic acid, and in alcaline solutions. It combines with the mineral 
 acids, forming bodies very sparingly soluble in water, which are pre- 
 cipitated by adding the acid to the solution of gluten in acetic acid, or 
 in potash. If these solutions be mixed with solutions of earthy, or 
 metallic salts, precipitates are formed, which are compounds of the 
 gluten with the metallic oxide. 
 
Gluten Albumen. Legumine. 771 
 
 In all these reactions, the gluten is accompanied by a slimy material, 
 termed mucin, which it is difficult to remove perfectly from the gluten; 
 it is best effected by boiling with water, when the mucin remains dis- 
 solved. Its solution is precipitated by sulphate of iron and infusion of 
 galls, but not by acetate of lead or corrosive sublimate. 
 
 Vegetable albumen remains behind after the rough gluten has been 
 boiled in alcohol. It is destitute of elasticity when softened, and dries 
 to a hard white mass ; it is moderately soluble in water, and its solu- 
 tion is coagulated by heat ; it dissolves in alcaline liquors. Its solu- 
 tions are precipitated by acids, except the phosphoric and acetic, and 
 by all earths and metallic salts ; these precipitates are white or coloured, 
 according to the nature of the metallic oxide ; with ferro-prussiate of 
 potash, and with infusion of galls, the solution of vegetable albumen 
 in acetic acid gives white precipitates. 
 
 Legumin. This substance, which exists in peas and beans, possesses 
 properties intermediate to those of the gluten and albumen of wheat. 
 When powdered peas are diffused through water, the starch settles to 
 the bottom, but the legumin is dissolved, and separates by evaporation, 
 on the surface of the liquor, in mucous transparent pellicles. Its so- 
 lution is not coagulated by heat ; it is insoluble in alcohol. It dis- 
 solves in solutions of the vegetable acids, and is precipitated on the 
 addition of a mineral acid. It dissolves in alcalies, and gives, with 
 the earthy and metallic salts, compounds insoluble in water. 
 
 All these substances differ from most vegetable bodies, in containing 
 a large quantity of nitrogen, and in the latter case, sulphur, as a con- 
 stituent. They leave behind, when burned, an ash consisting of phos- 
 phates of lime, magnesia, and iron, similar to the ash of animal sub- 
 stances. Indeed an almost perfect similarity of properties exists be- 
 tween these bodies, and fibrine, albumen, and casein among animal 
 products ; in the case of casein and legumine probably amounting to 
 identity. In contact with air and water, these bodies enter spontane- 
 ously into decomposition, evolving carbonic acid and ammonia, and 
 forming new products, and in this state of decomposition they super- 
 induce the alcoholic fermentation on those particles of sugar which lie 
 in contact with them. Hence, in fruits, the sugar may lie in contact 
 with these vegeto-animal substances without any change occurring, as 
 long as the investing membrane of the fruit-cells remains perfect ; but 
 if the fruit be crushed, so that the air have access, then oxygen is ab- 
 sorbed, the vegeto-animal body begins to putrefy, and the sugar is soon 
 engaged in the decomposition. It is remarkable, that the necessity 
 for oxygen is at the commencement of the decomposition ; when the 
 putrefaction of the albumen, or gluten, has once begun, it extends 
 
772 Nature of Yeast. Alcoholic Fermentation. 
 
 itself throughout its whole mass without requiring any further action 
 of the air. 
 
 The principles of the conservation of vegetable juices,, by inclosure 
 in vessels from which the air is excluded, can easily be understood from 
 this, as well as the utility of such agents as sulphurous acid, or sul- 
 phite of potash, which absorb any traces of oxygen that may be pre- 
 sent, and prevent it from acting on the organic substance. 
 
 The general characters of these natural ferments being thus sketched, 
 it is necessary to add the important facts of the history of artificial 
 ferment, or yeast. This is nothing more than the decomposing mass 
 of vegetable gluten, or albumen, produced in a previous fermentation. 
 If the yeast be too old, that is, if all the vegeto-animal matters be 
 already decomposed, its power of exciting action is destroyed ; it is 
 also destroyed by boiling, by alcohol, by many salts and acids, and 
 generally by all those means which give to the albumen and gluten an 
 insoluble form, and prevent their further putrefaction. 
 
 When a solution of pure sugar is fermented by contact with a cerfain 
 quantity of yeast, this last is found to be very much diminished in 
 quantity, and to have totally lost its activity. On the contrary, if in 
 place of pure sugar, grape or currant juice or an infusion of malt be 
 used, the quantity of ferment is found to be much increased, and to 
 preserve all its power. In this case the albumen and gluten of the 
 vegetable juices are themselves brought into the same train of decom- 
 position as the added portion of yeast, and thus form a new and larger 
 quantity of active fermenting material. Thus, in a brewery, the quan- 
 tity of yeast continually increases. If yeast be examined with the 
 microscope, it is found to contain a vast number of minute globular 
 bodies, possibly animalcules, which derive their nutriment from it ; 
 but recently some very unfounded attempts have been made to connect 
 these globules essentially with the process of fermentation, by the idea 
 that in the process of nutrition they absorbed the sugar, and that the 
 products of fermentation were excreted subsequently by them. But 
 this is shown to be absurd, by the simple fact, that the weight of the 
 alcohol and carbonic acid is greater than the weight of the sugar. 
 
 The phenomena of the alcoholic fermentation are best observed on 
 the clear expressed grape juice, kept at a temperature between 70 and 
 80, in a lightly-covered vessel. After a few hours, a slight efferves- 
 cence is observed, and the liquor becomes turbid, as if pipe-clay were 
 diffused through it. As the effervescence increases, the liquor becomes 
 warmer, and the precipitate forms flocculi, on which the gas-bubbles 
 are evolved, being thereby carried to the surface of the liquor, and 
 falling down again wh^n the gas-bubbles have broken. This circulation 
 
Alcoholic Fermentation. 773 
 
 continues until the fermentation has ceased, when the precipitate col- 
 lects at the bottom. The liquor no longer tastes sweet; it contains no 
 sugar, but in place of it, an equivalent quantity of alcohol. An in- 
 fusion of malt does not so readily ferment as the grape juice, unless 
 some yeast be first added. In its spontaneous fermentation, most of 
 the gum and sugar which it contains, passes into the mucous fermen- 
 tation, whilst but little alcohol is formed. In the practical manufac- 
 ture of malt drinks and spirits, therefore, the worts are always set to 
 ferment by the addition of a suitable quantity of the yeast formed in a 
 preceding operation. 
 
 Although the essential character of sugar is, to be capable of alco- 
 holic fermentation ; yet the different kinds of sugar enter on that pro- 
 cess with unequal facility. The sugar of milk requires the presence of 
 a very active ferment, and of an acid, by the influence of which it is 
 changed into sugar of grapes. Thus milk does not ferment until it 
 has become clotted and sour ; the casein then acts as yeast, in super- 
 inducing the alcoholic fermentation. Indeed, no matter what kind of 
 sugar is employed in this process, it is changed into grape sugar before 
 fermenting, as is shown by the action of the liquor upon polarized 
 light. The grape sugar, as dried at 2] 2, contains exactly the elements 
 of two atoms of alcohol, and four of carbonic acid, as 2(C 4 H 6 O 2 ) and 
 4.CO 2 arise from Ci 2 H 12 12 . As cane sugar takes an atom of water to 
 form grape sugar, it follows that cane sugar in fermenting should yield 
 more than its own weight of carbonic acid and alcohol, and it has been 
 ascertained by experiment that 100 parts actually give 104, whilst by 
 theory, 105 should be produced, consisting of 51*3 of carbonic acid 
 and 53' 7 of alcohol. This coincidence of numbers prove that these 
 bodies are the only products. The influence of the yeast is, therefore, 
 strictly what Berzelius terms catalytic, but its action becomes much 
 more definitely intelligible, by considering it as a case of the general 
 principle expressed by Liebig, that motion (decomposition) may be 
 communicated from the particles of one body (yeast) to those of another 
 (sugar) by virtue of proximity, as described more fully in pp. 229-234. 
 
 As further details of the circumstances of the alcoholic fermentation 
 should vary with the nature of the liquor to be produced, whether it 
 be for immediate drinking, as wine, ale, or porter, or for distillation, 
 and that these lead to purely technical descriptions of the arts of brew- 
 ing, &c., I shall not enter on them. 
 
 OF VINIC ALCOHOL AND THE ETHERS DERIVED FROM IT. 
 When any saccharine liquor, which has undergone the alcoholic fer- 
 mentation is distilled at a gentle heat, a very volatile liquid passes 
 
774 Rectified Spirit. Proof Spirit. 
 
 over, which by successive rectifications may be deprived of most of the 
 water which had been mixed with it. In various degrees of strength* 
 and contaminated by minute traces of essential oils, characteristic of the 
 plants from which the saccharine liquor had been obtained, it con- 
 stitutes the potato-spirit, brandy, malt-whiskey, arracJc, rum, &c. of 
 commerce. In a still stronger form it constitutes the spirit of wine, or 
 rectified spirit ; the term alcohol being applied to it only when it is 
 chemically pure. By mere distillation alcohol cannot be freed from all 
 the admixed water ; for which it exerts a strong affinity. When its 
 specific gravity is reduced to O813 at 60, in which state it still con- 
 tains 8*2 per cent, of water, or exactly half an equivalent, its boiling 
 point remains constantly at 172, and it distils over unchanged. In 
 the form of proof spirit of commerce its sp. gr. is about 0'920, 
 and it contains 48 per cent, of absolute alcohol ; the rectified spirit 
 containing about 83 per cent, and having the specific gravity 0'839 
 at 60 E. 
 
 To obtain real alcohol, or absolute alcohol, as it is generally termed, 
 rectified spirit is to be distilled at a moderate heat from some substance 
 having a stronger affinity for water ; as lime, caustic potash, carbonate 
 of potash, or chloride of calcium. Of these the last named should be 
 preferred. The water of the spirit combines with the body used and 
 forming a hydrate, the real alcohol distils over. The rectification 
 should be conducted in a water bath. 
 
 A singular mode of concentrating alcohol is founded on the fact that 
 alcohol does not moisten the animal tissues but corrugates, and rather 
 abstracts water from them. Hence if a bladder be filled with spirit of 
 sp. gr. O820 containing 90 per cent, of alcohol ; and if it be left for 
 a few days in a warm room, the spirit will be found to have its sp. gr. 
 reduced to O'SOO, containing 97 per cent of real alcohol. The water 
 permeates the bladder, and evaporates from the outer side, but as the 
 alcohol does not moisten the bladder, it cannot get through, and con- 
 sequently remains behind, freed from water. 
 
 The very ingenious way of obtaining alcohol, devised by Graham, by 
 evaporation in vacuo with quicklime, has been described in p. 111. 
 
 Alcohol thus obtained anhydrous, has a sp. gr. of 0'7947 at 60; 
 it boils at 168 ; the specific gravity of its vapour is 1598 ; it does not 
 become solid even in the most intense cold ; its taste is burning and 
 dry upon the tongue, owing to it abstracting water from its tissue. It 
 is highly inflammable, burns with little light ; from its volatility, if 
 some drops of it are poured into a jar of oxygen gas, its vapour forms 
 a powerfully explosive mixture. It does not conduct electricity. It 
 mixes with water in every proportion, contracts in volume, and evolves 
 
Constitution of Alcoliol. Uses of Alcohol. 775 
 
 heat. The sp. gr. of spirituous liquors is, therefore, always above the 
 mean sp. gr. of the alcohol and water they contain. The greatest 
 condensation occurs with 54 volumes of alcohol and 50 of water ; the 
 mixture occupies only 100 volumes ; and its sp. gr. is 0*927, being a 
 little denser than proof spirit. 
 
 The formula of alcohol is C,H 6 O 2 , and its composition is, 
 
 4 equivalents of carbon = 24-0 . . . 52'66 
 6 hydrogen = 6*0 . . . 12-90 
 
 2 oxygen = 16'0 . . . 34*44 
 
 The equivalent of alcohol = 46'0 . . . lOO'OO 
 
 This is confirmed by the products of its decomposition, and by the 
 specific gravity of its vapour : for, 
 
 4 vols. of carbon vapour (836'8^X 4) = 3347'2 
 
 12 hydrogen (69'3 x 12) = 831-6 
 
 2 oxygen (1105-6 X 2) ==2211-2 
 
 Give four volumes of alcohol vapour 6390 '0 
 Of which one volume weighs . . . 1597'5 
 
 It will be shown, however, that alcohol consists of ether united to 
 water, and that its formula is C 4 H 5 O -f- Aq. Its vapour is then 
 formed by the union of 
 
 volume of vapour of ether = 1286*4 ) 
 
 i volume of vapour of water = 311-1 j 15y7 ' 5 
 
 The uses of alcohol in chemistry and pharmacy are numerous and 
 important. It dissolves the caustic alcalies and most deliquescent salts, 
 combining with them to form akoates, which resemble very remarkably 
 the hydrates. Thus if dry chloride of calcium be dissolved in alcohol, 
 the alcoate crystallizes by cooling, in large transparent plates. By 
 heat, these are decomposed, and also by contact with water, which 
 expels the alcohol, and takes its place. The permanent and efflo- 
 rescent salts are generally insoluble in alcohol, and may be even precipi- 
 tated by it from their solution in water ; the alcohol seizing on the 
 water. 
 
 An important pharmaceutic use of alcohol is for the solution of the 
 resinous principles of plants, in the preparation of tinctures and 
 alcoholic extracts. The strength of the alcohol must in these cases be 
 regulated by the nature of the substances to be dissolved. Sometimes 
 rectified spirit, at other times proof spirit being more effectual. 
 
 The manufacture of alcohol is itself one of the most important arts ; 
 it is the basis also of the manufacture of vinegar, of the making of 
 resinous varnishes, and various other processes. To the chemist it is 
 
776 
 
 Preparation of Ether. 
 
 specially of interest as the type of a very interesting group of organic 
 bodies, and yielding by its decomposition a very numerous series of 
 products, which are of great importance in science, in pharmacy, and 
 in the arts: 
 
 When alcohol is exposed to the air it gradually absorbs oxygen, 
 aldehyd and acetic acid being formed. It is then said to undergo the 
 acetous fermentation. Under the influence of acids it loses an atom 
 of water, compounds being formed which are termed ethers, into the 
 composition of which the acid employed generally enters. 
 
 OF SULPHURIC ETHER. ETHER. OXIDE OF ETHYLE. 
 This substance may be prepared by any process which deprives 
 alcohol of the equivalent of water which it contains. Thus, if potas- 
 sium be placed in contact with absolute alcohol, hydrogen gas is 
 evolved, and a compound of ether and potash crystallizes, C 4 H 5 O-f HO 
 and K, giving C 4 H 5 O -f- KO and free H. If a current of gaseous 
 fluoride of boron (p. 453) be passed into alcohol, it is absorbed, and 
 boracic acid separates in crystals, whilst the liquor contains ether; 
 here also the water of the alcohol is decomposed, fluoric and boracic 
 acids being produced and ether liberated. By distillation with chloride 
 of zinc also, the water may be abstracted from alcohol and ether ob- 
 tained ; but the affinity of the other deliquescent salts is not sufficiently 
 intense to decompose it. 
 
 It is by the action of sulphuric acid upon alcohol that ether is, for 
 practical purposes, always obtained. Equal weights of rectified spirit 
 
Action of Sulphuric Acid on Alcohol. Ill 
 
 and of oil of vitriol, being well mixed, and avoiding any considerable 
 rise of temperature, are to be introduced into a glass globe, to which 
 heat may be applied by a sand bath, as represented in the figure. To 
 this may be attached the form of condenser devised by Liebig for the 
 distillation of very volatile liquids. It consists of a glass tube, three- 
 fourths or one inch wide, and twenty-four or thirty inches, long, dd, to 
 which is attached at one end by a good cork, a narrower tube passing 
 to the globe, and to the other end is soldered a smaller tube bent at an 
 obtuse angle, and conducting to the receiver m. The tube dd, fits 
 water-tight by corks into a tinned cylinder e, the proportions of which 
 may be judged from the figure ; this is kept full of cold water. When 
 the distillation commences, the hot vapours entering the condensing 
 tube at d } give out their latent heat to the surrounding water, and that 
 part of the condenser should soon get hot, was not the water constantly 
 changed ; by the funnel e, a stream of cold water flows from the 
 reservoir i } into the lower part of the tube d, and presses up before it 
 the warm and lighter water, until this is expelled by the tube/) when 
 it is collected at p. The supply of cold water should be so proportioned 
 to the supply of vapour, that, flowing away at^ it should not be sen- 
 sibly warm to the hand. With this precaution, most volatile liquids 
 may be perfectly condensed even in the midst of summer. The mix- 
 ture of acid and spirit in the globe being brought to a temperature of 
 about 260 as rapidly as possible, it begins to boil, and the ether 
 distilling over, accompanied by some water and unaltered alcohol, col- 
 lects in the receiver. 
 
 Since the quantity of sulphuric acid continually increases in the 
 globe, as the distillation proceeds, its action on the remaining alcohol 
 changes ; the mixture becomes dark coloured, an oily substance distils 
 over (oil of wine), and the quantity of ether formed diminishes rapidly. 
 Sulphurous acid and olefiant gases are then evolved, and finally the 
 mixture becomes thick and black, and froths up very much. When 
 the object is only the preparation of ether, these reactions may be 
 prevented, and a much larger product obtained, by admitting to the 
 globe by means of the bent funnel b, a continual, but minute stream of 
 rectified spirit. The action of the sulphuric acid is thus exercised upon 
 successive quantities of spirit, and the liberation of the ether continues 
 until the acid becomes so weak, as to be no longer able to decompose 
 the alcohol, which occurs when the whole quantity of rectified spirit 
 used, is about twice the weight of the oil of vitriol, which is then re- 
 duced to the strength of SO 3 + 4Aq. 
 
 Although we may represent the results of this reaction, by consid- 
 ering the sulphuric acid to take water directly from the alcohol, and set 
 
778 Continuous Formation of Ether. 
 
 the ether free, such is by no means really the case ; on the contrary, 
 when the alcohol acts on the oil of vitriol, the water of both is disen- 
 gaged, and the sulphuric acid and ether unite to form sulphate of 
 ether; (C 4 H 5 + Aq), and S0 3 + Aq, giving C 4 H 5 + SO 3 and 
 2.Aq. This body, which resembles very much sulphate of ammonia in 
 its tendency to combination, unites with an atom of oil of vitriol to 
 form bisulphate of ether, or as it is generally termed sulphovinic acid. 
 The two atoms of sulphuric acid thus engaged, change very much in 
 properties, forming salts with barytes and oxide of lead, which are very 
 soluble in water. The two equivalents of water, which, as above 
 described, are set free, dilute the remaining sulphuric acid to such a 
 degree, as that it cannot decompose more alcohol ; hence, if absolute 
 alcohol be used, 3(C 4 H 5 + Aq.), with 8(SO 3 .HO) produce, 3(C 4 H 5 O. 
 S0 3 + HO.S0 3 ) and 2(S0 3 + 4Aq.) ; one-fourth of the sulphuric 
 acid remaining over; if a weaker alcohol be used, the quantity of dilute 
 sulphuric acid formed becomes proportionally greater. An acid which 
 already contains four atoms of water, forms no sulphate of ether, when 
 put in contact even with absolute alcohol, except the temperature be 
 very high. 
 
 The ether obtained by distilling a mixture of alcohol and oil of 
 vitriol, results, therefore, not from the water being seized on by the oil 
 of vitriol, but from the decomposition of its compound with sulphuric 
 acid, the sulphate of ether; the ether being a base not much superior 
 in energy to water, is expelled by it in turn under favourable circum- 
 stances, especially when the water is present in excess. In this respect 
 it resembles, as Rose has remarked, the sesquioxides of iron, antimony 
 and bismuth, which form salts with sulphuric acid, that are totally 
 decomposed by a large quantity of water, especially if their solutions be 
 boiled ; the acid then combines with the water, and the metallic oxide 
 precipitates. Before deciding on this view of the production of ether, 
 it is necessary to describe some collateral phenomena. 
 
 If absolute alcohol and strong oil of vitriol be employed in the 
 preparation of ether, it is found that the distilled product consists of 
 ether and water, forming two distinct layers in virtue of their different 
 specific gravities ; but in quantity identical with those which constitute 
 alcohol; 100 parts of the mixed liquids consisting of 19*5 water and 
 79*5 ether, when separated from a quantity of alcohol which had 
 escaped decomposition. The oil of vitriol remains in the retort in its 
 original state of concentration, and hence might be applied to etherify 
 an infinite quantity of absolute alcohol, introduced in a continuous 
 stream. To explain this very remarkable result, Mitscherlich advanced 
 that the action of the sulphuric acid on the alcohol is merely catalytic, 
 
Theory of the Formation of Ether. 779 
 
 that it splits it, as it were, into ether and water, and these pieces not 
 being able to reunite, come over in vapour, merely mixed with each 
 other ; this idea is, however, quite inadmissible, as the whole quantity 
 of ether is proved to be united with the sulphuric acid in the first 
 place, and to distil over only after the decomposition of the compound 
 that had been so formed. The observations of Liebig and Eose have 
 removed the difficulty which this simultaneous evolution of water and 
 ether presented to the adoption of the theory which supposes the ether 
 to be expelled from its combination with the sulphuric acid, by the 
 water. In fact, it is only at a particular temperature that the ether 
 and water come over in atomic proportions, and this then results from 
 the identity of the boiling points of the solution of sulphovinic acid 
 and of the dilute sulphuric acid. Thus, when we heat together, sul- 
 phate of ether (C 4 H 5 + SO 3 ) and the dilute sulphuric acid, S0 3 + 4Aq, 
 the former is decomposed ; bihydrate of sulphuric acid, SO 3 -f- 2Aq. 
 being formed, and ether set free ; but at this temperature the sulphuric 
 acid begins to abandon its second atom of water, which then distils 
 over with the ether. If we conduct the distillation very slowly, and 
 retain the temperature below 212, the ether comes over, almost per- 
 fectly free from water ; but at a higher temperature, the ether, when 
 liberated, is immediately converted into elastic vapour, which bubbles 
 through the liquid, like a gas, and the water evaporates in the space 
 thus afforded, as it should evaporate in a current of air forced to bubble 
 through the liquid in the same way. 
 
 The production of ether depends, therefore, upon the facts, that 
 when alcohol and oil of vitriol are mixed, sulphate of ether is formed 
 and water is set free ; but on the application of heat, this action is 
 inverted, and the ether is expelled from the acid, with which the water 
 recombines. If the distillation be conducted so that the mixture boils, 
 the dilute sulphuric acid concentrates itself, at the same time, by giving 
 off an atom of w r ater, which condenses mixed with the ether, but had 
 its origin in a perfectly independent action. 
 
 If we heat alcohol in contact with glacial phosphoric or arsenic 
 acids, it is similarly acted on, and the ether forms a phosphovinic or 
 arseniovinic acid, which is decomposed by boiling, the ether being set 
 free. These acids would be too costly to admit of their employment 
 in the preparation of ether on the great scale, and besides, they do not 
 act as powerfully as oil of vitriol. Although this ether does not con- 
 tain any sulphuric acid, it is very generally called sulphuric ether, and 
 I shall often use that name, but the distinction between it and the 
 compound ethers formed by its union with acids, must be carefully 
 kept in mind. ^ 
 
780 Constitution of Ether. 
 
 The ether formed by the process now described is rendered impure 
 by admixture with alcohol and water, and sometimes oil of wine and 
 sulphurous acid. It is freed from these by rectification, from a water 
 bath, over some dry carbonate of potash. It is then a colourless 
 liquid, of an agreeable penetrating odour, and a pungent taste. Its sp. 
 gr. is 0-720 at 60; it does not conduct electricity; at 47 F. it 
 freezes into a crystalline mass; it boils at 96; the.sp. gr. of its vapour 
 is 2572*9. In evaporating it produces great cold, of which numerous 
 applications have been noticed under the head of vaporization. (Sect. 
 IV. Chap. III.) 
 
 Ether is very extensively used as a medicinal agent, and exercises a 
 very powerful action on the system. Its vapour if respired proves like 
 carbonic acid an intense narcotic, and has been hence employed to 
 produce torpor and prevent sensation during surgical operations. 
 
 Ether is very combustible; its vapour, diffused through air or 
 oxygen, forms powerfully explosive mixtures. Exposed to the air, it 
 gradually absorbs oxygen, forming acetic acid. Its flame is brighter 
 than that of alcohol, but it gives no smoke ; it dissolves sulphur and 
 phosphorus in small quantity; iodine and bromine are abundantly 
 dissolved, but they soon act on the ether ; most bodies that are soluble 
 in alcohol are dissolved by ether, except salts, of which only very few, 
 as the perchlorides of gold, of platina and of iron, are taken up by it. 
 Ether combines with almost all acids, forming well defined, neutral 
 salts, the compound ethers, which have a remarkable similarity to the 
 ammoniacal salts. It is, therefore, an organic base ; its composition is 
 expressed by the formula C 4 H 5 O, giving the numbers by weight : 
 
 4 equivalents of carbon . . 24 '00 . . . 65-31 
 
 5 ,, hydrogen . 5'00 . . . 13-33 
 1 oxygen . . 8'00 . . . 21-36 
 
 37-20 100-00 
 
 and by volume, 
 
 4 volumes of carbon vapour (836-8 x 4) = 3347 2 
 
 10 hydrogen , : (69'3 X 10) = 693-0 
 
 1 oxygen 1105-6 
 
 Produce two volumes of vapour of ether . 5145-8 
 Of which one weighs therefore .... 2572*9 
 
 In chemistry and pharmacy ether is of importance as a vehicle for 
 the solution of many resinous and other bodies, and from its action on 
 the animal economy. By the action of re-agents it yields a great 
 number of derived compounds, of which the most important will be 
 described in their proper place. 
 
Compounds of Ether and Sulphuric Acid. 781 
 
 The question of the intimate constitution of ether has been very 
 much discussed, and opinions have followed precisely the same course, 
 with regard to the theory of its compounds, as for that of the combi- 
 nations of ammonia ; thus it has been looked upon as an oxide of a 
 compound (metallic ?) radical, ethereum, or ethyle, as the salts of am- 
 monia were supposed to contain a compound metal, ammonium. The 
 formula of ethyle should be C 4 H 5 , and its symbol, Ae. On the other 
 hand, it may be considered to consist of olefiant gas, C 4 H 4 , united to 
 water, and the latter then takes the place of the arnmoniacal gas in the 
 theory of ammonia. I shall frequently employ for ether the symbol 
 Ae.O, and speak of it and other bodies as compounds of ethyle, as 
 oxide, chloride, &c. but without any other present object than con- 
 venience of language, for it would be impossible to discuss the com- 
 parative merits of these theories, without knowing the properties of 
 the compound ethers, of olefiant gas, of aldehyd, acetic acid, and many 
 other bodies, which are involved in the reactions by which we may 
 endeavour to test their value, and hence I shall postpone all details of 
 the principles of the ether-theories until the end of the present chapter. 
 
 COMPOUNDS OF ETHER WITH SULPHURIC ACID. 
 Sulphovinic Acid. Bisulphate of Ether. 
 
 Formula. C 4 H 5 O.S0 3 -f- HO.SO 3 or AeO.SO 3 + HO.SO 3 . Is pro- 
 duced by mixing alcohol with oil of vitriol, as described for the 
 preparation of ether, or by passing vapour of ether into oil of vitriol 
 as long as it is absorbed. By heat this solution is decomposed. The 
 sulphovinic acid cannot be obtained in a solid form ; if a solution of 
 sulphovinate of lead be decomposed by sulphuret of hydrogen, a 
 colourless and very acid liquor is obtained, which, when concentrated, 
 evolves ether, blackens, and is totally decomposed. Its salts are all 
 soluble, and generally deliquescent ; when boiled with muriatic acid, 
 alcohol is evolved and sulphuric acid set free. By a high temperature 
 they are decomposed, oil of wine, ether, olefiant gas, and sulphurous 
 acid being given off, whilst a metallic sulphate or sulphuret remains 
 behind mixed with some charcoal. By distilling a sulphovinate with a 
 potash salt of any volatile acid, a compound of ether with that acid 
 distils over, and sulphate of potash remains. By fusing a sulphovinate 
 with a caustic alcali, water and olefiaut gas are expelled, and all the 
 sulphuric acid remains combined with the alcali. 
 
 Sulphovinate of Potash. AeO.SO 3 + KO.S0 3 . Crystallizes in 
 colourless rhomboidal plates, which are anhydrous ; it is very soluble 
 in water, but sparingly soluble in alcohol. Sulphovinate of barytes, 
 
782 Siilphovinic, Ethionic, and Isethionic 
 
 AeO.SOg -f. BaO.SO 3 4- 2Aq. crystallizes in oblique rhomboidal prisms 
 unalterable in the air ; it tastes strongly acid ; in vacuo it abandons 
 its water, and is then not altered by a heat of 212, but if the hydrated 
 salt be heated to 21 2, alcohol is given off, and sulphuric acid set free. 
 Sulphovinate of lime, crystallizes in thin hexagonal plates, which are 
 very deliquescent ; it is soluble in less than its own weight of cold 
 water. Sulphovinate of lead forms large rhombic crystals, deliquescent, 
 very soluble in water and in alcohol ; it is gradually decomposed at 
 ordinary temperatures. Sulphovinate of copper, AeO.SO 3 -f CuO.S0 3 
 -f- 4Aq, forms large blue octagonal plates, permanent in the air, and 
 very soluble in alcohol and water ; heated to 212 it is totally decom- 
 posed. 
 
 Ethionic and Isethionic Acids. 
 
 These substances are formed by acting on alcohol, or ether, with the 
 vapours of anhydrous sulphuric acid; the liquor, neutralized by barytes, 
 gives the insoluble sulphate, and the soluble ethionate of barytes, which 
 last separates from the concentrated liquor, as a crystalline precipitate, 
 on the addition of alcohol. A solution of this salt, when decomposed 
 by sulphuric acid, gives free ethionic acid, which, by boiling, is decom- 
 posed into sulphovinic acid and isethionic acid, of which, indeed, 
 Liebig considers it to be, in reality, only a mixture. The isethionic 
 acid is formed more characteristically by the direct union of anhydrous 
 sulphuric acid and olefiant gas, and will be described as a compound of 
 that body. 
 
 Althionic and Methionic Acids. 
 
 "When the mixture of alcohol and oil of vitriol, for making ether, 
 has been distilled so far as that it has become black and began to froth, 
 it produces, when neutralized with bases, a series of salts, which, 
 though having the same per cent, composition as the sulphovinates, 
 differ very much from them in properties ; thus the Altliionate of lime 
 does not crystallize; the Altliionate of Barytes crystallizes in fine 
 needles, in place of the large plates of the sulphovinate ; the Altliionate 
 of copper is still more distinct, as its crystals are thin acute rhombs, 
 of a pale green colour. 
 
 If the ether, into which the vapours of sulphuric acid are passed, 
 be allowed to grow hot, it becomes black, sulphurous acid is evolved, 
 and an acid is formed different from any of the preceding ; it is called 
 the methionic acid, and is characterized by its barytes salt being totally 
 insoluble in alcohol, and but sparingly soluble in water. When its 
 salts are fused with caustic potash, merely sulphite of potash remains; 
 
Sulphate of Ether. Oil of Wine. Etherol and Etherine. 783 
 
 the formula of the acid contained in the barytes salt is C 2 H 3 S 2 O 7 . It 
 evidently does not contain any simple combination of alcohol or ether. 
 
 Heavy Oil of Wine Sulphate of Ether and Etherol. 
 
 Probable formula C 8 H 9 O -f 2SO 3 , or AeO.SO 3 + C 4 H 4 .SO 3 . When 
 one part of rectified spirit is distilled with two and a-half parts of oil 
 of vitriol, a little ether passes over, followed by an oily yellow liquid, 
 and water, with much sulphurous acid. The oil is to be washed with 
 a little water, and then dried in vacuo under a bell-glass, beside two 
 cups, one of oil of vitriol and the other of caustic potash ; the first 
 absorbs the water and ether, and the last the sulphurous acid. This 
 substance is then a thin oil, sometimes green and sometimes yellow ; 
 its odour aromatic and pungent; its specific gravity 1*133; when 
 heated it begins to boil, but is rapidly decomposed, blackening and 
 evolving sulphurous acid, and but little distilling over. It is scarcely 
 soluble in water, but abundantly so in alcohol and ether. When boiled 
 with water, or with an alcaline solution, sulphovinic acid is formed, 
 and etherol (light oil of \oine) set free, which floats upon the surface. 
 
 The composition of this body is not absolutely constant. It is 
 usually considered to be a mixture, in variable proportions, of true 
 sulphate of ether, AeO.SO 3 , with sulphate of etherol, C 4 H 4 .SO 3 . I 
 have found that when distilled with oxalate or acetate of potash, with 
 chloride or sulphuret of potassium, oxalic and acetic ethers, muriatic 
 ether, &c., are generated, and at the same time etherol remains indif- 
 ferent to these re-agents. It has been suggested that, as these heavy 
 and light oils of wine are produced but in such small quantities from 
 even large quantities of spirit, and that their relations to the true ether 
 are so doubtful, they may really belong to the amylic series, and be 
 products, not of the ether, but of the volatile oil which accompanies 
 and flavours the raw fermented spirits. 
 
 Another process for obtaining this heavy oil of wine consists in mix- 
 ing dry sulphovinate of lime with its own weight of quicklime, and 
 distilling at a heat not exceeding 520. The oil which comes over 
 mixed with alcohol is to be purified as already noticed. 
 
 Etherol and Etherine. C 4 H 4 . The oil, which is separated from the 
 foregoing substance, by hot water, or by alcalies, divides itself gene- 
 rally, after some time, into a liquid and a solid portion ; the first con- 
 stitutes the light oil of wine, etherol. It is pale yellow, and thick, 
 like olive oil ; its odour is aromatic ; its specific gravity = 0*921 ; it 
 boils at 500 ; at 35 it freezes. The etherine forms hard, brittle, 
 colourless prisms ; it is tasteless ; its specific gravity 0*980 ; it melts at 
 230 and boils at 464 ; it is soluble in alcohol and ether. The com- 
 
784 Saline Compounds of Ether. 
 
 position of both these bodies is the same, consisting of equal numbers 
 of atoms of carbon and hydrogen, but their atomic weights are not 
 known. It is very probable that the etherol is really a mixture of two 
 other bodies, for when a saturated solution of chloride of zinc in alco- 
 hol is distilled, an oily liquor is obtained, which, by rectification, may 
 be separated into two fluids, of which one, boiling at 212, has the 
 formula C 8 H 7 , and the other which boils only at 570o, has the formula 
 CsH 9 . A mixture of equal quantities of the two should have the com- 
 position assigned to etherol. 
 
 Liebig and Eegnault have found the etherol obtained by alcohol and 
 sulphuric acid, to have the formula C 4 H 3 , so that it must be looked 
 upon as an irregular mixture of several oils, which have not yet been 
 obtained pure. The etherol, or ethereal oil is employed to prepare 
 Hoffman's anodyne liquor, being dissolved in a mixture of one part of 
 ether and two of spirit of wine. 
 
 Compounds of Ether with the Phosphoric and Arsenic Acids. 
 
 Phosphovinic Acid. AeO.P0 5 -f- 2HO. When concentrated tri- 
 basic phosphoric acid is dissolved in alcohol, great heat is evolved, and 
 one atom of water replaced by an atom of ether. The acid salt thus 
 formed may be obtained crystallized, but when its solution is heated 
 strongly it is decomposed. It combines with two atoms of base to 
 form the phosphovinates, of which few are as yet well known. The 
 barytes salt, P0 5 + Ae0.2BaO + 12Aq. crystallizes in brilliant co- 
 lourless plates, and is remarkable for being equally soluble in water at 
 32 and 212, but three times more soluble in water at 104. 
 
 Arseniovinic Acicl.A.sO^ + AeO -f- 2HO. Is formed with arsenic 
 acid and alcohol, like the body last described. Its salts have been but 
 very slightly examined. 
 
 Compounds of Ether with the other Mineral Acids. 
 
 Muriatic Ether. Chloride of Ethyle. C 4 H 5 .C1. Is prepared by 
 distilling a mixture of three parts of oil of vitriol, four of fused common 
 salt, and two of absolute alcohol. The retort should be connected with 
 two two-necked bottles, of which the first should be immersed in a 
 vessel of water at 60, and the second be surrounded by ice, or a 
 freezing mixture. Some alcohol and common ether which pass over, 
 are condensed in the first bottle, whilst the muriatic ether is reduced 
 to the liquid state only in the second. By digestion with some chloride 
 of calcium it is rendered quite pure. 
 
 It is a colourless liquid of a pungent garlic odour; its specific 
 gravity = 0*874; it boils at 52; is neutral; sparingly soluble in 
 
Chloride, Iodide and Sulphuret of Ethyle. 785 
 
 water ; it bums with a bright flame, green at the edges, and gives off 
 muriatic acid gas. By passing through a red-hot tube, it affords equal 
 volumes of olefiant and muriatic acid gases, or by heating with potash, 
 it gives olefiant gas and chloride of potassium. Heated with alcaline 
 salts, it yields compound ethers and alcaline chlorides. When muriatic 
 ether is heated with potassium, Lowig states, that chloride of potas- 
 sium is formed and a light oily substance separates, which has the 
 formula C 4 H 5 . It should be ethyle, but so important an observation 
 has need of verification. This body is often called light muriatic ether, 
 to distinguish it from heavy muriatic ether, which results from the 
 action of chlorine on weak alcohol. 
 
 Hydrolromic Ether. Bromide of Ethyle. C 4 H 5 .Br. Is obtained 
 by distilling together two parts of bromine, one of phosphorus, and 
 six of alcohol. There is first formed bromide of phosphorus, which 
 instantly decomposes the water of the alcohol, and the nascent hydro- 
 bromic acid acting on the ether forms the hydrobromic ether. In 
 properties it perfectly resembles the following body : 
 
 Hydriodic Ether. Iodide of Ethyle. C 4 H 5 .I. Is formed by dis- 
 tilling iodine, alcohol, and phosphorus. It is a colourless liquid, of a 
 pungent ethereal smell; its specific gravity = 1*92 ; it boils at 161; 
 it is abundantly soluble in alcohol. Heated with potash, it gives pure 
 olefiant gas and iodide of potassium. The theory of its formation is 
 the same as in the former case. 
 
 Hydrosulphuric Ether. Sulphuret of Ethyle. C 4 H 5 .S. May be 
 formed by acting on muriatic ether, with an alcoholic solution of 
 sulphuret of potassium. It boils at 187 ; it combines with sul- 
 phuret of hydrogen to form the following very remarkable sub- 
 stance. 
 
 Sulphur-alcohol, or Mercaptan. C 4 H 6 S 2 , or Ae.S -j- HS. Which 
 is obtained directly by distilling in a water bath concentrated solutions 
 of sulphovinate of lime, and of potash saturated with sulphuret of 
 hydrogen, KS -f HS, and AeO.SO 3 + KO.SO 3 , producing 2.KO.SO 3 , 
 and AcS 4- HS ; the mercaptan distils over, aud sulphate of potash 
 remains in the retort ; it is a colourless thin liquid, of an insupportable 
 smell of onions; it boils at 96; its specific gravity is 0' 84 ; it dis- 
 solves in alcohol ; is perfectly neutral ; burns with a bright blue flame; 
 and by cold, freezes into a crystalline mass. In constitution, it is per- 
 fectly analogous to alcohol, the oxygen being replaced by sulphur. 
 When placed in contact with metallic oxides, water is formed, and a 
 double sulphuret of ethyle and the metal produced. This occurs 
 remarkably with oxide of mercury, whence the barbarous name given 
 to this body by Zeize, from mercurium captans, and to its compounds 
 50 
 
786 Hyponitrite and Nitrate of Ether. 
 
 of mercaptides. That of mercury is a crystalline solid, fusible at 
 110, and soluble in alcohol. 
 
 The properties of this body induced its discover, Zeize, to look 
 upon it as a compound of hydrogen with a compound radical which he 
 called mercaptum, which should be really the following compound. Its 
 formula then became C 4 H 5 S 2 + H. He extended this view also to 
 common alcohol, which he considers as C 4 H 5 2 + H. ; but this theory 
 has met with very few supporters. 
 
 Thialol. Bisulphuret of Ethyle. AeS 2 . Is formed by distilling a 
 mixture of sulphovinate of lime and persulphuret of potassium. It is 
 a limpid, oily fluid, with a strong garlic smell ; it boils at 124. Its 
 solution in alcohol precipitates the salts of lead and mercury. By 
 the action of nitric acid on these sulphurets of ethyle, acids are pro- 
 duced analogous to the sulphovinic, but which are not as yet accurately 
 known. 
 
 The Seleniuret and Telluret of Ethyle have been formed, but do not 
 require description. 
 
 Nitrous Ether. Hyponitrite of Ethyle. AeO.N0 3 . When alcohol 
 and strong nitric acid are directly mixed, the action is very violent ; 
 heat is evolved, red fumes are copiously given off, and acetic, oxalic 
 and carbonic acids formed. Even when the acid is dilute, its action is 
 very complex; giving up two atoms of oxygen to one portion of the 
 alcohol, it produces aldehyd, and acetic and oxalic acids, and it is only 
 the hyponitrous acid thus produced that acts on the remaining alcohol, 
 and, combining with the ether of it, forms the proper nitrous ether. 
 To avoid these oxidized products, the best plan is to generate red 
 fumes of hyponitrous acid, in a retort, and to conduct these fumes by 
 a bent tube to the bottom of a two-necked bottle containing alcohol. 
 They are copiously absorbed, and combine directly with the ether. 
 Erom the second neck of the bottle, a tube should pass to a condensing 
 apparatus and receiver ; enough of heat is evolved by the absorption of 
 the red fumes, to distil over the nitrous ether formed, which may be 
 thus obtained quite pure. 
 
 Another process, which may now be considered as obsolete, con- 
 sisted in distilling a mixture of oil of vitriol, nitrate of potash, and 
 rectified spirit, by the heat of a water bath, into a receiver cooled by 
 snow. The nitric acid acted very violently on the alcohol, and the 
 product was impure, and small in quantity. 
 
 Nitrous ether is a liquid, colourless, or pale yellow, of a pungent 
 odour of apples ; it usually reacts acid from slight decomposition, but 
 is neutral if quite pure; its specific gravity is 0-947 ; it boils at 61 
 Pah. Exposed to the air, it absorbs oxygen rapidly, and forms 
 
Preparation of Nitrous Ether. 787 
 
 aldehyd, acetic and formic acids, at the same time nitric oxide is given 
 off. By contact with any strong base, it is decomposed ; alcohol being 
 set free, and a hyponitrite formed. A solution of this nitrous ether in 
 spirit (spiritus nitri dulcis) is employed in pharmacy. It is prepared 
 by distilling a mixture of one part of nitric acid, and ten of rectified 
 spirit, collecting the first seven parts which come over, and digesting 
 them on a little dry carbonate of potash, to remove any traces of free 
 acid. Its specific gravity should be 0'850. It may be prepared 
 directly by dissolving one part of real nitrous ether in eight parts of 
 spirits of wine. 
 
 The method lately proposed by Kopp for the preparation of nitrous 
 ether, deserves preference to all of those hitherto described, for the 
 facility of its use and the quantity of its product. He introduces into 
 a retort some copper filings and the quantity of alcohol to be operated 
 on, to which is to be gradually added an equal volume of nitric acid. 
 Re-action takes place, but does not become violent, the copper dis- 
 solving with evolution of hyponitrous acid gas, which acts on the alcohol 
 producing hyponitrous ether. The action generates sufficient heat to 
 sustain itself until towards the end, when a gentle heat may be applied 
 by a water bath. The vapour of the ether is to be washed by passing 
 it through a bottle containing water, and then through a tube containing 
 chloride of calcium, in order to dry it, if it be required pure ; it is 
 to be finally condensed in a receiver surrounded by a powerful freezing 
 mixture. 
 
 The hyponitrous ether having the formula C 4 H 5 N0 4 , it may upon 
 the theory of substitutions be regarded as the hydrocarbon C 4 Hg, in 
 which one atom of hydrogen is replaced by NO 4 . It will be found 
 that several instances of this kind of substitution occur, and if such 
 bodies be acted on by sulphuretted hydrogen, an artificial organic alcali 
 is produced. Now when sulphuretted hydrogen acts on hyponitrous 
 ether, alcohol and ammonia are generated, besides water and sulphur 
 being set free, thus, 
 
 C 4 H 5 NC>4 and 6. HO give C 4 H6O 2 with NH 3 and 2HO with 6.S 
 
 Either therefore the analogy is unreal or the alcaloid has split from 
 C 4 H 9 1TO 2 into C 4 H 6 O 2 and NH 3 
 
 Nitric ether. C 4 H 5 O + NO 5 . The mutual action of nitric acid 
 and alcohol had been always found to be so violent that the production 
 of this ether was believed impossible, until Millon remarked that the 
 intense action is due to the nitrous acid which ordinary nitric acid 
 always contains, and that by using absolutely pure nitric acid, and pre- 
 venting the formation of any trace of nitrous acid, the real nitrate of 
 
788 Cyanates and Carbonates of Ether. 
 
 ether can be obtained with facility. To prevent the production of 
 nitrous acid he employs urea, which is immediately decomposed by and 
 destroys nitrous acid. When two ounces of absolute alcohol and one 
 ounce of strong nitric acid are mixed, and 20 grains of urea are added, 
 the re-action is very moderate, and after some time, a very heavy oily 
 liquid begins to separate, and is increased in quantity by the addition 
 of water. This is the true nitric ether. It is colourless ; sp. gr. I'll 2. 
 It boils at 184. Its odour and taste are agreeable. It is decomposed 
 by alcalies into alcohol and nitric acid. 
 
 Cyanogen Compounds of Ether. 
 
 Hydrocyanic Ether. Cyanide of Ethyle. Ae.Cy. Is prepared by 
 distilling a mixture of sulphovinate of potash and cyanide of potassium 
 at a moderate heat. It is a colourless liquid, of a strong garlic odour; 
 it boils at 179, and is lighter than water; it is very poisonous. 
 
 Allophanic Ether C 8 1N T 2 H 8 O 6 = C 4 H 5 -f C 4 N 2 H 3 5 . Is formed 
 when the vapours of hydrated cyanic acid are passed into ether, as 
 long as they are absorbed. After some time, the new compound 
 separates in crystals, which are colourless prisms, destitute of taste and 
 smell; soluble in water, and but sparingly soluble in ether. The 
 hydrated cyanic acid taking the elements of an atom of water from 
 the ether, forms allophanic acid, C^I^C^, which gives crystallizable 
 salts with alcalies and earths ; but if separated by a stronger acid, is 
 immediately resolved into carbonic acid and urea. 
 
 Rydrosulphocyanic Ether appears to be formed by distilling sulpho- 
 cyanide of potassium with sulphovinate of potash. It is a liquid 
 heavier than water. 
 
 Compounds of Ether with the Acids of Carbon. 
 
 Carbonic Ether. Carbonate of Ethyle. AeO.C0 2 . This ether can 
 only be produced by an indirect process, the theory of which is not 
 well understood. Metallic potassium or sodium is added, in small 
 pieces, to oxalic ether, as long as a disengagement of carbonic acid gas 
 occurs ; a thick brown mass is formed which is to be distilled, the 
 excess of metal being first destroyed by the addition of water ; the 
 carbonic acid distils over. It is a colourless liquid, of an aromatic 
 srncll, lighter than water. It boils at 260 ; it is insoluble in water, 
 but dissolves in alcohol; its alcoholic solution is decomposed by 
 potash, alcohol and carbonate of potash being formed. 
 
Oxalic Ether Oxamethan. 789 
 
 Carbonate of Ether and Water. Carbomnie Acid AeO.C0 2 -f-HO. 
 C0 2 . At one time it was considered that anhydrous sugar was actually 
 bicarbonate of ether, C 6 H 5 O 5 = C 4 H 5 O -f 2.CO 2 , and that the alco- 
 holic fermentation consisted in the separation of these bodies, the 
 nascent ether combining with water to form alcohol ; but that idea is 
 now inadmissible. The true carbovinic acid is prepared by dissolving 
 caustic potash in absolute alcohol, and passing dry carbonic acid gas 
 through the liquor as long as it is absorbed. A crystalline mass is 
 formed of carbonate and carbovinate of potash, which last is dissolved 
 out by cold alcohol ; and this solution being mixed with ether, deposits 
 the salt, whose formula is, AeO.CO 2 4-KO i C0 2 , in pearly plates, which 
 are immediately decomposed by water into alcohol and bicarbonate of 
 potash. The carbovinic acid is not known in an isolated form. 
 
 Oxalic Ether. Oxalate of Ethyle. AeO.C 2 O 3 . Is prepared by 
 distilling one part of alcohol with one of binoxalate of potash and 
 two of oil of vitriol. At first alcohol and common ether come over, 
 but then a heavy fluid, which sinks to the bottom of the receiver. The 
 portions last distilled are richest in product. It is rectified by another 
 distillation from off a little litharge. It is a colourless oily liquid, 
 denser than water, of a heavy but aromatic smell; it boils at 370. 
 In contact with water or bases it is gradually decomposed into alcohol 
 and oxalic acid. The sp. gr. of its vapour is 5C77. 
 
 Oxalomnic Acid. AeO.C 2 3 -f- HO.C 2 O3. This acid is not known 
 except in combination. It is produced by adding to a solution of 
 oxalic ether in alcohol, half as much potash as would suffice to decom- 
 pose it. The oxalovinate of potash separates as a crystalline powder, 
 being insoluble in alcohol. By an excess of base it is decomposed into 
 alcohol and an oxalate. Its other salts do not require special notice. 
 
 Oxamethan. AeO.C 2 O 3 + C 2 2 -Ad. When oxalic ether is acted on 
 by water of ammonia, it is totally decomposed, alcohol and oxamide 
 being formed, as already noticed, p. 7:28. If a solution of ammonia 
 in alcohol be used, but one-half of the oxalic ether is decomposed, and 
 the oxamide produced unites with the other half, forming a substance 
 soluble in alcohol and water, and crystallizing in brilliant prisms and 
 plates. It melts at 212, and sublimes unchanged at 430. Its solu- 
 tion in cold water does not precipitate lime water, but if it be boiled, 
 alcohol is expelled and the solution contains binoxalate of ammonia. 
 By water of ammonia it is totally changed into oxamide. 
 
 Chlor-oxycarbonic Ether. AeO.CO 2 -f- CO.C1. This substance is 
 formed by the action of chloro-carbonic acid gas on absolute alcohol. 
 It is a colourless liquid, perfectly neutral, heavier than water, and 
 boiling at 201 ; sparingly soluble in water. It consists, or at least 
 
790 Sulphocarbonate of Ether. 
 
 contains the elements, of "an atom of carbonic ether, and an atom of 
 phosgene gas. "When put in contact with water of ammonia, it is 
 dissolved violently and heat evolved; sal-ammoniac and a peculiar 
 substance termed Urethan being formed. The liquor is to be dried 
 down and the residue distilled in a dry retort, with an oil bath. The 
 urethan passes over and solidifies in the receiver to a crystalline mass 
 resembling spermaceti. In it the chlorine of the preceding substance 
 is replaced by amidogene, its formula being AeO.CO 2 -f- CO. Ad ; it 
 consists thus of carbonic ether and carbamide in the proportion of one 
 atom of each. 
 
 Sulphocarbonic Ether, Hydro-xanthic Acid. AeO.CS 2 -|- HO.CS2. 
 Is prepared by decomposing the xanthate of potash by dilute sulphuric 
 acid. A milky liquor is obtained, from which, after some time, a 
 heavy oil separates ; it is to be rapidly washed with water and dried by 
 chloride of calcium. It is then pale yellow, slightly acid, inflammable, 
 and burns with a blue sulphurous flame ; it is decomposed by warm 
 water into alcohol and sulphuret of carbon ; it decomposes the alcaline 
 carbonates, expelh'ng the carbonic acid. Of its salts, that of potash is 
 obtained directly, and from it, the others. Xanthate of potash AeO. 
 CS 2 -f- KO.OS 2 is formed by adding sulphuret of carbon to a warm 
 solution of caustic potash in alcohol. On cooling the liquor, it deposits 
 the salt in crystals, which are to be collected on a filter, washed with 
 ether, and dried between folds of bibulous paper, The salts of lead, 
 copper, &c., may be prepared by double decomposition j they are all 
 yellow, whence the ordinary name of the acid. 
 
 Mucate of Ether is solid and crystalline. It is formed by dissolving 
 mucic acid in oil of vitriol, and gradually adding an equal weight of 
 alcohol. The liquor yields after some time the mucic ether in crystals, 
 which are to be dried on a porous stone, and recrystallized from alcohol. 
 
 The remaining compounds of ether with acids will be described along 
 with the other salts of those acids. 
 
 OF OLEFIANT GAS AND ITS COMPOUNDS. 
 
 Etherene or .#%/. C 4 H 4 . Eq. 350 or 28. 
 
 This gas has been frequently mentioned as one of the products of 
 the action of sulphuric acid on alcohol. The usual process to obtain 
 it consists in heating one part of alcohol with six of oil of vitriol in a 
 flask b, from which a tube passes to the water pneumatic trough, as in 
 the figure ; the mass becomes dark ; ether, water, and oil of wine 
 
Preparatiwi of Etherene. 
 
 791 
 
 collect in the interposed globe a, and olefiant gas is copiously evolved, 
 mixed with an equal volume of sulphurous acid, which, however, being 
 absorbed by the water, the other gas remains pure. Towards the end 
 of the process the materials in the flask swell up very much, and might 
 boil over if not carefully attended to. The theory of this action ap- 
 pears, at first sight, very simple ; the alcohol losing an atom of water, 
 is first converted into ether, which, by the influence of the excess of 
 sulphuric acid, is deprived of the elements of another equivalent of 
 water, and olefiant gas remains ; C 4 H 5 O, giving C 4 H 4 and HO ; but 
 we cannot by this process generate the olefiant gas without, at the same 
 time, more complex products appearing, as etherol, sulphurous acid, 
 and the black matter which remains in the retort. This last, which 
 had been considered formerly as charcoal, appears to consist of C 2 7H 8 O 4 
 + S0 3 , it combines with bases, and is termed the tkiomelanic acid ; 
 it evidently results from the sulphuric acid, giving up oxygen to the 
 hydrogen of a portion of the alcohol. 
 
 Olefiant gas is generated on the large scale by the decomposition of 
 coal, pitch, oil, &c., at a red heat, and is employed for purposes of 
 illumination, being the most valuable constituent of the gas which is 
 burned in our streets and shops. To this source of it I shall have 
 occasion to return. 
 
 We may obtain this gas, however, by much more definite and simple 
 processes. Thus, if vapour of muriatic ether be passed through a red 
 hot porcelain tube, it is resolved into equal volumes of olefiant and 
 muriatic acid gases ; also if muriatic ether be heated with ammoniacal 
 gas, sal-ammoniac is formed, and olefiant gas evolved ; the same de- 
 composition is caused by caustic potash. If vapour of alcohol be 
 passed into oil of vitriol so far diluted as to boil at 320, and heated to 
 that degree, it is totally resolved into water and olefiant gas. In a theo- 
 retical point of view these sources of olefiant gas are peculiarly of interest. 
 
792 Properties of Olefiant Gas. 
 
 Olefiant gas when pure is colourless; its odour is very slightly 
 ethereal ; it is sparingly absorbed by water ; it burns with a brilliant 
 white flame producing much smoke. When mixed with twice its vo- 
 lume of chlorine, and set on fire in a tall narrow jar, a brilliant flame 
 descends rapidly, muriatic acid being formed, and charcoal, smelling 
 strongly of napthaline, separating in dense flocculi. Its specific gravity 
 is 974'6, as one volume of it contains a volume of carbon vapour and 
 two volumes of hydrogen (836*0 + ]38'6= 974'6). It consists of 
 an equal number of equivalents of hydrogen and carbon, but chemists 
 are not unanimous as to its real atomic weight. Berzelius, who looks 
 upon it as an organic radical, and the basis of a series of compounds 
 with oxygen, chlorine, &c., has proposed for it the name elayl, and the 
 formula C 2 H 2 . The name olefiant gas being very inconvenient, I shall, 
 in speaking of its compounds, term it for the present etherene'. The 
 principal support of the theory, which considers this gas to be the ra- 
 dical of the ethers and of alcohol, is derived from the great simplicity 
 of their constitution by volume, in the state of vapour, on that view. 
 Thus, two volumes of olefiant gas combine with two of vapour of 
 water to form alcohol ; with one of vapour of water to form ether ; 
 with two of muriatic or hydriodic acid gases to form the hydriodic or 
 muriatic ethers, and so in similarly simple proportions of volume in other 
 cases. But this evidence is very insecure, as we might show nearly as 
 simple gaseous relations upon other and very improbable points of view. 
 Its combinations are generally formed indirectly, as from alcohol or 
 ether, but it combines immediately with iodine, chlorine, and sulphuric 
 acid. 
 
 Anhydrous sulphuric acid absorbs etherene in large quantity, forming 
 white crystals, which, when dissolved in water, constitute isetJnonw 
 acid, identical in every respect with that formed as described (p. 782). 
 When dry, its composition is S 2 O 6 + C 4 H 4 ; but when in contact with 
 water, it combines with two atoms thereof and becomes isomeric with 
 sulphovinic acid. That it differs from it essentially in constitution is 
 shown, by its salts giving a mixture of sulphate and sulphite when 
 fused with potash ; the sulphurous element is therefore as hyposulphu- 
 ric and not sulphuric acid, and its rational formula is S 2 O 5 + C 4 H 4 O. 
 This isethionic acid is much more energetic than the sulphovinic ; it 
 decomposes all salts of organic acids ; its own salts are all soluble and 
 crystallizable; and sustain a heat of 450 without decomposition. 
 
 If a jar of olefiant gas c, be inverted in the pneumatic trough, over 
 a capsule b, as in the figure, and bubbles of chlorine be passed up into 
 it, both gases disappear, and a heavy oily liquid collects in the 
 capsule, the formation of which gave to the gas its common name 
 
Action of Chlorine on Etherene. 793 
 
 of olefiant yas. In this process a quantity of gas is 
 totally decomposed, and muriatic acid is evolved in 
 great quantity, but the oil results from the direct 
 union of the chlorine and etherene, its formula be- 
 ing C 4 H 4 .C1 2 . I will name it chlor-etherene, but it 
 is called the oil of the Dutch chemists, as it was first 
 formed by the members of a scientific association 
 in Holland. When quite pure it is colourless, of a 
 sweet ethereal odour. Its specific gravity = 1*25 ; 
 it boils at 180<>; it burns with a greenish flame, giving off muriatic 
 acid; the specific gravity of its vapour is 3421. Exposed to an excess 
 of chlorine it is decomposed, hydrogen being removed and replaced by 
 chlorine ; a volatile oily liquid C 4 H 2 C1 4 , and ultimately sesquichloride 
 of carbon C 4 .C1 6 are produced. 
 
 The chlor-etherene is not decomposed by a watery solution of potash, 
 but if it be dissolved in an alcoholic solution of that alcali, and gently 
 warmed, chloride of potassium is formed and a peculiar body produced, 
 whose composition is expressed by the formula C 4 H 3 C1. Tin's sub- 
 stance is gaseous ; of a garlic odour, burning with difficulty with a 
 smoky red flame ; its specific gravity is 2166. It is evident that the 
 chlor-etherene may be considered as a compound of this gas with mu- 
 riatic acid, C 4 H 3 Cl -j- HC1, in which case, the action of the potash is 
 easily explained. This gas itself is supposed to be a chloride of the 
 same carbo-hydrogen as is the basis of acetic acid and aldehyd, (C 4 H 3 ) 
 or acetyl, and the olefiant gas, on this view, is hydruret of acetyl, 
 C 4 H 3 + H, or Ac.H. The further discussion of this opinion will be 
 reserved for another place. If the gas, C 4 H 3 C1, be passed over per- 
 chloride of antimony, it combines with more chlorine and forms a 
 liquid, which boils at 240, and consists of C 4 H 3 C1 3 ; by an alcoholic 
 solution of potash this is decomposed into muriatic acid, and another 
 body also liquid, but boiling at 86, and having the formula C 4 H 2 C1 2 . 
 By contact with chlorine, this produces the liquid C 4 H 2 Cl4, noticed in 
 the preceding paragraph, as obtained directly from chlor-etherene, and, 
 as the next stage, the sesquichloride of carbon. 
 
 If a mixture of olefiant gas and vapour of ether be acted on by 
 chlorine, an oily liquid is obtained, which boils at 350, and consists 
 of C 4 H 4 C1O ; it is called chlor-etheral, but is properly a compound of 
 aldehyd and the chlor-etherene, C 4 H 4 C1 2 + C 4 H 4 O 2 , 
 
 Bromine combines with olefiant gas, with the same phenomena as 
 chlorine, and gives rise to a similar series of compounds, which it is 
 consequently unnecessary to detail. 
 
 Iodine absorbs olefiant gas abundantly, and forms a white crystalline 
 
794 Preparation of Aldeliyd. 
 
 substance, which melts at 180, and may be sublimed if air be not 
 present. It is soluble in alcohol, insoluble in water ; its formula is 
 C 4 H 4 I 2 , but the products of its decomposition are not similar to those 
 of the chlorine compound. 
 
 When bichloride of platinum is dissolved in alcohol, a very complex 
 reaction occurs, and a substance is produced, consisting of Pt.Cl -f C 2 H 2 . 
 This body combines with the chlorides of the alcaline metals to form 
 double salts. On Berzelius' view, the C 2 H 2 being a compound radical, 
 (elayl) may be supposed simply to replace the second atom of chlorine ; 
 and thus form an elayl-cliloride of platinum, which has the same power 
 of forming double salts as the ordinary bichloride. There are thus 
 (Pt + E1.C1) -f K.C1 and (Pt + E1.C1) + NaCl, &c. 
 
 PRODUCTS OF THE OXIDATION OF ALCOHOL SERIES OF ACETYL. 
 Aldehyd C 4 H4O 2 or AcO + HO. Eq. 550 or 44. 
 
 It has been mentioned, in speaking of nitrous ether, that by the 
 oxidation of alcohol, we obtain a crowd of products, as aldehyd and 
 acetic acid, formic, malic, and oxalic acids ; these last are secondary 
 products of the too violent reaction, and the result of the true oxidation 
 of alcohol is found to be aldehyd, or acetic acid, according to the point 
 at which the process stops. The formation of acetic acid thus directly 
 from alcohol, constitutes the acetic fermentation. 
 
 Although aldehyd is formed when nitric acid acts on alcohol, yet from 
 the other products being difficult to separate, it is not so prepared ; a 
 large quantity of it is generated in the destructive distillation of wood, 
 and it may be obtained in the rectification of the pyroxylic spirit. The 
 most ordinary process is that given by Liebig ; six parts oil of vitriol 
 with four of water, four of spirit of wine, and six of black oxide of 
 manganese, are to be distilled with a very gentle heat, and the product 
 collected in a receiver surrounded with melting ice. The apparatus de- 
 scribed for preparing ether, (p. 776), should be employed. The process 
 is completed as soon as the materials in the retort cease to froth up. I 
 have found a purer product to be obtained by distilling at a very gentle 
 heat, two parts of spirit of wine with three of bichromate of potash, 
 three of oil of vitriol, and six of water ; the two last being previously 
 mixed and allowed to cool. To obtain the aldehyd absolutely pure, it 
 is to be combined with ammonia, and the crystallized aldehyd-ammonia 
 decomposed by dilute sulphuric acid, distilled in a water bath at 120 
 with the greatest care, and rectified over fused chloride of calcium. 
 
 Aldehyd is a colourless liquid, of an agreeable but suffocating odour ; 
 it boils at 71; it is lighter than water; it mixes with water, alcohol, 
 and ether ; it is neutral, and inflammable, burning with a blue flame ; 
 
Preparation and Properties of Aldehyd. 795 
 
 in contact with oxidizing agents, it is changed into acetic acid, passing 
 through an intermediate state of aldehydic acid. On this fact is found- 
 ed its most characteristic property ; if any liquor containing aldehyd 
 be added to a solution of the ammoniacal nitrate of silver, and gently 
 heated, the silver is deposited as a brilliant metallic film, lining the 
 sides of the vessel like a mirror, and in the liquor is found aldehydate 
 of silver ; if to this potash be added, oxide of silver precipitates, and 
 on boiling for a moment, it is reduced to the state of metallic silver, 
 and acetate of potash is formed. Erom the composition of aldehyd, 
 these changes are at once explained. It is formed by the abstraction 
 of two atoms of hydrogen from alcohol, which are carried away, as 
 water, by the oxygen supplied ; its formula is hence, C 4 H 4 O 2 : now in 
 contact with AgO, it forms first, aldehydic acid, C 4 H 4 O 3 and metallic 
 silver, and then C 4 H 4 O 3 with AgO, gives hydrated acetic acid C 4 H 4 O 4 
 and another quantity of silver. The formation of acetic acid from al- 
 cohol consists, therefore in two stages, first, the abstraction of hydro- 
 gen by which aldehyd is formed, and second, the addition of oxygen 
 by which acetic acid is produced. 
 
 T\~hen aldehyd is heated in a solution of potash, this becomes brown, 
 and by an acid, a solid brown substance is separated, which is fusible 
 and possesses many properties of a resin. This also is a very distinctive 
 character of aldehyd. 
 
 When long kept, aldehyd undergoes an isomeric change into two 
 bodies, one liquid, elaldehyd, the other solid, metaldehyd ; they have 
 the same formula as aldehyd, C 4 H 4 O 2 but differ in all their properties. 
 
 The general characters of aldehyd show, that it contains the same 
 radical as acetic acid, acetyl, CJ5. y or Ac, combined with oxygen ; it 
 is therefore, hydrated ox-ide of acetyl, AcO + Aq. = C 4 H 4 O 2 ; it has 
 been called also hypoacetom acid, for it is capable of perfectly neutra- 
 lizing ammonia. Its compound with ammonia is indeed very remark- 
 able ; it is best prepared by dissolving aldehyd in ether, and passing 
 ammoniacal gas into the liquor ; the aldehyd-ammonia being very spa- 
 ringly soluble in ether, crystallizes as it forms in large hexagonal plates, 
 which are very brilliant and colourless. Their solution in water soon 
 decomposes, becoming brown and exhaling an animal smell. The dry 
 crystals may be fused and sublimed without alteration ; their formula 
 is, C 4 H 3 + HO.NH 3 . 
 
 Aldehyd is formed also by the direct action of the air on alcohol ; 
 this may be facilitated very much by means of spongy platina which 
 contains much oxygen condensed in its pores, but the process is of 
 more interest in consequence of another body which then forms, and 
 which cannot be otherwise generated ; it is acetal. To prepare it, a 
 
796 
 
 Aldehyd. Trigenic Acid. Tkialdine. 
 
 large bell-glass is taken, open above, and standing in a basin, so sup- 
 ported as to allow the air inside to be frequently renewed, as in the 
 fig. ; through the top passes the tube of a small fun- 
 nel a, under which is a watch glass, b, with a layer 
 of platina black (p. 576). Into the funnel strong 
 alcohol is poured, so that from time to time a drop 
 fall into the watch-glass ; being thus presented to 
 oxygen in a favourable condition, it is decomposed, 
 and aldehyd, acetic acid, and acetal are formed. 
 These liquids are vaporized by the heat evolved, but 
 condense on the sides of the bell-glass, and flowing 
 down, collect in the basin underneath. By processes 
 detailed in the systematic works, the acetal is puri- 
 fied. It is a colourless liquid, boiling at 230 ; its odour is agreeable; 
 its formula was given by Liebig as C 8 H 9 O 3 , but it appears to be a 
 mixture of acetic ether with the true acetal which Stass has shown to 
 consist of C 12 H 13 O 3 . 
 
 The aldeliydic acid acetous acid as already noticed, is formed by 
 the partial oxidation of aldehyd ; but it appears to be produced also 
 under the circumstances of slow combustion described in pp. 229, 237, 
 along with acetic and formic acids. It is obtained pure by decom- 
 posing its silver salt by sulphuret of hydrogen ; forming a liquor of an 
 agreeably acid taste. : /-*- - 
 
 When the vapour of hydrated cyanic acid is passed into aldehyd, a 
 substance is formed which has been termed trigenic acid from its con- 
 taining the elements of three bodies, cyanic acid, ammonia, and alde- 
 hyd, its formula being C 8 H 6 N 3 O 3 = 2CyO + NH 3 + C 4 H 3 O. When 
 heated this acid carbonizes and evolves quinoline, a base obtained also 
 in other more important reactions under which it shall be studied. 
 
 When sulphuretted hydrogen acts on a solution of ammonia aldehyd, 
 a crystalline body is formed termed thialdine. Its formula is C^H^NS^ 
 It is very volatile. It is soluble in water, but crystallizes beautifully 
 from its solution in alcohol or ether. It is a powerful base, forming 
 neutral crystalline salts with the strongest acids. If heated with lime 
 it yields quinoline, in which it resembles trigenic acid. By means of 
 seleniuretted hydrogen and ammonia-aldehyd, a similar base selen- 
 aldine is obtained. 
 
 Of Acetic Acid.Yinegar.-7&^. 750 or 51. 
 
 As all alcoholic liquors are liable to undergo spontaneous decom- 
 position, and form vinegar, this acid has been known from the earliest 
 ages, as produced by the acetous fermentation ; its origin was however 
 
Theory of the Acetous Fermentation. 797 
 
 7 / 
 
 long wrapped in obscurity, because the complex constitution of the 
 fermented liquors, in which it was originally produced, prevented the 
 simple nature of the change from being understood. It is now fully 
 established, that the change from alcohol to acetic acid consists simply 
 in the removal of two atoms of the hydrogen of the alcohol, and 
 addition of two atoms of oxygen; these actions not being simultaneous, 
 but successive, and aldehyd being the intermediate product, thus : 
 
 Alcohol C 4 H 6 O2 and Aldehyd C4H 4 O 2 
 
 gives by H 2 gives by + O 2 
 
 Aldehyd C 4 H 4 O 2 Hydrated Acetic Acid C 4 H 4 O 4 
 
 By means of chromic and nitric acids, but especially by the platinum 
 black as described just now, this reaction may be carried on with 
 perfect accuracy and distinctness. 
 
 But if we place ourselves in the actual condition of practice, the 
 theory of the acetous fermentation becomes much more difficult ; for 
 exactly as a pure solution of grape sugar will not break up into 
 alcohol and carbonic acid, and that a cause of disturbance is necessary 
 in order to enable the new arrangement of its particles to occur; so do 
 we find it to be in changing alcohol into acetic acid. Pure alcohol, 
 whether weak or strong, absorbs no oxygen by mere exposure to the 
 air, and hence forms no vinegar ; it is necessary there should be present 
 another body more liable to decomposition (ferment), which abstracting 
 oxygen from the air for the purpose of its own decomposition, may 
 confer upon the molecules of alcohol such instability of structure, as 
 will admit of, and cause the similar absorption of oxygen by them. 
 The ferment, in decomposing, evolves water and carbonic acid ; the 
 alcohol evolves water only, but absorbs the oxygen from the air. The 
 platinum black, in the process that has been described, supplies the 
 place of the ferment. In making vinegar from malt liquors or from 
 wine, they are placed in hogsheads, partially full, and left more or less 
 exposed to the air according to circumstances. To supply oxygen, the 
 air must have access, but if the air were very rapidly renewed, a large 
 quantity of the volatile aldehyd would be carried off. These solutions 
 contain abundance of organic matter, proper for acting as ferment, and 
 when the fermentation is complete, the products of their decomposition 
 collects upon the bottom and sides of the vats, in gelatinous mass, 
 termed mothers. 
 
 The manufacture of wine or malt vinegar by the old process of mere 
 partial exposure to the air in vats, consumed much time, and is almost 
 superseded by the German method, by which excellent fermented vinegar 
 
798 Preparation and Properties of Vinegar. 
 
 may be made in thirty-six hours. A cask is to be 
 filled, as in the figure, with wood shavings, and closed 
 at the top by a pan b, the bottom of which is per- 
 forated with a number of small holes, through which 
 short threads are passed to bring down the liquid 
 more rapidly. The shavings, before being used, are 
 well steeped in vinegar, which is, itself, one of the 
 most active ferments. Below, at c c, is a circle of 
 holes about half an inch diameter, by which the air may enter, which 
 then escapes above by a number of tubes which pass through the pan 
 and are left white in the figure. If now we take a spirit containing 
 abont one part of proof spirit to four of water, and having mixed 
 with it ,~th of honey or yeast, pour it into the pan above, it trickles 
 down the orifices by the threads, and spreading over the shavings, has 
 its surface enormously extended. It absorbs oxygen very rapidly, and 
 having been warmed to about 75 before being poured in, its tempera- 
 ture soon rises to 100 the interior being so hot, a current of air is 
 established through the vessels, by which a constant supply of oxygen 
 is kept up. According as the liquid passes down, it escapes through 
 the pipe at the bottom, and is collected in the vessel a ; when it has 
 passed through, three or four times, it is found to be converted into 
 excellent vinegar, and the whole time occupied is only between twenty- 
 four and thirty-six hours. 
 
 The manufacture of vinegar by the distillation of wood, now ex- 
 tensively carried on, will be described in another place. 
 
 The vinegar of commerce has frequently its pungency and acidity 
 increased by the addition of acrid herbs, as capsicum, and by sulphuric 
 acid. To obtain it free from these impurities it is redistilled. As, 
 however, its volatility is about the same as that of water, it cannot be 
 concentrated in that way, and hence the strong acetic acid must be 
 obtained by the decomposition of its salts by a stronger acid. !For 
 this purpose, one part of acetate of soda, which has been dried at a 
 gentle heat, is to be distilled with two parts of oil of vitriol; so much 
 heat is evolved by the mixture that a quantity of the acetic acid distils 
 over spontaneously, and to complete the decomposition only a very 
 moderate heat need be applied. In this process, S0 3 + Aq and NaO 
 + C 4 H 3 3 give S0 3 + NaO and C 4 H 3 O 3 -f Aq. The acid which 
 passes over generally contains some sulphurous acid, arising from its 
 secondary action on the oil of vitriol ; in order to separate this, it is 
 rectified over some peroxide of lead with which the sulphurous acid 
 forms sulphate of lead. The liquid acetic acid which distils is then to 
 be exposed to a cold of about 23, and the crystals which form are to 
 
Properties of Acetic Acid. 799 
 
 be separated from the liquid portion; these crystals are ti& protokydrate 
 of acetic acid, and its most concentrated form. 
 
 Acetic acid may be prepared also by distilling acetate of lead with 
 oil of vitriol, or by the destructive distillation of acetate of copper; 
 by this last method an acid is obtained (radical vinegar) of an agree- 
 able aromatic odour, from an admixture of acetone. The acetate of 
 potash is prescribed by the Dublin Pharmacopoeia, but as acetate of 
 soda is found abundant and cheap in commerce, it is now exclusively 
 employed. 
 
 The hydrated acetic acid, when free from any excess of water, crys- 
 tallizes at 50, in large white plates, which do not again become liquid 
 until heated above 60; it is hence called glacial acetic acid; its odour 
 is very characteristic and pungent ; its taste caustic ; it blisters the 
 skin ; it mixes with water, alcohol and ether, and dissolves camphor 
 and essential oils, which solution constitutes the aromatic vinegar of 
 the shops. When liquid, its sp. gr. is T063; but its specific gravity 
 does not indicate its strength, as it increases according as water is 
 added until it becomes 1-078, which is that of an acid, containing 34'6 
 per cent., or three atoms of water ; being a definite compound, C 4 H 3 O 3 
 -f HO -f 2Aq. On further dilution, the sp. gr. again diminishes, 
 and an acid containing 64 per cent, of water, has a sp. gr. of 1'063, 
 the same as that of the most concentrated acid. The strength of any 
 acetic acid may, however, be very simply found by immersing in it a 
 weighed piece of white marble, and weighing it again when the acid 
 has been completely neutralized ; the loss of weight gives pretty accu- 
 rately the quantity of acetic acid, as the atomic weight of CaO.CO 2 
 (50-) is nearly the same as that of C 4 H 3 O 3 . (51') ; of course, if the 
 acetic acid be not pure, this method cannot be employed. 
 
 The formula of hypothetic dry acetic acid is C 4 H 3 3 , and its equi- 
 valent = 51*. The acetate of water C 4 H 3 3 -f- Aq. consists of, 
 
 4 equivalents of carbon = 24-00 40-20 
 
 4 ,, hydrogen = 4-00 6-64 
 
 4 oxygen = 32'00 53-16 
 
 60-00 10000 
 
 The hydrated acetic acid boils at 240. The specific gravity of its 
 vapour presents very remarkable anomalies, as it changes so much for 
 small alterations of temperature, as to have made it be supposed that 
 this acid did not follow the usual law of combination by volumes. 
 But those anomalies have been explained, as described p. 292, and the 
 equivalent of acetic acid is represented by four volumes of vapour, the 
 specific gravity of which is 2080, when determined at or above 482 
 Pah. 
 
800 Salts of Acetic Acid. 
 
 The products of the decomposition of acetic acid by chlorine and 
 by bases will be hereafter noticed ; with powerfully oxidizing bodies, 
 it yields formic, oxalic, and carbonic acids. 
 
 Acetic acid is recognized by its peculiar odour and its volatility ; it 
 reddens litmus powerfully ; its solutions are precipitated by the nitrates 
 of silver and of black oxide of mercury, giving white crystalline salts, 
 sparingly soluble in cold water, and dissolving in boiling water without 
 decomposition. But even strong solutions are not affected by the 'salts 
 of lead or barytes. It combines with all bases forming salts, of which 
 none are quite insoluble in water, but generally very soluble and easily 
 crystallized. The most important of these will now be described. 
 
 Salts of Acetic Acid. Acetates. 
 
 Acetate of Potash. KO.C 4 H 3 3 . Is formed by neutralizing acetic 
 acid by means of pure carbonate of potash. The solution is generally 
 evaporated at once to dryness, and the salt fused at a dull red heat, in 
 order to obtain it quite white. It forms on cooling a foliated mass, 
 greasy to the feel. From its concentrated solution it may be obtained 
 also in delicate crystals. It is very deliquescent, and dissolves copiously 
 in alcohol. 
 
 Acetate of Socla.N^O.CJI^Os + 6Aq. May be obtained in the 
 same way as acetate of potash, but is made on the large scale in puri- 
 fying the rough wood-vinegar. The impure acetate of lime, obtained 
 by neutralizing the pyroligneous liquors with chalk, is decomposed by 
 6J times its weight of crystallized sulphate of soda. These are in the 
 proportion of two equivalents of Glauber's salt, as but one-half of the 
 quantity is decomposed by the acetate- of lime. It answers still better 
 to neutralize the acid liquors by sulphuret of sodium, prepared by roast- 
 ing Glauber's salt with small coal, as for making soda-ash, (p. 690). 
 
 When purified by successive crystallizations, the acetate 
 of soda forms oblique rhombic prisms, as i, u, in the 
 figure, with many secondary planes, as a, e, o. These 
 contain six atoms of water. It is permanent in the air ; 
 soluble in three parts of cold and in one of boiling 
 water; at a red heat it melts. Its principal use is in 
 the preparation of acetic acid. 
 
 Acetate of Barytes. BaO.C 4 H 3 O 3 . Is formed by neutralizing acetic 
 acid with carbonate of barytes, or sulphuret of barium. It crystallizes 
 in oblique rhombic prisms ; by heat it is completely decomposed into 
 carbonate of barytes and acetone, (BaO.CO^ and CaHaO). 
 
 Acetate of Lime is made on the large scale, but in a very impure 
 
Salts of Acetic Acid. 801 
 
 form, as one stage in the process of purifying the wood-vinegar. When 
 pure it crystallizes in needles, which do not deliquesce. It is decom- 
 posed by heat in the same way as the preceding salt. 
 
 Acetate of Alumina is of considerable technical importance from its 
 use as a mordant in dyeing. It is formed by mixing solutions of alum, 
 and of acetate of lead, when to be employed in the arts. The solution 
 then contains much acetate of potash. To obtain it pure, the simple 
 sulphate of alumina should be decomposed by acetate of barytes. 
 Evaporated at a very gentle heat, it dries into a transparent gummy 
 mass ; but if boiled, acetic acid passes off, and a basic acetate of alu- 
 mina is deposited as a white powder. This effect is produced also by 
 contact with linen or cotton cloth, the acetic acid becoming free, A 
 piece of calico is thus mordanted uniformly by immersion in a bath of 
 acetate of alumina, and then dried at about 80 ; or it is mordanted 
 partially, so as subsequently to form a coloured pattern, by being 
 printed with the solution of this salt, thickened with gum or starch 
 in order that it may not spread ; on being then dried by passing over 
 warm cylinders, the acetic acid passes off, and the alumina fixes itself 
 upon the tissue. 
 
 Acetate of Zinc. ZnO.C 4 H 3 3 -f- 3Aq. Metallic zinc dissolves in 
 acetic acid, evolving hydrogen ; but this salt is generally prepared by 
 mixing solutions of acetate of lead and sulphate of zinc, and separating 
 the sulphate of lead which is formed, by nitration. 
 On evaporating the solution, the acetate of zinc crys- 
 tallizes in brilliant soft hexagonal rhombic tables, as 
 in the figure, of which i, u, are primary and m a 
 secondary face. They are unalterable in the air, but 
 very soluble in water. When boiled with alcohol, a 
 "basic acetate of zinc precipitates, 3ZnO -f- C 4 H 3 3 . A solution of this 
 salt is completely decomposed by sulphuret of hydrogen. 
 
 Proto-acetate of Iron. FeO.C4H 3 3 . This salt, which may be pre- 
 pared by dissolving protosulphuret of iron in acetic acid, forms a 
 colourless solution, which yields, when evaporated in vacuo, pale green 
 prisms, which attract oxygen with great avidity. It cannot be formed 
 by decomposing protosulphate of iron by acetate of lead, as only a 
 portion of the lead salt precipitates, until the iron becomes peroxidized. 
 Sesgui-acetate of Iron. Fe 2 3 + 3(CJ1 3 O^). Is prepared by dis- 
 solving red oxide of iron in acetic acid, or by decomposing red sulphate 
 of iron with acetate of barytes. It forms a brownish red solution, 
 which when boiled, gives off acetic acid and oxide of iron separates. 
 By very cautious evaporation, a dark red gummy mass may be obtained, 
 which redissolves in cold water. It thus resembles closely acetate of 
 51 
 
80 Acetates of Iron and Lead. 
 
 alumina, and like it serves in dyeing as a mordant, to fix upon the 
 cloth oxide of iron with which the colouring matters may combine ; 
 being roughly prepared by digesting old iron in the impure acetic acid 
 from wood, it is commonly termed pyrolignite of Iron. 
 
 A Tincture of Acetate of Iron is employed in medicine, which, as 
 directed by the Dublin Pharmacopeia, is formed by triturating toge- 
 ther protosulphate of iron and acetate of potash, and digesting in 
 alcohol ; in order that the solution shall have the rich wine red colour 
 which is required, the mixture of the salts should be left for a little 
 time pasty, so as to absorb oxygen, and there should be present an 
 excess of acetate of potash. The iron is present in these tinctures, as 
 black oxide. If too much sesquioxide be formed, the solution decom- 
 poses very easily, red oxide of iron separating, and acetic ether and 
 aldehyd being produced. If the protoxide be present in excess, the 
 colour is a brownish-yellow, and the preparation is liable to spoil when 
 oxygen has subsequently access to it. Although the acetate of potash 
 does not form a true double salt in this case, yet it gives much greater 
 stability to the acetates of iron. 
 
 Acetates of Lead. Acetic acid forms with oxide of lead, four well 
 characterized salts. 
 
 Neutral Acetate of Lead. Sugar of Lead. PbO.C 4 H 3 3 -f- 3Aq. 
 Is prepared by dissolving litharge, or white lead, in acetic acid, of 
 which a slight excess should be used. The liquors yield by evaporation, 
 right rhombic prisms with dihedral summits, as in the figure, which 
 are very bright and colourless. Their taste is 
 sweet and astringent ; the solution in water red- 
 dens litmus, but turns sirup of violets green. 
 In very dry air they effloresce ; when heated to 
 136, they undergo aqueous fusion, but having 
 lost their water of crystallization become solid 
 again. The dry salt, thus obtained, fuses again 
 at a higher temperature, and, without blackening, is decomposed into 
 carbonic acid, acetone, and sesquibasic acetate of lead which remains : 
 3(PbO.C 4 H 3 O 3 ) giving CO 2 with C 3 H 3 and 3PbO + 2C 4 H 3 3 . 
 
 This neutral salt dissolves easily in alcohol ; it is very poisonous ; 
 the antidote to it is Glauber's or Epsom salt, which forms insoluble sul- 
 phate of lead. 
 
 Sesquibasic Acetate of Lead.WbQ + 2.C 4 H 3 O 3 . This salt, which 
 is formed as just described, dissolves in water, and the sirupy solution 
 crystallizes in pearly hexagonal plates ; its solution reacts alcaline. 
 
 Tribasic Acetate of Lead. 3PbO + C 4 H 3 3 . When ammonia is 
 added to a solution of neutral acetate of lead, so as to render it strongly 
 
Acetates of Lead and Copper. 803 
 
 alcaline, it does not combine with it, as with most other metallic salts, 
 but acetate of ammonia and tribasic acetate of lead are formed ; it may 
 also be prepared by boiling together six parts of crystallized acetate of 
 lead, seven of litharge, and thirty of water. This solution, known in 
 pharmacy as extractum saturni, gives, by evaporation, a mass of fine 
 crystalline needles; it reacts powerfully alcaline; it is insoluble in 
 alcohol. 
 
 Sexbasic Acetate of Lead. 6PbO -f C 4 H 3 O3. Is precipitated when 
 a solution of neutral acetate is added to a great excess of water of am- 
 monia ; it is formed also when acetic acid acts on metallic lead with 
 access of air, and is hence generally present in the ceruse of commerce. 
 (See p. G97.) It forms minute feathery crystals, when deposited from 
 boiling water, in which it is slightly soluble. 
 
 All these basic acetates of lead are decomposed by carbonic acid, 
 giving neutral acetate and carbonate of lead. 
 
 Acetates of Copper. The acetate of the suboxide of copper is not 
 important ; there are four acetates of the black oxide. 
 
 Neutral Acetate of Copper Distilled Verdigris. CuO. C-iHaOa -f- 
 Aq. It is prepared by dissolving verdigris in acetic acid ; it forms ob- 
 lique rhombic prisms, as in the figure, where i u u are primary and e e, 
 secondary faces of a fine deep green colour. It crystal- 
 lizes in another form with five atoms of water ; these 
 crystals are blue, like sulphate of copper, and when 
 heated to 26, give off 4 Aq. and change into the com- 
 mon green crystals ; it effloresces gradually in the air ; 
 when heated in close vessels it gives a mixture of acetic 
 acid and acetone ; in the air it takes fire, burning with a bright green 
 flame. 
 
 If a solution of this salt be mixed with sugar or honey, and heated, 
 it deposits a green powder of carbonate of copper, which changes into 
 minute crystals of the orange red suboxide ; the liquor contains then 
 abundance of formic acid. 
 
 Bibasic Acetate of Copper. Verdigris. 2CuO -f C 4 H 3 O 3 + 6Aq. 
 This salt is manufactured in wine countries by stratifying plates of cop- 
 per alternately with the residual stalks and pulp of the grapes, that 
 have passed into acetous fermentation ; oxygen is absorbed, and the 
 mass being occasionally turned over and moistened, to give access to 
 air, the plates of copper become covered with a crystalline crust of 
 basic acetate ; this is scraped off, made into a paste with vinegar, and 
 put into moulds, where it is allowed to dry ; the mass so formed con- 
 tains all the basic salts, mixed together. In this country it is prepared 
 by stratifying copper plates with cloths steeped in pyroligneous acid. 
 
,804 Acetates of Copper, Mercury, fyc. 
 
 When pure, the bibasic acetate is of a fine blue colour ; it is decom- 
 posed by water into the insoluble tribasic acetate, and the soluble ses- 
 guibasic acetate of copper, which forms a pale blue solution, whence it 
 may be precipitated in crystalline scales by alcohol. 
 
 Tribasic Acetate of Copper. S.CuO + C 4 H 3 3 + 2Aq. Remains 
 as an insoluble residue when verdigris is treated with water, or by di- 
 gesting a solution of neutral acetate with oxide of copper. It is a clear 
 green powder, which detonates feebly when heated. For emerald green, 
 see p. 646. 
 
 Acetate of Black Oxide of Mercury. Hg 2 + C 4 H 3 O 3 . May be 
 formed by mixing boiling solutions of acetate of potash and subnitrate 
 of mercury, and filtering rapidly. On cooling it is deposited in bril- 
 liant white crystalline scales, which are very sparingly soluble in cold 
 water, and insoluble in alcohol. The acetate of the red oxide is very 
 soluble in water, and does not crystallize. 
 
 Acetate of Silver. AgO.C 4 H 3 O 3 . Is formed by mixing boiling so- 
 lutions of nitrate of silver and acetate of potash, and filtering the 
 liquor whilst very hot. On cooling it crystallizes in pearly white nee- 
 dles, which are but very sparingly soluble in cold water. These last 
 salts serve as tests for the acetic acid in liquids. 
 
 Acetate of Ammonia. NH 4 0. C 4 H 3 O 3 . Is prepared by passing am- 
 rnoniacal gas over the crystalline hydrate of acetic acid, or by heating 
 moderately a mixture of equal parts of acetate of potash, and of sal- 
 ammoniac. The acetate of ammonia sublimes mixed with a little free 
 acetic acid ; it crystallizes in needles, which are very soluble in alcohol 
 and in water ; by exposure to the air it loses ammonia, and appears to 
 form an acid salt ; its solution in water, prepared by neutralizing dis- 
 tilled vinegar with carbonate of ammonia, is used in medicine by the 
 name of spirit of mindererus ; in its original form, when the carbonate 
 of ammonia, obtained by the distillation of bones (salt of hartshorn), 
 and which contained enpyreumatic animal oil, was used, it was a much 
 more powerful medicinal agent than when prepared as now, with pure 
 carbonate of ammonia. 
 
 Acetate of Ether. Acetic Ether. C 4 H 5 + C 4 H 3 3 . Is prepared 
 by distilling 16 parts of dry sugar of lead, 4 of alcohol, and 6 of 
 oil of vitriol ; the product should be rectified over some lime to remove 
 free acetic acid ; this ether is colourless and very inflammable ; it boils 
 at 165 ; it is lighter than water; it is remarkable for being isomeric 
 with aldehyd, their per cent composition being the same, but the sp. 
 gr. of the vapour of acetic ether is double that of aldehyd. 
 
Sulphoacetic Acid. Acetone. 805 
 
 If glacial acetic acid be acted on by anhydrous sulphuric acid, 
 a compound acid is produced, which is termed sulphoacetic acid, but its 
 formula appears to be C 4 H 2 O 2 + S 2 5 + Aq, and not to belong to the 
 acetic series. 
 PRODUCTS OF THE DECOMPOSITION OF ACETIC ACID BY HEAT. 
 
 A. Of Pyroacetic Spirit, Acetone. 
 
 When acetate of lime or barytes is heated to redness, the acetic acid 
 is completely decomposed, an earthy carbonate remaining, and a volatile 
 inflammable liquid, of an agreeable aromatic odour, distilling over; 
 C 4 H 3 O 3 separating itself into C0 2 and C 3 H 3 O. The metallic acetates 
 are similarly decomposed, but the products are not so pure, This li- 
 quid, for which I shall retain the name acetone, is formed also abun- 
 dantly, when the vapour of acetic acid is passed through a tube con- 
 taining charcoal, at a temperature just below redness. 
 
 Acetone is colourless, lighter than water ; it burns with a luminous 
 flame; it boils at 132; the specific gravity of its vapour is 2022. 
 When heated with hydrate of potash, it is totally converted into car- 
 bonic acid and marsh gas, C 3 H 3 O and HO, producing C 2 H 4 and CO 2 . 
 \\ hen treated by oxidizing agents, as permanganate of potash, or bi- 
 chromate of potash and sulphuric acid, it is totally converted into 
 a mixture of formic and acetic acids. 
 
 With sulphuric acid, acetone yields a series of products generally 
 analogous to those derived from alcohol, but still presenting such char- 
 acteristic differences as induce me to look upon them as not simply 
 extracted from acetone, but derived from its total decomposition. 
 Thus, it gives a hydrocarbon, mesitylene, whose formula is C 6 H 4 , and 
 also an ether, mesitic ether, C 6 H 5 O. With sulphuric acid this forms 
 the sulphomesitic and persulphomesitic adds, which are remarkable, as 
 the sulphuric acid retains all its power of saturating bases. With 
 phosphoric acid it produces plwsplwmesitic acid, and with hypophos- 
 phorous acid a very remarkable compound, whose barytes salt has the 
 formula C 6 H 5 O + 2BaO.PO. The anologue of which in the series of 
 wine alcohol has been very recently discovered by Wiirtz, and termed 
 Phosphovinous acid. The mesitic ether combines also with proto- 
 chloride of platinum. 
 
 T\ hen acetone is treated with chloride of phosphorus it gives 
 phosphoric acid and chloromesitic ether, C 6 H 5 C1 ; with iodide of phos- 
 phorus it produces iodomesitic ether, C 6 H 5 T, and when acted on by 
 chlorine it forms the mesitic chloral, of which the formula is C 3 H 2 C10, 
 and subsequently another body, also a heavy oily liquid, C 3 HC1 2 0. 
 
 When red fumes of hyponitrous acid are passed into acetone, and the 
 
806 Acetone. Alkarsine. 
 
 vessel is kept cool, they are copiously absorbed, and, on adding water, 
 a dense *nuid separates, which is nitrous mesitic ether, C 6 H 5 O + NO 3 . 
 
 By acting on mesitylene, CeH 4 , with nitric acid, a heavy liquid is 
 produced, which is termed mesitic aldehyd, its formula is C 6 H 3 O -f- Aq. 
 Its solution in alcaline liquors becomes brown after some time, and 
 precipitates most salts of the heavy metals. By chlorine the mesitylene 
 is converted into a crystalline body, soluble in ether, and separating 
 from it in brilliant colourless prisms. Its formula is C 6 H 3 C1. I have 
 termed it chloride of pteleyl. 
 
 In my original examination of this series of bodies, I looked upon 
 acetone as an alcohol (mesitic alcohol), Cell^ = C 6 H 5 O + Aq. from 
 which they were all derived ; but I do not now consider that either 
 mesitylene or mesitic ether pre-exists in acetone. The intimate nature 
 of that body remains yet to be examined. 
 
 B. Of the Bodies of the Kacodyl Series. 
 
 When equal weights of acetate of potash and arsenious acid are 
 mixed and distilled at a dull red heat, a dense colourless liquid is 
 obtained, which had been long known to the chemists as the filming 
 liquor of Cadet. The admirable researches of Bunsen have shown 
 that it is an oxide of a compound radical, kacodyl, which he has suc- 
 ceeded in isolating, and which, in the variety of its combinations and 
 the influence their discovery will doubtless exercise on science, ranks 
 with cyanogen. The kacodyl is however a powerfully electro-positive 
 radical, and relates itself rather to ammonium. This connexion is still 
 more evident from the discovery by Bunsen, that oxide of platinum 
 and kacodyl combine to form another compound Ta.dL\c,a\ } platinc-JcacodyI, 
 which corresponds to the compound bases of platino-ammonium, de- 
 scribed in pp. 720 et seq. Nevertheless as they are not of practical 
 importance, a short notice of them will suffice. 
 
 The fuming Liquor of Cadet or Alkarsin, when purified from acetone 
 and other accidental products of the distillation, is colourless ; much 
 heavier than water. It freezes at 9, and boils at 300. The spe- 
 cific gravity of its vapour is 7180; its odour is excessively disagreeable, 
 provoking weeping and nausea ; it is actively poisonous ; in contact 
 with the air it fumes very much, and absorbs oxygen so rapidly, that if 
 a large surface be exposed, it takes fire spontaneously and burns with 
 a large white flame, throwing off much arsenious acid. Its composition 
 is expressed by the formula C 4 H 6 AsO, and, in all the combinations 
 which it gives, the oxygen alone is replaced. Thus, when distilled 
 with strong muriatic acid, a dense liquid of an insupportable odour is 
 produced, which gradually changes into a crystalline mass, consisting 
 
Compounds of Kacodyl. 807 
 
 of C 4 H 6 AsCl. By digesting this liquid with zinc and water, in a 
 vessel kept full of pure carbonic acid, chloride of zinc is formed, and 
 the radical, C 4 H 6 As, is set free ; this is an oily -looking heavy liquid, 
 insoluble in water, and taking fire immediately on contact with air. 
 This is the kacodyl, and as its symbol I shall adopt that used by Bun- 
 sen, Kd = C 4 H 6 As. The alkarsine is therefore oxide of kacodyl, KclO, 
 and the body formed by muriatic acid is the chloride, KdCl. The 
 iodide, bromide, sulphuret, and cyanide of kacodyl, may be formed by 
 the simple process of distilling alkarsiue with the corresponding hydra- 
 cids, or the chloride of kacodyl with the iodides, &c. of potassium. 
 
 AVlien alkarsin is distilled with dilute muriatic acid, or when chloride 
 of kacodyl is treated with water, this is decomposed, and an oxy- 
 chloride obtained, the formula of which is KdO -f- S.KdCl. In a 
 similar manner a corresponding oxy-bromide, KdO -f S.KdBr may be 
 produced, and an oxy-iodide. 
 
 If alcoholic solutions of oxide of kacodyl and of corrosive sublimate 
 be mixed, a brilliant white precipitate is obtained, which is soluble in 
 water, and crystallizes therefrom in large but delicate rhombic tables, 
 of a satiny lustre. It is a direct combination ; its formula being KdO 
 -f- 2.HgCL A precisely similar compound is formed with the bromide 
 of mercury. 
 
 TThen alkarsine is exposed to the air, so that it may absorb oxygen, 
 but not burst into flame, it is changed totally into a white crystalline 
 mass ; at the same time arsenious acid and some volatile products are 
 formed. The crystals being dissolved in a small quantity of water, 
 this liquor is evaporated to dryness, and the residue dried by blotting 
 paper, and recrystallized from alcohol. The substance thus obtained is 
 termed alkargene ; it forms large oblique prisms, which are inodorous 
 and tasteless ; it deliquesces in moist air ; it combines with alcalies and 
 metallic oxides, forming very instable compounds ; it melts at 390, 
 and is decomposed by a stronger heat. By deoxidizing agents, as 
 protochloride of tin, or phosphorous acid, it is reduced to the state of 
 alkarsine ; it is not poisonous. Its composition is expressed by the 
 formula, C 4 H 7 AsO4, or Kd.0 3 + Aq. ; its proper name is therefore 
 kacodylic acid. The excessively disagreeable odour of alkarsine may 
 be taken advantage of to recognize the presence of small quantities of 
 arsenic. If a trace of arsenic be mixed with some acetate of potash 
 and water, then dried and ignited in a test tube, it will exhale the 
 odour of alkarsine, and if it be first moistened with muriatic acid the 
 odour of chloride of kacodyl will be produced. This reaction may be 
 useful in distinguishing arsenic from antimony, as according to Bunsen 
 the latter metal does not produce any similar compounds. 
 
808 Sources of Marsh Gas. Fire-Damp. 
 
 C. Of light carburetted Hydrogen, Marsh Gas. 
 
 This gas is formed by the decomposition of almost every organic 
 substance at a high temperature. Thus, it exists always, mixed with 
 olefiant gas, in the coal or oil gas used for illumination. It may be 
 formed by passing olefiant gas through a red-hot tube, when half of its 
 carbon is deposited and its volume doubled. It is produced also by 
 passing the vapours of alcohol, of ether, or of acetic acid, through 
 bright red-hot tubes in a similar manner. 
 
 A very interesting source of this gas is the decomposition of vege- 
 table matter in contact with water, but excluded from the air. By 
 assimilating the elements of four atoms of water the lignine breaks 
 up into carbonic acid, and this gas; C 12 H 8 O 8 , with 4. HO, giving 
 6.CO 2 and 6.CH 2 . As the origin of the great deposits of coal is to be 
 found in the slow decomposition of submerged forests of high antiquity, 
 this gas was then generated in large quantity, and being subjected to 
 enormous pressure under the mineral strata, which gradually settled 
 on the vegetable masses, it remained infiltrated through the coal, pro- 
 bably in a liquid condition. During the operations of mining, when 
 this great pressure is removed, it reassumes its gaseous condition, and 
 mixing with the air of the mine, creates the danger of explosion, 
 against which the genius of Humphrey Davy provided by the con- 
 struction of his safety lamp (see p. 242). Under the name of the 
 fire damp this gas is known and dreaded by the miners, whilst the 
 carbonic acid, which results simultaneously from the decomposition of 
 the wood, and is known also from its fatal effects when breathed, is 
 termed choke damp. 
 
 This decomposition of wood goes on in every muddy ditch. If the 
 mud be stirred, numerous gas bubbles will be seen to ascend, and when 
 collected will be found to consist of fire damp mixed with carbonic 
 acid ; hence this gas has got the name of pond or marsh gas. It is 
 obtained, however, most pure by the decomposition of acetic acid by 
 hydrate of potash. About equal parts of acetate of potash and caustic 
 potash are to be well mixed, and heated in a hard glass retort nearly to 
 redness. The acetic acid and water are simultaneously decomposed, 
 C 4 H 3 3 and HO, producing 2.CH 2 and 2.C0 2 . This last remains com- 
 bined with the potash, whilst the gas which passes off may be collected 
 over water. 
 
 It is colourless and transparent. It burns with a yellow flame, 
 possessing but little illuminating power; its sp. gr. is 557 ; its formula 
 being CHa and consisting of 
 
Chloral. Chloro-acetic Add. 809 
 
 One volume of carbon vapour . . . = 836 '8 
 Four volumes of hydrogen . . . . = 276*2 
 
 Forming two volumes of marsh gas . 1113*0 
 Of which one weighs, therefore . . 556*5 
 
 Or it may be considered as containing one volume of olefiant gas and 
 two hydrogen, condensed to two, (974'6 + 138-6) -r- 2 = 556'5. 
 
 The real atomic weight of the marsh gas is difficult to determine, as 
 it does not form any well defined combinations. There is reason to 
 suppose it to be C 2 H 4 . When acted on by chlorine, it gives muriatic 
 acid gas, and bichloride of carbon (p. 706), which has been already 
 noticed. 
 
 OF THE ACTION OF CHLORINE ON ALCOHOL, ALDEHYD, ACETIC 
 ACID, AND THE VARIOUS KINDS OF ETHERS. 
 
 When chlorine gas is passed into alcohol, not absolutely anhydrous, 
 a heavy oily liquid is obtained, known as heavy muriatic ether or 
 chlorine ether. It is a mixture of several substances in indeterminate 
 proportions. 
 
 Chloral and Chloroacetic Acid. 
 
 When the alcohol is anhydrous and the gas quite dry, the action is 
 definite, and gives rise to a remarkable result. Five-sixths of the 
 hydrogen of the alcohol are removed, and are replaced by three of 
 chlorine, and after the evolution of a large quantity of muriatic acid 
 gas a dense oily liquid is obtained, to which the name of chloral has 
 been given its formula is C 4 HC1 3 O2. The first operation of the chlorine 
 is to remove two equivalents gf hydrogen, and thus to reduce the 
 alcohol to the state of aldehyd, just as any other oxidizing agent should 
 have done ; but then it acts on the hydrogen of the radical acetyl, and 
 expelling it, takes its place, generating a new compound radical 
 acechloryl, C 4 C1 3 . This is combined with oxygen and water in chloral, 
 as acetyl is in ordinary aldehyd; the rational formula of chloral is 
 therefore C 4 C1 3 .O + Aq. 
 
 Chloral combines with water, forming a crystalline hydrate. It gra- 
 dually changes into an isomeric porcellanous-looking substance. The 
 equivalent change of common aldehyd has been described, (p. 794). 
 When chloral is acted on by a solution of potash, it yields formic acid 
 and chloroform, C 4 HC1 3 O 2 and HO, giving C2HC1 3 . 
 
 By the action of chlorine on aldehyd, chloral is directly formed. 
 
