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ELEMENTS 
 
 OF 
 
 CHEMISTKY, 
 
 , INCLUDING THE 
 
 MOST RECENT DISCOVERIES AND APPLICATIONS OF THE SCIENCE TO 
 MEDICINE AND PHARMACY, AND TO THE ARTS. 
 
 BY ROBERT^KANE, M.D., M.R.I.A., 
 
 PBOFESSOK OF NATURAL PHILOSOPHY TO THE BOYAL DUBLIN SOCIETY ; 
 
 PBOFBSSOB OF CHEMISTRY TO THE APOTHECARIES' HALL OF IRELAND ; MEMBER OF TBI 
 
 SOCIETY OF PHARMACY OF PARIS, AND OF THE GERMAN PHARMACEUTICAL 
 
 SOCIETY, ETC., ETC., ETC. 
 
 AN AMERICAN EDITION, 
 
 WITH ADDITIONS AND CORRECTIONS, AND ARRANGED FOR THE USE OF 
 
 THE UNIVERSITIES, COLLEGES, ACADEMIES, AND MEDICAL 
 
 SCHOOLS OF THE UNITED STATES, 
 
 BY JOHN WILLIAM DRAPER, M.D 
 
 PROFESSOR OF CHEMISTRY IN THE UNIVERSITY OF NEW- YORK, FORMERLT 
 
 PROFESSOR OF PHYSICAL SCIENCE AND PHYSIOLOGY IN HAMPDEN SIDNEY COLLEQB, 
 
 VIRGINIA; MEMBER OF THE LYCEUM OF NATURAL HISTORY OF NEW-YORK, 
 
 dec, &C., &C. 
 
 qD3o 
 
 NEW-YORK: 
 
 Published by Harper & Brothers, 
 No. 82 Clipf-Street. 
 
 185 1. 
 
 S4457 
 
A no 
 
 Entered, according to Act of Congress, in the year 184 , by 
 
 Harper & Brothers, 
 2R the Clerk's Office of the Sp-*hern District of New- York. 
 
 
 
PREFACE TO THE AMERICAN EDITION. 
 
 In preparing the work of Dr. Kane for the use of Amer- 
 ican students, I have preserved the original entire, and have 
 only made those alterations in it which the system of instruc- 
 tion pursued in the United States seems to require. 
 
 This work, which, as a text-book, is undoubtedly the best 
 extant in the English language, representing the present con- 
 dition of chemical science, necessarily contains much detail. 
 To give it completeness, it was needful to include the de- 
 scription of many bodies of little technical importance, to 
 describe experimental processes, and sometimes to dwell on 
 facts of minor value. 
 
 The period of instruction in the schools of this country is 
 short, so that many standard books are unavailable from 
 their extent. From an experience of several years in public 
 teaching, I have perceived the importance of separating, for 
 the student, the leading principles from the accompanying 
 detail. This will, perhaps, to a certain extent, be accom* 
 plished by the mechanical contrivance of printing such works 
 with different types, the important matter being in the larger 
 letters. 
 
 The magnitude of the original prevented me from making 
 additions to any great extent ; what has been introduced in 
 this way will be readily distinguished, from being inserted 
 between brackets. 
 
 From its having been repeatedly and carefully read, and 
 the errors and misprints revised, this will probably be found 
 more correct than the foreign edition. 
 
 John William Draper. 
 
 University of New-York, June 1st, 1843. 
 
PREFACE. 
 
 My object in the following pages is to present to the stu- 
 dent an account of the general principles and facts of Chem- 
 istry, and of its applications to Pharmacy, to Medicine, and 
 to the Useful Arts. 
 
 In the arrangement of a work like the present, if the gen- 
 eral principles of the science are first described, it is impos- 
 sible 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 princi- 
 ples of affinity and the laws of constitution is continually ne- 
 cessary, in order that the reactions of these bodies may be 
 understood. In both cases the student is liable to some em- 
 barrassment, 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 enter- 
 ing on the description of the chemical substances in detail. 
 
 Chemistry being itself but a department of Natural Philos- 
 ophy, 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 necessary for the proper understanding 
 of the nature of chemical phenomena. I have consequent- 
 ly embraced within the design of the present work a de- 
 scription 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 recognised, 
 and, upon the other, modify the affinities by which thp ac- 
 tion of chemical substances upon each other is determined. 
 With this twofold 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 substan- 
 ces of interest to Science, to Medicine, or to the Arts. But 
 in this part I will pass over very briefly the history of nu- 
 merous bodies which, from their rarity, are objects only of 
 
n PREFACE. 
 
 scientific curiosity, referring those who would wish to study 
 their history more closely to the extended works of Thomp- 
 son, of Graham, of Dumas, or of Berzelius. 
 
 In the department of Organic Chemistry my object will be 
 fully to discuss the history of all such bodies as are of im- 
 portance, from their bearing upon general principles or ex- 
 isting theories, from their use in medicine or pharmacy, their 
 employment 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 exist- 
 ence. 
 
 The relations of chemical action to the functions of organ- 
 ized matter, the applications of Chemistry to Physiology and 
 to Pathology, will be treated of so far as our accurate knowl- 
 edge extends ; and, finally, a succinct description of the mode 
 of analysis of organic and inorganic 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 quotations, which would needlessly 
 occupy much space ; for, in the larger works already men- 
 tioned, 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 hesi- 
 tated, in many instances, where the best consideration I" 
 could give the subject induced me to dissent from views 
 generally heldj to make this work the vehicle, in a popular 
 form, of such suggestions as I thought deserved to be adopted. 
 
 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 manufac- 
 turing laboratory of the Apothecaries' Hall of Ireland ; and 
 the apparatus figured in the woodcuts are generally similar 
 to those which I employ in experiments of research or at 
 lecture. 
 
CONTENTS. 
 
 Pago 
 
 INTRODUCTION. 
 Origin and Objects of Chemistry . 9 
 
 CHAPTER I. 
 
 or GRAVITY AND COHESIVE FORCES, AS 
 CHARACTERIZING CHEMICAL SUBSTAN- 
 
 Specific Gravities of Bodies . 
 
 . 11 
 
 Constitution of Matter . 
 
 . 17 
 
 Capillarity and Elasticity 
 
 . 19 
 
 Phenomena of Solution . 
 
 . 22 
 
 Crystallization 
 
 . 23 
 
 Systems of Crystallization 
 
 . 26 
 
 CHAPTER 11. 
 
 
 OF THE PROPERTIES OP LIGHT AS CHAR- 
 ACTERIZING CHEMICAL SUBSTANCES. 
 
 Reflection and Refraction of Light . 32 
 Double Refraction . . . .34 
 Polarization of Light . . .38 
 Circular Polarization . . .41 
 Wave Theory of Light ... 42 
 
 CHAPTER m. 
 
 OF HEAT CONSIDERED AS CHARACTERIZING 
 
 CHEMICAL SUBSTANCES. 
 
 Section I. 
 
 Of Expansion . . . .46 
 
 Nature of Temperature . . 49 
 
 Thermometers . . . .50 
 
 Pyrometers . . . .54 
 
 Expansion of Air and Gases . 56 
 
 Liquids . . .58 
 
 Solids ... 60 
 
 Section II. 
 
 Specific Heat . . . .63 
 Connexion of Specific Heat and 
 
 the Chemical Constitution . 66 
 
 Specific Heats of Gases . . 69 
 
 Section III. 
 
 Of liquefaction . . . .70 
 
 Latent Heat of Liquids . . 71 
 
 Freezing Mixtures . . .73 
 
 Sbction IV. 
 
 Of Vaporization . . . .75 
 
 Latent Heat of Vapours . . 76 
 
 Elasticities of Vapours . . 78 
 
 Nature of the Boiling Point . 83 
 
 Spontaneous Evaporation . . 87 
 Of Steam as a Moving Power . 89 
 
 Section V. 
 
 Of the Transmission of Heat through 
 
 Bodies 91 
 
 Conduction of Heat . . .92 
 
 Radiation of Heat . . .94 
 Absorption and Reflection of Heat 96 
 Researches of Melloni and Forbes 98 
 Polarization of Heat . . . 'Ol 
 Relations of Heat to Light . . 102 
 Section VI. 
 
 Of the Cooling of Bodies . . 103 
 Theory of Dew and Frost . . 104 
 Central Heat of the Earth . . 105 
 
 CHAPTER rV. 
 
 OF ELECTRICITY CONSIDERED AS CHA- 
 RACTERIZING CHEMICAL SUBSTAN- 
 CES 106 
 
 Section L 
 
 Of Statical Electricity . . . 107 
 Distribution of Electricity . .110 
 Electrical Attractions and Repul- 
 sions 113 
 
 Theories of Electricity . .114 
 Electrical Induction . . .118 
 Theory of the Leyden Jar . . 120 
 Nature of Induction . . . 122 
 Atmospheric Electricity . . 125 
 
 Section II. 
 
 Of Dynamical Electricity . .126 
 Simple Galvanic Circles . .128 
 Of Electrotype Copying . . 130 
 Theory of the Galvanic Battery .131 
 Volta's Theory of Contact . . 133 
 Construction of Galvanic Batteries 134 
 Constant Batteries . . .136 
 Thermo-electric Currents . . 139 
 
 Magnetism 143 
 
 Electro-magnetic Phenomena . 145 
 Of the Galvanometer . . . 147 
 
 CHAPTER V. 
 
 OF CHEMICAL NOMENCLATURE . 149 
 
 Names of the Simple Bodies . . 150 
 
 Primary Compounds . 152 
 
 Secondary Compounds 154 
 
 Symbolical Nomenclature . .156 
 
 CHAPTER VI. 
 
 OF CHEMICAL AFFINITY, AND ITS RELA- 
 TIONS TO HEAT, TO LIGHT, AND TO CO- 
 HESION. 
 
 Elective Decomposition . . .157 
 Order of Affinity not Constant . 159 
 Relation of Affinity to Cohesion . 163 
 Influence of Elasticity on Affinity . 168 
 Influence of Light on Affinity . . 172 
 Influence of the Chemical Rays of 
 Light 173 
 
VUl 
 
 CONTENTS. 
 
 Page 
 
 Photography and Daguerreotype 
 Drawing 175 
 
 CHAPTER VII. 
 
 or THE HEAT AND LIGHT DISENGAGED 
 
 DURING CHEMICAL COMBINATION . 178 
 
 Products of Slow Combustion . 179 
 
 Constitution of Flame . . .181 
 
 Of the Safety Lamp . . .183 
 
 Theories of Combustion . . . 185 
 
 CHAPTER VIII. 
 
 OF THE INFLUENCE OP ELECTRICITY 
 
 ON CHEMICAL AFFINITY . . 187 
 
 Electro-chemical Classification . 189 
 Electro-chemical Theories . .190 
 Electrolysis and Electrolytes . .194 
 Origin of the Galvanic Current . 197 
 Synthetic Action of Electricity . 199 
 Relations of Electricity to Affinity . 201 
 
 CHAPTER IX. 
 
 OP THE LAWS OF COMBINATION . 202 
 
 Scales of Chemical Equivalents . 205 
 
 . 207 
 
 . 210 
 
 . 213 
 
 Law of Multiple Proportions 
 Definiteness of Composition 
 Theory of Volumes 
 
 CHAPTER X. 
 
 OP THE RELATIONS OF CHEMICAL CONSTI- 
 TUTION TO THE MOLECULAR STRUCTURE 
 OF BODIES. 
 
 Section I. 
 
 Of the Atomic Theory . . .217 
 Physical and Chemical Atoms .218 
 
 Section II. 
 
 Of Isomorphism . . . .221 
 Isomorphous Groups . . . 223 
 Relation of Form to Constitution 226 
 
 Section III. 
 
 Of Dimorphism and Isomerism, and 
 
 of the Theory of Types . . 227 
 Approximate Dimorphism . . 230 
 Principle of Isomerism . .231 
 
 Compound Radicals . 233 
 
 Theory of Organic Types . . 234 
 
 Section IV. 
 
 Of Catalysis .... 235 
 
 Communication of Motion . . 237 
 
 CHAPTER XL 
 
 the CLASSIFICATION OP THE EL- 
 EMENTARY BODIES 
 
 CHAPTER XIL 
 
 238 
 
 at THE SIMPLE NON-METALLIC BODIES, 
 AND OP THEIR COMPOUNDS WITH EACH 
 OTHER. 
 
 1. Of Oxygen: Its Preparation and 
 Properties .... 241 
 
 a. Of Hydrogen : Its Preparation . 246 
 The Hydro-oxygen Blowpipe . 251 
 Of Water : its Composition . 253 
 
 Peroxide of Hydrogen . . 258 
 
 3. Of Nitrogen . . . .260 
 Of the Atmosphere . . . 262 
 Nitrous Oxide .... 272 
 Nitric Oxide .... 273 
 Hyponitrous Acid, Nitrous Acid . 275 
 Nitric Acid 277 
 
 4. Of Sulphur . . . .283 
 Sulphurous Acid .... 284 
 Sulphuric Acid .... 286 
 Hyposulphurous and Hyposulphu- 
 
 ric Acids 290 
 
 Sulphuret of Hydrogen . . 292 
 
 5. Of Selenium .... 294 
 Its Compounds with Oxygen, Hy- 
 drogen, and Sulphur . . 294 
 
 6. Of Phosphorus .... 295 
 Oxide of Phosphorus, Phosphor- 
 ous Acid 296 
 
 Phosphoric Acid .... 297 
 Phosphuret of Hydrogen . . 299 
 
 7. Of Chlorine .... 300 
 Hypochlorous and Chloric Acids . 304 
 Chlorous Acid .... 305 
 Hydrochloric or Muriatic Acid . 307 
 Chlorides of Sulphur and Phospho- 
 rus 310 
 
 8. Of Iodine 311 
 
 Iodic and Periodic Acids . .313 
 Hydriodic Acid .... 316 
 Iodine with Phosphorus, Sulphur, 
 
 &c 316 
 
 Hydriodate of Phosphuretted Hy- 
 drogen 316 
 
 9. Of Bromine . . . .317 
 Bromic and Hydrobromic Acids . 318 
 Other Compounds of Bromine .318 
 
 10. Of Fluorine . . . .319 
 Hydrofluoric Acid . . . 320 
 
 11. Of Silicon . . . .321 
 Silicic Acid or Silica . . . 322 
 Chloride of Silicon . . .323 
 
 ■ Fluoride of Silicon . . . 324 
 
 12. Of Boron 325 
 
 Boracic Acid .... 326 
 Chloride and Fluoride of Boron . 326 
 
 13. Carbon referred to Organic 
 Chemistry .... 327 
 
 CHAPTER XIL* 
 
 OF THE GENERAL CHARACTERS OP THB 
 METALS, AND OF THEIR COMPOUND* 
 WITH THE NON-METALLIC BODIES. 
 
 Classification of the Metals ; their 
 State in Nature ; the Mode of Re- 
 duction of their Ores . . . 327 
 
 CHAPTER XIII. 
 
 OP THE INDIVIDUAL METALS, AND OP THEIB 
 COMPOUNDS WITH OXYGEN, SULPHUR, 
 SELENIUM, AND PHOSPHORUS : THEIB 
 ALLOYS. 
 
 Section I. Metals of the First Class. 
 Potassium : its Preparation . 336 
 
 Potash, Peroxide of Potassium . 337 
 
CONTENTS. 
 
 IX 
 
 Page 
 
 Sulpharets of Potassium . . 339 
 Sodium and Soda . . .340 
 Sulphurets of Sodium . . .342 
 Lithium : its Oxide and Sulphuret 342 
 Barium : its Preparation . . 342 
 Barytes, Hydrate of Barytes . 342 
 Sulpiiuret of Barium . . .344 
 Strontium ; its Oxide and Sulphu- 
 ret 344 
 
 Calcium : its State in Nature . 345 
 Preparation and Properties of Lime 346 
 Sulphurets of Calcium . . 347 
 
 Magnesium, Magnesia, &c. . 348 
 
 iacTioN IL Metals of the Second Class. 
 Aluminum : its State in Nature . 349 
 Alumina, Sulphuret, &c. . . 350 
 Glucinum and its Compounds . 351 
 Tttrium, Thorium, Zirconium . 351 
 Cerium, Lanthanum . . .351 
 Of Manganese . . . .352 
 Oxides of Manganese . . . 353 
 Technical Valuation of Manganese 
 
 Ore 355 
 
 Manganic and Permanganic Acids 356 
 Other Compounds of Manganese . 357 
 Section IIL Metals of the Third Class. 
 Of Iron : its State in Nature . 357 
 Manufacture of Cast and Soft Iron 359 
 Manufacture of Steel . . .360 
 Passive Condition of Iron . .301 
 Oxides of Iron . . . .362 
 Sulphurets of Iron . . . 363 
 Of Nickel and its Compounds . 365 
 Of Cobalt and its Compounds . 366 
 Of Zhic and its Compounds . 367 
 or Cadmium. Of Tin . . 369 
 
 Oxides and Sulphurets of Tin . .370 
 Of Chrome : its Oxide. Chromic 
 
 Acid 371 
 
 Of Vanadium . . . . 373 
 Skction IV. Metals of the Fourth Class. 
 Tungsten and Molybdenum . 373 
 
 Osmium and its Compounds . 374 
 Columbium and Titanium . . 375 
 
 Of Arsenic 376 
 
 Arsenious Acid, Arsenic Acid . 377 
 Arseniuret of Hydrogen . . 378 
 Sulphuret of Arsenic . . . 379 
 Detection of Arsenic . . . 380 
 Of Antimony . . . .384 
 Compounds of Antimony with Ox- 
 ygen 385 
 
 Sulphurets of Antimony . . 386 
 Antimoniuret of Hydrogen . . 388 
 Of Tellurium and its Compounds 389 
 Of Uranium and its Compounds . 390 
 Section V. Metals of the Fifth Class. 
 Of Copper, Reduction from its 
 
 Ores 390 
 
 Oxides of Copper . . . 392 
 
 Sulphurets of Copper . . . 393 
 Brass, Bronze, Gun Metal, Specu- 
 lum Metal .... 393 
 Of Lead: its Oxides . . . 394 
 
 Sulphurets and Alloys of Lead . 395 
 Bismuth and its Compounds . 397 
 Section VI. Metals of the Sixth Class. 
 Of Silver, its Natural State and I 
 
 Properties .... 399 
 Oxides and Sulphurets of Silver . 401 
 Of Mercury : its Preparation and 
 
 Properties .... 402 
 Oxides and Sulphurets of Mercury 403 
 Of Gold : its Oxides and Sulphu- 
 rets 405 
 
 Of Palladium and its Compounds 406 
 Of Platinum : its Oxides and Sul- 
 phurets 407 
 
 Of Iridium and Rhodium . . 409 
 
 CHAPTER XIV. 
 OP the general properties and con- 
 stitution OF SALTS. 
 
 Neutral, Acid, and Basic Salts ; Dou- 
 ble Salts; Sulphur Salts; Theo- 
 ries of the intimate Constitution of 
 Acids and Salts ; Binary Theory 
 of Salts . . . , .410 
 
 CHAPTER XV. 
 
 SPECIAL HISTORY OP THE MOST IMPORTANT 
 SALTS OF THE INORGANIC ACIDS AND 
 BASES. 
 
 Of the Salts of Potash.— Chloiide, lo 
 dide, Bromide, and Fluoride of Po- 
 tassium ; Fluosilicate of Potash ; 
 Sulphates of Potash ; Nitrate of 
 Potash; Manufacture of Gunpow- 
 der ; Hypochlorite and Chlorate of 
 Potash ; ifercjilc^atei lodate, and 
 Sihcate of Potash . , . 421 
 
 Of the Salts of Sodium. — Chloride of 
 Sodium ; of Sea- water ; Bromide 
 and Iodide of Sodium ; Sulphate, 
 Nitrate, Hypochlorite, and Hypo- 
 nitrite of Soda; Various Phos- 
 phates of Soda ; Borate and Sili- 
 cate of Soda .... 426 
 
 Of the Salts of Lithium — Salts of Ba- 
 rium. — Chloride of Barium ; Sul- 
 phate and Nitrate of Barytes. Salts 
 of Strontium. — Chloride of Stron- 
 tium; Sulphate and Nitrate of 
 Strontian . . ; . . 429 
 
 Of the Salts of Calcium. — Chloride, 
 Bromide, Iodide, and Fluoride of 
 Calcium ; Sulphate and Nitrate of 
 Lime; Phosphateof Lime ; Hypo- 
 chlorite of Lime ; Manufacture of 
 Bleaching Salt ; Chlorometry . 430 
 
 Salts of Magnesia. — Epsom Salts . 434 
 
 Salts of Aluminum. — Manufacture of 
 
 Alum 435 
 
 Constitution of Glass and Porce- 
 lain; Manufacture of Glass; 
 Manufacture of Earthenware . 437 
 Of the Salts of Manganese . . 443 
 
 Of the Salts of /ron.— Chlorides of 
 
CONTENTS. 
 
 Page 
 
 Iron ; Manufacture of Copperas ; 
 Nitrates of Iron . . . 444 
 Salts of Nickel and Cobalt . . 446 
 Salts of Zinc and Cadmium . 447 
 
 Salts of Tin . . . .448 
 
 Salts of Chrome and Vanadium ; 
 
 Chromates .... 449 
 Salts of Tungsten, Molybdenum, 
 
 Osmium, and Columbium . 451 
 
 Salts of Arsenic, Arsenites, Ar- 
 
 seniates ..... 452 
 Salts of Antimony, Antimoniates 453 
 Salts of Titanium, Tellurium, and 
 
 Uranium 454 
 
 Salts of Copper. — Manufacture of 
 Blue Vitriol ; Scheele's Green ; 
 Emerald Green . . .. . 455 
 Salts of Lead ; Chrome Yellow ; 
 
 Chrome Red . . . . 457 
 Salts of Bismuth . . .458 
 
 Salts of Silver, Lunar Caustic . 459 
 Salts of Ji^rcury. — Corrosive Subli- 
 mate, Calomel, Iodides, Sul- 
 phates, and Nitrates of Mercury 461 
 Salts of Gold . . . .465 
 Salts of Palladium and Platinum 466 
 Salts of Iridium and Rhodium . 466 
 
 CHAPTER XVI. 
 
 OF THE GENERAL PRINCIPLES OP THE CON- 
 STITUTION OF ORGANIC BODIES. 
 
 Elements of Organic Bodies ; Rela- 
 tion of Vital Force to Affinity; 
 Compound Radicals ; Theory of 
 Organic Acids ; Theory of Types ; 
 Decomposition of Organic Bodies 467 
 
 CHAPTER XVn. 
 
 OF CARBON AND ITS COMPOUNDS WITH OX- 
 YGEN, SULPHUR, AND CHLORINE. 
 
 Forms of Carbon ; Organic Analysis 476 
 Carbonic Acid ; Carbonates of Pot- 
 ash and Soda ; Manufacture of 
 Potashes and Soda-ash ; Alkalim- 
 etry ; Earthy Carbonates ; Car- 
 bonates of Iron, Copper, Lead, 
 &c. ; of Carburets . . . 485 
 Carbonic Oxide, Oxalic Acid, and the 
 Oxalates ; Chlorocarbonic Acid ; 
 Oxycarburet of Potassium ; Rho- 
 dizonic, Croconic. and Mellitic 
 Acids ; Sulphuret of Carbon ; Chlo- 
 rides of Carbon . . . ^ . 492 
 
 CHAPTER XVIII. 
 
 OF THE COMPOUNDS OF NITROGEN 4ND HY- 
 DROGEN. OP AMMONIA, ITS DERIVATIVES 
 AND COMPOUNDS. 
 
 A.mmonia ; Amidogene ; Iodide and 
 Chloride of Azote ; Ammoniurets, 
 Amidides ; Azoturets ; Ammonia- 
 Salts of Zinc, Copper, Nickel, Co- 
 
 balt, Silver, Palladium, Platinum, 
 and Mercury; White Precipitate 498 
 Ammonia and Anhydrous Acids; 
 Common Ammoniacal Salts ; The- 
 ory of Ammonium ; Sal Ammoni- 
 ac, Sulphates, Phosphates, Oxal- 
 ates, &c., of Ammonia ; Double 
 Chlorides of Ammonium . . 507 
 
 CHAPTER XIX. 
 
 OF CYANOGEN AND ITS COMPOUNDS, AND 
 OF THE BODIES DERIVED PROM IT. 
 
 Cyanogen. Cyanic, Fulminic, and 
 Cyanuric Acids. Prussic Acid: 
 its Preparation and Detection; 
 Valuation of its Strength. Chlo- 
 rides and Iodides of Cyanogen . 613 
 
 Of the Metallic Cyanides, Potassium, 
 Mercury, Iron. Complex Cyan- 
 ides ; Prussian Blue ; Yellow and 
 Red Ferroprussiates of Potash ; 
 Theory of the Complex Cyanides 520 
 
 Of Sulphocyanogen and its Com- 
 pounds ; of Mellon, Melam, Mela- 
 mine, and their Derivatives . 525 
 
 CHAPTER XX. 
 
 OF STARCH, LIGNINE, GUM, AND SUGAE, 
 WITH THE PRODUCTS OF THEIR DECOM- 
 POSITION BY ACIDS AND ALKALIES. 
 
 Varieties of Starch ; Lignine ; Vari- 
 eties of Gum ; Varieties of Sugar ; 
 Action of Acids on Sugar ; Saccha • 
 rine Fermentation ; Lactine ; Mu- 
 cic Acid ; Mannite ; Lactic Acid; 
 Glycyrrhizine .... 527 
 
 CHAPTER XXL 
 
 OF THE ALCOHOLIC AND ACETIC FERMENT- 
 ATIONS. OF ALCOHOL ; THE ETHERS ; 
 ALDEHYD ; ACETIC ACID, AND OTHBB 
 BODIES DERIVED FROM IT. 
 
 Vegeto-animal Bodies ; Yeast ; Man- 
 ufacture of Spirit ; Preparation of 
 Ether; Theory of the Process; 
 Nature of Ether ; its Compounds 
 with Acids ; Sulphovinic Acid ; 
 Oil of Wine ; Compound Ethers ; 
 of defiant Gas and' the derived 
 Compounds .... 537 
 
 Oxidation of Alcohol; Aldehyd; Ace- 
 tous Fermentation ; Acetic Acid, 
 Acetates of Potash, Lime, &c , Su- 
 gar of Lead, Verdigris, other Ace- 
 tates ; of Acetone; Compounds of • 
 Kacodyl ; of Marsh Gas . , 553 
 
 Action of Chlorine on Alcohol, and 
 the Bodies derived from it ; The- 
 ory of the Ethers . . . 564 
 
 Secondary Products of the Alcoholic 
 Fermentation : GEnanthic Acid ; 
 Amilic Alcohol ; Corn Oil . . 567 
 
CONTENTS. 
 
 Xi 
 
 CHAPTER XXII. 
 
 Page 
 
 OP THE ESSENTIAL OILS, CAMPHORS, AND 
 RESINS. 
 
 Of the Oils forming Acids, not exist- 
 ing in the Plants ; Oil of Bitter 
 Almonds ; Amygdaline ; Benzoic 
 Acid ; Benzyl ;' Oils and Acids of 
 Cinnamon, Cloves, Mustard, and 
 Spirea 569 
 
 Oils pre-existing in the Plant, Prop- 
 erties not Acid .... 574 
 
 Camphors or Stearoptens of the Oils 
 of Resins . . . . • 576 
 
 Amber, Succinic Acid, Succinates; 
 Caoutchouc .... 579 
 
 CHAPTER XXIII. 
 
 OF THE SAPONIFIABLE FATS AND OILS. 
 
 Glycerine, Stearine, Oleine, Marga- 
 rine ; Products of the Action of 
 Acids on Fatty Bodies; Vegeta- 
 ble Fats and Oils ; Fish Oils : Man- 
 ufacture of Soaps and Plasters .581 
 
 Spermaceti, Ethal, and the derived 
 Bodies. Wax . . . .591 
 
 CHAPTER XXIV. 
 
 OP THE ORGANIC ACIDS WHICH DO NOT 
 PRE-EXIST IN PLANTS, AND DO NOT BE- 
 LONG TO ANY ESTABLISHED SERIES. 
 
 Tartaric Acid ; Tartrates of Potash, 
 Soda, Iron, Antimony, &c. . . 692 
 
 Action of Heat on Tartaric Acid ; 
 Raccmic Acid .... 595 
 
 Citric Acid ; Citrates ; its Decompo- 
 sition by Heat . . . '. 597 
 
 Malic, Maleic, and Fumaric Acids . 598 
 
 Meconic, Komenic, and Pyromecon- 
 ic Acids 599 
 
 Tannic Acid ; Valuation of Tannin ; 
 Tannates 600 
 
 Gallic Acid ; the Products of its De- 
 composition .... 601 
 
 Tannic Acid from Catechu, Cincho- , 
 na, and Kino .... 603 
 
 Other Vegetable Acids . . .604 
 
 CHAPTER XXV. 
 
 OF THE NEUTRAL ORGANIC SUBSTANCES, 
 AND OF THE PRODUCTS OF THEIR DE- 
 COMPOSITION. 
 
 Pectine ; Salicene ; Phloridzine ; As- 
 paragine ; Caffeine ; Piperine ; 
 Cantharadine ; Anemonine ; Ce- 
 trarine ; Picrotoxine ; Columbine ; 
 Cusparine; Elaterine; Meconine; 
 Peudecanine ; iEsculine ; Popu- 
 line ; Quassine ; Santonine ; Sapo- 
 nine ; Scillitine ; Senegine ; Smi- 
 lacine ; Absinthi'ine ; Lactucine . 605 
 
 Of Extractive Matter; Apotheme ; 
 Extracts 612 
 
 CHAPTER XXVI. 
 
 OF THE COLOURING MATTERS. 
 
 Of Madder; Anchusa ; Carthamine; 
 Carmine ; Logvi^ood ; Persian Ber- 
 ries ; Anotta ; other Yellow Bod- 
 ies ; Indigo, and the Substances 
 derived from it ; Lichen Colours ; 
 Archil and Litmus ; Colours of 
 Leaves and Flowers ; Theory of 
 Dyeing 613 
 
 CHAPTER XXVII. 
 
 OP THE VEGETABLE ALKALIES AND OF 
 THEIR SALTS. 
 
 Quinine ; Cinchonine ; Aricine ; Mor- 
 phia ; Narcotine ; Codeine ; The- 
 baine ; Narceine ; Pseudomor- 
 phine ; Strychnine ; Brucine ; Del- 
 phinine ; Veratrine ; Sabadilline ; 
 Jervine ; Colchicine ; Einetine ; 
 Solanine ; Chelerythrine ; Cheli- 
 donine ; Aconitine ; Atropine ; Bel- 
 ladonine ; Daturine ; Hyoscya- 
 raine ; Coneine ; Nicotine ; Men- 
 ispermine ; Cissampeline ; Glau- 
 cine ; of the Constitution of the 
 Vegetable Alkalies . . . 623 
 
 CHAPTER XXVIII. 
 
 OF THE PRODUCTS OF THE DECOMPOSITIOW 
 OP WOOD AND THE ALLIED BODIES. 
 
 Section I. 
 
 Of the slow Decomposition of Wood. 
 Constitution of Ulmine. Of Turf 
 
 and Coal 637 
 
 Section II. 
 
 Of the Products of the destructive 
 Distillation of Wood, Coal, and 
 Resin 646 
 
 Pyroxylic Spirit ; Compounds of 
 Methyl ; Formic Acid ; Coal 
 Gas ; Napthaline ; Kreosote, &c, 647 
 
 CHAPTER XXIX. 
 
 OF THE CHEMICAL PHENOMENA OF VEGE- 
 TATION. 
 
 Germination, Assimilation of the 
 Food of Plants ; Sources of Car- 
 bon and Nitrogen ; Ashes of Plants ; 
 Composition of Soils and Manures ; 
 Rotation of Crops ; Action of Light 
 on Plants 650 
 
 CHAPTER XXX. 
 
 OP ANIMAL CHEMISTRY. 
 
 Section I. 
 
 Of the Composition of the Animal 
 Tissues. 
 
 Of the Albuminous Constituents ; 
 Albumen ; Fibrine ; Proteine ; 
 Gelatine ; Chondrine ; Fats of 
 the Brain ; Ozmazome ; Zomi- 
 dine 663 
 
 Skin, Epidermis, Hair, Horn, 
 
xn 
 
 CONTENTS. 
 
 Feathers ; Cellular and Serous 
 Tissues ; Tendons ; Muscular 
 Tissue ; Brain ; Composition of 
 Bones, Teeth, and Enamel; 
 
 Shells 
 
 Section II. 
 
 Of the Composition of the Blood, and 
 the Phenomena of Respiration. 
 
 Blood Globules and Serum ; Clot ; 
 Hematosine. Blood in Disease ; 
 Respiration ; Modes of Action 
 of the Air ; Animal Heat 
 Section III. 
 
 Composition of the Digestive Or- 
 gans, and of their Secretions; 
 Chemical Phenomena of Diges- 
 tion. 
 
 Mucus ; Gastric Juice ; Pepsine ; 
 Analyses of the Bile; Bilin; 
 Taurine; Cholic and other 
 
 Fage 
 
 670 
 
 673 
 
 Acids; Bilifulvine; Chyle and 
 Lymph, Saliva and Pancreatic 
 
 Juice 
 
 Section IV. 
 
 Constitution of the Urine in Health 
 
 and in Disease. 
 Urea ; Uric Acid ; AUantoine, Al- 
 loxan, AUoxantine, and other 
 Products of the Decomposition 
 of Uric Acid ; Hippuric Acid 
 Urinary Deposites and Calculi 
 Mode of recognising Calculi 
 Urine in Diabetes and other 
 
 679 
 
 Section V. 
 
 Of various Natural and Morbid 
 
 Products. 
 Milk; Caseine; Eggs; Amnios; 
 Tissues of the Eye ; Earwax ; 
 Pus; Ambergris 
 
ELEMENTS OF CHEMISTRY. 
 
 The science of chemistry has its origin in the principle, that the 
 bodies which constitute the external world are composed of a va- 
 riety of elements, united according to certain laws. If we could 
 conceive a universe consisting only of iron, or quicksilver, or sul- 
 phur, 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 re- 
 ducing to precise laws the forces by which the motions of the 
 heavenly bodies might be produced, all the resources of his science 
 would still be brought into play. In like manner, the physical sci 
 ences could attain perfection, for the relations of these bodies to 
 heat, to light, to electricity, the various problems and laws of stat- 
 ical and dynamical forces, could have been known, and thus all 
 that is essential to the science of natural philosophy might be 
 attained. But not even an idea of chemistry could have been 
 formed. The duty of chemistry is to find the constituent ele- 
 mentary substances, which, by uniting, form the various compound 
 bodies which we observe ; to ascertain the nature of the forc-es 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 phenomena, independent of composition, which accom- 
 pany the exertion of chemical force. 
 
 This object of chemistry has been at all periods fully recognised ; 
 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 chemistry, and the reasonings to which they led, acquired a 
 better form, these elements, which had been assumed from specu- 
 lations in 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 decom- 
 . posing compound bodies. As more accurate ideas and better pro- 
 cesses were acquired, these elementary principles changed again 
 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 sim- 
 ple substances^ without pretending that they are elements ; for the 
 advance of science enables us to decompose, in each generation, 
 bodies which to our own predecessors had appeared simple ; 2d, 
 that we study to effect the recombination of those simple boJiej^, 
 
10 ORIGIif AND USES OF CHEMISTRY. 
 
 either in the same proportions, and thus regenerate the natural 
 compound bodies, or in new proportions, and t'hus add to the cata- 
 logue of bodies which may exist in nature. 
 
 Of these two operations, the first, or separation of a compound 
 body into the simple substances which constitute it, is termed anal- 
 ysis. The second, or combination of simple to form a compound 
 substance, is called synthesis. All chemical processes are conducted 
 upon the principle of one or other of these two, and occasionally 
 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 com- 
 position; 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 neg 
 lected or unknown; the alleviation 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 labora- 
 tory of the human frame may ultimately lead, ranks also among 
 the most important of its applications : and, although an abstract 
 science, which reveals some of the most beautiful of nature's laws, 
 deserves our best attention, yet it becomes invested 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 
 was first found as xw^^^i indicating the art of making gold and 
 silver among the Egyptians and Greeks of the Empire, at the com- 
 mencement of that extraordinary perversion of the idea of ele- 
 mentary constitution which fascinated mankind for nearly five hun- 
 dred years. From the Greeks it was naturally adopted, with the 
 rain 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 recognised, it was termed chemia or chemistry. 
 
 In studying those properties of the difierent kinds of matter by 
 which they are recognised to be distinct and independent chemical 
 substances, it is unavoidable to include those qualities which, al- 
 though common to all forms of matter, yet difier in degree among 
 the different kinds, and thus serve as distinguishing characteristics 
 of them. The physical properties of various bodies are hence in 
 common use among chemists, as serving to perfect their description j 
 and, indeed, the limit between properly physical and properly chem- 
 ical properties of substances is not always capable of being dis- 
 tinctly drawn. 
 
PECIFIC GRAVITY OP GASES. 11 
 
 CHAPTER L 
 
 OF GRAVITY AND COHESIVE FORCES AS CHARACTERIZING CHEMICAL SUB 
 
 STANCES. > 
 
 The physical forces which are of most importance in determin- 
 ing the characteristic properties of bodies are gravity and cohesion. 
 These differ, however, remarkably in principle from each other, 
 and are applied to quite independent purposes. Gravity is com- 
 mon to all forms of matter, and is totally independent of its 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 j and what we term weight is only the 
 gravitating force exerted by the substance which we weigh. By 
 no natural operation can the smallest particle of matter be annihi- 
 lated 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 operations, 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 j and when 
 a certain body is taken as a standard, and their density reduced to 
 numbers, 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 for its recognition. 
 
 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 as 1000, the spe- 
 cific gravities of the others become proportional to it ', as, 
 
 Water ... 480 : 1000 
 Ether ... 343 : 715 
 Sulphuric acid 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 pre- 
 cisely similar process may be had recourse to ; in place of a bottle 
 
12 SPECIFIC GRAVITY OP GASES. 
 
 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 pre- 
 viously be either perfectly dried or per- 
 fectly saturated with moisture, is admit- 
 ted 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 den- 
 sities, and hence the specific 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 5 hence the densities are as 8*5 to 12*8, and the specific 
 
 12-8 
 gravity of the gas, air being taken as 1000, is -^;^^ 1000= 1*506. 
 
 This brief description being intended only to explain the princi- 
 ple which the words " specific gravity" involve, it has been consid- 
 ered as not liable to alteration ; but, in reality, the volumes of bodies, 
 particularly of gases, are constantly in a state of change. Accord- 
 ing as the air is warmer or colder j according as the pressure to 
 which it is subjected, 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 refer- 
 ence to a certain standard of temperature and pressure, as 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 va- 
 pour, and hence the determination of the specific gravity of a gas, 
 although so simple in theory, is in practice a most delicate opera- 
 tion. 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 frag- 
 ments, 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 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 
 
SPECIF I«C GRAVITY OF SOLIDS. 13 
 
 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 j or, the 
 specific gravity of the water being taken as 1000, that of the solid 
 
 357 
 is X 1000, or 4958. If the solid be unsuited for that method, its 
 
 72 ' 
 
 volume is next determined by the principle that a solid body im- 
 mersed in a fluid 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 upward 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 entployed, 
 and it is only the overplus that is counterpoised by the weights 
 when we proceed to weigh the solid body immersed in any fluid. 
 A solid weighs, therefore, less when immersed in a fluid 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 op- 
 eration, a balance, as in 
 the figure, is taken, gen- 
 erally with one scale dish. 
 The solid is hung to the 
 other extremity of the 
 beam by a fine hair or 
 thread of cocoon-silk, ^, 
 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 j 
 let us suppose that it shall weigh 243 grains. This 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 
 
 295 
 is -—-x 1000=5673. 
 
 A variety of other instruments are made use of for measuring 
 the specific gravities of solids and of fluids, as areometers, hydrom- 
 eters, &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. 
 
 The specific gravity of compound gases is found to have a highly important rela- 
 tion to their ultimate constitution, and throws great light upon some of the most 
 general laws of chemistry ; but as yet, notwithstanding some interesting specula 
 lions of Perzoz and of Boullay which I shall hereafter notice, no connexion be 
 
 B 
 
14 
 
 SPECIFIC GRAVITY OF A^ A P O L" R S. 
 
 tvveen the chemical properties or composition of liquid or solid booies and their 
 specific gravities has been discovered. The physical constitution of vapours and 
 gases being, however, identical, those bodies which, being volatile, are capable of 
 assuming the form of vapour, may render, by the examination of the specific grav- 
 ities of their vapours, most interesting indications of the manner in which their 
 elements are combined, and methods of performing this operation have been con- 
 trived by some of the most illustrious of chemists, as by Dumas and by Gay Lussac. 
 The method of (Jay Lussac is the simpler of the two, and, for substances which 
 are volatilized at moderate temperatures, easily applied. A basin, c, is 
 taken, which rests upon a little furnace, and contains mercury. In 
 this basin the graduated bell glass, a, is inverted full of mercury. Let 
 us suppose we wish to determine the specific gravity of vapour of wa- 
 ter. 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 ijoint 
 dipped into the water; in this manner a little water gets admission ; 
 this is then boijed 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 tlius enclosed, 
 the little bulbs are passed under the edge of the jar, a, an'.l 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 furnace is then light 
 ed, and as the temperature of the oil and mercury rises, the vvater in the little bulbs 
 forms steam, which at last bursts the bulbs, and the level of the quicksilver in the 
 jar immediately falls, the steam occupying tlie space above it. When the mercury 
 ceases to descend, it is known that all liquid has been converted into vapour; the 
 temperature of the oil, which is necessardy the same as that of the vapour 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 is knovim, for it is the weight of 
 the vvater in the bulbs, and its volume at this high temperature is thus found. 
 Knowing thus the volume of a few grains of steam at 250", the volume at 33° 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 temperature 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 emj3loyed. 
 
 The method invented by Dumas has the advantage of being applicable to all tern 
 peratures 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 com- 
 plex in principle, though not less dehcate in practice. A globe holding from ten to fif- 
 teen cubic inches, and drawn out at its beak to a capillary orifice, is carefully weigh- 
 ed, containing, as usual, atmospheric air. It is then v/armed, and its beak being 
 dipped into the fluid to be tried, it is allowed to cool, until by the contraction of the 
 
 air a sufficient quantity of the 
 fluid 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 appli- 
 ed, and which may be water oi 
 oil, a solution of chloride of zinc, 
 ^.?s=^or, best of all, the fusible alloy 
 ^^^55^:=**^'^ of bismuth, tin, and lead. The 
 ^^f''''^ capillary beak of the tube just 
 
 (T projects over the surface of the 
 
 ^ bath, as in the figure. When the 
 
 . — I Jv.^ globe becomes sufliciently heat- 
 
 / Y — f ^\ ed, the liquid boils, and its va- 
 
 / \ ( /- \ ]) \ y P^*^*"' ^'^ passing away, carries oflF 
 
 I 1 — J ' O ^ L_ ^^-^ — ^ the air which had previously fill- 
 
DIVISIBILITY OF MATTER. 15 
 
 ed 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 pro- 
 ceeding from the capillary beak, and then by means of a blowpipe the orifice 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 break- 
 ing 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 quEintity of 
 the quicksilver being measured, the volume of the globe is known ; when this has 
 been done, all requisites for calculating 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 farther 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 detei- 
 mining 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 bodiea 
 with high boiling points, could have been tried. 
 
 The force of gravity is thus of importance in chemistry, by giv- 
 ing a measure of the quantity of matter upon which we experiment, 
 and by affording characteristics of individual substances, by the 
 comparison of the quantity of matter they possess in a standard 
 vokime. The force of cohesion, although not so universally exist- 
 ant as that of gravity, is of equal interest, from the numerous pecu- 
 liarities in its activity which almost everybody is capable of pre- 
 senting, and by which bodies are remarkably distinguished from 
 each other. To understand, however, the nature of cohesive forces, 
 and the causes of the variation of their energy, it is necessary to 
 notice those ideas of the peculiar constitution of matter on which 
 philosophers have generally agreed, and which result from, while 
 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 capable of infinite division, or whether, by continuing 
 to divide, a term should ultimately be found at which no farther sub- 
 division could be made j that thus the ultimate constituent and indi- 
 visible 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 
 powerful 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 
 degree, may be easily demonstrated by experiment. In gilding sil- 
 ver 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 ^-^^.J-- __- of a square inch in size, and yet possess 
 
16 DIVISIBILITY OF MATTER. 
 
 the colour and all otKer characters of the largest mass. If a graiB 
 of copper be dissolved in nitric acid, and then in water of ammonia, 
 it will give a decided violet colour to 392 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 con- 
 tains certainly 500*000 times the bulk of the drop of indigo solution, 
 the particles of the indigo must be smaller than jjuTTooiiooTrffoo ^^'' 
 twenty-five hundred millionth of a cubic inch. A rather more dig 
 tinct experiment is the following : if we dissolve a fragment of sil- 
 ver, of O'Ol of a cubic line in size, in nitric acid, it will render dis- 
 tinctly 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 men- 
 tion of so imperfectly 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, would require 31*675 years. 
 
 In the organized kingdoms of nature even this excessive tenuity 
 of matter is far surpassed. An Irish girl has spun linen yarn of 
 which a pound was 1432 English miles in length, and of which, con- 
 sequently, 17 lbs. 13 oz. would have girt the globe 5 a distinctly visible 
 portion of such thread could not have weighed more than tc;t o K o o o 
 of a grain. Cotton has been spun so that a pound of thread was 
 203*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 j 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 ca- 
 pable of possessing. Each new improvement in our instruments 
 displays to us new races of animals, too minute to be observed be- 
 fore, and of which it would require the heaping together of millions 
 upon millions to be visible to the naked eye. And yet these ani- 
 mals live and feed, and have their organs for locomotion and prehen- 
 sion, 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 organ- 
 ized, possessed of definite structure, lead us merely to a point where 
 all power of distinct conception ceases ; where we discover that 
 nothing is great or small but by comparison, 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 
 infinite divisibility quite untouched. There are, however, many and 
 
MOLECULAR CONSTITUTION. 17 
 
 powerful reasons' which have decided almost all modern philosophers 
 to consider the possible division as being finite. On the other view 
 the mind has no resting-place, until, by the total disappearance ot 
 material conceptions, the constitution of bodies resolves itself into 
 a collection of mathematical points, from which, as centres,- certain 
 forces are exerted ; but with such abstract speculation chemistry- 
 has no connexion. Its fundamental condition, that there exist many- 
 kinds of elementary matter, of which the quantity is measured by 
 their weight, is totally independent of our abstract idea of what mat 
 ter is, or how its properties have their source. 
 
 In proof of the division of matter having a limit, experiments 
 made principally by Faraday and Wollaston have been quoted. Thus, 
 it is ascertained that our atmosphere does not extend into spaced 
 but is confined within comparatively a trifling distance from the 
 earth, about 45 miles. Wollaston, considering the particles of air 
 as being balanced between their mutual repulsion and the general at- 
 traction towards the earth, suggested that, if these particles could be 
 divided to an infinite degree, there should be an infinite source of 
 repulsive power, and hence, at a certain distance, this repulsion over- 
 coming 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 recognised. 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, Faraday found that bodies, in evaporating, form atmo- 
 spheres of certain definite depths above the surface of the body, and 
 drew from hence the same conclusion. This argument cannot, how- 
 ever, be considered as decisive. It is not at all certain that, because 
 the elasticity of air is thus found to have a limit, the number of 
 particles of air, in a given space, might not be infinite. 
 
 I shall consider the masses of matter, whose properties we pur- 
 pose 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 di- 
 visible or not ; there is no fact in either chemistry or physics which 
 requires the positive 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 pro- 
 duced. One of these forces is attractive ; it is the attraction of ag- 
 gregation, as it has been termed, or cohesion. If it acted unimpeded, 
 the molecules of every portion of matter would cohere with insuper- 
 able power ; unconquerable solidity, hardness, and tenacity would 
 alone characterize external nature. The other force is one of repul- 
 sion, 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, would 
 change to atmospheres of vapours, and the beneficent uses to which 
 our earth is now adapted could not exist. 
 
 Such is, perhaps, approximatively what occurs in those extreme 
 
18 STATES OF AGGREGATION. 
 
 members of our planetary system, Herschel and Mercury. The for- 
 mer receiving from the Sun but j ^^ P^^* ^^ 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, are there 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 prevails are solid, and by their tenacity and resist- 
 ance 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 become? 
 gaseous, and its particles, devoid of the least trace of cohesive power, 
 repel each other. In intermediate cases, where the two forces ap- 
 pear 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, while 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 com- 
 mon 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, by the cohesion 
 becoming greater, be converted into a solid j or by increasing the 
 heat to which a solid is subjected, it may be converted into a li- 
 quid, 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, consid- 
 ered as effects of heat, will require and obtain hereafter a more 
 extended notice. 
 
 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 to- 
 gether 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 fluids, although the force of cohesion 
 is very nearly absent, yet it is not entirely so ; the viscidity of 
 fluids depending upon the traces of it which remain. The globular 
 form of a rain dtop, or of a drop of any fluid allowed to fall from 
 
COHESION.- 
 
 APILLARITY. 
 
 19 
 
 ti point) arises also from the cohesive attraction of its particles, and 
 different fluids difl^er remarkably in their relations to heat, from the 
 various degrees of force with which this residue of cohesion is ex- 
 erted. The particles of a fluid 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 fluids. 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 
 fluid, 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. From this cohe- 
 sion of fluids to solids, all the phenomena of capillary attraction 
 result, as the filtering of liquids in pharmacy and chemistry, to sep- 
 arate 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 ^ -JliL^^ .T/ ,.^-^.Ji^ ^^ 
 
 figure. A disk of any 
 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 be- 
 low. It will be found necessary to augment considerably the weights 
 in the scale dish opposite, to separate them j 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 
 others for the solid is found to be wetted by a layer of liquid par- 
 ticles 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. 
 
 [Clairaut found, as the result of his mathematical investigations, 
 that all the phenomena of capillary tubes depend upon the relation 
 of two forces : 1st, The cohesion of the particles of the fluid for 
 each other ; and, 2d, The attraction of the particles of the solid for 
 those of the fluid. When a glass tube is dipped into different 
 liquids: if the force of attraction of the glass is less than half the 
 force of cohesion of the fluid, the fluid will be 
 depressed, and not rise to its hydrostatic level ; ^ ^ 
 if it be equal to half, the fluid will come pre- 
 cisely to its level ; and if it be more than half, 
 the fluid will rise in the tube. a 
 
 Connected with these conditions is the figure 
 of the boundary surface of the fluid. If three 
 glass tubes, be, de, fg, be placed in fluids which ^ 
 respectively are depressed, at the true level, or at 
 
20 COMPRESSIBILITY. 
 
 an elevation, it will be seen that in h c the surface a a of the fluid 
 is convex, in c/ e it is plane, and in fg it is concave.] 
 
 The particles of a body being held at certain distances from each 
 other by the balance of their attraction and repulsion : if, by the ap- 
 plication of an external force, as pressure, they be brought nearer, 
 so as to occupy a smaller volume, the body is said to be compress- 
 ible. 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 in gases, the restoration to the origi- 
 nal 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 400 lbs. upon 
 each square inch of the surface of water to diminish its volume by 
 the joVo part. In gases, however, the repulsive force acting without 
 interference, and the particles being at much greater distances from 
 one another than in the liquid or solid form, the amount of com- 
 pressibility becomes very much increased, and the law by which it 
 is regulated extremely simple, being, that the volume of any gas 
 varies inversely as the pressure 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 20 lbs., 
 
 Then with pressures of 80 . 40 . 20 . 10 . 5 lbs. 
 The volume becomes 25 . 50 . 100 . 200 . 400. 
 
 The gases which are used in chemical operations are liable to 
 constant changes of volume, from the alterations in the weight of 
 the surrounding 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 atmo- 
 spheric pressure, and to allow for it. The pressure which the air 
 exercises is measured by the barometer, in which a column of quick- 
 silver balances the pressure 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 about 29-8 
 inches. For simplicity, a number very near this, 30 inches, is taken 
 as the standard pressure ; and whenever the specific gravity, or the 
 volume of a gas is given, without particular remark, this standard 
 height of the barometer is understood to be the pressure. 
 
 If, therefore, we have a gas at a different pressure, it is usual, and often neces- 
 sary, to reduce its volume to what it should have been under the standard pressure, 
 or, as it is generally termed, to correct for pressure : to do this, we use the rule 
 given above for the change of volume with the pressure. Thus, if, in an analysis 
 of morphia, we obtain 454 cubic inches of nitrogen gas when the barometer is at 
 285 inches, we say that, expressing the volume at 30 inches by V, 
 
 V • 28-5 : : 4-54 : 30, or V=— x4-54=4-313. 
 
LIQUEFACTION OF GASES. 
 
 21 
 
 Knowing, then, the weight of 100 cubic inches of nitrogen gas at 30 inches, the 
 weight of 4-313 is easily obtained. 
 
 In this manner, the corrections for pressure, alluded to in the description of the 
 modes of taking the specific gravities of gases and of vapours, are introduced. 
 Thus, in taking the specific gravity of steam by Gay Lussac's process (page 14), 
 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 diflference 
 between 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 
 example, this rule, of the volume being inversely as the pressure, 
 holds exactly ; but there are many other gases, in which, when the 
 compression is very great, the particles appear to be brought within 
 the sphere of their respective cohesive forces, and the volume di- 
 minishes 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 ex- 
 actly the same pressure, the volumes will not diminish in the same 
 degree when the pressure 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. Thus many gases have been liquefied 
 by a degree of pressure which differs for each gas, and is at 3?° 
 Fahrenheit as follows: 
 
 Name of gas. 
 
 Nitrous Oxide . . . 
 Carbonic Acid . . . 
 Muriatic Acid . . . 
 Sulphuretted Hydrogen 
 
 Ammonia 
 
 Cyanogen 
 
 Sulphurous Acid . . . 
 
 
 Pounds to 
 
 
 the Inch. 
 
 44 
 
 660 
 
 36 
 
 540 
 
 24 
 
 360 
 
 15 
 
 225 
 
 5 
 
 75 
 
 3 
 
 45 
 
 2 
 
 30 
 
 Other gases, such as oxygen, hydrogen, and nitrogen, have been 
 subjected to a pressure of 800 atmospheres, not only without becom- 
 ing liquid, but without even deviating from the rule which implies 
 perfect elasticity, and hence without even approximating to the 
 term at which they should abandon the gaseous state. Notwith- 
 standing this, we cannot •consider that there is any physical differ- 
 ence of constitution between those liquefiable and non-liquefiable 
 gases, and hence the conclusion is, that, by a suitable increase of 
 pressure, the molecules of all gases might be so brought into cohe- 
 rent approximation, and converted 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 such gases are generated, and such methods 
 will consequently 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 sep- 
 arate them to greater distances from each other than they had been 
 
22 
 
 PHENOMENA OF SOLUTION. 
 
 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 it- 
 self, the latter is not merely moistened by the fluid, but it abandons 
 altogether the solid form, and, becoming liquid, mixes uniformly with 
 the fluid, and is said to have been dissolved by it. By this peculi- 
 arity of cohesion, bodies are divided into the soluble and the insoluble. 
 Thus common salt and Glauber's salt are soluble, while chalk and 
 white lead are insoluble, in water. These classes are, however, con- 
 nected 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 al- 
 cohol. A great deal of the success of vegetable proximate analysis 
 depends on the skill with which the solvent powers of various fluids 
 may be successively applied. 
 
 From the tendency of heat to diminish the force of cohesion, it naturally 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, bvlt 74 at 212°. This, 
 however, i^ not always the case ; some bodies, as common salt, are exactly equally 
 soluble in water at all temperatures, while 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°, 502 ; at 52^, 1022 ; at 76o, 28 ; at 93°, 53; at 122°, 
 47 ; and at 212^, 42 : the solubility increasing up to 93°, and from thence dimin- 
 ishing. 100 parts of water dissolve of nitrate of soda, at 21°, 63 ; at 32°, 80 ; at 
 50°, 23 ; 60°, 55 ; and at 246°, 218 parts. Here the pecuharity is of the opposite 
 kind to what occurs with sulphate of soda : the solubility diminishing up to 50°, 
 and from thence progressively increasing. 
 
 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 rep- 
 resent the quantities of the salt dissolved by 100 parts of water, while the vertical 
 lines represent the temperatures. Thus the line of sulphate of soda commences 
 
 80 
 75 
 70 
 65 
 60 
 55 
 50 
 45 
 40 
 35 
 30 
 25 
 20 
 15 
 10 
 
 32^ 52° 72° 92° 112° 132° 152° 172° 192° 212° 232= 
 
 
 
 
 
 
 
 
 
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 ^ 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
FORMATION OFCRYSTALS. 23 
 
 at the temperature of 32° at the horizontal line 5, and, rising rapidly, cuts the hori- 
 zontal 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 43 
 parts dissolved. The line of chloride of sodium is horizontal, showing that it is 
 equally soluble at all temperatures, and in the other ceises the construction of the 
 scale is easily seen on inspection. 
 
 In general, when solid bodies dissolve in a fluid, there is cold produced, but oc- 
 casionally the solution is accompanied with a remarkable evolution of heat ; this 
 last occurs when bodies which naturally contain water, chemically combined, are 
 deprived of it by heat, and when thus dried, dissolved ; in such cases, it is probable 
 that the one portion of water is taken by the salt into a state of intimate chemical 
 combination, and thus more heat produced than counteracts the cold which should 
 arise from the mere solution of the hydrated salt thus formed. Such examples may 
 be found in dry chloride of calcium, the dry sulphates of copper, or of zinc and iron. 
 
 Solution is very much promoted by agitation, by the minute di- 
 vision of the solid, and generally by all causes which tend to facil- 
 itate 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 satu- 
 rated. The cohesion 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 
 cohesion of the particles of the solid to each other, a portion of 
 the solid separates, the amount of which depends on the new con- 
 ditions 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 muriatic 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 cer- 
 tain laws, and, assuming regular geometrical forms, are termed 
 crystals. Solid bodies, in separating slowly from liquids in which 
 they had been dissolved, 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 evaporation ; 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 formation of the crystals is not disturbed by the boiling of 
 the liquid, they form regularly, and may attain to considerable size. 
 
 In many cases the bodies which it is necessary to obtain crys- 
 
24 CRYSTALLIZATION. 
 
 tallized are not soluble, or it may be wished to obtain crystals oth- 
 erwise than by solution. By melting a solid substance, its particles 
 are allowed liberty of motion ', and when it again 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 
 afterward, there remains only a general crystalline structure, visi- 
 ble 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 moir^e 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 removed 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 
 then be made in the upper crust, and the fluid metal 
 remaining be poured out at the one aperture, while 
 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 generally found lined 
 with well-formed and characteristic crystals, as rep- 
 resented in the figure. 
 Bodies may also be crystallized by sublimation. When a sub- 
 stance has been converted into vapour, and that, in condensing, it 
 assumes at once the solid form, its particles arrange themselves so 
 as to form crystals. Thus are obtained in fine crystals, arsenic, 
 arsenious acid, corrosive sublimate, benzoic acid, &c. 
 
 It frequently happens that the same body may be obtained crys- 
 tallized by more than one of these processes. Thus, corrosive sub- 
 limate may be crystallized by solution or by sublimation j sulphur 
 may be crystallized either by fusion or by solution. It is remark- 
 able that, when this occurs, the crystals obtained by the two pro- 
 cesses are never of the same shape ; they have not even any simple 
 relation of figure to one another, but indicate a totally different 
 mode of arrangement of particles, induced probably, at least in 
 part, by the different temperatures at which the change of state of 
 aggregation may have occurred. A body which crystallizes thus 
 in two ways 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 ad- 
 vantageously applied. To favour the deposition of the particles, 
 a variety of artificial acids may be applied. Thus, crystallization 
 takes place better in a pan with some little roughness at the sides 
 
CRYSTALLIZATION. 25 
 
 than when it is quite smooth, and threads are hung in sirup to pro 
 mote the crystallization of the sugar-candy j a little crystal of the 
 same kind of salt is often introduced, to serve as a nucleus round 
 which the new crystals may gather j 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 divided between two similar 
 dishes j on a crystal of nitre being laid in one dish and a crystal 
 of Glauber's salt being laid in the other, a crystallization of pure 
 nitre will occur in the former, while 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 
 completely solid. Thus, when copper wire has been kept some 
 time in the laboratory, it becomes a mass of cubical crystals, and 
 its tenacity is almost completely lost. When sugar is melted and 
 allowed to cool, it forms a perfectly transparent hard mass, desti- 
 tute of any trace of crystalline arrangement, but after some months 
 it becomes opaque and white, having changed into ordinary crystal- 
 lized sugar. In cases, also, where bodies are dimorphous, one 
 form is generally unstable, and the body, when crystallized in it, 
 changes after some time into the other form. This takes place re- 
 markably with sulphur, and will hereafter be again referred to. 
 
 A solution of a salt, saturated at a high temperature, is found 
 occasionally to remain without crystallizing, although cooled to a 
 very low degree. In such case, on introducing a little crystal, or 
 agitating the liquor, it suddenly crystallizes, and frequently solidi- 
 fies into one mass. Sulphate of soda is remarkable for its tenden- 
 cy to assume this indifl^erence 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 j 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 va- 
 pour 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 portion of the vessel. 
 
 It has been noticed, that when a body has been obtained, crys- 
 tallized at difi^erent temperatures, as by solution and fusion, the 
 crystalline form is generally different, and the body is said to be 
 
26 
 
 PRIMARY AND SECONDARY CRYSTALS. 
 
 dimorphous. In this case, the two forms are totally different m 
 their geometrical character. But independent of this, a body may, 
 even simply by solution, be obtained, crystallized in a great variety 
 of forms. In a crop of crystals of sulphate of iron or of alum, obtain- 
 ed by cooling from a hot solution, a great many different figures may 
 be observed, which, however, are, on examination, all referrible to 
 one more regular and fundamental form. Each substance has thus 
 a characteristic form of crystal, which is termed its primary form j 
 and it may assume a great variety of figures, produced by modifi- 
 cations 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 there- 
 fore necessary, 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, and secondary 
 forms would be produced, by which the characteristic figure of the 
 crystal would be injured. 
 
 The most ordinary source of change of figure consists in the replacement 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 is to produce the secondary form b, and by replacing 
 the solid angles by planes, the form c ; when these replacements occur together, 
 
 
 .^^^ 
 
 the more complex figure d is produced. If the edges of the cube be replaced until 
 ail 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 
 
 inc same extent, there is formed a regular octohedron /. These last are again sim- 
 ple and primary forms, for by a similar move 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 determinatioft of the primary form of the crys- 
 
.REGULARSYSTEM. 27 
 
 f;al, for it often occurs that the same secondary form may be pro- 
 duced by two different primary forms, and in such case, the cleav- 
 age being simply related to the surfaces of the true primary form, 
 determines which it is. 
 
 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 par- 
 ticles being built up around certain axes, which pass through the centre of the crys- 
 tal, and the relative position and magnitude of which determine the manner in which 
 the particles are arranged. 
 
 In this way there may be formed six systems of crystallization, characterized as 
 follows : 
 
 1st System. The Regular System. The three axes are all equal in length, and 
 are at right angles to each other. 
 
 2d System. The Rhombokedral 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, while a fourth and unequal axis is at right angles to that plane. 
 
 3d 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, while 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 crystals 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 
 distances 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 /, of which each plane 
 is an equilateral triangle. When each face of the crystal cuts one axis at right an- 
 gles, and is hence parallel to the 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 positions 
 of sets of planes, other and more complicated (secondary) b, c, d, forms are produced, 
 arising from the partial coexistence of the conditions of the formation of two sim- 
 ple forms. 
 
 The crystals belonging to this system are generally veiy well defined and easily 
 recognised : a great number of important bodies crystallize ^ 
 in the forms belonging to it : thus common salt, fluor spar, /y 
 galena, and iron pyrites, are found in cubes ; alum in octohe- ^ ■ 
 drons ; the garnet is found in dodecahedrons. When pure 
 metallic substances are found crystallized, it is always in 
 forms belonging to this system ; thus, bismuth, copper, sil- 
 ver, gold, crystallize in cubes, and lead in octohedrons. 
 
 A peculiarity of crystals, belonging particularly to this sys- 
 tem and to the next, is, that every alternate face shall 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 sel- 
 dom truly octohedral ; it has usually the figure of g where 
 four of the sides of the octohedron have become very large, 
 while the other four remain very small. When the oblitera- 
 tion becomes complete, there is produced the tetrahedron, or 
 three-sided pyramid of fig. h, which is hence properly called 
 
28 
 
 RHOMBOHEDRAL AND SQUARE, SYSTEMS. 
 
 the hemioctohedron. Such crystals are called hemihedral, from their containing 
 half the proper number of sides. Certain bodies have a natural tendency to hemi- 
 hedral crystallization, 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 reg- 
 ular octohedron, but its crystals are universally hemihedral. 
 In the Rhambohedral system, the supplementary, or fourth axis, is taken as the 
 principal axis, and the crystals are formed 
 by the planes being apphed to these axes, 
 as in the former system. If the planes 
 be all inclined at the same angles to the 
 three horizontal axes, and cut the verti- 
 cal 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 (k) is produced. 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 modified forms than for those simple fig- 
 ures above described, although the six-sided prism and six- 
 sided pyramid are characteristic of very many substances. If 
 we suppose, 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 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 modification 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 ori- 
 ginally 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. 
 3. T7ie 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 re- 
 placement of the terminal edges of this prism, four-sided pyramids 
 may be formed on its base and summit. By this property 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 modified, while the top and bottom remain unaltered ; this never takes 
 place in the regular system, where, there being no one side particularly upper or 
 ower, all modifications must affect all sides alike. 
 
 ^ 
 
 f\ 
 
 V 
 
 Or/ 
 
 ■~"-Ov^ 
 
 
 
 
 vJ 
 
 ■? 
 
 
PRISMATIC SYSTEMS. 
 
 29 
 
 4. The right Prismatic System. — In this system the three axes 
 being all unequal, the length, breadth, and thickness of the crys- 
 tal may be different from each other. Thus, in the octohedron,j9, 
 formed by the application of planes, each connecting the extremi- 
 ties 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 in- 
 clined to the horizontal axes, and parallel to the vertical axis, a 
 prism with a rhombic base may be produced. This also, by com- 
 bination of the two forms, may obtain pyramidal terminations, as 
 in some forms of native sulphur. 
 
 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 aflfected 
 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. — From the manner in which 
 the crystals belonging to this system form, one of the oblique axes 
 is generally by much the most developed, and is taken as the prin- 
 cipal axis. The remaining axes, which are at right angles to each 
 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 ob- 
 lique rhombic octohedron, such as characterizes 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 inde- 
 pendence of each other, the front and back of the crystal may be 
 quite different in relation to the sides. The crystals of sulphate 
 of soda, of carbonate of soda, of borax, of sulphate of iron, and of 
 feldspar, may be taken as examples of the numerous forms deriva- 
 ble from this system. 
 
 6. The doubly oblique Prismatic System. — The axes are all une- 
 qual, and all form acute angles with each other, and it is hence in- 
 different which is taken as the principal axis of the crystal. The 
 consequence is complete absence of symmetry between any two surfaces of the 
 crystal, except 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 sulphur 
 of copper are examples of this system ; the octohedron of 
 this system is figured in the margin. 
 
 It might be at first supposed that the assumption of these axes, or lines round 
 which we have supposed the crystalline particles to be regularly 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 vari- 
 ety of sources agrees in demonstrating that this diversity of crystalline systems 
 arises from fundamental 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 peculiarly from the action of crystal- 
 lized bodies upon light that accurate and extraordinary information has been ob- 
 tained of their internal structure, and the discoveries that have been made in this 
 department were the means of advancing the physical theory of light to its present 
 ahnost perfect state. 
 
 Substances may assume crystalline forms which do not properly belong to them 
 in many ways. Thus, a group of crystals being imbedded in a rock, they may, by 
 the filtration of the water of springs across the rock, be dissolved out, leaving a hoi- 
 
 ^^©5* 
 
30 FORMS MODIFIED BY FOREIGN BODIES. 
 
 low mould of their form ; and, subsequently, substances of another kind may be in- 
 troduced 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's head, 
 can be said to have so crystallized. By cleavage, and by the operation of polarized 
 light, the unsuited internal structure is recognised, 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 crys- 
 tallized. 
 
 It has been thought that the presence of foreign bodies in a solution, even where 
 they did not enter into combination with the substances M^hich crystallized from it, 
 might modify their form. Thus, when common salt crystaUizes in a solution of 
 urea, it is deposited in octohedrons, and by dissolving alum in a solution of urea, it 
 may be obtained crystallized in cubes. But in this case, the substances which crys- 
 taUize 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 quanti- 
 ty of iodide of potassium, has been supposed to modify its form ; but it is more likely 
 that the mechanical presence of an impurity of the kind maybe supposed to produce 
 a tendency to macled crystals, and thus the external form be somewhat altered, al- 
 though the true constitution of the crystal may remain the same. 
 
 Certain bodies, when they exist together in solution, may re- 
 markably modify each other's form, by crystallizing together so* 
 completely that every individual crystal shall contain a quantity of 
 each. Yet these 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 potas- 
 sium and sulphate of soda, which belong to different systems of 
 crystallization, not crystallize together, but Glauber salt and car- 
 bonate of soda, which do belong to the same system, will not crys- 
 tallize together, because the relations of their angles and sides be- 
 ing completely different, they cannot mix together so as to form a 
 uniform solid. But sulphate of zinc and sulphate of magnesia be- 
 long not merely to the same crystalline system, but they are al- 
 most identical in their figures ; the eye cannot make any distinction 
 between their crystals ; and hence, when a crystal is being formed 
 in a solution containing these two bodies, the molecular and crys- 
 talline 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 crystal, its angle must be 90° 
 49'. Carbonate of lime and carbonate of magnesia are, like the 
 
ISOMORPHISM. 31 
 
 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° ¥, and that of carbonate 
 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 
 sulphates which crystallize in the same form, and which constitute 
 a well-defined crystalline genus. If an octohedral crystal of com- 
 mon alum be placed in a solution of the sulphate of alumina and 
 ammonia, the crystal augments in size by the addition of layers of 
 It. If it be then removed to a solution of sulphate of potash and 
 peroxide of iron, it acquires another layer ; by a solution of sul- 
 phate of ammonia and peroxide of iron another still ; and by means 
 of solutions 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 chemical constituents of the crystal may 
 thus vary, but it retains its form j the number of equivalents of 
 chemical substaiices contained in it remains also the same, although 
 they may not remain identical in nature. The potash and the am- 
 monia on the one hand, the oxide of iron, the alumina, and the ox- 
 ide of chrome on the other, agree in producing the same crys- 
 talline arrangement of particles ; in impressing upon their com- 
 pounds, with the same bodies, the same crystalline form. Bodies 
 so related are called isomorphous. Oxide of zinc and magnesia are 
 isomorphous j while 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 prop- 
 erties j they follow generally the same laws of combination, and 
 hence, as shall be farther 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 ar- 
 rangement 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, or wheth- 
 er 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 
 chemical combination, the crystalline form was determined by the number of mole- 
 cules or atoms present, and was independent of their nature. Neither of these 
 ideas has been found sufficient ; but the complete discussion 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 recognised and compared with one another, the 
 instruments by means of which their measurement is effected re- 
 
32 GONIOMETER S. L t G H T. 
 
 quire a few words' notice. They are called goniometers (yovioq^ an 
 angle ; fisrpo), I measure). The simplest form consists of a semicir- 
 cular 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 goniometer 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 exactly the same 
 direction. To the adoption of this principle of measurement 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 efl^ects which were pro- 
 duced by means of their action, were not such as to involve the 
 principle 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 most complex manifestation in a 
 double oblique crystal, 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 iden- 
 tification of chemical substances, and capable of modifying the cir- 
 cumstances of their mutual action in an eminent decree. 
 
 CHAPTER II. 
 
 OF THE PROPERTIES OF LIGHT AS CHARACTERIZING CHEMICAL SUBSTANCES 
 
 I SHALL not attempt to enter into the details of the history of the 
 mechanical 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 recognising chem- 
 ical 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, 
 
PROPERTIES OF LIGHT. 33 
 
 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 trans- 
 farent^ 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, though we cannot see anything through it. Where, in an 
 opaque body, the light is partly reflected to the eye and partly ab- 
 sorbed, there arises the diversity of colours which opaque bodies 
 may possess. 
 
 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 j and if its path be rep- 
 resented 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 lim- 
 iting 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 re- 
 fractive medium directly from an emptj?' 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 transmission of the luminous rays 
 which fall upon the surface of a body is, however, in no case abso- 
 lute 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 transmitted, 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 refraction 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 exceedinglj'- 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 solur ray contains, for 
 these differ in velocity, those which are least refrangible being trans- 
 mitted with the greatest quickness. The velocity of light is changed 
 when it passes from one substance to another, and it is this change 
 m which originates refraction. In general, the denser the medium 
 
 E 
 
34 
 
 REFRACTION. 
 
 dies in the follow 
 
 ing table : 
 
 
 . 2 549 
 
 Garnet 
 
 . 1 815 
 
 . 2-500 
 
 Oil of cassia 
 
 . 1-614 
 
 . 2-439 
 
 Plate glass 
 
 . 1-542 
 
 . 2-322 
 
 Oil of turpentine 
 
 . 1-475 
 
 . 2-224 
 
 Water 
 
 . 1-336 
 
 . 2-148 
 
 Chlorine . 
 
 . 1-000772 
 
 . 2-028 
 
 Air . 
 
 . 1 000294 
 
 . 1 830 
 
 Vacuum . 
 
 . 1-000000 
 
 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 undulatory theory of light was found. 
 
 The refractive power of a body is not connected with its chemical 
 constitution in any positive manner ; but inflammable substances 
 are generally possessed of high refractive powers. It was this 
 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 bodi 
 Realgar . 
 Octohedrite . 
 Diamond 
 Nitrate of lead 
 Phosphorus . 
 Sulphur . 
 Flint glass, from 
 to 
 
 In uncrystallized bodies, the molecular arrangement being irreg- 
 ular and indefinite, the action upon light is the same in every direc- 
 tion, and hence a ray of light undergoes, when passing from air into 
 water or glass, simple 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 regular system, where there are three precisely similar axes, 
 the molecular constitution, although subjected to definite laws, must 
 be the same in all directions, and hence a ray of light will be acted 
 upon, in such a crystal, in the same manner, no matter in what di- 
 rection it may go. Hence, in crystals of the regular system, there 
 is only ordinary refraction and a single image. 
 
 When a ray of light passes, however, into a crystal of the rhom- 
 bohedral system, it is diflerently 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 re- 
 fracted ray. But if the light pass in any other direction, it is divi- 
 ded into two portions, one of which is refracted according to the 
 ordinary law of the sines, while the other, following a totally new 
 law, is termed the extraordinary ray. The angle which these two 
 rays make with each other increases according as the path of the 
 incident fky is farther from the principal axis ; and when the light 
 falls perpendicular to the sides of the prism, and hence to the prin- 
 cipal axis, the divergence of the two refracted 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 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 
 follows a new and peculiar law. 
 
 The existence of double refraction, and the change in its amount, 
 according to the direction in which the light passes through the 
 
DECOMPOSITION OF LIGHT. 
 
 35 
 
 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 
 posidon of the eye, the distance between the two images of the dots 
 will be found to change j it will be greatest when the eye is in a line 
 connecting a solid angle and the centre of the opposite plane j but 
 to efface the double image and obtain single refraction, new sur- 
 faces 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 octohedron, 
 whether right or oblique, gives the predominant character to the forms, the exist- 
 ence of a molecular constitution, regulated by the same cause as the external fig- 
 ure, is displayed in a peculiarly striking manner. There is no longer a single line 
 in the crystal, in which ordinary 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 them, and which govern all 
 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 it, it is divided into two rays ; and 
 of these rays, both follow new and pecuhar laws of refraction, the proportionality of 
 the sines being totally abandoned. The real distinction of the crystalhne systems 
 is thus completely proved by the existence of these remarkable optical properties 
 by which they are characterized ; and so perfect is this distinction, that in cases 
 where the external form and cleavage would lead us totally astray, tha optical 
 properties of the body may show us its true crystalline position. Thus the mineral 
 boracite (borate of magnesia) crystallizes in cubes, which are remarkable, how- 
 ever, 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 rec- 
 tangular axes being exactly equal to each other. 
 
 When a ray of white light, S, P, admitted ^into a darkened room 
 
 L through an aperture, 
 
 H, passes mto a re- 
 fracting substance, «, 
 A, B, C, whose surfa- 
 ces 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 num.ber of rays of light, of 
 different colours and of different refrangibilities, as at g ; and if it 
 has been derived 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, the 
 same as that seen in the rainbow, is, 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 vv'^ith the nature of the refracting body, ac- 
 cording to what is termed its dispersive power. White light is, 
 therefore, not a simple, but a highly complex phenomenon, con- 
 
36 PRISMATIC COLOURS. 
 
 sisting 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 a uniform grayish- 
 white tinge is produced : if we had colours as perfect as those of 
 pure solar light, their reunion would form pure white, and this ac- 
 tually 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 spec- 
 trum, beyond the limits of the violet rays, other rays of a still 
 higher refrangibility, and of a colour which he proposes to term 
 lavender. This lavender light cannot be merely a weaker form of 
 violet light ; for, on 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 prismatic colours ; and although some peculi- 
 arity of vision, with regard to colours, may cause a difference of 
 opinion, yet the evidence obtained by Herschel of the real exist- 
 ence of simple lavender-coloured light appears to be satisfactory. 
 Of the seven prismatic colours, there are four which cannot be 
 considered 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 re- 
 maining in excess. There are, in fact, blue, red, and yellow lights 
 spread over every portion of the spectrum j and if they were so in 
 equal quantities, the spectrum would be white, and we could not 
 have any decomposition of light by refraction ; but, although there 
 are blue rays of every degree of refrangibility, yet the larger pro- 
 portion of them have a refrangibility greater than those of any 
 other colour, and they are hence collected nearer the upper extrem- 
 ity 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, while 
 the great proportion of the yellow rays, having a mean 
 refrangibility, occupy the centre. In every portion of 
 the spectrum there is therefore mixed, blue, red, yel- 
 N^ low, and hence white light ; but where these simple 
 lights prevail, the colours of the spectrum are pro- 
 duced, and where two are present in excess over the 
 quantities which form white light, the secondary col- 
 ours, 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, B, 
 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 
 
ABSORPTIO N. N ATURAL COLOURSOF BODIES. 37 
 
 yellow, and similarly in the blue ; at the point where the curves 
 of the red and yellow meet, the tint is orange j where the yellow and 
 blue are equal, the colour produced is green ; and where the red and 
 blue are both in excess over the intermediate yellow, there is violet. 
 This view of the constitution of the solar spectrum, leading to 
 the remarkable and unexpected consequence that there may be 
 white light unalterable by the prism, its coloured rays having all the 
 same degree of refrangibility, was obtained by Brewster, by means 
 of the absorliing 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 absorbed, 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 vi- 
 sion, 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 detect- 
 
 many 
 
 metallic substances, thus 
 
 Cobalt is known by colouring glass blue. 
 
 Nickel 
 
 i( 
 
 u 
 
 orange. 
 
 Chrome and vanad 
 
 ium 
 
 (C 
 
 green. 
 
 Copper " 
 
 (C 
 
 u 
 
 green or red. 
 
 Iron « 
 
 (C 
 
 (( 
 
 yellow or green. 
 
 Manganese 
 
 (( 
 
 C( 
 
 purple. 
 
 Silver « 
 
 (( 
 
 u 
 
 yellow or orange. 
 
 Gold 
 
 (( 
 
 u 
 
 crimson. 
 
 And these are not the only cases in which colours are produced. 
 
 The colours of chemical compounds are so varied, that there 
 cannot he 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, however, certain general facts worth bearing in 
 mind, in which classes of bodies, to a certain extent, are character- 
 ized by colour : thus, the ordinary compounds of copper are us»i 
 ally green or blue ; those of nickel, green; those of cobalt, ri^iit 
 or blue ; those of chrome, green or purple. A singular property 
 of certain bodies consists 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 complementary, or such as, 
 when mixed together, would form white light. This dichroism oc- 
 curs only in crystals which refract doubly, and in which the absorp- 
 tion 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 re- 
 flects, in considerable 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 sur- 
 
38 POLARIZATION OF LIGHT. 
 
 face, tinged like the transmitted portion, which, mixing with that 
 properly reflected at the first surface, modifies its colour. The 
 transmitted and reflected lights are sometimes truly complementa- 
 ry; 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^ 11', it acquires 
 peculiar properties which it had not previously possessed, and is 
 said to be polarized. If the ray be then made to falf upon a sec- 
 ond 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 an- 
 gles to the first, there is no light reflected : 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 which 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 re- 
 fraction or absorption. Even in ordinary refraction some of the 
 light transmitted is polarized, but it is mixed with so much ordina- 
 ry light that its properties are obscured : however, if the same 
 quantity of light be refracted often, it may be polarized completely j 
 and hence, transmitting a ray of ordinary light, at a certain angle, 
 through a pile of parallel glass plates, is a usual mode of polari- 
 zing it. In double refraction, the polarization of the refracted light 
 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 recompose the original ray of 
 common light ; but by contrivances, such as in Nichol's prism, one 
 may be turned aside or absorbed, and then the other used. In po- 
 larizing 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 tourma- 
 line be laid together, and the direction of their crystalline axes 
 be the same in both, they act similarly upon the light, and, the same 
 polarized ray being transmitted by both, the brightness of the im- 
 age 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 transmitted 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 the polarization has been complete 
 when the ray is totally absorbed by a tourmaline, the axis of which 
 is perpendicular to the plane of polarization 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 polarizing 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 phe- 
 
POLARIZED LIGHT. 
 
 39 
 
 nomena 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 refract- 
 ive 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 prismatic tints, 
 according as the plane of polarization of the ray of light is altered, and thus the ac- 
 tion 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 sup- 
 ported upon a frame, in a plane perpendicular to the direction of the ray ; or, if it be 
 fluid, a glass tube is filled with it, and, being closed by plates of glass with parallel 
 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 un- 
 dergone, by an apparatus termed the analyzing piece, which may be, where two 
 images are required, a doubly refracting prism, or, where only one, the Nichol's 
 prism, a doubly refracting 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 descri- 
 bed ; for the real difference of molecular ar- 
 rangement, in crystals belonging to these various 
 systems, is rendered still more remarkably dis- 
 tinct by the action which they exercise upon 
 light in this peculiar state of plane polarization. 
 , I If a ray of polarized light pass along the Princi- 
 pe pal axis of a crystal belonging to the rhombo- 
 hedral or to the square prismatic system, and 
 on issuing be examined by means of an analy- 
 zing plate, the axis of the crystal is seen to be 
 surrounded by a series of beautifully 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 
 uf colours similar to those which form the rings, as in quartz. / 
 
 If the crystal belong to any of the more complex systems, and 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 
 h, which is the phenom- 
 jCnon as seen with ni- 
 tre. The curves are fj 
 crossed by two bands, g 
 black or white, accord- 
 ing as the analyzing 
 plate revolves, but 
 which, when the crys- 
 tal is turned round on 
 its principal axis, open 
 out, revolving each on 
 its axis,, A or B, and 
 
40 
 
 OPTICAL PROIERTIES OF CRYSTALS. 
 
 bend with the convexity towards the centre of the figure. In substances, as topai 
 and carbonate of soda, where the axes make a large angle with each other, tho 
 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 purposes of the chemist, sufticient 
 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 system there ia 
 consequently no such result, and hence such crystals are recognised by the com 
 plete absence of coloured rings. 
 
 The optical properties of the different systems of crystallization may be thuf 
 summed up. 
 
 Single refraction. 
 . ) Double refraction 
 . J with one axis. 
 
 ' ( Double refraction 
 with two axes. 
 
 No rings by polarized light 
 Simple system of rings b} 
 polarized light. 
 
 Double system of rings by 
 polarized light. 
 
 Regular system. 
 
 2. Rhombohedral system 
 
 3. Square prismatic system 
 
 4. Right prismatic system 
 
 5. Oblique prismatic system . . > 
 
 6. Doubly oblique prismatic system ) 
 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 crys- 
 tals 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 macks, 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 pyramids ; and 
 such crystals of it occur with almos^ 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 hght, they show, in place 
 of the system of rings which a true crystal should pro- 
 duce, 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 
 imperfect joints, are found. A substance which il- 
 lustrates 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 ex- 
 ternal characters go, to the regular system. It has, 
 however, no distinct cleavage planes, and refracts 
 When examined by a ray of polarized light, the cube of analcime gives a 
 most beautiful appearance. The diagonals of each 
 surface become occupied by lines, which are alter- 
 nately black and white, according as the analyzer 
 is made to revolve, and in the intervening triangu- 
 lar spaces the richest colours of the rainbow sue 
 ceed one another, according to the optical laws. 
 This crystal is therefore made up of a great number 
 of other crystals belonging to some one of the 
 more complex systems ; but its structure is so ex- 
 traordinary, that the determination of the form of 
 its real crystal has been as yet impossible In 
 this instance, and in that of boracite alrea ly no- 
 ticed, the optical properties have been the means 
 of showing the true nature of bodies which, from their external form, should oth- 
 erwise 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 trav- 
 ersed by a cross, alternately black and white, as the analyzing plate revolves, but 
 
 doubly. 
 
ROTATIVE POWER OF LIQUIDS. 41 
 
 farther, 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 analyzing 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 opposite 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, which 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 na 
 ture of the molecules ; and, although some observations appeared to connect it with 
 the crystaUine structure, it is now fully established to be independent of it. In 
 fact, this property of circular polarization, as it is termed, belongs to certain bodies, 
 independent of their arrangement, and even in many cases accompanies them whei 
 they enter into combination. It is even found in liquids, particularly the volatilfi 
 oils ; and when oil of turpentine is converted into vapour, its molecules preserve 
 unaffected their rotative power. Its existence is, however, subjected to remarka- 
 ble anomalies ; thus, when oil of turpentine combines with muriatic acid and forms 
 artificial camphor, 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 disappeared. 
 
 [These phenomena of circular polarization may be readily traced. If from a 
 crystal of quartz a disk is cut transversely, a system of rings will be seen enclosing 
 a circular coloured space. If the disk be turned round, no change takes place ; but 
 if the analyzing plate turns, the colour passes through a series of tints, which, after 
 100° of rotation, may end in a sombre violet.. If, now, we cut from the same crys- 
 tal another disk twice the thickness of the former, and make use of it, we shall find 
 the tint different from what it last was ; but, by turning the analyzing plate 100°, 
 we may bring it back again to the same sombre violet : with a plate three times 
 as thick, we should have to turn 100° still farther to produce the same tint, and for 
 each additional thickness an additional 100°. We therefore infer that, when polar- 
 ized light passes along the axis of a crystal of quartz, its planes of polarization ro- 
 tate circularly, or, rather, spirally, in the crystal ; and this takes place in some spe- 
 cimens from right to left, and in others from left to right. Under these circum- 
 stances, light is said to undergo circular polarization.] 
 
 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 polarization 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, ac- 
 cording 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 45°< — ^, and of oil of lemons, in the same length, 
 84°9a»-^. The rotative power of quartz is about 685 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 high 
 ^8^ — >- power ; but it gradually changes into the sugar of grapes, the rotative power 
 of which is -< — ^:. Hence the action of the starch, when fermentation has com- 
 menced, rapidly diminishes, until there is so much sugar formed that the ^ — > and 
 < — ««s exactly balance, and the solution is totally without action upon a polarized 
 ray ; alter that, the quantity of sugar still increasing, the rotation becomes < — ^, 
 »nd 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 compared with their 
 specific gravities. This property of the circular polarization 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 produced by 
 chemical affinity, we shall find that the light which ordinary polarization throws upon 
 
 F 
 
fiS " WAVE THEORY OF LIGHT. 
 
 the internal mechanical stracture of the crystal is not more brilliant than that which 
 we obtain of the arrangement of the chemical constituents by their circularly po- 
 larizing power. 
 
 Some specimens of quartz appear destitute of this rotative power : 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 sohd angles of the pyr- 
 amid {k, page 28) are generally replaced by planes which are unequally inclined to 
 the axes ; and where these planes are present, the direction of the rotation can be 
 foretold, it being to the right or to the left, according as these unsymmetrical facea 
 are inclined. Such crystals are termed plagihedral ; as in the cases where no such 
 faces can be traced, the rotative power is generally absent, and this arises, as is re- 
 markably 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 uncrys- 
 tallized conditions, is devoid of all rotative power ; and, accordingly, until the dis- 
 covery of the power of rotation in liquids, and that this property was found to ac- 
 company the molecules of the body through all states of aggregation, it was con- 
 sidered 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 difference of crystalline arrangement, 
 but that this last is caused by actual difference of properties in the molecules them- 
 selves, of which the most remarkable is detected by the opposite actions upon light. 
 
 The impression of light was at one time considered to be produ- 
 ced by a series of exceedingly minute particles, of a peculiar sub- 
 stance, 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 v/hich, fill- 
 ing all space, and being diffused through the substance of the most 
 solid bodies, and occupying the spaces between their more substan- 
 tial molecules, transmits and modifies these vibrations, and confers 
 upon substances transparency or opacity, colour, and all other proper- 
 ties of acting upon light which they may possess. 
 
 This medium, or luminiferous ether, as it is termed, is supposed 
 capable 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 re- 
 frangible 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 col- 
 ours arises, therefore, precisely as the impression of different sounds 
 is produced, by a difference in the length of the waves in the vibra- 
 ting air j 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 Avhite light, there acts upon the eye in every 
 second 610-000000-000000 luminiferous vibrations. 
 
 In the case of doubly refracting crystals with one axis, that is, 
 those belonging to the rhombohedral and the square prismatic sys- 
 
WAVE THEORYOF LIGHT. 43 
 
 tern, the elasticity of the ether is supposed to be so far modified 
 by the arrangement 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 systems, the crystals of which have double refraction 
 with two axes, the elasticity of the ether is supposed to be differ- 
 ent in each of three perpendicular directions, and hence neither 
 refracted ray can follow the ordinary law. It is thus, as has been 
 already stated, that the classification of all crystallized bodies in 
 these systems is shown, not to be an arbitrary assumption, but a 
 principle based upon our most decisive evidence of molecular ar 
 rangement. 
 
 The rays of light derive some of their most remarkable proper 
 ties from the principle that the vibrations are accomplished in a 
 direction perpendicular to the direction of the rays. Thus, if we 
 conceive a ray of light moving from north to south, the little vi- 
 brations which constitute it are efiected in a direction east or west, 
 and in every other direction equally perpendicular to its path j and 
 ordinary light is characterized by the fact that its vibrations are 
 accomplished in every imaginable plane. If we reduce these vi- 
 bratory movements to a single plane, the light becomes polarized, 
 and is then in the condition for dissecting the interior of crystal- 
 lized bodies, and exhibiting the beautiful illustrations of their struc- 
 ture that have been already noticed. But it would lead us too far 
 away from our proper subject to enter into the description of polar- 
 izing apparatus, or even of its principles, in detail, as the indication 
 just given of its nature is suflicient. 
 
 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 an- 
 other point they may form light of double brilliancy. To effect 
 this, it is only necessary they should be in opposite states of vibra- 
 tion, that is, while the waves of one ray should be rising up, those 
 of the other should be falling down : these motions then compen- 
 sate each other, and the result is the same as if no vibratory mo- 
 tion 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 pro- 
 duced 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 pro- 
 duce 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 labrado- 
 rite, 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 5 the sun, the source of warmth to the surface of our globe, 
 being also the natural origin of light : and in most cases where light 
 is artificially produced, it is associated with heat, which is also ca- 
 
44 
 
 PHOSPHORESCENCE. 
 
 pable of being transmitted in a radiant form. It was, indeed, once 
 considered, that at certain temperatures heat became converted 
 into light, and that the colour of the light depended on the degree 
 of heat j 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 light 
 emitted is pure white, and similar in constitution to the solar ray. 
 The powers of emitting heat and of emitting light are, however, 
 although so frequently associated, quite independent and distinct j 
 and the rays of heat and those of light may be perfectly separated 
 from each other. It would anticipate too much the account of radi- 
 ant heat to describe the means of separating the heating from the 
 luminous qualities of ordinary light; but elsewhere they will be 
 described in full. A body may become luminous when very mod- 
 erately heated, as is the case with many 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 substance may be very 
 intensely heated. There are also many bodies which, when ex- 
 posed to the light of the sun after having been made red hot, ap- 
 pear to absorb a portion of it, and become capable of emitting it 
 slowly, giving a pale bluish light for some time afterward in the 
 dark. This occurs particularly with chloride of barium, native sul- 
 phate 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 putrefac- 
 tion has commenced. The light emitted is, in such cases, the re- 
 sult of an exceedingly slow but distinct process of combustion ; it 
 requires the presence of atmospheric air, or oxygen, although an 
 exceedingly small quantity may suffice, and it is extinguished and 
 revived by all such means as facilitate or retard the chemical ac- 
 tion of the air upon organic bodies. The light emitted by the glow- 
 worm and the fireflies, 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 at 
 mosphere, produces the light as a consequence of combustion 
 Animal phosphorescence is, therefore, to be ascribed to chemical 
 action. 
 
 The white light, derived from diflerent sources, does not always 
 possess the same physical constitution. If the coloured spectrum 
 produced by the solar ray be closely examined, it will be found 
 crossed by a multitude of black lines, indicating the total absence 
 in the sun's light of rays of certain refrangibilities. That this is 
 inherent in the light is shown by the fact, that when we change 
 the nature of the prism, the position of the space in which these 
 black lines occur may alter, but the lines preserve all their relative 
 
CHEMICAL RAYS IN THE SPECTRUM. 45 
 
 distances from each other totally unchanged. 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 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 re 
 markable dark lines in the blue. It is very curious, that if we ex- 
 amine the spectrum through certain coloured media, as the vapours 
 of iodine or bromine, we find additional black lines, and by using 
 gaseous nitrous acid these become almost innumerable, and in- 
 crease so much when the gas is heated that the spectrum is oblit- 
 erated and the gas becomes opaque. It is possible that such 
 takes place at the origin of the light of the heavenly bodies, and 
 that the sun and the fixed stars are involved in absorbing atmo- 
 spheres, 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 forever by means of such an impervious veil. 
 
 Some classes of chemical substances are, to a certain extent, 
 characterized by the facility with which they are decomposed when 
 under the influence of light. The salts of silver, of gold, of plati- 
 na, and, in some instances, of mercury, are subject to this influence. 
 A great variety 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 mod- 
 ify the affinity by which chemical combination is produced, has 
 been found to be exercised specially by the violet or more refran- 
 gible extremity of the spectrum, and even with great intensity by 
 invisible rays quite outside of the luminous space, and extending 
 beyond the lavender-coloured prismatic space of Herschel. It has 
 been also considered that the rays of the red extremity of the spec- 
 trum 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 
 certain. All that has been established is, that there exist 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 effects, the second of radiant heat, the nature of 
 which will be specially examined in the following chapter, and the 
 third of rays which, though neither luminous nor heating, exercise 
 an influence on chemical affinity, and the nature of which will be 
 discussed with more detail when the subject of chemical aflinity 
 and its relations to the other physical forces has been described. 
 
46 EFFECTS OF HEAT. 
 
 CHAPTER III. 
 
 OF HEAT CONSIDERED AS CHARACTERIZING CHEMICAL SUBSTANCES. 
 
 At almost every step of chemical inquiry it is necessary to in- 
 troduce the action of heat, either as modifying the results of the 
 chemical action of bodies upon each other, or as affording charac- 
 ters by which the substances we operate upon may be distinguished. 
 The doctrine of heat and the history of its effects have consequent- 
 ly, at all periods, formed an important portion of the studies of the 
 chemist ; and it is, indeed, only lately, since the brilliant course oi 
 discoveries that was opened, and so successfully prosecuted by 
 Melloni and by Forbes, 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 call- 
 ed, of heat. 
 
 Of all the physical sciences, however, that of Heat^ or Thermotia^, 
 as it is now termed, is the most important to the chemist in guiding 
 him in his operations, and in the accurate description of their results 
 On this account it will be necessary to describe the properties of heai 
 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. K::^ 
 pansion. 
 
 2d. Quantity of heat required to produce a given change of te¥> 
 perature. Specific heat. 
 
 3d. Temperature necessary for liquefaction. Melting points. 
 
 4th. Temperature necessary for giving a certain elasticity to j. 
 vapour. Boiling points. 
 
 5th. Quantity of heat required to produce a given change of a^' 
 gregation. Latent heat of liquids and vapours. 
 
 6th. Manner and rapidity of communicating or receiving he.-il 
 Conduction and radiation of heat. 
 
 The subject of heat will 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 rela- 
 tions of heat and light, and on the physical theory of heat. 
 
 SECTION I. 
 
 OF EXPANSION. 
 
 When describing the effects of cohesion, I have already noticed 
 that the molecular constitution of all bodies might be considered 
 
REPULSIVE POWER OF HEAT. 47 
 
 to depend on the relative power of the attractive force, cohesion^ 
 and the repulsive force of heat^ upon their particles. That where 
 the attraction was in excess, the molecules were knitted firmly to- 
 gether to form a solid body ; but that where repulsion was most pow- 
 erful, all cohesion was lost, and the body assumed the form of a va- 
 pour or a gas. In the intermediate condition, where the forces ap- 
 peared to be nearly in equilibrium, the liquid state was produced, 
 in which the molecules of the body appeared still to unite by a trace 
 of remaining cohesion, but that they 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 gradu- 
 ally heated until it shall begin to liquefy, its particles do not remaki 
 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 j the 
 molecules of the body gradually separate, occupy more space than 
 before, and from the very commencement of the increase of heat, 
 the body, though it may remain solid, yet expands. In the same 
 manner, if a liquid be heated, the change of aggregation does not 
 commence until the increase of heat has reached a certain degree ; 
 but from the beginning a change of volume occurs, the increase of 
 which marks the gradual diminution of cohesion. In gases there 
 can take place no farther change of form, and the only effect which 
 heat can produce upon them is expansion. 
 
 This power of repulsion which we suppose heat to exercise, in causing the tran- 
 sition from one state of aggregation to another, as well as the expansion which oc- 
 curs 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 dissi- 
 pated 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 de- 
 gree. 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 overcoming 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 state of tremulous 
 agitation, which being conveyed to the ear by the intervening air, gives a remark- 
 ably distinct and agreeable musical tone. The better conductor, the heated body, 
 and the worse conductor (provided both are metals), the cold body can be, the more 
 successful is the result. 
 
 This force of repulsion is iTxade still more distinct, and even measurable, 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 on 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 col- 
 oured ring, according as the temperature rises. 
 
 In gases, the expanding effect of heat is unaffected by any dis- 
 turbing cause 5 there is no cohesion remaining to impede its oper- 
 
48 MEASURE OF HEAT. 
 
 ation ; hence a certain increase of heat afTects all gases alike j and 
 no matter how hot or how cold a gas maybe, a certain increase of 
 heat produces the same increase of volume in every case. In sol- 
 ids and in liquids, however, it is different ; the expansion which oc- 
 curs is but the 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 cohe- 
 sion by which it is resisted, and which depends upon the nature of 
 the body. Consequently, every fluid and every solid expands in a 
 degree which is peculiar to it. There is yet another consequence 
 of the influence of cohesion upon the expansion 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 1|, and it will reduce the cohesion more than it did before, 
 as from 9 to 7^. 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 7| to 5, and 
 the increase of volume becoming, in place of 1^, 2. In solids and 
 liquids, the rate of expansion increases thus, with the temperature, 
 from the diminution of cohesion ; but in gases, where the cohesion 
 remains the same, or, rather, is completely absent, the expansion is 
 proportional to the additional 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 quanti- 
 ties of heat which we add or subtract from bodies to eflect their 
 expansion or contraction; to investigate, in fact, the principle on 
 which the thermometer and pyrometer are founded, and such de- 
 tails of their construction as shall hereafter be found necessary to 
 be known. 
 
 Let abhea glass bulb with a long and narrow neck, which is divided 
 
 o 
 
 ^ 
 
 M M i i I I i M M M M 
 
 KD 
 
 by a scale, as in the figure, of which each division is a certain part, as 
 ToV ^^ ^^^^ volume of the bulb. Let us suppose the bulb a to be fill- 
 ed 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 exactly settled at the commence- 
 ment of the scale. If, now, the instrument be warmed, the air in 
 the bulb expands, and, according as it increases in volume, pushes 
 before it into the tube the globule of mercury. This last serves, 
 therefore, 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 proper- 
 
NATURE OF TEMPERATURE. 49 
 
 tion. If the source of heat be water boiling, under ordinary cir- 
 cumstances, 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 glob-, 
 ule will be found to have arrived at the 365th division on the scale. 
 Therefore, 1000 measures of air, on being heated from the degree 
 of melting ice to that of boiling water, become 1365. 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 
 it received from the boiling water to be divided into 365 parts or 
 degrees, and each of these parts being applied separately to the 
 bulb, should have increased the volume of air by y ^V o P^^^j o^' should 
 have converted the 1000 volumes into 1001. There is thus obtain- 
 ed a scale of expansion which is quite artificial and arbitrary cer- 
 tainly, 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 de- 
 scribed, the expansion of the air will move the globule of mercury 
 to the degree 122, which is almost exactly the one third part of 
 the 365, and hence the water, in being heated from the degree of 
 melting ice to that of blood heat, received almost exactly one third 
 of the quantity of heat which should have made it boil, and its tem- 
 perature is one third as high. 
 
 I have here spoken of measuring the successive quantities^ of 
 heat which the air received, and in this case the manner of expres- 
 sion 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 temperature. The amount of expansion which a hot body is 
 capable of producing 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 tem- 
 perature the amount of expansion produced, marked off on any arbi- 
 trary scale which we may think proper to adopt. 
 
 Gases expanding more than any other bodies, the air thermom- 
 eter 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 cor- 
 rection, which is, that although the air, in being heated from the 
 degree of melting ice to that of boiling water, actually expands 
 fVVo ^^ ^^^ volume, yet that expansion is not all visible, for the glass 
 bulb expands also on being heated, although in a very small propor- 
 tion, and holds ^-^„^ more than it did when cold ; the visible expan- 
 sion on the scale is therefore only 363 degrees, and this must be 
 allowed for to have complete accuracy. The form of the air ther- 
 mometer 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 horizontal, which is quite 
 
 G 
 
50 
 
 AIR THERMOMETER. 
 
 impossible in the majority of practical cases, renders this kind of 
 an air thermometer too unmanageable ; and since the air changes its 
 volume very much for every change of pressure, and our atmo- 
 sphere varies in its weight almost every hour, an air thermometer 
 left open, as at the orifice ^, would change continually without ref- 
 erence to the degrees of heat at all, and would thus give false in- 
 dications. 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 proportional to the increase of heat, ceas- 
 es completely. For if the point b be closed, and the bulb a be 
 heated, the globule of mercury, in moving along the scale, con- 
 denses the air before it, and thus generates an elastic force, by 
 which the expansion is resisted and diminished in amount j the de- 
 grees would therefore be no longer equal, but rapidly diminish in 
 size, so that on the upper parts of the scale they could not be dis- 
 tinguished from one another, and would hence be useless. But by 
 having a second bulb, in the next figures, the elasticity of the air 
 'ompressed in the cold bulb increases much less rapidly, and the 
 *cale to be applied to the stem connecting the bulbs is easily con- 
 structed. 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 fluid there is also an ob- 
 jection, that the amount of expansion would be increased to 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 tem- 
 uerature only by the difference between the elasticity 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 
 balances the other. The 
 instrument indicates, there- 
 fore, such temperatures only 
 as affect one bulb and not 
 the other; the difference, in 
 fact, between the tempera- 
 tures of the two bulbs, and 
 hence is properly called the 
 differential 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 below, and plunges into the 
 fluid which the inferior bulb contains. This 
 lower bulb is soldered or cemented at its or- 
 ifice round the tube, so as perfectly to pre- 
 vent the action of the air. Fig C represents 
 
MERCURIAL THERMOMETER. 51 
 
 the most ordinary form j 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 in- 
 conveniences from the limited range of its scale, if it be not open 
 to the air, and from the complex form which the scale assumes if 
 the external air be prevented from communication, that it is never 
 made use of in practice except in some particular cases, which 
 shall hereafter be specially noticed. We are therefore obliged to 
 have recourse, for our accurate measures of temperature, to other 
 bodies, which, though not so sensible as air, ofier more practical 
 advantages. 
 
 The liquids which are generally used to measure, by their expan- 
 sion, change of temperature, are alcohol and mercury. The former, 
 in being raised from the melting point of ice to that at which itself 
 boils, expands y§^, whereas air within the same limits would have 
 expanded y^o) heing about three and a half times as much as alco- 
 hol : and mercury, in having its temperature raised from the melt- 
 ing point of ice to the boiling point of water, expands y^f oj ^^ 
 about ^V ^f ^^® 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 cold j and for this pur- 
 pose it is admirably fitted, as it is the 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 applica- 
 tion 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 admi- 
 rably suited to be a measure of heat, by the accidental circumstance 
 that its expansion, when contained in a glass bulb, is accurately 
 proportional to the temperature, and its indications therefore abso- 
 lutely true. 
 
 This is occasioned by the circumstance that, as in all liquids and solids the ex- 
 pansion 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 mer- 
 cury, 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 1-365, and 10000 measures of mercury become 10- 180. 
 If, then, they be both heated as much more, the air, expanding at the same rate, 
 becomes 1-730; but the mercury, expanding more rapidly, becomes 10-363: and 
 hence, if a scale was 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 example, 10 000 measures of mer- 
 cury ; but, on being heated to that of boiling water, it holds 10026. The mercury, 
 however, having become 10- 180, the difference, (10180 — 10026)=154 measures, 
 passes 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 10055 : and hence 
 the difference, (10-363 — 10-055)r=308 measures, passes into the stem and moves 
 along the scale. Thus the visible portion of the expansion is rendered exactly pro- 
 portional to the increase of heat ; and the mercurial thermometer becomes, not 
 merely the most convenient, but the most accurate measure of heat which we 
 
 In constructing a thermometer, the first requisite is, that the bore of the tube 
 shall be perfectly uniform, for otherwise the result above described, which gives all 
 
52 OF THE STANDARD INTERVAL. 
 
 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 some- 
 what 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 contraction of the internal, and the pressure of the exter- 
 nal, 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 in- 
 troduction 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 al- 
 lowed 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 blowpipe being directed upon the point which is to be the extremity of the tube, 
 it is melted, and the orifice completely closed. When the instrument then 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 365 parts. 
 This was, however, merely because the 1000 measures of air, in being heated 
 through that interval, 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 ta- 
 ken as the standard, is divided into 100 parts ; it is termed the centigrade scale, 
 and is 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 100°. On the scale generally used 
 in this country and 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, who was the inventor of this scale. He mixed together snow and salt, 
 and having thus produced a more intense cold than anybody 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 afterward called the absolute zero, and he called 
 that point 0° ; the melting point of ice was then 32°, and water boiling at 180^ 
 higher, its temperature was marked 212°. There is another scale, sometimes, but 
 not often used ; that of Reaumur, in which the melting point of ice is the com- 
 mencement 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 precautions 
 must be taken. I have frequently spoken of the melting point of ice and the freez- 
 ing point of water as meaning the same temperature, and under ordinary circum- 
 stances they do so ; but they do not so nece&sarily. The freezing of water is a 
 crystallization, and, like all other cases of crystallization, may take place with great- 
 er or less facility. If water be agitated, or if it be contained in rough vessels, af- 
 fording 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 
 be contained in smooth glass vessels, free from dust, it maybe easdy 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 plunging the bulb 
 of the thermometer into a mixture of ice and water, and marlcing 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 at- 
 tend to the condition of the barometer. It will be hereafter described how the boil- 
 ing 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 will be hereafter given, applied for any 
 difference of height which may exist. The water must boil also in a metallic ves- 
 sel, for water in a glass or porcelain vessel has its boiling point somewhat raised, 
 and as the thermometer 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 downward from the point of melting ice to obtain the zero ; for the zero 
 
THERMOMETRIC SCALES. 53 
 
 ctt^.-oi be truly got in the manner in which Fahrenheit is supposed originally to 
 have invented it, for a mixture of snow and salt is 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 upward, only 
 prefixing in the former case the — minus sign, whereas, in the degrees above zero, 
 the -|- plus sign is usually omitted. Thus, 4-50°, or simply 50°, is fifty degrees 
 above zero, but — 50° is the same number below zero. To construct the centi 
 grade 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 y-J-^ 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 vac- 
 uum 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. 
 
 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 ISO'* Fahrenheit, and into 100 centigrade degrees, and hence a degree 
 of the former is equal to j^^-, or |ths of a centigrade degree. To reduce any inter- 
 val in centigrade degrees to Fahrenheit's, it is therefore to be multiplied by 9 and 
 divided 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 calculation from the centigrade, and to subtract 32° from the num- 
 ber of degrees on Fahrenheit, which are to be converted into degrees upon the oth- 
 er scale. 
 
 Thus, to reduce 167° of Fahrenheit, we proceed : 
 
 167—32=135, and 135xf=75<=, 
 Jtiii find it to correspond to 75° centigrade. And to reduce 65° centigrade to Fah- 
 renheit's scale, we say, 
 
 65 X 1=117, and 117+32=149°, 
 corresponding, therefore, to 149° of Fahrenheit. 
 
 Reaumur's scale being to the centigrade scale as 4 to 5, similar reductions are 
 made to and from it, by using ^ in place of f , as has been employed in the example. 
 
 The range of temperatures observable with a mercurial thermom- 
 eter on Fahrenheit's scale is from — 39^ to +630°. The mercury- 
 freezes a little below — 40° ; and though it does not boil until it ar- 
 rives at 660°, yet the quantity of vapour which it forms when very 
 near its boiling point, prevents its indications from being quite ex- 
 act 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 de- 
 scribed 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 in- 
 vented for the purpose of determining the higher temperatures, 
 particularly of furnaces, and hence they have been called pyrome- 
 ters. Of these, the only one which appears to give accurate re 
 suits, and hence deserves description, is that of Daniell. 
 
 In this pyrometer, the change of temperature is shown by the excess of the ex- 
 pansion of an iron bar over the expansion of a black-lead case in which it is en- 
 closed. The iron rod a is somewhat shorter than the black-lead- ware case, and a 
 plug of earthenware, b, which fits tight in the case, abuts against the iron rod in- 
 side, and projects as at c in the figure. Let us suppose the length of the case to be 
 5 inches, that of the iron rod 4^ inches, and that of the earthenware plug to be 1 
 inch. If tlie 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., 
 
64 
 
 daniell's pyrometer. 
 
 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 12, the project- 
 ing portion is only 39. If the parts of the apparatus were all free to move, each 
 contracting again on cooling, the result would be that all would be restored to their 
 original position ; but this is not the case. The bar of iron, in expanding, 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 apparatus has become cold. The protrusion 
 of the earthenware plug is therefore a permanent index of the greatest amount of 
 expansion that had been produced while the instrument was exposed to heat. This 
 expansion is, however, very small. The three pieces being, as stated, 5, 4i, and 1 
 inch, the expansion, when heated from 32° to 212°, is only yf |^ of an inch ; and as 
 this indicates 180 degrees, the expansion for a degree is only about f-^o of an 
 inch. It is therefore necessary to magnify this expansion, in order that the indi- 
 cation maybe read off; and this is done by means of a graduated circular arch, d e 
 /, with a movable index, kept by means of a spring constantly at 0^ 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, c, catches in the prolonged heel 
 of the index, e, 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 absolute amount of expansion may vary, which, however, is re- 
 duced to the same proportion on the scale, by which, also, the increase in the rat« 
 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 de- 
 termined the melting point of most of the important metals, and also several other 
 temperatu] es at which remarkable phenomena occur. 
 
 The p Tometers of Wedgewood, of Guyton, and many others 
 that have been proposed, must be considered as now totally aban- 
 doned, and do not require notice. 
 
 The most delicate, and perhaps the most important, measure of 
 heat that has been contrived, is one totally independent of expan- 
 sion, and founded on the measurement of an electric current which 
 a change of temperature produces under certain circumstances. It 
 is the Thermo-multiplier invented by Nobili. The principle which 
 the instrument involves in its construction and its form will be de- 
 scribed under the head of electricity, and the remarkable results 
 obtained by means of it, and which have completely remoielled 
 
TABLE OP TEMPERATURES. 
 
 55 
 
 our ideas of the physical constitution of heat, will be noticed in 
 another place. 
 
 It may be of interest to subjoin the temperatures on Fahrenheit's 
 scale at which some of the most remarkable effects of heat are 
 produced : 
 
 — 135°. The greatest cold that has been produced. 
 
 — 121°. The solid compound of alcohol and carbonic acid 
 
 melts. 
 
 Greatest cold by ordinary freezing mixtures. 
 
 Temperature of the planetary spaces. 
 
 Greatest cold observed in the arctic regions. 
 
 Sulphuric ether congeals. 
 
 Nitric acid congeals. 
 
 Mercury congeals. 
 
 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. 
 
 Rose's metal melts. 
 
 Newton's metal melts. 
 
 Water boils. 
 
 Sulphur melts. 
 
 Mercury boils. 
 
 Antimony melts. 
 
 Red heat. 
 
 Heat of a common fire. 
 
 Brass melts. 
 
 Silver melts. 
 1996°. Copper melts. 
 2200°. Gold melts. 
 2786°. Cast iron melts. 
 The details which have been given, regarding the construction of the air ther- 
 a >meter, will show sufficiently the principle upon which the detennination of the 
 rhye of expansion of gaseous bodies has been effected. The exact amount of dila- 
 taion was first ascertained by Dalton and Gay Lussac nearly at the same time. 
 Tt«e apparatus of Gay Lussac consisted of a tin vessel, A, having five apertures^ 
 
 
 
 91°. 
 
 
 
 58°. 
 
 
 
 60°. 
 
 
 
 47°. 
 
 
 
 45°. 
 
 , 
 
 39°. 
 
 + 
 
 1°. 
 
 + 
 
 14°. 
 
 + 
 
 20°. 
 
 + 
 
 25°. 
 
 + 
 
 32°. 
 
 + 
 
 36°. 
 
 + 
 
 98°. 
 
 + 
 
 108°. 
 
 + 
 
 174°. 
 
 + 
 
 201°. 
 
 + 
 
 211°. 
 
 •4- 
 
 212°. 
 
 + 
 
 218°. 
 
 + 
 
 662°. 
 
 + 
 
 810°. 
 
 + 
 
 980°. 
 
 + 
 
 1141°. 
 
 + 
 
 1869°. 
 
 + 
 
 1873°. 
 
 By means of the aperture in the side, o', there is introduced the tube with the boH^ 
 
56 
 
 EXPANSION OF AIR. 
 
 fr 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 48. By the opposite orifice, o, is 
 fixed a thermometer, h s, the bulb b 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 so being 
 arranged, water, rendered ice-cold by some snow or ice floating on it, is introduced, 
 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 temper- 
 ature is indicated by the thermometer, t, the expansion by the motion of the index 
 globule, and at each degree the thermometer and air bulb may be compared to- 
 gether 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 by Dulong and Petit up to the boiling point of mercury. 
 
 From such experiments, conducted by Dalton, Gay Lussac, and Dulong, it result- 
 ed, that 1000 volumes of air, when heated from 32° to 212°, became 1375, and that 
 the change was in proportion for higher or lower temperatures. The numbers ac- 
 tually obtained may be stated as in the following table : 
 
 Temperature on a 
 Mercurial Ther- 
 monfeter by Fah- 
 renheit's Scale. 
 
 10000 Volumes 
 of Air at 32" 
 become 
 
 Expansion for one 
 Degree on F. Scale 
 in Parts of the Vol- 
 ume 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 these results gives the expansion for one degree at 20-81, or almosi 
 exactly ^1^ of the volume at 32°, which result had been adopted universally, with- 
 out any suspicion of its being imperfect. Circumstances having, however, induced 
 Rudberg to submit the subject to an accurate reinvestigation, conducted with ex- 
 ceeding care and attention, particularly to the state of dryness of the air employed, 
 he has found that the amount of expansion assigned by Gay Lussac and Dalton ia 
 somewhat too great, and that a volume of air, in being heated from 32° to 212°, 
 expands from 1000 volumes to 1365. 
 
 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 whic.'. 
 Avas drawn to a fine point, like that described, page 14, 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 
 blowpipe, 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 all the mercury which would 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 de- 
 scribed. The volume of the mercury which had entered into the globe was then 
 ascertained, and the volume of the globe itself also determined ; and by a compar- 
 ison 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 inferred that, in being 
 heated from 32° to 212°, 1000 volumes of air became between 1364 
 and ISGG'^ ; we may consider 1365, which is between the two, as 
 
CORRECTION FOR CHANGE OF TEMPERATURE. 57 
 
 being absolutely the most correct, and hence that for each degree 
 lOOd'volumes expand f|f =2-028, or ^f ^ of its volume at 32^ 
 
 In all operations upon gaseous mixtures, the rate of expansion 
 of air comes into play j for as all gases expand alike, and the vapours, 
 even of these bodies which are least volatile, as camphor and cor- 
 rosive sublimate, expand, while 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 va- 
 pour, it is also usual to reduce it to the same standard as those of 
 gases, that is, air at 32^, even where the substance is of- such a na- 
 ture 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 follows very simply from what has been de- 
 scribed. If there be a certain quantity, as 155 cubic inches of hydrogen gas at 142° 
 Fahrenheit, and we wish to know tlie 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 vol- 
 ume at 32°, and in addition to |-^| of it ; that being the quantity by which it is ex- 
 panded from 32° to 142°. Therefore, denoting the volume at 32° by the letter V, 
 there is the equation : 
 
 129-5 cubic inches are therefore the volume at 32°. 
 
 If, on the other hand, we have a gas at a low temperature, and we wish to as- 
 certain 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 origi- 
 nal volume. Thus, if the 155 cubic inches of hydrogen had been at 6° Fahrenheit, 
 then the equation should have been 32° — 6° being 26. 
 ,r^ Tr Tr26 ,. 155x493 ,^oo k •• u • 
 
 155=V — V-— -, or V=:- ^^ - ^ =1683 cubic mches in exact numbers. 
 493 493 — 26 
 
 It frequently happens that it is necessary to reduce a gas at one temperature 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 propor- 
 tion as the standard volume, 493, increased by the amount of expansion proper to 
 the temperatures. Thus, at the temperatures of 75° and 42°, the standard volume, 
 which is 493°, at 32° becomes respectively 536 and 503. 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 we wish to calculate its volume when at the temperature of 42°, we 
 say, calling the unknown volume V ; 
 
 V : 127 : : 503 : 536, and Y=^:^^I^^==ll9fi. 
 
 536 
 The formulae for these corrections may be very simply written in a general form . 
 thus, to reduce a volume to 32°, denoting the temperature on Fahrenheit's scale 
 by t ; by V, the volume of gas which we have measured at that temperature ; and 
 by Vi, the volume at 32°, the formula is : 
 
 y ^ 493. V 
 
 ^ 493 ± (f— 32°)' 
 And to reduce, without reference to 32° ; denoting the known volume by V, and 
 the unknown by Vi ; the temperature of V by /, and that of V, by ti, there is found : 
 V.__ 493± (^,-3 2) y, .,493-i: (^,-32) 
 
 V ~493± (i-32) ' ^""^ '- 493 :f ^-32)- 
 Air which has been heated becomes, from its great increase in 
 volume, specifically much lighter than cold air, in which it there- 
 fore ascends with a velocity due to the difference between their 
 
 H 
 
58 EXPANSION OF LIQUIDS. 
 
 specific gravities. It is thus that over every lamp or candle there 
 may be felt a current of heated air ascending from the flame j that 
 the heavy dark smoke 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 oppressively hot air, while 
 that near the floor will be quite cool. By the ascent of the heated 
 air from our furnaces and fireplaces, there is generated the draught 
 which gives the supply of air necessary for continued burning ; and 
 as the intensity of the combustion 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 regulate with accu- 
 racy 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, rising 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 fluid 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 ex- 
 pansion of a fluid is, in most cases, only the excess of its expansion 
 over the expansion of the solid vessel in which it may be contained. 
 To measure the amount of expansion in liquids, they may be introduced 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, 
 however, be more easily and more accurately done by means of the apparatus in 
 
 the figures, a d b is a glass tube, the neck of 
 f r ' * ' " ^ ^ ^ ^ which is very narrow, and bent as in either fig- 
 
 ' ure. This tube is to be filled completely, at the 
 
 lowest temperature, with the liquid, whose expansion is to be examined and then 
 ,_-...--„._....„.. weighed, the weight of the tube itself being previously 
 jj ^J]i_£ known, and the quantity of liquid which it contains is thus 
 I frj-^Ji-^ determined. The tube is to be then placed upright in a 
 I I IllJlIf cylinder of water or oil &, to which heat may be applied 
 I P^lf by a furnace below ; and the liquid expanding according 
 I l|i'|0 as its temperature is raised, the excess of volume flows 
 I 111 ^ out at the capillary beak c, and may be collected as in d, or 
 I 1 w let to waste. When the apparatus has been brought to the 
 I \|| - highest temperature required, and all farther expansion has 
 I I " ceased, as is known by no more liquid passing out at c, the 
 
 I /W '^fe t^be is to be removed from the bath, carefully cleaned, and, 
 ^^il^^^P when again cool, accurately weighed. The loss of weight 
 " is the quantity of liquid that had been expelled, and this, 
 
 compared with the whole original quantity of liquid, gives the proportion of expan- 
 sion. In this manner, however, the result appears to be less than it really is, for 
 the expansion of the glass tube itself diminishes the quantity 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 dilatable 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 ^, while its real expansion is -^■^. 
 The amount of expansion of different fluids in passing through 180° of Fahren- 
 heit is thus found to be : 
 
EXPANSION OF LIQUIDS. 
 
 59 
 
 Alcohol ^ 
 
 Nitric acid ^ 
 
 Fixed oils -j^ 
 
 Sulphuric ether • . • • t¥ 
 
 Oil of turpentine 
 Sulphuric acid . 
 Water . . . . 
 Mercury . . . 
 
 •51! 
 
 The actual amount of expansion, independent of the expansion of the containing 
 vessel, is best observed by the apparatus used by Dulong and Petit. It consists of 
 
 a glass tube a h c, bent in the form of a 
 U, of which the horizontal portion c is nar- 
 row, but the vertical legs pretty wide. 
 When mercury is poured into the tube, it 
 stands at the same height in both legs if 
 the 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 hquid column must in- 
 crease in order to balance the colder column of mercury in the proportion of the 
 augmented volume. The difference between the heights being read off, by means of 
 an accurate scale, with a telescope o, the amount of absolute expansion may be ea- 
 sily calculated from it. 
 
 By means of this instrument Dulong and Petit determined the rate at which the 
 expansion of mercury increases with the temperature, as has been noticed generally 
 in the description of the thermometer. Their result was, that between 32*^ and 212°, 
 measured on the air thermometer, the expansion is ■^^.-^. From 212° to 392°, it is 
 ^y.i_^ ; and from 392° to 572°, it is ^.o^. The consequence is, that, measured by 
 its own expansion, mercury boils at 680° Fahrenheit ; but from the expansion 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 is therefore taken as being 
 uniform for 180°. ^ of its volume. 
 
 Considerable simplicity is given to the laws of dilatation of liquids by an observa- 
 tion 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 con- 
 dition ; that is to say, the cohesive powers of the liquids we employ must be brought 
 into the same state. This is most nearly done by taking these liquids when heat- 
 ed to their boiling points, for then the cohesion of each liquid is about to cease alto- 
 gether. Thus alcohol boils at 173°, water at 212°, sulphuret of carbon at 134°, and 
 sulphuric ether at 963° ; and, taking 1000 volumes of each at their boiling points, 
 and aliowmg them to cool, they contract as follows : 
 
 By cooling 
 through 
 
 Water 
 
 contracts 
 
 Alcohol 
 contracts 
 
 Sulphuret 
 of Carbon 
 contracts 
 
 Ether 
 contracts 
 
 18° 
 36° 
 54° 
 72° 
 90° 
 108° 
 
 661 
 1315 
 18-85 
 2410 
 28-56 
 32 42 
 
 11-43 
 24 34 
 34-74 
 45-68 
 5602 
 65 96 
 
 1201 
 23-80 
 3506 
 45-77 
 56-28 
 6621 
 
 1617 
 31-83 
 46-42 
 58-77 
 7201 
 
 We by this means find a very interesting relation between alcohol and sul- 
 phuret of carbon, two fluids remarkably different in their specific gravities, and in 
 their chemical constitution and properties. It appears 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 farther 
 connexion is exhibited between their molecular conditions by the remarkable fact 
 that, in being converted into vapour, the augmentation of volume which they un- 
 dergo is the same. 
 
 Many liquids possess the property of contracting, by reduction 
 of temperature, only to a certain point ; below which, if the cool- 
 ing 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 recognised in water j but it has since been 
 
60 EXPANSIONOF SOLIDS. 
 
 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 extensive agency of that fluid in natural op- 
 erations. The point of maximum density of water has been deter- 
 mined by the experiments of very many persons to be 39.5" of Fah- 
 renheit. When water below that temperature is heated, it con- 
 tracts J when heated above it, it expands : when cooled from above 
 it, it contracts j Avhen cooled below it, it expands : and when the 
 experiment is made in glass vessels, the contraction of the glass has 
 . ne eflfect of rendering the expansion of cooling below, or of heat- 
 mg 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 by being heated from 39*5 to 46^, and the spe- 
 cific gravity of water at 46"^ and at 32° is consequently the same. 
 
 A great deal of the permanence of the existing order of nature 
 depends 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 surface acts as a screen to prevent the farther loss of heat, and 
 thus retains the deeper portions at a temperature sufliciently high 
 for the existence of its organized inhabitants j for, by the continued 
 action of the cold wind, the superficial water being cooled below 
 39*5°, 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 efix3ct- 
 ually prevented. If it w^ere not for this property of water, all large 
 collections of it in lakes and rivers would, 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 ex- 
 ceedingly 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, 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 sufliciently 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 tem- 
 perature is raised. In the arts, the expansion of solids, particularly 
 of the metals, in this way becomes the source of numerous incon- 
 veniences, 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 while 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 a useful meas- 
 ure of high temperatures j on the other hand, by the alternate ex- 
 pansions and contractions, under the successive influence of win- 
 
EXPANSION OF SOLIDS. 
 
 61 
 
 ters 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 me- 
 chanical arrangements have been constructed. As they are all 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 a very satisfactory idea of their gen- 
 eral construction: a 
 h is the bar of which 
 the expansion is to 
 be determined j it is 
 fastened securely at 
 the extremity «, and 
 rests at A 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 sec- 
 ond order, very near 
 the fulcrum, and this 
 transfers its motion 
 to the end of the lev- 
 er, increased in the proportion of the distance. This lever acts on 
 another similar one, (/, the extremity of which serves as an index 
 on the graduated circular arc e, 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 the end of the bar a 2it b moves 
 ToVir of an inch, the end of the index d will move on the scale e 
 
 through ~"fAA7r==Trj ^^ ^'i 'mc\ a space capable of being divided 
 
 by a microscope and vernier into 200 measurable spaces, so that an 
 expansion of the two hundred thousandth of an inch can be accu- 
 rately determined. For 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 tem- 
 perature 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 of a bar of 
 
 Glass varies from 
 to . 
 Copper . . . 
 Brass .... 
 
 • ToVo 
 
 Steel 
 
 Gold 
 
 SQver 
 
 Lead 
 
 Tin. 
 
 1 
 
 TT2 
 
 Softiron ^j 
 
 The increase in length is called the linear dilatation of a sub 
 
62 
 
 EXPANSION INCREASES WITH TEMPERATURE. 
 
 Stance, lut its increase of volume is called the cubical dilatation, 
 and is three times the former. Thus the cubical dilatation of glass 
 ^® 72^45 ^^ 4:ij' Hence a glass ball which holds 428 measures at 
 32°, becomes capable of holding 429 at 212° j or if it hold 10-000 at 
 32°, it holds 10-023 at 212°. In this manner the correction for the 
 expansion of glass is in all cases made. But it is necessary to ap- 
 ply the amount of expansion belonging to the particular sort of 
 glass j thus, in the account of the thermometer in page 51, the 
 cubic dilatation of glass was taken, not as 10*023, but 10-026. 
 
 [The reason that the cubic dilatation may be taken as equal to three times the 
 linear, without sensible error, is due to the circumstance that the linear dilatation 
 is always a small fraction of the primitive length. If l-\-l represent the dilated 
 length, (1-f /)% or 1-f 3 l-\-2 P-\-P will be the true volume ; but as / is a small 
 fraction, its triple square and cube may be neglected.] 
 
 Although it is abundantly proved that solid bodies expand more rapidly at high 
 than at low temperatures, yet, except in the case of some p£irticular substances, as 
 glass, iron, and platinum, whose utility as measurers of heat rendered a knowledge 
 of the law of their expansion necessary, the subject has been little examined ; the 
 degree to which the rate of expansion is affected by temperature will be sufficiently 
 shown in the table which follows. At the temperature of 212° Fahrenheit, as given 
 by an air thermometer, the dilatation for one degree is thus, for 
 
 Glass. 
 
 Platinum. 
 
 Iron. 
 
 Copper. 
 
 d'TToTo" 
 
 FtIs-o 
 
 S0T6 
 
 34I20 
 
 while at 572° of Fahrenheit it becomes, for 
 
 Glass. 
 
 Platinum. 
 65^40 
 
 Iron. Copper. 
 
 59220 
 
 4 0¥T7 3T1-60 
 
 and the temperature 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. 
 
 623° 
 
 572° 
 
 667° 
 
 592° 
 
 702° 
 
 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 maxi- 
 mum density, 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 ap- 
 plying 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 farther heated it contracts, until, 
 when at 156°, the volume is only 99-291, being less than at 32° 
 By a farther 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 it has no point of maximum density 
 when in the liquid state. 
 
 The diiferent rates of expansion of different solid bodies are sub- 
 servient to some very important uses in the arts and in scientific 
 research. Thus, the difference between the expansibilities of plati- 
 num and brass, or any other two metals which differ much, may be 
 used as a very delicate thermometric means. If we take a flat rule 
 
EXPANSION OF COMPOUND METALLIC BARS. 63 
 
 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 thermom- 
 eter. 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, while the platina rule will expand only 
 through 0'009 ; hence the end of the brass rule will project beyond 
 the platina rule by 0*0 10 of an inch j 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 minute to be easily 
 determined j but by modifying the form, and connecting the rules 
 through their whole length, the beautiful metallic thermometer of 
 Breguet has beeii invented. Its principle is as follows :• if the two 
 rules be soldered completely together, as in «, in place of being con- 
 nected only at a single point, the result of the unequal expansion is 
 to bend the bar, as in 6, until, the most expansible metal being on 
 the outside, it forms an arch longer than that 
 formed by the inside rule, by the difference 
 ^^ of their expansions. If the compound bar be 
 o 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 b, b, fastened at the upper end, 
 and having attached to its lower extremity an 
 index, c, which moves round a dial, dj d, 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 ordinary clock, 
 to measure time by its vibrations, being con- 
 stantly changing in length according as the ex- 
 ternal temperature varies, affects the rate of the 
 clock, making 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, while by the expansion 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 temper- 
 ature, and the clock becomes an exact measure of time at all sea- 
 sons. 
 
 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 
 
64 ME TH OD OF MIXT U RE S. 
 
 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 rel- 
 ative quantity of heat necessary to raise the temperature of any 
 body through a certain number of degrees, as ten, for example, is 
 termed its specific heat. 
 
 If we take a pint of water at 150°, and another pint of water at 
 50^, and mix them well in a very thin vessel, the temperature of 
 the mixture is found to be, if we allow for some sources of er- 
 ror to which this process is exposed, exactly 100°. Thus the one 
 part of the water has transferred to the other a quantity of heat 
 sufficient to raise its temperature 50° ; and whether this addition was 
 from 50° to 100"^, or from 100° to 150°, the result was the same. In 
 water, thej'efore, the specific heat does not change within these 
 limits J* but it will be found that in high temperatures a trifling in- 
 crease does occur ; for the present purpose, however, it may be neg- 
 lected. If, now, a pint of water be taken at 150° as before, and a 
 pint of mercury at 50°, and 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°, 
 while the water cools only through 32°, or not quite half as much, 
 so that the same quantity of heat can raise the temperature of mer- 
 cury through twice as many degrees as that of water. 
 
 Taking thus equal volumes, the specific heats of water and mer- 
 cury 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 is 0*47 nearly.^ Such bodies are, however, gener- 
 ally 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*mer- 
 cury, 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, nor 
 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 ex- 
 ceeding 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 ex- 
 periments 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 be then 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 
 aumbers, that of copper is found thus to be gVf— 0*096, water being 
 l-OOO. 
 One process employed by Dulong and Petit consisted in heating 
 
THECALORIMETER. 65 
 
 to the same degree the bodies to be tried, and allowing them to cool 
 exactly under 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 circumstanced in all re- 
 spects 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, and 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 cer- 
 tain 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 greatest 
 degree in one half of the time which the water required ; and also, 
 when both, equally hot, were removed from the fire, the mercury 
 cooled twice as fast. For 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 depend- 
 ant only on their difl^erent specific heats ; thus, equal weights of 
 the different bodies are placed in the same thin polished silver ves- 
 sel, so that their external surface may be the same in extent and na- 
 ture, 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 
 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, has been found on repetition to 
 have been rendered useless by the imperfections 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 au- 
 thority. 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 com- 
 bustion, these sources of error became less influential, and such results will be util- 
 ized 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 foUow- 
 inof table : 
 
 Water =1000 
 
 Ether =0520 
 
 Alcohol =0-660 
 
 Sulphuric acid . . . =0-333 
 
 Nitric acid .... =0-442 
 
 Sulphur =0-202 
 
 Carbon =0 241 
 
 Mercury =0 033 
 
 Iron =0114 
 
 Copper =0 095 
 
 Lead =0 031 
 
 Gold =0 032 
 
 Antimony . . . . . =0 051 
 
 Tin =0-056 
 
 Iodine =0 054 
 
 Phosphorus . . . . =0 188 
 
66 SPECIFIC HEAT. CHEMICAL CONSTITUTION. 
 
 Lime =0-205 
 
 Magnesia =0-276 
 
 Arsenic =0 081 Glass =0177 
 
 Platinum =0 032 Calomel =0 041 
 
 Silver =0057 Common salt . . . =0225 
 
 Zinc =:0095 Nitrate of soda . . . =0240 
 
 Tellurium =0051 
 
 Nickel =0109 
 
 Cobalt =0107 
 
 The numbers given are generally those lately obtained by Reg-» 
 
 nault. 
 
 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 following table : 
 
 Substance. 
 
 Sp. Heat from 
 320 to 212°. 
 
 Sp. Heat from 
 
 320 to 672°. 1 
 
 Mercury .... 
 
 0330 
 
 00350 
 
 Zinc 
 
 00927 
 
 01015 
 
 Antimony . . . 
 
 0507 
 
 00549 
 
 Silver .... 
 
 00557 
 
 00611 
 
 Copper .... 
 
 00949 
 
 01013 
 
 Platinum . . . 
 
 00355 
 
 00397 
 
 Glass .... 
 
 01770 
 
 01900 
 
 Iron 
 
 01098 
 
 01218 
 
 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 specific heat of water at 32° 
 being 1-000, that water at 212° is 1*010, consequently the equal dis- 
 tribution of heat between warm and cold water, which was described 
 at the commencement 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 heats of bodies are connected very intimately with 
 their chemical and molecular constitution, although we are not yet 
 able 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 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 num- 
 bers 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 : 
 
 
 
 Sp. Heat. 
 
 31 
 
 True 
 Kqulvalent. 
 
 
 Sp. Heat. 
 
 Lead .... 
 Tin . . . . 
 
 
 0031 
 056 
 0095 
 
 1000 
 55 4 
 326 
 
 1036 
 57-9 
 323 
 
 Zinc .... 
 
 Bismuth . . . 
 
 
 030 
 
 1007 
 
 710 
 
 Carbon . . . 
 
 
 0-24 
 
 129 
 
 61 
 
 1263 
 
 31-4 
 
 •108- 
 
 Iodine . . . 
 Phosphorus 
 Silver . . . 
 
 
 0054 
 •0188 
 0057 
 
 57-4 
 165 
 54-4 
 
 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 un- 
 
SPECIFIC HEATS OF ATOMS. 
 
 67 
 
 avoidable errors of experiment, they would coincide. In bismuth 
 the result is 1^ times the true equivalent. In carbon it is double 
 the true equivalent. In iodine, in phosphorus, and in silver, it is 
 one half. 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 
 equivalent number and the specific heat exists, although the connect- 
 ing 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 
 
 True 
 Equivalent- 
 
 Sp. Heat. 
 
 Carbonate of lime . . 
 Carbonate of iron . . 
 Carbonate of zinc . . 
 Magnesian limestone . 
 
 0-2044 
 0-1819 
 0-1712 
 0-2161 
 
 509 
 57-2 
 60-7 
 48-1 
 
 506 
 581 
 62-4 
 46-7 
 
 For certain sulphates the number is 12*4 Thus 
 
 Sulphate of barytes 
 Sulphate of strontia 
 Sulphate of lime 
 
 Sp. Heat. 
 
 01068 
 0-1300 
 01854 
 
 95-4 
 66-8 
 
 Sp. Heat. Equivalent. 
 
 116-1 116-1 
 
 91-9 
 68-6 
 
 For a number of metallic oxides, the constant appears to be 5'4 
 Thus: 
 
 Substances. 
 
 Sp. Heat. 
 
 0-276 
 0049 
 0132 
 0-137 
 
 5-4 
 Sp. Heat. 
 
 19.6 
 
 110-2 
 
 40.9 
 
 39-4 
 
 Equivalent. 
 
 20-7 
 
 109-4 
 
 40-3 
 
 396 
 
 Magnesia .... 
 Red oxide of mercury- 
 Oxide of zinc . . . 
 Oxide of copper . . 
 
 The relation between the specific heats of bodies and their chem- 
 ical equivalents is thus remarkably shown to extend not merely to 
 the simple substances, but even to saline bodies, and indicates a con- 
 nexion 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 contain- 
 ed in that weight ; and the constant numbers, which were divided 
 by the specific heats, are the specific heats of the ultimate chemi- 
 cally equivalent particles. Thus, the specific heat of chemical mole- 
 cules 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 j and that of 
 the sulphates of barytes, strontia, and lime, 12*4' Attempts have been 
 made to connect these constants together, but without good found- 
 ation ; 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 
 
68 HEAT BY CHEMICAL COMBINATION. 
 
 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 dif- 
 ferent bodies can be obtained perfectly consistent, for the various 
 bodies necessary cannot be examined exactly in the same state. 
 Regnault has well observed, that the quantity of heat which w« 
 measure as specific heat consists of several different portions : 1st, 
 the true specific heat ; 2d, the heat which produces dilatation ; 3d, 
 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 ac- 
 quire. These last three portions being very small, do not conceal 
 the law by which the true specific heat is regulated ; but they influ- 
 ence it so far as to prevent the law from being verified in its nu- 
 merical 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 mixtures 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. The excess, therefore, 0-665— 0-587=0-078, be- 
 comes free, and shows itself by raising the temperature of the mix- 
 ture ; 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 body contained might be determined by such an experi- 
 ment, thus : if the rise of temperature produced by 0.078 of heat 
 becoming free is expressed by 180^ above 32^, 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 con- 
 tain 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 abso 
 lute 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 neces- 
 sary, and the small quantity of material which can be operated on, 
 the results hitherto obtained have not acquired that degree of posi- 
 
SPECIFIC HEAT 
 
 OF GASES. 
 
 69 
 
 tive accordance which should render repetition unnecessary. The 
 principal experimenters in this department have been Delaroche and 
 Berard, Delarive and Marcet, Haycraft, Dulong, and, latterly, Apjohn 
 and Suerman. 
 
 The method adopted by Haycraft, 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, determining 
 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 pro- 
 cess of Delarive and Marcet was not such as could lead to results 
 worthy of much confidence. A glass globe full of gas, to which 
 was attached a thermometer, with the bulb exactly in the centre, 
 was plunged into a vessel of hot water, in the expectation that the 
 lime occupied by each gas, in having its temperature raised a cer- 
 tain number of degrees, would be proportional to the specific heat 
 under a constant volume. But the communication of the heat 
 would be so much and so variously affected by currents, according 
 to the density of the gas and the quantity of heat absorbed by the 
 gas, so trifling in comparison to that which would 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 note the same organ-pipe gave with 
 each : from this, by very ingenious methods, which, however, 
 need not here be introduced, farther than that the gases with higher 
 specific heats give more acute tones, he calculated the specific heats. 
 The calculations 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 va- 
 pour 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 • 
 
 [Apjohn, 
 
 Air . . . . 
 
 Nitrogen . . . 
 
 Oxygen . . . 
 
 Hydrogen . . 
 
 Carbonic acid . 
 Carbonic oxide . 
 
 Nitrous oxide . 
 
 1000 
 1048 
 
 •808 
 1-459 
 1195 
 
 •996 
 1193 
 
 1000 
 1006 
 •976 
 •900 
 1-258 
 1-034 
 1-350 
 
 Dulong. 
 
 1000 
 1-000 
 1000 
 1 300 
 1-172 
 1-000 
 1159 
 
70 * LIQUEFACTION. 
 
 These numbers show the diversity which exists among even the best expert 
 menters ; and they also show that the different gases follow no simple law regard- 
 ing their specific heats. The principle laid down by Haycraft, Delarive, and Marcet, 
 that in equal volumes all gases have 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 -900, 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 propor- 
 tional ; that is to say, when the volume of a gas is doubled, its spe- 
 cific 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 recog- 
 nising substances otherwise very similar in properties ; as, for ex- 
 ample, the numerous fatty acids can scarcely be otherwise distin- 
 guished from each other, exclusive of analysis, than by the tem- 
 peratures at which they melt. There has been already given a list 
 of the melting points of a number of solid bodies, and, in the his- 
 tory of each individual substance, its fusibility will be described. 
 
 The change from the solid to the liquid state is accompanied, 
 however, by a phenomenon difl^ering 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 
 thermometer precisely the same degree, and yet, independent of all 
 considerations of specific heat discussed in the last section, and 
 which we now lay aside, the water contains, in a state of intimate 
 
ABSORPTION OF HEAT DURING LIQUEFACTION. 71 
 
 combination, a great quantity of heat, by virtue of which it is liquid 
 water, and by losing which it would 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 sim- 
 ple kind. Thus, if a pound of ice be taken at 32% and added to a 
 pound of water at 172"", the ice dissolves immediately, but the tem- 
 perature of the resulting two pounds of water is found to be 32^ 
 There has thus disappeared a quantity of heat, which had previous- 
 ly raised the temperature of the water to 172^, or through 14>0^. 
 This heat has been absorbed by the ice in becoming liquid, and ren- 
 dered latent ; and it is therefore said that the latent heat of liquid 
 water is 140^. If a vessel of water, at the temperature of 52°, 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 j 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 cool- 
 ed from 52° 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 ten minutes to cool from 52° to 32°, it will be found to require 
 one hour and ten minutes 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 20° x 7=140°, 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 the ice has completely melted, the 
 temperature of the water will have risen to 172°. 
 
 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 ab- 
 sorbs 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 otherwise occur. If water passed from 32° to 
 31°, and became solid by losing only the same quantity of heat as 
 it gives out in cooling from 33° to 32°, the change of seasons would 
 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 lique- 
 faction might prove equally injurious, ice and snow, in melting, ab 
 sorb all excess of heat, and render the change gradual, and 'suitable 
 to the functions of those plants and animals to which a sudden tran- 
 sition 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 renaarkable 
 
72 HEAT EVOLVED IN SOLIDIFICATION. 
 
 pre-eminence of water in that respect. The numbers are given in 
 two cohimnsj 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 Measured by itself. Measured by Water 
 
 Water 140 140 
 
 Sulphur 144 2714 
 
 Lead 370 110 
 
 Zinc 493 483 
 
 Bismuth 550 ....... . 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 so- 
 lidifying. This is a phenomenon like that which has been (page 25) 
 noticed in the crystallization of sulphate of soda, where the solution 
 may remain perfectly liquid until agitated, and then suddenly crys- 
 tallizes with the evolution of considerable heat. If water, so cooled 
 below 32°, be 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 solidify- 
 ing, 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 sur- 
 face 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 substance of the rock, and causes 
 it gradually to fall to powder, thus generating the soft and porous 
 soil fitted for the reception and sustenance of the seeds and roots 
 of plants. It is also by the action of this force of expansion, exert- 
 ed by many bodies when*they crystallize, that we are enabled to 
 take accurate copies of the moulds into Avhich such substances, in 
 the liquid state, are poured. Cast iron, antimony, and the alloy of 
 antimony used for printers' types, the alloy used for stereotype 
 plates, brass, bronze, and all such bodies, are capable of making 
 good castings by virtue of this expanding power ; while 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 j and the ice mountains which form in the Polar Seas are 
 
COLD BY LIQUEFACTION. 73 
 
 found to be almost completely fresh. This principle has been ap- 
 plied also to the concentration of vinegar and lemon-juice by freez- 
 ing, a large quantity of mere ice being formed round the sides of 
 the vessel, and a central cavity remaining 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 surround 
 ing bodies the heat necessary to its liquefaction, and thus reduce 
 their temperature and its own. Hence, when salts are dissolved iit 
 water without any chemical combination, there is cold produced. 
 Thus, by mixing nitrate of ammonia with an equal weight of water, 
 the thermometer sinks 46° ; and carbonate and sulphate of soda, 
 dissolved in three times their weight of water, reduce the temper- 
 ature, 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 sal ammoniac 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 bisulphate of soda and chloride 
 of sodium, with which but i of the quantity of water remains ; and 
 the remaining | being disengaged, and abstracting from the sur- 
 rounding bodies the heat necessary for their liquefaction, depress 
 the temperature through 50°. 
 
 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 from. Thus crystallized chloride of calcium contains 
 half its weight of water, and, when mixed with an equal weight of 
 snow, the whole becomes liquid, and the quantity of heat absorbed 
 is proportionally large. By combining such freezing mixtures in- 
 tense 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. 
 
 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 mixtures a great deal of the success depends on 
 the rapidity with which the Uquefaction is produced ; the thinnest possible vessels, 
 and a tolerably large quantity of materials should be used. For producing a great 
 degree of cold, it is also necessary to cool the materials previously as much as pos- 
 sible ; thus, to produce the intense cold of — 91°, Mr. Walker had cooled the sub- 
 stances to be mixed down to — 68° by means of other freezing mixtures. 
 
 K 
 
74 ARTIFICIAL COLD BY FRIGORIFIC MIXTURES. 
 
 FRIGORIFIC MIXTURES WITHOUT ICE. 
 
 
 Mixtures. 
 
 Parts 
 
 Thermometer sinks 
 
 Degree 
 of cold. 
 
 Nitrate of ammonia 
 Water 
 
 
 
 1 
 1 
 
 5 
 
 5 
 
 16 
 
 1 from +50° to +4° 
 
 46° 
 40° 
 63° 
 
 Muriate of ammonia 
 Nitrate of potash . 
 Water 
 
 
 • 
 
 ( from 4-50° to +10° 
 
 Sulphate of soda . 
 Diluted nitric acid . 
 
 
 
 3 
 
 2 
 
 I from +50° to —3° 
 
 Sulphate of soda . 
 Muriate of ammonia 
 Nitrate of potash . 
 Diluted nitric acid . 
 
 
 
 6 
 4 
 
 2 
 4 
 
 1 
 
 Vfrom +50° to —10° 
 
 60° 
 
 Sulphate, of soda . . 
 Nitrate of ammonia . 
 Diluted nitric acid . . 
 
 
 
 6 
 5 
 
 4 
 
 ( from 50° to —14° 
 
 64° 
 
 Sulphate of soda . . 
 Muriatic acid . . . 
 
 
 
 8 
 5 
 
 : from +50° to 0° 
 
 50° 
 34° 
 
 Phosphate of soda . . 
 Nitrate of ammonia . 
 Diluted nitric acid . . 
 
 
 
 5 
 3 
 4 
 
 I from 0° to —34° 
 
 FRIGORIFIC MIXTURES WITH ICE. 
 
 
 Mixtures. 
 
 Parts. 
 
 Thermometer sinks 
 
 Degree 
 of cold. 
 
 * 
 ♦ 
 
 Snow or pounded ice 
 Common salt . . 
 
 
 
 2 
 1 
 
 > 
 
 1 
 S 
 
 to —5° 
 
 Snow or pounded ice 
 Common salt . . 
 Sal ammoniac . . 
 
 
 
 5 
 
 2 
 
 1 
 24 
 10 
 
 5 
 
 5 
 12 
 
 5 
 
 5 
 
 'Y 
 
 4 
 
 to —12° 
 
 Snow or pounded ice 
 Common salt . . 
 Sal ammoniac . . 
 Nitrate of potash . 
 
 
 
 > 
 
 to —18° 
 
 * 
 # 
 
 60° 
 
 82° 
 
 Snow or pounded ice 
 Common salt . . 
 Nitrate of ammonia 
 
 
 
 to —25° 
 
 Snow . . . . . 
 
 
 
 from +32° to —30° 
 
 Diluted nitric acid . 
 
 
 Snow 
 
 
 
 2 
 3 
 
 from +32° to —50° 
 
 Crys. muriate of lime 
 
 
 Snow 
 
 
 
 3 
 
 4 
 
 from +32° to— 51° 
 
 83° 
 46° 
 
 Potash 
 
 
 
 
 Snow 
 
 
 
 3 
 
 2 
 
 ; from 0° to —46° 
 
 Diluted nitric acid . 
 
 
 Snow 
 
 
 
 1 
 
 2 
 
 from 0° to —66° 
 
 66° 
 
 Crys. muriate of lime 
 
 
 Snow 
 
 
 
 8 
 10 
 
 > . 
 
 25° 
 
 Diluted sulphuric acid 
 
 r^ 
 
 om —66" to —91° 
 
 In the ordinary experiment of freezing mercury by a mixture of snow and crys- 
 tallized chloride of calcium, success is seldom obtained unless by having two por- 
 tions 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 
 without our being able positively to ascertain its source, and where, 
 
NATURE OF SPECIAL HEA T. V APORIZATION. 75 
 
 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 consid- 
 ered 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. Although our knowledge of this subject is 
 not at all as satisfactory as its importance merits, it has been ascer- 
 tained that, when iron is violently compressed, as in boring cannon 
 or by repeated hammering, its specific 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 distinguish between heat, cer- 
 tainly before latent, which may thus be rendered sensible, and the 
 true latent heat which is absorbed during liquefaction, and which 
 can be only given out again by the reassumption of the solid form j 
 and this might be done, perhaps, and its connexion 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 heat^ 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 measures the spe- 
 cific 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 appli- 
 cations of glass and iron in ordinary life depend. This has been 
 referred to a certain quantity of latent heat having already entered 
 into the body, and giving an intermediate condition, that of semiflu- 
 idity. 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 
 
76 
 
 LATENT HEAT OF VAPOURS. 
 
 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 silejitly, 
 or with violence and rapidity ; the hody 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 re- 
 quire to be specially examined ; but it is necessary to attend, in the 
 first place, to the phenomenon which accompanies and may be sup- 
 posed to produce the change of form, the absorption of the heat of 
 vaporization ; for precisely as a solid absorbs heat in becoming liquid, 
 so does a liquid, in assuming the vaporous condition, render heat la- 
 tent, 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 until the last drop of the water 
 shall have been boiled away. If we remark the time, we shall find 
 it to be in the following proportion. Let us suppose the temperature 
 of the water to have been originally 62°, and that at the end of six 
 minutes it began to boil, having attained the temperature of 212°. 
 In each minute, therefore, there entered into the water a quantity 
 of heat sufficient to raise its temperature ^-^^=^=25°. Now, the 
 source of heat remaining perfectly steady, it will be found neces- 
 sary to apply it during 40 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 25°, the total quantity of heat absorbed 
 by the water in being converted into steam would have raised its 
 temperature, had it remained liquid, 25x40=1000°, or just to red- 
 ness. 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, vvater 
 
 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 iu 
 the cold water, raises its tem- 
 perature ; 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 
 condensing may easily be cal- 
 culated. Thus : let us suppose that there were eight ounces of water, at 60°, ori- 
 ginally used, and that, at the termination of the experiment, there were nine ounces 
 at the temperature of 188°. It is then evident that one ounce of steam, in conden- 
 
INCREASE OF VOL U M E IN VAPORIZATION. 
 
 7-7 
 
 sing, had raised the temperature of the eight ounces 128°. The temperature of one 
 ounce might have been, therefore, raised 128x8=1024° : but this was not all la 
 tent heat ; for the steam, by merely condensing, should have formed liquid water at 
 212°, whereas it cooled to 188°. The difference, =24°, must be subtracted from 
 the 1024° ; and thus the latent heat of steam determined to be 1000°, 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 and 
 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 cii'culate 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 recon- 
 verted into steam. In large manufacturing 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 vege- 
 table preparations, such as extracts and inspissated juices, prepared 
 at temperatures which, being completely under the control of the 
 operator, allows 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 
 he&ts of the vapours of many fluids have been determined. 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 1000° 
 
 Alcohol 376° 
 
 Ether 163° 
 
 Oil of turpentine 138° 
 
 Nitric acid 335° 
 
 Tlie 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 changing from the liquid to the gaseous state, the volume is 
 increased in a very great degree ; the amount of increase, in some 
 instances, which may be taken as examples, is given in the following^ 
 table. 
 
 Water . . . , 
 Alchoi . . . , 
 Ether . . . , 
 Oil of turpentine 
 Mercury . . , 
 
 Spe. Gra. 
 
 Wafer = 
 
 1000. 
 
 1000 
 
 907 
 
 715 
 
 867 
 
 13500 
 
 Boiling 
 Point. 
 
 Volume 
 
 of Vapoiir 
 
 at boiling 
 
 Point. 
 
 212° 
 172° 
 97° 
 315° 
 660° 
 
 Volume 
 of Vapour 
 at 212°. 
 
 1696 
 488 
 240 
 221 
 
 3395 
 
 1696 
 519 
 289 
 192 
 
 1938 
 
 Specific 
 
 Gravity of 
 
 Vapour. 
 
 620 
 1601 \ 
 2583 
 4763 
 6969 
 
 In the first column are the names of the bodies ; in the second, theii 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 boiUng 
 point ; in the fifth, the number of volumes of vapour reduced to a standard temper- 
 ature, 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 
 
78 DETERMINATION OF ELASTICITIESOF VAPOURS- 
 
 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 
 distinguished from the change of a solid to a fluid, by the impor- 
 tant fact that, while liquefaction is definitely produced at one tem- 
 perature, and at that alone, vaporization occurs at all tempera- 
 tures j 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 5 even ice evaporates j and, in order to do so, it is not neces- 
 sary 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 melting point. 
 Other solid bodies also evaporate without previous melting, as cam- 
 phor ; and arsenic cannot be melted j for, when heated, it is convert- 
 ed at once from the solid to the vaporous 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 va- 
 pour, until they occupy completely the space in which the body is 
 contained, and exercise a pressure which is equal to the force of 
 their mutual repulsion, and which is termed the elasticity of the va- 
 pour. 
 
 The amount of elasticity, or, as it is often called, tension of a va- 
 pour, is determined by very simple methods. Thus, for elasticities 
 Ph&— — fflL below that of atmospheric air, a series of barom- 
 eter 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, d d, is to be 
 kept untouched, to measure the elasticity of the ex- 
 ternal 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, 
 counteracts a portion of the pressure of the exter- 
 nal air. The remaining pressure of the air is able 
 to support, therefore, only a shorter column of mer- 
 cury, 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 de- 
 pression 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 mer- 
 cury added to the elasticity of the vapour, and this 
 last is consequently 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 ofi' by the rule and index, r v r. Thus, if the barometer be at 
 30 inches and the temperature 80°, the mercury will stand in the 
 tube with watery vapour at 29 inches, in that with alcohol at 28-1, 
 and in that of ether at 10 inches. The elasticities of these vapours 
 are therefore at the temperature of 80°. 
 
DETERMINATION OF ELASTICITIES OF VAPOURS. 79 
 
 Vapour of water 10 inch. 
 
 " of alcohol 1-9 
 
 »• of ether 200 
 
 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 mercu- 
 rial 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 globe of water or oil to which heat may be applied, but the prin- 
 ciple remains the same. In this way a table of the elasticity of a 
 vapour at all temperatures below their boiling points may be form- 
 ed ', 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 f; 
 0-263 g 
 0-375 1 
 
 90° 
 
 1-36 ^ 
 1-86 g 
 
 40° 
 
 100° 
 
 50° 
 
 120° 
 
 3 33 53 
 
 55° 
 
 0-443 S. 
 
 140° 
 
 5-74 S 
 9-46 I 
 
 60° 
 
 0-524 t, 
 
 160° 
 
 65° 
 
 0-616 1 
 
 180° 
 
 15-15 1 
 
 70° 
 
 0-721 .S 
 
 200° 
 
 23-64 .S 
 
 80° 
 
 1000 .s 
 
 212° 
 
 30-00 S 
 
 When a liquid, in such an apparatus, is heated until the vapour 
 formed occupies all the tube and expels the mercury, the elastici- 
 ty of the vapour is equal to that of the air, and the liquid exposed 
 to the air boils j the phenomenon of boiling arising simply from 
 the fact that the elasticity of the vapour balances the pressure 
 of the air while the bubble is passing through the fluid: thus, 
 suppose a vessel of water exposed to the air at 200°, and a bub 
 ble of steam to form in it ; the pressure exercised by that bubble 
 being equal to its tension, is equivalent to a column of 23'64 inches 
 of mercury ; but the external pressure being 30 inches, the bub- 
 ble is crushed in by a force equal to the difference (6*36 inches 
 of mercury), and, consequently, dispersed. If the water, however, 
 be heated to 212°, the elasticity becomes equal to 30 inches, and 
 then the external and internal pressures being equal, the bubble 
 rises in the liquid without 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 constitutesthe simmering of a boiler or the sing- 
 ing 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 minute 
 bubbles j when these separate from the hot metal, they are immedi- 
 ately burst in by the greater external pressure, and the mass of 
 water is thus thrown into a state of exceedingly rapid and uniform 
 vibration, which fall upon the ear so regularly, in many cases, as to 
 produce a musical and often agreeable tone, which may become 
 
80 DETER MINATION OF ELASTICITIES OF VAPOURS. 
 
 graver or more acute, according 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 tem- 
 peratures the rate of increase is still more rapid. 
 To determine 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, a, into which is introduced by 
 the stopcock c/, the fluid to be experimented on, 
 as, for example, water. In the aperture c is 
 fitted a thermometer, the bulb of which dips 
 into the fluid near the centre, and shows its tem- 
 perature. A quantity of mercury being in the 
 bottom of the vessel, the tube b dips under its 
 surface, and, rising to the necessary height, has 
 attached to it the scale divided into inches and 
 their parts. When the apparatus is heated, as 
 the vapour produced cannot escape, all junc- 
 tures being perfectly steam-tight, the tempera- 
 ture rises continuously in place of stopping at 
 the boiling point, and the vapour formed press- 
 ing on the surface of the remaining liquid, and 
 by it on the mercury underneath, forces the. 
 mercury up the tube b until the mercurial col- 
 umn 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 equiv- 
 alent 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 212° 
 
 16 
 
 atmosph 
 
 Bres at 398° 
 
 2 atmospheres 
 
 at 250° 
 
 20 
 
 « 
 
 418° 
 
 3 « « 
 
 275° 
 
 25 
 
 « 
 
 « 439° 
 
 4 « « 
 
 294« 
 
 30 
 
 i< 
 
 457° 
 
 6 
 
 320° 
 
 40 
 
 « 
 
 " 486° 
 
 8 
 
 342° 
 
 50 
 
 (( 
 
 510° 
 
 12 
 
 374° 
 
 
 
 
 It is necessary, in order to understand such tables, to observe 
 that this great increase of the elasticity of steam, as the tempera- 
 ture 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 liquid water, were heated to 294°, it would tend to 
 expand precisely as air or any other gas, and the increase of elas- 
 ticity would be only from 30 to 34 inches, or from 1 atmosphere 
 to 1\ ; but if the globe contain liquid water, there is such an addi- 
 tional 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 
 
 vapour is made to vary, the result deviates from the rule laid down 
 
RELATIONS OF VAPOURS TO PRESSURE. 
 
 81 
 
 a 
 
 f ^ 
 
 in page 20, for the action of pressure upon gases ; for 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 liquid, 
 and there continues in the state of vapour only as much as occupies 
 with the same elasticity the diminished volume which the column 
 of mercury leaves. Thus, if we 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 bal- 
 ancing in the leg b a column of mercury thirty 
 inches high. If, now, without allowing the tem- .- 
 perature to change, mercury be poured in at the 
 orifice of b until it shall rise in a up to the line/ 
 g, and occupy exactly one half of that leg, the va- 
 pour 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 30 inches of mer- 
 cury precisely as it did before, and the pressing 
 column, counting from the line/g*, will terminate o 
 at h. 
 
 If, however, in place of attempting to increase the pressure on a 
 vapour, 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 
 proportioned 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 un- 
 condensed ; but, in reality, the relation is more complex, and may be calculated 
 upon the following principles. Thus, if we wish to know the specific gravity of va- 
 pour of water having an elasticity expressed by 742 inches of mercury, and the 
 temperature 150°, we proceed as follows : the specific gravity of steam at 30 inches 
 and 212° is 6202 ; and hence, if the volume did not change, the specific gravity of 
 the vapour at 150° should be 620-2 x ^^6^=1^^'^^ 5 but in cooling from 212° to 
 150°, the portion of steam which retains its elastic form is compressed within a 
 smaller volume, and hence has its specific gravity increased in proportion to the 
 change, and therefore the 153-39 obtained above must be increased in the propor- 
 tion 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 cal- 
 culated in that way, and accompanied by the temperatures, the elasticities, and the 
 weight in grains of 100 cubic inches of the vapour. 
 
 Temperature. 
 
 Elasticity in 
 Inches of 
 Mercury. 
 
 Specific Gravity. 
 Air=1000. 
 
 WeighioflOO 
 cubic Inches. 
 
 32° 
 
 0-200 
 
 5-68 
 
 01361 
 
 50° 
 
 0-375 
 
 10-17 
 
 0-2474 
 
 60° 
 
 0-524 
 
 14-03 
 
 0-3387 
 
 100° 
 
 1-860 
 
 46-36 
 
 1-1028 
 
 150° 
 
 7-420 
 
 169-24 
 
 4-0543 
 
 212° 
 
 30-000 
 
 62020 
 
 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 va- 
 pour of water to be at 67° 7-72, while 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 re-examination of the subject. At very high tempera- 
 
82 PROPERTIES OF COMPRESSED VAPOURS. 
 
 tures, 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 hquid, at the temperature of 320°, and its elasticity 
 in that state equals 38 atmospheres, whereas, by calculation, its elastic force should 
 be 168 atmospheres. Alcohol, enclosed in tubes hermetically sealed, is totally con- 
 verted into vapour, occupying only three times the volume of the liquid at 404°, and 
 then exerts a pressure only of 129 atmospheres, while by theory the pressure should 
 equal 221. Water, also, was obtained by Cagniard de la Tour gaseous in foui 
 times its hquid 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 be- 
 tween 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 not as yet 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 suddenly reduced in a re- 
 markable degree, even independent 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^ j there, however, the expansion does 
 not stop ; the impulse of the particles of vapour carries them much 
 farther ; and as the specific heat increases so as nearly to be doubled 
 when the volume becomes doubled, a considerable reduction of the 
 temperature below 212° occurs, which is still farther 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 heat- 
 ing 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 little volatile. Thus the space over the mercury in the 
 best barometers is not truly empty, but contains a quantity of mer- 
 curial vapour, exercising a certain elasticity, and, by depressing the 
 liquid column, making the pressure of the external air appear small- 
 er than it really is. It would appear, however, that there are, for 
 some bodies at least, temperatures 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 re- 
 search that the existence of a limit to evaporation was believed. 
 
 The boiling point of a liquid being that at which its vapour can 
 support the external pressure, it is liable to constant fluctuation gs 
 the pressure changes, and hence the fixing of the temperature of 
 boiling water upon the thermometer requires the care and attention 
 already noticed. If the barometer stood at 23'64, water would 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 abcre the 
 level of the sea may be determined by the temperature at which 
 
NATURE OF THE BOILING POINT. 83 
 
 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 or- 
 dinary calculation, the height of the mountain may be found with 
 as much accuracy as if the barometer itself had been carried up. On 
 the summit of Mount 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 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 would boil even at the 
 lowest possible temperature j but this is not practicable, as the va- 
 pour formed cannot be so perfectly removed but that it will exer 
 cise some pressure ; but, with a good air-pump, fluids may be got 
 to boil 145° below their ordinary boiling points j thus water will 
 boil at 67°, alcohol at 32°, ether at a temperature at which quicksil- 
 ver would freeze. If, at the moment that such a fluid is in violent 
 ebullition, the working of the pump be stopped, the vapour accumu- 
 lates, and, exercising on the surface of the fluid an amount of press- 
 ure corresponding to its elasticity at the existing temperature, rais- 
 es the boiling point, and thus stops the ebullition. 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 care- 
 fully 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, jo, be allowed 
 to play upon the flask, the vapour is condensed, 
 and, a vacuum being thus produced, the water 
 begins to boil ; if a jet of warm water be em- 
 ployed, 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 totally dependant 
 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 ordi- 
 nary 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 descri- 
 bing 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: 
 
84 ANOMALOUS PROPERTY OF LIQUIDS. 
 
 Muriatic ether .... 52° f Water 212° 
 
 Sulphuric ether ... 96° 
 
 Sulphuret of carbon . . 116° 
 
 Pyroacetic spirit . , . 132° 
 
 Water of ammonia . . 140° 
 
 Pyroxyhc spirit . . . 161° 
 
 Alcohol 173° 
 
 Nitric acid 248° 
 
 Oil of turpentine . . . 315° 
 
 Phosphorus .... 554° 
 
 Sulphur 601° 
 
 Sulphuric acid .... 630° 
 
 Mercury 660^ 
 
 The boiling point is influenced by some other circumstances than 
 the atmospheric pressure ; the nature of the vessel may alter it sev- 
 eral degrees. Thus, in a glass or glazed porcelain vessel, water 
 boils, under a pressure of 30 inches, not at 212°, but 214.° j and in 
 graduating a thermometer, it is hence necessary to use a metallic 
 vessel. This latter appears to favour ebullition by the minute irreg- 
 ularities 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 roughenfed 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 allowing it to cool a little, so that the boil- 
 ing shall completely cease ; if, then, a little filings of copper, or a 
 platina wire, be dipped into the liquid, if the cooling had not gone 
 too far, the boiling will immediately recommence, the steam forming 
 at the edges and angles of the rough substances introduced. 
 
 The temperature of the steam produced is not affected by the 
 boiling point of the liquid. Thus, although by dissolving salts, such 
 as chloride 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 bub- 
 ble which rises up through such a solution must be 264°, yet, as its 
 elasticity and latent heat are proportional to that temperature, it ex- 
 pands 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 increased 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 con- 
 taining 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 drop- 
 ping into it a small quantity of water ; the water remains on the red- 
 hot metal without 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 cohesive 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 
 
ARTIFICIAL COLD BY EVAPORATION. 85 
 
 upon glass, and is not 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. 
 At certain temperatures 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, in- 
 deed, more heat than it would render latent when converted into va- 
 pour by ordinary boiling. It has been found, by accurate experi- 
 ments with water, and there is good reason for supposing it to hold 
 also with liquids in general, that no matter at what temperature a 
 liquid vaporizes, it absorbs the same total quantity of heat. The 
 more of this that becomes sensible, the less is the portion which re- 
 mains 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 
 
 300°, » " 912, « " 1212 
 
 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 processes of the greatest value. Many vegetable substances 
 undergo important alterations in their chemical constitution and me- 
 dicinal properties 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, meas- 
 ured by a barometer gauge, may be established. In the manufacture 
 of sugar, this principle of evaporation at low temperatures, by re- 
 moval of the atmospheric pressure, was the source of great improve- 
 ment, as the true crystallizable sugar is converted into the uncrys- 
 tallizable sugar (treacle) with great rapidity at the temperature of 
 boiling sirup, and was hence, to a great extent, lost to the manu- 
 facturer. By later improvements in the mode of applying heat, the 
 necessity of evaporating the sirup 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 gener- 
 ated has been produced. The cold which is felt when a little ether 
 or spirits of wine is dropped on the hand, arises from this fact ; and 
 by surrounding the bulb of a mercurial thermometer with some loose 
 cotton, and moistening it with liquid sulphurous acid, the quicksilver 
 in the bulb may easily be frozen. By placing some ether in a shal- 
 low, 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 adhere firmly together by the intervening sheet of ice. 
 
 Water may be even frozen by its own evaporation, as in the cry- 
 ophorus, which consists of a long tube terminating in bulbs which 
 contain some water, and from which the air had been carefully ex- 
 
S6 SYNCHRONOUS FREEZING AND EVAPORATION 
 
 pelled by boiling before the apparatus was completely closed. The 
 
 space above the wa- 
 
 ter remains then oc- 
 cupied only by wa- 
 tery vapour. If all 
 the water be brought 
 into one bulb, and 
 the other bulb be im- 
 mersed in a freezing 
 mixture, the vapour 
 will condense there, 
 and new vapour be- 
 ^-' ing formed, a distil- 
 lation will be produced from the one to the other bulb. The vapour 
 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 j 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 arti- 
 ficial cold, water may be frozen by its own evapo- 
 ration. 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 converted into ice. Accordingly, as 
 any portion of vapour forms, it is immediately ab- 
 sorbed by the sulphuric acid, which has a great af- 
 finity for water j and the vapour being thus prevented 
 from collecting, the loss of heat by evaporation pro- 
 ceeds unceasingly, until so much heat has been re- 
 moved that the residual water is converted into ice. 
 
 In fluids more volatile than water, this synchronous freezing and 
 evaporation may occur still more simply. Thus, if strong prussic 
 acid be allowed to form a pendant 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 so- 
 lidification 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. 
 
 In warm climates, the evaporation of water is commonly employ- 
 ed to moderate the sultriness of the air, by the agreeable cold and 
 freshness it produces. The Spanish alcarrazas are earthen vessels, 
 so porous that any liquid which is put in 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 j and when describing these operations, the action of 
 this principle, in the construction of the apparatus used, will be re- 
 ferred to. 
 
 The conversion of a liquid into vapour at ordinary temperatures 
 
SPONTANEOUS EVAPORATION. 87 
 
 IS often called spontaneous evaporation ; and in the case of water, 
 from the great extent to which it becomes subservient to the econ- 
 omy of nature, this process is one of high importance. It was for- 
 merly supposed 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 cur- 
 rent is useful, not by supplying new quantities of air, but by re- 
 moving the vapour according as it is formed, and leaving fresh 
 spaces into which it may expand. When a liquid forms vapour, 
 the quantity formed is determined only 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 
 particles of watery vapour in the air are not subjected to the press- 
 ure of the atmosphere, but only influenced by the pressure of the 
 particles of the same kind ; and hence, that at 32'^, when the elas- 
 ticity 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 propor- 
 tional to its elasticity, and by the sum of all these pressures, the 
 pressure of the external air will be equilibrated. It is, consequent- 
 ly, possible to produce the rapid evaporation of one fluid, while an- 
 other 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, while the portion of the vapour of the second produ- 
 ced in the first instance shall remain, and prevent its farther change. 
 Thus, by placing a shallow dish of dilute alcohol under the receiv- 
 er of an air-pump, with a quantity of quicklime, the latter combines 
 with and absorbs the watery vapour as fast as formed ; and there 
 is, hence, a continual evaporation of the water, while the alcohol, 
 after generating as much vapour as once fills the receiver, is press- 
 ed upon by it, and cannot form any more. In this manner, alcohol, 
 almost quite pure, though much the 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 possesses the elasticity 
 belonging to its temperature ; but if there be not liquid enough to 
 form so much vapour, the vapour formed then expands, so as to oc- 
 cupy the entire space, and its elasticity diminishes in proportion to 
 the increase of volume ; vapours being regulated by the same law 
 of pressure which holds with gases. 
 
 If, thus, a bell glass of atmospheric air be confined over water at the tempera- 
 ture of 80°, a quantity of vapour diffuses itself through the air, and, as there is 
 water in excess, the elasticity of that vapour will be 100 inch. Now if we suppose 
 the elasticity of the air to have been previously 30 inches, it will become, by the 
 
88 MOIST-BULB HYGROMETER. 
 
 addition of the vapour, 29, for the vapour counteracts one inch of the external at- 
 mospheric 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 cor- 
 rected for the watery vapour that is mixed with them. Thus, in the analysis of a 
 substance containing nitrogen, let us suppose that 854 cubic inches of nitrogen have 
 been collected over water at the temperature of 63°, and the barometric pressure 
 being 29-35 inches ; at that temperature the elasticity of vapour is 058, and hence 
 that of the dry air is 2935 — 0-58=28-77. The volumes whi^h they occupy are as 
 these numbers, and hence the 854 of damp gas consists of •~^x8-54=017 of 
 watery vapour, and||;||x8-54— 8 37 of dry nitrogen. 
 
 This volume should still be corrected for temperature and pressure before the 
 quantity of nitrogen by weight could be obtained from it. 
 
 Where the air is not completely saturated with the watery va- 
 pour, it is not so easy to determine the exact quantity of vapour 
 which it contains. One of the best methods consists in cooling it 
 until its volume is so much diminished that the quantity of vapour 
 is sufficient to saturate 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 quantity of liquid water is deposited in the 
 form of dew upon the neighbouring cold bodies. This may be ea- 
 sily done by taking a tumbler of water somewhat too warm, and 
 cooling it gradually by dissolving in it a little mixed nitre and sal 
 ammoniac, until a slight deposition of dew is perceptible on the ex- 
 terior of the glass ; the water is then at the temperature of the dew 
 point. Another method consists in observing the rapidity of evap- 
 oration from the surface of the bulb of a thermometer which is 
 covered Avith muslin kept wet by water. The thermometer so ar- 
 ranged is always at a lower temperature than an ordinary thermom- 
 eter, from the quantity of heat carried away by evaporation, and 
 the temperature will be lower in proportion to the amount of evapo- 
 ration. In dry air, evaporation is quickest ; in air saturated with 
 moisture evaporation ceases, and in all intermediate degrees there is 
 a connexion between the quantity of moisture already present in the 
 air and the depression of temperature, which accompanies the forma- 
 tion of as much more as will saturate it. This method is peculiarly 
 of interest from the means which it afforded to Apjohn of ascertain- 
 ing the specific heats of the gases already noticed, and it is easy 
 now to understand the general principle upon which his process 
 was established. If we consider a certain space which may be fill- 
 ed by the different gases in succession, and these gases being dry, 
 they are made to saturate themselves with watery vapour, for the 
 formation of which they themselves supply the heat, it will be ea- 
 sily 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 with a high specific heat will only 
 require to cool 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 the watery vapoui 
 which the atmosphere contains are termed hygrometers, and that of Daniell is one 
 of the most elegant and most useful. It is a cryophorus, ah c, which in place of 
 
STEAM AS A MOVING POWER. 
 
 89 
 
 water contains ether, and in one bulb of 
 which, h d, is fixed a very delicate thermom- 
 eter. This bulb is made of blackened glass, 
 and the other bulb, a, is covered with a httle 
 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 anives at the point of satura- 
 tion, when a dew of liquid water begins to be 
 deposited, which is at once observed upon the 
 blackened glass. The internal thermometer 
 I 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 temperature of the external air. 
 
 When the dew point has been thus deter- 
 mined, the subsequent calculation 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 steam at 45° is 0316 ; and as the elasticity diminishes according as the volume 
 increases from 45° to 72°, the elasticity of the vapour in the air at 72° is 030 ; and 
 the atmospheric pressure of 30 inches is produced by the dry atmosphere, which 
 balances 29-70, and the watery vapour which balances 30 ; and the respective 
 volumes are as these pressures. 
 
 Gay Lussac has sought to establish a close relation between the manner in which 
 soUd bodies dissolve in liquids, and that in which vapours diffuse themselves through 
 space. Thus, if a sohd body dissolved only because the liquid diminished the co- 
 hesion of its particles, the diminution of that cohesion in another way should in- 
 crease the solubihty very much : this, however, does not occur. Wlien paralfine 
 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 com- 
 pares the diffusion of particles of the solid through the liquid to the diffusion of par- 
 ticles 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 in- 
 terest, as pointing out a similarity between solution and vaporization previously un- 
 noticed, and which may be applied to the explanation of many anomalous facts. 
 
 The employment of steam as a moving power is of so much im- 
 portance to science and to the arts, that it would be improper to 
 terminate a discussion of the properties of vapours without any 
 allusion to the manner in which it is utilized. The little steam cyl- 
 inder of Wollaston figured in the margin contains all 
 that is essential to the application of steam, in princi- 
 ple, to produce motion. A glass tube, terminating be- 
 low 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 repeated any number of times, 
 and is the essential element of the atmospheric steam 
 engine of Newcomen. It was in this form when Watt 
 commenced his improvements on it ; and by applying 
 all the resources of the exact knowledge of the properties of heat 
 
 M 
 
90 BOILING POINTS OF CONDENSED GASES. 
 
 then first obtained by himself and his illustrious associate Black, 
 he converted it, though still without changing its fundamental prin- 
 ciple, 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 considered as the most 
 powerful material agent of human improvement and civilization of 
 which mankind has O'ver obtained possession. 
 
 The similarity of constitution of gases and vapours has been already pointed out 
 on many occasions, and particularly, in page 21, the conversion of gases into liquids 
 by the application of great pressure has been detailed. A liquefied gas so con- 
 tained in a close vessel is precisely in the condition of water heated in a digester, 
 as in the apparatus figured in page 80, far above its boiling point, and generating 
 steam possessed of considerable tension. On this analogy has been founded an in- 
 teresting speculation concerning the temperatures at which the gases would, at or- 
 dinary pressures, assume their liquid form, that is, their boiling points when hquid, 
 thus : 
 
 At 44-5° the tension of liquid nitrous oxide is 50 atmospheres. 
 
 At 320° « " " 44 
 
 For 12-5° an increase of tension of ... 6 atmospheres. 
 
 Steam exerts a pressure of 50 atmospheres at . . . 511-5° 
 and of 44 " «... 4975° 
 
 For six atmospheres the difference is 140°, or just the same. 
 
 Liquid carbonic acid exerts a pressure of 25 atmos. at 32° ) -r,«- ^ one 
 
 and of 20 « " ^^o pifFerence, 20° 
 
 The tension of steam is 25 atmospheres at .... 4395° ) t^-o- o.n 
 
 20 - « . . . . 418-5° \ Difference, 21° 
 
 Muriatic acid exerts, when liquid, a tension of 25 atmos. at 25° > js-rr-^^^ „^ „„o 
 
 and of 20 " " 30 ^ umerence, 2^ 
 
 Steam balances 25 atmospheres at '^39 5° ) p,.^^^^ ^^ „,g 
 
 20 " " ^jg.go ^-L'merence, ^i 
 
 Ammonia liquefies and exerts a pressure of 65 atmos. at 50° ) pjiA-^^^ „„ , qo 
 
 and of 5 " « 32° S ^^nerence, 18 
 
 Steam exerts a pressure of 65 atmospheres at . . . 326° > rv;flv,__„-_ ^q eo 
 5-0 " "... 3075° ) ^'^^^^^^^f •'■°'" 
 
 It is hence evident that, in every case, the rate of increase of elasticity 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 at- 
 mosphere, the reduction of temperature necessary to effect it should be regulated 
 by the same law as that of watery vapour ; the gases should then, under the ordi- 
 nary pressure of 30 inches, become liquid, and when liquid, their boiling points 
 should be : 
 
 Nitrous oxide = — 252 4° Fahrenheit. 
 
