; i MEMCAL SCHOOL l f COLLEGE OF PHARMACY ' A MANUAL OF ELEMENTARY CHEMISTRY, THEORETICAL AND PRACTICAL. GEORGE FOWNES, F R.S., LATE PROFESSOR OF PRACTICAL CHEMISTRY IN UNIVERSITY COLLEGE, LONDON FROM THE TENTH REVISED AND CORRECTED ENGLISH EDITION. EDITED BY ROBERT BRIDGES, M.D., PROFESSOR OF CHEMISTRY IN THE PHILADELPHIA COLLEGE OF PHARMACY. 3!?2D of Pharmacy WITH ONE HUNDRED AND NINETY-SEVEN ILLUSTRATIONS. PHILADELPHIA: HENRY C. LEA. 1869. Entered according to Act of Congress, in the year 1869, by HENRY C. LEA, In the Clerk's Office of the District Court of the United States, in and for the Eastern District of Pennsylvania. AMERICAN PUBLISHER'S ADVERTISEMENT. SO recent and so thorough has been the revision which this work has enjoyed at the hands of the English Editors, that but little has remained to be done in preparing the present reprint ; while the enlargement which the volume has necessarily under- gone, in the introduction of the most modern views and discov- eries, has rendered it advisable to confine the additions to as moderate a compass as possible. The American Editor has there- fore added but few notes, together with a number of illustrations, and has directed his attention rather to secure the accuracy so essential to a treatise of this nature. Especial care has been devoted to the formulae, and errors have been corrected wherever a minute supervision has been able to detect them. In its present enlarged and improved form, it is hoped that the work fairly represents the existing condition of the science, and that it may be found worthy a continuance of the very remarkable favor which it has so long enjoyed. PHILADELPHIA, May, 1869. 418. ADVERTISEMENT TO THE TENTH EDITION. THE rapid progress of chemical discovery during the last few years has rendered it necessary to make considerable alterations and additions in almost every part of the present Edition. The chapter on the General Principles of Chemical Philosophy has been re-written. Some considerable additions have been made to the descriptions of the metals, especially those of rarer occurrence, several of which have acquired greatly increased importance by the more exact investigations of late years. The distinguishing reactions of the several metals are also given more fully than in former editions. The greater part of the Organic Chemistry has been re-written, espe- cially the sections relating to the Hydrocarbons, Alcohols, and Acids, upon which great light has been thrown by recent investigations. The section on Animal Chemistry has been entirely revised. The Atomic Weights used in this Edition are those which are now almost universally received among Chemists, and the Notation has been altered in accordance with them. The Nomenclature has been simplified by discarding the word " of " in the names of salts, &c., using, for example, the term "silver nitrate" instead of " nitrate of silver." The Weights and Measures used are those of the French decimal system ; and Temperatures are expressed on the Centigrade scale, ex- cepting where the contrary is expressly stated. A comparative Table of the two scales is given at the end of the volume. H. BENCE JONES. HENRY WATTS. LONDON, October, 1868. ADVERTISEMENT TO THE THIED EDITION. THE correction of this Edition for the Press was the daily occupation of Professor Fownes, until a few hours pre- vious to his death in January, 1849. His wish and his endeavor, as seen in his manuscript, were to render it as perfect and as minutely accurate as possible. When he had finished the most important part of the Organic Chemistry, where the most additions were required, he told me he should " do no more," he had " finished his work." At his request I have corrected the Press throughout, and made a few alterations that .appeared desirable in the only part which he had left unaltered, the Animal Chemistry. The Index and the Press have also been corrected throughout by his friend Mr. Robert Murray. H. BENCE JONES, M.D. 30 GROSVENOR STREET, Jan., 1850. vi PREFACE TO THE FIRST EDITION. design of the present volume is to offer to the student commencing the subject of Chemistry, in a compact and inexpensive form, an outline of the general principles of that science, and a history of the more important among the very numerous bodies which Chemical Investigations have made known to us. The work has no pretensions to be considered a complete treatise on the subject, but is intended to serve as an introduction to the larger and more comprehensive systematic works in our own language and in those of the Continent ; and especially to prepare the student for the perusal of original memoirs, which, in conjunction with practical instruction in the laboratory, can alone afford a real acquaintance with the spirit of research and the resources of Chemical Science. It has been my aim throughout to render the book as practical as possible, by detailing, at as great length as the general plan permitted, many of the working processes of the scientific labora- tory, and by exhibiting, by the aid of numerous wood-engrav- ings, the most useful forms of apparatus, with their adjustments and methods of use. As one principal object was the production of a convenient and useful class-book for pupils attending my own lectures, I have been induced to adopt in the book the plan of arrangement fol- lowed in the lectures themselves, and to describe the non-metallic vii viii PKEFACE. elements and some of their most important compounds before discussing the subject of the general philosophy of Chemical Science, and even before describing the principle of the equiva- lent quantities, or explaining the use of the written symbolical language now universal among Chemists. For the benefit of those to whom these matters are already familiar, and to render the history of the compound bodies described in the earlier part of the work more complete, I have added in foot-notes the view adopted of their Chemical Constitution, expressed in symbols. I have devoted as much space as could be afforded to the very important subject of Organic Chemistry ; and it will, I believe, be found that there are but few substances of any general interest which have been altogether omitted, although the very great number of bodies to be described in a limited number of pages rendered it necessary to use as much brevity as possible. GEO. FOWNES. UNIVERSITY COLLEGE, LONDON. October 5, 1847. CONTENTS. PAGE INTRODUCTION ........ 25 PART I. PHYSICS. OF DENSITY AND SPECIFIC GRAVITY ..... 27 Methods of determining the Specific Gravities of Fluids and Solids 27 Construction and Application of the Hydrometer . 32 OF THE PHYSICAL CONSTITUTION OF THE ATMOSPHERE, AND OF GASES IN GENERAL ....... 35 Elasticity of Gases; Construction and Use of the Air-pump . 36 Weight and Pressure of the Air Barometer ... 38 Law of Mariotte : Relations of Density and Elastic force: Cor- rection of Volumes of Gases for Pressure . . 39 HEAT ......... 42 Expansion Thermometers . . . . . 42 Different Rates of Expansion among Metals. Compensation- pendulum ....... 45 Daniell's Pyrometer ...... 47 Expansion of Liquids Absolute Expansion of Mercury Maxi- mum Density of Water ..... 48 Expansion of Gases Ventilation Movements of the Atmos- phere ........ 51 Conduction of Heat ...... 54 Change of State Latent Heat ..... 55 Ebullition Steam ...... 57 Distillation . ....... 61 Evaporation at low temperatures .... 62 Tension of Vapors at different temperatures ... 63 Vapor of Water in the Atmosphere Hygrometry . . 65 Liquefaction of Permanent Gases .... 66 Production of Cold by Evaporation .... 68 Capacity for Heat Specific Heat .... 69 Relations between the Specific Heat and Atomic Weight of Ele- mentary Bodies ...... 72 Sources of Heat ....... 74 Relation between Heat and Mechanical Force Mechanical Equivalent of Heat ...... 75 Dynamical Theory of Heat ..... 77 ix X CONTENTS. PAGE LIGHT ..... Reflection, Refraction, and Polarization of Light . . 83 Dispersion Relation between Color and Refrangibility Solar Spectrum Spectral Analysis . 85 Double Refraction and Polarization Circular Polarization Soleil's Saccharimeter ...... 91 Heating and Chemical Rays of the Spectrum Photography Radiation, Reflection, Absorption, and Transmission of Heat . 99 MAGNETISM ....... 107 Magnetic Polarity Natural and Artificial Magnets . . 107 Terrestrial Magnetism ..... 109 ELECTRICITY . . . * . . . 114 Electrical Excitation Polarity Induction Charge and Dis- charge . . . . . ' . Electrical Machines ...... 116 Accumulation of Electricity Leyden jar Electrophorus ....... 119 Electric Current Development of Electricity by Chemical Ac- tion Voltaic Battery . . . 119 Thermo-electricity ...... 121 Animal Electricity ...... 122 Electro-magnetism Galvanoscopes and Galvanometers Induc- tion of Magnetism by Electricity, and of Electricity by Mag- netism ........ 122 Electricity of Vapor ...... 126 PART II. CHEMISTRY OF ELEMENTARY BODIES. Nonmetallic Elements ...... 127 Oxygen ........ 128 Collection and Preservation of Gases Pneumatic Trough Gas-holder ....... 129 Oxides Acid, Basic, and Neutral Oxides Salts Chemical Nomenclature ...... 132 Ozone ........ 135 Hydrogen . . . . . . . 136 Diffusion, Effusion, Transpiration, and Occlusion of Gases . 137 Combination of Oxygen and Hydrogen Oxy-hydrogen Blow- pipe Slow Combustion of Hydrogen Surface action of Platinum ....... 140 Water Its Composition by Weight and Volume Natural Water Sea, River, and Spring Water Water of Hydra- tion Water of Crystallization Solubility of Salts . 143 Liquid Diffusion Dialysis Osmose Absorption of Gases by Water ........ 148 Hydrogen Dioxide . . . ... . 153 CONTENTS. XI PAGE Nitrogen . . . . . . . 153 Atmospheric air Eudiometry . ... 154 Oxides and Oxygen-acids of Nitrogen . . . 157 Nitrogen and Hydrogen Ammonia Ammoniacal salts . 162 Carbon ........ 163 Compounds of Carbon and Oxygen Carbonates . . 165 Compounds of Carbon and Hydrogen Methane, or Marsh-gas Ethene, or Olefiant gas Coal and Oil Gases . . 169 Combustion and the structure of Flame Furnaces Lamps Blowpipe ... . 172 Chlorine ........ 179 Hydrochloric acid . . . . . .181 Oxides and Oxacids of Chlorine .... 183 Chlorine and Nitrogen Chlorine and Carbon . . 187 Bromine ........ 188 Iodine ........ 188 Fluorine . . . . . . . 192 Sulphur . . . . . . . .193 Oxides and Oxacids of Sulphur .... 194 Compounds of Sulphur and Hydrogen .... 200 Compounds of Sulphur and Carbon .... 202 Compounds of Sulphur with Chlorine, Bromine, and Iodine . 203 Selenium ........ 204 Tellurium . . . . . -. . .205 Boron ........ 208 Boric Oxide and Acid ...... 208 Boron Nitride ...... 208 " Chloride and Bromide . . . . 209 Silicium or Silicon ...... 209 Silica or Silicic Oxide Silicates .... 210 Silicium Hydride Compounds of Silicium with Chlorine and Bromine . . . . . . . 211 Phosphorus . . . . . . . .212 Oxides and Oxacids of Phosphorus .... 213 Compounds of Phosphorus and Hydrogen . . . 215 Compounds of Phosphorus with Chlorine, Bromine, Iodine, Sulphur, and Selenium .... 216 ON THE GENERAL PRINCIPLES OP CHEMICAL PHILOSOPHY. The Laws of Combination by Weight. 1. Constancy of Compo- sition. 2. Law of Multiples. 3. Law of Equivalents . 219 Monogenic and Polygenic Elements .... 221 Atomic Weights Atoms and Equivalents Substitution 222 xii CONTENTS. Symbolic Notation ...... 225 Table of Elementary Bodies with their Symbols and Atomic Weights ........ 226 Physical and Chemical Relations of Atomic Weights . 227 Laws of Combination by Volume ..... 228 The Atomic Theory ...... 229 Equivalent or Saturating power of Elementary Bodies Ar- tiads and Perissads Monads Dyads, &c. . . 230 Constitutional Formulae ..... 231 Combination of Similar Atoms ..... 232 Variation of Equivalency ..... 233 Classification of Elementary Bodies according to their Equi- valent power or Atomicity ..... 236 Compound Radicals or Residues .... 237 Chemical Affinity . . . . . .239 Relations of Heat to Chemical Affinity ... 241 ELECTRO-CHEMICAL DECOMPOSITION OR ELECTROLYSIS ; CHEMISTRY OF THE VOLTAIC PILE ...... 245 Definite amount of Electrolytic Decomposition Voltameter . 248 Division of Bodies into Electro-positive, Basylous, or Ziricous and Electro-negative, Acid or Chlorous .... 251 Voltaic Batteries ...... 252 Heat developed by the Electric Current .... 255 Crystallization Crystalline Form .... 257 Systems of Crystallography ..... 260 Isomorphism ....... 264 Chemistry of the Metals . .... 267 Physical Properties of Metals ..... 267 Chemical Relations: Alloys ..... 270 Compounds of Metals with Metalloids Classification of Metals 271 Metallic Chlorides ...... 273 Bromides ....... 275 Iodides ...... 276 Fluorides ....... 276 Cyanides ...... 277 Oxides ....... 278 Oxygen-salts or Oxysalts .... 280 Basicity of Acids Normal, Acid and Double Salts 282 Phosphates Orthophosphates, Metaphosphates, and Pyrophosphates ..... 285 " Sulphides ...... 287 " Selenides and Tellurides 289 CLASS I. MONAD METALS. Potassium ........ 290 Sodium . . . . . . . .299 Alkalimetry . . . . . . . 303 Ammonium ........ 310 Ammoniacal Salts ...... 311 Amic Acids and Amides . . 314 CONTENTS. Xlll PAGE Lithium ........ 316 Ccesium and Rubidium ...... 316 Silver ........ 317 CLASS II. DYAD METALS. Group L Metals of the Alkaline Earths .... 323 Barium, 323 Strontium, 325 Calcium, 326. Group II. Metals of the Earths ..... 332 Aluminium (tetrad?), 333 Beryllium, or Glucinum (tetrad?), 337 Zirconium (tetrad), 338 Thorinum, or Thorium, 339. Cerium, Lanthanum, and Didymium, 340 Yttrium and Er- bium, 342. Reactions of the Earth-metals ..... 343 Manufacture of Glass, Porcelain, and Earthenware . . 344 Group III. Magnesium, 347 Zinc, 351 Cadmium . . 352 Group IV. Copper, 353 Mercury, 357 Ammoniacal Mercury- compounds . ..... 362 CLASS III. TRIAD METALS. Thallium ........ 365 Gold ........ 369 CLASS IV. TETRAD METALS. Group I. Platinum Metals ...... 372 Platinum, 372 Ammoniacal Platinum compounds, 374 Palla- dium, 378 Rhodium, 380 Iridium, 382 Ruthenium, 385. Osmium, 387. Group II. Tin, 389 Titanium .... 393 Group III. Lead ....... 344 Group IV. Iron Metals . . . . . . 397 Iron, 397 Nickel, 405 Cobalt, 407 Manganese, 410 Ura- nium, 414 Indium, 416. CLASS V. PENTAD METALS. Antimony, 418 Arsenic, 422 Bismuth, 427 Vanadium, 429. Tantalum, 432 Niobium or Columbium, 434. CLASS VI. HEXAD METALS. Chromium, 437 Tungsten or Wolfram, 441 Molybdenum . 444 PART III. ORGANIC CHEMISTRY. INTRODUCTION ....... 447 THE ELEMENTARY OR ULTIMATE ANALYSIS OF ORGANIC COMPOUNDS . 448 Empirical and Molecular Formulae . 457 XIV CONTENTS. PAGE DETERMINATION OF THE DENSITY OF VAPORS . . . 459 DECOMPOSITION AND TRANSFORMATION OF ORGANIC COMPOUNDS . 462 CLASSIFICATION OF ORGANIC COMPOUNDS ORGANIC SERIES . 466 Rational Formulae of Organic Compounds Isomerism . 472 HYDROCARBONS : First Series, C n H 2n _ 2 Paraffins . ... 474 Second Series, C n H 2 n Olefines . .... 480 Third Series, C n H 2n _ 2 : Ethine or Acetyline Propine or Allylene Quavtine or Cro- tonylene Quintine or Valerylene Sextine or Diallyl . 484 Fourth Series, C n H 2n _ 4 : Quintone or Valylene ...... 488 Terpenes, C 10 H, 6 Turpentine oil Volatile oils isomeric with Turpentine oil Caoutchouc Gutta-percha Volatile oils in general ....... 488 Fifth Series, C n H 2n _ 6 Aromatic Hydrocarbons . . . 492 Benzene or Benzol ...... 493 Toluene or Methyl-benzene ..... 495 Xylene or Dimethyl-benzene ..... 497 Ethyl-benzene ...... 498 Isomeric Hydrocarbons, C 9 H, 2 Cumene Mesitylene Isomeric Hydrocarbons, C 10 H 14 Cymene . . . 499 Amyl-benzene, C n H 16 . . . . .500 Sixth Series, C n H 2n _ 8 Phenylene Cinnamene . . 500 Seventh Series, C n H 2n _, Cholesterin . . . .502 Eighth Series, C n H 2n _ 12 Naphthalene . ... 502 Ninth Series, C n H 2n _ 14 Diphenyl Dibenzyl . . .503 Tenth Series, C n H 2n _, 6 Stilbene .... 604 Eleventh Series, C n H 2n _ 18 . Anthracene, or Paranaphthalene Pyrene Retene . . . . . . 504 Twelfth Series, C n H 2n _ 24 . Chrysene .... 505 Appendix to Hydrocarbons: Coal, Petroleum, Naphtha, and allied substances ....... 505 ALCOHOLS AND ETHERS , . . . . . 508 Monatomic Alcohols and Ethers . . . . . 510 1. Containing the Radicals C n H 2 n+l, homologous with Methyl . 510 Methyl alcohol and ethers , , , . . 512 Ethyl alcohol and ethers . , . . -515 Commercial Spirit Wine Beer Vinous Fermentation Ethyl Chloride or Chlorethane. , , , .522 Ethyl Bromide and Iodide . 522 Ethyl Oxide or Ethylic Ether 523 CONTENTS. XV Ethyl Nitrate ...... 526 Ethyl Sulphates . . . . . .526 Ethyl Sulphites ...... 527 Ethyl Phosphates and Borates . . . .528 Ethyl Silicates ...... 529 Ethyl Sulph-hydrate or Mercaptan .... 529 Ethyl Sulphides ...... 530 Triethylsulphurous compounds ..... 530 Propyl alcohols and ethers ... . . 531 Quartyl or Butyl alcohols and ethers .... 532 Quintyl or Amyl alcohols and ethers . . . 535 Sextyl or Hexyl alcohols and ethers . . . . 539 Septyl or Heptyl alcohols and ethers . . . 540 Octyl alcohols and ethers . . . . 541 Nonyl alcohol Sexdecyl or Cetyl alcohol . . 542 Ceryl alcohol Melissyl alcohol .... 542 2. Monatomic Alcohols, CnH 2n O. Vinyl alcohol Allyl alcohol .... 543 3. Monatomic Alcohols, OH 2n _ 2 0. Camphol . . . . . . .546 4. Monatomic Alcohols, C n H 2n _gO. Aromatic Alcohols . 547 Primary Aromatic Alcohols ..... 548 Benzyl alcohol ...... 518 Xylyl alcohol Cymyl alcohol Sycoceryl alcohol . . 549 Secondary Aromatic Alcohols ; Phenols . . . 550 Phenol, C 6 H 6 Methyl phenate or Anisol Chlorophenols Nitrophenols .. ... 7 550 Cresol, C 7 H 8 Eight-carbon or Xylylic phenols . . 553 Ten-carbon Phenols Thymol .... 556 5. Monatomic Alcohols, CnH 2n _ 8 . .... 554 Cinnyl alcohol Cholesterin .... 654 Diatomic Alcohols and Ethers ...... 555 1. Diatomic Alcohols, C n H 2 n+ 2 2 . Glycols . . 555 Ethene alcohol or Glycol, C 2 H 6 2 . . . . .556 Ethene Chloride . . 558 Products of the action of Chlorine on Ethene Chloride Chlorides of Carbon ..... 559 Ethene Bromide and Iodide .... 560 Oxygen-ethers of the Glycols Ethene Oxide . . 560 Polyethenic Alcohols ..... 561 2. Diatomic Phenols ...... 562 Oxyphenol, Oxyphenic acid, or Pyrocatechin Orcin . 562 Guaiacol and Creosol Creosote .... 563 Veratrol Anisic Alcohol .... 564 Triatomic Alcohols and Ethers ..... 565 Methenyl Ethers Methenyl Chloride or Chloroform Bromo- form lodoform ...... 565 Propenyl Alcohol or Glycerin, C 3 H 8 3 . . . .666 XVI CONTENTS. PAGE Polyglycerins ....... 569 Quintenyl Alcohol, or Amyl-glycerin .... 569 Triatomic Phenols Pyrogallol or Pyrogallic acid Phloro- glucin Frangulin ..... 570 Tetratomic Alcohols and Ethers . . . . .571 Erythrite Propylphycite ..... 571 Pentatomic Alcohols. ...... 572 Pinite and Quercite ...... 572 Hexatomic Alcohols and Ethers ..... 572 Saturated Hexatomic Alcohols- Mannite Dulcite . 572 Glucoses ........ 574 Ordinary Glucose Dextroglucose Dextrose . . 575 Maltose Levulose Mannitose .... 577 Galactose Inosite or Phaseomannite Sorbin, or Sorbite Eucalyn ....... 578 Glucosides ....... 578 Aesculin Amygdalin Chitin Gallotannic acid Gly cyr- rhizin Myronic acid Phlorizin Quercitrin Salicin Populin Helicin Solanine Thujin Xanthorhamnin Indican ....... 579 Polyglucosic Alcohols ..... 583 Cane-sugar or Saccharose Parasaccharose Melitose Melez- itose Trehalose Mycose Milk-sugar, Lactin, or Lactose 584 Gum ........ 588 Oxygen-ethers or Anhydrides of the Polyglucosic alcohols . 589 Starch Dextrin Starch from Iceland moss Inulin . 589 Cellulose Woody fibre Xyloidin and Pyroxylin . . 592 Glycogen ....... 594 ORGANIC ACIDS ....... 595 Monatomic Acids ...... 597 Fatty Acids, C n H 2n 2 ...... 597 Formic Acid . . . . . . 604 Acetic Acid ....... 606 Metallic Acetates ..... 607 Acetic Ethers ...... 610 Acetic Chloride and Oxide .... 611 Acids derived from Acetic Acid by substitution. Chloracetic, Bromacetic, and lodacetic acids Thiacetlc acid Amidacetic acid, or Glycocine Methyl-glycocine, or Sarcosine ...... 612 Propionic acid Chloropropionic and Bromopropionic acids Aniidopropionic acid, or Alanine . . 615 Butyric acid . . . . . . .616 Valeric or Valerianic acid .... 617 Caproic acid Amidocaproic, or Leucine . . 619 CEnanthylic acid ...... 619 Caprylic acid Pelargonic acid Kutic or Capric acid . 620 Laurie acid Myristic acid .... 621 Palmitic acid ....... 621 Margaric acid ...... 623 CONTENTS. Xvil PAC; E Stearic acid Stearates Soaps .... 623 Arachidic acid ...... 625 Benic or Belienic, Cerotic, and Melissic acids . . 625 Acrylic Acids, C n H 2n _ 2 2 ..... 626 Normal Acrylic acids : Acrylic, Crotonic, Angelic, Hypogacic, and Oleic acids . . . . . . 626 Iso-acrylic acids ...... 629 Monatomic Acids, C n H 2n _ 4 2 . Parasorbic, Sorbic, and Gamphic acids ........ 632 Monatomic Acid, C n H 2n _ 6 2 . Hydrobenzoic acid . . 632 Monatomic Acids, C n H 2n - 8 2 . Aromatic acids . .. 633 Benzoic acid ...... 633 Metallic Benzoates Benzoic Chloride and Iodide . . 634 Benzoic Oxides Benzoic Sulphide Dibenzoyl . 635 Chlorobenzoic, Bromobenzoic, and Nitrobenzoic acids . 636 Amidobenzoic acid Acetamidobonzoic acid Benzamid- acetic, or Hippuric acid .... 636 Toluic acid ....... 638 Xylic, Cumic, and Cymic acids .... 639 Monatomic Acids, CnH 2n _ 10 2 . Cinnamic acid Atropic acid . 640 Diatomic and Monobasic Acids ..... 642 1. Acids of the Lactic Series, C n H 2n 3 . . . .642 Glycollic acid ...... 644 Lactic acid ....... 644 Leucic acid ....... 648 Carbonic acid Carbonic ethers Sulphocarbonic ethers . 648 2. _ Pyruvic Scries, C n H 2n _ 2 3 .... 651 Pyruvic, Convolvulinoleic, Jalapinoleic, and Ricinoleic acids 651 3. Series C n H 2n _ 4 3 652 Guaiacic acid ....... 652 4. Series O n H 2n _ 8 3 . .... 652 Oxybenzoic, Para-oxybenzoic, and Salicylic acids . . 652 Carbocresylic, Cresotic, Formobenzoic, Anisic acids . 654 Phloretic, Thymotic, and Thymyl-carbonic acids . . 655 5. Series CJI, n - lQ O z 655 Coumaric acid ..... . 655 6. Series C^H^Og. . ... 656 Benzilic acid ....... 656 Diatomic and Bibasic Acids ..... 656 1 . Oxalic or Succinic Series, C n H 2n _ 2 4 .... 657 Oxalic acid ....... 657 Malonic acid . .661 2* XV111 CONTENTS. PAGE Succinic acid, Pyrotartaric, Adipic, Suberic . . 662 Anchoic or Lepargylic Sebic or Sebacic, and Roccellic acids 663 2. Fumaric Series C n H 2n _ 4 4 ..... 663 Fumaric and Maleic acids Itaconic, Citraconic, and Mesa- conic acids ...... 663 Camphoric acid ...... 664 3. Series CJ^^O^ ..... 665 Mellitic acid ....... 665 4. Smes C n H 2n _ 8 4 . 665 Quinonic or Quinoylic acid Orsellinic acid Evernic acid 665 5. Series C n H 2n _ 10 4 ...... 665 Phthalic, Terephthalic, and Insolinic acids . . 665 Triatomic and Monobasic Acids ..... 666 Glyoxylie acid ...... 666 Glyceric acid Oxysalicylic, Eugetic, and Piperic acids . 667 Triatomic and Bibasic Acids ..... 668 Malic acid ........ 668 Triatomic and Tribasic Acids . . . . . 669 Aconitic and Carballylic acids .... 670 Tetratomic and Monobasic Acids ..... 670 Gallic acid ....... 670 Appendix to Gallic Acid: Tannic acids, or Tannins . . 671 Opianic acid ....... 673 Tetratomic and Bibasic Acids ..... 673 Tartaric acid ....... 673 Paratartaric or Racemic acid ..... 677 Rhodizonic acid ...... 678 Tetratomic and Tribasic Acids ..... 678 Citric acid ....... 678 Meconic acid Comenic and Pyrocomenic acids . . 679 Pentatomic Acids. Quinic or Kinic acid Quinone Hydroqui- none ........ 680 Hezatomic Acids. Mannitic, Saccharic, and Mucic acids . 681 Sulpho-acids. Sulphacetic Disulphometholic or Methionic Sulphopropionic Disulphetholic Sulphobenzoic Sulphoben- zolic Disulphoberizolic Sulphonaphthalic Disulphonaphthalic Isethionic and Ethionic acids 683 CONTENTS. PAGE ALDEHYDES ....... 684 Aldehydes derived from Monatomic Alcohols . . . 684 Formic Aldehyde Acetic Acetal Chloral Acrylic Al- dehyde, or Acrolein ...... 686 Benzoic Aldehyde, or Bitter-almond Oil Toluic Aldehyde Cumic, Sycocerylic, and Cinnamic Aldehydes Camphor . 690 Aldehydes derived from Diatomic Alcohols . . . 692 Glyoxal Salicylic Aldehyde, or Salicylol Derivatives of Salicylol Coumarin Anisic Aldehyde Furfurol and Fu- cusol ........ 692 KETONES Acetone Benzone, or Benzophenone Methyl-benzoyl 696 ORGANIC COMPOUNDS CONTAINING NITROGEN. CYANOGEN COMPOUNDS ...... 700 Cyanogen and Paracyanogen ..... 700 Hydrogen Cyanide Hydrocyanic or Prussic acid . 701 Metallic Cyanides ...... 703 Ferrocyanides Ferricyanides Prussian blue Cabalticy- anides Nitro-prussides ..... 706 Alcoholic Cyanides, or Hydrocyanic Ethers . . . 710 Isocyanides ....... 711 Cyanic and Cyanuric acids Fulminic acid Fulminuric acid 712 Cyanogen Chlorides Bromide, Iodide, and Sulphide . 716 Sulphocynnic acid Sulphocyanic ethers . . . 717 Allyl Isosulphocyanate, or Volatile Oil of Mustard Sinapoline Thiosinamine Sinamine . . . . 719 Seleniocyanates Melam ...... 720 Mellone and Mellonides . ... . . 721 Urea ........ 721 Uric acid ....... 723 Derivatives of Uric acid Allan toi'n Alloxan Alloxanic acid Mesoxalic acid Mycomelic acid Parabanic acid Oxaluric acid Thionuric acid Uramile Alloxantin, Di- aluric acid Hydurilic, Dilituric, and Violuric acids Vio- lantin Dibromobarbituric acid, or Bromalloxan Barbi- turic acid Murexide . 724 XX CONTENTS. PAGE COMPOUND AMMONIAS OR AMINES ..... 732 Amines derived from Monatomic Alcohols ; Monamines . 733 Bases of the Ethyl Series. Ethylamine Biethylamine Tri- ethylamine Tetrethyl-ammonium hydrate . . 735 Bases of the Methyl Series. Methylamine Bimethylamine Trimethylamine Tetramethyl-ammonium hydrate . 737 38 Bases of the Amyl Series. Amylamine Biamylamine Tri- amylamine Tetramyl-ammonium hydrate . . . Bases of the Aromatic Series ..... 739 Aniline ....... 739 Paraniline Chloraniline Nitraniline . . 741 Diphenylamine and Triphenylamine Cyananiline Ethyl- aniline Diethylaniline Ethyl-amyl-aniline Methyl- ethyl-amyl-phenylammonium hydrate . . . 742 Toluidine and Benzylamine .... 742 Xylidine Cumidine and Cymidine . . . 743 Naphthalidene ...... 743 Diamines and Triamines ...... 743 Ethene-diamine and Diethene-diamine . . . 743 Diethene- and Triethene-triamine . . . 744 Diphenyl-ethene-diamine and Diphenyl-diethene-diamine . 744 Methenyl-diphenyl-diamine, or Formyl-aniline . . . 745 Phenylene-diamine ...... 745 Carbodiphenyl-triamine, or Melaniline .... 745 Carbotriphenyl-triamine, or Phenyl-melaniline . . 745 Aniline Colors: Aniline-purple or Mauve . . . 745 Aniline-red Rosaniline ..... 746 Aniline-blue and Aniline-violet Aniline-yellow Chrysaniline 747 Appendix to the Alcoholic Ammonias. I. Artificial Organic Bases obtained from various Sources . 748 Bases obtained by Destructive Distillation: Chinoline Lepidine Cryptidine Picoline ..... 748 Bases from Animal Oil : Petinine Pyridine Lutidine Colli- dine Parvoline . . . . . 749 Bases from Aldehydes: Furfurine Amarine Thialdine Ala- nine and its homologues ..... 750 II. Natural Organic Bases or Alkaloids . . .751 Morphine, and its salts ..... 751 Narcotine Opianic and Hemipinic acids Cotarnine Codeine 753 Thebaine Pseudo-morphine Narceine Meconin . . 754 Cinchonine and Quinine Quinoi'dine . . . 754 Strychnine and Brucine . 756 CONTENTS. xxi Veratrine Harmaline Caffeine or Theine Theobromine Xantliine ....... 756 Sarcine Guanine Guanidine Creatin Creatinine Sarco- sine ........ 758 Berberine Piperine Conine Hyoscyamine Atropine Solanine Aconitine Delphinine Emetine Curarine . 760 III. Phosphorus, Antimony, and Arsenic Bases . . 760 Phosphims. Triethylphosphine and Trimethylphosphine . 760 Antimony-bases or Stibines. Triethylstibine or Stibethyl Tetra- methylstibonium hydrate ..... 761 Arsenic-bases. Triethylarsine ..... 762 Arsendimethyl or Cacodyl ..... 763 Arsenmonomethyl ...... 766 Triethylbismuthine or Bismethyl ..... 767 Borethyl ........ 767 Diatomic Bases of the Phosphorus and Arsenic Scries . . 767 IV. Compounds of Alcohol-radicals with Bivalent and Quadrivalent Metals and Metalloids ..... 768 Zinc Ethyl or Zinc Ethide, 768 Zinc Methide, 769 Potassium Ethide and Methide, 769 Mercuric Ethide, 769 Aluminium Methide and Ethide, 769 Ethyl-compounds of Tin, 770 Plumbic Ethide, 770 Alcoholic compounds of Tellurium, Selenium, and Sulphur, 771. AMIDES: Amides derived from Monatomic Acids Acetamide Benza- mide Secondary and Tertiary Monamides . . . 772 Amides derived from Diatomic and Monobasic acids . . 774 Amides derived from Diatomic and Bibasic acids Amides of Carbonic and Oxalic acids ..... 775 Amides derived from acids of higher Atomicity Malamide and Malamio acid Asparagin and Aspartic acid Amides of Citric acid ....... 778 UNCLASSIFIED ORGANIC COMPOUNDS. Organic Coloring Principles ..... 781 Indigo, 781 Coloring Matters from Lichens, 785 Cochi- neal, 787 Madder-colors ; Alizarin, Purpurin, Garancin, 787 Safflower, 788 Brazil-wood Log-wood Yellow Dye- woods Aloes . .... 789 Eesins and Balsams . 790 XX11 CONTENTS. PAKT IV. ANIMAL CHEMISTRY. PAGE INTRODUCTION ........ 792 Albuminous Substances ...... 793 Serum Albumin, 793 Egg Albumin, 794 Casein and Albu- minate or Protein, 794 Paralbumin, 795 Syntonin or Para- peptone, 795 Myosin, 796 Fibrino-plastic substance and Fibrinogen, or Paraglobin, or Paraglobulin, 796 Coagulated Albuminous substances, 797 Amyloid substance, 797 Pep- tone, 797 Metalbumin, 798 Haemoglobin, Haematoglobulin, or Hoematocrystallin, 798 Hrematin, 799 Mucin, Pyin, Pep- sin, Sugar-forming Ferments of Saliva and Pancreatic Fluid, 800 Gelatin and Chondrin, Horny Matter or Elastin, 801 Keratin, Fibroin, Spongin, 803 Conchiolin, Chitin, Protagon and Neurine, 803 Inosinic acid, Cnlorohodic acid, Excretin, 804. Animal Fluids . . . . . .805 Blood, 805 Urine, 807 Urinary Calculi, 809 Sweat, Saliva, Gastric Juice, Bile, 811 Pancreatic Fluid, Intestinal Juice, Lymph, Mucus and Pus, 815 Milk, 816. The Animal Textures . . . . . . 81 8 Nervous Substance, Contractile Substance, Elastic Tissue ; Skin 818 Bones and Teeth, 818. On Chemical Functions in Animals. Eespiration ........ 820 Nutrition of Animals ...... 822 Nutrition of Plants . 825 APPENDIX. Hydrometer Tables ...... 827 Table of the Tension of Vapor of Water at different Temperatures 829 Tables of the proportions by Weight and Volume of Anhydrous Alcohol in Spirits of different Densities . . . 831 Analysis of Mineral Waters ..... 832 Analysis of Fresh Spring and River Water . . . 834 Weights and Measures . . . . . 836 Comparison of French and English Measures . . . 837 Tables for converting degrees of the Centigrade Thermometer into degrees of Fahrenheit's Scale . . 839 LIST OF ILLUSTRATIONS. FIG. PAGE 1 Specific gravity bottle 28 2 " " " 28 3 a 29 4 Theorem of Archimedes 29 5 " " 30 6 Specific gravity of heavy solids.. 30 7 " " light " .. 31 8 Lovis beads 32 9 Hydrometer 32 10 Urinometer 33 11 Specific gravity of liquids 33 12 Elasticity of gases 35 13 Single air-puinp 36 14 Double 36 15 Improved " 37 16 " " 38 17 Barometer 39 18 " 40 19 " 41 20 Expansion of solids 42 21 " liquids 42 22 " " gases 42 23 Thermometer, graduation 43 24 " air , 44 " differential 44 26 Difference of expansion in metals 45 27* Pendulum, gridiron........ 46 " mercury 46 29 Compensation balance 46 30 Darnell's pyrometer 47 31 Expansion of mercury 49 !2 Comparative expansion of liquids 49 33 Atmospheric currents 52 34 " 52 35 " . 53 36 Boiling paradox 58 37 Steam-bath 60 38 " engine 61 39 Distillation ,.. 62 40 " and condensation 62 41 Tension of vapor .. 63 42 64 i:'. Wet-bulb hygrometer 66 44 Condensation of gases (>(! " " carbon dioxide... 67 46 Cold by evaporation 68 FIG. PAGE 47 Wollaston's cryophorus 68 48 Daniell's hygrometer 69 49 Joule's apparatus 76 50 " " 76 51 " 76 52 Light, reflection 84 53 " refraction 84 54 " " 85 55 " " 85 56 Spectrum 86 57 " 87 58 of metals s/ 59 Spectroscope 88 60 Absorption-lines 91 61 " 91 62 Polarization of light 92 63 " " 92 64 " " 92 65 Saccharimeter 94 66 Reflection of heat 99 67 " " 100 68 Effect of electric current on the magnetic needle 102 69 " " 103 70 Thermo-electric pile 103 71 " " 103 72 Melloni's instrument for measur- ing transmitted heat 104 73 Magnetic polarity 108 74 " " 108 75 Electro-repulsion ....; 115 76 Electroscope 115 77 Electric polarity 115 78 Electric machine 116 79 " 117 80 Leyden jar 118 81 Electrophorus 119 82 Volta'spile 120 83 Crown of oups 120 84 Cruikshank's trough 121 85 Relation of magnetic needle to electric current 122 86 Galvanoscope 123 87 Magnetic effect of current 123 88 " " 124 89 Electro-magnet 125 xxiii XXIV LIST OF ILLUSTRATIONS. FIG. PAGE 90 Ruhmkorff's coil 126 91 Apparatus for oxygen 128 92 Hydro-pneumatic trough 130 93 Transferring gases 130 94 Pepys' hydro- pneumatic appara- tus 131 95 Apparatus for hydrogen 136 96 Levity of hydrogen 137 97 Diffusion of gases 138 98 Heming's safety-jet 141 99 Musical sounds by combustion of hydrogen 142 100 Catalytic effect of platinum 143 101 Decomposition of water 143 102 Cavendish's eudiometer 144 103 Analysis of water 145 104 Solubility of salts 147 105 Dialysis 149 106 " 149 107 " 149 108 149 109 Osmose 150 110 150 111 " 150 112 Preparation of nitrogen 154 113 " " 155 114 lire's eudiometer 156 115 Simple " 157 116 Preparation of nitrogen mon- oxide 160 117 Crystalline forms of diamond. ..164 118 Preparation of carbon dioxide. ..166 119 Formation of connecting tubes of india-rubber 166 120 Blast furnace 173 121 Reverberatory furnace 173 122 Structure of flame 175 123 Mouth blow-pipe 175 124 Structure of blow-pipe flame 176 125 Argand lamp 176 126 Spirit-lamp 176 127 Mitchell's lamp 176 128 Gas-lamp 177 129 Bunsen's burner 177 130 Davy's safety lamp 178 131 Hemming's safety jet 179 132 Preparation of chlorine 180 133 < " hydrogen chloride.182 134 Safety-tube 183 135 Preparation of hydrogen iodide.,190 136 Crystals of sulphur 193 137 " " 193 138 Apparatus for hydrogens ulphide 201 139 Preparation of silica 210 140 " " phosphorus 212 141 Electrolysis of hydrogen chlo- ride 247 142 " " " 247 143 Voltameter 249 144 Decomposition without contact of metals 250 FIG. PAGE 145 Wollaston's battery 252 146 Daniell's " 253 147 Grove's " 253 148 Carbon " 254 149 Electrotype 254 150 Lead-tree 255 151 Goniometer, common 258 152 " reflecting 258 153 " principles of 259 154 Crystals, regular system 260 155 " dinaetric < 261 156 " rhombohedral ' 261 157 " trimetric < 261 158 " monoclinic * 262 159 " triclinic ' 262 160 Passage of cube to octohedron...263 161 " octohedron to tetra- hedron 263 162 Wire-drawing 268 163 Preparation of potassium 291 164 Salt-cake furnace. 302 165 Alkalimeter 305 166 " Gay-Lussac's 305 167 " " " 305 168 " Mohr's 305 169 Mohr's clamp 306 170 Apparatus lor determining car- bon dioxide 306 171 " " '' 306 173 Iron manufacture. Blast-furnace.402 174 Subliming tube for arsenic 425 175 Marsh's apparatus 427 176 Organic analysis, weighing tube..449 177 " " decomposing " 449 178 " chauffer 450 179 " " water-tube 450 180 " " carbon dioxide bulbs 450 181 " " apparatus com- plete 450 182 Hofmann's gas-apparatus 451 183 " " 451 184 " " " 451 185 Bulb for liquid 452 186 Determination of nitrogen 453 187 Pipette 453 188 Determination of nitrogen, Du- mas 454 189 Determination of nitrogen as am- monia 456 190 Determination of density of va- pors 459 191 Preparation of ether 524 192 " of chlorides of carbon..559 193 Starch-granules 589 194 Mohr's apparatus for benzoic acid 634 195 Preparation of tannic acid 672 196 Preparation of cacodyl 764 197 Blood globules 806 MANUAL OF CHEMISTRY. INTRODUCTION. THE Science of Chemistry has for its object the study of the nature and properties of all the materials which enter into the composition or struc- ture of the earth, the sea, and the air, and of the various organized or liv- ing beings which inhabit these latter. Every object accessible to man, or which may be handled and examined, is thus embraced by the wide circle of Chemical Science. The highest efforts of Chemistry are constantly directed to the discovery of the general laws or rules which regulate the formation of chemical com- pounds, and determine the action of one substance upon another. These laws are deduced from careful observation and comparison of the proper- ties and relations of vast numbers of individual substances; and by this method alone. The science is entirely experimental, and all its conclusions the results of skilful and systematic experimental investigation. The applications of the discoveries of Chemistry to the arts of life, and to the relief of human suffering in disease, are, in the present state of the- science, both very numerous and very important, and encourage the hope of still greater benefits from more extended knowledge than that now enjoyed. In ordinary scientific speech, the term chemical is applied to changes which permanently affect the properties or characters of bodies, in oppo- sition to effects termed physical, which are not attended by such conse- quences. Changes of decomposition or combination are thus easily distin- guished from those temporarily brought about by heat, electricity, mag- netism, and the attractive forces, whose laws and effects lie within the province of Physics or Natural Philosophy. Nearly all the objects presented by the visible world are of a compound nature, being chemical compounds, or variously disposed mixtures of chemi- cal compounds, capable of being resolved into simpler forms of matter. Thus, a piece of limestone or marble, by the application of a red-heat, is decomposed into quicklime and a gaseous body, carbon dioxide. Both lime 3 25 26 INTRODUCTION. and carbon dioxide are in their turn susceptible of decomposition, the for- mer into a metal, calcium, and oxygen, and the latter into carbon and oxygen. For this purpose, however, simple heat does not suffice, the reso- lution of these substances into their components demanding the exertion of a high degree of chemical energy. Beyond this second step of decom- position the efforts of Chemistry have hitherto been found to fail; and the three bodies, calcium, carbon, and oxygen, having resisted all attempts to resolve them into simpler forms of matter, are accordingly admitted into the list of elements; not from any belief in their real oneness of nature, but from the absence of any evidence that they contain more than one description of matter. The partial study of certain branches of Physical Science, as the physi- cal constitution of gases, the chief phenomena of heat and electricity, and a few other subjects, forms so indispensable an introduction to Chemistry itself, that it is rarely omitted in the usual courses of oral instruction. A sketch of these subjects is, in accordance with these views, placed at the commencement of the present volume. PART I. -PHYSICS. OF DENSITY AND SPECIFIC GRAVITY. IT is of great importance at the outset to understand clearly what is meant by the terms density and specific gravity. By the density of a body is meant its mass, or quantity of matter, compared with the mass or quantity of matter of an equal volume of some standard body arbitrarily chosen. Specific grav- ity denotes the weight of a body, as compared with the weight of an equal bulk, or volume, of the standard body, which is reckoned as unity.* In all cases of solids and liquids, the standard of unity adopted in this country is pure water at the temperature of 15-5 C. (60 Fahr.) Anything else might have been chosen ; there is nothing in water to render its adoption for the purpose mentioned indispensable: it is simply taken for the sake of convenience, being always at hand, and easily obtained in a state of perfect purity. An ordinary expression of specific weight, therefore, is a number explaining how many times the weight of an equal bulk of water is con- tained in the weight of the substance spoken of. If, for example, we say, that concentrated oil of vitriol has a specific gravity equal to 1-85, or that perfectly pure alcohol has a density of 0-794 at 15-5 C., we mean that equal bulks of these two liquids and of distilled water possess weights in the proportion of the numbers 1-85, 0-794, and 1; or 1850, 794, and 1000. It is necessary to be particular about the temperature, for, as will be here- after shown, liquids are extremely expansible by heat; otherwise a constant bulk of the same liquid will not retain a constant weight. It will be pro- per to begin with the description of the mode in which the specific gravity of liquids is determined : this is the simplest case, and the one which best illustrates the general principle. In order to obtain at pleasure the specific gravity of any particular liquid compared with that of water, it is only requisite to weigh equal bulks at the standard temperature, and then divide the weight of the liquid by the weight of the water ; the quotient will of course be greater or less than unity, as the liquid experimented on is heavier or lighter than water. Now, to weigh equal bulks of two fluids, the simplest and best method is clearly to weigh them in succession in the same vessel, taking care that it is equally full on both occasions, a condition very easy of fulfilment. A thin glass bottle, or flask, with a narrow neck, is procured, of the form represented below (fig. 1), and of such capacity as to contain, when filled to about half-way up the neck, exactly 1000 grains of distilled water at 15-5 C. Such a flask is readily procured from any one of the Italian *Inothor words, density moans comparative mass, and specific gravity comparativ These expressions, although really relating to distinct things, are often used quite indifferently in chemical writings, and without practical inconvenience, since mass and weight are directly proportional to each other. 28 DENSITY AND SPECIFIC GRAVITY. artificers, to be found in every large town, who manufacture cheap ther- mometers for sale. A counterpoise of the exact weight of the empty bottle is made from a bit of brass, an old weight, or something of the kind, and carefully adjusted by filing. The bottle is then graduated, by introducing water at 15-5, until it exactly balances the 1000-grain weight and counter- poise in the opposite scale ; the height at which the water stands in the neck is marked by a scratch, and the instrument is complete for use. The liquid to be examined is brought to the temperature of 15-5, and with it the bottle is filled up to the mark before mentioned ; it is then weighed, the counterpoise being used as before, and the specific gravity directly ascertained. Fig. 1. Fig. 2. A watery liquid in a narrow glass tube always presents a curved surface, from the molecular action of the glass, the concavity being upwards. It is better, on this account, in graduating the bottle, to make two scratches, as represented in the figure, one at the top and the other at the bottom of the curve : this prevents any future mistake. The marks are easily made by a fine, sharp triangular file, the hard point of which, also, it may be observed, answers perfectly well for writing upon glass, in the absence of a proper diamond pencil. It will be quite obvious that the adoption of a flask holding exactly 1000 grains of water has no other object than to save the trouble of a very tri- fling calculation; any other quantity would answer just as well, and, in fact, the experimental chemist is often compelled to use a bottle of much smaller dimensions, from scarcity of the liquid to be examined. When the specific gravity of a liquid is to be determined with great accu- racy, a case which frequently occurs in chemical inquiries, a little glass bottle is used, of the form showed in fig. 2. This bottle is provided with a perforated conical glass stopper, most accurately fitted by grinding. By completely filling the little bottle with liquid, and carefully removing the portion of liquid which is displaced when the stopper is inserted, an unal- DENSITY AND SPECIFIC GRAVITY. 29 srable measure is obtained. The least possible quantity of grease applied to the stopper greatly promotes the exact fitting. When the chemist has only a small quantity of a fluid at his Fig- 3. disposal, and wishes not to lose it, the little glass vessel (fig. 3) is particularly useful. It is formed by blowing a bubble on a glass tube. On that portion of the tube which is narrowed by drawing the tube out over a lamp, a fine scratch is made with a diamond. The bubble is filled up to this mark with a liquid whilst it stands in water the temperature of which is exactly known. A very fine funnel is used for filling the bubble, the stem of the funnel being drawn out so as to enter the tube, and the upper opening of the funnel being small enough to be closed by the finger. The glass stopper is only wanted as a guard, and does not require to fit perfectly. The determination of the specific gravity of a solid body is made according to the same principles, and may be performed with the specific-gravity bottle (fig. 2). The bottle is first weighed full of water ; the solid is then placed in the same pan of the balance, and its weight determined; finally, the solid is put into the bottle, displacing an equal bulk of water, the weight of which is determined by the loss on again weighing. Thus the weights of the solid and that of an equal bulk of water are obtained. The former divided by the latter gives the specific gravity. For example, the weight of a small piece of silver wire was found to be . . . . . . . . 98-18 grains. Glass bottle filled with water 294-69 " After an equal volume of water was displaced by the sil- ver, the weight was ....... Hence the displaced water weighed . . From this, the specific gravity of the silver ) 98-18 Another highly ingenious, but less exact method of determining the specific gravity of solids, is based on the well-known theorem of Archimedes. This theorem may be thus expressed : When a solid is immersed in a fluid, it loses a por- tion of its weight ; and this portion is equal to the weight of the fluid which it displaces ; that is, to the weight of its own bulk of that fluid. It is easy to give experimental proof of this very im- portant proposition, as well as to establish it by reason- ing. Figure 4 represents a little apparatus for the former purpose. This consists of a thin cylindrical vessel of brass, into the interior of which fits very accu- rately a solid cylinder of the same metal, thus exactly filling it. When the cylinder is suspended beneath the bucket, as seen in the sketch, the whole hung from the arm of a balance and counterpoised, and then the cylinder itself immersed in water, it will be found to have lost a certain weight; and that this loss is pre- cisely equal to the weight of an equal bulk of water, may then he proved by filling the bucket to the brim, whereupon the equilibrium will be restored. 3* 392-87 383-54 30 DENSITY AND SPECIFIC GRAVITY. Fig. 5. The consideration of the great hydrostatic law of fluid pressure easily proves the truth of the principle laid down. Let the reader figure to himself a vessel of water, having immersed in it a solid cylindrical or rec- tangular body, and so adjusted with respect to density, that it shall float indifferently in any part beneath the surface (fig. 5.) Now the law of fluid pressure is to this effect: The pressure exerted by a fluid on any point of the containing vessel, or on any point of a body immersed beneath its surface, is dependent, firstly, upon the density of the fluid, and, secondly, upon the vertical depth of the point in question below the surface. It is independent of the form and lateral dimensions of the vessel or immersed body. Moreover, owing to the peculiar physical constitution of fluids, this pressure is exerted in every direction, upward, downward, and laterally, a with equal force. The floating body is in a state of equilibrium ; there- fore the pressure downward caused by its gravitation must be exactly compensated by the upward trans- mitted pressure of the column of water a, b. But this pressure downward is obviously equal to the weight of an equal quantity of water, since the body of neces- sity displaces its own bulk. Hence the weight which Fig. 6. a body loses when immersed in, or floated on water, is equal to the weight of the volume of water displaced by that body. Whatever be the density of the substance, it will be buoyed up to this amount : in the case supposed, the buoyancy is equal to the whole weight of the body, which is tlms, while in the water, reduced to nothing. A little reflection will show that the same reasoning may be applied to a body of irregular form ; besides, a solid of any figure may be divided by the imagination into a multitude of little perpendicular prisms or cylin- ders, to each of which the argument may be applied. What is true of each individually must necessarily be true of the whole together. This is the fundamental principle; its application is made in the following manner : Let it be required, for example, to know the specific gravity of a body of extremely irregular form, as a small group of rock crys- tals : the first part of the operation consists in determining its absolute weight, or, more correctly speaking, its weight in air ; it is next suspended from the balance-pan by a fine horsehair, immersed completely in pure water at 15-5, and again weighed. It now weighs less, the dif- ference being the weight of the water it displaces, that is, the weight of an equal bulk. This being known, nothing more is required than to find, by division, how many times the latter number is contained in the former; the quotient will be the density, water, at the tempera- ture of 15-5, being taken = 1. For example: The quartz-crystals weigh in air When immersed in water, they weigh 293-7 grains. 180-1 " Difference, being the weight of an equal volume of water 113-6 293-7 = 2-59, the specific gravity required. 113-6 DENSITY AND SPECIFIC GRAVITY. 81 The rule is generally thus written: " Divide the weight in air by the loss of weight in water, and the quotient will be the specific p . 7 gravity." In reality it is not the weight in air which is required, but the weight the body would have in empty space: the error introduced, namely, the weight of an equal bulk of air is so trifling, that it is usually neglected. Sometimes the body to be examined is lighter than water, and floats. In this case, it is first weighed, and afterwards attached to a piece of metal heavy enough to sink it, and suspended from the balance. The whole is then exactly weighed, immersed in water, and again weighed. The dif- ference between the two weighings gives the weight of a quantity of water equal in bulk to both together. The light substance is then detached, and the same operation of weighing in air, and again in water, repeated on the piece of metal. These data give the means of finding the specific gravity, as will be at once seen by the following example: Light substance (a piece of wax) weighs in air . . 133-7 grains. Attached to a piece of brass, the whole now weighs . 183-7 " Immersed in water, the system weighs .... 38-8 " Weight of water equal in bulk to brass and wax . . 144-9 " Weight of brass in air 50-0 " Weight of brass in water 44-4 " Weight of equal bulk of water 5-6 " Bulk of water equal to wax and brass .... 144-9 " Bulk of water equal to brass alone 5-6 " Bulk of water equal to wax alone 139-3 " 133-7 = 0-9598 1393 ' In all such experiments it is necessary to pay attention to the tempera- ture and purity of the water, and to remove with great care all adhering air-bubbles,* otherwise a false result will be obtained. Other cases require mention in which these operations must be modified to meet particular difficulties. One of these happens when the substance is dissolved or acted upon by water. The difficulty is easily overcome by substituting some other liquid of known density which experience shows is without action. Alcohol or oil of turpentine may generally be used when water is inadmissible. Suppose, for instance, the specific gravity of crys- tallized sugar is required, we proceed in the following way : The specific gravity of the oil of turpentine is first carefully determined ; let it be 0-87 ; the sugar is next weighed in the air, then suspended by a horsehair, and weighed in the oil ; the difference is the weight of an equal bulk of the lat- ter ; a simple calculation gives the weight of a corresponding volume of water : * A simple plan of avoiding altogether the adhesion of air-bubbles, which often are not easily pen-rived, consists in heating the water to ebullition, introducing the body which has been weighed in the. air into the still boiling water, which is then allowed to cool to 15-5, when the second weighing is performed. 32 DENSITY AND SPECIFIC GRAVITY. Weight of sugar in air ..... Weight of sugar in oil of turpentine Weight of equal bulk of oil of turpentine . 87 : 100=217-5 : 250, 400 grains. 182-5 217-5 " the weight of an equal bulk of water ; hence the specific gravity of the sugar, 400 == 1-6. 250 If the substance to be examined consists of small pieces, or of powder, then the method first described, namely, that of the specific-gravity bottle, can alone be used. By this method the specific gravities of metals in powder, metallic oxides, and other compounds, and salts of all descriptions, may be determined with great ease. Oil of turpentine may be used with most soluble salts. The crystals should be crushed or roughly powdered to avoid errors arising from cavities in their substance. The specific gravity of a solid can also be readily found by immersing it in a transparent liquid, the density of which has been so adjusted that the solid body remains indifferently at whatever depth it may be placed. The specific gravity of the liquid must now be determined, and it will, of course, be the same as that of the solid. It is necessary that the liquid chosen for this experiment do not dissolve or in any way act upon the solid. Solutions of mercuric nitrate, or corrosive sublimate, can be used for bodies heavier than water, while certain oils, and essences, and mixtures of alcohol and water, can be conveniently employed for such substances as have a lower specific gravity than water. This method is not only adapted to the exact determination of specific gravities, but also serves in many cases as a means of readily distinguishing substances much resembling one another. Suppose, for instance, a solution of mercuric nitrate to have a specific gravity 3; a red amethyst (2-67) will then float upon, and a topaz of the same color (3-55) will sink in thi liquid. The theorem of Archimedes affords the key to the general doctrine of the equili- brium of floating bodies, of which an application is made in the common hydro- meter, an instrument for finding the specific gravities of liquids in a very easy and expeditious manner. When a solid body is placed upon the surface of a liquid specifically heavier than itself, it sinks down until it displaces a quan- tity of liquid equal to its own weight, at which point it floats. Thus, in the case of a substance floating in water, whose specific weight is one half that of the liquid, the position of equilibrium will involve the immersion of one half of the body, inasmuch as its whole weight is counterpoised by a quantity of water equal to half its volume. If the same body were put into a liquid of one half the specific gravity of water, if such could be found, it would then sink beneath the surface, and remain indifferently in any part. A floating body of known specific gravity may thus be used as an indicator of the specific gravity of a liquid. In this manner little glass beads (fig. 8) of known specific gravities are some- times employed in the arts to ascertain in a rude manner the specific Fig. 8. Fig. 9. DENSITY AND SPECIFIC GRAVITY. 33 gravity of liquids; the one that floats indifferently beneath the surface, without either sinking or rising, has of course the same specific gravity as the liquid itself; this is pointed out by the number marked upon the bead. The hydrometer (fig. 9) in general use consists of a floating vessel of thin metal or glass, having a weight beneath to maintain it in an upright position, an a stem above bearing a divided scale. The use of the instru- ment is very simple. The liquid to be tried is put into a small narrow jar, and the instrument floated in it. It is obvious that the denser the liquid, the higher will the hydrometer float, because a smaller displacement of liquid will counterbalance its weight. For the same reason, in a liquid of less density, it sinks deeper. The hydrometer comes to rest almost im- mediately, and then the mark on the stem at the fluid-level may be read off. Very extensive use is made of instruments of this kind in the arts ; they sometimes bear different names, according to the kind of liquid for which they are intended ; but the principle is the same in all. The graduation is very commonly arbitrary, two or three different scales being unfortu- nately used. These may be sometimes reduced, however, to the true num- bers expressing the specific gravity by the aid of tables of comparison drawn up for the purpose. (See APPENDIX.) Tables are likewise used to reduce the readings of the hydrometer at any temperature to those of the normal temperature. The division of the instrument from below, upward, into 100 parts, is much to be preferred to these arbitrary scales. Half of these divisions must be made upon the stem. The 100th division indicates the point of immer- sion in distilled water at 15-5 C. (60 Fahr.) If in another liquid the instrument sinks less deeply, for example to 60, then 60 volumes of this liquid weigh as much as 100 volumes of water. Hence the weight of 100 volumes, that is, the specific gravity, is ^ = 1-67. By this arrangement of the scale, it is evident that the reduction of the specific gravity is so simple that no tables are required. A very convenient and useful instrument in the shape of a small hydro- meter, for taking the specific gravity of urine, has been put into the hands of the physician ;* it may be packed into a pocket-case, with a little jar and a thermometer, and is always ready for use.f Fig. 10. Fin. 11. [* The graduation of the urinometer is such that each degree represents 1-1000, thus giving tin- ac-tual specific gravity without calculation, for the number of degrees on the scale cut by the surface of the liquid when this instrument is at rest, added to 1e 1013, about the average density of healthy urine. R. B.] [f The mode of determining the specific gravity of a liquid by means of a solid has been omitted 34 DENSITY AND SPECIFIC GRAVITY. The determination of the specific gravity of gases and vapors of volatile liquids is a problem of very great practical importance to the chemist: the theory of the operation is as simple as when liquids themselves are con- cerned, but the processes are much more delicate, and involve besides cer- tain corrections for differences of temperature and pressure, founded on principles yet to be discussed. It will be proper to defer the considerations of these matters for the present. The method of determining the specific gravity of a gas will be found described under the head of Oxygen, and that of the vapor of a volatile liquid in the Introduction to Organic Chemistry. in the text. It results from the theorem of Archimedes, that if any solid be immersed in water and then in any other liquid, the loss of weight sustained in each case will give the relative weights of equal bulks of the liquids, and on dividing the weight of the liquid by the weight of the water, the quotient will be the specific gravity of the liquid experimented on. For in- etancc, Set a piece of glass rod (fig. 10) be suspended from the balance pan and exactly counter- poised, then immerse it in water and restore the equipoise by weights added to the pan to which the glass is suspended, the amount will give the loss of weight by immersion or the weight of a bulk of water equal to that of the stopper. Now wipe the glass dry, and having removed the additional weights, immerse it in the other liquid, and restore the equipoise as before; this latter weight is the weight of a bulk of the liquid equal to that of the water. The latter divided by the former gives the specific gravity. For example : The glass stopper loses by immersion in water 171 grains. The glass stopper loses by immersion in alcohol 143 " ^|3 - .83 6) the specific gravity required, R. B.] OF THE PHYSICAL CONSTITUTION OF THE ATMOS- PHERE AND OF GASES IN GENERAL. IT requires some little abstraction of mind to realize completely the con- dition in which all things at the surface of the earth exist. We live at the bottom of an immense ocean of gaseous matter, which envelops every- thing, and presses upon everything with a force which appears, at first sight, perfectly incredible, but whose actual amount admits of easy proof. Gravity being, so far as is known, common to all matter, it is natural to expect that gases, being material substances, should be acted upon by the earth's attraction, as well as solids and liquids. This is really the case, and the result is the weight or pressure of the- atmosphere, which is noth- ing more than the effect of the attraction of the earth on the particles of air. Before describing the leading phenomena of the atmospheric pressure, it is necessary to notice one very remarkable feature in the physical consti- tution of gases, upon which depends the principle of an extremely valuable instrument, the air-pump. Gases are in the highest degree elastic; the volume or space which a gas occupies depends upon the pressure exerted upon it. Let the reader imagine a cylinder, a, closed at the bottom, in which Fig. 12. moves a piston, air-tight, so that no air can es- cape between the piston and the cylinder. Sup- pose now the piston be pressed downward with a certain force ; the air beneath it will be com- pressed into a smaller bulk, the amount of this compression depending on the force applied; if c the power be sufficient, the bulk of the gas may be thus diminished to one hundredth part or less. When the pressure is removed, the elasticity or tension, as it is called, of the included air or gas, will immediately force up the piston until it ar- rives at its first position. Again, take fig. 12, b, and suppose the piston to stand about the middle of the cylinder,having air beneath in its usual state. If the piston be|| now drawn upward, the air below will expand, so as to fill completely the increased space, and this to an apparently unlimited extent. A volume of air, which, under ordinary circumstances, occupies the bulk of a cubic inch, might, by the removal of the pressure upon it, be made to expand to the capacity of a whole room, while a renewal of the former pressure would be attended by a shrinking down of the air to its former bulk. The smallest portion of gas introduced into a large exhausted vessel becomes at once diffused through the whole space, an equal quantity being present in every part ; the vessel is full, although the gas is in a state of extreme tenuity. This power of expansion which air possesses may have, and probably has, in reality, a limit; but the limit is never reached in practice. We are quite safe in the assumption that for all purposes of experiment, however refined, air is perfectly elastic. It is usual to assign a reason for this indefinite expansibility by ascribing 35 36 PHYSICAL CONSTITUTION to the particles of material bodies, when a in gaseous state, a self-repulsive agency. This statement is commonly made somewhat in this manner : Fig. 13. matter is under the influence of two opposite forces, one of which tends to draw the particles together, the other to separate them. By the prepon- derance of one or other of these forces, we have the three states called solid, liquid, and gaseous. When the particles of matter, in consequence of the direction and strength of their mutual attractions, possess only a very slight power of motion, a solid substance results; when the forces are nearly balanced, we have a liquid, the particles of which in the interior of the mass are free to move, but yet to a certain extent are held together ; and lastly, when the attractive power seems to be completely overcome by its antagonist, we have a gas or vapor. Various names are applied to these forces, and various ideas entertained Fig. 14. OF THE ATMOSPHERE. 37 concerning them: the attractive forces bear the name of cohesion when they are exerted between particles of matter separated by an immeasurably small interval, and gravitation when the distance is great. The repulsive principle is often thought to be identical with the principle of heat. We shall return to this subject in discussing the nature of heat. (See page 77.) The ordinary air-pump, shown in section in fig. 13, consists essentially of a metallic cylinder, in which moves a tightly fitting piston, by the aid of its rod. The bottom of the cylinder communicates with the vessel to be exhausted, and is furnished with a valve opening upward. A similar valve, also opening upward, is fitted to the piston : these valves are made with slips of oiled silk. When the piston is raised from the bottom of the cylinder, the space left beneath it must be void of air, since the piston- valve opens only in one direction; the air within the receiver having on that side nothing to oppose its elastic power but the weight of the little valve, lifts the latter, and escapes into the cylinder. So soon as the piston begins to descend, the lower valve closes, by its own weight, or by the transmitted pressure from above, and communication with the receiver is cut off. As the descent of the piston continues, the air inclosed in the cylinder becomes compressed, its elasticity is increased, and at length it forces open the upper valve, and escapes into the atmosphere. In this manner, a cylinder full of air is at every stroke of the pump removed from the receiver. During the descent of the piston, the upper valve remains open, and the lower closed, and the reverse during the opposite movement. In practice, it is very convenient to have two such barrels or cylinders, arranged side by side, the piston-rods of which are formed into racks, having a pinion, or small-toothed wheel, between them, moved by a winch. By this contrivance the operation of exhaustion is much facilitated and the labor lessened. The arrangement is shown in fig. 14, on the preceding page. A simpler form of air-pump is thus constructed: the cylinder, which may be of large dimensions, is furnished with an accurately fitted solid piston, the rod of which moves, air-tight, through a contrivance called a stuffing-box, at the top of the cylinder, where also the only valve essential to the apparatus is to be found : the latter is a solid conical plug of metal, shown at a in the figure, kept tight by the oil contained in the chamber into which it opens. The communication with the vessel to be exhausted is made by a tube which enters th,e cylinder a little above the bottom. The action is the following: let the piston be supposed in the act of rising from the bottom of the cylinder: as soon as it passes the mouth of the tube t, all communication is stopped between the air above the piston and the vessel to be exhausted ; the inclosed air suffers compression until it acquires sufficient elasticity to lift the metal valve and escape by bubbling through the oil. When the piston makes its descent, and , this valve closes, a vacuum is left in the upper part of the cylinder, into which the air in the receiver rushes so soon as the piston has passed below the orifice of the connecting tube. In the silk-valved air-pump, exhaustion ceases when the elasticity of the air in the receiver becomes too feeble to raise the valve : in that last described the exhaustion may, on the contrary, be carried to an indefinite extent, without, however, under the most favorable circumstances, be- coming complete. The conical valve is made to project a little below the cover of the cylinder, so as to be forced up by the piston when the latter reaches the top of the Fig. 15. 38 PHYSICAL CONSTITUTION cylinder; the oil then enters and displaces any air that may be lurking in the cavity. It is a great improvement to the machine to supply the piston with a relief-valve opening upward; this may also be of metal, and contained within the body of the piston. Its use is F'9- 16. to avoid the momentary condensation of the air in the receiver when the piston de- scends. The pump is worked by a lever in the manner represented in figure 16. The air-pump may be used for condens- ing instead of for rarefying the air. If the cylinder (fig. 15) is filled with air from the opening (t), it may be forced by the rise of the piston through the valve (a) into a communicating chamber, and this operation may be frequently repeated. To return to the atmosphere. Air pos- sesses weight: a light flask or globe of glass, furnished with a stopcock and ex- hausted by the air-pump, weighs consider- ably less than when full of air. If the capacity of the vessel be equal to 100 cubic inches, this difference may amount to nearly 30 grains. The mere fact of the pressure of the at- mosphere may be demonstrated by securely tying a piece of bladder over the mouth of an open glass receiver, and then exhausting the air from beneath it ; the bladder will become more and more concave, until it suddenly breaks. A thin square glass bot- tle, or a large air-tight tin box, may be crushed by withdrawing the support of the air in the inside. Steam-boilers have been often destroyed in this manner by collapse, in consequence of the accidental formation of a partial vacuum within. After what has been said on the subject of fluid pressure, it will scarcely be necessary to observe that the law of equality of pres- sure in all directions also holds good in the ' case of the atmosphere. The perfect mo- bility of the particles of air permits the transmission of the force generated by their gravity. The sides and bottom of an exhausted vessel are pressed upon with as much force as the top. If a glass tube of considerable length could be perfectly exhausted of air, and then held in an upright position, with one of its ends dipping into a vessel of liquid, the latter, on being allowed access to the tube, would rise in its interior until the weight of the column balanced the pressure of the air upon the surface of the liquid. Now, if the density of this liquid were known, and the height and area of the column measured, means would be furnished for exactly estimating the amount of pressure exerted by the atmosphere. Such an instrument is the barometer: a straight glass tube is taken, about 36 inches in length, and sealed by the blowpipe flame at one extremity ; it is then filled with clean, OF THE ATMOSPHERE. 