 When the crystallized acetic acid is exposed to the action of chlorine, 
 in bright sunshine, a substance is formed which crystallizes in brilliant 
 
810 Chloryl-Ether. Chlorojcamethan . 
 
 rhombs, and possesses strong acid properties ; its formula is C 4 HC1 3 4 . 
 It is formed by the replacement of the hydrogen of the radical, acetyl, 
 by chlorine, forming thus the chloro-acetic acid, C 4 C1 3 .O 3 + Aq. Its 
 salts crystallize with facility, and have great similarity to the acetates. 
 When the chloracetate of potash is heated with an excess of potash, 
 it is decomposed into carbonic acid and chloroform; C 4 C1 3 .O 3 and HO 
 giving 2.CO 2 and C 2 HC1 3 . This reaction is exactly similar to that of 
 the common acetate of potash, the chloroform replacing the pond gas. 
 
 Of the Series of Chlorine Ethers. 
 
 When chlorine acts upon sulphuric ether, a remarkable series of 
 bodies is produced ; the first formed is a dense oily liquor, having the 
 formula C 4 H 3 C1 2 O., which, by contact with water or an alcali, is decom- 
 posed into hydrochloric and acetic acids, 3(C 4 H 3 Cl.jO), and 6. HO, 
 producing 6.HC1 and 3.(C 4 H 3 O 3 .) This body is properly, therefore, 
 oxy chloride of acetyl j it is decomposed by sulphuret of hydrogen, 
 muriatic acid being given off, and an oxysulphuret of acetyl being 
 formed, which resembles it in properties. 
 
 In presence of a great excess of chlorine, this oxychloride is totally 
 decomposed, the chlorine entering into the place of the hydrogen in 
 the acetyl, and forming the same radical as exists in chloral and chloro- 
 acetic acid. The substance thus produced is solid and crystalline ; it 
 bears a very simple relation to sulphuric ether, as its formula is C 4 C1 5 0.; 
 being apparently ether, in which all hydrogen is replaced by chlorine. 
 It may be termed chloryl-ether. 
 
 The action of chlorine on the acetic and oxalic ethers, has thrown 
 much light on the theory of these bodies. 
 
 Acetic ether combines with two atQms of chlorine, and loses two 
 atoms of hydrogen, thus giving from C 4 H 3 O 3 + C 4 H 5 O, the chloracetic 
 ether C 4 H 3 O 3 + C 4 H 3 C1 2 0, an oxychloride of acetyl, containing twice 
 as much acetic acid as that just now described, and its rational formula 
 being, therefore, AcCl 3 + 2Ac0 3 . ; with potash it gives chloride of 
 potassium and acetate of potash. 
 
 By a stream of dry chlorine gas, oxalic ether is totally converted into 
 a mass of crystalline plates, which are tasteless and perfectly neutral ; 
 this body contains no hydrogen, its formula being C 6 C1 5 4 = C 4 C1 5 O 
 + C 2 O 3 . It is, therefore, a combination of oxalic acid with chloryl- 
 ether, and is termed chlor-oxalic ether. With water of ammonia it 
 gives oxamide ; by the action of dry ammonia, it forms a substance 
 also crystalline, which is soluble in alcohol and ether, sparingly soluble 
 in water, and the formula of which is C 8 H 2 C1 5 N0 6 . ; at the same time 
 chloryl-ether and water are evolved ; the rational formula of this body, 
 
Action of Chlorine on Muriatic Ether. 811 
 
 chloroxamethan, is at once seen by comparing it with, the oxamethan, 
 formed by ammonia on oxalic ether, (p. 788). Thus : 
 
 2 atoms oxalic ether, Ci2HioO8, give an atom of oxamethan, CgHyNOe. 
 
 1 ,, ammonia, NH 3 , ,, an atom of alcohol, C 4 H5O + Aq. 
 
 In like manner, 
 
 2 atoms of chloroxalic ether, C^ChoOs, give 1 of chloroxamethan, CsClsH^NOe. 
 1 ,, of ammonia, Nils, ,, 1 of chlorine alcohol, C^lgO+Aq. 
 
 The rational formula of the chloroxamethan is, therefore, C 4 C1 3 O.C 2 O3 
 4- C 2 O 2 .Ad. 
 
 When chloroxamethan is dissolved in water of ammonia, and the 
 solution evaporated, crystals are obtained, which are chloroxalovinate 
 of ammonia, their formula being C 8 H 4 C1 5 N0 8 , or in its rational form 
 C 4 C1 5 O.C 2 3 + C 2 3 .NH 4 O ; identical in constitution with the ordinary 
 oxalovinate of ammonia, except that it contains chloryl-ether in place 
 of common ether ; the chloroxalovinic acid itself has been isolated ; it 
 crystallizes in long needles, which react acid, and combines with all 
 bases to form well-defined salts ; its formula is C 4 C1 5 O.C 2 3 + C 2 O 3 Aq. 
 
 A crystallographic examination has rendered the isomorphism of the 
 ordinary oxamethane with the chloroxamethan exceedingly probable. 
 
 The results of the action of chlorine on the light muriatic ether, 
 have led to remarkable results. Eegnault considered this body as af- 
 fording a test experiment for the actual presence of olefiant gas in ether, 
 for if olefiant gas be AcH, and that muriatic ether be AcH.HCl, the 
 result of the action of chlorine should be the same on both bodies, as 
 the muriatic acid in the latter, could not influence such a reaction. 
 Now by acting on muriatic ether with chlorine, a series of bodies are 
 obtained, isomeric with those arising from olefiant gas, but quite dif- 
 ferent in properties. Thus there is first formed a liquid C 4 H 4 C1 2 ; this 
 has the composition of Dutch oil ; next a liquid forms, whose formula 
 is C 4 H 3 C1 3 ; afterwards bodies consisting of C 4 H 2 C1 4 and C 4 HC1 5 and 
 ultimately C 4 Cl6, sesquichloride of carbon. Now the bodies C 4 H 4 C1 2 
 and C^gCly as derived from olefiant gas, are separated by potash, 
 intoC 4 H 3 Cl with HQ, and into C 4 H 2 C1 2 with HC1; but the bodies 
 C 4 H 4 C1 2 and C 4 H 3 C1 3 from muriatic ether, are not decomposed by that 
 alcali. I do not, however, believe in the indefinite replacement of hy- 
 drogen by chlorine, which Eegnault assumes, and look upon the re- 
 lation of these series of bodies as being the following : 
 
 From olefiant Gas. From muriatic Ether. 
 
 C 4 H 4 C1 2 = 4 H 3 C1 + HC1. C 4 H4C1 2 = C 4 H 3 C1 + C 4 H 5 C1. 
 
 C 4 H 3 C1 3 = 2(C 2 HC1) and HC1 C 4 H 3 Cls. 
 
 C4H 2 C1 4 = 2(C 2 HC1 2 ) C4H 2 C1 4 = C4C15. Cl + 2(C4Hs. Cb) 
 
 C4HC1 5 = C 4 H 3 C1 3 + 2(C14.C1 5 .C1) 
 
812 Constitution of Alcohol and Ether. 
 
 Both these give finally sesquichloride of carbon, C 4 C1 5 C1. The 
 bodies from olefiant gas, which contain chloride of hydrogen, are de- 
 composed by an alcoholic solution of potash, but those in which the 
 chlorine is combined with an organic radical are not affected by that 
 reagent, 
 
 By the action of chlorine on mercaptan, a similar series of products 
 are obtained, of which the terminal body is C 4 HC1 4 S consisting of 
 C 4 H 3 .S 3 + 2(C 4 C1 5 .C1). 
 
 On the Theoretical Constitution of Alcohol, and the Bodies derived 
 
 from it. 
 
 The theory of alcohol and the ethereal combinations is of the more 
 importance as the principles of it regulate our ideas, not merely con- 
 cerning the bodies that have been now described, but a vast number of 
 others ; for the ordinary, or wine alcohol, is but one example of a nu- 
 merous family of bodies, which resemble it in all its general laws of 
 reaction, with, of course, peculiarities characteristic of each ; thus 
 wood-spirit, oil of potato-spirit, and ethal are alcohols. 
 
 The generic properties of an alcohol are, that its composition may 
 be represented by a hydrocarbon isomeric with olefiant gas, united with 
 two atoms of water ; that it gives an ether, which contains an atom of 
 water less, and acts as a base ; and that by combining the hydrocarbon 
 with four atoms of oxygen, an acid is formed. Thus, we have 
 
 Wine Alcohol. Wood Alcohol. Oil of Potato -Spirit. Ethal. 
 
 Alcohol, C4H 4 + 2HO C 2 II 2 + 2IIO. CioIIio + 2HO C 32 H 32 -f2HO 
 
 Ether, C 4 H4-|-HO C 2 H 2 + HO CioIIio+HO C 32 H 32 -{- HO 
 
 Acid, C 4 H 4 +O 4 . C 2 H 2 +O 4 CioH IO + O 4 C 32 H 32 + O 4 . 
 
 Such being the connexion of the bodies of this class, the proposi- 
 tions in which I shall now proceed to embody the principles of the 
 constitution of the substances derived from wine-alcohol, may be here- 
 after immediately applied to illustrate the history of the other alcohols. 
 
 1. Prom the action of sulphuric acid, of chloride of zinc, of fluor- 
 ide of boron, of potassium, and of chlorine on alcohol, it results that 
 it contains an atom of water ready formed, united with sulphuric ether ; 
 its formula is therefore C 4 H 5 + Aq. 
 
 2 The sulphuric ether is a base, neutralizing the strongest acids and 
 producing both oxy-salts and haloid salts, perfectly resembling those of 
 an alcali. The oxygen in ether may be replaced by all other electro- 
 negative bodies, whilst the carbo-hydrogen C 4 H 5 remains constant. By 
 the conditions laid down in p. 664 this, therefore, is a compound radical; 
 it is called ethyl, and its symbol is written Ae. Ether is oxide of ethyl, 
 and its symbol is A.eO. 
 
Theory of the Ethers. 813 
 
 3. By the action of oxidizing agents, hydrogen may be removed from 
 ethyl, and a new radical C 4 H 3 produced, which, by combining with 
 oxygen, forms aldehyd and acetic acid, its symbol being, Ac. Aldehyd 
 is protoxide, AcO, and acetic acid, peroxide of acetyl, Ac.0 3 ; both 
 being considered free from water. 
 
 4. From olefiant gas, by the action of oxidizing agents, we cannot 
 in any case pass to the series of bodies containing acetyl ; nor can we, 
 by bringing olefiant gas into contact with water or acids, produce any 
 form of alcohol or ether. On the contrary, the isethionic acid is 
 essentially distinct from these acids which contain ether, and yields 
 none by any form of decomposition ; olefiant gas, on the other hand, 
 given, by the action of chlorine, a series of bodies, which are quite 
 different from those given by muriatic ether, but which indicate that it 
 is itself a radical, having laws of combination peculiar to itself, and 
 independent, as Berzelius had already suggested, both of the alcohol 
 and acetic series. Its formula is, therefore, C 2 H 2 ; its symbol, El, and 
 the Dutch oil is truly chloride of elayl. The ethyl may change itself 
 readily into elayl by loss of hydrogen, sine C 4 H 5 = 2.C 2 H 2 and H, and 
 it is thus broken up when the hydriodic or muriatic ethers are decom- 
 posed by heat, or by potash, or ammonia ; or when sulphuric ether is 
 acted on by an excess of sulphuric acid. 
 
 5. Although from the decomposition of ether we obtain olefiant gas, 
 or light oil of wine, yet as ether cannot be in any way regenerated from 
 these bodies by the influence of water or otherwise, neither can the 
 other products derived from ether, as acetic acid, be produced from 
 them, we must abandon the theory which considered ether to be a 
 hydrate of C 4 H 4 , and consider it simply as an organic base, the oxide of 
 ethyl. 
 
 6. By the action of chlorine on the ethereal compounds and on 
 olefiant gas, radicals are regenerated, which are precisely equivalent to 
 the three, ethyl, acetyl, and elayl, but which contain chlorine in place of 
 hydrogen. Their formulae are C 4 Cl3.C 4 Cl5 and C 2 C1 2 . This last is the 
 protochloride of carbon, already described; the first, acechloryl, exists 
 in chlor-aldehyd and in chloro-acetic acid ; the second, ethcloryl, exists 
 combined with oxygen in chloryl-ether, which acts as a base similar to 
 common ether towards the oxalic and acetic acids. In contact with an 
 excess of chlorine, it breaks up, as ethyl does into olefiant gas and 
 hydrogen, into the protochloride of carbon and chlorine, and thus the 
 ultimate result is the sesquichloride of carbon, C 2 C1 3 . 
 
 7. The series of bodies formed by the action of chlorine on elayl and 
 on chloride of ethyl, are double combinations of bodies containing the 
 hydrogen and chlorine radicals, and hence results their isomerism. 
 
814 ^Enanthic Ether. 
 
 Thus the body (C 4 H 2 C 4 ), from elayl, consists of C 2 H 2 .C1 -f C 2 C1 2 .C1, 
 whilst the body (C 4 H 2 C1 4 ), from tlie muriatic ether,, is really 
 2(C 4 H 3 .C1 3 ) -f C 4 C1 3 C1 3 . The body, CiHaCl, from elayl, is 3(C 2 H 2 ) -f 
 C 2 C1 2 . 
 
 8. The relation of acetyl to ethyl is simply that of internal constitu- 
 tion, described in p. 665. Tor as benzoic acid contains benzoyl, 
 C 14 H 5 2 , whilst this again contains, as radical, the carbohydrogen, 
 C J4 H5. ; so ethyl, C 4 H 5 , contains within it, ready formed, the radical 
 acetyl, and its formula might be still more correctly written as, Ac.H 2 . 
 This is simply shown by the action of chlorine on ether, where 
 C 4 H 3 .H 2 .O, becomes first, C 4 H 3 .C1 2 .0, and subsequently changes to 
 C 4 C1 3 .C1 2 .O. The intermediate compound Ac.Cl 2 . relating itself to the 
 oxygen, as the sulphurous acid, S0 2 , or the benzoyl, C 14 H 15 .O2, in the 
 sulphuric and benzoic acids. Although the connexion of these two 
 radicals is thus analogous to that of amidogen, Ad, and ammonium, 
 Ad H 2 = Am, yet a broad line of distinction is drawn between the 
 ammonia and ether theories, by the very definite character of ether, 
 oxide of ethyl, as contrasted with the hypothetic oxide of ammonium ; 
 and on the other hand there does not appear to be any acetylide of 
 hydrogen, corresponding to ammonia, the amidide of hydrogen, for the 
 assumption of olefiant gas as being that body, is not based upon suffi- 
 cient evidence. 
 
 SECONDAEY PRODUCTS OF THE ALCOHOLIC FERMENTATION. 
 
 I have already noticed that besides the carbonic acid and alcohol, 
 which are derived from the sugar, other bodies are evolved in minute 
 quantities, and by their odour and taste characterize the spirit obtained 
 from particular vegetables. Thus, in the fermentation of grape juice, 
 02nanthic ether is produced; in the spirit distilled from potatoes, a 
 peculiar oil is found ; and in the fermentation of malted corn, both of 
 these bodies are generated, besides a third, to which the name of oleum 
 siticum or corn-oil has been given. 
 
 The cenanthic ether is a thin colourless liquid, of an almost stupifying 
 odour of wine, as to it the peculiar bouquet of wine is due ; its specific 
 gravity is 0'862; it boils at 445; when heated with caustic soda, it 
 evolves alcohol, and forms senanthate of soda, from which the cenanthic 
 acid may be separated by muriatic acid. This is a white crystalline 
 solid which melts at 88, and distils over at 560 unchanged ; its 
 formula is C 14 H 13 O 2 . ; it combines with water, forming a thick oil, 
 which solidifies only at 55, is tasteless and inodorous, but reddens 
 litmus sensibly. The formula of the. ether is AeO + C 14 H 13 O2; it is 
 
Ami lie Alcohol Amilene. 815 
 
 remarkable almost as the only ether that exists as a natural product, 
 but it may also be formed artificially by means of alcohol and senan- 
 thic acid. 
 
 The corn oil, of which the formula is C 42 H350 4 is lighter than water, 
 of a very penetrating odour, a biting taste, and cannot be distilled 
 without partial decomposition. 
 
 Amylic Alcohol Valerianic Acid. 
 
 The oil of potato-spirit has become of much interest from the dis- 
 covery, that it gives rise to a series of ethereal combinations similar to 
 those of wine alcohol ; the name of amilic alcohol may be applied to it; 
 it is colourless, oily, its odour at first pleasant, but subsequently 
 nauseous ; its taste acrid ; it burns with a blue flame ; its sp. gr. is 
 0'812 ; it freezes at 4, and boils at 294; it dissolves in alcohol and 
 ether ; its formula is C 10 H 12 O 2 . In this alcohol a compound radical is 
 assumed to exist, termed amyl, C 10 H U j its symbol is Ayl, and it is 
 combined with oxygen and water, Ayl. O -f- Aq. as ethyl is in wine 
 alcohol. 
 
 The amylic ether, Ayl. O, is not known except in combination with 
 acids ; its bisulphate, or sulph-amylic acid, is obtained by acting on 
 amilic alcohol with oil of vitriol; its formula is AylO.SO 3 -f- S0 3 .HO. ; 
 its barytes salt crystallizes in pearly plates, colourless, very soluble in 
 water and alcohol. This salt is decomposed when its solution is 
 boiled. The salts of lead and lime are completely similar in pro- 
 perties. 
 
 Chloride of Amyl, Ci H n Cl or Ayl.CL is prepared by acting on 
 amilic alcohol with chloride of phosphorus ; it is a colourless oil, which 
 boils at 217. By the action of bromine, or iodine, and phosphorus on 
 the amilic alcohol, the bromide and iodide of amyl are prepared ; they 
 possess properties similar to those of the chloride. 
 
 Acetate of AmyL Ayl O -f- AcO 3 . Is easily formed by distilling 
 acetate of potash, oil of vitriol and amilic alcohol; it is a volatile, 
 colourless liquid, which boils at 257. The oxalate of amyl may be 
 similary formed. 
 
 By distilling amilic alcohol with glacial phosphoric acid, a colourless, 
 aromatic liquid is obtained, having the formula C 10 Hi . It is, in this 
 series, what olefiant gas is in that of the wine alcohol ; it is termed 
 amilene ; the sp. gr. of its vapour in 4918. 
 
 Valerianic Add. C 10 HioO 4 . "When the amilic alcohol is exposed to 
 the air it absorbs oxygen, but its oxidation is more rapidly effected by 
 heating it with caustic potash. By a loss of hydrogen, and absorption 
 
816 Valerianic Acid Valerone. 
 
 of oxygen, precisely similar to that which wine alcohol forms acetic 
 acid, it produces a volatile, oily acid, remarkable as naturally existing in 
 the roots of the valeriana officinalis, and being extracted therefrom by 
 distillation; it is lighter than water; it boils at 347, and neutralizes 
 bases, forming soluble sweet-tasted salts; it must be considered as 
 containing a radical analogous to acetyl, valeryl = C 10 H 9 or Yl, and its 
 formula becomes VI. 3 -f Aq. 
 
 When valerianate of lime is heated, carbonate of lime is formed, and 
 a volatile liquid like acetone, distils over; it is termed valerone. 
 C 10 H90 3 giving CO 2 and CgH^O. The roots of the valerian contain, 
 besides the valerianic acid, another oil destitute of active properties. 
 
 By cautiously treating amilic alcohol with sulphuric acid and chro- 
 mate of potash, an oily liquid is obtained which is valerianic aldefiyd, 
 C 10 H 10 2 or Al.O + Aq. By an excess of chromate of potash it is 
 changed into valerianic acid. 
 
 Treated with chlorine, the amilic alcohol, and the various amilic 
 ethers, as well as the valerianic acid, give new products, which contain 
 chlorine, and are constituted on the same principles as have been fully 
 described for wine alcohol. 
 
 The valerianic acid is found naturally in the berries of the viburnum 
 opulus, and is the ingredient of fish oils, that had been termed Del- 
 phinic and Phocenic acids. It is also now found to be a very ordinary 
 product of the decomposition of organic bodies, as the putrefaction of 
 caseine, the oxidation of oleic acid, and of gelatine, and other bodies. 
 
817 
 
 CHAPTER XXII. 
 
 OP THE PRODUCTS OF THE DECOMPOSITION OF WOOD AND THE 
 ALLIED BODIES. 
 
 SERIES OF METHYL, PHENE AND ANILINE. 
 
 SECTION I. 
 
 OF THE SLOW DECOMPOSITION OF WOOD. CONSTITUTION OF ULMINE. 
 
 OF TURF AND COAL. 
 
 THE gradual decomposition of the woody tissues of plants gives origin 
 to a class of bodies which had been long confounded under the name 
 of ulmine, but which are now recognized to consist of several distinct 
 substances, differing in their origin and still more essentially in their 
 properties. From the influence which they exercise in agricultural ope- 
 rations, by forming an element of the soil, and their importance as fuel, 
 by constituting the great mass of turf, they deserve a somewhat de- 
 tailed notice. I have already stated, that by the action of acids upon 
 sugar, (p. 758), lignine, starch, and similar bodies, (p. 762), brown 
 substances are produced, the composition of which was not definitely 
 established. Mulder has, however, recently re-investigated the history 
 of this class of bodies, and from his known accuracy his results may 
 be looked upon as satisfactory. 
 
 When sugar is acted upon by a very dilute acid, and the liquor not 
 allowed to boil, two brown substances are formed, of which one is 
 soluble in solution of carbonate of soda, but the other not. Tor these 
 bodies the names sacchulmine and sacchulmic acid may be retained. 
 From the alcaline solution the latter may be precipitated by any stronger 
 acid. These bodies are insoluble in water and in alcohol. The formula 
 of the sacchulmine is C 40 H 16 O 14 ; that of the sacchulmic acid is 
 C^H^O^. They differ, therefore, in the former containing the ele- 
 ments of water, which, however, cannot be expelled without total de- 
 composition. 
 
 If the sacchulmic acid be dissolved in water of ammonia and preci- 
 pitated by an acid, it retains a quantity of the alcali; and if the 
 ammonia solution be decomposed by a metallic salt, the precipitate 
 which forms is a double compound of sacchulmic acid, ammonia and the 
 metallic oxide. It was the unsuspected existence of ammonia in these 
 cases which produced the discordance of former results. 
 52 
 
818 Ulmine Bodies from Wood. 
 
 If the sugar be acted on by a stronger acid and the solution kept 
 boiling for a considerable time, the ulmine bodies disappear, and are 
 replaced by two dark brown or black substances, possessing very analo- 
 gous properties, the sacckaro-humine and saccharo-hvimic acid. This 
 change takes place more readily if the air have free access. Both are 
 insoluble in water and alcohol ; they are separated by alcaline liquors 
 which dissolve the acid body. Prom this solution it is thrown down 
 by any stronger acid. The composition of saccharo-humine is expressed 
 by the formula, C 4 oH 15 O 15 ; that of the saccharo-humic acid by C 40 H 12 12 . 
 Like the former bodies these differ, therefore, in the elements of water. 
 
 Mulder found that access of air was not necessary for tli formation 
 of sacchulmine or its acid, but that without air no saccharo-humine nor 
 its acid could be produced. In this action, even without access of air, 
 formic acid appears, although not in large quantity ; at the same time, 
 glucic acid (p. 766), and another body first described by Mulder, 
 apoglucic acid, are generated. 
 
 When wood remains long in contact with air and moisture, it is 
 gradually converted into a mixture of two brown substances, which, 
 from their having been originally found as a product of the decompo- 
 sition of elm, are specially termed ulmine and ulmic acid. The latter 
 is insoluble in alcohol and water, soluble in alcaline solutions ; in its 
 natural state it contains ammonia, which can only be expelled by boiling 
 with caustic potash, by which the greater part of the ulmic acid is 
 itself decomposed. Its formula, as derived from the analysis of a 
 specimen furnished by a rotten willow, was C 40 H 12 O 12 , being isomeric 
 with saccharo-humic acid, but distinguished from it by many minor 
 characters, especially that when treated with acids it retains twice as 
 much ammonia as the artificial product. Mulder considers the natural 
 ulmine to contain more hydrogen ; its formula should then be C 4 oHi 4 O I2 , 
 arid by the continued action of the air it should change into ulmic 
 acid. The formation of these bodies from the woody fibre results 
 from the absorption of oxygen and the evolution of carbonic acid and 
 water : thus four atoms of ligriine, C 48 H 32 32 , with fourteen of oxygen, 
 produce 8X0. 2 with eighteen HO, and an atom of ulmine, C 40 H 14 Oi 2 . 
 
 Another kind of decomposition to which wood is subject, is the 
 conversion of the ligneous fibre into a white friable substance, which 
 is formed abundantly in the interior of dead trees ; its composition is 
 found to be expressed by the formula C 3 3H 27 O 2 4. It is evidently formed 
 by the lignine combining with oxygen from the air and with the ele- 
 ments of water, and then giving off carbonic acid gas ; C 36 H 24 24 with 
 3.O andS.HO, forming C 33 H 27 O 24 and 3.CO 2 . 
 
 The rotting of wood is, however, by no means necessarily induced by 
 
Ulmine Bodies of the Soil. 819 
 
 the mere presence of air and water, for lignine may be exposed to these 
 agents for centuries without being altered in any sensible degree. Pre- 
 cisely as in the alcoholic and acetous fermentations, it is necessary that 
 an azotized substance should be present, which being first decomposed 
 and forming, probably, crenic and apocrenic acids, communicates the 
 action to the lignine ; the albuminous juices which exist in the vessels 
 of the wood act thus as a ferment, and the decomposition of the wood 
 may be prevented by precisely the same methods as counteract the ten- 
 dency to the fermentation of sugar or of alcohol ; any deoxidizing sub- 
 stance, as sulphurous acid, any metallic salt, as corrosive sublimate, or 
 blue-stone, which may combine with the albumen, and render it insoluble, 
 will thus protect wood from decomposition, and are at present extensively 
 used as preservatives against what is technically termed the dry rot. 
 
 It is by similar decomposition that the roots and other remains of 
 plants are converted into a substance, which by virtue of its direct 
 absorption, or by means of the products of its further change, con- 
 tributes powerfully to the nutrition of the succeeding race of plants, 
 and thereby constitutes an essential element of every fertile soil ; but 
 though, like ulmine, derived from the rotting of vegetable matters, and 
 for the most part of the same composition, the organic substance of the 
 soil is by no means identical with it. It would even appear from. 
 Mulder's results, that the vegetable constituent of the soil varies in 
 composition according to the nature of the crop. For distinction I 
 shall apply to the ulmic acid of the soil the name of geic add, proposed 
 by Berzelius. To extract it, the soil is washed with boiling water until 
 this passed away quite clear, and then boiled with carbonate of soda ; 
 the brown filtered liquor is precipitated by muriatic acid, and the pre- 
 cipitate boiled with alcohol to dissolve out two organic acids, which 
 will be shortly described. In this state, the substance is really an 
 ammoniacal salt; its formula being C^H^O^ -f- NH 3 -f- 4.HO. and 
 even by caustic potash it cannot be completely deprived of ammonia. 
 In the geic acid of a meadow, the same organic element was found to 
 be united with twice as much ammonia, and in one case, where the 
 substance had been obtained from the soil of an orchard, the geic acid 
 had the formula C^H^On. The geic acid, C^H^O^, though isomeric 
 with the saccharo-humic and ulmic acids, is proved not to be identical 
 by numerous minor characters, which need not be described here. 
 
 In that decomposition of vegetable matter which gives origin to turf, 
 water is present in much greater quantity than in any of the former 
 cases ; in many instances, the plants being totally immersed, and so 
 matted together, from their mode of growth, that the access of air 
 must be very much prevented. Hence we no longer find in turf the 
 
820 Ulmine Bodies from Turf. 
 
 comparatively simple decomposition of the wood into an ulmine and an 
 ulmic acid, but in addition to these bodies, the turf allies itself to the 
 varieties of coal, in containing several kinds of fossil, resinous and waxy 
 substances, which are produced by secondary and more complicated 
 reactions. Here it is necessary, however, to describe only such con- 
 stituents of the turf as are analogous to those already noticed, and for 
 distinction I shall term them humous and kumic acids. The former is 
 found principally in the light pale brown turf, which is not imbedded 
 in water, the latter, on the contrary, in the heavy black turf, to which 
 water has had free access. They are prepared precisely as noticed for 
 the geic acid ; the turf containing in abundance the same organic acids 
 soluble in alcohol, as does the vegetable soil. 
 
 The Humous Add resembles perfectly in its properties the sacchulmic 
 acid, with which it is isomeric, its formula being C 40 H 12 O I2 , but it has 
 no tendency to retain ammonia when precipitated by an acid from its 
 combination with that alcali. The humic acid, on the contrary, com- 
 bines with ammonia, so intimately that they cannot be separated by any 
 re- agent, and it even absorbs ammonia in the laboratory, from the small 
 quantity of the gas which may be set free in other operations. As ex- 
 tracted from the black turf, its formula is C 4 oH 15 O 15 + NH 4 O. It is, 
 therefore, when free from ammonia, isomeric with the saccharo-humine, 
 but differs totally in composition from the saccharo-humic acid with 
 which it is so identified in properties. 
 
 The azotized acids which have been noticed as existing in vegetable 
 soil, and in turf, are termed the crenic and apocrenic acids ; they derive 
 their origin from the rotting of those elements of the plant which 
 contain nitrogen, as albumen, &c. and are formed also in the decom- 
 position of animal substances under peculiar circumstances ; thus 
 certain soft minerals, as polishing slate and rotten-stone, contain so 
 much organic matter as to be used for food in time of distress in the 
 north of Europe, and Berzelius found this to consist of crenic acid, 
 formed from the bodies of the microscopic animals, whose silicious 
 skeletons constitute the mineral portion of the rock. 
 
 These acids were first discovered in mineral springs, whence their 
 name (*ppn), and are most easily obtained pure from the ochery 
 deposits which form on the sides of the spring, and in which they are 
 combined with oxide of iron and silica. They are separated by means 
 of their copper salts, the white crenate of copper being soluble, whilst 
 the brown apocrenate of copper is insoluble in a liquor containing free 
 acetic acid ; from the copper salts they may be set free by sulphuretted 
 hydrogen. 
 
 The Crenic Acid is a pale yellow gummy mass, of an astringent 
 
Crenic Acid. Formation of Coal. 82] 
 
 taste, very soluble in alcohol and water ; its formula is NC 14 H 16 O 12 ; 
 by exposure to the air, it changes into apocrenic acid; this is brown, 
 of an astringent taste, reddens litmus, and is much less soluble in alco- 
 hol and water than the crenic acid ; its formula is N 6 C 28 H 14 O 6 . 
 
 The relations of these acids, and of the several species of ulmine to 
 the nutrition of plants will be hereafter considered. 
 
 The circumstances under which coal is formed have been already 
 noticed generally, in pp. 671 and 808, but it remains to examine 
 specially the mode of decomposition to which the wood is subjected 
 during that change. The coal appears to require for its production, 
 that the ligneous fibre should be in presence of water, with little or no 
 access of air, and that in most cases the temperature shall be elevated. 
 Thus whilst ulmine is produced when the woody material is on the 
 surface, or at least only immersed in water, the formation of any of the 
 varieties of coal requires the conjoined influence of moisture, of great 
 pressure, arising from the superposition of beds of rock or soil, of a 
 high temperature, given by the proximity of volcanic foci, or generated 
 by the decomposition of the wood itself, and finally, that the access of 
 air shall be much more limited than in the former cases. Then, accord- 
 ing to the age of the geological formation, the nature of the superin- 
 cumbent rock, and the degree to which the temperature is raised, the 
 coaly material varies in composition. The more recent species (lignite 
 or fossil wood) which peculiarly belong to the tertiary formations, are 
 characterized by the perfect preservation of the organized structure of 
 the wood, and a more or less deep brown, but not black colour. Their 
 composition may generally be expressed by formulae which indicate that, 
 without any absorption of oxygen from an external source, the wood 
 has given off carbonic acid and water. In the coals of the secondary 
 strata (the proper coal formation) great diversity of constitution exists, 
 depending on local circumstances. It would appear, that where the 
 conversion from lignine into true coal is perfect, the proportion of 
 carbon and hydrogen becomes uniformly C 3 2H 12 ; these elements being 
 united with small quantities of oxygen, generally amounting to from 
 three to five atoms. The cannell coal of Wigan, the splint coal of 
 TTorkington, and the caking coal of Newcastle have been ascertained, 
 by Johnstone, to be so constituted. Here, also, the change arises from 
 the elimination of the elements of water and carbonic acid from the 
 wood, as C36H24O24 produces exactly, 4.CO. 2 and 12. HO, with C 32 H 12 O 4 . 
 TThen the mass of decomposing vegetable matter has been subjected 
 to a very high temperature, as by the direct contact of volcanic rocks, 
 it becomes almost completely carbonized, and the variety of coal termed 
 anthracite is formed. The small quantity of hydrogen and oxygen 
 
822 
 
 Composition of Coal. 
 
 which anthracite contains, can only be referred to traces of the proper 
 coal that have escaped decomposition, and if pure, it should be a mineral 
 coke identical in nature with the coke artificially prepared. 
 
 The formulce here given as expressing the constitution of the pro- 
 ducts of the decomposition of wood, are to be considered only as 
 illustrative of the kind of re-action which goes on between its elements ; 
 for none of these products are pure chemical substances ; they form no 
 definite compounds ; they have no precise equivalent number, and 
 hence it is only for illustration that a formula can be legitimately em- 
 ployed to express their composition. 
 
 The following table contains the ordinary composition of the most 
 important varieties of coal and turf. The numbers given were selected 
 from those obtained in my own analyses. 
 
 Kind of Fuel. 
 
 Carbon. 
 
 Hydrogen. 
 
 Oxygen and 
 Nitrogen. 
 
 Ashes. 
 
 Economic 
 Value 
 Of 100 Parts. 
 
 Turf . . ; 
 
 58-09 
 
 5-93 
 
 31-37 
 
 4-61 
 
 171 
 
 Lignite . . 
 
 7171 
 
 4-85 
 
 21-67 
 
 1-77 
 
 208 
 
 Splint Coal . 
 
 82-92 
 
 6-49 
 
 10-86 
 
 0-13 
 
 262 
 
 Cannell Coal. 
 
 83-75 
 
 5-66 
 
 8-04 
 
 255 
 
 260 
 
 Cherry Coal . 
 
 84-84 
 
 5-05 
 
 8-43 
 
 1-68 
 
 258 
 
 Caking Coal . 
 
 87-95 
 
 5-24 
 
 5-41 
 
 1-40 
 
 271 
 
 Anthracite . 
 
 91-98 
 
 3-92 
 
 3 16 
 
 0-94 
 
 273 
 
 At the same time that the great masses of fossil fuel are thus gen- 
 erated by the decomposition of wood, a great number of other products 
 make their appearance, which, although much inferior in quantity, pos- 
 sess, at least in some cases, considerable interest. Thus the fire damp 
 of mines (p. 808) consists in most part of marsh gas, but contains in 
 some cases also olefiant gas and free hydrogen. 
 
 Interspersed through the masses of coal are found small quantities 
 of a great variety of bodies, principally carbo-hydrogens, resembling 
 the oils and stearoptens of plants closely in properties and constitution. 
 Thus, ozocherit, or fossil wax, is found in cavities in the rocks lying 
 upon coal; it is brown, of a foliated structure; it fuses at 143. 
 Paraffine, which is an important constituent of the tar, produced in 
 the destructive distillation of wood, is also found associated with coal. 
 It is white, crystallizes in brilliant plates ; it fuses at 111, and may 
 be distilled unaltered ; it dissolves readily in ether and alcohol ; it is 
 scarcely acted upon by re-agents, whence its name (parum affinisj. 
 Both these bodies have the same composition as olefiant gas, consisting 
 of CH. Many waxy fossil substances are isomeric with oil of turpen- 
 tine, and one, which is interesting, as being the matrix in which the 
 
Products of Destructive Distillation. 823 
 
 native cinnabar of Idria is imbedded, (p. 568), has the formula C 12 H 7 ; 
 it is termed idrialine. 
 
 Others of these products are liquid, and frequently issue forth from 
 the surface of the ground, constituting springs, which from their im- 
 flainmability have been invested in uncivilized countries with a sacred 
 character. Such liquids are known as rock oil or petroleum. Some 
 specimens of it that have been accurately examined are, like paraffine, 
 isomeric with olefiant gas, whilst others are isomeric with oil of tur- 
 pentine, and absorbing oxygen are gradually converted into a resinous 
 substance, asphalt, for which the formula, C^H^Oe, has been assigned. 
 
 SECTION II. 
 
 DESTRUCTIVE DISTILLATION OF WOOD OF THE PYROXYLIC SPIRIT, AND 
 
 ITS DERIVATIVES. 
 
 THE class of bodies upon the description of which I shall now enter, 
 although possessing the most remarkable analogies to the common 
 alcohol and the compounds derived from it, and to the acetic acid, are 
 separated from them by the circumstance of not being formed, so far 
 as is yet known, by any process of fermentation, but in the total 
 destruction of the organic constitution of ligneous fibre or wood, by a 
 strong heat. No material bearing to methylic alcohol the relation 
 which sugar has to common alcohol has been as yet discovered. The 
 methylic compounds are however met with in nature, although sparingly, 
 the volatile oil of the gualtheria procumbens being a methyle ether, 
 salicylate of methyl, and the product of the oxidation of pyroxylic 
 spirit, formic acid constituting the irritating material of the sting of 
 the common ant. 
 
 For practical purposes, however, the source of pyroxylic spirit is 
 altogether artificial. It was, in fact, first discovered as a volatile pro. 
 duct, appearing in the manufacture of an impure vinegar, by the dis- 
 tillation of wood ; and its collateral production in that process is the 
 source from whence the chemist always derives it. It will, therefore, 
 be necessary to describe the general conditions of that operation before 
 entering upon the study of the individual chemical products. 
 
 Preparation of Methylic Alcohol. 
 
 The results of the action of heat on an organic substance are strictly 
 analogous to those of an imperfect combustion. A quantity of carbon 
 is removed, as carbonic acid, and a quantity of hydrogen, as water. 
 
824 
 
 Products of the Distillation of Wood. 
 
 The other products contain, therefore, relatively less oxygen. If the 
 substance upon which we operate be pure, and the heat be carefully 
 managed, the result is in all cases perfectly simple and distinct, as 
 where acetic acid gives acetone and carbonic acid ; malic acid gives 
 water, carbonic acid, and maleic acid; but if the temperature change, 
 another set of reactions occur, and other products are generated, which 
 arise, properly speaking, from the decomposition of the first. Thus, 
 acetic acid gives marsh gas ; malic acid gives fumaric acid. Hence, 
 if substances be taken, through which, either from their mass or their 
 non-conducting power, the heat cannot be uniformly diffused, a number 
 of different reactions take place in different portions at the same time, 
 according to their respective temperatures ; the bodies generated in 
 the interior are altered according as they approach the surface ; and 
 hence a very high degree of complexity is given to the ultimate 
 results. 
 
 "When the substances operated on are not pure, but as common 
 wood, coal, turf, &c., contain various organic bodies of different na- 
 tures mixed together, it becomes quite impossible to express the precise 
 reactions which occur, and the number of bodies generated becomes 
 very great. It is to the classes of bodies thus produced that I wish 
 to direct attention in the present section, as in all cases where the 
 mode of origin of a pyrogenic product is accurately known, I have 
 described it in connexion with the body from whence it is usually 
 derived. 
 
 According as the object of the process is the manufacture of vinegar 
 or of tar, the distillation of wood is very differently managed. For 
 the first, a cast-iron cylinder, a, is built into a furnace, of which c is 
 
 the grate, d the fire door, and e, e, e, the flue, which winds spirally 
 round the cylinder, so as to heat it as uniformly as possible. The 
 wood, in pieces which fit accurately the interior of the cylinder, is in- 
 
Manufacture of Pt/roxylie Spirit. 825 
 
 troduced by an opening in the top, which is then closed by the plate b. 
 The volatile and gaseous products of the distillation pass off by the 
 tube g, which is bent zig-zag, and is surrounded at i, i, by larger tubes, 
 through which a stream of cold water constantly passes. This water is 
 supplied from a reservoir, n, by the tube I, and entering below at m, 
 passes from one jacket to another by the cross pipes 0, o, and escapes 
 ultimately above at p; this cooling arrangement being a form of 
 Liebig's condensing tube, (p. 776), convoluted, as it were, in order to 
 occupy less room. The liquids, which are thus condensed, collect in 
 the tubs r, and the gases which come over are allowed by the cock t 
 to issue from the tube s, and, being set on fire, play on the bottom of 
 the cylinder, and thus economize a certain quantity of fuel. 
 
 The liquid products separate, on standing, into two layers, the upper 
 formed of oily and tarry matters, the lower of water, acetic acid, 
 pyroxylic spirit, &c. By the connecting tube, this heavier liquid passes 
 into the second tub, while the tar remains in the first. The impure 
 acetous liquor is neutralized by carbonate of lime ; the acetate of lime 
 decomposed by sulphate of soda, or sulphuret of sodium ; the acetate 
 of soda crystallized and fused in order to expel the adhering tar, then 
 dissolved, recrystallized, and decomposed by oil of vitriol. Pure acetic 
 acid is thus obtained, which is then diluted with water to the various 
 degrees of strength required in commerce, (p. 796). 
 
 When the acetous liquor has been neutralized by the lime, it is con- 
 centrated by distillation, whereby a spirituous liquid is obtained, which 
 is ivn&& pyroxylic spirit, and has a close analogy to alcohol in its cha- 
 racters. In this state it is, however, a mixture of a variety of bodies ; 
 some of these, as aldehyd and acetone, have been already noticed, and 
 the others shall now be described. Mr. Scanlan first recognized the 
 various constituents of the impure pyroxylic spirit, and their history 
 was accurately investigated by Dumas and Peligot, by Lowig and by 
 myself. 
 
 The impure pyroxylic spirit having been deprived of water by re- 
 peated rectifications over lime, as much chloride of calcium as it can 
 dissolve is to be added to it, and the mixture allowed to stand for a 
 few days. Being then distilled in a water bath, the body to which the 
 name of pyroxylic spirit is specially applied, remains in the retort, com- 
 bined with the chloride of calcium, whilst there distils over a mixture 
 of two liquids, xylit and merit, which are separated from each other by 
 frequent rectification, as their boiling points differ. Besides these three 
 bodies, there exist in the rough liquor an oil, metkol, and a solid sub- 
 stance, discovered by Mr. Scanlan, and izTs&z&pyroxanthine. 
 
 This last body remains behind when the spirit is rectified over lime, 
 
826 XylUMesit.Methylic Alcohol. 
 
 from which it is separated by adding muriatic acid, and being then 
 dissolved in boiling alcohol, it crystallizes on cooling ; it forms deep 
 orange yellow needles ; it fuses at 350, and volatilizes in a current of 
 air or of vapour, but is decomposed if heated by itself : it is insoluble 
 in water, but dissolves in alcohol and volatile oils; sulphuric acid 
 colours it deep indigo blue ; its formula is C 2 iH 9 4 . No combinations 
 of it are known. 
 
 The Metkol contains no oxygen ; its formula being C 4 H 3 . It boils 
 at 356, and possesses the general characters of an essential oil. 
 
 XylU resembles alcohol closely in its properties. Its odour is 
 agreeable and ethereal; its specific gravity, 0*816; it boils at 143 ; 
 with acids it produces ethereal compounds, which have not been closely 
 examined ; its formula appears to be C 12 H 12 0.5. 
 
 Hesit can scarcely be considered as having been as yet obtained 
 pure; in its properties it closely resembles xylit, but has a higher 
 boiling point ; its formula has been stated to be C 6 H 6 O 2 . I shall 
 have on another occasion to notice the probable constitution of these 
 bodies. 
 
 The proper pyroxylic spirit is obtained pure from its combination 
 with chloride of calcium, by the addition of water, and distillation ; by 
 rectification in a water bath, with dry lime, it is freed from water. 
 "When quite pure, it is a colourless liquid, of a peculiar aromatic smell ; 
 it burns with a flame still less luminous than that of spirit of wine ; its 
 specific gravity is 0*798; it boils at 140; its formula is C 2 H 4 2 ; the 
 specific gravity of its vapour is 1*1105 ; in its action upon other bodies 
 this substance ranges itself completely with wine-alcohol, and it is 
 hence frequently termed methylic alcohol, from the Greek words /&w0u 
 and uX?j. In the history of its combinations it will, therefore, be suffi- 
 cient to fix attention on those points which are more specially charac- 
 teristic of it ; its series being in many respects more complete than that 
 of ordinary alcohol. 
 
 Pyroxylic spirit combines with bases and with salts to form com- 
 pounds similar to the alcoates. It is decomposed by the chlorides of 
 zinc and alcohol, by the fluorides of silicon and boron ; methylic ether 
 is evolved, the reactions being precisely such as occur in the case of 
 ordinary alcohol. 
 
 Methylic Ether and its Salts. 
 
 "When treated with sulphuric acid, the methylic alcohol produces an 
 ether, an organic acid, and a heavy oil, precisely similar to those formed 
 by spirit of wine. But the reaction is much more distinct, all the 
 
Methylic Ether. Sulphate of Methyl. 827 
 
 products remain properly in the series of the methylic alcohol ; no gas, 
 equivalent to olefiant gas, being evolved. 
 
 The methylic ether is, at ordinary temperatures and pressures, a 
 colourless gas, of an ethereal odour ; it burns with a blue flame. Water 
 absorbs thirty-seven times its volume of it ; its formula is C 2 H 3 O. ; it 
 hence is isomeric with wine-alcohol, with the vapour of which it has 
 the same specific gravity = 1597*5 ; but its atomic weight is only one- 
 half that of alcohol; it combines directly with anhydrous sulphuric 
 acid, forming a heavy oily liquid, and with the other acids to form com- 
 pound ethers. Tor the same reasons as have been fully discussed under 
 the head of wine-alcohol, it is assumed to be an oxide of a compound 
 radical, methyl, C 2 H 3 or Me, and the formula of the pyroxylic spirit is 
 therefore MeO + Aq. 
 
 The sulpho-methylic acid is formed precisely as the sulphovinic acid 
 which it closely resembles in properties, except that it may be obtained 
 crystallized in white needles, by cautious evaporation of its solution. 
 Its formula is MeO.S0 3 + SO 3 .HO. ; its salts are generally more per- 
 manent, and crystallize more easily than the sulphovinates. 
 
 Sulphate of Methyl. MeO + SO 3 . This substance passes over as 
 a heavy oil, when one part of pyroxylic spirit is distilled with five or 
 six parts of oil of vitriol, and is formed also by the direct union of 
 of methylic ether and dry sulphuric acid. It has a strong garlic colour; 
 its specific gravity is 1*324; it boils at 370. By boiling water, or 
 strong bases, it is immediately resolved into its constituents. "With dry 
 ammonia it forms a white crystalline mass, sulpho-methylan, which con- 
 sists of MeO.SO 3 + S0 2 .Ad. 
 
 The carlo methylic acid is prepared by adding solid carbonic acid to a 
 solution of barytes in pyroxylic spirit, or by passing a stream of dry 
 carbonic acid gas into the solution under pressure. The base becomes 
 perfectly neutralized, and the carbo-methylate of barytes may be 
 obtained crystallized in minute plates by evaporation and cooling. Its 
 formula is MeO.CO 2 + BaO.C0 2 . On decomposing this salt by 
 soluble carbonates or sulphates, the carbomethylates of the other 
 bases may be produced. The carbomethylates in solution rapidly de- 
 compose into a carbonate of the base, methylic alcohol and free 
 carbonic acid. If the salt be decomposed by a stronger acid, the 
 carbomethylic acid is set free, but very soon separates into its con- 
 stituents. 
 
 Xanthomethylic acid. MeO^ + CS 2 . On dissolving sulphuret of 
 carbon in a hot solution of potash in pyroxylic spirit, the xanthomethy- 
 late of potash crystallizes on cooling in very beautiful orange yellow 
 prisms. The other salts are prepared by double decomposition. 
 
82 8 Acetate of Methyl Nitrate of Methyl. 
 
 When vapours of hydrated cyanic acid are passed into pyroxylic 
 spirit it gives an allophanate of methyl analogous to the body described, 
 p. 788. 
 
 Acetate of Methyl. C 6 H g 4 = C^H/) -f C 4 H :) 3 . This body ap- 
 pears to be a product of the distillation of wood, and to constitute the 
 body already described as mesit. It is easily formed by distilling a 
 mixture of acetate of soda, pyroxylic spirit, and oil of vitriol. It is a 
 light liquid of an agreeable odour and a pungent taste, sp. gr. 0*920. 
 It boils at 136. This body is interesting as isomeric with the formiate 
 of ethyle, (formic ether), which is also C 6 H 6 4 = C 4 H.O + C 2 H0 3 . 
 
 Nitrate of Methyl. MeO.N0 5 . Is prepared by distilling nitrate of 
 potash, pyroxylic spirit, and oil of vitriol, mixed together in a capacious 
 retort. The receivers are to be carefully cooled, and a gentle heat 
 applied to the retort to commence the reaction, which then continues 
 to the end without any further external heat. The product, when puri- 
 fied by redistillation over some oxide of lead, is a colourless liquid, 
 neutral, of an ethereal odour ; it burns with a yellow flame ; its sp. gr. 
 is 1-182; it boils at 151. If a drop of it be heated to 300, it ex- 
 plodes, and this takes place much more easily if there be a quantity ; 
 hence its distillation must be very cautiously conducted. 
 
 With chloro-carbonic acid the pyroxylic spirit gives compounds 
 precisely similar to those already described in the series of ordinary 
 alcohol, and which with ammoniacal gas produce the uremethylane. 
 
 Oxalate of Methyl. MeO.C 2 O 3 . Is best formed by distilling a 
 mixture of equal parts of oxalic acid, pyroxylic spirit and oil of vitriol. 
 The product crystallizes in large rhombic plates; it fuses at 124, and 
 boils at 312 ; it dissolves easily in water and alcohol. With water of 
 ammonia it produces oxamid and methylic alcohol ; with dry ammonia 
 it forms a crystalline body, MeO.C 2 O 3 + C 2 O 2 .Ad. Oxamethylan. 
 
 The combinations of methylic ether with the other oxygen acids, 
 resemble so closely those of vinic ether, that they need not be specially 
 described. 
 
 Haloid Salts of Methyl Methyl Chloral. 
 
 Chloride of Methyl. C 2 H 3 .C1. Is obtained by distilling a mixture 
 of common salt, pyroxylic spirit and oil of vitriol. The product having 
 been washed by passing through water, is a colourless gas, sp. gr. 
 1'730; odour ethereal. When this gas is mixed with chlorine and 
 exposed to light, it produces a liquid isomeric with chloretherene, 
 (page 792), and with more chlorine, chloroform, C 2 HC1 3 . 
 
 Iodide of MethyL (C 2 H 3 .I.) Is produced as a very dense liquid 
 by distilling pyroxylic spirit with iodine and phosphorus. It boils at 
 104, sp. gr. 2-287. 
 
Haloid Salts of Methyl Methyl Chloral. 829 
 
 Sulphur et of Methyl. C 2 H 3 S. Is obtained by decomposing any of 
 the salts of methyl by an alcoholic solution of sulphuret of potassium. 
 It is a liquid of a very offensive odour, sp. gr. 0'850, boils at 107. It 
 is decomposed by chlorine. There is also obtained by decomposing sul- 
 pho-methylate of potash with hydrosulphuret of sulphuret of potassium, 
 a sulphomethylic alcohol or methylene mercaptan, C 2 H 4 S 2 . or C 2 H 3 S + 
 HS., which resembles perfectly in properties the mercaptan described 
 page 785. 
 
 "When pyroxylic spirit is acted on by chlorine, the action is very com- 
 plex, the liquor separating into a watery and a dense oily liquid. For 
 the latter, very complex formulse have been proposed. With the other 
 compounds of methyl chlorine produces decompositions, of which the 
 more important shall be described farther on. 
 
 Ammonia-Compounds of Methyl. 
 
 Oxamethylane. MeO.C 2 O 3 + C 2 O 2 . Ad. Ammoniacal gas is 
 absorbed by oxalate of methyl and a crystalline mass forms, which is 
 purified by solution in boiling alcohol, from which it is deposited in 
 brilliant plates. 
 
 Sufyhamethylane. MeO.S0 3 + SO 2 .Ad. If dry ammonia be 
 passed over sulphate of methyl, a white solid is produced, which may 
 be purified as above. It is formed also by dissolving sulphate of 
 methyl in water of ammonia in the cold, and evaporating in vacuo, 
 when it crystallizes. 
 
 Urethylane. MeO.CO 2 + CO.Ad. The oxide of methyl unites with 
 chloro-carbonic oxide, forming a gas closely resembling the chlorocar- 
 bonic ether described page 788, and this condenses with ammonia, 
 forming a crystalline mass, which is separated into muriate of ammonia 
 and the urethylane. 
 
 PRODUCTS OF THE OXIDATION OF PYROXYLIC SPIRIT. 
 
 Formic Acid. C 2 H.O 3 -f HO = FoO 3 + Aq. 
 
 If pyroxylic spirit be distilled with chromate of potash and sulphuric 
 acid, it is totally converted into carbonic acid and water. If black 
 oxide of manganese be used, and that after the first violent effervescence 
 has ceased, a gentle heat be applied, a liquid distils over, which, when 
 completely pure, has the formula, C 6 H 8 4 ; it boils at 104; its sp. gr. 
 is 0*855 ; it is termed methylal. 
 
 If pyroxylic spirit be brought into contact with oxygen by means of 
 spongy platinum, as described for ordinary alcohol in p. 796, hydrogen 
 
830 Products of the Oxidation ofPyroxylic Spirit. 
 
 is removed and oxygen absorbed in equivalent proportion, and the 
 methylic alcohol is totally converted into hydrated formic acid. 
 C 2 H 4 O 2 and 2O, giving 2-HO and C 2 H 2 4 . In this reaction there does 
 not appear to be any intermediate state, equivalent to that of aldehyd, 
 which body appears to be without a representative in the pyroxylic 
 series, at least except in combination. For practical purposes this 
 mode of preparing formic acid is not had recourse to, as it may be 
 derived more easily from the oxidation of most organic bodies. 
 
 The formic acid derives its name from existing in a very concentrated 
 form in the common ant, (formica rufa,) and produces the pain of their 
 sting, on being injected into the puncture which the animal makes; it was 
 formerly prepared by distilling the ants with a little water ; but the pro- 
 cess of Dobereiner is now generally followed. It consists in mixing one 
 part of starch, or sugar, or tartaric acid, with four of black oxide of man- 
 ganese, four of water, and four of oil of vitriol. Considerable efferves- 
 cence occurs owing to the escape of carbonic acid. When this is over^ 
 the mixture is to be distilled until four and one half-parts have passed 
 over ; this acid liquor is to be neutralized by carbonate of soda, and the 
 formiate of soda crystallized by evaporation and cooling. From this 
 salt the formic acid may be obtained in any required degree of concen- 
 tration, by distilling with oil of vitriol, in precisely the manner described 
 for acetic acid, p. 799. 
 
 If sugar, or starch, or barley, be simply heated with dilute sulphuric 
 acid, until it becomes brown, a certain quantity of formic acid is pro- 
 duced, along with ulmine and ulmic acid. The generation of this acid, 
 as a product of the decomposition of prussic acid, of chloral, and of 
 hydrated oxalic acid has been already noticed. 
 
 Pure hydrated formic acid is a limpid colourless liquid, which fumes 
 slightly in the air ; its odour is intensely pungent ; when cooled below 
 32, it crystallizes in brilliant plates; it boils at 212; its specific 
 gravity is 1*235. In this most concentrated form, it is an absolute 
 caustic, if applied to the skin, producing a sore very difficult to heal ; 
 its formula is C 2 HO 3 + HO, and like acetic acid, it is supposed to con- 
 tain a radical, formyl, C 2 H or Fo. and its rational formula to be Fo0 3 
 -f HO. Combining with water- it forms at least one other definite 
 hydrate ; the formula of which is FoO 3 + 2HO. 
 
 The resemblance of formic acid to acetic acid is very close, but they 
 are at once distinguished by their behaviour to certain re-agents. When 
 heated with an excess of oil of vitriol, it is decomposed with lively effer- 
 vescence into water and carbonic oxide, (C 2 HOa = C 2 O 2 and HO.) 
 If a solution of a formiate be mixed with a cold solution of nitrate of 
 silver, a white crystalline precipitate of formiate of silver falls, which, 
 
Formic Acid. Formiates. 831 
 
 when heated, is totally decomposed into metallic silver, water, and car- 
 bonic acid, C 2 HO 3 -f AgO, giving 2.CO 2 with HO, and Ag. If 
 formic acid be digested on red oxide of mercury, carbonic acid is given 
 off, and a sparingly soluble crystalline formiate of the black oxide of 
 mercury is produced, this, when boiled, is totally decomposed, metallic 
 mercury separating, and carbonic acid and water being evolved. 
 
 The alkaline formiates are soluble and crystallizable ; the formiate of 
 ammonia crystallizes in right rhombic prisms, which melt at 250, and 
 sublime without alteration. If its vapour be passed through a red-hot 
 porcelain tube, it is totally converted into prussic acid and water, 
 C 2 HO 3 + NH 4 O, giving C 2 N.H and 4.HO. 
 
 Formiate of Soda crystallizes in rhombic prisms, which have the 
 formula, NaO.FoOs + 2Aq. When heated it undergoes aqueous 
 fusion, and by a higher temperature is decomposed. A solution of this 
 salt, when boiled with the salts of silver, mercury, gold, palladium, or 
 platinum, precipitates the metal and is hence useful in analyses. 
 
 Formiate of Barytes. BaO.FoO 3 . It is obtained 
 in large rhombic prisms, as in the figure, where u, y 
 are primary, and i a secondary plane, which have a 
 bitter taste, and are not altered by the air. It is 
 very soluble in water, but insoluble in alcohol. 
 
 Formiate of Lime is easily produced by neutralizing 
 lime with dilute formic acid ; it is equally soluble in cold and in hot 
 water, so that it is only obtained crystallized by slow evaporation; it 
 dissolves in ten parts of cold water ; it is insoluble in alcohol. 
 
 Formiate of Lead. PbO.FoO 3 . If formic acid be added to a solu- 
 tion of acetate of lead, this salt separates after a short time in stellated 
 groups of brilliant needles, which are anhydrous, and require forty parts 
 of water for solution ; it is totally insoluble in alcohol. By the forma- 
 tion of this salt the formic acid is readily distinguished from the acetic 
 acid, and the two, if present together, may be thus separated. 
 
 Formiate of Copper crystallizes in large rhomboidal 
 prisms, as in the figure, where i, u, u are primary, and 
 m a secondary plane, which are very regular, trans- 
 parent, and of a fine clear blue colour. It effloresces in 
 dry air. 
 
 The Formiates of Mercury. That of the red oxide is 
 very soluble ; it can only exist at ordinary temperatures ; by a very 
 gentle heat it changes into the formiate of the black oxide, and this, 
 when boiled, gives metallic mercury, as already described among the 
 tests for formic acid. In this reaction 4HgO -f. 4.C 2 H0 3 produce 
 2.Hg 2 Of 2.C 2 H0 3 and C 2 4 whilst 2.C 2 H 2 4 become free, and further 
 
832 Formic Acid. Chlorides of Formyl. 
 
 2Hg 2 O + 2C 2 H0 3 produce C 2 O 4 with 2 Hg and C 2 H 2 O 4 free. The 
 formiate of the black oxide may also be prepared by mixing solutions of 
 formiate of soda, and of subnitrate of mercury ; it separates in small 
 pearly plates of four and six sides, which may be dried between folds of 
 blotting paper, and have a fine silky lustre. 
 
 Chlorine Bodies of the Formyl Series. 
 
 By the action of chlorine on the chloride of acetyle, a heavy oily 
 liquid is obtained, having the formula C 2 H.C1. = Fo.Cl. If the action of 
 the chlorine be prolonged, more is taken up and the bichloride of formyl 
 produced, C 2 HC1 2 = Eo.Ck. If the chloride of methyl be acted on by 
 chlorine, there is formed from C 2 H 3 C1 a very volatile dense liquid, 
 having the formula C 2 H 2 C1 2 , which corresponds to the chlore-etherene 
 of the other series, being PoCl -f HC1. If there be an excess of 
 chlorine, all these bodies are converted into the perchloride of formyle 
 or chloroform, which shall be immediately described. 
 
 When chlorine is made to act on the gaseous methylic ether, muriatic 
 acid gas is disengaged and a liquid compound obtained of a very irritat- 
 ing odour. Its formula C 2 H 2 C10. The further action of chlorine 
 produces a different body with the composition C 2 HC1 2 .O., and finally 
 by an excess of chlorine all hydrogen is removed, and the body C 2 C1 3 O 
 is generated; this is a liquid of a penetrating odour ; it boils at 212. 
 
 These several bodies may be considered as still representing the 
 methylic ether, its radical methyl C2H 3 being more or less transformed 
 by substitution of chlorine for hydrogen, as described in general prin- 
 ciple in page 668, and this view is taken by most of the modern 
 chemists ; but on the other hand Berzelius considers them as oxychlo- 
 rides of formyl, and the latter body as oxychloride of carbon. The 
 former opinion appears to me very much the more simple, and more in 
 harmony with the history of the corresponding bodies of the series of 
 vinic alcohol ; and it is shown by the following example that this chlo- 
 romethylic ether acts likewise as a base, and unites with and perfectly 
 neutralizes acids. 
 
 If oxalate of methyl be acted on by chlorine, a volatile liquid is pro- 
 duced, which, when mixed with water, produces oxalic acid, muriatic 
 acid, and carbonic oxide. Its formula is C 2 3 + C 2 HC1 2 O. = C 2 3 
 and C 2 2 with H 2 C1 2 . "With benzomethylic ether chlorine produces a 
 similar body, Bz.O + C2HC1 2 0., and the acetate of methyl gives 
 
 Ac0 3 + cjaciyO. 
 
 In all these cases we may also regard the acid as united with oxy- 
 chloride of formyl, but inorganic chemistry furnishes no example of 
 such a kind of combination. 
 
Preparation and uses of Chloroform. 833 
 
 Chloroform and its Analogues. 
 
 Chloroform, the perchloride of formyl. C 2 HC1 3 or Fo.Cl 3 has been 
 already noticed as the final product of a great variety of reactions in 
 which chlorine is engaged, with pyroxylic spirit and methylic ether, and 
 from ordinary alcohol ; for it is found that the acetyl, when strongly 
 acted on by chlorine or by oxygen, splits itself into formyl, C 4 H 3 giving 
 S.C^H, and hydrogen being removed, whilst in such cases the radical is 
 usually carried to its highest degree of combination, formic acid or 
 chloroform being produced. A precise instance of this is the decom- 
 position of chloral by strong alcalies, CX'laO -f- 2. HO, giving C2HC1 3 . 
 -f CkHOg. Owing to these properties, the chloroform may be prepared 
 in many ways, but the following are the best adapted for practice. 
 
 One pound of chloride of lime, (see page 611,) is to be mixed well 
 with four pounds of water in a capacious retort, and then four ounces of 
 alcohol added. It is nearly immaterial whether common alcohol, or 
 pyroxylic spirit, or pyroacetic spirit be used, but ordinary alcohol 
 appears to deliver usually a more satisfactory produce. The mixture is 
 to be distilled with a moderate heat into a well refrigerated receiver. 
 On mixing the distillate with water, a heavy oil subsides, which, being 
 separated by a funnel, is to be purified by distillation over some oil of 
 vitriol in a water bath. In this reaction it is pretty certain that the 
 alcohol is converted into chloral by the chlorine of the hypochlorite of 
 lime, and the chloral then decomposed by the lime into chloroform and 
 formic acid, which latter, with the excess of hypochlorite of lime, is 
 resolved into carbonic acid, water and chloride of calcium. 
 
 The chloroform is a colourless liquid, of a dense oily consistence, sp. 
 gr. 1*480. It boils at 142. By an alcoholic solution of potash, it is 
 converted into formic and muriatic acids, water being decomposed. By 
 a red heat it is converted into muriatic acid and chloride of carbon ; 
 acted on by chlorine, it gives chloride of carbon, C 2 C1 4 . 
 
 The chloroform has recently assumed very great importance as a 
 medicinal agent, from its being found to possess, on its vapour being 
 respired, narcotic or anesthetic powers even greater than those of sul- 
 phuric ether, (page 780.) If a sponge or handkerchief, moistened with 
 chloroform, be held under the mouth and nose, so that the inspired 
 air shah 1 , become mixed with a large proportion of the chloroform 
 vapour, total insensibility supervenes after a few minutes, and the 
 person can be kept thus narcotized for an indefinite time by arranging 
 that he shall breathe an atmosphere containing a proper proportion of 
 gaseous chloroform. On some temperaments, however, the action is 
 much more intense, and cases of death have occurred from the incautious 
 use of this material, which, however, when skilfully employed, has 
 
834 lodoform. Phene. Retinol. 
 
 enabled the most painful operations to be performed without the patient 
 being at all conscious of what was done. 
 
 The Perbromide of Formyl. C 2 HBr 3 or Po.Br 3 is prepared precisely 
 as the perchloride, which it closely resembles in properties. 
 
 The Persulphuret of formyl, C 2 HS 3 . is obtained by heating the perio- 
 dide with sulphuret of mercury. It is a yellow liquid, very dense, and 
 resolved by alcalies into formiate of potash and sulphuret of potassium. 
 
 Periodide of Formyl lodoform. Fo.I 3 . Is produced by adding 
 caustic potash to a solution of iodine in alcohol, until it is completely 
 decolororized, but avoiding an excess of alcali ; on then evaporating, 
 the iodoform is deposited in brilliant gold-coloured plates ; it is in- 
 soluble in water, but very soluble in alcohol and ether ; it volatilizes .at 
 218 ; with potash it gives iodide of potassium and formiate of potash. 
 There exist also bromides, cyanides, and sulphurets of formyl, which do 
 not require notice. 
 
 A substance which occurs accidentally among the formyl bodies, but is 
 not connected with them, furfurol, will be described when speaking of 
 the artificial preparation of organic alcaloids. 
 
 Products of the Distillation of Oil and Resin. 
 
 In preparing olefiant gas for the purposes of illumination, by the 
 destructive distillation of resin, a number of substances, some solid, 
 others liquid, are produced, which have been examined by Pelletier and 
 Walter. Those not already described are as follows : Retisteren, a 
 white crystalline solid, which melts at 152 and boils at 617. In its 
 properties it resembles napthaline ; its formula is C 32 Hi 4 . Retinol is a 
 colourless liquid, tasteless and inodorous ; specific gravity = 0'9 ; it 
 boils at 460 ; its formula is C 32 Hj6, being isomeric with benzin ; the 
 specific gravity of its vapour is 7*25. Retinaptha is a colourless 
 liquid, of an agreeable odour; its specific gravity is 0'86 ; it boils at 
 226 ; its formula is C J4 H 8 . Retinyl, also a liquid, boils at 300 ; it 
 consists of C, 8 Hi2, being polymeric with mesitylene. 
 
 When the gas, obtained by the destructive distillation of oil, is 
 strongly compressed, a liquid separates, which was found by Earaday to 
 contain three distinct substances. Of these the most abundant is 
 the benzin or phene, described (page 84 -2), and produced in the decom- 
 position of benzoic acid. Of the others, one is known as Faraday's 
 quadricarburet of hydrogen ; it is also formed abundantly in the distil- 
 lation of caoutchouc; its specific gravity is 0*627 ; it boils below 32; 
 it combines with chlorine, forming a heavy oil ; it is isomeric with 
 olefiant gas, its formula being C 4 H 4 and the specific of its vapour is 
 double that of the gas, being V962. The third liquid boils at 183. 
 Its formula is probably C 6 H 4 , being isomeric with mesitylene and retinyl. 
 
Constituents of Wood Tar. 835 
 
 Constituents of Wood Tar Kreosote PittaJcal. 
 
 During an elaborate examination of the nature of the tar produced 
 from the destructive distillation of wood, Beichenbach described a 
 number of bodies, of which one, kreosote, has become of much 
 interest, from its remarkable qualities ; but the others are still very 
 little known. 
 
 For the preparation of Tcreosote, the tar is rectified by successive dis- 
 tillations, until the oil which passes over becomes heavier than water, 
 and is then digested with a solution of caustic potash, which dissolves the 
 kreosote ; when this liquor is exposed to the air, it becomes brown, and 
 being then neutralized by an acid, the kreosote separates. This process 
 of solution in an alcaline liquor and precipitation by an acid, is to be 
 repeated until the solution is no longer browned by exposure to the air ; 
 the kreosote is then pure. It is an oily colourless liquid, with a pene- 
 trating odour of smoke ; its taste is sharp and burning ; its specific 
 gravity is T037 ; it boils at 400 ; it burns with a strong smoky flame; 
 with water it unites in two ways, 100 parts of water dissolve 1'25 of 
 kreosote, and TOO parts of kreosote take up ten of water; the solution 
 is quite neutral ; kreosote mixes with ether, alcohol, and acetic acid in 
 all proportions. It unites with alcalies and with acids, but without 
 appearing to form any definite compounds, and it is not certain that it 
 has ever been obtained really pure. The formula assigned to it is 
 
 C )4 HA. 
 
 The most remarkable property of kreosote is, that it coagulates 
 albumen and the colouring matter of the blood, and these bodies are 
 then no longer susceptible of putrefaction. Fibrine, or muscular flesh 
 immersed in a solution of kreosote for some minutes, has no tendency 
 to putrefy, even if exposed to the heat of the sun afterwards ; from 
 this is its name derived, (xgeu$ <rww). Kreosote is the antiseptic prin- 
 ciple in pyroligneous acid, and in turf or wood smoke. If placed on 
 the tongue, it makes a white mark, with violent pain. Its use as a 
 caustic remedy for toothache is well known. 
 
 Kapnomor accompanies kreosote in tar ; it is a colourless liquid ; it 
 smells like rum ; with oil of vitriol it forms a purple solution : it boils 
 at 360. Picamor is also liquid; it boils at 518; it combines with 
 bases. Cedrirct crystallizes in fine red needles, insoluble in all liquids, 
 except oil of vitriol, and kreosote, the former producing a blue, and 
 the latter a purple solution. Pi&akal forms a dark blue solid mass, 
 which, when rubbed, assumes a golden lustre ; it contains nitrogen ; 
 it is insoluble in water, but dissolves in acids, and is thrown down again 
 
836 Products of the Distillation of Coal. 
 
 by alcalies. With metallic salts, its solution gives blue precipitates, 
 which may be attached by mordants upon woollen and cotton cloths. 
 The constitution of these bodies has not been examined. 
 
 SECTION III. 
 
 PRODUCTS OF THE DISTILLATION OF COAL. 
 
 Organic bases of Coal Tar Naptkaline and Aniline. 
 
 The products of the distillation of coal in close vessels, possess a 
 remarkable analogy to those that have been now described, and, indeed, 
 in many instances, are identical with them. Thus the gaseous products 
 are, marsh gas, olefiant gas, and carbonic acid. The liquid products 
 consist of various bodies closely analogous to petroleum, and the solids 
 consist of napthaline and paraffine. The relative proportions of these 
 products vary with the temperature. The lower the heat employed, 
 the less gas, and the more solids and liquids are produced ; the higher 
 the temperature, the greater is the quantity of carburetted hydrogen ; 
 but for the purposes to which the practical process is applied, the tem- 
 perature must not be raised too high, for then the gas evolved would 
 be mostly marsh gas and pure hydrogen, which possess little illuminat- 
 ing power, whilst a great deal of illuminating power may be derived 
 from the vapours of some highly volatile liquid products. In the 
 manufacture of coal gas for the purpose of illumination, the object is, 
 therefore, to maintain a temperature too high for the production of 
 napthaline and paraffine, but not high enough to produce hydrogen or 
 marsh gas, and thus obtain the greatest possible quantity of a gaseous 
 product of olefiant gas, and vapours of liquid carbo-hydrogens. 
 
 Prom the albuminous constituents of the wood, coal always contains 
 a certain, though small quantity of nitrogen; and hence ammonia is 
 evolved in its distillation. The gas liquor so obtained is extensively 
 used in the manufacture of sal-ammoniac. From the sulphates existing 
 in the plants, or in water which has filtered through the bed of coal, or 
 from iron pyrites, which is generally associated abundantly with the 
 rocks of the coal formation (p. 616), a small quantity of sulphur always 
 exists in coal, which is evolved during the distillation as sulphuretted 
 hydrogen, and requires to be carefully separated from the other gases, 
 which is effected by washing them with the milk of lime, which absorbs 
 also the carbonic acid. The apparatus used for making coal gas, does 
 not differ in principle, although very much in arrangement, from that 
 figured in p. 824. The ammoniacal liquor and the tar are collected 
 in the tubs, and the gas, in place of being burned at the orifice of the 
 
Of Napthaline and its Derivatives. 837 
 
 tube s, is conducted to the purifiers, and thence to the gasometers for 
 use. 
 
 Many of the substances produced in this process have been already- 
 noticed. But there remains now to describe the properties of some 
 others which are important, as well from the uses to which they have 
 been applied, as from the remarkable light which their properties and 
 composition have thrown upon some of the most interesting questions 
 in the philosophy of organic chemistry. 
 
 Of Napthaline and its Derivatives* 
 
 This substance is a very usual product of the decomposition of 
 organic substances by heat ; it is obtained abundantly by rectifying 
 coal-gas tar ; it crystallizes in white silvery plates ; its specific gravity 
 is 1-048 ; it melts at 136, and boils at 413, but sublimes rapidly at 
 much lower temperatures ; it burns with a strong smoky flame ; its 
 smell is powerful and very peculiar ; it is insoluble in water, but abun- 
 dantly soluble in ether, alcohol, and oils ; its formula is CaoHg ; the 
 specific gravity of its vapour is 4488. It is remarkable for the 
 number of compounds to which it gives rise, and which more 
 than any other series of bodies have illustrated the necessity of 
 admitting in organic chemistry, some more extended principle 
 than that of binary electro-chemical combination, which had so long 
 sufficed for the explanation of the phenomena of inorganic che- 
 mistry. Accordingly, in discussing the constitution of the bodies 
 derived from napthaline, I shall of necessity adopt the views and 
 nomenclature of Laurent who discovered them, and taking the nap- 
 thaline C2oH 8 as a type, endeavour briefly, to trace the replacements 
 and modifications to which it is subject. Laurent's nomenclature, 
 and the principles of replacement in organic types, have been already 
 described in pages 202, 326, and 668. 
 
 Napthaline combines directly with chlorine, forming two chlorides, 
 one C 20 H 8 C1 4 , solid and crystalline, the other a dense oily liquid C 2 oH 8 Cl 2 . 
 If the latter be heated with an alcoholic solution of potash, an atom 
 of muriatic acid is removed, and chlornapthase C2oH 7 Cl formed. It 
 is however, from the decomposition of the perchloride, that the most 
 remarkable products of this chlorine series are produced. 
 
 When this solid chloride, C 20 H 8 C1 4 , is distilled, or is decomposed by 
 an alcoholic solution of potash, a body is produced having the formula 
 C 2 oH 6 Cl 2 by the loss of 2.HC1; but this product though constant in 
 composition, is not so in properties, and in fact this chtornapthese as 
 
838 Constitution of Chlornapthese. 
 
 it is termed, appears to exist in at least seven different isomeric states, 
 of which one is produced as well by distillation, as by potash, three 
 are formed only by distillation, two only by decomposition with potash, 
 and the seventh is generated by the action of chlorine on a body termed 
 nitronapthase. Five of these isomeric bodies are solid, but are distin- 
 guished by differences in their melting points, in their crystalline forms, 
 and in the products of their decomposition. Two are liquid, but are 
 quite different in densities, and in boiling points. 
 
 In order to afford any satisfactory explanation of these remarkable 
 facts, it is necessary to refer to what has been described in page 820, 
 where the isomerism of organic compounds was explained, by showing 
 that they possessed different rational formuloe, as in the case of the 
 acetate of methyl, and in the formiate of ethyl, or that they had 
 different equivalent masses, as in the cyanic and cyanuric acids. This 
 mode of explanation requires to be materially extended, in order to 
 embrace the class of bodies with which we are now occupied, and as 
 there is no reason for supposing, that the different forms of chlornap- 
 these admit of any dissection into compounds of different radicals, or 
 that the equivalent number of their molecule is not in all the same, 
 we must admit that not merely the amount of replacement of one 
 element by another can alter the chemical nature of an organic body, 
 but that the place of the substitution in the complex group of which 
 the equivalent consists, will also determine the properties of the body, 
 so that the same amount of one element, entering into the place of a 
 corresponding proportion of another, will yet produce totally different 
 substances, according to the place in the molecular group in which the 
 substitution takes place. Thus there is in the molecule of napthaline, 
 united to twenty equivalents of carbon, eight equivalents of hydrogen ; 
 Chlornapthese is formed by substituting two equivalents of chlorine for 
 two of hydrogen ; but for which two ? if it were indifferent, the product 
 should evidently be always the same ; but it is not so, and hence a 
 different new body is formed, an isomeric chlornaiithese, according to 
 the two atoms of hydrogen which are replaced. Thus marking the 
 atoms of hydrogen with the letters of the alphabet. If H a II b are 
 replaced, there is product A. If, H c H d , product B. If H e H f , pro- 
 duct C. If H g H h , product D. But also the replacement of H a H c 
 should give product E. If H a H d , product E, and so on. Also, if 
 H b H c still a different product, and finally as many different isomeric 
 forms of cklornapthese should be produced, all with the formula 
 C 20 H 6 C1 2 , as there are possible combinations of two equivalents of 
 hydrogen out of the eight which the molecule of napthaline contains, 
 hence there may evidently exist not merely the seven forms of chlor- 
 
.Derivatives of Napthaline. 839 
 
 naptbese already discovered, but twenty-one more, as tbe number of 
 possible combinations is twenty-eight. 
 
 By the still furtber action of chlorine, a body termed chlornapthise 
 is formed : its formula is C 2 oH 5 Cl3. There are six isomeric modifica- 
 tions of it known. The other more remarkable chlorine bodies of this 
 series are 
 
 Chlornapthose C2oH4Cl4. Four isomeric forms. 
 
 Chlornapthuse 
 
 Chlornapthalase 
 
 Chlornapthalise 
 
 Chloride of Chlornapthase C2oH7Cl + CU. 
 
 Chloride of Chloraapthese CsoHeCla -f Cl4. 
 
 Bromine acting on napthaline gives rise to a series of bodies not so 
 extended as those of chlorine, but still so analogous as to render any 
 detailed description unnecessary. Further, by acting with chlorine on 
 the bromine compounds, or by bromine on the chlorine bodies, another 
 series is brought into existence, in which the hydrogen of the naptha- 
 line is replaced partly by bromine and partly by chlorine, and as the 
 molecular place of the atoms so replaced may be different according to 
 the principle already described ; a great number of isomeric forms are 
 in most instances generated. Thus the same formula, C2oH 4 Cl 3 Br. 
 applies equally to what may be expressed as 
 
 Chlori-Bromnapthose C20H4BrCl3. 
 
 a. Broma-Chlornapthose C2oH4Cl3Br. 
 
 b. Broma-Chlornapthose C2oCl3BrH4. 
 
 Products of the Oxidation of Napthaline. 
 
 When napthaline is dissolved in nitric acid, it deposits on cooling a 
 body in long sulphur yellow prisms, which consist of C 2 oH 7 NO4. It is 
 termed nitronapthase. If the action of the nitric acid be prolonged 
 two other bodies are formed, nitronapthese, C 20 H 6 + 2N0 4 , and nitro- 
 napthise, C^Hs -f- 3N0 4 . These are solids, which crystallize, they are 
 insoluble in water but dissolve in alcohol, by which they may be puri- 
 fied and separated. If nitronapthase be heated with a great excess of 
 lime, a body sublimes which crystallizes in long needles, strikes a rich 
 blue colour with oil of vitriol, and has the formula C 2 oH 7 O. This is 
 the napthalase, so closely resembling pyroxanthine, described in p. 826. 
 On boiling any of the above nitrous acid bodies with alcoholic solution 
 of potash, brown bodies are produced possessing acid properties, and 
 somewhat analogous to humus or ulmine, but their nature is not yet 
 well known. 
 
840 Derivatives of Napthaline. 
 
 By the action of nitric acid on the chlorine compounds of napthaline, 
 a number of bodies are generated, such as 
 
 Oxide of chloroxenapthose = C2oH4Cl2O2 + 62. 
 Chloronapthesic acid = C2oH 5 ClO2 + 04. 
 
 Chloroxenapthalesic acid = C20HC15O2 + O4. 
 
 Nathalie acid. C 16 H 4 O 6 + 2.HO. When chloride of napthaline 
 is boiled with nitric acid all chlorine is removed ; and on cooling, the 
 liquor deposits the napthalic acid in brilliant plates. It is bibasic, and 
 forms easily crystallizable salts. If it be heated, it abandons water, 
 and the anhydrous acid sublimes in long delicate needles. If it be 
 distilled with lime, it is decomposed into carbonic acid, and the benzol 
 mphene, noticed p. 842. The Ci 6 H 6 O 8 giving 4C0 2 and C I2 H 6 . 
 
 There are two amide compounds derived from napthalic acid. Nap- 
 thalamide produced by acting on the anhydrous acid by ammonia, 
 C 16 H 4 6 and ]S T H 3 giving HO and C 16 H 6 6 N. Napthalimide \$ produced 
 by heating the napthalate of ammonia, C 16 H 4 6 + HO. NH40 when 
 4. HO separate, and C 16 H 5 N04 remain. 
 
 Prom the napthalic acid are also derived 
 
 Nitrapthalic acid = Ci 6 I-I 3 NO 10 + 2HO. 
 Chlorpthalic acid = Ci6HCl 3 4 . 
 
 by the agency of nitric acid or of chlorine. 
 
 Napthalidine. C 20 H 7 N. If nitronapthalase be decomposed by hy- 
 drosulphuret of ammonia, there is produced water, sulphur, and an 
 organic base, which forms colourless prisms, is soluble in alcohol and 
 ether, and forms neutral crystallizable salts with all the acids. If the ni- 
 tronapthalese be employed, the reaction is of the same kind, C 2 oH 6 N 2 O 8 , 
 producing with 8.HS. two atoms of semmaplhatidme, C 10 H 5 N. another 
 organic alcali, with 8.HO, and 8.S being set free. This last alcali forms 
 yellow prisms with metallic lustre, and gives neutral salts with acids. 
 
 Sulphuric Compounds of Napthaline. 
 
 The action of sulphuric acid on napthaline varies, as the acid is hy- 
 drated or anhydrous. In the latter case, sulphurous acid is evolved 
 and a series of products formed, which have been described by Berzelius 
 as follows : sulpho-napthaline S 2 iH 8 .S0 2 , crystallizes in white plates, 
 which melt below 212 to a colourless liquid ; sulpho-napthalid } C 24 H 10 . 
 S0 2 , is a snow-white powder, which may be separated from the former 
 by means of its insolubility in cold alcohol. In addition to these bodies 
 there are formed two acids, the sulpho -napthalic and the sulpJio-napthic ; 
 they are isolated by taking advantage of the insolubility of the barytes- 
 
Constituents of Coal Gas Tar. 841 
 
 salt of the latter in alcohol, and then by decomposing the barytes-salts 
 by dilute sulphuric acid, these organic acids may be obtained crystal- 
 lized. The sulpho-napthic acid forms soft crystalline scales, of a soapy 
 feel, like talc, which taste bitter and sour. Its formula is C 22 H 9 S4O 12 -f- 
 2Aq. ; it combines with two atoms of fixed base. . The sulpho-nap- 
 tJialic acid forms a hard crystalline mass, which is acid and bitter, 
 inodorous, fusible below 212; it is very deliquescent; its formula is 
 C 20 H g S 2 5 . The salts of these acids are all soluble in water. There 
 is still another acid product, termed by Berzelius sul/pho-glucic acid, 
 the constitution of which is not known. 
 
 Notwithstanding that few subjects have been so often investigated as 
 the history of napthaline and its derivatives, there are few bodies whose 
 theory is more obscure. It would appear that all its hydrogen, or at 
 least six atoms of it, are capable of replacement by chlorine or nitrous 
 acid, and there does not exist any distinct character by which the 
 existence of a compound radical, either primitive or derived, as a basis 
 of these combinations, could with reason be assumed. The hypothesis 
 of Marignac is, that napthaline itself is a compound of two carbo- 
 hydrogens, C 16 H 4 -f C 4 H4, by the diverse action of re-agents upon 
 which the various bodies may be derived, but tin's idea does not afford 
 sufficient advantages to justify its adoption. 
 
 Paranapthaline. Anthracene. This substance is associated with 
 napthaline in the gas tar, and is isomeric with it, its formula being 
 C3oH 12 ; it differs in its fusing and boiling points, which are very much 
 higher ; it may be distilled unaltered ; it is insoluble in water, very 
 sparingly soluble in alcohol or ether, but copiously so in oil of turpen- 
 tine ; its relations to other bodies are not well known ; with nitric acid 
 it produces a colourless crystalline body, the anthracenuse, having 
 the formula C3oH 7 O 5 . when the action of the acid is complete, 
 but previously a series of azotized compounds is generated, in 
 which the hydrogen of the anthracene is more or less replaced by 
 nitrous acid. It produces also chloranthracenese, of which the formula 
 is C3oHi Cl 2 . 
 
 Chrysene C 12 H 4 . %&&pyrene C 10 H 2 are found associated with anthra- 
 cene in coal tar. The former is a yellow, the latter a white crystalline 
 solid. They form azotized compounds by nitric acid, analogous to those 
 of anthracene. 
 
 Ampeline and ampelic acid have been obtained by distilling bituminous 
 schist. They are not important. 
 
842 Sources and Properties of Phene. 
 
 Constitution of Coal NaptJia and Tar. 
 PJienyl Series Aniline and Organic Bases. 
 
 The investigations of Range and of Laurent have demonstrated 
 among the constituents of coal gas tar, the existence of several bodies 
 of very great interest, from the varieties of compounds which they 
 form, and the light their history has shed upon the theory of the con- 
 stitution of the organic alcalies and other series of organic bodies. The 
 radical of this class of substances is assumed to have the formula 
 C 12 Hg, and is termed Phenyl. Its symbol is Ph. 
 
 The first body of this series which deserves notice is the carbo- 
 hydrogen, C 12 H 6 = Ph.H. It is termed Phene or Benzol, as it was 
 originally discovered as a product of the distillation of Benzoic acid 
 with lime, and is most usually prepared in that way. It was discovered 
 by Faraday to be a constituent of gas tar. When prepared from 
 Benzoic acid, this loses the elements of two atoms of carbonic acid, 
 Ci 4 H 6 4 , producing C 2 4 and C 12 H 6 . This reaction will be again 
 referred to in the History of Benzoic Acid. 
 
 The Pkene, Benzol or Benzine, is a liquid of an agreeable odour ; 
 boils at 196; its sp. gr. 0.86; it freezes at 32. By the action of 
 re-agents, it produces a numerous class of products. Thus 
 
 Sulphobenzid. Ph.S0 2 . is formed from Phene and anhydrous sul- 
 phuric acid. It is a solid which crystallizes ; it fuses at 212, is volatile 
 and insoluble in water. 
 
 Sulphobenzidic Acid. C 12 H 5 S 2 5 = Ph.S0 2 + S0 3 . is formed by 
 dissolving the preceding body in oil of vitriol, or by acting on Phene 
 with fuming oil of vitriol. A liquor is obtained, from which the body 
 crystallizes in prisms by evaporation. It is a well defined acid, neutra- 
 lizes bases, and forms well characterized salts, of which the sulpho-benzi- 
 date of copper is remarkable for crystallizing in large regular prisms. 
 
 Nitrobenzid. C 12 H 5 N0 4 = Ph.N0 4 . By dissolving Phene in fuming 
 nitric acid by heat, this substance precipitates as the liquid cools. 
 It is a dense sweet heavy liquid, which boils at 415, and congeals at 
 38 to a mass of needley prisms. By hydrosulphuret of ammonium, it 
 is converted into the remarkable body aniline, which shall be hereafter 
 described, C 12 H 5 N0 4 and 6.HS. giving C 12 H 7 N and 4Aq with 6.S. By 
 an excess of nitric acid, the Phene is converted into a crystalline body 
 Binitrobenzid, Ci 2 H 4 N 2 Og, which, decomposed with hydrosulphuret of 
 ammonium, gives another base, nitroaniline C I2 H 6 N 2 4 . 
 
 Azobendid. C] 2 H 5 N = Ph.N. Is produced by dissolving nitrobenzid 
 in an alcoholic solution of potash, and distilling, the azobendid forms 
 large crystals, which fuse at 150, and boil at 375. 
 
Hydrate of Pheny 1. Carbolic Acid. 843 
 
 With chlorine, Phene unites directly to form a crystalline solid, 
 having the formula C 12 H 6 C] 6 , which, when distilled with lime, abandons 
 half its hydrogen and chlorine, and produces a dense oily liquid, having 
 the formula C 12 H 3 C1 3 , which is evidently Phene with the hydrogen half 
 replaced by chlorine. 
 
 Hydrate of Phenyl, Carbolic Acid. C 12 H 6 2 = Ph.O + Aq. 
 
 This body, originally discovered by Runge, is obtained by acting 
 with a solution of potash on those portions of the gas tar oil which dis- 
 til between 300 and 400 P. Prom the alcaline liquor so obtained, 
 the addition of an acid separates the carbolic acid as a dense oily liquid 
 which may be purified by rectification over some lime which separates 
 the traces of the mineral acid. The carbolic acid appears to exist in 
 two isomeric conditions, one solid and one liquid. As a liquid, its sp. 
 gr. is about T062. It boils at 361. Its odour is strong, and like 
 that of kreosote. As a solid, it crystallizes in prisms, which fuse at 
 95 ; when liquefied, it resembles the liquid form. This body neutra- 
 lizes bases, and forms definite salts, which are as yet little known. 
 Prom this character Eunge gave it its original name ; but that given by 
 Laurent to it as a member of the Phenyl Series, is more consonant to its 
 general history. The properties of carbolic acid are almost identical 
 with those of kreosote, see page 835, and the latter body is probably 
 either an impure form or a mixture of carbolic acid. 
 
 By the action of chlorine upon this Hydrate of Phenyl, a series of 
 chlorinized acids is produced, in wliich the hydrogen is replaced by 
 chlorine, either in part or in the final term wholly, so that a compound 
 results which consists of carbon, chlorine and oxygen, combined with 
 basic water. These chlorine acids are also remarkable for being pro- 
 duced by the action of chlorine on isatine a constituent of indigo ; and 
 it will be seen that in almost all cases the products of the decomposition 
 of the bodies derived from indigo, belong to the phenyl group. These 
 chlorine compounds have the formulse : 
 
 Chloro phenesic acid = Ci 2 H 3 Cl 2 O + HO - 
 Chloro phenisic acid = Ci2H 2 Cl3O -j- HO. 
 Chloro phenusic acid = C 12 ClsO .J. HO. 
 
 With bromine similar bodies are formed. 
 
 By acting on hydrate of phenyl with nitric acid there is formed 
 Nitrophenesic acid C 12 H 3 N 2 09 + HO, in which two atoms of the 
 hydrogen are replaced by two of nitrous acid. If the action of the 
 nitric acid be continued the product is converted into Ritropkenisic 
 
844 Picric Acid. Nitrophenisic Acid. Carbazotic Acid. 
 
 acid, in which three atoms of the hydrogen of thephenyl are replaced by 
 nitrous acid, and which is known as a product of the oxidation of many 
 organic bodies under the name of Picric acid. 
 
 Picric Acid. NitropJienisic Acid. Carbazotic Acid. Formula 
 C 12 H 2 N 3 13 + HO = C 12 H 2 (3.NOJ O + HO. 
 
 This acid which is of considerable theoretical and practical interest 
 may be obtained by the action of boiling strong nitric acid on the 
 hydrate of phenyl, on indigo, on salicine, on silk and other materials. 
 The theory of its formation from the hydrate of pho3nyl has been just 
 stated ; the cheapest process for preparing it is from indigo, and the 
 readiest is from salicine. 
 
 Indigo is to be gradually added in fine powder to hot nitric acid, 
 and the liquor gently boiled as long as red fumes are given off. On 
 cooling the picric acid crystallizes. These crystals are to be dissolved 
 in a boiling solution of potash, and precipitated by nitric acid, then 
 again crystallized from solution in water ; it is then pure. It forms 
 brilliant yellow crystalline scales, sparingly soluble in water, abun- 
 dantly in alcohol and ether. It fuses; but if suddenly heated, it 
 deflagrates. Its salts crystallize easily. Its potash salt is very 
 sparingly soluble, especially in alcohol, and the acid is hence very fre- 
 quently employed as a re-agent for that alcali. The picrates mostly ex- 
 plode when heated, often with a flash of light. The picrate of potash 
 is sometimes employed in medicine. 
 
 Oxypicric Acid, or Nitrostephnic Acid. 
 
 This body is produced by the oxidation of most resins and gum 
 resins by nitric acid. The greatest quantity is obtained from gum 
 ammonia or from assafoetida. The material, in small lumps, is to be 
 digested in hot nitric acid until it partially dissolves ; the action is very 
 violent, and much red fumes are given off. The mass is then boiled 
 until solution is complete. The liquor so obtained is to be nearly 
 neutralized by potash to separate resins^ and the oxypicrate of potash 
 crystallizes. Prom this the acid is precipitated by nitric acid, and it is 
 purified by repeated crystallizations. It is an orange red crystalline 
 powder, sparingly soluble in water, strongly acid. Heated gently it 
 sublimes, but if heated suddenly explodes. Its formula is given by 
 Erdman and Will as C 12 H 2 N 3 15 + HO. It therefore contains, like 
 picric acid, phenyl, in which three atoms of hydrogen are replaced by 
 
Aniline and its Derivatives. 845 
 
 nitrous acid ; but there are two more atoms of oxygen than in picric 
 acid, whence the name oxypicric acid. 
 
 Berzelius proposes to consider it as a bibasic acid, and its formula 
 to be C, 2 HN 3 Oj 4 + 2. HO. This idea would imply that it is picric acid, 
 in which an atom of hydrogen is replaced by one of oxygen. 
 
 Aniline, C 12 H 7 N = Ph. Ad. 
 
 This body, which is a true organic alcali, appears as a very usual pro- 
 duct of the decomposition of azotized organic bodies by heat or under 
 deoxidizing influences. It was consequently met with by several che- 
 mists before its true history was established, and was described under 
 various names, as Crystalline, Benzidam, Kyanol. Its true constitu- 
 tion appears to be amidide of plienyl to be, in fact, an ammonia in 
 which the third atom of hydrogen is replaced by the organic radical 
 phenyl. With such diversity of origin, it is evident that aniline may 
 be prepared in many ways. It is had in largest quantity by extraction 
 from the volatile oils of gas tar. 
 
 By mixing the tar oil with muriatic acid, the alcaline oils are dis- 
 solved out and are separated from the liquor by the addition of potash. 
 The oil which separates is to be distilled, and that portion which distils 
 at 360 contains the aniline. It is to be converted into oxalate; and 
 on this being recrystaUized, and then distilled with potash, the aniline 
 comes over pure. 
 
 Aniline is obtained from indigo by mixture with a strong solution of 
 caustic potash and distilling. In this reaction the isatine, the colouring 
 matter of indigo, the formula of which is C, 6 H 5 NO4, is decomposed, 
 and with the elements of four atoms of water, produces aniline, carbonic 
 acid, and hydrogen gas. Thus : 
 
 Isatine, . Ci6HsNO4 Aniline, . . Ci 2 H 7 N 
 
 Water, . H4 O 4 produce Carbonic Acid, . C 4 Os 
 
 Hydrogen, . . H 2 
 
 Ci 6 H 9 N0 8 
 
 
 
 The origin of aniline from nitro-benzid will be found noticed, 
 (page 853). Its formation from salicine, and its relations to the indigo 
 substances, will be noticed under the history of those substances. 
 
 It is a colourless oily liquid; sp. gr. 1020; boils at 360. It does 
 not affect litmus nor turmeric. It neutralizes acids, and forms salts, 
 which all crystallize. Its characteristic reaction is, to form with a solu- 
 
846 Derivatives of Aniline. 
 
 tion of hypo-chlorite of lime, a deep purple colour, which, however, 
 soon disappears. 
 
 So complete is the analogy of aniline to ammonia, that its salts, with 
 the simple organic acids, produce by heat a series of bodies analogous 
 to the organic amides, being formed by the loss of an atom of oxygen 
 from the acid, and of hydrogen from the base, which separate under 
 the form of water. Thus, the oxalate of aniline, C I2 H 7 N.HO 4- 
 C 2 3 , gives oxanilide C 12 H 6 N -f C 2 2 ; and also a body having the 
 formula C^HyNCfo ; which is resolved by bases into formic acid and 
 aniline. It is, therefore, formanilide, C, 2 H 6 N -f C 2 H0 2 . With 
 cyanic acid, aniline forms, like ammonia, an anomalous cyanate; and 
 the aniline urea has the formula C^H^jOg, 
 
 The salts of aniline, like those of ammonia, contain an atom of 
 water essential to their composition; and if the ammonium theory 
 were fully carried out, a similar quasi-metallic radical should be as- 
 sumed, and the salts of aniline written (Ci 2 H 8 N) + O. 
 
 By the action of chlorine and of nitric acid, there is formed from 
 aniline a very extensive series of bodies, of some of which the names 
 and formulae are here given, so far as will serve to show their general 
 constitution. 
 
 Chloraniline Ci 2 H 6 ClN. 
 
 Dichloraniline CigHsCbN. 
 
 Chlor. Brom.Aniline Ci2H 4 ClBrN. 
 Nitraniline 
 
 The hydrogen of aniline may be replaced in part by sulphur ; and 
 the remarkable feature of these bodies is, that the alcaline character of 
 the aniline is preserved throughout ; the type of the radical phenyl 
 being unaltered, although its chemical constitution may have been 
 totally subverted ; the hydrogen being replaced by chlorine or nitrous 
 acid. The rational formula is still that of an amide of phenyl ; and 
 all these complex bodies must be looked upon as analogous to their 
 archetype, ammonia, and like it, forming, with acids, salts which contain 
 an atom of water. 
 
 I 
 Piccoline Leucoline. 
 
 These bodies are also organic bases found in coal gas tar ; but their 
 history being generally analogous to that of aniline, does not require to 
 be given in such detail. They are easily separted from aniline by their 
 different volatility. 
 
Animal OHPetanine 847 
 
 Piccoline is an oily liquid, sp. gr. 0*955; it boils at 272. It does 
 not colour solution of hypochlorite of lime. Its salts are usually acid, 
 and do not crystallize well. It has a very strong and disagreeable 
 smell. It was found by Anderson, its discoverer, to be isomeric with 
 aniline ; its formula being Ci 2 H 7 N. 
 
 Leucoline. The existence of this body in gas tar was recognized by 
 Bunge ; but it was prepared pure by Gerhardt, as a product of the 
 distillation of quinine with potash, and named Quinoline. It may be 
 formed also from cinchonine and from strychnine. It is a heavy oily 
 liquid ; it boils at 460 ; its formula is C 18 H 8 N. Its salts do not crys- 
 tallize well ; they retain, like those of ammonia, an atom of water. 
 
 The Pyrol of Eunge has not been as yet accurately examined. 
 
 The history of these alcaline bases of artificial organic origin is of 
 peculiar interest in regard to the theory of the constitution of the 
 vegetable alcalies, as quinine and morphia, found naturally existing in 
 plants ; and I shall have occasion to refer again to the consideration of 
 their properties under that head. 
 
 Products of the Distillation of Animal Substances DippelVs Oil. 
 
 When animal substances, particularly bones, are subjected to destruc- 
 tive distillation, a large quantity of liquid ammoniacal products are 
 evolved, much permanent and foetid gases generated, and there are also 
 produced oily and tarry materials analogous to those obtained from 
 coal, but distinguished by their peculiarly foetid and penetrating odour. 
 Formerly this process was carried on for medicinal purposes. The solid 
 and liquid ammoniacal products, which are carbonate of ammonia, 
 partly dissolved in water, constituting the salt of hartshorne and the 
 spirit of hartshorne of the older Pharmacopoeias ; and the oily pro- 
 ducts, when rectified, constituted the oil of hartshorne, or DippelVs 
 animal oil, which was considered by the physicians of the middle ages 
 one of the most sovereign remedies. The distillation of animal bodies 
 is now only carried on as a means of manufacturing ivory black by dis- 
 tilling bones in cylinders of iron, with a condensing apparatus almost 
 identical with that described, page 824, for the distillation of wood. 
 The phosphate of lime and excess of carbon which remains constitutes 
 the bone black or ivory black ; and the bone oil is also sent into com- 
 merce. 
 
 This bone oil contains aniline and piccoline. It contains also a large 
 quantity of the other products of the distillation of coal ; but its most 
 characteristic ingredient is an organic alcali discovered by Anderson, 
 and named by him Petanine. 
 
848 Piccoline Petanine. 
 
 Petanine is a colourless mobile liquid, its odour like decaying apples. 
 It tastes hot and pungent. It boils at 175. It is lighter than water. 
 It is a very powerful base, restores reddened litmus, gives white fumes 
 with muriatic acid gas, and neutralizes the strongest acids. It dissolves 
 in water, alcohol, and oils. Its solution precipitates the salts of copper, 
 and an excess redissolves the precipitate, giving a rich blue colour. 
 The salts of petanine crystallize well. The formula of petanine is 
 C 8 H 10 N. ; and Anderson considers that it is related, as aniline is to 
 phene, to the carbo-hydrogen C 8 H 9 , produced in the decomposition of 
 valerianic acid by a galvanic circuit. 
 
 The odorine discovered by Unverdorben in animal oil, has been 
 shown to be piccoline, at least in great part ; and the other bodies, 
 animine and alinine, will probably receive their exact examination in 
 the researches by Anderson, of which the discovery of petanine was the 
 first result. 
 
 CHAPTER XXIII. 
 
 OF THE ESSENTIAL OILS, CAMPHORS AND IIESINS. 
 
 THE bodies now to be described constitute three groups, very closely 
 allied in composition, in properties and in origin. For the most part 
 they exist ready formed in plants, as secreted by their proper organs, 
 or they are derived by reactions of a very simple kind, from substances 
 so circumstanced. They are employed in medicine for their aromatic 
 and stimulant properties, and in the arts, for the manufacture of a 
 variety of perfumes, varnishes, lacquers, &c. 
 
 A. Of the Essential or Volatile Oils. 
 
 These oils are so named from their solubility in alcohol, such solu- 
 tions being called essences, and from their volatility. In virtue of this 
 last property they are generally obtained by the distillation of the 
 plants with water. If the oil were extracted by the distillation of the 
 dry plant, the heat would rise so high as to destroy its odour and alter 
 its composition ; but by using a large quantity of water, the mixed 
 
General Characters of Essential Oils. 849 
 
 vapours of the oil and water pass over at a much lower temperature, as 
 at 212; for although the boiling point of the oil may be 400, yet it 
 forms a quantity of vapour at 212, proportional to its tension at that 
 degree. (See p. 99). To prevent even the injurious heat, which 
 might arise from the plant touching the sides of the still, when fragrant 
 flowers or leaves are operated on, they are suspended in a cage in the 
 centre of the still, and allowed only to come into contact with the 
 vapours. These oils are somewhat soluble in water, and giving to it 
 their odour and taste, form the various medicated waters. Hence, 
 often the same quantity of water must be distilled with fresh quantities 
 of the plant, before the oil is in such proportion as to separate. 
 
 Many essential oils, as those of turpentine, lemon, peppermint, &c. 
 exist actually in the plant, as secretions from peculiar glands; but 
 others are produced only at the moment of distillation, by the decom- 
 position of substances which did exist in the plant, and which undergo 
 a kind of fermentation. This is the case with the oils of bitter almonds, 
 of spiro3a, of mustard, and these oils possess much more active che- 
 mical properties than those of the former class. Another important 
 difference among essential oils is, that some, by absorbing oxygen 
 directly, produce well characterized acids, as occurs in the oils of bitter 
 almonds, of cinnamon, and of cloves; whilst others, as the oils of 
 turpentine, citron, and copaiva; by a much more indirect action of 
 oxygen, give origin to resins. On these principles I will arrange the 
 oils in two classes, for convenience of description : 
 
 IST CLASS. OILS FORMING ACIDS, NOT PRE-EXISTING IN THE PLANT. 
 Of Amygdaline and Oil of Bitter Almonds. 
 