 Carbonic acid = — 2308° " 
 
 Muriatic acid = — 2020° " 
 
 Ammonia = — 634° " 
 
 The great increase of elasticity which these liquefied gases acquire by a chang:e 
 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 importance. Thus, the manner in which 
 gases spread through each other, in virtue of their diffusive power, will be descri 
 bed under the head of Atmospheric Air, to the proper constitution of vi^hich this 
 law is indispensable. 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. 
 
CONDUCTIONOFHEAT. 91 
 
 SECTION V. 
 
 OF 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 be- 
 come so hot as to be intolerable to the hand j while, 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 tem- 
 perature raised in any remarkable degree. The extremity of a glass 
 rod may be melted by the flame of a blowpipe, 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 it- 
 self generally through its mass, and elevating the temperature of 
 its entire length almost to the same degree. Bodies which act like 
 silver are said to conduct heat well, and are termed conductors. 
 Bodies which intercept it, like wood or glass, are termed non-con- 
 ductors. 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 conduct- 
 ing power, is supposed to take place from particle to particle, pre- 
 cisely as, when we apply a heated to a cold ball of iron, the latter 
 becomes warmed 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 conducting 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 ar- 
 ranged in a variety of ways. Thus, if a number of similar rods, of 
 different substances, be coated to a certain distance from one ex- 
 tremity with wax, and then heat be applied to the other extremity, 
 the wax will melt according 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 sub- 
 stances 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 experiments 
 are only useful in giving the order of conducting power in a gen- 
 eral 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 experi- 
 ments were square prisms, and were all covered with the same black 
 
92 RELATIVE CONDUCTING POWER OF SOLIDS. 
 
 varnish, in order that the loss of heat from their surface might be 
 exactly similar. At every four inches of their length was a hole 
 bored to half the depth of the bar, which was filled with oil or mer- 
 cury, 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 of an experiment. The 
 temperature of the air of the room, which should scarcely at all 
 vary during that time, is known by a thermometer. 
 
 After the bar has been heated for two or three hours, each ther 
 mometer 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 prop- 
 agated along the bar from the lamp, and the quantity which is lost 
 by cooling. The excess of the temperatures of the thermometers 
 attached to the bar above the temperature of the room, forms, there- 
 fore, a series, the ratio of which depends upon the conducting pow- 
 er 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 for comparison. 
 
 Gold 1000 
 
 Silver 973 
 
 Copper 898 
 
 Platinum 381 
 
 Iron 374 
 
 Zinc 363 
 
 Tin 304 
 
 Lead 180 
 
 Marble 23 G 
 
 Porcelain 12-3 
 
 Fire clay 114 
 
 Although this series presents, when compared with the specific 
 gravities, 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 platina is, however, quite anomalous, and 
 must prevent any attempt at generalization. 
 
 The difference of the conducting power of solid bodies is of daily 
 utility in ordinary life, as well as in chemical operations. It is thus 
 that substances of exactly the same temperature may produce quite 
 opposite sensations 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 former, but the latter will feel 
 only moderately warm. If the metal and wood be both cooled to 
 32^, the former will feel intensely 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 conducting J)ower, the flow of heat takes 
 place so gradually in each direction as almost to escape notice. 
 The brickwork of a fireplace or of a furnace is for the purpose of 
 keeping the heat generated by combustion from spreading to the 
 surrounding bodies, and so being lost. It woi Id be difficult to light 
 
CONDUCTING POWER OF LIQUID S. 
 
 93 
 
 a fire in a massive metallic grate, for the heat would 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 power 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 experiment. Thus, if in ajar of water an air ther 
 mometer be inverted, so that its bulb shall be very 
 near the surface, and the 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 obtained, 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 even then 
 it is by the glass material of the tube that the heat is 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 con- 
 duction, 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, as- 
 cends in the mass, and is replaced by the colder and heavier por- 
 tions, which, being in their turn heated, ascend 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 tem- 
 perature quickly and uniformly gained. 
 
 In the case of water, and such liquids as have a point 
 of maximum density, this communication of heat, by as- 
 cending and descending currents, occurs in the inverse 
 order below that point. Thus, to warm water which is 
 below SQ'S"^, the heat should be applied above, or to cool 
 it farther 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 the mass of water becomes cooled to 39-5°, the su- 
 perficial layer becoming lighter as it cools more, prevents, 
 by its non-conducting power, the farther abstraction of 
 heat from the deeper portions ; but when the warm air of 
 spring plays on it, the heat is rapidly diffused from above down- 
 ward, until the temperature of the entire mass is raised to 39-5°. 
 
 ti 
 
94 COMMUNICATION OF HEAT BY RADIATION. 
 
 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 cold 
 particles, they abstract and communicate heat with great rapidity. 
 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 impor- 
 tance. The different kinds of clothing owe their warmth to the fact 
 that they prevent the heat of the body from escaping ; this they ef- 
 fect not so much by the power of their proper solid substance, as 
 by being of a loose and spongy texture, they imprison in their pores 
 a quantity of air, which, not being able to form those continual cur- 
 rents, acts as a non-conductor. The more loose and spongy, there- 
 fore, the tissue of a cloth may be, the more air does it confine and 
 the warmer it is. This is fully supported by the experiments of 
 Rumford, 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° with 
 
 Air in 576'' 
 
 Raw silk in 1284' 
 
 Fine lint " 1032" 
 
 Beaver's fur " 1296' 
 
 Cotton wool " 1046'' 
 
 Eider down " 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 
 transmission through its mass ; and since a current of air is passing 
 to the fire in order to supply its conduction and produce the draught 
 of the chimney, 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 quan- 
 tity of heat, is directed only upward. Heat is therefore propagated 
 by a third mode, distinct from diffusion and from combustion; 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. 
 
 Radiation 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 conduction as a kind of radiation from particle 
 to particle in the interior of the mass, and it is only with gases that 
 radiation is equal 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 
 
PROPERTIES OF RADIANT HEAT. 
 
 95 
 
 has yet been discussed, there exists 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 absorbed, or they pass through the body without loss. In 
 general, all these efiects are in part produced ; that is to say, one 
 portion of the incident rays will be transmitted, another portion re- 
 flected, and a third will disappear by being absorbed. There are 
 thus in relation to radiant heat four qualities, which various sub- 
 stances 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 re- 
 flection or refraction. By the former mode, that originally used by 
 Prevost and by Leslie, the properties of radiant heat may be de- 
 monstrated in a simple manner. 
 
 The form of apparatus generally employed for demonstrative ex- 
 periments on radiant 
 heat consists of re- 
 flecting mirrors of pol- 
 ished silvered copper, 
 of a paraboloid form, 
 A B ; the property of 
 this figure bein^ that 
 rays emanating from 
 the focus of one mir- 
 ror are reflected from 
 it in parallel directions, and falling thus parallel upon the other, are 
 brought to convergence in its focus. In this manner the heat ra- 
 diating from a body may be concentrated upon a single point, and 
 all 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 phos- 
 phorus for any length of time without affecting it ; but if the hot 
 ball be placed in the focus of one mirror, C, and the phosphorus in 
 the focus of the other, D, 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 
 bail, it feels cooled. It is thus not by the di- 
 rect 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 reflected from pol- 
 ished surfaces, and concentrated upon a focus, 
 and which will 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 imme- 
 diately indicates the rise of temperature, and 
 may serve to measure it. But it is only the ^^n^^' 
 air thermometer which is delicate enough for 
 
96 
 
 OF THE RADIATING, ABSORBING, 
 
 such experiments, and it is specially for this use that the differen- 
 tial air thermometer is constructed. One bulb being placed ^n the 
 focus, the difference of temperature between the two bulbs is in- 
 stantly shown ; and it is thus also proved that the rise of tempera- 
 ture 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 gen- 
 eral change of temperature, no matter how extensive. 
 
 By means of this apparatus, the radiating and absorbing, as well 
 as the reflecting and transmitting powers of bodies may be exam- 
 ined. The radiating power may be conveniently exhibited by filling 
 
 a tin cube, a, with boiling 
 water, and applying to the 
 surfaces of the cube the bod- 
 ies which are to be exam- 
 ined. Thus, one side being 
 left brightly polished, an- 
 other dimmed by being rub- 
 bed 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 c, 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, is measured 
 by its indication. Leslie thus found the radiating power of the 
 following surfaces to be relatively, 
 
 Lampblack 100 
 
 Writing paper 98 
 
 Crown glass ..... 90 
 
 Ice 85 
 
 Red lead 80 
 
 Plumbago 75 
 
 Tarnished lead .... 45 
 
 Clean lead 19 
 
 Polished iron 15 
 
 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 probable, 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 quan- 
 tity 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 press- 
 ure, the surface, although perfectly bright, radiates with a power of 22 ; but if it be 
 dimmed by rubbing with sand-paper, the compression, even though so slight, di- 
 minishes the radiating power to 12. Substances which are highly elastic, as ivory, 
 or very hard, as agate, radiate in the same degree, no matter what may 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 in all directions equally intense, 
 there should occur inequalities in the temperature of the surrounding bodies of the 
 most remarkable and intolerable kind. Thus, let us suppose two surfaces at right 
 angles radiating heat, as, for instance, two surfaces 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 
 
AND REFLECTING POWERS OF BODIES. 97 
 
 same points only the rays B M or C M'. But the rays 
 emanating not from the surface at M or M', but from N' and 
 N, at some depth below, the oblique ray N A has to pass 
 tlK-ough 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 sur- 
 rounding bodies to attain an equable 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 proportion of heat is lost in escaping 
 from below the surface of the body. 
 
 Th-e radiating powers of bodies are the foundation of numeroua 
 applications in the arts. Those bodies which radiate least cool 
 slowest 5 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 is 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 whitelead 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 cold 
 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 j 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 proper 
 tioned to one another by the following experiment. A large diflTerential thermom- 
 eter is arranged, whose bulbs are chambers of considerable size, presenting large 
 and equal plane surfaces on the sides that are towards each other. Of these, one 
 is polished and the other coated. Midway between them is placed a canister hav- 
 ing 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 ab- 
 sorbing one, and the worse radiating to the best absorbing, and the hquid in the tube 
 remains perfectly stationary, estabhshing thereby the exact equality of the absorb- 
 ing and radiating powers. 
 
 Although colour is without influence on the radiating power, it yet 
 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, v/ith reason that dark-coloured cloths are preferred 
 for winter use, and light colours for summer. It is, however, to be 
 
 N 
 
98 TRANSMISSION OF HEAT. 
 
 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 *ibsorbing power of a blackened and of a 
 metallic surface may easily be shown, by coating one bulb of a dif- 
 ferential thermometer with silver leaf and blackening the other. 
 W hen, 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 
 sensibly 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 there- 
 fore possessed by the surfaces of bodies in the inverse degree to the 
 absorbing and radiating powers, and hence the best absorbers are 
 those which reflect least. 
 
 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 arti- 
 ficial heat may be produced. The heat of the sun's rays may also be 
 concentrated 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 transmitting heat through their substance, it becomes necessary 
 to look farther to the source and intimate structure of the heat. For 
 the results which have as yet been described, we are indebted al- 
 most 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 advance of other sci- 
 ences had placed at the disposal of the experimenter measures of 
 temperature infinitely more sensible than any form of thermometer 
 formerly 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 subjoined figure. 
 
 On a steady table there rests a frame M M, along the middle of which a slip R R 
 IS cut, by which the various stands and supports may be moved back and forward, 
 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 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 P, from which the wires F F convey the electri- 
 city generated to the galvanometer 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 interposed, having an aper 
 ture 0, somewhat smaller than the plate to be employed. This last is then sup- 
 ported immediately behind the aperture by means of the little frame S', so that no 
 heat can reach the ttiermo-multiplier unless after having passed through it. As it 
 is of great importance to have the end of P farthest from the lamp uninfluenced by 
 any disturbing causes, the screen E" is placed immediately behind it, to protect it 
 
TRANSMISSION OF HEAT. 
 
 99 
 
 trom irregular radiation and from currents ; and as the action of the heat upon the 
 pile must be limited to the actual time of the experiment, the double scl:^en E' is 
 interposed immediately 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 is occasionally fitted with a conical tube of 
 plated brass, for the purpose of collecting the rays of heat in greater number ; birt 
 that is not often wanted. 
 
 The reflecting power of bodies has been exactly determined by 
 Buflfto 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 52 
 
 Polished brass varnished 41 
 
 Glass plate blackened on back 12 
 
 Looking-glass . , 20 
 
 Metal plate blackened 6 
 
 The power of a body to transmit heat is termed transcahscence^ 
 and of intercepting heat intranscahscence. These properties are to- 
 tally independent of the power of transmitting light, as will be at 
 once seen from the following table. Of 100 rays proceeding from 
 tbfl flame of an argand lamp, there are transmitted by 
 
 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 glass 
 
 . 
 
 black 
 
 16 
 
 Do. . . . . . 
 
 red 
 
 33 
 
 Citric acid . 
 
 . 
 
 colourless 
 
 15 
 
 Chromate of potash . 
 
 orange 
 
 33 
 
 Alcohol . . 
 
 
 do. 
 
 15 
 
 jBorax ...... 
 
 colourless 
 
 28 
 
 Alum . . 
 
 
 do. 
 
 12 
 
 1 Glass coloured . . . 
 
 green 
 
 23 
 
 Water . . 
 
 
 do. ^ 
 
 11 
 
 Rock salt is thus the most tran scale scent substance that has been 
 
100 
 
 PERMEABILITY OF BODIES TO HEAT. 
 
 found. Glass arrests more than one half of all the heat which it re- 
 ceives, while colourless and transparent alum, and the most limpid 
 water, arrest more of the heat which they receive than the deepest 
 coloured glasses, or topaz, or quartz, so brown as to be quite 
 opaque. 
 
 But not merely do different bodies act differently on rays pro- 
 ceeding from the same source, but the same body may allow the 
 heat from one source to pass freely through its substance, and inter- 
 cept partially or completely the heat radiating from another. Thus 
 using, in his experiments, the heat emanating from five kinds of 
 source, first, the argand lamp ; second, the lamp of Locatelli, which 
 is remarkable for the steadiness 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 
 m 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 
 Hlalina. 
 
 ,a% 
 
 a?2TI^ 
 
 100 
 
 Free radiation . 
 
 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 
 
 6 
 
 
 
 
 
 
 
 Rock salt is thus not only the most transcalescent body, but it is 
 that which alone is equally transcalescent to heat of all tempera- 
 tures. The rays of heat evidently acquire a greater power of trans- 
 missibility as the temperature of the source increases, and hence 
 glass arrests scarcely any portion of the direct solar heat, while 
 from the argand lamp it intercepts 47 j from Locatelli's lamp, 61 ; 
 from ignited platina, 72 ; from copper at 734°, 94 ; and from cop- 
 per at 212°, 100 per cent. The action of these media upon radi- 
 ant heat consists not merely in stopping a certain portion of it, but 
 in separating it into two portions, physically distinct, of which one 
 is capable of transmission, while 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 sub- 
 stance ; and calc spar, which transmits only yVo ^^ 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 
 tourmaline, which transmitted 18 out of 100 rays directly incident 
 upon it, intercepts //„ of those which had previously passed through 
 alum, but gives passage to jW 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 differ- 
 
ANALOGY OF HEAT TO COLOURED LIGHT. 101 
 
 ent refrangibility of the rays of heat emanating from sources of va 
 rious temperatures. If the rays of heat emanating from a lamp be 
 incident upon a rock-salt prism, they will undergo refraction, sub- 
 ject 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, while 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 that 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 
 peculiarities in their action will be at once observed. Rock salt al- 
 lows 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 re- 
 frangible 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 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 ab- 
 sorbing 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 coloured red that it is almost opaque, and trans- 
 mits 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 phenomena of colours in the case of light, must occur with 
 lieat, and be made sensible if our organs or our instruments were of a construc- 
 tion suitable for their appreciation. As yet, however, the fact which alone remains 
 wanting towards a physical theory of heat has not been observed — that of interfe- 
 rence ; up to the present time, the actual production 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 remark- 
 a!)le, 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 vibr^li<*n« -»f the 
 same ethereal medium which produces light, and in considering that Ih-, dJ3-»vence 
 
102 RELATIONS BETWEEN HEAT AND LIGHT. 
 
 between heat and light should be m the magnitude of the vibrations, and the conse- 
 quent refrangibility of their rays. On the contrary, it is not reasonable to sup- 
 pose, that while we are conscious of the waves in air, although they may vary in 
 length from 32 feet to ^ of an inch, the limits of our sensibihty 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, while the waves with- 
 m these limits produce upon the eye the sensation of coloured light, another range 
 of lengths, greater than those of light, should give to our organs the sensation of ra- 
 diant heat ; and that a third order of vibration, still shorter, and more refrangible 
 even than violet light, is capable of acting upon the elementary constituents of bod- 
 ies, 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 weU 
 imagine that, by whatever means the sun communicates to the ethweal 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 accompa- 
 nied by the heating power which animates all living nature, and without which the 
 universe would 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 de- 
 serve attentive study. If it were so, then the heating rays of the spectrum should 
 be thrown always below the coloured space, being less refrangible ; and it is found 
 that, with a flint glass prism, the greatest heat is produced outside the visible con- 
 fines of the spectrum at the limit of the red light. This is, however, only accident- 
 al, 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 col- 
 lected 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 distributed over the en- 
 tire visible spectrum a heating spectrum, which has its pecuhar point of greatest 
 energy, and which may be refracted more or less quite independently of the lumi- 
 nous space, and may be brought to overlap it at either end, or to lie evenly upon it. 
 The ethereal medium, if it be the means of transmitting radiant heat, must be ca- 
 pable 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 beautiful- 
 ly 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 to- 
 tally 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 thermoscope he couid apply, exhibited no trace of any 
 heating power whatsoever. 
 
 An interesting property of radiant heat, and one which shows the remarkable 
 distinction between it and light ia a very evident manner, is, that the heat may 
 change its degree of refrangibility ; and hence, if it be vibrations, one wave may 
 break it up into several, or several smaller waves may unite to form one. The 
 light of the aun, dep/ived 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 
 stat^ 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 hght. Red light has never 
 ihaiiged into blue, nor violet into orange ; and there must be in the physical theory 
 
EQUILIBRIUM OF TEMPERATURE. 103 
 
 ol 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 another occurs 
 m 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 jce or snow, and hence a layer of snow upon a field, ex- 
 posed 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 refrangibility, which 
 the snow absorbs completely, this is melted under the stick, 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 Uving vegetable, arises from this naerely 
 physical conversion. 
 
 From 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 97) melted the 
 snov^ 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 would be transmitted into the heat which would be ab- 
 sorbed by the snow on which they rested. 
 
 The construction of a theory of heat would be, even were an undulatory hypoth- 
 esis adopted for its radiant form, involved in difficulties which may require many 
 years of research to render them even clearly understood. The relation betw^een 
 radiation and conduction ; the connexion 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 comprehended 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 
 Jione of the views brought forward appear positi^ve 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 i^adiation. The rapid- 
 ity of cooling by the immediate contact of the hotter with the colder 
 body depends on the degree of intimacy of the contact, and on the 
 conducting powers of the bodies. Thus solids, which merely touch 
 at a few points, communicate their relative temperatures but very 
 slowly, while with liquids or gases which may mix completely with 
 each other, the establishment of a uniform temperature is almost 
 instantaneous. The colder body 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 j in other cases 
 the hotter body cools in proportion as the colder becomes warm, and 
 the resulting temperature depends on the specific h»at of each, as has 
 been described, page 62. In determining, therefore, the temperature 
 of a body by a thermometer, it must not be forgotten that the ther- 
 mometer, in becoming hot, cools the body, so that, unless there be a 
 continuous 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 
 
104 THEORY OF DEW AND FROST. 
 
 upon a plate of cold iron, abandons its excess of temperature so 
 rapidly, that a mean temperature 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 j no 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 radiated depends on the temperature of the bodyj 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 iif re- 
 turn, and will hence cool, while the surrounding colder bodies, ab- 
 sorbing 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 de- 
 pressed, tends ultimately to an equilibrium with all the neighbouring 
 bodies ; and hence, the instant we remove a substance from our fur- 
 naces or freezing mixtures, it begins to cool or to become less cold. 
 This principle explains, in a very perfect manner, a singular but in- 
 structive experiment which may be made with the concave mirror 
 apparatus described, page 95.* In the ordinary form, the thermom- 
 eter 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 sub- 
 stituted, the temperature of the thermometer in the focus of the op- 
 posite 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 sur- 
 face of the earth, we find the solution of many interesting natural 
 phenomena. The production of dew and frost are to be thus ac- 
 counted for. In the absence of the sun, the surface of the earth 
 losing by radiation a great quantity of heat, would have its temper- 
 ature considerably lowered, were it not that the canopy of clouds 
 which generally lies above it radiate in return, and thus maintains 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 degrees below that of tlie 
 atmosphere. The stratum of air whichlies in contact with the sur- 
 face of the ground is then cooled by contact, and a portion of the 
 watery vapour which it had possessed in its elastic form is depos- 
 ited as liquid water. If the temperature of the air be itself low, 
 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 
 
CENTRAL HEAT OF THE EARTH. 105 
 
 the fact that it is only on the surface of good radiators, and during 
 clear starlit nights, that dew or frost is found. If a plate of pol- 
 ished 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 interposition of a screen of any 
 substance which intercepts the passage of radiant heat, when the de- 
 position of dew or frost instantly ceases, and the surface cools no 
 more. Thus plants are protected by mats from the frost 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 tempera- 
 ture of the radiating bodies, but it is not proportional to this differ- 
 ence except within a very narrow range of temperature. Newton, 
 having experimented only within that limit, announced that law as 
 general j 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 con- 
 stant excess of temperature, 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 rapidly than they should do by New- 
 ton'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 vary- 
 ing position in the heavens, by which his rays strike upon the surface with different 
 inchnations, and, passing through the different thicknesses of atmosphere, undergo 
 absorption to a variable amount, the change of seasons as to temperature is pro- 
 duced ; and the alternation of vital activity and torpor which characterizes the ve- 
 getable world, and a great portion of the animal creation, is occasioned. Although 
 at the surface the temperature of the earth is solely dependant upon the radiating 
 power of the sun, yet it is found that it contains within itself a source of heat, which, 
 in ages excessively remote, must have retained the general mass of all 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 tem- 
 perature is in winter and in summer exactly the same. It is termed the stratum of 
 invariable temperature, and is in general of the mean temperature of the place ; that 
 is, the temperature of the surface falls in winter as much below that of the invari- 
 able 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 inward in virtue 
 of the conducting power of the ground ; and thus, each summer, a thin layer of ele- 
 vated temperature moves inward, those of successive summers being separated 
 from each other by the intervening colder shell, which marks the period of dimin- 
 ished heat in winter, until they mix and confound themselves in the layer of con- 
 stant temperature, below which the influence of the sun is felt no more. But, on 
 descending beyond this depth, the temperature steadily increases, and, although 
 subject to irregularities consequent on the different conducting powers of the rocks 
 of different countries, 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 would 
 
 o 
 
106 PROPERTIES OF ELECTRICITY. 
 
 be subjected: at four miles' depth tin and bismuth would naturally be liijuid"; ana 
 at five miles, lead. At a depth of thirty miles the temperature would be so high as 
 10 melt iron ; and still more easily, almost without exception, the rocks, which con- 
 stitute the solid earth which we inhabit. The central heat, therefore, although in- 
 sensible at the surface, is still, there is every reason to believe, in violent activity 
 at a small depth below : we hve upon a pellicle of sohd crystalline rocks, with which 
 the melted mass has become skinned over, and which extends but to y|^^ of the 
 distance to the centre. Hence we can well imagine, that in many places where 
 orifices or cracks in this sohd crust might form, violent manifestations of the inter- 
 nal fire should be produced, and the magnificent phenomena of volcanoes and 
 earthquakes should thus arise. 
 
 For artificial purposes, the source of heat is generally chemical combination. 
 The details of this mode of generating heat will require to be carefully and minutely 
 considfered hereafter, under the heads of Combustion, and the Relations of Heat to 
 Chemical Affinity. By mechanical 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 before and after the mechanical action ; and hence, although once considered 
 as influencing our ideas of the nature of heat, do not now require 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 dis- 
 cussed 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 de 
 scription of this interesting and important agent we shall now proceed. 
 
 CHAPTER IV. 
 
 OF ELECTEICITY CONSIDERED AS CHARACTERIZING CHEMICAL SUBSTANCES. 
 
 Among the various forces which concur to the production of nat- 
 ural 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 phi- 
 losophers 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, nor to attempt the detailed discussion of their causes ; as for a complete 
 examination of the subject, it must be considered as one, and certainly not one of 
 the least extensive branches of natural philosophy ; it is only with regard to the in 
 fluence which electricity exercises in the operations and the theory of chemistry, 
 and the means which the electrical properties of bodies afford for their recognition, 
 that it requires notice here ; and hence, although it is necessary to describe the pe- 
 culiar origin and characters of each form which electricity 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 
 properties of which we have to learn ; and in a future place the influence which it 
 exercises upon chemical affinity, and the opinions which have been advanced con- 
 cerning its relation to purely chemical forces, shall be carefully discussed. 
 
 Of the true nature of electricity nothing is positively known ; 
 whether it be a mere property of matter like attraction or cohesion, a 
 mere force acting independently of all interposed material, or wheth- 
 er, like light, it consists in the undulations of an ethereal medium fill- 
 
NATURE OF ELECTRICITY. 107 
 
 ing space, cannot be determined. Indeed, the ordinary views of its 
 nature consist in supposing the existence of one or of two fluids of 
 electricity, of exceeding tenuity and of perfect elasticity j and that, 
 according as ordinary bodies were supposed to contain more or less 
 of these fluids of electricity, they acquired or lost the properties of 
 electrical excitation. Of these opinions it is exceedingly diflicult 
 vO say which is the more reasonable or more consonant to experi- 
 mental truth, so far as the explanation 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 sep- 
 arated from the ordinary particles of matter, of which it appears 
 always as an additional property assumed under peculiar circumstan- 
 ces, 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 par- 
 ticles 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, although 
 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 ordi- 
 nary bodies, without being considered as at all believing in its actual 
 existence. 
 
 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 
 motion ; and the science of electricity may be thus divided into 
 electrodynamics and electrostatics. The electricity generated by 
 friction, or by change of state of aggregation, is ranked under the 
 latter head ; while the effects of electricity in motion are found to 
 include the phenomena of magnetism, of galvanism, and their rela- 
 tions to each other, electro-magnetism and magneto-electricity, and 
 also those of the electricity produced by a change of temperature in 
 bodies. Under these heads, therefore, the subject will be treated of 
 at present. 
 
 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 
 employed, 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 will become manifest ; and in the dark, the surface 
 of the glass rod will 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 
 approaching 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 
 
108 ELECTRICITY PRODUCED BY FRICTION. 
 
 will suddenly spring towards the rod, and be- 
 come attached to it for a moment ; after 
 which they will spring from it, and fall away 
 with equal power, assuming the positions of 
 I the dotted lines. The rod which has acquired 
 \ these properties is said to have been electri- 
 k fied by friction with the silk handkerchief j it 
 has become excited, and the phenomena pro- 
 duced are known j the phosphorescent appear- 
 ance, as the electrical light j the motion to 
 and from the rod by the light bodies, as elec- 
 trical 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 phenom- 
 ena may be produced ; two pieces of silk, by their mutual friction, 
 become electric also, particularly if they be of different colours ; 
 thus, on laying flat together slips of black and of white riband, 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 similar- 
 ly excited. Sulphur and amber, in which last, indeed, the property 
 was first discovered, and from the Greek name of which, 7]XeKTpov^ 
 the science electricity has its name, assume this excited state with 
 remarkable facility and power. 
 
 It is not every substance which may be thus electrified by fric- 
 tion, and even the same substance may often become incapable of 
 being excited ; thus, if the silk or flannel be not completely dry, 
 if the glass rod be damp, no elebtric properties can be conferred 
 upon them. But it matters not how much care we use in drying a 
 metallic surface which rests upon the ground, or which we support 
 by the hand, it cannot be electrically excited by any amount of fric- 
 tion. Such a body is termed a non-electric ; dry glass, resin, sul- 
 phur, 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 appara- 
 tus 5 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 
 
RELATIVE CONDUCTING POWERS. 109 
 
 retained in its elastic form upon their surface, and produces all the 
 effects of excitation. They are electrics because they are non-con- 
 ductors 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-conducting 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-con- 
 ductor of electricity, and by rubbing a stick of ice it becomes ex- 
 cited ; but it must not melt upon the surface, for liquid water, al- 
 though inferior to the metals in conducting power, is yet so excel- 
 lent a conductor, that it allows the electricity which we might de- 
 velop to pass totally away. Hence the necessity of drying care- 
 fully 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 as- 
 certained with accuracy enough to justify their being expressed in 
 numbers, at least for the non-metallic bodies. The general order 
 appears to be, commencing with the best insulators or worst con- 
 ductors : 
 
 Strong acids. 
 Fused saline bodies. 
 Charcoal. 
 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, 
 becomes heated in proportion to the resistance offered to the motion 
 of the electricity, and therefore the rise of temperature is inversely 
 proportional to the conducting power. By such experiments Harris 
 found that, with 
 
 Dry air. 
 
 Glass. 
 
 Shell-lac. 
 
 Spermaceti. 
 
 Resins. 
 
 Damp organic bodies 
 
 Oil of turpentine. 
 
 Damp air. 
 
 Sulphur. 
 
 Water. 
 
 Silver . . . 
 
 The Heat 
 evolved. 
 
 . . . 6 . . . 
 
 The conduct 
 JDg Power. 
 
 . ... 120 
 
 Copper . . . 
 Gold . . . . 
 
 . . . 6 . . . 
 . . . 9 , . . 
 
 , ... 120 
 . ... 80 
 
 Zinc . . . . 
 
 . . . 18 . . . 
 
 . ... 40 
 
 Platinum . . 
 Iron .... 
 
 . . . 30 . . . 
 . . . 30 . . . 
 
 . ... 24 
 .... 24 
 
 Tin . . . . 
 
 . . . 36 . . . 
 
 .... 20 
 
 Lead . . . . 
 
 . . . 72 . . . 
 
 . ... 12 
 
 These numbers are merely comparative, and can only be looked 
 upon as approximations. 
 
 The difference of the conducting power explains the fact that, 
 when 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 ex- 
 
110 DISTRIBUTION OF ELECTRICITY. 
 
 tensive 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 inter- 
 val filled by any non-conducting matter. 
 
 The rapidity with which the electric impulse is propagated has 
 been examined by Wheatstone in a very ingenious manner, the de- 
 tails of which could not be well introduced here, but which enabled 
 him to determine an interval of the xs 2V¥o- ^^ ^ 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 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 constantly to break away and pass to other bodies which 
 are not excited. It thus passing through air produces the electric 
 spark, and is accompanied 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 electricity to pass away will be quad- 
 rupled, 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 appa- 
 ratus 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 diffu- 
 sed over the whole external surface ; and if the hemispheres be sud- 
 denly removed by means of the handles, the globe A will remain total- 
 ly 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 j 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 everywhere of equal thickness, but in an elongated body 
 
OPPOSITE CONDITIONS OF EXCITATION, 111 
 
 it accumulates more at the extremities of the longest axis. Hence 
 on a wire or a needle, the electricity is accumulated almost exclu- 
 sively 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. Hence electrical apparatus should be completely 
 smooth except where a point or projection is intentionally attached, 
 and many remarkable experiments 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 the attraction of the light bodies, which 
 demonstrates its excited state, by concentrating 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, will be hereafter 
 fully noticed ; at present it is sufficient to refer it to the thickness 
 and high elasticity of the layer of electric fluid which forms upon 
 them. 
 
 It has been already stated that, when two slips of silk riband are 
 excited by rubbing against each other, the electricity appeared to be 
 equally evolved upon each. This occurs in all cases of excitation 
 by means of friction. Thus, when silk and glass are rubbed together, 
 the silk acquires as much electricity as the glass, but by the silk 
 being held in the hand, the electricity escapes by the dampness which 
 is always present, and is lost. If, however, the silk be insulated ; 
 if a disk of dry wood covered 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 light bodies, the odour and the phospho- 
 rescence 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 difference between the two condi- 
 tions : 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 remarkable evidence of ten- 
 sion, giving sparks and shocks ; but when combined, 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 called into 
 existence. The states of the two bodies are therefore so far op- 
 posed 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 suspended 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 man- 
 aging the distance, perfectly at rest. If there be the glass alone, it instantly at- 
 tracts 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 have been sufficient, and for this purpose the gold-leaf 
 4cctroscope is best adapted : deferring the description of its principle to another 
 
112 ELECTRICAL ATTRACTIONS AND REPULSIONS. 
 
 place, I shall here only notice its construction and the indications 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 in- 
 side of the glass, and rising so far that the gold leaves, on open- 
 ing out, may come into contact with them. When this occurs 
 there is evidently a free conducting medium from the upper me- 
 tallic 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 exci- 
 ted body, the gold leaves diverge, and remain so, in the position of the figure, as 
 long as the excited body be kept near. 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 act- 
 ing 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 together, the gold leaves remain quiescent. If 
 -they be made to separate by the influence of the glass, and the excited silk be then 
 slowly approximated, 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 neutrahzed 
 condition, the leaves diverge, from that remaining 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 con- 
 ditions of two bodies rubbed by a third, as if a glass be rubbed with silk, and an in- 
 sulated metal rod be 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 will assume op- 
 posite 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 ex- 
 citation 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 of 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 farther 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 bring near it an excited body, the cylinder is at- 
 tracted, 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 mutually 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 cyhnder which has been, as above described, re- 
 pelled 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 
 iwwerful than if the body had previously been neutral. If two such gilt paper cyl- 
 inders be touched, both vi'ith 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 excita- 
 tion neutralize each other, and they become inactive. 
 
 When bodies are rubbed together, therefore, they become elec- 
 tric, and with such properties, that while each when separate gives 
 signs of powerful excitation, together they destroy each other's 
 power. Bodies when thus oppositely electrified attract each other j 
 
LAW OF ELECTRICAL ATTRACTIONS. 
 
 113 
 
 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 gravitation, diminishes in intensity ac- 
 cording 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 electrometer. The gold-leaf appara- 
 tus, though ex;ceedingly sensible 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. From the top of this tube is hung, by 
 a fine thread of glass or of cocoon silk, a very light wooden beam, 
 c, 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 counterpoise, 
 and by its 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, d, 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 car- 
 rying ball, to an excited body, we charge it with electricity, and, 
 having inserted it in the aperture, it touches the ball of the bal- 
 ance, which is immediately repelled : in moving away, this twists 
 the thread by which it is suspended, and the amount of the twisting which is ne- 
 cessary in the opposite direction to bring it back again, ^d maintain it at a certain 
 distance, measures the force of repulsion the balls then exercise. This measure- 
 ment 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 de- 
 gi-ees 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 distribu- 
 tion of electricity on bodies, its accumulation on and escape from points, that have 
 been noticed, might be deduced. 
 
 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 re- 
 lated 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 consideration 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 exist 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, accord- 
 ing 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 contains 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 togethd^, the re- 
 
114 THEORIES OF ELECTRICITY. 
 
 suit is, that one electric fluid accumulates in excess upon the olie, 
 and the other upon the other body. They are thus both brought 
 into a state of excitation ; and as the excess of the one fluid musi 
 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 language of Du- 
 fay, 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 consequence of the necessity of accompanying these flu- 
 ids in their action on each other. Hence the electric attractions 
 and repulsions which manifest themselves in all cases of excitation, 
 and hence the bodies return to their indiflMerent condition as soon 
 as the excess of electricity they contain is neutralized. It was for 
 a long time supposed that the atmosphere, by its mechanical press- 
 ure, assisted in retaining the free electricities upon the surface of 
 the excited bodies ; but this is not the case. The air acts as an in- 
 sulator 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 as- 
 sumed to exist but one electric fluid, of which, in its ordinary state, 
 every substance contains a certain quantity. This fluid is consid- 
 ered to be highly elastic, to repel its own particles with a force 
 varying as the inverse square of the distance, and to attract the par- 
 ticles 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 ordinarily attribute to it. 
 But when two such bodies are rubbed together, a quantity of elec- 
 tricity 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 ori- 
 ginal ordinary state. The excitation being produced, according to 
 this view, by one body having electricity in excess, while 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 -f- and — are often used as abbre- 
 viations for these words. 
 
 The particles of the electric fluid being mutually repulsive, and at- 
 tracting those of matter, it is natural that two bodies having elec- 
 tricity in excess shall mutually repel, and that a body having an 
 excess of electricity shall attract one having an excess of matter. 
 Bodies both -\- therefore repel, a + and a — body attract each other. 
 But, to ^explain the mutual repulsion of bodies both in the negative 
 
ELECTRICAL MACHINES. 
 
 115 
 
 condition, an assumption is required which at first sight appears to 
 militate considerably against our reason j for as it is matter which 
 is in excess in that condition, Ave 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 con- 
 tains its natural quantity of electricity j and it affords no grounds 
 for supposing that, if matter were deprived of that natural electri- 
 city, it would 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 phenom- 
 ena as that of the two fluids before described. 
 
 Already, indeed, considerable progress has been made towards a theory of elec- 
 tricity upon this idea. In order to account for the ordinary 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, ac- 
 cording as the distance between the particles is made to vary ; and Mosotti has 
 shown that it is only necessary to assume that the mutual repulsion of matter, 
 wlien 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 neces- 
 sary 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 ac- 
 ceptation. 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 words positive and negative 
 fluids in place of vitreous and resinous ; 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 dis- 
 cussion of the principles of electricity which yet remain, it is ne- 
 cessary to notice the construction of some electrical apparatus, which 
 is employed in all ca- 
 ses where it is desira- 
 ble 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 mod- 
 ification of the glass 
 tube which, by fric- 
 tion with a piece of 
 silk, evolved the elec- 
 tricity in the first ex- 
 periments described. 
 It consists of a glass 
 having such a form 
 as to expose a great 
 extent of surface, and 
 generally being used 
 in the shape of a cyl- 
 
116 
 
 ELECTRIJAL MACHINES. 
 
 inder, A, or of a plate. There are hence the cylinder and the plate 
 machines. To produce the friction, an elastic rubber, B, is covered 
 with silk, and made to press against the surface of the glass accord- 
 ing as the plate or cylinder is turned round by means of the handle. 
 The rubber being generally insulated, 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 diftused upon the glass passes from its sur- 
 face to that of a brass cylin- 
 der, termed the prime con- 
 ductor, C, being collected by 
 means of a series of pointed 
 wires, which graze the sur- 
 face of the cylinder accord- 
 ing as it is turned round. The 
 prime conductor is also insu- 
 lated ; and in the case of a 
 cylinder machine, the glass 
 itself is often supported upon 
 insulating pillars, by which 
 the loss of electricity is pre- 
 vented. To increase the en- 
 ergy 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 con- 
 duct the electricity to the points, and prevent its being carried away 
 by the air. 
 
 Although I shall have occasion, when we have examined the rel- 
 ative action of excited bodies and conductors somewhat better, to 
 notice the true theory of the prime conductor, yet for the present it 
 may be considered 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 in- 
 tensely 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 a peculiar phosphorescent odour. To prevent 
 this recombination, which would, of course, render accumulation up- 
 on the prime conductor impossible, the rubber, when the machine is 
 required for active work, is 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. 
 
PHENOMENA OF THE ELECTRICAL MACHINE. 117 
 
 By means of a machine of such construction, the opposing prop- 
 erties of the electricities of the bodies rubbed together may be sim- 
 ply and completely shown. 
 
 The degree of excitation of the prime conductor is generally, 
 though not very accurately, shown by means of the quad- 
 rant 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, as in the figure. To this is attached 
 an ivory semicircular scale, of which a portion is graduated, 
 from whence the name ; on an axis at the centre of the 
 ivory 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 elec- 
 trical condition with it when the instrument is placed on the 
 prime conductor and the machine worked. The stem and the pith 
 ball then repel each other, and the ball being consequently set in mo- 
 tion 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 excitation. Now if, when this instru- 
 ment 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 excitation 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 devel- 
 oped on the rubber, and the two being evolved in equal quantities, 
 complete neutralization is produced. That bodies similarly electri- 
 fied 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 the prime conductor. 
 
 To prove on a large scale, by means of the machine, that the op- 
 posite electricities attract each other, it is only necessary to place 
 in connexion 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 oth 
 er 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, while 
 they move towards those oppositely excited. Numerous experi- 
 ments of an amusing kind, which it Avould 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, hy friction^ which is, indeed, the only 
 true direct excitation. 2d, by contact ; as when an insulated 
 brass disk excited by friction is touched to another, also insulated 
 and neutral, a spark passes between them at the moment previous 
 to actual contact, and the first is found to have divided its electri- 
 city with the second in proportion to its surface. In this case the 
 two bodies, after contact, are in the same state of excitation. 3d. 
 as where the prime conductor, which is neither itself rubbed, nor 
 
118 EXCITATION BY INDUCTION. 
 
 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 indicate a pow- 
 er of action and excitation even at considerable distances ; and this 
 mode, which results from the attraction and repulsion of the elec- 
 tric 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 hj 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 
 
 neutral, and having 
 their natural electri- 
 cities combined, and 
 distributed uniform- 
 ly over their surface. 
 ^^^If a globe, A, exci- 
 *^ ted, say with posi- 
 tive electricity., be brought near, it will attract the opposite electri- 
 city 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 re- 
 maining. The positively excited end of B influencing C in a cor- 
 responding way, brings it also into an excited state, and this com- 
 munication 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 be- 
 come 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 only the termination of the inductive action. 
 For suppose that A had 10 parts of + electricity, and that, by in- 
 duction, 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 destroy- 
 ing 4-5 of the body A, the two bodies should remain each with 
 -}-5, and thus the results of contact described already should be 
 produced. 
 
 The distance at which the combination of the electricities of the 
 inducing and the induced body may occur, depends upon the inten- 
 sity 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 proportion of the liberated fluid, as has been already de- 
 scribed, becomes accumulated, the fluid escapes from thence before 
 
THEORY OF THE GOLD LEAF ELECTROSCOPE. 119 
 
 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 de- 
 scribed as the power of points to gather and to disperse the elec- 
 tric fluid. If a pointed body be excited by friction, it induces an 
 opposite state in the particles of air by which it is surrounded, and 
 communicates to them, with great rapidity, the charge which it had 
 received. The prime conductor of the machine, being insulated, 
 has its electricities separated by the inductive action of the excited 
 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 -j- to the air as fast as the oth- 
 er points give the — to the glass ; a point held near the prime con- 
 ductor also prevents its excitation, by giving to it by induction — 
 electricity as fast as it obtains -j- electricity from the glass of the 
 machine. 
 
 In all these cases of induction where the electricities attract and 
 repel 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 ex- 
 plained upon this principle. The variety of dancing figures, ring- 
 ing bells, revolving wheels, afli-ighted heads, and so on, that are ex- 
 hibited in popular lectures on this subject, 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 Bennet's gold leaf electrometer, with which some of the most 
 important principles of statical electricity are demonstrated, 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 
 diverge. If the exciting body be -4-, it is the -{- fluid by which the instrument ap- 
 pears affected ; if it be — , the leaves diverge from the presence of — electricity. 
 Hence if, when it is under the influence of a glass rod rubbed with silk, a stick of 
 seahng-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 negative electricity as there had been positive brought into action by the 
 glass, and hence the gold leaves coming into their natural and indifferent 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 diver- 
 gence increases, indicating the superaddition of electricity of the same aame from 
 the inducing power of the resin. 
 
 If, as in the figure (page 118), the cylinder C be connected with the ground by 
 means of a wire or a wetted thread, D, the positive electricity 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 
 returns 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 
 
120 CONSTRUCTION OF THE LEYDEN JAR. 
 
 the removal of the wire or thread, the body C cannot get its positive electricity back, 
 and hence remains in a state of negative excitation. In this manner a substance 
 may, by induction, be made to receive a permanent charge. This is often useful in 
 experiments with the electroscope, and the manipulation to charge it permanently is 
 as follows : If it be desired to charge it positively, an excited stick of resin is held 
 near, and the cap of the electroscope is touched with the finger. The negative elec- 
 tricity then escapes by the hand into the ground, and the positive electricity, accu- 
 mulating 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 the charge of the leaves is temporary, 
 its electricity is the same as that of the exciting body ; but where the charge is per- 
 manent, the electricity 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 charge, by secondary inductive action, various forms of the electroscope have been 
 contrived for rendering it more sensible, and are described in special treatises on 
 electricity under the name of DouUcrs 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 farther consideration. 
 
 One of the most interesting instruments in statical electricity, 
 founded on the principle of induction, is the Ley den Jai\ so called 
 from the city where its construction was discovered. 
 It consists of a glass hottle, 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 cork stopper, 
 through which passes a stout wire, touching at the bot- 
 tom 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 de- 
 gree. This, then, reacting by induction upon the electricities of the 
 external coating, separates them, attracting the negative to the side 
 next the glass, repelling the positive to the outer side. The posi- 
 tion becomes, therefore, -|- — + j and when the + fluid inside 
 makes up by its greater quantity for the thickness of the ^ass 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 j and the electricities 
 of the external coating, although separated 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 posi- 
 tive escapes and the negative remains behind, held by the attraction 
 across the glass to the positive fluid inside. New quantities of pos- 
 itive electricity entering continually from the machine, the accu- 
 mulation of negative electricity on the outer coating proceeds, un- 
 til the 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 discharges itself. To discharge a jar in which the elec- 
 
ELECTROPHORUS OF VOLT A. 121 
 
 tricities 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 quantities of electricity in large jars or 
 in sets of jars (electrical batteries), the most beautiful and remark- 
 able phenomena of electrical force may be exhibited. 
 
 The principle of the construction of the Leyden jar may be ex- 
 perimentally 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 accumu- 
 late upon its outer surface, the other shall be dissipated on the ground. 
 Second, a light body placed between two balls, connected, one with 
 the internal, and one with the external coating, is alternately attract- 
 ed 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 applying the knob of a second 
 jar which is not insulated to its outer surface ; 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 capa- 
 ble 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 electrophorus of Volta. It con- 
 sists of a flat cake of resin, &, which is generally spread on a circu- 
 lar 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 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 knob. The resin- 
 ous 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 negative electricity j 
 of this passes, then, into the ground, and the positive 
 accumulates on the surface next the resin, of which 
 it, by induction, increases the negative charge. This new portion 
 of negative fluid decomposes 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 obtain- 
 ed from it 3 the instrument may be repeatedly charged and dischar- 
 
122 TRANSMISSION BY INDUCTION. 
 
 ged in a few minutes, and retains its charge better than the electrify- 
 ing machine. 
 
 This inductive action of electricity would at first appear to be 
 exercised 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 5 but a more exact 
 ■ examination shows that this is not the case. The substances inter 
 posed in the path of the inductive action are necessary to its trans- 
 mission, and modify, by their nature, its direction and amount ; and 
 it is, indeed, only from molecule to molecule of any substance, gas- 
 eous 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 
 turpentine, 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 be- 
 comes excited by induction. 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. 118) j and attaching themselves 
 mutually by their extremities, they transmit the electricity of the 
 machine, by a series of decompositions, to the ball which is con- 
 nected with the ground. If the excitation be very violent, the at- 
 tractions and repulsions become too strong to be regularly trans- 
 mitted; and this induction is accompanied by a powerful current 
 of the particles of the oil from the first ball to the second. The 
 particles immediately in contact with the directly excited ball ac- 
 quire its state, and, being repelled, immediately pass off' to that which 
 has obtained, by induction, the opposite condition, and there become 
 neutralized. Now what here occurs with the oil of turpentine takes 
 place in ordinary induction with the air ; every molecule of it inter- 
 posed between the solid bodies becomes itself subjected to the in- 
 ductive action, and forms a chain of alternate positive and negative 
 poles, by which the efi^ect may be transmitted to any distance. If 
 t'he excitation be very great, the neutralization may occur with vi- 
 olence and rapidity, and generate currents, as in the oil of turpen- 
 tine. 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 experi- 
 ments of revolving flies. A still more violent and rapid recomposi- 
 tion of the electricities of the air molecules, which had been sep- 
 arated 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 efl^ect- 
 ed in this manner, from particle to particle of the interposed sub- 
 stance, is beautifully shown in the results obtained by Faraday con- 
 cerning the influence of the nature of the medium on the amount 
 of inductive charge transmitted. The instrument, which he has 
 termed a.n inductometer, consists of a hollow sphere of brass, a a b, 
 and a sphere of smaller size, A, also of brass, which is placed exact- 
 
SPECIFIC INDUCTIVE CAPACITY. 
 
 123 
 
 ly concentric with it. The interval between 
 these, o, may be occupied by any substance, 
 as air, or glass, or sulphur ; and then the central 
 sphere being insulated from the outer by the 
 shell-lac column b, and having been excited from 
 +he machine through the ball and wire B, the 
 uter one is uninsulated, and the whole becomes 
 a Leyden jar, in which the material may be va- 
 ried at the will of the experimenter. By means 
 of the tube and stopcock / J, the air in o o may 
 be removed, and any other gas substituted for it. ^j 
 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 exci- 
 tation 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 molecular excitation was transmitted in proportion to these 
 numbers, which express, therefore, the degree of excitation that 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 constitution, even though the temperature and press- 
 ure do not remain the same, possessed the same specific inductive 
 capacity as air. 
 
 This principle is farther 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 them- a\ W 
 
 selves considered centres of inductive force. V / 
 
 Thus, if a cylinder, a, of shell-lac be excited by- 
 friction, and a brass hemisphere. A, placed on top 
 of it, the intensity of the induced electricity will 
 
 be found to depend not merely on the distance d 
 from the excited source and the nature of the 
 interposed material, but to be more energetic 
 in certain positions in the air, as when the car- 
 rier ball of Coulomb's torsion electrometer was 
 placed at o, than when it was lower or higher at 
 n or p. 
 
 Faraday has been led by his experiments to conclude that the 
 difference between conducting and non-conducting bodies is, that 
 the former assume with exceeding rapidity, under an inductive in- 
 fluence, this condition of molecular excitation, and hence appear to 
 
124 OTHER CAUSES OF STATICAL EXCITATION. 
 
 allow the electricity to pass actually and instantly through their 
 substance, whereas, in reality, it is only that the separation and re- 
 composition of the electricities of the chain of molecules has been 
 so accomplished. They lose also this condition as soon as the ex- 
 citing cause has been removed, 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 coat- 
 ings of a Leyden jar were connected by a metallic wire, the induct- 
 ive action would be propagated immediately across it j but the in- 
 stant that the source of the excitation was removed, the electrici- 
 ties of the two coatings would recombine, from the facility with 
 which the molecules of the wire can assume the inverse condition. 
 But with an interposed plate of glass the result is different ; the in- 
 ductive 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 coatings 
 may be removed, and yet the accumulated electricities be not dis- 
 turbed ; the tin foil serving only to discharge at the same moment 
 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 explains 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 investiga- 
 tions that the permanent excitation of an electrified body has its 
 origin also in the inductive influence of the bodies that are around. 
 
 The source of the electricity evolved by the electrical machine 
 cannot be considered as being positively known. Wollaston in- 
 stituted a series of experiments, by which it appeared to be demon- 
 strated that there was no electricity evolved except where chemical 
 combination took place, and the superior power given to the ma- 
 chine 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 propor- 
 tional only to the amount of friction, and was the same under va 
 rious circumstances of liability to the presence or absence of chem 
 ical action of the materials rubbed. It is therefore likely that, at 
 least, the electricity of the machine may be generated by the sim- 
 ple molecular derangement and vibration which friction necessarily 
 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 elec- 
 tricity may be produced. 
 
 In almost all cases where the particles of bodies are suddenly and violently dis- 
 arranged, 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 temperature causes a manifestation of electrical 
 
ATMOSPHERIC ELECTRICITY. ^ 125 
 
 polarity in a very remarkable degree ; thus, if a long prism of tourmaline be heater?, 
 one extremity becomes positive and the other negative ; when the temperature at- 
 tains its highest point and becomes stationary, all symptoms of electricity 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 par- 
 ticles, in the internal motion which the expanding force of heat produces in them, 
 acquired the same condition of polarity as they would have done by an external 
 friction. 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 
 which likewise become electric on being heated, as boracite, are exceptions to the 
 general law of crystalline symmetry, and in other respects, as with regard to light, 
 indicate a kind of structure which is very complex and peculiar. In such cases, an 
 internal friction by the action of expansion on the unsymmetrically situated mole- 
 cules 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 universahty 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 con 
 dition, or in the reverse order, from being solid or being gaseous becomes liquid, dis- 
 turbance 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 me- 
 tallic plate, the bodies after sohdification will be found excited. If a cup of watei 
 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 influ- 
 ence 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 mj»st 
 abundant sources of electricity ; for as at all ordinary temperatures evaporation 
 takes place from the surface of all the water of the globe, and the vapour produced, 
 carrying with it the prodigious quantity of positive electricity which is thus set free, 
 mixes with the air, our atmosphere is almost continually in an electrical condition, 
 generally 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 constitutes a mass of cloud, and 
 therein is thus concentrated all the electricity evolved by evaporation at the sur- 
 face. The clouds are, therefore, intensely electric ; and when attracted by indue 
 tion 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, while the report, 
 re-echoed from the surfaces of the remaining clouds, or by the sides of the adja- 
 cent 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 combination 
 and decomposition electricity in its statical form may be evolved ; thus Pouillet 
 proved decisively, that when charcoal is burned, the carbonic acid which passes ofT 
 is in a state of positive excitement, and the residual mass of charcoal becomes neg- 
 atively charged. When hydrogen burns in air, the vapour of water carries off the 
 positive electricity, while the negative fluid distributes itself on the hydrogen re- 
 maining, 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 complex 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 im- 
 bedded becomes negative. It would appear, however, that frequently electricity 
 that had been imagined to arise from the chemical relation of the bodies brought 
 into contact, arose from their merely mechanical action on each other ; thus the 
 electricities produced by sifting lime and oxalic acid together on the plate of the 
 electrometer are produced. 
 
 The mere contact of bodies has been supposed sufficient to evolve electricity upon 
 
126 DYNAMICAL ELECTRICITY. 
 
 their surface. The trace of excitation in such experiments is so small, and dimin- 
 ishes 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 ; while it is only with difficulty that we can obtain, by means 
 of it, the slightest chemical decomposition. In the language of the theory of elec- 
 trical fluids, the electricity is developed in exceedingly small quantities by friction 
 or change of aggregation, and hence can perform but feebly such offices as chemi- 
 cal decomposition, which depend on the quantity that passes in a given time ; but 
 this small quantity is gifted with immense tension ; the few molecules which be- 
 come polarized are so to an intense degree, and the attractive 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 
 circulating form, so that its properties shall result from its uninter- 
 rupted motion, must necessarily consist in arrangements from which 
 all insulating substances are to be carefully excluded. In statical 
 electricity, the connexion, by a conducting medium, of the opposite 
 extremities of an inductively excited body, caused all electrical in- 
 dications instantly to disappear, while that kind of connexion is ab- 
 solutely necessary to the continuous flowing of the electricity which 
 constitutes its dynamical condition ; 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 stat- 
 ical condition. 
 
 1st. Electricity thus circulating through conductors is found 
 naturally existing in those substances which thereby possess mag- 
 netic 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. 2d. When any closed conducting 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 ob- 
 stacle is greatest to that part where it is least. 3d. When sub- 
 stances capable of mutual chemical combination or decomposition 
 act on one another, there is a current of electricity produced. In 
 the case of simple union or double decomposition, the circle is in- 
 ternally closed, like that of a steel magnet ; but where there is sim- 
 ple decomposition or replacement, the current may be directed 
 through any kind of circuit ; and thus constituting the most impor- 
 tant branch of dynamical electricity, is called Galvanism or Voltaism, 
 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 transmit- 
 ting a current of electricity across even imperfect conductors, and 
 employ, instinctively, the efl^ect of this current upon the living 
 frame of smaller animals in order to obtain them for food. The 
 
GALVANIC ELECTRICITY. 127 
 
 identity of the electricity from this animal origin, with the fluid of 
 the other dynamic sources, has been completely proved, particular 
 ly by Faraday j and as the question of the anatomical 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 ihat will be described as characterizing galvanic 
 electricity of very high tension, and allude no farther to it. 
 
 To the chemist, the electricity of the Galvanic or Voltaic battery 
 is the most interesting of all the forms which this agent may as- 
 sume, from the intimate relation which exists between it and the 
 force by which the elements of bodies are bound together in chem- 
 ical combination. To it, therefore, I shall especially direct atten- 
 tion, and consider the remaining sources only so far as the electri- 
 city 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 has been described. 
 
 Galvanic Electricity, — The manner in which this form of excita- 
 tion 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 appearance of electrical disturbance 5 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 uninterruptedly supplied, while 
 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 which 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 described. We may suppose, simply, that the 
 chemical relations of the zinc and muriatic acid are such, that when 
 placed in contact they mutually induce on each other a development 
 of electricity : that part of the zinc which is immersed becoming -}-, 
 and that out of the acid — , while the molecules of the acid near the 
 zinc become - — , and the general mass of the fluid obtains -\- excita- 
 tion ; the + electricity of the zinc being, however, balanced between 
 the fluids of its own mass and of the acid, and the — fluid 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 apparptus being in the condition of a very feebly 
 charged Leyden jar : and on applying the slip of copper by which 
 
 tk 
 
128 
 
 SIMPLE GALVANIC CIRCLES. 
 
 the excited surfaces, the zinc and acid, are placed in communication, 
 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 cop- 
 per to produce neutralization j 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 positively to the body which is neg 
 atively 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 copper in the acid under- 
 neath. At every moment, according as the neutral 
 ization of the electricities is effected, the system is 
 competent to generate new quantities, and hence the 
 analogy of the weakly-charged Leyden jar, noticed above, does not 
 completely hold ; for, to be accurate, it would require the jar to pos- 
 sess a power of charging itself as rapidly as it could be discharged 
 The passage of the current is accompanied by the solution of tho 
 zinc and the liberation of the hydrogen. This hydrogen accompa 
 nies the positively electrified molecules of the acid across the fluid, 
 «ind is discharged under the form of gas upon the surface of the 
 copper plate. 
 
 The essential elements of an arrangement by which a current of 
 electricity 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 conduct- 
 or was a slip of copper ; but it may be of any form, or 
 almost any substance 5 thus, as in the figure, a wire 
 may be soldered to the end of each slip, and on bring- 
 ing 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 circle. 
 It is not even necessary that the conductor should be solid or me- 
 tallic ; it is, indeed, only for convenience that the ordinary conduct- 
 ing plates and wires are metallic. Thus, in the figure, 
 A Z W, a plate of zinc is in contact on the one side witk 
 muriatic acid, A, and on the other with water, W, to 
 which a better conducting power has been given by dis- 
 solving in it a little common salt. The current is then es- 
 tablished, being from the conductor to the zinc, and from 
 the zinc to the acid, precisely as in the former instances. 
 The passage of the current under these various circumstances 
 may be shown, and also that, for its origin and transfer, metallic 
 communication 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 
 
 f 
 
 Z 
 
 ^ 
 
 
 
 
 A. 
 
 
 
GALVANIC AND CHEMICAL ACTION. 
 
 129 
 
 n. 
 
 f^^\ 
 
 \l 
 
 a bit of paper moistened with iodide of potassium be laid 
 upon it, and the wire from A be then brought to touch the k 
 upper surface of the moistened paper, the current passes in A 
 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, it will be found to be 
 alkaline, 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 chem- 
 ical action which is produced at the period of its passage, and on 
 this principle is founded one of the most cogent and reasonable ar- 
 guments in favour of the idea that the current is produced by the 
 chemical decomposition, 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 immersed in a strong solution of am- 
 monia, which acts upon the copper, but not upon the iron, the cur- 
 rent is produced in the reverse direction. If persulphuret of lime, 
 dissolved in water, be used as the exciting fluid with iron and cop- 
 per, the current is from the copper to the iron through the fluid ; 
 but on using zinc and copper with the same fluid, the direction 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 es- 
 caped action, and the current would 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 
 chemical action is of the most intimate nature possible ; the one, as 
 Faraday and others have decisively shown, cannot exist in such ar- 
 rangements without the other, and the nature and tendencies of one 
 determine 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 ; tlie 
 current through the fluid is, of course, in the opposite direction. The metals ar- 
 range 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 
 
 Strong Nitric 
 
 Muriatic Acid. 
 
 Soiuiinn of 
 
 Yellow Hydrosul- 
 
 Acid. 
 
 Acid. 
 
 
 Caustic Potash. 
 
 phuret of Hotassiuii:. 
 
 Platinum. 
 
 Platinum. 
 
 Platinum. 
 
 Platinum. 
 
 Platinum. 
 
 Silver. 
 
 Nickel. 
 
 Antimony. 
 
 Silver. 
 
 Iron. 
 
 Copper. 
 
 Silver. 
 
 Silver. 
 
 Nickel. 
 
 Nickel. 
 
 Antimony. 
 
 Antimony. 
 
 Nickel. 
 
 Copper. 
 
 Bismuth. 
 
 Bismuth. 
 
 Copper. 
 
 Bismuth. 
 
 Iron. 
 
 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. 
 
 R 
 
130 PRINCIPLE OF ELECTROTYPE COPYING. 
 
 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 upper 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 
 antimony and zinc, and with persulphuret of potassium with iron and zinc. 
 
 If the metals in contact with the exciting hquid be such as that one is totally 
 without chemical action on it, it serves only as a means of mechanically transmit- 
 ting 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, then 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 hquid, 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 cun-ent, wtiile with dilute acids, which act very differently 
 on each, the current is very powerful ; and thus platinum, which is inattackable by 
 ahnost all liquids, forms the best possible element in every instance. 
 
 The metal which is used as the conducting medium conducts by having its natu- 
 ral polarity inverted ; and hence, in place of a disposition to combine with the oxy- 
 gen 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 protect- 
 ing the copper sheathing of ships, by attaching small portions of iron of about j^ 
 of the surface ; the chlorine of the salt in the sea-water being thus transferred to 
 the iron, and the copper, in place of becoming covered with the green rust of 
 oxychloride 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, lime and magnesia, were depos- 
 ited 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 materially to in- 
 jure their saihng powers. The process at present so extensively employed, of fix- 
 ing a layer of zinc upon iron surfaces, acts in protecting them from rust in the 
 same manner. 
 
 This transfer of the elemeitts of the exciting liquids has become recently, in the 
 hands of Spencer, the basis of one of the most beautiful and important of the ap- 
 plications of science to the arts. If one of the exciting liquids be a solution of sul- 
 phate of copper, as in Daniell's battery (page 136), the metallic copper which sep- 
 arates 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 homogeneous as the best hammered copper. 
 Any prominences or depressions, even a scratch of a pin, drawn on the plate on 
 which the deposite forms, are accurately represented on its internal surface : and ii 
 IS only necessary to use as the negative metallic element a medal in relievo or in- 
 tagho, to reproduce, with an accuracy equalling the powers of the most finished 
 hand or machine, the finest w^orks of art. This principle has been shown by Mr. 
 Spencer to be applicable to the copying of all varieties of designs, and 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 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 powerful 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 
 
COMPOUND VOLTAIC CIRCLE 
 
 131 
 
 great source of failure and uncertainty in our experiments, inter- 
 cepts 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 becoming evi 
 dent j and yet the disproportion in quantity between the fluid, which 
 bursts through the strongest insulating bonds of our apparatus, 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, the im- 
 mersion 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 di- 
 lute sulphuric acid for three seconds, gave as much electricity as 
 could be generated by thirty turns of the most powerful machine 
 of the Royal Institution. Indeed, Faraday has shown that, in the 
 current which passes during the decomposition of a grain of water, 
 there is contained more electricity than in the brightest flash of 
 lightning. 
 
 If the metallic elements of a simple circle be connected, not di- 
 rectly by metallic contact or by a wire, but by means of one or more 
 other similar simple circles, interposed in the course of the current o 
 its electricity, it is not at all interfered with, but the quantity of elec- 
 tricity which circulates is precisely equal to what is generated by 
 the chemical action Avhich takes place in each cell. For, consider- 
 ing the circle of four cells, represented in the figure, consisting of 
 
 copper and zinc plates, 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, 6, and c, and it is only the amount of elec- 
 tricity liberated upon the copper and zinc plates in the terminal 
 cells that passes along the wires, and, recombining at d, produces 
 the phenomenon of the current ; but this is the same quantity as 
 should be evolved by any one of these simple cells by itself, and 
 hence the remarkable result, which has been fully demonstrated 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 ip. all the cells, there 
 passes little more electricity than what is generated where the de- 
 composition is least active ; for, as the excess would have to pen- 
 etrate through the liquid conductor in all the cells, the obstacle af- 
 forded to its progress is so great that it is almost totally absorbed. 
 Although the increase in number of the elements ojf the galvanic 
 
182 RELATION OF INTENSITY AND QUANTITY. 
 
 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 no matter of what magnitude, it never can possess. 
 It has been seen, that by the state of mutual excitation into which the 
 zinc and acid are thrown before the circuit is compileted, the inten- 
 sity of the evolved fluids is limited to that which will 
 not suffice to enable the excited particles of acid to dis- 
 charge themselves upon the oppositely excited particles 
 of zinc j for if this discharge occurred, all should be 
 brought back to the neutral condition. Now, if there be 
 interposed a second cell, containing an equal quantity of 
 the same liquid as the first, its particles must be brought into an 
 equally excited state before discharge can occur ; and as the elec- 
 tricity has then to pass through a bad conductor of double the 
 length, it will require much greater intensity to penetrate it. The 
 process, in virtue of which, therefore, the electric equilibrium is in 
 the first instance disturbed, continues, even before contact is made, 
 until the intensity accumulated is sufficient to propel the current 
 across the interposed retarding liquid, and is hence proportional 
 to the number of cells, or, as it is usually stated, to the number of 
 pairs of plates. The peculiar character of intensity may be suppo- 
 sed to arise, also, from the electricity generated by the outside 
 plates obtaining additional velocity, in passing across the intermedi- 
 ate cells, in each of which it meets an equal quantity of fluid moving 
 in the same direction, and Wiose motion it absorbs, restoring them 
 to rest, and being thereby hurried itself onward in proportion. 
 
 1^6 intensity of the electricity which is thus excited is very slight, even where 
 the number of combinations is considerable ; thus, it requires a series of at least 
 300 pairs of plates, four inches square, immersed in dilute sulphuric acid, to cause a 
 sensible divergence of the gold leaves of the most delicate electroscope. It is only 
 where the arrangement involves some thousands of couples that electricity is 
 evolved 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 recognised ; to obtain 
 these effects also, the circuit must be broken, for even with the most powerful com- 
 binations the current of electricity is without any action of intensity. Where, how- 
 ever, 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, are exceedingly minute. This is exemplified 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 ap- 
 parent 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 tvventy thousand, 
 
 care being taken to turn all the gilt surfaces 
 the same way. These are enclosed in a glass 
 tube, and terminated at each end by a brass 
 cap with a pressure screw. The paper con- 
 taining 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 recom 
 bination through the disks internally, and by 
 the atmospheric air outside, attains a degree 
 of intensity so high that it acts decidedly upon 
 the electroscope, as shown in the figure, and 
 is amusingly applied to produce various at- 
 tractive and repulsive motions, such as ringing 
 
volta's theory of contact. 133 
 
 bell->, (Si-o. ; for there being a continual source of electricity in the action of the 
 moisture of the paper on the zinc, these phenomena 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 before 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 extrem- 
 ities, and vanishing at the centre where these last are equal, precisely as there ex- 
 ists 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 dissipated, 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 consequences 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 Voltaic 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 subsequent improvement 
 in the domain of electricity, for without its agency it is hard to see how the steps 
 which followed could have been made. 
 
 The form in which the Voltaic pile was first constructed was sim- 
 ilar to that of the dry pile noticed above. The disks were of zinc 
 and silver 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 common cloth, 
 which were interposed between 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 afiects 
 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 131 ; for 
 the outer copper plate at the one end, and the outer zinc plate at 
 the other, having no communication with the exciting acid, trans- 
 mit 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, while 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 Volta, and even at the present moment sup- 
 ported by some illustrious men, ascribed the origin of the electri- 
 city not to the action of the acid upon the zinc, but to the contact 
 of the zinc with the copper ; the point ^vhere the metals touched 
 being supposed to be a continual source of positive electricity to 
 the copper. It was even attempted to prove this by soldering to- 
 gether plates of zinc and copper, and testing their electrical condi- 
 tion 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 contact experiments are made with increased care, the re- 
 sults become less evident in favour of that theory. Such trials tend 
 to show the evolution of minute traces of statical electricity, where- 
 
134 VARIOUS FORMS OF GALVANIC BATTERIES. 
 
 as 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 affecting the gold-leaf electro- 
 scope, it would be as far from accounting for the totally different 
 kind of electrical excitement by which the galvanic battery is cre- 
 ated, 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 Volta, must be carefully distinguished from the 
 capability of inductive excitement, which bodies capable of chemi- 
 cal action, as a slip of zinc and muriatic acid, mutually confer upon 
 each other. 
 
 This last arises from the possible substitution of the zinc for the 
 hydrogen of the acid, which does occur as soon as the interchange 
 of the electricities allows of the transfer of elements j for on the 
 first immersion of the zinc, the equilibrium of the chlorine and hy- 
 drogen, which had previously been totally engaged with each other, 
 is interrupted, and that of the particles of the zinc, which had be- 
 fore been all circumstanced alike, is disturbed by some of them be- 
 ing nearer the acting muriatic acid than the others, and thus the in- 
 duced 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 ac- 
 company the passage of the current, yet, for the only purpose which 
 we here require, of studying the manner in which the current of 
 electricity of the battery has its rise, the peculiar and important in- 
 fluence exercised by the chemical reaction among 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 Volta consisted in placing it 
 horizontally in a wooden trough, 
 and replacing by cells containing 
 dilute acid the moistened disks of cloth employed by the original 
 inventor. It being difficult to cleanse the surfaces of the plates, 
 
 which in that form were per- 
 manently cemented into the 
 trough, this was made of delft- 
 ware 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 wante'd, 
 they may be immersed with 
 great rapidity, and withdrawn 
 as easily from the liquid when 
 the battery is not wanted. The 
 power of such troughs is in- 
 
INTERFERING ACTION OF COMMON ZINC. 135 
 
 creased by one half when the copper slip is doubled over so as to 
 oppose both surfaces of the zinc. Batteries intended rather for in- 
 tensity than for quantity, and which consequently consist of a great 
 number of plates of moderate dimensions, are generally employed 
 on this last construction : each delftware trough holding ten pairs of 
 plates, and any number of troughs that may be required being rap- 
 idly and easily arranged together. When a current of electricity 
 of great quantity, but not of intensity, is required, it is usual to em- 
 ploy a few, or even only one pair 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 separated by ropes of horsehair, have 
 been rolled up together and immersed into a large tub of acid, form- 
 ing 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 containing the acid : cylindric^ 
 batteries of moderate size are very frequently so constructed. 
 
 I have supposed, in the description of the nature of simple and 
 compound Voltaic circles, that the zinc employed was completely 
 pure, in which state, when first immersed in the acid, there is no chem- 
 ical action, but only the preparatory inductive state produced, the 
 decomposition 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 pre- 
 venting to a great extent the formation of the proper current. For 
 suppose that there is on the centre of a plate of zinc a little piece of 
 iron or of copper, this serves to return to the zinc from the acid the 
 positive electricity, which had passed away from it precisely as if 
 it had been a copper wire, which touched the acid with the one end, 
 and the zinc plate with the other. Such a plate is therefore occu- 
 pied almost solely with its own self-contained currents, 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 evolv- 
 ing hydrogen upon its own surface. It evolves the hydrogen upon 
 those points of its surface on which foreign metals being deposited, 
 serve to complete its circuits. This injurious property of ordinary 
 zinc is remedied by coating the surface of the plate with mercury, 
 or, as it is termed, amalgamating it. By this means the whole sur- 
 face 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 acted on until the circuit is completed, and then all hy- 
 drogen 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 
 dilute nitric acid, to which a small quantity of nitrate of mercury 
 
136 
 
 FORMS OF CONSTANT BATTERIES. 
 
 has 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. Before 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 sur- 
 face which, by rubbing with a little flannel, may be rendered com- 
 pletely uniform. The zinc should not be too highly mercurialized, 
 for then it becomes extremely 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 bat- 
 teries 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, neutralizes a certain proportion of 
 the power of the circle, and may even destroy 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 of Mullins ; the mechani- 
 cal construction is most perfect in Daniell's constant battery. Mul- 
 lins' battery consists of a delftware trough, D, in 
 jC^JL 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 j round the upper edge 
 of the copper cylinder C is tied a bladder, into vvhich 
 fluid may be introduced by means of a row of ap- 
 ertures 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 commences, the hydrogen is transfer- 
 r-fi red through the membrane, and, meeting there 
 the solution of sulphate of copper, is absorbed 
 in the production of metallic copper. The cop- 
 per 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. 
 Daniell's battery has the advantage that the cop- 
 per is outside, and hence is capable, with ex- 
 posure of the same surface of zinc, of producing 
 a much more pow^erful current. The cell con- 
 
CONSTANT BATTERIES, 137 
 
 sists of a copper cylinder, a, c, near the top of which is attached 
 a perforated platp, P, on which, when the cell has been filled with 
 the solution of sulphate of copper, a quantity of crystals are laid, 
 to be dissolved according as they are required. A solid zinc rod, 
 ffi, supported at the top of the copper cylinder by a wooden cross- 
 piece, is contained in a membranous bag, formed of the gullet of an 
 ox, g, A, 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 per- 
 fectly unaltered ; and thus the laws of action of the current have 
 been determined, particularly in its chemical relations, with com- 
 plete success, and views of the analogies between affinity and elec- 
 tricity, equally novel and important, which will be discussed in an- 
 other 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 biscuit-ware, such as is represented in the figure by 
 
 Some forms of battery have recently been proposed, in which, 
 under a small compass, very great power is obtained, by, 1st, bring- 
 ing the plates very near each other j 2d, selecting solid elements, 
 which difier as much as possible in their chemical relations ; and, 
 3d, using as the exciting fluids those of the most intense action, 
 and of the highest conducting power. In this way, the most pow- 
 erful Voltaic combination that has been yet made is that of Mr. 
 Groves. Plates 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 dissolved ; and the metals, being 
 those most opposite in their electrical relations, give the most pow- 
 erful current possible. 
 
 The conducting powers of various bodies for this form of electri- 
 city 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 
 Silver . , 
 Gold . . 
 Copper 
 Platina 
 Bismuth . 
 
 5791 
 
 Brass from . . 
 
 . . 900 
 
 5152 
 
 to . . 
 
 . 200 
 
 3975 
 
 Cast steel from 
 
 . 800 
 
 3838 
 
 to . . 
 
 . 500 
 
 855 
 
 Iron .... 
 
 . 600 
 
 384 
 
 Mercury . . 
 
 . 100 
 
138 RELATIVE CONDUCTING POWERS. 
 
 He ascertained, also, the relative conducting powers of the saline 
 solutions usually contained in the cells of the Galvanic battery j 
 and it appears that the conducting power of platina is two million 
 and a half times that of a saturated solution of sulphate of copper, 
 and hence that of copper is sixteen million times as great. The 
 conducting power of the saturated solution of the sulphate of cop- 
 per 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 ^o¥oo 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 under- 
 stood. Pure water may be considered, with feeble circles, as an 
 absolute non-conductor ; and even with the most powerful combi- 
 nations 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 in- 
 sufficient conducting medium, the centre of the conductor becomes 
 hot, and thus the most brilliant effects of heat and light may be pro- 
 duced ; even the most refractory metals, as gold and platina, being, 
 when in thin foil or wire, dissipated actually in smoke. By termi- 
 nal 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 carbonic 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 induc- 
 tively excited particles of charcoal, which, in a state of intense ig- 
 nition, abandon the positive to attach themselves to the negative 
 extremity of the conductor. 
 
 The action of galvanic electricity upon the animal frame does not 
 properly fall within the scope of the present work, but in termina- 
 ting 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 Bo- 
 logna, and, while preparing frogs for 
 some physiological experiments, he hap- 
 ^Wl Wl^^ pened to touch, by one extremity of a 
 
 metallic wire, the lumbar nerves which 
 still remained attached to the spine, while 
 
G A L V A N I S M. T HERMO-ELECTRICITY. 139 
 
 the Other extremity of the wire was in contact with the muscles of 
 the leg j these last were instantly thrown into strong convulsions. 
 To perform this experiment with 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 to- 
 gether at one end, the nerves are to be touched with one wire, 
 while the other is to be applied to the muscles of the leg. 
 
 Galvani erred in the explanation of this remarkable effect j he look- 
 ed upon the body as being in the stat* of a charged Leyden jar, of 
 which the nerves and muscles were the external and internal coat- 
 ings, and that, on connecting these by the conducting wire, the elec- 
 tricities recombined, and the passage renewed for the instant the 
 phenomena of life. Volta 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 con- 
 vulsive 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 chemical 
 action on the wires ; but it was so fruitful in results, of which the 
 construction of the Voltaic pile is the most remarkable, that Volta 
 is, with justice, looked upon as the true originator of this branch of 
 electricity 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 
 Galvanic current ; it is truly a galvanoscope, corresponding to the 
 gold-leaf electroscope for ordinary electricity ; but it does not meas- 
 ure the quantity or intensity of the electricity which passes. As 
 yet we have no exact measure of the intensity of Galvanic electri- 
 city ; 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 de- 
 flect the magnetic needle from its natural position of north and 
 south, for the angle of deflection is connected with the quantity 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 tex- 
 ture and thickness, 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 in the wire, exist, a cur- 
 rent will be established, of which the direction will be 
 from the point of the circuit to which the heat is applied 
 towards the point where the retarding cause exists. If 
 in place of merely causing an artificial obstacle on a 
 uniform wire, two metals, a b, be selected, which differ 
 in conducting power, and 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 
 
140 THERMO-ELECTRIC CURRENTS. 
 
 the metal which is the worst conductor. The more unlike the met- 
 als are in molecular constitution, and the greater the difference be- 
 tween 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 sys- 
 tems. Bismuth and antimony, which are the worst conductors of 
 the metals, are also among the most crystalline ; and while bismuth 
 crystallizes in cubes, the form of antimony is a rhombohedron j these 
 metals, therefore, combine ajl 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 wri- 
 ting them down in the following 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 following or- 
 der : bismuth, platinum, lead, tin, copper or silver, zinc, iron, anti- 
 mony. The molecular texture would appear from this list to have 
 more influence on the production of the current than the mere dif- 
 ference of conducting power. 
 
 The intensity of the thermo-electric current so excited is exceed- 
 ingly small ', it is only capable of passing through very good con- 
 ductors, 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 the place where the two unite ', if the 
 current pass from the bismuth to the antimony, the junction becomes 
 heated j but if the electricity pass in the opposite direction, the junc- 
 tion 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 ob- 
 tained 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 dis- 
 covered, and may influence our theories of the nature of heat in no 
 inconsiderable degree. 
 
 The principle of strengthening the thermo-electric current, by 
 
 combining 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 i, 
 soldered together alternately at their 
 ends, so that every alternate soldering 
 shall be in the same plane, and the 
 extremities of the terminal bars be 
 
CONSTRUCTION OF THE THERM OSCOPE. 141 
 
 connected by a wire, on applying heat to the alternate solderings, 
 a current is generated at each, which, being all in the same direc- 
 tion, travel together through the system, and thus increase its en- 
 ergy in proportion to the number of combinations. The important 
 distinction between this and the combination of elements in the 
 Voltaic 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 aug- 
 mented also. 
 
 It is this principle which has been applied by Nobili to the con- 
 struction 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 con- 
 sists of fifty small bars of bismuth and antimony, placed parallel be- 
 side one another, and forming a single prismatic bundle, F, F', about 
 1^ inch long and f 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 sep- 
 arated all through their length by an insulating substance. To the 
 
 CnflC 
 
 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 ex- 
 tremities of the two wires are put in communication with the ter- 
 minal wires of a magnetic galvanometer, the needle of which indi- 
 cates 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 99.) 
 
 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 
 soldering, 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 varies 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 3 ^Vo- 
 of a degree on Fahrenheit's scale. 
 
 The electricity which is thus evolved by change of temperature 
 in conducting bodies, although so feeble in quantity and intensity 
 as to be utterly devoid of those brilliant qualities which attach much 
 popularity to the phenomena of Galvanism and of machine electri- 
 city, has thus been found the means of assigning the true laws of 
 some of the most interesting and important branches of the ph^ical 
 Bciences j and it will be hereafter seen that thermo-electric currents, 
 
142 
 
 RELATIONS OF 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 properties on which are founded the com- 
 mercial intercourse of civilized nations, but, by influencing the affin- 
 itary powers of the elementary constituents of our planet, may have 
 been the agent in silently, but effectively, regulating the constitution 
 of inorganic nature. 
 
 [From the extensive employment of thermo-electric currents as measures of tem- 
 perature, it is desirable to understand their habitudes. Dr. Draper has shown that 
 equal quantities of heat do not set in motion equal quantities of electricity ; with 
 certain combinations of metals the proportion increases, and with others decreases. 
 For this reason, temperatures estimated in this way must always undergo correc- 
 tion, as the following table shows : 
 
 M 5 
 
 £5" 
 
 Mercurial thermometer . 
 
 Copper and iron . . . 
 
 Silver and palladium 
 
 ^ ^ Iron and palladium . . 
 
 S :^ I Platina and copper . . 
 
 S -2 Iron and silver . . . 
 
 H 6 I Iron and platina . . . 
 
 Water boils. 
 
 Mercury boils. 
 
 212 
 
 662 
 
 202 
 
 257 
 
 235 
 
 880 
 
 211 
 
 539 
 
 244 
 
 1030 
 
 170 
 
 279 
 
 212 
 
 829 
 
 We therefore infer, that in these six systems of metals, the developments of electii- 
 city do not increase proportionally with the temperatures, but in some with greater 
 rapidity, and in others with less. 
 
 The tension of these currents undergoes a slight increase with increase of tem- 
 perature : a phenomenon due to the increased resistance to conduction of metals 
 when their temperature rises. In hydro-electric pairs, the quantity of electricity 
 evolved depends on the surface of the plates ; but in thermo-electric arrangements, 
 the quantity of electricity is independent of the amount of heated surface, a mere 
 point being just as efficacious as an indefinitely extended surface. And in a com- 
 pound series of many pairs, the quantity of electricity evolved is directly proportional 
 to the number of pairs. 
 
 Thermo-electric currents traverse metallic masses only on account of differences 
 of temperature existing at different points. When a current flowing from the poles 
 of a battery is made to traverse a wide metallic sheet, the whole of it does not 
 
 pass in a straight line from one pole to 
 the other, but diffuses itself through the 
 metal, diverging from one pole and con- 
 verging to the other. For these reasons, 
 there are certain forms of construction 
 which give thermo-electric arrangements 
 peculiar advantages. For example, the sur- 
 faces united by soldering must not be too 
 massive. Let a, fig. 1, be a bar of anti- 
 mony, and h a bar of bismuth ; let them be 
 soldered together along the line c d, and at 
 the point d let the temperature be raised, 
 a current is immediately excited ; but this 
 does not pass round the bars a b, inasmuch as it finds a shorter and readier chan- 
 nel through the metals between c and d, circulating, therefore, as indicated by the 
 arrows. Nor will the whole current pass round the bars until the temperature of 
 the soldered surface has become uniform. 
 
 An obvious improvement on such a combination is shown in fig. 2, which con- 
 sists of the former arrangement cut out along the dotted lines ; here the whole cur- 
 rent, as soon as it exists, is forced to pass along the bars. And because the mass 
 of metal has been diminished along the hne of junction, such a pair will change its 
 temperature very quickly. 
 
 One of the very best forms for a thermo-electric couple is given in fig. 3, where a 
 is a semi-cylindrical bar of antimony, b one of bismuth, united together by the oppo- 
 site ^rners of a lozenge-shaped piece of copper, c. From its exposing so much 
 surface, the copper becomes hot and cold with the greatest promptitude ; and from 
 its good conducting power, it may be made very thin without injury to the current.] 
 
MAGNETIC PROPERTIES OF IRON AND STEEL. 143 
 
 Magnetic Electricity. — The properties which are now known as 
 magnetic were first recognised 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 ineft with regard to all other bodies, attracts 
 iron and steel with great power ; and the pieces of iron and steel, 
 while in contact 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, although magnetic while in contact with the loadstone, 
 loses all its properties when it is removed; while steel, which is at 
 first attracted with inferior power, when it has become magnetic by 
 contact with that mineral, retains that condition after separation, 
 and thus becomes a permanent artificial magnet. A steel magnet 
 thus formed may in its turn be used in place of a loadstone to form 
 others j and almost all the magnets we employ in experiments have 
 thus obtained their power, as native loadstone is not found in suf- 
 ficient 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 horseshoe 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 ^ I f^^ 
 
 all to the centre ; the magnetic power is '^^gppw-*'A^'-t^'i*'JJi^^iJl|Nf^ 
 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 an order 
 which is termed the magnetic curves, and from the disposition of 
 these curves it is evident that the action of the magnet emanates 
 from a single point, P, near each 
 extremity; these points being the 
 centres of action of the magnet, 
 are termed iX?, 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 diverging 
 lines, which, uniting on the inner 
 side, form the magnetic 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 indifferently, 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, while 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 
 
 
 
144 INTIMATE STRUCTURE OF MAGNETS. 
 
 attract, a condition precisely 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 superficial 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 explained 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 south- 
 ern 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 ex- 
 plained, however, by supposing it to be a simple magnet with a pole at each ex- 
 tremity. It possesses at least two centres of force or poles in the north, one in 
 Siberia and one in North America, while the exact distribution of the centres of 
 magnetic force in the southern hemisphere has not been yet made out, These cen- 
 tres themselves are, however, not fixed ; the needle is continually changing in di- 
 rection ; at present it points to 24i° 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 
 phenomena, a theory similar for the most part to that of the two 
 electrical 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 th|j head of statical electricity, the constitution 
 of iron being such that the fluids recombined on the disturbing cause 
 being removed ; the constitution of steel, on the contrary, prevent- 
 ing their reunion. There existed, however, one great difference 
 between a magnetic bar and a body excited by induction with ma- 
 
 ^ C B chine electricity. If the bar A, C, B, excited 
 
 C 1 ) by induction, and of which the portion A is 
 
 /\ jjj /\ positive, and B negative, the middle C being 
 
 neutral, be cut in two at C, the portions A 
 
 1 j ^ and B retain their peculiar states, one posi- 
 
 tive and the other negative. But if the mag- 
 netic bar A, C, B be broken across at the 
 neutral portion C, then each half becomes 
 
 k 
 
 ^^3[^':; a perfect magnet of half the strength of the 
 '■'/?i?\v ^ entire j the points C and C, which had 
 
 ■•s jM^vjJC -'- teen neutral, acquire magnetic power ', and 
 if these portions be again broken, each frag- 
 ment is a perfect magnet. Magnetism be- 
 longs, in this way, to the inmost particles of the body, and in the 
 general mass each magnetic molecule is still active and independ- 
 ent ; a magnet resembles, therefore, an exceedingly bad conductor, 
 which has been inductively excited by common electricity, and the 
 particles 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 
 
MAGNETIC QUALITIES OF GALVANIC CURRENT. 145 
 
 Fig. 3. 
 
 Fig. 4. 
 
 never leaves the magnetic element, or molecule of iron or steel, in 
 which it has its origin ; in fact, every current of electricity possess- 
 es magnetic properties, and simulates the action of a magnet situ- 
 ated transversely to it. Thus, if a needle be held transversely on a 
 wire carrying an electric current, it becomes magnetic precisely as 
 if it had been laid parallel to a magnet ; and by bending the wire 
 round so as to form a coil, the magnetism which it confers being 
 increased in proportion to the number of turns, may be rendered 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 magnetism is conferred upon the 
 bar of steel inside. And 
 in fig. 2, a large horse- 
 shoe of soft iron, by being covered by a helix of many 
 hundred turns, may become able to raise a weight of 
 some hundreds of pounds by the magnetism it ac- 
 quires. 
 
 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 magnetic 
 pole at each end. A flat coil, as in fig. 4, 
 is also found to be magnetic, the poles be- 
 ing indefinitely near each other at the cen- 
 tre of the coil. A beautiful form of the ex- 
 Fig. 5. periment consists ,...■>., 
 in a long wire, ^^^^^ 
 which is made into a close coil, and connect- 
 ed at the ends with a pair of little plates of 
 zinc and copper, as in fig. 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 nee- 
 dle, and behaves in all respects like a mag- 
 net situated in the centre of the coil, and 
 perpendicular 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 might 
 represent its action. If A B be a wire in which a current ^ 
 is descending, as marked by the arrow, and a needle, N S, 
 is placed transverse to it, the right-hand end of the needle 
 ^ becomes the north, and left-hand end of the nee- 
 zqii die the south 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, conse- 
 quentljr, easily seen; the current A B, which descends in front 
 
 T 
 
 lA 
 
 B 
 
KS 
 
 146 MAGNETIC ACTION OF A GALVANIC CURRENT. 
 
 of, and ascends behind the needle, produces in the bar, N S, a 
 northern polarity to the right, and a southern to the left ; the ac- 
 tion of magnetic currents upon each other supplies the explana- 
 tion of these phenomena. If two wires carrying Galvanic currents 
 be brought near each other, there is attraction or repulsion, accord- 
 ing to the direction of the currents ; if the two currents be in the 
 same direction, the wires attract j if in opposite directions, the wires 
 ^ m repel each other. The cause is evident on inspecting 
 ^'^ the figure : the upper wires being arrows which carry 
 ^2S currents in the same direction, they act on each other, 
 as should a pair of magnets placed transverse to their 
 direction j the ends of the magnets which are juxtaposed 
 have opposite polarities, and attract ; while in the lower 
 arrows, where the currents are in opposite directions, 
 the effect is the same as would result from the magnets 
 of which the contiguous poles are of the same name, and hence re- 
 pulsion. 
 
 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 department, termed electro-magnetism ; but 
 being unimportant in detail except in physical relations, I shall 
 only notice the experiments by which CErsted 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 the 
 needle be movable 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 repre- 
 sents J and hence, in the figure, the 
 motion would 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. )f the current had been in the opposite di- 
 rection, the action would have been reversed, and the north pole 
 would have been turned up from the paper j 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 por- 
 tion, 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 ultimate position would 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 assumes is the resultant of the two 
 forces. 
 
 The deflection of the needle being thus an indication of the pas- 
 sage of an electric current through the wire, it is desirable in prac 
 
 )i 
 
ASTATIC COMBINATIONS OF MAGNETS. 147 
 
 tice to give the power of the current as much eifect as possible, 
 and at the same time to diminish as much as can he done the action 
 of the terrestrial magnetism. The first is effected easily by increas- 
 mg to the desired degree 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 num- 
 ber of coils 5 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 j but the object is effected by using a combi- 
 nation 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. 
 
 Du 
 
 the remote and weaker opposing action of the j^^ 
 earth becomes almost insensible. A current 
 
 C = 
 
 air 
 
 & 
 
 3]sr 
 
 passing in the direction of the arrows, C, E, g, 
 
 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 deflection of such a system of needles will still be 
 regulated by residual terrestrial influence ; but as this may be ren- 
 dered 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 would be af- 
 fected by trivial and accidental causes ; but by leaving a small resi- 
 due of terrestrial magnetic efiect, 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 quan- 
 tity 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 
 uniformity of action, the system of needles is in all good instruments 
 hung by a thread of glass or of silk, like the beam of Coulomb's 
 balance (page 113). The deflecting force then acts against the force 
 of torsion, and the resistance to be overcome is reduced to its sim- 
 plest possible conditions. 
 
 The galvanometer, such as, with the thermo-pile, constitutes the 
 thermo-multiplier, is represented in section and in perspective in 
 the following 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 hor- 
 izontal plate D, E, which can turn in its own plane around its cen- 
 tre by means of a toothed wheel and endless screw, which are 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, 
 
148 CONSTRUCTION OF THE GALVANOMETER. 
 
 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 movement 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 deri- 
 ved 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 false indications of its quantity, unless an am- 
 ple path were opened through the best conductors for it ; the num- 
 ber of coils for a thermo-electric galvanometer should also, for the 
 same reason, be as 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 98, 
 and its use in measuring the quantity of electricity flowing from 
 galvanic sources, which has been already partly noticed, will be far- 
 ther 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 pass- 
 ed, shown to be suflicient 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-existing current, which would have con- 
 ferred 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 another, or that a 
 body statically excited may induce the electric condition on the 
 
bodies in its neighbourhood ; but such peculiar infiu^ces are too 
 removed from the proper domain of chemistry to justify any detail- 
 ed description of them. 
 
 In concluding this section of the subject of electricity, it is, however, important 
 to prevent its being supposed that, by the omission of such considerations, they are 
 to be considered as of inferior interest in the phenomena of nature. It is so much 
 the reverse,, that perhaps one of the most active sources of the electricity which 
 we shall find to play a most important part in chemical combination, is derived from 
 the induction of the magnetic influence of the earth itself : for the earth being ren- 
 dered 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, in- 
 deed, amazingly from the brilliant excitation of the thunder-cloud, but surpassing 
 it far 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 mani- 
 festing its tendency to escape by the attractions, the flashes, the mechanical vio- 
 lence which characterize machine electricity ; while, 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 suc- 
 ceed in demonstrating its heating, its luminous, or its mechanical effects ; but we 
 recognise in it, nevertheless, the untiring agent by which the inorganic superstruc- 
 ture of the habitable glob* 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 par- 
 amount 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 advancement of science. 
 
 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 
 liitherto avoided as much as possible involving any ideas of chemical decomposition 
 in the account of electricity just given, restricting myself to narrate such circum- 
 stances as might serve for the recognition of bodies by means of their electrical 
 properties, independent of their chemical constitution. But the question whether 
 electrical influence and affinity are identical, or what are their exact relations, 
 and the discussion of the theory of electro-chemical combination, still remain, and 
 will be examined when, first, the nature of affinity and the distinction between it 
 and the action of cohesive force have been described, and the general system of nom 
 eaclature by which chemical substances are designated has been briefly noticed 
 
 CHAPTER V. 
 
 OF CHEMICAL NOMENCLATURE. 
 
 The general properties and laws of the physical agents, cohesion, 
 light, heat, and electricity, having been now described so far as was 
 necessary, that we may avail ourselves of those properties in char- 
 acterizing the substances, elementary or compound, whose more pe- 
 culiarly chemical relations we shall now proceed to study, it is ne- 
 
150 
 
 PRINCIPLES OF NOMENCLATURE. 
 
 cessary to prefix to the description of the forces by wliich 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 occasion to refer have been con- 
 structed. 
 
 There are at present known fifty-five substances which the chemist 
 has not been as yet able to separate into other elements. These are 
 distinguished by the following names : 
 
 Oxygen, 
 
 0. 
 
 Potassium, 
 
 K. 
 
 Arsenic, 
 
 As. 
 
 Hydrogen, 
 
 H. 
 
 Sodium, 
 
 Na. 
 
 Antimony, 
 
 Sb. 
 
 Nitrogen, 
 
 N. 
 
 Lithium, 
 
 Li. 
 
 Tungsten, 
 
 W. 
 
 Carbon, 
 
 C. 
 
 Barium, 
 
 Ba. 
 
 Molybdenum, 
 
 Mo. 
 
 Boron, 
 
 B. 
 
 Strontium, 
 
 Sr. 
 
 Tantalum, 
 
 Ta. 
 
 Silicon, 
 
 Si. 
 
 Calcium, 
 
 Ca. 
 
 Chromium, 
 
 Cr. 
 
 Sulphur, 
 
 s. 
 
 Magnesium, 
 
 Mg. 
 
 Vanadium, 
 
 V. 
 
 Selenium, 
 
 Se. 
 
 Aluminum, 
 
 Al. 
 
 Uranium, 
 
 U. 
 
 Phosphorus, 
 
 P. 
 
 Glucinum, 
 
 G. 
 
 Gold, 
 
 Au. 
 
 Chlorine, 
 
 CI. 
 
 Zirconium, 
 
 Zr. 
 
 Iridium, 
 
 Ir. 
 
 Iodine, 
 
 I. 
 
 Thorium, 
 
 Th. 
 
 Osmium, 
 
 Os. 
 
 Bromine, 
 
 Br. 
 
 Yttrium, 
 
 Y.' 
 
 Platinum, 
 
 PI. 
 
 Fluorine, 
 
 F. 
 
 Cerium, 
 
 Ce. 
 
 Tin, 
 
 Sn. 
 
 Tellurium, 
 
 Te. 
 
 Lanthanum, 
 
 Ln. 
 
 Lead, 
 
 Pb. 
 
 Mercury, 
 
 Hg. 
 
 Manganese, 
 
 Mn. 
 
 Bismuth, 
 
 Bi. 
 
 Zinc, 
 
 Zn. 
 
 Iron, 
 
 Fe. 
 
 Silver, 
 
 Ag. 
 
 Cadmium, 
 
 Cd. 
 
 Copper, 
 
 Cu. 
 
 Palladium, 
 
 Pd. 
 
 Cobalt, 
 
 Co. 
 
 Titanium, 
 
 Ti. 
 
 Rhodium, 
 
 R. 
 
 Nickel, 
 
 Ni. 
 
 
 
 
 
 By the combination of these bodies among 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-me- 
 tallic elements. The first thirteen in the list are non-metallic ; the 
 remaining bodies are metallic. It is found, however, that this di- 
 vision is only popularly correct ; no matter how we may define a 
 metal, we cannot avoid breaking through connexions of the most in- 
 timate and important kind if we endeavour to retain the class of 
 metals as one founded on really existing chemical principles. Thus, 
 in density and 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 assim 
 ilate themselves most perfectly, one to sulphur, and the other to 
 phosphorus. In selenium, also, the metallic characters are so feebly 
 marked, that even did we not know that by its properties it must 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 
 chemistry 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 fa- 
 cilitated by departing from it, I shall not hesitate to do so. In order 
 to avoid confusion 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 upou 
 
NOMENCLATURE OF LAVOISIER AND GUYTON. 151 
 
 which the names of these objects are founded should be clearly- 
 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, at a time 
 when, by a mal-application to chemistry of the analogy of the human 
 body and 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 Lavoi- 
 sier, 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 con- 
 ditions which it is very difficult to successfully combine ; that the 
 name shall not only tell us that the substance is an independent sub- 
 stance, but that it shall give to us an idea of its most important chem- 
 ical character, its composition ; thus the name prussic acid is less 
 strictly scientific than that of hydrocyanic acid, which shows us 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 nom- 
 enclature 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 impor- 
 tance to the accurate ideas of combination in which it had its origin. 
 The removal of the unconnected and unfounded names, which had 
 been invented 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 acid^ base, and salt. 
 The word acid signifying originally sour, was applied to all bodies 
 which tasted like vinegar. The word base signifies any substance 
 which, uniting with an acid, forms a compound, of which it is the 
 basis or foundation ; 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 
 
152 SIMPLE BODIES AND PRIMARY COMPOUNDS. 
 
 name should be derived from its most characteristic property, La- 
 voisier formed the word " oxygen" from o^vg^ acid, and yevvao), 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 forming acids. In like manner, he constructed the word 
 "hydrogen" from vdcop, water, and yevvaio^to express its most im- 
 portant property, of being an element of water. This principle can, 
 however, seldom be rigidly acted on j 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 a7}?i7jV7], the moon ; 
 vanadium and thorium from Vanadis and Thor, deities of Scandi- 
 navian mythology ; chlorine from x^<^pog, yellowish green (its col- 
 our) ; and similarly iodine from loetdrjg (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 j if it be an acid, 
 the word acid is added to that of the other body to which the ter- 
 mination ic is joined. Thus the acid compound of sulphur and 
 oxygen is sulphuric acid ; the acid compound of phosphorus and 
 oxygen is phosphoric acid. It frequently happens that the same 
 body forms with oxygen two acids, in which case, that containing 
 most oxygen retains the terminal zc, while that in which there is 
 least oxygen ends in ous. Thus there is sulphurous acid^ and phos- 
 phorous acidj 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 introduced: the words 
 ?;7ro, hypo, and vnepj hyper, under and over, are prefixed to the de- 
 grees terminating as before stated. Thus there is an acid of sul- 
 phur containing less oxygen than the sulphurous acid, and it is call- 
 ed 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 acid ; 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 short- 
 er Latin per for the Greek virep, perchloric acid. 
 
 In cases where the compound formed with oxygen is not an acid, 
 it is termed 2iXi oxide of the substance with which the oxygen is uni- 
 ted. Thus oxide of lead, oxide of iron, oxide of copper, are re- 
 spectively the compounds of oxygen with lead, with iron, and with 
 copper. In many cases, where oxygen unites with bodies in more 
 than one proportion, one compound may be an acid, and the other 
 not. Thus manganese, uniting with oxygen,gives manganic acid and 
 permanganic acid, but in a lower degree of oxidation it forms several 
 
VARIOUS CLASSES OF PRIMARY COMPOUNDS. 153 
 
 oxides of manganese. For as a substance uniting with oxygen may- 
 form many acids, so may it form many oxides also 3 and in such 
 cases it becomes necessary to distinguish them from one another. 
 This is done by the adoption of the Greek words nporog, devrepog, 
 TpLTog (first, second, third), prefixed to the word oxide. Thus we 
 say protoxide of lead, deutoxide of lead, tritoxide of iron ; the ox- 
 ide 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 in- 
 termediate between protoxides and deutoxides, but the nomenclature 
 then involves numerical proportions, which will require to be de- 
 scribed herafter. 
 
 Some other simple non-metallic bodies, in combining with the met- 
 als, 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 forms 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 termination is adopted for that body and some others. 
 Thus, 
 
 Sulphur gives Sulphurets. 
 Selenium " Seleniurets. 
 Tellurium " Tellurets. 
 Carbon " Carburets. 
 
 Nitrogen, gives 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 dcuto- chloride of manga- 
 nese ; also perchlorides and subchlorides. 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 chloruret in place of chloride, and sulphide in 
 place of sulphuret, are frequently employed ; but as these are found- 
 ed on certain theoretical ideas that have not yet been discussed, the 
 propriety of adopting such additional terminations cannot be con- 
 sidered until we have proceeded 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 phos- 
 phorus or phosphuret of chlorine 1 This is decided by referring to 
 the classification 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 
 
 U 
 
154 NAMES OF SECONDARY COMPOUNDS. 
 
 peculiar 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. Arse- 
 nic and tellurium are so far removed from the metals by their 
 chemical characters, that their compounds with the proper metals 
 have the peculiar termination in uret. 
 
 By the union of two primary compounds there is formed a sec- 
 (mdary compound. These secondary compounds are generally termed 
 saks. The word salt is, however, applied to numerous classes of 
 primary compounds. Thus, the metallic iodides, chlorides, bromides, 
 and fluorides are recognised as salts. It is now also a debated ques- 
 tion whether the bodies formed by the direct union of an acid and 
 an oxide are really primary or secondary compounds ; but I shall 
 now describe only the ordinary nomenclature of those bodies, post- 
 poning the discussion of their intimate constitution to another place. 
 When an acid and a metallic oxide, both primary compounds, com- 
 bine 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 ; the generic name is taken from the 
 acid, the word acid being omitted, and the final ic being changed into 
 ate, or the final ous into ite. There is thus formed from sulphuric 
 acid and soda sulphate of soda. From nitric acid and oxide of lead, 
 nitrate of oxide of lead: From sulphurous acid and potash, sulphite 
 of potash. From hypochlorous 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 injuri- 
 ous ; this mode of naming salts is so universal, that breaking in on 
 it might be productive of more injury than allowing it to remain j I 
 shall therefore say, for example, nitrate of lead, understanding, how- 
 ever, that the nitric acid is combined not with lead, but with oxide 
 of lead. 
 
 It frequently happens that a metal forming with oxygen two ox- 
 ides, 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 proto-sulphate of iron, persulphate of iron ', 
 indicating that there is in 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 dtg, rpic^ 
 &CC., as di-sulphate of zinc, tri-sulphate of mercury ; or still iDctter 
 by the words bi-basic, tri-basic, &c., to indicate the quantity of base ; 
 there is thus tribasic-sulphate of mercury, quadribasic-sulphate of 
 copper, and so on. 
 
TERNARY AND QUATERNARY COMPOUNDS. 155 
 
 Th«re 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 many different ca- 
 pacities, and its nomenclature must be varied accordingly, as will 
 be seen under its proper head ; but where we wish to indicate that 
 a body contains water, 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 com- 
 pounds, which are called oxychlorides, as the oxychlorides of mercury^ 
 the oxychloride of lead. Oxides and sulphurets combining form oxy 
 sulphurets, as oxysulphuret 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 sodi- 
 um, 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, uniting with a sulphuret of a basic metal (a sulphur 
 base), forms 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 prefix oxy is, however, not usedj 
 the ordinary salts are supposed to contain the oxygen acid, and it 
 is only where a salt does not contain an oxygen acid that an addi- 
 tional word is necessary to point out what sort of acid it does con- 
 tain. Tellurium and selenium act like sulphur ; there are tellurium 
 acids and tellurium bases, selenium acids and selenium bases, and hence, 
 in place of calling the compound of seleniuret of antimony and se- 
 leniuret of sodium a double seleniuret, it is called the selenio-sti- 
 biate of sodium. 
 
 An attempt was made to assimilate the nomenclature of the chlorine and iodine 
 bodies to that of the oxygen and sulphur compounds ; thus, to call chloride of mer- 
 cury a chlorine acid, and chloride of sodium a chlorine base, and the compound 
 which they form a chlorine salt, chlorohy drargyrate of sodium. This idea, howev- 
 er, has not been received into science ; for, indeed, now the direction of the ideas 
 most popular am.ong chemists points precisely contrary, 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 
 than one proportion. Alum combining with water to produce the 
 crystallized alum, generates a quaternary compound; and even more 
 complicated stages may be attained ; but they are so rare, and of so 
 little scientific importance, that they do not require notice here. 
 
 In organic chemistry, the principles of nomenclature are for the 
 most part identical with those now stated ; where deviations occur, 
 they will be noticed under their proper heads. The progress of sci 
 
156 SYMBOLICAL NOMENCLATURE. 
 
 ence has, however, introduced remarkable changes in the mode ot 
 representing the constitution of bodies, particularly by means of the 
 symbolical nomenclature now universally adopted after Berzelius. 
 
 In the list of the simple bodies in page 150, the name of each 
 substance is accompanied by its symbol, which is generally the in- 
 itial 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 gen- 
 erally selected to be denoted by the single letter, as C. and P. for 
 .carbon and phosphorus, while the metals whose symbols have the 
 same letter are denoted by Ca., Co., Cd., Ce., and PL, Ph., 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, while 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 
 compound of oxygen and lead ; C.H.N.O. a compound of carbon, 
 hydrogen, nitrogen, and oxygen. The algebraic sign of addition is 
 frequently used to connect symbols, as Cl.-f-S., chloride of sulphur ; 
 I H-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 infe- 
 rior degree of affinity ; thus Cl.Ca. is chloride of calcium dry, but 
 when crystallized it becomes Cl.Ca.+6H.O., in which the -f- sign is 
 used to show that the water is united with the Ca. CI. by a power 
 distinct from, and inferior to, that which retains Ca. and CI. in com- 
 bination. Water thus combined is often represented by the symbol 
 Aq., for water is capable of acting in a variety of ways in combina- 
 tion, and, as will be shown when we come to 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 
 relations. 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 sym- 
 bol Pb.O. 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 Pb.Oj, or Pb.-f 20., which rep- 
 resents also a compound 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. Pb.O. is 
 therefore protoxide, and Pb.Oi is the peroxide of lead. 
 
 The details of the application of those symbols involve thus the 
 numerical laws of constitution, which have yet to be described ,* and 
 
NATURE OF CHEMICAL AFFINITY. 157 
 
 hence it is unnecessary to develop their arrangement farther at 
 present. It was 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. 
 
 CHAPTER VI. 
 
 OF CHEMICAL AFFINITY, AND ITS RELATIONS TO HEAT, TO LIGHT, AND TO 
 
 COHESION. 
 
 The peculiar power by which we suppose chemical phenomena to 
 be produced, is specially distinguished from cohesion, and from aU 
 other forces in nature, by exerting in the different kinds of element- 
 ary or compound substances various degrees of energy j and by its 
 capability of acting upon certain bodies exclusively, and in prefer- 
 ence 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 magnesia, the 
 lime will all dissolve in the acid before any trace of the magnesia 
 will be taken up. If a slip of iron be placed in a cup of nitric acid, 
 a large quantity of deep red fumes is 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 sub- 
 stances 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, there- 
 fore, presented equally to lime and magnesia, 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 prefer- 
 ence 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 char- 
 acteristic of chemical force. It is decomposition. The copper can- 
 not dissolve in the nitric acid without the expulsion of another sub- 
 stance. By a simpler example, the decomposition may be rendered 
 more evident. Sulphuret of hydrogen consists of sulphur and hy- 
 drogen ; 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 affinity for the iodine caused the decomposition. 
 Hydrogen has, however, a still more decided tendency to combine 
 
158 PRINCIPLES OF ELECTIVE DECOMPOSITION, 
 
 with chlorine ; and if chlorine be brought into contact with iodide 
 of hydrogen, the iodine is in its turn expelled, and chloride of hy- 
 drogen 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 combination, contain- 
 ing that for which its affinity was strongest. But when an uncom- 
 bined 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 ex- 
 periments 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, 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 the elective affinity were 
 constructed. 
 
 It has been stated that, if lime and magnesia be placed together 
 in contact with muriatic acid, the acid will dissolve all the lime be- 
 fore it acts upon the magnesia j the affinity of lime for muriatic acid 
 is therefore greater than that of magnesia for the same acid, and 
 hence, if to a solution of magnesia there be lime added, the mag- 
 nesia will be expelled and the lime will take its place. If to the 
 lime solution of soda be added, the lime will separate, and soda may 
 be in turn expelled by potash. On the other hand, there are many 
 metallic oxides which enjoy a still more feeble affinity than magne- 
 sia ; 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 j and by 
 observing the order of decomposition by each other, a view of the 
 relative affinities which they exercise may be fovmed. 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 
 oi potash is exposed to the air, it absorbs carbonic acid, for which, 
 therefore, the potash has an affinity of a certain energy j 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 potash 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 
 
ORDER OF ELECTIVE DECOMPOSITION. 159 
 
 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. 
 Sulphuric acid. 
 Nitric acid. 
 Muriatic acid. 
 Acetic acid. 
 Carbonic acid. 
 
 Muriatic Acid. 
 
 Potash. 
 
 Soda. 
 
 Lime. 
 
 Magnesia. 
 
 Oxide of iron. 
 
 For the simple bodies similar lists might be constructed : thus, in 
 the same way as the series of affinities for hydrogen already noticed, 
 a table of affinites of the diffisrent 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 dissolves, 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 copper 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 expressed, taking hydrogen and oxygen as illus 
 trations, by the following columns : 
 
 Hydrogen. 
 Chlorine. 
 Iodine. 
 Sulphur. 
 
 Oxygen. 
 Zinc. 
 Lead. 
 Copper. 
 Mercury. 
 Silver. 
 
 m which any one body in the list may expel all below it from com- 
 bination, 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 bod- 
 ies, 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 5 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 carbonate of lime. The nature of the de- 
 composition may be more clearly shown from the figure : 
 
 i Nitric acid. Potash. > 
 
 ( Lime. Carbonic acid. 3 
 
 The bodies existing before mixture being composed of those writ- 
 ten above one another, and those formed by decomposition consist- 
 ing of those which are in the same horizontal line. 
 
 This action is termed double decomposition. In the example just 
 stated, the diffisrence between it and simple decomposition may 
 
s 
 
 160 DOUBLE DECOMPOSITION. 
 
 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 com- 
 bined together J but the peculiarity of double decomposition is, 
 that by means of it reactions may occur which could not have 
 been produced by simple affinity, and which, on the contrary, ap- 
 pear to have been produced in opposition to it. Thus, ammonia 
 cannot decompose nitrate of lime ; on the contrary, lime will take 
 nitric acid from ammonia ; and yet, if we mix a solution of nitrate 
 of lime and carbonate of ammonia, they decompose each other, 
 and, by double elective affinity, there are formed nitrate of ammo- 
 nia and carbonate of lime. As in the former diagram, the com- 
 pounds, before and after mixture, are found arranged in the hori- 
 zontal and vertical lines of the diagram : 
 
 Nitric acid. Ammonia. 
 Lime. Carbonic acid. 
 
 In fact, m order to understand the cause of such double decompo- 
 sition, 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 ammo- 
 nia ; 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 decomposi- 
 tion are the affinities of nitric acid for lime, and of carbonic acid 
 for ammonia; that is, 80+30 = 110; while 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 ex- 
 change places. The former affinities are termed the quiescent, the 
 latter the divellent affinities ; and whenever the sum of the divel- 
 lent is greater than that of the quiescent affinities, decomposition 
 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 chlorine 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 : 
 
 30 
 
 ««{SX^: f^hurh* 
 
 10 
 
 the force producing decomposition being 30-|-10=40, and greater than those, 
 204-15=35, 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 form ; 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 
 
CAUSES WHICH INFLUENCE AFFINITY. 161 
 
 should tind tneh place, and all possible cases of chemical decompo 
 sition might be loretold with the same accuracy as the law of grav- 
 itation allows the disturbing effects of a new planet to be calculated ; 
 but, unlortunateiy tor tiie simplicity of expression which the laws of 
 chemical aifinity would thus assume, new and unexpected compli- 
 cations arise, and embarrasjs all cur explanations ; thus, if we take 
 muriatic acid, and form a table oi the affinities of bases for it, we 
 «hail find that it is as given m Jyo. i, aud constructing for sulphuric 
 iccid an independent column, we sh&Jl liW 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 strong- 
 est base in one column, is the weakest in the other j and barytes 
 and strontia, which manifest the most intense affinity for sulphuric 
 dcid, are found but midway among the bases arranged in order of 
 strength for muriatic acid. Which column must be taken as repre* 
 senting the true order of affinities'? What principle is there by 
 which these conflicting testimonies of experiments may be brought 
 to correspond 1 The answer is, that neither table is exclusively 
 correct j that these lists, although showing the order of decomposi- 
 tion, and thus exhibiting to the eye, most usefully, the result of a 
 great number of experiments, must not be supposed as strictly show- 
 ing to us the order of the affinities of these bodies, unless we apply 
 thereto a number 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 unim- 
 peded, 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 fre- 
 quently 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; according as the cohesion of the acting bodies may pre- 
 vail, decompositions, simple or compound, may be produced in op- 
 posite ways j and thus a chemical result is not the simple conse- 
 (juence 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 ob- 
 ject, 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 organized 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 
 
 X 
 
162 CAUSES WHICH INFLUENCE AFFINITY. 
 
 had there been no means of dissolving their connexion when once formed, immedi- 
 ately 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 tendency to combine, and long since all nature would 
 have been arranged into some few chemical combinations, the breaking up of vi'hich 
 could not be accomphshed 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 would have revolved in space a barren and uninhabitable ball. 
 
 The action of these modifying causes may be easily exhibited by one or two ex- 
 amples. It has been already described how a solution of muriate of hme is decora- 
 posed 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 hme remains behind. If watery vapour be brought into contact with me- 
 tallic 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 af- 
 finity 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 re- 
 moved by the hydrogen in the state of water, and metallic 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 decomposi- 
 tion was not the order of affinity, and pointed out the importance 
 of attending to the other forces that modify it, was led by his ob- 
 servations to assert that the power to which we have attached so 
 much importance, elective affinity, had no real existence ; he said 
 that chemical union differed from mechanical cohesion only in being 
 exerted between the particles of different substances, and that in all 
 cases where certain bodies combined in preference to others, the 
 source was to be found in the accidental and external circumstances. 
 On his ideas, the force by which the particles of a fragment of sul- 
 phate of soda are united, differs from the force by which the sulphu- 
 ric acid is united to the soda only in the fact that the cohesion 
 unites particles of the same kind, while affinity unites particles of 
 different kinds. A salt dissolved in water is thus 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, Avhich, although sup- 
 ported by the amazing talents of Berthollet, has been finally and to- 
 tally given up. We do not now consider such phenomena as solu- 
 tion to be produced by chemical affinity, for we require that a chem- 
 ical compound should have parted with the properties of its constit- 
 uents, 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 ag- 
 gregation is one of the most common evidences of chemical combi- 
 nation, as where muriatic acid and ammonia, both gases, become sol- 
 id; oxygen and hydrogen, both gases, become liquid; water and 
 bichloride of tin, both liquid, become solid, and innumerable other 
 
AFFINITY AND COHESION. 163 
 
 cases. The production of heat, and often light, is one of the most 
 universal attributes of chemical action 3 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 conse- 
 quent on this change of volume, a change, generally an increase, of 
 the specific gravity of the body from the mean specific gravity of its 
 constituents 3 thus, when oxygen and nitrogen unite to form nitrous 
 oxide, the volume of the compound is but | of that of the mixed 
 constituents ; when nitrogen and hydrogen unite to form ammonia, 
 the resulting volume is but ^ of that of the gases mixed before com- 
 bining ; if 100 volumes of alcohol be mixed with 100 volumes of 
 water, the mixture will occupy but 196 volumes 5 and on mixing 
 similar quantities 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 explained 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 
 characteristic 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 de- 
 grees. On the contrary, 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 hard- 
 ness, 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 j but it is not in the na- 
 ture of cohesive forces to render the hardness of one body opposite 
 to the hardness of another, so that together they shall produce soft- 
 ness. Yet such is the nature of the sources of chemical activity ; 
 thus sulphuric acid and soda are actuated by affinities for each oth- 
 er ; 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 
 character of a powerful alkali ; yet these forces are so peculiarly 
 related to each other, that, when the bodies have combined, the 
 acid and the alkaline properties disappear, and there results a sub- 
 stance, formed by their union (Glauber's salt), innocent, inactive, 
 with little tendency to combine, 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 solu- 
 tion are found most active where the resemblance between the 
 bodies is most complete. Thus metals adhere most powerfully to 
 
164 AFFINITY AND COHESION. 
 
 Other metals, and for their sohition, mercury, a liquid metal, can 
 alone be used j salts dissolve in water always most easily when they 
 show their resemblance to it by already containing water of crystal- 
 lization in their mass ; inflammable bodies, as sulphur and phospho- 
 rus, 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 con- 
 trary with chemical combination , the more complete 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 proper- 
 ties is its effect. Thus the gases, ammonia, and muriatic acid, a 
 caustic alkali, 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 farther combination with 
 oxide of iron and with potash, may 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, 
 produces agreeable intoxication (nitrous oxide) ; in other propor- 
 tions, a deep orange-coloured gas (nitrous acid), which, by int^se 
 cold, may be obtained liquid j and in an intermediate form, a gas 
 colourless and transparent (nitric oxide), which, when mixed with 
 air, produces, by combining 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 proper 
 ties 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 observed between them arose solely from external cir- 
 cumstances. This principle has been rejected ; but the discussion 
 to which it was subjected showed the importance of attending to 
 the influence which external circumstances really do exercise, and 
 which is frequently, in practice, more powerful than the force of af- 
 finity itself. It is therefore necessary to study in detail the influ- 
 ence of the external physical agents upon 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 influ- 
 ence of cohesion by the Latin proverb : Corpora non agunt 7iisi sint 
 soluta ; bodies do not act unless they be dissolved. And of all 
 forms of matter, liquidity is that in which chemical action is most 
 rapid and most energetic. 
 
INFLUENCE. OF COHESION. 165 
 
 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, is even slightly 
 touched, detonation follows. In these cases, the original arrange- 
 ment of particles must have been so instable, that the imperfect ap- 
 proach produced by mechanical mixture, or the slight change of po- 
 sition 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 with- 
 out chemical action on one another. 
 
 In the gaseous form of matter, chemical affinity appears to be 
 controlled and weakened by the mutual mechanical repulsion of the 
 gaseous particles. Thus, oxygen and hydrogen, bodies whose af- 
 finities are so strong, may remain in contact as gases for an indefi- 
 nite period. Nitrogen and hydrogen have no apparent tendency to 
 unite when mixed. Hydrogen, in the form of a gas, is without ac- 
 tion on carbon, or arsenic, or phosphorus, although under other 
 circumstances it unites with them, forming characteristic bodies. 
 In order to obtain the full chemical 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 hydrogen is liberated, there is a 
 moment before the hydrogen actually assumes the permanently elas- 
 tic form ; and being then, perhaps, liquid, and in a highly concentra- 
 ted condition, its affinities are manifested with extraordinary force. 
 It is the same with other gases j they act always with their full 
 power only in their nascent state. 
 
 The influence of cohesion in determining chemical action is, 
 however, of much greater importance in another way, as serving, 
 upon the principles of Berthollet, to explain the anomalous discord- 
 ance between those experiments upon which the tables of the affin- 
 ities 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 ; while, if the relation of the bases 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 influ- 
 ence 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 mo- 
 ment by both bases, and each base by both acids, so that there oc- 
 curs 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 while the solution is dilute, all remain so ; but if the liquor be 
 very much concentrated, the sulphate of potash, being a sparingly 
 soluble salt, is deposited in crystals, and a new distribution takes 
 
166 ARRANGEMENT OF ACIDS AND BASES. 
 
 place in the mother liquid. Supposing all sulphate of potash re- 
 moved, 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 continued, 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 de- 
 composition which actually occurs, and the manner in which it real- 
 ly 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 j and on 
 continuing the evaporation, all sulphuric acid may be removed in 
 combination with the lime. But the acids and bases being divided 
 among one another in solution, there coexist sulphate of lime, sul- 
 phate 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, all its constituents are eliminated in 
 combination, precisely as the sulphate 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 sujphate of barytes ap- 
 pears instantaneous to the senses, it yet may, in point of fact, be 
 just as gradual as in other cases. Thus there may have been a mo- 
 ment 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 detected, the quantity of ba- 
 rytes in the solution is reduced to the mere trace of sulphate Avhich 
 the quantity of water can dissolve, and which is too small to be de- 
 tected by our ordinary tests. 
 
 The nature of double decomposition depends thus on the relative 
 solubility of the compounds formed. In whatever w^ay the most in- 
 soluble 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 j 
 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 
 
DISTRIBUTION NOT INVARIABLE. 167 
 
 The inversion of affinity which is produced by the influence of 
 cohesion 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 potash in alcohol, the salt is decomposed, acetic acid be- 
 ing set free, and carbonate of potash formed. The cause of this is 
 the insolubility of the carbonate of potash in alcohol j for, on the 
 first action of the carbonic acid, the potash divides itself between 
 the two acids, and there is formed some carbonate, which is thrown 
 down ; then another quantity, 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. 
 
 By this principle of distribution of acids and bases, we are thus 
 enabled to account for a variety of facts, which appear totally op- 
 posed to affinity, if it were not subject to such modifications j but, 
 although it is so convenient for explanation, it should not be ad- 
 mitted as a principle in science if there could not be adduced evi- 
 dence 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 emerald green. Now, on mixing mu- 
 riatic 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 solu- 
 ble of the two. Also, on mixing a solution of sulphate of iron with 
 sulpho-cyanic acid, the liquor becomes intensely blood-red colour- 
 ed, showing that a quantity of sulpho-cyanide of iron has been 
 formed, although the sulpho-cyanic acid is much weaker than the 
 sulphuric, and no precipitation occurs to favour its production. 
 
 These, and many other such examples which might be brought 
 forward, show that the opinion of Berthollet, that the acids and 
 bases, when mixed together in solution, arrange themselves so 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 ex- 
 periments ; 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 abandon the idea of chemical affinity being 
 elective. 
 
 The answer to this question has been long since received in sci- 
 ence. The principle of Berthollet does not hold always, for nn- 
 merous 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, while 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 '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 
 
168 INFLUENCE OF ELASTICITY ON AFFINITY. 
 
 changing the red to that of the onion-skin, no sign of it is found 
 until all the boracic acid has been expelled. Here, therefore, there 
 is no partition of the base between two acids ; all the sulphuric acid 
 which is added unites with the soda, and all the boracic acid is ex 
 pelled. 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 no division of base between the two. The carbonic acid is to- 
 tally expelled, 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 BerthoUet 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 for the absolute order of affinities. 
 
 To sum up the details that have been given of the influence of 
 cohesion on the affinities of bodies acting on each other in solution, 
 it may be said that, 1st, In almost all cases of precipitation, the na- 
 ture of the double decomposition is determined much more by the 
 fact of one of the bodies formed being insoluble, than by the result- 
 ant of the united affinities of the bodies which are engaged. 2d, 
 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 strong- 
 est base, and the weakest acid with the weakest base ; and if there 
 be not base sufficient to neutralize all of the acids, a corresponding 
 quantity of the weakest acid being left out of combination alto- 
 gether 5 but, 3d, 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, the number of com- 
 pounds in solution will be equal to the whole number of acids mul- 
 tiplied by the whole number of bases present. 
 
 2d. The Influence of Elasticity. — The absence of cohesion, or, still 
 more, the substitution for cohesion of its antagonist power repul- 
 sion, 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 substance 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 otlfer bodies. In all such cases the same 
 principle of distribution, so fully described already, may be suppo- 
 sed to hold : thus a solution of sulphate of magnesia is perfectly 
 
INFLUENCE OF COHESION AND ELASTICITY. 169 
 
 decomposed by ammonia, the magnesia being precipitated ; but, on 
 mixing sulphate of ammonia with dry magnesia, and applying heat, 
 the ammonia is expelled, and the sulphuric acid remains, united 
 exclusively with the magnesia. Supposing that there is little dif 
 ference 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 mag- 
 nesia is insoluble, and it is expelled j in the dry way the excess ot 
 ammonia is gaseous, and it is driven off; and thus, with the same 
 substances and the same affinities, precisely opposite decomposi- 
 tions are produced by the influence of cohesion and elasticity. 
 The decomposition of muriate of lime by carbonate of ammonia 
 in solution has been already noticed, where carbonate of lime is 
 formed in consequence of its insolubility. If the carbonate of 
 lime and the muriate of ammonia so produced be dried and heated, 
 the precisely reversed decomposition 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 in- 
 terchange of elements is complete. 
 
 The boracic acid has been already noticed, as being one so fee- 
 ble in its affinities that the law of the division of acids and bases 
 does not hold with it, but 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, while the fixed boracic acid will remain combined with 
 the whole quantity of base. The white, inert, earthy substance, sil- 
 ica (powdered flints), the acid properties of which are so feeble 
 that it is only from analogy that it is recognised 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 j 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 j and admitting 
 that in the commencement a partition of the base between the two 
 took place, even to a very small extent, the final and complete ex- 
 pulsion of the more volatile must result. 
 
 From 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 upon water as being a base of considerable force, and 
 entering into combination in forms which should possess consider- 
 able 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 
 
 Y 
 
170 INFLUENCE OF VARIOUS MODIFYING CAUSES. 
 
 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 re- 
 main 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 sub- 
 stance, the decomposition 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 de- 
 composed. The removal of the carbonic acid is accomplished, in 
 burning lime on the large scale, by the limestone beiiig heated in a 
 kiln, through which there is a continuous draught, by which the car- 
 bonic acid is carried ofT 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 redness 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 com- 
 pletely caustic. 
 
 It is in this way, also, that we may explain the contrary order of 
 decomposition 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 kept full 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 al- 
 lowed full play, the reduction of the metal is completed. 
 
 Independent of its influence on cohesion, a change of tempera- 
 ture 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 producing the explosion of gaseous mixtures, de- 
 pends 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 
 
BERTHOLLETS THEORY OF AFFINITY. 
 
 171 
 
 often to diminish the affinity of bodies ; thus the explosion of de 
 tonating compounds was so explained ; but this appears to arise 
 from the heat really exalting the affinity of the more powerful con- 
 stituents, 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 exam- 
 ples of mere separation of elements on the application of heat j but 
 Marchand and 1 have found that these bodies contain hydrogen, and 
 that they are decomposed in consequence of the formation of hy- 
 drochloric or hydriodic acid To produce many bodies of instable 
 nature, it is necessary to avoid the use of heat 5 not that heat dimin- 
 ishes the affinities of their elements in general, but that the heat 
 enables those elements to satisfy their affinities better, by combining 
 in a more stable form. 
 
 It has been mentioned that Berthollet considered affinity as be- 
 ing not elective, but that the combination of one body to another 
 was determined 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 
 thejr 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 pro- 
 portion to their masses, but of their affinities ; and hence might ap- 
 pear to admit that bodies had different degrees of affinity, and that 
 this might, therefore, be elective j but, if I conceive his opinions 
 rightly, the affinity of which he spoke was not the force to which 
 we assign the power of choice of one body over another, but he car- 
 ried 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 Ber- 
 thollet recognises 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 numeri- 
 cal laws in chemistry, deserves notice. He looked upon the neutralizing power of 
 a body as being the measure of its affinity for anoth^, and considered that the de- 
 viations from this rule arose from the influence of cohesion or of elasticity : thus 
 the same quantity of potash is saturated by 
 
 Sulphuric acid . 
 
 . 40 parts. 
 
 Muriatic acid . . 
 
 . 36-5 parts 
 
 Nitric acid . . 
 
 . 54 " 
 
 Acetic acic . . 
 
 . 51 
 
 Carbonic acid . 
 
 . . 22 " 
 
 Oxalic acid . . 
 
 . 36 
 
 Hence, if mere affinity was allowed to act, carbonic acid should be the strongest, 
 and nitric acid the weakest in the list ; in like manner, the same quantity of sul- 
 phuric acid neutralizes 
 
 Potash 48 parts. 
 
 Soda 32 " 
 
 Ammonia 17 " 
 
 Lime 28 parts. 
 
 Barytes 76 *' 
 
 Magnesia 18 " 
 
172 INFLUENCE OF LIGHT ON AFFINITY. 
 
 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 substan- 
 ces that are equivalent to each other in combination, are fully recognised as totally 
 independent of the force of affinity exercised by each body. As yet we have no 
 other measure of affinity than the order of decomposition, controlled by the esti- 
 mate 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. 
 
 Of the Influence of Light on Chemical Affinity. — Although attention 
 has latterly been very much directed to the influence of light on 
 chemical affinity, from the accidental discovery of some very re- 
 markable 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 contem- 
 plated from any general point of view at the present moment. So 
 far, however, as positive facts have been discovered, and as even 
 plausible explanations of those facts have been suggested, I shall en- 
 deavour to represent, briefly, the actual condition of our knowledge 
 of this department. 
 
 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 diff'use daylight, 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 into chloride of hydrogen, water being decompo- 
 sed, and oxygen eliminated 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 dis- 
 coverer. Dr. Davy. Chlorine and sulphurous acid unite also only 
 when exposed to brilliant sunshine ; so much so, that in Dublin but 
 few days in summer are found bright enough to form it. The de- 
 composing action of chlorine, iodine, and bromine upon organic 
 bodies, which consists in the separation of hydrogen, and the as- 
 sumption 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 Cg H3 0., the body C3H2C]. 
 0. ; but in Paris, in summer, the chlorine removed another equiva- 
 lent of hydrogen, and Dumas and I succeeded in obtaining the body 
 C3 H. CI2 0. In like manner, in bright sunshine, the action of 
 chlorine on pyroxylic spirit is so violent, that unless the vessel be 
 carefully shaded, the decomposition proceeds by a series of explo- 
 sions, while I have found it exceedingly difficult in gloomy weather 
 to produce any action whatsoever. Instances of this kind might be 
 very much multiplied, but those described are sufficient to point out 
 the general manner in which light is found to act. 
 
PHOTOGRAPHIC DRAWING. 173 
 
 The action of light appears occasionally limited to the simple 
 separation 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, containing less cyanogen, is also an example of this 
 principle. 
 
 Setting aside, for the present, the influence of light on the pro- 
 duction of colouring matters in organic bodies, which will be de- 
 scribed as a portion of the chemical history of the individual sub- 
 stances, I shall now only advert to the action of light upon the com- 
 pounds of the easily-reducible metals, particularly silver, by the study 
 of which such 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 distilled water contains in small quantity. Chloride of silver 
 also is afl^ected 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 de- 
 stroying the organic matter therein dissolved. I apprehend that in 
 most, if not all cases of the decomposition of a metallic salt and the 
 reduction of the metal under the influence of light, a substance con- 
 taining 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 of obtaining accurate outlines, and is called photography^ or 
 'photographic drawing. If a sheet of paper be washed with a very di- 
 lute solution of 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 exposure even to moderate light. If an opaque body 
 be laid betvyeen a sheet of such paper and the light, the portions to 
 which the light arrives become dark, while that under the object re- 
 mains 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 re- 
 move the silver compound under the pattern j for if it remained, the 
 blackness would gradually become uniform over the entire surface, 
 and the picture would be efl'aced. This is effected by washing the 
 paper, after the image has been completely formed, by a solution of 
 some substance capable of dissolving out all of the undecomposed 
 salt of silver j for this purpose, ammonia, hypo-sulphite of soda, and 
 strong solution of common salt are those generally employed. 
 
 The most remarkable features connected with the chemical agen- 
 cies of light result from the recent experiments of Herschel. He 
 
174 
 
 COLOURING EFFECTS O.F THE CHEMICAL RAYS. 
 
 has shown, as was slightly noticed when describing the general char- 
 acters 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 substance employed to show their decomposing ac- 
 tion, 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 ac- 
 tion 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 CHi the paper. 
 Thus the colours impressed were in one experiment : 
 
 Spectrum Colours. 
 
 Colours formed on the Paper. | 
 
 Extreme red. 
 
 None. 
 
 Mean red. 
 
 None. 
 
 Orange. 
 
 Faint brick red. 
 
 Orange yellow. 
 
 Brick red, pretty strong. 
 
 Yellow. 
 
 Red, passing into green. 
 
 Yellow green. 
 
 Dull bottle green. 
 
 Green. 
 
 Do., passing into bluish. 
 
 Blue green. 
 
 Very sombre blue. 
 
 Blue. 
 
 Black, passing into metallic yellow. 
 
 Violet. 
 
 Do. Do. 
 
 Beyond the violet. 
 
 Violet, or purplish black. 
 
 It is in the lavender-coloured space that the chemical effects are 
 generally most intense ; when the light of it had been concentrated 
 by a lens, and received on a piece of prepared paper, the blacken- 
 ing was instantaneous, precisely as if a red-hot body had been ap- 
 plied behind, or a smoky flame directed on the paper over all the 
 space illuminated, and accurately marking 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 be- 
 yond the red space, in which the darkening action of the diffuse 
 light appears to have been suspended. The opposite extremities of 
 the spectrum appear, therefore, to have different powers, the dark- 
 ening 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 unalter- 
 ed 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 si- 
 multaneously on the paper, the neutralizing power of the opposite 
 ends of the spectrum was beautifully shown. The blackening pow- 
 er of the more refrangible rays was suspended over all the space 
 
PROCESS OF TAKING IMAGES. 175 
 
 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. 
 
 The paper with which those results were obtained derived its 
 sensibility to light from chloride of silver ; but the action of other 
 salts of silver gives 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 spectrum, and the whitening effect is produced 
 beyond it to a considerable distance. The subject has been shown 
 by Herschel to be one of considerable importance and great extent j 
 and from the popular interest it excites, some clew to a more gen- 
 eral knowledge of its principles will probably 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 
 deserves attention, as being founded upon the chemical agencies of 
 light, although hitherto there has been but little success in the at- 
 tempts made to assign a theory of it. It is not complicated in de- 
 tail. A plate of silvered copper is cleaned with dilute nitric acid, 
 so that the surface of silver may be absolutely pure, and is then ex- 
 posed to the vapour of iodine until a gold-coloured pellicle of iodine 
 of excessive tenuity is deposited upon it. In this state it is very 
 sensible to light. The plate so prepared is placed in a camera-ob- 
 scura, 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 submit- 
 ted to the action of the vapour of mercury, by which the picture is 
 rendered visible. As there still remains, however, a general sensi- 
 bility to the farther influence of light, this is removed by dissolving 
 away all the iodine and iodide of silver by a solution of hyposul- 
 phite of soda. The shadows remain then marked by smooth amal- 
 gamated surfaces, and the lights, by the corresponding portions be- 
 ing of a dull gray colour, possessing only a power of diffuse reflec- 
 tion. 
 
 The explanation of this process, which, from my own observations, I am disposed 
 to suggest, is, that the iodine combines with the silver, and forms iodide of silver, 
 which is spread in an amorphous state, forming an excessively thin layer, like var- 
 nish, over the surface of the plate. Under the influence of the light, I consider that this 
 crystallizes as melted sugar does, but so minutely as to be invisible to the eye, and 
 the closeness and completeness of the crystalline structure being proportional to the 
 duration and intensity of the light to which it had been exposed. When, then, the 
 vapour of mercury attacks the plate, the iodide of silver in both conditions is de- 
 composed, and the iodine being replaced by mercury, an amalgam of silver is form- 
 ed, uniform in surface, and perfectly metallic in its lustre, over the shaded portions ; 
 but the crystalline iodide, in being decomposed, gives a crystalline amalgam, which, 
 from the minuteness of its particles, presents only a grayish tint, and, being mixed 
 with interspersed points of bright, smooth amalgam where the light had been less 
 powerful, shades off proportionally all the intermediate effects. 
 
 The application of the mercurial fumes cannot be pushed far enough to decom- 
 pose all the iodide of silver, for it would injure the picture by depositing itself irreg- 
 ularly and in excess. It is therefore necessary, as soon as enough has been acted 
 on by the mercury to bring out the picture in a distinct manner, to remove the re- 
 mainder by the washing which has been described. 
 
 The influence of colour on the production of pictures by Da- 
 guerre's process is very marked ; the images of green objects are 
 scarcely at all defined, so that the method is scarcely applicable to 
 
176 PROCESS FOR TAKING PORTRAITS. 
 
 taking landscapes. Red and orange are also very feeble in their ef- 
 fect ', but blue, even so intense 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 col- 
 ours in a manner similar to that discovered by Herschel, and already 
 noticed, has been remarked in Daguerre's process, although so ir- 
 regularly 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 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. 
 
 [Since the preceding paragraphs were written by Dr. Kane, nu- 
 merous improvements have been made in this beautiful chemical 
 art in America and elsewhere : the theory of the process is also 
 much better understood. The most important of these improve- 
 ments is the application of Daguerre's process to taking portraits 
 from the life. This is due to Dr. Draper, who succeeded with it 
 soon after the French process was known in this country. At first 
 the direct or reflected rays of the sun were required ; but modes of 
 preparation, giving the plate more sensitiveness, have been since dis- 
 covered, so that the ordinary diffused light of day is now sufficient. 
 
 The best process for obtaining portraits is as follows : The plate, 
 having been carefully cleaned, is iodized to a pale lemon colour ; it 
 is then exposed to the vapour of bromine for a sufficient length of 
 tjme to bring it to a golden yellow. It is a great advantage to keep 
 it in total darkness for three or four hours before using it. The 
 person whose portrait is to be taken, having been seated in a suita- 
 ble chair, with a support to keep the head perfectly steady, before a 
 window, so that the light shall illuminate all those portions seen in 
 the camera with proper strength, the plate is to be exposed to the 
 focal image for a time, which may be determined by previous trials. 
 
 Much of the beauty of the picture depends on the object-glass of 
 the camera j very good proofs may be had by an arrangement of 
 uncompensated convex lenses four inches in diameter and eight 
 inches in focus ; but the most finished pictures are obtained by the 
 use of achromatics, which ought always to be preferred. 
 
 The process of exposing the proof to the mercurial vapour is one 
 of great delicacy j sometimes the object is suddenly evolved, some- 
 times it requires the mercury to be maintained at 175^ Fahrenheit 
 for a long time. Experience alone can determine when the full ef- 
 fect has been obtained. 
 
 After the picture has been brought out, and the coating of iodide 
 of silver removed, it remains only to efiect the gilding. This is ac- 
 complished by pouring all over the silver surface a very weak solu- 
 tion of the chloride of gold in hyposulphite of potash, and warming 
 it gently with the flame of a spirit-lamp. At a particular tempera- 
 ture, the shadows increase in depth and the lights in brillancy ; the 
 plate is then to be thoroughly washed. The gilding serves to render 
 
THEORY OF THE PR^OCESS OF DAGUERRE. 177 
 
 the picture immovable by ordinary exposure or accident, and im- 
 parts to it a beautiful satiny lustre, and chatoyant play of colour. 
 
 The great difficulty in the management of the Daguerreotype lies 
 in the circumstance that the iodide of silver is not affected corre- 
 spondingly by lights that are of different degrees of brilliancy, if 
 they should be of different colours. And it is only under particular 
 circumstances, not easy to reproduce, that lights of the same colour, 
 but of different strengths, produce a corresponding degree of white- 
 ness on the plate. Often, whtn the light is too active, the proof 
 takes on an unpleasant slate-blue colour, from the exterior portions 
 of the iodide assuming a state of solarization before those beneath 
 have had time to undergo change ; a phenomenon resembling what 
 takes place when a sheet of paper is held before a very bright fire, 
 the exposed surface becoming scorched, while the back has scarce- 
 ly had time to become warm. 
 
 As respects the theory of this process, 1 do not coincide with the 
 views expressed by Dr. Kane. In the shadows no mercury exists ; 
 the lights are an amalgam. When a Daguerreotype is exposed to 
 the vapour of mercury to bring out its picture, a decomposition of 
 all those portions of the iodide which have Iseen exposed to the 
 light ensues ; an amalgam is formed, and the iodine expelled unites 
 with the metallic silver behind, effecting, therefore, a corrosion of 
 the plate ; no iodine is evolved, and for obvious reasons such an 
 event is impossible. The light therefore imparts to those portions 
 of iodide on which it has impinged, the quality of being decomposed 
 at a lower temperature by the vapour of mercury than the temper- 
 ature at which an unexposed iodide can be decomposed ; an amal- 
 gam therefore forms on such positions when the temperature does 
 not rise beyond 175° F., though the whole surface might be decom- 
 posed and whitened if the temperature were carried high enough. 
 
 The chemical rays which affect the iodide of silver are chiefly 
 those of high refrangibility, and these rays manifest many habitudes 
 resembling those of radiant heat. They are absorbed and lost in 
 effecting the change, so that a ray of light which has once fallen 
 on a Daguerreotype plate, and is reflected by it, has lost all its activ- 
 ity. Whatever, therefore, will interfere with the absorption, will in- 
 terfere with the sensitiveness of different compounds. Thus it has 
 long been known that there is a proper colour to which the plate 
 may be brought when it possesses the maximum of sensitiveness : 
 this is the golden yellovN^ ; when it is red, or green, or blue, it is 
 much less sensitive j and when of a lavender colour, hardly sensitive 
 at all. This arises from the circumstance that under these condi- 
 tions the optical character of the plate is such that it reflects the 
 active raj^s in part or altogether. • 
 
 I have already remarked that lights which vary in intensity do 
 not affect these plates in a corresponding way ; this arises from the 
 circumstance that, as the iodide of silver is undergoing change, a 
 large quantity of light becomes latent, precisely as a piece of ice in 
 the act of melting absorbs a large quantity of heat, not discoverable 
 by the thermometer ; this phenomenon accompanies the blueness 
 which the compound assumes as it changes into the condition of a 
 subiodide.] 
 
 Z 
 
178 NATURE OP COMBUSTION. 
 
 CHAPTER VII. 
 
 OF THE LIGHT AND HEAT DISENGAGED DURING CHEMICAL COMBINATION. 
 
 It has been already noticed that the union of substances having 
 chemical affinity for each other is accompanied by increase of tem- 
 perature ; 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 con- 
 sidering the relations of this phenomenon to affinity, it will be ne- 
 cessary to notice, first, the general circumstances of combustion; 
 secondly, the relation between the amount of affinity and the quan- 
 tity of heat evolved; and, finally, the explanations that have been 
 ofl^ered 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 ac- 
 companying phenomena are in general those on which popular at- 
 tention becomes fixed, and for which the process is generally car- 
 ried on ; and hence, to the world at large, combustion is of impor- 
 tance only as a source of heat and light. One of the bodies, as hy- 
 drogen or sulphur, is termed the burning or combustible body, and 
 the oxygen is said to be the supporter of combustion ; but this lan- 
 guage, although convenient for common use, is incorrect as a scien- 
 tific expression ; for oxygen may be burned in a vessel of hydrogen, 
 as w^ell as hydrogen may be burned in a vessel of oxygen gas, the 
 one and the other being equally active in the process, and being re- 
 lated 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 analyzed 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 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 
 oxygen 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, when burning at common temperatures, emits but 
 little light, and forms phosphorous acid ; if it be heated, it bursts 
 into brilliant fiame, and forms phosphoric acid, which contains 
 
PRODUCTS OF SLOW COMBUSTION. 179 
 
 fths more oxygen. Potassium combines at common temperature 
 with oxygen, forming potash ; but when heated it burns with flame, 
 and combines 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.H.O., combines with 
 20. to form C.O2 and H.0. 5 and alcohol, which is C2H3O., combines 
 with 60. to form 2(C.02) and 3(H.O.). But at common tempera- 
 tures the slow oxidizement of woody fibre produces the black ve- 
 getable mould, a form of ulmine, the C.H.O. taking O. to form C.H.O2. 
 At common temperatures alcohol becomes acetic acid, the C2H3O. 
 combining with 20. to form C2H2O2 and H.O. The pyroxylic spirit 
 at common temperatures becomes, by slow combustion, formic acid, 
 C2H4O2 taking O4 to form C2H2O4 and 2(H.O.). 
 
 This slow combustion produces heat, although so much less than 
 is evolved by the more rapid process that it may easily be over- 
 looked. 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 into vivid flame. The oils and tallow, if there be a 
 large surface exposed to the air, as when cotton or linen rags im 
 bibed in oil lie in a heap, combine so rapidly with oxygen as to 
 form a sort of resin, that by the heat evolved the mass will be set 
 on fire ; and hence the origin of those spontaneous fires, so called, 
 which consumed the naval arsenal at St. Petersburgh, 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 decomposi- 
 tion has just commenced. The energy of this slow combustion 
 may be much increased by heat applied below the point which pro- 
 duces 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 brilliant combustion, forming then the ultimate products, wr • 
 ter and carbonic acid. 
 
 On this fact of the increased energy in the process of slow com- 
 bustion produced by a heat below that at which the body is in- 
 flamed, is founded the construction of the lamp without flame, or 
 the aphlcgistic lamp. If a wine-glass be taken, and rinsed inside 
 with strong alcohol 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 re- 
 mains, 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 atmo- 
 sphere, in which the ball of platina is immersed and works. 
 
180 CONSTRUCTION OF THE PLATINA GAS LAMP. 
 
 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 particles of whatever gaseous mixture it is immersed in. Hence, 
 if its surface is in the slightest degree soiled, it ceases to exert this 
 action ; and by increasing the surface, its energy may be augmented 
 in a remarkable 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 j 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 ex- 
 plode ; for the oxygen and hydrogen, being absorbed by the spongy 
 platina, are brought into intimate contact upon its surface, and unite, 
 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 pipe- 
 clay, 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 temper- 
 atures, 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 
 instantaneous light by means of the hydrogen gas 
 lamp. A vessel,/, contains dilute sulphuric acid, into 
 which the tube of the vessel g h dips nearly to the bot- 
 tom, having attached a piece of ordinary zinc, e. The 
 vessels being ground air-tight where they fit to one 
 another, when the stopcock b is closed, and the acid 
 S* acts on the zinc, the hydrogen evolved cannot escape, 
 and, pressing on the liquid in /, forces it up into A, 
 until the acid falling below the level of the zinc, the 
 action ceases. To the stopcock b 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 ox- 
 ygen, 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 prop- 
 erty to a slight extent, particularly when hot ; but in none is it ac- 
 tive enough to be usefully applied, except in platinum. 
 
 The temperatures at which bodies enter into rapid combustion 
 are very various ; thus phosphorus inflames at a temperature of 
 120° F., and sulphur at 300^ F. Phosphuretted hydrogen gas in- 
 flames at all ordinary temperatures, while hydrogen requires a dull 
 red, and carburetted hydrogen a bright red heat before they will 
 take fire. The inflammability 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 sub- 
 limed 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 
 
CONSTITUTION OF FLAME. 181 
 
 which enter into union are in contact. Thus, in an ordinary flame, 
 the true combustion is limited to a thin sheet, the 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 i? 
 dark, although full of inflammable vapour, which passes through un 
 inflamed, and may be ignited on the opposite side of the gauze. L 
 the flame of an ordinary candle, a, four distinct portions may be ob 
 served, having totally distinct constitutions ; at the base 
 of the flame, i i, a pale, blue-coloured light is emitted, for 
 there the air is in excess, and the combustion is at once 
 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, while the inside of 
 the flame, Z>, remains completely black, and is occupied only 
 by vapour incapable of burning from having no access to 
 the external air. The light emitted arises also from the 
 circumstances of the combination j the temperature of flame is in 
 all cases exceedingly 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 casef 
 where bright light is produced in combustion, one of the bodies en- 
 gaged must be solid, and the light is really derived from its becom- 
 ing 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 form- 
 ed, in both cases gaseous. Phosphorus, when it, in burning, forms 
 a volatile body, gives but little light, but when it forms a fixed prod- 
 uct, is one of the most brilliant instances of combustion. Iron and 
 zinc, which form solid oxides, burn with great light, and carbon, al- 
 though 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 decompo- 
 sition 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 actually cools the flame. 
 When, therefore, a high temperature, or a clear flame without smoke 
 is required, all the carbon must be consumed. This is efl^ected by 
 a variety of contrivances : in the burner of the Argand lamp or gas 
 
182 HEATING EFFECTS OF FLAME. 
 
 jet, a current of air is established through the centre of the flame, 
 and thus the combustion of the inflammable vapour much accelera- 
 ted ; in the flame of the blowpipe 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 fac- 
 tories situated in large cities. In the employment of the blowpipe, 
 the constitution of the flame is of great importance ; for according 
 as the body to be heated is placed at 6, where the 
 ^ oxygen of the air preponderates, or between a and 
 
 \\fi^^^^^::^='b ^j where it is immersed in an atmosphere of inflam- 
 
 ^?j2^ mable material, the most opposite effects of violent 
 
 I llll oxidation, and of reduction from the state of oxide, 
 
 ill ^^y ^® produced. Thus a glass of copper be- 
 
 ^^^ comes green at b, and red from a to b ; a glass of 
 
 manganese is rendered purple at 5, but colourless from a to b j there 
 being few bodies whose relations to the blowpipe can be completely 
 known without a comparison of the effect of the oxidizing and re- 
 ducing flames. 
 
 During combustion, the heat evolved is at first absorbed by the body which is 
 then produced ; but it is afterward distributed through the mass of all neighbour- 
 ing 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 tempera- 
 ture of the vapour produced should be, since one part of oxygen heats twenty-nine 
 parts of water, 180 degrees =| (29xl80)=:4640 above the freezing point ; but the 
 capacity of watery vapour in equal weight is only 0-847, and therefore it is more ea- 
 sily heated in that proportion than liquid water ; hence the temperature really pro- 
 duced is r=4640x0 847, or 5478 above the freezing point of water. If, however, in 
 place of pure oxygen, atmospheric air had been made use of, then 23- 1 parts of 
 oxygen are mixed therein with 769 parts of nitrogen, which must be heated to the 
 same temperature with the watery vapour, and, of course, at its expense. The ca- 
 pacity 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 
 exactly three times as much nitrogen, so that precisely one half of the quantity of 
 heat produced is absorbed by the nitrogen, and the temperature 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 
 ihe open air ; but the temperature of 5478°, given by hydrogen burning in oxygen, 
 is very nearly double that, and passes, therefore, far beyond the melting point of 
 platinum, and exceeds the heat of all our other artificial fires ; it is only in the dis- 
 charge 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 communi- 
 cating the combustion to the mass. In this manner, the combustibility 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 defiant gas, 
 two of ammonia, three of carbonic acid ; but with eight volumes of hydrogen, 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 re 
 
CONSTRUCTION OF THE SAFETY-LAMP. 
 
 183 
 
 ceive, enables them, in a still more remarkable 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 ig- 
 nited coal gas, the flame will be arrested at the low- 
 er 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 
 mixture of air and gas be allowed to pass through 
 the metallic gauze, and then ignited at its upper 
 surface, it will burn there ; but, although the space 
 between the jet and gauze be occupied by inflam- 
 mable material, the flame cannot pass down, the me- 
 tallic tissue conducting away the heat so rapidly as to prevent the 
 temperature froni 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 cov- 
 ers 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 
 considered, 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 negli- 
 gence, 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 Avhich the principle of cooling orifices may be most successfully 
 applied. The candle or lamp, Z», by 
 which light is to be obtained for work- 
 ing in the mine, is surrounded by a cyl- 
 inder of wire gauze, of about 1500 ori- 
 fices in the square inch. Inside of this 
 the inflammable mixture may explode, 
 but the flame cannot pass out ; the com- 
 bustion 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 emission of a spark would 
 cause destruction, and measures, by the 
 appearance of the lamp, the actual con- 
 dition of the air he breathes, the phe- 
 nomena of the flame indicating also its 
 fitness for Respiration. If the air be 
 pure, the lamp burns clear, as in the 
 upper air 3 if some fire-damp be present, 
 
184 QUANTITY OF HEAT EVOLVED IN COMBUSTION. 
 
 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 becomes extinguished, and the cylinder of metallic gauze is 
 filled by a sheet of lurid flame j the miner being then enveloped by 
 an atmosphere fully explosive, and even fatal to life if it be long 
 respired. If he proceed still farther, all flame is lost ; for, as the 
 fire-damp then predominates, 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 use 
 ful beacon glow, until an atmosphere is obtained where there is ox- 
 ygen enough to support a rapid combustion, 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 
 combustion of a given quantity of combustible substance is a prob- 
 lem 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 substances by means of the smallest quantity of air 
 which is suflicient, in a vessel surrounded, as far as possible, with 
 water. If it be found that the burning of a pound of wood heats 
 37 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 
 74? pounds of water through the same range, it follows that the char- 
 coal 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 ; but, by the late researches of Des 
 pretz and of Bull, which appear to have been conducted with more 
 attention to accuracy than former ones, a very interesting rule has 
 been obtained : it is, that in all cases of combustion 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°, 291 lbs. of water. 
 " *' " charcoal, " " 29 " 
 
 " " " alcohol, " " 28 
 
 a u .. gji^gj.^ u u 281 
 
 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 light upon the former differences. When phosphorus burns slowly, so as to 
 form phosphorous acid, it heats, in combining with a pound of oxygen, S8 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 remark, that in the cases where the smaller proportion of heat 
 is evolved, the products of combustion are all volatile, and where the larger propor- 
 tion is produced, the products are fixed and solid ; even in the case of phosphorus, 
 when it combines, producing least heat, it forms a volatile product, but one which 
 resists a full red heat in the case where the combination has been complete. 
 
 Hess has lately pointed out a relation between the amount of chemical action 
 
THEORY OF COMBUSTION. 185 
 
 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 un- 
 combined condition, as where vapour of anhydrous sulphuric acid produces, by con- 
 tact with dry barytes, brilliant ignition ; but, although the barytes generates, by con- 
 tact with dilute sulphuric acid, much less heat, yet, if the two quantities 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. Witli Water. Sum. 
 
 Oil of vitriol . . . 5958 5958 
 
 First dilution . . . 518-9 . . 778 . . . 5967 
 Second dilution . . 480 5 . . 116-7 . . . 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 chem- 
 ical combination may be connected with the equivalent number and the electrical 
 condition of the substances by a definite law, which farther investigation may dis- 
 <*lose. 
 
 At all periods in the history of chemistry, the explanation of the phenomena 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 un- 
 philosophical ideas of the existence of inflammability which prevailed before Lavoi- 
 sier'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 oper- 
 ate 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 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 a heat, a solid be- 
 comes a gasj and should produce an equivalent degree of cold. Lavoisier here 
 brought in 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 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 thr 
 contrary, the carbonic acid has a specific heat greater than that of the oxygen g. 
 it was formed from, in the proportion of 1195 to 808 ; and hence, on Lavoisier'a, 
 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 chem- 
 ical combination by an application of the law of Dulong regarding specific heats 
 (described page 66). 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 tem- 
 perature. Thus, considering oil of vitriol to contain seven combining equivalents, 
 two of hydrogen, four of oxygen, and one of sulphur, and that the specific heat of 
 all of these is the same, 31, as results from Dulong's law if it be supposed rigidly 
 
 exact, the specific heat of oil of vitriol should be ^^ =0442, 491 being the 
 
 Aa 
 
186 
 
 HEAT OF COMBir^ATION, WHENCE DERIVED. 
 
 equivalent number of oil of vitriol ; but the specific heat found by experiment Is 
 only 352 ; so that exactly 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 farther than Dr. Thompson appears to 
 have contemplated its application, some coincidences, with results already known, 
 are found, which give it an aspect of considerable theoretic interest. Thus we 
 may consider certain metallic oxides as consisting of an equivalent of each constit- 
 uent, and hence their proper specific heat should be, if none were lost by combina- 
 tion, 3-lx2=6-2 ; but the specific heat of the compound molecule is experimentally 
 found to be 54, and thus that 08 of heat had been lost, producing the phenomena 
 of combustion in combination. In this manner we can understand why Despretz 
 found that a certain quantity of oxygen evolves the same quantity of heat in com- 
 bining with very many bodies. If we examine the sulphates noticed, p. 67, in re- 
 lation to the same principle, we find that as there are in each six molecules, the 
 specific heat should be 18-6=3-lx6 ; 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 
 it is from the oxygen that the portion set free is taken, the experimental result 
 arises from the heat of each oxygen molecule being reduced by 1-6, and hence that 
 when oxygen 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 phosphorus into phosphoric acid, com- 
 pared with what is evolved when it forms only phosphorous acid, may have its ori- 
 gin 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 mole- 
 cules, 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 
 carbonic acid 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 therefore 9-3-j-6-9-j-5=:20-7; or, re- 
 duced to the equivalent number used in p. 67, it is 10 35, the experimental number 
 being 104. 
 
 The results in these three cases may be shown in the form of the following table, 
 in which the first column contains the equivalent molecule 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. 
 
 M. 0. 
 
 6-2 
 
 31-1-23 
 
 5.4 
 
 12-2 
 
 54 
 12-4 
 
 M. O4S. 
 
 18-6 
 
 (2x31)-f(4xl-5) 
 
 M2O6C. 
 
 279 
 
 (3x31)-|-(3x2-3)-f3xl-5) 
 
 20.7J20-8| 
 
 The coincidences refer only to the bodies already selected, p. 67, as exam- 
 ples 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 there- 
 fore be accidental ; but there is yet so much likelihood of some physical law of the 
 kind being to be discovered, that everything that may assist in its detection is of 
 importance. 
 
 Laying aside altogether the attempt at deducing the phenomena of combustion 
 from any change in the amount of latent or of specific heat in the bodies which 
 enter into combination, it remains only to be admitted as a general and independent 
 principle that chemical combination is a source of heat and light. It is, however, 
 impossible to arrest inquiry at that point, and, accordingly, the speculations of phi- 
 losophers have been directed in seeking a cause for the phenomena of combus- 
 tion 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 produced by the separation or combination 
 of the electric fluids. The evidence in favour of this view will be best described 
 among the relations of electricity to affinity. 
 
INFLUENCE OF ELECTRICITY ON AFFINITY. 187 
 
 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 elements 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 gen- 
 erated without, by the chemical action of the more oxidizable met- 
 al, the liquid being decomposed, and some one element of it expell- 
 ed, in place of which a corresponding quantity of zinc may be sub- 
 stituted. 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 of electricity 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 communication 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- 
 gen would have been evolved as gas at the zinc extremity, and chlo- 
 rine 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 
 is 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 + extrem- 
 ity of the wires, occurs similarly ; protochioride 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 elec- 
 tricity pass through a solution of sulphate of soda, the sulphuric 
 acid appears upon the +, and the alkali upon the — wire. With 
 sulphate of magnesia, the earth passes to the negative, and the acid 
 to the positive extremity of the liquid circuit j in these cases water 
 
188 CHEMICAL AFFINITY ELECTRICAL ATrRACTION. 
 
 is also decomposed, of which the hydrogen accompanies the hase, 
 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 de- 
 posited in crystals upon the — wire, while 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 
 superseded during the passage of the electric current. The elements 
 previously 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 
 decomposed. 
 
 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, while this 
 last is more powerfully attracted by the negative pole than by the ox- 
 ygen. The elementary 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 ap- 
 plied to all such cases. Oxygen, chlorine, iodine, sulphur, as well 
 as the various acids, are attracted by the positively electric pole, 
 while hydrogen, potassium, sodium, copper, silver, lead, and the 
 various bases, are attracted to the negative pole of the battery. But 
 one force cannot completely supersede 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 elec- 
 trical force which makes them separate 1 The cause was easily 
 found : they are identical. The oxygen and hydrogen united ori- 
 ginally from being in opposite electrical states, and they are forced 
 to separate from being subjected to the action of still more power- 
 ful attractions ; 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 depended on which electricity it was 
 naturally excited by when in combination 5 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 di- 
 vided 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 ran- 
 ged as in the following list : 
 
ELECTRO-CHEMICAL CLASSIFICATION. 
 
 189 
 
 Electro-negative. 
 
 Mercury. 
 
 Palladium. 
 
 Electro-positive, j 
 
 Oxygen. 
 
 Potassium. 
 
 1 Fluorine. 
 
 Chrome. 
 
 A Silver. 
 
 Sodium. 
 
 t Chlorine. 
 
 Vanadium. 
 
 i Copper 
 
 1 Lithium. 
 
 1 Bromine. 
 
 i Iridium. 
 
 iLead. 
 
 T Barium. 
 
 Iodine. 
 
 T Rhodium. 
 
 Tin. 
 
 y Strontium. 
 
 Sulphur. 
 
 Y Uranium. 
 
 Bismuth. 
 
 Calcium. 
 
 Selenium. 
 
 Osmium. 
 
 Cobalt. 
 
 Magnesium. 
 
 A Tellurium. 
 
 Platinum. 
 
 Nickel. 
 
 Glucinum. 
 
 T Nitrogen. 
 
 Titanium. 
 
 .Iron. 
 
 Yttrium. 
 
 1 Phosphorus. 
 
 iGold. 
 
 t Manganese. 
 
 1 Thorium. 
 
 Arsenic. 
 
 T Molybdenum. 
 
 4 Cadmium. 
 
 T Aluminum. 
 
 Antimony. 
 
 ' Tungsten. 
 
 '"Zinc. 
 
 t Zirconium. 
 
 Silicon. 
 
 Columbium. 
 
 Hydrogen. 
 
 Lanthanum. 
 
 Boron. 
 
 J 
 
 Carbon. 
 
 Cerium. 
 
 Tht 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 arrows. Any substance in the list is positive with re- 
 gard 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 pre- 
 ceding 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. 129. 
 
 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 1 and why, if their condition resem- 
 bles that of ordinary electricity, do they remain combined, when 
 their opposite fluids might unite, and neutralization being produced, 
 all combination cease 1 
 
 These two questions have not yet been answered. Several times their explana- 
 tion has been attempted ; and thus the electro-chemical theories of Davy, Ampdre, 
 and Berzelius have been proposed. I shall briefly notice the leading features of 
 these before "proceeding to discuss the remarkable advance recently made in our 
 ideas of the electro-chemical relations 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 be- 
 come excited. Thus a disk of sulphur touched to a disk of copper becomes nega- 
 tive, 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 lecombme, carrying with them the molecules of the sulphur and cop- 
 per 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 forffied, 
 is no longer electric ; it remains permanent in virtue of a force which Davy does 
 not strictly define, but which he appears to have considered an intimate cohesion 
 between the particles which had been closely approximated by their electrical at- 
 tractions ; 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 sep- 
 arate. This view supposes, therefore, the electrical excitation to be only moment- 
 ary, dunng 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 
 
190 THEORIKS OF DAVY, AMPERE, AND BERZELIUS. 
 
 completely proved that it is not the contact which evolves electricity, but the 
 chemical action ; and also, on Davy's views, the electrical disturbance only suffi- 
 ces to account for the secondary phenomena of union, the light and heat, leaving 
 the act of combination to be ascribed to a different and independent force of affin- 
 ity 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 substance 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 them- 
 selves must remain permanently combined, 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 elec- 
 tro-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 proportions 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 are 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 combina- 
 tion 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 sulphur or arsenic be heated with potassium, 
 there is similarly combustion, showing 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 there- 
 fore at one time positive, and at another negative. There is, indeed, no substance 
 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 suggested 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 
 negative 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 contact with sulphur, the naturally feeble negativity of 
 the latter is heightened by induction, while, if the sulphur be acted on by oxygen, it 
 is its positive charge that is increased ; and thus any substance near the midd'e of 
 the electro-chemical series may become positive or negative, according as it com- 
 bines with a body situated nearer to the negative or positive extremity. 
 
DISENGAGEMENT OCCURS AT LIMITING SURFACES. 191 
 
 This ^iew 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 all 
 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 com- 
 bine, 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 with potas- 
 sium, bodies so far separated in the electro-chemical scale founded on their reactions, 
 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 com- 
 pleted ; the former is generally termed the generating, and the latter 
 the decomposing cell. 
 
 The decompositions hitherto described have been considered as 
 resulting 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 accumula- 
 tion can exist ; once the current passes, it is everywhere present 
 in equal quantity and of uniform tension ; and such forces of attrac- 
 tion and repulsion, acting upon molecules already electrically exci- 
 ted, were only imagined for the foundation of the imperfect theories 
 already noticed, and, when impartially examined, are found to have 
 no real existence. It is also fatal to the idea of attractive forces ex- 
 ercised by the poles, that the substances evolved upon their surface 
 do not necessarily combine with them ; thus, if one platina pole have 
 such attraction for oxygen as to separate 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 j 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, takes 
 place in all cases at the bounding surfaces 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 5 a strong solution of sulphate 
 of magnesia is poured in until it rises a little above 
 the edge of the partition, 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 magne 
 
192 ELEMENTS NOT EVOLVED ON POLES. 
 
 sia 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 e, 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 b, the hydrogen gas upon the plate e ; but, although 
 the sulphuric acid is liberated freely upon the plate b, no magnesia 
 travels farther than the limiting surface of the saline liquor c. Here 
 the metal e serves as a pole to the hydrogen, but not to the magne- 
 sia ; and the water on which the magnesia has evolved has no power 
 to prevent the farther passage of the hydrogen. 
 
 If A, C, B be filled with solution of sulphate of soda, and by means 
 -^ >^^ of the plates P and N, a current from a battery 
 
 A^ ^ T . . ^g 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 b, 
 the vessel be divided into three compartments 
 A, C, and B, and the central one being filled 
 with a solution of sulphate of soda, dilute nitric acid is poured 
 into those at the side in order to aflfbrd a conducting medium, 
 the acid and alkali do not appear at the metallic poles when the cur- 
 rent 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 de- 
 monstrated : if a slip of paper moistened with solution of iodide of 
 potassium be held near the insulated prime conductor of the elec- 
 trical machine while in action, and 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, while hydrogen and potash may 
 be traced as liar a» any liquid conductor admitting of their passage 
 goes. Here there is nothing that can be termed a pole ; the iodine 
 is discharged upou 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 ex- 
 plaining the decomposition of the liquid elements of the circuit must 
 be obtained. The word poles must first be laid aside, and the ex- 
 pressions proposed by Faraday in their place deserve universal adop- 
 tion. 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 {jiXen-pov^ o(5of), they being the routes through 
 which the electricity makes its way. I shall therefore, in future, 
 speak of the positive and negative electrodes in relation to the sur- 
 faces, generally of metal, by which the battery is brought to act upon 
 the substance which is to be decomposed. 
 
 Since there are thus no attractive forces by which the chemical 
 affinities of the substances in the decomposing cell can be overcome, 
 to what mechanism can we attribute the separation of elements 
 which occurs 1 Concerning this, as yet, there is only speculation to 
 
ELECTRO-CHEMICAL DECOMPOSITION. 193 
 
 be presented. 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 diiferent mole- 
 cule gives off its hydrogen 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 an- 
 other along the line, all particles of oxygen advancing a step against 
 the current, and the molecules of hydrogen moving in a correspond- 
 ing manner in the direction of it. Thus, if a line of particles of 
 water in a decomposing cell be represented ^ ^ 
 
 before the current passes, the electrodes be- -}-0.H. O.H. O.H. — 
 ing represented by the plus and minus signs, 
 on the current passing, a molecule of oxygen ^ ^ 
 
 will be evolved upon the positive, and one of — H. * xj* ' tt' * 0.-\- 
 hydrogen upon the negative side, as in the 
 second line 5 and as this motion is participated 2«» — v 
 
 in by every molecule of oxygen and hydrogen 4"0.H. O.H. — 
 in the circuit, they will come into the final po- .^ ^ 
 
 sition of the third line. The current still pass- O. ^ , 
 
 ing, another molecule of each will be evolv- "• * H. * 
 
 ed, as in the fourth; and, ultimately, all the 
 intervening water may be decomposed ; the , ^tt* 
 
 separation of the elements being thus accom- "^ ' * 
 
 panied by a continual rotation on each other of the intermediate 
 molecules, each molecule of oxygen being successively united with 
 every molecule of hydrogen in the series, and each molecule of hy- 
 drogen combining in turn with every particle of oxygen as it passes 
 along. In Faraday's words, the current is an axis of power, equal, 
 and exerted in opposite directions, by which, in every case of a 
 true binary compound, the molecules of one element are carried in 
 one direction, while those of the other constituent move in the re- 
 verse course. 
 
 From this idea, the evolution of the iodine, the soda, the magne- 
 sia 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 particles is broken, although there may be other con- 
 ductors to complete the circuit. The iodine is evolved where the 
 air touches the surface of the paper, because the air has no potas- 
 sium by which it could be carried farther. The decomposition ap- 
 pears 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 de- 
 composition 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 b, and water in the glass c, and they be connected together vj^ith slips of 
 amianthus, moistened to allov^r the passage of the current, and the positive electrode 
 
 Bb 
 
194 ELECTROLYSIS AND ELECTROLYTES. 
 
 imMH rifc. ' i tif ^ ^ ^ ^^ ^ battery be immersed in a, and the nega- 
 
 ^^iSr~~^^^^^~MS^^^~^^ ^i"*'® ^^ ^» ^^^ sulphate of soda will be decom- 
 
 , ^HM^ liteipi rallSH posed, and its alkali will appear in c, although 
 
 V^Sr 'BSli' ^IB^^ the acid in b, through which it must have 
 
 '^miffr ^^^ypgr /!Sg passed, retains all its power. Here, then, was 
 
 ^Vi^i S^S^^ ^J^^^ ^^^ affinity of the acid in b for soda complete- 
 
 — jS^^ — JL- v._„seE=- j^ annulled by the superior attraction of the 
 
 negatively electric pole in c, and this was considered to be farther proved by the 
 
 acid preventing the passage of barytes, for which its affinity was so much stronger ; 
 
 when a contained nitrate of barytes, the earth, on entering into b, combined with 
 
 the sulphi»ric acid, and went no farther. But in these experiments, considered at 
 
 the time so decidedly in favour of Davy's theory, that which was believed to be the 
 
 obstacle »o the passage of the soda is in reality the cause of it. Had there been no 
 
 acid in b, no alkali could have passed across it, and the barytes remained combined 
 
 only because, becoming insoluble, it no longer formed any portion of the hquid-con- 
 
 ducting medium. 
 
 It has been, indeed, found, that although a feeble current may- 
 be transmitted through liquid conductors without any sign of de 
 composition, yet, in general, the passage of a more powerful cur- 
 rent can only be accomplished by means of bodies which are at the 
 same time decomposed by its influence. Faraday proposes to term 
 the decomposition by the current electrolysis [TjXetcrpoVj Avw], and 
 such bodies as undergo electrolysis electrolytes. It is, therefore, 
 only electrolytes that are capable of conducting, and they do so by 
 the opposite directions in which the chains of liberated particles 
 move. That electrolysis may occur, it is necessary that the sub- 
 stance be in the liquid state, and hence all conducting power is lost 
 when the body becomes solid; ice is a non-conductor, and it is only 
 by being melted that the chlorides and iodides of lead and silver, 
 and such bodies, become capable of conduction, and of being hence 
 decomposed. But there are many bodies which insulate when cold, 
 and yet, when heated, allow the current to pass even before they 
 fuse, its passage being unattended by any electrolysis, even though 
 the current be very powerful. Sulphuret of silver, iodide and chlo- 
 ride of mercury, and fluoride of lead, are remarkable examples of 
 this anomaly. 
 
 Faraday, considering that the words 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 in- 
 correct, proposed 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 interrupt- 
 ed by a decomposing cell, the surface at which the current enters 
 the liquid may be termed the anode (dvd, upward), and the other the 
 cathode (fcard, downward) ; oxygen, chlorine, and such bodies are 
 evolved upon the surface of the anode, while from the cathode hy- 
 drogen and the metals are liberated. The elements which, by their 
 combination, form electrolytes, Faraday proposes to term ions, ir}\ii, 
 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 Far- 
 
THE CHEMICAL VOLTAMETER. 195 
 
 aday'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, 
 connecting the agencies of electricity and affinity, is the law of def- 
 inite electro-chemical decomposition. If the same current of elec- 
 tricity 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 
 
 8 grains of Oxygen and 1 of Hydrogen from 9 parts of water. 
 35-4 " Chlorine and 1 *' Hydrogen " 364 " muriatic acid. 
 35-4 " Chlorine and 108 "Silver " 1434 " chloride of silvei. 
 
 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 re- 
 duced. 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 sol- 
 dered the platina electrodes in connex- 
 ion with the battery ; the vessel and 
 tube being filled with water, which is A^ 
 rendered easily decomposible by the 
 addition of sulphuric acid, 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 meas- 
 ured. 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 in- 
 sisted on, then, in all electrolytes, the elements must be held togeth- 
 er by the same force, since they require the same amount of elec- 
 tricity to produce decomposition ; and we should return nearly to 
 the principles of Berthollet, that chemical affinity was equally pow- 
 erful for all bodies, and merely appeared to vary from external in- 
 fluences ; but this would be a rash and unphilosophical conclusion ; 
 the electrolytes are but one class of chemical bodies, those which 
 are primary compounds, of an equivalent of each element j the cur- 
 rent does not act upon deutoxides or bichlorides, and on double 
 salts its agency is exceedingly complicated. All that can be infer- 
 red from this very beautiful result is, that the elements of bodies 
 combine, in separating from each other under the influence of a cur- 
 rent, 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 electrici- 
 ties 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 oc- 
 curs in the generating cell, where the current which passes through 
 
196 ACTION IN THE GENERATING CELL. 
 
 the Other is 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 froni 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 be- 
 coming positively excited, and those of chlorine becom- 
 ing negative. This condition has been already described 
 (page 132) 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 excita- 
 tion referrible to one, and its negative to the other extremity, must 
 also, like the magnet, be looked upon as consisting of a great num- 
 ber of excited elements, each of which has its positive and nega- 
 tive extremities ; or, for greater definiteness, they may be consid- 
 ered as grouped in pairs, of which one molecule is positively and 
 the other negatively excited. The condition of the slip of zinc of 
 the last figure may therefore be represented as in the figure at the 
 A side, the particles of zinc being con- 
 
 W V. Y ▼j.^/0\(^/^~^(^i^ t^ii^^d ^^ the shaded bar, and those 
 ^^J^i^^^J^j^V-J V^v^^vly of the liquid, consisting of chlorine 
 Zn. Zn. Zn. Zn. CI. H. CI. H. and hydrogen, represented outside 
 of it. The terminal particle of 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 ««• o <:omplete the circuit, and to allow the passage of 
 the galvar' ^arrent, it is easy to see how the decomposition of the 
 exciting nuid follows 5 for although, in the arrangement above de- 
 scribed, the inductive excitement is most active at A, and diminish 
 es from thence as it extends 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 be- 
 comes equally powerful all through ; the particles 
 of copper assume 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 inductively polarized particles 
 being established, precisely such as are represented 
 by cuttings of silk thread which convey a current 
 from an electric machine through oil of turpentine ; the molecular 
 arrangement being represented in the following figure. Such be- 
 
ORIGIN OF THE GALVANIC CURRENT. 197 
 
 ing the position of the mutually-excited 
 molecules, the electricities of the particles 
 of zinc and chlorine nearest to each other 
 comhine, and their neutralization is follow- zn. 
 ed by that of the entire chain ; the adjacent 
 particles of zinc and 
 chlorine then unite, ^|#C)(+YCY+^ 
 ZmQ.JkTI T \ \Cop. and the hydrogen, dis- ^^kJ\J^^ 
 
 engaged, is thrown ^^^^• 
 
 upon the second particle of chlorine, its hy- 
 drogen upon the third chlorine molecule, by 
 which the hydrogen it had previously been 
 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. 2d, The completion of the chain of inductively polar- 
 ized particles, by the intervention of the copper plate and connect- 
 ing wire. 3d, The passage of the current, and the consequent de- 
 composition 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 de- 
 composition of the acid, for it precedes it ; but the quantity of chem- 
 ical action in the generating cell is proportional to the quantity of 
 electricity which passes, for it is produced entirely by its agency. 
 There is, therefore, 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 proportionally less. 
 
 Such is the theory of galvanism which I believe to be most con- 
 sistent 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 how much the circumstances of contact maybe changed; 
 and by every alteration of the conditions of chemical action, it va- 
 ries in direction and in power, although the relations of the solid 
 bodies which are in contact are not affected. Neither does the cur- 
 rent arise from the transfer of elements which occurs in the gener- 
 ating 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 mu- 
 riatic acid. In fact, although I have hitherto considered 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 sur- 
 
198 COMPOUND BODIES FORMED BY THE CURRENT. 
 
 face 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 presence of two substances for which its affinity is equal- 
 ly intense, it is disposed 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 ox- 
 ygen 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 sul- 
 phuric acid ; but when the zinc has become thus sheathed in metal- 
 lic copper, the decomposition would 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 decompo- 
 sition 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 consti- 
 tution, such as would enable it to act as the positive element of a 
 simple galvanic circle, then, no doubt, the purest zinc would decom- 
 pose 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 de- 
 pends 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 the nature of chemical affinity, 
 than it becomes as a means of presenting to each other, under the most favourable 
 circumstances for union, the different elements of the voltaic 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 produced, the se- 
 cretion of the raetalhferous ores into the veins and cavities of rocks accurately rep- 
 resented, and bodies, whose affinities for each other rank as the most intense, com- 
 pletely, though silently and gradually, separated from each other. It is to Becque- 
 rel that we owe almost all our knowledge of this important function of electricity ; 
 from him we have also received the important lesson, that it is not in the brilliant 
 effects of the great batteries of Davy or of Daniell that we must seek a clew to the 
 history of the electrical processes of chemical affinity, but in the slow but uninter- 
 mitting action of currents of such low intensity that a drop of pure water would be 
 an insuperable obstacle in their path. The electricity to be employed in the artifi- 
 cial 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 de- 
 tJiil, are best observed by means of a tube bent into a U shape, and at the bottom 
 of which is interposed a porous partition 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 con- 
 necting the hquids with the p^es of a feeble battery, or by im- 
 mersing 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 car- 
 bonate of soda and of sulphate of copper be thus brought to act 
 on one another, a double carbonate of copper and soda crys- 
 tallizes on the plate immersed in the copper liquor ; and if then 
 
SYNTHETIC ACTION OF ELECTRICITY. 
 