39 Fig. 17. dry mercury, care being taken to displace all air-bubbles, the open end stopped with a finger, and the tube inverted in the basin of mercury. On removing the finger, the fluid sinks away from the top of the tube, until it stands at the height of about 30 inches above the level of that in the basin. Here it remains supported by, and balancing the atmospheric pressure, the space above the mercury in the tube being of necessity empty. The pressure of the atmosphere is thus seen to be capable of sustaining a column of mercury 30 inches in height, or thereabouts: now such a column, having an area of one inch, weighs between 14 and 15 pounds: consequently such must be the amount of the pressure exerted upon every square inch of the surface of the earth, and of the objects situated thereon, at least near the level of the sea. This enormous force is borne without inconvenience by the animal frame, by reason of its perfect uniformity in every direction; and it may be doubled, or even tripled, without injury. A barometer may be constructed with other liquids besides mercury ; but as the height of the column must always bear an inverse proportion to the density of the liquid, the length of tube required will be often considerable; in the case of water it will exceed 33 feet. It is seldom that any other liquid than mercury is employed in the construction of this instru- ment. The Royal Society of London possessed a water barom- eter at their apartments at Somerset House. Its construction was attended with great difficulties, and it was found impos- sible to keep it in repair. It will now be necessary to consider a most important law which connects the volume occupied by a gas with the pressure made upon it, and is thus expressed: The volume of gas is inversely as the pressure ; the density and elastic force are directly as the pressure, and inversely as the volume. For instance, 100 cubic inches of gas under a pressure of 30 inches of mercury would expand to 200 cubic inches were the pressure reduced to one half, and shrink, on the contrary, to 50 cubic inches if the original pressure were doubled. The change of density must necessarily be in the inverse proportion to -that of the volume, and the elastic force follows the same rule. This, which is usually called the law of Mariotte, though really discovered by Boyle (1661), is easily demonstrable by direct experiment. A glass tube, about 7 feet in length, is closed at one end, and bent into the form represented in fig. 18, the open limb of the syphon being the longer. It is next attached to a board fur- nished with a movable scale of inches, and enough mercury is introduced to fill the bend, the level being evenly adjusted, and marked upon the board. Mercury is now poured into the tube until it is found that the inclosed air has been reduced to one half of its former volume ; and on applying the scale, it will be found that the level of the mercury in the open part of the tube stands very nearly 30 inches above that in the closed portion. The pressure of an additionnl "atmosphere" has consequently reduced the bulk of the contained air to one half. If the experiment be still continued until the volume of air is reduced to a third, it will be found that the column measures 60 inches, and so in like proportion as far as the experiment is carried. The above instrument is better adapted for illustration of the principle than for furnishing rigorous proof of the law; this has, however, been 40 PHYSICAL CONSTITUTION done. MM. Arago and Dulong published, in the year 1830, an account of certain experiments made by them in Paris, in which the law in question had been verified to the extent of 27 atmospheres. And with rarefied air, of whatever degree of rarefaction, the law has been found true. All gases are alike subject to this law, and all Fig. 18. vapors of volatile liquids, when remote from their points of liquefaction.* It is a matter of the greatest importance in practical chemistry, since it gives the means of making corrections for pressure, or deter- mining by calculation the change of volume which a gas would suffer by any given change of external pressure. Let it be required, for example, to solve the follow- ing problem: We have 100 cubic inches of gas in a graduated jar, the barometer standing at 29 inches; how many cubic inches will it occupy when the column rises to 80 inches? Now the volume must be inversely as the pressure: consequently a change of pressure in the proportion of 29 to 30 must be accompanied by a change of volume in the proportion of 30 to 29, the 30 cubic inches of gas contracting to 29 cubic inches under the conditions imagined. Hence the answer: 30 : 29 = 100 : 96-67 cubic inches. The reverse of the operation will be obvious. The pupil will do well to familiarize himself with the sim- ple calculations of correction for pressure. From what has been said respecting the easy com- pressibility of gases, it will be at once seen that the atmosphere cannot have the same density, and cannot exert equal pressures at different elevations above the sea-level, but that, on the contrary, these must dimin- ish with the altitude, and very rapidly. The lower strata of air have to bear the weight of those above them; they become, in consequence, denser and more compressed than the upper portions. The following table, which is taken from Prof. Graham's work, shows in a very simple manner the rule followed in this respect: Height above the sea, in miles. 2-705 5-41 . 8-115 10-82 . 13-525 16-23 Volume of air. 1 . 2 . 4 . 8 . 16 . 32' 64 , Height of barometer, in inches. . 30 15 . 7-5 3-75 . 1-875 0-9375 0-46875 The numbers in the first column form an arithmetical series, by the con- stant addition of 2-705; those in the second column an increasing geomet- rical series, each being double its predecessor; and those in the third, a decreasing geometrical series, in which each number is the half of that standing above it. * Near the liquefying point the law no longer holds ; the volume diminishes more rapidly than the theory indicates, a smaller amount of pressure being then sufficient. OF THE ATMOSPHERE. 41 In ascending into the air in a balloon, these effects are well observed; the expansion of the gas within the machine, and the fall of the mercury in the barometer, soon indicate to the voyager the fact of his having left below him a considerable part of the whole atmosphere. The invention of the barometer, which took place in the year 1643, by Torricelli, a pupil of the celebrated Galileo, Fig.19. speedily led to the observation that the atmospheric pressure at the same level is not constant, but possesses, on the con- trary, a small range of variation, seldom exceeding in Europe 2 or 2-5 inches, and within the tropics usually confined within much narrower limits. Two kinds of variations are distin- guished: regular or horary, and irregular or accidental. It has been observed that in Europe the height of the barometer is greatest at two periods in the twenty-four hours, depending upon the season. In winter, the first maximum takes place about 9 A. M., the first minimum at 3 p. M., after which the mercury again rises and attains its greatest elevation at 9 in the evening: in summer these hours of the aerial tides are somewhat altered. The accidental variations are much greater in amount, and render it extremely difficult to trace the regu- lar changes above mentioned. The barometer is applied with great advantage to the mea- surement of accessible heights, and it is also in daily use for foretelling the state of the weather ; its indications are in this respect extremely deceptive, except in the case of sudden and violent storms, which are almost always preceded by a rapid fall in the mercurial column. It is often extremely useful in this respect at sea. To the practical chemist a moderately good barometer is an indispensable article, since in all experiments in which volumes of gases are to be estimated, an account must be taken of the ;itniospheric pressure. Fig. 19 represents a very convenient and economical syphon-barometer for this purpose. A piece of new and stout tube, of about one third of an inch in diam- eter, is procured at the glass-house, sealed at one extremity, and bent into the syphon-form, as represented. Pure and warm mercury is next introduced by successive portions until the tube is completely filled, and the latter being held in an upright position, the level of the metal in the lower and open limb is conveniently adjusted by displacing a portion with a stick or glass rod. The barometer is, lastly, attached to a board, and furnished with a long scale, made to slide, which may be of box-wood, with a slip of ivory at each end. When an observation is to be taken, the lower extremity or zero of the scale is placed exactly even with the mercury in the short limb, and then the height of the column is at once read off. 4* 42 HEAT. HEAT. IT will be convenient to consider the subject of heat under several sec- tions, and in the following order : 1. Expansion of bodies, or effects of variations of temperature in alter- ing their dimensions. 2. Conduction, or transmission of heat. 3. Change of state. 4. Specific heat. 5. Sources of heat. 6. Dynamical theory of heat. The phenomena of radiation must be deferred until a sketch has been given of the science of light. EXPANSION. If a bar of metal of such magnitude as to fit accurately to a gauge, when cold, be heated considerably, and again applied to the gauge, it will be found to have become enlarged in all its dimensions. When cold, it will once more enter the gauge. Again, if a quantity of liquid contained in a glass bulb, furnished with a narrow neck, be plunged into hot water, or exposed to any other source Fig. 20. Fig. 21. Fig. 22. of heat, the liquid will mount in the stem, showing that its volume has been increased. The bulb, however, has likewise expanded by the heat, and its capacity has consequently been augmented. The rise of the liquid in the tube, therefore, denotes the difference between these two expansions. Or, if a portion of air be confined in any vessel, the application of a slight degree of heat will suffice to make it occupy a space sensibly larger. This most general of all the effects of heat furnishes in the outset a principle, by the aid of which an instrument can be constructed capable of taking cognizance of changes of temperature in a manner equally ac- curate and convenient : such an instrument is the thermometer. A capillary glass tube is chosen, of uniform diameter: one extremity is closed and expanded into a bulb, by the aid of the blowpipe flame, and the HEAT. 43 Fig. 23. other somewhat drawn out, and left open. The bulb is now cautiously heated by a spirit-lamp, and the open extremity plunged into a vessel of mercury, a portion of which rises into the bulb when the latter cools, replacing the air which had been expanded and driven out by the heat. By again applying the flame, and causing this mercury to boil, the remain- der of the air is easily expelled, and the whole space tilled with mercurial vapor. The open end of the tube must now be immediately plunged into the vessel filled with mercury ; as the metallic vapors condense, the pres- sure of the external air forces the liquid metal into the instrument, until finally the tube is completely filled with piercury. The thermometer thus filled is now to be heated until so much mercury has been driven out by the expansion of the remainder, that its level in the tube shall stand at common temperatures at the point required. This being satisfactorily adjusted, the heat is once more applied, until the column rises quite to the top; and then the extremity of the tube is hermetically sealed by the blowpipe. The retraction of the mercury on cooling now leaves an empty space, which is essen- tial to the perfection of the instrument. The thermometer has yet to be graduated; and to make its indications comparable with those of other instruments, a scale, having at the least two fixed points, must be adapted to it- It has been observed, that the temperature of melting ice, that is to say, of a mixture of ice and water, is always constant; a thermometer, already graduated, plunged into s^uch a mixture, always marks the same degree of temperature, and a simple tube filled in the manner described and so treated, exhibits the same effect in the unchanged height of the little mercurial column, when tried from day to day. The freezing- point of water, or melting-point of ice, constitutes then one of the invariable temperatures demanded. Another is to be found in the boiling-point of water, or, more accurately, in the temperature of steam which rises from boiling water. In order to give this temperature, which remains perfectly constant whilst the baro- metric pressure is constant, to the mercury of the thermometer, distilled water is made to boil in a glass vessel with a long neck, when the pressure is at 30 inches (fig. 23). The thermometer is then so placed that all the mercury is surrounded with steam. It quickly rises to a fixed point, and there it remains as long as the water boils, and the height of the barometer is unchanged. The tube having been carefully marked with a file at these two points, it remains to divide the interval into degrees: this division is entirely arbi- trary. The scale now most generally employed is the Centigrade, in which the space is divided into 100 parts, the zero being placed at the freezing- point of water. The scale is continued above and below these points, numbers below being distinguished by the negative sign. In England the division of Fahrenheit is still in use: the above-mentioned space is divided into 180 degrees; but the zero, instead of starting from the freezing-point of water, is placed 32 degrees below it, so that the tem- perature of ebullition is expressed by 212. The plan of Reaumur is nearly confined to a few places in the north of Germany and to Russia: in this scale the freezing-point of water is made 0, and the boiling-point 80. It is unfortunate that a uniform system has not been generally adopted in graduating thermometers: tliis would render unnecessary the labor which now so frequently has to be performed of translating the language 44 HEAT. of one scale into that of another. To effect this, presents, however, no great difficulty. Let it be required, for example, to know the degree of Fahrenheit's scale which corresponds to 60 C. Consequently, 100 C 180 F, or 5 C = 9 F. 5 : 9 = 60 : 108. But then, as Fahrenheit's scale commences with 32 instead of 0, that number must be added to the result, making 60 C = 140 F. The rule then will be the following : To convert Centigrade degrees into Fahrenheit degrees, multiply by 9, divide the product by 5, and add 32; to convert Fahrenheit degrees into Centigrade degrees, subtract 32, multiply by 5, and divide by 9. The reduction of negative degrees, or those below zero of one scale into those of another scale, is effected in the same way. For example, to con- vert 15 C. into degrees of Fahrenheit 9 We have 15 X + 32 = 27 + 32 = + 5 F. 5 In this work, temperatures will always be given in Centigrade degrees, unless the contrary is expressly stated. Mercury is usually chosen for making thermometers, on account of its regularity of expansion within certain limits, and because it is easy to have the scale of great extent, from the large interval between the freezing and boiling points of the metal. Other substances are sometimes used; alcohol is employed for estimating very low temperatures, because this liquid has not been frozen even at the lowest degree of cold which has been artificially produced. Air-thermometers are also used for some few particular purposes; indeed, the first thermometer ever made was of this kind. There are two modifica- tions of this instrument: in the first, the liquid into which the tube dips is open to the air; and in the second, shown in fig. 24, the atmosphere is completely excluded. The effects of expansion are in the one case compli- cated with those arising from changes of pressure, and in the other cease to be visible at all when the ivhole instrument is subjected to alterations of temperature, because the air in the upper and lower reservoir being equally affected by such changes, no alteration in the height of the fluid column Fig. 24. Q Fig. 25. HEAT. 45 can occur. Accordingly, such instruments are called differential thermom- eters, since they serve to measure differences of temperature between the two portions of air, while changes affecting both alike are not indicated. Fig. 25 shows another form of the same instrument. The air-thermometer may be employed for measuring all temperatures from the lowest to the highest; M. Pouillet has described one by which the heat of an air-furnace could be measured. The reservoir of this instru- ment is of platinum, and it is connected with a piece of apparatus by which the increase of volume experienced by the included air is determined. An excellent air-thermometer has been constructed and used by Rudberg, and more recently by Magnus and Regnault, for measuring the expansion of the air. Its construction depends on the law, that when air is heated and hindered from expanding, its tension increases in the same proportion in which it would have increased in volume if permitted to expand. All bodies are enlarged in their dimensions by the application of heat, and reduced by its abstraction, or, in other words, contract on being artifi- cially cooled: this effect takes place to a comparatively small extent with solids, to a larger amount in liquids, and most of all in the case of gases. Each solid and liquid has a rate of expansion peculiar to itself; gases, on the contrary, expand nearly alike for the same increase of heat. Expansion of Solids. The difference of expansibility among solids is very easily illustrated by the following arrangement: a thin, straight bar of iron is firmly fixed, by numerous rivets, to a similar bar of brass: so long as the temperature at which the two metals were united remains unchanged, the compound bar preserves its straight figure ; but any alteration of tem- perature gives rise to a corresponding curvature. Brass is more dilatable than iron; if the bar be heated, therefore, the former expands more than the latter, and forces the straight bar into a curve, whose convex side is the brass ; if it be artificially cooled, the brass contracts more than the iron, and the reverse of this effect is produced. Fig. 26. This fact has received a most valuable application. It is not necessary to insist on the importance of possessing instruments for the accurate mea- surement of time; such are absolutely indispensable to the successful cultivation of astronomical science, and not less useful to the navigator, from the assistance they give him in finding the longitude at sea. For a long time, notwithstanding the perfection of finish and adjustment be- stowed upon clocks and watches, an apparently insurmountable obstacle presented itself to their uniform and regular movement: this obstacle was the change of dimensions to which the regulating parts of the machine were subject by alterations of temperature. A clock may be defined as an instrument for registering the number of beats made by a pendulum : now the time of oscillation of a pendulum depends principally upon its length; any alteration in this condition will seriously affect the rate of the clock. The material of which the rod of the pendulum is composed is subject to expansion and contraction by changes of temperature ; so that a pendulum HEAT. adjusted to vibrate seconds at 15-5 would go too slow if the temperature rose to 20, from its becoming longer, and too fast if the temperature fell to 10, from the opposite cause. This great difficulty has been overcome by making the rod of a number of bars of iron and brass, or iron and zinc, metals whose rates of expan- sion are different, and arranging these bars in such a manner that the expansion in one direction of the iron shall be exactly compensated by that in the opposite direction of the brass or zinc, it is possible to maintain under all circumstances of temperature an invariable distance between the points of suspension and of oscillation. This is often called the gridiron pendulum; fig. 27 will clearly illustrate its principle; the shaded bars are supposed to be iron and the others zinc. Fig. 27. Fig. 28. Fig. 29. A still simpler compensation-pendulum is thus constructed. The weight or bob, instead of being made of a disc of metal, consists of a cylindrical glass jar containing mercury, which is held by a stirrup at the extremity of the steel pendulum-rod, fig. 28. The same increase of temperature which lengthens this rod, causes the volume of the mercury to enlarge, and its level to rise in the jar: the centre of gravity is thus elevated, and by properly adjusting the quantity of mercury in the glass, the virtual length of the pendulum may be made constant. In watches, the governing power is a horizontal weighted wheel, set in motion in one direction by the machine itself, and in the other by a fine spiral spring. The rate of going depends greatly on the diameter of this wheel, and the diameter is of ne- cessity subject to variation by change of tempera- ture. To remedy the evil thus involved, the cir- cumference of the balance-wheel is made of two metals having different rates of expansion, firmly soldered together, the more expansible being on the outside. The compound rim is also cut through in two places, as repre- sented in the drawing. When the watch is exposed to a high temperature, ana the diameter of the wheel becomes enlarged by expansion, each seg- HEAT. 47 Fig. 30. ment is made, by the same agency, to assume a sharper curve, whereby its centre of gravity is thrown inward, and the expansive effect completely compensated. Many other beautiful applications of the same principle might be pointed out: the metallic thermometer of M. Breguet is one of these. Mr. Daniell very skilfully applied the expansion of a rod of metal to the measurement of temperatures above those capable of being indicated by the thermometer. A rod of iron or pla- tinum, about five inches long, is dropped into a tube of black lead earthenware; a little cylinder of baked porcelain is put over it, and secured in its place by a pla- tinum strap and a wedge of porcelain. When the whole is exposed to heat, the ex- pansion of the bar drives forward the cylinder, which moves with a certain de- gree of friction, and shows, by the extent of its displacement, the lengthening which the bar has undergone. It remains, there- fore, to measure the amount of its displace- ment, which must be very small, even when the heat has been exceedingly intense. This is effected by the contrivance shown in figure 30, in which the motion of the longer arm of the lever carrying the vernier of the scale is multiplied by 10, in consequence of its superior length. The scale itself is made comparable with that of the ordinary thermometer, by plunging the instrument into a bath of mercury near its point of congela- tion, and afterwards into another of the same metal in a boiling state, and marking off the interval. By this instrument the melting-point of cast iron was fixed at 1530 C. (2786 F.), and the greatest heat of a good wind- furnace at about 1815 C. (3390 F.) The actual amount of expansion which different solids undergo by the same increase of heat has been carefully investigated. The following are some of the results of the best investigations, more particularly those of Lavoisier and Laplace. The fraction indicates the amount of expansion in length suffered by rods of the undermentioned bodies in passing from to 100 : Firwood* . English flint glass Platinumf Common white glass! Common white glass| Glass without lead Another specimen . Steel untempered 23TT TsVff Tempered Soft iron Gold steel ti *: TT7TT TTW rfc TtfW *7 Copper . Brass Silver . Lead Zinc . . i From the linear expansion, the cubic expansion (or increase of volume) may be calculated. When the expansion of a body in different directions is equal, as, for example, in glass, hammered metals, and generally in most uncrystallized substances, it will be sufficient to triple the fraction expressing the increase in one dimension. This rule does not hold true * In the direction of the vessels Kater. J Duloug and Petit. t Borda. Lavoisier and Laplace ; also Magnus. 48 HEAT. for crystals belonging to irregular systems, for they expand unequally in the direction of the different axes. Metals appear to expand pretty uniformly for equal increments of heat within the limits stated ; but above the boiling-point of water the rate of expansion becomes irregular and more rapid. The force exerted in the act of expansion is very great. In laying down railways, building iron bridges, erecting long ranges of steam-pipes, and in executing all works of the kind in which metal is largely used, it is indispensable to make provision for these changes of dimensions. In consequence of glass and platinum having nearly the same amount of expansion, a thin platinum wire may be fused into a glass tube, without any fear that the glass will break on cooling. A very useful little application of expansion by heat is that of the cut- ting of glass by a hot iron : this is constantly practised in the laboratory for a great variety of purposes. The glass to be cut is marked with ink in the required direction, and then a crack, commenced by any convenient method, at some distance from the desired line of fracture, may be led by the point of a heated iron rod along the latter with the greatest precision. Expansion of Liquids. The dilatation of a liquid may be determined by filling a thermometer with it, in which the relation between the capacity of the ball and that of the stem is exactly known, and observing the height of the column at different temperatures. It is necessary in this experiment to take into account the effects of the expansion of the glass itself, the observed result being evidently the difference of the two. Liquids vary exceedingly in this particular. The following table is taken from Pe"clet's Elements de Physique: Apparent Dilatation in Glass between and 100. Water ^ Hydrochloric acid, sp. gr. 1-137 . . . . ^V Nitric acid, sp. gr. 1-4 . . . . . . ^ Sulphuric acid, sp. gr. 1-85 ^ Ether T J Olive oil . j 1 ^ Alcohol ......... ^ Mercury -fa Most of these numbers must be taken as representing mean results ; for there are few liquids which, like mercury, expand regularly between these temperatures. Even mercury above 100 shows an unequal and increasing expansion, if the temperature indicated by the air-thermometer be used for comparison. This is shoWi by the following abstract of a table given by llegnault : Reading of Air Thermometer. 100 200 300 350 Reading of Mercurial Thermometer. 100 200 301 354 Temperature deduced from the absolute expansion of Mercury. 100 202-78 308-34 362-16 Tlxe absolute amount of expansion of mercury is, for many reasons, a point of great importance: it has been very carefully determined by a method independent of the expansion of the containing vessel. The ap- paratus employed for this purpose, first by MM. Dulong and Petit, and later by Regnault, is shown in fig. 31, divested, however, of many of its HEAT. subordinate parts. It consists of two upright glass tubes, connected at their bases by a horizontal tube of much smaller dimensions. Since a free communication exists between the two tubes, mercury poured into the one will rise to the same level in the other, provided its temperature is the same in both tubes ; when this is not the case, the hotter column will be the taller, because the expansion of the metal diminishes its specific gravity, and the law of hydrostatic equilibrium requires that the height of such columns should be inversely as their densities. By the aid of the outer cylinders, one of the tubes is maintained constantly at 0, while the other is raised, by means of heated water or oil, to any required temperature. The perpendicular heights of the columns may then be read off by a hori- zontal micrometer telescope, moving on a vertical divided scale. These heights represent volumes of equal weight, because volumes of equal weight bear an inverse proportion to the densities of the liquids, so that the amount of expansion admits of being very easily calculated. Thus, let the column at be six inches high, and that at 100, 6-108 inches; the increase of height, 108 on 6000, or 7 i- part of the actual cubical expansion. Fig. 31. The indications of the mercurial thermometer are inaccurate when very high ranges of temperature are concerned, from the increased expansi- bility of the metal. The error thus caused is, however, nearly compen- sated for temperatures under 204-5 by the expansion of the glass tube. For higher temperatures a small correction is necessary, as the above table shows. To what extent the expansion of different liquids may vary between the same temperatures is obvious from a glance at fig. 32, which represents the expansion of mercury (M), water (W), oil of turpentine (T), and alcohol (A). A column of these several liquids, equalling at the tenfold height of the line 01 in the diagram, would rxhj^it. when heated to a temper- ature of 10, 20, 30, &c., an expansion indicated by the distances at Fig. 32. 10 20 30 40 50 00 70 80 90 100 s^hich the perpendicular lines drawn over the numbers 10, 20, 30, &c., are intersected by the curves belonging to each of these liquids. Thus it is 6 50 HEAT. seen that oil of turpentine, between and 100, expands very nearly T ^j of its volume, and that mercury, between the same limits of temperature, expands uniformly, while the rate of expansion of the other liquids increases with the rise of the temperature. An exception to the regularity of expansion in liquids exists in the case of water; it is so remarkable, and its consequences so important, that it is necessary to advert to it particularly. Let a large thermometer-tube be filled with water at the common tem- perature of the air, and then artificially cooled. The liquid will be ob- served to contract, until the temperature falls to about 4 C. (39-2 F., or 8) above the freezing-point. After this a further reduction of tempera- ture causes expansion instead of contraction in the volume of the water, and this expansion continues until the liquid arrives at its point of con- gelation, when so sudden and violent an enlargement takes place that the vessel is almost invariably broken. At the temperature of 4, water is at its maximum density;* increase or diminution of heat produces upon it, for a short, time, the same effect. A beautiful experiment by Dr. Hope illustrates the same fact. If a tall jar filled with water at 10 or 15, and having in it tAvo small thermometers, one at the bottom and the other near the surface, be placed at rest in a very cold room, the following changes will be observed : The thermometer at the bottom will fall more rapidly than that at the top, until it has at- tained the temperature of 4, after which it will remain stationary. At length the upper thermometer will also mark 4, but still continue to sink as rapidly as before, while that at the bottom remains stationary. It is easy to explain these effects : the water in the upper part of the jar is rapidly cooled by contact with the air; it becomes denser in consequence, and falls to the bottom, its place being supplied by the lighter and warmer liquid, which in its turn suffers the same change ; and this circulation goes on until the whole mass of water has acquired its condition of maximum density, that is, until the temperature has fallen to 4. Beyond this, loss of heat occasions expansion instead of contraction, so that the very cold water on the surface has no tendency to sink, but rather the reverse. This singular anomaly in the behavior of water is attended with the most beneficial consequences in shielding the inhabitants of the waters from excessive cold. The deep lakes of the North American continent never freeze, the intense and prolonged cold of the winters of those regions being insufficient to reduce the temperature of such masses of water to 4. Ice, however, of great thickness forms over the shallow portions and the rivers, and accumulates in mounds upon the beaches, where the waves are driven up by the winds Above the freezing-point, s^-water has no point of maximum density. The more it is cooled the denser it becomes, until it solidifies at -2 6.f The gradual expansion of pure water cooled below 4 must be carefully distinguished from the great and sudden increase of volume it exhibits in the act of freezing, in which respect it resembles many other bodies which * According to the latest researches of Kopp, the point of greatest density of the water is 4-08 C. (39-34 F.). According to the determinations of this physicist, the volume of water = 1 at C. changes when heated to the following volumes : 2 0-99991 4 99988 0-99990 0-99999 1-00012 1-00031 1-00056 10 12 14 16 1-00085 18 1-00118 20 1-00157 22 1-00200 1-00247 1-00272 1-00406 24 25 35 40 45 50 55 60 65 1-00570 1-00753 1-00954 1-01177 1-01410 OO1659 1-01930 70 1-02225 75 1.02544 80 1-02858 85 1-03189 90 1-03540 95 1-03909 500 1-04299 J Neumann, PoggewJorff's Aunajen., cxiij. 382, HEAT. expand on solidifying. The force thus exerted by freezing water is enor- mous. Thick iron shells quite filled with water, and exposed, with their fuse-holes securely plugged, to the cold of a Canadian winter night, have been found split on the following morning. The freezing of water in the joints and crevices of rocks is a most potent agent in their disintegration. Expansion of Gases. This is a point of great practical importance to the chemist, and happily we have very excellent evidence upon the subject. The following four propositions exhibit, at a single view, the principal facts of the case: 1. All gases expand nearly alike for equal increments of heat; and all vapors, when remote from their condensing points, follow the same law. 2. The rate of expansion is not altered by a change in the state of com- pression, or elastic force of the gas itself. 3. The rate of expansion is uniform for all degrees of heat. 4. The actual amount of expansion is equal to ^| or 7 ^ 7 or 0-03666 of the volume of the gas at Centigrade, for each degree of the same scale.* It will be unnecessary to enter into any description of the methods of investigation by which these results have been obtained; the advanced student will find in Pouillet's Elements dc Physique, and in the papers of Magnus and Regnault,f all the information he may require. In the practical manipulation of gases, it very often becomes necessary to make a correction for temperature, or to discover how much the volume of a gas would be increased or diminished by a particular change of tem- perature ; this can be effected with great facility. Let it be required, for example, to find the volume which 100 cubic inches of any gas at 10 would become on the temperature rising to 20. The rate of expansion is ^\^ or ^J- 7 of the volume at for each degree; or 3000 measures at become 3011 at 1, 3022 at 2, 3110 at 10, and 3220 at 20. Hence Meas. at 10. Meas. at 20. Moas. at 10. Meas. at 20. 3110 : 3220 = 100 : 103-537 If this calculation is required to be made on the Fahrenheit scale, it mtist be remembered that the zero of that scale is 32 below the melting- point of ice. Above this temperature the expansion for each degree of the Fahrenheit scale is T | of the original volume. This, and the correction for pressure, are operations of very frequent occurrence in chemical investigations, and the student will do well to become familiar with them. Note. Of the four propositions stated in the text, the first and second have recently been shown to be true within certain limits only; and the third, although in the highest degree probable, would be very difficult to demonstrate rigidly; in fact, the equal rate of expansion of air is assumed in all experiments on other substances, and becomes the standard by whick the results are measured. The rate of expansion for the different gases is not absolutely the same, but the difference is so small that for most purposes it may with perfect safety be neglected. Neither is the state of elasticity altogether indifferent, * The fraction 3^ jy^ is very convenient for calculation. t Poggentlorff'H Annalen, iv. 1. Ann. Chim. Phys., 3d series, iv. 5, and v. 52. See also Watts's Dictionary ot Chemistry, art. HEAT, vol. iii. p. 46. 52 HEAT. the expansion being sensibly greater for an equal rise of temperature when the gas is in a compressed state. It is important to notice that the greatest deviations from the rule are exhibited by those gases which, as will hereafter be seen, are most easily liquefied, such as carbon dioxide, cyanogen, and sulphur dioxide; and that the discrepancies become smaller and smaller as the elastic force is lessened ; so that, if means existed for comparing the different gases in states equally distant from their points of condensation, there is reason to believe that the law would be strictly fulfilled. The experiments of Dalton and Gay-Lussac give for the rate of expan- sion ^ly of the volume at 0: this is no doubt too high. Those of Rudberg give 27 5-; those of Magnus and of Regnault ^ 7 ^. The ready expansibility of air by heat gives rise to the phenomena of winds. In the temperate regions of the earth these are very variable and uncertain, but within and near the tropics a much greater regularity prevails; of this the trade-winds furnish a beautiful example. The smaller degree of obliquity with which the sun's rays fall in the localities mentioned, occasions the broad belt thus stretching round the earth to become more heated than any other part of the surface. The heat thus acquired by absorption is imparted to the lower stratum of air, which, becoming expanded, rises, and gives place to another: and in this manner an as- cending current is established, the colder and heavier air streaming in laterally from the more temperate regions, north and south, to supply the partial vacuum thus occa- sioned. A circulation so commenced will be completed, in obedience to the laws of hydrostatics, by the establishment of counter-currents in the higher parts of the atmosphere, having directions the reverse of those on the surface. Such is the effect produced by the unequal heating of the equatorial parts ; or, more correctly, such would be the effect were it not greatly modified by the earth's movement of rotation. As the circumference of the earth is, in round numbers, about 24,000 miles, and since it rotates on its axis, from west to east, once in 24 hours, the equatorial parts must have a motion of 1000 miles per hour; this velocity diminishes rapidly toward each pole, where it is reduced to nothing. The earth in its rotation carries with it the atmosphere, whose velocity of movement corresponds, in the absence of disturbing causes, with that part of the surface immediately below it. The air which rushes toward the equator to supply the place of that raised aloft by its diminished density, brings with it the degree of momen- tum belonging to that portion of the earth's surface from which it set out, and as this mo- mentum is less than that of the earth under its new position, the earth itself travels faster than the air immediately over it, thus pro- ducing the effect of a wind blowing in a con- trary direction to that of its own motion. The original north and south winds are thus devi- ated from their primitive directions, and made to blow more or less from the eastward, so that HEAT. the combined effects of the unequal heating and of the movement of rota- tion is to generate in the northern hemisphere a constant north-east wind, and in the southern hemisphere an equally constant south-east wind. In the same manner the upper or return current, is subject to a change of direction in the reverse order; the rapidly moving wind of the tropics, transferred laterally towards the poles, is soon found to travel faster than the earth beneath it, producing the effect of a westerly wind, which modi- fies the primary current. The regularity of the trade-winds is much interfered with by the neigh- borhood of large continents, which produce local effects upon a scale suffi- ciently great to modify deeply the direction and force of the wind. This is the case in the Indian Ocean. They usually extend from about the 28th degree of latitude in both hemispheres to within 8 of the equator, but are subject to some variations in this respect. Between them, and also beyond their boundaries, lie belts of calms and light variable winds; and beyond these latter, extending into higher latitudes in both hemispheres, westerly winds usually prevail. The general direction of the trade-wind of the Northern hemisphere is E.N.E., and that of the Southern hemisphere E.S.E. The trade-winds, it may be remarked, furnish an admirable physical proof of the reality of the earth's movement of rotation. The theory of the action of chimneys, and of natural and artificial ven- tilation, belongs to the same subject. Let the reader turn to the demonstration given of the Archimedean hydrostatic theorem : let him once more imagine a body immersed in water, and having a density equal to that of the water; it will remain in equilibrium in any part beneath the surface, and for these reasons: The force which presses it downward is the weight of the body added to the weight of the column of water above it; the force which presses it upward is the weight of a column of water equal to the height of both conjoined ; the density of the body is that of water, that is, it weighs as much as an equal bulk of that liquid; consequently, the downward and upward forces are equally balanced, and the body remains at rest. Next, let, the circumstances be altered; let the body be lighter than an equal bulk of water; the pressure upward of the column of water a c is no longer compensated by the downward pres- sure of the corresponding column of solid and Fig. 35. water above it; the former force preponderates, and the body is driven upward. If, on the con- trary, the body be specifically heavier than wa- ter, then the latter force has the ascendency, and the boily sinks. All things so described exist in a common chimney ; the solid body, of the same density as that of the fluid in which it floats, is represented by the air in the chimney funnel; the space ft i' represents the whole atmosphere above it. When the air inside and outside the chimney is at the same temperature, equilibrium takes place, be- cause the downward tendency of the air within is counteracted by the upward pressure of that without. Now, let the chimney be heated; the air suffers expansion, and a portion is expelled ; the chimney therefore contains a smaller weight of air than it did before ; the external and internal columns no longer balance each other, and the warmer and lighter air is forced upward from below, and its place supplied by cold air. If the brick-work, or other material of which the chimney is constructed, retain its temperature, this second por- 5* 54: HEAT. tion of air is disposed of like the first, and the ascending current continues, so long as the sides of the chimney are hotter than the surrounding air. Sometimes, owing to sudden changes of temperature in the atmosphere, the chimney may happen to be colder than the air about it. The column within forthwith suffers contraction of volume ; the deficiency is filled up from without, and the column becomes heavier than one of similar height on the outside; the result is, that it falls out of the chimney, just as the heavy body sinks in the water, and has its place occupied by air from above. A descending current is thus produced, which may be often no- ticed in the summer season, by the smoke from neighboring chimneys find- ing its way into rooms which have been for a considerable time without fire. The ventilation of mines has long been conducted upon the same prin- ciple, and more recently it has been applied to dwelling-houses and assembly- rooms. The mine is furnished with two shafts, or with one shaft divided throughout by a diaphragm of boards ; and these are so arranged, that air forced down the one shall traverse the whole extent of the workings before it escapes by the other. A fire kept up in one of these shafts, by rarefy- . ing the air within, and causing an ascending current, occasions fresh air to traverse every part of the mine, and sweep before it the noxious gases > but too frequently present. CONDUCTION OF HEAT. Different bodies possess very different conducting powers with respect to heat : if two similar rods, the one of iron, the other of glass, be held in the flame of a spirit-lamp, the iron will soon become too hot to be touched, while the glass may be grasped with impunity within an inch of the red- hot portion. Experiments made by analogous but more accurate methods have estab- lished a numerical comparison of the conducting powers of many bodies. The following may he taken as a specimen : Silver . . . 1000 Copper . . 736 Gold . . .532 Brass ... 236 Tin ... 145 Iron 119 Steel . . .116 Lead ... 85 Platinum ... 84 German silver . 63 Bismuth 18 As a class, the metals are by very far the best conductors, although much difference exists between them ; stones, dense woods, and charcoal follow next in order : then liquids in general, and gases, whose conducting power is almost inappreciable. Under favorable circumstances, nevertheless, both liquids and gases may become rapidly heated : heat applied to the bottom of the containing vessel is very speedily communicated to its contents : this, however, is not so much by conduction as by convection, or carrying. A complete circu- lation is set up ; the portions in contact with the bottom of the vessel get heated, become lighter, and rise to the surface, and in this way the heat becomes communicated to the whole. If these movements be prevented by dividing the vessel into a great number of compartments, the really low conducting power of the substance is made evident ; and this is the reason why certain organic fabrics, as wool, silk, feathers, and porous bodies in general, the cavities of which are full of air, exhibit such feeble powers of conduction. The circulation of heated water through pipes is now extensively applied to the warming of buildings and conservatories; and in chemical works a serpentine metal tube containing hot oil is often used for heating stills and evaporating-pans: the two extremities of the tube are connected with the HEAT. OO ends of another spiral built into a small furnace at the lower level, and an unintermitting circulation of the liquid takes place as long as heat is applied. CHANGE OF STATE. Solid bodies when heated are expanded; many are liquefied, t. e., they fuse. The fusion of solids is frequently preceded by a gradual softening, more especially when the temperature approaches the point of fusion. This phenomenon is observed in the case of wax or iron. In the case of other solids of zinc and lead, for instance and several other metals, this softening is not observed. Generally, bodies expand during the pro- cess of fusion ; an exception to this rule is water, which expands during freezing (10 vol. of water produce nearly 11 vol. of ice), while ice when fusing produces a proportionately smaller volume of water. The expansion of bodies during fusion, and at temperatures preceding fusion, or the con- traction during solidification and further refrigeration, is very unequal. Wax expands considerably before fusing, and comparatively little during fusion itself. Wax, when poured into moulds, fills them perfectly during solidification, but afterwards contracts considerably. Stearic acid, on the contrary, expands very little before fusion, but rather considerably during fusion, and consequently pure stearic acid when poured into moulds solidi- fies to a rough porous mass, contracting little by further cooling. The addition of a little wax to stearic acid prevents the powerful contraction in the moment of solidification, and renders it more fit for being moulded. Latent Heal of Fusion. During fusion bodies absorb a certain quantity of heat, which is not indicated by the thermometer; at a given tempera- ture the fusing-point, for instance a certain weight of substance con- tains when solid less heat than when liquid. If equal weights of water at and water at 79 be mixed, the tempera- ture of the mixture will be the mean of the two temperatures, or 39-5. If the same experiment be repeated with snow or finely-powdered ice at 0, and water at 79, the temperature of the whole will be only 0, but the ice will have been melted, 1 ! b b ; :f : ^?;} =2 '-. ^e r at 39.50 IS: In the last experiment, therefore, as much heat has been apparently lost as would have raised a quantity of water equal to that of the ice through a range of 79. The heat, thus become insensible to the thermometer in effecting the liquefaction of the ice, is called latent heatj or, better, heat of fluidity. Again, let a perfectly uniform source of heat be imagined, of such intensity that a pound of water placed over it would have its temperature raised 5 per minute. Starting with water at 0, in rather less than 10 minutes its temperature would have risen 79; but the same quantity of ice at 0, exposed for the same interval of time, would not have its tem- perature raised a single degree. But, then, it would have become water; the heat received would have been exclusively employed in effecting the change of state. This heat is not lost, for when the water freezes it is again evolved. If a tall jar of water, covered to exclude dust, be placed in a situation where it shall be quite undisturbed, and at the same time exposed to great cold, the temperature of the water may be reduced 10 or more below its freez- 56 HEAT. ing-point without the formation of ice ; * but then, if a little agitation be communicated to the jar, or a grain of sand dropped into the water, a por- tion instantly solidifies, and the temperature of the whole rises to ; the heat disengaged by the freezing of a small portion of the water will have been sufficient to raise the whole contents of the jar 5. This curious condition of instable equilibrium shown by the very cold water in the preceding experiment, may be reproduced with a variety of solutions which tend to crystallize or solidify, but in which that change is for a while suspended. Thus, a solution of crystallized sodium sulphate in its own weight of warm water, left to cool in an open vessel, deposits a large quantity of the salt in crystals. If the warm solution, however, be filtered into a clean flask, which when full is securely corked and set aside to cool undisturbed, no crystals will be deposited, even after many days, until the cork is withdrawn and the contents of the flask violently shaken. Crystallization then rapidly takes place in a very beautiful manner, and the whole becomes perceptibly warm. The law thus illustrated in the case of water is perfectly general. Whenever a solid becomes a liquid, a certain fixed and definite amount of heat disappears, or becomes latent ; and conversely, whenever a liquid be- comes a solid, heat to a corresponding extent is given out. The following table exhibits the melting points of several substances, and their latent heats of fusion expressed in gram-degrees that is to say, the numbers in the column headed "latent heat" denote the number of grams of water the temperature of which would be raised 1 Centigrade by the quantity of heat required to fuse one grain of the several solids: Substance. Melting Point. Latent Heat. Substance. Melting Point. Latent Heat. 39 2-82 Tin 235 14-25 44 5-0 Silver 1000 21-1 332 5-4 Zinc . . 433 28-1 Sulphur . . Iodine . . 115 107 9-4 11-7 Calcium chloride ") (CaCl 2 GH 2 0) / 28-5 40-7 Bismuth . . 270 12-6 Potassium nitrate . 339 47-4 Cadmium 320 13-6 Sodium nitrate . . 310-5 63-0 When a solid substance can be made to liquefy by a weak chemical attraction, cold results, from sensible heat becoming latent. This is the principle of the many frigorific mixtures to be found described in some of the older chemical treatises. When snow or powdered ice is mixed with common salt, and a thermometer plunged into the mass, the mercury sinks to 17-7C. (0 F.), while the whole after a short time becomes fluid by the attraction between the water and the salt ; such a mixture is very often used in chemical experiments to cool receivers and condense the vapors of volatile liquids. Powdered crystallized calcium chloride and snow pro- duce cold enough to freeze mercury. Even powdered potassium nitrate, * Fused bodies, when cooled down to or below their fusing point, frequently remain liquid, more especially when not in contact with solid bodies Thus, water in a mixture of oil of almonds and chloroform, of specific, gravity equal to its own, remains liquid to 10: in a simi- lar manner fused sulphur or phosphorus, floating in a solution of zinc chloride of appropriate concentration, retains the liquid condition at temperatures 40 below its fusing point. Liquid bodies, thus cooled below their fusing point, frequently solidify when touched with a solid sub- stance, invariably when brought in contact with a fragment of the same body in the solid condition. HEAT. 57 or sal-ammoniac, or ammonium nitrate, dissolved in water, occasions a very notable depression of temperature : in every case, in short, in which solution is unaccompanied by energetic chemical action, cold is produced. No relation can be traced between the actual melting-point of a sub- stance, and its latent heat when in the fused state. Latent Heat of Vaporization. A law of exactly the same kind as that described affects universally the gaseous condition ; change of state from solid or liquid to gas is accompanied by absorption of sensible heat, and the reverse by its disengagement. The latent heat of steam and other vapors may be ascertained by a mode of investigation similar to that employed in the case of water. When water at is mixed with an equal weight of water at 100, the whole is found to possess the mean of the two temperatures, or 50 ; on the other hand, 1 part by weight of steam at 100, when condensed in cold water, is found to be capable of raising 5-4 parts of the latter from the freezing to the boiling-point, or through a range of 100. Now 100 X 5-4=540 ; that is to say, steam at 100, in becoming water at 100, parts with enough heat to raise a weight of water equal to its own (if it were possible) 540, of the thermometer. When water passes into steam, the same quantity of sensible heat becomes latent. The vapors of other liquids seem to have less latent heat than that of water. The following table is by Dr. Th. Andrews, and serves well to illustrate this point. The latent heats are expressed, as in the last table, in gram-degrees: Vapor of water 535-90 alcohol 202-40 ether 90-45 oxalic ether . . . . . 72-72 acetic ether . . . . . 92-68 ethylic iodide .... 46-87 pyroxylic spirit ..... 263-70 carbon bisulphide .... 86-67 tin tetrachloride . 30-35 bromine ...... 45-66 oil of turpentine .... 74-03 Ebullition is occasioned by the formation of bubbles of vapor within the body of the evaporating liquid, which rise to the surface like bubbles of permanent gas. This occurs in different liquids at very different tempera- tures. Under the same circumstances, the boiling-point is quite constant, and often becomes a physical character of great importance in distinguish- ing liquids which much resemble each other. A few cases may be cited in illustration : Substance. Boiling-point. Aldehyde 20-8 Ether 34-9 Carbon bisulphide ...... 46-1 Alcohol 78-4 Water 100 Nitric acid, strong ...... 120 Oil of turpentine . . . . . .157 Sulphuric acid 326-6 Mercury 350 For ebullition to take place, it is necessary that the elasticity of the vapor should be able to overcome the cohesion of the liquid and the pres- 58 HEAT. sure upon its surface : hence the extent to which the boiling-point may be modified. Water, under the usual pressure of the atmosphere, boils at 100 (212 F.) : in a partially exhausted receiver or on a mountain-top it boils at a much lower temperature: and in the best vacuum of an excellent air- pump, over oil of vitriol, which absorbs the vapor, it will often enter into violent ebullition while ice is in the act of forming upon the surface. On the other hand, water confined in a very strong metallic vessel may be restrained from boiling by the pressure of its own vapor to an almost unlimited extent; a temperature of 177 or 204 is very easily obtained; and, in fact, it is said that it may be made red-hot, and yet retain its fluidity. There is a very simple and beautiful experiment illustrative of the effect of diminished pressure in depressing the boiling-point of a liquid. A p { 36 little water is made to boil for a few minutes in a flask or retort placed over a lamp, until the air has been chased out, and the steam issues freely from the neck. A tightly fitting cork is then inserted, and the lamp at the same moment withdrawn. When the ebullition ceases, it may be renewed at pleasure for a considerable time by the affusion of cold water, which, by condensing the vapor within, occasions a partial vacuum. The nature of the vessel, or, rather, the state of its surface, exercises an influence upon the boiling-point, and this to a much greater extent than was formerly supposed. It has long been noticed that in a metallic vessel water boils, under the same circumstances of pressure, at a temperature one or two degrees below that at which ebullition takes place in glass: but it has lately been shown * that by particular management a much greater difference can be observed. If two similar glass flasks be taken, the one coated in the in- side with a film of shellac, and the other completely cleansed by hot sul- phuric acid, water heated over a lamp in the first will boil at 99-4, while in the second it will often rise to 105 or even higher; a momentary burst of vapor then ensues, and the thermometer sinks a few degrees, after which it rises again. In this state, the introduction of a few metallic filings, or angular fragments of any kind, occasions a lively disengagement of vapor, while the temperature sinks to 100, and there remains stationary. These remarkable effects must be attributed to an attraction between the surface of the vessel and the liquid. When out of contact with solid bodies, liquids not only solidify with re- luctance, but also assume the gaseous condition with greater difficulty. Drops of water or of aqueous saline solutions floating on the contact- surface of two liquids, of which one is heavier and the other lighter, may be heated from 10 to 20 degrees above the ordinary boiling-point; explo- sive ebullition, however, is instantaneously induced by contact with a solid substance. A cubic inch of water in becoming steam under the ordinary pressure of the atmosphere expands into 1696 cubic inches, or nearly a cubic foot. Steam, not in contact with ivater, is affected by heat in the same manner as the permanent gases ; its rate of expansion and increase of elastic force are practically the same. When water is present, the rise of temperature increases the quantity and density of the steam, and hence the elastic force increases in a far more rapid proportion. This elastic force of steam in contact with water, at different tempera- * Marcet ' Ann. Chim. Phys.' 3d scries, v. 449. HEAT. 51) lures, has been very carefully determined by Arago and Dulong, and lately by Magnus and llegnault. The force is expressed in atmospheres : the ab- solute pressure upon any given surface can be easily calculated, allowing 14 6 Ib per square inch to each atmosphere. The experiments were carried to twenty-five atmospheres; at which point the difficulties and danger became so great as to put a stop to the inquiry: the rest of the table is the result of calculations founded on the data so obtained: Pressure of Steam iu atmospheres. 1-5 2 2-5 5 5-5 6 6-5 7 , 7-5 8 9 10 11 12 , 13 14 15 16 Corresponding temperature. Pressure of Steam in atmospheres. 100 3 . 112 3 5 122 4 . 129 4 5 153 17 j 157 18 160 19 t 163 20 167 21 t 169 22 172 23 . 177 24 182 25 . 186 30 190 35 m 194 40 197 45 200-5 50 203 Corresponding temperature. 135 140-5 145 5 149 207 209 212 214 217 219 222 224 226 236 245 253 255 266 It is very interesting to know the amount of heat requisite to convert water of any given temperature into steam of the same or another given temperature. The most exact experiments on this subject have been made by Regnault. He arrived at this result, that when the unit-weight of steam at the temperature t is converted into water of the same temperature, and then cooled to 0, it gives out the quantity of heat T, which is represented by the formula: T = 606 5 -f 305 t. This formula appears to hold good for temperatures above and below the ordinary boiling-point of water. The following table gives the values of T, corresponding to the respective temperatures in the first columns: t 50 100 150 200 T 606 5 621-7 637-0 652-2 667-5 T is called the total heat of steam, being the heat required to raise water from to t, together with that which becomes latent by the transformation of water of t into steam at t. Regnault states, as a result of some very deli- cate experiments, that the heat necessary to raise a unit-weight of water from to t is not exactly denoted by t; the discrepancy, however, is so small that it may be disregarded. Employing the approximate value, the 60 HEAT. latent heat of steam, L, at any temperature will be found by subtracting t from the total heat; or, according to the formula: L= 606 5 0-595 t. This equation shows us the remarkable fact that the latent heat of steam diminishes as the temperature rises. Before Regnault's experiments were made, two laws of great simplicity were generally admitted, one of which, however, contradicted the other. Watt concluded, from experiments of his own, as well as from theoretical speculations, that the total heat of steam would be the same at all temperatures. Were this true, equal weights of steam passed into cold water would always exhibit the same heating power, no matter what the temperature of the steam might be. Exactly the same absolute amount of heat, and consequently the same quantity of fuel, would be required to evaporate a given weight of water in vacuo at a temperature which the hand can bear, or under great pressure, and at a high tempera- ture. Watt's Law, though agreeing well with the rough practical results obtained by engineers, is only approximately true ; and the same may be said of the deductions which have just been made from it. The second law, in opposition to Watt's, is that of Southern, stating the latent heat of steam to be the same at all temperatures. Regnault's researches have shown that neither Watt's law (T constant), nor Southern's law (L constant) is correct. The economical applications of steam are numerous and extremely valu- able: they may be divided into two classes: those in which the heating power is employed, and those in which its elastic force is brought into use. The value of steam as a source of heat depends upon the facility with which it may be conveyed to distant points, and upon the large amount of latent heat it contains, which is disengaged in the act of condensation. An invariable temperature of 100, or higher, may be kept up in the pipes or other vessels in which the steam is contained by the expenditure of a very small quantity of the latter. Steam-baths of various forms are used in the arts with great convenience, and also by the scientific chemist for drying filters and other objects where excessive heat would be hurtful: a very good instrument of the kind was contrived by Mr. Everitt. It is merely a small kettle (fig. 37), surmounted by a double box or jacket, into which the substance to be dried is put, and loosely covered by a card. The appa- ratus is placed over a lamp, and may be left without attention for many hours. A little hole in the side of the jacket gives vent to the excess of steam. The principle of the steam-engine may be described in a few words: its mechanical details do not belong to the design of the present volume. The machine consists essentially of a cylinder or metal Fig. 37. a (fig. 38), in which a closely fitting solid piston works, the rod of which passes, air-tight, through a stuffing-box at the top of the cylinder, and is connected with the machinery to be put in motion, directly, or by the intervention of an oscillating beam. A pipe communicates with the interior of the cylinder, and also with a vessel surrounded with cold water, called the condenser b, into which a jet of cold water can at pleasure be introduced. A sliding-valve arrangement, shown at c, serves to open a communication between the boiler and the cylinder, and between the cylinder and the con- denser in such a manner that while the steam is allowed to press with all its force upon one side of the piston, the other, open to the condenser, is necessarily vacuous. The valve is shifted by the HEAT. 61 Fig. 38. engine itself at the proper moment, so that the piston is alternately driven by the steam up and down against a vacuum. A large air-pump, not shown in the engraving, is connected with the condenser, and serves to remove any air that may enter the cylinder, and also the water produced by condensation, together with that which may have been injected. Such is the vacuum or condensing steam- engine. In what is called the high-pres- sure engine, the condenser and air-pump are suppressed, and the steam is allowed to escape at once from the cylinder into the atmosphere. It is obvious that in this arrangement the steam has to overcome the whole pressure of the air, and a much greater elastic force is required to produce the same effect; but this is to a very great extent compensated by the absence of the air-pump and the increased simplicity of the whole machine. Large engines, both on shore and in steamships, are usually constructed on the condensing principle, the pressure seldom exceeding six or seven pounds per square inch above that of the atmosphere; for small engines the high- pressure plan is, perhaps, preferable. Locomotive engines are of this kind. A peculiar modification of the steam- engine, employed in Cornwall, for draining the deep mines of that counti^y, is now get- ting into use elsewhere for other purposes. In this machine, economy of fuel is carried to a most extraordinary extent, engines having been known to perform the dull/ of raising more than 100, 000, 000 Ibs. of water one foot high by the con- sumption of a single bushel of coals. The engines are single-acting, the down- stroke, which is made against a vacuum, being the effective one, and em- ployed to lift the enormous weight of the pump-rods in the shaft of the mine. When the piston reaches the bottom, the communication both with the boiler and the condenser is cut off, while an equilibrium-valve is opened connecting the upper and lower extremities of the cylinder, whereupon the weight of the pump-rods draws the piston to the top and makes the up-stroke. The engine is worked expansively, as it is termed, steam of high tension being employed, which is cut off at one-eighth or even one- tenth of the stroke. The process of distillation, which may now be noticed, is very simple: its object is either to separate substances which rise in vapor at different temperatures, or to part a volatile liquid from a substance incapable of volatilization. The same process applied to bodies which pass directly from the solid to the gaseous condition, and the reverse, is called sublimation. Every distillatory apparatus consists essentially of a boiler, in which the vapor is raised, and of a condenser, in which it returns to the liquid or solid condition. In the still employed for manufacturing purposes, the latter is usually a spiral metal tube immersed in a tub of water. The common retort and receiver constitute the simplest arrangement for distil- lation on the small scale; the retort is heated by a gas lamp, and the re- ceiver is kept cool, if necessary, by a wet cloth, or it may be surrounded with ice. (Fig. 39.) 6 62 HEAT. Liebig's condenser* (fig. 40) is a very valuable instrument in the labora- tory; it consists of a glass tube tapering from end to end, fixed by per- forated corks in the centre of the metal pipe, provided with tubes so ar- ranged that a current of cold water may circulate through the apparatus. By putting ice into the little cistern, the water may be kept at 0, and extremely volatile liquids condensed. Fig. 40. Liquids evaporate at temperatures below their boiling-points: in this case the evaporation takes place slowly from the surface. Water, or alco- hol, exposed in an open vessel, at the temperature of the air, gradually disappears; the more rapidly, the warmer and drier the air. This fact was formerly explained by supposing that air and gases in general had the power of dissolving and holding in solution certain quan- [* Invented by Weitzel, the elder, of Stockholm, and well described and figured in Gray'a Operative Chemist. R. B.] HEAT. 63 titles of liquids, and that this power increased with the temperature: such an idea is incorrect. If a barometer-tube be carefully filled with mercury and inverted in the usual manner, and then a few drops of water passed up the tube into the vacuum above, a very remarkable effect will be observed; the mercury will be depressed to a small extent, and this depression will increase with increase of temperature. Now, as the space above the mercury is void of air, and the weight of the few drops of water quite inadequate to ac- count for this depression, it must of necessity be imputed to the vapor which instantaneously rises from the water into the vacuum ; p . 41 and that this effect is really due to the elasticity of the aqueous vapor, is easily proved by exposing the barometer to a heat of 100 C. (212 F.), when the depression of the mercury will be complete, and it will stand at the same level within and with- out the tube; indicating that at that temperature the elasticity of the vapor is equal to that of the atmosphere a fact which the phenomenon of ebullition has already shown. By placing over the barometer a wide open tube dipping into the mercury below, and then filling this tube Avith water at different temperatures, the tension of the aqueous vapor for each degree of the thermometer may be accurately deter- mined by its depressing effect upon the mercurial column; the same power which forces the latter down one inch against the pressure of the atmosphere, would of course elevate a column of mercury to the same height against the vacuum, and in this way the tension may be conveniently expressed. The following table was drawn up by Dalton, to whom we owe the method of investigation: Temperature. Tension in inches F. C. of mercury. ?)'2 . 0-200 40 . 4-4 . 0263 50 . 10 . 0-375 60 . 15-5 . 0-524 70 . 21-1 . 0721 80 . 26-6 . 1-000 90 . 32-2 . 1-360 100 . 37-7 . 1-860 110 . 43-3 . 2-530 120 . 48-8 . 3-330 Temperature. Tension in inches F. C. c >f mercury. 130 . 54-4 . 434 140 . 60 5-74 150 . 65-5 . 7-42 160 . 71-1 . 9-46 170 . 76-6 . 12-13 180 . 82-2 . 15-15 190 . 87-7 . 19-00 200 . 93-3 . 23 64 212 . 100 3000 Another table representing the tension of the vapor of water, drawn up by llegnault, is given at the end of the work. Other liquids tried in this manner are found to emit vapors of greater or less tension, for the same temperature, according to their different degrees of volatility : thus, a little ether introduced into the tube depresses the mercury 10 inches or more at the ordinary temperature of the air; oil of vitriol, on the other hand, does not emit any sensible quantity of vapor until a much greater heat is applied ; and that given off by mercury itself in warm summer weather, although it may be detected by very delicate moans, is far too little to exercise any effect upon the barometer. In the case of water, the evaporation is quite distinct and perceptible at the lowest temperatures, when frozen to solid ice in the barometer-tube: snow on the ground, or on a house-top, may often be noticed to vanish, from the same cause, day by day in the depth of winter, when melting is impossible. There exists for each vapor a state of density which it cannot pass with- out losing its gaseous condition, and becoming liquid; this point is called 64 HEAT. the condition of maximum density. When a volatile liquid is introduced in sufficient quantity into a vacuum, this condition is always reached, and then evaporation ceases. Any attempt to increase the density of this vapor by compressing it into a smaller space will be attended by the liquefaction of a portion, the density of the remainder being unchanged. If a little ether be introduced into a barometer, and the latter slowly sunk into a very deep cistern of mercury (fig. 42), it will be found that the height of the column of mercury in the tube above that in the cistern remains un- altered until the upper extremity of the barometer ap- preaches the surface of the metal in the column and all the ether has become liquid. It will be observed also, that, as the tube sinks, the stratum of liquid ether in- creases in thickness, but no increase of elastic force oc- curs in the vapor above it, and, consequently, no increase of density; for tension and density are always, under ordinary circumstances at least, directly proportionate to each other. The point of maximum density of vapor is dependent upon the temperature; it increases rapidly as the tem- perature rises. This is well shown in the case of water. Thus, taking the spec, grav, of atmospheric air at 100 =1000, that of aqueous vapor in its greatest state of compression for the temperature will be as follows: Temperature. Specific gravity. "Weight of 100 cubic C. F. inches. . 