 All plants which yield prussic acid on distillation produce, at the 
 same time, a volatile oil, which is known as the oil of Utter almonds, 
 it being most abundantly obtained from that fruit. The leaves of the 
 cherry laurel, peach kernels, &c. also yield it. The oil and the acid 
 both arise from the decomposition of another substance, amygdaline. 
 This is prepared by bruising bitter almonds, and pressing them 
 strongly between plates of hot iron, to force out the fixed oil; the 
 residue is treated by alcohol of 93 per cent, and the solution evapo- 
 rated in a water bath to the consistence of a sirup ; this is then diluted 
 with water and a little yeast added, which, by inducing fermentation, 
 destroys a quantity of sugar. When this is over, the liquor is to be 
 again evaporated to a sirupy consistence, from which the amygdaline is 
 precipitated by the addition of cold strong alcohol, in which it is 
 54 
 
850 Amygdaline Its Decomposition. 
 
 scarcely soluble ; being dissolved in boiling alcohol, it is finally ob- 
 tained pure by crystallization. 
 
 The formula of amygdaline is C^E^NC^. ; it forms short silky 
 needles, which are anhydrous, tasteless, and inodorous; it is very 
 soluble in water, and crystallizes therefrom in large colourless prisms, 
 containing 6Aq. By contact with nitric acid it produces ammonia, 
 oil of bitter almonds, benzoic, and formic acids. 
 
 When amygdaline is acted on by caustic alcalies it is decomposed 
 into ammonia and amygdalic acid. C^H^C^ + Aq. the elements of 
 water being absorbed. This acid does not crystallize ; it forms soluble 
 salts; with oxidizing agents it produces oil of bitter almonds and. formic 
 acid. 
 
 When bruised, bitter almonds are distilled with water, all amygdaline 
 disappears, and a number of products, as prussic acid and volatile oil, 
 are evolved. Pure amygdaline may, however, be boiled in water with- 
 out being altered. It is the animo-vegetal principle which constitutes 
 the mass of the cotelydon of the almond that induces the reaction ; it 
 has been called emulsine or synaptase, and appears very similar in pro- 
 perties and constitution to the vegetable albumen or legumine, described 
 as the active principle in the alcoholic fermentation. (See p. 771). 
 The emulsine is soluble in water, but insoluble in alcohol. It is pre- 
 cipitated neither by acids nor by salts of lead. It coagulates by heat, 
 and by strong alcalies is decomposed into ammonia and a peculiar acid. 
 If solutions of 10 parts of amygdaline in 100 of water, and of 1 of 
 emulsine in 10 of water, be mixed, immediate decomposition occurs ; 
 the liquor becomes milky, smells of bitter almonds, it contains sugar, 
 prussic acid, formic acid, and volatile oil, and the emulsine coagulates. 
 It is most probable that the emulsine is itself also decomposed in this 
 reaction, but we may explain the origin of these bodies from the amyg- 
 daline alone, thus : 
 
 1 equiv. of prussic acid Cg HN -N 
 
 2 volatile oil C 2 8Hi2O 4 I = C^BfoNOs?, 
 
 1 ,, sugar CG H 5 O 5 > one equivalent 
 
 2 ,, formic acid 4 Hg OG I of amygdaline 
 7 water H? O7 J 
 
 In the cotelydon of the almond, the amygdaline and emulsine are in 
 distinct cells, and have no means of acting on each other, but when 
 bruised in water, both dissolve and decomposition immediately occurs. 
 The preparation of the oil, by distillation, can hence be fully under- 
 stood. 
 
 The mixture of amygdaline and emulsine has been employed as a 
 
Oil of Sifter Almonds. Benzyl. 851 
 
 means of producing a prussic acid of standard strength for medicinal 
 purposes, and it is owing to the decomposition of this principle that 
 the liquors distilled from the cherrylaurel leaves, peach kernels, etc., 
 contain the prussic acid. The quantity of prussic acid present in laurel 
 water may, however, be very variable, and a dilute prussic acid of de- 
 finite strength is much preferable for medicinal use. 
 
 Oil of Sitter Almonds Hydruret of Benzyl. 
 FormulaC 14 H 6 O 2 , or Bz.H = Eq. 106. 
 
 Prepared by distilling bruised bitter almonds with water. In this 
 rough state it contains a great quantity of prussic acid, from which it is 
 freed by distillation with some water, chloride of iron and lime. It is 
 then colourless, of a strong peculiar smell, sp. gr. 1*043 ; it boils at 
 356 ; when exposed to the air it absorbs oxygen, and forms crystals 
 of benzoic acid; when heated with hydrate of potash, hydrogen is 
 evolved, and benzoate of potash formed. The formula of this oil is 
 C H H 6 O 2 , but from the series of compounds to which it gives rise, it is 
 believed to contain an organic radical C 14 H 5 O 2 termed benzyl, and its 
 rational formula is, therefore, BzH. See p. 664. 
 
 Chloride of Benzyl. Bz.Cl. Is formed by acting on the hydruret 
 with chlorine. It is a liquid, heavier than water; it boils at 383; 
 when heated with water it gradually changes into benzoic and muriatic 
 acids. By heating chloride of benzyl with iodide of potassium, iodide 
 of benzyl is formed ; and by using the bromide, sulphuret, or cyanide 
 of potassium, compounds of benzyl with these electro-negative bodies 
 may be formed. 
 
 Amidide of Benzyl Benzamide. Bz.Ad. Is formed by acting on 
 chloride of benzyl with dry ammonia, 2(HAd) and Bz.Cl gives Bz.Ad 
 and AdH.HCl; it forms rhomboidal prisms, whch melt at 240 and 
 may be distilled unaltered ; heated with potash it gives ammonia and 
 benzoate of potash. 
 
 Oxideof Benzyl Benzoic Acid.- C 14 H 5 O 3 -f HO = BzO + Aq. Eq. 
 122. This acid is found ready formed in the resin of benzoin and in 
 dragon's blood ; it sometimes appears in the urine of herbivorous ani- 
 mals, in place of hippuric acid, and is formed by the oxidation of oil 
 of bitter almonds, and of amygdaline. 
 
 The following process for obtaining it pure was devised at the same 
 time by Mohr and Hennell; 1 Ib. of benzoin resin, in powder, is to be 
 spread on the bottom of a metal dish, eight or nine inches diameter, 
 and two inches deep, which is to be covered with a drum of blotting 
 
S52 Benzole Acid Benzoates. 
 
 paper, pasted to the edge of the dish ; the whole is to be covered with 
 a cylindrical cap of stout packing paper. To render the heat uniform, 
 the dish is to be placed on a metal plate, covered with sand, resting on 
 a furnace ; heat being cautiously applied, for three or four hours, the 
 cap is found full of splendid crystals of benzoic acid ; the empyreu- 
 matic oil, which usually contaminates the sublimed product, being ar- 
 rested by the drum of blotting paper, through which the vapour of the 
 acid passes freely. 
 
 It may be also extracted from the resins by boiling these with lime ; 
 a soluble benzoate of lime is produced, from which the benzoic acid is 
 precipitated by the addition of muriatic acid ; it is then to be dissolved 
 in boiling water, and allowed to crystallize by cooling slowly. 
 
 Benzoic acid crystallizes in hexagonal needles ; when pure it is ino- 
 dorous ; it reddens litmus feebly ; melts at 248 ; the fused acid boils 
 first at 462, but it sublimes freely at 293 ; it dissolves in 25 parts; 
 of boiling water, but requires 200 parts of cold water for its solution; 
 it is soluble in twice its weight of alcohol or ether ; it forms a very ex- 
 tensive series of salts, of which few require special notice. 
 
 Benzoate of Lime. CaO.BzO + Aq. Crystallizes in brilliant prisms ; 
 at a dull red heat, it is decomposed into carbonate of lime and benzone, 
 the formula of which is Ci 3 H 5 O. Another liquid, benzin, or benzole, 
 Ci 2 H 6 , is at the same time formed by virtue of a much more complex 
 process, napthaline, carbonic acid, and carbonic oxide being evolved. 
 
 Benzoate of Ammonia. AdH. 2 .O.BzO, crystallizes in brilliant plates. 
 This salt is employed in mineral analysis, to separate iron from manga- 
 nese ; a solution of protoxide of iron, not containing any excess of acid, 
 being completely precipitated by neutral benzoate of ammonia, whilst 
 the salts of manganese are not affected by it. 
 
 Benzoate of Silo er. AgO.BzO. Obtained by double decomposition, 
 crystallizes from a boiling solution, on cooling, in brilliant colourless 
 needles. 
 
 Formo-benzoic Acid. HBz -f Fo.0 3 . If water, saturated with the 
 impure oil of bitter almonds, be mixed with muriatic acid and evapo- 
 rated, this substance crystallizes. The prussic acid is decomposed into 
 formic acid and ammonia (p. 738), and the nascent formic acid com- 
 bines with the hydruret of benzyl ; in this body, all the saturating power 
 of the formic acid is preserved. 
 
 If a current of chlorine be passed through a solution of impure oil 
 of bitter almonds in water, a similar body is formed, consisting of ben- 
 zoic acid and hydruret of benzyl. Bz.H + BzO. This will be again 
 referred to as an acid of a peculiar radical stilbene, and called stilbous 
 acid. C 28 H 12 O 5 . 
 
Complex Bcnzoic Compounds. 853 
 
 Hypo-sulpho-benzoic Acid. C 14 H 8 3 -f- S 2 O 5 -f- 2Aq. This body is 
 formed by the action of dry sulphuric acid on benzoic acid. A viscid 
 mass results which, when neutralized by barytes, yields a salt perma- 
 nent in the air, crystallizing in rhomboidal prisms, and having the for- 
 mula C 14 H 5 3 + S 2 O 5 4- 2BaO -f- 3Aq. From this the pure acid may 
 be obtained ; it is decomposed if its solution be boiled, but when eva- 
 porated in vacuo it crystallizes. The sulpho-benzoate of copper crys- 
 tallizes in large rhombs of a rich blue colour. 
 
 Bromo-benzoic Acid. C 28 H 9 Br0 8 -f- 2Aq. Is formed when benzoate 
 of silver is decomposed by bromine. It is a crystalline solid, very 
 soluble in water, fuses at 212 and sublimes at 482; its salts are all 
 soluble and contain two atoms of base. 
 
 Of the liquids produced by the distillation of benzoate of lime, 
 lenzone, C 13 H 5 O does not form any compounds. It is a heavy oily 
 liquid, decomposed by chlorine, but not by alcaldes. It is produced by 
 the abstraction of an atom of carbonic acid from benzoic acid, or may 
 be regarded as a compound of carbonic oxide, with the following body, 
 benzin or pkene. C 12 H 6 which produces with sulphuric acid, nitric acid, 
 and chlorine, a series of bodies, of which the formula alone need be 
 here given, they are, as described by Mitscherlish, their discoverer 
 
 Sulpho-benzide C] 2 H5SO 2 Chlor-benzin C 12 H 6 Cl6 
 
 Sulpho-benzidic acid Ci2H 5 S 2 O 5 Chlor-benzid Ci 2 H 3 Cl3 
 Nitro-benzide CuHsNO* Azo-benzid Ci2HsN 
 
 I have had occasion to refer to benzin as a product of the distilla- 
 tion of resin and coal. It is colourless, of an agreeable ethereal odour ; 
 it boils at 187; its specific gravity 0*85 ; that of its vapour is 2378 ; 
 at 32 it freezes into a crystalline mass which melts first at 43 It 
 has latterly assumed much theoretical importance as the basis of a series 
 of very numerous derivatives, including picric acid and aniline. It 
 has been recently termed phene, and its radical C 12 H 5 phenyl. The 
 above noticed bodies may therefore be looked upon as compounds of 
 phenyl. See p. 842. 
 
 Oil of Utter Almonds with Ammonia. By the action of water of 
 ammonia on hydruret of benzyl, all oxygen is removed, and a crystal- 
 line body, hydro-benzamide, produced; its formula is C 42 H 18 N 2 . It is 
 soluble in alcohol, and by boiling the solution is decomposed into 
 ammonia and hydruret of benzyl. The nitrogen here enters into the 
 constitution of the radical, replacing the oxygen, and the body is 
 kydruret of azobenzyl (C 14 H 5 .|N) + H. This azobenzyl is itself also 
 formed in the same process as the former, and also the azobenzoilic 
 acid (C u H 5 .f N) + JN, which is benzoic acid, in which all oxygen is re^ 
 
854 Complex Benzyl Compounds. 
 
 placed by nitrogen. The origin of these bodies is explained by the 
 constitution of the radical benzyl, as described in p. 666. 
 
 Among the products of the action of ammonia on hydruret of benzyl 
 is one termed Amarine. It is an organic alcali, its composition, C 42 H 18 ]Sr, 
 being isomeric with the hydro-benzamide. It is dissolved by muriatic 
 acid, and precipitated by ammonia. It crystallizes in fine needles, and 
 forms with acids well defined neutral and cry stalliz able salts. By dis- 
 tilling hydro-benzamide, there is produced another organic base, termed 
 Lophine ; ammonia, and a volatile oil are given off. The mass in the 
 retort, after treatment with ether, is to be digested with muriatic acid, 
 which dissolves the lophine ; and on the addition of ammonia to the 
 liquid the lophine precipitates. It forms white silky crystals. Its 
 formula is C 46 H 16 N2. With hot nitric acid it gives an orange- coloured 
 body, Nitrt>loptyle 3 C 46 N" 5 H 13 0,2. The mass from which muriatic acid 
 dissolved the lophine contains Amarone, C^Hnl^. 
 
 The hydro-benzamide, when heated with caustic potash, gives 
 Benzostilbene, C 3l H. n 2y and Benzolone, C U H0 4 ., whilst ammonia is 
 given off. These bodies are both crystalline. 
 
 In the impure oil of bitter almonds, a substance exists, termed 
 lenzoine, which is isomeric with the oil, its formula being Ci4lI G 02 ; it 
 crystallizes in colourless prisms. By potash it gives benzoic acid and 
 hydrogen. By ammonia it forms a substance isomeric with kydro- 
 benzamide. By chlorine it gives muriatic acid, and in place of chloride 
 of benzyl, a crystalline body which is isomeric with that radical, its 
 formula being Ci4H 6 2 . This is termed benzoil. When heated with 
 potash it gives the benzoilic acid, which has the formula C28ll n 05+Aq. 
 
 By acting on oil of bitter almonds with a solution of sulphuret of 
 ammonium in alcohol, Laurent has obtained a series of bodies in which 
 the oxygen of the radical benzyl is replaced by sulphur, and in some 
 cases partly by azote. There should thus be sulpJio-benzyl (C 14 H 5 S2) 
 corresponding to the azobenzyl. It is unnecessary in an elementary 
 work to enumerate the individual substances ; but I look upon their 
 formation as corroborating very much Berzelius' idea, that the true 
 radical of the benzoic series, is the carbo-hydrogen Ci 4 H 5 , and that the 
 chloride, &c. of benzyl, are really oxy-chlorides, &c. (see p. 667). 
 Certainly, the element which remains truly constant in those reactions, 
 (and hence satisfies the definition of a radical, p. 666), is Ci 4 H 5 , and 
 not Ci 4 H 6 2 . 
 
 Stilbene. If the hydruret of sulphobenzyl be distilled, it gives sul- 
 phuretted hydrogen ; and by a higher temperature there sublimes a 
 body termed stilbene, which is looked upon by Laurent as the radical 
 of a great number of these complex benzoyl bodies. The stilbene 
 
Derivatives of Stilbene. 855 
 
 crystallizes from its solution in hot alcohol or ether, in colourless pearly 
 prisms, like the mineral stilbite. It melts at 230, and volatilizes at 
 568. Its formula is C 28 H 12 , being polymeric with benzin or phene, 
 C I2 H 6 . It forms a very extensive series of compounds, of which it 
 will suffice to give the names and formulae of the more important. 
 From stilbene, C 28 Hi 2 , there are 
 
 Chloride of Stilbene 
 Chlorstilbase 
 Nitrostilbase 
 
 Oxide of Stilbene, Benzoine 
 Azostilbene, Benzoinamide 
 Stilbous Acid, BzO -f BrH. 
 Stilbic Acid, Benzilic Acid 
 Nitrostilbic Acid 
 Chlorostilbic Acid 
 
 These are only examples of the range of bodies so formed. 
 
 Picryle, C4 2 H 15 N0 4 . Is also produced by acting on oil of bitter 
 almonds with hydro-sulphuret of ammonia. It is an organic base. It 
 crystallizes in colourless octohedrons, soluble in water. Its salts have 
 not been studied. 
 
 Oil of Cinnamon and the Derived Compounds. 
 
 Tins oil is found in the bark and flower buds of the laurus cinna- 
 momum and laurus cassia. It is heavier than water, and possesses the 
 odour of the plant in the highest degree. It boils at 428 ; its formula 
 is CijoHnO-j, and for distinction I shall term it the a oil. When exposed 
 to the air it absorbs oxygen, and forms another oil, which is that gene- 
 rally found in the shops, the oil, the formula of which is C ]8 H 8 2 . 
 Two resins, a and ft are at the same time produced. 
 
 r a. resn = 
 
 3 atoms of a oil =C6oH33O6 absorbing 7 \ (3. resin = Ci2H 5 O 
 
 6 atoms of oxygen = O 6 produce S ^ oil __ C]9 H 8 O 2 
 
 (. 5 atoms water HsOs 
 
 The j8 oil of cinnamon, although thus only a product of the decom- 
 position of the true oil, is very important from the variety of com- 
 pounds it gives rise to. It is heavier than water ; it dissolves in water 
 of potash or of barytes, a cinnamate of the base being formed, and an 
 oil lighter than water separating. 2.(Ci8H 8 2 ) and HO giving C l8 Hi O 2 
 and CisHrOs. The properties of this oil indicate that it contains an 
 
856 Compounds of Cinnamyl. 
 
 organic radical, cinnamyl, C J8 H 7 O 2 , united to hydrogen. It is hydruret 
 of cinnamyl, Ci.H, and the oil lighter than water, is Ci.H>. 
 
 Hydruret of cinnamyl combines directly with muriatic acid, with 
 nitric acid, and with ammonia, forming compounds which are solid and 
 crystalline. Their formula are CiH.HCl,CiH.HAd, and CiH.HO+NO 6 . 
 By chlorine one-half of the hydrogen of the j8 oil is removed, and a white 
 crystalline body formed, C 18 H 4 C1 4 O 2 . The chlorine here enters into the 
 constitution of the radical. 
 
 Oil of cinnamon combines with iodide of potassium and iodine to 
 form a substance which crystallizes in large needles of a brilliant bronze 
 colour, like permanganate of potash. Its formula is CiH.I 3 + K.I. 
 Once formed it is decomposed by water. It was discovered by Moore, 
 of Dublin, and analyzed by Apjohn. 
 
 Cinnamic Acid. Ci.O + Aq. May be abundantly obtained by the 
 action of potash on the alcoholic solutions of the class of bodies 
 termed balsams. It is also simply formed by exposing the hydruret of 
 cinnamyl to the air ; it absorbs two atoms of oxygen, and forms crys- 
 tallized cinnamic acid. It forms colourless groups of plates, of an 
 acid taste ; it is almost insoluble in water, but easily soluble in alcohol 
 and ether. It melts at 264, and distils over at 554 unchanged. Its 
 salts are exceedingly similar to the benzoates. 
 
 By the action of an excess of hot nitric acid, both oil of cinnamon 
 and cinnamic acid are converted into oil of bitter almonds and an acid 
 closely resembling the benzoic, but having the formula Ci 5 H 15 5 . With 
 cold nitric acid, cinnamic acid directly combines, forming the nitro- 
 cinnamic acid Ci.O + 
 
 Nature of the Balsams. 
 
 The origin of the Balsam of Peru is closely related to the oil of 
 cinnamon. It consists of resinous substances (the a and $ cinnamic 
 resins ?) and of an oil which may be obtained pure by distillation. It 
 is called cinnameine ; its formula is Ci 8 H 8 2 , being isomeric with the 
 j8 of oil of cinnamon. It is neutral ; but when its alcoholic solution 
 is boiled with potash, it forms cinnamate of potash ; or by simple 
 boiling of its alcoholic solution, cinnamic ether is produced, and another 
 oil, jperuvine, is separated, the formula of which is C 18 H 12 2 . In these 
 cases, three atoms of cinnameine and two of water produce two atoms 
 of dry cinnamic acid and one of peruvine. 
 
 These researches on the nature of this balsam are due to Fremy 
 but Richter has advanced that the balsam of Peru contains two oils, 
 
Constitution of Balsams. 857 
 
 which he terms myriospermine and myroxyline, the relation of which to 
 peruvine and cinnameine is not yet established. 
 
 The Balsam of Tolu. This substance yields like the former, cinna- 
 meine, but also benzoic acid, and a heavy oil isomeric with oil of bitter 
 almonds. By destructive distillation it yields a carbohydrogen, toluol 
 whose formula is C 14 H 8 ; the theoretical position of which is very inte- 
 resting, as it may be considered the true origin of the benzyl series, as 
 C 14 H 8 = Bz. H 3 ; and the different bodies of that series may be sup- 
 posed to be formed by the replacement in different ways of the three 
 atoms of hydrogen ; thus, Bz.H0 2 . Bz.H 3 . Bz.C10 2 etc., as the phene or 
 benzol has been described (p. 842). With nitric acid toluol forms a 
 compound nitrotoluol C 14 H 7 jSTO 4 . It is liquid. When heated with 
 lime the elements of carbonic acid are removed, and the very important 
 organic basis is formed, aniline t Ci 2 H 7 N, which has been already de- 
 scribed. If nitrotoluidine be decomposed by hydrosulphuret of ammo- 
 nia, sulphur is deposited, and a base toluidine formed, the composition 
 of which is C 14 H 9 K 
 
 The toluole forms further compounds with nitric acid, with chlorine, 
 and with sulphuric acid, in all of which, more or less, hydrogen is re- 
 placed by the other electro-negative elements. 
 
 The resin storax yields by distillation with water a volatile oil, a 
 carbo-hydrogen, C 16 H 8 . which may also be produced by the distillation 
 of the cinnamic acid, which from C 18 H 8 4 , yields C 16 H 8 and C 2 4 . This 
 styrol gradually changes, when heated, into a solid metastyrol. With 
 nitric acid, bromine, and chlorine, it forms a series of compounds in 
 which hydrogen is more or less replaced, and which determine its mole- 
 cule to be C 16 H 8 , while that of metastyrol appears to be C 14 H 7 . 
 
 The resin gnaiacum yields by distillation a volatile oil, having distinctly 
 acid properties. Its formula is CuHgO*, and it is supposed to be hy- 
 druret of guiacyl, C U H 7 O 4 -f- H. Another body obtained from the 
 resin is the guiacic acid, C 12 H 8 6 , and a neutral oil, guiacene, the for- 
 mula of which is C 10 H 8 O 2 . 
 
 Oil of Cloves, Eugenic Acid, fyc. 
 
 The oil obtained by distillation from the undeveloped flowerbuds of 
 the eugenia caryophyllata, is a mixture of several bodies. By the action 
 of potash it is separated into a volatile oil which does not possess active 
 properties, is lighter than water, and consists of C 10 H 8 , whilst an 
 eugenate of potash dissolves. Prom this solution the eugenic acid is 
 precipitated by any strong acid. 
 
858 Oil of Cloves Oil of 8p*r$* Salicyl. 
 
 Eugenic Acid. Heavy Oil of Cloves. C 24 H 15 O 5 . Is a colourless 
 oil, sp. gr. 1*079; it boils at 470; its taste and smell are those of 
 cloves. It forms with the metallic oxides well defined salts, most of 
 which are soluble and crystallizable. 
 
 "When the common oil of cloves is kept for some time, it deposits a 
 crystalline substance, caryophylline, C 20 Hi6O 2 ; it is soluble in alcohol; 
 insoluble in water. It is volatile. Erom water, distilled with cloves, 
 a different body separates in pearly scales, having the formula C 20 H 12 O 4 . 
 It is called eugenme. 
 
 The eugenic acid and eugenine are rendered blood-red by contact 
 with nitric acid. 
 
 The Light Oil of Cloves has sp. gr. = 0*918 ; it boils at 287. 
 
 Oil of Spiraea Ulmaria Salicide of Hydrogen. 
 
 The oil distilled from the flowers of the meadow-sweet is a mixture 
 of a light and of a heavy oil, with a solid body like camphor. The 
 heavy oil is of much interest, from the number of compounds which it 
 forms, and from our being able to form it at will, although from a 
 body, salicine, which has not been found to exist in the spiraea. The 
 impure oil of spirsea is purified by adding potash, by which the light 
 oil is separated, and salicide of potassium formed, which, when acted on 
 by sulphuric acid, yields the salicide of hydrogen pure. 
 
 To form it artificially, equal parts of salicine and bichromate of potash 
 are to be distilled with 2 parts of oil of vitriol and 20 of water. 
 There is heat evolved and much gas disengaged. On then distilling, 
 the heavy oil passes over. Two atoms of dry salicine (C 42 H 2 40 18 ), 
 without any oxygen, might yield three atoms of oil, 3(Ci 4 H 6 4 ), and 
 six of water ; but the reaction is far more complicated in reality, as 
 four parts of salicine yield but one of oil. 
 
 The properties of this oil show it to be a compound of a radical, 
 (C 14 H 5 4 ), salwyle, Syl, with hydrogen ; it acts as a hydracid in com- 
 bining with metallic oxides; its specific gravity is 1*173; it boils at 
 380. The specific gravity of its vapour is 4260. In this and in 
 composition it agrees with crystallized benzoic acid, with which it is 
 isomeric. The alcaline salicides are soluble and crystallizable ; those 
 of lead, zinc, and mercury are insoluble. If a solution of any salicide 
 be mixed with a solution of a sesqui-salt of iron, the liquor assumes a 
 fine purple colour, by which the oil is well characterized. 
 
 When salicide of hydrogen is heated with caustic potash, hydrogen 
 .is evolved and salicylic acid, Syl.O, formed; the potash salt being 
 dissolved in water, and muriatic acid added, the new acid is precipitated 
 
Compounds of Salicyl. Oil of Mustard. 859 
 
 and is purified by recrystallization; it dissolves in boiling water; it may 
 be sublimed, and condenses in long needles, like benzoic acid ; it 
 possesses the usual acid properties ; its salts are generally soluble, and 
 resemble closely the benzoates. 
 
 By the action of chlorine on salicide of hydrogen, chloride of salicyle 
 is formed, Syl. Cl. ; it crystallizes in rhomboidal tables, which melt 
 and sublime undecoinposed ; bromine and iodine give similar com- 
 pounds ; with nitric acid it produces nitrosalicylic acid, Syl.NO^ 
 which crystallizes in long prisms, and unites with bases forming salts. 
 
 The connection of salicyl with benzyl is very remarkable, they con- 
 tain the same hydrogen and carbon, C 14 H 5 , but it is combined in salicyl 
 with 4, and in benzyl with but 2 atoms of oxygen. By the action of 
 ammonia on the chloride of salicyl and on the oil, this relation is more 
 clearly shown, for the oxygen in the radical may be brought to the 
 composition of benzyl. Thus, the chlorosalicamide is C4 2 Hi5Cl 3 6 N2, 
 or properly 3(C 14 H 5 O 2 .]Xi)Cl; that is (Bz.fN).Cl. By the direct 
 action of ammonia on the salicide of hydrogen, the corresponding 
 C 14 H 5 O 2 .|N) H- H may be formed. To this new radical, which is 
 evidently nitruret of benzyl, the name azosalicyl might be given, 
 (seep. 853.) 
 
 If salicylic acid or salicylate of barytes be carefully distilled, the acid 
 resolves itself into carbonic acid, and a new liquid product carbolic acid 
 C 14 H 6 O 6 producing C 2 4 and C 12 H 6 O 2 . This carbolic acid is also found 
 as an ingredient in the volatile oils produced in the distillation of coal, 
 and is looked upon by Laurent as hydrate of phenyl, the radical of the 
 pliene series already so often noticed. The history of this body has 
 been fully given when describing the products of destructive distil- 
 lation in the former chapter. 
 
 Sulphur Essential Oils Allyle Series. 
 
 When the seeds of either black or white mustard are subjected to 
 processes similar to those by which amygdaline is extracted from bitter 
 almonds, substances are obtained which appear to have the same relation 
 to the formation of oil of mustard as the amygdaline and emulsine have 
 to the evolution of hydruret of benzyle, but their chemical history is 
 as yet very imperfect, and their exact composition unknown. The sub- 
 stances that have been described are as follows : 
 
 Sulphosinapisine is, when pure, white, solid, and crystalline. It 
 dissolves in alcohol and water. It contains carbon, hydrogen, nitrogen, 
 oxygen, and sulphur, but its formula is not known. With an alcoholic 
 solution of potash it yields a sulphuret and a sulphocyanide of potassium, 
 and ammonia is given off. 
 
860 Sinapisine Myronic Acid. Allyle. 
 
 It has recently been stated that the so-called sulphosmapisine con- 
 tains potash, and is really a salt of an acid myronic acid, the properties 
 of which are the same as those just described. It forms salts which 
 have a bitter taste. 
 
 The albuminous principle existing in the mustard seeds is termed 
 myrosine, its precise formula is not known ; in properties it is quite 
 analogous to emulsine or synaptase. When added to a solution of 
 rnyronic acid it induces a kind of fermentation, and oil of black mustard 
 is evolved. Fremy states that both white and black mustard contain 
 myronic acid, but if so the same oil should be obtained from both by 
 distillation with water, which is not the case. 
 
 Another body obtained from the seeds of black mustard is sinapisine, 
 it is solid and crystalline ; it does not contain sulphur, and resembles 
 very closely an unsaponifiable fat. It does not appear to have any 
 share in the production of the oil. 
 
 When the seeds of black mustard are distilled with water a heavy 
 volatile oil is produced by the decompsition of the myronic acid or sul- 
 phosinapisine. This oil has a sp. gr. 1035 ; its taste is pungent, and 
 odour sharply irritating ; it contains sulphur and nitrogen ; its formula 
 being C 8 H 5 NS 2 . The sp. gr. of it impure is 3370. When acted on 
 by nitric acid it forms sulphuric acid and organic products. With 
 potash it gives a mixture of sulphuret and sulpho-cyanide of potassium, 
 and evolves ammonia and organic products. With sulphuret of po- 
 tassium it produces sulphocyanide of potassium, and a heavy oil identi- 
 cal with that obtained from garlic and from assafoetida. 
 
 If oil of mustard be treated with ammonia it forms a crystalline 
 product, having the formula CsH 8 N 2 S2. This body acts as an organic 
 base ; it is called thiosinnamine. When it is put into contact with 
 oxide of lead it loses all its sulphur and some hydrogen, and is 
 converted into another base sinnamine, the formula of which is 
 CsH 6 N 2 . 
 
 If oil of mustard be decomposed by barytes or by oxide of lead, the 
 reaction is more regular than with potash, and the products are found 
 to be sulphuret of carbon, and a new base having the formula 
 C 14 Hi2N 2 2 . and termed Sinapoline. This formula I believe indicates a 
 compound of amide and cyanate of allyle, C 6 H 5 Ad + C 6 H 5 O.CyO. 
 
 The volatile oils obtained from the pungent cochlearias, as horse- 
 radish, and from the alliaria afficinalis are identical with that from 
 black mustard. 
 
 When the common garlic, allium sativum, is distilled with water a 
 heavy oil is obtained having the odour of the plant, and closely con- 
 nected with the oil of mustard. If assafatida be distilled it is found 
 
Oils containing Sulphur. Allyle Series. 861 
 
 to yield two oils one lighter and the other denser than water. The 
 heavy oil is identical with oil of garlic, as is also oil of onions, allium 
 cepa. These oils have all the formula C 6 H 5 S. They may be artificially 
 produced by distilling the oil of mustard with sulphuret of potassium, 
 thus showing the organic radical of both oils to be the same. Indeed 
 there appears no doubt but that oil of mustard is the sulphocyanide, 
 and oil of garlic the sulphuret of a radical C 6 H 5 , to which the name 
 allyle has been given. Thus 
 
 Sulphuret of Allyle, Al.S =CeH 5 S. OH of Garlic. 
 Sulphocyanide Allyle, Al.Scy = C&Hs^S. Oil of Mustard. 
 
 This allyle series is probably extensive although as yet but little 
 studied. The formula and origin of the base sinapoline, above des- 
 cribed, indicates the probable existence of amides and cyanates of allyle, 
 and it may be remarked that the carbohydrogen, termed mesityl, and 
 assumed as the basis of the series of bodies derived from acetone, is 
 either identical or isomeric with allyle ; thus presenting a point of 
 view remarkably worthy of being accurately examined. (See page 
 805.) 
 
 2ND CLASS. OILS PRE-EXISTING IN THE PLANT PROPERTIES 
 
 NOT ACID. 
 
 These oils are very numerous, and so similar in properties that a 
 special description is quite unnecessary for each. They are characterized 
 by not dissolving in solution of potash, by being lighter than water, 
 and by a less energetic action on the animal system than the oils of the 
 first class. They combine with muriatic acid to form heavy oily sub- 
 stances, in some cases crystalline. When put in contact with iodine, 
 they frequently combine with it so energetically, as to produce a feeble 
 explosion. By chlorine, hydrogen is removed, and an oily liquid heavier 
 than water is produced. The oil, as yielded by the plant, consists of 
 two substances, one solid (stearopten ) , the other liquid (elaopten) ; the 
 former generally crystallizes when the oil is long kept. I prefer to term 
 the liquid simply the oil, and the solid portion the camphw of the 
 plant. We sometimes observe these oils forming the camphor, arti- 
 ficially, by contact with water. 
 
 These oils may be very naturally divided into two groups, according 
 as they contain oxygen or not. The following table includes all the 
 
862 
 
 Series of Oil of Cumin. 
 
 important facts of the history of the oils (elaoptens) containing 
 oxygen : 
 
 Plant yielding the Oil. 
 
 Sp. gr. 
 as Liquid. 
 
 Boiling 
 Point. 
 
 Formula. 
 
 Sp. gr. 
 of Vapour. 
 
 Cajeput . .- . ' ;' . 
 
 0-927 
 
 347 
 
 CioH90 
 
 
 Lavender ,. . . . . . . 
 
 0-897 
 
 397 
 
 Cl5Hl4O2 
 
 
 Rosmary ; . ; ' ' : : s ! 
 
 0-897 
 
 365 
 
 C45H 38 2 
 
 
 Pennyroyal 
 
 0-925 
 
 395 
 
 CioHSQ 
 
 
 Camphor tree 
 
 0-910 
 
 ... 
 
 C2oHi 6 O 
 
 
 Valerian 
 
 ... 
 
 518 
 
 C2oHi 2 O 
 
 
 Spearmint 
 
 0-914 
 
 ... 
 
 C35H 2 8O 
 
 
 Marjoram 
 
 0-867 
 
 354 
 
 > C5oH 4 oO 
 
 
 Asarum 
 
 ... 
 
 ... 
 
 C16H9Q2 
 
 
 Fennell 
 
 0-997 
 
 ... 
 
 C20H12O2 
 
 
 Anise 
 
 ... 
 
 ... 
 
 C20H12O2 
 
 
 Peppermint 
 
 0-902 
 
 ... 
 
 C2lH20O 2 
 
 
 Rue 
 
 0-837 
 
 446 
 
 C 2 8H 2 8O 3 
 
 7690 
 
 Olibanum . 
 
 0-866 
 
 323 
 
 C35H28O 
 
 
 Cumhi 
 
 0-860 
 
 418 
 
 C2oHi 2 O 2 
 
 5094 
 
 Erom the recent experiments of Gerhardt and Cahours, it appears that 
 by the action of fused hydrate of potash, most essential oils, containing 
 oxygen, may be separated into an acid, and an oil destitute of oxygen. 
 Some of the results obtained by those chemists are of great interest ; 
 thus, from the oil of valerian C 20 Hi 2 O, valerianic acid is obtained, and 
 an oil which absorbs oxygen with great rapidity and generates common 
 camphor. The oil of chamomile also yields valerianic acid. 
 
 The oil of cumin (cuminum cyminum), of which the characters have 
 been given in the table, yields, when treated with hydrate of potash, a 
 peculiar acid, cumenic acid, whose formula is C2oH n O3 + Aq. ; it is 
 perfectly white, crystallizes in fine prismatic tables, tastes sour, fuses at 
 197, and may be distilled unchanged. If cumenate of barytes be 
 distilled at a dull red heat, a colourless liquid oil is obtained, which 
 boils at 292; it is termed cymen ; its formula is C 18 H 12 , being isomeric 
 with mesitylene ; with sulphuric acid cymen unites, forming cymensul- 
 phuric acid, C 18 H 12 S 2 6 , which forms well characterized soluble salts. 
 By the action of chlorine and of bromine on the oil of cumen, heavy 
 oily compounds are obtained, whose formulae are CjoHnO^G^ and 
 C 20 H n 2 .Br. 
 
 It is evident that in these compounds a radical (cumyl) C 20 H n O 2 , 
 exactly analogous to benzyl, may be assumed, aud the cymen has the 
 place of benzin. The carbo-hydrogen of the oil of cumin is termed by 
 Cahours, cumen ; its formula is C 20 Hi4 ; its specific gravity 0'860; it 
 boils at 330 ; it may be prepared artificially also from common cam- 
 phor ; with sulphuric acid it forms cumensulphuric acid, which resem- 
 bles completely the other acids of that class. 
 
Isomeric Essential Oils. 
 
 863 
 
 The stearopteus or camphors containing oxygen, will be described bye 
 and bye. 
 
 The following table contains a similar view of the most important oils 
 not containing oxygen : 
 
 Plant yielding the 
 Oil. 
 
 Sp. Gr. 
 as liquid. 
 
 Boiling 
 Point. 
 
 Formula. 
 
 Sp.Gr. as 
 Vapour. 
 
 Circular polarizing 
 power. 
 
 Citron 
 
 0-847 
 
 343 
 
 2 K i 
 
 i 1 
 
 + 80 9, right 
 
 Copaiva 
 
 0-878 
 
 473 
 
 ** *a 
 
 ^ Q-^ 
 
 + 34 2, left 
 
 Parsley 
 
 ... 
 
 410 
 
 > O O 
 
 ~i .i-t ^ 
 
 ?^ en ^*^ 
 S C^ II 
 
 
 
 Juniper 
 
 0-839 
 
 311 
 
 g +a ^3 
 
 
 3 5, left 
 
 Savine . 
 
 ... 
 
 315 
 
 ^ El ^ "* 
 
 ^2 ^ >% 
 
 
 
 Cubebs 
 
 0-929 
 
 ... 
 
 "o g - W 
 
 "o S-'g 
 
 40 1 left 
 
 Black Pepper 
 
 ... 
 
 ... 
 
 g ^ o 
 
 CJ ^ d 
 
 
 
 Bergamotte 
 
 ... 
 
 ... 
 
 , W ^S 
 
 ^ s ^ 
 
 -f 29" 3','righ't 
 
 Turpentine 
 
 0-864 
 
 315 
 
 llfl 
 
 i a< 
 
 _ 43 3, left 
 
 Although these oils have all the same per cent, composition, they 
 differ in the formula of their atom ; that of turpentine being C 20 H 1G ; 
 that of cubebs, Ci 3 H 12 , and all the other being C 10 H 8 . Although even 
 as given in the table, they constitute a remarkable group of isomeric 
 bodies, yet each is capable of changing its molecular condition in va- 
 rious ways, and thus generating other bodies, still more closely isomeric, 
 as they differ only in their action on polarized light. Of these changes 
 I shall describe only those of oil of turpentine, which will serve as an 
 example. 
 
 By contact with oil of vitriol, oil of turpentine changes into another 
 liquid, which has the same specific gravity both in the state of liquid 
 and of vapour, the same boiling point, and the same atomic weight, 
 but is totally without action on polarized light. This new liquid is 
 called terebene. If the oil of turpentine be acted on by muriatic acid 
 gas, it combines therewith, forming a dense liquid, which is muriate 
 of terebene, and which has no action on light ; but another portion of 
 the turpentine unites with the muriatic acid, unchanged, and forms a 
 solid, which crystallizes in fine white prisms, and from its remarkable 
 odour, is called artificial camphor. In this solid, the oil of turpentine 
 preserves all its action upon light, and for convenience it may obtain 
 the name of campliene, and the solid is then muriate of camphene. Now 
 if this solid be distilled with lime, the muriatic acid is removed and an 
 oil obtained, which differs from camphene only in having no action on 
 light, whilst it differs from terebene in forming with muriatic acid, a 
 solid product. This oil is termed camphilene and the muriate of cam- 
 pliilene is distinguished from the muriate of camphene, in being quite 
 
864 Isomeric forms of Oil of Turpentine. 
 
 destitute of rotatory power. From none of these products can the true 
 oil of turpentine, or camphene, be regenerated. There are thus three 
 forms of oil of turpentine, of which two give solid compounds, and the 
 third a liquid, with muriatic acid ; two are without action on light, but 
 the camphene rotates powerfully to the left : with chlorine they all 
 give heavy liquids, all of which have the formula C 20 Hi 2 Cl4, but are dis- 
 tinguished from each other by their action upon polarized light ; the 
 chlo-camphene presenting the anomalous character of a rotatory power 
 to the right. 
 
 When oil of turpentine is mixed with nitric acid and gently heated, 
 a thick and heavy oily substance is produced, apparently by their direct 
 union, and may be separated by the addition of cold water. If, how- 
 ever, the materials be left to themselves, after some time violent, almost 
 explosive action sets in, copious red fumes are given off, and a resinous 
 material formed, which by boiling with nitric acid, dissolves, and the 
 solution on cooling yields crystals of turpentinic acid, Its composition 
 was found by Bromeis to be C 14 H 9 7 + Aq. The exact theory of its 
 formation has not been as yet ascertained. 
 
 The other oils of this class are capable of similar metamorphoses 
 which need not be specially detailed. 
 
 The type C 5 H 4 exists probably in all essential oils, for it will be seen 
 by reference to the former table, of oils containing oxygen, that their 
 formulae consist in multiples of C 5 H4, combined with oxygen, or with 
 the elements of water. 
 
 B. Of the Camphors or Stearoptens of the Oils. 
 
 The most remarkable substances of this class are the common cam- 
 phors which are extracted from the wood of the laurus camphora and 
 of the dryabalanops camphora, by distillation with water. In the 
 plants they are mixed with the camphor-oil (C 28 H 16 ) from the gradual 
 oxidation of which the common camphor appears to be produced. 
 
 The laurel camphor forms a white semitransparent mass, crystallized 
 in regular octohedrons. It is very tough and difficult to powder ; its 
 specific gravity is 0.986 ; its taste is bitter; its odour is well known; 
 it melts 347 and boils at 390, subliming unaltered ; it is sparingly 
 soluble in water, but easily so in alcohol and ether ; its formula is 
 C 2 oH 16 2 . The specific gravity of its vapour is 5317, which might 
 be considered as formed by one volume of vapour of camphene and 
 and half a volume of oxygen (4776 + 55T3). Hence camphor and 
 camphor-oil may be looked upon as oxides of an oil of the turpentine 
 family. 
 
Camphor Camphoric Acid. 
 
 865 
 
 The dryabalanops or Borneo camphor resembles completely, in physical 
 properties, the common camphor, but it contains more hydrogen, its 
 formula being C 10 H 9 O. By strong nitric acid it is converted first into 
 common camphor, and then into camphoric acid, water being produced. 
 
 When camphor is heated with lime, water, and an oil, camphron 
 (CsoH^O), are produced. With muriatic acid it unites, forming a 
 colourless liquid, whose formula is C 2 oH 17 O 2 Cl. By boiling with strong 
 nitric acid it is completely converted into camphoric acid. 
 
 This acid crystallizes in small rhomboidal tables, which tastes sour 
 and bitter ; it melts at 145, gives off water, and leaves the anhydrous 
 acid, which melts at 423 and distils over at 518 without alteration. 
 The formula of the anhydrous acid is C 10 H 7 O 3 ; the crystals contain an 
 atom of water. The salts of camphoric acid are not important, and 
 appear to differ in properties according as the dry or hydrated acid was 
 employed to form them. The camphor ate of ether is a dense liquid, 
 which, with camphoric acid, forms the camphovinic acid, a thick 
 heavy liquid which is decomposed by heat, and forms unimportant salts. 
 
 When camphor is distilled with glacial phosphoric acid, water is 
 formed, and a volatile oil passes over, having the formula C 20 H 14 , and 
 identical in every respect with the cymen obtained from oil of cumin, as 
 described in p. 862. 
 
 When camphor in vapour is passed over hydrate of potash, heated 
 to about 700, an acid is formed, which has the formula C 2 oH 17 O 3 -f Aq. 
 This campholeic acid fuses at 176 and boils at 482 ; it may be dis- 
 tilled unchanged. It is insoluble in water, but dissolves abundantly 
 in alcohol and ether, and crystallizes from these solutions on cooling. 
 When it is heated with phosphoric acid, a volatile oil is produced, 
 campJiolen, having the formula Ci 8 Hi6. When campholeate of lime 
 is distilled, another oily fluid is formed, whose formula is C 19 H 17 O. 
 
 Of the camphors of the other volatile oils, only a few require any 
 detailed notice. The characters of most of them are given in the 
 following table : 
 
 Plant giving the 
 Camphor. 
 
 Sp. Gr. 
 as liquid. 
 
 Melting 
 Point. 
 
 Boiling 
 Point. 
 
 Sp. Gr. 
 of Vapour. 
 
 Formula. 
 
 Rose (Otto) 
 
 
 77 
 
 550 
 
 
 CH 
 
 Parsly 
 
 
 70 
 
 552 
 
 
 Cl2H 7 O4 
 
 Iris Florentina 
 
 
 ... 
 
 ... 
 
 m 
 
 CHO 
 
 Elicampane 
 
 
 108o 
 
 ... 
 
 . 
 
 Ci5H 10 O 2 
 
 Asarum 
 
 
 104 
 
 530 
 
 
 Cl6H H O4 
 
 Fennell 
 
 1014 
 
 680 
 
 428o 
 
 
 C2oH 12 CH 
 
 Anise 
 
 
 64 
 
 430o 
 
 5680 
 
 C2oH 12 O-2 
 
 Peppermint 
 
 
 91 
 
 406o 
 
 5455 
 
 C2IH-20O2 
 
 Cubebs 
 
 
 ... 
 
 ... 
 
 . 
 
 CieHuO 
 
 Turpentine 
 
 1 -057 
 
 302" 
 
 31l 
 
 
 C2oH 2 oO 4 
 
 55 
 
866 Camphors of the Essential Oils. 
 
 On comparing these formulae with those of the corresponding oils 
 (p. 86] ), it is seen that the camphors arise from various causes ; in 
 some cases they are isomeric with the oils, in others oxides of them, 
 and in others hydrates; thus, the camphor of turpentine may be 
 formed at will, by agitating the oil with water and then exposing it to 
 cold ; the hydrate crystallizes out in colourless prisms, sometimes of 
 great size. 
 
 The peppermint camphor has been found to yield, by the action of 
 re-agents, a series of compounds. Thus, by the action of glacial phos- 
 phoric acid, or of oil of vitriol, a light oil was obtained, having the 
 formula C 21 H 18 , which is termed menthen. By the action of chlorine, 
 a thick heavy liquid is produced, C2iHj 4 Cl 6 O 2 . By nitric acid, menthen 
 yields a heavy oily liquid, C 21 H 18 9 ., which possesses acid properties ; 
 and with chlorine, menthen yields a sirupy yellow liquid, having the 
 formula C 2 iH I3 Cl 5 . 
 
 The anise-camphor yields with bromine a crystalline substance 
 C 20 H 9 Br 3 2 , and with sulphuric acid an oily substance, aniso'ine, isomeric 
 with itself. By nitric acid it is converted into a body which crystal- 
 lizes in long needles, anisic acid C 16 H 6 O 5 -f- Aq. which forms salts with 
 metallic oxides, and gives by further action the nitranisic acid, C 16 H 5 
 + Aq. and nitranisid, C 20 H 10 N 2 10 . 
 
 C. Of the Resins. 
 
 The bodies of this class approach closely to the camphors in composi- 
 tion and properties, but are distinguished by not being volatile without 
 decomposition, and being generally capable of acting as acids. The 
 most important will be first specially noticed, and the properties and 
 formulae of those remaining expressed in a table. 
 
 Resins of Turpentine. The ordinary white resin co-exists, in the dif- 
 ferent species of pine, with oil of turpentine, and is obtained by making 
 incisions through the bark, when the thick tenacious turpentine flows 
 out. This, when distilled with water, gives off the oil, whilst the resin 
 remains, and is called colophony. It is a mixture of two resins which, 
 though having the same composition, differ in properties, and are termed 
 the pinic and sylvic acids. 
 
 The Pinic Acid is obtained by digesting colophony reduced to fine 
 powder, in cold spirit of sp. gr. 0*865, which does not dissolve sylvic 
 acid. The solution is to be mixed with a spirituous solution of acetate 
 of copper, as long as a precipitate forms. Thispinate of copper is to be 
 dissolved in strong boiling spirit, decomposed by a little muriatic acid, 
 and then mixed with water ; the pinic acid precipitates as a resinous 
 powder which may be dried at a moderate heat. 
 
Pinic Acid Sylvic A' id. Pimaric Acid. 867 
 
 When quite pure, pinic acid is colourless ; it melts at 257, but 
 becomes soft at 149 ; its solution in alcohol reacts acid. It expels 
 carbonic acid from bases ; its alcaline salts are soluble ; its earthy and 
 metallic salts insoluble in water, but many of them soluble in spirit ; its 
 formula is C^H^O^ 
 
 When a solution of pinic acid in alcohol is long exposed to the air, 
 it absorbs oxygen, and forms oxypinic acid, the formula of which is 
 QoHsoOg ; it is a stronger acid than the pinic. When heated with 
 lime, pinic acid is decomposed, and three different volatile oils obtained, 
 whicli need not be specially noticed. 
 
 The Sylvic Acid remains when the pinic acid is dissolved by weak 
 alcohol. As it is not pure, the residue is to be dissolved in two parts 
 of boiling spirit of 0*865 ; on cooling the sylvic acid separates. By a 
 second solution all the traces of pinic acid may be removed. The pure 
 sylvic acid crystallizes from its alcoholic solution in colourless rhombic 
 prisms; it melts at 212; it is easily soluble in strong alcohol and in 
 ether, but insoluble in water ; its formula is C 4 oH3oO 4 . Its salts are 
 exactly similar to those of pinic acid. 
 
 When either pinic or sylvic acids are kept melted for some time, they 
 become brown, and change into a resin very sparingly soluble in alcohol, 
 and possessed of stronger acid properties than either : it is termed co- 
 lophonic acid ; it exists in small quantity in common resin. 
 
 The turpentine of the pinus maritima contains an acid isomeric with 
 pinic acid, pimaric acid, which, when distilled, yields pyromaric acid, 
 and pimarone. With hot nitric acid there is produced azomaric acid 
 having the formula C 2 oH n ]N"O 8 . 
 
 The resin of the spruce fir has been found by Johnstone to be a mix- 
 ture of two resins which are separated by means of alcohol. The more 
 soluble, or A resin, has the formula C 40 H 31 O 6 , the less soluble, or B 
 resin, that of C 4 oH 39 O 5 ; they both possess acid characters. 
 
 For the manufacture of tar and pitch, the pine wood containing tur- 
 pentine is exposed to a kind of destructive distillation, in kilns hollowed 
 out in the ground. Although a large quantity of the resin flows out 
 undecomposed (as colophonic acid), yet the important components of 
 the tar are bodies belonging to a different series, which will be described 
 hereafter. 
 
 A great variety of resins, of important use in medicine and in the 
 arts, exude from trees, either pure, or mixed with oils, or with gums 
 (gum resins), sometimes with benzoic or cinnamic acids, constituting 
 balsam*. -Frequently there are many kinds of resins mixed together, 
 but they all possess the characters of fusibility, insolubility in water, 
 
868 
 
 Composition of Resins. 
 
 and of being dissolved by alcohol, ether, essential oils, and alcaline 
 solutions. Their composition is given in the following table : 
 
 Anime Resin 
 Elemi Resin 
 
 'j- C4oH 33 O 
 
 B. Sandarach 
 A. Euphorbium 
 
 } C^.0, 
 
 Fossil Copal 
 B. Mastic Resin 
 
 . C49H 3 ]O2 
 
 Asphaltene . 
 A. Olibanum 
 
 
 | C40H3206 
 
 Antiar Resin 
 
 . C4oH 3 oO 
 
 Labdanum 
 
 
 CwHssO? 
 
 B. Copal Resin 
 
 "\ C4()HsiO 
 
 Pasto Resin 
 
 
 C40H32O8 
 
 Birch Resin 
 
 C4()H 3 30 
 
 Sagapenum 
 
 
 C40H'^9O9 
 
 A. Mastic Resin .1 . TT . ^, 
 
 Scammony 
 
 
 C40H33O20 
 
 Copaiva Resin 
 A. Elemi Resin 
 
 r 040-CL31V; 
 
 Jalap Resin 
 Galbanum 
 
 
 C40H34O20 
 C40H2707 
 
 B. Olibanum Resin J ^^ 
 
 Dragon's Blood 
 
 
 C4<H2tO 8 
 
 C. Sandarach 
 
 CioHaOfi 
 
 Gamboge 
 
 
 C40H230 8 
 
 Ammoniac Resin . CioH^sOg 
 
 A. Assafcetida 
 
 
 C4oH2eOi9 
 
 B. Assafcetida 
 
 CioHseOg 
 
 Acaroid Resin 
 
 
 C40H20O12 
 
 Guaiacum 
 
 C4oH23OlO 
 
 Opoponax 
 
 
 C4()H250l4 
 
 Bdellium Resin 
 A. Sandarach 
 
 ; ;J C4oH 3 i0 5 
 
 B. Benzoin Resin 
 A. Benzoin Resin 
 
 
 
 In all this series of resins it is evident that the carbon remains un- 
 altered, and Johnstone has shown that they may all be considered as 
 derived from oils having the turpentine constitution = C 40 H 3 2. 
 
 Amber Succinic Acid Succinone. 
 
 A substance which is connected with the preceding in many ways is 
 amber. This body is found in rounded pieces, mixed with or attached 
 to fragments of decomposing wood in the lignite beds of the north of 
 Europe. It is also found cast on shore by the waves, along the coasts 
 of the Baltic. It is yellow, transparent, and often contains imbedded in 
 it, insects, and parts of plants, so as to prove it to have been perfectly 
 liquid when first formed. It is, in fact, the turpentine of unknown 
 trees belonging to a former geological epoch ; its specific gravity is 
 1-067 ; when heated it melts, and is then totally decomposed; its re- 
 lations to electricity have been fully noticed, p. 173. Amber is found 
 to be a mixture of two resins, which are soluble in alcohol and ether, a 
 bitumen insoluble in those liquids, a volatile oil, and a peculiar acid, 
 the succinic acid. It is used very extensively in the arts as a material 
 for varnishes ; but to the chemist its principal interest is its electrical 
 properties, and as a source of its acid. 
 
 Succinic Acid is obtained by the destructive distillation of amber ; it 
 partly sublimes into the neck of the retort in discoloured crystals, and 
 partly dissolves in the water which comes over ; by solution in nitric 
 acid it may be freed from the resinous colouring matters. It may also 
 be obtained from the amber by digestion with alcohol or solution of 
 potash ; it hence pre-exists in the amber, and is not produced by the 
 
Amber Succinic Acid. 869 
 
 heat. It is found in small quantity also in colophony, and is abun- 
 dantly produced by the action of nitric acid on the fatty acids, as the 
 stearic or margaric. 
 
 Succinic acid crystallizes, from its solution in water, in 
 colourless right rhombic prisms, as m t a in the figure, which 
 have the formula C 4 H 2 3 -f- Aq. ; when heated to 350 it 
 melts, abandoning half its water, and at 450 sublimes in 
 an anhydrous state ; its solution in water is markedly acid ; 
 when heated with lime, a volatile liquid is produced, succinone, 
 the exact formula of which is not established. 
 The salts of succinic acid are mostly soluble and crystallizable. 
 The Succinate of Soda, prepared by neutralizing the acid by carbo- 
 nate of soda, crystallizes in doubly oblique rhombic prisms, of which 
 i u v are primary, and z n secondary faces in the figure ; it is permanent 
 in the air, and very soluble in water. The succinate of am- 
 ^ monidj which is much used in mineral analysis, for the se- 
 2 paration of iron from manganese, crystallizes in nearly the 
 / same form as the soda salt figured above. The succinates 
 of barytes, lime, and lead, are white powders, insoluble in 
 water. The succinate of manganese forms rose-red, four-sided pris- 
 matic crystals, permanent in the air, and soluble in ten parts of cold 
 water. The succmate of the peroxide of iron is precipitated when an 
 alcaline succinate is added to any per-salt of iron,not containing an excess 
 of acid ; it forms a pale brownish-red powder, insoluble in cold water, 
 but decomposed by boiling water which dissolves out the acid with a 
 small quantity of the iron ; it dissolves readily in acid liquors. 
 
 The Bisuccinate of Ammonia gives off water when heated, and a 
 white crystalline solid sublimes, which is termed succinamid. Its 
 formula is C 8 H 5 O 4 N. 
 
 The rare mineral mellite (see p. 702), is only found accompanying 
 amber in the deposits of lignite. 
 
 Caoutchouc Caoutchene Gutta Percha. 
 
 Caoutchouc Indian Rubber. This substance, now so much used in 
 the laboratory for connecting pieces of apparatus, and so extensively 
 employed in the arts, possesses much similarity to the resins. It dis- 
 solves but imperfectly even in ether ; its proper solvent being the vola- 
 tile oils into which it is converted by distillation, or the so-called nap- 
 tha, or volatile oils obtained by the destructive distillation of wood or 
 coal. One of these is the lightest liquid known, its specific gravity 
 being but C'654; it boils at 92; it has been termed faradyn. Ano- 
 
870 Caoutchouc. Gutta Percka. 
 
 ther, known as caoutckene, has a specific gravity of 0.842; it boils at 
 340. The composition of these liquids, or of caoutchouc itself is not 
 well known, as they have not been as yet obtained absolutely pure ; but 
 so far as I can judge, some appear to have the same composition as oil 
 of turpentine, and others that of olefiant gas and etherene. 
 
 When caoutchouc is heated with sulphur to a temperature of 250 to 
 300, it appears to dissolve or combine with a large quantity of that 
 substance forming a material, now known in the arts as Vulcanized In- 
 dian Rubber, and usefully applied to many purposes 'from the elasticity 
 it possesses. Volatile sulphurets, as the sulphuret of carbon or of 
 arsenic, appear to have the same power of volcanizing or sulphuretting 
 the caoutchouc. 
 
 Gutta Pereha. This material, recently introduced into commerce, 
 is like indian rubber, the juice of trees, whose botanical history is, how- 
 ever, still unknown. It is imported from Borneo. It appears to be a 
 mixture of several hydro-carbons, and by distillation yields volatile 
 liquid products analogous to those of indian rubber. When heated to 
 120 it softens, and becoms so plastic that it may be moulded or 
 stamped, and from its accurately preserving, when cold, the forms so 
 given to it, objects of ornamental design are made of it. It is very 
 tough, and bands of it are employed in place of leather for connecting 
 machinery. It is, however, totally destitute of the adhesive quality of 
 indian rubber. Pieces of it cannot be united except by being melted 
 together. 
 
871 
 
 CHAPTER XXIV. 
 
 OF THE SAPONIFIABLE FATS AND OILS. 
 
 THE substances of this class are found both in the animal and vegetable 
 kingdoms very extensively distributed. In animals, the various fats 
 are deposited in the cavities of the cellular tissue, but often also diffused 
 through the mass of the glandular organs. In plants, the oils or fats 
 are generally found in the investing membranes of the seed, or in the 
 cellular texture of the fruit. The leaves or roots seldom contain any 
 fatty matter. The fats and oils, as they exist in nature, are mixtures 
 of a few simple fatty and oily bodies in variable proportions ; their 
 degree of consistence depending on the relative preponderance of the 
 solid or liquid constituent. The greater number of fats consist of two 
 simple fats, stearine and margarine, and a simple oil, oleln ; but these 
 three bodies, which may be considered as the bases of all fats and oils, 
 are accompanied generally by smaller quantities of solid or liquid fats, 
 which are often peculiar to a particular animal or plant. These fatty 
 bodies are all fixed ; that is, they cannot be distilled without decom- 
 position ; but they are totally converted by heat into volatile bodies, 
 undergoing, in some cases, singular metamorphoses, which will be de- 
 scribed in the history of the individual fats. 
 
 Exposed to the air, the fatty bodies gradually absorb oxygen, and 
 evolve carbonic acid ; they at the same time obtain an acid reaction, 
 and a smell well known as rancid. Most of this change appears to 
 result from minute quantities of azotized organic tissues which remain 
 interspersed through the fats. A great number of oils, however, ab- 
 sorb oxygen very rapidly, and, evolving carbonic acid, change into a soft 
 resinous body ; they are hence termed drying oils, and are used so in 
 painting. This drying quality is increased by combining the oil with a 
 small quantity of the base, as oxide of lead. 
 
 The most important fact in the history of the fixed oils and fats is, 
 that by the action of alcalies they are converted into soaps ; whence the 
 name of saponifiable given to the class. By means of the alcali, the fat 
 or oil is decomposed into an acid which combines with the base, form- 
 ing a true salt, which is the soap, and a substance soluble in water, of 
 
872 Compounds of Glycerine. Acrole'ine. 
 
 a sweet taste, which is the same, no matter what kind of fat had been 
 employed. This substance, the sweet principle of the oils, or glycerine, 
 is united in each fat with a different acid, and hence as the fats are best 
 described as salts of glycerine, I shall first notice the composition and 
 properties of the base itself, and of some important products of its de- 
 composition by re-agents and by heat. 
 
 Glyceryl Lipyl Acryl. 
 
 Glycerine. C 6 H 7 5 -f Aq. or 2.C 3 H 2 + 4Aq. To obtain glyce- 
 rine, any fatty matter is to be saponified by a caustic alcali. The solu- 
 tion being decomposed by tartaric acid, which precipitates the fatty 
 acid, is to be evaporated, and the glycerine dissolved out by strong 
 alcohol. It may also be obtained by saponifying the fat by oxide of 
 lead, and treating the watery solution with sulphuretted hydrogen to 
 precipitate some oxide of lead which dissolves ; the glycerine may then 
 be obtained by evaporation. 
 
 Glycerine cannot be obtained solid. When brought to its greatest 
 degree of consistence by evaporation in vacuo over sulphuric acid, it is 
 a colourless syrup, sp. gr. = 1'26 ; it dissolves in water and alcohol, 
 but is insoluble in ether ; it is decomposed by heat. With nitric acid 
 it produces oxalic and formic acids. Boiled with solutions of copper 
 it precipitates metallic copper. 
 
 With chlorine it forms a white flocculent solid, having the formula 
 Ci 2 HnO ]0 Cl 3 , and with bromine it gives a dense oily liquid, whose for- 
 mula is CjgH^OjoBr.g. When glycerine is mixed with oil of vitriol, 
 they unite without blackening, and form an acid compound, sulpho- 
 glyceric acid, the formula of which is C 6 H 7 5 .2S0 3 .HO. With 
 bases this acid forms soluble salts, having considerable analogy to the 
 sulphovinates. The glycerate of lime crystallizes in long delicate 
 needles whose formula is C H 7 5 .S03 -f S0 3 .CaO. With phosphoric 
 acid it produces the glycero-plwspJioric acid, of which the lime salt has 
 the formula PO 5 + 2CaO + C 6 H 7 5 . 
 
 The compounds of glycerine with the fatty acids constitute the 
 various kinds of fats and oils ; but the base does not appear to have 
 exactly the same composition in all. A certain quantity of water ap- 
 pears to separate, and the equivalent of the glycerine to be in some fats 
 but one half what it is in others. Thus, the glycerine of palm oil has 
 the formula C 6 H 4 O 2 , and the glycerine of rnyristine or nutmeg butter 
 to be C 3 H 2 0., of which bodies the common glycerine should be 
 hydrates. As the different fats have been considered as analogous to 
 the ethers, the glycerine C 6 H 7 O 5 -f- HO was looked upon as an alcohol, 
 
Metacetonic Arid Acrylic Acid. 873 
 
 and to be the hydrated oxide of a radical, glyceryl, C 6 H 7 O 4 . But this 
 radical could not exist in the other forms of glycerine; and hence 
 Berzilius proposed to consider the true anhydrous glycerine, C 3 H 2 O, to 
 be the oxide of a radical, lipyl, C 3 H 2 = Lp. The glycerine of palm oil 
 should represent two equivalents of this body, and the glycerine of 
 the ordinary fats be = 2LpO + 4HO. 
 
 When a solution of glycerine is mixed with yeast, and kept in a warm 
 place for some weeks, it is gradually decomposed, and converted into 
 metacetonic acid. This change has no resemblance to the conversion of 
 common alcohol into acetic acid, but closely resembles the lactic fer- 
 mentation described, page 768. The glycerine C 6 H 7 5 forming meta- 
 cetonic acid, CgHjjOg, as sugar C 6 H 6 O 6 does lactic acid C 6 H 5 5 by loss 
 of the elements of water. 
 
 Metacetonic Acid, as thus formed, is the body previously noticed as 
 prepared by the action of oxidizing agents on sugar, or on the metace- 
 tone prepared from sugar. It is most simply obtained by heating sugar 
 with an excess of potash, or distilling metacetone with bichromate of 
 potash and dilute sulphuric acid. It is a volatile liquid so closely re- 
 sembling acetic acid, as well when free as in its salts, that they are 
 scarcely distinguished except by analysis. Its formula when hydrated 
 is C 6 H 6 O 4 = C 6 H 5 3 H- Aq. ; and it is peculiarly interesting, as it con- 
 nects the acetic and formic acids with the butyric and other volatile 
 fatty acids that shall be hereafter described. 
 
 The metacetonic acid cannot be prepared from acetone, which, on 
 oxidizement, delivers only acetic and formic acids, and has apparently 
 no connection with metacetone, although their formulae are so allied. 
 
 Acroleine Acroleic Acid. When any fatty substance is subjected to 
 destructive distillation, a volatile oil is produced, destitute of acid pro- 
 perties, but of a most virulently acrid and penetrating odour. This 
 material is derived solely from the decomposition of the glycerine. It 
 is termed acroleon ; its formula is C 6 H 4 O 2 . It is therefore produced by 
 the abstraction of the elements of water from glycerine, and is isomeric 
 with the glycerine of palm oil and myristine, from which, however, it 
 totally differs in properties ; and it cannot be by any means reconverted 
 into glycerine. 
 
 Pure acroleine, which is best prepared by distilling glycerine with 
 anhydrous phosphoric acid, is a colourless oil of extreme pungency, 
 and so rapidly absorbing oxygen, that if air be allowed access to it, it 
 becomes totally decomposed, forming acrylic acid. It is very volatile. 
 It changes like aldehyd, with which body it ha.s much relation, into a 
 white solid disacryle. The acrylic acid very closely resembles acetic 
 
874 Stearine and Stearic Acid. 
 
 acid. Its formula is C 6 H 4 4 , or C 6 H 3 -f. HO, being formed by the 
 union of two atoms of oxygen to one of acroleine. The acrylic acid, 
 when heated with potash, yields acetic and formic acids. In these 
 bodies a radical acryl = CgHg, analogous to acetyl, is assumed to exist, 
 and the acroleine is hydrated oxide of acryl = AcrO + HO, and the 
 acrylic acid is AcrO 3 -f- HO. 
 
 Of Stearine and Stearic Acid. 
 
 Stearine is the essential constituent of all solid fats, and preponde- 
 rates in proportion to their consistence. It is best obtained from mut- 
 ton-suet, either by washing it with ether as long as anything is dis- 
 solved, or by mixing up melted suet with six times its volume of ether, 
 and subjecting the mass when cold to strong pressure. In both cases 
 the stearine remains behind ; it is generally crystalline, like spermaceti, 
 not at all greasy between the fingers, and is easily powdered ; it melts 
 at 143 ; it is insoluble in water and in cold ether ; it dissolves in 
 boiling alcohol or ether; and crystallizes out as it cools. The formula 
 of stearine is C] 4 2H 141 17 , consisting of 
 
 1 atom of glycerine = Ce Hy O 5 ^ 
 
 2 atoms of stearic acid = CiseH^Oio > = Ci^H^O^. 
 2 atoms of water = H2 62 J 
 
 By the action of strong bases, or of strong acids, it is separated into 
 these constituents. A similar decomposition is effected by heat. 
 
 Stearic Acid is obtained pure by saponifying stearine by potash, and 
 decomposing the solution by means of warm dilute muriatic acid. The 
 stearic acid, which precipitates, is to be washed with water, and dis- 
 solved in boiling alcohol, whence the pure acid crystallizes on cooling, 
 in brilliant white plates. It may, however, be more simply prepared 
 from the stearic acid candles of commerce by solution in boiling alcohol, 
 and crystallization several times, until the fusing point ceases to rise. 
 
 When mutton.suet is directly saponified, very troublesome operations 
 are necessary to free the stearic acid from the other fatty acids which 
 accompany it. 
 
 Pure stearic acid is tasteless and inodorous. It does not melt below 
 158; the melted acid forms a crystalline mass on cooling; it is appa- 
 rently volatile, and may be distilled, unaltered in close vessels ; it is in- 
 soluble in water, but dissolves in hot alcohol ; the solution reddens 
 litmus ; its composition when crystallized is C C 8H660 5 -f- 2Aq. When 
 heated in contact with lime, carbonic acid is formed, and a volatile 
 liquid, stearon, whose formula is C 66 H 66 O. 
 
Margarine and Marganc Add. 875 
 
 Stearic acid is but feeble in its action ; it expels the carbonic acid 
 from the alcalies only when the solution is boiling. It is bibasic, 
 forming two classes of salts, the bistearates, which contain one atom of 
 water and one of fixed base, and the neutral stearates, which contain 
 two atoms of fixed base. The alcaline stearates are the only salts 
 soluble in water ; they dissolve also in alcohol. If neutral stearate of 
 potash be mixed with a large quantity of boiling water, it is decom- 
 posed, one-half of the potash becoming free, and the bistearate of 
 potash precipitating in minute crystalline scales. A solution of soap 
 precipitates all earthy and metallic salts, producing insoluble stearates. 
 
 The Stearic ether is exceedingly remarkable, as it corresponds exactly 
 to stearine in composition, the glycerine being replaced by ether. Thus 
 its formula is 
 
 1 atom of ether = 4 H 5 O. ^ 
 
 2 atoms of stearic acid = Ci36Hi 32 C]o Ci 40 Hi39Oi3 = 1 atom of stearic ether. 
 2 atoms of water = H 2 Og ' 
 
 Stearic acid is now very extensively used for making candles. The 
 tallow is saponified by boiling with a thin paste of lime. The glycerine 
 is washed out, and the soap being decomposed by muriatic acid, the 
 oleic acid is removed from the stearic acid by violent pressure between 
 folds of cloth. The pure stearic acid, when solidifying, assumes a 
 crystalline structure, which would spoil the appearance of the candle - 
 and this tendency is removed by the very improper addition of one part 
 of arsenious acid to about 2000 of stearic acid. 
 
 Of Margarine and Marganc Add. 
 
 Margarine exists along with stearine in most fats, particularly human 
 fat, goose fat, and olive oil, but is most characteristic of human fat. 
 It is prepared from the ethereal solution, which has left the stearine 
 undissolved. This liquor is to be evaporated, and the residue dissolved 
 in boiling alcohol, from which the margarine crystallizes as the solution 
 cools ; it melts at 118. In all other properties it resembles stearine, 
 but is much more soluble in ether and alcohol ; it consists of C 74 H 74 O 12 . 
 
 1 atom of glycerine = C& Ify O 5 ^ 
 
 2 atoms of margaric acid = CesHeeOo > C74H7 4 Oi2 = 1 atom of m.irgarine. 
 1 atom of water = H O 3 
 
 By the action of bases it is separated into glycerine and margaric 
 acid. 
 
876 Constitution of Oleic and Margaric Adds. 
 
 The preparation of margaric acid is precisely similar to that of the 
 stearic acid, which it resembles very closely, being most different in its 
 melting point, which is 140. On solidifying, it crystallizes in white 
 needles. When carefully heated, it volatilizes without alteration. The 
 formula of margaric acid is Cg^aaOg + Aq. If it be mixed with lime 
 and distilled, carbonic acid is produced, which combines with the lime, 
 and a volatile substance is obtained, which is termed margaron. Its 
 formula is CsgHggO. It is a white solid, of a pearly lustre, which melts 
 at 170, and forms, on cooling, a crystalline mass like spermaceti. By 
 repeated distillation with lime, all oxygen is removed as carbonic acid 
 and a volatile oily substance obtained, having the composition of 
 olefiant gas. 
 
 The experiments of Eedtenbacher have indicated a remarkable source 
 of margaric acid in the distillation of stearic acid. The distilled pro- 
 duct, though in appearance unchanged stearic acid, yet does not in 
 reality contain any trace of it, being a mixture of margaric acid, of 
 margarone, and of the volatile oily carbo-hydrogen. The reaction being 
 that 
 
 ;^Q atoms of margaric acid 204^204024 
 I 1 atom of water H O 
 
 produce J 1 ,, margaron 33 HSS O 
 
 7 1 ,, carbonic acid C Og 
 
 v_The oily carbohydrogen 34 Hs4 
 
 Eedtenbacher doubts the real existence of stearone, as none of it is 
 produced in this reaction. 
 
 Another remarkable and simple mode of preparing margaric acid is, 
 by heating stearic acid with its own weight of nitric acid for a few mi- 
 nutes, oleic and margaric acids are formed, and are separated by pressure 
 between folds of bibulous paper. The solid product is to be then 
 crystallized from alcohol until it becomes pure. In this process the 
 simple transference of oxygen converts the stearic acid into the other 
 fatty acids of the same series, as shall be further shown. 
 
 The salts of margaric acid resemble perfectly the stearates in their 
 properties; but the acid being monobasic, there is but one class of 
 margarates. The pearly lustre of the crystalline scales of the margarate 
 of potash gave occasion to the name of this acid, from the word 
 
 /Aagyagirys, a pearl. 
 
 If we compare the formulae of the bodies now described, we find 
 them capable of being expressed by a very simple theory : thus, indi- 
 cating an hypothetic carbo-hydrogen, C 34 H 33 , by E, the stearic acid be- 
 comes E 2 + O 5 , and the margaric acid E + Oa., being related as 
 hyposulphuric and sulphuric acids. Also, as Eedtenbacher has re- 
 
Product* of the Decomposition of Olein. 877 
 
 marked, all the results obtained might be accounted for, by ascribing 
 to maragone the formula C^H^O, in which case it becomes E + O, 
 and the volatile oil may be K 4- H. The stearic acid can be converted 
 into the margaric, not merely by nitric acid, but also by other oxidizing 
 agents, as by sulphuric acid and by bichromate of potash ; and it has 
 been shown that by heat the stearic acid is resolved into margaric acid 
 and margarone, a higher and a lower degree of oxidation precisely as 
 hyposulphuric acid S 2 5 is resolved by heat into S0 2 and S0 3 . 
 
 Of Olein and Oleic Acid. 
 
 Olein exists in small quantity in the various solid fats, but consti- 
 tutes the great mass of the liquid fixed oils, which are not drying oils. 
 It holds dissolved more or less stearine and margarine, of which the 
 greatest part may be separated by exposure to cold when they crystal- 
 lize. Olive oil contains a large quantity of margarine, and hence 
 freezes very readily. The expressed oil of sweet almonds is the purest 
 native olein ; next to it is rape oil. 
 
 To obtain pure olein, almond oil is dissolved in hot ether, and the 
 solution exposed to great cold ; the traces of margarine crystallize out 
 completely, and by evaporation the ether is removed. Olein remains 
 liquid at 0. Fah. In constitution it resembles the solid fats, containing 
 a peculiar acid, oleic acid, combined with glycerine and water. 
 
 1 atom of glycerine CG H? O 5 ^ 
 
 2 atoms of oleic acid C72H66O6 > produce 1 atom olein CygEtaOia 
 2 atoms of water Hg O2 3 
 
 Oleic acid is obtained by saponifying olei'n with a strong solution of 
 potash, then decomposing the oleate of potash by muriatic acid, washing 
 the oil which separates, and drying it with chloride of calcium ; when 
 cooled below 23 P., it congeals as a mass of needly crystals. Its 
 specific gravity at 68 is 0*898 ; it is tasteless and inodorous when 
 pure ; it is insoluble in water, but abundantly soluble in alcohol and 
 ether ; these solutions react strongly acid ; its composition has been 
 determined by Yarentrapp to be CggH^O., -f Aq. ; its alcaliue salts are 
 soluble, and form soft masses, destitute of tendency to crystallize ; they 
 are still more soluble in alcohol. The earthy and metallic salts are 
 white plastery substances, insoluble in wafer. The oleate of lead is 
 soluble in ether, by which it may be perfectly separated from the 
 stearate or margarate of lead. The oleic ether was formed by Varen- 
 trapp by passing muriatic gas into a solution of oleic acid in alcohol. 
 It is a colourless liquid, sparingly soluble in alcohol, lighter than water, 
 
878 Sebacic Acid Pimelic Acid. 
 
 but heavier than alcohol, from which it is deposited as it forms ; its 
 formula is C 36 H 30 3 + Ae.O. 
 
 "When oleic acid is distilled, a portion of it passes over unaltered, 
 but the greater part is decomposed, and some charcoal remains in the 
 retort. The distilled products are very numerous and complex, but 
 consist principally of sebacic acid and a liquid carbo-hydrogen, isomeric 
 with olefiant gas ; sebacic acid is not produced by the distillation of any 
 other fatty substance than oleic acid, and hence may be considered as 
 characteristic of it. The decomposition may be expressed by stating 
 that 
 
 1 atom of sebacic acid 
 
 2 atoms of hydrated f 3 2 atoms of carbonic acid C 2 O* 
 
 oleic acid C 72 H 68 8 f P roduce 1 carbo-hydrogen C 59 H 59 
 
 * residual charcoal C 
 
 Sebacic Acid. C 10 H 8 3 + HO. Eq. 92 + 9. 
 
 This body had been considered as a product of the destructive dis- 
 tillation of all fatty bodies ; but it has been shown by Eedtenbacher to 
 arise only from oleic acid ; the distilled product is to be washed with 
 boiling water, which dissolves the sebacic acid ; on the addition of 
 aeetate of lead, a white precipitate is obtained, which, being decomposed 
 by sulphuretted hydrogen, gives sulphuret of lead, whilst the pure 
 sebacic acid dissolves, and may be obtained crystallized by the evapora- 
 tion and cooling of its solution. 
 
 The crystallized sebacic acid closely resembles the benzoic acid in 
 properties and appearance ; its solution reddens litmus ; its alkaline 
 salts are very soluble ; its lead, silver, and mercury salts are insoluble 
 in water ; from a strong solution of an alcaline sebacate, the acid is 
 precipitated in voluminous crystalline flocks, on the addition of a 
 stronger acid. When completely pure, the sebacic acid is totally without 
 odour; the strong smell of heated oil being due to the formation of 
 the totally different substance, acroleon, already described. The dry 
 sebacic acid has the formula C IO H 8 3 , when crystallized it becomes 
 Ci H 8 3 + Aq. 
 
 Of the Action of Nitric Acid on Stearic, Margaric, and Oleic Acids. 
 
 By the gradual oxidation of those fatty acids, a series of bodies result, 
 which have so much connexion with each other, as to be most conve- 
 niently studied in relation to their origin. 
 
 A. If stearic acid be digested with two or three times its weight of 
 
Succinic, Suberic, and Adipic Acids. 879 
 
 common aquafortis, at a moderate heat, a very lively action commences 
 after some time, and copious red fumes are given off. When the mix- 
 ture has ceased to froth up, and the action of the acid ceases, the only 
 product forms a colourless layer on the surface of the acid liquor, and 
 is found to be pure margaric acid. The change here is evidently a 
 simple oxidation, as E^ -f- O 5 and O give 2(E + 3 ) as described in 
 p. 876. 
 
 If the fatty acid be acted on by successive quantities of the nitric 
 acid until it disappears, the watery liquor deposits, on cooling, abun- 
 dance of crystallized succinic acid, already described in page 868, and 
 the mother liquor of these crystals being evaporated to one-half, forms, 
 on cooling, a thick mass of crystals, which may be washed with cold 
 water, and being purified by recrystallization, are found to be identical 
 with the acid formed by the action of nitric acid on the peculiar woody 
 tissue which exists in cork, Suberine, and which will be hereafter de- 
 scribed. This acid is termed the Suberic acid; it is white, inodorous, 
 and of. a feebly acid taste; easily soluble in alcohol and water; the 
 crystals melt at 248, and when heated more strongly, are decomposed 
 in great part ; it precipitates solution of acetate of lead ; its alcaline 
 salts are soluble, and crystallizable ; when crystallized, the formula of 
 the acid is C 8 H 6 O3 + Aq. The suberic ether was prepared as described 
 for the oleic ether, (p. 877), it is liquid, and its formula is C 8 H 6 O 3 -f- 
 AeO. By the distillation of the suberate of lime, a volatile liquid, 
 sulerone, is obtained, whose formula is C 7 H 6 O. 
 
 The artificial formation of the succinic and suberic acids in this way 
 is exceedingly curious ; but Brorneis and Laurent, to whom the obser- 
 vation is due, have not been able to trace the precise reaction in which 
 they originate. 
 
 B. The action of nitric acid on oleic acid is much more violent than 
 on the stearic acid. Among the products of the reaction are found the 
 succinic and suberic acids, but in addition, several other acid bodies, of 
 which, however, a very slight notice will suffice. 
 
 Pelargonic Acid. C 18 H 17 3 . HO. Exists naturally in the juice of the 
 Pelargonium Roseum, but is more abundantly formed in the process 
 now described. Its barytes salt crystallizes in plates. The (Enanthylic 
 or Pemnanthic acid will be more fully noticed as a product of the oxi- 
 dation of castor oil. 
 
 The Pimelic Acid forms white crystalline grains, which melt at 273, 
 and sublime easily in brilliant needles ; its alkaline salts are soluble 
 but its earthy and metallic salts insoluble in water; the formula of the 
 acid is CyHsOa + Aq. 
 
 Adipic Acid resembles closely the former; it dissolves in water, alco- 
 
880 Elaidine ElaUic Acid. 
 
 hoi, and ether ; melts at 223 ; it sublimes in very beautiful crystals ; 
 its formula is Ci 4 H 9 7 -f-2 Aq. ; it being a bibasic acid. 
 
 The Lipic and Azoleic acids are still less important, and our know- 
 ledge of their constitution very imperfect. All these bodies are ob- 
 tained from the mother liquors, from which the succinic and suberic 
 acids have crystallized. 
 
 Elaidine Elaidic Acid. 
 
 The most important product of the action of nitric acid on oleic 
 acid, or on olein, is Elaidine and the Elaidic acid j as these bodies are 
 of pharmaceutic interest, from their constituting the citrine ointment, 
 or unguentum nitratis Jiydrargyri of the Dublin and London pharma- 
 copeias. 
 
 Elaidine is prepared by the action of nitric acid, or still better, of the 
 red fumes of the nitrous acid on olein ; the oil gradually becomes thick, 
 and finally congeals into a butyraceous mass of a deep yellow colour. 
 By digestion with warm alcohol, a deep orange-red oil is dissolved out, 
 and the pure elaidine is obtained perfectly white; it melts at 97, is 
 insoluble in water, and but sparingly so in alcohol ; it dissolves readily 
 in ether ; with caustic alcalies, it saponifies completely, glycerine being 
 set free. The whole action of the nitric acid in this reaction is exerted 
 on the oleic acid, and the elaidine is a true fat consisting of elaidic acid, 
 united to glycerine. 
 
 Elaidic acid may be prepared by saponifying elaidine, and decom- 
 posing the alcaline elaidate by a stronger acid, but it is obtained in a 
 much purer form, by passing nitrous acid fumes, generated by heating 
 nitrate of lead (p. 378) into pure oleic acid, prepared from oil of sweet 
 almonds ; after some time, the liquid becomes a nearly solid mass of 
 crystalline plates, of a fine yellow colour ; this mass is to be boiled in 
 water to remove adhering nitric acid ; then dissolved in boiling alcohol 
 and allowed to cool. The orange-red oil remains in solution whilst the 
 elaidic acid crystallizes in large brilliant white rhombic tables. This 
 body, when pure, fuses at 113 ; it dissolves readily in alcohol and in 
 ether ; these solutions redden litmus ; when boiled with a solution of 
 carbonate of potash, carbonic acid is expelled and elaidate of potash 
 formed ; its earthy and metallic salts are insoluble in water. The cry- 
 stallized elaidic acid has the formula C^HeeOs + 2Aq. ; it is a bibasic 
 acid. The elaidate of silver is hence C 72 H 66 5 -f 2.AgO, and the 
 elaidic ether, which is a colourless fluid, lighter than water, consists of 
 C 72 H 66 O 5 + HO. AeO. 
 
 The orange-red oil, which is formed simultaneously with the elaidic 
 
Action of Nitrous Acid on Oleine. 881 
 
 acid, has not been as yet accurately examined, and hence we cannot 
 explain by precise formulae the mode in which these bodies are gene- 
 rated. It is this oil which gives to the citrine ointment its characteristic 
 colour and smell ; it is lighter than water, and dissolves in alcaline 
 liquors, but does not form true soaps. 
 
 In the formation of citrine ointment, the conversion of the olein into 
 elaidine is effected by the nitrous acid, which the solution of the mer- 
 curial salt always contains, it being formed by the deoxidation of the 
 nitric acid, and there being no heat used to expel it. The subnitrate of 
 mercury is then mechanically mixed with the elaidine and with the 
 yellow oil. Some of the mercurial salt is often decomposed, however, 
 as metallic mercury may usually be detected interspersed through the 
 ointment. 
 
 Both olei'c and elaidic acids give origin, when heated with fused 
 hydrate of potash, to a peculiar fatty acid, discovered by Yarentrapp ; it 
 is white, solid, and crystalline, melts at 144, and has the formula 
 C 32 H 3 oO3 + Aq. There is formed at the same time, a large quantity 
 of acetic acid. Another point of connexion between the oleic and 
 elaidic acids, is that by distiDation, both furnish sebacic acid. 
 
 It has been found by Redtenbacher, that the products of the oxida- 
 tion of oleic acid by nitric acid are even more numerous than those just 
 described, and include the acetic, metacetonic, butyric, valerianic, 
 caproic, enanthylic, caprylic, pelargonic and capric acids; all which 
 bodies have, however, the very simple connexion, that they are repre- 
 sented by a carbo-hydrogen isomeric with olefiant gas, united in an equi- 
 valent of the acid with four atoms of oxygen, but each acid being 
 characterized by the number of atoms of carbon and hydrogen in its 
 molecule. 
 
 Action of Sulphuric Acid on Margarine and Oleine. 
 
 When olein is mixed with oil of vitriol, the sulphuric acid combines 
 with both the glycerine and the oleic acid, forming sulpho-glyceric and 
 sulph-oleic acids. This last is soluble in water, but insoluble in dilute 
 sulphuric acid, and hence by adding water gradually to the mixture of 
 oil of vitriol and oleine, it separates, floating as a thick sirup on the 
 surface, whilst the sulpho-glyceric acid and the excess of sulphuric 
 acid dissolves. The sulph-oleic acid, thus obtained, forms, with lime 
 and barytes, soluble salts, which are analogous to the sulpho-vinates ; 
 when its solution in water is heated, it is decomposed, sulphuric acid 
 becoming free, and the oleic acid being converted into two acids, which 
 have been named the meta-oleic and the kydroleic acids. 
 56 
 
88*2 Action of Oil of Vitriol on Olein. 
 
 These acids are both liquid like oleic acid ; they are principally dis- 
 tinguished as to properties by the sparing solubility of the former in 
 alcohol, and are thus separated. The constitution of these bodies had 
 been examined by Eremy, at a time when the true constitution of the 
 oleic acid had not been established, and the formula? he assigned to 
 them are not now admissible. They are isomeric with each other ; 
 when distilled, they produce carbonic acid, and two volatile liquids, 
 oleen and elaen, which are isomeric with olefiant gas. Erom the cir- 
 cumstances of the formation of these acids, the change must consist 
 in the fixation of the elements of water, as no other body containing 
 carbon is produced ; but, from his analysis, the anhydrous meta-oleic 
 acid has evidently the same composition as the hydrated oleic acid, and 
 its formula is therefore CaeH^O^ when in combination, and C 36 H33O 3 , 
 when free. Its decomposition by heat consists in the separation of 
 2.CO 2 , and C 34 H 34 remaining, which contains the elements of the two 
 volatile oily liquids. 
 
 With margarine, oil of vitriol does not combine directly; but if 
 margarine and olein together, as they are in olive oil, be mixed with 
 oil of vitriol, union occurs, and a sulpho-margaric acid is produced, 
 which being treated similarly to the sulph-oleic acid, gives two other 
 acids, the meta-margaric and Jiydro-margaric. These are soluble in 
 alcohol, from which they crystallize by cold, so combined as to produce 
 distinct salts, and to affect all the characters of an independent acid, 
 called by Eremy the Jiydro-margaritic. 
 
 If the mixed solutions of sulpho-margaric and sulpho-oleic acids be 
 left to decompose without heat, in place of being boiled, the meta- 
 margaric and met-oleic acids separate and float on the top, but the 
 hydro-margaric and hydro-oleic acids remain dissolved, and separate 
 only by bringing the solution to boil. Each of the products thus ob- 
 tained is to be dissolved in alcohol, and the modified margaric acids 
 crystallize on cooling, whilst the modified oleic acids remain dissolved. 
 The meta-margaric acid is polymeric with the margaric acid ; its for- 
 mula is C 68 H 66 6 + 2Aq., but the hydro-margaric acid contains the 
 elements of four atoms of water more, its formula being C 68 H 70 10 + 
 2Aq. 
 
 Olein of the Drying Oils. 
 
 The oils which possess the property of rapidly absorbing oxygen and 
 evolving carbonic acid, thereby being changed into a kind of transpa- 
 rent resinous varnish, consist of glycerine united to a liquid acid, quite 
 distinct from the ordinary oleic acid ; treated with nitric acid, it yields 
 first a resinous substance, and then oxalic acid. The drying properties 
 
Cocoa-Stearine Palmitine Palmitic Acid. 883 
 
 of these oils are known to be much increased by boiling on litharge, 
 of which a quantity dissolves ; in this case, however, Liebig has shown 
 that no saponification occurs; the litharge serving only to combine 
 with, and coagulate a quantity of vegetable mucus, which being diffused 
 through the oil, prevented its acting as rapidly on the air as it does 
 when pure. 
 
 Of Cocoa-tallow, and Cocoa-stearic Acid. 
 
 The albumen of the cocoa-nut contains a solid fat, which is extracted 
 from it, and imported largely into these countries, to be used in the 
 manufacture of candles. It is a mixture of ordinary olein with a 
 stearine, which contains a peculiar acid. The olein and stearine are 
 separated by pressure or by ether, or by solution in boiling alcohol, 
 from which the stearine crystallizes on cooling, exactly as described for 
 ordinary stearine. 
 
 The cocoa-stearine is white and crystalline; its specific gravity O925; 
 insoluble in water, it dissolves but sparingly in alcohol, except when 
 boiling; it is more soluble in ether; it melts at 77. The products of 
 its decomposition by heat have not been well examined. With caustic 
 alkalies it forms soaps, from which by a stronger acid, the cocoa-stearic 
 acid is separated. 
 
 This acid, purified by repeated crystallizations from alcohol, is bril- 
 liant white ; it fuses at 95, and cannot be distilled without total de- 
 composition. Its formula was found by Bromeis to be C 27 H26O3 -f- Aq. ; 
 its alcaline salts are soluble, but the earthy and metallic salts are inso- 
 luble in water. By the process described for oleic ether, the cocoa- 
 stearic ether was prepared by Bromeis ; it is a clear oil, lighter than 
 water ; its formula is C 2 7H 2 6O 3 + AeO. 
 
 Palm-Oil and Palmitic Acid. 
 
 This solid oil, which is now extensively employed in the manufacture 
 of yellow soap, is prepared in Africa, by pressing and boiling the fruits 
 of the cocos butyracea, or of the avoira elais ; it is of the consistence of 
 butter, reddish-yellow colour, and an aromatic odour. When kept, it 
 acquires a rancid smell, and becomes white ; the colour results from a 
 small quantity of a substance which may be decomposed, and the palm- 
 oil bleached, by chlorine, or any oxidizing agents. Besides ordinary 
 oleine, this oil contains a peculiar stearine, palmitine, which has been 
 accurately examined by Fremy and Stenhouse. 
 
 Pure palmitine melts at 118 and is crystalline. It is insoluble in 
 water, very sparingly soluble even in boiling absolute alcohol, but abun- 
 
884 Palmitic and Myristic Acids. 
 
 clantly soluble in ether. It is quite neutral ; when saponified by potash, 
 and the soap decomposed by an acid, palmitic acid is set free. The 
 palm-oil of commerce usually contains a large quantity of free palmitic 
 acid, and hence is more easily saponified than any other fat ; it also 
 contains free glycerine, so that the palmitine would appear to undergo a 
 spontaneous decomposition. 
 
 Palmitic Acid melts at 140 ; it dissolves in hot alcohol and crys- 
 tallizes therefrom by cooling. Its formula in crystals is C 64 H 62 6 + 
 2 HO it is a bibasic acid ; its silver salt is C64H 62 O 6 + 2AgO. The 
 palmitic ether, which may be prepared by heating palmitic acid with 
 alcohol and oil of vitriol, is solid and crystallizes in fine prisms which 
 melt at 70, and have the formula C 64 H 62 06 + 2.AeO. By distillation 
 the palmitic acid is not altered ; by the action of chlorine, hydrogen is re- 
 moved from it, and an acid containing chlorine produced, the formula 
 of which appears to be C^H^ClgOe. 
 
 The constitution of palmitine was found, by Stenhouse, to be ex- 
 pressed by the formula C7 H 66 8 , from which should follow, that the 
 substance united with the palmitic acid, is formed of C 6 H 4 O2, and hence 
 differs from common glycerine, C 6 H 7 O 5 , in having lost the elements of 
 three atoms of water. This has been already referred to in the history 
 of glycerine, page 872. 
 
 Nutmeg -butter. Myristic Acid. 
 
 This substance is a mixture of an aromatic volatile oil, with three 
 fats, of which two are easily soluble in alcohol, and are thus simply se- 
 parated from the third, which has been termed by Playfair, myristicine. 
 Of the fats soluble in the alcohol, one is liquid, and the other solid, but 
 we do not know whether they are peculiar, as the analyses of Playfair 
 have been confined to the third. 
 
 Pure myristicine is obtained by crystallization from its ethereal solu- 
 tion ; it has a silky lustre, and melts at 88. When saponified, it yields 
 glycerine and myristic acid f This substance is snow-white and crys- 
 talline, easily soluble in hot alcohol, and then reddening litmus ; it melts 
 at 120; its composition is expressed by the formula C 28 H 2 70 3 + Aq. 
 its compounds are very well characterized and crystallizable. The my- 
 ristic ether is analogous in constitution to the stearic ether, (875) con- 
 sisting of 
 
 2 atoms of ether 
 
 1 atom of ether = C 4 Hs O C 1 atom of myristic ether CeoHeoOg. 
 
 1 atom of water 
 
 = see -\ 
 = C 4 Hs O C 
 = H O 3 
 
Preparation and Properties of Butyric Acid. 885 
 
 The myristicine was found by Playfair, to have the formula C 118 H 113 
 O 15 , consisting of 
 
 4 atoms of myristic acid = Ci 12 H 108 O 
 1 atom of dry glycerine = CG H 4 O 2 
 1 atom of water = HO 
 
 By distilling myristicine, much acroleon is generated, but no sebacic 
 acid. 
 
 Ordinary Butter. Butyric, Caproic, and Cdpric Acids. 
 
 9 
 
 Butter is a mixture of six different fats, viz., common stearine, mar- 
 garine, and olein, with butyrine, caproin and caprine ; by melting the 
 butter, and keeping it for some days at a temperature of 68, the stear- 
 ine and margarine crystallize, whilst the others remain liquid. By 
 means of alcohol the oleine is then separated from the other fats, 
 which are more easily soluble in that menstruum ; their further puri- 
 fication depends on successive solutions in alcohol, but none of them 
 can be considered as having been obtained completely pure. 
 
 Butyrine is a colourless oil, with the odour of heated butter. It soli- 
 difies at 32 ; with alcalies it gives a soap, and sets glycerine free. Its 
 elementary composition is not known. 
 
 Caprome and Caprine cannot be obtained sufficiently free from buty- 
 rine, or from each other, to be described. 
 
 When butter is saponified, and the soap decomposed by tartaric acid, 
 stearic, margaric and oleic acids separate, whilst the other acids remain 
 dissolved. On distilling this liquor, the butyric, capric, and caproic 
 acids pass over along with the water, and being neutrallized by barytes, 
 the three barytic salts are separated by repeated crystallizations. 
 
 The butyric acid is, however, prepared most conveniently, and in 
 quantity, not from butter, but by that fermentation of sugar, which 
 has been described in page 769 as the best process for obtaining lactic 
 acid. In that process, according as the transformation of the sugar 
 proceeds, the sparingly soluble lactate of lime precipitates ; and if the 
 object be to prepare lactic acid, the process should be arrested then, 
 for soon after another action sets in, the precipitate in part redissolves 
 with a copious evolution of the carbonic acid and hydrogen gases, and 
 finally the liquor contains only butyrate of lime. In this action, two 
 atoms of lactic acid, C 12 H 12 O 12 , produce butyric acid, C 8 H 8 04, carbonic 
 acid, C 4 O 8 , and hydrogen gas, H 4 . The solution of butyrate of lime 
 so obtained is to be distilled with muriatic acid, and fused chloride of 
 calcium is to be adde'd to the distilled liquor. The butyric acid then 
 separates as an oily layer, which is purified by distillation. This origin 
 
886 Volatile Acids of Butter. 
 
 of butyric acid is of peculiar interest, as it accounts for the formation in 
 the animal system of this and other similar fatty acids, from the starchy 
 or saccharine ingredients of our food. 
 
 The butyric acid is also formed during the putrefaction of cheese and 
 of most vegetables. Its origin in the oxidation of oleic acid by nitric 
 acid, has been already mentioned. 
 
 The butyric acid, so prepared, is a clear oily liquid, of a penetrating 
 sour smell of rancid butter ; tastes pungent and acid, and leaves a white 
 mark on the tongue. Its specific gravity is 0*976 ; its boiling point is 
 above 212; it burns , with a brilliant white flame, and is abundantly 
 soluble in water, alcohol, and ether. Its formula is C 8 H 7 O 3 + Aq. ; 
 when distilled with lime it gives a neutral volatile liquid, butyrone, 
 whose formula is CrHyO. and a volatile liquid tutyral, C 8 H 8 O 2 , which 
 appears to be to butyric acid, as aldehyd is to acetic acid. 
 
 The other acids existing in butter, and associated also with the bu- 
 tyric acid, as products of oxidation, require but little notice. The 
 caproic acid boils at 396. It has a peculiarly characteristic odour of 
 sweat; its formula is C 12 H n O3 -f- HO. Its barytes salt crystallizes in 
 long needles. The cajprylic acid boils at 465 , and has the formula 
 C 16 H 15 O 3 + HO. The capric acid forms a solid mass of crystals at 44, 
 which then melt only at above 60. The liquid capric acid, boils at 
 534, and has the odour of a goat. Its barytes salt is insoluble in cold 
 water. Its formula is, C 2 oH 19 O 3 + HO. 
 
 Under some undetermined circumstances, butter, in place of yielding 
 butyric and caproic acids, yields a different body, vaccinic acid, which 
 has the formula C 2 oH 18 O 5 + HO, which, however, decomposes with 
 absorption of oxygen into the butyric and caproic acids, C 8 H 7 03 and 
 C 12 H n 3 . 
 
 A very simple relation exists between the composition of these several 
 butter acids and also acetic acid. Thus, if we denote the carbo-hydro- 
 gen, C 4 H 4 by E, the several acids in their hydrated forms are 
 given as 
 
 Acetic acid = M -f 40- 
 
 Butyric acid = 2M + 4O 
 
 Caproic acid = 3M + 4O 
 
 Caprylic acid = 4M + 4O 
 
 Capric acid = 5M + 4O 
 
 I shall have occasion, however, to return to the consideration of this 
 family of acids in a still more general point of view. 
 
 Of Fish-Oils, DelpMnine, and DelpJimic Acid. 
 These oils are generally composed of ordinary margarine, stearirie, 
 
Palm in e -Del^h lulu e Rici/i me. 887 
 
 and oleiue; but some, as whale and dolphin oil, contain a peculiar fat 
 delpkinine, which yields delphinic acid. Eroin the fish-oil the delphi- 
 nine is extracted by cold alcohol, which dissolves it more readily than 
 the other oils; it is liquid, of specific gravity, - 954 ; it is not acid, 
 but becomes so by exposure to the air ; it saponifies readily. From the 
 soap the delphinic acid is separated by tartaric acid, and may be obtained 
 pure by distillation. It is a thin oil, of specific gravity, 0'932 ; it 
 boils above 212, and distils unchanged; it has a peculiar aromatic 
 smell ; tastes acid, and reddens litmus strongly ; it dissolves in twenty 
 parts of water ; its formula is C IO H 9 3 -f- Aq. arid when distilled with 
 lime, it gives a volatile neutral liquid delpMnon, C 9 H 9 O. 
 
 The delphinic acid has been found in the berries of the viburnum 
 opulus, and its composition being the same, and its properties closely 
 resembling those of the valerianic acid, I hazarded an opinion in the 
 former edition of this work, that a re-examination of it would demon- 
 strate its identity with that remarkable vegetable acid, which has subse- 
 quently been completely verified by recent experiments. 
 
 Of Castor Oil and its Products. 
 
 The oil of the ricinus communis (castor oil) is, according to Lecanu 
 and Bussy, a mixture of three fats, ricino-stearine, ricino-oleine, and 
 ricinine, which are all easily soluble in alcohol. Like the fats of butter, 
 they can be but imperfectly separated, but when saponified, they yield 
 acids, which can be more accurately examined ; the soap, being decom- 
 posed by muriatic acid, yields an oil, from which, by cooling, the ricino- 
 stearic acid crystallizes, and the remaining oil, when distilled, separates 
 into the ricinic acid, which passes over, and the ricin-ole'ic acid which 
 is not volatile. 
 
 Purified by recrystaUization from alcohol, the ricino-stearic acid forms 
 pearly scales, which are easily soluble in alcohol, reddens litmus, and does 
 not melt below 266. The ricin-oleic acid freezes a few degrees below 
 32. The ricinic acid is solid and crystalline, melts at 71, and distils 
 unchanged at a temperature but little higher. 
 
 "When castor oil is acted on by nitrous acid, it is converted into a 
 solid substance, termed by Boudet, palmine ; it is white, of a waxy 
 appearance, and melts at 151 ; it is easily soluble in alcohol and ether ; 
 with alcalies it yields glycerine and palmic acid. The formula of which 
 is, according to Playfair, C 3 2H34O 5 -f HO. 
 
 The products of the complete oxidation of castor oil by nitric acid, 
 have been accurately examined by Mr. Tilly. The action is violent, and 
 much nitrous acid fumes are given off. Besides suberic and lipic 
 
888 Products of the oxidation of Castor Oil. 
 
 acids, a peculiar fatty acid is formed, which is colourless, of an agreeable 
 smell, and a sweet stimulating taste; it boils at 300, but cannot be 
 distilled with being in great part decomposed. Its formula was found 
 to be C 14 Hi30 3 + Aq. ; he formed the ether of this acid, in the way de- 
 scribed for oleic ether, and ascertained its formula to be C 14 H ]3 O 3 -f- 
 AeO. This body is termed the per-eenanthic add, or cenanthylic acid, 
 as it contains the same carbon and hydrogen as the oenanthic acid, which 
 exists in wine as described in page 814, but combined with an atom 
 more oxygen. 
 
 By the distillation of castor oil there is formed a large quantity of an 
 oil termed cenantkol. It boils at 312, and has the formula Ci 4 H 14 O2. 
 It is, therefore, to cenanthylic acid as aldehyd is to acetic acid, and the 
 cenanthic acid of wine may be a compound of those bodies, as 
 2.C 14 H 14 3 = C 14 HiA + C 14 H 14 4 . 
 
 Oil of Tiglium. Crotonine Crotonic Acid. 
 
 The experiments that have been made on this oil have not given very 
 satisfactory results ; by saponification it yields an acid which is exceed- 
 ingly volatile ; but whether the active properties of the oil reside in this 
 crotonic acid is not established, nor have any analytical results been ob- 
 tained as to its constitution. 
 
 Of the Manufacture of Soaps and Plasters. 
 