 199 
 
 the solution of soda be replaced by ordinary water, a new current is generated 
 which decomposes the first product, and forms a liew crystallization 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 cop- 
 per upon the metallic surface in the other tube. 
 
 By using two liquids which have unequal chemical actions on a 
 strip 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 nitrate 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 Uquids, generates a current which passes up through its mass, 
 and down from the lighter to the denser fluid : the copper dissolves, (c\ 
 therefore, above, and the salt formed being electrolyzed by the current, 
 its metal is deposited on the lowest surface under the form of crystals, 
 and this is continued until the free acid, and hence the electromotive 
 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 iso- 
 lated form, those simple bodies, as boron, silicon, potassium, &c., whose compounds 
 resist ordinary means most obstinately. It consists of a generating and of a decom- 
 posing cell. This last is a glass cylin- 
 der, a, within another glass cylinder, 
 b. The inner one, a, is four inches 
 long, and an inch and a half in diame- 
 ter, and is closed at the lower end by 
 a plug of plaster of Paris, 07 inch in 
 tliickness. This cylinder is supported 
 within the other, b, which is an ordi- 
 nary jar, about eight inches deep and 
 two inches diameter, by means of 
 wedges of cork. A piece of sheet cop- 
 per, c, four inches long and three inch- 
 es wide, having a copper conducting 
 wire soldered to it, is loosely coiled up 
 and placed in the inner cylinder, while 
 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 so- 
 lution 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, fre- 
 quently 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 cyhnder, especially on that part where 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 in- 
 tended to hold the metallic solution submitted to experiment, 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, while 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 beUeve, so far as to demonstrate a complete identity of cause. It 
 is possible that, hereafter, some sublime generalization may embrace the phenom- 
 ena of heat, of light, and of electricity, of cohesion and gravity, as well as of chem- 
 ical 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 
 
200 ELECTRO-CHEMICAL THEORY PROPOSED. 
 
 such a state of science, we dare not rashly seek to anticipate its approach ; 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 combi- 
 nation. 
 
 Where 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 electri- 
 city does appear, although in quantity bearing no proportion to that of the feeblest 
 galvanic battery. If I were to suggest an electro-chemical theory, such as might 
 agree with the facts that have hitherto been discovered, I should consider that bod- 
 ies in their free state are perfectly destitute of excitation ; 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 ori- 
 gin to the electricity employed in our experiments. When united, bodies are like- 
 wise destitute of electrical properties ; in iodide of potassium, the bond is the afiin- 
 ity of iodine and potassium for each other, and not that the iodine is in a perma- 
 nent state of negative excitation while the potassium remains positive. 
 
 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 Pouil- 
 let. 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, and the negative rests upon the carbon. The evolution of 
 heat may be in these cases an independent effect of combination, 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 combus- 
 tion, 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 po- 
 larized molecules becomes necessary ; for the particles of zinc and hydrogen, which 
 become oppositely united, 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, I conceive, fatal to those views which 
 assume the identity of chemical and electrical, or, as they call it, current or induc- 
 tive 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 excitation and dis- 
 charge before it is completed, and the permanent combination 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 excita- 
 tion, and while their elements, oppositely excited, were yet separate from each 
 other. A compound body is therefore, as I apprehend, decomposed by the bat- 
 tery, from having this electrical state given to it by the current ; and the transfer 
 of its elements across the liquid is accomphshed by a series of neutralizations and 
 excitations, accompanying the unions and decompositions by which they pass to the 
 electrodes, on which 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 the 
 same. That this actually occurs appears probable from the analogy of heat ; 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 quan- 
 tity of this evolved should be the same also. It appears, likewise, that an equiva- 
 lent of sulphuric acid, in combining with different bases, evolves the same quantity 
 of heat, and to decompose the various salts thus formed, the same quantity of 
 electricity should be required ; and hence, that the two actions, so completely equiv- 
 alent to each other, may satisfactorily be referred to the same source. 
 
 Such is the interpretation I put upon the phenomena of electro-chemical decOTO 
 
becquerel's electro-chemical theory. 201 
 
 position, 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 representing he actions of the bodies on each other 
 proposed by Graham, but I consider it too hypothetical to assume that such mole- 
 cular 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 polarities, which are them- 
 selves 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 accom- 
 panied by an electrical phenomena, 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 admirable a philosopher, I shall 
 endeavour, in concluding this section, to give a short description of them. In the 
 main, they do not differ much from the principles of electro-chemical combination 
 which I have long since adopted, and which have been already noticed. 
 
 M. Becquerel considers that in all bodies there is distributed a quantity of elec- 
 tricity indefinitely great, which is so intimately connected with their molecular 
 constitution, that it is disturbed, and excitation produced in all cases where molci- 
 cular 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 acid com- 
 bines with an alkali, the first sets free positive electricity, and the second an equal 
 quantity of negative electricity ; these two combine immediately in the liquor, form- 
 ing neutral fluid, and produce as many currents as there had been particles in ac- 
 tion ; now this multitude of little currents ought to determine the production of a 
 quantity of heat, depending on the energy with which 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 alkali the positive electri- 
 city ; 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 indispen- 
 sable 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 ap- 
 pears 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 
 inverse 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 Am- 
 pere's idea of electrical atmospheres, although he denies that any bodies are natu- 
 rally or permanently in a positive or negative condition ; but he supposes that the 
 neutral condition of a body consists in the molecule being either positive or nega- 
 tive, 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 re- 
 main excited while in union, although the union is the cause of the electrical dis- 
 turbance, and not its effect. Now, when zinc is put in contact with water, this last 
 is decomposed, and there is hence a disturbance of electricity ; the particle of zinc 
 abandons its negative atmosphere, and unites in a positive condition with the neg- 
 ative and nascent oxygen ; the hydrogen is liberated nascent also, and highly pos- 
 itive ; in this state the oxygen would be balanced between the two equally positive 
 particles of zinc and hydrogen, and the decomposition could ^ot proceed; but, if a 
 slip of copper be introduced, this supplies a negative atmosphere to the 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 com- 
 pound 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. 
 
 M. Becquerel has endeavoured to apply the agency of electricity to determine the 
 
 Cc 
 
202 
 
 LAWS OF COMBINATION. 
 
 relative affinities which bodies have for each other. His principle is as follows : ii 
 nitrate of copper and nitrate of silver be dissolved together in equal quantities, and 
 decomposed by a galvanic current, the nitrate of silver alone is at first affected, be- 
 cause the affinity of the silver for the oxygen and acid is so much less than that 
 of the copper for the same. But, when the quantity of nitrate of copper is gradually 
 increased, a term is arrived at when the electric current is exactly 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 solu- 
 tion 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 
 copper and J 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 
 galvanic current. His results appear to show that the affinities are expressed by 
 the nmnbers ; for - 
 
 Hydrogen. 
 
 For Chlorine 922 
 
 Bromine 712 
 
 Iodine 212 
 
 Oxygen. 
 
 For Chlorine 169 
 
 Bromine 380 
 
 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 ingenuity and ac- 
 curacy 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. 
 
 CHAPTER IX. 
 
 ON THE LAWS OF COMBINATION. 
 
 The gensral nature of affinity, and the modifications which it un- 
 dergoes from the influence of the physical agents, having been now 
 stated, I shall proceed to discuss the numerical laws to which its re- 
 sults are subjected, the discovery of which was the first step in con- 
 ferring 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 proportions, 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 chloride and the sodium, which con- 
 stitute the salt, form it only in certain proportions which are inva- 
 riable, 100 parts containing always 39-66 of sodium and 60-34i 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 inde- 
 terminate proportions, or had the properties which we recognise in 
 chloride of sodium been ascribable to compounds of those elements 
 
CHEMICAL EQUIVALENTS. 203 
 
 in every possible proportion, no accurate ideas regarding the con- 
 stitution or properties of bodies could have been acquired, and none 
 of the benefits derivable from experience or experiment could have 
 been attained. The first law of constitution is, therefore, that the 
 composition and properties of any given substance are always the 
 same. 
 
 When, by the intervention of superior affinities or by double de- 
 composition, a compound body is decomposed and a new compound 
 formed, the proportions by weight of the various substances brought 
 mto action have a constant relation to one another, and, as they rep- 
 resent 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 hy- 
 drogen gas, it is reduced, and the hydrogen, uniting with the oxygen 
 which it contained, forms water. In the 100 of oxide there were 79*83 
 of metallic copper and 20-17 of oxygen, which last, taking 2*52 of 
 hydrogen, forms 22-69 of water. Now, in this case, the 2-52 of hjr 
 drogen produce the same result of satisfying the combining power of 
 the 20-17 of oxygen as the 79-83 of copper ; and hence these quanti- 
 ties of hydrogen and copper are equivalent to each other. This ex- 
 ample may be, however, brought much farther. If, in place of treat- 
 ing the oxide of copper by hydrogen gas, it had been acted on by 
 cliloride of hydrogen, the oxygen should have been carried off by the 
 hydrogen, which would abandon its chlorine for that purpose j 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 re- 
 action would be so proportioned that the quantity of copper reduced 
 by the hydrogen of the chloride of hydrogen would be exactly suf- 
 ficient to unite with all the 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 decomposition 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 combination, to 20-17 of 
 oxygen. 
 
 Starting from this point, we may proceed to a still more extend- 
 ed range of instances. If we treat sulphuretted hydrogen gas with 
 iodine, we find that it is totally decomposed, sulphur being pre- 
 cipitated, and iodide of hydrogen being formed. Now, taking the 
 quantity of the sulphuret of hydrogen, containing the weight obtain- 
 ed in the former example, 2-52 of hydrogen, we find it to be 43-09, 
 and hence to contain 40-57 of sulphur, which separates by the action 
 of the iodine, of which 318-28 parts, uniting with the 2-52 of hydro- 
 gen, 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 throus:h a variety of decompositions, in all of 
 
204 SCALES OF CHEMICAL EQUIVALENTS. 
 
 which the quantities engaged effect the same purpose of satisfying the 
 tendency to combine, we found for the numbers which express the 
 equivalent quantities of the simple bodies employed the following : 
 
 Copper 79-83 
 
 Hydrogen 2-52 
 
 Oxygen 20- 17 
 
 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 : 
 
 Chlorine 89-21 
 
 Sulphur 40-57 
 
 Iodine 318-28 
 
 Oxide of copper . . . 100-00 
 Oxide of hydrogen . . 22-69 
 Chloride of hydrogen . 9 1 • 73 
 
 Sulphuret of hydrogen . 4309 
 Iodide of hydrogen . . 320-79 
 Chloride of copper . . 16904 
 
 It is evident that if, in place of oxide of copper, any other metal- 
 lic oxide reducible by hydrogen had been employed, its equiv- 
 alent should have been obtained, and in this way the equivalents of 
 the majority of 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, oxygen or hydrogen, the most 
 important bodies, are selected. 
 
 Any number experimentally obtained, as the above, may be re- 
 duced to the standard scale by the rule of simple proportions : thus, 
 the equivalent of copper being 79'83, oxygen being 20*17, and hy- 
 drogen 2*52, it is 
 
 20-17 : 79-83 : : 100-=395-7 Oxygen =100 
 and 2-52 : 79-83 : : 1 = 31-71 Hydrogen =1 
 
 It is difficult to decide which of the two scales thus formed de- 
 serves 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, how- 
 ever, for use, the more convenient, as, in consequence of the greal 
 preponderance of bodies in which oxygen exists, the calculations 
 are much simplified by its number being 100 ; and there are but 
 two or three bodies which, on that scale, require to be expressed 
 in a fractional form. 
 
 When the study of these equivalent proportions first occupied the 
 minds of chemists. Doctors Prout and Thompson were led, from 
 speculations regarding the physical constitution of gaseous bodies, 
 to suggest that the equivalent numbers of all substances were sim- 
 ple multiples of that of hydrogen ; and as, representing hydrogen 
 by 1, the other numbers therefore became all whole numbers, the 
 spale acquired thereby considerable 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 follow- 
 ing list, no trace of such a law can be detected: later researches 
 have also, in the hands of Turner and of Penny, afforded additional 
 support to this opinion ; but Phillips has lately reopened the dis- 
 cussion, and Dumas is inclined to consider the original views of 
 Prout as being probably correct. In any case, the numbers given 
 
SCALES OF CHEMICAL EQUIVALENTS. 
 
 205 
 
 in the list must be looked upon as being, in a slight degree, still 
 open to revision. 
 
 In the following table, the equivalents of all the simple bodies are 
 expressed on each of these scales ; and throughout this work the 
 two equivalent numbers will be given for each compound body, ex 
 cept where it is otherwise remarked. 
 
 1VTn«nAA nf TPIa 
 
 
 Equivalents. l 
 
 IVr^moe nf CiiKc 
 
 
 
 
 Equivalents. | 
 
 riames of Lileiueuis. 
 
 O.= 100 
 
 H.= l 1 
 
 JNames oi oubsiiuuca. 
 
 O.=100 
 
 H.= l 
 
 Aluminum . . . 
 
 171-2 
 
 13-7 
 
 Mercury .... 
 
 12658 
 
 101-43 
 
 Antimony 
 
 
 1612-9 
 
 129-2 
 
 Molybdenum 
 
 
 
 598-5 
 
 47-96 
 
 Arsenic . 
 
 
 940 1 
 
 7534 
 
 Nickel . . 
 
 
 
 369-7 
 
 29-62 
 
 Barium . 
 
 
 856-9 
 
 68 66 
 
 Nitrogen 
 
 
 
 
 1750 
 
 1400 
 
 Bismuth 
 
 
 886-9 
 
 7110 
 
 Osmium 
 
 
 
 
 1244-5 
 
 99-72 
 
 Boron . 
 
 
 136-2 
 
 10-91 
 
 Oxygen . 
 
 
 
 
 1000 
 
 801 
 
 Bromine 
 
 
 978-3 
 
 7839 
 
 Palladium 
 
 
 
 
 665-9 
 
 53 36 
 
 Cadmium 
 
 
 696-8 
 
 55 83 
 
 Phosphorus 
 
 
 
 
 392-3 
 
 31-44 
 
 Calcium . 
 
 
 2560 
 
 20-52 
 
 Platinum 
 
 
 
 
 1233-5 
 
 98-84 
 
 Carbon . 
 
 
 76 
 
 608 
 
 Potassium 
 
 
 
 
 489-9 
 
 39-26 
 
 Cerium . 
 
 
 5747 
 
 46 05 
 
 Rhodium 
 
 
 
 
 651-4 
 
 52-2 
 
 Chlorine 
 
 
 442-6 
 
 35-47 
 
 Selenium 
 
 
 
 
 494-6 
 
 39-63 
 
 Chromium 
 
 
 351-8 
 
 2819 
 
 Silicon . 
 
 
 
 
 277-3 
 
 22-22 
 
 Cobalt . 
 
 
 369-0 
 
 29-57 
 
 Silver . 
 
 
 
 
 1351-6 
 
 108-3 
 
 Columbium 
 
 
 2307-4 
 
 184-90 
 
 Sodium . 
 
 
 
 
 290-9 
 
 23-31 
 
 Copper . 
 
 
 395-7 
 
 31-71 
 
 Strontium 
 
 
 
 
 5473 
 
 43-85 
 
 Fluorine . 
 
 
 233-8 
 
 18-74 
 
 Sulphur . 
 
 
 
 
 20117 
 
 1612 
 
 Glucinum 
 
 
 331-3 
 
 26-54 
 
 Tellurium 
 
 
 
 
 801-76 
 
 64-25 
 
 Gold . . 
 
 
 24860 
 
 199-21 
 
 Thorium 
 
 
 
 
 744-9 
 
 59-83 
 
 Hydrogen 
 
 
 12-5 
 
 1-00 
 
 Tin . . 
 
 
 
 
 735 29 
 
 58 92 
 
 Iodine . 
 
 
 1579-5 
 
 126-6 
 
 Titanium 
 
 
 
 
 30366 
 
 24 33 
 
 Iridium . 
 
 
 12335 
 
 98-84 
 
 Tungsten 
 
 
 
 
 11830 
 
 94-80 
 
 Iron , . 
 
 
 339-2 
 
 27-18 
 
 Vanadium 
 
 
 
 
 856-9 
 
 68 66 
 
 Lanthanum 
 
 
 
 
 Uranium 
 
 
 
 
 2711-4 
 
 217-26 
 
 Lead . . 
 
 
 1294-5 
 
 103-73 
 
 Yttrium . 
 
 
 
 
 4025 
 
 32 25 
 
 Lithium . 
 
 
 803 
 
 6-44 
 
 Zinc . . 
 
 
 
 
 403-2 
 
 3231 
 
 Magnesium . . 
 
 1583 
 
 1269 
 
 Zirconium 
 
 
 
 
 4202 
 
 3367 
 
 Manganese . , . 
 
 3459 
 
 27-72 
 
 
 
 
 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 noti- 
 ced to the scales, there are : 
 
 Substances. 
 
 Equivalents. | 
 
 Substances. 
 
 Equivalents. | 
 
 O. = I00 
 
 H.= I 
 
 O.=100 
 
 H.=l 
 
 Oxide of copper . . 
 Oxide of hydrogen . 
 Chloride of hydrogen . 
 
 495-7 
 112-5 
 4451 
 
 39-72 
 
 9-01 
 
 36-47 
 
 Chloride of copper . 
 Iodide of hydrogen 
 Sulphuret of hydrogen 
 
 838-3 
 
 15920 
 
 213-7 
 
 6718 
 
 127-57 
 1712 
 
 It IS m 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 ni- 
 trate of barytes we add a solution of sulphate of soda, there is im- 
 mediate decomposition, by the mutual interchange of acids and ba 
 ses, and the neutrality of the solution remains completely undisturb 
 ed J the salts which exist after mixture are equally neutral with 
 
206 
 
 EQUIVALENTS OF COMPOUND BODIES. 
 
 those which had existed previously, and the quantities of acids and 
 bases which are involved in the decomposition are hence equiva- 
 lent to each other. Thus, if we take 130'7 parts of nitrate of ba- 
 rytes, we find that they require for their decomposition exactly 71-3 
 parts of dry sulphate of soda, and that there are formed 116-7 parts 
 of sulphate of barytes and 85*3 parts of nitrate of soda. The com- 
 position of these four salts is : 
 
 Sulphate of Barytes. 
 Sulphuric acid . . 40 
 Barytes .... 767 
 116-7 
 
 Nitrate of Barytes. 
 Nitric acid ... 54 
 Barytes .... 767 
 130-7 
 
 Nitrate of Soda. 
 Nitric acid ... 54 
 
 Soda 31-3 
 
 85 3 
 
 Sulphate of Soda. 
 Sulphuric acid . . 40 
 
 Soda 31-3 
 
 71-3 
 
 All four are neutral ; the acids and bases are in all equally neutral- 
 ized, 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, are equivalent quantities, and represent the combining 
 proportions of these acids j and the 76*7 of barytes and the 31-3 of 
 soda being likewise 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 pres- 
 ent, 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 
 would 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. 
 
 Nitric acid . . 540, producing Sulphuric acid . . 40- 1 
 Oxide of lead . 111-7, « Oxide oflead . . . lU-7 
 Nitrate of lead 165-7 Sulphate of lead 151.8 
 
 If, in place of sulphate of soda, we take oxalate of soda, we shall 
 jRnd 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 ba- 
 rytes. 36 of oxalic acid are therefore equivalent to 40- 1 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, 
 
 Substasoefl. 
 
 Equivalents. 
 
 ■■ 
 
 Substances. 
 
 Equivalents. | 
 
 O.= 100. 
 
 H.= I. 
 
 540 
 40- 1 
 360 
 
 = 100. 
 
 H. = l. 
 
 Nitric acid . . 
 Sulphuric acid . 
 Oxalic acid 
 
 6770 
 501-1 
 4529 
 
 Soda .... 
 Barytes . . . 
 Oxide of lead . 
 
 3901 
 
 956-9 
 
 1394-5 
 
 31-3 
 
 76-7 
 111-7 
 
 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 
 assigning the numerical conditions of chemical action. 
 
LAW OF MULTIPLE PROPORTIONS. 207 
 
 The mode of determining the equivalent number of a new sub- 
 stance can now be easily understood. If it be an acid, it is to be 
 combined with some base of which the equivalent is known j if it be 
 a base, it must be united with an acid. If it be a metal, it may be 
 united with chlorine or oxygen. If it be a simple non-metallic body, 
 it may be united with a metal. In any case, a well-defined com- 
 pound 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 neu- 
 tral 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, as, 37*3 : 62*7 : : 40*1 : x=67-4, which is the equiva- 
 lent of the body, 40*1 being that of sulphuric acid, and hydrogen 
 being =1. 
 
 A calculation of this kind requires, however, to be checked by a 
 knowledge of the next law of combination, that of multiple propor- 
 tions ; for, as has been stated, we presume, in the example, the salt 
 analyzed 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 would become 
 134<*8 5 or two equivalents of base to one of acid, which would make 
 the number 33*7. The proportions might be even still more com- 
 plex ; and hence, before attempting to decide on the equivalent num- 
 ber 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 com- 
 pounds, unite with the same quantity of the first. Thus, taking man- 
 ganese and nitrogen, which are remarkable for the number of com- 
 pounds which they form with oxygen, there are, 
 
 345-9 of manganese unite with 100 of oxygen, forming protoxide. 
 345-9 " 150 " sesquioxide. 
 
 345-9 " 200 " peroxide. 
 
 346-9 " 250 " manganous acid. 
 
 345-9 " 300 " manganic acid. 
 
 345-9 " 350 " permanganic acid. 
 
 And with nitrogen, 
 
 175 of nitrogen unite witli 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 manganese 
 are as the numbers 2, 3, 4, 5, 6, 7, and those which combine with the 
 nitrogen are as 1, 2, 3, 4, 5. In the last case they are all simple 
 multiples 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 ex- 
 tremely probable that, though it has not been yet discovered, there 
 
52-2 chromic 
 
 acid- 
 
 104-4 
 
 - 
 
 156-6 
 
 H 
 
 208 LAW OF MULTIPLE PROPORTIONS. 
 
 exists a compound of 348*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 
 ^proportions, forming by 
 
 •47.3 potash, neutral chromate of potash. 
 -47-3 " bichromate of potash. 
 ■47-3 " terchromate of potash. 
 
 Sulphuric acid combines with potash in two proportions, 
 
 40- 1 sulphuric acid -|-47-3 potash, neutral sulphate. 
 80-2 " 4-47-3 " bisulphate. 
 
 It was, indeed, by the verification of it in the carbonates and ox- 
 alates 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 - -47-3 potash, form oxalate of potash. 
 72 " 4-47-3 " binoxalate of potash. ' 
 
 144 " -|-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 
 
 39-7 oxide of copper -{-401 sulphuric acid, form neutral sulphate. 
 
 79-4 " 440-1 " bibasic sulphate. 
 
 158-8 " 4-40 1 " quadribasic sulphate. 
 
 317-6 " 4-401 " octobasic sulphate. 
 
 In other cases the series, though not so complete, evidently follows 
 the same law. 
 
 The great use of the symbolical nomenclature, noticed already in 
 page 156, consists in its supplying an exact expression of this law 
 of multiple proportions. The ordinary symbol of a simple body in- 
 dicating an equivalent of it, the number by which that symbol is 
 multiplied, in the formula of each compound body, represents the 
 number of equivalents therein contained. Thus, for manganese and 
 nitrogen, already used as instances, the symbolical expression of the 
 law is given in 
 
 N.O. Nitrous oxide. 
 N.O2 Nitric oxide. 
 N.O3 Hyponitrous acid. 
 N.O4 Nitrous acid. 
 N.O5 Nitric acid. 
 
 Mn.O. Protoxide of manganese. 
 MuaOa Sesquioxide. 
 Mn.O, Peroxide. 
 Mn.Oa Manganic acid. 
 MugOy Permanganic acid. 
 
 The numerical coefficient is sometimes placed, as here, below 
 and to the right of the letter symbol; by other chemists it is placeld 
 to the left and on the same line, asPb. + 20. Cr.+30., and sometimes 
 to the right and above the letter, as Pb.O^ Cr.O^. This makes no 
 difference m chemistry ; but the student must be careful not to 
 confound chemical with mathematical symbols, in which the posi- 
 tion of the number might alter its power and meaning altogether. 
 It must be noticed, however, that numbers written as the above af- 
 fect only the immediate symbol to which they are attached j but 
 
RESEARCHES OF PROUST. 209 
 
 sometimes a number affects a group of symbols: thus, 3Mn.O. is 
 three equivalents of protoxide of manganese =Mn303: thus, also, 
 S.O3 K.O.+AI2O3. 3S.O3, the formula of dry alum, contains four fig- 
 ures of 3, of which the first, second, and fourth only affect the O., 
 to which they are subjoined, but the third affects the S.O3, 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 
 quantities in which one body may unite with another are multiples 
 of the first by a whole number j and the cause of this is at once 
 seen, and a simple and positive meaning given to this law, by say- 
 ing that the first body contains an equivalent of each element ; the 
 second, one equivalent of one and two equivalents of the other, and 
 so on ; the successive steps being formed by the number of com- 
 bining proportions of the second body which unite with one com- 
 bining 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, at- 
 tacked by BerthoUet, to whose exclusive doctrines it was quite fatal. BerthoUet, 
 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 
 formation of the bodies actually produced resulted. Thus he asserted that sulphu- 
 ric acid and barytes actually unite in all proportions ; but those of 40- 1 of acid tc 
 76-7 of base forming the body of the least solubility, the whole quantity of acid is 
 determined to unite with the barytes in those proportions, and in none others 
 Thus he imagined, also, that mercury and oxygen should unite in all proportions 
 and that it was only by the intervention of external causes that their union was de- 
 termined in preference to occur in the proportions of 101-4 of mercury to 4 of oxy- 
 gen, and 101 -4 of metal to eight of oxygen. We owe to Proust the complete refu- 
 tation of BerthoUet's views in this respect ; he cleared away a heap of incorrect 
 ideas which had prevailed regarding compound bodies, showing that numerous de- 
 grees of oxidation, which had been looked upon as intermediate, and connecting 
 the extreme limits, as BerthoUet thought they ought to be connected, were impure 
 and badly prepared mixtures of the true compounds, and that, when pure, the tran- 
 sition 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, how- 
 ever, as an example of how easily a great discovery in science may be lost, that, al- 
 though Proust had in his hand all materials necessary for establishing the laws ot 
 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 
 
 Oxygen 11-22 
 
 Copper 88-78 
 
 1 St Oxide of mercury 
 
 Oxygen 3-80 
 
 Mercury 96 20 
 
 I St Sulphuret of iron 
 
 Sulphur 37-23 
 
 Iron 62-77 
 
 2d Oxide of copper cpntained 
 
 Oxygen 20- 17 
 
 Copper 79-83 
 
 2d Oxide of mercury 
 
 Oxygen 7-32 
 
 Mercury 92-68 
 
 2d Sulphuret of iron 
 
 Sulphur ,54-26 
 
 Iron 45-74 
 
 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 calcu- 
 lation ; had he taken a certain weight of one element as the standard, and not 100 
 parts of the compound body, his numbers would have become, 
 1st Oxide of copper 
 
 Oxygen 100-0 
 
 Copper 791-4 
 
 Dd 
 
 2d Oxide of copper 
 
 Oxygen 2000 
 
 Copper 791-4 
 
210 
 
 METHODS OF DETERMINING THE 
 
 1st Oxide of mercury 
 
 Oxygen 1000 
 
 Mercury 2531-6 
 
 1st Sulphuret of iron 
 
 Sulphur 201-2 
 
 Iron 339-3 
 
 2d Oxide of mercury 
 
 Oxygen 2000 
 
 Mercury 2531-6 
 
 2d Sulphuret of iron 
 
 Sulphur 402-4 
 
 Iron 339-2 
 
 And thus the fact of the quantity of oxygen or sulphur in the second 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 exist- 
 ence 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 be- 
 fore noticed, is rendered difficult, sometimes, when the substances 
 in question unite in more proportions than one. Thus it is evident 
 that the manganese series might be represented as 
 
 100 of oxygen -|-345-9 of manganese, forming protoxide. 
 
 100 " 230-5 " " sesquioxide. 
 
 100 " 172-9 " " peroxide. 
 
 100 " 138-3 " " manganous acid. 
 
 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 
 
 Oxygen 1000 
 
 Copper 791-4 
 
 1st Oxide of mercury 
 
 Oxygen 1000 
 
 Mercury 2531-6 
 
 1st Sulphuret of iron 
 
 Sulphur 201-2 
 
 Iron 339-2 
 
 2d Oxide of copper 
 
 Oxygen 100-0 
 
 Copper 395-7 
 
 2(L Oxide of mercury 
 
 Oxygen 1000 
 
 Mercury . . . .1265 8 
 
 2d Sulphuret of iron 
 
 Sulphur 201-2 
 
 Iron 1696 
 
 There might thus be deduced from each kind of compound a dif- 
 ferent equivalent for each simple body, and it is therefore neces- 
 sary 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 
 are good reasons 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 pro 
 portions, as a metal with oxygen, and 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 and of oxygen to unite is pretty well satiated 
 by the combination of an equivalent of each, if the protoxide so 
 formed unite with another equivalent of either metal or of oxygen, 
 this will be retained with inferior power, and when the substance 
 80 produced is exposed to decomposing agencies, it may be resolved 
 
EQUIVALENT CONSTITUTION OF BODIES. 211 
 
 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, while the red oxide undergoes no change except total de- 
 composition into mercury and free oxygen. Red oxide of copper 
 decomposes 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 manganese is heated by deoxidizing agents, it 
 abandons one half of its oxygen, but the oxide so formed cannot be 
 farther reduced. In this way, therefore, we conclude that 
 
 Red oxide of copper is suboxide. CuzO. 
 Black oxide of jcopper is protoxide. Cu.O. 
 Black oxide of mercury is suboxide. HggO. 
 Red oxide of mercury is protoxide. Hg.O. 
 Yellow oxide of lead is protoxide. Pb.O. 
 Brown oxide of lead is deutoxide. Pb.Oa. 
 Olive oxide of manganese is protoxide. Mn.O. 
 Black oxide of manganese is deutoxide. Mn.Og. 
 
 Thus, also, hydrogen and oxygen unite in two proportions, to form, m 
 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 provo- 
 ked by the slightest causes, and is explosively violent. It is hence 
 concluded that 
 
 Water is protoxide of hydrogen. H.O. 
 Oxygenated water is deutoxide. H.Og. 
 
 If there be still more degrees of combination of the two bodies, 
 these principles apply still more determinately to their characteristic 
 properties. 
 
 Third. The constitution of an acid may be frequently determin- 
 ed by the consideration that an equivalent of it is the quantity 
 which neutralizes an equivalent of a well-characterized base. Thus 
 the equivalent number of potash on the hydrogen scale is 47*3, and 
 this combining with 40*1 of sulphuric acid to form neutral sulphate 
 of potash, this number is determined to be the equivalent of the 
 acid; and as it is made up of 16*1 of sulphur and 24 of oxygen, the 
 acid is considered to be composed of one equivalent of sulphur 
 16-1, and three equivalents of oxygen 8x3 = 24. Its formula is 
 therefore S.O3. In the same way, on analyzing hyposulphate of 
 potash, it is found to consist of 47-3 of potash, united to 72-2 of the 
 acid, which is, therefore, its equivalent number. But this number 
 is made up of 32-2, or two equivalents of sulphur, and 40, or five 
 equivalents of oxygen, and the formula expressing its constitution 
 is S2O5. 
 
 Where an acid forms several classes of salts, it is difficult to de- 
 termine which is that containing an equivalent of each element, and 
 
212 METHODS OF DETERMINING THE 
 
 hence this mode of ascertaining the constitution of the acid may be 
 occasionally at fault. This happens particularly with the acids of 
 phosphorus and arsenic j and in these cases it is necessary to recur 
 to considerations regarding 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 which 
 the bodi-es combine does not follow the simple proportion of 1 : 2 : 3, 
 &c., but assumes the more complex form 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 uncertainty. Thus there are two oxides of iron 
 which may be looked upon as consisting, either 
 
 the 1st of 27*9 of iron + 8 oxygen, 
 the 2d 27-9 " +12 " 
 or the 2d 18-6 " +8 " 
 the 1st 27-9 " + 8 « 
 
 In the first mode of view the oxygen varies as 2 : 3, but in the sec- 
 ond 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 27*9 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 Fe.O. The per- 
 oxide of iron then becomes Fe.O 1^ ; but as the equivalent of oxygen 
 cannot be considered to be divided, we look upon it as being rather 
 FciOg, and having its equivalent 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 propor- 
 tion of Fe203, dry iron alum being S.O3, K.O.+Fe203, 3S.O3 ; and as 
 this is the only proportion in which these two salts unite, it is rea- 
 sonable 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 j the 
 
 Green oxide of chrome consists of 18-79 chrome + 8 oxygen. 
 Chromic acid « 18-79 " +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 
 substance 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, resembling in all characters and constitution the iron 
 alum already noticed, and hence oxide of chrome corresponds to 
 peroxide of iron, and its formula is CraOg. This is farther 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 
 
EQUIVALENT CONSTITUTION OF BODIES. 213 
 
 of 28-2 of chrome and 24 of oxygen ; and hence the formula of 
 chromic acid is Cr.Oa, resembling that of sulphuric acid S.O3. 
 
 Fifth. In cases where there is only one compound of a body with 
 oxygen, we may be induced to consider it not to be composed of an 
 equivalent of each element from analogical grounds, such as those 
 now described. Thus aluminum and oxygen form only one com- 
 pound, alumina j 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 AI2O3. 
 
 Sixth. When bodies are found combined in proportions expressed 
 by high numbers, they are generally looked upon as secondary com- 
 pounds, formed by the reunion of others, the ratio of whose elements 
 are simple. Thus lead forms with oxygen compounds intermediate 
 to the two 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^Os^SPb.O.+Pb.Oa, and Pb304-2Pb.O.+Pb.02. 
 
 In like manner, between the two proper oxides of iron there inter- 
 vene the two magnetic oxides, the formulae of which are Fe^O^ and 
 Fe304, being compounds of protoxide and peroxide, as, 
 
 FeA=2Fe.O.+Fe203, and Fe304=Fe.O.+Fe203. 
 
 By this means the constitution of an extensive class of complex bod- 
 ies is reduced to very simple forms. 
 
 If we take oxygen, hydrogen, chlorine, and nitrogen in the pro 
 portions by weight which correspond to their equivalent numbers, 
 and measure the volumes which, as gases, they occupy, an exceed- 
 ingly striking relation 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 va- 
 pour, they occupy precisely the same voliime as the equivalent of 
 hydrogen gas at the same temperature and pressure. On convert- 
 ing into gas equivalent weights of arsenic and phosphorus, they oc- 
 cupy precisely the same volume, which is equal to that of the equiv- 
 alent of oxygen gas 5 and by similarly treating an equivalent of sul- 
 phur, its volume becomes one third that of the oxygen. Finally, 
 when a quatitity of mercury, representing its equivalent number, 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 uncon- 
 nected, 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 proportion of the other bodies mentioned are ; 
 
214 EQUIVALENT VOLUMES OF COMPOUND BODIES. 
 
 Name of Substance, 
 
 Equivalent Weight. 
 
 Equivalent 
 Volume. 
 
 Sp.Gr.ofV^po,r. 
 
 Oxygen . • 
 
 1000 
 
 1 
 
 1102-6 
 
 Hydrogen . • 
 Chlorine . . 
 
 12-5 
 442-6 
 
 2 
 2 
 
 68-8 
 24700 
 
 Iodine . . . 
 
 1579-5 
 
 2 
 
 8701-0 
 
 Bromine . • 
 
 978-3 
 
 2 
 
 53930 
 
 Nitrogen . • 
 Sulphur . . 
 Phosphorus . 
 Arsenic . . 
 
 175-0 
 201-2 
 3923 
 940 1 
 
 2 
 
 1 
 1 
 
 9760 
 
 • 6048-0 
 
 4327-0 
 
 10362-0 
 
 Mercury . . 
 
 1265-8 
 
 4 
 
 69690 
 
 Not merely does this simple proportion of equivalrat 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 
 equivalent 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 forma- 
 tion of water, one volume of oxygen unites with exactly two of hy- 
 drogen, and the volume of watery vapour which is formed is equal 
 to that of the hydrogen employed. To form ammonia, one volume 
 of nitrogen unites with three of hydrogen, and the four volumes are 
 condensed into two by the combination. 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 unconnect- 
 ed numbers, like those of the equivalents by weight, but are found 
 to be, as the weights should become if the suggestion of Proust were 
 verified, simple multiples of the equivalent of some standard body 
 which may be selected, as oxygen in the table. 
 
 Name of the Compound Vapour. 
 
 Water 
 
 Nitrous oxide . . . 
 Nitric oxide . . . 
 Sulphurous acid . . 
 Sulphuric acid . . . 
 Sulphuretted hydrogen 
 Muriatic acid . . . 
 Hydriodic acid . , . 
 Hydrobromic acid 
 Ammonia .... 
 Arseniuretted hydrogen 
 Terchloride of arsenic 
 
 Calomel 
 
 Corrosive sublimate . 
 Arsenious acid . . 
 Sulphuret of mercury 
 Chloride of sulphur . 
 Protochloride of phosphorus 
 Perchloride of phosphorus . 
 
 Formula. 
 
 H.O. 
 N.O. 
 N.O2 
 S.O2 
 S.O3 
 S.H. 
 Cl.H. 
 
 I.H. 
 
 Br.H. 
 
 N.H3 
 
 AS.H3 
 
 AS.CI3 
 
 Hg2Cl, 
 
 Hg.Cl. 
 
 AS.O3 
 
 Hg.S. 
 
 S2CI. 
 
 P.CP 
 
 P.CI5 
 
 1125 
 
 275-0 
 
 375-0 
 
 401-2 
 
 501-2 
 
 213-7 
 
 455 1 
 
 1592-0 
 
 990-8 
 
 214-5 
 
 9526 
 
 2268-0 
 
 2974-3 
 
 1708-5 
 
 1240- 1 
 
 1467-0 
 
 845-0 
 
 1720-1 
 
 2505-3 
 
 Equivalent 
 Volume of 
 Constituents. 
 
 3 
 3 
 
 4 
 7 
 
 10 
 7 
 4 
 4 
 4 
 4 
 7 
 7 
 6 
 8 
 4 
 7 
 4 
 7 
 
 11 
 
 Up. Gr. ol 
 the Vapour. 
 Air=10000. 
 
 620-2 
 1527-3 
 1039-3 
 22106 
 2761-9 
 1177-0 
 1269-5 
 4385-0 
 2731-0 
 
 591-5 
 2694-0 
 6295-0 
 82040 
 9439 
 136700 
 5384-0 
 4686 
 4741 1 
 4788-1 
 
 The simplicity thus shown to exist between the volumes of the 
 constituent and compound vapour enables us very often to calculate 
 beforehand what the specific gravity of a vapo^ur should be, and thus 
 
SPECIFIC GRAVITIES OF COMPOUND VAPOURS. 215 
 
 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, aiid the weights of these volumes being as their specific 
 gravities, the weight of the ammonia formed should be 976+(3x 
 69)= 1183 if the four volumes of constituents were condensed into 
 one ; but as the condensation is into two, the specific gravity of 
 the ammonia is 1183-^2=591-5, as given in the table. Sulphur 
 and hydrogen unite in the proportion of one volume of sulphur to 
 six of hydrogen, and hence, if there were but one volume of result- 
 ing gas, the specific gravity should be 6648+ (6 X 69)=7062 j but as 
 there are six volumes of gas formed, the true specific gravity of sul- 
 phuretted hydrogen is 7062H-6 = 1177. The general rule being to 
 multiply the specific gravities of the simple gases or vapours re- 
 spectively by the volumes in which they combine, to add those 
 products together, and then to divide the sum by the number of vo]- 
 umes of the compound gas produced. 
 
 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 pos- 
 sible to weigh their vapours experimentally. Thus the temperature 
 at which antimony is volatile is so high that the specific gravity of 
 its vapour may possibly never be determined by experiment ; but 
 the chloride of antimony 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 chlo- 
 ride of antimony, which is 8106-5, by four, we obtain 324260, and 
 subtracting from it the weight of six volumes of chlorine =14820, 
 there remains 17606, which, if the analogy between the 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 
 specific gravity which carbon should possess if it were converted 
 into vapour. This number would be of great importance in all cal- 
 culations 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, chem- 
 ists are not agreed upon the precise number, some making it the 
 double of what it is estimated at by others. If we look upon car- 
 bonic acid as consisting of equal volumes of vapour of carbon and 
 oxygen, the two condensed into one, the specific gravity of carbon 
 is 1524-1 — 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 con- 
 sists of two volumes of carbon vapour and one of oxygen, the three 
 
216 CHEMICAL AND MOLECULAR CONSTITUTION. 
 
 condensed to two (2x421-5 + 1102-6)-^2=972-8 ; and on the latter, 
 of equal volumes united without condensation (843'0 + 1102'6)-7-2= 
 972'8. It is this latter view 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 sulphur had been experimentally determined, it was considered, 
 from 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 com- 
 pounds of carbon. 
 
 In the combination by volume, the same laws of multiple propor- 
 tion hold as in combination by equivalents; thus the compounds of 
 chlorine and oxygen, which are by weight CI. O., CI.O4, CI. O5, and 
 CI. O7, are by volume two of chlorine to one, to four, to five, and to 
 seven volumes of o. ygen respectively, and so in all other instan- 
 ces ; and, consequently, all remarks that have been made regard- 
 ing the law of multiple proportions in equivalents by weight, apply 
 to combinations of equivalents by volume also. 
 
 CHAPTER X. 
 
 OF THE RELATIONS OF CHEMICAL CONSTITUTION TO THE MOLECULAR 
 STEUCTURE 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 that 
 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 additional evidence of the intimate 
 relation of chemical to molecular constitution ; and in the present 
 chapter I purpose to conclude the description of the general histo- 
 ry of chemical action, by an account of such principles as have 
 been advanced, and such facts as have been discovered illustrative 
 of this connexion. They are as follow : 
 
 1st. The connexion between the molecular constitution and the 
 equivalent numbers of bodies. The atomic theory. 
 
 2d. The connexion between the crystalline form and the chemical 
 equivalency of bodies. Isomorphism. 
 
 3d. The relation of constitution to composition. Of Dimorphism 
 and Isomerism. The theory of types. 
 
 4th. Of chemical action independent of affinity. Catalysis. 
 
THEATOMICTHEORY. 217 
 
 SECTION I. 
 OF THE ATOMIC THEORY. 
 
 It was natural that, as soon as the remarkable laws of combination 
 discussed 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 
 proved chemical action to be subjected 5 accordingly, such theoreti- 
 cal 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 practi 
 cal 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 had 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 chem- 
 ical action, were yet overlaid by a tissue of hypotheses so irregular 
 and so unnecessary, that for a long time the real dignity and excel- 
 lence of the experimental laws were underrated and misunderstood. 
 These accessory speculations have now, however, passed away, and 
 the theory of combination laid down by Dalton may, in all its essen- 
 tial conditions, be very briefly expressed as follows : 
 
 All substances are supposed to be constituted of particles per- 
 fectly indivisible, and hence truly atoms. In different kinds of mat- 
 ter, 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 j 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 de- 
 grees 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 5 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 35-4i parts of chlorine, because, when an atom of 
 hydrogen leaves the atom of oxygen, it combines with an atom of 
 chlorine in its place, which is heavier than that of oxygen in the 
 proportion of 35-4 to 8, and the quantity must be consequently so 
 determined. When a second atom of oxygen combines with hy- 
 drogen, 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 ne- 
 cessary 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 ; 2d, the 
 principle of equivalent proportion ; and, 3d, the law of multiple com- 
 
 Ee 
 
218 PHYSICAL AND CHEMICAL ATOMS. 
 
 bination. It is therefore, even in this form, the most embracing and 
 perfect generalization that has ever been proposed in chemistry; but, 
 before committing ourselves implicitly to its adoption, it is neces- 
 sary to examine into its bases with some detail. 
 
 Dalton assumes that matter is constituted of indefinitely small 
 particles, atoms, but he advances no proof that it is so j 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 explanation 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 as- 
 certain in what manner 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 existence 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 consti- 
 tution, inconsistencies are found which must prevent our coming 
 too hastily to a conclusion. 
 
 When Gay Lussac first determined the existence of those simple 
 relations which have been described as existing between the volumes 
 of gases which combine together, it was considered certain that 
 all gases contained in the same volume the same number of atoms. 
 The gases are remarkable for all possessing the same physical con- 
 stitution. Their relations to pressure and to heat are governed by 
 the same law in all 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 con- 
 sists 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 chlo- 
 rine ; all physical evidence would lead us to believe that muriatic 
 acid gas contained in the same volume the same number of atoms 
 as its constituents, 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 hydrogen ; and as water is formed by the 
 union of one volume of oxygen with two of hydrogen, it should 
 
\ 
 PHYSICAL AND CHEMICAL ATOMS. 219 
 
 consist of one atom of oxygen and two atoms of hydrogen 3 but the 
 most perfect chemical evidence we possess proves that water is 
 composed of an equivalent of each element. The number of chem- 
 ical 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 the 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 spe'cific heats, on the remarkable law of which, regarding the 
 simple bodies, as discovered by Dulong and Petit, and extended to 
 many compound bodies by Nauman and Avogadro, I have already 
 fixed attention (page 67). 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 consid- 
 erations. 
 
 In the great majority of cases, the atomic weights of the solid sim- 
 ple bodies, deduced from their specific heats, coincide with those 
 adopted from chemical considerations ; and in some of the excep- 
 tional instances, as bismuth and silver, there is 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* 1, 
 while 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 
 31*4«; but when we calculate the atomic weights from their specific 
 heats, we find as the result for arsenic 37*7, and for phosphorus 
 15*7, 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 consider 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 equal volumes (p. 69) of oxygen and 
 of hydrogen have been proved by Apjohn to be as 808 to 1459, 
 while on chemical grounds that of oxygen should be double, and 
 on molecular considerations 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 par- 
 ticles unite, and to the phenomena of chemical combination when 
 the union is between 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 all considerations as to whether the masses which 
 combine are indivisible or the reverse. The word atom, if interpret 
 ed in its strict and proper sense, is unnecessary, and may be inju 
 rious if employed with any vague or undefined meaning. 
 
220 VARIOUS ORDERS OF MOLECULAR GROUPS. 
 
 I consider, as I have already stated (page 17), that sensible masses 
 of matter are constituted of a number of lesser masses, which again 
 may be made up of similar constituent groups, proceeding down- 
 ward 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 combining groups may be supposed to subdi- 
 vide themselves, in order to generate a set of groups of an inferior 
 class. The specific heats of bodies may be considered to have ref- 
 erence to an order of groups of particles often, but not ne*cessarily, 
 coincident with those which combine to produce chemical com- 
 pounds ; and the third, probably the most remote, engaged in the or- 
 dinary properties of matter, may be such as, being uniformly distrib- 
 uted 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 j for 
 these groups, engaged in chemical combination, and indivisible by 
 chemical means, are, in all chemical relations, atoms. Their relative 
 weights are our equivalent numbers. From 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 relations 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 volume that 
 fhey respectively occupy in hydrogen, chlorine, and iodine. In 
 most of the simple bodies the same groups produce chemical com- 
 bination, and determine the specific heat j but in iodine, in arsenic, 
 and in phosphorus, the group which enters into chemical combina 
 tion contains 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 fol- 
 lowing page^, but I do so only as an abbreviation for the terms 
 equivalent quantity or combining masses. Of the ultimate particles of 
 matter, or true atoms, we know nothing j and all of the discussions 
 that have taken place, from the earliest and vaguest speculations of 
 Democritus or Leucippus, to the modern experiments of WoUaston 
 and Faraday, must be considered as absolutely without influence on 
 the positive decision of the question. 
 
RELATION OF CONSTITUTION TO FORM. 221 
 
 SECTION II. 
 OF ISOMORPHISM. 
 
 The general principles of the isomorphism of crystallized sub- 
 stances have been already noticed, with relation to the fact of their 
 substitution for each other (page 31), and of the advantage with 
 Avhich this property may be applied to determine equivalent num- 
 bers (page 212) j it now remains to study this character, as indica- 
 tive of the molecular constitution of the body. 
 
 It must, in the first place, be carefully observed, that identity of 
 crystalline form does not imply similar chemical constitution, un- 
 less 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 be- 
 ■comes more complex, and the conditions necessary for its forma- 
 tion, 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 arrangement belonging to 
 it be the same, or, at least, similar in both. Hence, in the regular sys- 
 tem, there can be no inference whatsoever drawn with regard to 
 constitution from the crystalline form alone. Bodies the most con- 
 trasted possible in their properties and composition have identical 
 external figures, as fluor spar, bismuth, alum, sulphuret of lead, com- 
 mon 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 con- 
 stituents is allowable. 
 
 In the other systems of crystallization, where the double refrac- 
 tion and the rings produced by polarized light, transmitted along 
 their principal axis, indicate a much greater complexity of struc 
 ture, it becomes highly improbable that the molecules of two bod- 
 ies shall be so similar to each other as to produce identity of crystal- 
 line 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 struc- 
 ture 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, in the sulphuric, chromic, selenic, telluric, and 
 manganic acids, which contain each three equivalents of oxygen, 
 the molecules of sulphur, chrome, tellurium, selenium, and manga- 
 nese have all the same form. The perfect determination of wheth- 
 er those elements are really thus isomorphous, is very difficult, from 
 the fact of comparatively very few being crystallizable. Thus tel- 
 lurium and sulphur are those of which, alone, we know the crystal- 
 line form, for the only crystals of selenium that have been observ- 
 ed are microscopic and imperfect, and neither chrome nor manga- 
 nese can be had crystallized at all. We must, therefore, be guided 
 
222 ISOMORPHISM OF COMPOUND BODIES. 
 
 by analogy in such cases ; and if we examine another group of com- 
 pounds into which chrome and manganese enter, we find that Crg 
 O3 and Mn203 are isomorphous with FejOa, and Mn.O. and Fe.O. are 
 isomorphous with Cu.O. Now we here arrive, by a chain of iso- 
 morphous conditions, at a metal which may be obtained crystallized, 
 but the crystalline form of copper is always one of the regular sys- 
 tem, as the cube, octohedron, rhombohedron, dodecahedron, «Scc. ; 
 while sulphur, with which it should be isomorphous, if this princi- 
 ple were absolutely true, crystallizes in two forms, of which one be- 
 longs to the oblique prismatic, and the other to the right prismatic 
 system j while tellurium belongs to the rhombohedral system, af- 
 fecting a totally different form altogether. Numerous other instan- 
 ces might be taken ; thus the periodic, perchloric, and permanga- 
 nic acids are isomorphous (I.O7, CI.O7, and MngO;), while the ele- 
 ments themselves are certainly not necessarily isomorphous, as 
 iodine belongs to the right prismatic system. Also the isomorphx 
 ism of the phosphoric and arsenic acids (P.O5 and As.O.) is one 
 of the best examples that has been found ; but phosphorus and arse- 
 nic are so far from being isomorphous, that phosphorus crystallizes 
 in the regular, and arsenic in the rhombohedral system. The prin- 
 ciple that compound bodies are isomorphous, because their repla- 
 cing 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 
 isomorphism is, that the crystalline form of a body is completely 
 independent 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 ar- 
 rived 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 also among the 
 simple bodies, that the replacement should be always by an equal 
 number of ultimate molecules, which is also negatived by experi- 
 ment. Thus we find that an equivalent of a simple body, K., is re- 
 placed by a group of five equivalents, N.H4, and that the simple atom, 
 CI., is replaced by the two atoms Mua. This suggestion cannot, there- 
 fore, be considered as satisfactory, and we must examine farther 
 into the conditions of isomorphous replacement before we attempt 
 the farther discussion of the source from whence it has its rise. 
 
 It is necessary first to study the crystalline relations of the unde 
 composed 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 : 
 
ISOMORPHOUS GROUPS. 
 
 223 
 
 Regular System. 
 Carbon. 
 Phosphorus. 
 Selenium. 
 Copper. 
 Silver. 
 Gold. 
 Platinum. 
 Mercury. 
 Bismuth. 
 Titanium. 
 Lead. 
 
 Rhomhohedral, 
 Carbon. 
 Tellurium. 
 Arsenic. 
 Antimony. 
 
 Right Prismatic. 
 Sulphur. 
 Iodine. 
 
 Oblique Prismatic. 
 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. Car- 
 bon and sulphur are known also to have each two forms of diiBTerent 
 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 
 circumstances 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 elliptical polarization j 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 dia- 
 mond 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 octohedrons of lead, silver, and 
 zinc, may therefore belong to the square or right prismatic systems, 
 the three axes being equal among each other, and hence the iso- 
 morphism of the simple bodies be rendered still less probable. 
 
 The examples of isomorphism in compound bodies, which are most deserving ot 
 attention, are the following : 
 
 Sulphuric acid 
 Telluric acid . 
 Selenic acid . 
 Chromic acid . 
 Manganic acid 
 
 Magnesia 
 
 Protoxide of iron . . 
 Protoxide of manganese 
 Oxide of copper . . . 
 Protoxide of cobalt . . 
 Protoxide of nickel . . 
 Oxide of zinc .... 
 » Oxide of cadmium . . 
 
 These acids, the composition of which 
 is similar in all, form salts, which, when 
 they contain the same base, and the 
 Cr 0^ Tsame proportion of base and of water of 
 Mn n^ crystallization, have the same crystalline 
 ^"•^^'yform. 
 
 S.O3 
 Te.Og 
 Se.O, 
 
 GROUP 
 
 Mg.O 
 Fe.O 
 Mn.O 
 Cu.O 
 
 These protoxides combine with acids 
 and form salts, which, when in the same 
 degree of saturation with base and water 
 
 QqQ /*of crystallization, have the same form. 
 
 Ni.O. 
 Zn.O. 
 CdO 
 
 The sulphates of these oxides combine 
 with sulphate of potash to fonn isomorph- 
 ous double salts. 
 
224 ISOMORPHOUS GROUPS. 
 
 GROUP III. 
 
 Sesquioxide of iion .... Fe203^ These sesquioxides, combined with 
 , Sesquioxide of manganese . . Mn203 I sulphuric acid, with sulphate of potash, 
 
 Oxide of chrome Cr203 [and with water, form the different spe- 
 
 Alumina AI2O3 7 cies of alum, which have all the octohe- 
 
 dral form. They are themselves also isomorphous. 
 
 GROUP IV, 
 
 Potash K.O. -N These fixed alkalies may be substitu- 
 
 Soda Na.O. I ted for each other in the different spe- 
 
 Hydrated ammonia .... N.H3H.O. r cies of alum. The hydrated ammonia. 
 Hydrate of lime Ca.O.H.O.; H.O.N.H3 (often called oxide of ammoni- 
 um, N.H4O.), 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 min 
 erals, and in some forms of alums, potash is replaced by an atom of any oxide in 
 Group II., united with an atom of water, as hydrate of hme, or by two atoms of 
 such compound without water. 
 
 GROUP V, 
 
 Phosphoric acid P.O5 ^ These acids combine with bases in 
 
 Arsenic acid AS.O5 5 different proportions to form each three 
 
 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 Mit- 
 scherlich first established the principle of isomorphism, although the true laws of 
 their constitution escaped his notice, and were only brought into view by the later 
 excellent researches of Graham. Even now there is no example of isomorphism 
 between two complete series of compounds so well established as that of the ar- 
 seniates and phosphates. 
 
 GROUP VI. 
 
 Perchloric acid C1.07^ The corresponding salts of these acids 
 
 Permanganic acid Mn207 >are truly isomorphous, and this gi-oup af- 
 
 Periodic acid LO7 j fords an example of a form to which I 
 
 shall recur, that of one equivalent of one body being replaced by two of another, as 
 CI. by Mng. 
 
 GROUP VII. 
 
 Sulphuret of antimony . . . . Sb.Sa^ These bodies, which are found crystal- 
 
 Sulphuret of arsenic As.Ss >lized in nature, have the same form. 
 
 vSulphuret of bismuth .... Bi2S3 / The oxide of antimony and the arsenious 
 acid, Sb.Os and AS.O3, though they are not found crystallized in the same form, ap- 
 pear to replace each other in some salts without changing its figure, and may, 
 therefore, be sometimes isomorphous. 
 
 GROUP VIII. 
 
 Stannic acid Sn.02 ) These are found native crystallized in 
 
 Titanic acid Ti.02 5 the same form. 
 
 There are many other cases in which similarity of crystalline form has been ob- 
 served between bodies of more or less analogous constitution ; 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 sup- 
 posed 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 carbonates of lime and magnesia, the angles of the rhombs 
 differ by 2° 36' ; 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 plesiomorphism^ 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 
 
ISOMORPHISM IMPORTANT TO THE CHEMIST. 225 
 
 changes in external circumstances might prevent the absolute iso- 
 morphism of two bodies, particularly as it is found that the value 
 of the angles in different specimens of even the same substance is 
 liable to fluctuation even to nearly a degree. I apprehend thai we 
 must seek the cause of these plesiomorphic differences in the pecu- 
 liar circumstances under which the body forms, particularly with 
 regard to temperature j for when a crystallized body, not of the reg- 
 ular system, is heated or cooled, it expands in different degrees, ac- 
 cording to the direction of its axis, and may even contract in one 
 direction while it is expanding in another j thus, when carbonate of 
 lime is heated from 32^ to 212^, the linear expansion in the direction 
 of the principal axis is 0*001961, while in the direction of each hor- 
 izontal axis a contraction of 0*00056 occurs ; in consequence of this, 
 the obtuse angle of the rhomb, which at 50^ Fah. is equal to 105° 
 4', becomes more acute by 8^', 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 were thus coincident ; but by change of figure, when brought 
 to ordinary temperatures, the small plesiomorphic differences may 
 have occurred. 
 
 Isomorphism, considered as thus sketched, affords to the chemist 
 the most valuable criterion at present at his disposal for determin- 
 ing those substances which replace each other most truly in com- 
 bination ; and where a number of bodies are so connected by exter- 
 nal form, very important conclusions may be obtained as to the in- 
 ternal arrangement of their constituents. In this manner it has 
 been satisfactorily established, that bodies may replace each other 
 in proportions quite different from their ordinary equivalents, and 
 thus pass, as it were, by a doubling or trebling of their atomic 
 weights, into a different natural group j and that even two bodies, 
 combined in an equivalent of each, may form a complex group, ca- 
 pable of being substituted for one of simpler structure. Thus an 
 equivalent of chlorine is replaced by two equivalents of manganese ; 
 mi equivalent of silver is replaced by two equivalents of copper j an 
 equivalent of soda or of potash is replaced by two equivalents of 
 lime, or of one of lime and one of water, or by one of Ihne and one 
 of oxide of manganese or of iron, or by ammonia and water united 
 to each other, or to an equivalent of a protoxide of the magnesian 
 group. By such observations we obtain the foundations of a philo- 
 sophical classification of bodies, with which the analogies drawn 
 from purely chemical characters are found remarkably to corre- 
 spond. 
 
 But it is important to ascertain whether the isomorphism of various bodies rs- 
 tabhshes necessarily, or even probably, in the absence of other reasons, grounds for 
 assimilating the formulae of the bodies, or imagining that their chemical constitu- 
 ents 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 anhydrous sulphate of soda crystallizes in the same form as perchlorate of 
 barytes and permanganate of barytes ; and if it be necessary, as a consequence of 
 isomorphism, that these bodies should have similar constitutions, we must change 
 the formula, S.O3 . Na.O. into S2O7 . Na20., in order to make it resemble Mn207 . 
 Ba.O. This requires us to compare the sulphates whose elements are most oow. 
 
 Ff 
 
226 PRINCIPLES OF ISOMORPHOUS REPLACEMENT. 
 
 erfully united, with some of the most easily decomposed salts that we know ; it re- 
 quires us to consider the alkalies as being suboxides, which is opposed by every 
 circumstance in their history ; and it requires us to consider two equivalents of so- 
 dium as being equivalent to one of barium, for which no other evidence can be had 
 from other examples. But, again, the anhydrous sulphate of soda is isomorphous 
 with sulphate of silver, and hence the formula of this last should be S2O7 . Ag-aO., 
 which is so totally unsupported by other evidence that it has been proposed to sub- 
 divide the atomic weight of silver and sodium, for the purpose of explaining the iso- 
 morphism of Cu2 and Ag. These examples are sufficient to show how unphilosoph- 
 ical 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 crys- 
 talline form also. Even without speaking of the regular system, where fluor spar 
 and alum, Ca.F. and K.O. . S.O3-I-AI2O3 . 3S.03-f 24H.O., have the same form, we 
 find numerous examples of this fact ; nitrate of soda and. carbonate of lime are iso- 
 morphous in the rhorabohedral system, and nitrate of potash and carbonate of lead 
 in the right prismatic system ; the chemical constitution of the formulae N.O5 . Na.O., 
 and C.O2 . Ca.O., and that of the formulae N.O5 . K.O., and C.O2 . Pb.O., are 
 widely different, but the forces by which the assumption of crystalline form is gov- 
 erned are alike. Even in these instances the attempts at generalizing the chemical 
 formulae have been tried, and the nitrates of soda and potash have been written 
 N.Oe K. and N.Oe . Na., with which the formulae of the carbonates, when doubled, 
 C206Ca2 and C206Ba2, have been compared. In this way one equivalent of soda is 
 made isomorphous with two of barytes, while by a former and similar reasoning, 
 one of barytes was made isomorphous with two of soda. Bisulphate of potash, 
 K.O. . S.O3-I-H.O. . S.O3, crystaUizes in two forms, one of which is that of sul- 
 phur, a simple body, and the other of which is that of feldspar, K.O. . Ss-j-AkOs . 
 3S03. Here, in neither case is there the shghtest 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 
 structure of the bodies shall be alike, but has no necessary reference 
 to the chemical nature or composition of these molecules. Exam- 
 ples. — Nitrate of soda and carbonate of lime, sulphate of soda and 
 perchlorate of barytes, bisulphate of potash and sulphur. 
 
 2d. When the physical molecules consist of chemical elements 
 which follow the same laws 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. Examples. — Sulphate of zinc and sulphate of magnesia, 
 carbonate of lime and carbonate of zinc, sulphate of barytes and sul- 
 phate of strontia. 
 
 3d. But identity of molecular structure may result from the ag- 
 gregation of substances the most different in their chemical relations, 
 and hence isomorphous bodies are not necessarily of similar chem- 
 ical constitutions. 
 
 4th. As the influence of the chemical constitution does not extend 
 to the absolute determination of the molecular structure, a body, 
 chemically 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 isodimorphous. Examples. — Sulphur, bisulphate of potash, 
 nitrate of potash and carbonate of lime, garnet and idocrase, arse- 
 nious acid and oxide of antimony. 
 
 5th. We cannot assert that the similarity of form of truly isomorph- 
 
OF DIMORPHISM AND ISOMERISM. 227 
 
 ous bodies results from the isomorphism of their elements ; for, 
 BO 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 aggre- 
 gation of the same number of simple molecules j 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 exam- 
 ples 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. 
 
 Finally. Isomorphism does result from the aggregation, according 
 to the same laws, of similar molecular groups, which are most gen- 
 erally formed by the reunion of similar chemical substances in the 
 same state of combination. 
 
 SECTION III. 
 
 OF DIMOEPHISM AND ISOMERISM, AND OF THE THEORY OF TYPES. 
 
 The fact of the same body being capable of crystallizing in forms 
 belonging to two different systems has been already frequently re- 
 ferred to, but, for convenience of reference, a more detailed list of 
 such cases is here inserted, taken from Professor Johnston's excel- 
 lent report on the subject made to the British Association. 
 
228 
 
 LIST OF DIMORPHOUS BODIES. 
 
 I. Elementary bodies 
 Sulphur . , 
 
 Carbon 
 
 Symbol or Form. 
 
 II. Bi-elementary Compounds : 
 Dioxide of Copper . A l 
 
 B 
 
 Disulphur. of Copper A 
 
 :i 
 
 Sulphuret of Silver . A 
 
 1 . B 
 
 Sulph. of Manganese A 
 
 Bisulphuret of Iron 
 
 i\ 
 
 A 
 B 
 
 Biniodide of Mercury A 
 
 B 
 
 Bichlor. of Mercury . A 
 
 . B 
 
 Arsenious acid 
 
 . A> 
 . Bf 
 
 Oxide of Antimony . A \ 
 
 . B S 
 
 III. Compounds of 2 Elements : 
 Carbonate of Lime . A \ 
 
 . B^ 
 
 Carbon, of Magnesia A ) 
 
 B S 
 
 A^ 
 
 Carbonate of Iron 
 
 Carbonate of Lead 
 
 Nitrate of Potash 
 
 Chromate of Lead 
 
 IV. Compounds of A or mare 
 Eh 
 
 
 laments : 
 Sulphate of Nickel . A 
 
 . B 
 
 Seleniate of Zinc . A 
 
 . B 
 
 Bisulphate of Potash A 
 
 _ B 
 
 Biphosphate of Soda A 
 
 a A) 
 
 - bS 
 
 Garnet A 
 
 Idocrase 6 
 
 Baryto-Calcite . A 
 
 Sulphato- Tricarbon- i 
 ate of Lead . . S 
 
 S. 
 C. 
 
 CujO. 
 
 Cu.S.orCuaS. 
 
 Ag.S. or AgaS. 
 Mn.S. 
 Fe.Sz. 
 Hg.Ia. 
 Hg.Cla. 
 AS2O3. 
 SbjOj. 
 
 Ca.O.+C.Og. 
 Mg.O.+C.Os. 
 Fe.0.+C.02. 
 Pb.O.+C.Og. 
 K.O.+N.Os. 
 Pb.O.+Cr.Os. 
 
 Ni.O.+S.03+7H.O. 
 Zn.O.+Se.03+7H.O. 
 
 K.O.+S.Oa+H.O.+S.Oj 
 
 Na.O.+P2 05+4H.O. 
 or Na.H2P.+2H. 
 
 Ca,si.+— 
 
 Si. 
 
 Fe. 
 
 Pb.S.+3Pb.C. 
 
 Crystalline Form. 
 
 j Rt. Rh. Pr., M. on M. 101-59, Haid. 
 \ Oblique Rh. Pr. of 90° 32', M. 
 I Reg. Octohedron. 
 I Rhombohedral. 
 
 iCube. 
 Rh. of 99° 15', 6 sid. Pr. Rhomb. 
 cleav., Sk. 
 I Do., Primary a Rhomb., P. on P'. 
 ^ =71° 30'. 
 ( Reg. Octohedrons. 
 ( Cube in Silver glance. 
 \ Rhomboid. 
 ( Cubes. 
 ( Rhomboid. 
 i Cubes. 
 
 \ Rt. Rh. R., M. on M'. 106° 2'. 
 5 Octohed. with square base. 
 ^Rt. Rh. Pr., M.M.=zll4o. 
 i Rt. Rh. Pr., M.M.=71-55. 
 \ Octohed. with rect. base. 
 j Reg. Octohedrons. 
 \ Rt. Rh. Pr. 
 \ Do., M. on M'. 136° 58'. 
 ( Reg. Octohedrons. 
 
 5 Rhomb, of 105° 4', M. 
 
 ^Rt. Rh. Pr. ofI16° 16', Xm. 
 
 < Rhomb, of 106° 15'. 
 
 \ Rt. Rh. Pr. 
 
 j Rhomb, of 107-0. 
 
 I Rt. Rh. Pr., 108° 26', 118° 0'? 
 
 j Rhomboid, 104° 53^'? 
 
 \ Rt.Rh.Pr. of 117° 14', Xu. 
 
 \ Rt. Rh. Pr., M.on M'.=118° 52', Lv. 
 
 I Rhomboid of 106-36, Fm. 
 
 \ Ob. Rh. Pr. 
 
 \ Square Prism. 
 
 ( Rt. Rh. Pr., M. on M'. 91° lO', Bk. 
 
 \ Square Prism. 
 
 \ Rt. Rh. Pr. 
 
 ( Square Prism. 
 
 I Rhombic Octohed. (form of sulphur) 
 
 < M. 
 
 i Ob. Rh. Pr. (form of feldspar), M. 
 
 C Rt. Rh. Pr. of M. on M'.93° 54'. 
 
 / Do. of 78° SC. 
 
 Reg. Dodecahedron. 
 
 Square prism, 
 
 i Oblique Rh. Prism. 
 Right Rh. Prism (form of arrago- 
 nite). 
 5 Acute rhomboid of 72° 30'. 
 I Rt. Rhomb. Prism,* M. on.M=120. 
 
 * Haidinger sajrs an oblique rhombic prism, which, according to the subsequent moasorement of Brooke, i« in 
 norrect. Bi., Brooke id*., Kupfer ; Ziv., Levy ; JJf ., Mitscherlich ; Si., Suckow. 
 
VARIOUS STRUCTURE OF DIMORPHOUS B O D I E S. 229 
 
 The molecular arrangements which produce this diversity of form 
 are not in general of equal stability j on the contrary, one figure ap- 
 pears 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 carbonate of lime commences to be decomposed j 
 but no alteration of temperature can convert calc spar back again 
 into arragonite. Indeed, arragonite appears to be formed only be 
 tween very narrow limits of temperature. When chalk is melted, 
 it forms, on cooling, marble, whose fracture shows it to have the 
 rhombohedral structure ; and when carbonate of lime is precipitated 
 at ordinary temperatures, the microscopic crystals produced are 
 rhombohedrons ; but when it is precipitated from a boiling solution, 
 it deposites minute crystals of arragonite, which a hi her or a lower 
 temperature would 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 accom- 
 panied 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 ex- 
 ternal circumstances admit of their suitable motion among each 
 other. 
 
 Independent of the change in external figure, dimorphous bodies 
 present remarkable differences in physical properties j thus the den- 
 sity is generally different ; in one form the substance is more solu- 
 ble than in the other 5 they differ also in hardness, and, generally 
 speaking, in all characters derived from the physical arrangement 
 of molecules. 
 
 A body in its dimorphous conditions presents frequently a differ- 
 ence of chemical properties deserving of particular notice. The 
 bisulphuret of iron, in its cubical form, is remarkably permanent, 
 not being acted on either by air or water j but in its right rhombic 
 form, when exposed to moist air, it absorbs oxygen with avidity, 
 and is converted into a crystalline mass of copperas. On this prin- 
 ciple 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 boiling oil of vitriol, and this change is 
 generally accompanied by the spontaneous ignition of the body, 
 which the temperature applied would be quite insuflicient to pro- 
 duce. 
 
 Independent of crystalline form, we must refer to circumstances 
 
230 CHANGILS APPROACHING DIMORPHISM, 
 
 similar to those which produce dimorphism, a variety of differences 
 in phj^sical constitution observable in certain bodies ; thus melted 
 sulphur is, at 230"^ F., perfectly liquid j on being heated to 430° it 
 becomes thick, and so tenacious that the vessel containing it may 
 be inverted without it running out j when heated farther to 480°, it 
 becomes again liquid, and continues so till it begins to boil. When 
 the red oxide of mercury is heated nearly to redness, it becomes 
 almost quite black. If the red iodide of mercury, formed by pre- 
 cipitation, be sublimed, it becomes yellow j 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 liquid hyponitrous 
 acid (N.O3) is deep green at 60°, but at 4° it is quite colourless ; 
 and the deep red gas of nitrous acid (N.OJ 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 molecular 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 equiva- 
 lent to that to which dimorphism may be referred, is capable of being 
 produced by very simple means. Thus, when a plate of glass is com- 
 pressed 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 yi^ 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 differences of chemical properties may, however, proceed 
 much farther, so that in place of considering that there is one chem- 
 ical substance which may exist in two molecular conditions, we are 
 obliged to 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 al- 
 cohol, we obtain a gas consisting of carbon and hydrogen, in the 
 proportion of an equivalent of each. In the destructive distillation ol 
 wood, a solid substance is obtained, 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, preseni, 
 
PRINCIPLE OF ISOMERISM. 231 
 
 therefore, a difference in molecular arrangement still greater than 
 those which have heen observed among merely dimorphous bodies, 
 and when we examine their chemical relations, the diversity becomes 
 still more marked. The gas (olefiant gas) is remarkable for the num- 
 ber of compounds to which it gives rise, and has been, from the va- 
 riety of its reactions, 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 dif- 
 ferently placed, but that the molecules are different ; the carbon and 
 hydrogen which unite to constitute the chemical equivalent of the 
 body are themselves differently arranged, and thus give rise to dif- 
 ference 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 laog 
 [ispog) because they have the same ultimate composition, but in all 
 their chemical 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 dimorphous bodies are produced ; but when 
 the difference of arrangement extends to the chemical constituents 
 of these molecular groups, independent, but isomeric bodies are 
 produced. 
 
 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 C5H4 j but when 
 we combine these oils with muriatic acid, we find that the equiv- 
 alent group of oil of turpentine contains C2oH,6, while that of oil of 
 citron is only CioHg ; it is remarkable that, though the chemical 
 group of oil of citron is only one half the weight of that of oil of 
 turpentine, it exercises the same power of circular polarization, but 
 in the opposite direction. 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 C4H6O2, 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 com- 
 posed of ether and water, C4H30.-[-H.O., while methylic ether cannot 
 be resolved into those substances. Formiate of methylene and glacial 
 acetic acid are each C4H4O4, not differing even in the w^eight of their 
 equivalent ,• but all the properties of these bodies show that glacial 
 acetic acid is C4H3O3+H.O., while formiate of methylene is C^H.Oa-f 
 C2H3O. Instances of this kind might be multiplied to any extent, 
 ^ut these will be sufficient to illustrate the principle. 
 
232 CONNEXION OF DIMORPHISM AND ISOMERISM. 
 
 It is necessary, however, in studying such cases of isomerism, 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 total- 
 ly unappreciable, except in the most rigidly accurate analysis, may 
 change so completely the properties of bodies that they will sim- 
 ulate 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, 
 P.H3 ', but the first may be changed into the second by mere admix- 
 ture with a very small quantity of the vapour of ether, and the sec- 
 ond may be converted into the first by the most minute bubble of 
 nitrous acid gas. Such bodies, therefore, 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 in- 
 dications of dimorphism, to the complete difference of structure and 
 properties constituting isomerism, it becomes an interesting ques- 
 tion 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 evidence of difference in chem- 
 ical arrangement. May not 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 difference in equivalents be the source of diversity in formi 
 When sulphur crystallizes in the form of bisulphate of potash, may 
 we not reasonably suppose that its molecules are grouped into a 
 complex figure, like that of the compound salt, and that its equiv- 
 alent 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 hydro- 
 gen or copper 1 Manganese replacing chlorine, is to manganese re- 
 placing 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 Fe.S2, and, like Mn.02, 
 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 equiv- 
 alent be Fe2S4, resembling CI.O4, and, like it, be decomposed by the 
 slightest causes 1 
 
 The circumstance that isomeric bodies are almost universally con- 
 nected by simple relations between their atomic weights, coupled 
 with the idea that even among the simple bodies a kind of isomer- 
 ism may be the cause of their dimorphous conditions, acquires re- 
 markable 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 : 
 
NATURE OF COMPOUND RADICALS. 
 
 233 
 
 1 equivalent of zinc = 32-31 
 
 1 " yttrium . . . 3225 
 \ " antimony . . . 32 40 
 1 " tellurium . . . 32 13 
 
 2 " sulphur . . . 32-24 
 
 1 equivalent of cobalt . , . . 29 57 
 
 1 " nickel .... 29-62 
 
 ^ " tin .... . 29-46 
 
 1^ equivalent of bismuth = 106-65 
 
 2 " palladium. . . 106-72 
 
 2 equivalent of osmium . . . 199-72 
 
 1 " gold .... 199-21 
 
 1 equivalent of platina . . .' . 98-84 
 
 I " iridium . . . 9884 
 
 L equivalent of molybdenum . . 4796 
 
 i " tungsten . . . 47-40 
 
 May it not be possible that science shall hereafter find the metals 
 so connected to be truly isomeric 1 In no case are their properties 
 more different j and we find in the racemic and tartaric acids an 
 example of the general similarity of properties in the compounds 
 of isomeric bodies, which is so remarkable in the combinations of 
 sulphur and tellurium, or of cobalt and nickel, among the simple 
 substances. 
 
 Considerable probability is given to the idea of the compound na- 
 ture of bodies at present considered simple, by the existence of 
 certain compound bodies which simulate the properties of, and 
 enter into combination subject to the same laws as the undecom- 
 pounded 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 cyanides, as chlorine is of a series of chlorides, and 
 it is hence called a compound radical. The discovery of this prin- 
 ciple 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 
 contain different radicals, precisely as the salts of nickel and the 
 salts of cobalt will remain quite distinct, even should nickel and co- 
 balt be hereafter shown to be isomeric bodies. This 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 dif- 
 ference of properties was to be explained, the formulae of organic 
 bodies were perhaps too hastily grouped, by the assumption of a 
 hypothetic radical, of which the different bodies of the series were 
 supposed to be combinations. It is certain that, in many cases, this 
 plan has been of great use to science, as in the benzyle theory of 
 Liebig, and in the ether and ammonia theories proposed by Ber- 
 zelius and myself; but I consider the degree to which it has latterly 
 been extended, 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 con- 
 ceal 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 union has been considered as resulting 
 from their antagonistic and mutually neutralizing properties, and 
 the successive stages of composition being 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 
 
 Gg 
 
234 
 
 CONSTITUTION OF ORGANIC BODIES. 
 
 alumina; these respectively, compounds of sulphuric acid and a base 
 which consists of oxygen united to a metal ; the sulphuric acid it 
 self being formed by the union of oxygen and sulphur. This view 
 results necessarily from what has been said of the nature of chem- 
 ical affinity, and expresses faithfully the principle upon which the 
 electro-chemical theory has been formed ; there is no doubt but that 
 the constitution of inorganic bodies is regulated in this way, but we 
 meet with considerable difficulty in applying its principles to or- 
 ganic chemistry. Thus I myself suggested a few years ago, that 
 the formic and acetic acids should be looked upon as oxides of com- 
 pound radicals, formyle and acetyle, C2H.03=Fo.03 and C4H303= 
 AC.O3, by which means a variety of bodies of analogous constitution 
 were simply connected together, as the formyle or acetyle, which 
 combine with oxygen to form those vegetable acids, combine with 
 iodine, chlorine, sulphur, and cyanogen to form binary compounds, 
 precisely as manganese (a simple radical) combines with oxygen to 
 form manganic acid, and with chlorine, &c., to form an analogous 
 series of bodies. I am far from abandoning this view : the question 
 of its full applicability will be discussed among the general laws of 
 organic chemistry, but at present we will attend to only one circum- 
 stance connected with it. Hydrated acetic acid is formed from al- 
 cohol, 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 H2 and gaining O2, 
 thus: 
 
 Alcohol C4H6O2 
 
 gives by . . — H2-}-Q2 
 Hydrated acetic acid , C4H4O4. 
 
 Pyroxylic spirit . . C2H4O2 
 
 gives by . . — H2-{-Q2 
 
 Hydrated acetic acid . C2H2O4. 
 
 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 itl 
 
 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 consti 
 tution 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 proposition which merits profound attention. He considers 
 that the elements 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, elements of the most di- 
 verse characters may be substituted for each other, and yet the 
 molecular group remain unaltered in structure and physical consti- 
 tution. Thus the molecular group of alcohol (C4H6O2) contains 
 twelve chemical atoms. When it is changed into acetic acid ('C4H4O4), 
 the numbei of chemical atoms is the same ; the mechanical type of 
 
OF ACTIONS BY CONTACT. 23o 
 
 the body is unaltered, although its chemical properties are complete- 
 ly 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 while the nature of the elements changes, the bodies have 
 the same mechanical type ; but if the substitution of elements is ac- 
 companied by a change of properties, the chemical type of the ori- 
 ginal body is destroyed. Thus alcohol and acetic acid have not the 
 same chemical type. 
 
 When acetic acid is treated with chlorine, it loses three equiva- 
 lents of hydrogen and gains three of chlorine (C4H4O4 — H3+Cl3= 
 C4CI3H.O4), forming chloroacetic acid. The sum of the molecules 
 is here twelve, and this substance has the same mechanical type as 
 alcohol and common acetic acid ; but in changing to this body, com- 
 mon acetic acid scarcely changes its properties, and hence is said 
 to retain its chemical type. When ether (C4H5O.) is treated with 
 chlorine, its hydrogen is totally replaced by chlorine, and the body 
 (C4CI5O.), chlorine ether, is produced 5 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 is undisturbed, notwithstanding the 
 total substitution of chlorine for hydrogen, a body differing from it 
 so much in general characters. 
 
 The question how far this theory of types should be adopted, and 
 how far the law of substitution on which it rests is verified by ex- 
 periment, will be hereafter examined. The theory is here only no- 
 ticed as involving important relations between the mechanical struc- 
 ture and the chemical constitution of organic bodies. 
 
 SECTION IV. 
 
 OF CATALYSIS. 
 
 The decomposition of compound bodies is frequently eflfected by 
 the intervention of causes which cannot be referred to ordinary af- 
 finity ; and in many cases, bodies which have but little tendency to 
 unite, enter into combination when brought into contact with a sub- 
 stance 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 platinum, 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 supposing that the platinum 
 condenses powerfully on its surface a layer of mixed gaseous par- 
 ticles, and thus brings them within the sphere of their mutual attrac- 
 tion. But this explanation does not apply to other cases. If we 
 boil starch (Ci2H,oO,o) with diluted sulphuric acid, it is converted suc- 
 cessively into dextrine, gum, starch-sugar, and, finally, crystallizable 
 grape-sugar (Ci^HiaO,^), hiiving associated to itself the constituents 
 of two equivalents of water. At the termination of the process, the 
 sulphuric acid is found unaltered in properties and in quantity, so 
 
236 ANALYSTS AND CATALYSIS. 
 
 that the smallest portion of sulphuric acid is sufficient to convert 
 into sugar an indefinitely great quantity of starch. If oxamide 
 (C2O2N.H2) be diffused through water, in contact with the smallest 
 possible quantity of oxalic acid, it gradually disappears, and, appro- 
 priating to itself the elements of an equivalent of water, is converted 
 into neutral oxalate of ammonia, (C2O3+N.H3), the small quantity of 
 oxalic acid originally added remaining unaltered and in excess. 
 
 Among instances of decomposition by forces of this kind, the ox- 
 ygenated water (H.O2) 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 in- 
 stantaneous 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 re- 
 mains quite unaltered ; no affinity can be traced between it and the 
 oxygenated water, the mere presence of the foreign body appearing 
 to cause the decomposition. 
 
 Berzelius, who first directed general attention to these phenomena, 
 proposed to attribute them to a peculiar force, differing from ordi- 
 nary 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 
 expelled. It is in this way that we obtain the constituents of bodies 
 by or dinar Y analysis ; and for distinction, he proposes to term such 
 decompositions as those just described, operations of catalysis, and 
 to name the power which these bodies have of acting by mere con- 
 tact, 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 phenomena, and it is, indeed, 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 conditions 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 sat- 
 isfied ; but it is natural to suppose that, while 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 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 decompo- 
 sition resolves itself into a means of disturbing the molecular equi- 
 librium of a compound body, so that it can be only restored when 
 the particles are differently arranged. Catalysis may, therefore, be 
 produced not merely by the presence of various bodies, but stil^ 
 more remarkably by the action of physical agents, among which 
 heat is the most powerful ; thus, when acetate of lime (C4H304Ca.) 
 is strongly heated, the equilibrium of its molecular group is over 
 
COMMUNICATION OF MOTION. 237 
 
 turned, and when the affinities again satisfy themselves, two new 
 bodies result, acetone and carbonate of lime (C3H3O. and COgCa.). 
 Destructive distillation is therefore a catalytic process, and the or- 
 igin 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 decomposi- 
 tion of explosive bodies by an elevation of temperature or by a 
 slight blow, is traceable to the same disturbance of the old equilib- 
 rium, and establishment of the new. A most important means of 
 thus setting into motion the particles of bodies, and enabling them 
 to rearrange 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 sil- 
 ver, the decomposition is propagated to the latter, which is com- 
 pletely resolved into oxygen and metallic silver ; if peroxide of lead 
 be used, it is converted into protoxide by the escape of half its ox- 
 ygen, and even the black oxide of manganese may be reduced 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 com- 
 municated 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 (CiaHnO,,) be 
 brought into contact with a little decomposing gluten or yeast, it 
 unites with the elements of an equivalent of water, and divides it- 
 self into two equivalents of alcohol, 2 (C^eOg), and four of carbonic 
 acid, 4 (C.O2). If a solution of urea (C.O.N.H2) be put in contact 
 with yeast, it unites also with an atom of water, and is then decom- 
 posed into an equivalent of ammonia (N.H3) and one of carbonic 
 acid. The conversion of starch into sugar in the processes of ger- 
 mination and of malting, is effected by a substance which accompa- 
 nies 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 
 necessary 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 with- 
 out leaving any residue. Pure copper is not acted upon by dilute 
 sulphuric acid j but when it is alloyed with nickel and zinc, as in 
 the argentine, or German silver of commerce, it dissolves complete- 
 ly. In these cases, the molecular action which produces the com- 
 bination with the acid was not possessed by the platina or copper 
 when alone, but is acquired by them, being transmitted from the 
 other metals with which ihey are alloyed. 
 
 It may not be easy to reduce to the action of this principle all 
 phenomena of catalysis; for, in the imperfect light by which we 
 contemplate them, it is possible that we may rank together circum- 
 stances whose real nature is very different ; but, at all events, we 
 must recognise in this principle, the definite introduction of which 
 into science is due to Liebig, a cause of chemical decomposition 
 
238 CLASSIFICATION OF BODIES. 
 
 peculiarly important in explaining the complex reactions of organic 
 bodies. It is remarkable, also, that this law, of which the simplest 
 expression is, that where two chemical substances are in contact, 
 any motion occurring among the particles of the one may be com- 
 municated to the particles of the other, is of a more purely mechan- 
 ical nature than any other principle as yet received in chemistry ; 
 and when more definitely established by succeeding research, it 
 may be the basis of a dynamical theory in chemistry, as the law of 
 equivalents and of multiple combination expresses the statical con- 
 dition of bodies which unite by chemical force. 
 
 We must, at least, look upon these actions of catalysis^, the con- 
 ditions of molecular arrangement which give rise to isomerism and 
 dimorphism, and the introduction of the principle of types in oppo- 
 sition to that of mere binary combination, as tending towards a 
 change in our ideas of the nature of chemical affinity, which may^ 
 before long, remodel the whole constitution of the science. 
 
 CHAPTER XI. 
 
 ON THE CLASSIFICATION OF THE ELEMENTARY 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 
 I on-supporters of combustion. It has, however, been fully shown, 
 that in combustion each body is mutually a supporter and a com- 
 bustible : oxygen burns in hydrogen or in the vapour of sulphur, just 
 as much as hydrogen or sulphur burn in oxygen ; Thompson's prin- 
 ciple is therefore radically defective ; and the electro-chemical the- 
 ory, although far superior as a principle, is liable to weighty objec- 
 tions of a somewhat similar kind. These have been already, how- 
 ever, so far noticed, and the arrangement of the simple bodies in that 
 series so fully given, p. 188, that it is unnecessary to recur farther 
 to the subject. 
 
 The kind of classification that is suited to the present wants of 
 chemistry must be founded upon the general analogy of properties 
 between substances belonging to the same class, and on their iso- 
 morphous replacement of one another. This last character is not 
 absolute j 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 last three is com- 
 plete, and their compounds are strictly isomorphous j their similar- 
 ity 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. 
 
CLASSIFICATION OP ELEMENTS. 239 
 
 The second class comprises magnesium, calcium, manganese, iron, 
 cobalt, nickel, zinc, cadmium, copper, hydrogen, bismuth, chromi- 
 um, 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 
 aliali. Chromium, aluminum, glucinum, vanadium, and zirconium 
 do not form protoxides, but sesquioxides, the salts of which are iso- 
 morphous with those of the sesquioxides of iron and manganese. A 
 remarkable connexion is established between this class and the prece- 
 ding by the ismorphism of the manganic acid (Mn.Oa) and chromic 
 acid (Cr.Oa) with sulphuric acid (S.O3), indicating that under cer 
 tain circumstances these metals may change from one natural fam- 
 ily 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 soluble in water, while the sulphates of this 
 class are almost insoluble. Calcium approximates to this condition 
 by the sparing solubility of sulphate of lime ; and the connexion be- 
 tween the two families is still more fully shown by the dimorphism 
 of carbonate of lime, it having in one form the figure of the carbon- 
 ates 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 suffi- 
 ciently evident ; and although their compounds are not frequently 
 isomorphous, yet there is good reason for attributing that to the di- 
 morphism of each. Silver differs remarkably in its chemical rela- 
 tions from potassium and sodium, and the only grounds for inserting 
 it in this class is the isomorphism of sulphate of silver with anhy- 
 drous sulphate of soda. 
 
 The salts of potash are perfectly isomorphous with the salts of 
 ammonia which contain an atom of water ; and. hence, if the base 
 of the ammoniacal salts (N.H3+H.O.) be written N.H^ . 0., it may 
 be considered as an oxide of a compound radical which is isomorph- 
 ous with potassium, and would rank, did we not know its compo- 
 sition, in the present group. This view of the composition of the 
 ammoniacal salts was suggested by Berzelius, who gave to that com- 
 pound radical the name ammonium ; but I have since shown that 
 the replacement is really by two equivalents of a hydrogen com- 
 pound, 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 com- 
 plete. It is connected with the first and second classes by means 
 of manganese, of Which two equivalents replace, in truly isomorph- 
 ous compounds, one of chlorine. 
 
 Sixth class, nitrogen, phosphorus, arsenic, and antimony. In their 
 chemical history these compounds exhibit considerable, though not 
 complete similarity. The corresponding compounds of arsenic, an- 
 timony, and phosphorus are generally isomorphous, but in no case 
 
240 CLASSIFICATION OF ELEMENTS. 
 
 has isomorphism 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 marly cases in the proportion of one third of its equiva- 
 lent 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 me- 
 tallic state. 
 
 Ninth class, platinum, palladium, iridium, and osmium, from the 
 isomorphism of their double chlorides, by which also Graham con- 
 siders this class to be connected with the seventh. 
 
 Tenth class, tungsten and molybdenum ; the tungstates and mo- 
 lybdates being isomorphous. These metals Avill probably be found 
 to be of the same family with chrome, as chromate of lead has been 
 found crystallized in the same form as the molybdate. 
 
 Eleventh class, carbon, boron, and silicon: of these substances 
 no isomorphous relations are known ; they are brought together by 
 a general, though imperfect analogy of properties. 
 
 Graham makes no attempt at classifying mercury, cerium, colum- 
 bium, lithium, rhodium, or uranium. 
 
 I agree completely with the general principles of this classifica- 
 tion, but, in a few cases, researches made since it was drawn up by 
 Graham render some alterations necessary 5 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 sul- 
 phate of silver as being a sufficient ground for ranking the latter 
 metal in the fourth class. We have already seen numerous examples 
 of isomorphism among substances of totally different chemical con- 
 stitution, and the properties of the compounds of silver resemble so 
 completely those of lead, as to demonstrate positively that it be- 
 longs to the same natural group. "When copper enters into combi- 
 nation in a double equivalent Cuj, it becomes likewise a member of 
 the lead and barytes group, as is shown by the sparing solubility of 
 its sulphate and chloride ; and its being isomorphous with silver fur- 
 nishes 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 
 copper ; it therefore must be separated from platinum, and removed 
 to the second class. When mercury enters into combination with 
 the equivalent 10 1,4 (Hg.), it coincides in the nature of its com- 
 pounds with palladium and copper, and attaches itself to the second 
 
NON-METALLIC BODIE S.— O X Y G E N . 
 
 241 
 
 class ; but when its equivalent is 202,8 (Hgj), its compounds resem- 
 ble those of lead and silver, and, like copper, it then becomes a mem- 
 ber of the third class. 
 
 A classification such as this, although necessary for the philosoph- 
 ical study of the relations of the simple bodies, could not, without 
 considerable inconvenience, be strictly adhered to in an elementary 
 work like this j I shall, therefore, having thus laid down these gen- 
 eral 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 that may be useful towards understanding or illustra- 
 ting: those that follow. 
 
 ■J 
 
 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 numer- 
 ous processes into which it enters as an agent, and the influence 
 which its discovery 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 existing in great quanti- 
 ty 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 pro- 
 cesses of combustion and of respiration 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 5 it is colourless and 
 transparent; its specific gravity is 1102-6; 100 cubic inches of it 
 weigh 34-2 grains; its refractive index is 0-8616, that of air beintr 
 1-0000. It is very spa- 
 ringly dissolved by wa- 
 ter, 100 cubic inches of 
 water taking up only be- 
 tween three and four of 
 the gas. It is, conse- 
 quently, in most cases, 
 collected over water, by 
 forms of apparatus that 
 shall be now described. 
 
 For the collection and pres- 
 ervation of gases, such as ox- 
 ygen, the instruments gener- 
 ally employed are the pneu- 
 matic trough and the gasom- 
 eter The former is any ves- 
 
 Hh 
 
^42 GASOMETERS. — 'PREPARATION OF OXYGEN. 
 
 sel, 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 sustained upon a shelf, the water descends according as the bubbles 
 of gas ascend ; and when the jar in the water 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 below. The tube m passes down nearly to the 
 bottom of the cyhnder, but the other, n, only extends to 
 the upper surface ; both are provided with stopcocks, so 
 that the communication between the cylinder and the 
 upper vessel may be opened or cut off at pleasure. At / 
 there is also a small tube with a stopcock, 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 
 3losed, and all the stopcocks, m, n, I, left open. Water 
 being then poured into the upper vessel, it flows in through 
 the tubes m and n, while the air issues at /. When water 
 begins to flow out at I, that stopcock is to be closed, and 
 then the air which still remains escapes by the tube n, bub- 
 bling through the water in the upper vessel. When this 
 also ceases, the stopcocks 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 pur- 
 pose of obtaining oxygen gas ; one, which is very simple in theory, 
 and of great interest in history, from being that by which the impor- 
 tant agencies of oxygen in chemistry were first recognised, al- 
 though it is not at present practicably useful, is the following : 
 
 Some red oxide of mercury (Hg.O.) is to be introduced into a 
 retort, a, of hard glass, to which is then attached a receiver, b^ with 
 
 a tube, c, passing to the pneumatic trough. On applying the heat of 
 the argand 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 receiv- 
 er. The substance used is thus resolved into mercury and oxygen; 
 from 1094 grains, there would have been obtained 101'4^ 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 
 
PREPARATION OF OXYGEN. 
 
 243 
 
 experiment of this kind that Lavoisier demonstrated the true con- 
 stitution 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 ox- 
 ygen, 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 peroxides 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 manga- 
 nese (Mn.Oa) abandons, when at a red heat, one third of its oxygen, 
 and a complex oxide, Mn304, remains, analogous to the black mag- 
 netic oxide of iron, and formed by the union of equivalents of pro 
 
 <Z 
 
 toxide and of sesquioxide (Mn.O. + MnaOa). For this purpose tne 
 manganese is introduced in an iron bottle, a, to the neck of which 
 is attached a piece of gun-barrel, 6, 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 c? 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, and frequently. 
 
 from the occurrence of carbonate of lime and of ammonia in the 
 substance, the first portions of gas are mixed ivith carbonic acid or 
 with nitrogen ; these should be allowed to pass away, and the oxy- 
 gen 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 
 consists of 27-7 of manganese, united to sixteen of oxygen, of which 
 5*3 are given off, and hence 1 lb. troy of it is capable of furnishing 
 about 700 grains, or nearly 2000 cubic inches, equal to seven impe- 
 
244 
 
 PREPARATION OF OXYGEN. 
 
 rial 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, while the manganese, with the remainder, forms protoxide, 
 which combines with the sulphuric acid thus : H.O. . S.03-hMn.02= 
 H.O. . S.O3 . Mn.O.+O. 
 
 This operation is conducted by placing the manganese in a flask, 
 
 a, supported in a little 
 cup of sand, 6, over a 
 lamp, and mixing it with 
 twice its weight of oil of 
 vitriol; a tube, c, bent, as 
 in the figure, passes to 
 the pneumatic trough, 
 and dips under the edge 
 of the jar in Avhich the 
 gas is to be collected. 
 When the flask is heat- 
 ed, oxygen gas is rapid- 
 ly disengaged, but care 
 must be taken that, to- 
 ^ wards the close, the wa- 
 ter 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 con- 
 sist 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, 
 Mn.Oj, into protoxide, Mn.O., and permanganic acid, Mn207 (SMn.Oj 
 = 3Mn.O.+Mn207). This last is decomposed, when the temperature 
 rises, into 2(Mn.03), manganic acid, giving out one equivalent of ox- 
 ygen ; but the temperature must be raised very much to complete 
 the separation of the Mn.Og into O2 and Mn.O. Hence, in this pro- 
 cess, as ordinarily conducted, the residue in the flask is found to be 
 green, from manganic acid ; and, although in theory a more abun- 
 dant source of oxygen than that by simple ignition, in the propor- 
 tion 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 con- 
 sists of chloric acid united to potash Cl.Os-j-K.O., 
 and when heated somewhat above its melting 
 point, it is decomposed, all the oxygen it con- 
 tains being evolved in the state of gas, and the 
 other elements remaining combined as chloride 
 of potassium. The constituents of this salt are 
 by weight 35-4 chlorine, 39*7 potassium, and 48 
 of oxygen. Hence 100 parts of it give 39 of 
 oxygen by weight, or an ounce troy, 187 grains, 
 
PROPERTIES OF OXYGEN. 
 
 245 
 
 or 543 cubic inches. An ounce of it is therefore equivalent in ef- 
 fect to six ounces of ordinary peroxide of manganese. 
 
 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 re- 
 peated several times in succession. A bit of charcoal, heated' to 
 redness at a single point, burns, when immersed in oxygen, with 
 rapid scintillations of exceeding brilliancy ; and when phosphorus 
 is inflamed in oxygen, the splendour of the combustion is insupport- 
 able to the eye. Even bodies which are not combustible under or- 
 dinary circumstances, may be made to burn in oxygen. Thus, if an 
 iron wire be tipped at its extremity Avith 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 disengage- 
 ment of m.ost 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 in drops from the extremity of the burning wire, 
 which, even after having passed through a layer of water, fuse them- 
 selves 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 bv 
 simple methods. If a jet, u, be attached to the lat- 
 eral stopcock, I, of the gasometer, and the flame of a 
 spirit-lamp, h, be urged by the issuing stream of gas, 
 as by a blov^pipe, the most refractory substances 
 may be fused by it. If the tube be curved Aoyvn- 
 
 ward, the jet may be brought to bear on a little cup ^^^^^^^ u _A 
 of red-hot charcoal, in which the body to be fused ~ 
 
 may be laid, and thus, upon a small scale, the con- 
 struction and effect of the most powerful wind fur- 
 naces may be imitated. 
 
 Oxygen gas is. necessary to the support 
 of animal life. It is the oxygen which ex- 
 ists 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 car- 
 bonic acid, in a manner of which the exact details will be hereafter 
 studied. This change occurs even with blood which has been re- 
 moved from the body. If a quantity of dark blood, drawn from a 
 vein, be agitated in a vessel of oxygen gas, it is immediately changed 
 into the vermilion-coloured arterial blood. An animal can live long- 
 er in a vessel of pure oxygen than in the same volume of atmosphe- 
 ric 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 
 [i symptoms of general inflammatory fever, even though there may re- 
 main still a quantity of oxygen gas capable of supporting the life of 
 ^another animal for a considerable time. 
 
 The name of oxygen was given to this body from the idea of its 
 
246 PREPARATION OF HYDROGEN. 
 
 peculiar power of conferring acid properties on its compounds j and, 
 in reality, most of the bodies recognised by chemists among 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 recur- 
 ring to it when describing the properties of those bodies. 
 
 Of Hydrogen, 
 
 Hydrogen exists abundantly in nature as a constituent of animal 
 and vegetable substances, and is particularly of interest by forming 
 a constituent of water. From this fact it derives its name, vduip 
 yevvao) (I form water), and it is by the decomposition of water that 
 hydrogen is almost always obtained for experimental purposes. 
 
 If 1 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 ap- 
 pears 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 decomposi- 
 tion of water can be exhibited, the reaction being K.+H.O.=K.O. 
 
 If the circuit of the electrical current from a voltaic battery be 
 completed through water, which has been rendered a good con- 
 ductor by the addition of sulphuric acid, or common or Glauber salt, 
 the two constituents of the water are evolved at the opposite elec- 
 trodes, or terminating 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 compe- 
 tent to explain it, in a former chapter. 
 
 These methods, although the simplest, are yet-not applicable to 
 ordinary 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 hy- 
 drogen, and so to decompose water at ordinary temperatures; but 
 at a red heat the decomposition rapidly takes place. For this pur- 
 pose iron is generally employed. A gun-barrel, or an iron tube, c c, 
 is taken, and the interior having been loosely filled with iron turn- 
 ings 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 extrem 
 ity 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 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 immedi- 
 ately occurs, and the iron is oxidized, while 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 
 
PREPARATION OF HYDROGEN. 
 
 247 
 
 scales that are formed at the smith's forge by the action of the at- 
 mospheric air on iron, and which is also formed when iron is burn- 
 ed in oxygen gas. The action may, however, be simply represent- 
 ed as follows : 
 
 Fe.-f H.0.= H.-fFe.O. Protoxide of iron. 
 2Fe.H-3H.O.=:3H.+FeA P eroxide of iron. 
 3Fe.+4H.O.=4H.+Fe304 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 ot 
 hydrogen gas, acting at a red heat, oxide of iron may be decomposed, 
 the iron separating in the metallic state, and water being produced j 
 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 direct- 
 ed to one or the other object, according as one or the other sub- 
 stance 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 hydrogen gas, it is decompo- 
 sed, 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 tenden- 
 cy of a metal to combine 
 with water, so that the de- 
 composition 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, /, is 
 adapted, as in the appara- 
 tus represented in the fig- 
 ure, and then oil of vitri- 
 
248 PREPARATION AND PROPERTIES OF HYDROGEN. 
 
 ol, diluted with eight times its weight of water, be poured upon it 
 through the funnel, an abundant effervescence occurs, arising from 
 the escape of hydrogen gas, and the zinc or iron rapidly dissolves. 
 The action continues 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, while the 
 hydrogen is set free. The process may be thus represented, zinc 
 being used, Zn.+S.Oa+H.O.^H.-f (S.Oa+Zn.O.) 
 
 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 decompose the water, because the oxide of zinc, when formed 
 by the decomposition, 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 passed away. It ap 
 pears to me that the explanation is of a 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 ox- 
 ide which is formed, being insoluble in water, coats over the metallic 
 surface with a varnish impermeable to the fluid, and thus prevents 
 its farther 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 hinderance. 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 commercial zinc or iron may be referred to decompo- 
 sition by the electric currents which circulate from one portion of 
 the impure metal to the other, through the liquid. See page 135. 
 
 Hydrogen gas, when it has been prepared by any of these process- 
 es, is seldom pure. The iron and zinc of commerce contain gen- 
 erally traces of carbon, of sulphur, and sometimes of arsenic, which, 
 combining with some hydrogen, form gaseous or volatile products, 
 which give to the hydrogen a peculiar disagreeable odour, and col- 
 our its flame. Occasionally, also, traces of potassium and zinc, in 
 very minute division, are carried up with the hydrogen by the me- 
 chanical force of the effervescence, but by repose these latter impu- 
 rities 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 of 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 quicksilver, 
 so as to moderate the rapidity of the decomposition. Zinc, which 
 
PROPERTIES OF HYDROGEN. 24^ 
 
 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 com- 
 bines with the oxygen of the air, and forms water. If a jar of hy- 
 drogen gas be suddenly turned with the orifice upward, and infla- 
 med, 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 combustion of the mixture is instantaneous, and ac- 
 companied with an explosive report. The proper proportions are two 
 volumes of hydrogen gas to five of air. If a lighted taper be plunge^l 
 into a jar of hydrogen, it is immediately extinguished, the gas not 
 being able to support combustion. 
 
 Hydrogen gas is colourless and transparent ; it is absorbed by wa 
 ter in very small quantity, and hence, for ordinary purposes, is al- 
 ways collected over that liquid. It refracts light strongly, its re- 
 fractive 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 1-00 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 j or, more accurately, its specific gravity is 68*8, 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 over water, its specific gravity may be so much in- 
 creased by the watery vapour it may contain, that, although good enough for a 
 larger balloon, 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 ; consequently, the 
 hydrogen should be dried, which may be effected by causing 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 
 considerably lighter than atmospheric air under the same volume. 
 
 By the same experiment, the three most remarkable properties of hydrogen may 
 be exhibited in an interesting form. If a jar of hydrogen be held vertically, with 
 the orifice downward and open, it will remain filled by the hydrogen for a certain 
 time, as the air, being so much heavier, mixes itself with the lighter gas but very 
 slowly. If a lighted taper be now appUed, the gas will inflame at the surface 
 where it is in contact with the atmosphere, but, on plunging the taper upward 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 horizontal 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 upward, the residual gas will at once rush out, and, mixmg 
 with the air, will burn 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, but 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 ; 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 briUiant light and deafening explosion, the strongest bladder being torn to 
 shreds by the expansive force of the ignited gases. In this experiment the bladder 
 
 I I 
 
250 
 
 PROPERTIES OF HYDROGEN. 
 
 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 elec- 
 tric spark ; for this purpose a strong tube, closed at the top, 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 a eudiometer, 
 as it is frequently used to measure the quantity of 
 oxygen in the atmosphere, and generally for the 
 analysis 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 proportions had been 
 accurately observed, no residue is found ; if one 
 or the other gas had been in excess, the excess 
 remains behind, one third of the volume which 
 disappears being oxygen, and the other two thirds 
 being hydrogen. 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 tlje external ends, being connected by long wires with the 
 coatings of a charged Leyden jar, the spark passes between the terminal knobs in 
 the bladder, and the explosion 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 into contact with the platinum, and follows 
 the same course. If the platinum be in the form of a 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. Pla- 
 tinum in form of sponge always contains a quantity of air in this con- 
 densed condition, and hence, when a jet of hydrogen gas is caused 
 to play upon a morsel of spongy platina, it is absorbed, and water be- 
 ing 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 p. 179 and 235. 
 Spongy platinum introduced into a mixture of oxygen and hydro- 
 gen 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 produce their union in the slow and silent way. This mode 
 is accordingly often used in the analysis of mixtures of gases, and 
 
HYDRO-OXYGEN BLOWPIPE. 251 
 
 tne energy of the platinum balls can be graduated by the proportions 
 of metal and of pipe-clay which are employed. Hydrogen and oxy- 
 gen, however, are not the only gases which can be made to unite by 
 the agency of platinum -surfaces, 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 most serious 
 accidents. The safest form for experiment on a large scale con- 
 sists 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 will 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 resembling that of a candle, into the interior of which is in- 
 jected a stream of air by the blowpipe in common use. Another form 
 consists 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 condensing 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 cur- 
 rent is sufficient to prevent the passage backward of the flame. 
 This form is now, however, almost totally superseded 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 closely. The interstices between the wires form thus a col- 
 lection of exceedingly minute tubes, through which the gas must 
 pass. To one end of this cylinder is connected a bladder contain- 
 ing the mixed gases j the other end terminates in a jet from which 
 the gas issues ; the flame, in passing backward 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 
 farther 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 hydro-oxygen blowpipe, the most infusible sub- 
 stances are melted ; flint, pipe-clay, 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, par- 
 ticularly the former, become, in the flame of the mixed gases, so 
 
252 CHEMICAL RELATIONS OF HYDROGEN. 
 
 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 lighthouses, and has been actually employ- 
 ed for signals in connecting the trigonometrical surveys of the Brit- 
 ish 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 hydrogen, al- 
 though 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 musi- 
 cal note is heard. The explosions set the air in the tube to vibrate, at first irregu- 
 larly, 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. Occasionally, also, a distinct beat, or alternations of sound and silence, 
 may be heard, as in two organs, .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, while 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, cy- 
 anogen, iodine, &c., form one class of acids by combining with ox- 
 ygen, so they jformed 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 phospho- 
 ric acids. In the year 1832, 1 proved that this view was totally incor- 
 rect, and that all the properties of the compounds of hydrogen com- 
 bined to show that it was an eminently electro-positive body ; that it 
 took a place along with iron, manganese, and zinc ; and that the com- 
 pounds of hydrogen with chlorine, oxygen, iodine, and sulphur were 
 almost universally electro-positive in combination, and possessed ba- 
 sic characters derived from the pre-eminent positive energies of the 
 hydrogen itself. These views have, since that period, been still far- 
 ther corroborated by the researches of Graham, and by additional 
 investigations of my own ; and although the old familiar nomencla- 
 ture 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 de- 
 
CONSTITUTION OF WATER. 253 
 
 prived of the commonplace qualities of lustre, hardness, or brillian- 
 cy, than is the mercurial atmosphere which fills the apparently empty 
 top of the tube of a barometer, or the salivating atmosphere of a 
 quicksilver mine or of a gilder's workshop. 
 
 Of Water — Oxide of Hydrogen. 
 H.O. 
 It has been already shown that water consists of hydrogen ana 
 oxygen combined, in the proportions of two volumes of the former 
 gas to one volume of the latter, and by weight of one part of hy- 
 drogen united to eight of oxygen, or of ll-l 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 constit- 
 uents of water. It has, consequently, attracted the attention of many 
 distinguished chemists. But, although the determination of the re- 
 spective volumes in which the oxygen and hydrogen unite, as de- 
 termined by Gay Lussac, gave a very accurate result, yet the most 
 positive determination was obtained by Berzelius, with the method 
 now to be described. 
 
 A known weight of black oxide of copper is introduced into a 
 glass tube, on which a bulb is blo^vn, and to the extremity of which 
 a flask, containing the materials for generating' pure hydrogen gas, 
 is connected. As, however, the hydrogen gas passes off in a damp 
 condition, and thus introducing water might falsify the result, there 
 is interposed a tube containing fragments of fused chloride of cal- 
 cium, by which 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 
 containing 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 necessary, 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 connector, and the stream of 
 hydrogen gas is allowed to continue through the apparatus 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 com- 
 pletely absorbed and retained. The oxide of copper tube having 
 been weighed before and after the experiment, the loss found is the 
 oxygen 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 : 
 
254 CONSTITUTION OF WATER. 
 
 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 j 
 
 consequently, 22*67 of water consist of 
 
 20.15 of oxygen, 
 2*52 of hydrogen ; 
 
 or in 100 parts, 
 
 88-9 of oxygen, 
 11*1 of hydrogen. 
 
 To determine the combining equivalents of these substances, or, 
 in theoretical language, their atomic weights, it is first necessary to 
 ascertain what grounds there are for deciding on the atomic consti- 
 tution 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 oxy- 
 gen and two of hydrogen, it was considered by some chemists to 
 consist of one atom of oxygen united to two of hydrogen ; there- 
 fore, 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*48= weight of two atoms of hydrogen ; and hence the atomic 
 weight of hydrogen should be 6*24. 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 false, as the same volumes of all 
 gases certainly do not contain the same number of chemical atoms ; 
 and, although hydrogen enters so much into combination, it is but 
 very rarely that it does so in the proportion of 6*24. Likewise wa- 
 ter, in all the modes in which it is capable of combining, does so in 
 a quantity containing 12*48 and not 6*24 ; and, finally, water in com- 
 bination 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 100*00 8 
 
 One atom of hydrogen ... 12*24 1 
 
 112*24 "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 freez- 
 ing ; if it be then touched or shaken, a portion is immediately con- 
 verted 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 surfaces of the hardest rocks are gradually crum- 
 bled into soil fit for the support of vegetable life ; the water perco- 
 
SOLUTION OF GASES IN WATER. 255 
 
 latmg into minute crevices and fissures during the warmer months, 
 and, when frozen in winter, breaking down, by repeated and in- 
 creasing expansive efforts during successive years, the substance 
 of masses which would appear, from compactness and hardness, fit- 
 ted 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 620-1, atmospheric air be- 
 ing lOOO'O. Two volumes of steam contain two of hydrogen and 
 one of oxygen ; hence 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 . 68-8 X 2= 137-6 
 
 One volume of oxygen — 1102-6 
 
 give two volumes of vapour of water — 1240-2 
 hence one volume of vapour of water = 620-1 
 
 In forming steam at 212°, and a pressure of 30 inches mercury, 
 water expands to 1696 times its volume according to the determina- 
 tion 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 prin 
 ciples 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 ammonia; and 
 in these cases the condensation of the gases by the water is accom- 
 panied by the evolution of considerable heat. But in other cases, 
 particularly where the quantity of gas is small, the result appears 
 to be merely a mechanical distribution of the molecules of the gas 
 throughout the mass of the liquid. The following is a table of the 
 quantity of these gases absorbed by water without combination 
 100 volumes of water at 60° Fahr. and 30 inches bar. absorb of 
 
 Sulphuretted hydrogen 253 volumes 
 
 Sulphurous acid 438 " 
 
 Chlorine 206 « 
 
 Carbonic acid 100 " 
 
 Nitrous oxide 76 " 
 
 defiant gas 12-5 » 
 
 Oxygen 37 " 
 
 Nitrogen ) 16 « 
 
 Hydrogen 5 
 
 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 corresponding 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 exam- 
 ple of this fact consists in taking a glass half full of Champagne, and 
 
/ 
 
 256 CHEMICAL RELATIONS OF WATER. 
 
 having formed the palm of the hand into a hollow 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 compressed, and a por- 
 tion is then absorbed, under pressure, by the fluid, from which a 
 quantity of carbonic acid is expelled, greater than that of air absorb- 
 ed in the proportion of 1060 to 16, and thus the effervescent char- 
 acter of the wine restored. 
 
 Notwithstanding this character of neutrality, which renders wa- 
 ter so useful as a vehicle or solvent for more energetic bodies, wa- 
 ter is actively engaged in a great variety of chemical reactions, in 
 which its elements, separating from one another, appear in an iso- 
 lated state, or, by combining with other substances which may be 
 present, generate new compounds. Even, however, independent of 
 decomposition, water plays a most important part in chemical theory, 
 from the numerous classes of compounds of which it forms a con- 
 stituent. 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 crystallization even at ordinary temperatures, if the air be 
 moderately dry ; some, such as the carbonate and sulphate of soda, 
 losing all j others, as the phosphate of soda, only a portion of that 
 constituent : these are termed efflorescent salts ; when the efilores- 
 cence is complete, they lose their crystalline arrangement and fall 
 to powder. 
 
 Graham has shown, that in many classes of salts, particularly in 
 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 crystallized sulphate of copper there are five atoms of wa- 
 ter, 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 Cu.O. . S03 + 5H.O., but Cu.O. . S.O3 H.0.H-4H.0., the 
 four atoms being water of crystallization j now if this salt be com- 
 bined with sulphate of potash, this fifth atom of water disappears, 
 and the double salt is (Cu.O. . S.O3) (K.O. . S.O3) +4H.0. ; the K.O. 
 S.O3 having entered into the place of the water which had been ex- 
 pelled ; water thus circumstanced is termed constitutional water, 
 as being necessary to the complete constitution of the substance. 
 
 Water, in combination with the stronger acids, is capable of act- 
 mg as a base, and, indeed, Ave 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 of these acids with water — salts of water. Oil 
 
WATER IN CHEMICAL COMBINATION. 25? 
 
 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 sul- 
 phate of copper combines with more oxide of copper to produce a 
 corresponding basic salt. The salts of water possess the most com- 
 plete similarity with those of zinc and copper, and it is from their 
 comparative study that the evidence in favour of the view inculca- 
 ted already, of hydrogen being a volatile metal, has been in greatest 
 part derived. 
 
 Water combines also with bases : the majority of metallic oxides 
 combine with water, often with the evolution of considerable heat. 
 The slacking 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 Avith 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 slacking, still more heat^ 
 Potash retains water so strongly that it can only be obtained free 
 from it by the direct combustion of the metal, potassium, in dry 
 oxygen gas or air. In relation to these powerful bases, water ap- 
 pears, 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 func- 
 tions performed by water, in the various modes of combination it 
 affects, render it necessary to adopt a definite principle of nomen- 
 clature in this respect. In the subsequent pages I shall employ the 
 wovdJiydrate only where the water is combined with a base, such 
 as a metallic oxide ; thus, hydrate of lime, hydrate of potash, hy- 
 drated oxide of lead. Where 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 u^ater, 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 pecu- 
 liarly applicable to the form of compounds which contains constitu- 
 tional water, but it will serve as well to characterize the absence or 
 deprivation of this water by the word anhydrous, the ordinary 
 name of the substance being supposed to include the combined wa- 
 ter j thus, common sulphate of zinc, freed from water of crystalliza- 
 tion, is Zn.O. . S.O3 . H.O. ', anhydrous sulphate of zinc is Zn.O. . S.O3. 
 When there exists water of crystallization in a salt, it is of course 
 included when the salt is spoken of as crystallized. In formula?, 
 for the 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 
 CA . H.0.4-2Aq. The phosphate of soda is PA+^Na.O. . H.0.+ 
 24Aq. 
 
 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 com 
 
 K K 
 
258 MINERAL WATERS. PEROXIDE OP HYDROGEN. 
 
 mon salt, sulphates and carbonates of lime, and chloride of magne- 
 sium, are the most important. In particular localities, the water is- 
 suing from the earth contains iron, and often sulphuretted hydrogen ; 
 also traces of iodine and bromine j and occasionally the quantity of 
 these foreign matters present is so great as to confer upon the wa- 
 ter medicinal properties, 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 mount- 
 ains and general crust of the earth are composed, 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 ex- 
 plained 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 wafer. 
 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 j if free from lime, it will not be affected by oxalic 
 acid 5 and if it be not rendered turbid by nitrate of barytes, it can 
 not contain sulphuric acid. 
 
 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 
 economy of nature, it is taken as the standard with which the prop- 
 erties 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 I'OOO. 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 j and hence, for 
 this class of bodies, a better suited standard substance is found in 
 atmospheric air. 
 
 Of Oxygenated Water. Peroxide of Hydrogen, 
 H.O. + O., or H.O,. 
 This singular substance was first discovered by Thenard ; its 
 preparation is somewhat circuitous and indirect, oxygen and hydro- 
 gen not combining \/ith each other directly in any other proportions 
 but those which form water. 
 For its preparation, peroxide of jarium must be first procured ; this is prepared 
 
PEROXIDE OF HYDROGEN, PREPARATION, ETC. 259 
 
 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 Ba.O. becomes Ba.02 
 
 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 disen- 
 gagement of oxygen from the chlorate of potash has set in, the mass becomes 
 glowing red at one point, and this appearance spreads over the whole mass like tinder. 
 The barytes burns, as it were, in the atmosphere of oxygen, and forms the deutox- 
 ide of barium. If, then, the residual mass be washed with water, the chloride of 
 potassium, which remains from the chlorate of potash, is dissolved, and the deutox- 
 ide of barium, combining with an equivalent of water to form a bulky, white, insol- 
 uble hydrate, remains behind, and may be collected on a filter. 
 
 The best mode of obtaining peroxide of hydrogen from this substance is that pro- 
 posed 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, while all the oxy- 
 gen is transferred to the hydrogen, which the fluoric acid abandons ; thus, 
 H.F.-l-Ba.02=Ba.F.-|-H.02. 
 
 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. 
 Fluosilicic 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 in- 
 soluble white powder, and the peroxide of hydrogen remains dissolved. 
 
 Thenard'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 hquor 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 vegeta- 
 ble 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 manganese is one of the most active. If a 
 little of this substance, in powder, be introduced ipto strong peroxide of hydrogen, in 
 a graduated tube, over mercury, the latter is decomposed almost explosively, disen- 
 gaging 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 these metals, as oxide of silver, it is not mere- 
 ly 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 mbe becomes red hot. The decompo- 
 sition of the oxide of silver cannot, however, be referred 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 separa- 
 tion 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 combinatipn, 
 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 de- 
 composing it with rapidity, while albumen is without effect. It is highly probable, 
 that in the decomposition of water by the voltaic pile, some of this compound may 
 
260 PREPARATION OF NITROGEN GAS. 
 
 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 condi- 
 tion, gradually decomposes, oxygen being given off, and water remaining behind. 
 The presence of an acid in the liquor retards this action very much, while the pres- 
 ence of an alkah accelerates it. It w^as in great part from the remarkable charac- 
 ters 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 JVitrogen. 
 N. 
 It has been already noticed, that the substance by which the ox- 
 ygen is diluted in atmospheric air, so as to render it suitable to the 
 respiration 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 characteristic, and it alone will be hereafter used. 
 As nitrogen exists in great quantity in the air we breathe, it is 
 most easily obtained by acting upon a con- 
 fined portion of the air so as to 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 
 c/, floating on water, be set on fire, and a bell 
 glass, a, be inverted over it, the phosphorus, 
 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 dissolving 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 pur- 
 pose, 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 hy- 
 drogen, combine with the oxygen of the air, forming carbonic oxide 
 and water, the nitrogen remaining behind. The gas thus obtained 
 must be washed well with water, or, better, a little solution of pot- 
 ash, to remove the carbonic acid, and even then the nitrogen con- 
 tains some oxygen unconsumed ; 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 impeding 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 mav 
 
PREPARATION OF NITROGEN GAS. 
 
 261 
 
 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 hydroge* 
 of the animal substance, forming different compounds according to 
 the temperature and the proportions, while the nitrogen of both is 
 disengaged. 
 
 If a gas, termed nitrous oxide, which will be described in a sub- 
 sequent section, be put into contact with a slip of metallic zinc, at 
 the moment of its formation the zinc deprives it of its oxygen, form- 
 ing oxide of zinc, and the nitrogen is set free. The apparatus used 
 for this purpose consists of a tubulated retort, into which is intro- 
 duced the salt (nitrate of ammonia), which, when heated, yields ni- 
 trous 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 pneu- 
 matic 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 sur- 
 face of the melted mass. The effervescence immediately 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 N. 
 0., and acted on by Zn. their products are N. and Zn.O. 
 
 If ammonia dissolved in water be exposed to the action of a cur- 
 rent of chlorine, it is decomposed, sal ammoniac is formed, and ni- 
 trogen gas is disengaged. The solu- 
 tion 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 is disengaged, and opening under 
 the surface of the liquid near the bot- 
 tom, the other projecting but little 
 under the cork, and leading to the 
 pneumatic trough. The action of the 
 chlorine upon the ammonia 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, how- 
 ever, 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. Am- 
 monia 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 sal ammoniac (muriate of 
 ammonia). Thus (N.+3H.) and 3C1. give N. and (3C1.H.), which 
 
262 PROPERTIES OF NITROGE N. A T M O S P H E R I C AIR. 
 
 combine with 3N.H3 to form 3(C1.H. . N.H3), one equivalent of ni- 
 trogen becoming free. 
 
 Nitrogen, when obtained by any of these processes, is a perma- 
 nent gas, colourless and transparent ; it is absorbed by water only 
 Jti very small quantity. It is lighter than atmospheric air, its specific 
 gravity being 976, air being 1000. It is characterized by the com- 
 plete absence of the positive properties which distinguish other 
 gases. Thus, it does not support combustion or respiration ; it ex- 
 tinguishes a taper, and animals are suffocated in it ; but these ef- 
 fects appear to be due only to the absence of oxygen. 
 
 Although nitrogen is thus incapable of combining directly with 
 oxygen, yet by indirect methods they may be made to unite, and 
 the compounds formed of these elements are surpassed in number 
 and importance by few series of binary combinations. When oxy- 
 gen and nitrogen combine, their result is almost universally that 
 which contains most oxygen, nitric acid ; their union may be effect- 
 ed by the electric spark, provided water, or a solution of an alkali 
 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 neutralized 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, 
 however, 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 chemical 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 
 themselves, and hence the names of instruments originally devised 
 for examining 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 good- 
 ness of the air j and from the interest which the problem presented, 
 numerous methods were early invented, although it is only recently 
 that very great precision has been obtained. It was at first believed 
 that the relative salubrities of districts, and even of different local- 
 ities in the same neighbourhood, could be determined by the pro- 
 portions of oxygen and nitrogen whicn 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 oi 
 
ANALYSIS OF AIR. 263 
 
 an hospital or of a jail, might be recognised, and means discov- 
 ered 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 recognised as being almost 
 absolutely the same throughout its entire mass 5 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, at- 
 mospheric air contains some carbonic acid and watery vapour ; the 
 quantitjr of the latter is determined by methods almost entirely 
 physical, and forms a practical department in the theory of vapours, 
 termed hygrometry. I shall, thereifore, not touch upon it here, refer- 
 ring 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 at- 
 mospheric air has been made accurately by Saussure, who found 
 that, in general, 10,000 volumes of air contain 4*15 of carbonic acid j 
 the maximum 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 of the 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 experiments of Saussure and of Boussingault have made it 
 probable 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 quan- 
 tity of carbonic acid equal to nearly one part in 2000 of the air em- 
 ployed ; and, although employing other methods, the results of Bous» 
 singault 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 ef- 
 fect 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 amaunt of 
 absorption the quantity of oxygen may be ascertained. Thi& isth.e 
 
264 COMPOSITION OP THE ATMOSPHERE. 
 
 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 sulphate of iron, with a measured quan- 
 tity of atmospheric air ; but it is now abandoned. An excellent 
 mode of using these bodies as eudiometers 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 
 int© 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 press- 
 ure 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 ox- 
 ide, all oxygen may easily be removed from atmospheric air, but 
 the composition 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. 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 stout as in the common form, is taken 
 about twice as long, and bent into the form of a U. Having been 
 tilled with mercury, the mixture of 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 cork. 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 foil, moistened with muriatic acid, absorb oxygen 
 with great avidity, and have been proposed by Gay Lussac for the 
 analysis of atmospheric air. Saussure has used in his accurate re- 
 searches 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 a eudiometer. It may be used either by 
 slow or by rapid combustion. In the former mode, a stick of moist- 
 ened phosphorus, placed in a graduated tube of air, deprives it com- 
 pletely of its oxygen in about twenty hours 5 the residue is nitro- 
 gen, 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 combustion 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 
 
CONSTITUENTS OF ATMOSPHERIC AIR. 265 
 
 on. This disadvantage has been obviated by the mode proposed by 
 Brunner, and used by him in some determinations lately made, in 
 which the liability to error has been reduced to 0*20 per cent. In 
 the figure, a, Z>, c is a tube, consisting of a wide por- 
 tion, bj and a narrower, c ; the wider part being 
 drawn in a to a capillary opening. Into it is intro- 
 duced a quantity of loose cotton and some bits of 
 phosphorus, and being then warmed, the melted 
 phosphorus is 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 ves- 
 sel c?, which is graduated and filled with mercury ; 
 a cock at e allows the mercury to flow out on oc- 
 casion. To use this apparatus, the tube a, 6, c is 
 weighed, and then attached to the vessel d ; the 
 cock e is then slig^itly opened j the mercury issues 
 out in a properly graduated stream, and its place is supplied by air, 
 which, entering at the capillary orifice a, streams over the surface 
 of the phosphorus, by which all its oxygen is removed, and the re- 
 sidual nitrogen passing into the graduated vessel, its volume can be 
 easily read off; or the mercury which flows ofl* being caught in a 
 graduated glass, its volume is equal to that of the nitrogen which 
 has passed in. Besides extending the surface of the phosphorus, 
 and thus quickening the absorption of the oxygen, the mass of cot- 
 ton serves as a filter to collect the white fumes or flakes of phos- 
 phorous acid formed. When a sufficient quantity of air has passed 
 through the apparatus, the tube a, 6, 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 eflected by securing to the tube 
 a, bj c, by means of a caoutchouc connector, a small tube contain- 
 ing fragments of fused chloride of calcium, through which the air 
 streaming deposites the moisture it may contain. 
 
 The result of all these methods indicates that atmospheric air con- 
 tains from 20-79 to 21-08 of oxygen gas in 100 volumes ; and from 
 experiments 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, 8020 
 feet above the level of the sea, the constitution appears to be iden- 
 tical at all heights. By weight, the constituents of the atmospheric 
 air in 100 parts are, omitting carbonic acid and water. 
 
 Oxygen gas =23-04 
 
 Nitrogen gas =76-96 
 
 .Too^o"o 
 
 This permanency of constitution of atmospheric air, together 
 with many other circumstances which I shall briefly notice, led to 
 the opinion among many chemists of its being a compound, and not 
 a mere mixture of its constituents. The analysis not being then so 
 accurately made, it was supposed to consist of one volume of oxy- 
 gen united to four volumes of nitrogen, a simplicity of proportion 
 
 Ll 
 
26Q VELOCITY OF DIFFUSION OF GASES. 
 
 which characterizes chemical union among gases. It was also re 
 marked, that if the nitrogen and oxygen were merely mixed, their 
 different densities should cause them to separate ; the heavier oxy- 
 gen accumulating near the earth, while 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 among 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 mean 
 qualities of the oxygen and nitrogen which form it ; circumstances 
 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 atmo- 
 spheric 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 stopcocks, 6, c, c/, and al- 
 lowed to stand for a few hours, the bottle containing the 
 heavy gas being lowest, they will be found to mix, the light- 
 er 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 recognised by Dobereiner, and then studied 
 by Mitchell, but finally examined, and its laws accurately assigned, 
 by Graham. When gases of unequal densities are placed in con- 
 tact with each other, they tend to mix ultimately in a uniform 
 manner ; but the rapidity with which they penetrate each other's 
 volume, or, as it is termed bjr 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 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 India rubber, a bell glass of air 
 be inverted over it, the hydrogen passing out of the glass more rap- 
 idly than air enters to supply its place, the sheet of India rubber 
 is gradually bent into the glass, and ultimately burst by the external 
 pressure. On the contrary, if the small glass contain air and the 
 bell glass hydrogen, the membranous cover is gradually forced up- 
 ward by means of the excess of hydrogen which passes in, and 
 which finally breaks through it by the elasticity thus produced in- 
 side. 
 
LAW OF DIFFUSION OF GASES. 267 
 
 The exact law of the diffusion of gases is, that the velocity of diffusion is inverse- 
 ly proportional to the square roots of the specific gravities of the gases. This is ex- 
 hibited in the following table. 
 
 Specific Gravities. Square Roots of S. G. DiflFusion Velum* 
 
 Hydrogen .... 00688 .... 02623 . . 
 
 Ammonia .... 05898 .... 07681 . . 
 
 Air 10000 .... 10000 . . 
 
 Carbonic acid . . . 1-6239 . . . 1-2345 
 
 Chlorine .... 2-4700 .... 15716 
 
 457 
 130 
 100 
 81 
 64 
 
 By this table it will be seen, that in the same time in which 100 volumes of at- 
 mospheric 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 is, however, entirely departed from when the gases are separated 
 from one another by a plug or barrier which exerts upon them a condensing action, 
 and the diffusion volumes are found to be other than those indicated in the forego- 
 ing table. A plug of stucco exerts#)ut little condensing effect upon the gases, and 
 hence their diffusion takes place into one another with a velocity inversely propor- 
 tional to the square roots of their densities ; but a thin lamina of India rubber, ef- 
 fecting a powerful condensation, presents the two gases to each other with densi- 
 ties that are abnormal, and hence disturbs their rate of diffusion. 
 
 Phenomena of this kind may be very beautifully shown by means of soap-bub- 
 bles. If a vial that has had a film of soap- water spread over its mouth be exposed 
 under a jar to an atmosphere of ammonia or protoxide of nitrogen, its horizontality 
 is instantly disturbed, and it begins to assume a spherical convexity, and continues 
 expanding until, after passing through a series of brilliant colours, it may become 
 so thin as to be almost invisible. To show the great rapidity with which a gas or 
 vapour will pass through such barriers, if a soap-bubble be expanded in a vial con- 
 taining a little aqua ammonias, and the air from its interior be immediately with- 
 drawn into the mouth, the strong caustic taste of the ammonia will be immediately 
 perceived. 
 
 Through thin pieces of India rubber gases will diffuse into each other, though 
 resisted by any given pressure. I have found that sulphuretted hydrogen will thus 
 pass into atmospheric air against a pressure of more than fifty atmospheres.] 
 
 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 different 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 de- 
 monstrated 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 mechani- 
 cal obstruction. 
 
 This general principle had, however, been laid hold of by the keen intellect of 
 Dalton, and announced long before its truth had been accurately proved in the man- 
 ner 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 recognise, and exercising pressures upon the surface of the earth pro- 
 portional to their quantities. Thus, if we suppose 100 parts of atmospheric air to 
 consist by weight of, 
 
 Nitrogen gas . . ... 75-88 "\ 
 
 Oxygen gas . ... 23041 ,„^.^^ 
 
 Watery vapour ... 103 f^"""" 
 
 Carbonic acid . .... 05^ 
 
 the pressure of the air being taken at thirty inches of mercurj', the respective 
 pressures of the independent atmospheres will be as follows : 
 
268 CONSTITUTION OF THE ATMOSPHERE PERMANENT. 
 
 Pressure of the nitrogen gas 22 764 inches, 
 
 " oxygen gas 6912 " 
 
 " watery vapour 0309 " 
 
 " carbonic acid gas 0015 " 
 
 30 000 
 
 The different constituents of air are thus in the state best suited 
 to the purposes for which the atmospliere is destined ; no one gas 
 can interfere with, or retard the others' action j there are no affini- 
 ties 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 continu- 
 ed and happy existence of animal and vegetable life depends, from 
 which arises the diversity of aspect of our ever varying sky, and 
 the gradual detrition of the solid rocky materials of the earth's sur- 
 face giving a fruitful soil. 
 
 By the processes of combustion and of respiration which are in ac- 
 tion on the surface of the earth, the 'Oxygen of the atmosphere is 
 continually removed, and an equal volume of carbonic acid gener- 
 ally 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, 720 cubic 
 feet of atmospheric air, that is, a mass of air eleven feet square and 
 six feet thick. The burning 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 render- 
 ed unfit for respiration 3,185,760 cubic yards of air, which would 
 cover to the depth of six feet a space a quarter of a mile square. 
 Nevertheless, it has been already mentioned, that even in cities, the 
 relative proportions of oxygen, nitrogen, and carbonic acid in the 
 air are but little altered, and it becomes an object of great interest 
 to ascertain in what manner that permanency, on which the stabili- 
 ty, in truth, of all organized nature seems ultimately to depend, has 
 been secured. 
 
 In the first place, from the frequent occurrence of storms and vio- 
 lent currents, which agitate vast tracts of air, accumulation of nox- 
 ious 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 indicating 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 immensity 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 j 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 , 2V0 part, a quantity 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 com- 
 
ATMOSPHERIC PRESSURE. 269 
 
 positior., science has pointed out, in the peculiar relations of the 
 lunctions of vegetable and aninnal 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 sunlight, 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 vegetable world, and 
 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, while the same element which the 
 plant absorbs, and from which it forms its tissues, has been thrown 
 out as useless by the animal, and would, if not removed, accumulate 
 in the end, and destroy all animal existence. 
 
 The most accurate experiments have determined that 100 cubic 
 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 at 40*5° Fahrenheit, when water is at its gre9test 
 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 
 surface. The existence of this pressure may be shown 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 al- 
 lowed to act against the other ; a pair of brass hemispheres, which 
 are easily separated while filled by air, are pressed most firmly to- 
 gether 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 ba- 
 rometer^ or pressure measurer, is thus constructed, to register, at ev- 
 ery moment, the pressure which the atmosphere exercises. A tube 
 closed at one end, and about thirty-two inches long, is to be care- 
 fully filled with pure mercury ; it is then inverted in a basin of mer- 
 cury, 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 above it a space which is, at low temper- 
 atures, the most perfectly empty that can be experimentally pro- 
 cured. From the name of the inventor of this instrument, it 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 mo 
 tions in the air, which produce changes fn the weather also, the 
 barometer is popularly regarded as a weather-glass, although no ac- 
 curate indications of approaching changes can be at all reckoned on 
 from its use. 
 
270 PRESSURE AND EXTENT OP THE ATMOSPHERE. 
 
 If the atmosphere preserved throughout its entire mass the same 
 density and elasticity which it possesses at the surface of the earth, 
 its height would be about five miles. But such is not the case j 
 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 geo- 
 metrical proportion when the heights are taken in an arithmetic 
 series j and on this principle is founded one of the most accurate 
 modes of estimating heights that has 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 prac- 
 tice there are corrections depending on temperatures and other 
 causes, to which it is not necessary to allude. So rapid is this dimi- 
 nution of density, that one half of the w^hole 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 j 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 an 
 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 our earth as having 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 defi- 
 nite 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 atmosphere ; 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 farther 
 expanding tendency bein^ overcome, the atmosphere should be ter- 
 minated by a definite surffce, 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, produce the regular 
 variations in the height of the barometer, which, though involved 
 by the irregular motions of much larger amount, have been detected 
 
S ATMOSPHERIC THEORY. 271 
 
 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 vir- 
 tue 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 observation has shown 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, likewise, the gravitating centre of our sys- 
 tem, 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 experiment 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's 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 at- 
 mosphere derives its heat is not the sun, but the solid earth ; the solar rays passing 
 through the air as they pass through glass and all transparent bodies, without com- 
 municating 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. Farthest from the level of the sea at the equator, being 15,000 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 mountains with perpetual 
 snow, the line of congelation being 6000 feet above the surface. 
 
 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 proportional to its temperature ; and when the air, 
 thus mixed with vapour, rises to a higher and colder stratum, the elasticity of the 
 vapour is diminished, and a portion separates either as cloud or rain. Thus, if air 
 becomes loaded with vapour at the surface having a temperature of 80°, and, on 
 ascending, it becomes cooled to 40°, the quantity of water separated is thus found • 
 
 The elasticity at 60° is 0524 inch of mercury. 
 40° is 0263 
 
 the difference is . . 0.261 " 
 
 But 524 : 261 : : 100 : 498, 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 is deposited as liquid water, from the circumstance 
 of the diminution in volume of the mixture of gas and vapour produced by the low- 
 ering of its temperature ; this is equal to about four per cent., so that there remains 
 as invisible vapour only about forty-six, while fifty-four per cent, are engaged in the 
 production of the cloudy masses. The farther properties of clouds, the circum- 
 stances which determine the production of rain, snow, or hail, are of so httle refer- 
 ence to chemistry that I shall pass from them without remark. 
 
 Reasoning from the principle that all gases ma^by suitable reduction of their 
 temperature, be reduced to the sohd form, Poisson proposes to consider the atmo- 
 sphere as being extended above the earth, gradually becoming more attenuated and 
 more cold, until it arrives at a point at which it freezes ; there then should be a 
 shell of transparent colourless air-ice, lined on its concave surface with a sea of 
 
272 
 
 NITROUS OXIDE, 
 
 liquid oxygen and nitrogen mixed or combined together. From such assumption, 
 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 collat- 
 eral 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 tem- 
 perature 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 be- 
 coming liquid, far less solid ; and hence the supposition of such a hollow sphere 
 of frozen air cannot be granted. 
 
 Compounds of Jfitrogen and Oxygen. 
 Nitrous oxide . . . N. = 14-0-{- 0.=- 8=N.O =22-0 
 
 Nitric oxide . . 
 Hyponitrous acid 
 Nitrous acid . . 
 Nitric acid . . . 
 
 N.=:14-0H-2O. = 16=N.O2=30-0 
 N. = 14-0+3O.=24=N.O3=38-0 
 N. = 14-0+4O.=32=--N.O4=46-0 
 N.==14-0+5O.=40=N.O5=54-0 
 
 JVitrous Oxide. Protoxide of Jfitrogen. 
 
 This substance, which exists, under ordinary pressure, in the gab 
 eous 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 
 effervescence 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: 
 
 N.O,+N.H40.=2(N.O.)+4(H.O.) 
 
 The nitrate of ammonia may be placed in the flask a, imbedded 
 
 in the little cup of sand. 
 A bent tube conducts the 
 gas evolved to the pneu- 
 matic trough, as in the 
 figure, or to the gasom- 
 eter, if the quantity be 
 large. In this process 
 the temperature should 
 not be allowed to rise be- 
 yond the point at which 
 the effervescence is mod- 
 erately brisk ; for when 
 the salt becomes much 
 hotter, the decomposi- 
 '"i i'wii"H'i'" i "i i ii'ii ; iy ' ^ ^ ^^tion is tumultuously rap- 
 
 id, and the gas obtained may not be at all pure. 
 
 The nitrous oxide gas so obtained is perfectly colourless and 
 transparent ; it is absorbed by water in moderate quantity, and hence 
 the water over which it i# 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 1-527. 
 
 A lighted taper burns with increased brilliancy in this gas j and if 
 
ITS PROPERTIES AND COMPOSITION. 273 
 
 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 hydrogen, it may be inflamed by a taper or by an electric spark, 
 and then 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 com 
 bination. It is decomposed by the high temperature of the burning 
 body and the affinity of this last for oxygen, and the combustion is 
 maintained 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 analyzed. 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 be cooled 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 vol- 
 umes of nitrogen and one of oxygen condensed to two volumes, and hence its spe- 
 cific gravity may be calculated thus : 
 
 Two volumes of nitrogen 976x2=19520 
 One volume of oxygen . . . 1102-6 
 give two volumes of nitrous oxide 3054-6 
 and one volume weighs, therefore 1527.3 
 
 By weight, the composition of nitrous oxide and its equivaletit 
 number on each scale are expressed as follows : 
 
 Nitrogen, 63*9 One equivalent, 140 or 175 
 
 Oxygen, 36-1 « _8^ " 100 
 
 "100^ 22-0 275 
 
 and its formula is N.O. 
 
 The most singular property of this gas is, that when breathed 
 pure for a few minutes it produces a lively and agreeable into'xica- 
 tion, which does not leave any lassitude or disagreeable sensation 
 when it goes off*. To prepare gas for being breathed, it is necessa- 
 ry to attend to the purity of the nitrate of ammonia used, as very 
 frequently the salt found in commerce contains muriate of ammo- 
 nia, in which case the gas obtained may be contaminated by nitrous 
 acid and chlorine, and prove very irritating to the lungs. To ob- 
 tain 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. 
 
 J^itric Oxide. Deutoxide of Kitrogen. 
 
 This substance exists naturally under the form of a gas, which 
 chemists 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 decomposition of nitric acid by the metals. 
 
 If a small quantity of quicksilver, or of cd^per cut into small bits, 
 be placed in the gas bottle in the figure, and diluted nitric acid, pre- 
 pared by mixing equal volumes of the aquafortis of commerce and of 
 water, be poured in by the funnel a, efl!ervescence is immediately pro- 
 
 Mm 
 
274 PREPARATION, ETC., OF NITRIC OXIDE. 
 
 duced, even without the 
 application of heat, and 
 the metal dissolves in the 
 acid, which becomes pale 
 green-coloured if quicksil- 
 ver had been employed, 
 but of a rich blue if cop- 
 per had been used. From 
 greater economy, the lat- 
 ter metal is almost always 
 that employed. For some 
 time after the action commences, the space in the bottle over the 
 liquid is occupied by reddish fumes ; but these gradually pass away, 
 and the gas may be collected when the upper part of the generating 
 flask is occupied by it 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 ni- 
 trogen is evolved in combination with the remainino- two fifths, 
 forming nitric oxide. The copper, being thus oxidized, 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 crys- 
 tallized. For complete decomposition, four equivalents of nitric 
 acid and three of copper are required, and the action may be then 
 expressed as follows : 4N.O5 and 3Cu. give SrN.Og . Cu.O.) and 
 (N.O,). 
 
 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 
 water, and may hence be, on all occasions, collected over it. It is 
 a little heavier than air, its sp. gr. being 1039 ; its refractive index 
 is 0*876 1. A lighted taper plunged into this gas is extinguished, and 
 a red-hot wire maybe 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 
 oxygen, 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 re- 
 mains untouched. 
 
 In this way nitric oxide may be analyzed, and is found to consist of equal vol- 
 umes of nitrogen and oxygen united without any condensation. From this its spe- 
 cific gravity may be calculated : 
 
 One volume of nitrogen . . .=976 
 One volume of oxygen . . . rr=ll02 6 
 give two volumes of nitric oxide 2078 6 
 of which one is found to weigh . 1039 3 
 
 Its equivalent volume is therefore 4, and its composition by weight 
 and its equivalent number on each scale are as follows: 
 
HYPONITROUSACID. 275 
 
 Nitrogen, 46-95 One equivalent, =175 or 14-0 
 Oxygen, 53-05 Two equivalents, =200 or 16-0 
 loFOO 375 30^ 
 
 and Its formula is N.O2. 
 
 Nitric oxide may be deprived of one half of its oxygen, and so be 
 reduced to the state of nitrous oxide, by remaining in contact for 
 some days with moist iron or zinc filings 5 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 (N.O3) or nitrous acid (N.O4), and they are both 
 generally formed in uncertain proportions. Hence we cannot ex- 
 actly calculate the quantity of oxygen that had been present ; and 
 this process does not answer well for gaseous analysis, but it is 
 useful for removing oxygen from a gaseous 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. 
 
 Nitric oxide combines with a great number of salts and with some 
 acids to form compounds, which in some respects possess consid- 
 erable interest : these shall be noticed under those heads to which 
 their history more particularly belongs. 
 
 Hyponitrous Acid. 
 
 The red fumes which are formed when niiric 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 form- 
 ed, 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*iiito 
 contact with water, it is in great part decomposed, being resolved into nitric oxide 
 and nitric acid, three equivalents of hyponitrous acid (SN.Og) giving 2(N.02) and 
 N.O5. 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, N.O5 . K.O. giving off 
 20., and leaving N.O3 . K.O. This is known by the hyponitrite being decomposed 
 by acetic acid, and giving off copious red fumes, while the nitrate of potash is unal- 
 terable 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 hyponitrous acid 
 formed. 
 
 The specific gravity of the vapour of this acid has not been experimentally deter- 
 mined. It consists of two volumes of nitrogen united to three of oxygen, but of 
 their condensation we know nothing. 
 
 Its composition by weight and its equivalent constitution are, 
 
S76 PREPARATION, ETC., OF NITROUS ACID. 
 
 Nitrogen, 37*11 One equivalent, =175 or 14*0 
 
 . Oxygen, 62-89 Three equivalents, =300 or 24-0 
 
 iOO-00 - 475 38^ 
 
 JSTitrous Jicid. Jfitroso-nitric Acid. 
 
 This substance presents itself, like the last, under the form of deep 
 red fumes, and is produced when the oxygen is in excess with regard 
 to the nitric oxide. By a cold of about 0° on Fahrenheit's scale, it 
 raay 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 byiieat. 
 
 A quantity of finely-powdered and dry nitrate of lead is to be pla- 
 ced in an earthenware or hard glass retort, and heated to full red- 
 hess. The red vapours that are produced are to be conducted into 
 a receiver, carefully cooled by a mixture of snow and salt. They 
 then condense into a liquid, while 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 : N.O5 . Pb.O. gives Pb.O., free N.O4 and O. 
 
 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 various 
 coloured states, it exercises remarkable absorbing power on light. 
 The specific gravity of the liquid acid is 1*451. 
 
 Nitrous acid is the most stable compound of nitrogen and oxy- 
 gen; 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(N.04) give N.O^ and 2(N.05). The nitric acid 
 formed always protects'a portion of the nitrous acid from this reac 
 tion. 
 
 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 3181-2 ; thus, 
 
 One volume of nitrogen 976 
 
 Two volumes of oxygen 2205 2 
 
 One volume of nitrous acid .... 31812 
 
 Its composition by weight and the constitution of its equivalent 
 are as follows : 
 
 Nitrogen, =30*33 One equivalent, =175 or 14*0 
 
 Oxygen, =69.6 7 Four equivalents, =400 or 32*0 
 
 100*00 575 4^0 
 
 Considerable doubt has been thrown upon the nature of this substance, 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(N.04)=N.05-4-N.03. 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 hyponitrous acid really contain this substance ; thus, the yellow basic salt, formed 
 '^y 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 peroiude 
 of nitrogen, proposed for it by Graham, is frequently applied to nitric oxide 
 
NITRIC ACID. 277 
 
 Mitric Acid. 
 N.O3. 
 
 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, that is 
 found to be a solution of pure nitric acid. Looking to the compo- 
 sition 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 com- 
 bining under certain circumstances ; and there is no doubt but that 
 the great, if 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 hydro- 
 gen, 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 alkaline reaction, 
 and after a time crystals of saltpetre (nitrate of potash) form in it. 
 This may be shown, 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 shown 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 pass- 
 ing through the air, and this uniting with the ammonia which is al- 
 ways present in our atmosphere from decomposing animal remains. 
 
 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, and the nitrate of ammonia being washed down by the rains 
 into the porous limestone soils, the ammonia is again given ofl*, while 
 the ground becomes coated with an efflorescence of earthy nitrates 
 when it dries on the cessation of the ram \ a small quantity of ni- 
 trate 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 Continent, this process is 
 imitated in artificial nitre-beds, and large quantities of home-made 
 saltpetre are used in France and Germany for the manufacture of 
 gunpowder. In South America, particularly in Chili and Peru, there 
 are found immense deposites of nitrate of soda upon the surface of 
 the soil, and it is now extensively imported into these countries; 
 the source of the nitric acid is, in this case also, the union of the 
 elements of the atmosphere, although the circumstances which sup- 
 plied the alkali cannot be distinctly seen. 
 
278 
 
 PREPARATION OF NITRIC ACID. 
 
 It is from the nitrates of soda or potash so produced that the 
 nitric acid is always obtained. True nitric acid has never been iso- 
 lated ; that substance which is generally spoken of as nitric acid, 
 and which I shall, unless especially remarked otherwise, be under- 
 stood to mean in the following account of its properties and prepar- 
 ation, 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 vit- 
 riol are mixed in a glass re- 
 tort, 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 wa- 
 ter, and by the reaction 
 which ensues, the sulphu- 
 ric acid combines with the 
 potash of the nitre, while 
 the water of the oil of vit- 
 riol uniting with the nitric 
 acid, forms the liquid nitric acid, which distils over, and is conden- 
 sed in the receiver, B. To render the condensation more complete, 
 this is surrounded by a net, and placed in a trough, c c ; a stream of 
 cold water flows continually on it from the pipe «, and being dis- 
 tributed evenly over the surface by the network, flows out by the 
 exit pipe of the trough, /, and escapes into d e. Using the propor- 
 tions just noticed (equal weights), the quantity of sulphuric acid 
 present is double that necessary to neutralize the potash of the ni- 
 tre, and completely expel the nitric acid ; for 
 
 The nitre consists of 
 One atom nitric acid, 54*0 
 One atom potash . -iT'S 
 
 loTs 
 
 Oil of vitriol consists of 
 One atom sulph. acid, 40*1 
 One atom water . 9*0 
 
 49^ 
 
 These, reacting upon each other, should produce, 
 
 Sulphate of potash consisting of Liquid nitric acid formed of 
 One atom sulph. acid, 40*1 One atom nitric acid, 54*0 
 
 One atom potash . 47-3 One atom water . 9*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. r 
 
 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(S.03 . H.O.) and K.O. . 
 N.O5 give 
 
 (S.O3 . H.O.+K.O. . S.O3) and H.O. N.O5. 
 
 If there be oil of vitriol enough, the nitre is thus perfectly decom- 
 
PREPARATION OF NITRIC ACID. 
 
 279 
 
 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 equiva- 
 lent 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 decomposed; 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 increases very much the risk of 
 the apparatus breaking. 
 
 The scientific chemist and the apothecary, however, do not prepare nitric acid ; it 
 IS made on the large scale for the purposes of the arts, and the processes of purify- 
 ing the acid of commerce is so simple that no other source is required. On the 
 great scale the nitric acid is prepared, not in glass retorts, but in iron cylinders, 
 connected with condensers, as represented in the figures, one being a section per- 
 pendicular to the axes of the cylinders, and the other a section paraUel to the axes : 
 the same letters apply to both. 
 
 a is the grate, and d the ashpit of the furnace, h. In each furnace two cast iron 
 cylinders, c, c, are set, of such capacity that about li 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,/, 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 conducted to the range of condensing jars of earthenware, fitted with safety 
 tubes, of which the first is seen in the figure, as h, I, k. The flues, w, m, m, pass 
 from the furnaces to the chimney, n. As in this apparatus the temperature can be 
 raised to dull redness without injury, and as 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 540 
 
 One equivalent of soda 31-3 
 
 and hence 100 parts of it yield about 74 parts of liquid nitric acid, while 100 parts 
 of nitrate of potash yield but 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 free. At the termination of the process, if the tem- 
 
280 PR OPE R TIE S, ETC., OF LIQUID NITRIC ACID. 
 
 perature pass much beyond 300°, there is a new evolution of red 
 fumes, for the nitric acid is then similarly decomposed into N.O4 
 and O. 
 
 The strongest nitric acid that can be thus made is of specific gravity 1-521, and 
 consists of N.Os-f-H.O. 
 
 One equivalent of nitric acid . . . 540 or per cent. 8571 
 One equivalent of water .... 90 " 14 29 
 
 63^ 10000 
 
 It boils at 187° F., but cannot be distilled without partial decomposition. 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 2N.05-|-3H.O. 
 
 Two equivalents of nitric acid . . 1080 or per cent. 8000 
 Three equivalents of water . . . 270 " 20 00 
 
 1350 100 00 
 
 When the nitric acid is gradually mixed with water, the boiling point rises until 
 when the specific gravity is 1-420, it boils at 248°. If it be farther diluted, the 
 boiling point is again lowered. At this point the acid has a definite chemical con- 
 stitution ; it consists of N.05-{-4H 0. 
 
 One equivalent of nitric acid . . . 540 or per cent. 6022 
 Four equivalents of water .... 360 " 39 78 
 
 900 10000 
 
 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, while oxygen gas is disen- 
 gaged j the same decomposition into nitrous acid and oxygen gas 
 may be instantly effected 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 ulti- 
 mately 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. The decomposition of the acid is gener- 
 ally accompanied by the production 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 inac 
 tive acid may be brought into activity by various means, as by touch- 
 ing the immersed metal with another different one. These phenom- 
 ena appear to involve conditions probably electrical, which are not, 
 as yet, completely understood. 
 
 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 
 
DETECTION OF NITRIC ACID. 281 
 
 useful, as it gives off oxygen still more easily than the pure acid, 
 and is hence sometimes applicable as an oxidixing 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 acidj it 
 is absorbed in great quantity, and the liquor assumes successively 
 various shades of yellow, green, and red, according to its state of 
 dilution. The nitric oxide (N.O2) decomposes the nitric acid (N.O5), 
 and forms nitrous acid (N.O4), which dissolves in the excess of liquid 
 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 impuri- 
 ties of it are, generally, chlorine, arising from the nitre employed 
 having contained common salt ; sulphuric acid, from some having 
 been distilled over by too great heat j and some iron, arising from 
 the cylinders or stoneware bottles in which the acid is preserved. 
 These may be easily detected ; on mixing a few drops of the com- 
 mercial acid with half an ounce of distilled water, a drop of solution 
 of nitrate of barytes will give a precipitate if sulphuric acid be pres- 
 ent ; nitrate of silver will indicate, by a precipitate, the presence of 
 chlorine ; while a little solution of yellow prussiate of potash will 
 form Prussian blue if the acid contained any iron. From these im- 
 purities the acid may be freed by being redistilled 3 the chlorine 
 passes off along with the portions which first come over, and by 
 thus testing from time to time the acid which is thus obtained, it 
 will be found no longer to precipitate the nitrate of silver, and may 
 then be considered pure ; the iron and sulphuric acid 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. 
 
 The detection of nitric acid is not difficult; it cannot be recog- 
 nised by forming precipitates, as all its neutral salts are soluble, but 
 its properties are very marked. 1st, The production of red fumes 
 by nitric oxide when it is brought into contact with a metal, is char- 
 acteristic of it. 2d, 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. 3d, 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 pro- 
 duces with a crystal of morphia. 
 
 For the detection of a small quantity of nitric acid, the best plan 
 
 Nn 
 
282 SOURCES, PROPERTIES, AND 
 
 is to neutralize the liquor, if it be acid, by a solution of potash, and 
 to evaporate to dryness. The salt so obtained crystallizes in 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 of pro- 
 tosulphate of iron, produces the olive-coloured liquor already noticed. 
 All solid compounds of nitric acid, such as the basic nitrates, may 
 be recognised in this way. 
 
 The nitric acid not being isolable, we do not know the state of 
 condensation of its elements, which are united in the proportion of 
 two 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 
 
 100^0 675 54^ 
 
 The specific gravity of the vapour of the liquid nitric acid, H.O. . N.O5, is not known ; 
 but Bineau has found the sp. gr. of the vapour of the liquid acid, which boils at 248*^, 
 H.O. . N.Os+SH.O., to be 1243, which might result from 
 
 Two volumes of nitrogen 976x2=19520 
 
 Five volumes of oxygen 1102 6x5=55130 
 
 Eight volumes of watery vapour .... 6201X 8 =4960 8 
 
 condensed into ten volumes 12425 8 
 
 of which one, therefore, should weigh 1242-6 
 
 This result requires confirmation. 
 
 Sulphur. 
 
 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 5 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 sul- 
 phuret of hydrogen, arising probably from the decomposition of me- 
 tallic sulphurets by the high temperature in the interior of the earth. 
 The native sulphur so produced, condensing in fissures, constitutes 
 the great deposites of volcanic sulphur of Sicily and other places, 
 which supply a large proportion of that employed in commerce. It 
 exists also native, combined 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. 
 
 At ordinary temperatures sulphur 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 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 heat- 
 ed farther 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 
 
PREPARATION OF SULPHUR. 
 
 28£ 
 
 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 second- 
 ary faces, and the surfaces of the octohedron, 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 be- 
 come opaque, sulphur yellow, and friable, 
 being then changed into the dimorphous 
 state. 
 
 If the thick tenacious sulphur at 400^ be suddenly cooled by im- 
 mersion 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 India rubber j after some time, however, it changes 
 into the ordinary state. 
 
 Sulphur is used in pharmacy under two forms, that of roll and 
 flowers ; 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 va- 
 pour of sulphur so rapidly that the molecules have not time to form 
 crystals of any perceptible size, so that the condensed sulphur, al- 
 though really crystalline, appears to the sight and touch as an im- 
 palpable soft powder. 
 
 For the manufacture of flowers of sulphur, the apparatus is arranged as in 
 the subjoined figures, in which A is a vertical and B a horizontal section, to which 
 
 the same letters refer. In an apartment and shed, M, M, a chamber, A, is con 
 structed, which must have at least 2000 cubic feet capacity. Outside T)f this cham- 
 ber is an iron pan, c, in which, by a fire at o, the sulphur is kept gently boiling. The 
 boiler and fireplace must be completely surrounded by brickwork, 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 supplied 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 con- 
 densed, and falls like a fine snow shower upon the floor underneath. When a sul- 
 ficient quantity of the flowers of sulphur have been thus formed, they are removed 
 by the door at p. If, at the commencement of the process, the mixture of sulphur- 
 vapour and air should inflame, the explosion 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 oc- 
 tohedron, of which a common modification is represented in the 
 
284 RELATIONS OF SULPHUR TO OXYGEN. 
 
 margin. Sulphur is found crystallized in this form on 
 the edges of the craters of most volcanoes, the crys- 
 tals being transparent, and sometimes of considerable 
 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 themselves. 
 
 Sulphur may be obtained, however, in a state of 
 much more minute division, and destitute of all crys- 
 talline structure, by precipitation from solution. Thus, if the per- 
 sulphuret of potassium, K.S^, be decomposed by muriatic acid, four 
 equivalents of sulphur are set free, and separate as a milk-white 
 powder. This constitutes the Sulphur Precipitatum of pharmacy. 
 In all cases where sulphur is precipitated from a cold solution, it is 
 pure white. 
 
 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 will be studied hereafter. 
 
 When sulphur is boiled it forms a deep yellow vapour, the specific 
 gravity of which is 6648. Sulphur evaporates, however, very rap- 
 idly long before it boils, and even forms some vapour below ita 
 melting point. At a temperature of about 300° it takes fire, burning 
 with a bluish violet flame, and forming sulphurous acid (S.Og). 
 
 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 gener 
 ate 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. 
 
 K.O. . C.O2 Carbonate of potassium. 
 
 and with arsenic and potassium, 
 As.Qs Arsenic acid. 
 K.O. Oxide o f potassium. 
 K.O. . AS.O5 Arseniate of potassium. 
 
 C.S2 Sulpho-carbonic acid. 
 K.S. Sulphuret of potassium. 
 K.S. .C.S2 Sulpho-carbonate of potaf*- 
 sium. 
 
 As.Ss Sulpharsenic acid. 
 K.S. Sulphuret of potassium. 
 K.S. . As.So Sulpharseniate of potas- 
 sium. 
 
 In like manner, the similar compounds Fe304 and Fe3S4 are not altered by heat, 
 but are magnetic, while Fe.Sa and Mn.Os give out oxygen and sulphur, and are re- 
 duced to Fe3S4 and Mn304. I shall have frequent occasion to revert to these con- 
 siderations, which have already been noticed under another point of view (p. 238). 
 
 The equivalent number of sulphur is 16*1 or 201*2, and its com- 
 bining volume one third that of oxygen. 
 
 Sulphur combines with oxygen, forming 
 
 Sulphurous acid ...... S.O2. 
 
 Sulphuric acid S.O3, or S.O2 . O. 
 
 Hyposulphurous acid .... S2O2, or S.O2 . S. 
 
 Hyposulphuric acid .... S2O5, or 2S.O2 . O. 
 
 Sulphurous Acid. 
 
 Sulphurous acid exists at ordinary temperature and pressure 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 
 
 m pure oxygen, sulphur not being capable of passing directly to a 
 
PREPARATION, ETC., OF SULPHUROUS ACID. 285 
 
 higher degree of oxidation. In the burning of sulphur, the volume 
 of sulphurous acid gas formed is exactly equal to that of the oxygen 
 consumed. 
 
 When required pure, it is prepared generally by decomposing 
 sulphuric acid by means of a metal not very easily oxidized, as 
 mercury or copper. The metal combines with one atom of the ox- 
 ygen 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, S.O3 and Hg. give S.O2 and Hg.O., and Hg.O. unites 
 with S.O3 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 (Hg20.), but above that degree the red oxide (Hg.O.) 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 manga- 
 nese. The reaction is very simple ; one part of the sulphur uniting 
 with the metal, and another with the oxygen, form sulphuret of man- 
 ganese and sulphurous acid ; thus, Mn.Oi and 2S. give Mn.S. and 
 S.O2. The apparatus used in these processes may be that figured 
 under the heads of oxygen (p. 244) or nitrous oxide (p. 272). 
 
 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 pe- 
 culiarly irritating (the smell of burning sulphur), and cannot be 
 breathed. It is not combustible, 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 substance, 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 ex- 
 posed to the fumes of burning sulphur, it becomes completely white 5 
 but if washed in dilute sulphuric acid, its red colour is perfectly 
 renewed. 
 
 TJie specific gravity of sulphurous acid gas is 2210'6, and it is 
 formed by 
 
 One volume of sulphur-vapour 6648*0 
 
 Six volumes of oxygen 6615*6 
 
 The seven volumes condensed to six, give . . 13263.6 
 Weight of one volume of S.O2 2210-6 
 
 When this gas is exposed to a cold of 0° F., it condenses into 
 liquid heavier than water, which boils at 14°, and produces by its 
 evaporation a very intense cold ; it ^^,„„-,.^^ 
 
 is easily obtained in the liquid form ^ ^.^^-^^"'^l^^^^^'''^^^^^^^^^-^ i 
 
 by putting a quantity of mercury and ^^ ^^^^j^^ ""^"''^ ^ n ./^x 
 oil of vitriol into a tube, and sealing ^^^^"'^ ^^ 
 
 up the ends, as in the figure ; on applying heat to the extremity a, 
 
286 
 
 PROPERTIES, ETC., OF SULPHUROUS ACID. 
 
 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 b. 
 When a large quantity of sulphurous acid is required dissolved in water, or wheu 
 
 it is to be employed to form com- 
 pounds with bases, it may be pro- 
 duced in a much cheaper way than 
 those described above. Into a mat- 
 rass, a, placed in a furnace, is in- 
 troduced a quantity of well-burned 
 charcoal, in bits about the size of a 
 hazel-nut, and by means of the safe- 
 ty-funnel I, as much oil of vitriol is 
 poured in as that the mixture shall 
 half fill the vessel ; a tube passes to 
 a bottle, i, containing some water to 
 v.'ash the gas from any adhering sul- 
 phuric acid, and it is then conduct- 
 ed by the tube /, which passes to 
 the bottom of the vessel h, contain- 
 ing 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 2S.O3 there are 
 formed C.O2 and 2S.O2 ; there is produced a mixture of two volumes of sulphur- 
 ous 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 j 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 e:^pelled 
 from its combinations by almost all but the carbonic acid. Of its 
 salts, those which are soluble, all possess alkaline reaction. 
 
 The sulphurous acid passes into the state of sulphuric acid by 
 absorbing 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 j 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 are as follows : 
 
 Sulphur, 50-14 
 
 Oxygen, J^-86 
 
 100^ 
 
 One equivalent, 
 Two equivalents, 
 
 = 201-2 or 16-1 
 
 = 2000 or 16-0 
 
 40F2 32-1 
 
 Sulphuric Acid. 
 S.O3. 
 Sulphuric acid, one of the most important compound bodies, from 
 the energy of its action, and the variety of combinations which it 
 forms, 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 reducible metallic oxides, sulphuric acid is produced. 
 This principle is beautifully shown by passing a mixture oi sulphur- 
 
PREPARATION OF SULPHURIC ACID. 
 
 287 
 
 ous 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 nitro- 
 gen of the air j 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 ', these unite 
 to form a white crystalline solid, which appears to be a compound 
 of sulphurous acid and nitrous acid (S.02H-N.04), united with a quan- 
 tity of sulphuric acid and water which is not constant. The forma- 
 tion of this substance may be 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, sul- 
 phurous acid gas generated in the 
 flask a, and nitric oxide formed in 
 6, are introduced, to the latter of 
 which the oxygen is supplied by 
 the air to form nitrous acid fumes ; 
 the interior of the vessel becomes 
 gradually covered with a deposite 
 like hoar-frost, consisting of this 
 substance; and, in order that its 
 production may proceed without 
 interruption, the vessel may be filled with fresh atmospheric air by 
 blowing through one of the tubes c, d, while 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 
 generated, is resolved into sulphuric and hyponitric acids j thus S. 
 Oa+N.Ot gives S.O3 and N.O3, which last is decomposed by the 
 water into nitric acid and nitric oxide, SN.Og giving N.O5 and 2 
 N.O2; the nitric acid remains combined with the water along with 
 the sulphuric acid, while the nitric oxide escaping with effervescence, 
 generates, on arriving at the air, a new quantity of red fumes, and 
 oxidizes 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 contains no water. Sulphurous and 
 nitrous acids do not act on each other when in the gaseous form, unless water be 
 present; but they combine if placed in contact under considerable pressure, and 
 liquid, even when completely dry. A portion of the nitrous acid converts an equiv- 
 alent of the sulphurous acid into sulphuric acid, it being itself reduced to the state 
 of hyponitrous acid, while another quantity of nitrous and sulphurous acid unites 
 directly ; there are thus formed from 2S.O2 and 2N.O4 a white crystalline solid 
 S.O2 . N.O4-I-S.O3, and a quantity of N.O3, which is given off on the tube in 
 which the combination is produced being opened. 
 
 It may be questioned, however, whether this substance, for the discovery and 
 analysis of which we are indebted to M. de Prevostaye, 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 the manufacture of sulphuric acid, the apparatus consists of a long leaden 
 chamber consisting of two portions ; the lower a tray of about li feet deep, the 
 
288 
 
 MANUFACTURE OF OIL OF VITRIOL. 
 
 Other a quadrangular bell, which, being suspended on a wooden framework, h, 6, 
 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, a, 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 sulphur- 
 ous acid passes into the chamber by the chimney/; the heat necessary is supplied 
 by the fireplace under e ; the nitrous acid is obtained by placing over the burning 
 sulphur in g a pan containing a quantity of nitrate of soda and oil of vitriol, the ni- 
 tric acid evolved from which directly oxidizes a portion of sulphurous acid, and 
 then, being brought to the state of N.O4, acts on the mass of sulphurous acid as has 
 been just described : ^ 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, sul- 
 phurous acid gas and nitrous acid fumes, which produce, as in the apparatus figured 
 already, the white crystalline solid, by which, when decomposed by the water at 
 the bottom of the chamber, the sulphurous 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 decomposition by the water the nitric oxide 
 is again evolved with little loss ; and thus the oxygen of the air is gradually trans- 
 ferred 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 proportion 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 c, 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 complete mixture inside, and in due proportions, but which 
 does not carry them away until their action is completed. 
 
 The inclination given to the bottom of the chamber is for the purpose of allow- 
 ing the water, which, having dissolved most of the sulphuric acid, and become 
 heavy, to flow down to the farthest end ; and thus there is, on the surface has next 
 the front, a layer of the weakest acid, ready to absorb and decompose the great 
 
MANUFACTURE OF OIL OP VITRIOL. 289 
 
 ^jntity of the crystalline body formed when the mixed sulphurous and nitrous 
 acid gases meet the damp atmosphere of the chamber. 
 
 Ttie water in the chamber is allowed to remain unchanged until it has attained 
 a specific gravity of about 1600 ; it is then removed by leaden pipes, and concen 
 traled by evaporation in leaden cisterns, until its specific gravity is increased to 
 about 1-76. At this strength it begins to act upon 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 gravity 
 is 1-847, and it contains 81 54 of real acid in 100. 
 
 Thus is the oil of vitriol of commerce manufactured. At present, a midification 
 of the process has been introduced, in consequence of the extensive use of the iron 
 pyrites (bisulphuret of iron, Fe.Sa) in place of sulphur, as the source of the sul- 
 phurous 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 sulphurous acid, which is 
 conducted into the chamber, while the iron remains behind as 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. As the combus- 
 tion proceeds, new quantities of pyrites are introduced by apertures high up in the 
 kiln, while the residue of adherent rock and oxide of iron is raked out from the 
 ashpits at the bottom. 
 
 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 sulphur- 
 ous 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, spe- 
 cific gravity about 19, and consisting generally of about 90 of real acid and 10 of 
 water in 100, approaching closely to the formula 2S.03-J-H.O. At the same time, 
 a quantity (one half) of the acid is decomposed, the iron becoming peroxidized, 
 and sulphurous acid gas being evolved. Thus 4(S.03+Fe.O.) and H.O. give 
 2S.03-J-H.0. and 2S.O2, leaving behind ZFejOa, known in commerce as colcothar 
 of vitriol. 
 
 This process is carried on in a long furnace, in which are ranged about 120 
 
 earthen retorts, as I, in rows of 20, containing the ^.-— ^ — — ~-^ 
 
 partially-dried sulphate of iron. They are gradu- f I ^ "^ J 
 
 ally heated until the fumes of sulphuric acid begin — ""^ — "-^ 
 
 to appear, and the receiver A 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 or- 
 dinary oil of vitriol and real sulphuric acid. This last, being very 
 volatile, distils over in colourless vapours, which, on coming into 
 contact w^ith moist air, form dense white fumes of liquid acid. If 
 the colourless vapour be received in a dry vessel, cooled by a freez- 
 ing mixture, it condenses in beautiful white satiny fibres, consti- 
 tuting the dry sulphuric acid. This acid melts at 77^, and very 
 little above that temperature it boils. The specific gravity of its 
 vapour is 2762, formed by 
 
 One volume of vapour of sulphur =6648 
 
 Nine volumes of oxygen 1102-6x9= 99234 
 
 The ten volumes forming six =16571-4 
 
 Of which one weighs, therefore 2761 9 
 
 When this dry sulphuric acid in vapour is brought into contact 
 
 Oo 
 
290 SULPHURIC ACID. H Y P O S U L P H U R O U S ACID. 
 
 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 strong- 
 est oil of vitriol made in this country, and contains an equivalent 
 of acid united to one of water ; its formula is S.O3 + H.O. ; its most 
 important properties have been already described. The other con- 
 tains twice as much water ; its formula being S.03-J-2H.O. ; its spe 
 cific gravity is 1780. When exposed to the temperature of melting 
 ice, this acid forms large and regular crystals, while 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 j and it has been 
 already shown (page 185) that, no matter what combination a cer- 
 tain 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 lead ; from these it may freed by redistilla- 
 tion, 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 precip- 
 itates from the diluted acid. 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. If the smallest quantity of sulphuric acid be 
 present, a white precipitate is formed, which is insoluble in 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 solu- 
 tions are not, however, of any independent interest. 
 
 Hyposulphurous Acid. 
 SA, or S.O,-fS. 
 
 When a stream of sulphurous acid gas (S.O2) is passed into a sohition of sul- 
 phuret of calcium, it is absorbed, a quantity of sulphur is precipitated, 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 had been combined with the calcium is 
 set free, 2Ca.S. and 2S.O2 giving 2Ca.0.4-S202, while 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 3Na.O. and 4S. giving 
 Na.O.-f-SzOa and 2Na.S. 
 
 This acid itself is very easily decomposed ; it may, however, be obtained, at 
 
HYPOSULPHURIC ACID. 291 
 
 least fot a time, in a free state, by adding to any of its salts a stronger acid, or, bet- 
 ter, by bringing sulphurous acid and sulphuretted hydrogen gas to meet in water ; 
 the reaction which occurs is that 4S.O2 and 2S.H. give 3S2O2 and 20. 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 hyposulphurous acid 
 possess is, that they dissolve those compounds of silver which are insoluble in 
 water, as the chloride and iodide, and form a solution possessing an intensely sweet 
 taste ; upon this property is founded their use in Daguerreotype and photogenic draw- 
 ing. This acid is also recognised by its silver salt being decomposed, when boiled, 
 into black sulphuret of silver and free sulphuric acid, SaOa+Ag.O. giving S.O3 and 
 Ag.S. It is an important fact, also, in the history of the hyposulphuric acid, that 
 its salts do not always contain metaUic oxides, but that it may form salts with me- 
 tallic sulphurets ; thus there are two hyposulphites of sodium, of which one con- 
 tains oxide of sodium (soda), the other sulphuret of sodium. Their formulae are 
 S202-}-Na.O., and SzOa-l-Na.S Each of these, in crystallizing, combines with ten 
 atoms of water, like common sulphate of soda ; they possess, like it, a point of max- 
 imum solubility, and the crystals of all three appear to be isomorphous. There 
 are, therefore, three salts, 
 
 S.O2 . S.+Na.S.-[-10H.O., 
 S.O2 . S.-l-Na.O.-flOH.O., 
 S.O2 . 0.-i-Na.O.+lOH.O., 
 
 the similar constitution of which evidences the relation of sulphur and oxygen in a 
 remarkable degree, and will furnish the ground of speculations of great interest, to 
 which I shall again recur. 
 
 Hyposulphuric Acid. 
 
 S2O5, or S2O4+O. 
 
 When sulphurous acid gas is passed through water in which pure peroxide of 
 manganese is diffused, this dissolves, and the solution contains neutral hyposul- 
 phate of manganese. The reaction by which it is produced is simply that the sec- 
 ond atom of oxygen of the peroxide of manganese converts two equivalents of sul- 
 phurous acid into hyposulphuric acid, which is exactly neutralized by the protoxide 
 of manganese that is evolved, Mn.Oa and 2S.O2 giving Mn.O.-}-S205. 
 
 When a salt of hyposulphuric acid is heated, it is resolved into sulphurous acid, 
 which passes off as gas, and a neutral sulphate which remains behind, S2 05-J-R.O. 
 giving S.O2 and S-Og-j-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 rapidly 
 forms stilphuric acid by absorbing oxygen. 
 
 Remarks on the Constitution of the Compounds of Oxygen and Sulphur, 
 The progress of science has gradually brought into view a num- 
 ber 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, sulphurous acid must be considered as pre-existing. 
 The reasons for this are very numerous. By the direct union of 
 sulphur and oxygen we can never obtain any other ^compound than 
 sulphurous acid ; the others being always formed from it, 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 necessity of the indirect process of manufacture 
 of sulphuric acid becomes evident. The sulphur, when it forms sul- 
 phurous acid, is fully saturated with oxygen, and cannot combine 
 with any more ; but the sulphurous acid (S.O2) acts as a compound 
 radical, like cyanogen, as described in p. 233, and may unite with 
 
\ 
 
 292 PREPARATION AND PROPERTIES 
 
 any of the simple and compound bodies. It does not unite directly 
 with oxygen, but it does so with nitrous acid, and the body so form- 
 ed is decomposed by water, producing sulphuric acid, as has been 
 fully described. In like manner, to form hyposulphurous acid, the 
 radical, sulphurous acid, combines with sulphur ; the compound is 
 a sulphur acid, S.02-}-S., and combines with sulphur bases to form a 
 distinct class of salts. The hyposulphuric acid contains also sul- 
 phurous acid as its basis ; but there are two equivalents of the rad- 
 ical to one of oxygen : it is 28.02 + 0. This hypothesis is render- 
 ed still stronger by the fact that sulphurous acid combines with 
 chlorine and with iodine to form the chloro-sulphurous acid S.O^ 
 -j-Cl., and the iodo-sulphurous acid S.O^+I. It combines also 
 with nitric oxide to form the nitro-sulphurous acid S.O2+N.O2. 
 The chloro-sulphurous acid is produced by the direct combination 
 of chlorine and sulphurous acid, when exposed to strong sunlight. 
 The iodo-sulphurous acid is formed by passing sulphurous acid gas 
 through a solution of iodine in pyroxylic spirit, and the nitro-sul- 
 phuric 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 exten- 
 sive range of combinations, in which it serves as a compound radi- 
 cal, and of which the formulae are as follows : 
 
 Sulphuric acid S.Oa-f-O. 
 
 Hyposulphuric acid gSOj-j-O. 
 
 Hyposulphurous acid S.Og-j-S. 
 
 Chloro-sulphurous acid S.O2-J-CI. 
 
 Iodo-sulphurous acid S.02-|-I- 
 
 Nitro-sulphurous acid S.Oa-f-N.Oa. 
 
 The ordinary salts of sulphurous acid, the Sulphites^ I 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. 
 
 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 protosulphuret of iron 
 (Fe.S.) is acted on by dilute sulphuric acid, in the apparatus figured 
 in p. 24'7. A lively effervescence occurs from the escape of sul- 
 phuretted hydrogen gas, and the solution contains sulphate of pro- 
 toxide 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 j the 
 result may be expressed as follows : Fe.S. and S.Oj-f-jfl.O. give 
 H.S. and S.Og+Fe.O. This gas may also be obtained by acting on 
 sulphuret of potassium by dilute sulphuric or muriatic acid, in which 
 case the theory is the same as that already given. Sulphuret of 
 antimony and liquid muriatic acid produce, when heated, very pure 
 sulphuretted hydrogen, the reaction being that Sb^Sg and 3(H.C1.) 
 give Sb^Cla and 3(H.S.). 
 
OF SULPHURETTED HYDROGEN. 293 
 
 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 pneu- 
 matic 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 j 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 66480 
 
 Six volumes of hydrogen 688x6= 412-8 
 
 the seven volumes are condensed to six 70608 
 
 of which one weighs, therefore 1176-8 
 
 The sulphuretted hydrogen gas dissolves in water, forming a so- 
 lution 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 recognised. Thus 
 antimony gives an orange, manganese a flesh red, arsenic and cad- 
 mium a canary yellow, and several, as lead, mercury, and bismuth, 
 black or brown precipitates. 
 