32 . 5-690 . 0-180 grains. 10 50 10-293 . 0'247 15-5 . 60 . 14-108 . 0-338 37-7 . 100 . 46-500 . 1-113 65*5 . 150 . 170-293 . 4'076 100 . 212 . 625-000 . 14-962 The last number was experimentally found by Gay- Lussac; the others are calculated from that by the aid of Dalton's table of tensions, on the assumption that steam, not in a state of saturation, that is, below the point of greatest density, obeys the laws of Mariotte (which is, however, only approximately true), and that when it is cooled it contracts like the permanent gases. Thus, there are two distinct methods by which a vapor may be reduced to the liquid form pressure, by causing increase of density until the point of maximum density for a given temperature is reached ; arid cold, by which the point of maximum density is itself lowered. The most powerful effects are produced when both are con- joined. For example, if 100 cubic inches of vapor of water at 100 F., in the state above described, had its temperature reduced to 50 F., not less than 0-89* grain of liquid water would necessarily separate, or very nearly eight-tenths of the whole. Evaporation into a space filled with air or gas follows the same law as evaporation into a vacuum : as much vapor arises, and the condition of maximum density is assumed in the same manner, as if the space were perfectly empty ; the sole difference lies in the length of time required. * 100 cub. inch, aqueous vapor at 100 F., weighing 1-113 grain, would at 50 F. become reduced to 91-07 cub. inch., weighing 0-225 grain. HEAT. 65 When a liquid evaporates into a vacuum, the point of greatest density is attained at once, while in the other case some time elapses before this happens : the particles of air appear to oppose a sort of mechanical resist- ance to the rise of the vupor. The ultimate effect is, however, precisely the same. When to a quantity of perfectly dry gas confined in a vessel closed by mercury a little water is added, the latter immediately begins to evaporate, and after some time as much vapor will be found to have risen from it as if no gas had been present, the quantity depending entirely on the tempera- ture to which the whole is subjected. The tension of this vapor will add itself to that of the gas. and produce an expansion of volume, which will be indicated by an alteration of level in the mercury. Vapor of water exists in the atmosphere at all times and in all situations, and there plays a most important part in the economy of nature. The pro- portion of aqueous vapor present in the air is subject to great variation, and it often becomes important to determine its quantity. This is easily done by the aid of the foregoing principles. Deiv-Point. If the aqueous vapor be in its condition of greatest possible density for the temperature, or, as it is frequently, but most incorrectly, expressed, the air be saturated with vapor of water, the slightest reduction of temperature will cause the deposition of a portion in the liquid form. If, on the contrary, as is almost always in reality the case, the vapor of water be below its state of maximum density, that is, in an expanded con- dition, it is clear that a considerable fall of temperature may occur before liquefaction commences. The degree at which this takes place is called the dew-point, and it is determined with great facility by a very simple method. A little cup of thin tin plate or silver, well polished, is filled with water at the temperature of the air, and a delicate thermometer inserted. The water is then cooled by dropping in fragments of ice, or dissolving in it powdered sal-ammoniac, until moisture begins to make its appearance on the outside, dimming the bright metallic surface. The temperature of the dew- point, is then read off upon the thermometer, and compared with that of the air. Suppose, by w^ of example, that the latter were 70 F., and the dew- point 50 F., the elasticity of the watery vapor present would correspond to a maximum density proper to 50 F., and would support a column of mercury 0-375 inch high. If the barometer on the spot stood at 30 inches, therefore, 29-025 inches would be supported by the pressure of the dry air, and the remaining 0-375 inch by the vapor. Now a cubic foot of such a mixture must be looked upon as made up of a cubic foot of dry air, and a cubic foot of watery vapor, occupying the same space, and having tensions indicated by the numbers just mentioned. A cubic foot, or 1728 cubic inches of vapor, at 70 F., would become reduced by contraction, according to the usual law, to 1062-8 cubic inches at 50 F. ; this vapor would be at its maximum density, having the specific gravity pointed out in the table ; hence 1602-8 cubic inches would weigh 4-11 grains. The weight of the aqueous vapor contained in a cubic foot of air will thus be ascertained. In this country the difference between the temperature of the air and the dew- point seldom reaches 30 F. (16-6 C.) degrees; but in the Deccan, with a temperature of 90 F. (32-2 C.), the dew-point sinks as low as 29 F., mak- ing the degrees of dryness 61 F.* Another method of finding the proportion of moisture present in the air is to observe the rapidity of evaporation, which is always in some relation to the degree of dryness. The bulb of a thermometer is covered with mus- lin, and kept wet with water; evaporation produces cold, as will presently be seen, and accordingly the thermometer soon sinks below the actual tem- * Daniel!, Introduction to Chemical Philosophy, r- 15-*- 6* HEAT. Fig. 43. perature of the air. When it comes to rest, the degree is noticed, and from a comparison of the two temperatures an approximation to the dew-po^nt can be obtained by the aid of a mathematical formula con- trived for the purpose. This is called the wet-bulb hygrom- eter: it is often made in the manner shown in fig. 43, where one thermometer serves to indicate the temperature of the air, and the other to show the rate of evaporation, being kept wet by the thread dipping in the water reservoir. Liquefaction of Gases. The perfect resemblance in every respect which vapors bear to permanent gases, led, very naturally, to the idea that the latter might, by the application of suitable means, be made to assume the liquid condition, and this surmise was, in the hands of Mr. Faraday, to a great ex- tent verified. Out of the small number of such substances tried, not less than eight gave way; and it is quite fair to infer that, had means of sufficient power been at hand, the rest would have shared the same fate, and proved to be nothing more than the vapors of volatile liquids in a state very far re- moved from that of their maximum density. The subjoined table represents the results of Mr. Faraday's first investiga- tions, with the pressure in atmospheres, and the temperatures at which the condensation takes place.* Sulphur dioxide Hydrogen sulphide Carbon dioxide Chlorine Nitrogen monoxide Cyanogen Ammonia Hydrochloric acid Atmospheres. 2 . 17 . 36 4 . 50 . 3-6 6-5 . , 40 , Temperatures. C. I 1 . 7-2 45 10 15-5 7-2 7-2 10 10 50 32 60 45 45 50 50 The method of proceeding was very simple : the materials were scaled up in a strong, narrow tube, together with a little pressure-gauge, consist- ing of a slender tube, closed at one end, and having within it, near the open extremity, a globule of Fig. 44. mercury. The gas being dis- engaged by heat, accumulated in the tube, and by its own pressure brought about con- densation. The force required for this purpose was judged of by the diminution of volume of the air in the gauge. Mr. Faraday has since resumed, with the happiest results, the subject of the liquefaction of the permanent gases. By using narrow green glass tubes of great strength, powerful condensing syringes, and an extremely low temperature, produced by means to be presently described, olefiant gas, hydriodic and hydrobromic acids, phosphoretted hydrogen, and the gaseous fluorides of silicon and boron, were successively liquefied. Oxygen, hydro- gen, nitrogen, nitrogen dioxide, carbon monoxide, and marsh gas, refused to liquefy at 166 F., while subjected to pressures varying from 27 to 58 atmospheres. Sir Isambard Brunei, and, more recently, M. Thilorier, of Paris, succeeded Phil. Trans, for 1823, p. 189. HEAT. 67 in obtaining liquid carbon dioxide (commonly called carbonic acid) in great, abundance. The apparatus of M. Thilorier consists of a pair of ex- tremely strong metallic vessels, one of which is destined to serve the pur- pose of a retort, and the other that of a receiver. They are made either of thick cast iron or gun-metal, or, still better, of the best and heaviest boiler-plate, and arc furnished with stop-cocks of a peculiar kind, the workmanship of which must be excellent. The generating vessel or retort has a pair of trunnions upon which it swings in an iron frame. The joints are secured by collars of lead, and every precaution taken to prevent leak- age under the enormous pressure the vessel has to bear. The receiver re- sembles the retort in every respect; it has a similar stop-cock, and is con- nected with the retort by a strong copper tube and a pair of union screw- joints; a tube passes from the stop-cock downwards, and terminates near the bottom of the vessel. The operation is thus conducted : 2| Ib. of acid sodium carbonate, and 6lb. of water at 100 F., are introduced into the generator; oil of vitriol to the amount of 1^ Ib. is poured into a copper cylindrical vessel, which is Fig. 45. lowered down into the mixture, and set upright; the stop-cock is then screwed into its place, and forced home by a spanner and mallet. The machine is next tilted up on its trunnions, that the acid may run out of the cylinder and mix with the other contents of the generator; and this mix- ture is favored by swinging the whole backward and forward for a few minutes, after which it may be suffered to remain a little time at rest. The receiver, surrounded with ice, is next connected with the generator, and both cocks opened; the liquefied carbon dioxide distils over into the colder vessel, and there again in part condenses. The cocks are now closed, the vessels disconnected, the cock of the generator opened to allow the contained gas to escape; and, lastly, when the issue of gas has { 657 5-85 Sulphur 0-2026 32 6-48 Potassium 0-1696 39 6-61 Iron .... 0-1138 56 6-37 Nickel .... 0-1086 58-7 6-37 Cobalt 0-1070 58-7 6-28 Copper .... 0-9515 63-5 6-04 Zinc .... 0-9555 65 6-24 Arsenic .... 0-8140 75 6-10 Selenium 0-7616 79 6-02 Bromine (solid) 0-8432 80 6-75 Palladium . 0-5928 106-5 6-31 Silver .... 0-5701 108 6-16 Cadmium . 0-5669 112 6.35 Tin . 05623 118 6-63 Antimony . 0-5077 122 6-19 Iodine .... 0-5412 127 6-87 Tellurium . 0-4737 128 6-06 Gold .... 0-3242 196-7 6-38 Platinum . 0-3113 197-4 6-15 *{$* ' . ' 0-3192 0-3332 } 200 { 6-38 6-66 Lead .... 0-3140 207 6-50 Bismuth 0-3084 210 6-48 A comparison of the numbers in the fourth column of this table shows that for a considerable number of elementary bodies in the solid state the specific heats are very nearly proportional to the atomic weights, so that the products of the specific heats of the elements into their atomic weights give nearly a constant quantity, the mean value being 6-4. This quantity may be taken to represent the atomic heat of the several elements in the solid state, or the quantity of heat which must be imparted to or removed from atomic proportions of the several elements, in order to produce equal variations of temperature. Nevertheless, this law must not be understood as perfectly general, for there are three elements, namely, carbon, boron, and silicon, which exhibit decided exceptions to it, as shown by the following numbers: 7 HEAT. Elements. Specific Heat. Atomic Weights. Product of Sp. Heat X At. Weight. Boron, crystallized 0-2500 11 2-75 ( wood charcoal Carbon ^ graphite ( diamond . 0-2415 0-2008 0-1469 t " { 2-90 2-41 1-76 Si!ic '>{Sd allized - . 0-1774 0-1750 ) i 497 4-70 The specific heats and molecular weights of similarly constituted com- pounds exhibit, for the most part, the same relation as that which is observed between the specific heats and atomic weights of the elements. SOURCES OF HEAT. The first and greatest source of heat, compared with which all others are totally insignificant, is the sun. The luminous rays are accompanied by rays of a heating nature, which, striking against the surface of the earth, elevate its temperature ; this heat is communicated to the air by convection, as already described, air and gases in general not being sensibly heated by the passage of the rays. A second source of heat is supposed to exist in the interior of the earth. It has been observed that in sinking mine-shafts, boring for water, &c., the temperature rises in descending, at the rate, it is said, of about | C. (1 F.) for every 45 feet, or 65 C. (117 F.) per mile. On the supposition that the rise continues at the same rate, the earth, of the depth of less than two miles, would have the temperature of boiling water ; at nine miles it would be red-hot; and at 30 or 40 miles depth all known substances would be in a state of fusion.* According to this idea, the earth must be looked upon as an intensely heated fluid spheroid, covered with a crust of solid badly conducting matter, cooled by radiation into space, and bearing somewhat the same proportions in thickness to the ignited liquid within, that the shell of an egg bears to its fluid contents. Without venturing to offer any opinion on this theory, it may be sufficient to observe that it is not positively at variance with any known fact ; that the figure of the earth is really such as would be assumed by a fluid mass ; and, lastly, that it offers the best explanation we have of the phenomena of hot springs and volcanic eruptions, and agrees with the chemical nature of their products. Among the other sources of heat are chemical combination and mechani- cal work. The disengagement of heat in the act of combination is a phenomenon of the utmost generality. The quantity of heat given out in each particular case is fixed and definite; its intensity is dependent upon the time over which the action is extended. Many admirable researches on this subject have been published ; but their results will be more advantageously con- sidered at a later part of this work, in connection with the laws of chemical combination. * The Artesian well at Crenelle, near Paris, has a depth of 1794-5 English feet; it is bored through the chalk basin to the sand beneath. The temperature of the water, which is exceed- ingly abundant, is 82 F.; the mean temperature of Paris is 51 F.; the difference is 31 F.; which gives a rate of about 1 for 58 feet. HEAT. 75 Heat produced by Mechanical Work. Heat and motion are convertible one into the other. The powerful mechanical effects produced by the elasticity of the vapor evolved from heated liquids afford abundant illustration of the conversion of heat into motion ; and the production of heat by friction, by the hammering of metals, and in the condensation of gases (p. 72), shows with equal clearness that motion may be converted into heat. In some cases the rise of temperature thus produced appears to be due to a diminution of heat-capacity in the body operated upon, as in the case of a compressed gas just alluded to. Malleable metals, also, as iron and copper, which become heated by hammering or powerful pressure, are found thereby to have their density sensibly increased and their capacity for heat dimin- ished. A soft iron nail may be made red-hot by a few dexterous blows on an anvil; but the experiment cannot be repeated until the metal has been annealed, and in that manner restored to its former physical state. But the amount of heat which can be developed by mechanical force is, in most cases, out of all proportion to what can be accounted for in this way. Sir H. Davy melted two pieces of ice by rubbing them together in a vacuum at the temperature of ; and Count Rumford found that the heat developed by the boring of a brass cannon was sufficient to bring to the boiling-point two and a half gallons of water, while the dust or shavings of metal, cut by the borer, weighed only a few ounces. In these and all similar cases the heat appears as a direct result of the force expended ; the motion is converted into heat. The connection between heat and mechanical force appears still more in- timate when it is shown that they are related by an exact numerical law, a given quantity of the one being always convertible into a definite amount of the other. The first approximate determination of this most important numerical relation was made by Count Rumford in the manner just alluded to. A brass cylinder enclosed in a box containing a known weight of water at 60 F. was bored by a steel borer made to revolve by horse-power, and the time was noted which elapsed before the water was raised to the boiling- point by the heat resulting from the friction. In this manner it was found that the heat required to raise the temperature of a pound of water by 1 F. is equivalent to 1034 times the force expended in raising a pound weight one foot high, or to 1034 "foot pounds," as it is technically expressed. This estimate is now known to be too high, no account having been taken of the heat communicated to the containing vessel, or of that which was lost by dispersion during the experiment. For the most exact determinations of the mechanical equivalent of heat we are indebted to the careful and elaborate researches of Mr. J. P. Joule. From experiments made in the years 1840-43 on the relations between the heat and mechanical power generated by the electric current, Mr. Joule was led to conclude that the heat required to raise the temperature of a pound of water 1 F. is equivalent to 838 foot-pounds; this he afterwards reduced to 772 ; and a nearly equal result was afterwards obtained by ex- periments on the condensation and rarefaction of gases ; but this estimate has since been found to be likewise too great. The most trustworthy results are obtained by measuring the quantity of heat generated by the friction between solids and liquids. It was for a long time believed that no heat was evolved by the friction of liquids and gases. But in 1842 Meyer showed that the temperature of water may be raised 22 or 23 F. by agitating it. The warmth of the sea after a few days of stormy weather is also probably an effect of fluid friction. The apparatus employed by Mr. Joule for the determination of this im- portant constant, by means of the friction of water, consisted of a brass paddle-wheel furnished with eight sets of revolving vanes, working between four sets of stationary vanes. This revolving apparatus, of which fig. 49 76 HEAT. shows copper Fig. 49. Fig. 50. motion pended a vertical, and fig. 50 a horizontal section, was firmly fitted into a vessel (see fig. 51) containing water, in the lid of which were two necks, one for the axis to revolve in without touching, the other for the insertion of a thermometer. A similar apparatus, but made of iron, and of smaller size, having six rota- tory and eight sets of stationary vanes, was used for the experiments on the friction of mercury. The apparatus for the friction of cast- iron consisted of a vertical axis car- rying a bevelled cast-iron wheel, against which a bevelled wheel was pressed by a lever. The wheels were enclosed in a cast-iron vessel filled with mercury, the axis passing through the lid. In each apparatus was given to the axis by the descent of leaden weights w (fig. 51) sus- by strings from the axis of two wooden pulleys, one of which is Fig. 51. TV- at p, their axis being supported on friction wheels d d, and the pulleys were connected by fine twine with a wooden roller r, which, by means of a pin, could be easily attached to or removed from the friction apparatus. The mode of experimenting was as follows : The temperature of the frictional apparatus having been ascertained, and the weights wound up, the roller was fixed to the axis, and the precise height of the weights as- certained; the roller was then set at liberty, and allowed to revolve till the weights touched the floor. The roller was then detached, the weights wound up again, and the friction renewed. This having been repeated twenty times, the experiment was concluded with another observation of the temperature of the apparatus. The mean temperature of the apart- ment was ascertained by observations made at the beginning, middle, and end of each experiment. Corrections were made for the effects of radia- tion and conduction; and, in the experiments with water, for the quantities of heat absorbed by the copper vessel and the paddle-wheel. In the ex- periments with mercury and cast-iron, the heat-capacity of the entire ap- paratus was ascertained by observing the heating effect which it produced on a known quantity of water in which it was immersed. In all the ex- HEAT. 77 periments, corrections were also made for the velocity with which the weights came to the ground, and for the friction and rigidity of the strings. The thermometers used were capable of indicating a variation of tempera- ture as small as ^ of a degree Fahrenheit. The following table contains a summary of the results obtained by this method; the second column gives the results as they were obtaine in air; in the third column the same results corrected for a vacuum : Material Equivalent Equivalent employed. in air. in vacno. Mean. Water . . 773-640 772-692 772-692 Mercury. . {* |} 774-083 Cast-iron. . 774,87 In the experiments with cast-iron, the friction of the wheels produced a considerable vibration in the frame-work of the apparatus, and a loud sound ; it was therefore necessary to make allowance for the quantity of force expended in producing these effects. Tae number 772-692, obtained by the friction of water, is regarded as the most trustworthy ; but even this may be a little too high ; because even in the friction of fluids it is impos- sible entirely to avoid vibration and sound. The conclusions deduced from these experiments are: 1. That the quantity of heat produced by the friction of bodies, whether solid or liquid, is always proportional to the force expended. 2. That the quantity of heat capable of increasing the temperature of lib. of wafer (weighed in vacuo, and between 55 and 60) by 1 F., requires for its evo- lution the expenditure of a mechanical force represented by the fall of 772lbs. through the space of 1 foot. Or, the heat capable of increasing the temperature ofl gram of water by 1 C., is equivalent to a force represented by the fall of 423-55 grams through the space of 1 metre. This is consequently the effect of " a unit of heat. ^ Experiments made by other philosophers on the work done by a steam- engine, on the heat evolved by an electro-magnetic engine at rest and in motion, and on the he.at evolved in the circuit of a voltaic battery and in a metallic wire through which an electric current is passing, have given values for the mechanical equivalent of heat very nearly equal to the above. DYNAMICAL THEORY OF HEAT. For a very long time two rival theories have been held regarding the nature of heat: on the one hand, heat has been viewed as having a material existence, though differing from ordinary matter in being without weight, and in other respects; on the other hand, it has been regarded as a state or condition of ordinary matter, and generally as a condition of motion. From the latter part of the last century, until the modern researches upon the mechanical equivalent, the former view had by far the greater number of adherents. Its popularity may be chiefly traced to the teaching of Black and Lavoisier. By the former of these philosophers, the various capacities for heat, or specific heats of- different bodies, seem to have been regarded as analogous to the various proportions of the same acid required to neu- tralize equal quantities of different bases, while the solid, liquid, and gaseous states were explained by Black as representing so many distinct proportions in which heat was capable of combining with ordinary matter. Very similar views were advocated by Lavoisier: he regarded all gases as compounds of a base characteristic of each, with caloric, and supposed that when, as the result of chemical action, they assumed the liquid or solid state, this caloric was set free and appeared as sensible heat. 7* 78 HEAT. Heat was compared by these philosophers to a material substance, in order to explain its then known quantitative relations ; and from this point of view the conception introduced by them had the great advantage of being more easily grasped than any which the advocates of the immaterial nature of heat had to offer in its place. It was much easier to conceive of definite quantities of an exceedingly subtile substance or fluid, than of definite quantities of motion, which was itself undefined as to its nature. It was a direct consequence of the material view, that heat should be considered as indestructible and as incapable of being produced, and therefore that the total quantity of heat in the universe should be regarded as at all times the same. But, on the other hand, this hypothesis did not afford a satisfactory ex- planation of the production of heat by mechanical means. Here it was not easy to deny the actual generation of heat, or to explain the effects as de- pending merely on its altered distribution. Nevertheless, the evolution of heat by friction and percussion was generally considered, by the advocates of the material view, as in some way resulting from a diminution in the capacities for heat of the bodies operated upon ; and this explanation de- rived considerable support from the remark, made by Black, that a piece of soft iron, which has been once made red-hot by hammering (see p. 75), cannot be so heated a second time until it has been heated to redness in a fire and allowed to cool. In this case, certainly, it seemed as though the hammering forced out heat from the mass of iron, like water from a sponge, and that a fresh supply was taken up when the iron was put in the fire. This explanation, however, did not satisfy Rumford, who, in the investi- gation described above, made direct experiments upon the specific heat of the chips of metal detached by the friction, and found it to be identical with that of brass under ordinary circumstances. Still more decisive proof that the heat generated by friction cannot be ascribed to a diminution of specific heat in the substances operated on was afforded by Davy's experiment on the liquefaction of ice by friction ; for in this case the ice was converted into a liquid having twice the specific heat of the ice itself. Hence Davy * drew the conclusion that, "The immediate cause of the phenomena of heat is motion, and the laws of its communication are precisely the same as the laws of the communication of motion." The mechanical, or dynamical theory, which regarded heat as consisting in a state of molecular motion, cannot however be said to have been defi- nitely established, until it also was made quantitative, until it was shown that exact numerical laws regulate the production of heat by work or of work by heat, equally with its production during solidification and disap- pearance during fusion. To illustrate the general nature of the dynamical theory of heat, we give an outline of the view of the constitution of gases, first put forward, in its present form, by Joule ; f and subsequently developed by Kronig,J and Clausius,$ and of the explanation of the relations existing between solids, liquids, and gases, which has been deduced from it by the last-named philosopher. First, then, it is assumed that the particles of all bodies are in constant motion, and that this motion constitutes heat, the kind and quantity of mo- tion varying according to the state of the body, whether solid, liquid, or gaseous. In gases, the molecules each molecule being an aggregate of atoms are supposed to be constantly moving forward in straight lines, and with a * Elements of Chemical Philosophy, 1812, pp. 94, 95. f Ann. Ch. Phys. [3] 1. 381. J Pogg. Ann. xcix. 315. \ Ibid. 353. HEAT. 79 constant velocity, till they impinge against each other, or against an im- penetrable wall. This constant impact of the molecules produces the ex- pansive tendency or elasticity which is the peculiar characteristic of the pisrous state. The rectilinear movement is not, however, the only one with which the particles are affected. For the impact of two molecules, unless it takes place exactly in the line joining their centres of gravity, must give rise to a rotatory motion; and, moreover, the ultimate atoms of which the molecules are composed may be supposed to vibrate within certain limits, being, in fact, thrown into vibration by the impact of the molecules. This vibratory motion is called by Clausius, the motion of the constituent atoms. The total quantity of heat in the gas is made up of the progressive motion of the molecules, together with the vibratory and other motions of the con- stituent atoms; but the progressive motion alone, which is the cause of the expansive tendency, determines the temperature, Now, the outward pressure exerted by the gas against the containing envelope arises, according to the hypothesis under consideration, from the impact of a great number of gaseous molecules against the sides of the vessel. But at any given tem- perature, that is, with any given velocity, the number of such impacts taking place in a given time, must vary inversely as the volume of the given quan- tity of gas ; hence the pressure varies inversely as the volume or directly as the density, which is Boyle's law. When the volume of the gas is constant, the pressure resulting from the impact of the molecules is proportional to the sum of the masses of all the molecules multiplied into the squares of their velocities; in other words, to the so-called vis viva or working force of the progressive motion. If, for ex- ample, the velocity be doubled, each molecule will strike the sides of the vessel with a twofold force, and its number of impacts in a given time will also be doubled : hence the total pressure will be quadrupled. Now, we know that when a given quantity of any perfect gas is main- tained at a constant volume, it tends to expand by ^y-g- of its bulk at zero for each degree Centigrade. Hence the pressure or elastic force increases proportionally to the temperature reckoned from 273 C. ; that is to say, to the absolute temperature. Consequently, the absolute temperature is pro- portional to the working force of the progressive motion. Moreover, as the motions of the constituent particles of a gas depend on the manner in which its atoms are united, it follows that in any given gas the different motions must be to one another in a constant ratio ; and, there- fore, the vis viva or working force of the progressive motion must be an aliquot part of the entire working force of the gas: hence also the absolute temperature is proportional to the total working force arising from all the motions of the particles of the gas. From this it follows that the quantity of heat which must be added to a gas of constant volume in order to raise its temperature by a given amount, is constant and independent of the temperature. In other words, the specific heat of a gas referred to a given volume is constant, a result which agrees with this experiments of Regnault, mentioned at p. 72. The result may be otherwise expressed, as follows : The total or working force of ihe gas is to the ivorking force of the progressive motion of Ihe molecules, which is the measure of the temperature, in a constant ratio. This ratio is different for dif- ferent gases, and is greater as the gas is more complex in its constitution : in other words, as its molecules are made up of a greater number of -atoms. The specific heat referred to a constant pressure is known to differ from the true specific heat only by a constant quantity. The relations just considered between the pressure, volume, and temper- ature of gases, presuppose, however, certain conditions of molecular con- stitution, which are, perhaps, never rigidly fulfiled ; and. accordingly, Ilie experiments of Magnus and Regnault show (p. 52) that gases do exhibit 80 HEAT. slight deviations from Gay-Lussac and Boyle's laws. What the conditions are which strict adherence to these laws would require, will be better under- stood by considering the differences of molecular constitution which must exist in the solid, liquid, and gaseous states. A movement of molecules must be supposed to exist in all three states. In the solid state, the motion is such that the molecules oscillate about certain positions of equilibrium, which they do not quit, unless they are acted upon by external forces. This vibratory motion may, however, be of a very complicated character. The constituent atoms of a molecule may vibrate separately; the entire molecules may also vibrate as such about their centres of gravity, and the vibrations may be either rectilinear or rotatory. Moreover, when extraneous forces act upon the body, as in shocks, the molecules may permanently alter their relative positions. In the liquid state the molecules have no determinate positions of equili- brium. They may rotate completely about their centres of gravity, and may also move forward into other positions. But the repulsive action arising from the motion is not strong enough to overcome the mutual attrac- tion of the molecules and separate them completely from each other, A molecule is not permanently associated with its neighbors, as in the solid state; it does not leave them spontaneously, but only under the influence offerees exerted upon it by other molecules, with which it then comes into the same relation as with the former. There exists, therefore, in the liquid state, a vibratory, rotatory, and progressive movement of the molecules, but so regulated, that they are not thereby forced asunder, but remain within a certain volume Avithout exerting any outward pressure. In the gaseous state, on the other hand, the molecules are removed quite beyond the sphere of their mutual attractions, and travel onward in straight lines according to the ordinary laws of motion. When two such molecules meet, they fly apart from each other, for the most part with a velocity equal to that with which they came together. The perfection of the gaseous state, however, implies: 1. That the space actually occupied by the mole- cules of the gas be infinitely small in comparison with the entire volume of the gas. 2. That the time occupied in the impact of a molecule, either against another molecule or against the sides of the vessel, be infinitely small in comparison with the interval between any two impacts. 3. That the influence of the molecular forces be infinitely small. When these con- ditions are not completely fulfilled, the gas partakes more or less of the nature of a liquid, and exhibits certain deviations from Gay-Lussac and Boyle's laws. Such is, indeed, the case with all known gases; to a very slight extent with those which have not yet been reduced into the liquid state ; but to a greater extent with vapors and condensable gases, especially near the points of condensation. Let us now return to the consideration of the liquid state. It has been said that the molecule of a liquid, when it leaves those with which it is as- sociated, ultimately takes up a similar position with regard to other mole- cules. This, however, does not preclude the existence of considerable ir- regularities in the actual movements. Now, at the surface of the liquid, it may happen that a particle, by a peculiar combination of the rectilinear, rotatory, and vibratory movements, may be projected from the neighboring molecules with such force as to throw it completely out of their sphere of action* before its projectile velocity can be annihilated by the attractive force which they exert upon it. The molecule will then be driven forward into the space above the liquid, as if it belonged to a gas, and that space, if originally empty, will in consequence of the action just described, become more and more filled with these projected molecules, which will comport themselves within it exactly like a gas, impinging and exerting pressure upon the sides of the envelope. One of these sides, however, is formed by HEAT. 81 the surface of the liquid, and when a molecule impinges upon this surface, it will, in general, not be driven back, but retained by the attractive forces of the other molecules. A state of equilibrium, not static, but dynamic, will therefore be attained, when the number of molecules projected in a given time into the space above, is equal to the number which in the same time impinge upon and are retained by the surface of the liquid. This is the process of vaporization. The density of the vapor required to insure the compenzation just mentioned, depends upon the rate at which the par- ticles are projected from the surface of the liquid, and this again upon the rapidity of their movement within the liquid, that is to say, upon the tem- perature. It is clear, therefore, that the density of a saturated vapor must increase with the temperature. If the space above the liquid is previously filled with a gas, the molecules of this gas will impinge upon the surface of the liquid, and thereby exert pressure upon it; but as these gas-molecules occupy but an extremely small proportion of the space above the liquid, the particles of the liquid will be projected into that space almost as if it were empty. In the middle of the liquid, however, the external pressure of the gas acts in a different manner. There also it may happen that the molecules may be separated with such force as to produce a small vacuum in the midst of the liquid. But this space is surrounded on all sides by masses which afford no passage to the disturbed molecules ; and in order that they may increase to a permanent vapor-bubble, the number of molecules projected from the inner surface of the vessel must be such as to produce a pressure outwards equal to the ex- ternal pressure tending to compress the vapor-bubble. The boiling of the liquid will, therefore, be higher as the external pressure is greater. According to this view of the process of vaporization, it is possible that vapor may rise from a solid as well as from a liquid; but it by no means necessarily follows that vapor must be formed from all bodies at all tempera- tures. The force which holds together the molecules of a body may be too great to be overcome by any combination of molecular movements, so long as the temperature does not exceed a certain limit. The production and consumption of heat which accompany changes in the state of aggregation, or of the volume of bodies, are easily explained, ac- cording to the preceding principles, by taking account of the work done by the acting forces. This work is partly external to the body, partly internal. To consider first the internal work : . When the molecules of a body change their relative positions, the change may take place either in accordance with or in opposition to the action of the molecular forces existing within the body. In the former case, the molecules, during the passage from one state to the other, have a certain velocity imparted to them, which is immediately converted into heat; in the latter case, the velocity of their movement, and consequently the tempera- ture of the body, is diminished. In the passage from the solid to the liquid state, the molecules, although not removed from the spheres of their mutual attractions, nevertheless change their relative positions in opposition to the molecular forces, which forces have, therefore, to be overcome. In evapo- ration, a certain number of the molecules are completely separated from the remainder, which again implies the overcoming of opposing forces. In both cases, therefore, work is done, and a certain portion of the working force of the molecules, that is, of the heat of the body, is lost. But when once the perfect gaseous state is attained, the molecular forces are com- pletely overcome, and any further expansion may take place without inter- nal work, and, therefore, without loss of heat, provided there is no external resistance. But in nearly all cases of change of state or volume, there is a certain amount of external resistance to be overcome, and a corresponding loss of 82 HEAT. heat. When the pressure of a gas, that is to say, the impact of its atoms, is exerted against a movable obstacle, such as a piston, the molecules lose just so much .of their moving power as they have imparted to the piston, and, consequently, their velocity is diminished and the temperature lowered. On the contrary, when a gas is compressed by the motion of a piston, its molecules are driven back with greater velocity than that with which they impinged on the piston, and, consequently, the temperature of the gas is raised. When a liquid is converted into vapor, the molecules have to overcome the atmospheric pressure or other external resistance, and, in consequence of this, together with the internal work already spoken of, a large quantity of heat disappears, or is rendered latent, the quantity thus consumed being, to a considerable extent, affected by the external pressure. The liquefac- tion of a solid not being attended with much increase of volume, involves but little external work; nevertheless the atmospheric pressure does in- fluence, to a slight amount, both the latent heat of fusion and the melting- point. LIGHT. 83 LIGHT. nnWO views have been entertained respecting the nature of light. Sir Isaac Newton imagined that luminous bodies emit, or shoot out, infi- nitely small particles in straight lines, which, by penetrating the transparent parts of the eye and falling upon the nervous tissue, produce vision. Other philosophers drew a parallel between the properties of light and those of sound, and considered that, as sound is certainly the effect of undulations, or little waves, propagated through elastic bodies in all directions, so light might be nothing more than the consequence of similar undulations trans- mitted with inconceivable velocity through a highly elastic medium, of ex- cessive tenuity, filling all space, and occupying the intervals between the particles of material substances. To this medium they gave the name of ether. The wave hypothesis of light is at present generally adopted. It is in harmony with all the known phenomena discovered since the time of Newton, not a few of which were first deduced from the undulatory theory, and afterwards verified by experiment. Several well-known facts are in direct opposition to the theory of emission. A ray of light emitted from a luminous body proceeds in a straight line, and with extreme velocity. Certain astronomical observations afford the means of approximating to a knowledge of this velocity. The satellites of Jupiter revolve about the planet in the same manner as the moon about the earth, and the time required by each satellite for the purpose is exactly known from its periodical entry into or exit from the shadow of the planet. The time required by one is only 42 hours. Homer, the astronomer of Copenhagen, found that this period appeared to be longer when the earth, in its passage round the sun, moved from the planet Jupiter ; and, on the contrary, he observed that the periodic time appeared to be shorter when the earth moved in the direction towards Jupiter. The difference, though very small for a single revolution of the satellite, increases, by the addition of 'many revolutions, during the passage of the earth from its nearest to its greatest distance from Jupiter, that is, in about half a year, till it amounts to 16 minutes and 16 seconds. Homer concluded from this, that the light of the sun, reflected from the satellite, required that time to pass through a distance equal to the diameter of the orbit of the earth ; and since this place is little short of 200 millions of miles, the velocity of light cannot be less than 200,000 miles in a second of time. It will be seen hereafter that this rapidity of transmission is rivalled by that of electricity. Another astronomical phenomenon, observed and correctly explained by Bradley, the aberration of the fixed stars, leads to the same result. Phy- sicists have, moreover, succeeded in measuring the velocity of light for terrestrial, and, indeed, comparatively small distances; the results of these experiments essentially correspond with those given by astronomical observations. When a ray of light falls upon a boundary between two media, a part of it, and, in exceptional cases, the whole, is reflected into the first medium, whilst the other part penetrates the second medium. The law of regular reflection is extremely simple. If a line be drawn perpendicular to the surface upon which the ray falls, and the angle con- tained between the ray and the perpendicular measured, it will be found, LIGHT. Fig. 52. Fig. 53. that the ray, after reflection, takes such a course as to make with the per- pendicular an equal angle on the opposite side of the latter. A ray of light, R, falling at the point p, will be reflected in the direction PR', making the angle R'PP' equal to the angle RPP X ; and a ray from the point r falling upon the same spot will be reflected to r f in virtue of the same law. Further, it is to be observed that the incident and reflected rays are always con- tained in the same normal plane. The same rule holds good if the mirror be curved, as a portion of a sphere, the curve being considered as made up of a multitude of little planes. Parallel rays cease to be so when reflected from curved surfaces, becoming divergent or convergent according as the reflecting surface is convex or concave. Bodies with rough and uneven surfaces, the smallest parts of which are inclined towards each other without order, reflect the light diffused. The perception of bodies depends upon the diffused reflected light. It has just been stated that light passes in straight lines ; but this is true only so long as the medium through which it travels pre- serves the same density and the same chemi- cal nature : when this ceases to be the case, the ray of light is bent from its course into a new one, or is said to be refracted. Let E be a ray of light falling upon a plate of some transparent substance with parallel sides, such as a piece of thick plate glass, in short, any transparent homogeneous ma- terial which is either non-crystalline, or crys- tallizes in the regular system ; and let A be its point of contact with the upper surface. The ray, instead of holding a straight course and passing into the glass in the direction A B, will be bent downwards to c ; and, on leaving the glass, and issuing into the air on the other side, it will again be bent, but in the opposite direction, so as to make it parallel to the continuation of its former track, provided there be one and the same medium on the upper and lower side of the plate. The general law is thus expressed: When the ray passes from a rare to a denser medium, it is usually refracted towards a line perpendicular to the surface of the latter; and conversely, when it leaves a dense medium for a rarer one, it is re- fracted from a line perpendicular to the surface of the denser substance ; in the former case the angle of incidence is greater than that of refraction ; in the latter it is less. In both cases the direction of the refracted ray is in the plane R A s, which is formed by the falling ray and the perpendicular s A drawn from the spot where the ray is refracted ; the angle RAS = BAS / , is called the angle of incidence. The angle c A s / is called the angle of re- fraction. The difference of these two angles, that is, the angle CAB, is the refraction. The amount of refraction, for the same medium, varies with the obliquity with which the ray strikes the surface. When perpendicular to the latter, the ray passes without change of direction at all; and in other positions, the refraction increases with the obliquity. Let R represent a ray of light falling upon the surface of a mass of plate glass at the point A. From this point let a perpendicular fall and be con- tinued into the new medium ; and around the same point, as a centre, let \ \ LIGHT. 85 Fig. 54. a circle be drawn. According to the law just stated, the refraction must be towards the perpendicular; in the direction A B/, for example. Let the }i nes a rtj a f a', at right angles to the per- pendicular, be drawn, and their length com- pared by means of a scale of equal parts, and noted; their length will in the case supposed be in the proportion of 3 to 2. These lines are termed the sines of the angles of incidence and refraction respectively. Now let another ray be taken, such as r ; it is refracted in the same manner to r', the bending being greater from the increased obliquity of the ray; but what is very re- markable, if the sines of the two new angles of incidence and refraction be again com- pared, they will still be found to bear to each other the proportion of 3 to 2. The fact is expressed by saying, that so long as the light passes from one to the other of the same two media, the ratio of the sines of the angles of incidence and re- fraction is constant. This ratio is called the index of refraction. Different bodies possess different refractive powers ; generally speaking, the densest substances refract most. Combustible bodies have been noticed to possess greater refractive power than their density would indicate, and from this observation Sir I. Newton predicted the combustible nature of the diamond long before anything was known respecting its chemical nature. The method adopted for describing the comparative refractive power of different bodies, is to state the ratio borne by the sine of the angle of inci- dence in the first medium, and on the boundary of the second, to the sine of the angle of refraction in this second medium ; this is called the index of refraction of the two substances; it is greater or less than unity, according as the second medium is denser or rarer than the first. In the case of air and plate glass the index of refraction is 1-5. When the index of refraction of any particular substance is once known, the effect of the latter upon a ray of light entering it in any position can be calculated by the law of sines. The following table exhibits the indices of refraction of several substances, supposing the ray to pass into them from the air : Substances. Tabasheer* Ice Water Index of refraction. . . 1-10 . . 1-30 1-34 Fluor spar 1-40 Plate glass .... 1-50 Rock-crystal . . . .1-60 Chrysolite . . . . 1-69 Bisulphide of carbon . 1-70 Substances. Index of refraction. Garnet 1-80 Glass, with much oxide of lead 1-90 Zircon 2-00 Phosphorus 2-20 Diamond 2-50 Chromate of lead . . . 3-00 Cinnabar 3-20 Fig. 55. When a luminous ray enters a mass of substance differing in refractive power from the air, and whose surfaces are not parallel, it becomes permanently deflected from its course and altered in its direction. It is upon this principle that the properties of prisms and lenses depend. To take an example. Fig. 55 represents a triangular prism of glass, upon the side of which the ray of light R may be supposed to fall. This ray will 8 * A siliceous deposit in the joints of the bamboo. 86 LIGHT. of course be refracted, on entering the glass, towards a line perpendicular to the first surface, and again, from a line perpendicular to the second sur- face on emerging into the air. The result is the deflecton a c R, which is equal to the sum of the two deflections which the ray undergoes in passing through the prism. A convex lens is thus enabled to converge rays of light falling upon it, and a concave lense to separate them more widely ; each separate part of the surface of the lens producing its own independent effect. The light of the sun and celestial bodies in general, as well as that of the electric spark and of all ordinary flames, is of a compound nature. If a ray of light from any of the sources mentioned be admitted into a dark room by a small hole in a shutter, or otherwise, and suffered to fall upon a glass prism in the manner shown in fig. 56, it will not only be refracted from its straight course, but will be decomposed into a number of colored rays, which may be received upon a white screen placed behind the prism. When solar light is employed, the colors are extremely brilliant, and spread into Fig. 56. an oblong space of considerable length. The upper part of this image, or spectrum, will be violet and the lower red, the intermediate portion, com- mencing from the violet, being indigo, blue, green, yellow, and orange, all graduating imperceptibly into each other. This is the celebrated experi- ment of Sir Isaac Newton ; from it he drew the inference that white light is composed of seven primitive colors, the rays of which are differently re- frangible by the same medium, and hence capable of being thus separated. The violet rays are most refrangible, and the red rays least.* Bodies of the same mean refractive power do not always equally disperse or spread out the differently colored rays to the same extent; because the principal yellow or red rays, for instance, are equally refracted by two prisms of different materials, it does not follow that the blue or the violet will be similarly affected. Hence, prisms of different varieties of glass, or other transparent substances, give, under similar circumstances, very dif- ferent spectra, both as respects the length of the image, and the relative extent of the colored bands. The appearance of the spectrum may also vary with the nature of the source of light: the investigation of these differences, however, involves the use of a more delicate apparatus. Fig. 57 shows the principle of such an apparatus, which is called a spectroscope. The light, passing through a fine slit, s, impinges upon a flint-glass prism, p, by which it is dispersed. The decomposed light emerges from the prism in several directions between r (red rays) and v (violet rays) ; and the spectrum thus produced is observed * The colors of natural objects are supposed to result from the power possessed by their surfaces of absorbing some of the colored rays, while they reflect or transmit, as the case may be, the remainder of the rays. Thus an object appears red because it absorbs or causes to disappear the yellow and blue rays composing the white light by which it is illuminated. Any color which remains after the deduction of another color from white light, is said to be cnmpJenifntari/ to the latter. Complementary colors, when acting simultaneously, reproduce white light. Thus in the example already quoted, red and green the latter resulting from yellow and blue are complementary colors. The fact of complementary colors giving rise to white light may be readily illustrated by mixing in appropriate quantities a rose-red solu.^ ticm of cobalt and green solution of nickel; the resulting liquid is nearly colorless. LIGHT. 87 by the telescope t, which receives only part of it at once ; but the several parts may be readily examined by turning slightly either the prism, j?, or the telescope, t. Fig. 57. If the solar spectrum be examined in this manner, numerous dark lines parallel with the edge of the prism are observed. They were discovered in 1802 by Dr. Wollaston, and subsequently more minutely investigated by Fraunhofer. They are generally known as Fraunhofer's lines. These dark lines, which exist in great numbers, and of very varying strength, are ir- regularly distributed over the whole spectrum. Some of them, in con- sequence of their peculiar strength and their mutual position, may always be easily recognized ; the more conspicuous are represented in fig. 58. The same dark lines, though paler, and much more difficult to recognize, are Fig. 58. Red. Orange. Yellow. Green. Blue. Indigo. Tiolet. A B C D "E"^ F G H Sun Na Dark lines. Sr Bright lines. observed in the spectrum of planets lighted by the sun ; for instance, in the light emanating from Venus. On the other hand, the dark lines ob- served in the spectra, which are produced by the light emanating from fixed stars from Sirius, for instance differ in position from those previously mentioned. Sources of light which contain no volatile constituents incandescent platinum wire, for example furnish continuous spectra, exhibiting no such lines. But if volatile substances be present in the source of light, bright lines are observed in the spectrum, which are frequently characteristic of the volatile substances. Professor Pliicker, of Bonn, has investigated the spectra which are pro- duced by the electric light when developed in very rarefied gases. He found the bright lines and the dark stripes between the lines varying con- siderably with different gases. When the electric light was developed in a 88 LIGHT. mixture of two gases, the spectrum thus obtained exhibited simultaneously the peculiar spectra belonging to the two gases of which the mixture con- sisted. When the experiment was made in gaseous compounds capable of being decomposed by the electrical current, this decomposition was indicated by the spectra of the separated constituents becoming perceptible. Many years ago the spectra of colored flames were examined by Sir John Herschel, Fox Talbot, and W. A. Miller. Within the last few years results of the greatest importance have been obtained by Kirchhoff and Bunsen, Fig. 59. who have investigated the spectra furnished by the incandescence of vola- tile substances: these researches have enriched chemistry with a new method of analysis, the analysis by spectrum observations. In order to recognize one of the metals of the alkalies or of the alkaline earths, it is generally sufficient to introduce a minute quantity of a moderately volatile compound of the metal on the loop of a platinum wire into the edge of the very hot, but scarcely luminous flame, of a mixture of air and coal-gas, and to examine the spectrum which is furnished by the flame containing the vapor of the metal or its compound. Fig. 59 exhibits the apparatus which is used in performing experiments of this description. The light of the flame in which the metallic compound is evaporated passes through the fine slit in the disc, s, into a tube, the opposite end of which is provided with a convex lens. This lens collects the rays diverging from the slit, and throws them parallel upon the prism, p. The light is decomposed by the prism, and the spectrum thus obtained is observed by means of the telescope, which may be turned round the axis of the stand carrying the prism. Foreign light is excluded by an appropriate covering. The limits of this elementary treatise do not permit us to describe the ingenious arrangements which have been contrived for sending the light from different sources through the same prism at different heights, whereby their spectra, the solar spectrum, for instance, and that of a flame, may be placed in a parallel position, the one above the other, and thus be compared.* The spectra of flames in which different substances are volatilized frequently exhibit such characteristically distinct phenomena, that they may be used with the greatest advantage fcfr the discrimination of these substances. Thus the spectrum of a flame containing sodium (Na) exhibits a bright line on * See the article " Spectral Analysis," by Prof. Roscoe, in Watts's Dictionary of Chemistry, vol. i. LIGHT. 89 the yellow portion, the spectrum of potassium .(K) a characteristic bright line at the extreme limit of the red, and another at the opposite violet limit of the spectrum. Lithium (Li) shows a bright brilliant line in the red, and a paler line in the yellow portion ; strontium (Sr) a bright line in the blue, one in the orange, and six less distinct ones in the red portion of the spec- trum. The diagram (fig. 58) exhibits the most remarkable of the dark lines (Fraunhofers lines), and the position of the bright lines in the spectra of flames containing the vapors of compounds of the several metals enumerated. The delicacy of these spectral reactions is very considerable, but unequal in the case of different metals. The presence of YTre.imT.Tnnj' S ra i n f sodium in the flame is still easily recognizable by the bright yellow line in the spectrum. Lithium, when introduced in the form of a volatile compound, imparts to the flame a red color; but this coloration is no longer perceptible when a volatile sodium compound is simultaneously present, the yellow coloration of the flame predominating under such circumstances. On the other hand, when a mixture of one part of lithium and 1000 parts of sodium is volatilized in a flame, the spectrum of the flame exhibits, together with the bright yellow sodium line, likewise the red line characteristic of lithium. The observation of bright lines not belonging to any of the pre- viously known bodies has led to the discovery of new elements. Thus, Bunsen and Kirchhoff, when examining the spectrum of a flame in which a mixture of alkaline salt was evaporated, observed some bright lines, which could not be attributed to any of the known elements, and were thus led to the discovery of the two new metals, caesium and rubidium. By the same method a new element, thallium, has been more recently discovered by Mr. Crookes. For the examination of the bright lines in the spectra of metals, the electric spark, passing between two points of the metal under examination, may be conveniently employed as a source of light. Small quantities of the metal are invariably volatilized ; and the spectrum developed by the electric light exhibits the bright lines characteristic of the metal employed. These lines were observed by Wheatstone as early as 1835. This method of investigation is more especially applicable to the examination of the spectra of the heavy metals. By a series of theoretical considerations, Professor Kirchhoff has arrived at the conclusion that the spectrum of an incandescent gas is reversed i. e., that the bright lines become dark lines, if there be behind the incandescent gas a very luminous source of light, which by itself furnishes a continuous spectrum. Kirchhoff and Bunsen have fully confirmed this conclusion by experiment. Thus a volatile lithium salt produces, as just pointed out, a very distinct bright line in the red portion of the spectrum ; but if bright sunlight, or the light emitted by a solid body heated to the most powerful incandescence, be allowed to fall through the flame upon the prism, the spectrum exhibits, in the place of this bright line, a black line similar in every respect to Fraunhofers lines in the solar spectrum. In like manner the bright strontium line is reversed into a dark line. Kirchhoff and Bunsen have expressed the opinion that all the Fraunhofer lines in the solar spec- trum are bright lines thus reversed. In their conception, the sun is sur- rounded by aluminous atmosphere, containing a certain number of volatilized substances, which would give rise in the spectrum to certain bright lines, if the light of the solar atmosphere alone could reach the prism ; but the intense light of the powerful incandescent body of the sun which passes through the solar atmosphere, causes these bright lines to be reversed, and to appear as dark lines on the ordinary solar spectrum. Kirchhoff and Bunsen have thus been enabled to attempt the investigation of the chemical constituents of the solar atmosphere, by ascertaining the elements which, 8* 90 LIGHT. when in the state of incandescent vapor, develop bright spectral lines, co- inciding with Fraunhofer's lines in the solar spectrum. Fraunhofer's line D (fig. 58) coincides most accurately with the bright spectral line of sodium, and may be artificially produced by reversing the latter; sodium would thus appear to be a constituent of the solar atmosphere. Kirchhoff has proved, moreover, that sixty bright lines perceptible in the spectrum of iron cor- respond, both as to position and distinction, most exactly with the same number of dark lines in the solar spectrum; and, accordingly, he believes iron, in the state of vapor, to be present in the solar atmosphere. In a similar manner this physicist has endeavored to establish the presence of several other elements in the solar atmosphere. Absorption Spectra. The relative quantities of the several colored rays absorbed by a colored medium of given thickness may be observed by view- ing a line of light through a prism and the colored medium ; the spectrum will then be seen to be diminished in brightness in some parts, and perhaps cut oif altogether in others. This mode of observation is often of great use in chemical analysis, as many colored substances when thus examined afford very characteristic spectra, the peculiarities of which may often be dis- tinguished, even though the solution of the substance under examination contains a sufficient amount of colored impurities to change its color very considerably. The following method of making the observation is given by Professor Stokes.* A small prism is to be chosen of dense flint glass, ground to an angle of 60, and just large enough to cover the eye comfortably. The top and bottom should be flat, for convenience of holding the prism between the thumb and fore-finger, and laying it down on a table, so as not to scratch or soil the faces. A fine line of light is obtained by making a vertical slit in a board six inches square, or a little longer in a horizontal direction, and adapting to the aperture two pieces of thin metal. One of the metal pieces is movable, to allow of altering the breadth of the slit. About the fiftieth of an inch is a suitable breadth for ordinary purposes. The board and metal pieces should be well blackened. On holding the board at arm's length against the sky or a luminous flame, the slit being, we will suppose, in a vertical direction, and viewing the line of light thus formed through the prism held close to the eye, with its edge vertical, a pure spectrum is obtained at a proper azimuth of the prism. Turning the prism round its axis alters the focus, and the proper focus is got by trial. The whole of the spectrum is not, indeed, in perfect focus at once, so that in scrutinizing one part after another it is requisite to turn the prism a little. When daylight is used, the spectrum is known to be pure by its showing the principal fixed lines ; in other cases the focus is got by the condition of seeing distinctly the other objects, whatever they may be, which are presented in the spectrum. To observe the absorption-spec- trum of a liquid, an elastic band is put round the board near the top, and a test-tube containing the liquid is slipped under the band, which holds it in its place behind the slit. The spectrum is then observed just as before, the test-tube being turned from the eye. To observe the whole progress of the absorption, different degrees of strength must be used in succession, beginning with a strength which does not render any part of the spectrum absolutely black, unless it be one or more very narrow bands, as otherwise the most distinctive features of the absorption might be missed. If the solution be contained in a wedge- shaped vessel instead of a test-tube, the progress of the absorption may be watched in a continuous manner by sliding the vessel before the eye. Some observers prefer using a wedge-shaped vessel in combination with the slit, * Chem. Soc. Journ. xvii. 306. LIGHT. 91 the slit being perpendicular to the edge of the wedge. In this case each element of the slit forms an elementary spectrum corresponding to a thick- ness of the solution which increases in a continuous manner from ihe edg of the wedge, where it vanishes. This is the mode of observation adopted by Gladstone.* Fig. 00 represents the effect produced in this way by a solution of chromic chloride, and fig. 61 that produced by a solution of potassium permanganate. Fig. 60. Fig. SI. C d F 3E D OB The right-hand side of these figures corresponds with the red end of the spectrum ; the letters refer to Fraunhofer's lines. The lower part of each figure shows the pure spectrum seen through the thinnest part of the wedge ; and the progress of the absorption, as the thickness of the liquid increases, is seen by the gradual obliteration of the spectrum towards the upper part of the figures. Fluorescence. An examination into a peculiar mode of analysis of light, discovered by Sir John Herschel, in a solution of quinine sulphate, has within the last few years led to the discovery of a most remarkable fact. Mr. Stokes has observed that light of certain refrangibility and color is capable of experiencing a peculiar influence in being dispersed by certain media, and of undergoing thereby an alteration of its refrangibility and color. This curious change, called fluorescence, can be produced by a great number of bodies, both liquid and solid, transparent and opaque. Frequently the change affects only the extreme limits; at other times larger portions, and in a few cases even the whole, or, at all events, the major part of the spec- trum. A dilute solution of quinine sulphate, for instance, changes the violet and the dark-blue light to sky-blue ; by a decoction of madder in a solution of alum all rays of higher refrangibility than yellow are converted into yellow; by an alcoholic solution of the coloring matter of leaves all the rays of the spectrum become red. In all cases in which this peculiar phe- nomenon presented itself in a greater or less degree, Mr. Stokes observed that it consisted in a diminution of the refrangibility. Thus, rays of so high a degree of refrangibility, that they extend far beyond the extreme limits of the spectrum visible under ordinary circumstances, may be ren- dered luminous, and converted into blue and even red light. DOUBLE REFRACTION AND POLARIZATION. A ray of common light made to pass through certain crystals of a particular order is found to undergo a .very remarkable change. It becomes split or divided into two rays, one of * Chem. Soc. Journ. x. 79. 