 Although the general principles of the constitution of soaps have been 
 frequently alluded to in the description of individual fatty substances, 
 and that a detailed account of their manufacture would be out of place 
 in the present work, yet it may not be uninteresting to notice, briefly, 
 some circumstances of the processes employed which could not be de- 
 duced from the mere theory of their nature, and yet are essential to 
 practical success. 
 
 There are found in commerce, three varieties of soap; 1st, hard white 
 soap, which is made from tallow and caustic soda ; 2d, hard yellow soap, 
 which is made from soda with tallow, palm oil, and resin ; 3rd, soft soap, 
 in which the alcali is potash, combined with whale or seal oil, and some 
 tallow. The difference of consistence depends principally upon the 
 alcali ; as the fatty salts of soda unite with water to form true hydrates, 
 which are completely solid, whilst the potash salts absorb water and form 
 a semitransparent gelatinous mass, such as the ordinary soft soap. 
 
 For the preparation of the hard white soap, a solution of caustic soda 
 is prepared, of specific gravity 1-050, by decomposing soda-ash by the 
 proper quantity of lime ; the soda ley being brought to boil, the tallow 
 is added in small portions at a time, until the free alcali has been all 
 
Manufacture of White, Yellow, and Soft Soaps. 889 . 
 
 combined with fatty acids, and the ley will saponify no more. The 
 liquor contains then free glycerine, and the fatty salts of soda, all dis- 
 solved together in the water, and as the soap scarcely crystallizes, a pe- 
 culiar method is necessary to separate it from the solution. This is 
 founded on the fact, that soap is insoluble in a solution of common salt. 
 If to a solution of soap in water, as much common salt be added as the 
 water can dissolve, the soap is separated, and floats on the surface of the 
 liquor completely deprived of water. But this is not the state in which 
 the manufacturer wishes it to be. Hence the salt is added but gradu- 
 ally to the soap ley, and the water then dividing itself between the salt 
 and the soap, a point is obtained, at which the soap is in its proper hy- 
 drated condition, and this being recognized by the appearance of the 
 boil, and the texture of the layer of soap, the latter is run into wooden 
 boxes where it congeals, and is then cut by a wire into the forms it pos- 
 sesses in commerce. 
 
 The hard white soap thus made generally contains from forty to fifty 
 per cent, of water. When very hard it still retains above thirty, and 
 may hold seventy per cent without being very soft. 
 
 The formation of the Yellow, or Resin Soap, depends on the direct 
 combination of an acid resin (colophony, p. 866) with soda. In this 
 case no glycerine is set free, as there is no proper saponification. A 
 mere compound of resin and soda would be, however, too soft, and also 
 act too powerfully on clothes ; and hence there is always a quantity of 
 a fat added, generally tallow, and some palm-oil, which brightens the 
 colour, and masks the disagreeable odour of the resin. A good soap 
 should contain two parts of fatty matter to one of resin. 
 
 The Soft Soap is manufactured by heating the oils in shallow pans, 
 and gradually adding a strong solution of caustic potash, boiling and 
 continually agitating the mass until the milkiness produced by the oil 
 vanishes, the mass becomes transparent, and the froth subsides. As 
 this soap cannot be separated from the liquor by the addition of com- 
 mon salt, which would decompose it, forming a soda-soap and chloride 
 of potassium, the liquor is evaporated until the operator recognizes that 
 it has attained the proper strength, and it is then cooled as speedily as 
 possible. The glycerine of the oils exists, therefore, mixed through 
 the substance of the soap. To give it greater consistence some tallow 
 is generally employed, and the stearate of potash crystallizing gradually 
 forms the white points which are seen in most specimens of soft soap. 
 
 Plasters are metallic soaps. Of those the only one of pharmaceutic 
 importance is the litharge plaster, prepared by boiling litharge, olive 
 oil, and water together ; oleate and margarate of lead are formed, and 
 float upon the surface ; when the mass has obtained the proper consis- 
 
890 Constitution of Cetine Etkal. 
 
 tence, it is removed and formed into rolls for use. The watery solution 
 contains glycerine and a large quantity of oxide of lead dissolved. If 
 litharge plaster be digested in ether, oleate of lead dissolves, and the 
 margarate of lead is left behind. 
 
 Of Spermaceti, Ethal, and the Derived Bodies. 
 
 Spermaceti exists in the cavities of the head of the physeter macro- 
 cephalus, and some allied species of whales, dissolved in the spermaceti 
 oil, from which it separates by crystallization, after the death of the 
 animal. To obtain it pure, it is to be crystallized repeatedly from its 
 alcoholic solution by cooling ; it is a remarkably beautiful crystalline 
 fat, melting at 120, and volatilizing at 680 without change, if the air 
 be excluded. In this pure state it is usually termed cetine, and its 
 formula is C 16 H 1G O, in its simplest form. By boiling with very strong 
 alcaliue solutions, it gradually saponilies ; but it differs totally from the 
 ordinary fats, as it contains none of the acids so far described, nor gly- 
 cerine, but yields a peculiar acid, the cetylic acid, and a peculiar base, 
 ethal, or hydrated oxide of cetyl. The cetine may be, in fact, regarded 
 as cetylate of cetyl, or still more simply as oxide of cetene. 
 
 Cetylic Acid. C3 2 H 31 O 3 -f Aq. Although this acid may be pre- 
 pared by the saponification of cetine, yet as its purification is then diffi- 
 cult, it is best obtained by heating cetine with a mixture of fused potash 
 and quicklime to about 350, hydrogen is given off, and the whole is 
 converted into cetylate of potash. The mass boiled in water is decom- 
 posed by chloride of barium, and the cetylate of barytes heated with 
 ether, to remove unaltered ethal or cetine. The residue is then decom- 
 posed by a strong acid, and the cetylic acid is obtained pure. It fuses 
 at 130. It is volatile, soluble in alcohol and ether. It appears to be 
 monobasic. It is remarkable as having the same formula and half the 
 equivalent of palmitic acid. See page 884. 
 
 Ethal. C 32 H330 -f- HO. To obtain this substance pure the 
 spermaceti is to be saponified, by being fused with half its weight of 
 potash ; the resulting mass being digested with water and muriatic acid, 
 the cetylic acid and the ethal separate from the liquor, and float upon 
 the surface. Being then mixed with lime, which combines with the 
 cetylic acid, and boiled in absolute alcohol, the ethal dissolves, and 
 crystallizes out on cooling, 
 
 It is a solid crystalline white substance, destitute of taste or smell ; 
 neutral to test paper ; it melts at 119, and volatilizes rapidly at 250; 
 it is insoluble in water ; its formula is C 32 H 34 O 2 , or C 32 H 3 3O + Aq. 
 
 The ethal is remarkable for its analogy, in composition and proper- 
 
Cetyl Series Nature of Wax. 891 
 
 ties, to the bodies of the alcohol group ; like them, it may be looked 
 upon as formed of water united to a carbo-hydrogen, isomeric with ole- 
 fiant gas, and by distilling ethal with glacial phosphoric acid, this body 
 is actually obtained, and has been termed cetene. It is an oily liquid, 
 colourless, soluble in alcohol and ether ; it boils at 527. Prom its 
 reactions, and the specific gravity of its vapour, 7846, it results that its 
 formula is C 32 H 3 2. 
 
 If ethal be heated with perchloride of phosphorus, a heavy liquid is 
 obtained, having the formula C^H&Cl; and by fusing ethal with 
 potassium, hydrogen is evolved, and a white solid substance formed, 
 consisting of C 32 H33O + KO, which with water gives hydrate of potash 
 and ethal. With sulphuric acid ethal forms sulpho-ethalic acid, which 
 resembles the sulpho-vinic acid, and has the formula C^H^O.SOg -j- 
 S0 3 .HO. Further, if the ethal be heated with potash, hydrogen gas is 
 given off, and an acid formed, the formula of which is C 32 H 31 O 3 + Aq.; 
 it is the cetylic acid. 
 
 From this analogy of ethal to wine-alcohol, a compound radical, 
 cetyl, similar to ethyl, may be assumed to exist in these combinations, 
 and its formula be written CsaH^ or Ct. Ethal is then Ct.O -f Aq. 
 On considering the whole history of cetine, it appears more probable 
 that the cetylic acid and the ethal are products of its decomposition, 
 and not its constituents. It is thus a simple material like cholesterine, 
 which by bases is broken up into two bodies, the oxygen and hydrogen 
 dividing themselves unequally, and producing an acid and a basic 
 substance, thus, 4.Ci6Hi 6 O, producing C 32 H 31 O 3 , and C^H^O, and each 
 of these assuming an atom of water in their isolated form. 
 
 Wax. Ordinary bees'-wax is a mixture of two substances which are 
 separated by boiling alcohol. Cerin dissolves ; it is quite white ; its 
 specific gravity is 0*969 ; it is less fusible than wax ; it does not com- 
 bine with bases : its formula is C 2 oH 20 O 2 . The substance insoluble in 
 alcohol is myracine, which melts at 95 ; its formula is C 20 H 20 O. In 
 yellow wax a colouring matter is present which has not been examined. 
 When wax is bleached by nitric acid, oxygen is absorbed, and a peculiar 
 substance formed, ceraic acid, which has the formula C^H^Og. All 
 these bodies are probably derived from oils, isomeric with otto of roses, 
 which exist in the flowers of odoriferous plants. 
 
 When cerin is boiled with solution of potash, a soap is formed, and 
 from this a peculiar waxy substance (ceram) is obtained, as ethal is from 
 spermaceti : its properties are but very little known ; from an analysis 
 by Ettling its formula would appear to be C 18 H 19 O 7 . A peculiar kind 
 of wax, termed ceroslne, has been found in the sugar cane ; its formula 
 
892 
 
 CHAPTER XXV. 
 
 OF THE ORGANIC ACIDS WHICH PRE-EXIST IN PLANTS., AND DO NOT 
 BELONG TO ANY ESTABLISHED SERIES. 
 
 Tartaric Acid. C 8 H 4 0, -f- 2Aq. 
 
 This important acid exists in most kinds of fruit, occasionally free, but 
 more usually combined with potash, forming cream of tartar, or as tar- 
 trate of lime. For the purposes of commerce it is almost exclusively 
 prepared from the bi-tartrate of potash. This salt exists abundantly in 
 grape juice, and being but very slightly soluble in spirituous liquors, it 
 gradually separates as the alcoholic fermentation proceeds, and collects 
 in irregularly crystallized layers on the insides of the casks in which the 
 wine is made. It is purified, as will be elsewhere described. 
 
 When one part of carbonate of lime is added to a solution of four 
 parts of bitartrate of potash, one-half of the tartaric acid combines with 
 the lime, carbonic acid being expelled with effervescence. Tartrate of 
 lime precipitates as a white powder and neutral tartrate of potash re- 
 mains dissolved. By the addition of chloride of calcium to the liquor, 
 this portion also of tartaric acid is thrown down, and chloride of potas- 
 sium is formed. The whole quantity of tartrate of lime being then col- 
 lected and washed, it is to be digested with a quantity of oil of vitriol 
 equal to half the weight of the cream of tartar employed, and diluted with 
 four parts of water ; sulphate of lime is formed and tartaric acid set free. 
 The mixture having been boiled for a short time is to be strained, and 
 the liquor evaporated gently to a pellicle ; the tartaric acid then crystal- 
 lizes on cooling. 
 
 The tartaric acid forms colourless oblique rhombic prisms, generally 
 tabular, as in the figure, where i, u, n, are primary, and 
 a, c, m, secondary faces ; it is permanent in the air, 
 and dissolves readily in half its weight of water ; it 
 is also easily soluble in ale ohol ; its taste and reaction 
 is strongly acid. When heated, it abandons water and forms two acids 
 which will be again noticed. When a solution of it is long exposed to 
 the air, it absorbs oxygen, and forms carbonic and acetic acids. This 
 
Tartaric Acid Tartrate of Potash. 893 
 
 effect may be instantly produced by boiling it with an excess of oxide 
 of silver, metallic silver being set free. 
 
 Tartaric acid is known by its not being volatile, and by leaving a 
 copious coaly residue when heated. If it be fused with potash, it is de- 
 composed, acetic and oxalic acids being produced (p. 670) ; with other 
 oxidizing agents, as black oxide of manganese and sulphuric acid, it 
 gives carbonic and formic acids. A solution of tartaric acid precipitates 
 lime water ; but the precipitate is redissolved by an excess of acid, or by 
 solution of sal-ammoniac. The soluble neutral tartrates give white pre- 
 cipitates, which are not crystalline, with the neutral salts of lead, lime 
 and silver, which all re-dissolve in an excess of acid. 
 
 The tartaric acid is bibasic; its formula being C 8 H 4 Oio+2Aq. ; 
 several of its salts are of considerable importance. 
 
 Bi-tartrate of Potash Cream of Tartar. 
 C 8 H 4 Oio -f KO.Aq. 
 
 This salt, just now noticed as being deposited from grape-juice, ac- 
 cording as alcohol is formed, is sent into commerce under the name of 
 argol, which is red or white according to the kind of wine it was depo- 
 sited from. This is dissolved in 'boiling water, and mixed with some 
 pipe-clay, which, combining with the colouring matter of the grape, 
 renders it insoluble ; the clear liquor is then allowed to cool slowly, and 
 the cream of tartar is deposited in irregular crystals on the sides of the 
 vessel, still containing a small quantity of tartrate of lime. It 
 crystallizes in right rhombic prisms, as in the figure j,w,ra, being 
 primary, and a,a,i,m, secondary planes. It is but very 
 sparingly soluble in cold water, requiring 80 parts 
 at 60 ' anc ^ ^ P^ 8 at 212; hence an excess of tar- 
 taric acid produces a crystalline precipitate in solutions 
 of potash, which are not very dilute. By calcining cream of tartar either 
 alone or with nitre, the black or white fluxes employed in metallurgy are 
 formed (p. 546), Its calcination furnishes also the purest source of 
 carbonate of potash, which hence derives its name of salt of tartar 
 (p. 688). 
 
 Neutral Tartrate of Potash Soluble Tartar. C s Hfl }0 -f KO.KO. 
 This salt is formed by adding cream of tartar to a hot solution of car- 
 bonate of potash, until this be completely neutralized. It crystallizes 
 with difficulty in right rhombic prisms, which when pure are not deli- 
 quescent. 100 parts of water dissolve 130 parts of it at 60, and 268 
 parts at 212. Any strong aci d added to its solution takes half the potash, 
 and precipitates cream of tartar. 
 
894 
 
 Eochelle Salt Tartar of Iron. 
 
 The Tartrates of Ammonia resemble closely those of potash. The 
 neutral tartrate of soda crystallizes in large rhombic prisms like nitre ; 
 it is very soluble in water, its formula C 8 H 4 O 10 +2.NaO-f-4Aq. 
 
 Tartrate of Potash and Soda Eochelle Salt. C g H 4 O 10 + KO. 
 NaO +10Aq. Is prepared by neutralizing a hot solution 
 of carbonate of soda with cream of tartar ; by evaporation 
 and cooling it forms large prismatic crystals, with many 
 sides, of the right rhombic system ; p, u, u, being primary 
 and i, i, t, e, e, being secondary faces. These crystals are 
 remarkable for being often but half formed, so as to present 
 the aspect represented in the lower figure. Its taste is 
 mildly saline, and not very disagreeable, whence its popu- 
 larity as a medicine. It is permanent in the air except it be 
 very dry, when it effloresces slightly on the surface; it dis- 
 solves in two parts of cold water. 
 The Tartrate of Lime is very sparingly soluble in water, and is pre- 
 cipitated as a white powder, when solutions of a neutral tartrate and of 
 a salt of lime are mixed. It dissolves in an excess of acid ; and if this 
 solution be neutralized, it is deposited in small octohedral crystals, 
 which have the formula C g H 4 Oi + CaO.CaO + 8Aq. Nolner has 
 asserted, that when tartrate of lime is mixed with yeast a fermentation 
 sets in by which a new acid, pseudo-acetic acid, is produced ; this 
 requires, however, confirmation. 
 
 Proto-tartrate of Iron. C 8 H 4 Oi + 2.EeO. Is a white powder, 
 very sparingly soluble in water ; it is formed in minute crystals when 
 hot solutions of protosulphate of iron and of cream of tartar are mixed 
 together. The prototartrate of iron and potash, C 8 H 4 10 + FeO.KO, 
 is formed by digesting cream of tartar and water with metallic iron. 
 Hydrogen gas is evolved, and a white, sparingly soluble, salt is obtained, 
 which, when exposed to the air, rapidly absorbs oxygen, and becomes 
 greenish brown or black. In this state it contains magnetic oxide of 
 iron, and is much more soluble. 
 
 Pertartrate of iron, formed by dissolving the freshly precipitated red 
 oxide of iron in a solution of tartaric acid, gives by evaporation a brown 
 jelly. If the red oxide of iron be boiled with a solution of cream of 
 tartar, it dissolves abundantly, giving a fine brown -red liquor, from 
 which, by cautious evaporation, small ruby-red crystals may be obtained ; 
 but it is generally dried down completely, when it forms a translucent 
 brown mass, deliquescent in damp air. An excess of tartaric acid 
 should be avoided, as it acts on the peroxide of iron during the evapo- 
 ration, reducing it to the state of protoxide, and carbonic acid being 
 given off. Hence the pharmacopoeias direct perfect neutrality of the 
 
Tartrate of Antimony and Potash. 895 
 
 liquor to be secured by the addition of a small quantity of ammonia. 
 The formula of this salt is C 8 H 4 O 10 + KO.Fe 2 O 3 . It is very soluble in 
 water, and its solution is not precipitated by an excess of potash. 
 Another form of tartarized iron, is formed according to the pharmaco- 
 poeias by digesting cream of tartar with iron filings and water 
 until it is saturated. Its constitution is not very definite, the iron 
 should finally be peroxidized, but the product contains usually a great 
 deal of iron as protoxide or magnetic oxide. 
 
 Tartrate of Antimony. 3(C g H 4 O 10 ) + SbO 3 . This salt is obtained 
 by the solution of the sesquioxide of antimony in tartaric acid ; it is 
 colourless and crystallizes in short deliquescent prisms. 
 
 Tartrate of Potash and Antimony. Tartar -Emetic. C 8 H 4 C 10 + 
 KO.Sb0 3 -}- 2Aq. This salt, the most important compound of antimony, 
 is prepared by boiling together in water, equal weights of sesquioxide 
 of antimony and cream of tartar. In the Dublin and Edinburgh 
 pharmacopoeias, the powder of algarotti (p. 642) is employed as the 
 source of oxide of antimony ; but by the London college, an impure 
 oxide is prepared by gently deflagrating together sulphuret of antimony 
 and nitre, with a little muriatic acid, and washing out the soluble 
 products. In either case the oxide of antimony replaces the second 
 atom of base (water) in the cream of tartar, and by evaporation and 
 cooling, it may be obtained in crystals, which are right rhombic octohe- 
 drons, with many secondary planes, as in the figure. 
 This salt dissolves in fourteen parts of cold, and in 
 two of boiling water. In dry air it effloresces, losing 
 the 2Aq. Its solution is not affected by alcalies ; but 
 the oxide of antimony is precipitated by sulphuric or 
 muriatic acids, and by ammonia. In the preparation 
 of tartar emetic, the whole product from the materials 
 used can never be obtained crystallized, the mother 
 liquor contains a substance which dries down to a 
 transparent mass, like gum arabic. By alcohol it is 
 decomposed into tartar emetic, and free tartaric acid. According to 
 Knapp's analysis, this salt is the neutral tartrate of potash and anti- 
 mony, having the formula C 4 H 2 O 5 .KO + (3.C 4 H 2 O 5 + SbO 3 ) + 2Aq. 
 It may be formed by dissolving tartar-emetic in a strong solution of 
 tartaric acid, and then crystallizes in minute oblique rhombic prisms. 
 In order to form this salt, however, from cream of tartar, and oxide of 
 antimony, a quantity of potash must enter into some form of combination 
 which has not been as yet explained. 
 
 Owing to the occasional presence of arsenic in the ores of antimony, 
 the tartar-emetic of commerce is not unfrequently contaminated by its 
 
896 Tartar-Emetic j Borotartrates, and Arseniotartrates. 
 
 presence, and should in such case be absolutely rejected from medi- 
 cinal use. 
 
 If tartar-emetic be exposed to a temperature of 480, it abandons, 
 besides its crystal-water, two equivalents of water, the elements of which 
 are abstracted from the constitution of the tartaric acid as generally 
 assumed. In this dried tartar-emetic, therefore, the organic element is 
 not C 8 H 4 Oio, but C 8 H 2 O 8 . When redissolved in water, it resumes the 
 two atoms of water, forming ordinary tartar-emetic again. Of the 
 other salts of tartaric acid, but one possesses this property ; the boro- 
 tartrate of potash being also reduced by loss of water at 480 to the 
 formula C 8 H 2 8 + KO.B0 3 . Chemists are not unanimous in ex- 
 plaining this peculiarity. The simplest idea is, that these two atoms 
 of water exist ready formed in these salts, and that tartaric acid is 
 really quadribasic ; being in its crystallized form CsH^Og + 4HO ; 
 the cream of tartar being C 8 H 2 O 8 + KO.3HO; Eochelle salt, C 8 H 2 O 8 + 
 KO.NaO.2HO; and for tartar-emetic, the oxide of antimony replacing 
 three atoms of a protoxide, the formula is C 8 H 2 O8 + KO.SbOa + &Aq 
 + 2Aq, and the two portions of water being retained by very unequal 
 forces are given off at very different temperatures. Berzelius considered 
 that in this change the nature of the acid is totally altered; and as 
 opinion is so much divided on the subject, I shall not enter further into 
 its discussion. 
 
 Borotartrate of Potash. Cream of tartar and boracic acid unite in 
 two proportions, forming compounds precisely resembling the two tartar- 
 emetics, the antimony being replaced by boron. These salts are used 
 in medicine. They are very soluble in water, sparingly soluble in 
 alcohol. The boracic acid here certainly enters into the constitution of 
 the acid, as it cannot be considered to act as a base. 
 
 Arsenio-tartrate of Potas/i. The arsenious acid also combines with 
 cream of tartar, forming a salt which does not crystallize well, but 
 appears to be constituted precisely as tartar emetic. 
 
 Action of Heat on Tartaric Acid. 
 
 When tartaric acid is cautiously heated, it fuses into a mass like gum, 
 and gives off water. In this state it combines with bases forming salts 
 quite different from the tartrates ; it retains its bibasic character, but its 
 atomic weight is increased to one and a half times that of tartaric acid ; 
 its formula being C 12 H 6 15 -f-2Aq. It thus constitutes tartralic acid; 
 it does not crystallize, and in solution gradually passes back into tartaric 
 acid. If the tartralic acid be kept long melted at 360, it abandons 
 still more water, and forms tartrelic acid, in which the bibasic character 
 
Pyrotartaric Acid Racemic Acid. 897 
 
 remains, its formula being C 16 H 8 O2o. + 2Aq. This acid is characterized 
 by forming insoluble salts with lime and barytes, thereby differing from 
 the tartralic acid. If the heat be still longer kept up, a porous white 
 mass is formed, which is insoluble in water and in alcohol. It is anhy- 
 drous tartaric acid ; its formula is C 8 H 4 O 10 . If left long in contact with 
 water it changes successively into the tartrelic, tartralic, and common 
 tartaric acid. This change is produced more rapidly by boiling with a 
 solution of potash : this substance appears to hold the same relation 
 to tartaric acid that the white sublimate does to the proper lactic 
 acid (p. 769). 
 
 If tartaric acid be distilled at a still higher temperature, it abandons 
 water and carbonic acid; and forms pyrotartaric acid ; C 8 H 4 O 10 , giving 
 off 3.CO 2 and HO, and C 5 H 3 O 3 remaining. The process succeeds 
 best at about 400. This acid is white ; it crystallizes from the dis- 
 tilled liquors in prisms which are to be purified from empyreumatic oil 
 by recrystallization and digestion with animal charcoal ; it reacts very 
 acid; it melts at 210, and sublimes at .360 ; is very soluble in water 
 and alcohol. It is a monobasic acid, forming salts which, with few 
 exceptions, are soluble and crystallizable. 
 
 Racemic Acid. C8H 4 O J0 4-2Aq. 
 
 This acid is found in grape juice, replacing tartaric acid to a greater 
 or less extent ; its formation appears to depend on very peculiar circum- 
 stances, as it has never been found except in the district about the 
 Vosges Mountains, and only in some seasons. It is combined with 
 potash, forming a kind of cream of tartar, which is bi-racemate of 
 potash, and from, which it is prepared by the same methods as have been 
 described for tartaric acid. 
 
 It crystallizes in colourless oblique rhombic prisms, which contain 
 water, of which one-half is lost by efflorescence in warm dry air ; the 
 remaining hydrate is identical in composition with crystallized tartaric 
 acid ; it tastes and reacts as strongly acid. In its relation to salts, it 
 follows nearly the same rules as the tartaric acid, but their crystalline 
 form is completely different ; it also is a bibasic acid, and its formula, 
 when crystallized, is C 8 H 4 O 10 -f 2.HO + 2Aq. The characters by which 
 it is distinguished from tartaric acid are; First, racemic acid requires ten 
 times as much water for solution, and they are hence easily separated 
 by crystallization. Second, that the corresponding salts are not of the 
 same crystalline form. Third, the racemate of potash and soda is 
 uncrystallizable, giving merely a gummy mass, whilst the Rochelle salt 
 forms very large crystals. Fourth, the racemate of lime is insoluble in 
 57 
 
898 Racemic Acid Citric Acid. 
 
 a solution of sal-ammoniac. The two acids, however, form a most 
 perfect example of isomerism, as not merely their composition, but their 
 atomic weight is absolutely the same. 
 
 When heated, racemic acid passes through precisely the same changes 
 as have been described for tartaric acid, abandoning water, and forming 
 two bibasic acids, whose formulae are respectively Ci 2 H 6 Oi 5 -f- 2HO and 
 C 16 H 8 20 -f- 2HO. They are distinguished by their salts, which differ 
 in characters from each other, and from those of the bodies formed by 
 tartaric acid. 
 
 By the destructive distillation of racemic acid, is generated the pyro- 
 racemic acid, in which the isomerism with the tartaric acid series is 
 broken through ; its formula being C 6 H 3 5 . It differs totally in pro- 
 perties from the pyrotartaric acid; it does not crystallize; it tastes 
 acid ; its salts are all soluble and crystallizable ; but pass also into a 
 gummy condition. If a little crystal of copperas be laid in a solution of 
 one of these salts, it becomes coloured bright red. 
 
 Citric Acid. C 12 H 5 O n + 3HO + 2Aq. 
 
 This acid exists in the juices of fruits, especially the lemon, orange, 
 currant, and quince. It is usually prepared from lemon juice, which is 
 clarified by rest, then saturated with chalk, and the neutral solution is 
 boiled until the citrate of lime is completely deposited ; this is then 
 washed and decomposed by a quantity of oil of vitriol, equal in weight 
 to the chalk employed, and diluted with six volumes of water. After 
 the sulphate of lime has been removed by straining, the liquor is eva- 
 porated, and allowed to crystallize by very slow cooling; the crystal-form 
 is generally that of a right rhombic prism, very much modified, as in the 
 figure, in which iu' u are primary, and n, y, r } are secon- 
 dary planes. In this case its formula is that given above ; 
 but if its solution be evaporated at 212 to a pellicle, it 
 crystallizes whilst hot, in a totally different form, and its 
 formula is C 12 H 5 On -f 3HO. By exposing the hydrated 
 crystals in vacuo to sulphuric acid, or to a gentle heat, the 2Aq. may 
 also be removed. 
 
 The citric acid possesses an agreeably sour taste : it dissolves in less 
 than its own weight of cold, and in half its weight of boiling water ; it 
 is sparingly soluble in alcohol ; when heated it fuses, becomes yellow, 
 and ultimately gives the usual pyrogenic products of organic acids. It 
 is a tribasic acid, and gives rise to three classes of salts, which, as they 
 may contain different quantities of combined water, rendered their his- 
 
Products of the Decomposition of Citric Add, 899 
 
 tory very confused until Liebig explained their true constitution. Very 
 few of these salts are, however, of practical or medicinal interest. 
 
 Citrate of Soda crystallizes in efflorescent prisms, having the formula 
 Ci 2 H 5 0,i + 3NaO -f 4Aq + 7Aq. By exposure to a heat of 212, 
 the 7Aq. are removed, and at 400 the remaining 4Aq. are driven off: 
 Berzelius is of opinion, that in this action the real constitution of the 
 citric acid is changed, and that it is partly converted into aconitic acid, 
 but the point is not yet experimentally decided, and Liebig^s views ex- 
 plain the phenomena with such beautiful simplicity that I have no hesi- 
 tation in adopting them, at least provisionally. 
 
 The Citrate of Lime is obtained by mixing solutions of a soluble 
 citrate and of salt of lime ; it forms a white powder, sparingly soluble 
 in pure water, but much more so if the liquid be acid. Its constitution 
 isC 12 H 5 O n -f 3CaO + 4Aq. When boiled with an excess of lime 
 water, citric acid forms a basic citrate of lime, which is less soluble than 
 the neutral salt. 
 
 The Citrates of Lead and Barytes are white powders, insoluble in 
 water, formed by double decomposition, and resembling in constitution 
 the citrate of lime ; there are also basic salts, the formation of which, 
 as in that of lime, appears to result from the crystal- water (2Aq.) of the 
 acid being more or less replaced by metallic oxide, in addition to that 
 which fulfils the proper basic function. 
 
 The Citrate of Silver is a white powder, its formula is C 12 H 5 O n + 
 3AgO. It therefore shows the true constitution of the anhydrous citric 
 acid. 
 
 There is a potash citrate of antimony analogous to tartar emetic. 
 
 The citric acid is easily recognized by forming no precipitate with 
 liine water, unless the liquor be heated. Its potash salt is also very 
 soluble, even with an excess of acid ; it is thus distinguished from the 
 racemic and tartaric acids. 
 
 Aconitic , Itakonic, and Citrakonic Acids. 
 
 When citric acid is heated it fuses, gives off water, and is converted 
 into an acid, which, from being found in the aconitum napellus, is 
 called aconitic acid, but it exists also abundantly in various species of 
 equisetum, and was hence often called equisetic acid. To complete the 
 change of the citric acid it must be distilled until the gases which coine 
 over cease to be inflammable, and oily drops appear in the receiver ; 
 the process is then to be interrupted, the mass remaining in the retort 
 to be dissolved in water, the solution filtered and evaporated to a pellicle. 
 On cooling, it forms a crystalline mass, from which ether dissolves out 
 
Aconitic, Itakonic and Malic Acids. 
 
 the aconitic acid, and leaves unaltered citric acid behind ; the former 
 may then be obtained crystallized by evaporation. In this reaction, be- 
 sides the aconitic acid, there are produced acetone, and a mixture of 
 carbonic oxide and carbonic acid gases. 
 
 Aconitic acid is soluble in water, alcohol, and ether ; its formula is 
 C 12 H 3 O 9 +'3.Aq. ; like citric acid it is tribasic; it forms well cha- 
 racterized salts; the aconitate of ether had been mistaken for citric 
 ether, for when citric acid is put in contact with alcohol and oil of vi- 
 triol, it changes into aconitic acid. 
 
 If aconitic acid be heated until it boils, it gives off carbonic acid, and 
 forms ita&onic acid, which distils as an oily liquid, and forms a crystalline 
 mass as it cools ; by solution in alcohol and slow evaporation, it may be 
 obtained in long prismatic needles ; its salts, of which there are two 
 classes, (it being bibasic), generally crystallize very well ; its formula 
 is C 10 H 4 06 + 2Aq ; formed by the aconitic acid losing C 2 O 4 , but an 
 atom of water, previously basic, entering into the organic element. 
 When the itakonic acid is redistilled, it is converted into water and a 
 heavy oil liquid, citrakonic acid, the formula of which is C 10 H 3 5 + Aq. 
 In contact with water it forms a crystalline mass containing 2Aq. 
 
 All these products are simultaneously and successively formed in the 
 distillation of common citric acid. Acetone is also generated, C 12 H 12 Oj 2 
 giving 3(C 3 H 3 0), with 3.HO and 3(C0 2 .) 
 
 Malic Acid.V*R>i + 2HO. 
 
 This acid exists in most fruits associated with citric and tartaric 
 acids ; but it is found purest and most abundant in the berries of the 
 mountain ash, and in the house leek. The best mode of extraction is 
 the following, devised by Liebig. The juice of the berries of the moun- 
 tain ash (sorbus aucuparia) is to be nearly but not completely neutralized 
 by lime, and the liquor then boiled for some hours, during which the 
 malate of lime precipitates as a sandy white powder ; when no more falls 
 down, the neutralization is completed by adding a little lime, and on 
 cooling the remainder of the salt is obtained. This malate of lime is to 
 be dissolved by boiling, in the smallest possible quantity of very dilute 
 nitric acid. On cooling, the acid malate of lime crystallizes, and is to 
 be purified by recrystallization. This salt being then decomposed by 
 acetate of lead, malate of lead is formed, which, being acted on by sul- 
 phuretted hydrogen, gives sulphuret of lead and free malic acid ; by 
 evaporation of the liquor and cooling, a sirup thick liquid is obtained, 
 which, after long repose, forms a white crystalline mass. 
 
 Malic acid is deliquescent, and very soluble in water. It tastes and 
 reacts strongly acid ; its relations to bases are very curious ; thus, mag- 
 
Maleic Add Fumaric Acid. 901 
 
 nesia is the only earth by whose carbonate it can be completely 
 neutralized. This arises from its tendency to form salts, in which one 
 atom of basic water is preserved ; it befhg a bibasic acid. Another pe- 
 culiarity pointed out by Hagen is, that it forms with many bases two 
 neutral salts, of which one retains water with obstinacy at 212. at which 
 temperature the other at once abandons it. When crystallized, it 
 appears to contain only basic water ; its formula is hence C 8 H 4 O 8 + 
 2Aq. None of its salts are of technical or medicinal interest, and hence 
 require but brief notice. 
 
 The alcaline malates are very soluble in water, scarcely crystallizable, 
 sparingly soluble in alcohol. 
 
 The Malate of Lime forms as a granular white precipitate, when malic 
 acid is neutralized by lime. Its formula is C 8 H 4 O 8 + 2.CaO ; it sepa- 
 rates in hard brilliant crystals, which contain 5 Aq., when the following 
 salt is neutralized by an alcaline carbonate. Bi-malate of lime, 
 C 8 H 4 O 8 -f CaO.HO + 6Aq. crystallizes in large right rhombic octo- 
 hedrons. "Water dissolves it abundantly when boiling, but very 
 sparingly when cold. 
 
 The Malate of Lead C 8 H 4 O 8 + 2PbO, precipitates, on mixing so- 
 lutions of a soluble malate with acetate of lead, as a white curdy mass, 
 which, after some- time, changes into minute but brilliant crystalline 
 scales. By boiling in water, a small quantity of it is dissolved, which 
 separates in brilliant plates on cooling. It fuses below 212, and is then 
 nearly insoluble in water. 
 
 Malic Acid is distinguished both from tartaric and citric acids, by not 
 giving any precipitate with lime water either by heat or when cold. 
 
 When malic acid is heated to a temperature of about 400, it aban- 
 dons water and gives origin to two acids, of which one is remarkable as 
 being found naturally existing in several plants. They are the maleic 
 acid and fosfumaric acid, the latter so called from having been first dis- 
 covered in the fumaria officinalis. These acids are isomeric, the reaction 
 being in both cases, that C 8 H 4 8 produces 2 HO and C 8 H 2 6 . Both 
 acids may be formed in the same process ; the maleic acid passes over 
 with the water, ' and crystallizes from the condensed liquor ; the less 
 volatile fumaric acid constitutes the residue in the retort, which solidifies 
 into a crystalline mass as it cools. From the plants which contain this 
 acid, it may be obtained by precipitating the clarified juices by acetate 
 of lead, and decomposing the salt of lead by sulphuretted hydrogen. 
 The liquors yield the acid by crystallization when concentrated to the 
 necessary degree. 
 
 The Maleic Acid, which had been thought identical with the aconitic 
 acid, already noticed, forms crystals of a sour bitter taste, soluble in 
 
902 Meconic Acid and its Salts 
 
 water, alcohol, and ether. When heated it abandons water, and the 
 anhydrous acid remains, which, if the water be allowed to flow back, 
 gradually changes into fumaric acid. This anhydrous acid melts at 167 
 and sublimes at 350. Of its salts, that of barytes alone is remarkable, 
 it is a white precipitate which changes soon into a mass of brilliant plates. 
 
 The Fnmaric Acid, which exists also in Iceland moss, crystallizes in 
 fine long prisms, which fuse with difficulty, and volatilize first at 400. 
 It requires 200 parts of water for its solution. When heated, it is de- 
 composed into water and anhydrous maleic acid. The fumarate of 
 silver is so insoluble that one part of the acid, dissolved in 200,000 
 parts of water, is precipitated by nitrate of silver, but the precipitate 
 dissolves in nitric acid. The salts, with copper, iron, and lead, are also 
 very sparingly soluble. 
 
 When muriatic acid gas is passed into a solution of malic acid in ab- 
 solute alcohol, Hagen found that the ether formed contains fumaric and 
 not malic acid. It is a liquid, heavier than water, of an agreeable 
 smell. With potash it gives alcohol and fumarate of potash. Its 
 formula is C 4 H0 3 O + AeO. On adding water of ammonia to this ether, 
 a substance is deposited in brilliant white scales, insoluble in cold water 
 and in alcohol, but dissolved by boiling water. It isfumaramid ; its 
 formula being C 4 H0 2 .Ad. By potash, ammonia is set free, and fuma- 
 rate of potash formed. 
 
 Meconic Acid C 14 HO n + 3.HO -f 6Aq. 
 
 This acid is found only in opium ; it is best extracted by adding 
 chloride of calcium to an infusion of opium in cold water. A white 
 precipitate of mixed meconate and sulphate of lime occurs. This 
 being washed with hot water and with alcohol, it is to be treated 
 with dilute muriatic acid, heated to about 180. The meconate of lime 
 dissolves, and from the liquor on cooling, bi-meconate of lime separates 
 in brilliant crystalline plates. On dissolving these in warm strong mu- 
 riatic acid, and cooling the solution, the pure meconic acid crystallizes. 
 It may be freed from any adhering colouring matter by combination 
 with potash, decomposing the crystallized mecouate of potash by muri- 
 atic acid and recrystallization. 
 
 When pure, meconic acid is in brilliant white crystalline scales, con- 
 taining 6.Aq., which they give off at 212 ; it is soluble in four parts 
 of boiling water; it is a tribasic acid, forming salts, of which those 
 with the earths and heavy metallic oxides are generally insoluble in 
 water. There are three classes of meconates, according as the quantity 
 of fixed base is one, two, or three atoms. Few of them are specifically 
 of importance. The most characteristic properties of this acid are, 
 
Derivative* of Meconic Acid Tannin. 903 
 
 1st, that it produces with solutions of the peroxide of iron a blood-red 
 colour, analogous to that of the sulphocyanide of iron, from which it is 
 distinguished by the fact, that on the addition of the acetate of lead, a 
 white precipitate is formed, which, when heated to full redness with a 
 little sulphur and potassium, and treated with water, gives no red colour 
 with the salts of iron (see page 751) ; 2nd, that with nitrate of silver 
 it gives a white precipitate, which is dissolved by dilute nitric acid ; the 
 liquor, however, when boiled, becomes milky, and deposits cyanide of 
 silver. 
 
 If a strong solution of meconic acid be boiled for a long time, or if 
 the crystallized acid be dissolved in strong boiling muriatic acid, it is 
 converted into Jcomenic acid ; carbonic acid being given off. The crys- 
 tallized meconic acid undergoes the same change, when heated to 400. 
 This acid forms granular crystals, which are soluble only in sixteen 
 parts of boiling water, and have the formula C 12 H 2 O 8 + 2HO, as the 
 Ci 4 HO H loses CO 2 and gains HO. This acid is bibasic ; the third 
 atom of water, which was basic in the meconic acid, entering into the 
 radical here. It also reddens the per-salts of iron. It forms two series 
 of salts, which in properties resemble closely the corresponding meco- 
 nates. When it is heated to 500, it gives off water and carbonic acid, 
 and forms pyro-meconic acid, of which the formula is C 10 H 3 O 5 -f HO. 
 This acid forms crystalline plates, which fuse at 240, and are volatilized 
 by a heat little higher. It is very soluble in water, alcohol, and ether ; 
 it is a monobasic acid, forming salts, which, with the exception of that 
 of lead, are all soluble in water. Like the acids, from which it is de- 
 rived, it strikes a blood-red colour with solutions containing peroxide 
 of iron. 
 
 Tannic Acid or Tannin. C 18 HO 9 + 3HO. 
 
 This important substance exists in the bark of most exogenous trees, 
 particularly the oak and horse-chesnut, . accumulated principally in the 
 inner layers of bark. It is found also in the roots of the tormentilla 
 and bistort, in the leaves of roses and pomegranates; but its most 
 abundant source is the gall-nut of the oak (quercus infectoria). 
 
 To distinguish this from the other kinds of tannin, of which there 
 are a great number, it may be suitably termed gallo-tannw acid, and I 
 shall generally, though, perhaps, not uniformly, employ that name. 
 
 The method given by Pelouze for its extraction, and which serves for 
 the preparation of a variety of other vegetable principles, is as follows : 
 into a globular funnel, b, which can be closed at the top by a stopper, 
 
904 Preparation and Properties of Tannin. 
 
 and rests in a bottle, a, as in the figure, is to be introduced a quantity 
 of nut-galls, in powder, moderately compressed, after the 
 tube of the funnel has been stopped with a little cotton. 
 The upper empty part of the funnel is to be then filled with 
 ether, as it is usually found in the shops, containing about 
 one-tenth of water dissolved in it, and the apparatus allowed 
 to stand for some days. The bottle is then found to contain 
 two layers of liquid. The inferior, sirup-thick, is a concen- 
 trated solution of tannic acid in water, with very little 
 ether. The upper is ether, containing but a small trace of 
 tannic and gallic acids. Being separated, the lower layer is 
 to be washed once or twice with a little ether, and then 
 evaporated in vacuo, with a capsule of sulphuric acid. A faintly 
 yellowish white mass remains, of a distinctly crystalline structure, which 
 is pure gallo-tannic acid. The theory of this process is, that the tannic 
 acid is so greedy of water as to withdraw it from the ether, and to dis- 
 solve in it to the exclusion of every other constituent of the gall-nut. 
 
 The watery solution of gallo-tanuic acid reddens litmus ; it is pro- 
 bably insoluble in absolutely anhydrous alcohol and ether ; its taste is 
 intensely astringent, but not bitter. The most characteristic property 
 of tannic acid is, that it combines with the animal substance, gelatine, 
 and forms a compound insoluble in water, which is the basis of most 
 kinds of leather ; hence any tissue, as skin, which contains gelatine, 
 removes gallo-tannic acid from its watery solution, on which is founded 
 the art of tanning. It is a tribasic acid, and forms three classes of 
 salts, which are of interest, from the colours of the precipitates it gives 
 with metallic solutions, being often useful as a test for the presence of 
 certain metals. Hence an infusion, or tincture of galls, is always found 
 in the laboratory as a re-agent ; it does not affect the solutions of zinc, or 
 cadmium, or the protoxides of iron, and manganese, nor any of the alka- 
 line or earthy salts. "With the other metals it gives precipitates which 
 with lead and antimony are white ; with copper, grey ; with tin, nickel, 
 cobalt, cerium, tellurium, and silver, are various shades of yellow ; with 
 tantalum, and bismuth, are orange ; with titanium, blood red ; with 
 platinum, green; with chrome, molybdenum, uranium, and gold, are 
 brown ; and with osmium and peroxide of iron, are rich bluish -purple. 
 This last is the most important of all from its great delicacy and dis- 
 tinctness. If the solutions be very strong, the liquor appears absolutely 
 black, and constitutes the material of ordinary writing ink. 
 
 The insolubility and consequent inactivity of tannate of antimony is 
 taken advantage of in medicine ; infusion of oak-bark, or galls, being 
 employed as an antidote in poisoning by tartar-emetic. I shall have 
 
Derivatives of Tannin Gallic Acid-. 905 
 
 occasion hereafter to notice its use in the detection and neutralization of 
 the vegetable alcaloids. 
 
 The gallo-tannic acid is not the only kind of tanning material em- 
 ployed in the manufacture of leather ; yet as the others will hereafter 
 come under notice, I shall here give Humphrey Davy's estimate of the 
 comparative power of such substances as contain true tannic acid. He 
 found the quantity of active material in 100 parts of the following 
 bodies to be 
 
 Gall nuts 27'4 White inner oak bark . . . 16'0 
 
 Oak bark entire .... 6*3 White inner horse-chesnut . . 15'2 
 
 Horse chesnut bark entire . . 4'3 Sicilian sumac 16'2 
 
 Elm bark entire . 2'7 Malaga sumac 10.4 
 
 These numbers are but approximative, and such as are given by very 
 rough processes ; the true quantity of tannic acid present being much 
 larger ; thus the nut galls easily yield by Pelouze's method forty per 
 cent, of pure product. 
 
 When a solution of tannic acid is exposed to the air it is decom- 
 posed, absorbing oxygen and evolving carbonic acid ; the liquor becomes 
 coloured, and a large quantity of gallic acid is found to be produced. 
 
 Tannoxylic and Tannomelanic Acids. 
 
 When a solution of tannin with an excess of potash is exposed to 
 the air, oxygen is absorbed and the liquor becomes black. It then 
 gives with acetate of lead a crimson red precipitate. This is said to be 
 a salt of an acid, tannoxylic acid, having the formula C 15 H5O n . If the 
 potash liquor be boiled for a long time the gallic acid and tannoxylic 
 acids first formed disappear, and there is produced a new acid which 
 separates on the addition of a stronger acid as a brown powder insoluble 
 in water. The formula C I4 H 6 9 has been proposed for it. 
 
 The bodies are evidently produced by the absorption of oxygen from 
 the air and the removal of carbon from the tannin, under the form of 
 carbonic acid. 
 
 Gallic AcM.Gt'HOi + 2HO + Aq. 
 
 This remarkable substance does not appear to exist naturally formed 
 in plants, except in the seeds of the mango, but is generated by the 
 decomposition of gallo-tannic acid. Powdered galls are to be made 
 into a thin paste with water and exposed to the air for some weeks, at 
 a temperature of about 80, water being supplied according as it eva- 
 porates away ; the resulting mass is to be boiled with water, and the 
 
906 Sources and Preparation of Gallic Add. 
 
 gallic acid crystallizes out of the liquor as it cools. By digestion with 
 ivory black and re-crystallization, it is obtained completely pure. 
 
 In this process the reaction is very simple, as an atom of tannic acid 
 C 18 H 8 O 12 , absorbing from the air eight atoms of oxygen, produces 
 4.CO 2 and 2(C 7 H0 3 + 8Aq.) 
 
 The conversion of gallo-tannic acid into gallic acid, may occur, 
 however, without the access of air, and indeed be effected almost 
 instantaneously ; thus if tannic acid be boiled in a strong solution of 
 potash for a few minutes, and an excess of sulphuric acid be then 
 added, a copious product of gallic acid is obtained crystallized on 
 cooling; or if sulphuric acid be added to a strong solution of gallo- 
 tannic acid, and the precipitate thus formed be washed with a small 
 quantity of water, and then added gradually to boiling dilute sulphu- 
 ric acid, it dissolves, and on cooling, the gallic acid crystallizes. In 
 these reactions, which succeed also perfectly with infusion of galls, 
 some other substances must be simultaneonsly formed, which are as yet 
 not known. Gallo-tannic acid contains exactly the constituents of 
 gallic acid and acetic acid, as C 18 H 5 9 = 2(C 7 H0 3 ) -f C 4 H 3 3 , but 
 Liebig has determined that acetic acid is not produced. 
 
 It has been stated by Braconnot that in the fermentation of gall 
 nuts to produce gallic acid, alcohol is given off, and this would indicate 
 the presence or liberation of sugar from the gall nut. In fact, three 
 atoms of tannin represent six atoms of gallic acid and one of sugar, but 
 Braconnot's observation has not been since verified. 
 
 This change may occur in the nut gall itself, which it is very proba- 
 ble contains a principle analogous to yeast, which, under favourable 
 circumstances, induces this kind of decomposition in the gallo-tannic 
 acid. This idea, first suggested by Robiquet, has derived much support 
 from the experiments of Larocque, who found that the matter of the 
 nut gall which remains after the extraction of the tannin, has the power 
 of exciting the alcoholic fermentation in solutions of sugar. As yet, 
 however, we possess no accurate knowledge of the theory of this inter- 
 esting transmutation. 
 
 Pure gallic acid crystallizes in colourless doubly oblique rhombic 
 prisms, as u, z. in the figure, where i, is a secondary plane ; it tastes 
 bitter and slightly acid, and requires 100 parts of cold, but 
 much less of boiling water for its solution ; it is less soluble 
 in alcohol; its crystals contains three atoms of water, of which 
 one is expelled at a temperature of 230, but the remaining 
 two are only removed when replaced by bases. It is a biba- 
 sic acid, forming two classes of salts ; those with the alcalies 
 are very soluble ; the earthy and metallic salts are insoluble 
 
Pyrogallic Acid Melangallic Acid. 907 
 
 in water. With a per-salt of iron, gallic acid gives a blackish blue 
 precipitate, which differs from the tannate of iron in becoming gradu- 
 ally colourless, the acid being decomposed and the iron reduced to the 
 state of protoxide ; this is effected instantly by boiling, carbonic acid 
 gas being evolved. The gallic acid is further distinguished from the 
 tannic by not precipitating gelatine nor any of the vegetable alcalies. 
 
 Products of the Decomposition of Gallic Acid. 
 
 Pyrogallic Acid. When gallic acid is carefully heated to about 
 400, it is totally decomposed into carbonic acid, and pyrogallic acid, 
 (C7H 3 5 = C 6 H 3 O 3 + C 2 O,) which sublimes in brilliant white plates ; 
 it is easily soluble in ether, alcohol, and water ; it reacts feebly acid ; it 
 fuses at 240, and sublimes at 400. If a solution containing peroxide 
 of iron be added to a solution of pyrogallic acid, a black colour is 
 struck, but the iron is rapidly reduced to the state of protoxide, and 
 the liquor assumes a rich red tint. If, however, a salt of pyrogallic 
 acid be used, the solution remains permanently blue. 
 
 Melangallic Acid. If in the distillation of pyrogallic acid the tem- 
 perature be allowed to rise beyond 450, it is decomposed, water is 
 given off, and a shining jet-black mass like coal remains in the retort, 
 which is this body ; its formula is C }2 H 3 O y being formed from 
 2(C 6 H 3 O3) by loss of 3. HO; it is insoluble in water, alcohol and ether; 
 at a temperature of 500 it is totally decomposed into the ordinary 
 pyrogenic products ; it dissolves in alcaline solutions, forming salts of 
 a black colour, which do not crystallize ; these salts give black preci- 
 pitates with solutions of earthy and metallic salts. 
 
 If gallo-tannic acid be heated to about 400, it is resolved totally 
 into pyrogallic, melangallic and carbonic acids, and water. 
 
 Ellagic Acid. In the formation of gallic acid by the slow fermen- 
 tation of tannic acid, a certain quantity of ellagic acid generally though, 
 not constantly, appears. Being insoluble in water, it remains when the 
 gallic acid has been dissolved out, and by digesting the residue with a 
 weak solution of potash it is taken up, and may then be precipitated by 
 muriatic acid. 
 
 It forms minute crystals, whose formula is C ? H0 3 -f- HO + Aq. 
 The Aq. is driven off by a heat of 212, and the dry acid is then 
 isomeric with the gallic acid, but it is monobasic ; it is very feebly 
 acid, not expelling carbonic acid from its salts ; the earthy and metallic 
 ellagates are all insoluble, and all white or yellow. 
 
 A curious occurrence of ellagic acid is in the calculi called Bezoar 
 stones, employed in India, in medicine and as talismans. They are the 
 
908 Bezoar Stones Ellagic Acid Artificial Tannin. 
 
 intestinal concretions of some species of deer and of apes, and consist in 
 some cases of the Lithofellic acid to be hereafter described. In other 
 instances they are found to consist of ellagic acid, derived probably 
 from the animals having fed on vegetables rich in Tannin. 
 
 If gallic acid be heated to 880 with oil of vitriol, it dissolves, and 
 on cooling, brilliant crystals of a dark scarlet colour are deposited, 
 which, constitute par-ellagic add. This body is isomeric with ellagic 
 acid ; it forms with bases salts which are generally red. It is worthy 
 of notice, that ellagic acid acted on by oil of vitriol, gives no par- 
 ellagic acid. 
 
 It is here probably best to notice the formation of what has been 
 termed artificial tannin ; it is produced by mixing one part of almost 
 any kind of vegetable substance with five parts of oil of vitriol, letting 
 the mixture stand for some days, and then heating it as long as any 
 sulphurous acid gas is evolved. A black mass remains, from which the 
 remaining acid is to be washed with water, and then the tannin dis- 
 solved out by alcohol ; the solution is dark brown, and when evaporated 
 gives a black extractive matter, which tastes astringent, smells of burned 
 sugar, and dissolves in water; it precipitates gelatine, but does not 
 affect the salts of iron like true tannin. 
 
 Another and very singular manner of producing artificial tannin con- 
 sists in boiling pure charcoal in nitric acid as long as any reaction 
 occurs ; the liquor is then brown ; being evaporated to the consistence 
 of a sirup, and mixed with water, a brownish yellow substance falls, 
 and the filtered solution gives, by evaporation, a hard black mass, which 
 reddens litmus, tastes astringent, is soluble in water and in alcohol, and 
 copiously precipitates gelatine ; when heated it smells like horn, and 
 contains nitrogen ; it precipitates most metallic salts brown. The true 
 nature of these bodies is not well known, as they have not been much 
 studied since the methods of organic chemistry acquired their present 
 exactness ; they are probably mixtures of many bodies, as ulmine in its 
 various forms, with crenic and apocrenic acids. 
 
 Catechuic Acid, and Catecku-tannic Acid. 
 
 The Catechu, or Terra Japonica, a brown extract prepared from the 
 wood of the mimosa catechu, appears to contain at least four bodies, the 
 precise composition and connexion of which have not yet been definitely 
 established. The rough catechu, as imported, is of extensive use in 
 medicine, and in the arts, for tanning and for giving a rich permanent 
 brown dye. Davy estimated that 100 parts of Bengal catechu contain 
 
Ca tech u Ca teck u tan n in Ca tech ine. 909 
 
 forty-eight, and of Bombay catechu about fifty-four per cent, of useful 
 tanning material. 
 
 If catechu be treated with ether, by the method of displacement, as 
 described for tannic acid, the liquor does not separate into two layers, 
 but a strong solution of catechu-tannic acid in ether is obtained, which, 
 by evaporation, yields it as a pale yellow, scarcely crystalline, mass, in 
 taste and appearance similar to tannic acid ; its solution in water pre- 
 cipitates gelatine, but not tartar-emetic ; with the salts of peroxide of 
 iron it strikes an intensely olive-green colour, which is best marked 
 with the perchloride, being somewhat purple with the persulphate ; ex- 
 posed to the air, its solution rapidly absorbs oxygen, becomes red, and 
 finally brown, depositing a brown insoluble matter. This change is in- 
 stantly effected by any oxidizing agent. 
 
 The catechu-tannic acid has been analyzed by Pelouze, who ascribes 
 to it the formula C 18 H 8 O 8 -f Aq. ; it would thus appear to be formed 
 by the abstraction of four atoms of oxygen from tannic acid; but from 
 researches with which I am now occupied on these bodies I consider it 
 to be properly represented by the formula C 2 oH 12 9 , in which the quan- 
 tity of water is not positively determined. 
 
 When catechu has been deprived of the catechu-tannic acid by ether 
 or continued washings with cold water, the residual mass is to be boiled 
 in alcohol, and the filtered liquor evaporated to one-third of its volume; 
 on cooling, catechuic acid crystallizes. If coloured, it is to be dissolved 
 in boiling water, precipitated by acetate of lead, the catechuate of lead 
 diffused through boiling water, and decomposed by sulphuretted hydro- 
 gen ; the liquor being filtered gives, on cooling, a perfectly white and 
 pure catechuic acid ; it forms satiny flakes, indistinctly crystallized ; it 
 is very little soluble in cold water, but abundantly in boiling water and 
 in alcohol ; it is insoluble in ether ; its solution is not acid ; it appears 
 to exist in very different states of hydration, or possibly different kinds 
 of catechu contain substances which are totally distinct, for the formulae 
 assigned to it are quite discordant, and chemists are not agreed quite as 
 to its properties. Svanberg, who examined the catechu from the 
 mimosa catechu, gives as its formula, C ]5 H 5 O 5 -f- Aq. Zwenger, who 
 states the substance he worked with to be the produce of the nauclea 
 gambir, gives C 2 oH 9 O 8 -f Aq. ; and Hagen, who used Bengal catechu, 
 found the catechuic acid to be C 14 H 6 O 6 -4- 3Aq., and its lead salt 
 C 14 H 6 6 + 2PbO. Delffs again has proposed the formula C 7 H 4 O 4 + 
 Aq. My own researches would tend to prove the equivalent of cate- 
 chine to be, when dried in vacuo at ordinary temperatures, C 20 H 12 12 + 
 Aq. But the extreme difficulty of preparation of its salts has prevented 
 
910 Pyrocatechine Oxy catechine Japonic Add. 
 
 me from as yet obtaining positive evidence of the amount of water 
 which may be replaced therein. 
 
 When catectmic acid is heated it fuses, gives off water, and finally a 
 white crystalline sublimate, pyrocatecUn, which has the formula C 6 H 2 O 
 -f- Aq.; its characteristic property is that of forming a bright green 
 solution with alcohol. 
 
 If a solution of either of the acids now described be exposed to the 
 air, oxygen is absorbed, and much more rapidly in presence of an alcali. 
 The substance formed is termed japonic acid; it makes up the mass of 
 the coloured portion of catechu ; it is almost insoluble in water ; soluble 
 in caustic, but not in carbonated alcalies. Svanberg gives for it the 
 formula C 12 H 2 O 4 -f- Aq. If catechuic acid be boiled with a solution 
 of carbonate of potash, rulinic acid is formed, whose formula is said 
 to be C, 8 H 6 O 9 . By further absorption of oxygen it forms japonic acid. 
 None of these results, however, can be considered as definitely estab- 
 lished. 
 
 When a solution of catechine is heated with a solution of bichromate 
 of potash, a very rich brown powder is formed, perfectly insoluble in 
 water, and of much technical interest, as being employed in calico 
 printing as a mode of dying a fast brown. This reaction is very defi- 
 nite, no other product appearing to be formed. The formula of this 
 body I found to be C 20 H 12 18 -fr 2Cr 2 3 + 6.Aq., which might be 
 written as an equivalent of catechine and two equivalents of chromic acid. 
 On boiling this brown powder in strong muriatic acid, oxide of chrome 
 is dissolved out, and a dark powder remains, which I found to consist 
 of C 20 H 6 O 12 -|- Aq. The action of the chromic acid is, therefore, not 
 to oxidize the catechine, but to remove from it six atoms of hydrogen. 
 
 The same body, which may be termed oxycateckine, appears also to 
 be formed as the product of the oxidation of the moist salts of cate- 
 chine, or of catechine itself exposed moist to the air. I have thus 
 found for the brown lead salts produced by the spontaneous oxidation 
 of the catechine salts the formula, when dried, at 212, C 2 oH 6 12 + 
 PbO, which may combine with 3Aq. and with 12Aq. 
 
 The products of oxidation of catechine noticed above as japonic and 
 rubinic acids, do not appear to be really distinct, as their formulae differ 
 only in proportions of the elements of water. I have found but one 
 product to be formed in that way, probably the true japonic acid. It was 
 prepared by dissolving catechine in solution of caustic potash, and leaving 
 the liquor exposed to the action of the air until it had become intensely 
 dark-red brown coloured, and the catechine had totally disappeared. 
 Muriatic acid then precipitated a brown powder, which had the formula 
 
Catechu Cinchona Tannin. 911 
 
 C ]0 H 6 15 , and the lead salt had the composition C JO H 3 O 12 PbO, or 
 C2oH 6 24 . If the quantity of carbon in the equivalent of these bodies 
 remains unaltered/ which I am disposed to believe, their relations are as 
 follows : 
 
 Catechu-tannin 
 
 Catechine = C 2 oHi 2 Oi2 + Aq. 
 
 Oxycatechine = Cgo^e O]2 + Aq. 
 
 Japonic acid = 20^6 Og4 + Aq. 
 
 These researches are, however, not as yet concluded; and I merely 
 describe those results as tending to remove some of the obscurity which 
 it has been remarked invests the history of this group of bodies. 
 
 Cinchona-tannic Acid and Kinic Acid. 
 
 These substances exist in the barks of various species of cinchona 
 combined with quinia and cinchonia. The first is extracted by digestion 
 in dilute muriatic acid and precipitation with magnesia. The precipitate 
 is to be dissolved in acetic acid and precipitated with acetate of lead, 
 which leaves the alcaloids dissolved ; the cinchona-tannate of lead being 
 decomposed by sulphuretted hydrogen, the filtered liquor yields, on 
 evaporation, the cinchona-tannic acid pure, and of a very pale yellow 
 colour, not crystalline. In properties it resembles closely ordinary 
 tannic acid ; it precipitates gelatine and tartar-emetic. An infusion of 
 cinchona is hence recommended as an antidote in cases of poisoning by 
 tartar-emetic. It colours solutions of the per-salts of iron, green. By 
 exposure to the air, it is converted into a rust-coloured substance, 
 termed cinchona-red. Nothing is known of the composition of these 
 bodies. 
 
 The Kinic Acid, which Berzelius believes to exist in the inner bark 
 (albumen) of fir and of most trees, is obtained by adding lime in small 
 quantity to a cold infusion of cinchona bark. The alcaloids being thus 
 separated, the liqudr is filtered and evaporated very carefully to the con- 
 sistence of a sirup. On standing for a few days, the kinate of lime 
 crystallizes in needles, which are to be decomposed by an exact equiva- 
 lent of the sulphuric acid. The gypsum being removed by the filter, the 
 solution is to be concentrated, and the kinic acid crystallizes. It forms 
 small acid needles, is very soluble in water ; its salts are all soluble in 
 water; it affects neither gelatine, tartar emetic, nor the per-salts of 
 iron ; its formula appears to be C H H 8 O 8 -f- 4Aq. 
 
 By distilling the kinic acid with sulphuric acid, peroxide of manga- 
 nese and water, a compound sublimes in beautiful yellow crystals, which 
 
912 Kinone and its Derivatives. 
 
 is termed kinone. Its formula is C ]2 H 4 O 4 . It is soluble in water, and 
 volatile. By the influence of deoxydizing agents it decomposes water, 
 and unites with hydrogen, producing two bodies, the green and the 
 white, kydrokinone. The green Jiydrokmone forms exceedingly beau- 
 tiful greenish-yellow needles, of a brilliant metallic lustre. Its formula 
 is C J2 H 6 O 4 . The white hydrokinone crystallizes in prisms, with the 
 formula Ci 2 H 5 O 4 , and can be produced either by oxidizing the green 
 compound or by mixing solutions of it and of kinone. 
 
 By the action of chlorine and of sulphuretted hydrogen on the hydro- 
 kinones, there is generated a numerous class of derived compounds, 
 according as the hydrogen is replaced by chlorine and the oxygen by 
 sulphur. Their properties need not, however, be described, and their 
 formulae may be expressed as follows ; 
 
 Chlor kinone C12.H3C1.O4. 
 
 Chlor hydrokinone Ci2.H 5 Cl.O4 
 
 Sulph hydrokinone Ci 2 H60 4 S4 
 
 Chloro Sulph hydrokinone C24H8C1.O8S4 
 
 The derivation of kinone from the oxidation of the kinic acid is easily 
 explained, as by the addition of four equivalents of oxygen, and the loss 
 of four atoms of water and two of carbonic acid, the CnHgOs becomes 
 converted into C 12 H 4 4 . 
 
 Kinoic Acid, or Cocco-tannic Acid. 
 
 The substance known in pharmacy as gum kino, which is an extract 
 of the wood of the coccoloba uvifera, is to be dissolved in cold water, the 
 solution precipitated by sulphuric acid, the precipitate washed, dis- 
 solved in boiling water, and solution of barytes added until the sulphuric 
 acid is all removed ; the liquor is then carefully evaporated to dryness. 
 The kinoic acid forms a crimson transparent mass ; soluble in alcohol 
 and water, but not in ether ; its taste is astringent, but not bitter. The 
 salts of this acid are not known, nor has its composition been examined. 
 It does not precipitate solution of tartar emetic. 
 
 Of the following acids we possess little more than a knowledge of 
 their probable existence. 
 
 Lactucic Acid is said to exist in the lactuca virosa. The expressed 
 juice is precipitated by acetate of lead, and the lactucate of lead decom- 
 posed by sulphuretted hydrogen. From the liquor the acid crystallizes 
 by evaporation and cooling, like oxalic acid ; it tastes acid, and gives 
 with proto-salts of iron, a green, and with salts of copper, a brown 
 precipitate. 
 
 Fungic Acid exists in most mushrooms; their expressed juice is 
 
Chelidonic and other Organic Acids. 913 
 
 boiled, and the coagulated albumen removed by filtration ; the liquor is 
 then evaporated to a sirup, and treated with alcohol. Eungate of pot- 
 ash remains uudissolved, from which the acid is obtained by acetate of 
 lead and sulphuretted hydrogen. The fungic acid is colourless, sour, 
 deliquescent, and not crystalline. 
 
 Boletic Acid is obtained from the boletus igniarius, in the same way 
 as the last acid is from other mushrooms. It crystallizes readily and 
 sublimes without decomposition. 
 
 Krameric Acid exists in rhatauy root (krameria triandria). The 
 watery infusion is precipitated, first by gelatine, and then by copperas. 
 The filtered liquor is concentrated, neutralized by lime, precipitated by 
 acetate of lead and the kramerate of lead decomposed by sulphuret of 
 hydrogen ; it crystallizes irregularly, and tastes strongly acid and astrin- 
 gent ; it formula is probably C 10 H 8 05, by Liebig's analysis. 
 
 Caincic Acid exists in the root of the chiococca racemosa. Its mode 
 of extraction resembles that of the krameric acid; it crystallizes in 
 needles ; is but sparingly soluble in water ; its solution reacts acid ; it 
 appears to have the same formula as krameric acid, and perhaps they 
 are really identical. 
 
 Verdous and Verdic Acids exist in a variety of plants of the families, 
 dipsacea3, composite, and eupatorise ; it is best prepared from the roots 
 of the scabiosa succisa. They are to be digested in alcohol, and the 
 solution mixed with ether. Impure verdous acid is thrown down ; it 
 is to be dissolved in water, and the liquor precipitated by acetate of 
 lead; the verdite of lead being collected and decomposed by H.S gives 
 the pure verdous acid, which remains after evaporation as a clear yellow 
 mass, which is not altered by the air ; it reddens litmus strongly. If 
 it be neutralized by an alcali, it then absorbs oxygen rapidly, and the 
 solution becomes deep green; from this, acids throw down a brown-red 
 powder, which is verdic acid. Eunge, who observed these facts, con- 
 siders that the two acids are different oxides of the same radical, but no 
 exact researches have been made about them. 
 
 Chelidonic Add. C 14 H 2 Oi + 3Aq. This acid has been discovered 
 in the juice of the chelidonium majus. Its mode of preparation is 
 analogous to that of malic acid. It crystallizes in silky needles. It is 
 a tribasic acid ; but by a moderate heat it abandons one atom of water, 
 and becomes bibasic. It consequently forms two classes of salts, each 
 including numerous varieties. A very simple relation appears to exist 
 between this acid and the meconic acid, C 14 HOn, indicating a substitu- 
 tion of an atom of oxygen for hydrogen ; and as both acids belong to 
 the same class of plants, papaveraceas, their origin may possibly be con- 
 nected. 
 
 58 
 
914 Neutral Organic Substances. 
 
 Acids have been discovered in the leaves of digitalis and of tobacco, 
 in the roots of angelica, in the leaves of achillea, and in the roots of 
 robinia. In the Iceland moss, and in some other lichens, a fatty acid 
 is found, to which the name lichen-stearic acid has been given. 
 
 The Digitalic acid is solid, crystallizes in needles, reacts strongly 
 acid. It does not contain nitrogen. 
 
 The Tabacic acid. C 3 H0 3 + HO. Can be obtained crystallized. 
 Its properties are yet but little known- 
 
 Angelic acid. C 10 H 7 O 3 + HO. Is separated from the rough oil of 
 angelica by an alcaline solution, and then sulphuric acid being added, 
 and the liquor distilled, the angelic acid passes over, and partly crystal- 
 lizes in the neck of the retort. It crystallizes in long prisms, melts at 
 113, and sublimes at 374, when dry. It is sparingly soluble in 
 water, but abundantly so in alcohol, ether, and oils. 
 
 Other acids, of which the existence has been only indicated, will be 
 noticed in describing the more important bodies with which they are 
 associated in the plants. 
 
 CHAPTER XXVI. 
 
 OF THE NEUTRAL ORGANIC SUBSTANCES AND THE PRODUCTS OF THEIR 
 
 DECOMPOSITION. 
 
 THE bodies to be described in this chapter are distinguished by the 
 absence of distinct acid or basic characters, and also that they are at least 
 so destitute of colour, as not to be included in the list of colouring 
 matters. In other respects they possess no direct connexion with each 
 other, and are united only for convenience of arrangement. 
 
 Pectin or Vegetable Jelly. 
 
 This substance, which is to be carefully distinguished from animal 
 jelly or gelatine, to which it by no means bears the relation that the 
 albumen of plants does to that of animals, is very extensively diffused, 
 
Modifications of Pectin Pectic Acid 915 
 
 being found in almost every kind of plant, and distributed through all 
 their parts. It is very easily prepared from the expressed juice of white 
 beet, celery, parsley, currants, cherries, or plums. It is sufficient to 
 filter the juice and mix it with alcohol : after some hours, the pectin 
 separates as a consistent jelly, which is to be collected on a filter, washed 
 with alcohol and dried by a very moderate heat. It forms a transparent 
 mass, like isinglass, and is almost insipid. When immersed in water it 
 swells up ; one part gives a firm jelly with 100 parts of water. When 
 acted on by nitric acid it produces the pectic and the rnucic acids. It pre- 
 cipitates the salts of barytes, lead, copper, and sesquioxide of iron, but 
 does not affect solutions of silver, of protosulphate of iron, of tartar- 
 emetic, of tannic acid, or of silicate of potash. Its formula, as from 
 the experiments of Fremy, is C 24 H 17 O 22 . By long boiling, or by 
 contact with powerful acids or bases, it changes into the following sub- 
 stance. 
 
 Pectic Acid appears to exist naturally combined with lime in many 
 plants, and is precipitated from their juice on the addition of muriatic 
 acid. The precipitate is to be boiled with a little lime, and the solution 
 again decomposed by muriatic acid. The pectic acid which then sepa- 
 rates pure, is to be washed with distilled water and dried. It does not 
 crystallize, but forms white transparent scales, tastes distinctly acid, and 
 reddens litmus. It dissolves very sparingly in cold, but more copiously 
 in boiling water; the solution is colourless, and does not gelatinize on 
 cooling, but is coagulated to a transparent jelly by acids, by lime water, 
 alcohol, and many salts. Sugar gradually converts the solution into a 
 firm jelly, and is thus useful in the manufacture of the preserves of juicy 
 fruit. 
 
 The pectic acid is isomeric with pectin ; its formula being C 2 JInO ss . 
 It appears to be bibasic, the pectate of lead being 0241^7022 + 2PbO. 
 Its alcaline salts are soluble in water, but the others are insoluble, and 
 form transparent jellies whilst moist. 
 
 If pectin or pectic acid be boiled in a solution of potash, the alcali 
 being in excess, until the liquor ceases to give any precipitate on the 
 addition of muriatic acid, metapectic acid is formed. On the addition 
 of sugar of lead, metapectate of lead is thrown down, which being de- 
 composed by sulphuretted hydrogen, the metapectic acid dissolves, and 
 is obtained by cautious evaporation to dryness. Its taste and reaction 
 are strongly acid ; it deliquesces and dissolves easily in alcohol and 
 water ; it is not volatile. When dry it is isomeric with the preceding 
 bodies, its formula also being C 2 4H n O 2 2 ; but its salts contain five atoms 
 of base. Those of the alcalies are soluble and uncrystallizible ; but 
 those of the earths and Jieavy metallic oxides are insoluble in water. 
 
916 Salicine Saliretine Saligenine 
 
 Of Salicine and the Bodies derived from it. 
 
 This substance exists in the leaves and bark of a great variety of 
 trees, but is particularly abundant in those species of salix which have 
 a bitter taste. The bark is to be boiled three or four times with water, 
 the decoction evaporated till it amounts to but three times the weight 
 of the bark employed ; then digested for twenty -four hours with oxide 
 of lead, and the clear liquid evaporated to the consistence of a sirup. 
 After a few days this becomes a mass of crystalline fibres, which, sepa- 
 parated by pressure from the mother liquor, are to be purified by solu- 
 tion, digestion with animal charcoal and recrystallization. 
 
 When pure, salicine is in the form of small white rectangular crys- 
 talline plates or prisms ; its taste is very bitter. It dissolves in eighteen 
 parts of cold and in one of boiling water ; it is soluble in alcohol, but 
 not in ether ; at 212 it melts, and on cooling solidifies into a crystalline 
 mass. The composition of salicine has been very accurately determined, 
 its formula is, when crystallized, C26Hi 8 Oi4 + 2Aq. ; it precipitates the 
 basic acetate of lead, forming a white compound, the formula of which is 
 C 26 H 18 lt +3PbO. 
 
 The products of the decomposition of salicine are exceedingly re- 
 markable. When it is boiled with dilute sulphuric acid it is decom- 
 posed into grape sugar, and a resinous substance, termed saliretin. 
 One atom of salicine C 2 6Hi 8 O 14 giving saliretin, C l4 H 6 O 2 , and sugar, 
 C l2 H 12 Oj 2 -f. 2Aq. When quite pure this body is white or pale yellow. 
 It is insoluble in water, but soluble in alcohol and ether. The salire- 
 tine is thus isomeric with oil of bitter almonds and with benzoine. 
 
 Saligenine. If, in place of acting on salicine by acids, which con- 
 vert it into saliretine, a solution of it be mixed with synaptase, and 
 kept at a moderate temperature, fermentation sets in, and it is totally 
 converted into sugar, and a new body, saligenine, which crystallizes out 
 as the decomposition proceeds. This body forms beautiful pearly plates, 
 very soluble in water, alcohol, and ether. Its formula is C 14 H 8 O 4 . 
 Under the influence of acids it abandons two atoms of water, and forms 
 saliretine CuHeOa. If a solution of it be mixed with platinum black, 
 it unites with oxygen, and forms water and oil of spirea, hydruret of 
 salicyle, C 14 H 6 4 . Owing to this property it is that when a solution 
 of salicine is distilled with sulphuric acid and bichromate of potash, 
 formic and carbonic acids are evolved from the oxidation of the grape 
 sugar, and oil of spirea from the oxidation of the saligenine or salire- 
 tine. 
 
 When salicine is boiled with nitric acid, some gaseous products are 
 formed, and so large a quantity of picric, or nitrophenesic acid, is pro- 
 
A&lion of Re-agents on Salicine, 917 
 
 duced as to constitute this one of the most useful methods of obtaining 
 this body. See page 858. The salicine, by the oxidizement from the 
 nitric acid, first yields hydmret of salicyl, which, being CuHeO^ con- 
 tains the elements of carbonic oxide and hydrated oxide of phenyl ; 
 and hence, by replacement of hydrogen with nitrous acid, the picric 
 acid is produced along with oxalic acid, and red fumes from nitric oxide 
 are disengaged. 
 
 If, however, the action of the nitric acid be kept moderate, other 
 products are generated, by the union of the saligenine, the hydruret of 
 salicyl, and the grape sugar. Thus the oil of spirea forms with the 
 sugar a body, helieine, which crystallizes easily. Its formula is 
 CggHieOu = Ci4H6O4 + C^HioOio ; and if the oxidation be still less 
 advanced, there is produced helicodine, which has the formula C 5 oH 34 O 28 , 
 formed evidently by the union of saligenine, C U H 8 O 4 , oil of spirea, 
 C U H 6 O 4 , and two equivalents of sugar, C 2 4H 20 O 2 o. 
 
 Other acid products of this reaction, as the anilotic and the anilic 
 acids, belong more peculiarly to the indigo series, and shall be described 
 hereafter. 
 
 By the action of chlorine on salicine, two bodies are produced, one 
 crystalline, whose formula is C 2 iH,2Cl 2 09, and the other a heavy oil, 
 consisting of C 21 H 8 C1 4 9 . They are both soluble in alcohol, but 
 sparingly soluble in water; treated with dilute acids they produce 
 resins analogous to saliretine, but containing chlorine. 
 
 If strong oil of vitriol be poured on salicine, it is decomposed into 
 water and a deep olive-green powder, olivin, the formula of which is 
 C 2 iH 9 6 . This action is accompanied by the disengagement of much 
 heat. Olivin is crystalline, insoluble in water, alcohol, and ether. 
 If the oil of vitriol be in great excess, it becomes red-coloured, and the 
 salicine dissolves. The red substance thus formed is termed rtifin ; it 
 is obtained more simply from phloridzine. If a large quantity of 
 salicine be acted on by sulphuric acid, it forms a tenacious mass, which, 
 when treated with water and the liquor neutralized by lime, gives a 
 brown resinous body which is termed rutilin. This contains sulphuric 
 acid, its formula being C 28 H 12 4 -f- S0 3 . 
 
 Of Phloridzine and its Products. 
 
 This remarkable substance exists in the bark of the roots of the 
 various species of apple, pear, plum, and cherry trees. It is prepared 
 by infusing the root-bark in weak spirit for eight or ten hours at 120. 
 The greater part of the spirit may then be distilled off, and on cooling 
 the phloridzine crystallizes from the remaining liquor. It forms bril- 
 liant silky plates and needles, perfectly white when pure. It is easily 
 
918 Derivatives of Phloridzine. 
 
 soluble in alcohol, ether, and in boiling water, but requires 1000 parts 
 of cold water for its solution. Its taste is bitter and astringent. The 
 formula of the crystals is C 2 iH n 8 -f4Aq. At 212 it gives off 2.Aq.; 
 it melts at 260 and boils at 350, but is decomposed, water being 
 evolved and a new substance produced. The solution of phloridzine 
 precipitates some metallic salts. The persulphate of iron gives a brown 
 precipitate, but the perchloride of iron produces a blood-red liquor and 
 no precipitate. 
 
 The decomposition of phloridzine by heat is not complete unless the 
 temperature rises to 450; it then forms a red mass of rwfin, the same 
 substance as is produced by the action of oil of vitriol on salicine ; it 
 is very soluble in alcohol, insoluble in ether ; boiled with water it dis- 
 solves, but loses its red colour, and the liquor on cooling becomes 
 milky. It dissolves in water of ammonia or *potash with a rich red 
 colour, and is precipitated on the addition of an acid ; its formula is 
 C 14 H 7 5 ; it combines with oil of vitriol, forming rufin- sulphuric acid 
 which unites with the metallic oxides, forming red or brown salts which 
 possess considerable analogy to the sulpho-vinates. 
 
 When phloridzine is dissolved in dilute sulphuric acid, and the liquor 
 boiled, a white crystalline substance separates, which is termed pJiloretm ; 
 the liquor then contains much grape sugar. The formula of phloretin 
 is C 51 H260 17 ; its taste is sweet ; it is sparingly soluble in water, but very 
 soluble in alcohol ; it melts at 300 ; when heated with nitric acid it 
 forms phloretic acid, the formula of which is C 51 H 24 ]N~2O25, it is a yellow- 
 brown powder, of a velvety aspect but not crystalline, insoluble in 
 water, and soluble in alcohol. Since the more recent investigations 
 which have altered the view formerly held of the constitution of salicine 
 and its derivatives, no examination of these bodies has taken place ; 
 and hence all their formula will probably require to be modified. 
 
 The most remarkable action of phloridzine is, that exercised by 
 ammonia with access of air. Over a capsule containing water of 
 ammonia, are arranged several capsules containing phloridzine in very 
 thin layers, and the whole is so covered with a large bell-glass, as that 
 the air shall have free access ; after a few days the contents of the cap- 
 sules are changed into a thick sirupy liquor, nearly black ; the excess 
 of ammonia being removed by exposure in vacuo with sulphuric acid, 
 the excess of phloridzine is dissolved out by the alcohol, and the residue 
 then being dissolved in water, gives a magnificent blue liquor, from 
 which the colouring substance, phloridzem, is precipitated by the cau- 
 tious addition of acetic acid ; it is not crystalline ; it forms a transparent 
 resinous mass of a rich crimson colour; its taste is bitter; boiling 
 water dissolves enough of it to be coloured red, but cold water, alcohol, 
 or ether, appear scarcely to act upon it. 
 
Phloridzeine Asparagine. 919 
 
 The formula of phloridzein is C 21 H 14 O 13 N-f-Aq. ; it is formed, there- 
 fore, by the combination of phloridzine with five atoms of oxygen and 
 one of ammonia ; it is not, however, a salt of ammonia, for the alcalies 
 dissolve phloridzein without alteration, forming magnificent blue solu- 
 tions ; from metallic solutions it precipitates purple or blue lakes, the 
 composition of which renders it probable that the equivalent of phlo- 
 ridzein is C 42 H 28 2G N2 -f 2Aq. then the 
 
 Phloridzeinate of ammonia = C42H2sN2O26 + NH 3 
 Phloridzemate of silver = C 42 H 28 N2O2G + 2AgO 
 Phloridzemate of lead = C4 2 H28"N" 2 O26 2PbO. 
 
 If the blue solution of phloridzeinate of ammonia be put in contact 
 with a slip of zinc, protochloride of tin, sulphuretted hydrogen, or any 
 other deoxidizing agent, it is deprived of colour ; but by exposure to 
 the air, it rapidly reassumes the tint ; with chlorine the colour is in- 
 stantly and permanently destroyed. 
 
 Asparagine Aspartic Acid. 
 
 Asparagine is found in the young shoots of asparagus and of potatoes, 
 in the roots of liquorice, and marsh-mallow. From the latter it is easily 
 prepared. The decorticated roots are to be digested in cold water for 
 forty-eight hours, and the liquor then strained and evaporated to the 
 consistence of a sirup. By standing for some time the asparagine gra- 
 dually crystallizes, and the crystals are to be purified in the ordinary 
 manner by animal charcoal. It forms rectangular octohedrons, and 
 prisms ; it is colourless and tasteless ; it requires about sixty parts of 
 cold, but much less of hot water for solution ; it is insoluble in alcohol ; 
 it contains nitrogen, its formula being NC 4 H 4 03 + Aq. ; the water 
 passes away at a heat of 230. 
 
 When asparagine is boiled with a strong solution of barytes, am- 
 monia is expelled, and aspartate of barytes formed ; by cautiously 
 adding sulphuric acid the barytes may be precipitated, and the liquor 
 yields, on evaporation and cooling, crystallized aspartic acid. In this 
 reaction 2(NC 4 H 4 O 3 ) produces NH 3 and NCgHgOg, which is the for- 
 mula of aspartic acid. This substance is tasteless, sparingly soluble in 
 cold, but abundantly in boiling water, and being deposited as a white 
 crystalline powder as the solution cools ; it reddens litmus. Its salts 
 are generally soluble, except those of lead, silver, and black oxide of 
 mercury. 
 
 It is not easy to decide whether the ammonia exists ready-formed or 
 
920 Neutral Organic Substances 
 
 not in the asparagine ; if so, the remaining organic element may be 
 aconitic acid (see p. 899) and then there should be, 
 
 Asparagine = anhydrous aconitate of ammonia =C4H03 + 
 Aspartic acid = anhydrous binaconitate of ammonia=2(C4HO3) + 
 
 In the case of the anhydrous compounds of ammonia with the mineral 
 acids, it is retained with the same obstinacy as in asparagine (see 
 page 721. 
 
 Caffein or Them. Theolromine. 
 
 This has been found only in the coffee-berry, the tea-leaf, the ilex 
 paraguayensis, and the paulinia sorbalis (guarana). To prepare it, raw 
 coffee or green tea is to be boiled in water, and the decoction treated 
 with subacetate of lead as long as the precipitate which forms is co- 
 loured. The caffei'n crystallizes from the filtered liquor, by evaporation 
 and cooling ; if it be coloured, it is to be boiled with oxide of lead and 
 ivory-black, and again crystallized ; when pure, it forms brilliant long 
 needles of a rich satiny lustre ; its taste is purely bitter ; it dissolves in 
 fifty parts of cold, but in much less of boiling water ; it is very soluble 
 in proof spirit, but insoluble in absolute alcohol ; its solutions react nei- 
 ther acid nor alcaline ; it is not precipitated by any metallic salt. Caf- 
 fein is remarkable for the large quantity of nitrogen it contains (29 per 
 cent.), being more than any other vegetable substance; its formula is 
 N 2 C 8 H 5 O 2 + Aq. When caffein is boiled with solution of barytes, 
 cyanuric acid, ammonia, formic, and carbonic acids are produced. 
 
 The coloured precipitate produced in the decoction of raw coffee by 
 basic acetate of lead, contains two peculiar substances, which may be 
 extracted from it by treatment with a stream of sulphuretted hydrogen 
 gas, evaporation to the consistence of a sirup, and digestion of the re- 
 sidue in strong alcohol. That which dissolves is caffe-tannic acid ; it is 
 dark brown ; tastes acid and astringent ; colours the per-salts of iron 
 emerald green ; it precipitates the salts of barytes and lime yellow, of 
 copper green, but does not affect tartar emetic. Its composition is ex- 
 pressed by the formula C 16 H 8 O 7 + HO. The substance insoluble in 
 alcohol is a white powder, which, when heated, evolves the characteristic 
 aromatic smell of roasted coffee ; its solution in water reddens litmus ; 
 it is termed caffe'ic acid. Its formula has been given as C 14 H 8 7 . A 
 crystalline compound of caffeic acid, caffein and potash has been ex- 
 tracted from the coffee berry by Payen, which is probably the form in 
 which these bodies naturally exist in the plant. 
 
 Theohromine. The nuts of the chocolate tree, Theobroma Cacao, from 
 
Naturally existing in Plants. 921 
 
 which the chocolate of commerce is prepared, have been found to contain a 
 principle analogous to theine, to which the above name has been given. 
 It is prepared by digesting the chocolate nuts in hot water, precipitating 
 from the liquor the colouring extractive and tanning materials by ace- 
 tate of lead, and evaporating the filtered liquor to dryness. The residue 
 is treated with boiling alcohol, from which the theobromine separates 
 on cooling, as a crystalline powder, and only requires to be re-crystallized 
 to be obtained pure. 
 
 It is but little soluble in water or cold alcohol. It is not acted on 
 by acids or alcalies. It unites with tannin and with chloride of mer- 
 cury. Its composition is expressed by C9H 5 N 3 2 . So that it is equally 
 remarkable with the principle of the tea and coffee plants, for the large 
 quantity of nitrogen which it contains. 
 
 Piperin. NC 24 H 19 6 . 
 
 This substance exists in white, black, and long pepper ; it is prepared 
 from white pepper by digestion in spirit of wine, and distilling the 
 liquor to the consistence of an extract, from which, by digestion 
 in a solution of caustic potash, a quantity of resin is to be re- 
 moved ; the residue is then to be dissolved in alcohol, and the solution 
 abandoned to spontaneous evaporation, when the piperin gradually 
 crystallizes in transparent rhombic prisms. It melts at 212, is taste- 
 less, and inodorous ; destitute of either acid or basic properties ; nitric 
 acid colours it red ; when heated strongly, it yields ammoniacal products. 
 It was recently announced that piperin consists of one equivalent of 
 aniline with two of a nitrogenous acid, and that piperin has been arti- 
 ficially formed by the union of these bodies. 
 
 Cantharidin. C 10 H6O 4 . This substance is extracted from the blis- 
 tering fly (various species of cantharis and lytta) by digesting a watery 
 extract of the flies in alcohol, evaporating the solution to dryness, and 
 treating the residue with ether, which dissolves out the cantharidin. 
 By spontaneous evaporation, it is obtained crystallized ; it forms colour- 
 less, pearly scales, which fuse when gently heated, and sublime unal- 
 tered at a higher temperature ; it is, when pure, insoluble in water and 
 cold alcohol j it is perfectly neutral, and has no affinity either to acids 
 or bases. 
 
 Anemonine Anemonic Acid. 
 
 This substance exists in various species of anemone ; it is extracted 
 by distilling the plant with water ; it separates, after some time, from 
 the distilled water, in brilliant white needles ; it melts and volatilizes 
 
922 Neutral Organic Substances 
 
 at a high temperature, yet not without partial decomposition ; its for- 
 mula is C 6 H 3 4 ; when it is dissolved in strong muriatic acid, and the 
 liquor evaporated to dryness, anemonic acid is formed; its formula is 
 C 6 H 4 05 -f- Aq. It is not important. 
 
 Cetrarine or Lichen Bitter. 
 
 This substance is found in Iceland moss ; to extract it, the lichen, 
 being well crushed, is to be digested in alcohol as long as this acquires 
 a bitter taste ; the liquor may then be distilled in great part off, and the 
 cetrarine is deposited, on cooling, in granular crystals ; these are to be, 
 while still moist, washed with ether and cold alcohol, by which they are 
 rendered white, and then being dissolved in 200 times their weight of 
 boiling alcohol, the pure cetrarin separates on cooling, as a white pow- 
 der of a highly crystalline aspect. It is but sparingly soluble in any 
 menstruum ; its only remarkable character is, that by digestion with 
 muriatic acid it forms a deep blue mass, but the nature of the reaction 
 is not known, as the constitution of these bodies has not been accurately 
 investigated. 
 
 Picrotoxine or Cocculm. 
 
 This substance exists in the seeds of the menispermum cocculus (coc- 
 culus Indicus) constituting their active ingredient ; to prepare it, the 
 seeds, freed from the capsules, are to be digested in alcohol, and the 
 solution evaporated to an extract : this is to be then treated with water 
 as long as any thing is dissolved ; and then some muriatic acid added 
 to the liquor ; by cooling, the cocculin crystallizes in brilliant white 
 needles. Its reaction is neutral ; its taste intensely bitter ; it dissolves 
 moderately in boiling, but sparingly in cold water. The portion of the 
 alcoholic extract which does not dissolve in water contains another sub- 
 stance, picrotoxic acid, which is brown, and possesses the properties of 
 a resin ; it dissolves in alcaline liquors, from which acids throw it down 
 unchanged. The formula C IO H 6 4 has been assigned to picrotoxine, 
 and that of CnH 6 4 to picrotoxic acid. 
 
 Columbin. Pound in the roots of the menispermum palmatum. 
 The coarsely-powdered columbo roots are to be digested in ether, and 
 by the spontaneous evaporation the columbin crystallizes; or by digest- 
 ing the roots in alcohol, and decolorizing the liquors by animal char- 
 coal, it may also be prepared ; it forms brilliant right rhombic prisms ; 
 its taste is intensely bitter; its reaction neutral; it dissolves but 
 
Naturally existing in Plants. 923 
 
 sparingly in water, alcohol, or ether ; its solution does not precipitate 
 any metallic salt ; its formula appears to be C 2 4H 12 7 . 
 
 Cusparin. This is the active principle of the true angustura (cuspa- 
 ria febrifuga.) The bark is to be extracted by alcohol, and the solution 
 concentrated very much by spontaneous evaporation ; on cooling then 
 below 32, granular crystalline masses of cusparine separate, from 
 which the liquor is to be strained ; by redissolving in alcohol, and pre- 
 cipitation of the colouring matter by acetate of lead, it is ultimately 
 obtained pure. "When crystallized from a solution, some degrees below 
 32, cusparine forms colourless but irregular needles ; by a very gentle 
 heat it melts and gives off twenty-three per cent, of water of crystalli- 
 zation ; it dissolves readily in water and alcohol, but it is insoluble in 
 ether ; by heat it is totally decomposed ; its solutions precipitate most 
 metallic salts. Its composition is not known. 
 
 Elatenn is the active material of the expressed juice of the momor- 
 dica elaterium : the juice being evaporated to the consistence of an 
 extract, is to be digested in strong alcohol ; the solution thus formed is 
 to be distilled to a small bulk, and then on being mixed with water, it 
 deposits the elaterin as a white crystalline powder. It melts at about 
 3&0, but is totally decomposed by a stronger heat; its taste is intensely 
 bitter; it is almost insoluble in water, but abundantly so in alcohol; 
 it possesses no characteristic chemical property. 
 
 Meconine. This substance exists mixed with the more important 
 ingredients in opium ; it is most abundant in the inferior kinds ; its 
 preparation is very circuitous, and will be described in the general 
 analysis of opium, under the head of narceine. Meconine crystallizes 
 in white six-sided prisms ; it melts at 194, and may be sublimed 
 unaltered; it dissolves sparingly in cold, but moderately in boiling 
 water, abundantly in alcohol and ether; its formula appears to be 
 C 20 H 9 7 -f Aq. By nitric acid it is dissolved, and a substance crys- 
 tallizes from the liquor in long needles, which is termed nitromeconic 
 acid ; its formula is NC 20 H 9 O 12 ; its solution in water reddens litmus ; 
 it volatilizes at 370, but is partly decomposed. By contact with chlo- 
 rine, meconine is coloured red, and substances formed whose constitu- 
 tion is not well known. 
 
 Peudecanine. This substance is found in the roots of the peudeca- 
 num officinale, and is extracted by digestion with alcohol and evapo- 
 ration ; it crystallizes in delicate, white needles, of a slightly aromatic 
 taste ; it fuses at 140 ; it is insoluble in water, and but sparingly in 
 cold alcohol ; it dissolves copiously in boiling alcohol, in ether, and 
 the oils. 
 
924 Neutral Organic Principles 
 
 j or Polychrome. 
 
 A great number of vegetables give, when treated with hot water, a 
 solution which appears yellow by transmitted, but violet or blue by 
 reflected light. This phenomenon results from the presence of a body 
 hence called polychrome, or also awwline, being most abundant in the 
 bark of the horse chesnut. The bark is to be digested in alcohol, 
 and the liquor to be concentrated by distillation to the consistence of a 
 sirup, in which, when set aside for some weeks, the aesculine crystal- 
 lizes ; by washing with ice-cold water it is freed from the liquid extrac- 
 tive matter ; the impure crystals are to be dissolved in a boiling mixture 
 of five parts alcohol with one of ether, from which, by cooling, the pure 
 substance separates, perfectly colourless, and generally as a light 
 powder, like magnesia alba. It tastes bitter; it dissolves in 672 parts 
 of water at 50, and in thirteen parts at 112 ; its cold watery solution 
 is perfectly colourless by transmitted, but slightly blue by reflected 
 light ; if spring water be used the blue becomes much stronger ; acids 
 destroy this property, but it is restored to the solution by the addition 
 of a few drops of any alcali. 
 
 The watery solution of sesculin reddens litmus, yet it does not neu- 
 tralize the alcalies, nor precipitate any of the ordinary metallic salts ; 
 it dissolves abundantly in alcaline liquors, and the solutions give 
 a magnificent play of colours with reflected light; its formula is 
 C 16 H 9 10 . 
 
 Populin exists in the bark and leaves of different species of populus, 
 along with salicine ; the latter is removed from the liquors by precipi- 
 tation with acetate of lead, and then by evaporation the populin 
 is obtained crystallized; its taste is bitter-sweet, like liquorice; it 
 is very sparingly soluble in water; when heated it fuses, and 
 is then decomposed ; like salicine, it gives with nitric acid, 
 picric acid, and with sulphuric acid rutilin; its composition is not 
 known. 
 
 Quassme constitutes the bitter principle of the quassia amara and 
 excelsa. The rasped wood is to be boiled several times with water, 
 and the filtered decoction evaporated down to three-fourths the weight 
 of the wood employed. The liquid, when cold, is to be mixed with 
 slaked lime, and after twenty-four hours, filtered and evaporated nearly 
 to dryness ; the residue is to be treated with alcohol, arid the solution 
 distilled in a water bath to dryness ; it is then impure quassine ; it is to 
 be washed with ether, and then redissolved in alcohol, and this treatment 
 repeated until it becomes completely white. 
 
Naturally existing in Plants. 925 
 
 Quassine forms small white prisms of an intense but purely bitter 
 taste; but sparingly soluble in water or in ether, it dissolves abundantly 
 in alcohol ; when heated it fuses like a resin ; its solution is not pre- 
 cipitated by any metallic salt, but abundantly by tannic acid ; its for- 
 mula is C 2 oHi 2 O 6 . 
 
 Santonin. This substance exists in the flowering tops and seeds of 
 a number of species of artemisia, from one of which (art. santonica) it 
 derives its name. To prepare it, four parts of the seeds are to be mixed 
 with one and a-half of dry lime and boiled in twenty parts of alcohol, 
 three times ; the united decoctions are to be distilled to fifteen parts ; 
 the residue, when cold, is to be filtered, evaporated to one-half, and, 
 having been rendered slightly acid by vinegar, boiled for some time ; 
 on cooling, the sautonine crystallizes in large feathery crystals, which 
 are to be purified from an adhering resinous substance by washing with 
 alcohol. Being then redissolved, and the solution slowly cooled, the 
 santonine crystallizes in colourless rectangular prisms and plates ; it is 
 tasteless ; it is very sparingly soluble in water ; more so in alcohol and 
 ether ; at 328 it melts ; and by a carefully applied heat may be sub- 
 limed without decomposition, otherwise it becomes brown, and a yellow 
 crystalline substance is formed. Santonin appears to possess feeble 
 acid properties; it produces with the alcalies soluble, and with the earths 
 and ordinary metallic oxides insoluble compounds, but they are of 
 instable constitution. The formula of santonine is C 10 H 6 O 2 . 
 
 By exposure to light, santonine undergoes a change apparently, iso- 
 meric ; it becomes gold-coloured, and forms yellow solutions, which, 
 however, soon becomes colourless. 
 
 Saponin. This substance is most easily extracted from the roots of 
 the saponaria officinalis, by boiling in weak spirit; on cooling, the sapo- 
 nine separates ; it is purified by digestion with animal charcoal ; it is a 
 white powder, of a sharp piquant taste ; very soluble in water, it is spa- 
 ringly soluble in alcohol and insoluble in ether ; its formula appears to 
 be C 2 6H 2 3O 16 . By the action of nitric acid, saponine forms mucic acid, 
 and a resinous substance ; when dissolved in solution of caustic potash, 
 it forms saponinic acid, which is precipitated as a white powder on 
 adding a stronger acid to the liquor. The formula of saponinic 
 acid is Qj 6 H 22 O 12 . It is insoluble in cold, but soluble in boiling 
 water. 
 
 Scillitin is the active principle of the squill (scilla maritima.) The 
 fresh juice is evaporated, and the extract treated with alcohol. The 
 spirituous solution is to be dried down, and the residue being dissolved 
 in water, is to be precipitated with acetate of lead and filtered ; sulphu- 
 retted hydrogen being passed through the clear liquor removes the 
 
926 Neutral Organic Substances. 
 
 excess of lead, and then, by filtration and evaporation, the scillitin may 
 be crystallized. 
 
 It forms a hard, brittle mass, like resin, of an intensely bitter taste ; 
 it deliquesces and dissolves readily in alcohol and water, but not in ether. 
 
 Senegin* This substance is extracted from the roots of polygala se- 
 nega, by boiling with water, precipitating the concentrated decoction 
 with the acetate of lead, filtering and removing the excess of lead from 
 the solution by sulphuretted hydrogen, and evaporating cautiously to 
 dryness ; the residue is to be digested in alcohol, and this solution being 
 dried down, the product is to be digested in ether. The material, which 
 remains undissolved, is then to be passed through the same series of 
 operations until it becomes a white pulverulent mass, which is pure sene- 
 gin. It is sparingly soluble in cold, but abundantly in boiling water ; 
 it is very soluble in alcohol, but insoluble in ether. With sulphuric 
 acid it produces a curious play of colours, becoming first yellow, after 
 some time rose-red, and then dissolving ; the solution gradually becomes 
 violet, and after some time greyish-blue, and finally colourless, whilst a 
 grey precipitate falls down. Senegin appears to possess feeble acid 
 properties. 
 
 Smilacine, or .Sarsaparilline. This substance is found in the roots of 
 smilax sarsaparilla and the bark of China nova. It is obtained by boiling 
 with alcohol and distilling the decoction to two-thirds ; on cooling, the 
 smilacine crystallizes and is purified by animal charcoal and recrystalliza- 
 tion. It is white, in very minute needles ; its taste nauseous and slightly 
 bitter ; very sparingly soluble in water, more so in alcohol, most in ether ; 
 with sulphuric acid it gives colours like those of senegin. 
 
 Alsinthin. The bitter principle of the worm-wood, (artemisia ab- 
 sinthium) . It is prepared by a succession of operations almost identical 
 with those described for obtaining senegin ; it is hence unnecessary to 
 repeat their description. When completely pure, it is white and crys- 
 talline ; its taste is intensely bitter ; it fuses at a high temperature, and 
 closely resembles a resin ; its best solvent is alcohol. It possesses the 
 characters of a weak acid, being much more soluble in alcaline liquors 
 than in pure water, and being precipitated from such solutions on the 
 addition of an acid. With oil of vitriol, it is coloured first yellow, and 
 then dark reddish purple. 
 
 Lactudne is obtained by digesting the insipissated juice of the lactuca 
 virosa (lactucarium) in ether ; by the spontaneous evaporation of the 
 solution, it forms a mass of crystalline needles, slightly coloured yellow ; 
 it has a strong bitter taste, is fusible and may be partly volatilized ; it 
 is soluble in water, alcohol, and ether. It is decomposed by strong 
 acids, and appears not to have any tendency to form salts. 
 
Preparation of Vegetable Extracts. 927 
 
 Of Extractive Matter Apotheme Extracts. 
 
 If from any plant, or portion of a plant, the soluble ingredients be 
 dissolved out by water, a variety of substances exist in the liquor, some 
 acid, others basic, others indifferent ; of these bodies, the majority pos- 
 sess the property of absorbing oxygen, when the solution is exposed to 
 the air, and often, also, of evolving carbonic acid, changing thereby into 
 substances insoluble, or scarcely soluble in water. Thus gallo-tannic 
 acid first forms gallic acid, and is then converted into a brown insoluble 
 mass ; so gum and sugar ultimately produce certain forms of ulmine, 
 and there are few of the neutral principles described in the present 
 chapter, that do not rapidly undergo a similar change. 
 
 During the evaporation of a vegetable infusion, or decoction, these 
 reactions rapidly occur, being promoted by the heat ; the liquor which 
 had been at first clear, becomes turbid and brown ; a deposit forms, and 
 when finally it has been evaporated to the consistence of a thick sirup, 
 what remains is termed an extract ; it is a mixture of the constituents 
 of the plant in great part decomposed. If this extract be treated with 
 water, and the soluble portion again evaporated, the same changes 
 occur, so that no matter what may have been the original nature of the 
 vegetable substances, they are ultimately reduced to this insoluble and 
 inert condition. This brown substance is termed apotheme ; its true 
 nature is not known, but it is probable that its composition and pro- 
 perties vary in some degree with the nature of the substance it is 
 formed from ; we do not even know of its relations to the various 
 kinds of ulmine ; though from its solubility in alcaline liquors, and its 
 precipitating metallic salts, its being separated from these by acids, and 
 obstinately retaining a portion of the acid used to precipitate it, its 
 identity with ulmic acid, or humic acid, is not improbable. 
 
 When the conversion of the real constitution of the plant into apo- 
 theme is yet incomplete, the material which dissolves equally in water 
 and dilute alcohol, but not in absolute alcohol or in ether, is termed 
 extractive. Such a mixture can have no distinctive chemical properties; 
 it is more or less coloured, and uncrystallizable ; it precipitates metallic 
 salts; it absorbs oxygen, forming apotheme (oxidized extractive). The 
 different classes of plants are considered by pharmaceutic writers to 
 contain different kinds of extractive matter ; there are thus bitter ex- 
 tractive, gummy extractive, astringent extractive, and so on ; but, to the 
 chemist, these names convey only the idea of absolute ignorance of the 
 real nature of these bodies ; the chemist recognises no such substance 
 as extractive matter, or apotheme ; they are merely complex products of 
 decomposition of other bodies, and have not as yet been accurately 
 
928 Products of the Oxidation of Aloes. 
 
 examined. In the preparation of an extract of a plant, the ambition 
 of the operator should be, not to have either extractive or apotheme 
 produced, but, by employing the lowest possible temperature, and ex- 
 cluding air as much as possible, to obtain the constituents of the plant 
 in a concentrated form, but not destroyed, as they too frequently are, 
 by the operation : accordingly, in the manufacturing laboratory of the 
 Apothecaries' Hall of Ireland, the greatest precautions are taken to 
 ensure success in the preparation of extracts, but details of the me- 
 thods belong to pure pharmacy, and are unfitted for the present work. 
 