 Sulphuretted hydrogen is highly inflammable ; if burned in a lim- 
 ited quantity of air, the hydrogen is consumed, while most of the 
 sulphur is deposited. By means of nitric acid or chlorine it may be 
 completely decomposed j hence chlorine acts as a disinfectant and 
 purifier of sewers or rooms impregnated with the odour of sulphu- 
 retted hydrogen. This gas is very poisonous ; air being capable of 
 producing death to large animals, if respired, though it may not con- 
 tain more than ^i^ of this gas. Many of the metals decompose sul- 
 phuretted hydrogen, particularly when heated in this gas, combining 
 with the sulphur, and setting the hydrogen free. This occurs slow- 
 ly, even at common temperatures ; 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 Har- 
 rowgate, Lucan, and Golden-bridge. They are easily recognised 
 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 it- 
 self closely to water ; its composition and equivalent numbers are 
 as follows : 
 
 Sulphur, 94-18 One equivalent, =201-2 or 16-1 
 
 Hydrogen, 5-82 One equivalent, = 12-5 or 1-0 
 
 100-00 ns^ Wl 
 
 Bisulphuret of Hydrogen. — To prepare this substance, bisulphuret of potassium 
 ia to be dissolved in water, and the solution gently poured into dilute muriatic acid ; 
 
294 SELENIUM, ITS COMPOUNDS WITH OXYGEN, ETC. 
 
 the potassium combines with the chlorine, and the hydrogen unites with the sul- 
 phur, K.S2 and H.Cl. giving K.Cl. and H.S2 ; the latter sinlis to the bottom of the 
 vessel as a heavy yellow liquid, insoluble in water, but decomposed rapidly by con- 
 tact 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 sul- 
 phur beyond two atoms, which, precipitating along with this true compound, dis- 
 solves 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 hy- 
 drogen condensed into a hquid, is to seal up, in a strong tube, a quantity of this bi- 
 sulphuretted hydrogen, which, after a short time, is decomposed ; the gas, not being 
 able to escape, is liquefied by the pressure it exercises, \vhile the sulphur separates 
 in octohedral crystals. 
 
 This body is decomposed by all substances which decompose deutoxide of hydro- 
 gen. Black oxide of manganese, or oxide of silver put in contact with it, evolve 
 sulphuretted hydrogen gas, and often with the appearance of hght and heat ; it 
 corrodes the skin, and appears to possess bleaching properties. 
 
 Sulphurets of Nitrogen have been discovered and described ; they are solid and 
 crystallizable, but are of no importance. 
 
 Of Selenium. 
 
 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 
 substance : 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 
 density is 4-32 ; its fracture is crystalline ; it melts a little above 
 the boiling point of water, and boils at 650^ 5 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 (Se.O.), a colourless 
 gas, which is remarkable for its pungent odour of horseradish. By this means 
 selenium may be recognised, 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 equivalents of oxy- 
 gen, and forms selenious acid, Se.Og- This may be also produced by burning se- 
 lenium in oxygen gas at a high temperature. It is solid, white, volatile, and may 
 be^ obtained crystaUized by sublimation, or from its watery solution. Selenious 
 acid may be deprived of its oxygen by contact with zinc or iron filings, or by sul- 
 phurous acid : selenium is set free as a crimson precipitate. When selenite of am- 
 monia 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, the selenic acid is formed (Se.Oa), which has the 
 most remarkable analogy with sulphuric acid. All their similar salts are isomorph- 
 ous, and almost identical in properties. Indeed, 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. 
 
 Seleniurctted Hydrogen is formed by the action of acids upon metallic seleniurets, 
 in precisely the same manner as that described under the head of sulphuretted hy- 
 drogen. It is a colourless gas, of an extremely fetid odour, irrespirable, soluble 
 in water, and precipitating, from the solutions of many of the metals, metallic sel- 
 eniurets ; these are generally black or brown ; but the seleniuret of manganese is, 
 like the sulphuret, 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 analogous to selenious acid, its 
 formula being Se.^-Sa- It is a canary yellow powder, insoluble in water. 
 
PHOSPHORUS, ITS PREPARATION, ETC. 
 
 295 
 
 Of Phosphorus. 
 
 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 quan- 
 tity in London and Paris. In the latter city it is computed that 
 about 200,000 lbs. of phosphorus are annually obtained. 
 
 The principal source of pliosphorus is the earthy material of bones (phosphate of 
 lime). The bones are first burned until they become completely white, and 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, while the remainder forms, with the whole of the phosphoric acid, 
 a soluble salt, which is obtained in the hquor, 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 powdered 
 charcoal, about one fourth the weight of the 
 bones that had been used, and the whole com- 
 pletely dried at a temperature just below redness. 
 The niass 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, 6, the other extremity 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 carbon 
 of which combines with the oxygen to form car- 
 bonic acid, while the phosphorus becomes free ; 
 this being volatilized by the high temperature, 
 passes in the state of vapour into the copper 
 tube, where it is condensed, and, flowing down 
 in the liquid form into the bottle, collects under the surface of the water. The cop- 
 I)er 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 cylin- 
 drical form in which it is found in commerce. 
 
 Phosphorus, when pure, is transparent and colourless j but, as 
 generally found, it is of a pale yellow, or even of a reddish col- 
 our. At ordinary 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 vol- 
 atile oils, in ether, and in sulphuret of carbon, from which last it 
 may be obtained in crystals of considerable size, 
 which are regular dodecahedrons, as in the figul'e. 
 It has also been obtained crystallized by fusion, 
 under the form of octohedrons. At 108^ phos- 
 phorus melts into a colourless liquid, and at 550° 
 it boils, forming a colourless vapour, the sp. gr. 
 of which is 4327. Phosphorus appears to assume 
 an anomalous condition like that of sulphur ; when 
 strongly heated and suddenly cooled, it becomes jet black and 
 opaque, but gradually returns to its ordinary aspect. 
 
 Phosphorus is exceedingly inflammable. Even at ordinary tem- 
 peratures, when exposed to the air, it burns slowly, forming phos- 
 
296 COMPOUNDS OF PHOSPHORUS AND OXYGEN. 
 
 phorous acid, and emitting light visible in the dark, from whence 
 its name (^o)^ 0epw, I bring light). It, at the same time, emits a 
 remarkable and penetrating garlic smell. It is hence that phospho- 
 rus is used to analyze atmospheric air, and that it must always be 
 preserved under water. When heated to 120^ phosphorus bursts 
 into brilliant flame, and unites with oxygen to form phosphoric acid. 
 The combustibility of phosphorus is influenced by the presence of 
 various gaseous bodies in a very remarkable degree. Thus, in 
 pure oxygen, phosphorus does not burn nor 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. 
 This influence even extends, under some circumstances, to much 
 higher temperatures. 
 
 The atomic weight of phosphorus had been formerly taken as 
 15*7 (H. = l) in consequence of some views of the constitution of 
 its compounds, which are now generally abandoned, and I consider 
 the true equivalent number to be 31'4, double the former. 
 
 Phosphorus combines with oxygen in four proportions, forming an oxide anr* 
 Uiree acid compounds, the constitution of which follows : 
 
 Oxide of phosphorus . . . =2P.+0.=62 8-f- 80=70 8 
 Hypophosphorous acid . . . = P.-i-0.=31-4-|- 80=39-4 
 Phosphorous acid . . . . = P.4-03=31 -44-24 0=55-4 
 Phosphoric acid = P.-i-O5=31-4-|-400=71-4 
 
 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 com- 
 pound of phosphorus with water ; but there forms, at the same time, a reddish sub- 
 stance, 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 
 pjissing 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 combina- 
 tion that it can form. It may be obtained purer by other processes, which are, how- 
 ever, too complicated to be introduced in this place. 
 
 The oxide of phosphorus so formed is a red or yellow powder, insoluble in water ; 
 it is exceedingly inflammable in some forms, but in others does not take fire until 
 heated to near the boiling point of mercury. 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 P2O. is that 
 obtained from the yellow matter ; Pelouze considers the reddish matter to be ex- 
 pressed by P3O2. 
 
 Hypophosphorous Acid. — This acid is very little known ; it is formed when phos 
 phorus is heated in a solution of an alkali or earth : water is decomposed ; one por- 
 tion of phosphorus combining with the hydrogen, and another with the oxygen, 
 produce phosphuretted hydrogen gas, which passes off, and hypophosphorous acid, 
 which remains combined with the alkali or earth employed ; the reaction may be 
 shown thus with phosphorus and solution of barytes : 4P., 3H.0., and 3Ba.O., give 
 3(P.O.+Ba.O.) and P.H3. 
 
 The hypophosphite of barytes, so obtained, may be decomposed by sulphuric acid, 
 and the sulphate of barytes being removed by filtration, the hypophosphorous acid 
 remains uncombined ; its solution may be evaporated to the consistence of a sirup, 
 but it cannot l^e obtained solid ; it is decomposed, by continuing the heat, into 
 phosphuretted hydrogen, phosphoric acid, and some phosphorus is set free. 
 
 Its salts are all soluble in water, and most of them crystallize and contain water 
 of crystallization ; when heated strongly, they give phosphuretted hydrogen and a 
 phosphate of the base. 
 
 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 ia 
 
PHOSPHORIC ACID^ ITS PREPARATION, ETC. 297 
 
 drawn out at one end to a point, with an aperture large enough to admit a pin, and 
 bent at an obtuse 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 excess 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 Uquid form ; for this purpose, a 
 quantity of phosphorus is placed in a thin glass vessel, covered 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 protochloride of phosphorus ; this substance 
 is immediately decomposed by the water, phosphorous acid and muriatic acid being 
 produced ; the P.CI3 and 3H.0. giving P.O3 and 3H.C1. ; both acids dissolve in the 
 water, but by evaporating the solution to the consistence of a sirup, the muriatic 
 acid passes off as gas, and the hydrate of phosphorous acid, P.Og-j-SH.O., remains 
 behind. This hydrated acid cannot be freed from water by farther heat, it being 
 then decomposed into phosphoric acid, and the variety of phosphuretted hydrogen 
 which is not spontaneously inflammable. Thus 4(P.03-l-3H.O.)give BP.Os-j-SH.O.) 
 and P.H3. 
 
 The solution of phosphorous acid absorbs oxygen rapidly from the air, and, with 
 the assistance of heat, reduces to the metalUc state the salts of mercury, silver, 
 gold, and platina. It is hence occasionally used as a deoxidizing agent. 
 
 Phosphoric Acid, 
 
 When this acid is required in large quantity, it is generally pre- 
 pared from the earth of bones, which are acted on by sulphuric acid, 
 as was described for the preparation of phosphorus. The acid so- 
 lution of superphosphate of lime is decomposed by carbonate of am- 
 monia, by which the lime is thrown down in combination with car- 
 bonic acid, and the phosphoric acid remains in solution as phosphate 
 of ammfinia. This salt may be crystallized, but it is generally 
 evaporated to dryness, and ignited ; the ammonia passes off, and 
 the phosphoric acid remains behind melted, and solidifies on cool- 
 ing into a colourless glass, the glacial phosphoric acid. 
 
 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 
 evaporated to dryness, and the residual phosphoric acid ignited, to 
 expel all traces of nitric acid. This process is somewhat danger- 
 ous, as sometimes fragments of phosphorus are projected by the 
 effervescence out of the liquid, and burning in the nitric oxide gas, 
 may burst the retort. 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 contained air forms phosphoric acid, which is 
 deposited in white flakes on the inside of the glass and on the sup- 
 porting plate. In all these cases, the acid so obtained 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, 
 
 phosphates of water ^ the constitution of which is as follows: 
 
 Monobasic phosphate of water . . P.O54- H.O. 
 
 Bibasic phosphate of water . . . P.O,-f-2H.O. 
 
 Tribasic phosphate of water . . . P.Os-f-SH O. 
 
 Pp 
 
298 PHOSPHATES OF WATER. 
 
 This relation was first established by the researches of Graham, 
 whose admirable memoir on the arseniates and phosphates formed 
 an important 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^ another 
 class oi bihasic 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 metallic oxides. 
 
 A solution of phosphoric acid in water may contain any one of 
 the three phosphates of water that have been described, and, when 
 neutralized by bases, may hence produce totally different salts. 
 The properties of a solution of phosphoric acid may therefore be 
 totally different, according to the manner in which it had been pre- 
 pared, and hence this acid was at one time ranked as a remarkable 
 instance of isomerism j but Graham has beautifully shown 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 P.O5-I-R.O., and a soluble salt of it 
 produces, in solutions of silver, a white, soft precipitate, P.Oj-f- 
 Ag.O. This is the least stable of the phosphates of water; it grad- 
 ually passes into the other forms, particularly when its solution is 
 boiled. 
 
 Bibasic Phosphate of Water. — This form of the acid may be pre- 
 pared by decomposing bibasic phosphate of lead by sulphuretted 
 hydrogen-. It is characterized by combining always with two equiv- 
 alents of base, forming salts, whose formula is P.O5 + 2R.O. ; its 
 salts give, with nitrate of silver, a white precipitate, P.Oj-fSAg.O., 
 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 may 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 moderate heat with the water 
 of crystallization, but requiring a temperature approaching to igni- 
 tion 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 
 characterized by not precipitating albumen, and by combining with 
 three equivalents of base when fully neutralized. In the majority 
 of cases, of the three equivalents of base, one is water ; thus the com- 
 mon phosphate. of soda is a tribasic phosphate, its formula being 
 (P.05H-2Na.O.H.O.)-f 24-Aq. ; when moderately heated, or even by 
 long exposure to dry air, it loses the 24.Aq., 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 
 
PHOSPHURETTED HYDROGEN. 
 
 299 
 
 changed into bibasic phosphate of soda, the formula of which is 
 (P.O5 f 2Na.0.)+ lOAq. The difference is remarkably shown by 
 the action of these salts on solution of silver ; common phosphate 
 of soda precipitates nitrate of silver of a canary yellow, and the so- 
 lution 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 ex- 
 pressed : 
 
 P.05+2Na.O.H.O. and 3(N.05-LAg.O.) 
 give R05+3Ag.O. . . 2(N.O,+Na.O.) and N.O5+H.O. 
 If, on the other hand, bibasic phosphate of soda be used, the liquor 
 remains neutral, for P.05 + 2Na.O. and 2(N.05-f Ag.O.) give P.O5 + 
 2Ag.O. and 2(^0^ + Na.O.). 
 
 In the tribasic phosphates it frequently occurs that there is but 
 one equivalent of fixed base, the other two being water ; such salts 
 have frequently an acid reaction, and were formerly termed biphos- 
 phates. Thus one tribasic phosphate of soda is P.Os + Na.O. . 2H. 
 O. ; the biphosphate of ammonia is tribasic, its formula beinff P.Os 
 + N.H,0..2H.O. 
 
 These salts of phosphoric acid were originally designated by 
 Graham metaphosphates, pyrophosphates, and common phosphates, 
 but the systematic names which he has since proposed should be 
 universally adopted. 
 
 In the general remarks on the constitution of salts, and on some 
 other occasions, I shall have opportunities to return to the consid- 
 eration of this subject. 
 
 Compounds of Phosphorus and. Hydrogen. 
 
 Although it is probable that there exist at least two compounds 
 of phosphorus and hydrogen, yet I shall describe only that which 
 is gaseous (P.H3), as of it alone do we possess 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 decom- 
 posed, gives its oxygen to one portion of the phosphorus to form 
 hypophosphorous acid, and its hydrogen to another, forming phos- 
 phuretted hydrogen gas: 2d, when the hydrated phosphorous acid 
 is heated, the water is decomposed, and phosphoric acid and phos- 
 phuretted 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 
 second the B variety. 
 If the A gas, evolved 
 from the retort a, 
 be allowed to bub- 
 ble through the wa- 
 ter of the pneumatic 
 trough, each bubble 
 of gas, as it bursts in 
 
300 PHOSPHURETTED HYDROGEN. 
 
 the air, takes fire spontaneously, and, burning 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 apart- 
 ment be still, without its form being broken up. The structure of 
 this ring is exceedingly curious and pretty ; it consists of an ama- 
 zing 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 phos- 
 phuretted 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 J but slightly absorbed by water, and precipitating the generali- 
 ty of metallic salts, giving insoluble phosphurets. The specific grav- 
 ity is the same for both, being 1185, which arises from 
 
 One volume of phosphoms- vapour =43270 
 
 and six volumes of hydrogen 68-8x6= 412-8 
 
 being condensed to four 4739-8 
 
 of which one weighs, therefore 1184-9 
 
 Their constituents by weight, and equivalent numbers, are as fol- 
 lows : 
 
 Phosphorus, =91-29 One equivalent, =392-3 or 31-4? 
 
 Hydrogen, 8-71 Three equivalents, = 37-5 or 3-0 
 
 100-00 429^ 34¥ 
 
 These two varieties were naturally looked upon as isomeric, but 
 Graham has shown that the difference of properties may arise from 
 the 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 inflammable. Graham considers that, in 
 obtaining the gas from phosphorus and milk of lime, &c., it is accom- 
 panied 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 inflammable, and, acting as a 
 match, inflames the general mass of gas (see p. 296.) 
 
 Phos2)huret of Nitrogen. — Tliis compound has been discovered and described by 
 Rose, but possesses no important properties. 
 
 Sulphur et of Phosphorus is formed by melting together sulphur and phosphorus in 
 equivalent weights. It appears that these elements unite in more proportions than 
 one. The compound is much more inflammable than phosphorus, and is the mate- 
 rial used in the phosphorus match-boxes. 
 
 Of Chlorine, 
 Chlorine exists in large quantity in nature, principally combined 
 with sodium, forming immense deposites of rock-salt (chloride of 
 
CHLORINE, ITS PREPARATION. 
 
 301 
 
 8odmm) in England, in Poland, and elsewhere j and in the same 
 state it communicates the saltness, and constitutes the chief ingre- 
 dient 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 tht 
 peroxide of manganese passes to the sodium, the chlorine being expelled, and the 
 soda and protoxide of manganese both unite with the sulphuric acid. Thus Mn.Oj 
 and Na.Cl., treated with 2S.O3, produce S.O3 . Na.O.-f-SOg . Mn.O., and CI. i& 
 evolved. By weight, about six parts of oxide of man- 
 ganese and eight of chloride of sodium are employed 
 with thirteen of oil of vitriol ; and as the manufactu- 
 rers of chloride of lime are generally makg;rs of oil of 
 vitriol also, a proportionate quantity of acid of 1 600 
 from the chamber (p. 289) is generally used in place 
 of strong oil of vitriol, the expense of concentration 
 being thus saved. Into a leaden still, h, h, such as is 
 represented in the figure, the mixed salt and manga- 
 nese are introduced at the aperture z, which is then 
 tightly closed ; the sulphuric acid enters by the bent 
 funnel b, and these materials 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, e, into which steam is conducted by 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. 
 
 When chlorine is required in small quantity in the laboratory, it 
 may be more conveniently prepared from the muriatic acid of com- 
 merce, which is a solution of chloride of hydrogen gas in water. 
 This is completely decomposed by peroxide of manganese 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 protochloride and free chlorine. Thus, at first, 
 Mn.Oa and 2C1.H. give Mn.Cl^ and 2H.0., and then Mn.Cla sep- 
 arates into Mn.Cl. and CI., which is evolved as gas. For this it is 
 only necessary to introduce about one part of peroxide and three of 
 muriatic acid into an apparatus, such as those already often figured, 
 and the gas may be obtained. 
 The collection of the chlorine 
 requires some remark. It is ab- 
 sorbed rapidly by cold water, 
 and it cannot be collected over 
 mercury, as it combines rapid- 
 ly with it, forming calomel; wa- 
 ter 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 
 
302 BLEACHING POWER OF CHLORINE. 
 
 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, pre- 
 cisely as, by conducting a stream of water to the bottom of a vessel 
 containing oil, this might be perfectly expelled, and the vessel filled 
 with water. The colour of the chlorine allows the gradual filling of 
 the bottle to be seen, and by stopping its aperture Avith a greased 
 stopple, the gas may be preserved unaltered for a long time. 
 
 The chlorine, when thus prepared, is a greenish yellow gas, 
 whence its name (^/Iwpoc) ; of an extremely suffocating odour, ir- 
 ritating the air passages when respired, even 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 phosphorus, although with little light. A 
 paper dipped in oil of turpentine takes fire spontaneously, the hy- 
 drogen 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 common temperatures, 
 and suddenly, with explosion if set on fire by a taper or by the 
 electric spark. In consequence of this affinity for hydrogen, chlo- 
 rine decomposes most organic substances, one half of the chlorine 
 removing an equivalent quantity of hydrogen, and the other half 
 going in its place j thus ether and chlorine give chloride of hydro- 
 gen and chlorine ether, C4H5O. and lOCl. giving C4CI5O. and 5H.C1. 
 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 re- 
 moving the colour of organic substances ; its bleaching properties. 
 Formerly it was considered that water was necessary for this bleach- 
 ing, and that the chlorine combined with the hydrogen, while 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, that this is not the case, but that the chlorine enters 
 into the constitution of the new substance formed, sometimes repla- 
 cing hydrogen, at others simply combining with the coloured body, 
 and in some, the reaction being so complex that its immediate stages 
 cannot be completely traced. I shall notice this agency of chlorine 
 again when describing the chloride of lime, and also when discuss- 
 ing its relations to organic chemistry. 
 
 From this action on organic bodies, chlorine is extensively em- 
 ployed as a disinfectant, to remove the miasmata and infectious im- 
 purities by which the atmosphere of an hospital may be contaminated. 
 For this purpose, it is desirable to evolve the gas slowly, but con- 
 tinuously ; 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. 
 
OXIDIZING POWER OF CHLORINE. 303 
 
 When chlorine is brought into contact with water at 32°, they 
 combine, 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 lib- 
 erated, exercises 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 be- 
 comes 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 employed 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 chlo 
 ro-selenious acid, Se.O^ . CL, which, in contact with water, is resolv- 
 ed into Se.Og . O. and Cl.H. 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 pro- 
 toxide of iron is converted into peroxide by chlorine, because 6Fe. 
 0., acted on by 3C1., produce Fe2Cl3 and 2Fe203. The direct decom- 
 position of water by chlorine I consider to occur very seldom. 
 
 The combinations of chlorine form, perhaps, next to those of ox- 
 ygen, the most complete series which exists in chemistry. Its af- 
 fiirities 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 gener- 
 ally 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 possesses also the property of combining with metallic 
 oxides, apparently without decomposition in many cases, and form- 
 ing compounds resembling peroxides, in which a portion of the ox- 
 ygen is replaced by chlorine. Thus, w4th lime it forms Ca.O. . CI., 
 with protoxide of lead Pb.O. . CI., withbarytes Ba.O. . CI., which cor- 
 respond probably to Pb.Oa and Ba.Oa. In the hydrate of chlorine, 
 which is Cl. + IOH.O., it is likely that a compound corresponding to 
 peroxide of hydrogen may exist, and that the constitution of the 
 crystals may be H.O. . Cl. + QH.O., and that bleaching compounds in 
 general may have that type. 
 
 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, soluble 
 inwater 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 prop- 
 erties and smell are absent. 
 
304 HYPOCHLOROUS ACI D. C ULORIC ACID. 
 
 Compounds of Chlorine with Oxygen. 
 These are four, constituted as follows : 
 
 Hypochlorous acid .... =C1.4- 0.r:r35-4-|-8 =434 
 
 Chlorous acid =Cl.-|-40.=35 4-|-32=67-4 
 
 Chloric acid =C1.4-50.=35 4-1-40=75 4 
 
 Percliloric acid ..... =Cl.-j-70.=354-j-56=91-4 
 
 Hypochlorous Acid. 
 
 If red oxide of mercury, diffused through a small quantity of wa- 
 ter, be introduced into bottles containing chlorine, and the whole 
 be agitated, the gas is rapidly absorbed, and, combining with both 
 constituents of the oxide, forms chloride of mercury and hypochlo- 
 rous 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. 4- 3Hg.O., which separates, and the hypochlorous 
 acid remains nearly pure in solution in the water. By a very mod- 
 erate heat it may be distilled in a dilute form, and so obtained quite 
 pure from sublimate, 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 j 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 green- 
 ish yellow gas, very similar to chlorine in all respects ; water ab- 
 sorbs 100 volumes of it j by raising its temperature even slightly, it 
 explodes, and its volume is increased by one half: 100 volumes of 
 it produce 100 of chlorine and fifty of oxygen. Its specific gravity 
 is by theory 3021*3, and its equivalent numbers 542-6 or 43.4: its 
 formula is Cl.O. 
 
 The hypochlorous acid combines with bases to form salts, hypo- 
 chlorites, which possess 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. 
 When chlorine is brought into contact Avith an alkaline solution, 
 it is absorbed with great avidity, and the liquor acquires powerful 
 bleaching properties. Concerning the nature of the reaction, the 
 opinions of chemists are not completely settled j it may be sup- 
 posed, on the one hand, that the chlorine unites directly with the 
 alkali, forming simply, if potash be employed, chloride of potassa, 
 K.O. . CI. But, on the other hand, it is possible that a quantity of 
 alkali may be decomposed, as certainly occurs with oxide of mer- 
 cury, and that chloride of potassium and hypochlorite of potash may 
 coexist in the liquor; thus, that 2K.0. and 2C1. should produce K. 
 CI. and Cl.O.-j-K.O. The majority of chemists incJine to the latter 
 view, but the subject will hereafter receive detailed consideration. 
 
CHLORIC ACID. CHLOROUS ACID. 305 
 
 In any case, this bleaching alkaline liquor is completely decomposed 
 by boiling, particularly if it be very concentrated. Oxygen is then 
 evolved in considerable quantity, while chloride of potassium and 
 chlorate of potash are produced: thus 9(K.0.-}-C1.0) evolve 120., 
 and form 8K.C1. and K.O.-f-Cl.O^. It is in this way that the chlorate 
 of potash of commerce is obtained, and from it the chemist prepares 
 chloric acid. 
 
 A solution of this acid is readily prepared by decomposing a so 
 lution 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 chlorine, oxygen, and perchloric acid. It does not bleach ; it does 
 not precipitate a solution of nitrate of silver : when in its strongest 
 form, 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 recognised, by yielding, 
 when heated, oxygen and a metallic chloride ; thus the chlorate of 
 potash is used in the preparation of oxygen (p. 244), CI.O5+K.O. 
 giving Cl.K. and 60. When mixed with sulphur and rubbed in a 
 warm mortar, they explode, and if thrown upon an ignited coal, they 
 deflagrate 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 chemist obtains the remaining compounds of chlorine and ox- 
 ygen. 
 
 The constitution and equivalent numbers of chloric acid are as 
 follows : by weight. 
 
 Chlorine, 46-95 One equivalent, =442'6 or 35-4 
 
 Oxygen, 53-05 Five equivalents, =500-0 or 40-0 
 
 iWoO 942-6 75^ 
 
 its formula is CI.O5, and, like the nitric acid, which it resembles m 
 so many other properties, it consists of five volumes of oxygen uni- 
 ted to two of the other element. 
 
 Chlorous Acid. — When chlorate of potash in fine powder is decom- 
 posed 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 
 chlorous, and the latter the perchloric acid, 3CI.O5 giving 2(C1. 
 Oj) and CI.O7. This process must be conducted very cautiously, and 
 the retort warmed very gently in a water bath. The chlorous acid 
 may be collected over mercury, or, from its great density, like chlo- 
 rine, in a dry jar ; there remains in the retort a mixture of bisul- 
 phate and of perchlorate of potash. 
 
 This acid gas is of a rich yellowish-green colour, and an aromatic 
 odour ; it is rapidly absorbed by water ; it bleaches strongly, and is 
 u powerful oxidizing agent, its elements separating from the slightest 
 causes. If it be heated above 212^, it explodes with a flash of light ; 
 phosphorus immersed in it takes fire spontaneously, and burns brill- 
 iantly in the mixture of chlorine and oxygen which results from its 
 decomposition. This may be very well shown by placing some 
 crystals of chlorate of potash and some phosphorus together, at 
 
 Qq 
 
306 PERCHLORICACID. 
 
 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 chlorous 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 chlorous acid combines with bases to form salts, chlorites, 
 which possess bleaching properties, but are not of much importance, 
 as they do not enter into practical use. 
 
 Perchloric Acid. — This acid is formed in the process for obtaining 
 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 therein ; this may then be dissolved in boiling 
 water, from which it crystallizes as the solution cools. When the 
 object is only the preparation of perchloric acid, and not of chlorous 
 acid, the process becomes easier by heating chlorate of potash with 
 dilute nitric acid ; the elements of the chlorous acid are then sep- 
 arated, 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 j this arises 
 from the salt being at first decomposed into oxygen, chloride of 
 potassium, and perchlorate of potash, 3(K.O.C1.05) giving 2(C1.K.) 
 and K.O.CI.O7, while 80. are evolved as gas. This is exactly half 
 of the oxygen which the salt contains. If the saline mass then re- 
 maining 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 wa- 
 ter, and distilling ; the acid passes over Avith the 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, how- 
 ever, 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 chlo- 
 ric acid is immediately decomposed, a mixture of chlorous acid and 
 chlorine being evolved ; CI.O5 and Cl.H. giving H.O. and a mixture 
 of CI.O4 with CI., which was described by Sir Humphrey Davy as a 
 peculiar gas, Euchlorine. By this means the salts of perchloric and 
 of chloric acid may be distinguished. It is not decomposed by al- 
 cohol, nor has it any spontaneous action on organic bodies. It is 
 well characterized by the very sparing solubility of its potash salt 
 whence it has been employed as a reagent to detect that alkali. 
 
 The constitution and equivalent numbers of perchloric acid are as 
 follows : 
 
 Chlorine, 38-74 One equivalent, =442-6 or 35-4 
 
 Oxygen, 61-26 Seven equivalents, =700-0 or 56-0 
 
 100-00 ll4¥6 9F4 
 
CHLORIDE OF HYDROGEN. 307 
 
 Compound of Chlorine and Hydrogen. 
 
 This compound exists naturally as a gas, of which a solution m 
 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 li- 
 quid or gaseous muriatic acid, according as it is free or combined 
 with water ; but in cases where its functions in combination are dis- 
 cussed, I shall term it chloride of hydrogen. 
 
 To prepare the gaseous muriatic acid, a sigfiall 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 sulphuric acid, while its hydrogen, uniting with the chlo 
 rine, produces the chloride of hydrogen, which is given off as a gas ; 
 the reaction may be thus expressed: S.O3H.O. and Na.Cl. give S. 
 OaNa.O. and H.Cl. 
 
 This gas may also be formed by putting together chlorine and hy- 
 drogen in equal volumes. Even in diffuse light they combine 
 completely in some hours, but in the direct sunshine the union 
 is instant and explosive. The mixture may also be fired by the ta- 
 per 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 cases of the action of chlorine on or- 
 ganic matters, this substance is also formed j indeed, the agency of 
 chlorine in bleaching, and in decomposing organic compounds, ap- 
 pears generally to result from its disposition to unite with hydro- 
 gen. 
 
 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 has been browned by an alkali 5 hence 
 it is generally looked upon as a powerful acid. When mixed with 
 damp air it forms heavy white fumes by uniting with the wa- 
 tery vapour, and condensing 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 5 
 thus Cu.O. and H.Cl. give Cu.Cl. and H.O. If any of the more oxi- 
 dable metals, as iron, zinc, or potassium, be heated in a current of 
 the gas, it is decomposed, a metallic chloride being formed and hy- 
 drogen gas evolved. This occurs, also, when these metals are im- 
 mersed in the liquid acid ; a copious effervescence is produced by 
 the escape of hydrogen, 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 hydrogen and chlorine united without condensa 
 tion. Its specific gravity is, by theory, 
 
308 
 
 PREPARATION AND PROPERTIES OP 
 
 One volume of chlorine =2470 
 
 One volume of hydrogen = 68-8 
 
 give two volumes of muriatic acid .... =2538 8 
 of which one weighs, therefore 12694 
 
 Its constitution and equivalent numbers are therefore, 
 
 Chlorine, 97-26 One equivalent, =442-6 or 35-4 
 
 Hydrogen, 2*74 One equivalent, = 12-5 or 1-0 
 
 100^ 
 
 455-1 
 
 36-4 
 
 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 re- 
 search. 
 
 To prepare liquid muriatic acid in the laboratory, chloride of sodium is to be in- 
 troduced into a glass globe, placed in a sand-bath on the furnace, and then an equal 
 weight of sulphuric acid and water, mixed together, are to be introduced by the fun- 
 nel : the decomposition proceeds as already explained, and the gas evolved passes 
 
 »y the tube into the first of a range of three-necked bottles, as in the figure. Eact 
 bottle is about half full of water. When that in the first has become completely sat- 
 urated 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 spir- 
 its of salt of commerce. When this is placed in a distilling apparatus, arranged as 
 that figured in p. 278, and 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 is nearly empty, and an acid so obtained completely 
 pure, and of a very convenient strength for the general range of applications. 
 
 The manufacture of this acid is carried on on a very large scale more generally 
 with a view to the extraction of the alkali from the residual sulphate of soda than foi 
 the sake of the muriatic acid, the great difficulty in a soda factory being how to get rid 
 of tlic muriatic acid which is produced. When the object is. however, to prepare the 
 
MURIATICACID. 309 
 
 liquid acid, precisely the same apparatus is employed as for the manufacture of nitric 
 acid, which has been already figured and described (p. 278), the cylinders being 
 somewhat larger, as from four to five cwts. of common salt are generally decom- 
 posed 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 e e in the figure are very fi-equently constructed, not of metal, but of free- 
 stone 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 
 aci^, 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 H.C1.-J-6H.0., or in 
 numbers, 
 
 Muriatic acid . 40 27 One equivalent . =4551 or 364 
 
 Water . . . 59 73 Six equivalents . =6750 or 54 
 
 10000 11301 904 
 
 When this concentrated acid is heated, it evolves a large quantity of gas, and 
 the boiUng 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 
 H.C1.-J-16H.0., or in numbers, 
 
 Muriatic acid . 2013 One equivalent . . . = 4551 or 36-4 
 
 Water . . . 79 87 Sixteen equivalents . . =18000 or 144.0 
 
 100 00 22551 180l 
 
 Graham has found that the strong acid, when evaporated in the open air, aban- 
 dons a quantity of gas, while the remaining liquid becomes H.Cl.-|-12H.O. 
 
 The metallic character of hydrogen, and the analogy of its combinations with 
 those of zinc, are completely shown 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 shown that the hydrates of oxy- 
 chloride of zinc are as follows : 
 
 Zn.Cl.-|-6Zn.O. 
 Zn.Cl.-f6Zn.0.4- 6Aq. 
 Zn.Cl.-l-6Zn.O.4-10Aq. 
 
 and the definite states of liquid muriatic acid are 
 
 H.Cl.-f6H.O. 
 H.Cl.-f 6H.0.-f 6Aq. 
 H.Cl.-i-6H.O.-|-10Aq. 
 
 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 solutions 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, 
 find always a trace of iron, derived from the metal cylinders in 
 which it is fabricated. Occasionally, sulphurous acid is formed in 
 it in small quantity. These impurities are detected thus : by dilu- 
 ting the muriatic 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 ; while solu- 
 tion of protochloride of tin produces a brown precipitate of sulphuret 
 of tin if sulphurous acid had been present. 
 
 Muriatic acid is easily recognised, as a gas, by its action on moist 
 litmus paper, its fuming in the air, its forming with ammonia dense 
 
310 
 
 NITRO-MURIATIC ACID. 
 
 white clouds of sal ammoniac, 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. 
 
 Mitromuriatic Acid. Aqua Hegia. — 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.Cl. and N.O5 giving CI. and N.O4, 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 decom- 
 posed. Thus the nitromuriatic 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 sulphurets) 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. 
 
 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 con- 
 denses in the receiver /, which 
 must be kept very cool ; any uncon- 
 densed gas is conducted away by 
 the tube I. 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. It consists of one equivalent of 
 chlorine united to two of sulphur, S2CI., and in contact with water, muriatic acid, 
 sulphur, and hyposulphurous acid are formed by mutual decomposition. 
 
 It is probable that there is another chloride of sulphur consisting of one equiva- 
 lent of each, S.Cl. 
 
 Chlorides of Phosphorus. — Chlorine unites with phosphorus in two proportions, 
 forming a liquid protochloride, P. CI 3, and a solid perchloride, P.CI5. 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 will be described hereafter, I will introduce the description 
 
CHLORIDES OF PHOSPHORUS. IODINE. 311 
 
 of it here. The chlorine is generated by hquid muriatic acid and peroxide of man- 
 ganese, in the flask a, supported on a sand-bath over the lamp ; from it a bent tube 
 passes to the receiver b, in which a quantity of watery vapour is condensed, and 
 serves to absorb any muriatic acid gas that might escape decomposition. The pure 
 chlorine passes then through the tube c, which is filled with fragments of fused 
 cliloride 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 conden- 
 ses ; 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 tempeiature 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. While there is an excess of phosphorus, the protochloride is princi- 
 pally 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 
 perchloride. 
 
 The Protochloride of Phosphorus is obtained pure by stopping the process before 
 all the phosphorus has been consumed, and rectifying the colourless liquid by dis- 
 tilling it in a retort containing some bits of phosphorus, which bring back any per- 
 chloride it might contain dissolved, to the state of protochloride. This body is 
 heavier than water, by which it is completely decomposed, P.CI3 and 3H.0. giving 
 P.O3 and 3H.C1. It is thus that the liquid phosphorous acid is obtained, as de- 
 scribed in p. 297. 
 
 The Perchloride of Phosphorus is a white solid, volatile under 212°, and conden- 
 sing in a crystalline form. In contact with water, it is decomposed with the evo- 
 lution of great heat, producing phosphoric acid and muriatic acid, P.CI5 and 5H.0. 
 giving P.O5 and 5H.0. ; 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. 
 
 Iodine is found principally in sea- water, associated 'wjth chlorine, 
 combined with sodium and magnesium. It has been also discover- 
 ed in the mineral kingdom, united with silver. For the purposes of 
 commerce it is always extracted from kelp^ which is a semifused 
 mass of saline ashes remaining after the burning of various species 
 of fiici (sea-weed). 
 
 For this purpose, the powdered kelp is lixiviated in water, to 
 which it yields about half its weight of salts. The solution is evap- 
 orated down in an open pan, and Avhen concentrated to a certain 
 point, begins to deposite its soda-salts, namely, common salt, car- 
 bonate and sulphate of soda, which are removed from the boiling 
 liquid by means of a shovel pierced with holes like a colander. 
 The liquid is afterward run into a shallow pan to cool, in which 
 It deposites a crop of crystals of chloride of potassium j the same 
 operations are repeated on the mother-ley of these crystals until it 
 is exhausted. A dense, dark-coloured liquid remains, which con- 
 tains 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, sulphuric acid is gradually added in such quantity 
 as to leave the liquid very sour, which causes an evolution of car- 
 bonic acid, sulphuretted hydrogen, and sulphurous acid gases, with 
 a considerable 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, 
 
;u2 
 
 PREPARATION OF IODINE. 
 
 fl, of a cylindrical form, 
 supported in a sand-bath, 
 which is heated by a 
 small fire below. The 
 retort has a large open 
 ing, to which a capital, 
 b^ c, resembling the head 
 of an alembic, is adapt- 
 ed, and luted with pipe- 
 clay. In the capital it- 
 self there are two open- 
 ings, a larger and a small- 
 er, at b and c, closed by 
 leaden stoppers. A se- 
 ries of bottles, J, having 
 each two openings, con- 
 nected together, as rep- 
 resented in the figure, 
 and with their joinings luted, are used as condensers. The prepa- 
 red ley being heated to about 140° in the retort, 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 collect- 
 ed ', the progress of its evolution is watched by occasionally re- 
 moving the stopper at c ; and additions of sulphuric acid or man- 
 ganese are made by ^, if deemed necessary. This description of 
 the manufacture of iodine iipon the large scale at Glasgow is due 
 to Professor Graham. 
 
 In this operation, the peroxidvs i)f 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 de- 
 compose the iodides, but not the chlorides. If both were decom- 
 posed, the chlorine and iodine simultaneously evolved would unite 
 to form chloride of iodine, by which the iodine would be lost j but 
 as the chlorine remains combined, the action becomes simply, that 
 the metal of the iodide present is oxidized by the oxide of manga- 
 nese, and the iodine set free ; thus, with iodide of sodium, S.O,-f- 
 Mn.02 and Na.I. give Mn.O. . S.O3 . Na.O. and I. 
 
 Another mode of preparing iodine consists in adding to the solu- 
 tion containing iodide of sodium, a solution of sulphate of copper, 
 in which the copper is reduced to the state of sub-oxide (CU2O.) bv 
 means of protosulphate of iron dissolved along with it. By the in- 
 terchange of elements, sulphate of soda is formed, and a sub-iodid« 
 of copper of a very pale yellow colour, and quite insolubl<» 
 in water, is produced, S.Og+CuaO. and Na.I. giving S.Og-h 
 Na.O. and Cugl. 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 sca.es of a bluish 
 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 
 
PROPERTIES OF IODINE. IODIC ACID. 313 
 
 iodine is 4948 ; it fuses at 225°, and boils at 347° j but it evaporates 
 at the usual temperature, and more rapidly when damp than when 
 dry, diffusing 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 loeidTjg, violet-coloured. The vapour of iodine is 
 one of the heaviest of gaseous bodies, its density being 8707*7, ac- 
 cording to calculation from its atomic weight. 
 
 Pure water dissolves about l-7000th of its weight of iodine, and 
 acquires a brown colour. In general, iodine comports itself like 
 chlorine, 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 deli- 
 cate test of iodine. If the iodine be free, starch produces at once 
 the blue precipitate ; but if it be in combination as a soluble iodide, 
 no change takes place till chlorine is added to liberate the iodine. 
 If more chlorine, however, be added than is necessary for that pur- 
 pose, 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, but recovers its blue colour 
 if immediately cooled. The soluble iodides give, with nitrate of 
 silver, an insoluble iodide of silver, of a pale yellow colour, insoluble 
 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 sim- 
 ilarity 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. 
 
 Compounds of Iodine and Oxygen. 
 
 Iodine appears to combine with oxygen in three proportions, form 
 ing the iodous acid^ the iodic acid, and the periodic acid. Of the con- 
 stitution of the first there is nothing positively known; it has not 
 been isolated, and the substances that have been supposed to contain 
 it may also be considered as compounds of an iodide with an iodate. 
 The description of these compounds will be found in the chapter 
 on the salts; and I shall, therefore, at present, only notice the other 
 two acids. 
 
 Iodic Acid. — This acid may be very easily prepared by boiling 
 iodine in fuming nitric acid until it is all dissolved, and then distil 
 ling off the excess of acid; the iodic acid remains as a white crys 
 talline 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 dissolved ; the acid liquor so obtained is to be 
 neutralized by carbonate of soda, by which a quantity of iodine ia 
 
314 PROPERTIES OF IODIC ACID. PERIODIC ACID. 
 
 precipitated ; the chlorine is then passed through until this iodine 
 disappears, and then more carbonate of soda added, and this alter- 
 nation continued until the addition of the carbonate of soda produces 
 no deposite of iodine ; the solution contains then iodate of soda and 
 chloride of sodium, generated by the decomposition of the soda by 
 the chloride of iodine first formed. Thus 5C1. and I. produce I.CI5, 
 which, with 6Na.O., give 5Na.Cl. and Na.O. -I-I.O5. 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 its weight of oil of vitriol and 1^ times its weight 
 of water j the sulphate of barytes may be then separated by the fil- 
 ter, and the solution of iodic acid evaporated gently to dryness. 
 
 Iodic acid is very soluble in water; from a strong solution it crys 
 tallizes in rhombic plates and 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 oxi- 
 dizing 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 and iodide of sulphur. By an 
 excess of these agents, the iodine is finally converted into iodide of 
 hydrogen. By these means the iodic acid may be recognised, and 
 also by its peculiar action upon morphia, which it decomposes, io- 
 dine being set free. This is more valuable as a character of mor- 
 phia 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 com- 
 merce is founded on this property. Iodine is dissolved in a solution 
 of potash, and, when dried down, gives a mixture of 5K.I. and I.O5 . 
 K.O. When this mass is fused, oxygen is given off in abundance, 
 and ultimately pure K.I. remains. The commercial salt prepared in 
 this way has been shown by Mr. Scanlan frequently to contain iodate 
 of potash, either fradulently or accidentally, left undecomposed. 
 
 The composition and equivalent numbers of the iodic acid are as 
 follows, its formula being I.O5 : 
 
 Iodine, 75-96 One equivalent, =1579-5 or 126-6 
 
 Oxygen, 24-04 Five equivalents, -■ 500-0 or 40-0 
 
 100^ ■2079^ 166^ 
 
 Its elements are united in the proportion, by volume, of two vol- 
 umes of vapour of iodine to five volumes of oxygen. 
 
 Periodic Acid, I.O7. — 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, while its oxygen, being added 
 to the iodic acid, converts it into the periodic acid, which combines with two equiv- 
 alents of soda. Thus, 2C1. acting on 3Na.O. and I.Os-f-Na.O., produce 2Na.Cl. and 
 1.07-f 2Na.O. On adding to the solution of this salt nitrate of silver, a basic peri- 
 odate of silver is produced, which, being dissolved in nitric acid, gives yellow crys- 
 tals of neutral periodate of sil\^r When put in contact with water, these crystals 
 are decomposed, half of the periodic acid precipitating with the whole of the oxide 
 of silver as the insoluble salt, I.07-}-2Ag.O., while 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 temperature 
 
HYDRIODIC ACID, ITS PREPARATION. ^±0 
 
 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, =15795 or 126-6 
 
 Oxygen, 30 -69 Seven equivalents, = 700-0 or 56 
 
 100 00 "2279^ 182^6 
 
 Compound of Iodine and Hydrogen. Hydriodic Acid. 
 
 There is but one compound of iodine with hydrogen : this exists 
 under ordinary temperatures and pressure 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 ^^^^~a\ 
 glass, it filters through to the bottom, and there, 
 acting violently on the iodide of phosphorus, is 
 decomposed j 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 issu- 
 ing from it may be collected. This gas is obtain- Jn 
 ed by the method of displacement, as has been 
 described for chlorine (p. 302) ; and as it fumes 
 like muriatic acid in contact with the air, it can 
 easily be recognised when the bottle is full. ^ 
 
 The specific gravity of this gas is 4385, produced by 
 
 One volume of vapour of iodine =87010 
 
 One volume of hydrogen = 68 8 
 
 united without condensation 8769-8 
 
 and one volume weighing, therefore 4384 9 
 
 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 pro- 
 duced ; 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 126-6 
 
 Hydrogen, 0-78 One equivalent, = 12-5 or 1-0 
 
 100-00 Y592^0 l27^ 
 
316 lODO-PH O SPHURE T OF HYDROGEN. 
 
 A solution of hydriodic acid or of a metal produces, with nitrate 
 of silver, a curdy pale yellow precipitate, which is insoluble in acids 
 and in water of ammonia j by this character the iodides are distin- 
 guished from the chlorides, even without the aotion 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 phosphorus, 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, hy- 
 driodic and hypophosphorous acids ; its composition is therefore P.I. : the second is 
 gray ; it fuses at 84°, and gives, with water, hydriodic and phosphorous acids ; its 
 formula is hence P.I3. The third, which produces, when decomposed by water, 
 hydriodic acid and phosphoric acid, consists of P.I5, is black, and melts at 114^. 
 
 Hydriodic acid combines with phosphuretted hydrogen, forming a white sohd 
 compound, the constitution of which is of considerable interest. It cannot be pre- 
 pared 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 phos- 
 phorus, 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 hypophosphorous acid are produced, which last is re- 
 solved, by contact with the water at that temperature, into phosphorous acid and 
 phosphuretted hydrogen. 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 hy- 
 driodate of ammonia, to which this formula, in one way, might assimilate it, 
 H.I.-f-P-Hg corresponding to H.I.-j-N.Hg, 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, N.Hg, but that it con- 
 tains amidogene (N.H2), being amidide of hydrogen, Ad.H. It has been also shown 
 that the crystals of the body H.I.-j-PHg are not cubes, but belong 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 hydrogen may, with great reason, be 
 supposed to be, not P.H3, but that a quantity of phosphorus equal to one third of 
 its ordinary atomic weight unites with an equivalent of hydrogen, its formula being 
 3.H., and the commonly received equivalent of phosphuretted hydrogen being in 
 reality three equivalents, =3.?.H. I therefore consider the compound which I have 
 just described as having for its true constitution H.I.-[-3-.H., as there will be here- 
 after described the bodies Hg.Cl.-|-3.|.,Hg., and 2Hg.Cl.-{-3.j.Hg. : the equiva- 
 lent of nitrogen being capable of the same subdivision by three. 
 
 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 spontane- 
 ously inflammable condition. It burns when heated in air, but, in a dry tube con- 
 taining no oxygen, it may be sublimed from place to place unaltered. 
 
 Chlorides of Iodine. — I have shown that chlorine and iodine unite in three pro- 
 portions, forming bodies having the formulae I.-fCl., I.-}-3Cl., and I.-f 5C1. By 
 much water the first and second are decomposed, 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 psriodic 
 acids, as already noticed. 
 
PROPERTIES OF BROMINE. 317 
 
 Of Bromine. 
 
 This substance, which is intermediate in almost all chemical prop- 
 erties 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 deposites 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 cur- 
 rent 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 produced ; when this is acted on by pot- 
 ash, there is formed 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 preparation of chlorine or of 
 iodine, the bromine is set free and may be distilled over. It is ne- 
 cessary 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 2S.O3, Mn.02, and K.Br, produce (S.O3 . Mn.O+K.O. . S.O3) 
 and Br. 
 
 Bromine is a liquid at ordinary temperatures, but at 4° it solidi- 
 fies ; it is deep red by transmitted, but black by reflected light ; it is 
 much heavier than water, its specific gravity being 2-97 ] its odour 
 is like that of chlorine, but much more disagreeable, whence its 
 name (from BpWjUOf). 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 grav 
 ity 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 spa- 
 ringly in water, but copiously in alcohol and ether. A taper is ex- 
 tinguished 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 5 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. 
 
 With 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 hyponitrous acid, from which its other characters completely 
 separate it. A solution containing bromine or a metallic bromide 
 gives, Avith nitrate of silver, a white, curdy precipitate, insoluble in 
 nitric acid, but dissolved by ammonia. This precipitate is distin- 
 guished from the chloride of silver by giving vapours of bromine 
 when heated with a little chlorine water 
 
318 B R O M I C A C I D. H YDROBROMIC ACID. 
 
 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 im- 
 perfect. When bromine is dissolved in a solution of potash, bro- 
 mide of potassium and bromate of potash are formed, 6Br. and 
 6K.0. giving 5K.Br. and Br.O^+K.O. On adding a solution of a 
 salt of barytes to the liquor so obtained, bromate of barytes is pre- 
 cipitated, 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 j it is still more 
 easily decomposed by deoxidizing agents than the chloric acid \ thus 
 the sulphurous 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 Br.05, its composition by weight and equivalent 
 numbers being, 
 
 Bromine, 66-18 One equivalent, =978-2 or 78-40 
 
 Oxygen, 33-82 Five equivalents, ^500-0 or 40-00 
 
 100^0 1478-2 11840 
 
 These elements are united by volume in the ratio of two vol- 
 umes of bromine-vapour to five volumes of oxygen. 
 
 Hydrobromic Acid. — The processes for obtaining the bromide of 
 hydrogen 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. 315), bromine being substituted for iodine in 
 every case. This gas is colourless ; it is rapidly absorbed by wa 
 ter, the solution reacting acid ; it is not decomposed by oxygen, 
 nor does bromine decompose 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 po- 
 tassium be acted on by oil of vitriol, the result is partly as occurs 
 with a chloride, water being decomposed and hydrobromic acid 
 evolved, and partly as occurs with an iodide, bromine and sulphur- 
 ous 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 . . . 53930 
 
 One volume of hydrogen 68 8 
 
 united without condensation .... 5461 8 
 and hence one volume weighs .... 2730-9 
 
 The Bromide of Sulphur is a heavy reddish liquid, like chloride of sulphur, prob- 
 ably SaBr. 
 
 There are two Bromides of Phosphorus, one liquid, P.Brn, and the other solid, 
 P.Brs, which present complete analogy with the chlorides of phosphorus. Neither 
 of these bodies presents particular interest. 
 
 The bromide of hydrogen unites with phosphuretted hydrogen, forming a com- 
 pound similar to that already noticed, containing hydriodic acid. It is sufficient to 
 mix the two gases together over mercury ; a dense white cloud forms, which con- 
 denses on the sides of the glass in small crystals, which appear to be cubes, but are 
 
OF FLUORINE. 319 
 
 not so really. This substance can also be formed in the indirect manner described 
 for the iodine compound. It consists of an equivzdent of each element, its for- 
 mula being H.Br.-j-P.Hg, or, as I prefer to write it, for the reasons already stated, 
 H.Br.-f3|.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 decom- 
 
 The Chloride of Bromine and the Bromides of Iodine resemble in general charac 
 ters the compounds of chlorine and iodine. The first, when decomposed by water^ 
 produces hydrochloric and bromic acids ; the latter, on the contrary, gives hydro- 
 bromic and iodic acids. These bodies are not otherwise of interest. 
 
 Of Fluorine. 
 
 Although the existence of this body is rendered exceedingly prob- 
 able by analogical reasoning, and recent experiments have gone 
 very far in establishing its distinctive characters, yet it cannot 
 be prepared in an isolated form, or exhibited like all 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 enters 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 substances on which fluorine is incapable of acting be- 
 ing such as already are fully saturated with it, Messrs. Knox had 
 vessels constructed of fluor spar (fluoride of calcium), which were 
 filled with pure dry chlorine gas. Into these vessels was then in- 
 troduced 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 CI. giving 
 Hg.Cl. 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 arrangement 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, as it was liberated, it might have 
 combined with the excess of chlorine present, and that the colour- 
 less gas may have been chloride of fluorine, and not the mere fluo 
 rine itself. 
 
 The specific gravity of gaseous fluorine, calculated from the 
 analogy of its compounds to those of chlorine, is 1289 3 its equivalent 
 number is 233-8, or 18.7. 
 
 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 cool by ice. An acid liquor distils over, of an excessively suf- 
 focating odour, and so intensely corrosive, that a drop let fall upon 
 the hand produces a sore very difficult to heal. This liquid is hy- 
 drofluoric acid, the reaction be ng that H.O. .S.O3 and Ca.F. give 
 Ca.O. . S.O3 and H.F. Sulphate f lime remains in the retort. 
 
320 HYDROFLUORIC ACID. 
 
 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 formation 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 gener- 
 ally 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 decomposes, Si.Og and 3H.F. producing 
 3H.0. and Si.Fg. This fluoride of silicon is a gas, decomposed by 
 water in a way that will 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 con- 
 ducted: 1st, by the liquid acid j 2d, by the acid in vapour. For the 
 first, the glass plate being covered with a uniform coating 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 through- 
 out 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 engraving required, is poured on 
 the plate to the depth of two or three lines, and left for a time de- 
 pendant on the judgment of the operator. When it has remained 
 long enough, the remaining acid is poured ofl*, 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 cer- 
 tain incidences of the light. A glass plate so prepared may be used 
 as 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 
 ah 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 ao gently as not to melt the wax or injure the accuracy of 
 the design 3 the hydrofluoric acid, which rises in vapour, acts upon 
 the surface of glass 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, will 
 be described hereafter. 
 
 The composition and equivalent numbers of the hydrofluoric acid 
 ire as follows: 
 
OF SILICON. 321 
 
 Fluorine, 94-93 One equivalent, =233-8 or 18-7 
 
 Hydrogen, 5-07 One equivalent, = 12-5 or 1-0 
 
 'lOO^O 246-3 l9^ 
 
 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 decomposed by water, produces hydrofluoric acid 
 and phosphorous acid ; it is, therefore, P.F3. When heated in the air, it bums, but 
 the product of the combustion has not been examined. 
 
 Of Silicon. 
 
 This substance is one of the most extensively distributed of the 
 undecomposed 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 Vith various metallic 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 j 
 even by ignition with potassium it is but imperfectly decomposed. 
 To prepare silicon, therefore, a somewhat complex body is selected 
 to be acted on, the double fluoride of silicon and potassium (2Si.Fj 
 4-3K.F.), 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 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, through- 
 out the entire mass ; when cool, the residual 
 brown matter is to be washed carefully with wa- 
 ter : fluoride of potassium dissolves, and the silicon remains behind j 
 the 2Si.F3+ 3K.F., acted on by 6K., give 9K.F. and 2Si. To have the 
 silicon quite pure, numerous precautions are necessary, which need 
 not be detailed here. 
 
 The silicon so obta:ined is a dull brown powder, which when 
 heated in air or in oxygen, takes fire and burns, forming silicic 
 acid. If it be ignited in a closely covered vessel, it shrinks in vol- 
 ume, increases very much in density, and becomes insoluble in 
 acids or alkalies, Avhich, 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 chlo- 
 rine, combining with these bodies. When ignited with carbonate 
 of potash, the silicon burns brilliantly, setting carbon free, and form- 
 ing, with the oxygen of the carbonic acid, silicic acid, which com- 
 bines with the potash. The equivalent number of silicon is 277-31 
 or 22-22, according as the oxygen or the hydrogen standard may be 
 adopted. 
 
 S s 
 
322 SILICIC ACID. 
 
 Silicic Jlcid. 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 sys- 
 tem 5 their ordinary form is represented in the mar- 
 gin. It is exceedingly hard, and, in order to be re- 
 duced to powder, requires to be heated first to red- 
 ness, and then thrown into a large mass of cold water. 
 The piece of quartz cracks in every direction by be- 
 ing 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 carbonate of soda, and ad- 
 ding thereto powdered flint, by small quantities at a 
 time ; the silica dissolves in the melted alkali, while carbonic acid 
 gas is given off. When the alkaline silicates, so formed, are dis- 
 solved in water, and a stronger acid added, the silicic acid is pre- 
 cipitated 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 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 j it is 
 fusible only by the oxyhydrogen blowpipe, in the flame of which 
 it melts into a colourless glass ; when once dried it is totally in- 
 soluble in water, but in its gelatinous form it is soluble to a small ex- 
 tent ; hence many mineral waters contain silica, which, being grad- 
 ually precipitated in the substance of decomposed organic matter, 
 produces the silicious petrifactions in which the most delicate vege- 
 table 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 lit- 
 tle affinity. When a dilute alkaline 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 in- 
 soluble condition, and remains behind when the saline constituent 
 is dissolved. On the other hand, by the presence of an alkali, the 
 insoluble silica is made to assume the soluble state. 
 
 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 one, having the formula 2Si.03 + H.O., as being certain ; 
 I have found the light spongy masses of silica deposited from vol- 
 canic springs, and on the edges of volcanic craters from Iceland and 
 Tenerifl^e, to have accurately that constitution. 
 
 It is probable that a great deal of the silica which exists in nature 
 has been originally deposited in the soluble condition. The struc 
 ture of the agates, chalcedony, and many other minerals, proves 
 that they Avere formed by a solution of silica having penetrated 
 
CHLORIDE OP SILICON. 
 
 323 
 
 into a cavity in the surrounding rock, and having then gradually- 
 dried down or crystallized. It is even pretty certain that the crys- 
 tallized quartz is also of this aqueous origin. 
 
 In the arts, silica is of exceeding importance, being an essential 
 constituent of glass, porcelain, and every kind of delft and earthen- 
 ware. 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 as fol- 
 lows, its formula being Si.Og. 
 
 Silicon, 48-04 One equivalent, =277-3 or 22-22 
 
 Oxyge n, 51-96 Three equivalents, =3000 or 24-00 
 
 100-00 5773 46-22 
 
 Silicon does not combine with hydrogen nor with nitrogen : there 
 exists a sulphuret of silicon, which is probably Si.Sg, as when acted 
 on by water it produces soluble silica and sulphuretted hydrogen. 
 
 Chloride of Silicon. — This substance, Eilthough not itself important, is yet inter- 
 esting 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 at 
 
 tached at h, a current of dry chlorine be made to stream over the ignited mixture, 
 decomposition ensues, the oxygen of the silica combining with the carbon to form 
 carbonic oxide gas, while the chlorine and sihcon unite, producing the chloride of 
 sihcon, which, being a very volatile liquid, requires to be carefully condensed ; for 
 this purpose, the tube c / is wrapped up in a cloth, or a paper kept constantly wetted 
 by a stream of water from the reservoir e, and the liquid produced then collects 
 
 in the bottle /, while the oxide 
 of carbon and the excess of 
 chlorine pass off by the tube 
 m. In this process the reac- 
 tion is such, that 3C1. acting 
 on Si.Og and 3C., give rise to 
 3C.0. and Si.Cls- 
 
 The stream of dry chlorine 
 may be very conveniently ob- 
 tained by the apparatus here 
 figured ; the muriatic acid and 
 peroxide of manganese are 
 placed in the flask a, arid the 
 gas evolved, depositing the ac- 
 companying liquid in the re- 
 ceiver b, passes through the 
 tube c, which, being filled with 
 
324 
 
 FLUORIDE OF SILICON. 
 
 fragments of recently-fused chloride of calcium, absorbs all the watery vapoui 
 The gas issues dry from the extremity, where it is connected with the end b 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 siUca and hydrochloric acid, from whence 
 its formula must be Si.Cls. 
 
 Fluoride of Silicon. — This is the most remarkable compound of 
 silicon after silicic acid j 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 
 maybe explained in either way. Thus the oxygen of the silica may 
 combine with the calcium, forming lime, and this with the sulphuric 
 acid, while the silicon unites with the fluorine of the fluor spar. Or, 
 water being decomposed, hydrofluoric acid and lime may be first 
 produced, and the former, reacting on the silica, may reproduce wa- 
 ter, and form fluoride of silicon. I prefer to omit here, as I did 
 when describing the formation of chlorine, all the unnecessary the- 
 oretic agency of the water, and to express the decomposition as 
 3(S.03 . H.O.) with Si.Oa and 3(Ca.F.) give SrS.Og . Ca.O. . H.O.) and 
 Si;F3. 
 
 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 
 
 Si.Fg. 
 
 Silicon, 28-32 One equivalent, =277-3 or 22-22 
 
 Fluorine, 71-68 Three equivalents, =701-4 or ,56-22 
 
 lOCHOO 978^7 78^4" 
 
 The hydrofluosilicic acid, or the double fluoride of hydrogen and 
 silicon, cannot be obtained free from water, but its solution is of 
 considerable importance as a chemical reagent, and hence its prep- 
 aration 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 
 siphon funnel /, the oil of vitriol is then 
 poured in, and the gas evolved is conduct- 
 ed by the tube to the water in the ves- 
 sel d e. If the tube opened into the wa- 
 ter directly, so much silica would be de- 
 posited at its orifice as to stop it up every 
 moment; and hence a quantity of mer- 
 cury, e, is placed at the bottom, and the 
 end of the tube dips into it. The gas bub- 
 ble, therefore, does not touch the water 
 until completely separated from the tube : 
 it escapes from the surface of the mercu- 
 ry, and then it becomes invested with a 
 
OF BORON. 325 
 
 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 con- 
 tinued until the water becomes thick from the quantity of silica sep- 
 arated j 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 silicon to form the hydrofluosilicic acid, the formula of which is 
 2(Si.F3)-f3H.F. 
 
 When a solution of this acid is heated, fluoride of silicon is given 
 ofl*, and hydrofluoric acid remains. Hence, although the hydrofluo- 
 silicic 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, 
 compounds, Jluosilicates, 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 transpa- 
 rent that it can be recognised 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 formula 2Si.F3-f3K.F. 
 
 The composition of hydrofluosilicic acid is easily known from that 
 of the hydrofluoric acid and fluoride of silicon. Its equivalent num- 
 ber is 2696-4. or 216-2. 
 
 Of Boron. 
 
 The history of this substance presents a very close analogy with 
 that of silicon. It was first obtained by decomposing boracic acid by 
 galvanism, but is best prepared by acting on the fluoborate of pot- 
 ash 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 electri- 
 city. It is insoluble in water and all other neutral fluids. When 
 heated to 600^ in the air or oxygen, it takes fire, and burning, forms 
 boracic acid ; the same eflect 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 imperfect way, was brought into commerce under the name 
 of tinkal, or crude borax. The boracic acid is also found, and in 
 much larger quantity, 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 these 
 
326 BORACIC ACI D. C HLORIDE OF BORON. 
 
 lakes is evaporated, and the boracic acid being crystallized, is im- 
 ported into these countries for the manufacture of borax (borate of 
 soda) and other salts. 
 
 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 crystallization is necessary 
 to have it pure. 
 
 The crystals of boracic acid, so prepared, contain 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 5 when completely dry it is fixed, but in the presence of wa- 
 ter it is carried ofi' 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 212^ for their solution. Alcohol dissolves boracic acid 
 copiously ; and the solution, when set on fire, burns with a beauti- 
 ful 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 alkaline reaction, and all are decomposed by 
 the weakest acids. It does not redden litmus, but gives it a port- 
 wine colour, and a strong solution of it browns turmeric paper like 
 an alkali. At high temperatures, however, boracic acid may decom- 
 pose the salts of the nitric, or even of the sulphuric acids, from the 
 principles that have been already explained in the chapter on Affin- 
 ity (p. 169). 
 
 The composition and equivalent numbers of boracic acid are as 
 follows, its formula being B.O3 : 
 
 Boron, 31-22 One equivalent, ==136 2 or 10-9 
 
 Oxygen, 6878 Three equivalents, = 300*0 or 24-0 
 
 lOO^O 436^ 34^ 
 
 Boron does not combine with hydrogen or nitrogen j its com- 
 pounds with sulphur and selenium are not important. 
 
 Chloride of Boron. — Boron burns spontaneously in chlorine gas, but the best way 
 to prepare the compound of chlorine and boron is to proceed as described for ma- 
 king 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 exhaled. The chloride of boron is 
 rapidly absorbed and decomposed by water ; its specific gravity is 4079 ; it contains 
 1^ times its volume of chlorine ; its formula is B.CI3. 
 
 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 
 
GENERAL CHARACTERS OF THE METALS. 327 
 
 water, and generating hydrofiuoboric acid, which is perfectly anal- 
 ogous to the hydrofluosilicic acid. It hence forms dense white 
 fumes when mixed with damp air. Its specific gravity is 2362. 
 
 The hydrofiuoboric 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 li- 
 quor be evaporated 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 con- 
 stitution, its formula being 2(B.F3)-f-3H.F. 
 
 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 entering upon it until 
 after the description of the metals and their salts, and other compounds with the 
 non-metallic bodies. I will then commence 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 
 among 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 will consequently be 
 found. The hypothetical compounds of nitrogen and hydrogen (amidogene and am- 
 monium) will be associated with it. 
 
 The substances hitherto described as chloride and iodide of nitrogen having been 
 found to contain hydrogen, and to range themselves in an important series of or- 
 ^ ganic combinations, have not been noticed in the chapter now closed, but will be 
 ' '' found in their true position hereafter. 
 
 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 con- 
 sidered as forming a class of bodies, united by such analogies of 
 chemical properties and laws of combination as would constitute a 
 natural family, yet in their physical characters, and the most prom- 
 inent facts of their technical history, they have so much in common 
 as to render a notice of the conditions in which they exist in na- 
 ture, the methods by which they are extracted upon the large scale, 
 and the physical and chemical properties by which they are distin- 
 guished as a great division of the elementary bodies, necessary, be 
 fore proceeding to the detailed history of the individual metals. 
 
 The metals are forty-two in number ; their names have been al- 
 ready given in more than one place (p. 150 and 189). They reflect 
 light powerfully, and hence possess what is termed metallic lustre. 
 If the incident light be plane polarized, it undergoes a remarkable 
 change, produced only by the metals and by diamond, becoming 
 elliptically polarized on reflection. The metals are characterized 
 very completely by their power of conducting heat and electricity, 
 in which, although they differ among each other, yet the worst 
 excels all non-metallic bodies. Lists of their relative eonducting 
 
328 GENERAL CHARACTERS OF THE METALS. 
 
 powers in these respects have been already given (p. 92, 109, and 
 137). By the combination of these characters, the histre and con- 
 ducting- power, the metallic or non-metallic nature of a body is al- 
 ways determined. 
 
 In the other properties of the metals there is found remarkable 
 diversity j thus in colour, although silver is purely white, the major- 
 ity of the metals are of various shades of bluish-white or gray, 
 while copper and titanium are reddish coloured, and gold is yellow. 
 In specific gravity, 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 of potassium only -^^ that of water. 
 
 Some of the most important applications of the. metals in the arts 
 depend on their malleability and ductility. Those metals are malle- 
 able which admit of being rolled or beaten out into thin leaves ; 
 tho§e being ductile which can be drawn into wire. Gold is the 
 most malleable of metals ; gold leaf may be obtained of -j^-^- of 
 an inch in thickness, and is hence the only metal in which any trace 
 of transparency has been found j 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 j platinum wire was made by Wollaston of 3 q^^^ o ^^^^ diame- 
 ter ; but a met^l 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 con- 
 ditions, depends closely upon temperature. Thus zinc is malleable 
 and ductile at 300^ ; it loses this power, but remains tough, at GO"', 
 while at 600^ it becomes so brittle that it powders as easily as bis- 
 muth. In the drawing of lead pipe, and in making most of the me- 
 tallic wires, there is a peculiar temperature required 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 strong- 
 est metal ; 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 about one half so strong j then platinum, silver, and gold : 
 tin and lead are the weakest of the metals. The tenacity depends 
 also on the molecular 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 t 
 but one metal is liquid at ordinary temperatures. All the metal? 
 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 manv metals 
 as platinum, are infusible in the most intense heat of a blast furnace 
 and yield only to the flame of the oxyhydrogen blowpipe. 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 
 furnaces ; but mercury, zinc, cadmium, arsenic, tellurium, potassium, 
 and sodium may be volatilized. 
 
CLASSIFICATION OF THE METALS. 
 
 329 
 
 The generality of metals, when exposed to the air, particularly 
 when damp, absorb oxygen and form oxides j some becoming mere- 
 ly 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 pret- 
 tiest lecture experiments. Mercury also, which does not tarnish 
 when exposed to oxygen at common temperatures, becomes oxi- 
 dized when heated to near its boiling point, but the oxide is resolv- 
 ed again at a red heat into oxygen and metallic mercury. 
 
 It is owing to their affinity for oxygen that many of the metals 
 decompose 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 pro- 
 ceeds. Thus, 
 Potassium, 
 
 Sodium, 
 
 liithium, 
 
 Barium, 
 
 Strontium, 
 
 Calcium, 
 
 Magnesium, 
 
 Aluminum, 
 
 Glucinum, 
 
 Thorium, 
 
 Yttrium, 
 
 Zirconium, 
 
 Lanthanum, 
 
 Cerium, 
 
 Manganese, 
 
 Iron, 
 
 Nickel, 
 
 Cobalt, 
 
 Zinc, 
 
 Cadmium, 
 
 Tin, 
 
 Chromium, 
 
 Vanadium, 
 
 Tungsten, 
 
 Molybdenum, 
 
 Osmium, 
 
 Columbium, 
 
 Titanium, 
 
 Arsenic, 
 
 Antimony, 
 
 Tellurium, 
 
 I Uranium, 
 Copper, 
 Lead, 
 Bismuth, 
 Silver, 
 Mercury, 
 Gold, 
 
 Palladium, 
 Platinum, 
 Rhodium, 
 Iridium, 
 
 . The first class consists of metals which decompose water with 
 ^lively effervescence, even at 32°. 
 
 The second class consists of metals which do not decompose watei 
 >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 decompose vapour of 
 > water energetically at a red heat, but which do not decompose it at 
 common temperature, even in contact with strong acids. 
 
 "v The fifth class consists of metals which decompose water at a red 
 Vheat but very feebly, but whose oxides are not reducible to the me- 
 J tallic state by heat alone. 
 
 The sixth class consists of metals whose oxides are decomposea 
 > alone at a high temperature, and which do not decompose water 
 under any circumstances. 
 
 Tt 
 
\ 
 
 330 CLASSIFICATION OF THE METALS. 
 
 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 
 popular considerations, is yet so far consonant with the simplest 
 characters 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 
 noble 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 j and of their oxides, only 
 potash, soda, barytes, lime, magnesia, and alumina were known. 
 From the old name of potash, Kali^ with the Arabic prefix a/, potash 
 and soda, at one time confounded together, were termed alkalies^ 
 and ammonia, resembling them very much when dissolved in water 
 or combined with acids, was also called an alkali ; it was the vol- 
 atile alkali, potash and soda being fixed alkalies ; it was also termed 
 the animal alkali, while soda was the mineral alkali, being derived 
 from rock-salt or from the ocean ; and potash received the name of 
 the vegetable alkali, from its source being the ashes of plants grow- 
 ing upon land. The alkalies are characterized by being very soluble 
 in water, and by neutralizing the strongest acids. They hence re- 
 store 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 alkali, 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 alkaline earths ; they are 
 soluble in water, but much less so than the alkalies ; these solutions 
 brown turmeric paper, and neutralize acids ; but they are complete- 
 ly distinguished from the alkalies by their combinations with car- 
 bonic acid, which are insoluble in water, while the alkaline carbon- 
 ates are very soluble in that liquid. These phrases of alkalies and 
 earths are of constant recurrence in descriptions of chemical pro- 
 cesses and results, and are thus seen to be founded on, and express- 
 ive of, some of the most important characters in those bodies. 
 
 Most of the metals combine with oxygen in more than one pro- 
 portion, and the characters of the oxides are found to be regulated 
 in a great degree by their composition. All protoxides (R.O.) (R. 
 representing an equivalent of any metal) appear capable of combi- 
 ning with acids to form neutral salts ; they constitute, properly, the 
 metallic basis, but in many cases suboxides, (RaO*)? such as those 
 of copper and mercury, form well-characterized salts, and sesqui- 
 oxides, (R2O3), as those of iron, manganese, aluminum, and chrome, 
 produce well-defined classes of salts also, which, however, in solu- 
 tion always possess an acid reaction. Peroxides, (R.O^), as those 
 
AFFINITY OF METALS FOR CHLORINE, ETC. 331 
 
 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, Mn.Og, and the chro- 
 mic acid (Cr.Og). 
 
 The different oxides of the same metal frequently unite with each 
 other, producing compounds wWch 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 require 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 gener- 
 ally, after the oxides, the most important metallic compounds. 
 Towards iodine, bromine, and fluorine, the metals are related near- 
 ly 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 of those of chlorine. 
 
 The compounds of sulphur with the metals constitute a very ex- 
 tensive and important series, which, as has been more fully noticed 
 in p. 284, resembles in a very striking manner the series of oxides 
 of the same metal. Many metals, at a high temperature, combine 
 with sulphur with brilliant combustion ; and even at common tem- 
 peratures, 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 
 some conditions as in forming sulphurets, but the history of those 
 compounds is not nearly so complete. As yet but very little has 
 been done towards the history of the compounds of the metals with 
 nitrogen, silicium, or boron. 
 
 Some of the metals, 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 ele- 
 ment, the metal playing the part of the sulphur or of oxygen. 
 
 The circumstances under 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 oth- 
 ers. Many exist combined with arsenic, the sources of cobalt and 
 nickel being almost exclusively their native arseniurets. Some me- 
 tallic chlorides and iodides exist also native, but the most abundant 
 forms in which the metals are to be found are combinations with 
 
332 GENERAL PRINCIPLES OF THE 
 
 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 com- 
 bined with acids, forming salts. Thus lead, copper, iron, zinc, tin, 
 manganese, antimony, are all found in abundance 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 importance 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 be mineralized by the substance with which it is united. 
 
 The processes followed in the extraction of the metals must be, of 
 course, regulated by the composition of the ores in which it is con- 
 tained ; and as it will save the necessity of frequent repetition here- 
 after, 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 improper. 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. 
 
 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 with the oxygen, and the metal is set free. It is not often that 
 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 deoxidizing action of the ignited fuel. Thus the native car- 
 bonates of lead, of copper, of zinc, and especially of iron, are simply 
 reduced in this way: the last mentioned is the ore which consti- 
 tutes the great iron deposite of the neighbourhood of Glasgow. 
 
 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 arseniurets 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 car- 
 bon, for the oxygen of the acid and base being simultaneously re- 
 moved 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, S.Og-l-Pb.O. and4C. giving S.+Pb 
 and 4C.0. 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 anti- 
 mony is very generally obtained by the fusion of the native sulphu- 
 ret with iron j SbaSg and 3Fe. giving 3Fe.S. and Sb^. On the large 
 
REDUCTION OF THE METALS. 
 
 333 
 
 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 converted into sulphurous and sulphuric acid, 
 while the metal is oxidized. This process is tQTvaeA calcination. A 
 great part of the sulphuric acid formed is carried off with the cur- 
 rent 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 ox 
 ygen, 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 com- 
 mences, and this is effected by mixing up a proper quantity of lime 
 with the calcined mass. The lime decomposes the metallic sulphate, 
 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, while the sul- 
 phate of lime, by losing its oxygen, is brought to the state of sul- 
 phuret of calcium, and remains as glassy scoria upon the surface 
 without injury. This kind of operation is generally carried on in a 
 sort of furnace termed reverberatory, from its office of beating down 
 the flames from the fireplace upon the materials strewed upon itp, 
 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 apply, a is the fireplace, and 
 b the ash-pit ; at c a low wall is rais- 
 ed, termed the bridge, and the flames 
 and heated air ascending from the 
 fire are reflected downward by the 
 low, vaulted roof, and, impinging up- 
 on the hearth, or sole of the furnace, 
 d, produce the greatest heating ef- 
 fect 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 cond* 
 cive to the success of the operation 
 regulates the draught, and hence the intensity of the fire. 
 
 In this furnace, the calcining or oxidizing, and the reducing op 
 deoxidizing effect is produced, according as the supply of fuel and 
 of air is regulated ; and thus the two stages just described, in the 
 extraction 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 opera- 
 tion is concluded. 
 
 In the case of sulphuret of lead, a very simple and beautiful pro 
 
 The damper, p, in the fluw, 
 
334 GENERAL PRINCIPLES OF THE 
 
 cess of reduction consists in roasting the ore at a moderate temper- 
 ature, so that about one half of it shall be converted into sulphate 
 of lead by oxidizement, without any of the sulphuric acid being driv- 
 en offj and then, having mixed this up well with the unaltered por- 
 tion 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 com- 
 bining with the sulphur and oxygen of that portion which had been 
 oxidized. Thus S.Oa+Pb.O. and S.+Pb. produce exactly 2S.O2 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 of greater or less purity, 
 combined with alumina and silica. Now, as carbon cannot deprive 
 silica of oxygen except under very peculiar circumstances, such as 
 those described in page 323, so the metal cannot be obtained by 
 mere deoxidation ; and even if the oxygen were removed, the result 
 would not be pure iron, but a compound of silicon and iron, which, 
 indeed, is formed in small quantity, and is found generally in cast 
 iron. It is necesifeary, therefore, to decompose the silicate of iron 
 of which the ore is constituted, 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 set 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 being melted together, form a substance of 
 a nature somewhat between glass and porcelain, which floats upon 
 the mass of melted metal, and constitutes the slags or scorise of the 
 iron furnaces. 
 
 In the case of ores containing arsenic, of which only the arseniu- 
 rets of cobalt and nickel are of technical importance, the method 
 followed is to roast the ore in a furnace so constructed that a pow- 
 erful oxidizing action shall be produced by a current of air stream- 
 ing over the ignited ore 5 both metals being thus oxidized, arsenious 
 acid, and oxide of cobalt or of nickel are produced ; the greater 
 part of the former 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 re- 
 mains 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 fa- 
 miliarly termed black flux. The theory of this process is very sim* 
 pie. 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, Sb2S3 and 3Ca.O. giving 
 SCa.S. and SbjOs. This last is then decomposed by the charcoal, 
 the oxygen combining with the carbon, and the metallic antimony 
 separates. 
 
REDUCTION OF THE METALS. 335 
 
 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 remains 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 used in 
 processes where the deoxidizing effect of the carbon is not required. 
 Thus, for the reduction 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 j the formula of the reaction 
 being that K.O. . C.O^ and Gl.Ag. give K.Ch and free Ag., while O. 
 and C.O2 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 va- 
 rieties of metallic combinations, whether oxides, chlorides, or sul- 
 phurets ; and that the results it gives are so accurate as to serve as 
 bases 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 investigations, the isolation of a metal, by decom- 
 posing its chloride or sulphuret in a stream of hydrogen gas, is 
 frequently employed. The deoxidizing action of hydrogen is oc- 
 casionally used in an indirect manner. 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, while 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 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 holds sulphate of copper dissolved, by dipping therein pieces 
 of iron, and, indeed, all cases of the precipitation of one metal by 
 another, are referrible to the same source. 
 
 The physical agent, electricity, which has been already found to 
 influence chemical action to so remarkable a degree, has been em- 
 ployed with considerable success in the reduction of certain met- 
 als. It was first applied by Davy, who thereby made his wonderful 
 discoveries of the composition of the alkalies 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. 
 
 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. 
 
336 POTASSIUM. 
 
 CHAPTER XIII. 
 
 OF THE INDIVIDITAL METALS, AND OF THEIR COMPOUNDS WITH OXVGEN, 
 SULPHUR, SELENIUM, AND PHOSPHORUS. 
 
 SECTION I. 
 METALS OF THE FIRST CLASS. 
 
 Of Potassium. 
 
 Potassium is the metallic basis of the alkali potash. It was ongi 
 nally discovered by Sir Humphrey Davy, who obtained it by sub- 
 mitting a piece of caustic potash, slightly moistened, so as to be a 
 conductor of electricity, to the action of a powerful galvanic bat- 
 tery J the water and the potash were simultaneously decomposed, 
 oxygen being evolved at the positive electrode, while hydrogen and 
 potassium were separated at the negative wire. From the heat 
 generated by the intense power used, the metallic globules gener- 
 ally burned as soon as they came into contact 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 de- 
 composition can be effected by a much weaker force, and even 
 with a single pair of plates, as in the arrangement of Dr. Bird, de- 
 scribed in p. 199. 
 
 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 
 carbonate of potash mixed wdth carbon in a state of very minute 
 division, and this mass is to be intimately mixed, while still hot, 
 with a quantity of coarsely-powdered wood charcoal, which serves 
 to render the w^hole porous, so as to allow of the escape of the 
 gases generated in its interior without its swelling up. The mate- 
 rial 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, while 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 re- 
 ceiver 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 
 
PREPARATION AND PROPERTIES OF POTASSIUM. 337 
 
 in globules, which are protected by the naptha, in which they sink, 
 while the oxygen of the potash and of the carbonic acid combines 
 with carbon, forming carbonic acid, which, escaping under the par- 
 titions in the receiver, passes away j K.O.-I-C.O2 and 2C. producing 
 K. and 3C.0. The great difficulty and loss in this process arise, 
 however, from a cause which is not at first apparent ; it is, that 
 carbonic oxide and potassium unite to form a dark gray mass, 
 which sublimes, and, condensing in the short iron tube, renders the 
 screw necessary to keep the passage clear, and frequently causes 
 the failure of the process. Even in the most successful results, 
 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 J 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 in 
 stantly becomes gray when exposed to the air, owing to the absorp- 
 tion 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 decomposes water, and even ice, with great vio- 
 lence, 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. 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 re- 
 port, and instantly then dissolves. 
 
 Potassium is remarkably characterized by its great affinity for ox- 
 ygen, which it abstracts from almost all bodies ; thus its use in the 
 preparation of boron and silicon has been already noticed ; and al- 
 though, 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 
 ^rom the one, and metallic iron separated from the other. 
 
 The symbol of potassium is K., the initial of the word Kalium, 
 6y which the metal is designated by most of the Continental chem- 
 ists; the old name kali being still retained in preference to the word 
 notash, which has been adopted only in Great Britain and in France. 
 the equivalent is 490 or 39-3, according to the scale. 
 
 Oxides of Potassium. — Potassium combines with oxyo-en in two 
 proportions, forming a protoxide K.O., and a peroxide K O3. 
 
 The protoxide of potassium constitutes the important alkali pou 
 ash ; A\ can only be obtained free from water by exposing potassium 
 
 U u 
 
338 PREPARATION AND PROPERTIES OF POTASH. 
 
 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 sub- 
 stance 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 ot 
 potash; the dry potash, in uniting with water, becomes ignited. 
 Before the discovery of carbonic acid, the alkalies and their carbon- 
 ates were distinguished from each other by the epithets of mild 
 and caustic, and hence for medicinal purposes, and in some phar 
 macoposias, 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 slacked 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 shows that all the alkaline carbonate has been decom- 
 posed, the pan is to be removed, and being laid aside, carefully cov- 
 ered, until the carbonate of lime has been well settled, the clear li- 
 quor may be siphoned off. The decomposition of the carbonate of 
 potash by the lime would take place also at ordinary temperatures, 
 but the precipitate would be in the rhombohedral form, and being 
 specifically lighter and more finely divided, would occupy much 
 more room, and would not separate so well. Jf the carbonate of 
 potash be dissolved in less than six parts of water, it is not decom- 
 posed by lime ; on the contrary, when a strong solution of caustic 
 potash is boiled with carbonate of lime, carbonate of potash is pro- 
 duced, 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^ K.O. . H.O. This liquid is gener- 
 ally 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 sul- 
 phate and carbonate of potash, chloride and peroxide of potassium, 
 and oxide of iron, which it generally contains, by being dissolved 
 in absolute alcohol, the solution evaporated to dryness, and the re- 
 maining 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 decom- 
 posing them, and hence its use in surgery, and its name of caustic 
 potash. It dissolves in water, with the evolution of considerable 
 heat J a concentrated solution of it crystallizes when exposed to 
 cold, in rhombic octohedrons, whose composition is K.0.4-5H.O. 
 
 The solution of potash is pre-eminently alkaline ; it neutralizes the 
 strongest acids, browns turmeric paper, and restores the blue coloui 
 
SULPHURETS OP POTASSIUM. 339 
 
 of litmus paper reddened by an acid. It absorbs carbonic acid rap- 
 idly from the air, and must hence be preserved in close vessels. It 
 acts rapidly on glass containing much alkali 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 all cases of saline 
 decomposition, and its various compounds are of great importance 
 in the chemical arts, of which many will be noticed hereafter in de- 
 tail. 
 
 Potash is distinguished, when free, first, by its general alkaline 
 characters, and by its not being precipitated by carbonate of soda, 
 which separates it from everything but soda and ammonia. From 
 the latter it is known by the brown stain produced on turmeric paper 
 being permanent, whereas the brown colour produced by ammonia 
 disappears when the paper is warmed; and from soda it is known 
 by giving with an excess of the perchloric, tartaric, and hydrofluo- 
 silicic 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 alkali in excess, the action on vegetable colours is not 
 that of an alkali. 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, while those of potash are fixed, and give to the flame 
 of the blowpipe a distinct 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 =490 or 39-3 
 
 Oxygen, 16-95 One equivalent =100 or 8-0 
 
 100^ 590 47^ 
 
 Peroxide of Potassium. K.O3. — 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 hy- 
 drate of potash is heated to redness in 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. 
 
 Siilphureis of Potassium. — When potassium is gently heated in 
 contact with sulphur, they unite with brilliant combustion, and, ac- 
 cording to the proportions in which they are employed, form the 
 sulphurets of potassium, of which there are altogether four. These 
 bodies are, however, always prepared in practice by more econom- 
 ical 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 K.O. . S.O3 and 411. produce 
 4H.0. and K.S. The same result follows from igniting strongly, in a crucible, a 
 mixture of charcoal and sulphate of potash ; all the oxygen is removed as carbonic 
 oxide, and the sulphur and the potassium remain in combination, K.O. . S.O3 and 4C, 
 giving 4C.(). and K.S. 
 
340 SULPHURETS OP POTASSIUM. SODIuAl. 
 
 This protosulphuret is of a brown colour, fusible below a red heat, easily solu- 
 ble, and its solution is yellow, and reacts higlily alkaline and caustic. When ex- 
 posed to the air, it absorbs oxygen rapidly ; and in preparing it from sulphate of pot- 
 ash, by carbon, if lampblack be used, so that the product shall be in a state r-f very 
 minute division, it takes fire spontaneously on coming into contact with the air, 
 constituting a pyrophorus. 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 re- 
 mains united with the acid, and the sulphuret 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 
 aulphurets being formed. It absorbs sulphuretted hydrogen in such proportion that 
 a compound is produced, K.S.-j-H.S., exactly similar to the hydrate of potash, 
 K.O.+H.O. 
 
 The tersulphuret o/;?ofa55mm corresponds to the peroxide, its formula being K.S3. 
 It constitutes the mass of the hcpar sulphuris, liver of sulphur, of the pharmaco- 
 poeias. It may be prepared by fusing, at a low red 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 hyposulphurous or sul- 
 phuric acid, according to the temperature, while the remainder of the sulphur com- 
 bines with the potassium, producing a sulphuret, the composition of which is de- 
 termined by the quantity of sulphur present. With the above proportions the reac- 
 tion may be considered thus : 4(K O.-fCOa) and lOS. give 3K.S3 and K.O. . S.O3, 
 which constitute the fused mass, while 40. O2 is driven off with effervescence. If, 
 however, equal weights of carbonate of potash and of sulphur be employed, the 
 sulphuret formed contains five equivalents of sulphur : it is the pentasulphuret. 
 
 These sulphurets resemble each other completely in external appearance ; they 
 are liver-brown ; they deliquesce in the air, and absorb oxygen rapidly. Their solu- 
 tions, 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 pentasulphuret be treated with an acid, water is decomposed, and 
 potash being formed, sulphuret of hydrogen is produced ; the remaining sulphur 
 then separates in a state of very minute division, and of a milk-vi^hite colour, con- 
 stituting the lac sulphuris, or the sulphur precipitatum of jiharmacy. If the acid em- 
 ployed be strong and in great excess, a quantity of bisulphuret of hydrogen is form- 
 ed, as explained in page 293. 
 
 Rose is of opinion that the whiteness of precipitated sulphur depends not merely 
 upon its minute division, but that it is owing to the presence of a trace of bisul- 
 phuret of hydrogen. When the hepar sulphuris is decomposed by an acid, it is not 
 merely that the excess of sulphur is set free, but in addition, as there is always hy- 
 posulphurous acid present ; this, when evolved, acts on the sulphuretted hydrogen, 
 and the sulphur of both is precipitated, water being formed ; S.O2 and 2PI.S. giving 
 3H.0. and 2S. 
 
 The Pentasulphuret of Potassium is prepared perfectly pure by decomposing sul- 
 .phate of potash by sulphuret of hydrogen, at a red heat. Thus K.O. . S.O3 and 
 4H.S. give K.S3 and 4H.0. 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.S5 may be constituted of K.S. and S.S3. 
 
 The seleniurets of potassium are similar in constitution to the sulphurets. They 
 evolve seleniuret of hydrogen when treated Jy acids, with precipitation of seleni- 
 um when it is present in greater proportion than one equivalent. 
 
 Of Sodium. 
 Sodium exists in great quantities in the mineral kingdom, es- 
 pecially combined with chlorine, as common salt, of which enor- 
 mous deposites 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. 
 Tt is, indeed, from the chloride of sodium that we derive, whether 
 directly or indirectly, all the supplies of the various compounds o( 
 this metal. 
 
SODIUM AND SODA. 341 
 
 The discovery of sodium was made in the same manner, and im 
 mediately subsequent to that of potassium, by Humphrey Davy, 
 and it is now prepared in exactly the same manner as that metal. 
 It is, however, 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 
 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 
 globule be prevented from moving about, the water becomes heat- 
 ed, and the action increases so much 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 
 thickened 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 equiva- 
 lent numbers are 291 or 23-3. 
 
 Sodium unites with oxygen in two proportions, forming the pro- 
 toxide, or soda, Na.O., and the peroxide, of which the constitution 
 is not exactly known. This last is prepared just as the peroxide of 
 potassium, which it resembles completely in its properties. The 
 former only requires detailed notice. 
 
 The preparation of dry soda is effected like that of potash, by 
 heating the metal in dry air or oxygen. It is grayish white, and 
 absorbs water with excessive power. From the hydrate of soda 
 the water can be expelled only by an acid. The caustic soda is, 
 therefore, always like caustic potash, a hydrate of the alkali. For 
 the preparation of caustic soda, the same process is to be followed 
 as for that of potash. The carbonate of soda of commerce, dissolv- 
 ed in boiling water, is decomposed by slacked lime, it being neces- 
 sary, however, to use one third more lime, from the smaller equiv- 
 alent number of soda. The solution of caustic soda resembles that 
 of caustic potash in all its alkaline characters, but its action is not 
 so intense. It is a weaker alkali, its salts being decomposed in 
 all cases by potash. 
 
 The soda consists of an equivalent of each element j its formula 
 is Na.O., and its composition, 
 
 Sodium, 74-42 One equivalent =291 or 23-3 
 
 Oxygen , 25-5 8 One equivalent =100 or 8.0 
 
 100-00 391 SFS 
 
 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 
 alkali. On then applying the various tests for potash and for am- 
 monia detailed in the last section, if no evidence of their presence 
 
342 L I T H I U M. B A R I U M. 
 
 be obtained, the alkali must be soda ; and even where potash also 
 is present, a small quantity of soda may be recognised, by its tin- 
 ging the flame of the blowpipe of a fine yellow colour. 
 
 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 a^ 
 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. Thia 
 mineral is a double silicate of the alkali 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 be- 
 comes oxidized immediately on exposure to the air. Its symbol is 
 L., and its equivalent number 80*3 or 6'4i. 
 
 To obtain lithia, the simplest process is to mix the mineral containing it (gener- 
 ally lepidolite or spodumene), previously reduced to very fine powder, with fluor 
 spar, and digest the mass with oil of vitriol, until it is completely decomposed ; the 
 silica is carried off by the hydrofluoric acid (see page 324), and the hme, 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 ig- 
 nited, 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 alkalies by the sparing sol- 
 ubility 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 recognised 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. Lithia is a protox- 
 ide, its formula being L.O. ; its equivalents 180*3 or 144. 
 
 The sulphurets and seleniurets of lithium do not possess any in- 
 terest. 
 
 The alkali ammonia might, on one hypothesis of its nature, be described here. 
 When combined with hydrogen, it is considered by BerzeUus and many other chem- 
 ists to form a remarkable compound metal, ammonium, N.H4, whose relations to 
 potassium are of an exceedingly intimate kind ; and the salts of ammonia, which 
 contain ammonia and water, N.H3-4-H.O., are looked upon as consisting of an oxide 
 of that metal, N.H4 . 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. 
 
 Bariuvu 
 
 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 imme- 
 diately after the discovery of the basis of the alkalies. It may be 
 prepared by voltaic action, as described under the head of potassium, 
 
PREPARATION OF BARYTES. 343 
 
 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, evolv- 
 ing hydrogen gas and forming barytes (oxide of barium). 
 
 The name barium is derived from jSapv^j heavy ; the native sul- 
 phate of barytes having been called formerly terra ponderosa, or heavy 
 spar. Its symbol is Ba. ; its equivalent numbers 856*9 or 68*7. 
 
 Barium combines with oxygen in two proportions, forming a pro- 
 toxide, which is the earth barytes, Ba.O., and a deutoxide, Ba.Oo. 
 The preparation of this last has been described so fully when ex- 
 plaining its only important use, the formation of deutoxide of hy- 
 drogen (p. 258), that it need not be farther 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, 
 and boils briskly from the rapid escape of oxygen ; when this has 
 terminated, there remains a gray loosely coherent powder, which 
 is barytes. The melted salt is in this process very apt to froth up, 
 so much as to overflow, unless the vessel be of considerable size ; 
 this is very simply avoided by mixing the nitrate of barytes, before- 
 hand, 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 re- 
 sidual mass with water, all the pure barytes dissolves, the sulphate 
 remaining totally unacted on. 
 
 If the native carbonate of barytes, Ba.O, . C.O2, be strongly heated with carbon, the 
 carbonic acid is converted into carbonic oxide, which passes off, and pure barytes 
 remains behind, Ba.O. . C.O2 and C. giving Ba.O. and 2C.0. ; the former process is, 
 however, so much easier, that it alone is now usually employed. Graham has sug- 
 gested the employment of iodate of barytes as a substitute for the nitrate : other 
 processes will be described under the head of sulphuret of barium. 
 
 Pure barytes is a heavy gray powder ; when exposed to the air, 
 it absorbs water rapidly, giving out much heat, and falling into a fine 
 white powder, hydrate of barytes^ Ba.O.+H.O. Another hydrate may 
 be obtained crystallized, by dissolving barytes in three parts of boil- 
 ing water, and allowing the solution to cool slowly; it contains nine 
 equivalents of water. The solution of barytes is very caustic and 
 alkaline ; 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 (p. 263), 
 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 sulphuretted hydrogen gas in water. The sulphate of 
 barytes is not merely insoluble in water, but also in nitric and mu- 
 riatic acids, which is a farther characteristic of this earth. 
 
 The formula of barytes is Ba.O., and its composition, 
 
344 SULPHUR ET OP BARIUM. STRONTIUM. 
 
 Barium, 89-55 One equivalent =856-9 or 68-7 
 
 Oxygen, 10-45 One equivalent =100-0 or 8-0 
 
 100^ 95T9 7^7 
 
 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 j the sulphate of barytes then produced is 
 absolutely inert. 
 
 Sulphuret of Barium. Ba.S. — This body is of considerable inter- 
 est, as the source of barytes and of most of its ordinary compounds j 
 to prepare 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; carbonic oxide is evolved, and sulphuret of barium remains; 
 Ba.O. . S.O3 and 4C. giving 4C.0. and Ba.S. The mass thus ob- 
 tained is to be boiled in water j a deep yellow solution is then pro- 
 duced, from which the sulphuret of barium crystallizes on cooling ; 
 it is then a hydrate, but its water of crystallization may be removed 
 by a moderate heat. 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 labora- 
 tory 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, while 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. 
 
 Of Strontium, 
 
 This metal is the basis of the earth strontia, protoxide of stron- 
 tium, which exists native combined with sulphuric and carbonic 
 acids. The native carbonate of strontia was first found at Strontian 
 in Scotland, 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 outline 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 
 ascertained. 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 
 carbonate or sulphate of strontia for the compounds of barytes. The 
 strontia is gray, slacks on exposure to the air, forming a hydrate, 
 Sr.O. . H.O., and by crystallization from its watery solution, another 
 hydrate, Sr.O. -\- 9H.0. Strontia is less soluble than barytes, its tast^ 
 is not so caustic, nor is it so poisonous 
 
COMPOUNDS OF CALCIUM. 345 
 
 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 the preparation. 
 Like barytes, the soluble salts of strontia are precipitated by sul- 
 phuric acid, but the sulphate of strontia is not so very insoluble as 
 sulphate of barytes j 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 3 
 the chromic acid acts in a similar manner. 
 
 The sulphuret and seleniuret of strontium resemble perfectly thos» 
 of barium, and are prepared in the same way. 
 
 Of Calcium. 
 
 The existence of this metal was first recognised by Sir Humphrey 
 Davy, it being obtained from lime by the same method as that de- 
 scribed under the head of barium; it is white like silver; it sinks in 
 water, which it decomposes rapidly, evolving hydrogen, and uniting 
 with oxygen, forms lime (protoxide of calcium). The symbol of 
 calcium is Ca., and its equivalent number 256 or 20'5. 
 
 Calcium combines with oxygen only in one proportion, forming 
 lime, the most important of the earths. It is found very extensively 
 distributed in the mineral kingdom, principally combined with sul- 
 phuric and carbonic acids, forming sulphate of lime (gypsum, plas- 
 ter of Paris) and carbonate of lime (marble, limestone, chalk). These 
 substances exist as rocks or crystallized, the last constituting the 
 mineral species, arragonite 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 com- 
 pounds of fluorine. ^^ 
 
 Notwithstanding the immense quantities of carbonate of lime 
 which are found constituting a great portion of the surface of the 
 globe, as, for instance, the whole centre of Ireland is one vast plain 
 of limestone, 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 compo- 
 sition in this respect is found to coincide in a remarkable degree 
 with the most natural physiological classification. The skeletons of 
 the vertebrated animals consist principally of phosphate of lime, 
 while 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 min- 
 eral apatite. 
 
 Now it is remarkable that all the great geological formations 
 which contain carbonate of lime are found to consist of the aggre- 
 
 X X 
 
346 PROPERTIES OP LIME. 
 
 gated skeletons (shells) of myriads of the tribes of invertebrated an- 
 imals, which had existed in some former period of the world's his- 
 tory. From the densest and hardest limestone to the softest chalk, 
 the entire mass resolves 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 crys- 
 talline 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 render- 
 ed the texture of the mass completely uniform. 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 king- 
 doms. 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, af- 
 ford materials for the proper development of the skeleton. When 
 the animal dies, the materials of its tissues either serve for the nu- 
 trition of some other animal, or, being totally decomposed, its ele- 
 ments return to the mineral kingdom, to be, in after ages, the sub- 
 ject of similar alternations. 
 
 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 mar- 
 ble 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. 170. 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 sui|able proportions j 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 limestone 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 
 absorbs water, and falls into a white powder (slacked lime), which 
 is a hydrate, Ca.O. . H.O. 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 cracks, and falls into the powder of 
 hydrate, evolving so much heat as to char wood and inflame gun- 
 powder 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 j one part of lime requiring 778 of wa- 
 ter at«60^, and 1270 at 212^ for its solution ; hence, when lime-water 
 is boiled, it becomes turbid. The solution of lime has an acrid, slight- 
 ly caustic taste ; it reacts alkaline ; exposed to the air, it absorbs 
 carbonic acid, becoming covered with a crystalline pellicle of car- 
 bonate of lime. On breathing into lime-water through a glass tube, 
 it is immediately rendered turbid by the carbonate of lime produced 
 
SULPHURETS OF CALCIUM. ^ 347 
 
 by respiration 5 an excess of the carbonic acid, however, dissolves 
 the precipitate. It is in this way that carbonate of lime is held dis- 
 solved 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 slacked, 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 Ca.O. . C.02+Ca.O. . H.O. being probably formed, but after that 
 point it advances very slowly. 
 
 Lime being a protoxide, its formula is Ca.O., and its composition 
 and equivalent numbers are as follows ; 
 
 Calcium, 71'91 One equivalent =256-0 or 20-5 
 
 Oxygen, 28-09 One equivalent =^ 1Q0-Q or 8-0 
 
 lOO^OO 356-0 28-5 
 
 Lime is easily distinguished by its dilute solutions not being pre- 
 cipitated by sulphuric acid or sulphate of soda, but giving a white 
 precipitate of oxalate of lime on the addition of a solution of oxalic 
 acid j an excess of oxalic acid does not redissolve this precipitate. 
 The nitrate of lime is deliquescent and soluble in alcohol, in 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 
 mortar, and in agriculture from its application as a manure. The 
 lime in mortar is not as carbonate, and its coherent property ap- 
 pears to depend only on the gradual drying of the hydrate by which 
 the stones are retained 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 read- 
 ily taken up by the 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 ben- 
 eficial effects of lime are peculiarly marked. 
 
 There is a deutoxide of calcium, Ca.02, prepared by adding a solution of deutoxids 
 of hydrogen to lime-water ; it resembles deutoxide of barium, but is of no impor 
 tance. 
 
 There are three compounds of sulphur and calcium known ; the first, or proto- 
 sulphuret of calcium, Ca.S., may be prepared by heating sulphate of lime to redness 
 in a stream of hydrogen gas, or, more simply, by igniting sulphate of lime with one 
 third of its weight of lampblack ; all the oxygen of the salt is carried off as watei 
 m the one, or as carbonic oxide in the other case, and the suljihur and calcium re- 
 main united. It is a white powder, but very sparingly soluble in water. It plays 
 an important part in the manufacture of carbonate of soda, as will be hereafter ex- 
 plained. When flowers of sulphur and slacked 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 bisulphuret of calcium, 6S. 
 and 3Ca.O. producing S202+Ca.O. and 2Ca.S2. If the solution be concentrated, thia 
 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, sulphu- 
 ret of hydrogen is evolved from the sulphuret of calcium in such proportion as to 
 decompose the hydros ulphurous acid, and all the sulphur is precipitated, while the 
 lime remains in combination with the acid which is employed. If the sulphur be 
 in great excess in proportion to the lime, a pentasulphuret of calcium may be formed. 
 
 The seleniuret of calcium is not important. If phosphorus in vapour be passed 
 
348 PREPARATION OF MAGNESIUM. 
 
 through a red-hot tube loosely filled with lime, a brown substance is produced, pop- 
 ularly 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 hy- 
 drogen being produced ; this last being evolved in its spontaneously inflammable 
 condition, it is an interesting experiment to throw a fragment of the brown sub- 
 stance into a glass of water ; numerous gas bubbles are immediately formed, which 
 explode when they reach the air, as described in p. 300. 
 
 Of Magnesium. 
 
 This metal, like the bases of the other earths, was first recog- 
 nised by Humphrey Davy, but the process by which it is best pre- 
 pared 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 chloride of magnesium in small fragments to be laid upon 
 them i the part of the tube containing the earthy chloride is to be 
 heated to near its point of fusion, and the metal converted into va- 
 pour by the application of the lamp, as in the figure, p. 321 ; as 
 soon as the vapour of the potassium comes into contact with the 
 heated salt, vivid ignition ensues, and chloride of potassium being 
 formed, the magnesium is liberated 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 warm wa- 
 ter; the chloride of potassium dissolves, and leaves the magnesium, 
 with perfect metallic properties, behind. It is Avhite like silver, mal- 
 leable 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 water without 
 this being decomposed. If magnesium be heated to redness in air 
 or oxygen, it burns with brilliancy, forming magnesia, and it in- 
 flames spontaneously in chlorine ; it dissolves in dilute acids with 
 the evolution of hydrogen gas, and the formation of a salt of mag- 
 nesia. 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 constituent of a great variety of minerals ; it is found as hydrate, 
 as carbonate, sulphate, and silicate, but its most abundant source is 
 the magnesian limestone, common both in Ireland and in England, 
 which consists of an equivalent of each carbonate, its formula being 
 Ca.O. . C.Oa + Mg.O. . C.O2. 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, without taste or smell ; it is almost per- 
 fectly infusible ; but it and lime are remarkable for becoming beau- 
 tifully 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 solu- 
 ble in water, and still less so in hot than in cold water ; its solution 
 browns turmeric paper very slightly. It is remarkably inferior to 
 lime in basic power, but still neutralizes the strongest acids perfect- 
 ly, forming excellently characterized classes of salts. 
 
 The formula of magnesia is Mg.O., and its composition and equiv- 
 alent numbers are, 
 
PREPARATION OF ALUMINUM. 849 
 
 Magnesium, 61-29 One equivalent rr 158-3 or 12-7 
 
 Oxygen, 38-81 One equivalent =^0^ or 8-0 
 
 lOOOO' 258-3 20-7 
 
 Magnesia is recognised by its sulphate being very soluble in wa- 
 ter, and a solution containing it being precipitated by the alkalies 
 and their 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 sus- 
 pected to contain it alkaline 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 alkaline liquor. A solid substance containing mag- 
 nesia 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 impor- 
 tance ; they resemble, almost perfectly, those of calcium already 
 noticed. 
 
 SECTION II. 
 
 METALS OF THE SECOND CLASS. 
 
 Of Aluminum. 
 
 This metal is prepared by the action of potassium upon its chlo- 
 ride, exactly as described for magnesium in the last division, but the 
 operation 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 gray melted mass of chloride of potas- 
 sium and metallic aluminum 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 alkalies, with the 
 evolution of hydrogen gas, from the water being decomposed. The 
 synrbol of aluminum is Al., and its equivalent numbers are 171*2 or 
 13-7, according to the scale. 
 
 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 kinds of limestone ; it constitutes 
 the great mass of the ordinary clays and soils, these deposites bemg 
 produced by the gradual decomposition and detrition of various kinds 
 of rocks. In all these forms the alumina is generally combined with 
 silica, and sometimes 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 
 
350 PREPARATION AND PROPERTIES OP ALUMINA. 
 
 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 kinds of por- 
 celain, and is extensively used as the basis or mordant for some of 
 the most brilliant and durable colours 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 decom- 
 posed 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 sul- 
 phate of potash, from which it must be separated by being dissolved 
 in dilute muriatic acid, and again precipitated by carbonate of am- 
 monia ; being then well washed, until the water passes from the fil- 
 ter completely free from sal ammoniac, it may be looked upon as 
 pure. The alumina so obtained, when dried at common tempera- 
 tures, constitutes a bulky gummy mass, which is a hydrate, the earth 
 and the 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 contrac- 
 tion 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 reten- 
 tive quality 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 alkalies, but if 
 it be very strongly heated, particularly if fused by the oxy hydrogen 
 blowpipe, it dissolves much more slowly. It is particularly remark- 
 able for its tendency to unite with organic matters. If a cotton cloth 
 be immersed in a solution of acetate of alumina, the earth will de- 
 posite itself completely on the fibres of the cotton, and leave the acetic 
 acid free. The most important proces^s 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 de- 
 scribed, pages 213 and 223, the isomorphous and other relations which 
 establish its constitution to be similar to that of peroxide of iron. 
 It is hence a sesquioxide, and its formula is AI2O3. Its composition 
 and equivalent numbers are, 
 
 Alumina, 53-3 Two equivalents, =342-4 or 27-4 
 
 Oxygen, 46-7 Three equivalents, =300-0 or 24-0 
 
 1000 "6424 51-4 
 
 Alumina is easily recognised. Its solution is precipitated by the 
 alkalinb carbonates, and the precipitate is dissolved by the caustic 
 
GLUCINUM, YTTRIUM, THORIUM, ETC. 351 
 
 fixed alkalies, but not by ammonia. It is also precipitated white by 
 hydrosulphuret of ammonia. If a solid substance containing alumina 
 be moistened with a trace of nitrate of cobalt, and ignited by the 
 blowpipe, it becomes of a beautiful blue colour. 
 
 If aluminum be heated in the vapour of sulphur, it takes fire, and forms a gray 
 mass of sulphur et of aluminum. This is decomposed by water, producing alumina 
 and sulphuretted hydrogen, showing that its formula was AI2S3, which with 3H.0. 
 give AI2O3 and 3H.S. This sulphuret, 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 sulphuret of hy- 
 drogen. 
 
 The seleniuret and phosphuret of aluminum are known, but are of no importance. 
 
 Of Glucinum, 
 
 The earth of which this metal is the basis has been found but in a few rare min- 
 erals, 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 suf- 
 fice. 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 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 car- 
 bonate of ammonia, in which the glucina dissolves. On boiling the filtered liqdor 
 so obtained, the glucina separates in combination with carbonic acid, from which it 
 is freed by ignition, and so obtained 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 {yTiVKvg). 
 It is easily recognised by its relation to pure and carbonated ammonia, described in 
 the details of its preparation. The metal glucinum is prepared from its chloride 
 precisely as aluminum and magnesium, which it resembles very closely in all its 
 properties. Its symbol is G., and its equivalent numbers are .3314 or 265. 
 
 Glucina is considered to be, like alumina, a sesquioxide, and its formula being 
 G2O3, its composition and equivalents may easily be calculated. 
 
 Of Yttrium^ 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, short 
 notice of their characters only need be given. 
 
 Yttrium. — The earth yttria, oxide of yttrium, exists in some rare Swedish min- 
 erals, which were its only sources until the very remarkable discovery, by Apjohn, 
 of its presence in the ordinary Bohemian garnet or pyrope. The method of its ex- 
 traction is too complicated for description here. It is insoluble in the fixed caustic 
 alkalies, and is precipitated by the yellow prussiate of potash, by which it is com- 
 pletely distinguished from the^other earths. It is a protoxide. Its formula is 
 hence Y.O. 
 
 Thorium. — The earth thoria, oxide of thorium, Th.O., has been found but in two 
 very rare minerals. It is the heaviest of all the earths, its sp. gr. being 9 4, It re- 
 sennbles yttria closely in its properties. 
 
 Zirconium. — The earth zirconia, sesquioxide of zirconium, Zr203, is found in two 
 rare minerals, the hyacinth and zircon. It resembles alumina very closely in all its 
 properties, and in some respects assimilates 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 zirco- 
 nium is obtained, by a process identical with that which is described in page 321, 
 for the preparation of silicon. 
 
 Cerium. Lanthanum. 
 
 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 
 
352 MANGANESE, ITS PREPARATION, ETC. 
 
 nafure. Their history does not possess any particular interest, and need hence be 
 noticed but very briefly. 
 
 Tlie metallic cerium is obtained by igniting the protochloride of cerium with po- 
 tassium, as has been already described 'for other metals. It is a shghtly coherent 
 brown powder, which decomposes water slowly, evolving hydrogen, particularly if 
 the water be hot, and forming oxide of cerium. It combines with oxygen in two 
 proportions, forming a protoxide and a sesquioxide, Ce.O. and Ce203. 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 analyzed 
 as compounds of cerium, and on its received atomic weight. The protoxide of 
 cerium is of a pale fawn colour. If it be heated in the open air, it absorbs oxygen, 
 and changes into the dark brown peroxide ; and if this be reduced by hydrogen 
 gas, at a red heat, it forms a yellow complex oxide, probably Ce304. 
 
 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 ni- 
 tric 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 {XavOavu), but its detailed his- 
 tory remains yet undeveloped. 
 
 Of Manganese. 
 This metal exists very extensively diffused through nature, al- 
 though not in very great quantity. Traces of it are found in the an- 
 imal 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 modifi- 
 cation of magnesia, for the native peroxide was once termed magne' 
 sia nigra ; but when the peculiar metal which it contained was recog- 
 nised, the present appellation was given to it. 
 
 Manganese is one of the metals most difficult to reduce, from its 
 great affinity for oxygen, and the liigh 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 lampblack, 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 foimd occupying its lowest portion. 
 
 The metallic manganese is grayish white, granular, and brittle ; 
 its sp. gr. 8*013. It is exceedingly infusihJe. 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 .... Mn.O. 
 
 Sesquioxide of manganese . . . MngOg. 
 
 Peroxide of manganese .... Mn.Oa. 
 
 Manganic acid Mn.Og. 
 
 Permanganic acid MnzOy. 
 
OXIDES OF MANGANESE. 353 
 
 In addition, there are two complex oxides : 
 
 The red oxide .... MnaO,, or Mn-O.+Mn^Og. 
 Varvicite Mn40„ or Mn203+2Mn.02. 
 
 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 
 quantities, 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 na- 
 tive peroxide, which is usually associated with a large quantity of 
 oxide of iron, consists 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 solution of protochloride of man- 
 ganese is obtained. From this the various other preparations may 
 be easily formed. 
 
 Protoxide of Manganese — ^]\In.O. ; equivalent 446 or 35*7 — may 
 be prepared in many ways. If to a solution of protochloride of 
 manganese an excess of a caustic alkali 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 ox- 
 ides 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 protoxide of manganese behind. The oxide 
 so obtained is of a greenish gray colour ; it does not absorb oxygen 
 at all so rapidly as the hydrated oxide j but if it be exposed to the 
 air while 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 kind of platinum 
 crucible to a full red heat. The chloride of manganese is decom- 
 posed by the carbonate of soda, chloride of sodium and carbonate 
 of manganese being formed j Mn.Cl. and Na.O. . C.Og giving Na. 
 CI. and Mn.O. . COg. 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 hy- 
 drogen, is prevented from passing to a higher degree of oxidation. 
 The oxide obtained at this high temperature has no tendency to 
 combine farther with oxygen under ordinary circumstances, and 
 may hence be easily preserved. • 
 
 The oxide is of various shades of grayish 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 def- 
 initeness and neutrality. These salts are generally colourless, but 
 often of a peculiar rose colour, which is not due to the presence of 
 
 Yy 
 
d-J-\ SESQUIOXIDE AND PEROXIDE OF MANGANESfi. 
 
 any higher degree of oxidation, but to a peculiar (isomeric) con- 
 dition of the salt itself. 
 
 Sesquioxide of Manganese. — MuaOg. 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 man- 
 ganite. 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 de- 
 composition of that substance so that it shall not proceed too far. 
 The sesquioxide is of a dark brown colour j 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. Its salts are immediately decolorized by sulphur- 
 ous acid and by sulphuretted 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. — Mn.Og. Equivalent 546 
 or 43.7. This substance, which is the most abundant source of 
 manganese, and that from which all its technical applications are 
 derived, exists in nature in a variety of forms. Crystallized and pure, 
 it forms the m.mQX^\ pyrolusite ; combined with water, 2Mn.02 + H. 
 O., it constitutes the mineral Wadd^ which, in an impure form, con- 
 taminated 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 ar- 
 tificially by decomposing the protochloride of manganese, by a solu- 
 tion of chloride of lime, Mn.Cl. and 2Ca.0. + Cl. producing 2Ca.Cl. 
 and Mn.Oa. It is also produced when permanganate of potash is de- 
 composed by any organic substance. In these cases it is precipita- 
 ted in combination with one equivalent of water, Mn.024-H.O., 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 alkalies j 
 but, when heated with strong sulphuric acid, it is decomposed in the 
 manner fully described under the head of oxygen, in page 244. Its 
 use in the preparation of chlorine has been also noticed, page 301. 
 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 Mn.Oa on 2Fe.O. there are formed Mn.O. and Fe203, two 
 substances which have no injurious effect upon the glass ; if, how- 
 ever, 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 caus- 
 
ANALYSIS OF PEROXIDE OF MANGANESE. 355 
 
 tic alkali, the precipitate, cautiously washed and ignited in an open 
 crucible, gives the quantity of red oxide corresponding to the quan- 
 tity of manganese present. The varvacite, the other complex oxide, 
 is a mineral of rare 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, are, generally speaking, due exclusively 
 to the quantity of oxygen it is capable of yielding, a ready mode of effecting its anal- 
 ysis becomes of great importance. There are two modes in which this may be ac- 
 complished upon very simple principles, and in a short time, with sufficient accu- 
 racy 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 man- 
 ganese contains ; for Mn.02 and C2O3 produce Mn.O. and 2C.O2. 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 this 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 included 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 dissolved ; a small quantity of a light brownish sediment, w^hich generally forms, 
 is easily distinguished from the particles of black oxide : as soon as the action is 
 quite over, the flask is suffered 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 con- 
 tents, 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 conversion into pro- 
 toxide, which remains combined with sulphuric acid in the liquor, and the quantity 
 of peroxide in the 100 grains of the ore is thus directly found. Thus, taking as 
 an example an actual determination, the flask and materials weighed altogether 
 1876 grains; after the action had terminated it weighed 18165 grains; the loss 
 was, therefore, 59 5. This consisted of 16 3 of carbon and 432 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. 
 
 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 difTused ; 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 availa- 
 ble in the mineral, are known. The theory of the process may be still more simply 
 expressed by the formulae of the bodies engaged, as follows : Mn.Oj and 2H.C1., 
 acting together, produce Mn.Cl. and 2H.0., while CI. is given ofFas gas ; this combines 
 with Ca.O. When the compound Ca.O.Cl. is brought in contact with 2(Fe.O. . S.O3), 
 the oxygen passing from the hme to the iron, we have Ca.Cl. and FcaOg . 2S.O3 pro- 
 duced. 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 opera- 
 tion will complete this explanation. 100 grains of commercial oxide of manganese 
 were placed in a flask with about one ounce of strong spirits of salt, and the chlo- 
 rine evolved was conducted by a bent tube to the bottom of a deep jar containing 
 1600 grains of water with 100 grains of slacked lime ; when the oxide of manga- 
 nese 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 grains 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 lime added thereto by droj*9 
 
356 MANGANIC AND PERMANGANIC ACIDS. 
 
 from an accurately graduated tube, until, by the test of red prussiate of potash, am 
 the iron was peroxidized. It required 1300 grains of the dilute solution, and henco 
 433 of the strong solution. Now, as 100 grains of the mineral had given 1600 
 grains of this strong solution, the 433 grains corresponded to 27 grains ; the avail- 
 able oxygen of which was exactly equivalent to transfer the iron of the protosul- 
 phate to the state of peroxide. Now the 100 grains contain 456 of water, 289 of 
 acid, and 255 of protoxide of iron, consisting of 19-7 of iron and 58 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 29, and the 
 quantity of pure peroxide consequently 158 grains, or 58*7 per cent. This whole 
 process, although, when thus described in detail, it may appear complex, is exceed- 
 ingly simple in execution, and does not occupy much time. In accuracy, the two 
 metliods 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 sul- 
 phate of iron directly to the muriatic acid and oxide of manganese 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 em- 
 ployed ; 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 hmits 
 may be considered as being between 60 and 70 per cent, of pure peroxide in 100. 
 Frequently, the commercial substance contains sesquioxide, or one of the complex 
 oxides ; but in all these cases, the methods given, as they determine the quantity of 
 available oxygen, show the true value of the specimen, no matter what the state oJ 
 combination of the metal may be. 
 
 Manganic Acid. — Mn.Og. Equivalent 646 or 51-7. If peroxide 
 of manganese be mixed with caustic potash, or carbonate or nitrate 
 of potash, in a crucibk, and ignited strongly, 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 dilated, it gradually changes colour, a brown precipitate separ- 
 ates, and the liquor becomes of a splendid red colour. This sub- 
 stance 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 man- 
 ganic acid, which unites with the potash. If potash, caustic or car- 
 bonated, be used, the oxygen is derived from the air ; if nitre, it sup- 
 plies oxygen ; but the best source consists in mixing four parts of 
 peroxide of manganese in fine powder with 3| 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 dry- 
 ness, powdered, and afterward 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 evap- 
 oration 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 exhibited in an isolated form. 
 
 Permanganic Acid, — MnaO^. Equivalent 1392 or 111-4. When a 
 /olution of manganate of potash is diluted with boiling water, a co- 
 pious precipitate of hydrated peroxide of manganese forms, and a 
 
DETECTION OF MANGANES E. 1 RON. 357 
 
 tine crimson solution of permanganate of potash is obtained. 
 SMn.Og produces Mn.Og and MnaO^. By rapidly evaporating this 
 solution until a pellicle forms, an abundant crop of crystals of per- 
 manganate of potash is obtained on cooling: these are isomorphous 
 with the perchlorate of potash, and are almost completely black, 
 but with a very peculiar bronze lustre. The salts of this acid are 
 very stable, and by treating the permanganate of barytes with a 
 proper quantity of dilute sulphuric acid, a deep crimson solution of 
 permanganic acid is obtained. This acid cannot be had solid, ac- 
 cording 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 perman- 
 ganic acid by some chemists contained some other matter combined 
 with it. 
 
 The formation of these acids by the action of sulphuric acid on 
 peroxide of manganese has been already noticed, and the most 
 delicate test of the presence of manganese in minerals consists in 
 fusing a fragment of the substance with a little carbonate of soda 
 on a slip of platina foil, by means of the oxidizing flame of the blow- 
 pipe. The mass, on cooling, becomes apple-green, from the forma- 
 tion of manganate of soda, if there be the smallest trace of manga- 
 nese in the substance used. 
 
 There is but one sulphuret of manganese. It is found as a min- 
 eral, and formed also by heating oxide of manganese and sulphur 
 (page 285). It is precipitated in a hydrated state, when a solution 
 of manganese 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 recognised 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 col- 
 ourless, and yields with the caustic alkalies a white precipitate (Mn. 
 O.), rapidly becoming brown QilnsO^) : with the alkaline carbonates, 
 a white precipitate, Mn.O. . C.O2 ; and with hydrosulphuret of am- 
 monia, a flesh red hydrated sulphuret. The yellow prussiate of pot- 
 ash precipitates the salts of manganese pure white, if there be no 
 trace of iron present. When the manganese is not in the state of 
 protoxide, the solution is always coloured red or green. These so- 
 lutions are decolorized by sulphurous acid and by sulphuretted hy- 
 drogen, which absorbs oxygen from all the higher degrees of oxida- 
 tion, and a colourless solution of protoxide is then obtained, which 
 gives the reactions already described. 
 
 SECTION III. 
 
 METALS OF THE THIRD CLASS. 
 
 Of Iron. 
 
 This is the most extensively distributed, and also the most im- 
 portant of the metals ; it may, indeed, be considered as being, after 
 those elements necessary to the functions of animal existence, that 
 ■«vhich is most indispensable to man for the wants of ordinary life. 
 •)n its employment and applications is founded every important 
 
358 STATE OP IRON IN NATURE. 
 
 Step which marks the gradual progress of the human race from har 
 barism 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 advan- 
 tage it possesses over every other metal for the construction equally 
 of the simplest tool and the most complex machine, for the imple- 
 ments of war as well as peace, all combine 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 great- 
 est 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 Russia and America. Its most 
 abundant form is that of oxide, either pure, forming the various 
 black and magnetic oxides, the haematite, or red oxide, &c., or com- 
 bined 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 native arseniates, phosphates, sulphates, 
 and other salts have been found. 
 
 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 igni- 
 tion and combustion j they move generally with great velocity ob- 
 liquely towards the ground, and generally, before touching, or at the 
 moment of contact with the surface, burst with an explosion, scat- 
 tering their fragments to considerable distances. These masses are 
 termed cerohthes ; 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 violently from the active volcanoes which 
 telescopic research has proved to exist in great numbers on the sur- 
 face of the moon, and that, passing beyond the limits of the attrac- 
 tion of our satellite, they come under the influence of this earth, and 
 fall towards its surface. No such substances are ever found pro- 
 jected from terrestrial volcanoes. 
 
 The general principles of the smelting of the clay iron stone 
 have been already noticed (p. 334), both considering it as a mere car- 
 bonate 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 appli- 
 cations — 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.4-4Fe., and forming cast 
 iron, which is easily fusible, while the pure metal is almost quite 
 infusible. The cast iron is, however, not by any means a pure car- 
 buret of iron j it contains small quantities of silicon and phosphorus, 
 
PREPARATION OF MALLEABLE IRON. 359 
 
 according to the proportions of which it varies in properties, so as 
 to constitute a number of varieties, known in the arts by their col- 
 our and texture, but of which it would be superfluous to speak here. 
 When cast iron remains under water for a considerable time, it be- 
 comes gradually oxidized, magnetic oxide of iron being formed, 
 and the carbon remaining under the form of a spongy mass, pre- 
 serving, 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 li- 
 quid state, and its multifarious uses for making castings, from 
 whence it derives its name. 
 
 Pure or malleable iron is made from cast iron 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 reverberatory furnace (see p. 333), 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 aggluti- 
 nate, and are worked up into a ball about the size of a large loaf, 
 which is taken out of the furnace 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, un- 
 altered cast iron that might remain are squirted out, as water 
 would be by pressure from the pores of a sponge ; this lump of 
 malleable iron is then passed through a succession of rollers, driven 
 by powerful steam engines ; each pair of rollers having a smaller in- 
 terval 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 enormous pressure to which the metal is subjected in this pro- 
 cess 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 pudling^ 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. Fe304 and 
 Fe^C^ produce Fe,, and C2O4. 
 
 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 temperatures, and then becomes only semifluid. It is, con- 
 sequently, 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 undistinguishable. 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 
 
360 MANUFACTURE OF STEEL. 
 
 all parts which require to possess peculiar tenacity, such as anchors, 
 &c., are always made, not in a single piece, but by thus welding to 
 gether 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 constitution, containing generally about 1-5 per cent, of carbon. 
 Steel may be formed directly from the ore or from cast iron by pro- 
 portioning the action of the fuel and of the air in the furnaces so as 
 to leave combined 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 car- 
 bon 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 es- 
 cape 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 trans- 
 ferred from particle to particle of the iron until the entire mass as- 
 sumes 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 j it is then exceedingly 
 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 de- 
 gree, and then allowed to cool slowly. By this means the excess 
 of hardness is got rid of, and the steel remains of the quality re- 
 quired. 
 
 The peculiar property of iron and steel of becoming magnetic, 
 has been described in page 143. 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 charac- 
 ter ; of these, one constitutes, 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 specific grav- 
 ity is 7-8. It becomes pasty when intensely heated, whence its re- 
 markable power of welding, which belongs, besides, to platinum and 
 sodium. 
 
 When iron in mass is exposed to dry air, it does not become ox. 
 idized ; but when 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. 
 
PASSIVE CONDITION OF IRON. 361 
 
 it burns with exceeding brilliancy, and forms globules of black ox- 
 ide of iron, Fe304. The true product of the combustion is peroxide, 
 FcaOa, but this loses one ninth of its oxygen by the intense tempera- 
 ture, and forms the black magnetic oxide. It is hence that, when 
 iron is burned in oxygen gas, the oxide, which is thrown off in mi- 
 nute grains, collects on the inside of the jar as peroxide, but the lar- 
 ger 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 pro- 
 duces 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 descri- 
 bed in p. "246. If iron be immersed in water holding potash, lime, 
 or soda in solution, or if the iron be covered up in quicklime, all 
 rusting is prevented, probably from any carbonic acid present being 
 totally taken up by the base. 
 
 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, hecom'mg passive ; although, 
 under ordinary circumstances, it is rapidly dissolved by that acid 
 with evolution of nitric oxide. This passive condition may be pro- 
 duced in many ways. 1st. If one end of a long iron wire be igni- 
 ted, and then, when cool, the wire be immersed in the acid, the ig- 
 nited end being dipped first, it remains unaltered. 2d. If a piece 
 of platina wire be fastened to a piece of iron wire, and then immer- 
 sed in the acid, the platina first. 3d. By placing a platina wire in 
 the acid, then immersing an iron wire in contact with it, the platina 
 wire maybe 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 con- 
 tact with it, and the first then withdrawn, 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 ap- 
 pears to have lost all tendency to unite with oxygen ; it does not 
 dissolve in acids; it does not precipitate copper from its solutions; 
 and when used as a positive electrode for 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 relations to the noble metals. It is possible that this 
 property may be connected with the equivalency of two equivalents 
 of the iron and manganese group of metals to one of chlorine, and 
 that when, by a change of molecular arranoement, like isomerism^ 
 
 Zz 
 
362 VARIOUS OXIDES OF IRON. 
 
 the particle becomes Fca in place of Fe., it is incapable of acting as 
 the positive element in galvanic ot chemical combinations. 
 
 The equivalent of iron is not so accurately known as those of 
 metals much less important and less common. The best determi- 
 nations make it about 339 upon the oxygen, and 27*2 upon the hy- 
 drogen 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. 
 
 Protoxide of Iron. — Fe.O. Equivalent 439 or 35"2. 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 protosalts of iron. From their solutions, it is 
 precipitated by an alkali as a white hydrate, which rapidly becomes 
 green, and finally brown-red, from absorption of oxygen. If we at- 
 tempt to form the protoxide by processes similar to those described 
 for obtaining protoxide of manganese, the iron is reduced either to 
 black oxide or to the metallic state. This oxide exists native, com- 
 bined 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. — Ye^O^. Equivalent 978 or 78*4. This substance 
 exists in very great abundance in nature, crystallized in rhombohe- 
 drons, 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 decom- 
 posed, abandoning its acid, and absorbing oxygen. It is thus that 
 the margins of chalybeate springs become coated with an ochrey 
 deposite j the carbonate of iron originally dissolved being gradually 
 converted into red oxide, while, the carbonic acid passes off. 
 
 The peroxide of iron may be artificially prepared by precipitating 
 a solution of any of its salts with an alkali 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 j 
 and, indeed, by an intense heat it loses some of its oxygen, 3(Fe203) 
 giving 2(Fe304), and O. escaping, being decomposed just as the ses- 
 quioxide of manganese, but requiring much greater heat. The per- 
 oxide 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. 
 
 When a solution of a protosalt of iron is exposed to the air, it 
 gradually absorbs oxygen until two thirds of the iron become per- 
 oxidized, and then the decomposition ceases. The liquor then con- 
 tains a compound oxide, Fe.O. -j-FeaOg, and on the addition of a caus- 
 
SULPHURETS OF IRON. 363 
 
 tic alkali this is precipitated as a black powder, which, when dry, is 
 powerfully 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 precip- 
 itate is a hydrate, but may be deprived of the water without altera- 
 tion. 
 
 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 smithies and forges during the successive heat- 
 ings and hammerings to which the metal is subjected. These scales 
 of iron are, however, not uniform in constitution, and are hence in- 
 ferior as a steady medicinal" agent to the oxide artificially prepared 
 by precipitation. 
 
 Sulphurets of Iron. — Sulphur combines with iron in three propor- 
 tions, forming the protosulphuret, the sesquisulphuret, and the bi- 
 sulphuret. These again combine, so as to produce complex (mag- 
 netic) sulphurets. Other degrees (subsulphurets) are problematical. 
 
 Protosulphuret of Iron. — Fe.S. Equivalent 540*4 or 43*3. The af- 
 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 
 combine with energy, and the sulphuret of iron flows down in copi- 
 ous 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 pro- 
 tosulphuret 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 j 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 form- 
 ing 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 292. This protosulphuret of iron ex- 
 ists sometimes, though rarely, in nature, and is dangerous, particu- 
 larly in coal mines, from the avidity with which, when moist, it ab- 
 sorbs oxygen, forming protosulphate of iron, Fe.S. and 40. giving 
 Fe.O. . S.O3 ; during which process it occasionally becomes so heat- 
 ed as to set fire to the beds of coal near it, and thus cause consid- 
 erable loss. 
 
 This sulphuret may be prepared in the moist way by adding hy- 
 drosulphuret of ammonia to a protosalt of iron. Thus Fe.Cl. and 
 S.H.+N.H3 produce Fe.S. and CI.H.+N.H3. It is a jet black pow- 
 der, which dissolves readily in acids, and when exposed moist to 
 the air, rapidly absorbs oxygen, forming green copperas. 
 
 Sesquisulphuret of Iron. — FcgSg. Equivalent 1282 or 102-7. This 
 compound, which corresponds to the peroxide, is very instable in 
 constitution. 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 
 
364 SULPHURETS OF IRON. 
 
 produced by heating peroxide of iron in a current of sulphuretted 
 hydrogen gas, water being formed. It is not attracted by the mag- 
 net. It dissolves in acids, but one third of the sulphur is precipita- 
 ted, two thirds only combining with hydrogen, and the iron existing 
 in solution as a protosalt. Thus FcaSs^and 2H.C1. give 2(Fe.Cl.) 
 and 2H.S. with deposition of S. This arises from the circumstance 
 that peroxide of iron is reduced by sulphuretted hydrogen to pro- 
 toxide, water being formed, and sulphur set free. 
 
 Bisulphuret of Iron. — Fe-Sg. Equivalent 741-5 or SQ-^. This 
 substance 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 229-232), and in its two forms 
 possesses very 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 remains a voluminous yellow powder, noi 
 acted on by the magnet, and insoluble in acids, which is the bisul- 
 phuret 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 fig- 
 ures of a variety of organic remains, as nautili, &c., where, proba- 
 bly, the animal having perished in water holding traces of sulphate 
 of iron in solution, the hydrogen compounds evolved by its decom- 
 position have reacted on the sulphate of iron, abstracting its oxygen 
 and producing a deposite of pyrites. 
 
 Magnetic Sulphurets of Iron. — Of these the most remarkable is that 
 which corresponds to the magnetic oxide, having the formula Fcg 
 04=Fe.S.-|-Fe2S3. It is found native at Barege, and may be formed 
 by exposing to a red heat, in close vessels, the bisulphuret or sesqui- 
 sulphuret : the pyrites 3(Fe.S2) producing Ye^i and S2, precisely 
 as peroxide of manganese 3(Mn O^) produces O2 and MngO^. If, 
 however, the heat be raised too high, more sulphur is expelled, and 
 another kind of magnetic sulphuret, Fe7S8=5Fe.S.+Fe2S3, formed, 
 which is also found native, and which corresponds to the black 
 scales of oxide of iron, which are 5Fe.O.+Fe203. 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 
 sulphurets. 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 oxiclip, or peroxide ; and as the 
 application 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 5 with sulphocyan- 
 ide of potassium, a deep blood-red colour, but no precipitate j with 
 
r REPARATION OF NICKEL. 365 
 
 a solution of tannin or tincture of galls, a deep violet or black. 
 With sulphuret of hydrogen there is no effect except the separation 
 of a deposite of pure sulphur, but with hydrosulphuret of ammonia 
 a black precipitate of sesquisulphuret of iron. 
 
 If the solution contain the iron only as protoxide, ammonia pro^ 
 duces a precipitate, at first whitish, but rapidly becoming bluish- 
 green. The yellow prussiate of potash, a precipitate, at first white, 
 but rapidly becoming blue. The sulphocyanide of potassium, thfe 
 tannin, and the sulphuret of hydrogen are without effect, but the hy- 
 drosulphuret of ammonia forms the black protosulphuret. The char- 
 acteristic reagent for protoxide of iron is the red prussiate of pot- 
 ash, which gives Prussian blue, but does not act upon the solution 
 of peroxide. 
 
 If the solution contain at the same time both oxides, the precipi- 
 tate 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 MckeL 
 
 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-nickely or de- 
 ceitful copper. Subsequently it was found to consist of a peculiar 
 metal united to arsenic, and this metal retained the name nickel, its 
 meanincr being forgotten or lost sight of. A substance found in 
 commerce, termed speiss, a residue from the manufacture of smalts, 
 is also an arseniuret of nickel, and from either of these sources the 
 metal is generally extracted. 
 
 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 li- 
 quor, 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 
 redissolved . On then evaporating and cooling, a double sulphate of nickel and pot- 
 ash 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 sulphuretted hydrogen, and from the last by the 
 solubility of the oxide of nickel in water of ammonia. From the ammoniacal so- 
 lution, the oxide of nickel may be precipitated by oxalic acid, as an insoluble ox- 
 alate, which, when dried and heated, gives off carbonic acid, and leaves metallic 
 nickel, Ni.O.-f C2O3, producing 2O.O2 and Ni. The metallic nickel is then in the 
 form of a very light sponge. 
 
 It is somewhat more fusible than cast iron ; of a silvery white 
 colour. It does not rust when exposed even to damp air. Its sp. 
 gr. is about 85. It is nearly as magnetic as iron, and retains its mag- 
 netism, 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. It is hence that, 
 added to brass in the proportion of one to five, it is employed as a 
 substitute for silver, constituting the German silver, nickel silver, 
 argentine, and British plate of commerce, as well as the packfong 
 long used in China. 
 
 The symbol of nickel is Ni. ; its equivalent 369-7 or 29-6. 
 
 Oxides of JVickel. — This metal combines with oxygen in two pro- 
 portions, forming a protoxide and a sesq;::ioxide. 
 
366 COBALT AND ITS OXIDE 3. 
 
 The protoxide, Ni.O., is prepared by precipitating a salt of nickel by caustic potas^i ; 
 a grass-green hydrated oxide of nickel separates, Ni.O.-|-H.O., which, wlien dry, gives 
 the pure ash-gray 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 dissolved on adding an excess of 
 the alkali, forming a blue solution, in a great degree characteristic of this metal. 
 
 The Peroxide of Nickel, NiaOg, is a black powder, prepared by boiling the pro- 
 toxide in a solution of chloride of lime ; the oxygen of the lime changes the pro- 
 toxide into peroxide, 2Ni.O. and Ca.O.Cl. producing Niz . O3 and Oa.Cl. When igni- 
 ted, this oxide gives oxygen and protoxide ; with muriatic acid it forms protochloride 
 and chlorine. It does not form any true salts. 
 
 Nickel is easily recognised by its solutions giving with ammonia 
 a 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 sul- 
 phuretted hydrogen, but give a black sulphuret of nickel with hy- 
 drosulphuret of ammonia. 
 
 The sulphuret, seleniuret, and phosphuret of nickel do not present 
 any point of interest. 
 
 Of Cobalt. 
 
 The name of this metal has 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 ex- 
 pect an abundant produce, but the modes of reduction then in use 
 were employed without avail ; it was hence imagined that these 
 ores were especially protected by the guardian spirits of the mines, 
 or Kobolds, and these minerals were termed Die Kobold's erze^ the 
 Kohold'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. 334. The residual impure oxide of cobalt is 
 sold in commerce under the name of Zaffre. This zaflre is dissolved in muriatic 
 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 met- 
 als, I must refer to more extended works. 
 
 The oxalate of cobalt, when ignited, yields carbonic acid and 
 metallic cobalt in a spongy form. Cobalt melts into a button more 
 easily than cast iron ; it is reddish-gray ; specific gravity 8-5 j when 
 perfectly pure, it is not susceptible of becoming magnetic. It acts 
 upon water and acids more rapidly than nickel, but much less ac 
 tively than iron or zinc. The symbol of cobalt is Co., and its equiv 
 alent 369 or 29-6. 
 
 Oxides of Cobalt. — Cobalt combines with oxygen to form two well 
 defined oxides, a protoxide and sesquioxide; there are also a com- 
 plex oxide, and a compound of which the constitution is not well 
 known, but which is probably a deutoxide. 
 
 Protoxide of Cobalt, Co.O., is prepared by adding caustic potash to a solution of a 
 
USES OF COBALT IN THE ARTS. ZINC. 367 
 
 salt of cobalt ; a fine blue powder falls, which is a hydrate, Co.O. . H.O. ; when de- 
 prived of its water, it becomes ash-gray : it is the only oxide of cobalt which forma 
 salts with acids. 
 
 Sesquioxide of Cobalt, C02O3, is prepared as the sesquioxide of nickel ; it is a black 
 powder, which, with hydrochloric acid, gives chlorine and protochioride : it does 
 not form salts. 
 
 The complex oxide is Co304=:::Co.O.-|-Co203, similar to the magnetic oxide of 
 iron and red oxide of manganese. 
 
 Cobalt is recognised in solution by producing with water of am- 
 monia a blue precipitate, which redissolves in an excess of the al- 
 kali, 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 sulphuretted hydrogen, but is thrown down black by hydrosul- 
 phuret of ammonia. The most remarkable test for cobalt is its 
 power of colouring glass blue. The most minute trace of this metaJ 
 may be thus recognised 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 impal- 
 pable powder, constitutes the smalts used to give to writing paper 
 and to linen a delicate shade of blue. The blue colours upon por- 
 celain and delft are also produced by cobalt j when speaking of 
 magnesia (p. 349) ai^ alumina (p. 351), 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 blue colours of cobalt are spoiled if brought into contact with chlorine or ox- 
 ygen, 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 acquirmg a brown tinge ; and by melting together cobalt-glass and hlack oxide 
 of manganese, a deep black glass is formed, 2(Co.O.) and Mn.02 giving C02O3 and 
 Mn.O. 
 
 The sulphuret and seleniuret of cobalt consist of an equivalent of each element^ 
 bat do not require notice. 
 
 Of Zinc. 
 
 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 reverberatory furnace. In England the crucibles are closed 
 above, but perforated 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 the water, solidifies. In Silesia very large 
 earthen retorts are employed, not unlike those figured in page 289 
 for the preparation of German oil of vitriol. 
 
 The zinc of commei^ce, 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 
 
368 OXIDE OF ZINC. 
 
 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 sulphuric acid, as explained in page 135. It is 
 a brilliant bluish-white metal, of a very crystalline texture ; its sin- 
 gular variations of tenacity are described in page 328. 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 wa- 
 ter, zinc is not continuously oxidized. It becomes covered with a 
 varnish of a gray substance, probably a definite suboxide, which is 
 not farther altered by exposure, and hence this metal is admirably 
 fitted for the various purposes of domestic and technical 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 corro- 
 sion is, however, in this case, not diminished, but rather augmented 
 in amount j 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 acids ; all that is known#f its relations in this 
 respect has been already described in pages 198 and 248. 
 
 The symbol for zinc is Zn. Its equivalent number 403*2 or 32-3. 
 
 Oxide of Zinc. — Zn.O. Equivalent 503-2 or 40*3. Although 
 there is some reason to suppose the existence of other oxides of 
 zinc, yet at present w^e possess accurate knowledge only of the 
 protoxide. This is formed when the metal is burned in air or oxy- 
 gen. It is produced, also, when the zinc is oxidized by the decom- 
 position of water, either at a red heat or assisted by an acid. To 
 form the oxide by combustion, it is sufficient to proj'ect a small frag- 
 ment 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 by the 
 current of air, is deposited on the inside of the upper crucible as 
 a loose cottony mass, which, while very hot, is of a fine canary col- 
 our, but becomes pure white when completely cold. 
 
 Such is the tendency of oxide of zinc to enter into combination, 
 that the precipitates given by the caustic alkalies in a solution of 
 a salt of zinc are basic salts, and not the mere 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 strongest acids, and its salts are some of the most 
 definite and characteristic that exist : they are easily recognised. 
 In their solutions, the caustic alkalies all produce voluminous white 
 precipitates, which are redissolved by an excess of the alkali. An 
 alkaline carbonate gives a similar precipitate, which, however, is 
 not redissolved by an excess, except it be carbonate of ammonia. 
 Hydrosulphuret of ammonia produces a white precipitate of hydra 
 
C A D M I U M. T I N. 369 
 
 ted sulphuret of zinc, if the solution be not very acid. Sulphuret- 
 ted hydrogen does so only if the solution be completely neutral 
 A solution of zinc with much free acid is not affected by sulphuret- 
 ted hydrogen, either free or combined. 
 
 The native Sulphuret of Zinc^ Zn.S., is found in crystals of a va- 
 riety of colours ; it is a protosulphuret, and may be artificially 
 formed by melting zinc and sulphur together. It is decomposed by 
 acids, sulphuretted hydrogen being given off, and a salt of zinc pro 
 duced. 
 
 Of Cadmium* 
 
 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 j 
 it accompanies almost universally, though in small quantities only, 
 the ores of zinc, and is obtained in the working of zinc ores by ta 
 king advantage of its greater volatility. The details of its purifi- 
 cation need not be inserted. It is white like tin j it is more fusible 
 and more volatile than zinc ; its specific gravity is 869 j it dissolves 
 very slowly in dilute sulphuric acid, but rapidly in dilute nitric acid j 
 it combines with oxygen only in one proportion. Its symbol is Cd., 
 and its equivalent 696'8 or 55'8. 
 
 The Oxide of Cadmium, Cd.O., equivalent 796 8 or 63 8, is obtained by processes 
 exactly such as described for oxide of zinc. When anhydrous, it is an orange pow 
 der ; its salts, which are very stable, resemble closely those of zinc, from which 
 they are distinguished by giving with sulphuretted hydrogen a fine yellow precipi- 
 tate, and with carbonate of ammonia a white precipitate, insoluble in an excess : 
 its salts, like those of zinc, are all colourless. 
 
 Sulphuret of Cadmium, Cd.O., is found native near Greenock; it is yellow like 
 orpiment, but is not volatile ; it does not dissolve in water of ammonia nor of pot- 
 ash. 
 
 Of Tin. 
 
 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 instruments 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 substitute for it. It was from the tin mines 
 of Cornwall that England first became known to the then more civ- 
 ilized nation of Phoenicia. A great quantity of the tin of commerce 
 is still obtained from that county j 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 the 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. 332. The met- 
 al thus obtained is still farther purified from any admixture of for- 
 eign metals by the process 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 
 
 A A A 
 
370 OXIDES OF TIN. 
 
 from rising higher, the pure metal melts completely out, leaving 
 behind the impurities combined with a proportion 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 col- 
 umns, like those formed by starch, or by basalt, as in the Giant's 
 Causeway, and emitting, when bent, a peculiar creaking sound. 
 The block tin possesses these characters in a very small degree, or 
 not at all. 
 
 Tin, when pure, is white like silver, brilliant, and after gold, sil- 
 ver, and copper, the most malleable of the metals. It is very soft, 
 may be bent easily, and has but little tenacity. Its specific gravity 
 is 7*3. It is one of the most fusible of the metals, melting at 442" 
 Fah. Tin oxidizes but very slowly in contact with air and water, 
 and is hence used to protect the surface of the more easily oxida- 
 ble 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 concentra- 
 ted, forming the peroxide. 
 
 The symbol of tin is Sn., derived from its Latin name siannum. 
 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 proper- 
 ties. 
 
 Protoxide of Tin. — Sn.O. Equivalent 835-3 or 66-9. On adding 
 water of ammonia to a solution of protochloride of tin, a copious 
 vi^hite precipitate is obtained, which does not contain ammonia, but 
 is the hydrated oxide, Sn.O. . H.O. The same precipitate is pro- 
 duced by an alkaline 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 re- 
 mains as a dense black powder. 
 
 If the hydrate be heated in the open air, it absorbs oxygen, and becomes perox- 
 ide ; and if the black protoxide be touched when cold with a red-hot coal or wire, 
 it inflames and burns like tinder, forming peroxide. The salts of tin may be formed 
 by digesting the hydrated oxide in acids. It also dissolves in solutions of the caus- 
 tic fixed alkalies, but after some time metallic tin is deposited, and a compound of 
 the alkali with peroxide of tin remains dissolved, 2Sn.O. producing Sn. and Sn.Oz. 
 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, 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^Og, 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, 2Sn CI. and 
 FcjOa producing SuiOg and 2Fe.Cl. It is a gray powder ; it absorbs 
 oxygen readily, and appears to form salts, which have been, as yet, 
 little examined. 
 
 Peroxide of Tin. Stannic jlcid.—Sn.O^. Equivalent 935-3 or 74-9. 
 This substance is produced in all cases w^here 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 artificial- 
 ly by pouring the liquid nitric acid, sp. gr. 1-42, on metallic tin> in 
 
SULPflURETS 1=^ TIN. CHROME. 371 
 
 foil or powder j 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 alkali, a white precipitate of hy- 
 drated 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 
 npon them as isomeric bodies. He calls that by nitric acid, a peroxide, and that 
 from the perchloride, j3 peroxide, and their properties may be contrasted as follows 
 
 The a modification is totally insoluble in nitric acid and in sulphuric acid, wheth 
 er strong or dilute. It is insoluble in muriatic acid, but is changed by it into an in 
 soluble basic salt. 
 
 The /3 modification dissolves while 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 original properties. These 
 modifications are also capable of being transformed into each other; the a into /? 
 by distillation with strong muriatic acid, and the /? into a by boiling with nitric acid. 
 
 The hydrated peroxide of tin reddens litmus, and combines with alkalies 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 pulty, and in glass and enamelling, in order to give the 
 milk whiteness used for dials of watches and other purposes. 
 
 There are three sulphurets of tin corresponding to the oxides 
 
 The Protosulphurct, 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 Sesquisidphuret, SngSg, is of no impor- 
 tance. 
 
 The Bisulphuret of Tin, Sn.S«, equivalent 1137-6 or 91-1, may be prepared by 
 decomposing a solution of perchloride of tin by sulphuretted hydrogen, which it 
 precipitates of a golden yellow colour. This is a strong sulphur acid. It dissolves 
 readily in solutions of the sulphurets of the alkaline metals, forming sulphur salts. 
 If it be'strongly heated, it abandons an atom of sulphur, and is converted into the 
 protosulphurct. It may be also prepared in the dry way, and then possesses con- 
 siderable interest as being one of those substances which, being obtained from the 
 common metals, and simulating the appearance and some of the properties of gold, 
 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 its 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 mer- 
 cury 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 recognised in solution by the action of hydrosulphu- 
 ret 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 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 Chromium, or Chrome. 
 
 This metal derives its name from the variety and brilliancy of the 
 colours of its compounds (Xpw/ioc). It exists as chromic acid com- 
 bined with lead or with copper in some rare minerals, but abundant- 
 
372 OXIDE AND ACID OF CHROME. 
 
 ly as chromic oxide in the chrome-iron ore (Fe-O.+CraOg). 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 com- 
 merce, 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 grayish-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 dissolves in hydrofluoric acid 
 with evolution of hydrogen gas. 
 
 Chrome combines with oxygen in two proportions, forming an ox 
 ide and an acid. Its symbol is Cr., and its equivalent numbers are 
 351-8 or 28-19. 
 
 Oxide of Chrome, CraOg, equivalent 1003-6 or 80-4, may be ob- 
 tained by a great variety of processes. Thus, if chromate of mer- 
 cury be heated to redness, the oxide of mercury and half the oxy- 
 gen of the chromic acid are expelled, and the chromic oxide remains 
 of a beautiful green colour. 
 
 If bichromate of potash be mixed with sal ammoniac and heated to redness, chlo- 
 ride 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, 
 SCr.Og+K.O. and CI.N.H4 produce K.Cl., N., 4H.0., and Ct^O^. The oxide so 
 obtained is pulverulent, but it may be obtained crystallized as follows : the vapour 
 of a compound which will be hereafter described, chlovochromic acid, is to be pass- 
 ed 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 in rhombic 
 octohedrons, isomorphous with those found native of alumina (corundum) and per- 
 oxide of iron ; the chlorochromic acid, 2(Cr.0£Cl.) giving off 2C1. and 0., and 
 CraOg remaining. 
 
 This oxide of chrome is the basis of an extensive class of salts, 
 and it may also be obtained by precipitation from any solution con- 
 taining it. Its salts are generally made from the bichromate of pot- 
 ash 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 sul- 
 phuric 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 alkali, as a pale green hydrate. In this condition, 
 the oxide of chrome dissolves readily in acids, and also in solutions 
 of the fixed caustic alkalies, 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 more than 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 solu- 
 bility in acids, except they be hot and concentrated. It is remark- 
 able that sulphate of chrome, made from the ignited oxide, will not 
 combine with sulphate of potash to form a chrome alum. 
 
 Chromic Acid. — Qr.O^. Equivalent 651-8 or 52-2. To prepare 
 'his acid, a solution of bichromate of potash is to be treated by hy- 
 drofluosilicic acid gas, until the potash has been precipitated com- 
 pletely. The resulting liquor is to be cautiously evaporated to dry- 
 
V A N A D I U M. T U N G S T E N. 373 
 
 * 
 
 ness, and then redissolved in a small quantity of water. The solu- 
 tion 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.Fg and 3H.0. produce 3 
 H.F. and Cr.Oa, which last is deposited on the surface of the paper 
 in crimson scales and needles of great brilliancy. This acid, when 
 heated strongly, gives up half its oxygen, being reduced to the state 
 of oxide. It combines with bases, forming several important classes 
 of salts, in which it is isomorphous with the sulphuric and manganic 
 acids. Its salts are all coloured, generally yellow, orange, or red. 
 They will be described in another chapter. 
 
 Chromium is characterized by the remarkable colours of its com 
 pounds when dissolved, and by giving, when in the state of oxide, 
 a green precipitate with the alkalies. In the state of acid, it is known 
 by producing, with the salts of lead, a yellow, and with the salts of 
 the black oxide of mercury, an orange precipitate. It is at once 
 recognised 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, or 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, Cr.Oa, which this matter may possibly be. When it is washed with 
 much water, or digested in alkaline liquors, chromic acid is dissolved out and oxide 
 of chrome remains, CraOa-f-Cr.Og^aCr.Oz. 
 
 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 Scan- 
 dinavian 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 suf- 
 fice, although it forms a great variety of combinations, which resemble very remark- 
 ably 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 
 are 856 9 or 68 7. 
 
 The Protoxide of Vanadium, V.O., is a black powder, formed by acting 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, V.O2, which is a base combining with 
 acids and forming salts which are generally blue. It acts also as an acid, forming 
 frystallizable salts with the fixed alkalies. 
 
 The Vanadic Acid, V.O3, resembles very much the chromic and manganic acids. 
 It is a red powder, which may be melted at a red heat without losing oxygen. It 
 is very slightly soluble in water. It forms various classes of salts, of which some 
 are while, 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 solution, while that from chrome is green. 
 
 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 lime in strong mu- 
 riatic acid, the lime is dissolved out, and tungstic acid remains as a yellow powder, 
 which may be farther purified by solution in water of ammonia, and igniting the 
 
I-J74 T U N G S T E N. M OLYBDENU M. O S M I U M. 
 
 tungstate of ammonia. It is a deep yellow powder, which forms well-defined crys- 
 taliizable salts with the alkalies. The symbol of tungsten is W., from its German 
 name Wolfram, and its equivalents 1183 or 94-8. The tungstic acid resembles the 
 chromic acid, being W.O3. 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 
 tu/ngstic oxide, W.O2, of a copper-red colour. This may be also formed by diflusing 
 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 175. 
 
 The most curious fact in the history of tungsten is its producing a substance hav- 
 ing an extraordinary similarity to gold. It is prepared by adding to fused tungstate 
 of soda as much tungstic iacid as it will dissolve, and exposing the product at a full 
 red heat to a current of hydrogen gas ; the residual tungstate of soda is then to be 
 dissolved out. The new compound, which consists of tungstic oxide united to soda, 
 Na.O.-|-2W.02, remains in scales and cubes of a splendid gold colour. It resists the 
 action of acids and alkalies, 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 transmuta- 
 tion. 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 alkalies or acids. 
 
 There exist two sulphurets of tungsten, W.S2 and W.Sa, of which the latter is the 
 most interesting. It is formed by dissolving tungstic acid in hydrosulphuret of am- 
 monia, and precipitating by an acid. It is a blackish-brown powder, and one of the 
 strongest sulphur acids. Many of its compounds with the sulphurets of the alka- 
 line 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 considerable interest. When ob- 
 tained in the metallic state it is white, sp. gr. 8-6, acted on only by concentrated ni- 
 tric 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, M0.O3, 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 
 alkaline liquors, forming salts which are neutral and crystallizable. 
 
 Molybdic Oxide, M0.O2, 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 alkalies, of which some may be 
 crystallized. A molybdate of molybdenum, or, rather, a complex oxide, also exists, 
 Mo.O2-i-2Mo.O3— -M03O8. It is a blue powder. 
 
 When a solution of molybdate is decomposed by as much muriatic acid as redis- 
 solves the molybdic acid, which is at first thrown down, and a slip of zinc is immer 
 sed in the liquor, the hydrogen evolved deoxidizes the molybdic acid, and a precipi 
 tate is formed upon the zinc, at first blue, then brown, and finally black ; thus passing 
 through all the intermediate degrees to the last, the Molybdoiis Oxide, Mo.O. This 
 is a very feeble base, forming with acids salts which do not crystallize. 
 
 Sulphur combines with molybdenum in three proportions, forming M0.S2, M0.S3, 
 and M0.S4. Of these the bisulphuret, M0.S2, is important, as being the native ore 
 from which the metal and its compounds are generally prepared. It is a soft gray 
 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 circui- 
 tous that I shall not introduce them here. In the systematic works, a complete ac- 
 count of the processes pursued will be found. 
 
 The most interesting property of osmium is its forming a highly x^olatile oxide of 
 an exceedingly penetrating odour, whence the name {oaix-n). 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 compres- 
 sion it may be rendered coherent, and of a brilliant white colour. In the state of 
 powder, osmium bums when heated to redness in the air, and is oxidized by nitric 
 
COLUMBIUM AND TITANIUM. 375 
 
 acid, but loses both these characters when ignited. The symbol of osmium is Os. 
 Its equivralent is 1244-5 or 99-7. It combines with oxygen in three proportions. 
 
 The Osniic Add, or Peroxide of Osmium, OS.O4, is always formed when osmi- 
 um is burned in air or in oxygen gas. It condenses in long white needles. _ Us 
 odour is remarkably acid and pungent. It melts at 212°, 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 alkalies, forming osvdates. 
 
 The Osmic Oxide, Deutoxide of Osmium-, OS.O2, is produced by the decomposi- 
 tion of a solution of osmiate of ammonia, by a temperature 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, powder is thrown down, in which 
 the oxide is combined with water and traces of the alkali. 
 
 The sulphurets of osmium are not known. 
 
 Columbium, or Tantalum, 
 
 This metal was discovered first in an American mineral, from whence its name, 
 it was subsequently, but independently, discovered in some very rare Swedish min- 
 erals, and from the difficulty of its extraction, the name tantalum was given to it, 
 which it still bears upon the Continent, and from whence its symbol is Ta. The 
 process required to prepare it need not be described, as it is similar to that for ob- 
 taining silicon. 
 
 Metallic Columbium, or Tantalum, is a black powder, which, when burnished, 
 appears iron gray. 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 nimibers are 
 230-7 or 185. It combines with oxygen in two proportions. 
 
 Tayitalic, or Columbic Acid, Ta.Os, exists native in all the minerals 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 lit- 
 mus 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, Ta.02. This substance is gray. 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. 
 
 Titanium. 
 
 This metal, although not met with in large quantities, is yet found in a great va- 
 riety of minerals. It is not found native in a metallic state, but combined with ox- 
 ygen, forming titantic acid. To obtain metallic titanium, the volatile perchloride 
 is employed. This body absorbs ammonia, forming a white substance, Ti.Cl2+2 
 N.H3, which, when heated to redness, gives metallic titanium, with sal ammoniac 
 and nitrogen, the hydrogen carrying off the chlorine. It 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, crystal- 
 lized 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 by air or 
 water. Its symbol is Ti. Its equivalent numbers are 303*7 or 24-3, and it com- 
 bines with oxygen in two proportions. 
 
 Titanic Acid, Ti.02, exists native, constituting the mineral rutile, isomorphous 
 with tin stone (Sn.02), and also in the mineral anatase. More abundantly it is found 
 in the titanic iron, ilmenite, the formula of which is Fe.O. . Ti.02, and, which is 
 very remarkable, from having the same crystalline form as peroxide of iron, Fe203, 
 sf:; that the titanium would appear to replace the second atom of iron, and the formu- 
 la to be Fe.Ti.+Oa. This is merely speculative, however, as iron is never iso- 
 morphous with tin, and in no other case with titanium, and I hence consider this 
 histance as one of the coincidences of form described in pages 221 and 236. 
 
 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 be- 
 hind. It requires other processes to render it absolutely pure, which need not be de- 
 scribed here. It is a pure white powder, resembling silica very remarkably in its 
 propel ties, and, like it, having a soluble and an insoluble modification. It is remark- 
 
376 ARSENIC, ITS PREPARATION, ETC. 
 
 aJt)ly characterized by its solution in muriatic acid, giving with tincture of gall^ 
 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 powdej, insoluble in all acide. 
 The Bisulphuret of Titanium, Ti.S2, is a strong sulphur acid, but not otherwise 
 important. 
 
 Of Arsenic. 
 
 This metal exists in nature in a great variety of forms, and m 
 considerable quantity. It is found native, but more generally com- 
 bined with other metals, as nickel, cobalt, iron j being considered, 
 like oxygen and sulphur, as a mineralizer of other metals. Combined 
 with sulphur, it constitutes the native orpiment 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. 334. 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 grayish 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 be- 
 come so hot that the arsenious acid, in condensing, 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 ways, but best by mixture with three times its weight of black 
 flux (p. 334) 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 condenses, but with a retort it is deposited in the neck as 
 an irregular mass of rhombohedrons, variously modified. It is very 
 brittle j its sp. gr. 5*96. It sublimes at 356"^ F. without previously 
 melting. The sp. gr. of its vapour is 10362. Its vapour, if in con- 
 tact with the air, has a very characteristic garlic odour j 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 gradu- 
 ally absorbs oxygen, and falls into gray powder {suboxide^ fly powder). 
 By nitric acid it is rapidly oxidized, and deflagrates violently in 
 melted nitre. In fine powder it burns spontaneously in chlorine 
 gas, with a brilliant -^vhite flame, and burns similarly when heated 
 in oxygen gas. The symbol of arsenic is As., and its equivalent 
 numbers are 940*1 or 75-34. 
 
 Arsenic combines with oxygen in three proportions, forming a 
 suboxide^ 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 im- 
 portance. 
 
 Arsenious Acid. White Arsenic. Oxide of Arsenic — As.Og, equiv- 
 alent 1240" 1 or 99*34 — is found in commerce in masses, which, if 
 recently sublimed, are perfectly colourless and transparent, but 
 
r 
 
 A R S E N I O UVS A OI D. A RSENIC ACID. 377 
 
 gradually become milk-white and opaque. In general, the outer 
 portions of the commercial masses have thus changed, while the in- 
 terior retains its original transparency. This alteration is probably 
 connected with the dimorphism of arsenious acid (p. 228), for the 
 acid in these conditions differs in density and in solubility. The 
 transparent is sp. gr. 3-74i, 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 vit- 
 reous 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 arsenious acid is not marked, but rather 
 slightly sweet : it leaves upon the palate, however, an acrid sensa 
 tion. 
 
 The arsenious acid sublimes at 380^ F. without previously melt- 
 ing. 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 
 
 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 
 rhombohedral). 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 pe- 
 culiar ; but if it had been the transparent variety, the deposition of 
 every crystal is accompanied by a sudden flash of light, very brill- 
 iant 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 alter- 
 ation in molecular constitution 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 sub- 
 stance, administered to produce death. Its recognition is, there- 
 fore, 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. 
 
 Jlrsenic Acid. — As.O^. 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, while 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 re- 
 tort to the consistence of a sirup, 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 
 
 Bbb 
 
378 ARSENIUREr OF HYDROGEN. 
 
 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 alkalies perfectly neutral salts. At a high temperature it is ca- 
 pable of expelling all the volatile acids, even the sulphuric acid, 
 from their combinations. In its compounds it resembles very close- 
 ly the phosphoric acid j but it appears capable of forming only one 
 of the three classes of salts which phosphoric acid produces. The 
 arseniates are all tribasic, but as the quantity of fixed base varies, 
 there are some neutral and others acid arseniates j the latter were 
 formerly called binarseniates. Thus there are, 
 
 3Na.0.-f As.Oj-f-24 aq. called subarseniate of soda, 
 
 2Na.O. . H.O.+As.O^-j-M aq. " neutral arseniate of soda, 
 
 Na.O. . 2H.O.-I-AS.O5 + 2 aq. " binarseniate of soda j 
 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 recognised by being precipitated golden yel- 
 low 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, arse- 
 niate of silver, 3Ag.O.+As.05, the formation of which is easily ex- 
 plained. An insoluble arseniate heated in a glass tube with char- 
 coal powder gives a sublimate of metallic arsenic. 
 
 Arseniuret of Hydrogen. — It has been supposed, that when metal- 
 lic arsenic is used as the negative electrode of a voltaic battery, 
 the hydrogen evolved combines with it, ajid forms a brown powder, 
 hydruret of arsenic. The same body was supposed to be generated 
 in other ways j but it is now known that this substance is only me- 
 tallic arsenic finely divided, and that there is but one compound of 
 arsenic and hydrogen, the gaseous arseniuret of hydrogen. As.Hg. 
 
 This compound is easily obtained whenever nascent hydrogen 
 comes into contact with naetallic 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(S.03-[-H.O.) 
 and ZuaAs. producing 3(S.03+Zn.O.) and H As. It is still more 
 easily prepared by adding muriatic acid to a solution of arsenious 
 acid in water, and immersing therein a piece of zinc ; the hydrogen 
 first evolved reduces the arsenious acid, and the metal is then sep- 
 arated as a fine brown powder, with which the hydrogen next 
 evolved combines. This gas is generally stated to have a very dis- 
 agreeable odour, which, however, I have not found it to possess. 
 It is excessively 'poisonous; it burns with a brilliant white flame, 
 water being formed, and arsenious acid or metallic arsenic being 
 deposited according to the supply of oxygen to the gas j it is not 
 absorbed by water ; its specific gravity is 2694, formed by 
 
 One volume of arsenic vapour . . =10362 
 Six volumes of hydrogen 68 8 X 6 . = 4128 
 The seven being condensed to four . 107748 
 Of which one weighs 26937 
 
SUL PHUKETS OF ARSENIC. 379 
 
 Arseniuret of hydrogen decomposes most metallic solutions, pre- 
 cipitating metallic arseniurets of corresponding constitution (RoAs.). 
 If a current of it be passed over chloride of copper, heated to about 
 400-, it is decomposed, HgAs. and 3Cu.Cl. giving CugAs. and 3H.C1. 
 This gas is absorbed by dry sulphate of copper, which it decompo- 
 ses, 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 con- 
 taining arsenic. If a fragment of chloride of mercury be heated 
 in this gas, it is rapidly decomposed, muriatic acid gas and arse- 
 niuret of mercury being formed. At a full red heat the gas is de- 
 composed completely by itself, so that if a single point of a tube, 
 through which it streams, be ignited, all the arsenic is deposited a 
 little beyond that point, in the metallic state, and only pure hydro- 
 gen passes on. 
 
 Sulphur and arsenic combine in several proportions : the Bisulphu- 
 ret of Arsenic^ AS.S2, exists native, forming the mineral rea/g-ar. It is 
 prepared by fusing the following sulphuret with metallic arsenic, 
 and subliming the product. It is a ruby-red crystalline mass ; when 
 it is digested in solution of caustic potash, a blackish powder re- 
 mains, which may be looked upon as a subsulphuret ; its definite 
 nature is problematical. The Tersulphuret of Arsenic^ As. S3, yellow 
 arsenic, orpiment, is found native, and may be easily prepared by de- 
 composing a solution of arsenious acid with sulphuret of hydrogen, 
 AS.O3 and 3H.S. giving As. S3 and 3H.0. It is a rich yellow powder j 
 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, com- 
 bining with the sulphur bases to form salts, sulpho-arsenites. It 
 hence dissolves readily in hydrosulphuret of ammonia, and also in 
 the. caustic alkalies. In the last case there exists in solution an 
 ordinary arsenite besides the sulphur salt ; for, using potash, 2As. 
 S3 and 6K.0. produce (AS.S3+3K.S.) and (AS.O3 + 3K.O.). When 
 sulphuret of arsenic is ignited with black flux, metallic arsenic sub- 
 limes ; and the separation of the metal is still more elegantly efl^ect- 
 ed by heating the sulphuret, mixed with carbonate of potash, in a 
 current of dry hydrogen gas. 
 
 The Persulphuret of Arsenic, As.Sj, 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 5 sub- 
 limes without alteration in close vessels j is a strong sulphuric acid, 
 and hence dissolves in solutions of the alkaline hydrosulphurets, 
 forming sulpho-arseniates ; the metal may be eliminated from it by 
 the same means as those described for orpiment. 
 
 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 j but much of 
 it consists merely of white arsenic coloured by some sulphur mixed 
 with it. From 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. 
 
380 DETECTION OF ARSENIC. 
 
 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 satis- 
 factory and complete. In a question 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 iso- 
 lation 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 j I shall afterward notice the peculiarities of its other prep- 
 arations. 
 
 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 substan- 
 ces vomited by the person suspected to be poisoned should be care- 
 fully examined for the same object j and in case of death, the mate- 
 rials in the stomach and its mucous surface must be similarly search- 
 ed. The little grains of arsenious acid adherent to the surface of 
 the stomach are frequently tinged yellow at the surface by sulphu- 
 retted hydrogen, if the examination be deferred until some time af- 
 ter death. 
 
 In case of such traces of white powder being found, the examina 
 tion is very simple. Their porperties are : 
 
 1st. Heated alone in a glass tube, the powder sublimes and con- 
 denses in minute brilliant octohedrons. 
 
 2d. Mixed, in a tube closed at one end, with a little black flux, 
 and ignited, metallic arsenic sublimes, forming a steel-gray 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 in- 
 spiring, a garlic odour is perceived. 
 
 3d. On cutting off the sealed end of the tube, and then heating 
 the part containing the metallic crust, the tube being slightly incli- 
 ned, 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. 2. 
 
 4th. The white powder dissolves in water. It yields precipitates 
 with the following reagents : 
 
 A. Sulphuretted Hydrogen. — A rich yellow : soluble in ammonia, 
 and precipitated on the addition of an acid. This precipitate is or- 
 
LIQUID TESTS FOR ARSENIC. 381 
 
 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 reagents is liable to fallacy, which must be 
 guarded against. 
 
 A. Sulphuretted Hydrogen gives precipitates more or less resem- 
 bling that from arsenic with the following metals : 
 
 Cadmium. Antimony. 
 
 Tin (persaltsj. 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 pro- 
 duct. 
 
 B. Ammonia-nitrate of Silver. — Phosphate of soda produces a yel- 
 low 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 ar- 
 senite gives off oxygen and arsenious acid, while metallic silver re- 
 mains ; 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 reagents are, therefore, in themselves posi- 
 tive, unless by extraction of the metal j and this is the more impor- 
 tant when the operator has to work, not with the clear solutions 
 prepared intentionally 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 arseniuret of hydrogen. I will 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 precip- 
 itate 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 be- 
 ing strained or filtered, is to be well boiled to expel the excess of 
 chlorine, and then submitted to the action of a current of sulphuret- 
 ted 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 
 
382 marsh's test for arsenic. 
 
 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 pre- 
 cipitate produced. This is to be then collected on a filter, washed 
 carefully with water acidulated by muriatic acid, and 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 sides of the tube ; metallic arsenic sublimes, which is recog- 
 nised by the characters given already in pages 376, 380. 
 
 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 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 horizontally for a few inches, turns up and forms a 
 jet J a piece of zinc being introduced into the acid liquor, hydrogen 
 is evolved, which combines with any arsenic that may be present, 
 and, forming the gaseous arseniuret of hydrogen, passes ofi'. 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 on holding over the jet 
 a fragment of glass or porcelain, or a film of mica, a deposite is pro- 
 duced, which may be white from arsenious acid, or brown from me- 
 tallic arsenic, according to the height at which the plate is held, 
 and the consequent completeness of the combustion, or the reverse. 
 If the quantity of arsenic be too small to produce this eftect in a cer- 
 tain time, it may be better detected by igniting a portion of the hori 
 zontal arm of the tube. All the arseniuretted hydrogen, in passing 
 that point, deposites 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 em- 
 ployment of the methods just described. In this case the liquid 
 should be made so feebly 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 terminating 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 subsequently 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 ar- 
 seniuretted hydrogen being then absorbed and decomposed, metallic 
 
SOURCES OF ERROR. 383 
 
 arsemurets are produced, which easily yield, by the application of 
 heat, the arsenic in the metallic form. 
 
 In this mode of detecting the presence of arsenic, it is necessary 
 to avoid some sources of error, into which, without previous knowl- 
 edge of their existence, an operator might easily fall. If the effer- 
 vescence 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 suspicion, or perhaps wrong conclusions. This 
 may be avoided by either moderating the effervescence, or by pass- 
 ing 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 sul- 
 phuret, 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 
 sulphuric 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 con- 
 sidered 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 pre- 
 cisely similar gas, antimoniuret of hydrogen. It would anticipate too 
 much the history of that metal to enter into the details of the means 
 of distinguishing that gas from the arseniuretted hydrogen, but they 
 will be fully described in their proper place. 
 
 Arsenious acid possesses the power of preventing the putrefac- 
 tion 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 com- 
 pounds, which are not susceptible of alteration under ordinary cir- 
 cumstances. 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 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 committed 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 survi- 
 ved for a length of time sufficient for the complete permeation of the 
 tissues by the absorption of the poison ; in the others, death had 
 occurred while it was yet only in the intestinal tube. The absorp- 
 tion 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 
 
384 ANTIDOTE TO ARSENIOUS ACI D. A N T I M O N Y. 
 
 of a single dose, but by frequently repeated doses, each insufficient 
 to produce rapid poisoning. The decision in such cases is rendered, 
 however, extremely difficult by the fact, recently established, that 
 the resemblance of function, so often alluded to, between arsenic 
 and phosphorus, is such, that the latter element, which character 
 izes the animal tissues by its almost constant presence, may be 
 replaced as a constituent of our organs by arsenic. Thus, the 
 bones may contain arseniate of lime as a substitute for some of 
 their proper phosphate of lime, and in the phosphoric salts, which 
 are found in the blood, a similar replacement 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 poi- 
 soning, the analysis of the organs might lead to useful evidence, 
 ret the discovery of arsenic out of the alimentary canal should, as 
 conceive, not without great caution, be considered as necessarily 
 involving its having been administered. 
 
 The sulphuret of arsenic of commerce, king's yellow^ when taken 
 as a poison, is recognised by its solubility in ammonia, from which 
 It is again thrown down by an excess of any acid. Its reduction to 
 the metallic 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 so- 
 lution of arsenious acid, this disappears, being changed into arsenic 
 acid, and the iron into protoxide, 2Fe203 and As.Og producing 4Fe.O. 
 ~f- As.Og. This arseniate of iron has no action on the system , and 
 hence, in cases of poisoning by arsenic, this hydrated peroxide 
 should be administered as largely and as rapidly as possible. It 
 may be made in a few moments 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. 
 
 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 dyeing. It has many other less exten- 
 sive uses. 
 
 Of Antimony. 
 
 This metal was first discovered, and its preparations introduced 
 into medicine by Basil Valentine, from the unpleasant results of 
 whose experiments upon his fellow monks it got the name of 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 obtaining it by means of iron is no- 
 ticed p. 332, but it is had purer by fusing the sulphuret at a bright 
 red heat with black flux. Sulphuret of potassium and oxide of an- 
 timony are first formed, and this last being decomposed by the car- 
 
OXIDES OF ANTIMONY. 385 
 
 bon, carbonic oxide is evolved, and metallic antimony separates; 
 this process is farther detailed in p. 334. 
 
 The antimony thus obtained is a brilliant white metal, of a highly 
 crystalline fracture, and may be obtained crystallized in rhombohe- 
 drons, like those of arsenic, by fusion, as described in p. 23 ; its 
 specific gravity is 6*8 ; it melts at about 800^, just below redness, 
 and may be volatilized by a white heat. If heated violently in con- 
 tact 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 ipowder, flowers of antimony. Antimony in powder takes 
 fire spontaneously in chlorine, burning with a yellowish flame ; the 
 antimony is not oxidized by exposure to the air nor by water ; it 
 is not acted on by sulphuric nor muriatic acids, but is rapidly oxi- 
 dized by nitric acid. The symbol of antimony is Sb. ; its equiva- 
 lent numbers are 1613 or 129*2 ; it combines with oxygen in three 
 proportions. 
 
 Oxide of jlntimony — Sb.Og ; equivalent 1913 or 153'2 — may be 
 prepared by adding to an acid and boiling solution of chloride of 
 antimony in water, carbonate of soda in excess. The carbonic acid 
 does not combine with oxide of antimony, which therefore precip- 
 itates 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 which it is, therefore, isodimorphous ; both the metal and 
 this oxide, when ignited 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 veg- 
 etable acids, double salts of remarkable constitution ; of these the 
 potash tartrate of antimony (tartar emetic) is the most important ; it 
 also acts as a feeble acid ; thus, if in its preparation caustic potash 
 be used to decompose the chloride, a granular white powder is ob- 
 tained, in which the oxide of antimony is combined with potash ; 
 it is on this account called hypo-antimonious acid by many chemists. 
 
 xy sulphur et of Antimony. — Sb.O3H-2Sb.Ss. 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 dis- 
 solved 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 pro- 
 duced ; this, when melted, constitutes the glass of antimony, and 
 the oxysulphuret is the crocus of antimony of the older pharmaco- 
 poeias. 
 
 Antimonious Acid. Peroxide of Antimony. — Sb.04. Equivalent 
 2013 or 161-2. This is the most stable compound of oxygen and an- 
 timony ; 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 ; 
 
 Ccc 
 
386 SU LP BURETS OF ANTIMONY. 
 
 it combines with alkalies, forming salts insoluble in water, and from 
 which, by a stronger acid, it is separated as a hydrate, Sb.04+H.O. 
 This hydrate dissolves in strong muriatic acid. 
 
 Antimonic j^cid.—Sh.O^. Equivalent 2113 or 169-2. This sub- 
 stance is first formed when metallic antimony is oxidized by an ex- 
 cess 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, as just described j it is, however, more 
 stable in combination, and may hence be prepared by deflagrating 
 antimony with nitre j when the resulting mass is digested in cold 
 water, nitrate and nitrite of potash dissolve out, and leave the anti- 
 moniate of potash as a white powder j 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 hy- 
 drochloric acid. 
 
 Antimony and sulphur combine in three proportions, forming sul- 
 phurets, which resemble completely, in constitution, the oxygen 
 compounds ; they are sulphur acids, dissolving in a solution of the 
 alkaline sulphurets, and forming sulphur salts. 
 