92 LIGHT. Fig. 62. which follows the general law of refraction, while the other takes a new and extraordinary course, dependent on the position of the crystal. This effect, which is called double refraction, is beautifully illustrated in the case of Iceland spar, or crystallized calcium carbonate. On placing a rhomb of this substance on a piece of white paper on which a mark or line has been made, the object will be seen double. Again, if a ray of light be suffered to fall on a plate of glass at an angle of 56 45', the portion of the ray which suffers reflection will be found to have acquired properties which it did not before possess ; for on throwing it, at the same angle, upon a second glass plate, it will be observed that there are two particular positions of the latter, namely, those in which the planes of incidents are at right angles to one another, when the ray of light is no longer reflected, but entirely refracted. Light which has suffered this change is said to be polarized. The light which passes through the first or polarizing plate is, also, to a certain extent, in this peculiar condition, and by employing a series of similar plates held parallel to the first, this effect may be greatly increased ; a bundle of fifteen or twenty such plates may be used with great convenience for the experiment. It is to be remarked, also, that the light polarized by transmission in this manner is in an oppo- site state to that polarized by reflection; that is, when examined by a second or analyzing plate, held at the angle before mentioned, it will be seen to be reflected when the other is transmitted, and to be dispersed when the first is reflected. It is not every substance which is capable of polar- izing light in this manner; glass, water, and certain other bodies bring about the change in question, each having a particular polarizing angle at which the effect is greatest. The metals also can, by reflection, polarize the light, but they do so very imperfectly. The two rays into which a pencil of common light divides itself in passing through a doubly refracting crystal are found on examination to be polarized in a very complete manner, and also transversely, the one being capable of reflection when the other vanishes or is transmitted. The two rays are said to be polarized in op- posite directions. With a rhomb of transparent Iceland spar of tolerably large dimensions, the two oppositely polarized rays may be widely separated and examined apart. Certain doubly refracting crystals absorb the one of these rays, but not the other. Through a plate of such a crystal one ray passes and becomes entirely polarized ; the other, which is likewise polarized, but in another plane, is removed by absorption. The best known of these media is tour- maline. When two plates of this mineral, cut parallel to the axis of the crystal, are held with their axes parallel, as in fig. 63, light traverses them both freely; but when one of them is turned round in the manner shown in fig. 64, so as to make the axes cross at right angles, the light is almost Fig. 03. Fig. 64. LIGHT. 93 wholly stopped, if the tourmalines are good. A plate of the mineral thus becomes an excellent test for discriminating between polarized light and that which has not undergone the change. Some of the most splendid phenomena of the science of light are ex- hibited when thin plates of doubly refracting substances are interposed between the polarizing arrangement and the analyzer. Instead of the tourmaline plate, which is always colored, frequent use is made of two Nichol's prisms, or conjoined prisms of calcium carbonate, which, in consequence of a peculiar cutting and combination, possess the property of allowing only one of the oppositely polarized rays to pass. A more advantageous method of cutting and combining prisms has been given by M. Foucault. His prisms are as serviceable as and less expensive than those of Nichol. If two Nichol's or Foucault's prisms be placed one behind the other in precisely similar positions, the light polarized by the one goes through the other unaltered. But when one prism is slightly turned round in its setting, a cloudiness is produced ; and by continuing to turn the prism, this increases until perfect darkness ensues. This happens, as with the tour- maline plates, when the two prisms cross one another. The phenomenon is the same with colorless as with colored light. CIRCULAR POLARIZATION. Supposing that polarized light, colored, for ex- ample, by going through a plate of red glass, has passed through the first Nichol's prism, and been altogether obstructed in consequence of the posi- tion of the second prism, then, if between the two prisms a plate of rock- crystal formed by a section at right angles to the principal axis of the crystal, be interposed, the light polarized by the first prism will, by passing through the plate of quartz, be enabled partially to pass through the second Nichol's prism. Its passage through the second prism can then again be interrupted by turning the second prism round to a certain extent. The rotation re- quired varieg with the thickness of the plate of rock-crystal, and also with the color of the light employed. It increases from red in the following order yellow, green, blue, violet. This property of rock-crystal was discovered by Arago. The kind of polarization has been called circular polarization. The direction of the rotation is with many plates towards the right hand ; in other plates it is towards the left. The one class is said to possess right-handed polarization, the other class left-handed polarization. For a long time quartz was the only solid body known to exhibit circular polarization. Others have since been found which possess this property in a far higher degree. Thus, a plate of cinnabar acts fifteen times more powerfully than a plate of quartz of equal thickness. Biot observed that many solutions of organic substances exhibit the property of circular polarization, though to a far less extent than rock- crystal. Thus, solutions of cane-sugar, glucose, and tartaric acid, possess right-handed polarization; whilst albumen, uncrystallizable sugar, and oil of turpentine, are left-handed. In all these solutions the amount of circular polarization increases with the concentration of the liquid and the thickness of the column through which the light passes. Hence circular polarization is an important auxiliary in chemical analysis. In order to determine the amount of polarization which any liquid exhibits, it is put into a glass tube not less than from ten to twelve inches long, which is closed with glass plates. This is then placed between the two Nichol's prisms, which have previously been so arranged with regard to each other that no light could pass through. An apparatus of this description, the saccharimeter, is used for determining the concentration of solutions of cane-sugar. The form of this instrument may be seen in fig. (35. The two Nichol's prisms are enclosed in the corresponding fastenings a and 6. Between the two there is a space to receive the tube, which is filled with the solution of 94 LIGHT. sugar. If the prisms are crossed in the way above mentioned before the tube is put in its place, that is, if they are placed so that no light passes them, then by the action of the solution of sugar the light is enabled to pass, and the Nichol's prism, a, must be turned through a certain angle before the light is again perfectly stopped. The magnitude of this angle is observed on the circular disk s s, which is divided into degrees, and upon which, by the turning of the prism, an index z is moved along the division. When the tube is exactly ten inches long, and is closed at both ends by flat glass plates, and when it is filled with solution containing 10 per cent, by weight of cane-sugar, and free from any other substance possessing an ac- tion on light, the angle of rotation is 13-35. Since the magnitude of this angle stands in direct relation to the length of the column of liquid and also to the quantity of sugar in solution, it is clear that the quantity of sugar in any given solution, when the length of the column of liquid is I inches, and the angle of rotation is a degrees, can be determined by the a X I equation ' = 33^-. This process is not sufficient when the solution contains cane-sugar and uncrystallizable sugar : for the latter rotates the ray to the left ; in that Fig. 65. c dud* case only the difference of the two actions is obtained. But if the whole quantity of sugar be changed into uncrystallizable sugar, and the experi- ment be repeated, then from the results of the two observations the quan- tity of both kinds of sugar can easily be calculated. It is difficult to find exactly that position of the Nichol's prisms in which LIGHT. 95 the greatest darkness prevails. To make the measurements more exact and easy, Soleil has made some additions to the apparatus. At tained by mixing 65 parts mercury, 24 tin, and 11 zinc. It is better applied to silk than to iitltnr obtained by leather. 118 ELECTRICITY. Another form of the electrical machine .consists of a circular plate of glass (fig. 79) moving upon an axis, and provided with two pairs of cush- ions or rubbers, attached to the upper and lower parts of the wooden frame, covered with amalgam, between which the plate moves with con- siderable friction. An insulated conductor, armed as before with points, discharges the plate as it turns, the rubber being at the same time con- nected with the ground by the wood-work of the machine, or by a strip of metal. This modification of the apparatus is preferred in all cases where considerable power is wanted. In the practical management of electrical apparatus, great care must be taken to prevent deposition of moisture from the air upon the surface of the glass supports, which should always be varnished with fine lac dissolved in alcohol; the slightest film of water is sufficient to destroy the power of insulation. The rubbers also must be carefully dried, and, like the plate, cleansed from adhering dust before use, and the amalgam renewed if need- ful: in damp weather much trouble is often experienced in bringing the machine into powerful action. When the conductor of the machine is charged with electricity, it acts in- directly on, and accumulates the contrary electricity to its own, at the sur- face of all the surrounding conductors. It produces the greatest effect on the conductor that is nearest to it and is in the best connection with the ground, whereby the electricity of the same kind as that of the machine may pass to the earth. As the inducing electricity attracts the induced electricity of an opposite kind, so, on the other hand, is the former attracted by the latter. Hence, the electricity which the conductor receives from the machine must especially accumulate at that spot to which another good conductor of electricity is opposed. If a metal disc is in connection with the conductor of a machine, and if another similar disc, which is in good connection with the earth, is placed opposite to it, we have an arrange- ment by which tolerably large and good conducting surfaces can be brought close to one another: thus the positive condition of the first disc, as well as the negative condition of the other, must be increased to a very con- siderable degree: the limit is in this case, however, soon reached, because the intervening air easily permits spark-discharge to take place through its substance. With a solid insulating body, as glass or lac, this happens with much greater difficulty, even when the plate of insulating matter is very thin. It is on this principle that instruments for the accumulation of electricity depend, among which the Leyden jar is the most important. A thin glass jar is coated on both sides with tinfoil, care being taken to leave several inches of the upper part un- covered (fig. 80) ; a wire, terminating in a metallic knob, communicates with the internal coating. When the out- side of the jar is connected with the earth, and the knob put in contact with the conductor of the machine, the inner and outer surfaces of the glass become respectively positive and negative, until a very great degree of in- jrgiii" '~~^JJL tensity has been attained. On completing the connec- 'll 1 ifi t * on Between the two coatings by a metallic wire or rod, dischai'ge occurs in the form of an exceedingly bright spark, accompanied by a loud snap ; and if the human body be interposed in the circuit, the peculiar and dis- agreeable sensation of the electric shock is felt at the moment of its completion. By enlarging the dimensions of the jar, or by connecting together a num- ber of such jars in such a manner that all may be charged and discharged simultaneously, the power of the apparatus may be greatly augmented. Thin wires of metal may be fused and dissipated ; pieces of wood may be ELECTRICITY. 119 shattered ; many combustible substances set on fire ; and all the well-known effects of lightning exhibited upon a small scale. The electric spark is often very conveniently employed in chemical inquiries for firing gaseous mixtures in closed vessels. A small Leyden jar charged by the machine is the most effective contrivance for this purpose; but, not unfrequently, a method may be resorted to which involves less preparation. The most convenient means of generating electricity is that proposed by Blinsen. A large porcelain tube, which is dry and warm, is wrapped round and rubbed briskly by a dry silken cloth. After each rub the tube is brought in the immediate neighborhood of the knob of a small Leyden jar, the outer coating of this vessel being in connection with the earth. The electrophorus is also frequently used for this purpose. This instrument consists of a round tray or disli of tinned plate, having a stout wire Fig. 81. round its upper edge ; the width may be about twelve inches, and the depth half sin inch. This tray is filled with melted shellac, and the surface rendered as even as possible. A brass disc, with rounded edge, of about nine inches diameter, is also provided, and fitted with an insulat- ing handle. When a spark is wanted, the resinous plate is excited by striking it with a dry, warm piece of fur, or a silk handkerchief; the cover is placed upon it, and touched by the finger, to- gether with the rim of the plate. When the cover is raised, it is found so strongly charged by induction with positive electricity, as to give a bright spark; and, as the resin is not discharged by the cover, which merely touches it at a few points, sparks may be drawn as often as may be wished. It is not known to what cause the disturbance of the electrical equili- brium of the atmosphere is due: experiment has shown that the higher regions of the air are usually in a positive state, the intensity of which reaches a maximum at a particular period of the day. In cloudy and stormy weather the distribution of the atmospheric electricity becomes much deranged, clouds near the surface of the earth often appearing in a negative state. The circumstances of a thunder-storm exactly resemble those of the charge and discharge of a coated plate or jar; the cloud and the earth represent the two coatings, and the intervening air the bad conducting body or dielectric. The polarities of the opposed surface and of the in- sulating medium between them become raised by mutual induction, until violent disruptive discharge takes place through the air itself, or through any other bodies which may happen to be in the interval. When these are capable of conducting freely, the discharge is silent and harmless; but in other cases it often proves highly destructive. These dangerous effects are now in a great measure obviated by the use of lightning-rods attached to buildings, the erection of which, however, demands a number of pre- cautions not always understood or attended to. The masts of ships may be guarded in like manner by metal conductors : Sir W. Snow Harris has devised a most ingenious plan for the purpose, which is now adopted, with the most complete success, in the Koyal Navy. ELECTRIC CURRENT; ELECTRIC BATTERY. When two solid conducting bodies are plunged into a liquid which acts upon them unequally, the electric equilibrium is also disturbed, the one acquiring the positive condition, and the other the negative. Thus, pieces 120 ELECTRICITY. of zinc and platinum put into dilute sulphuric acid, constitute an arrange- ment capable of generating electrical force: the zinc being the metal at- tacked, becomes negative ; and the platinum remaining unaltered, assumes, the positive condition ; and on making a metallic communication in any way between the two plates, discharge ensues, as when the two surfaces of a coated and charged jar are put into connection. No sooner, however, has this occurred, than the disturbance is repeated; and as these successive charges and discharges take place through the fluid and metals with inconceivable rapidity, the result is an apparently con- tinuous action, to which the term electrical current is given. It is necessary to guard against the idea, which the term naturally sug- gests, of an actual bodily transfer of something through the substance of the conductors, like water through a pipe: the real nature of all these phenomena is entirely unknown, and may perhaps remain so; the expres- sion is convenient notwithstanding, and consecrated by long use; and with this caution, the very dangerous error of applying figurative language to describe an effect, and then seeking the nature of the effect from the common meaning of words, may be avoided. The intensity of the electrical excitement developed by a single pair of metals and a liquid is too feeble to affect the most delicate gold-leaf electroscope; but, by arranging a number of such alternations in a con- nected series, in such a manner that the direction of the current shall be the same in each, the intensity may be very greatly exalted. The two in- struments invented by Volta, called the pile and crown of cups, depend upon this principle. Upon a plate of zinc is laid a piece of cloth, rather smaller than itself, steeped in dilute acid, or any liquid capable of exerting chemical action upon the zinc ; upon this is placed a plate of copper, silver, or platinum; then a second piece of zinc, another cloth, and a plate of inactive metal, until a pile of about twenty alternations has been built up. If the two termi- nal plates be now touched with wet hands, the sensation of the electrical shock will be experienced ; but, unlike the momentary effect produced by the discharge of ajar, the sensation can be repeated at will by repeating the contact, and with a pile of one hundred such pairs, excited by dilute acid, it will be nearly insupportable. When such a pile is insulated, the two extremities exhibit strong positive and negative states; and when connection is made between them by wires armed with points of hard charcoal or plumbago, the discharge takes place in the form of a bright enduring spark or stream of fire. The second form of apparatus, or crown of cups, is precisely the same in principle, although different in appearance. A number of cups or ELECTRICITY. 121 glasses are arranged in a row or circle, each containing a piece of active arid a piece of inactive metal, and a portion of exciting liquid zinc, cop- per, and dilute sulphuric acid, for example. The copper of the first cup is connected with the zinc of the second, the copper of the second with the zinc of the third, and so to the end of the series. On establishing a communication between the first and last plates by means of a wire, or otherwise, discharge takes place as before. When any such electrical arrangement consists merely of a single pair of conductors and an interposed liquid, it is called a simple circuit; when two or more alterations are concerned, the term "compound circuit" is applied: they are called also, indifferently, voltaic batteries. In every form of such apparatus, however complex it may appear, the direction of the current may be easily understood and remembered. The polarity or disturbance may be considered to commence at the surface of the metal attacked, and to be propagated through the liquid to the inactive conductor, and thence back again by the connecting wire, these extremities of the battery being always respectively negative and positive when the appara- tus is insulated. In common language, it is said that the current in every battery in an active state starts from the metal attacked, passes through the liquid to the second metal or conducting body, and returns by the wire or other channel of communication: hence, in the pile and crown of cups just described, the current in the battery is always from the zinc to the copper ; and out of the battery, from the copper to the zinc, as shown by the arrows. In the modification of Volta's original pile, made by Mr. Cruikshank, the zinc and copper plates are soldered together and cemented water-tight into a mahogany trough, which thus becomes divided into a series of cells or compartments capable of receiving the exciting liquid. This apparatus is well fitted to exhibit effects of tension, to act upon the electroscope, and give shocks: hence its advantageous employment in the application of electricity to medicine, as a very few minutes suffice to prepare it for use. Fig. 84. The crown of cups was also put into a much more manageable form by Dr. Babingtori, and still further improved, as will hereafter be seen, by Dr. Wollaston. Subsequently, various alterations have been made by different experimenters with a view of obviating certain defects in the common batteries, of which a description will be found towards the middle of the volume. The term " galvanism," sometimes applied to this branch of electrical science, is used in honor of Professor Galvani, of Bologna, who, in 1790, made the very curious observation that convulsions could be produced in the limbs of a dead frog when certain metals were made to touch the nerve and muscle at the same moment. It was Volta, however, who pointed out the electrical origin of these motions; and although the explanation he offered of the source of the electrical disturbance is no longer generally adopted, his name is very properly associated with the invaluable instru- ment his genius gave to science. In the year 1822, Professor Seebeck, of Berlin, discovered another source of electricity, to which allusion has already been made namely, in- equality of temperature and conducting power in different metals placed 11 122 ELECTKO-MAGNETISM. in contact, or in the same metal in different states of compression and density. Even with a great number of alternations, the current produced is exceedingly feeble compared with that generated by the voltaic pile. Some animals of the class of fishes, as the torpedo or electric ray, and the electric eel of South America, are furnished with a special organ or appa- ratus for developing electrical force, which is employed in defence, or in the pursuit of prey. Electricity is here seen to be closely connected with nervous power: the shock is given at the will of the animal, and great ex- haustion follows repeated exertion of the power. ELECTRO-MAGNETISM; INDUCTION. Although the fact that electricity is capable, under certain circum- stances, both of inducing and of destroying magnetism, has long been known from the effects of lightning on the compass-needle and upon small steel articles, as knives and forks, to which polarity has suddenly been given by the stroke, it was not till 1819 that the laws of these phenomena were discovered by Oersted, of Copenhagen, and shortly afterwards fully devel- oped by Ampere. The action which a current of electricity, proceeding from any so.urce, exerts upon a magnetized needle, is quite peculiar. The poles or centres of magnetic force are neither attracted nor repelled by the wire carrying the current, but made to move around the latter by a force which may be termed tangential, and is exerted in a direction perpendicular at once to that of the current, and to the line joining the pole and the wire. Both poles of the magnet being thus acted upon at the same time, and in con- trary directions, the needle is forced to arrange itself across the current, so that its axis, or the line joining the poles, may be perpendicular to the wire; and this is always the position which the needle will assume when the influence of terrestrial magnetism is in anyway removed. This curious angular motion may even be shown by suspending a magnet in such a way that only one of its poles shall be subjected to the current; a perma- nent movement of rotation will continue as long as the current is kept up, its direction being changed by altering the pole, or reversing the current. The movable connections are made by mercury, into which the points of the conducting wires dip. It is often of great practical consequence to be able to predict the di- rection in which a particular pole shall move by a given current, because in all galvanoscopes and other instruments involving these principles, the movement of the needle is taken as an indication of the direction of the cir- culating current. And this is easily done by a simple mechanical aid to the memory: Let the current be supposed to pass through a watch from the face to the back; the motion of the Fig. 85. north pole will be in the direction of the hands. Or a little piece of apparatus may be used if reference is often required : this is a piece of pasteboard, or other suitable material, cut into the form of an arrow for indicating the current, crossed by a magnet having its poles marked, and arranged in the true position with respect to the current. The direction of the lat- ter in the wire of the galvanoscope can at once be known by placing the representative magnet in the direction assumed by the needle itself. The common galvanoscope (fig. 86), consisting of a coil of wire having a compass-needle suspended on a point within it, is greatly improved by the addition of a second needle, as already in part described (p. 102), and by ELECTRO-MAGNETISM. 123 a better mode of suspension, a long fibre of silk being used for the purpose. The two needles are of equal size, and magnetized as nearly as possible to the same extent; they are then immovably fixed together parallel, and Fig. 86. with their poles opposed, and hung with the lower needle in the coil and the upper one above it. The advantage gained is twofold: the system is astatic, unaffected, or nearly so, by the magnetism of the earth ; and the needles, being both acted upon in the same manner by the current, are urged with much greater force than one alone would be, all the actions of every part of the coil being strictly concurrent. A divided circle is placed below the upper needle, by which the angular motion can be measured; and the whole is enclosed in glass, to shield the needles from the agitation of the air. The whole is shown in fig. 86. The action between the pole and the wire is mutual, as may be shown by rendering the wire itself movable, and placing a magnet in its vicinity: on completing the circuit, the wire will be put in motion, and, if the arrangement permits, it will rotate around the magnetic pole. A little consideration will show that, from the peculiar nature of the electro-dynamic force, a wire carrying a current, bent into a spiral or helix, must possess the properties of an ordinary mag- netized bar, its extremities being attracted and repelled by the poles of a magnet. Such is really found to be the case, as may be proved by a va- riety of arrangements, among which it will bo sufficient to cite the beautiful little apparatus of Professor de la Rive. A short wide glass tube is fixed into a cork ring of considerable size (fig. 87) ; a little voltaic battery, consisting of a single pair of copper and zinc plates, is fitted to the tube, and to these the ends of the spiral are soldered. On filling the tube with dilute acid, and floating the whole in a large basin of water, the helix will be observed to arrange itself in the magnetic meridian, and on trial it will be found to obey a magnet held near it in the most perfect manner, as long as the current circulates. When an electric current is passed at right angles to a piece of iron or steel, the latter acquires magnetic polarity, either temporary or permanent, as the case may be, the direction of the current determining the position Fig. 87. 124 ELECTRO-MAGNETISM. of the poles. This effect is prodigiously increased by causing the current to circulate a number of times round the bar, which then acquires extra- ordinary magnetic power. A piece of soft iron, worked into the form of a horse-shoe (fig. 88), and surrounded by a coil of copper wire covered with silk or cotton for the purpose of insulation, furnishes an excellent illus- tration of the inductive energy of the current in this re- spect: when the ends of the wire are put into commu- nication with a small voltaic battery of a single pair of plates, the iron instantly becomes so highly magnetic as to be capable of sustaining a very heavy weight. Ampere discovered, in the course of his investigations, a number of extremely interesting phenomena resulting from the action of electrical currents on each other, which become evident when arrangements are made for giving mobility to the conducting wires. He found that when two currents, flowing in the same direction, are made to approach each other, strong attraction takes place between them, and, when in opposite directions, an equally strong repulsion. These effects, which are not difficult to demonstrate, have absolutely no relation, that can be traced, to ordinary electrical attractions and repulsions, from which they must be carefully distinguished; they rfre purely dynamic, having to do with electricity in motion. Ampere founded upon this discovery a most beautiful and ingenious hypothesis of magnetic actions in general, which explains very clearly the influence of the current upon the needle. A current of electricity can thus develop magnetism in a transverse direction to its own ; in the same manner, magnetism can call into activity electric currents. If the two extremities of the coil of the electro-magnet above described be connected with a galvanoscope, and the iron magnetized by the application of a permanent steel horse-shoe magnet to the ends of the bar, a momentary current will be developed in the wire, and pointed out by the movement of the needle. It lasts but a single instant, the needle returning after a few oscillations to a state of rest. On removing the mag- net, whereby the polarity of the iron is at once destroyed, a second current or wave will become apparent, but in the opposite direction to that of the first. By employing a very powerful steel magnet, surrounding its iron keeper or armature with a very long coil of wire, and then making the armature itself rotate in front of the faces of the magnet, so that its induced polarity shall be rapidly reversed, magneto-electric currents may be pro- duced, of such intensity as to give bright sparks and most powerful shocks, and exhibit all the phenomena of voltaic electricity. Fig. 89 represents a very powerful arrangement of this kind. When two covered wires are twisted together or laid side by side for some distance, and a current transmitted through the one, a momentary electrical wave will be induced in the other in the reverse direction ; and on breaking connection with the battery, a second single wave will become evident by the aid of the galvanoscope, in the same direction as that of the primary current. In the same way, when a current of electricity passes through one turn in a coil of wire, it induces two secondary currents in all the other turns of the coil; when the circuit is closed, the first is mov- ing in the opposite direction to the primary current; the second, when the circuit is broken, has a motion in the same direction as the primary current. The effect of the latter is added to that of the primary current. Hence, if a wire coil be made part of the conducting wire of a weak electric pile, and if the primary current, by means of an appropriate arrangement, ELECTRO-MAGNETISM. 125 be made and broken in rapid succession, we can increase in a remarkable manner the effects which are produced at the moment of breaking the cir- Fig. 89. cuit either at the place of interruption, such as the spark-discharges, or in secondary closing conductors, as in the action on the nerves or the decom- position of water. If two copper wires, the one above the other, be twisted round the same hollow cylinder, and one of these wires for instance, the inner one be made part of a galvanic circuit, a current of short duration is induced in the outer wire, both by making and by breaking contact. The strength of this current can be very appreciably increased by filling the hollow cylinder with a bundle of thin iron rods, when magnetic and electrical induction are made to co-operate. The more frequently contact is alternately made and broken, the greater is the number of induced currents that follow each o.ther, and the more powerful, within certain limits, is the action. Dr. Neef has constructed an ingenious contrivance, in which contact is made and broken by the current itself, whereby his induction apparatus actually becomes an electrical machine. Fig. 90 exhibits the original apparatus slightly modified. The arrangement consists essentially of an elastic copper strip a a', which is fixed at a', and carries at b a small plate of soft iron." The latter hangs over the iron rods of the induction coil, which are some- what raised in this particular point, but without touching them. The end, a, of the copper strip is covered with a little plate of platinum, which presses against a platinum point of the screw c. The current, having trav- ersed the inner coil, passes from the point c, to the plate a, in order to return through the copper strip a a', and the wire s f . By the passage of the current the iron rods have become magnetic and attract the iron plate, 6, whereby the end, #, of the copper strip is removed from the platinum point, and contact is broken. But as soon as the current ceases, the iron rods lose their magnetism, the elastic copper strip returns to its former position, and establishes again the current for a short time. The screws, c and d, regulate the position of the spring and the time of its oscillations, the velocity of which may be estimated by the pitch of the notes produced. This apparatus, which was first made by Dr. Neef, in 1830, has been con- 126 ELECTRICITY OF VAPOK. siderably improved within the last few years. Ruhmkorff especially, by a more perfect isolation of the wire coils, has succeeded to a much greater extent in preserving the electrical induction. He has thus obtained a state Fig. 90. of electrical tension which resembles that produced by frictional electricity ; the spark is capable of crossing the air in measurable distances, not in isolated discharges, but in streams of brilliant light. The shocks of this apparatus resemble those of a moderate Leyden jar, but diifer from the latter by the rapidity with which they may be repeated at pleasure. By means of Ruhmkorff 's coil, Grove has lately effected decompositions in water and other bad conducting liquids, which resemble those obtained many years ago by Wollaston by means of the electrical machine. Those phenomena of decomposition, which in water, for instance, furnish oxygen and hydrogen at the same pole, must be distinguished from true electrical decompositions ; they are, in fact, effects of heat, as Grove has pointed out. ELECTRICITY OF VAPOR. The electricity exhibited under certain peculiar circumstances "by a jet of steam, first observed by mere accident, but since closely investigated by Sir W. Armstrong, and also by Faraday, is now referred to the friction, not of the pure steam itself, but of particles of condensed water, against the interior of the exit-tube. It has been proved with certainty in the last few years that evaporation alone is not capable of disturbing the electrical equilibrium, and the hope first entertained, that these phenomena would throw light upon the cause of electrical excitement in the atmosphere, is now abandoned. The steam is usually positive, if the jet-pipe be constructed of wood or clean metal, but the introduction of the smallest trace of oily matter causes a change of sign. The intensity of the charge is, cseleris paribus, increased with the elastic force of the steam. By this means effects have been obtained very far surpassing those of the most powerful plate electrical machines ever constructed. Although no electricity can be directly evolved by evaporation, yet va- por possesses in a high degree the property of discharging into the at- mosphere that electricity which often accumulates in bodies from which it arises. The fresh branches and leaves of trees do this to the greatest ex- tent. When moistened with rain or dew, their surfaces become positively electrical, whilst the internal parts, even to the roots, become negatively electrical. PAKT II. CHEMISTRY OF ELEMENTARY BODIES. rpHE term element or elementary substance is applied in chemistry to those X forms of modifications of matter which have hitherto resisted all at- tempts to decompose them. Nothing is ever meant to be affirmed concern- ing their real nature; they are simply elements to us at the present time; hereafter, by new methods of research, or by new combinations of those already possessed by science, many of the substances which now figure as elements may possibly be shown to be compounds; this has already hap- pened, and may again take place. The elementary bodies, at present recognized, amount to sixty-four in number ; of these, about fifty belong to the class of metals. Several of these are of recent discovery, and as yet very imperfectly known. The distinction between metals and non-metallic substances, or metalloids, al- though very convenient for purposes of description, is entirely arbitrary, since the two classes graduate into each other in the most complete manner. It will be proper to commence with the latter and less numerous division. The elements are named as in the subjoined table, the most important be- ing distinguished by the largest and most conspicuous type, those next in importance by medium type, whilst the names of elements which are either of rare occurrence, or of which our knowledge is very imperfect, are printed in the smallest type. METALLOIDS. BORON. BROMINE. CARBON. CHLORINE. FLUORINE. HYDROGEN. IODINE. NITROGEN. OXYGEN. PHOSPHORUS. Selenium. SILICIUM. SULPHUR. Tellurium. METALS. ALUMINIUM. ANTIMONY. ARSENIC. BARIUM. Beryllium. BISMUTH. Cadmium. Caesium. CALCIUM, Cerium. CHROMIUM. COBALT. COPPER. Didymium. Erbium. GOLD. Indium. Iridium. IRON. Lanthanum. LEAD. Lithium. MAGNESIUM. MANGANESE. MERCURY. Molybdenum. NICKEL. Niobium. Osmium. PALLADIUM. PLATINUM. POTASSIUM. Rhodium. Rubidium. Ruthenium. SILVER. SODIUM. STRONTIUM. Tantalum. Terbium. Thallium. Thorinum. TIN. TITANIUM. TlTNGSTK.V. URANIUM. Vanadium. Yttrium. ZINC. Zirconium. 127 128 OXYGEN. OXYGEN. Whatever plan of classification, founded on the natural relations of the elements, be adopted, it will always be found most advantageous, in the practical study of chemistry, to commence with the consideration of the great constituents of the ocean and the atmosphere. Oxygen was discovered in the year 1774, by Scheele, in Sweden, and Dr. Priestley, in England, independently of each other, and described under the terms empyreal air and dephlogislicated air. The name oxygen* was given to it by Lavoisier some time afterward. Oxygen exists in a free and un- combined state in the atmosphere, mingled with another gaseous body, ni- trogen. No very good direct means exist, however, for separating it from the latter; and, accordingly, it is always obtained for purposes of experi- ment by decomposing certain of its compounds, which are very numerous. The red oxide of mercury, or red precipitate of the old writers, may be employed with this view. In this substance the attraction which holds together the mercury and the oxygen is so feeble, that simple exposure to heat suffices to bring about decomposition. The red precipitate is placed Fig. 91, in a short tube of hard glass, to which is fitted a perforated cork, furnished with a piece of narrow glass tube, bent as in fig. 91. The heat of a spirit- lamp being applied to the substance, decomposition speedily commences; globules of metallic mercury collect in the cool part of the wide tube, which answers the purpose of a retort, while gas issues in considerable quantity from the apparatus. This gas is collected and examined by the aid of the pneumatic trough, which consists of a vessel of water provided with a shelf, upon which stand the jars or bottles destined to receive the gas, filled with water and inverted. By keeping the level of the liquid above the mouth of the jar, the water is retained in the latter by the pres- sure of the atmosphere, and entrance of air is prevented. When the jar is brought over the extremity of the gas-delivering tube, the bubbles of gas rising through the water, collect in the upper part of the jar, and displace the liquid. As soon as one jar is filled, it may be removed, still keeping its mouth below the water-level, and another substituted. The whole ar- rangement is shown in fig. 91. * From <5uf, acid, and yev, a root signifying production. OXYGEN. 129 The experiment here described is more instructive as an excellent, case of the resolution by simple means of a compound body into its constituents,* than valuable as a source of oxygen gas. A better and more economical method is to expose to heat in a retort, or flask furnished with a bent tube, a portion of the salt called potassium chlorate. A common Florence flask serves perfectly well, the heat of a spirit-lamp being sufficient. The salt melts and decomposes with ebullition, yielding a very large quantity of oxygen gas, which may be collected in the way above described. The first portion of the gas often contains a little chlorine. The white saline residue in the flask is potassium chloride. This plan, which is very easy of execu- tion, is always adopted when very pure gas is required for analytical pur- poses. f A third method, very good when perfect purity is not demanded, is to heat to redness, in an iron retort or gun-barrel, the black manganese oxide of commerce, which under these circumstances suffers decomposition, al- though not to the extent manifest in the red precipitate. J If a little of the black manganese oxide be finely powdered and mixed with potassium chlorate, and the mixture heated in a flask or retort by a lamp, oxygen will be disengaged with the utmost facility, and at a far lower temperature than when the chlorate alone is used. All the oxygen comes from the chlorate, the manganese remaining quite unaltered. The materials should be well dried in a capsule before their introduction into the flask. This experiment affords an instance of an effect by no means rare, in which a body seems to act by its mere presence, without taking any obvi- ous part in the change brought about. Methods for the preparation of oxygen on a large scale will be found described under the heads of sulphuric acid and barium dioxide. Whatever method be chosen and the same remark applies to the col- lection of all other gases by similar means the first portions of gas must be suffered to escape, or be received apart, as they are contaminated by the atmospheric air of the apparatus. The practical management of gases is a point of great importance to the chemical student, and one with which he must endeavor to familiarize himself. The water-trough just described is one of the most indispensable articles of the laboratory, and by its aid all experiments on gases are carried on when the gases themselves are not sensibly acted upon by water. The trough is best constructed of japanned copper, the form and dimensions being regulated by the magnitude of the jars. It should have a firm shelf, so arranged as to be always about an inch below the level of the water, and in the shelf a groove should be made about half an inch in width, and tbe same in depth, to admit the extremity * Chemists are in the habit of representing the elements by symbols, and their compounds by formulas. The same symbolical language, which is fully explained in a subsequent section of the work ((Jeneral Principles of Chemical Philosophy), is used for representing the changes which the chemical compounds undergo. For the benefit of the advanced student, the formula} expressing the more- important decompositions are now given in, foot-notes. The decomposition of mercuric oxide is thus represented: HgO = Mercuric oxide. KC10 3 Potassium chlorate. Potassium chloride. ."MnOo = Mn 3 4 Manganese dioxide. MangaxxMO-man- Oxygen. ganic oxide. [The manganese oxide should not contain any combustible matter, or an explosion will result. Accidents have occurred from this cause, anil a preliminary trial should lie made by heat- ing a small quantity in a metal cup, should there be any doubt of the purity of the oxide. R. U.J 130 OXYGEN. of the delivery-tube beneath the jar, which stands securely upon the shelf. When the pneumatic trough is required of tolerably large dimensions, it may with great advantage have the form and disposition represented in Fig. 92. Fig. 93. fig. 92. The end of the groove spoken of, which crosses the shelf or shal- low portion, is shown at a. Gases are transferred from jar to jar with the utmost facility, by first filling the vessel, into which the gas is to be passed with water, inverting it, carefully retaining its mouth below the water-level, and then bringing beneath it the aperture of the jar containing the gas. On gently inclining the latter, the gas passes by a kind of inverted decantation into the second vessel. When the latter is narrow, a funnel may be placed loosely in its neck, by which loss of gas will be prevented. Ajar wholly or partially filled with gas at the pneumatic trough may be removed by placing beneath it a shallow basin, or even a common plate, so as to carry away enough water to cover the edge of the jar : and many gases, especially oxygen, may be so preserved for many hours without material injury. Gas-jars are often capped at the top, and fitted with a stop-cock for transferring gas to bladders or caoutchouc bags. When such a vessel is to be filled with water, it may be slowly sunk in an upright position in the well of the pneumatic trough, the stop-cock being open to allow the air to escape, until the water reaches the brass cap. The cock is then to be turned, and the jar lifted upon the shelf, and filled with gas in the usual way. If the trough be not deep enough for this method of proceeding, the mouth may be applied to the stop-cock, and the vessel filled by sucking out the air until the water rises to the cap. In all cases it is proper to avoid as much as possible wetting the stop-cocks and other brass apparatus. Mr. Pepys contrived, many years ago, an admirable piece of apparatus for storing and retaining large quantities of gas. It consists of a drum or reservoir of sheet copper, surmounted by a shallow trough or cistern, the communication between the two being made by a couple of tubes, a i, fur- nished with stop-cocks, one of which, A/, passes nearly to the bottom of the drum, as shown in fig. 94. A short wide open tube, c, is inserted obliquely near the bottom of the vessel, into which a plug may be tightly screwed. OXYGEN. 131 Fig. 94. A stop-cock, g, near the top, serves to transfer gas to a bladder or tube- apparatus. A glass water-gauge, d e, affixed to the side of the drum, and communicated with both top and bottom, indicates the level of the liquid within. To use the gas-holder, the plug is first screwed into the lower opening, and the drum completely filled with water. All three stop-cocks are then to be closed and the plug removed. The pressure of the atmosphere retains the water in the gas- holder, and if no air-leakage occurs, the escape of water is inconsiderable. The extremity of the delivery-tube is now to be well pushed through the open aperture into the drum, so that the bubbles of gas may rise without hindrance to the upper part, displacing the water, which flows out in the same proportion into a vessel placed for its reception. When the drum is filled, or enough gas has been collected, the tube is withdrawn and the plug screwed into its place. When a portion of the gas is to be transferred to a jar, the latter is to be filled with water at the pneumatic trough, carried by the help of a basin or plate to the cistern of the gas-holder, and placed over the shorter tube. On opening the cock of the neighboring tube, the hydrostatic pressure of the column of water will cause compression of the gas, and increase its elastic force, so that, on gently turning the cock beneath the jar, it will ascend into the latter in a rapid stream of bubbles. The jar, when filled, may again have the plate slipped beneath it, and be removed without dif- ficulty. Oxygen, when free or uncombined, is known only in the gaseous state, all attempts to reduce it to the liquid or solid condition by cold and pressure having completely failed. When pure, it is colorless, tasteless, and in- odorous. It is the sustaining principle of animal life, and of all the ordinary phenomena of combustion. Bodies which burn in the air, burn with greatly increased splendor in oxygen gas. If a taper be blown out, and then introduced while the wick remains red-hot, it is instantly rekindled: a slip of wood or a match is relighted in the same manner. This effect is highly characteristic of oxygen, there being but one other gas which possesses the same property; and this is easily distinguished by other means. The experiment with the match is also constantly used as a rude test of the purity of the gas when it is about to be collected from the retort, or when it has stood some time in contact with water exposed to air. When a bit of charcoal is affixed to a wire, and plunged with a single point red-hot into a jar of oxygen, it burns with great brilliancy, throwing off beautiful scintillations, until, if the oxygen be in excess, it is completely consumed. An iron wire, or, still better, a steel watch-spring, armed at its extremity with a bit of lighted amadou, and introduced into a vessel of oxygen gas, exhibits a most beautiful phenomenon of combustion. If the experiment be made in a jar standing on a plate, the fused globules of black iron oxide fix themselves in the glaze of the latter, after falling through a stratum of water half an inch in depth. Kindled sulphur burns with great beauty in oxygen; and phosphorus, under similar circumstances, exhibits a splendor which the eye is unable to support. In these an4 many other similar cases which might be mentioned, the 132 OXYGEN. same ultimate effect is produced as in atmospheric air ; the action is, how- ever, more energetic, from the absence of the gas which, in the air, dilutes the oxygen and enfeebles its chemical powers. The process of respiration in animals is an effect of the same nature as common combustion. The blood contains substances which slowly burn by the aid of the oxygen thus introduced into the system. When this action ceases, life becomes extinct. Oxygen is bulk for bulk a little heavier than atmospheric air, its specific gravity being 1-10503, referred to that of air as unity, and 16 referred to that of hydrogen as unity. A litre of oxygen at the standard temperature and pressure, that is to say, at C., and 700 millimetres barometric pres- sure, weighs 1-43028 gram. At 15-5 C. (60 F.), and under a pressure of 30 inches, 100 cubic inches of the gas weigh 34-29 grains.* It has been already remarked, that to determine with the utmost degree of accuracy the specific gravity of a gas, is an operation of very great practical difficulty, but at the same time of very great importance. There are several methods which may be adopted for this purpose : the one de- scribed below appears, on the whole, to be the simplest and best. It re- quires, however, the most scrupulous care, and the observance of a number of minute precautions which are absolutely indispensable to success. The plan of the operation is as follows: A large glass globe is to be filled with the gas to be examined in a perfectly pure and dry state, having a known temperature, and an elastic force equal to that of the atmosphere at the time of the experiment. The globe so filled is to be weighed. It is then to be exhausted at the air-pump as far as possible, and again weighed. Lastly, it is to be filled with dry air, the temperature and pressure of which are known, and its weight once more determined. On the supposition that the temperature and elasticity are the same in both cases, the specific gravity is at once obtained by dividing the weight of the gas by that of the air. The globe or flask must be made very thin, and fitted with a brass cap, surmounted by a small but excellent stop-cock. A delicate thermometer should be placed in the inside of the globe, secured to the cap. The gas must be generated at the moment, and conducted at once into the previously exhausted vessel, through a long tube filled with fragments of pumice moistened with oil of vitriol, or some other extremely hygroscopic substance, by which it is freed from all moisture. As the gas is necessarily generated under some pressure, the elasticity of that contained in the filled globe will slightly exceed the pressure of the atmosphere ; and this is an ad- vantage, since, by opening the stop-cock for a single instant, when the globe has attained an equilibrium of temperature, the tension becomes ex- actly that of the air, so that all barometrical correction is avoided, unless the pressure of the atmosphere should sensibly vary during the time oc- cupied by the experiment. It is hardly necessary to remark that the greatest care must also be taken to purify and dry the air used as the standard of comparison, and to bring both gas and air as nearly as possible to the same temperature, to obviate the necessity of a cor- rection, or at least to diminish almost to nothing the errors involved by such a process. Oxides. The compounds formed by the direct union of oxygen with other bodies bear the general name of oxides : these are very numerous and important. They are conveniently divided into three principal groups or classes. The first division contains all those oxides which resemble in their chemical relations the oxides of potassium, sodium, silver, or lead : these are denominated alkaline or basic oxides. The oxides of the second group have properties opposed to those of the bodies mentioned ; the oxides * Dumas, Ann. Chim. Phys. [3], iii. 275. OXYGEN. 133 of sulphur and phosphorus may be taken as the typical representatives of the class: they are called acid oxides, and are capable of uniting with the basic oxides, and forming compounds called salts. Thus, when the oxide of sulphur, called sulphuric oxide, is passed in the state of vapor over heated barium oxide, combination takes place, attended with vivid incan- descence, and a salt called barium sulphate is produced, containing all the elements of the two original bodies, namely, barium, sulphur, and oxygen. There is also an intermediate group of oxides called neutral oxides, from their slight disposition to enter into combination. The black oxide of manganese, already mentioned, is an excellent example. It must not be supposed, however, that the three groups of oxides just mentioned are separated from each other by decided lines of demarcation ; on the con- trary, they blend into one another by imperceptible degrees, and the same oxide may, in many cases, exhibit either acid or basic relations according to the circumstances under which it is placed. Among salts, there is a particular group, namely, the hydrogen salts, con- taining the elements of an acid oxide, and water (hydrogen oxide), which are especially distinguished as acids, because many of them possess in an eminent degree the properties to which the term acid is generally applied, such as a sour taste, corrosive action, solubility in water, and the power of reddening certain blue vegetable colors. A characteristic property of these acids, or hydrogen salts, is their power of exchanging their hydrogen for a metal presented to them in the free state, or in the form of oxide. Thus, sulphuric acid, which contains sulphur, oxygen, and hydrogen, readily dissolves metallic zinc, the metal taking the pluce of the hydrogen, which is evolved as gas, and forming a salt containing sulphur, oxygen, and zinc ; in fact, a zinc sulphate, produced from a hydrogen sulphate by substitution of zinc for hydrogen.* The same substitution and formation of zinc sulphate take place when zinc oxide is brought in contact with sul- phuric acid; but in this case the hydrogen, instead of being evolved as gas, remains combined with the oxygen derived from the zinc oxide, form- ing water, f A series of oxides containing quantities of oxygen in the proportion of the numbers 1, 2, 3, united with a constant quantity of another element, are distinguished as monoxide, dioxide, and trioxide respectively, the Greek numerals indicating the several degrees of oxidation. A compound inter- mediate between a monoxide and a dioxide is called a sesquioxide, e. g. : Chromium. Oxygen. Chromium monoxide . . . . . 62-5 -f- 16 Chromium sesquioxide ..... 52-5 -f- 24 Chromium dioxide 52-5 -f- 32 Chromium trioxide 52-5 -f 48 When a metal forms two basic or salifiable oxides, they are distinguished by adjectival terms ending in ous for the lower, and ic for the higher de- gree of oxidation, e. g. : Iron. Oxygen. Iron monoxide, or Ferrous oxide . . . . 56 -j- lt> Iron sesquioxide, or Ferric oxide . . . 56 -f- 24 The salts resulting from the action of acids on these oxides are also dis- tinguished as ferrous and ferric salts respectively. Acid oxides of the same element, sulphur for example, are also dis- tinguished by the terminations ous and ic, applied as above ; their jicids, * S0 4 H 2 + Zn = S0 4 Zn + H 2 t S0 4 H 2 + Zn = S0 4 Zn + OIL, 12 134 OXYGEN. or hydrogen salts, receive corresponding names; and the salts formed from these acids are distinguished by names ending in ite and ale respec- tively. Thus, for the oxides and salts of sulphur : Sulphur. Oxygen. Sulphurous oxide 82 4- 32 Hydrogen. Hydrogen sulphite, or Sulphurous acid . 32 4. 48 -f- 2 Lead. Lead sulphite 32 -f 48 -f 207 Sulphuric oxide 32 -f- 48 Hydrogen. Hydrogen sulphate, or Sulphuric acid . . 32 -\- 64 -f- 2 Lead. Lead sulphate 32 -f 64 -f 207 The acids above spoken of are oxygen-acids; and formerly it was sup- posed that all acids contained oxygen that element being, indeed, re- garded as the acidifying principle; hence its name (p. 128). At present, however, we are acquainted with many bodies which possess all the char- acters above specified as belonging to an acid, and yet do not contain oxygen. For example, hydrochloric acid (formerly called muriatic acid, or spirit of salt) which is a hydrogen chloride, or compound of hydrogen and chlorine is intensely sour and corrosive; reddens litmus strongly; dissolves zinc, which drives out the hydrogen and takes its place in com- bination with the chlorine, forming zinc-chloride ; and dissolves most me- tallic oxides, exchanging its hydrogen for the metal, and forming a metal- lic chloride and water.* Bromine, iodine, and fluorine also form, with hydrogen, acid compounds analogous in every respect to hydrochloric acid. Compounds of chlorine, bromine, iodine, fluorine, sulphur, selenium, phosphorus, &c., with hydrogen and metals, are grouped, like the oxygen compounds, by names ending in ide: thus we speak of zinc chloride, cal- cium fluoride, hydrogen sulphide, copper phosphide, &c. The numerical prefixes, mono, di, iri, &c., as also the terminations ous and ic, are applied to these compounds in the same manner as to the oxides, thus : Hydrogen bromide Potassium monosulphide . Potassium disulphide Potassium trisulphide Potassium tetrasulphide Potassium pentasulphide . Hydrogen. 1 Potassium. 78-2 . 78-2 78-2 . 78-2 78-2 Iron. 56 Bromine. 4- 80 Sulphur, -f 32 -f 64 4- 96 -f 128 -}- 160 Chlorine. 4- 71 . 56 4- 105-5 Stannous sulphide Tin. 118 118 Sulphur. 4- 64 4- 128 The Latin prefixes uni,bi,ter, quadro, &c., are often used instead of the corresponding Greek prefixes ; there is no very exact rule respecting their * Action of hydrochloric acid on zinc : 2HC1 + Zn ZnCl 2 + H 2 Action of hydrochloric acid on zinc oxide : 2HC1 + ZnO = ZnClg + OH a OXYGEN. 135 use : but, generally speaking, it is best to employ a Greek or Latin prefix, according as the word before which it is placed is of Greek or Latin origin ; thus, c&'oxide corresponds to bisulphide ; on the whole, however, the Greek prefixes are most generally employed. OZONE. It has long been known that dry oxygen, or atmospheric air, when exposed to the action of a series of electric sparks, emits a peculiar and somewhat metallic odor. The same odor may be imparted to moist oxygen by allowing phosphorus to remain for some time in it, and by several other processes. A more accurate examination of this odorous air has shown that, in addition to the smell, it possesses several properties not exhibited by oxygen in its ordinary state. One of its most char- acteristic effects is the liberation of iodine from potassium iodide. This odorous principle has been the subject of many researches, in particular by Schonbein, of Basle, who proposed for it the name of ozone.* An easy method of exhibiting the production of ozone is to transmit a current of oxygen through a tube into which a pair of platinum wires is sealed, with the points at a little distance apart; on connecting one of the wires with the prime conductor of an electrical machine in good action, and the other with the ground, the characteristic odor of ozone is im- mediately developed in the issuing gas ; but, notwithstanding the powerful odor thus produced, only a small portion of the oxygen undergoes this change. Andrews and Tait have shown that, to obtain the maximum of ozone, it is necessary to transmit the discharge silently, between very fine points; if sparks are allowed to pass, a considerable portion of the ozone is reconverted into ordinary oxygen as fast as it is formed. Siemens pre- pares ozone by induction: he forms a sort of Leyden jar, by coating the interior of a long tube with tin-foil, and passes over this tube a second wider tube coated with tin-foil on its outer surface. Between the two tubes a current of pure dry oxygen is passed, which becomes electrified by in- duction, on connecting the inner and outer coating with the terminal wires of an induction-coil; by this means it is said that from 10 to 15 per cent, of the oxygen may be converted into ozone. Ozone may also be obtained in several ways, without the aid of elec- tricity; thus it is formed in small quantity when a stick of phosphorus is suspended in a bottle filled with moist air; by the slow oxidation of ether, oil of turpentine, and other essential oils ; in the electrolytic decomposition of water; and by the action of strong sulphuric acid on potassium per- m'anganate.^ There has been considerable discussion about the nature and composition of ozone; but the most trustworthy experiments seem to show that, in whatever way produced, it is merely a modified form of oxygen. Ozone is insoluble in water and in solutions of acids or alkalies, but is absorbed by a solution of potassium iodide. Air charged with it exerts an irritating action on the lungs. Ozone is decomposed by heat, gradually at 100 C. (212 F.,) instantly at 290 C. (554 F.) It is an extremely power- ful oxidizing agent; possesses strong bleaching and disinfecting powers; corrodes cork, caoutchouc, and other organic substances ; and rapidly oxidizes iron, copper, and even silver when moist, as well as dry mercury and iodine. It is remarkable that the absorption of ozone by these and other agents is not attended with any contraction of volume. The expla- nation of this fact appears to be, that oxygen when ozonized diminishes in volume (in the proportion of 3 to 2, according to Soret), and that when the ozone is decomposed by a metal or other substance, one portion of it enters into combination, while the remainder, which is set free as ordinary oxygen, occupies the same bulk as the ozone itself. * From 8$civ, to emit an odor. [f Also, according to A. Houseau.by the action of sulphuric acid on barium dioxide. R. B.] 136 HYDROGEN. The most delicate test for the presence of ozone in any gas is afforded by a strip of paper moistened with a mixture of starch and solution of po- tassium iodide. On exposing such paper to the action of ozone, the po- tassium iodide is decomposed, its potassium combining with oxygen, while the iodine is liberated, and forms a deep blue compound with the starch. Now, when paper thus prepared is exposed to the open air for five or ten minutes, it often acquires a blue tint, the intensity of which varies on dif- ferent days. Hence it has been plausibly supposed that ozone is present in the air in variable quantity. But iodine may be liberated from po- tassium iodide by many other agents, especially by certain oxides of ni- trogen, which are very likely to be present in the air in minute quantities: hence the existence of ozone in the air cannot be proved to be present by this reaction alone. HYDROGEN. Hydrogen may be obtained for experimental purposes by deoxidizing water, of which it forms a characteristic component.* If a tube of iron or porcelain, containing a quantity of filings or turnings of iron, be fixed across a furnace, and its middle portion be made red-hot, and then the vapor of water transmitted over the heated metal, a large quantity of permanent gas will be disengaged from the tube, and the iron will become converted into oxide, and acquire an increase in weight. The gas is hydrogen: it may be collected over water and examined. Hydrogen is, however, more easily obtained by decomposing hydrochloric or dilute sulphuric acid with zinc, the metal then displacing the hydrogen in the manner already explained (p. 133). The simplest method of preparing the gas is the following : A wide-necked bottle is chosen, and fitted with a sound Fig. 95, cork, perforated by two holes for the reception of a small tube-funnel reach- ing nearly to the bottom of the bottle, and a piece of bent glass tube to convey away the disengaged gas. Granulated zinc, or scraps of the malleable metal, are put into the bottle, together with a little water, and sulphuric acid slowly added by the funnel, the point of which should dip into the liquid. The evolu- tion of gas is easily regulated by the supply of acid; and when enough has been discharged to expel the air of the vessel, it may be collected over water in a jar, or passed into a gas-holder. In the absence of zinc, filings of iron or small nails may be used, but with less advantage. A little practice will soon enable the pupil to construct and arrange a variety of useful forms of. apparatus, in which bottles, and other articles always at hand, are made to supersede more costly instruments. Glass tube, purchased by weight of the maker, Hence the name, from vdwp, water, and ysv. HYDROGEN. 137 may be cut by scratching with a file, and then applying a little force with both hands. It may be softened and bent, when of small dimensions, by the flame of a spirit-lamp, or a candle, or, better, by a gas jet. Corks may be perforated by a heated wire, and the hole rendered smooth and cylindrical by a round file ; or the ingenious cork-borer of Dr. Mohr, now to be had of all instrument-makers, may be used instead. Lastly, in the event of bad fitting, or unsoundness in the cork itself, a little yellow wax melted over the surface, or even a little grease applied with the finger, renders it sound and air-tight, when not exposed to heat. Hydrogen is colorless, tasteless, and inodorous when quite pure. To ob- tain it in this condition, it must be prepared from the purest zinc that can be obtained, and passed in succession through solutions of potash and silver nitrate. When prepared from commercial zinc, it has a slight smell, which is due to impurity, and when iron has been used, the odor is very strong and disagreeable. It is inflammable and burns, when kindled, with a pale, yellowish flame, evolving much heat, but very little light. The result of the combustion is water. It is even less soluble in water than oxygen, and has never been liquefied. Although destitute of poisonous properties, it is in- capable of sustaining life. Hydrogen is the lightest substance known ; Dumas and Bous- Fig.QQ. singault place its density between 0-0691 and 0-0695,* referred to that of air as unity. The weight of a litre of hydrogen at C., and under a barometric pressure of 0-760 metre, is 0-08961 gram ; consequently, a gram of hydrogen occupies a space of 11-15947 litres. f At 15-5 C. (60 F.), and 30 inches barometric pressure, 100 cubic inches weigh 2-14 grains. When a gas is much lighter or much heavier than atmos- pheric air, it may often be collected and examined without the aid of the pneumatic trough. A bottle or narrow jar may be filled with hydrogen without much admixture of air, by invert- ing it over the extremity of an upright tube delivering the gas. In a short time, if the supply be copious, the air will be wholly displaced, and the vessel filled. It may now be removed, the vertical position being carefully retained, and closed by a stop- per or glass plate. If the mouth of the jar be wide, it must be partially closed by a piece of cardboard during -the operation. This method of collecting gases by displacement is often extremely useful. Hy- drogen was formerly used for filling air-balloons, being made for the pur- pose on the spot from zinc or iron and dilute sulphuric acid. Its use is now superseded by that of coal-gas, which may be made very light by employ- ing a high temperature in the manufacture. Although far inferior to pure hydrogen in buoyant power, it is found in practice to possess advantages over that substance, while its greater density is easily compensated by in- creasing the magnitude of the balloon. There is a very remarkable property possessed by gases and vapors in general, which is seen in a high degree of intensity in the case of hydrogen ; this is what is called diffusive power. If two bottles containing gases which do not act chemically upon each other at common temperatures be connected by a narrow tube and left for some time, the gases will be found, at the ex- piration of a certain period, depending much upon the narrowness of the tube and its length, uniformly mixed, even though they differ greatly in density, and the system has been arranged in a vertical position, with the heavier gas downwards. Oxygen and hydrogen can thus be made to mix, in a few hours, against the action of gravity, through a tube a yard in * Ann.Chim. Phys., 3d series, viii. 201. f- A-; ii near approximation, it nuiy li remembered that a litre of hydrogen weighs 0-09 gram, or '.) < fiiti-rains, and a gram of hydrogen occupies 11-1 litres. 