 A great number of bodies, that have been from time to time an- 
 nounced as the active principles of many plants containing them, are 
 really only such extracts, properly prepared, but still not the pure che- 
 mical substances. Thus, from colocynth, colocynthine ; from hippo, 
 emetine; from rhubarb, rhe'in, &c. It is on this account that many 
 bodies, to which distinct names have been given by their discoverers, 
 as chemical species, are not here noticed as such. 
 
 Bitter Principle of the Aloes. 
 
 Although this body has never been obtained chemically pure, yet, 
 the very remarkable products of the action of nitric acid on it, show 
 that it is a truly distinct substance. When socotorine or hepatic aloes 
 is digested with hot nitric acid, red fumes are abundantly evolved, and 
 four different acids produced, for the accurate examination of which 
 we are indebted to Schunk. They are, the aloetic add, the aloe-resinic 
 acid, the chrysammic acid, and the chrysolepic acid, and they are gene- 
 rated by successive oxidation of the bitter principle of the aloes, in the 
 order in which their names stand. 
 
 The aloetic acid is a yellow powder, insoluble in water, but forming 
 soluble salts, of which that with potash crystallizes in ruby-red 
 needles. The aloeresinic acid is soluble in water; its potash salt 
 uncrystallizable ; its combinations with the metallic oxides insoluble, 
 and generally brownish-red. The analyses of these bodies are not yet 
 published. 
 
 The chrysammic acid is a greenish-yellow crystalline powder ; it is 
 very sparingly soluble in water, yet tinges it purplish-red ; it is more 
 soluble in alcohol, ether, and acids ; when heated it fuses, and is then 
 decomposed with a slight explosion and a bright but smoky flame ; it 
 contains nitrogen; its formula is Ci5H 2 N 3 Oi2 + Aq. The chrysammate 
 of barytes is a red insoluble powder. The chrysammate of potash is 
 the most insoluble of all the salts of potash, requiring 1250 parts of 
 water, at 60, for solution, and may hence serve as an excellent re-agent 
 
Organic Colouring Matters. 929 
 
 for that alcali ; it is a dark red crystalline powder when precipitated, 
 but when it crystallizes from a hot dilute solution, it forms gold- 
 coloured plates. 
 
 The chrysoleptic acid is distinguished by its solubility in water ; it 
 crystallizes in beautiful gold-coloured plates closely resembling picric 
 acid, with which it is isomeric ; its formula being C 12 H 2 N 3 O 13 -f Aq. 
 It is distinguished, however, by the much greater solubility of its 
 potash-salt, and by the action of heat, as it may be fused and volatilized 
 without decomposition, if cautiously heated. 
 
 CHAPTER XXVII. 
 
 OF THE COLOURING MATTERS. 
 
 THE substances to be now described may be arranged in two classes, 
 according as they pre-exist in the plant, or as they are merely products 
 of the decomposition of other bodies which are not coloured ; of these 
 last an example has already been given in the formation of pfaloridzein 
 from phloridzin. 
 
 OF THE PRE-EXISTING COLOURING MATTERS. 
 
 Colouring Principles of Madder. 
 
 The dried roots of the rubia tinctomm constitute the madder of 
 commerce, which, furnishing the well known Turkey red, is perhaps the 
 most important of the dye-stuffs. The constitution of madder is very 
 complex ; it contains five different colouring matters, and two colourless 
 acids, the general preparation and properties of which are as follows. 
 
 Madder Purple, or Purpurine. Madder roots are to be well washed 
 with water at 80, then boiled several times in a strong solution of 
 alum, and each liquor filtered whilst very hot. On cooling a red-brown 
 59 
 
930 Constituents of Madder. 
 
 substance precipitates, which is impure madder red ; it is to be sepa- 
 rated by the filter. On adding to the clear red solution some sulphuric 
 acid, the madder-purple is thrown down. To obtain it quite pure, it is 
 to be dissolved in boiling alcohol, and the solution allowed to evaporate 
 slowly. It separates as a fine lively cherry-red crystalline powder; 
 sparingly soluble in cold, but more easily in boiling water. The solu- 
 tion is rose-red ; its solutions in ether and alcohol are bright red. 
 Acids turn it yellow ; alcalies dissolve it with a rich red colour. It is 
 fusible, and when more strongly heated a portion sublimes as a red 
 powder, but the greater part is decomposed. It has recently been 
 analysed by Schiel, who proposes for it the formula C2 8 H 10 O 15 . 
 
 Madder Red, or Alizarine, as precipitated in the preparation of pur- 
 purine, is to be purified by repeated boiling with solution of alum, and 
 then crystallized by solution in ether and spontaneous evaporation. It 
 is a pure but dark yellow crystalline powder. When heated it sublimes, 
 forming brilliant orange needles ; it is sparingly soluble in water, more 
 so in alcohol and ether. Ammonia dissolves it with a purple-red, and 
 potash or lime with a violet colour. The formula C 28 H 9 O9 has been 
 assigned to this body by the analyses of Schiel. 
 
 Madder Orange. The roots are to be digested for sixteen hours in 
 eight parts of water at 70; the infusion is to be filtered and set aside; 
 small orange crystals gradually form ; these are to be collected and dis- 
 solved in boiling alcohol. On cooling, the madder orange crystallizes 
 as a yellow powder. When heated it fuses and is decomposed in great 
 part, some of it subliming in yellow fumes ; it is most easily soluble in 
 ether ; it dissolves in alcalies forming brown red liquors. 
 
 Madder Yellow or Xantkin. The cold infusion of madder is to be 
 mixed with an equal volume of lime water. The dark red precipitate 
 is to be treated with dilute acetic acid ; the lime and the yellow madder 
 dissolve ; any traces of the other colouring matters are removed from the 
 liquor by a woollen cloth mordanted with alum. The solution is to be 
 then evaporated ; the residue dissolved in alcohol, and precipitated by 
 sugar of lead ; the scarlet precipitate separated and decomposed by sul- 
 phuretted hydrogen. The liquor so obtained gives, on evaporation, the 
 xanthine pure ; it is yellow, uncrystallizable, and very soluble in alco- 
 hol and water. 
 
 Madder Brown is totally insoluble both in alcohol and water. The 
 acids which exist in madder are but very little known, and do not pos- 
 sess any interest either technical or scientific. 
 
 Of these colouring matters, the red or alizarine, is the most impor- 
 tant, as it forms with an alumina mordant the magnificent Turkey red. 
 With an iron mordant it gives a permanent black, and with mixed 
 
Red Colouring Substances. 931 
 
 mordants of the two, various intermediate shades of purple. The great 
 complexity of the process for dyeing Turkey red arises from the difficulty 
 of dissolving away the other four bodies, so that only pure madder red 
 may remain. 
 
 Alcanna-red, or Anckusic Acid. 
 
 This substance exists in the roots of the anchusa tinctoria. They 
 are to be well boiled in water, and then digested in a solution of carbo- 
 nate of potash ; on the addition of an acid to this liquor the colouring 
 matter precipitates ; it may also be obtained by digesting the roots in 
 alcohol and evaporating ; it is a dark red resinous body, insoluble in 
 water, soluble in alcohol, ether, and essential oils: it combines with 
 alcalies, forming blue solutions, which give blue or crimson lakes with 
 metallic salts. The formula C l? H l0 O4 has been assigned to this body. 
 
 Braziline is the colouring matter of various species of csesalpina 
 (Brazil wood, fernambouc wood). The decoction of the wood in water 
 is to be agitated with hydrated oxide of lead, then filtered and evapo- 
 rated to dryness. The residue is to be treated with alcohol, the solution 
 mixed with water and gelatine, which throws down a quantity of tannic 
 acid ; then filtered, again dried, mixed with alcohol and filtered to se- 
 parate the excess of gelatine, then again evaporated, and set aside to 
 crystallize. 
 
 When pure, braziline forms orange crystals : it is soluble in water, 
 alcohol, and ether; the solutions are reddish-yellow; alcalies and most 
 metallic salts give purple and alum a red precipitate with the solution of 
 braziline. 
 
 Santaline exists in the red sanders wood (pterocarpus santalinus). 
 Its extraction and properties are precisely similar to that of the alcanna- 
 red. Its formula is C 16 H 8 3 . 
 
 Hamatoxylin This substance, the colouring principle of the logwood 
 (hpematoxylon campechianum) is frequently met with naturally crystal- 
 lized in stellated groups of prisms, sometimes of considerable size, in 
 clefts of the wood ; it may also be prepared by a process similar to that 
 described for braziline ; it is slightly bitter and astringent ; it is very 
 sparingly soluble in water, but copiously in alcohol and ether, forming 
 brownish-red liquids. Acids colour its solutions yellow, alcalies purple ; 
 with the earths or metallic oxides it forms purple or blue lakes. The 
 recent investigations of Erdmann have shown that the substance which 
 really exists in the fresh wood of the hsematoxylon is a substance crys- 
 tallizing in white needles, and which forms with water a colourless so- 
 lution ; which, however, rapidly absorbs oxygen from the air, generating 
 thereby the red heematoxyline. This white body dissolves more readily 
 
932 Substances used in Dyeing. 
 
 in water of ammonia, and the liquor becomes almost instantly purple 
 from the absorption of oxygen and the formation of the colouring body. 
 The solutions of logwood become decolorized by sulphuretted hydrogen 
 and by sulphurous acid, from the deoxidation of the colouring material 
 and the regeneration of the white hsematoxyline. 
 
 Safflower-red, or Carthamine. 
 
 The petals of the safflower (carthamus tinctorius) contain a red and 
 a yellow material ; the former alone is of technical importance. The 
 flowers are to be washed with water acidulated with acetic acid, until 
 all the safflower-yellow is removed. By digestion then, in a solution of 
 carbonate of soda, the carthamine is dissolved, and may be precipitated 
 by any acid, but citric acid answers best ; it forms a dark red powder, in- 
 soluble in water and in acids, and but sparingly soluble in alcohol or 
 ether ; it reddens litmus, and gives with the alcalies yellow solutions ; 
 its compound with soda crystallizes in silky needles ; with alumina it 
 forms a beautiful red lake, rouge, used as a cosmetic and in dyeing. 
 This substance is much employed for dyeing silk, of various shades of 
 pink and rose colour. Its formula is C 14 H 8 7 . 
 
 I have found in the petals of the salvia fulgens a colouring matter, 
 possessing considerable analogy to carthamin, and capable of being 
 substituted for it. 
 
 Quercitrin. This substance is extracted from the bark of the quercus 
 infectoria, by simple decoction in water ; after some days, the colouring 
 matter separates in crystals ; or better by digesting the bark in alcohol, 
 precipitating the tannin by gelatine and evaporation. "When pure, it 
 resembles very minute crystals of yellow prussiate of potash; it is 
 easily soluble in water and in alcohol; and appears to possess feeble acid 
 properties. Its formula, by Boulley's analysis, appears to be C I6 H 9 9 + 
 Aq. "With metallic oxides it gives brilliant yellow lakes. 
 
 Chryso-rhamnine Xantho-rhamnine. 
 
 I have found the unripe berries of the rhamnus tinctorius (Persian 
 berries, grains d' Avignon,) to contain a substance, soluble in alcohol 
 and ether, and crystallizing from its ethereal solution in minute silky 
 needles of a brilliant yellow colour ; it gives with metallic oxides yellow 
 lakes. When cautiously heated it fuses, but is not volatile. In the 
 ripe berry, this substance, to which I have given the name chryso- 
 rhamnine, is totally replaced by another, which I term xantho-rJiamnine, 
 which is of a much less beautiful yellow, and does not crystallize ; this 
 
Yellow Colouring Substances. 933 
 
 .change is effected also by boiling the chryso-rhamnine for a few minutes 
 with water, or by contact with alcalies. The xantho-rhamnine is totally 
 insoluble in ether, but easily soluble in alcohol and water. It is formed 
 by the union of the elements of water with chryso-rhamnine. Its 
 silver salt is yellow when first thrown down, but rapidly becomes black ; 
 metallic silver separating, 'and a colourless organic substance being 
 formed. The Persian berries are much used for dyeing yellow, but 
 from the processes employed, the xantho-rhamnine alone is actually 
 brought into play. 
 
 Luteolin is the colouring principle of the weld (reseda luteola) and 
 probably of the dyer's broom, (genista tinctoria). Its mode of prepa- 
 ration resembles that of quercitrine. It is soluble in water, alcohol, 
 and ether ; it combines with both acids and alcalies, forming yellow 
 compounds. With alumina and the oxides of tin and lead, it gives 
 brilliant yellow lakes ; with iron a dark brown precipitate. 
 
 Morin is the colouring principle of the yellow-wood (morus tinc- 
 torius) ; it is prepared like quercitrine, with which its properties accu- 
 rately agree. 
 
 Orellin.TliG seed of the bixa orellana are imbedded in an orange- 
 red colouring matter, which is separated by washings and a kind of 
 fermentation ; when deposited from the liquors, so as to form a consis- 
 tent paste, it is sent into commerce under the names of rocou, Orleans, 
 or anotto. To obtain the colouring principle pure, the orange-red mass 
 is digested in alcohol, and the solution distilled nearly to dry ness ; the 
 residue is then treated with ether, which dissolves .the orelline, and 
 yields it on evaporation, as an orange-red, somewhat crystal- 
 line powder; it colours water pale yellow; it is more soluble in 
 alcohol, but gives with ether or oils deep red solutions ; it dissolves in 
 alcalies, and is precipitated therefrom by acids. "With alumina, oxide 
 of tin, and oxide of lead, it gives fiery red precipitates. It is exten- 
 sively used in dyeing, and also to heighten the colour of cheese and 
 butter. 
 
 Curcumin is found in the roots of the curcuma longa (turmeric), and 
 is obtained by treatment with boiling alcohol, evaporation to dryness, 
 and digestion of the residue in ether, which dissolves the pure colour- 
 ing matter, and yields it by spontaneous evaporation. Curcumin melts 
 at 104; it possesses the properties of a resin; alcalies brown it, on 
 which its employment for a test-paper rests ; acids render its proper 
 yellow much paler, except boracic acid, which stains it yellowish-red. 
 
 Berberin exists in the roots of the berberis vulgaris ; it is prepared 
 by boiling the roots in water, and evaporating the decoction to the con- 
 sistence of an extract, which is to be treated with spirit of wine as long 
 
934 Organic Colouring Matters. 
 
 as this acquires a bitter taste. The spirit is to be distilled in great part 
 off, and the residue let to stand in a cool place for twenty-four hours ; 
 the crystals which form are to be recrystallized, first from water and 
 then from alcohol. Pure berberin forms a light crystalline yellow 
 powder of a strongly bitter taste ; it is very sparingly soluble in cold, 
 but very abundantly in boiling water and in alcohol ; it is insoluble in 
 ether. At 268 it melts; and if further heated, it is decomposed, 
 giving ammoniacal products ; by chlorine it is converted into a brown- 
 red substance ; it combines with bases, acting feebly as an acid ; its 
 alcaline compounds crystallize ; those with the earths and heavy metallic 
 oxides are insoluble, and generally very yellow ; a solution of it pre- 
 cipitates the iodide, cyanide, ferro-cyanide, and sulpho-cyanide of po- 
 tassium. Berberin contains nitrogen ; its formula being NCaaH^O^. 
 
 Cochineal-red, or Carmine. 
 
 This very remarkable substance differs from all of the other colouring 
 matters here described, in being a product of the animal kingdom. It 
 exists in many insects of the genus coccus, as the coccus cacti, (the 
 true cochineal), the coccus ilicis, (kermes,) the coccus ficus, (lac-dye), 
 &c. For its preparation the cochineal is to be digested in ether, to re- 
 move a quantity of fat, and then boiled in alcohol as long as this is 
 coloured. The alcoholic liquors being mixed, are to be concentrated 
 by distillation, and then cautiously dried ; the impure carmine thus ob- 
 tained is digested in alcohol, and the solution mixed with ether, which 
 precipitates the colouring matter quite pure. 
 
 It is a purple red powder, easily soluble in water and alcohol ; in- 
 soluble in ether. It melts at 122 ; but is decomposed by a high heat; 
 chlorine turns it yellow ; alcalies colour cold solutions of carmine red ; 
 but it becomes yellow by exposure to the air, or by boiling. With 
 alumina it forms a precipitate, which is crimson when prepared with a 
 cold, but violet if with a hot solution. All metallic salts give lakes 
 with the alcaline solution of carmine ; that of the protoxide of tin is 
 a rich scarlet. The carmine of commerce is an alumina lake, more or 
 less pure ; that called Chinese carmine is the compound with oxide of 
 tin. 
 
 The carmine contains nitrogen ; the formula, NC 32 H2GO 2 o, has been 
 assigned to it, but cannot be considered as definitely established. 
 
 Of Indigo and the Bodies Derived from it. * 
 
 The blue indigo of commerce is obtained from the leaves of a variety 
 of plants of different genera. The genus indigofera includes a number 
 
Indigo and Us Derivatives. 935 
 
 of productive species, also the genera, nerium, and isatis, marsdenia, 
 asclepias, and polygonum, galega, spilanthus, and amorpha. Of these 
 the great majority are natives of the tropics ; but a few, as the isatis 
 tinctoria, and the poljgonum tinctorium, belong to temperate regions, 
 the former being indigenous both to Ireland and to England. 
 
 The indigo is secreted in the cellular tissue of the leaf, in a form 
 (white indigo) which can also be artificially produced ; it is then colour- 
 less, and remains so as long as the tissue of the leaf is perfect. When 
 the leaf begins to wither oxygen is absorbed, and the indigo assuming 
 its colour, the leaves become covered with a number of blue points, the 
 first appearance of which shows that the period for collecting them has 
 arrived. The fresh leaves are thrown into large vats with some water, 
 and pressed down by weights, After some time a kind of mucous fer- 
 mentation sets in, carbonic acid, ammonia, and hydrogen gases are 
 evolved, and a yellow liquor is obtained, which holds all the indigo 
 dissolved. This is separated, mixed with lime water, and then exposed 
 to the air until the indigo becomes blue *and insoluble, and is com- 
 pletely deposited as a precipitate. The theory of this action is, that 
 by the putrefaction of the vegeto-animal matter of the leaves, the 
 indigo is kept in the same white, soluble condition in which it exists in 
 the plant ; and a clear solution of it being thus obtained, it is precipi- 
 tated, according as it absorbs oxygen, in a much purer form than other- 
 wise could be effected. 
 
 The putrefying pasty mass of leaves, obtained from the isatis tinc- 
 toria, constitutes the woad or wad employed in the hot indigo bath for 
 dyeing cloth. 
 
 The blue indigo, as thus obtained, is still a mixture of several bodies, 
 as indigo-red, indigo-brown, indigo-gluten, which are removed by re- 
 peated treatment with alcohol and dilute acids and alcalies. When 
 pure, the precipitated indigo is a rich blue powder, which, when rubbed 
 by a knife, assumes the colour of metallic copper ; it is perfectly insoluble; 
 when cautiously heated, it sublimes in rectangular prisms, of a dark pur- 
 ple colour and metallic lustre ; its vapour is of a rich purple ; it contains 
 nitrogen, its formula, as fully established by Dumas, being NC 16 H 5 O 2 . 
 
 White Indigo. When indigo is acted upon by deoxidizing agents, 
 as protochloride of tin, protoxide of iron, or sulphurous acid, it loses 
 its blue colour, and the white indigo, which is insoluble in water, but 
 soluble in alcaline solutions, is produced. Its mode of preparation is 
 simple ; one and one-half parts of commercial indigo ; two and one- 
 half parts of slaked lime, and two parts of green copperas are to be 
 well mixed up with sixty parts of water in a vessel from which the 
 air is carefully excluded. The protoxide of iron, formed by the action 
 

 936 Indigo and its Derivatives. 
 
 of the lime on the copperas, peroxidizes itself at the expense of the 
 indigo and water, and the white indigo thus formed dissolves in com- 
 bination with lime. On adding muriatic acid to the clear solution, the 
 white indigo precipitates, and may be obtained dry, as a crystalline 
 powder, by suitable precautions to prevent the access of air. 
 
 The simplest theory of this process should be, that the oxide of iron 
 directly abstracted oxygen from the indigo, hence the names of 
 deoxidized indigo and indigogene were given to the white substance ; 
 but the analyses of l)umas have proved, that the white indigo is a 
 compound of hydrogen with the blue indigo, its formula being 
 C J6 H 5 N0 2 -f H. In its formation, therefore, water is decomposed, 
 the elements of it combining respectively with the blue indigo, and the 
 deoxidizing body. 
 
 On the properties of this white indigo depend the important appli- 
 cation of indigo as a dyeing material. The indigo is rendered soluble 
 either by lime and copperas (cold indigo bath), or, being diffused 
 through warm water with a quantity of woad, by the fermentation of 
 which ammonia and hydrogen are evolved, a soluble compound of am- 
 monia and white indigo is obtained (hot indigo bath) ; the former is 
 employed for cotton, and the latter for woollen cloth. The cloth is 
 immersed in the bath until it has fullyjmbibed the solution ; it is then 
 exposed to the air, the oxygen of which carries off the hydrogen of the 
 white indigo, and the blue insoluble indigo attaches itself to the fibres 
 of the cloth so firmly at the moment of its formation, as to constitute 
 the most permanent and the most beautiful of our blue dyes. 
 
 Sulphate of Indigo. "When blue indigo, in very fine powder, is di- 
 gested with strong oil of vitriol, for which purpose the German, or 
 fuming sulphuric acid answers best, it dissolves in great part, and two 
 acids are formed, the mlpho-purpuric and sulph-indylic ; the former is 
 the principal product when the indigo is in excess, the latter when the 
 oil of vitriol preponderates ; they are separated by dilution with water, 
 the sulpho-purpuric acid being insoluble, whilst the sulph-indylic acid 
 dissolves. 
 
 The sulpho-purpuric acid, though insoluble in dilute acids, dissolves 
 readily in pure water; it forms, with the alcalies and earths, blue com- 
 pounds, which are sparingly soluble in water, but soluble in alcohol. 
 By the analysis of Dumas it appears to consist of C 32 H 10 N 2 O 4 + 2. 80s, 
 and in its potash salt to contain one atom of alcali. 
 
 The sulph-indylic acid, C 16 H 5 NO 2 + 2S0 3 , when dried from its 
 solution in water, forms a dark blue mass. Its salts are of a rich blue 
 colour ; those of the alcalies are soluble, those of the earths and me- 
 tallic oxides insoluble in water. They consist, according to Dumas' 
 
Anilic AM Picric Acid Idoptene. 937 
 
 analysis, of an atom of indigo, two of sulphuric acid, and one of 
 base. The sulpho-purpuric and sulph-indylic acids thus contain the 
 same organic element (indigo), but in different proportions, united to 
 sulphuric acid. 
 
 Berzelius considers that, besides these two, there are generated, by 
 the action of sulphuric acid on indigo, several other acids of complex 
 nature ; but as we possess no exact results concerning them, and that 
 they are of no technical importance, it is unnecessary to describe them 
 in detail. 
 
 This solution of indigo in oil of vitriol constitutes the Saxon Hue ; 
 or cliemic blue, used extensively in dyeing; on neutralizing the liquor by 
 an alcali (carbonate of soda), and immersing the tissue, whether wool, 
 silk, or cotton, the indigo combines with the fibre of the cloth, and the 
 sulphuric acid remains combined with the alcali. 
 
 Anilic AM Picric AM Anthranilic AM. 
 
 By the gradual oxidation of indigo, a substance is formed which 
 crystallizes in large red prisms, and is termed by Laurent, isatine ; its 
 formula is Ci 6 H 5 NO 4 . If the process be more violently carried on, the 
 constitution of the indigo is broken up and a new type formed, thus : 
 by the action of an excess of nitric acid on indigo two remarkable bodies 
 are formed, the anilic and the picric acids. For the formation of the 
 anilic acid, or as it is also often termed the indigotic acid } or the nitro- 
 salicylic acid, the following process is well adapted. A mixture of one 
 part of fuming nitric acid and ten of water being brought to boil, indigo 
 is to be added in fine powder as long as any effervescence occurs ; the 
 liquor is to be then filtered whilst hot. Both acids crystallize on cool- 
 ing ; the crystals are to be drained, redissolved in water, and precipitated 
 by acetate of lead; picrate of lead falls ; anilate of lead remains dissolved, 
 and being decomposed by sulphuretted hydrogen, the anilic acid crys- 
 tallizes in white needles; its taste is bitter and acid; it requires 1000 
 parts of cold, and but ten of boiling water ; its salts are all soluble ; its 
 formula is C 14 H 4 NO 9 + Aq. 
 
 The Picric Acid may be obtained by diffusing the picrate of lead 
 through boiling water, and decomposing it by sulphuretted hydrogen 
 gas ; on filtering and cooling, the picric acid crystallizes. It may be 
 obtained, however, much purer and more abundantly by digesting sali- 
 cine in nitric acid (p. 844) and directly from the substance which exists 
 in coal gas naptha, termed by Laurent, hydrate of phenyl ; it forms 
 yellow prisms, sparingly soluble in cold water ; when heated it explodes, 
 as do also its salts ; its potash salt requires 260 parts of cold water for 
 
938 Products of the Decomposition of Indigo. 
 
 solution, and it is hence sometimes used as a re-agent for that alcali ; 
 its formula is C 12 H 2 N 3 13 + Aq. 
 
 When indigo is mixed with a strong boiling solution of caustic potash, 
 it dissolves and chrys-anilic acid is formed, which may be precipitated 
 by muriatic acid as an orange-red powder ; it dissolves in alcohol and 
 ether, and crystallizes by the evaporation of the solutions ; its formula 
 appears to be C 28 H 10 NO 5 -f Aq. By exposure to the air, whilst hot, 
 or directly by contact with peroxide of manganese, this acid is converted 
 into another, anthranilic acid, the properties of which are remarkable ; 
 it is soluble, crystallizes, gives very well marked and crystallizable salts, 
 fuses at 275, and sublimes a little above that temperature unchanged ; 
 if it be strongly heated, however, it is decomposed, the sole products 
 being carbonic acid and a volatile liquid, aniline. The formula of the 
 hydrated anthranilic acid is, C 14 H 7 NO 4 , and it gives 2.C0 2 and 
 C 12 H 7 N. 
 
 This liquid, aniline, acts as a powerful base, combining with the hy- 
 dracids directly, and with the oxacids by including an atom of water ; 
 it thus resembles ammonia. It is the remarkable artificial alcaloid 
 whose history has been already fully described, p. 845. 
 
 Action of Chlorine on Indigo. 
 
 This subject, so important in relation to the theory of the bleaching 
 of colouring matters, has been very minutely investigated by Erdman, 
 of whose numerous and complex results the elementary nature of this 
 work will allow but a general notice to be given. Dry chlorine has no 
 action on indigo, but in presence of water it converts it into a yellow 
 mass, from which is separated by distillation a substance, termed chlo- 
 rindopten, which sublimes in white scales and needles ; its formula is 
 C 16 H 4 O 2 C1 4 ; it is sparingly soluble in water, copiously in alcohol and 
 ether. This appears to be a secondary product. The substance which 
 remains behind in the retort, on being dissolved in boiling alcohol, yields 
 on cooling, red prismatic crystals of chlorisatin ; its formula is C 16 H 4 C1. 
 N0 3 , it is hence indigo in which an equivalent of hydrogen is replaced 
 by chlorine, and united to an atom of oxygen ; with an excess of chlo- 
 rine it gives lichlorisitine, which consists of C 16 H 4 C1 2 N0 3 . If these 
 bodies be treated with sulphuretted hydrogen, sulphur is set free, and 
 the hydrogen enters into combination ; in contact with potash, the ele- 
 ments of an atom of water are assimilated, aud an acid formed, which 
 unites with the potash. In this way chlorisatin give chlorisatyd, 
 CieHsClNOg, and chlorisatic acid, C 16 H 5 C1N0 4 , and bichlorisatin 
 gives two corresponding bodies. 
 
Relations of Indigo to Phenyl. 939 
 
 If chlorisatyd be heated, it produces water, chlorisatin, and a violet 
 powder, chlorindm, which has the formula C 16 H 5 C1NO2, and is hence a 
 compound of indigo-blue with chlorine. By heating bichlorisatyd, the 
 bichlorindin C 16 H 5 NO 2 .Cl2 is similarly formed. 
 
 By passing chlorine through a solution of chlorisatin in alcohol, all 
 hydrogen is removed, and a substance formed which crystallizes in pale 
 yellow plates, and has the formula C 6 O 2 C1 2 ; it is termed chloraniL 
 By the secondary reactions of these bodies, a number of others are ge- 
 nerated, which it is not necessary specially to describe. 
 
 Notwithstanding the attention devoted by the most distinguished 
 chemists to the compounds and derivatives of indigo, the theory of that 
 body remains very obscure. The derivation of picric acid from the 
 body C ]2 H 5 D -f Aq. (hydrate of phanyl) discovered as a product of de- 
 structive distillation by Laurent, may serve as a connecting point for 
 many of the bodies derived from indigo, and which otherwise had ap- 
 peared totally unconnected. Thus the picric acid is evidently formed by the 
 substitution of S.NCU for 3H in C ]2 H 5 O, and the aniline is probably 
 CigHs -f NH 2 ; other speculative ideas might be brought forward, but 
 I shall only mention that the blue indigo contains exactly the elements 
 of cyanogen and benzyl, C 2 N + C 14 H 5 O 2 , and that as the cyanogen is 
 converted so easily into oxalic acid and ammonia, the derived bodies 
 which contain Ci^ may thus have their origin. The relations of the 
 bodies of the indigo series to those of the series of phenyl, derived from 
 the destructive distillation of organic bodies, has been further exhibited 
 in Chapter xxv., page 842. 
 
 Indian Yellow. Purree and its Derivatives. 
 
 A yellow colouring material is brought into commerce from the East, 
 known as Indian yellow ', or purree. It is extracted from camel's urine, 
 but appears to be derived only from the urine of such camels as feed on 
 the mangistana mangifer. It is a compound of magnesia with a yellow 
 body, which may be prepared pure by boiling the mass with water, to 
 which small quantities of muriatic acid are added, until the whole dis- 
 solves, and then filtering. On cooling, the liquor deposits the colour- 
 ing matter in brilliant yellow scales, which are termed purreic add. 
 They are very sparingly soluble in cold, but abundantly in boiling wa- 
 ter. They are distinctly acid, and neutralize bases. Their formula is 
 C 40 H 16 O 21 + 2Aq. "When carefully heated, the purreic acid is decom- 
 posed and a new body sublimes in yellow needles, which is termed 
 purron, its formula is C 13 H 4 04. The same body appears to be pro- 
 duced from purreic acid under the influence of strong acids or bases. 
 
940 -fndian Yelloiv and its Derivatives. 
 
 With chlorine and bromine the purreic acid gives derived cliloro- 
 purreic and Iromopurreic adds, of which the formulae are respectively 
 C 4 oH 14 Cl20 2 i and C 4 oH 14 Br 2 O 21 . The former crystallizes in gold 
 yellow plates, the latter appears only in amorphous grains. They form 
 well defined neutral salts. With oil of vitriol, purreic acid forms sulplw- 
 purreic acid, and purron ; C 40 H 16 O 2 i, producing two atoms of C 13 H 4 O 4 
 and C I4 H 8 Oi3, which with S0 3 produce the combined acid in its anhy- 
 drous form. The sulphopurreic acid can be obtained as a thick sirup, 
 but does not crystallize and very soon decomposes. 
 
 When acted on by nitric acid, there are produced from purreic acid 
 three acids, the nitropurreic acid, the nitrococcic acid, and the styphnic 
 acid, which last has been already described page 844, as a product of 
 the oxidation of many gum resins. The nitropurreic acid is formed by 
 the action of cold nitric acid ; this is not decomposed, and no red fumes 
 are given off. The purreic acid changes into crystalline grains in which 
 the elements of an atom of water of the purreic acid are replaced by an 
 atom of nitric acid, so that the formula of the product is, C 40 Hi 5 NO 25 . 
 r= C 40 H 15 O 2 o + N0 5 . If the purreic acid and nitric acid be heated 
 together a very violent reaction occurs ; red fames are abundantly given 
 off, and on cooling the nitro-coccic acid separates in yellow grains. Its 
 formula is not well determined, as it is very difficult to obtain it quite 
 pure from nitro-purreic acid on the one hand, and from styphnic acid 
 on the other. Its characteristic quality is to produce with the alcalies 
 scarlet red salts. 
 
 The purron produces, with re-agents, a series of compounds. Thus, 
 cklorpurron is a yellow powder, having the formula C 13 H 3 C1O 4 . Brom- 
 purron is similarly constituted. With nitric acid the purron produces 
 nitropurronic acid, the formula of which is CaeHgNgOjg. It is inso- 
 luble in water, but soluble in alcohol, from which it crystallizes in 
 small reddish-yellow prisms. It forms with bases red salts, of which 
 that of ammonia is remarkable, as it forms blood-red grains sparingly 
 soluble in water, even when boiling. 
 
 The relation of the bodies of this purree series to the products of the 
 oxidation of aloes, described page 928, will be easily observed on com- 
 parison, and deserves further enquiry. 
 
 OF THE COLOURING MATTERS DERIVED FROM THE LICHENS. 
 
 Many kinds of lichen contain substances which, although colourless 
 themselves, produce, by contact with air and ammonia, the rich purple 
 or blue colouring matters,'constituting the archil and litmus of commerce. 
 The more important species have been in this respect very accurately 
 
Constituents of the Lichens. 
 
 examined, and the material facts of their history may be considered as 
 now satisfactorily established by the researches of Dumas, of Schunk, 
 of Steuhouse, and myself. The species most studied have been the 
 variolaria dealbata, the parmelia roccella, the usnea tinctoria, and the 
 roccella tinctoria. 
 
 Orcine and Orceine. 
 
 The useful substance in the variolaria is termed orcine, it is obtained 
 by digesting the lichen in alcohol, evaporating to dryness, dissolving 
 the extract in water, concentrating the solution to the thickness of a 
 sirup, and setting it aside to crystallize ; it forms, when quite pure, 
 colourless prisms, of a nauseous-sweet taste ; it fuses easily, and may be 
 sublimed unaltered ; its formula is C 16 H 8 O 4 -|- 3Aq. when sublimed ; 
 when crystallized from its aqueous solution, it contains 5Aq. 
 
 If orcin be exposed to the combined action of air and ammonia, ex- 
 actly as described for phloridzin, (p. 918), it is converted into a crimson 
 powder, orceine, which is the most important ingredient in the archil 
 of commerce. The orceine may also be obtained by digesting dried 
 arclu'l in strong alcohol, evaporating the solution in a water bath to 
 dryness, and treating it with ether as long as anything is dissolved ; it 
 remains as a dark blood-red powder, being sparingly soluble in water or 
 ether, but abundantly in alcohol ; its formula is C 16 H 9 N0 7 . The orceine 
 in archil is, however, frequently found to contain less oxygen, and to be 
 represented by the formula C 16 H 9 N0 4 . I have termed the first kind 
 alpha-orcein, and the second beta-orce'in ; in properties they are iden- 
 tical. 
 
 Orcein dissolves in alcaline liquors, with a magnificent purple colour ; 
 with metallic oxides it forms lakes also of rich purple, of various shades. 
 In contact with de-oxidizing agents it combines with hydrogen, as in- 
 digo does, and forms leuc-orcein, C 16 H 9 NO 7 -f H. When bleached by 
 chlorine, a yellow substance is formed, chlor-orceine, the formula of 
 which I have found to be C 16 H 9 N0 7 + Cl analogous to the other. 
 
 Lecanoric acid Erythric acid. 
 
 The examination by Schunk, of various species of Lecanora, and 
 some other lichens, has proved that although under the influence of 
 ammonia, and of air they ultimately produce Orceine, these lichens do not 
 contain Orcine ready found ; but another body termed Lecanoric acid, 
 which under the influence of bases, breaks itself up into Orcine and 
 carbonic acid. It is most easily extracted by digesting the lichen in 
 
942 Colouring Principles of the Lichens. 
 
 very cold dilute water of ammonia with exclusion of air, and then pre- 
 cipitating it from its solution by an acid. It forms minute crystals 
 nearly insoluble in water, and but sparingly soluble in cold alcohol, or 
 ether. By boiling alcohol it is rapidly altered. Its formula is found 
 to be C 18 H 8 O 8 -f- Aq. If it be heated orcine sublimes, and if boiled 
 with solution of barytes, carbonate of barytes is produced, and orcine, 
 which is thus proved to C ]6 H 8 4 when anhydrous. If Lecanoric 
 acid be dissolved in boiling alcohol, it unites with ether, forming Lcca- 
 noric ether. This body crystallizes beautifully in pearly scales. Its 
 formula is C 22 H 13 O 9 = C 18 H 8 8 + C 4 H 5 O. This body was described 
 by Heeren and by myself, under the names of Erythrine and Pseudo- 
 erythrine, and the formula, C 5 H 4 O 2 , was proposed for it by Liebig; but 
 the true empirical formula for it, C 22 H 13 O 9 , was established by my ana- 
 lyses and was verified afterwards by SchunFs discovery that it con- 
 sisted of Lecanoric acid and ether. 
 
 The Erythric acid is found principally in the rocella tinctoria, and 
 in the evernia prunastri ; it is extracted by boiling water from which 
 it deposits on cooling, and may be purified by a repetition of the 
 process. It forms small soft crystalline masses ; it is sparingly soluble 
 in cold water, abundantly in boiling. By long boiling it is decomposed 
 into Lecanoric acid, and a material termed Amarythrine, or Erythrine- 
 bitter. The formula of the Erythric acid was first given by Schunk 
 as C 34 H 1 9O 1 5 and it was supposed to decompose into Lecanoric acid 
 and Orcine, C 18 H 8 8 -f- C 16 H n 7 = C 34 H 19 O 15 , But this does not 
 explain the formation of the Erythrine bitter which I showed to be pro- 
 duced in this reaction, and Schunk lately proposed for the Erythric 
 acid the formula C 42 H 23 21 , formed of 
 
 Lecanoric Acid = Ci 8 H 8 O 8 , \ 
 Amarythrine = C 2 4H, 5 O,3. J <W* 
 
 Stenhouse, however, whose analyses of Erythric acid appear worthy 
 of confidence, proposes for it the formula C^H^O^, and it appears to 
 consist of lecanorine with erythrine-bitter, having the formula C 22 Hi 4 Oi 2 , 
 when anhydrous. 
 
 Amarythrine, Picrerythrine, or Erythrine bitter, is formed when ery- 
 thric acid is boiled. I considered it as a product of the oxidation of 
 erythrine, but it has been shown to be a natural constituent of the 
 lichen in the erythric acid. It is soluble in water, particularly when 
 hot ; it forms compounds with bases ; I proposed for it the formula 
 C 22 H I3 O 14 , but the specimens examined were not quite pure, and I am 
 disposed to adopt from Mr. Stenhouse' s analyses of the erythric acid, 
 of which it is a constituent, the formula C 22 H 14 O 12 + HO, when crys- 
 tallized ; the composition deduced from which coincides with the empi- 
 rical formula proposed by Mr. Stenhouse, C 34 H 23 O 2 o. 
 
Derivatives of Erythrinc. 943 
 
 When Amareythrine is boiled in contact with a base it abandons the 
 elements of carbonic acid and produces a substance termed Pseudo- 
 orcine, discovered by Stenhouse. This body crystallizes in prisms for 
 which Mr. Stenhouse proposed the formula C 10 H 13 O 10 . Mr. Schunk 
 has proposedj for this body the formula C22H 28 O 22 ; but I prefer Mr. 
 Stenhouse' s formula, merely doubling the equivalent =C 20 B. 26 O 2 Q. By 
 which its formation is perfectly explained, as 
 
 Amarythrine = C22HuOi2 
 
 Losing carbonic acid Cs O4 
 And taking water + 
 
 Produces Pseudo-orcine = 
 
 Orsellic Acid. Mr. Steuhouse has shown that some varieties of the 
 roccella tinctoria, contain in place of lecanoric acid, a different body 
 which he has termed as above. Under the influence of bases it is 
 converted into carbonic acid and orcine, and by boiling in alcohol it 
 forms lecanoric ether ; its formula is C^H^O^ and it appears to be a 
 coupled body consisting of hydrated lecanoric acid C 18 H 9 O 9 , and hy- 
 drated orcine Ci 6 H 9 O 5 . 
 
 In the examination of the evernia prunastri, Mr. Stenhouse also 
 found that in place of pure lecanorine, a body was obtained which he 
 termed evernic acid, which ultimately yielded orcine under the influence 
 of a base, but which also produced a different substance evernesic acid. 
 It would appear, therefore, that the latter, for which Mr. Stenhouse 
 assigns the formula C 18 H 9 O 7 , unites with lecanoric acid C 18 H 8 8 to 
 form evernic acid, for which Schunk has proposed the formula C^H^O^, 
 in place of that of Stenhouse C^H^On. This question must however 
 be considered as still undecided. 
 
 Telerytherine. In my examination of the lichen bodies, I disco- 
 vered that after the complete decomposition of the erythrine there 
 might be obtained a crystallizable material which I termed telerythe- 
 rine, having the formula C 2 oH 9 Oi 8 + Aq. This body however does 
 not appear to form any part of the series of substances producing 
 colour. 
 
 Roccellic Acid. This body which has the strongest analogy to the 
 fatty acids, is extracted from the lichen by water of ammonia, and is preci- 
 pitated on the addition of chloride of calcium as rocellate of lime, which 
 being decomposed by muriatic acid, the rocellic acid may be dissolved 
 by boiling alcohol, from which it crystallizes on cooling. Liebig 
 assigned to this acid the formula Ci 7 Hi 6 4 ; but I showed that its pro- 
 
944 Colouring Principles of the Lichens. 
 
 perties indicated the formula CgeH^Og to be the true one. Latterly 
 Schnnk has proposed to modify slightly this also, making it C24H 23 O 6 . 
 
 Erythryline. This substance was obtained in my researches on these 
 bodies ; it is very sparingly soluble in water ; but abundantly in alco- 
 hol and ether ; with boiling alcohol it produces lecanoric ether, and 
 with ammonia and access of air produces the crimson colour of orceine. 
 I proposed for it the formula C 22 H 16 O 6 , which must however, from 
 later investigations, be doubled. It is a coupled body consisting of 
 lecanorine and roccellic acid, and hence according to the formula as- 
 sumed for that body, it becomes C4 4 H3o0 12 or C 42 H 29 O 12 . The elements 
 of two atoms of water being evolved. 
 
 Usnic Acid. This body exists in a great variety of lichens, which 
 have naturally more or less of a red or yellow colour. It is extracted 
 by ether, from which, when mixed with alcohol, it deposits in crystals 
 of a rich yellow colour. With alcalies it forms red compounds, but does 
 not yield orceine. Its formula is C 38 H 17 O H . Another similar body is 
 the chrysophanic acid, which forms golden-yellow crystals, and gives 
 with the alcalies rich purple and red solutions. Its formula is C 10 H 8 O 3 . 
 
 Constitution of Archil and Litmus as found in Commerce. 
 
 It is known that these bodies are prepared by the digestion of differ- 
 ent species of lichens with ammonia, generally derived from putrid 
 urine. I found them to contain two classes of colouring materials, one 
 characterized by the presence of nitrogen as a constituent, and evi- 
 dently formed by the agency of the ammonia, and the other class desti- 
 tute of nitrogen in their composition. The orceine, which is the most 
 important of the series, has been already noticed as derived from orcine, 
 the others require only brief notice. 
 
 The ingredients in the archil or orseille of commerce are the orceine, 
 of which the two varieties already noticed may be recognized, and which 
 form the important and characteristic ingredients; and further, two 
 bodies, one containing nitrogen, azoerythrine, and the other, erythroleic 
 acid, destitute of azote. 
 
 The azoerythrine is insoluble in alcohol and in water, it dissolves in 
 alcalies, giving wine-red solutions, which are precipitated by acids and 
 by metallic salts. At the time that the erythrine was supposed to 
 have the formula C 22 H 13 O 9 , I proposed for azoerythrine the formula 
 C 2 2H6N0 19 -f- 3Aq., but the composition of this body would now 
 require a new examination. 
 
 The erythroleic acid is separated from the other bodies present in 
 archill by means of ether, in which it dissolves abundantly, forming a 
 
Nature of Archil and Litmus. 945 
 
 rich crimson solution. It gives with alcalies purple liquors., and with 
 the earthy and metallic salts coloured lakes. Its formula is C26H22O8 . 
 It appears to be capable, under circumstances not yet well understood, 
 to break up into two bodies which have not been found in archill, but 
 which exist in litmus, the erythrole'in and the erythrolitmine. 
 
 The litmus, which is to the chemist a colouring material of so much 
 interest, from its use as a test for acids, consists of a mass of the earthy 
 and alcaline compounds of colouring bodies, which being themselves red 
 when free, form blue salts and lakes. Hence htm us paper is reddened 
 by an acid, the red colouring matter being set free, and again blued by 
 an alcali, from the lake or alcaline compound being again formed. The 
 important ingredients of litmus are azolitmine, erythrolitmine, and 
 erythrolein. The latter exists but in small quantity. 
 
 The azolitmine is a dark red powder, which is insoluble in alcohol 
 and ether, and but sparingly soluble in water. It dissolves better in 
 acid liquors, which render it a pale red, and with alcalies it gives the 
 fine blue colour of litmus. It appears to be derived from the further 
 oxidation of orce'ine, and to have the formula C 16 H 9 NO 9 . With the 
 earths and metallic oxides it forms purple or black lakes; with deox- 
 idizing agents it is decolorized, forming leucolitmine, and with chlorine 
 it is destroyed and bleached, a yellow substance being formed, chlor- 
 azolitmine, to which the formula C 16 H 9 NO 9 + Cl. may be assigned. 
 
 The erythrolein possesses exactly the properties already described for 
 the erythroleic acid, from which it differs only in composition, its for- 
 mula being C 26 H 2 2O4. The erythrolitmine, however, is much more dis- 
 tinctly characterized. It is very sparingly soluble in water or in ether, 
 but easily soluble in alcohol. Alcalies turn it bright blue. In a solu- 
 tion of potash it dissolves, but its compound with ammonia is insoluble 
 in water. The formula of erythrolitmine is C^H^O^. Its blue ammonia 
 salt has the formula C 26 H 22 12 + NEUO. By heat, one-half of the 
 ammonia is expelled, and a very dark red compound remains. This 
 change of colour may be easily observed by warming ordinary litmus 
 paper. 
 
 The brief history of these substances now given will render intel- 
 ligible the process of manufacture of archil and litmus, and the prin- 
 ciples of their use in the arts and in the laboratory. The lichens em- 
 ployed are ground up with water to an uniform pulp, and this is then 
 mixed with as much water as makes the whole thick fluid. Ammo- 
 niacal liquors from the gas, or ivory-black works, or even stale urine, 
 are from time to time added, and the mass frequently stirred so as to 
 promote the action of the air. The orcine or erythrine which existed 
 in the lichen absorbs oxygen and ammonia and forms orcein ; the 
 60 
 
Nature of Archil and Litmus. 
 
 roccelline absorbs oxygen and forms erythroleic acid ; these being kept 
 in solution by the excess of ammonia, the whole liquid is of an in- 
 tensely rich purple tint, and constitutes ordinary archil. If the oxidizing 
 action of the air be allowed to go too far, we have the purple colour 
 replaced by a shade more or less blue ; the orcei'ne changes to azolit- 
 mine, and the erythrolein gives erythrolitmine ; a quantity of chalk and 
 plaster of Paris is then added to the liquor, so as to form a consistent 
 paste, and this cut into little cubical masses and dried, forms the litmus 
 of commerce. From the constitution of archil and litmus, such must 
 be the general principles of the manufacture, although, particularly 
 for litmus, the details are kept very secret by those engaged in the 
 trade. 
 
 The use of litmus paper, as a test for the presence of a free acid, 
 arises from the blue colour belonging to compounds of the erythrolit- 
 mine and azoerythrine with an alcali ; and as this is taken by even the 
 weakest acid, the red colouring materials are set free. 
 
 Of the Colouring Matters of Leaves and Flowers. 
 
 The green colour of plants is due to the presence of a substance 
 termed chlorophyl. Even deeply coloured plants contain but very little 
 of it ; and it has not been as yet obtained in a state of such purity 
 as that any formula can be assigned to it. It does not contain nitro- 
 gen ; it is insoluble in water, soluble in alcohol and ether ; it is dis- 
 solved by strong acids, and precipitated therefrom by dilution ; it enters 
 into union with bases, and gives pale green lakes. With deoxidizing 
 agents it shows the same process of decoloration as most other bodies 
 of this class. 
 
 Berzelius has noticed that there are really three kinds of chlorophyl ; 
 the first, which exists in fresh leaves, dissolves in acetic acid, with a 
 rich grass-green colour ; the second, formed from the first by drying, 
 gives an indigo-blue solution with the same acid ; and the solution of 
 the third, which exists principally in the pyrus aria, and other dark 
 leaved plants, is brownish-green. So excessive is the colouring power 
 of this body, that Berzelius has calculated that the entire mass of leaves 
 of a large tree seldom contains ten grains of chlorophyl. 
 
 It is known that in autumn the leaves of many trees, as the sorbus 
 aucuparia, cornus sanguinea, &c., assume a fine red colour; whilst the 
 foliage of others, particularly of forest trees, becomes bright yellow. 
 Berzelius, who has examined the nature of this change, found the chlo- 
 rophyl to be replaced in such leaves by a red and yellow colouring 
 matter, to which he gave, respectively, the names erythrophyl and 
 
Colouring matter of Leaves and Flowers. 947 
 
 xanthophyl. The former is an extractive matter, easily soluble in 
 alcohol and water ; by the air it is gradually changed into a brown in- 
 soluble matter : with alcalies it forms rich green solutions, and with 
 metallic oxides, green lakes ; by acids the red colour is restored ; a 
 green leaf containing chlorophyl is, however, not reddened by an acid. 
 It is remarkable that all trees in whose leaves erythrophyl forms in 
 autumn, bear red fruit, as the cherry, currant, &c. 
 
 Xanthophyl is a deep yellow, fatty substance, which melts between 
 100 and 120; it is insoluble in water, but dissolves copiously in 
 alcohol and ether; its solution, exposed to the air and light, is rapidly 
 bleached. Alcalies dissolve it sparingly with a yellow colour, which is 
 bleached by light. 
 
 We possess but very little accurate knowledge of the colouring mat- 
 ter of flowers : they constitute a very remarkable group of bodies, 
 closely related to each other, and distinct from the colouring matters 
 that have been as yet examined. It has been stated that the colours of 
 all flowers result from two ; one blue (anthocyari), which is soluble in 
 water and alcohol, reddened by acids, rendered green by alcalies ; and 
 from these changes producing the red, and all intermediate shades of 
 purple and violet. The yellow substance (anthoxanthin) is likewise 
 easily soluble in alcohol and water, and is coloured intensely blue by 
 oil of vitriol. These substances possess most analogy to hematoxylin 
 and to safflower-yellow ; but it is highly probable that a great number 
 of species of colouring matters exist in flowers as they do in woods. 
 The quantity present in the flower is generally so excessively minute, 
 that the accurate examination of their properties is exceedingly 
 difficult. 
 
 On some general Characters of Colouring Matters, and on the 
 Principles of Dyeing. 
 
 In addition to the detailed history of the individual colouring matters, 
 there are a few remarks belonging to them, as a class, which deserve 
 notice. 
 
 Under the heads of indigo and of orceine I have described the 
 formation of white compounds, by the action of deoxidizing agents, 
 and that in those, which are the only cases that have been accurately 
 examined, it resulted from the direct combination of hydrogen with the 
 colouring matter. This character of forming a colourless compound 
 with hydrogen appears to belong to all coloured substances. If an in- 
 fusion of logwood, of cochineal, of violets, of turmeric, be rendered 
 acid by muriatic acid, and a slip of zinc immersed therein, the liquor 
 
948 Principles of the Art of Dyeing. 
 
 becomes gradually colourless, and on adding ammonia, a white lake is 
 precipitated, consisting of the hydruret of the colouring matter com- 
 bined with oxide of zinc. 
 
 "With oxygen all colouring matters appear also to combine to form 
 bodies quite or nearly destitute of colour. Thus, if the chryso-rham- 
 nate of silver be boiled in water, metallic silver separates, and the 
 oxidized colouring matter dissolves. This illustrates the manner in 
 which colours fade, and they are more or less fugitive, according as 
 their tendency thus to combine with oxygen is greater. On this prin- 
 ciple was founded the old process of bleaching, by exposing the cloth 
 to the conjoined agencies of water, air, and light. The bodies whose 
 colour injured the whiteness of the cloth were gradually changed by 
 oxidation into others, less coloured and more easily removable by 
 washing. In the majority of cases, however, the process is not limited 
 to simple oxidation, but carbonic acid is evolved, and the colouring 
 matter is totally broken up in constitution. 
 
 The colour of many substances, as logwood, archil, litmus, indigo, 
 of most flowers, &c., is removed by sulphuretted hydrogen, and by sul- 
 phurous acid. In these cases there is direct combination, and the 
 colour is restored by expelling the combined gas by heat, or by a strong 
 acid. Tor commerce, many bodies, particularly those of a yellow 
 colour, are given a temporary whiteness, by stoving or smoking with 
 sulphurous acid, by placing them in a room where sulphur is burned; 
 this is done with corn, with straw for hats, with sponges, &c. The 
 sulphurous acid gradually goes off afterwards, and the yellow colour 
 returns. 
 
 The destruction of colours, by means of chlorine, is the most 
 important decomposition to which this class of bodies is subject, as on 
 it the modern processes of bleaching all our woven tissues, paper, &c. 
 is founded. Innumerable niceties in the application of coloured pat- 
 terns on cloth would be impossible, and the art of the calico printer 
 restrained to very narrow limits, was it not for the power which 
 chlorine gives him of removing the original colour from any chosen 
 space, and replacing it by others of various tints. The theory of this 
 action of chlorine, which had been formerly thought to depend upon 
 a mere oxidation of the colouring matter, water being decomposed, has 
 been shown by my results with orceine, and confirmed by those of 
 Erdman on indigo, to consist in the formation of new substances con- 
 taining chlorine. The chlorine in some cases replaces hydrogen ; in 
 others it combines directly with the colouring matter ; in others again, 
 water is decomposed, and the product, besides containing chlorine, is 
 also more highly oxidized. The action of chlorine on colouring matters 
 
Theory of the Process of Bleaching. 949 
 
 is, therefore, subjected to the same laws as when it acts upon other 
 organic substances, the series of bodies derived from indigo by chlo- 
 rine having much analogy to the series of bodies formed by chlorine 
 with alcohol or olefiant gas. 
 
 In relation to the processes of dyeing, colouring substances are 
 divided into two classes, the substantive and adjective. The substan- 
 tive colours are those which being very sparingly soluble in water, and 
 having a strong affinity for the fibre of the cloth, combine directly with 
 it ; such are carthamine, and indigo ; the adjective colours are inca- 
 pable of so permanently fixing themselves, and the necessary insolubi- 
 lity and affinity for the cloth is given through the intervention of a 
 base with which the colouring substance may combine. The cloth is 
 mordanted with alumina (p. 490,) or iron (p. 521,) or tin (p. 758,) or 
 mixtures of these metallic oxides, and as the lakes so formed are of 
 different colours, a great variety of tints may be produced. The 
 field of application of substantive colours also is greatly enlarged by 
 the use of mordants ; the simple colouring matter could, of course, 
 give but its own tints, whilst it forms, with the bases, lakes of various 
 colours. 
 
 The resources of the dyer are by no means limited even by the vast 
 number of coloured substances described in the present chapter. From 
 the mineral kingdom, some of the richest colours are now procured, as 
 has been already noticed in the special history of the salts of chrome, 
 of iron, of copper, of lead, of manganese, and of antimony. It is 
 remarkable that hitherto no true green colouring matter has been 
 found capable of application in the processes of dyeing; the only greens 
 which exist in nature being the chlorophyl, and the green of the stems 
 of buckthorn, (sap-green) neither of which are capable of being attached 
 to the cloth : all greens are therefore in practice formed by the super- 
 position of a blue (indigo, or Prussian blue) and a yellow (chromate of 
 lead or chryso-rhammine.) 
 
 The details of the processes of dyeing and printing in patterns, 
 although embracing some of the most refined applications of the pro- 
 perties of the colouring matters, do not enter into the plan of an ele- 
 mentary and general work, like the present. 
 
950 
 
 CHAPTER XXVIII. 
 
 OF THE VEGETABLE ALCALIES. 
 
 THE substances now to be described constitute a very remarkable family 
 of bodies. They exist naturally in the plants from which they are de- 
 rived, and confer upon them their most active medicinal properties ; they 
 act as bases, forming, with few exceptions, well characterized and neutral 
 salts even with the strongest acids, and they are distinguished from 
 most substances of vegetable origin by containing nitrogen. The pre- 
 sence of this element, indeed, has been considered as standing in imme- 
 diate connexion with the source of their alcaline power, and has given 
 rise to theories of their intimate constitution, of which I shall notice the 
 most important, at the conclusion of their special histories. 
 
 Quinine (NC 20 H 12 2 ) or Qu. 162, or 2025. 
 
 The bark of the various species of cinchona, contains three vegetable 
 alcalies, combined with the cinchonic and cinchona-tannic acids already 
 described. These are quinine, cinchonine, and aricine ; of these the 
 quinine is by far the most important, and is generally extracted from the 
 yellow bark. The coarsely powdered bark is to be boiled with eight or 
 ten parts of water, to which two parts of muriatic acid have been added. 
 When the liquor will dissolve no more, it is to be allowed to cool and to 
 be strained ; lime is then to be added in very fine powder, until the liquor 
 has a marked alcaline reaction ; the precipitate is to be collected on a 
 linen cloth, washed once or twice with water, and then dried ; from this 
 boiling alcohol dissolves out quinine and cinchonine ; the solution being 
 mixed with water, the alcohol may be distilled off and saved ; the resi- 
 due is then to be neutralized by dilute sulphuric acid, and a slight ex- 
 cess added to form acid salts. On evaporating this liquor to the proper 
 
Sulphates of Quinine. 95 1 
 
 point, the sulphate of quinine crystallizes whilst the sulphate of cin- 
 chonine remains in solution. 
 
 To obtain pure quinine, solution of sulphate of quinine is to be 
 decomposed by caustic potash, and the white curdy precipitate, being 
 carefully dried, is to be dissolved in the smallest possible quantity of 
 spirit of wine. By then allowing it to evaporate spontaneously in a 
 warm place, the pure quinine crystallizes, with an atom of combined 
 water. 
 
 When heated cautiously, the quinine abandons its crystal-water, and 
 then fuses ; its taste is intensely bitter ; it requires 200 parts of boiling 
 water for solution, and is almost insoluble in cold water; it dissolves 
 easily in alcohol and ether. 
 
 The salts of quinine are generally crystallizable, and soluble in alcohol 
 and water ; those with the oxygen acids contain an atom of water, in 
 which they agree with the salts of ammonia, of melamine, and of ani- 
 line ; it combines directly with the hydracids. 
 
 The Muriate of Quinine. (Qu. -f- HC1). Forms pearly needles. 
 It dissolves easily in water ; with corrosive sublimate, and with bich- 
 loride of platinum it forms double salts soluble in water, and crys- 
 tallizable. 
 
 The Basic Sulphate of Quinine is the most important preparation of 
 this base ; its manufacture is conducted on a very large scale, according 
 to the process just now given for preparing quinine, or various ana- 
 logous methods. When crystallized it contains water : its formula 
 being (Qu 2 . -}- SO 3 -f- 8 Aq.) It effloresces when gently heated, or in 
 very dry air, giving off six atoms of water and retaining two, which can- 
 not be expelled without partial decomposition ; it is but sparingly solu- 
 ble in water, requiring thirty parts of boiling and 740 parts of cold 
 water ; it requires eighty parts of cold alcohol, but much less of hot ; 
 its crystals are small pearly plates or needles, which when heated phos- 
 phoresce strongly and fuse ; by a strong heat it is, of course, totally 
 decomposed. 
 
 The Neutral Sulphate of Quinine crystallizes in rectangular prisms, 
 which have the formula (Qu. -f. SOs -f 8Aq.) They effloresce easily, 
 dissolve in ten parts of water, at 60. and undergo aqueous fusion at 
 212. It is also very soluble in alcohol ; though neutral in constitu- 
 tion its solution reddens litmus. 
 
 The sulphate of quinine of commerce is sometimes adulterated with 
 sulphate of lime, and with boracic acid, which are known by remaining 
 when the organic substance is burned away, and also with sugar and 
 with margaric acid. The latter is detected by its insolubility in dilute 
 acids ; the former by washing the sample with a little water, and pre- 
 
95 Salts of Quinine. 
 
 cipitating the quinine that is dissolved by a drop of solution of carbonate 
 of soda, when the taste of the sugar is recognized. 
 
 Phosphate of Quinine crystallizes in small but very brilliant needles, 
 which are soluble in water and alcohol. 
 
 The Tannate of Quinine is formed by adding solution of tannic acid, 
 or infusion of galls to any salts of quinine. A white precipitate appears 
 which is totally insoluble in water, but dissolves in acetic and muriatic 
 acids. 
 
 Ferro-prussiate of Quinine is formed by boiling together one part of 
 sulphate of quinine, and one and one-half of yellow prussiate of potash 
 with seven parts of water. The newly formed salt separates as a green- 
 ish-yellow oily substance. When the liquor is cold it is to be poured 
 off, and the ferro-prussiate of quinine dissolved in boiling alcohol, from 
 which it crystallizes in greenish-yellow needles by spontaneous eva- 
 poration. 
 
 When quinine is distilled with a very strong solution of potash, a 
 dense oil is produced which was termed quinoline, but it has been found 
 to be identical with the substance leucoline, found in gas tar, and de- 
 scribed in page 847 ; it possesses the characters of an organic alcali. 
 
 The action of chlorine on quinine and its salts is very characteristic. 
 If sulphate of quinine be dissolved in a large quantity of chlorine water, 
 and some water of ammonia added, a deep green precipitate is formed, 
 and the liquor becomes also intensely green. To the body so formed 
 the name Thalleiochin has been given. If the green solution be evapo- 
 rated with contact of air, it becomes dark-red coloured, sal-ammoniac is 
 formed, and two bodies, of which one is soluble in alcohol and the other 
 not ; the former is called rusiochin, and the latter melanochin. For- 
 mulae have been proposed for these bodies, but as no security for their 
 accuracy has been given, I think it better not to bring them forward. 
 These reactions, combined with the action of tannic acid, serve as 
 tests for quinine. 
 
 Cinchonine. NCaoH^O or Ci. Equiv. 154, or 1925. 
 
 This alcali exists most abundantly in the grey bark (cinchona mi- 
 crantha), from which it may be obtained by the same kind of process 
 as the yellow bark is subjected to for the extraction of quinine ; but it 
 is usually prepared from the mother liquors which remain after the 
 crystallization of the sulphate of quinine, as just now described ; from 
 its alcoholic solution it crystallizes in thin colourless prisms ; its taste 
 is peculiar and bitter; it requires 2500 parts of boiling water for solu- 
 tion, but dissolves easily in alcohol and in ether. At 330 it fuses, 
 without losing weight. Its salts resemble very closely those of quinine. 
 
 
Cinchonine Aricine. 953 
 
 Muriate of Cinchonine. Ci + HC1. Crystallizes easily in brilliant 
 interwoven needles ; it forms double salts with the metallic chlorides, 
 similar to those of quinine. 
 
 Sulphate of Cinchonine. The basic sulphate, Ci 2 + SO 3 -f- 2Aq. crys- 
 tallizes in rhombic prisms ; it requires fifty-four parts of cold water for 
 solution. The neutral salt Ci. + 80s + 8Aq. is much more soluble, 
 and crystallizes in large, well-formed rhombic octahedrons. The tannate 
 of clnchonine is a white insoluble powder. 
 
 In contact with chlorine, cinchonine forms a dark-red solution, and 
 after some time a brown precipitate appears. If iodine and ciuchonine 
 be dissolved together in alcohol, and the liquor evaporated spontaneously, 
 a compound crystallizes in saffron-coloured needles, which is described 
 as iodide of cinchonine, which it cannot be, as hydriodic acid is formed. 
 
 Aricine. NC 2 oH 12 3 . or Ar. Equiv. 170, or 2125. 
 
 This alcaloid is found in the bark known as China de cusco or arica 
 bark, with which the genuine cinchona bark is often adulterated ; the 
 tree yielding it not known. It is obtained by precisely the same pro- 
 cesses as those by which cinchonine and quinine are procured from the 
 pale and yellow barks. 
 
 It crystallizes in brilliant white needles; it is totally insoluble in 
 water, but easily dissolves in alcohol and ether. These solutions have 
 an intensely bitter taste ; by nitric acid it is coloured green ; its salts 
 have been very little examined, but they appear to correspond very 
 closely in constitution and properties, to the salts of quinine and cin- 
 chonine. 
 
 Morphia. NCa^Og, or Mr. Equiv. 286, or 3562-3. 
 
 To this body is due in most part the medicinal activity of opium, as 
 a substitute for which it is prepared upon a very large scale. The pro- 
 cesses adopted in the British pharmacopoeias for this purpose are very 
 simple, and deliver a product which, although by no means chemically 
 pure, is yet sufficiently so for all medical objects ; as they are, however, 
 more especially applied to the preparation of the muriate of morphia, I 
 shall describe them under that head. 
 
 To obtain pure morphia, the process invented by Wittstock, is per- 
 haps the best. One part of opium, eight of water, and two of muriatic 
 acid are to be digested together for six hours ; when the mixture has 
 cooled, the brown solution is to be poured off, and the residue treated 
 twice more with water and acid. The liquors so obtained being mixed 
 are to be saturated with common salt, on which they become milky, 
 
954 Properties of Morphia* 
 
 and after a few hours, a brown clotty precipitate forms ; this being re- 
 moved by the filter, ammonia is to be added in slight excess, and the 
 whole allowed to stand for twenty-four hours. The precipitate which 
 forms in this time is to be collected on a filter, washed with a little 
 water, dried, and digested in spirit of specific gravity, 0*820, which 
 dissolves out the morphia. By distillation, the greater part of the 
 spirit is removed, and the morphia being dissolved in a small quantity 
 of boiling alcohol, crystallizes on cooling. In this process, the narcotin 
 is separated by the addition of the common salt, in a solution of which 
 it is insoluble ; the meconic acid, codein and thebain remain dissolved 
 after the addition of the ammonia in excess, and the other principles 
 present in the opium remain in the mother liquor after the morphia 
 crystallizes. 
 
 The process of Merck is founded on the insolubility of morphia in a 
 solution of sal-ammoniac, and its solubility in lime water. Opium is to be 
 digested in three times its weight of water, then expressed, and this re- 
 peated three or four times ; these solutions being mixed, are brought to 
 boil, and milk of lime added in slight excess ; the precipitate which 
 forms, is to be collected in a strainer and strongly pressed : the liquor 
 is then to be evaporated until it is about twice the weight of the opium 
 employed, and to be then filtered, brought to boil, and for each pound 
 of opium, one ounce of sal-ammoniac added in powder. The morphia 
 separates in crystals, and may be purified by boiling with some lime and 
 ivory black and precipitation again by sal-ammoniac. 
 
 Morphia crystallizes in right rhombic prisms, as in the figure; ?', u, 
 being primary, and m, a secondary plane, containing 2.Aq. which they 
 lose by efflorescence in a gentle heat, and become opaque ; 
 its taste is strongly and permanently bitter; it is almost 
 insoluble in water, requiring 400 parts when boiling and 
 separating almost completely as the liquor cools. The 
 solution reacts strongly alcaline ; it dissolves readily in al- 
 cohol, but very sparingly in ether. It dissolves in solutions of the 
 caustic alcalies or earths. If morphia or any of its salts be brought 
 into contact with nitric acid, they become coloured red ; this property 
 belongs also to some other vegetable alcalies, and appears not to be 
 possessed by morphia when absolutely pure. With chlorine water, 
 morphia is first coloured orange-red, and then dissolved. If iodic acid 
 be brought into contact with morphia, it is immediately decomposed 
 and iodine set free. 
 
 If morphia or any of its salts be added to a solution of sesquichloride 
 of iron, the solution assumes a rich blue colour, which is removed by an 
 excess of acid, but returns on the neutralization of it by an alcali. 
 
Salts of Morphia Narcotine. 955 
 
 With tannic acid it gives a copious white precipitate. By these remark- 
 able reactions, the recognition of morphia is rendered more simple than 
 that of any other body of its class. 
 
 Morphia completely neutralizes the strongest acids, forming salts, 
 which are generally soluble and crystallizable. 
 
 Muriate of Morphia. Mr. -f* H.C1. Is, for medicinal objects, the 
 most important compound of morphia ; its preparation as directed by 
 the British pharmacopoeias, is as follows : the soluble parts of opium 
 having been dissolved out by digestion in water, the united liquors are 
 to be evaporated to the consistence of a sirup and then cold water 
 added by which a quantity of feculent matter (apotheme) is separated ; 
 the clear liquor is to be decomposed by a slight excess of chloride of 
 lead (London), or of chloride of calcium (Edinburgh.) The meconate 
 of morphia, which exists in the opium, being decomposed, meconate of 
 lime or lead is precipitated, and muriate of morphia remains dissolved ; 
 the liquor is to be carefully strained and evaporated to a pellicle ; on 
 cooling, the salt crystallizes ; this is to be pressed between folds of cloth, 
 to remove the dark mother-liquor, and then dissolved in boiling water, 
 digested by ivory black, and re-crystallized until the crystals become 
 perfectly white. 
 
 The product of this method, although not chemically pure, is suf- 
 ficiently so for medicinal uses. It contains codeine, and sometimes 
 others of the opium alcaloids. To obtain the pure salts, pure morphia 
 should be dissolved in dilute muriatic acid, and the solution crys- 
 tallized. 
 
 Sulphates of Morphia, The neutral sulphate which crystallizes in 
 groups of soft needles, and dissolves in twice its weight of water ; has 
 the formula Mr.HO.SOs + 5 Aq. The "bisulphate of morphia does not 
 crystallize. 
 
 Acetate of Morphia is formed by dissolving the alcali in acetic acid, 
 or by decomposing muriate of morphia by acetate of lead; it crystallizes in 
 small feathery needles interwoven into masses. It is soluble in water and 
 in alcohol, and after the muriate is the most important salt of morphia. 
 
 Morphia is precipitated by ammonia and by tannic acid from solu- 
 tions of any of these salts. 
 
 Narcotine. NCtfH^Ou, or Nr. Equiv. 5362-5, or 429. 
 
 This alcaloid may be obtained at once from opium by digestion with 
 ether, or when the impure morphia is thrown down by ammonia, ether 
 dissolves out the narcotine from it. It crystallizes in colourless rhom- 
 bic prisms, which are generally larger than those of morphia ; it fuses 
 
956 Narcotine Narcogenine Co famine. 
 
 at 338, and remains liquid until cooled to 266, when it congeals as a 
 mass of radiated needles. It is almost insoluble in water, but easily 
 soluble in alcohol and ether ; its salts have but little stability, few of 
 them crystallize, and most are decomposed by dilution with much water. 
 By ammonia and tannic acid they are precipitated. 
 
 From morphia, narcotine is very easily distinguished by its solubi- 
 lity in ether, insolubility in caustic alcalies and earths ; its not giving 
 the reactions characteristic of morphia with nitric acid, or with sesqui- 
 chloride of iron. But if narcotine be put in contact with sulphuric 
 acid, and that oxygen is supplied either by the air or by a trace of 
 nitric acid, it becomes red. Under these circumstances, however, mor- 
 phia becomes green. 
 
 Products of the Decomposition of Narcotine. 
 
 When narcotine is subjected to the action of oxidizing agents, as by 
 distillation with peroxide of manganese and dilute sulphuric acid, it 
 gives origin to new products, differing according to the degree to 
 which the action has been carried. Various means of oxidation may 
 be employed, as treatment with caustic potash, or with bichloride of 
 platinum, and corresponding differences in the nature of the products 
 are found to occur. 
 
 The first result appears to be that narcotine, with five atoms of oxy- 
 gen, produces opianic acid, narcogenine and water. The formula of 
 opianic acid is CgoHgOg + Aq. It crystallizes in slender prisms and 
 forms well defined cry stalliz able salts. The opianate of ammonia, when 
 heated, gives off water, and produces opiammon C 20 H 17 NO 16 , a pale 
 yellow powder, which by boiling with water, is converted into binopi- 
 anate of ammonia. Under the influence of caustic potash opiammon 
 gives off ammonia and forms another acid, xanthopenic acid, which is a 
 yellow substance containing nitrogen. 
 
 Narcogenine has the formula C 36 H 19 NOio. It crystallizes in a dou- 
 ble salt with bichloride of platinum ; but can scarcely be examined in an 
 isolated form as it breaks up into narcotine and another alcali which 
 has been termed cotarnine. This body has the formula C 25 Hi3N0 6 . It 
 is the usual product of the oxidation of narcotine, the narcogenine 
 being destroyed by the continued action. The cotarnine crystallizes in 
 deep yellow radiated needles. It is soluble in alcohol and water ; it is 
 bitter and strongly alcaline, forming crystallizable salts with acids and 
 with the bichloride of platinum. By the decomposition of cotarnine, 
 apopkyllic acid is produced, of which the properties are not well 
 known. 
 
Different Alcaloids contained in Opium. 957 
 
 The opianic acid yields a numerous series of derivatives, which, how- 
 ever, require but a brief notice. By oxidation it produces the hemi- 
 pinic acid, which crystallizes in prisms, and has the formula C 10 H 4 O 5 , 
 With sulphurous acid it produces opianmlpJiurous acid, C 2 oH 6 OnS 2 -j- 
 Aq., which is opianic acid, in which the elements of two equivalents of 
 water are replaced by two of sulphurous acid. By the action of sul- 
 phuretted hydrogen opianic acid is converted into sulphopianic acid, 
 C 20 H 8 7 S 2 + Aq, in which two atoms of water are replaced by 2.HS. 
 "Woehler considers these two atoms of water to be really ready formed 
 in the opianic acid, and the anhydrous acid to have the formula C2oH G 07. 
 He also considers narcotine to contain opianic acid ready formed, united 
 with an organic alcali of which the oxidation produces narcogenine and 
 cotarnine. 
 
 When decomposed by heating with caustic potash narcotine is con- 
 verted into a body apparently isomeric, termed narcotianic acid. When 
 heated alone narcotine gives a dark brown material not containing 
 nitrogen, it has been called humopinic acid, but its real nature is not 
 known. 
 
 Codeine. NC 36 H 21 O 6 , or Cdn. Equiv. 3737'5, or 299. 
 
 This alcali remains dissolved after the morphia, narcotine, and other 
 substances have been precipitated by ammonia. The filtered liquor is 
 to be evaporated to dryness, and digested in solution of potash, a sub- 
 stance remains undissolved which gradually becomes crystalline. This 
 is to be washed with water, and then dissolved in boiling ether, from 
 which, by spontaneous evaporation, the codein separates in colourless 
 prismatic crystals, which contain 2Aq. 
 
 Crystallized codein fuses at 300, giving off its crystal water. It 
 dissolves copiously in water, the solution reacts strongly alcaline ; it is 
 insoluble in alcaline liquors, but forms with acids perfectly neutral 
 crystallizable salts. These are precipitated copiously by tannic acid, 
 but not by ammonia ; it does not produce any of the reactions described 
 as characterizing morphia. As none of its salts are employed in phar- 
 macy or medicine, they need not be specially noticed. 
 
 Thelaine. ^NC 25 H 14 O 3 , or Tb. Equiv. 2525, or 202. 
 
 The watery infusion of opium being treated with milk of lime, so 
 that the morphia may rest dissolved, the precipitate is to be washed 
 with water until it becomes white, and then dissolved in a dilute acid. 
 Prom this solution thebain is precipitated by ammonia. The preeipi- 
 
9 5 8 Thebaine Narceme Strychnine. 
 
 tate being dissolved in ether, and the solution evaporated, pure thebai'n 
 crystallizes in colourless short rhombic prisms, which taste sharp and 
 styptic, and have a strong alcaline reaction. At 300 it fuses, and 
 solidifies then only when cooled to 230. It is scarcely soluble in water, 
 but abundantly so in alcohol and ether. 
 
 By acids thebaine is decomposed, a resinous substance and a salt of 
 ammonia being formed. In its other characters it completely resembles 
 narcotin. 
 
 Narceme. The watery solution of opium is to be heated first by 
 ammonia, which throws down morphia, narcotin, thebaine, and some 
 other bodies, and these being removed, by filtrations, the meconic acid 
 and codein are to be precipitated by an excess of solution of barytes. 
 The excess of barytes being then removed by a current of carbonic acid 
 gas, the filtered liquor is to be evaporated to the consistence of a sirup 
 and set aside ; after some time crystals form, which are a mixture of 
 meconine, (see p. 923), and narceine. These are separated by ether, 
 which dissolves the meconine, and the residual narceine being dissolved 
 in alcohol and decolorized by animal charcoal, crystallizes by the cooling 
 of its solution in delicate needles. 
 
 It tastes bitter, fuses at 200, and forms a crystalline solid on cool- 
 ing ; it dissolves in 230 parts of boiling water ; it is very soluble in 
 alcohol, but insoluble in ether ; its solution does not react alcaline, and 
 it is decomposed by strong acids. In its constitution, however, it re- 
 sembles the true vegetable alcalies, its formula being NCasHgoO^. 
 
 Pseudomachine. NC 2 4H 18 12 ? Occurs but very rarely in opium. 
 For its mode of preparation, when present, I shall refer to the larger 
 systematic works ; in its reaction it is absolutely identified with mor- 
 phia, from which it is distinguished, however, by its composition, by 
 crystallizing in plates, and by not forming any well characterized salts, 
 although it dissolves very readily in dilute acids. 
 
 Strychnine. 'N,^>i. Stc. Equiv. 4325, or 346. 
 
 This alcaloid exists associated with brucine in several species of 
 strychnos (nux vomica,ignatia, colubrina, &c.), also in the substance used 
 by the natives of Borneo for poisoning their arrows, and termed upas- 
 tieuta, or woorara ; it is obtained most easily from the Ignatius' beans, 
 which contain but little brucine, but as these are not often found in 
 commerce, the nux vomica is most generally employed. The seeds are 
 to be boiled for some time in strong alcohol, which dissolves out a 
 quantity of fatty matter ; being then dried in a stove, they are easily 
 reduced to powder ; this powder is to be then boiled two or three times 
 
Preparation and Salts of Strychnine. 959 
 
 in alcohol, and the liquors distilled until the greater part of the alcohol 
 has come over. To the residue, acetate of lead is to be added as long 
 as any precipitate occurs ; by this means more fat, colouring matter, 
 and some organic acids are removed. The filtered liquor is to be then 
 evaporated so far, that from sixteen ounces of nux vomica it amounts 
 to six or eight ounces. To this quantity two drachms of magnesia are 
 to be added, and the whole allowed to stand aside for some days ; the 
 precipitate which forms is to be collected on linen, pressed, dried, and 
 dissolved in alcohol, from which the strychnine crystallizes on cooling, 
 whilst the brucine remains in the mother liquor. As the strychnine, 
 however, is not yet pure, it is to be dissolved in dilute nitric acid, and 
 the solution evaporated to a pellicle. On cooling the nitrate of strych- 
 nine crystallizes in brilliant white, soft, feathery prisms, whilst the 
 nitrate of brucine separates afterwards in large hard rhombic prisms. 
 From sixteen ounces of nux vomica, forty grains of nitrate of strych- 
 nine, and fifty grains of nitrate of brucine may be obtained ; from the 
 solution of the pure nitrate in water, the strychnine may be precipitated 
 by ammonia, and being dissolved in spirit of wine, it crystallizes by 
 spontaneous evaporation in small, white, four-sided prisms. 
 
 Strychnine has an intensely bitter, somewhat metallic taste ; it re- 
 quires 7000 parts of cold water for solution, and yet if one part of this 
 be diluted with 100- parts more of water, this liquor tastes strongly 
 bitter ; it is insoluble in absolute alcohol and in ether, but dissolves 
 readily in spirit of wine. With acids strychnine unites, forming well 
 characterized and crystallizable salts ; it differs from the other vegetable 
 alcalies, in containing two atoms of nitrogen in its equivalent. With 
 chlorine strychnine gives a white precipitate ; also with tannin ; when 
 completely pure, it is not reddened by nitric acid, but such as it exists 
 in commerce, it generally is so, owing to the presence of traces of 
 brucine. Under the influence of caustic potash, strychnine, like quinine 
 and cinchonine, yields the quinoline or leukol. 
 
 Muriate of Strychnine.. Stc. -f- HC1. Crystallizes in crowded rhom- 
 bic needles, which dissolve readily in water. With corrosive sublimate, 
 with bichloride of platinum, and with cyanide of mercury it gives in- 
 soluble double salts. 
 
 Hydrocyanate of Strychnine is obtained by dissolving strychnine in 
 prussic acid ; it crystallizes in needles, which are decomposed even by 
 a gentle beat. If solution of sulphocyanide of potassium be added to 
 a solution of any salt of strychnine, the liquor, when agitated, deposits 
 the sulphocyanate of strychnine in fine radiated needles, which are inso- 
 luble in water. By this means one part of strychnine may be recog- 
 nized in 375 of water, and hence Artus has proposed this reaction as 
 the best medico-legal test for strychnine. 
 
960 Brucine and Curarine. 
 
 Sulphate of Strychnine forms small cubic crystals, which contain 
 4 Aq. and are soluble in ten parts of water. 
 
 The characters of the nitrate of strychnine have been described in 
 the method of preparing the alcaloid. 
 
 Strychnine is, perhaps, after pure prussic acid, the most intense of 
 poisons. It kills by producing tetanus. 
 
 J3rucine.N 2 C 4B H. 26 08 or Br. Equiv. 406, or 5075. 
 
 This substance is found associated with strychnine, as already de- 
 scribed, and also in the bark of the false angustura, which is now 
 known to be the strychnos nux vomica, though formerly supposed to 
 be the brucia antidysenterica, whence the name of this alcaloid is de- 
 rived. Its mode of preparation from the nux vomica has been suffici- 
 ently described in the preceding article. 
 
 From its solution in spirit, brucine crystallizes in colourless rhombs, 
 containing water, which they abandon on melting at 280. It dissolves 
 in 850 parts of cold, and in 500 parts of boiling water ; these solutions 
 react alcaline, and taste intensely bitter ; it dissolves readily in alcohol, 
 but is insoluble in ether. 
 
 With nitric acid, brucine becomes of a rich red colour, which, on 
 the addition of protochloride of tin, changes to a fine violet ; this dis- 
 tinguishes it from the red of morphia, which is completely bleached by 
 protochloride of tin and by sulphurous acid. 
 
 "With chlorine, brucine gives a yellowish-red, and with iodine a 
 chocolate brown precipitate. 
 
 The salts of brucine have a bitter taste, are generally crystallizable, 
 and give with tannin and with ammonia white precipitates. 
 
 A curious result is said to be produced by heating brucine with nitric 
 acid, vapours of nitrous ether are given off, and a peculiar yellow body 
 formed, termed by Laurent cacotheline. To the latter product has been 
 assigned the formula CajHnNaO^; it appears to possess alcaline pro- 
 perties, and it combines with ammonia to form a crystallizable material, 
 which has not yet been accurately examined, but which appears to be 
 a powerful alcali. 
 
 The Curara, or Urari poison, used in the Indian Archipelago for 
 poisoning arrows, contains a vegetable alcaloid, curarine, which forms 
 a yellow uncrystallizable mass, which dissolves easily in water and in 
 alcohol, but is insoluble in ether ; it reacts alcaline and combines with 
 acids ; its salts do not crystallize ; its solution is precipitated by tannic 
 acid. 
 
 The tree from which curara is derived, is not accurately known, but 
 is supposed to be a strychnos. 
 
Vegetable Alcalies. 961 
 
 Delphinin. NC 27 H 19 2 or De. Equiv. 2637'5 or 211. 
 
 This substance is extracted from the seeds of the stavesacre, delphi- 
 nium staphisagriaj by digestion in water, to which some sulphuric acid 
 had been added. The acid liquor is to be decomposed by a slight excess 
 of magnesia, and the precipitate being washed and dried, is to be boiled 
 in alcohol, which dissolves the delphinine. To obtain it quite pure it 
 is to be redissolved in a dilute acid, boiled with animal charcoal, filter- 
 ed, precipitated with ammonia, and the precipitate dissolved in alcohol, 
 from which the delphinine separates on cooling as a white crystalline 
 powder. 
 
 It is soluble in ether and alcohol ; almost insoluble in water ; its 
 solution has an intolerably sharp taste; it melts at 250; chlorine 
 turns it green ; oil of vitriol colours it red, and then carbonizes it ; 
 its salts are very soluble, but crystallize badly ; Courbe states that the 
 stavesacre contains also a substance stcpkysain, (NO^H^C^. ?), which 
 is distinguished by its insolubility in ether ; it is a yellow resinous mass, 
 insoluble in water, but dissolving in dilute acids without neutralizing 
 them. 
 
 Veratrine. NC&H^Og. or Ve. Equiv. 3589 or 287. 
 
 This alcaloid is found in the roots of the veratrum album, and in 
 the seeds of the veratrum sabadilla ; the best process for its extraction 
 is that given by Yasmer. 
 
 The sabadilla seeds are to be infused in water, containing an ounce 
 of oil of vitriol for each pound of seeds, as long as anything is dis- 
 solved. The filtered liquor is wine-yellow ; it is to be accurately neu- 
 tralized by carbonate of soda, and evaporated to the consistence of an 
 extract. While yet warm, alcohol is to be poured on it, and digested 
 until every thing soluble is taken up. From this solution the alcohol 
 is then to be distilled off, the residue digested in dilute sulphuric acid, 
 and from this liquor the veratria precipitated by carbonate of soda. 
 The precipitate must be redissolved in a dilute acid, digested with ivory 
 black, and again precipitated by a carbonated alcali in order to obtain 
 it pure. 
 
 Pure veratrine appears as a white uncrystallized resinous powder ; it 
 melts at 230, reacts alcaline, has no smell, but produces violent 
 sneezing ; its taste is exceedingly sharp, but without bitterness ; it is 
 insoluble in water, but dissolves readily in alcohol and ether ; its salts 
 are mostly crystallizable and neutral, but if mixed with much water 
 they are decomposed, acid being set free and a basic salt precipitating. 
 Yeratrine itself is actively poisonous, and is much used in medicine, 
 but none of its salts are important. 
 61 
 
96 2 Jervin Colchicine JSmetin. 
 
 Saladilline.--NV zo H.i 3 5 , or Sa. Equiv. 2338, or 187. 
 
 This body which accompanies veratrine, is separated from it by boil- 
 ing the precipitate produced by the carbonate of soda with water. 
 From the liquor the sabadilline gradually separates in radiated crys- 
 talline needles, of a pale rose colour, but when purified it becomes white ; 
 its taste is intolerably sharp ; it is sparingly soluble in water or in ether, 
 but abundantly soluble in alcohol ; it reacts strongly alcaline, and forms 
 crystallizable salts with acids. 
 
 Jervin. NC 3 oH 2 3O 2 , or Je. Equiv. 2912, or 233. 
 
 This alcaloid accompanies veratrine in veratrum album ; it is pre- 
 pared by a process similar to that for veratrine, from which it is sepa- 
 rated by the facility with which it crystallizes from its alcoholic solution, 
 and by the very sparing solubility of its sulphate. "When pure it is 
 white, easily fusible, totally decomposed at 400, slightly soluble in 
 water, but copiously soluble in alcohol. Of its salts, the sulphate, nitrate 
 and muriate, are sparingly soluble in water or in mineral acids ; the 
 acetate dissolves readily. Muriate of jervin forms with bichloride of 
 platinum a very sparingly soluble double salt. Crystallized jervin con- 
 tains 4 Aq. 
 
 Colchicine. (Formula not established.) 
 
 This alcaloid is obtained from the seeds of the meadow saffron (col- 
 chicum autumnale), by digestion in a mixture of weak alcohol and sul- 
 phuric acid. The excess of acid in the liquor is to be 'then neutralized 
 by kme, and the alcohol distilled off. The residual liquor is to be de- 
 composed by carbonate of potash in excess, the precipitate washed, 
 dried, dissolved in absolute alcohol, decolorized by animal charcoal, and 
 gently evaporated ; a few drops of water being added. The pure col- 
 chicine crystallizes in colourless needles. Its taste is intensely bitter, 
 but not biting, like that of veratrine, nor does it produce the violent 
 sneezing ; it is pretty soluble in water, and very soluble in alcohol and 
 ether ; its solution reacts feebly alcaline, but neutralizes acids perfectly. 
 Tincture of iodine precipitates it of a rich orange colour. Nitric acid 
 colours it dark violet and blue. Though most abundant in the seeds, 
 all parts of the meadow saffron contain colchicine. 
 
 Emetin. (Formula not established.) 
 
 This substance exists in all those plants, whose roots are sent into 
 commerce under the name of ipecacuanha, or hippo. The roots are to 
 
Solanine Chelerythrine. 963 
 
 be powdered and digested in ether, by which a fatty substance is taken 
 up. They are then to be boiled with alcohol, the decoction mixed with 
 water and the spirit distilled off. The residual liquor is to be filtered 
 and then boiled with magnesia ; the precipitate is to be dried and di- 
 gested in alcohol, which dissolves the emetin. This solution is to be 
 evaporated to dryness, the residue dissolved in a dilute acid, the liquor 
 boiled in ivory black, until completely decolourized, then filtered, and 
 the emetin precipitated by an alcali. 
 
 When completely pure, emetin is white and nearly tasteless ; it is 
 very poisonous; scarcely soluble in water or in ether; it dissolves 
 readily in alcohol ; it possesses strong alcaline properties ; its salts are 
 completely neutral, but cannot be crystallized ; they dry down to gummy 
 masses. Tannic acid and corrosive sublimate produce white precipi- 
 tates ; iodine and bichloride of platinum form brownish-yellow precipi- 
 tates, with the salts of emetin. 
 
 Solanine. NC 48 H73O 2 8 or So. Equiv. 7519, or 601. 
 
 This alcaloid is found in the berries of the solanum nigrum; in 
 the berries, leaves, and stems of the solanum dulcamara (bitter-sweet), 
 and tuberosum (potato). 
 
 The powdered stems of bitter-sweet are to be digested with spirit of 
 sp. gr. 0.865, mixed with one-third of sulphuric acid. This liquid is 
 to be supersaturated with milk of lime, the spirit distilled off, the re- 
 sidue washed with water, and what remains treated with dilute sulphuric 
 acid. Erom the solution thus obtained the solanine is to be precipitated 
 by an alcali, washed with water, dissolved in alcohol, decolorized by 
 animal charcoal, and then obtained by evaporation. It forms a white 
 brilliant powder, of a slightly bitter, nauseous taste ; it does not brown 
 turmeric, but restores the blue colour of reddened litmus ; it melts a 
 little above 212 ; it is almost insoluble in water, sparingly soluble in 
 ether, but copiously in alcohol. "With acids it forms neutral salts, which 
 do not crystallize, and are strong narcotic poisons. 
 
 The injurious properties of unripe potatoes result from the presence 
 of this body. It exists abundantly in the early shoots (underground) 
 and buds of the tubers. 
 
 Chelerytkrine. (Formula not estabb'shed). 
 
 This substance is extracted from the roots of the chelidonium majus, 
 by digestion with dilute sulphuric acid. The liquor so obtained is to 
 be evaporated and mixed with ammonia. The brown precipitate which 
 falls is to be washed, pressed between folds of paper, and digested ill 
 
964 Chelidonine Aconitine. 
 
 alcohol, with some sulphuric acid. The alcoholic solution being mixed, 
 with water, and the spirit distilled off, the residual liquor is precipitated 
 by ammonia, and the precipitate being washed and dried by pressure is 
 to be digested in ether, and the ethereal solution evaporated to dryness. 
 The mass so obtained is then digested in dilute muriatic acid, which 
 leaves a resinous substance undissolved. The deep red liquor evapo- 
 rated to dryness, and washed with ether, leaves a mixture of muriate of 
 chelerythrine and muriate of chelidonine ; the former of which is dis- 
 solved by washing with a small quantity of water, whilst the latter re- 
 mains undissolved. 
 
 From the solution of the muriate, chelerythrine is precipitated by 
 ammonia, as a white curdy powder. From its ethereal solution it re- 
 mains as a resinous mass, which continues soft for a long time; it is inso- 
 luble in water ; its solutions in alcohol and ether are pale yellow. With 
 acids it forms salts of a rich crimson colour which generally crystallize. 
 Tannic acid produces in their solutions a precipitate soluble in alcohol. 
 
 C/ielidonine. C^H^oOe, or Ch. 
 
 The preparation of this substance has been in great part described in 
 the preceding article. By digesting the sparingly soluble muriate with 
 ammonia, then dissolving in sulphuric acid and precipitating with mu- 
 riatic acid, it is freed from all traces of chelerythrine, and finally the 
 pure chelidonine, separated by ammonia, is dissolved in boiling alcohol, 
 from which it crystallizes, on cooling, in brilliant colourless tables. It 
 is insoluble in water, soluble in alcohol and ether ; it tastes bitter and 
 reacts alcaline; its salts are colourless, and those with the mineral 
 acids crystallize ; its solutions give with tannic acid a precipitate. 
 
 Aconitin. (Formula not established). 
 
 The fresh expressed juice of the monkshood (aconitum napellus) is to 
 be boiled and filtered, and the clear liquor mixed with an excess of car- 
 bonate of potash. The mixture is to be agitated with ether as long as 
 anything is taken up, and by evaporating this solution the aconitin 
 remains. From the dry plant, as from the seeds, the aconitin may be 
 obtained by processes similar to those described for veratrine and 
 colchicin. 
 
 Aconitin partly crystallizes from its ethereal or alcoholic solution in 
 white grains, but for the most part, forms a colourless, vitreous-looking 
 mass ; it tastes sharp and bitter, and is intensely poisonous ; it reacts 
 strongly alcaline, and neutralizes the strongest acids ; alcalies precipi- 
 
Atropine Bclladonnine. 965 
 
 tate its solution white ; chloride of gold and tannic acid also give white 
 precipitates, and iodine throws it down orange. 
 
 Atropine. NCgjH^Og, or At. 
 
 This alcaloid exists in all parts of the atropa belladonna, but most 
 abundantly in the roots. To prepare it, the fresh roots are to be pow- 
 dered and digested in alcohol, of specific gravity, 0'820. The liquor 
 obtained is to be mixed with lime, in the proportion of one part to 
 twenty-four parts of roots, and laid aside for twenty-four hours with 
 frequent agitation ; the mixture is to be then filtered, and the deposit 
 treated with dilute sulphuric acid : the filtered solution is distilled, and 
 the spirit being thus removed, the residual liquor is concentrated by 
 evaporation, until it equals one-twelfth of the roots employed. To this 
 liquor, when cold, is to be added a strong solution of carbonate of 
 potash, until a dirty brown precipitate occurs, which is to be removed 
 by the filter, and then more carbonate of potash added as long as any 
 precipitate is formed. This last, which is impure atropine, is to be 
 washed with water, then dried, and dissolved in strong alcohol, the 
 solution decolorized by boiling with animal charcoal, filtered, and 
 gradually evaporated, whereby the atropin separates in small white silky 
 prisms. 
 
 The taste of atropin is sharp, bitter, and metallic. It dilates the 
 pupil permanently and strongly ; if impure, it is brown, does not crys- 
 tallize, and has a horrible smell, but if quite pure, it has no smell ; it 
 requires 2000 parts of cold water for solution, but dissolves in thirty- 
 four parts of boiling water, from which some crystallizes by cooling, 
 but the greater part is totally decomposed; it dissolves readily in 
 alcohol and ether. 
 
 The alcaline properties of atropin are feeble; most of its salts are 
 decomposed by boiling with water into ammonia and a substance of an 
 excessively disagreeable smell ; this decomposition is instantly effected 
 by the caustic fixed alcalies. Most of the salts of atropin crystallize ; 
 tannic acid precipitates their solutions white ; the chlorides of platinum 
 and gold, yellow ; and iodine orange-yellow. 
 
 Belladonnine. (Formula not established). The dried root of bella- 
 donna, is to be mixed with a strong solution of caustic potash and 
 rapidly distilled ; the distilled liquor is to be decomposed by bichloride 
 of platinum, and the white precipitate which forms being washed and 
 dried, is to be mixed with carbonate of potash and gently heated. 
 Belladoimine sublimes and condenses in colourless rectangular prisms, 
 with a penetrating odour like ammonia ; it dissolves in water, the solu* 
 
966 Daturine. Hyoscyamine. 
 
 tion reacts alcaline ; it is not very poisonous ; its salts resemble closely 
 the corresponding salts of ammonia. 
 
 It appears to be likely, that this substance is a product of the decom- 
 position of the atropine by the caustic potash, and does not exist in the 
 plant. 
 
 Daturine. 
 
 This substance is obtained from the seeds of the thorn apple (datura 
 stramonium), by the same process as has been described for the pre- 
 paration of aconitine. From its solution in spirit, it crystallizes in very 
 brilliant, colourless groups of needles. When perfectly pure, it is 
 inodorous, but when impure, it smells -disgustingly narcotic ; its taste 
 is bitter, and like that of tobacco ; it dissolves in seventy- two parts of 
 boiling, and in 250 of cold water; in twenty-one of ether, and in three 
 of alcohol; it melts below 212, and volatilizes unchanged at a stronger 
 heat in white clouds. 
 
 A solution of daturine reacts strongly alcaline, and forms crystalli- 
 zable neutral salts, which like pure daturine are very poisonous. 
 Towards re-agents it acts like atropin. 
 
 Hyoscyamine. 
 
 This alcaloid, which is the active principle of the henbane (hyoscy- 
 amus niger and albus), is best prepared from the seeds, in the same 
 way as atropine, except that to the spirit in which the seeds are digested 
 some sulphuric acid should be added. It crystallizes in radiated groups 
 of silky needles, but is more usually obtained as a transparent vitreous 
 mass. In its properties it resembles so perfectly atropin and daturin, 
 that they need not be specially detailed. It neutralizes acids perfectly; 
 its salts are intensely poisonous ; they are decomposed very easily even 
 by boiling with water. 
 
 Coneme. Ci 7 H 17 N or Cn. Equiv. 1589, or 127*. 
 
 This remarkable substance is the active principle of the hemlock 
 (conium maculatum), in all parts of which it exists, but is more easily 
 extracted from the seeds. These are to be bruised, mixed with one- 
 fourth of a strong solution of caustic potash, and eight parts of water, 
 and distilled as long as the water which comes over has any smell. 
 This is to be neutralized by dilute sulphuric acid, and evaporated to the 
 consistence of a sirup. The residue is treated two or three times with 
 a mixture of one part of ether and two of alcohol, sp. gr. 0*820, 
 wherein the sulphate of coneine dissolves. From this solution the 
 
Coneine Nicotin. 967 
 
 ether and spirit are distilled off, then some water added, and the liquor 
 evaporated to dryness. The residue is to be mixed with half its weight 
 of strong solution of potash, and rapidly distilled to dryness. The 
 receiver should be carefully cooled. The oily coneine should be sepa- 
 rated from the watery liquor, and this last distilled again with some 
 lime. If the coneine contain ammonia, it may be gotten rid of 
 by exposure for a few hours in vacuo, beside a capsule of oil of 
 vitriol. 
 
 Pure coneine is a colourless transparent liquid, of sp. gr. 0'89 ; its 
 odour is highly penetrating and nauseating, partly like that of the plant; 
 its taste is disgustingly sharp * it is extremely poisonous. 100 parts 
 of cold water dissolve one of coneine, and the solution becomes turbid 
 when heated. Coneine itself dissolves one-fourth of water, and tin's 
 liquor becomes milky even by the heat of the hand ; it mixes with 
 alcohol, ether, and oils in all proportions ; in close vessels it distils 
 unaltered at 370, but at a much lower temperature if water be present. 
 When completely anhydrous, coneine has no alcaline properties, but acts 
 very powerfully when water is present ; it saturates acids completely. Its 
 salts crystallize but imperfectly ; they are decomposed by much water ; 
 they dissolve readily in water, alcohol, or a mixture of alcohol and 
 ether ; but in pure ether they are insoluble. Their watery solution is 
 precipitated by iodine, saffron-yellow ; and by tannic acid white. Co- 
 neine itself is coloured by nitric acid blood-red ; by exposure to the air, 
 especially if warm, coneine is decomposed ; it becomes brown, ammonia 
 is evolved, and a bitter, inodorous, resinous substance is produced, 
 which has no poisonous properties. 
 
 Nicotin. (Formula C 10 H 7 1S T ). Eq. 1012-5 or 81. 
 
 This substance is the characteristic ingredient of tobacco, (nicotiana 
 tabacum, and many other species). Eor its preparation, the following 
 process is to be followed : Tobacco leaves are to be digested in water 
 with a small quantity of sulphuric acid. The liquor is to be evaporated 
 to a sirupy consistance, and the residue distilled with about one-sixth 
 its bulk of a strong solution of caustic potash. That product is a 
 mixture of nicotine and ammonia, the former partly separated as a yellow 
 oil. It is to be saturated with oxalic acid, and evaporated to dryness on 
 a water bath, the brown crystalline residue boiled with absolute alcohol 
 which takes up the oxalate of nicotine. This alcoholic liquor is to be 
 evaporated to a sirupy consistence, then decomposed by caustic potash, 
 and the mixture agitated with ether which takes up the pure uicotin, and 
 
968 Nicotin. Menispermine. 
 
 leaves it quite pure when the ether is separated by distillation in a water 
 bath. 
 
 The easy decomposition of nicotin has prevented its analysis in a 
 separate form., but its muriate combines with bichloride of platinum 
 forming a double salt Ci H 8 NCl -f PtCl 2 , and it combines with corro- 
 sive sublimate, forming a body C 10 H 7 N -f- HgCl, from which its own 
 formula is inferred to be C 10 H 7 N. It is intensely poisonous. 
 
 When pure, nicotin is a colourless oily liquid, of a pungent tobacco 
 smell, and a sharp burning taste ; it differs from all other organic bases 
 in mixing with water in all proportions ; it mixes also with alcohol and 
 ether. When anhydrous, it gives off white fumes at 212, and distils 
 at 480 ; but the greater part of it is decomposed. If water be present 
 it distils easily at a much lower temperature. 
 
 Nicotin possesses a strong alcaline reaction, and neutralizes acids 
 perfectly. Its salts are generally very soluble, some crystallizable, ino- 
 dorous, but with a strong tobacco taste. With alcalies they evolve 
 the characteristic odour of the plant. 
 
 It is now very generally admitted that nicotin does not pre-exist in 
 tobacco leaves, but that it is produced by the decomposition of a sub- 
 stance, nicotmnme, which the leaves contain. This body forms white 
 crystals. It resembles a fat, is insoluble in water, soluble in alcohol 
 and ether, has a strong tobacco odour, and contains nitrogen. 
 
 Menispermine. NC 18 H 12 O 2 . 
 
 This substance is found in the capsules of the cocculus indicus, asso- 
 ciated with picrotoxine (page 922). The alcoholic extract is to be 
 boiled with acidulated water, and when the picrotoxine has crystallized 
 from the filtered liquor, an excess of an alcali is to be added. The 
 precipitate is to be dissolved in alcohol, decolorized by animal charcoal, 
 and evaporated to dry ness. The residue is to be digested with ether, 
 which dissolves menispermine, and leaves another body, paramenisper- 
 minej undissolved. 
 
 From the ethereal solution, menispermine crystallizes in white square 
 prisms. It is tasteless and not poisonous ; it forms neutral crystalli- 
 zable salts. The paramenisperinine dissolves in acids but does not neu- 
 tralize them. 
 