 Sulphuret of Antimony. — Sb.Sg. Equivalent 2216-6 or 177*5. This 
 substance constitutes the common gray ore of antimony, and crys- 
 tallizes 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 sulphu- 
 retted hydrogen ; it is then an orange powder, Avhich becomes darker 
 on being dried, and has the same composition as the native sulphu- 
 ret, with which it becomes identical in appearance by fusion. This 
 sulphuret dissolves in alkaline solutions, on which circumstance are 
 founded the various pharmacopoeial processes for its formation. It 
 has been used in medicine ever 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 sul 
 phur and the other oxygen, united to antimony and potassium. For 
 one half of each substance is decomposed, the oxygen passing to 
 the antimony, and the sulphur to the potassium, so that oxide of an 
 timony and sulphuret of potassium result, and these respectively 
 combine with the quantities of potash and sulphuret of antimony 
 that had not been altered ; in this way, 
 
 C Sb.Sa 3K.0. ) C Sb.Sg-f 3K.S. ) 
 
 < and V produce < and > 
 
 ( Sb.Sa 3K.0. ) I Sb.03+3K.O. ) 
 
 When the solution cools, both compounds are partly decomposed, 
 so that a quantity of sulphuret and of oxide of antimony precipitate 
 mixed together j and hence an opinion has generally prevailed, and, 
 indeed, been supported by the high authorities of Leibig and Gay 
 Lussac, that these bodies are chemically united in the precipitate 
 
PREPARATION OF KERMES MINERAL. 387 
 
 SO obtained, and that it is an oxysulphuret, identical in constitution 
 with that already described. It is, however, quite established, par- 
 ticularly by the experiments of Berzelius and H. Rose, that the ox- 
 ide and the sulphuret are but mechanically mixed ; under the mi- 
 croscope, the former is seen as brilliant white crystals, mixed with 
 the fine amorphous brown powder of the latter} and, besides, the 
 quantity of oxide is completely variable, and in no case so great as 
 the composition of the true oxysulphuret 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 temperature, and the degree of concentration of the liquor. 
 It is termed in pharmacy kermes mineral^ from a very remote analogy 
 of its colour to that afforded by the insect kermes {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 pro- 
 portion of base, is precipitated by adding an acid in excess. The 
 sulphuret of potassium is decomposed, and the sulphuret of anti- 
 mony, with which it had been combined, separates ; at the same 
 time, the sulphuretted hydrogen, evolved from the sulphuret of po- 
 tassium, reacts on the oxide of antimony, converting it into sul- 
 phuret. This precipitate is much lighter-coloured generally than 
 the kermes, and is sometimes called the golden sulphuret of anti- 
 mony^ although that name properly belongs to a different substance, 
 to be described farther on. In many cases, in place of collectinof 
 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 constitutes the 
 brown sulphuret^ or orange sulphuret of antimony of the British phar- 
 macopoeias. 
 
 In place of caustic potash, the native sulphuret of antimony is 
 frequently boiled with carbonate of soda. In this case the whole 
 of the carbonic acid unites with one half of the soda, forming bicar- 
 bonate, and the other half of the soda acts with the sulphuret of 
 antimony precisely 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- 
 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 circumstance which, though occurring in all cases, is 
 more marked in this process than the others. It is, that some anti- 
 mony separates in the metallic state, while another portion is 
 changed into persulphuret j thus SSb.Sg produces SSb.Sg, 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 car- 
 ries down with it also some sulphuret of potassium, and hence the 
 
388 ANTIMONIURET OF HYDROGEN. 
 
 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.S4. This substance is produced as 
 a yellow powder when the solution of antimonious acid is decom- 
 posed by sulphuretted hydrogen. 
 
 Sulpho-antimonic Acid — Persulphuret of Antimony^ Sb.S^ — is obtain- 
 ed when a solution of antimonic acid in muriatic acid is treated 
 with sulphuretted hydrogen. It is of a fine golden orange colour. 
 Its formation 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 sul- 
 phuret 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.Hg. When hydrogen is evolved 
 in contact with antimony in a nascent or finely divided state, th^y 
 combine and form a gas, which, in properties and constitution, has 
 a remarkable similarity to arseniurct of hydrogen. The. easiest mode 
 of effecting this is to dissolve zinc in dilute sulphuric acid to which 
 tartar emetic has been added. The gas so evolved is colourless, in- 
 soluble in water, has neither acid nor alkaline reaction. It precip- 
 itates the salts of mercury and most metals, but not copper, by 
 which it is distinguished from the arseniuret of hydrogen. Its 
 specific gravity has not been experimentally determined ; but if it be 
 composed, like arseniuretted 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, according 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 
 heating a point of the tube through which it passes to redness, 
 deposites the metal at the heated part, while arsenic settles at a 
 certain distance beyond, where the tube is colder. 
 
 2d. The metallic crust is not volatilized at any temperature which 
 can be applied to glass. 
 
 3d. If the metallic scale be deposited on a porcelain plate, and ox- 
 idized by the outer flame of the blowpipe, it forms a powder yel- 
 low while hot, but white when cold, which is not volatilized by 
 any farther application of the flame. Arsenic, on the contrary, be- 
 comes 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 theie 
 cases they may be separated 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. 
 
 The detection of antimony is generally simple ; in all its combi- 
 nations it is immediately recognised by the formation of its com- 
 
TELLURIUM AND ITS COMPOUNDS. 889 
 
 pound 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 hydrogen are more yellow, but are all easily distinguish- 
 ed from orpiment by not being volatile, and from the bisulphuret 
 of tin by yielding the antimoniuret of hydrogen. From the sul- 
 phuret of cadmium they are known by their solubility in hydrosul- 
 phuret of ammonia. 
 
 Of Tellurium, 
 
 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 in- 
 ferior to the others, it ranks naturally with sulphur and selenium, to which last it 
 assimilates completely in its properties. It exists in nature, native, and combined 
 with a variety of metals, gold, silver, antimony, lead, &c., forming ores of very in- 
 definite constitution. Its extraction, which is still farther complicated by the pres- 
 ence of sulphur and selenium, would require too detailed description, and is too sel- 
 dom an object with chemists to require description here. Its properties and princi- 
 pal compounds alone deserve attention. 
 
 Pure tellurium is silver white and very brilliant. It crystallizes easily in rhom- 
 bohedrons. It is brittle and easily powdered. Its sp. gr. is 6-14:. It is about as fu- 
 sible as antimony, and at a very high temperature 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 potas- 
 sium; 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 tel- 
 luric acids. The former, telltirous acid, Te.O^, is prepared by decomposing the bi- 
 chloride of tellurium by water, Te.Clz and 2H.O. producing 2H.C1. and Te.02. 
 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 alkaline solutions, forming compounds of a very instable character. 
 When its solution in water is heated to about 110=', it deposites the tellurous acid in 
 an anhydrous form. The water is also expelled by a moderate heat from the hy- 
 drated acid in powder. The anhydrous acid thus obtained differs essentially from 
 the hydrated form. It is insoluble in water, in acids, and in alkalies, 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 hydra- 
 ted tellurous acid is thrown down on the addition of an acid. 
 
 Berzelius considers these remarkable differences of properties as indicating 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. 
 
 Tdluric Acid, Te.Oa, is prepared by deflagrating tellurous acid with nitre; a sol- 
 uble tellurate of potash is thus obtained, which, when mixed with nitrate of ba- 
 rytes, 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 ofl' 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 ofl', it becomes 
 orange, and undergoes a change of properties like stannic acid. It becomes insolu- 
 ble in water, in acids, and alkaline solutions; when very strongly heated, it gives 
 off oxygen, and tellurous acid remains ; but if this anhydrous acid be fused with 
 potash, tlie 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 
 resembles in its characters sulphuret of hydrogen, particularly in its odour; it red- 
 
890 URANIUM AND ITS COMPOUND S. C O P P E R. 
 
 dsns litmus, is soluble in water, decomposes the alkalies and earths, forming soluble 
 tellurets, and precipitates insoluble tellurets from solutions of the other metals. 
 
 Tellurium combines with sulphur in two proportions, forming sulphurets, which 
 do not require detailed notice. Its compounds with the metals resemble so com- 
 pletely 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 tellu- 
 rets are soluble or insoluble in water, precisely as the sulphurets of the same metals 
 are. 
 
 Of Uranium. 
 
 This metal exists in some rather rare minerals, particularly mpeckblende, combined 
 with oxygen; the processes for its extraction are rendered very complex by the 
 presence of a great number of other metals, and I shall refer, therefore, to the sys- 
 tematic works for the details of its extraction ; the metal itself is easily obtained 
 pure by the action of hydrogen gas on either of its oxides at a red heat. It is of a 
 dark gray colour, difficultly fusible, specific gravity 90. Its symbol is U., its equiv- 
 alents are 2711 or 217-3, being the largest numbers for any oi the simple bodies; it 
 combines with oxygen in two proportions. 
 
 Protoxide of Uranium, U.O., is obtained by decomposing any salt of uranium by 
 a caustic alkali ; it precipitates as a greenish hydrate, which rapidly becomes yel- 
 low, forming the peroxide by absorbing oxygen : the protoxide of uranium is dis- 
 solved by an excess of ammonia. Peroxide of uranium, U.O3, is formed when the 
 protoxide is heated in air ; it is yellow, and possesses some of the characters of an 
 acid, uranic acid ; it reddens litmus ; it enters into combination as well with alka- 
 lies as with acids ; the alkaline 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. 
 
 SECTION V. 
 METALS OF THE FIFTH CLASS. 
 
 Of Copper. 
 
 Copper is one of the most important of the metals, and one, also, 
 of the most extensively diffused through nature. It exists native in 
 veins, and frequently crystallized, in forms belonging- to the regular 
 system ; in the state of oxide it is found, both uncombined and form- 
 ing arseniates, phosphates, carbonates, and other salts, but its most 
 abundant source is the native sulphuret. The ordinary copper ore, 
 copper pyrites^ is a double sulphuret of copper and iron, CuaS.+FegSa, 
 and from this the metal is extracted for the purposes of commerce. 
 
 The general processes for the reduction of a metallic sulphuret 
 have been already described (p. 333), but, from the composition of 
 the copper ore, some additional management is required ; there are 
 two metals present in the ore, and as neither is volatile, the product 
 after complete reduction should be, if the process was simply man- 
 aged as for a simple sulphuret, not pure copper, but an alloy of one 
 equivalent of copper and two of iron ; this is avoided by arresting 
 the process of reduction at a certain stage ; the copper, having less 
 affinity for oxygen than the iron, assumes the metallic state first, 
 and, if it were possible to work so accurately, the whole of the cop- 
 per might be reduced before any iron, and this last metal left alto- 
 gether in the scoriae as oxide or silicate ; but this not being feasible, 
 the copper first obtained is rendered impure by the presence of a 
 quantity of iron, and also of sulphur ; this impure copper is then 
 calcined ; the iron and sulphur, being the more combustible bodies, 
 are first oxidized, and then again, by other reductions and calcina- 
 tions, the copper is ultimately brought to a state of complete purity 
 
PROPERTIES OF COPPER. 391 
 
 The separation of the iron is facilitated by adding a small quantity 
 of sand to the calcined mass before the process of reduction j the 
 silicic acid unites exclusively with the oxide of iron, and the silicate 
 of iron not being reducible under ordinary circumstances, the puri- 
 fication of the copper is more rapidly effected. 
 
 Though the copper is thus rendered quite pure from iron, great 
 care is still required in these operations, in order to secure the 
 proper softness, ductility, and tenacity necessary in the employ- 
 ment of this metal in the arts j thus, if it has been too long in con- 
 tact with the fuel, it combines with a small quantity of carbon ; if, on 
 the other hand, the deoxidizing 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 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 reservoirs in which the drainage water of the mine is col- 
 lected, and by electro-chemical action, as described p. 193, 195, 
 and 335, the iron is dissolved and the copper precipitated in irreg- 
 ularly crystallized masses. 
 
 Pure copper is of a peculiar well-known reddish colour. It is 
 very malleable and ductile ; after iron, it is the strongest of the met- 
 als. It crystallizes 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 cop- 
 per. 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 gen- 
 erated. In this way the feeblest acids may act upon copper, as the 
 acetic acid and the acids contained in the various fatty bodies, and 
 the metal be thus introduced into culinary preparations, and so pro- 
 • duce 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 j its equivalent 
 395-7 or 31-7. 
 
 Copper combines with oxygen in two proportions, forming a sub- 
 oxide and a protoxide. 
 
 Protoxide of Copper. — Cu.O. Equivalent 495-7 or 39-7. This ox- 
 ide 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 
 
392 OXIDESOFCOPPER. ' 
 
 dull black powder, which, by a very high temperature, m^y be melt- 
 ed, and crystallizes on cooling. It dissolves but slowly in acids, 
 forming the ordinary blue or green salts of copper. When heated, 
 even below redness, in a stream of hydrogen gas, it is perfectly re- 
 duced, water being formed. It is thus that, as described in p. 253, 
 the composition of water is best determined. At a dull red heat, 
 this oxide is reduced completely 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 con- 
 taining nitrogen, to prevent the formation of nitrous or nitric oxides. 
 
 When a solution of caustic potash is added in excess to a solu- 
 tion of a salt of copper, the protoxide is thrown down as a hydrate, 
 Cu.O. . H.O. It is a fine blue powder, which is decomposed by a 
 very gentle heat, so that even if a liquor containing it be boiled, it 
 becomes brown and anhydrous, 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. 
 
 Suboxide of Copper. — CugO. 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 cop- 
 per and four of copper filings j half of the oxygen of the former 
 passes to the latter, and the whole becomes suboxide. It is like- 
 wise made by fusing together three parts of subchloride of copper 
 and two of dry carbonate of soda ; chloride of sodium and suboxide 
 of copper result, CU2CI. and Na.O. giving CugO. and Na.Cl., while 
 the carbonic acid is given off. This suboxide of copper is a red- 
 dish-brown powder, which is much less acted on by moist air than 
 pure copper ; and hence, under ordinary circumstances, when cop- 
 per 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 Fe203 giving CU2O. and 2Fe.O. j 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 
 metallic 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 J thus sulphurous acid converts the hydrate of the black oxide 
 into sulphate of the suboxide, S.O2 and 2Cu.O. producing S.O3 + 
 CuaO. From the solution of this salt, a fine orange hydrate of the 
 red oxide is thrown down by the caustic alkalies. Protochloride 
 of tin and protosulphate of iron also reduce the salts of copper to 
 this state of oxidation. 
 
 Sulphur combines with copper in two proportions, forming sul- 
 phurets equivalent to the oxides just described; they are both found 
 
DETECTION OF COPPER. 393 
 
 native, and constitute, particularly the subsulphuret, 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 appli- 
 ed 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 subsul- 
 phuret J these bodies are not of importance, except as the great 
 sources of metallic 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 CU2S. or Cu.S., according as the solution contain- 
 ed 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 am- 
 monia, a precipitate is produced, bluish or green, according to the 
 acid with which the oxide had been combined, but in all cases pro- 
 ducing with an excess of the ammonia a deep violet-coloured solu- 
 tion. 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 broAvn precipitate of ferrocyanide of copper. With sul- 
 phuret 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 re- 
 duced, 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 differ- 
 ent; 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 con- 
 stitution changes. The colourless solution of suboxide of copper in 
 ammonia becomes violet blue in the act of pouring it from one bot- 
 tle to another ; and hence, for the mere detection of copper, the 
 properties of the protoxide alone need be taken into account. 
 
 Like the oxides of cobalt and nickel, the oxides of copper are not, 
 by themselves, soluble in water of ammonia. The solutions of these 
 metallic compounds in water of ammonia are basic salts, to the con- 
 stitution of which the acid, with which the metallic oxide had been 
 originally 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 dis- 
 tinct. Fused 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 reducing flame and suddenly cooled, is deep ruby 
 red, generally opaque. This change of colour arises from the cop- 
 per being reduced to the state of suboxide The colour given to 
 glass by this suboxide is a pure prismatic red, so homogeneous that 
 red light may be obtained for optical experiments by transmitting 
 
 Ddd 
 
rsKPUi. AI.I.OTS or copper. — lead. 
 
 m^ke B^ tkio«gk tlus endowed ^ass^ and tht tint is so fine that 
 tkis raby gkss is tlw nofit valaaUe that can be used for ornamental 
 
 TWe salits of cofiptK geaeiaDy tinge tlie flame of tlie blowpipe 
 U«e tMT gieea, acemdia|r to tlie other bodies that Biay be present. 
 
 ladepeadcat of die direct aapkyymeiit of copper in the arts, for 
 %Aich its pn^erties eminentlf qnalify it, A enters into the compo- 
 cifagreatnaBberofallojscif^reatiHiportaiice. Thosbronze, 
 r vaed as a iwbaritnte fw sle^ aid still employed in the 
 _ of stataes aad mowuDamtSk from the aocoracy with which it 
 adapts itsetf to the moald, and its dnrabilitj, consists of ninety pans 
 <if copper and ten of tia in 100. It is curkHis, that from the Tery 
 ^i^rltffa* ages, this, which is stiU the best {m^ortiott, should hare been 
 employed ^ the bronze swords fr«m ancient l^ypt, from Scandina- 
 Tia, and those found in Ireland, haTing aU this constitution. Gwt 
 rngtalf or dmt of which cannons are cast, is an inferior kind of bronze. 
 
 The elasticitj and sonoronancss td these aDoys are very remark- 
 able. That naed for hefk^ Ml mmmi, couists of 80 parts of copper 
 and 20 of tin. The Indian g w ^i hare this composiiion, bat com- 
 mon bdk contain less tin, and, in place of it, some lead and zinc. 
 In Ae pn^mtion of two parts of eopfct to one of tin, or, more 
 accnratety, of four atoms of copper to one of tin, 127 to 59, an 
 aBoy is formed of exceeding hritdaiesB and hardness, and so brill- 
 iant, when traly jioKshrd, as to be nsed for ^e mirror surface in 
 Tcflectii^telesi^^ies; it is hence called ^pccWnm wcte/. The quality 
 of this aHoj is rwnarkaMy detcn<»ated by a slight deriation to ei- 
 tha side erf" thetrae atomic proportions. 
 
 The alloys of zinc and copper are Tery numerous and important, 
 conslitnting the diftrent varieties of brmn. The best brass consists 
 of four atoms of coppn to one of zinc; but, bj changing the pro- 
 
 of Ac mcials, a ranety of shades of gold lustre, 
 countofeit jewidrj, are obtained, b dw prc^portion of equal parts 
 of copper and zine, imd MtUkr is prodnced| this is used in solder- 
 ing togeAer sm&ces of bnai and copper. 
 
 OfUmL 
 
 This metal exists in nature, Tery extensirely difinsed, and in a 
 Turiety of forms. The Hulphsff, phosphate, arseaiate, car- 
 and chloride of lead are found natiTe ; but it is exclosirely 
 die salphuret of lead, g«2ena, that the metal is extracted for 
 1^ puiposes «^ covnmerce. The methods used in its redaction 
 huTe bran Tery fully descrihed in die preceding chapter, p. 3^. 
 Lead is one of due softest and least tenacious of the metals ; it is 
 white, and Tery brilliant, hut rapidly tarnishes in the air, be- 
 c<rrered with a gnjidft coating, beyond which the action 
 does not a^ear to extend; its ^ecific graTitr is 11-44 ; it melts at 
 613^, and in solidifying diminiiAes in Tolume, so that it is unfit for 
 accunte castings ; it may, howerer, be obtained, by fusion, crystal- 
 lized in octobedrons ; it is not Tolatile ; it is not sensiblT acted on 
 by muriatic nor sulphuric acids, exc^ at Tery high temperatures, 
 Iwt by nitric aeid it is rapidly oxidized and disK^lred. 
 
OXIBES OF LBAH. 
 
 Whes lead is cnoMd at dKauwiiaie to air a 
 oeceda witk gieaf nfidilj, ao as to be 
 air ^2^). The cxnie so fonBed is 
 Ua, so that a^en pare mter, laia, or erem 
 preaenred ia leadea ctitenis, aa i a qaegaa l km vilk lead i 
 
 habitaalij as a ^oA, Foftvaatelf , this is ohratfad, 
 
 tile aaiall qaaatities of 
 
 aH 
 
 ofitfioai 
 OBtheiateriorortiMs 
 
 it froBi ihe oiidiil a g aetioB af the air ; ao daager is tM tnJmm. to 
 he ^ipicheBded froat the sapplf of vater to a otj 
 
 lefas;for 
 tke%cnoriociB 
 
 for its i iro tc c t iom. 
 
 ThesyabolofleadisFbsftoaiitaLatiaaaaie; ite 
 t3t94r9 or 103^. It r iwdiiai ■ vi& ozjgcB ia two 
 
 af Lm£— Fh.0. Eqairdeaft 139^ or 111-7. TUa 
 ■Mjbe prepared hf riposiag ■tli l lii lead at a red heat to a car- 
 
 ao prodaeed laaea. It foraM, oa coalii^ crjatailBe aaaaes of a 
 
 arhich is gemeaStf obtnaed ia the capdbtioo of lead for tke par- 
 pose of extiattia^ feat it the sBaU qotitjr of alver vhicb its ana 
 gcBerallj eoataiB. Wkea the fitharge is kept lor ssbk tiaM. Ae 
 
 heat. This 
 
 of thecryalaBiaeforaiofthelilharge. TW tcIIow lbr» 
 to be wne aeraaaeat if the r 
 
 bepndaeedoffhe 
 ofleadata 
 the fasiaa of the oxide. 
 
 Tins oxide any also be prepared by 
 of lead by eaaade potash ; a vhke 
 
 akydrateof theo9ade,2FbL-fH.O.; byagicatexceasof< 
 ashthepncip^ateaiajbeiediaMdved. The oxide of 
 to ha^e the power af aaitiaff wi^ oMMt of tke 
 to forai coBipoaai 
 
 ed by bofliap Ine aad filbuge toveiher, is capable af • 
 and is aaed to dye the hair blade The 
 a Uaek aalpharet of lea 
 
 <Aaage. The protoxide of lead icqaiies 12,000 parts of 
 dissolve k ; the solatioa reads fc^lr daliae ; it is a 
 aad the oaiy oxide of kwd which co^Ums with 
 adeari^lVOU»«bl»a.db, 
 
396 OXIDES AND SULPHURET OF LEAD. 
 
 in chlorine water, or in a solution of chloride of lirrie. In the first 
 case, 2Pb.O. and CI. produce Pb.Oa and Pb.Cl. In the second case, 
 Pb.O. and Ca.O.Cl. produce Pb.O^ and Ca.Cl. ; another simple plan 
 consists in heating 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 obtained is of a dull dark brown colour j 
 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 absorbs, neutral white sul- 
 phate of lead, Pb.Oa and S.O^ producing Pb.O. + S.Og. This oxide 
 of lead does not form salts. 
 
 The Red Lead, or Minium, Pb304=2Pb.O. + Pb.02, 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, increas- 
 ing 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 pro- 
 toxide ; with muriatic acid it forms protochloride and chlorine. It 
 does not form any proper salts, but it dissolves in acetic acid com- 
 pletely, giving a colourless liquor, from which, after a little time, 
 peroxide of lead separates. 
 
 It is probable that there exist other oxides of lead ; thus the gray 
 coating which forms on lead exposed to the air is looked upon by 
 many chemists as a suboxide ; and on heating oxalate of lead to low 
 redness, a gray powder is obtained of a similar nature, and yields, 
 on analysis, the formula PbaO. In general, these bodies have been 
 considered as mixtures of the metal in powder with the real pro- 
 toxide J but I think the evidence of their definite constitution very 
 strong. 
 
 From the similarity of the formula of red lead, Pb304, to those of 
 the black oxide of iron, FcgO^, and of the red oxide of manganese, 
 Mn304, it has been suggested that it may contain sesquioxide of lead, 
 PbaOg, similar to FcaOa and MnjOg. The formula of red lead should 
 then become Pb.O.+PbiOa ; but this idea, though interesting, is only 
 hypothetical. 
 
 Sulphuret 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 
 sulphuretted hydrogen gas or hydrosulphuret of ammonia. It is 
 then a black powder, insoluble in water, and in alkalies, and dilute 
 acids. It is rapidly 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 re- 
 spectively the most delicate reagents for each other. 
 
 There are some indications of the existence of other sulphuret* 
 of lead, which, however, do not require special notice. If a salt o[ 
 
DETECTION AND USES OF LEA D. B I S M U T H. 397 
 
 lead be decomposed by bisulphuret of calcium, a red precipitate ap- 
 pears, possibly a bisulphuret of lead^ analogous to the deutoxide, and 
 galena may be fused with metallic lead, forming a homogeneous 
 mass, in which, probably, 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 recog- 
 nised by giving, with caustic potash, a white precipitate, soluble in 
 excess ; with carbonate of potash, one also white, but insoluble in 
 excess; with sulphuretted hydrogen, one dark brown or black, 
 whose characters are described above ; Mdth a solution of bichro- 
 mate of potash, the salts of lead produce a fine yellow precipitate, 
 chrome yellow ; 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 acids. If 
 the solution contain much lead, any soluble chloride throws down 
 sparingly soluble chloride of lead, which, however, remains dissolv- 
 ed, 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 
 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 
 antimony. The inferior sorts of pewter are alloys of lead and tin, 
 but the fine kinds should be tin with very little lead, and some anti- 
 mony and bismuth. The solder used for soldering surfaces of lead, 
 or of tinned iron, to each other, consists of lead and tin, the propor- 
 tions 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 it is. Fine solder fuses at 360°, 
 coarse solder at 500°. 
 
 Of Bismuth. 
 
 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 bis- 
 muth is too rare to be of technical interest. ' It is extracted from 
 the rocks through which it is disseminated by reducing them 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 pla- 
 ced 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 
 considerable 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 scoriae which form on the surface. The crys- 
 tals so obtained have frequently beautiful rainbow tints on their sur- 
 face, 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 vio- 
 
398 BISMUTH AND ITS COMPOUNDS. 
 
 lently, 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, Bi.O,, 
 the last a teroxide, Bi.Oa. 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 show that this analogy is not at all 
 so strong as had been supposed, and that their diiierence is more remarkable 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 bis- 
 muth are exceedingly instable, and, like those of antimony, are decomposed by wa- 
 ter, so that, while it allies itself to that metal in every important point of physical 
 and chemical characters, it recedes in all the important facts of its history from cop- 
 per, iron, zinc, and the other metals of the magnesian class, I therefore think 
 these are suflicient grounds for abandoning the numbers 8869 and 71-1, given in the 
 table, p. 205, and to assume 2660-7 and 213-3, as the equivalents of bismuth on the 
 oxygen and hydrogen scales respectively. 
 
 Oxide of Bismuth — Bi.Og ; equivalent 2960*7 or 237*3 — may be 
 prepared by the combustion of bismuth at a high temperature, or by 
 the ignition of the subnitrate of bismuth. It is a bufl*-coloured pow- 
 der, which may be melted. It combines with acids to form well- 
 characterized salts. 
 
 The Superoxide of Bismuth, Bi.Og, is prepared by boiling finely- 
 levigated oxide of bismuth in a 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 decom- 
 posed 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 would be a sesquioxide, Bi203, like the 
 sesquioxides of cobalt and nickel, which it resembles so much in 
 properties ; but the formula, Bi.Oa, agrees as well with the analyti- 
 cal results, and I look upon it as corresponding to antimonic acid. 
 
 Sulphuret of Bismuth, Bi.Sg, 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 alkalies pro- 
 duce a white precipitate of hydrated oxide of bismuth, which is in- 
 soluble in excess. A strong solution of a salt of bismuth is decom- 
 posed by the addition of water, whereby a white basic salt is pre- 
 cipitated, 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 bismuth j and by increasing the quantity of bismuth, the fusibil- 
 
EXTRACTION OF SILVER FROM ITS ORE. 399 
 
 ity 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 fu- 
 sible metal used for the bath in taking the specific gravities of va- 
 pours, as described p. 14, and for supplying a steady source of 
 heat for other purposes. 
 
 SECTION VI. 
 
 METALS OF THE SIXTH CLASS. 
 
 Of Silver. 
 
 This metal exists native, and in the state of sulphuret, in a great 
 variety of places j and from the facility with which it may be ex- 
 tracted, 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 remark- 
 able. 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 fine- 
 ly disseminated to be simply melted out. It is washed out by mer- 
 cury, this fluid metal dissolving the silver, and being then distilled 
 off, leaves the precious metal behind. A very remarkable process 
 is used to extract the silver from the sulphuret. This ore is roast- 
 ed in a reverberatory furnace with chloride of sodium, by which 
 chloride of silver and sulphuret of sodium are formed, Ag.S. and 
 Na.Cl. giving Ag.Cl. and Na.S. 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 decomposes the chloride of silver, 
 forming chloride of iron and setting the silver free, and this dis- 
 solves in the mercury, forming a fluid amalgam ; this is strained 
 through leather bags, by which a great part of the mercury passes 
 off, and a pulpy mass of amalgam of silver is obtained, which is then 
 submitted to distillation, by which the mercury is separated, 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 re- 
 duced 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. 395, 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 by the metal thus flashing or 
 lightening^ as it is technically termed. This is the process of cupeU 
 lation. 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 
 
400 PROPERTIES OF SILVER. 
 
 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 sil- 
 ver, is melted, and allowed to cool very slowly, so as to crystallize, 
 the portions which first solidify are pure lead, and these being re- 
 moved with iron colanders, all the silver remains in the mother li- 
 quor. 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 oxi- 
 dized at the cupel diminished in a corresponding degree. 
 
 The silver of commerce is never pure, and hence, for chemical 
 purposes, must be freed from the metals, generally copper, associa- 
 ted with it. For this purpose it is dissolved in nitric acid, and its 
 solution precipitated by common salt. Chloride of silver separates, 
 which is then reduced by any of the methods described in p. 332, 
 333. The method of assaying may also be used to obtain pure sil- 
 ver. 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 malle- 
 able. Its sp. gr. is 10 5; it fuses at 1873^. It is not altered byair 
 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 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, laut 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 rap- 
 idly dissolved by nitric acid, with evolution of nitric oxide gas. 
 
 Silver combines with oxygen in three proportions, forming ox- 
 ides, of which only one, the protoxide, is well known. The equiv- 
 alent of silver is 1351-6 or 108-3, and its symbol is'Ag., from the 
 Latin name. 
 
 Protoxide of Silver — Ag.O. ; equivalent 145 1-6 or 116-3 — 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 even at ordinary temperatures. 
 
SULPHURET OF SILVER. 401 
 
 if It be in contact with organic matter. It neutralizes the strongest 
 acids, as the sulphuric and nitric, and forms well-characterized salts. 
 It is not acted on by the fixed alkalies, 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 oxygen is removed, and the citric acid 
 remains combined with the suboxide of silver^ AgjO. This salt dis- 
 solves in water, the solution being brown, and giving a brown pre- 
 cipitate of suboxide with potash. When a solution of this salt is 
 heated, it becomes colourless, contains a salt of the peroxide, and 
 metallic silver separates. Some other silver salts of organic acids 
 give the same result with hydrogen gas. When a solution of ni- 
 trate of silver is decomposed by the battery, a substance is deposited 
 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 
 chlorine. They are, therefore, crystals oi peroxide of silver^ proba- 
 bly Ag.O,. 
 
 Although silver does not combine with oxygen directly, yet when 
 it is heated in contact with glass, it stains this of a deep yellow or 
 orange colour, being converted into oxide. 
 
 Sulphuret of Silver, equivalent 1552*8 or 124''4), exists native 
 pure, and also in combination with other metallic sulphurets, par- 
 ticularly those of lead, antimony, copper, and arsenic, forming a va- 
 riety of minerals. It is the most common o*e of silver. It may 
 be formed artificially by fusing together sulphur and silver, the ex- 
 cess of sulphur being expelled by the heat. Silver has, indeed, a 
 remarkable affinity for sulphur, so that it even decomposes sulphu- 
 retted hydrogen, and hence arises the tarnishing of silver when ex- 
 posed to the atmosphere. An exceedingly delicate test for sulphur 
 in a solid body consists in igniting a minute fragment of it on char- 
 coal, in the reducing flame of the blowpipe ; 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 associa- 
 ted 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 precipi- 
 tated by the sulphites, by protosulphate of iron, and by protochlo- 
 ride of tin, the silver being reduced. A solution of common salt 
 or muriatic acid gives a white curdy precipitate of chloride of sil- 
 ver, 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. 173. The solutions of silver give, with 
 
 E E E 
 
402 MERCURY, ITS EXTRACTION FROM ITS ORE. 
 
 iodide of potassium, a canary-yellow precipitate, insoluble in ammo- 
 nia, and with sulphuretted hydrogen a deep brown sulphuret of 
 silver. 
 
 The uses of silver are well known j its advantages as a medium 
 of exchange depend on the steadiness of the quantity of it brought 
 into commerce, which preveiits great changes in its value, and on 
 its not being corroded or worn down by ordinary agents. In 'i 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 o'' 
 copper. 
 
 Of Mercury y or Quicksilver. 
 
 From the remarkable properties of this metal, and its occurring in 
 the metallic state in nature, it has attracted much attention from 
 the earliest ages, and formed the object of the most elaborate in- 
 quiries of the older chemists. Its volatility and the variety of its 
 compounds made it enter into the theories of that period as an im- 
 portant element, and hence there is, perhaps, no metal concerning 
 which so much valuable 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 con- 
 sists in distilling the ore with lime, or with iron in small pieces ; in 
 the first case, Hg.S. and Ca.O. produce Ca.S., while Hg. and 0. pass 
 off, the temperature being too high to allow of the formation of ox- 
 ide of mercury ; in the second case, Hg.S. and Fe. produce Fe.S. 
 and Hg. j this process is carried on in long furnaces, in which are 
 arranged numbers of earthen or iron retorts, to which are adapted 
 receivers, in which the mercurial vapours condense. The other 
 plan, which is that now adopted in the hest arranged works, con- 
 sists of a kiln, like that in which the pyrites is roasted for the man- 
 ufacture 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 nu 
 merous perforations, and on this js arranged the cinnabar, the poor- 
 est kinds being placed below, until the kiln is filled nearly to the 
 orifice of the chimney, which passes off at the side ; the fire com- 
 municating to the ore, the sulphur contained in it burns, and the 
 mercury is set free, Hg.S. and 20. producing S.O2 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 
 draught into the chimney, which leads into a wide chamber of brick- 
 work, the sides of which are hung with leather ; on these the mer- 
 cury condenses in drops, which gradually flow down and collect on 
 the floor, while the sulphurous acid gas passes away by a small 
 chimney at the farther end, by means of which the continuous com 
 bustion of the ore is sustained; at certain periods, an aperture in 
 the side of this chamber is opened, and the mercury which had col- 
 lected is withdrawn. 
 
 The mercury is sent into commerce in iron bottles, but generally 
 
OXIDES OP MERCURY. 403 
 
 in a very impure state, it being intentionally adulterated with the 
 alloy of tin, lead, and bismuth, already noticed p. 398, of which it 
 can dissolve 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. 
 
 Mercury is distinguished by being liquid at ordinary tempera- 
 tures j this, together with its resemblance to silver in brilliancy, is 
 the origin of its various names, hydrargyrum (ydoyp apyvpeog), quick- 
 silver^ 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 the other metals present. At 39^ it becomes solid, 
 and crystallizes in octohedronsj it then contracts very much; its 
 sp. gr. being 135 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. 
 
 Mercurj'^ is not acted on at common temperatures by sulphuric or 
 muriatic acid ; nitric acid oxidizes it rapidly, the nature of the pro- 
 duct varying with the circumstances. Boiling oil of vitriol is de- 
 composed by mercury, sulphurous acid being evolved, and oxide of 
 mercury produced. 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 1265'8 or 101*4. 
 
 Suboxide of Mercury.— Yig^O. Equivalent 2631-6 or 210-8. This 
 oxide is the basis of many important preparations, and is best pre- 
 pared by decomposing calomel (subchloride of mercury) by a solu- 
 tion 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, HgaCl. and K.O. produce 
 K.Cl. and Hg^O. 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 ex- 
 posed to the light. This oxide combines with acids and forms well 
 characterized salts. 
 
 Protoxide of Mercury — Hg.O. j equivalent 1365*8 or 109*4 — 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. 2d. By heating crystals of nitrate of mercury until 
 all the water and nitric acid have been expelled, the oxide remam- 
 ing is a crystalline powder of an orange-red colour, the red precipi- 
 tate by nitric acid. 3d. When a solution of chloride of mercury (cor- 
 rosive sublimate) is decomposed by caustic potash or lime water, 
 Hg.Cl. and K.O. produce K.Cl. and Hg.O. It is thus obtained as a 
 canary-yellow hydrate, which, however, when dried, becomes deeper 
 coloured. The red precipitate also, when finely divided, assumes the 
 same yellow tint. 
 
404 SULPHURETS OF MERCURY. 
 
 This oxide of mercury is slightly soluble in water. The solution 
 browns turmeric paper slightly, and restores the blue colour of red- 
 dened litmus. It combines with acids, forming a numerous and im- 
 portant class of sdlts. At a full red heat it is totally resolved into 
 mercury and oxygen, as described fully in page 242. It changea 
 its colour remarkably with the temperature, becoming nearly black 
 when very hot. 
 
 Subsulphuret of Mercury^ Hg^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 protosulphuret and metallic mercury. 
 
 Protosulphuret of Mercury — Hg.S. j equivalent 1467 or 117*5 — con 
 stitutes the native cinnabar, the usual ore of quicksilver. It may 
 be prepared artificially by fusing sulphur in a crucible, and adding 
 thereto six times its weight of mercury; they combine with the 
 evolution of considerable heat. The mass must be stirred frequent- 
 ly to favour their union, and covered in order to prevent the sul- 
 phur from burning away. In this state it is black, but when sub- 
 limed at a red heat in glass vessels, it becomes deep red, constitu- 
 ting factitious cinnabar^ and this, when levigated, and exposed to 
 strong light, in flat dishes covered with a thin layer of water, grad- 
 ually assumes a very brilliant colour, and forms the pigment vermil- 
 ion. 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 then 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 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 precipi- 
 tated in the metallic state, as a gray powder on the surface of the 
 copper. With a magnifying-glass, this is found to consist of mi- 
 nute but brilliant globules, 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 recognised. Any solid body 
 containing mercury gives, when ignited in a tube of hard glass, par- 
 ticularly 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 gray powder, but is found to consist of brilliant glob- 
 ules when inspected with a lens. 
 
 The two classes of salts which quicksilver forms are very dis- 
 tinctly characterized by their behaviour to reagents. The salts of 
 the suboxide give with the caustic alkalies black or gray precipi- 
 tates. Sulphuretted hydrogen produces the black subsulphuret. 
 Solution of chloride of sodium gives a white precipitate, which is 
 calomel, and the bichromate of potash produces an orange chromate 
 of the suboxide. 
 
EXTRACTION AND PROPERTIES OF GOLD. 405 
 
 The salts of the red oxide are precipitated, yellowish by an excess 
 of caustic potash, and white by ammonia ; with sulphuretted hydro- 
 gen in excess, a black precipitate of protosulphuret ; and with iodide 
 of potassium, 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 j 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 trit- 
 urating mercury with other inactive substances. In these the mer 
 cury is only reduced to a state of very minute division j it is not 
 oxidized. By triturating mercury with sulphur, however, a certain 
 quantity of sulphuret is formed, although the great mass of the met- 
 al and of the sulphur remains uncombined. 
 
 Of Gold. 
 
 This valuable metal is found only in the metallic state, either 
 pure or alloyed with other metals, particularly silver, tellurium, and 
 mercury ; the rocks in which it is found distributed are generally 
 those of igneous origin, but the greater part of the gold of com- 
 merce is obtained by washing the sands of the rivers which have 
 their source in such mountains, 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 amalgamation, similar to that de- 
 scribed, p. 399, 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 term- 
 ed 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 coin- 
 age, 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. 15. 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 ni- 
 tromuriatic acid, and by a mixture of nitric and hydrofluoric acids. 
 
 The symbol of gold is Au., from its Latin name, and its equiva- 
 lent numbers are 2486 or 199*2. 
 
 There are two oxides of gold, obtained by the decomposition of 
 the corresponding chlorides, which will be hereafter described. 
 The deutoxide of gold, Au.Oa, is a green powder, which does not 
 combine with acids, but dissolves in solution of caustic potash, and 
 soon separates into the higher oxide and metallic gold. The perox 
 ide of gold, auric acid, Au.Og, is best prepared by decomposing per 
 
 :| 
 
406 PROPERTIES OF GOL D. P A L L A D I U M. 
 
 chloride 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 j by muriatic acid 
 it is decomposed, perchloride of gold being formed j it combines 
 , with alkalies strongly, so that the precipitate given by a solution of 
 gold with a caustic alkali is always a compound of auric acid with 
 the base ; there 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. 
 
 Gold is deposited from its solutions by means of any of the de- 
 oxidizing 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 j protochloride of tin produ- 
 ces a fine purple precipitate, the purple of Cassius^ which is not me- 
 tallic gold, but it appears to be a compound of oxide of tin and a 
 suboxide of gold, for it is perfectly soluble in water of ammonia, 
 and mercury digested on it does not dissolve out any metallic gold. 
 Various processes are given for this preparation, which it is not 
 easy to obtain of the proper depth and purity of colour ; when ex- 
 posed to a red heat, it is changed into a mixture of peroxide of tin 
 and metallic gold, but its purple colour remains j it is hence employ- 
 ed for painting on glass and porcelain. When metallic gold is heat- 
 ed on the surface of glass, it appears to become oxidized, and in 
 that state to combine with the glass, staining it a rich purple col- 
 our. 
 
 Sulphur and gold combine to form sulphurets similar in constitu- 
 tion to the oxides; they are produced by decomposing the corre- 
 sponding chlorides by sulphuretted hydrogen ; they are brown pow- 
 ders, which are strong sulphur acids, and dissolve in hydrosulphu- 
 ret of ammonia. 
 
 The uses of gold are well known. The commercial value of its 
 alloys is ascertained, either by cupellation, p. 399, by quartation, p. 
 405, or by the touchstone, which is a variety of flinty slate (Lydian 
 stone) or basalt, of a 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 wheth- 
 er 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 consti- 
 tutes more than one per cent, of the ore. After the platinum has 
 been precipitated from the solution in aqua regia, by means of sal 
 ammoniac, cyanide of mercury is added, by which all the palladium 
 
COMPOUNDS OF PALLADIU M.-»-P L A T I N U M. 407 
 
 is thrown down as cyanide; this, when ignited, is totally decom- 
 posed, 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 forma- 
 tion of a thin layer of suboxide ; but by a stronger heat this is re- 
 duced, 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 — Pd.O. ; 
 equivalent 7659 or 61-4 — has been as yet studied with much care ; this oxide is form- 
 ed 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 palladium, 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 half itis 
 oxygen, and a suboxide, PdzO.jis 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 potash, the deuiox- 
 ide, Fd.02, is obtained as a yellowish brown powder; it appears to combine both with 
 acids and alkalies, but of its properties very little is known. 
 
 There are sulphurets of Palladimn, which correspond to the oxides, but farther 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 recognised by giving with ammonia a flesh-red 
 precipitate, which redissolves in an excess, giving a colourless solution ; with cya- 
 nide 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 
 American 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 
 Russian 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 four, 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 as the working of it has be- 
 come a branch of manufacture, the chemist always obtains 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 hydro-oxygen 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 com- 
 bustion, as noticed in p. 180, 250, 287. The finely-divided platinum 
 18 of two kinds, spongy platinum and platinum-black. The former is 
 
408 COMPOUNDS OF PLATINUM. 
 
 prepared by dissolving chloride of platinum and sal ammoniac sep- 
 arately in alcohol, and mixing the solutions; the double chloride of 
 platinum and ammonium is thus produced as a fine yellow powder, 
 which, while yet moist, is to be made into balls like peas, and heat- 
 ed to full redness. The chlorine is all carried off by the hydrogen 
 of the ammonia, and the platinum remains as a light gray sponge, 
 in the form of the little balls ; it is this kind of platinum that is 
 used in the aphlogi&tic lamp, in the eudiometer, and for other pur- 
 poses 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, bet- 
 ter, by dissolving protochloride of platinum in a boiling solution of 
 potash, and adding thereto alcohol, in small quantities at a time, 
 until all effervescence ceases ; a jet-black precipitate is produced, 
 which is to be boiled successively with alcohol, muriatic 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 pow- 
 der. 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. Dccbereiner 
 terms it an oxyphorus from this property. Many interesting reac- 
 tions 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-hydrofiuoric acids, and in these it dis- 
 solves more slowly than gold. 
 
 The symbol of platinum is PI. 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— Ft. O. ; equivalent 1333-5 or 1068 — is produced by digest- 
 ing the protochloride with as much potash as exactly suffices 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, fonning salts, which have been as yet but little studied. 
 
 Deutoxide of Platinum. — Pt.02. 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 alkali 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 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 alkalies and earths, in 
 which it is the acid. In another place I shall notice them farther. 
 
 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, Pt.Sg, is produced 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 in- 
 tense action into sulphate of platinum. 
 
 Phosphurets and seleniurets of platinum have been formed, but they are not im- 
 portant. 
 
 The detection of platinum is effected easily by precipitating its 
 solution by a slip of zinc, when a black powder separates, soluble 
 
IRIDIUM AND RHODIUM. 409 
 
 only in aqua regia, and then giving with reagents the following re- 
 sults. A solution of sal ammoniac in alcohol gives a fine yellow 
 crystalline precipitate ', 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 pla- 
 tinum j and with protochloride of tin, a chocolate precipitate or a 
 deep reddish solution, according to the quantity present. 
 
 The action of this last reagent is founded on the reduction of the 
 bichloride of platinum to the state of protochloride by the first por- 
 tion 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 appli- 
 cation of iodide of potassium in excess, the liquor is not coloured 
 red, but becomes so on the addition of a drop of nitric acid or chlo- 
 rine water. 
 
 The great use of platinum is for the manufacture of the large 
 boilers used in the concentration of oil of vitriol j it is also univer- 
 sally employed as the material for the crucibles used in the more 
 delicate operations 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 ac- 
 casionally used in enamelling on glass and porcelain. 
 
 Of Iridium and Rhodium. 
 
 These metals are, like palladium and iridium, found only associated with plati- 
 num, 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 platina ore is dissolved in aqua regia, the iridium and os- 
 mium ore remains undissolved, and requires to be treated by fusion with caustic 
 potash ; the iridium then becomes oxidized, and combines with the alkali. The pro- 
 cesses of puriticalion 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 gravity 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 becomess lightly oxidizedf, 
 and is soluble in aqua regia. 
 
 Iridium combines with oxygen in four proportions ; its symbol is Ir., and its equiv- 
 alent 1233-5 or 98-8, the same as that of platinum. 
 
 Protoxide of Iridium, Ir.O., is obtained by decomposing the protochloride by car- 
 bonate of potash; it appears as a greenish-grav hydrate ; this oxide combines with 
 acids. The scsquioxide, IriOs, is tliat 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 decom- 
 posed 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 deuloxide of Iridium, Ir.O 2, exists com- 
 bined with acids, but has not been isolated. The peroxide, Ir.Oa, is formed in small 
 quantity when iridium is ignited with nitre, but is best prepared by the decomposf 
 tion of the perchloride. Solutions containing salts of the protoxide and of the per- 
 oxide together, present a great variety of shades of purple and blue, and hence gave 
 origin to the name oi the metal (Iris). 
 
 Rhodium.— This metal remains dissolved in the nitromuriatic solution of the pla- 
 tinum 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 sys- 
 tematic 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. 
 
 Fff 
 
410 GENERAL CHARACTERS OF SALTS. 
 
 237; for, when alloyed with copper, lead, or platina, it dissolves along with the othei 
 metal in aqua regia. Rhodium derives its name from the beautiful rose (podo^) col- 
 our of its solutions ; it combines with oxygen in two proportions ; its symbol is R., 
 and its equivalent 661-4 or 52.2. 
 
 Of the protoxide of Rhodium, it is only known that it exists in certain salts that 
 have been but little examined ; the sesquioxide, R^Os, is the basis of the most impor- 
 tant compounds of this metal. It is prepared by igniting metallic rhodium with a 
 mixture of caustic potash and nitre; a brown mass is formed, Avhich, when decom- 
 posed by muriatic acid, yields the oxide as a gray hydrate, insoluble in acids. Ber- 
 zelius 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 sup- 
 posed to exist, also, complex oxides of rhodium, resembling, probably, the complex 
 oxides of iron and manganese. The equivalent of rhodium is so nearly equal to 
 that of palladium, that some relations might be expected in the constitution of their 
 combinations, which, as yet, does not appear to have been experimentally investi- 
 gated. 
 
 CHAPTER XIV. 
 
 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 
 constitution j the first comprehends such as are formed by the union 
 of a simple body of the chlorine family with a metal ; thus chloride 
 of sodium, 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 pos- 
 sessed 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 suffi- 
 ciently described in many places already (p. 151, 154, 157), and 
 need not be here repeated. In general, the acids and bases so en- 
 gaged contain oxygen as their electro-negative ingredient ; but there 
 are classes of salts formed by the Union of sulphur acids and sul- 
 phur bases, and, as noticed in p. 238 and 294, selenium and tellurium 
 resemble oxygen and sulphur in this respect. The history of the 
 metallic compounds in the last chapter affords many cases of the 
 existence of such salts, and in the detailed history of the more im- 
 portant salts which will follow, others will 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, and the 
 relations between their several subdivisions, which I shall now pro- 
 ceed to notice as briefly as the subject will admit. 
 
 I have frequently adverted to the circum«tance that the bodies 
 termed hydracids were in reality not acids, but compounds of hy- 
 drogen, in which that element acted as a positive metallic constitu- 
 ent ; and that, when they act on a metallic oxide, double decomposi- 
 tion generally occurs, precisely as when a chloride or iodide of 
 zinc or copper is decomposed by potash or by soda. Thus Cl.H. 
 and K.O. produce Cl.K. and H.O., precisely as when Cl.Cu. and K.O. 
 
GENERAL CHARACTERS OF SALTS. 411 
 
 produce Cl.K. and Cu.O. 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 constitu- 
 tion. 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. From Cl.H. and Zn. there are 
 produced Cl.Zn., and H. becomes free, precisely as chloride of cop- 
 per, Cu.CL, is decomposed by zinc, copper being precipitated. 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 cor- 
 responding compounds 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: 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, S.O3-I-H.O., 
 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 met- 
 al, this may be dissolved either by substitution for, and displacement 
 of the hydrogen, as in the ordinary cases of obtaining that gas, 01' 
 by the direct decomposition of a part of the acid, as in the process- 
 es for obtaining sulphurous acid and nitric oxide (p. 285, 274). 
 
 Salts may be either neutral^ acid, or basic. A salt is neutral which 
 does not manifest, in its action on vegetable colours, acid or alka- 
 line 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 acid with which metallic oxides are disposed to 
 unite in their most neutral salts, is subject to a remarkable propor- 
 tion, being one equivalent for each atom of oxygen which the base 
 contains. Thus a protoxide or suboxide combines with one equiv- 
 alent of acid. The sulphate of zinc is Zn.O. . S.O3 j sulphate of cop 
 per Cu.O. . S.O3 J the subnitrate of mercury, Hg^O. . N.O5. A sesqui- 
 oxide unites with three equivalents of acid, as sulphate of alumina, 
 AI2O3+3S.O3. Salts in which this law is observed to hold are gen- 
 erally 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 chan- 
 ging turmeric or litmus, but the state in which the characteristic 
 properties of acid and base are most neutralized, the definition of 
 a neutral 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 acid salts : 1st, those in which the excess 
 of acid is present in its hydrated form j and, 2d, those in which 
 the dry acid is in excess. These differ remarkably in nature, those 
 
412 GENERAL CHARACTERS OP SALTS. 
 
 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 K.O. . S.O3 + H.O. . S.O3, is one of a family of double 
 salts, in which sulphate of potash is united to a sulphate of a pro- 
 toxide, 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 carbonate of potash and water, K.O. . C.O^-j- 
 H.O. . C.O2, to which similar analogies exist. These salts resemble 
 completely the acid salts of the hydracids, described in the begin- 
 ning of this chapter J K.O. . S.Oa-f-H.O. . S.O3 corresponding exact- 
 ly 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 K.O.-j- 
 Cr.Oa, K.O.+2Cr.03, and K.O. + SCr.Oa- 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 
 equivalent of base for each equivalent of acid ; thus, in turbeth min- 
 eral there is 3Hg.O. + S.03j in basic nitrate of copper, 3Cu.O. + N. 
 Og.H.O.; in basic sulphate of copper, 4CU.O.-I-S.O3-I-4H.O. It has 
 been thought that the proportion of base in basic salts bore a sim- 
 ple 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 5 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 Gra- 
 ham, 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 evi- 
 dence of the basic nitrates adduced by Graham, and has been ex- 
 tended to the chlorides and sulphates by my own investigations. 
 Thus nitrate of copper, in its crystallized and neutral condition, is 
 Cu.O. . N.O5 + 3H.O., and the basic nitrate is formed by H.O. . N.Oj 
 + 3Cu.O. Comparing these two with the hydrated nitric acid, sp. 
 gr. 1*42, the formulas 
 
 Nitrate of water, =H.O. . N.O5+3H.O. 
 
 Nitrate of copper, =Cu.O. . N.O5+3H.O. 
 
 Basic nitrate of copper, =H.O. . N.Oa-j-SCu.O. 
 
 evidently correspond, the only difference being that, in place of 
 oxide of hydrogen, there is oxide of copper substituted, in a pro- 
 portion continually increasing. From these conditions it follows, 
 that with the same acid and base there may be formed a great va- 
 
SALTS OF POLYBASIC ACIDS. 
 
 413 
 
 riety 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 
 o( acid j and in its common crystallized form, these consist of one of 
 oxide of zinc and seven of water; but in becoming basic, the quan- 
 tity of oxide of zinc gradually increases, and a series of basic salts 
 is formed, as 
 
 S.03+Zn.O.-{-7H.O., 
 S.03 + 4Zn.O.+4H.O., 
 
 S.03+6Zn.O. + 2H.O., 
 
 S.Oa+SZn.O. 
 
 The salts, consisting of a simple body of the chlorine family uni- 
 ted with a metal, as chloride of sodium, iodide of potassium, &c., 
 and which, from the analogy of common sah, are termed haloid salts 
 (dXg and eidog), combine frequently with the oxide of the metal 
 which they contain, and form basic haloid salts. Thus we have Cu. 
 CI. + 3Cu.O., basic chloride of copper; Hg.Cl.-{-3Hg.O., basic chlo- 
 ride of mercury ; Pb.I. + 2Pb.O., basic iodide of lead. Such com- 
 pounds are, however, generally termed oxychlorides, oxyiodides, &c. ; 
 they are subjected to precisely the same laws of derivation and con- 
 stitution as the basic sahs of the same metals with ordinary acids. 
 
 From 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 im- 
 portant distinction requires 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 phos- 
 phoric acid, which, according as it has 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 
 p. 297 and 377. In addition, therefore, to ordinary neutral salts, 
 which are monobasic, or contain an equivalent of base and one of 
 acid, there are bibasic and tribasic salts, containing respectively two 
 and three equivalents of base to one of acid, and yet being neutral j 
 by which is meant, not that they are without action on test paper, 
 since one tribasic salt may redden litmus, while another may brown 
 turmeric paper, but that they are derived from a definite combination 
 of the acid with basic water, and not by the replacement of the wa- 
 ter 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, while 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 
 
414 ~ > i. DOUBLE SALTS. 
 
 * ■ 
 
 phosphate of soda, ammonia, and water j another of magnesia, am- 
 monia, and water j others of potash and water. The presence ol 
 two or more bases of different 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 
 philosophical 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 similarly circumstanced. 
 
 Double salts are formed by the union of two simple salts. In gen- 
 eral, both salts contain the same acid, but different bases, and the 
 two bases belong to different natural groups j as when sulphate of 
 potash combines 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 sul* 
 phate of zinc, Zn.O. . S.O3 . H.0.-|-6Aq., gives with K.O. . S.O3 the 
 double salt (Zn.O. . S.O3+K.O. . S.03)+6Aq.; and sulphate of cop- 
 per, Cu.O. . S.O3 . H.0.-f4Aq., gives (Cu.O. . S.Oa-^K.O. . S-OJ^- 
 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 alkaline 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 double salts, but in crystallizing are mechanically mix- 
 ed (p. 31). This rule, however, is not without exception, as the 
 constant composition of the magnesian limestone, Ca.O. . C.02+Mg. 
 O. . C.O2, 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 ex- 
 amples, though few, of a double salt containing two acids and two 
 bases. 
 
 The relations of salts to water have been fully discussed under 
 the heads of solution and crystallization (p. 22, et seq.), and of the 
 chemical properties of water (p. 253), 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 potassium, 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 produ- 
 ced. 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 not be with- 
 out exception. The difference of properties of the chlorides of 
 magnesium and of aluminum in the anhydrous state and when crys- 
 tallized with water, is so great as to give reason to suppose that 
 these chlorides decompose water, and that the crystallized hydrated 
 sails are not AI2CI3-I-3H.O. and Mg.Cl.-f H.O., but AlA-f 3H,C1. and 
 
CONSTITUTION OF ACIDS AND SALTS. 415 
 
 Mg.O.-}-H.Cl. Hence it is probable that magnesia and alumina 
 combine with hydracids without decomposition. 
 
 The sulphur salts consist of a sulphur acid, which is generally a 
 sulphuret of an electro-negative metal or of carbon, combined with 
 a 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 (p. 282, 386). 
 
 The positive metallic sulphurets combine frequently with the ha- 
 loid, or oxygen salts of the same metal, to form basic salts \ this is 
 the case particularly with mercury. Thus there is Hg.O. . S.O3 + 
 2Hg.S., similar to Hg.O. . S.03-|-2Hg.O., ordinary turbeth mineral. 
 
 It had been long remarked as curious, that bodies so totally dif- 
 ferent 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 mo- 
 ment of union a new arrangement of elements takes place, by which 
 the structure of the resulting salt is assimilated to that of a com- 
 pound 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 exten- 
 sively received by chemists; and I shall proceed, therefore, to de- 
 scribe, with some detail, the form which it has assumed, and the ev- 
 idence 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 N.OgH. ; to acetic acid, the crystalline body C4H4O4 ; and 
 to oxalic acid, the sublimed crystals C2O4H. ; we look upon these 
 bodies as being combinations of the dry acid with water, and we 
 write their formulae N.O5+H.O., and C4H303-f-H.O., and CA+H.O. i 
 but that these dry acids exist at all is a mere assumption. Hence, 
 with regard to these 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 the- 
 oretical. 
 
 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 
 S.Og-f H.O. gives with zinc S.Oa+Zn.O. ; and where a metal is 
 acted on by a hydrated acid, the hydrogen is thus evolved either 
 directly as gas, or it reacts on the elements of the acid, and givea 
 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 hy- 
 
416 THEORY RESPECTING THE INTIMATE 
 
 drogen and the formation of a neutral salt. But in this respect the 
 action becomes completely analogous to that of the metal on a hy- 
 dracid, except that in the latter case a haloid salt is formed ; and 
 hence we assimilate the two classes in constitution by a very sim- 
 ple 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 stannic, the arsenic, the phosphoric, &c. ; and when they com- 
 bine with bases, it is most natural to consider the union as beintr 
 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 circumstances intervene. These acids, al- 
 though 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 combination 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 (P.O5) which is 
 found in the liquor, but its terhydrate (P.Os-j-SH.O.), as is shown 
 by its forming with oxide of silver the yellow phosphate, P.Os+ 
 3Ag.O. In the case of telluric acid, its hydrate (Te.Os-'rSH.O ) 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 (Te.Og-fH.O.) is still acid and soluble in wa- 
 ter, perfectly neutralizing the alkalies ; 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 alkaline 
 solutions, and can only be brought back to its former state by be- 
 ing fused with potash at a red heat. Here it is evident 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 v/ith other 
 bases would 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 im- 
 pediment would exist to their union which would not occur with 
 cold barytes and dry sulphuric acid in vapour, and yet cold barytes 
 and oil of vitriol will combine with such intensity as to produce 
 ignition, while the barytes must be heated before it begins to com- 
 bine 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 1 
 
 When muriatic acid (H.Cl.) acts on zinc, the metal is taken up, 
 forming Zn.Cl., and hydrogen is expelled ; and if, in place of zinc, 
 oxide of zinc be taken, the effect is the same, except that the hy- 
 drogen combining with the oxygen of the oxide forms water, H.Cl. 
 and Zn.O. giving Zn.Cl. and H.O. Now we have in oil of vitriol 
 
CONSTITUTION OF ACIDS AND SALTS. 417 
 
 the elements S.O4H. combined together j when put in contact with 
 zinc, H. is expelled, and S.04Zn. is formed ; and with Zn.O. and 
 S.O4H., there are produced S.04Zn., and H.O. is set free. In both 
 cases, of which the former may be taken as the type of all the ha- 
 loid 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 
 combined with an electro-negative element 5 which may be simple^ 
 as chlorine, iodine, fluorine 5 or may be compound, as cyanogen, 
 N.C^, and yet capable of being isolated ; or, as occurs in the great 
 majority of cases, its elements may be such as can only remain to- 
 gether when in combination. Thus oil of vitriol does not contain 
 S.Oj and H.O., but consists of hydrogen united to a compound rad- 
 ical S.O4. Liquid nitric acid does not contain N.0,5 and H.O., but 
 consists of hydrogen united to a compound radical N-Og, and the 
 acetic acid is written C4H3O44-H., the oxalic acid CiO^-^-H., and 
 so on. 
 
 The elegance and simplicity with which the laws of saline com- 
 bination 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 was propor- 
 tional 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.+O. and H. + R. produce H. + O. and M.-fR. ; 
 
 and in the neutral salt, there is an equivalent of each. Now in the 
 case of a sesquioxide, in order that water shall be formed, and so 
 neither acid nor base in excess, the reaction is that 
 
 M2-I-O3 and 3(H.+R.) produce 3(H. + 0.) and M2-I-R3, 
 
 a sesqui-compound being formed perfectly analogous to a sesqui 
 oxide, and the number of atoms of acid, 3(H.4-R.), is equal to the 
 number of atoms of oxygen in the base (M2O3), because that number 
 of atoms of hydrogen is required for the decomposition of the base. 
 In like manner, for a deutoxide, there is 
 
 M. + O, and 2(H.+R.) producing 2(H.O.) and M. + R^. 
 
 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. + O. with K. + S.O4, than where H.O. was contrasted 
 with the complex formula K.O. + S.O3. 
 
 The circumstance that on the new theory (or, as it is now often 
 called, the Binarij theory of salts) it is necessary to admit the ex- 
 istence 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 
 
 G G G 
 
418 BINARY THEORY OF SALTS. 
 
 to the salts of phosphoric acid. For it has been ah-eady described 
 that this acid forms three distinct classes of salts, all neutral, and 
 which have their origin in the three hydrated states of the phos- 
 phoric acid. These states are written on the two views as follows: 
 
 Old Theory. New Theory. 
 
 Monobasic acid, P.O,+H.O. . . . P.Og+H. 
 Bibasicacid, P.O3-I-2H.O. . . . F.O^+H^. 
 
 Tribasic acid, P.O5-I-3H.O. . . . P.Os+Ha. 
 
 Now it appears very useless, where 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 inexplicable, on the idea of their being merely three de- 
 grees 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 al- 
 ways the same Glauber's salt ; while phosphoric acid, when neutral- 
 ized by soda, gives a different kind of salt according to the state it 
 may be in. Also, the permanence of these conditions of phospho- 
 ric acid is a powerful proof that they do not consist in the adhesion 
 of mere water. The idea that the phosphoric acid is a different hy- 
 dracid in each of its three conditions, on the other hand, not mere- 
 ly explains the fact of these differences of properties, but it renders 
 the formation of bibasic and tribasic salts, which is such an anoma- 
 ly on the old theory, a necessary consequence of the new; for the 
 phosphoric salt r'ldicals, P.Og, P.O^, and P.O., differ not merely in 
 the quantity of oxygen they contain, but are combined with differ- 
 ent quantities of hydrogen, and hence, in acting on metallic oxides 
 (bases), there is a different number of atoms required for each to 
 replace the hydrogen ?nd form water. Thus, 
 
 P.OgET. and Na.O. give R O, and P.OgNa., monobasic phosphate of 
 
 soda ; 
 P.O.H^ and 2Na.O. give 2H.O. and P.0,Na2, bibasic phosphate ; 
 P.0«H3 and 3Na.O. give 3H.0. and P.O.Na,, tribasic phosphate. 
 
 A circumstance which gives additional reason to infer that the wa 
 ter 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 tribssic phosphates of the alka- 
 lies should be those least likely to retain any portion of the basic 
 water; but the reverse is the fact; while oxide of silver, a very 
 weak base, is that which most easily and totally replaces the water. 
 On the idea, however, of hydracids, this is easUy understood, for 
 the oxide of silver is one most easily reduced by hydrogen, and, 
 consequently, one on which the action of a hydrogen 'icid, as P.O, 
 -I-H3, or P.07-hH2, would be most completely exercised. 
 
 A remarkable verification of this theory has been recently found 
 in the decomposition of solutions of the oxysalts in water by voltair 
 electricity. It has been already explained (p. 1S7, et seq.) that it re- 
 
EVIDENCE IN FAVOUR OP THE NEW THEORY. 419 
 
 quires the same quantity of electricity to decompose an equivalent 
 of any binary compound, such as iodide of lead, chloride of silver, 
 muriatic 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 j oxygen 
 and sulphuric acid being evolved at one pole, and soda and hydro- 
 gen 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, how- 
 ever, 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 decomposed 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 so- 
 lution having the formula Na.S.04, is resolved by the current into its 
 elements Na. and S.O4, as chloride of sodium would also be ; the 
 sodium, on emerging at the negative electrode 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 S.O4 also decomposes water, and produces H.S.O4 
 and 0. The appearance of the oxygen and hydrogen is thus but 
 secondary, and the body really decomj^osed by the current is only 
 Na.S.04. 
 
 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 elec- 
 trode, and the quantity of copper separated represents exactly the 
 energy of the current which has passed; for the salt being Cu.S.O^, 
 is simply resolved into its elements, but S.O4 reacting on the water, 
 produces H.S.O4, and O. at the positive electrode. On the old view 
 it was supposed that water and sulphate of copper were both de- 
 composed, oxygen and acid being evolved at one side, and oxide of 
 copper and hydrogen being separated at the other j 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 
 decomposition are precisely similar. Chloride of copper gives sim- 
 ply chlorine and copper, no water being decomposed. Chloride of 
 sodium or iodide of potassium give chlorine or iodine at the one 
 electrode, and alkali 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 arc due, considers 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 
 o£ salts will become necessary. Graham has proposed that the 
 
420 VIEWS RESPECTING DOUBLE SALTS. 
 
 name of the salt-radical should be formed by prefixing to the wo»d 
 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 eJ. 
 O4, suljphatoxygen^ gives sulphatoxides ; the sulphates, N.Oe, nitrat- 
 oxygen, gives nitratoxides, the nitrates, and so on ; but I consider 
 that the form of nomenclature proposed by Daniell deserves the 
 preference. It has been described (p. 194) that Faraday proposed 
 to term the elements which pass to the electrodes of the battery, 
 ions ; acting on this, Daniell proposes to term the electro-negative 
 element of the sulphates, oxysuliihion ; that of the nitrates, oxynitri- 
 on, and so on, and the salts may be termed oxysulphion of copper, 
 oxynitrion of sodium, &c. It would be desirable, however, for a 
 long time, to introduce these names only where theoretical consid- 
 erations 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 composi- 
 tion without any reference to the discussion in which we have been 
 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 forma- 
 tion of double salts, the salts which unite had the same relation to 
 each other that the 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 alka- 
 line sulphate acted as a base to the sulphate of copper when these 
 two salts combined to form the double sulphate of potash and cop- 
 per, and so on in other instances; but, in addition to the circum- 
 stance that all we have said as to the constitution of the salts mili- 
 tates 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 cop- 
 per or magnesian class, which water nobody would contend to act 
 in them as a base j and, second, that when a solution of such a dou- 
 ble salt is decomposed by the battery, the two salts are not separa- 
 ted as if they were acid and base, but are decomposed independent- 
 ly in the proportions 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 potassi- 
 um, &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 Cu.Cl. does not resemble S.O3, 
 but Cu.S.O^ and Cu.Cl.-f K.Cl. are analogous, not to S.O3 . K.O., but 
 to the double salt, C0.S.O44-K.S.O4. Bonsdorft^'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, while the progress of science has led us to the 
 opposite generalization of reducing all salts to the simple haloid 
 type. 
 
SALTS OF POTASH. 421 
 
 CHAPTER XV. 
 
 BPECIAL HISTORY OF THE MOST IMPORTANT SALTS OF THE INCEGANIC 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 ele- 
 ment. 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 his- 
 tory of each metal, and influences only the compounds of chrome 
 Rnd arsenic to any degree. 
 
 Of the Salts of Potash. 
 
 Chloride of Potassium. — K.Cl. Eq. 932 6 or 74-7. 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 ashes of plants. It is very soluble in water, producing so 
 much cold as to be employed as a freezing mixture j it crystallizes 
 in cubes, which are anhydrous j its principal use is in the manufac- 
 ture of alum. 
 
 Iodide of Potassium. — K.I. Eq. 2069*4 or 165*8. A variety of 
 processes may be employed to prepare this salt. One of the sim- 
 plest consists in dissolving iodine in solution of potash until this is 
 completely neutralized. The potash being decomposed, there is 
 formed from 61. and 6K.0., 5K.I. and K.O. . I.O5. 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 re- 
 sidual 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, io- 
 date of potash may remain undecomposed ; 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, farther 
 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 recognised 
 by means of starch. 
 
 Another process, adopted by the London and Edinburgh Phar- 
 macopeias, 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 
 
422 IODIDE, BROMIDE, AND SULPHATE OF POTA.SH. 
 
 by the carbonate of potash. Iodide of potassium is produced with 
 oxide of iron and carbonic acid ; a quantity of the latter combines 
 with the oxide of iron, but as this is not pure protoxide, most of 
 the carbonic acid is evolved as gas. The reaction consists in Fe.I. 
 and K.O. . C.O^, giving rise to K.I. and Fe.O. . C.O2. The liquor be- 
 ing 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 this means it is 
 known to be free from carbonate of potash. It is sometimes adul- 
 terated by chloride of potassium, which may be detected by decom- 
 posing its solution by nitrate 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, chloride of potassium was present, 
 and its amount may be thus determined. 
 
 The iodide of potassium is extensively used in medicine, by the 
 chemist as a reagent, and for the preparation of other metallic io- 
 dides. 
 
 A solution of iodide of potassium dissolves iodine in large quan- 
 tity, forming a brown liquor used in medicine. It is not certain, 
 however, that in this case any definite compound (as a biniodide) 
 is formed. 
 
 Bromide of Potassium. — ^K.Br. Eq. 14.68-3 or 117-6. This salt 
 may be prepared exactly as the iodide of potassium, which it re- 
 sembles in most of its physical characters. It is recognised by 
 giving, with oil of vitriol, orange-red fumes of bromine. The com- 
 mercial article is frequently 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 tillit 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 chloride of potassium would have the 
 effect (from the smaller equivalent of chlorine) of increasing the 
 weight ; therefore, if the precipitate, when quite dry, weighs more 
 than 158-8 grains, the sample is impure, and the quantity of chloride 
 present may be calculated from the overplus weight, for 100 grains 
 of pure chloride of potassium should give 192-6^ grains of precipi- 
 tate. Thus, if there were 10 per cent, of impurity, 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-Jiuoride of Potas- 
 sium are not of importance beyond what has been already said in 
 p. 321, 323, and 324. 
 
 Sulphate of Potash.— K.O. . S.O3 Eq. 109 11 or 87-43. This salt 
 is produced upon the large scale in the manufacture of the sulphu- 
 ric and nitric acids, where nitrate of potash is employed. It may be 
 prepared by the direct union of its constituents, and, being but spa- 
 ringly soluble, it precipitates as a fine crystalline powder when oil 
 of vitriol is mixed with a strong solution of potash. It is more sol- 
 
SULPHATE AND NITRATE OF POTASH. 423 
 
 uble 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 de- 
 scribed in p. 28. In the figures, A represents the manner in which 
 the three rhombic prisms adhere together, the letters A 
 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 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 sul- 
 phuric acid to form a bisulphate of potash, K.O.-h 
 2S.O3, which may be prepared by exposing the neu- 
 tral salt to the vapour of dry sulphuric acid, or by 
 dissolving it with 1| equivalents of oil of vitriol in 
 the smallest possible quantity of distilled water. 
 This bisulphate of potash crystallizes in small prisms, wliich are 
 gradually decomposed by water, the following salt being formed. 
 
 Common Bisulphate of Potash. Double Sulphate of Water and Pot- 
 ash.— K.O. .S.O.fU.O. .S.O,. Eq. 1704-7 or 136-6. 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 gen- 
 tly heated with half its weight of oil of vitriol to just below red- 
 ness. It may be obtained crystallized from a strong solution in 
 right rhombic prisms. It is decomposed 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 rhom- 
 bic crystals ; it is thus dimorphous (see p. 227j ; at a higher tem 
 perature it abandons its excess of acid, and neutral sulphate re- 
 mains. 
 
 There exists also a hydrated sesquisulphate of potash^ 2(K.O. . S.O3) 
 -}-H.O. . S.O;,, which crystallizes in fine needles. Similar com- 
 pounds of sulphate of potash with hydrated nitric and phosphoric 
 acids have also been described. 
 
 Mtrate of Potash. Saltpetre. Mlre.—K.O. . N.O5. Eq. 1266-9 or 
 101-5. 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 lixivi- 
 ating the materials thus obtained, whether naturally or from arti- 
 ficial nitre beds, with water, a solution is obtained, containing, 
 among other saline matters, a considerable quantity of nitrate of 
 lime j this is then decomposed 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 dihe- 
 dral summits, derived from the right rhombic system. It is anhy- 
 drous ; 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 (wnployed for the preparation of fireworks, and espe- 
 cially of gunpowder. The action of gunpowder depends upon its generating, when 
 decomposed, a large quantity of gases, which occupy more than lOOO times its vol- 
 
424 MANUFACTURE OF GUNPOWDER. 
 
 ume. If this took place instantaneously, all bodies near, which could not resist 
 this force, would be burst or broken; as takes place with chloride of azote, which, if 
 placed in a gun, would burst it, but have no power to propel a ball ; the decomposi- 
 tion 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 ul- 
 timate efiect of the whole quantity of gas produced. When gunpow der is completely 
 decomposed, the products are found to be sulphuret of potassium, nitrogen, and car- 
 bonic acid gas, and from these the proportions by weight of its constituents mav be 
 calculated, for S., K.O. . N.O5, and 3C., produce K.S., N., and 3C.0z. The parts by 
 weight are, therefore, 
 
 Tlieorv. French. English. Prussian. 
 
 S.= 161 — il-8 12-5 100 11-5 
 
 30.= 18-3 — 13-5 12-5 15 135 
 
 K.O. . N.Q5= 101-5 — 74-7 750 75 750 
 
 135-9 1000 1000 1000 1000 
 
 The proportions employed in the government factories of the most important coun- 
 tries are given also above. The Prussian mixture agrees best with theory. For 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 salt- 
 petre, 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, 
 it 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 gunpowder, but totally without explosion. It is therefore the sul- 
 phur which determines the violence and rapidity of the deflagration of gunpowder, 
 while the charcoal produces the great volume of gas on which iis mechanical elfeci 
 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 cyl- 
 inders, 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 recrystalli- 
 zations, and by washing the crystals with water already saturated with saltpetre, 
 which dissolves out any common salt that may be present, but does not act on tlte 
 crystals of saltpetre. The description of the mechanical operations of the manufac- 
 ture would be out of place here. 
 
 Hypochlarite nf Potash. — When gaseous chlorine is passed into a solution of carbon- 
 ate of potash, it is abundantly absorbed, but no carbonic acid is disengaged until 
 the liquor contains an atom ol' chlorine for every two atoms of alkaline carbonate. 
 On examination, it is then found to contain hypochlorite of potash, chloride of potas- 
 sium, and bicarbonate of potash, which are mixed in solution, and may be partially 
 separated by crystallization. The reaction has been such that 2C1. and 4K.0. . C. 
 02give K.Cl.,K.O. .C1.0.,and 2(K.O.-i-C.02-i-H.O. .C.O2). If the stream of chlo- 
 rine be continued, carbonic acid is copiously evolved, and as much more clijorine is 
 absorbed, giving ultimately a mixture of K.Cl. and K.O. . Cl.O. 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. 
 
 Farther details of the theory of these bleaching compounds are given under the 
 head of chloride of lime. 
 
 Chlorate of Potash.— K.O. . CI.O5. Eq. 1532-6 or 122-81. When 
 chlorine gas is passed into a strong solution of potash, it is absorbed 
 rapidly until the alkali is completely neutralized, and chloride of 
 potassium and hypochlorite of potash are formed ; 2K.0. and 2C1. 
 giving K.Cl. and K.O. . Cl.O. If, then, this liquor be boiled for some 
 time, oxygen gas is given off, the hypochlorite being decomposed, 
 and chloride of potassium and chlorate of potash being formed ', 
 9(K.O. . Cl.O.) producing 120. with 8K.C1. and K.O. . Cl.O,. If car- 
 bonate of potash has been employed, the tibsorption of the chlorme 
 is rapid until half of the salt has been decomposed und the remain- 
 
CHLORATE OF POTASH. 425 
 
 der converted into bicarbonate, from combining^ with the evolved 
 carbonic acid, as described under the preceding head ; but a high 
 temperature and a great excess of chlorine being necessary to com- 
 plete the reaction, render the operations tedious and very trouble- 
 some ; and as, owing to the large quantity of oxygen evolved, there 
 is but one equivalent of chlorate of potash obtained by the action 
 of eighteen equivalents of chlorine on eighteen of potash, the pro- 
 cess is one of considerable expense. 
 
 We owe to Graham a method which is free from these disadvan- 
 tages. If an equivalent of carbonate of potash be mixed with one 
 of hydrate of lime (by weight about 2 of K.O. . CO to 1 of Ca.O. . 
 H.O.), and exposed to a current of chlorine, the gas is absorbed with 
 avidity, and the solid mass becomes very hot, while water is given 
 off abundantly. When saturated, it may be gently heated to com- 
 plete the decomposition. No oxygen is given off, the reaction being 
 that 6(K.O. . C.OJ and 6(Ca.O. . H.O.), acted on by 6Cl., produce 
 5K.C1., 6Ca.O. . C.O^, and K.O. . Cl.O,, while 6H.0. are evolved. 
 By digesting the mass in water, the potash salts are dissolved 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 j when heated, 
 it melts and evolves oxygen gas, being decomposed into chloride of 
 potassium and hyperchlorate of potash ; on increasing the heat, this 
 also is decomposed, and chloride of potassium remains pure. Its 
 uses in preparing oxygen, and the compounds of chlorine and oxy- 
 gen, have been already noticed. From its supplying oxygen still 
 more readily than nitre, it is the basis of a variety of deflagrating 
 mixtures. When rubbed in a mortar with sulphur or with sulphu- 
 ret 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 
 gumarabic, 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. 
 
 Perchloratc of Potash — K.O. .Cl.O?; Eq. 1732-6 or 138-8 — is of importance only 
 from being one of the least soluble salts of potash, and, consequentl}^, that the per- 
 chloric acid may be used as a test for the presence of potash in solution, it giving 
 a granular crystalline precipitate if that alkali be present. Its preparation is su^ 
 ficiently noticed in page 306. 
 
 Tlie Sihcaie of Potash is of considerable importance as a constituent of glass, and 
 will be noticed as such hereafter. 
 
 lodate of Potash. — K.O. . I.O5. This salt, which is but sparingly soluble in water, 
 may be obtained by neutralizing the perchloride of iodine with caustic potash ; I, 
 CI5 and 6K.0. produce 5K.C1. and K.O. . I.O5. This last separates in crystalline 
 grains. It may also be obtained by adding iodide of potassium 10 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 
 crystallization. This salt has a remarkable tendency to form acid and double salts, 
 of which, however, none are specially interesting. 
 
 H H H 
 
426 CHLORIDE OF SODIUM. 
 
 Salts of Sodium. 
 
 Chloride of Sodium. Common Salt. Sea Salt— Nn.Cl j Eq. 733-6 
 or 58*8 — exists in great abundance in nature ; solid, as rock salt^ 
 and in solution in the water of the ocean, and of many inland seas 
 and lakes. The deposites 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 Northwich, 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 deposites at Wie- 
 liczka, in Poland, appear to be still larger. The origin of these de- 
 posites of salt is probably to be found in the gradual drying up, by 
 evaporation, of salt lakes, to which fresh quantities of salt were con- 
 tinually supplied by the surrounding springs. Owing to admixture 
 of earthy matters, the rock salt, as quarried, is generally brownish- 
 coloured, and hence requires to be dissolved in water and crystal- 
 lized 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 
 France, salt is obtained by the spontaneous evaporation of sea-wa- 
 ter, 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 concentrated, and, finally, the evaporation being finished by 
 means of artificial heat. The sea-water is not evaporated to dry- 
 ness, 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 > q.^^ \ 100-00, 
 Carbonate of magnesia ) 
 
 Sulphate of lime .... 0-01 
 
 Water 96-54 J 
 
 vvith generally some traces of iodide and bromide of magnesium. 
 According as the evaporation proceeds, the common salt is depos- 
 ited in crystals, and the mother liquor, or bittern^ being rich in salts 
 of magnesia, 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 car- 
 bonate of soda by muriatic acid. In practice, however, this is never 
 done. 
 
 Chloride of sodium crystallizes in cubes. Its taste is purely sa- 
 line. It is equally soluble in water at all temperatures, 100 of wa- 
 ter dissolving 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 de« 
 
427 
 
 crepitation. A strong solution of salt does not freeze at 0^, but de- 
 posites 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 
 source from whence the other compounds of sodium, such as the 
 carbonate and sulphate, are obtained. It is employed also in the 
 manufacture 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.—Na.O. . S.O3+ 10 Aq. Eq. 892-1 
 4-1125 or 71'48+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. 307). 
 
 As 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. 333. 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 grad- 
 ually until all the muriatic acid gas has been expelled, and the reside 
 ual 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 con- 
 densed by meeting with a stream of water, and the weak liquid acid 
 thus formed is suffered to run to waste. The greater part of the 
 sulphate of soda thus produced is immediately used to make car- 
 bonate of soda ; but to form Glauber's salt, it is only necessary to 
 dissolve it in warm water, and let it crystallize 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 maxi- 
 mum solubility at 93 \ as figured in page 22. Its 
 ordinary crystals contain 56 per cent, of water ; 
 by exposure to the air it loses all its water by 
 eftlorescence, and falls into a white powder j from 
 a hot saturated solution opaque rhombic octohe- 
 dral 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. 224. A 
 bisulphate and a sesquisulphate 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 sul- 
 phates of potash. 
 
 Xitrate of Soda. Cubic JViVre.— Na.O. . N.O,. Eq. 1067-5 or 85-57. 
 The spontaneous formation of this salt by the atmospheric influence, 
 probably on a soil containing chloride of sodium, has been noticed 
 
428 PHOSPHATES OF SODA. 
 
 p. 277. It may also be obtained by means of nitric acid and carbon- 
 ate of soda. It crystallizes in rhombs, isomorphous with calc spar 
 (p. 224). It is very soluble in water, and is slightly deliquescent ; 
 hence it cannot be employed in the manufacture of gunpowder. It 
 (s used for the manufacture of nitric and sulphuric acids, and as a 
 manure. 
 
 Hyposulphite of Soda. — Na O. . S^O^H- 10 Aq. This salt, which 
 oas 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 pass- 
 ing a stream of sulphurous acid gas through the liquor until it smells 
 strongly of it. Na.O. . C.O^, with S. and S.O2, produce Na.O. . S.Oz, 
 while C.O2 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 colourless liquor on filtration, the salt is 
 more simply produced, the necessary quantity of oxygen being ab- 
 sorbed 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. 291. 
 
 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 farther 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 (P.O- + 2Na.O. -hH.0.)4- 
 24< Aq. It is prepared by decomposing the solution of acid tribasic 
 phosphate of lime obtained from bones (as described in p. 295) 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 oblique rhombic prisms, as in the fig- 
 ure, which react alkaline. When exposed to the 
 air, it .loses some of its water by efflorescence (ten 
 atoms 1), 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 subphos- 
 phate of soda (P.O-, + 3Na.O + 24 Aq.) crystallizes in 
 long prisms ; and by the addition of hydrated phos- 
 phoric acid to its solution, and cautious evaporation, 
 the acid tribasic phosphate (P.05 4-Na.O.-i-2H.O.) + 2 Aq., which 
 crystallizes 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 Py- 
 rophosphate of Soc/«,(P.O:^-|-2Na.O.)-[- 10 Aq., is of interest, as its dis- 
 covery led the way to the true history of these bodies. It is form- 
 ed by fusing the common phosphate of soda, (P.05-l-2Na.O. + H.O.) 
 -1-24 Aq., 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 expelled, and, when the salt is then redissolved, the 
 phosphoric acid does not recombine with basic water, but remains 
 
BORATES OF SOD A. S ALTS OF BARIbM. 429 
 
 united only with the soda. ' It is recognised by giving a white pre- 
 cipitate with nitrate of silver. 
 
 C. The Monobasic Phosphate of Soda, P.05-fNa.O., is obtained by 
 heating the acid tribasic or bibasic phosphates of soda to redness. 
 All the volatile base being thus expelled, the phosphoric acid re- 
 mains combined with one equivalent of soda. This salt fuses into 
 a transparent glass j is deliquescent ; its solution does not crystal- 
 lize. It is easily recognised by throwing down from solutions of 
 lead and silver, precipitates, which are not powders, but soft, tena- 
 cious pastes. 
 
 Borates of Soda. — Boracic acid combines with soda in many pro- 
 portions, forming salts, of which the most important is the biborate, 
 the borax of commerce (Na.O.-f^B.O^)-!- 10 Aq. It exists in the 
 water of several lakes in Thibet and China, also in Hungary, and 
 was imported 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. 326, 
 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 crystallizes in oblique rhombic prisms, as z, w, My 
 
 in the hgure. If a strong solution of borax be kept at 
 
 SS"", the salt crystallizes in regular octohedrons with f(T_f_~p 
 only five atoms of water. Although this salt contains 1 
 two equivalents of acid, it has an alkaline reaction : i 
 when heated, it froths up very much, abandoning its |>- 
 water. The dry salt melts at a red heat into a colour- ^ 
 less glass, which dissolves most metallic oxides very readily, and 
 hence is serviceable in experiments with the blowpipe, as enabling 
 the metals to produce the coloured glasses by which they are rec- 
 ognised ; under the head of glass and porcelain, its use in these 
 branches of art will be again noticed. 
 
 The remaining compounds of boracic acid with soda, as the neu- 
 tral borate, Na.O. . B.O3 + 8 Aq., and acid salts, as Na.O.-{-4.B.03 and 
 Na.O.+6'B.03, 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 farther notice 
 than that its carbonate is but very sparingly soluble in water, yet its solution pos- 
 sesses an alkaline reaction. It thus serves to connect the alkaline with the earthy 
 bases. 
 
 Salts of Barium, 
 
 Chloride of Barium.— Bsi.Cl-^^ Aq. Eq. 1299-64-225 or 104-8-h 
 18. This salt may be prepared by decomposing the native carbon 
 ate of barytes with dilute muriatic acid, or, more economically, by 
 decomposing the sulphuret of barium, the preparation of which is 
 described in p. 342, 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 rhom- 
 boidal tables which contain 14'7 of water. 
 
 Sulphate of Barytes.— Ba.O. . S.O3. Eq. 1458 or 119-5. This salt 
 exists native, in great abundance, being the most common source 
 of barytes. It is very generally associated with sulphuret of lead, 
 
430 SALTS OF BARIUM, STRONT 
 
 and serves as an indication of the prol)able 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 
 i and e are planes ; the secondary planes, p 
 and w, belong 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. WheA 
 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 it having the opacity or body neces- 
 sary in a good pigment. It may be prepared artificially by adding 
 sulphuric acid to any solution containing barytes ; it falls as a heavy 
 white crystalline powder. Its total insolubility renders its constit- 
 uents excellent reagents for each other. 
 
 Mtrate of Barytes^Ba.O.-{-'N.O,; Eq. 1633-9 or 130-9— may be 
 produced by acting on carbonate of barytes with dilute nitric acid, 
 or, more cheaply, by mixing strong hot solutions of sulphuret of ba- 
 rium and nitrate of soda. The sparingly soluble nitrate of barytes 
 crystallizes as the mixed liquors cool, but the sulphuret of sodium 
 remains dissolved. In this process, from Ba.S. and Na 0. . N.O5 we 
 obtain Ba.O. . N.O5 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 octohedrons. 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. CI + 6 Aq. 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.— -Sr.O. . S.O3. Eq. 1148-4 or 91-9. This, the 
 most abundant source of strontia, is found native crystallized, iso- 
 morphous with sulphate of barj'^tes. It may be produced artificial- 
 ly as a white powder, by adding sulphuric acid to any solution con- 
 taining strontia. It is dissolved by 3600 parts of boiling water, and 
 remains dissolved after cooling. It is fused by a strong heat j with 
 charcoal it gives sulphuret of strontium. 
 
 JV-itrate of Strontia — Sr.O. . N.O- — 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 application of heat, these crystals evolve oxygen and nitro- 
 gen, and leave pure strontia. 
 
 Salts of Calcium, 
 
 Chloride of Calcium— C'd.C].-\- 6 Aq. ; Eq. 698-7 + 675 or 55984- 
 54 — is obtained by decomposino- carbonate of lime with muriatic 
 acid. In the laboratory it is abundantly procured as the residue of 
 
FLUORIDE OF CALCIU M. S ULPHATE OF LIME. 431 
 
 the preparation of carbonic acid, ammonia, &c. It is very soluble 
 in water j its solution, evaporated to the consistence of a sirup, 
 gives, by cooling, long, striated, rhombic prisms, which deliquesce 
 with great rapidi'v, and when heated undergo watery fusion, soon 
 after which it abandons two thirds of its water of crystallization, 
 and a powder is obtained, Ca.Cl.-[-2 Aq., in which form it is best 
 adapted for freezing mixtures. Heated still farther, it becomes an- 
 hydrous, and at a red heat fuses. In this state it is phosphorescent 
 in the dark, forming Homberg's pyrophorus. It has a very great 
 affinity for water, combining with two atoms of it, with the evolu- 
 tion of much heat, and is hence employed to dry gases for experi- 
 mental purposes, and to remove water from liquids, as in the recti- 
 fication of alcohol. 
 
 This salt combines with lime, forming an oxychloride of calci 
 um, Ca.Cl. l-3Ca.O., which is obtained by boiling a solution of it 
 with an excess of lime, and filtering. The new substance crystal- 
 lizes, 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^ Ca.F., is an abundant mineral known as fluor 
 spar, found crystallized in cubes and octohedrons, but principally 
 massive. 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 p. 319, 324, 
 and 327. It appears as a gelatinous precipitate when hydrofluoric 
 acid is added to any soluble salt of lime. When heated in contact 
 with silicious or aluminous minerals, it forms easily fusible com- 
 pounds, and being thus of use as a flux in the smelting of metallic 
 ores, its name of fluor spar was thence derived. 
 
 Sulphate of Lime— Ca.O. . S.O3+2 Aq. ; Eq. 857-2-f-225 or 68-69 + 
 18 — may be prepared artificially, by mixing a solution of any solu- 
 ble salt of lime with Fulphuric 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 vari- 
 ous forms : 1st, in distinct colourless crystals j 2d, in semi-transpa- 
 rent 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. From this plaster of Paris 
 is prepared, bj'^ calcining the gypsum, broken into small pieces, in 
 ovens at a temperature 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 expand- 
 ing 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 be heated, in ba- 
 king, above 300 , it is changed in nature, and no longer combines 
 with water so as to set ; it is then converted into a form which exists 
 in nature crystallized, and which is termed anhydrite. 
 
432 
 
 MANUFACTURE OF CHLORIDE OF LIME. 
 
 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. 291. 
 
 The Mitrate 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 trihasic Phosphate of Lime^ or 
 Earth of Bones. This salt, which constitutes the inorganic portion 
 of the skeletons of the mammalia, mixed only with small quantities 
 of carbonate and sulphate of lime, and of fluoride of calcium, has the 
 formula 8Ca.O. -f 3P.O5. It may be obtained precipitated by dis- 
 solving bone earth in muriatic acid, and exactly neutralizing the so- 
 lution by caustic ammonia. It falls as a gelatinous powder contain- 
 ing 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(3Ca.O. . P.O,-f Aq.)-}-(H.O. . 2Ca.O. . P.O,-f 
 Aq.). Each of these tribasic phosphates of lime may be obtained 
 separate, by decomposing solutions of chloride of calcium by solu- 
 tion 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 hypochlorite of potash, I have had occasion to notice the diver- 
 sity of opinion regarding the nature of the bleaching substance^ 
 formed by the action of chlorine on the alkalies and on lime. Ot 
 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. Iij, as described p. 301 
 the materials being kept constantly mixed by means of an ngitator moved round b^ 
 the handle d. The gas is conducted by the tube e e \o the upper part of a wood;- 
 en reservoir or apartment, as in the iigure, made very tight, i, i, on the floor 
 
 11 
 
 of which pure hydrate of lime is exposed to the action of the gas. The lime is 
 introduced by the door A:, ^, and the surface is changed occasionally by stirring 
 with rakes by means of the apertures /, Z, /: the absorption should take place so slow- 
 ly as no. to evolve any sensible heat. In this way 100 parts of slacked lime combine 
 generally with from fifty to sixty of chlorine. If the process be carried on too rap- 
 idly, a quantify of lime is decomposed, chlorate of lime and chloride of calcium be- 
 ing formed, which may be recognised by the product getting damp when exposed 
 to the air 
 
VALUATION OF CHLORIDE OF LIME. 433 
 
 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 con- 
 stitution ; 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 disadvantages of the dry way which prevents the absorption of the 
 gas reaching this limit, and the best bleaching powder may be looked upon as a mix- 
 ture of true chloride of lime, with about eighteen per cent, of hydrate of lime in ex- 
 cess. Accordingly, when ordinary bleaching powder is treated with water, the true 
 atomic compound is dissolved out, and the excess of lime remains. The composi- 
 tion of the theoretical and best practical substances may, therefore, be expressed as 
 follows : 
 
 Theoretical. _ Best practical 
 
 1 atom chlorine, 3547 48-63 
 
 1 " lime, 28-57 39-04 
 
 I " water, 9-00 12-3 3 
 
 73-04 100-00 
 
 Chlorine 4032 
 
 Lime 4540 
 
 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 liberates chlorine, and enables 
 it to destroy the colouring matter. It is thus that the colour can be removed from 
 certain points without injuring 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 applied, while the general surface remains deep red. A solu- 
 tion 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 prop- 
 erties. 
 
 As the technical value of bleaching powder depends on the total quantity of chlo- 
 rine 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 Chloromctry. The earliest method employed consisted in prepa- 
 ring 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 evidently, 
 the richer the bleaching powder was in chlorine, the more solution of indigo a certain 
 weight of it could bleach. The. action of chlorine on indigo is, however, so com- 
 plex, that this method was found exposed to numerous fallacies, and may be con- 
 sidered 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, de- 
 composing water, converts the arsenious acid into arsenic acid, and itself forms hy- 
 drochloric acid; As.Oa with 2C1. and 2H.0. producing As.Os and 2H.CI. 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 the bleaching powder to be tested 
 are to be diifused through lOOO 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 unalter- 
 ed, the blue colour of the drop is instantly destroyed, and the addition of the arsenic 
 liquor is to be continued until the blue drop remains unaltered. Then the quantity 
 of chlorine present in the 100 grains of bleaching powder is represented by j^-^iYi of 
 
 tthe quantity of the test liquor employed ; thus, if there were 2565 grains of the test 
 liquor necessary to destroy the bleaching power of the 100 grains of chloride of lime, 
 tlie quantity of chlorine would be 25-65. This is not absolutely correct ; for in theo- 
 ry, the true quantity of chlorine indicated would be 26-08 ; but as a few drops of the 
 solution are always employed, more than what should by theory be necessary, the 
 practical proportion of -J^^th comes very close to the truth. Even one half part 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. 355 for determining the technical value of black oxide of man- 
 
434 CONSTITUTION OFTHE BLEACHING SALTS. 
 
 ganese by means of copperas (green sulphate of iron). The proportion and meth- 
 od 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 solu- 
 tion to the volume of 5000 grains of water. On the other hand, 100 grains of the 
 chloride of lime are 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 isyl^th of the 
 quantity of the standard copperas liquor employed; thus, if 2783 grains measure of 
 the volume of the solution be foynd necessary, the sample contains 2783 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 prussiate into red prussiate of potash, by means of the chlo- 
 rine of the bleaching powder; and others, by decomposing the bleaching powder by 
 means of an excess of water of ammonia, and measuring the nitrogen gas evolved; 
 but these are more troublesome 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 ne- 
 cessary to form peroxide. Thus, that with lead,^ a chloroxide Pb.O. 
 CI. ; that with iron, a chloroxide FcaOaCl. The chloride of lime, 
 Ca.O.Cl., would thus be equivalent to deutoxide of calcium, Ca.0.0. 
 It has been found, however, that the evidence is not yet satisfac- 
 tory. The peroxide of potassium is K.O3, while chloride of potash 
 is not K.O.CI2, but K.O.Cl. 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 2Ca.O. and 2C1. may 
 give Ca.O. + Cl.O. and Ca.Cl. But, if this happens, the chloride of 
 calcium certainly remains combined, forming a double salt 5 for the 
 bleaching powder, if properly prepared, has no tendency to deli- 
 quesce, and only becomes damp when long kept ; and then chlorate 
 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^ corre- 
 sponding 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, CI.O4, 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 — Mg.Cl. ; Eq. 600 9 or 48.16— may be ob- 
 tained in solution by acting on the carbonate of magnesia with mu- 
 riatic acid ; by evaporation, it may be obtained in prisms with 6 
 Aq., which are very deliquescent. These crystals cannot be de- 
 prived of water without total decomposition, the chlorine passing 
 off as muriatic acid, and magnesia remaining behind. The chloride 
 may, however, be obtained anhydrous, by previously mixing its so- 
 
SALTS OF MAGNESIUM AND ALUMINUM. 
 
 435 
 
 lution 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.^Ug.O. . S.O3. Eq. 759-4 or SO-8. This salt 
 exists abundantly in saline mineral springs, as those of Seidlitz, Sel- 
 lers, and Epsom, from whence it derives its common name of Epsom 
 salt. It is extracted principally from the magnesian limestone, 
 which is calcined, and the mixed lime and magnesia treated with 
 dilute sulphuric acid ; the sulphate of lime, being very sparingly sol- 
 uble, is easily separated from the sulphate of magnesia by washing 
 with water ; the latter is dissolved out, and the liquor evaporated 
 and crystallized. A great deal is also made from the mother liquor 
 of sea-water, or bittern (p. 426). This is decomposed by sulphuric 
 acid, and the salt formed separated by crystallization. 
 
 The sulphate of magnesia crystallizes in eight 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 Mg.O. . S.O3 . 
 H.O. + 6 Aq. ; when heated to 212^ it easily aban- 
 dons the 6 Aq., but retains the seventh atom of wa- 
 ter even at 400^. It combines with the sulphate 
 of potash to form a double salt, (Mg.O. . S.O3+K. 
 O. . S.03)-t-6 Aq., the atom of constitutional water 
 being replaced by the alkaline sulphate. The sul- 
 phates of soda and of ammonia act in the same way. " 
 
 Nitrate of MagTiesia, Mg.O. . N.O5, is very soluble and deliquescent. It cannot be 
 obtained dry, as it crystallizes with six equivalents of water, of which five are ex- 
 pelled by a moderate heat, and by a higher temperature the nitric acid itself passes 
 off, and magnesia remains behind ; Mg.O. . N.O5 . H.O. producing Mg.O. and H.O. . 
 N.O5. 
 
 The Borate of Magnesia constitutes the mineral boracite, whose electrical and 
 crystalline properties have been already noticed. 
 
 There exists a great number of combinations of silicic acid with magnesia, con- 
 stituting the steatite, or soapstone ; the meerschaum, of which pipe-bowls are cut ; oli- 
 vine and serpentine, which exist abundantly in the green marble of Galway : these 
 are simple silicates of magnesia ; others, as amphibole and pyroxene, are double sili- 
 cates of magnesia and lime, more or less replaced by protoxide of iron. 
 
 Salts of Aluminum. 
 
 Chloride of Aluminuvi.—AhCh. Eq. 1670-3 or 133-84. In a hydrated form this 
 salt may be prepared by dissolving alumina in muriatic acid, a solution being ob- 
 tained, which, when evaporated, yields very deliquescent crystals, containing twelve 
 atoms of water. On applying 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. 323. 
 Pure alumina is mixed with lampblack and ignited in a porcelain tube, while a 
 stream of dry chlorine is passed over it : the oxygen of the alumina combines witlT 
 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 palcrgreen 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. 349. 
 
 The Fluoride of Aluminum is found in the mineral kingdom. The beautiful gem, 
 the topaz, is a double fluoride and silicate of alumina. 
 
436 MANUFACTURE OF ALUM. 
 
 4 
 
 Sulphate of Alumina (AI2O3 + SS.Og)-}- 18 Aq. — This salt is obtain- 
 ed by dissolving alumina in dilute sulphuric acid ; it has a sweetish 
 styptic taste, is very soluble in water, and crystallizes in thin flexi- 
 ble 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 con- 
 stituting the mineral aluminite is the most important ; its formula is 
 AI2O34-S.O34-3 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. 351). 
 
 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 for- 
 mula of which is (K.O. . S.03-L-A1A4-3S.03) + 24< Aq. 
 
 From the large quantities of this salt employed in the processes of dyeing, its man- 
 ufacture is conducted upon the great scale. In the coal districts, and underlying 
 the beds of good coal, strata of clay-slate are generally found, containing a certain 
 quantity of coally material, and through which abundance of bisulphuret of iron is 
 disseminated in the instable rhombic form (see p. 332 and 358). 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 establish- 
 ed ; 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 bums, becoming brick red ; 
 according as the process is carried through, successive quantities of mineral are ad- 
 ded 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 powdered and lixiviated with 
 water ; a large quantity of sulphate of alumina and sulphate of iron dissolve out, 
 and the liquor is brought by evaporation 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, while the 
 iron remains as chloride in the liquor. 
 
 In some volcanic countries, as Italy, a mineral is found already containing potash 
 and sulphuric acid united to alumina, from which is obtained a very pure alum, 
 rock-alum, which is valued very much by dyers, on account of its total freedom from 
 sulphate of iron, of which English alum generally contains a small trace, which in- 
 jures 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 py- 
 rophorus, 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 lamp- 
 black, alumina, and sulphuret of potassium, which last, being in a 
 ytate of exceedingly minute division, takes fire when a little of the 
 product is shaken out of the bottle, and emits considerable light. 
 Basic Mum. Cubical Mum.—M^O^ . SS.Og-f K.O. . S.O3. This 
 
GLASS AND PORCELAIN. 437 
 
 substance, which is preferred as a mordant to ordinary alum, is pre- 
 pared by adding carbonate of potash to a solution of alum, as long 
 as the precipitate 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 
 hereafter noticed. 
 
 The Phosplmte 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 pharmaceutic value are 
 noticed under the heads of the uses to which they are applied. For a description of 
 the others, I refer to the ordinary works on mineralogy. 
 
 One substance, however, of which the constitution is very curious, may, from its 
 technical importance, here be noticed, the Mpis-lazuli, ultramariTie. It is found in 
 veins in igneous rocks in Siberia, but particularly 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, 23-2; sulphur, 3-1 ; carbonate of lime, 3-1 : it is difficult to de- 
 duce a formula from these numbers, and the state of combination of the sulphur is 
 not well understood. Attempts at imitating 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 proportions above 
 given, and the mixture dried down ; the resulting mass is placed in a covered cruci- 
 ble 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, 
 
 1 deferred the description of the silicates of potash, soda, and 
 lime, because they stand so closely allied with the silicate of alumi- 
 na, in relation to the important manufactures of glass and earthen- 
 ware, 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 liquo?- 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 de- 
 liquesces 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. 321. In this preparation, soda may be substi- 
 tuted for potash in a proportion one third less, and a mixture of 
 seventy parts of carbonate of potash, fifty-four of dry carbonate of 
 soda, and 152 of fine quartz sand, gives a still more fusible and sol- 
 uble 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 bein^ 
 melted, very gradually, and to pass through a condition of pasti- 
 ness, which admits of its being blown out, cut, and fashioned in ev- 
 ery way ; and, second, to remain, when solid, quite transparent, and 
 destitute of any tendency to crystalline structure. Its composition 
 
438 
 
 MANUFACTURE OF GLASS. 
 
 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 ; 2d, lime, used sometimes pure, 
 sometimes slacked j occasionally chalk is employed in place of lime j 
 3d, carbonate of potash (pearl ashes of commerce) ; 4th, carbonate 
 of soda, or a salt of soda, as Glauber's salt or common salt j 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 va- 
 rious kinds of glass difiering very much, as is shown in the following table of th« 
 best analyses of glass. 
 
 Constituents. 
 
 Hard while 
 Glass. 
 
 Crown Glass. | Bottle Glass. 
 
 Crys- 
 tal. 
 
 Flint Glass. 1 
 
 No. 1. 
 
 No. 2. 
 
 No. 3. 
 
 No. 4. No. 5. 
 
 No. 6. 
 
 53-5 
 
 No. 7. 
 
 59-2 
 
 No. 8. 
 
 No. 9. 
 
 Silicic Acid . . . 
 
 71-7 
 
 69-2 
 
 62-8 
 
 69-260-4 
 
 51-9 
 
 42-5 
 
 Potash 
 
 12-7 
 
 158 
 
 221 
 
 80 3-2 
 
 5-5 
 
 90 
 
 13-8 
 
 11-7 
 
 Soda 
 
 2-5 
 
 30 
 
 
 30! . . 
 
 
 
 
 
 Lime 
 
 10-3 
 
 7-6 
 
 12-5 
 
 130:20-7 
 
 29-2 
 
 
 
 05 
 
 Alumina .... 
 
 0-4 
 
 1-2 
 
 ) 
 
 36 
 
 10-4 
 
 60 
 
 
 
 1-8 
 
 Magnesia .... 
 
 
 20 
 
 ^2-6 
 
 0-6 
 
 0-6 
 
 . . 
 
 . . 
 
 , , 
 
 
 Oxide of Iron . . . 
 
 b-3 
 
 0-5 
 
 S 
 
 1-6 
 
 3-8 
 
 5-8 
 
 0-4 
 
 . . 
 
 , . . 
 
 Oxide of Manganese 
 
 0-2 
 
 
 
 
 
 
 10 
 
 . . 
 
 
 Oxide of Lead . . 
 
 
 
 
 990 
 
 991 
 
 1000 
 
 28-2 
 97-8 
 
 33-3 
 99-0 
 
 43-5 
 1000 
 
 
 981 
 
 99-3 
 
 1000 
 
 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 Bohe- 
 mian glass, is much more fusible, and is that in ordinary use. No. 3 is English 
 plate, and No. 4 German plate glass, Nos. 5 and 6 are both French. Nos. 7 and 
 § are English glass for 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 difierent 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 gradu- 
 ally 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 oi 
 alumina. In this 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 lieaumur's Porcelain. 
 
 The arrangement of the furnaces for the manufacture of glass varies according to 
 the materials and the kind of product. The materials, reduced to the state of very 
 fine powder, are intimately mixed, and fused in crucibles of very refractory clay. 
 The silica decomposes the carbonates of lime and potash or soda, and, expelling the 
 carbonic acid, combines 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 decom- 
 posed, sulphurous and carbonic acids being evolved (p. 292), otherwise the silica 
 could not completely expel the sulphuric acid. From the presence of minute quan- 
 tities of protoxide of iron in the materials, the glass has. at first, a pale-greenish tint, 
 which is counteracted 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 pre- 
 vent its employment. More generally peroxide of manganese is used, which, acting 
 on protoxide of iron, produces peroxide of iron and protoxide of manganese, neither 
 of which bodies gives any sensible tint to glass. If there be too much manganese 
 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 employ- 
 ed in the manufacture of the fine crown glass of Germany. In the oval furnace 
 A. which is covered by a dome, the crucible.s are arranged in two rows, on barJcs, 
 
MANUFACTURE OF GLASS. 
 
 439 
 
 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 by a hood, pre- 
 senting only an aperture ex- 
 ternal to the furnace for 
 the workman, as the glass 
 would require to be thus pro- 
 tected from the smoke and 
 combusti])le gases of the fur- 
 nace, which would reduce 
 the lead to the metallic state. 
 Between the banks is a rec- 
 tangular space for the fire, 
 resting on the gratings b b, 
 which are separated by the 
 partition wall F, and have 
 apertures 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 e e. The 
 flame of the fuel, which should be either wood or a very bituminous coal, issues 
 partly through the apertures in front of the crucibles o o, and partly passes by g into 
 the wings and chimney ; by means of the wings, a great quantity of the heat is 
 economized for preparatory operations. Next the furnace are placed the fresh cru- 
 
 r 
 
 cibles e e, 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 1 1; these being brought to a dull red heat, undergo a commencement of 
 vitrefaction, and are thus fritted, or prepared for the perfect combination by fusion 
 in the crucibles. This operation of fritting was formerly 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 pass- 
 ing 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 pass off freely, and then be suffered 
 to cool until it acquires the pasty consistence which fits it for being worked into the 
 necessary fonns. In thus cooling down, however, those glasses which contain 
 oxide of lead frequently separate into two or more layers of glass of different den- 
 sities, 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 impefection 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 insol- 
 
440 COMPOSITION OF CLA'^. 
 
 ubility in water ; its resisting the action of acids and the generality of chemical re- 
 agents under all ordinary circumstances ; its transparency and lustre, and the rela- 
 tions 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 sudden- 
 ly cooled, as by being laid, while soft, on a i)late of cold iron, or being dropped into 
 water, the internal portions being prevented from contracting, remain in a state of in- 
 stable arrangement, on which depends its double refracting and polarizing properties 
 (p. 230). 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 dis- 
 position, and, flying asunder, the mass crumbles into powder with an explosion. 
 Priiice Rupert's drops, with which this property of glass may be exemplified, are pre- 
 pared by taking up on an iron 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 pro- 
 jecting 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 un- 
 fit 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. For this purpose, the 
 vessels, when formed, are placed in the aiinealing fiirnace, or leer, which is a long gal 
 lery 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. Accord- 
 ing 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 pas- 
 sage down occupying from 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 ex- 
 posed, 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 reagents best. The 
 oxide of lead in flint glass is acted on by a variety of chemical sub- 
 stances, which unfits it for many laboratory uses. Where alkali 
 predominates, the glass is rapidly acted on by the air, attracting 
 moisture, and thus frequently embarrassing electrical experiments. 
 Bottle glass which contains much alumina 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. 37) ; on this principle is founded the art of 
 painting on, or staining glass, and also the manufacture of artificial gems. These 
 arts I shall 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 
 principles, first, that of the plasticity and fusibility of clay, and, sec- 
 ondly, 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, is a neutral silicate of alumina, Al203H-3Si.03 ; but 
 as the great deposites 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 feldspar contained in granitic and syenitic 
 rocks. The feldspar has the formula K.O. . Si.03-{-(AlA+3*Si.03) i 
 by the action of water, the silicate of potash is dissolved out as sol- 
 uble glass (p. 437), and the silicate of alumina remains as a fine 
 
MANUFACTURE OF EARTHENWARE. 
 
 441 
 
 powder, perfectly white, impalpable, forming with water a paste 
 capable of being moulded into any form, and, when heated, abandon- 
 ing 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 j 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, con- 
 sequently, when burned, assume a red or yellow colour, are em- 
 ployed for common earthenware. In the clays which contain very 
 little iron, and hence burn white, there are present, almost univer- 
 sally, certain quantities of alkali, remaining from the decomposed 
 feldspar ; this is generally potash, but may be soda when the clay 
 is formed from albite (Na.O. . Si.O -fSAlaOa-f-SSi.Oa) ; and when the 
 source of the clay is not a pure granitic rock, the associated miner- 
 als generally yield a certain quantity of lime which mixes with it. 
 Hence the composition of the following clays, from various coun- 
 tries, used in the manufacture of porcelain, can easily be account- 
 ed for : 
 
 Clay from 
 
 Mori. 
 
 Schnee- 
 berg. 
 
 Limoges. 
 
 Silica .... 
 
 71-42 
 
 436 
 
 46-8 
 
 Alumina . . . 
 
 26 07 
 
 377 
 
 373 
 
 Lime .... 
 
 13 
 
 
 
 Potash .... 
 
 045 
 
 
 25 
 
 Water .... 
 
 
 120 
 
 13-0 
 
 Oxide of Iron . . 
 
 1-93 
 
 1-5 
 
 
 If clay alone were used in the fabrication of earthenware, al- 
 though, from its plasticity, it would assume perfectly the required 
 form, yet, from its infusibility, it would, when baked, have so little 
 coherence, and, from its great 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 tem- 
 perature, cement together the particles of clay, and enable the dif- 
 ferent portions of the vessel to hold together during the bakings. 
 Thus, to form the body of ironstone chinaware, forty parts of Dev- 
 onshire 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 pro- 
 cess 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 re- 
 ception 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 surface, 
 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 of its porosity. The composition of the glaze 
 may vary much in different establishments ; an ordinary one, for ironstone china, 
 consists of feldspar 36, quartz 20, white lead 40, flint glass 8. These materials are 
 flitted 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 ar- 
 ranged 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 
 
 K K K 
 
442 BAKING AND GLAZING OF EARTHENWARE. 
 
 Taulted 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 ar- 
 rows ; 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 sec;ond, the ar- 
 ticles are dried to the de- 
 gree 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 perform- 
 ed. The operation com- 
 mences, first, with a moder- 
 ate fire, the fuel being in- 
 troduced into the cavity A, 
 and supplied with air by 
 the apertures e s; the heat 
 being allowed to rise grad- 
 ually for six or eight hours, 
 the space 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 k. The temperature is thus kept uniform- 
 ly intense 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 en- 
 graved 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 de- 
 sign. 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 j the crimson 
 by gold ; and gold and platina are applied also in their metallic 
 state, by dissolving their chlorides in oil of turpentine, and apply- 
 ing this varnish with a pencil, then burning, and burnishing the me- 
 tallic surface. 
 
 A coarse kind of glazing, given to the common articles of earth- 
 enware, 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 sur- 
 face of the earthenware decomposes the common salt, which is con- 
 verted into vapour by the heat ; Si.Og with Na.Cl. and H.O., produ- 
 cing Na.O. . Si.Oa, which forms a transparent glassy varnish on their 
 surface, while H.Cl. passes off with the excess of w^atery vapour, 
 forming copious white fumes. 
 
SALTS OF MANGANESE. 443 
 
 The general characters of the salts of glucinum, thorium, yttrium, zirconium, Ixm- 
 thanum, and ceiium have been noticed under the heads of these respective metals 
 (p. 351, et seq.)f and do not require farther 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 
 noticed in p. 356, and it remains only to describe the former. 
 
 Protochloride of Manganese. — Mn.Cl.-l-4 Aq. Eq. 788-5-1-450 or 
 63- 19-1-36. This salt maybe obtained by digesting the commercial 
 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 form- 
 ed 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 digesting the melted mass in water, protochloride of 
 manganese dissolves, and all the iron remains insoluble. The solu- 
 tion, 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^ Mn.Cl2, 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. — Mn.O. . S.O3-I-7 Aq. 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 contains 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, 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 con- 
 stitutional, 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, Mn2034-3S.03 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 octohedrons, which are manganese alums, similar in constitution 
 to the ordinary alum, but with AI2O3 replaced by MuaOa. 
 
 No other salt of manganese requires special notice. 
 
444 SALTSOFIRON. 
 
 Salts of Iron. 
 
 There are two series of iron salts, corresponding to the two ox- 
 ides, proto-salts and sesqui-salts. 
 
 Protochloride of Iron. — Fe.Cl.+4H.O. This salt is formed when 
 metallic iron is dissolved in muriatic acid, hydrogen being evolved j 
 the solution, which is of a pale bluish-green colour, yields, on evap- 
 oration, 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 per- 
 chloride is formed and the whole decomposed. The anhydrous 
 protochloride is very elegantly prepared by passing a stream of dry 
 chloride of hydrogen over fine iron wire, coiled up in a tube of hard 
 Bohemian glass, and heated to bright redness : hydrogen gas ia 
 evolved, and protochloride 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. — FeaClg. 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 sirup, gives large red crys- 
 tals of hydrated chloride, which are very deliquescent. On the ap- 
 plication of heat, this salt is totally decomposed j muriatic acid is 
 given off, and the red oxide of iron remains behind, with some un- 
 altered chloride, as a basic salt. To obtain the anhydrous sesqui- 
 chloride, 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 ammo 
 niac, 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 chlo- 
 ride of iron. 
 
 Protoiodide of.Iron, Fe.I., is formed by digesting iodine in wa 
 ter on an excess of iron filings. Considerable heat is evolved, and 
 a colourless solution is obtained, which, when evaporated, yields a 
 crystalline mass containing water of crystallization, and which is 
 decomposed by a farther action of the heat, iodine being evolved. 
 It absorbs oxygen very rapidly. A solution of protoiodide of iron 
 dissolves iodine abundantly, becoming brown, and possibly contain- 
 ing the sesqui-iodide, Fcala ; but it is more likely that the iodine is 
 not combined, as it is sensible to the test of starch. 
 
 The bromides of Iron resemble perfectly the iodides. 
 
 Protosulphate of Iron. Green Copperas. — Fe.O. . S.Oa-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. 436). Oxygen is rapidly absorbed both 
 by the iron and the sulphur, sulphuric acid and oxide of iron being 
 
SALTS OF IRON. 445 
 
 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 ex- 
 cess 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 dissolving iron wire in dilute sulphuric acid, as in the 
 process for preparing hydrogen gas (page 247). The protosulphate 
 of iron generally crystallizes with seven atoms of water, of which 
 one is constitutional, and may be replaced by an alkaline sulphate, 
 forming double salts. The form of its crystal is a short oblique 
 rhombic prism, z, w, u, with numerous secondary faces, as j3, 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 spa- 
 ringly 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 used in the arts, under the names of rouge and colcothar^ 
 as a polishing material. On these properties is founded the manu- 
 facture of fuming oil of vitriol, described in page 247. The proto- 
 sulphate of iron absorbs oxygen rapidly even when dry, and becomes 
 covered with a reddish crust of basic persulphate, whence its com- 
 mercial name. In solution, the absorption of oxygen proceeds 
 quickly, until two thirds of the iron are peroxidized and a reddish 
 solution obtained, from which alkalies throw down the black mag- 
 netic oxide (see page 363). This solution does not crystallize. 
 
 Se^^w^w/pAa^e o//ro?^.— FeA+3S.03. Eq. 2481-9 or 198 9. This 
 salt is found native in large quantities in Chili, combined with 9 Aq. 
 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 ex- 
 pel 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, 
 which may be driven off by a heat just below redness. The persul- 
 phate then appears as a white powder, which dissolves but very 
 slowly in water. By a strong heat this salt is totally decomposed. 
 The protosulphate may be converted into persulphate by adding to 
 a boiling solution nitric acid in small quantities, as long as any ni- 
 tric 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 2Fe203-(-S.03-f-3 Aq. 
 
 The persulphate of iron combines with the alkaline sulphates to 
 form a class of alums^ which contain FegOg in place of AL2O3. These 
 iron alums are generally pale red in colour, but have the form, sol- 
 ubility, and nearly the taste of common alum. 
 
 Protonitrate of Iron may be formed by dissolving sulphuret of iron 
 in cold dilute nitric acid ; it crystallizes in pale-green rhombs, 
 which, when heated, evolve nitric oxide gas, and form a basic ni- 
 
446 SALTS OF IRON, NICKEL, AND COBALT. 
 
 trate of the peroxide. Metallic iron dissolves in dilute nitric acid 
 without the evolution of any gas, water and nitric acid being si* 
 multaneously decomposed, and oxide of iron and ammonia produced. 
 Thus N.O3 with 3H.0. and 6Fe., give 6Fe.O. and N.H3. 
 
 Pernitrate of Iron is produced when iron is dissolved in hot nitric 
 acid ; the solution is reddish brown, and gives, by drying, a deli- 
 quescent 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 StahVs alkaline tincture of Iron. 
 
 Protophosphate of Iron^ Tribasic — H.O. . 2Fe.0.4-P-03 — may be 
 formed by decomposing a solution of protosulphate of iron with tri- 
 basic 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^ and may be produced ar- 
 tificially by adding solution of phosphate of soda to the solution of 
 mixed sulphate of iron, from which alkalies precipitate the black 
 oxide (p. 363). The precipitate which forms is of a rich blue col- 
 our, and is not changed by exposure to the air. Its formula is (H. 
 0..2Fe.O.-(-P.05) + (2FeA.P.05). It is used in medicine. 
 
 Sesquiphosphate of Iron, 2Fe203+P.05, is obtained by decompo- 
 sing a 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 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 
 gives Fe, + Cl^ . N.O2, and the protosulphate (Fe24- O, • N.O,) -f 2S.O3, 
 analogous to Fez + Cl.a and (Fca-j- 03)4-28.03. The utility of this 
 olive liquor as a test for nitric acid and in eudiometry, has been 
 noticed in p. 264^ and 281. 
 
 Salts of JVickel and Cobalt. 
 
 Chloride of Nickel, Ni.Cl., may be obtained by dissolving oxide of nickel in dilute, 
 muriatic acid, or by acting on the metal with the hot concentrated acid. It crystal- 
 lizes 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. 
 
 Sulp/iaie of Nickel. — Ni.O. . S.Os. This salt is obtained by dissolving the oxide 
 in dilute sulphuric acid, or by acting on the metal with a mixture of nitric and sul- 
 phuric acids diluted with water; the nitric acid then supplies oxygen. This solu- 
 tion gives fine emerald green crystals, which vary in Ibrm according to the quanti- 
 ty of water ihey contain. When they form below 60^, they are long rhombic prisms, 
 containing 7 Aq., and isomorphouswith the sulphates of zinc and magnesia; 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, arid becomes oqaque 
 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. CI., is formed by dissolving oxide of co- 
 balt, or the zaffre of commerce, in muriatic acid. The solution ia 
 
SALTS OF COBALT AND ZINC. 447 
 
 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 pre- 
 pared from zafTre, the colour becomes green, and it is thus that 
 sympathetic inks of cobalt are produced, and summer and winter 
 scenes in landscapes alternated j 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. 
 
 Sulphate of Cobalt, Co.O.+S.Oa, 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, H.O. . 2C0.O.+P.O5, is precipitated in dark violet flocks when 
 solution of sulphate of cobalt and phosphate of soda are mixed together. This sub- 
 stance is the basis of a very beautiful pigment, Thenard^s Bliie, which is prepared by 
 mixing intimately one part of phosphate of cobalt with two or thr6e 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 p. 349 and 351). 
 
 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 Sax- 
 ony 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 (p. 366, 376). From the zafFre a sulphate of cobalt is 
 prepared, and on the other hand a silicate of potash, by melting to- 
 gether fine sand and carbonate of potash ; these solutions being 
 mixed, silicate of cobalt i^ precipitated, while sulphate of potash 
 remains dissolved. This precipitate is the best material for colour 
 ing porcelain and glass ; but the ordinary smalts are formed by melt- 
 ing impure carbonate of cobalt with potash and quartz into a blue 
 glass, which is then reduced to impalpable powder, and sorted ac- 
 cording to the quality, for commerce. 
 
 Salts of Zinc and Cadmium. 
 
 Chloride of Zim — Zn.Cl. ; Eq. 845-9 or 67-78 — may be prepared by burning metal- 
 lic zinc in chlorine, or by dissolving the metal in muriatic acid. The solution is 
 colourless; when evaporated, it yields rhombic crystals, Avhich 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 some- 
 times applied as a bath in place of oil or fusible metal, in taking the specific gravity 
 of vapours (p. 14). From its fusibility and softness, it had formerly the name of 
 Butter of Zinc. From its affinity for water, it acts powerfully as a caustic on the liv- 
 ing tissues, and is employed in medicine as such. 
 
 Chloride of zinc combines with oxide of zinc in many proportions, forming oxy- 
 chlorides, 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 for. 
 mula is Zn.Cl.+3Zn.O.+4 Aq. The second results from the action of water on 
 the amraoniacal chloride of zinc; its formula is Zn.Cl. +6Zn.O.+10 Aq., and is that 
 whose analogies to the liquid muriatic acid have been pointed out in p. 309. The 
 third is formed by acting on chloride of zinc with an excess of potash ; its formula 
 is Zn.Cl.+9Zn.O.+l4 Aq. 
 
 The brovii'le and iodide of Zinc resemble completely the chloride in general char- 
 acters : a solution of iodide of zinc is capable of dissolving a large quantitv of iodine. 
 Sulphate of Zinc, Zn.O. . S.O3+7 Aq., may be produced by dis 
 solving 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, bletide 
 
448 SALTS OF TIN. 
 
 The metal and sulphur both combining with oxygen, a neutral sul- 
 phate of the oxide is formed, which being then dissolved out by- 
 water, the solution is evaporated to a pellicle, and allowed to crys- 
 tallize. Sometimes the blende, in place of being roasted, is exposed 
 on sloping beds to the action of the air and moisture, when it grad- 
 ually 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 com- 
 mercial name is white vitriol. The crystals of sul- 
 phate of zinc are eight 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 replace its con- 
 stitutional water, forming double salts, and with ox- 
 ide 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. 368. 
 
 Nitrate of Zinc, Zn.O. . N.O5, is obtained by dissolving the metal in dilute nitric 
 acid ; it crystallizes in flat four-sided prisms. It is deliquescent, and soluble in al- 
 cohol. 
 No other salt of zinc is of importance. 
 
 Cfdm-ide of Cadmium, Cd.CL, crystallizes in large four-sided prisms ; it is not de- 
 liquescent. The other salts of cadmium resemble completely the corresponding 
 salts of zinc, and do not require notice. 
 
 Salts of Tin.* 
 
 Protochloride of Tin.~Sn.Cl. + 3 Aq. Eq. 1 177-9 -f 337-5 or 94-39 
 +27. This salt is obtained anhydrous by heating tin in a current 
 of muriatic acid gas, hydrogen being evolved ; or by distilling a 
 mixture of equal parts of tin and corrosive sublimate in a glass re- 
 tort, the metallic mercury first passes over, and, finally, the proto- 
 chloride of tin sublimes at a strong red heat. It forms a gray 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 crystallizes in long prisms, which contain three atoms of 
 water. When these crystals are heated, they first lose water, but 
 afterward muriatic acid passes off, and a basic salt remains. This 
 crystallized protochloride, under the name o{ salt of tin^ is used ex- 
 tensively in dyeing as a mordant ; in its preparation on a large 
 scale, copper vessels may be employed, 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, Sn.Cl + Sn.O., 
 being thrown down ; hence, in order to have a dilute solution clear, 
 it requires the addition of a few drops of muriatic acid. Protochlo- 
 ride 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, orceine 5 forming colourless compounds, which 
 have some important applications in the art of dyeing. 
 
SALTS OF TIN, CHROMIUM, AND VANADIUM. 449 
 
 The protochloride of tin combines with chloride of potassium and 
 with sal ammoniac to form double salts, which were analyzed by 
 Apjohn. 
 
 Perchloride of Tin^ Sn.Cli, 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 bichloride of tin, the fuming liquor of Libavius. Metallic 
 mercury remains in the retort. This singular compound boils at 
 248^ Fah. j the specific gravity of its vapour is 9*12. When mixed 
 with one third of 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 dis- 
 solving 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, muriat- 
 ic acid being given off, and peroxide of tin remaining. 
 
 Protoiodidc of Tin, Sn.L, 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 orange colour. It is decomposed by a large quantity of wa- 
 ter. It combines with the iodide of potassium to form a soluble double iodide. The 
 biniodide of tin crystallizes in yellow needles, which are decomposed by much water. 
 
 The bromides of Tin are not important. 
 
 ProtomlpJiate of Tin, Sn.O. . S.Od, is formed when tin is dissolved in strong sul- 
 phuric acid. A saline mass is obtained, which dissolves in water, giving a brown 
 solution, from which the salt crystallizes in small needles. Bancroft's niardant, for 
 dyers, is prepared by digesting two parts of tin with three of strong muriatic acid for 
 an hoar, 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 solution, on cooling, forms a crys- 
 talline 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-precipitated 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 described in p. 371. 
 
 The sulphurets of tin act as sulphur acids, combining with the sulphurets of the 
 alkaline metals. The bisulphuret forms vnth. sulphuret of sodium a crystallizable 
 salt, 2Na.S.-|-Sn.S2+12 Aq., sulphostannate of Sodium. 
 
 Salts of Chromium and Vanadium. 
 
 There are two kinds of salts of chrome, one in which the oxide of chrome is the 
 base, and the other in which the chromic acid is combined with bases. 
 
 A. Salts of Oxide of Chrome. 
 
 Cliloride of Ckrorrie.—Gi^Ch. Eq. 2031-6 or 162-8. When oxide of chrome is mix- 
 ed with lampblack, and treated by a current of dry chlorine at a red heat, as de- 
 scribed 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 
 exceeding beauty. It may also be obtained by dissolving oxide of chrome in muri- 
 atic acid, and evaporating the solution ; it remains as a green mass, in which it is 
 combined with 3H.0. 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 pro- 
 cess first described. 
 
 C/ilorochromic tIciVA— Cr.Cl3-j-2Cr.O3. 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 ap- 
 paratus 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 produci distils 
 ever, without the application of external heat. This substance is a thin bl od-red 
 
 Lll 
 
450 CHROMATES OF POTASH. 
 
 aquid appearing black by reflected light; it fumes much by exposure to the air; it« 
 vapour IS red like nitrous acid. When its vapour is heated to redness, it is decom 
 posed, as described in p. 373. It is decomposed by water. Alcohol placed in coiv 
 tact 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, Cr.Cla+SCr.Os, or as a compound of chlorine with a 
 deutoxide of chrome, Cr.OaCl. The analogy of the sulphuric to the chromic acid 
 is supposed to favour this latter view, as also the sp. gr. of its vapour, which is 5-9. 
 
 Sulphate of Chrome, Cr203+3S.03, 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 chroine alums, which crystallize in dark purple octohedrons, and which contain 
 ihe same proportion 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 it becomes green, and the elements of the salt are then found to be no 
 longer united, as by evaporation they may be separated. 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 abundant- 
 ly by setting aside for a few days the residue of the process for making aldehyd, as 
 described farther on. 
 
 The Perjluoride of Chrome, Cr.Fs, is formed by acting with oil of vitriol on a mix- 
 ture 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 in- 
 verted in the quicksilver trough. Its decomposition by water, and the consequent 
 formation of chromic acid, has been already noticed, p. 373. 
 
 B. Salts of Chromic Acid. 
 
 Chromates of Potash. — The manufacture of the bichromate of pot- 
 ash, K.O.-)-2Cr.03, 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 prepared. It is made from the only abundant ore of chrome, 
 ihe chrovie-iron^ Fe.O.+CraOg, by the following process. Two parts 
 oi 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 sev- 
 eral 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 crys- 
 tallized 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 crystalli- 
 zation in tanks lined wdth lead. 
 
 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 
 chromate of potash. 
 
 The neutral Chromate of Potash, K.O. . Cr.O;,, may be prepared by 
 
 t adding to a solution of bichromate of potash as much 
 more alkali as it already contained. It is soluble in twice 
 its weight of cold water. Its solution is intense golden 
 yellow ; it crystallizes in rhombic prisms, isomorphous 
 with those of sulphate of potash, as in the figure, of which 
 n n and u, u are primary, and z, m are secondary planes. 
 
SALTS OF TUNGSTEN, MOLYBDENUM, ETC. 451 
 
 If bichromate of potash be dissolved in hot dilute nitric acid, a 
 terchromate of potash, K.O. . +3Cr.03, 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 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 equiva- 
 lent of chloride of potassium united to two of chromic acid, K.Cl. 
 i-2Cr.03. 
 
 None other oi 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 ex- 
 ceeding rarity of the metal, have been but little studied. The salts containing the 
 vanadic oxide are generally splendid blue ; those containing the vanadic add as basis 
 are red or yellow, while 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 bichlo- 
 ride and perchloride, according as the metal or the gas is in excess. Both are vol- 
 atile, and condense in red needles. They are decomposed by water, giving muriatic 
 acid and tuogstic oxide, W.O2, or tungstic acid, W.O3. A chlorotungstic acid exists, 
 W.O2CI., 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 already in p. 374, 
 
 Molybdenum takes fire when heated in "a stream of chlorine gas, and forms the ter- 
 chloride, M0.CI3, 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 metaJ, Mo. 
 CI. and M0.CI2, are known to exist. 
 
 The protoxide of molybdenum forms salts with the oxygen acids, which are pur- 
 ple or black coloured, and are very easily decomposed by heat. Thus the sulphate 
 is resolved into sulphurous acid gas and molybdic oxide. The molybdic oxide also 
 forms a series of salts, generally red coloured, which do not possess any special in- 
 terest. 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 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; while the latter, being carried much farther by the current of gas, is depos- 
 ited 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 com- 
 bine wi*h the oxygen acids to form salts which do not crystallize, and have been 
 very little studied. 
 
 Coluvibimi forms a volatile chloride. Its oxide, ^Ta,02, does not combine with 
 acids, and the columbic acid forms salts which are not of practical importance. 
 
 Salts of Arsenic, 
 
 Chloride of Arsenic— As. Ch] Eq. 2268-0 or 181-74 — is formed when the metal bums 
 spontaneously in chlorine ; it is a volatile liquid, which forms dense white fumes on 
 exposure to the air. It may be obtained, also, by mixing intimately one part of ai» 
 senious acid and three of common salt; putting'them into a retort to which a con 
 denser 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. In, is best prepared by digesting one part of arsenic witli 
 five of iodine and fifty of water, until the iodine disappears; on cooling, the ioaide 
 separates in orange-red crystals. It is decomposed by water into hydriodic and a^ 
 senious acids. The bromide of arsenic may be similarly formed. 
 
 Arsenic does not form any compound with chlorine, bromine, or iodine analogoui 
 to arsenic acid. 
 
452 SALTS OF ARSENIC. 
 
 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 -wiiich 
 they constitute the electro-negative element. 
 
 Arsenious Acid is dissolved in large quantities by the caustic and 
 carbonated alkalies, but the salts thus formed cannot be obtained 
 crystallized, and appear to be very indefinite in constitution. The 
 combinations of arsenious acid with the earths are white powders, 
 of which the only one of interest is arsenite of Lime^ H.O. . 2Ca.0.-f-, 
 As.Os, 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. 
 
 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 ar- 
 senious acid (see p. 384). 
 
 The arsenite of Cobalt is found native, as a rose-red powder, and 
 the arsenite of JK'ickel exists as a mineral of a pale-green colour j both 
 contain combined water. The arsenites of copper and silver will be 
 described under the heads of these metals, and have been already 
 Doticed in p. 381, et seq. 
 
 The constitution of the salts of arsenic acid has been already 
 mentioned in p. 377. 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 pot- 
 ash, H.O. . 2K.O.-I-AS.O5, forms a deliquescent saline mass. The 
 binarseniate of Potash^ 2H.0. . K.O. +AS.O5, is formed by adding to 
 the former as much arsenic acid as it already contained, or by ig- 
 niting 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 octohedrori. 
 
 There are three arseniates of Soda, which resemble the three triba- 
 sic phosphates of soda. The first, (3Na.O.+As.05)-f 24 Aq., is ob- 
 tained by igniting arsenic acid wdth an excess of carbonate of soda. 
 When a solution of arsenic acid is neutralized by carbonate of soda, 
 the salt H.O. . 2Na.0.-f As.Oj 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, 2H.0. . Na.O.-f-As.Oj, resem- 
 bles the corresponding salt of phosphoric acid. 
 
 The arseniates of the earths are white powders, insoluble in wa- 
 ter, but soluble in an excess of any acid. 
 
 Arseniates of Iron.— That of the protoxide, H.O. . 2Fe.-l-As.O5, 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 magnetic oxide. This salt corresponds to the blue phosphate 
 of iron, its formula being (2Fe.O. . H.O. -f- As.Og) + 2Fe203 . As.Og-f- 
 12 Aq. 
 
 The per arseniate of Iron is a white powder, which, when heated, 
 gives off 12 Aq. and becomes red ; it has the singular property of 
 dissolving totally in water of ammonia. 
 
 ArseniaM of Nickel is a pale green powder. Arseniate of Cobalt is a rose- red pow- 
 dor, and mav be used in place of phosphate of cobalt in preparing Thenard's blue 
 
CHLORIDE OF ANTIMONY. 453 
 
 fp. 447). It is prepared on the large scale by roasting the native arseniuret of co- 
 balt, CosAs. 
 
 The sulphur salts of arsenic are some of the best characterized among that class 
 (p. 379). There are three sidphoarscniaks of Potassium, having respectively the for- 
 muke (SK.S.+As.Sj), (SK.S.+As.Si), and (K.S.+As.Sa). They are all deliques- 
 cent, 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 char- 
 acter of the first. The sulphoarseniates of Sodium resemble those of potassium. The 
 basic salt (3Na.S.+As.S5-i-15 Aq.) crystallizes in large colourless rhomboidal ta- 
 bles. When orpiment is dissolved in solution of sulphuret of potassium, sulphoarse- 
 mfe of potassium is obtained, K.S.H-As.Sa, which, when evaporated, is decomposed, 
 and deposites a brown powder, which consists of K.As.Ss, and appears to contain a 
 bisulphuret of arsenic, As.Sz, combined with K.S., which is decomposed when sep- 
 arated from the state of combination. 
 
 Salts of Antimony. 
 
 Sesquichloride of Antimony. — Sb.Clg. Eq. 3383-5 or 271-1. To 
 obtain this salt completely pure, sulphuret of antimony in fine pow- 
 der 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 exposure to the air, whence its old name of Butter of Anti- 
 mony ; 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. 385), 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 antimony. In this operation, the crocus 
 antimonii being 2Sb.S3-j-Sb.O3, the former remains passive ; but the 
 latter, acting On 3Na.Cl. and 3S.O3, produces Sb.Clg and 3Na.O. . S. 
 O3. As there is, however, some water supplied by the oil of vitri- 
 ol, the product is not solid. It is, however, quite strong enough 
 for its successful application as a caustic. 
 
 When chloride of antimony is put in contact with much water, 
 both are decomposed, and a white oxychloride is precipitated, call- 
 ed Powder of Algarotti^ from the name of its discoverer. If the wa- 
 ter be hot, the precipitate is distinctly crystallized. In it one fourth 
 of the metal is combined with chlorine, and three fourths with oxy- 
 gen ; it contains also water, its formula being, according to Berze- 
 lius, Sb.Clj + SSb.Og-l-S Aq. The formula given by Malaguti and 
 Johnstone is 2Sb.Cl3-l-9Sb.O3, and it is possible that there are two 
 oxychlorides, which may be produced separately or mixed, accord- 
 ing to the circumstances of the precipitation. This oxychloride is 
 employed to furnish oxide of antimony 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 constituent. 
 
 Perchloride of Antimony^ Sb.Cls, is formed when metallic anti- 
 mony 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 wa- 
 ter 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. 
 
454 SALTS OF TITANIUM, TELLURIUM, ETC. 
 
 The bromide and iodide of Aviimony are prepared by the direct combination 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 (p. 387, 388), 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 hyposulpho- 
 antimo'iiite of Potassium which remains in solution after the precipitation of Kermes 
 by cooling, crystallizes on evaporation in colourless deliquescent plates. 
 
 The sesqaioxide of antimony combines with oxygen acids to Ibrm salts, which 
 possess but little interest. Metallic antimony decomposes hot oil of vitriol, evolv- 
 ing sulphurous acid gas, and forming the sulphate of Anti'tnony, a white salt, which is 
 decomposed by water. 
 
 Antimonial Powder. James's Powder. — This preparation, to which, 
 at one time, the highest medicinal virtues were attached, is pre- 
 pared by mixing together equal parts of sulphuret of antimony and 
 hartshorn shavings, and calcining them together 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 j it is then to 
 be reduced to a fine powder. In this process the sulphur, and the 
 carbon and hydrogen of the hartshorn, are burned away, and the an- 
 timony is converted into antimonious acid, of which a small quan- 
 tity unites with the lime that had been as carbonate in the bone j 
 the rest of the lime remains as phosphate, mixed with the antimo- 
 nite of lime and the antimonious acid. Its composition varies very 
 much J it seldom contains more than one per cent, of antimonite 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, 
 
 Chlmide of Titanium, Ti.Cl2, is best prepared by treating a mixture of titanic acid 
 and lampblack by chlorine, as for the preparation of chloride of silicon. It is a col- 
 ourless 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, Te.Cl2, 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 de- 
 composed by water into tellurous and muriatic acids, and combines with the alka- 
 line chlorides to form double salts. The protochloride is prepared by melting togeth- 
 er equal weights of the bichloride and of tellurium, and distilling; it condenses as 
 a deep yellow liquid, which solidifies, but does not appear crystalline. 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 important. The relations of tellu- 
 rous and telluric acids to bases have been already noticed at sufficient length (p. 389). 
 
 The chlorides of Uranium, U.Cl. and U2CI3, give yellowish green solutions, but 
 do not crystallize. With the alkaline chlorides they unite, forming crystallizablc 
 double salts. 
 
 Protosulphate of Uranium crystallizes in green prisms. 
 
 Sesquisulphale of Uranium, U2O3+3S.O3, is not itself crystallizable, but combine* 
 vith sulphate of potash in several proportions to form double salts of very complex 
 ■constitution. 
 
 The Sesquinitrate of Uraninm, U203-F3N.05, crvstallizes in large tabular crystab 
 ti a bright yellow colour. This salt is remarkable as the most definite nitrate of a 
 %csquioxide that is known to chemists. 
 
 All these salts are prepared by dissolving the oxides of uranliun in the dilute acids. 
 
SALTS OF COPPER. 455 
 
 Salts of Copper. 
 
 Copper forms two series of salts, one corresponding to the sub- 
 oxide, and tiie other to the black oxide. The former are generally 
 white, and the latter blue or green. 
 
 Chloride of Copper, Cu.CL, 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, Cu.Cl.-}-2 Aq., which are slightly deliquescent, and are solu- 
 ble in alcohol. When heated they give off water, and the dry chlor 
 ride remains as a brown powder, which recombines with water, with 
 the evolution of much heat. Strongly heated, it fuses, gives off half 
 its chlorine, and the subchloride remains, melted into a brown resin- 
 ous-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 Cu.Cl.-f3Cu.0.-|-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 Cu.Cl.-f2Cu.O. -f 3 Aq., and Cu. 
 Cl.-j-4Cu.O.-l-6H.O., prepared by the decomposition of the ammo- 
 niacal chlorides of copper. 
 
 The Subchloride of Copper, CuaCl., may be prepared either by heat- 
 ing the chloride as above, or by digesting the clippings of thin cop- 
 per in a strong solution of chloride of copper, to which some muri- 
 atic acid had been added. The liquor gradually acquires an olive 
 colour, and the subchloride is deposited in the form of a white pow- 
 der. In this case the Cu.Cl. combines with a second equivalent of 
 copper, forming CuaCl. It also precipitates when chloride of copper 
 is acted on by protochloride of tin, 2Cu.Cl. and Sn.Cl. producing 
 CU2CI. and Sn.Clj. This subchloride is insoluble in water ; it dis- 
 solves 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 alka 
 line metals to form double salts. 
 
 The Brmnide and Subhromide of Copper, Cu.Br. and CuaBr., resemble in every re- 
 spect the chlorides just described. 
 
 The Iodide of Copper, Cu.L, does not appear to exist except in combination. If so- 
 lutions of iodide of potassium and chloride of copper be mixed, the subiodide is pre- 
 cipitated, while half the iodine is set free, 2Cu.Cl. and 2K.L producing 2K.C1. and 
 CU2I., with free I. But if an excess of iodide of potassium be added, these elements 
 recombine, and a double salt, Cu.I.-f-K.L, 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 io- 
 dine then precipitated as subiodide. Thus made, it is a pale yellow powder, unal- 
 tered by the air. 
 
 Sulphate of Copper.— Cu.O. . S.O3 . H.O. +4 Aq. Eq. 996-9 -f 562-5 
 or 79-9-1-45. For 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 
 
456 SCHEELe's green and emerald GREEl^^ 
 
 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, «, v marking the 
 primary planes in each. These crystals dis- 
 solve 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 re- 
 placed 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 Cu.O. . S.Og-f-SCu.O.-l- 
 4 Aq. J and another, containing Cu.O. . S.O^-|-7Cu.O.H-12 Aq., is oc- 
 casionally observed to form. 
 
 Jfitrate of Copper. — Cu.O. . N.O54- 3 *Aq. This salt is obtained 
 when copper is dissolved in dilute nitric acid ; it crystallizes in ob- 
 lique rhombs of a rich blue colour, and sometimes in paler rhom- 
 boidal 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 tin foil, 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 ammonia to a solution 
 of the neutral salt. The formula of the basic salt is H.O. . N.Os-f- 
 3Cu.O. 
 
 Phosphate of Copper^ H.O. . 2Cu.O. +P.0-, and the arseniate of Cop- 
 per^ H.O. . 2Cu.O. -hAs.O,, are pale green powders, obtained by dou- 
 ble decomposition. 
 
 Arsenite of Copper^ H.O. . 2Cu.O-f-As.O3, 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 ar- 
 senic, has been already discussed (p. 381). 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 cop- 
 per in twelve quarts of water, previously heated in a copper pan. 
 In another pan tAvo 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 so- 
 lution is gradually added to the solution of copper. The precipi- 
 tate is collected on a cloth and carefully dried. The produce 
 should be 1 lb. 6i oz. A still more beautiful pigment, which may 
 be best described here, is prepared under the name of Schweinfurt 
 Green, or Emerald Green ; it is a compound of acetate of copper and 
 arsenite of copper, Cu.O. . a4-3(H.O. . 2Cu.O. + AS.O3). It is pre- 
 pared 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 arsenious acid 
 are to be then dissolved in 100 parts of boiling water, and while 
 boiling, the verdigris pulp is to be gradually added thereto, con- 
 tinually stirring. At first a mere arsenite of copper falls, and all 
 the acetic acid remains in the liquor ,• it being only after much agi- 
 
SALTS OF LEAD. 457 
 
 tation that the double salt is produced, which is known by the light 
 flocculent precipitate changing into a heavy granular powder of a 
 brilliant green colour. 
 
 The salts of the suboxide of copper with the oxj'^gen acids pos 
 sess no practical interest. 
 
 ' Saks of Lead, 
 
 Chloride of Lead^ Pb.Cl., may be produced by boiling lead in 
 strong n)uriatic acid, or by acting on oxide of lead with the same 
 acid ; but more simply by adding to any soluble salt of lead a so- 
 lution 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 semi-transparent mass like horn, whence the old name, plumbum 
 corneum. By the action of ammonia on chloride of lead, several 
 oxychlorides may be formed, of which none are now of interest. 
 
 Bromide of Lead resembles perfectly the chloride. 
 
 Iodide of Lead, Pb.L, 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 
 dissolve it. The solution is colourless, and, on cooling, deposites 
 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. — Pb.O. . S.O3. This salt is found in the mineral 
 kingdom in large transparent rhombs, isomorphous with sulphate 
 of barytes, and of which the octohedron z, y, in the figure, is the 
 primary form. It may be also formed by adding to 
 any solution containing lead sulphuric acid or a sul- 
 phate. 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, manu- 
 factured in leaden chambers, generally contains a small quantity of 
 it dissolved, which is precipitated on the addition of water. 
 
 J^itrate of Lead, Pb.O. . N.O5, is obtained by dissolving lead in di- 
 lute nitric acid, and evaporating. It crystallizes in regular octohe- 
 drons, often modified, which are generally opaque j it is soluble in 
 seven and a half parts of cold, and much less of boiling water. It 
 is not soluble in nitric acid. When heated, it gives out a mixture 
 of oxygen and nitrous acid gases (p. 276), and leaves melted pro- 
 toxide 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 Jead, this dissolves, and on cooling, brilliant yellow plates 
 are deposited, which are basic nitrite of Lead, 2Pb.0.-f N.O4. By 
 adding sulphuric acid to a solution of this salt, a neutral nitrite is 
 
 M M M 
 
458 CHROMATES OF LEA D. S ALTS OF BISMUTH. 
 
 obtained, Pb.O. . N.O4+H.O., which crystallizes in yellow octohe- 
 drons. If an excess of lead be used in the preparation of the ni- 
 trite, the acid is still farther deoxidized, and a hyponitrite of Lead, 
 SPb.O.-j-N.Oa+S Aq., is produced, which crystallizes in rose-red 
 scales. These salts are of interest, as it was doubted whether the 
 nitrous acid (N.O4) 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. 
 
 Phosphate of Lead, HO. . 2Pb.O.-|-P-05, 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 3Pb. 
 O.+P.O,. 
 
 Silicate of Lead has been noticed in relation to crystal and to flint 
 glass. 
 
 Chromate of Lead — Pb.O. . Cr.Os. — Chrome Yellow is formed by 
 mixing together solutions of nitrate of lead and bichromate of pot- 
 ash. It precipitates as a fine lemon-yellow powder, insoluble in 
 water. It occurs native in ruby-red crystals, constituting the red 
 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 neutral chromate, prepared as above, with the 
 basic chromate of Lead, 2Pb.O.-|-Cr.03, 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 there- 
 to, 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, becomes 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, Bi^Clg, 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 
 decomposed, giving the oxychloride of bismuth, a white powder, 
 having the composition BiaCla-f-^BiaOa-l-SH.O. In the arts this pow- 
 der is sometimes employed under the name of Spanish White or Pearl 
 White. 
 
 The chloride of bismuth combines with the chlorides of the alka 
 line 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 observed, and hence it furnishes additional proof that the 
 chloride of bismuth is a sesquichloride, on which idea the Tormulse 
 ■^come 2K.Cl.+Bi,Cl3+2 Aq. and 2Na.Cl.-fBi,Cl3-f 3 Aq. 
 
SALTS OF SILVER. 459 
 
 Sulphate of Bismuth^ BigOa + SS.Oa, is formed by dissolving bis- 
 muth in hot sulphuric acid. It forms a deliquescent mass of acicu- 
 lar crystals, which are decomposed by water, giving a white pow- 
 der, the basic sulphate of Bismuth^ Bi^Oa+S.Og. 
 
 The Mtrate of Bismuth^ Bi^Oa+SN.Os+O Aq., is formed by dis- 
 solving 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 precipi- 
 tate has the composition 4Bi203+3N.05+9H.O. ; while, if an acid 
 liquor be decomposed by water, the precipitate has the formula Bi. 
 O3 + N.O5. Both of these salts yield very nearly the same quantity 
 of oxide of bismuth on analysis, and were hence long confounded 
 together. Many reasons for considering the oxide of bismuth to be 
 a sesquioxide have been given (p. 398). These subnitrates of bis- 
 muth are used indiscriminately in medicine, but the latter form is 
 more generally found in the shops. The names Pearl White, &;c., 
 are also applied to these bodies. 
 
 Salts of Silver. 
 
 Chloride of Silver — Ag.Cl. ; Eq. 1794*3 or 143*8 — exists native as 
 an ore of silver, horn silver, and may be formed by mixing a solu- 
 tion of common salt with a soluble salt of silver. It forms a curdy 
 white precipitate, perfectly insoluble in water and in acids, but easi- 
 ly soluble in water of ammonia. When heated, it fuses below red- 
 ness, 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 re- 
 action, it is necessary that organic matter or water should be pres- 
 ent, with the hydrogen of which the chlorine may combine, and that 
 thus a thin layer of subchloride 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 p. 173, et seq. The processes for the reduction of chlo- 
 ride of silver to the metallic state have been described in p. 399, 
 400. 
 
 Iodide of Silver, Ag.L, 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 j at least it requires 
 2500 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. 175). It is reduced to the metallic state by the 
 same means as the chloride. 
 
 Bromide of Silver, AgBr., resembles the chloride in every par- 
 ticular respect. 
 
 Sulphate of Silver ^ Ag.O. . S.O3, is formed by boiling metallic sil 
 
460 &ALTS OF SILVER. 
 
 ver in oil of vitriol; sulphurous gas is given off, and a white saline 
 mass formed, which, when more strongly heated, is totally decom- 
 posed, leaving metallic silver. This salt dissolves in eighty-eight 
 parts of boiling water, and crystallizes, on cooling, in small needles. 
 Hyposulphite of Silver. — 2Ag.O. -f S2O2. 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 
 subsequently becomes permanent. It soon loses its pure colour, 
 especially if heated, and at last becomes black from sulphuret of 
 silver, while the liquor contains sulphate of silver; thus 2Ag.0.4- 
 S2O2 produce Ag.S. and Ag.O. . S.O3. 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 dissolve all the salts of silver insoluble iu 
 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. 
 
 mtrateof Silver.— Ag.O. . N.O^. 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 caus- 
 tic 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 mat- 
 ter 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 oxy- 
 gen 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 ham- 
 mer, it explodes violently. Its solution is reduced to the metallic 
 state by all deoxidating agents. 
 
 Hyponitrite of Silver, Ag.O. . N.O3, is obtained in granular crys» 
 tals by adding the soda salt prepared by melting nitrate of soda (p. 
 428) to a boiling solution of nitrate of silver, and filtering while 
 very hot. 
 
 Tribasic Phosphate of Silver, SAg.O. + P.O^, is the canary-yellow 
 precipitate, produced by adding a tribasic phosphate of soau to a 
 solution of nitrate of silver. Its relations to the other phosphates 
 
SALTS OF MERCURY. 461 
 
 of silver, and to the silver test for arsenic, have been noticed in p. 
 298 and 381. 
 
 Arseniate of Silver^ 3Ag.0.-f As.Og, 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 
 properties of arsenic acid. 
 
 Arsenite of Silver^ H.O. . 2Ag.O. -f As.Oa, is produced, as has been 
 noted in p. 401, by adding a solution of arsenious acid to the am- 
 moniacal nitrate of silver, or of arsenite of potash to nitrate of sil- 
 ver. It is a canary-yellow powder, soluble in ammonia and in ni- 
 tric acid. When heated, it first yields water and becomes brown j 
 then it gives oxygen, arsenious acid, and leaves metallic silver. 
 
 Salts of Mercury. t 
 
 Chloride of Mercury. Corrosive Sublimate — Hg.Cl. j Eq. 1708'5 or 
 136'9 — 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 pre- 
 pared 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, gen- 
 erally prepared, for pharmaceutic purposes, by the dry way, as fol- 
 lows : sulphate of mercury, Hg.O. . S.O3, is to be well mixed with 
 its own weight of common salt, Na.Cl., and the mixture introduced 
 into a wide-necked glass retort, 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; decom- 
 position occurs, the chlorine of the common salt combining with Xht 
 mercury, while the sodium takes the oxygen and acid ; we have 
 therefore formed Hg.Cl., which sublimes into the head, forming a 
 mass of prismatic crystals, which, being partly fused by the heat, co- 
 here strongly together, and sulphate of soda, which remains behind ', 
 Hg.O. . S.O3 and Na.Cl. giving Hg.Cl. and Na.O. . S.O3. 
 
 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 509^, and boils at 563\ The specific gravity 
 of its vapour is 9420. It dissolves in two parts of 
 boiling and in 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 dimorph- 
 ous ; it is soluble in 2^ parts of cold alcohol, and in 
 three parts of cold ether ; it dissolves much more 
 readily in muriatic acid and in solutions of the alka- _ 
 
 line 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, sa/ alembroth, 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 mer- 
 cury, described in p. 403. When a small quantity of potash is ad- 
 ded to a solution of sublimate, a brown precipitate falls, which by 
 boiling becomes black and crystalline ', the same substance may be 
 
462 
 
 PREPARATION OF CALOMEL. 
 
 formed by boiling red oxide of mercury in a solution of sublimate } 
 it is an oxychloride of mercury^ whose formula is Hg.Cl. + 3Hg.O. 
 
 If a solution of sublimate be treated by a small quantity of sulphu* 
 ret of hydrogen, a precipitate forms, at first brownish, but which ul- 
 timately becomes quite white, provided there be sublimate in excess ; 
 it is a chlorosulphuret^ of which the formula is Hg.C1.4-2Hg.S. 
 
 Subchloride of Mercury. Calomel.— Rg^Cl Eq. 2974-3 or 238-3 
 This important medicinal agent may be prepared either by precipi- 
 tation or by sublimation. For the former object, nine parts of mer- 
 cury are to be digested in eight parts of nitric acid, sp. gr. 1*25, 
 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 abso- 
 lutely pure. The mercury dissolving in the nitric acid, forms pitrate 
 of the suboxide, and by the chloride of sodium, nitrate of soda and 
 subchloride of mercury are formed ; HgaO. . N.O5 and Na.Cl. giving 
 Hg^Cl. and Na.O. . N.O^. 
 
 To obtain calomel by sublimation, four parts of corrosive subli- 
 mate may be rubbed up with three parts of mercury, so intimately 
 that no trace of metal shall be visible ; and the mixture being intro- 
 duced 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, Hg.Cl. combining directly with Hg., gives HgaCl. 
 The union is never perfected by the first sublimation, and the prod- 
 uct is to be again powdered, well mixed, and again sublimed. The 
 process followed by the British pharmacopoeias is difl^erent, and is 
 best carried on in the following proportions : Thirty-one parts of 
 dry sulphate of the red oxide of mercury (persulphate) are tobe in- 
 timately mixed with twenty and one third parts of metallic mercury 
 and twenty parts of fused common salt, and the whole rubbed to- 
 gether until the mercurial globules totally disappear. This method 
 is the same as the former in principle, except that the corrosive 
 sublimate is generated only when required to combine with the ad- 
 ditional quantity of mercury to form calomel. The sublimation is 
 carried on as described above. The sublimed mass is always con- 
 taminated 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 wa- 
 ter of ammonia. 
 
 The precipitated calomel is a pure white pow- 
 der. 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 mi- 
 nute 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 excessively fine powder. Its specific gravi- 
 ty is 6-5. The presence of sublimate in the cal- 
 omel of the shops is detected by boiling for a fev/ 
 minutes in alcohol, and adding to the alcoholic li* 
 
^ IODIDES OP MERCURY. 463 
 
 quor some water of ammonia, 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. 
 
 T/ie Bromide and Subbromide of Mercury, Hg.Br. and Hg2Br., may be prepared, 
 the first by acting directly on mercury with bromine, when a colourless solution is 
 obtained, which gives prismatic crystals by evaporation ; the second, by decompo- 
 sing nitrate of the suboxide by bromide of potassium. These bodies resemble com- 
 pletely sublimate and calomel in their properties. 
 
 Iodide of Mercury. Red Iodide— Kg.l. ; 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 precipi- 
 tating a solution of corrosive sublimate with an equivalent of iodide 
 of potassium. An excess of the latter redissolves the precipitate, 
 as it forms a double salt (K>I. + Hg.I.), soluble in water, and crystal 
 lizable in octohedrons. The iodide of mercury is insoluble in wa- 
 ter ; when heated, it fuses and sublimes, condensing in a crystalline 
 mass, formed of rhomboidal plates, which, when broken or scratch- 
 ed, 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 j 
 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 proportions. It forms a 
 class of double salts, equally extensive with that produced by cor- 
 rosive sublimate. 
 
 Subiodide of Mercury^ Hg2l., may be formed by triturating iodine 
 with mercury, or by precipitating a solution of iodide of potassium 
 by a slight excess of nitrate of the suboxide of mercury. It is an 
 olive-green powder, which is resolved by heat into metallic mercu- 
 ry and iodide, and is similarly decomposed by a solution of iodide 
 of potassium, with which the iodide of mercury formed combines. 
 
 Sesquiodide of Mercury^ or Yellow Iodide. — Hg4l3 or 2Hg.I. -J- Hggl. 
 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 solu- 
 tion of iodide of*'potassium, it is resolved into red iodide and me- 
 tallic mercury. The reaction by which it is formed is that, of the 
 subiodide first produced, by the K.I. and Ug^O. . ISi.O^, one half is 
 converted into red iodide by the additional atom of iodine which 
 is supplied; 2(K.I.)-f I. and 2(Hg20. . N.O,) giving 2(K.O. . N.O5) 
 and Hg.2l.-{-2Hg.I. This preparation is employed in pharmacy. 
 
 A preparation which has been proposed by Donovan, under the 
 name of lodo-hydrargyrate of Arsenic^ is prepared by rubbing togeth- 
 er 6-08 grs. arsenic, 15-38 grs. of mercury, and 50 grs. iodine, v/ith 
 a few drops of alcohol, until they combine, and then adding eight 
 ounces of water with a few drops of hydriodic acid ; a solution 18 
 obtained, at first colourless, but soon becoming yellowish-brown by 
 
464 OXYGEN SALTS OF MERCURY. *' 
 
 light, from iodine being set free. This preparation is not a cnem- 
 ical compound ; but the iodide of arsenic being decomposed by the 
 water, the iodide of mercury is dissolved by the hydriodic acid 
 formed, while arsenious acid exists free in the solution. 
 
 Sulphate of Mercury— Eg. 0. . S.O3; Eq. 1867 or 149-6— is produ- 
 ced by boiling oil of vitriol on mercury, until it is converted into a 
 white saline mass, which requires to be finally heated nearly to red- 
 ness to expel the excess of acid. Sulphurous acid is evolved, Hg. 
 and ^S.Og giving Hg.O. . S.O3 and S.O2 j 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 crys- 
 talline ; at a full red heat it is resolved into merc+iry, sulphurous 
 acid, and oxygen. Its use is extensive in preparing calomel and 
 sublimate. By a large quantity of water it is decomposed into free 
 acid and basic sulphate^ turpeth mineral^ SHg.O. + S.Og, which is a 
 bright yellow powder, which, when heated with muriatic acid, gives 
 neutral sulphate and corrosive sublimate, 2H.C1. and (3Hg.0.-t-S. 
 O3) producing 2Hg.Cl. and Hg.O. . S.O3, water being formed (see 
 p. 461). 
 
 Subsulphate of Mercury— Eg^O. . S.O3 — Sulphate of the Black Ox- 
 ide 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 powder, very sparingly soluble in water, by which it is 
 not decomposed, and is thereby distinguished from the preceding 
 salt. 
 
 Kitrute of Mercury. J^itrate of the Red Oxide. — 2Hg.O. . N.O5+ 
 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 so- 
 lution is decomposed when diluted, a basic nitrate of the Red Oxide 
 being precipitated of a bright canary colour, and having the formu- 
 la HO. . N.Oj-I-SHg.O. If this powder be boiled with much water, 
 a still more basic salt is formed, which has the formula N.05-]-6Hg. 
 O. Both this salt and the sulphate, when heated by sulphuretted 
 hydrogen not in excess, give white basic compounds, like the chlo- 
 rosulphuret (p. 464), having the formulae Hg.O. . N.05H-2Hg.S. and 
 Hg.O..S.03 + 2Hg.S. 
 
 Subnitrate of Mercury. J^itrate of the Black Oxide. — When mercu- 
 ry is dissolved in dilute nitric acid, without any heat, or with only 
 as much as sustains a very moderate action, the black oxide formsj 
 and may unite with the nitric acid in various proportions. 1st. If 
 there be nitric acid in excess, the solution gives by cautious evapo- 
 ration clear transparent rhombs of neutj-al subnitrate, huviug the for- 
 mula HgaO. . N.O5+2H.O. 2d. If there be an excess of mercury, 
 large opaque white rhombic prisms sometimes form, which have the 
 composition (3Hg.,0. + 2N.O,,+3H.O.). 3d. 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 H.O. . N.05-l-2Hg, 
 O. This salt may also be formed by the action of water on either 
 the first or second j both being decomposed into free acid, and the 
 
SALTS OF GOLD AND PALLADIUM. 465 
 
 basic salt, which is not farther altered even by boiling water. The 
 second salt may be looked upon as a compound of the first and third, 
 since (3Hg,0.4-2N.05+3H.O.)=(Hg,0. . N.03+2H.O.) + (:H.O. .N. 
 0,+ 2Hg,0.). 
 
 S'.ibchromate of Mercury, Hg20.+Cr.03, produced by mixing solutions of chro- 
 mate of potash and subriitrate 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. 372). 
 
 Red nitrate of mercury combines with iodide of mercury to form a double salt, 
 which is formed by half precipitating a solution of the mercuric salt by iodide of po- 
 tassium, and boiling until the precipitate redissolves ; on cooling, the new salt is de- 
 posited in brilliant red crystalline scales, which are decomposed by much water. 
 
 Salts of Gold. 
 
 Perchloride of Gold. — Au.Clg. When gold is dissolved in nitro- 
 muriatic acid, and the solution evaporated very cautiously to dry- 
 ness, 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 depos- 
 ited 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 combines with many other chlorides, 
 forming double salts. The chloride of gold and potassium, AU.CI3+ 
 K.C1.-I-5 Aq., crystallizes in orange-red striated rectangular prisms. 
 It efhoresces in the air, and may be obtained anhydrous; it is then 
 ruby-red. Chloride of gold and sodium (Na.Cl. + Au.Cl3+4 Aq.) 
 forms crystals of the same form and colour, but which do not ef- 
 floresce : when heated, they fuse in their water of crystallization. 
 
 Subchloride of Gold, Au.Ch, 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 subiodid^ of Gold, Au.L, while 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 crystal- 
 lizes, and which contains iodide of Gold; its formula is K.I.-fAu.Ia; by the cautious 
 addition of chloride of gold to a solution of this salt, a greenish precipitate 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. 406. 
 
 Salts of Palladium. 
 
 Chloride of Palladntm, Pd.Cl., is formed by dissolving palladium in nitromuriatic 
 acid. Its solution is deep brown, and it forms, by evaporation, a crystalline mass; 
 by the action of a small quantity of caustic alkali, a basic salt, or oxycMoride of Pal- 
 ladium, Pd.Cl.+3Pd.O.+4 Aq., is produced ; it is a brown powder, insoluble in wa- 
 ter. The chloride of palladium combines with other chlorides to form double salts ; 
 when heated to about 600°, it abandons half its chlorine, and subcfdffride of Palladi- 
 um remains, an olive-brown powder insoluble in water. By a strong red heat this 
 is totally decomposed. 
 
 Deutockloride of Palladium, Pd.Cla, is formed when the chloride of palladium is 
 gently heated with aqua regia ; it forms a dark brown liquor, which gives, with a 
 
 N N N 
 
466 SALTS OF PLATINUM, IRIDIUM, AND RHODIUM. 
 
 solution of chloride of potassium, a sparingly soluble double salt, K.Cl.+Pd.Cla. 
 This deutochloride cannot be obtained solid, its solution giving off chlorine, and 
 chloride remaining. 
 
 Iodide of Palladium, Pd.I., is a black powder, obtained by double decomposition. 
 It forms double salts with other iodides. By heat it is decomposed, without form- 
 ing any subiodide. 
 
 Sulphate of PaUadium, Pd.O. . S.O3, is produced by dissolving the metal in a mix- 
 ture of nitric and sulphuric acids. By evaporation, a saline mass is obtained, 
 which is decomposed by water. 
 
 Nitrate of Palladium;'? A. O. . N.O5, 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 N.O2, and becomes brown. The nitrate of palladium 
 is decomposed by water, giving basic salts. 
 
 Salts of Platinum. 
 
 Protochloride of Platinum, Pt.Cl., is formed by exposing the bi-' 
 chloride, in fine powder, to a temperature of about 500"^ in a porce- 
 lain 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 resolved into 
 chlorine and metallic platinum. If the bichloride be exposed only 
 to a temperature of about 400^, water dissolves from out of the re- 
 sulting mass, a substance which colours it intensely brown, and 
 which is, probably, a sesquichloride, PtaCla. 
 
 Bichloride of Platinum. — Pt.Cl2. This salt is produced by dis- 
 solving platinum in nitromuriatic acid. The solution, when free 
 from excess 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. 339). It combines 
 with other chlorides, forming double salts, of which some possess 
 considerable interest. Those with chloride of potassium, K,C1.4- 
 Pt.Cli, and with sal ammoniac, N.H4C1.H- Pt.Cl,, are precipitated as 
 yellow powders from strong solutions, or as minute octohedral or- 
 ange-red crystals from dilute solutions of those alkalies, and are 
 hence used for their detection. These salts are insoluble in alco- 
 hol. The sodium double salt (Na.Cl.+Pt.Cy 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 K.I.-fPt.Iz, 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 systematic books 
 (sulphate, nitrate, &cl), I consider that we possess no accurate knowledge whatever 
 of that class of combinations. 
 
 Salts of Iridium and Rhodium. 
 
 There are four chlorides of iridium. The pytochloride, Ir.Cl., is prepared by 
 heating metallic iridium to redness in chlorine ; it is an olive-green body, which is 
 insoluble in water, but combines with other chlorides to form double salts. The 
 sesquichloride, IraCla, is formed by dissolving the sesquioxide in muriatic acid. It iJ 
 a brown crystalline substance, volatile, and forming double salts. The bichloride^ 
 Ir.Cl2, 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 crys- 
 tals. The perchloride, I.CI3, is not known except in the state of a double salt, K.Cl. 
 +I.CI3, which is produced by processes, for which I refer to the larger systematic 
 works. 
 
 The protoxide, sesquioxide, and deutoxide of iridium form salts with the oxygen 
 
ELEMENTS OF ORGANIC BODIES. 467 
 
 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 Indium to the metal; they are not otherwise important. 
 
 Sesquichloride of Rhodium, R2CI3, 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 com- 
 pletely decomposed. It combines with other chlorides to form well-defined double 
 salts, such as that 2K.Cl.+R2Cl3-f 2 Aq. 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 sim- 
 ilar compound of protochloride and sesquichloride of rhodium, R4Cl5=2R.Cl.+ 
 R2CI3. 
 
 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. 
 
 k 
 
 CHAPTER XVI. 
 
 ON THE GENERAL PRINCIPLES OF THE CONSTITUTION OF ORGANIC BODIES. 
 
 Organic bodies are distinguished generally by a much greater 
 complexity of composition than occurs in substances of mineral or- 
 igin. 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 organ- 
 ic atom being formed by three elementary atoms. On the contrary, 
 the number of simple atoms entering into the composition of an or- 
 ganic body is sometimes very great : thus an equivalent of oleic acid 
 contains 270 simple atoms j an atom of albumen is formed of 883 
 simple atoms; an atom of spermaceti includes 468 simple atoms; 
 Clumbers to which we find no form of combination approaching in 
 inorganic compounds. 
 
 Besides this greater complexity of constitution, organic bodies 
 ure distinguished by the nature of their elements. I have had oc- 
 casion already to describe as inorganic fifty-four undecompounded 
 bodies, which, by their reunion in various proportions, generate the 
 compound substances which constitute the mineral crust of the 
 globe ; but among organic bodies we meet with few of these. Al- 
 though equalling in number and surpassing in variety of properties 
 the mineral species, the products of the animal and vegetable king- 
 dom 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 extensively 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 henco 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 is the ba- 
 sis. With the constituents of inorganic bodies it has but an acci- 
 dental connexion ; for, as I shall hereafter show, there is no form o{ 
 
468 CLASSES OF ORGANIC BODIES. 
 
 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 func- 
 tions, without being really constituents of their organic tissues or 
 secretory products. Thus iodine and bromine exist in many ma- 
 rine 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 carbo- 
 nate of lime the testaceous covering of another tribe of animals, 
 while silica forms the solid basis of some of the lower tribes of zo- 
 ophytes. In the red colouring matter of the blood, iron is an essen- 
 tial 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, ex- 
 cept the one fact of the iron element of red blood, we find these 
 saline substances to be contained in fluids in a condition of mere 
 physical solution, or to be deposited as solids in the bones or teeth 
 in a purely inorganic form, clearly to be distinguished from the 
 proper state of organic combination, in which the carbon, hydro- 
 gen, oxygen, and nitrogen of the tissues and secretory products are 
 united. 
 
 Among organic bodies, it is necessary to distinguish three class- 
 es, which differ no less in complexity of composition than in the 
 circumstances under which they are formed, and their relation to 
 organic bodies. These are, first, those bodies which are directly 
 elements of an organized and living being, and which, while in con- 
 nexion with it, appear to possess the power of elaborating, from 
 certain nutritious juices, additional material similar to themselves. 
 Such are the organic constituents of the animal and vegetable tis- 
 sues and of the blood, which, while in connexion with, and form- 
 ing portions of the animal or plant, participate to a certain degree 
 in its vitality, and do not obey the laws of ordinary affinity, unless 
 by being, in the first instance, killed; these bodies should be more 
 properly called organized than merely organic ; their chemical rela- 
 tions commence only when they have been deprived of their most 
 essential character, life. They are organs ; their constitution can- 
 not be expressed in formulse, nor their properties accounted for by 
 analysis. 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 combi- 
 nation 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, per- 
 form their functions in virtue of vital power, and not of any chen>- 
 ical properties they possess. The albumen of the egg is not a chem- 
 ical substance, but a delicatelj^-constructed mass, destined to be 
 transmuted into the organs of the chick, and by participating in its 
 life, protected from putrefaction. But when albumen is precipitated 
 by corrosive sublimate, it is killed, and the product of its decompo- 
 sition combines with the oxide of mercury. 
 
 This class of bodies have their origin, therefore, in actions purely 
 
RELATION OF ORGANIC FORCE TO AFFINITY. 469 
 
 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 decomposi- 
 tion, 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 putrefy, probably from not being in any de- 
 gree soluble in water. The formation and growth of nails and 
 hoofs, hair and horns, are examples of the important 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 (se- 
 creted) 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 or proportioned 
 to be assimilated to the organized tissues of the living being itself. 
 It is thus that, by a plant which uses water, carbonic acid, and at- 
 mospheric air as nutriment, after the assimilation of a certain quan- 
 tity of their constituents to its proper tissues, sugar, starch, and al- 
 bumen, adapted for the nutrition of its young, may be formed as 
 secreted products, and oils, resins, colouring matters, &c., rejected 
 as useless or injurious. 
 
 The third class of organic bodies contains those which are evolv- 
 ed by the chemical decompositions, whether spontaneous or arti- 
 ficial, to which substances of the first and second class are subject- 
 ed. Thus sugar, by fermentation, yields alcohol and carbonic acid ; 
 alcohol, by oxidation, yields acetic acid, or aldehyd ; acetic acid, 
 variously treated, produces acetone, or alkarsin ; while 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 regu- 
 lated, as compared with the simpler forms of affinity by which the 
 actions of inorganic elements are controlled. In the first there is 
 found nothing referrible to chemical attraction ; all affinity is an- 
 nulled by the supremacy of life and organization. Hence it is only 
 when dead that such bodies can be analyzed, and by treatment with 
 reagents a crowd of products belonging to the third class be obtain- 
 ed from their 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 or- 
 ganized cell ; it would require not merely the combination of its el- 
 ements, 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 j although we cannot trace, precisely, 
 
470 THEORY OF COMPOUND RADICALS. 
 
 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 circumstan- 
 ces of their formation 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. 236, 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 easi- 
 ly imitated, and the reactions by which they are evolved, although 
 often catalytic, fall, in the majority of cases, under the rules of or- 
 dinary 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 crystallized, and 
 the liquid substances possess 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 properties also. The great classes of acids and bases ex- 
 ist, 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 character- 
 istic distinction of mineral substances is to consist of a series of el- 
 ements 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 bi- 
 nary 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 remains. It is from the discovery of cyanogen, and the dis- 
 cussions as to the nature of the ethers and of the ammoniacal salts, 
 that we must date the positive introduction of this theory of com- 
 pound radicals into chemistry. Its utility has not been limited to 
 the explanation of the constitution of organic bodies ; on the con- 
 trary, it has been applied successfully to explain the phenomena pre- 
 sented by numerous classes of inorganic compounds, such as the 
 compounds of sulphur and oxygen, noticed p. 292, 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 in- 
 discriminately to explain the constitution of organic bodies, we 
 should be liable to fall into continual error. The criterion which 1 
 would assume as decisive of the constitution of an organic body is, 
 whether certain of its elements may be exchanged for others, in ac- 
 cordance 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, 
 
THEORY OF COMPOUND RADICALS. 471 
 
 and from which again, by suitable reactions, the original substance 
 can be obtained unaltered. In such case 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 ex- 
 tensive. Thus, if we treat oil of bitter almonds, C14H6O2, by chlorine, 
 we obtain a compound C^Ji:iOJ^\.J which gives, with iodide or sul- 
 phuret of potassium, bodies whose formulae are respectively C14H3O2 
 I. and 0,4115028. Again acted on by oxygen, it gives crystallized 
 benzoic acid, C,4Ho04, or, rather, C,4H503-|-Aq. Now it will be seen 
 that, throughout this whole series, the element C,4H502 has remained 
 unaltered. In the oil it was combined with hydrogen ; in benzoic acid 
 it unites with oxygen ; in the other 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,4H502 are united, first with each other, by an affin- 
 ity which ordinary reagents cannot overcome, and that this com- 
 pound 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 denomina- 
 ting the group, 0,411^02, 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 formula of its combinations, respectively, Bz. 
 H., Bz.Cl., Bz.L, and Bz.O.+Aq. 
 
 But we must not be induced, by the brilliancy shed on certain 
 branches of organic chemistry through the application of this prin- 
 ciple, 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 character- 
 ized by a remarkable indifference to combination, and which, when 
 decomposed by the influence of reagents, lose not merely one con- 
 stituent 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 reagent that had been applied fre- 
 quently appears indifferent, so that the action appears to have more 
 the character of catalysis than of true chemical affinity. Such bod- 
 ies 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 decomposed, but bod- 
 ies 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 se- 
 ries of compounds, acts as a simple body, but it does so only in re- 
 lation to the nature and intensity of the forces that act upon it ; it 
 may be decomposed, and frequently it cannot be separated from 
 combination without total decomposition ; hence iew compound 
 radicals can be isolated. But they can be decomposed, even while 
 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 
 
472 ITS APPLICATION LIMITED. 
 
 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 admit 
 ting benzyle, C^HiO., to be the radical of the oil of bitter almondis 
 and of benzoic acid ; but if we digest oil of bitter almonds with 
 ammonia, all oxygen is removed, and we obtain a compound of ni 
 trogen with the body, C H^, which may also be obtained in other 
 forms of combination. Now this organic substance, C14H5, 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 (Cj^ 
 H5-I-O2) [-0. The considerations described in p. 291 point out a 
 perfect analogy to this in the constitution of sulphuric acid. Ee- 
 duced to its ultimate elements, its formula is S.O3 ; but powerful evi- 
 dence shows that its real basis is sulphurous acid, and not sulphur, 
 its rational formula being S.O2+O. Now here the primary radical, 
 CiJi^y corresponds to sulphur, and benzyle to sulphurous acid ; the 
 total quantity of oxygen in such acids being divided into two por- 
 tions, differing in order and intensity of combination with the ulti- 
 mate radical. If we add to these considerations the view of salt- 
 radicals, and consider the salts of benzoic acid as expressed by the 
 formula Bz.Oa+M., as that of the sulphates has been shown to be 
 S.O2 . 02+^., 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 or- 
 ganic acids, that the theory of compound radicals, as employed in 
 the new views of the constitution of oxygen salts, appears most in- 
 teresting, as the anomalies of properties and composition presented 
 by the salts of the organic acids were more numerous and more ex- 
 traordinary than any which the mineral acids presented, and were, 
 indeed, totally unintelligible, until illustrated by the conjoined in- 
 vestigations of Dumas and of Liebig. An example of this may easi- 
 ly be selected. Of the organic acids, the majority are monobasic, 
 but there are also many bibasic and tribasic ; thus the citric acid, 
 whose formula is C|2H^0,,, combines with three atoms of base ; the 
 meconic acid, C14H.O,,, is also tribasic; the tartaric acid, 0^1140,0, 
 and the mucic acid, C,2HgO|4, are bibasic. In these instances, the 
 quality of combining with many atoms of base, which is so anoma- 
 lous on the older view, necessarily follows from the formulae of the 
 hydrated acids, which become respectively, for citric acid, C12H5O14 
 .-f-Haj for meconic acid, C14H.O 4+H3; for tartaric acid, C^jOia+Hj; 
 and for mucic acid, CijHsOie-fHi. By its means many other singu- 
 lar properties of organic acids are explained : thus there appear to 
 exist three acids, having absolutely the same composition of C2N. 
 O., 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 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, 
 
CONSTITUTION OF COMPOUND RADICALS. 473 
 
 when we study the salts formed by these acids. The cyanic acid 
 is monobasic ; its hydrate is C2N.O. + H.O. : the fulminic acid is bi- 
 basic; its hydrate is C4N2O2+2H.O. : the cyanuric acid is tribasic ; 
 its formula is CsNaOg+SH.O. 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 to- 
 tally distinct internal structure. When expressed in formulae on 
 the binary theory, we have C2N.O2+H. for the cyanic, C4N2O4+H2 
 for the fulminic, and CyNaOe+Hg for the cyanuric acid; and not 
 merely the difference in nature of the acids, but also the distinctive 
 characters bf 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 w^hen 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 importance. He considers that the compound rad- 
 icals 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 j he considers the only radical to be the carbo- 
 hydrogen, Ci4H5, and benzoic acid to be directly C,4H5-f-03. He 
 looks upon the oil of bitter almonds as containing ready-formed 
 benzoic acid, combined with the true hydruret of the radical, as 3 
 (C,4HA)==2(C»4H5-f 03)4-(C,4H5+H3). The chloride of benzyle he 
 looks upon as an oxychloride, 3(C,4H5 . O2CI.) being equal to 2(C,4Hs 
 -}'Oj)-|-(Ci4H5-f CI3). 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 chlorosulphu- 
 rous acid is, according to him, a compound of sulphuric acid with 
 a terchloride of sulphur, 3(S.02Cl.)=2S.03 + S.Cl3; and so in all 
 other bodies similarly circumstanced. 
 