138 HYDKOGEN. length, and not more than one quarter of an inch in diameter : and the fact is true of all other gases which are destitute of direct action upon each other. If a vessel be divided into two portions by a diaphragm or partition of porous earthenware or dry plaster of Paris, and each half filled with a dif- ferent gas, diffusion will immediately commence through the pores of the dividing substance, and will continue until perfect mixture has taken place. All gases, however, do not permeate the same porous body, or, in other words, do not pass through narrow orifices with the same degree of facility. Professor Graham, to whom we are indebted for a very valuable investiga- tion of this interesting subject, has established the existence of a very simple relation between the rapidity of diffusion and the density of the gas, which is expressed by saying that the diffusive power varies inversely as the square root of the density of the gas itself. Thus, in the experiment supposed, if one half of the vessel be filled with hydrogen and the other half with oxygen, the two gases will penetrate the diaphragm at very dif- ferent rates ; four cubic inches of hydrogen will pass into the oxygen side, while one cubic inch of oxygen travels in the opposite direction. The den- sities of the two gases are to each other in the proportion of 1 to 16; their relative rates of diffusion will be inversely as the square roots of these numbers, i. e., as 4 to 1. In order, however, that this law may be accurately observed, it is neces- sary that the porous plate be very thin ; with plates of stucco an inch thick or more, which really consist of a congeries of long capillary tubes, a dif- ferent law of diffusion is observed.* An excellent material for diffusion experiments is the artificially compressed graphite of Mr. Brockedon, of the quality used for making writing- pencils. It may be reduced by cutting and grinding to the thickness of a wafer, but still retains considerable tenacity. The pores of this substance appear to be so small as entirely to prevent the transmission of gases in mass, so that, to use the language of Mr. Graham, it acts like a molecular sieve, allowing only molecules to pass through. The simplest and most striking method of exhibiting the Fig. 97. phenomenon of diffusion is by the use of Graham's diffu- sion-tube. This is merely a piece of wide glass tube ten or twelve inches long, having one of its extremities closed by a plate of plaster of Paris about half an inch thick, and well dried. When the tube is filled by displacement with hydrogen, and then set upright in a glass of water, the level of the liquid rises in the tube so rapidly, that its movement is apparent to the eye, and speedily attains a height of several inches above the water in the glass. The gas is actually rarefied by its superior diffusive power over that of the external air. It is impossible to over-estimate the importance in the economy of Nature of this very curious law affecting the constitution of gaseous bodies: it is the principal means by which the atmosphere is preserved in a uniform state, and the accumulation of poisonous gases and exhalations in towns and other confined localities prevented. A partial separation of gases and vapors of unequal diffusibility may be effected by allowing the mixture to permeate through a plate of graphite or porous earthenware into a vacuum. This effect, called atmolysis, is best ex- hibited by means of an instrument called the tube-afmoh/ser. This is simply a narrow tube of unglazed earthenware, such as a tobacco-pipe stem, two feet long, which is placed within a shorter tube of glass, and secured in its * See Bunsen's Gasometry, p. 203 ; Graham's Elements of Chemistry, 2d ed., ii. 624 ; Watts's Dictionary of Chemistry, ii. 815. HYDROGEN. 139 position by corks. The glass tube is connected with an air-pump, and the annular space between the two tubes is made as nearly vacuous as possible. Air or other mixed gas is then allowed to flow along the clay tube in a slow stream, and collected as it issues. The gas or air atmolysed is, of course, reduced in volume, much gas penetrating through the pores of the clay tube into the air-pump vacuum, and the lighter gas diffusing the more rap- idly, so that the proportion of the denser constituent is increased in the gas collected. In one experiment, the proportion of oxygen in the air, after traversing the atmolyser, was increased from 20-8 per cent., which is the normal proportion, to 24-5 per cent. With a mixture of oxygen and hy- drogen, the separation is, of course, still more considerable.* A distinction must be carefully drawn between real diffusion through small apertures, and the apparently similar passage of gases through membran- ous diaphragms, such as caoutchouc, bladder, gold-beater's skin, etc. In this mode of passage, which is called osmose, the rate of interchange de- pends partly on the relative diffusibilities of the gases, partly on the differ- ent degrees of adhesion exerted by the membrane on the different gases, by virtue of which the gas which adheres most powerfully penetrates the diaphragm most easily and, attaining the opposite surface, mixes with the other. A sheet of caoutchouc tied over the mouth of a wide-mouthed bottle filled with hydrogen, is soon pressed inwards, even to bursting. If the bottle be filled with air, and placed in an atmosphere of hydrogen, the swelling and bursting takes place outwards. If the membrane is moist, the result is likewise affected by the different solubilities of the gases in the water or other liquid which wets it. For example, the diffusive power of carbonic acid into atmospheric air is very small, but it passes into the latter through a wet bladder with the utmost ease,in virtue of its solubility in the water with which the membrane is moistened. It is by such a process that the function of respiration is performed ; the aeration of the blood in the lungs, and the disengagement of the carbonic acid, are effected through wet membranes ; the blood is never brought into actual contact with the air, but receives its supply of oxygen, and disembarrasses itself of carbonic acid, by this kind of spurious diffusion. The high diffusive power of hydrogen against air renders it impossible to retain that gas for any length of time in a bladder or caoutchouc bag ; it is even unsafe to keep it long in a gas-holder, lest it should become mixed with air by slight accidental leakage, and rendered explosive. The passage of gases through membranes like caoutchouc or varnished silk, as well as through wet membranes like bladder, appears to depend upon an actual liquefaction of the gases, which then become capable of pen- etrating the substance of the membrane (as ether and naphtha do), and may again evaporate on the surface and appear as gases. The unequal absorp- tion of gases in this manner often effects a much more complete separation of the components of a gaseous mixture than can be attained by the atmo- lytic method above described. Thus, Graham has shown that oxygen is ab- sorbed and condensed by caoutchouc two-and-a-half times more abundantly than nitrogen, and that when one side of a caoutchouc film is freely ex- posed to the air, while a vacuum is produced on the other side, the film allows 41-6 per cent, of oxygen to pass through, instead of 21 per cent, usually present in the air, so that the air which passes through is capable of rekindling wood burning without flame. Even metals appear to possess this power of absorbing and liquefying gases. Deville and Troost have observed the remarkable fact that hydrogen gas is capable of penetrating platinum and iron tubes at a red heat, and Graham is of opinion that this effect may be connected with a power resi- dent in these and certain other metals to absorb and' liquefy hydrogen, possibly in its character as a metallic vapor. Platinum in the form of * Graham, Phil. Trans. 1863 140 HYDROGEN. wire or plate, at a low red heat, can take up 3-8 volumes of hydrogen measured cold, and palladium foil condenses as much as 643 times its vol- ume of hydrogen at a temperature below 100 C. In the form of sponge, platinum absorbed 1-48 times its volume of hydrogen, and palladium 90 volumes. This absorption of gases by metals is called occlusion.* The meteoric iron of Lenarto contains a considerable quantity of oc- cluded hydrogen. When placed in a good vacuum, it yields 2-85 times its volume of gas, of which 85-68 per cent, consist of hydrogen, with 4-46 carbon monoxide and 9-86 nitrogen. Now, hydrogen has been recognized by spectrum analysis in the light of the fixed stars, and constitutes, ac- cording to the observations of father Secchi, the principal element in the atmosphere of a numerous class of stars. " The iron of Lenarto," says Mr. Graham, "has, no doubt, come from such an atmosphere, in which hydrogen greatly prevailed. This meteorite may be looked upon as holding imprisoned within it, and bringing to us, the hydrogen of the stars." f The rates of effusion of gases, that is to say, their rates of passage through a minute aperture in a thin plate of metal or other substance into a vacuum, follow the same law as their rates of diffusion, that is to say, they are inversely as the square roots of the densities of the gases. Never- theless, the phenomena of diffusion and effusion are essentially different in their nature, the effusive movement affecting masses of a gas, whereas the diffusive movement affects only molecules ; and a gas is usually carried by the former kind of impulse with a velocity many thousand times greater than by the latter. Mixed gases are effused at the same rates as one gas of the actual density of the mixture: and no separation of the gases oc- curs, as in diffusion into a vacuum. The law of effusion just stated is true only under the condition that the gas shall pass through a minute aperture in a very thin plate. If the plate be thicker, so that the aperture becomes a tube, very different rates of efflux are observed; and when the capillary tube becomes considerably elongated, so that its length exceeds its diameter at least 400 times, the rates of flow of different gases into a vacuum again assume a constant ratio to each other, following, however, a law totally distinct from that of effusion. The principal general results observed with relation to this phenomenon of "Capillary Transpiration" are as follows: 1. The rate of transpiration of the same gas increases, cseteris paribus, directly as the pressure: in other words, equal volumes of gas at different densities require times inversely proportional to their densities. ^ 2. With tubes of equal diameter, the volume transpired in equal times is inversely as the length of the tube. 8. As the temperature rises, the transpiration of equal volumes becomes slower. 4. The rates of transpiration of different gases bear a constant relation to each other, totally independent of their densities, or, indeed, of any known property of the gases. Equal weights of oxygen, nitrogen, and carbon monoxide are transpired in equal times ; so likewise are equal weights of nitrogen, nitrogen dioxide, and carbon mon- oxide ; and of hydrogen chloride, carbon dioxide, and nitrogen monoxide. J COMBINATION OF HYDROGEN WITH OXYGEN. It has been already stated that, although the light emitted by the flame of pure hydrogen is exceedingly feeble, yet the temperature of the flame is very high. The temperature may be still further exalted by previously mixing the hydrogen with as much oxygen as it requires for combination, * Graham, Phil. Trans. 1866; Journal of the Chemical Society, [2] v. 235. t Proceorlinsjs of the Royal Society, xv. 502 J Graham, Phil. Trans. 1846, p. 591 ; and 1S49, p. 349 ; also Elements of Chemistry, 2d ed. i. 82. HYDROGEN. that is, as will presently be seen, with half its volume. Such a mixture burns like gunpowder, independently of the external air. When raised to the temperature required for combination, the two gases unite with explo- sive violence. If a strong bottle, holding not more than half a pint* be filled with such a mixture, the introduction of a lighted match or red-hot wire determines in a moment the union of the gases. By certain precau- tions, a mixture of oxygen and hydrogen can be burned at a jet without communication of fire to the contents of the vessel; the flame is in this case solid. A little consideration will show, that all ordinary flames burning in the air or in pure oxygen are, of necessity, hollow. The act of combustion is nothing more than the energetic union of the substance burned with the surrounding oxygen ; and this union can take place only at the surface of the burning body. Such is not the case, however, with the flame now under consideration ; the combustible and the oxygen are already mixed, and only require to have their temperature a little raised to cause them to combine in every part. The flame so produced is very different in physical characters from that of a simple jet of hydrogen or any other combustible gas; it is long and pointed, and very remarkable in appearance. The safety-jet of Mr. Hemming, the construction of which involves a principle not, yet discussed, may be adapted to a common bladder contain- ing the mixture, and held under the arm, and the gas forced through the jet by a little pressure. Although this jet, properly constructed, is believed to be safe, it is best to use nothing stronger than a bladder, for fear of in- jury in the event of an explosion. The gases are often contained in sepa- rate reservoirs, a pair of large gas-holders, for example, and only suffered to mix in the jet itself, as in the contrivance of Professor Daniell: in this way all danger is avoided. The eye speedily becomes accustomed to the peculiar appearance of the true hydro-oxygen flame, so as to permit the supply of each gas to be exactly regulated by suitable stop-cocks attached to the jet (fig. 98). Fig. 98. Fig. 99, P* A piece of thick platinum wire introduced into the flame of the hydro- oxygen blowpipe melts with the greatest ease; a watch-spring or small 142 HYDROGEN. Bteel file burns with the utmost brilliancy, throwing off showers of beautiful sparks; an incombustible oxidized body, as magnesia or lime, becomes so intensely ignited as to glow with a light insupportable to the eye, and to be susceptible of employment as a most powerful illuminator, as a sub- stitute for the sun's rays in the solar microscope, and for night-signals in trigonometrical surveys. If a long glass tube, open at both ends, be held over a jet of hydrogen (fig. 99), a series of musical sounds are sometimes produced by the partial extinction and rekindling of the flame by the ascending current of air. These little explosions succeed each other at regular intervals, and so rapidly as to give rise to a musical note, the pitch depending chiefly upon the length and diameter of the tube. Although oxygen and hydrogen may be kept mixed at common tempera- tures for any length of time, without combination taking place, yet, under particular circumstances, they unite quietly and without explosion. Many years ago, Professor Dobereiner, of Jena, made the curious observation, that finely divided platinum possessed the power of determining the union of the gases; and, more recently, Mr. Faraday has shown that the state of minute division is by no means indispensable, since rolled plates of the metal have the same property, provided their surfaces are absolutely clean. Neither is the effect strictly confined to platinum ; other metals, as palla- dium and gold, and even stones and glass, exhibit the same property, al- though to a far inferior degree, since they often require to be aided by a little heat. When a piece of platinum-foil, which has been cleaned by hot oil of vitriol and thorough washing with distilled water, is thrust into a jar containing a mixture of oxygen and hydrogen standing over water, combination of the two gasas immediately begins, and the level of the water rapidly rises, while the platinum becomes so hot that drops of water acci- dentally falling upon it enter into ebullition. If the metal be very thin and exceedingly clean, and the gases very pure, its temperature rises after a time to actual redness, and the residue of the mixture explodes. But this is an effect altogether accidental, and dependent upon the high temperature of the platinum, which high temperature has been produced by the pre- ceding quiet combination of the two bodies. When the platinum is reduced to a state of minute division, and its surface thereby much extended, it be- comes immediately red-hot in a mixture of hydrogen and oxygen, or hydro- gen and air; a jet of hydrogen thrown upon a little of the spongy metal, contained in a glass or capsule, is at once kindled, and on this principle machines for the production of instantaneous light have been constructed. These, however, act well only when constantly used; the spongy plati- num is apt to become damp by absorption of moisture from the air, and its power is then for the time lost. The best explanation that can be given of these curious effects is to sup- pose that solid bodies in general have, to a greater or less extent, the prop- erty of condensing gases upon their surfaces, or even liquefying them (as shown p. 139), and that this faculty is exhibited preeminently by certain of the non-oxidizable metals, as platinum and gold. Oxygen and hydrogen may thus, under these circumstances, be brought, as it were, within the sphere of their mutual attractions by a temporary increase of density, whereupon combination ensues. Coal-gas and ether or alcohol vapor may be made to exhibit the phenom- enon of quiet oxidation under the influence of this remarkable surface-ac- tion. A close spiral of slender platinum wire, a roll of thin foil, or even a common platinum crucible, heated to dull redness, and then held in a jet of coal-gas, becomes strongly ignited, and remains in that state as long as the supply of mixed gas and air is kept up, the temperature being maintained by the heat disengaged in the act of union. Sometimes the metal becomes white-hot, and then the gas takes fire. HYDROGEN. Fig. 100. A very pleasing experiment may be made by attaching such a coil of wire to a cord, and suspending it in a glass containing a few drops of ether, having previously made it red-hot in the flame of a spirit- lamp. The wire continues to glow until the oxygen of the air is exhausted, giving rise to the production of an irritating vapor which attacks the eyes. The combustion of the ether is in this case but partial ; a portion of its hydrogen is alone removed, and the whole of the carbon left untouched. A coil of thin platinum wire may be placed over the wick of a spirit-lamp, or a ball of spongy platinum sus- tained just above the cotton: on lighting the lamp, and then blowing it out as soon as the metal appears red-hot, slow combustion of the spirit drawn up by the capillarity of the wick will take place, accompanied by the pungent vapors just mentioned, which may be modified, and even rendered agreeable, by dissolving in the liquid some sweet-smelling essential oil or resin. Hydrogen forms numerous compounds with other bodies, although it is greatly surpassed in this respect, not only by oxygen, but by many of the other elements. The chemical relations of hydrogen tend to place it among the metals. The great discrepancy in physical properties is perhaps more apparent than real. Hydrogen is not yet known in the solid state, while, on the other hand, the vapor of the metal mercury is as transparent and colorless as hydrogen itself. This vapor is only about seven times heavier than atmospheric air, so that the difference in this respect is not nearly so great as that in the other direction between air and hydrogen. There are two oxides of hydrogen namely, water, and a very peculiar substance, discovered in the year 1818 by M. Thenard, called hydrogen dioxide. It appears that the composition of water was first demonstrated in the year 1781 by Cavendish ; * but the discovery of the exact proportions in which oxygen and hydrogen unite in generating that most important com- pound has, from time to time to the present day, occupied the attention of some of the most distinguished cultivators of chemical science. There are two distinct methods of research in chemistry the analytical, or that in which the com- pound is resolved into its elements, and the synthetical, in which the elements are made to unite and produce the compound. The first method is of much more gen- eral application than the second ; but in this particular instance both may be employed, although the results of the synthesis are the more valuable. The decomposition of water may be effected by voltaic electricity. When water is acidulated so as to render it a conductor,! and a portion interposed between a pair of platinum plates connected with the extremities of a voltaic apparatus of moderate power, decomposition of the liquid takes place in a very interesting manner ; oxy- gen, in a state of perfect purity, is evolved from the wa- ter in contact with the plate belonging to the copper end of the battery, and hydrogen, equally pure, is disengaged at the plate con- * A claim to the discovery of the composition of water, on behalf of James Watt, has been very strongly urged, and supported by such evidence that the reader of the controversy may be led to the conclusion that the discovery was made by both parties, nearly simultaneously, and unknown to each other. See the article " Gas," by Dr. Paul, in Watts's Dictionary of Chem- istry, ii. 780. t See the section on " Electro-chemical Decomposition." Fig. 101. 144 HYDROGEN. Fig. 102. nected with the zinc extremity, the middle portions of liquid remaining ap- parently unaltered. By placing small graduated jars over the platinum plates, the gases can be collected, and their quantities determined. The whole arrangement is shown in fig. 101 ; the conducting wires pass through the bottom of the glass cup, and away to the battery. When this experiment has been continued a sufficient time, it will be found that the volume of the hydrogen is a very little above twice that of the oxygen : were it not for the accidental circumstance of oxygen being sensibly more soluble in water than hydrogen, the proportion of two to one by measure would come out exactly. Water, as Mr. Grove has shown, is likewise decomposed into its constit- uents by heat. The effect is produced by introducing platinum balls, ignited by electricity or other means, into water or steam. The two gases are obtained in very small quantities at a time. When oxygen and hydrogen, both as pure as possible, are mixed in the proportions mentioned, passed into a strong glass tube standing over mercury, and exploded by the elec- tric spark, all the mixture disappears, and the mercury is forced lip into the tube, filling it completely. The same experiment may be made with the explosion-vessel or eudi- ometer of Cavendish (fig. 102). The instrument is exhausted at the air-pump, and then filled from a capped jar with the mixed gases; on passing an electric spark by the wires shown at a, explosion ensues, and the glass becomes bedewed with moisture ; and if the stop-cock be then opened under water, the latter will rush in and fill the vessel, leaving merely a bubble of air, the result of imperfect exhaustion. The process upon which most reliance is placed, is that in which pure copper oxide is reduced at a red-heat by hy- drogen, and the water so formed is collected and weighed. This oxide suffers no change by heat alone, but the momen- tary contact of hydrogen, or any common combustible mat- ter, at a high temperature, suffices to reduce a corresponding portion to the metallic state. Fig. 103 will serve to convey some idea of the arrangement adopted in researches of this kind. A copious supply of hydrogen is procured by the action of dilute sulphuric acid upon the purest zinc that can be obtained ; the gas is made to pass in succession through so- lutions of silver and strong caustic potash, by which its purification is completed. After this it is conducted through a tube three or four inches in length, filled with fragments of pumice-stone steeped in concentrated oil of vitriol, or with anhydrous phosphoric acid. These substances have so great an attraction for aqueous vapor, that they dry the gas completely during its transit. The extremity of this tube is shown at a. The dry hydrogen thus arrives at the part of the apparatus containing the copper oxide represented at b; this consists of a two-necked flask of very hard white glass, main- tained at a red-heat by a spirit-lamp placed beneath. As the decomposition proceeds, the water produced by the reduction of the oxide begins to con- dense in the second neck of the flask, whence it drops into the receiver c, provided for the purpose. A second desiccating tube prevents the loss of aqueous vapor by the current of gas which passes in excess. Before the experiment can be commenced, the copper oxide, the purity of which is well ascertained, must be heated to redness for some time in a HYDJiOGEN. 145 current of dry air ; it is then suffered to cool, and very carefully weighed with t lie flask. The empty receiver and second drying-tube are also weighed, the disengagement of gas set up, and when the air has been displaced, heat Fig. 103. is slowly applied to the oxide. The action is at first very energetic ; the oxide often exhibits the appearance of ignition; but as the decomposition proceeds, it becomes more sluggish, and requires the application of a con- siderable heat to effect its completion. When the process is at an end, and the apparatus perfectly cool, the stream of gas is discontinued, dry air is drawn through the whole arrange- ment, and, lastly, the parts are disconnected and reweighed. The loss of the copper oxide gives the oxygen; the gain of the receiver and its drying-tube indicates the water; and the difference between the two, the hydrogen. A set of experiments, made in Paris in the year 1820,* by Dulong and Berzelius, gave as a mean result, for the composition of water by weight, 8-009 parts oxygen to 1 part hydrogen ; numbers so nearly in the proportion of 8 to 1, that the latter have usually been assumed to be true. More recently the subject has been reinvestigated by Dumas, f with the most scrupulous precision, and the above supposition fully confirmed. The composition of water may therefore be considered as established ; it con- tains by weight 8 parts oxygen to 1 part hydrogen, and by measure, 1 vol- ume oxygen to 2 volumes hydrogen. The densities of the gases, as already mentioned, correspond very closely with these results. The physical properties of water are too well known to need lengthened description : it is, when pure, colorless and transparent, destitute of taste and odor, and an exceedingly bad conductor of electricity of low tension. It attains its greatest density towards 4-5 C. (40 F.), freezes at C. (32 F.),J and boils under the ordinary atmospheric pressure at or near 100 C. (212 F.). It evaporates at all temperatures. The weight of a cubic centimetre of water at the maximum density is chosen as the unit of weight of the metrical system, and called a gram; consequently a litre or cubic decimetre = 100 cubic centimetres of water, at the same temperature, weighs 1000 grams, or 1 kilogram. A cubic inch of water at 16-7 C. (62 F.) weighs 252-45 grains; a cubic foot weighs nearly 1000 ounces avoirdupois; and an imperial gallon weighs 70,000 grains, or 10 Ibs. avoirdupois. Water is 825 times heavier than air. To all ordinary observations, it is incompressible; very accurate experi- ments have nevertheless shown that it does yield to a small extent when the power employed is very great, the diminution of volume for each atmo- sphere of pressure being about 51-millionth of the whole. Clear water, although colorless in small bulk, is blue like the atmosphere when viewed in mass. This is seen in the deep ultramarine tint of the * Ann. Chim. Phys. XT. 386. t Ibid. 3d series, viii. 1S9. J According to Dufonr. the specific gravity of ice is 09175; water, therefore, on freezing, expands by JUth of its volume. 13 146 HYDROGEN. ocean, and perhaps in a still more beautiful manner in the lakes of Switzer- land and other Alpine countries, and in the rivers which issue from them, the slightest admixture of mud or suspended impurity destroying the effect. The same magnificent color is visible in the fissures and caverns found in the ice of the glaciers, which is usually extremely pure and transparent within, although foul upon the surface. The specific gravity of steam or vapor of water is found by experiment to be 0-625, compared with air at the same temperature and pressure, or 9 as compared with hydrogen. Now, it has been already shown that water is composed of two volumes of hydrogen and one volume of oxygen ; and if the weight of one volume of hydrogen be taken as unity, that of two volumes hydrogen (== 2) and one volume oxygen (= 16) will together make 18, which is the weight of two volumes of water-vapor. Consequently water in the state of vapor consists of two volumes of hydrogen and one volume of oxygen condensed into two volumes. A method of demonstrating this important fact by direct experiment has been devised by Dr. Hofmann. It consists in exploding a mixture of two volumes hydrogen and one volume oxygen, by the electric spark, in a eudiometer tube enclosed in an atmosphere of the vapor of a liquid (amylic alcohol) which boils at a temperature considerably above that of boiling water, so that the water produced by the combination of the gases remains in the state of vapor instead of at once condensing to the liquid form. It is then seen that the three volumes of mixed gas are reduced after the explosion to two volumes.* Water seldom or never occurs in nature in a state of perfect purity: even the rain which falls in the open country contains a trace of ammoniacal salt, while rivers and springs are invariably contaminated to a greater or less extent with soluble matters, saline and organic. Simple nitration through a porous stone or a bed of sand will separate suspended impurities, but distillation alone will free the liquid from those which are dissolved. In the preparation of distilled water, which is an article of large consump- tion in the scientific laboratory, it is proper to reject the first portions which pass over, and to avoid carrying the distillation to dryness. The process may be conducted in a metal still furnished with a worm or condenser of silver or tin ; lead must not be used. The ocean is the great recipient of the saline matter carried down by the rivers which drain the land: hence the vast accumulation of salts. The following table will serve to convey an idea of the ordinary composition of sea-water ; the analysis is by Dr. Schweitzer, j- of Brighton, the water being that of the British Channel : 1000 grains contained Water ..... 964-745 Sodium Chloride . . . 27-059 Potassium Chloride . . . 0-766 Magnesium Chloride . . . 3-666 Magnesium Bromide . . . 0-029 Magnesium Sulphate . . . 2-296 Calcium Sulphate .... 1-406 Calcium Carbonate . . . 0-033 Traces of Iodine and Ammoniacal salt 1000-000 Its specific gravity was found to be 1-0274 at 15-5 C. (60 F.). Sea-water is liable to variations of density and composition by the influ- * For a description of the apparatus, see Hofmann'a " Modern Chemistry " (1865), p. 51. f Philosophical Magazine, July, 1839. HYDROGEN. 147 ence of local causes, such as the proximity of large rivers, or masses of melting ice, and other circumstances. Natural springs are often impregnated to a great extent with soluble substances derived from the rocks they traverse: such are the various mineral waters scattered over the whole earth, and to which medicinal virtues are attributed. Some of these hold ferrous oxide in solution, and are effervescent from carbonic acid gas ; others are alkaline, probably from traversing rocks of volcanic origin ; some contain a very notable quantity of iodine or bromine. Their temperatures, also, are as variable as their chemical nature. A tabular notice of some of the most remarkable of these waters will be found in the Appendix. Water enters into direct combination with other bodies, forming a class of compounds called hydrates; the action is often very energetic, much heat being evolved, as in the case of the slaking of lime, which is really the production of a hydrate of that base. Sometimes the attraction be- tween the water and the second body is so great that the compound is not decomposable by any heat that can be applied ; the hydrates of potash and soda, and of phosphoric oxide, furnish examples. Oil of vitriol is a hy- drate of sulphuric oxide, from which the water cannot be thus separated. Water very frequently combines with saline substances in a loss inti- mate manner than that above described, constituting what is called water of crystallization, from its connection with the geometrical figure of the salt. In this case it is easily driven off by the application of heat. Lastly, the solvent properties of water far exceed those of any other liquid known. Among salts a very large proportion are soluble to a greater or less extent, the solubility usually increasing with the temperature, so that a hot saturated solution deposits crystals on cooling. There are a few exceptions to this law, one of the most remarkable of which is coin- 10 20 30 40 50 60 70 80 90 100 110 F. 32 50 68 86 104 122 140 158 176 194 212 230 C. Temperature. mon salt, the solubility of which is nearly the same at all temperatures: the hydrate and certain organic salts of calcium, also, dissolve more freely in cold than in hot water. 148 HYDROGEN'. The diagram (fig. 104) exhibits the unequal solubility of different in water of different temperatures. The lines of solubility cut the verticals raised from points indicating the temperatures, upon the lower horizontal line, at heights proportioned to the quantities of salt dissolved by 100 parts of water. The diagram shows, for example, that 100 parts of water dissolve, of potassium sulphate 3 pts. at C., 17 pts. at 50, and 26 pts. at 100. There are salts which, like sodium chloride, possess, as already mentioned, very nearly the same degree of solubility in water at all tem- peratures ; in others, like potassium sulphate or potassium chloride, the solubility increases directly with the increment of temperature ; in others, again, like potassium nitrate or potassium chlorate, the solubility aug- ments much more rapidly than the temperature. The diagram exhibits the differences in the deportment of these different salts very conspicuously, by a straight horizontal line, by a straight inclined line, and lastly by curves, the convexity of which is turned toward the lower horizontal line. In the diagram, the solubility of salt is represented by the quantity of anhydrous salt dissolved by 100 parts of water. This is, in fact, the com- mon mode of stating the solubility of salts. It is obvious, however, that salts containing water of hydration or water of crystallization cannot, within certain limits of temperature, dissolve in water in the anhydrous state, but must be dissolved as hydrates. The solubility of a hydrated salt frequently differs very considerably from that of the same salt in the anhy- drous state. Again, many salts form more than one hydrate ; and these several hydrates may also differ in their solubility. Sodium sulphate forms a peculiar hydrate, consisting, in 100 parts, of 53 parts of anhy- drous salt and 47 parts of water, which is obtained in crystals, when a solution of sodium sulphate, saturated at 100 C. (212 F.), is considerably cooled out of contact with the air: this hydrate is much more soluble than Glauber's salt, the other hydrate of sodium sulphate, which differs from the former one in its crystalline form, and consists, in 100 parts, of 44-2 parts of anhydrous salt and 55-8 parts of water. When a solution of sodium sulphate is saturated at the boiling-point of water, and cooled to the common temperature without depositing any crystals, the salt exists in the form of the more soluble hydrate. This salt, when coming in contact with the dust of the air, or with a small crystal oC common Glauber's salt, is suddenly transformed into the less soluble hydrate, part of which sepa- rates from the solution, in the form of Glauber's salt. From to 33 C. (32 to 91 F.) sodium sulphate dissolves as Glauber's salt, the solubility of which increases with the temperature; hence the rapid rise of the curve representing the solubility of the salt in the diagram. Above 33 C. (91 F.) the hydrate of sodium sulphate is, even in solution, decomposed, being more and more thoroughly converted into the anhydrous salt as the temperature increases. Sodium sulphate appears, however, far less solu- ble in the anhydrous state, and hence the diminution of solubility of the salt when its solution is heated above 33 C. (91 F.), which is exhibited by the diagram. Liquid Diffusion. Dialysis. When a solution having a sp. gr. greater than water is introduced into a cylindrical glass vessel, and then water very cautiously poured upon it, in such a manner that the two layers of liquid remain unmoved, the substance dissolved in the lower liquid will gradually pass into the supernatant water, though the vessel may have been left un- disturbed, and the temperature remain unchanged. This gradual passage of a dissolved substance from its original solution into pure water, taking place notwithstanding the higher specific gravity of the substance which opposes this passage, is called the diffusion of liquids. The phenomena of this diffusion have been lately investigated by Mr. Graham, who has arrived at very important results. Different substances, when in solution of the same HYDROGEN. 149 concentration, and under other similar circumstances, diffuse with very unequal velocity. Hydrochloric acid, for instance, diffuses with greater rapidity than potassium chloride, potassium chloride more rapidly than sodium chloride, and the latter, again, more quickly than magnesium sul- phate ; gelatin, albumin, and caramel diffuse very slowly. Diffusion is generally found to take place more rapidly at high than at low temperatures. Diffusion is more particularly rapid with crystallized substances, though not exclusively, for hydrochloric acid and alcohol are among the highly diffusive bodies. Diffusion is slow with non-crystalline bodies, which, like gelatin, are capable of forming a jelly, though even here exceptions are met with. Mr. Graham calls the substances of great diffusibility crystal- lot Is y the substances of low diffusibility colloids. The unequal power of diffusion with which different substances are endowed frequently furnishes the means of separating them. When water is poured with caution, so as to prevent mixing, upon a solution containing equal quantities of potassium chloride and sodium chloride, the more diffusible potassium chloride travels more rapidly upwards than the less diffusible sodium chloride, and very considerable portions of potassium chloride will have reached the upper layers of the water before the sodium chloride has arrived there in ap- preciable quantity. The separation of rapidly diffusible crystalloids and slowly diffusible colloils succeeds still better. A more perfect separation of crystalloids and colloids may be accom- plished in the following manner: Mr. Graham has made the important ob- servation, that certain membranes, and also parchment paper, when in contact, on the one surface, with a solution containing a mixture of crys- talloilal and collilal substances, and, on the other surface, with pure water, will permit the passage to the water of the crystalloids, but not of the colloids. To carry out this important mode of separation, which is des- ignated by the term dialysis, the lower mouth of a glass vessel, open on both sides (fig. 105), is tied over with parchment paper placed upon an .ap- propriate support (fig. 106), and transferred, together with the latter, into a larger vessel filled with water (fig. 107) ; or the vessel may be suspended, as shown in fig. 108. The liquid containing the different substances in Fig. 105. Fig. 108. solution is then poured into the inner vessel, so as to form a layer of about half an inch in height upon the parchment paper. The crystalloidal substances gradually pass through the parchment paper into the outer 150 HYDROGEN. water, which may be renewed from time to time : the colloidal substances are almost entirely retained by the liquid in the inner vessel. In this man- ner Mr. Graham has prepared several colloids, free from crystalloids; lie has shown, moreover, that poisonous crystalloids, such as arscnious acid or strychnine, even when mixed with very large proportions of colloidal substances, pass over into the water of the dialyzer in such a state of purity that their presence may be established by re-agents with the utmost facility. Osmose. When two different liquids are separated by a porous dia- phragm, as, for instance, by a membrane, and the liquids mix through this diaphragm, it is found that in most cases the quantities travelling in op- posite direction are unequal. Suppose three cylinders, the lower mouths of which are tied over Avith bladders, filled respectively with concentrated solutions of copper sulphate, sodium chloride, and alcohol, and let them be immersed in vessels containing water to such a depth that the liquids inside and outside are level (fig. 109). After some time the liquid within the tube is found to have risen appreciably above the level of the water (fig. 110). On the other hand, if the cylinder tilled with pure water be im- mersed in a solution of copper sulphate, or of sodium chloride, or in al- cohol, the liquid in the cylinder is seen to diminish after sometime (fig 111). A larger quantity of water passes through the bladder into the solution of Fig. 110. Fig. 111. copper sulphate, of sodium chloride, or into alcohol, than the amount of either of these three liquids which passes through the bladder into the water. The mixing of dissimilar substances through a porous diaphragm is called osmose. The passage in larger proportion of one liquid into an- other is designated by the term exosjnose. These phenomena are due to the attraction which the two liquids have for each other, and to the difference of the attraction exercised by the diaphragm upon these liquids. Bladder takes up a much larger quantity of water than of a solution of salt or of alcohol. Very rarely only one of the liquids traverses the diaphragm; generally two currents of unequal strength move in opposite directions. When water is separated by an animal membrane from a solution of salt or from alcohol, not only is a transition of water to these liquids observed, but a small quantity of hydrochloric acid and of alcohol also passes over into the water. In some cases, however, when colloidal substances in concentrated solutions are on one side of the diaphragm and water on the other, the latter alone traverses the diaphragm, not a trace of the former passing through to the water. Water likewise dissolves gases. Solution of gases in water (or in other liquids) is called absorption, unless this solution gives rise to the formation of chemical compounds in definite proportions. The phenomena of absorp- HYDROGEN. 151 tion have been more particularly studied by Bunsen, and it is to this phi- losopher that we are indebted for the most accurate examination of this subject. Water dissolves very unequal quantities of the different gases and very unequal quantities of the same gas at different temperatures. 1 vol. of water absorbs, at the temperatures stated in the table, and under the pres- sure of 30 inches of mercury, the following volumes of different gases, measured at C. and 30 inches pressure : 10 20 0C. 10 20 30 40 Oxygen. 0-041 0-033 0-028 Chlorine. 2-59 2-16 1-75 1-37 Nitrogen. 0-020 0-016 0-014 Hydrogen Sulphide. 4-37 3-59 2-91 2-33 1-86 Hydrogen. 0.019 0-019 0-019 Sulphurous Oxide. 53-9 3G-4 27-3 20-4 15-6 Nitrogen Monoxide. 1-31 0-92 0-67 Hydrochlo- ric Acid. 505 472 441 412 387 Carbon Dioxide. 1.80 1-18 0-90 Ammo- nia. 1180 898 680 536 444 When the pressure increases, a larger quantity of the gases is absorbed. Gases moderately soluble in water follow in their solubility the law of Henry and Dalton, according to which the quantity of gas dissolved is pro- portional to the pressure. At 10 C. 1 vol. of water absorbs under a pres- sure of 1 atmosphere 1-18 vol. of carbon dioxide, measured at and under a pressure of 30 inches mercury. The quantity of carbon dioxide dissolved under a pressure of 2 atmospheres, and measured under conditions pre- cisely similar to those of the previous experiments, equals 2-36 vol. Again, 1 vol. of water dissolves under a pressure of *- atmosphere, 0.59 vol. of carbon dioxide also measured at and under 30 inches of mercury. Gases which are exceedingly soluble in water do not obey this law, except at higher temperatures, when the solubility has been already considerably diminished. It deserves, however, to be noticed, that the pressure which determines the rate of absorption of a gas is by no means the general pressure to which the absorbing liquid is exposed, but that pressure which the gas under consideration would exert if it were alone present in the space with which the absorbing liquid is in contact. Thus, supposing water to be in contact with a mixture of 1 vol. of carbon dioxide and 3 vol. of nitrogen, under a pressure of 4 atmospheres, the amount of carbon dioxide dissolved by the water will be by no means equal to that which the water would have absorbed if it had been at the same pressure of 4 atmospheres in contact with pure carbon dioxide. In a mixture of carbon dioxide and nitrogen in the stated proportions, the carbon dioxide exercises only }, the nitrogen only f, of the total pressure of the gaseous mixture (4 atmospheres); the partial pressure due to the carbon dioxide is in this case 1 atmosphere, that due to the nitrogen 3 atmospheres; and water, though exposed to a pressure of 4 atmospheres, cannot, under these circumstances, absorb more carbon dioxide than it would if it were in contact with pure carbon dioxide under a pressure of 1 atmosphere. It is necessary to bear this in mind in order to understand why the air which is absorbed by water out of the atmosphere differs in composition from atmospheric air. The latter consists very nearly of 21 vol. of oxygen and 79 vol. of nitrogen In atmospheric air which acts under a pressure of 1 atmosphere, the oxygen exerts a partial pressure of T ? ^, the nitrogen a 152 HYDROGEN. partial pressure of T ^ 9 7 atmosphere. At 10 C. (50 F.) 1vol. of water (see the above table) absorbs 0-033 vol. of oxygen, and 0-016 vol. of nitrogen, supposing these gases to act in the pure state under a pressure of 1 atmo- sphere. But under the partial pressures just indicated, water of 10 C. cannot absorb more than T 2 J^ X 0-033 = 0-007 of oxygen, and T 7 ^- x 01G = 0-013 vol. of nitrogen. In 0-007 -j- 0-013 = 0-020 vol. of gaseous mixture absorbed by water there are consequently 0-007 vol. of oxygen, and 0-013 vol. of nitrogen, or in 20 vol. of this mixture, 7 vol. of oxygen and 13 vol. of nitrogen, or in 100 vol. of the gaseous mixture, 35 vol. of oxygen and 69 vol. of nitrogen. The air contained at the common temperature in water is thus seen to be very much richer in oxygen than ordinary atmo- spheric air. Water containing a gas in solution, when exposed in a vacuum or in a space filled with another gas, allows the gas absorbed to escape until the quantity retained corresponds with the share of the pressure belonging to the gas evolved. If the latter be constantly removed by a powerful ab- sorbent or by a good air-pump, it is in most cases easy to separate every trace of gas from the water. The same result is obtained when water con- taining a gas in solution is exposed in a space of comparatively infinite size filled with another gas. Water in which nitrogen monoxide is dis- solved loses the latter entirely by mere exposure to the atmosphere, and the gas evolved cannot, at any moment, exert more than an infinitely small share of the pressure. If water be freed from gases by ebullition, the separation depends partly upon the diminution of the solubility by the in- crease of temperature, partly also upon the formation above the surface of the liquid of a constantly renewed atmosphere into which the gas still retained by the liquid may escape. Some gases which are absorbed in large quantities, and very quickly by water, hydrochloric acid, for instance, cannot be perfectly ex'pelled either by the protracted action of another gas (exposure to the atmosphere) or by ebullition : in such cases the liquid still charged with gas evaporates as a whole when it has assumed a certain composition. This composition varies, however, if the liquid be submitted to a current of air, with the temperature ; and if it be boiled, with the pressure under which ebullition takes place. Liquids also lose the gas they contain in solution by freezing: hence the air-bubbles in ice, which consist of the air which had been absoi'bed from the atmosphere by the water. Gas is retained by liquids at the freezing temperature only when it forms a chemical combination in definite propor- tion with the liquid. Water containing chlorine or sulphurous acid in so- lution freezes without evolution of gas, with formation of solid hydrates of chlorine or sulphurous acid. Pure water generally dissolves gases more copiously than water contain- ing solid bodies in solution (salt water, for instance). If in some few cases exceptions are observed to take place, they appear to depend upon the for- mation of feeble but true chemical compounds in definite proportion ; the fact that carbon dioxide is more copiously absorbed by water containing sodium phosphate in solution than by pure water may perhaps be explained in this manner. When water is heated in a strong vessel to a temperature above that of the ordinary boiling-point, its solvent powers are still further increased. Dr. Turner inclosed in the upper part of a high-pressure steam-boiler, worked at 149 C. (300 F.), pieces of plate and crown glass. At the ex- piration of four months the glass was found completely corroded by the action of the water; what remained was a white mass of silica, destitute of alkali, while stalactites of siliceous matter, above an inch in length, depended from the little wire cage which enclosed the glass. This experi- NITROGEN. 153 ment, tends to illustrate the changes which may be produced by the action of water at a high temperature in the interior of the earth upon felspathic and other rocks. The phenomenon is manifest in the Geyser springs of Iceland, which deposit siliceous sinter.* HYDROGEN DIOXIDE, f sometimes called oxygenated water, is an exceedingly interesting substance, but very difficult of preparation. It is formed by dis- solving barium dioxide in dilute hydrochloric acid carefully cooled by ice, and then precipitating the barium by sulphuric acid; the excess of oxygen of the dioxide, instead of being disengaged as gas, unites with a portion of the water, and converts it into hydrogen dioxide. This treatment is repeated with the same solution, and fresh portions of the barium dioxide, until a considerable quantity of the latter has been consumed, and a cor- responding amount of hydrogen dioxide formed. The liquid yet contains hydrochloric acid, to get rid of which it is treated in succession with silver sulphate and baryta-water. The whole process requires the utmost care and attention. The barium dioxide itself is prepared by exposing pure baryta, contained in a red-hot porcelain tube, to a stream of oxygen. The solution of hydrogen dioxide may be concentrated under the air-pump receiver until it acquires the specific gravity of 1-45. In this state it pre- sents the aspect of a colorless, transparent, inodorous liquid, possessing remarkable bleaching powers. It is very prone to decomposition; the least elevation of temperature causes effervescence, due to the escape of oxygen gas; near 100 it is decomposed with explosive violence. Hydrogen dioxide contains exactly twice as much oxygen as water, or 16 parts to 1 part of hydrogen. A trioxide of hi/drogen is said to exist, although it has never been obtained in the pure state. It is likewise a powerful oxidizing agent, and altogether similar in its properties to the dioxide. According to the researches of Dr. Baumert, minute quantities of this substance are formed in the decom- position of water by electricity, and impart the odor by which the prod- ucts of this process are characterized ; but, according to the experiments of Andrews and others, already referred to (p. 135), the supposed trioxide really consists of active oxygen or ozone, with a small quantity of hydrogen dioxide. NITROGEN. Nitrogen J constitutes about four-fifths of the atmosphere, and enters into a great variety of combinations. It may be prepared by several methods. One of the simplest of these is to burn out the oxygen from a confined por- tion of air by phosphorus, or by a jet of hydrogen. A small porcelain capsule is floated on the water of the pneumatic trough, and a piece of phosphorus is placed in it and set on fire. A bell-jar is then inverted over the whole, and suffered to rest on the shelf of the * Philosophic,-)] Mnpa/ino. Oct. 1834. f In symbols the composition of water and hydrogen dioxide is thus expressed: Wator OH 2 . Hydrogen dioxide 2 H/;. J 7. c. Generator of nitre; also called Azote, from a, privative, and w >j, life. 154 NITROGEN. trough, so as to project a little over its edge. At first the heat causes expansion of the air of the jar, and a few bubbles are expelled, after which the level of the water rises considerably. When Fig.\\1. the phosphorus becomes extinguished by exhaustion of the oxygen, and time has been given for the sub- sidence of the cloud of finely divided snow-like phos- phoric oxide which floats in the residual gas, the nitrogen may be transferred into another vessel, and its properties examined. Prepared by the foregoing process, nitrogen is con- taminated with a little vapor of phosphorus, which communicates its peculiar odor. A preferable method is to fill a porcelain tube with turnings of copper, or, still better, with the spongy metal obtained by redu- cing the oxide with hydrogen; to heat this tube to red- ness, and then pass through it a slow stream of at- mospheric air, the oxygen of which is entirely removed during its progress by the heated copper. If chlorine gas be passed into solution of ammonia, the latter substance, which is a compound of nitrogen with hydrogen, is decomposed ; the chlorine combines with the hydrogen, and the nitrogen is set free with effervescence. In this manner very pure nitrogen can be obtained. In making this ex- periment, it is necessary to stop short of saturating or decomposing the whole of the ammonia ; otherwise there will be great risk of accident from the formation of an exceedingly dangerous explosive compound, produced by the contact of chlorine with an ammoniacal salt. Another very easy and perfectly safe method of obtaining pure nitrogen is to decompose a solution of potassium nitrite with ammonium chloride (sal-ammoniac). The potassium nitrite is prepared by passing the red vapors of nitrous acid obtained by heating dilute nitric acid with starch into a solution of caustic potash. On boiling the resulting solution with sal-ammoniac, nitrogen gas is evolved, while potassium chloride remains in solution. * Nitrogen is destitute of color, taste, and odor; it is a little lighter than air, its density being, according to Dumas, 0-972. A litre of the gas at C. and 760 mm. barometric pressure weighs 1-25658 gram. 100 cubic inches, at 60 F. and 30 inches barometer, weigh 30-14 grains. Nitrogen is in- capable of sustaining combustion or animal existence, although, like hydro- gen, it has no positive poisonous properties; neither is it soluble to any notable extent in water or in caustic alkali; it is, in fact, best character- ized by negative properties. The exact composition of the atmosphere has repeatedly been made the subject of experimental research. Besides nitrogen and oxygen, the air contains a little carbon dioxide (carbonic acid), a very variable proportion of aqueous vapor, a trace of ammonia, and, perhaps, a little carburetted hydrogen. The oxygen and nitrogen are in a state of mixture, not of com- bination, yet their ratio is always uniform. Air has been brought from lofty Alpine heights, and compared with that from the plains of Egypt; it has been brought from an elevation of 21.000 feet by the aid of the bal- loon; it has been collected and examined in London and Paris, and many other places; still the proportion of oxygen and nitrogen remains unaltered, the diffusive energy of the gases being adequate to maintain this perfect uniformity of mixture. The carbon dioxide, on the ccntrary, being much * The reaction is represented by the equation, NQ2K + NII4C1 - KC1 -f 20II 2 + N 2 Potassium Ammonium Potassium "Water. Nitrogen nitrite. chloride. chloride. gas. NITROGEN, s 155 influenced by local causes, varies considerably. In the following table the proportions of oxygen and nitrogen are given on the authority of Duinas, and the carbon dioxide on that of De Saussure: the ammonia, the discovery of which in atmospheric air is due to Liebig, is too small in quantity for direct estimation. Nitrogen Oxygen Composition of the Atmosphere. By weight. 77 parts 23 " By measure. 79-19 20-81 100 100-00 Carbon dioxide, from 3-7 measures to 6-2 measures in 10,000 measures of air. Aqueous vapor variable, depending much upon the temperature. Ammonia, a trace. Dr. Frankland has analyzed samples of air taken by himself in the valley of Chamouni, on the summit of Mont Blanc, and at the Grands Mulcts. The following are the results of his analyses: Chamouni (3000 feet) Grands Mulcts (11,000 feet) Mont Blanc (15,732 feet) . Carbon dioxide. . 0-OC3 0-111 . 0-061 Oxygen. 20-894 20-802 20-903 Fig. 113. A litre of pure and dry air at C. and 760 mm. pressure weighs 1-29366 grams. 100 cubic inches at 60 F. and 30 inches barom. weigh 30-935 grains: hence a cubic foot weighs 536-96 grains, which is ^-^ of the weight of a cubic foot of water at the same temperature. The analysis of air is very well effected by passing it over finely divided copper contained in a tube of hard glass, carefully weighed and then heated to redness: the nitrogen is suffered to flow into an ex- hausted glass globe, also previously weighed. The in- crease of weight after the experiment gives the informa- tion sought. An easier, but less accurate method consists in intro- ducing into a graduated tube, standing over water, a known quantity of the air to be examined, and then passing into the latter a stick of phosphorus affixed to the end of a wire. The whole is left about twenty-four hours, during which the oxygen is slowly but completely absorbed, after which the phosphorus is withdrawn, and the residual gas read off. Liebig has proposed to use an alkaline solution of py- rogallic acid (a substance which will be described in the department of organic chemistry) for the absorption of oxygen. The absorptive power of such a solution, which turns deep black on coming in contact with the oxygen, is very considerable. Liebig's method combines great ac- curacy with unusual rapidity and facility of execution. Another plan is to mix the air with hydrogen and pass an electric spark through the mixture: after explosion the volume of gas is read off and compared with that of the air employed. Since the analysis of gaseous bodies by explosion is an operation of great importance in practical chem- istry, it may be worth while describing the process in detail, as it is appli- cable, with certain obvious variations, to a number of analogous cases. 156 NITROGEN. A convenient form of apparatus for the purpose, when great accuracy is not required, is the syphon eudiometer of Dr. Ure : this consists of a stout glass tube, having an internal diameter of about Fig. 114. one third of an inch, closed at one end, and bent into the form represented in fig. 114. Two pieces of platinum wire, melted into the glass near the closed extremity, serve to give passage to the spark. The closed limb is carefully graduated. When required for use, the instrument is filled with mercury, and inverted in a vessel of the same liquid. A quantity of the air to be examined is then introduced, the manipulation being precisely the same as with expe- riments over water; the open end is stopped with the thumb, and the air transferred to the closed ex- tremity. The instrument is next held upright, and after the level of the mercury has been made equal on both sides by displacing a portion from the open limb by thrusting down a piece of stick, the volume of air is read off. This done, the open part of the tube is again filled up with mercury, closed with the finger, inverted into the liquid metal, and a quantity of pure hydrogen introduced, equal, as nearly as can be guessed, to about half the volume of the air. The eudiometer is once more brought into the erect position, the level of the mercury equalized, and the volume again read off; the quantity of hydrogen added is thus accurately ascertained. All is now ready for the explosion; the instrument is held in the way represented, the open end being firmly closed by the thumb, while the knuckle of the fore-finger touches the nearer platinum wire; the spark is then passed by the aid of a charged jar or a good elec- trophorus, and the explosion ensues. The air confined by the thumb in the open part of the tube acts as a spring and moderates the explosive effect. Nothing now remains but to equalize the level of the mercury by pouring a little more into the instrument, and then to read off the volume for the last time. What is required to be known from this experiment is the diminution the mixture suffers by explosion ; for since the hydrogen is in excess, and since that body unites with oxygen in the proportion by measure of two to one, one-third part of that diminution must be due to the oxygen contained in the air introduced. As the amount of the latter is known, the proportion of oxygen it contains thus admits of determination. The case supposed will render this clear. Air introduced 100 measures. Air and hydrogen . . . . . 150 Volume after explosion .... 87 Diminution ...... 63 63 21 ; oxygen in the hundred measures. 3 The syphon eudiometer in the simple form above described is not well adapted for accurate analysis, especially when, as in the analysis of many gaseous mixtures, caustic potash and other re-agents have to be introduced into the closed limb, to absorb some of the components of the mixture, or of the products resulting from the explosion; but it forms the essential part of the more exact and complex forms of eudiometer devised by Reg- NITROGEN. 157 Fig. 115. n.'iult, and by Frankland and Ward, in which provision is made for accu- rately adjusting the level of the mercury, and for quickly transferring the gas to another tube in which it may be subjected to the action of absorbing agents, and then returning it to the syphon tube for measurement.* The simplest, and, on the whole, the most convenient form of eudiometer consists of a straight graduated glass tube (fig. 115) closed at the top, and having platinum wires inserted near the closed end. This tube is filled with mercury, and inverted in a mercurial pneumatic trough. A quantity of air, sufficient to fill about one sixth of the tube, is then in- troduced, and its volume accurately as- certained by reading off with a telescope the number of divisions on the tube to which the mercury reaches, whilst the height of the column of mercury in the tube above the trough, together with that of the barometer, and the tempera- ture of the air, are also read off. A quantity of pure hydrogen gas is now added, more than sufficient to unite with all the oxygen present; and the volume of the gas and the pressure exerted upon it, are then determined as before. An electric spark is npw passed through the mixture, care being taken to prevent any escape, by pressing the open end of the eudiometer against a piece of sheet caoutchouc under the mercury in the trough. After the explosion, the volume is again determined as before, and is found to be less than that before the ex- plosion. One third of the diminution gives, as already explained, the volume of oxygen contained in the air taken for analysis. Compounds of Nitrogen and Oxygen. There are five distinct compounds of nitrogen and oxygen, thus named and constituted : Composition. Nitrogen monoxide f Nitrogen dioxide Nitrogen trioxide, or Nitrous oxide . Nitrogen tetroxide Nitrogen pentoxide, or Nitric oxide . By weight. By volume. Nitrogen. Oxygen. Nitrogen. Oxygen. 28 . 16 2.1 . 28 . 32 2.2 28 . 48 2.3 . 28 . 64 2.4 28 , 80 2.5 A comparison of these numbers Vill show that the quantities of oxygen which unite with a given quantity of nitrogen are to one another in the ratio of the numbers 1, 2, 3, 4, 5. See the article " Analysis of Gases," by Dr. Russell, in Watts's " Dictionary of Chemistry," f In symbols the composition of these bodies is thus expressed: Nitrogen monoxide . . . N 2 O Nitrogen dioxide .... N 2 2 or NO Nitrogen trioxide . . . N 2 O 3 Nitrogen tetroxide .... N 2 ' 4 orN0 2 Nitrogen pentoxide . . . N 2 5 . 158 NITROGEN. The third and fifth of the compounds in the table are capable of taking up the elements of water and of metallic oxides to form salts (p. 133), called respectively nitrites and nitrates, the hydrogen salts being also called nitrous and nitric acid.* The other three nitrogen oxides do not form salts. It will be convenient to commence the description of these compounds with the last on the list, viz., the pentoxide, as its salts, the nitrates, are the sources from which all the other compounds in the series are obtained. NITROGEN PENTOXIDE or NITRIC OXIDE (also called Anhydrous Nitric Acid OT Nitric Anhydride]. This compound was discovered in 1849 by Deville, who obtained it by exposing silver nitrate, which may be regarded as a compound of nitrogen pentoxide with silver and oxygen, to the action of chlorine gas. Chlorine and silver then combine, forming silver chloride, which remains in the apparatus, while oxygen and nitrogen pentoxide separate. } The latter is a colorless substance, crystallizing in six-sided prisms, which melt at 30 and boil between 45 and 50, when they begin to decompose. Nitrogen pentoxide sometimes explodes spontaneously. It dissolves in water with great rise of temperature, forming hydrogen nitrate or nitric acid. NITRATES NITRIC ACID. In certain parts of India, and in other hot dry climates where rain is rare, the surface of the soil is occasionally covered by a saline efflorescence, like that sometimes apparent on newly plastered walls : this substance collected, dissolved in hot water, and crystallized from the filtered solution, furnishes the highly important salt known in commerce as nitre or saltpetre, and consisting of potassium nitrate. To obtain nitric acid, equal weights of powdered nitre and strong sulphuric acid are in- troduced into a glass retort, and heat is applied by means of an Argand gas- lamp or charcoal chauffer, (see fig. 38). A flask, cooled by a wet cloth, is adapted to the retort to serve for a receiver. No luting of any kind must be used. As the distillation advances, the red fumes which first arise disappear, but towards the end of the process they again become manifest. When this happens, and very little liquid passes over, while the greater part of the saline matter of the retort is in a state of tranquil fusion, the opera- tion may be stopped; and when the retort is quite cold, water maybe introduced to dissolve out the saline residue. The reaction consists in an interchange between the potassium of the nitre and half the hydrogen of the sulphuric acid (hydrogen sulphate), whereby there are formed hydro- gen nitrate which distils over, and hydrogen and potassium sulphate which remains in the retort. J In the manufacture of nitric ac.id on the large scale, the glass retort is replaced by a cast-iron cylinder, and the receiver by a series of earthen condensing vessels connected by tubes. Sodium nitrate, found native in Peru, is now generally substituted for potassium nitrate. Nitric acid thus obtained has a specific gravity of from 15 to 1-52; it has a golden-yellow color, due to nitr.ogen trioxide, or tetroxide, which is held in solution, and, when the acid is diluted with water, gives rise by its decomposition to a disengagement of nitric oxide. Nitric acid is ex- * Hydrogen nitrate, or Nitrous acid .... N 2 3 .OH 2 or NOH 2 Potassium nitrate N 2 O 3 .OK 2 or NOK 2 Hydrogen nitrate, or Nitric acid .... N 2 O 5 .OII 2 or N0 3 H Potassium nitrite N 2 5 .OK 2 or N0 3 K. t N0 3 Ag + Cl a = 2AgCl + + N 2 5 . j N0 3 K + S0 4 H 2 = N0 3 H + S0 4 HK Potassium Hydrogen Hydrogen Hydrogen and po- nitrate. sulphate. nitrate. tassium sulphate. NITROGEN. 159 coedingly corrosive, staining the skin deep yellow, and causing total dis- organization. Poured upon red-hot powdered charcoal, it causes brilliant combustion; and when added to warm oil of turpentine, acts upon that substance so energetically as to set it on fire. Pure nitric acid, in its most concentrated form, is obtained by mixing the above with about an equal quantity of strong sulphuric acid, redistil- ling, collecting apart the first portion which conies over, and exposing it in a vessel slightly warmed and sheltered from the light, to a current of dry air made to bubble through it, which completely removes the nitrous acid. In this state the product is as colorless as water: it has the sp. gr. 1-517 at 15-5 (60 F.), boils at 84-5 (184 F.), and consists of 54 parts nitrogen pentoxide and 9 parts water. Although nitric acid in a more dilute form acts very violently upon many metals, and upon organic sub- stances generally, this is not the case with the most concentrated acid: even at a boiling heat, it refuses to attack iron or tin; and its mode of action on lignin, starch, and similar substances is quite peculiar and very much less energetic than that of an acid containing more water. On boiling nitric acid of different degrees of concentration, at the ordi- nary atmospheric pressure, a residue is left, boiling at 120/5 and 29 inches barometer, and Laving the sp. gr. 1-414 at 15-5. This acid was formerly supposed to be a definite compound of nitric acid with water; but Roscoe has recently proved this assumption to be incorrect, the composition of the acid varying according to the pressure under which the liquid boils. The nitrates form a very extensive and important group of salts, which are remarkable for being all soluble in water. Hydrogen nitrate is of great use in the laboratory, and also in many branches of industry. The acid prepared in the way described is apt to contain traces of chlorine from common salt in the nitre, and sometimes of sulphate from accidental splashing of the pasty mass in the retort. To discover these impurities, a portion is diluted with four or five times its bulk of distilled water, and divided between two glasses. Solution of silver nitrate is dropped into the one, and solution of barium nitrate into the other; if no change ensue in either case, the acid is free from the impurities men- tioned. Nitric acid has been formed in small quantity by a very curious process, namely, by passing a series of electric sparks through a portion of air in' contact with water or an alkaline solution. The amount of acid so formed after many hours is very minute; still it is not impossible that powerful discharges of atmospheric electricity may sometimes occasion a trifling production of nitric acid in the air. A very minute quantity of nitric acid is also produced by the combustion of hydrogen and other sub- stances in the atmosphere ; it is also formed by the oxidation of ammonia. Nitric acid is not so easily detected in solution in small quantities as many other acids. Owing to the solubility of all its compounds, no precip- itant can be found for this substance. An excellent mode of testing it is based upon its power of bleaching a solution of indigo in sulphuric acid when boiled with that liquid. The absence of chlorine must be insured in this experiment by means which will hereafter be described: otherwise the result is equivocal. The best method for the detection of nitric acid is the following. Tho substance to be examined is boiled with a small quantity of water, and the solution cautiously mixed with an equal volume of concentrated sul- phuric acid; the liquid is then allowed to cool, and a strong solution of ferrous sulphate carefully poured upon it, so as to form a separate layer. If large quantities of nitric acid are present, the surface of contact, first, and then the whole of the liquid, becomes black. If but small quantities of nitric acid are present, the liquid becomes reddish-brown or purple. 