 Cissampelin exists in the roots of the cissampelos pareira (pareira 
 brava,) and is prepared by the same kind of process that has been fre- 
 quently described. Prom the evaporation of its ethereal solution, it 
 remains as a yellowish, transparent, vitreous mass, which combines with 
 water, forming a white powder like magnesia. It is very easily decom- 
 
Cissampeline Glaucine. 969 
 
 posed ; it is a powerful organic base ; its salts form gummy masses, 
 but scarcely crystallize. 
 
 Glaucin exists in the glaucium luteum (horned poppy). Its prepa- 
 ration is similar to that of aconitin ; it crystallizes in pearly scales ; it 
 possesses the same range of properties as the other vegetable bases, and 
 forms crystallizable salts. The horned poppy contains another crys- 
 talline principle, (glauco-picrine^} which appears also to act as a base. 
 
 A great number of plants are stated to contain organic bases, which, 
 however, have been as yet so imperfectly examined and described, as to 
 render their introduction here useless. Of such substances, the most 
 important are ; in the croton tiglium, crotonine, which is crystalline, 
 but is not the active principle ; in the sethusa cynapium, cynapin, crys- 
 talline ; and in the digitalis purpurea, digitaline, which appears most to 
 resemble coneine. . 
 
 Harmaline. Formula, C 2 4Hi 3 N 2 O. 
 
 This substance has been discovered in the seeds of the peganum 
 harmala ; its process of extraction is similar to that already given for 
 other alcaloids. It forms yellowish brown crystals, sparingly soluble in 
 water but abundantly so in alcohol. It produces well characterized 
 salts. The infusion of the plant is used for dyeing yellow and also 
 brilliant reds, which latter colours have been traced to products of the 
 oxidation of the harmaline. 
 
 OF THE ARTIFICIAL PRODUCTION OF ORGANIC ALCALIES, AND 
 OF THE CONSTITUTION OF THE VEGETABLE ALCALOIDS. 
 
 In studying the constitution of the class of bodies of organic origin 
 which act as bases, and appear to possess properties more or less analo- 
 gous to those of the ordinary alcalies or earths, we perceive at once that 
 they form two essentially distinct groups, according as they do or do not 
 contain nitrogen in their composition. The history of the latter class 
 has been referred to in detail in describing the theory of the ethers, and 
 may be summed up in the general principle that they act as oxides of 
 compound, quasi-metallic radicals, which in those derived from alcohols, 
 are all marked by the condition of forming powerful acids, by replace- 
 ment of two atoms of hydrogen by oxygen. Thus the vinic, methylic 
 and amylic ethers, deliver the acetic, formic and valerianic acids, by 
 C 4 H 3 H 2 O., giving C 4 H 3 O 3 : C 2 HH 2 O, giving C 2 HO 3 , and C 10 H 9 H 2 O, 
 giving C 10 H 9 3 . 
 
 To the other more numerous and peculiar class of organic bases, we 
 
970 Nature of the Organic Bases. 
 
 may also attach the two very remarkable bodies, the alkarsine (p. 806,) 
 and the phosphor-alcaloid noticed by M. Thenard. In those bodies the 
 arsenic and phosphorus must replace nitrogen, and their alcaloids bear 
 to the proper azotized organic bases, the relation which phosphuretted 
 hydrogen, and which arseniuretted hydrogen have been shown to bear 
 to ammonia. Their theoretic history, as far as we can judge of it, will, 
 therefore, be included in the following remarks on the constitution of 
 the azotized alcaloids, to which question the attention of chemists has 
 been specially directed by the interest and importance of the numerous 
 bodies of this class, found naturally existing and constituting the 
 active principles of those plants, most distinguished for medicinal or 
 poisonous qualities. 
 
 Prom the period of the first discovery of this class of bodies, chemists 
 have endeavoured to ascertain on what depended the basic properties by 
 which they are so remarkably characterized. The assertion by Liebig, 
 that each equivalent of an organic base contained an equivalent of 
 nitrogen, suggested the very plausible idea that they contained ammonia 
 ready formed, and that in their salts the acid was neutralized by the 
 ammonia, and the organic substance remained combined with the salt 
 as it had been with the ammonia before. This idea, however, cannot 
 be sustained, as we cannot obtain ammonia from any vegetable alcaloid 
 unless by processes, which totally destroy its constitution, and which, 
 indeed, eliminate ammonia from many organic substances, containing 
 nitrogen, but certainly not containing ammonia as such. Moreover, it 
 is now known that Liebig's rule is not universally true, the equivalents 
 of strychnine and of brucine probably contain each two atoms of 
 nitrogen, and we know of other organic bases, as melamine, ameline, 
 jervin and urea, in which the quantity of nitrogen in the equivalent 
 goes much beyond one atom. We may hence conclude that there is no 
 reason to suppose that the vegetable alcalies contain ammonia as such, 
 or owe their basic properties to its presence. 
 
 Some remarkably simple relations of composition appeared to occur 
 among certain bodies of this class, which at first were expected to 
 throw light upon their constitution. Thus, morphine and codein were 
 supposed to differ in composition, only by morphia containing an atom 
 of oxygen more ; and if we supposed (NC 3 5H 20 O 4 ) to be a compound 
 radical, E, then codeine should be protoxide, E -f O, and morphia 
 deutoxide, E -f- 20, more accurate researches has, however, disproved 
 this idea. However, if we take the cinchona alcalies, we shall really 
 find them to differ only in the quantity of oxygen they contain, 
 and making (jNC 2 oH 12 ) a compound radical, cinchonine should be 
 E + O, quinine, E + 20, and aricine, E + 30. These remarkable 
 
Nature of the Organic Bases. 971 
 
 facts might lend considerable support to the idea, that these alkaloids 
 are oxygen bases, oxides of compound radicals, but a closer examination 
 of their relations does away with all probality of its truth. Thus if 
 morphia were R -f 2.O, then by muriatic acid we should have a bichlo- 
 ride formed, R + 2C1, and water separated ; in place of which the 
 morphia combines directly with, one atom of muriatic acid, and so in all 
 other cases ; we cannot find in the compounds of these vegetable alca- 
 lies any of the laws which govern the formation of salts by metallic 
 oxides. In addition, the salts formed by these alcaloids with the oxygen 
 acids contain an atom of water, which cannot be expelled without de- 
 composition. 
 
 The theory of the constitution of the organic alcalies has, however, 
 been remarkably illustrated by the important discoveries lately made in 
 the artificial formation of alcaloids, so closely resembling in characters 
 and modes of combination those found naturally existing, that it is im- 
 possible to avoid referring all to the same class. In order, therefore, 
 to exhibit the views which may be taken of the nature of the organic 
 alcalies, it is proper to refer slightly to the general nature of those 
 artificially generated, which have been already described as members 
 of the series of bodies by whose decompositions they have their origin. 
 
 The group of alcaloids first to be noticed is that which is destitute 
 of oxygen, containing only carbon, hydrogen and nitrogen, as ele- 
 ments. Of this class the aniline, napthaline, leukol, piccoline, toluidine, 
 petanine, sinnamine, lophine, and others are members. They are all 
 under the influence of strong acids and alcalies resolved into ammonia, 
 and an organic body destitute of nitrogen. They all unite with the 
 hydracids directly, and with the oxygen acids with the intervention of 
 an atom of water, to form well characterized salts, and in fact in every 
 respect they represent the history of ammonia, in which the hydrogen 
 is more or less replaced by a more complex organic element. Now it is 
 not advancing too far on hypothetical grounds to apply to this class of 
 alcaloids, the theory which I have advanced of the constitution of the 
 aminoniacal compounds, and to look upon them as organic amidides ; 
 as ammonia, in which the third atom of hydrogen is replaced by an 
 organic radical ; thus there should be formed, 
 
 Aniline = Ci 2 H 5 + Ad. = Ci 2 H7N. 
 Napthalidine = C 20 H 7 + Ad. = C 20 H 9 N. 
 Toluidine = Ci 4 H 7 + Ad. = Ci 4 H 9 N. etc. 
 
 This view discloses that the organic radical of the alcaloid is that of 
 the series from which the alcaloid is produced, as phcenyl is of aniline, 
 and that napthalidiue is napthaline, in which H is replaced by NH 2 . 
 
972 Artificial Formation of Organic Bases. 
 
 It also explains why, in this group, an atom of the alcaloid contains one 
 atom of nitrogen, and why also the oxygen salts involve an atom of 
 water; which if the ammonia theory be followed out, furnishes the 
 hydrogen to produce the hypothetic metallic radical, and the oxygen to 
 form its oxide as described for ammonia in p. 722. 
 
 The natural alcaloids attaching themselves to this group are nicotine 
 and coneine, and it is only necessary to look to their history to observe 
 their resemblance to aniline. They are even still more easily 
 resolved into ammonia and an organic body, and it is very proba- 
 ble that they do not really pre-exist in those plants, but are products of 
 the decomposition of some material not yet isolated. 
 
 We further know that organic amides, as the oxamide and the urea, 
 fulfil, in many cases, in regard to acids, the function of alcaloids in the 
 most perfect manner. 
 
 The types of the second group of alcaloids are formed by the action 
 of re-agents on the first. In nature those alcaloids are marked by con- 
 taining oxygen, but in those artificially formed, oxygen is but one of 
 the variety of elements which may be inserted in their constitution 
 without the alcaline character or their rational type being disturbed. 
 Thus, from aniline a great series of artificially derived alcaloids may be 
 formed, substituting for the hydrogen of the organic element other 
 electro-negative bodies to a greater or less extent. Thus are produced. 
 
 With Chlorine, from, C^Hg + Ad. 
 
 Chloraniline = Ci 2 H 4 Cl + Ad. 
 
 Dichloraniline = C^HsC^ -f- Ad. 
 
 Bromaniline = Ci2H4Br _J_ Ad. 
 
 Bibromaniline = Ci2H3Br2 _L Ad, 
 
 "When the substitution of the chlorine or bromine is carried further 
 the alcaline character is lost, but the above are true organic alcalies, and 
 it is evident, as already noticed in page 846, that the body still con- 
 tinues amidide of phenyl. but the radical is altered in its chemical 
 nature, though not in its type, by the hydrogen being more or less re- 
 placed by chlorine or by bromine. 
 
 The permanence of the radical type throughout all these substitutions, 
 has been beautifully proved by the late experiments of Hoffman and of 
 Melsens, who have succeeded in regenerating the original radicals from 
 the chloroacetic acid, and from the chlorauiline by removing the chlo- 
 rine and substituting hydrogen. The agent employed was a very feeble 
 amalgam of potassium, which, taking the chlorine whilst at the same 
 time water was slowly decomposed, the nascent hydrogen replaced the 
 chlorine in the radical, and the chloracetic acid was restored to the con- 
 dition of the acetic acid, and the chloranilinc to the state of ordinary 
 
Nature of the Organic Alealies. 973 
 
 aniline. In no way has the congruity and consistency of the theory 
 of types and the theory of compound radicals been more satisfactorily 
 shown than by those researches. 
 
 The derivation of alcaloids by nitrous acid requires some additional 
 remark, as it influences the theory of the formation of another group. In 
 a variety of reactions it is manifest that nitric acid, N0 5 ,must be looked 
 upon as constituted of NO 4 -f- 0, precisely as the basis in the ammo- 
 niacal salts may be considered as NH 4 + O, and the nitrous acid NO^ 
 may replace an equivalent of ammonium. Now this occurs in the de- 
 composition of a vast number of organic bodies by nitric acid, thus 
 assuming as an abbreviated symbol for N0 4 = X, as is now usual, we 
 may write, 
 
 From Napthaline 
 
 Nitronapthase C 2 oH 7 X 
 
 Nitronapthese C 2 oHG X2 
 
 Nitronapthise C2oH 5 Xs 
 
 From Phene C 2 oHe 
 
 Nitrobenzid Ci 2 H 5 X 
 
 Picric acid Ci 2 H 2 X 3 O 
 
 Now from the several alcaloids of the first group we may obtain, by 
 the substitution of nitrous acid, just as in the above instance, alcaloids, 
 which in constitution exhibit a very remarkable analogy to those 
 found naturally existing in plants, thus 
 
 From Aniline = CigH 5 4. Ad. 
 Nitraniline = C ]2 H 4 X 4. Ad. 
 
 the phenyl type being still preserved. 
 
 The artificial formation of the third group of alcaloids depends on a 
 kind of decomposition nearly the inverse of that just described. That 
 is to say, on the reduction by sulphuretted hydrogen of an organic 
 compound containing nitrous acid. The perfect action should be to 
 transform the nitrous acid into ammonium, NO 4 and 8HS, producing 
 NH4, and 4HO and 8.S becoming free, but practically we find in this 
 as in all the other phenomena of the ammonia bodies, that the ammo- 
 nium enjoys but an ephemeral and questionable existence; it is amido- 
 gene that is really formed, and which, uniting with the organic elements, 
 produces the new alcali, which thereby becomes analogous to the gase- 
 ous ammonia ; whilst it is only in subsequently forming salts that the 
 alcali obtains the hydrogen, which could assimilate its constitution to 
 the theory of ammonium. There are, therefore, required to convert 
 N04 = X into NH 2 = Ad., six atoms of HS, and 4HO are separated 
 with 6.S, and it would almost appear that from every organic body 
 
974 Nature of the Organic Bases. 
 
 which contains N04, an artificial alcali can be by this process ob- 
 tained. 
 
 There are as examples the production from 
 
 Nitro-benzid = Ci^Hs X Aniline = CioHs Ad. 
 
 Nitro-benzoene = C] 4 H7 X Toludine = CnHy Ad. 
 
 Nitro-napthalide = 20^7 X Napthalidene == Csolfy Ad. 
 
 In the case of the organic bodies which contain more than one 
 equivalent of nitrous acid, there are produced of course as many 
 equivalents of amidogene, and it would appear that the organic radical 
 then breaks up, and two or more equivalents of another alcali are formed, 
 of which each contains one equivalent of amidogene with one of the 
 new radical. 
 
 Thus there is from 
 
 Binitro-benzid Ci2H 4 X Semi-aniline. 2.C6 H 2 . Ad. 
 Nitro-napthalese CgoH^X^ Semi-napthalide 2.CioH3. Ad, 
 
 This subdivision of the organic radical is also very remarkably illus- 
 trated by the action of sulphuretted hydrogen on the nitrous alcalies of 
 the second group, derived from those of the first, thus 
 
 Aniline C^Hs. Ad. gives 
 
 Nitra-aniline Ci2H4. X Ad. and this 
 Semi-aniline CeHg. Ad. 
 
 by conversion of N04 into NH 2 , and the partition of the organic 
 radicals between the two atoms of amidogene. 
 
 A fourth class of artificial organic alcalies is derived from the oxi- 
 dizing influence of hydrate of potash, at an elevated temperature on 
 azotized organic bodies, whether neutral or alcaline. It is in this way 
 that the quinoline (Leukol,) is produced by heating quinine, cinchonine 
 or strychine with potash ; carbon, hydrogen and oxygen being removed, 
 as carbonic acid and water, and the new alcali remaining, C 18 H 7 N. In 
 this way also is produced aniline, from the isatine of Indigo, and the 
 derivative alcalies of aniline from the corresponding derivatives of 
 isatine, by means of potash. It is most probable also that the vegetable 
 alcalies, nicotine and coneine, which ally themselves in composition and 
 properties to aniline, are products of decomposition, by the alcaline 
 liquors used, of bodies existing in the plants, and of which the body 
 termed nicotianine is an instance. 
 
 Finally, a large class of artificial alcalies have their origin in the 
 transformation of ammoniacal compounds, or of other alcaloids under 
 the influence of acids, or of caustic mineral alcalies. Of organic alca- 
 
Nature of Furfurol and Furfurine. 975 
 
 lies thus artificially formed, a great number have been already noticed '. 
 The formation of urea from cyanate of ammonia p. 732; that of 
 thiosinnamine from oil of mustard ; of amariiie and lophine from hydro- 
 benzamide. One of the most interesting of this series is the furfurine, 
 which has not yet been noticed as it does not attach itself to any 
 definite series, and I shall therefore briefly state the facts of its history 
 here. 
 
 In the process for preparing formic acid from starch, oxide of man- 
 ganese and sulphuric acid, described p. 830, a dense oily matter distils 
 over in small quantities, which when purified has the formula C 15 H 6 O 6 . 
 When this is acted on by ammonia it is converted into a crystalline 
 solid termed furfur amide, having the formula Ci 5 HcNO 3 ; this, however, 
 possesses perfectly neutral properties, but on boiling it in a solution of 
 potash it is converted, without changing its composition, into a power- 
 ful artificial alcaloid furfurine. The equivalent appears, however, to be 
 doubled, and the formula of furfurine to be C 30 H 12 N 2 O 6 . It dissolves 
 in boiling water and crystallizes on cooling, it exerts a powerful alcaline 
 action on vegetable colours. If boiled with the salts of ammonia it 
 expels that gas and takes its place in combination. 
 
 Such being the general circumstances under which the artificial alca- 
 loids have their origin, we may proceed to apply the principles so revealed 
 to explain the possible constitution of the alcaloids found naturally ex- 
 isting. In these, therefore, it is consistent with our knowledge to 
 recognize two groups. 
 
 In the first group, the nitrogen being but in the proportion of one 
 equivalent to an equivalent of alcali, if we apply the analogy of aniline 
 or of furfurine, we should consider those as amides of an organic radical, 
 and we should write 
 
 Quinine C2oHi 2 NO-2. =C2oHi O 2 -f Ad. 
 Strychnine C22Hi2NO4 = C22HioO 4 -j- Ad. 
 
 And in the oxidizing influence by which quinoline is formed, the 
 organic radical alone should be decomposed, the product being the amide 
 of a new radical. 
 
 Quinoline, CisH 7 N = CisH 5 -f. Ad. 
 
 In other cases, as in caffeine, in chelidonine, in theobromine, where 
 the quantity of nitrogen is more than one equivalent in an equivalent 
 of the alcaloid, we may have in reality something resembling the type 
 presented by nitraniline, C^He^Qi, in which the organic radical con- 
 tains NO 4 , or the mellamine, C 3 H 3 N 3 , or ammeline, CeHsNsOa, in which 
 there is little doubt but that the radical contains cyanogen NC 2 , or 
 
976 Nature of the Organic Bases. 
 
 mellon N 2 C 3 . It would be, however, useless to attempt to group the 
 formula of the natural vegetable alcaloids, on merely hypothetic 
 assumptions of this kind. 
 
 The idea of Woehler that narcotine consists of opianic acid united 
 to the true alcaloid, and that it is analogous in constitution to opiam- 
 mon, (p. 953,) presents to us another view of the constitution of 
 organic alcalies, and one recently supported by additional results. Thus, 
 Kochleder and Eedtenbacher have announced that piperine consists of 
 aniline with two equivalents of an azotized acid, and they have pro- 
 duced it artificially from aniline. Also that narcogenine consists of the 
 opianic acid with two equivalents of the same base that exists in nar- 
 cotine. This form of saline or binary constitution may exist very ex- 
 tensively in those bodies, and it is to be hoped that the researches now 
 being undertaken in this highly important field, will soon enable us to 
 reduce the natural alcaloids to the same principles of classification as I 
 have shown to regulate the alcalies of artificial origin. 
 
 In concluding this subject it is important to record that for the 
 researches on aniline, which were the basis of all subsequent exact 
 inquiry in this branch, science is principally indebted to Professor Hoff- 
 man, with whom was associated in many of his investigations Dr. 
 Muspatt of Liverpool, and that the theoretical views of the constitu- 
 tion of the organic bases, are founded mostly on those advocated by 
 Fresernius. 
 
977 
 
 CHAPTER XXIX. 
 
 OF THE CHEMICAL PHENOMENA OF VEGETATION. 
 
 IN the seed of a plant, the germ of the future individual is associated 
 with one or more organs termed cotyledons, which contain, in general, 
 starch and some form of azotized matter, as albumen, gluten, or legu- 
 mine, which substances are so disposed in order to supply the nutri- 
 ment necessary for the development of the embryo, until its organs are 
 fitted for the collection of nutriment from external sources. 
 
 The first act of growth in the seed is termed germination, and is 
 accompanied by a remarkable change in the constitution of the cotyle- 
 donous mass. For perfect germination, it is necessary that the seed be 
 moderately supplied with water and with air, and that it be either in 
 the dark or exposed but to little light ; all these circumstances are per- 
 fectly secured by the ordinary -mode of sowing seeds, in a moistened 
 soil, which shall be so loose as to admit air, and yet exclude the 
 light. 
 
 A seed so circumstanced, gradually swells to much beyond its origi- 
 nal volume, and its temperature rises ; it absorbs oxygen from the air, 
 and evolves water and carbonic acid, and the starch of the cotyledon 
 gradually disappears, being changed into sugar. From the point of 
 the seed where the embryo is situated, two shoots spring forth, one of 
 which, the radical, takes its direction downwards into the soil, whilst 
 the other, iheplumula, strikes up towards the air, to become the origin 
 of the stem ; according as this growth proceeds, the quantity of sugar 
 in the seed diminishes, and by the time that the radical is fit for the 
 performance of its functions, as root, in absorbing nutriment from the 
 soil, nothing remains of the seed but its ligneous part, which in some 
 cases completely perishes underground, but in others rises, and assum- 
 ing the functions of leaves, (seed leaves), assists in providing nutriment 
 for the young plants, until the stem shall have been furnished with leaves 
 by which it may act upon the surrounding air. 
 62 
 
978 Germination Malting. 
 
 This process of germination is artificially produced, for the purposes 
 of the arts, by the operation of malting ; the grain is steeped in water, 
 until it has absorbed the proper quantity of it; it is then spread on the 
 floor of the malt-house, and its temperature prevented from rising too 
 high by the mass being frequently spread out, and new surfaces exposed 
 to the air. When the seed contains the maximum quantity of sugar, 
 that is, when the conversion of the starch is most complete, and yet 
 before much sugar has been assimilated by the germ, which is practi- 
 cally found to be when the radical has grown as long as the grain, but 
 does not project beyond it, the young plant is killed, by exposing the 
 malted corn to a current of hot dry air in the malt-kiln, and the malt 
 is then employed as a source of sugar, in the fermentative processes of 
 the brewer anc! distiller. 
 
 The saccharine fermentation which thus furnishes nutriment for the 
 young plant in the first stage of its existence, resembles the transforma- 
 tion of starch by means of sulphuric acid, described in p. 761, and 
 is excited by the presence of a peculiar ferment produced by the decom- 
 position of the vegetable albumen which the seed contains. This active 
 substance is termed diastase ; it does not pre-exist in the seed, but is 
 itself produced by the action of the air and water upon the albumen ; 
 it is not identical with the ferment which induces the alcoholic fermen- 
 tation, yet they appear to be but successive stages of the decomposition 
 of the same substance. The diastase may be obtained solid by bruising 
 malt with a small quantity of water and expressing the liquor ; to this 
 alcohol is to be added, which precipitates a quantity of unaltered albu- 
 men, and on evaporating the filtered liquor to dryness, the diastase re- 
 mains, though by no means pure ; it is a white gummy mass ; it is 
 precipitated by infusion of galls and most metallic salts ; one part of 
 it rapidly and completely converts a solution in water of 2000 parts 
 of starch, first into dextrine, and finally into grape sugar. It has been 
 suggested by Saussure, that diastase is identical with the substance 
 termed mucin, in p. 771, but this is doubtful ; it contains nitrogen, 
 and is most probably, as already stated, the first product of the putre- 
 faction of the gluten or albumen. 
 
 When the process of germination is over, the plant is found provided, 
 by its roots and leaves, with the means of procuring such nutriment as 
 its future offices require, from the atmosphere and the soil. For the 
 constitution of its proper ligneous tissue, carbon, hydrogen and oxygen 
 are required, and these serve also for the formation of the majority of 
 its excreted products, as sugar, gum, starch, resin, .oils, and acids ; but, 
 in addition, nitrogen is required ; and although the proportion of nitro- 
 gen in any plant is small, compared with that pf the other elements, 
 
Constitution of Plants. 979 
 
 yet it is of great importance as a constituent of the active principles of 
 most medicinal plants, as the vegetable alcalies, amygdaline, &c. ; and 
 of still higher interest, as Boussingault has shown, the nutritive power 
 of each plant, when used as food, to be proportional to the quantity of 
 nitrogen and phosphates which it contains. In every plant there exists 
 also certain inorganic elements, acids, and bases, which, though small 
 in quantity, are yet essential to its healthy growth. The examination 
 of the modes, chemical and vital, by which these various substances 
 are supplied to the plant, and assimilated by its organs, constitutes an im- 
 portant branch of vegetable physiology, which can here be but superfi- 
 cially sketched ; and, in its relation to practice, the manner of supply- 
 ing these materials so as to favour the growth of plants, and develope 
 their most useful principles, must be the basis of every system of en- 
 lightened agriculture. 
 
 Of the Assimilation of Carbon by Plants. 
 
 In describing the constitution of the atmosphere, (p. 362), I have 
 had already occasion to notice the beautiful provision by which the two 
 great classes of organized beings mutually compensate for the change 
 which each produces in its nature, and thus retain it in the condition 
 most conducive to the healthful existence of both. That whilst the 
 animal, in his respiration, throws off carbonic acid, and absorbs oxygen, 
 the plant from the surfaces of its green leaves, in sunlight, absorbs car- 
 bonic acid and gives out oxygen. It only remains here to examine the 
 circumstances of its change, with reference to the other functions of 
 the plant. 
 
 As water is abundantly absorbed by plants, both with the roots and 
 leaves, the assimilation of carbon from the air should, with it, supply at 
 once the elements of the woody matter, as well as of those other bodies, 
 as sugar, starch, and gum, which contain oxygen and hydrogen, in the 
 proportions to form water. But this respiratory function of the leaves 
 does not in reality possess the simplicity and uniformity of effect, which 
 has been just assigned to it. It is found, that the absorption of car- 
 bonic acid and the liberation of oxygen occur only under the influence 
 of sunlight, and from the green portions of the plant, whilst the co- 
 loured portions, as the flowers and fruits, and even the green leaves, 
 during the night, absorb oxygen and give out carbonic acid ; thus tend- 
 ing to increase the vitiation of the atmosphere, produced by animals, 
 in place of counteracting it. The existence of these opposing actions 
 had induced some physiologists to doubt whether they did not neu- 
 tralize each other, and hence to seek for the source of the carbon of the 
 
980 Formation of Woody Tissue. 
 
 plant, in the action of the roots upon the organic substances of the 
 soil. But the experiments of Daubeny have conclusively established, 
 that a healthy plant evolves so much more oxygen in the day than it 
 absorbs during the night, and inversely absorbs so much more carbonic 
 acid during the day than it evolves at night, as may satisfactorily ac- 
 count for the growth of the woody material of the plant, and com- 
 pensate for the influence of animal respiration and combustion upon 
 the air. 
 
 It has been already shown, that the grains of starch, when elaborated 
 by the organs of the plant, possess a structure totally different from that 
 which characterizes bodies constituted in virtue of mere affinity, and 
 more analogous to certain animal organs, as the crystalline lens of the 
 eye. In the different varieties of starch, it is not difficult to trace the 
 gradual transition to lignine, and, as stated in page 758, ordinary wood 
 still retains in the tubes and cells formed by the arrangement of the 
 particles of lignine, a considerable quantity of unaltered starch. In 
 the medulla of various trees, the passage from starch to lignine is still 
 more evident. Now for the formation of starch there are required but 
 water and carbon, its formula being C 12 H 10 IO and this I consider is the 
 actual result of the true respiratory process of the plant ; carbonic acid 
 being absorbed, and an equal volume of oxygen being exhaled, the car- 
 bon is assimilated by the vital power of the plant, and with the elements 
 of the water, produces a substance partially organized in structure, the 
 starch globule. The outer layer of this gradually increasing in density, 
 and water being separated from the internal portion, should give a cell, 
 or by the reunion of many, a continuous fibre, or tube, of true lig- 
 nine. The change being simply the loss of water, the formula of the 
 lignine becomes Ci 2 H 8 O 8 . The nature of the starch globule, and hence 
 the structure and physical properties of the ligneous fibre varies in dif- 
 ferent plants. Thus, I consider, in the adult plant, starch to be the 
 first product of the assimilation of carbon and water, and being already 
 possessed of a low degree of organization, is, in structure and com- 
 position, adapted for the change (growth rather than transformation) 
 into true wood. 
 
 By contact with the albuminous, or fermentative principles, the starch, 
 whether accumulated in the seed or roots, or distributed throughout 
 the substance of the plant, undergoes changes of an opposite kind. 
 Its organized character is lost ; it successively forms gum and sugar. 
 We cannot yet form cane sugar artificially from starch, but we can have 
 no doubt that it arises, as grape sugar does, from the catalytic meta- 
 morphosis of the starch, arrested, in virtue of the vital power of the 
 plant, at a point where we cannot seize it in the laboratory. These are 
 
Secretions of Plants. 981 
 
 the truly nutritious elements of the plant, whether designed for the 
 support of the adult individual, or collected in proper reservoirs, to 
 serve for the sustenance of the future individual in the seed. 
 
 In the conversion of the starch into the numerous secondary pro- 
 ducts, as acids, colouring matters, oils, &c., the presence of which 
 characterise the generality of plants, we may find the source of that 
 inverse respiratory action which so much masks the real and simple 
 nutritive process. Of the circumstances of the formation of these 
 bodies, we have an example admirably illustrative of the point, in the 
 conversion of lignine into ulmine. Here, though the change should at 
 first appear to require only the loss of the elements of water, we find it 
 to be much more profound ; the constitution of the lignine is totally 
 broken up ; oxygen is abundantly absorbed from the air ; a quantity of 
 its carbon is carried off as carbonic acid, and a quantity of its hydrogen 
 as water. This action, which may be looked upon as equivalent to the 
 various processes of secretion performed upon the blood by the organs 
 of animals, by which substances adapted to the use or structure of dif- 
 ferent parts are there deposited, whilst others unfitted for the purposes 
 of the organized being are thrown off, is carried on by the leaves, pro- 
 bably by all portions of the surface of the plant, and is the source of 
 the continued exhalation of water and carbonic acid which occurs. 
 During the day, and especially in bright sunshine, the assimilating 
 power of the plant being in full action, carbonic acid is taken in and 
 oxygen given out ; during the night, whilst the plant is in repose, this 
 nutritive action ceases. Through the whole time, however, the pro- 
 cess of the secretion is carried on, water and carbonic acid given off, 
 though in such proportion only as to secure at the end of the twenty- 
 four hours, an excess of assimilated carbon sufficient fully to secure and 
 account for the rapidity of growth. 
 
 The changes of constitution which accompany the ripening of fruit, 
 deserve to be considered more in detail than those of which the gene- 
 ral nature has been just noticed. If we examine the composition of a 
 young apple, we find it nearly tasteless, and to consist of a loose 
 ligneous tissue, in which is imbedded a quantity of ordinary starch ; as 
 the growth proceeds, the starch appears to diminish in relative amount, 
 and the fruit becomes sour, from the presence of tartaric acid ; after some 
 time the acidity becomes of a much less disagreeable kind, and the 
 tartaric acid is found to be replaced by malic acid ; whilst the tissue is 
 found to be infiltrated with pectin or pectic acid ; finally, in the next 
 and concluding stage of maturity, the malic acid disappears, its place 
 being taken by more fully developed pectine and sugar. Some of 
 these reactions appear to be due to the decomposition of the acid con- 
 stituents of the fruit. 
 
982 Ripening of Fruit. 
 
 Fremy has shown that the origin of the pectin of the fruit is to be 
 found in a body having a great analogy to lignine or cellulose, and 
 which he terms pectose ; when this is boiled it changes into pectine, and 
 this change naturally takes place in the fruit under the influence of a 
 natural ferment, pectase, which is analogous to diastase. This by its 
 further action converts the pectine into pectic acid, or into other derived 
 acids which resemble it in properties, and only differ in constitution by 
 the abstraction or addition of the element of water. The pectic fer- 
 mentation being like the lactic (p. 768,) unaccompanied by the evo- 
 lution or absorption of any gas. Premy found the formula of pectine 
 to be C 6 4H 4 sO 6 4, and that of metapectine C 64 H 46 06 2 , in his new researches. 
 The pectine of the ripe fruit, therefore, has no relation either to the 
 starch or to the acid the unripe fruit contained. 
 
 The sugar of the ripe fruit is derived, according to all appearance, 
 from the starch which the green fruit contains ; either by the pectase 
 ferment or by the contact of the organic acid, the saccharine fermen- 
 tation is induced, and grape sugar, which is the sugar of fruits, is 
 generated. It is not known whether the tartaric acid is first secreted as 
 such by the plant, or whether it arises from the decomposition of any 
 previously existing body, but it is easy to see how the malic acid is 
 formed from it. Thus, malic acid, C 8 H 4 O 8 , may be produced by the 
 direct abstraction of oxygen from the tartaric acid, C 8 H 4 O 10 , or, at those 
 periods when the reverse action takes place and carbonic acid is given 
 off, six atoms of tartaric acid, C 48 H 24 60 , may produce five atoms of 
 malic acid, C 40 H 2 o0 4 o, with eight atoms of carbonic acid C 8 O 16 , and four 
 of water, H 4 4 . 
 
 When our knowledge of the ultimate effect of the complex actions 
 of plants upon the atmosphere was still uncertain, it was considered, 
 and upon very rational grounds, that the plant was indebted for its 
 carbon to the organic substances of the soil, and the necessity for a 
 continued supply of animal or vegetable manure, to keep up the fer- 
 tility of the soil, was thus satisfactorily explained ; it was considered 
 that the roots and leaves remaining from the preceding crop, or inten- 
 tionally mixed up with the soil, were converted, as already described, 
 into ulmine, which, either by itself, or in combination with inorganic 
 bases, was taken up by the absorbing rootlets of the plant, carried into 
 its vessels and assimilated to the constituents of its tissues ; for, in fact, 
 if we examine at any moment any kind of fertile soil, we find it to con- 
 tain abundance of a kind of ulmine (geic acid, p. 819) ; we find this 
 ulmine to be a product of the decomposition of the organic substances 
 used as manure ; we find, that in barren soils the ulmine is either 
 absent, or it exists in another isomeric form (humine, &c.), and hence 
 
Source of Carbon in Plants 983 
 
 the vegetation appeared distinctly connected with, and attributable to 
 the quantity of geine present. But, notwithstanding such plausible 
 evidence, Liebig has brought forward very strong proof that the action 
 of the ulmine can be but secondary towards the nutrition of the plant, 
 His arguments are derived from the facts ; first, that the pknt may 
 fully vegetate, though totally unconnected with the ground, as has been 
 proved by experiments upon cellular plants, suspended in the air, and 
 supplied with water ; second, that from the insolubility of every kind 
 of ulmine, either free or when combined with earthy bases, which alone 
 are presented in sufficient quantity in the soil, it cannot be directly 
 absorbed by the rootlets of the plant, which totally reject every kind of 
 solid matter ; and third, that if we compare the quantity of ulmine in 
 a soil before the growth, and after the collection of a crop, we find the 
 diminution to be so small when compared with the great quantity of 
 carbon contained in the mass of vegetable matter that has been ob- 
 tained, as fully to prove the produce of carbon in the crop to bear but 
 an indirect, if any proportion to the quantity of ulmine in the soil. 
 According to the conclusions I have drawn from the different facts ob- 
 served, the true office of the organic matter in the soil, appears to be, 
 that by its gradual decomposition, a constant supply of carbonic acid 
 is afforded to the plant, by which, during the first stages of its devel- 
 opment, and whilst destitute of the expanse of leaf requisite to collect 
 the necessary quantity of nutriment from the air, a more concentrated, 
 and, as it were, richer food is applied to the absorbing roots, and, its 
 healthful and rapid growth thus provided for ; it is not, therefore, the 
 ulmine of the soil, but the organic matter generally, in changing into 
 ulmine, that may supply carbon to the young plant ; the office of the 
 soil-ulmine (geic acid) being different, as shall be shortly shown ; and, 
 even in this action of the organic matters, the functions of the plant 
 remain the same, being the absorption of carbonic acid, and evolution 
 of oxygen. That the organic matter of the soil is at least so far active, 
 and indeed necessary to the growth of plants, has been abundantly 
 proved by the practical evidence of the insufficiency of merely inor- 
 ganic manures, applied to the soil to obtain agricultural crops, which 
 should be left solely to the atmosphere for their supply of carbon. 
 
 Assimilation of Nitrogen by Plants. 
 
 The organic substances which contain nitrogen belong to two classes ; 
 those of the first, which constitute the active, or characteristic princi- 
 ples of many plants, although of much interest in relation to medicine, 
 and to abstract science, are of very little importance with reference to 
 
984 Assimilation of Nitrogen. 
 
 the growth of the plant, and its use as food. The bodies whose origin 
 and properties are here of interest, belong to that class of vegeto- 
 animal substances, as albumen, gluten, legumine, of whose extraor- 
 dinary power in inducing catalytic decompositions of other bodies, I 
 have so often spoken ; they are found in all parts of the plant, dissolved 
 or diffused through its juices, but especially collected where transfor- 
 mations necessary for growth, or germination, are to be accomplished. 
 Although present in but small quantity, no function of the plant, in 
 any stage of its existence, could be accomplished without their aid. 
 The conversion of starch into sugar, for the nutrition of the germ; of 
 starch or lignine into the vast variety of secretory products in the 
 adult plants ; the elaboration of the fruit, its ripening, and even the 
 ultimate destruction of the vegetable tissues, have their origin in a 
 series of actions, induced and maintained by communication from the 
 active fermentation of these azotized materials. 
 
 Not merely does the presence of this class of bodies regulate the 
 proper performance of the functions of the plant, but they play an 
 equally important part in favouring the assimilation of vegetable matter 
 when used as food by animals. Boussingault has shown by experi- 
 ments, to which I shall have occasion again to refer, that in herbivorous 
 animals, the total quantity of nitrogen assimilated for the growth of 
 its muscular and other tissues is derived from and equal to that con- 
 tained in the vegetable substances used as food, and that hence to ascer- 
 tain, as far as practical results are concerned, in any of the ordinary 
 articles of food, the nutritive value of any organic substance, it is only 
 necessary to determine the quantity of nitrogen which it contains. The 
 results so calculated agree with the mean experimental results of the 
 most enlightened agriculturists, within limits as narrow as could be 
 expected in experiments of that kind, and may by further research be 
 brought to still greater accuracy. 
 
 Like the carbon, the nitrogen of plants is obtained in great part by 
 absorption from the air, but yet it is not merely gaseous nitrogen which 
 is assimilated. The atmosphere always contains a quantity of ammonia, 
 derived from the putrefaction of organic bodies. This is absorbed and 
 passes into the constitution of a new set of plants, and from them to 
 animals, to be again thrown into the air after their death, and thus 
 circulate from age to age, entering into the constitution of each succes- 
 sive race of organized beings. It has been, however, objected, to refer 
 the total quantity of nitrogen in plants to this one source ; for it has 
 been said, that if the produce of one year derived its nitrogen only 
 from the decomposition of the plants of the previous year the total 
 quantity should be constant, whereas experience teaches, that by proper 
 
Source of tie Nitrogen of Plants. 985 
 
 methods, the quantity of vegetables produced on a soil may be continu- 
 ously increased, and for this the nitrogen must be derived strictly by 
 absorption from the air. In regard to the quantity of ammonia de- 
 rivable from the air or from rain water, accurate investigations have 
 shewn that it is so great as fully to account for any production of vege- 
 tables that occur in practice, and the earthy soil has been found, even 
 when highly silicious, to be itself naturally so absorbant of ammonia 
 from the air, as to contain a supply fully sufficient for the crops of 
 ordinary years. 
 
 Plants vary exceedingly in the facility with which they derive nitro- 
 gen from the air, whether by direct absorption of gas, or as ammonia. 
 Thus trefoil vegetates and thrives nearly as well when planted in pure 
 sand, and supplied only with water and air, as when sown in ordinary 
 soil ; and when fully grown, the quantity of nitrogen is found to be in- 
 creased twenty-six per cent. ; but, on the contrary, wheat grows but 
 slowly under the same circumstances, makes no attempt to flower, and 
 on analysis the whole plant is found to contain even less nitrogen than 
 had originally existed in the seed. "Wheat has, therefore, no power to 
 assimilate nitrogen from the air, while trefoil possesses that character in 
 probably its greatest vigour. Yet wheat when fully grown is rich in 
 nitrogen ; its seed is more nutritious than that of any other corn, as it 
 contains more gluten; its nitrogen must therefore, be derived from 
 another source, it is extracted from the organic matters of the soil, or 
 from ammonia, which a natural soil had previously absorbed from the 
 air or from rain water. 
 
 Without entering here into the question of the nature of manures, 
 which will require especial consideration, it may be stated, that though 
 wheat is thus peculiar in deriving its supply of nitrogen exclusively from 
 the soil, yet all plants do so in a greater or less degree. In the soil 
 however, the nitrogen is not present uncombined. It is evolved as 
 ammonia from the decomposing organic substances of the manures, and 
 hence animal manures, as producing more of it, are proportionally 
 richer. It has been already noticed, (p. 819), that the ulmine of the 
 soil is always combined with ammonia, which it retains with exceeding 
 force. But in presence of strong bases, such as lime, which all fertile 
 soils contain, the ulmine is slowly decomposed, the elements of car- 
 bonic acid and of ammonia are eliminated from it, and these both being 
 in a state fit for absorption by the rootlets of the plant, are assimilated 
 and supply carbon, nitrogen, and water. Independent of the ammonia 
 derived from the organic substances actually contained in the soil, much 
 of that diffused through the atmosphere is carried to the roots of plants 
 by showers of rain, and by the direct absorption of the gas by the por- 
 
986 Inorganic Elements of Plants. 
 
 ous clay. There are few specimens of clay, especially if they contain 
 iron, which do not give out ammonia when heated, and the absorption 
 occurs with greater power when the clay has been strongly dried. 
 Hence arises the increased fertility often given to a soil by burning the 
 surface to the depth of a few inches. 
 
 Assimilation of Hydrogen. 
 
 I have described (p. 979) as the source of the carbonic acid evolved 
 by plants during the night, the conversion of the starchy substance, 
 which I conceive to be that first elaborated by the plant, into the various 
 secretory products, acids, colouring matters, &c. But there are many 
 classes of important vegetable products in which hydrogen so far pre- 
 dominates, that we must conceive for their formation water to be de- 
 composed, and its oxygen to be evolved either free or in combination 
 with carbon. Of such bodies, glycerine, all of the fixed and many of 
 the volatile oils, wax, and caoutchouc, are examples. The secretory 
 action may thus, in place of opposing that of the respiration of the plant, 
 coincide with it in result, according to the nature of the substances 
 formed, since if all of the carbon of the starch remains in the constitu- 
 tion of the secretion, oxygen is evolved from the water which is de- 
 composed to supply the necessary quantity of hydrogen. 
 
 Of the Inorganic Constituents of Plants. 
 
 If we make a plant vegetate in water which holds dissolved small 
 quantities of inorganic salts, we find that as long as the plant remains 
 in health it exercises upon these salts a remarkable discretionary power 
 of absorption, taking up some and rejecting others which pass into its 
 substance only when by the death or weakness of the plant the liquor 
 enters the tubes by merely physical capillarity. If a plant, whose tis- 
 sues have been thus imbibed with saline matters, by its own spontaneous 
 power of absorption, be placed in a vessel of pure water, it will be 
 found to give out certain of the saline matters it had taken up, but to 
 retain others. In this manner we may recognize the action of inorganic 
 salts upon plants to be of three kinds; 1st, directly poisonous, which 
 are rejected by the plant as long as it is in health, and to this class be- 
 long most substances poisonous to man ; 2nd, those to which the 
 plant appears indifferent, which are taken up by it and given off again, 
 without any apparent influence on its growth ; and 3rd, those which 
 when absorbed by the plant are assimilated to its proper tissues, and 
 are not given up by the plant to water in which it may be immersed. 
 
Relation of Soil to Plant. 987 
 
 The bodies of this last class are all combinations of alcalies and 
 earths, with sulphuric and phosphoric acids, in some cases nitric and 
 muriatic acids, also largely with organic acids ; they form the ashes of 
 the plant when the organic matter is burned away, and then usually 
 possess an alcaline reaction from the formation of carbonates. As a 
 general principle we may say, that each plant requires for its healthy 
 growth inorganic substances in certain quantity, and of certain nature ; 
 but replacement of one base by another may occur in certain cases, 
 without positive injury to the plant. Thus, the plants which yield 
 soda when grown upon the sea-shore (salsola, salicornia), if transplanted 
 to the interior, gradually lose the soda, and acquire potash in its place ; 
 so that after a generation no trace of the former alcali remains. The 
 ashes of oaks or pines grown upon a granitic or basaltic soil, contain 
 an abundance of magnesia and of potash, whilst trees of the same spe- 
 cies will flourish on a limestone soil, and in their ashes, lime will be 
 the predominant ingredient. But these cases of substitution of one 
 base for another in a plant are still but rare exceptions to the prin- 
 ciple, that each kind of plant requires for its vigorous and healthy 
 growth to be supplied with inorganic substances of a specific nature and 
 in certain quantity. 
 
 It is this principle which determines the more successful cultivation 
 of certain plants in certain soils. Thus, if we examine the composition 
 of the ashes of wheat, we find abundance of silica, phosphoric acid, 
 magnesia, lime and potash. If we sow wheat in a soil which contains 
 neither potash nor phosphoric acid, some of the materials necessary for 
 the perfection of the plant being absent, the crop cannot be productive ; 
 but if we previously manure the soil with bone dust, with ashes of 
 weeds, or other substances which may supply the necessary inorganic 
 elements, these will be absorbed, and the plants obtain their full de- 
 velopement. Even when the quantity of the required inorganic base is 
 but exceedingly minute, it will still be collected by the vital action of 
 the plant in the necessary quantity. Thus, in most sea plants, iodide 
 of magnesium exists in such proportion as that it affords the universal 
 source of iodine for all technical and scientific objects ; and yet, that 
 salt, which is excessively soluble, is removed by the plant from the sea- 
 water, which contains but minute traces of it, and it is retained in the 
 vegetable tissue by a power which prevents it being washed out again. It 
 is this power of a plant to search for and remove from the soil all traces 
 of those inorganic bases which it most requires that renders many soils 
 incapable of bearing successive crops of the same kind, without the in- 
 termediate application of suitable mineral manures. But if the soil be 
 of such nature as to contain itself those elements, it may become truly 
 
988 Composition of Soil, 
 
 inexhaustible for the growth of most species of plants. Jt is hence that 
 soils formed by the decomposition of basaltic rocks, or of modern lavas, 
 are some of the most productive for every kind of crop ; the facility 
 with which these rocks are decomposed, by the action of air and water 
 provides a constant supply of soil absolutely new, and from the consti- 
 tution of these rocks, the great variety of their mineral components 
 renders such soils abundant in every element that plants in general 
 require. 
 
 Of the Constitution of Soils and of Manures. 
 
 From what has been already said, it is easy to judge of the circum- 
 stances which render a soil barren or productive, but from the impor- 
 portance of the subject to vegetable physiology and to agriculture, it 
 requires more detailed examination. 
 
 The organic elements of the plant being derived for the most part 
 from the atmosphere, the office of the soil, so far as they are concerned, 
 is reduced to supplying to the root, during those periods when there is 
 not a sufficient expanse of foliage to absorb nutriment from the air, 
 the carbonic acid produced by the gradual rotting of the ligneous 
 matter, and ulmine, as well as ammonia from the azotized elements of the 
 manure. For this purpose the soil is, in respect to its mineral composition, 
 unimportant ; it should be porous, in order to admit of the easy penetra- 
 tion of the rootlets, and to allow free access of oxygen to the organic 
 matter to form carbonic acid ; it should yet be close enough to retain 
 moisture in the average intervals of rain, in order that the water neces- 
 sary for vegetation may not be absent. 
 
 These physical conditions are not, however, combined in any one kind 
 of mineral material. If we take a soil of pure sand, or of pure limestone, 
 we find them so loose and porous, that the water filters off almost 
 immediately after falling, and the plants should necessarily perish. If a 
 soil consist of pure clay, its tenacity would be such,, as totally to pre- 
 vent the access of air, and all growth of the absorbing filaments of the 
 roots. To combine the two proper conditions of a soil, the clay should 
 be mixed with the porous material, in proportions which vary with the 
 nature of the plant to be cultivated ; and thus the simplest soil, in order 
 to fulfil its physical conditions, as supplemental to the atmosphere, 
 should contain two mineral substances, of which one should be clay, 
 and the other lime or silica, and as in practice, unless for some special 
 object, the presence of caustic lime would prove injurious to the ab- 
 sorbing rootlets, this should be present combined with carbonic acid, as 
 in any of the usual varieties of limestone rocks. 
 
Action of Mineral Manures. 989 
 
 The proper action of the soil, that which it exercises independently of 
 its office in replacing the atmosphere, is to supply to the plant those 
 inorganic constituents, the importance of which has been already 
 shown. For this purpose, a far greater complexity of constitution is 
 required. Thus there is no plant that does not contain both lime and 
 silica, and hence, in the simplest soil, both must be present. There is 
 scarcely a plant whose ashes do not contain a fixed alcali, generally pot- 
 ash, and hence minerals which may yield, by their decomposition, the 
 necessary quantity of that base, should be present in the fertile soil. 
 For most plants also magnesia must be supplied, and for all vegetables 
 that are employed in any important degree, as food for man, or the other 
 animals, and especially in the various kinds of corn, phosphoric acid. In 
 average soils, most of these bodies are naturally present in the necessary 
 degree. When the soil has originated in the decomposition of granitic, 
 or of slaty rocks, the silica, the alumina, and the potash are abundantly 
 supplied from feldspar and from mica : lime and magnesia also may be 
 derived from associated minerals ; but in general, it is necessary to add 
 lime to such soils in order that the quantity necessary to full fertility 
 may be present. In purely limestone soils, clay and silicious gravel 
 must be added ; and to make up the deficiency in potash, the ashes of 
 other plants and cinders of coals. If the soil be purely silicious, the 
 addition of clay and lime (marl) may bring it to the proper composition. 
 In clays or marl, phosphoric acid is supplied from the contained mi- 
 nerals or fossil remains of animals, but the most practical source is to 
 restore as dung the materials of preceding vegetables which have served 
 as food, and thus give back to the soil the several mineral ingredients 
 which the crop of the previous year had taken from it. 
 
 In these few words are contained the theory of what are termed 
 mineral manures, with few exceptions. In adding lime, or marl, bone 
 dust or guano to a soil, we either render its physical condition of poro- 
 sity and tenacity more suitable to the circumstances of the plant, or we 
 supply some ingredient which was either primitively deficient in the 
 soil, or had been removed from it by a previous crop of the same kind. 
 On this last condition is founded also the necessity, in an economic 
 agriculture, of alternating crops which take up from the ground mate- 
 rials of different kinds. Thus, if wheat be grown upon a soil, the rocky 
 substance of which is rich in potash and phosphoric acid, the crops 
 will, after a few years, be unproductive, and the soil impoverished, be- 
 cause the rock decomposes too slowly to supply materials for the wheat 
 as fast as they are required ; but if we take from that soil a crop of 
 wheat but once in three years, and interpose some other plant, as trefoil, 
 which takes up but little potash, and phosphoric acid, the soil has 
 
990 Excretions of Plants. 
 
 time to recover its constitution, and the series of crops thus arranged 
 in rotatory order, so far from impoverishing the soil, may bring it to a 
 higher degree of richness, by the additions made to its azotized organic 
 components, by the roots and rejected leaves of the various plants which 
 are left upon it, and the manure derived from the consumption of its 
 produce by animals. 
 
 The advantage of a rotation of crops may be thus deduced from the 
 necessity of the soil renewing its mineral constituents, by the gradual 
 decomposition of the subjacent rocky matter (subsoil.) But the obser- 
 vations of Macaire and Decandolle, indicate another and possibly not 
 less important reason for its use. These physiologists have found, that 
 from the rootlets of a plant the same process of excretion is carried on, 
 as by its stem and leaves, and that brown-coloured substances are 
 exuded, which possess much analogy with tannin, and which are poison- 
 ous to plants of the same kind, when dissolved in the water with which 
 their roots are supplied. On the other hand, the excretory products of 
 one plant may be used without injury, and even advantageously for the 
 growth of another plant of a different natural family, and in this respect 
 the grasses, and the leguminous plants, are most remarkable. It is 
 hence, probably, for example, that wheat unfits the soil for the growth 
 of another crop of wheat, not merely by removing the potash and phos- 
 phoric acid which are required for the perfection of its parts, but it also 
 gives out a substance poisonous to a plant of the same kind, but which 
 acts beneficially upon the rootlets of a leguminous plant, favouring its 
 growth, whilst the soil has time to regain from the subsoil the inorganic 
 materials of which it had been deprived. 
 
 The utility of manures may now be easily understood ; their action 
 is either as bone-earth, marl, lime, guano or silicious gravel, to supply 
 to the soil some mineral ingredient in which it had been deficient, or to 
 provide as by the ordinary vegetable or animal manures, soot, &c., 
 organic matter, which, by its decomposition, may give out carbonic acid 
 and ammonia for the nutrition of the young plants. In some few cases 
 the action of manures is more indirect ; thus, the leguminous plants 
 (trefoil) require but little inorganic matter, but much ammonia, and yet 
 there is no manure so efficient, in the promotion of their growth as 
 plaster of Paris, (sulphate of lime). The plant, however, contains no 
 sulphate of lime ; it is not absorbed. The action of this manure ap- 
 pears to be, as was first suggested by Liebig, that acting on those sub- 
 stances of the ulmine family, which always retain a large quantity of 
 ammonia intimately united in the soil, it forms by double decomposition, 
 ulmate of lime and sulphate of ammonia, which last being soluble, is 
 easily absorbed by the rootlets of the plant, and the nitrogen assimilated 
 
Action of Organic Manures. 991 
 
 to its tissues. Another view is, however, supplied by the observations 
 of Boussingault. The leguminous plants grow rapidly and require a 
 great deal of lime, which they could not take up as carbonate, but the 
 gypsum is so far soluble that by means of it the lime is carried into the 
 tissues of the plant, and the sulphuric acid is then decomposed and 
 probably exhaled as sulphuretted hydrogen or returned to the soil. 
 
 With regard to organic manures, their great value depends on the 
 proportion of nitrogen they supply. In plants, the great mass of nitro- 
 gen is always deposited in organs, as the seed, the tuber, &c., which for 
 that very reason are sought after and collected by man, either as food, 
 or for medicinal purposes, from the active (azotized) principles they 
 contain. The roots, stems and leaves of the plants, such as are rejected 
 in the collection of the crop, contain little nitrogen, they being rejected 
 as useless for that very reason. Hence the residue of a former season 
 may manure the land abundantly, so far as carbon is concerned, but be 
 quite incapable of supplying nitrogen, and in providing materials for a 
 future abundant crop. The object of the agriculturist must be, so far 
 as organic material is concerned, to supply nitrogen, especially for such 
 plants as the different species of corn, which are incapable of deriving 
 that important element directly from the atmosphere. The value of an 
 organic manure may, therefore, for particular purposes, be considered as 
 being measured by the quantity of nitrogen which it contains, and the 
 directness or indirectness of the benefit derivable from it, depends upon 
 the manner in which the nitrogen is combined. If mere ammoniacal 
 salts be used, or materials, as animal manures, urine, &c., which soon 
 form ammoniacal salts by their putrefaction, the whole benefit of the 
 manure is given to the crops immediately succeeding its application ; 
 but if organic substances be employed which resist decomposition, their 
 nitrogen is evolved but slowly, and though little immediate amelioration 
 be observed from their addition to the soil, their influence is gradually 
 and steadily exerted, and becomes ultimately sensible to the fuU degree, 
 proportional to the nitrogen they contain. 
 
 A mode of restoring to the soil the principles it had lost by ir discreet 
 cultivation, is that of falloiving. It is a method synonymous with an 
 ignorant and improvident agriculture. The soil having, by over work 
 lost, on the one hand, some of its essential mineral ingredients, requires 
 time to gather, by the decomposition of the underlying subsoil, or rock, 
 a proper quantity of them to supply the elements of the succeeding 
 crops, and having been deprived of its organic elements, especially the 
 nitrogen, it must be allowed to gain from the atmosphere a suitable 
 quantity of ammonia, or by the gradual rotting of the roots of the pre- 
 ceding crop, a quantity of carbonic acid suitable to the wants of that 
 
992 Action of Organic Manures. 
 
 which is to follow. But all these effects may be more perfectly and 
 more profitably secured by the intervention, in a succession suitably 
 arranged, of other crops which exercise upon the soil actions alternately 
 opposed. 
 
 Thus by alternating cereal or white crops which remove from the soil 
 large quantities of silica, of alcalies, and of phosphoric acid, with her- 
 bage or green crops, or root crops, which require abundance of lime 
 and magnesia, there are brought into play such diversified chemi- 
 cal actions as may allow the soil to restore itself from time to time, by 
 replacing, from the continuous weathering of its materials, the elements 
 it had lost; whilst by the varied mechanical processes which the several 
 crops involve, according as they are fibrous or taprooted, and penetrate 
 to different depths beneath the surface, the action of air and water upon 
 the rocky material of the soil becomes accelerated, and the renewed 
 provision of freshly-formed soil becomes more rapidly available. The 
 various systems of rotation of crops founded upon those principles, 
 have been founded in practice by eminent agriculturists to give results 
 fully conformable in advantage to what theory indicates, and there is 
 absolutely no other reason assignable for allowing a field to lie idle 
 every second or third year in fallow, but ignorance on the part of the 
 farmer of what could otherwise be effected on it. 
 
 It remains only to notice, in relation to the theory of the growth of 
 plants, a few additional circumstances connected with the formation of 
 some of their peculiar principles. It is not unusual to hear, from even 
 intelligent agriculturists, objections to the cultivation of certain plants, 
 on the grounds of their exhausting the soil too much. A plant ex- 
 hausts the soil only in consequence of its forming in proportional 
 quantity some substance, the. elements of which are derived from the 
 soil, and which constitute in almost every case the valuable portion 
 of the plant. Wheat exhausts the soil, because it derives therefrom the 
 large quantity of nitrogen and phosphoric acid which its grain contains; 
 but it is precisely that great quantity of nitrogen and phosphoric acid 
 which renders wheat more valuable in the market than oats or barley. 
 Tobacco exhausts the soil, because it takes up abundance of nitrogen, 
 with which it forms its nicotin ; the more of the active principle the 
 plant produces, the more it exhausts the soil, but in the same proportion, 
 the greater value does it possess when sold. To produce indigo, nitro- 
 gen must be supplied to the plants by abundance of rich manure ; no 
 crop is more exhausting ; but without the nitrogen no colouring matter 
 could be formed, and the plant should be completely worthless. 
 Examples of this kind might be adduced in any number, but these 
 suffice to place in a distinct, though popular aspect, the general principle 
 
Economy of Residues of Crops. 993 
 
 that where a plant exhausts the soil, especially as to its nitrogen, it 
 is for the production of the substance which gives the plant its com- 
 mercial value and importance, and that hence the quantity of manure 
 necessary for the production of an abundant crop, is fully repaid by the 
 improved quality of the produce. 
 
 To this general principle there exists, however, a practical exception 
 which requires some notice as it embraces the cultivation of some very 
 important plants. The substances, sugar and starch, as well as the 
 forms of ligneous fibre, which constitute the commercial flax and hemp, 
 do not contain nitrogen, and yet the plants which are cultivated for 
 their production are rich in nitrogen, and may be considered as, after the 
 cereal plants, the most powerful exhausters of a soil. The nitrogen, as 
 well as the large quantity of phosphoric acid which these plants con- 
 tain, exists therein in forms which do not concur to the commercial 
 value of the produce, and under the imperfect modes of agriculture, 
 which for the most part prevail, these materials are sacrificed and 
 thrown away; but it becomes an important object to utilize them, 
 and were it done to the degree easily feasible in practice, the exhausting 
 quality of such crops as flax, hemp, &c. might be materially dimin- 
 ished if not removed, and the cost of their cultivation lessened in a 
 corresponding degree. 
 
 In the starch manufactories near Paris, for example, it has become 
 usual to top-dress meadows with the water that has been used to wash 
 the potato pulp or wheaten flour, from which the starch was prepared. 
 A similar plan has been lately adopted in this country, and with the 
 same success. The potash, lime, phosphoric acid and nitrogen of the 
 plant, none of which belong to the starch, were dissolved in the water, 
 and being absorbed by the soil, afforded the materials of growth to the 
 succeeding crop, by which the amount of produce obtained was ren- 
 dered manifold what otherwise could have been expected. In the flax 
 cultivation, the steep water is so very rich in azotized and saline sub- 
 stances, that if let run into rivers it kills the fish, and such practice is 
 prohibited, but if it be spread over the land, it affords a most nutri- 
 tive top-dressing, restoring almost completely the materials which the 
 previous crop had taken out of the soil. 
 
 Intimately connected with the restoration of the fertile qualities of 
 the soil, is the promotion of the weathering of its rocky constituents 
 under the action of the atmosphere, by means of drainage. The pro- 
 minent object of drainage in this country, is of course to give to the 
 cultivated plants something analogous to the condition of climate which 
 they possess in those localities, whence they originally were derived. 
 All of the important plants which we employ as food, are natives of 
 63 
 
994 General Principles of Drainage. 
 
 climates, naturally drier than that of this country, and hence in order 
 that they may vegetate with proper luxuriance, the soil should not be 
 wet. Further, the dampness of this country throws back the period of 
 ripening of the grain crops to so late a period, as to expose the harvest 
 to all the uncertainty of late autumnal weather, when the temperature 
 falls so low that the conditions of true ripening cannot take place. 
 Moreover, the constant evaporation from the surface of a wet soil, pre- 
 vents its becoming warmed by the sun's heat; it remains cold, and vegeta- 
 tion is arrested. The richer grasses cannot exist in it, and hence 
 those tenacious clays which retain water closely within their mass are 
 particularly termed cold soils, even by the practical farmer, whose expe. 
 rience of the result has enabled him to anticipate the judgment of 
 science as to the cause. 
 
 To these physical and mechanical advantages of draining the soils 
 of countries naturally so moist as the British Islands, are to be added 
 the very important chemical results of the percolation of water through- 
 out the mass of soil which takes place in well conducted drainage. 
 The water which falls from the atmosphere always holds dissolved car- 
 bonic acid, oxygen and ammonia. 'In passing through the soil, these 
 gases are absorbed by the plants and by the soil, and serve directly to 
 their nutrition, they also acting on the organic matters of the soil 
 favour their decomposition, and the supply of food to the young root- 
 lets. Further the rocky or gravelly materials of the soil, acted upon by 
 the continuous contact of this aerated water, are decomposed, lime is 
 dissolved, potash, magnesia, and phosphoric acid are set free from the 
 minerals in which previously they had been locked up, and thus by 
 means of drainage, new soil is formed, the loss of elements by cropping 
 may be restored, and from the porosity which the free passage of the 
 water throughout the soil necessarily produces, the rootlets of the 
 plants are enabled to spread far deeper into the soil in search of nutri- 
 ment, and thus to render available a depth of soil that by no other 
 means could be made useful to the agriculturist. 
 
 Without seeking to enter into the general question of the influence 
 of the physical agents on vegetation, which, for its discussion would 
 require more extended limits, and lead to considerations too far removed 
 from chemistry to justify its introduction, I shall, in concluding this 
 sketch of the chemistry of vegetation, notice the peculiar action which 
 light exercises upon plants. It is not merely that it acts as a general 
 stimulus, and thus provokes the activity of nutrition, which determines 
 the ultimate result of the purification of the atmosphere by plants, and 
 that its withdrawal is followed, with plants as with higher beings, by a 
 torpor and tendency to rest, which closes their petals, and folds their 
 
Action of Light on Plants. 995 
 
 leaves at night ; but in the production of the coloured parts of plants 
 the agency of light is indispensable. A plant which grows in darkness, 
 as in the gallery of a mine, no matter to what size its form may reach 
 by means of a copious supply of food, remains soft, its wood unformed, 
 its colour pale ; the chlorophyll not being generated, unless under the 
 influence of light. For culinary purposes precisely this effect is pro- 
 duced by covering up the stems of celery and asparagus, the softness 
 and whiteness admired upon the table being the evidence of the sick 
 and abortive organization of the stem. 
 
 The action of light in favouring the production of colour in plants 
 is, however, accompanied by a more material change. The petals, and 
 all coloured parts of plants, except the leaves, absorb oxygen from the 
 air. This is precisely what we find a number of bodies to effect, when 
 passing from their colourless condition to that in which their proper 
 colour is displayed. Thus, white indigo becomes blue by absorbing 
 oxygen. Thus rocelline, by absorbing oxygen and giving off water, forms 
 erythrolitmic acid. It is thus, too, that, by deoxidizing agents we may 
 remove the colour from logwood, archil, and the flowers of most plants, 
 and restore their tints by again admitting it. Frequently also the gene- 
 ration of the coloured substance is accompanied not merely by an ab- 
 sorption of oxygen, but by an escape of carbonic acid ; this, which is 
 shown in the laboratory in forming orceine from erythrine, appears to 
 take place in the tissue of most flowers, which rapidly give out carbonic 
 acid for some time after they have first opened. 
 
 In similar actions, carried on in the laboratory by means of chlorine, 
 the influence of light in furthering the removal of hydrogen, and even 
 of carbon, if water be present, is most remarkable, and illustrates the 
 operation of that physical agent in producing the colours of plants in a 
 distinct and satisfactory way. This action has been, however, so fully 
 noticed in describing the general chemical agencies of light (p. 51) 
 and the action of chlorine on colouring matters, (p. 948,) that I 
 deem it necessary only to refer to what has been there said upon the 
 subject. 
 
CHAPTER XXX. 
 
 OF ANIMAL CHEMISTRY. 
 
 IN describing the various classes of organic bodies which have hitherto 
 come under our notice, I have made no distinction as to their animal or 
 vegetable origin, for the point of view under which they were then con- 
 sidered, and the properties which they manifested, were independent of 
 their source. It was thus with ethal, the fatty acids, and colouring 
 matters, and indeed, in many instances, the same substances were found 
 to be products of both kingdoms of organized nature. In the present 
 chapter I purpose to describe, so far as our accurate knowledge extends, 
 the chemical history of those bodies, which I characterized in another 
 place (p. 662,) as being rather organized than organic, as constituting, 
 not merely a product of the vital operations of the being, but the 
 mechanism itself by which these vital operations are carried on, as 
 making part of the tissues essential to its proper organization and life, 
 and as being, whilst in connexion with the animal and participating in 
 its life, protected from the truly chemical reactions of their proper ele- 
 ments, which, after the death of the animal, especially in contact with 
 air and water, rapidly assume simpler forms of union, and breaking up 
 the complex animal tissue into a crowd of binary compounds, induce 
 the change well known as putrefaction. 
 
 In connexion with these substances, which form the basis of the 
 tissues and organs of the animal frame. I will bring under survey 
 the processes by which, from the atmosphere, or from the materials of 
 our food, the substance of our organs is continually renewed, their 
 growth provided for, and the conditions necessary for the continuance 
 of health and life maintained. The functions of respiration and of 
 digestion, so far as the chemical phenomena which they embrace are 
 known, the composition of those secretions and excretions, whose 
 agency in the furtherance of those processes has been studied, will here 
 be described, and finally, the composition of those excretions, which 
 have for their office the separation of elements unfit for the nutrition 
 of the being, or which are not intended for its support. 
 
Composition of the Tissues. 997 
 
 In each of these divisions, I shall add to the description of the com- 
 position and properties of these tissues or secretions in the state of 
 health, such facts, in reference to the modifications introduced by dis- 
 ease, as have been observed with proper accuracy. 
 
 SECTION I. 
 
 OF THE COMPOSITION OF THE ANIMAL TISSUES. 
 
 A. Of the Albuminous Materials of the Tissues. 
 Of Fibrine. 
 
 This substance constitutes the basis of the muscular tissue, and forms 
 an important constituent of the blood. In the latter, it exists dissolved 
 during life, but separates after death, or extraction from the body, pro- 
 ducing, with the colouring material, the phenomenon of coagulation. 
 In the muscles, the fibrine is arranged in a truly organized and living 
 condition, constituting the contractile fibres, in which it is so inter- 
 woven with nervous and vascular filaments as to render its isolation im- 
 possible. To obtain pure fibrine, therefore, we have recourse to blood, 
 which, if immediately on being drawn it be briskly agitated with a little 
 bundle of twigs, does not coagulate, but the fibrine is deposited on the 
 twigs in soft tenacious masses ; these, being washed to remove any ad- 
 hering colouring matter, and digested in alcohol and ether to remove 
 some traces of fatty substances that adhere to it, constitute pure 
 fibrine, which may be dried by a gentle heat, and appears then as a 
 yellowish opaque mass, hard, tasteless, and inodorous : if it be at all 
 transparent, this results from traces of adhering fat. It is insoluble in 
 water, alcohol and ether ; it absorbs, however, so much water as to 
 treble its weight, and thereby recovers the volume, softness and flexi- 
 bility it possessed before being dried. This moisture is not sensible to 
 the hand, but by strong pressure between folds of bibulous paper, it 
 may be removed and the fibrine rendered completely dry. When boiled 
 with water for a great length of time, fibrine is decomposed and dis- 
 solves, but it does not form any kind of gelatine. 
 
 Fibrine is remarkable for decomposing deutoxide of hydrogen rapidly 
 by catalytic force, (pp. 229, 357), evolving oxygen. Several of the 
 animal tissues produce this effect, though not containing fibrine. Albu- 
 men is, however, totally destitute of it. 
 
 Fibrine absorbs cold oil of vitriol, and swells up to a yellow trans- 
 parent jelly. On the addition of water, it shrinks up and becomes 
 
998 Fibrine Albumen. 
 
 hard ; but if all the excess of acid be washed away, the residual mass, 
 which is a neutral compound of fibrine and sulphuric acid, dissolves in 
 pure water. With nitric acid fibrine evolves nitrogen and nitric oxide, 
 and forms a yellow powder, xanthoproteic acid, to which I shall shortly 
 recur. Tribasic phosphoric acid, and acetic acid dissolve fibrine. The 
 solution is precipitated by the mineral acids and by caustic potash, an 
 excess of which last, however, redissolves the precipitate. The mono, 
 or bibasic phosphoric acids, act as sulphuric acid towards fibrine. If 
 perfectly dry fibrine be digested in strong muriatic acid, it swells up, 
 and after a few minutes dissolves into a rich dark blue liquid. No 
 gas is evolved. This blue liquor is precipitated by the yellow prus- 
 siate of potash. 
 
 Fibrine is dissolved even by a dilute solution of caustic potash, and 
 appears thereby to neutralize the alcali almost completely. This solu- 
 tion is coagulated by alcohol and by acids, but not by heat. The pre- 
 cipitates given by acetic and tribasic phosphoric acids are redissolved by 
 an excess. 
 
 If sulphate of soda, or nitrate of potash be added to newly drawn 
 blood, its coagulation is prevented ; and if fibrine be digested in a 
 strong solution of nitre, it dissolves, forming a thick liquid, which is 
 coagulated by heat, by alcohol and acids, and is precipitated by the salts 
 of mercury, lead and copper, and by yellow prussiate of potash. This 
 property of fibrine will again come under notice. 
 
 The composition of fibrine has been expressed by the formula 
 C8ooH62o^iooO 2 4o -f PS 2 . It contains, besides, minute quantities of lime 
 and magnesia, so that when icinerated, it leaves 0'77 per cent of sul- 
 phates and phosphates of those bases, but as I have already explained 
 it is one of these substances of which, though we may by analysis deter- 
 mine their absolute per centage constitution, yet we cannot attempt to 
 assign by a rational formula any theory of the mode of union of their 
 elements. Under the head of protein this point will be more specially 
 discussed. 
 
 Of Albumen. 
 
 This substance is even more extensively distributed through the 
 animal frame than fibrine. Like fibrine it exists in two conditions, one 
 soluble, and the other insoluble in water; but whereas the fibrine 
 loses its solubility almost instantly on being withdrawn from the body, 
 albumen may retain that state for an indefinite time, and its history is 
 therefore more complete. In its soluble form it exists in the blood, 
 the egg, in the serous secretions, in the humours of the eye, &c. ; in 
 
States of Albumen. 999 
 
 the insoluble or coagulated form, it constitutes a portion of most of the 
 solid tissues. Albumen derives its name from its constituting the mass 
 of white of egg. 
 
 Soluble Albumen. This is obtained in the solid form by evaporating 
 to dryness, at a temperature which shall not exceed 120, the serum of 
 blood or white of egg, the membranous investments of the latter having 
 been torn up by triturating with some angular fragments of glass. The 
 dry mass is yellow, transparent, hard, tough, and contains, besides the 
 albumen, the salts and some other constituents of the blood, or white of 
 egg, in minute quantity. These are extracted by digestion in alcohol 
 and ether, which leave the albumen pure. When thus completely dry, 
 it may be heated beyond 212 without passing into the coagulated con- 
 dition. If digested in cold water, it gradually swells up and finally 
 dissolves. This solution, when heated to a temperature between 140 
 and 150, coagulates. If dilute, the solution may even be heated to 
 1 65 without coagulating, and when present in very small quantity, the 
 albumen may not separate until the water boils. When once coagulated 
 in this manner, albumen is totally insoluble in water ; it is changed into 
 its second form. The solution of albumen is precipitated by alcohol, 
 by acids, and metallic salts, exactly as the solution of fibrine in salt- 
 petre. The only distinction that can be drawn between the two is, that 
 the saline solution of fibrine is partially decomposed by the addition of 
 a large quantity of water. 
 
 The precipitates yielded by solution of albumen with metallic salts, 
 are mixtures of two distinct substances; one a compound of albumen 
 with the acids, the other a compound of albumen with the metallic 
 oxide ; the former is generally somewhat soluble, the latter insoluble, 
 and hence results the application of albumen, as an antidote to mineral 
 poisons, such as corrosive sublimate and blue-stone. 
 
 Albumen is also coagulated by many organic bodies, as tannic acid 
 and kreasote, which last acts catalytically, as a very minute quantity of 
 it coagulates a large quantity of albumen, without entering into combi- 
 nation with it. 
 
 Coagulated Albumen is obtained by heating serum of the blood, or 
 white of egg, to between 140 and 150, so that they solidify ; washing 
 the mass with water, digesting with alcohol and ether until all soluble 
 is removed, and then drying with care. Thus prepared, it retains some 
 inorganic salts, principally phosphate of lime, from which it may be 
 obtained free as follows : The serum of blood is to be coagulated by 
 muriatic acid ; the coagulum washed with acidulated water, and then so 
 much pure water added as may dissolve it. This solution being then 
 decomposed by carbonate of ammonia, the pure albumen is separated as 
 a flocculent white precipitate. 
 
1000 Properties of Protem. 
 
 When dry it is yellow and transparent ; in every chemical character, 
 except its relation to deutoxide of hydrogen, it identifies itself with 
 fibrine, and it is hence unnecessary to repeat the details of these 
 reactions ; in its composition it is very closely related to it ; their 
 organic element is almost absolutely the same, and they differ only in 
 the quantity of sulphur; the formula assigned for albumen being 
 C 8 ooH 62 o^ r iooO24o + P&t- The quantity of ashes remaining from albu- 
 men is greater than from fibrine. 
 
 Proteine Its Derivatives. 
 
 The comparative history of the above bodies as now given leads to 
 considerable doubt, as to -how far they are chemically distinct, although 
 their physiological characters are so different. Mulder, to whose accu- 
 rate researches we are indebted for the greater part of our knowledge 
 of the constitution of these bodies, looks upon both as compounds of 
 the real organic substance, which he terms proteine, with sulphurets of 
 phosphorus. In fact, as he states, the sulphur and phosphorus may be 
 removed by very simple methods, and the body (proteine) which then 
 remains deserves attentive study. 
 
 When albumen, fibrine, cheese or flesh, is freed by digestion in water, 
 alcohol and ether, from all bodies soluble in these liquids, and that by 
 dilute muriatic acid all earthy salts have been removed, it is to^be dis- 
 solved in a dilute solution of caustic potash, and heated to 120, 
 whereby the sulphur and phosphorus form phosphate of potash and 
 sulphuret of potassium. From the filtered liquor the protein may then 
 be precipitated by acetic acid, which must be added only in very slight 
 excess, otherwise the precipitate would be redissolved. 
 
 Protein, according to Mulder, forms greyish-white gelatinous flocks, 
 which, when dried, become hard and yellow, and give an amber- 
 coloured powder. It absorbs water, swells up, and regains the appear- 
 ance it had before being dried. By long boiling with water it is decom- 
 posed and dissolved. 
 
 Proteine dissolves in all very dilute acids, forming neutral compounds 
 which are insoluble in strong acid liquors, and are hence precipitated on 
 the addition of strong acids, except the acetic and tribasic phosphoric 
 acids. With oil of vitriol it combines as described under the head of 
 fibrine, and forms proteo-sulpliuric acid. It combines also with earthy 
 and metallic oxides, .forming insoluble compounds, which are identical in 
 characters with those obtained with albumen. 
 
 The composition of proteine, as found by Mulder, and confirmed by 
 the analyses of its acid and basic combinations, is expressed by the 
 
Compounds of Protein . 1001 
 
 formula C 4 oH3 ] N 5 O 1 2. We may evidently consider albumen and fibrine 
 as compounds of protein, for if we represent proteine by the symbol 
 Prt. albumen becomes Prt.29 -f- PS 4 and fibrine is Prt <2 o + PS 2 . I 
 consider, however, that the state of combination of these bodies requires 
 some further consideration. 
 
 Mulder asserts that proteine constitutes the basis, not merely of 
 the animal substances now under examination, but that it exists 
 also in vegetable albumen, gluten and legumine, (p. 771,) and con- 
 stitutes the pure caseous matter of milk, considering that the similarity 
 of properties and composition in these bodies, proves their organic 
 element to be identical. "We have seen, indeed, that between albumen 
 and fibrine, the distinctive chemical characters are, if any, so trivial, as 
 to leave no firm ground for their distinction in that way, but if we ex- 
 amine the evidence of their being compounds of protein with sulphur 
 and phosphorus, we shall find them inconclusive. First, it is not cer- 
 tain that such sulphurets of phosphorus exist as PS 2 and PS 4 ; second, 
 the compounds of sulphur and phosphorus, do not manifest any ten- 
 dency whatsoever to combination ; and third, in all the reactions of 
 albumen and fibrine, the protein on the one hand, the sulphur and 
 phosphorus on the other, act as if they were totally distinct. I look 
 upon albumen and fibrine, whilst in connexion with the body, as 
 organized and living substances, in whose functions the minute quantity 
 of sulpjiur and phosphorus may act an important part, as a catalytic 
 body. The proteine, I consider, not with Mulder as the basis of our 
 tissues, but as the simplest product of their decomposition. It enters 
 into combination with acids and with bases, as indigo or morphia do, 
 which I look upon as totally foreign to the character of a body possessed 
 of vital properties. 
 
 The view which has been just described and which I advanced in the 
 first edition of this work, at the time when the protein theory was uni- 
 versally admitted, has recently received full confirmation from the 
 researches of Liebig and other chemists of the German school, who have 
 experimentally established the fallacy of the protein theory, at least 
 as Mulder first proposed it. 
 
 It is in fact now admitted that the albuminous bodies contain much 
 more sulphur and phosphorus than Mulder had supposed, and that his 
 formula above given, do not satisfactorily express their constitution. 
 It is now even a disputed point whether any such body as protein, free 
 from sulphur and phosphorus, can be obtained. Although it is difficult 
 to judge among the conflicting statements on the subject, I do believe 
 that by treatment with reagents all sulphur and phosphorus may be 
 removed, and an organic product will remain, which may be called 
 
1002 
 
 Theory of Protein, 
 
 protein, if it be so wished ; but I consider, as I long since announced, 
 that such body is in no way the basis of the albuminous tissues, but 
 merely a product of their decomposition, an opinion which is corrobo- 
 rated by the experimental researches carried on in Giessen, and may now 
 be considered as an established analytical fact. 
 
 It is indeed rendered highly doubtful whether the isomerism of the 
 albuminous substances upon which Mulder's protein theory was founded 
 is true, all the other analyses of these bodies shewing differences of com- 
 position, which can scarcely be supposed to arise from error. To show 
 this and to exhibit also the nature of those bodies, which the formula 
 already quoted can scarely indicate, the per-cent composition is here 
 given, including caseine, although the detailed history of that body 
 belongs to another place. 
 
 Fibrine. Albumen. Caseine. 
 
 Carbon 54-45 
 
 55-46 
 
 54.66. 
 
 Hydrogen 7'07 
 
 7'20 
 
 7-15. 
 
 Nitrogen 17 '21 
 
 16-48 
 
 15-72. 
 
 Oxygen 19-35 
 
 18-27 
 
 21-55. 
 
 Sulphur 1-59 
 
 2-16 
 
 92. 
 
 Phosphorus -33 
 
 43 
 
 ... 
 
 100-00 
 
 100-00 
 
 100-00 
 
 Although caseine is thus found not to contain phosphorus as such, 
 yet it contains a large quantity of phosphate of lime and potash, some- 
 times so much as six per cent., which is destined for the bones of the 
 young sucking animal, but which is independant of its organic con- 
 stitution. 
 
 Having thus described what I consider to be the true place of 
 protein, in relation to albumen and fibrine, I shall briefly notice some of 
 its derived compounds. 
 
 Chloroproteic Acid is formed by passing chlorine into a solution of 
 albumen. It is a white powder. Its formula is C 40 H 31 N 6 12 + C1O 4 . 
 By ammonia it is decomposed, nitrogen being evolved, and a white 
 substance formed, oxyprotein, the formula of which is C^H^NsO^. 
 
 The formation of xantkoproteic acid, by the action of nitric acid on 
 fibrine, has been already noticed. It is an orange-yellow powder, when 
 washed from adhering acid, tasteless and inodorous, but reddens moist 
 litmus paper. Insoluble in water, alcohol and ether, it unites with 
 acids, forming compounds which are pale, yellow and insoluble ; with 
 bases it forms soluble salts, generally deep -red coloured. Its formula is 
 C 34 H 25 N 4 12 . 
 
Source of Gelatine. 1003 
 
 B. Of the Gelatinous Constituents of the Tissues. 
 Of Gelatine. 
 
 When the skin, cellular , orserous tissues, tendons and some forms 
 of cartilage, as that of bones, are boiled in water, they dissolve in great 
 part, and form a solution which gelatinizes on cooling. Some of these 
 tissues, as the skin, dissolve easily, and almost completely, others dis- 
 solve but partly, and leave behind a quantity of coagulated albumen. 
 In most kinds of cartilage a very prolonged boiling is necessary to ex- 
 tract any sensible quantity of gelatine. These various tissues are thus 
 found to consist of albumen and gelatine, united in various proportions, 
 and each presenting various degrees of condensation of texture, but by 
 boiling they may be completely separated from each other. 
 
 The gelatine is known in commerce as the material of isinglass and 
 common glue. When pure it is colourless and transparent, very 
 sparingly soluble in cold water, by contact with which, however, it swells 
 up and softens. In hot water it dissolves readily, and on cooling forms 
 so strong a jelly, that with T ^Q part it is a consistent solid. It is in- 
 soluble in alcohol and ether. When a solution of gelatine is long ex- 
 posed to the air, or frequently heated and cooled, it undergoes a com- 
 mencement of putrefaction, and loses its property of gelatinizing. The 
 composition of gelatine, by Mulder's analyses is expressed by the 
 formula, C^H^Ni-Os. 
 
 When acted on by chlorine, gelatine is converted into a white floccu- 
 lent substance, insoluble in water, but dissolved by an excess of gelatine. 
 Its composition is expressed by the formula C52H 4 oN 8 O.2o + ClO^ con- 
 sisting, therefore, of four atoms of unaltered gelatine, and one atom of 
 of chlorous acid. Gelatine is not precipitated either by solutions of 
 ordinary or of basic alum, but if a solution of common salt be also 
 mixed, the gelatine falls down, combined with alumina, as it decom- 
 poses the muriate of alumina which is then formed. On this principle 
 is founded the manufacture of white leather, by a kind of tanning with 
 alum. 
 
 The most important compound of gelatine is that with tannic acid, 
 which constitutes ordinary leather. This reaction is so distinct, that 
 one part of gelatine in 5000 of water, is at once detected by infusion of 
 galls. The constitution of the precipitate varies according as one or 
 other of these materials are employed in excess, the tannic acid and 
 gelatine being capable of uniting in at least three different proportions; 
 100 parts of dry gelatine combine with 136 parts of tannic acid, when 
 
1004 Gelatine Chondrine. 
 
 the latter is in great excess ; this compound contains an atom of each 
 ingredient. 
 
 The technical applications of gelatine are numerous, and for the most 
 part well known. For glueing together wood, paper, &c., thickening 
 colours, filling up the pores of writing paper, and as isinglass in calves' 
 feet jelly, an article of food, it is abundantly employed ; but its most 
 important use is in the manufacture of leather. The skins are cleaned 
 by digestion with lime and scraping with a knife, from the hair and epi- 
 dermis on the one, and the loose cellular tissue on the other side, and 
 steeped in pits containing an infusion of oak bark, valonia, sumac, or 
 others of the substances rich in tannic acid (p. 904). At first the tan- 
 ning liquor is used very weak, or otherwise the surface of the skin 
 would become impervious, and the interior could not afterwards be 
 tanned ; but having passed through a succession of liquors gradually 
 becoming stronger, the skins are in the last pit interstratified with oak 
 bark, and so for a considerable time submitted to the action of the 
 tannic acid in its higest state of concentration, until the conversion into 
 leather is complete throughout the entire substance. They are then 
 removed and subjected to finishing and cleaning processes, which I need 
 not notice. 
 
 Many chemists consider that gelatine is merely a product of the de- 
 composition of albumen or fibrine by boiling water, and not a true 
 constituent of the tissues. I believe this idea to be incorrect on the 
 following grounds. First, pure fibrine, or albumen, gives no gelatine by 
 boiling ; second, in the process of tanning, the tannic acid combines 
 with gelatine in a skin which has never been boiled ; and third, that we 
 can easily understand why some tissues give gelatine more easily than 
 others by the different degrees of condensation in their structure ; but 
 I rather consider that gelatine bears the same relation to the organized 
 tissue of the skin or cellular membrane that protein does to the fibrine 
 of the blood ; being really a product of its death and decomposition, 
 though the only representative of it which we can have. 
 
 Chondrine. Those cartilages in which bone is not deposited are re- 
 solved by boiling into a substance possessing much analogy to gelatine, 
 but still distinguished from it by the following properties ; it precipitates 
 solution of alum, sulphate of iron, and acetate of lead, and is precipi- 
 tated by acetic acid, none of which bodies have any action on ordinary 
 gelatine, which, however, chondrine resembles in all its other characters; 
 in composition, however, it differs, its formula being, by Mulder's 
 analysis, Ci6H ]3 N 2 O 7 , it, however, contains a trace of sulphur, its com- 
 plete formula being C 3 2oH 2 GoN4oOi4o + S The physiologist Miiller, to 
 whom the discovery of chondrin is due, considers that the skeleton of 
 cartilaginous fishes yields a third variety of gelatine. 
 
Leucine Sugar of Gelatine. 1005 
 
 Glycocoll Leucine Valeronitrile. 
 
 The action of re-agents on gelatine is in some cases of high interest. 
 By digestion with strong sulphuric acid, as with caustic potash the same 
 results are obtained. Ammonia is evoked, a white crystalline body 
 (leucine) and a sweet substance (sugar of gelatine) are formed. They 
 are separated from each other, and from some less important products, 
 by repeated crystallizations. Prom its alcoholic solution leucine sepa- 
 rates in brilliant colourless plates. It feels greasy, is tasteless and 
 inodorous ; heated to 336 it sublimes totally unchanged. It dissolves 
 in twenty-eight parts of cold water, but requires 625 parts of alcohol, 
 and is insoluble in ether ; its formula is Ci 2 H 12 N0 4 . It combines with 
 nitric acid to form nitro-leucic acid, which crystallizes in brilliant needles, 
 and forms with bases neutral salts. Its formula is C 12 H 12 1NX) 4 -f- NO 5 . 
 Aq. 
 
 The Glycocoll is an organic base of very great interest, it has a strong 
 sweet taste, is very soluble in water, but sparingly in alcohol or ether. 
 It forms crystallizable salts with acids, and has a remarkable tendency 
 to form binary compounds with the different classes of neutral salts. 
 When crystallized from its watery solution it has the formula C 4 NH 5 O 4 
 = C 4 NH 4 O 3 + Aq., of which the water is replaced by acids in its salts, 
 but it appears to exist in a combined form containing an atom of water 
 less in some important organic compounds. Thus if we represent truly 
 anhydrous glycocoll as C 4 NH 3 2 , there is formed from 
 
 One Atom of Glycocoll 
 
 One Atom Benzole acid CuH 5 O3 + HO. 
 
 One Atom Hippuric Acid CisHVNOs -f HO. 
 
 and into these constituents the hippuric acid is resolved by strong 
 muriatic acid. Further, there is formed from 
 
 One Atom Glycocoll C 4 H 3 NO 2 . 
 One Atom Cholalic acid C48H 4 oOio. 
 
 One Atom Cholic acid C52H 4 aNOi2. 
 
 the most characteristic ingredient in bile, and which is so decomposed 
 under the influence of re-agents. 
 
 The salts of Glycocoll, like those of the other organic bases, contain 
 an atom of water with the oxygen acids. 
 
 When gelatine is oxidized by bichromate of potash and sulphuric acid, 
 there are formed a croud of products, as acetic, valerianic and benzoic 
 acids, and oily products, which appear to be related to valerianic acid as 
 
1006 Cerebrate Cephalol Cholesterine. 
 
 azobenzyle,(p. 853,) is to the benzoic acid; they are valeronitrile, having 
 the formula C 10 H 9 N. which is converted by boiling with a solution of 
 potash into valerianate of ammonia and valeracetonitrile, the rational 
 formula of which is 3(C 4 H 3 O 3 ) + 4(C 10 H>N.) Oil of bitter almonds 
 is also formed in this reaction, but is usually converted into benzoic 
 acid. 
 
 C. Of the fatty Constituents of the Tissues. 
 Composition of the Brain 
 
 The fatty bodies already described in Chapter XXIII. although con- 
 tributing essentially to the support of the animal frame, are mere secre- 
 tions, and do not form any portion of its organized tissues. The sub- 
 stances properly included under the present head, are the constituents 
 of the nervous tissue, such as are found in the brain, the spinal cord and 
 nerves. 
 
 In the composition of the brain Couerbe has announced the existence 
 of at least three, perhaps five, distinct substances of a fatty nature; 
 the most characteristic and important is termed Cerebrate ; its mode of 
 preparation can easily be gathered from its characters ; it is a white 
 powder, tasteless and inodorous, feeling not all greasy, but like starch ; 
 when heated it does not melt until it has become brown, and in great 
 part decomposed ; it is insoluble in water, sparingly soluble in alcohol 
 or ether when cold, but abundantly when hot ; on cooling it is deposited 
 from its alcoholic solution as a white powder, not at all crystalline ; it 
 is not acted upon by alcalies. In composition it resembles albumen, 
 containing a large quantity of nitrogen, with sulphur and phosphorus 
 in minute quantity, but its precise formula cannot be considered as 
 being yet established. This body has recently been shewn by Freiny to 
 possess acid properties, and to exist in the brain in the state of a soda 
 salt. It is, therefore, now more usually termed cerebric acid. 
 
 Cerebrol is a liquid reddish oil, having the odour of fresh brain, and 
 a disagreeable rancid taste. It is soluble in all proportions in ether and 
 in oils, but only moderately so in alcohol. It contains the same ele- 
 ments as the cerebrote, and apparently in nearly, if not exactly, the 
 same proportions, but the analyses of Couerbe, who alone has examined 
 their composition, are not authentic enough to be brought forward. 
 The cerebrol is not saponifiable, nor is it in any way altered by digestion 
 with caustic alcalies. 
 
 This result, however, is controverted by Premy, who has described 
 this cerebrol under the name of oteophosphoric acid. He states that it 
 forms soaps with alcalies ; when long boiled with water it is converted 
 
Juice of Flesh Ozmazome Zomidine. 1007 
 
 into phosphoric acid and oleine ; this change takes place also by putre- 
 faction. It contains 2 per cent of phosphorus. 
 
 In addition to these bodies, the brain contains a large quantity of a 
 substance, which, from having been first discovered as a constituent of 
 biliary calculi, is termed cholesterine ; it is insoluble in water, but dis- 
 solves abundantly in boiling alcohol from which it crystallizes on cool- 
 ing in brilliant plates ; it melts at 290, and sublimes partially by a 
 stronger heat ; it dissolves readily in ether ; it is not altered by caustic 
 alcalies ; its formula is CseH^oO. By treatment with hot nitric acid, it 
 is converted into a substance which crystallizes in yellow needles, and 
 forms with bases, yellow salts. This is cholesteric add, the formula of 
 which appears to be C 26 H 2 oN0 12 . 
 
 Couerbe has described as constituents of the brain two other fatty 
 bodies, cepJialot and stearocenot ; they are brown coloured resinous 
 bodies, which, I consider, will most probably, on re-examination of the 
 subject, be found to be impure or decomposed mixtures of cerebrote 
 and cephalol. I hence only indicate their supposed existence. The 
 cholesterine, I look upon as' being deposited in the brain as ordinary 
 fat is in the cellular tissue, or in the substance of other organs, and 
 not as making up an essential portion of the nervous tissue. This idea 
 is strengthened by the fact, that the cholesterine frequently aggregates 
 in the brain in masses, forming one variety of the fatty tumours of 
 that organ. 
 
 D. Of t/ie Saline and Extractive Constituents of the Tissues. 
 Nature of the Juice of Flesh. 
 
 "We find in all of the animal tissues small quantities of a great 
 variety of salts, which differ in some important characters, according as 
 they belong to the proper flesh, or belong to those which shall be here- 
 after noticed as existing in the blood, to the presence of which in the 
 substance of the tissues they are probably due. In the tissue of the 
 bones and teeth, however, these saline matters are deposited in much 
 greater quantity, and in disease and in old age bony deposits occur in 
 all those tissues which yield true gelatine on boiling. The composition 
 of the bones and teeth will be hereafter noticed. 
 
 The extractive matters of the tissues, like the extractive matter of 
 plants, (p. 927), do not pre-exist as such, but are formed by the de- 
 composition, by protracted boiling in water, of the fibrine, albumen, 
 gelatine, &c., which they really contain. Berzelius has pointed out the 
 existence of a great number of different substances which are thus gene- 
 
1008 Constituents of the Juice of Flesh. 
 
 rated, of which two need here only require notice. For the first the 
 name ozmazome may be retained, and the name zomidine applied to the 
 second. Ozmazome is soluble in water, and also in absolute alcohol. 
 The zomidine is insoluble in alcohol, it dries down to a brown extract 
 of a strong and agreeable odour of soup. It dissolves in water in all 
 proportions. 
 
 These results have, however, been rendered unimportant by the re- 
 cent remarkable discoveries of Liebig, as to the composition of the 
 liquid, by which the muscular flesh of all animals is infiltrated, and 
 which he has shewn to contain definite ingredients, and to act an im- 
 portant part in the phenomena of digestion and respiration. He veri- 
 fied the fact noticed by Berzelius, of the existence in the juice of flesh 
 of free lactic acid, and of the organic base discovered by Chevreul, and 
 termed kreatine, and he studied the products of decomposition of the 
 latter with his usual ability. His results are briefly as follow : 
 
 Kreatine Kreatimne Inosinic Acid. 
 
 To prepare kreatine, the finely chopped flesh, for which that of fowls 
 is best, is to be well kneaded with its own weight of water, and then 
 the liquid expelled by strong pressure. This is to be done several 
 times, and the re-united liquors then heated to 160 to coagulate the 
 albumen and hematosine of any intermixed blood. The liquor, filtered 
 from the coagnlum, is strongly acid, it is to be mixed with as much 
 solution of barytes as will make it slightly alcaline, an abundant preci- 
 pitate of phosphate of barytes falls, whilst lactate and inosinate of 
 barytes remain dissolved, the filtered liquor is to be evaporated very 
 carefully at about 130 Fahrenheit, until it has been very much re- 
 duced in bulk, and that mucilaginous skins form on the surface ; if it 
 be then laid aside in a cold place for some days, the kreatine separates 
 in brilliant prismatic crystals. 
 
 The quantity of kreatine in flesh appears to be very small, varying 
 from one to three parts in 1000. The kreatine forms very brilliant 
 prisms, which contain 2 aq. very soluble in hot, but sparingly in cold 
 water and in alcohol. In properties it is perfectly neutral, its formula 
 is CgNaHgC^ + 2 aq. Under the influence of strong acids, the krea- 
 tine is resolved into another body, losing the elements of water. This 
 body is a strong organic base, it is termed Jcreatinine, its formula is 
 CgNaEM^. This body has been shown to exist also naturally in the 
 juice of flesh, and also in urine, perhaps from a spontaneous transfor- 
 mation of the kreatine. Kreatinine forms prismatic crystals, dissolves 
 readily in water, less so in alcohol, neutralizes acids forming crystallizable 
 
Skin EpidermisHorn . 1009 
 
 salts, with nitrate of silver, corrosive sublimate, and bichloride of 
 platinum, it produces crystalline saline compounds. It is peculiarly 
 remarkable for forming with chloride of zinc, a very sparingly soluble 
 body which deposits in granular crystals, and led by its formation to the 
 discovery of kreatinine and kreatine, as constituents of urine, from 
 which the alcaloid can usually be easily prepared. 
 
 When kreatine is boiled with a great excess of caustic barytes, 
 ammonia is given off, the barytes precipitates as carbonate, and the 
 liquor contains a new organic base, which is termed sarcosine. In this 
 re-action the ammonia and carbonic acid are products of the decompo- 
 sition of urea, which is first formed ; the hydrated kreatine C 8 H n 1^3O 6 
 separating into urea C 2 O 2 N 2 H 4 , and sarcosine, which has the formula 
 C 6 H 7 N0 4 . This body possesses distinct but feeble basic properties, it 
 forms neutral salts with acids. It is specially remarkable as isomeric 
 with urethan and with lactamide, pp. 789, 769, from which, however, 
 its properties quite separate it. 
 
 The inosinic add, is found in the sirupy liquor of the juice of flesh, 
 which had deposited the kreatine. It is thrown down by alcohol, and 
 the precipitate being redissolved in water, and decomposed by chloride 
 of barium, gives inosinate of barytes, which crystallizes in silvery scales ; 
 from it the acid is set free by any mineral acid. Its formula is 
 C, H 6 N2O IO -f HO. It is decomposed when its solution is boiled. 
 
 The inorganic ingredients in the juice of flesh consist of the chlor- 
 ides of potassium and sodium, minute traces of lime, phosphate of 
 magnesia, and what is specially characteristic, the acid phosphate of 
 potash, P0 5 -f K0.2.HO. This salt possesses the property when 
 acted on by common salt, of producing common phosphate of soda, 
 P0 5 + HO. 2 NaO, which has an alcaline reaction, and as this latter 
 compound is found abundantly in blood, Liebig has based on this re- 
 action a theory of digestion and respiration to which I shall again 
 refer. 
 
 OF THE COMPOSITION OF THE TISSUES, AND OF THE SECRE- 
 TIONS IN HEALTH AND IN DISEASE. 
 
 Having described thus the constituents of the tissues individually, I 
 shall now present such results as have been hitherto obtained as to the 
 quantitative composition of the organized tissues formed by their re- 
 union, their secretory products and morbid alterations. 
 
 Of the Skin, Epidermis, and its Modifications. The skin of animals 
 is a congeries of finely constructed organs, sensitive and secretory, im- 
 bedded in a peculiar tissue, which is one of those most easily yielding 
 64 
 
1010 Constitution of Horn and Hair. 
 
 gelatine, whence the process of tanning skins. The relative propor- 
 tions of solid and liquid matter in a skin freed from adhering fat and 
 cellular membrane, but soft and imbibed with its natural proportion of 
 water, was found by Wierihault to be 
 
 Proper cutaneous tissues including blood-vessels and nerves 32 '53 
 Albumen .... . 1*54 
 
 Extractive soluble in alcohol .... 0*83 
 
 Do. soluble only in water . . . .7*60 
 
 Water ... . 57'50 
 
 100.00 
 
 On the surface of the skin there is secreted a substance, which 
 though varying in anatomical structure and appearance exceedingly, as 
 it forms the fine epidermis, the nails, proper horn, the tortoise-shell, 
 feathers, hairs, &c., is yet, throughout all these shapes, identical in 
 chemical character, and may be described as the same substance. The 
 best example of horn is that which covers the process of the frontal 
 bone in the ox. It varies in colour, is translucent, tough and elastic. 
 When heated beyond 212 it softens without being decomposed, and 
 may then be bent, moulded, and soldered, on which properties many of 
 its uses depend. It is scarcely further acted on by water even after an 
 ebullition of several days. When treated by strong acids, horn is 
 softened and becomes soluble in water. Heated with solution of caus- 
 tic potash it evolves ammonia, dissolves, and the liquor contains sulphu- 
 ret of potassium and an organic substance, precipitable by an acid. 
 The composition of these products, or of horn itself, has not been 
 accurately examined. 
 
 The principal mass of hair is composed of the same substance as 
 horn, but the colour is due to an oil, which may be extracted by ether. 
 It is by virtue of the sulphur contained in hair, that a solution of litharge 
 in lime water blackens the hair. Nitrate of silver blackens the hair 
 also, but by the deposition of the metal. When horn or hair is 
 strongly heated they fuse, give off carbonate of ammonia, and gases of 
 a characteristic disagreeable smell ; if air be present they burn with a 
 brilliant flame. The perspiration from the surface of the skin varies in 
 nature according to the part of the body, it is generally acid, contains 
 traces of albumen, fatty matter, and the salts of the blood. It often 
 contains a volatile odorous principle characteristic of the animal by 
 which it is secreted. 
 
 Of the Cellular and Serous Tissues. These tissues are constituted 
 of gelatinous material, similar to that in the skin, and hence dissolve 
 by boiling in water, being converted into gelatine. In the natural con- 
 dition of these membranes their surfaces are moistened by a watery 
 
Nervous, Cellular and Muscular Tissues. 1011 
 
 liquid, which accumulating in excessive quantity gives rise to the drop- 
 sies of the cavities or of the cellular tissue. This serum of the cavi- 
 ties is clear and colourless. It reacts alcaline; its specific gravity, 
 I'OIO to 1'020 its composition, though liable to fluctuate, is, in gene- 
 ral, as found by Berzelius, 
 
 Albumen . . .1-66 
 
 Substance soluble in alcohol . 3*32 
 Free soda . . . 0-28 
 
 Alcaline chlorides . , ' 6-09 
 
 Earthy phosphates . . 0'09 
 
 Water . 987 '56 J 
 
 1000-00 
 
 In the serum of dropsical effusions I have found stearine, elaine, and 
 urea. This observation has also been made by Marchand. 
 
 The cells of the cellular tissue, in which fat is usually deposited, are 
 often filled up by an albuminous material, having considerable analogy 
 to caseum. It is thus that the diffused hardening of the cellular tissue, 
 and the local white tumours have their origin. Tendons, aponeuroses, 
 and fibrous membranes are similar in their chemical relations to the 
 cellular and serous tissues. 
 
 Of the Muscular Tissue. From what has been already said of 
 fibrine, it is evidently the essential element of the muscular tissue, and 
 it only remains here to give the numerical results of two analyses 
 of beef muscle, made by Berzelius and Braconnot. They found in 100 
 parts, 
 
 Muscular fibre, (with vessels and nerves) . 15'807 ig'18 
 
 Cellular tissue giving gelatine . .1 -90 3 
 
 Soluble albumen and colouring matter . 2*20 . 1 '70 
 Alcoholic extract with salts . ....,.- 1*80 . 1-94 
 
 Watery extract with salts . , . 1-05 . 015 
 
 Phosphate of lime ... ... . *"-* O' 08 
 
 Water and loss * . *_ 1 . 77'17 . 77 '03 
 
 Composition of the Brain. The most exact analyses of the brain 
 that we possess are those by Lassaigne. The differently coloured por- 
 tions differ essentially in their nature, as he found in 100 parts. 
 
 Medullary Substance. Cortical Substance. 
 
 Albumen ."'" . . . 1H> . . 7*5 
 
 Colourless fat .-. -.': .'.. ; .. 1S-9 .. .,..'. 1-0 
 
 Red fat . . . . 0* ..> 37 , 
 
 Osmazome and organic salts . . I'D 'V . . 1'4 
 
 Phosphates . "' i : . '. ' !$ v ". 1-2 
 
 Water . 73-0 85'2 
 
1012 Composition of the Brain Bones Teeth Enamel. 
 
 The nerves or spinal marrow have not been specially analyzed. 
 