 The opinions of a man to whose extraordinary industry and ge- 
 nius we owe some of thennost important additions, both theoretical 
 and practical, that science has received since the epoch of Lavoisier, 
 should not be rejected without much consideration j but on apply- 
 ing those ideas to express the constitution of the crowd of bodies, 
 containing four or five elements, which have recently been discov- 
 ered, we are led to suppositions destitute of experimental proof, and 
 yet which, assuming the existence of numerous hypothetic bodies 
 of anomalous constitution, 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 con- 
 clude, 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. 234) 
 
 Ooo 
 
474 THEORY OF CHEMICAL TYPES. 
 
 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 fol- 
 low necessarily from the theory of compound radicals, nor does the 
 conservation of the type require that the radical be preserved unal- 
 tered, but only the type of the radical. Thus, when aldehyd is 
 changed into chloral (C4H4O2 into C4H. . CI3O2), the type is preserved, 
 since the hydrogen is replaced by an equivalent of chlorine ; the 
 radical is altered, since acetyl, C4H3, is changed into C4CI5, but the 
 new radical is still constructed 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 un- 
 derstand it, and as I believe it to have been proposed by Dumas. 
 The bases u^on which it rests may be announced 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 C4H3 may be formed 040)3, and 
 these, combining with oxygen and water, form 04H3O.-j-Aq. or O4 
 HgOg-l-Aq., and O4OI3O -j-Aq. or O4OI3O34- Aq. : also, by uniting 
 with chlorine, they produce C4H3OI. and C4OI3OI. 
 
 2d. 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 composi- 
 tion 5 thus C4H4O4, when heated with potash, gives 2C.O2 and CJi^ ; 
 and C4H. . CI3O4, similarly treated, gives 2C.O2 and C2H.CI3 j the 
 types of C2H.H3 and C2H.CI3 being the same, and containing equiv- 
 alent radicals. 
 
 3d. When bodies of the same chemical, though of different me- 
 chanical types, or, as I would term them, bodies of the same natural 
 families, as the alcohols, are submitted to the action of affinities of 
 equal power, the bodies generated have *he same relation to one 
 another as the original bodies had ; and the radicals are either un- 
 changed, or all changed in a similar degree. Thus from wine alco- 
 hol (C4H6O2), methylic alcohol (C2H4O2), essential oil of potato 
 spirit, CioHiaOj, and ethal, C32H34O2, there are produced by the ac- 
 tion of potash a series of acids, each having the same type and 
 containing the same radical as its alcohol ; thus the acetic acid (C4 
 H4O4), the formic acid (C2H2O4), the valerianic acid (CJ0H10O4), and 
 the ethalic acid, C32H32O4. 
 
 Considered in this way, the theory of types is an important ad- 
 dition 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 com- 
 plex and anomalous, 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 o{ 
 still more important additions to our knowledge. 
 
 Although each organic substance gives, when acted on by re- 
 
PRINCIPLE OF ACTION OF REAGENTS. 475 
 
 agents, 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 eithei 
 combines directly with the gas, or, as more frequently happens, hy- 
 drogen is removed to an amount equivalent to that of the chlorine 
 absorbed. Even in the first case, the direct union is often but ap- 
 parent, and arises from the muriatic acid formed combining with 
 the true product. Thus olefiant gas, C4H4, gives the oily liquid C4 
 H4CI2 ; but this, in place of being a direct combination, consists of 
 C4H^C1., which is the true product formed by substitution of CI. 
 for H., but is united with the H.Cl. thus generated. 
 
 If water be present, it influences the reaction very much, being 
 generally decomposed. In some cases, all the chlorine unites with 
 its hydrogen, while the oxygen combines with the organic sub- 
 stance ; but, generally, the chlorine unites with both elements of 
 the water, forming muriatic acid, which remains free, and hypochlo- 
 rous or chlorous acids, which enter into the composition of the or- 
 ganic 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 ; while the new products formed contain usually a smaller 
 number of molecules than the original organic substance. Thus 
 gum (CioHioOio), when acted on by nitric acid, gives, first, by sim- 
 ple oxidation, mucic acid (C,2H,oO,6) ; but, if the action of the acid 
 be more violent, all hydrogen is removed, and two atoms of oxygen 
 substituted, thus producing CijOig, the elements of six atoms of ox- 
 alic acid. 
 
 In many cases, the action of nitric acid is not limited to the oxi- 
 dation, 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 organ- 
 ic elements, and forms new products. Thus, from napthaline and 
 benzine, numerous substances containing nitrogen are derived. 
 This fixation of nitrogen may occur even with bodies which already 
 contain it ; thus indigo, treated with iwtric 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 or- 
 ganic bodies in a more regulated manner than nitric acid, the new 
 substance combining with the protoxide of the metal ; thus, by Pb. 
 O2, uric acid is decomposed into allantoin, urea, and oxalic acid. 
 
 By fusion with hydrate of potash, the oxidizement of organic 
 substances is very powerfully effected ; water being decomposed, 
 its hydrogen evolved, and the oxygen uniting with the organic body 
 to form an acid^ which remains combined with the potash. Thus 
 alcohol, C4H6O2 and 2H.0 , produce acetic acid, C4H4O4, and H4 be- 
 comes free. Often the organic substance is merely broken up into 
 other bodies of simpler constitution, as when tartaric acid, C8H4OJ0, 
 
476 
 
 ORGANIC ORIGIN OF CARBON. 
 
 by fusion with potash, is decomposed into acetic acid, C4H4O4, and 
 oxalic acid, 2(C203). In every case, if the temperature be much 
 raised, carbonic acid is one of the products j thus acetic acid (C4H4 
 O4) separates into C4H4 and 2C.O2. 
 
 The action of sulphuric acid on organic bodies may be very dif- 
 ferent, according to circumstances j thus from starch we may ob- 
 tain, by a merely catalytic influence, gum, grape-sugar, and ulti- 
 mately sacchulmine. 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 sul- 
 phovinic and sulphomethylic 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, S2O5. It is thus that 
 the sulphurous element exists in the *sulphobenzoic acid, the isethi- 
 onic acids, &c. 
 
 If an organic substance containing nitrogen be acted on by these 
 reagents at a high temperature, this is generally separated under 
 the form of ammonia ; water being decomposed, and its hydrogen 
 so applied, while its oxygen forms the ordinary oxidized organic 
 products. If potash be the reagent, the ammonia is expelled, and a 
 salt of potash with the new organic acid remains ; if sulphuric acid 
 be the reagent, the organic acid is set free, and a sulphate of am 
 monia 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 pyrogen- 
 ic products are always richer in hydrogen and carbon than the bod- 
 ies they are formed from, and of less acid characters. This kind 
 of decomposition will, however, require to be described in a dis- 
 tinct chapter. 
 
 CHAPTER XVII. 
 
 OF CARBON, AND ITS COMPOUNDS WITH OXYGEN, SULPHUR, AND CHLORINE. 
 
 Carbon exists in large quantities, and 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 difl^erent varieties of coal have been produced by the ag- 
 gregation of great quantities of wood, the materials of primeval for- 
 ests, which, being submerged in water, and covered by the gradual- 
 ly-deposited layers of sand and mud, have been elevated, in connex- 
 ion with the strata of clay and sandstone so produced, to their pres- 
 ent 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 
 
NATURE OF LIMESTONE ROCK. DIAMOND. 477 
 
 coal, has thus its origin. This formation 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 quan- 
 tity, and hence the probable source, in the air and in mineral wa- 
 ters, 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 car- 
 bonate of lime, which, under the form of chalk, oolite, coral, mount- 
 ain limestone, &c., constitutes a large proportion of the geological 
 formations of our globe. In all these cases, the rock is formed of 
 shells of animals, aggregated together in great masses ; these geo- 
 logical 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 superincumbent 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 great- 
 er or less degree. In this way the crystalline marbles are formed, 
 in which few or no traces of organic origin remain. The compara- 
 tively small quantity of carbonate of lime, which is found separately 
 and 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 depos- 
 iting, 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 (page 225). The other native carbonates, ol 
 which the quantity is very small in comparison with that of the car- 
 bonate 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 deposite of sulphate of lime, and, 
 at a certain distance, carbonate of iron or of copper would be sep- 
 arated. Those instances suffice to point out the reasons for consid- 
 ering 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 dis- 
 seminated in alluvial strata in Golconda, Brazil, &;c., and is separa- 
 ted 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 scratching it as a file. Its crystals are 
 generally hemihedral, and frequently rough and discoloured at the 
 surface. These crystals all cleave parallel to the faces of a regular 
 octohedron (fig./, p. 26), 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, indicating that the crystal had 
 
478 ORIGIN AND NATURE OP PLUMBAGO. 
 
 been originally soft, and only concreted by degrees ; and in the re* 
 cent 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 fulJy 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*439), whence its great brilliancy. 
 It conducts heat and electricity very badly j it resists most chemi- 
 cal 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 combus- 
 tion; 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 Borrodale, in Cumberland. It is 
 perfectly opaque, crystallized in rhombohedrons, or six-sided ta- 
 bles ; but its usual appearance is in brilliant leaves or spangles ; it 
 is soft and unctuous to the touch, and gives, on paper, a continuous 
 gray streak, whence its name of blacklead^ and its use in making pen- 
 cils. 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 sup- 
 posed to be a carburet of iron. Graphite may be formed artificial- 
 ly 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 gravity 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 
 obtained by the application of a very high temperature to animal 
 or vegetable substances in close vessels. The kinds of carbon thus 
 produced still difl^er 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. By the proximity of igneous rocks to coal 
 under the earth, a similar expulsion of its volatile matters may be 
 effected, and a form of carbon nearly pure, anthracite^ results. These 
 fuels are difficult to light, but, when once ignited, give out an in- 
 tense heat by their combustion. 
 
 If an organic substance, which contains hydrogen and carbon, be 
 set on fire, and there be a copious supply of air, it is totally con- 
 verted 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 wa- 
 ter. By this method of imperfect combustion, several forms of car- 
 bon are prepared, such as wood-charcoal and lampblack. If we 
 
CHARCOAL AND LAMPBLACK. 479 
 
 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 n 
 mass of charcoal forms inside, and remains unaltered as long as, be- 
 ing 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 fig- 
 ure, as the combustion advances along the stick b, the burn- 
 ed portion a be gradually plunged into a narrow tube, this J 
 becomes filled with carbonic acid, which does not support 
 combustion, and the cylinder of 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 j 
 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 car- 
 bonization has been completed, the whole mass is covered up and 
 allowed to cool perfectly before being opened. In this country, 
 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 decomposition, 
 while, when slowly charred, they may yield twenty-five or twenty- 
 six. The mode of conducting the process, therefore, must be chan- 
 ged according as the residual charcoal, or the volatile materials, are 
 the most valuable products. The charcoal preserves, in a remark- 
 able manner, the structure of the wood from which it is produced, 
 so that by the microscope some of the most delicate forms of vege- 
 table organization may be traced in charcoal that has been slowly 
 prepared. 
 
 Lampblack is formed by a still more direct application of the principle of imper- 
 fect 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, while by some apertures 
 a small quantity of air is allowed to sweep over its sur- 
 face ; the sides of the round chamber are lined with leath- 
 er, and above is a conical cover of coarse linen, d, 
 through which the draught from the furnace passes, 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 
 t9 boil ; it takes fire, and, as the quantity of air which 
 has access to it is very smaH, the hydrogen alone bums, 
 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, 
 
 jJnimal charcoal is produced by the decom- 
 position of animal mafters in close vessels. 
 From its properties, which I shall just now notice, it is manufactured 
 
480 
 
 PROPERTIES OF' ANIMAL CHARCOAL. 
 
 in large quantities for the arts, especially from bones, and is hence 
 called Ivory-black or Bone-black. The bones are placed in iron cyl- 
 inders, which are arranged, vertically or horizontally, in a furnace, 
 in connexion with a series of condensing vessels containing water ; 
 the volatile constituents of the animal matter being expelled prin- 
 cipally as carbonate of ammonia, of which a large quantity is thus 
 made, the excess of carbon remains in a state of very minute divis- 
 ion, mixed with the earth of bones (phosphate of lime). 
 
 Some of the most important uses of carbon are founded on prop- 
 erties which the various forms of it possess in different degrees. 
 Its inflammability varies with its density and closeness of aggrega- 
 tion ; being least in graphite, and becoming so great when wood 
 charcoal, prepared at a low temperature, has been reduced to pow- 
 der for the preparation of gunpowder, as to inflame sometimes spon- 
 taneously, and give rise to destructive accidents. Carbon possesses 
 a remarkable tendency to unite with colouring and odorous substan- 
 ces. This property is specially possessed by ivory-black, in conse- 
 quence of the extreme degree of division of its particles. When a 
 purely organic body yields carbon, the molecules of the latter ag- 
 gregate themselves to a degree which depends on the temperature ; 
 and if, as in wood, there be a fusible ash present, this acts as a ce- 
 ment, and diminishes the porosity very much. If the organic sub- 
 stance 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 
 po'ssible 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 j and barrels in which water is to be kept are charred on 
 the insides, in order to remove any organic matter described in the 
 water, which might be liable to putrefy. 
 
 The following table contains some numerical results of the rela- 
 tive decolorizing power of equal quantities of carbon in various 
 forms ; the first column containing the number expressing the pow- 
 er 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 : 
 
 Kind> of Charcoal. 
 
 Common ivory-black 
 
 Well ignited lampblack 
 
 Lampblack ignited with pot ashes 
 
 Charcoal from the decomposition of acetate of potash . 
 
 Starch ignited with pot ashes 
 
 Blood ignited with phosphate of lime 
 
 Ivory-black digested in muriatic acid 
 
 Ivory-black digested in muriatic acid, and afterward 
 
 ignited v^^ith pot ashes 
 
 Blood ignited with pot ashes 
 
 Sugar. 
 
 1 
 
 10 
 44 
 89 
 
 10 
 1-7 
 
 20 
 20 
 
ATOMIC WEIGHT OF CARBON. 481 
 
 The decolorizing power is thus not the same for all bodies. If 
 charcoal that had once been used be again ignited, it does not re- 
 cover its 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 introduced into a tube containing ammoniacal gas, in the 
 mercurial pneumatic 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 char 
 coal, which is the most active, absorbing 
 
 90 cubic inches of ammonia. 
 85 " " muriatic acid. 
 
 65 " " sulphurous acid. 
 
 55 " " sulphuretted hydro- 
 
 35 " " olefiant gas. [gen. 
 
 40 cubic inches of nitrous oxide 
 35 " " carbonic acid. 
 
 9-25 " oxygen. 
 
 75 " nitrogen. 
 
 175 " hydrogen. 
 
 These gases in this absorption undergo no chemical change, but 
 appear 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 not at 
 present exactly known. By Drs. Prout and Thompson it was fixed 
 at seventy-five upon the oxygen, and six upon the hydrogen scale j 
 but the investigations of Berzelius and Dulong induced the majority 
 of chemists to adopt a higher number, 76'4< or 6-13. The latest 
 experiments of Dumas and Stass directed to the determination of 
 this point, induce those eminent chemists to recur to the original 
 number, 75 ; while Liebig and Redtenbachar have deduced from 
 their researches the numbers 75-8. Dr. Clarke, from a re-exami- 
 nation of Berzelius's results, finds that they give, when corrected 
 for some minute sources of error, 75*6 ; and, until opinion becomes 
 more unanimous upon this important point, I shall assume as the 
 number expressing the equivalent of carbon, 75'6 upon the oxygen, 
 and 6-05 upon the hydrogen scale. 
 
 If we admitted the truth of Dulong and Petit's law (p. 66, 219), 
 connecting the specific heat with the atomic weights of bodies, we 
 should consider the ei^uivalent of carbon to be double that above 
 given, as Regnault 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 
 equivalents, taking the number as 6-05. But the force of this result 
 is totally 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 ap- 
 plication of the theory of volumes, carbon vapour is frequently spo- 
 ken of by chemists, although its existence is purely hypothetical. 
 I have mentioned (p. 215) the difference of opinion as to its specific 
 
 Ppp 
 
482 ANALYSIS OF ORGANIC BODIES, 
 
 gravity, which I assume at 843. The new results would appear to 
 show that it is really but 836*8 upon the one, or 4184 upon the 
 other view. 
 
 General Principles of Organic Analysis. 
 
 Substances which contain much carbon are, in general, easily recognised, 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 car- 
 bonate of potash. 
 
 Altliough it is not within the scope of the present work to embrace the details ol 
 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 ni- 
 trogen, which enter into the constitution of organic bodies. The general principle 
 npon 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 progressive, as to admit of the products being 
 collected with accuracy. The nitrogen is always determined by an independent 
 operation, in w^hich 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 constit- 
 uents from that of the substance employed. For the analysis of an organic sub- 
 stance, there are, therefore, two processes ; the first, to determine the carbon and hy- 
 drogen, and the second to determine the amount of nitrogen. 
 
 The substance generally used to supply oxygen is the black oxide of copper, pre- 
 pared by gently igniting the nitrate. Sometimes chromate of lead is employed, par- 
 ticularly for bodies rich in chlorine. Where the substance to be analyzed bums 
 with difficulty, it is often necessary, in order to be certain of the complete combus- 
 tion of the carbon, 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 
 
 one third to half an inch 
 
 I I '' yj ^ diameter, is to be drawn 
 
 I i I y^ out at one end to a point, 
 
 {^^^^y|j]|]jnpj|[[|jCT which is to be sealed and 
 
 . turned up, as in the fig- 
 
 ure. 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 
 Dxide of copper as will occupy about six inches of the tube is to be then intimately 
 mixed with the substance to be analyzed, if it be solid, by rubbing in a mortar, and 
 this mixture then introduced. The mortar is next to be rinsed out with as much ox- 
 ide 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 materials thus intro- 
 duced will occupy about fourteen inches of the tube, when it is shaken down by tap- 
 ping 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 sub- 
 stance must be made absolutely dry, and the oxide of copper, being powerfully hy- 
 groscopic, 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 while very hoi 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 tra- 
 ces of damp which might have been absorbed by exposure to the air during the mix- 
 ing in the mortar. This is done by means of a small exhausting syringe, which is 
 attached to the combustion tube by a cork, a tube containing fused "chloride of cal- 
 cium being interposed. The combustion tube is bedded in warm sand, and by 
 means of the syringe, the damp air it contains is withdra\^m, and replaced by air, 
 which, passing'over the chloride of calcium, becomes completely dry. After a lew 
 repetitions of this process, all moisture is removed, and the combustion tube is 
 ready to be attached to the other parts of the apparatus. 
 
 a 6 ton wool is dropped at «, and it is then filled 
 
ANALYSIS OP ORGANIC BODIES. 483 
 
 with recently-fused chloride of calcium in fragments of the size of a split pea. At * a 
 little cotton wool is also placed, and a small lube is connected with it by a cork. 
 To its smallei end a cork is adapted, which accurately fits the end of the combus- 
 tion tube, and which has been carefully dried. This apparatus (but without the last 
 cork) is carefully weighed before the operation. 
 
 The second apparatus is ihe potash bulb4ube, the invention of which by Liebigwas 
 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 re- 
 markable 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 proportions of the respective bulbs may be collected 
 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. 1-25), and the apparatus attached to the small 
 tube, b, of the v^ater tiibe by a caoutchouc connector 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 dan- 
 ger 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 Q.\ inches) a*! 
 
 that the cork by which the water tube is attached shall not be in any danger of be- 
 ing charred, but yet shall be so hot that no water can condense upon it. The joint- 
 ings 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 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, contains some traces" of the organic substance, is to be simi- 
 larly 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 car- 
 bon, 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 char- 
 coal on the remaining space. 
 
 The combustion being thus completed, the tube remains, ho\^ever, 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 carries the v/ater 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 carbonic acid and of water collected, and 
 hence, by simple calculation, the proportions of carbon and hydrogen contained in 
 the quantity of substance that had been operated on. 
 
 If the substance had been one very difficult to burn, and hence requiring 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 car- 
 bon 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 operation, in order to 
 obtain the high degi'ee of accuracy which alone confers value on numerical results. 
 These can be learned omy in the laboratory, and not even from the most detailed <Ip- 
 
484 
 
 DETERMINATION OF NITROGEN. 
 
 O 
 
 scription. My object is merely to afford an idea of the general principles of the 
 method. 
 
 If the substance to be analyzed be liquid and vol- 
 atile, it is introduced into small bulbs of the size of 
 the figure, by the method given in page 11. 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 
 
 Jj across in the act of introducing 
 
 •H, mmsms\'^ ^( ^ >^« kmm%%%w^^ \#.a^ them, so that the liquid may 
 
 f < easily flow out, when, by the 
 
 approach of a piece of red-hot charcoal, it is gently heated, so as to form a vapour. 
 The peculiar precautions necessary in the management of the analysis of such bod- 
 ies, and the methods adopted for non-volaiile liquids and other bodies of peculiar 
 Sroperties, can only be learned by experience, and do not fall within my purpose to 
 escribe. 
 
 To determine the nitrogen of an organic substance, a long combustion tube is 
 taken (2 or 25 feet), sealed at one end, but not drawn out, as in the figure. Next 
 
 tne sealed end is placed carbonate 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-di- 
 vided 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 ap- 
 plied to the closed end of the tube, where it disengages carbonic acid from the carbon- 
 ate 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 Math 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 backward, just as in the former 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 remain- 
 ing may then be measured. The volume of gas is next to be corrected for temper- 
 ature and pressure, as directed in p. 57 and 20, and its 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 form- 
 ed, which would falsify the result, as its volume is double that of the nitrogen it con- 
 tains ; 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 is thus a very delicate operation, and occupies 
 several hours. If the substance contain a large quantity of nitrogen, its amount 
 may be indirectly ascsrtained 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, 
 "ome of the mixture next the sealed end is first ignited, and the gas allowed to es- 
 cape, 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 ti>bes that is required for the result. The volume of gas in a tube being 
 
CARBONIC ACID, ITS PREPARATION, ETC. 485 
 
 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 as outside the tube. The 
 relative volumes of the carbonic acid and nitrogen gases are thus found ; and as cin 
 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, C2N., mellon, C3N2, caffeine and taurine, C4N., this method 
 gives very accurate results. 
 
 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 con- 
 stituents "then determined in the ordinary way. In organic salts the metallic basis 
 is determined by igniting the substance, burning away the organic element, and de- 
 termining 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 the most de- 
 tailed description. 
 
 Of Carbonic Acid. Eq. 275-6 or 22-05. 
 
 Carbonic acid exists in the atmosphere as a product of combus- 
 tion 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 impor- 
 tant. It is a result, also, of the slow decomposition of most vege- 
 table 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. For 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 frag- 
 ments 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, p. 247, and the gas which is evolved is con- 
 ducted by the bent tube, to be made use of as required. The re- 
 action consists in H.Cl. and Ca.O. . C.O2 producing H.O. and Ca.Cl., 
 which remains in the bottle, while C.O2 is driven off. Carbonic acid 
 being dissolved by water, and it being generally required in larger 
 quantity than it is convenient to collect over mercury, we take ad- 
 vantage of the density of the gas to collect it in dry jars, as de- 
 scribed and figured for chlorine in p. 301. The jar is known to be 
 full when a lighted taper, applied near the mouth, is instantly ex- 
 tinguished. 
 
 The properties of carbonic acid are very remarkable ; it is per- 
 fectly 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 1-521. It hence, when disengaged in large 
 quantities, whether by natural operations or in processes of manu- 
 facture, accumulates in all cavities within its reach, and may cause 
 fatal accidents to animals who enter unadvisedly. Thus workmen 
 
486 LIQUID AND SOLID CARBONIC ACID. 
 
 engaged in cleaning out dry wells or vaults, or the large vats from 
 which fermenting liquors have been run off, should carefully ob- 
 serve whether a candle can remain for some time burning brightly 
 at the bottom. In volcanic countries, caverns are frequently occu- 
 pied to the level of their surface by this gas, exhaled from the 
 ground ; and an experiment often tried, to amuse the traveller, con- 
 sists in walking into such a cavern with a dog, which, holding the 
 head near the floor, is almost instantly asphixiated by the layer of 
 carbonic acid, while the 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 the 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 car- 
 bonic 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 
 solution of an agreeably acidulous taste, which sparkles when agi- 
 tated J it colours blue litmus paper of a wine-red, which disappears 
 on exposure to the air or by heat. By means of pressure, water 
 can be made to absorb a large quantity of carbonic acid, which es- 
 capes 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 carbonates, which redissolve in an excess of the car- 
 bonic 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 exces- 
 sive expansibility 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 ra- 
 pidity that, one portion absorbing heat from the other, this latter is 
 rendered solid (see page 86). Solid carbonic acid can thus be ob- 
 tained in large quantity by the apparatus contrived by Thilorier. 
 It is a white body, in filamentous masses, like asbestus ; it evaporates 
 but slowly ; it is very soluble in alcohol and ether ; the ethereal so- 
 lution produces by its evaporation the most intense cold known, es- 
 timated at — 180 degrees of Fahrenheit. 
 
 The composition of carbonic acid may be determined 
 by very simple experiments. If into a bottle of pure ox- 
 ygen 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 contains its 
 own volume of oxygen. It co'nsists, therefore, of 
 
MANUFACTURE OF POTASHES. 
 
 487 
 
 Two volumes of oxygen . 1102-6x2=2205 2 
 
 One volume of carbon vapour .... 8430 
 
 Forming two volumes of carbonic acid 2-^-3048-2 
 
 Of which one volume weighs, therefore, =1524- 1 
 
 The corrected specific gravity of carbonic acid, 1*521, indicates 
 that the theoretical density of carbon vapour should rather be taken 
 as 83G 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 
 globule of potassium. The metal takes fire, burning with a brilliant 
 violet flame, and forms potash, while carbon is abundantly deposit- 
 ed 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 combine 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 now 
 described. 
 
 Carbonate of Potash.— K.O. . CO,. Eq. 866-3 or 694. 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 
 growing 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 compositas 
 and crucifera3 are the richest ; the grasses rank next ; and among 
 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 potash is derived. 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 American pearlashes sel- 
 dom contain more than eighty-five per cent., and Russian potash 
 often not sixty per cent, of true carbonate of potash. 
 
 The purification of pearlashes being difficult, carbon- 
 ate of potash is best prepared for chemical purposes by 
 calcining cream of tartar ; the tartaric acid which it con- 
 tains 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 
 
488 
 
 CARBONATE OF SODA. 
 
 N 
 
 1 
 
 
 
 ! 
 
 I 
 1 
 
 i 
 
 1 
 
 oblique rhombic octohedrons, a, a\ a", a"\ as in the figure (K.O. 
 C.O2+2 Aq.). It reacts strongly alkaline. It is almost insoluble 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 manufactures 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 alkalimetry. 
 The best method of performing it will be described under the head 
 of "Carbonate of Soda." 
 
 Bicarbonate of Potash, K.O. . C.O2 + H.0. . C.O2, 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\ On 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 alkaline. 
 
 Carbonate of Soda—lSi^.O. . C.O^+IO Aq. 5 Eq. 667-3 + 1125 or 
 
 53*4i7-f-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 427. 
 
 The dry sulphate of soda is to be mixed with its own weight of 
 limestone or chalk, and half its weight of small coal, and the mix- 
 ture being reduced to fine powder, is introduced into a reverbera- 
 tory furnace, such as is figured in page 333, in charges of about 2 cwt. 
 each. After being exposed to a full red heat for about an hour, on 
 the floor of the furnace, the mass fuses, and being well stirred for a 
 few minutes, is raked off' through the opening in the side, and re 
 ceived in metal boxes. It forms a black mass, which is known iv 
 commerce as black-ash, or British barilla. The theory of this process 
 is very remarkable ; the sulphate of soda being melted in contact 
 with the coally matter, is deoxidized, its oxygen being carried off by 
 the carbon, and sulphuret of sodium remaining. This is immediately 
 decomposed by the carbonate of lime, sulphuret of calcium and 
 carbonate of soda being produced. S.O3 . Na.O. and 2C. form 
 aCO^and Na.S., which, vvith Ca.O. . C.O^, gives Ca.S. and Na.O. . C. 
 Og. 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 
 black-ash generally contains about 22 per cent, of real alkali. To 
 obtain the soda under a purer form, the masses of black-ash are 
 broken up, and digested in warm water until all soluble matter is 
 extracted. The residue consists of sulphuret of calcium and the 
 excess of coally matter. The liquor is then evaporated to dryness, 
 and the saline mass obtained is calcined in a reverberatory furnace 
 with one fourth of its weight of sawdust, in order to convert all of 
 the alkali into carbonate, and to burn out some traces of sulphur 
 which still remain j on being then redissolved in water, and the clear 
 
METHOD OF ALKALIMETRY. 489 
 
 solution dried down, it constitutes white-ash^ or soda-ash of the best 
 quality, containing from 45 to 50 per cent, of real alkali. 
 
 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 pure carbonate of soda crystallizes in flat, oblique rhomboidal 
 prisms, as in the figure, which contain 
 ten atoms of water, Na. . C.O.-f- 10 Aq. 
 In a dry atmosphere, they lose by efflo- 
 rescence all their water, and fall into a ^"x^x^ V^^ ^ — Ili^ 
 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 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 alkali may 
 now be considered as extinct. Graham states, on the authority of 
 Mr. Muspratt, that in 1838 there were manufactured from common 
 salt 50,000 tons of soda-ash and 20,000 tons of crystallized carbon- 
 ate, and the manufacture is continually on the increase. 
 
 To the practical chemist and the manufacturer, it is important to be able to deter- 
 mine, by a rapid and easily executed process, the real quantity of alkali present in 
 any sample of pearlashes or soda-ash that may be in the market. All such pro- 
 cesses* depend on measuring the quantity of sulphuric acid necessary to produce a 
 neutral salt with a certain weight of the sample; but in the management of the de- 
 tails considerable difference may exist. A mode which I have found to be very ac- 
 curate, and easily executed even by ordinary persons, consists in preparing before- 
 hand 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 are 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 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 alkaline liquor in the capsule is to be exactly neutral- 
 ized. 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 sensiblv, it may be done in order 
 to secure complete neutralization. The graduations of the glass being numbered 
 from above downward, 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 al- 
 kali be soda, or forty-seven if the alkali be potash, and divide in each case by 100, 
 to obtain the quantity of real alkali 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 measures 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 alkali in a sample neutralized by, 
 for example, 137 measures of acid, we say, 
 
 For potash, 100 : 47 : : 137 : .'C=[3ix 47=64-4 ; 
 And for soda, 100 : 31 : : 137 : x=\p^x3l=^-5, , 
 
 Qqq 
 
490 
 
 CARBONATE OF LIME. 
 
 A. table may easily be constructed beforehand on those principles, so as to save 
 even this little calculation. Tiie 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 commercial purposes ; thus, in the examples above 
 taken, if the quantity of acid had been measured wrongly at 138, the indications 
 would be, for potash, 64-9, and for soda, 42-8; the error in no case exceeding half a 
 part per cent., and being exactly counterbalanced by taking the numbers 31 and 47 
 instead of the correct equivalents, 31-3 and 47-3. 
 
 Bicarbonate of Soda^ H.O. . C.Oa + Na.O. . C.Oj, is formed by pass- 
 ing a current of carbonic acid gas through a cold solution of carbon- 
 ate 'y the new salt precipitates in small opaque crystals, having the 
 appearance of starch. It requires fifteen parts of cold water for its 
 solution j it has an alkaline reaction, but is not disagreeable to the 
 taste. 
 
 Sesquicarbonate of Soda occurs native on the banks of certain lakes 
 in northern Africa, whence it is exported under the name of trona. 
 Its formula is 2Na.O. . C.02 + 3C.024-4H.O. It cannot be formed 
 at will. 
 
 Carbonate of Barytes. — Ba.O. . C.O2. This salt exists native, crys- 
 tallized in oblique rhombic prisms; it is insoluble in pure water, but 
 dissolves 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 analysis of minerals containing alkali, and for the prep- 
 aration of various salts of barytes. It has been used in the manu 
 facture of glass. 
 
 Carbonate of Strontia resembles perfectly the former. 
 
 Carbonate of Lime.—Csi.O. . CO,. Eq. 632-5 or 50-7. The cir- 
 cumstances and forms under which this salt exists in nature have 
 been so frequently noticed (p. 477, 225), and the molecular consti- 
 tution and peculiar relations to light of its crystals so fully described, 
 that it is not necessary to enter upon its history here farther. It 
 may be prepared 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 in- 
 soluble in pure water. It is thus that carbonate of lime is held dis- 
 solved 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 exposure 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. — Mg.O. . CO,. This salt exists anhydrous 
 in nature, crystallized in rhombohedrons like calc spar. 
 By dissolving magnesia in water by a stream of car- 
 bonic acid, it may be formed, and is gradually deposit- 
 ed in rhomboidal prisms of six or eight sides, as »», «, 
 «, in the fisfure, which contain three atoms of water. It 
 is this salt, Mg.O. . C.O.-fS Aq., which exists in Mur- 
 ray's solution of magnesia. When acted on by pure hot 
 water, this salt is decomposed, carbonic acid escaping, 
 
CARBONATE OF IRON, ETC. 
 
 491 
 
 and basic carbonate of magnesia being produced. It is this basic car- 
 bonate which constitutes 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 al- 
 most totally insoluble in water. One fourth of the carbonic acid is 
 given off in this reaction, and the precipitate is found to be a com- 
 pound of carbonate and of hydrate of magnesia, Mg.O. . H.O. -f-3 
 (Mg.O. . C.O,.H.O.), or 4Mg.O. + 3C.O, + 4 Aq. 
 
 The nature of dolomite or magnesian limestone has been already 
 sufficiently noticed (p. 348). 
 
 Carbonate of Manganese, Mn.O. . C.O2, is a white powder formed 
 by double decomposition, and decomposed by a red heat. 
 
 Protocarbonate of Iron, Fe.O. . C.O2, exists native in rhombs iso- 
 morphous with calc spar. It may be prepared by decomposing 
 protosulphate of iron by carbonate of soda ; it forms a white pre- 
 cipitate, 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 obtained pure ; but by mixing the fresh precipitate with 
 sugar, and evaporating 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 carbonic 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 
 (Zn.O. . C.02)4"3Zn.O. .H.O. if the solutions were warm, but of Zn. 
 O. . C.02+2Zn.O. .H.O. if cold j carbonic acid gas is given off in 
 both cases. 
 
 There are two carbonates of Copper, both basic ', the green carbon- 
 ate exists native (malachite), and is used as a pigment. It may be 
 formed by mixing solutions of a salt of copper and an alkaline car- 
 bonate 5 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 2Cu.O. + C.024-H.O. The blue carbonate exists also 
 native (Copper-azure), but cannot be prepared artificially so as to be 
 permanent: its formula is SCu.0. 4-20.02 H-H.O. 
 
 Carbonate of Lead, Pb.O. . C.O2, 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 formulae 3Pb,0. + 2C.024-H.O. and 4Pb.O+3C. 
 O2 + H.O. 
 
 For the manufacture of white lead, very thin sheets of the metal 
 are exposed to the fumes arising from vessels containing weak vin- 
 egar, which are kept moderately warm by being imbedded in fer- 
 menting tan J the lead, absorbing oxygen from the air, combines 
 
492 CARBONIC OXIDE. 
 
 with the acetic acid, forming a basic acetate of lead, which is de- 
 composed by the carbonic acid of the surrounding air, basic carbon- 
 ate 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 acet- 
 ic acid thus serving to produce a very large quantity of ceruse. 
 This process has lately been much improved by exposing litharge, 
 finely ground and mixed 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 successively 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 un- 
 combined 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. 360), and the 
 carburet of silver is a gray powder, which remains when certain 
 silver salts of organic acids, as the citrate and tartrate, are imper- 
 fectly burned away. 
 
 Carbonic Oxide. — CO. Atomic Weight 14i'05 % 
 
 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 car- 
 bonic oxide 5 in place of charcoal, iron filings or zinc may be used ; 
 the metal, in this case, takes half of the oxygen from the carbonic 
 acid, C.O2 and Zn. giving Zn.O. and CO. 
 
 A very simple and elegant way of obtaining this gas consists m 
 warming strong oil of vitriol with crystals of oxalic acid, in a flask, 
 o 6, from which a tube,/, passes to a bottle containing solution of 
 
 caustic potash, «, as in the figure ; 
 ^1/ from this another tube conducts to 
 
 the pneumatic trough. The oxalic 
 acid, C2O3-I-H.O., 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 car- 
 bonic acid (CA^C.O. + CO.), 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 is combustible, and, burning 
 with a pale blue flame, forms carbonic acid. It is this gas which 
 produces, on the top of a clear coke fire, a blue flame, which ap- 
 
MANUFACTURE OP OXALIC ACID. 493 
 
 pears purple when seen with the red background of the glowing 
 cinders. It contains half its volume of oxygen j 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. 
 
 Oxalic Acid.—Qfi^ or 2(C.0.) + 0. Eq. 451-2 or 36-1. 
 
 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 rhubarb, and in a variety of lichens. It was formerly 
 extracted principally from the oxalis acetosella, from whence its 
 name is derived, but is now manufactured in larger quantities arti- 
 ficially. It is generally a product of the oxidation of vegetable sub- 
 stance^ by nitric acid, on which fact its mode of preparation is 
 founded. The substances employed 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 oxidized, and nitrous fumes giv- 
 en off abundantly ; when the action has become slow, one part more 
 of acid is to be added, and the heat increased. The liquors so ob- 
 tained, are mixed, evaporated to a pellicle, and set aside to crystal- 
 lize, and the crystals are purified by re-solution and crystallization. 
 From the mother liquors new quantities of oxalic acid may be ob- 
 tained by heating with more nitric acid. 
 
 If we consider the sugar in its dryest form as being CiaHgOg, the 
 action of the nitric acid should consist in first removing the nine 
 equivalents of hydrogen, and substituting for them nine equivalents 
 of oxygen; thus CizHgOg and 6N.O5 should give 6(CA) with 9H.0. 
 and 6N.O2. But the action is not so simple, as other products, es- 
 pecially the Saccharic Acid, are at the same time formed. By means 
 of permanganate of potash, however, the carbon of sugar may be 
 very elegantly and directly changed into oxalic acid, CjaHgOg and 
 6(Mn20,+K.O.) producing 12(Mn.O,) with 9H.0. and 6(C203+K. 
 O.), the oxalic acid formed exactly neutralizing the potash of the 
 manganic salt employed. 
 
 The oxalic acid crystallizes from its solution in oblique rhombic 
 
 prisms, of which those planes marked i c are prima- k- ■. ^^^ 
 
 ry, and af secondary : the summit is often dihedral, /K """ — '\' \ 
 in which case the plane a, and that vertically oppo- kKX \ % 
 
 site to it, are absent. These crystals contain three (j^-A ^- \j j 
 
 atoms of water, of which one is basic : CaOa-f H.O. A^iZZI—J 
 H-2 Aq. When warmed, they give off" 2 Aq., and the hydrate of 
 oxalic acid remains as a white powder, which melts at 350^, and 
 when heated farther sublimes, a portion being, however, decompo- 
 sed; the products of the reaction of oil of vitriol on oxalic acid have 
 been already noticed (p. 492). Oxalic acid is converted into car- 
 bonic acid by contact with many peroxides, as the peroxide of man- 
 ganese, by which means the technical value of manganese ores may 
 be determined (see p. 355). By contact with a great excess of hot 
 nitric acid or of chlorine, it is also converted into carbonic acid. 
 
494 OXALATES OP POTASH. 
 
 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 neutrali- 
 zes the alkalies 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 con- 
 verted into carbonic acid and metal, C^Oa+M.O. giving C204andM. 
 Those of the earths and alkalies evolve carbonic oxide, and produce 
 a carbonate, CA+M.O. giving CO. and C.O^+M.O. The former 
 action is usefully applied to obtain cobalt and nickel in the metal- 
 lic 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 ox- 
 alic acid, or of any organic acid. It precipitates, also, the solu- 
 tions of barytes and lead. It acts violently on animals as a poison j 
 for an antidote magnesia 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 Wollas- 
 ton satisfied himself of the truth of the law of multiple combination, 
 p. 208, their proportions of acid being as 1 : 2 : 4. 
 
 The neutral Oxalate of Potash, K.O. . CaOg + 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, K.O. . C2O3+H.O. . C2O3 + 2 Aq., exists nat- 
 urally 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 ob- 
 lique 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. 
 
 Quadroxalate of Potash, K.O. .C2O3+3H.O. . CaOg-f^ Aq., is form- 
 ed 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 
 prepared by dissolving the binoxalate in muriatic acid, which takes 
 half of the alkali, and the quadroxalate crystallizes out. This and 
 the last salt are indiscriminately sold in commerce as salt of sor- 
 rel, 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 is but one oxalate of Soda ; it is not important. 
 
 Oxalate of Lime, Ca.O. . C2O34-2 Aq., exists abundantly in nature, 
 forming the hard earthy basis of many lichens, and may be prepared 
 
DOUBLE OXALATES OP POTASH, ETC. 495 
 
 by mixing solutions of oxalate of ammonia and of any soluble salt 
 of lime. It forms a white flocculent precipitate, which, by boiling, 
 becomes heavy and granular. It is totally insoluble in water, and 
 is hence used as a means of removing lime from solutions, and de- 
 termining its quantity. It dissolves in the mineral acids, but is in- 
 soluble in all organic acids, even the acetic. When heated, it leaves 
 a perfectly white residue of carbonate of lime. 
 
 The remaining simple oxalates are not important, except the ox-. 
 alate of Silver, which is a white powder, prepared by double decom- 
 position, and remarkable for being decomposed by a moderate heat, 
 with a slight explosion, into carbonic acid and metallic silver. 
 
 There are several double oxalates of interest. 
 
 Oxalate of Potash and Peroxide of Iron, (Fe203+3C203)+3K.O. . C2O3+6 Aq., 
 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 Chrmne, (Cr203+3C203)+3K.O. . C2O3+6 Aq., is prepared 
 by dissolving together in hot water one part of bichromate of potash, two of crys- 
 tallized oxalic acid, and two of binoxalate of potash, A copious evolution of car- 
 bonic 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 li- 
 quor 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, K.O. . C2O3+CU.O. . CaOs-f-S Aq., is formed by di- 
 
 gesting a solution of binoxalate of potash on oxide of copper. It crystallizes in fine 
 lue prisms. It may be obtained with 4 Aq. 
 
 Ckloro-carbonic ^cid. —CO. -\- CI Eq. 619-1 or 49-5. When 
 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 mu- 
 riatic 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 car- 
 bonic acid gas. The metal is converted into a blackish-green po- 
 rous mass. If the air be admitted to this while hot, it inflames j 
 when brought into contact with water, it is immediately decomposed, 
 a peculiar gas being given ofl^, and a rhodizonate of potash formed. 
 This oxycarburet of potassium is obtained in quantity in the process 
 by which potassium is procured, and constitutes the great obstacle 
 to obtaining that metal, as described in page 337. 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 ex- 
 pressed 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 prop- 
 erty is to detonate with a brilliant flash, and deposite charcoal when 
 mixed with chlorine, even in the dark. He assigns to it the formula 
 C.H. 
 
496 ISOMERIC OXIDES OF CARBON. 
 
 Rhodizonic Acid. — This is formed when the oxycarburet of potas- 
 sium is dissolved in cold water. It is, when dry, isomeric with 
 carbonic oxide, C7O7, but it appears to be a tribasic hydracid, and 
 its formula CvOio-j-Hs. Its salts are of a fine scarlet red colour, 
 whence its name. 
 
 Croconic Acid, C5O4, 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^Ot+SK.O. giving K.O. and 
 CaOg-f K.O., with C5O4+K.O. The salts of croconic acid are bright 
 yellow coloured, but do not require other notice. 
 
 Mellitic Acid, C4O3, when dry, is found only native, combined 
 with alumina, in a very rare mineral, mellite or honeystone. It crys- 
 tallizes with water, C403-fH.O., and from its characters, especially 
 the properties of the mellate of silver, it appears to be properly a 
 hydrogen acid, having carbonic oxide as its radical, and its formula 
 to be C4O4-J-H. When its ammonia salt is decomposed by heat, it 
 is resolved 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 
 appears to play. From the composition of its chlorine compound, 
 it is certain that the equivalent of the gas is CO., and, combining 
 with oxygen, it forms carbonic acid, C.O2. 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 
 C2O2, 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 O7, or of the croconates or mellates ; but the gas is changed into 
 these more complex bodies by an isomeric action, which appears to 
 occur at the moment that it combines with the potassium. I look 
 upon the carbonic oxide gas, therefore, 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. 
 
 OfSulphuret of Carbon.— CS^. Eq. 478-7 or 38-3. 
 
 This remarkable substance is formed whenever sulphur comes 
 into contact with red-hot charcoal. It may be prepared by means 
 of the apparatus figured in page 323 ; the tube a, c being filled with 
 pieces of charcoal about the size of almonds, and bits of sulphur 
 introduced from time to time at h, which is to be then tightly clo- 
 sed with a cork. The sulphur fuses, and the tube being a little in- 
 clined, runs down upon the ignited charcoal, combines with it, and 
 the product passing as vapour into the long glass tube e, /, is con- 
 densed, 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 boiile), two iron tubes, one long, b, 
 reaching nearlv to the bottom, and projecting a foot above the top, and the other 
 short, c, and bent at a right angle, serving to convey the product to the condensing 
 apparatus. By means of the tube c, the bottle may be filled with small fragments 
 
SULPHURET OF CARBON. 
 
 497 
 
 of charcoal, and then, being placed in a furnace, the wide glass tube c, and the nai- 
 rower /, are to be attached by corks. From the cock d a stream of water flows^ 
 which, gl^ided by the tin-plate gTitter o, cools the tube/, 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 cf, collects in the bottle n, which 
 is half filled with ice in order more perfectly to preserve it. Any incondensible gas- 
 es 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 sulphur were 
 allowed to be present to 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 redistillation at a very 
 moderate heat (in a water bath) ; when about nine tenths have dis 
 tilled over, by allowing the residue to evaporate spontaneously in a 
 capsule, very fine right rhombic crystals of sulphur may be obtain- 
 ed (p. 284). 
 
 The sulphuret of carbon is a colourless liquid, of a very disagree- 
 able garlic smell. It does not mix with water, but dissolves in al 
 cohol and ether. It dissolves sulphur and phosphorus in large 
 quantity. Its specific gravity is 1272. It boils at 108"^ "Fah., and 
 forms a colourless vapour, whose specific gravity is 2*621. From 
 its volatility, it obtained the name of Alcohol of Sulphur. In evap- 
 orating it produces great cold ; mercury may be frozen by suspend- 
 ing under a bell-glass a thermometer, the bulb of which is envel- 
 oped by cotton moistened by 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 hydro- 
 gen. 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 sul- 
 phur, and its formula to be C.So. 
 
 It is a powerful sulphur acid, combining with the sulphurets of 
 the alkaline metals and forming sulphur salts, which are crystalli- 
 zable ; with the sulphurets of lead, silver, copper, &;c., it forms in- 
 
 R PvR 
 
498 CHLORIDES OF CARBO N. A M M O N I A. 
 
 soluble compounds, which* correspond closely in composition to the 
 ordinary carbonates. This substance is, in fact, exactly equivalent 
 to carbonic acid, C.O2, the sulphur being replaced by oxygen, with 
 which its analogies have been already noticed in p. 291. The sul- 
 phuret of carbon is hence often called Sulphocarbonic Jlcid. 
 
 Moist chlorine converts this body into a crystalline substance ]iike 
 camphor j but this, as well as the products of the action of nitric 
 acid and of strong alkalies, have not yet been accurately examined 
 
 Chlorides of Carbon, 
 
 Subchloride of Carbon, C2CI., is formed by passing the vapour of the protochlorirte 
 many times through an ignited glass tube ; chlorine is given off, ana the subchlo- 
 ride deposited in silky crystals, which are fusible, and sublime at about 300^ un- 
 changed. 
 
 Protochloride of Carbon, C2CI2, is also formed from the sesquichloride 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 re- 
 moves one third of the 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, C2CI3, is produced by the action of a great excess of chlo- 
 rine in bright sunshine on olefiant gas or on muriatic ether; all the hydrogen of 
 these bodies is removed, and the carbon remains united with chlorine. It forms a 
 white crystalline mass like camphor, which is insoluble in water, but soluble in al- 
 cohol and ether. It melts at 320'', and sublimes at 360"^ unchanged ; at a red heat it 
 abandons chlorine, and forms the bodies last described. 
 
 Bichlaride of Carbon, C2CI4, is formed by exposing a body termed chloroform, 
 whose formula is C2H.CI3, or marsh gas, C2H4, to an excess of chlorine in bright sun- 
 light. 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 DERIV- 
 ATIVES AND COMPOUNDS. 
 
 Although there is very perfect evidence that hydrogen and ni- 
 trogen unite in two, perhaps in three proportions, we as yet know 
 but one of these in an isolated form, which is the volatile alkah\ 
 Ammonia. This was known to the earliest chemists, but the im- 
 portance 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 thun- 
 der-storms contains nitrate of ammonia. It is evolved in large 
 quantities in the putrefaction of organic substances containing ni- 
 trogen, 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 is mixed with hydrogen, and passed 
 through a tube containing red-hot spongy platinum, ammonia is 
 formed j and, lastly, it is produced abundantly when iron or tin is 
 
PREPARATION OF AMMONIA. 499 
 
 oxidized violently by nitric acid, the oxygen being taken both from 
 the acid and water, the nascent hydrogen and nitrogen unite. Am- 
 ttionia 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 
 muriate of ammonia, or sal ammoniac, which is manufactured in 
 large quantities for commerce, by processes to be hereafter de- 
 scribed. Equal parts of the s^l ammoniac, in powder, and slacked 
 lime are to be intimately mixed and heated in a flask, from which 
 a bent tube passes ; the gas which issues is to be conducted through 
 a tube, as in the figure (p. 310), containing dry lime or fused pot- 
 ash, by which adhering moisture is removed, and it may then be 
 collected over mercury. It is colourless and transparent. Its odour 
 is strong, pungent, and irritating, well known as the smell of harts- 
 horn. When perfectly dry, it has no action on vegetable colours ; 
 but if damp, it reacts powerfully alkaline. The brown colour which 
 it produces on turmeric disappears when heat is applied, by which 
 it is distinguished from the browning by the fixed alkalies or earths. 
 By a pressure of 6i atmospheres^ or at a temperature of — 61°, gas 
 eous ammonia is liquefied. When inspired pure, it proves excess 
 ively caustic and poisonous. 
 
 Ammonia is slightly combustible. It does not support combus 
 lion. When a series of electric sparks is passed through a quan 
 tity of the gas confined over mercury, its volume enlarges, and ul- 
 timately becomes double. It is then totally decomposed, and the 
 resulting gas consists of three volumes of hydrogen and one of ni- 
 trogen: tJhe specific gravity of ammonia is therefore 591*5, as de- 
 duced in p. 215, and its formula N.H3. If a current of ammoniacal 
 gas be passed through a red-hot tube filled with iron wire, it is de- 
 composed in the same way as by electricity. If the tube contain 
 red-hot charcoal, carbon is taken up, and prussiate of ammonia and 
 carburet of hydrogen produced. 
 
 Ammoniacal gas is rapidly absorbed by water, which takes up 
 780 times its volume at 32^. Great heat is thereby evolved, and 
 the solution, 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 ammonia, and approximates to the formula N.Hg-f 4 Aq. 
 This solution is termed Water of Ammonia^ or, improperly, Liquid 
 Ammonia, To prepare it upon a larger scale, the matrass and se- 
 ries of three-necked bottles, described and figured in p. 308, may 
 be employed. Five parts of lime, slacked, and mixed with as much 
 water as will convert it into a thin paste, are to be introduced, witli 
 four 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 is left empty, in order to catch any wa- 
 ter 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 bot- 
 tles 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 contain more than 18 per 
 cent, of gas j it then has a specific gravity of 0-930. 
 
500 CONSTITUTION OF AMMONIA, 
 
 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 chlorine is very violent, and accompanied by flame ; sal ammo- 
 niac is formed and nitrogen set free, as described in p. 261. 
 
 Ammonia is very easily recognised : its odour, the brown colour 
 given to turmeric paper, which is removed by a gentle heat, and its 
 forming dense white fumes on the approach of a glass rod moisten- 
 ed with strong muriatic acid, characterize it when free ; all sub- 
 stances which contain ammonia are either volatilized by heat, or 
 decomposed, the ammonia being generally liberated j 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*1, and hence its formula is N.Hg, 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, how- 
 ever, is, that, in acting on metallic compounds, and on certain or- 
 ganic acids, it abandons an atom of hydrogen, and the remaining 
 N.Hg combines with the metal, or with the radical of the acid. Thus, 
 with Hg.Cl. and N.Hg there result Hg.N.H2 and H.Cl. j with Pt.Cl^ 
 and 2N.H3 there are formed Pt. + SN.H^ and 2H.C1. ; from Hg. . N.O, 
 and N.H3 are produced Hg.N.Ha and H.N.Og. Of organic bodies, 
 oxalate of ammonia gives, when heated, C2O2 + N.H2, and benzoate 
 of ammonia produces similarly C,4H502 + N.H2. It is hence evident 
 that the third atom of hydrogen is not so intimately combined with 
 the nitrogen as the remaining two ; it may be eliminated by the 
 simplest reactions, but the N. and H2 remain much more firmly 
 united, and separate only when the constitution of the ammonia is 
 totally broken up. I hence concluded that the N.H2 should be con- 
 sidered as the radical of ammonia, and proposed to term it Amido- 
 gene, and its symbol Ad. The ammonia is then Jlmidide of Hydro- 
 gen, and its rational formula N.H2H. 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 adopt- 
 ed 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.N.H2. It is Amidide of Potassium. When put into water, 
 potash and ammonia are produced, K.Ad. and H.O. giving K.O. and 
 H.Ad. When this olive substance is heated nearly to redness, am- 
 monia is expelled and Jfitruret of Potassium remains, 3K. . N.H, giv- 
 
COMPOUNDS OF AMIDOGENE. , 501 
 
 ing 2N.H3 and K3N. 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 necessary to dis- 
 tinguish those in which ammonia acts simply as amidide of hydro- 
 gen, 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 farther, but shall first describe the most 
 important members of the former class. 
 
 Ammonia and Chlorine. — If a bottle full of chlorine gas be in- 
 verted in a cup containing a solution of sulphate or muriate of am- 
 monia, it is gradually absorbed, and a heavy yellow 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 creasy body, or with phosphorus, it explodes with 
 intense violence j a globule as large as a pin-head, on being exploded 
 in a teacup, shatters 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 decom- 
 posed over mercury, it gives nitrogen and chlorine in the propor- 
 tions by volume of 1:3, and hence it was concluded to be Chloride 
 of Azote^ N.CI3, 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 probably be bichloride of Amidogene^ Ad.Cl2, which, when 
 decomposed, should produce N. and CI3, besides Ad.H. . H.Cl. 
 
 Iodine and Ammonia. — When the semi-fluid compound of iodine 
 and ammonia is put into water, it is decomposed into hydriodato 
 of ammonia, and a brown powder which is usually described as Io- 
 dide of Azote ^ N.I3. This substance may also be prepared by digest- 
 ing iodine in water of ammonia, the iodine gradually changing into 
 the brown substance, and the solution containing hydriodate of am- 
 monia : this body must be collected on filters in very small quantity, 
 and dried merely by exposure to the air j if it be rubbed, even un- 
 der Avater, it explodes with a violent detonation, though not so pow- 
 erfully as the previous body. The cloud of hydriodate of ammonia, 
 formed by its decomposition, is very evident ; it therefore contains 
 hydrogen, and I look upon it as a hiniodide of Amidogene^ Ad.l2« 
 
 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 properties ; they all contain combined water. It is im- 
 possible to say, positively, whether the ammonia exists undecom- 
 posed in tiiese bodies 5 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 is prepared by digesting recently-prepared oxide of sil- 
 ver in water of ammonia, or by dissolving nitrate of silver in an ex- 
 cess of water of ammonia, and precipitating the solution by caustic 
 potash. It is a brown powder, which detonates violently by the 
 slightest shock or friction j when exploded, it is said to produce 
 
502 NITRURETS AND AMMONIURETS. 
 
 water, azote, and metallic silver, which should give for its formula 
 N.Ha+BAg.O.-f-Aq. But the facility of its decomposition, which 
 has been the cause of many serious accidents, has prevented it be- 
 ing accurately analyzed. 
 
 Ammoniuret of Gold^ Au.Oa-f-SAd.H., is produced by the action 
 of water of ammonia on peroxide of gold. It is a brown powder, 
 nearly as explosive as the former body, but it has been accurately 
 analyzed 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 analyzed, and quite different from the impure substance 
 described in books as Davy's fulminating platinum. 
 
 I have examined the ammoniurets of Copper aiui Mercury formed by digesting the 
 oxides of these metals in water of ammonia : the first is blue, the second yellow ; 
 their formulae are 3Cu.O.+2Ad.H.+6 Aq., and 3Hg.O+Ad.H.+2 Aq. They de- 
 tonate feebly when heated. There exist, also, compounds of ammonia with the ox- 
 ides 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 anhy- 
 drous oxide of copper at a temperature of 480° Fah. ; 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 elements. Its formula 
 appears to be CueN., which corresponds to the suboxide CU2O., as w^hen replacing 
 oxygen | is equivalent to O. (see p. 262) and CueN.— 3(Cu2+|). Schrseter, to whom 
 the discovery of the above compound is due, formed also a 7iitrurd of Chrome, whose 
 formula is not quite ascertained. 
 
 Ammonia is absorbed in large quantities by the chlorides of phosphorus and of 
 sulphur, and substances produced which possess singular properties. 
 
 Ammoniacal Protochloride of Phosphorus, P.Cl3+5Ad.H., is obtained by exposing the 
 liquid chloride of phosphorus to a current of dry ammonia. It forms a white pow- 
 der, which, when put in contact with water, produces sal ammoniac, and an insol- 
 uble white substance that has not been analyzed; the reaction is probably that 
 S(C1.H. . Ad.H.) and P.N2H3 result. If the ammoniacal protochloride of phosphorus 
 be calcined without access of air, a very remarkable body, phosphwret of Azote, the 
 formula of which is P.Nz, is produced, while phosphorus, hydrogen, ammonia, and 
 sal ammoniac are expelled. The phosphuret of azote is insoluble in water, and re- 
 sists the action of the most powerful acids and alkalies. The composition of the 
 ammoniacal perchlorides of Phosphorus is not quite certain, as these bodies appear to 
 decompose each other. The formula is P.Cl5H-2Ad.H. When calcined they yield 
 phosplmret of azote. 
 
 Gaseous ammonia and chloride of sulphur combine in two proportions, according 
 as each ingredient is in excess. The formulae of these bodies are S.Cl.-fAd.H. and 
 8.Cl.-|-2Ad.H. The former is a brown powder, soluble in alcohol and ether ; the 
 latter is a citron-yellow powder. They are remarkable for delivering as a product 
 of their decomposition, by water or by heat, the sulphuret of Azote (S3N.), which is a 
 volatile yellow powder, decomposed "by the prolonged action of water into ammonia 
 r;nd hyposulphurous acid, 2(S3N.) and 6H.0. giving 3S2O2 and 2Ad.H. 
 
 When chloride of sulphur is digested with water of ammonia, a brown substance 
 is formed, whose composition is CI.S4 . N3H6. It is probably formed of chloride and 
 amidide of sulphur, S.Cl.-K3(S.Ad.) 
 
 Ammoniacal gas is absorbed in great quantity by the volatile chlorides 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 exposed to a 
 current of the dry gas; but certain metals are specially distinguished by the charac- 
 ter that ammonia added to their solutions produces precipitates which either contain 
 ammonia or amidogene, as is the case with mercury, palladium, and platinum, or 
 by an excess of the ammonia the precipitate is redissolved, and soluble compounds 
 containing ammonia are produced, as occurs with zinc, copper, nickel, cobalt, and 
 also palladium and platinum. The number of combinations thus formed is so very 
 
AMMONIA-SALTS OF ZINC, COPPER, ETC. 503 
 
 great that it would be tedious to describe all, and I shall hence notice only such aa 
 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(Zn.O. . S.03)+5Ad,H., which dissolves perfectly in water. 
 
 If water of ammonia be added to a solution of chloride of zinc, a basic chic ride is 
 precipitated, which being redissolved by an excess of ammonia, a colourless solu- 
 tion js obtained, which crystallizes on cooling. According to the proportion of am- 
 monia 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 con- 
 sists of Zn.Cl.+2Ad.H.+H.O., the former of 2(Zn.Cl.)+2Ad.H.+H.O. In these 
 salts, as in ail such as are produced by the action of an excess of ammonia on 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 di- 
 rect absorption of ammonia by a salt, in which I conceive the union of the acid and 
 oxide not to be distuibed. Hence I write the formula of the tabular ammonia-chloride 
 of Zinc as Ad.H. . H.Cl.+Ad.H. . Zn.O. When heated it gives off ammonia and 
 water, and a white powder, Ad.H. . Zn.Cl., remains. 
 
 By the action of an excess of ammonia on a solution of sulphate of zinc, the am- 
 monia sulphate of Zinc is formed : its formula is Ad.H. . H.O. . S.Og+Ad.H. . Zn.O. 
 It crystallizes in short prisms ; when heated it evolves Ad.H, . H.O., and a wliite 
 powder, Ad.H. . Zn.O. . S.O3 remains. In crystals it contains 3 Aq., of which it 
 loses two by efilorescence, and the third by a moderate heat. 
 
 2. Ammonia-Salts of Copper. 
 
 Chloride of copper absorbs dry ammonia, forming a blue compound, Cu.Cl,-4-3Ad. 
 
 H., 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 for- 
 mula is Ad.H. . H.Cl.+Ad.H. . Cu.O. When heated, these crystals evolve am- 
 monia and water, and a blue powder, Ad.H. . H.Cl., remains, which is totally decom- 
 posed by a strong heat. 
 
 Dry sulphate of copper exposed to a current of dry ammonia forms a fine purple 
 powder, whose formula is 2(Cu.O. . S.03)+5Ad.H. 
 
 An excess of ammonia gives, with a strong solution of sulphate of 
 copper, a rich purple liquor, from which the ammoniucal sulphate of Cop- 
 per cr3^stallizes on cooling in large right rhombic prisms, u, u\ with 
 dihedral summits, ?", i, as in the figure, m being a secondary plane. I 
 consider these crystals, however, to be macles. The formula of this 
 salt is Ad.H. . H.O. . S.Oa+Ad.H. . Cu.O. When heated, it gives off 
 ammonia and water, and a green powder, Ad.H. . Cu.O. . S.O3, remains. 
 
 Under the name of cuprum ammoniatum, the ammoniacal sulphate of copper is em- 
 ployed 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, and carbonic acid is giv- 
 en 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 octohedrons of a fine purple colour: its formula is Ad.H. . H.O. .N.Os-H 
 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 J^ickel and of Cobalt. 
 
 These resemble the corresponding salts of copper so perfectly, that it is sufficient 
 to refer to the foregoing for their properties ; and their composition is obtained bf 
 substituting Ni. or Co. for Cu. in the formulae. 
 
504 AMMONIA-SALTS OF SILVER, PALLADIUM, ETC. 
 
 4. Ammonia-^ alts of Silver. 
 
 The chloride of silver is soluble in water of ammonia. The solution gives opaque 
 white rhombic crystals, which exhale ammonia when exposed 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 evaporation double salts, 
 in rhombic prisms, having the formulce Ad.H. . H.O. . S.Oa+Ag.Ad, and Ad.H, . H. 
 O. . N.Os+Ag.Ad. In both salts the silver is combined with amidogene, Chromate 
 of silver and ammonia gives a similar salt. The ammonia-nitrate of silver is employ- 
 ed in testing for arsenic and in preparing fulminating silver. A remarkable prop- 
 erty 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-col- 
 oured precipitate is produced, having fhe formula Pd.Cl. . Ad.H. When more am- 
 monia is added, it dissolves, and from the solution the second salt crystallizes in 
 long rectangular prisms, having the formula Ad.H. . H.Cl.-fPd.O. . H.Ad. 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 mu- 
 riatic acid, a yellow crystalline precipitate forms, which has the same formula as the 
 first salt, Pd.Cl.+H.Ad. 
 
 With solution of sulphate of palladium and water of ammonia, a precisely similar 
 series of salts is formed; the first being flesh-red, Pd.O. . S.Oa-l-H.Ad. ; the second 
 salt in colourless prisms, Ad.H. . H.O. . S.Oa+Pd.O. . H.Ad., and, when dried, the 
 last member becoming Pd.Ad. ; and by a small quantity of an acid, a crystalline 
 precipitate, which consists also of Pd.O. . S.Os+H.Ad, 
 
 The iodide of palladium gives similar salts. With the nitrate no other than the 
 cokurless crystalline salt can be obtained, whose form is thin rhombic plates. Ad. 
 H..H.O. .N.Os+Pd.Ad. When heated, it deflagrates like loose gunpowder, and 
 leaves behind metallic palladium as a black powder. 
 
 In the red and yellow insoluble ammonia-salts of palladium, although the experi- 
 mental composition is the same, I consider that an important difierence of constitu- 
 tion 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, Pd.Cl.+H.Ad. But 
 when we form the yellow salt by adding an acid to a solution of the soluble ammo- 
 nia-salt, I conceive that the acid unites directly with the amidide of the metal, and 
 thus forms, for example, Pd.Ad.+H.Cl. The yellow ammonia-iodide, Pd.Ad. -fH.L, 
 gradually changes itself b^ck into the red substance, Pd.I,-f-H,Ad. 
 
 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 de- 
 serve more detailed notice than 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 
 2Hg.C1.4-H.Ad. By contact with water, this body is decomposed into sal alem- 
 broth and white precipitate ; the former, a compound of sublimate and sal ammo- 
 niac, dissolving, and the latter, whose composition will be next studied, separating 
 as a whi:e powder. 
 
 If we add to a cold solution of corrosive sublimate a very slight excess of ammo- 
 nia, a copious white precipitate is produced, and the liquor is found to contain exact- 
 ly half the chlorine of the sublimate combined with hydrogen and ammonia as sal 
 ammoniac ; the v/hite powder, which had been known to the early chemists as White 
 Precipitate of Mercury, contains all the mercury and the remaining half of the chlo- 
 rine 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 
 
PRECIPITATES OF MERCURY. 505 
 
 formula is Hg.Cl.+Hg.Ad., it being a true chloro-amidide of mercury. The theory 
 of its formation is very simple, 2Hg.Cl. and 2H.Ad. producing, by interchange of 
 the elements of one equivalent of each body, Hg.Cl.+Hg.iVd., which precipitates, 
 and H.Cl.+H.Ad., 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 recognised. 
 
 W/iitc Precipitate is insoluble in cold water. It is decomposed by boiling water, 
 two atoms of which, reacting on two of white precipitate, produce sal ammoniac, 
 which dissolves, and a heavy yellow powder, which is insoluble in water, and has 
 the formula Hg.Cl.+2Hg.0.+Hg.Ad. This body is completely analogous to the 
 oxychloride of mercury, Hg.Cl.+3Hg.O., from which it may be prepared by the ac- 
 tion of ammoniacal gas, the third atom of Hg.O. and H.Ad. giving Hg.Ad. and 
 H.O., 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 ofi", and a red powder remains, which is a 
 compound of chloride and nitruret of mercury, Hg.Cl.+HgaN. ; or, rather, as the ni- 
 trogen here replaces oxygen, and has hence the one third atomic weight, Hg.Cl.4- 
 3Hg.j, exactly analogous to the oxychloride j by careful management, all the subli- 
 mate may be expelled, and the azoturd of Mercury, Hg.f , is obtained as a brown pow- 
 der, which detonates with great violence when struck. 
 
 The white precipitate which has been now described must be distinguished from 
 another body which has been confounded with it in the pharmacopoeias, until the 
 difference was shown by Woehler's observations 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 form- 
 ed by boiling alpha- white precipitate in a solution of sal ammoniac. It has a crys- 
 talline aspect, and is not decomposed by boiling water ; when heated, it fuses, and 
 gives off ammonia and azote, while a mixture of calomel, sublimate, and sal ammo- 
 niac sublimes. Its formula is very simple, Hg.Cl.+H.Ad. ; but it may also be look- 
 ed upOn as a compound of alpha-white precipitate and sal ammoniac, (Hg.Cl.-f- 
 Hg.Ad.)+(H.Cl.+H.Ad.)=2(Hg.C].-t-H.Ad.). 
 
 When calomel absorbs dry ammonia, it forms a dark gray powder, which is 2 
 HgaCl.+H.Ad. ; by a gentle heat all ammonia may be expelled, 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 gray powder results, which is a com- 
 pound of subchloride and subamidide of mercury, Hg2Cl.-f Hg2Ad. This body, 
 which I have termed Black Precipitate, is formed by a similar reaction to that by 
 which alpha-white precipitate is produced, 2Hg2Cl. and 2H.Ad. giving Hg2Cl.-f- 
 Hg2Ad. and H.Cl.-f-H.Ad. By several chemists, the action of water of ammonia 
 on calomel is given as a means of preparing black oxide of mercury, which is quite 
 incorrect. The compound formed contains no oxygen. 
 
 The action of the bromides of mercury with ammonia has not been s& 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 amadide, Hg, 
 Br.+Hg.Ad., and analogous to the alpha- white precipitate. The subbromide of 
 mercury produces with water of ammonia a black powder, consisting of Hg2Br.-|- 
 Hg2Ad. 
 
 Iodide of mercury dissolves plentifully in hot water of ammonia, and the solution 
 deposites, 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 pseu- 
 domorphous crystals. This white body has the formula SHg.I.-f-H.Ad. 
 
 There is no iodine compound analogous to alpha-white precipitate ; but when that 
 substance is warmed in a solution of iodide of potassium, ammonia is evolved and a 
 brown powder is formed, having the formula Hg.I.-|-2Hg.0.-|- Hg.Ad. 
 
 B. Action of Ammonia on the Oxygen Salts of Mercury, 
 
 Wlien 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-turpeth. It is not act- 
 ed on by water nor by alkalies. Its formula is SHg.O.+S.Oa-l-Hg.Ad. It is there- 
 fore ordinary turpeth mineral combined with amadide of mercury. 
 
 When water of ammonia is added to a solution of nitrate of mercury, being cold 
 and not in excess, a white precipitate is formed, a basic ammonia-nitrate, which is 
 found to consist of H.Ad. . N.05-4-3Hg.O. It is therefore a basic nitrate of mercu- 
 ry, analogous to the ordinary basic nitrate, H.O. . N.05+3Hg.O., except that ant 
 
 Sss 
 
506 AMMONIA-SALTS OF PLATINUM. 
 
 monia (amidide of hydrogen) is substituted for water (oxide of hydrogen). If an ex- 
 cess of ammonia be added, and the mixture boiled, the white precipitate becomes 
 heavier and granular, and is then found to consist of Hg.Ad. , N.Os+SHg.O. This 
 substance, the ^ basic ammonia-nitrate, is evidently analogous to the former, the hy- 
 drogen being replaced by mercury, and it corresponds accurately in constitution also 
 to the ammonia-turpeth. 
 
 If either of these basic ammonia-nitrates be boiled in water containing much 
 nitrate of ammonia, they dissolve and form double salts ; that usually formed is in 
 short opaque white prisms, having the very simple composition 4Hg.O.+3(H.Ad. . 
 H.O. . N.O5); but as it is decomposed by water into the /? basic ammonia-nitrate, 
 its formula must be (Hg.Ad. , N.05+3Hg.O.)+2(H.Ad. . N.Os+SH.O.). The dou- 
 ble salt, which forms less frequently, is in yellow plates, and has the formula (Hg. 
 Ad. . N.05+3Hg.O.)+(H.Ad. . N.O5 . H.O.). 
 
 These double salts may also be generated by boiling oxide of mercury in solution 
 of nitrate of ammonia. If the common basic nitrate of mercury be boiled in a solu- 
 tion of nitrdte of ammonia, this is decomposed ; the ammonia being employed in 
 forming amidide of mercury, and the nitric acid being set free, as may be recog- 
 nised by litmus. 
 
 The subsulphate of mercury, Hg20. . S.O3, acted on by water of ammonia, pro- 
 duces a black powder, the formula of which is Hg20. . S.03+Hg2Ad. : it is easily 
 decomposed. 
 
 By acting on a solution of subnitrate of mercur}' in water with ammonia added 
 dilute, and in such quantities as to leave a portion of the mercurial salt undecompo- 
 sed, a fine velvet black precipitate is obtained, known in pharmacy as Hahnemann's 
 solvJjle 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 of mercury should he precipitated. 
 When quite pure, I have found its formula to be H.Ad. . N.Os+SHggO., it being 
 perfectly analogous to the common basic subnitrate H.O. . N.054-2Hg20,, the ox- 
 ide 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 ol 
 ammonia added, a green precipitate is produced, composed of Pt.Cl.-f-H.Ad. 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 ammonia. By boiling this green substance in strong water of am- 
 monia, it forms a white powder, the formula of which is Pt.Cl.-f2H.Ad. 
 
 The action of amm.onia on a solution of bichloride of platinum is very complex ; 
 it gives origin to a series of bodies, composed of bichloride, binoxide, and binami- 
 dide of platinum, in proportions which vary with the temperature and proportions 
 used. The ultimate effect is the formation of a colourless solution, when the ammo- 
 nia is boiling and in considerable excess, from which a white powder separates by 
 cooling, or by the addition of alcohol. This powder, which consists of (Pt.Ck+Pt. 
 Ad2)-f 3H.Ad.-f2 Aq., combines with acids, and generates a very remarkable series 
 of double salts, discovered by Gros, who formed them differently, having obtained 
 the nitric acid salt by heating the green substance Pt.Cl.+H.Ad. with nitric acid, 
 and the other salts by double decomposition. Liebig proposed to consider, that in 
 these salts there exists a compound radical, Pt.Cl. . N2H6, which combines with chlo- 
 rine and with oxygen, and the oxide of which unites with acids. Thus the oxa- 
 late contains Pt.Cl. . N2H6O.+C2O3, &c. But as the gradual formation of this sup- 
 posed oxide can be traced from the bichloride of platinum, we must admit it to con- 
 tain a compound of bichloride and binamidide, similar, in many respects, to white 
 precipitate, and we must look upon the salts formed by Gros as consisting of that 
 compound united to ordinary ammoniacal salts, just as are the double ammonia-ni- 
 trates of mercury. 
 
 The formulas of Gros's salts are upon my view : 
 
 fPt.Cl2+Pt.Ad2)+2(H.O. . HAd.), the base of the series. 
 (Pt.C]2-|-PtAd2)-|-2(H.Cl. . H Ad.), the muriatic salt. 
 (Pt.Cl2+PtAd2)+2(H.O. . N.O5 . H Ad.), the nitric salt. 
 (Pt.Cl24-PtAd2)-f 2(H.O. . S.O3 . H.Ad.), the sulphuric salt. 
 (Pt.Cl2+Pt.Ad2)-j-2(H.O. . C2O3 . H.Ad.), the oxalic salt. 
 
AMMONIACAL SALTS. 507 
 
 The action of ammonia on biniodide of platinum is more simple ; a deep red pow- 
 der is formed, which has the formula Pt.l2+Pt.Ad2+4 Aq. 
 
 Our knowledge of the action of ammonia on the oxygen salts of platinum is yet 
 too inexact to justify me in bringing forward here the statements that have been 
 made concerning the results. 
 
 By the action of ammonia on perchloride of gold, an olive-brown powder is pro- 
 duced, which fulminates when rubbed. It is decomposed by water, and its real for- 
 mula has not yet been established. 
 
 Products of the Action of Jlmmonia on the Anhydrous Acids. 
 
 When chloro-sulphurous acid, S.O2CI., is exposed to dry ammonia, it is converted 
 into a white saline mass, which is a mixture of sal ammoniac and sidph-amide, S. 
 O2CI. and 2Ad.H. giving S.02Ad. and H.Cl+H.Ad. 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, 2H.0. and S.02Ad. giving S.Oa+Ad.H. . H.O. 
 
 "When dry sulphurous acid and ammonia gases are mixed, they combine to form 
 a reddish substance, which is decomposed by water; there appear to be two propor- 
 tions, giving the bodies S.O2 . H.Ad. and 2S.O2 . H.Ad. 
 
 Dry sulphuric acid unites with dry ammonia in two proportions, forming S.O3 . H. 
 Ad. and 2S.O3 . H.Ad. 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 be- 
 comes changed into ordinary sulphate of ammonia. 
 
 It was supposed that the chloro-carbonic acid, C.O.Cl., combined directly with 
 ammonia, but Regnault has found that decomposition occurs, and that sal ammo- 
 niac and amidide of carbonic oxide result. This body, which he terms carb-amide^ 
 C.O.Ad., is white, soluble in water, is not deliquescent, and resists the action of al- 
 kalies and acids, unless they be very concentrated. 
 
 Of the Common Ammoniacal Salts. 
 
 From the great number of classes of compounds described in the 
 preceding sections, it is evident that ammonia enters into combina- 
 tion 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 alkalies, 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 the Animal 
 Alkali. The characteristic distinction is, that in all cases where it 
 acts as an alkali, ammonia is associated with water : it is not x'^.d.H., 
 which is the alkali, but Ad.H. + H.O., or, rather, N.H4O., the ele- 
 ment which replaces potassium in the isomorphous salts being sub- 
 amidide of Hydrogen, Ad.Hg, or N.H4. 
 
 At the time when Mitscherlich showed the isomorphism of the 
 potash and ammonia salts, nothing was known of the true constitu- 
 tion of ammonia or of amidogene ; and, in order to explain the ne- 
 cessity of the presence of water, a very ingenious theory was pro- 
 posed by Berzelius and Ampere. It was, to consider that these 
 ammoniacal salts do not contain ammonia at all, but another com- 
 pound of nitrogen and hydrogen, N.H4, which is metallic, and re- 
 sembles potassium in all general characters, and for which the name 
 Ammonium was proposed. This view squared accurately with ex- 
 periment, as in every oxygen salt of ammonia there is just so much 
 water as may form with the ammonia Oxide of Ammonium, N.H4 
 O. J and in every haloid salt, the electro-negative body is combined 
 
508 
 
 AMMONIACAL AMALGAM. 
 
 with as much hydrogen as may convert the ammonia into the com- 
 pound metal; thus N.Hg . H.O. + S.O3 and N.H34-H.CI. would give 
 N.H40.-fS.03 and N.H4CI. Not merely was this theory conso- 
 nant to numbers, but experiment gave very good reason to believe 
 in the real existence of this compound metal, by the remarkable 
 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 volume, becomes semi-fluid and covered with warty excrescen- 
 ces, and finally becomes so light as to float on water. No hydro- 
 gen is evolved from its surface, but oxygen is copiously given off 
 from the positive electrode. If the current be interrupted, a copi- 
 ous disengagement of hydrogen occurs from this metallic sponge, 
 which also gives off ammonia, 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 crys- 
 tallize in cubes at a cold of 0^ ; and if decomposed when dry over 
 mercury, it evolves ammonia and hydrogen, by volume in the pro- 
 portion of 2 : 1. This indicates that the mercury is therein com- 
 bined with a body which consists of N.H4, and as the mercury re- 
 tains its lustre, the compound formed is properly an alloy, and the 
 body N.H4 is of a metallic nature. It may be the metal Ammonium^ 
 almost perfectly isolated. All these phenomena may be observed 
 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 N.H4CI., there are pro- 
 duced K.Cl. and Hg.N.H4 ; the globule of mercury swells up rapid- 
 ly, 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.Ha ; but whether the water which 
 is found in the common ammoniacal salts exists therein as such, or 
 whether these salts contain true oxide of ammonium, is not thus 
 decided. In fact, among the metallic compounds of ammonia al- 
 ready 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 Ave^ compare sal ammoniac with other 
 similar bodies, as in the following formulae, 
 
 1. CI.N.H4, 5. Cl.N..H3Ni., 
 
 2. Cl.N. . H3CU., 6. Cl.N. . HaHg., 
 
 3. Cl.N. . HaZn., 7. Cl.N. . H^Hg^, 
 
 4. Cl.N. . HaPd., 8. Cl.N. . HaPt^, 
 
 and 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 am- 
 monia on chloride of hydrogen, we must admit their similarity of 
 constitution j and if we say that in No. 1, N.H4 forms a compound 
 metal, we must consider all the others as chlorides of compound 
 radicals also. Still more, the connexion is so perfect from these 
 bodies to such as resemble the yellow powder, Hg.Cl.-f-2Hg.0.-f 
 Hg.Ad., and from that to the oxychloride, Hg.Cl. + 3Hg.O., that if 
 we insist on assuming the compound metal ammonium to exist 
 ready formed in the salts of ammonia, we must lay down as a gen- 
 
MANUFACTURE OF SAL AMMONIAC. 509 
 
 eral principle that all basic salts are salts of compound metals, 
 which could not be tolerated in an exact science for a moment. At 
 the same time, therefore, that I consider the ammoniacal 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 magne- 
 sian sulphates, but more intimately. Thus, sulphate of ammonia, 
 S.Oa+Ad.H. .H.O., I consider to resemble the bihydrated sulphuric 
 acid, S.Og+H.O. . H.O. 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 or- 
 dinary salts of ammonia. 
 
 Muriate of Ammonia. Sal Ammoniac. — Cl.HaAd. 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 destruc- 
 tive distillation of horns, bones, coals, and such other organic mat- 
 ters as contain nitrogen. Those liquors which contain ammonia, 
 combined principally 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 obtain- 
 ed in small crystals, deeply coloured with tarry matter. They are 
 purified by re-crystallization, 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 100 lbs., 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 ammo- 
 niac separated by crystallization. 
 
 Sal ammoniac is very soluble in water ; it crystallizes both by 
 sublimation and solution, in cubes and octohedrons ; it is slightly 
 deliquescent, and is soluble in alcohol ; it volatilizes below a red 
 heat. When heated with lime or potash, it yields ammonia, as de- 
 scribed in p. 499. It consists of an equivalent of each element, its 
 formula being H.Cl. . H.Ad. It may be formed by their direct com- 
 bination. When equal volumes of dry muriatic acid gas and am- 
 monia are mixed together, the two gases disappear, and a snow- 
 white powder of sal ammoniac results. Hence arise the white 
 fumes when a rod dipped in water of ammonia is brought where 
 cblorine 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 Ad.H2Cl.+Mg.Cl., 
 which is used in preparing metallic magnesium. 
 
 With perchloride of iron, it crystallizes in fine red octohedrons, Fe2Cl3+3('Ad.Ha 
 CL). When these are heated, sal ammoniac sublimes, coloured by some cnloride 
 of iron, and forms thus the Flvres 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 Cu.Cl.-l-Ad.HaCL-f 
 8Aq. 
 
510 HYDROSULPHURET, ETC., OF AMMONIA. 
 
 Corrosive sublimate unites in two proportions with sal ammoniac. The first salt, 
 of which the formula is Hg.Cl.+Ad.H2Cl.+Aq., is very soluble in water, and crys- 
 tallizes in flat rhomboidal tables, which effloresce when exposed to the air. This is 
 the Sal Alembroth of the older chemists. The second salt crystallizes in rhomboidal 
 
 Erisms, which sublime unchanged, and have the formula 2Hg.Cl.+Ad.H2Cl. It is 
 y 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 
 Pt.Cl2+Ad.H2Cl. It precipitates as a bright yellow powder when solutions of iU 
 constituents are mixed, and especially if alcohol be added, in which it is quite in- 
 soluble. It is but very sparingly soluble 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 crystallines in 
 orange-red cubes, having the formula Au.Cls-f Ad.H2Cl.-f-2 Aq. 
 
 The hydrobromate and hydriodate of ammonia do not require notice. They re- 
 semble the sal ammoniac in all important characters, and combine with the metal- 
 lic bromides and iodides to form similar double salts. 
 
 Hydrosulphuret 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 
 ordina'^y temperatures. The formula of this compound is S.H. + H. 
 Ad., or S.N.H4, analogous to protosulphuret of potassium, S.K. Like 
 that, it combines with as much more sulphuret of hydrogen, forming 
 a volatile crystalline compound, Ad.HgS.-f-H.S. This hihydrosul^ 
 phuret of Ammonia is formed also when sulphuretted hydrogen is 
 passed into water of ammonia, as long as it is absorbed. For 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 quantity of sulphur, forming com- 
 pounds analogous to the higher sulphurets of potassium. This hy- 
 drosulphuret of ammonia is of great importance in the detection of 
 the metals, from the formation of metallic sulphurets. It is a sul- 
 phur base, and forms salts with the sulphur acids, analogous to those 
 formed by sulphuret of potassium. 
 
 Sulphate of Ammonia. — Ad.Hg . O.S.Og-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 j it 
 
 t crystallizes in flat rhomboidal prisms, as in the figure, or in 
 macles, isomorphous with the crystals of sulphate of pot- 
 ash. It is very soluble in water, but insoluble in alcohol ; 
 when heated, it gives off water, ammonia, and azote, and 
 sulphite of ammonia sublimes. It combines with the sul- 
 phates of copper, zinc, iron, alumina, &c., forming double salts ex- 
 actly analogous to those formed by sulphate of potash. With oil 
 of vitriol it unites to form bisulphate of Ammonia, which is deliques- 
 cent and soluble in alcohol. 
 
 Kitratt of Ammonia, Ad.HaO. . N.O5, is formed by neutralizing ni- 
 tric acid by ammonia. It crystallizes in striated hexagonal prisms, 
 isomorphous with nitre, of a bitter saline taste ; they are deliques- 
 cent and very soluble in water. When heated, they fuse at 230°, 
 and at about 460^ are rapidly decomposed into nitrous oxide and 
 water, as described p. 2.72. By the presence of a large excess oi 
 sulphuric acid, this action takes place at much lower temperatures. 
 
PHOSPHATES OP AMMONIA. 511 
 
 When heated with combustible bodies, it deflagrates with extreme 
 violence. 
 
 Phosjihates of Ammonia. — The tribasic phosphoric acid forms with 
 ammonia two salts; the first, whose formula is (P.O^+Ad.HaO.-f 
 H.O.)-{-Aq., is prepared by adding the acid in excess to water of 
 tmmonia j it crystallizes in rhombic prisms, which are very soluble 
 'n water. Their reaction to test-paper is strongly acid. If the amr 
 monia be added in excess, a salt crystallizes, possessing nearly the 
 isame characters, except that its reaction is alkaline, and its formula 
 P.03-]-2(Ad.H20.)-l-H.O. Both of these salts yield, by ignition, 
 phosphoric acid. 
 
 AmmoniacO'Magnesian Phosphate. — When a solution of a salt of 
 •magnesia is added to any soluble phosphate, and the liquor rendered 
 alkaline by ammonia, a crystalline precipitate is formed, which is 
 soluble in acids, sparingly soluble in water, but insoluble in alkaline 
 .iquors. Its formula is P.05-|-(Ad.H,0.-|-2Mg.O.) + 12 Aq. Its 
 formation is often of use for the detection of magnesia, and it is 
 occasionally generated in urine by the action of ammonia, produced 
 oy the spontaneous decomposition of urea upon the soluble phos- 
 phates of magnesia which it contains. It then constitutes a com- 
 mon variety of calculus. 
 
 Phosphate of Ammonia and Soda. — This salt, of which the formula 
 IS P.0,+(Ad.H,0. + Na.0.+H.0.)-{-8 Aq., is easily produced by 
 mixing 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, 
 produce chloride of calcium and carbonate of ammonia, which sub- 
 limes, 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, Ad.H^Cl. and Ca.O. . C.Og giving 
 Ca.Cl. and Ad.H^O. . C.O^ ; but a quantity of ammonia and water is 
 given off", and the sublimed salt was considered to be a sesquicarbon- 
 ate, consisting of 2(Ad.H20.)-f-3C.02, until Scanlan showed that 
 it was a mixture of two different salts, which may be separated by 
 water. Rose has recently thoroughly examined the carbonates of 
 ammonia, of which there are a great number, but only four sufficient- 
 ly important to be noticed here. 
 
 The proper neutral carbonate of ammonia, Ad.H20. . CO., does 
 not exist except in combination, but its compounds are very nu 
 merous 5 it forms, 
 
 1st. With carbonate of water, the ordinary bicarbonate of Ammonia^ 
 Ad.H.O. . C.O.4-H.O. . C.O2. This is prepared by washing the com- 
 mercial 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 
 
512 CARBONATES AND OXALATES OF AMMONIA. 
 
 weak odour of ammonia. Its solution reacts feebly alkaline. By 
 pouring on the commercial 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 rhom- 
 boidal crystals, which contain one and a half atoms of water. 
 
 2d. 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 
 Ad.H. . C.O2, and the ordinary sesquicarbonate is a mechanical mix 
 ture 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 Ad.HaO. . C.Oa+H.Ad. . C.O2, being a compound of neutral carbo- 
 nate with dry carbonate, or a bicarbonate in which the basic oxide of 
 hydrogen is replaced by amidide of hydrogen, the two double salts, 
 
 Ad.HaO. . C.Oa-f-H.O. . C.O2, water-bicarbonate of ammonia, 
 Ad.HaO. . C.O^+H.Ad. . C.O2, ammonia-bicarbonate of ammonia, 
 
 being precisely equivalent in composition. The less volatile product 
 is of very complex composition j its formula is 4(Ad.H20.)-j-5C.02, 
 or it consists of an atom of neutral carbonate united to an atom of 
 each of the different bicarbonates, thus : 
 
 Ad.H20. . C.O2 ) 
 
 Ad.H20. . C.O2+H.O. . C.O2 > =4(Ad.H20.) + 5C.02. 
 
 Ad.H20. . C.02+H.Ad.Co2 ) 
 
 Oxalate of Ammonia, Ad.H20. . C2O3, may be prepared by neutral- 
 izing oxalic acid by water of ammonia ; it crystallizes in 
 right rhombic prisms, as in the figure, where p, w, 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^O. . C^ 
 O3 producing 2H.0. and Ad. 0202- This neutral oxalate of ammonia 
 combines 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, ox- 
 alic acid and ammonia being regenerated. Its discovery by Dumas 
 laid the foundation of our present knowledge of the nature of am- 
 monia, by leading him to the idea of the probable existence of ami- 
 dogene. 
 
PREPARATION OF CYANOGEN. 513 
 
 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 cj'^anogen as their 
 basis. The powerful affinities which this radical exerts, the simpli- 
 city of its constitution, and, above all, 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 anal- 
 ogy of mineral bodies and the theory of compound radicals is most 
 undeniably applicable. 
 
 Cyanogen does not exist in nature ready formed j the kernels of 
 peaches, plums, bitter almonds, &c., and the leaves of the cherry- 
 laurel, yield, by simple distillation, abundance of prussic acid (cy- 
 anide of hydrogen), but this is only then produced by the decompo- 
 sition 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 
 organic substance containing nitrogen is calcined with potash, the 
 nascent carbon and nitrogen unite, and cyanide of potassium is 
 formed ; even with pure charcoal this occurs, nitrogen being derived 
 from the air ; and Mr. Fownes has shown, that when a mixture of 
 pure charcoal and potash is 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 K.O. 
 and N. giving CO. and C^N.K. 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 2N.H3 produce C^H.+N.Hj, and 
 H2 become free. It is by virtue of these processes that cyanogen 
 is produced for its various applications in the arts j but, as I shdl re- 
 turn to them in detail, l shall now only consider farther the mode 
 of obtaining it free and pure. 
 
 Cyanide of silver, or cyanide of mercury, of which the prepara- 
 tion 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 temperature of decomposition has been lower. The 
 gas which comes over is, however, cyanogen completely pure. 
 
 Its properties are very marked. It is colourless, of a sharp smell, 
 which irritates the eyes. Its sp. gr. is 1819. If a quantity of cya- 
 nide 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 apress- 
 
 Ttt 
 
514 CYANIC ACID. 
 
 ure of about four atmospheres, and 
 ^ collects at the other end, b, as a col- 
 ourless liquid. It is combustible, 
 burning with a beautiful rose-colour- 
 ed flame, and producing- two volumes of carbonic acid and one of 
 nitrogen. It is constituted, therefore, of equal volumes of carbon 
 vapour and nitrogen, the two volumes being condensed to one j 
 hence 843 + 976 = 1819 is its sp. gr. It dissolves abundantly in al- 
 cohol 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 in- 
 soluble matter.' A similar decomposition is produced much more 
 rapidly by contact with water of ammonia. The composition of 
 this brown matter appears to be C4N2 . H.O. It dissolves in alkalies, 
 and gives precipitates with the metallic salts ; it has been termed 
 hence Azulmic Jicid. 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 ni- 
 tric acid, and the solution gives, with water, a yellow precipitate, 
 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 
 ate three compounds of cyanogen and oxygen, which are all acids, 
 and are polymeric bodies. It unites also with sulphur, and its com- 
 pounds have a remarkable tendency to form double and triple com- 
 binations. 
 
 The formula of cyanogen is indifferently written CgN. or Cy. Its 
 equivalent number is 328*6 or 26-05. 
 
 SECTION I. 
 
 NON-METALLIC COMPOUNDS OF CYANOGEN. 
 
 Compounds of Cyanogen and Oxygen. 
 
 Cyanic Acid — Cy.O. ; Eq. 428*6 or 34*05 — is very easily obtained 
 in combination, by calcining the cyanide of potassium in contact 
 Avith 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 em- 
 ployed, as the cyanide of iron which it contains is totally decom- 
 posed, and the cyanide of potassium then acts as if it were com- 
 pletely pure. The cyanic acid cannot, however, be isolated from 
 these salts by a stronger acid, as it then rapidly changes into bicar- 
 bonate of ammonia, uniting with the elements of three atoms of 
 water ; thus C.2N.O. and 3H.0. produce N.H3 and 2C.0,. 
 
 The cyanic acid can be obtained free only by distilling the cyan- 
 uric acid, CysOg+SH.O., which then transforms itself into the hy- 
 drated cyanic acid, Cy.O. -[-H.O. , and is to be collected in a receiv- 
 er surrounded with snow. It is a colourless liquid, of a very pun- 
 
SALTS OF CYANIC ACID, ETC. 515 
 
 gent odour, cauterizes the skin, and, when mixed with water, is 
 decomposed as above stated. When preserved in its most concen- 
 trated form, it soon transforms itself into a white mass, like porce- 
 lain, of the same composition, C^N. . H.O2, which has been termed 
 Cyanamelide. This body is insoluble in water, but by heat is trans- 
 formed 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 j 
 those of the alkalies are soluble j the others are white insoluble 
 powders. 
 
 Cyanate of Potash. — Cy.O. . K.O. 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 digested with alcohol, from which the pure cyanate crys- 
 tallizes, on cooling, in rhombic tables like chlorate of potash. In 
 contact with 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, ox- 
 alate of potash is formed, and the cyanic acid changes into cya- 
 namelide. 
 
 Cyanic Acid and Ammonia. — 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 Cy.O. + H.O. + 2N.H3. If it be gently heated it 
 gives ofFanjmonia, and is transformed into an important substance, 
 Urea^ which, though thus capable of being artificially produced, will 
 be specially described as a product of the organization, in another 
 chapter. Whenever we attempt to form the neutral cyanate of 
 ammonia, Cy.O. . N.H3 . H.O., urea is produced j thus, by acting on 
 cyanate of silver with muriate of ammonia, or by mixing solutions 
 of sulphate of ammonia and cyanate of potash. But still we cannot 
 consider urea to be merely cyanate of ammonia, to which it bears 
 the same relation that cyanamelide does to hydrated cyanic acid. 
 
 Fulminic Acid. — Cy202+2H.O. This acid, which has attracted 
 much attention from the detonating properties of its salts, is pre- 
 pared by the action of nitric acid on alcohol, 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 two equiva 
 lents of alcohol and two of nitric acid, producing one of acetic acid, 
 one of fulminic acid, and eight of water j thus 2N.O3 and 2(C4H602) 
 give C,H404 and C^N^O^, besides 8H.0. 
 
 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 cyan- 
 ogen, are produced. The fulminic acid is bibasic, and forms two 
 series of salts, of which the neutral contains two equivalents of fixed 
 base, the acid salts containing one of fixed base and one of water 
 
516 FULMINATES OF SILVER AND MERCURY, ETC. 
 
 Fulminate of Silver. — CyaOi + SAg.O. It is prepared by dissolv- 
 ing silver in ten parts of nitric acid, specific gravity 1-35, and pour- 
 ing 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 crystals, 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 alkali, as potash, half of the silver separates 
 as oxide, and a salt is formed, Cy202 + K.O. . Ag.O. If it be dissolv 
 ed in warm dilute nitric acid, half of the silver is also removed an<5 
 replaced by water, and on cooling, the acid fulminate of silver, Cy< 
 O^-f-H.O. . Ag.O., crystallizes out. This explodes more readilj 
 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 o; 
 copper, fulminates of these metals with two atoms of oxide are ob 
 tained ; and by acting on these salts with an alkali or barytes, salt*' 
 with two different bases may be formed. In no case, however, caa 
 a fulminate containing two atoms of an alkaline base be produced. 
 All these salts possess detonating properties more or less violent. 
 
 Fulminate of the Suboxide of Mercury. — Cy202+2Hg20. This, the 
 most important salt of fulminic acid, is prepared by dissolving mer- 
 cury in nitric acid, and treating it by alcohol, as in preparing ful- 
 minate of silver. As the solution cools, some metallic mercury 
 precipitates, and the fulminate of the suboxide is deposited in hard, 
 opaque, white crystals, generally very minute. It is to be washed 
 and redissolved in boiling water, and crystallizes then in fine silky 
 needles. This salt detonates violently when struck between two 
 hard bodies. It is extensiv^ely used in the manufacture of the per- 
 cussion caps used for firearms. 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, from containing a large quan- 
 tity of prussic acid. 
 
 Cyanuric ^cid. — CyaOg-j-SH.O. 
 
 This acid is produced under a variety of circumstances where 
 the elements of cyanic acid become free. Thus, if the solid chlo- 
 ride of cyanogen be treated with water, Cy.Cl. and H.O. produce 
 H.Cl. and Cy.O., but this transforms itself immediately into cyanu- 
 ric acid. It is formed abundantly, as a white sublimate, in the dry 
 distillation of uric acid, and may be very simply produced by heat- 
 ing urea a little above its point of fusion in a glass retort ; ammo- 
 nia is given off, and the urea changes into a dry, gray mass, which 
 is to be dissolved in strong sulphuric 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(C2H4 . NgOJ, contain the elements of three atoms of am- 
 monia and one of cyanuric acid, CgNsOg+SH.O. 
 
 By means of a substance which will be hereafter noticed, termed 
 
PREPARATION OF PRUSSIC ACID. 517 
 
 Melam^ cyanuric acid may be formed simply and in quantity. The 
 details of the process will be given when describing the properties 
 of that body. 
 
 Cyanuric acid is colourless and nearly tasteless, possessing a very 
 slight acid reaction. It crystallizes in oblique rhombic prisms, which 
 have the formula Cy3034-3H.O.+4 Aq. By a moderate heat, the 4 
 Aq. are expelled, and when more strongly heated, the dry acid chan- 
 ges 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. 
 
 Cyanide of Hydrogen. Hydrocyanic Acid. Prussia Acid. 
 
 This remarkable substance may be formed by the direct combina- 
 tion 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 forraiate of ammonia (C2H.O3+N.H4O.) be passed in va- 
 pour through a red-hot porcelain tube, it is totally converted into 
 prussic acid and water, C2N.H. and 4H.0. Also, by passing ammo- 
 nia over red-hot charcoal, hydrocyanate of ammonia is formed in 
 such quantity that prussic acid may be economically pTepared from 
 it. If cyanide of silver be decomposed by muriatic acid, chloride 
 of silver and cyanide of hydrogen are produced (Ag.Cy. and H.CI. 
 giving Ag.Cl. and H.Cy.) j and by sulphuret of hydrogen, cyanide 
 of mercury gives sulphuret of mercury and prussic acid. For its 
 preparation 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, 
 consists of cyanide of iron united to cyanide of potassium ; by the 
 action of sulphuric acid, three fourths of the latter are decomposed, 
 bisulphate of potash being formed, and prussic acid liberated, 2(S. 
 O3+H 0.) and Cy.K. giving (K.O. . S.^+HO. . S.O3) and Cy.H. 
 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 cyanogen which existed in the salt employed. The 
 precise decomposition is, that two equivalents of the yellow ferro- 
 prussiate of potash, 2(Fe.Cy. + 2K.Cy.), acted on by six atoms of oil 
 of vitriol, 6(S.0;iH-H O.), produce three atoms of bisulphate of pot- 
 ash, 3(H.O. . S.O3+K.O. . S.O3), and three atoms of prussic acid, 3H. 
 Cy. ; there remains then an atom of Everitt's salt, 2(Fe.Cy. + 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 an- 
 hydrous acid, three parts of yellow prussiate of potash, in fine pow- 
 der, are to be decomposed by a mixture of two parts of oil of vit- 
 riol and two of water, in a small retort, at a very gentle heat, and 
 
518 TROPERTIES OF PRUSSIC ACID. 
 
 the product collected in a receiver, surrounded by ice, and contain- 
 ing some fragments of 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 cyan- 
 ide 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 anhydrous by the latter j 
 the vapour is then condensed in a receiver, surrounded by ice. 
 
 Pure prussic acid is a colourless liquid ; its specific gravity at 
 67^ is 0*6969 ; at 5'^ Fah. it congeals into a mass of fibrous crystals, 
 and at 80' 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 943-9, consisting of equal volumes of 
 cyanogen and hydrogen, united without condensation, as (1819'0-{- 
 68'8)-i-2=943'9. It reddens litmus paper feebly, and the tint dis- 
 appears by heat. Its odour is extremely 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 poi- 
 son of intense activity, the greatest care should be used in manipu- 
 lating 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. 514, but of which the composi- 
 tion is not well known. By contact with a strong acid, prussic acid 
 assimilates the elements of three atoms of water, and produces for- 
 mic acid and ammonia (C2N.H. and 3H.0. giving C2H.O3 and N. 
 H3). 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. 
 
 For medicinal use, the prussic acid is prepared in a very dilute 
 condition. The directions sometimes given in pharmacoposias to 
 distil over an acid of a specific strength, are, in practice, very dif- 
 ficult to execute, and might give rise to serious errors. The prop- 
 er method is to prepare an acid stronger than that required ; then, 
 to ascertain by accurate analysis its strength, and dilute it with dis- 
 tilled 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 : 1 lb. of crystallized yellow 
 prussiate of potash, in fine powder, is placed in a capacious retort, 
 and 2 lbs. of water poured on it ; to this is added a mixture of 12 
 ozs. of oil'of vitriol and 2 lbs. 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 lbs. of dilute acid are dis- 
 tilled over into a receiver containing already 1 lb. of distilled water j 
 there are obtained thus 3 or 4 lbs. of an acid containing from 6 to 
 8 per cent, of real acid. 200 grs. of this are weighed and decom- 
 posed by an excess of nitrate of silver j the cyanide of silver pre* 
 
DETECTION OF PRUSSIC ACID. 519 
 
 cipitated 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 pharmacopoeia, 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 1495 of cyanogen, the 200 
 grs. contained 15-53 of real acid, or 7-76 per cent. ; now, to reduce this to the Dublin 
 standard, divide 7-76 by 1-6, which gives 485; indicating that by adding 3-85 lbs. 
 of distilled water to each pound of acid, the mixture will have accurately the strength 
 directed by the pharmacopoeia. Some of this calculation may be spared by consid- 
 ering the cyanide of silver to be equivalent to one fifth of its weight of real prussic 
 acid ; the quantity per cent, in the supposed example should then be one tenth of 
 the weight of cyanide of silver obtained!^ from the 200 grs., that is, 7-4 per cent.; and 
 the water necessary 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 pharma- 
 copoeias differs very much : that prescribed by the London College 
 contains about 2 per cent, of real acid ; that of the Edinburgh Col- 
 lege contains about 4> per cent. ; while 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 prassic acid, by digest- 
 ing it on a known quantity of red oxide of mercury ; when the prussic acid has sat- 
 urated itself with the oxide, what remains is to be washed, dried, and weighed. 
 Now, as 116-4 of oxide of mercury is converted into cyanide by 27-1 of prussic acid, 
 which proportion 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 analyti- 
 cal purposes. 
 
 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 insoluble 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. 2d. 
 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 pre- 
 cipitate is produced, from which muriatic acid dissolves out the ex- 
 cess of oxide of iron, and leaves Prussian blue (cyanide of iron) of 
 a very rich colour : it is essential to the proper action of this test, 
 that both protoxide and peroxide of iron be present in the solution. 
 3d. If a solution of sulphate of copper be added to the liquor con- 
 taining 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 decompo- 
 sition occurs, sulphate of potash and a metallic cyanide being form- 
 ed. As the potash is always added in excess, a quantity of metal- 
 lic 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 recognised very elegantly by 
 heating them with a little potash and sulphur, and dissolving the 
 
520 CYANIDE OF POTASSIUM. ETC. 
 
 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. 
 
 There are two ddarides 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 cyanogen dissolves. This gas, which is very irritating and poisonous, 
 may be obtained crystallized in needles by exposure to a very low temperature. II 
 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 current of chlorine. It sub- 
 limes in white transparent needles. It dissolves unaltered in alcohol and ether, and 
 is decomposed by hot water into hydrochloric and cyanuric acids. 
 
 Iodide of Cyanogen is prepared by distilling, in a retort, a mixture of iodine, cyan- 
 ide 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°. 
 
 SECTION II. 
 
 OF THE 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 
 produced also whenever carbonaceous matter is calcined in contact 
 with potash, provided nitrogen be present. The best mode of ob- 
 taining 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 de- 
 composed, nitrogen being given off, and carburet of iron remaining 
 with the unaltered cyanide of potassium. The half-melted mass is 
 to be coarsely powdered, and digested in boiling, weak spirit of 
 wine, from which the salt crystallizes in cubes on cooling. Spirit 
 of specific gravity 0900 at 60^, is remarkable for dissolving a large 
 quantity of cyanide of potassium when boiling, but depositing it 
 nearly totally when it cools. 
 
 This salt in solution reacts alkaline, and smells of bitter almonds, 
 and hence probably decomposes water when dissolved. Its crystals 
 deliquesce and are decomposed, even in close vessels, after a short 
 time, by contact with water, into ammonia and formiate of potash. 
 
 The properties of the cyanide of sodium and of the hydrocyanate 
 of ammonia are quite similar. 
 
 The Cyanides of Barium, strontium, calcium, and magnesium are soluble in wa- 
 ter, 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 ©f copper to form an oxycyanide of a lively green colour. 
 It forais double salts with the alkaline cyanides. 
 
 Cyanide of Mercury — Hg.Cy. ;" Eq. 1594-4 or 127-45 — 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 recrystallized. The best 
 
f 
 
 CYANIDE OF MERCURY, ETC. 521 
 
 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 dry- 
 ness, and to digest the prussic acid so obtained with twelve parts 
 of finely-powdered oxide of mercury, until this is completely dis- 
 solved. 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 Prus- ^,.<-;55^^v. 
 sian blue may be obtained. 0^^^\ 
 
 Cyanide of mercury crystallizes in colourless rectan- 
 gular prisms, as q q, in the figure, terminated by numer- 
 ous secondary faces, as e e. These crystals are anhy- 
 drous, and occasionally opaque. When heated, it is re- 
 solved into mercury and cyanogen, of which a portion is resolved 
 into the brown powder (paracyanogen). It is sparingly soluble in 
 alcohol. It tastes as the other mercurial salts. So great is the 
 affinity of mercury to cyanogen, that cyanide of potassium, when 
 boiled with oxide of -mercury, is decomposed, and caustic potash 
 liberated. In a solution 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 mercury, combines 
 with it in two proportions, forming the oxycyanixles of Mercury, Hg.Cy.+Hg.O. and 
 Hg.Cy.+3Hg.O. These bodies are soluble in water, and crystallize in prismatic 
 needles. 
 
 With iodide of potassium, cyanide of mercury combines, forming a substance, 2 
 Hg.Cy.-fK.L, 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 simi- 
 lar compound is formed, •2Hg.Cy.4-K.Cy.S2. 
 
 Cyanide of mercury combines with the alkaline cyanides, and with the alka- 
 line 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 occasionally employed in 
 medicine. 
 
 Cyanide of Silver, Ag.Cy., 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 resembles mercury. 
 Every soluble salt of palladium is decomposed by prussic acid, a pale yellow precip- 
 itate 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 extensive class of double salts. 
 
 Cyanide of Gold, Au.Cya, is a pale yellow powder, forming double salts with the 
 alkaline cyanides. 
 
 Protocyanide of Iron, Fe.Cy., is not known in an isolated fou" lat 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 alkali, and hence may be looked upon as an element of the neg- 
 ative constituent ; they are hence often termed ferrocyanides, or ferroprussiates of 
 whatever other metal they may contain. 
 
 Ferrocyanide of Hydrogen. Ferrocyanic Jlcid. — Fe.Cy. -f-2H.Cy 
 When the ferrocyanide of lead is decomposed by sulphuret of hy 
 drogen, 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 ferrocy- 
 anides. If the solution be boiled, it is resolved into prussic acid, 
 
 Uuu 
 
522 FERROCYANIDE OF POTASSIUM. 
 
 and a white precipitate, which becomes blue in the air. The crys- 
 tals undergo the same change spontaneously after some time. 
 
 Ferrocyanide of Potassium. — Fe.Cy. + 2K.Cy. + 3 Aq. Eq. 2656*9 
 or 212*5. 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 pearl ashes 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 oper- 
 ation 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 j 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 dissolved iron enough, some copperas 
 is added as long as the Prussian blue, which at first forms, is found 
 to redissolve. After what has been said of the formation of cyan* 
 ogen (p. 513), the theory of this process may easily be understood. 
 
 The ferrocyanide of potassium crystallizes in truncated octohe- 
 
 A/^Z ~f~~^ 73 drons with a rectangular base, e e e', 
 
 /K e \ ''V /$^~7^^^^^c'''^) ^® ^^ ^^^ figure, of which A represents 
 
 l^ \ .XJ \>^^^^^^=^~^ the usual simple, and B a more com- 
 
 ^^/ ^ " -/^ ^^ — - — <C^ plicated form ; the secondary plane n 
 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 farther 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. With sulphate of mercury it gives sulphate of pot- 
 ash, cyanide of mercury, and Everitt's yellow salt. 
 
 With cyanide of mercury, ferrocyanide of potassium forms a 
 double salt, whose formula I found to be SHg.Cy. + (Fe.Cy. -f2K 
 CyO + '^ Aq. It crystallizes in pale yellow rhombic tables. 
 
 In the arts, the ferrocyanide of potassium is of importance for 
 dyeing various shades of blue j to the chemist it is specially of in- 
 terest, as from it all the cyanogen compounds are most economi- 
 cally formed, and from the peculiar precipitates it gives with solu- 
 tions 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 mercu- 
 ry gradually becomes blueish, and that of manganese reddish. With 
 copper, the precipitate is of a rich chocolate colour ; with cobalt, 
 greenish, changing to red ; with uranium and molybdenum, brown ; 
 and with chrome, grayish-green. All these precipitates contain cy- 
 anide of iron, united to two atoms of cyanide of the other metal, 
 being true ferrocyanides. 
 
 It is on solutions of iron that the action of this reagent is the most 
 remarkable. With solution of protosulphate of iron, a whitish pre- 
 cipitate is obtained, which consists of the cyanides of iron and po- 
 
PREPVRATION OF PRUSSIAN BLUE, ETC. 523 
 
 tassium, united in proportions which are not well known. Exposed 
 to the air, this body absorbs oxygen and becomes blue. With a so- 
 lution of sulphate of iron pure Prussian Blue is precipitated. This 
 substance is insoluble in water and in muriatic acid, and gives with 
 caustic alkalies oxide of iron and ferrocyanide of potassium ; its 
 formula is Fe7Cy9, or it consists of 3Fe.Cy.4-2Fe2Cy3. Its forma- 
 tion involves 3(Fe.Cy. + 2K.Cy.) and 2(FeA + 3S.03), and there re- 
 main dissolved six atoms of sulphate of potash. For the manufac- 
 ture of Prussian blue for the purposes of the arts, the impure liquor 
 obtained by digesting in water the calcined mass of animal matter, 
 potash and iron, described p. 522, 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 yel- 
 low prussiate of potash, is exposed moist to the air. It is termed 
 basic Prussian Blue. As Everitt's salt consists of 2Fe.Cy.4-K.Cy., 
 and 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 formed remaining united with the Prussian blue. From 9 
 Fe.Cy. and 30. there is thus formed 3(Fe.Cy.4-2Fe2Cy3H-Fe203), the 
 basic compound. 
 
 The ferrocyanides of Sodium, Barium, &c., possess all the essential characters of 
 the potassium salt, and need not be farther noticed. 
 
 The ferrocyanides in many cases combine with each other, forming salts, which 
 contain three different metals combined with cyanogen. 
 
 Sesqtiicyanide of Iron, FeaCy^, is not known in an isolated form, but, like the pro- 
 tocyanide, enters into a number of combinations with the other metallic cyanides, 
 which may be called either pe7 ferrocyanides or ferridcyanides, as proposed by Lie big. 
 
 Ferridcyanide of Potassium — Red Prussiate of Potash^ Fe2Cy3-f-3K. 
 Cy., is formed by passing chlorine through a solution of yellow prus- 
 siate 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 crys- 
 tals, which are generally macles. The products of its decomposi- 
 tion by heat are the same as those of the yellow salt. It dissolves 
 in thirty-eight parts of cold water j its solution, if pure, is yellow, 
 but more commonly is green. 
 
 This salt rivals that already described in its utility as a reagent 
 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 man- 
 ganese, brown. It is, however, with the salts of iron that its reac- 
 tion 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.Cyg, or of Fe^Cyg + SFe.Cy. ; thus containing the 
 same protocyanide with half as much sesquicyanide as exists in 
 common Prussian blue. This ferridcyanide of Iron is made for 
 commerce, and sold as TurnbulVs Prussian Blue. 
 
 Ferridcyanide of Hydrogen. — If we digest ferridcyanide of lead 
 
524 THEORY OF THE COMPLEX CYANIDES. 
 
 with dilute sulphuric acid, a red liquor is obtained, which yields on 
 evaporation a mass of minute brownish-yellow needles, the formula 
 of which is FeaCya-f-SCy.H. This body reddens litmus, and has a 
 sour astringent taste ; upon another theory it is considered to be a 
 compound of hydrogen with a compound radical, (FcaCye), and is 
 termed Ferridcyanic Acid. 
 
 In the history of these complex cyanides we meet three facts, on which the the- 
 ories of their constitution must be founded. 1st. The extraordinary tendency to 
 double combination^ which no other body possesses in the same degree. 2d. In 
 almost all cases, the cyanogen enters into the compound in the proportion of three, 
 six, or nine atoms ; and, 3d. One metallic element, as iron, in each compound, 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 con- 
 structed, 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, {Fe.Cy^) or Cfy., and Ferridcyanogen, (FejCye) or Cfya, these 
 two being isomeric ; Cohaltocyanogen, (CozCye) or Cky., and many others ; and these 
 radicals combine with hydrogen to form polybasic hydracids, from which, the hy- 
 drogen 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 salts formed by Mosander are produced : thus, the salt writ- 
 ten on Berzelius's view as (Fe.Cy.4-2K.Cy.)-f (Fe.Cy.-i-2Ca.Cy.) becomes Cfy.-{- 
 Ca.K., and similarly there is Cfy.-f Ca.K., &c. 
 
 The red prussiate of potash Liebig supposes to contain a radical, (FcoCye) or 
 Cfy 2, isomeric with, but of double tlie atomic weight of ferrocyanogen ; this fer- 
 ridcyanogen forms with hydrogen a tribasic acid, Cfya+Hs, by replacement of the 
 hydrogen, in which, by three atoms of the same or of different metals, the various 
 ferridcyanides are produced, as Cfya-j-Ks, Cfy2-f-3Cu., &c. 
 
 The Prussian blues, on this theory, are considered to be compounds of ferro- 
 cyanide with ferridcyanide of iron ; thus, 
 
 SCfy.Fca+CfyaFea expresses common Prussian blue. 
 CfyaFcg " Turnbull's Prussian blue. 
 
 SCfy.Fea-hCfyjFea-l-FezOa " basic Prussian blue. 
 
 This theory accounts very strictly for the first and third of the fundamental 
 facts which I have described as characterizing the cyanogen compounds. 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 re- 
 lation to metals, but to oxygen, as in cyanuric acid, and hence we may assume 
 that cyanogen, as Cyg, with three times its ordinary atomic weight, forms a dis- 
 tinct radical {paracyan ?), which forms with oxygen and with hydrogen tribasic 
 acids, CygOg and CygHg. 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, 
 
 Cyg-|-Fe.2K. . . . yellow prussiate of potash. 
 Cys-j-Fe.K.Ca. . . ferroprussiate of lime and potash. 
 Cy3-\-Fe.2Il. . . . ferroprussic acid. 
 
 The basis of the red prussiate of potash should be, then, another polymeric cyano- 
 gen, Cye, which would form, with hydrogen, a pentabasic acid, Cye-j-Hs, in which 
 more or less of replacement by metals should give the various ferridcyanides. 
 Thus ferridprussic acid should be Cys+FesHa, and red prussiate of potash Cye-f 
 FejKs, and so on ; Turnbull's Prussian blue becomes, on this theory, simply Cye-f 
 Fcg ; the common Prussian blue is (Cy3-4-Fe2)4-Cy6Fe5 ; and, by the addition of 
 Fe203 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 Cyg. 
 
METALLIC S U L P 11 O C y A X I D E S. 525 
 
 Of Sulpho cyanogen^ 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 ves- 
 sel to perfect fusion, which takes place at a dull red heat, the sul- 
 phur combines with all the cyanogen, forming sulphocyanogen, 
 which unites with the potassium, while the iron is converted into 
 sulphuret. By digesting the fused mass in water, the former dis- 
 solves, and is obtained, by evaporation and cooling, in long striated 
 prisms, similar to those of nitre. If the temperature be not raised 
 too high, the iron forms also sulphocyanide, which dissolves, and 
 may be decomposed by the addition of a slight excess of carbonate 
 of potash ; by this means one half more product may be obtained 
 than is yielded if the sulphocyanide of iron be too violently heated, 
 and thereby converted into sulphuret. 
 
 Sulphocyanogen is prepared by 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 sulphui* and cy- 
 anogen of the salt, its formula being Cy.So. It is very light, and 
 insoluble in water. It combines with all the metals and with hy- 
 drogen, forming well-defined salts. 
 
 Hydrosulphocyanic Acid, Cy.Sa + H., is formed by decomposing 
 sulphocyanide 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. 
 
 Sulphocyanide of Potassium. — Cy.S^+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 labor- 
 atory as a test for peroxide of iron. 
 
 Sulphocyanide of Lead is a crystalline powder, prepared by mix- 
 ing solutions of a salt of lead and of sulphocyanide of potassium. 
 
 Of the sulphocyanides of Iron, the protosalt, Fe. + Cy.S^, forms a 
 colourless solution, which becomes red on exposure to the air. The 
 sesquisalt, Fe2+3Cy.S2, forms a deep blood-red liquor, when a sol- 
 uble sulphocyanide 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 prus- 
 sic acid, as noticed p. 520. 
 
 These sulphocyanides may be considered either as double sul- 
 phurets of cyanogen and of a metal, as Cy.S.+S.K., &c., or as salts 
 of the compound radical sulphocyanogen, Cy.S2+K., &c. The 
 latter view has been almost universally adopted by chemists. 
 
 It appears, however, from the researches of Parnell, that al- 
 though sulphocyanogen really exists in these salts, yet the yellow 
 substance extracted from them by chlorine or by nitric acid, as de- 
 scribed just now under that name, is only a product of the decom- 
 position of the real sulphocyanogen, which has not been as yet iso- 
 lated. The formula of the yellow powder he finds to be S.^CiaNg . 
 H3O. When acted on by alkalies or by nitric acid, it produces an 
 acid which he terms the Thiocyanic, which is polybasic. It is a 
 
526 MELLON, M E L A M, ETC. 
 
 pale yellow powder, sparingly soluble in water, more so in alcohol. 
 Its formula is SjaCioNj . H^02. 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 ; the others have not been 
 examined. 
 
 Mellon. — When sulphocyanogen is heated, it is decomposed, 
 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 is a compound radical, analogous to cyanogen in 
 its characters. It is insoluble in water, alcohol, or dilute acids. Its 
 formula is C6N4 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. 
 
 Hydromellonic Acid, H.Ml., 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, H.Ml.-j-Aq. 
 
 Mellotiide of Potassium, K.Ml., is produced by adding mellon to sulphocyanide 
 of potassium, fused .in a porcelain capsule ; sulphur and sulphuret of carbon are 
 evolved. On dissolving the brown mass thus formed in boiling water, the mellon- 
 ide of potassium crystallizes, on cooling, in fine colourless needles. 
 
 If we take the formula of sulphocyanogen at C2N.S2, the formation of mellon con- 
 sists in 4(C2N.S2), producing 2(C.S2) with 4S., and leaving C6N4 ; but, on Mr. Par- 
 nell's view, the decomposition is by no means so simple. 
 
 When mellon is boiled with strong nitric acid, it dissolves, and, on cooling, the 
 liquor yields octohedral crystals of Cyanilic Acid. This substance has the same for- 
 mula as cyanuric acid, CyaOa-f-S Aq., but its relations to bases are not well under- 
 stood. Nitrate of ammonia is formed ; mellon, C6N4, and three atoms of water, 
 giving CeNsOa and N.H3. 
 
 Melam. — C12H9N11. Sulphocyanide of ammonium, on being heated, is decom- 
 posed into ammonia, sulphuret of carbon, and sulphuret of hydrogen, which pass off, 
 while a grayish-white powder remains, which is Melam. The same result is ob- 
 tained by heating to fusion a mixture of sulphocyanide of potassium and sal am- 
 moniac : 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 alkaline solutions, giving origin to a series of 
 remarkable bodies. 
 
 Melamine, CeCeNe, 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 be- 
 gins to deposite small crystalline plates, and being then allowed to cool, the mel- 
 lamine crystallizes out in colourless 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. — CeNs . H5O2. After the alkaline 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 C12H11 . NnOj producing CeHeNs and CeNs . H5O2. 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 acid, and the 
 solution be precipitated by alcohol, a white powder is obtained, insoluble in water 
 and alcohol, but soluble in strong acids and alkalies. 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 C12H7 . N904-|-2 Aq. When this body is boiled for a long 
 time with dilute sulphuric or nitric acid, it is resolved into ammonia and Cyanuric 
 Acid, which last is the ultimate product of the similar treatment of all the bodies of 
 this series. 
 
OP STARCH, ETC. 527 
 
 The theoretical constitution of these bodies remains exceedingly obscure. The 
 bases, melamine and ammeline, are of great importance, from their close analogy 
 to the alkaloids, 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 muck 
 notice. Cyanogen and sulphuretted hydrogen combining, form orange crystals, in- 
 soluble in water. 
 
 CHAPTER XX. 
 
 OF STARCH, LIGNINE, GUM, AND SUGAR, WITH THE PRODUCTS OF THEIR 
 DECOMPOSITION BY ACIDS AND ALKALIES. 
 
 The substances now to be described form a very remarkable class 
 of organic bodies. They are found abundantly in most plants, but 
 varying somewhat in characters, according to their immediate 
 source, and are subservient to the most important offices of the 
 vegetable organization, 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 compo- 
 sition, 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 reagents, or by the organic power -of the plant. 
 In these bodies, also, we find an example of the difficulty of distin- 
 guishing between a constitution derived from physical, and that re- 
 sulting from vital force. In the different kinds of sugar, the crys- 
 talline condition, solubility, &c., indicate that the elements are 
 combined by forces merely chemical ; but in the different varieties 
 of starch, and especially in lignine, 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 j^rrow-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 struc- 
 ture. They differ in size in almost every plant. Those of the po- 
 tato, which are the largest, do not exceed in diameter o j^^^ of an 
 inch ; those of arrow-root, which are some of the smallest, do not 
 exceed ^ ^o^^* ^^ form, these grains vary also, some being globular, 
 
528 PRE PAR AT I O'N OF STARCH, ETC. 
 
 Others ovoidal,, and often, eve^^. 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 solu- 
 tion 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 
 grinding, 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 deposite themselves when the liquors are left at 
 rest. In obtaining starch from wheat, this liquor is allowed to fer- 
 ment 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 temperature of about 140^, 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 fer- 
 mentation. It is artificially induced by malting the grain, for the 
 preparation of alcoholic liquors by brewers and distillers. The cir- 
 cumstances .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 British Gum. 
 
 The action of reagents on starch is very remarkable. By boiling 
 with dilute sulphuric or muriatic acids, a kind of saccharine ferment- 
 ation is induced, it being changed successively into gum, sugar, 
 and sacchulmine. By boiling with nitric acid, it gives saccharic 
 and oxalic acids. These reactions will be hereafter studied in de- 
 tail. 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 add- 
 ed 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 alco- 
 hol to a very strong aqueous solution, and collecting the precipi- 
 tate on a filter. It is decomposed by alkalies and hy chlorine ,• in- 
 deed, by all bodies which combine with iodine ; and its formation 
 serves, therefore, as a test only for free iodine, as described in p. 
 
I 
 
 INULIN, LICHENINE, AND LIGNINE. 529 
 
 313. When a solution of iodide of starch is heated, it becomes 
 quite colourless below 200°, and, if it be not boiled, regains its col- 
 our 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 combination it had formed. 
 
 The composition of starch, no matter what plant it may be deri- 
 ved from, is C,2H,oO,o, as confirmed by a variety of reactions. Its 
 combination with oxide of lead, Amylate of Lead, is Cj2HioOjo4-2 
 Pb.O. 
 
 Jnulin. — This kind of starch is found in the roots of the inula, dahlia, angelica, 
 leontodon, and many other plants. It may be prepared in the same way as common 
 starch. It is a white and very fine powder, almost insoluble in cold water, but easi- 
 ly dissolved by boiling water ; forming a liquor which becomes thick, but not gelati- 
 nous, when it cools, and deposites 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 pecu- 
 liarly 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 ex- 
 amined. Its formula is C12H10O10, like that of common starch, but in combining 
 with oxide of lead it appears to lose one atom of water, and to become C12H9O9, as 
 remarked by Parnell. 
 
 Licheniyie. — This variety of starch, which is found in many lichens, especially the 
 Iceland moss and the carrigeen (sphcero coccus 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 carbonate of soda, to dissolve the bitter resinous princi- 
 f)le, 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 gray 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 fonnula as the others, C12H10O10. 
 
 Of Lignine. Principle of Woody Fibre, 
 
 When any kind of wood is treated successively and repeatedly 
 by dilute acids and alkalies, 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 CjaH^Oj;. 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 con- 
 stitute the materials of our most important woven textures, of pa- 
 per, &-C. Although the lignine is thus rather the remains of an or- 
 ganized body than a mere chemical substance, it forms some com- 
 binations 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 o-xides have a similar, though 
 weaker affinity for lignine, and thus serve as mordants for various 
 colours. 
 
 Lignine, when quite pure, is white ; the bleaching of linen, cot- 
 ton, paper, &c., being eflfected 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 j the lignine it- 
 self resists these agents, unless applied in a very concentrated form 
 
 X X X 
 
530 ARABINE AND TRAGACANTHINE. 
 
 With cold nitric acid lignine combines directly, forming a very re- 
 markable substance, Xylo'idine, which may be produced by immer- 
 sing 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. Hot 
 nitric acid converts lignine into oxalic acid ; with sulphuric acid it 
 is changed into gum, and ultimately into sugar, as will be detailed 
 farther on. 
 
 If sawdust be heated with a warm solution of potash for some 
 hours, 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 decom- 
 posed. 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 ace- 
 tate and oxalate of potash results 5 C,2Hs08 and 4H.0. giving 6H., 
 with 2(C,03) and 2(0^03). 
 
 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, lig- 
 nine 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 the different Varieties of Gum. 
 
 It is necessary to distinguish three varieties of gum, to which 
 the names of Arahine^ Cerasine^ and Dextrine may be given. The 
 first two are natural, the last is a product of the transmutation of 
 starch. 
 
 Arahine is found in the juices of many species of acacia and pru- 
 nusj it exudes from crevices in the bark, and forms lumps, in which 
 state it is found in commerce (^Gum Arabic and Gum Senegal). The 
 roots of mallow, comfrey, and many other plants contain a great 
 deal of arabine. It is never crystalline, and is colourless and trans- 
 parent, 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. 41). 
 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 afterward 
 oxalic acid ; another characteristic property of it is, that of giving 
 a precipitate with solution of silicate of potash (soluble glass, p. 
 437). Its composition is expressed by the formula Ci^HnO,,. 
 
 Tragacanthine^ or Vegetable Mucus, exists in cherry-tree gum mix- 
 ed with arabine, but is purer in gum tragacanth, in flaxseed, and in 
 quince- seed. It is extracted by digestion in water, when it gradu- 
 
DEXTRINE. CANE-SUGAR. 531 
 
 ally swells up and appears rather to imbibe the water than to dis- 
 solve ; 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 vit- 
 riol 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 sul- 
 phuric 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 
 aftected by silicate of potash. If dextrine be boiled too lo«ng with 
 the sulphuric acid, it passes into a substance more analogous to 
 tragacanthine, 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 CiaHjoOio. 
 
 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 charac- 
 terized by being capable of undergoing the alcoholic fermentation. 
 
 Cane-sugar. — C,2HioO,o+Aq. when crystallized. This species of 
 sugar is found abundantly in the juices of many plants. It is ex- 
 tracted for use from the sugar-cane, the maple, and the beet-root. 
 The juice, when fresh, runs into fermentation with great quick- 
 ness, and is therefore clarified by being warmed to 150^, with a lit- 
 tle lime, by which the vegetable albumen is coagulated, and the fer- 
 mentation checked. The juice is then evaporated with as little 
 heat as possible, and allowed to 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 li- 
 quid uncrystallizable portion constitutes Molasses, or Treacle. To ob- 
 tain the sugar pure, it is redissolved, and the liquor having been 
 cautiously evaporated (in some establishments, in vacuo, see p. 85) 
 to the necessary degree, is poured into cones of unglazed earthen- 
 ware, 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 
 
532 SACCHULMINE. SACCHARIC ACID. 
 
 crystals very minute and close, the plug below is removed, and tha 
 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 throuo-h. 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 heat- 
 ed, it fuses at 350^ into a clear yellow liquid, and congeals, on cool- 
 inor, into a hard brittle mass (barley-sugar), which, after some weeks, 
 becomes 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 decom- 
 posed. Sugar dissolves in one third of its weight of cold, and in all 
 proportions 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 uncrystalli- 
 zable sugar; hence arises the most important source of loss in the 
 manufacture and refining of sugar. It is sparingly soluble in abso- 
 lute alcohol, and but moderately in weak spirit. 
 
 Suga? combines with some bases and salts, acting as a feeble acid j 
 the compound with oxide of lead is insoluble, and has the formula 
 C,2H,oO,o4-2Pb.O. ; that with barytes is crystalline: its formula is 
 C,2H,oO,o+Ba.O. With common salt sugar combines, forming crys- 
 tals, easily soluble in water, and consisting of Ci^HioOio + Na.Cl. 
 
 The action of acids on cane-sugar is very remarkable. When di- 
 gested 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 alkaline liquors. The former is termed Sacchulmine^ 
 the latter, Sacchulmic Acid. These bodies are formed even with 
 very dilute acids if the digestion be continued for a long time. Ac- 
 cording as the reaction proceeds, the sacchulmine separates in mi- 
 nute 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 established, as it appears to be influ- 
 enced by the strength of the acid used and other circumstances. 
 The best-grounded idea is, that they have both the same composi- 
 tion, CaoH,50|5, being isomeric with ulmine. If in this reaction the 
 atmospheric air have access, oxygen is absorbed, and a large quan- 
 tity of formic acid generated. • 
 
 The preparation of oxalic acid by means of nitric acid and sugar 
 has been already described (p. 493). If 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 de- 
 composed by acetate of lead, a white precipitate 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 so- 
 lution. This is termed the Saccharic Acid. It gives an extensive 
 series of salts, being a pentabasic acid. Its formula is Q^JlfS^u-\-^ 
 H.O. when crystallized. Its potash salt is CjzHiOa-fK.O. . 4H.0. 
 
GRAPE-SUGAR. 533 
 
 Its lead salt CizHsOn+SPb.O. 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 sac- 
 charate of silver is decomposed by heat ; metallic silver being de- 
 posited, and forming a mirror-surface on the interior of the vessel. 
 
 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 com- 
 bines with bases j its formula is CiaHgOg. The sugar, in forming it, 
 therefore, loses the elements of an atom of water, besides its water 
 of crystallization. By heating sugar with lime, a volatile liquid is 
 obtained, which has the formula CeHjO., and is termed Metacetone. 
 
 Grape'SVgar. Glucose. — C12H,, 0,1+3 Aq. 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 ger- 
 mination, and by artificial processes. In consequence of this vari- 
 ety of sources, it is better to term it glucose, as suggested by Du- 
 mas, 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 Qgg^ and evaporated to crystallization. 
 
 From starch, gum, or cane-sugar, it may be prepared by the ac- 
 tion of sulphuric acid as follows : one part of potato-starch is to be 
 boiled with four parts of water and -V^^ ^^ ^i^ ^^ 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 will be de- 
 tailed 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 convert- 
 ed into a 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 3 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, ia granular crystals, which contain alcohol combined. It 
 
534 CONSTITUTION OF GRAPE-SUGAR. 
 
 combines with bases, forming compounds analogous to those given 
 by cane-sugar. 
 
 The composition of crystallized grape-sugar is C,2H,40i4, or CigHn 
 Oh + 3 Aq. When fused at 212°, it becomes C,2H,^0,2, or C,2H„0h 
 +Aq. Its compound with chloride of sodium, which crystallizes 
 in fine double six-sided pyramids, consist of 2(C|2H,20i2)4-Na.Cl.+ 
 2 Aq. With a solution of basic acetate of lead it gives a white 
 precipitate, the formula of which is C,2Hi,Oi, + 3Pb.O., correspond- 
 ing to the crystallized 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 contained in the grape-juice or in the juice of the flowering 
 grasses, rotates 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, receives its name of dextrine from that 
 quality. 
 
 As lignine, starch, gum, and cane-sugar all contain the same quan- 
 tity of carbon (C,2), their transformation into grape-sugar consists 
 evidently in the fixation of the elements of water j thus lignine, 
 Ci^HgOs takes 4H.0., and 100 parts of sawdust have been found to 
 give 115 of sugar; starch (C|2H,oOio) takes 2H.0., 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 Sulphosaccharic. Sugar of starch or grapes is to be 
 fused at a low heat, and 1| 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,2HHO„) + S.03+4^Pb.O. 
 
 In acting on grape-sugar, nitric acid gives rise to the same pro- 
 ducts, 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 de- 
 rived from the latter. On this view its formation is more easily 
 explained ; for as the dry glucose is C,2H,|0|„ and the saccharic acid 
 is C,2H^0,,, the oxygen of the nitric acid simply removes six atoms 
 of the hydrogen of the grape-sugar, and the elements of the acid re- 
 main. 
 
 By contact even with the strongest bases, cane-sugar is but slowly 
 altered, and hence lime may be employed to clarify the vegetable jui- 
 ces which contain it ; but, under the same circumstances, grape-su- 
 gar is rapidly decomposed and an acid formed, which is termed Glu- 
 cic Acid. It is very soluble in water, and does not crystallize ; with 
 lime, barytes, and lead, it forms neutral soluble salts, but it precip- 
 itates a solution of basic acetate of lead. Its taste is purely acid. 
 
L A C T I N E. M A N N I T E. 535 
 
 and it reddens litmus. Its composition is CiaHgOg, and it is isomeric, 
 therefore, in its dry state, with lignine. When a strong solution of 
 caustic potash is added to fused grape-sugar boiled, the glucic acid 
 which at first forms is decomposed. The liquor becomes deep 
 brown, and yields, on the addition of muriatic acid, a black fioccu- 
 lent precipitate of Melassic Acid. The formula Ca^HiaOjo has been 
 assigned to it, but its nature is not well know^n. 
 
 Lacfine, 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, semi- 
 transparent, 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 270°, 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 C24H19O19, and of the crystals 
 C24H19O194-5 Aq. By mixing solutions of sugar of milk and of basic acetate of 
 lead, a wliite precipitate is produced, the formula of which is C24Hi90i9-f-5Pb.O. 
 
 By digestion with dilute sulphuric acid, sugar of milk is changed into grape-sugar, 
 and then produce the other reactions already described. With alkalies the decom- 
 position is also the same as that of glucose, but the action of nitric acid on lactine 
 differs from that on any other sugai, 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 cool- 
 ing. It is a crystalline powder, gritty under the teeth, and feebly acid. It dissolves 
 in six parts of boiling water, but is insoluble in alcohol. Its crystals have the form- 
 ula C)2HioOi6, being formed from gum by the simple addition of six equivalents of 
 oxygen. This formula contains, however, 2 Aq., as it is a bibasic acid, and its salts 
 consist of C2iH80i4-|*2M.O. The alkaline mucates are soluble, the earthy and me- 
 tallic 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 evolv- 
 ed, and a sublimate forms in brilliant white plates, which are soluble in alcohol and 
 water ; CuHioOie giv^ 20. O2 and 6H.0., besides C10H4O6, 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 equivalent of base ; those of lead, 
 barytes, and silver are insoluble ; those of the alkalies are very soluble in water. 
 
 With this acid a certain quantity of chlorine may be combined, forming Chloro- 
 pijromucic Acid, C10H3 . CI4O5, which is prepared by acting with chlorine on Pyro- 
 mucic Ether. 
 
 Sugar of Mushrooms 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 C12H13O13, but little is known accurately of this va- 
 riety of sugar. 
 
 Of Mannite and Glycyrrhizine. 
 
 These bodies are connected so closely with the true sugars, that, although want- 
 ing in the characteristic of forming alcohol by fermentation, they may be best de- 
 scribed here. 
 
 Mannite, CeHvOs, 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 while 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 it crystallizes in 
 brilliant white prisms of silky lustre. When heated gently, it fuses without losing 
 
536 LACTIC ACID. GLYC YRRHIZINE. 
 
 weight. With nitric acid it gives oxaUc and saccharic acids. It does not appeal 
 to combine with bases. 
 
 If the unclarified juice of the beet or carrot root be kept at a temperature of 100^ 
 for some time, a tumultuous decomposition sets in, which is termed the mucous fer- 
 mentation. Ail 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 aU 
 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 
 reaction 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 ; 
 while, by abstracting two atoms of oxygen from an equivalent of crystallized grape- 
 sugar, the constituents of two atoms of mannite remain. 
 
 Lactic acid is most easily prepared by means of this mucous fermentation, but 
 may be also obtained abundantly from sour whey, or the sour waters obtained in 
 making wheaten starch. The acid liquor is to be neutralized by carbonate of lead, 
 and the solution of lactate of lead evaporated until it is tolerably concentrated. It 
 is then to be decomposed by sulphate of zinc, and the precipitated sulphate of lead 
 being removed by the filter, 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 dis- 
 solves. The solution is to be placed in vacuo over sulphuric acid ; it gives a sirup- 
 thick liquor, which has the formula CeHsOe or CeHsOa-^Aq., as it contains an atom 
 of basic water ; it tastes strongly acid. When heated to 480° it gives off water, 
 and a white smblimate forms in brilliant white rhomboidal plates, which is Paralac 
 tic Acid. It is purified by solution in boiling alcohol, from which it crystallizes. 
 The composition of this body is C6H4O4 ; 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 crys 
 tallize. 
 
 The lactic acid coagulates albumen ; it mixes with milk when cold, but coagu- 
 lates it when boiled. It forms monobasic salts, in which its formula is CeHsOs, 
 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, C6H505-i-Fe.O.-f3 Aq., may be obtained crystal- 
 lized 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 medicine. 
 
 The lactic acid will be again noticed as a constituent of the animal system. 
 
 Glycyrrhizine. — This substance, which is found in the liquorice-root, and in some 
 other sweet woods, is obtained by boiling the root or liquorice in water, and, after 
 concentrating the liquor, adding thereto sulphuric acid. A white precipitate, con- 
 taining the glycyrrhizine combined with sulphuric acid and albumen, is formed. 
 This is to be washed with acid water, and then with pure water, -and to be dissolv- 
 ed in alcohol, which leaves the albumen. The alcoholic solution is to be decom- 
 posed by carbonate of potash, which throws down ths sulphuric acid, and by evap- 
 orating the filtered liquor, the sweet principle remains pure as a yellow transparent 
 
 Its most remarkable property is that of combining very definitely with acids and 
 bases, and with several neutral salts. Almost every acid precipitates a compound 
 from a solution of glycyrrhizine. It expels the carbonic acid from the carbonates 
 of potash, soda, and barytes, combining with the base, and it precipitates the solu- 
 tions of most of the ordinary metallic salts. Neither the pure substance nor any 
 of its compounds have been accurately analyzed. 
 
GLUTEN, MUCIN, AND ALBUMEN. 537 
 
 CHAPTER 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 al- 
 cohol is generated. If, however, the solution of sugar be brought in con- 
 tact with any organic substance which is itself in the act of slow decom- 
 position, 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 albu- 
 men 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 off, 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 collected and dried. 
 
 Vegetable Gluten so obtained is pale yellow, and forms, when soft, an 
 adhesive mass, very extensive and elastic. Its solution in alcohol ia 
 thick-fluid when concentrated ; insoluble in ether ; it dissolves in acetic 
 acid, and in alkaline solutions. It combines with the mineral acids, 
 forming bodies very sparingly soluble in water, which are precipitated 
 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. 
 
 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 dissolv- 
 ed. 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 solution is 
 coagulated by heat ; it dissolves in alkaline liquors. Its solutions 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 
 
 Y T Y 
 
538 L E G U M I N. N ATURE OF YEAST. 
 
 infusion of galls, the solution of vegetable albumen in acetic acid gives 
 white precipitates. 
 
 Legumin. — This substance, which exists in pease and beans, possesses 
 properties intermediate to those of the gluten and albumen of wheat. 
 When powdered pease 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 solution 
 is not coagulated by heat ; it is insoluble in alcohol. It dissolves in so- 
 lutions of the vegetable acids, and is precipitated on the addition of a 
 mineral acid. It dissolves in alkalies, 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 prod- 
 ucts ; in the case of casein and lupuline probably amounting to identity. 
 In contact with air and water, these bodies enter spontaneously into 
 decomposition, evolving carbonic acid and ammonia, and forming new 
 products ; and in this state of decomposition they superinduce the alco- 
 holic 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 absorbed, the vegeto-animal 
 body begins to putrefy, and the sugar is soon engaged in the decomposi- 
 tion. It is remarkable, that the necessity for oxygen is at the com- 
 mencement of the decomposition : when the putrefaction of the albu- 
 men or gluten has once begun, it extends itself throughout its whole 
 mass without requiring any farther action of the air. 
 
 The principles of the conservation of vegetable juices, by enclosure 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 sulphite 
 of potash, which absorb any traces of oxygen that may be present, 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 fer- 
 ment^ 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 farther putrefaction. 
 
 When a solution of pure sugar is fermented by contact with a certain 
 quantity of yeast, this last is found to be very much diminished in quan- 
 tity, 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 decomposition as the added 
 
ALCOHOLIC FERMENTATION. 539 
 
 portion of yeast, and thus form a new and larger quantity of active fer- 
 menting material. Thus, in a brewery, the quantity of yeast continu- 
 ally 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. Alter a few hours a slight effervescence is 
 observed, and the liquor becomes turbid, as if pipeclay 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 
 when the gas- bubbles have broken. This circulation continues until the 
 fermentation has ceased, when the precipitate collects at the bottom. 
 The liquor no longer tastes sweet ; it contains no sugar, but in place of 
 it an equivalent quantity of alcohol. An infusion of malt does not so 
 readily ferment as the grape juice, unless some yeast be first added. Id 
 its spontaneous fermentation, most of the gum and sugar which it con 
 lains passes into the mucous fermentation, while but little alcohol is 
 formed. In the practical manufacture of malt-drinks and spirits, there- 
 fore, 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 alcoholic 
 fermentation, yet the different kinds of sugar enter on that process 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 superinducing the al- 
 coholic 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 212°, contains exactly the elements of two atoms of alcohol 
 and four of carbonic acid, as 2(C4H602) and 4C.O2 arise from CiaHigOu. 
 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 car- 
 bonic acid and alcohol ; and it has been ascertained by experiment that 
 100 pans actually give 104, while by theory 105 should be produced, 
 consisting of 51*3 of carbonic acid and 53*7 of alcohol. This coinci- 
 dence of numbers proves that these bodies are the only products. The 
 influence of the yeast is, therefore, strictly what Berzelius terms cata- 
 lytic, but its action becomes much more definitely intelligible by consid- 
 ering it as a case of the general principle expressed by Liebig, that mo- 
 tion (decomposition) may be communicated from the particles of one 
 body (yeast) to those of another (sugar) by virtue of proximity, as de- 
 scribed more fully in p. 235-237. 
 
 As farther details of the circumstances of the alcoholic fermentatioa 
 
540 CONSTITUTION OF ALCOHOL. 
 
 would 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 
 as these lead to purely technical descriptions of the arts of brewing, 
 &c., I shall not enter on them. 
 
 Of 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 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 con- 
 taminated by minute traces of essential oils, characteristic of the plants 
 from which the saccharine liquor has been obtained, it constitutes the 
 potato-spirit, brandy, malt-whiskey, arrack, rum, &c., of commerce. In 
 a still stronger form it constitutes the sjpirit 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 redu- 
 ced to 0*813 at 60°, in which state it still contains 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 ab 
 solute alcohol ; the rectified spirit containing about 83 per cent., and 
 having the specific gravity 0*839 at 60° F. 
 
 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 
 a-lcohol 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. 0*820, 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 0-800, 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 conse- 
 quently 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. 87. 
 
 Alcohol thus obtained anhydrous has a sp. gr. of 0*7947 at 60° ; it 
 boils at 168° ; tne specific gravity of its vapour is 1601 ; it does not 
 become solid even in the most intense cold ; its taste is burning and dry 
 upon the tongue, owing to its abstracting water from its tissue. It is 
 highly inflammaole, and 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 mix- 
 es with water in every proportion, contracts in volume, and evolves 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 occu- 
 
USES OF ALCOHOL. 541 
 
 pies only 100 volumes, and its sp. gr. is 0;927, being a little denser 
 than proof spirit. 
 The formula of alcohol is C^HeOz, and its composition is, 
 
 4 equivalents of carbon, =24-2 . . . 5266 
 
 6 " " hydrogen, = 60 . . . 12 90 
 
 2 " " oxygen, =160 . . . 34-44 
 
 The equivalent of alcohol, =462 . . . 10000 
 
 This is cwfifirmed by the products of its decomposition, and by the specific giavit? 
 ©fits vapouf; for, 
 
 4 volumes of carbon vapour . (843x4)=3372 
 12 " hydrogen . . (688x12)= 825-6 
 
 2 « oxygen . . (1102-6 x2) =22052 
 
 Give four volumes of alcohol vapour . 64028 
 Of which one volume weighs . . . . 1600 7 
 
 It will be fcuown, however, that alcohol consists of ether united to water, and that 
 Its formula is C4H50.-|-Aq. Its vapour is then formed by the union of 
 
 i volume of vapour of ether, =12906 ) iqqq.j 
 ^ volume of vapour of water, = 310- 1 J 
 
 The uses of alcohol in chemistry and pharmacy are numerous and 
 important. It dissolves the caustic alkalies and most deliquescent salts, 
 combining with them to form alcoatesy 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 efflorescent salts are 
 generally insoluble in alcohol, and may be even precipitated 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 res- 
 inous varnishes, and various other processes. To the chemist it is 
 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 com- 
 position of which the acid employed generally enters. 
 
 Of Sulphuric Ether, Ether, Oxide of Ethyle, 
 
 This substance may be prepared by any process which deprives alco- 
 hol of the equivalent of water which it contains. Thus, if potassium be 
 placed in contact with absolute alcohol, hydrogen gas is evolved, and a 
 compound of ether and potash crystallizes, 041150. -j-H.O. ahd K. giving 
 C4H6O.+K.O. and free H. If a current of gaseous fluoride of boron 
 
542 
 
 PREPARATION OF ETHER. 
 
 (p. 326) be passed into alcohol, it is absorbed, and boracic acid separates 
 in crystals, while 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 obtained ; 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 
 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, d d, 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 e. The tube d d fits water- 
 tight by corks into a tinned cylinder c, the proportions of which may be 
 judged from the figure ; this is kept full of cold water. When the distil- 
 lation 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 would soon get hot, were not the water constantly changed ; 
 by the funnel/, a stream of cold water flows from the reservoir i into the 
 lower part of the tube c, and presses up before it the warm and lighter 
 water, until this is expelled by the tube h, when it is collected at h. 
 The supply of cold water should be so proportioned to the supply of va- 
 pour, thai, flowing away at h, it should not be sensibly warm to the 
 hand. With this precaution, most volatile liquids may be perfectly con- 
 densed even in the midst of summer. The mixture 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, collects in the receiver. 
 
 Since th^ quantity of sulphuric acid continually increases in the globe 
 as the distillation proceeds, its action on the remaining alcohol changes, 
 
CONTINUOUS FORMATION OF ETHER. 543 
 
 the mixture becomes dark coloured, an oily substance distils over (oil of 
 wine), and the quantity of ether formed diminishes rapidly. Sulphurous 
 acid and defiant 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 lar- 
 ger product obtained, by admitting to the globe, by means of the bent 
 funnel, 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 reduced to the strength of S.03-f4 Aq. 
 
 Although we may represent the results of this reaction by considering 
 the sulphuric acid to take water directly from the alcohol, and set 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 disengaged, 
 and the sulphuric acid and ether unite to form Sulphate of Ether, (C4H5 
 O. + Aq.) and S.Oa+Aq. giving C4H5O. + S.O3 and 2 Aq. This body, 
 which resembles very much sulphate of ammonia in its tendency to com- 
 bination, 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 sul- 
 phuric 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 decom- 
 pose more alcohol ; hence, if absolute alcohol be used, 3(C4H50.-{-Aq.) 
 with 8(S.03 . H.O.) produce 3(C4H50. . S.O3+H.O. . S.O3) and 2(S. 
 O3-I-4 Aq.), one fourth of the sulphuric acid remaining over ; if a weak- 
 er 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 vi^iol 
 results, therefore, not from the water being seized on by the oil of vimol, 
 but from the decomposition of its compound with sulphuric acid, the sul- 
 phate of ether; the ether being a base not much superior in energy to 
 water, is expelled by it in turn under favourable circumstances, 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. Be- 
 fore 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 prepara- 
 tion 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 decompo- 
 sition. The oil of vitriol remains in the retort in its original state of 
 concentration, and hence might be applied to etherify an infinite quantity 
 
544 THEORY OF THE FORMATION OF ETHER. 
 
 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 ; 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, how- 
 ever, 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 Rose 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 sulphate of ether, (C4H5O. -I-S.O3), and the dilute sulphuric 
 acid, S.O34-4 Aq., the former is decomposed, bihydrate of sulphuric 
 acid, S.O3+2 Aq., being formed, and ether set free ; but at this temper- 
 ature 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 perfectly free from water; but at a higher temperature,* 
 the ether, when liberated, is immediately converted into elastic vapour, 
 which bubbles through the liquid lil^e 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 wa- 
 ter 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 water, 
 which condenses mixed with the ether, but had its origin in a perfectly 
 in*pendent 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 arseniovi- 
 flic acid, which is decomposed by boiling, the ether being set free. These 
 acids would be too costly to admit of their employment in the prepara- 
 tion of ether on the great scale, and, besides, they do not act as power- 
 fully as oil of vitriol. Although this ether does not contain 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. 
 
 The ether formed by the process now described is rendered impure by 
 admixture with alcohol and water, and sometimes oil of wine and sul- 
 phurous 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 
 2581 'S. In evaporating it produces great cold, of which numerous ap- 
 plications have been noticed under the head of vaporization. (Sec. IV., 
 Chap. III.) 
 
CONSTITUTION OF ETHER. 
 
 545 
 
 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 dis- 
 solved 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, there- 
 fore, an organic base ; its composition is expressed in the formula C4H5O 
 giving the numbers by weight : • 
 
 4 equivalents of carbon . 
 
 5 " " hydrogen 
 1 " " oxygen . 
 
 24-20 
 500 
 800 
 
 37-20 
 
 65-31 
 
 1333 
 
 21-36 
 
 10000 
 
 and by volume, 
 
 4 volumes of carbon vapour, (843x4)=:38720 
 10 " hydrogen " (68-8x10)=: 6880 
 
 1 " oxygen " . . . . =1102-6 • 
 
 Produce two volumes of vapour of ether . 5162-6 
 Of which one weighs, therefore . . . .25813 
 
 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 reagents it yields a great number 
 of derived compounds, of which the most important will be described in 
 their proper place. 
 
 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 combinations 
 of ammonia ; thus it has been looked upon as an oxide of a compound 
 (metallic ?) radical, Ethereum or Ethyle, as the salts of ammonia were sup- 
 posed to contain a compound metal. Ammonium. The formula of ethyie 
 should be C4H5, and its symbol Ae. On the other hand, it may be con- 
 sidered to consist of olefiant gas, C4H4, united to water, and the latter 
 then takes the place of the ammoniacal 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 ethyie, as oxide, chloride, &c., but without 
 any other present object than convenience of language, for it would be 
 impossible to discuss the comparative merits of these theories, without 
 knowing the properties of the compound ethers, of olefiant gas, of al- 
 dehyd, acetic acid, and many other bodies, which are involved in the re- 
 actions 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, 
 
 Sulphovime Acid. Bisulphate of Ether, C4H5O. . S.O3-J-H.O. . S.O3, is produced by 
 Miixing 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 
 splution is decomposed. The sulphovinic acid cannot be obtained in a sohd form^ 
 if a eolation of sulphovinate of leaid be decomposed by sulphuret of hydrogen, a col • 
 
 Zzz 
 
546 SULPHOVINATE OF POTASH, ETC. 
 
 ourless and very acid liquor is obtained, which, when concentrated, evolves ether, 
 blackens, and is totally decomposed. Its salts are all soluble, and generally deli- 
 quescent ; 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, while a metallic sulphate or sulphuret re- 
 mains behind, mixed with some charcoal. By distilling a sulphovinate with a pot- 
 ash 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 alkali, water 
 and olefiant gas are expelled, and all the sulphuric acid remains combined with the 
 alkali. 
 
 Sulphovinate of Potash, Ae.O. . S.Og-j-K-O. . S.O3, crystallizes in colourless rhom- 
 boidal plates, which are anhydrous ; it is very soluble in water, but sparingly solu- 
 ble in alcohol. Sulphovinate of Barytes, Ae.O. . S.Og-j-Ba.O. . S.O3-4-2 Aq., crystal- 
 lizes in obligue 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 212°, alcohol is given off, and sulphuric acid set free. 
 Sulphovinate of Lime crystallizes in thin hexagonal plates, which are very deliques- 
 cent ; it is soluble in less than its own weight of cold water. Sulphovinate of Lead 
 forms large rhombic crystals, dehquescent ; very soluble in water and in alcohol ; 
 it is gradually decomposed at ordinary temperatures. Sulphovinate of Copper, 
 Ae.O. . S.O3-I-CU.O. . S.O3-I-4 Aq., forms large blue octagonal plates, permanent 
 in the air, and very soluble in alcohol and water ; heated to 212° it is totally de- 
 composed. 
 
 ^thionic and Isethionic Acids. — These substances are formed by acting on alco- 
 hol 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 addi- 
 tion of alcohol. A solution of this salt, when decomposed by sulphuric acid, gives 
 free Ethionic ^.a^Z, which, by boiling, is decomposed into sulphovinic acid and isethi- 
 onic 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 anhy- 
 drous 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 begun 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 Althionate of Lime does not crystallize ; the Althionate 
 of Barytes crystallizes in fine needles, in place of the large plates of the sulphovi- 
 nate ; the Althionate 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 dif- 
 ferent from any of the preceding ; it is called the Methionic Acid, and is character- 
 ized 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 ; the formula of the acid contained in the barytes salt is C2H3 . S2O7. It 
 evidently does not contain any simple combination of alcohol or ether. 
 
 Heavy Oil of Wine. Sulphate of Ether and Etherol. — CsH9O.-l-2S.O3, or Ae.O. . 
 S.03-)-C4H4 . S.O3. 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 alkaline solution, 
 sulphovinic acid is formed, and Etherol {light oil of wine) set free, which floats upon 
 the surface. 
 
 The composition of this body is not absolutely constant. I consider it to be a 
 mixture, in variable proportions, of true Sulphate of Ether, Ae.O. . S.O3, with Sulphate 
 of Etherol, C4H4 . S.O3. I have found that when distilled with oxalate or acetate 
 
COMPOUNDS OP ETHER. 547 
 
 nt potash, with chloride or sulphuret of potassium, oxalic and acetic ethers, muriat- 
 ic ether, &c., are generated, and, at the same time, etherol remains indifferent to 
 these re-agents. 
 
 Another process for obtaining this heavy oil of wine consists in mixing dry sul 
 phovinate of lime with its own weight of quicklime, and distilling at a heat not ex- 
 ceeding 520'^. The oil which comes over mixed with alcohol is to be purified as 
 already noticed. 
 
 Etherol and Etherine. — C4H4. The oil which is separated from the foregoing 
 substance by hot water or by alkalies, divides itself generally, after some time, into 
 a liquid and a sohd portion ; the first constitutes the light oil of wine, Etherol. It is 
 pale yello\Y, 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, col- 
 ourless 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 composition 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 re- 
 ally a mixture of two other bodies ; for when a saturated solution of chloride of zinc 
 in alcohol is distilled, an oily liquor is obtained, which, by rectification, may be sep- 
 arated into two fluids, of which one, boiling at 212°, has the formula CgH?, and the 
 other, which boils only at 570°, has the formula CsHg. A mixture of equal quanti- 
 ties of the two should have the composition assigned to etherol. 
 
 Liebig and Regnault have found the etherol obtained by alcohol and sulphuric 
 acid to have the 'formula C4H3, so that it must be looked upon as an irregular mix- 
 lure of several oils, which have not yet been obtained pure. The etherol, or Ethe- 
 real Oil, is employed to prepare Hoffman'' s Anodyne Liquor, being dissolved in a mix- 
 ture of one part of ether and two of spirit of wine. 
 
 Compounds of Ether icith the Phosphoric and Arsenic Acids. 
 
 Phosphovinic Acid. — Ae.O. . P.O5+2H.O. When concentrated tribasic phos- 
 phoric acid is dissolved in alcohol, great heat is evolved, and one atom of water re- 
 placed by an atom of ether. The acid salt thus formed may be obtained crystal- 
 lized, 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, P.Os-j-Ae.O. . 2Ba.O.-|-12 Aq., crystallizes in brilliant colourless 
 plates, and is remarkable for being equally soluble in water at 32° and 212°, but 
 three times more soluble in water at 104°. 
 
 Arseniovinic Acid, As.05-|-Ae.O.-j-2H.O., 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, C4H5CI., 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, while 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 water ; it 
 burns 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 ole- 
 fiant s^as and chloride of potassium. Heated with alkaline salts, it yields 
 compound ethers and alkaline chlorides. When muriatic ether is heated 
 with potassium, Lovvig states that chloride of potassium is formed and a 
 light oily substance separates, which has the formula C4H5. It should be 
 EthylCf but so important an observation has need of verification. This 
 
548 
 
 HYDROBROMIC ETHER, ETC. 
 
 body is often called ligTit Muriatic Ethers to distinguish it from heavy 
 Muriatic Ether, which resuhs from the action of chlorine on weak alco- 
 hoi. 
 
 Hydrobromic Ether, Bromide of Ethyle, C4H5Br., is obtained by dis. 
 tilling together two parts of bromine, one of phosphorus, and six of alco- 
 hoi. There is first formed bromide of phosphorus, which instantly de- 
 composes the water of the alcohol, and the nascent hydrobromic acid 
 acting on the ether forms the hydrobromic ether. In properties it per- 
 fectly resembles the following body : 
 
 Bydriodic Ether. Iodide of Ethyle, C4H5I., is formed by distilling 
 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 abun- 
 dantly 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. Sulphur et of Ethyle, C4H5S., may be formed 
 by acting on muriatic ether with an alcoholic solution of sulphuret of 
 potassium. It boils at 187°^ it combines with sulphuret of hydrogen to 
 form the following very remarkable substance : 
 
 Sulphur-alcohol, or Mercaptan, 04^1^29 or Ae.S. + H.S., which is obtain- 
 ed directly by distilling in awater-bath concentrated solutions of sulpho- 
 vinate "of lime and of potash saturated with sulphuret of hydrogen, K.S.-f 
 H.S. and Ae.O. . S.O3+K.O. . S.O3 producing 2K.0. . S.O3 and Ae.S. 
 -j-H.S. ; the mercaptan distils over, and 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 dissolves in al- 
 cohol ; is perfectly neutral ; burns with a bright blue flame ; and by cold, 
 freezes into a crystalline mass. In constitution, it is perfectly analogous 
 to alcohol, the oxygen being replaced by sulphur. When placed in con- 
 tact 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 of Mercapiides. That of mercury is a 
 crystalline solid, fusible at 110^, and soluble in alcohol. 
 
 The properties of this body induced its discoverer, 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 0411582-1- H. He extended this view also to common alco- 
 hol, which he considers as C4H502-hH. ; but his theory has met with 
 very few supporters. 
 
 Thialbl. Bisulphuret of Ethyle, Ae.Sj, is formed by distilling a mix- 
 ture of sulphovinate of lime and persulphuret of potassium. It is a lim- 
 pid, 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 produced analogous to 
 the sulphovinic, but which are not, as yet, accurately known. 
 
 The Seleniuret and Telluret of Ethyle have been formed, but do not re- 
 quii'e description. 
 
 Nitrous Ether. Hyponitrite of Ethyle. — Ae.O. . N.Oa- When alco- 
 hol and nitric acid are directly mixed, the action is very violent ; heat 
 is evolved, red fumes are copiously given off*, and acetic, oxalic, and car- 
 i>onic acids formed. Even when the acid is dilute, its action is very 
 
NITROUS ETHER, ETC. 549 
 
 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 hypo- 
 nitrous acid thus produced that acts on the remaining alcohol, and, com- 
 bining with the ether of it, forms the proper nitrous ether. To avoid 
 these oxidized products, the best plan is to generate red fumes of hypo- 
 nitrous acid, by acting on starch by nitric acid in a retort, and to conduct 
 these fumes by a bent tube to the bottom of a two-necked bottle contain- 
 ing alcohol. They are copiously absorbed, and combine directly with 
 the ether. From the second neck of the bottle a tube should pass to a 
 condensing apparatus and receiver ; enough of heat is evolved by the ab- 
 sorption 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, consisted 
 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 ucid acted very violently on the alcohol, and the product was im- 
 pure, 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^ Fah. Exposed 
 to the air, it absorbs oxygen rapidly, and forms 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. 
 
 Cyanogen Compounds of Ether, 
 
 Hydrocyanic Ether. Cyanide of Ethyle, Ae.Cy., is prepared by distil- 
 ling 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. 
 
 Cyanuric Ether, SAe.O.+SCysOs+B Aq.,is formed when the vapours of hydrated 
 cyanic acid are passed into ether, as long as they are absorbed. After some time, 
 xHiQ new compomid separates in crystals, which are colourless prisms, destitute of 
 taste and smell, soluble in water, and but sparingly soluble in ether, 
 
 Hydrostdphocyanic Ether appears to be formed by distilling sulphocyanide of potas- 
 sium with sulphovinate of potash. It is a liquid heavier than water. 
 
 Compounds of Ether with the Acids of Carbon, 
 
 Carbonic Ether. Carbonate of Ethyle. — Ae.O. , C.O2. This ether can only be pro- 
 duced 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 disen- 
 •gagement of carbonic oxide 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 smell, lighter 
 than water. It boils at 2G0° ; it is insoluble in water, but dissolves in alcohol ; its 
 alcoholic solution is decomposed by potash, alcohol and carbonate of potash being 
 formed. 
 
 Carbonate of Ether and Water. Carbovinic Acid. — Ae.O. .C.O24-H.O. .C.O2. At 
 one time it was considered that anhydrous sugar was actually bicarbonate of ether, 
 C6H503=C4H50.+2C.02, and that the alcoholic fermentation consisted in the sep. 
 
550 OXALIC ETHER, ETC. 
 
 aration 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 dissolv- 
 ing 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, deposites the salt, whose formula is Ae.O. . C.O2+K.O. . Q. 
 O2, 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, Ae.O. . C2O3, 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 heavv 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 5077. 
 
 Oxalovinic Acid. — ^Ae.O. . C2O3+H.O. . C2O3. 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 decompose it. The Oxalovinate of Potash sep- 
 arates 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. 
 
 Oxaniethan. — Ae.O. . C203+C202Ad. When oxalic ether is acted on by water 
 of ammonia, it is totally decomposed, alcohol and oxamide being formed, as already 
 noticed. 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 solution in cold wa- 
 ter 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 chan- 
 ged into oxamide, 
 
 Chloroxycarbonic Ether. — Ae.O. . C.O2+C.O.CI. This substance is formed by the 
 action of chlorocarbonic acid gas on absolute alcohol. It is a colourless liquid, 
 perfectly neutral, heavier than water, and boiling at 201° ; sparingly soluble in wa- 
 ter. It consists, or, at least, 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 dis- 
 , solved 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 Ae.O.. C.Oa+C.O.Ad. ; it 
 consists thus of carbonic ether and carbamide in the proportion of one atom of each. 
 
 Sulphocarhonic Ether. Hydroxanthic Acid, Ae.O. .C.S24-H.O. .C.S2, 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, slight- 
 ly acid, inflammable, and burns with a blue sulphurous flame ; it is decomposed by 
 warm water into alcohol and sulphuret of carbon ; it decomposes the alkaline car- 
 bonates, expelling the carbonic acid. Of its salts, that of potash is obtained direct- 
 ly, and from it the others. Xanthate of Potash, Ae.O. . C.Sa+K.O. . C.S2, is formed 
 by adding sulphuret of carbon to a warm solution of caustic potash in alcohol. On 
 cooling the liquor, it deposites the salts in crystals, which are to be collected on a fil- 
 ter, washed with ether, and dried between folds of bibulous paper. The salts of 
 lead, copper, &c., may be prepared by double decomposition; they are all yellow, 
 whence tne ordinary name of the acid. 
 
 Mucate of Ether is solid and crystalline. It is formed by dissolving mucic acid in 
 cil of vitriol, and gradually adding an equal weight of alcohol. The liquor 3-ields, 
 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. 
 
 This gas has been frequently mentioned as one of the products of the ac- 
 tion of sulphuric acid on alcohol. The usual process to obtain it consists 
 
PREPARATION OF OLEFIANT GAS. 
 
 551 
 
 in heating one part of alcohol with six of oil of vitriol in a flask, J, from 
 which a tube passes to the water pneumatic trough, as in the figure ; the 
 mass becomes dark ; 
 ether, water, and oil 
 of wine collect in the 
 interposed globe, a, 
 and olefiant gas is co- 
 piously evolved, mix. 
 ed with an equal vol- 
 ume of sulphurous 
 acid, which, however, 
 being absorbed by the 
 water, the other gas 
 remains pure. To- 
 wards the end of the 
 process the materials 
 in the flask swell up very much, and might boil over if not carefully at- 
 tended to. The theory of this action appears, 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 ele- 
 ments of another equivalent of water, and olefiant gas remains, C4H5O. 
 giving C4H4 and H.O. ; but we cannot by this process generate the ole- 
 fiant 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, ap- 
 pears to consist of C27H804-f-S.03; it combines with bases, and is termed 
 the Thiomelanic 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 the purpose of il- 
 lumination, being the most valuable constituent of the gas which is burn- 
 ed 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 muri- 
 atic acid gases ; also, if muriatic ether be heated with ammoniacal gas, 
 sal ammoniac is formed, and olefiant gas evolved ; the same decomposi- 
 tion 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 theoretical point of 
 view, these sources of olefiant gas are peculiarly of interest. 
 
 Olefiant gas, when pure, is colourless ; its odour is very slightly ethe- 
 real ; it is sparingly absorbed by water ; it burns with a brilliant white 
 flame, producing much smoke. When mixed with twice its volume 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 980*8, as 
 one volume of it contains a volume of carbon vapour and two volumes of 
 hydrogen (843'0 + 137*6 = 980'6). 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 
 
552 COMPOUNDS OF ETilERENE. 
 
 radical, and the basis of a scries of compounds with oxygen, chlorine, 
 &c., has proposed for it the name Elayl, and the formula CgHj. The name 
 Olejiant Gas being very inconvenient, I shall, in speaking of its com- 
 pounds, term it, for the present, Etherene. The principal support of the 
 theory, which considers this gas to be the radical of the ethers and of al- 
 cohol, is derived from the great simplicity of their constitution by volume, 
 in the state of vapour, on that view. Thus, two volumes of defiant 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 similar simple propor- 
 tions 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 indi- 
 rectly, as from alcohol or ether, but it combines immediately with iodine, 
 chlorine, and sulphuric acid. 
 
 Anhydrous sulphuric acid absorbs etherene in large quantity, form- 
 ing white crystals, which, when dissolved in water, constitute Iselhionic 
 Acid, identical in every respect with that formed as described p. 546. 
 When dry, its composition is 8206+0404; 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 hyposulphuric, and 
 not sulphuric acid, and its rational formula is S20g+C4H40. This ise- 
 thionic 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 defiant gas, c, be inverted in the pneumatic trough, over a 
 capsule, h, 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 of Olejiant Gas. 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 being C4H4CI2. 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 col- 
 ourless, 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, C4H2CI4, and ultimately sesquichloride of Carbon, C4 
 Clg, 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 alkah, and gently 
 warmed, chloride of potassium is formed, and a peculiar body produced, 
 whose composition is expressed by the formula C4H3CI. This substance 
 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 muriatic acid, C4H 
 
PREPARATION OF ALDEHYD. 553 
 
 Cl. + H.Cl., in which case the action of the potash is easily explained. 
 This gas itself is supposed to be a chloride of the same carbohydrogen 
 as is the basis of acetic acid and aldehyd, (C4H3), or Acetyl ; and the ole- 
 fiant gas, on this view, is Hydruret of Acetyl, G4H3-I-H., or Ac.H. The 
 farther discussion of this opinion will be reserved for another place. If 
 the gas, C4H3CI., be passed over perchloride of antimony, it combines 
 with more chlorine and forms a liquid, which boils at 240°, and consists 
 of C4H3CI3 ; by an alcoholic solution of potash this is decomposed into 
 muriatic acid, and another body, also liquid, but boiUng at 86°, and hav- 
 ing the formula C4H2CI2. By contact with chlorine, this produces the 
 liquid C4H2CI4, 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 C4H4 . Cl.O. ; it is called Chlor- 
 etheral, but is properly a compound of aldehyd and the chlor-etherene, C4H4CI24- 
 C4H4O2. 
 
 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 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 C4H4I2, but the products of its decompo- 
 sition are not similar to those of the chlorine compound. 
 
 When bichloride of platinum is dissolved in alcohol, a very complex reaction oc- 
 curs, and a substance is produced consisting of Pt.Cl.-|-C2H2. This body combines 
 with the chlorides of the alkaline metals to form double salts. On Berzelius's view, 
 the C2H2 being a compound radical (Elayl), may be supposed simply to replace the 
 second atom of chlorine, and thus form an Elayl-chloride of platinum, which has 
 the same power of forming double salts as the ordinary bichloride. They are thus 
 (Pt.+El.Cl.)+K.Cl. and (Pt.+El.Cl.)-|-Na.Cl., &c. 
 
 Of the Products of the Oxidation of Alcohol, Aldehyd, Hypoacetous 
 Acid.—Eq. 555-6 or 44*2. 
 
 It has been mentioned, in speaking of nitrous ether, that by the ox- 
 idation 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 alco. 
 hoi 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 al- 
 cohol 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 of oil of vitriol 
 with four of water, four of spirit of wine, and six of black oxide of man- 
 ganese, are to be distilled with a very gentle heat, and the product col- 
 lected in a receiver surrounded with melting ice. The apparatus de- 
 scribed for preparing ether (p. 542) 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 last two 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 decom- 
 
 4 A 
 
554 
 
 PROPERTIES OF ALDEHY D. A C E T A L. 
 
 posed 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 ; in 
 contact with oxidizing agents, it is changed into acetic acid, passing 
 through an intermediate state of Aldeliydic 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 heat- 
 ed, the silver is deposited as a brilliant metallic film, hning 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. From the composition of aldehyd, these changes are 
 at once explained. It is formed by the abstraction of two atoms of by. 
 drogun from alcohol, which are carried away, as water, by the oxygen 
 supplied ; its formula is hence C4H4O2 : now, in contact with Ag.O., it 
 forms, first, aldehydic acid, C4H4O3, and metallic silver, and then C4H4O3 
 with Ag.O. gives hydrated acetic acid, C4H4O4, and another quantity of 
 silver. The formation of acetic acid from alcohol consists, therefore, in 
 two stages ; first, the abstraction of hydrogen, by which aldehyd is form- 
 ed, and, second, the addition of oxygen, by which acetic acid is produced. 
 When aldehyd is heated in a solution of potash, this becomes brown, 
 and by an acid a solid brown substance separates, 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, Elaldehydy the other solid, Metaldehyd ; they have the 
 same formula as aldehyd, C4H4O2, but difler in all their properties. 
 
 The general characters of aldehyd show that it contains the same rad- 
 ical as acetic acid, Acetyl, C4H3 or Ac, combined with oxygen; it is, 
 therefore, Hydrated Oxide of Acetyl, Ac.O. + Aq. =0411402; it has been 
 called, also, Hypoacetous Acid, for it is capable of perfectly neutralizing 
 ammonia. Its compound with ammonia is, indeed, very remarkable ; 
 it is best prepared by dissolving aldehyd in ether, and passing ammo- 
 niacal gas into the liquor ; the aldehyd-ammonia, being very sparingly 
 soluble in ether, crystallizes as it forms in large hexagonal plates, which 
 are very brilliant and colourless. Their solution in water soon decom- 
 poses, becoming brown, and exhaling an animal smell. The dry crystals 
 may be fused and sublimed without alteration ; their 
 formula is C4H3O.4-H.O. . N.H3. 
 
 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 oxy- 
 gen 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 large bell-glass is ta- 
 ken, open above, and standing in a basin, so sup- 
 ported as to allow the air inside to be frequently re- 
 newed, as in the figure ; through the top passes the 
 tube of a small funnel, a, under which is a watch- 
 
 ^ 
 
FORMATION OF ACETIC ACID. 555 
 
 glass, b, with a layer of platina black (p. 407). Into the funnel strong 
 alcohol is poured, so that from time to time a drop falls 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 purified. 
 It is a colourless hquid, boiUng at 200° ; its odour is agreeable ; its for- 
 mula is CgHgOg, and it appears to be a compound of aldehyd and ether, 
 C^HA+aH^O. 
 
 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 p. 179, along with 
 acetic and formic acids. It is obtained pure by decomposing its silver 
 salt by sulphuret of hydrogen, forming a liquor of an agreeably acid 
 taste. 
 
 Of Acetic Acid, Vinegar, — Eq. 755-6 or 51*2. 
 As all alcoholic liquors are liable to undergo spontaneous decomposi- 
 tion, and form vinegar, this acid has been known from the earliest ages 
 as produced by the acetous fermentation ; its origin was, however, long 
 wrapped in obscurity, for the complex constitution of the fermented 
 liquors, in which it was ordinarily produced, prevented the simple na- 
 ture of the change from being understood. It is now fully established, 
 that the change from alcohol to acetic acid consists simply in the remo- 
 val 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 : 
 
 A.lcohol, C4H6O2, and Aldehyd, C4H4O2, 
 
 gives by — H2, gives by -J-Oz, 
 
 Aldehyd, "cIhIo^ Hydrated Acetic Acid, C4H4O4. 
 
 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 oi practice, the the- 
 ory of the acetous fermentation becomes much more difficult ; for exactly 
 as a pure solution of grape-sugar will not break up into alcohol and car- 
 bonic acid, and 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 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 al- 
 cohol 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 
 
556 MANUFACTURE OF VINEGAR. 
 
 rapidly renewed, a large quantity of the volatile aldehyd would be car. 
 ried off. These solutions contain abundance of organic matter, proper 
 for acting as ferment ; and when the fermentation is complete, the prod, 
 ucts of their decomposition collect upon the bottom and sides of the 
 vats, in a gelatinous mass, termed mothers. 
 
 The manufacture of wine or malt vinegar by the old process of mere partial ex- 
 posure to the air in vats consumed much time, and is almost superseded by the 
 German method, by which excellent 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 perforated 
 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 in 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 about one part of proof spirit to four of water, 
 and, having mixed with it joVo^h 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 veiy rapidly, and, having been warmed to about 75° before being poured in, 
 its temperature soon rises to 100° ; the interior being so hot, a current of air is es- 
 tablished 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 will be described in an- 
 other place. 
 
 The vinegar of commerce has frequently its pungency and acidity in- 
 creased by the addition of acrid herbs, as capsicum, and by sulphuric 
 acid. To obtain it free from these impurities, it is redistilled. As, how- 
 ever, its volatility is about the same as that of water, it cannot be con- 
 centrated 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 ap- 
 plied. In this process, S.Os-j-Aq. and Na.O.-j-C4H303 give S.Og+Na.O. 
 and C4H303-|-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 be separated from the liquid portion ; these 
 crystals are the Prolohydrate of Acetic Acid, and in 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 agreeable aromat- 
 ic odour, from an admixture of Acetone, The acetate of potash is pre- 
 scribed 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, crvs- 
 
PROPERTIES OF ACETIC ACID, ETC. 557 
 
 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 essen- 
 tial oils, which solution constitutes the aromatic vinegar of the shops. 
 When liquid, its sp. gr. is 1*063 ; but its specific gravity does not indi- 
 cate its strength, as it increases according as water is added until it be- 
 comes 1*078, which is that of an acid containing 34*6 per cent., or three 
 atoms of water ; being a definite compound, C4H3034-H.O. + 2 Aq. On 
 farther 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 accurately the quantity of acetic acid, as 
 the atomic weight of Ca.O. . C.Og (50*5) is nearly the same as that of 
 C4H3O3 (51*2) ; of course, if the acetic acid be not pure, this method 
 cannot be employed. 
 