100 NITROGEN. The ferrous sulphate reduces the nitric acid to nitrogen dioxide, which, dissolving in the solution of ferrous sulphate, imparts to it a dark color. NITROGEN MONOXIDE (sometimes called Nitrous Oxide; also Laughing- Gas}. When solid ammonium nitrate is heated in a retort or flask,* fig. 116, furnished with a perforated cork and bent - H6. tube, it is resolved into water and nitrogen mon- oxide. f No particufar precaution is required in the operation, save due regulation of the heat, and the avoidance of tumultuous disengagement of the gas. Nitrogen monoxide is a colorless, transparent, and almost inodorous gas, of distinctly sweet taste. Its specific gravity is 1-525; a litre of it weighs 0-97172 grams ; 100 cubic inches weigh 47-29 grains. It supports the combustion of a taper or a piece of phosphorus with almost as much energy as pure oxygen : it is easily distinguished, however, from that gas by its solubility in cold water, which dis- solves nearly its own volume : hence it is necessary to use tepid water in the pneumatic trough or gas- holder; otherwise great loss of gas will ensue. Nitrous oxide has been liquefied, but with diffi- culty: it requires, at 7-2 C. (45 F.), a pressure of 50 atmospheres : the liquid, when exposed under the bell-glass of the air-pump, is rapidly converted into a snow-like solid. When mixed with an equal volume of hydrogen, and fired by the electric spark in the eudi- ometer, it explodes with violence, and liberates its own measure of nitrogen. Every two volumes of the gas must consequently contain two volumes of nitrogen and one volume of oxygen, the whole being condensed or con- tracted one third a constitution resembling that of vapor of water. The most remarkable property of this gas is its intoxicating power iipon the animal system. If quite pure, or merely mixed with atmospheric air, it may be respired for a short time without danger or inconvenience. The effect is very transient, and is not followed by depression. NITROGEN DIOXIDE (sometimes called Nitric Oxide). Clippings or turn- ings of copper are put into the apparatus employed for preparing hydrogen (p. 137), together with a little water, and nitric acid is added by the funnel until brisk effervescence is excited. The gas may be collected over cold water, as it is not sensibly soluble. The reaction is a simple deoxidation of some of the nitric acid by the copper: the metal is oxidized, and the oxide so formed is dissolved by an- other portion of the acid. Nitric acid is very prone to act thus upon certain metals. J The gas obtained in this manner is colorless and transparent: in contact with air or oxygen gas it produces deep red fumes, which are readily ab- sorbed by water: this character is sufficient to distinguish it from all other * Florence oil-flnsks, which may be purchased at a very trifling sum, constitute exceedingly useful vessels lor chemical purposes, and often supersede retorts or other expensive apparatus. They are rendered still more valuable by cutting the neck smoothly round with a hot iron, Foftening it in the flame of a good Argand gas-lamp, and then turning over the edge so as to form a lip, or border. The neck will then bear a tightly fitting cork without risk of splitting. f N0 3 NII 4 = OII 2 + N 2 Ammonium Water. Nitrogen nitrate. monoxide. % 8N0 3 H + Cu 3 = N 2 2 + 3(N0 8 y3n + 4H 2 Nitric acid. Copper. Nitrogen dioxide. Copper nitrate. Water. NITROGEN. 161 gaseous bodies. A lighted taper plunged into the gas is extinguished; lighted phosphorus, however, burns in it with great brilliancy. The specific gravity of nitrogen dioxide is 1-039; a litre weighs 1-34343 grams. It contains equal measures of oxygen and nitrogen gases united without condensation. When this gas is passed into the solution of a fer- rous salt, it is absorbed in large quantity, and a deep-brown or nearly black liquid produced, which seems to be a definite compound of the two sub- stances (p. 159). The compound is again decomposed by boiling. NITROGEN TRIOXIDE, or NITROUS OXIDE. When four measures of ni- trogen dioxide are mixed with one measure of oxygen, and the gases, per- fectly dry, are exposed to a temperature of 18, they condense to a thin mobile blue liquid, which emits orange-red vapors. Nitrous oxide, sufficiently pure for most purposes, is obtained by pouring concentrated nitric acid on lumps of arsenious acid, and gently warming the mixture, in order to start the reaction. Nitrous oxide is then evolved as an orange-red gas, arsenic acid remaining behind. Nitrous oxide is decomposed by water, being converted into nitric acid and nitrogen dioxide.* For this reason it cannot be made to unite directly with metallic oxides; potassium nitrite may, however, be prepared by fusing potassium nitrate, whereby part of its oxygen is driven off; and many other salts of nitrous acid may be obtained by indirect means. Thus a solution of potassium or sodium nitrite may be prepared by passing the vapor of nitrogen trioxide, obtained as above by heating nitric acid with arsenious acid (or with starch), into a solution of caustic potash or soda. NITROGEN TETROXIDE (also called Nitric Peroxide}. This is the principal constituent of the deep-red fumes always produced when nitrogen dioxide escapes into the air. When carefully dried lead nitrate is exposed to heat in a retort of hard glass, it is decomposed, lead oxide remaining behind, while a mixture of oxygen and nitrogen tetroxide is evolved. By surrounding the receiver with a very powerful freezing mixture, the latter is condensed in trans- parent crystals, or if the slightest trace of moisture is present, as a color- less liquid, which acquires a yellow and ultimately a red tint, as the tem- perature rises. At 27-8 it boils, giving off its well-known red vapor, the intensity of the color of which is greatly augmented by elevation of tem- perature. Its vapor is absorbed by strong nitric acid, which thereby ac- quires a yellow or red tint, passing into green, then into blue, and after- wards disappearing altogether on the addition of successive portions of water. The deep-red fuming acid of commerce, called nitrous acid, is simply nitric acid impregnated Avith nitrogen tetroxide. Nitrogen tetroxide is decomposed by water at very low temperatures in such a manner as to yield nitric and nitrous acid ; f but when added to excess of water at ordinary temperatures, it yields nitric acid, and the products of decomposition of nitrous acid, namely, nitric acid and nitrogen dioxide. In like manner, when passed into alkaline solutions, it forms a nitrate and a nitrite of the alkali-metal; but it has been also supposed to unite directly, under certain circumstances, with metallic oxides lead oxide, for example forming definite crystalline salts, and has hence been called hyponitric acid; but it is most probable that these salts are compounds of nitrates and nitrites. | * 3N 2 3 + OIL, - 2N0 3 II + 2NOo Nitrogen trioxide. Water. Nitric acid. Nitrogen dioxide, t N.,0 4 -f Olio = NOjH + NO.JI Nitrogen tetroxide. Water. Nitric acid. Nitrous acid. I E.g., 2("Nn0 4 -n>0) - (NO.y.,1'1) + (NO._,)oPh Lead byponitrate. Li-ad nitrate. Lead nitrite. 14* 162 NITROGEN AND HYDROGEN; AMMONIA. Nitrogen appears to combine, under favorable circumstances, with metals. When iron is heated to redness in an atmosphere of ammonia, it becomes brittle and crystalline, and shows an increase in weight, said to vary from 6 to 12 per cent. ; while, according to other observers, the physical charac- ters of the metal are changed without sensible alteration of weight. By heating copper in ammonia, no compound of nitrogen with copper is pro- duced. But when ammonia is passed over copper oxide heated to 800, water is formed, and a soft brown powder produced, which, when heated further, evolves nitrogen, and leaves metallic copper. The same effect is produced by the contact of strong acids. A similar compound of chromium with nitrogen appears to exist. NITROGEN AND HYDROGEN ; AMMONIA. When powdered sal-ammoniac is mixed with moist calcium hydrate (slaked lime), and gently heated in a glass flask, a large quantity of gas- eous matter is disengaged, which must be collected over mercury, or by displacement, advantage being taken of its low specific gravity. Ammonia gas thus obtained is colorless ; it has a strong pungent odor, and possesses in an eminent degree those properties to which the term alkaline is applied ; that is to say, it turns the yellow color of turmeric to brown, that of reddened litmus to blue, and combines readily with acids, neutralizing them completely; by these reactions it is easily distinguished from all other bodies possessing the same physical characters. Under a pressure of 6-5 atmospheres at 15-5, ammonia condenses to the liquid form.* Water dissolves about 700 times its volume of this gas, forming a solution which in a more dilute state has long been known under the name of liquor ammonise; by heat, a great part is again expelled j- The solution is decomposed by chlorine, sal-ammoniac being formed, and ni- trogen set free. Ammonia has a density of 0-589; a litre weighs 0-76271 grams. It can- not be formed by the direct union of its elements, although it is sometimes produced under rather remarkable circumstances by the deoxidation of nitric acid.J The great sources of ammonia are the feebly compounded azotised principles of the animal and vegetable kingdoms, which, when left to putrefactive change, or subjected to destructive distillation, almost in- variably give rise to an abundant production of this substance. The analysis of ammonia gas is easily effected. When a portion is con- fined in a graduated tube over mercury, and electric sparks passed through it for a considerable time, the volume of the gas gradually increases until it becomes doubled. On examination, the tube is found to contain a mixture of 3 measures of hydrogen gas and 1 measure of nitrogen. Every two volumes of the ammonia, therefore, contained three volumes of hydrogen and one of nitrogen, the whole being condensed to the extent of one half. The weight of the two constituents is in the proportion of 3 parts hydrogen to 14 parts nitrogen, g * [At the temperature of 75 F.. liquid ammonia freezes into a colorless solid, heavier than the liquid itself (Faraday.) K. B.] t A concentrated solution of ammonia has recently been applied by M. Carr6 for producing intense cold (for the manufacture of ice). The apparatus used for this purpose consists of two strong iron cylinders connected by tubes, the one cylinder containing the solution of am- monia, the other being empty, and the whole apparatus being perfectly air-tight. The empty cylinder is now cooled with* water, and the other cylinder is gently warmed. The ammonia escapes from the solution, and is condensed by its own pressure in the cooled cylinder. If the source of heat be now removed, the liquefied ammonia is again absorbed by the water, and the heat necessary for its transformation into vapor being taken from the iron vessel, the water eurrounding it is converted into ice: by this process the temperature may be reduced to 15 C. (+ 5 F.) J A mode of converting the nitrogen of the atmosphere into ammonia, by a succession of chemical operations, will be found under the head of Cyanogen. The formula of ammonia is NH 3 . CARBON. 163 Ammonia may also be decomposed into its elements by transmission through a red-hot tube. Solution of ammonia is a very valuable reagent, and is employed in a great number of chemical operations, for some of which it is necessary to have it perfectly pure. The best mode of preparation is the following: Equal weights of sal-ammoniac and quicklime are taken ; the lime is slaked in a covered basin, and the salt reduced to powder. These are mixed and introduced into the flask employed in preparing solution of hydrochloric acid,* together with just enough water to damp the mixture, and cause it to aggregate into lumps ; the rest of the apparatus is arranged exactly as in the former case, with an ounce or two of water in the wash-bottle, or enough to cover the ends of the tubes, and the gas conducted afterwards into pure distilled water, artificially cooled as before. The cork joints are made tight with wax ; a little mercury is put into the safety-funnel, heat cautiously applied to the flask, and the whole left to itself. The disen- gagement of ammonia is very regular and uniform. Calcium chloride, with excess of calcium hydrate (slaked lime), remains in the flask. The decomposition of the salt may be represented in the manner shown by the following diagram : ( Ammonia Ammonia. Sal-ammoniac < Hydrochloric) Hydrogen ^^*~ Water. ( acid . . ) Chlorine. T . f Oxygen ^*\^^ f Calcium { Calcium ^ j chloridc.f Solution of ammonia should be perfectly colorless, leave no residue on evaporation, and when supersaturated by nitric acid, give no cloud or mud- diness with silver nitrate. Its density diminishes with its strength, that of the most concentrated being about 0'875 ; the value in alkali of any sample of liquor ammonia) is most safely inferred, not from a knowledge of its density, but from the quantity of acid a given amount will saturate. The mode of conducting this experiment will be found described under Alka- limetry. When solution of ammonia is mixed with acids of various kinds, salts are generated, which resemble in the most complete manner the corresponding potassium and sodium compounds: these are best discussed in connection with the latter. \ Any ammoniacal salt can at once be recognized by the evolution of ammonia which takes place when it is heated with slaked lime, or solution of potash or soda. CARBON. This substance occurs in a state of purity, and crystallized, in two distinct and very dissimilar forms namely, as diamond, and as graphite or plum- * See fig. 132, p. 182. f 2NII 4 C1 + CaO = 2Nir 3 -f- CaCl 2 + H.,0 Sill-ammoniac. Limo Ammonia. Calcium Water. chloride. t The ammonia salts may be regarded either as direct compounds of ammonia, NII 3 , with acids (IICI. fur example), or as resulting from the replacement of the hydrogen of an acid by the group NH 4 . called timmtmiitni, which in this sense is a compound metal, chemically equiv- alent to potassium, sodium, silver, etc. Thus: Ammonia bydroehlorate NIT 3 .TrCl = NTT 4 .C1 Ammoniujn chloride. " nitrate NHo.HNO, = NIT 4 .\0 3 " nitrite. sulphate (NI^-HoSC^ = (NII 4 ) 2 .S0 4 " sulphate. The formula; in the second column arc exactly analogous to those of the potassium salts, KCK KN0 3 , K 2 S0 4 . 164: CARBON. bago. It constitutes a large proportion of all organic structures, animal and vegetable : when these latter are exposed to destructive distillation in close vessels, a great part of their carbon remains, obstinately retaining some of the hydrogen and oxygen, and associated with the earthy and alka- line matter of the tissue, giving rise to the many varieties of charcoal, coke, etc. This residue, when perfectly separated from all foreign matter, con- stitutes a third variety of carbon. The diamond is one of the most remarkable substances known : long prized on account of its brilliancy as an ornamental gem, the discovery of its curious chemical nature confers upon it a high degree of scientific in- terest. Several localities in India, the island of Borneo, and more espe- cially Brazil, furnish this beautiful substance. It is always distinctly crys- tallized, often quite transparent and colorless, but now and then having a shade of yellow, pink, or blue. The origin and true geological position of the diamond are unknown ; it is always found embedded in gravel and transported materials whgse history cannot be traced. The crystalline form of the diamond is that of the regular octohedron or cube, or some fig- ure geometrically connected with these. Many of the octohedral crystals exhibit a very peculiar appearance, arising from the faces being curved or rounded, which gives to the crystal an almost spherical figure. The diamond is infusible and unalterable even by a very intense heat, provided air be excluded ; but when heated, thus protected, between the poles of a strong galvanic battery, it is converted into coke or graphite ; heated to whiteness in a vessel of oxygen, it burns with facility, yielding carbonic acid gas. Fig. 117. The diamond is the hardest substance known : it admits of being split or cloven without difficulty in certain particular directions, but can only be cut or abraded by a second portion of the same material ; the powder rubbed off in this process serves for polishing the new faces, and is also highly use- ful to the lapidary and seal-engraver. One very curious and useful appli- cation of the diamond is made by the glazier: a fragment of this mineral, like a bit of flint, or any other hard substance, scratches the surface of the glass ; a crystal of diamond having the rounded octohedral figure spoken of, held in one particular position on the glass namely, with an edge formed by the meeting of two adjacent faces presented to the surface and then drawn along with gentle pressure, causes a split or cut, which penetrates to a considerable depth into the glass, and determines its fracture with per- fect certainty. Graphite or plumbago appears to consist essentially of pure carbon, al- though most specimens contain iron, the quantity of which varies from a mere trace up to five per cent. Graphite is a somewhat rare mineral : the finest and most valuable for pencils is brought from Borrowdale, in Cumber- land, where a kind of irregular vein is found traversing the ancient slate beds of that district.* Crystals are not common : when they occur, they * The graphite which can be directly cut for pencils occurring only in limited quantity, powdered graphite, obtained from the inferior varieties of the mineral, is now frequently consolidated lor this purpose. The mechanical division of graphite presents considerable CARBON. 165 have the figure of a short six-sided prism a form bearing no geometric relation to that of the diamond. Graphite is often formed artificially in certain metallurgic operations: the brilliant scales which sometimes separate from melted cast-iron on cooling, called by the workmen "kish," consist of graphite. Lampblack, the soot produced by the imperfect combustion of oil or resin, is the best example that can be given of carbon in its uncrystallized or amorphous state. To the same class belong the different kinds of char- coal. That prepared from wood, either by distillation in a large iron retort, or by the smothered combustion of a pile of fagots partially covered with earth, is the most valuable as fuel. Coke, the charcoal of pit-coal, is much more impure ; it contains a large quantity of earthy matter, and very often sulphur, the quality depending very much upon the mode of .preparation. Charcoal from bones and animal matters in general is a very valuable sub- stance, on account of the extraordinary power it possesses of removing coloring matters from organic solutions; it is used for this purpose by the sugar-refiners to a very great extent, and also by the manufacturing and scientific chemist. The property in question is possessed by all kinds of charcoal in a small degree. Charcoal made from box, or other dense wood, has the property of con- densing gases and vapors into its pores: of ammoniacal gas it is said to absorb not less than ninety times its volume, while of hydrogen it takes up less than twice its own bulk, the quantity being apparently connected with the property in the gas of suffering liquefaction. This property of absorb- ing gases, as well as the decolorizing power, no doubt depends in some way upon the same peculiar action of surface so remarkable in the case of pla- tinum in a mixture of oxygen and hydrogen. The absorbing power is, in- deed, considerably increased by saturating charcoal with solution of pla- tinum, and subsequently igniting it, so as to coat the charcoal with a thin film of platinum. Dr. Stenhouse, who suggested this plan, finds that the gases thus absorbed undergo a kind of oxidation within the pores of the charcoal.* Compounds of Carbon and Oxygen, There are two direct inorganic compounds of carbon and oxygen difficulties, which may be entirely obviated by adopting a chemical process suggested by Sir Benjamin Brodie, applicable, however, only to certain varieties, such as Ceylon graphite. This process consists in introducing the coarsely powdered graphite, previously mixed with ^ of its weight of potassium chlorate, into 2 parts of concentrated sulphuric acid, which is heated in a water-bath until tlie evolution of acid fumes ceases. The acid is then removed by water, and the graphite dried. Thus prepared, this substance, when heated to a temperature ap- proaching a red heat, swells up to a bulky mass of finely divided graphite. The. graphite lately discovered in Siburi-i, which attracted such general attention at the Exhibition of 1862, likewise admits of being purified by Sir B. Brodie's process. [* It removes from solution in tatter the vegetable bases, bitter principles, and astringent subst mres when employed in excess, requiring from twice to twenty times their weight for total precipitation. A soiurio:i of iodine in w.ite.r, or of iodide of potassium, is quickly deprived Of color. .Metallic salts dissolved in water, or diluted alcohol, are precipitated, though not entirely, requiring about thirty times their weight of animal charcoal. Arsenious acid is totally carried out of solution. In these cases it acts in three different ways : the salt is ab- Korbed unaltered; the oxide in til salt may be reduced; or, the salts precfpitated in a basic condition, the solution showing an acid reaction as soon as the carbon begins to act. It is in this last cas csp-ciilly th if traces of the bases can be detected, the acid set free preventing thttir total precipitation. The precipitation may hence be prevented by adding an excess of acid, and the bases after precipitation may be dissolved out by boiling with an acid solution. Warrington, M >m Oliiin. Soc. 1845: G irrod. I'harrn. Journ. 1845; Weppen, Ann. dft Chim. 1846. Carbon is a combustible uniting with oxygen and producing carbonic acid. Its different forms exhibit much difference in this respect: in the very porous condition of charcoal it burns readily, while in its most dense form, the diamond, 'it requires a bright-red heat and pure oxygen gas. In the form of charcoal, it conducts heat slowly and electricity readilv. Carbon is insoluble in water and not liable to be affected by air and moisture. It retards putrefac- tion. 11. B.] 166 CARBON. called carbon monoxide and carbon dioxide : their composition may be thus stated: Composition by weight. Carbon monoxide Carbon dioxide Carbon. . 12 12 Oxygen. 16 32 CARBON DIOXIDE, or CARBONIC OXIDE (commonly called Carbonic Acid], is always produced when charcoal burns in air or oxygen gas : it is most conveniently obtained, however, for study, by decomposing a carbonate with one of the stronger acids. For this purpose, the apparatus for gen- erating hydrogen may again be employed: Fragments of marble are put into the bottle with enough water to cover the extremity of the funnel- tube, and hydrochloric or nitric acid is added by the latter, until the gas is freely disengaged. Chalk-powder and dilute sulphuric acid may be used instead. The gas may be collected over water, although with some loss; or very conveniently by displacement, if it be required dry, as shown in fig. 118. The long drying-tube is filled with fragments of calcium chloride, Fig. 118. and the heavy gas is conducted to the bottom of the vessel in which it is to be received, the mouth of the latter being lightly closed.* Carbon dioxide is a colorless gas ; it has an agreeable pungent taste and color, but cannot be respired for a minute without insensibility following. Its specific gravity is 1-524,-j- a litre weighing 1-96664 grams and 100 cubic inches weighing 47-26 grains. Fig. 119. This gas is very hurtful to animal life, even when largely diluted with air; it acts as a nar- * In connecting tube-apparatus for conveying gases or cold liquids, not corrosive, little tubes of caoutchouc about an inch long are inexpressibly useful. These are made by bending a piece of sheet india-rubber loosely round a glass tube or rod, and cutting off the superfluous portion with sharp scissois. The fresh-cut edges of the caoutchouc, pressed strongly together, cohere com- pletely, and the tube is perfect, provided they have not been soiled by touching with the finders. The connectors are secured by two or three turns of thin silk cord. Tubes of various sizes, made of vulcanized india-rubber, are now articles of commerce, and may be conveniently substituted for those made in the labo- ratory. The glass tubes are sold by weight, and are easily bent in the flame of a spirit-lamp, and, when necessary, cut by scratching with a file, and broken asunder. f Dulong and Berzelius. CARBON. 167 cotic poison. Hence the danger arising from imperfect ventilation, the use of fireplaces and stoves of all kinds unprovided with proper chimneys, and the crowding together of many individuals in houses and ships without efficient means for renewing the air; for carbon dioxide is constantly disengaged during the process of respiration, which, as we have seen (p. 131), is nothing but a process of slow combustion. This gas is sometimes emitted in large quantity from the earth in volcanic districts, and it is constantly generated where organic matter is in the act of undergoing fermentive decomposition. The fatal "after-damp" of the coal-mines contains a large proportion of carbon dioxide. A lighted taper plunged into carbon dioxide is instantly extinguished even to the red-hot snutf. When diluted with three times its volume of air, it still retains the power of extinguishing a light. The gas is easily known from nitrogen, which is also incapable of supporting combustion, by its rapid absorption by caustic alkali, or by lime-water ; the turbidity communicated to the latter from the production of insoluble calcium car- bonate is very characteristic. Cold water dissolves about its own volume of carbon dioxide, whatever be the density of the gas with which it is in contact (comp. p. 151); the solution temporarily reddens litmus-paper. In common soda-water, and also in eifervescent wines, examples may be seen of the solubility of the gas. Even boiling water absorbs a perceptible quantity. Some of the interesting phenomena attending the liquefaction of carbon dioxide have been already described: it requires for the purpose a pres- sure of between 27 and 28 atmospheres at 0, according to Mr. Adams. The liquefied oxide is colorless and limpid, lighter than water, and four times more expansible than air: it mixes in all proportions with ether, alcohol, naphtha, oil of turpentine, and carbon disulphide, and is insoluble in water and fat oils. In this condition it does not exhibit any of the properties of an acid. Carbon dioxide exists, as already mentioned, in the air: relatively its quantity is but small ; but absolutely, taking into account the vast extent of the atmosphere, it is very great, and fully adequate to the purpose for which it is designed, namely, to supply to plants their carbon, these lat- ter having the power, by the aid of their green leaves, of decomposing carbon dioxide, retaining the carbon, and expelling the oxygen. The presence of light is essential to this effect, but of the manner in which it is produced we are yet ignorant. The carbonates form a very large and important group of salts, some of which occur in nature in great quantities, as the carbonates of calcium and magnesium. They contain the elements of carbon dioxide and a me- tallic oxide: calcium carbonate, for example, being composed of 44 parts by weight of carbon dioxide and 56 parts of calcium oxide or lime, or of 12 carbon, 48 oxygen, and 40 calcium ; * but they are never formed by the direct union of dry carbon dioxide with a dry metallic oxide, the inter- vention of water being always required to bring about the combination. Potassium carbonate (pearlash) is the chief constituent of wood-ashes; sodium carbonate is contained in the ashes of marine plants, and is manu- factured on a very large scale by heating sodium sulphate with lime and coal. These carbonates are soluble in water. The other metallic carbon- ates, which are insoluble, may be formed by mixing a solution of potas- sium or sodium carbonate with a soluble metallic salt; thus, when solu- tions of lead nitrate and sodium carbonate are mixed together, the lead and sodium change places, forming sodium nitrate, which remains dis- solved, and lead carbonate, which, being insoluble in water, is precipi- * C0 3 Ca or COg.CaO. 168 CARBON. tated * in the form of a white powder. This is an example of double de- composition, the most frequent of all forms of chemical action. The solution of carbon dioxide in water may be supposed to contain hydrogen carbonate, or carbonic acid, consisting of 12 parts by weight of carbon, 48 oxygen, and 2 hydrogen ; f but this compound is not known in the separate state, only in aqueous solution. CARBON MONOXIDE, or CARBONOUS OXIDE (commonly called Carbonic Oxide). When carbon dioxide is passed over red-hot charcoal or metallic iron, one-half of its oxygen is removed, and it becomes converted into carbon monoxide. A very good method of preparing this gas is to intro- duce into a flask fitted with a bent tube some crystallized oxalic acid, or salt of sorrel, and pour upon it five or six times as much strong oil of vitriol. J On heating the mixture, the organic acid is resolved into water, carbon dioxide, and carbon monoxide ; and by passing the gases through a strong solution of caustic potash, the first is withdrawn by absorption, while the second remains unchanged. Another and, it may be, preferable method, is to heat finely powdered yellow potassium ferrocyanide with eight or ten times its weight of concentrated sulphuric acid. The salt is entirely decomposed, yielding a most copious supply of perfectly pure carbonous oxide gas, which may be collected over water in the usual manner. $ Carbon monoxide is a combustible gas ; it burns with a beautiful pale- blue flame, generating carbon dioxide. It has never been liquefied. It is colorless, has very little odor, and is extremely poisonous much more so than carbon dioxide. Mixed with oxygen, it explodes by the electric spark, but with some difficulty. Its specific gravity is 0-973; a litre weighs 1-2515 grams; 100 cubic inches weigh 30-21 grains. The relation by volume of these oxides of carbon may thus be made in- telligible: carbon dioxide contains its own volume of oxygen, that gas suffering no change of bulk by its conversion. One measure of carbon monoxide, mixed with half a measure of oxygen and exploded, yields one measure of carbon dioxide ; hence carbon monoxide contains half its volume of oxygen. Carbon monoxide unites with chlorine under the influence of light, form- ing a pungent, suffocating compound, possessing acid properties, called phosgene gas, or carbonyl chloride. It made by mixing equal volumes of carbon monoxide and chlorine, both perfectly dry, and exposing the mix- ture to sunshine: the gases unite quietly, the color disappears, and the volume becomes reduced to one half. A more convenient method for pre- paring this gas consists in passing carbon monoxide through antimony pentachloride. It is decomposed by water. * COgNa^ + (N0 3 ) 2 Pb = 2N0 3 Na + C0 3 Pb Sodium Lead Sodium Lead carbonate. nitrate. nitrate. carbonate, t C 3 II 2 or C0 2 OII 2 . % 2C0 4 TT 2 = CO + C0 2 + OTT 2 Oxalic Carbon Carbon "Water. acid. monoxide. dioxide. g The reaction is represented by the equation : C 6 N K 4 Fe + 60H a + 6S0 4 H 2 = 6CO + 2S0 4 K 2 + 3S0 4 (NH 4 ) 2 + S0 4 Fe Potassium Water. Sulphuric Carbon Potassium Ammonium Ferrous ferrocyanide. acid. monoxide, sulphate. sulphate. sulphate. See a paper by the author in the Memoirs of the Chemical Society, i. 251. COMPOUNDS OF CARBON AND HYDROGEN. 169 Compounds of Carbon and Hydrogen. The compounds of carbon and hydrogen already known are exceedingly numerous: perhaps all, in strictness, belong to the domain of organic chemistry, as they cannot, except in very few cases, be formed by the di- rect union of their elements, but always arise from the decomposition of a complex body of organic origin. It will be found convenient, notwith- standing, to describe two of thorn in this part of the volume, as they very well illustrate the important subjects of combustion and the nature of flame. METHANE or MARSH GAS ; LIGHT CARBONETTED HYDROGEN ; FIRE-DAMP. This gas is but too often found to be abundantly disengaged in coal- mines from the fresh-cut surface of the coal, and from remarkable aper- tures or "blowers," which emit for a great length of time a copious stream or jet of gas, probably existing in a state of compression, pent up in the coal. The mud at the bottom of pools in which water-plants grow, on being stirred, suffers bubbles of gas to escape, which may be easily collected. This, on examination, is found to be chiefly a mixture of light carbonetted hydrogen and carbon dioxide : the latter is easily absorbed by lime-water or caustic potash. For a long time, no method was known by which the gas in question could be produced in a state approaching to purity by artificial means; the various illuminating gases from pit-coal and oil, and that obtained by passing the vapor of alcohol through a red-hot tube, contain large quan- tities of light carbonetted hydrogen, associated, however, with other sub- stances which hardly admit of separation; but Dumas has discovered a method by which that gas can be produced at will; perfectly pure, and in any quantity.* A mixture is made of 40 parts crystallized sodium acetate, 40 parts solid sodium hydrate, and 60 parts quicklime in powder. This mixture is trans- ferred to a flask or retort, and strongly heated ; the gas is disengaged in great abundance, and may be collected over water, while sodium carbonate remains behind. f Methane is a colorless and nearly inodorous gas, which does not affect vegetable colors. It burns with a yellow flame, generating carbon dioxide and water. It is not poisonous, and may be respired to a great extent without apparent injury. The density of this compound is about 0-559, a litre weighing 0.71558 grams, and 100 cubic inches weighing 17-41 grains; it contains carbon and hydrogen associated in the proportion of 12 parts by weight of the former to 4 of the latter. J When 100 measures of this gas are mixed with 200 of pure oxygen in the eudiometer, and the mixture exploded by the electric spark, 100 measures of gas remain, which are entirely absorbable by a little solution of caustic potash. Now, carbon dioxide contains its own volume of oxygen: hence one-half the oxygen added that is, 100 measures must have been con- sumed in uniting with the hydrogen. Consequently, the gas must contain twice its own measure of hydrogen, and enough carbon to produce, when completely burned, an equal quantity of carbon dioxide. * Ann. Chim. Phys. Ixxiii. 93. j- The reaction is repi-osi-nted by the equation: C 2 H 3 2 Na + NallO = CH 4 + C0 8 Na 3 Sodium Sodium Marsh Sodium acetate. hydrate. gas. carbonate. The use of the lime is merely to prevent the sodium hydrate from fusing and attacking the lass. J The two carbides of hydrogen here described are represented by the following formula : Methane or Marsh gas . . CH 4 . Ethene or Olefiant gas . . C 2 H 4 . 15 170 COMPOUNDS OF CARBON AND HYDROGEN. When chlorine is mixed with marsh gas over water, no change follows, provided light be excluded. The presence of light, however, brings about decomposition, hydrochloric acid, carbon dioxide, and sometimes other products, being formed. It is important to remember that this gas is not acted upon by chlorine in the dark. ETHENE or OLEFIANT GAS. Strong spirit of wine is mixed with five or six times its weight of oil of vitriol in a glass flask, the tube of which passes into a wash-bottle containing caustic potash. A second wash-bottle, partly filled with oil of vitriol, is connected with the first, and furnished with a tube dipping into the water of the pneumatic trough. On the first applica- tion of heat to the contents of the flask, alcohol, and afterwards ether, make their appearance ; but, as the temperature rises, and the mixture blackens, the ether-vapor diminishes in quantity, and its place becomes in great part supplied by a permanent inflammable gas ; carbon dioxide and sulphurous oxide are also generated at the same time, besides traces of other products. The two last-mentioned gases are absorbed by the alkali in the first bottle, and the ether-vapor by the acid in the second, so that the olefiant gas is delivered tolerably pure. The entire reaction is too complex to be discussed at the present moment ; it will be found fully described in another part of the volume ; but the ethene may be regarded as resulting from a simple dehydration of the alcohol by the oil of vitriol.* Olefiant gas thus produced is colorless, neutral, and but slightly soluble in water. Alcohol, ether, oil of turpentine, and even olive oil, as Faraday has observed, dissolve it to a considerable extent. It has a faint odor of garlic. On the approach of a kindled taper, it takes fire, and burns with a splendid white light, far surpassing in brilliancy that produced by marsh gas. This gas, when mixed with oxygen, and fired, explodes with extreme violence. Its density is 0-981 ; a litre w r eighs 1-25194 grams; 100 cubic inches weigh 30-57 grains. By the use of the eudiometer, as already described, it has been found that each measure of ethene requires for complete combustion exactly three of oxygen, and produces under these circumstances two measures of carbon dioxide ; whence it is evident that it contains twice its own volume of hy- drogen combined with twice as much carbon as in methane. By weight, these proportions will be 24 parts carbon and 4 parts hydrogen. Ethene is decomposed by passing it through a tube heated to bright red- ness; a deposit of charcoal and tar takes place, and the gas becomes con- verted into marsh gas, or even into free hydrogen, if the temperature be very high. This latter change is, of course, attended by increase of volume. Chlorine acts upon ethene in a very remarkable manner. When the two bodies are mixed, even in the dark, they combine in equal measures, and give rise to a heavy oily liquid, of sweetish taste and ethereal odor, to which the name of ethene chloride, or Dutch liquid,-}- is given. It is from this peculiarity that the term olefiant gas is derived. A pleasing and instructive experiment may also be made by mixing in a tall jar two measures of chlorine and one of ethene, and then quickly ap- plying a light to the mouth of the vessel. The chlorine and hydrogen unite with flame, which passes quickly down the jar, while the whole of the carbon is set free in the form of a thick black smoke, COAL AND OIL GASES. The manufacture of coal-gas is. at the present moment, a branch of industry of great interest and importance in several points of view. The process is one of great simplicity of principle, but requires, in practice, some delicacy in management to yield a good result. *C 2 IT 6 = CH 4 -f OH 2 Alcohol. Ethene. Water. COMPOUNDS OF CARBON AND HYDROGEN. 171 When pit-coal is subjected to destructive distillation, a variety of products show themselves permanent gases, steam, and volatile oils, besides a not inconsiderable quantity of ammonia from the nitrogen always present in the coal. These substances vary very much in their proportions with the temperature at which the process is conducted, the permanent gases be- coming more abundant with increased heat, but, at the same time, losing much of their value for the purposes of illumination. The coal is distilled in cast-iron retorts, maintained at a bright-red heat, and the volatilized product is conducted into a long horizontal pipe of large dimensions, always half filled with liquid, into which the extremity of each separate tube dips: this is called the hydraulic main. The gas and its accompanying vapors are next made to traverse a refrigerator usually a scries of iron pipes, cooled on the outside by a stream of water; here the condensation of the tar and the ammoniacal liquid becomes complete, and the gas proceeds onward to another part of the apparatus, in which it is deprived of the sulphuretted hydrogen and carbonic acid gases always pres- ent in the crude product. This was formerly effected by slaked lime, which readily absorbs the compounds in question. The use of lime, however, has been almost superseded by that of a mixture of sawdust and iron oxide. This mixture, after having been employed, is exposed for some time to the atmosphere, and is then fit for use a second time. The purifiers are large iron vessels, filled either with slaked lime or with the iron oxide mixture. The gas is admitted at the bottom of the vessel, and made to pass over a large surface of the purifying agents. The last part of the operation, which, indeed, is often omitted, consists in passing the gas through dilute sulphuric acid, in order to remove ammonia. The quantity thus separated is very small, relatively, to the bulk of the gas, but, in an extensive work, becomes an object of importance. Coal-gas thus manufactured and purified is preserved for use in immense cylindrical receivers, closed at the top, suspended in tanks of water by chains to which counterpoises are attached, so that the gas-holders rise and sink in the liquid as they become filled from the purifiers or emptied by the mains. These latter are made of large diameter, to diminish as much as possible the resistance experienced by the gas in passing through such a length of pipe. The joints of these mains are still made in so im- perfect a manner that immense loss is experienced by leakage when the pressure upon the gas at the works exceeds that exerted by a column of water an inch in height.* Coal-gas varies very much in composition, judging from its variable den- sity and illuminating powers, and from the analyses which,have been made. The difficulties of such investigations are very great, and unless particular precaution be taken, the results are merely approximative. The purified gas is believed to contain the following substances, of which the first is the most abundant, and the second the most valuable : Methane, or Marsh gas. Ethene, or Olefiant gas. Hydrogen. * It may give some idea of the extent of this species of manufacture, to mention that in the year 1838, for lighting London and the suburbs alone, there were eighteen public gas-works, and 2,800,000 invested in pipes and apparatus. The yearly revenue amounted to 450.000, and the consumption of coal in the same period to 180,000 tons, 1460 millions of cubic feet of g;i$ being made in the year. There were 134,300 private lights, and 30,400 street lamps. SMI tons of coal were used in the retorts in the space of twenty-four hours at mid-winter, and 7,l-0,uu) cubic feet of gas consumed in the longest night. Ure, Dictionary of Arts and Manufacture!. Since that time, the production of gas has been enormously increased. The amount of coal used in London for gas-making in 1857 is estimated at more than 800,000 tons, yielding not less than 7,000,000 of cubic feet of gas. In the same year, the mains in the London streets had reached the extraordinary length of 2000 miles. 172 COMBUSTION, AND Carbon Monoxide. Nitrogen. Vapors of volatile liquid Hydrocarbons.* Vapor of Carbon Bisulphide. Separated by Condensation and by the Purifiers. Tar and Volatile Oils. Ammonium Sulphate, Chloride, and Sulphide. Hydrogen Sulphide. Carbon Dioxide. Hydrocyanic acid, or Ammonium Cyanide. Sulphocyanic acid, or Ammonium Sulphocyanate. A far better illuminating gas may be prepared from oil, by dropping it into a red-hot iron retort filled with coke ; the liquid is in great part decom- posed and converted into permanent gas, which requires no purification, as it is quite free from the ammoniacal and sulphur compounds which vitiate gas from coal, ^lany years ago, this article was prepared in London ; it was compressed for the use of the consumer into strong iron vessels, to the extent of 30 atmospheres ; these were furnished with a screw-valve of pe- culiar construction, and exchanged for others when exhausted. The com- parative high price of the material, and other circumstances, led to the abandonment of the undertaking. On the Continent, gas is now extensively prepared from wood. COMBUSTION, AND THE STRUCTURE OF FLAME. When any solid substance capable of bearing the fire is heated to a cer- tain point, it emits light, the character of which depends upon the tempera- ture, Thus, a bar of platinum or a piece of porcelain, raised to a particu- lar temperature, becomes what is called red-hot, or emissive of red light : at a higher degree of heat, this light becomes whiter and more intense, and when urged to the utmost, as in the case of a piece of lime placed in the flame of the oxyhydrogen blowpipe, the light becomes exceedingly powerful, and acquires a tint of violet. Bodies in these states are said to be incan- descent or ignited, Again, if the same experiment be made on a piece of charcoal, similar effects will be observed ; but something in addition : for whereas the plati- num or porcelain, when removed from the fire, or the lime from the blow- pipe flame, begin immediately to cool, and emit less and less light, until they become completely obscure, the charcoal maintains to a great extent its high temperature. Unlike the other bodies, too, which suffer no change whatever, either of weight or substance, the charcoal gradually wastes away until it disappears. This is what is called combustion, in contradis- tinction to mere ignition ; the charcoal burns, and its temperature is kept up by the heat evolved in the act of union with the oxygen of the air. In the most general sense, a body in a state of combustion is one in the act of undergoing intense chemical action : any chemical action whatsoever, if its energy rise sufficiently high, may produce the phenomenon of combus- tion, by heating the body to such an extent that it becomes luminous. In all ordinary cases of combustion, the action lies between the burning body and the oxygen of the air ; and since the materials employed for the economical production of heat and light consist of carbon chiefly, or that substance conjoined with a certain proportion of hydrogen and oxygen, all common effects of this nature are cases of the rapid and violent oxidation of carbon and hydrogen by the aid of the free oxygen of the air. The heat * These bodies increase the illuminating power, and confer on the gas its peculiar odor. THE STRUCTURE OF FLAME. 173 must be referred to the act of chemical union, and the light to the elevated temperature. By this principle, it is easy to understand the means which must be adopted to increase the heat of ordinary fires to the point necessary to melt refractory metals, and to bring about certain desired effects of chemical decomposition. .If the rate of consumption of the fuel can be increased by a more rapid introduction of air into the burning mass, the intensity of the heat will of necessity rise in the same ratio, the quantity of heat evolved being fixed and definite for the same constant quantity of chemical action. This increased supply of air may be effected by two distinct methods: it may be forced into the fire by bellows or blowing-machines, as in the com- mon forge and in the blast, and cupola-furnaces of the iron-worker, or it may be drawn through the burning materials by the help of a tall chimney, the fireplace being closed on all sides, and no entrance of air allowed, save between the bars of the grate. Such is the kind of furnace generally em- ployed by the scientific chemist in assaying and in the reduction of metallic oxides by charcoal : the principle will be at once understood by the aid of the sectional drawing (fig. 120), in which a crucible is represented arranged in the fire for an operation of the kind mentioned. Fig. 121. The "reverberatory " furnace (fig. 121) is one very much used in the arts when substances are to be exposed to heat without contact with the fuel. The fire-chamber is separated from the bed or hearth of the furnace by a low wall or bridge of brick-work, and the flame and heated air are re- flected downward by the arched form of the roof. Any degree of heat can be obtained in a furnace of this kind from the temperature of dull red- ness to that required to melt very large quantities of cast-iron. The fire is urged by a chimney provided with a sliding-plate, or damper, to regulate the draught. Solids and liquids, as melted metal, possess, when sufficiently heated, the faculty of emitting light: the same power is exhibited by gaseous bodies, but the temperature required to render a gas luminous is incom- parably higher than in the cases already described. Gas or vapor in this 15* 174 COMBUSTION, AND condition constitutes flame, the actual temperature of which generally ex- ceeds that of the white heat of solid bodies. , The light emitted from pure flame is often exceedingly feeble ; but the illuminating power may be immensely increased by the presence of solid matter. The flame of hydrogen, or of the mixed gases, is scarcely visible in full daylight; in a dusty atmosphere, however, it becomes much more luminous by igniting to intense whiteness the floating particles with which it comes in contact. The piece of lime in the blow-pipe flame cannot have a higher temperature than that of the flame itself; yet the light it throws off is infinitely greater. On the other hand, it is possible, as recently pointed out by Dr. Frank- land, to produce very bright flames in which no solid particles are present. Metallic arsenic burnt in a stream of oxygen produces an intense white flame, although both the metal itself and the product of its combustion (arsenious oxide) are gaseous at the temperature of the flame. The com- bustion of a mixture of nitrogen dioxide and carbon bisulphide also pro- duces a dazzling white flame, without any separation of solid matter. The conditions most essential to luminosity in a flame are a high tem- perature, and the presence of gases or vapors of considerable density. The effect of high temperature is seen in the greater brightness of the flame of sulphur, phosphorus, and indeed all substances, when burnt in pure oxygen, as compared with that which results from their combustion in com- mon air; in the former case the whole of the substances present take part in the combustion and generate heat, whereas in the latter the temperature is lowered by the presence of a large quantity of nitrogen, which contrib- utes nothing to the effect. The relation between the luminosity of a flame and the vapor-densities of its constituents may be seen from the following table, in which the vapor-densities are referred to that of hydrogen as unity. Relative Densities of Gases and Vapors. Hydrogen ... 1 Water 9 Hydrochloric acid . . 18|- Carbon dioxide . . .22 Sulphur dioxide . . 32 Arsenious chloride . . 9f Phosphoric oxide . 71, or 142 Metallic arsenic . . . 150 Arsenious oxide 198 A comparison of these numbers shows that the brightest flames are those which contain the densest vapors. Hydrogen burning in chlorine produces a vapor more than twice as heavy as that resulting from its combustion in oxygen, and accordingly the light produced in the former case is stronger than in the latter; carbon and sulphur burning in oxygen produce vapors of still greater density, namely, carbon dioxide and sulphur dioxide, and their combustion gives a still brighter light; lastly, phosphorus, which has a very dense vapor, and likewise yields a product of great vapor-density, burns in oxygen with a brilliancy which the eye can scarcely endure. Moreover, the luminosity of a flame is increased by condensing the sur- rounding gaseous atmosphere, and diminished by rarefying it. The flame of arsenic burning in oxygen may be rendered quite feeble by rarefying the oxygen; and on the contrary the faint flame of an ordinary spirit-lamp becomes very bright when placed under the receiver of a condensing pump. Frankland has also found that candles give much less light when burning on the top of Mont Blanc than in the valley below, although the rate of combustion in the two cases is nearly the same. The effect of condensa- tion in increasing the brightness of a flame is also strikingly seen in the combustion of a mixture of oxygen and hydrogen, which gives but a feeble THE STRUCTURE OF FLAME. 175 Fig. 122. V C Fig. 123. light when burnt under the ordinary atmospheric pressure, as in the oxy- hydrogen blowpipe, but a very briglit flash when exploded in the Cavendish eudiometer (p. 144), in which the water-vapor produced by the combustion is prevented from expanding. Flames burning in the air, and not supplied with oxygen from another source, are, as already stated, hollow, the chemical action being necessarily confined to the spot where the two bodies unite. That of a lamp or candle, when carefully examined, is seen to consist of three separate portions. The dark central part, easily rendered evident by depressing upon the flame a piece of fine wire-gauze, consists of combustible matter drawn up by the capillarity of the wick, and volatilized by the heat. This is surrounded by a highly luminous cone or envelope, which, in contact with a cold body, deposits soot. On the outside, a second cone is to be traced, feeble in its light-giving power, but having an exceedingly high temperature. The most probable explanation of these appearances is as follows : Carbon and hydrogen are very unequal in their attraction for oxygen, the latter greatly exceeding the former in this respect: consequently, when both are present, and the sup- ply of oxygen limited, the hydrogen takes up the greater portion of the oxygen, to the exclusion of a great part of the carbon. Now, this happens, in the case under consideration, at some little distance within the outer surface of the flame namely, in the luminous portion; the little oxygen which has penetrated thus far inward is mostly consumed by the hydrogen, and hydro -carbons are separated, rich in carbon and of great density in the state of vapor (naphthalene, chryscne, pyrene, etc.). These hydro-carbons, which would form smoke if they were cooler, and are depos- ited on a cold body held in the flame in the form of soot,* become intensely ignited by the burning hydro- gen, and evolve a light whose whiteness marks a very elevated temperature. In the exterior and scarcely visible cone, these hydro-carbons undergo combustion. A jet of coal-gas exhibits the same phenomena ; but if the gas be previously mingled with air, or if air be forcibly mixed with, or driven into the flame, no such separation of carbon occurs; the hydrogen and carbon burn together, forming vapors of much lower density, and the illuminating power almost disappear-s. The common mouth blowpipe is a little instrument of great utility ; it is merely a brass tube fitted with an ivory mouthpiece, and terminated by a jet having a small aperture, by which a current of air is driven across the flame of a candle. The best form is per- haps that contrived by Mr. Pepys, and shown in fig. 123. The flame so produced is very peculiar. Instead of the double envelope just described, two long pointed cones are observed (fig. 124), which, when the blowpipe is good, and the aperture smooth and round, are very well defined, the outer cone being yellowish and the inner blue. A double combustion is, in fact, going on, by the blast in the inside, and by the external air. The space between the inner and outer cones is filled with exceedingly hot combustible matter, possessing strong reducing or deoxidiz- ing powers ; while the highly heated air just beyond the point of the exterior * Soot is not pure carbon, but a mixture of heavy hydro-carbons. 176 COMBUSTION, AND Fig. 124. cone oxidizes with great facility. A small portion of matter, supported on a piece of charcoal, or fixed in a ring at the end of a fine platinum wire, can thus in an instant be exposed to a very high degree of heat under these contrasted circumstances, and observations of great value made in a very short time. The use of the instrument requires an even and uninterrupted blast of some dura- tion, by a method easily acquired with a little patience : it consists in employing for the pur- pose the muscles of the cheeks alone, 'respira- tion being conducted through the nostrils, and the mouth from time to time replenished with air, without intermission of the blast. The Argand lamp, adapted to burn either oil or spirit, but especially the latter, is a very useful piece of chemical appa- ratus. In this lamp the wick is cylindrical, the flame being supplied with air both inside and outside : the combustion is greatly aided by the chim- ney, which is made of copper when the lamp is used as a source of heat. Fig. 125 exhibits, in section, an excellent lamp of this kind for burning alcohol or wood-spirit. It is constructed of thin copper, and furnished with ground caps to the wick-holder and aperture,* by which the spirit is intro- Fig. 125. Fig. 126. duced, in order to prevent loss when the lamp is not in use. Glass spirit- lamps (fig. 126), fitted with caps to prevent evaporation, are very convenient for occasional use, being always ready and in order.f In London, and other large towns where coal-gas is to be had, it is con- stantly used with the greatest economy and advantage in every respect as a source of heat. Retorts, flasks, capsules, and other vessels, can be thus Fig. 127. * When in use, this aperture must always be open, otherwise an accident is sure to happen ; the heat expands the air in the lamp, and the spirit is forced out in a state of inflammation. f [A modification of the Argand lamp con- trived by the late Professor J. K. Mitchel is ad- vantageous, from the wick-holder being kept constantly cool by the current of air always passing between it and the body of the lamp. " It is made of tinned iron. The alcohol is poured out by means of the hollow handle, arid is ad- mitted to the cylindrical burner by two or three tubes which are placed at the very bottom of the fountain. By such an arrangement of parts, the alcohol may be added as it is consumed, and the flame kept uniform ; and as the pipes which pass to the burner are so remote from the flame, the, alcohol never becomes heated so as to fly off through the vent-hole, and thus to cause greater waste and danger of explosion." K. B.] THE STRUCTURE OF FLAME. 177 Fig. 128. Fig. 129. exposed to an easily regulated and invariable temperature for many succes- sive hours. Small platinum crucibles may be ignited to redness by placing them over the flame on a little wire triangle. The arrangement shown in fig. 127, consisting of a common Argand gas-burner fixed on a heavy and low foot, and connected with a flexible tube of caoutchouc or other material, is very convenient. A higher temperature, and perfectly smokeless flame, is, however, obtained by burning the gas previously mixed with air. Such a flame is easily produced by placing a cap of wire-gauze on the chimney of the Ar- gand burner just described, and setting fire to the gas above the wire-gauze. The flame does not penetrate below, but the gas in passing up the chimney becomes mixed with air, and this mixture burns above the cap with a blue, smokeless flame. Another kind of burner for producing a smokeless flame has been contrived by Professor Bunsen, and is now very generally used in chemical laboratories. In this burner (fig. 129) the gas, supplied by a flexible tube, t, passes through a set of small holes into the box at a, in which it mixes with atmospheric air entering freely by a number of holes near the top of the box. The gaseous mixture passes up the tube b, and is inflamed at the top, where it burns with a tall, blue, smokeless flame, giving very little light, but much heat. By arranging two or more such tubes, together with an air-box containing a sufficient number of holes, a very powerful burner may be constructed. Considerable improvements in this form of burner have been made by Mr. Griffin, who has also con- structed, on the same principle, powerful gas-fur- naces, affording heat sufficient for the decomposition of silicates, and the fusion of considerable quantities of copper or iron.* The principle of burning a mixture of gas and air is also applied in Hof- manu's gas-furnace for organic analysis, which will be described under Or- ganic Chemistry. The kindling-point, or temperature at which combustion commences, is very different with different substances : phosphorus will sometimes take fire in the hand ; sulphur requires a temperature exceeding that of boiling water; charcoal must be heated to redness. Among gaseous bodies the same fact is observed : hydrogen is inflamed by a red-hot wire ; light carbonetted hydrogen requires a white heat to effect the same thing. When flame is cooled by any means below the temperature at which the rapid oxidation of the combustible gas occurs, it is at once extinguished. Upon this depends the principle of Sir H. Davy's invaluable safety-lamp. Mention has already been made of the frequent disengagement of great quantities of light carbonetted hydrogen gas in coal-mines. This gas, mixed with seven or eight times its volume of atmospheric air, becomes highly explosive, taking fire at a light and burning with a pale-blue flame ; and many fearful accidents have occurred from the ignition of large quan- tities of mixed gas and air occupying the extensive galleries and workings of a mine. Sir H. Davy undertook an investigation with a view to discover some remedy for this constantly occurring calamity : his labors resulted in some exceedingly important discoveries respecting flame, which led to the construction of the lamp which bears his name. * See the article on Gas-burners and Furnaces in Watts's "Dictionary of Chemistry," ii. 782. 178 COMBUSTION, AND When two vessels filled with a gaseous explosive mixture are connected by a narrow tube, and the contents of one fired by the electric spark, or otherwise, the flame is not communicated to the other, provided the diameter of the tube, its length, and the conducting power for heat of its material, bear a certain proportion to each other; the flame is extinguished by cool- ing, and its transmission rendered impossible. In this experiment, high conducting power and diminished diameter compensate for diminution in length ; and to such an extent can this be carried, that metallic gauze, which may be looked upon as a series of very short square tubes arranged side by side, when of sufficient degree of fine- ness, arrests in the most complete manner the passage of flame in explosive mixtures depending upon the inflammability of the gas. Now the fire-damp mixture has an exceedingly high kindling-point ; a red heat does not cause inflammation ; consequently, the gauze will be safe for this substance, when flame would pass in almost any other case. The miner's safety lamp is merely an ordinary oil-lamp, the flame of which is enclosed in a cage of wire-gauze, made double at the upper part, Fig. 130. Fig. 131. containing about 400 apertures to the square inch. The tube for supplying oil to the reservoir reaches nearly to the bottom of the latter, while the wick admits of being trimmed by a bent wire passing with friction through a small tube in the body of the lamp ; the flame can thus be kept burning for any length of time, without the necessity of unscrewing the cage. When this lamp is taken into an explosive atmosphere, although the fire-damp may burn within the cage with such energy as sometimes to heat the metallic tissue to dull redness, the flame is not communicated to the mixture on the outside. These effects may be conveniently studied by suspending the lamp in a large glass jar, and gradually admitting coal-gas below. The oil-flame is at first elongated, and then, as the proportion of gas increases, extin- guished, while the interior of the gauze cylinder becomes filled with the burning mixture of gas and air. As the atmosphere becomes purer, the wick is once more relighted. These appearances are so remarkable that CHLORINE. 179 the lamp becomes an admirable indicator of the state of the air in different parts of the mine.* The same great principle has been ingeniously applied by Mr. Hemming to the construction of the oxy-hydrogen safety-jet before mentioned. This is a tube of brass about four inches long, filled with straight pieces of fine brass wire, the whole being tightly wedged together by a pointed rod, for- cibly driven into the centre of the bundle, (fig. i31.) The arrangement thus presents a series of metallic tubes, very long in proportion to their diam- eter, the cooling powers of which are so great as to prevent the possibility of the passage of flame, even with oxygen and hydrogen. The jet may be used, as before mentioned, with a common bladder, without a chance of explosion. The fundamental fact of flame being extinguished by contact with a cold body, may be elegantly shown by twisting a copper wire into a short spiral, about 0-1 inch in diameter, and then passing it cold over the flame of a wax candle; the latter is extinguished. If the spiral be now heated to redness by a spirit-lamp, and the experiment repeated, no such effect follows. - CHLORINE. This substance is a member of a very important natural group, containing also iodine, bromine, and fluorine. So great a degree of resemblance exists between these bodies in all their chemical relations, especially between chlorine, bromine, and iodine, that the history of one will almost serve, with a few little alterations, for that of the rest. Chlorine f is a very abundant substance: in common salt it exists in com- bination with sodium. It is most easily prepared by pouring strong hy- drochloric acid upon finely powdered black oxide of manganese contained in a retort or flask, arid applying a gentle heat ; a heavy yellow gas is dis- engaged, which is the substance in question. It may be collected over warm water, or by displacement: the mercurial trough cannot be employed, as the chlorine rapidly acts upon the metal, and becomes absorbed. The reaction is very easily explained. Hydrochloric acid is a compound of chlorine and hydrogen: when this is mixed with a metallic monoxide, double interchange of elements takes place, water and chloride of the metal being produced. But when some of the dioxides are substituted, an addi- tional effect ensues namely, the decomposition of a second portion of hydrochloric acid by the oxygen in excess, the hydrogen of which is with- drawn and the chlorine set free. Hydrochloric f Chlorine Chlorine. acid { Hydrogen _____ Water. I Manganese __^ Manganese Chloride. ( Oxygen Hydrochloric f Chlorine acid \ Hydrogen ::::::: =*- Water 4 * This is the true use of the lamp namely, to permit the viewer or superintendent, with- out n-k to himself, to examine the state of the air in every part of the mine; not to enable workmen to continue their labors in an atmosphere habitually explosive, which must be unfit for human respiration, although the evil effects may be slow to appear. Owners of coal-mines should be compelled cither to adopt efficient means of ventilation, or to close workings of thia dangerous character altogether. f From xAwpoj, yellowish^green, the name given to it by Sir H. Davy. t Mn0 2 + 4HC1 = G3 2 + MnCl 2 + 20H a Manganese Hydrochloric Chlorine. Manganese Water, dioxide. acid. chloride. 180 CHLORINE. Fig. 132. Chlorine was discovered by Scheele in 1774, but its nature was long mis- understood. It is a yellow gaseous body, of intolerably suffocating proper- ties, producing very violent cough and irritation when inhaled even in ex- ceedingly small quantity. It is soluble to a considerable extent in water, that liquid absorbing at 15-5 (60 F.)> about twice its volume, and acquiring the color and odor of the gas. When this solution is exposed to light, it is slowly changed, by decomposition of water, into hydrochloric acid, the oxygen being at the same time liberated. When moist chlorine gas is exposed to a cold of 0, yellow crystals are" formed, which consist of a definite compound of chlorine and water, containing 35-5 parts of the former to 90 of the latter. Chlorine has a specific gravity of 2-47; a litre of it weighs 3-17344 grams; exposed to a pressure of about four atmospheres, it condenses to a yellow limpid liquid. Chlorine has but little attraction for oxygen, its chem- ical energies being principally exerted towards hydro- gen and the metals. A lighted taper plunged into the gas, continues to burn w-ith a dull-red light, and emits a large quantity of smoke, the hydrogen of the wax being alone consumed, and the carbon separated. If a piece of paper be wetted with oil of turpentine, and thrust into a bottle filled with chlorine, the chemical action of the latter upon the hydrogen is so violent as to cause inflammation, accompanied by a copious deposit of soot. Although chlorine can, by indirect means, be made to combine with carbon, yet this never occurs under the circumstances described. Phosphorus takes fire spontaneously in chlorine, burning with a pale and feebly luminous flame. Several of the metals, as copper leaf, powdered antimony, and arsenic, undergo combustion in the same manner. A mix- ture of equal measures of chlorine and hydrogen explodes with violence on the passage of an electric spark, or on the application of a lighted taper, hydrochloric acid gas being formed. Such a mixture may be retained in the dark for any length of time without change : exposed to diffuse day- light, the two gases slowly unite, while the direct rays of the sun induce instantaneous explosion. The most characteristic property of chlorine is its bleaching power; the most stable organic coloring principles are instantly decomposed and de- stroyed by this remarkable agent: indigo, for example, which resists the action of strong oil of vitriol, is converted by chlorine into a brownish sub- stance, to which the blue color cannot be restored. The presence of water is essential to these changes, for the gas in a state of perfect dryness is incapable even of affecting litmus. Chlorine is largely used in the arts for bleaching linen and cotton goods, rags for the manufacture of paper, &c. For these purposes, it is employed, sometimes in the state of gas, sometimes in that of solution in water, but more frequently in combination with lime, forming the substance called bleaching-powder. When required in large quantities, it is often made by pouring slightly diluted oil of vitriol upon a mixture of common salt and manganese oxide contained in a large leaden vessel. The decomposition which ensues may be thus represented : CHLORINE. 