 Composition of the Bones. Muller has found that prior to ossifica- 
 tion, the cartilage of the bones is in that condition which yields chon- 
 drin, although it is afterwards totally changed into the gelatine-carti- 
 lage. In the vertebrated animals, with osseous skeletons, the earthy 
 material, in all cases, consists principally of phosphate of lime with 
 some phosphate of magnesia, carbonates of lime and soda, and fluoride 
 of calcium. By digesting a bone in dilute muriatic acid, all of these 
 inorganic salts are removed, and the cartilage remains, preserving per- 
 fectly the form of the bone. By burning the bone in a moderate cur- 
 rent of air, all animal matter may be consumed, and the earthy mate- 
 rial then remains, in the form of the bone, and perfectly white; 
 100 parts of burned bone of the following animals have been found to 
 contain, 
 
 Human Bone. Beef Bone. Lion. Sheep. 
 
 Phosphate of lime and fluoride 7 g g. 4 90'70 95'0 80-0 
 
 of calcium T- "> . .3 
 
 Carbonate of lime . . 10'3 2-16 2-5 19-3 
 
 Carbonate of magnesia V, 0'3 1-10) 2 -5 Q-7 
 Carbonate of soda . V : 3'0 5'74> 
 
 But these proportions vary in the bones of different individuals of the 
 same kind of animal. 
 
 The quantity of animal matter in the bones varies in different classes 
 of animals. In the mammalia it is generally about thirty-three per 
 cent. Thus human and ox bones, deprived of their marrow and peri- 
 osteum, and dried until they ceased to lose weight, gave Berzelius : 
 
 Human Bone. Beef Bone. 
 
 Cartilage soluble in water . . 32-17? 33-30 
 
 Vessels M3> 
 
 100-0 
 
 Vessels 
 
 Phosphate of Lime and fluoride of calci um 53-04 57*45 
 
 Carbonate of Lime . . 11 "30 3 -85 
 
 Phosphate of magnesia . . 1-16 2-85 
 
 Soda and a little common salt 1-20 3'45 
 
 The teeth present, in their constitution, the closest analogy to bone. 
 The principal and organized substance of the teeth is indeed true bone, 
 containing, however, less cartilage (twenty-nine per cent.) and more 
 phosphate of lime (sixty-four per cent.) than the other bones. The 
 enamel, which is an inorganic secretion from the upper surface of the 
 bony tooth, is almost destitute of a#y animal matter, the analyses of 
 Berzelius giving: 
 
Nature of the Blood, the Bile and Lymph. 1013 
 
 Human Enamel. Beef Enamel. 
 
 Phosphate of lime and fluoride of calcium 88-5 85'0\ 
 
 Carbonate of lime . . . 8-0 7'1 
 
 Phosphate of magnesia . . 1-5 3 -0 VI 00 00 
 
 Soda , 1-4 
 
 Animal matter and water . -\ 2'0 3'5J 
 
 The proportion of fluoride of calcium is greater in enamel than in 
 common bone, and the animal membrane appears to belong only to the 
 connexion of the enamel with the subjacent bony tissue of the tooth. 
 The exterior crusta petrosa of the teeth, which exists most developed 
 in herbivorous animals, has the same composition as bone. 
 
 In the inveterate animals the internal skeleton is replaced by an ex- 
 ternal shell, which contains cartilage, with earthy salts, similar to those 
 of proper bone, but in different proportions ; the carbonate of lime pre- 
 ponderating. Thus the shells of crabs and lobsters contain from fifty 
 to sixty per cent, of carbonate, and but from three to six of phosphate 
 of lime, the rest being animal matter. Oyster shells contain but a 
 trace of animal matter, being almost pure carbonate of lime, and the 
 substance termed cuttle-fish bone, has the same composition nearly as 
 crab shells. 
 
 SECTION II. 
 
 OF THE COMPOSITION OF THE BLOOD, THE BILIARY SECRETION, 
 THE CHYLE AND LYMPH. 
 
 Blood is, in the higher classes of animals, an opaque, thick, red 
 fluid : its specific gravity about T055 ; it has a salty and nauseous 
 taste, and a peculiar smell, resembling that of the animal whence it had 
 been derived. 
 
 When the blood of any red-blooded animal is allowed to rest, it 
 gradually forms a soft jelly, from which, after some time, a thin yellow- 
 ish fluid (serum) separates, whilst the red jelly, or coagulum. contracts 
 in volume, and acquires greater consistence. If this coagulation of 
 the blood takes place slowly, the upper portion of the coagulum be- 
 comes white or pale yellow, forming thus the huffy coat. There is no 
 doubt that the blood, whilst in connexion with the animal, participates 
 in its life, and the phenomena of coagulation are to be referred 
 to a new arrangement of its materials consequent on the loss of that 
 vitality. 
 
 The serum of the blood, when coagulation has been perfect, is of a 
 yellowish, sometimes greenish colour ; its taste is dull and salty ; its 
 
1014 
 
 Blood Coagulum Serum. 
 
 specific gravity about 1<028; it is thick fluid, like olive oil; when 
 heated to 140 it coagulates. 
 
 If we examine under the microscope the appearance presented by 
 blood, we find that it consists of a great number of minute red parti- 
 cles swimming in a nearly colourless liquor. These red particles are 
 flattened disks, in man and the mammalia round, in other animals ellip- 
 tical. Their size is variable, being in man from ^Vo to Voov f an 
 inch in diameter, but larger in most other animals. In the frog they 
 are about y^o- They consist of a central colourless nodule, and an 
 investing ring, which is coloured red by a material (Hematosine ) , which 
 may be dissolved out without the constitution of the globule being 
 otherwise essentially altered. 
 
 The blood contains a large quantity of albumen, partly dissolved, and 
 remaining in the serum after coagulation ; partly in a solid state, form- 
 ing the great mass of the globules. In the living body the blood con- 
 tains also fibrine in solution, but this separates soon after extraction 
 from the body ; it assumes a solid form, and investing, as a sponge, the 
 red globules, forms with them the coagulum. The fibrine is thus the 
 element active in the coagulation of the blood, the globules being but 
 passively engaged in it. In addition to these essential organic ele- 
 ments, the bl6od contains a variety of salts, as common salt, phosphates 
 of ammonia, lime, of soda and manganese, of these the phosphate of 
 soda is the most important ; the alcalinity of the serum being now 
 supposed to depend on it, as it is very doubtful whether the blood con- 
 tains any carbonates or lactates. This question will be discussed when 
 describing the chemical phenomena of respiration. 
 
 The best analyses of the blood are those by Lecanu, and the results 
 for blood and serum are, that they contain 
 
 Blood globules 
 Fibrine 
 Albumen 
 Fatty substances 
 Extractive matters 
 Alcaline salts 
 Earthy salts 
 Water 
 Loss 
 
 Blood of Man. 
 
 Serum of Man, 
 
 13-30 
 
 
 21 
 
 
 6-51 
 
 8-12 
 
 37 
 
 34 
 
 30 
 
 46 
 
 .84 
 
 .75 
 
 21 
 
 .09 
 
 78.02 
 
 90.10 
 
 24 
 
 14 
 
 100.00 
 
 100.00 
 
 He found these proportions liable to fluctuation, and to vary accord- 
 ing to the sex. The maxima and minima of each constituent which he 
 found for the human subject of each sex were 
 
Composition of the Blood. 
 
 1015 
 
 
 Male. 
 
 Female. 
 
 c* *** 
 
 
 
 
 Max. 
 
 Min. 
 
 Max. 
 
 Mia. 
 
 Water 
 
 80-5 
 
 73-2 
 
 84-84 
 
 75-00 
 
 Albumen . 
 
 6-3 
 
 4-85 
 
 6-80 
 
 5-00 
 
 Globules . 
 
 18-6 
 
 11-05 
 
 1671 
 
 7-14 
 
 Fibrine 
 
 4 
 
 20 
 
 31 
 
 20 
 
 The fatty substance of the blood is a mixture of cholesterine with 
 stearic and oleic acids, and a peculiar fatty substance termed serolin y 
 the history of which is yet incomplete, and wliich differs from choleste- 
 rine most in containing nitrogen. None of the phosphuretted fats of 
 the brain appear to exist in blood. 
 
 The chemical history of fibrine and albumen have been already 
 given, it remains only to describe the peculiar colouring matter, for the 
 most accurate knowledge we possess concerning which, we are indebted 
 to Lecanu's elaborate researches on blood. His method of preparing 
 hematosine is as follows : 
 
 Blood, which has been freed from fibrine by beating with a twig, is 
 to be mixed, by continual agitation, with sulphuric acid diluted with 
 its own weight of water, until the whole mass solidifies to a brown pulp, 
 from which the acid liquor is to be then drained off on filtering paper, 
 and the last portion removed by washing with alcohol. The mass thus 
 obtained, which is a mixture of sulphates of albumen and of hematosine, 
 is to be boiled in successive portions of alcohol, as long as this becomes 
 brown. The liquors, being filtered when cold, are to be neutralized by 
 ammonia, by which albumen, and much sulphate of ammonia are pre- 
 cipitated, whilst a compound of hematosine and ammonia remains dis- 
 solved. This solution is to be then evaporated in a water bath to dry- 
 ness, and the residue washed with water, alcohol and ether, to remove 
 the salts and fatty matters which were contained in it. Being then 
 redissolved in alcohol by means of ammonia, evaporated to dryness, 
 and washed again with water, the hematosine remains pure, but in its 
 coagulated form. 
 
 It is a dark brown mass, tasteless and inodorous ; when heated, it 
 does not melt, but swells up and evolves ammoniacal products ; it is 
 insoluble in water, alcohol and ether ; it forms with the mineral acids 
 compounds, which are insoluble in water, but soluble in alcohol. By 
 caustic alcalies it- is dissolved with a blood-red colour, and these combi- 
 nations are soluble in water, alcohol and ether. Hematosine contains 
 neither phosphorus nor sulphur, but iron in large quantity, (6'64 per 
 cent.) By Mulder's analyses, the formula of hematosine is C44H22N 3 O G "Fe. 
 
1016 Serolin Hematosine Globuline. 
 
 It hence lias no connexion with protein or albumen. The state in 
 which the iron exists in hematosine has been, even up to the present 
 day, an object of much discussion among chemists, but with the 
 knowledge we now possess of hematosine in its pure form, we must con- 
 sider the iron to be an integral part of its organic constitution, as 
 sulphur is in albumen, or arsenic in alkarsin ; and the opinion of its 
 being oxidized, and combined with the true organic element as a kind 
 of salt, can no longer be supported. If a solution of hematosine be 
 acted on by chlorine gas, a white flocculent precipitate is produced, and 
 the solution contains chloride of iron, but if hematosine be digested 
 with strong sulphuric acid it is found that iron is dissolved out, and yet 
 the organic matter remain red-coloured. The exact nature of this iron- 
 free hematosine has not been determined, and it is most likely that a 
 change in its constitution has been effected. 
 
 Although hematosine is the colouring material of the globules of the 
 blood, it is present but in very small quantity ; 100 parts of dried 
 globules containing but from four to five of pure hematosine. In the 
 blood globule, the hematosine is in its uncoagulated state, and possesses 
 properties somewhat different from those of its coagulated form, as pre- 
 pared by the process above given. A solution of the coloured blood 
 globules in water, when exposed to the air, becomes of a bright red 
 colour, being thus partially arterialized. When evaporated at a tempe- 
 rature of 120, it gives a dark red mass which is completely soluble in 
 in cold water. Its solution coagulates at 155, leaving the liquor 
 clear yellow. It is coagulated also by alcohol and by acids. The 
 hematosine then passes into the insoluble condition already described. 
 
 I have hitherto spoken of the colourless ingredient in the blood 
 globules as being albumen, with which indeed it is almost identical in 
 properties, but still differs in some points. It has been termed globulin. 
 In its uncoagulated condition it cannot be separated from hematosine, 
 and is there distinguished from albumen principally, by being insoluble 
 even in a very dilute saline solution, which dissolves albumen readily. 
 It is hence that the globules swim unaltered in the serum of the blood, 
 but are readily dissolved by pure water. On this principle is founded 
 a method of isolating the blood globules. If the blood, when extracted 
 from the vein, be received in a vessel containing a solution of glauber's 
 salt, coagulation is prevented as the fibrine remains dissolved, and by 
 filtering the liquor so obtained the serum and water pass off, and the 
 globules remain mixed only with a little of the salt. The globulin can- 
 not, however, be separated from the hematosine, except by acids, 
 which, as described in the preparation of hematosine, then combine 
 with the globuline. Mulder found the organic element in the sulphate 
 of globuline, to have the composition of protein (see p. 1001), 
 
Alterations of the Blood in Disease. 1017 
 
 Alteration of the Blood in Disease. The examination of the state 
 of the blood in disease, although presenting important relations to 
 pathology and to practice, has been hitherto conducted in a manner too 
 disconnected and superficial to afford satisfactory results. This branch 
 of chemical pathology has, however, been taken up by the illustrious 
 Andral, who, in conjunction with Gavaret and Rodier, has published the 
 results of the analysis of the blood in numerous cases of disease, in 
 memoirs, from whose publication may be dated the commencement of a 
 true pathology of this fluid. 
 
 In the method which, by the advice of Dumas, they adopted, the 
 quantity of fibrine, of globules, of the solid materials of the serum, 
 (which may be considered as albumen,) and the quantity of water, in 
 each specimen of blood, were determined. The pure hematosine was 
 not isolated, and the salts were considered as sufficiently important to 
 necessitate their separation, only in certain cases. For point of com- 
 parison they assume as the standard of healthy blood, that 1000 parts 
 contain 790 of water, 127 of globules, three of fibrine, and eighty of solid 
 constituents of the serum, of wliich eight are inorganic ; which num- 
 bers almost coincide with Lecanu's analysis, as already given. Their 
 researches have enabled them to recognize four classes of disease, in 
 wliich the composition of the blood is essentially altered, though in 
 different ways. 
 
 The first class presents as a constant alteration, an increase in the 
 quantity of fibrine ; it includes diseases remarkably different in their 
 locality and form, but all belong to the class of acute inflammations. 
 In some cases of morbid deposition, as in tubercle and cancer, a similar 
 increase in the quantity of fibrine is found, but it may be doubted 
 whether it be due to the abnormal growth, or to the inflammatory 
 action which accompanies it. 
 
 In the second class, the fibrine remains stationary, or even diminishes 
 in quantity, whilst the globules increase in proportion to the fibrine. 
 The diseases which belong to this class are continued fevers without 
 local infiamrnation, and some form of cerebral ham&rrhagies. The 
 increase in quantity of globules, though exceedingly frequent, is not 
 so universal, as that the fibrine does not increase, which was invariably 
 found. 
 
 In the third class, the fibrine remaining unchanged, there is a re- 
 markable diminution in tlie quantity of the globules ; of these diseases 
 chlorosis may be taken as the example ; and in the fourth class, it is no 
 longer the fibrine or globules, which are the subject of the morbid 
 change, but the quantity of albumen in the serum is diminished. Of this 
 class of affections, Bright' s disease is the type. 
 
1018 
 
 Observations on Andral and Gavaret. 
 
 Without entering into the details of these researches, which are ex- 
 cluded by the limited extent of this work, I shall merely present in the 
 following table an example of the constitution of blood in each of these 
 classes of morbid alteration. 
 
 Constituents. 
 
 Health. 
 
 1st Class. 
 
 2ndClass. 
 
 3rdClass. 
 
 4thClass. 
 
 Fibrine 
 
 3 
 
 7 
 
 2 
 
 3 
 
 3 
 
 Globules 
 
 127 
 
 125 
 
 136 
 
 47 
 
 82 
 
 Albumen 
 
 72 
 
 78 
 
 69 
 
 75 
 
 58 
 
 Salts 
 
 8 
 
 7 
 
 7 
 
 8 
 
 7 
 
 Water 
 
 790 
 
 783 
 
 786 
 
 867 
 
 850 
 
 The appearance of albumen in the urine in Bright' s disease is evi- 
 dently connected with its diminution in the serum. The oily materials 
 which are usually found in the blood, and the remarkable diminution 
 which occurs, not so much in the globules as in the hematosine, had 
 not attracted AndraTs attention in the memoirs now described. These 
 oily substances are of the same nature as the proper fatty matters of 
 the blood, but present in excessive quantity. 
 
 It has been observed, that in cholera the blood becomes so thick as 
 to arrest the circulation, and contains from thirty to forty-live per cent, 
 of solid matter; it is then also less strongly alcaline than healthy 
 blood. This is connected probably with the matters vomited and 
 evacuated, which are strongly alcaline, and contain a quantity of 
 albumen. 
 
 The blood has been found occasionally, in cases of diabetes mellitus, 
 to contain traces of sugar ; the great discordance of the results obtained 
 may, perhaps, result from the sugar being contained in the blood only 
 for a short time after meals, and then being rapidly evacuated by the 
 kidneys. In jaundice the green colouring matter of the bile has been 
 observed in the serum of the blood. Other observations of morbid 
 constituents of the blood are too indefinite to justify me in occupying 
 space with them. The observations of Barruel, that by heating the 
 blood of any animal with a little oil of vitriol, the odour of the animal 
 is so powerfully evolved as to be easily recognized; appears well 
 founded, and may be useful in medico-legal questions, where, however, 
 it should be employed with exceeding circumspection. 
 
 Composition of the Bile Choleic and Cholic Acids Products of their 
 
 Although the precise part which this remarkable secretion performs 
 in the animal economy is not yet fully known, it has been the subject 
 
Composition of the Bile. 1U19 
 
 of repeated and accurate chemical examination, although from the 
 facility with which its elements are transformed into other bodies, by 
 the action of the re-agents employed, every succeeding analysis has led 
 to different results. I shall only notice the researches of Gmelin, 
 X)emar9ay, Berzelius, and Strecker. 
 
 In the elaborate work on digestion, undertaken in conjunction with 
 Tiedemann, Gmelin analyzed principally the bile of the ox, from which, 
 however, as far as observations have been made, human bile does not 
 appear essentially to differ. He obtained from it a volatile body having 
 the odour of musk, cholesterine, margaric and oleic acids, a peculiar 
 acid, the cliolic acid ; colouring matters, liliary resin, biliary sugar, 
 taurine, a glutinous substance, caseum, salivary matter, ozmazome, and 
 a number of salts of organic or inorganic acids. Demar^ay looked 
 upon all these substances as being produced by the reactions used, and 
 denies that any of them really exist in the bile. He considered the 
 bile to be a soda-soap of a peculiar fatty acid, the cJiole'lc add, that is, 
 a choleate of soda. The choleic acid is obtained by dissolving one part 
 of the alcoholic extract of ox-gall in 100 parts of water, and mixing 
 the solution with two parts of sulphuric acid diluted with ten of water. 
 By gradual evaporation of the liquor, oily drops separate. It is to be 
 then cooled, and these drops, which are common fat, removed. On 
 then standing for eight or ten hours, the choleic acid gradually sepa- 
 rates, and being digested with ether, to remove some adhering fat, is 
 pure. It is a brittle yellowish white mass, tastes bitter, softens by a heat 
 of 250, but does not really melt; it is slightly soluble in water, but 
 abundantly in alcohol and ether. It forms, with bases, salts which do 
 not crystallize. 
 
 When the alcoholic extract of the gall is boiled for a long time in 
 contact with an excess of muriatic acid, the choleic acid is decomposed, 
 and the most remarkable products are the taurine of Gmelin, and a 
 new acid, the choloidic acid. The latter is a fatty acid, not volatile, 
 yellow, of a bitter taste ; it forms a soft mass with warm water, but 
 without dissolving; it dissolves readily in alcohol and ether, and these 
 solutions redden litmus. 
 
 If the bile be treated with an excess of a strong alcali. the choleic 
 acid is totally broken up into ammonia, and an acid termed by Dema^ay, 
 ckolic acid. It crystallizes from its hot aqueous solution in delicate 
 silky needles, of a brilliant white colour ; its taste is at once acid and 
 sweet ; by heat it is melted and decomposed ; it is very slightly soluble 
 in water, but copiously in alcohol; its solutions redden litmus; it 
 contains no azote. This body is now termed, Cholalic acid. 
 
 Dema^ay's examination of the bile appears thus quite satisfactory 
 
1020 Berzelius' Analysis of the Bile. 
 
 in showing that the cholic acid, and the taurine are secondary products, 
 and he considered the other substances found by Gmelin to be choleic 
 or choloidic acids in an impure form. But Berzelius, who had been 
 occupied in the je-examination of the subject, has asserted that the 
 choleic acid of Demargay is really the body which is impure, being a 
 mixture of the true biliary substance (bilin, Gmelin' s biliary sugar) 
 with the biliary resins. He found that when the alcoholic extract of 
 the bile is mixed with sulphuric acid, no precipitate appears for a con- 
 siderable time, showing that the substance, which really exists in the 
 bile, combined with soda, is completely soluble in water, and it is only 
 by its gradual change that the precipitate (choleic acid) occurs. By 
 digesting this substance with ether, he removed from it a resin which, 
 by possessing acid properties, and by means of combination with 
 barytes, is shown to be a mixture of two distinct acid resins, fellic 
 acid and cholinic acid. The material insoluble in ether, is the true 
 dilin ; it is not acid, of a bitter taste, soluble in alcohol and water in 
 all proportions, but insoluble in ether ; when heated, it becomes soft, 
 and burns like a resin ; its watery solution is rapidly decomposed, espe- 
 cially if warmed ; by contact with acids or alkalies, it is immediately 
 changed in constitution : the substances produced are different accord- 
 ing as the degree of alteration is more or less advanced. 
 
 The biliary matter, which is the state in which the greater part of 
 tbe bilin exists in ordinary bile, being the first product of its decompo- 
 sition, is a white bitter substance which has a marked acid reaction, 
 and is decomposed by oxide of lead into bilin and bilifellic acid, 
 which is the choleic acid of Deraargay. The formation of taurine is 
 accompanied by that of another body dyslysin, which is a colourless 
 resinous substance, very sparingly soluble in water. The fellinic and 
 cholinic acid, have been noticed above. 
 
 According to Berzelius, when the bile has been kept for a long time, 
 it is decomposed by a kind of fermentation, and two acids formed, 
 termed the fellanic and cholanic acids, they are wh its earthy powders, 
 sparingly soluble in water; the former melts only far above 212; the 
 latter is very easily fusible. 
 
 The researches by Berzelius had appeared to receive their full confir- 
 mation from the experiments of Mulder, when the subject was again 
 examined by Strecker, whose results are probably the most satisfactory as 
 to the real nature of this secretion. He considers with Demar^ay, that 
 the bile is of simple constitution, the great number of products obtained 
 by Gmelin and Berzelius being products of decomposition, but on the 
 other hand he does not consider the bile to be merely choleate of soda, 
 but to contain two acids, the choleic acid, which is rich both in sulphur 
 
Strccktfs Analysis of the Bile. 1021 
 
 and in nitrogen, and the true cholic acid which contains nitrogen but 
 no sulphur. These bodies are in the bile combined with soda, and from 
 their decomposition all the other bodies are derived. 
 
 The true cholic acid is identical with the body described by Gmelin 
 under that name. It is prepared by precipitating purified bile with 
 sulphuric acid and treating the precipitate with ether. The cholie acid 
 forms a mass of very minute crystalline needles arranged in stellated 
 clusters. It is slightly soluble in water, very much so in alcohol. It 
 reacts acid. Its formula is C 52 H4 3 NO 1 2. It appears to exist in some 
 isomeric form producing paracholic acid. Its internal constitution ap- 
 pears to be very remarkable, under the influence of strong alcalies or 
 acids, it is broken up into another acid, and the glycocoll already des- 
 cribed as obtained from gelatine. The acid so formed is termed by 
 Strecker, cholalic acid, but it appears to be identical with the cholic 
 acid of Demarcay, which latter name should be abandoned. Hence we 
 may explain the decomposition as 
 
 Cholic Acid. Glycocoll. Cholalic Acid. 
 
 The properties of the cholalic acid have been already noticed 
 sufficiently. 
 
 The cholate of soda crystallizes in square prisms, and it can be ob- 
 tained from bile directly by mixing an alcoholic solution of bile with a 
 quantity of ether, a crystalline deposit gradually forms which is cholate 
 of soda, and indicates the natural existence in the bile of that 
 material. 
 
 The choleic acid is admitted by Strecker to have the properties des- 
 cribed by Demarcay, and already noticed. Its composition is remarka- 
 ble as it contains sulphur, and is the origin of the taurine. The 
 formula of the choleic acid is C 5 2H4 5 NO I4 S 2 , and under the influence 
 of strong acids or bases it separates into cholalic acid and taurine. 
 
 Choleic Acid. Taurine. Cholalic Acid. 
 
 C 5 2H 4 5NOl4S2. = C4H 5 NO 4 S 2 . + C48H40O10. 
 
 In this combination two atoms of water which taurine usually con- 
 tains, are supposed evolved, as took place also with the glycocoll referred 
 to as produced from cholic acid. 
 
 By the prolonged action of muriatic acid, cholalic acid is converted 
 into the choloidic acid already described, and which has the formula 
 C4 8 H39O 9 , water being separated, and by still more prolonged action 
 the dyslysin of BerzeKus is generated, which is a resinous body having 
 the formula C^HgeOg, more water being removed. 
 
1022 Taurine Carlothialdine. 
 
 Taurine. Formula, C 4 H 7 NO 6 S 2 . 
 
 This body the origin of which as a product of the decomposition of 
 choleic acid, has been already noticed, deserves special notice from its 
 remarkable properties. It may be prepared either by boiling bile for a 
 long time with muriatic acid, or by mixing bile with some yeast, and 
 allowing it to ferment and putrify. In either case the taurine can be 
 crystallized from the liquors. It forms six-sided prisms which are per- 
 fectly neutral. It dissolves readily in water, but very sparingly in alco- 
 hol. It is scarcely acted on even by the strongest acids, and its solu- 
 tion is not acted on by any re-agent. It contains all the sulphur and 
 nitrogen of the choleic acid from which it was formed. When tau- 
 rine is heated with a strong solution of caustic potash, ammonia is 
 evolved, and a saline mass obtained, from which a strong acid expells 
 sulphurous acid and acetic acid. The acetic acid is here a product of 
 oxidation, but Eedtenbacher has shown that the sulphur must exist in 
 taurine as sulphurous acid, the rational constitution being 
 
 Two atoms sulphurous acid, 6482. 
 
 One atom hydrated aldehyd, C4H4O2. 
 One atom ammonia, 
 
 Taurine, C4H7NOGS2- 
 
 Eedtenbacher therefore considers taurine to be bisulphite of aldehyd 
 ammoniac, analogous to the cyanate of aldehyd ammonia, described in 
 p. 796, but as the taurine exists in the choleic acid with the elements 
 of two atoms of water less, the organic constituent is evidently amid- 
 acetyl, thus 
 
 Taurine. Amid Acetyl. Sulphurous Acid. 
 
 C 4 H 5 NO 4 S 2 + 2HO = C 4 H 3 .Ad + 2SO 2 + 2. HO. 
 
 To verify this idea of the constitution of taurine, Eedtenbacher 
 passed sulphurous acid gas into an alcoholic solution of aldehyd- 
 ammonia ; a white crystalline body formed, a true bisulphite of the base, 
 isomeric with taurine, but by no means identical with it. Similarly on 
 adding bisulphuret of carbon to an alcoholic solution of aldehyd am- 
 monia, a crystalline body forms, carlotliialdine having the formula 
 C 5 H 5 NS 2 , which is an organic alcaloid, forming well denned salts. All 
 these bodies belong evidently to the family which include the thialdine 
 and selenaldine noticed in p. 796. 
 
 The colouring matter of the bile is present during health in but small 
 quantity, but in disease it sometimes accumulates so as to produce solid 
 
Colouring Matters of the Bile. 1023 
 
 masses. When pure it is a reddish yellow powder, which is scarcely 
 soluble in water or in alcohol, but dissolves easily in solution of caustic 
 potash. This solution is of a clear yellow colour, but when exposed to 
 the air it becomes deep green, absorbing oxygen. This change is re- 
 markably produced by nitric acid, and it is indeed the reaction by which 
 the presence of the bile in the serum of the blood, in the urine, in the 
 skin and eyes, &c., may be shown in case of jaundice. If too much 
 nitric acid be not added at once, the yellow liquor becomes at first 
 green, then blue, violet and finally red, all these changes occurring in a 
 few seconds. After a moment the red colour also disappears, the solu- 
 tion becomes yellow, and the colouring matter is found to be totally 
 decomposed. The solution of the colouring matter in potash is precipi- 
 tated by muriatic acid in deep green flocculi, which dissolve in nitric 
 acid with the effect already noticed, and are soluble in caustic ammonia 
 and potash, with a rich emerald green colour. These reactions show, 
 that by a process of oxidizement from the original yellow substance, 
 green and red materials may be generated, in which forms the colouring 
 matter exists naturally in various animals, according as their bile is 
 yellow, green or reddish, and also gives rise to the concretions of 
 various kinds that are deposited in disease. The most common kind of 
 gall-stone consists however, of cholesterine. 
 
 The bile contains generally about nine per cent, of solid matter, 
 but in the present state of our knowledge of its constituents, it is 
 evidently impossible to assign the numerical proportions in which they 
 exist. 
 
 The examination of the further products of digestion involves con- 
 siderations too purely physiological to be entered into. 
 
 Chyle and Lymph. 
 
 The nutritive material extracted from the food by the absorbing 
 Vessels of the intestine is thrown into the thoracic duct, where it meets 
 with another fluid, which is transmitted to the same vessel from all 
 parts of the body by the colourless veins, or lymphatics. The fluid 
 from the intestines is termed chyle, that from the body generally, is 
 termed lymph. It is the mixture of these that alone has been exam- 
 ined, for the vessels which carry either separately are too minute to 
 allow of the extraction of their contents in a pure form. 
 
 When taken from the thoracic duct a few hours after a meal, when, 
 probably; the chylous element prevails, it is a whitish opaque liquid 
 like milk, with generally a reddish shade ; a short time after sepa- 
 ration from the body it coagulates ; the clot is at first pale, but it soon 
 
1024 Nature of Chyle and Lymph. 
 
 becomes light cinnabar red ; the milkiness of the serum is due to the 
 presence of oil ; it contains albumen, and coagulates by heat. Except 
 that it is more dilute, and that the hematosine is for the most part ab- 
 sent, (not yet formed), the chyle and lymph have the same composition 
 as the blood. It appears to vary, however, with the nature of the 
 food, as Dr. Prout found the chyle of dogs fed on vegetables to con- 
 tain a much smaller quantity of albumen that when they had had ani- 
 mal food. Dr. Prout also indicates in chyle the existence of a sub- 
 ject which he terms incipient albumen, which is not coagulated by heat, 
 except after the addition of acetic acid. The properties of this form 
 of albumen, however, are not fully known. The results of three analy- 
 ses of chyle are here given ; that by Berzelius was the chyle of a horse, 
 killed some time after having fed abundantly with oats ; and of those 
 by Dr. Prout, No. 1 was from a dog, supported on vegetable, and No. 
 2, of a dog supported on animal food. 100 parts contained 
 
 Berzelius. Prout, No. 1. No. 2. 
 
 Dry Clot . . . 0'78 Fibrine . . 0'6 0'8 
 
 Albumen . . . 4-49 Incipient Albumen 4'6 4*7 
 
 Fatty matters . . 1 '67 Albumen . . 0'4 4'6 
 
 Extractive Matters and) . 1<44 Oil and Sugar . trace trace 
 
 Salts . . 3 Salts . .0-8 0'7 
 
 Water . 91-62 Water . . 93-6 8'92 
 
 SECTION III. 
 
 CHEMICAL PHENOMENA OF THE PROCESSES OF RESPIRATION AND 
 
 DIGESTION. 
 
 Phenomena of Respiration. 
 
 In the living body the blood in the veins and arteries is well 
 known to differ remarkably in colour, in the former being of a 
 dark purple red, and in the latter of a bright vermilion colour. 
 The change from the venous to the arterial state, is effected during 
 the passage of the blood through the capillary vessels of the lungs, 
 where it is exposed to the action of an extensive surface of atmos- 
 pheric air, whilst the arterial blood, in traversing the general capil- 
 lary system of the body, assumes the dark red condition in which 
 it is returned to the heart by the veins. Even out of the body, this 
 change of colour is produced when venous blood is exposed to the air, 
 especially if agitated therewith, and still more with pure oxygen ; even 
 
Phenomena of Respiration. 1025 
 
 the globules, when separated from the serum, and dissolved in water, 
 become brighter in colour, and partially arterialized by exposure to the 
 air. Yet, although the vital properties of the blood depend essentially 
 upon this change of colour, we are not yet able to connect it with any 
 alteration in the composition of the constituents of the blood, or even 
 in their relative proportions. Arterial and venous blood contain sensi- 
 bly the same quantity of water, fibrine, globules, albumen and salts, 
 and by analysis the composition of these bodies is found to be identical, 
 no matter what kind of blood they are derived from. To trace the 
 difference of nature between arterial and venous blood, it is therefore 
 necessary to study it under other points of view than its proximate or 
 elementary composition, so far as we have yet examined it. 
 
 The air which has been employed in respiration, is found to have 
 undergone an important change of constitution; its volume is but 
 slightly, if at all altered, but a quantity of oxygen has disappeared, and 
 is replaced by carbonic acid, in generally an equal volume. Air, which 
 has been once respired, is found to contain from three to four per cent, 
 of carbonic acid; and if the same quantity of air be continually 
 breathed, the animal dies with all symptoms of narcotic poisoning, 
 when the carbonic acid has accumulated to from eight to ten per cent. 
 The action of the air in expiration is therefore to remove carbon from 
 the blood. The quantity so taken from the system in twenty-four hours, 
 is very large, and makes up theprincipal portion of that element which 
 we take in with our food ; yet, such is the activity with which its assimi- 
 lation proceeds, that no perceptible change in the solid elements of the 
 blood can be detected. 
 
 It was at one time a much-disputed point, whether the carbon so 
 separated from the system was directly secreted from the lungs, and 
 burned off, as it were, by contact with the oxygen of the air ; or whether 
 the oxygen was first absorbed by the blood, and carried by the circula- 
 tion to every portion of the body, where it combined with the carbon, 
 which was there present in excess, and the carbonic acid so produced, 
 being dissolved by the venous blood, was thrown off on arriving at the 
 surface of the atmosphere, in the lungs. The progress of science has, 
 however, finally decided in favour of the latter view, to which the 
 fullest confirmation has been given by the careful and elaborate experi- 
 ments of Magnus. He found that both arterial and venous blood hold 
 dissolved quantities of gases, oxygen, nitrogen, and carbonic acid, 
 wliich amount to from one-tenth to one-twentieth of the volume of the 
 blood. The proportions of these gases to each other are different in 
 arterial and venous blood ; the oxygen in arterial blood being about 
 one-half of the carbonic acid, whilst in the venous blood it seldom 
 65 %'" 
 
1026 Theory of Respiration. 
 
 amounts to more than one-fifth. The difference is greatest in young 
 animals, and probably is proportional to their activity of nutrition. 
 The quantity of nitrogen appears to be the same in both kinds of 
 blood, making from one-fifth to one-tenth of the gaseous mixture. 
 
 The physico-chemical conditions of respiration are simply explicable 
 upon these results. By the principle of gaseous diffusion, (p. 365), 
 the fine lining pulmonary membrane being permeable to gases, when the 
 venous blood arrives at the surface of the lungs, a portion of the car- 
 bonic acid which it contains is evolved, and a quantity of oxygen gas 
 absorbed in place of it. These two quantities are not necessarily equal 
 at each moment, though, ultimately, they become so, and hence the 
 volume of oxygen absorbed is generally, though not universally, equal 
 to that of the carbonic acid given eut. There appears, from the pre- 
 sence of nitrogen in equal quantity in both kinds of blood, to be an 
 absorption and evolution of that gas, simply from physical laws, and 
 independent of any direct application of it to the nutrition of the 
 animal ; hence the volume of nitrogen in air is sometimes increased, 
 and at others diminished by respiration, and an animal evolves much 
 nitrogen when respiring an artificial atmosphere of oxygen and hydro- 
 gen, whilst Boussingault has shown the rate of nutrition of an animal 
 to be proportional to the quantity of nitrogen it receives as food, and 
 that none of that principle is really assimilated from the air. 
 
 It is still not by any means easy to decide upon the cause of the 
 change of colour which occurs in the blood during respiration ; for this 
 .should appear connected, not merely with the presence of certain gases 
 in the blood, but upon a true change in the constitution of the hema- 
 tosine, which analysis cannot direct. Stevens first directed attention to 
 the remarkable influence which saline bodies have upon the colour of 
 the blood. If dark venous blood be put in contact with a solution of 
 common salt, Glauber's salt, nitre, or carbonate of soda, it becomes as 
 vermilion-coloured as if it had been truly arterialized. On the contrary, 
 the presence of carbonic acid impedes this action, and gives to blood, 
 so reddened by a salt not in excess, the dark tint of venous blood. If 
 we consider, therefore, the arterial tint to be due to the natural combi- 
 nation of the colouring matter with the saline constituents of the serum, 
 this will be darkened when, by passing through the capillary system, 
 the blood takes up an excess of carbonic acid ; and again, in the lungs, 
 when the carbonic acid is replaced by oxygen, the vermilion colour is 
 restored, not by any active agency of the oxygen, but by the natural 
 tint of saline-hematosine becoming evident. Although this theory 
 of the change of colour is by no means free from objections, it 
 appears to me to be better founded than any other that has been 
 proposed. 
 
Sources of Animal Heat. 1027 
 
 The relation of the saline constituents of the blood to the processes 
 of respiration and digestion, has been very beautifully shown by Liebig, 
 in his late researches on the chemistry of food. He has demonstrated 
 that the blood contains no potash salts, nor any alcaline carbonate, but 
 that the alcaline reaction of the serum of the blood is due to the pre- 
 sence of the tribasic phosphate of soda, with two atoms of fixed 
 base, HO. 2NaO + PO 5 , a salt which absorbs carbonic acid with 
 great force, but under the agency of diminished pressure, or by ex- 
 posure to air, gives up again totally the carbonic acid it had ab- 
 sorbed. Now as the juice of flesh reacts distinctly acid from the 
 presence of the acid tribasic phosphate of potash, it becomes evident 
 that the instinct which compels animals to seek for common salt either 
 as a constituent or as a condiment to their food, is to convert by double 
 decomposition the acid phosphate of potash of the flesh into the alcaline 
 phosphate of soda, which passing into the blood takes up the carbonic 
 acid formed by the wearing out of the organic tissues, and conveys 
 that gas to the pulmonary surface, where it is diffused into the mass of 
 the inspired air, and is given out. The chloride of potassium produced 
 at the same time is taken into the excreted liquids, and together with 
 other constituents of the juice of flesh, as kreatine, may be detected 
 abundantly in the urine. 
 
 Animal Heat. The phenomena of respiration consisting mainly in 
 the conversion of carbon into carbonic acid by union with oxygen, the 
 source of the heat which is developed in the body of all red-blooded 
 animals has been naturally referred to that source ; and as we know- 
 that the change from the arterial to the venous condition of the blood 
 occurs at every point of the system, the almost complete equality of 
 temperature throughout the body in health is explained. That the 
 great source of heat is the respiratory process, is abundantly proved by 
 the temperature being highest in those animals, and in the same animal 
 at those periods, when the circulation is most rapid and the quantity of 
 air consumed the greatest, but it has been calculated that the heat 
 evolved by the combustion of the quantity of carbon thrown off from the 
 body in twenty-four hours, is not more than eight-tenths of the quantity 
 generated in the bodpr during that time, and the origin of the remainder 
 must be found in the action of the muscles and in the nervous power, 
 which appears of itself to be a distinct source of animal heat. 
 
1028 Mucus Gastric Juice. 
 
 Chemical Phenomena of Digestion. 
 
 The lining membrane of the alimentary canal is moistened with a 
 liquid possessing many characters of the vegetable mucus, (tragacan- 
 thine, p. 761), but containing nitrogen. It is a thick tenacious sub- 
 stance, which contains, dissolved in the water through which it is 
 diffused, the ordinary salts of the serum of the blood ; it swells up with 
 water to a considerable mass, but without dissolving ; it dissolves in 
 alcaline liquors, and is precipitated therefrom on the addition of an 
 acid and by tincture of galls ; the mucus from different parts of the 
 mucous membrane is, however, by no means identical in properties. 
 
 The liquid secreted by the internal surface of the stomach, the 
 gastric-juice, which exercises an important influence on digestion, differs 
 essentially in its characters from mucus. When the stomach is empty 
 and contracted, it contains only ordinary mucus, but if even indigestible 
 substances be introduced, and still more after taking proper food, a 
 liquid is abundantly poured out, which is colourless or very pale yellow, 
 and contains a very small quantity of solid matter, (two per cent.), 
 which consists principally of inorganic salts, (common salt and sal- 
 ammoniac, with a trace of a salt of iron) ; it is especially characterized 
 by the presence of a notable quantity of free muriatic acid, the pro- 
 portions of which appear to vary with the activity of the digestive 
 powers at the time. This gastric juice possesses the remarkable 
 property of softening down and dissolving fibrine and albumen, and 
 thus converts the masses of food into the uniform pulp, (chyme) } from 
 which the absorbing vessels of the small intestines take up the nutritious 
 elements. 
 
 If we form an artificial gastric juice by mixing together the muriatic 
 acid and salts in the proper proportions, it is found to be totally in- 
 capable of dissolving the materials of the food, and indeed, to be quite 
 inactive towards digestion. The organic material of the gastric juice, 
 although its quantity be so minute, is therefore essential to its powers, 
 and these may be perfectly conferred upon the previously inactive arti- 
 ficial juice, by the addition of a little of the mucus of the stomach, or 
 by steeping in the acid liquor, for a short time, a small portion of a 
 mucous membrane, and filtering the liquor. For this purpose it is not 
 even necessary to use the mucous membrane of the stomach, for that of 
 the bladder has been found to act equally well. The substance which 
 is dissolved out of the membrane in these cases has been termed pep- 
 sine. It has not been obtained in a truly isolated or pure form, but its 
 properties are very remarkable. For its full activity it requires the 
 presence of a free acid, as the artificial gastric juice becomes much less 
 
Pepdne Saliva. 1029 
 
 active in dissolving food, when neutralized by an alcali, though it 
 retains other properties, as that of coagulating milk like rennet. If 
 the artificial gastric juice be precipitated by acetate of lead, the precipi- 
 tate washed and then decomposed by sulphuret of hydrogen, the solu- 
 tion thus obtained possesses all the digestive powers of the juice. Hence 
 the pepsine and muriatic act together in combining with oxide of lead. 
 The process given by Schwacn for preparing the best artificial gastric 
 juice, is to mix water with 2| per cent, of muriatic acid, of specific 
 gravity 1'13, and digest therein the mucous membrane of a stomach for 
 twenty-four hours, then to filter. 
 
 Pepsine appears to be completely decomposed by contact with alco- 
 hol, or by the heat of boiling water. Its powers are destroyed also by 
 deoxidizing substances. The solution of albumen and fibrine in gas- 
 tric juice is essentially different from their solution in muriatic acid, as 
 in the former case the quantity of acid is very minute in relation to the 
 quantity of material dissolved, and after solution the acid still remains 
 quite uncombined. 
 
 Fremy has discovered that the peculiar fermentative process, which 
 sometime spoils the manufacture of sugar, and which I have described, 
 (p. 768), as the mucous fermentation, is capable of being induced by 
 contact with mucous membrane, (by pepsine?). He has found that 
 sugar of milk may thus be converted to an unlimited extent into 
 lactic acid; no other product appearing. The vegetable ferments 
 are able to produce the same effect, but in a different stage of de- 
 composition from that in which they induce the saccharine or alcoholic 
 fermentations. 
 
 The action of the stomach in digestion appears, therefore, to be, so 
 far as our actual knowledge extends, a purely catalytic fermentative 
 action; one in which the active excitant is an organic substance 
 (pejisinej secreted by the mucous surface, and whose properties are 
 developed by the presence of muriatic acid, which is secreted at the 
 same time. The new products into which the food, fibrine, albumen, 
 gluten, starch, oils, sugar, &c., are converted, and which collectively 
 constitute the white uniform pulp, termed by physiologists, chyme, 
 have not been made the subject of accurate chemical research. 
 
 In the mouth the mass of nutritive material is acted on by a liquid 
 which is secreted by the salivary glands, the saliva. It is alcaline, and 
 holds in solution about one per cent, of solid matter, which contains 
 some carbonate of soda, and common salt, admixed mucus, a trace of 
 sulpho-cyanide of potassium, and a peculiar organic body termed by 
 Tiedemann and Gmelin, salivary matter. This last substance is soluble 
 in water ; its solution is not coagulated by heat, nor precipitated by 
 
1030 
 
 Composition of Urine. 
 
 tincture of galls, corrosive sublimate, acetate of lead, nor by acids. 
 The pancreas, though so similar in structure to the salivary glands, has 
 a different secretion ; it contains no salivary matter, nor any sulpho- 
 cyanide of potassium, but albumen and some salts; it is generally 
 slightly acid. 
 
 SECTION IV. 
 
 CONSTITUTION OF THE URINE IN HEALTH AND DISEASE. 
 
 The nature of this secretion has at all periods been an object of 
 considerable interest to the physician and to the chemist, from the 
 indications which changes in its composition give of disease of impor- 
 tant organs, and from the number and interest of the organic sub- 
 stances it contains. As in almost all other branches of animal chem- 
 istry, Berzelius first determined accurately its constitution, and lately 
 Lecanu has ascertained with great care the limits to which the propor- 
 tions of its ingredients may vary in health, and thus established 
 a correct basis of comparison for urine in the various conditions of 
 disease. 
 
 The specific gravity of urine varies from 1016 to 1030. In general, 
 if the excretion exceeds in quantity thirty-two ounces in twenty-four 
 hours the specific gravity falls proportionally below ] 030 ; but if the 
 quantity be under thirty-two ounces, the specific gravity for a man in 
 active health is generally 1030, but less for women. The important 
 organic constituents of the urine are urea and uric acid, which will 
 require a detailed and special examination ; the other principles, though 
 numerous, being of less moment, need be only noticed in the following 
 statement of Berzelius's general analysis of the urine. He found 100 
 parts to contain : 
 
 Water . , 933-001 
 
 Urea ...... 30-10 
 
 Free lactic acid, lactate of ammonia, and animal extract 17*14 
 
 Uric acid . . . . . . . 1 -00 
 
 Mucus of the bladder ..... 0*32 
 
 Sulphates of potash and soda . .... .,, . . 6*87 100 "00 
 
 Phosphates of soda and ammonia . . . 4 '59 
 
 Common Salt . . . . . ' : . 4-45 
 
 Sal-ammoniac . .' " ''*''' '*?. /" . '.' 1-50 
 
 Phosphates of lime and magnesia .. ,. > .-.., ...... ' 1*00 
 
 Silica ,_-. r ;.. ,, . . \. , ; v . o-03 
 
Salts of Urea Uric Acid. 1031 
 
 Urea. N 2 C 2 2 H 4 or Ur. Eq. 60, or 750. 
 
 The chemical history and modes of preparation of this interesting 
 substance have been already fully described, page 732 et seq. and 
 it is hence only here necessary to mention its physiological relations. 
 
 The quantity of urea secreted in health appears pretty regular in the 
 same individual, when the diet remains the same, and not to depend 
 upon the quantity of liquor excreted. It varies, however, very much 
 in different individuals, and is much more abundant in men in active 
 age, than in women or in old men. Thus, Lecanu found the quantity 
 of urea secreted in twenty-four hours, by men in the prime of age, to 
 vary from 350 to 500 grains; in women, it varies from 150 to 430 
 grains; whilst with old men the limits were 80 and 180 grains. In 
 children the quantity is still smaller, and infants secrete scarcely a trace 
 of urea. 
 
 Uric Acid and ike Bodies derived from it. 
 
 The uric acid exists in the urine of all carnivorous animals. In 
 birds, reptiles, and many insects, it is voided with the excrements, and 
 the urine is in such a state of concentration as to form a white mass 
 nearly solid, which consists almost totally of urate of ammonia. In 
 the small islands of the South Sea, which are inhabited by great 
 flocks of aquatic birds, it accumulates in such quantity as to be an 
 article of commerce, being brought to South America, and even to 
 Europe, under the name of guano, and used as manure. In many 
 diseases it is generated by the system in abnormal quantity, and consti- 
 tutes, free or combined with bases, the gouty and arthritic concretions, 
 and many forms of vesical calculus. 
 
 For the purposes of the chemist the uric acid is most easily obtained 
 from the white solid excrements of the larger serpents in the mena- 
 geries. This is to be boiled in a solution of caustic potash, and the 
 filtered liquor decomposed by the addition of muriatic acid in excess. 
 The precipitate should be boiled in water for some time, then well 
 washed and dried. It crystallizes in minute brilliant white scales, 
 which are very slightly soluble in boiling water ; the solution reddens 
 litmus ; it is tasteless ; it dissolves in oil of vitriol, forming a crystal- 
 lizable compound, which is decomposed on the addition of water : the 
 action of nitric acid is different. When heated, it is decomposed, 
 giving a great variety of products, urea, hydrocyanic and cyanuric acids, 
 carbonate of ammonia &c. Its formula is NAoH^Og; its salts are 
 not well characterized ; those of the alcalies are very sparingly soluble, 
 
1032 Uric AcidAllanto'in. 
 
 and are decomposed by all acids except the carbonic acid. The urate 
 of ammonia is the material of the white excrement (dry urine) of birds 
 and serpents. The urate of soda is the principal material of gouty 
 deposits. The uric acid is specially interesting for the number of im- 
 portant bodies to which it gives origin by the action of re-agents, and of 
 which some are also products of the organization ; for our accurate 
 knowledge of these we are indebted to the recent investigations of Liebig 
 and Wohler. 
 
 Allantoin. This substance exists in the waters of the allantois of 
 the cow, being contained in the urine of the foetus, from which it may 
 be extracted by evaporation and crystallization. It is, however, much 
 more easily formed from uric acid. Freshly prepared peroxide of lead 
 is to be added to uric acid, diffused through twenty parts of boiling 
 water, as long as its colour is destroyed. The boiling liquor is to be 
 filtered, evaporated till crystals begin to form, and then allowed to cool. 
 The allantoin crystallizes, and the mother liquor contains abundance of 
 urea. At the same time, oxalate of the protoxide of lead is produced. 
 2(JV 4 Ci H 4 O 6 ) and 5 HO with 4.Pb0 2 , producing 4 (C 2 O 3 + PbO) ; 
 with urea, 2(N 2 C 2 H 4 O 2 ), and allantoin, N 4 C 8 H 5 5 . On this reaction 
 Liebig founds a theory of the constitution of uric acid, to which I shall 
 have occasion again to recur. He considers it to contain urea ready 
 formed, and a hypothetic substance for which he proposes the names of 
 uril or cyanoxalic acid, it being oxalic acid in which oxygen is replaced 
 by cyanogen, C 2 O 2 + Cy. Thus, uric acid, N 4 C 10 H 4 O 6 = N 2 C 2 H A + 
 2(C 2 02.Cy). In forming allantoin on this view, the urea is set free, 
 and the cyanoxalic acid with oxygen and water, gives oxalic acid and 
 allantoin. 
 
 Allantoin forms rhombic prisms, which contain an atom of water. 
 It is sparingly soluble in water, and perfectly neutral. By boiling with 
 a strong alcali, it combines with the elements of water, giving oxalic 
 acid and ammonia. It does not form a definite compound with any 
 base but oxide of silver. 
 
 Alloxan. The products of the action of nitric acid on uric acid, 
 present considerable interest, from their number and connexion. On 
 adding one part of uric acid gradually to four parts of strong nitric 
 acid, it is dissolved with much heat, and copious disengagement of car- 
 bonic acid and nitrogen. The rise of temperature being prevented as 
 much as possible, the liquor solidifies on cooling to a mass of granular 
 crystals, which are to be drained and then recrystallized from the smallest 
 possible quantity of boiling water. This is alloxan, its crystals are 
 short right rhombic prisms, brilliant and colourless. In dry air they 
 effloresce, losing 6Aq. ; at a higher temperature, it crystallizes in oblique 
 
Bodies Derived from Alloxan. 1033 
 
 rhombic prisms, which are anhydrous, and have the formula 
 its solution in water reddens litmus, and stains the skin purple ; when 
 neutralized by an alcali, it strikes an indigo-blue colour with a proto- 
 salt of iron ; it is decomposed by almost all re-agents, producing a series 
 of bodies that will be successively examined ; its origin consists probably 
 in the uryl being oxidized by oxygen from the nitric acid, leaving hypo- 
 nitrous acid, which, reacting on the urea, gives the mixture of carbonic 
 acid and nitrogen gases. The alloxan may thus be considered as a hy- 
 drated deutoxide of uryl. 
 
 Alloxanic Acid is formed by acting on alloxan with strong alcalies, 
 or by barytes ; when separated from its combinations by a stronger acid, 
 it crystallizes in colourless needles, which have a strong acid reaction ; 
 its alcaline salts are soluble ; those with the earths and heavy metallic 
 oxides sparingly soluble; it is insoluble in water; its formula is 
 N 2 C 8 H 2 8 when dry; the alloxan having lost the elements of two 
 atoms of water. When a solution of alloxanate of barytes is boiled, 
 or when a solution of alloxan is gradually added to a boiling solution 
 of sugar of lead, another acid is formed, mesoxalic acid, which in the 
 latter case precipitates as an insoluble salt of lead, and the liquor con- 
 tains urea, the alloxan breaking up into N 2 C 2 H 4 O 2 and 2.C 3 O 4 ; this last 
 is the constitution of the mesoxalic acid, which has probably therefore 
 an isomeric oxide of carbon (C 3 O 3 ) for its base, and belongs to the 
 same group as the mellitic and rhodizonic acids (p. 702.) By oxi- 
 dizing agents the mesoxalic acid is converted into carbonic acid ; thus 
 with a solution of nitrate of silver, it gives a clear yellow precipitate, 
 which, when boiled, is converted into carbonic acid and metallic 
 silver. 
 
 Mycomelinic Acid. If a solution of alloxan in water of ammonia 
 be heated, a brownish-yellow precipitate falls, which is mycomelinate of 
 ammonia, by boiling which, or by washing with dilute sulphuric acid, 
 the ammonia is removed, and the rmycomeliuic acid remains as a yellow 
 jelly, which dries to a coarse yellow powder. It is sparingly soluble 
 in water ; its salts are gelatinous, sparingly soluble flocks ; the 
 formula of the acid is N 4 C 8 H 5 O 5 , being isomeric with anhydrous 
 allantoin. 
 
 Parabanic Acid. If alloxan be heated with an excess of nitric acid, 
 it dissolves, nitrogen gas is evolved and on cooling the new acid sepa- 
 rates ; it is also easily procured from uric acid by using an excess of 
 nitric acid ; it forms colourless, transparent, six-sided prisms, and tastes 
 like oxalic acid. It is partly volatilized and partly decomposed by heat. 
 If the crystals be heated to 212 they assume a reddish colour; the 
 formula of the crystallized acid is N 2 C 6 O 4 -f 2Aq. hence alloxan with 
 
1034 Oxaluric Acid Thionuric Acid. 
 
 2.0 produces 2.C0 2 , with 4.HO and N 2 C 6 O 4 . By contact with bases, 
 this acid is decomposed, producing the oxaluric acid. This is best 
 prepared by dissolving parabanic acid in caustic ammonia, boiling, and 
 then letting the liquor cool; it forms a mass of small brilliant white crystals 
 of oxalurate of ammonia. The oxaluric acid is also a product of 
 other reactions on uric acid, some of which will be specially noticed 
 hereafter. It is a strong acid, and is obtained free, by dissolving its 
 ammonia salt in boiling water, adding an excess of dilute muriatic acid, 
 and rapidly cooling, when the oxaluric acid separates, as a white or 
 slightly yellow powder ; if long boiled in water, it is decomposed into 
 oxalic acid and oxalate of urea, of which it contains the elements, its 
 formula being C 2 N 6 H 3 7 -f- Aq. 
 
 Thionuric Acid. If sulphurous acid gas be passed through a satu- 
 rated solution of alloxan until the liquor begins to smell strongly of the 
 gas, and then ammonia be added in excess, after some time brilliant 
 white rhombic tables form, which are thionurate of ammonia. By 
 recrystallization, this salt generally becomes pale rose-red, but is not 
 altered in constitution. To obtain the acid free, a solution of this 
 ammonia salt is to be precipitated by acetate of lead, and the thionurate 
 of lead decomposed by sulphuretted hydrogen. By evaporation of the 
 liquor, the acid remains as a white semi-crystalline mass ; it is easily 
 soluble in water, reddens litmus strongly ; its formula is N3C 8 H 7 14 S2 : 
 it contains thus the elements of one atom of alloxan, one of ammonia 
 and two of sulphurous acid ; it is a bibasic acid. If a strong solution 
 of thionuric acid be boiled, it becomes turbid, and soon solidifies to a 
 mass of brilliant silky crystals, whilst the liquor contains much sulphuric 
 acid; the crystalline substance being drained and washed with cold 
 water, in which it scarcely dissolves, is termed uramil ; it is white, 
 soluble in dilute alcaline liquors, and precipitated therefrom unchanged 
 by the addition of an acid, but by strong alcalies it is decomposed, 
 ammonia being evolved and uramilic acid formed. The formula of 
 uramil is N 3 C 8 H 5 O 6 ; the thionuric acid might be considered as bi-sul- 
 phate of uramil. The uramilic acid is formed by the action of acids 
 and alcalies on uramil, it crystallizes in colourless needles, which dissolve 
 in acids and alcalies, forming with the latter, well defined salts; its 
 formula is N 5 C 16 H 10 15 . 
 
 Alloxantine. This substance is formed as a product of the moderate 
 oxidation of uric acid, or it may be obtained by acting on alloxan with 
 deoxidizing agents. Uric acid is to be diffused through boiling water, 
 and dilute nitric acid added until a perfect solution is obtained. On 
 filtering and cooling, the alloxantine gradually crystallizes. The mother 
 liquor contains much urea. If sulphuretted hydrogen gas has been 
 
Alloxantine Dialuric Add. 1035 
 
 passed through a solution of alloxan, sulphur is deposited, and alloxan- 
 tine formed, and the same effect is produced by acidulating the solution 
 of alloxan, and immersing therein a slip of zinc ; the alloxan is deoxi- 
 dized by the nascent hydrogen. By the galvanic battery, alloxan is 
 resolved into oxygen and alloxantine. It is sparingly soluble in cold, 
 but much more in boiling water, and crystallizes in short oblique rhom- 
 bic prisms, which contain 3Aq., which they lose only by a heat above 
 300. The solution of alloxantine reddens litmus but does not form 
 salts with bases, being immediately decomposed by contact with them. 
 Its formula is N. 2 C 8 H 5 O 10 . 
 
 By oxidizing bodies, as nitric acid, chlorine or oxide of silver, it is 
 immediately converted into alloxan. If treated by an excess of sulphu- 
 retted hydrogen, more sulphur is set free, and the liquor becomes 
 strongly acid. The body thus formed, if mixed with alloxan, regene- 
 rates alloxantine from both. If neutralized by carbonate of ammonia, 
 a white crystalline precipitate forms, which is a salt of ammonia, of 
 which the formula is N 3 C 8 H 7 O 8 . Liebig considers it to contain a body 
 which he terms the dialuric acid, the formula of which is N 2 C 8 O4, being 
 isomeric with the cyanoxalic acid or uryl, already noticed. The 
 dialurate of ammonia is therefore N 2 C 8 4 -f- NH 4 -f. 3Aq. It may 
 be produced by adding hydrosulphuret of ammonia to a saturated solu- 
 tion of uric acid in dilute nitric acid, or by acting on alloxan with zinc 
 and muriatic acid in excess. Though white when first produced, it 
 becomes rose-red by drying, and at 212 blood-red, and loses ammonia. 
 It is by no means established that this body is a true ammoniacal 
 salt, as described by Liebig, or that the dialuric acid really exists. 
 Berzelius looks upon it as a compound of alloxantine and alloxantine- 
 amide. 
 
 By boiling with sal-ammoniac, alloxantine is converted into urarail 
 and alloxan, whilst muriatic acid becomes free. By the action of oxy- 
 gen upon an ammoniacal solution of alloxautine, uramil, oxaluric acid, 
 and mycomelinic acid are generated. 
 
 Murexid. This remarkable substance may be produced by a variety 
 of reactions, none of which are, however, quite constant in their result. 
 On evaporating a solution of uric acid in very dilute nitric acid, until 
 the liquor becomes flesh red, and then adding dilute water of ammonia 
 in slight excess, and cooling, the murexid crystallizes. In this process, 
 a very slight excess or deficiency of any of the ingredients prevents 
 success, and Gregory proposes as the most certain method, to dissolve 
 four parts of alloxantine, and seven of hydrated alloxan, in 240 parts 
 of boiling water, and eighty of solution of carbonate of ammonia, 
 when the murexid crystallizes by gradual cooling. By the action of 
 
1036 Murexid Mitrexan. 
 
 uramil and ammonia it may also be generated, and is the ordinary 
 source of the purple colours that are produced in many of the reac- 
 tions already described. 
 
 The murexid, the name of which is derived from the murex, the 
 shell fish furnishing the tyrian purple, crystallizes in short rhombic 
 prisms, of a garnet-red colour, and by reflected light have a green 
 metallic lustre. It dissolves sparingly in cold, copiously in boiling 
 water : it is insoluble in ether and alcohol. Gregory has found, 
 that it is sometimes soluble, and at others insoluble in water of 
 ammonia, whence he suggests that two different bodies have been 
 confounded under this name. It dissolves in caustic potash, with 
 an indigo-blue colour which disappears by heat, ammonia being 
 evolved ; it does not appear to combine with bases ; its formula 
 is N 5 Ci 2 H 6 O 8 . By the mineral acids and by sulphuretted hydrogen 
 it is decomposed, ammonia, alloxantine, alloxan, and dialuric acid 
 being evolved, besides another body termed murexan. This sub- 
 stance is more abundantly produced by dissolving murexid in a boiling 
 solution of potash, and when the blue colour has totally disappeared, 
 adding sulphuric acid in excess. It precipitates in white silky crystal- 
 line scales ; its formula is N 2 C 6 H 4 O 5 ; it dissolves in caustic alcalies 
 without neutralizing them. If its solution in ammonia be exposed to 
 the air, oxygen is absorbed and murexid regenerated. 
 
 The murexid was long since described by Prout under the name of 
 purpurate of ammonia ; and Fritzsche has revived the idea that it is 
 really an ammoniacal salt of a distinct acid, purpuric add. By the 
 double decomposition of murexid with salts of potash, barytes, lead 
 and silver, he has obtained purpurates of these bases, the formula of 
 which shows the acid to be composed of N 5 C 16 H 4 10 . The murexid 
 is, according to this chemist, composed of N 6 C l6 H 8 O n = N 5 C 16 H 4 10 -f- 
 NH 4 0. The evidence brought forward by Eritzsche against Liebig's 
 view is very strong. 
 
 Urine of Herbivorous Animals Hippuric Acid = C 18 H 8 N0 5 + Aq. 
 
 In the urine of herbivorous animals, and occasionally of children, 
 the uric .acid is replaced by a different body, the Jiippuric acid, which 
 exists therein combined with soda. The urine of horses and cows is 
 to be evaporated to one-eighth of its volume, and mixed with muriatic 
 acid, which produces, after some time, a yellowish crystalline precipi- 
 tate. This is to be dissolved by boiling with some lime ; chloride of 
 lime is to be added to the liquor, until it is nearly decolorized, and the 
 smell of urine has disappeared ; being then digested with ivory black 
 and filtered, the pure acid is separated by muriatic acid. By the cool- 
 
Guano Guanine. 1037 
 
 ing of the liquor it crystallizes in delicate silky needles, or rhombic 
 prisms ; its taste is very slightly bitter, but it reddens litmus strongly. 
 When heated, it melts and is then decomposed, giving a crystalline 
 sublimate of benzoic acid with ammonia and prussic acid. It is very 
 sparingly soluble in cold, but copiously in boiling water : very soluble 
 in alcohol. By nitric acid, and other oxidizing agents, it is decom- 
 posed and benzoic acid is formed. Its salts are all soluble and crys- 
 tallize ; they resemble the benzoates exactly. The formula of the crys- 
 tallized acid is NC 18 H 8 5 + Aq. 
 
 It has been already noticed, p. 1005, that this acid is decomposed byre- 
 agents into benzoic acid and glycocoll; Ci 8 H 9 N0 6 producingC 14 H 5 O 3 and 
 C 4 H 4 N03. This reaction is prevented by the presence of a feeble base, 
 and hence the quantity of hippuric acid obtained from cow's urine is 
 very much increased by adding milk of lime during the evaporation, 
 so as to preserve constantly an alcaline reaction in the liquor. 
 
 Guano Guanine. 
 
 It has been already mentioned, that the urine of birds and reptiles 
 being voided in a highly concentrated form, furnishes the most available 
 source of uric acid from its concreting into masses of urate of ammonia. 
 The deposits of sea birds accumulating for ages on the Islands of the 
 Southern Ocean, and on the Coasts of Peru, in those latitudes where 
 there falls but little rain, have recently afforded a most valuable source 
 of manure for agricultural purposes, under the name of Guano. 
 
 The Guano properly speaking is but the dried urine and excrement of 
 the sea fowl, but as it is practically mixed with the remains of the 
 animals themselves and of their food and eggs, it presents a mass of 
 very complex and very variable composition, but always, when not adul- 
 terated, very rich in nitrogen, partly as uric acid and partly as am- 
 monia ; also rich in phosphate of lime, and even of magnesia and pot- 
 ash, and smaller quantities of other ingredients, which add to its value 
 as a manure. The various deposits of it which had been discovered, 
 have been already to a great extent exhausted by the enormous demand 
 created for it by the necessities of agriculture in these countries ; and 
 it will be the office of the chemist to imitate the natural guano by 
 proper admixtures of other materials, derived from the sources of ani- 
 mal excretions which are now rejected as waste, and which injure the 
 sanitary condition of our ill-drained and imperfectly cleansed towns, 
 in place of restoring to the country, the fertility which the constant 
 removal of food crops must tend gradually to deteriorate. 
 
 The spontaneous decomposition of the uric acid of the guano, has 
 
1038 Urine in Disease. 
 
 been found to produce some interesting bodies. Thus guano is found 
 to contain a large quantity of oxalate of ammonia. It also contains a 
 peculiar body termed guanine. This material is a white crystalline 
 powder ; its formula is C 10 H 5 N 2 5 . It is an organic base, but its salts 
 are very peculiar, thus it forms with nitric acid, no less than five ni- 
 trates. It forms also two muriates. If guanine be powerfully oxi- 
 dized as by treatment with chlorate of potash and muriatic acid, it pro- 
 duces a body in brilliant crystals, sparingly soluble in water and acids, 
 this is the liyperuric add. Its formula is stated to be C 10 lNr 4 H3O 7 + 
 2 Aq. but its history and composition requires to be more exactly 
 studied. 
 
 Of the Urine in Disease Urinary Calculi. 
 
 To the pathologist and physician the indications of disease of the 
 urinary and digestive organs, furnished by changes in the composition 
 of the urine, are most valuable. The majority of the substances which 
 are taken into the circulation, but are incapable of assimilation to our 
 organs, are thrown off by this secretion and hence a variety of medi- 
 cinal substances may be traced to it after having been ingested, some- 
 times quite unaltered, at others modified in their nature. Thus, if 
 alcaline salts of organic acids be taken into the stomach, the organic 
 material is oxidized, probably during the action of respiration, whilst 
 the alcali passes into the urine in the state of carbonate. If, however, 
 the organic acid be taken uncombined, it escapes decomposition, and 
 passing into the urine, produces an abundant precipitate of salts of 
 lime, in the case of the tartaric and oxalic acids. 
 
 Iodide of potassium and iodine pass into the urine, the latter as 
 hydriodic acid. Some organic bodies, as asparagine and oil of turpen- 
 tine, are decomposed, and the products which they form are excreted, 
 giving to the urine peculiar odours, in the latter case like that of vio- 
 lets. Nitrate of potash, yellow prussiate of potash, and most other 
 alcaline and earthy salts pass into the urine unchanged. The majority 
 of colouring matters are thrown out of the system by means of this 
 secretion, whilst others, as cocchineal and litmus, are not so given oft'. 
 
 The mineral acids, alcohol, camphor, most metallic salts, do not pass 
 into the urine in any sensible degree. 
 
 Urine in Diabetes. The most remarkable change in the nature of 
 the urine, occurs in diabetes mellitus. It is voided in great quantity. 
 Its specific gravity is very high, from ] 030 to 1050, and it is found to 
 contain a very large quantity of grape sugar, and very little urea. It 
 was supposed that in this disease, urea ceased to be formed by the sys- 
 
Urine in Disease. 1039 
 
 tern, and was replaced by sugar ; but I have shown, that although the 
 quantity of urea is very small in any one specimen of the urine, yet, 
 the total quantity of that liquid is so much increased, that in twenty-four 
 hours the natural quantity of urea is secreted ; the secretion of sugar 
 being an act of faulty digestion, and totally unconnected with the urea. 
 These results have been fully confirmed by Macgregor. The diabetic 
 urine sometimes contains albumen, which arises from complication of 
 other forms of disease. 
 
 As the average composition of urine in diabetes, the following may 
 be taken, from an analysis by myself. Its specific gravity was 1*0363, it 
 contained in 1000 parts, water 913, sugar 60, urea 6*5, salts, ex- 
 tractive matters, and uric acid 20*5. This patient made in volume 
 about four times the healthy quantity of urine, in twenty-four hours. 
 
 Urine in Dropsies. In those diseases, particularly where associated 
 with disease of the kidneys, the urine is not increased in quantity ; its 
 specific gravity is very low, 1005 to 1015, and it contains but very 
 little urea, but generally albumen, and sometimes caseum. In these 
 cases, the urea which is deficient in the urine is found in the serum of 
 the blood, and in the dropsical effusions. In some states of the sys- 
 tem, which do not appear connected with any distinct disease, milk 
 passes into the urine, in which as well the butter as the caseum may be 
 detected. Such cases have even been met with in males. In jaundice 
 the colouring material of the bile passes abundantly into the urine, and 
 may be detected by nitric acid. The natural elements of the urine are, 
 however, not altered in quantity. 
 
 Slue and Black Urine. The urine has been observed coloured deeply 
 blue by a peculiar organic substance, which, however, has not been accu- 
 rately examined. Braconnot found it contained nitrogen, and was red- 
 dened by acids, and the colour restored by alcalies. But Spangeuberg 
 found, in the case he observed, that acids dissolved the blue sub- 
 stance without changing its colour. Marcet observed in the urine 
 of a child, a black matter insoluble in water, but soluble in alcalies. 
 Prout, who also observed this substance, termed it melanic acid. 
 
 In many states of the system, particularly in arthritic rheumatism, 
 there is a great tendency to the formation of uric acid, and the urate 
 of ammonia is deposited under the form of a crystalline precipitate, 
 when the urine cools. It is usually mixed with more or less of a yel- 
 lowish-red body, which is not purpurate of ammonia, (murexid), as 
 Prout supposed, but a peculiar organic substance, soluble in alcohol, 
 which deserves more minute examination. The deposition of this 
 excess of matter, in the joints and sheaths of the tendons, pro- 
 duces the gouty concretions, which consist for the most part of urate 
 of soda. 
 
1040 Urinary Calculi. 
 
 In other conditions of the system, the formation of phosphatic salts 
 predominates, and precipitates occur in the urine, which are generally 
 more crystalline, and less highly coloured, than those of uric acid, or of 
 urates. As these different conditions of the secreting organs require 
 different modes of treatment, it is necessary to be able simply to 
 distinguish between these two kinds of sediment. It is sufficient 
 to remark, that the uric acid deposit is soluble in alcalies, and inso- 
 luble in dilute acids, whilst the phosphatic sediments dissolve in 
 dilute acids, but not in alcaline liquors, even though decomposed by 
 them. 
 
 The uric acid, and the inorganic salts of the urine, are afterwards de- 
 posited in the bladder, and form urinary calculi. 
 
 The Uric Acid Calculus is probably the most common. It is re- 
 cognized by being decomposed by heat ; being soluble in caustic alca- 
 lies, and precipitated by acids. When dissolved in nitric acid, evapo- 
 rated and moistened with water of ammonia, it gives the rich purple 
 colour of murexid. 
 
 The Urate of Ammonia Calculus, in addition to the character of 
 uric acid, gives off ammonia, when dissolved in solutions of caustic 
 potash. 
 
 The Phosphate of Lime Calculus fuses with difficulty, or not at all, 
 before the blowpipe. It is dissolved by muriatic acid, and precipi- 
 tated by caustic ammonia from this solution, as a white powder not 
 crystalline. 
 
 The Ammoniaco-magnesian Phosphate Calculus, is generally crys- 
 talline in structure ; before the blowpipe, it gives off ammonia, and 
 ultimately melts, though with difficulty. It also gives off ammonia, 
 when boiled with caustic potash. It dissolves in dilute acids, and 
 is precipitated as a crystalline powder, on the addition of caustic am- 
 monia. 
 
 The two latter calculi often form together, and produce the triple 
 phosphate or fusible calculus. This melts readily before the blowpipe, 
 and if dissolved in a dilute acid, it gives with oxalic acid a precipitate 
 of oxalate of lime, and then with an alcali, a crystalline deposit of am- 
 moniaco-magnesian phosphate. 
 
 All of these various deposits may occur in the bladder, either suc- 
 cessively, and form the alternating calculus, or together, forming the 
 mixed calculus. The recognition of these species will depend on the 
 careful application of the methods by which each component may be 
 known, as already described. 
 
 It is not very unfrequent to meet with calculi formed of materials 
 which do not exist in healthy urine, but are produced by the decompo- 
 
Cystic Oxide Xantkic Oxide. 1041 
 
 sition of its natural constituents. . Thus the mulberry calculus, so called 
 from its usual external form, consists of oxalate of lime. When igni- 
 ted it leaves caustic lime, which browns wet turmeric paper strongly, 
 dissolves in muriatic acid, and is precipitated by adding oxalate of am- 
 monia. Calculi have been found also, though rarely, consisting of car- 
 bonate of lime, and of carbonate of magnesia. 
 
 The most remarkable calculi of this class, however, are those formed 
 of the cystic oxide, and xanthic oxide ; substances of purely organic 
 nature. The latter body is yellow, soluble in alcalies, and is precipi- 
 tated by the addition of an acid. It dissolves in nitric and sulphuric 
 acids, but not in muriatic or oxalic acids. Its formula is N 4 Ci H4O 4 . 
 It contains, therefore, the same carbon, nitrogen, and hydrogen, as 
 uric acid, but less oxygen, whence the name uric oxide has been pro- 
 posed for it. The cystic oxide calculus consists of small yellow crys- 
 talline plates, which dissolve in alcalies, and crystallize out again, on the 
 addition of an acid, by an excess of which the cystic oxide is, however, 
 redissolved. When heated strongly it is decomposed, evolving sulphu- 
 rous acid and ammonia. It forms definite salts with the nitric and 
 muriatic acids. Its formula is NC 6 H 6 O 4 S 2 . 
 
 When blood is effused into the bladder, the fibrine is occasionally 
 aggregated as a calculus, the recognition of which is very simple, from 
 what has been said of the properties of fibrine, (p. 997). 
 
 Those who would wish for more detailed information of the proper- 
 ties of calculi, and of the composition of the urine in health and dis- 
 ease, I would refer to the truly classical work of Doctor Prout, on the 
 Diseases of the Stomach and Urinary Organs. 
 
 SECTION Y. 
 
 OF THE MILK, AND OTHER NATURAL AND MORBID PRODUCTS NOT 
 INCLUDED IN THE PRECEDING SECTIONS. 
 
 Some f the most remarkable constituents of milk have been already 
 described as lactic acid, (p. 768) ; the sugar of milk, (p. 766) ; the 
 butter fats, (p. 885.) It only remains to notice the general compo- 
 sition of milk, and the properties of the caseum or curd. It is well 
 known that, by standing, milk abandons the greater part of its butter, 
 which separates, with other substances, as cream. Berzelius found the 
 cream from cows' milk, to have specific gravity T0244, and to consist, 
 in lOO'O parts, of 4'5 of butter, separated by agitation, 3*5 of caseum, 
 with some butter, separated by coagulation, and 92 of whey. The 
 66 
 
1042 
 
 Composition of Milk Caseine. 
 
 skimmed milk had a specific gravity of T0348, and contained in lOO'O 
 parts : 
 
 Caseous matter with some butter 
 Sugar of milk .... 
 
 Alcoholic extract with lactic acid 
 Chloride of potassium 
 Alcaline phosphates ,. . ' , 
 Earthy phosphates and a trace of iron 
 Water 
 
 2-6001 
 3-500 
 0-600 
 0-170f 
 0*025 
 0-230 I 
 92-875J 
 
 100-000 
 
 The following table presents the best results that have been as yet 
 obtained on the average composition of the milk of different animals : 
 
 
 Human. 
 
 Mares. 
 
 Asses. 
 
 Cows. 
 
 Sheep. 
 
 Dogs. 
 
 Specific Gravity 
 
 1-0323 
 
 1-0395 
 
 1-0322 
 
 1 -0320 
 
 1-0380 
 
 
 Water . >. .:; 
 Extractive 
 
 88-36 
 1-24 
 
 88-68 
 
 90-47 
 
 85-91 
 
 53-2 
 
 (Cream 
 
 65-74 
 2-90 
 
 Casein . jf^< 
 Butter 
 Sugar 
 Ashes 
 
 340 
 2-53 
 4-25 
 0-22 
 
 1-82 
 0-75 
 
 8-75 
 
 1-95 
 1-29 
 6-29 
 
 7-00 
 3.93 
 
 287 
 0-29 
 
 11-5) 
 15-3 
 5-8 
 4-2 
 
 17-40 
 16-20 
 
 (Salts 
 1.50) 
 
 The butter of human milk is more solid than that of the cow, and 
 appears to contain no butyrine. 
 
 Caserne Leucine Tyrosine. 
 
 The caseum or caserne is capable of existing in a soluble and an in- 
 soluble condition like albumen. In milk it is principally dissolved, but a 
 part is insoluble, and united with the butter, produces the emulsive appear- 
 ance of the milk. On adding sulphuric acid to skimmed milk, the 
 caseine precipitates combined with the acid, as a white coagulum, which 
 being washed with water, so as to remove all adhering milk, and then 
 digested with carbonate of barytes, the caseine dissolves in the water, and 
 may by nitration be freed from all traces of the butter, sulphuric acid, 
 or barytes. The caseine may also be precipitated by alcohol, and when 
 the curd is digested with ether to remove ah 1 traces of butter, it may be 
 looked upon as pure. 
 
 The solution of caseine in water is thick, like mucilage ; it smells as 
 boiled milk, and dries down to an amber-coloured mass, which is again 
 soluble in water. The solution is coagulated by all acids, even acetic 
 acid, particularly when hot, and by alcohol. In relation to acids, caseine 
 is similar to albumen, except that as to acetic acid ; the constitution of 
 its precipitates being precisely similar. 
 
Leucine Tyrosine Eggs. 1043 
 
 The coagulated condition of casein is not produced by boiling, but 
 only by the digestive principle (rennet, pepsine), as already described 
 (p. 1029). When thus coagulated, casein is absolutely undistinguished 
 from coagulated albumen in its properties. It contains a considerable 
 quantity of bone-earth, (phosphate of lime,) amounting to five or six 
 per cent, in intimate combination. Its organic element was found by 
 Mulder to be protein, of which ten atoms are combined with one of 
 sulphur; the formula of caseine being C^oH^oNgoO^o 4- S. It contains 
 no phosphorus, but to each atom so expressed, two atoms of bibasic 
 phosphate of lime are united. 
 
 When coagulated casein, containing water, (cheese,) is kept for a 
 long time, it undergoes a remarkable kind of decomposition, and a sub- 
 stance, crystallizable and soluble in water, is obtained, termed by Bra- 
 connot aposepedine. By Mulder's experiments it appears, however, to 
 be impure leucine (p. 1005,) and the caseous oxide and caseic acid of 
 Prout appear also to be the same bodies as have been already noticed 
 as formed from the decomposition of the other protein substances. 
 
 By contact with casein, sugar of milk is rapidly converted into lactic 
 acid, which precipitates the caseine without, however, really coagulating 
 it, hence on neutralizing the acid, the caseine redissolves and may 
 react on a new quantity of sugar. In this manner Fremy has shown 
 that the lactic fermentation may be carried on to an indefinite extent. 
 
 It has lately been suspected that caseine is not itself a homogenous 
 body but a mixture of at least two closely resembling azotized sub- 
 stances. Thus, if freshly precipitated caseine be dissolved in water the 
 liquor yields by the addition, first of carbonate of ammonia and then 
 of muriatic acid, precipitates, which essentially differ in their composition 
 and properties. If caseine be fused with caustic potash it evolves 
 hydrogen and ammonia gases, and the residue dissolved in water yields, 
 on the addition of acetic acid, an organic body crystallizing in brilliant 
 needles, which is termed tyrosine. This body has the formula Cj 6 H 9 NO 5 . 
 It forms compounds as well with acids as with bases, but has been little 
 examined. From the mother liquor of the tyrosine there is deposited, 
 by evaporation, abundance of the leucine^ which has been already des- 
 cribed in page 1005. 
 
 Constitution of Eggs. 
 
 The shell of liens' eggs consists of from 90 to 95 per cent, of car- 
 bonate of lime, one to five of phosphate of lime, and two to five of 
 animal matter. Internally it is lined by a membrane analogous to epi- 
 dermis. The white of egg is a concentrated solution of albumen, con- 
 
1 OM Amnios Allantois Eye Cerumen. 
 
 tained in the cells of a delicate membrane, in the centre of which the 
 yolk is suspended. The nutritive material of the yolk consists of albu- 
 men and an oil, also a yellow colouring matter, analogous to that of 
 bile. The oil of eggs is obtained by expressing the egg boiled, and 
 partly torrefied ; it is reddish-yellow, thick, and solidified by cold ; it 
 soon becomes rancid ; the solid portion of it appears to be cholesterine; 
 the liquid contains phosphorus and nitrogen, and is with difficulty sapo- 
 nifiable. It appears to contain a large quantity of oleophosphoric acid. 
 When the young animal is developed during incubation, the quantity 
 of phosphoric acid in its bones is exactly represented by the quantity of 
 phosphorus in the yolk and white, but as these bodies contain very little 
 lime, that earth must be derived from the shell, which becomes thin and 
 brittle as the animal advances in growth. 
 
 Liquor of the Amnios. This fluid, in which the fetus is immersed 
 before birth, appears to be identical in constitution with the liquor 
 effused from the serous surfaces in dropsy, (p. 1011). The liquor of 
 the allanto'is of the cow, which is really the urine of the fetus, is of 
 the same nature, but contains in addition a small quantity of allantoin, 
 the artificial formation of which is described p. 1032. 
 
 Black Pigment of the Eye. This substance is insoluble in water and 
 alcohol. It is decomposed by strong acids and alcalies. Caustic potash 
 dissolves it, forming a yellow liquor, from which acids throw down a 
 clear brown powder. The action of nitric acid is nearly the same. 
 The cuttle-fish ink has much analogy with the black matter of the eye, 
 giving, when dried, a black powder, insoluble in water, alcohol and 
 ether, which dissolves in nitric acid and potash, with a reddish-yellow 
 colour, from which solution a yellowish powder falls when it is neutral- 
 ized. The true nature of these black colouring matters, and their 
 relation to the melanic acid of Prout, which sometimes appears in the 
 urine, would deserve attentive study. 
 
 The Humours of the Eye consist of water, holding in solution albu- 
 men in small quantity, with the salts which usually accompany it. The 
 crystalline lens consist of albumen, in a state of beautiful and complex 
 organization, amounting to about thirty-eight per cent, of the entire 
 mass, which contains about sixty of water. 
 
 Cerumen Wax of the Ear. This substance contains an albuminous 
 material insoluble in water, a solid and a liquid fat soluble in ether, and 
 a deep yellow matter, soluble in alcohol, and insoluble in ether, to 
 which its colour and very disgusting taste is due ; another constituent 
 which appears to be peculiar to this secretion is brown, insoluble in 
 caustic potash ; it most resembles horn in its properties, but is still 
 quite distinct from that body. 
 
GallStones Lithqfelic Acid Pus Ambergris. 1045 
 
 Pus. This remarkable morbid secretion has generally a specific 
 gravity of 1-030. It consists of a clear liquor, in which float a great 
 number of yellow globules, of various sizes, the largest of which are 
 about twice the size of the globules of the blood. Pus loses by drying 
 86 '1 of water in 100 parts, and hence contains 13' 9 of solid material, 
 from which alcohol takes 5'9 of fatty and extractive matters, and leaves 
 7 '4 per cent, of a residue, which consists of coagulated albumen, the 
 solid globules and a substance peculiar to pus. 
 
 The globules of pus appear to consist of coagulated albumen. The 
 serum contains two liquids, both coagulated by heat. One is albumen, 
 the other pyin, which is characterized by being coagulated both by heat, 
 by acetic acid, and by a solution of alum. Giiterbach who has recently 
 examined pus with great care, finds the only certain distinction between 
 pus and mucus to be that the pus globules sink always in water, whilst 
 the mucus swims. If the suspected liquid be dried, the extraction of 
 the fatty substance by ether should decide very positively. 
 
 Ambergrue. This substance, which is generally found floating on 
 the sea- coasts of tropical islands, is known to be an intestinal concretion 
 of the spermaceti whale, analogous to the gall-stones of cholesterine in 
 other animals. Its principal ingredient is the ambrein, which is obtained 
 by solution in boiling alcohol, whence it crystallizes on cooling in fine 
 needles. It is white, tasteless, of a very agreeable odour ; it is not 
 saponifiable ; its formula is C^H^O. By boiling with nitric acid it 
 produces ambreic acid, which crystallizes from its solution in alcohol in 
 small colourless tables ; it reddens litmus, but is scarcely soluble in 
 water ; it forms well defined yellow salts with the alcalies ; its formula 
 appears to be C 2 cH 2 oNO 12 . 
 
 The calculi formed by the deposition of solid materials in the gall 
 bladder or ducts, consist usually of cholesterine (see p. 1007), or 
 colouring matters, but recently a peculiar substance has been disco- 
 vered, forming biliary calculi in large animals, and termed Lithofellic 
 acid. This body possesses the general characters of a resin, its for- 
 mula is C 40 H 36 O 8 . Its most important character is that like sulphur, 
 it may exist in a crystallized or in an amorphous condition, and its 
 melting points in these states differ by 180 Fahrenheit; the melting 
 point of the crystals being 205 C, and that of the amorphous form 
 105 C. 
 
 SECTION VI. 
 
 OF THE PRESERVATION AND PUTREFACTION OE ANIMAL MATTERS. 
 
 Prom the greater complexity of composition of animal substances, 
 their decomposition is more rapid, and its products more diverse than 
 
1046 Phenomena of Putrefaction. 
 
 in the case of organic bodies of vegetable origin ; and whilst the carbon, 
 hydrogen and oxygen give origin to the various kinds of ulinine and 
 other substances of the same class, the nitrogen is generally evolved 
 as ammonia, and the sulphur as sulphuretted hydrogen. It is the pre- 
 sence of these bodies that give to putrefying animal substances the 
 disagreeable odour by which that process is distinguished from mere 
 mouldering or rotting. 
 
 Even during life the constituent particles of the body are in a con- 
 tinual state of change, being absorbed and thrown out of the system 
 whilst others are assimilated^ in their place. Any part of our consti- 
 tuents, liquid or solid, which becomes unfitted for this vital function is 
 thereby killed, and must, if not gotten rid of, induce the death of the 
 individual. Hence precisely the same means which give to animal sub- 
 stances the fixity of constitution, which belongs to true chemical com- 
 pounds, and thus preserve them from decomposition by the disturbing 
 action of their own elements, (as when we coagulate albumen by an 
 acid, by corrosive sublimate, or by sulphate of copper), produce, if 
 applied to the living body, the death of the part or of the whole being, 
 by depriving the blood or the tissue of the mutability of constitution 
 which is required for the functions of the animal frame. 
 
 It is thus that the generality of metallic poisons act in producing 
 death. Being absorbed into the system, they unite with the albumen 
 and fibrine of the blood, and converting them into the insoluble com- 
 pounds which we form in the laboratory, unfit them for the continual 
 absorptive and secretive offices which as organs while they live they 
 must fulfil. If the injury be local and limited in extent, the part 
 so coagulated may be thrown off, and after a certain time the functions 
 return to their proper order. If the mass, or the importance of the 
 affected parts be greater, the system cannot so get rid of the portions 
 which have thus been removed from the agency of life to submit to 
 merely chemical laws; on the contrary, the vital powers of the remaining 
 portions of the animal are so much weakened in the effort that general 
 death is caused. 
 
 Tor putrefaction it is thus necessary 1st, that the force of vitality, 
 which governs so completely the mere chemical tendencies of the ele- 
 ments of our tissues, be removed ; 2nd, that there should not be pre- 
 sent any powerful chemical re-agent, with which the organized material 
 may enter into combination, and thus the divellant tendencies of the 
 affinities of its elements be overcome ; 3rd, that water be present in 
 order to give the necessary mobility ; 4th, that oxygen be present, or 
 at least some other gas, into the space occupied by which the gaseous 
 products may be diffused ; and, lastly, that the temperature shall be 
 
Conservation of Animal Bodies. 1047 
 
 within moderate limits, putrefaction being impossible below 32, and 
 above 182. 
 
 The agency of the first of these preventive powers need not be fur- 
 ther noticed. The second is extensively employed in the preparation of 
 bodies for anatomical purposes, by baths, or injections into the arteries, 
 of solutions of corrosive sublimate, acetate of alumina, sulphate of 
 iron, tannin, wood vinegar, and kreosote; this last body, however, 
 does not appear to act by direct combination, but by the complete 
 (catalytic) coagulation it produces in all the tissues of the body that 
 have protein for their base. The necessity for the presence of water is 
 shown by the fact, that by drying the animal substances they are com- 
 pletely preserved. It is thus that the bodies of those perishing in the 
 Arabian deserts, are recovered years subsequently, dried, but com- 
 pletely fresh. Alcohol and common salt act in preserving animal 
 bodies by their affinity for water. If a piece of flesh be covered with 
 salt, the water gradually passes from the pores of the flesh, and dissol- 
 ving the salt, forms a brine, which does not wet the flesh, but trickles 
 off its surface ; the water necessary for putrefaction is thus removed. 
 The mode of strengthening alcohol in a bladder (p. 774), rests on the 
 same principle. Fourth, by excluding oxygen, the putrefactive process 
 is retarded, precisely as the fermentative action of the gluten in grape 
 juice (p. 772) cannot begin until a small quantity of oxygen be ab- 
 sorbed. It is thus, that meat which is sealed up in close vessels, and 
 then boiled for a moment, is preserved ; the small quantity of oxygen 
 of the air remaining then in the vessel is absorbed, and the product of 
 that minute change being coagulated by the heat, it cannot proceed 
 further. A high temperature stops putrefaction by coagulating the 
 azotized materials ; a temperature below 32, by freezing the water, 
 acts as if the tissue had been dried; in both cases putrefaction is 
 arrested. 
 
 During putrefaction, at a stage prior to any fetid gas being evolved, 
 a peculiar organic substance is generated, possessed of intensely 
 poisonous properties, and the blood of persons who have died from its 
 effects, is found to be quite disorganized, and irritating when applied 
 to wounds. The blood of over-driven cattle is found to produce effects 
 similar to those of venemous reptiles, and the wounds received in dis- 
 section are sometimes followed by similar fatal consequences. The 
 communication of disease, in this way, has recently been very ingen- 
 iously ascribed by Liebig to the general principle of the communica- 
 tion of decomposition by contact, (p. 229). The small quantity of 
 diseased organic matter originally introduced into the system by absorp- 
 tion, acts as a ferment, and reproduces itself in the mass of blood 
 
1048 Phenomena of Putrefaction, 
 
 until this becomes unfitted for the performance of its functions, and the 
 animal is killed ; the active principle being thus copiously present, is 
 exuded from the skin and lungs, and gives a contagious character to 
 the disease, or it remains only in the blood, or is secreted in pustules, 
 &c v constituting infection by which the disease may be communicated 
 to another person. 
 
 In the decomposition of vegetable matter, in marshes, similar male- 
 ficent products may be evolved, and throwing the blood of the animal, 
 by which they are absorbed, into fermentative decomposition, produce 
 the effects of malaria and marsh miasm. 
 
INDEX. 
 
 Absinthiin, 926. 
 Absorption of Light, 34-50. 
 
 of Heat, 121-124. 
 
 Acechloryl, 809. 
 Acetates of Alumina, 801. 
 Ammonia, 804. 
 
 of Barytes, Lime, 800. 
 
 Lead, 802. 
 
 Copper, 803. 
 
 Silver. Mercury, 804. 
 
 Potash, Soda, 800. 
 
 Acetal, 796. 
 
 Acetone, 805. 
 Acetyl, 794, 812. 
 Achromanides, 752. 
 Acids, Poly basic, 412, 666. 
 Acid, Acetic, 797. 
 
 Acrylic, 873. 
 
 Adipic,879. 
 
 Akonitic, 899. 
 
 Aldehydic, 796. 
 
 Alloxanic, 1033. 
 
 Althionic, 782. 
 
 Aloetic, 928. 
 
 Ambreic, 1045. 
 
 Amygdalic, 850. 
 
 Anilic, 937. 
 
 Angelic, 914. 
 
 Anthranilic, 938. 
 
 Anemonic, 921. 
 
 Antimonious Antimonic, 544. 
 . Apoglucic, 818. 
 
 Arsenious, 532. 
 
 . Arseniovinic, 784. 
 
 Arsenic, 535. 
 
 Aspartic, 919. 
 
 Auric, 572. 
 
 Azoleic, 880. 
 
 - Azulmic, 731. 
 
 Benzoic, 851. 
 
 , Benzoylic, 854. 
 
 Boletic, 913. 
 
 Boracic, 455. 
 
 Bromic, 443. 
 
 Butyric, 885. 
 
 Caprylic, 886. 
 
 Acid Carbonic, 687. 
 
 Carbovinic, 789. 
 
 Carbomethylic, 827. 
 
 Camphoric. Camphovinic, 864. 
 
 Capric. Caproic, 886. 
 
 , Catechu-tannic. Catechuic, 908. 
 
 Caincic, 913. 
 
 Caifeic, 920. 
 
 Caseic, 1043. 
 
 Cetylic, 891. 
 
 Chelidonic, 913. 
 
 Chlorous, 425. 
 
 Chloric, 423. 
 
 Chloro-carbonic, 701. 
 
 Chloro-acetic, 809. 
 
 Chlorisatic, 938. 
 
 Chloro-chromic, 636. 
 
 Chlornapthalic, 840. 
 
 Chloro-phenic, 843. 
 
 Chloroxalovinic, 811, 
 
 Chloroproteic, 1002. 
 
 Choleic, 1019. 
 
 Cholalic, 1021. 
 
 Cholesteric, 1007. 
 
 Chrysanilic, 938- 
 
 Chlorosochloric, 426. 
 
 Chloronitrous, 432. 
 
 Chromic, 524. 
 
 Chrysammic, 928. 
 
 Chrysanilic, 938. 
 
 Chrysolepic, 929. 
 
 Cinnamic, 855. 
 
 Citric, 898. 
 
 . Citrakonic, 899. 
 
 Cinchonic. Cinchona-tannic, 
 
 911. 
 
 Coccotannic, 912. 
 
 Coccostearic, 883. 
 
 Colophonic, 867. 
 
 Columbic, 529. 
 
 Crenic. Apocrenic, 821, 
 
 Crotonic, 888. 
 
 Cumenic. Cumen-sulphuric, 
 
 867. 
 
 Croconic, 702. 
 
 Cyanic, 73 1 . 
 
1050 
 
 INDEX. 
 
 Acid Cyanuric, 736. 
 
 Cyanilic, 753. 
 
 Cyanoxalic, 1032. 
 
 Cymensulphuric, 867. 
 
 Delphinic, 887. 
 
 Dialuric, 1035. 
 
 Deutothionic, 400. 
 
 Elaidic, 880. 
 
 Ellagic, 907. 
 
 Equisetic, 899. 
 
 Erythric, 942. 
 
 Ethionic, 782. 
 
 Ethalic, 890. 
 
 -. Eugenic, 857. 
 
 Evernesic, 943. 
 
 Ferric, 509. 
 
 Formic, 829. 
 
 Formo-benzoic, 852. 
 
 Fulminic, 734. 
 
 Fumaric, 902. 
 
 Fungic, 912. 
 
 Gallic, 905. 
 
 Gei'c, 819. 
 
 Glucic, 766. 
 
 Glycerosulphuric, 872. 
 
 Hippuric, 1036. 
 
 Humous. Humic, 918. 
 
 Hydrochlorocyanic, 736. 
 
 Hydro-bromic, 444. 
 
 Hydro-chloric, 427. 
 
 Hydrocyanic, 737. 
 
 Hydro-fluoric, 445.- 
 
 Hydro-fluoboric, 456. 
 
 Hydro-fluosilicic, 453. 
 
 Hydriodic, 440. 
 
 Hydroleic. Hydro-margaric, 
 
 882. 
 
 Hypo-antimonious, 543. 
 
 Hypo-chlorous, 422. 
 
 Hypo-nitrous, 377. 
 
 Hypo-phosphorous, 410. 
 
 Hypo-sulphuric, 400. 
 
 Hypo-sulphurous, 399. 
 
 lodic, 437. 
 
 . . Inosinic, 1110. 
 
 lodous, 437. 
 
 Isethionic, 782. 
 
 Itakonic, 899. 
 
 Japonic, 910. 
 
 Kacodylic, 807. 
 
 Kinoic, 912. 
 
 Komenic, 903. 
 
 Krameric, 913. 
 
 Lactucic, 912. 
 
 Lecanoric, 941. 
 
 Lichen-stearic, 914. 
 
 . Lithofellic, 908, 1045. 
 
 Lipic, 880. 
 
 Malic, 900. 
 
 Acid Maleic, 901. 
 . Manganic, 500. 
 
 Meconic, 902. 
 
 Melanic, 1039. 
 
 Melassic, 766. 
 
 Margaric, 875. 
 
 Melangallic, 907. 
 
 Mellitic, 702. 
 
 Mesoxalic, 1033. 
 
 Metacetonic, 873. 
 
 Methionic, 782. 
 
 Metoleic Metamargaric, 
 882. 
 
 Metapectic, 916. 
 
 Metaphosphoric, 412. 
 
 Molybdic, 528. 
 
 Mucic, 767. 
 
 Muriatic, 427. 
 
 Mycomelinic, 1033. 
 
 Myristic, 884. 
 
 Myronic, 860. 
 
 Nitrosonitric, 384. 
 
 Nitranilic, 938. 
 
 Nitrostyphic, 845. 
 
 Nitrococcic, 940. 
 
 Nitranisic, 866. 
 
 Nitric, 380. 
 
 Nitro-leucic, 
 
 Nitro-meconic, 923. 
 
 Nitro-phenesic, 844. 
 
 Nitro-muriatic, 432. 
 
 Nitrous, 378. 
 
 (Enanthic, 814. 
 
 CEnanthylic, 888. 
 
 Oleic, 877. 
 
 Opianic, 957. 
 
 Orsellic, 943: 
 
 Osmic, 529. 
 
 Oxamic, 729. 
 
 Oxypicric, 845, 
 
 Oxalic, 698. 
 
 Oxalovinic, 789. 
 
 Oxaluric, 
 
 Oxypinic, 867. 
 
 Palmic, 887. 
 
 Palmitic, 883. 
 
 Parellagic, 907. 
 
 Paracyanic, 732* 
 
 Parabanic, 1033. 
 
 Parellagic, 908. 
 
 Paralactic, 764. 
 
 Pelargonic, 940. 
 
 Perchlorous, 424. 
 
 Perchloric, 425. 
 
 Pectic, 915. 
 
 Periodic, 437. 
 
 Permanganic, 501. 
 
 Phosphomesitilic, 805. 
 
 Phosphoric, 412. 
 
INDEX. 
 
 1051 
 
 Acid Phosphorous, 411. 
 
 Phosphogly eerie, 872. 
 
 Phosphomethylic, 828. 
 
 Phospho-vinic, 784. 
 
 Pinic, 866. 
 
 Pimelic, 879. 
 
 Picric, 844 937. 
 
 Proteosulphuric, 1000. 
 
 Prussic, 737. 
 
 Purreic, 940. 
 
 Purpuric, 1036. 
 
 Pyromucic, 767. 
 
 Pyro-racemic, 898. 
 
 Pyro-tartaric, 897. 
 
 Pyro-meconic, 903. 
 
 Pyro-gallic, 907. 
 
 Pyromucic, 767. 
 
 Racemic, 897. 
 
 . Rhodizonic, 702. 
 
 Ricino-stearic. Ricinic, 887. 
 
 Rubinic, 910. 
 
 Rufin-sulphuric, 917. 
 
 Saccharic, 763. 
 
 Saccharohumic, 818. 
 
 Sacchulmic, 763. 
 
 Salicylic, 858. 
 
 Sebacic, 878. 
 
 Selenious. Selenic, 407. 
 
 Silicic, 449. 
 
 Stannic, 521. 
 
 Stearic, 874. 
 
 Suberic, 879. 
 
 Succinic, 868. 
 
 Sulpho-benzoic, 953. 
 
 Sulpho-amilic, 815. 
 
 Sulpho-ethalic, 889. 
 
 Sulpho-glyceric,872. 
 
 Sulphindylic, 936. 
 
 Sulpholeic-Sulpho-margaric, 
 
 882. 
 
 Sulpho-mesitic, 805. 
 
 Sulpho-methylic, 827. 
 
 Sulpho-napthalic, 840. 
 
 Sulpho-purpuric, 936. 
 
 Sulpho-vinic, 781. 
 
 Sulpho- carbonic, 704. 
 
 Sulphuric, 392. 
 
 Sulphurous, 390. 
 
 Sylvic, 867. 
 
 Tannoxylic, 905. 
 
 Tannomelanic, 905. 
 
 Tannic, 903. 
 
 Tantalic, 529. 
 
 Tartaric, 892, 
 
 Tartralic-Tartrelic, 896. 
 
 Tellurous. Telluric, 549. 
 
 Tetrathionic, 400. 
 
 Thiocyanic, 752. 
 
 Thionuric, 1034. 
 
 Acid Titanic, 531. 
 
 Trigenic, 796. 
 
 Trithionic, 400. 
 
 Tungstic, 527. 
 
 Turpentinic, 864. 
 
 Ulmic, 818. 
 
 Usmic 944. 
 
 Vaccinic, 886. 
 
 Vanadic, 526. 
 
 Valerianic, 816. 
 
 Verdous and verdic, 913. 
 
 Xanthoproteic, 1002. 
 
 Hydroxanthic, 790. 
 
 Hydrosulpho- cyanic, 750. 
 
 Acaroid Resin, 868. 
 Aconitine, 964. 
 
 Acroleon, 873. 
 
 Acidimetry, 624. 
 
 Acryl-series, 873. 
 
 Actinic Forces, 229. 
 
 Action of Magnets on Light, 47. 
 
 Actions by Contact, 229. 
 
 Adhesion of Solids to Liquids, 9. 
 
 JSsculine, 924. 
 
 Uroliths, 503. 
 
 Affinity, Chemical, 204. 
 
 Order of, 209. 
 
 influenced by Cohesion, 214. 
 Elasticity, 218. 
 Light, 224. 
 
 Measure of, 222, 273. 
 
 Aggregation, States of, 8. 
 Agricultural Chemistry, 977. 
 Air, Atmospheric, 360. 
 
 Expansion of, 67. 
 
 Alabaster, 609. 
 Albumen, Animal, 998. 
 
 Vegetable, 771. 
 
 Alcohol, Ordinary, 774. 
 
 Methylic, 823. 
 
 Amylic, 815. 
 
 Alcoates, 776. 
 
 Alcalies from Aniline, 846. 
 
 Organic, Artificial, 972. 
 
 production of, 969. 
 
 Alkanna-red, 931. 
 Alizarine, 930. 
 Alembroth, Salt of, 725. 
 Algarotti, Powder of, 642. 
 Alkaline Earths, 461. 
 Alkarsin. Alkargene, 806. 
 Alkalimetry, 693. 
 Alkalies, 461. 
 Allantoin, 1032. 
 Alloxantine, 1035. 
 Allophanic Ether, 788. 
 Allotropy and Isomerism, 320. 
 Allotropic Conditions, 305. 
 Allotropy, Cause of, 317. 
 