 The formula of hypothetic dry acetic acid is C4H3O3, and its equiva- 
 lent =51*2. The acetate of water, C4H303+Aq., consists of 
 
 4 equivalents of carbon, =2420 . . 4020 
 4 " hydrogen, = 4 00 . . 664 
 
 4 " oxygen, =3200 . . 5316 
 
 60-20 10000 
 
 The hydrated acetic acid boils at 240°. The specific gravity of its 
 vapour is 2278, and is anomalous as showing that its equivalent volume 
 is 3, in place of 4 or 2, as occurs with almost all other organic bodies. 
 
 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 recognised 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. But even strong solutions are not af- 
 fected by the salts of lead or barytes. It combines with all bases form- 
 ing salts, of which none are quite insoluble in water, but generally very 
 soluble and easily crystallized. The most important of these acetates 
 will now be described. 
 
 Acetate of Potash^ K.O. . C4H3O3, 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 l;ieat, 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 Soda^ Na.O. . C4H4O3+6 Aq., may be obtained in the 
 same way as acetate of potash, but is made on the large scale in purify- 
 ing the rough wood-vinegar. The impure acetate of lime, obtained by 
 neutralizing the pyroligneous liquors with chalk, is decomposed by 6^ 
 times its weight of crystallized sulphate of soda. These are in the pro- 
 portion of two equivalents of Glauber's salt, as but one half of the quan^ 
 tity added is decomposed by the acetate of lime. It answers still better 
 
558 
 
 ACETATE OF BARYTES, LIME, ETC. 
 
 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. 488). 
 
 When purified by successive crystallizations, the acetate 
 of soda forms oblique rhombic prisms, as z, 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, Ba.O. . C4H3O3, 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 
 (Ba.O. . C.O2 and CgHaOA 
 
 Acetate of Lime is made on the large scale, but in a very impure form, as one 
 stage in the process of purifying the wood-vinegar. When pure, it crystallizes in 
 needles, which do not deliquesce. It is decomposed 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 f ure, the simple 
 sulphate of alumina should be decomposed by acetate of barytes. Evap- 
 orated at a very gentle heat, it dries into a transparent gummy mass ; 
 but if boiled, acetic acid passes off, and a hasic acetate of Alumina is de- 
 posited 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 subse- 
 quently 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, Zn.O. . C4H3O3-I-3 Aq. 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 filtration. On evapora- 
 ting the solution, the acetate of zinc crystallizes in brilliant, soft, 
 hexagonal rhombic tables, as in the figure, of which i, u are pri- 
 mary, 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, 3Zn.O.-l-C4H303. A solution of this 
 salt is completely decomposed by sulphuret of hydrogen. 
 
 Protoacetate oflron.—Fe.O. . C4H3O3. This salt, which may be prepared by dis- 
 solving 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 ace- 
 tate of lead, as only a portion of the lead salt precipitates until the iron becomes 
 peroxidized. 
 
 Sesquiacetate of Iron,¥e203 + S(CJisOs), is prepared by dissolving 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 boil- 
 ed, 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 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 
 
ACETATES OF LEAD. 559 
 
 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 Pharmacopoeia, is formed by triturating together 
 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 re- 
 quired, 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 decomposes 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 ac- 
 cess 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, Pb.O. . C4H3O34-3 Aq., 
 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 
 i\ figure, which are very bright and colourless ; 
 -|-J\ their taste is sweet and astringent ; the solution 
 j in water reddens litmus, but turns sirup of vio* 
 
 I J lets green. In very dry air they effloresce ; 
 '^^y^'^ when heated to 136° they undergo aqueous fu- 
 sion, but, having lost their water of crystalli- 
 ^"^V^ zation, 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(Pb.O. . C4H3O3) giving C.O2 with C3H.O. and 
 3Pb.0.4-2C4H303. 
 
 This neutral salt dissolves easily in alcohol ; it is very pois .ous ; the 
 antidote to it is Glauber's or Epsom salt, which forms insolu .e sulphate 
 of lead. 
 
 Sesquihasic Acetate of Lead. — 3Pb.O.+2C4H303. This salt, which 
 is formed as just described, dissolves in water, and the sirupy solution 
 crystallizes in pearly hexagonal plates ; its solution reacts alkaline. 
 
 Trihasic Acetate of Lead. — 3Pb.O. +04^303. When ammonia is 
 added to a solution of neutral acetate of lead, so as to render it strongly 
 alkaline, it does not combine with it as with most other metallic salts, 
 but acetate of ammonia and trihasic 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 Satumi, gives, by evaporation, a mass of fine 
 crystalline needles; it reacts powerfully alkaline; it is insoluble in 
 alcohol. 
 
 Sexbasic Acetate of Lead, 6Pb.O.-|-C4H303, is precipitated when a 
 solution of neutral acetate is added to a great excess of water of ammo- 
 nia ; 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 
 
560 ACETATES OF COPPER, MERCURY, ETC. 
 
 p. 491.) It forms minute feathery crystals when deposited from boiling 
 water, in which it is shghtly 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, Cu.O. . C4H303+Aq., 
 is prepared by dissolving verdigris in acetic acid. It forms 
 /<^</^^X^ oblique rhombic prisms, as in the figure, where i, u, u are 
 ^"^y^^ "^ primary, and e, e secondary faces of a fine deep green col- 
 our. It crystallizes in another form with five atoms of 
 water : these crystals are blue, like sulphate of copper, 
 ^^^^^ and when heated to 86°, give off 4 Aq., and change into 
 ^^^<^^^^^^5^ the common 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 
 deposites 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. — 2CU.O.+C4H3O3+6 Aq. 
 This salt is manufactured in wine countries by stratifying plates of 
 copper 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 contains all the basic 
 salts mixed together. In this country it is prepared by stratifying cop- 
 per plates with cloths steeped in pyroligneous acid. When pure, the 
 bibasic acetate is of a fine blue colour ; it is decomposed by water into 
 the insoluble tribasic acetate, and the soluble sesquihasic acetate of cop- 
 per, which forms a pale blue solution, whence it may be precipitated in 
 crystalline scales by alcohol. 
 
 Tribasic Acetate of Copper, 3CU.O.+C4H3O3+2 Aq., remains as an 
 insoluble residue when verdigris is treated with water, or by digesting 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. 456. 
 
 Acetate of Black Oxide of Mercury, Hg.02+C4H303, may be formed 
 by mixing boiling solutions of acetate of potash and subnitrate of mer- 
 cury, and filtering rapidly. On cooling, it is deposited in brilliant 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 wa- 
 ter, and does not crystallize. 
 
 Acetate of Silver, Ag.O. . C4H3O3, is formed by mixing boiling solu- 
 tions of nitrate of silver and acetate of potash, and filtering the liquor 
 while very hot. On cooling, it crystallizes in pearly white needles, 
 which are but very sparingly soluble in cold water. These last salts 
 serve as tests for the acetic acid in liquids. 
 
 Acetate of Ammonia^ N.H4O. . C4B3O8, is prepared by passing ammo- 
 
ACETATE OF ETHER. ACETONE. 561 
 
 niacal gas over the crystalline hydrate of acetic acid, or by heating 
 moderately a mixture of equal parts of acetate of potash and of sal 
 amnnoniac. 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 neutrahzing distilled 
 vinegar with carbonate of ammonia, is used in medicine by the name of 
 Sjiirit of Mindererus ; in its original form, when the carbonate of ammo- 
 nia, obtained by the distillation of bones (salt of hartshorn), and which 
 contained empyreumatic animal oil, was used, it was a much more pow- 
 erful medicinal agent than when prepared, as now, with pure carbonate 
 of ammonia. 
 
 Acetate of Ether. Acetic Ether, C4H5O.+C4H3O3, is prepared by 
 distilling 16 parts of dry sugar of lead, 4i 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 (3063) is double that of aldehyd (1531). 
 
 Products of the Detomposition 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, C4 
 H3O3 separating itself into C.O^ and C3H3O. The metallic acetates are 
 similarly decomposed, but the products are not so pure. This liquid, 
 for which I shall retain the name Acetone, is formed also abundantly 
 when the vapour of acetic acid is passed through a tube containing 
 charcoal, at a temperature just below redness. 
 
 x^cetone is colourless, and lighter than water ; it burns with a lumin- 
 ous flame ; it boils at 132° ; the specific gravity of its vapour is 2022. 
 When heated with hydrate of potash, it is totally converted into carbonic 
 acid and marsh gas, C3H3O. and H.O. producing C2H4 and COj. When 
 treated by oxidizing agents, as permanganate of potash, or bichromate of 
 potash and sulphuric acid, it is totally converted into acetic acid. 
 
 With sulphuric acid, acetone yields a series of products closely analogous to those 
 derived from alcohol, but still presenting such characteristic 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, Mesilijlene, whose formula is 
 C6H4, and also an ether, Mcsitic Ether, CeHaO. With sulphuric acid, this forms the 
 Sulphomcsitic and Persulphomesitic Acids, which are remarkable, as the sulphuric 
 acid retains all its power of saturating bases. With phosphoric acid, it produces 
 Phospho mcsitic Acid, and with hypophosphorous acid a very remarkable compound, 
 whose barytes salt has the formula CeHsO.-j-SBa.O. . P.O. The series of wine-alco- 
 hol contains no similar body. The mesitic ether combines also with protochloride 
 of platinum. 
 
 When acetone is treated with chloride of phosphorus, it gives phosphoric acid 
 and ChloTomesitic Ether, CeHsCl. ; with iodide of phosphorus it produces lodomesitic 
 Ether, CcHsI. ; and, when acted on by chlorine, it forms, first, the Mesitic Chloral, of 
 which the formula is C3H2 . Cl.O., and subsequently another body, also a heavy, 
 oily liquid, C3H. . CI2O. 
 
 When red fumes of hyponitrous acid are passed into acetone, and the vessel is 
 kept cool, they are copiously absorbed, and, on adding water, a dense fluid separ- 
 ates, which is Nitrous Mesitic Ether, CeHsO.-j-N.Os. 
 
 By acting on mesitylene, C6H4, with nitric acid, a heavy liquid is produced, 
 
 4 B 
 
562 BODIES OF THE KACODYL SERIES. 
 
 which is termed Mesitic Aldehyd ; its formula is CeHaO.-f-Aq. Its solution in alka« 
 line 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 CeHaCl. I have termed it Chloride of Pleleyl. 
 
 In my original examination of this series of bodies, I looked upon acetone as an 
 alcohol {Mesitic Alcohol), C6H602=(C6H50.-|-Aq.), from which they were all derived ; 
 but I do not now consider that either mesitylene or mesitic ether pre-exists in ace- 
 tone. 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 mix- 
 ed and distilled at a dull red heat, a dense colourless liquid is obtained, 
 which had been long known to chemists as the Fuming Liquor of Cadet. 
 The admirable researches of Bunsen have shown that it is an oxide of 
 a compound radical, which he has succeeded in isolating, and which, in 
 the variety of its combinations, and the influence their discovery will 
 doubtless exercise on science, ranks with cyanogen. Nevertheless, as 
 they are not of practical importance, a short notice of them will suffice. 
 
 The Fuming Liquor of Cadet, or Alkarsine, 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 specific 
 gravity of its vapour is 7180 ; its odour is excessively disagreeable, pro- 
 voking 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 ofT much arsenious acid. Its composition is ex- 
 pressed by the formula C4H6 . As.O., 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 of C4H6 . As. CI. 
 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 C4H6AS. is set 
 ire^ ; 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 1 shall adopt that used by Bunsen, Kd.=C4H6As. The alkar- 
 sine is therefore oxide of kacodyl, Kd.O., and the body formed by mu- 
 riatic acid is the chloride, Kd.Cl. The iodide, bromide, sulphuret, and 
 cyanide of kacodyl, may be formed by the simple process of distilling al. 
 karsine with the corresponding hydracids, or the chloride of kacodyl with 
 the iodides, &;c., of potassium. 
 
 When alkarsine is distilled with dilute muriatic acid, or when chloride 
 of kacodyl is treated with water, this is decomposed, and an oxychloride 
 obtained, the formula of which is Kd.O. + SKd.Cl. In a similar man- 
 ner, a corresponding oxybromide, Kd.O. + SKd.Br., may be produced, 
 and an oxyiodide. 
 
 If alcoholic solutions of oxide of kacodyl and of corrosive sublimate be 
 mixed, a brilliant white precipitate is obtained, which is soluble in wa- 
 ter, and crystallizes therefrom in large but delicate rhombic tables, of a 
 satiny lustre. It is a direct combination, its formula being Kd.O.-f 
 2Hg.Cl. A precisely similar compound is formed with the bronnide of 
 mercury. 
 
 When 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 
 
SOURCES, ETC., OF MARSH GAS. 563 
 
 termed. 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 
 •dlkargene ; it forms large oblique prisms, which are inodorous and taste- 
 less ; it deliquesces in moist air ; it combines with alkalies and metallic 
 oxides, forming very instable compounds ; it melts at 390°, and is de- 
 composed 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 C4H7 . As. 
 O4, or Kd.Os+Aq. ; its proper name is therefore Kacodylic Acid. 
 
 C. Of light Carburetted Hydrogen, Marsh Gas, 
 
 This gas is formed by the decomposition of almost every organic sub- 
 stance at a high temperature. Thus it exists always mixed with defi- 
 ant 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 vegetable 
 matter in contact with water, but excluded from the air. By assimila- 
 ting the elements of four atoms of water, the lignine breaks up into car- 
 bonic acid and this gas, CigHgOg with 4H.0. giving 6C.O2 and GCHg. 
 As the origin of the great deposites of coal is to be found in the slow de- 
 composition 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 mass- 
 es, it remained infiltrated through the coal, probably in a liquid condi- 
 tion. During the operations of mining, when this great pressure is re- 
 moved, 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 construction of his safety-lamp (see p. 
 183). Under the name of Fire-damp, this gas is known and dreaded 
 by the miners, while the carbonic acid, which results simultaneously from 
 the decomposition of the wood, and is known, also, from its fatal eflfects 
 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, C4H3O3 and 
 H.O. producing 2C.H2 and 2C.O2. This last remains combined with 
 the potash, while the gas which passes off may be collected over water. 
 
 It is colourless and transparent. It burns with a yellow flame, pos- 
 sessing but little illuminating power ; its sp. gr. is 559 ; its formula be- 
 ing C.H2, and consisting of 
 
 One volume of carbon vapour =8430 
 
 Four volumes of hydrogen =275-2 
 
 Forming two volumes of marsh gas .... 11182 
 Of which one weighs, therefore 559 1 
 
564 C H L O R A L. C HLOROACETIC ACID. 
 
 Or it may be considered as containing one volume of olefiant gas and two of hydro- 
 gen, condensed to two, (980-4-f-137-6)-r-2=559. 
 
 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 Cjtl^. When acted on by chlorine, it gives muriatic 
 acid gas and bichloride of carbon (p. 498), which has been already no- 
 ticed. 
 
 Of the Action of Chlorine on Alcohol., Aldehyde Acetic Acid, and the va- 
 rious Kinds of Ethers. 
 
 When cljlorine 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. 
 
 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 C4H. . CI3O2. The first operation of the 
 chlorine is to remove two equivalents of hydrogen, and thus to reduce the alcohoJ 
 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, C4CI3. This is combined with oxy- 
 gen and water in chloral, as acetyl is in ordinary aldehyd ; the rational formula of 
 chloral is therefore C4Cl30.-|-Aq. 
 
 Chloral combines with water, forming a crystalline hydrate. It gradually chan- 
 ges into an isomeric porcellaneous-looking substance. The equivalent change of 
 common aldehyd has been described (p. 554). When chloral is acted on by a 
 solution of potash, it yields formic acid and chloroform, C4H. . CI3O2 and H.O. giv- 
 ing C2H.O3 and C2H.CI3. 
 
 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 rhombs, and pos- 
 sesses strong acid properties ; its formula is C4H. . CI3O4. It is formed by the 
 replacement of the hydrogen of the radical acetyl by chlorine, forming thus the 
 Chloroacctic Acid, C4Cl3034-Aq. Its salts crystallize with facility, and have great 
 similarity to the acetates. When the chloroacetate of potash is heated with an ex- 
 cess of potash, it is decomposed into carbonic acid and chloroform ; C4Cl30^ and 
 H.O. giving 2C.O2 and C2H.CI3. This reaction is exactly similar to that of the 
 common acetate of potash, the chloroform replacing the pond gas. 
 
 When chlorine acts upon sulphuric ether, a remarkable series of bodies is pro- 
 duced ; the first formed is a dense oily liquor, having the formula C4H3 . CI2O., 
 which, by contact with water or an alkali, is decomposed into hydrochloric and 
 acetic acids, 3(C4H3 . CI2O.) and 6H.0. producing 6H.C1. and 3(C4H303). This 
 body is properly, therefore, Oxychloride of Acetyl ; 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 tht 
 name radical as exists in chloral and chloroacetic acid. The substance thus pro 
 duced is solid and crystalline ; it bears a very simple relation to sulphuric ether, 
 as its formula is C4CI5O., 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 h£is thrown much light on 
 the theory of these bodies. 
 
 Acetic ether combines with two atoms of chlorine and loses two atoms of oxy 
 gen, thus giving from C4H303+C4H50.,the Chloroacctic Ether, C4H3O34-C4H3. CI2O., 
 an oxychloride of acetyl, containing twice as much acetic acid as that just now 
 described, and its rational formula being, therefore, Ac.Cl3-}-2Ac.03; 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 C6Cl504=C4Cl50.-|-C203. It is, therefore, a combina- 
 
ACTION OF CHLORINE ON MURIATIC ETHER. 565 
 
 tion ol oxalic acid with chloryl ether, and is termed Chloroxalic Ether. With water 
 of ammonia it gives oxamide ; by the action of dry ammonia it forms a substance 
 also crystaUine, which is soluble in alcohol and ether, sparingly soluble in water, 
 and the formula of which is CSH2CI3 . N.Oe ; at the same time, chloryl ether and 
 water are evolved ; the rational formula of this body, Chloroxamethan, is at once 
 seen by comparing it with the oxamethan, formed by ammonia on oxalic ether 
 (p. 550). Thus, 
 
 2 atoms of oxalic ether, C12H10O8, give an atom of oxamethan, CsH? . N.Oe. 
 1 atom of ammonia, N.H3, gives an atom of alcohol, C4H50.-i-Aq. 
 
 In like manner, 
 
 2 atoms of chloroxalic ether, C,2Clio08, give 1 of chloroxamethan, C8CI5H2 . N.O5. 
 1 atom of ammonia, N.H3, gives 1 of chlorine alcohol, C4Cl50.-|-Aq. 
 
 The rational formula of the chloroxamethan is therefore C4CI5O. . C203+C202Ad. 
 
 When chloroxamethan is dissolved in water of ammonia, and the solution evap- 
 orated, crystals are obtained, which are Chloroxalovinate of Ammonia, their formula 
 being CgHiCb . N.Og, or, in its rational form, C4CI5O. . C2O3+C2O3. N.H4O. , 
 identical in constitution with the ordinary oxalovinate of ammonia, except that it 
 contains chloryl ether in place of common ether; the C hloroxalovinic Aciditself hsis 
 been isolated ; it crystallizes in long needles, which react acid, and combines with 
 all bases to form well-defined salts ; its formula is C4CI5O. . C203-|-C203Aq. 
 
 A crystallographic examination has rendered the isomorphism of the ordinary 
 oxamethan with the chloroxamethan exceedingly probable. 
 
 The results of the action of chlorine on the light muriatic ether have led to re- 
 markable results. Regnault considered this body as affording a test experiment 
 for the actual presence of defiant gas in ether; for if defiant gas be Ac.H., and 
 muriatic ether be Ac.H. . H.Cl., 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 is 
 obtained, isomeric with those arising from defiant gas, but quite different in prop- 
 erties. Thus there is first formed a liquid, C4H4CI2 ; this has the composition of 
 Dutch oil ; next, a liquid forms whose formula is C4H3CI3 ; afterward, bodies con- 
 sisting of C4H2CI4 and C4H CI5, and ultimately C4CI6, Sesquichloride of Carbon. Now 
 the bodies C4H4CI2 and C4H3CI3, as derived from defiant gas, are separated by pot- 
 ash into C4H3CI. with H.Cl, and into C4H2CI2 with H.Cl. ; but the bodies C4H4Cla 
 and C4H3CI3, from muriatic ether, are not decomposed by that alkali. I do not> 
 however, believe in the indefinite replacement of hydrogen by chlorine, which 
 Regnault assumes, and look upon the relation of these series of bodies as being the 
 following : 
 
 From defiant Gas. From Muriatic Ether. 
 
 C4H4Cl2=C4H3Cl.-fH.Cl. C4H4Cl2=C4H3CI.+C4H5Cl. 
 
 C4H3Cl3:=2(C2H.Cl.) and H.Cl. C4H3CI3. 
 
 C4H2Cl4=2(C2H.Cl2). C4H2Cl4=C4Cl5Cl.-i-2(C4H3Cl3). 
 
 C4H.Cl5=C4H3Cl3-|-2(Cl4Cl5Cl.). 
 
 Both these give, finally, sesquichloride of carbon, C4CI6CI. The bodies from 
 olefiant gas, which contain chloride of hydrogen, are decomposed by an alcoholic 
 solution of potash, but thof5«^ 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 is obtained, 
 of which the terminal body is C4H. . CUS., consisting of C4H3S34-2(C4Cl5Cl.). 
 
 On the Theoretical Constitution of Alcohol, and the Bodies derived from it. 
 
 The theory of alcohol and the ethereal combinations is of the more 
 impoitance, as the principles of it regulate our ideas, not merely concern- 
 ing 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 numerous 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 po- 
 tato-spirit, and ethal are alcohols. 
 
 The generic properties of an alcohol are, that its composition may be 
 
 I 
 
666 THEORY OF THE ETHERS. 
 
 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, C4H44-2H.O. C2H24-2H.O. C,oH,o-j-2H.O. C32H32-I-2H.O. 
 Ether, C4H4+H.O. C2H2+H.O. C.oH.o+H.O. C32H32H-H.O. 
 
 Acid, C4H4O. C2H2O4 CioH,o04 C32H32O4. 
 
 Such being the connexion of the bodies of this class, the propositions 
 in which I shall now proceed to imbody the principles of the constitution 
 of the substances derived from wine-alcohol, may be hereafter immedi- 
 ately applied to illustrate the history of the other alcohols. 
 
 1. From the action of sulphuric acid, of chloride of zinc, of fluoride 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 C4H50. + 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 alkali. The oxygen in ether may be replaced by all other electro- 
 negative bodies, while the carbohydrogen, C4Hg, remains constant. By 
 the conditions laid down in p. 467, 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 Ae.O. 
 
 3. By the action of oxidizing agents, hydrogen may be removed from 
 ethyl, and a new radical, C4H3, produced, which, by combining with oxy- 
 gen, forms aldehyd and acetic acid, its symbol being Ac. Aldehyd is 
 protoxide, Ac.O., and acetic acid, peroxide of acetyl, AcOg, 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 in contact with water or acids, produce any 
 form of alcohol or ether. On the contrary, the isethionic acid is essen- 
 tially distinct from these acids, which contain ether, and yields none by 
 any form of decomposition ; olefiant gas, on the other hand, gives, 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 radi- 
 cal, 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 C2H2 ; its symbol El. ; and the Dutch oil is truly 
 Chloride of Elayl. The ethyl may change itself readily into elayl by loss 
 of hydrogen, since C4H5=2C2H2 and H., and it is thus broken up when 
 the hydriodic or muriatic ethers are decomposed by heat, or by potash, 
 or ammonia ; or when sulphuric ether is acted on by an excess of sul 
 phuric 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 C4H4, 
 and consider it simply as an organic base, the oxide of ethyl. 
 
 6. By the action of chlorine on the ethereal compounds and on ole- 
 fiant gas, radicals are generated, which are precisely equivalent to the 
 
THEORY OF THE ETHERS, ETC. 567 
 
 Inree, ethyl, acetyl, and elayl, but which contain chlorine in place of hy- 
 drogen. Their formulae are C4CI3, CI4C5, and C2CI2. This last is the pro- 
 tochloride of carbon, already described ; the first, Acechloryl, exists in 
 chloraldehyd and in chloroacetic acid; the second, Ethchloryl, 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 defiant gas and hy- 
 drogen, into the protochloride of carbon and chlorine, and thus the ulti- 
 mate result is the sesquichloride of carbon, C2CI3. 
 
 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. Thus 
 the body (C4H2CI4), from elayl, consists of C2H2CI.4-C2CI2CI., while the 
 body (C4H2CI4), from the muriatic ether, is really 2(C4H3Cl3)-fC4Cl3Cl3. 
 The body, C4H3CI., from elayl, is 3(C2H2)4-C2Cl2. 
 
 8. The relation of acetyl to ethyl is simply that of internal constitu- 
 tion, described in p. 467. For as benzoic acid contains benzoyl, C,4H502, 
 while this, again, contains, as radical, the carbohydrogen, C,4H5, so ethyl, 
 C4H5, contains within it, ready formed, the radical acetyl, and its formula 
 might be still more correctly written as Ac.Hz. This is simply shown 
 by the action of chlorine on ether, where C4H3 . H2O. becomes first 
 C4H3 . CI2O., and subsequently changes to C4CI3 . CI2O. ; the intermediate 
 compound, AcClg, relating itself to the oxygen, as the sulphurous acid, 
 S.O2, or the benzoyl, C^Hi^Oa, in the sulphuric and benzoic acids. Al- 
 though the connexion of these two radicals is thus analogous to that of 
 amidogen. Ad., and ammonium, Ad.H2=Am., yet a broad line of distinc- 
 tion is drawn between the ammonia and ether theories, by the very defi- 
 nite 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 sufficient evidence. 
 
 Secondary Products of the Alcoholic Fermentation. 
 
 I have already noticed that, besides the carbonic acid and alcohol which are de- 
 rived 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, (Enanthic Ether is produced ; in the spirit dis- 
 tilled 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 (Enanthic 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 0862 ; it 
 boils at 445° ; when heated with caustic soda, it evolves alcohol, and forms cenan- 
 thate of soda, from which the (Enanthic Acid may be separated by muriatic acid. 
 This is a white crystalline solid, which melts at 88°, and distils over at 560° un- 
 changed ; its formula is C14H13O2; 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 Ae.O.-|-Ci4Hi302 ; it is remarkable as the only ether 
 that exists as a natural product, but it may also be formed artificially by means of 
 alcohol and cenanthic acid. 
 
 The Corn Oil, of which the formula is C42H35O4, is lighter than water, of a very 
 penetrating odour, a biting taste, and cannot be distilled without partial decompo- 
 sition. 
 
 The Oil of Potato-spirit has become of much interest, from the discovery that it 
 gives rise to a series of ethereal combinations similar to those of wine alcohol ; the 
 name of A milic Alcohol may be applied to it ; it is colourless, oily, its odour at first 
 
568 AMILIC ETHER, ETC. 
 
 pleasant, but subsequently nauseous ; its taste acrid ; it burns with a blue flame 
 its sp. gr. is 08 12 ; it freezes at 4°, and boils at 294° ; it dissolves in alcohol and 
 ether ; its formula is C10H12O2. In this alcohol a compound radical is assumed to 
 exist, termed Anulyl, CioHn ; its symbol is Ayl., and it is combined with oxygen 
 and water, Ayl.0.4-Aq., as ethyl is in wine-alcohol. 
 
 The Amilic Ether, Ayl.O., is not known except in combination with acids ; its 
 bisulphate, or Sulph-amilic Acid, is obtained by acting on amilic alcohol with oil 
 of vitriol; its formula is Ayl.O. . S.Os-j-S.Os . H.O. ; its barytes salt crystallizes in 
 pearly plates, colourless, very soluble in water and alcohol. This salt is decom- 
 posed when its solution is boiled. The salts of lead and lime are completely sim- 
 ilar in properties. 
 
 Chloride of Amilyl, CioHnCl. or Ayl. CI., 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 Amilyl are prepared ; they possess properties similar to those of the chlo- 
 ride. 
 
 Acetate of Amilyl, Ayl.O.-j-Ac.Oa, 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 Amilyl may be similarly formed. 
 
 By distilling amilic alcohol with glacial phosphoric acid, a colourless aromatic 
 liquid is obtained, having the formula CioHio. 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 is 4918. 
 
 Valerianic Acid. — C10H10O4. When the amilic alcohol is exposed to the air, it ab- 
 sorbs oxygen, but its oxidation is more rapidly effected by heating it with caustic 
 potash. By a loss of hydrogen and absorption of oxygen precisely similar to that 
 by 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, z^CioHg or VI., and its formula becomes VI.O3 
 4-Aq. 
 
 When valerianate of lime is heated, carbonate of lime is formed, and a volatile 
 liquid like acetone distils over ; it is termed Valeron, C10H9O3 giving C.O2 and 
 C9H9O. 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 chromate of potash, 
 an oily liquid is obtained, which is Valerianic Aldchyd, C10H10O2 or Al.O.-j-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 constitu- 
 ted according to the same principles as have been fully described for wine-alcohol 
 
 CHAPTER XXII. 
 
 OF THE ESSENTIAL OILS, CAMPHORS, AND RESINS. 
 
 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 solutions 
 being called essences^ and from their volatility. In virtue of this last prop. 
 
PREPARATION, ETC., OF AMYGDALINE. 569 
 
 erty, 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 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. 78.) To pre- 
 vent even the inj*urious 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 
 U) come into contact with the vapours. These oils are somewhat solu- 
 *ile in water, and, giving to it their odour and taste, form the various 
 dedicated waters. Hence often the same quantity of water must be 
 distilled with fresh quantities of the plant before the oil is in such pro- 
 portion as to separate. 
 
 Most essential oils, as those of turpentine, lemon, peppermint, &c., 
 exist actually in the plant, as secretions from peculiar glands ; but oth- 
 ers are produced only at the moment of distillation, by the decompo- 
 sition of substances which did exist in the plant, and which undergo 
 a kind of fermentation. This is the case with the oils of bitter al- 
 monds, of spircea, of mustard, and these oils possess much more active 
 chemical properties than those of the former class. Another impor- 
 tant 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 ; while others, as the oils of tur- 
 pentine, 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. 
 
 1st 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 Bitter Almonds, it being 
 most abundantly obtained from that fruit. The leaves of the cherry-lau- 
 rel, peach-kernels, &c., also yield it. The oil and the acid both arise 
 from the decomposition of another substance, Amygdaline. This is pre. 
 pared 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 evaporated 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 scarcely soluble ; being 
 dissolved in boiling alcohol, it is finally obtained pure by crystallization. 
 
 The formula of amygdaline is C40H27 . N.O22 ; it forms short silky nee- 
 dles, which are anhydrous, tasteless, and inodorous ; it is very soluble in 
 water, and crystallizes therefrom in large colourless prisms, containing 
 6 Aq. By contact with nitric acid it produces ammonia, oil of bitter 
 almonds, benzoic and formic acids, and by caustic alkalies it is decom- 
 posed into ammonia and Amygdalic Acid, C4oH26024+Aq. 
 
 When bruised bitter almonds are distilled with water, all amygdaline 
 
 4C 
 
570 OIL OF BITTER ALMONDS. 
 
 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, and appears very similar in properties and con- 
 stitution to the vegetable albumen or legumine, described as the active 
 principle in the alcoholic fermentation. (See p. 538.) The emulsine 
 is soluble in water, but insoluble in alcohol. If solutions of ten parts of 
 amygdaline in 100 of water, and 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 amygdaline alone thus : 
 
 1 equivalent of prussic acid, C2H.N., "\ 
 
 2 " Sloaoid, gSS; f lentofamygdalme. 
 7 " water, H7O7, ) 
 
 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 bruis- 
 ed in water both dissolve, and decomposition immediately occurs. The 
 preparation of the oil by distillation can hence be fully understood. 
 
 The mixture of amygdaline and emulsine has been employed as a 
 means of producing a prussic acid of standard strength for medicinal 
 purposes. 
 
 Oil of Bitter Almonds, Hydruret of Benzyl, 
 
 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 evolv- 
 ed, and benzoate of potash formed. The formula of this oil is C14H6O2; 
 but, from the series of compounds to which it gives rise, it is believed to 
 contain an organic radical, C14H5O2, termed Benzyl, and its rational for- 
 mula is therefore Bz.H. (See p. 471.) 
 
 Chloride of Benzyl, Bz.CI., 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 potassi- 
 um, 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(H.Ad.) and Bz.CI. give Bz. 
 Ad. and Ad.H. . H.Cl. ; it forms rhomboidal prisms, which melt at 
 240°, and may be distilled unaltered ; heated with potash, it gives am- 
 monia and benzoate of potash. 
 
 Oxide of Benzyl. Benzoic Acid. — Bz.O.-f-Aq. This acid is found 
 ready formed in the resin of benzoin and in dragon's blood ; it some 
 
COMPLEX BENZOIC COMPOUNDS. 571 
 
 times appears in the urine of herbivorous animals, 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 lb. 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 paper, 
 pasted to the edge of the dish ; the whole is to be covered with a cylin- 
 drical cap of stout packing paper. To render the heal 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 empyreumatic oil, which 
 usually contaminates the sublimed product, being arrested by the drum 
 of blotting paper, through which the vapour of the acid passes freely. 
 
 It may also be extracted from the resins by boiling these with lime ; a 
 soluble benzoate of lime is produced, from which the benzoic acid is pre- 
 cipitated 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 extensive series 
 of salts, of which few require special notice. 
 
 Benzoate of Lime, Ca.O. . Bz.O.+ Aq., crystallizes in brilliant prisms ; 
 at a dull red heat it is decomposed into carbonate of lime and Benzene, 
 the formula of which is C13H5O. Another liquid, Benzin, CizHg, 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, Ad.HgO. . Bz.O., crystallizes in brilliant plates. 
 This salt is employed in mineral analysis to separate iron from manga- 
 nese ; a solution of peroxide of iron, not containing any excess of acid, 
 being completely precipitated by neutral benzoate of ammonia, while the 
 salts of manganese are not affected by it. 
 
 Benzoate of Silver, Ag.O. . Bz.O., is obtained by double decomposi- 
 tion ; crystallizes from a boiling solution, on cooling, in brilliant colourless 
 needles. 
 
 Formobenzoic Acid. — H.Bz.-j-Fo.Oa. If water, saturated with the impure oil of 
 bitter almonds, be mixed with muriatic acid and evaporated, this substance crystal- 
 lizes. The prussic acid is decomposed into formic acid and ammonia (p. 517), and 
 the nascent formic acid coml)ines 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 al 
 monds in water, a similar body is formed, consisting of benzoic acid and hydruret 
 of benzyl, Bz.H.-l-Bz.O. 
 
 Sulphobenzoic Acid. — Ci4H803-l-S205-}-2 Aq. This body is formed by the action 
 of dry sulphuric acid on benzoic acid. A viscid mass results, which, when neutral- 
 ized by barytes, yields a salt permanent in the air, crystallizing in rhomboidal 
 prisms, and having the formula Ci4H803+S205H-2Ba.0.4-3 Aq. From this the 
 pure acid may be obtained ; it is decomposed if its solution be boiled, but when 
 evaporated in vacuo it crystallizes. The sulphobenzoate of copper crystaUizes in 
 large rhombs of a rich blue colour. 
 
 Bromobenzoic Acid, C28H9 . Br.08-|-2 Aq., is formed when benzoate of silver is dty 
 composed 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, Benzonc, CwHsO.* 
 does not form any compounds ; but Benzin, CuHe, produces with sulphuric acid, 
 
57^ OIL OF CINNAMON. 
 
 nitric acid, and chlorine, a series of bodies, of which the formulae alone need be 
 here given ; they are, 
 
 Sulpnobenzide, Ci2l^ • S.O2. Chlorbenzin, Ci2H6C]6. 
 
 Sulphobenzidic acid, C12H3 . S2O5. Chlorbenzid, CijHsCb. 
 
 Nitrobenzide, C12H5.N.O4. Azobenzid, C12H5N. 
 
 I shall have occasion to refer to benzin as a product of the distillation of resm 
 and coal. It is colourless, of an agreeable ethereal odour ; it boils at 187° ; its 
 specific gravity is 85 ; that of its vapour is 2378 ; at 32° it freezes into a crystal- 
 line mass, which melts first at 43°. 
 
 Oil of Bitter Almonds with Ammonia. — By the action of water of ammonia on hy- 
 druret of benzyl, all oxygen is removed, and a crystalline body, Hydrobenzamide, 
 produced ; its formula is C42H1SN2. It is soluble in alcohol, and by boiling the so- 
 lution is decomposed into ammonia and hydruret of benzyl. The nitrogen here en- 
 ters into the constitution of the radical, replacing the oxygen, and the body is Hy- 
 druret of Azobenzyl (C14H5 . fN)-|-H. This azobenzyl is itself also formed in the 
 same process as the former, and also the Azohenzoilic Acid (C14H5 . |N.)-j-gN., which, 
 is benzoic acid, in which all oxygen is replaced by nitrogen. The origin of these 
 bodies is explained by the constitution of the radical benzyl, as described in p. 471, 
 
 In the impure oil of bitter almonds a substance exists, termed Bcnzo'ine, which is 
 isomeric with the oil, its formula being C14H6O2 ; it crystallizes in colourless prisms. 
 By potash it gives benzoic acid and hydrogen ; by ammonia it forms a substance 
 isomeric with Hydrobenzamide. By chlorine it gives muriatic acid, and in place of 
 chloride of benzyl, a crystalline body, which is isomeric with that radical, its form- 
 ula being C14H5O2 ; this is termed Benzcril : when heated with potash it gives the 
 BenzoiHc Acid, which has the formula C24Hii054-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 sulphur and partly by 
 azote ; there should thus be Sulphobenzyl (C14H5S2), corresponding to the azoben- 
 zyl. It is unnecessary, in an elementary work, to enumerate the individual sub- 
 stances, but I look upon their formation as corroborating very much Berzelius's 
 idea, that the true radical of the benzoic series is the carbohydrogen, C14H5, and 
 that the chloride, &c., of benzyl are really oxychlorides, &c. (See p. 471.) Cer- 
 tainly the element which remains truly constant in those reactions (and hence sat- 
 isfies the definition of a radical, p. 467) is C14H5, and not C14H5O2. 
 
 Oil of Cinnamon and the derived Compounds. 
 This oil is found in the bark and flower-buds of the laurus cinnamomum and lau- 
 rus cassia. It is heavier than water, and possesses the odour of the plant in the 
 highest degree. It boils at 428° ; its formula is C2oHn02, 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 generally found in the shops, the (3 oil, the formula of which is 
 C18H8O2. Two resins, a and /?, are at the same time produced. 
 
 o * ^ ■^ r> XT n. f (^ rCSiu, =C3oH|504, 
 
 3 atoms of a oil, ^CeoHaaOe, ) U ..g^^ =.c 2H O. 
 
 The j8 oil of cinnamon, although thus only a product of the decomposition of the 
 true oil, is very important, from the variety of compounds 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(C]8H802) and H.O. 
 giving C)8Hio02 and C18H7O3. The properties of this oil indicate that it contains 
 an organic radical, Cinnamyl, CigHvOz, united to hydrogen. It is Hydruret of Cin 
 namyl, Ci.H., and the oil lighter than water is Ci.Ha. 
 
 Cinnamic Acid, Ci.O.-f-Aq., is formed by exposing the hydruret of cinnamyl to 
 the air ; it absorbs two atoms of oxygen, and forms crystallized 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°, distils over at 554° un 
 changed. Its salts are exceedingly similar to the benzoates. 
 
 Hydruret of cinnamyl combines directly with muriatic acid, with nitric acid, and 
 with ammonia, forming compounds which are solid and crystalline. Their formulae 
 are Ci.H. . H.Cl., Ci.H. . H.Ad., and Ci.H. . H.O.+N.Os. By chlorine one half 
 of the hydrogen of this /3 oil is removed, and a white crystalline body formed, Cis 
 H4 . CI4O2. The chlorine here enters into the constitution of the radical. 
 
OIL OF CLOVFS AND SPIRiEA. 573 
 
 Oil of cinnamon combines with iodidn of potassium and iodine to form a sub- 
 stance which crystallizes in large needles of a brilliant bronze colour, like perman- 
 ganate of potash. Its formula is Ci.H.la-j-K.I. Once formed, it is decomposed by 
 water. It was discovered by Moore, of Dublin, and analyzed by Apjohn. 
 
 The origin of the Balsams of Peru and Tolu is closely related to the oil of cinna- 
 mon. They consist of resinous substances (the a and (3 cinnamic resins'?), and of 
 an oil which may be obtained pure by distillation. It is called Cinnameine ; its for- 
 mula is CigHsOz, being isomeric with the 8 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, Peruvine, is separated, the formula of which is CigHuO;. 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 the balsams are due to Fremy ; but Richter 
 has advanced that the balsam of Peru contains two oils, which he terms Myrio- 
 spermine and Myroxyline, the relation of which to peruvine and cinnameine is not 
 yet established. 
 
 By the action of an excess of nitric acid, both oil of cinnamon and cinnamic acid 
 are converted into oil of bitter almonds and benzoic acid. 
 
 Oil of Cloves, Eugenic Acid, SfC. 
 
 The oil obtained by distillation from the undeveloped flower-buds of the eugenia 
 caryophyllata is a mixture of several bodies. By the action of potash, it is separa- 
 ted into a volatile oil which does not possess active properties, is hghter than 
 water, and consists of CioHs, while a eugenate of potash dissolves. From this 
 solution the Eugenic Acid is precipitated by any strong acid. 
 
 Eugenic Acid. Heavy Oil of Cloves, C24H15O5, is a colourless oil, sp. gr. 1079; it 
 boils at 4700 ; 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 deposites a crystalline 
 substance, Caryophylline, C20H16O2 ; it is soluble in alcohol, insoluble in water. It 
 is volatile. From water distilled with cloves a different body separates in pearly 
 scales, having the formula C20H12O4. It is called Eugcnine. 
 
 The eugenic acid and eugenine are rendered blood-red by contact with nitric acid. 
 
 The Light Oil of Cloves has sp. gr. =0918 ; it boils at 287°. 
 
 Oil of Spirma 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 Hke camphor. The heavy oil is of much in- 
 terest, 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 spiraea 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 (C42H21O18), without any oxygen, might yield three atoms of oil, 
 3(Ci4H604), 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 (C14H5O4), Sali- 
 cyle, Syl., with hydrogen ; it acts as a hydracid in combining with metallic oxides ; 
 its specific gravity is 1173 ; 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 alkaline 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, and is purified by recrystalliza- 
 tion ; 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. 
 
574 OIL OP MUSTARD, ETC. 
 
 By the action of chlorine on salicide of hydrogen, Chloride of Salicyle is formed, 
 Syl.Cl. ; it crystalUzes in rhomboidal tables, which melt and sublime undecom- 
 posed ; bromine and iodine give similar compounds ; with nitric acid it produces 
 Nitrosalicylic Acid, Syl.N.04, which crystallizes in long prisms, and unites with 
 bases forming salts. 
 
 The connexion of salicyl with benzyl is very remarkable ; they contain the same 
 hydrogen and carbon, C14H5, 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 ChlorosaUcamide is C42H15CIS . 
 O6N2, or, properly, SCCnHsOa . |N.)CL ; that is, (Bz.f N.)C1. By the direct action 
 of ammonia on the salicide of hydrogen, the corresponding (C14H5O2 . |N.)-{-H. 
 may be formed. To this new radical, which is evidently Nitruret of Benzyl, the 
 name Azosdicyl might be given (see p. 572). 
 
 Essential Oil of Mustard. 
 
 The oil obtained by distilling the seeds of the sinapis nigra with water is remark- 
 able for an unusually complex constitution, as it contains five elements ; its for- 
 mula being C32H20N4 . S5O5. When pure, it is colourless ; it boils at 289° ; ita 
 specific gravity is 1015 ; that of its vapour is 3370 ; when acted on by nitric acid, 
 it yields sulphuric acid and an organic product ; with caustic potash it forms sul- 
 phuret and sulphocyanuret of potassium, and organic products which have not been 
 examined. With ammonia it forms a substance in large white crystals, the for- 
 mula of which is C32H20N4 . S5O5+4N.H3. Our knowledge of the chemical nature 
 of this oil is yet imperfect. It has been only established that it does not exist in 
 the seeds, being, like oil of bitter almonds, formed at the moment of distillation. 
 
 The seeds of mustard contain two crystalline substances. Of these, Sulphosin- 
 apisine is obtained by a process similar to that used for preparing amygdaline. It 
 is, when pure, white ; soluble in alcohol and water ; it contains the same five ele- 
 ments as the oil, which is probably formed from it by the action of the emulsin of 
 the seed, as is the case with amygdaline. The principle of the mustard seed to 
 which it appears to owe most of its pungency has been termed Sinapisine ; its 
 preparation is complex ; it does not contain any sulphur, and hence can act but 
 indirectly in the formation of the essential oil. Fremy considers the essential oil 
 to be formed by the action of the albumen of the seed on a peculiar acid body, 
 which he terms Myronic Acid ; but this has not been analyzed, and we do not know 
 its relations to sinapisine, with which it may possibly be identical. The formula 
 given above for the oil is that of Dumas ; Lowig has since analyzed it, and denies 
 that it contains oxygen, assigning to it the formula N.Cg . H5S2. Accurate re- 
 searches on the constitution of these bodies are very much to be desired. 
 
 2d Class. — Oils pre-existing in the Plant, Properties not Acid, 
 
 These oils are very numerous, and so similar in properties that a spe- 
 cial 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 substances, 
 in some cases crystalline. When put in contact with iodine, they fre- 
 quently 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 substan- 
 ces, one solid (Slearopten), the other liquid (Elaopten) ; the former gener- 
 ally crystallizes when the oil is long kept. I prefer to term the liquid 
 simply the oi7, and the solid portion the camphor of the plant. We some- 
 times observe these oils forming the camphor artificially, 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 im- 
 portant facts of the history of the oils (elaoptens) containing oxygen r 
 
NEUTRAL ESSENTIAL OILS, ETC. 
 
 575 
 
 Plant yielding the oil. 
 
 Cajeput . . 
 Lavender . 
 Rosemary . 
 Pennyroyal 
 Camphor-tree 
 Valerian 
 Spearmint . 
 Marjoram . 
 Asarura . . 
 Fennel . . 
 xlnise . . 
 Peppermint 
 Rue . . . 
 Olibanum . 
 Cumin . . 
 
 Sp.gr. 
 as Liquid. 
 
 0-927 
 0-896 
 0-897 
 0-925 
 0-910 
 
 0-914 
 0-867 
 
 0-997 
 
 0-902 
 0-837 
 0-866 
 0-860 
 
 Boiling 
 
 347° 
 397° 
 365° 
 395° 
 
 518° 
 
 354° 
 
 446^ 
 323^ 
 
 418= 
 
 Sp.gr. 
 of Vapour. 
 
 C10H9O. 
 C15H14O2 
 C45H38O2 
 
 CoHsO. 
 C20H16O, 
 
 C20H,2O. 
 
 C3.5H280. 
 
 C50H40O. 
 C16H902 
 
 C2oHi20^ 
 
 C20H12O2 
 C21H20O2 
 C28H2803 
 C35H280. 
 C20H12O2 
 
 7690 
 
 5094 
 
 From 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, C2oH,20., 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 pe- 
 culiar acid, Cumenic Acid, whose formula is CaoHjiOa+Aq. ; it is per- 
 fectly white, crystallizes in fine prismatic tables, tastes sour, fuses at 
 197°, and may be distilled unchanged. If cumenate of barytes be dis- 
 tilled at a dull red heat, a colourless liquid oil is obtained, which boils at 
 292° ; it is termed Cymen ; its formula is CigHig, being isomeric with 
 mesitylene ; with sulphuric acid cymen unites, forming Cymensulphuric 
 Acid, Ci8H,2 . S2O6, which forms well-characterized soluble salts. By the 
 action of chlorine and of bromine on the oil of cumin, heavy oily com- 
 pounds are obtained, whose formulae are C20H,, . O2CI., and CaoHn . OgBr. 
 
 It is evident that in these compounds a radical (Cumyl), C2oH,i02, ex- 
 actly analogous to benzyl, may be assumed, and the cymen has the place 
 of benzin. The carbohydrogen of the oil of cumin is termed by Ca- 
 hours Cumen ; its formula isCaoH^; its specific gravity 0'860; it boils 
 at 330° ; it may be prepared artificially also from common camphor ; 
 with sulphuric acid it forms Cumensulphuric Acid, which resembles com- 
 pletely the other acids of that class. 
 
 The stearoptens, or camphors containing oxygen, will be described by- 
 and-by. 
 
 The following table contains a similar view of the most important oils 
 not containing oxygen : 
 
 Plants yielding the Oil. 
 
 Citron . . . 
 
 Copaiva . . 
 
 Parsley . . 
 
 Juniper . . 
 
 Savine . . . 
 
 Cubebs . . 
 Black Pepper 
 
 Bergamotte . 
 
 Turpentine . 
 
 0-847 
 0-878 
 
 0-839 
 0929 
 
 0-864 
 
 343° 
 4730 
 410O 
 311° 
 315° 
 
 315^ 
 
 Formula 
 
 Sp. gr. as 
 Vapour. 
 
 Circular Polarizing 
 Power. 
 
 al 
 
 
 4-80° 9', right. 
 
 > >> 
 
 4-34° 3', left. 
 
 fi 
 
 —3° 5'', left. 
 
 ^^^ 
 
 >% 
 
 
 °.2o 
 
 
 * 460 V, left. 
 
 III 
 
 If 
 
 +29° 3', light. 
 
 -8a 
 
 < 
 
 —43° 3', Ir.fl. 
 
576 ISOMERIC OILS OF TURPENTINE. 
 
 Although these oils have all the same per cent, composition, they dif- 
 fer in the formula of their atom, that of turpentine being CaoHje, that 
 of cubebs, C,5Hi2, and all the others being CioHg. Although, even as giv- 
 en in the table, they constitute a remarkable group of isomeric bodies, 
 yet each one is capable of changmg its molecular condition in various 
 ways, and thus generating other bodies, still more closely isomeric, as 
 they differ only in their action on polarized light. Of these changes 
 J 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 to- 
 tally without action on polarized light. This new liquid is called Tere- 
 bene. If the oil of turpentine be acted on by muriatic acid gas, it com- 
 bines 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 Camphene, 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, while it differs from 
 terebene in forming with muriatic acid a solid product. This oil is 
 termed Camphilene, and the Muriate of Camphilene is distinguished from 
 the muriate of camphene in being quite 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 power- 
 fully to the left : with chlorine they all give heavy liquids, all of which 
 have the formula C2oH,2Cl4, but are distinguished from each other by their 
 action upon polarized light; the Chlorcamphene presenting the anom- 
 alous 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, however, 
 the materials be left to themselves, after some time, violent, almost ex- 
 plosive action sets in, copious red fumes are given off, and a resinous ma- 
 terial formed, which, by boiling with more nitric acid, dissolves, and the 
 solution, on cooling, yields crystals of Turpentinic Acid. Its composition 
 was found by Bromeis to be CHHeOy-f-Aq. The exact theory of its for- 
 mation 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 C5H4 exists probably in all essential oils, for it will be seen, 
 by reference to the former table of oils containing oxygen, that their for- 
 mulse consist in multiples of C5H4, combined with oxygen, or with the 
 elements of water. 
 
 B. Of the Camphors or Stearoptens of the Oils. 
 The most remarkable substance of this class is the common camphor. 
 
CAMPHOR. CAMPHORIC ACID. 
 
 577 
 
 whicli is extracted from the wood of the laurus and dryabalanops cam- 
 phora by distillation with water. In the plant it is mixed with the cam- 
 phor-oil (CasHifiO.), from the gradual oxidation of which it appears to be 
 produced. 
 
 Camphor forms a white semitransparent mass, crystallized in irregu- 
 lar 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 at 
 347°, and boils at 390°, subliming unaltered ; it is sparingly soluble in 
 water, but easily so in alcohol and ether ; its formula is CaoHigOg. The 
 specific gravity of its vapour is 5317, which might be considered as form- 
 ed by one volume of vapour of camphene and half a volume of oxygen 
 (4776+ 551 'S). Hence camphor and camphor-oil may be looked upon 
 as oxides of an oil of the turpentine family. 
 
 When camphor is heated with lime, water, and an oil, Camphron 
 (C30H22O.), are produced. With muriatic acid it unites, forming a col- 
 ourless liquid, whose formula is CaoH,, . O2CI. By boiling with strong 
 nitric acid, it is completely converted into Camphoric Acid, 
 
 This acid crystallizes in small rhomboidal tables, which taste 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 C10H7O3 ; 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 Camphorate 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 form- 
 ed, and a volatile oil passes over, having the formula C2oH,4, and identical 
 in every respect with the Cymen obtained from oil of cumin, as descri- 
 bed in p. 575. 
 
 When camphor in vapour is passed over hydrate of potash, heated to 
 about 700°, an acid is formed, which has the formula CgoHi-Oa+Aq. 
 This Camphoric Acid fuses at 176°, and boils at 482° ; it may be distil- 
 led unchanged. It is insoluble in water, but dissolves abundantly in al- 
 cohol and ether, and crystaUizes from these solutions on cooling. When 
 it is heated with phosphoric acid, a volatile oil is produced, Campholen, 
 having the formula CigHig. When campholeate of lime is distilled, an- 
 other oily fluid is formed, whose formula is CigH^O. 
 
 Of the camphors of the other volatile oils, only a few require any de. 
 tailed notice. The characters of most of them are given in the follow, 
 ing table : 
 
 Plant giving the Camphor. 
 
 Sp. Gr. 
 as Liquid, 
 
 Melting 
 Point. 
 
 Boiling 
 Point. 
 
 Sp. Gr. 
 
 of Vapour. 
 
 Rose (Otto) . 
 Parsley . . 
 Iris Florentina 
 Elicampane . 
 Asarum . . 
 Fennel . . 
 Anise . • . 
 Peppermint . 
 Cubebs . . 
 Turpentine . 
 
 77° 
 70° 
 
 550° 
 552° 
 
 1014 
 
 108° 
 
 104° 
 
 68° 
 
 64° 
 
 91° 
 
 530° 
 
 428 3 
 430° 
 406° 
 
 1057 
 4D 
 
 311' 
 
 5680 
 5455 
 
 C.H. 
 
 C]2H704 
 C4H4O. 
 C7H6O. 
 Ci6H,i04 
 
 C20HI2O2 
 
 C20H;2O2 
 C21H20O2 
 C16H14O. 
 
 CaoH2o04 
 
578 RESINS OF TURPENTINE. '' 
 
 On comparing these formulae with those of the corresponding oils 
 (p. 575). 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 phosphoric 
 acid or of oil of vitriol, a light oil was obtained, having the formula Cg, 
 Ills, which is termed Menthen. By the action of chlorine, a thick, heavy 
 liquid is produced, C21H14 . ClgOa. By nitric acid, menthen yields a heavy 
 oily liquid, CaiHjgOg, which possesses acid properties ; and with chlorine, 
 menthen yields a sirupy yellow liquid, having the formula C21H13CI5. 
 
 The anise-camphor yields with bromine a crystalline substance, C20H9 . 
 BrjOg, and with sulphuric acid an oily substance, Aniso'ine, isomeric with 
 itself. By nitric acid it is converted into a body which crystallizes in 
 long needles, Anisic Acid, CieHgOs+Aq., which forms salts with metal- 
 lic oxides, and gives by farther action the Nitranisic Acid, Ci^s • N.O3+ 
 Aq., and Nitranisid, C20H10 . N2O10. 
 
 C. Of the Resins. 
 
 The bodies of this class approach closely to the camphors in compo- 
 sition 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 the remaining expressed in a table. 
 
 Resins of Turpentine. — The ordinary white resin coexists, 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, while 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. This Pinate 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 resin- 
 ous powder, which may be dried at a moderate heat. 
 
 When quite pure, pinic acid is colourless ; it melts at 257°, but be- 
 comes soft at 149° : its solution in alcohol reacts acid. It expels car- 
 bonic acid from bases ; its alkaline salts are soluble ; its earthy and me- 
 tallic salts insoluble in water, but many of them soluble in spirit ; its for- 
 mula is C40H30O4. 
 
 When a solution of pinic acid in alcohol is long exposed to the air, it 
 absorbs oxygen and forms Oxypinic Acid,i\\Q formula of which is C40H3B 
 Og ; it is a stronger acid than the pinic. When heated with lime, pinic 
 acid is decomposed, and three different volatile oils obtained, which need 
 not be specially noticed. 
 
 The Sylvic Acid remains when the pinic acid is dissolved by weak al- 
 cohol. As it is not pure, the residue is to be dissolved in two parts of 
 
COMPOSITION OP RESINS. 
 
 579 
 
 boiling spirit of 0*865 ; on cooling, the sylvic acid separates. By a sec- 
 ond solution, all the traces of pinic acid may be removed. The pure syl- 
 vic 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 C40H30O4. Its salts are ex- 
 actly 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 Colo- 
 phonic Acid ; it exists in small quantity in common resin. 
 
 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 C40H31O6; the less soluble, or B res- 
 in, that of C40H39O5 ; 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 un- 
 decomposed (as colopholic 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 Balsams. 
 Frequently there are many kinds of resins mixed together, but they all 
 possess the characters of fusibility, insolubility in water, and of being 
 dissolved by alcohol, ether, essential oils, and alkaline solutions. Their 
 composition is given in the following table : 
 
 Anime Resin . . . . ? /-• TT._r\ B. Sandarach 
 
 Elemi Resin . . 
 
 Fossil Copal . . 
 
 B, Mastic Resin . 
 
 Antiar Resin . . 
 
 B. Copal Resin . 
 
 Birch Resin , . . 
 
 A. Mastic Resin . 
 
 Copaiva Resin 
 
 A. Elemi Resin . 
 
 B. Olibanum Resin 
 
 C. Sandarach . . 
 Ammoniac Resin . 
 B. AssafoBtida . . 
 Guiacuin .... 
 Bdellium Resin . 
 A. Sandarach . . 
 
 C40HS3O. 
 
 C40H32O. 
 . C49H31O2 
 
 C40tl3oC2 
 . C40H31O3 
 . C40H33O3 
 
 ' ]• C40H31O4 
 
 •;;C4oH320i 
 
 . C)4oH3o06 
 
 . C40H25O9 
 
 C40H26O9 
 
 . C45H23O10 
 
 C40H31O5 
 
 A.Euphorbium . \ '. | C40H31O6 
 
 Asphaltene } C40H32O6 
 
 A. Olibanum .... 5 
 
 Labdanura C48H33O7 
 
 Pasto Resin C40H32O8 
 
 Sagapenum C4oH2909 
 
 Scammony C4oH330ao 
 
 Jalap Resin C4oH340a) 
 
 •Galbanum C40H27O7 
 
 Dragon's Blood . . . C4oH2i08 
 Gamboge C40H23O8 
 
 A. Assafcetida .... C4oH260i9 
 Acaroid Resin .... C40H20O12 
 Opoponax C40H25OU 
 
 B. Benzoin Resin . . . C40H22O9 
 A. Benzoin Resin . . . C40H26O7 
 
 In all this series of resins, it is evident that the carbon remains unal- 
 tered, and Johnstone has shown that they may all be considered as deri- 
 ved from oils having the turpentine constitution =C4oH32. 
 
 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 Eu- 
 rope. It is also found, cast on shore by the waves, along the coast 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, be- 
 longing to a former geological epoch; its specific gravity is 1*067; 
 
580 
 
 AMBER, SUCCINIC ACID, ETC. 
 
 when heated it melts, and is then totally decomposed ; its relations to 
 electricity have been fully noticed, p. 108. Amber is found to be a mix. 
 ture of two resins, which are soluble in alcohol and ether, a bitumen in- 
 soluble 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 varnish- 
 es, but to chemists 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 
 heat. It is found in small quantity also in colophony, and is abundantly 
 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 tw, t, a in the figure, which 
 have the formula C4H2O34- Aq. ; when heated to 350° it melts, 
 abandoning half its water, and at 450° sublimes in an anhy- 
 drous state ; its solution in water is markedly acid ; when 
 heated with lime, a volatile hquid is produced, Succinone, the 
 exact formula of which is not established. 
 The salts of succinic acid are mostly soluble and crystalU- 
 zable. 
 
 The Succinate of Soda, prepared by neutralizing the acid by carbon- 
 ate 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 per- 
 manent in the air, and very soluble in water. The Succinate 
 of Ammonia, which is much used in mineral analysis for the 
 separation 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 Succinate of the Peroxide of Iron is precipitated when an 
 alkaline succinate is added to any 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 
 
 QHg . O4N. 
 
 The rare mineral, Mellite (see p. 498), is only found accompanying 
 amber in the deposites of lignite. 
 
 Caoutchouc. Indian Rubber. — This substance, now so much used in 
 the laboratory for connecting pieces of apparatus, and so extensively em- 
 ployed in the arts, possesses much similarity to the resins. It dissolves 
 but imperfectly even in ether, its proper solvent being the volatile oils, 
 into which it is converted by distillation. One of these is the lightest 
 liquid known, its specific gravity being but 0.654 ; it boils at 92° ; it has 
 been termed Faradyn. Another, known as Caouichene, has a specific 
 
CONSTITUTION OF FATTY BODIES. 581 
 
 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, they appear all to 
 have the same composition as oil of turpentine. 
 
 CHAPTER XXIII. 
 
 OF THE SAPONIFIABLE FATS AND OILS. 
 
 The substances of this class are found both in the animal and vegeta- 
 ble 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 cellu- 
 lar texture of the fruit. The leaves or roots seldom contain any fatty 
 matter. The /ats 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 li- 
 quid constituent. The greater number of fats consist of two simple fats, 
 Stearine and Margarine, and a simple oil, Olein ; but these three bodies, 
 which may be considered as the bases of all fats and oils, are accompa- 
 nied generally by smaller quantities of solid or liquid fats, which are 
 often peculiar to a particular animal or plant. These fatty bodies are 
 all faced ; that is, they cannot be distilled without decomposition ; but 
 they are totally converted by heat into volatile bodies, undergoing, in 
 some cases, singular metamorphoses, which will be described in the his- 
 tory 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 inter- 
 spersed through the fats. A great number of oils, however, absorb ox- 
 ygen very rapidly, and, evolving carbonic acid, change into a soft resin- 
 ous body ; they are hence termed Drying Oils, and are used so in paint- 
 ing. This drying quality is increased by combining the oil with a small 
 quantity of a base, as oxide of lead. 
 
 The most important fact in the history of the fixed oils and fats is, 
 that, by the action of alkalies, they are converted into soaps ; whence 
 the name o^ saponijiahle given to the class. By means of the alkali, 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 
 a sweet taste, which is the same, no matter what kind of fat had been 
 employed. This substance, the swee't 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. 
 
 Of Glycerine. — CgllA+Aq. Eq. 1157-4 or 92-3. To obtain gly- 
 cerine, any fatty matter is to be saponified by a caustic alkali. The 
 solution being decomposed by tartaric acid, which precipitates the fatt}- 
 
f'JSS GLYCERINE, STEARIN E, AND STEARIC ACID. 
 
 acid, is to be evaporated, and the glycerine dissolved out by strong alco- 
 hol. It may also be obtained by saponifying the fat by oxide of lead, 
 and treating the watery solution with sulphuretted hydrogen to precipi. 
 tate some oxide of lead, which dissolves ; the glycerine may then be ob- 
 tained 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 sirup, 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 CjaH,, . O10CI3, and with bromine it gives a 
 dense oily liquid, whose formula is CigHu . OjoBrg. 
 
 When glycerine is mixed with oil of vitriol, they unite without black- 
 ening, and form an acid compound, Sulphoglyceric Acid, the formula of 
 which is CfiHyOs . 2S.O3 . H.O. With bases this acid forms soluble 
 salts, having considerable analogy to the sulphovinates. The Sulpho- 
 glycerate of Lime crystallizes in long delicate needles, whose formula is 
 C6H7O5 . S.O3+S.O3 . Ca.O. The compounds of glycerine with the 
 fatty acids constitute the various kinds of fats and oils. 
 
 Of Stearine and Stearic Acid, 
 
 Stearine is the essential constituent of all solid fats, and preponder- 
 ates in proportion to their consistence. It is best obtained from mutton- 
 suet, either by washing it with ether, as long as anything is dissolved, 
 or by mixing up melted suet with six times its volume of ether, and sub- 
 jecting the mass, when cold, to strong pressure. In both cases the stea- 
 rine 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 
 Ci42Hi4iOi7, consisting of 
 
 1 atom of glycerine, =C6H705, ^ 
 
 2 atoms of stearic acid, =rCi36Hi320io, > =Ci42Hi4iOi7. 
 2 atoms of water, =H202, 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 dissolved 
 in boiling alcohol, whence the pure acid crystallizes, on cooling, in brill- 
 iant white plates. 
 
 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 lit- 
 mus ; its composition, when crystallized, is CgsHeeOs+S Aq. When heat- 
 ed in contact with lime, carbonic acid is formed, dnd a volatile liquid, 
 Stearon, whose formula is CegHeeO. 
 
MARGARINE AND MARGARIC ACID. 583 
 
 Stearic acid is but feeble in its action : it expels the carbonic acid 
 from the alkalies only when the solution is boiling. It is bibasic, form- 
 ing two classes of salts, the Bistearates, which contain one atom of water 
 and one of fixed base, and the Neutral Stearaies, which contain two atoms 
 of fixed base. The alkaline 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 decomposed, one half of the 
 potash becoming free, and tlie Bistearate of Potash precipitating in minute 
 crystalline scales. A. solution of soap precipitates all earthy and metal- 
 lic 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, =C4H50., \ 
 
 2 atoms of stearic acid, =Ci36Hi320io, > Ci4oHi390i3=l atom of stearic ethei. 
 2 atoms of water, =H202, ) 
 
 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 ten- 
 dency is removed by the very improper addition of one part of arsenious 
 acid to about 2000 of stearic acid. 
 
 Of Margarine and Margaric Acid, 
 
 Margarine exists along with stearine in most fats, but is most char- 
 acteristic 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 crys- 
 tallizes 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 C74H74OJ2. 
 
 1 atom of glycerine, =C6H705, i 
 
 2 atoms of margaric acid, ^CesHeeOs, > =C74H740i2, 1 atom of margarine. 
 1 atom of water, =H.O., ) 
 
 By the action of bases it is separated into glycerme and margaric acid. 
 
 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 C34H33O3+ 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 C33H33O. 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 vol- 
 atile oily substance obtained, having the composition of defiant gas. 
 
 The experiments of Redtenbacher have indicated a remarkable source 
 of margaric acid in the distillation of stearic acid. The distilled product, 
 though in appearance unchanged stearic acid, yet does not in reality 
 
584 OLEIN AND OLEIC ACID. 
 
 contain any trace of it, being a mixture of margaric acid, of margarone, 
 and of the volatile oily carbohydrogen. The reaction being that 
 
 (6 atoms of margaric acid, C204H204O24, 
 1 atom of water, H.O., 
 
 1 " margarone, CasEUaO., 
 1 " carbonic acid, C.O2, 
 The oily carbohydrogen, C34H34. 
 
 Redtenbacher doubts the real existence of slearone, as none of it is 
 produced in this reaction. 
 
 The salts of margaric acid resemble perfectly the stearates in their 
 properties, but the acid being monobasic, there is but one class of marga- 
 rates. The pearly lustre of the crystalline scales of the margarate of 
 potash gave occasion to the name of this acid, from the word fiapyapi' 
 TTjg, 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, indicating an 
 hypothetic carbohydrogen, C34H33, by R., the stearic acid becomes R2 + 
 O5, and the margaric acid, R. + O3, being related as hyposulphuric and 
 sulphuric acids. Also, as Redtenbacher has remarked, all the results 
 obtained might be accounted for by ascribing to margarone the formula 
 C34H33O., in which case it becomes R. + O., and the volatile oil may be 
 R.+H. Farther researches are, however, wanted to give experimental 
 evidence on these points. 
 
 Of Olein and Oleic Acid. 
 
 Ole'in exists in small quantity in the various solid fats, but constitutes 
 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 great- 
 est part may be separated by exposure to cold, when they crystallize. 
 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 so. 
 lution 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, CgHyOs, 
 
 2 atoms of oleic acid, CssHtsOs, \ produce 1 atom olein, C94H87O15. 
 2 atoms of water, H2O2, 
 
 H7O5, i 
 bHtsOs, > 
 O2, ) 
 
 Oleic Acid is obtained by saponifying olein 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 20° F., it congeals as a mass of needly crystals. Its spe- 
 cific gravity at 60° 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 determin- 
 ed by Varrentrapp to be C44H3904-f-Aq. ; its alkaline 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, plas- 
 tery substances, insoluble in water. The Oleate of Lead is soluble in 
 ether, by which it may be perfectly separated from the stearate or mar- 
 
SEBACIC ACID, ETC. > 585 
 
 garate of lead. The Oleic Ether was formed by Varrentrapp by passing 
 muriatic acid gas into a solution of oleic acid in alcohol. It is a colour- 
 less liquid, sparingly soluble in alcohol, lighter than water, but heavier 
 than alcohol, from which it is deposited as it forms; its formula is 
 C«H39044-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 Sebacic Acid and a liquid carbohydrogen, 
 isomeric with defiant gas ; sebacic acid is not produced by the distilla- 
 tion of any other fatty substance than oleic acid, and hence may be con- 
 sidered as characteristic of it. The decomposition consists in that 
 
 r 1 atom of sebacic acid, C10H9O4, 
 
 2 atoms of hydrated oleic acid, ) „-^j„„_J 3 atoms of carbonic acid, C3O6, 
 CggHgoOio, $ proauce< carbohydrogen, C71H71, 
 
 V residual charcoal, C4. 
 
 Sehacic Acid had been considered as a product of the destructive dis- 
 tillation of all fatty bodies ; but it has been shown by Redtenbacher 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 ace- 
 tate of lead, a white precipitate is obtained, which, being decomposed by 
 sulphuretted hydrogen, gives sulphuret of lead, while the pure sebacic 
 acid dissolves, and may be obtained crystallized by the evaporation 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 alkaline sebacate, the acid is pre- 
 cipitated 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 a totally dif- 
 ferent substance, Acroleon, The dry sebacic acid has the formula 
 CjoH O3 ; when crystallized it becomes CioHgOa+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 conveniently studied in re- 
 lation to their origin. 
 
 A. If stearic acid be digested with two or three times its weight of common 
 aquafortis at a moderate heat, a very lively action commences after some time, and 
 copious red fumes are given off. When the mixture has ceased to froth up, and 
 the action of the acid ceases, the only product forms a colourless layer on the sur- 
 face of the acid liquor, and is found to be pure Margaric Acid. The change here is 
 evidently a simple oxidation, as R2-I-O5 and 0. give 2(R.-{-03), as described in p. 584 
 
 If the fatty acid be acted on by successive quantities of the nitric acid until it 
 disappears, the watery liquor deposites, on cooling, abundance of crystallized Suc- 
 cinic Acid, 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 form- 
 ed by the action of nitric acid on the peculiar woody tissue which exists in cork, 
 Suberine, and which will be hereafter described. 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 decom- 
 posed in great part ; it precipitates solution of acetate of lead ; its alkaline salts are 
 soluble and crystaUizable ; when crystallized, the formula of the acid is CsHeOg-j- 
 Aq. The Suberic Ether was prepared as described above for the oleic ether ; it 
 is liquid, and its formula is C8H603-|-Ae.O. By the distillation of the suberate of 
 lime, a volatile liquid, Suberone, is obtained, whose formula is C7H6O. 
 
 4E 
 
586 HMELIC, ADIPIC, LIPIC ACIDS, ETC. 
 
 The artificial formation of the succinic and suberic acids in this way is exceed- 
 ingly curious ; but Bromeis and Laurent, to whom the observation 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, four other acid bodies, of which, however, a very slight notice will 
 suffice. 
 
 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 C-jHeOs-^-Aq. 
 
 Adipic Acid resembles closely the former ; it dissolves in water, alcohol, and 
 ether ; melts at 223° ; it sublimes in very beautiful crystals ; its formula is ChH* 
 Or-j-a Aq., it being a bibasic acid. 
 
 The Lipic and Azoleic acids are still less important, and our knowledge of their 
 constitution very imperfect. All these bodies are obtained from the mother liquors, 
 from which the succinic and suberic acids have crystallized. 
 
 The most important products of the action of nitric acid on oleic acid, or on olein, 
 are Eldidine and the Eididic Acid ; these bodies are of pharmaceutic interest, from 
 their constituting the Citrine Ointment, or Unguentum Nitratis Hydrargyri of the 
 Dublin and London pharmacopoeias. 
 
 Eldidine 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 alkalies, 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 decomposing the alka- 
 line 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. 276) 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, while the elaidic acid crystallizes 
 in large, briUiant, 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 crys- 
 tallized elaidic acid has the formula C72H6605-|-2 Aq. ; it is a bibasic acid. The 
 Elaidate of Silver is hence C72H6605+2Ag.O. ; and the Elaidic Ether, which is a 
 colourless fluid lighter than water, consists of CvaHeeOs-j-H.O. . Ae.O. 
 
 The orange-red oil, which is formed simultaneously with the elaidic acid, has not 
 been, as yet, accurately examined, and hence we cannot explain by precise formulae 
 the mode in which these bodies are generated. It is this oil which gives to the 
 Citrine Ointment its characteristic colour and smell ; it is lighter than water, and 
 dissolves in alkaline 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 mercurial salt always con- 
 tains, 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 tha 
 ointment. 
 
 Both oleic and elaidic acids give origin, when heated with fused hydrate of pot- 
 ash, to a peculiar fatty acjd, discovered by Varrentrapp ; it is white, solid, and crys- 
 talline ; melts at 144°, and has the formula C32H3o03-j-Aq. There is formed, at the 
 game time, a large quantity of acetic acid. Another point of connexion between 
 the oleic and elaidic acids is, that by distillation both furnish sebacic acid. 
 
 The Acroleon, to which is due the exceedingly sharp and disagreeable smell of 
 highly heated oil or fat, is generated by the decomposition of the glycerine, and in 
 Buch exceedingly small quantity, that its isolation has not yet been successfully at- 
 tempted. According to the observation of Brandes, it is a colourless oil, of sp. gr 
 
ACTION OF SULPHURIC ACID ON MARGARINE, ETC. 587 
 
 578, which, when distilled with caustic soda, becomes inodorous, while the soda 
 combines with a fatty acid ; no analytical investigation of it has been as yet made. 
 
 Action of Sulphuric Acid on Margarine and Ole'ine. 
 
 When olein is mixed with oil of vitriol, the sulphuric acid combines with both 
 the glycerine and the oleic acid, forming sulphoglyceric and sulphole'ic 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, while the sulphoglyceric acid and the excess of sulphuric 
 acid dissolve. The sulphole'ic acid thus obtained forms, with lime and barytes, 
 soluble salts, which are analogous to the sulphovinates ; 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 Metaole'ic and the Hydroleic 
 Acids. 
 
 These acids are both liquid like oleic acid ; they are principally distinguished, as 
 to properties, by the sparing solubihty of the former in alcohol, and are thus separa- 
 ted. The constitution of these bodies had been examined by Fremy at a time 
 when the true constitution of the oleic acid had not been established, and the formu- 
 lae he assigned to them are not now admissible. They are isomeric with each other ; 
 when distilled, they produce carbonic acid, and two volatile liquids, Olein and Elaen, 
 which are isomeric with olefiant gas. From the circumstances 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 
 metaoleic acid has evidently the same composition as the hydrated oleic acid, and 
 its formula is therefore C44H40O5 when in combination, and C44H41O6 when free. Its 
 decomposition by heat consists in the separation of 3C.O2, and C41H41 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 sulphomargaric acid is produced, which, being treated similarly to the sulph- 
 ole'ic acid, gives two other acids, the Metamargaric and Hydromargaric. These 
 are soluble in alcohol, from which they crystallize by cold, so combined as to pro- 
 duce distinct salts, and to affect all the characters of an independent acid, called by 
 Fremy the Hydro mar gar itic. 
 
 If the mixed solutions of sulphomargaric and sulphole'ic acids be left to decom- 
 pose without heat, in place of being boiled, the metamargaric and metaoleic acids 
 separate and float on the top, but the hydromargaric and hydroleic acids remain 
 dissolved, and separate only by bringing the solution to boil. Each of the products 
 thus obtained is to be dissolved in alcohol, and the modified margaric acids crystal- 
 lize on cooling, while the modified oleic acids remain dissolved. The metamarga- 
 ric acid is polymeric with the margaric acid ; its formula is C68H6606-[-2 Aq., but 
 the hydromargaric acid contains the elements of four atoms of water more, its 
 formula being CesHvoOio-}-^ Aq. 
 
 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 transparent 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 of these oils is 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 coag- 
 ulate 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 boil- 
 ing alcohol, from which the stearine crystallizes on cooling, exactly as described for 
 ordinary stearine. 
 
 The cocoa-stearine is white and crystalline ; its specific gravity is 0925 ; insolu- 
 
588 PALMITINE, PALMITIC ACID, ETC. 
 
 ble in water ; it dissolves but sparingly in alcohol, except when boiling ; it is moro 
 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 brilliant white ; it 
 fuses at 95°, and cannot be distilled without total decomposition. Its formula was 
 found by Bromeis to be C27H2603-[-Aq. ; its alkaline salts are soluble, but the earthy 
 and metallic salts are insoluble in water. By the process described for oleic ether, 
 the cocoa-stearic ether was prepared by Bromeis ; it is a clear oil, lighter than wa 
 ter ; its formula is C27H2603-j-Ae.O. 
 
 Palm Oil and Palmitic Acid, 
 
 This solid oil, which is now extensively employed in the manufacture of yellovr 
 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 abundantly 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 crystallizes therefrom 
 by cooling. Its formula in crystals is C64H6206-t-2H.O. ; it is a bibasic acid ; its 
 silver salt is C64H6206-|-2Ag.O. 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 C64H6206-|-2Ae.O. By distilla- 
 tion, the palmitic acid is not altered ; by the action of chlorine, hydrogen is removed 
 from it, and an acid containing chlorine produced, the formula of which appears to 
 be C64H54 . ClgOe. 
 
 The constitution of palmitine was found by Stenhouse to be expressed by the 
 formula C^oHeeOg, from which should follow, that the substance united with the pal- 
 mitic acid is formed of C6H4O2, and hence diflfers from common glycerine, CeHrOs, 
 in having lost the elements of three atoms of water. This would be a very impor- 
 tant fact to reinvestigate. 
 
 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 separated from the third, 
 which has been termed by Playfair Myristicine. Of the fats soluble in 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 crystaUization from its ethereal solution ; it has 
 a silky lustre, and melts at 88°. When saponified, it yields glycerine and Myristi* 
 Acid. This substance is snow-white and crystalline, easily soluble in hot alcohol 
 and then reddening litmus ; it melts at 120° ; its composition is expressed by the 
 formula C28H2703-|-Aq. ; its salts are very well characterized and crystallizable. 
 The Myristic Ether is analogous in constitution to the stearic ether (583), consist' 
 ing of 
 
 Two atoms of myristic acid, =C56H5406, i 
 
 One atom of ether, =C4H50., > One atom of myristic ether, CeoHeoOg. 
 
 One atom of water, =H.O., ) 
 
 The myristicine was found by Playfair to have the formula CusHnsOis, consis^ 
 ing of 
 
 Four atoms of myristic acid, =Ci,2Hio80i2, ) 
 
 One atom of dry glycerine, =C6H402, > CnsHnsOjs. 
 
 One atom of water, =H.O., J 
 
 Bv distilling myristicine, much acroleon is generated, but no sebacic acid. 
 
BUTYRINE, CAPROINE, ETC. 589 
 
 r)rdinary Butter. Butyric, Capro'ic, and Capric Acids, 
 
 iiutief is a mixture of six different fats, viz., common stearine, margarine, and 
 wleine, with butyrine, caproine, and caprine ; by melting the butter, and keeping it for 
 some days at a temperature of 68°, the stearine and margarine crystaUize, while 
 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 farther pu- 
 rification depends on successive solutions in alcohol, but none of them can be con- 
 sidered as having been obtained completely pure. 
 
 Butyrine is a colourless oil, with the odour of heated butter. It solidifies at 32° ; 
 with alkalies, it gives a soap, and sets glycerine free. Its elementary composition 
 is not known. 
 
 Caproine and Caprine cannot be obtained sufficiently free from butyrine, or from 
 each other, to be described. 
 
 When butter is saponified, and the soap decomposed by tartaric acid, stearic, 
 margaric, and oleic acids separate, while the other acids remain dissolved. On dis- 
 tilling this liquor, the butyric, capric, and caproic acids pass over along with the 
 ^ater, and, being neutralized by barytes, the three barytic salts are separated by 
 repeated crystallizations. Of these acids, the history of the Butyric Acid is most 
 complete. It 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 0976 ; 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 
 CTHeOs-j-Aq. ; when distilled with lime, it gives a neutral volatile liquid, Butyrone, 
 whose formula is CeHeO. The Caproic Acid agrees in properties closely with the 
 butyric acid, but has a characteristic odour of sweat ; its formula is Ci2H903=:Aq. 
 The Capric Acid crystallizes in fine needles, which melt at 66°, and have the for- 
 mula CisHuOa-j-Aq. 
 
 Of Fish Oils, Delphinine, and Delphinic Acid. 
 
 These oils are generally composed of ordinary margarine, stearine, and oleine ; 
 but some, as whale oil and dolphin oil, contain a peculiar fat, Delphinine, which 
 yields Delphinic Acid. From the fish oil the delphinine is extracted by cold alcohol, 
 which dissolves it more readily than the other oilg; it is liquid, of specific gravity 
 0954 ; 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 CioHgOs-j-Aq., 
 and when distilled with lime, it gives a volatile neutral liquid, Delphinon, C9H9O. 
 
 The delphinic acid has been found in the berries of the viburnum opulus, and its 
 composition being the same, and its properties very closely resembling those of the 
 valerianic acid, I think it very likely that a re-examination of it would demonstrate 
 its identity with that remarkable vegetable acid. 
 
 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 ricine, 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 decomposed 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-oleic Acid, which is not vol- 
 atile. 
 
 Purified by recrystallization from alcohol, the ricino-stearic acid forms pearly 
 scales, which are easily soluble in alcohol, redden litmus, and do 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 sub- 
 stance, termed by Boudet Palmine ; it is white, of a waxy appearance, and melts at 
 1510 ; it is easily soluble in alcohol and ether ; with alkalies, it yields glycerine 
 and Palmic Acid. We do not possess any knowledge of the elementary composi- 
 tion of these bodies. 
 
590 MANUFACTURE OP SOAP. 
 
 The products of the complete oxidation ot castor oil by nitric acid have been ac- 
 curately examined by Mr. Tilly. The action is violent, and much nitrous acid 
 fumes are given off. Besides suberic and lipinic 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 without being in great part decomposed. 
 Its formula was found to be CuHiaOa-l-M- ; he formed the ether of this acid in the 
 way described for oleYc ether, and ascertained its formula to be CuHiaOa-j-Ae. 0. This 
 body is termed the Peroenanthic Acid, as it contains the same carbon and hydrogen 
 as the oenanthic acid which exists in wine, as described in page 567, but combined 
 with an atom more of oxygen*. 
 
 Oil of Tiglium, Crotonine. Crotonic Acid. 
 The experiments that have been made on this oil have not given very satisfac- 
 tory results : by saponification, it yields an acid which is exceedingly volatile ; but 
 whether the active properties of the oil reside in this crotonic acid is not estab- 
 lished, nor have any analytical results been obtained 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 
 a detailed account of their manufacture would be out of place in the pres- 
 ent work, yet it may not be uninteresting to notice briefly some cir- 
 cumstances of the processes employed, which could not be deduced 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 ; 2ol, hard yellow soap, 
 which is made from soda with tallow, palm oil, and resin ; 3d, soft soap, 
 in which the alkali is potash, combined with whale or seal oil, and some 
 tallow. The difference of consistence depends principally upon the af- 
 kali ; as the fatty salts of soda unite with water to form true hydrates, 
 which are completely solid, while the potash salts absorb water, and form 
 a semitransparent gelatinous mass, such as is 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 Hme ; the soda-ley being brought to boil, the tallow 
 is added in small portions at a time, until the free alkali has been all 
 combined with fatty acids, and the ley will saponify no more. The li- 
 quor contains then free glycerine, and the fatty salts of soda, all dissolved 
 together in the water ; and as the soap scarcely crystallizes, a peculiar 
 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 li- 
 quor completely deprived of water. But this is not the state in which 
 the manufacturer wishes it to be. Hence the salt is added but gradually 
 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 hyd rated 
 condition, and this being recognised 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 has 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. 578) with soda. In this 
 
SPERMACET I. E T H A L. 591 
 
 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 
 fat added, generally tallow, and some palm oil, which brightens the col- 
 our, 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 con- 
 tinually agitating the mass until the milkiness produced by the oil van- 
 ishes, the mass becomes transparent, and the froth subsides. As this 
 soap cannot be separated from the liquor by the addition of common salt, 
 which would decompose it, forming a soda-soap and chloride of potassi- 
 um, the hquor is evaporated until the operator recognises that it has at- 
 tained the proper strength, and it is then cooled as rapidly 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 these, 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 consistence, 
 it is removed, and formed into rolls for use. The watery solution con- 
 tains glycerine and a large quantity of oxide of lead dissolved. If lith- 
 arge plaster be digested in ether, oleate of lead dissolves, and the mar- 
 garate 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 ani- 
 mal. To obtain it pure, it is to be crystallized repeatedly from its alco- 
 holic solution by cooling ; it is a remarkably beautiful crystalline fat, 
 melting at 120°, and volatilizing at 680° without change, if the air be 
 excluded. By boiling with very strong alkaline solutions, it gradually 
 saponifies, a margarate and an oleate being formed ; but, in place of 
 glycerine, a peculiar base, which is termed Ethal, being set free. To 
 obtain it pure, spermaceti is saponified by being fused with half its 
 weight of potash ; the resulting mass being digested with water and mu- 
 riatic acid, the oily acids and the ethal separate from the liquor and float 
 upon the surface. Being then mixed with lime, which combines with the 
 oily acids, and boiled in absolute alcohol, the ethal dissolves, and crystal- 
 lizes 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 C32H34O2, or CaaHgaO. + Aq. The 
 spermaceti itself consists of 
 
 2 atoms of margaric acid, =C68H6606 ) r>, tt r» • i * 
 1 atom of oleic acid, =C,,uZo: i C208H207p,6, one equivalent 
 
 3 atoms of ethal, =C69H,a206, S ^^ spermaceti. 
 
 The ethal is remarkable for its analogy, in composition and properties, 
 to the bodies of the alcohol group ; like them, it may be looked upon as 
 
592 WAX, CERINE, MYRICINE, AND TARTARIC ACID. 
 
 formed of water united to a carbohydrogen, isomeric with defiant 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°. From its reactions and 
 the specific gravity of its vapour, 7846, it results that its formula is 
 
 If ether be heated with perchloride of phosphorus, a heavy liquid is 
 obtained, having the formula C32H33CI. ; and by fusing ethal with potassi- 
 urn, hydrogen is evolved, and a white solid substance formed, consisting 
 of C32H33O. + K.O., which, with water, gives hydrate of potash and ethal. 
 With sulphuric acid ethal forms sulphoethalic acid, which resembles the 
 sulphovinic acid, and has the formula C32H33O. . S.Og-f-S.Oa . H.O. 
 Farther, if the ethal be heated with potash, hydrogen gas is given oflT, 
 and an acid formed, the formula of which is CagHgiOg+Aq. : it is term- 
 ed the Ethalic 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 C32H33 or Ct. Ethal is then Ct.O.-j-Aq. (See p. 
 566.) 
 
 Wax. — Ordinary beeswax is a mixture of two substances, which are 
 separated by boiling alcohol. Cerine dissolves ; it is quite white ; its 
 specific gravity is 0*969 ; it is less fusible than wax ; it does not combine 
 with bases ; its formula is C20H20O2. The substance insoluble in alcohol 
 is Myricine, which melts at 95° ; its formula is C20H20O. 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 C20H20O3. 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 (Cerdine) 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 CigHigOy. 
 
 CHAPTER XXIV. 
 
 OF THE ORGANIC ACIDS WHICH PRE-EXIST IN PLANTS, AND DO NOT BELONS 
 TO ANY ESTABLISHED SERIES. 
 
 Tartaric Acid. — C8H40,o+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 bitartrate 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. 
 
TARTARIC ACID. CREAM OF TARTAR. 593 
 
 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 remainvS 
 dissolved. By the addition of chloride of calcium to the liquor, this por- 
 tion, also, of tartaric acid is thrown down, and chloride of potassium is 
 formed. The whole quantity of tartrate of lime being then collected and 
 washed, it is to be digested with a quantity of oil of vitriol, 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 mix- 
 ture, having been boiled for a short time, is to be strained, and the liquor 
 evaporated gently to a pellicle ; the tartaric acid then crystallizes on 
 cooling. 
 
 The tartaric acid forms colourless oblique rhombic prisms, generally 
 tabular, as in the figure, where i, w, u 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 alcohol; its taste and reaction are n^ u ^)w{^ 
 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 effect may be instantly produced by boiling it with an ex- 
 cess of oxide of silver, metallic silver being set free. 
 
 Tartaric acid is known by its not being volatile, and by leaving a co- 
 pious coaly residue when heated. If it be fused with potash, it is de- 
 composed, acetic and oxalic acids bemg produced (p. 475) ; 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 so- 
 lution 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 redissolve in an excess of acid. 
 
 The tartaric acid is bibasic, its formula being C8H40io+2 Aq. ; sev 
 eral of its salts are of considerable importance. 
 
 Bitartrate of Potash, Cream of Tartar, — C8H,o04-{-K.O.Aq. 
 
 This salt, just now noticed as being deposited from grape-juice, accord- 
 ing 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 deposited 
 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, jp, u, u being primary, 
 and a, a\ i, m secondary planes. It is but very sparingly 
 soluble in cold water, requiring 80 parts at 60°, and 7 
 parts at 212° ; hence an excess of tartaric 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. 334). Its 
 
 4F 
 
594 
 
 TARTRATES OF POTASH, AMxMONiA, ETC. 
 
 calcination furnishes also the purest source of carbonate of potash, which 
 hence derives its name of Salt of Tartar (p. 487). 
 
 Neutral Tartrate of Potash. Soluble Tartar.— C^YiJd.^-irK.O. . K.O. 
 This salt is formed by adding cream of tartar to a hot solution of car- 
 bonate of potash, until this be completely neutralized. It crystallizea 
 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 acid added to its solution takes half the potash, and 
 precipitates cream of tartar. 
 
 The Tartrates of Ammonia resemble closely those of pota§h. The 
 neutral Tartrate of Soda crystallizes in large rhombic prisms like nitre ; 
 it is very soluble in water; its formula is C8H40io+Na.O. . Na.O. 
 , , .. +4Aq. 
 
 i^L^^ Tartrate of Potash and Soda. Rochelle Salt, CsH^Piq-^- 
 K.O. . Na.O. + lO Aq., is prepared by neutralizing a hot 
 solution of carbonate of soda with cream of tartar : by evap- 
 'p oration and cooling it forms large prismatic crystals, with 
 many sides, of the right rhombic system, p, u, u being 
 X[~\^ primary, and ^, i, t, e, e being secondary faces. These 
 ^v•T■'"v-.-— ^ 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 popularity as a medicine. It is permanent in the air ex- 
 cept it be very dry, when it effloresces slightly at the sur- 
 face ; it dissolves in two parts of cold water. 
 The Tartrate of Lime is very sparingly soluble in water, and is precipitated 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 
 m small octohedral crystals, which have the formula C8H40io-}-Ca.O. . Ca.O.-f 8 
 Aq. Nolner has asserted that, when tartrate of lime is mixed with yeast, a ferment- 
 ation sets in, by which a new acid, Pseudo-acetic Acid, is produced ; this requires, 
 however, confirmation. 
 
 Prototartrate of Iron, C8H40io-f2Fe.O., is a white powder, very sparingly solu- 
 ble 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 Pot- 
 ash, C8H40io-4-Fe.O. . K.O., is formed by digesting cream of tartar and water with 
 metallic iron. Hydrogen gas is evolved, and a white, sparingly soluble salt is ob- 
 tained, which, when exposed to the air, rapidly absorbs oxygen, and becomes green- 
 ish 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 abun- 
 dantly, 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 evLporation, 
 reducing it to the state of protoxide, and carbonic acid being given off. Hence the 
 pharmacopoeias direct perfect neutrality of the liquor to be secured by the addition 
 of a small quantity of ammonia. The formula of this salt is C8H4O10-I-K.O. . IVOs. 
 It is very soluble in water, and its solution is not precipitated by an excess of potash. 
 Tartrate of Antimony. — 3(C3H40]o)-|-Sb.03. 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. — C8H4C,o+K.O. . 
 Sb.05+2 Aq. This salt, a 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 pharma- 
 
PROPERTIES OF TARTAR-EMETIC. 595 
 
 Copceias, the Powder of Algarotti (p. 453) is employed as the source of 
 oxide of antimony, but by the London college an impure oxide is pre- 
 pared, 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 octohedrons, 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 2 Aq. Its solution is 
 not affected by alkalies ; but the oxide of antimony is 
 precipitated by sulphuric or muriatic acids, and by am- 
 monia. 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 Ara- 
 bic. 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 antimony, having the formula 
 C4HA . K.O.+(3C4H205+Sb.03)+2 Aq. It may be formed by dissolv- 
 ing tartar-emetic in a strong solution of tartaric acid, and then crystal- 
 lizes 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 
 explained. 
 
 Owing to the occasional presence of arsenic in the ores of antimony, 
 the tartar-emetic of commerce is not unfrequently contaminated by its 
 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, be- 
 sides 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 C8H4O10, but CgHaOg. 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 borotartrate 
 of potash being also reduced by loss of water at 480° to the formula 
 C8H208+K!'0* • B.O3. Chemists are not unanimous in explaining 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, C8H20s-f4H.O. ; the cream of tartar 
 being CsHA+K.O. . 3H.0. ; Rochelle salt, CgHaOs+K.O. . Na.O. . 2 
 H.O. ; and for tartar-emetic, the oxide of antimony replacing three atoms 
 of a protoxide, the formula is CgHgOs+K.O. . Sb.03+2 Aq.-i-2 Aq., and 
 the two portions of water being retained by very unequal forces, are given 
 off at very different temperatures. Berzelius considers 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 farther into its discussion. 
 
 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 for- 
 mula being CiiHeOis-l-^ Aq. It thus constitutes Tartralic Acid; it does not crys- 
 
598 RACE MIC kcm and its salts. 
 
 tallize, and in solution gradnally passes back into tartaric acid. If the tartralic acm 
 be kept long melted at 360°, it abandons still more water, and forms Tartrelic Acid, 
 in which the bibasic character remains, its formula being Ci6H802o-|-2 Aq. This 
 acid is characterized by forming insoluble salts with lime and barytes, thereby dif- 
 fering 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 Anhydrous Tar- 
 taric Acid; its formula is CSH4O10. 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 prop- 
 er lactic acid (p. 536). 
 
 If tartaric acid be distilled at a still higher temperature, it abandons water and 
 carbonic acid, and forms Pyrotartaric Acid, CSH4O10 giving off 30. O2 and H.O., 
 and C5H3O3 remaining. The process succeeds best at about 400°. This acid is 
 white ; it crystallizes from the distilled 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 wate. 
 and alcohol. It is a monobasic acid, forming salts which, with few exceptions, are 
 soluble and crystallizable. 
 
 Racemic Acid, — C8H40,oH-2 Aq. This acid is found in grape-juice, 
 replacing tartaric acid to a greater or less extent ; its formation appears 
 to depend on very peculiar circumstances, as it has never been found 
 except in the district about the Vosges Mountains, and only in some sea- 
 sons. It is combined with potash, forming a kind of cream of tartar, 
 which is biracemate 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 exactly the same rules as the tartaric acid, but their crystalline 
 form is completely different ; it is a bibasic acid, and its formula, when 
 crystallized, is C8H4O10+2H.O.+2 Aq. 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 un- 
 crystallizable, giving merely a gummy mass, while the Rochelle salt 
 forms very large crystals. Fourth, the racemate of lime is insoluble 
 in 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 
 bibasic acids, whose formulae are respectively C12H6O15+2H.O. and Cie 
 H8O20+2H.O. They are distinguished by their salts, which differ in 
 characters from each other, and from those of the bodies formed by tar- 
 taric 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 CgHaOg. It differs totally in proper- 
 ties from the pyrotartaric acid ; it does not crystallize ; it tastes acid ; its 
 salts are all soluble and crystallizable, but pass also into a gummy con- 
 dition. If a little crystal of copperas be laid in a solution of one of these 
 salts, it becomes coloured bright red. 
 
CITRIC ACID AND ITS SALTS. 597 
 
 Citric ^cM.— C,2H50ii+3H.O.+2 Aq. 
 
 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 wash- 
 ed 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 sul- 
 phate of lime has been removed by straining, the liquor is evaporated, 
 and allowed to crystallize by very slow cooling ; its form is generally 
 that of a right rhombic prism, very much modified, as in the figure, 
 where i, u\ u are primary, and n', y, r are secondary planes, ^^^^p^^-v^^^ 
 In this case its formula is that given above ; but if its solu- /i^v.,..^>S\ 
 tion be evaporated at 212° to a pellicle, it crystallizes while Qy^ j 
 hot in a totally different form, and its formula is then CiaLH^Us. 1 4>.J 
 H5O11+3H.O. By exposing the hydrated crystals in vacuo ^^<^^^iti>^ 
 to sulphuric acid or to a gentle heat, the 2 Aq. 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 i* 
 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 ; and, as these con- 
 tain different quantities of combined water, their history was very confu- 
 sed 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 Ci2H50n-f- 
 3Na.0.4-4 Aq.4-7 Aq. By exposure to a heat of 212° the 7 Aq. are removed, and 
 at 400° the remaining 4 Aq. are driven off: Berzelius is of opinion that in this ac- 
 tion the real constitution of the citric acid is changed, and that it is partly convert- 
 ed into aconitic acid ; but the point is not yet experimentally decided, and Liebig's 
 views explain the phenomena with such beautiful simplicity, that I have no hesita- 
 tion in adopting them, at least provisionally. 
 
 The Citrate of Lime is obtained by mixing solutions of a soluble citrate and of a 
 salt of lime ; it forms a white powder, sparingly soluble in pure water, but much 
 more so if the liquor be acid. Its constitution is Ci2H50ii4-3Ca.O.-j-4 Aq. 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 of Barytcs are white powders, insoluble in water, form- 
 ed 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 re- 
 sult from the crystal- water (2 Aq.) of the acid being more or less replaced by metal- 
 lic oxide, in addition to that which fulfils the proper basic function. 
 
 The citric acid is easily recognised by forming no precipitate with lime-water un- 
 less 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. 
 
 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 is hence often called 
 Equisetic Acid. To complete the change of the citric acid, it must be distilled un- 
 til the gases which come over cease to be inflammable, and oily drops appear in the 
 receiver ; the process is to be then interrupted, the mass remaining in the retort to 
 be dissolved in water, the solution filtered and evaporated to a pellicle. On cool- 
 ing, it forms a crystalline mass, from which ether dissolves out the aconitic acid, 
 and leaves unaltered citric acid behind ; the former may then be obtained crystal- 
 lized by evaporation. 
 
 Aconitic acid is soluble in water, alcohol, and ether ; its formula is C12H3O9-4- 
 3 Aq. ; like citric acid, it is tribasic ; it forms well-characterized salts : the aconi- 
 tate of ether had been mistaken for citric ether ; for, when citric acid is put in con- 
 tact with alcohol and oil of vitriol, it changes into aconitic acid. 
 
598 MALIC ACID AND ITS SALTS. 
 
 If aconitic acid be heated until it boils, it gives off carbonic acid, and forms Itor- 
 konic 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 crys- 
 tallize very well ; its formula is CioHiOe-l-^ Aq. ; formed by the aconitic acid losing 
 C2O4, but an atom of water, previously basic, entering into the organic element. 
 When the Itakonic Acid is redistilled, it is copverted into water and a heavy oily 
 liquid, Citrakonic Acid, the formula of which is CioHsOs-^-Aq. In contact with wa-^ 
 ter, it forms a crystalline mass containing 2 Aq. 
 
 All these products are simultaneously and successively formed in the distillation 
 of common citric acid. Acetone is also generated, C12H12O12 giving 3(C3H30.), with 
 3H.0. and 3(C.02). 
 
 Malic ^ciVZ.— C8H4O8+2H.O. 
 
 This acid exists in most fruits, associated with citric and tartaric acids, 
 but is found purest and most abundant in the berries of the mountain ash 
 and in the houseleek. The best mode of extraction is the following, de- 
 vised by Liebig. The juice of the berries of the mountain 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 more lime, and on cooling, 
 the remainder of the salt is obtained. This malate of lime is to be dis- 
 solved 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 ace- 
 tate of lead, malate of lead is formed, which, being acted on by sulphu- 
 retted hydrogen, gives sulphuret of lead and free malic acid ; by evapo 
 ration 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- 
 nesia is the only earth by whose carbonate it can be completely neutral- 
 ized. This arises from its tendency to form salts, in which one atom of 
 basic water is preserved, it being a bibasic acid. Another peculiarity 
 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 tempera- 
 ture the other at once abandons it. When crystallized it appears to con- 
 tain only basic water ; its formula is hence C8H4O8+2 Aq. None of its 
 salts are of technical or medicinal interest, and hence require but brief 
 notice. 
 
 The alkaline malates are very soluble in water, scarcely crystalliza- 
 ble, sparingly soluble in alcohol. 
 
 The Malate of Lime forms as a granular white precipitate when malic acid is 
 neutralized by lime. Its formula is C8H408+2Ca.O. ; it separates in hard, brilliant 
 crystals, which contain 5 Aq., when the following salt is neutralized by an alkaline 
 carbonate. Bimalate of Lime, C8H408-|-Ca.O. . H.O.-f 6 Aq., crystallizes in large 
 right rhombic octohedrons. Water dissolves it abundantly when boiling, but very 
 sparingly when cold. 
 
 The Malate of Lead, C8H408-f 2Pb.O., precipitates, on mixing solutions of a solu- 
 ble 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 abandons water and 
 
MECONIC ACID AND ITS SALTS. 599 
 
 gives origin to two acids, of which one is remarkable as being found naturally ex- 
 isting in several plants. They are the Maleic Acid and the Fumaric Acid, the latter 
 so called from having been first discovered in the fumaria officinalis. These acids 
 are isomeric, the reaction being in both cases that C8H4O8 produces 2H.0. and 
 CsHzOe. 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 con- 
 centrated to the necessary degree. 
 
 The Maleic Acid, which had been thought identical with the Aconitic Acid, al- 
 ready noticed, forms crystals of a sour, bitter taste, soluble in 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 Fumaric 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 decomposed into water and anhydrous 
 maleic acid. The fumarate of silver is so insoluble, that one part of the acid, dis- 
 solved in 200,000 parts of water, is precipitated by nitrate of silver, but the precipi- 
 tate 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 maUc acid in absolute alco- 
 hol, 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 C4H.034-Ae.O. On adding water of am- 
 monia to this ether, a substance is deposited in brilliant white scales, insoluble in 
 cold water and in alcohol, but dissolved by boiling water. It is Fumaramid, its 
 formula being C4H. . 02Ad. By potash, ammonia is set free, and fumarate of potash 
 formed. 
 
 Meconic ^aVZ.— C,4H.Oh+3H.O.+2 Aq. 
 
 This acid is found only in opium ; it is best extracted by adding chloride of cal- 
 cium 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, 
 is to be treated with dilute muriatic acid, heated to about 180°. The meconate of 
 lime dissolves, and, from the liquor on cooling, bimeconate of lime separates in 
 brilliant crystalline plates. On dissolving these in warm, strong muriatic 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 
 meconate of potash by muriatic acid, and recrystalhzation. 
 
 When pure, meconic acid is in brilliant white crystalline scales, containing 2 Aq., 
 which they give oflfat 212° ; it is soluble in four parts of boiling water; it is a triba- 
 sic 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 specifi- 
 cally of imp6rtance. The most characteristic properties of this acid are, 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 Uttle sulphur and potassium, and treated with water, 
 gives no red colour with the salts of iron (see page 525) ; 2d, 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 deposites 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 Komenic Acid, 
 carbonic acid being given off. The crystallized meconic acid undergoes the same 
 phange when heated to 400°. This acid forms granular crystals, which are soluble 
 only in sixteen parts of boiling water, and have the formula Ci2H208-{-2H.O., as the 
 C14H.O11 loses C2O4 and gains H.O. This acid is bibasic ; the third atom of water, 
 which was basic in the meconic acid, entering into the radical here. It also red- 
 
(>00 PREPARATION OF TANNIN. 
 
 dens the per-salts of iron. It forms two series of salts, which in properties resem- 
 ble closely the corresponding meconates. When it is heated to 500°, it gives off 
 water and carbonic acid, and forms Pyromekonic Acid, of which the formula is Cio 
 H3O5+H.O. This acid forms crystalhne plates, which fuse at 240°, and are vola- 
 tilized 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 derived, it strikes a blood-red 
 colour with solutions containing peroxide of iron. 
 
 Tannic Acid, or Tannin. — CigHsOg + SH.O. 
 
 This important substance exists in the bark of most exogenous trees, 
 particularly the oak and horse-chestnut, 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 infecloria). 
 
 To distinguish this from the other kinds of tannin, of which there is a 
 great number, it may be suitably termed GaUo-tannic 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, and rests in a bottle, a, as in the figure, is to be intro- 
 duced a quantity of nut-galls in powder, moderately compress- 
 ed, 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 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 lay- 
 ers of liquid. The inferior, sirup-thick, is a concentrated so- 
 lution of tannic acid in water, with very little ether. The 
 upper is ether, containing but a 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 crystalhne 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 dissolve it to the exclusion of every 
 other constituent of the gall-nut. 
 
 The watery solution of gallo-tannic acid reddens litmus ; it is probably 
 insoluble in absolutely anhydrous alcohol and ether ; its taste is intense- 
 ly 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 inter- 
 est from the colours of precipitates it gives with metallic solutions, being 
 often useful as a test for the presence of certain metals. Hence an in- 
 fusion, or tincture of Galls, is always found in the laboratory as a rea- 
 gent ; it does not affect the solutions of Zinc or Cadmium, or the 'protox- 
 ides of Iron and Manganese, nor any of the alkaline or earthy salts. 
 With the other metals it gives precipitates which, with Lead and Anti^ 
 mony, are white ; with Copper, gray ; with Tin, Nickel, Cohalt, Cerium, 
 Tellurium^ and Silver, are various shades of yellow ; with Tantalum and 
 
PREPARATION OF GALLIC ACID. 601 
 
 Bismuth, are orange ; with Titanium, blood-red ; with Platinum, greerf , 
 with Chrome, Molybdenum, Uranium, and Gold, are brown ; and with Os- 
 mium and peroxide of Iron, are rich bluish purple. This last is the most 
 important of all, from its great delicacy and distinctness. If the solu- 
 tions be very strong, the liquor appears absolutely black, and constitutes 
 the material of ordinary writing ink. 
 
 The insolubility, and consequent inactivity of tartrate of antimony, is 
 taken advantage of in medicine, infusion of oak-bark or galls being em- 
 ployed as an antidote in poisoning by tartar-emetic. I shall have occa 
 sion hereafter to notice its use in the detection and neutralization of the 
 vegetable alkaloids. 
 
 The gallo-tannic acid is not the only kind of tanning material employ- 
 ed in the manufacture of leather ; yet, as the others will hereafter come 
 under notice, I shall 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 
 
 Oak bark entire 63 
 
 Horse-chestnut bark entire . . 4-3 
 Elm bark entire 2-7 
 
 "White inner oak bark . . . 16*0 
 
 White inner horse-chestnut . 15-2 
 
 Sicilian sumach 16-2 
 
 Malaga sumach 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 lar- 
 ger ; thus the gall-nuts easily yield, by Pelouze's method, forty per cent 
 of pure product. 
 
 VVhen a solution of tannic acid is exposed to the air, it is decomposed , 
 absorbing oxygen and evolving carbonic acid, the liquor becomes colour 
 ed, and a large quantity of gallic acid is found to be produced. 
 
 Gallic ^cifZ.— C7H.03-f2H.O. + Aq. 
 
 This remarkable substance does not appear to exist naturally formed 
 in plants, 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 evaporates away ; the resulting mass is to be 
 boiled with water, and the gallic acid crystallizes out of the liquor as it 
 cools. By digestion with ivory black and recrystallization, it is obtain- 
 ed completely pure. 
 
 In this process the reaction is very simple, as an atom of tannic acid, 
 Cii-HgOiz, absorbing from the air eight atoms of oxygen, produces 4C.O2 
 and 2(C7H.03-f3 Aq.). 
 
 The conversion of gallo-tannic acid into gallic acid may occur, howev- 
 er, without the access of air, and, indeed, be effected almost instantane- 
 ously ; 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 sulphu- 
 ric acid be added to a strong solution of gallo-tannic acid, and the pre- 
 cipitate thus formed be washed with a small quantity of water, and then 
 added gradually to boiling dilute sulphuric acid, it dissolves, and on cool- 
 ing the gallic acid crystallizes. In these reactions, which succeed also 
 perfectly with infusion of galls, some other substances must be simulta- 
 neously formed, which are as yet not known. Gallo-tannic acid contains 
 exactly the constituents of gallic acid and acetic acid, as Ci8H509=2(C- 
 
 4 G 
 
602 PYROGALLIC, MELANGALLIC ACIDS, ETC. 
 
 H.03)+C4H303 ; but Liebig has determined that acetic acid is not pro- 
 duced. 
 
 This change may occur in the nut-gall itself, which it is very probable 
 contains a principle analogous to yeast, which, under favourable circum- 
 stances, induces this kind of decomposition in the gallo-tannic acid. This 
 idea, first suggested by Robiquet, has derived much support from the ex- 
 periments 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 pos- 
 sess no accurate knowledge of the theory of this interesting transmuta- 
 tion. 
 
 Pure gallic acid crystaUizes in colourless oblique rhombic prisms, as 
 tt, 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 
 y^^Y^^^^ water for its solution ; it is less soluble in alcohol ; its crys- 
 tals contain three atoms of water, of which one is expelled at a 
 temperature of 230°, but the remaining two are only remov- 
 I i ed when replaced by bases. It is a bibasic acid, forming two 
 M;~-.J,_J classes of salts ; those with the alkalies are very soluble ; the 
 ^--^^ earthy and metallic salts are insoluble in water. With a 
 per-salt of iron, gallic acid gives a blackish-blue precipitate, which dif- 
 fers from the tannate of iron in becoming gradually 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 gal- 
 lie acid is farther distinguished from the tannic by not precipitating gela- 
 tine nor any of the vegetable alkalies. 
 
 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 (C7H305=C6H603-|-C.02), 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 contain- 
 ing 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 as- 
 sumes 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 temperature be al- 
 lowed 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 
 C12H3O3, being formed from 2(C6H303) by loss of 3H.0. ; it is insoluble in water, 
 alcohol, and ether ; at a temperature of 500° it is totally decomposed into the ordi- 
 nary pyrogenic products ; it dissolves in alkaline solutions, forming salts of a black 
 colour, which do not crystallize ; these salts give black precipitates with solutions 
 of the 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 fermentation 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 C7H.O3-4-H.O.+ Aq. The Aq. is driven 
 ofTby 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 Ellagatcs are all insoluble, and all white or yellow. 
 
 If gallic acid be heated to 280° with oil of vitriol, it dissolves, and on cooling, 
 brilliant crystals of a dark scarlet colour are deposited, which constitute Parellagic 
 Acid. This body is isomeric with ellagic acid ; it forms with bases salts which are 
 
CATECHUIC AND C A T E C H U T'A N N I C ACIDS. 603 
 
 generally red. It is worthy of notice, that ellagic acid acted on by oil of vitriol 
 gives no parellagic acid. 
 
 It is here probably best to notice the forntiation 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 dissolved out by alcohol ; 
 the solution is dark brown, and when evaporated gives a black extract- 
 ive 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 a very singular manner of producing artificial tannin 
 consists 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 red- 
 dens litmus, tastes astringent, is soluble in water and alcohol, and copi- 
 ously 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 aprocrenic acids. 
 
 Caiechuic Acid and Catechutannic Acid, 
 
 The Catechu, or Terra Japonica, a brown extract prepared from the wood of the 
 mimosa catechu, appears to contain at least four acids, 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 giv- 
 ing a rich permanent brown dye. Davy estimated that 100 parts of Bengal catechu 
 contain forty-eight, and of Bombay catechu about fifty-four per cent, of useful tan- 
 ning material. 
 
 If catechu be treated with ether, by the method of displacement as described lor 
 tannic acid, the liquor does not separate into two layers, but a strong solution of 
 Catechutannic 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 precipitates 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 ; exposed to the air, 
 its solution rapidly absorbs oxygen, becomes red, and finally brown, depositing a 
 brown insoluble matter. This change is instantly effected by any oxidizing agent. 
 
 The catechutannic acid has been analyzed by Pelouze, who ascribes to it the 
 formula CigHsOs-l-Aq. ; it would thus appear to be formed by the abstraction of four 
 atoms of oxygen from tannic acid. 
 
 When catechu has been deprived of the catechutannic acid by ether or continued 
 washings with cold water, the residual mass is to be boiled in alcohol, and the fil- 
 tered liquor evaporated to one third of its volume ; on cooling, Catechuic Acid crys- 
 tallizes. 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 hydrogen ; 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 in- 
 soluble 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 CisHsOs+Aq. Zwenger, who states 
 the substance he worked with to be the produce of the nauclea gambir, gives 
 
604 CINCHONATANNIC AND CINCHONIC ACIDS, ETC. 
 
 C2oH908-|-Aq. ; and Hagen, who used Bengal catechu, found the catechuic acid to 
 be CuHeOe-j-'^ Aq., and its lead salt Ci4H606-|-2Pb.O. Additional researches are 
 required to clear up this confusion. 
 
 When catechuic acid is heated, it fuses, gives off water, and, finally, a white crys- 
 talline sublimate, Pyrocatechin, which has the formula CeHjO.-l-Aq. , its character- 
 istic 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 alkali. 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 alkalies. 
 Svanberg gives for it the formula Ci2H204-}-Aq. If catechuic acid be boiled with a 
 solution of carbonate of potash, Rubinic Acid is formed, whose formula is said to be 
 CisHeOg. By farther absorption of oxygen it forms japonic acid. None of these re- 
 sults, however, can be considered as definitely established. 
 
 Cinchonatannic Add and Cinchonic 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 alkaloids dissolved ; the cincho- 
 natannate of lead being decomposed by sulphuretted hydrogen, the filtered liquor 
 yields, on evaporation, the Cinchonatannic Acid pure, and of a very pale yellow col- 
 our, not crystalline. In properties it resembles closely ordinary tannic acid; it 
 precipitates gelatine and tartar-emetic. An infusion of cinchona is hence recom- 
 mended 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 Cinchonic 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 infu- 
 sion of cinchona bark. The alkaloids being thus separated, the liquor is filtered and 
 evaporated very carefully to the consistence of a sirup. On standing for a few days, 
 the cinchonate of lime crystallizes in needles, which are to be decomposed by an 
 exact equivalent of sulphuric acid. The gypsum being removed by the filter, the 
 solution is concentrated, and the cinchonic acid crystallizes. It forms small acid 
 needles ; is very soluble in water ; its salts are all soluble in water ; it affects nei- 
 ther gelatine, tartar-emetic, nor the per-salts of iron ; its formula appears to be 
 C14H8O8-I-4 Aq. When it is heated, a substance sublimes in brilliant yellow nee- 
 dles, which is termed Chinoyl, and consists of C3H.O. 
 
 Kinoic Acid, or Coccotannic 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 precipi- 
 tated by sulphuric acid, the precipitate washed, dissolved in boiling water, and solu- 
 tion of barytes added until the sulphuric acid is all removed ; the liquor is then care- 
 fully 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 httle more than a knowledge of their probable 
 existence. 
 
 Lactucic Acid is said to exist in the lactuca virosa. The expressed juice is pre- 
 cipitated by acetate of lead, and the lactucate of lead decomposed by sulphuretted 
 hydrogen. From the hquor the acid crystaUizes by evaporation and cooling, like 
 oxalic acid ; it tastes acid, and gives with protosalts of iron a green, and with salts 
 of copper a brown precipitate. 
 
 Fungic Acid exists in most mushrooms ; their expressed juice is boiled, and the 
 coagulated albumen removed by filtration ; the liquor is then evaporated to a sirup, 
 and treated with alcohol. Fungate of potash remains undissolved, 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 ignarius, in the same way as the last acid 
 is from other mushrooms. It crystallizes readily, and sublimes without decompo- 
 sition. 
 
KRAMERIC ACID, ETC. PECTIN. 605 
 
 Kramcric Acid, exists in rhatany root (krameria triandria). The watery infusion 
 IS precipitated, first by gelatine, and then by copperas. The filtered liquor is con- 
 centrated, 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 astringent ; its formula is probably CioHsOs, by Liebig's analysis. 
 
 Cdincic 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 sol- 
 uble in water ; its solution reacts acid ; it appears to have the same formula as kra 
 meric acid, and perhaps they are really identical. 
 
 Verdous aiid Verdic Acids exist in a variety of plants of the families (Mpsaceae, 
 compositae, and eupatoriae ; it is best prepared from the roots of the scabiosa succi- 
 sa. 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 precip- 
 itated 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 yel- 
 low mass, which is not altered by the air ; it reddens htmus strongly. If it be neu- 
 tralized by an alkaU, it then absorbs oxygen rapidly, and the solution becomes deep 
 green ; from this, acids throw down a brown-red powder, which is Verdic Acid. 
 Runge, who observed these facts, considers that the two acids are different oxides 
 of the same radical, but no exact researches have been made about them. 
 
 Other acids, of which the existence has been only indicated, will be noticed in de • 
 scribing the more important bodies with which they are associated in the plants. 
 
 CHAPTER XXV. 
 
 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, 
 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, wash- 
 ed with alcohol, and dried by a very moderate heat. It forms a trans- 
 parent 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 pectic and the mucic acid. It 
 precipitates 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 C24Hn022. By long boiling, or by contact with 
 any powerful acid or base, it changes into the following substance : 
 
606 PECTIC AND METAPECTIC ACIDS. S A L I C I N E. 
 
 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 separates 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 mamifacture of the preserves of juicy fruits. 
 
 The pectic acid is isomeric with pectin, its formula being C24H17O22. It appears 
 to be bibasic, the pectate of lead being C24Hi7022H-2Pb.O. Its alkaUne salts are 
 soluble in water, but the others are insoluble, and form transparent jellies while 
 moist. 
 
 If pectin or pectic acid be boiled in a solution of potash, the alkali being in ex- 
 cess, 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 decomposed 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 C24H17O22 ; but its salts contain five atoms of base. Those of the alka- 
 lies are soluble and uncrystailizable, but those of the earths and heavy metallic ox- 
 ides are insoluble in water. 
 
 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, separated 
 by pressure from the mother liquor, are to be purified by solution, diges- 
 tion with animal charcoal, and recrystallization. 
 
 When pure, salicine is in the form of small white rectangular crystal- 
 line 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 determin- 
 ed ; its formula is, when crystallized, C2iH,209+2 Aq. ; it precipitates the 
 basic acetate of lead, forming a white compound, the formula of which is 
 C2,H,A+3Pb.O. 
 
 The products of the decomposition of salicine are exceedingly remarkable. 
 When it is boiled with dilute sulphuric acid, it is decomposed into grape-sugar, and 
 a resinous substance termed Saliretine. Three atoms of salicine, C63H36O27, giving 
 saliretine, C51H24O15, and sugar, C12H12O12. When quite pure, this body is white or 
 pale yellow. It is insoluble in water, but soluble in alcohol and ether. 
 
 With sulphuric acid and chromate of potash, salicine gives hydruret of salicyl 
 (oil of spiraea), as described page 573. Although the evolution of formic and car- 
 bonic acids, which occur in this reaction, show that it is in reality complex, yet its 
 result may be expressed by the simple abstraction of water from the salicine, as 
 2(C2iH,209)— 6H.O.=^3(C,4H604). 
 
 When salicine is boiled with nitric acid, it is totally converted into picric acid. 
 As this body is, however, more closely connected with indigo, it will be there fully 
 described. 
 
 By the action of chlorine on salicine two bodies are produced, one crystalline, 
 whose formula is C21H12 . CI2O9, and the other a heavy oil, consisting of CaiHs . 
 CI4O9. They are both soluble in alcohol, but sparingly soluble in water. 
 
 If strong oil of vitriol be poured on salicine, it is decomposed into water and a 
 
PHLORIDZINE AND ITS PRODUCTS. 607 
 
 deep olive-green powder, Olivin, the formula of which is C21H9O6. This action is 
 accompanied by the disengagement of much heat. Olivin is crystalline, insoluble 
 in M^ater, 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 
 Rujin ; it is obtained more simply from phloridzine. If a large quantity of sahcine 
 be acted on by sulphuric acid, it forms a tenacious mass, which, when treated with 
 water, and the liquor neutralized by hme, gives a brown resinous body, which is 
 termed Rutilin. This contains sulphuric acid, its formula being C28Hi2044-S.03. 
 
 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 brilliant silky plates and needles, perfectly white when pure. It is easily 
 soluble in alcohol, ether, and in boihng water, but requires iOOO parts of cold water 
 for its solution. Its taste is bitter and astringent. The formula of the crystals is 
 C2iHiiOg-|-4 Aq. At 212° it gives off 2 Aq. ; it melts at 226°, and boils at 360°, 
 but is decomposed, water being evolved, and a new substance produced. The solu- 
 tion 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 until the temperature 
 rises to 450° ; it then forms a deep red mass of Rujin, the same substance as is 
 produced by the action of oil of vitriol on salicine ; it is very soluble in alcohol, in- 
 soluble in ether ; boiled in water, it dissolves, 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 C14H7O5 ; 
 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 sulphovinates. 
 
 When phloridzine is dissolved in dilute sulphuric acid, and the liquor boiled, a 
 white crystaUine substance separates, which is termed Phloretine ; the liquor then 
 contains much grape-sugar. The formula of phloretine is C51H26O17 ; 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 PUoretic Acid, the formula of which is C51H24 . 
 N2O25 ; it is a yellow-brown powder, of a velvety aspect, but not crystalline ; insol- 
 uble in water, and soluble in alcohol. 
 
 The most remarkable action on 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, anri the whole is so covered 
 with a large bell-glass as that the air shall have free acress ; after a few days the 
 contents of the capsules 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 alcohol, and the residue then being dis- 
 solved in water, gives a magnificent blue liquor, from which the colouring substance, 
 Phloridze'in, is precipitated by the cautious addition of acetic acid ; it is not crys- 
 talline ; 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, al- 
 cohol, or ether appear scarcely to act upon it. 
 
 The formula of phloridzein is C21H14 . OisN.-fAq. ; it is formed, therefore, by the 
 combination of phloridzine with five atoms of oxygen and one of ammonia ; it is 
 not, however, a salt of ammonia, for the alkalies dissolve phloridzein without alter- 
 ation, forming magnificent blue solutions ; from metallic solutions it precipitates 
 purple or blue lakes, the composition of which renders it probable that the equiva- 
 lent of phloridzein is C42H28 . 026N2-f 2 Aq. ; then the 
 
 Phloridzelnate of ammonia, =C42H28 . N2O26-I-N.H3. 
 Phloridzeinate of silver, =C42H28 . N20264-2Ag.O. 
 Phloridzeinate of lead, =042X128 • N2026-|-2Pb.O. 
 
 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 its tint ; with 
 chlorine the colour is instantly and permanently destroyed. 
 
608 ASPARAGINE, CAFFEINEj AND PIPERINE, 
 
 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 li- 
 quor then strained and evaporated to the consistence of a sirup. By standing foi 
 some time, the asparagine gradually 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 N.C4 . H4034-Aq. ; the water goes away by a heat of 230°. 
 
 When asparagine is boiled with a strong solution of barytes, ammonia is expell- 
 ed, and aspartate of barytes formed ; by cautiously adding sulphuric acid, the bary- 
 tes may be precipitated, and the liquor yields, on evaporation and cooling, crystal- 
 lized aspartic acid. In this reaction 2(N.C4 . H4O3) produces N.H3 and N.Cs . H5O6, 
 which is the formula of aspartic acid. This substance is tasteless, sparingly solu- 
 ble in cold, but abundantly in boiling water, and is deposited as a white crystal- 
 line powder as the solution cools ; it reddens litmus. Its salts are generally solu- 
 ble, except those of lead, silver, and black oxide of mercury. 
 
 It is not easy to decide whether the ammonia exists ready formed or not in the 
 asparagine ; if so, the remaining organic element may be aconitic acid (see p. 597), 
 and then there should be, 
 
 Asparagine=ranhydrous aconitate of ammonia=C4H.03-|-N.H3. 
 Aspartic acid=anhydrous binaconitate of ammonia=2(C4H.03)-|-N.H3. 
 
 In the case of the anhydrous compounds of ammonia with the mineral acids, it is 
 retained with the same obstinacy as in asparagine (see p. 508). 
 
 Caffeine or The'ine. Caffeic Acid, 
 
 This has been found only in the coffee-berry, the tea-leaf, and the paulinia sor- 
 baUs (guarana). To prepare it, raw coffee is to be boiled in water, and the decoc- 
 tion treated with subacetate of lead as long as the precipitate which forms is col- 
 oured. The caffeine 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 solu- 
 tions react neither acid nor alkaline ; it is not precipitated by any metallic salt. 
 Caffeine is remarkable for the large quantity of nitrogen it contains (29 per cent.), 
 being more than any other vegetable substance ; its formula is NzCg. H502H-Aq. 
 When caffeine 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 acetate of 
 lead contains two peculiar substances, which may be extracted from it by treat- 
 ment with a stream of sulphuretted hydrogen gas, evaporation to the consistence of 
 a sirup, and digestion of the residue in strong alcohol. That which dissolves is 
 Caffetannic 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. 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 Caffeic Acid. 
 
 These bodies have not been accurately examined. It is not known if the tannic 
 acid of tea and coffee be the same, 
 
 Piperine. — N.C34 . HigOe. 
 
 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 removed ; the residue is then to be dissolved in alcohol, and the solu- 
 tion abandoned to spontaneous evaporation, when the piperine gradually crystallizes 
 in transparent rhombic prisms. It melts at 212° ; is tasteless and inodorous ; des- 
 titute of either acid or basic properties ; nitric acid colours it red ; when heated 
 strongly, it yields ammoniacal products. 
 
ONIA'E, CETRARINE, PICROTOXINE, ETC. 
 
 609 
 
 CanZ/ianiirac— C10H6O4. This substance is extracted from the blistering fly (va- 
 rious species of cantharis and lytta) by digesting a watery extract of the flies in al- 
 cohol, evaporating the solution to dryness, and treating the residue with ether, 
 which dissolves out the cantharidine. By spontaneous evaporation it is obtained 
 crystallized ; it forms colourless pearly scales, which fuse when gently heated, 
 and sublime unaltered at a higher temperature ; it is, when pure, insoluble in water 
 and in cold alcohol ; it is perfectly neutral, and has no aftinity 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 at a high temperature, yet not with- 
 out partial decomposition ; its formula is C6H3O4 ; when it is dissolved in strong 
 muriatic acid, and the liquor evaporated to dryness, Anemonic Acid is formed ; its 
 formula is CeR40r^-\-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 li- 
 quor may then be distilled in great part off, and the cetrarine is deposited, on cool- 
 mg, m 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 cetrarine separates on cooling as a 
 white powder of a slightly 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 con- 
 stitution of these bodies has not been accurately investigated. 
 
 Picrotoxine, or Cocculine. 
 
 This substance exists in the seeds of the menispennum cocculus (cocculus Indi- 
 cus), 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 anything is dissolved, and then 
 some muriatic acid added to the liquor ; by cooling, the cocculine crystalhzes in 
 brilliant wliite needles. Its reaction is neutral ; its taste intensely bitter ; it dis- 
 solves moderately in boiling, but sparingly in cold water. The portion of the alco- 
 holic extract which does not dissolve in water contains another substance, Picro- 
 toxic Acid, which is brown, and possesses the properties of a resin ; it dissolves in 
 alkahne liquors, from which acids throw it down unchanged. The formula C10H6O4 
 has been assigned to picrotoxine, and that of CiiHc04 to picrotoxic acid. 
 
 Cciumbine. — Found in the roots of the menispermum palmatum. The coarsely- 
 powdered columbo-roots are to be digested in ether, and by the spontaneous evap- 
 oration the columbine crystallizes ; or by digesting the roots in alcohol, and decol- 
 orizing the liquors by animal charcoal, it may also be prepared ; it forms brilliant 
 right rhombic prisms ; its taste is intensely bitter ; its reaction neutral ; it dissolves 
 but sparingly in water, alcohol, or ether ; its solution does not precipitate any me- 
 tallic salt ; its formula appears to be C24H12O7. 
 
 Cusparinc. — This is the active principleof the true angustura (cusparia 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 precipitation of the colouring matter by acetate of lead, it is ultimately 
 obtained pure. When crystallized from a solution some degrees below 32°, cuspa- 
 rine forms colourless but irregular needles ; by a very gentle heat it melts and gives 
 off twenty-three per cent, of water of crystallization ; it dissolves readily in water 
 and alcohol, but is insoluble in ether ; by heat it is totally decomposed ; its solu- 
 tions precipitate most metallic salts. Its composition is not known. 
 
 Elatcrine is the active material of the expressed juice of the momordica 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 deposites the elaterine as a white crystalline powder. 
 It melts at about 320°, but is totally decomposed by a stronger heat ; its taste is 
 
 4H 
 
610 MECONINE, PEUDECANINE, iESCULINE, ETC. 
 
 intensely bitter ; it is almost insoluble in water, but abundantly in alcohol ; it pos- 
 sesses no characteristic chemical property. 
 
 Meconine. — This substance exists mixed with the more important ingredients m 
 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 sub- 
 limed unaltered ; it dissolves sparingly in cold, but moderately in boiling water, 
 abundantly in alcohol and ether ; its formula appears to be C2oH907-j-Aq. By nitric 
 acid it is dissolved, and a substance crystallizes from the liquor in long needles, 
 which is termed Nitromeconic Acid; its formula is N.C20 • H9O12 ; its solution in watei 
 reddens litmus ; it volatilizes at 370°, but is partly decomposed. By contact with 
 chlorine, meconine is coloured red, and substances formed whose constitution is^not 
 well known. 
 
 Peudecanine. — This substance is found in the roots of the peudecanum officinale, 
 and is extracted by digestion with alcohol and evaporation ; it crystallizes in deli- 
 cate 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. 
 
 jEscuUne, or Polychrome. 
 
 A great number of vegetables give, when treated with hot water, a solution which 
 appears yellow by transmitted, hut violet or blue by reflected light. This phenom- 
 enon results from the presence of a body hence called Polychrome, and aXsoJEsculine^ 
 being most abundant in the bark of the horse-chestnut. 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 crystallizes ; by wash- 
 ing with ice-cold water it is freed from the liquid extractive matter ; the impure 
 crystals are to be dissolved in a boiling mixture of five parts of 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 212° ; 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 alkali. 
 
 The watery solution of aesculine reddens litmus, yet it does not neutralize the al- 
 kalies, nor precipitate any of the ordinary metallic salts ; it dissolves abundantly in 
 alkaline liquors, and the solutions give a magnificent play of colours with reflected 
 light ; its formula is CieHgOio- 
 
 Populine exists in the bark and leaves of different species of populus, along with 
 salicine ; the latter is removed from the liquors by precipitation with acetate of 
 lead, and then, by evaporation, the populine is obtained crystallized ; its taste is bit- 
 ter-sweet, like liquorice ; it is very sparingly soluble in water ; when heated, it fu- 
 ses, and is then decomposed ; like salicine, it gives with nitric acid, picric acid, and 
 with sulphuric acid, rutilin ; its composition is not known. 
 
 Quassine constitutes the bitter principle of the quassia amara and excelsa. The 
 rasped wood is to be boiled several times with water, and the fihered decoction 
 evaporated down to three fourths the weight of the wood employed. The liquid, 
 when cold, is to be mixed with slacked lime, and, after twenty-four hours, filtered 
 and evaporated nearly to dryness ; the residue is to be treated with alcohol, and 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. 
 
 Quassine forms small white prisms of an intense but purely bitter taste ; but spa- 
 ringly soluble in water or in ether, it dissolves abundantly in alcohol ; when heated, 
 it fuses like a resin ; its solution is not precipitated by any metallic salt, but abund 
 antly by tannic acid ; its formula is C20H12O6. 
 
 Santonine. — 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 santonine crystallizes in large featherv crystals, which are to be puri- 
 fied from an adhering resinous substance by washing with alcohol. Being then re- 
 
SAPONINEj-^SCILLITINE, SENEGINE, ETC. 611 
 
 dissolved, 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 338° it melts, and by a carefully-applied heat may 
 be sublimed without decomposition, otherwise it becomes brown, and a yellow crys- 
 talline substance is formed. Santonine appears to possess feeble acid properties ; it 
 produces with the alkalies soluble, and with the earths and ordinary metallic oxides 
 insoluble compounds, but they are of instable constitution. The formula of santo- 
 nine is CioHsOa. 
 
 By exposure to light, santonine undergoes a change apparently isomeric ; it be- 
 comes gold-coloured, and forms yellow solutions, which, however, soon become 
 colourless. 
 
 Saponine. — This substance is most easily extracted from the roots of the sapona- 
 ria officinalis by boiling in weak spirit ; on cooling, the saponine 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 sparingly soluble in alcohol, and insoluble in ether; 
 its formula appears to be C26H230)6. By the action of nitric acid, saponine forms 
 mucic acid and a resinous substance ; when dissolved in solution of caustic pot- 
 ash, 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 C26H22O12. It is in- 
 soluble in cold, but soluble in boiling water. 
 
 Scillitine 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 ace- 
 tate of lead, and filtered ; sulphuretted hydrogen being passed through the clear li- 
 quor removes the excess of lead, and then, by filtration and evaporation, the scillitine 
 may be crystallized. 
 
 It forms a hard, brittle mass, like resin, of an intensely bitter taste ; it deliques- 
 ces and dissolves readily in alcohol and water, but not in ether. 
 
 Senegine. — This substance is extracted from the roots of the polygala senega 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 hydro- 
 gen, 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 ma- 
 terial which remains undissolved is then to be passed through the same series of 
 operations until it becomes a white pulverulent mass, which is pure Senegine. It is 
 sparingly soluble in cold, but abundantly in boiling water ; it is very soluble in alco- 
 hol, but insoluble in ether. With sulphuric acid it produces a curious play of col 
 ours, becoming first yellow, after some time rose-red, and then dissolving; the so- 
 lution gradually becomes violet, after some time grayish-blue, and finally colourless, 
 while a gray precipitate falls down. Senegine appears to possess feeble acid prop- 
 erties. 
 
 Smilacine, or Sarsaparilline. — This substance is found in the roots of the smilax 
 sarsaparilla and the bark of the 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 recrystallization. It is white, in very minute nee- 
 dles ; 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 sen- 
 egine. 
 
 Absinthiine. — The bitter principle of the wormwood (artemisia absinthium). It is 
 prepared by a succession of operations almost identical with those described for ob- 
 taining senegine ; it is hence unnecessary to repeat their description. When com- 
 pletely pure, it is white and crystalline ; 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 alkaline 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. 
 
 Lactucinc is obtained by digesting the inspissated juice of the lactuca virosa (lac- 
 tucarium) 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 fusi- 
 ble, 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. 
 
612 APOTHEME. EXTRACTIVE. 
 
 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 re- 
 actions rapidly occur, being promoted by the heat ; the liquor, which had 
 been at first clear, becomes turbid and brown, a deposite 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 tl^e 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 con- 
 dition. This brown substance is termed Apotheme ; its true nature is 
 not known, but it is probable that its composition and properties 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 alkaline liquors, and its precipitating metallic salts, 
 its being separated from these by acids, and obstinately retaining a por- 
 tion of the acid used to precipitate it, its identity with ulmic acid or 
 humic acid is not improbable. 
 
 When the conversion of the real constituents 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 con- 
 tain different kinds of extractive matter; there are thus hitter extractive, 
 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 ex- 
 amined. 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 excluding 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 methods belong to pure phar- 
 macy, and are unfitted for the present work. 
 
 A great number of bodies, that have been from time to time announced as the 
 active principles of many plants containing them, are really but such extracts, prop- 
 
COLOURING MATTERS. 613 
 
 eriy prepared, but still not the pure chemical substances. Thus, from colocynth, 
 Colocynthine ; from hippo, Emetine ; from rhubarb, Rheine, &c. It is on this account 
 that many bodies, to which distinct names have been given by their discoverers, as 
 chemical species, are not noticed as such by me. 
 
 The bitter principle of the Aloes is one of these which have never been obtained 
 chemically pure, and yet the very remarkable products of the action of nitric acid 
 on it show that it is a truly distinct substance. When socotrine or hepatic aloes 
 are digested with hot nitric acid, red fumes are abundantly evolved, and four dif- 
 ferent acids produced, for the accurate examination of which we are indebted to 
 Schunk. They are, the Alo'ttic Acid, the Alo'e-resinic Acid, the Chrysammic Acid, 
 and the Chrysolepic Acid, and they are generated by successive oxidation of the bit- 
 ter principle of the aloes, in the order in which, their names stand. 
 
 The Alo'etic Acid is a yellow powder, insoluble in water, but forming soluble salts, 
 of which that with potash crystallizes in ruby-red needles. The Alo'e-resinic Acid 
 is soluble in water ; its potash salt uncrystallizable ; its combinations with the me- 
 tallic 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 spa- 
 ringly 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 C15H2 . N2O12+ 
 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 wa- 
 ter at 60° for solution, and may hence serve as an excellent reagent for that alkali ; 
 it is a dark red crystalline powder when precipitated, but when it crystallizes from 
 a hot dilute solution, it forms gold-coloured plates. 
 
 The Chrysolepic Acid is distinguished by its solubility in water ; it crystallizes ni 
 beautiful gold-coloured plates, closely resembling Picric Acid, with which it is isom- 
 eric, its formula being C12H2 , NaOia-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 XXVI. 
 
 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 phloridzeine 
 from phloridzine. 
 
 SECTION I. 
 
 OF THE PRE-EXISTING COLOURING MATTERS. 
 
 Colouring Principles of Madder, 
 
 The dried roots of the rubia tinctorum constitute the madder of com- 
 merce, which, furnishing the well-known Turkey red, is perhaps the 
 most important of the dyestufFs. 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 while very hot. On cooling, a red-brown sub- 
 stance precipitates, which is impure Madder Red; it is to be separated 
 
G14 COLOURING PRINCIPLES OF MADDER. 
 
 by trie 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 orange-red crystalline powder, sparingly soluble 
 in cold, but more easily in boiling water. The solution is rose-red ; its 
 solutions in ether and alcohol are bright red. Acids turn it yellow ; al- 
 kalies 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. 
 
 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 brownish -yellow crystalline powder. When heated, it sublimes, form- 
 ing 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 CarHjaOio has been assigned 
 to this body. 
 
 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 for4Ti ; 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 
 eth^r ; it dissolves in alkaline, forming brown-red liquors. 
 
 Madder Yellow, or Xanihin. — 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 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 sulphuret- 
 ted hydrogen. The liquor so obtained gives, on evaporation, the xan- 
 thine pure; it is yellow, uncrystaUizable, and very soluble in alcohol 
 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 possess 
 any interest either technical or scientific. 
 
 Of these colouring matters, the Red, or Alizarine, is the most important, 
 as it forms with an alumina mordant the magnificent Turkey Red. With 
 an iron mordant it gives a permanent black, and with mixed mordants 
 of the two, various intermediate shades of purple. The great complexity 
 of the process for dyeing Turkey red arises from the difficulty of dis- 
 solving away the other four bodies, so that only pure madder red may 
 remain. 
 
 Alkanna Red, or Anchusic 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 carbonate of potash ; on the ad- 
 dition 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 resin- 
 ous body, insoluble in water, soluble in alcohol, ether, and the essential oils ; it 
 combines with alkalies, forming blue solutions, which give blue or crimson lakes 
 with metallic salts. The formula C17H10O4 has been assigned to this body. 
 
 Braziliine is the colouring matter of various soeries of ca-sabina (Brazil wood, 
 
SAFFLOWER RED, ETC. 615 
 
 fernambouc wood). The decoction of the wood in water is to be agitated with hy- 
 drated oxide of lead, then filtered and evaporated 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 separate the excess of gelatine, then again evaporated, and set aside to 
 crystallize. 
 
 When pure, brazilii'ne forms orange crystals ; it is soluble in water, alcohol, and 
 ether ; the solutions are reddish-yellow ; alkalies and most metallic salts give pur- 
 ple, and alum a red precipitate, with the solution of braziliine 
 
 Santaline exists in the red sanders wood (pterocarpus santalinus). Its extraction 
 and properties are exactly similar to that of the Alcanna Red. Its formula is 
 CigHsOs. 
 
 Hcematoxyline. — This substance, the colouring principle of the logwood (haema- 
 toxylon Campechianum), is frequently met with naturally crystaUized 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 braziliine ; it is slightly bitter 
 and astringent ; it is very sparingly soluble in w^ater, but copiously in alcohol and 
 ether, forming brownish-red liquids. Acids colour its solutions yellow, alkalies 
 purple ; with the earths and metallic oxides it forms purple or blue lakes. 
 
 Saffiower Red, or Carthamine, 
 
 The petals of the safQower (carthamus tinctorius) contain a red and a yellow ma- 
 terial ; the former alone is of technical importance. The flowers are to be washed 
 with water acidulated with acetic acid until all the Saffiower 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, insoluble in water and in acids, and but sparingly soluble in alcohol oi 
 ether ; it reddens litmus, and gives with the alkalies yellow solutions ; its com- 
 pound 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 em 
 ployed for dyeing silk of various shades of pink and rose colour. 
 
 I have found in the petals of the salvia fulgens a colouring matter possessing con- 
 siderable analogy to carthamine, and capable of being substituted for it. 
 
 Qmrcitrine. — 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 gel- 
 atine 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 pos- 
 sess feeble acid properties. Its formula, by BoUey's analysis, appears to be CieHgO 
 -|-Aq. With metaUic oxides it gives brilliant yellow lakes. 
 
 Chrysorhamnine. Xanihorhamnine, 
 
 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 
 Chrysorhamnine, is totally replaced by another, which I. term Xanthorhamnine, 
 which is of a much less beautiful yellow, and does not crystallize ; this change is 
 effected, also, by boiling the chrysorhamnine for a few minutes with water, or by 
 contact with alkalies. The xanthorhamnine is totally insoluble in ether, but easily 
 soluble in alcohol and water. It is formed by the union of the elements of water 
 with chrysorhamnine. Its silver salt is yellow when first thrown down, but rap- 
 idly 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 xanthorhamnine alone is actually brought into play. 
 
 Luteoline is the colouring principle of the weld (reseda luteola), and probably of 
 the dyers' broom (genista tinctoria). Its mode of preparation resembles that of 
 quercitrine. It is soluble in water, alcohol, and ether ; it combines with both acids 
 and alkalies, forming yellow compounds. With alumina and the oxides of tin and 
 lead, it gives brilliant yellow lakes ; with iron, a dark brown precipitate. 
 
 Morinc is the colouring principle of the yellow-wood (morus tinctorius) ; it is pre 
 pared like quercitrine, with which its properties accurately agree. 
 
 OreUina.—ThQ seed of the bixa orellana are imbedded in an orange-red colouring 
 
616 COCHINEAL RED, ETC, 
 
 matter, which is separated by washings and a kind of fermentation ; when deposit- 
 ed from the hquors, so as to form a consistent paste, it is sent into commerce under 
 the names of Kocou, Orleans, or Anotta. To obtain the colouring principle pure, the 
 orange-red mass is digested in alcohol, and the solution distilled nearly to dryness ; 
 the residue is tlien treated with ether, which dissolves the orelline, and yields it, on 
 evaporation, as an orange-red, somewhat crystalline powder ; it colours water pale 
 yellow ; it is more soluble in alcohol, but gives with ether or oils deep red solutions ; 
 it dissolves in alkalies, and is precipitated therefrom by acids. With alumina, ox- 
 ide of tin, and oxide of lead, it gives fiery red precipitates. It is extensively used 
 in dyeing, and also to heighten the colour of cheese and butter. 
 
 Curcumine 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 resi- 
 due in ether, which dissolves the pure colouring matter, and yields it by spontane- 
 ous evaporation. Curcumine melts at 104° ; it possesses the properties of a resin ; 
 alkahes 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. 
 
 Berberine exists in the roots of the berberis vulgaris ; it is prepared by boiling the 
 roots in water, and evaporating the decoction to the consistence of an extract, 
 which is to be treated with spirit of wine as long as this acquires a bitter taste. 
 The spirit is to be distilled in great part off, and the residue suffered 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 berberine forms a lig-ht crystalline yel- 
 low pov/der of a strongly bitter taste ; it is very sparingly soluble in cold, but abun- 
 dantly in boiling water and in alcohol ; it is insoluble in ether. At 268° it melts, 
 and, if farther heated, 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 alkaline compounds crystalhze ; those with the earths and heavy me- 
 tallic oxides are insoluble, and generally yellow ; a solution of it precipitates the 
 iodide, cyanide, ferrocyanide, and sulphocyanide of potassium. Berberine contains 
 nitrogen, its formula being N.C33 . HisOja. 
 
 Cochineal Red, or Carmine. 
 
 This veiy remarkable substance diflfers from all of the other colouring matters 
 here described, in being a product of the animal kingdom. It exists in many in- 
 sects 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 remove 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 dis- 
 tillation, and then cautiously dried ; the impure carmine thus obtained is digested 
 in alcohol, and the solution mixed with ether, which precipitates the colouring mat 
 ter quite pure. 
 
 It is a purple red powder, easily soluble in water and alcohol, insoluble in ether. 
 It melts at 122°, but is decomposed by a high heat ; chlorine turns it yellow ; al- 
 kalies colour cold solution 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 pre- 
 pared with a cold, but violet if with a hot solution. All metallic salts give lakes 
 with the alkaline 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 Chi- 
 nese Carmine is the compound with oxide of tin. 
 
 The carmine contains nitrogen ; the formula N.C32 . H26O20 has been assigned to 
 it, but cannot be considered as definitely estabhshed. 
 
 Of Indigo, and the Bodies derived from it. 
 
 The blue indigo of commerce is derived from the leaves of a variety 
 of plants of difFereni genera. The genus indigofera includes a number 
 of productive species, also the genera nerium and isatis, marsdeiiia, as- 
 clepias, and polygonum, galega, spilanthus, and amorpha. Of these the 
 great majority are natives of the tropics ; but a few, as the isatis tincto- 
 ria and the polygonum tinctorium, belong to temperate regions, the for- 
 mer being indigenous both to Ireland and to England. 
 
 The indigo is secreted in the cellular tissue of the leaf, in a form (white 
 
BLUE A^D WHITE INDIGO. 61 
 
 mdigo) which can also be artificially produced ; it is then colourless, 
 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 arri- 
 ved. The fresh leaves are thrown into large vats with some water, and 
 pressed down by weights. After some time, a kind of mucous ferment- 
 ation 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 un- 
 til the indigo becomes blue and insoluble, and is completely 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 solu- 
 tion of it being thus obtained, it is precipitated, according as it absorbs 
 oxygen, in a much purer form than otherwise could be effected. 
 
 The putrefying pasty mass of leaves obtained from the isatis tinctoria 
 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 repeat- 
 ed treatment with alcohol and dilute acids and alkalies. 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 purple col- 
 our and metallic lustre ; its vapour is of a rich purple ; it contains nitro- 
 gen, its formula, as fully established by Dumas, being N.C,6. H5O2. 
 
 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 
 alkaline solutions, is produced. Its mode of preparation is simple : one 
 and a half parts of commercial indigo, two and a half parts of slacked 
 lime, and two parts of green copperas, are to be well mixed up with six- 
 ty parts of water, in a vessel from which the air is carefully excluded. 
 The protoxide of iron, formed by the action of the lime on the copperas, 
 peroxidizes itself at the expense of the indigo and v/ater, and the white 
 indigo thus formed dissolves in combination with lime. On adding mu- 
 riatic acid to the clear solution, the white indigo precipitates, and may 
 be obtained dry, as a crystalline powder, by suitable precautions to pre- 
 vent 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 o^ Deoxidized 
 Indigo and Indigogene were given to the white substance ; but the anal- 
 yses of Dumas have proved that the white indigo is a compound of hy- 
 drogen with the blue indigo, its formula being CieHj . N.Oi+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 application 
 of indigo as a dyeing material. The indigo is rendered soluble either by 
 lime and copperas (cold indigo bath), or, being diffused through warm wa- 
 ter with a quantity of woad, by the fermentation of which ammonia and 
 hydrogen are evolved, a soluble compound of ammonia and white indigo 
 
 4 I 
 
618 SULPHATES OF INDIGO, ETC. 
 
 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 
 fully imbibed 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 ajid the most beau- 
 tiful of our blue dyes. 
 
 Sulphate of Indigo, — When blue indigo, in very fine powder, is digest- 
 ed with strong oil of vitriol, for which purpose the German or fuming sul- 
 phuric acid answers best, it dissolves in great part, and two acids are 
 formed, the Sulphopurpuric and Sulphindylic ; the former is the prin- 
 cipal product when the indigo is in excess, the latter when the oil of vit- 
 riol preponderates ; they are separated by dilution with water, the sul- 
 phopurpuric acid being insoluble, while the sulphindylic acid dissolves. 
 
 The sulphopurpuric acid, though insoluble in dilute acids, dissolves 
 readily in pure water ; it forms, with the alkalies 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 C32H10. N2O4+2S.O3, and 
 in its potash salt to contain one atom of alkali. 
 
 The sulphindylic acid, CigHg. N.02-{-2S.03, when dried from its solu- 
 tion in water, forms a dark blue mass. Its salts are of a rich blue col- 
 our ; those of the alkalies are soluble, those of the earths and metallic ox- 
 ides insoluble in water. They consist, according to Dumas's analysis, of 
 an atom of indigo, two of sulphuric acid, and one of base. The sulpho- 
 purpuric and sulphindylic 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 as 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 Blue, or 
 Chemic Blue, used extensively in dyeing ; on neutralizing the liquor by 
 an alkali (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 alkali. 
 
 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 CieHs . N.O4. If 
 tlie 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. 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 while hot. Both acids crystallize on cooling ; the crystals are to be drain- 
 ed, 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 crystallizes 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 for- 
 mula is C14H4 . N.Og-fAq. 
 
 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 salicine in nitric acid (p. 606), and directly from the sub- 
 stance 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, a.^ 
 do also its salts ; its potash salt requires 260 parts of cold water for solution, and 
 it is hence sometimes used as a reagent for that alkaU ; its formula is C12H3 . N3O13 
 +Aq. 
 
ACTION OF CHLORINE ON INDIGO. 619 
 
 When indigo is mixed with a strong boiling solution of caustic potash, it dissolves, 
 Q.m.,ChrysanUic 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 evap- 
 oration of the solutions ; its formula appears to be C28H10 . N.Os-f-Aq. By exposure 
 to the air while 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 
 375°, 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 vol- 
 atile liquid, Anilene. The formula of the hydrated anthranilic acid is C14H7 . N.O4, 
 and it gives 2C.O2 and C12H7N. 
 
 This liquid, anilene, is a body closely analogous to the melamine (p. 526) ; it acts 
 as a powerful base, combining with the hydracids directly, and with the oxacids by 
 mcluding an atom of water ; it thus resembles ammonia. These important sub- 
 stances, for whose discovery we are indebted to Fritzche, are still under examina- 
 tion. 
 
 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 Erd- 
 man, 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 Chlorindopten, which sublimes in white scales 
 and needles ; its formula is CieHj . O2CI4 ; 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 Chlorisatine : its formula is C16H4CI. . N.O3; it is 
 hence indigo, in which an equivedent of hydrogen is replaced by chlorine, and united 
 to an atom of oxygen ; with an excess of chlorine it gives Bichlorisatine, which con- 
 sists of C16H4CI2 . N.O3. If these bodies be treated with sulphuretted hydrogen, 
 sulphur is set free, and the hydrogen enters into combination ; in contact with pot- 
 ash, the elements of an atom of water are assimilated, and an acid formed, which 
 unites with the potash. In this way chlorisatine gives Chlorisatyd, C16H5CI. . N.O3, 
 and Chlorisatic Acid, CieHsCl. . N.O4, and bichlorisatine gives two corresponding 
 bodies. 
 
 If chlorisatyd be heated, it produces water, chlorisatine, and a violet powder, CMo- 
 rindine, which has the formula C16H5CI. . N.O2, and is hence a compound of indigo- 
 blue with chlorine. By heating bichlorisatyd, the Bichlorindine, C16H5N. . O3CI2, is 
 similarly formed. 
 
 By passing chlorine through a solution of chlorisatine in alcohol, all hydrogen is 
 removed, and a substance formed which crystallizes in pale yellow plates, anc^ has 
 the formula OeOzCla ; it is termed Chloranil. By the secondary reactions of these 
 bodies, a number of others are generated, which it is not necessary specially to de- 
 scribe. 
 
 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 Ci2H50.-|-Aq. (Hydrate of Phanyl), dis- 
 covered as a product of destructive distillation by Laurent, may serve as a connect- 
 ing 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 sub- 
 stitution of 3N.O4 for 3H. in C12H5O., and the anilene is probably C12H5-J-N.H2 ; 
 other speculative ideas might be brought forward, but I shall only mention that the 
 blue indigo contains exactly the elements of cyanogen and benzyl, C2N.-I-C14H5O2, 
 and that, as the cyanogen is converted so easily into oxahc acid and ammonia, the 
 derived bodies, which contain C,4, may thus have their origin. 
 
 Of the Colouring Matters derived from the Lichens, 
 Many species of lichen contain substances which, although colourless themselves, 
 produce, by contact with air and ammonia, the rich purple or blue colouring mat- 
 ters constituting the archil and litmus of commerce. The species of lichen that 
 have been in this respect most accurately examined are the variolaria dealbata by 
 Robiquet and Dumas, and the rocella tinctoria by myself. 
 
 The useful substance in the variolaria is termed Orcine ; it is obtained by digest- 
 ing 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 crvs- 
 
620 ORCEIN E, ERYTHRYLINEj ETC. 
 
 tallize ; it forms, when quite pure, colourless prisms of a nauseous-sweet taste i it 
 fuses easily, and may be sublimed unaltered ; its formula is Ci8H703-j-2 Aq. vsKen 
 sublimed ; when crystallized from its aqueous solution, it contains 5 Aq. 
 
 If orcine be exposed to the combined action of air and ammonia, exactly as de- 
 scribed for phloridzine (p. 607), 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 archil 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 CigHio . N.Og. The orceine in archil is, 
 however, frequently found to contain less oxygen, and to be represented by the 
 formula CisHio . N.O5. I have termed the first kind Alpha-orce'ine, and the second 
 Beta-orcetne ; in properties they are identical. 
 
 Orceine dissolves in alkaUne liquors, with a magnificent purple colour ; with me- 
 tallic oxides it forms lakes, also, of rich purple, of various shades. In contact with 
 deoxidizing agents it combines with hydrogen, as indigo does, and forms Leucor- 
 cetne, CigHio . N.08-|-H. When bleached by chlorine, a yellow substance is formed, 
 Chlororcdne, the formula of which I have found to be CisHio.N.Os-^-Cl., analogous 
 to the other. 
 
 In the rocella tinctoria there is no orcine ; the origin of the coloured substances 
 is a body which I have termed Erythryline ; it is soluble in ether and alcohol, insol 
 uble in water, but is gradually decomposed by it ; its formula is C22H16O6. By the 
 action of the air it is gradually changed into Erythrine, a substance which dissolves 
 sparingly in cold, but abundantly in boiling water, from which it separates on cool- 
 ing in brilliant micaceous plates ; it is very soluble in alcohol and ether ; its formula 
 is C22H13O9. By prolonged boiling in water, erythrine is changed into a substance 
 very soluble in water and in alcohol, Amarythrine, the formula of which is C22Hi30i4; 
 and, finally, by the still farther action of the air, Telerythrine is formed, which crys- 
 tallizes in small grains, and has the formula C22H9O18. 
 
 If, however, in addition to the air, ammonia have access to these bodies, the 
 crimson colour is produced, and the two varieties of orceine are formed. I conceive 
 the oxidizing stage to proceed as far as amarythrine, and that, by combination with 
 ammonia and oxygen, a substance is formed, to which I have given the name of 
 Azoerythrine. Its formula is C22H16 . N.Oi9-j-3 Aq. By the loss of 4C.O2 and 
 6H.0., it gives alpha-orcei'ne, CigHio . N.O5, which, absorbing oxygen, gradually 
 forms the true or beta-orceine, CigHio . N.Og. 
 
 When an alkaline solution of orceine is exposed to the air, it absorbs more oxy- 
 gen, and a substance is produced which constitutes a great part of the colouring 
 material of litmus. I have termed it Azolitmine ; its formula is CisHio . N.Oio ; it is 
 a dark red powder, which is insoluble in alcohol or ether, and but sparingly soluble 
 in water ; it dissolves better in acid liquors, which render it a pale red, and with 
 zilkalies it gives the rich blue colour of htmus. With the earths and metallic ox- 
 ides it forms purple or blue lakes ; with deoxidizing agents it is decolorized, form 
 ing Leucolitmine, and by chlorine a yellow substance is produced, having the foi 
 mulaCisHio.N.Oio-fCl. 
 
 Besides the bodies of the erythrine series, the lichen rocella contains a substance, 
 termed Rocclline, which is white, fusible, insoluble in water, soluble in alcohol and 
 ether ; its formula is C26H24O6. By exposure to the air, it is converted into a fatty 
 substance of a rich crimson colour, which I have termed Erythrolcic Acid ; this body 
 exists in archil, and is separated from the orceine by means of its solubility in ether. 
 Its formula is C26H22O8 ; it is capable, under circumstances which are not yet well 
 understood, of being broken up into two substances, which are both found to exist 
 in litmus ; they are Erythroleine, which has the formula C26H22O4, and Erythrolit- 
 viine, which consists of C26H22O12. The erythroleine and erythroleic acid are, like 
 the alpha and beta orceines, distinguished only by their composition ; they have the 
 same colour, are sparingly soluble in water, but copiously in alcohol and ether; they 
 dissolve in alkaline liquors with a rich crimson colour, and give crimson lakes with 
 the metallic salts. The erythrolitmine, on the other hand, is bright red, very spa- 
 ringly soluble in water or ether, but soluble in alcohol. Alkalies turn it bright blue ; 
 in a solution of potash it dissolves, but its compound with ammonia is insoluble, 
 and consists of C26H220i2-t-N.H40. 
 
 The brief history of these substances now given will render intelligible the process 
 of manufacture of archil and litmus, and the principles of their use in the arts and 
 in the laboratory. The lichens employed are ground up with water to a uniform 
 
COLOURING MATTERS OP LEAVES, ETC. 621 
 
 pulp, and this is then mixed with as much water as makes the whole thick- fluid. 
 Amraoniacal 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 orceine ; the rocelline absorbs oxygen, and forms erythroleic 
 acid ; these being kept in solution by the excess of ammonia, the whole liquid is of 
 an intensely rich purple tint, and constitutes ordinary archil. If the oxidizing ac- 
 tion of the air be allowed to go too far, we have the purple colour replaced by a 
 shade more or less blue ; the orceine changes to azoliimine, and the erythroleine 
 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 erythrolitmine and azoerythrine with an 
 alkali, 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 ChloT- 
 ophyll. Even deeply-coloured plants contain but very little of it, and it has not, as 
 yet, been obtained in a state of such purity as that any formula can be assigned to 
 it. It does not contain nitrogen ; it is insoluble in water, soluble in alcohol and 
 ether ; it is dissolved 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 chlorophyll : the first, 
 which exists in fresh leaves, dissolves in acetic acid with a rich grass-green col- 
 our ; 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 chlorophyll. 
 
 It is known that in autumn the leaves of many trees, as the sorbus aucuparia, 
 cornus sanguinea, &c., assume a fine red colour, while the foliage of others, partic- 
 ularly of forest-trees, becomes bright yellow. Berzelius, who has examined the 
 nature of this change, found the chlorophyll to be replaced in such leaves by a red 
 and a yellow colouring matter, to which he gave respectively the names Erythro- 
 fhyll and Xanthophyll. The former is an extractive matter, easily soluble in alcohol 
 and water ; by the air it is gradually changed into a brown insoluble matter; with 
 alkalies it forms rich green solutions, and with metaUic oxides, green lakes ; by 
 acids the red colour is restored ; a green leaf containing chlorophyll is, however, 
 not reddened by an acid. It is remarkable, that all trees in whose leaves erythro- 
 phyll forms in autumn bear red fruit, as the cherry, currant, &c. 
 
 Xanthop/iyll 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 so- 
 lution, exposed to the air and light, is rapidly bleached : alkalies dissolve it sparing- 
 ly v/ith a yellow colour, which is bleached by light. 
 
 We possess but very little accurate knowledge of the colouring matters of flow- 
 ers : 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 {Anthocy- 
 an), which is soluble in water and alcohol, reddened by acids, rendered green by 
 alkalies, and from these changes producing the red, and all intermeidiate shades of 
 purple and violet ; the yellow substance {Anthoxanthine) is likewise easily soluble 
 in alcohol and water, and is coloured intensely blue by oil of vitriol. These sub- 
 stances possess most analogy to hematoxylin and to safiiower-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 excess- 
 ively minute, that the accurate examination of their properties is exceedingly dif- 
 ficult 
 
622 
 
 THEORY OF DYEING, ETC. 
 
 On some general Characters of Colouring Matters, and on the Principle* 
 
 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 forma- 
 tion 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 hydro- 
 gen appears to belong to all colouring substances. If an infusion of log- 
 wood, of cochineal, of violets, of immerin, be rendered acid by muriatic 
 acid, and a slip of zinc immersed therein, the liquor becomes gradually 
 colourless, and on adding ammonia, a white lake is precipitated, consist- 
 ing of the hydruret of the colouring matter combined with oxide of zinc. 
 
 With oxygen all colouring matters appear also to combine to form bod- 
 ies quite or nearly destitute of colour. Thus, if the chrysorhamnate of 
 silver be boiled in water, metallic silver separates, and oxidized colour- 
 ing 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 principle 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, how- 
 ever, 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 sulphur- 
 ous 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. 
 For 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 afterward, 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 patterns on cloth 
 would be impossible, and the art of the calico printer restrained to very 
 narrow limits, were it not for the power which chlorine gives him of re- 
 moving 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 col- 
 ouring 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 containing 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 prod- 
 uct, besides containing chlorine, is also more highly oxidized. The 
 
FIXING OF COLOURS ON CLOTH, ETC. 62'6 
 
 action of chlorine on colouring matter is therefore subjected to thfe same 
 laws as when it acts upon other organic substances, the series of bodies 
 derived from indigo by chlorine having much analogy to the series of 
 bodies formed with alcohol or olefiant gas. 
 
 In relation to the processes of dyeing, colouring substances are divi- 
 ded into two classes, the substantive and adjective. The substantive 
 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 incapable 
 of so permanently fixing themselves, and the necessary insolubility 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. 436), or iron (p. 558), or tin (p. 448), 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, while 
 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 remarka- 
 ble, 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 chlorophyll and the green of the stems of buck-thorn 
 (sap-green), neither of which is capable of being attached to cloth : all 
 greens are, therefore, in practice, formed by the superposition of a blue 
 findigo or Prussian blue) and a yellow (chromate of lead or chrysotham- 
 mine). 
 
 The details of the processes of dyeing and printing in patterns, al- 
 though embracing some of the most refined applications of the properties 
 of the colouring matters, do not enter into the plan of an elementary and 
 general work, such as this should be. 
 
 CHAPTER XXVII. 
 
 OF THE VEGETABLE ALKALIES. 
 
 The substances now to be described constitnte a very remarkable 
 family of bodies. They exist naturally in the plants from which they 
 are derived, and confer upon them their most active medicinal prop- 
 erties ; they act as bases, forming, with few exceptions, well-char- 
 acterized and neutral salts even with the strongest acids, and they 
 are distinguished from most substances of vegetable origin by con 
 taining nitrogen. The presence of this element, indeed, has been 
 considered as standing in immediate connexion with the source of 
 their alkaline power, and has given rise to theories of their intimate 
 
624 QUININE AND ITS SALTS. 
 
 constitution, of which I shall notice the most important at the con- 
 clusion of their special histories. 
 
 Quinine:— (N.C^o . HisO^) or Qu. Eq. 163-1 or 2039. 
 
 The bark of the various species of cinchona contains three vege- 
 table alkalies, combined with the cinchonic and cinchonatannic 
 acids already described. These are quinine, cinchonine, and ari- 
 cine ; of these, the quinine is by far the most important, and is gen- 
 erally 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 strained ; lime is then to 
 be added in very fine powder until the liquor has a marked alkaline 
 reaction j the precipitate is to be collected on a linen cloth, washed 
 once or twice with water, and then dried ; from this, boiling alco- 
 hol dissolves out quinine and cinchonine j the solution being mixed 
 with water, the alcohol may be distilled off and saved; the residue 
 is to be then neutralized by dilute sulphuric acid, and a slight ex- 
 cess added to form acid salts. On evaporating this liquor to the 
 proper point, the sulphate of quinine crystallizes, while the sulphate 
 of cinchonine remains in solution. 
 
 To obtain pure quinine, solution of sulphate of quinine is to be 
 decomposed by caustic potash, and the white curdy precipitate, be- 
 ing carefully dried, is to be dissolved in the smallest possible quan- 
 tity of spirit of wine. By then allowing it to evaporate spontane- 
 ously 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 j 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 anilene ; it combines directly with the hydracids. 
 
 The Muriate of Quinine, (Qu.-f-H.CL), forms pearly needles. It 
 dissolves easily in water ; with corrosive sublimate and with bichlo- 
 ride of platinum it forms double salts, soluble in water, and crys- 
 tallizable. 
 
 The Basic Sulphate qf 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 analogous methods. When crystallized, it contains water, 
 its formula being (Qua+S.Og+S Aq.). It effloresces when gently 
 heated or in very dry air, giving off six atoms of water and retain- 
 ing two, Avhich cannot be expelled without partial decomposition ; 
 it is but sparingly soluble in water, requiring thirty parts of boiling 
 and 740 parts of cold water ; it requires eighty parts of cold alco- 
 hol, but much less of hot ; its crystals are small pearly plates or 
 needles, which, when heated, phosphoresce strongly and fuse ; by 
 a strong heat it is, of course, totally decomposed. 
 
 The JVeutral Sulphate of Quinine crystallizes in rectangular prisms 
 
SALTS OF QUININE. C I N C H O N I N E. 625 
 
 which have the formula (Qu. + S.O3 + 8 Aq.). 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 consti- 
 tution, 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 precipitating the quinine that is dissolved by a 
 drop of solution of carbonate of soda, when the taste of the sugar 
 is recognised. 
 
 Phosphate of Quinine crystallizes in small but very brilliant nee- 
 dles, 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 salt of quinine. A white precipi- 
 tate appears, which is totally insoluble in water, but dissolves in 
 acetic and muriatic acids. 
 
 Ferroprussiate of Quinine is formed by boiling together one part 
 of sulphate of quinine and one and a half of yellow prussiate of 
 potash with seven parts of water. The newly-formed salt separates 
 as a greenish-yellow oily substance. When the liquor is cold, it is 
 to be poured off, and the ferroprussiate of quinine dissolved in 
 boiling alcohol, from which it crystallizes in greenish-yellow nee- 
 dles by spontaneous evaporation. 
 
 The action of chlorine on quinine and its salts is very character- 
 istic. 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 Dalleiochin has been given. If 
 the green solution be evaporated 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. Formulae 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.—N.Q>2o - HjzO. or Ci. Eq. 155-1 or 1939. 
 
 This alkali exists most abundantly in the gray bark (cinchona 
 micrantha), from which it may be obtained by the same kind of 'pro- 
 cess 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 de- 
 scribed I from its alcoholic solution it crystallizes in thin colourless 
 prisms ; its taste is peculiar and bitter ; it requires 2500 parts of 
 boiling water for solution, but dissolves easily in alcohol and in 
 ether. At 330° it fuses, without losing weight. Its salts resemble 
 very closely those of quinine. 
 
 Muriate of Cinchonine^ Ci.-f H.CL, crystallizes easily in brilliant 
 
 4K 
 
626 A R I C I N E. M O R P H I A. 
 
 interwoven needles ; it forms double salts with the metallic chlo- 
 rides, similar to those of quinine. 
 
 ^ulyhate of Cinchonine. — The basic sulphate, Cij-}-S.034-2 Aq., 
 crystallizes in rhombic prisms j it requires fifty-four parts of cold 
 water for solution. The neutral salt, Ci. -f S.O3-I 8 Aq., is much more 
 soluble, and crystallizes in large, well-formed rhombic octohedrons. 
 The Tannate of Ci?ickomne 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 
 cinchonine be dissolved together in alcohol, and the liquor evap- 
 orated 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.—N.G^, . H,A or Ar. Eq. 171-1 or 2139. 
 
 This alkaloid is found in the bark known as China de cusco, or 
 arica bark, with which the genuine cinchona bark is often adulter- 
 ated; the tree yielding it is not known. It is obtained by precisely 
 the same process as 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 but very little examined, but they appear to cor- 
 respond very closely in constitution and properties to the salts of 
 quinine and cinchonine. 
 
 JlforpAt«.— N.C35 . H20O6 or Mr. Eq. 293-8 or 3673. 
 
 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 processes adopted in the British pharmacopoeias for this pur- 
 pose are very simple, and deliver a product which, although by no 
 means chemically pure, is yet sufficiently so for all medicinal ob- 
 jects ; as they are, however, more especially applied to the prep- 
 aration of the muriate of morphia, I shall describe them under that 
 head. 
 
 To obtain pure morphia, the process invented by Wittstock is 
 perhaps 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, and after a few hours, a brown clotty 
 precipitate forms ; this being removed by the filter, ammonia is to 
 be added in slight excess, and the whole allowed to stand for twen- 
 ty-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, crys- 
 tallizes on cooling. In this process the narcotine is separated by 
 the addition of the common salt, in a solution of which it is insolu- 
 
PROPERTIES OF MORPHIA. 627 
 
 l)le ; the meconic acid, codeine, and thebaine 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 ex- 
 pressed, and this repeated three or four times j these solutions be- 
 ing mixed, are brought to boil, and milk of lime added in slight ex- 
 cess j the precipitate which forms is to be collected on a strainer 
 and strongly pressed j the liquor is then to be evaporated until it is 
 about twice the weight of the opium employed, and to be then fil- 
 tered, 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, 2, 
 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 permanent- 
 ly bitter j it is almost insoluble in water, requiring 400 
 parts when boiling, and separating almost completely as 
 the liquor cools. The solution reacts strongly alkaline ; it dissolves 
 readily in alcohol, but very sparingly in ether. It dissolves in so- 
 lutions of the caustic alkalies 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 alkalies, 
 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 sesquichlo- 
 ride of iron, the solution assumes a rich blue colour, which is re- 
 moved by an excess of acid, but returns on the neutralization of it 
 by an alkali. With tannic acid it gives a copious white precipitate. 
 By these remarkable reactions, the recognition of morphia is ren- 
 dered 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. + H.Cl., is, for medicinal objects, the 
 most important compound of morphia ; its preparation, as directed 
 by the British pharmacopoeias, is as follows : the soluble parts o( 
 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 ex- 
 cess of chloride of lead (London) or of chloride of calcium (Edin- 
 burgh). The meconate of morphia, which exists in the opium, be- 
 ing decomposed, meconate of lime or lead is precipitated, and mu- 
 riate of morphia remains dissolved 5 the liquor is to be carefully 
 strained and evaporated to a pellicle ; on cooling, the salt crystalli- 
 nes J this is to be pressed between folds of cloth, to remove the 
 
628 NARCOTINE. CODEINE. 
 
 dark mother liquor, and then dissolved in boiling water, digested 
 with ivory black, and recrystallized until the crystals become per- 
 fectly 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 alkaloids. To obtain the pure salt, pure mor- 
 phia should be dissolved in dilute muriatic acid, and the solution 
 crystallized. 
 
 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.H.O. . S.Og+S Aq. The Bisulphate of Morphia 
 does not crystallize. 
 
 Acetate of Morphia is formed by dissolving the alkali in acetic 
 acid, or by decomposing muriate of morphia by acetate of lead ; 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 so- 
 lutions of any of these salts. 
 
 JVarcoifme.— N.C46 . H^aOja or Nr. Eq. 5230 or 418. 
 
 This alkaloid may be obtained at once from opium by digestion 
 with ether, or when the impure morphia is thrown down by ammo- 
 nia, ether dissolves out the narcotine from it. It crystallizes in col- 
 ourless rhombic prisms, which are generally larger than those of 
 morphia 5 it fuses at 338^, and remains liquid until cooled to 266°, 
 when it congeals as a mass of radiated needles. It is almost insol- 
 uble in water, but easily soluble in alcohol and ether j its salts have 
 but little stability, few of them crystallize, and most are decompo- 
 sed by dilution with much water. Bj'^ ammonia and tannic acid they 
 are precipitated. 
 
 From morphia, narcotine is very easily distinguished by its solu- 
 bility in ether, insolubility in caustic alkalies and earths, and its not 
 giving the reactions characteristic of morphia with nitric acid or 
 with sesquichloride of iron. But if narcotine be put in contact with 
 sulphuric acid, and oxygen is supplied either by the air or by a 
 trace of nitric acid, it becomes red. Under these circumstances, 
 however, morphia becomes green. 
 
 Cotfeme.— N.C35 . H20O5 or Cdn. Eq. 3573 or 285-8. 
 
 This alkali 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 substance 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 codeine 
 separates in colourless prismatic crystals, which contain 2 Aq. 
 
 Crystallized codeine fuses at 300°, giving off its crystal water. It 
 dissolves copiously in water ; the solution reacts strongly alkaline ; 
 it is insoluble in alkaline 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 
 
T H E B A I N E. ^N A R C E I N E. S T R Y C H N I N E. 629 
 
 are employed in pharmacy or medicine, they need not be specially 
 noticed. 
 
 TAeiame.— N.C25 . H.A or Tb. Eq. 2542 or 203-4. 
 
 The watery infusion of opium being treated with milk of lime, so 
 that the morphia may rest undissolved, the precipitate is to be 
 washed with water until it becomes white, and then dissolved in a 
 dilute acid. From this solution thebaine is precipitated by ammo- 
 nia. The precipitate being dissolved in ether, and the solution 
 evaporated, pure thebaine crystallizes in colourless short rhombic 
 prisms, which taste sharp and styptic, and have a strong alkaline 
 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 narcotine. 
 
 J^arceine. — The watery solution of opium is to be heated first by 
 ammonia, which throws down morphia, narcotine, thebaine, and 
 some other bodies, and these being removed by filtrations, the me- 
 conic acid and codeine are to be precipitated by an excess of solu- 
 tion 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 crys- 
 tals form, which are a mixture o{ meconine (see p. 610) 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 deli- 
 cate needles. 
 
 It tastes bitter, fuses at 200°, and forms a crystalline solid on 
 cooling ; it dissolves in 230 parts of boiling water ; it is very solu- 
 ble in alcohol, but insoluble in ether j its solution does not react al- 
 kaline, and it is decomposed by strong acids ; in its constitution, 
 however, it resembles the true vegetable alkalies, its formula being 
 
 Pseudomorphine^ N.C54 . H,sOj4, occurs but very rarely in opium. 
 For its mode of preparation, when present, I shall refer to the lar- 
 ger systematic works ; in its reactions it is absolutely identified 
 with morphia, from which it is distinguished, however, by its com- 
 position, by crystallizing in plates, and by not forming any well- 
 characterized salts, although it dissolves very readily in dilute acids 
 
 Strychnine.— N^C,^ . H22O4 or Stc. Eq. 4355 or 348. 
 
 This alkaloid exists associated with brucine in several species of 
 strychos (nux vomica, ignatia, colubrina, «fec.), also in the substance 
 used by the natives of Borneo for poisoning their arrows, and term- 
 ed Upas-tieuta^ or Woorara ; it is obtained most easily from the Ig- 
 natius's beans, which contain but little brucine ; but, as these are not 
 often found in commerce, the nux vomica is most generally em- 
 ployed. The seeds are to be boiled for some time in strong alco- 
 hol, which dissolves out a quantity of fatty matter ; being then dried 
 in a stove, they are easily reduced to powder j this powder is to be 
 
630 STRYCHNINE, ITS PROPERTIES, ETC. 
 
 then boiled two or three times in alcohol, and the liquor distilled 
 until the greater part of the alcohol has come over. To the resi- 
 due, acetate of lead is to be added as long as any precipitate oc- 
 curs ; 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 lineu, pressed, dried, 
 and dissolved in alcohol, from which the strychnine crystallizes on 
 cooling, while the brucine remains in the mother liquor. As the 
 strychnine, how^ever, 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 strychnine crystallizes in brilliant white, soft, feathery 
 prisms, while the nitrate of brucine separates afterward in large, 
 hard, rhombic prisms. From sixteen ounces of nux vomica, forty 
 grains of nitrate of strychnine 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 dissolv- 
 ed in spirit of wine, it crystallizes, by spontaneous evaporation, in 
 small white four-sided prisms. 
 
 Strychnine has an intensely bitter, somewhat metallic taste j it 
 requires 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 j it differs from 
 the other vegetable alkalies 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. 
 
 Muriate of Strychnine^ Stc.-j-H.Cl., crystallizes in crowded rhom 
 bic needles, which dissolve readily in water. With corrosive sub- 
 limate, with bichloride of platinum, and with cyanide of mercury, 
 it gives insoluble double salts. 
 
 Hydrocyanate of Strychnine is obtained by dissolving strychnine in 
 prussic acid ; it crystallizes in needles, which are decomposed even 
 by a gentle heat. If solution of sulphocyanide of potassium be ad- 
 ded to a solution of any salt of strychnine, the liquor, when agitated, 
 deposites the Sulphocyanate of Strychnine in fine radiated needles, 
 which are insoluble in water. By this means one part of strychnine 
 may be recognised in 375 of water, and hence Artus has proposed 
 this reaction as the best medico-legal test for strychnine. 
 
 Sulphate of Strychnine forms small cubic crystals, which contam 
 4 Aq., and are soluble in ten parts of water. 
 
 The characters of the JS'^itrate of Strychnine have been described in 
 the method of preparing the alkaloid. 
 
 Strychnine is, perhaps, after pure prussic acid; the most intense 
 of poisons. It kills by producing tetanus. 
 
B R U C I N E. D E L P H I N I N E. V E R A T R I N E. 631 
 
 Brucine.—N,C,s . H^gOg or Br. 'Eq. 408 or 5107. 
 
 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 alkaloid 
 is derived. Its mode of preparation from the nux vomica has been 
 sufficiently described in the preceding article. 
 
 From its solution in spirit, brucine crystallizes in colourless 
 rhombs, containing water, which they abandon on melting at 220°. 
 It dissolves in 850 parts of cold and in 500 parts of boiling water ; 
 these solutions react alkaline, 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 
 distinguishes 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 crystalliza- 
 ble, and give with tannin and with ammonia white precipitates. 
 