181 Sodium chloride Sulph. oxide Manganese dioxide. Sulph. oxide. f Chlorine 1 Sodium -Chlorine. Sodium sulphate. | Manganese \ sulphate.' Chlorine is one of the best and most potent substances that can be used for the purpose of disinfection, but its employment requires care. Bleach- ing-powder mixed with water, and exposed to the air in shallow vessels, becomes slowly decomposed by the carbonic acid of the atmosphere, and the chlorine is evolved: if a more rapid disengagement be wished, a little acid of any kind may be added. In the absence of bleaching-powder, either of the methods for the production of the gas described may be had recourse to, always taking care to avoid an excess of acid. HYDROGEN CHLORIDE; HYDROCHLORIC, CIILORHYDRIC, OR MURIATIC ACID. This substance, in a state of solution in water, has been long known. The gas is prepared with the utmost ease by heating in a flask fitted with a cork and bent tube, a mixture of common salt and oil of vitriol diluted with a small quantity of water ; it must be collected by displacement, or over mercury. It is a colorless gas, which fumes strongly in the air from con- densing the atmospheric moisture ; it has an acid, suffocating odor, but is much less offensive than chlorine. Exposed to a pressure of 40 atmospheres, it liquefies. Hydrochloric acid gas has a density of 1-269 compared with air, or 18-25 compared with hydrogen as unity. It is exceedingly soluble in water, that liquid taking up at the temperature of the air about 418 times its bulk. The gas and solution are powerfully acid. The action of oil of vitriol on common salt, or any analogous substance, is thus easily explained : f Sodium chloride Sulphuric acid f Chlorine \ Sodium f Hydrogen 4 Oxygen ^Sulphur Hydrochloric acid. Sodium sulphate. The composition of this substance may be determined by synthesis : when a measure of chlorine and a measure of hydrogen are fired by the electric spark, two measures of hydrochloric acid gas result, the combination being unattended by change of volume. By weight it contains 35-5 parts of chlorine and 1 part of hydrogen. Solution of hydrochloric acid, the liquid acid of commerce, is a very im- portant preparation, and of extensive use in chemical pursuits: it is best prepared by the following arrangement: A large glass flask, containing a quantity of common salt, is fitted with a cork and bent tube, in the manner represented in fig. 132: this tube passes through and below a second short tube into a wide-necked bottle, containing a little water, into which the open tube dips. A bent tube is adapted to another hole in the cork of the wash-bottle, so as to convey the purified gas * 2NaCl -f Mn0 2 + 2S0 4 H 2 = C1 2 + S0 4 Nju> + S0 4 Mn + 20Ho Sodium Manganese Hydrogen Chlorine. Sodium Manganous Water, chloride. dioxide. sulphate. sulphate, sulphate. f 2NaCl + S0 4 H 2 = 2TIC1 + SO 4 Na Sodium Hvdroiron Hvdroffen Sodium Sodium chloride. 16 Hydrogen sulphate. Hydrogf-n chloride. 4 a2 Bodtam sulphate. 182 CHLOKINE. into a quantity of distilled water, by which it is instantly absorbed the joints are made air-tight by melting a little yellow wax over the corks. A quantity of oil of vitriol, about equal in weight to the salt, is then slowly introduced by the funnel; the disengaged gas is at first wholly absorbed by the water in the wash-bottle, but when this becomes saturated, it passes into the second vessel and there dissolves. When all the acid has been added, heat may be applied to the flask by a charcoal chauffer, until its contents appear nearly dry, and the evolution of gas almost ceases, when the process may be stopped. As much heat is given out during the condensa- tion of the gas, it is necessary to surround the condensing vessel with cold Fig. 133, The simple wash-bottle, shown in the last figure, will be found an ex- ceedingly useful contrivance in a great number of chemical operations. It serves in the present, and in many similar cases, to retain any liquid or solid matter mechanically carried over with the gas, and it may be always employed when a gas of any kind is to be passed through an alkaline or other solution. The open tube dipping into the liquid prevents the pos- sibility of absorption, by which a partial vacuum would be occasioned, and the liquid of the second vessel lost by being driven into the first. The arrangement by which the acid is introduced also deserves a moment's notice. The tube is bent twice upon itself, and a bulb blown in one portion : the liquid poured into the funnel rises upon the opposite side of the first bend until it reaches the second ; it then flows over and runs into the flask. Any quantity can then be got into the latter without the introduction of air, and without the escape of gas from the interior. The funnel acts also as a kind of safety-valve, and in both directions ; for if by any chance the delivery-tube should be stopped, and the issue of gas prevented, its in- CHLORINE. 183 creased elastic force soon drives the little column of liquid out of the tube, the gas escapes, and the vessel is saved. On the other hand, any absorp- tion within is quickly compensated by the entrance of air through the liquid in the bulb. The plan employed on the large scale by the manufacturer is the tt same in principle as that described; he merely substitutes a large iron cylinder, or apparatus made of lead, for the flask, and vessels of stoneware for those of glass. On distilling an aqueous solution of hydrochloric acid, an acid is produced boiling at 110 (230 F.) which contains 20-22 per cent, of anhydrous hydrochloric acid: a more concentrated solution when heated gives off hydrochloric acid gas; a weaker solution loses water. Roscoe and Dittmar have proved that the composition of the distillate varies with the atmospheric pressure; it cannot, therefore, be viewed as a chemical compound. Pure solution of hydrochloric acid is transparent and colorless : when strong, it fumes in the air by evolving a little gas. It leaves no residue on evaporation, and gives no precipitate or opacity with diluted solution of barium chloride. When saturated with the gas, it has a specific gravity of 1-21, and contains about 42 per cent, of real acid. The commercial acid, which is obtained in immense quantity as a secondary product in the manufacture of sodium sulphate by the action of sulphuric acid upon common salt, has usually a yellow color, and is very impure, containing salts, sulphuric acid, chloride of iron, and organic matter. It may be rendered sufficiently pure for most purposes by diluting it to the density of 1-1, which happens when the strong acid is mixed with its own bulk or rather less of water, and then distilling it in a retort furnished with a Liebig's condenser. A mixture of nitric and hydrochloric acids has long been known under the name of aqua regia, from its property of dissolving gold. When these two substances are heated together, they both undergo decomposition, nitro- gen tetroxide and chlorine being evolved. This, at least, appears to be the final result of the action: at a certain stage, however, two peculiar sub- stances, consisting of nitrogen, oxygen, and chlorine (chloronitric acid gas* and chloronitrous gasf), appear to be formed. It is only the chlorine which attacks the metal. The presence of hydrochloric acid, or any other soluble chloride, is easily detected by solution of silver nitrate. A white curdy precipitate is pro- duced, insoluble in nitric acid, freely soluble in ammonia, and subject to blacken by exposure to light. Oxides and Oxacids of Chlorine. There are four oxacids of chlorine, which may be regarded as oxides of hydrochloric acid; thus: Composition by weight.f Chlorine. Hydrogen. Oxygen. Hydrochloric acid . . . 35-5 -f- 1 Hypochlorous acid .... 35-5 1 -j- 16 Chlorous acid .... 35-5 -f 1 32 Chloric acid 35-5 -f * 48 Perchloric acid .... 35-5 +1 + 64 * NOC1 2 . t NOC1. J Hypochlorous acid . . . . CIIIO Chlorous acid C1H0 2 Chloric acid C1HO 3 Perchloric acid C1HO V 184: CHLORINE. The anhydrous chlorine oxides corresponding to hypochlorous and chlorous acids are known, namely: * - Chlorine. Chlorine. Oxygen. Chlorine monoxide, or Hypochlorous oxide . . 35-5 -f- 35-5 -f- 16 Chlorine trioxide, or Chlorous oxide .... 35-5 -j- 35-5 -j- 48 Also an oxide to which there is no corresponding acid, namely : Chlorine. Oxygen. Chlorine tetroxide . . . . 2 X 35-5 -j- 64 The oxides corresponding to chloric and perchloric acid have not been ob- tained. Hypochlorous and chloric acids are produced by the action of chlorine on certain metallic oxides in presence of water; hypochlorous and chlorous acids also by direct oxidation of hydrochloric acid. Perchloric acid and chlorine tetroxide result from the decomposition of chloric acid. HYPOCHLOROUS OXIDE, ACID, AND SALTS. The oxide is best prepared by the action of chlorine gas upon dry mercuric oxide. This oxide, prepared by precipitation, and dried by exposure to a strong heat, is introduced into a glass tube kept cool and well washed, dry chlorine gas is slowly passed over it. Mercuric chloride and hypochlorous oxide are thereby formed ; the latter is collected by displacement. The reaction by which it is pro- duced may be thus illustrated: Chlorine ___^- Hypochlorous oxide. Mercuric f Mercury oxide \ Oxygen Chlorine - Mercuric chloride, j- The mercuric chloride, however, does not remain as such ; it combines with another portion of the oxide when the latter is in excess, forming a peculiar brown compound, an oxychloride of mercury. It is remarkable that the crystalline mercuric oxide prepared by calcining the nitrate, or by the direct oxidation of the metal, is scarcely acted upon by chlorine under the circumstances described. Hypochlorous oxide is a pale-yellow gaseous body, containing, in every two measures, two measures of chlorine and one of oxygen, and is there- fore analogous in constitution to water. It explodes, although with no great violence, by slight elevation of temperature. Its odor is peculiar, and quite different from that of chlorine. When the flask or bottle in which the gas is received is exposed to artificial cold by the aid of a mix- ture of ice and salt, the hypochlorous oxide condenses to a deep-red liquid, slowly soluble in water, and very subject to explosion. J Hypochlorous acid is produced by the solution of hypochlorous oxide in water ; also by passing air saturated with hydrochloric acid gas through a solution of potassium permanganate acidulated with hydrochloric acid and heated in a water bath : the distillate is a solution of hypochlorous acid, formed by oxidation of the hydrochloric acid; thirdly, by decomposing a metallic hypochlorite with sulphuric acid or other oxacid; fourthly, by passing chlorine gas into water holding in suspension a solution containing metallic oxides, hydrates, carbonates, sulphates, phosphates, &c., the most * Chlorine monoxide or Hypochlorous oxide .... C1 2 Chlorine trioxide or Chlorous oxide C1 2 3 Chlorine tetroxide C1 2 4 . f 2HgO + CU HgCVHgO + C1 2 Mercuric Chlorine. Mercuric Hypochlorous oxide. oxychloride. oxide. % Pelouze Ann. Chim. Phys. [3], vii. 112. CHLOROUS OXIDE. 185 advantageous for the purpose being mercuric oxide, or calcium carbonate (chalk).* The aqueous solution of hypochlorous acid has a yellowish color, an acid taste, and a characteristic sweetish smell. The strong acid decomposes rapidly even when kept in ice. The dilute acid is more stable, but is de- composed by long boiling into chloric acid, water, chlorine, and oxygen. Hydrochloric acid decomposes it, with formation of chlorine. f It is a very powerful bleaching and oxidizing agent, converting many of the ele- ments iodine, selenium, and arsenic, for example into their highest oxides, and at the same time liberating chlorine. Metallic hypochlorites may be obtained in the pure state by neTitralizing hypochlorous acid with metallic hydrates, such as those of sodium, cal- cium, copper, &c. ; but they are usually prepared by passing chlorine gas into solutions of alkalies or alkaline carbonates, or over the dry hydrates of the earth-metals dry slaked lime, for example. In this process a metallic chloride is formed at the same time.J The salts thus obtained constitute the bleaching and disinfecting salts of commerce. They will be more fully described under the head of calcium salts. CHLOROUS OXIDE, ACID, AND SALTS. The oxide is prepared by heating in a flask filled to the neck, a mixture of 4 parts of potassium chlorate and 3 parts of arsenious acid, or oxide, with 12 parts of nitric acid pre- viously diluted with 4 parts of water. During the operation, which must be performed in a water-bath, a greenish-yellow gas is evolved, which is permanent in a freezing mixture of ice and salt, but liquefiable by extreme cold. It dissolves freely in water and in alkaline solutions, forming chlorous acid and metallic chlorites. The reaction by which chlorous oxide is formed is somewhat complicated. The arsenious acid deprives the nitric acid of part of its oxygen, reducing it to nitrous acid, which is then reoxidized at the expense of the chloric acid, reducing it to chlorous oxide. $ Chlorous Acid may be prepared by condensing chlorous oxide in water, or by decomposing a metallic chlorite with dilute sulphuric or phosphoric acid. Its concentrated solution is a greenish-yellow liquid having strong bleaching and oxidizing properties. It does not decompose carbonates, but acts strongly with caustic alkalies and earths to form chlorites. < CHLORINE TETROXIDE. When potassium chlorate is made into a paste with concentrated sulphuric acid, and cooled, and this paste is very cau- tiously heated by warm water in a small glass retort, a deep-yellow gas is evolved, which is the body in question; it can be collected only by dis- placement, since mercury decomposes and water absorbs it. Chlorine tetroxide has a powerful odor, quite different from that of the preceding compounds, and of chlorine itself. It is exceedingly explosive, being resolved with violence into its elements by a temperature short of the boiling-point of water. Its preparation is, therefore, always attended with danger, and should be performed only on a small scale. It is com- posed by measure of one volume of chlorine and two volumes of oxygen, * COgCa + OH 2 -f C1 4 = C0 2 -f CaCl 2 + 2C1IIO Calcium Water. Chlorine. Carbon Calcium Hypochlorous carbonate. dioxide. chloride. acid, f C1HO + C1H = 2 II C1 2 . % CaII 2 2 + C1 4 =" CaCloOo" + CaCL> + OIL, Calcium Chlorine. Calcium Calcium Water. hydrate. hypochlorite. chloride, g 2C10 ? TI + 2NOoH 2N0 3 H + OIL, -}- C1 2 3 Chloric acid. Nitrons acid. Nitric acid. Water. Chlorous oxide. 10* 186 CHLORIC ACID. condensed into two volumes.* It may be liquefied by cold. The solution of the gas in water bleaches. The euchlorine of Davy, prepared by gently heating potassium chlorate with dilute hydrochloric acid, is probably a mixture of chlorous acid arid free chlorine. The production of chlorine tetroxide from potassium chlorate and sul- phuric acid depends upon the spontaneous splitting of the chloric acid into chlorine tetroxide and perchloric acid, which latter remains as u potas- sium salt.f When a mixture of potassium chlorate and sugar is touched with a drop of oil of vitriol, it is instantly set on fire, the chlorine tetroxide disengaged being decomposed by the combustible substance with such violence as to cause inflammation. If crystals of potassium chlorate be thrown into a glass of water, a few small fragments of phosphorus added, and then oil of vitriol poured down a narrow funnel reaching to the bot- tom of the glass, the phosphorus will burn beneath the surface of the water, by the assistance of the oxygen of the chlorine tetroxide disen- gaged. The liquid at the same time becomes yellow, and acquires the odor of that gas. CHLORIC ACID. This is the most important compound of the series. When chlorine is passed to saturation into a moderately strong hot solution of potassium hydrate or carbonate, and the liquid concentrated by evaporation, it yields, on cooling, flat tabular crystals of a colorless salt, consisting of potassium chlorate. The mother-liquor contains potassium chloride. J From potassium chlorate, chloric acid may be obtained by boiling the salt with a solution of hydrofluosilicic acid, which forms an almost insoluble potassium salt, decanting the clear liquid, and digesting it with a little silica, which removes the excess of the hydrofluosilicic acid. Filtration through paper must be avoided. By cautious evaporation, the acid may be so far concentrated as to assume a sirupy consistence ; it is then very easily decomposed. It sometimes sets fire to paper, or other dry organic matter, in consequence of the facility with which it is deoxidized by combustible bodies. The chlorates are easily recognized ; they give no precipitate when in solution with silver nitrate ; they evolve pure oxygen when heated, passing thereby into chlorides ; and they afford, when treated with sulphuric acid, the characteristic explosive yellow gas already described. The dilute solu- tion of the acid has no bleaching power. PERCHLORIC ACID. When powdered potassium chlorate is thrown by small portions at a time into hot nitric acid, a change takes place of the same description as that which happens when sulphuric acid is used, but with this important difference : that the chlorine arid oxygen, instead of being evolved in a dangerous state of combination, are emitted in a state of mixture. The result of the reaction is a mixture of potassium nitrate and perchlorate, which may be readily separated by their difference of solubility. Perchloric acid is obtained by distilling potassium perchlorate with sul- phuric acid. Pure perchloric acid is a colorless liquid, of 1-782 sp. gr. at 15-5 (60 F.), not solidifying at 35 (31 F.) ; it soon becomes colored * Its formula is C1 2 4 . t eClOgK + - 3S0 4 II 2 = 2C1 2 4 + 2C10 4 TI + 3S0 4 K 2 + 2H0 Potassium Hydrogen Chlorine Hydrogen Potassium Water. chlorate. sulphate. tetroxide. perchlorate. sulphate. J 3K 2 + C1 6 = 5KC1 + C10 3 K Potassium Chlorine. Potassium Potassium oxide. chloride. chlorate. PERCHLORIC ACID. 187 even if kept in the dark, and after a few weeks decomposes with explosion. The vapor of perchloric acid is transparent and colorless: in contact with moist air, it produces dense white fumes. The acid, when cautiously mixed with a small quantity of water, solidities to a crystalline mass, which is a compound of perchloric acid with one molecule of water.* When brought in contact with carbon, ether, or other organic substances, perchloric acid explodes with nearly as much violence as chloride of nitrogen. COMPOUND OF CHLORINE AND NITROGEN. When sal-ammoniac or ammonia nitrate is dissolved in water, and a jar of chlorine inverted in the solution, the gas is absorbed, and a deep-yellow oily liquid is observed to collect upon the surface of the solution, ultimately sinking in globules to the bottom. This is nitrogen chloride, the most dangerously explosive substance known. The following is the safest method of conducting the experiment: A somewhat dilute and tepid solution of pure sal-ammoniac in distilled water poured into a clean basin, and a bottle of chlorine, the neck of which is quite free from grease, inverted into it. A shallow and heavy leaden cup is placed beneath the mouth of the bottle to collect the product. When enough has been obtained, the leaden vessel may be withdrawn with its dangerous contents, the chloride remaining covered with a stratum of water. The operator should protect his face with a strong wire-gauze mask when experimenting upon this substance. The change may be explained by the following diagram: Chlorine __ ^Nitrogen chloride. Chlorine ^^ ^-"""^^- Hydrochloric acid. !l Nitrogen ^ \ Hydrogen ' Hydrochloric acid Hydrochloric acid.f Nitrogen chloride is very volatile, and its vapor is exceedingly irritating to the eyes. It has a specific gravity of 1-653. It may be distilled at 71 (160 F.), although the experiment is attended with great danger. Between 93 (200 F.) and 105 (221 F.) it explodes with the most fearful violence. Contact with almost any combustible matter, as oil or fat of any kind, de- termines the explosion at common temperatures ; a vessel of porcelain, glass, or even of cast-iron, is broken to pieces, and the leaden cup receives a deep indentation. This body has usually been supposed to contain nitrogen and chlorine in the proportion of 14 parts of the former to 106-5 parts of the latter, but recent experiments upon the corresponding iodine compound (p. 191) induce a belief that it contains hydrogen. J CHLORINE AND CARBON. Several compounds of chlorine and carbon are known. g They are obtained indirectly by the action of chlorine upon certain organic compounds, and will be described under Organic Chemistry. * C10 4 H + OH 2 . f NH 4 C1 + 6C1 - NC1 3 + 4IIC1 Ammonium Chlorine Nitrogen Hydrochloric chloride. trichloride. acid. % Instead of NC1 3 , it may in reality be NHC1 2 , or NH a Cl. g C 2 C1 2 , C 2 C1 4 , C 2 C1 6) and CC1 4 . 188 BROMINE. IODINE. BROMINE, BROMINE* was discovered by Balard in 1826. It is found in sea-water, and is a frequent constituent of saline springs, chiefly as magnesium bro- mide : a celebrated spring of the kind exists near Kreuznach in Prussia. Bromine may be obtained pure by the following process, which depends upon the fact that ether, agitated with an aqueous solution of bromine, removes the greater part of that substance. The mother-liquor, from which the less soluble salts have separated by crystallization, is exposed to a stream of chlorine, and then shaken up with ether; the chlorine decomposes the magnesium bromide, and the ether dissolves the bromine thus set free. On standing, the ethereal solu- tion, having a fine red color, separates, and may be removed by a funnel or pipette. Caustic potash is then added in excess, and heat applied ; potassium bromide and bromate are formed. The solution is evaporated to dryness, and the saline matter, after ignition to redness to decompose the bromate, is heated in a small retort with manganese dioxide and sul- phuric acid diluted with a little water, the neck of the retort being plunged into cold water. The bromine volatilizes in the form of a deep- red vapor, which condenses into drops beneath the- liquid. Bromine is at common temperatures a red thin liquid of an exceedingly intense color, and very volatile; it freezes at about 7 (19 F. ), and boils at 63 (143 F.) The density of the liquid is 2-976, and that of the vapor 5 -54 compared with air, and 80 compared with hydrogen. The odor of bromine is very suffocating and offensive, much resembling that of iodine, but more disagreeable. It is slightly soluble in water, more freely in alcohol, and most abundantly in ether. The aqueous solution bleaches. HYDROGEN BROMIDE, or HYDROBROMIC ACID.-}- This substance bears the closest resemblance to hydriodic acid: it has the same constitution by volume, very nearly the same properties, and may be prepared by means exactly similar, substituting the one body for the other (see page 189). The solution of hydrobromic acid has also the power of dissolving a large quantity of bromine, thereby acquiring a red tint. Hydrobromic acid contains by weight 80 parts bromine and 1 part hydrogen. BROMIC AciD.J Caustic alkalis in presence of bromine undergo the same change as with chlorine, a metallic bromide and bromate being pro- duced: these may often be separated by the inferior solubility of the lat- ter. Bromic acid, obtained from barium bromate, closely resembles chloric acid; it is easily decomposed. The bromates, when heated, lose oxygen and become bromides. A hypobromous acid corresponding to hypochlorous acid is likewise known. IODINE. This element was first noticed in 1812 by M. Courtois, of Paris. Minute traces are found in combination with sodium or potassium in sea-water, and occasionally a much larger proportion in that of certain mineral springs. It seems to be in some way beneficial to many marine plants, as * From /3f>w/*0f, a noisome smell : a very appropriate term, f IIBr. J Br0 3 H. IODINE. 189 these latter have the power of abstracting it from the surrounding water, and accumulating it in their tissues. It is from this source that all the iodine of commerce is derived. It has lately been found in minute quan- tity in some aluminous slates of Sweden, arid in several varieties of coal and turf. Kdp, or the half-vitrified ashes of sea-weeds, prepared by the inhabi- tants of the Western Islands and the northern shores of Scotland and Ire- land, is treated with water, and the solution filtered. The liquid is then concentrated by evaporation until it is reduced to a very small volume, the sodium chloride, sodium carbonate, potassium chloride, and other salts being removed as they successively crystallize. The dark-brown mother-liquor left contains very nearly the whole of the iodine, as iodide of sodium, magnesium, &c. : this is mixed with sulphuric acid and manganese dioxide, and gently heated in a leaden retort, when the iodine distils over and condenses in the receiver. The theory of the operation is exactly analogous to that of the preparation of chlorine; in practice, however, it requires careful management, otherwise the impurities present in the solution interfere with the general result.* The manganese is not absolutely necessary; potassium or sodium iodide, heated with an excess of sulphuric acid, evolves iodine. This effect is due to a secondary action between the hydriodic acid first produced and the excess of the sulphuric acid, in which both suffer decomposition, yielding iodine water, and sulphurous acid. Iodine crystallizes in plates or scales of a bluish-black color and imper- fect metallic lustre, resembling that of plumbago: the crystals are some- times very large and brilliant. Its density is 4-918. It melts at 107 (2i>5 p.), and boils at 175 (347 F.), the vapor having an exceedingly beautiful violet color.f It is slowly volatile, however, at common temper- atures, and exhales an odor much resembling that of chlorine. The den- sity of the vapor is 8 716 compared with air, 127 compared with hydro- gen. Iodine requires for solution about 7000 parts of water, which never- theless acquires a brown color; in alcohol it is much more freely soluble. Solutions of hydriodic acid and the iodides of the alkaline metals also dissolve a large quantity : these solutions are not decomposed by water, which is the case with the alcoholic tincture Iodine stains the skin, but not permanently ; it has a very energetic action upon the animal system, and is much used in medicine. One of the most characteristic properties of iodine is the production of a splendid blue color by contact with starch. The iodine for this purpose must be free or uncombined. It is easy, however, to make the test available for the purpose of recognizing the presence of the element in question when a soluble iodide is suspected ; it is only necessary to add a very small quantity of chlorine-water, when the iodine, being displaced from combi- nation, becomes capable of acting upon the starch. HYDROGEN IODIDE, or HYDRIODIC ACID. The simplest process for pre- paring hydriodic acid gas is to introduce into a glass tube, sealed at one extremity, a little iodine, then a small quantity of roughly powdered glass moistened with water, upon this a few fragments of phosphorus, and lastly more glass: this order of iodine, glass, phosphorus, glass, is repeated until the tube is half or two-thirds filled. A cork and narrow bent tube are then fitted, and gentle heat applied. The gas is best collected by displace- ment of air. The experiment depends on the formation of an iodide of *-KI -f Mn0 2 + 2S0 4 IL, = I. 2 + S0 4 K 2 + S0 4 Mn + 20IT 2 Potassium Manganese Hydrogen Iodine. Potassium Manganese Water, iodide. dioxide. sulphate sulphate. sulphate. f Whence the name, from fu<5>7?, violet-colored. 190 IODINE. phosphorus and its subsequent decomposition by water, whereby hydrogen phosphite, or phosphorous acid, and hydrogen iodide are produced.* The glass merely serves to moderate the violence Fi 0- 135 - of the action of the iodine upon the phos- phorus. Hydriodic acid gas greatly resembles the corresponding chlorine compound; it is color- less, and highly acid ; it fumes in the air, and is very soluble in water. Its density is about 4-4 compared with air, 64 compared with hydrogen. By weight, it is composed of 127 parts iodine and 1 part hydrogen; and by measure of equal volumes of iodine vapor and hydrogen united without con- densation. Solution of hydriodic acid may be pre- pared by a process much less troublesome than the above. Iodine in fine powder is suspended in water, and a stream of washed hydrogen sulphide passed through the mixture; sul- phur is deposited, and the iodine converted into hydriodic acid. When the liquid has become colorless, it is heated, to expel the excess of hydrogen sulphide, and filtered. The solution cannot be kept long, especially if it be concentrated ; the oxygen of the air grad- ually decomposes the hydriodic acid, and iodine is set free, which, dissolving in the remainder, communicates to it a brown color. Compounds of Iodine and Oxygen. The most important of these are the iodic and periodic oxides. Composition by weight.f Iodine. Oxygen. Iodic oxide 127 40 Periodic oxide ...... 127 56 Both these are acid oxides, uniting with water and metallic oxides, and forming salts called iodates and periodates. The composition of the hydro- gen salts is as follows : J Iodine. Oxygen. Hydrogen. Iodic oxide. Water. Hydrogen lodate or Iodic acid 127 -f 48 -f 1 or 834 -f 18 Hydrogen Periodate or Periodic acid 127 -j- 56 -f 1 or 386 + 18 Iodic acid may be prepared by the direct oxidation of iodine with nitric acid of specific gravity 1-5; 5 parts of dry iodine with 200 parts of nitric acid are kept at a boiling temperature for several hours, or until the iodine has disappeared. The solution is then cautiously distilled to dryness, and the residue dissolved in water and made to crystallize. Iodic acid is a very soluble substance ; it crystallizes in colorless, six- sided tables. At 107 (224 F.) it is resolved into water and iodic oxide, which forms tabular rhombic crystals, and when heated to the temperature of boiling olive oil, is completely resolved into iodine and oxygen. The solution of iodic acid is readily deoxidized by sulphurous acid. The iodates * p 2 + i 6 + eoilo = 6HI + 2P0 3 H 3 Phosphorus. Iodine. Water. Hydrogen iodide. Hydrogen phosphite, f I 2 5 and laOy. J I 2 6 .OH 2 = 2I0 3 H; I 2 7 .OH 2 = 2I0 4 H. IODINE. 191 much resemble the chlorates: that of potassium is decomposed by heat into potassium iodide and oxygen gas. Periodic Acid. When solution of sodium iodate is mixed with caustic soda, and a current of chlorine transmitted through the liquid, two salts are formed namely, sodium chloride and a compound of sodium periodate with sodium hydrate, which is sparingly soluble.* This is separated, con- verted into a silver-salt, and dissolved in nitric acid : the solution yields, on evaporation, crystals of yellow silver periodate, from which the acid may be separated by the action of water, which resolves the salt into free acid and insoluble basic periodate. Periodic acid crystallizes from its aqueous solution in deliquescent oblique rhombic prisms, which melt at 130 (266 F.), and are resolved at 170 (338 F.) into water and a white mass of periodic oxide, which at 180 or 190 (356 374 F.) gives off oxygen with great rapidity, and leaves iodic oxide. The solution of periodic acid is reduced by many organic substances, and instantly by hydrochloric acid, sulphurous acid, and hydrogen sul- phide. With hydrochloric acid it forms water, iodine chloride, and free chlorine. The metallic periodates are resolved by heat into oxygen and metallic iodide. Compounds of Iodine and Nitrogen. When finely powdered iodine is put into caustic ammonia, it is in part dissolved, giving a deep-brown solution, and the residue is converted into a black powder, called nitrogen iodide.\ The brown liquid consists of hydriodic acid, holding iodine in solution, and is easily separated from the solid product by a filter. The latter, while still wet, is distributed in small quantities upon separate pieces of bibulous paper, and left to dry in the air. Nitrogen iodide is a black insoluble powder, which, when dry, explodes with the slightest touch even that of a feather and sometimes without any obvious cause. The explosion is, however, not nearly so violent as that of nitrogen chloride, and is attended with the production of violet fumes of iodine. According to Dr. Gladstone, this substance contains hy- drogen, and may be viewed as ammonia in which two thirds of the hy- drogen are replaced by iodine.| According to the researches of Bunsen, it must be viewed as a combination of nitrogen tri-iodide with ammonia. It appears, however, that the substance called nitrogen iodide varies in composition. Gladstone, by changing the mode of preparation, obtained several compounds of nitrogen tri-iodide with ammonia. Compounds of Iodine and Chlorine. Iodine readily absorbs chlorine gas, forming, when the chlorine is in excess, a solid yellow compound, and when the iodine preponderates, a brown liquid. The solid iodide is decomposed by water, yielding hydrochloric and iodic acids. || Another definite compound is formed by heating in a retort a mixture of 1 part iodine and 4 parts potassium chlorate ; oxygen gas and iodine chloride are disengaged, and the latter may be condensed by suitable means. Potassium iodate and perchlorate remain in the retort. This iodine chloride is a yellow oily liquid, of suffocating smell and astringent taste ; it is soluble in water and alcohol without decomposition. It probably consists of 127 parts iodine and 35-5 parts chlorine.^ * HtyVa + SXaTIO + C1 2 = 2Na.Cl + Sodium Sodium Chlorine Sodium Basic sodium iodate. hydrate. chloride. periodate. t NI 3 . t NHIfr g NI 3 .N% || Hence it is doubtless ICI 5 . f Id. 192 FLUORINE. FLUORINE. This element has never been isolated at least, in a state fit for exam- ination; its properties are consequently in great measure unknown; but from the observations made, it is presumed to be gaseous, and to pos- sess color, like chlorine. The compounds containing fluorine can be easily decomposed, and the element transferred from one body to another; but its intense chemical energies towards the metals and towards silicium, a component of glass, have hitherto baffled all attempts to obtain it pure in the separate state. As calcium fluoride, it exists in small quantities in many animal substances, such as bones. Several chemists have endeavored to obtain it by decomposing silver fluoride by means of chlorine in vessels of fluor-spar, but even these experiments have not led to a decisive result. HYDROGEN FLUORIDE, or HYDROFLUORIC ACID.* When powdered cal- cium fluoride (fluor-spar) is heated with concentrated sulphuric acid in a retort of platinum or lead connected with a carefully cooled receiver of the same metal, a very volatile colorless liquid is obtained, which emits copious white and highly suffocating fumes in the air. This was formerly believed to be the acid in the anhydrous state. Louyet, however, states that it still contains water, and that hydrofluoric acid, like hydrochloric acid, when anhydrous, is a gas. The anhydrous acid may be prepared, according to Fremy, by distilling hydrogen and potassium fluoride in a platinum vessel. The acid is gaseous at ordinary temperatures. In a frigorific mixture it exists as a liquid, which acts violently on water and evolves white fumes. When hydrofluoric acid is put into water, it unites with the latter with great violence: the dilute solution attacks glass with great facility. The concentrated acid, dropped upon the skin, occasions deep and malignant ulcers, so that great care is requisite in its management. Hydrofluoric acid contains 19 parts fluorine arid 1 part hydrogen. In a diluted state, this acid is occasionally used in the analysis of siliceous minerals, when alkali is to be estimated: it is employed, also, for etching on glass, for which purpose the acid may be prepared in vessels of lead, that metal being but slowly attacked under these circumstances. The vapor of the acid is also very advantageously applied to the same object in the following manner : The glass to be engraved is coated with etching- ground or wax, and the design traced in the usual way with a pointed instrument. A shallow basin made by beating up a piece of sheet-lead is then prepared, a little powdered fluor-spar placed in it, and enough sul- phuric acid added to form with the latter a thin paste. The glass is placed upon the basin, with the waxed side downward, and gentle heat applied beneath, which speedily disengages the vapor of hydrofluoric acid, lu a very few minutes, the operation is complete: the glass is then re- moved and cleaned by a little warm oil of turpentine. When the experi- ment is successful, the lines are very clean and smooth. No combination of fluorine and oxygen has yet been discovered. *HP SULPHUR. 193 SULPHUB. This is an elementary body of great importance and interest. It is often found in the free state in connection with deposits of gypsum and rock-salt; its occurrence in volcanic districts is probably accidental. Sicily furnishes a large proportion of the sulphur employed in Europe. In a state of combination with iron and other metals, and as sulphuric acid united to lime and magnesia, it is also abundant. Pure sulphur is a pale-yellow brittle solid, of well-known appearance. It melts when heated, and distils over unaltered, if air be excluded. The crystals of sulphur exhibit two distinct and incompatible forms namely, first, an octohedron with rhombic base (fig. 136), which is the figure of native sulphur, and that assumed when sulphur separates from solution at common temperatures, as when a solution of sulphur in carbon bisulphide is exposed to slow evaporation in the air ; and, secondly, a lengthened prism having no relation to the preceding: this happens when a mass of sulphur is melted, and, after partial cooling, the crust on the surface is broken and the fluid portion poured out. Fig. 137 shows the result of such an experi- ment. ig. 136. Fig. 137. The specific gravity of sulphur varies according to the form in which it is crystallized. The octohedral variety has the specific gravity 2-045; the prismatic variety the specific gravity 1-982. Sulphur melts at 111 (232 F.) (at 114-5, according to Brodie): at this temperature it is of the color of amber, and thin and fluid as water; when further heated, it begins to thicken, and to acquire a deeper color; and between 221 (430 F.) and 249 (480 F.) it is so tenacious that the vessel in which it is contained may be inverted for a moment without the loss of its contents. If in this state it be poured into water, it retains for many hours a remarkably soft and flexible condition, which should be looked upon as the amorphous state of sulphur. After a while it again becomes brittle and crystalline. From the temperature last mentioned to the boiling-point about 400 (792 F.) sulphur again becomes thin and liquid. In the preparation of commercial flowers of sulphur, the vapor is conducted into a large cold chamber, where it condenses in minute crystals. The specific gravity of sulphur vapor is 2-22, referred to that of air as unity, or 32 com- pared with that of hydrogen (Deville). Sulphur is insoluble in water and alcohol ; oil of turpentine and the fat oils dissolve it, but the best substance for the purpose is carbon bisulphide. In its chemical relations sulphur bears great resemblance to oxygen: to very many oxides there are corresponding sulphides, and the sulphides often unite among themselves, forming crystallizable compounds analogous to oxysalts. 17 194 SULPHUB. Sulphur is remarkable for the great number of modifications which it is capable of assuming. Of these, however, there are two principal well- characterized varieties, one soluble, and the other insoluble in carbon bi- sulphide, and many minor modifications. The soluble variety is distinguished by Berth elot* by the name of electro-negative sulphur, because it is the form which appears at the positive pole of the voltaic battery during the decom- position of an aqueous solution of hydrogen sulphide, and is separated from the combinations of sulphur with the electro-positive metals. The insolu- ble variety is distinguished as electro-positive sulphur, because it is the form which appears at the negative pole during the electric decomposition of sulphurous acid, and separates from compounds of sulphur with the electro- negative elements, chlorine, bromine, oxygen, &c. The principal modifications of soluble sulphur are the octohedral and prismatic varieties already mentioned, and an amorphous variety which is precipitated as a greenish-white emulsion, known as milk of sulphur on adding an acid to a dilute solution of an alkaline polysulphide, such, for example, as is obtained by boiling sulphur with milk of lime.f This amor- phous sulphur changes by keeping into a mass of minute octohedral crystals. Sublimed sulphur appears also to be allied to this modification, but it always contains a small portion of one of the insoluble modifications. The chief modifications of insoluble sulphur are : 1. The amorphous in- soluble variety, obtained as a soft magma by decomposing chlorine bisul- phide with water, or by adding dilute hydrochloric acid to the solution of a hyposulphite. J 2. The plastic sulphur already mentioned as obtained by pouring viscid melted sulphur into water. A very similar variety is pro- duced by boiling metallic sulphides with nitric or nitro-muriatic acid. Magnus g obtained a black modification of sulphur by repeatedly heating sulphur to 300 (572 F.), cooling suddenly, and exhausting with carbon bi- sulphide; and this black sulphur, heated to a temperature between 130 and 150, passed into a red modification. According to Mitscherlich, how- ever, pure sulphur does not exhibit these modifications ; but various highly colored products may be obtained by melting sulphur with small quantities of fatty matters. Even the grease imparted by touching sulphur with the fingers is sufficient to alter its color considerably when melted. When solutions of hydrogen sulphide and ferric chloride are mixed together, a blue precipitate is sometimes formed, which is said to be a peculiar modification of sulphur. Compounds of Sulphur and Oxygen. There are two oxides of sulphur whose names and composition are as follows : Composition by weight. Sulphur. Oxygen. Sulphur dioxide or Sulphurous oxide . . . 32 -f- 32 Sulphur trioxide or Sulphuric oxide . . . 32 -f 48 Both these oxides unite with water and metallic oxides, or the elements thereof, producing salts; those derived from sulphurous oxide are called * Ann. Chim Phys. [3], xlix. 430. f CaS 5 + 2HC1 = CaCl 2 + SH 2 -f S 4 Calcium Hydrochloric Calcium Hydrogen Sulphur, pentasulphide. acid. chloride. sulphide. % 2C1 2 S 2 + 30H 2 = 4IIC1 + S 2 3 H 2 + 83 Chlorine Water. Hydrochloric Hypo'sulphurous Sulphur, bisulphide. acid. acid. g Poggendorff s Annajen, xcii. 308. SULPHUR. 195 sulphites, and those derived from sulphuric acid, sulphates. The composi- tion of the hydrogen salts, or acids, is as follows : * Sulphur. Oxygen. Hydrogen. Sulphurous oxide. Water. Hydrogen Sulphite | 32 + 48+2 = 64 +18 or Sulphurous acid / Sulphuric oxide. Water. Hydrogen Sulphate, j 32 + 64 + 2 = 80 +18 or Sulphuric acid / The replacement of half or the whole of the hydrogen in these acids, by metals, gives rise to metallic sulphites and sulphates. There are also several acids of sulphur, with their corresponding metal- lic salts, to which there are no corresponding anhydrous oxides, viz. : 1. Hyposulphurous or Thiosulphuric Acid, having the composition of sul- phuric acid in which one fourth of the oxygen is replaced by sulphur.f Its composition by weight is : Sulphur. Oxygen. Hydrogen. 04 + 48 + 2 2. A series of acids called Polythionic Acids,\ in which the same quanti- ties of oxygen and hydrogen are united with quantities of sulphur in the proportion of the numbers 2. 3, 4, 5,g viz.: Sulphur. Oxygen. Hydrogen. Dithionic, or Hyposulphuric acid . . 64 + 96+2 Trithionic acid 96 + 96 + 2 Tetrathionic acid 128 + 96 + 2 Pentathionic acid . . . . 160 + 96 + 2 SULPHUR DIOXIDE, or SULPHUROUS OXIDE. This is the only product of the combustion of sulphur in dry air or oxygen gas. It is most conveniently prepared by heating sulphuric acid with metallic mercury or copper clip- pings ; a portion of the acid is decomposed, one third of the oxygen of the sulphuric oxide being transferred to the metal, while the sulphuric oxide is reduced to sulphurous oxide which escapes as gas.|| Another very simple method of preparing sulphurous oxide consists in heating concentrated sul- phuric acid with sulphur ; a very regular evolution of sulphurous oxide is thus obtained. Sulphurous oxide is a colorless gas, having the peculiar suffocating odor of burning brimstone ; it instantly extinguishes flame, and is quite irrespirible. Its density is 2-21; a litre weighs 2-8605 grams; 100 cubic inches weigh 68-69 grains. At 17-8 (0 F.), under the ordinary pressure of the atmosphere, this gas condenses to a colorless, limpid liquid, very expansible by heat. Cold water dissolves more than thirty times its volume of sulphurous oxide. The solution, which contains hydrogen sul- phite or sulphurous acid, maybe kept unchanged so long as air is excluded, but access of oxygen gradually converts the sulphurous into sulphuric acid, although dry sulphurous oxide and oxygen gases may remain in contact * The composition of these oxides and acids is thus expressed in symbols : Sulphurous oxide .... S0 2 Sulphurous acid S0 3 II 2 = S0 2 .OH 2 Sulphuric oxide S0 3 Sulphuric acid S0 4 FI 2 rr S0 3 .OH 2 f Sulphuric acid Thiosulphuric acid $ From TroXfif, many, and 6uov, sulphur. 2 In symbols: Dithionic acid ... Trithionic acid . . . . Tetrathionic acid .... S 4 O fl ll a Pentathionic acid . . . S 6 6 H 2 I 2(S0 3 .On 2 ) + Cu = S0 3 .CuO + 20H 2 + S0 2 Sulphuric acid. Copper. Copper sulphate. Water. Sulphurous oxide. 196 SULPHUR. for any length of time without change. When sulphurous oxide and aqueous vapor are passed into a vessel cooled to below 8-3 or 6 (17 or 21 F.), a crystalline body forms, which contains about 24-2 sulphurous oxide to 75-8 of water. One volume of sulphurous oxide gas contains one volume of oxygen and half a volume of sulphur vapor, condensed into one volume. Gases which, like the present, are freely soluble in water, must be col- lected by displacement, or by the use of the mercurial pneumatic trough. The manipulation with the latter is exactly the same in principle as with the ordinary water-trough, but rather more troublesome, from the great density of the mercury, and its opacity. The whole apparatus is on a much smaller scale. The trough is best constructed of hard, sound wood, and so contrived as to economize as much as possible the expensive liquid it is to contain. Sulphurous acid has bleaching properties ; it is used in the arts for bleach- ing woollen goods and straw-plait. A piece of blue litmus paper plunged into the moist gas is first reddened and then slowly bleached. The salts of sulphurous acid are not of much importance: those of the alkalies are soluble and crystallizable ; they are easily formed by direct combination. The sulphites of barium, strontium, and calcium are insol- uble in water, but soluble in hydrochloric acid. The stronger acids de- compose them ; nitric acid converts them into sulphates. Sulphurous oxide unites, under peculiar circumstances, with chlorine, and also with iodine, forming compounds, which have been called chloro- and iodo-sulphuric acids. They are decomposed by water. It also combines with dry ammoniacal gas, giving rise to a remarkable compound ; and with nitric oxide also, in presence of an alkali. SULPHUR TRIOXIDE or SULPHURIC OXIDE (also called Anhydrous Sulphuric acid, or Sulphuric anhydride]. This compound maybe formed directly by passing a dry mixture of sulphurous oxide and oxygen gases over heated spongy platinum; or it may be obtained by distilling the most concentrated sulphuric acid with phosphoric oxide, which then abstracts the water and sets the sulphuric oxide free. It is usually prepared, however, from the fuming oil of vitriol of Nordhausen, which may be regarded as a solution of sulphuric oxide in sulphuric acid. On gently heating this liquid in a retort connected with a receiver cooled by a freezing mixture, the sulphuric oxide distils over in great abundance, and condenses into beautiful white silky crystals, resembling those of asbestos. "When thrown into water, it hisses like a red-hot iron, from the violence with which combination occurs: the product is sulphuric acid. When exposed to the air, even for a few moments, it liquefies by absorption of moisture. It unites with ammoniacal gas, forming a salt called ammonium sulphamate, the nature of which will be explained further on. SULPHURIC ACID. This acid has been known since the fifteenth century. There are two distinct processes by which it is at present prepared namely, by the distillation of ferrous sulphate (copperas or green vitriol), and by the oxidation of sulphurous acid with nitrous and hyponitric acids. The first process is still carried on in some parts of Germany, especially in the neighborhood of Nordhausen in Prussia, and in Bohemia. The fer- rous sulphate, derived from the oxidation of iron pyrites, is deprived by heat of the greater part of its water of crystallization, and subjected to a high red heat in earthen retorts, to which receivers are fitted as soon as the acid begins to distil over. A part gets decomposed by the very high tem- perature ; the remainder is driven off in vapor, which is condensed by the cold vessel, containing a very small quantity of water or common sulphuric acid. The product is a brown oily liquid, of about 1-9 specific gravity, fum- SULPHUR. 197 ing in the air, and very corrosive. It is chiefly made for the purpose of dissolving indigo. The second method, which is, perhaps, with the single exception men- tioned, always followed as the more economical, depends upon the fact that, when sulphurous oxide, nitrogen tetroxide, and water are present together in certain proportions, the sulphurous oxide becomes oxidized at the expense of the nitrogen tetroxide, which by the loss of one-half of its oxygen, sinks to the condition of nitrogen dioxide. The operation is thus conducted: A large and very long chamber is built of sheet-lead supported by timber- framing: on the outside, at one extremity, a small furnace or oven is con- structed, having a wide tube leading into the chamber. In this, sulphur is kept burning, the flame of which heats a crucible containing a mixture of nitre and oil of vitriol. A shallow stratum of water occupies the floor of the chamber, and a jet of steam is also introduced. Lastly, an exit is pro- vided at the remote end of the chamber for the spent and useless gases. The effect of these arrangements is to cause a constant supply of sulphur- ous oxide, atmospheric air, nitric acid vapor, and water in the state of steam, to be thrown into the chamber, there to mix and react upon each other. The nitric acid immediately gives up a part of its oxygen to the sulphurous oxide, and is itself reduced to nitrogen tetroxide; it does not remain in this state, however, but suffers further deoxidation until it be- comes reduced to nitrogen dioxide. That substance, in contact with free oxygen, absorbs a portion of the latter, and once more becomes tetroxide, which is again destined to undergo deoxidation by a fresh quantity of sul- phurous oxide. A very small portion of nitrogen tetroxide, mixed with at- mospheric air and sulphurous oxide, may thus in time convert an indefinite amount of the latter into sulphuric acid, by acting as a kind of carrier be- tween the oxygen of the air and the sulphurous oxide. The presence of water is essential to this reaction. We may thus represent the change: * 46 Oxygen 16 Oxygen 16 Sulphurous oxide ( Sulphur 32 64 \ Oxygen 32 Water 18 Nitrogen dioxide 30. Sulphuric acid 98. Such is the simplest view that can be taken of the production of sulphuric acid in the leaden chamber ; but it is too much to affirm that it is strictly true ; the reaction may be more complex. When a little water is put at the bottom of a large glass globe, so as to maintain a certain degree of hu- midity in the air within, and sulphurous oxide and nitrogen tetroxide are introduced by separate tubes, symptoms of chemical action become im- mediately evident, and after a little time a white crystalline matter is observed to condense on the sides of the vessel. This substance appears to be a compound of sulphuric acid, nitrous acid, and a little water. j- When thrown into water, it is resolved into sulphuric acid, nitrogen * N0 2 + S0 2 + OH 2 = NO + S0 4 H 2 Nitrogen Sulphurous Water. Nitrogen Sulphuric tetroxide. oxide. dioxide. acid. f Gaultier do Claubry assigned to this curious substance the composition expressed by tho formula 2(N 2 3 .'20II 2 ').:'>S03, and this view has generally been received by recent chemical writers. De la Provostaye has since shown that a compound possessing all the essential prop- erties of the body it> question may be formed by bringing together, in a sealed glass tube, liquid sulphurous oxide and liquid nitrogen tetroxide, both free from water. The white crys- talline solid noon begins to form, and at the expiration of twenty-six hours the reaction ap- pears complete. The new product is accompanied by an exceedingly volatile greenish liquid 17* 198 SULPHUR. dioxide, and nitric acid. This curious body is certainly very often pro- duced in large quantity in the leaden chambers ; but that its production is indispensable to the success of the process, and constant when the operation goes on well, and the nitrogen tetroxide is not in excess, may perhaps ad- mit of doubt. The water at the bottom of the chamber thus becomes loaded with sul- phuric acid: when a certain degree of strength has been reached, the acid is drawn off and concentrated by evaporation, first in leaden pans, and afterwards in stills of platinum, until it attains a density (when cold) of 1*84, or thereabouts; it is then transferred to carboys, or large glass bot- tles fitted in baskets, for sale. In Great Britain this manufacture is one of great national importance, and is carried on to a vast extent. Sulphuric acid is now more frequently made by burning iron pyrites, or poor copper ore, or zinc-blende, as a substitute for Sicilian sulphur: it very frequently contains arsenic, from which it may be freed, however, by heating it with a small quantity of sodium chloride, or by passing through the heated acid a current of hydrochloric acid gas, whereby the arsenic is volatilized as trichloride. The most concentrated sulphuric acid, or oil of vitriol, as it is often called, is a definite combination of 40 parts sulphuric oxide, and 9 parts water.* It is a colorless oily liquid, having a specific gravity of about 1-85, of intensely acid taste and reaction. Organic matter is rapidly charred and destroyed by this substance. At the temperature of 26 ( 15 F.) it freezes; at 327 (620 F.) it boils, and may be distilled without decom- position. Oil of vitriol has a most energetic attraction for water ; it with- draws aqueous vapor from the air, and when it is diluted with water, great heat is evolved, so that the mixture always requires to be made with cau- tion. Oil of vitriol is not the only hydrate of sulphuric oxide; three others are known to exist. When the fuming oil of vitriol of Nordhausen is exposed to a low temperature, a white crystalline substance separates, which is a hydrate containing half as much water as the common liquid acid. Then, again, a mixture of 98 parts of strong liquid acid and 18 parts of water f congeals or crystallizes at a temperature above 0, and remains solid even at 7-2 (45 F.). Lastly, when a very dilute acid is concentrated by evaporation in a vacuum over a surface of oil of vitriol, the evaporation stops when the sulphuric oxide and water bear to each other the proportion of 80 to 54. J When the vapor of sulphuric acid is passed over red-hot platinum, it is decomposed into oxygen and sulphurous acid. St. Claire Deville and De- bray have recommended this process for the preparation of oxygen on the large scale, the sulphurous acid being easily separated by its solubility in water or alkaline solutions. Sulphuric acid acts readily on metallic oxides; converting them into sulphates. It also decomposes carbonates with the greatest ease, expelling carbon dioxide with effervescence. With the aid of heat it likewise de- composes all other salts containing acids more volatile than itself. The sulphates are a very important class of salts, many of them being exten- sively used in the arts. Most sulphates ate soluble in water, but they are all insoluble in alcohol. The barium, calcium, strontium, and lead salts having the characters of nitrous acid. The white substance, on analysis, was found to contain the elements of two molecules of sulphuric oxide and one of nitrous oxide, or N 2 3 .2S0 3 . M. de la Provostaye very ingeniously explains the anomalies in the different analyses of the leaden chamber product, by showing that the pure substance forms crystallizable combina- tions with different proportions of sulphuric acid. (Ann. Chim. Phys. Ixxiii. 362.) See also Weber (Jahresbericht fur Chemie, 1863, p. 738; 1865, p. 93; Bull. Soc. Chim. de Paris, 1867, i. 15.) * S0 3 .OH 2 = S0 4 Ho. t S0 3 .20H 2 = S0 4 H 2 .OH 2 . t S0 3 30H 2 = S0 4 H 2 .20H 2 . SULPHUR. 199 are insoluble, or very slightly soluble, in water; and are formed by pre- cipitating a soluble salt of either of those metals with sulphuric acid, or a soluble metallic sulphate. Barium sulphate is quite insoluble in water; consequently sulphuric acid, or its soluble salts, may be detected with the greatest ease by solution of barium nitrate or chloride ; a white precipi- tate is thereby produced which does not dissolve in nitric acid. HYPOSULPHUROUS, or THIOSULPHURIC ACID. By digesting sulphur with a solution of potassium or sodium sulphite, a portion of that substance is dissolved, and the liquid, by slow evaporation, furnishes crystals of hypo- sulphite.* The acid itself is scarcely known, for it cannot be isolated : when hydrochloric acid is added to a solution of a hyposulphite, the acid of the latter is almost instantly resolved into sulphur, which precipitates, and sulphurous acid, easily recognized by its odor. In very dilute solu- tion, however, it appears to remain undecomposed for some time. The most remarkable feature of the alkaline hyposulphites is their property of dissolving certain insoluble salts of silver, as the chloride a property which has lately conferred upon them a considerable share of importance in relation to the art of photography. They are also much used as anti- chlores for removing the last traces of chlorine from bleached goods. DITHIONIC, or HYPOSULPHURIC ACID. This acid is prepared by sus- pending finely divided manganese dioxide in water artificially cooled, and then transmitting a stream of sulp'mrous acid gas; the dioxide becomes monoxide, half its oxygen converting the sulphurous into dithionic acid.-}- The manganese dithionate thus prepared is decomposed by a solution of pure barium hydrate, and the barium salt, in turn, by enough sulphuric acid to precipitate the base. The solution of dithionic acid may be con- centrated by evaporation in a vacuum, until it acquires a density of 1 -347 ; pushed further, it decomposes into sulphuric and sulphurous acids. It has no odor, is very sour, and forms soluble salts with baryta, lime, and lead oxide. TRITHIONIC ACID. A substance accidentally formed by Langlois, J in the preparation of potassium hyposulphite, by gently heating with sulphur a solution of potassium carbonate saturated with sulphurous acid. It is also produced by the action of sulphurous oxide on potassium hyposulphite. g Its salts bear a great resemblance to those of hyposulphurous acid, but differ completely in composition, while the acid itself is not quite so prone to change. It is obtained by decomposing the potassium salt with hydro- fluosilicic acid: it may be concentrated under the receiver of the air-pump, but is gradually decomposed into sulphur, sulphurous and sulphuric acids. TETRATHIONIC ACID. This acid was discovered by Fordos and Gelis. || When iodine is added to a solution of barium hyposulphite, a large quantity of that substance is dissolved, and a clear colorless solution obtained, * S0 3 K 2 + S = SaOgKa Potassium Sulphur. Potassium sulphite. hyposulphite. t Mn0 2 + 2S0 3 H 2 = S 2 6 Mn + 20H 2 Manganese Sulphurous Manganese Water. dioxide. acid. dithionate. t Ann. Chim. Phys. [2], Ixxiv. 250. 2S 2 3 K 2 + 3S0 2 - 2S 3 6 K 2 + S Potassium Sulphurous Potassium hyposulphite. oxide. trithionate. || Ann. Ch. Pharm. xliv. 247. 200 SULPHUR. which, besides barium iodide, contains barium tetrathionate.* By suitable means, the acid can be eliminated, and obtained in a state of solution. It very closely resembles dithionic acid. The same acid is produced by the action of sulphurous acid on chlorine disulphide. PENTATHIONIC ACID. Another acid of sulphur was discovered by Wack- enroder,f who formed it by the action of hydrogen sulphide on sulphurous acid.J It is colorless and inodorous, of acid and bitter taste, and capable of being concentrated to a considerable extent by cautious evaporation. Under the influence of heat, it is decomposed into sulphur, sulphurous and sulphuric acids, and hydrogen sulphide. The salts of pentathionic acid are nearly all soluble. The barium salt crystallizes from alcohol in square prisms. The acid is also formed when lead dithionate is decomposed by hydrogen sulphide, and when chlorine monosulphide is heated with sul- phurous acid. Sulphur with Hydrogen. HYDROGEN MONOSULPHIDE ; SULPHYDRIC ACID ; HYDROSULPHURIC ACID ; SULPHURETTED HYDROGEN. There are two methods by which this important compound can be readily prepared, namely, by the action of dilute sulphuric acid upon iron monosulphide, and by the decomposition of antimony tri- sulphide with hydrochloric acid. The first method yields it most easily, the second in the purest state. Iron monosulphide is put into the apparatus for hydrogen, already several times mentioned, together with water, and oil of vitriol is added by the funnel, until a copious disengagement of gas takes place. This is to be collected over tepid water. The reaction is thus explained : Iron sulphide. Water . . . Sulphuric oxide / Sulphur \ Iron f Hydrogen \ Oxygen Hydrogen sulphide. Ferrous sulphate. By the other plan, finely powdered antimony trisulphide is put into a flask to which a cork and bent tube can be adapted, and strong liquid hydrochloric acid poured upon it. On the application of heat, a double interchange occurs between the bodies present, hydrogen sulphide and antimony trichloride being formed. The action lasts only while the heat is maintained. Hydrochloric acid Antimony sulphide, Hydrogen sulphide. Antimony chloride. | Hydrogen sulphide is a colorless gas, having the odor of putrid eggs ; it is most offensive when in small quantity, when a mere trace is present in the air. It is not irritating, but, on the contrary, powerfully narcotic. * 2S 2 3 Ba + Barium hyposulphite. Iodine. = BaT 2 Barium iodide. + S 4 6 Ba Barium tetrathionate. f Ann. Ch Pharm . Ix. 189. J 5S0 3 H 2 + Sulphurous acid. 5SH 2 = Hydrogen sulphide. S 5 6 H 2 = Pentathionic acid. 90H 2 + S 6 Water. Sulphur. \ FeS + Ferrous sulphide. S0 4 H 2 Hydrogen sulphate. = SH 2 Hydrogen sulphide. = S0 4 Fe Ferrous sulphate. II SbgSg + Antimonious sulphide. GHC1 Hydrogen chloride. = 3SII 2 Hydrogen sulphide. + 2SbCl 3 Antimonious chloride. SULPHUR. 201 When set on fire, it burns with a blue flame, producing sulphurous acid when the supply of air is abundant; and depositing sulphur when the oxygen is deficient. Mixed with chlorine, it is instantly decomposed, with separation of the whole of the sulphur. This gas has a specific gravity of 1-171 referred to air, or 17 referred to hydrogen as unity ; a litre weighs 1-51991 grams. A pressure of 17 atmospheres at 10 (50 F.) reduces it to the liquid form. Cold water dissolves its own volume of hydrogen sulphide, and the solution is often directed to be kept as a test ; it is so f . 13g prone to decomposition, however, by the oxygen of the air, that it quickly spoils. A much better plan is to keep a little apparatus for generating the gas always at hand, and ready for use at a moment's notice. A small bottle or flask, to which a bit of bent tube is fitted by a cork, is supplied with a little iron sulphide and water ; when required for use, a few drops of oil of vitriol are added, and the gas is at once evolved. The experiment completed, the liquid is poured from the bottle, replaced by a little clean water, and the apparatus is again ready for use. Potassium heated in hydrogen sulphide burns with great energy, becoming converted into sulphide, while pure hydrogen remains, equal in volume to the original gas. Taking this act into account, and comparing the density of the gas with those of hydrogen and sulphur vapor, it appears that every volume of hydrogen sulphide contains one volume of hydrogen and half of a volume of sulphur-vapor, the whole condensed into one volume, a constitution precisely analogous to that of water-vapor. This corresponds very nearly with its composition by weight, determined by other means namely, 16 parts sulphur and 1 part hydrogen. When a mixture of 100 measures of hydrogen sulphide and 150 measures of pure oxygen is exploded by the electric spark, complete combustion ensues, and 100 measures of sulphurous oxide gas result. Hydrogen sulphide is a frequent product of the putrefaction of organic matter, both animal and vegetable ; it occurs also in certain mineral springs, as at Harrogate, and elsewhere. When accidentally present in the atmosphere of an apartment, it may be instantaneously destroyed by a small quantity of chlorine gas. There are few reagents of greater value to the practical chemist than this substance: when brought in contact with many metallic solutions, it gives rise to precipitates, which are often exceedingly characteristic in appearance, arid it frequently affords the means of separating metals from each other with the greatest precision and certainty. The precipitates spoken of are insoluble sulphides, formed by the mutual decomposition of the metallic oxides or chlorides and hydrogen sulphide, water or hydro- chloric acid being produced at the same time. All the metals are in fact precipitated, whose sulphides are insoluble in water and in dilute acids. Arsenic and cadmium solutions thus treated give bright yellow precipi- tates, the former soluble, the latter insoluble, in ammonium sulphide; tin salts give a brown or a yellow precipitate, according as the metal is in the form of a stannous or a stannic salt; both soluble in ammonium sulphide. Antimony solutions give an orange-red precipitate, soluble in ammonium sulphide. Copper, lead, bismuth, mercury, and silver salts give dark- brown or black precipitates, insoluble in ammonium sulphide ; gold and platinum salts, black precipitates, soluble in ammonium sulphide. Hydrogen sulphide possesses the properties of an acid ; its solution in water reddens litmus-paper. 202 SULPHUR. The best test for the presence of this compound is paper wetted with solution of lead acetate. This salt is blackened by the smallest trace of the gas. Hydrogen duulphide. lhis substance corresponds m constitution and instability to the hydrogen dioxide; it is prepared by the following means: Equal weights of slaked lime and flowers of sulphur are boiled with 5 or G parts of water for half an hour, when a deep orange-colored solution is produced, containing, among other things, calcium disulphide. This is filtered, and slowly added to an excess of dilute sulphuric acid, with con- stant agitation. A white precipitate of separated sulphur and calcium sulphate makes its appearance, together with a quantity of yellow oily- looking matter, which collects at the bottom of the vessel: this io hydro- gen disulphide.* If the experiment be conducted by pouring the acid into the solution of the sulphide, then nothing but finely divided precipitated sulphur is ob- tained. The disulphide is a yellow, viscid, insoluble liquid, exhaling the odor of sulphuretted hydrogen; its specific gravity is 1-769. It is slowly de- composed even in the cold into sulphur and hydrogen monosulphide, and instantly by a higher temperature, or by contact with many metallic oxides. Carbon and Sulphur. CAKBON DISULPHIDE OR BISULPHIDE, f A white porcelain tube is filled with pieces of charcoal which have been recently heated to redness in a covered crucible, and fixed across a furnace in a slightly inclined position. Into the lower extremity a tolerably wide tube is secured by the aid of a cork: this tube bends downward, and passes nearly to the bottom of a bottle filled with fragments of ice and a little water. The porcelain tube being heated to a bright redness, fragments of sulphur are thrown into the open end, which is immediately afterwards stopped by a cork. The sulphur melts, and becomes converted into vapor, which at that high tem- perature combines with the carbon, forming an exceedingly volatile com- pound, which is condensed by the ice and collects at the bottom of the vessel. This is collected and redistilled at a ^ery gentle heat in a retort connected with a good condenser. For preparation on the large scale, a tubulated earthen retort is filled with charcoal, and the sulphur is dropped in through a porcelain tube passing through the tubulus and reaching nearly to the bottom ; or the charcoal is contained in a large iron cylinder, and the sulphur introduced through a pipe fitted into the lower part. * The reaction which ensues when calcium hydrate, sulphur, and water are boiled together is rather complex, disulplride or pentasulphide of calcium being formed, together with calcium hyposulphite, arising from the transfer of the oxygen of the decomposed lime to another por- tion of sulphur. 3CaO + S 6 = 2CaSa -f S 2 3 Ca Lime. Sulphur. Calcium Calcium disulphide. hyposulphite. The calcium disulphide, decomposed by an acid under favorable circumstances, yields a cal- cium salt and hydrogen disulphide. CaS 2 + S0 4 IT a = SH 2 + S0 4 Ca Calcium Sulphuric Hydrogen Calcium disulphide. acid. disulphide. sulphate. When the acid is poured into the sulphide, sulphuretted hydrogen, water, and calcium sul- pliatr arc. produced, while the excess of sulphur is thrown down as a fine white powder, the "precipitated sulphur" of the Pharmacopoeia. When the object is to prepare the latter sub- stance, hydrochloric acid must be used in place of sulphuric acid. tcs* SULPHUR. 