1052 
 
 INDEX. 
 
 Allyle Series, 859. 
 Aloes, Acids from, 928. 
 Alum, 616. 
 Aluminum. Alumina," 489. 
 
 Salts of, 615. 
 
 Almonds, fixed Oil of, 877. 
 
 volatile Oil of, 850. 
 
 Amber, 868. 
 
 Ambergris. Ambreine, 1045. 
 Amnios, Liquid of the, 1044. 
 Amidide of Hydrogen, 709. 
 ' Mercury, 716. 
 
 Amilene, 815. 
 Amidogene, 709. 
 Ammonia, 706. 
 
 Ordinary Salts of, 722. 
 
 Metallic Salts of, 713. 
 
 Anhydrous Salts of, 721. 
 
 Metallic bases, 720. 
 
 Salts of Copper, 713. 
 
 Mercury, 716. 
 
 Palladium, 715. 
 
 : Platinum, 719. 
 
 Silver, 714. 
 
 Zinc, 713. 
 
 Amarythrine, 942. 
 
 Aniline, 845. 
 Ammonium, 723. 
 Ammoniurets, 711. 
 Ammoniacal Amalgam, 723. 
 Ammeline, 753. 
 Amilic Alcohol, 815. 
 Ammoniacum, 844. 
 Amygdaline, 850. 
 Anhydrite, 609. 
 Anemonine, 921. 
 Animal Chemistry, 996. 
 
 Charcoal, 676. 
 
 Electricity, 181, 164. 
 Anatase, 531. 
 Analcime, 45. 
 Analysis, Nature of, 2. 
 
 Organic, 678. 
 
 Antimonial Powder, 641. 
 
 Antimoniates 544. 
 
 Antimony Crocus. Glass of, 544. 
 
 Anthracite, 822. 
 
 Antimony, 542. 
 
 Oxide of, 543. 
 
 Sulphurets of, 546. 
 
 Detection of, 548. 
 
 Salts of, 638. 
 
 Antimoniuret of Hydrogen. 547. 
 Anime, resin, 868. 
 
 Anise, Oil of, 862. 
 
 Camphor, 866. 
 
 Antiar Resin, 868. 
 Apotheme, 927. 
 Aqua-regia, 423. 
 
 Arrow Root, 755. 
 rterialization, 1025. 
 .rsenic, 534. 
 
 Acids of, 535. 
 
 Sulphurets of, 536. 
 
 Detection of, 538. 
 
 Antidote to, 542. 
 
 Salts of, 639. 
 
 .rseniate of Potash, 640. 
 
 Iron, 639, 
 
 Silver, 651. 
 
 A.rsenite of Potash, 640. 
 Copper, 646. 
 Silver, 651. 
 
 Arseniuret of Hydrogen, 535. 
 Arabin, 760. 
 Archil], 945. 
 A.ricine, 935. 
 Artificial Tannin, 908. 
 Asarum, Oil of, 862. 
 
 Camphor, 865. 
 Asparagine. Aspartic Acid, 919. 
 Asphaltene, 868. 
 Assafoetida, 868. 
 Asphalt, 824. 
 
 Atomic Volumes, Theory of, 300. 
 of Salts, 593. 
 
 of Isomorphous Bodies, 310. 
 
 and Densities, 304. 
 
 Atmosphere, 360. 
 
 Composition of, 364. 
 
 Effect of Respiration on, 
 
 Pressure of, 369. 
 Extent and Form of, 
 
 371. 
 
 Atmospheric Electricity, 161. 
 Atomic Theory, 294. 
 Atoms, Physical and Chemical, 297- 
 Specific Heat of, 85. 
 
 Atropine, 965. 
 Aurates, 573. 
 Azote, 357. 
 Azobenzyl, 853. 
 Azolitmine, 945. 
 Azure Blue. 696. 
 Azosalicyl, 859. 
 Azoturets, 711. 
 
 B. 
 
 Battery of Groves, 179. 
 Gas, 179. 
 
 Balance, Electrical, 146. 
 Balsams, Nature of, 856. 
 Barium, 480. 
 Chloride of, 607. 
 
INDEX. 
 
 1053 
 
 Barium, Sulphuret of, 482. 
 Barilla, 691. 
 Barytes, 481. 
 
 Salts of, 607. 
 
 Bases Platinum, 721. 
 Basic Salts, 583. 
 Barometer, 369. 
 Batteries, Galvanic, 174. 
 
 Constant, 178. 
 
 Bdellium, Resin, 868. 
 Belladonine, 965. 
 
 Bell Metal, 557. 
 Benzoates, 852. 
 Benzyle Compounds, 853. 
 Benzin. Benzone, 854. 
 Benzone Resin, 868. 
 Benzid Series, 842, 853. 
 Berberine, 933. 
 Bergamotte, Oil of, 863. 
 Bile, Constitution of the, 1018. 
 
 Acids in, 1020. 
 
 Bilein, Bilifulvine, 1019. 
 Biliary Calculi, 1045. 
 Binary Theory of Salts, 590. 
 Birch Resin, 868. 
 Bismuth, 561. 
 
 Oxides of, 562. 
 
 Salts of, 648. 
 
 Sulphuret of, 563. 
 
 Bittern, 603. 
 Bleaching Powder, 61 1. 
 
 Theory of, 949. 
 
 Black Pepper, Oil of, 863. 
 Black Flux, 469. 
 
 Black Lead, 673. 
 
 Blood, Composition of the, 1013. 
 
 Globules, 1016. 
 
 Serum of the, 1014. 
 
 . in Disease, 1017. 
 
 Phosphates in, 1027. 
 
 Blue, Prussian, 746. 
 
 Azure, 696. 
 
 Thenards, 632. 
 
 Verditer, 696. 
 
 Blende, 518. 
 
 Bodies, Diamagnetic, 192. 
 Boiling Points of Liquids, 106. 
 Bone, Earth, 610. 
 
 Oil, 847. 
 
 Boracite, 615. 
 
 Bones, Composition of, 1012. 
 B orates of Soda, 606. 
 Boracic Acid. Boron, 454. 
 Boron, Fluoride of, 456. 
 Borax, 606. 
 Brass, 557. 
 Bromine, 442. 
 
 Chloride of, 445. 
 
 Bromide of Sulphur, 444. 
 
 Bromide of Potassium, 595. 
 Mercury, 653. 
 
 Sromates, 444. 
 
 Sraziliin, 931. 
 Brucine, 960. 
 
 Srain. Fats of the, 1006. 
 
 Jutyrine. Butyrone, 885. 
 Bronze, 557. 
 
 C. 
 
 Cadmium and its Compounds, 518. 
 
 Salts of, 633. 
 
 Caffeine, 920. 
 3ajeput, Oil of, 861. 
 Dalamine, 516. 
 dale Spar, 484, 695. 
 Calcium and its Oxides, 483. 
 Sulphuret, 486. 
 Salts of, 608. 
 Calcination of Ores, 466. 
 
 alculi, Biliary, 1045. 
 
 Vesical, 1040. 
 
 Calomel, 652. 
 
 alorimeter, 82. 
 Cameleon Mineral, 501. 
 Camphene, 863. 
 Camphors of the Oils, 864. 
 Camphor, Common, 863. 
 Camphor Tree, Oil of, 862. 
 Camphilene, 863. 
 Campholen, 864. 
 Caoutchouc. Caoutchine, 869. 
 Caprine. Caproine, 886. 
 Capacity of Bodies for Heat, 80. 
 Catalysis, 229. 
 Carbon, forms of, 672. 
 Carbonic Acid, 686. 
 
 Oxide, 697. 
 
 Carbon, Sulphuret of, 703. 
 
 Chlorides of, 705. 
 
 Carbonates of Potash, 688. 
 Soda, 691. 
 
 Lime, 695. 
 
 Barytes, 695. 
 
 Magnesia, 695. 
 
 Iron, 696. 
 
 Copper, 696. 
 
 Lead, 697. 
 
 Ammonia, 727. 
 
 Carburets, 697. 
 Caramel, 762. 
 Cane Sugar, 761. 
 Carmine, 934. 
 Carthamine, 932. 
 Cartilage, 1004. 
 Caseum. Caseine, 1042. 
 Cassius, Purple of, 573. 
 
1054 
 
 INDEX. 
 
 Cantharidine, 921. 
 
 Catechine, 908. 
 
 Capillary Force, 10. 
 
 Catalysis, Theories of, 232. 
 
 Calcium, Phosphuret of, 487. 
 
 Carbonate of Manganese, 696. 
 
 Calomel, 653. 
 
 Carbaldine, 796. 
 
 Cementation, 505. 
 
 Cerin. Ceraine,891. 
 
 Cedririt, 835. 
 
 Cellular Tissue, 1010. 
 
 Cerebrot. Cerebrol, 1006. 
 
 Cerium and its Compounds, 493. 
 
 Ceruse, 697. 
 
 Cetene, 890. 
 
 Cetrarine, 922. 
 
 Cerium, 493. 
 
 Cetine. Cetene, 890. 
 
 Charcoal, 672. 
 
 Chalk, 695, 672, 
 
 Chelerythrine, 963. 
 
 Chelidonine, 964. 
 
 Chemical Action of Galvanism, 252. 
 
 Theory of Galvanism, 266. 
 
 Affinity, 204. 
 
 Rays of Light, 226. 
 
 Voltameter, 263. 
 
 Equivalents, 276. 
 
 Chemistry, Origin and Object, of, 1. 
 
 Derivation of, 3. 
 
 Agricultural, 977- 
 
 Animal, 996. 
 
 Chemical Nomenclature, 194. 
 
 . Formulae, 203. 
 
 Chinone, 912. 
 
 Chlorine, 418. 
 
 Properties of, 420. 
 
 Compounds with Oxygen, 
 
 422. 
 Chloride of Hydrogen, 427. 
 
 Sulphur, 432. 
 
 Phosphorus, 433. 
 
 . Iodine, 441. 
 
 Silicon, 451. 
 
 Potassium, 594. 
 
 Sodium, 602. 
 
 Boron, 456. 
 
 Barium, 607. 
 
 Strontium, 608. 
 
 Calcium, 608. 
 
 Lime, 610. 
 
 Magnesium, 614. 
 
 Aluminum, 615. 
 
 Manganese, 626. 
 
 Iron, 627. 
 
 Nickel, 631. 
 
 Cobalt, 631. 
 
 Zinc, 632. 
 
 Chloride of Tin, 633. 
 . Chrome, 636. 
 
 Arsenic, 639. 
 
 Antimony, 641. 
 
 Titanium, 643. 
 
 Copper, 644. 
 
 Lead, 646. 
 
 Bismuth, 648. 
 
 Silver, 649. 
 
 Mercury, 652. 
 
 Gold, 656. 
 
 Palladium, 657. 
 
 Platinum, 658. 
 
 Rhodium, 659. 
 
 Cyanogen, 740. 
 
 Carbon, 705. 
 
 Ammonium, 724. 
 
 Chlorate of Potash, 423, 596. 
 Chlorometry, 611. 
 Chlorine and Indigo, 938. 
 Chloral, 809. 
 Chloryl-ether, 810. 
 Chloroxalic Ether, 810. 
 Cholesterine, 1007. 
 Chondrine, 1004. 
 Chlorophyll, 946. 
 Chrysorhamnine, 932. 
 Choke Damp, 808. 
 Chromium, 523. 
 Chromium Oxide, Acid of, 524. 
 
 Salts of, 635. 
 
 Chromates of Potash, 637. 
 
 Lead, 648. 
 
 Mercury, 656. 
 
 Chrome Alum, 636. 
 
 Iron, 523. 
 
 Chyle and Chyme, 1024. 
 Chloroso Chloric Acid, 426. 
 Chloronitrous Acid, 432. 
 Chlorometry, 612. 
 Chrome, Yellow, 648. 
 Chloroxalic Ether, 810. 
 Chlorether Series, 811. 
 Chloroform, 833. 
 Chlorindigo, 938. 
 Cinnamyl, 856. 
 Cinnameine, 857. 
 Cinnamon, Oil of, 855. 
 Cinchona Red, 911. 
 Cinchonine and its Salts, 952. 
 Circular Polarization, 45. 
 Circles, Galvanic, 166. 
 Cissampelline, 968. 
 Cinnabar, 568. 
 
 Factitious, 570. 
 
 Citrates, 899. 
 Citron, Oil of, 863. 
 Citrine Ointment, 883. 
 Coal, Constitution of, 822. 
 
INDEX. 
 
 1055 
 
 Coal Gas, Nature of, 836. 
 Cobalt, 514. 
 
 Compounds of, 516. 
 
 Salts of, 631. 
 
 Clay, Composition of, 624. 
 Cloves, Oil of, 857. 
 Cobalto -cyanides, 750. 
 Cocoa Stearine, 883. 
 Cocculin, 922. 
 Cochineal Red, 934. 
 Codeine, 957. 
 
 Cohesion, Force of, 9. 
 
 Relation to Heat, 15, 54. 
 
 and Affinity, 212. 
 
 Colours, Prismatic, 38. 
 
 of Natural Bodies, 40. 
 
 Cold by Liquefaction, 90. 
 Classification of Bodies, 327. 
 Columbine, 922. 
 Colchicine, 962. 
 
 Colouring Matters, 929. 
 Colophony, 866. 
 Combustion, Slow, 235. 
 
 Theories of, 249. 
 
 Combination, Laws of, 274. 
 Conduction of Heat, 118. 
 
 of Electricity, 140. 
 
 and Induction, 152 
 
 Communication of Motion, 232. 
 Constant Battery, 177. 
 Contact, Actions by, 229. 
 Contagion, 1047. 
 
 Cooling of Bodies, 81, 133. 
 Columbium, 529. 
 
 Salts of, 638. 
 
 Coneine, 966. 
 Copaiva Resin, 868. 
 
 Oil of, 863. 
 
 Copal Resin, 868. 
 Copper, 552. 
 
 Oxides of, 554. 
 
 Sulphurets of, 555. 
 
 Alloys of, 556. 
 
 Salts of, 644. 
 
 Pyrites, 552. 
 
 Ammonia, Salts of, 713. 
 Corn Oil, 814. 
 Constitution of Salts, 580. 
 Combustion, Slow, 236. 
 
 Laws of, 244. 
 
 Corrosive Sublimate, 651. 
 Cobaltocyanides, 750. 
 Cotton, Gun, 758. 
 Coals, Composition of, 822. 
 Cotarnine, 956. 
 Cream, 1042 . 
 Crotonine, 888. 
 Cryophorus, 109. 
 Crystallization, 20. 
 
 Crystalline Forms, 22. 
 Crystals, Systems of, 24. 
 
 Polarization by, 42. 
 
 Mackled, 44. 
 
 Plagihedral, 47. 
 
 Isomorphous, 305. 
 
 Dimorphous, 314. 
 
 Plesiomorphous, 309. 
 
 Crystals, Optical Properties of, 44. 
 
 Currents, Galvanic, 165, 252. 
 
 Cupellation, 565. 
 
 Cumen, 862. 
 
 Cusparine, 923. 
 
 Curcumine, 1040. 
 
 Cubebs, Oil of, 863. 
 
 Camphor, 866. 
 
 Cumen, Oil of, 862. 
 Cuttle Fish Ink, 1 044. 
 Curves of Solubility, 19. 
 Cube, Modifications of, 25. 
 Cupric Acid, 555. 
 Curd, 1041. 
 Cuticle, 1009. 
 Cyanol, 845. 
 Cyanogen, 729. 
 
 Compounds with Oxygen. 
 
 731. 
 
 Chlorides of, 740. 
 
 Iodides of, 741. 
 
 Sulphuret of, 750. 
 
 Cyanamelide, 732. 
 Cyanide of Hydrogen, 737. 
 
 Potassium, 741. 
 
 Mercury, 742. W 
 
 Iron, 744. 
 
 Cyanides, Complex, 743. 
 Cymen, 862. 
 
 Cystic Oxide, 1041. 
 
 D. 
 
 Daguerrotype Images, 227. 
 
 Daturine. 966. 
 
 Definite Proportions, 274. 
 
 Deliquescence, 352. 
 
 Delphinine, (Fat), Delphinone, 886. 
 
 Delphinine, (Alcaloid), 961. 
 
 Destructive Distillation, 823, 834, 
 
 836. 
 Detonating Silver, 735. 
 
 Mercury, 735. 
 
 Powder, 599. 
 
 Dextrine, 761. 
 
 Dew, Nature of, 135. 
 Deutothionic Acid, 400. 
 Detection of the Metals, 463. 
 Diamond, 673. 
 Diastase, 772, 988. 
 
1056 
 
 INDEX. 
 
 Dichroism, 40. 
 Diabetes, Blood in, 1018. 
 
 Urine in, 1038. 
 
 Differential Thermometer, 59. 
 Diamagnetic Force, 192. 
 Didymium, 493. 
 Digestion, 1024. 
 Digestive Principle, 1029. 
 Diffusion of Gases, 365. 
 Dimorphous Bodies, 23, 315. 
 Dimorphism, 305. 
 Dippell's Animal Oil, 847. 
 Distillation, 98. 
 Distilling Apparatus, 776. 
 Disinfecting Liquor, 605. 
 Divisibility of Matter, 6. 
 Divellent Affinities, 209. 
 Double Decomposition, 207. 
 Double Refraction, 36. 
 
 Salts, 585. 
 
 Dragon's Blood, 868. 
 Dyeing Substances, 929. 
 
 Theory of, 947. 
 
 Dynamic Electricity. 163. 
 
 E. 
 
 Ear-wax, 1044. 
 Earths, Proper, 460. 
 
 Alcaline, 461. 
 
 Earthenware, 624. 
 Eblanine, 825. 
 Ebullition, *00. 
 Efflorescence, 352. 
 Eggs, Composition of, 1043. 
 Eleen, 877. 
 Elaidine, 880. 
 Elaidates,881. 
 Elecampane Camphor, 866. 
 Elaoptens, 861. 
 Elaterine, 923. 
 Elasticity of Gases, 16. 
 
 Vapours, 100. 
 
 and Affinity, 218. 
 Elayl, 790. 
 
 Elective Decomposition, 205. 
 Electricity, Nature of, 137. 
 
 of Steam, 162. 
 
 Statical, 139. 
 
 Animal, 164, 181. 
 
 Dynamic, 163. 
 
 of the Air, 161. 
 
 Theories of, 147. 
 
 Positive and Negative, 
 
 148. 
 
 Distribution of, 142. 
 
 Interference of, 145. 
 
 Velocity of, 142. 
 
 Electrical Conductors, 141. 
 
 Attraction, 145. 
 
 Machines, 149. 
 
 Balance, 146. 
 
 Induction, 152, 158. 
 
 Battery, 155. 
 
 Electrics and Non-electrics, 140. 
 Electrometer, 151. 
 Electrophorus, 156. 
 Electroscope, 144. 
 Electrotype, 169. 
 Electro-magnetism, 188. 
 
 chemical Theories, 252. 
 
 metallurgy, 470. 
 
 of Ampere, 256. 
 
 Berzelius, 257. 
 
 Davy, 255. 
 
 Faraday, 260. 
 
 Graham, 258. 
 
 Kane, 264. 
 
 Decomposition, 260. 
 
 Electrolysis and Electrodes, 262. 
 Elemi, 868. 
 
 Elements, Nature of, 2. 
 
 Classification of, 327.' 
 
 Emetine, 962. 
 Epsom Salt, 614. 
 Equivalent Decomposition, 278. 
 Electro-chemical, 263. 
 
 Chemical, 274. 
 
 Thermochemical, 246. 
 
 Erythrolein. Erythrolitmine, 945. 
 Erythrine. Erythryline, 946. 
 Erythrogen, 1019. 
 Erbium and Erbia, 492. 
 Essential Oils, Acid, 849. 
 
 Neutral, 860. 
 
 Essences, 898. 
 Ethal, 890. 
 
 Ether, Lumniferous, 48. 
 Sulphuric, 776. 
 
 Etherene, 790. 
 
 Etherine. Ether ol, 783. 
 
 Ether eum, 812, 
 
 Ethyl, 812. 
 
 Ethchloryl, 811. 
 
 Ethers, Theory of the, 812. 
 
 Acetic, 804. 
 
 Camphoric, 865. 
 
 Carbonic, 788. 
 
 Chloro-carbonic, 789. 
 
 Cinnamic, 856. 
 
 Cyanuric, 788. 
 
 Elaidic, 880. 
 
 Hydriodic, 785. 
 
 Hydro-bromic, 785. 
 
 Hydro-sulphuric, 785. 
 
 Hydro-chloric, 784. 
 
 Hydro-cyanic, 788. 
 
INDEX. 
 
 105? 
 
 Ethers, Hyponitrous, 786. 
 
 Mucic, 790. 
 
 . Myristic, 885. 
 
 Nitric, 786. 
 
 Oleic, 877, 
 
 Oxalic, 789. 
 
 Palmitic, 884. 
 
 Sulpho-carbonic, 790. 
 
 Sulphuric, True, 783. 
 
 Stearic, 875. 
 
 Sulpho-cyanic, 788. 
 
 Suberic, 879. 
 
 Xanthic, 785. 
 
 Ethyl, Sulphurets of, 786. 
 
 Chloride of, 784. 
 
 Iodide of, 785. 
 
 Eudiometer, Use of the, 361. 
 of Davy and Scheele,362. 
 
 ofVolta, 344. 
 
 ~ Ure, 362. 
 
 Brunner, 363. 
 
 Euphorbium, 869. 
 Euchroic Acid, 703. 
 Evaporation, 96. 
 
 ,- Spontaneous, 100. 
 
 Cold by, 109, 
 
 Excitation, Electrical, 140. 
 Expansion by Heat, 54. 
 
 of Gases, 67. 
 
 Liquids, 72. 
 
 Solids, 76. 
 
 Extractive Matter, 927. 
 
 Animal, 1007. 
 
 Eye, Humours of the, 1004. 
 Black Pigment of the, 1004. 
 
 F. 
 
 Fallowing, Theory of, 991. 
 Fats of the Brain, 1006, 1011. 
 Fatty Bodies, 871. 
 Feathers, 1010. 
 Fennel, Oil of, 861. 
 
 Camphor, 866. 
 
 Fermentation, Acetic, 794. 
 
 Alcoholic, 772. 
 
 Butyric, 885. 
 
 . Gly eerie, 873. 
 
 Lactic, 768. 
 
 Mucous, 769. 
 
 Putrefactive, 1046. 
 
 Saccharine, 764. 
 
 Ferrocyanide of Hydrogen, 744. 
 
 Iron, 746. 
 
 Potassium, 745. 
 
 Ferridcyanide of Potassium, 747. 
 Ferro-cyanogen, 748. 
 
 Ferric Acid, 509. 
 67 
 
 Ferro-cyanides, 744. 
 Ferridcyanides, 747. 
 Filtration of Water, 355. 
 Fibre, Ligneous, 758. 
 Fibrine, 977. 
 
 State of, in the Blood, 1014. 
 Fire Damp, 808. 
 Fixed Oils, 871. 
 Flashing, 565. 
 
 Flame, Constitution of, 240. 
 Flesh, Muscular, 1011. 
 
 Juice of, 1009. 
 Flints, 447. 
 
 Liquor of, 618. 
 
 Flowers, Colours of, 946. 
 
 Fluidity 89. 
 
 Fluoborates, 456. 
 
 Fluorine, 445. 
 
 Fluoride of Aluminum, 615. 
 
 Boron, 456. 
 
 Calcium, 609. 
 
 Hydrogen, 446- 
 
 Phosphorus, 447. 
 
 Potassium, 597. 
 
 Silicon, 452. 
 
 Fluo-silicate of Potash, 597. 
 Fluor Spar, 609. 
 Flux, White and Black, 469. 
 Force, Diamagnetic, 192. 
 Forces, Tithonic, 229. 
 Formic Acid, 829. 
 Formyl, Compounds of, 829. 
 Formiate of Copper, 831. 
 
 Barytes, 830. 
 
 Lead, 831. 
 
 Mercury, 832. 
 
 Soda, 830. 
 
 Fossil Copal, 868. 
 
 Frost, Nature of, 135. 
 
 Freezing Mixtures, 94. 
 
 Fulminating Silver, 711. 
 
 Fulminates, 735. 
 
 Furnace, Reverberatory, 467. 
 
 Fusion. Liquefaction, 89. 
 
 Watery, 352. 
 
 Fusion, Crystallization by, 21. 
 Furfurine. Furfurol, 975. 
 
 G. 
 
 Galena, 560. 
 
 Galvanic Electricity, 163. 
 
 Circles, 166. 
 
 Intensity, 170, 173. 
 
 Batteries, by Groves, Callan 
 
 and Bunsen, 179. 
 
 Galvanism, Chemical Theories,of, 
 171. 
 
1058 
 
 INDEX. 
 
 Galvanism, Contact Theory of, 174. 
 Galvanic Batteries, Common, 175. 
 
 Constant, 179. 
 
 Galvanism, Discovery of, 181. 
 
 Galvanoscope, 181, 191, 264. 
 
 Gallates, 906. 
 
 Gamboge, 868. 
 
 Gases, Conduction of Heat by, 120. 
 
 Correction, for Moisture of, 
 
 112. 
 
 Temperature, 70. 
 
 Pressure, 16. 
 
 Diffusion of, 365. 
 
 Expansion of, 68. 
 
 Relation to Vapours, 111, 115. 
 
 Specific Gravity of, 11. 
 
 Heat of, 87. 
 
 Liquefaction of, 17. 
 
 Absorption by Water, 351. 
 
 Absorption by Charcoal, 677. 
 
 Mode of Drying, 452. 
 
 Gasometers, 332. 
 
 Gas, Battery of Groves, 179. 
 
 Garlic, Oil of, 860. 
 
 Galbanum, 868. 
 
 Gastric Juice, ^+1 
 
 Gelatine, 1003. 
 
 Sugar of, 1005. 
 
 German Silver, 513. 
 
 Germination, 988. 
 
 Glass, Composition of, 619. 
 
 Manufacture of, 618. 
 
 Annealing of, 620. 
 
 ... . of Antimony 544. 
 
 . Expansion of, 77. 
 Glauber's Salt, 604. 
 Glucinum. Glucina, 491. 
 Glucose, 764. 
 Glaucine, 754, 969. 
 Gluten, 771. 
 Glycerine, 973. 
 Glycyrrhizine, 767. 
 Glaucene, 752. 
 
 Glycero-phosphoric Acid, 872. 
 Glyceric Fermentation, 873. 
 Glycocoll, 1005. 
 Gold, 571. 
 
 Oxides of, 572. 
 
 Salts of, 656. 
 
 Double Chlorides of, 657. 
 
 - Ammonia Chloride, 721. 
 
 Fulminating, 711. 
 
 Mosaic, 522. 
 
 Golden Sulphuret of Antimony, 546. 
 
 Goniometers, 33. 
 
 Gouty Concretions, 1039. 
 
 Graphite, 673. 
 
 Grape Sugar, 764. 
 
 Gravity, Nature of, 6. 
 
 Gravity, Specific, of Gases, 16. 
 
 Liquids, 10. 
 
 Vapours, 13. 
 
 : Solids, 12. 
 
 Green, Brunswick, 644. 
 
 Emerald, 646. 
 
 Mineral, 696. 
 
 Scheele's 646. 
 
 Growth of Plants, 977. 
 Guaiacum, 868. 
 Gum, 760. 
 
 British, 756. 
 
 Resins, 868. 
 Gunpowder, 599. 
 Gun Cotton, 758. 
 Gutta Percha, 870. 
 Gypsum, 609. 
 
 H. 
 
 Hair, Horn, 1010. 
 
 Haloid Salts, 581, 592. 
 
 Hartshorn, Spirits of, 707, 727, 847. 
 
 Harmaline, 969. 
 
 Heat, Repulsive Power of, 54. 
 
 Measure of, 57. 
 
 Specific of Solids, 81. 
 
 Gases, 87. 
 
 of Atoms, 84. 
 
 Evolution of, 235. 
 
 Latent of Liquids, 90. 
 
 Latent of Vapours, 97. 
 
 Transmission of, 116. 
 Conduction of by Gases, 120. 
 
 Liquids, 119. 
 
 Solids, 117. 
 
 Radiation of, 121. 
 
 Reflection and Absorption of, 
 
 123. 
 
 Polarization of, 1 32. 
 
 Relation of, to Light, 126, 131 
 
 Interference of, 130. 
 
 Theories of, 133. 
 
 Central of the Earth, 136. 
 
 Sources of, 137. 
 
 of Liquefaction, 91. 
 
 . Latent and sensible constant, 
 103. 
 
 Permeability of Bodies to, 128. 
 
 Analogy of, to Light, 130. 
 
 Catalytic Effects of, 231. 
 
 Helicine, 917. 
 
 Heavy Spar, 607. 
 Hematosine, 1015. 
 Hematoxylin, 93 1 . 
 Hematite, 508. 
 Hepar Sulphuris, 476. 
 Honey, 764. 
 
INDEX. 
 
 1059 
 
 Honeystone, 702. 
 
 Humine and Humous Acid, 820. 
 
 Hydrates, 353. 
 
 Hydrogen, 338. 
 
 Hydrogen, Oxide of, 347. 
 
 Peroxide of, 355. 
 
 Amidide of, 706. 
 
 Sulphuretted, 404. 
 
 Seleniuretted, 407. 
 
 Phosphuretted,4l6. 
 
 Arseniuretted, 535. 
 
 Antimoniuretted, 547. 
 
 Hydriodic Acid, 439. 
 
 Hydriodate of Phosphuretted Hy- 
 drogen, 441. 
 
 Hydrobromic Acid, 444. 
 
 Hydro-chloric Acid, 427. 
 
 Hydro-cyanic Acid. 737. 
 
 Hydro-fluoric Acid, 446. 
 
 Hydro-fluosilicic Acid, 453. 
 
 Hydro-mellonic Acid, 752. 
 
 Hydrogen, Carburet of, Faraday's, 
 834. 
 
 Metallic Nature of, 347. 
 
 Salts of, 581. 
 
 Hydroxygen Blowpipe, 345. 
 
 Hydrogen Harmonicon, 347. 
 
 Hydruret of Arsenic, 535. 
 
 Hydrokinone, 912. 
 
 Hygrometry, 371. 
 
 Hygrometers, 113. 
 
 Hydro-benzamide, 854. 
 
 Hyoscyamine, 966* 
 
 Hydro-sulphuret of Ammonia, 846. 
 
 Hypochlorite of Lime, 610. 
 
 Potash, 600. 
 
 Soda, 605. 
 
 Hyponitrite of Potash, 376. 
 
 Silver, 651. 
 
 Hyposulphite of Silver, 651, 225. 
 of Soda, 605. 
 
 I. 
 
 Idrialine, 823. 
 Ilmenium, 529. 
 Incipient Albumen, 1024. 
 Indigo, Blue, 934. 
 
 White, 935. 
 
 Sulphates of, 936. 
 
 with Chlorine, 938. 
 
 Indian Yellow, 939. 
 Indigogene, 935. 
 
 Indigo Bath, 936. 
 Induction, Electric, 152. 
 Inductive Capacity, 158. 
 Inductometer, 157. 
 
 Induction, Magneto-electric, 188. 
 
 Infection, 1047, 
 
 Inuline, 757. 
 
 Ink, 904. 
 
 Insolubility, 214. 
 
 Insulation, 141. 
 
 Interference of Heat, 130. 
 
 Light, 49. 
 
 Electricity, 145. 
 
 Photographic, 228. 
 
 lodate of Potash, 602. 
 Iodide of Arsenic, 639. 
 
 Amidogen, 710. 
 
 Copper, 645. 
 
 Cyanogen, 740. 
 
 Gold, 657- 
 
 Hydrogen, 439. 
 
 Iron, 628. 
 
 Lead, 647. 
 
 Mercury, 654. 
 
 Palladium, 657. 
 
 Platinum, 658. 
 
 Potassium, 595. 
 
 Silver, 649. 
 
 Sulphur, 440. 
 
 Iodine, 434. 
 
 Compounds of, 437. 
 
 lodous Acid, 437. 
 Ipecacuanha, 962. 
 Iridium, 577. 
 
 Salts of, 658. 
 
 Iris Florentina Camphor, 867. 
 Iron, 502. 
 
 Commercial Varieties, 504 . 
 
 Composition of, 505. 
 
 Detection of, 511. 
 
 Magnetic Oxide of, 507. 
 
 Malleable, 504. 
 
 Oxides of, 507. 
 
 Passitivity of, 507. 
 
 Pyrites, 510. 
 
 Smelting, of, 468, 503. 
 
 Sulphurets of, 509. 
 
 Salts of, 628. 
 
 Isatine, 937. 
 Isomerism, 305, 321. 
 Isomorphism, 32, 305. 
 Isomorphous Groups, 308, 314. 
 
 J. 
 
 Jalap, Resin, 868. 
 Jelly, Vegetable, 914. 
 
 Animal, 1003. 
 
 Jervin, 962. 
 Juniper, Oil of, 863. 
 Juice of Flesh, 1008, 
 
1060 
 
 INDEX. 
 
 K. 
 
 Kalium, 471. 
 
 Kacodyl Compounds, 806. 
 
 Kacodylic Acid, 807. 
 
 Kermes Mineral, 546. 
 
 Animal, 934. 
 
 Kapnomor, 835. 
 
 Kelp, 692. 
 
 King's Yellow, 536. 
 
 Kreatine, 1008. 
 
 Kreatinine, 1009. 
 
 Kupfer Nickel, 512. 
 
 L. 
 
 Labdanum Resin, 838. 
 
 Labarraque, Liquor of, 605. 
 
 Lac-sulphuris, 388, 476. 
 
 Lactates, 769. 
 
 Lactine, 766. 
 
 Lactucine, 926. 
 
 Lactic Fermentation, 768. 
 
 Lampblack, 675. 
 
 Lanthanum, 493. 
 
 Lana Philosophica, 517. 
 
 Lamp Aphlogistic, 235. 
 
 Safety, 242. 
 
 Lapis Lazuli, 617. 
 
 Latent Heat of Liquids, 90. 
 
 Vapours, 97* 
 
 Lavoisierian Nomenclature, 194. 
 Laws of Combination, 274. 
 Lavender, Oil of, 861. 
 Lead, 557. 
 
 Black, 673. 
 
 Compounds of, 559. 
 
 -_ Red, 559. 
 
 Salts of, 646. 
 
 Uses of, 561. 
 
 White, 697. 
 
 Yellow, 648. 
 
 Leather, Manufacture of, 1009. 
 Legumine, 771. 
 
 Leucine, 1005, 1043. 
 Leucolitmine, 946. 
 Leyden Jar, 155. 
 Leucoline, 847. 
 Lecanorine, 942 
 Lichenine, 757. 
 Lichen Bitter, 922. 
 
 Colours, 940. 
 
 Colouring Bodies from the, 
 
 940. 
 
 Lignine, 758. 
 Lignite, 821. 
 Lipyl, 872. 
 Ligno-sulphuric Acid, 760. 
 
 Light, 34. 
 
 Composition of, 38. 
 
 Polarization of, 41. 
 
 Wave-Theory of. 48. 
 
 Chemical Rays of, 51, 227. 
 
 _ Relation to Heat, 121, 240. 
 
 Velocity of, 35. 
 
 Magnetic Relations of, 47. 
 
 Analogy to Heat, 130. 
 
 Interference of, 49. 
 
 Influence on Affinity, 224. 
 
 Action on Vegetation, 993. 
 
 Refraction of, 35. 
 
 Double Refraction of, 41. 
 
 Absorption of, 39. 
 
 Action on Metallic Salts, 226. 
 
 Chemical Rays of, 229.^ 
 
 Heating Rays of, 127. 
 
 Sources of, 53. 
 
 Simple and Compound, 38. 
 
 Lightning, Nature of, 161. 
 Lime, 483. 
 
 Phosphuret of, 487. 
 
 Salts of, 608. 
 
 Limestone, 484, 695. 
 Liquation, 519. 
 Liquefaction, 89. 
 
 Cold produced by, 93. 
 
 Liquids, Specific Gravity of, 10. 
 
 Expansion of, 72. 
 
 Conduction of, 119. 
 
 Liquor of Flints, 618. 
 Liquorice, 767.- 
 
 Litharge, 558. 
 Lithium, 479. 
 
 1 Compounds of, 480. 
 
 Salts of, 607. 
 
 Litmus, 944. 
 Logwood, 931. 
 Luteoline, 933. 
 Lymph, 1024. 
 
 M. 
 
 Machines, Electrical, 150. 
 
 Steam Electric, 162. 
 
 Macled Crystals, 44. 
 
 Madder, Colouring Bodies of, 929. 
 
 Magnesium, 487. 
 
 Compounds of, 489. 
 
 Salts of, 614. 
 
 Magnesian Limestone, 488, 696. 
 Magnetism, 185. 
 Magnetic Attraction, 187. 
 
 Relations of Light, 47. 
 
 Magneto-electricity, 189. 
 Magnets, Nature of, 186. 
 Malaria, 1048. 
 
1061 
 
 Malates, 901. 
 Malachite, 696. 
 Malting, 988. 
 Manganese, 494. 
 
 Carbonate of, 696. 
 
 Oxide of 496. 
 
 Sulphurets of, 501 . 
 
 Salts of, 626. 
 
 Valuation of, 498, 694, 
 
 Mannite, 768. 
 
 Margarine. Margaron, 875. 
 Margarates, 876. 
 Manures, Organic, 992. 
 
 Mineral, 989. 
 
 Marsh Gas, 808. 
 Mariotte, Law of, 16. 
 Marjoram, Oil of, 862. 
 Mastic, 868. 
 Massicot, 559. 
 Matter, Divisibility of, 5. 
 
 Constitution of, 7. 
 
 Meconates, 902. 
 Meconine, 923. 
 Membrane, Cellular, 1010. 
 Menthene, 866. 
 Mercury, 567. 
 
 Ammonia-chlorides, 716. 
 
 Ammonia Nitrates, 719. 
 
 - Cyanide of, 742. 
 
 Detonating, 735. 
 
 Detection of, 571. 
 
 Fulminating, 711. 
 
 Oxides of, 569. 
 
 Salts of, 651. 
 
 Mercurial Preparations, 570. 
 Mesit, 826. 
 
 Mesitylene, 805. 
 Mesitic Ether, 805. 
 Melam, 752. 
 Melamine, 753. 
 Mellates, 702. 
 Mercaptan, 785. 
 Menispermine, 968. 
 Metals, Properties of, 457. 
 
 Compounds with Oxygen, 
 
 459. 
 Chlorine, 462. 
 
 Classification of, 460, 
 
 . Noble and Imperfect, 461. 
 
 Natural State of, 465. 
 
 Reduction of Ores of, 466. 
 
 Alcaline and Earthy, 461. 
 
 Conduction of Heat by, 117. 
 
 Electricity, 141. 
 
 Metal Gun, 557. 
 
 Speculum, 557. 
 
 Bell, 557. 
 
 Meteoric Stones, 503. 
 Methylic Alcohol, 825. 
 
 Methylic Ether, 827. 
 Methyl Salts of, 828. 
 Methylal, 829. 
 Metacetone, 763, 873. 
 Metallic Sulphurets, 463. 
 Metallurgic Processes, 465. 
 Metallurgy, Electric, 470. 
 Mesoxalic Acid, 703. 
 Melam, 736, 753. 
 Mellon, 752. 
 
 Milk, Composition of, 1041. 
 Sugar of, 766. 
 
 Miasm, 1048. 
 Mindererus, Spirit of, 804. 
 Mineral Chameleon, 500. 
 
 Kermes, 546. 
 
 Minium, 559. 
 Molybdenum, 528. 
 
 Salts of, 638. 
 
 Molybdates, 529. 
 
 Molecular Laws of Specific Heat, 84. 
 
 Molecular Decomposition, 229, 233. 
 
 Constitution, 294, 305, 319, 
 
 7,45. 
 
 Groups, 297, 325. 
 
 Cohesion, 9. 
 
 Electrical Arrangement, 
 
 265. 
 
 Mordants, Action of, 949. 
 Morphia, 953. 
 
 Salts, of, 955. 
 
 Morine, 933. 
 
 Mosaic Gold, 522. 
 
 Mucus, 1028 
 
 Mulberry Calculus, 1041. 
 
 Multiple Proportions, 28 1 . 
 
 Murexan, 1035. 
 
 Murexid, 1036. 
 
 Muriatic Acid, 427. 
 
 Muriates of Metallic Oxides, 585. 
 
 Muriate of Ammonia, 724. 
 
 Cinchonine, 953. 
 
 Morphia, 955. 
 
 Strychnine, 959. 
 
 Quinine, 951. 
 
 Muscular Tissue, 1011: 
 Mustard, Essential Oil of, 859. 
 Oil of, 860. 
 
 Mushroom Sugar, 767. 
 Mucous Fermentation, 768. 
 Myracine, 891. 
 Myristicine, 884. 
 Myriospermine, 857. 
 
 N. 
 
 Nails of Animals, 1010. 
 Naptha, Coal Gas, 836. 
 
1062 
 
 Naptha or Petroleum, 823. 
 Napthaline, 837. 
 
 Compounds of, 840. 
 
 Napthalic Acid, 839. 
 Narceine, 958. 
 Narcotine, 955. 
 Natrium. Natron, 477. 
 Napthaline and Chlorine, 837. 
 
 Nitrogen, 840. 
 
 Oxygen, 839. 
 
 Sulphur, 841. 
 
 Narcogenine, 956. 
 Neutral Salts, 581. 
 Neutralization of Affinities, 206. 
 Nitro-napthalese, 840. 
 Nickel, 5 12. 
 
 Compounds of, 513. 
 
 Salts of, 631. 
 
 Ammonia Salts of, 714. 
 
 Nicotine, 967. 
 
 Nitrate, of Ammonia, 724. 
 
 Barytes, 607. 
 
 Brucine, 960. 
 
 Bismuth, 649. 
 
 Copper, 645. 
 
 Iron, 630. 
 
 Lead, 647. 
 
 Lime, 610. 
 
 Magnesia, 615. 
 
 Mercury, 655. 
 
 Palladium, 658. 
 
 Potash, 598. 
 
 Soda, 605. 
 
 Strontia, 608. 
 
 Strychnia, 960. 
 
 Silver, 650. 
 
 Zinc, 633. 
 
 Water, 380. 
 
 Nitre, 598. 
 
 Nitrite of Lead, 647. 
 Nitrogen, 357. 
 
 Properties of, 359. 
 
 Oxides of, 373. 
 
 Chloride of, 7 10. 
 
 Iodide of, 710. 
 
 Nitric Oxide, 375. 
 
 Nitrous Oxide, 373. 
 
 Nitruret of Mercury, 711, 717. 
 
 Copper, 712. 
 
 Chrome, 711. 
 
 Nicotianine, 968. 
 
 Nitrogen, Estimate of, 684. 
 
 Nitre, Valuation of, 600. 
 
 Niobium, 529. 
 
 Nitrifaction, 380. 
 
 Non-electrics and Electrics, 139. 
 
 Nomenclature, 194. 
 
 of Lavoisier, 167. 
 
 of Laurent, 202. 
 
 INDEX. 
 
 Nutmeg-butter, 884. 
 
 O. 
 
 Oblique Prismatic System, 29. 
 Oil, Dippel's Animal, 847. 
 
 of Vitriol, 394. 
 
 of Wine, 783. 
 
 Potato-spirit, 815. 
 
 of Hartshorn, 847. 
 
 Corn, 815. 
 
 of Turpentine, 863. 
 
 Oils, Fixed, 871. 
 
 Essential, Acid, 849, 
 
 Essential, Neutral. 861. 
 
 Ointment, Citrine, 881. 
 Olefiant Gas, 790. 
 Oleine, 877. 
 Oleates, 878. 
 Olein, 882. 
 Olibanum Resin, 839. 
 
 Oil of, 861. 
 
 Olivin, 917. 
 Ologist Iron, 508. 
 Opium, Constituents of, 953. 
 Organic Analysis, 678. 
 
 Bodies, 662. 
 
 Radicals, 325, 664. 
 
 Types, 326, 668, 972. 
 
 Organized Bodies, 662. 
 
 Orcine. Orceine, 941. 
 
 Orelline, 933. 
 
 Optic Axes of Crystals, 36. 
 
 Opoponax Resin, 839. 
 
 Orpiment, 536. 
 
 Organic Alcalies, Artificial formation 
 
 of, 969. 
 Osmium, 528. 
 
 Oxides of, 529. 
 
 Salts of, 638. 
 
 Oxalates of Ammonia, 728. 
 
 Lime, 701. 
 
 Potash, 700. 
 
 of Potash and Iron, 700. 
 
 Chrome, 701. 
 
 Copper, 701. 
 
 Silver, 700. 
 
 Oxides of Aluminum, 490. 
 
 Ammonium, 722. 
 
 Antimony, 543. 
 
 Arsenic, 533. 
 
 Bismuth, 562. 
 
 Barium, 48 1 . 
 
 i Cadmium, 518. 
 
 Calcium, 485. 
 
 Cystic, 1041, 
 
 Chrome, 523. 
 
INDEX. 
 
 1063 
 
 Oxides of Cobalt, 515. 
 
 Copper, 553. 
 
 Carbon, 679. 
 
 Cerium, 493. 
 
 Ethyl, 776. 
 
 Grlucinum, 491. 
 
 Iron, 508. 
 
 Lead, 558. 
 
 Lithium, 479. 
 
 Manganese, 495. 
 
 Methyl, 826. 
 
 . Mercury, 569. 
 
 Molybdenum, 528. 
 
 Nickel, 513. 
 
 Nitrogen, 373. 
 
 Osmium, 528. 
 
 Palladium, 574. 
 
 Phosphorus, 410. 
 
 Platinum, 575. 
 
 Potassium, 473. 
 
 Iridium, 577. 
 
 Gold, 572. 
 
 . Rhodium, 578. 
 
 Silver, 566. 
 
 Sodium, 478. 
 
 Strontium, 483. 
 
 Tin, 520. 
 
 Titanium, 531. 
 
 Thorium, 492. 
 
 Tungsten, 527. 
 
 Uranium, 551. 
 
 Uric, 1041. 
 
 Vanadium, 526. 
 
 Xanthic, 1041. 
 
 Yttrium, 492. 
 
 Zinc, 517. 
 
 Zirconium, 492. 
 
 Hydrogen, 347. 
 
 Chlorine, 422. 
 
 Magnesium, 488. 
 
 Oxygen, 331. 
 
 Preparation of, 333. 
 
 Properties of, 336. 
 
 Consumed by Animals, 1025 : 
 
 337. 
 
 Evolved by Plants, 368, 979. 
 
 Oxygen of the Atmosphere, 366. 
 Oxyhydrogen Blowpipe, 345. 
 Oxyphorus, 576. 
 Oxamethylane, 829. 
 Oxamethane, 789. 
 
 Oxamide, 728. 
 
 Oxy-chloride of Calcium, 609. 
 
 . Chrome, 636. 
 
 Antimony, 642. 
 
 Copper, 644. 
 
 - Bismuth, 648. 
 
 Lead, 646. 
 
 Merciuy, 652. 
 
 Oxycatechine, 910. 
 Oxy-chloride of Palladium, 657. 
 Oxy-cyanide of Mercury, 742. 
 Oxy-protei'n, 1002. 
 Oxalic Acid, 698. 
 Oxanilide, 846. 
 Ozocherite, 822. 
 Ozone, 338. 
 
 P. 
 
 Palladium, 574. 
 
 Compounds of, 575. 
 
 Salts of, 657. 
 
 Ammonia, Salts of, 715. 
 
 Cyanide of, 743. 
 Palmine, 887. 
 Palmitine, 883. 
 Pancreatic Juice, 1030. 
 Paraffine, 822. 
 Para cyanogen, 731. 
 Para-napthaline, 841. 
 Parsley Camphor, 865. 
 
 Oil of, 863. 
 
 Pasto-Resin, 868. 
 Paraban, 703. 
 Pearlashes, 689. 
 Pectine, 914, 980. 
 Pennyroyal, Oil of, 862. 
 Peppermint, Oil of, 862. 
 
 Camphor, 865. 
 
 Peudecanine, 923. 
 Perchlorates, 426. 
 
 of Potash, 602. 
 
 Periodates, 438. 
 
 Permanganates, 501. 
 
 Peruvine, 856. 
 
 Petroleum, 823. 
 
 Pewter, 561. 
 
 Pentathionic Acid, 401. 
 
 Perchlorous Acid, 424. 
 
 Pelopium, 525. 
 
 Petanine, 848. 
 
 Pectase, Pectose, 980. 
 
 Phenyl, Hydrate of, 843. 
 
 Phloretin. Phloridzein, 919. 
 
 Phloridzine, 917. 
 
 Phosphates of Ammonia, 726. 
 
 of Ammon. and Magnes. 727. 
 
 Ammonia and Soda, 727. 
 
 Cobalt, 632. 
 
 Copper, 646. 
 
 Iron, 630. 
 
 Lime, 610. 
 
 Soda, 605. 
 
 Silver, 651. 
 
 Phosphates of Water, 413. 
 __ Alumina, 617. 
 
1064 
 
 INDEX. 
 
 Phosphates in the Urine, 1040. 
 Phosphatic Calculi, 1040. 
 Phosphuret of Azote, 712. 
 
 Metallic, 462. 
 
 of Hydrogen, 416. 
 
 Phosphites, 411. 
 Phosphorus, 408. 
 
 Compounds of, 410. 
 
 Phosphorescence, 50. 
 
 Phosphuretted Fats, 1006, 1011. 
 
 Photography, 225. 
 
 Photographic Interference, 228. 
 
 Phosphoric Acid, 412. 
 
 Phosphurets of Hydrogen, 417. 
 
 Phosphuret of Calcium, 487. 
 
 Phene, 842. 
 
 Phenyl, Hydrate of, 859, 843. 
 
 Phenyl, Amidide of, 845. 
 
 Piccamar, 835. 
 
 Picrotoxine, 922. 
 
 Piperine, 921. 
 
 Pittacal, 835. 
 
 Pictures, Negative and Positive, 225. 
 
 Picric Acid, 844. 
 
 Piccoline, 846. 
 
 Picryle, 855. 
 
 Plagihedral Crystals, 47. 
 
 Plants, Digestion of, 984. 
 
 Food of, 979. 
 
 Germination of, 977. 
 
 Ashes of, 986. 
 
 Growth of, 988. 
 
 Plaster of Paris, 609. 
 Plasters, 888. 
 Platinum, 575. 
 
 Gas Lamp, 237. 
 
 Spongy, 576. 
 
 Oxides, &c., of, 577. 
 
 Salts of, 658. 
 
 Ammonia, Salts of, 719. 
 
 Fulminating, 711. 
 
 Plesiomorphism, 309. 
 Plumbago, 673. 
 
 Platinum, Ammonia Bases, 719. 
 Platinocyanides, 749. 
 Platinocacodyl, 806. 
 Platinum Bases, 721. 
 Polarization of Heat, 132. 
 
 Light, 41. 
 
 Circular, 47. 
 
 Populin, 924. 
 Polychrome, 923. 
 Polybasic Acids, 588. 
 Porcelain, Nature of, 623. 
 
 Manufacture of, 625. 
 Potashes, 688. 
 
 Potash, 473. 
 
 Hydrates of, 474. 
 
 Potassium, 471. 
 
 Potassium, Oxides of, 473. 
 
 Sulphur ets of, 475. 
 
 Salts of, 594. 
 
 Amidide, 709. 
 
 Cyanide, 741. 
 Ferro-cyanide, 744. 
 
 Potato-starch, 755. 
 Potassium, Iodide of, 596. 
 Precipitate, Black, 717. 
 
 Red, 569. 
 
 White, 716. 
 
 Pressure on Gases, Law of, 16. 
 Vapours, 100. 
 
 Prismatic Colours, 38. 
 Prime Conductor, 153. 
 Proof-spirit, 774. 
 Prussian Blue, 746. 
 Prussiate of Potash, Yellow, 744. 
 Red, 747. 
 
 Prussine, 749. 
 Prussic Acid, 737. 
 
 Preparation of, 738. 
 
 Valuation of, 739. 
 
 Detection of, 740. 
 
 Protein, 1000. 
 
 Prismatic Systems of Crystals, 28, 
 
 Prussic Acid, Valuation of, 739. 
 
 Pseudomorphine, 959. 
 
 Pseudomorphism, 30. 
 
 Pseudorcine, 943. 
 
 Pteleyl Compounds, 806. 
 
 Puddling, 504. 
 
 Pus, 1045. 
 
 Putrefaction, 1045. 
 
 Purpurates, 1036. 
 
 Putty, 521. 
 
 Purple of Cassius, 572, 656. 
 
 Purree and its Derivatives, 938. 
 
 Pyrites, Copper, 552. 
 
 Iron, 5 10. 
 
 Pyro-acetic Spirit, 805. 
 Pyrometer, Daniell's, 65. 
 
 Expansion in, 67. 
 
 Pyro-catechine, 909. 
 Pyrogenic Bodies, 823. 
 Pyroxylic Spirit, 825. 
 Pyrophorus, 476. 
 Pyrolusite, 497. 
 
 Q. 
 
 Quantity, Influence of, on Affinity, 
 
 214. 
 
 Quartz, 449. 
 Quartation, 572. 
 Quassine, 924. 
 Quercitrine, 932 
 Quicksilver, 567. 
 
INDEX. 
 
 1065 
 
 Quinine, 950. 
 Quinoline, 796, 847. 
 
 K. 
 
 Radiation of Heat, 121. 
 
 of Light, 34. 
 
 Radical of the Seed, 976. 
 Radicals, Compound, 325. 
 
 Nature of, 664. 
 
 Rays, Tithonic in Light, 229. 
 Realgar, 536. 
 
 Red Lead, 559. 
 
 Precipitate, 569. 
 
 Cinchona, 911. 
 
 Colouring Matters, 930. 
 
 Reduction of Metallic Oxides, 465. 
 
 Sulphurets, 467. 
 
 ,. Arseniurets, 468. 
 
 Reflection of Heat, 123. 
 
 Light, 34. 
 
 Refraction of Heat, 132. 
 
 Single, 35. 
 
 Double, 41. 
 
 Indices of, 36. 
 
 Regular System, 25. 
 Rennet, 1028. 
 
 Resins, 867. 
 
 Distillation of, 834. 
 
 Respiration of Plants, 980. 
 
 Animals, 1025. 
 
 Retisteren. Retinol, 834. 
 Rhein, 928. 
 
 Rhombohedral Crystals, 27. 
 Rhodium, 577. 
 
 Salts of, 658. 
 
 Rhodizonates, 702. 
 Rhodan, 751. 
 
 Ricinostearine. Ricine, 888. 
 Ripening of Fruits, 982. 
 Rochelle Salt, 894. 
 Rosemary, Oil of, 861. 
 Rose, Otto of, 866. 
 Rotation of Crops, 989. 
 Rouge, 932. 
 
 Rutile, 531. 
 Rutilin. Rufin, 917. 
 Rue, Oil of, 861. 
 Ruthenium, 577. 
 
 Sabadilline, 962. 
 
 Saccharine Fermentation, 756, 764. 
 Sacchulmine, 772, 817. 
 Saccharohumine, 818. 
 Safety Lamp, 242. 
 68 
 
 Safflower, Red, 932. 
 Sago, 755. 
 Salop, 761. 
 Sal-ammoniac, 724. 
 Salicine, 916. 
 Salicyl Compounds, 859. 
 Saliretine, 917. 
 Saliva, 1029. 
 Salivary Matter, 1029. 
 Sagapanum, 869. 
 Salt, Common, 602. 
 
 Glauber's, 604. 
 
 Epsom, 614. 
 
 Microcosmic, 727. 
 
 Petre, 596. 
 
 Rochelle, 894. 
 
 Spirits of, 427. 
 
 of Sorrel, 700. 
 
 of Lemons, 701. 
 Salt, Radicals, 590. 
 Salts, Constitution of, 587. 
 
 Classes of, 582. 
 
 Polybasic, 589. 
 
 Double, 585, 592. 
 
 Water in, 353. 
 
 Crystallization of, 30, 20. 
 
 Isomorphism of, 305, 314. 
 
 Solubility of, 19. 
 
 Salts of Alumina, 615. 
 
 . Ammonia, 722. 
 
 Antimony, 641. 
 
 Arsenic, 639. 
 
 P Barium, 607. 
 
 Bismuth, 648. 
 
 Brucine, 960. 
 
 Calcium, 608. 
 
 Cadmium, 632. 
 
 i Cinchonine, 935. 
 
 Cobalt, 631. 
 
 Chrome, 635. 
 
 Copper, 644. 
 
 Iridium, 658. 
 
 Iron, 627. 
 
 Lead, 646. 
 
 Magnesium, 614. 
 
 Manganese, 626. 
 
 Mercury, 651. 
 
 Morphia, 955. 
 
 Molybdenum, 638. 
 
 Nickel, 631. 
 
 Osmium, 638. 
 
 Narcotine, 957- 
 
 Gold, 656. 
 
 Palladium, 657. 
 
 Platinum, 658. 
 
 - Quinine, 951. 
 
 Rhodium, 659. 
 
 Potassium, 594. 
 
 Silver, 649. 
 
1066 
 
 INDEX. 
 
 Salts of Sodium, 602. 
 
 Strontium, 608. 
 
 Strychnine, 959. 
 
 Tin, 633. 
 
 Zinc, 632. 
 
 Santaline, 932. 
 Sandarach, 869. 
 Santonine, 925. 
 Saponine, 925. 
 Saponifiable Fats, 871. 
 Savine, Oil of, 863. 
 Saxon Blue, 937. 
 
 Salts, Atomic Vols. of, 593. 
 
 Basic Nature of, 594. 
 
 Saltpetre, Assay of, 600. 
 
 Saligenine, 916. 
 
 Sarcosine, 1010. 
 
 Scammony Resin, 869, 
 
 Scillitine, 925. 
 
 Sea Water, Composition of, 603. 
 
 Secretions of Plants, 981. 
 
 Animals, 1041. 
 
 Sediments in Urine, 1039. 
 Selenite, 609. 
 Selenium, 407. 
 
 Compounds of, 408. 
 
 Senegin, 926. 
 Serous Tissues, 1010. 
 
 Secretion, 1011. 
 
 Serum of the Blood, 1013. 
 
 Serolin, 1014. 
 
 Selenaldine, 796. 
 
 Shells, Composition of, 1013. 
 
 Silica, 449. 
 
 Silicate of Alumina, 617, 624. 
 
 Cobalt, 632. 
 
 Potash, 602, 617. 
 
 Soda, 607, 619. 
 
 Silicon, 448. 
 
 Chloride of, 451. 
 
 Fluoride of, 452. 
 
 Silver, 565. 
 
 Oxides of, 566. 
 
 Sulphurets of, 567. 
 
 Salts of, 649. 
 
 Ammonia, Salts of, 714. 
 
 -Cyanide of, 742. 
 
 Sinapisine, 860. 
 
 Simple Bodies, 2. 
 
 Table of, 195. 
 
 Sinnamine, 860. 
 Sinapoline, 860. 
 
 Skin, Nature of, 1009. 
 
 Slaked Lime, 484. 
 
 Slags or Scoriae, 465. 
 
 Smalts, 632. 
 
 Smilacine, 926, 
 
 Soap, Manufacture of, 889. 
 
 Soda, 478. 
 
 Soda, Detection of, 479. 
 Sodium, 477. 
 
 Salts of, 602. 
 Soda-ash, 691. 
 Solanine, 963. 
 Solids, Specific Gravity of, 12. 
 
 Expansion of, 76. 
 
 Conduction of Heat by, 117. 
 
 Solder, 561. 
 
 Solubility, 1& 
 
 Solution, Phenomena of, 20. 
 
 like Vaporization, 114. 
 
 Sources of Heat, 137. 
 of Light, 53. 
 of Electricity, 163. 
 Solubility, Curves of, 19. 
 Soda-ash, Assay of, 693. 
 Spar-calc, 695. 
 Fluor, 608. 
 Heavy, 606. 
 Special Heat, 86. 
 Specific Gravity of Gases, 11. 
 Liquids, 10. 
 Solids, 12. 
 Vapours, 13. 
 
 Specific Heat, 81. 
 Spearmint, Oil of, 861 . 
 Spectrum, Prismatic, 38. 
 Speiss, 512. 
 Spiraea, Oil of, 858. 
 Spermaceti, 890. 
 Speculum Metal, 557. 
 Spectrum, Luminous, 38. 
 
 Chemical, 226. 
 
 Spirit of Wine, 775. 
 
 Salts, 427. 
 
 Hartshorn, 727, 847. 
 
 Mindererus, 804. 
 
 Pyroxylic, 823. 
 
 Pyro -acetic, 805. 
 
 Starch, 755. 
 
 Stannic Acid, 521. 
 
 Steam, Motive Force of, 114. 
 
 Latent Heat of, 97. 
 
 Elasticity of, 101. 
 
 Compressed, 115. 
 
 Stearine, 873. 
 Stearates, 874. 
 Stearoptens, 861. 
 Steel, 504. 
 Stibium, 542. 
 Strontium, 482. 
 
 Oxides of, 483. 
 
 Salts of, 607. 
 
 Strychnine, 958. 
 
 Steam, Electric Machine, 162. 
 Stilbene, Series, 855. 
 Suberine, 879. 
 Suberon, 879. 
 
INDEX. 
 
 1067 
 
 Succinates, 868. 
 Succinon, 869. 
 Sugar-Cane, 761. 
 
 of Grapes, 764. 
 
 Milk, 766. 
 
 Mushrooms, 767. 
 
 Starch, 764. 
 
 Gelatine, 1005. 
 
 Lead, 802. 
 
 Liquorice, 767. 
 
 Sulphates of Alumina, 616. 
 Ammonia, 723. 
 
 Barytes, 606. 
 
 Bismuth, 648. 
 
 Cinchonine, 935. 
 
 Cohalt, 631. 
 
 Copper, 644. 
 
 Chrome, 636. 
 
 Iron, 628. 
 
 Lead, 646. 
 
 Lime, 608. 
 
 Magnesia, 614. 
 
 Manganese, 626. 
 
 .. Mercury, 654. 
 
 Morphia, 955. 
 
 Nickel, 631. 
 
 Palladium, 657. 
 
 ^ Quinine, 951. 
 
 Potash, 595. 
 
 Silver, 649. 
 
 . Soda, 604. 
 
 Strontium, 608. 
 
 . Strychnia, 959. 
 
 Tin, 633. 
 
 Zinc, 632. 
 
 Sulphites, 390. 
 Sulpho- cyanides, 752. 
 Sulpho-cyanogen, 750. 
 Sulpho-sinapisine, 860. 
 Sulpho-methylan, 827. 
 Sulphur, 386. 
 
 Analogy with Oxygen, 389. 
 
 Oxygen, Compounds of, 390. 
 
 Sulphurets of Aluminum, 491. 
 
 Ammonium, 725. 
 
 Antimony, 545. 
 
 Arsenic, 536. 
 
 Barium, 482. 
 
 Bismuth, 563. 
 
 Cadmium, 519. 
 
 Calcium, 486. 
 
 Chrome, 526. 
 
 Cobalt, 516. 
 
 Copper, 555. 
 
 Carbon, 703. 
 
 Ethyl, 785. 
 
 Gold, 574. 
 
 Hydrogen, 404. 
 
 Iron, 510. 
 
 Sulphurets of Lead, 560. 
 
 Magnesium, 489. 
 
 Manganese, 501. 
 
 Mercury, 570. 
 
 Methyl, 828. 
 
 Molybdenum, 528. 
 
 Nickel, 514. 
 
 Nitrogen, 407. 
 
 Palladium, 575. 
 
 Platinum, 577. 
 
 Phosphorus, 418. 
 
 Potassium, 475. 
 
 Silver, 566. 
 
 Selenium, 408. 
 
 Sodium, 479. 
 
 Strontium, 483. 
 
 Tin, 522. 
 
 Zinc, 518. 
 
 Sulphuric Ether, 776. 
 Sulphur Salts, 586. 
 Substitutions, Theory of, 326, 668. 
 Thermic, 247. 
 
 Sulpho -mellon, 752. 
 
 Sulphovinic Acid, 782. 
 
 Sweat, 1010. 
 
 Synthesis, Nature of, 2. 
 
 Synthetic Action of Galvanism, 267. 
 
 Systems of Crystallization, 24. 
 
 T. 
 
 Tallow, 873. 
 
 Tannin, 903. 
 
 Tannates, 905. 
 
 Tanning Materials, Value of, 904. 
 
 Art of, 904, 1004. 
 
 Tantalum, 529. 
 Tapioca, 755. 
 Tannoxylic Acid, 905. 
 Tar, Constituents of, 834. 
 
 Wood, 835. 
 
 Coal, 836. 
 
 Tartar, Cream of, 893. 
 
 Emetic, 895. 
 
 of Iron, 894. 
 
 Tartrates of Potash, 893. 
 
 Soda, 894. 
 
 Lime, 894. 
 
 Antimonv, 896. 
 
 Tartrate, Boron, 896. 
 
 Stibion, 895. 
 
 Arsenic, 896. 
 
 Tartralets, 897. 
 Teeth, 1012. 
 Tellurium, 548. 
 
 Compounds of, 549. 
 
 Telluret of Hydrogen, 550. 
 Salts of, 643, 
 
1068 
 
 INDEX. 
 
 Temperature, Nature of, 57. 
 
 Balance of, 133. 
 
 ,- Table of, 66. 
 
 Tendons,. Composition of, 1011. 
 
 Terebene, 863. 
 
 Tetrathionic Acid, 401. 
 
 Terbium and Terbia, 482. 
 
 Theirie, 920. 
 
 Thebaine, 959. 
 
 Thermometer, Nature of the, 56. 
 
 ; Kinds of, 60. 
 
 Thermometric Scales, 63. 
 Thermometer of Breguet, 79. 
 
 Differential, 122. 
 
 Thermo-multiplier, 126, 184. 
 Thermo-electricity, 182. 
 Thermo- chemistry, 244, 250. 
 Theory, Atomic, 294. 
 , Binary of Salts, 590. 
 
 of Compound Radicals, 325, 
 
 664. 
 of Chemical Types, 326, 668, 
 
 972. 
 
 of Organic Acids, 666. 
 
 of Volumes, 289. 
 
 of the Ethers, 812. 
 
 of Ammonia, 709, 723. 
 
 of Respiration, 1024. 
 
 Thialol, 785. 
 Thorinum, 492. 
 
 Salts of, 626. 
 
 Thermochemical Equivalents, 246. 
 Thermic Substitutions, 248. 
 Thionic Acids, 403. 
 Thialdine, 796. 
 Thiosinnamine, 860. 
 Theobromine, 920. 
 Tin, 518. 
 
 Grain, 519. 
 
 Oxides of, 520. 
 
 Stone, 520. 
 
 Sulphurets of, 521. 
 
 Salts of, 633. 
 
 Tincal, 606. 
 
 Titanium, 530. 
 
 . Compounds of, 531. 
 
 Salts of, 643. 
 
 Tithonicity, 229. 
 Tithonic Rays of Light, 52. 
 Transfer of Elements, 258. 
 Treacle, 761. 
 
 Trona, 695. 
 Transcalescence, 127. 
 Tragacanthine, 761. 
 Tungsten, 527. 
 
 Saits of, 638. 
 
 Turpentine, 867. 
 
 Oil of, 863. 
 
 Camphor, 866. 
 
 Turf, Nature of, 819. 
 
 Types, Chemical, 326, 668, 972. 
 
 U. 
 
 Ulmine, from Soil, 819. 
 
 Sugar, 772, 819. 
 
 -Turf, 820. 
 
 .Wood, 818. ( 
 
 Ultramarine, 617. 
 Uranium, 551. 
 
 Salts of, 643. 
 
 Urea, 732. 
 
 Salts of, 733. 
 
 Uryl, 1032. 
 Uramil, 1034. 
 
 Urine of Carnivora, 1030. 
 
 of Reptiles, 1031. 
 
 Herbivora, 1036. 
 
 Diabetic, 1038. 
 
 in other Diseases, 1039. 
 
 Urinary Sediments, 1040. 
 Calculi, 1041. 
 
 Uranyle, 551. 
 
 V. 
 
 Vacuum, Barometric, 369. 
 
 Evaporation in, 109. 
 
 Boiling in, 106. 
 
 Valerian, Oil of, 861. 
 Valerianic Aldehyd, 816. 
 Valeron, 816. 
 
 Vapour, Electricity of, 162. 
 Vapours, latent Heat of, 97. 
 --- Volumes of, 99. 
 
 Elasticities of, 101. 
 
 Compared with Gases, 
 
 115. 
 
 Specific Gravity of, 13. 
 
 Vaporization, 96 
 Vanadium, 526. 
 
 Salts of, 638. 
 
 Ill, 
 
 Vegetable Jelly, 914. 
 
 Alcaloids, Nature of the, 
 
 969. 
 
 Vegetation, Phenomena of, 977. 
 Velocity of Light, 35. 
 Electricity, 142. 
 
 Vegetable Soil, 819, 988. 
 Veratrine, 961. 
 Verdigris, 803. 
 Vermillion, 570. 
 Vegetable Alcalies, 950, 969. 
 
 Extracts, 927. 
 
 Albumen, 771. 
 
 Vinous Fermentation, 772. 
 Vinegar, 797. 
 
INDEX. 
 
 1069 
 
 Vitriol, Oil of, 392. 
 
 White, 632. 
 
 Vinegar Mothers, 797. 
 Volatile Alcali, 706. 
 Voltaic Electricity. 163. 
 
 Circles, 166. 
 
 Voltameter, 264. 
 
 Volta's Theory of Contact, 174. 
 Volumes, Theory of, 289. 
 
 of Atoms, 300. 
 
 Atomic, of Salts, 573. 
 
 Isomorpic, 302. 
 
 W. 
 
 Water, Composition of, 348. 
 
 Solution of Gases in. 351. 
 
 of Solids in, 20. 
 
 Chemical Properties of, 352. 
 
 Combinations of, 353. 
 
 Oxygenated, 355. 
 Phosphates of, 413. 
 
 - Expansion of, 73. 
 
 Freezing of, 93. 
 
 . Vapour of, 97. 
 
 Filtration of, 355. 
 
 of Ammonia, 708. 
 
 Waters, Mineral, 354. 
 
 Sea/603. 
 
 Wax, 891. 
 
 Wave-Theory of Light, 48. 
 
 of Heat, 133. 
 
 Welding, 504. 
 
 Weld, 933. 
 White Lead, 697. 
 
 Pearl. 648. 
 
 Vitriol, 632. 
 
 Wine, Oil of, 783. 
 
 Wood, Fossil, 821. 
 
 Rotting of, 818. 
 
 Distillation of, 823. 
 
 Tar, 835. 
 
 Woody Fibre, 758, 980. 
 Woad, 934. 
 
 X. 
 
 Xanthic Oxide, 1041. 
 Xanthophyll, 946. 
 Xanthorhamnine, 932. 
 Xanthine, 930. 
 Xyloidine, 759. 
 ! Xylit, 826. 
 
 Y. 
 
 Yeast, 772. 
 Yellow, King's, 536. 
 
 Chrome, 648. 
 
 Yellow-colouring Matters, 933. 
 Yellow Wood, 934. 
 Yttrium, 492. 
 Salts of, 626. 
 
 Z. 
 
 Zaflre, 514. 
 Zinc, 516. 
 
 Butter of, 633. 
 
 Compounds of, 517. 
 
 Salts of, 632. 
 
 Blende, 518. 
 
 Zirconium, 494. 
 Salts of, 626. 
 
 THE END. 
 
DUBLIN : 
 GOODWIN, SON & NETHERCOTT, 
 
 79, Marlborough-sl, 
 
A CATALOGUE OF WORKS 
 
 IN THE VARIOUS BRANCHES OF 
 
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 of Contents, 
 
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 Pereira's (Dr.) Elements of Materia Medica 
 
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 "In the parts now before us [XIII. and XIV.] we find articles extending, in alphabetical 
 order, from Poisons to Scirrhous Tumors; and when we say that they are ot such a character 
 as to justify the description of the work which we have just quoted from the title-page, we 
 have awarded praise of no ordinary kind. Dr. Copland is indeed one of the most remarkable 
 of living authors : he not only brings to bear upon his subjects a vast we had almost said an 
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 mind of the reader, by the soundness with which he applies his personal experience. For one 
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 CURLING.-A PRACTICAL TREATISE ON THE DISEASES 
 
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 sulted as distinct treatises. Vol. I. External Diseases ; Vol. II. Internal ; Vol. III. Lameness. 
 
PUBLISHED BY MESSRS. LONGMAN, BROWN, AND CO. 
 
 PERCIYALL.-THE ANATOMY OF THE HORSE; 
 
 Embracing the Structure of the Foot. By WILLIAM PERCIVALL, M.R.C.S. Veterinary 
 Surgeon 1st Life Guards. 8vo. 20s. cloth. 
 
 PEREIRA.-THE ELEMENTS OF MATERTA MEDICA AND 
 
 THERAPEUTICS. By JONATHAN PEREIRA, M.D. F.R.S. and L.S. ; Fellow of the Royal 
 College of Physicians in London ; Vice-President of the Royal Medical and Chirurgical 
 Society ; Honorary Member of the Pharmaceutical Societies of Great Britain, St. Petersburg, 
 and Portugal ; of the Medical and Physical Society of Erlangen ; and of the Natural History 
 Association of Hesse ; Corresponding Member of the Society of Pharmacy of Paris ; Examiner 
 in Materia Medica and Pharmacy to the University of London; and Assistant Physician to, 
 and Lecturer on Materia Medica at, the London Hospital. New Edition, enlarged and im- 
 proved, including Notices of most of the Medicinal Substances in Use in the Civilized World, 
 and forming an Encyclopaedia of Materia Medica. With numerous Wood Engravings. Vol. I. 
 comprising Psychical or Mental Remedies, and Physical but Imponderable Remedies. 8vo. 
 25s. cloth. [Vol. II. it in thepretf. 
 
 PEREIRA.-A TREATISE ON FOOD AND DIET. 
 
 With Observations on the Dietetical Regimen suited for Disordered States of the Digestive 
 Organs : and an Account of the Dietaries of some of the principal Metropolitan and other 
 Establishments, for Paupers, Lunatics, Criminals, Children, the Sick, &c. By JON. PEREIRA, 
 M.D. F.R.S. & L.S. &c. 8vo. 16s. cloth. 
 
 PESCHEL.-THE ELEMENTS OF PHYSICS. 
 
 By C. F. PESCHEL, Principal of the Royal Military College, Dresden. Translated from the 
 German, with Notes, by E. WEST. 3 vols. fcp. 8vo. with Woodcuts and Diagrams, 21s. cloth. 
 
 ( Part I. The Physics of Ponderable Bodies. Fcp. 8vo. 7s. 6d. 
 Separately < Part II. Imponderable Bodies Light, Heat, Magnetism, Electricity, and Electro- 
 
 (. Dynamics. 2 vols. fcp. 8vo. 13s, 6d. 
 
 "Mr. West has enhanced the value of this work by his notes, and the woodcuts and 
 diagrams illustrative of the subject are very neatly and clearly executed. The body of infor- 
 mation comprised in these three closely-printed volumes is enormous. The last portion is 
 devoted to the investigation of the Physics of Imponderable Bodies; in the handling of which 
 very difficult and delicate subject the author exhibits peculiar acumen." 
 
 CHURCH OF ENGLAND QUARTERLY REVIEW. 
 
 PHILLIPS .-AN ELEMENTARY INTRODUCTION TO 
 
 MINERALOGY ; comprising a Notice of the Characters, Properties, and Chemical Consti- 
 tution of Minerals: with Accounts of the Places and Circumstances in which they are found. 
 By WILLIAM PHILLIPS, F.L.S. M.G.S. &c. New Edition, corrected, enlarged, and im- 
 proved, by H. G. BROOKE, F.R.S., and W. H. MILLER, M.A. F.R.S. Professor of Mineralogy 
 in University of Cambridge. 8vo. with numerous Wood Engravings [Nearly ready. 
 
 THE POCKET AND THE STUD ; 
 
 Or, Practical Hints on the Management of the Stable. By HARRY HIEOVER. Author of 
 " Stable-Talk and Table-Talk ; or, Spectacles for Young Sportsmen." Fcp. 8vo. with Portrait 
 of the Author on his favourite Horse " Harlequin." 5s. half-bound. 
 
 REES (DR. G. OWEN).-ON THE NATURE AND TREAT- 
 MENT of DISEASES of the KIDNEY connected with ALBUMINOUS URINE (MORBUS 
 BRIGHTII). By GEORGE OWEN REES, M.D. F.R.S. Assistant- Physician to, and Lecturer 
 on Materia Medica at, Guy's Hospital ; Physician to the Pentonville Prison. 8vo. 5s. cloth. 
 
 " Dr. Owen Rees has been long known to the profession as an able and indefatigable labourer 
 in the field of animal chemistry. This little work will add justly to his reputation. It is 
 altogether practical, and may be said fairly to embrace, in a moderate compass all that is at 
 present known on the subject of which it treats." LANCET. 
 
 " The appearance of a treatise by Dr. G. O. Rees, who is well known to have devoted consi- 
 derable attention to this subject, is a most welcome addition to our medical literature. By 
 the aid of sound chemical knowledge, accurate observation, and a clear manner of expressing 
 his views, the author has succeeded in compressing into a small octavo a large amount of in- 
 formation, which cannot fail to prove valuable to the medical practitioner who has neither the 
 
 time nor the inclination to read a bulky treatise With this we conclude our notice of 
 
 this admirable practical treatise. We entertain no doubt that it will find a wide circulation 
 in the profession." MEDICAL GAZETTE. 
 
 REES (DR. G. 0EN).-THE TREATMENT OF RHEUMATIC 
 
 DISEASES by LEMON-JUICE: with Illustrative Cases from Hospital Practice. By 
 G. OWEN REES, M.D. F.R.S., Fellow of the Royal College of Physicians ; Assistant-Physician 
 to, and Lecturer on Materia Medica at, Guy's Hospital ; Physician to the Pentonville Prison, 
 &c. 8vo. Is. 6d. sewed. 
 
12 MEDICAL, SURGICAL, AND SCIENTIFIC WORKS, 
 
 REES (DR. G. OWENX-ON THE ANALYSIS OF THE BLOOD 
 
 AND URINE, AND ON THE TREATMENT OF URINARY DISEASES. By G.OWEN REES, 
 M.D. F.R.S. Fellow of the Royal College of Physicians, Principal Medical Officer to the 
 Pentonville Prison, and Assistant-Physician to Guy's Hospital. New Edition. 8vo. with Plates, 
 7s. 6d. cloth. 
 
 RYND.-PATHOLOGICAL AND PRACTICAL OBSERVATIONS 
 
 on STRICTURES, and some other DISEASES of the URINARY ORGANS. Br FRANCIS 
 RYND, Esq. M.A. M.R.I.A., Fellow and Member of Council of the Royal College of Surgeons 
 in Ireland ; Surgeon to the Meath Hospital, and County of Dublin Infirmary ; Her Majesty's 
 Medical Superintendent of Convicts in Ireland ; Member of the Royal Medical Society of 
 Edinburgh, of the Pathological Society, &c. 8vo. 7s. 6d. cloth. 
 
 " Mr. Rynd presents us in the present volume with a very clear and intelligent treatise, In 
 which thought is blended with experience, and research with practice : and from the perusal 
 of which, although we do not agree in all the opinions that are advanced, we have derived 
 
 both profit and gratification It is, without doubt, an able and thoughtful production, 
 
 and has our cordial recommendation as one of the best of the modern contributions to this 
 branch of surgery." MEDICO-CHIRURGICAL REVIEW. 
 
 "The selections we have given from Mr. Rynd's book are intended as specimens of his 
 style and matter, and more for the purpose of inducing others to peruse his volume, than 
 with the view of affording anything like a general analysis of it. The author has exhibited 
 considerable industry and care in the arrangement of his work, and the practical precepts 
 with which it is replete will amply remunerate the reader for the time expended in its study. 
 We' again repeat it as our deliberate opinion, that these pathological and practical observations 
 on stricture reflect great credit upon the author." DUBLIN MEDICAL JOURNAL. 
 
 SANDBY.-MESMERISM AND ITS OPPONENTS. 
 
 By GEORGE SANDBY, M.A. Vicar of Flixton, Suffolk. New Edition, considerably enlarged ; 
 with an Introductory Chapter on the Hostility of Scientific and Medical Men to Mesmerism. 
 16mo. 5s. cloth ; or in 2 Parts, 2s. each. 
 
 SCHLEIDEN.-PRINCIPLES OF SCIENTIFIC BOTANY; 
 
 or, Botany as an Inductive Science. By Dr. J. M. SCHLEIDEN, Extraordinary Professor of 
 Botany in the University of Jena. Translated by EDWIN LANKKSTER, M.D. F.R.S. F.L.S. 
 Lecturer on Materia Medica and Botany at the St. George's School of Medicine, London. 
 With Plates and Wood Engravings. 8vo. 21s. cloth. 
 
 *' More might be said in favour of this remarkable work ; valuable on account not so much 
 of the vast accumulation of facts contained in it, as of the comprehensive manner in which 
 they are strung together. The explanatory comments aid materially to render the text intel- 
 ligible The author is gn atly indebted to Dr. Lankester for the skill with which he has 
 
 made his labours known in this country, and especially for the ease with which the botanical 
 terms are made conformable to our habitual technicalities in the science." ATHENAEUM. 
 
 "This work is undoubtedly the most valuable systematic exposition of the structural de- 
 partment of botany which has yet been given to the world. The thanks of the botanists of 
 this country are therefore due to Dr. Lankester for the present translation, which although 
 by no means free from blemishes, may be received, on the whole, as a fair average rendering 
 of a work which is admitted to present considerable difficulties The volume is well illus- 
 trated wholly from the author's own drawings, a rather unusual circumstance, but of course 
 greatly adding to its value. No one interested in scientific botany should be without the 
 work." JABDINE'S ANNALS OF NATURAL HISTORY. 
 
 " The treatise no\y placed before us in an English dress is already in its third German 
 edition, which sufficiently indicates the appreciation it has acquired in the country which 
 gave it birth. It differs in its general character and arrangement from all preceding treatises 
 on botany ; and presents the anatomical and physiological departments of the subject in a far 
 more scientific aspect than they have ever before been made to exhibit. It is full of original 
 observations of great value ; and has this remarkable merit, that the author has taken very 
 little upon trust, but has examined into almost every point for himself. We need not say, 
 then, that its reproduction in our own language, under the able editorship of Dr. Lankester, 
 (who has had the advantage of Mr. Henfrey's assistance,) is a great boon to the British bota- 
 nist We regard the plan of his work, and the method of investigation on which it is 
 
 based, as far superior to that of any other systematic treatise on the subject ; and no one can 
 rightly comprehend the present aspect of botanical science, without a careful study of it." 
 
 MEDICO-CHIRURGICAL REVIEW. 
 
 SEYMOUR (DR. EDWARD) -THOUGHTS ON THE NATURE 
 
 and TREATMENT of several SEVERE DISEASES of the HUMAN BODY ; including 1. 
 Diseases of the Stomach. 2. Gout.- 3. Melancholy (Mental Derangement). 4. Epilepsy. 
 5. Neuralgic Affections Brow Ague, Sciatica, &c. By EDWARD J. SEYMOUR, M.D. F.R.S. 
 late Senior Physician to St. George's Hospital. 8vo. 10s. cloth. 
 
PUBLISHED BY MESSRS. LONGMAN, BROWN, AND CO. 13 
 
 SMITH.-AN INTRODUCTION TO THE STUDY OF BOTANY. 
 
 By Sir J. E. SM ITH, late President of the Linnaean Society. New Edition, corrected, in which 
 the object of Smith's "Grammar of Botany" is combined with that of the " Introduction." 
 By Sir W. J. HOOKER, K.H. LL.D. &c. 8vo. with 36 Plates, 16s. ; with the plates coloured, 
 j6 J 2. 12s. 6d. cloth. 
 
 SMITH-COMPENDIUM OF THE ENGLISH FLORA. 
 
 By Sir J. E. SMITH. New Edition, with Additions and Corrections, by Sir W. J. HOOKER. 
 12mo. 7s. 6d. cloth. 
 
 THE SAME IN LATIN. New Edition. 12mo. 7s. 6d. cloth. 
 
 SOLLY (SAMUEL). -THE HUMAN BRAIN: ITS STRUC- 
 
 TURE, PHYSIOLOGY, and DISEASES ; with a description of the Typical Forms of Brain 
 in the Animal Kingdom. By SAMUEL SOLLY, F.R.S. Senior Assist.-Surgeon to St. Thomas's 
 Hospital, and Lecturer on Clinical Surgery, Senior Surgeon to the Aldersgate Dispensary. 
 New Edition, greatly enlarged. 8vo. with numerous Wood Engravings, 21s. cloth. 
 
 "The most complete account of the anatomy, physiology, and pathology of the brain that 
 has hitherto appeared. Mr. Solly has enriched the descriptive portion of his volume with'a 
 large number of wood-engravings, many of them the product of his own pencil ; and which, 
 being intercalated with the text, give an increased interest and clearness to the details they 
 so admirably illustrate. We earnestly advise all our professional brethren to enrich their 
 libraries with this admirable treatise, which bears the stamp of extensive observation and 
 careful research ; and which has in addition this peculiar advantage, that it combines, in a 
 moderate compass, a scientific and practical account of the anatomy, physiology, and pathology 
 of the brain." MEDICO-CHIRURGICAL REVIEW. 
 
 " The reputation of the first edition of this treatise has been maintained up to the present 
 time. Additions from recent observations by numerous anatomists have been amply supplied, 
 to brinz the work up to the standard of our present knowledge ; and these, together with all 
 that gave interest and value to the former edition, comprehend, we will venture to say, as 
 nearly as possible the whole of the information of importance already established with regard 
 to the anatomy, physiology, and diseases of the brain. The work is one which fully deserves, 
 and will certainly obtain, a place among our medical classics. The subjects of which it treats, 
 like almost all questions in anatomy and pathology, will doubtless, as science advances, 
 receive numerous additions and modifications ; but the scope of the treatise is so ample, and 
 the arrangement of its various topics so judicious, that we believe it need never be superseded 
 as a standard work of reference." MEDICAL GAZETTE. 
 
 STAFFORD THE TREATMENT OF SOME AFFECTIONS 
 
 of the PROSTATE GLAND. By R. A. STAFFORD, F.R.C.S. Surgeon -Extraordinary to 
 H.R.H. the Duke of Cambridge, Senior Surgeon to St. Marylebone Infirmary, &c. New 
 Edition. 8vo. 5s. cloth. 
 
 STAFFORD. OBSERVATIONS ON DISEASES OF THE 
 
 URETHRA, and more particularly on the Treatment of Permanent Stricture. By R. A. 
 STAFFORD, F.R.C.S. Surgeon-Extgaordinary to H.R.H. the Duke of Cambridge, Senior 
 Surgeon to St. Marylebone Infirmary, &c. New Edition. 8vo. 9s. cloth. 
 
 STANLEY.-A TREATISE ON DISEASES OF THE BONES. 
 
 By EDWARD STANLEY, President of the Royal College of Surgeons of England, and Surgeon 
 to St. Bartholomew's Hospital. Accompanied by an Atlas of Plates illustrating the Diseases 
 and Injuries of the Bones. 8vo. with folio Atlas of Plates, 42s. cloth. 
 
 V The 8vo. volume may be had separately, price fos. 6d. ; the Atlas of Platea 
 separately, price 1. 2s. 
 
 " We are sure that the present works will be looked upon as filling up a hiatus in surgical 
 literature ; more especially as they are the productions of a gentleman who has possessed so 
 many opportunities of gaining information respecting the pathology and treatment of these 
 
 diseases We cannot but express our opinion, that this treatise is one of great merit, and 
 
 that it will be appreciated as it deserves to be by those who make themselves acquainted with 
 it. Some of the subjects are, perhaps, not treated so fully as they might be, but yet, taking 
 the work as a whole, a large amount of valuable information will be found therein. The 
 numerous cases related by the author form a prominent feature in the work, and shew that 
 he has exercised great industry in collecting the proper materials, and that he has not thrown 
 away the vast opportunities which he has possessed, as surgeon to one of the largest hospitals 
 in London. We have no doubt that this treatise will be estimated in the same light as are 
 the admirable works of Hodgson, Lawrence, and Sir Astley Cooper works of which British 
 surgeons may well be proud. With regard to the handsome folio volume of illlustrations, 
 we can only say, without making particular mention of any delineation, that it forms an 
 admirable companion to the practical treatise: the drawings are vivid and expressive, and we 
 strongly recommend both works to be studied together." LANCET. 
 
14 MEDICAL, SURGICAL, AND SCIENTIFIC WORKS, 
 
 THE STUD, FOR PRACTICAL PURPOSES AND PRACTICAL 
 
 MEN : being a Guide to the Choice of a Horse, for use, more than for show. By HARRY 
 HIEOVER, Author of "Stable Talk and Table Talk," and "The Pocket and the Stud." 
 With two Plates, one representing "A pretty good sort for most purposes;" the other, 
 " ' Rayther' a bad sort for any purpose." Fcp. Svo. 5s. half-bound. 
 
 TAMPLIN (MR. R. .) LECTURES ON THE NATURE AND 
 
 TREATMENT OF DEFORMITIES, delivered at the Royal Orthopaedic Hospital, Bloomsbui y 
 Square. By R. W. TAMPLIN, F.R.C.S.E. Surgeon to the Hospital. Fcp. 8vo. with Wood 
 Engravings, 7s. 6d. cloth. 
 
 TEALE (T. P. ESQJ-A PRACTICAL TREATISE ON 
 
 ABDOMINAL HERNIA. By THOMAS PRTDGIN TEALE, F.L.S. Fellow of the Royal College 
 of Surgeons, and Surgeon to the Leeds General Infirmary. 8vo: with numerous Illustrations, 
 15s. cloth. 
 
 THOMAS'S MODERN PRACTICE OF PHYSIC : 
 
 Exhibiting the Character, Causes, Symptoms, Diagnostics, Morbid Appearances, and Improved 
 Method of Treating Diseases of all Climates. By the late Dr. ROBERT THOMAS. New 
 Edition, thoroughly revised, and brought up to the present day, by ALGERNON FRAMPTON, 
 M.D. Fellow of the Royal College of Physicians, and Physician to the London Hospital. Svo. 
 
 [In the press. 
 
 THOMSON (DR. R. D.)-EXPERIMENTAL RESEARCHES 
 
 on the FOOD of ANIMALS and. the FATTENING of CATTLE; with Remarks on the 
 Food of Man. By ROBERT DUNDAS THOMSON, M.D. Master in Surgery in the University of 
 Glasgow; Lecturer on Chemistry in the same University; and formerly in the Medical 
 Service of the Honourable East India Company. Fcp. Svo. 5s. cloth. 
 
 THOMSON-SCHOOL CHEMISTRY ; 
 
 or, Practical Rudiments of the Science. By ROBERT DUNDAS THOMSON, M.D. Master in 
 Surgery in the University of Glasgow ; Lecturer on Chemistry in the same University ; and 
 formerly in the Medical Service of the Honourable East India Company. Fcp. Svo with 
 Woodcuts, 7s. cloth. 
 
 " The book has a two-fold aim; viz. to furnish a text-book suitable for the instruction of 
 the youngest persons at all competent fo take an interest in chemistry, and likewise to supply 
 a manual such as shall enable the professional student, and especially the student of medicine, 
 to follow University lectures It discusses sufficiently and fully all the important depart- 
 ments of chemistry. The style is simple and perspicuous ; the experiments suggested are 
 well devised ; and the mode in which they should be performed is made manifest by a plentiful 
 use of woodcuts, illustrating apparatus and manipulation. In addition to its substantial 
 merits as a text-book, its pages are lightened by a variety of curious and frequently amusing 
 details, to be found in few other treatises on Chemistry." 
 
 MONTHLY JOURNAL OF THE MEDICAL SCIENCES. 
 
 THOMSON (DR. ANTHONY TODD). -A PRACTICAL 
 
 TREATISE on DISEASES affecting the SKIN. By ANTHONY TODD THOMSON, M.D. F.L.S. 
 Fellow of the Royal College of Physicians; Physician to University College Hospital; and 
 Professor of Materia Medica and Forensic Medicine in University College, &c. With a 
 Memoir by Mrs. THOMSON. Svo. [Nearly ready. 
 
 THOMSON-CONSPECTUS OF THE PHARMACOPEIAS. 
 
 By Dr. ANTHONY TODD THOMSON, F.L.S. &c. New Edition, thoroughly revised and greatly 
 improved ; containing the alterations and additions of the last London Pharmacopoeia and 
 the New French and American Remedies. 18mo. 5s. 6d. cloth ; or, with roan tuck, as a pocket- 
 book, 6s. 6d. 
 
 THOMSON.-THE LONDON DISPENSATORY : 
 
 Containing Translations of the Pharmacopoeias of London, Edinburgh, and Dublin ; the 
 Elements of Pharmacy; the Botanical Description, Natural History, and Analysis of the 
 Substances of the Materia Medica, &c. &c. : with a copious Index of Synonyms. "Forming a 
 Practical Synopsis of Materia Medica, Pharmacy, and Therapeutics: with Tables and Wood- 
 cuts. By ANTHONY TODD THOMSON, M.D. F.L.S. Fellow of the Royal College of Physicians, 
 Professor of Materia Medica, &c. in University College, London. New Edition, corrected 
 throughout, and materially improved. Svo. 21s. cloth. 
 
 THOMSON- ELEMENTS OF MATERIA MEDICA AND 
 
 THERAPEUTICS ; including the Recent discoveries and Analysis of Medicines. By Dr. 
 ANTHONY TODD THOMSON, F.L.S. &c. &c. New Edition, enlarged and improved. Svo. with 
 upwards of 100 Wood Engravings, \. 11s. 6d. cloth. 
 
PUBLISHED BY MESSRS. LONGMAN, BROWN, AND CO. 15 
 
 THOMSON.-THE DOMESTIC MANAGEMENT OF THE SICK 
 
 ROOM, necessary, in Aid of Medical Treatment, for the Cure of Diseases. By A. TODD 
 THOMSON, M.D. F.L.S. &c. New Edition. Post 8vo. 10s. 6d. cloth. 
 
 THOMSON.-ATLAS OF DELINEATIONS OF CUTANEOUS 
 
 ERUPTIONS ; illustrative of the Descriptions in Dr. Bateman's Synopsis of Cutaneous 
 Diseases. By A. TODD THOMSON, M.D. &c. Royal 8vo. with 29 Plates, comprising 128 Illus- 
 trations, carefully coloured after nature, =3. 3s. boards. 
 
 TODD (DR. R. B.)-THE CYCLOPEDIA OF ANATOMY AND 
 
 PHYSIOLOGY. Edited by ROBERT B. TODD, M.D. F.R S. Fellow of the Royal College of 
 Physicians, Professor of Physiology, and of General and Morbid Anatomy, in King's College, 
 London, and Physician to King's College, Hospital. Illustrated with numerous Engravings 
 on Wood. 
 
 Vol. I. ABDOMEN to DEATH. 8vo. with numerous Wood Engravings, 4^s. 
 
 II. DIAPHRAGM to IXSECTIVORA. 8vo. with numerous Wood Engravings, 50s. 
 III. INSTINCT to PLACENTA. 8vo. with numerous Wood Engravings, 50s. 
 And Parts XXX. to XXXVIII. POLYOASTRIA to THORAX,* with numerous Wood Engrav- 
 ings. 8vo. 5s. each. Part XXXIX. is nearly ready. 
 
 ** The Cyclopaedia is now in course of publication with as ranch regularity as the nature of 
 the work wul admit, seven Parts having appeared since Messrs. Longman and Co. became 
 the proprietors of it : it is rapidly drawing to a conclusion, and Messrs. Longman and Co. 
 are assured that it will be completed in four or five more Parts. 
 
 This work is especially dependent on the support of medical men, and of those who take an 
 interest in anatomical and physiological science. It has greatly exceeded the extent origi- 
 nally assigned to it at its commencement, chiefly in consequence of the rapid strides which 
 Physiology has made during the last ten years, which rendered it necessary to introduce 
 many entirely new articles, and partly because a much larger number of illustrations has been 
 given than was originally contemplated. 
 
 It is hoped that when completed the work will contain such a series of essays, anatomical, 
 physiological, and zootomical, as is not to be found in any other publicatiou, whether British 
 or foreign ; and as it had been commenced at a low price, and conducted with a liberality 
 which precludes the possibility of remuneration without an extended sale, Messrs. Longman 
 and Co. trust that they may look to the medical and scientific public to lend their patronage 
 to this great and important work. 
 
 " As this great work proceeds, the same proofs are given of the talent and elaborateness of 
 which so highly characterised its commencement, and have run through its numerous 
 
 numbers We have expressed our admiration of the book on many previous occasions, 
 
 so that additional panegyric would be but the reiteration of past praise. It is a work that 
 must abide as long as the language in which it is written ; and every member of the profes- 
 sion wishing to possess some of the best monographs on the various subjects which it con- 
 tains, should possess the Cyclopeedia of Anatomy and Physiology. The work is a library on 
 the subjects ot anatomy and physiology." LANCET. 
 
 TRANSACTIONS OF THE ROYAL MEDICAL AND CHIRUR- 
 
 GICAL SOCIETY of LONDON; comprising many valuable and important Papers on Medi- 
 cine and Surgery- Vol. XXXII. (1850), or Vol. XIV. of the New Series. With Lithographic 
 Plates and Wood Engravings. 8vo. 8s. 6d. cloth. 
 
 TURNER A TREATISE. ON THE FOOT OF THE HORSE, 
 
 And on a New System of Shoeing, by one-sided nailing; also on the Nature, Origin, and Symp- 
 toms of the Navicular Joint Lameness, with Preventive and Curative Treatment. By 
 J.TURNER, M.R.V.C. Royal 8vo. 7s. 6d. boards. 
 
 URE.-DICTIONARY OF ARTS, MANUFACTURES, & MINES: 
 
 Containing a clear Exposition of their Principles and Practice. By ANDREW URE, M.D. 
 F.R.S. M.G.S. M.A.S. Lond. ; M. Acad. N.L. Philad. ; S. Ph. Soc. N. Germ. Hanov.; Mulii. 
 &c. &c. 3d Edition, corrected. 8vo. with 1,241 Engravings on Wood, 50s. cloth. 
 
 URE.-RECENT IMPROVEMENTS IN ARTS, MANUFAC- 
 
 TURES, and MINES; being the 2d Edition of a Supplement to the 3d Edition of his Dictionary. 
 By ANDREW URE, M.D. F.R.S. &c. 8vo. with numerous Wood Engravings, 14s. cloth. 
 
 THE VETERINARIAN ; 
 
 Or, Monthly Journal of Veterinary Science. Edited by Mr. PERCIVALL, in communicatien 
 with M. LEBLANC, Editor of the " Clinique V6te'rinaire," at Paris. 8vo. Is. 6d. sewed. 
 
 THE VETERINARY RECORD, 
 
 And Transactions of the Veterinary Medical Association. Edited by Messrs. SPOONER, 
 SIMON DS, and MORTON. 8vo. 2s. 6d. sewed. 
 
 V Published Quarterly On the 1st of January, April, July, and October. 
 
16 SCIENTIFIC WORKS PUBLISHED BY MESSRS, LONGMAN & CO. 
 
 VINCENT (J. P.)-OBSERYATIONS ON SOME OF THE 
 
 PARTS of SURGICAL PRACTICE ; to which is prefixed, an Inquiry into the Claims that 
 Surgery may be supposed to have for being classed as a Science, By JOHN PAINTER 
 VINCENT, late 'Senior Surgeon to St. Bartholomew's Hospital. 8vo. with Plate, 12s. cloth. 
 
 " A book which contains many valuable remarks, useful hints, and observations, which few 
 engaged in the active duties of their profession can read and reflect on without profit. The 
 whole tone of Mr. Vincent's treatise is characteristic of the gentleman and the scholar." 
 
 MEDICO-CHIRURGICAL REVIEW. 
 
 " Every page of this learned treatise bears the impress of the scientific surgeon and accom- 
 plished scholar. The introductory chapter upon the claims of surgery to be considered as a 
 science, evidences an intellect of a superior order, and a highly cultivated and reflecting 
 
 before he has ventured to lay before the profession the results of his observations. We shall 
 make but a few extracts from the work, for the entire treatise should be carefully read both 
 by the student and the practitioner." DUBLIN MEDICAL JOURNAL. 
 
 WEST (DR. CHARLESX-LECTURES ON THE DISEASES OF 
 
 INFANCY and CHILDHOOD. By CHARLES WEST, M.D. Fellow of the Royal College of 
 Physicians, Senior Physician to the Royal Infirmary for Children, Physician-Accoucheur *:> 
 the" Middlesex Hospital, and Lecturer on Midwifery at St. Bartholomew's Hospital. 8vo. 
 14s. cloth. 
 
 " We take leave of Dr. West with great respect for his attainments, a due appreciation of 
 his acute powers of observation, and a deep sense of obligation for this valuable contribution 
 to our professional literature. His book is undoubtedly in many respects the best we possess 
 on diseases of children. The extracts we have given will, we hope, satisfy our readers of its 
 value ; and yet in all candour we must say that they are even inferior to some other parts, 
 the length of which prohibited our entering upon them. That the book will shortly be in the 
 hands of most of our readers we do not doubt, and it will give us much pleasure if our strong 
 recommendation of it may contribute towards this result'" DUBLIN MEDICAL JOURNAL. 
 
 '"These lectures comprise a very able summary of the pathology and treatment of the 
 leading diseases incident to the periods of infancy and childhood. While the author has 
 availed himself of the labours of those who have cultivated the most successfully this parti- 
 cular department of medical inquiry, the value of his lectures is greatly enhanced by the 
 comparison of the opinions and practice advocated by the more authoritative writers on the 
 
 diseases of which he treats, with tlie results of his own observations Every portion of 
 
 these lectures is marked by a general accuracy of description,- and by the soundness of 'the 
 views set forth in relation to the pathology and therapeutics of the several maladies treated of.". 
 
 AMERICAN JOURNAL OF THE MEDICAL SCIENCES. 
 
 "In taking leave of Dr. West, we can scarcely do more than reiterate our former praise of 
 him. We have given, we fear, but a very faint notion of the scope of his work, and of its 
 excellent execution. It is one standing by itself upon its important subject, in our language 
 
 unapproached unrivalled His knowledge of what others have done is equalled only 
 
 by his own extensive experience ; and the results of both are combined in his valuable p-ac 
 tical lectures now offered for the guidance of others. ; .... The works of Maunsell and Evan- 
 son, Rees, Underwood, and others, must now relinquish the field they have occupied for some 
 time past. It will be long before that of Dr. West finds a rival in this country In con- 
 clusion, we may be excused if we say to the student and junior practitioner, let the pathology 
 of children's diseases, and a treatment based upon that pathology, be your earnest study for 
 the future, and let your guide be the lectures of Dr^West." MEDICO-CHIR. REVIEW. 
 
 WHITEr-A COMPENDIUM OF THE VETERINARY ART; 
 
 Containing plain and concise Observations on the Construction and Management of the 
 Stable ; a brief and popular Outline of the Structure and Economy of the Horse ; the Nature, 
 Symptoms, and Treatment of the Diseases and Accidents to which the Horse is liable ; the 
 Best Methods of performing various Important Operations ; with Advice to the Purchasers 
 of Horses ; and a copious Materia Medica and Pharmacopoeia. By JAMES WHITE, late Vet. 
 Surg. 1st Dragoons. New Edition, entirely reconstructed, with considerable Additions and 
 Alterations, bringing the work up to the present State of Veterinary Science, by W. C. 
 SPOONER, Veterinary Surgeon. 8vo. with coloured Plate, 16s. cloth. 
 
 WHITE. -A COMPENDIUM OF CATTLE MEDICINE; 
 
 Or, Practical Observations on the Disorders of Cattle and the other Domestic Animals, except 
 the Horse. By the late J. WHITE. 6th Edition, re-arranged, with copious Additions and 
 Notes, by W. C. SPOONER, Veterinary Surgeon. 8vo. 9s. cloth. 
 
 WILSON.-PRACTICAL AND SURGICAL ANATOMY. 
 
 By W. J. ERASMUS WILSON, F.R.S. Teacher of Practical and Surgical Anatomy and Phy- 
 siology. 12mo. with 50 Engravings on Wood by Bagg, 10s. Gd. cloth. 
 
 [ March 30, 1850. 
 
 WiUon and O^ilvy, 57, Skinner Street, Suowir.ll, London. 
 
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