 The Curara, or Urari poison, used in the Indian Archipelago for 
 poisoning arrows, contains a vegetable alkaloid, Curarine^ which 
 lorms a yellow uncrystallizable mass, which dissolves easily in wa- 
 ter and in alcohol, but is insoluble in ether ; it reacts alkaline, and 
 combines with acids ; its salts do not crystallize 5 its solution is pre- 
 cipitated by tannic acid. 
 
 The tree from which curara is derived is not accurately known, 
 but is supposed to be a strychnos. 
 
 Delphinine.—N.C,, . H, A or De. Eq. 2659 or 2124.— This sub- 
 stance is extracted from the seeds of the stavesacre, delphinium 
 staphisagria^ 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 ani- 
 mal charcoal, filtered, 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 j almost insoluble in water; its 
 solution has an intolerably sharp taste ; it melts at 250^ ; chlorine 
 turns it green j 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, Stephysaine, (N.C32 . H23O4 1), 
 which is distinguished by its insolubility in ether ; it is a yellow 
 resinous mass, insoluble in water, but dissolving in dilute acids with- 
 out neutralizing them. 
 
 Veratnne.—'N.Cs^ . H2i06 or Ve. Eq. 3647 or 289. 
 
 This alkaloid is found in the roots of the veratrum album, and in 
 the seeds of the veratrum sabadilla j the best process for its extrac- 
 tion is that given by Vasmer. 
 
632 SABADILLIN E. J E R V I N E. C O L C H I C I N E, 
 
 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 5 it is to be accurately 
 neutralized 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 everything 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 car- 
 bonate of soda. The precipitate must be redissolved in a dilute 
 acid, digested with ivory black, and again precipitated by a carbon- 
 ated alkali in order to obtain it pure. 
 
 Pure veratrine appears as a white uncrystallized resinous powder ; 
 it melts at 230°, reacts alkaline, has no smell, but produces violent 
 sneezing ; its taste is exceedingly sharp, but without bitterness j it 
 is insoluble in water, but dissolves readily in alcohol and ether 5 its 
 salts are mostly crystallizable and neutral, but if mixed with much 
 water they are decomposed, acid being set free, and a basic salt pre- 
 cipitated. Veratrine itself is actively poisonous, and is much used 
 in medicine, but none of its salts are important. 
 
 Sabadilline.—'N.C^o . H.aO^ or Sa. Eq. 2351 or 188-1. 
 
 This body, which accompanies veratrine, is separated from it by boiling the pre- 
 cipitate produced by the carbonate of soda with water. From the liquor the sabadil- 
 line gradually separates in radiated crystalline 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 alkaline, 
 and forms crystallizable salts with acids. 
 
 Jervine.— 1^2^00 - HsOg or Je. Eq. 5952 or 476. 
 
 This alkaloid accompanies veratrine in veratrum album; it is prepared by a pro- 
 cess similar to that for veratrine, from which it is separated 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°, 
 nearly insoluble in water, but copiously soluble in alcohol. Of its salts, the sul- 
 phate, nitrate, and muriate are sparingly soluble in water or in mineral acids; the 
 acetate dissolves readily. Muriate of jervine forms, with bichloride of platinum, a 
 very sparingly soluble iouble salt. Crystallized jervine contains 4 Aq. 
 
 Colchicine. — (Formula not established.) 
 
 This alkaloid is obtained from the seeds of the meadow saffron (colchicum autum- 
 nale) by digestion in a mixture of weak alcohol and sulphuric acid. The excess 
 of acid in the liquor is to be then neutralized by lime, and the alcohol distilled oif. 
 The residual liquor is to be decomposed by carbonate of potash in excess, the pre- 
 cipitate washed, dried, dissolved in absolute alcohol, decolorized by animal charcoal, 
 and gently evaporated, a few drops of water being added. The pure colchicine 
 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 wa- 
 ter, and very soluble in alcohol and ether; its solution reacts feebly alkaline, but 
 neutralizes acids perfectly. Tincture of iodine precipitates it of a rich orange col- 
 our. Nitric acid colours it dark violet and blue. Though most abundant in the 
 seeds, all parts of the meadow saffron contain colchicine. 
 
 Emetine. — (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 be powdered and digest- 
 ed 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 j the precipitate is to be dried and digested in 
 
SOLANINE. CH E LERYTHR INE, ETC. 633 
 
 alcohol, which dissolves the emetine. This solution is to be evap- 
 orated to dryness, the residue dissolved in a dilute acid, the liquor 
 boiled with ivory black until completely decolorized, then filtered, 
 and the emetine precipitated by an alkali. 
 
 When completely pure, emetine is white and nearly tasteless j it 
 is very poisonous ; scarcely soluble in water or in ether, it dis- 
 solves readily in alcohol ; it possesses strong alkaline properties ,* 
 its salts are completely neutral, but cannot be crystallized j they 
 dry down to gummy masses. Tannic acid and corrosive sublimate 
 produce white precipitates ; iodine, bichloride of platinum, brown 
 ish-yellow precipitates with the salts of emetine. 
 
 Solanine.—lS(.C,s . H^aO^s or So. Eq. 7519 or 601. 
 
 This alkaloid 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. The liquid is to be supersaturated with 
 milk of lime, the spirit distilled off, the residue washed with water, and what remains 
 treated with dilute sulphuric acid. From the solution thus obtained the solanine is 
 to be precipitated by an alkali, 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 insolu- 
 ble 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 (under ground) and buds of the tubers. 
 
 Chelerythrine. — (Formula not established.) 
 
 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, prised between 
 folds of paper, and digested in 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 sub- 
 stance undissolved. The deep red liquor evaporated to dryness and washed with 
 ether, leaves a mixture of muriate of chelerythrine and muriate of cheledoline, the 
 fojrmer of which is dissolved by washing with a small quantity of water, while the 
 latter remains undissolved. 
 
 From the solution of the muriate, the chelerythrine is precipitated by ammonia 
 as a white curdy powder. From its ethereal solution it remains as a resinous mass, 
 which remains soft for a long time; it is insoluble 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. 
 
 Chelidonine. — N3C40 . HgoOg or Ch. 
 
 The preparation of this substance has been in great part described in the prece- 
 ding article. By digesting the sparingly soluble muriate with ammonia, then dis- 
 solving in, sulphuric acid, and precipitating with muriatic 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 c'ol- 
 ouriess tables. It isj insoluble in water, soluble in alcohol and ether; it tastes bitter, 
 and reacts alkaline ; its salts are colourless, and those with the mineral acids crys* 
 tallize ; its solutions give with tannic acid a precipitate. 
 
 Aconitine. — (Formula not established.) 
 
 The fresh-expressed juice of the monkhood (aconitum napellus) is to be boiled 
 and filtered, and the clear liquor mixed with an excess of carbonate of potash. The 
 
 4L 
 
634 A T R O P I N E. B ELLADONIN E. D A T U R I N E. 
 
 mixture is to be agitated with ether as long as anything is taken up, and by evapo- 
 rating this solution the aconitine remains. From the dry plant or from the seeds, 
 the aconitine may be obtained by processes similar to those described for veratrine 
 and colchicine, 
 
 Aconitine 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 alkaline, and neutralizes the 
 strongest acids ; alkalies precipitate its solution white ; chloride of gold and tannic 
 acid also give white precipitates, and iodine throws it down orange. 
 
 Atropine. — N.C34 . HgaOg or At. 
 
 This alkaloid exists in all parts of the atropa belladonna, but most abundantly in 
 the roots. To prepare it, the fresh roots are to be powdered and digested in alcohol, 
 of specific gravity 0820. The liquor obtained is to be mixed with lime, in the pro- 
 portion 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 deposite 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 boil-, 
 ing with animal charcoal, filtered, and gradually evaporated, whereby the atropine 
 separates in small white silky prisms. 
 
 The taste of atropine is sharp, bitter, and metallic. It dilates the pupil perma- 
 nently and strongly ; if impure, it is brown, does not crystallize, and has a horrible 
 smell, but if quite pure it has no smell ; it requires 2000 parts of cold water for so- 
 lution, but dissolves in thirty-four parts of boiling water, from which some crystalli- 
 zes by cooling, but the greater part is decomposed ; it dissolves readily in alcohol 
 and ether. 
 
 The alkaline properties of atropine 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 eflfected by the caustic fixed alkalies. Most 
 of the salts 1^ atropine crystallize; tannic acid precipitates their solutions white ; 
 t^e chlorides of platinum and gold, yelloAv ; and iodine, orange-yellow. 
 
 Belladonine. — (Formula not established.) The dried root of belladonna 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. Belladonine sublimes and condenses in colourless rectangular prisms, with 
 a penetrating odour like ammonia ; it dissolves in water ; the solution reacts alka- 
 line ; it is not very poisonous ; its salts resemble closely the corresponding salts yf 
 ammonia. 
 
 It appears to me likely that this substance is a product of the decomposition 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 preparation of aconi- 
 tine. 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 dis- 
 gustingly narcotic ; its taste is bitter, and like that of tobacco ; it dissolves in seven- 
 ty-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 alkaline, and forms crystallizable neutral 
 salts, which, like pure daturine, are very poisonous. Towards reagents it acts like 
 atropine. 
 
 Hyoscyamine. — This alkaloid, which is the active principle of the henbane (hyos- 
 cyamus" niger and albus), is best prepared from the seeds, in the same way as atro- 
 pine, 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 atropine and daturine, that they need not be specially detailed. It neutral- 
 izes acids perfectly; its salts are intensely poisonous; they are decomposed very 
 easily, even by boiling with water. 
 
C O N E I N E. N I C O T I N E. 635 
 
 Coneine.—'N.C,^ . OhH. or Cn. Eq.^ 1359 or 108-7. 
 
 This remarkable substance is ihe active principle of the hemlock (conimn macui 
 latum), 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 pot- 
 ash 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 mix- 
 tui-e of one part of ether and two of alcohol, sp, gr. 0820, wherein the sulphate of 
 coneine dissolves. From this solution the 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 separated 
 from the watery liquor, and this last distilled again with some lime. If the coneine 
 contain ammonia, it may be got rid of by exposure for a lew hours in vacuo, beside 
 a capsule of oil of vitriol. 
 
 Pure coneine is a colourless transparent liquid, of sp. gr. 089 ; 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 oi 
 water, and this 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 an- 
 hydrous, coneine has no alkaline properties, but acts very powerfully if water is 
 present ; it saturates acids completely, and has the smallest atomic weight of any 
 organic alkali known. 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. Coneine itself is coloured by 
 nitric acid blood- red ; by exposure to the air, especially if warm, coneine is decom- 
 posed ; it becomes brown, ammonia is evolved, and a bitter, inodorous, resinous 
 substance is produced, which has no poisonous properties. 
 
 J^icotine. — (Formula not established.) 
 
 This substance is the characteristic ingredient of tobacco (nicotiana tabacum, 
 and many other species). For its preparation, precisely the same process is to be 
 followed as has been described for coneine, to which it has a very great similarity. 
 When pure, nicotine 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. 
 Jf water be present, it distils easily at a much lower temperature. 
 
 Nicotine possesses a strong alkaline reaction, and neutralizes acids perfectly. Its 
 salts are generally very soluble, some crystallizable, inodorous, but with a strong 
 K)bacco taste. With alkalies they evolve the characteristic odour of the plant. 
 
 Menispcnni'ne. — N.Cis . H12O2. This substance is found in the capsules of the coc- 
 culus Indicus, associated with picrotoxine (page 609). The alcoholic extract is to be 
 boiled with acidulated water, and when the picrotoxine has crystallized from the fil- 
 tered liquor, an excess of alkali is to be added. The precipitate is to be dissolved 
 in alcohol, decolorized by animal charcoal, and evaporated to dryness. The residue 
 is to be digested with ether, which dissolves Menispermine, and leaves another body, 
 Paramenispermine, undissolved. 
 
 From the ethereal solution, menispermine crystallizes in white square prisms. It 
 is tasteless, and not poisonous ; it forms neutral crystallizable salts. The parame- 
 nispermine dissolves in acids, but does not neutralize them. 
 
 Cissampdinc exists in the roots of the cissampelos pareira (pareira brava), and is 
 prepared by the same kind of process that has been frequently described. From 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 decomposed ; it is a powerful organic base ; its salts form gummy masses, 
 but scarcely crystallize. 
 
 Glaucine exists in the glaucium luteum (homed poppy). Its preparation is sim- 
 ilar to that of aconitine ; it crystallizes in pearly scales ; it possesses the same range 
 of properties as the other vegetable bases, and forms crystallizable salts. The 
 homed poppy contains another crystalline principle (^Glauco-picritie), which appears 
 also to act as a base. 
 
636 CONSTITUTION OF VEGETABLE ALKALOIDS. 
 
 A great number of plants are stated to contain organic bases, which, howevef, 
 have been as yet so imperfectly examined and described as to render their intro- 
 duction 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 aathusa 
 cynapium, Cynapine, crystalline ; and in the digitalis purpurea, Digitalhie, which ap- 
 pears most to resemble coneine. 
 
 Of the Constitution of the Vegetable Alkaloids. 
 
 From the period of the first discovery of this class of bodies, 
 chemists have endeavoured to ascertain on what depended the ba- 
 sic properties by which they are so remarkably characterized. The 
 discovery, by Liebig, that each equivalent of an organic base con- 
 tained 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 ob- 
 tain ammonia from any vegetable alkaloid, unless by processes 
 which totally destroy its constitution, and which, indeed, eliminate 
 ammonia from any organic substance containing nitrogen. More- 
 over, it is now known that Liebig's rule is not universally true ; the 
 equivalents of strychnine and of brucine contain each two atoms of 
 nitrogen, and we know of other organic bases, as melanine, amiline, 
 jervine, and urea, in which the quantity of nitrogen in the equiva- 
 lent goes much beyond one atom. We may hence conclude that 
 there is no reason to suppose that the vegetable alkalies contain 
 ammonia, or owe their basic properties to its presence. 
 
 Some remarkably simple relations of composition occur among 
 certain bodies of this class, which would at first appear to throw 
 light upon their constitution. Thus morphine and codeine differ 
 in composition only by morphia containing an atom of oxygen 
 more 5 and if we supposed (N.C35 . H20O4) to be a compound radical 
 R., then codeine should be protoxide, R. + O., and morphia deutox- 
 ide, R.4-20. In like manner, if we take the cinchona alkalies, we 
 find them to differ only in the quantity of oxygen they contain, and 
 making (N-CjoHia) a compound radical, cinchonine should be R.-f 
 O., quinine R.-f-^O., and aricine, R.4-30. These remarkable facts 
 might lend considerable support to the idea that these alkaloids are 
 oxygen bases, oxides of compound radicals j but a closer examina- 
 tion of their relations does away with all probability of its truth. 
 Thus, if morphia were R.-|-20., then by muriatic acid we should 
 have a bichloride formed, R.-}-2Cl., 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 alkalies any of the laws which govern the formation 
 of salts by metallic oxides. In addition, the salts formed by these 
 alkaloids with the oxygen acids contain an atom of water, which 
 cannot be expelled without decomposition. In this they resemble 
 ammonia, and I think that it is the only analogy which we can estab- 
 lish by the facts at present known ; but whether, in these vegetable 
 alkalies, the nitrogen makes part of a compound radical analogous 
 to amidogene, remains to be decided by future investigations 
 
ULMINE BODIES FROM SUGAR. 637 
 
 CHAPTER XXVIII. 
 
 OF THE PRODUCTS OF THE DECOMPi)SITION OF WOOD AND THE ALLIED 
 
 BODIES. 
 
 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 recognised to consist of 
 several distinct substances, differing in their origin, and still more 
 essentially in their properties. From the influence which they ex- 
 ercise in agricultural operations, by forming an element of the soil, 
 and their importance as fuel, by constituting the great mass of turf, 
 they deserve a somewhat detailed notice. I have already stated, 
 that by the action of acids upon sugar (p. 532), lignine, starch, and 
 similar bodies (page 528), brown substances are produced, the com- 
 position of which was not definitely established. Mulder has, how- 
 ever, recently reinvestigated the history of this class of bodies, and, 
 from his known accuracy, his results may be looked upon as satis- 
 factory. 
 
 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. For 
 these bodies the names Sacchulmine and Sacckulmic Acid maybe re- 
 tained. From the alkaline 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 C4oHi60,4 ; that of the 
 Sacckulmic Acid is C4oH,40i2. They differ, therefore, in the former 
 containing the elements of water, which, however, cannot be expell- 
 ed without total decomposition. 
 
 If the sacchulmic acid be dissolved in water of ammonia and pre- 
 cipitated by an acid, it retains a quantity of the alkali ; and if the 
 ammoniacal solution be decomposed by a metallic salt, the precipi- 
 tate which forms is a double compound of sacchulmic acid, ammo- 
 nia and the metallic oxide. It was the unsuspected existence of 
 ammonia in these cases which produced the discordance of former 
 results. 
 
 If the sugar be acted on by a stronger acid, and the solution kept 
 boiling for a considerable time, the ulmine bodies disappear, and ar6 
 replaced by two dark brown or black substances, possessing very 
 analogous properties, the Saccharo-humine and Saccharo-humic Acid. 
 This change takes place more readily if the air have free access. 
 Both are insoluble in water and alcohol ; they are separated by al- 
 kaline liquors, which dissolve the acid body. From this solution it 
 is thrown down by any stronger acid. The composition of saccha- 
 
638 ULMINE BODIES FROM WOOD. 
 
 ro-humine is expressed by the formula C4oH,50i5 ; that of the sac» 
 charo-humic acid by C4oH,20i2. Like the former bodies, these differ, 
 therefore, in the elements of water. 
 
 Mulder found that access of air was not necessary for the forma- 
 tion of sacchulmine or its acid, but that without air no saccharo- 
 humine nor its acid could be produced. In this action, even with- 
 out access of air, formic acid appears, although but in small quantity ; 
 at the same time, glucic acid (p« 534), and another body first de- 
 scribed by Mulder, Jlpoglucic Jlcid^ 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 decom- 
 position of elm, are specially termed Ulmine and Ulmic Acid. The 
 latter is insoluble in alcohol and water, soluble in alkaline 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 ul 
 mic acid is itself decomposed. Its formula, as derived from the 
 analysis of a specimen furnished by a rotten willow, was C4oHj20i2, 
 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 C4oH,40,2, and 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 evo 
 lution of carbonic acid and water : thus four atoms of lignine, C48 
 H32O32, with fourteen of oxygen, produce 8C.O2 with 18H.0., and an 
 atom of ulmine, C4oH,40,2. 
 
 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 C33H27O24. It is evidently 
 formed by the lignine combining with oxygen from the air and 
 with the elements of water, and then giving ofT carbonic acid gas, 
 C3GH24O24 with 30. and 3H.0. forming C33H27O24 and 3C.O2. 
 
 The rotting of wood is, however, by no means necessarily in- 
 duced by the mere presence of air and water ; for lignine may be 
 exposed to these agents for centuries without being altered in any 
 sensible degree. Precisely as in the alcoholic and acetous ferment- 
 ations, 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 albu- 
 minous 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 tendency to the fer 
 mentation of sugar or of alcohol ; any deoxidizing substance, as 
 sulphurous acid; any metallic salt, as corrosive sublimate or blue- 
 stone, which may combine with the albumen and render it insolu- 
 ble, 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 a similar decomposition that the roots and other remains 
 
ULMINE BODIES FROM THE SOIL, ETC. 639 
 
 of plants are converted into a substance which, by virtue of its di 
 rect absorption, or by means of the products of its farther change, 
 contributes powerfully to the nutrition of the succeeding race of 
 plants, and thereby constitutes the 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 Ge'ic Acid^ proposed by Berzelius. To extract it, the soil 
 is washed with boiling water until this passes away quite clear, and 
 then boiled with carbonate of soda ; the brown filtered liquor is 
 precipitated by muriatic acid, and the precipitafe boiled with alco- 
 hol to dissolve out two organic acids, which will be shortly descri- 
 bed. In this state the substance is really an ammoniacal salt, its 
 formula being C40H12O12+N.H3 + 4H.O., and even by caustic potash 
 it cannot be completely deprived of ammonia. In the ge'ic acid of 
 a meadow, the same organic element was found to be united with 
 twice as much ammonia j and in one case, where the substance had 
 been obtained from the soil of an orchard, the geic acid had the 
 formula C4oH,20,4. The geic acid, C4oH,20i2, though isomeric with 
 the saccharo-humic and ulmic acids, is proved not to be identic£il 
 hy 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 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 sec- 
 ondary and more complicated reactions. Here it is necessary, how- 
 ever, to describe only such constituents of the turf as are analogous 
 to those already noticed, and for distinction I shall term them Hu- 
 mous and Humic 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, sol- 
 uble in alcohol, as does vegetable soil. 
 
 The Humous Acid resembles perfectly in its properties the sac- 
 chulmic acid, with which it is isomeric, its formula being C4oH,40,2, 
 but it has no tendency to retain ammonia when precipitated by an 
 acid from its combination with that alkali. The Humic Acid, on 
 the contrary, combines with ammonia so intimately that they can- 
 not be separated by any reagent ; and it even absorbs ammonia in 
 the laboratory, from the small quantity of the gas which may be set 
 free in other operations. As extracted from the black turf, its for- 
 mula is CjoHj50,5 + N.H40. It is, therefore, when free from ammo- 
 nia, isomeric with the saccharo-humine, but differs totally in com- 
 
640 FORMATION OF COAL. 
 
 position from the saccharo-humic acid, with which it is so identified 
 in properties. 
 
 The azotized acids which have been noticed as existing in vege- 
 table 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 decomposition of animal substances under peculiar circum- 
 stances 5 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 (KprjvT]), and are most easily obtained pure from the 
 ochery deposites 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 cop- 
 per being soluble, while the brown apocrenate of copper is insolu- 
 ble in a liquor containing free acetic acid 3 from the copper salts 
 they may be set free by sulphuretted hydrogen. 
 
 The Crenic Acid is a pale yellow gummy mass, of an astringent 
 taste, very soluble in alcohol and water ; its formula is N.C,4 . Hie 
 0,2; 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 alcohol and water than the crenic acid j its formula is 
 NA3.H„0«_. 
 
 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 p. 476 and 563, but i* remains to examine spe- 
 cially 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, while ulmine is produced when the woody mate- 
 rial is on the surface, or, at least, only immersed in water, the for- 
 mation of any of the varieties of coal requires the conjoined influ- 
 ence of moisture, of great pressure, arising from the superposition 
 of beds of rock or soil, of a high temperature, given by the prox- 
 imity 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, according to the age of 
 the geological formation, the nature of the superincumbent rock, 
 and the degree to which the temperature is raised, the coaly mate- 
 rial 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 lees 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. 
 
COMPOSITION, ETC., OF COAL 
 
 641 
 
 In the coals of the secondary strata (the proper coal formation) 
 great diversity of constitution exists, depending on local circum- 
 stances. It would appear that, where the conversion from lignite 
 into true coal is perfect, the proportion of carbon and hydrogen be- 
 comes uniformly CgaHis, these elements being united with small 
 quantities of oxygen, generally amounting to from three to five 
 atoms. The cannel coal of Wigan, the splint coal of Workington, 
 and the caking coal of Newcastle, have been ascertained, by John- 
 stone, 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 40. O2 and 12H.0., with C32 
 H,20,. 
 
 AVhen the mass of decomposing vegetable matter has been sub- 
 jected to a very high temperature, as by the direct contact of vol- 
 canic rocks, it becomes almost completely carbonized, and the va- 
 riety of coal termed Anthracite is formed. The small quantity of 
 hydrogen and oxygen which anthracite contains, can only be refer- 
 red to traces of the proper coal that have escaped decomposition, 
 and if pure, it would be a Mineral Coke, identical in nature with the 
 coke artificially prepared. 
 
 The formulae 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 reaction which goes on between its ele- 
 ments 5 for none of these products are pure chemical substances ; 
 they form no definite compounds j they have no precise equivalent 
 number, and hence it is only for illustration that a formula can be 
 legitimately employed to express their composition. 
 
 The following table contains the ordinary composition of the most 
 Important varieties of coal and turf. The numbers given were se- 
 lected from those obtained in the analyses byEichardson and Reg- 
 lault. 
 
 Turf . . . 
 Lignite . . 
 Splint Coal 
 Cannel Coal 
 Cherry Coal 
 Caking Coal 
 Anthracite 
 
 68 09 
 71-71 
 82-92 
 83 75 
 84-84 
 87-95 
 91 98 
 
 Hydrogen. 
 
 593 
 485 
 6-49 
 566 
 5 05 
 524 
 3-92 
 
 Oxygen and 
 Mtrogen. 
 
 31 37 
 21 67 
 10-86 
 8 04 
 8-43 
 541 
 3 16 
 
 Asbes. 
 
 4-61 
 1 77 
 13 
 255 
 1-68 
 1-40 
 94 
 
 Economic 
 Value of 
 100 Parts. 
 
 171 
 208 
 262 
 260 
 258 
 271 
 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 pro- 
 ducts make their appearance, which, although much inferior in quan- 
 tity, possess, at least in some cases, considerable interest. Thus 
 the fire-damp of mines (p. 563) 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 va- 
 riety of bodies, principally carbohydrogens, resembling the oils and stearoptens of 
 plants closely in properties and constitution. Thus Ozocherit, or jTossil Wax, is found 
 in cavities in the rocks lying upon coal ; it is brown, of a foliated structure ; it fuses 
 at 143*^'. Paroffifie, which is an important constituent of the tar produced in the 
 destructiv^e distillation of wood, is also found associated with coal. It is while, 
 crystallizes in brilliant plates ; it fuses at 111*^, and maybe distilled unaltered; it 
 dissolves readily in ether and alcohol ; it is not acted upon by any reagent, whence 
 
 4M 
 
642 
 
 MANUFACTURE OF WOOD VINEGAR. 
 
 its name {parum affinis). Both these bodies have the same composition as olefiam 
 gas, consisting of C.H. Many waxy fossil substances are isomeric with oil of tur- 
 pentine, and one, which is interesting as being the matrix in which the native cin • 
 nabar of Idria is imbedded (page 402), has the formula C2iH'7; it is termed Idria- 
 line. 
 
 Others of these products are liquid, and frequently issue forth from the surface of 
 the ground, constituting springs, which, from theirinflammability, have been invested 
 in uncivilized countries with a sacred character. Such liquids are known as Rock 
 OU, or Petroleum. Some specimens of it that have been accurately examined are, 
 like paraffine, isomeric with olefiant gas, while others are isomeric with oil of tur- 
 pentine, and, absorbing oxygen, are gradually converted into a resinous substance 
 Asphalt, for which the formula C40H32O6 has been assigned. 
 
 SECTION II. 
 
 OF THE PRODUCTS OF THE DESTRUCTIVE DISTILLATION OF WOOD, COAL, 
 
 AND RESIN. 
 
 The results of the action of heat on an organic substance are 
 strictly analogous to those of an imperfect combustion. A quanti 
 ty of carbon is removed, as carbonic acid, and a quantity of hydro- 
 gen, as water. 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 carbon- 
 ic acid ; malic acid gives water, carbonic acid, and maleic acid ; but 
 if the temperature change, another set of reactions occurs, and oth- 
 er products are generated, which arise, properly speaking, from the 
 decomposition of the first. Thus acetic acid gives marsh gasj ma- 
 lic acid gives fumaric acid. Hence, if substances be taken, through 
 which, either from their mass or their non-conducting power, the 
 jieat cannot be uniformly diffused, a number of different reactions 
 takes place in different portions at the same time, according to their 
 irespective 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 natures mixed together, it becomes 
 quite impossible to express the precise reactions which occur, and the number ot 
 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 connex- 
 ion 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 
 
 rdistiilation of wood is very differently managed. For the first, a cast iron cylinder, 
 
 — — ^ «, is built into a furnace, 
 
 \llSy < . , r pP r hff^ of which c is the grate, d 
 
 ^^ CT ' < -XJLbe I f^ n.^'""^ -g^,^^ the fire-door, and e, e, e the 
 
 5^1^ R5JSK ^^^jg^ which winds spiral- 
 
 ly round the cylinder, so 
 as to heat it as uniformxy 
 as possible. The wood, in 
 pieces which fit accurate- 
 ly the interior of the cylin- 
 der, is introduced by an 
 opening in the top, which 
 is then closed by the plate 
 b. The volatile and gas- 
 eous products of the dis- 
 tillation 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, 
 
PYROXYLIC SPIRIT, ETC. 643 
 
 entering below at w, passes from one jacket to another by the cross pipes o, o, and 
 escapes ultimately above atp; this cooling arrangement being a form of Liebig's 
 condensing tube (p. 543), convoluted, as it were, in order to occupy less room. The 
 Jiquids 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, re- 
 crystallized, 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 com- 
 merce (p. 557). 
 
 When the acetous liquor has been neutralized by the lime, it is concentrated by 
 distillation, whereby a spirituous liquid is obtained, which is termed Pyroxylic Spirit^ 
 and has a close analogy to alcohol in its characters. 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 will now be described. Mr. Scanlan first recognised 
 the various constituents of the impure pyroxylic spirit, and their history was accu- 
 rately investigated by Dumas and Peligot, by Lowig and by myself. 
 
 The impure pyroxylic spirit having been deprived of water by repeated rectifica- 
 tions 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, combined with the chloride of calcium, while there distils over a mixture of 
 two liquids, Xylit and Mesit, which are separated from each other by frequent rectifi- 
 cation, as their boiling points difier. Besides these three bodies, there exist in the 
 rough liquor an oil, Methol, and a solid substance, discovered by Mr. Scanlan, and 
 termed Eblanine. 
 
 This last body remains behind when the spirit is rectified over lime, 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 col- 
 ours it indigo blue; its formula is C21H9O4. No combinations of it are known. 
 
 The Methol contains no oxygen, its formula being C4H3. It boils at 350°, and 
 possesses the general characters of an essential oil. 
 
 Xylit resembles alcohol closely in its properties. Its odour is agreeable and ethe- 
 real; its specific gravity, 0816; it boils at 143°; with acids it produces ethereal 
 compounds, which have not been closely examined; its formula appears to be 
 
 Cl2H,205. 
 
 Medt 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 C6fe602. I shall have, on another occasion, to notice tne probable 
 constitution of these bod ies. 
 
 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 bums 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 
 C2H4O2; 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 Mdhylic Alcohol, from the Greek words [j.edv and vIt], In the history of its 
 combinations, it will, therefore, be sufficient to fix attention on those points which 
 are more specially characteristic of it, its series being in many respects more com- 
 plete than that of ordinary alcohol. 
 
 Pyrox}dic spirit combines with bases and with salts to form compounds 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 as in 
 the case of ordinary alcohol. 
 
 When treated with sulphuric acid, the methylic alcohol produces an ether, an or- 
 ganic acid, and a heavy oil, precisely similar to those formed by spirit of wine. 
 But the reaction is much more distinct; all the products remain properly in the se- 
 ries of the methylic alcohol, no gas equivalent to olefiant gas being evolved. 
 
644 METHYLIC ETHER AND ITS COMPOUNDS. 
 
 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 C2H3O.; it hence is isomeric with Vine-alcohol, 
 with the vapour of which it has the same specific gravity, =1601-5, but its atomic 
 weight is only one half that of alcohol ; it combines directly with anhydrous sul- 
 phuric acid, forming a heavy oily liquid, and with the other acids to form compound 
 ethers. For 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, C2H3 or Me., 
 and the formula of tha pyroxylic spirit is theretbre Me.O.-f-Aq. 
 
 The Stilphomethijlic 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 Me.O. . S.O3+S.O3. 
 H.O. ; its salts are generally more permanent, and crystallize more easily than the 
 sulphovinates. 
 
 Sulphate of Methyl. — Me.O.+S.Os. 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 methylic ether and dry sulphuric acid. It 
 has a strong garlic odour; its specific gravity is 1-324; it boils at 370°. By boiling 
 water or strong bases, it is immediately removed into its constituents. With dry 
 ammonia it forms a white crystalline mass, Sulphomethylan, which consists of Me> 
 O. . S.03+S.02Ad. 
 
 Chloride of Methyl, C2H3CI. or Me.Cl., is formed by heating a mixture of common 
 salt, pyroxylic spirit, and oil of vitriol. A permanent gas is evolv6d, which may be 
 collected over water, which absorbs but twice its volume of it; it burns with a 
 greenish-white flame. 
 
 Iodide of Methyl, C2H3I. or Me. I., is prepared by distilling a mixture of phospho- 
 rus, iodine, and pyroxylic spirit. On the addition of water to the distilled liquor, 
 the iodide of methyl separates as a heavy oily liquid, of sp. gr. 2-237 ; it boils at 
 about 112^. 
 
 Fluoride of Methyl, C2H3F. or Me.F., is formed by heating a mixture of sulphate 
 of methyl and fluoride of potassium, and collecting the gas evolved over water. It 
 is colourless, and burns with a M^hitish flame, evolving fumes of hydrofluoric acid. 
 
 Methylene-mercaptan. Sulphuret of Methyl. — These bodies are prepared precisely 
 as the corresponding substances in the series of ordinary alcohol. 
 
 Nitrate of Methyl, Me.O. . N.O5, is prepared by distilling nitrate of potash, pyrox- 
 ylic 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 farther external heat. The 
 product, when purified by redistillation over some oxide of lead, is a colourless li- 
 quid, 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 explodes, and this takes place 
 much more easily if there be a quantity; hence its distillation must be very cau- 
 tiously conducted. 
 
 Carbomethylic Acid is formed by passing a jtream of dry carbonic acid into a so- 
 lution of barytes in pyroxylic spirit. Carbomethylate of bar5rtes forms in minute 
 plates, which are insoluble in spirit, but dissolve easily in wate'r. This salt rapidly 
 decomposes into carbonate of barytes, free carbonic acid, and methylic alcohol. 
 With chlorocarbonic acid and sulphuret of carbon, the pyroxylic spirit gives com- 
 pounds precisely similar to those already described in the series of ordinary alcohol. 
 
 Oxalate of Methyl, Me.O. . C2O3, 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, Me.O. . C203+C202Ad., OxavietJiylan. 
 
 Acetate of Methyl. — Me.O. . AC.O3. Formed by distilling together oil of vitriol, 
 pyroxylic spirit, and acetate of soda. It forms a colourless liquid, which boils at 
 l36°;"^its specific gravity is 0-919, The substance known as Mesit may be consid- 
 ered as a compound of methylic alcohol and aldehyd, C2H30,^-C4H30., and the 
 xylit is probably a mixture of that body with the acetate of methyl. 
 
 The combinations of methylic ether with the other acids resemble so closely 
 those of vinic ether that they need not be specially described. 
 
 Products of the Oxidation of Pyroxylic Spirit. 
 
 If pyroxylic spirit be distilled wnth chromate of potash and sulphuric acid, it 
 is totally converted into c:irbonic acid and water. If black oxide of manganese 
 be used, and, after the first violent efiervescence has ceased, a gentle heat be ap- 
 
PREPARATION OF FORMIC ACID, ETC. 645 
 
 plied, a .liquid distils over, which, when completely pure, has the formula GfrHaO^ ; 
 U boils at 104° ; its sp. gr. is 0-855 ; it is termed MetkylaL 
 
 Ifpyroxylic spirit be brought into contact with oxygen by means of spongy plati- 
 uum, as described for ordinary alcohol in p. 554, hydrogen is removed and oxygen 
 absorbed in equivalent proportion, and the melhylic alcohol is totally converted into 
 hydrated Farniic Acid, C2H4O2 and 20. giving 2H.0. and C2H2O4. In this reac- 
 tion 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 co/nbination. Fox practical purposes, tliis 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 in- 
 jected into the puncture which the animal makes ; it was Ibrmeriy prepared by dis- 
 tilling the ants with a little water; but the process 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 manganese, four of water, and four of oil of vitriol. Con- 
 siderable etiervescence occurs, owing to the escape of carbonic acid. When this is 
 over, the mixture is to be distilled until four and a half parts have passed over j 
 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 ob- 
 tained in any required degree of concentration, by distillation with oil of vitriol, in 
 precisely the manner described for acetic acid (p. 556). 
 
 If sugar, or starch, or barley be simply heated with dilute sulphuric acid until it 
 becomes brown, a certain quantity of formic acid is produced, along with ulmine and 
 ulmic acid. The generation of this acid as a product of the decomposition of prus- 
 sic acid, of chloral, and of hydrated oxalic acid, has been already noticed. 
 
 Pure hydrated ibrmic acid is a limpid colourless liquid, which fumes slightly in 
 the air; its odour is intensely pungent; when cooled below 33°, it crystallizes in 
 brilliant plates; it boils at 212°; its specific gravity is 1-235. In this most concen- 
 trated form it is an absolute caustic if applied to the skin, producing a sore very 
 difficult to heal ; its formula is C2H.O3+H.O., and, like acetic acid, it is supposed 
 to contain a radical, Formyl, C2H, or Fo., and its rational formula to be F0.O3+H. 
 O. Combining with water, it forms at least one other definite hydrate, the formula 
 ofwhichisFo.03+2H.O. 
 
 The resemblance of formic acid to acetic acid is very close, but they are at once 
 distmguished by their behaviour to certain reagents. When heated with an excess 
 of oil of vitriol, it is decomposed, with lively effervescence, into water and carbonic 
 oxide (C2H.03=C202 and H.O.). If a solution of formiate be mixed with a cold so- 
 lution of nitrate of silver, a white crystalline precipitate of formiate of silver falls, 
 which, when heated, is totally decomposed into metallic silver, water, and carbonic 
 acid, C2H.03+Ag.O. giving 2C.O2 with H.O. and Ag. If formic acid be digested 
 on red oxide of mercury, carbonic acid is given off, and a sparingly soluble crystal- 
 line formiate of the black oxide of mercury is produced : this, when boiled, is total- 
 ly decomposed, metallic mercury separating, and carbonic acid and water being 
 evolved. 
 
 The alkaline formiates are soluble and crystallizable ; that of ammonia crystal- 
 lizes 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, C2H.O3+N.H4O. giving C2N.H. and 4H.6. 
 
 Formiate of Soda crystallizes in rhombic prisms, which have the formula Na.O. . 
 F0.O3-I-2 Aq. When heated, it undergoes aqueous fusion, and by a higher tempera- 
 ture 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 
 analysis. 
 
 Fonniate of Barytes. — Ba.O. . F0.O3. It is obtained in large 
 rhombic prisms, as in the figure, where w, y are primary, and i a 
 secondary plane, which have a bitter taste, and are not altered 
 by the aif. 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. — Pb.O. . Fo.Os. If formic acid be added to a 
 solution 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 fcr solu- 
 
1)40 PRODUCTS OF DISTILLATION OF COAL. 
 
 tion ; it is totally insoluble in alcohol. By the formation of this salt, the formic 
 iicid is readily distinguished from the acetic acid, and the two, if present together, 
 may be thus separated. 
 
 Foriniate 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, transparent, and of a fine, clear blue colour. 
 It eflioresces in dry air. 
 
 The Formiaies of Mercury. — That of the red oxide is very soluble; 
 it can only exist at ordinar}^ 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. The formiate of the black oxide may also be prepared 
 by mixing solutions of formiate of soda and of subnitrale 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. 
 
 Chlorides and Iodides of Formyl. — When, under the Influence of powerful reagents, 
 the constitution of the compounds of acetyl or elayl is broken up, a series of bodies 
 is generally produced, which are supposed to contain as their radical formyl. Thus, 
 by the action of chlorine on the chloride of elayl, a heavy oily liquid is formed, C2 
 H.CI2 or F0.CI2, Bichloride of Formyl; and by acting on chloral by caustic potash, 
 formic acid is produced, and a heavy oily liquid, which is termed Chlorofoi-m, and 
 consists of C2H.CI3 or F0.CI3, being Perchloride of Formyl. This, which is the most 
 interesting of these bodies, is easily prepared by distilling alcohol, acetone, or py- 
 roxylic spirit with chloride of lime ; it is colourless, of an agreeable ethereal odour; 
 its specific gravity is 1-480; it boils at 141°; the specific gravity of its vapour is 
 4-llb; with an excess of chlorine it gives bichloride of carbon. 
 
 Periodide of Formyl. Iodoform, F0.I3, is produced by adding caustic potash to a 
 solution of iodine in alcohol until it is completely decolorized, but avoiding an ex- 
 cess of alkali; on then evaporating, the iodoform is deposited in brilliant gold-col- 
 oured plates; it is insoluble in water, but very soluble in alcohol and ether; it vola- 
 tilizes 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. 
 
 By acting on the methylic ether and on the chloride of methyl with chlorine, 
 Regnault obtained two series of bodies, which follow precisely the same principles 
 of constitution as have been described fully when speaking of wine-alcohol (p. 565). 
 Malaguti also obtained, from the oxalate and acetate of methyl, bodies similar to 
 those generated by chlorine with the ordinary oxalic and acetic ethers, and hence 
 it is only necessary to say that all the conclusions there drawn respecting the nature 
 of these bodies, and the theory of the chlorine radicals, may be applied to explain 
 tlie origin of the bodies derived from the methylic alcohol also. 
 
 "Products of the Distillation of Coal. 
 
 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 gas- 
 eous products are marsh gas, olefiant gas, and carbonic acid. The 
 liquid products consist of various bodies closely analogous to pe- 
 troleum, 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 j the higher the temperature, the greater 
 is the quantity of carburetted hydrogen ; but, for the purposes to 
 which the practical process is applied, the temperature must not 
 be raised too high, for then the gas evolved would be mostly marsh 
 gas and pure hydrogen, which possess little illuminating power, 
 while a great deal of illuminating power may be derived from the 
 vapours of some highly volatile liquid products. In the manufac- 
 ture of coal gas for the purpose of illumination, the object is, there- 
 fore, to maintain a temperature too high for the production of much 
 napthaline or paraffine, but not high enough to produce hydrogen 
 
COMPOUNDS OF NAPTHALINE. 647 
 
 or marsh gas, and thus ohtain the greatest possible quantity of a 
 gaseous product of olefiant gas and vapours of liquid carbohydro- 
 gens. 
 
 From the albuminous constituents of the wood, coal always con- 
 tains a certain, though small quantity of nitrogen, and hence ammo- 
 nia is evolved in its distillation. The gas liquor so obtained is ex- 
 tensively used in the manufacture of sal ammoniac. From the sul- 
 phates 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. 363), a small 
 quantity of sulphur always exists in coal, which is evolved during 
 the distillation as sulphuretted hydrogen, and requires to be care- 
 fully 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. 642. 
 The ammoniacal liquor and the tar are collected in the tubs, and 
 the gas, in place of being burned at the orifice of the tube 5, is con- 
 ducted to the purifiers, and thence to the gasometers for use. 
 
 Most of the substances produced in this process have been already noticed. It 
 only remains now to describe, as briefly as possible, the properties of such others as 
 are important. 
 
 Of Napthaline aTid 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 abundantly soluble in ether, alcohol, and oils ; its formula is 
 CmHs; the specific gravity of its vapour is 4488. It is remarkable for the number 
 of compounds to which it gives rise. When digested with nitric acid, it forms two 
 combinations ; the first, Nitrofiapthalid, crystallizes in sulphur-yellow prisms ; its 
 formula is C20H7. N.O4; the second, Nltronaphdehyd^ is a white crystalline powder, 
 having the formula C10H3 . N.O4, Both these bodies are insoluble in water, but dis- 
 solve easily in alcohol and ether, from which solutions they crystallize on cooling. 
 When nitronapthalid is distilled with lime, a substance is obtained which resem- 
 bles eblanine (p, 643) in properties, but consists of C20H7O. Laurent termed it 
 Oxvk of Napthcdese. 
 
 Chlorine forms with napthaline a heavy oily liquid, which has the formula C20H8 
 CI2. It gradually evolves muriatic acid gas, and deposites a crystalline substance. 
 This change is effected immediately by heat or by a base. This solid body is tenn- 
 ed ChlornaptMid ; it consists of C20H7CI. If this be melted and submitted to the 
 continued action of chlorine, hydrogen is removed and a crystalline solid formed, 
 Cfdornaptlidehyd, C 0H4CI2. By acting on napthaline with an excess of chlorine,' 
 and distilling the product, a solid substance is obtained, which crystallizes in large 
 prisms, and has the formula C20H6CI2. All of these bodies are insoluble in water, 
 but dissolve in alcohol and ether. 
 
 When these chlorine compounds are boiled in nitric acid, a series of substances 
 are obtained containing chlorine and oxygen. Thus from C20H8CI2 is formed C20 
 H5.O3CI2, which is a brilliant yellow crystalline matter, insoluble in water, and 
 melting at 206°. By farther treatment with nitric acid, the Chloronapthalic Acid is 
 formed, the formula of which is C20H5 . O6CI2. This body is insoluble in water, but 
 dissolves in ether, and crystallizes, on cooling, in short, brilliant yellow prisms ; It 
 melts at 400°, and may be sublimed unchanged. With bases it forms well-charac- 
 terized salts, which are orange or red-coloured ; those of the alkalies and earths are 
 soluble and crystallizable ; those of the heavy metals are insoluble in water. In 
 this process there is also formed a substance which does not contain chlorine ; it re- 
 sembles closely benzoic acid ; it is termed Napthalic Acid-, but its composition is not 
 yet decided ; another product noticed by Marignac is an acid possessing the remark- 
 able constitution of C.Cl. .N.O4. 
 
 The action of sulphuric acid on napthaline varies, as the acid is hydrated or an- 
 hydrous. In the latter case, sulphurous acid is evolved and a series of products 
 
648 BODIES OF THE PHENYL SERIES. 
 
 formed, vrhich have been described by Berzelius as follows: Sulphonapthaline, Cu 
 Hg. S.O2, crystallizes in white plates, which melt below 212o to a colourless liquid; 
 Sidphonapthalid, C24H10 • S.O2, 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 Sidfkonwplhalic and the Sulplwnapthic ; they 
 are isolated by taking advantage of the insolubility of the barytes salt of the latter in 
 cold alcohol, and then, by decomposing the barytes salts by dilute sulphuric acid, 
 these organic acids may be obtained crystallized. The SulpJionapthic Acid forms 
 soft crystalline scales, of a soapy feel, like talc, which taste bitter and sour. Its for- 
 mula is C22H9 . S4O12+2 Aq. ; it combines with two atoms of fixed base. The SuU 
 'phanapihalic Acid forms a hard crystalline mass, which is acid and bitter, inodorous, 
 tiisible below 21*2='; it is very deliquescent; its formula is C20H8 . S2O3. The salts 
 of these acids are all soluble in water. There is still another acid product, termed 
 by Berzelius Sidphoglucic 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, is capable of re- 
 placement by chlorine or nitrous acid, and there does not exist any distinct charac- 
 ter 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 carbohydrogens, C16H4+ 
 C4Bb', by the diverse action of reagents upon which the various bodies may be de- 
 rived ; but this idea does not afford sufficient advantages to justify its adoption. 
 
 Paranaptkaline. — This substance is associated with napthaline in the gas-tar, and 
 is isomeric with it, its formula being C20H8; 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 turpentine ; its 
 relations to other bodies are not well known; with nitric acid it produces a colour- 
 less crystalline body, having the formula C15H4O2. 
 
 The liquid products of the distillation of coal have been as yet studied only by 
 Laurent, of the most interesting of whose results, as yet, but the general nature has 
 been published. This liquid, which is properly termed Gas-7iaptha, contains a crys- 
 talline solid, which volatilizes without decomposition, and acts as an acid; its for- 
 mula is Ci2H50.+Aq. Its discoverer considers it as a hydrated oxide of a com- 
 pound radical, which he terms Phenyl; it combines with potash and barytes, forming 
 crystalline compounds. With sulphuric acid it forms Sulphophe7iic Acid, C12H5O. . 
 S.O3+S.O3 . H.O., which forms salts resembling the sulphovinates ; with chlorine it 
 forms, first, Cfilorophenesic Acid, C12H3 . Cl20.-f-Aq., which crystallizes in rhombo- 
 hedrons, and possesses a very nauseous odour; and afterward Chlo'rophenic Acid, 
 the formula of which is C12H2 . ClsO.+Aq. 
 
 With nitric acid, the hydrated oxide of phenyl produces, first, Nitrophencsic Acid, 
 Ci2H3(N208)0.-i-Aq., and by continuing the action, the Nitrophenic Add, C12H2 
 (N30i2)0.+Aq., which is the Picric Acid described p. 618, as formed from indigo 
 and salicine. This phenyl series appears, therefore, to be the final result of the ox- 
 idation of a great number of organic bodies. As yet, our knowledge of the proper- 
 lies of these bodies is not sufficiently detailed to justify any discussion of their na- 
 ture, but the connexion with the bodies derived from indigo is exceedingly remark- 
 able. If we consider the radical as C12H5, then amilene is Amidide of Phenyl, and 
 all the characters of its salts are easily explained. The substance termed by Lau- 
 rent ChloraWine, CaHeCb, is probably CzHsCl.+H.Cl. 
 
 In preparing olefiant gas for the purposes of illumination, by the destmctive dis- 
 tillation 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 
 (517®. In its properties it resembles napthaline ; its formula is C32H14. Betinol is 
 a colourless liquid, tasteless and inodorous ; specific gravity =:0-9 ; it boils at 400° ; 
 its formula is C32H1 , being isomeric with benzin ; the specific gravity of its vapour 
 is 7-25. Retinaptha is a colourless liquid, of an agreeable odour; its specific gravi- 
 ty is 0-86; it boils at 226®; its formula is CmHs. Reti^iyl, also a liquid, boils at 
 300° ; it consists of C18H12, being polymeric with mesitylene. 
 
 When the gas obtained by the destructive distillation of oil is strongly compress- 
 ed, a liquid separates, which was found by Faraday to contain three distinct sub- 
 stances. Of these the most abundant was the benzin described already (page 571), 
 as produced in the decomposition of benzoic acid. Of the others, one is known as 
 Faraday's Quadricarhv/ret of Hydrogen ; it is also formed abundantly in the distillation 
 of caoutchouc ; its specific gravity is 0627 ; it boils below 32'' ; it combines with 
 
KREOSOTE, KAPNOMOR, ETC. 649 
 
 chlorine, forming a heavy oil ; it is isomeric with olefiant gas, its formula being Ca 
 H4, and the specific gravity of its vapour is double that of the gas, being 1-962. The 
 third liquid boils at 183°. Its formula is probably C6H4, being isomeric with mesit- 
 ylene and retinyl. 
 
 During an elaborate examination of the nature of the tar produced 
 from the destructive distillation of wood, Reichenbach described a 
 number of bodies, of which one, Kreosote^ has become of much in- 
 terest, from its remarkable properties, but the others are still very- 
 little known. For the preparation of kreosote, the tar is rectified by- 
 successive distillations, until the oil which passes over becomes 
 heavier than water, and then digested with a solution of caustic 
 potash, which dissolves the kreosote 5 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 alkaline 
 liquor and precipitation by an acid, is to be repeated until the solu- 
 tion is no longer browned by exposure to the air ; the kreosote is 
 then pure. It is an oily, colourless liquid, with a penetrating odour 
 of smoke ; its taste is sharp and burning ; its specific gravity is 
 1037 J 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 100 parts of kreosote take up ten of water ; the solu- 
 tion is quite neutral ; kreosote mixes with ether, alcohol, and acetic 
 acid in all proportions. It unites with alkalies and with acids, but 
 without appearing to form any definite compounds, and it is not cer- 
 tain that it has ever been obtained really pure. The formula as- 
 signed to it is C,4H902. 
 
 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 after- 
 ward ; from this is its name derived (xps^f aw^w). Kreosote is the 
 antiseptic principle 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. 
 
 Kiipnomor 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''. Picamar is 
 also liquid; it boils at 518° ; it combines with bases. Cedriret crystallizes in fine red 
 needles, insoluble in all liquids except oil of vitriol and kreosote, the former pro- 
 ducing a blue, and the latter a purple solution. Pittakal forms a dark blue solid 
 mass, which, when rubbed, assumes a golden lustre ; it contains nitrogen ; it is in- 
 soluble in water, but dissolves in acids, and is thrown down again by alkalies. 
 With metallic salts, its solution gives blue precipitates, which may be attached by 
 mordants upon Avoollen and cotton cloths. The constitution of these bodies has not 
 been examined. 
 
 By the action of reagents on the coal-gas naptha, Runge obtained a series of bod- 
 ies, a re-examination of which would be of the highest interest to science ; they are 
 liquid, and appear to possess strong alkaline properties, and generate salts, which 
 with one ( Cyatiot) are of a rich blue colour. They belong apparently to the same 
 class of bodies as anilene. 
 
 By the destructive distillation of animal substances, a series of oily bodies is gen- 
 erated, of a strong odour {Animal Oil of Dippel, Oil of Hartshorn), which is described 
 by Unverdorben as a mixture of several bodies, to which he has given names; but, 
 as we possess no accurate knowledge whatsoever of their properties, I do not think 
 it necessary to give his account of their preparation. 
 
 4N 
 
H50 GERMINATIO N. M A L T I N G. 
 
 CHAPTER XXIX. 
 
 OF THE CHEMICAL PHENOMENA OF VEGETATION. 
 
 In the seed of a plant, the gerrne 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 nutriment 
 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 perfectly 
 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 original 
 volume, and its temperature rises ; it absorbs oxygen from the air, and 
 evolves water and carbonic acid, and the starch of the cotyledon gradu- 
 ally 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 downward into the soil, while the other, the 
 plumula, 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 re. 
 mains of the seed but its ligneous husk, which in some cases completely 
 perishes under ground, but in others rises, and, assuming the functions of 
 leaves (seed-leaves), assists in providing nutriment for the young plants, 
 until the stem has been furnished with leaves by which it may act upon 
 the surrounding air. 
 
 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 malthouse, and its temperature prevented from rising too 
 high by the mass being frequently spread out, and new surfaces ex- 
 posed 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 germe, which 
 is practically 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 ex- 
 posing 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 pro- 
 cesses of the brewer and 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. 528, and is ex- 
 
CONSTITUTION OF PLANTS. 651 
 
 cited by the presence of a peculiar ferment produced by the decomposi- 
 tion 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 fermenta- 
 tion, but 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 pre- 
 cipitated by infusion of galls and most metallic salts ; one part of it rap- 
 idly and completely converts a solution of 2000 parts of starch in water, 
 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. 537, but this is doubtful ; it contains nitrogen, and is most proba- 
 bly, as already stated, the first product of the putrefaction 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 nitrogen 
 in any plant is small, compared with that of the other elements, yet it 
 is of great importance as a constituent of the active principles of most 
 medicinal plants, as the vegetable alkalies, amygdaline, &c. ; and of still 
 higher interest, as Bousingault has shown the nutritive power of each 
 plant, when used as food, to be proportional to the quantity of nitrogen 
 which it contains. In every plant there exists also certain inorganic 
 elements, acids, and bases, which, though small in quantity, are yet es- 
 sential 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 important branch of vege- 
 table physiology, which can here be but superficially sketched ; and, in 
 its relation to practice, the manner of supplying these materials so as to 
 favour the growth of plants, and develop their most useful principles, 
 must be the basis of every system of enlightened agriculture. 
 
 Of the Assimilation of Carbon hy Plants. 
 
 In describing the constitution of the atmosphere (p. 269), 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 while the animal, in 
 his respiration, throws off" carbonic acid and absorbs oxygen, the plant, 
 from the surfaces of its green leaves, in sunlight, absorbs carbonic acid 
 and gives out oxygen. It only remains here to examine the circumstan- 
 ces of this 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 
 
652 FORMATION OF WOODY TISSUE. 
 
 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 carbonic 
 acid and the liberation of oxygen occur only under the influence of sun- 
 light, and from the green portions of the plant, while the coloured por. 
 tions, as the flowers and fruits, and even the green leaves during the 
 night, absorb oxygen and give out carbonic acid, thus tending to in- 
 crease 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 neutralize each other, 
 and hence to seek for the source of the carbon of the plant in the action 
 of the roots upon the organic substances of the soil. But the experi- 
 ments 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 account for the growth of 
 the woody material of the plant, and compensate for the influence of ani- 
 mal 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 diflTerent varieties of starch, it is not diflficult to trace the 
 gradual transition to lignine, and, as stated in page 530, ordinary wood 
 siiU retains in the tubes and cells formed by the arrangement of the par- 
 ticles of lignine, a considerable quantity of unaltered starch. In the me- 
 dulla 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,2HioO,o, and this I consider as the actual 
 result of the true respiratory process of the plant ; carbonic acid being 
 absorbed, and an equal volume of oxygen being exhaled, the carbon is 
 assimilated by the vital power of the plant, and, with the elements of 
 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 lignine. The 
 change being simply the loss of water, the formula of the lignine becomes 
 C12H8O8. The nature of the starch globule, and, hence, the structure and 
 physical properties of the ligneous fibre, varies in different plants. Thus 
 1 consider, in the adult plant, starch to be the first product of the assimi- 
 lation of carbon and water, that it is already possessed of a low degree 
 of organization, and is, in structure and composition, 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 or- 
 ganized 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 metamorphosis 
 of the starch, arrested, in virtue of the vital power of the plant, at a point 
 
SECRETION OF PLANTS, ETC. 653 
 
 where we cannot seize it in the laboratory. These are the truly nutri- 
 tious 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 products, 
 as acids, colouring matters, oils, &c., the presence of which characterizes 
 the generality of plants, we may find the source of that inverse respira- 
 tory action which so much masks the real and simple nutritive process. 
 Of the circumstances of the formation of these bodies, we have an exam- 
 ple admirably illustrative of the point, in the conversion of lignine into 
 ulmine. Here, though the change would at first appear to require only 
 the loss of the elements of water, we find it to be much more profound j 
 the constitution of the lignine is totally broken up ; oxygen is abundant- 
 ly absorbed from the air ; a quantity of its carbon is carried off as car- 
 bonic 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 diflTerent parts are there deposited, 
 while others unfitted for the purposes of the organized being are thrown 
 off, is carried on by the leaves, probably by all portions of the surface of 
 the plant, and is the source of the continued exhalation of water and car- 
 bonic acid w4Hch occurs. During the day, and especially in bright sun- 
 shine, the assimilating power of the plant being in full action, carbonic 
 acid is taken in, and oxygen given out ; during the night, while the plant 
 is in repose, this nutritive action ceases. Through the whole time, how- 
 ever, the process 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 se- 
 cure 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 general 
 nature has been just noticed. If we examine the composition of a young 
 apple, we find it to be nearly tasteless, and to consist of a loose ligneous 
 tissue, in which is imbedded a quantity of ordinary starch ; as its growth 
 proceeds, the starch diminishes in proportional amount, and the fruit be- 
 comes intensely 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 ; and in the next and conclu- 
 ding stage of maturity, this acid disappears, its place being taken by pec- 
 tine and by sugar. During the whole of these actions, oxygen is absorb- 
 ed from the air, and water and carbonic acid given off. Their theory is 
 simply indicated : thus starch, which is C,2H,oO,o, absorbing 140., pro- 
 ^ duces 6 Aq. and 4C.O2, with tartaric acid, CsH40,o ; and of this, three 
 atoms, absorbing 60., produce 8C.O2 and 4 Aq., with two atoms of malic 
 acid, 2(C8H408). The change of tartaric to malic acid may also occur 
 without the absorption of oxygen from the air, as 6(C8H40,o) may pro- 
 duce 5(C8H408) with 8C.O4 and 4 Aq. ; but as fruits do not ripen in close 
 vessels, unless when they absorb oxygen, the former is more probably 
 the process which actually takes place. The formation of the pectine 
 and sugar from the malic acid may be produced by the absorption of ox- 
 ygen and the giving off of water and carbonic acid, as 8(C8H408) with 
 9H.0. and 50., produce pectine, C24H17O22, sugar, 2(C,2Hi20j2) with 16C 
 
654 SOURCE OF CARBON IN PLANTS. 
 
 O2. That neither pectine nor sugar is derived originally from the starch, 
 is evident, as the starch abounds but in the very earliest stage, and 
 gives place to the tartaric acid, while the increase in quantity of the 
 gelatinous and saccharine matter is proportional to the disappearance 
 of the acid constituents of the fruit. 
 
 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 sup- 
 ply of animal or vegetable manure to keep up the fertility of the soil, was 
 thus satisfactorily explained ; it was considered that the roots and leaves 
 remaining from the preceding crop, or intentionally 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 ab- 
 sorbing 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 contain abundance of a kind of ul- 
 mine (geic acid, p. 639) ; we find this ulmine to be a product of the de- 
 composition 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 the vegetation appeared distinctly con- 
 nected with, and attributable to the quantity of geine present. But, not- 
 withstanding 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 plant may fully vegetate, though totally unconnected with 
 the ground, as has been proved by experiments upon cellular plants, sus- 
 pended in the air, and supplied with water ; second, that, from the insol- 
 ubility of every kind of ulmine, either free or when combined with earthy 
 bases, which alone are presented in sufficient quantity in the soil, it can- 
 not 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 quanti- 
 ty 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. 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 development, and while destitute 
 of the expanse of leaf requisite to collect the necessary quantity of nutri- 
 ment 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 
 will be shortly shown ; and, even in this action of the organic matters, 
 the functions of the plant remain the same, being the absorption of car- 
 bonic acid and evolution of oxygen. 
 
 Assimilation of Nitrogen hy Plants. 
 The organic substances which contain nitrogen belong to two classes ; 
 
SOURCE OF NITROGEN IN PLANTS. 655 
 
 those of the first, which constitute the active or characteristic principles 
 of many plants, although of much interest in relation to medicine and to 
 abstract science, are of very little importance with reference to the growth 
 of the plant, and its use as food. The bodies whose origin and proper- 
 ties are here of interest, belong to that class of vegeto-animal substan- 
 ces, as albumen, gluten, legumine, of whose extraordinary power in in- 
 ducing 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 transformations 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 witltout their aid. The conversion of starch into sugar for 
 the nutrition of the germe ; of starch or lignine into the vast variety of 
 secretory products in the adult plants ; the elaboration of the fruit, its ri- 
 pening, and even the ultimate destruction of the vegetable tissues, have 
 their origin in a series of actions, induced and maintained by communi- 
 cation from the active fermentation of these azotized materials. 
 
 Not merely does the presence of this class of bodies regulate the prop- 
 er performance of the functions of the plant, but they play an equally im- 
 portant part in favouring the assimilation of vegetable matter when used 
 as food by animals. Bousingault has shown by experiments, to which 
 I shall have occasion again to refer, that in herbivorous animals, the to- 
 tal quantity of nitrogen assimilated for the growth of its muscular and 
 other tissues is derived from, and equal to that contained in the vegeta- 
 ble substances used as food, and that hence, to ascertain the nutritive 
 value of any organic substance, it is only necessary to determine the quan- 
 tity 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 farther 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 organifc bodies. This is absorbed, and 
 passes into the constitution of a new set of plants, and from them to an- 
 imals, to be again thrown into the air after their death, and thus circulate 
 from age to age, entering into the constitution of each successive race of 
 organized beings. We cannot refer, however, the total quantity of ni* 
 trogen in plants to this one source ; for if the produce of one year deri- 
 ved its nitrogen only from the decomposition of the plants of the previous 
 year, the total quantity should be constant ; whereas experience teaches 
 us that, by proper methods, the quantity of vegetables produced on a soil 
 may be continuously increased, and for this the nitrogen must be derived 
 strictly by absorption from the air. 
 
 Plants vary exceedingly in the faciUty with which they derive nitrogen 
 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 increased 
 twenty-six per cent. ; but, on the contrary, wheat grows but slowly un- 
 der the same circumstances, makes no attempt to flower, and, on analy- 
 sis, the whole plant is found to contain even a little less nitrogen than 
 
iJ56 ASSIMILATION OF HYDROGEN, ETC. 
 
 had originally existed in the seed. Wheat has, therefore, no power to 
 assimilate nitrogen from the air, while trefoil possesses that character in 
 probahly 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 an- 
 other source : it is extracted from the organic matters of the soil. 
 
 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, how- 
 ever, the nitrogen is not present uncombined. It is evolved as ammonia 
 from the decomposing organic substances of the manufes, and hence an- 
 imal manures, as producing more of it, are proportionally richer. It 
 has been already noticed (p. 639) 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 carbonic acid and of am- 
 monia are eliminated from it, and these both being in a state fit for ab- 
 sorption by the rootlets of the plant, are assimilated, and supply carbon, 
 nitrogen, and water. Independent of the ammonia derived from the or- 
 ganic 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 porous 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 the increased fer- 
 tility often given to a soil by burning the surface to the depth of a few 
 inches. 
 
 .Assimilation of Hydrogen^ 
 
 I have described (p. 653) 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 se- 
 cretory products, acids, colourirTg 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 decom- 
 posed, 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 vol- 
 atile oils, wax, and caoutchouc, are examples. The secretory action 
 may thus, in place of opposing that of the respiration of the plant, coin- 
 cide with it in result, according to the nature of the substances formed, 
 since, if all the carbon of the starch remains in the constitution of the 
 secretion, oxygen is evolved from the water which is decomposed to sup- 
 ply the necessary quantity of hydrogen. 
 
 Of the Inorganic Constituents of Plants. 
 
 If we make a plant vegetate in water which holds dissolved small quan- 
 tities 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 sub- 
 stance only when, by the death or weakness of the plant, the liquor enters 
 the tubes by merely physical capillarity. If a plant, whose tissues have 
 
RELATION OF SOIL TO PLANT. 657 
 
 »jeen 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 recognise the action of inorganic salts upon plants 
 to be of three kinds : first, directly poisonous, which are rejected by the 
 plant as long as it is in health, and to this class belong most substances 
 poisonous to man ; 2d, 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, 3d, those which, when absorbed by the plant, are assim- 
 ilated to its proper tissues, and are not given up by the plant to water in 
 which it may be immersed. 
 
 The bodies of this last class are all combinations of alkalies and earths, 
 and principally with organic acids ; they form the ashes of the plant 
 when the organic matter is burned away, and then always possess an al- 
 kaline reaction from the formation of carbonates. As a general princi- 
 ple, we may say that each plant requires for its healthy growth inorganic 
 substances in certain quantity and of a 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 
 seashore (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 alkali remains. The ashes of oaks or pines grown 
 upon a granitic or basaltic soil contain abundance of magnesia and of 
 potash, while trees of the same species 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 the other in a plant are still but rare 
 exceptions to the principle, that each kind of plant requires for its vigor- 
 ous 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, magne- 
 sia, lime, and potash. If we sow wheat in a soil which contains neither 
 potash nor phosphoric acid, some of the materials necessary for the per- 
 fection of the plant being absent, the crop cannot be productive ; but if 
 we previously manure the soil with bonedust, with ashes of weeds, or 
 other substances which may supply the necessary inorganic elements, 
 these will be absorbed, and the plants obtain their full development. 
 Even when the quantity of the required inorganic base is but exceeding, 
 ly 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 ex- 
 ists in such proportion as that it affords the universal source of iodine for 
 all technical and, scientific objects ; and yet that salt, which is excess- 
 ively soluble, is removed by the plant from the sea-water, which con- 
 tains but minute traces of it, and is retained in the vegetable tissue by a 
 power which prevents its 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 bear- 
 ing successive crops of the same kind, without the intermediate applica- 
 tion of suitable mineral manures. But if the soil be of such nature as to 
 contain itself those elements, it may become truly inexhaustible for the 
 growth of most species of plant. It is hence that soils formed by the de- 
 
 40 
 
658 CONSTITUTION OF SOILS. 
 
 composition of basaltic rocks or of modern lavas are, for every kind of 
 crop, some of the most productive ; the facility with which these rocks 
 are decomposed by the action of air and water, provides a constant sup. 
 ply of soil absolutely new, and from the constitution of these rocks, the 
 great variety of their mineral components renders such soil 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 importance 
 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 re- 
 duced to supplying to the roots, during those periods when there is not 
 a sufficient expanse of foliage to absorb nutriment from the air, the car- 
 bonic acid produced by the gradual rotting of the ligneous matter, and 
 ulmine, and ammonia from the azotized elements of the manure. For 
 this purpose the soil is, in respect to its mineral composition, unimpor- 
 tant ; it should be porous, in order to admit of the easy penetration 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 necessary for vegeta- 
 tion 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 imme- 
 diately after falling, and the plants necessarily perish. If a soil consist 
 of pure clay, its tenacity wf)uld be such as totally to prevent the access 
 of air, and all growth of the absorbing filaments of the roots. To com- 
 bine 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 absorbing rootlets, this should 
 be present, combined with carbonic acid, as in any of the usual varieties 
 of limestone rocks. 
 
 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 in- 
 organic constituents, the importance of which have 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 alkali, generally potash ; and 
 hence minerals which may yield, by their decomposition, the necessary 
 quantity of that base, should be present in a fertile soil. For most plants, 
 also, magnesia must be supplied ; and for many, and especially the vari- 
 ous kinds of corn, phosphoric acid. In average soils, most of these bodies . 
 are naturally present in the necessary degree. When the soil has origi- 
 nated in the decomposition of granitic or of slaty rocks, the silica, the al 
 
EXCRETIONS OF PLANTS, ETC. 659 
 
 umina, and the potash are abundantly supplied from feldspar and from 
 mica : ^.ime 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 defi- 
 ciency in potash, the ashes of other plants and cinders of coal. If the 
 soil be purely silicious, the addition of clay and lime (marl) may bring it 
 to the proper composition. 
 
 In these few words are contained the theory of what are termed miner- 
 al manures, with few exceptions. In adding lime or marl, bonedust or 
 cinders, to a soil, we either render its physical condition of porosity 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 materials 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, afler a few years, be 
 unproductive, and the soil impoverished, because 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 in- 
 terpose some other plant, as trefoil, which takes up but little potash and 
 no phosphoric acid, the soil has 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 crops which are left upon it, and the manure derived from the con- 
 sumption 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 not less im- 
 portant 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 poisonous 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 remarka«b]e. It is hence, 
 probably, for example, that wheat unfits the soil for the growth of an- 
 other crop of- wheat, not merely by removing the potash and phosphoric 
 acid which is 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 bene- 
 ficially upon the rootlets of a leguminous plant, favouring its growth, 
 while the soil has time to regain from the subsoil the inorganic mate- 
 rials of which it had been deprived. 
 
 The utility of manures may now be easily understood; their action is 
 either as bone-earth, marl, lime, cinders, 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., or- 
 
660 ACTION OF ORGANIC MANURES. 
 
 ganic matter, which, by its decomposition, may give ot:it trmtbonpr -Ai^id 
 and ammonia for the nutrition of the young plants, kn some few *.a«es 
 the action of manures is more indirect; thus the leguminous plants (tre- 
 foil) require but little inorganic matter, but much ammonia, and yet 
 there is no manure so efficient in the promotion of their growth as plas- 
 ter of Paris (sulphate of lime). The plant, however, contains no sul- 
 phate of lime ; it is not absorbed. The action of this manure appears 
 to be, as was first suggested by Liebig, that, acting on those substances 
 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 ab- 
 sorbed by the rootlets of the plant, and the nitrogen assimilated to its 
 tissues. 
 
 With regard to organic manures, their great value depends on the pro- 
 portion of nitrogen they supply. In plants, the great mass of nitrogen 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 plants, such as are rejected in the col- 
 lection 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 mate- 
 rial 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 practical purposes, be considered as being measured 
 by the quantity of nitrogen which it contains, and the directness or in- 
 directness 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 sub- 
 stances 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 full degree proportional to the 
 nitrogen they contain. 
 
 A mode of restoring to the soil the principles it had lost by indiscreet 
 cultivation, is that of fallowing. 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 undenying 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 am- 
 monia, or by the gradual rotting of the roots of the preceding crop, a quan- 
 tity of carbonic acid suitable to the wants of that which is to follow. But 
 all of these effects may be more perfectly and more profitably secured by 
 .he intervention, in a succession suitably arranged, of other crops, which 
 exercise upon the soil actions alternately opposed. Thus, if we arrange 
 
ACTIVE PRINCIPLES OF PLANTS. 661 
 
 that wheat, which probably removes from the soil a greater quantity and 
 a greater number of elements than any other crop, shall be succeeded by 
 sown grasses, for forage or hay, which, as they are not allowed to mature 
 their seeds, exercise but little deteriorating action ; these, again, by oats, 
 the exhausting power of which is but one sixth that of wheat ; then pease 
 or beans manured ; that these be followed by barley, the exhausting power 
 of which is one third, and this by a manured green crop, the soil may be 
 brought into a condition superior to that from which we had set out, and 
 the series may be recommenced with wheat, the soil being every season 
 economized. This is but one of the many kinds of rotation which have 
 been found by experienced agriculturists to be as beneficial in practice as 
 theory indicates that they ought to be ; and no other reason can be assign- 
 ed for allowing a field to lie idle every second or third year, but ignorance 
 on the part of the farmer of what could otherwise be done with 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 exhausts the 
 soil only in consequence of its forming in proportional quantity some sub- 
 stance, the elements of which are derived from the soil, and which con- 
 stitute in almost every case the valuable portion of the plant. Wheat 
 exhausts the soil, because it derives therefrom the large quantity of nitro- 
 gen which its grain contains ; but it is precisely that great quantity of 
 nitrogen 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 nicotine ; the more of the active princi- 
 ple 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, nitrogen must be supplied to the plants by abundance of rich 
 manure ; no crop is more exhausting ; but without the nitrogen no col- 
 ouring matter could be formed, and the plant would be completely worth- 
 less. Examples of this kind might be adduced in any number; but these 
 suffice to place in a distinct, though popular aspect, the general principle, 
 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 commercial 
 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. 
 
 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 exer- 
 cises upon plants. It is not merely that it acts as a general stimulus, and 
 thus provokes the activity of nutrition, which determines the ultimate re- 
 suh of the purification of the atmosphere by plants, and that its withdraw- 
 al is followed, with plants as with higher beings, by a torpor and tendency 
 to rest, which closes their petals,' and folds their leaves at night. But in 
 the production of the coloured parts of plants the agency of light is indis- 
 pensable. 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 
 
662 ACTION OF LIGH T. A NIMAL CHEMISTRY. 
 
 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 produced 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 j^eaves, absorb oxygen from the air. 
 This is precisely what we find a number of bodies to effect, when pass- 
 ing 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 ery- 
 throlitmic acid. It is thus, too, 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 generation of the 
 coloured substance is accompanied not merely by an absorption of oxy. 
 gen, but by an escape of carbonic acid ; this, which is shown in the la- 
 boratory in forming orceine from erythrine, appears to take place in the 
 tissues 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 ineans 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 opera- 
 tion 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. 172) and the ac- 
 tion of chlorine on colouring matters (p. 622), that 1 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 mat- 
 ters ; and, indeed, in many instances, the same substances were found to 
 be products of both kingdoms of organized nature. In the present chap- 
 ter I purpose to describe, so far as our accurate knowledge extends, the 
 chemical history of those bodies which I characterized in another place 
 (p. 468) 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, 
 while in connexion with the animal, and participating in its life, protect- 
 
' FIBRIN E, ITS PROPERTIES. 663 
 
 ed from the truly chemical reactions of their proper elements, whi^h, 
 after the death of the animal, especially in contact with air and water, 
 rapidly assume simpler forms of union, and, breaking up the complex an- 
 imal 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 com- 
 position of those excretions which have for their office the separation of 
 elements unfit for the nutrition of the beings, or which are not intended 
 for its support. 
 
 In each of these divisions I shall add to the description of the compo- 
 sition Smd properties of these tissues or secretions in the state of health, 
 such facts in reference to the modifications introduced by disease, 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, produ- 
 cing, with the colouring material, the phenomenon of coagulation. In 
 the muscles, the fibrine is arranged in a truly organized and living con- 
 dition, constituting the contractile fibres, in which it is so interwoven 
 with nervous and vascular filaments as to render its isolation impossible. 
 To obtain pure fibrine, therefore, we have recourse to blood, which, if im- 
 mediately 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, which, being washed to remove any adhering colouring matter, 
 and digested in alcohol and ether to remove some traces of fatty substan- 
 ces which 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 ad- 
 hering fat. It is insoluble in water, alcohol, and ether ; it absorbs, how. 
 ever, so much water as to treble its weight, and thereby recovers the 
 volume, softness, and flexibility 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 complete- 
 ly dry. When boiled with water for a great length of time, fibrine is de- 
 composed and dissolves, but it does not form any kind of gelatine. 
 
 Fibrine is remarkable for decomposing deutoxide of hydrogen rapidly 
 by catalytic force (p. 235, 258), evolving oxygen. Several of the animal 
 tissues produce this effect, though not containing fibrine. Albumen is, 
 however, totally destitute of it. 
 
664 ALBUMEN. 
 
 Fibrine absorbs cold oil of vitriol, and swells ap to a yellow transpa- 
 rent jelly. On the addition of water, it shrinks up and becomes hard ; 
 but if all the excess of acid be washed away, thb 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 snail shortly recur. Tri- 
 basic phosphoric acid and acetic acid dissolve librme. 'I'he solution is 
 precipitated by the mineral acids and by caustic potash, an excess of 
 which last, however, redissolves the precipitate. The mono, or bi basic 
 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 yellow prussiate of potash. 
 
 Fibrine is dissolved even by a dilute solution of caustic potash, and 
 appears thereby to neutralize the alkali 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 is expressed by the formula CgooHgio . N,oo 
 O240-I-P.S2. It contains, besides, minute quantities of lime and magne- 
 sia, so that, when incinerated, it leaves 0*77 per cent, of sulphates and 
 phosphates of those bases. 
 
 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 becomes insol- 
 uble 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 the soluble or coagulated 
 form, it constitutes a portion of most of the solid tissues. Albumen de- 
 rives 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 does 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 
 «gg, 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 condi 
 tion. If digested in cold water, it gradually swells up, and finally dis- 
 solves. This solution, when heated to a temperature between 140** and 
 150°, coagulates. If dilute, the solution may even be heated to 165° 
 without coagulating, and when present in very small quantity, the albu- 
 
STATES OF ALBUM E N. P R O T E I N E, 6^6 
 
 men may not separate until the water boils. When once coagulated in 
 this manner, albumen is totally insoluble in water j 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 saltpetre. 
 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 quan- 
 tity of water. 
 
 The precipitates yielded by solution of albumen with metallic salts a?© 
 mixtures of two distinct substances, one a compound of albumen with the 
 acid, the other a compound of albumen with the metallic oxide ; the for- 
 mer is generally somewhat soluble, the latter insoluble ; and hence results 
 the application of albumen as an antidote to mineral poisons, as corrosive 
 sublimate and bluestone. 
 
 Albumen is also coagulated by many organic bodies, as tannic acid 
 and kreosote, which last acts catalytically, as a very minute quantity of 
 it coagulates a large quantity of albumen, without entering into combina- 
 tion 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 the 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 car- 
 bonate of ammonia, the pure albumen is separated as a flocculent white 
 precipitate. 
 
 When dry, it is yellow and transparent ; in every chemical character 
 except its relation to deuloxide 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 
 the same, and they diflfer only in the quantity of sulphur, the formula of 
 albumen bemg CsooHe^ . N,oo024o+P.S4. The quantity of ashes remain- 
 ing from albumen is greater than from fibrine. 
 
 The comparative history of these bodies, as now given, leads to con- 
 siderable doubt as to how far they are chemically distinct, although their 
 physiological characters are so different. Mulder, to whose accurate 
 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 Prote'ine, with sulphurets of phos- 
 phorus. In fact, 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 wa- 
 ter, alcohol, and ether, from all bodies soluble in these Hquids, and, 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 proteine may then be precipi- 
 tated by acetic acid, which must be added only in very slight excess, as 
 oftherwise the precipitate would be redissolved. 
 
 Proteine forms grayish-white gelatinous flocks, which, when dried, be* 
 
 4 P 
 
666 COMPOUNDS OF PROTEIN E. 
 
 come hard and yellow, and give an amber-coloured powder. It absorbs 
 ^ater, swells up, and regains the appearance it had before being dried. 
 By long boiling with water it is decomposed 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 Proteosulphuric 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 for. 
 mula C40H32 . N5O12. We may evidently consider albumen and fibrine 
 as compounds of proteine ; for if we represent proteine by the symbol 
 Prt., albumen becomes Prt2o+P.S4, and fibrine is Prtgo+P.Sa- I consider, 
 however, that the state of combination of these bodies requires some far- 
 ther consideration. 
 
 It is found that proteine constitutes the basis, not merely of the animal 
 substances now under examination, but that it is obtained also from ve- 
 getable albumen, gluten, and legumine (p. 538), and constitutes the pure 
 caseous matter of milk, and that the similarity of properties and compo- 
 sition in these bodies is such as to justify us in looking upon them as 
 identical. We have seen that, between albumen and fibrine, the dis- 
 tinctive chemical characters are, if any, so trivial as to leave no firm 
 ground for their distinction in that way ; and if we examine the evidence 
 of their being compounds of proteine with sulphur and phosphorus, wo 
 shall find them quite inconclusive. First, it is not certain that such sul- 
 phurets of phosphorus exist as P.S2 and P.S4; second, the compounds of 
 sulphur and phosphorus do not manifest any tendency whatsoever to 
 combination ; and, third, in all the reactions of albumen and fibrine, the 
 proteine on the one hand, the sulphur and phosphorus on the other, act 
 as if they were totally distinct. I look upon albumen and fibrine, while 
 in connexion with the body, as organized and living substances, in whose 
 functions the minute quantity of sulphur and phosphorus may act an im. 
 portant 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 in combination with acids and with bases, as 
 indigo or morphia do, which I look upon as totally foreign to the char- 
 acter of a body possessed of vital properties. 
 
 Having thus described what I consider to be the true place of proteine, 
 m relation to albumen and fibrine, I shall briefly notice some of its de- 
 rived compounds. 
 
 Chloroproieic Acid is formed by passing chlorine into a solution of al- 
 bumen. It is a white powder. Its formula is C40H3, . N50i2+C1.04. 
 By ammonia it is decomposed, nitrogen being evolved, and a white sub- 
 stance formed, Oxyproteine, the formula of which is C40H3, . N5O15. 
 
 The formation of Xanthoproteic 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 CsiHj, . 
 
SOURCES, ETC., OF GELATINE. 667 
 
 B. Of the Gelatinous Constituents of the Tissues. 
 Of Gelatine. 
 
 When the skin, cellular or serous 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, 
 ciS the skin, dissolve easily, and almost completely ; others dissolve but 
 partly, and leave behind a quantity of coagulated albumen. In most 
 kinds of cartilage, a very prolonged boiling is necessary to extract 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 boiliffg they 
 may be completely separated from each other. 
 
 The gelatine is known in commerce as the material of isinglass and of 
 common glue. When pure it is colourless and transparent, very spa- 
 ringly 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 yf^th part it is a consistent solid. It is insolu- 
 ble in alcohol and ether. When a solution of gelatine is long exposed 
 to the air, or frequently heated and cooled, it undergoes a commencement 
 of putrefaction, and loses its property of gelatinizing. The composition 
 of gelatine, by Mulder's analyses, is expressed by the formula CnHio 
 
 The action of reagents 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 evolved, a white crystalline body 
 {Leuci7ie) and a sweet substance (Sugar of Gelatine) are formed. They 
 are separated from each other, and from some less important products, 
 by repeated crystallizations. From its alcoholic solution, Leucine sep- 
 arates in brilliant colourless plates. It feels greasy, is tasteless and ino- 
 dorous ; heated to 336°, it sublimes totally unchanged. It dissolves ia 
 twenty-eight parts of cold water, but requires 625 parts of alcohol, and is 
 insoluble in ether ; its formula is C,2H,2 . N.O4. It combines with nitric 
 acid to form Nitroleucic Acid, which crystallizes in brilliant needles, and 
 forms with bases neutral salts. Its formula is CjaHia . N.04-}-N.05Aq. 
 
 The Sugar of Gelatine crystallizes from its solution in alcohol, by spon- 
 taneous evaporation, in large prisms, which are colourless, taste sweet, 
 and feel gritty between the teeth. It is decomposed by heat. At 60° it 
 dissolves in five parts of water, but it is sparingly soluble in alcohol and 
 ether. The crystals consist of C,6H,5 . N40„-l-3 Aq. It forms, with 
 bases, well-characterized compounds, and unites also with nitric acid. 
 
 When acted on by chlorine, gelatine is converted into a white floccu- 
 lent substance, insoluble in vvater, but dissolved by an excess of gelatine. 
 Its composition is expressed by the formula C-^U^q . N8029H-C1.04, con- 
 sisting, therefore, of four atoms of unaltered gelatine and one atom of 
 chlorous acid. Gelatine is not precipitated either by solutions of ordina- 
 ry or of basic alum ; but if a solution of common salt be also mixed, the 
 gelatine falls down, combined with alumina, as it decomposes the muri- 
 ate 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 
 
668 MANUFACTURE OP LBATHE R. C HONDRINE. 
 
 part of gelatine in 5000 of water is at once detected by the infusion of 
 galls. The constitution of the precipitate varies according as one or 
 other of these materials is employed in excess, the tannic acid and ge- 
 latine being capable of uniting in at least three different proportions ; 100 
 parts of dry gelatine combine with 136 parts of tannic acid, when the 
 latter is in great excess : this compound contains an atom of each ingre- 
 dient. 
 
 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 and calves* 
 feet jelly, an article of food, it is abundantly employed ; but its most im. 
 portaift use is in the manufacture of leather. The skins are cleaned by 
 digestion with lime and scraping with a knife, from the hair and epider- 
 mis on the one, and the loose cellular tissue on the other side, and then 
 gteeped in pits containing an infusion of oak bark, valonia, sumach, or 
 other of the substances rich in tannic acid (p. 601). At first the tan- 
 ning liquor is used very weak, as otherwise the surface of the skin would 
 become impervious, and the interior could not afterward be tanned ; but 
 having passed through a succession of liquors gradually becoming strong- 
 er, 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 high, 
 est 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 boihng water, and not a true con- 
 stituent of the tissues. I believe this idea to be incorrect on the follow, 
 ing grounds : First, pure fibrine, or albumen, gives no gelatine by boil- 
 ing ; second, in the process of tanning, the tannic acid combines with ge- 
 latine 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 proteine 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 
 solutions of alum, sulphate of iron, and acetate of lead, and is precipita. 
 ted by acetic acid, none of which bodies have any action on ordinary ge- 
 latine, which, however, chondrine resembles in all its other characters ; 
 in composition, however, it differs, its formula being, by Mulder's anal- 
 ysis, CigHja. NgO,; it, however, contains a trace of sulphur, its complete 
 formula being C220H260 • N40O140+S. The physiologist Miiller, to whom 
 the discovery of chondrine is due, considers that the skeleton of cartila- 
 ginous fishes yields a third variety of gelatine. 
 
 C. Of the fatty Constituents of the Tissues, 
 
 The fatty bodies already described in Chapter XXIIL, 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- 
 
CEREBROTE, CEREBROL, CHOLESTERINE, ETC. 669 
 
 Stances properly included under the present head are the constituents of 
 the nervous tissue, such as it is found in the brain, the apinal cord, and 
 nerves. 
 
 In tlie composition of the brain it is possible to distinguish at least 
 three, perhaps five, distinct substances of a fatty nature ; the most char- 
 acteristic and important is termed Cerebrate : its mode of preparation 
 can easily be gathered from its characters ; it is a white powder, taste- 
 less and inodorous, feeling not at all greasy, but like starch ; when heat- 
 ed, it does not melt until it has become brown, and in great part decom- 
 posed ; it is insoluble in water, sparingly soluble in alcohol or ether when 
 cold, but abundantly when hot ; on cooling, it is deposited from its alco- 
 holic solution as a white powder, not at all crystalline ; it is not acted 
 upon by alkalies. In composition it resembles albumen, containing a 
 large quantity of nitrogen, with sulphur and phosphorus in minute quan- 
 tity, but its precise formula cannot be considered as being yet established. 
 
 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 elements 
 as the cerebrote, and apparently in nearly, if not exactly, the same pro- 
 portions ; but the analyses of Couerbe, who alone has examined their 
 composition, are not authentic enough to be brought forward. The cer- 
 ebrol is not saponifiable, nor is it in any way altered by digestion with 
 caustic alkalies. 
 
 In addition to these two bodies, the brain contains a large quantity of 
 a substance, which, from having been first discovered as a constituent of 
 biliary calcuU, 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 
 alkalies ; its formula is CagHaoO. 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 Acid, the formula of 
 which appears to be CzeHao . N.0,2. 
 
 Couerbe has described as constituents of the brain two other fatty bod- 
 ies, Cephalot and StearocenoL: 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 cepha- 
 lol. I hence only indicate their supposed existence. The cholesterine 
 I look upon as being deposited in the brain as ordinary fat is in the cel- 
 lular 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 the Saline and Extractive Constituents of the Tissues, 
 
 We find in all the animal tissues small quantities of a great variety of 
 salts, the same as those which will be hereafter 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 sa- 
 line matters are deposited in much greater quantity, and in disease and 
 in old age bony deposites occur in all those tissues which yield true ge- 
 latine on boiling. The composition of the bones and teeth will be here- 
 after noticed. 
 
670 S K I N. E P I D E R M I S. H O R N. 
 
 The extractive matters of the tissues, like the extractive matter of 
 plants (p. 612), do not pre-exist as such, but are formed by the decom- 
 position, by protracted boiling in water, of the fibrine, albumen, gelatine, 
 (fee, which they really contain. Berzelius has pointed out the existence 
 of a great number of different substances that are thus generated, of 
 which two need here only require notice. For the first, the name Ozma- 
 zome may be retained, and the name Zomidine applied to the second. 
 Ozmazome is soluble in water, and also in absolute alcohol ; it cannot 
 be dried by heat, but forms a semifluid of an acid and salty taste, which 
 evolves powerfully the odour of concentrated decomposing urine. Its 
 solution in water is yellow ; it is precipitated by the salts of mercury, 
 lead, and tin. 
 
 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. Its solutions are precipitated by the salts of lead and tin, 
 but not by corrosive sublimate or tincture of galls. When heated it 
 gives out an odour of roasting meat, the taste and smell of which are 
 indeed due to its formation. Both ozmazome and zomidine contain ni- 
 trogen. 
 
 Of the Composition of the Tissues, and of the Secretions in Health and tn 
 
 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 reunion, 
 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 
 gelatine, whence the process of tanning skins. The relative proportions 
 of solid and liquid matter in a skin freed from adhering fat and cellular 
 membrane, but soft and imbibed with its natural proportions of water, 
 was found by Wienhalt to be, 
 
 Proper cutaneous tissues, including blood- > 33,53' 
 
 vessels and nerves 5 
 
 Albumen 1-54 
 
 Extractive soluble in alcohol 083 
 
 Do. soluble only in water .... 760 
 Water 57-50J 
 
 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 their shapes, identical in chem- 
 ical 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 farther acted on by water even after an ebulli- 
 tion of several days. When treated by strong acids, horn is softened, 
 And becomes soluble in water. Heated with solution of caustic potash, 
 it evolves ammonia, dissolves, and the liquor contains sulphuret of potas- 
 
 10000. 
 
CELLULAR, SEROUS, AND MUSCULAR TISSUES. 671 
 
 sium and an organic substance, precipitable by an acid. The composi- 
 tion of these products, or of horn itself, has not been accurately exam- 
 ined. 
 
 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. If, 
 by virtue of the sulphur contained in hair, 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, 
 it fuses, gives off carbonate of ammonia, and gases of a characteristic 
 disagreeable smell ; if air be present, it burns 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 condition 
 of these membranes their surfaces are moistened by a watery liquid, 
 which, accumulating in excessive quantity, gives rise to the dropsies of 
 the cavities or of the cellular tissue. This serum of the cavities is clear 
 and colourless. It reacts alkahne ; its specific gravity 1*010 to 1*020; 
 its composition, though liable to fluctuate, is, in general, as found by 
 Berzelius, 
 
 Albumen 166^ 
 
 Substance soluble in alcohol . . 3-32 
 
 Free soda 0-28 
 
 Alkaline chlorides 609 
 
 Earthy phosphates 009 
 
 Water 98756 
 
 .100000 nearly. 
 
 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 caseiim. 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 cel- 
 lular 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 re- 
 mains 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) . 15-80 > iq.iq 
 
 Cellular tissue giving gelatine 1-90 J ^^ 
 
 Soluble albumen and colouring matter . . 2-20 . 1-70 
 
 Alcoholic extract with salts 1-80 . 1-94 
 
 Watery extract with salts 105 . 0-15 
 
 Phosphate of lime 008 . 
 
 Water and loss 77*17 . 77-03 
 
 Composition of the Brain. — The most exact" analyses of the brain thai 
 we possess are those by Lassaigne. The differently coloured portions 
 differ essentially in their nature, as he found in 100 parts, • 
 
d72 composition of the bones. 
 
 Medullary Cortical 
 
 Substance. Substance, 
 
 Albumen 99 . . 7-5 
 
 Colourless fat 13-9 . . 1-0 
 
 Red fat 09 . . 3-7 
 
 Ozmazome and organic salts , 1-0 .. 1-4: 
 
 Phosphates 1-3 .. 1-2 
 
 Water 730.. 852 
 
 10000. 
 
 Lion. 
 
 Sheep. 
 
 950 
 
 800 
 
 2-5 
 
 19-3 
 
 2-5 
 
 0-7 
 
 The nerves or spinal marrow have not been specially analyzed. 
 
 Composition of the Bones. — Miiller has found that, prior to ossification, 
 the cartilage of the bones is in that condition which yields chondrine, al- 
 though it is afterward totally changed into the gelatine cartilage. 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 thes# inorganic salts are 
 removed, and the cartilage remains, preserving perfectly the form of the 
 bone. By burning the bone in a moderate current of air, all animal mat- 
 ter may be consumed, and the earthy material then remains in the form 
 of the bone, and perfectly white ; 100 parts of burned bone of the follow- 
 ing animals have been found to contain, 
 
 Human Bone. Beef Bone. 
 
 Phosphate of lime and fluoride ) og.j^ qo-70 
 
 of calcium J cso i 
 
 Carbonate of lime . .... 103 2-16 
 
 Carbonate of magnesia ... 03 110). 
 
 Carbonate of soda 30 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 pei 
 cent. Thus human and ox bones, deprived of their marrow and perioa 
 team, and dried until they ceased to lose weight, gave Berzelius, 
 
 Human Bone. Beef Bone. 
 
 Cartilage soluble in water . . 32- 17 ) 33 30 
 
 Vessels 1-13 ) 
 
 Phosphate of lime and fluoride > m.qa 57-45 
 
 of calcium 5 
 
 Carbonate of lime 11-30 3-85 
 
 Phosphate of magnesia . . . 1-16 285 
 
 Soda and a little common salt . 1-20 3-45 
 
 The teeth present, in their constitution, the closest analogy to boh<; 
 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 almo&t destitute of any animal matter, the analyses of Ber- 
 zelius giving, 
 
 Human Enamel. Beef Enamel. 
 
 Phosphate of lime and fluoride of) oq.r o^.q' 
 
 calcium ) 
 
 Carbonate of lime 8-0 7-1 
 
 Phosphate of magnesia .... 15 3-0 
 
 Soda " 1-4 
 
 Animal matter and water ... 2-0 3-5 ^ 
 
 The proportion of fluoride of calcium is greater in enamel than in com- 
 mon bone, and the animal membrane appears to belong only to the con- 
 nexion of the enamel with the subjacent bony tissue of the tooth. The 
 
 100-00. 
 
 Uoooo. 
 
BLOOD C O A G U L U M. S E R U M. 673 
 
 exterior crusla petrosa of the teeth, which^exists most developed in her- 
 biferous animals, has the same composition as bone. 
 
 In the invertebrate 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 prepon- 
 derating. 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 sul)stance 
 termed cuttle-fish bone has the same composition nearly as crab-shells. 
 
 SECTION 11. 
 
 OF THE COMPOSITION OF THE BLOOD, AND THE PHENOMENA OF RESPI- 
 RATION. 
 
 Blood is, in the higher classes of animals, an opaque, thick, red fluid ; 
 its specific gravity about 1*055 ; 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 grad- 
 ually forms a soft jelly, from which, after some time, a thin yellowish fluid 
 (serum) separates, while 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 becomes white or pale 
 yellow, forming thus the bvffy coat. There is no doubt that the blood, 
 while in connexion with the animal, participates in its life, and the phe- 
 nomena 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 yel- 
 lowish, sometimes greenish colour ; its taste is dull and salty ; its spe- 
 cific 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 particles 
 swimming in a nearly colourless liquor. These red particles are flatten- 
 ed disks, in man and the mammalia round, in other animals elliptical. 
 Their size is variable, being in man from ^^Vo^^ ^^ ? oVo^^^ ^^ ^" ^'^^^^ ^"^ 
 diameter, but larger in most other animals. In the frog they are about 
 rrVe^h. 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 es- 
 sentially altered. 
 
 The blood contains a large quantity of albumen^ partly dissolved, and 
 remaining in the serum after coagulation, partly in a solid state, forming 
 the great mass of the globules. In the living body the blood contains 
 also fibrhie in solution, but this separates soon after extraction from the 
 body ; it assumes a solid form, and investing, as a sponge, the red glob- 
 ules, 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 elements, the blood 
 contains a variety of salts, as common salt, phosphates of magnesia, am- 
 monia, and lime, lactates of soda and magnesia. The best analyses of 
 the blood are those by Lecanu, and the results for blood and serum are, 
 that they contain, 
 
 4Q 
 
674 
 
 S E R O L I N E. H EMATOSINE. 
 
 Blood or Man. Serum of Mas. 
 
 BJood globules 1330 
 
 Fibrine -21 
 
 Albumen . ». C'5l 8-12 
 
 Fatty substances . '37 -34 
 
 Extractive matters -30 -40 
 
 Alkaline salts -84 -75 
 
 Earthy salts -21 -OD 
 
 Water 7802 9010 
 
 Loss . ;24 -14 
 
 10000 100-00 
 
 He found these proportions liable to fluctuation, and to vary according 
 to the sex. The maxima and minima of each constituent which he found 
 for the human subject of each sex were, 
 
 Constitnents. 
 
 Male. 1 Female. 
 
 Max. 
 
 Mm. j Max. 
 
 Mm. 
 
 Water .... 
 
 80-5 
 
 733 184-84 
 
 75 00 
 
 Albumen. . . . 
 
 6-3 
 
 4-85| 68 
 
 500 
 
 Globules .... 
 
 18-6 
 
 1105 1671 
 
 714 
 
 Fibrme .... 
 
 •4 
 
 •20j -31 
 
 •20 
 
 The fatty substance of the blood is a mixture of chqiesterine with stearic 
 and oleic acids, and a peculiar fatty substance, termed Seroline, the history 
 of which is yet incomplete, and which differs from cholesterine most in 
 containing nitrogen. None of the phosphuretted fats of the brain appear 
 to exist in blood. 
 
 The chemical history of fibrine and albumen having 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 the 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, with 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 portions 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 precip- 
 itated, while a compound of hematosine and ammonia remains dissolved. 
 This solution is to be then evaporated in a wateV-bath to dryness, 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 al- 
 cohol by means of ammonia, evaporated to dryness, and washed again 
 w'llh 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 alkalies 
 it is dissolved with a blood-red colour, and these combinations 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 
 analysis, the fotmula of hematosine is C44H22N3 . OgFe. It hence has no 
 connexion with proteine or albumen. The state in which the iron exists 
 
HEMATOSINE, GLOBULIN E, ETC. 675 
 
 in hcmatosine 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 consider the iron to be an integral 
 part of its organic constitution, as sulphur is in albumen, or arsenic in 
 alkarsine ; 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 j^ 
 solution of hematosine be acted on by chlorine gas, a white flocculent 
 precipitate is produced, and the solution contains chloride of iron. 
 
 Although hematosine is the colouring material of the globules of the 
 blood, it is present but in very small quantity ; 100 parts of dried glob- 
 ules containing but from four to five of pure hematosine. In the blood 
 globule, the hematosine is in its uncoagulated state, and possesses prop- 
 erties somewhat different from those of its coagulated form, as prepared 
 by the process above given. A solution of the coloured blood globules 
 in water, when exposed to the air, becomes of a brighter red colour, be- 
 ing thus partially arterialized. When evaporated at a temperature of 
 120°, it gives a dark red mass, which is completely soluble in cold water. 
 Its solution coagulates at 155°, leaving the liquor clear yellow. It is co- 
 agulated 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 glob- 
 ules as being albumen, with which, indeed, it is almost identical in proper- 
 ties, but still differs in some points. It has been termed Glohuline, 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 ia 
 hence that the globules swim unaltered in the serum of the blood, but arc 
 readily dissolved by pure water. On this principle is founded a method 
 of is'jjciting the blood globules. If the blood, when extracted from the 
 vein, be received in a vessel containing a solution of Glauber's salt, coag- 
 ulation 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 globuline cannot, 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 com- 
 position of prote'ine (see p. 666). 
 
 Alteration of the Blood in Disease. — The examination of the state of 
 the blood in disease, although presenting important relations to patholo- 
 gy and to practice, has been hitherto conducted in a manner too discon- 
 nected and superficial to afford satisfactory results. This branch of 
 chemical pathology has, however, been taken up by the illustrious An- 
 dral, who, in conjunction with M. Gavaret, has published the results of 
 the analysis of the blood in 360 cases of disease, in a memoir, from whose 
 publication may be dated the commencement of a true pathology of this 
 fluid. 
 
 In the method whicl^ by the advice of Dumas, they adopted, the' quan- 
 tity 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. As a point of comparison, they assume 
 
676 ALTERATION OF THE BLOOD IN DISEASE. 
 
 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 whicii eight are inorganic ; which numbers almost coincide with 
 Lecanu's analysis, as already given. Their researches have enabled 
 them to recognise four classes of diseases in which 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 jibrine ; it includes diseases remarkably different in their lo. 
 cality and form, but all belonging 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 wheth. 
 er 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, while the globules increase in proportion to the fibrine. The 
 diseases which belong to this class are continued fevers without local 
 inflammation, and some form oi cerebral haemorrhages. 
 
 In the third class, the fibrine remaining unchanged, there is a remark- 
 able diminution in the 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 af- 
 fections Brighi's disease is the type. 
 
 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. 
 
 Const iiuems. 
 
 Heallh. 
 
 1st CUs-. 
 
 2d Class. 
 
 3d Class. 
 
 4!h Class. 
 
 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 evident- 
 ly connected with its diminution in the serum. The oily materials which 
 are usually found in the blood, and the remarkable diminution which oc- 
 curs, not so much in the globules as in the hematosine, had not attracted 
 Andral's attention in the memoir now described. These oily substances 
 are of the same nature as the proper fatly matters of the blood, but pres- 
 ent 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-five per cent, of 
 solid matter ; it is then, also, less strongly alkaline than healthy blood. 
 This is connected probably with the matters vomited and evacuated, 
 which are strongly alkaline, and contain a quantity of albumen. 
 
 The blood has been found occasionally, in cases of diabetes melUtuSj 
 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 tlte kid- 
 neys. In jaundice the green colouring matter of the bile has been ob- 
 served in the serum of the blood. Other observations of morbid constit- 
 uents of the blood are too indefinite to justify me in occupying spac<» 
 
PHENOMENA OF RESPIRATION. 677 
 
 with them. The observation of Barruel, that, by heating the blood of 
 any animal with a little oil of vitriol, the odour of the animal is so pow- 
 erfully evolved as to be easily recognised, appears well founded, and may 
 be useful in medico-legal questions, where, however, it should be em- 
 ployed with exceeding circumspection. 
 
 Of Respiration, — in the living body, the blood in the veins and arter- 
 ies 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 pas- 
 sage of the blood through the capillary vessels of the lungs, where it is 
 exposed to the action of an extensive surface of atmospheric air, while 
 the arterial blood, in traversing the general capillary 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 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. Ar- 
 terial and venous blood contain sensibly 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 un- 
 dergone an important change of constitution ; its volume is but slightly, 
 if at all, altered ; but a quantity of oxygen has disappeared, and is re- 
 placed 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 car- 
 bonic 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 the principal portion of that element which we take in 
 with our Ibod ; yet such is the activity with which its assimilation pro- 
 ceeds, 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 separ- 
 ated 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 circulation 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 confirma- 
 tion has been given by the careful and elaborate experiments of Magnus. 
 
678 THEORY OF RESPIRATION. 
 
 He found that both arterial and venous blood hold dissolved quantities 
 of gases, oxygen, nitrogen, and carbonic acid, which 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 j the 
 oxygen in arterial blood being about one half of the carbonic acid, while 
 in the venous blood it seldom amounts to more than one fifth. The dif- 
 ference 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. 267), 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 ab- 
 sorbed 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 out. There appears, from the presence of ni. 
 trogen 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 ar. 
 tificial atmosphere of oxygen and hydrogen, while Bousingault has 
 shown the rate of nutrition of an animal to be proportional to the quan- 
 tity 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 hematosine, which 
 analysis cannot direct. Stevens first directed attention to the remarka- 
 ble 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-col- 
 oured 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, there- 
 fore, the arterial tint to be due to the natural combination of the colour- 
 ing matter with the saline constituents of the serum, this will be darken- 
 ed 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 be- 
 coming 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. 
 
 Animal Heat. — The phenomena of respiration consisting mainly in 
 the conversion of carbon into carbonic acid by union with oxygen, 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 
 
MUCUS. GASTRIC JUICE. 679 
 
 from the arterial to the venous condition of the blood occurs at every 
 point of the system, the ahuost complete equality of temperature through- 
 out the body in health is explained. That the great source of heat 
 is the respiratory process, is abundantly proved by the temperature be- 
 ing highest in those animals, and in the same animal at those periods 
 4Hien The circulation is most rapid, and the quantity of air consumed the 
 greatest ; but it has been calculated that the heat evolved by thecombus. 
 tion 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 body 
 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. 
 
 SECTION III. 
 
 COMPOSITION OF THE DIGESTIVE ORGANS AND OF THEIR SECRETIONS. 
 CHEMICAL PHENOMENA OF DIGESTION. 
 
 Mucus. — The lining membrane of the alimentary canal is moistened 
 with a liquid possessing many characters of the vegetable mucus (traga- 
 canthine, p. 530),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 alkaline li- 
 quors, 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 Gasinc 
 Juice, which exercises an important influence on digestion, differs essen- 
 tially in its characters from mucus. When the stomach is empty and 
 contracted, it contains only ordinary mucus ; but if even indigestible sub- 
 stances be introduced, and still more after taking proper food, a liquid is 
 abundantly poured out, which is colourless or very pale yellow, and con- 
 tains 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 "s specially characterized by the presence of a 
 notable quantity of free muriatic acid, the proportions 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 uni- 
 form pulp [Chyme), from which the absorbing vessels of the small intes- 
 tines 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 incapa- 
 ble of dissolving the materials of the food, and, indeed, to be quite inac- 
 tive towards digestion. The organic material of the gastric juice, al- 
 though its quantity be so minute, is therefore essential to its powers, and 
 these may be perfectly conferred upon the previously inactive artificial 
 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 
 ia these cases has been termed Pepsine. It has not been obtained in a 
 
680 PEPSIN E, SALIVA, ETC. 
 
 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 gas- 
 tric juice becomes much less active in dissolving food, when neutralized by 
 an alkali, though it retains other properties, as that of coagulating milk like 
 rennet. If the artificial gastric juice be precipitated by acetate of lead, 
 the precipitate washed, and then decomposed by sulphuret of hydrogen, 
 the solution thus obtained possesses all the digestive powers of the juice. 
 Hence the pepsine and muriatic acid act together in combining with oxide 
 of lead. The process given by Schwann for preparing the best artificial 
 gastric juice, is to mix water with 2^ per cent, of muriatic acid, of spe- 
 cific 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 alcohol, 
 or by the heat of boiling water. Its powers are desti'oyed, also, by de- 
 oxidizing substances. The solution of albumen and fibrine in gastric 
 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 un- 
 combincd. 
 
 Fremy has discovered that the peculiar fermentative process, which 
 sometimes spoils the manufacture of sugar, and which I have described 
 (p. 536) as the mucous fermentation, is capable of being induced by con- 
 tact 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 decomposition 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 {Pepsine) secre- 
 ted 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, 
 <Sz;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 alkaline, and 
 holds in solution not one per cent, of solid matter, which contains some 
 carbonate of soda and common salt, admixed mucus, a trace of sulphocy- 
 anid? of potassium, and a peculiar organic body termed by Tiedemann 
 and 3melin Salivary Matter. This last substance is soluble in water; 
 its solution is not coagulated by heat, nor precipitated by 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 sulphocyanide of potassium, but 
 albumen and some salts ; it is generally slightly acid. 
 
 Composition of the Bile. — The precise part which this remarkable se- 
 cretion performs in the animal economy is not yet fully known. It 
 has been the subject of repeated and accurate chemical examination, 
 although, from the facility with which its elements are transformed into 
 other bodies, by the action of the reagents employed, every succeeding 
 
ANALYSES OF THE BILE. 681 
 
 analysis has led to different results. I shall only notice the late researches 
 of Gmelin, Demar9ay, and Berzelius. 
 
 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 diifer. He obtained from it a volatile body having 
 the odour of musk, cholesterine, margaric and oleic acids, a peculiar acid, 
 the Chollc Acid; colouring matters. Biliary Resin, Biliary Sugar, TaU' 
 rine, a glutinous substance, caseiim, salivary matter, ozmazome, and a 
 number of salts of organic and inorganic acids. Dema^^ay looks upon 
 all of these substances as being produced by the reactions used, and de- 
 nies that any of them really exist in the bile. He considers the bile to 
 be a soda-soap of a peculiar fatty acid, the Chole'ic Acid, that is, a Cho. 
 ledte of Soda, The cholei'c 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 separates, and, being digest- 
 ed with ether to remove some adhering fat, is pure. It is a brittle yel- 
 low-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 ; its formula 
 was found to be C42H36 . N.0,2. 
 
 When the alcoholic extract of the gall is boiled for a long time in con- 
 tact 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 Cholo'idic 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 lit- 
 mus. By Dumas's analysis the formula of this body appears to be C33 
 H33O7. It does not contain nitrogen^ The Taurine, which remains in 
 the acid liquor from which the cholofdic acid separates, is obtained by 
 evaporation, and mixing with alcohol, from which solution it crystallizes 
 gradually in six-sided prisms, which are perfectly neutral ; it fuses and is 
 decomposed by a strong heat ; it dissolves in twelve and a half parts of 
 cold, and in less of boiling water, but requires 573 parts of spirit of wine 
 for solution : it is scarcely acted on even by the strongest acids, and is 
 not precipitated by any metallic salt; its formula is remarkable, being 
 C4H7 . N.0,0, including the elements of binoxalate of ammonia and 2 Aq. 
 
 If the bile be treated with an excess of a strong alkali, the choleic acid 
 is totally broken up into ammonia and the Cholic Acid of Gmelin. 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 copious- 
 ly in alcohol ; its solutions redden litmus ; it contains no azote ; its for- 
 mula being, as determined by Dumas, C42H360,o. 
 
 Demar^ay's examination of the bile appears thus quite satisfactory 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 cho- 
 loidic acids in an impure form. But Berzelius, who has been occupied in 
 the re-examination of the subject, has decided that the choleic acid of 
 
 4R 
 
682 COLOURING aiATTER OF THE BILE. 
 
 Demar9ay is really the body which is impure, being a mixture of the true 
 biliary substance {Bilin, GmcWn's Biliary Sugar) with the biliary resins. 
 He found that when the alcoholic extract of the bile is mixed with sul- 
 phuric acid, no precipitate appears for a considerable time, showing that 
 the substance, which really exists in the bile combined with soda, is conti- 
 pletely soluble in water, and it is only by its gradual change that the pre- 
 cipitate (choleic acid) occurs. By digesling 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 dis- 
 tinct acid resins, Fellic Acid and Cholinic Acid, The material insolu. 
 ble in ether is the true Bilin; it is not acid, of a bitter taste, soluble in 
 alcohol and water in all proportions, but insoluble in ether ; when heat- 
 ed, it becomes soft, and burns like a resin ; its watery solution is rapidly 
 decomposed, especially if warmed ; by contact with acids or alkalies, it 
 is immediately changed in constitution ; the substances produced are dif- 
 ferent, according as the degree of alteration is more or less advanced. 
 Those more important are the following : 
 
 The Biliary Matter^ which is the state in which the greater part of the 
 bilin exists in ordinary hile, being the first product of its decomposition, 
 is a white, bitter substance, which has a marked acid reaction, and is de- 
 composed by oxide of lead into bilin and Bilifellmic Acid, which is the 
 choleic acid of Demarcay. The formation of taurine is accomj)anied by 
 that of another body, Dyslysin, which is a colourless resinous substance, 
 very sparingly poluble in water. The fellinic and cholinic acid have 
 been noticed o.bove. 
 
 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 
 Cholam'c Acids : they are white earthy powders sparingly soluble in wa- 
 ter ; the former melts only far above 212° ; the latter is very easily fu- 
 sible. 
 
 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 
 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 cases 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 solution becomes yel- 
 low, and the colouring matter is found to be totally decomposed. The 
 solution of the colouring matter in potash is precipitated by muriatic acid 
 in deep green flocculi, which dissolve in nitric acid with the effect al- 
 ready 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 gallstone consists, however, of 
 cholesterine. 
 
NATURE OF CHYLE AND LYMPH. 683 
 
 This, yellow malerial Berzelius names BUifulvin. He considers the 
 greeiT''colouring matter present in healthy bile to be identical with chlo- 
 rophyll (p. 62i). 
 
 Tne bile contains generally about nine per cent, of solid matter ; but in 
 the present state of our knowledge of its constituents, it is evidently im- 
 possible to assign the numerical proportions in which they exist. 
 
 The substance found in the bile, and termed Erythrogen by Bizio, is 
 too apocryphal to require any notice. 
 
 The examination of the farther processes of digestion involves consid- 
 erations too purely physiological to be entered into. 
 
 Chyle and Lymph. — The nutritive materials 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 examined, 
 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 thw 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 separation from 
 the body it coagulates ; the clot is at first pale, but it soon 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 absent (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 contain a much smaller quantity of albumen 
 than when they had had animal food. Dr. Prout also indicates in chyle the 
 existence of a substance which he terms Incipient Albumen, which is not 
 coagulated by heat, except after the addition of acetic acid. The prop, 
 erties of this form of albumen, however, are not fully known. The re- 
 sults of their analyses 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 con- 
 tained. 
 
 Berzeliui. Front. No. 1. No. 2. 
 
 Dry Clot .... 078 
 
 Albumen .... 4*49 
 
 Fatty matters . . 1-67 
 
 Extractive matters 
 
 and salts . . ( ^ "" 
 Water 01 62 
 
 Fibrine 06 0-8 
 
 Incipient Albumen . 46 47 
 
 Albumen .... 04 46 
 
 Oil and Sugar . . trace trace 
 
 Salts 0-8 0-7 
 
 Water 93-6 892 
 
 SECTION IV. 
 
 CONSTITUTION OF THE URINE IN HEALTH AND IN DISEASE. 
 
 The nature of this secretion has at all periods been an object of con- 
 siderable interest to the physician and to the chemist, from the indica- 
 tions which changes in its composition give of disease of important or- 
 gans, and from the number and interest of the organic substances it con- 
 tains. As in almost all other branches of animal chemistry, Berzelius 
 first determined accurately its constitution, and lately Lecanu has ascer* 
 
10000 
 
 b84 COMPOSITION OF URINE. UREA. 
 
 tained with great care the limits to which the proportions of its ingredi- 
 ents may vary in health, and thus established a correct basis of compar 
 ison 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 1030; but if the 
 quantity be under thirty-two ounces, the specific gravity for a man in ac- 
 tive heahh is generally 1030, but less for women. The important organ- 
 ic constituents of the urine are JJrea and Uric Acid^ which will require 
 a detailed and special examination ; the other principles, though numer- 
 ous, being of less moment, need be only noticed in the following state- 
 ment of Berzelius's general analysis of the urine. He found 100 parts 
 to contain, 
 
 Water 93S00^ 
 
 Urea 3010 
 
 Free lactic acid, lactate of ammonia, and ) v^\i 
 
 animal extract ) 
 
 Uric acid 1-00 
 
 Mucus of the bladder 0'33 
 
 Sulphates of potash and soda 6-87 
 
 Phosphates of soda and ammonia .... 4-59 
 
 Common salt 4-45 
 
 Sal ammoniac 1-50 
 
 Phosphates of lime and magnesia . ... 1-00 
 
 Silica 003 
 
 C7rea.— NA . O2H4 or Ur. Eq. 60 or 750. 
 
 The artificial formation of this remarkable substance in various ways, 
 has been noticed already in many places (as 511, 515). It may be ob- 
 tained from urine by evaporation to the consistence of a thick sirup in a 
 water-bath, and mixing the mass remaining with three times its volume 
 of nitric acid, specific gravity about 1*25, which had been perfectly freed 
 from all traces of nitrous acid which it might contain, as this last instant- 
 ly decomposes urea. The liquor forms a crystalline pulp, which, being 
 kept carefully cool, may be freed from the liquor by draining and press- 
 ure between folds of paper. The impure crystallized nitrate of urea thus 
 obtained is to be dissolved in a small quantity of boiling water, and re- 
 crystallized by cooling. These crystals being again dissolved in water, 
 are to be digested with animal charcoal to remove the colouring matter, 
 and then with an excess of carbonate of lead, until completely neutral. 
 The solution so obtained, being evaporated very carefully in a water- bath 
 to dryness, is to be treated with boiling alcohol, and filtered. The pure 
 urea separates from the alcoholic solution, on cooling, in brilliant white 
 four-sided prisms. 
 
 Urea is much more simply and economically obtained by the transform- 
 ation of cyanate of ammonia, for which purpose the process given by 
 Liebig answers best. 
 
 An impure cyanate of potash is prepared by roasting yellow prussiate 
 of potash (as described p. 515), and this is mixed with a solution of sul- 
 phate of ammonia in water, and the whole then boiled with alcohol, which 
 dissolves out urea, and leaves the sulphate of potash undissolved. On 
 cooling, the urea crystallizes, and may be obtained quite pure by anoth- 
 er crystallization from alcohol. 
 
 The taste of urea is fresh like nitre ; its reaction is quite neutral ; it 
 is inodorous. When heated to 220°, it melts, and at a higher tempera- 
 
SALTS OF UREA. URIC ACID. 685 
 
 ture is decomposed, giving carbonic and cyanuric acids and ammonia. 
 It dissolves in less than its own weight of water at 60°," producing great 
 cold ; it is soluble in much less boiling water. If the urea be quite pure, 
 its solution remains for a long time unaltered ; but if it contains any tra- 
 ces of an azotized substance which putrefies, this acts as a ferment, and 
 the decomposition extending to the urea, this assimilates the elements of 
 water, and is totally converted into carbonate of ammonia, N C2 . O2H4 
 and H4O4 producing 2(G.O +N.H4O.). It is this decomposition that 
 renders urine alkaline in a few hours, generally, after it is voided. Urea 
 dissolves in five parts of cold and one of boiling alcohol. In ether it is 
 almost insoluble. 
 
 In contact with strong acids, urea is decomposed, giving oflf carbonic 
 acid, and forming an ammoniacal salt. When the acids are dilute, it unites 
 with them, although without neutralizing them, and forms crystalline 
 compounds, of which but a few have been accurately examined. The 
 oxygen salts of urea resemble those of the vegetable alkalies, melamine, 
 ammonia, &;c., in containing an atom of associated water. 
 
 Nitrate of Urea (Ur.H.O. -f-N.Og) crystallizes in large brilliant plates 
 by the cooling of its solution. It is pleasantly acid, and is soluble in al- 
 cohol, but much more so in water ; if heated rapidly, it explodes. It is 
 sparingly soluble in dilute nitric acid, whence the addition of a great ex- 
 cess of nitric acid serves as a test for the presence of urea, this salt be- 
 ing precipitated in bright pearly scales. 
 
 Oxalate of Urea (Ur.H.O.-j-CgOa) crystallizes in long rhomboidal 
 tables. It tastes acid ; it is copiously soluble in boiling water, but crys- 
 tallizes almost completely out on cooling, as 100 of water retain but 4 of 
 the salt. It is still less soluble in alcohol. 
 
 Lactate of Urea crystallizes in fine plates and needles ; it is very solu- 
 ble. There is reason to consider that the urea is naturally combined 
 with lactic acid in the urine. The other salts of urea are not important. 
 
 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 differ, 
 ent 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 ; while 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 the Bodies derived from it. 
 
 The uric acid exists in the urine of all carnivorous animals. In birds, 
 leptiles, and many insects, it is voided with the excrements, and the urine 
 is in such a slate 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 o^ guano, 
 and used as manure. In many diseases it is generated by the system in 
 abnormal quantity, and constitutes, 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 
 
686 URIC A C I D. ^A L L A N T O I N. A L L O X A N. 
 
 from the white solid excrements of the larger serpents in the menageries. 
 This is to be boiled in a solution of caustic potash, and the filtered Jiquoi 
 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 solu- 
 ble in boiling water ; the solution reddens litmus ; it is tasteless ; it dis- 
 solves in oil of vitriol, forming a crystallizable compound, which is de- 
 composed 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 formu- 
 la is N4C,o . H^Og ; its salts are not well characterized ; those of the al- 
 kalies are very sparingly soluble, 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 deposites. The uric acid is specially inter- 
 esting for the number of important bodies to which it gives origin by the 
 action of reagents, and of which some are also products of the organiza- 
 tion ; for our accurate knowledge of these we are indebted to the recent 
 investi"[ations of Liebig and VVohler. 
 
 Allantdin. — This substance exists in the waters of the allantoi's of the 
 cow, being contained in the urine of the foetus, from which it may be ex- 
 tracted 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, evapora- 
 ted till crystals begin to form, and then allowed to cool. The allantom 
 crystallizes, and the mother liquor contains abundance of urea. At the 
 same time, oxalate of the protoxide of lead is produced, 2(N4C,o . H4O6) 
 and 5H.0. with 4Pb.02, producing 4(C203+Pb.O.) ; with urea, 2(Nj 
 Cg . H4O.2), and allantoin, N4C8 . H5O5. 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 hy- 
 pothetic substance, for which he proposes the names of Uril, or Cyanox- 
 alic Acid, it being oxalic acid in which oxygen is replaced by cyanogen, 
 CA+Cy. Thus uric acid, N4C,o . H406=N2C2 . H402+2(C20,Cy.). 
 In forming allantoin on this view, the urea is set free, and the cyanox- 
 alic 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 alkali, it combines with the elements of water, giving oxalic acid 
 and ammonia. It does not form a definite competed with any base but 
 oxide of silver. 
 
 Alloxan. — The products of the action of nitric acid on uric acid present consider- 
 able interest, from their number and connexion. On adding one part of uric acid 
 gradually to four pans of strong nitric acid, it is dissolved with much heat, and co- 
 pious disengagement of carbonic acid and nitrogen. The lise 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 6 Aq. ; at a higher 
 temperature it crystallizes in oblique rhombic prisms which are anhydrous, and have 
 the formula NjCs . H4O10; its solution in M-ater reddens litmus, and stains the skin 
 purple; when neutralized by an alkali, it strikes an indigo-blue colour with a protc 
 salt of iron; it is decomposed by almost all reagents, producing a series of bodies 
 that will be successively examined; its origin consists, probably, in the uryl beicg 
 
ALLOXANIC AND MYCOMELINIC ACIDS, ETC. 687 
 
 oxidized by oxygen from the nitric acid, leaving hyponitrous acid, which, reacting 
 on the urea, gives the mixture of the carbonic acid and nitrogen gases. The allox- 
 an may thus be considered as a hydrated deutoxide of uryl. 
 
 AUoxanic Addis formed by acting on alloxan with strong alkalies or by barytesj 
 when separated from its combinations by a stronger acid, it crystallizes in colour- 
 less needles, which have a strong acid reaction; its alkaline salts are soluble; those 
 with the earths and heavy metallic oxides sparingly soluble ; it is insoluble in wa- 
 ter ; its formula is N2C3 . H2O8 when dry, tiie alloxan having lost the elements of 
 two atom.> 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, JVLsoxaitc Acid, which in the latter case precipitates an insoluble salt 
 of lead, and the liquor contains urea; the alloxan breaking up into N2C2 . H4O2 and 
 2C3O4, which is the constitution of the mesoxalic acid, which has probably, there- 
 fore, an isomeric oxide of carbon (C3O3) for its base, and belongs to the same group 
 as the mellitic and rhodizonic acids (p. 496). By oxidizing agents, the mesoxalic 
 acid is converted into carbonic acid ; thus, with a solution of nitrate of silver, ii 
 gives a clear yellow precipitate, which, when boiled, is converted into carbonic 
 acid and metallic silver. 
 
 Mijconidtmc 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 
 mycomelinic 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 N4C8 . H5O5, being isomeric with anhydrous allantoVn. 
 
 Panibanic Acid. — If alloxan be heated with an excess of nitric acid, it dissolves, 
 nitrogen gas is evolved, and, on cooling, the new acid separates; it is also easily 
 procured from uric acid by using an excess of nitric acid ; it forms colourless, trans- 
 parent, six-sided prisms, and tastes like oxalic acid. It is partly volatilized and 
 partly decomposed by heat. If the crystals he heated to 212", they assume a reddish 
 colour ; the formula of the crystallized acid is N2C6O4-1-2 Aq. ; hence alloxan with 
 20. produces 2C.O2, with 4H.0. and N2C6O4. By contact with bases, this acid is 
 decomposed, producing the Oxaluric Acid. This is best prepared by dissolving pa- 
 rabanic 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 special- 
 ly noticed hereafter. It is a strong acid, and is obtained free by dissolving its am- 
 monia 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 NoCe . HaOT-fAq. 
 
 Tiiiomiric Acid. — If sulphurous acid gas be passed through a saturated 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 re- 
 mains as a white semicrystalline mass; it is easily soluble in water, reddens lit- 
 mus strongly; its formula is N3C3 . H7O14S2: it contains thus the elements of one 
 atom of alloxan, one oli ammonia, and two of sulphurous acid ; it is a bibasic acidi 
 If a strong solution of thionuric acid be boiled, it becomes turbid, and soon solidifies 
 to a mass of brilliant silky crystals, while 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 alkaline liquors, 
 and precipitated therefrom unchanged by the addition of an acid, but by strong al- 
 kalies it is decomposed, ammonia being evolved, and uramilic acid formed. The 
 formula of uramil is N3C8 . H-,06; the thionuric acid might be considered as bisul- 
 phate of uramil. The Uramilic Add is formed by the action of acids and alka.lies 
 on uramil ; it crystallizes in colourless needles, which dissolve in acids and alkalies, 
 forming with the latter well-defined salts; its formula is N.^Cie . H10O15. 
 
 AU.vxuitin-'. — This substance is formed as a product of the moderate oxidation 
 of unc acid, or it may be obtained by acting on alloxan with deoxidizing agents. 
 Uric acid is to be diffused through boiling water, and the dilute nitric acid added 
 until a perfect solution is obtained. On filtering and cooling, the alloxantine grad- 
 ually crystaHizes. The mother liquor contains much urea. If sulphuretted hydro- 
 gen g is'has been passed through a solution of alloxan, sulphur is deposited, and al- 
 loxantine formed, and the same effect is produ:;ed by acidulating the solution of al- 
 
683 DIALURIC ACID, MUREXID, ETC. 
 
 loxan, and immersing therein a slip of zinc ; the alloxan is deoxidized by the nas- 
 cent hydrogen. By the galvanic battery alloxan is resolved into oxygen and allox- 
 antine. It is sparingly soluble in cold, but much more in boiling water, and crys- 
 tallizes in short oblique rhombic prisms which contain 3 Aq., which tliey lose only 
 by a heat above 300"^. The solution of alloxaritine reddens litmus, but docs not 
 form salts with bases, being immediately decomposed by contact with them. Its 
 formula is N2C8 . H5O10. 
 
 By oxidizing bodies, as nitric acid, chlorine, or oxide of silver, it is immediately 
 converted into alloxan. If treated by an excess of sulphuretted hydrogen, more sul- 
 phur is set free, and the liquor becomes strongly acid. The body thus formed, if 
 mixed with alloxan, regenerates alloxantine from both. If neutralized by carbonate 
 of amm.onia, a white crystalline precipitate forms, which is a salt of ammonia, of 
 which the formula is NsCb . H-Os. Liebig considers it to contain a body which he 
 terms the DiaUric Acid, the formula of which is N2C8O4, being isomeric with the 
 cyanoxalic acid or uryl already noticed. The Dialurate of Ammonia is therefore 
 N2C8O4+N.H4O.+3 Aq. It may be produced by adding hydrosuiphuret of ammo- 
 nia to a saturated solution 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 be- 
 comes 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 uramil and alloxan, 
 while muriatic acid becomes free. By the action of oxygen upon an ammoniacal 
 solution of alloxantine, uramil, oxaluric acid, and mycomelinic acid are generated. 
 
 Murezid. — This remarkable substance may be produced by a variety of reactions, 
 none of which are, however, quite constant in their result. On evaporating a solu- 
 tion 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 ingre- 
 dients prevents success, and Gregory proposes, as the most certain method, to dis- 
 solve four parts of alloxantine and seven of hydrated alloxan in 240 parts of boil- 
 ing water and eighty of solution of carbonate of ammonia, when the murexid crys- 
 tallizes by gradual cooling. By the action of uramil and ammonia it may also be 
 generated, and is the ordinary source of the purple colours that are produced in 
 many of the reactions already described. 
 
 The Murexid, the name of which is derived from the murex, the shell-fish furnish- 
 ing the Tyrian purple, crystallizes in short rhombic prisms of a garnet-red colour, 
 and by reflected light have a green metallic lustre. It dissolv^es 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 insolulile 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 
 NbCh . HeOg. By the mineral acids and by sulphuretted hydrogen it is decompo- 
 sed, ammonia, alloxantine, alloxan, and dialuric acid being evolved, besides an- 
 other body termed Murexan. This substance is more abundantly produced by dis- 
 solving murexid in a boiling solution of potash, and when the blue colour has to- 
 tally disappeared, adding sulphuric acid in excess. It precipitates in white silky 
 crystalline scales; its formula is N2C6 . H4O5; it dissolves in caustic alkalies with- 
 out 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 Puvpnratc of 
 Ammonia ; and Fritzsche has revived the idea that it is really an ammoniacal salt 
 of a distinct acid, Purpuric Acid. By the double decomposition of murexid with 
 salts of potash, barytes, lead, and silver, he has obtained purpurates of these bases, 
 the formula of whibh shows the acid to be composed of N5C16 . H40i(. The mu- 
 rexid is, according to this chemist, composed of NeCie. H80ii=N5Ci6 . H4O10-I- 
 N.H4O. The evidence brought forward by Fritzsche against Liebig's view is very 
 strong. 
 
 In the urine of herbivorous animals, and occasionally in children, the uric acid is 
 replaced by a different body, the Hipjpiric Acid, which exists therein combined with 
 soda. The urine of horses and com'S is to be evaporated to one eighth of its volume, 
 and mixed with muriatic acid, which produces, after some time, a yellowish crys- 
 talline precipitate. This is to be dissolved by boiling with some lime; chloride of 
 iime 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 
 
URINE IN DISEASE. 689 
 
 separated by muriatic acid. By the cooling of the liquor it crystallizes in delicate 
 silky needles or rhombic prisms; its taste is very slightly bitter, but it reddens lit- 
 mus 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 decomposed, and benzoic acid is formed. Its 
 salts are all soluble and crystallize ; they resemble the benzoales exactly. The for- 
 mula of the crystallized acid is N.Cis • HgOs+Aq. The constant transformation of 
 this acid into benzoic acid has given origin to many theories of its constitution. It 
 has been supposed by some to contain benzoic acid ready formed, by others benza- 
 mid, and by others oil of bitter almonds, but none of these views have even much 
 probability in their favour. 
 
 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 medicinal 
 substances may be traced to it after having been ingested, sometimes quite 
 unaltered, at others modified in their nature. Thus, if alkaline salts of or- 
 ganic acids be taken into the stomach, the organic material is oxidized, 
 probably during the action of respiration, while the alkali 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, pro- 
 duces 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 hy- 
 driodic acid. Some organic bodies, as asparagine and oil of turpentine, 
 are decomposed, and the products which they form are excreted, giving 
 to the urine peculiar odours, in the latter case like that of violets. Ni- 
 trate of potash, yellow prussiate of potash, and most other alkaline and 
 earthy salts, pass into the urine unchanged. The majority of colouring 
 matters are thrown out of the system by means of this secretion, while 
 others, as cochineal and litmus, are not so given off. 
 
 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 1030 to 1050, and it is found to con- 
 tain a very large quantity of grape-sugar, and very little urea. It wsis 
 supposed that, in this disease, urea ceased to be formed by the system, 
 and was replaced by sugar ; but I have shown that, although the quantity 
 of urea is very small 4n any one specimen of the urine, yet the total 
 quantity 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 con- 
 tains albumen, which arises from complication of other forms of disease. 
 
 As the average composition of urine in diabetes, the following may be 
 taken, analyzed by myself. Its specific gravity was 1'0363 ; it contained 
 in 1000 parts, water 913, sugar 60, urea 6*5, salts, extractive 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 these diseases, particularly where associated 
 
 4S 
 
690 URINARY DEPOSITES AND CALCULI 
 
 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 caseiim. 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 system, which do 
 not appear connected with any distinct disease, milk passes into the urine, 
 in which as well the butter as the caseiim 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. 
 
 Blue and Black Urine. — The urine has been observed coloured deeply 
 blue by a peculiar organic substance, which, however, has not been ac- 
 curately examined. Braconnot found that it contained nitrogen, and was 
 reddened by acids, and the colour restored by aJkahes. But Sprangen- 
 berg found, in the case he observed, that acids dissolved the blue sub- 
 stance without changing its colour. Moncet observed in the urine of a 
 child a black matter insoluble in water, but soluble in alkalies. 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 yellowish-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, produces the gouty concretions, which 
 consist, for the most part, of urate of soda. 
 
 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 distin- 
 guish between these two kinds of sediment. It is sufficient to remark, 
 that the uric acid deposite is soluble in alkalies and insoluble in dilute 
 acids, while the phosphatic sediments dissolve in dilute acids, but not in 
 alkaline liquors, even though decomposed by them. 
 
 The uric acid and the inorganic salts of the urine are afterward de- 
 posited in the bladder, and form urinary calculi. 
 
 The Uric Acid Calculus is probably the most common. It is recog- 
 nised by being decomposed by heat ; being sellable in caustic alkalies, 
 and precipitated by acids. When dissolved in nitric acid, evaporated 
 and moistened with water of ammonia, it gives the rich purple colour of 
 murexid. 
 
 The Urate of Ammonia Calculus, in addition to the characters 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 precipitated 
 by caustic ammonia from this solution as a white powder not crystal- 
 line. 
 
 The Ammoniaco-magnesian Phosphate Calculus is generally crystal- 
 line in structure ; before the blowpipe it gives off ammonia, and ulti- 
 
CYSTIC AND XANTHIC OXIDES, ETC. 691 
 
 mately melts, though with difficultj'. It also gives off ammonia when 
 boiled with caustic potash. It dissolves in dilute acids, and is precipita- 
 ted as a crystalline powder on the addition of caustic ammonia. 
 
 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 alkali, a crystalline deposite of ammo- 
 niaco-magnesian phosphate. 
 
 All of these various deposites may occur in the bladder, either success- 
 ively, 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 decomposition of 
 its natural constituents. Thus the Mulberry Calculus, so called from its 
 usual external form, consists of oxalate of lime. When ignited it leaves 
 caustic lime, which browhs wet turmeric paper strongly, dissolves in 
 muriatic acid, and is precipitated by adding oxalate of ammonia. Cal- 
 culi have been found also, though rarely, consisting of carbonate 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 na- 
 ture. The latter body is yellow, soluble in alkalies, and is precipitated 
 by the addition of an acid. It dissolves in nitric and sulphuric acids, but 
 not in muriatic or oxalic acids. Its formula is N4C,o . H4O4. It con- 
 tains, therefore, the same carbon, nitrogen, and hydrogen as uric acid, 
 but less oxygen, whence the name Uric Oxide has been proposed for it. 
 The Cystic Oxide Calculus consists of small yellow crystalline plates, 
 which dissolve in alkalies, 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 sulphurous acid and 
 ammonia. It forms definite salts with the nitric and muriatic acids. Its 
 formula is N.CeHe . O^. 
 
 When blood is effused into the bladder, the fibrine is occasionally ag- 
 gregated as a calculus, the recognition of which is very simple, from what 
 has been said of the properties of fibrine (p. 663). 
 
 Those who would wish for more detailed information of the properties 
 of calculi, and of the composition of the urine in health and disease, I 
 would refer to the truly classical work of Doctor Prout on the Diseases 
 of the Stomach and Urinary Organs. 
 
 SECTION V. 
 
 OF THE MILK, AND OTHER NATURAL AND MORBID PRODUCTS, NOT 
 INCLUDED IN THE PRECEDING SECTIONS. 
 
 Some of the most remarkable constituents of milk have been al- 
 ready described, as lactic acid (p. 536), the sugar of milk (p. 535), 
 the butter, fats (p. 589). It only remains to notice the general com- 
 position of milk, and the properties of the Caseiim 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 
 
692 
 
 COMPOSITION OF MILK, ETC. 
 
 found the cream from cows' milk to have specific gravity 1'0244', 
 and to consist, in 100 parts, of 4*5 of butter, separated by agitation, 
 3'5 of caseiJm, with some butter, separated by coagulation, and 92 
 of whey. The skimmed milk had a specific gravity of 1*0348, and 
 contained in 100 parts : 
 
 Caseous matter with some butter .... 2-600"\ 
 
 Sugar of milk 3-500 
 
 Alcoholic extract with lactic acid .... 0-600 
 
 Chloride of potassium 0-170 !► 100-00. 
 
 Alkaline phosphates 0-025 
 
 Earthy phosphates and a trace of iron . . 0230 
 Water f . 92-875, 
 
 The following table presents the best results that have been as yet 
 obtained on the average composition of the milk of diflferent animals : 
 
 Specific gravity . . 
 
 Water 
 
 Extractive . . > 
 
 Caseine .... 
 
 Butter 
 
 Sugar 
 
 Ashes .... 1 
 
 Human. 
 
 Mares. 
 
 Asses. 
 
 Cowrs. 
 
 Sheep. 
 
 1-0380 
 
 nog,. 
 
 10323 
 
 10395 
 
 88-68 
 
 1-82 
 0-75 
 8 75 
 
 10322 
 
 10320 
 
 
 88-36 
 
 1-24 
 
 340 
 253 
 4-25 
 
 022 
 
 90 47 
 
 1-95 
 1-29 
 629 
 
 85-91 
 
 700 
 393 
 
 2-87 
 
 029 
 
 532 
 
 (Cream 
 
 11-5) 
 
 153 
 
 5-8 
 
 4-2 
 
 65-74 
 
 290 
 
 17-40 
 1620 
 
 (Salts 
 1-50) 
 
 The butter of human milk is more solid than that of the cow, and appears to con- 
 tain no butyrine. 
 
 The Caseilm or Caseine is capable of existing in a soluble and an 
 .nsoluble condition, like albumen. In milk it is principally dissolved, 
 3ut a part insoluble, united with the butter, produces the emulsive 
 appearance of the milk. On adding sulphuric acid to skimmed milk, 
 the caseine precipitates, combined with the acid, as a white coagu- 
 -um, which, being washed with water so as to remove all adhering 
 milk, and then digested with carbonate of barytes, the caseine dis- 
 solves in the water, and may, by filtration, 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 all traces of butter, it miy be looked ipon as pure. 
 
 The solution of caseine in water js 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 to acetic acid ; 
 the constitution of its precipitates being precisely similar. 
 
 The coagulated condition of caseine is not produced by boiling, 
 but only by the digestive principle (rennet, pepsine), as already de- 
 scribed (p. 679). When thus coagulated, caseine is absolutely un- 
 distinguished from coagulated albumen in its properties. It con- 
 tains a considerable quantity of bone-earth (phosphate of lime), 
 amounting to five or six per cent., in intimate combination. Its or- 
 ganic element was found by Mulder to be proteme, of which ten at- 
 oms are combined with one of sulphur, the formula of caseine being 
 C400H310 • N5oO,2o + S. It contains no phosphorus, but to each atom 
 so expressed, two atoms of bibasic phosphate of lime. 
 
 When coagulated caseine containing water (cheese) is kept for 
 
EGGS, AMNIOS, CONTENTS OF THE EYE, ETC. 693 
 
 a long time, it undergoes a remarkable kind of decomposition, and 
 a substance, crystallizable and soluble in water, is obtained, termed 
 by Braconnot jlposepedine. By Mulder's experiments it appears, 
 however, to be impure leucine (p. 667) ; and the Caseous Oxide and 
 Case'ic Acid of Prout appear also to be the same bodies as have been 
 already noticed as formed from the decomposition of the other pro- 
 te'ine substances. 
 
 By contact with caseine, sugar of milk is rapidly converted into 
 lactic acid, which precipitates the caseine, without, however, really 
 coagulating it j hence, on neutralizing the acid, the caseine redis- 
 solves, and may react on a new quantity of sugar. In this manner 
 Freiry lias shown that the Lactic Fermentation may be carried on to 
 an indefinite extent. 
 
 Constitution of Eggs. — The shell of hens' eggs consists of from 
 90 to 95 per cent, of carbonate 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 epidermis. The white of egg is a concen- 
 trated solution of albumen, contained in the cells of a delicate mem- 
 brane, in the centre of which the yolk is suspended. The nutritive 
 material of the yolk consists of albumen and an oil ; also a yellow 
 colouring matter analogous to that of bile. The Oil of Eggs is ob- 
 tained by expressing the Ggg boiled, and partly torrefied j it is red- 
 dish-yellow, thick, and solidified by coldj it soon becomes rancid; 
 the solid portion of, it appears to be cholesterine ; the liquid con- 
 tains phosphorus and nitrogen, and is not saponifiable. When the 
 young animal is developed during incubation, the quantity of phos 
 phoric acid in its bones is exactly represented by the quantity of 
 phosphorus in the yoJk 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 foetus is immersed 
 before birth, appears to be identical in constitution with the liquor 
 effused from serous surfaces in dropsy (p. 671). The Liquor of the 
 Allanto'is of the cow, which is really the urine of the foetus, is of 
 the same nature, but contains, in addition, a small quantity of allan- 
 toin, the artificial formation of which is described p. 686. 
 
 Black Pigment of the Eye. — This substance is insoluble in water 
 and alcohol. It is decomposed by strong acids and alkalies. Caus- 
 tic 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, insol- 
 uble in water, alcohol, and ether, which dissolves in nitric acid and 
 potash with a reddish-yellow colour, from which solution a yellow- 
 ish powder falls when it is neutralized. 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 atten- 
 tive study. 
 
 The Humours of the Eye consist of water, holding in solution al 
 bumen in small quantity, with the salts which usually accompany 
 it. The crystalline lens consists of albumen, in a state of beautiful 
 
694 CERUMEN, PUS, AMBERGRIS, ETC. 
 
 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 albumi- 
 nous 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 i(.'h\c\\ its colour and very disgusting taste are due ; an- 
 other 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. 
 
 Pus. — This remarl^able 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 o^ which 
 are about twice the size of the globules of the blood. Pus Joses 
 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 7'4i 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 coagulable by heat. One is 
 albumen, the 9ther Pyin^ which is characterized by being coagula- 
 ted both by heat, by acetic acid, and by a solution of alum. Giiter- 
 bach, who has recently examined pus with great care, finds the only 
 certain distinction between pus and mucus to be, that the pus glob- 
 ules sink always in water, while the mucus swims. If the suspect- 
 ed liquid be dried, the extraction of the fatty substance by ether 
 should decide very positively. 
 
 Jlmbergris. — This substance, which is generally found floating on 
 the seacoasts of tropical islands, is known to be an intestinal con- 
 cretion of the spermaceti whale, analogous to the gallstones of 
 cholesteVine in other animals. Its principal ingredient is the Am- 
 bre'ine, 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 j it is not saponifiable ; its formula is C33H32O 
 By boiling with nitric acid it produces ambreic acid, which crystal 
 lizes from its solution in alcohol in small colourless tables ; it red- 
 dens litmus, but is scarcely soluble in water ; it forms well-defined 
 yellow salts with the alkalies j its formula appears to be C26H20 . 
 N.0.2. 
 
 SECTION VI. 
 
 OF THE PRESERVATION AND PUTREFACTION OF ANIMAL MATTERS. 
 
 From the greater complexity of composition of animal substances, 
 their decomposition is more rapid, and its products more diverse, 
 than in the case of organic bodies of vegetable origin ; while the 
 carbon, hydrogen, and oxygen give origin to the various kinds of 
 ulmine and other substances of the same class, the nitrogen is gen- 
 erally evolved as ammonia, and the sulphur as sulphuretted hydro- 
 gen. It is the presence of these bodies that give to putrefying sub- 
 stances the disagreeable odour by which that process is distinguish- 
 ed from mere mouldering or rotting. 
 
PUTREFACTION. 695 
 
 Even during life the constituent particles of the "body are in a 
 continual state of change, being absorbed and thrown out of the 
 system, while others are assimilated in their place. Any part of 
 our constituents, liquid or solid, which becomes unfitted for this 
 vital function, is thereby killed, and must, if not got rid of, induce 
 the death of the individual. Hence precisely the same means w:hich 
 give to animal substances the fixity of constitution which belongs 
 to true chemical compounds, and thus preserve them from decom- 
 position 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 albu- 
 men and fibrine of the blood, and, converting them into the insolu- 
 ble compounds which we form in the laboratory, unfit them for the 
 continual absorptive and secretive offices which, as organs, vi'hile 
 they live they must fulfil. If the injury be local, and limited in ex- 
 tent, 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. 
 
 For putrefaction it. is thus necessary, 1st, that the force of vitali- 
 ty, which governs so completely the mere chemical tendencies of 
 the elements of our tissues, be removed ; 2d, that there shall not be 
 present any powerful chemical reagent with which the organized 
 material may enter into combination, and thus the divellant tenden- 
 cies of the affinities of its elements be overcome ; 3d, that water be 
 present in order to give the necessary mobility j 4th, that oxygen 
 be present, or at least some other gas, into the space occupied by 
 which the gaseous products may be diffused j and, lastly, that the 
 temperature shall be within moderate limits, putrefaction being im- 
 possible below 32° and above 182°. 
 
 The agency of the first of these preventive powers need not be 
 farther noticed. The second is extensively employed in the prepar- 
 ation 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 combinations, but by the 
 complete (catalytic) coagulation it produces in all the tissues of the 
 body that have proteine for their base. The necessity for the pres- 
 ence of water is shown by the fact that, by drying the animal sub- 
 stances, they are completely preserved. It is thus that the bodies 
 of those perishing in the Arabian deserts are recovered years sub- 
 sequently, dried, but completely 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 wator gradually passes from 
 
69(^ MIASM S. C O N T A G I O N. 
 
 the pores of the flesh, and, dissolving the salt, forms a brine, which 
 does not wet the flesh (p. 540), but trickles off' its surface; the wa- 
 ter necessary for putrefaction is thus removed. The mode of 
 strengthening alcohol in a bladder (p. 540) rests on the same prin- 
 ciple. Fourth, by excluding oxygen, the putrefactive process is re- 
 tarded, precisely as the fermentative action of the gluten in grape- 
 juice (p. 538) 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 ol 
 oxygen of the air remaining then in the vessel is absorbed, and the 
 product of that minute change being coagulated by the heat, it can- 
 not proceed farther. A high temperature stops putrefaction by co- 
 agulating the azotized materials ; a temperature below 32^, by freez- 
 ing the water, acts as if the tissue had been dried j in both cases 
 putrefaction is arrested. 
 
 During putrefaction, at a stage prior to any fetid gas being evolv- 
 ed, 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 ap- 
 plied to wounds. The blood of over-driven cattle is found to pro- 
 duce efl^ects similar to those of venomous reptiles, and the wounds 
 received in dissection are sometimes followed by similar fatal con- 
 sequences. The communication of disease in this way has recently 
 been very ingeniously ascribed by Liebig to the general principle 
 of the communication of decomposition by contact (p. 663). The 
 small quantity of diseased organic matter originally introduced into 
 the system by absorption, acts as a ferment, and reproduces itself 
 in the mass of blood 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., constituting infection, by which 
 the disease may be communicated to another person. 
 
 In the decomposition of vegetable matter in marshes, similar 
 maleficent products may be evolved, and throwing the blood of the 
 animal, by whom they are absorbed, into fermentative decomposi- 
 tion, produce the effects of Malaria and Marsh Miasm, 
 
INDEX. 
 
 Absinthiine, 611. 
 Absorption of Light, 45. 
 
 of Heat, 96. 
 
 Acechloryl, 564. 
 Acetal, 554. 
 Acetone, 561. 
 Acetyl, 654. 
 Acid, Acetic, 555. 
 
 Adipic, 586. 
 
 Aldehydic, 555. 
 
 Althionic, 546. 
 
 Aloetic, 612. 
 
 Anchusic, 614. 
 
 Anilie, 618. 
 
 Antiraonious, Antimonic, 385. 
 
 Arsenic, 377. 
 
 Arsenious, 376. 
 
 Auric, 405. 
 
 Azulmic, 518. 
 
 Boletic, 604. 
 
 ^ Boracic, 326. 
 
 Bromic, 318. 
 
 Butyric, 589. 
 
 Carbonic, 485. 
 
 — — Capric, Caproic, 589. 
 
 Catechutannic, Catechuic, 603. 
 
 Caincic, 605. 
 
 Chloric, 304 
 
 Chloroacetic, 564. 
 
 Chlorochromic, 450. 
 
 Chlorous, 305. 
 
 Chromic, 372. 
 
 Chrysammic, 613. 
 
 Chrysolepic, 613. 
 
 Cinchonic, Cinchonatannic, 604. 
 
 • Cinnamic, 572. 
 
 Citric, 597. 
 
 Colophonic, 579. 
 
 Columbic, 375. 
 
 Crenic, Apocrenic, 640. 
 
 Croconic, 496. 
 
 Crotonic, 590. 
 
 Cumenic, Cumen-sulphuric, 575. 
 
 Cyanic, 514. 
 
 Cyanuric, 516. 
 
 Delph>nic, 589. 
 
 Elaidic, 586. 
 
 Ellagic, 602. 
 
 Ethionic, 546. 
 
 Eugenic, 573. 
 
 — — Formic, 645. 
 
 Fulminic, 515. 
 
 Fungic, 604. 
 
 Galhc, 601. 
 
 Glucic, 534. 
 
 4T 
 
 Acid, Hippuric, 688. 
 
 Humous, Humic, 639. 
 
 Hydriodic, 315. 
 
 Hydrobromic, 318. 
 
 Hydrochloric, 307. 
 
 Hydrocyanic, 517. 
 
 Hydrofluoboric, 327. 
 
 Hydrofluoric, 319. 
 
 Hydrofluosilicic, 325. 
 
 Hydroxanthic, 550. 
 
 Hypoantimonius, 385. 
 
 Hypochlorous, 304. 
 
 Hyponitrous, 275. 
 
 Hypophosphorous, 296. 
 
 Hyposulphuric, 291. 
 
 Hyposulphurous, 290. 
 
 Iodic, 313. 
 
 Isethionic, 546. 
 
 Kinoic, 604. 
 
 Krameric, 605. 
 
 Lactucic, 604. 
 
 Lipic, 586. 
 
 Manganic, 356. 
 
 Margaric, 583. 
 
 Mellitic, 496. 
 
 Metaphosphoric, 299. 
 
 Methionic, 546. 
 
 Molybdic, 451. 
 
 Muriatic, 307. 
 
 Myristic, 588. 
 
 Nitric, 277. 
 
 Nitromuriatic, 310. 
 
 Nitrous, 276. 
 
 Oleic, 584. 
 
 Osmic, 374. 
 
 Oxalic, 493. 
 
 Oxalovinic, 550. 
 
 Palmitic, 588. 
 
 Paracyanic, 514. 
 
 Perchloric, 306. 
 
 Periodic, 314. 
 
 Permanganic, 356. 
 
 Phosphomesitic, 561. 
 
 Phosphoric, 297. 
 
 Phosphorous, 296. 
 
 Picric, 618. 
 
 Pimelic. 586. 
 
 Pinic, 578. 
 
 Purpuric, 688. 
 
 Racemic, 596. 
 
 Rhodizonic, 496. 
 
 Saccharic, 532. 
 
 Saccharohumic, 637. 
 
 Sacchulmic, 532. 
 
 Sebacic, 586, 
 
698 
 
 INDEX. 
 
 Acid, Selenious, Selenic, 294. 
 
 Silicic. 322. 
 
 Stannic, 370 
 
 Stearic, 582. 
 
 Succinic, 580. 
 
 Sulphomesitic, 561. 
 
 Sulphuric, 286. 
 
 Sulphurous, 284. 
 
 Sylvic, 578. 
 
 Tannic, 597. 
 
 Tantalic, 375. 
 
 Tartaric, 592. 
 
 Tellurous, Telluric, 389. 
 
 Titanic, 375. 
 
 Tungstic, 374. 
 
 Valerianic, 568. 
 
 Vanadic, 373. 
 
 Verdous and Verdic, 605. 
 
 Acids, Poiybasic, 413. 
 
 Acroieon, 585. 
 
 Actions by Contact, 235. 
 
 Adhesion of Solids to Liquids, 19. 
 
 Uroliths, 357. 
 
 Affinity, Chemical, 157. 
 
 Order of, 159. 
 
 influenced by Cohesion, 164. 
 
 Elasticity, 168. 
 
 Light, 172. 
 
 Measure of, 202. 
 
 Aggregation, States of, 16. 
 Air, Atmospheric, 262. 
 
 Expansion of, 48. 
 
 Alabaster, 431. 
 Albumen, Animal, 663. 
 Alcohol, Ordinary, 540. 
 Alem broth, Salt of, 461. 
 Algarotti, Powder of, 453. 
 Alkalies, 330. 
 Alkalimetry, 489. 
 Alkaline Earths, 330, 
 Alkarsine, Alkargene, 563. 
 AUantoine, 686. 
 Alloxan, 686. 
 Alloxantine, 687. 
 
 Alum, 436. 
 
 Aluminum, Alumina, 349. 
 
 Salts of, 435. 
 
 Amber, 579. 
 
 Ambergris, Ambreine, 694, 
 
 Amldogene, 500. 
 
 Amilic Alcohol, 5671 
 Ammeline, 526. 
 Ammonia, 498. 
 
 Ordinary Salts of, 507. 
 
 Amygdaline, 569. 
 Analcime, 40. 
 Analysis, Nature of, 10, 
 
 Organic, 482. 
 
 Anatase, 375. 
 Anhydrite, 431. 
 Animal Charcoal, 480. 
 
 Electricity, 138. 
 
 Antimonial Powder, 454, 
 Antimoniuret of Hydrogen, 388. 
 
 Antimony, 384. 
 
 Detection of, 388. 
 
 Oxide of, 385. 
 
 Salts of, 453. 
 
 Sulphurets of, 386. 
 
 Antimony Crocus, Glasses of, 385. 
 
 Apotheme, 612. 
 
 Aqua-regia, 310. 
 
 Arabine, 530. 
 
 Aricine, 625, 
 
 Arseniate of Iron, 452, 
 
 Potash, 452. 
 
 Silver, 461. 
 
 Arsenic, 376, 
 
 Acids of, 377. 
 
 Antidote to, 384. 
 
 Detection of, 381. 
 
 Salts of, 451. 
 
 Sulphurets of, 379. 
 
 Arsenite of Copper, 456. 
 
 Potash, 452. 
 
 Silver, 461. 
 
 Arseniuret of Hydrogen, 378. 
 Atmosphere, 262. 
 
 Composition of, 263, 
 
 Effect of Respiration ou, 
 
 268. 
 
 Extent and Form of, 270. 
 
 Pressure of, 269. 
 
 Atmospheric Electricity, 126. 
 Atomic Theory, 217. 
 Atoms, Physical and Chemical, 219. 
 Specific Heat of, 66. 
 
 Atropine, 634. 
 Aurates, 405. 
 Azote, 260. 
 Azure Blue, 447. 
 
 113. 
 
 Balance, Electrical, 
 Barium, 342. 
 
 Chloride of, 429. 
 
 Sulphuret of, 344. 
 
 Barytes, 342. 
 Salts of, 429. 
 
 Batteries, Constant, 136. 
 Galvanic, 131. 
 
 Bell Metal, 393. 
 Benzyle Compounds, 570. 
 Bile, Constitution of the, 680. 
 Bileine, Bilifulvine, 682. 
 Bismuth, 397. 
 
 Oxides of, 398. 
 
 Salts of, 458, 
 
 Sulphuret of, 398. 
 
 Blende, 367. 
 Blue, Azure, 447. 
 
 Thenard's, 447. 
 
 Boihng Points of Liquids, 83. 
 
 Boracic Acid, Boron, 326. 
 
 Boracite, 435, 
 
 Borax, 428, 
 
 Boron, Fluoride of, 327. 
 
 Brass, 394, 
 
 Bromates, 318. 
 
INDEX. 
 
 69^ 
 
 Bromide of Sulphur, 318. 
 Bromine, 317. 
 
 Chloride of, 318. 
 
 Bronze, 393. 
 Brucine, 631. 
 
 Cadmium and its Compounds, 369. 
 
 Salts of, 448. 
 
 Caffeine, 608. 
 
 Calamine, 367. 
 
 Calc Spar, 345. 
 
 Calcium and its Oxides, 345. 
 
 Salts of, 430. 
 
 Sulphuret, 347. 
 
 Camphene, 576 
 Cantharidine, 609. 
 Caoutchouc, Caoutchine, 580. 
 Capacity of Bodies for Heat, 63. 
 Caramel, 533. 
 Carbon, Forms of, 476. 
 Carbonates, 485. 
 Carbonic Acid, 485. 
 
 Oxide, 492. 
 
 Carburets, 485. 
 
 Carmine, 616. 
 
 Carthamine, 615. 
 
 Caseiim, Caseine, 691. 
 
 Catalysis, 235. 
 
 Cementation, 360. 
 
 Cerebrot, Cerebrol, 669. 
 
 Cerium and its Compounds, 351. 
 
 Chalk, 345. 
 
 Chameleon Mineral, 356. 
 
 Chemical Action of Galvanism, 129. 
 
 Affinity, 156. 
 
 Formulae, 166. 
 
 Nomenclature, 149. 
 
 Rays of Light, 173. 
 
 Chemistry, Origin and Object of, 9. 
 
 Derivation of, 10. 
 
 Chloral, 564. 
 
 Chlorate of Potash, 304, 424. 
 
 Chloride of Aluminum, 435. 
 
 Antimony, 453. 
 
 Arsenic, 452. 
 
 Barium, 429. 
 
 Bismuth, 458. 
 
 Boron, 326. 
 
 Calcium, 430. 
 
 Chrome, 449. 
 
 Cobalt, 446. 
 
 Copper, 455. 
 
 Gold, 465. 
 
 Hydrogen, 307. 
 
 Iodine, 317. 
 
 Iron, 444. 
 
 Lead, 457. 
 
 Magnesium, 434, 
 
 ■ Manganese, 443. 
 
 Mercury, 461. 
 
 Nickel, 446. 
 
 Palladium, 466. 
 
 Platinum, 466. 
 
 Potassium, 421. 
 
 Chloride of Rhodium, 466. 
 
 Selenium, 311. 
 
 Silicon, 323. 
 
 Silver, 459. 
 
 Sodium, 426. 
 
 Strontium, 429. 
 
 Sulphur, 310. 
 
 Tin, 448. 
 
 ■ Titanium, 454. 
 
 Zinc, 447. 
 
 Chlorine, 300. 
 
 Compounds v^rith Oxygen, 304 
 
 Chlorophyll, 621. 
 Chondrine, 668. 
 Chromates of Lead, 458. 
 
 Mercury, 464. 
 
 Potash, 449. 
 
 Chrome Alum, 449. 
 Iron, 371. 
 
 Chromium, 371. 
 
 Oxide, Acid of, 371. 
 
 • Salts of, 449. 
 
 Chrysorhamnine, 615. 
 Chyle and Chyme, 679. 
 Cinchonine and its Salts, 625. 
 Cinnabar, 402. 
 
 Factitious, 403. 
 
 Circular Polarization, 41. 
 Classification of Bodies, 238. 
 Cobalt, 366. 
 
 Salts of, 446. 
 
 Cocculine, 609. 
 Cohesion and Affinity, 163. 
 Columbine, 609. 
 Columbium, 375. 
 
 Salts of, 451. 
 
 Combination, Laws of, 202. 
 Combustion, Slow, 173. 
 
 Theories of, 185. 
 
 Communication of Motion, 235. 
 Conduction of Heat, 91. 
 Coneine, 635. 
 Constant Battery, 136. 
 Contact, Actions by, 235. 
 Cooling of Bodies, 103. 
 Copper, 390. 
 
 Alloys of, 393. 
 
 Oxides of, 392. 
 
 Pyrites, 390. 
 
 Salts of, 453. 
 
 Sulphurets of. 
 
 Crystalline Forms, 23. 
 Crystals, Dimorphous, 227. 
 
 Isomorphous, 221. 
 
 Polarization by, 38. 
 
 Systems of, 26. 
 
 Currents, Galvanic, 126, 197. 
 Cyanogen, 513. 
 
 Daguerreotype Images, 
 Definite Proportions, 2( 
 Dew, Nature of, 104. 
 Dex rine, 331. 
 Diamond, 477. 
 
 175. 
 
700 
 
 INDEX. 
 
 Diastase, 651. 
 
 Differential Thermometer, 60. 
 Dimorphism, 237. 
 Distillation, 83. 
 Divellent Affinities, 157. 
 Divisibility of Matter, 17. 
 Double Decomposition, 157. 
 
 Refraction, 34. 
 
 Dynamic Electricity, 126. 
 
 Ebullition, 83 
 Elasticity of Gases, 19. 
 
 Vapours, 78. 
 
 and Affinity, 168 
 
 Elaterine, 609. 
 
 Elayl, 552. 
 
 Elective Decomposition, 157. 
 
 Electrical Attraction, 112. 
 
 Balance, 113. 
 
 Battery, 120. 
 
 Induction, 118. 
 
 Electricity, Distribution of, 110. 
 
 Dynamic, 126. 
 
 Interference of, 112. 
 
 Nature of, 106. 
 
 — of the Air, 125. 
 
 — Positive and Negative, 114. 
 
 — Statical, 107. 
 Theories of, 113. 
 
 Electrics and Non- electrics, 107. 
 Electro-chemical Theories, 187. 
 Electro-magnetism, 145. 
 Electrolysis and Electrodes, 194. 
 Electrotype, 130. 
 Elements, Nature of, 9. 
 
 Classification of, 238. 
 
 Emetine, 632. 
 
 Epsom Salt, 434. 
 
 Equivalent Decomposition, 206. 
 
 Ethal, 591. 
 
 Ether, Luminiferous, 42. 
 
 Sulphuric, 541. 
 
 Etherene, 547. 
 
 Ethers, Theory of the, 544. 
 Ethyl, 545. 
 
 Eudiometer, Use of the, 262. 
 Evaporation, 77. 
 
 Spontaneous, 87. 
 
 Excitation, Electrical, 106. 
 Expansion by Heat, 46. 
 of Gases, 56. 
 
 Liquids, 58. 
 
 Solids, 60. 
 
 Fermentation, 539. 
 
 Fibrine, 603. 
 
 Flame, Constitution of, 181. 
 
 Flashing, 399. 
 
 Flints, 321. 
 
 Liquor of, 437. 
 
 Fluidity, 70. 
 Fluoborates, 327. 
 Fluoride of Boron, 327 
 Calcium, 430. 
 
 Fluoride of Hydrogen, 320. 
 
 Phosphorus, 321. 
 
 Silicon. 324. 
 
 Fluorine, 319. 
 Fluor Spar, 430. 
 Freezing Mixtures, 71. 
 Frost, Nature of, 104. 
 Fulminates, 513. 
 Fusion, Liquefaction, 70. 
 
 Galena, 395. 
 
 Galvanic Batteries, Common, 134. 
 Constant, 136. 
 
 — Circles, 128. 
 
 — Electricity, 126. 
 Intensity, 131. 
 
 Galvanism, Contact Theory of, 133. 
 
 Galvanoscope, 147, 195. 
 
 Gases, Conduction of Heat by, 92. 
 
 Liquefaction of, 20. 
 
 Specific Gravity of, 11. 
 
 Heat of, 69. 
 
 Gelatine, 667. 
 
 Glass, Composition of, 437. 
 of Antimony, 385. 
 
 Glucinum, Glucina, 351. 
 Glucose, 533. 
 Glycerine, 581. 
 Glycyrrhizine, 535. 
 Gold, 405. 
 
 Gravity, Nature of, 11. 
 Green, Brunswick, 455. 
 
 Emerald, 455. 
 
 Scheele's, 455. 
 
 Heat, Central, of the Earth, 104. 
 
 Conduction of by Solids, 92. 
 
 Interference of, 101. 
 
 Latent of Liquids, 70. 
 
 Vapours, 76. 
 
 of Liquefaction, 70. 
 
 Polarization of, 101. 
 
 Radiation of, 94. 
 
 Reflection and Absorption of, 9!4. 
 
 Relation of to Light, 102. 
 
 Repulsive Power of, 46. 
 
 Sources of, 105. 
 
 Specific of Atoms, 66. 
 
 Gases, 69. 
 
 Solids, 63. 
 
 Transmission of, 91. 
 
 Heavy Spar, 342. 
 
 Hematite, 362. 
 
 Hematosine, 674. 
 
 Hematoxyline, 615. 
 
 Hepar Sulphuris, 339. 
 
 Hydriodate of Phosphuretted Hydrogen, 
 
 316. 
 Hydriodic Acid, 315. 
 Hydrobromic Acid, 318. 
 Hydrochloric Acid, 307. 
 Hydrofluoric Acid, 320. 
 Hydrofluosilic Acid, 324. 
 Hydrogen, 246. 
 
INDEX. 
 
 701 
 
 Hydrogen, Antimoniuretted, 388. 
 
 Arseniuretted, 378. 
 
 Oxide of, 253. 
 
 Peroxide of, 25|* 
 
 Phosphuretted, 299. 
 
 Seleniuretted, 294. 
 
 Sulphuretted, 292. 
 
 Hydro-oxygen Blowpipe, 251. 
 Hydruret of Arsenic, 378. 
 
 Indigo, Blue, 616. 
 Inuline, 529. 
 Iodine, 311. 
 
 Compounds of, 313. 
 
 Iridium, 409. 
 
 Salts of, 466. 
 
 Iron, 357. 
 
 Magnetic Oxide of, 362. 
 
 Malleable, 359. 
 
 Oxides of, 362. 
 
 Passitivity of, 361. 
 
 Pyrites, 363. 
 
 Salts of, 444. 
 
 Smelting of, 359. 
 
 Sulphurets of, 363. 
 
 Isomerism, 231. 
 Isomorphism, 221. 
 Isomorphous Groups, 223. 
 
 Kacodyl Compounds, 562. 
 Kalium, 337. 
 Kermes Mineral, 386. 
 King's Yellow, 379. 
 Kupfer Nickel, 365. 
 
 Lac-sulphuris, 339. 
 Lactine, 535. 
 Lactucine, 611. 
 Lamp, Aphlogistic, 179. 
 
 Safety, 183. 
 
 liampblack, 479 
 
 Lana Philosophica, 367. 
 
 Lanthanum, 351. 
 
 Latent Heat of Liquids, 70. 
 
 Vapours, 76. 
 
 Laws of Combination, 202. 
 
 Lead, 394. 
 
 Legumine, 538. 
 
 Lichenine, 529. 
 
 Light, Chemical Rays of, 173. 
 
 Wave Theory of, 42. 
 
 Lignine, 529. 
 Lime, 345. 
 
 Salts of, 430. 
 
 Liquefaction, 70. 
 Lithium, 342. 
 
 Salts of, 429. 
 
 Lymph, 683. 
 
 Madder, Colouring Bodies of, 613. 
 Magnesium, 348. 
 
 Salts of, 434. 
 
 Magnetism, 143. 
 Manganese, 352. 
 
 Manganese, Salts of, 443. 
 Mannite, 535. 
 Marsh Gas, 563. 
 Meconine, 609. 
 Melam, 526. 
 Melamine, 526. 
 Membrane, Cellular, 671. 
 Menthene, 578. 
 Mercury, 402. 
 
 Salts of, 461. 
 
 Mesitic Ether, 561. 
 Mesitylene, 561. 
 Metal, Bell, 393. 
 
 Gun, 393. 
 
 Speculum, 393. 
 
 Metals, Properties of, 327. 
 Methyl, Salts of, 644. 
 Minium, 395. 
 Molecular Cohesion, 19. 
 Molybdates, 373. 
 Molybdenum, 373. 
 
 Salts of, 451. 
 
 Mordants, Action of, 622. 
 Morine, 615. 
 Morphia, 627. 
 Mosaic Gold, 370. 
 Mucus, 679. 
 
 Multiple Proportions, 207. 
 Murexid, 688. 
 Muriatic Acid, 307. 
 Myriospermine, 573. 
 
 Napthaline, 647. 
 Narcotine, 628. 
 Natrium, Natron, 342. 
 Nickel, 365. 
 
 Salts of, 446. 
 
 Nicotine, 635. 
 Nitric Oxide, 273. 
 Nitrogen, 26. 
 Oxides of, 272. 
 
 Nitrous Oxide, 272. 
 Nomenclature, 149. 
 
 Oleine, 581. 
 Olivine, 607. 
 Ologist Iron, 362. 
 Orcine, Orceine, 619. 
 Organic Analysis, 476. 
 Bodies, 467. 
 
 Orpiment, 379. 
 Osmium, 374. 
 
 Oxides of, 374. 
 
 Salts of, 451. 
 
 Oxamethane, 350. 
 Oxides of Aluminum, 349. 
 
 Antimony, 385. 
 
 Arsenic, 377. 
 
 Barium, 342. 
 
 Bismuth, 397. 
 
 Cadmium, 369. 
 
 Calcium, 346. 
 
 Cerium, 351. 
 
 Chlorine, 304. 
 
W2 
 
 7NDEX. 
 
 Oxides of Chrome, 371. 
 
 Cobalt, 366. 
 
 Copper, 392. 
 
 Glucinum, 351. 
 
 Gold, 405. 
 
 Hydrogen, 253. 
 
 Iridium, 409. 
 
 Iron, 362. 
 
 Lead, 394. 
 
 Lithium, 342. 
 
 Magnesium, 348. 
 
 Manganese, 353. 
 
 Mercury, 403. 
 
 Molybdenum, 373. 
 
 Nickel, 365. 
 
 Nitrogen, 272. . 
 
 Osmium, 374. 
 
 Palladium, 406. 
 
 Phosphorus, 296. 
 
 . — Platinum, 407. 
 
 Potassium, 337. 
 
 . Rhodium, 409. 
 
 Silver, 401. 
 
 Sodium, 340. 
 
 Strontium, 344. 
 
 Thorium, 351. 
 
 Tin, 369. 
 
 . Titanium, 375. 
 
 Tungsten, 373. 
 
 Uranium, 390. 
 
 Vanadium, 373. 
 
 Yttrium, 351. 
 
 Zinc, 367. 
 
 Zirconium, 351 
 
 Oxychloride of Antimony, 453 
 . Bismuth, 458. 
 
 i^ Calcium, 430. 
 
 . Chrome, 449. 
 
 . Copper, 455. 
 
 Lead, 457. 
 
 Mercury, 462. 
 
 PaUadium, 466. 
 
 Oxygen, 241. 
 
 Preparation of, 241. 
 
 Oxyhydrogen Blowpipe, 251. 
 
 Palladium, 406. 
 
 Compounds of, 406. 
 
 Paracyanogen, 514. 
 Pectirie, 605 
 Perchlorates, 306. 
 Periodates, 313. 
 Permanganates, 357. 
 Pewter, 397. 
 Phenyl, Hydrate of, 648. 
 Phloridzine, 607. 
 Phosphates of Water, 297. 
 Phosphites, 297. 
 Phosphorus, 295. 
 
 Compounds of, 296. 
 
 Photography, 175. 
 Piperine. 608. 
 Platinum, 407. 
 Polarization, Circular, 41. 
 
 Polarization of Heat, 102, 
 — Light, 38. 
 
 Polychrome, 610. 
 Populine, 610. 
 Porcelain, Nature of, 437. 
 Potash, 337. 
 Potassium, 336. 
 
 Oxides of, 337. 
 
 Salts of, 421. 
 
 Sulphurets of, 339. 
 
 Proteine, 665. 
 Puddling, 359. 
 Purpurates, 688. 
 Pus, 694. 
 Putty, 370. 
 Pyrites, Copper, 390. 
 Iron, 363. 
 
 Pyrometer, Daniell's, 54. 
 Pyrophorus, 339. 
 Pyroxylic Spirit, 643. 
 
 Quartation, 405. 
 Quartz, 322. 
 Quassine, 610. 
 Quicksilver, 402. 
 Quinine, 624. 
 
 Radiation of Heat, 94. 
 Light, 32. 
 
 Radicals, Compound, 
 Nature of, 233. 
 
 Realgar, 379. 
 Red Lead, 394. 
 
 Precipitate, 403. 
 
 Reflection of Heat, 96. 
 
 : Light, 32. 
 
 Refraction of Heat, 100. 
 
 Double, 34. 
 
 Single, 32. 
 
 Regular System, 26. 
 Respiration of Animals, 677. 
 Rhodium, 409. 
 
 Salts of, 466. 
 
 Rutile, 375. 
 Rutiline, Rufine, 607. 
 
 Safety Lamp, 183. 
 Salop, 531. 
 
 Salicyl Compounds, 573. 
 Salts, Constitution of, 410. 
 
 Crystallization of, 23. 
 
 Isomorphism of, 221. 
 
 Solubility of, 22. 
 
 Salts of Alumina, 435. 
 
 Antimony, 453. 
 
 Arsenic, 452. 
 
 Barium, 429. 
 
 Bismuth, 458. 
 
 Cadmium, 448. 
 
 Calcium, 430. 
 
 Chrome, 449. 
 
 Cobalt, 446. 
 
 Copper, 455. 
 
 Gold, 465. 
 
INDEX. 
 
 703 
 
 Salts of Iridium, 466. 
 Iron, 444. 
 
 Lead, 457. 
 
 Magnesium, 434. 
 
 Manganese, 443. 
 
 Mercury, 461. 
 
 Molybdenum, 451. 
 
 Nickel, 446. 
 
 Osmium, 451. 
 
 Palladium, 466. 
 
 Platinum, 466. 
 
 Potassium, 421. 
 
 Rhodium, 466. 
 
 Silver, 459. 
 
 Sodium, 426. 
 
 Strontium, 439. 
 
 Tin, 448. 
 
 Zinc, 447. 
 
 Santaline, 615. 
 Santonine, 610. 
 Saponine, 611. 
 Scillitine, 611. 
 Selenium, 294. 
 
 Compounds of, 294. 
 
 Senegine, 611. 
 
 Silica, 322. 
 
 Silicate of Alumina, 437. 
 
 Cobalt, 447. 
 
 Potash, 426. 
 
 Soda, 429. 
 
 Silicon, 321. 
 
 Chloride of, 323. 
 
 Fluoride of, 324. 
 
 Silver, 399. 
 
 Oxides of, 401. 
 
 Salts of, 459. 
 
 Sulphurets of, 401. 
 
 Simple Bodies, 9. 
 
 Table of, 149. 
 
 Skin, Nature of, 670. 
 Slacked Lime, 346. 
 Smalts, 447. 
 Smilacine, 611. 
 Soap, Manufacture of, 590. 
 Soda, 340. 
 
 Detection of, 340. 
 
 Sodium, 340. 
 
 Salts of, 426. 
 
 Solanine, 633. 
 Solder, 396. 
 
 Solids, Conduction of Heat by, 92. 
 
 Expansion of, 60. 
 
 Specific Gravity of, 11. 
 
 Specific Heat, 63. 
 Speculum Metal, 393. 
 Speiss, 365. 
 Spermaceti, 591. 
 Spirit of Salts, 307. 
 Starch. 527. 
 Steam, Elasticity of, 78. 
 
 Latent Heat of, 76. 
 
 Motive Force of, 89. 
 
 Stearine, 582. 
 Steel. 360. 
 
 Stibium, 384. 
 Strontium, 344. 
 
 — Oxides of, 345. 
 
 Salts of, 429. 
 
 Strychnine, 629. 
 Sugar of Liquorice, 536. 
 Sugarcane, 531. 
 Sulphites, 284. 
 Sulphocyanogeu, 525. 
 Sulphosinapisine, 574. 
 Sulphur, 282. 
 Sulphurets of Aluminum, 350. 
 
 Antimony, 386. 
 
 Arsenic, 379. 
 
 Barium, 344. 
 
 Bismuth, 398. 
 
 Cadmium, 369. 
 
 Calcium, 347. 
 
 . Chrome, 371. 
 
 Cobalt, 367. 
 
 Copper, 393. 
 
 Gold, 405. 
 
 Hydrogen, 292. 
 
 Iron, 363. 
 
 Lead, 395. 
 
 Magnesium, 348. 
 
 Manganese, 357, 
 
 Mercury, 404. 
 
 Molybdenum, 373. 
 
 — Nickel, 366. 
 
 Palladium, 407. 
 
 Platinum, 407. 
 
 Phosphorus, 299. 
 
 — Potassium, 339. 
 
 — Selenium, 295. 
 
 Silver, 401. 
 
 • Sodium, 342 
 
 Strontium, 344. 
 
 Tin, 370. 
 
 ■ Zinc, 368. 
 
 Synthetic Action of Galvanism, 
 Systems of Crystallization, 26. 
 
 Tantalum, 375. 
 Telluret of Hydrogen, 389. 
 Salts of, 454. 
 
 199 
 
 Tellurium, 389. 
 
 Compounds of, 389. 
 
 Temperature, Nature of, 49. 
 Thebaine, 629. 
 Theory, Atomic, 217. 
 
 of Volumes, 213. 
 
 Thermo-electricity, 139. 
 Thermometer, Nature of the, 49. 
 Kinds of, 50. 
 
 Thermometric Scales, 53. 
 Thialol, 548. 
 Thorium, 351. 
 Tin, 369. 
 
 Grain, 369. 
 
 Oxides of, 369. 
 
 Tincal, 429. 
 Titanium, 375. 
 Transcalescence, 98. 
 
704 
 
 INDEX 
 
 Tragacanthine, 530. 
 Transfer of Elements, 194 
 Tungsten, 373. 
 
 — Salts of, 451. 
 
 Types, Chemical, 234. 
 
 Ulmine, from Soil, 637. 
 Uranium, 390. 
 
 Salts of, 454. 
 
 Urea, 684. 
 Urine, 689. 
 
 Vanadium, 373. 
 
 Salts of, 451. 
 
 Vaporization, 75. 
 Vapours, Elasticities of, 78. 
 
 Latent Heat of, 76. 
 
 Volumes of, 77. 
 
 Veratrine, 631. 
 Vermilion, 404. 
 Vitriol, Oil of, 286. 
 Voltaic Electricity, 126. 
 
 Volta's Theory of Contact, 13S. 
 Volumes, Theory of, 213. 
 
 Water, Composition of, 253. 
 Wave Theory of Light, 42. 
 Heat, 102. 
 
 Wax, 592. 
 Welding, 359. 
 White, Pearl, 458. 
 Vitriol, 447. 
 
 Xyloidine, 530. 
 
 Yeast, 538. 
 Yttrium, 351. 
 Salts of, 443. 
 
 Zaflre, 366. 
 Zinc, 367. 
 
 Butter of, 447. 
 
 Zirconium, 351. 
 Salts of, 44S. 
 
 THE END 
 
i 
 
12^A57 
 
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