203 Carbon disulphide is a transparent, colorless liquid of great refractive and dispersive power. Its density is 1-27'J, that of its vapor is 2-67. It boils at 43 (110 F.), and emits vapor of considerable elasticity at com- mon temperatures. This substance has a very repulsive odor. When set on fire in the air, it burns with a blue flame, forming carbon dioxide and sulphur dioxide gases; and when its vapor is mixed with oxygen, it be- comes explosive. Carbon disulphide, when heated with water in a sealed tube to about 153 (307 F.), is converted into carbon dioxide and hydrogen sulphide. In contact with nascent hydrogen (when heated with zinc and dilute sulphuric acid), it is converted into a white crystalline substance containing carbon, hydrogen, and sulphur,* crystallizing in square prisms, insoluble in water, alcohol, and ether, but soluble in carbon disulphide, subliming at 150 (302 F.), and decomposing at 200. Carbon disulphide freely dissolves sulphur, and by spontaneous evaporation deposits the latter in beautiful crystals; it also dissolves phosphorus, iodine, camphor, and caoutchouc, and mixes easily with oils. It is extensively used in the vul- canization of caoutchouc, and in the manufacture of gutta-percha, also for extracting bitumen from mineral substances, and oil from seeds. Carbon disulphide unites with metallic sulphides, forming salts called sulphocarbonates, which have the composition of carbonates with the oxygen replaced by sulphur. By treating the ammonium salt with dilute sulphuric or hydrochloric acid, an oily acid liquid is precipitated, consisting of hydrogen sulphocarbonate, or sulphocarbonic acid.f Compounds of Sulphur with Chlorine. When dry chlorine is passed over the surface of sulphur kept melted in a small glass retort connected with a good condensing arrangement, a deep orange-yellow mobile liquid distils over, having a peculiar and disagree- able odor, and boiling at 136 (276 F.). As this substance dissolves both sulphur and chlorine, it is not easy to obtain it in a pure and definite state. It contains 32 parts sulphur and 35-5 chlorine, and is called sulphur monochloride (or subchloride), also chlorine bisulphide. J It is instantly decomposed by water, hydrochloric and hyposulphurous acids being formed, and sulphur separated. The hyposulphurous acid in its turn decomposes into sulphur and sulphurous acid.| By exposing the above compound for a considerable time to the action of chlorine, and then distilling it in a stream of the gas, a deep-red liquid is obtained, at a cer- tain stage of the distillation, heavier than water, boiling at 164, and con- taining twice as much chlorine as the monochloride, hence called sulphur dichloride or chlorine mono sulphide.\\ It appears, however, to be not a definite compound of sulphur and chlorine, but a mixture of the preceding with the following compound. A compound called sulphur tetrachloride,^ containing 32 parts of sulphur to 142 parts of chlorine, appears to exist in combination with certain me- tallic chlorides, but is not known in the separate state. According to Carius,** the red-brown liquid, obtained as above mentioned by saturating chlorine disulphide with chlorine, is a mixture of the monochloride and * CSH 2 . f Calcium carbonate . . . C0 3 Ca = C0 2 .CaO Calcium sulpho-carbonate . CS 3 ra = CS 2 .CaS Hydrogen sulpho-carbonate CS a II 2 CSjj.H 2 S 2 3IT 2 = 4IIC1 + So + Ss0 8 Ha (or S0 3 H 2 + S) Sulphur Water. Hydrochloric Sulphur. Hyposul- Sulphurous Sulphur. monochloride. acid. phurous acid. acid. I* Ann^Ch. Pharm. cvi. 291 ; ex. 209; see also Watts's Pictionary of Chemistry, v. 633. 204 SELENIUM. tetrachloride in various proportions, according to the temperature at which the saturation is effected. CARBON OXYCHLORIDE.* This compound, also called phosgene gas, has been already mentioned. It is produced by the direct combination of chlorine and carbon monoxide under the influence of sunshine; but is more easily prepared by passing carbon monoxide into boiling antimony pentachlorides. It must be received over mercury, as water decomposes it. CARBON SULPHOCHLORIDE.| This compound, the sulphur-analogue of the preceding, is produced, together with chlorine monosulphide, by the action of dry chlorine on carbon disulphide,J or by passing a mixture of hydrogen sulphide and vapor of carbon tetrachloride through a red-hot tube.$ It is a yellow liquid having a very irritating odor, not acted upon by water or acids, but decomposed by potash, yielding potassium sulphide, potassium carbonate, and carbon tetrachloride. || SULPHUR AND BROMINE. Bromine dissolves sulphur, forming a brown- red liquid probably containing a sulphur bromide analogous to sulphur monochloride ; but it has not been obtained pure. SULPHUR AND IODINE. These elements combine when heated together, even under water. The resulting compound, containing 32 parts of sulphur and 127 parts of iodine, ^[ is a blackish-gray radio-crystalline mass, resem- bling native antimony sulphide. It decomposes at higher temperatures, gives off iodine on exposure to the air, and is insoluble in water. By heating 254 parts of iodine with 32 parts of sulphur,** a compound is obtained which smells like iodine, and is said to be a powerful remedy in skin-diseases. A cinnabar-red sulphur iodide is obtained, according to Grosourdi, by precipitating iodine trichloride with hydrogen sulphide. SELENIUM. This is a very rare substance, much resembling sulphur in its chemical relations, and found in association with that element in some few localities, or replacing it in certain metallic combinations, as in the lead selenide of Clausthal in the Hartz. Selenium is a reddish-brown solid body, somewhat translucent, and hav- ing an imperfect metallic lustre. Its specific gravity, when rapidly cooled after fusion, is 4-3. At 100, or a little above, it melts, and boils. It is insoluble in water, and exhales, when heated in the air, a peculiar and disagreeable odor, which has been compared to that of decaying horse- radish: it is insoluble in alcohol, but dissolves slightly in carbon bisulphide, from which solution it crystallizes. Two oxides of selenium are known. The one containing the smallest proportion of oxygen is formed by the imperfect combustion of selenium in air or oxygen gas. It is a colorless gas which is the source of the pe- culiar horse-radish odor above mentioned. Its composition is not known. The higher oxide, called selenious oxide, is produced by burning selenium * COC1 2 . t CSC1 2 . t CS 2 + C1 4 = CSC1 2 + ' SCI* 1 CC1 4 + SH 2 - 2HC1 + CSC1 2 . I 2CSC1 2 + 3K 2 = 2K 2 S -f C0 3 K 2 + CC1 4 . TELLURIUM. 205 in a stream of oxygen gas; it contains 79-5 parts, by weight, of selenium, and 32 of oxygen. It is a white solid substance which absorbs water rapidly, forming a hydrate, viz. : Selenium. Oxygen. Hydrogen. Selenious Water. oxide. Selenious acid, or ) n A Hydrogen selenite } ' ' 79 ' 4 + 48+2 or 111-4 + 18 This acid, analogous in composition and properties to sulphurous acid, is likewise produced by dissolving selenium in nitric or nitro-muriatic acid. It is deposited from its hot aqueous solution by slow cooling in prismatic crystals like those of saltpetre; but when the solution is evaporated to dryness, the selenious acid is resolved into water and selenious oxide, which sublimes at a higher temperature. Selenious acid is a very powerful acid, approximating to sulphuric acid in the energy of its reactions. It reddens litmus, decomposes carbonates with effervescence, and decomposes nitrates and chlorides with aid of heat. Its solution precipitates lead and silver salts, and is decomposed by hydro- gen sulphide, yielding a precipitate of selenium sulphide.* The metallic selenites resemble the sulphites. When heated with sodium carbonate in the inner blowpipe flames, they emit the characteristic odor of selenium. They are not decomposed by boiling with hydrochloric acid. Selenic Acid is a more highly oxidized acid of selenium, analogous to sulphuric acid, and containing 79-4 parts, by weight, of selenium, 64 of oxygen, and 2 of hydrogen. f The corresponding anhydrous oxide is not known. Selenic acid is prepared by fusing potassium or sodium nitrate with selenium, precipitating the selenate so produced with a lead salt, and then decomposing the compound with hydrogen sulphide. The acid strongly resembles oil of vitriol; but, when very much concentrated, decomposes, by the application of heat, into selenious acid and oxygen. The selenates bear the closest analogy to the sulphates in almost every particular. They are decomposed by boiling with hydrochloric acid, chlorine being evolved and a salt of selenious acid being produced. HYDROGEN SELENIDE ; SELENHYDRIC ACID ; SELENETTED HYDROGEN. This substance is produced by the action of dilute sulphuric acid upon po- tassium or iron selenide. It very much resembles sulphuretted hydrogen, being a colorless gas, freely soluble in water, and decomposing metallic solutions like that substance : insoluble selenides are thus produced. This gas is said to act very powerfully upon the lining membrane of the nose, exciting catarrhal symptoms, and destroying the sense of smell. It contains 79-4 parts selenium and 2 parts hydrogen. J TELLURIUM. This element possesses many of the characters of a metal, but it bears so close a resemblance to selenium, both in its physical properties and its chemical relations, that it is most appropriately placed in the same group with that body. Tellurium is found in a few scarce minerals in association * Se0 3 H 2 + 2SH 2 = 30II 2 + 8683. Selenious Hydrogen Water. acid. sulphide, f Selenic acid, Se0 4 H 2 - 206 TELLURIUM. with gold, silver, lead, and bismuth, apparently replacing sulphur, and is most easily extracted from the bismuth sulpho-telluride of Chemnitz in Hungary. The finely powdered ore is mixed with an equal weight of dry sodium carbonate, the mixture made into a paste with oil, and heated to whiteness in a closely covered crucible. Sodium telluride and sulphide are thereby produced, and metallic bismuth is set free. The fused mass is dis- solved in water, and the solution freely exposed to the air, when the sodium and sulphur oxidize to sodium hydrate and hyposulphite, while the tellu- rium separates in the metallic state. Tellurium has the color and lustre of silver ; by fusion and slow cooling it may be made to exhibit the form of rhombohedral crystals similar to those of antimony and arsenic. It is brittle, and a comparatively bad con- ductor of heat and electricity: it has a density of 6-26, melts at a little below a red-heat, and volatilizes at a higher temperature. Tellurium burns when heated in the air, and is oxidized by nitric acid. Tellurium forms two oxides, analogous in composition to the oxides of sulphur, and likewise forming acids by combination with water. Composition by weight.* Tellurium. Oxygen. Hydrogen. Tellurous oxide . . .128 82 acid . . 128 + 48 + Telluric oxide . . .128 + 48 - acid . . . 128+64 + 2 TELLUROUS OXIDE may be prepared by heating the precipitated acid to low redness. It also separates in semi-crystalline grains from the aqueous solution of the acid when gently heated ; more abundantly and in well defined octohedrons from the solution of tellurous acid in nitric acid. It is fusible and volatile, slightly soluble in water, but does not redden litmus. When fused with alkaline hydrates or carbonates, it forms tellurites. TELLUROUS ACID is best obtained by decomposing tellurium tetrachloride with water. It may also be prepared by dissolving tellurium in nitric acid of spec. gr. 1-25, and pouring the solution, after a few minutes, into a mass of water. By either process it is obtained as a somewhat bulky pre- cipitate, which, when dried over oil of vitriol, appears as a light, white, earthy mass, having a bitter metallic taste. It is slightly soluble in water, more easily soluble in alkalies and acids, the nitric acid solution alone being unstable. Sulphurous acid, zinc, phosphorus, and other reducing agents, precipitate metallic tellurium from the acidified solution of tellurous acid. Like selenious acid, it is decomposed by hydrogen sulphide and alkaline sulph-hydrates, with formation of a dark-brown tellurium sulphide, which dissolves readily in excess of alkaline sulph-hydrate, forming a sulpho- tellurite. Tellurous acid is a hydrate in which the acid and basic tendencies are nearly balanced ; in other words, the tellurium of the compound can replace the hydrogen of an acid to form tellurous salts, and the hydrogen of the compound can be replaced by the basylous metals, to form metallic tellu- rites.f The tellurites of potassium, sodium, barium, strontium, and cal- * Tellurous oxide Te0 9 acid Te0 3 H 2 = Te0 2 .OH 2 . f TELLURIUM SALTS. Te(S0 4 ) 2 Sulphate. Te(N0 3 ) 4 Nitrate. Te(C 2 4 ) 2 Oxalate. Chloride. Telluric oxide Te0 3 acid Te0 4 H 2 = Te0 3 .OH 2 . ssr TELLURITES. Te0 3 H 2 Hydrogen tellurite. Te0 3 K 2 Potassium tellurite. To0 3 KH Hydrogen and potassium tellurita (Te0 3 ) 2 KH 8 Trihydropotassic tellurite. TELLURIUM. 207 cium, are formed by fusing tellurous oxide, or acid, with the carbonates of the several metals in the required proportions. These tellurites are all more or less soluble in water. The tellurites of the other metals, which are insoluble, are obtained by precipitation. TELLURIC OXIDE AND ACID. Equal parts of tellurous oxide and sodium carbonate are fused, and the product is dissolved in water; a little sodium hydrate is added, and a stream of chlorine passed through the solution. The liquid is next saturated with ammonia, and mixed with solution of barium chloride, by which a white insoluble precipitate of barium tellurate is thrown down. This is washed and digested with a quarter of its weight of sulphuric acid, and diluted with water. The filtered solution gives, on evaporation in the air, large crystals of telluric acid, containing water of crystallization.* Crystallized telluric acid is freely, although slowly, soluble in water ; it has a metallic taste, and reddens litmus-paper. The crystals give off their water of crystallization at 100, and the remaining acid, when strongly heated, gives off more water and yields the anhydrous oxide, which is then insoluble in water, and even in a boiling alkaline liquid. At the temperature of ignition, telluric oxide loses oxygen, and passes into tellurous oxide. The tellurates of the alkali-metals f are soluble in water, and are prepared by dissolving the required quantities of telluric acid and an alkaline car- bonate in hot water. The other tellurates are insoluble, and are obtained by precipitation. TELLURIUM SULPHIDES. J Tellurium forms two sulphides, analogous in composition to the oxides ; they are formed by the action of hydrogen sul- phide on solutions of tellurous acid and telluric acid respectively. They are brown or black substances, which unite with metallic sulphides, forming salts called sulphotellurites and sulphotellurates. HYDROGEN TELLURIDE. Tellurhydric acid, Hydrotelluric add, or Telluretled Hydrogen. \ This compound is a gas, resembling sulphuretted and seleni- etted hydrogen. It is prepared by the action of hydrochloric acid on zinc telluride. It dissolves in water, forming a colorless liquid, which precipi- tates most metals from their solutions, and deposits tellurium on exposure to the air. TELLURIUM CHLORIDES. || Tellurium forms a dichloride and a tetra- chloride, both volatile and decomposable by excess of water, the latter being completely resolved into tellurous and hydrochloric acids. \ The tetra- chloride unites with the chlorides of the alkali-metals, to form crystallizable double salts. The bromides and iodides of tellurium correspond to the chlorides in prop- erties and composition. * Crystallized telluric acid, Te0 4 H*20H s ; acid dried at 100, Te0 4 Hfc. t Neutral potassium tellurate .... TV0 4 K 3 T Acid Te0 4 KII Quadracid . Te0 4 KH.Te0 4 H a Anhydrous quadri tellurate Te0 4 K 2 .3Te0 4 . t TeS and TeS 2 . TeH. || TeCl 2 and TeCl 4 . fiTeC'li + 3H 2 = 411C1 + Te0 8 H 2 . 208 BOKIC OXIDE. BORON. This element, the basis of boric or boracic acid, is prepared by heating the double fluoride of boron and potassium with metallic potassium in a small iron vessel, and washing out the soluble salts with water. It is a dull, greenish-brown powder, which burns in the air when heated, producing boric oxide. Nitric acid, alkalies in the fused state, chlorine, and other agents, attack it readily. By a process analogous to that adopted for the preparation of the diamond variety of silicium, Wohler and Deville have procured also the correspond- ing modification of boron. It crystallizes in square octohedrons, generally of a brownish color, possessing very nearly the hardness and refractive power of diamond. It is infusible in the flame of the oxy-hydrogen blow- pipe, but burns in oxygen at the same temperature at which the diamond is oxidized. Its specific gravity is 2-68. By fusing boric oxide with aluminium, Wohler and Deville likewise ob- tained, together with diamond boron, a small quantity of graphite-like substance which they at first regarded as a graphitoidal modification of boron ; but by more recent experiments, they have found that it is a com- pound of boron with aluminium. This compound is obtained in larger quantity by passing the vapor of boric chloride over fused aluminium. It crystallizes in thin opaque six-sided plates, having a pale copper-color, and perfect metallic lustre. BORIC OXIDE AND ACID.* There is but one oxide of boron, namely, boric oxide, containing 11 parts of boron and 48 of oxygen. It unites with water and metallic oxides, forming boric acid and metallic borates. Boric or Boracic Acid, or Hydrogen Borate, contains 11 parts boron, 48 oxygen, and 3 hydrogen, or 7 parts boric oxide, and 54 water. It is found in solution in the water of the hot volcanic lagoons of Tuscany, whence a large supply is at present derived. It is also easily made by decomposing with sulphuric acid a hot solution of borax, a salt brought from the East Indies, consisting of sodium borate. Boric acid crystallizes in transparent colorless plates, soluble in about 25 parts of cold water, and in a much smaller quantity at the boiling heat; the acid has but little taste, and feebly affects vegetable colors. When heated, it loses water, and melts to a glassy transparent mass of anhydrous boric oxide, which dissolves many metallic oxides with great ease. The crystals dissolve in alcohol, and the solution burns with a green flame. Glassy boric oxide, in a state of fusion requires for its dissipation in vapor a very intense and long-continued heat ; the aqueous solution cannot, however, be evaporated without very appreciable loss by volatilization: hence it is probable that the acid is far more volatile than the anhydrous oxide. By heating in a glass flask or retort, 1 part of vitrified boric oxide, 2 of fluor-spar, and 12 of oil of vitriol, a gaseous boron fluoride^ may be obtained, and received in glass jars standing over mercury. It is a transparent gas, easily soluble in water, and very heavy ; it forms a dense fume in the air, like the fluoride of silicium. BORON NITRIDE. J This compound, containing 11 parts of boron and 14 t nitrogen, is produced by heating boric oxide with metallic cyanides, or * Boric oxide, B 2 3 . Boric acid, B 2 3 , 3H 2 0, or B0 3 H 3 . B *3- J BN. SILICIUM. 209 by heating to bright, redness a mixture of sal-ammoniac and pure anhy- drous borax.* It is a white amorphous powder, insoluble in water, infus- ible and non-volatile. When heated in a current of steam, it yields ammonia and boric oxide,f and likewise gives off a large quantity of ammonia when fused with potash. Boron Chloride^ was formerly believed to be a permanent gas : recent re- searches have proved that it is a liquid, boiling at 17, decomposed by water, with production of boric and hydrochloric acids, and fuming strongly in the air. It may be most easily obtained by exposing to the action of dry chlorine at a very high temperature an intimate mixture of glassy boric oxide and charcoal. It resembles in constitution the lower chloride of phosphorus. There is also a Boron bromide $ of similar constitution. SILICIUM. Silicium, sometimes called silicon, in union with oxygen constituting silica, or the earth of flints, is a very abundant substance, and one of great importance. It enters largely into the composition of many of the rocks and mineral masses of which the surface of the earth is composed. The following process yields silicium most readily. The double fluoride of si- licium and potassium is heated in a glass tube with nearly its own weight of metallic potassium ; violent reaction ensues, and silicium is set free. When cold, the contents of the tube are put into cold water, which removes the saline matter and any residual potassium, and leaves the silicium un- touched. So prepared, silicium is a dark-brown powder, destitute of lustre. Heated in the air, it burns, and becomes superficially converted into silica. It is also acted upon by sulphur and by chlorine. When silicium is strongly heated in a covered crucible, its properties are greatly changed; it becomes darker in color, denser, and incombustible, refusing to burn even when heated by the flame of the oxy-hydrogen blowpipe. According to recent researches by Wohler and Deville, silicium, like carbon, is capable of existing in three different modifications. The modi- fication above mentioned corresponds to the amorphous variety of carbon (lampblack). The researches just quoted have established the existence of modifications corresponding to the diamond, and to the graphite variety of carbon. The diamond modification of silicium is most readily obt a ined by introducing into a red-hot crucible a mixture of 3 parts of potassium silico-fluoride, 1 part of sodium in small fragments, and 1 part of granu- lated zinc, and heating to perfect fusion. On slowly cooling, there is formed a button of zinc, covered and interspersed with needle-shaped crystals consisting of octohedrons, joined in the direction of the axis. This crystallized silicium, which may be readily freed from zinc by treatment with acids, resembles crystallized haematite in color and appearance: it scratches glass, and fuses at a temperature approaching the melting-point 2NH 4 C1 ^ nnii 1 )iiintu - 2BN + B-Os Boron Boric Sodium chloride. nitride. oxide. chloride. 30H 2 Water. 2XTI :i + Ammonia. R,0, Boric oxide. I BBr a . * Nao0.2B 2 3 -t- 2NII 4 C1 = 2BN B,O, h wn, Anhydrous ~.-...ii n,>r.ti Boric sodium borate. t 2BN + Boron nitride. J BC1,. 18* 210 SILICA. of cast iron. The graphite modification of silicium is prepared by fusing, in a Hessian crucible, 5 parts of soluble glass (potassium silicate), 10 parts of cryolite (sodium and aluminium fluoride), with 1 part of aluminium. On treating the resulting button of aluminium with hydrochloric acid, the silicium remains in the form of scaly crystals, resembling graphite, but of somewhat brighter color, scratching glass, like the previous modification. It is infusible. Its specific gravity is 2-49. SILICA, or SILICIC OXIDE. This is the only known oxide; it contains 28 parts silicium and 82 parts oxygen.* Color- less transparent rock-crystal consists of silica very nearly in a state of purity; common quartz, agate, chalcedony, flint, and several other minerals, are also chiefly composed of this substance. The experiment about to be described furnishes silica in a state of complete purity, and at the same time exhibits one of the most remarkable properties of silicium namely, its at- traction for fluorine. A mixture is made of equal parts fluor- spar and glass, both finely powdered and introduced into a glass flask, with a quantity of oil of vitriol. A tolerably wide bent tube, fitted to the flask by a cork, passes to the bottom of a glass jar, into which enough mercury is poured to cover the extremity of the tube. The jar is then half filled with water, and heat is applied to the flask. The first effect is the disengagement of hydrofluoric acid : this sub- stance, however, finding itself in contact with the silica of the powdered glass, undergoes decomposition, water and silicium fluoride being produced. The latter is a permanent gas, which escapes from the flask by the bent tube. By contact with a large quantity of water, it is in turn decomposed, yield- ing silica, which separates in a beautiful gelatinous condition, and an acid liquid, which is a double silicium and hydrogen fluoride, commonly called hydrofluosilicic or silicofluoric acid.f The silica may be collected on a cloth filter, well washed, dried, and heated to redness to expel water. The acid liquid is kept as a test for barium and potassium, with which it forms nearly insoluble precipitates, the double fluoride of silicium and potassium being used, as was stated, in the preparation of silicium. Sili- cium fluoride, instead of being condensed into water, may be collected over mercury : it is a permanent gas, destitute of color, and very heavy. Ad- mitted into the air, it condenses the moisture of the latter, giving rise to a thick white cloud. It is important in the experiment above described to keep the end of the delivery-tube from touching the water of the jar, other- wise it almost instantly becomes stopped : the mercury effects this object, Pure silica may also be prepared by another method, which is very in- structive, inasmuch as it is the basis of the proceeding adopted in the ana- lysis of all siliceous minerals. Powdered rock-crystal or fine sand is mixed with about three times its weight of dry sodium carbonate, and the nixture fused in a platinum crucible. When cold, the glassy mass is boiled with water, by which it is softened and almost entirely dissolved. An ex- it hydrochloric acid is then added to the filtered liquid, and the whole * Si0 2 . t (1) Reaction of hydro-fluoric acid upon silica + Si0 2 - 20II 2 + SiF 4 Hydrofluonc gUfol Water. * Silicfum acid - fluoride. (2) Decomposition of fluoride of silicium by water: SiP 4 + OJJ - S i silicic acid. COMPOUNDS OF SILICIUM. 211 evaporated to complete drynes.s. By this treatment the gelatinous silica thrown down by the acid becomes completely insoluble, and remains behind when the dry saline mass is treated with acidulated water, by which the alkaline salts, alumina, ferric oxide, lime, and many other bodies which may happen to be present, are removed. The silica is washed, dried, and heated to redness. The most prominent characters of silica are the following: it is a very fine, white, tasteless powder, having a density of about 2 -60, fusible only by the oxy-hydrogen blowpipe. When once dried, silica is not sensibly soluble in water or dilute acids (with the exception of hydrofluoric acid). But on adding hydrochloric acid to a very dilute solution of potassium sili- cate, the liberated silica remains in solution. From this mixed solution of silica and potassium chloride, the latter may be separated by diffusion (comp. p. 149), whereby a moderately concentrated solution of silica in water is obtained. This solution has a distinctly acid reaction : it presents, however, but little stability. When kept for some time, it gelatinizes, the silica separating in the insoluble modification. The same effect is produced by the addition of a few drops of sulphuric or nitric acid, or of a solution of salt. Silica is essentially an acid oxide, forming salts with basic metallic oxides, and decomposing all salts of volatile acids when heated with them. In strong alkaline liquids it is freely soluble. When heated with bases, especially those which are capable of undergoing fusion, it unites with them and forms salts, which are sometimes soluble in water, as in the case of the potassium and sodium silicates, when the proportion of base is con- siderable. Common glass is a mixture of several silicates, in which the reverse of this happens, the silica being in excess. Even glass, however, is slowly acted upon by water. Finely divided silica is highly useful in the manufacture of porcelain. SILICIUM HYDRIDE, or SILICATED HYDROGEN, was discovered by Buff and Wohler, who obtained this gas by passing an electric current through a solution of sodium chloride, the positive pole employed consisting of alu- minium containing silicium. More recently Wohler and Martius produced this gas by treating magnesium containing s-dlicium with hydrochloric acid. Both methods yield silicium hydride mixed with free hydrogen. Friedel and Ladenburg, however, by a process which will be described further on, have obtained it pure, and shown that it consists of 28 parts by weight of silicium and 4 parts of hydrogen.* Silicium hydride is a colorless gas. In the impure state, as obtained by the two processes above given, it takes fire spontaneously on coming in contact with the air, and burns with a white flame evolving clouds of silica. Pure silicium hydride, however, does not ignite spontaneously under the ordinary atmospheric pressure ; but on passing a bubble of air into the rarefied gas standing over mercury, it takes fire, and yields a deposit of amorphous silicium mixed with silica. On passing silicium hydride through a red-hot tube, it is decomposed, silicium being deposited. COMPOUNDS OF SILICIUM AND CHLORINE. Silicium unites directly with chlorine, forming a tetrachloride.f This compound is obtained by mixing finely divided silica with charcoal powder and oil, strongly heating the mixture in a covered crucible, and then exposing the mass so obtained in a porcelain tube heated to full redness, to the action of perfectly dry chlorine gas. A good condensing arrangement, supplied with ice-cold water, must be connected with the porcelain tube. The product is a colorless and very volatile liquid, boiling at 50, of pungent, suffocating odor. In contact * SiH<. t Si01 4 . 212 PHOSPHORUS. with water, it yields hydrochloric acid and gelatinous silica. This sub- stance contains 28 parts silicium and 142 chlorine. When hydrochloric acid gas is passed over crystallized silicium, heated to a temperature below redness, a very volatile inflammable liquid is ob- tained, which, when purified by distillation, has the composition of silicium hydrolrichloride,* containing 28 parts silicium, 1 hydrogen, and 106-5 chlorine. This compound is decomposed by water, forming a white oxy- genated body, probably silicium hydrotrioxide,^ which by prolonged contact with water is further decomposed, with evolution of hydrogen and forma- tion of silica. A mixture of silicium hydrotrichloride and bromine, heated to 100 in a closed vessel, becomes dark-colored, and is converted into the bromotri- chloride. J Silicium tetrabromide,% obtained like the tetrachloride, resembles that compound, but is less volatile. PHOSPHORUS, Phosphorus in the state of phosphoric acid is contained in the ancient unstratified rocks, and in the lavas of modern origin. As these disintegrate and crumble down into fertile soil, the phosphates pass into the organism of plants, and ultimately into the bodies of the animals to which these latter serve for food. The earthy phosphates play a very important part- in the structure of the animal frame, by communicating stiffness and in- flexibility to the bony skeleton. Phosphorus was discovered in 1669 by Brandt, of Hamburg, who pre- pared it from urine. The following is an outline of the process now adopted. Thoroughly calcined bones are reduced to powder, and mixed with two thirds of their weight of sulphuric acid diluted with a considerable quantity of water: this mixture, after standing some hours, is filtered, and the nearly insoluble calcium sulphate is washed. 14 - The liquid is then evaporated to a syrupy con- sistence, mixed with charcoal powder, and the desiccation completed in an iron vessel exposed to a high temperature. When quite dry, it is transferred to a stoneware retort, to which a wide, bent tube is luted, dipping a little way into the water contained in the receiver. A narrow tube serves to give issue to the gases, which are conveyed to a chimney. This manu- facture is now conducted on a very large scale, the consumption of phosphorus, for the appar- ently trifling article of instantaneous-light matches, being something prodigious. Phosphorus, when pure, very much resembles in appearance imperfectly bleached wax, and is soft and flexible at common temperatures. Its density is 1-77, and that of its vapor 4-35, air being unity, or 62 referred to hydrogen as unity. It melts at 44 (111 F.), and boils at 280 (536 F.). On slowly cooling melted phosphorus, well formed dodecahedrons are some- times obtained. It is insoluble in water, and is usually kept immersed in * SiHCl 3 . SiBr<. PHOSPHORUS. 213 that liquid, but dissolves in oils, in native naphtha, and especially in car- bon bisulphide. When set on fire in the air, it burns with a bright flame, generating phosphoric oxide. Phosphorus is exceedingly inflammable; it sometimes takes fire by the heat of the hand, and demands great care in its management ; a blow or hard rub will very often kindle it. A stick of phosphorus held in the air always appears to emit a whitish smoke, which in the dark is luminous. This effect is chiefly due to a slow combustion which the phosphorus undergoes by -the oxygen of the air, and" upon it depends one of the methods employed for the analysis of air, as already described. It is singular that the slow oxidation of phosphorus may be entirely prevented by the presence of a small quantity of olefiant gas, or the vapor of ether, or some essential oil; phosphorus may even be distilled in an atmosphere containing vapor of oil of turpentine in considerable quantity. Neither does the action go on in pure oxygen at least, at the temperature of 15-5 (60 F.), which is very remarkable; but if the gas be rarefied, or diluted with nitrogen, hydrogen, or carbonic acid, oxidation is set up. A very remarkable modification of this element is known by the name of amorphous phosphorus. It was discovered by Schrotter, and may be made by exposing common phosphorus for fifty hours to a temperature of from 240 to 250, (464-482 F .), in an atmosphere which is unable to act chem- ically upon it. At this temperature it becomes red and opaque, and insol- uble in carbon bisulphide, whereby it may be separated from ordinary phosphorus. It may be obtained in compact masses when common phos- phorus is kept for eight days at a constant high temperature. It is a coher- ent, reddish-brown, infusible substance, of specific gravity between 2-089 and 2-106. It does not become luminous in the dark until its temperature is raised to about 200, nor has it any tendency to combine with the oxygen of the air. When heated to 260 (500 F.), it is reconverted into ordinary phosphorus. Compounds of Phosphorus and Oxygen. When phosphorus is melted beneath the surface of hot water, and a stream of oxygen gas forced upon it from a bladder, combustion ensues, and the phosphorus is converted in great part into a brick-red powder, which was formerly believed to be a peculiar oxide of phosphorus ; but Schrotter has shown that it is a mixture, consisting chiefly of amorphous phosphorus. There are two definite oxides of phosphorus, in which the quantities of oxygen united with the same quantity of phosphorus are to one another as 3 to 5,* viz. : Composition by weight. Phosphorus. Oxygen. Phosphorus Trioxide, or Phosphorous oxide 62 -4- 48 Phosphorus Pentoxide, or Phosphoric oxide 62 -\~ 80 Both these are acid oxides, uniting with water and metallic oxides to form salts, called phosphites said phosphates respectively; the hydrogen salts being also called phosphorous and phosphoric acid. There is also another oxygen-acid of phosphorus, containing a smaller proportion of oxygen, called hypophosphorous acid, to which there is no corresponding anhydrous oxide. Hypophosphorous Acid, f When phosphorus is boiled with a solution of * In symbols : Phosphorous oxide .... Pa0 3 Phosphoric oxide PS^B- f Hypophosphorous acid . . . P0 2 H 3 . 214 PHOSPHORUS. potash or baryta, water is decomposed, giving rise to phosphoretted hy- drogen, phosphoric acid, and hypophosphorous acid; the first escapes as gas, and the two acids remain as barium salts.* By filtration the soluble hyp'ophosphite is separated from the insoluble phosphate. On adding to the liquid the quantity of sulphuric acid necessary to precipitate the base, the hypophosphorous acid is obtained in solution. By evaporation it may be reduced to a syrupy consistence. The acid is very prone to absorb more oxygen, and is therefore a powerful deoxidizing agent. All its salts are soluble in water. PHOSPHOROUS OXIDE is formed by the slow combustion of phosphorus in the atmosphere; or by burning that substance by means of a very limited supply of dry air, in which case it is anhydrous, and presents the aspect of a white powder. Phosphorous acid is most conveniently prepared by adding water to the trichloride of phosphorus, when mutual decomposition takes place, the oxygen of the water being transferred to the phosphorus, generating phosphorous acid, and its hydrogen to the chlorine, giving rise to hydrochloric acid.f By evaporating the solution to the consistence of syrup, the hydrochloric acid is expelled, and the residue, on cooling, crj-stallizes. Phosphorous acid is very deliquescent and very prone to attract oxygen and pass into phosphoric acid. When heated in a close vessel, it is resolved into phosphoric acid and pure phosphoretted hydrogen gas. It is composed of 110 parts of phosphorous oxide and 54 parts of water, or, 31 phosphorus, 48 oxygen, and 3 hydrogen.;); The phosphites are of little importance. PHOSPHORIC OXIDE (also called Anhydrous Phosphoric Acid, or Phosphoric Anhydride). When phosphorus is burned under a bell-jar by the aid of a copious supply of dry air, snow-like phosphoric oxide is produced in great quantity. This substance exhibits as much attraction for water as sulphuric oxide: exposed to the air for a few moments, it deliquesces to a liquid, and when thrown into water, combines with the latter with explosive violence. The water then taken up cannot again be separated. When nitric acid of moderate strength is heated in a retort with which a receiver is connected, and fragments of phosphorus are added singly, taking care to suffer the violence of the action to subside between each addition, the phosphorus is oxidized to its maximum, and converted into phosphoric acid. By distilling oif the greater part of the acid, transferring the residue in the retort to a platinum vessel, and then cautiously raising the heat to redness, the acid may be obtained pure. This is the glacial phosphoric acid of the Pharmacopoeia. A third method consists in taking the acid calcium phosphate produced by the action of sulphuric acid on bone-earth, precipitating it with a slight excess of ammonia carbonate, separating by a filter the insoluble calcium- salt, and then evaporating and igniting in a platinum vessel the mixed phosphate and sulphate of ammonia. Phosphoric acid alone remains behind. The acid thus obtained is not remarkable for its purity. One of the most advantageous methods of preparing phosphoric acid on the large scale in a state of purity is to burn phosphorus in a stream of dry atmos- pheric air, by the aid of a proper apparatus, not difficult to contrive, in which the process may be carried on continuously. The phosphoric oxide * P 8 + Phosphorus. t PC1 3 Phosphorus trichloride. = 2P0 3 II 3 . 3BaH 2 2 Barium + 6H 2 = Water. 3BaH 4 (P0 2 ) 2 4 Barium - 2PH 3 Hydrogen hydrate. hydrophosphite. phosphide. 30H 2 Water. = P0 3 H 3 - Phosphorous f 3HC1 Hydrochloric acid. acid. PHOSPHORUS. 215 obtained may be preserved in that state, or converted into hydrate or glacial acid, by the addition of water and subsequent fusion in a platinum vessel. The glacial phosphoric acid is exceedingly deliquescent, and re- quires to be kept in a closely stopped bottle. It contains 142 parts of phos- phoric oxide and 18 parts of water, or 31 phosphorus, 48 oxygen, and 1 hydrogen.* Phosphoric oxide is readily volatilized, and may be sublimed by the heat of an ordinary spirit-lamp. The acid may be fused in a platinum crucible at a red heat; at this temperature, it evolves considerable quan- tities of vapor, but is still far from its boiling-point. Phosphoric acid is a very powerful acid : being less volatile than sulphuric acid, it expels the latter at higher temperatures, although it is displaced by sulphuric acid at the common temperature. Its solution has an intensely sour taste, and reddens litmus-paper; it is not poisonous. The best reagent for the detection of phosphoric acid is molybdate of ammonia. A solution of this salt is treated with hydrochloric or nitric acid until the precipitate at first formed is redissolved. A very small quantity of the liquid to be tested for phosphoric acid is then added to this solution. If phosphoric acid be present, the liquid becomes yellow, and a yellow deposit, consisting of molybdic acid, phosphoric acid, and ammonia, is formed, even if the quantity of phosphoric acid be very small. There are few bodies that present a greater degree of interest to the chemist than this substance : the changes its compounds undergo by the action of heat, chiefly made known to us by the admirable researches of Professor Graham, will be described in connection with the general his- tory of saline compounds. Compounds of Phosphorus and Hydrogen. PHOSPHORUS TRIHYDRIDE. PHOSPHINE. PHOSPHORETTED HYDROGEN. This body is analogous in some of its chemical relations to ammoniacal gas ; its alkaline properties are, however, much weaker. It may be obtained in a state of purity by heating phosphorous acid in a small retort, the acid being then resolved into phosphoretted hydrogen and phosphoric acid.f Thus obtained, the gas has a density of 1-24. It contains 31 parts phos- phorus and 3 parts hydrogen, and is so constituted that every two volumes contain 3 volumes of hydrogen and half a volume of phosphorus vapor, condensed into two volumes. It possesses a highly disagreeable odor of garlic, is slightly soluble in water, and burns with a brilliant white flame, forming water and phosphoric acid. Phosphoretted hydrogen may also be produced by boiling together, in a retort of small dimensions, caustic potash or slaked lime, water, and phos- phorus: the vessel should be filled to the neck, and the extremity of the latter made to dip into the water of the pneumatic trough. In the reaction which ensues, the water is decomposed, and both its elements combine with the phosphorus. f Hydrogen __ -^-- j Phosphoretted hydrogen. ' I Oxygen Phosphorus Phosphorus Lime ~ ' Cnl" 1 '" hypophosphite.J * P 2 6 .H 2 2P0 3 H. t 4P0 3 H 3 Phosphorous = PH 3 + Phosphine. 3P0 4 TI 3 Phosphoric acid. acid. t PS H Phosphorus. 3CaH 2 2 Calcium hydrate. + 60H 2 Water, = 2PH 3 -4 Phosphine. 3P 2 4 CaTI 4 Calcium hypo- phosphite. 216 PHOSPHOEUS. The phosphoretted hydrogen prepared by the latter process has the sin- gular property of spontaneous inflammability when admitted into the air or into oxygen gas ; with the latter, the experiment is very beautiful, but requires caution : the bubbles should be admitted singly. When kept over water for some time, the gas loses this property, without otherwise suffer- ing any appreciable change ; but if dried by calcium chloride, it may be kept unaltered for a much longer time. M. Paul Thenard has shown that the spontaneous combustibility of the gas arises from the presence of the vapor of a liquid hydrogen phosphide, which can be procured in small quantity, by conveying the gas produced by the action of water on calcium phosphide through a tube cooled by a freezing mixture. This substance forms a colorless liquid of high refractive power and very great volatility. It does not freeze at 17-8 (0 F.) In contact with air, it inflames instantly, and its vapor in very small quantity communicates spontaneous inflamma- bility to pure phosphoretted hydrogen, and to all other combustible gases. It is decomposed by light into gaseous phosphoretted hydrogen, and a solid phosphide which is often seen on the inside of jars containing gas which, by exposure to light, has lost the property of spontaneous inflam- mation. Strong acids occasion its instantaneous decomposition. It is as unstable as hydrogen dioxide. It is to be observed that the pure phospho- retted hydrogen gas itself becomes spontaneously inflammable if heated to the temperature of boiling water.* Phosphoretted hydrogen decomposes several metallic solutions, giving rise to precipitates of insoluble phosphides. With hydriodic acid it forms a crystalline compound somewhat resembling sal-ammoniac. Compounds of Phosphorus with Chlorine. Phosphorus forms two chlorides, analogous in composition to the oxides, the quantities of chlorine combined with the same quantity of phosphorus being to one another in the proportion of 3 to 5. PHOSPHORUS TRICHLORIDE, or PHOSPHOROUS CHLORIDE, } is prepared in the same manner as sulphur bichloride, by gently heating phosphorus in dry chlorine gas. the phosphorus being in excess; or by passing the vapor of phosphorus over fragments of calomel (mercurous chloride) contained in a glass tube, and strongly heated. It is a colorless, thin liquid, which fumes in the air, and has a powerful and offensive odor. Its specific gravity is 1.45. Thrown into water, it sinks to the bottom of that liquid, and is slowly decomposed, yielding phosphorous acid and hydrochloric acid.J It contains 31 parts phosphorus and 106-5 parts chlorine. PHOSPHORUS PENTACHLORIDE, or PHOSPHORIC CHLORIDE, $ is formed when phosphorus is burned in excess of chlorine. Pieces of phosphorus are in- troduced into a large tubulated retort, which is then filled with dry chlorine gas. The phosphorus takes fire, and burns with a pale flame, forming a white volatile crystalline sublimate, which is the pentachloride. It may be obtained in larger quantity by passing a stream of dry chlorine gas into the preceding liquid trichloride, which becomes gradually converted into a solid crystalline mass. Phosphorus pentachloride is decomposed by water, yielding phosphoric and hydrochloric acids. || * Ann. Chim. Phys., 3d scries, xiv. 5. According to M. P. Thgnard, the liquid phosphide of hydrogen contains PH 2 and the solid P 2 H. The gas is represented by the formula PH 3 . t PC1 8 . I PC1 8 + 30H 2 = 3HC1 + P0 3 H 3 . ? PC1 5 . | PC1 5 + 40H 2 = 5HC1 + P0 4 H 3 . PHOSPHORUS. 217 PHOSPHORUS OXYCHLORIDE.* When phosphorus pentachloride is heated with a quantity of water insufficient to convert it into phosphoric acid, it yields, together with hydrochloric acid, a compound of phosphorus, chlo- rine, and oxygen. This body may also be prepared by distilling the pen- tachloride with dehydrated oxalic acid, or by distilling a mixture of phos- phorus pentachloride and phosphoric oxide. Phosphorus oxychloride is a colorless liquid of sp. gr. 1-7, possessing a very pungent odor, and boiling at 110 (230 F.). It is readily decomposed by water into hydrochloric and phosphoric acids. A sulphochloride f of analogous composition is produced by the action of hydrogen sulphide on the pentachloride. It is a colorless, oily liquid, decomposed by water. Two bromides of phosphorus, an oxybromide and a sulphobromide, are known, corresponding in composition and properties with the chlorine compounds, and obtained by similar processes. Phosphorus forms also two iodides^ containing 31 parts of phosphorus with 2 X 127 and 3 X 127 parts of iodine. The latter is analogous in composition to the trichloride ; the former has no chlorine representative. Both these compounds are obtained by dissolving phosphorus and iodine together in carbon bisulphide, and cooling the liquid till crystals are de- posited. Whatever proportions of iodine and phosphorus may be used, these two compounds always crystallize out, mixed with excess either of iodine or of phosphorus. The di-iodide melts at 110 (230 F.), forming a red liquid which condenses to a light red solid. The tri-iodide melts at 55 (131 F.), and crystallizes on cooling in well denned prisms. Both are decomposed by water, yielding hydriodic and phosphorous acids, the di-iodide also depositing yellow flakes of phosphorus. Compounds of Phosphorus with Sulphur and Selenium. SULPHIDES. When ordinary phosphorus and sulphur are heated together in the dry state, or melted together under water, combination takes place between them, attended with vivid combustion and often with violent ex- plosion. AVhen amorphous phosphorus is used, the reaction is not explosive, though still very rapid. Six compounds of sulphur and phosphorus have been prepared, contain- ing the following proportions of sulphur and phosphorus, g Composition by weight. Phosphorus. Sulphur. Hemisulphide . . . . . 31 -(- Monosulphide . . . . . 31 -j- 16 Sesquisulphide 31 24 Trisulphide 31 48 Pentasulphide 31 Dodecasulphide . . . . 31 -j- -^2 The fourth and fifth are analogous to phosphorus and phosphoric oxides respectively ; the others have no known analogues in the oxygen series. They may all be formed by heating the two bodies together in the required proportions; but the trisulphide and pentasulphide are more easily pre- pared by warming the monosulphide with additional proportions of sulphur. Moreover, the two lower sulphides exhibit isomeric modifications, each being capable of existing as a colorless liquid and as a red solid. The * POC1 3 . t PSC1 2 . t P1 2 and I>1 3 . P 4 S, P 2 S, P 4 S 3 , P 2 S3, P 2 S 5 , and 19 218 PHOSPHORUS. mono-, tri-, and pentasulphides of phosphorus unite with metallic sulphides, forming sulphur-salts.* SELENIDES OF PHOSPHORUS, f analogous in composition to the first, second, fourth, and fifth of the sulphides -above mentioned, are produced by heat- ing ordinary phosphorus and selenium together in the required proportions in a stream of hydrogen gas. The hemiselenide is a dark-yellow, oily, fetid liquid, solidifying at 12; the other compounds are dark-red solids. The mono-, tri-, and pentaselenides unite with metallic selenides, forming selenium-salts analogous to the sulphur-salts above mentioned. * Copper Hyposulphophosphite P 2 S2Cn = CuS.P 2 S. Copper Siilphophosphite P 2 S 4 Cu =: CuS.P 2 S 3 . Copper Sulphophosphate P~ 2 S 6 Cu = CuS.P 2 S 6 . f PSe, P 2 Se, P 2 Se 3> and P 2 Se 6 . ON THE GENERAL PRINCIPLES OF CHEMICAL PHILOSOPHY. rpHE study of the non-metallic elements can be pushed to a very consider- l able extent, and a large amount of precise and exceedingly important information acquired, without much direct reference to the great funda- mental laws of chemical union. The subject cannot be discussed in this manner completely, as will be obvious from frequent cases of anticipation .in many of the foregoing foot-notes : still, much may be done by this simple method of proceeding. The bodies themselves, in their combinations, fur- nish admirable illustrations of the general laws referred to ; but the study of their leading characters and relations does not of necessity involve a previous knowledge of these laws themselves. It is thought that by such an arrangement the comprehension of these very important general principles may become, in some measure, facili- tated by constant reference to examples of combinations, the elements and products of which have already been described. So much more difficult is it to gain a clear and distinct idea of any proposition of great generality from a simple enunciation, than to understand the bearing of the same law when illustrated by a single good and familiar instance. Before proceeding further, however, it is absolutely necessary that these matters should be discussed: the metallic compounds are so numerous, that the establishment of some general principle, some connecting link, becomes indispensable. The doctrines of equivalence and combining pro- portions, and the laws which regulate the formation of saline compounds, supply this deficiency. THE LAWS OP COMBINATION BY WEIGHT. (1.) Constancy of Composition. This is the main distinction between chemical combination and mechanical mixture, or that kind of adhesion which gives rise to the solution of a solid in a liquid. Metals may be fused together to form alloys; water may be mixed with alcohol, alcohol with ether, and diiferent oils one with the other, in any proportions whatever, the mixture always exhibiting properties intermediate between those of its constituents, and in regular gradation according to the quantity of each that may be present; a solid body may be dissolved in a liquid salt or sugar in water, for example in any proportion up to a certain limit, the solution likewise exhibiting a regular gradation of physical properties, according to the quantity of the solid taken up. But in a true chemical compound, the properties of the constituent elements admit of no variation whatever. Water, whether obtained from natural sources, or formed by direct combination of its elements, always contains in 100 parts, 88-9 parts of oxygen and 11-1 parts of hydrogen; and a piece of flint, or rock-crystal, obtained from any part of the world, invariably contains 46-6 per cent, of silicium to 53-4 of oxygen. When two or more compounds are formed of the same elements, as the oxides of carbon and the chlorides of phosphorus (pp. 1G4, 216), there is no gradual blending of one into the other, as in the case of mixtures ; but each compound is sharply defined and separated, as it were, from the others by an impassable gulf, exhibiting properties dis- 220 GENERAL PRINCIPLES OF tinct from those of the others, and of the elements themselves in the sepa- rate state. Thus of the two oxides of carbon, the monoxide is an inflam- mable gas, lighter than air, and not absorbed by solution of potash, whereas the dioxide is non-inflammable, heavier than air, and easily absorbed by potash; and both compounds differ entirely in their characters, both from carbon and from oxygen in the free state. The composition of chemical compounds is ascertained, as already ob- served, by analysis, and in some cases also by synthesis. The results are usually stated in percentages (thus, 100 parts of zinc oxide contain 80-1 parts zinc and 19 9 oxygen), which for many purposes is as convenient a method as can be adopted. But when it is desired to compare the compo- sition of several compounds of the same elements, or of the compounds formed by one element with several others, it is more convenient to start with a fixed quantity of the first element, and specify the relative quan- tities of the other element or elements which combine with it. This will be easily seen by comparing the following tabular statements of the com-, position of the five nitrogen oxides already described, first, in percentages, secondly, by stating the several quantities of oxygen which unite with 100 parts of nitrogen. ! 100 part, Nitrogen. Oxygen. Nitrogen. Oxygen. Monoxide . . 63-64 36-36 100 175 Dioxide . . . 46-67 53-33 100 350 Trioxide . . 36.85 63-15 100 525 Tetroxide . . 30-44 69-56 100 700 Pentoxide . . 25-93 74-07 100 875 The numbers on the left-hand side of the table do not exhibit any simple relation ; but on looking to the right-hand side, it is immediately seen that the quantities of oxygen which unite with the same quantity of nitrogen, are to one another as the numbers 1, 2, 3, 4, 5. And this leads us to the second general law of chemical combination, viz. : (2.) The Law of Multiples. This law may be thus stated: If two ele- ments, A and B, are capable of uniting in several proportions, the quan- tities of B which unite with a given quantity of A, usually bear a simple relation to one another, such as : A + B, A -f 2B, A + 3B, A -f- 4B, &c. ; or, 2A -f 3B, 2A -f- 5B, 2A + 7B, &c. ; or, A -f B, A + 3B, A -f 5B, &c. Numerous examples of this law are afforded by the compounds of the non-metallic elements one with the other; as, for example, the oxides of hydrogen, carbon, chlorine, sulphur, and phosphorus, the chlorides of phosphorus, &c. ; and still more numerous examples will be met with, in treating of the compounds of metals with non-metallic elements. It must be observed, however, that more complex relations are by no means unfrequent. The compounds of carbon and hydrogen, for example, are very numerous; and on comparing together the quantities of hydrogen H, which unite with a fixed quantity of carbon C, we meet with such rela- tions as 50 -f 17H, 7C + 16H, 11C + 24H, 15C + 32H, &c. In short, the simple relations above mentioned must be looked upon merely as particular instances of a large number of possible relations, although they happen to hold good with reference to a considerable number of important compounds. CHEMICAL PHILOSOPHY. 221 (3.) Law of Equivalents. If a body A unites with certain ether bodies B, C, D, then the quantities B, C, D, which combine with A, or certain simple multiples of them, represent for the most part the proportions in which they can unite amongst themselves. For example, 8 parts by weight of oxygen are known to unite with the following quantities of hydrogen, nitrogen, &c. : Oxygen 8 Hydrogen 1 Nitrogen 14 Carbon 6 Sulphur 8 Phosphorus . . . . 10J or y Chlorine 35-5 Iodine . . . . . 25f or *f Potassium .... 39 Iron 28 Copper 31-7 Lead 103-5 Silver 108 &c. &c And it is found, moreover, that hydrogen and chlorine combine in the pro- portions 1 to 35-5; hydrogen and sulphur, 1 to 2X8; chlorine and silver, 35-5 to 108; iodine and potassium, 127 parts of the former to 39 of the latter, &c. ; phosphorus and chlorine, 31 parts of the former to 3 x 35-5 and 5x355 of the latter, &c. Now, on comparing the relative quantities of the elements contained in all known chemical compounds, it is found: 1. That there is a certain number of elements which combine with one another in one proportion only. 2. That by far the greater number of elements are capable of uniting in two or more proportions. The elements of the former class may be con- veniently called monogens, those of the latter polygons.* Hydrogen and chlorine unite in the proportion of 1 part, by weight, of the former, to 35-5 p$,rts of the latter, and in no other. The same quantity of chlorine combines with 39-1 parts of potassium, 23 of sodium, and 108 of silver. These several quantities of sodium, potassium, and silver, are capable of saturating the same quantity of chlorine that is saturated by 1 part of hydrogen. They are, therefore, in this respect equivalent to 1 part by weight of hydrogen and to each other. They may, in fact, be made directly to replace one another in combination with chlorine. Thus, when sodium or potassium is heated in hydrochloric acid gas, hydrogen is set free, and sodium or potassium chloride is formed, 23 parts of sodium or 31H parts of potassium always taking the place of 1 part of hydrogen. Again, when a solution of sodium chloride is mixed with silver nitrate, the sodium and silver change places, forming a solution of sodium nitrate and a precipitate of silver chloride; and in this case 108 parts of silver take the place of 23 parts of sodium. The above-mentioned quantities of hy- drogen, chlorine, sodium, potassium, and silver, are therefore called equiva- lent weights. There are a few other monogenic elements, the names and equivalent weights of which are given, together with the preceding, in the following table : * Erlenmeyer, " Lehrbuch der organischen Chemie." 10* 222 GENERAL PRINCIPLES OF CHEMICAL PHILOSOPHY. Hydrogen ... 1 Chlorine . . . 35-5 Bromine . . .80 Fluorine ... 19 Silver . . 108 Potassium . . . 89-1 Sodium . . . 23 Lithium ... 7 Caesium . . . 133 Rubidium . 85-4 All other elements are polygenic, uniting with the monogens and with one another in more than one proportion. With regard to these elements the question of equivalence appears at first to be somewhat indeterminate; in fact, according to the idea of equivalency above defined, the equivalent value of a polygenic element must vary according to the proportions in which it unites with others. Thus iron forms two chlorides, containing 28 and 18f parts of iron to 35.5 parts of chlorine. Either of these quantities of iron may therefore be regarded as equivalent to 1 part of hydrogen ; in other words, as the equivalent weight of iron. Again, 1 part of hydrogen unites with 8 parts of oxygen to form water, and with 16 parts to form hy- drogen dioxide. Which of these is the equivalent weight of oxygen ? The former number has perhaps the best right to be so regarded, because water is a more stable compound than hydrogen-dioxide, and, moreover, 8 parts by weight of oxygen frequently take the place of 1 part of hydrogen in processes of oxidation, as when alcohol, a compound of 12 parts carbon, 3 hydrogen, and 8 oxygen, is oxidized to acetic acid, containing 12 parts car- bon, 2 hydrogen, and 16 oxygen. But what number shall we fix upon as the equivalent of nitrogen ? This element forms only one compound with hydrogen, namely, ammonia, which contains 14 parts of nitrogen to 3 of hydrogen, or 4f nitrogen to 1 hydrogen. Accordingly, the equivalent weight of nitrogen appears to be 4f , and, in fact, this quantity of nitrogen can be made to take the place of 1 part of hydrogen in many organic compounds. But if we look to the compounds of nitrogen with oxygen, we find that these elements unite in five different proportions, 8 parts of oxygen (which we have seen to be in most cases equivalent to 1 part of hydrogen) uniting with 14, 7, !/, |, or ^ parts of nitrogen, either of which numbers may therefore be regarded as equivalent to 1 part of hydrogen. Lastly, with regard to carbon, the problem appears still more indefinite, inasmuch as that element forms with hydrogen a very large number of compounds, and appears to be capable of uniting with it in almost any proportion. We may, however, obtain a set of comparable values by assuming as the equivalent weight of each polygenic element, the smallest quantity of it which unites with 1 part of hydrogen, or with 35-5 of chlorine, or generally with the equivalent weight of any monogenic element. Thus of all the compounds of hydrogen and carbon, marsh-gas, or methane, which is composed of 12 parts carbon to 4 hydrogen, or 3 parts carbon to 1 hydrogen, contains the largest quantity of hydrogen in proportion to the carbon ; in other words, 3 parts of carbon is the smallest quantity that can unite with 1 part of hydrogen This, then, we shall regard as the equivalent weight of carbon ; and by similar considerations the equivalent weight of oxygen will be found to be 8, that of sulphur 16, of nitrogen 4f or V, of phosphorus V or 64, of iron 18f, of lead 103-5, &c. ATOMIC WEIGHTS. Let us now compare the hydrogen compounds of monogenic and polygenic elements, with regard to the manner in which the hydrogen contained in them may be replaced by other elements. Com- pare first hydrochloric acid and water. When hydrochloric acid is acted upon by certain metals, as sodium, zinc, or magnesium, the whole of the hydrogen is expelled, and the chlorine enters into combination with an equivalent quantity of the metal; thus 36-5 parts of hydrochloric acid (= 1 part hydrogen -f- 35-5 chlorine) and 23 sodium yield 1 part of free ATOMIC WEIGHTS. 223 hydrogen and 23 -f- 35-5 (= 58 5) sodium chloride; there is no such thing as the expulsion of part of the hydrogen, or the formation of a compound containing both hydrogen and metal in combination with the chlorine. With water, however, the case is different. When sodium is thrown upon water, 9 parts of that compound (= 1 hydrogen -f- 8 oxygen) are decom- posed, in such a manner that half of the hydrogen is expelled by an equiv- alent quantity of sodium, , and sodium hydrate is formed containing : Sodium. Hydrogen. Oxygen. .'";+ I + 8 This compound remains in the solid state when the liquid is evaporated to dryness; and if it be further heated in a tube with sodium, the remaining half of the hydrogen is driven off, and anhydrous sodium-oxide remains, composed of 23 parts sodium -j- 8 oxygen. Water differs, therefore, from hydrochloric acid in this respect, that its hydrogen may be replaced by a monogenic metal in two equal portions, yielding successively a hydrate and an anhydrous oxide, the relations of which to the original compound may be thus represented : Water. Sodium-hydrate. Sodium-oxide. Hydrogen. Oxygen. Hyd. Sod. Ox. Sodium. Ox. or, multiplying by 2, to avoid fractions of equivalent weights: Water. Sodium-hydrate. Sodium-oxide. Hydrogen. Oxygen. Hyd. Sod. Ox. Sodium. Ox. (1 + 1) + 16 (1 + 23) + 16 (23 + 23) + 16. It appears from this that 2 x 8, or 16 parts of oxygen, is the smallest quantity of oxygen that can be supposed to enter into the reaction just considered, if we would avoid speaking of fractions of equivalents; and we shall find hereafter that the same is true with regard to all other well- defined reactions in which oxygen takes part. Hence this quantity of .oxygen 16 parts by weight (hydrogen being the unit), is called an indivisible weight, or atomic weight, or an atom of oxygen.* Let us now consider the hydrogen compound of nitrogen, that is to say, ammonia. This is composed of 1 part of hydrogen united with 4| or J g 4 of nitrogen. Now in this compound the hydrogen is replaceable by thirds. When potassium is heated in ammonia gas, a compound called potassamine is formed, in which one third of the hydrogen is replaced by potassium. Another compound, called tri-potasxamine, is also known, con- sisting of ammonia in which the whole of the hydrogen is replaced by an equivalent quantity of potassium: Nit. Hydrogen. Nit. Hydrogen. Ammonia . . + - - |- -- or 14 + 1 + 1 + 1 O O o Nit. Hydrogen. Pot. Nit. Hydrogen. Pot. 1 j 1 1 ^0 Potassamine . - + + - - + -5- or 14 + 1 + 1+39 6 & o o Nit. Potassium. Nit. Potassium. Tripotassamine ~ +??+-+-! or 14 + 39 + 39 + 89 o o o o * Aro/wj, indivisible. 224 ATOMIC WEIGHTS. There is also a large class of compounds derived from ammonia in like manner by the replacement of , f , or the whole of the hydrogen by equi- valent quantities of certain groups of elements called compound radicals (see page 237). Hence, by reasoning similar to that which was above applied to water, it is inferred that ammonia is composed of 14 parts by weight, or 3 equivalents, of nitrogen combined with 3 parts or 3 equivalents of hydro- gen, and that the atomic weight of nitrogen is 14. Next take the case of marsh-gas or methane, a compound of 1 part hydro- gen with 3 parts carbon. When this gas is mixed with chlorine, and ex- posed to diffused daylight, a new compound is formed, in which one fourth of the hydrogen belonging to the marsh-gas is replaced by an equivalent quantity of chlorine ; and if the chlorine is in excess, and the mixture ex- posed to sunshine, three other compounds are formed, in which one half, three fourths, and all the hydrogen, are thus replaced. The results may be thus expressed : Methane. Carbon. Hydrogen. Carbon. Hydrogen. + Carbon. Hydrogen. ior 12 + 1+1-j- Chloromethane. Chlorine. Carbon. Hydrogen. Chlorine. 35-5 or 12 +1+1+1 35-5 Carbon. Hydrogen. Dichloromethane. Chlorine. Carbon. Hydrogen. Chlorine. ~T~ + ~4~ or 12 + 1 + 1 + 35-5 + 35-5 3 4- 4- ^ Carbon. Hyd. Trichloromethane or Chloroform. Chlorine. Carb. Hyd. Chlorine. _ 1 , 35-5 , 35-5 + 5 35 ' 5 Chlorinje. 35 ' 5 + 35 ' 5 + 35 ' 5 Hence, by reasoning similar to the above, it is inferred that marsh-gas is composed of 12 parts by weight, or 4 equivalents of carbon, and 4 parts, or 4 equivalents of hydrogen, and that the atomic weight of carbon is 12. According to the preceding explanations, the equivalent weight of a poly- enic element is the smallest auantitv of it, thnt, n.n nnUo uii , 1 --"& v/^.^iu,Li,uiviio, i,uc cyuivuieiti iveiurti ui a poiy- genie element is the smallest quantity of it that can unite with an equiva- ic. element, that is, with 1 part of hydrogen, 35-5 parts lent of a monogenic , __ , , ilAA plll - t ux ^.u-ogen, 00 - parts )1 chlorine, &c. ; and the atomic weight, or atom, is the smallest, quantity of an element that can unite with others without introducing fractions of equivalents. In the case of a monogenic element, the atomic and equiva- lent weights are identical, but the atomic weight of a polygenic element is always greater than the equivalent weight in the ratio of 1 to 2 3 4 &c ATOMIC WEIGHTS. 225 Te have shown in three cases how the atomic weight of an element may be determined by the proportion in which equivalent substitution takes place in its compounds with hydrogen or other monogenic elements. Sul- phur, selenium, and tellurium form hydrogen compounds exactly analogous in tins respect to water, the hydrogen being replaceable by halves; their atomic weights are therefore double of their equivalent weights. Silicon forms with chlorine a compound containing 7 parts silicon with 35-5 parts chlorine ; and in this one fourth of the chlorine is replaceable by hydro- gen or by bromine: hence the atomic weight of silicon is, like that of carbon, equal to four times the equivalent weight, its numerical value being 28. There are also some elements in which the atomic weight is equal to five times, and others in which it is equal to six times, the equivalent weight; higher ratios have not been observed. It must not be supposed that the atomic weights of elementary bodies are always actually determined in the manner above described. There are several other methods of determining their numerical values, as will be presently explained ; and the values obtained by different methods do not always agree ; but the atomic weights of all the more important elements may be regarded as definitely fixed within small numerical errors. The equivalent value of an element or the ratio of the equivalent to the atomic weight, is also subject to some variation, as will be presently explained, according to the view which may be taken of the constitution of particular compounds. The table on the next page exhibits the values of the atomic weights of the elementary bodies in which chemists are now for the most part agreed ; also the abbreviated symbols (the first or first two letters of their Latin names) by which they are designated in chemical formulae. SYMBOLIC NOTATION. The symbols, H, 0, N, etc., stand, not for the names of the several elements, but for quantities of them proportional to the atomic weights. Combination between elements is represented by the juxtaposition of the symbols; thus NaCl represents sodium chloride, a compound of 23 parts by weight of sodium with 36-5 parts of chlorine. Two or more atoms of an element are represented by placing a small figure to the right of the symbol, and a little below ; thus H 2 denotes 2 atoms of hydrogen; OH 2 denotes water, a compound of 2 atoms hydrogen with 1 atom oxygen; PC1 5 , phosphorus pentachloride ; Fe 2 3 , iron sesquioxide, etc. The elements in a compound are usually placed in the order of their equi- valencies, the highest to the left; but this order is often departed from when, by so doing, the relation between two or more compounds under con- sideration can be more clearly brought to light. The union of two atomic groups, or molecules, is represented by placing their symbols together, with a point or comma between them; thus sal-am- moniac, formed by the union of ammonia, N1I 3 , and hydrochloric acid, HC1, is represented by the formula NH 8 .HC1: sulphuric acid, or hydrogen sul- phate, which may be regarded as sulphur trioxide combined with water, may be represented by the formula S0 3 .OH 2 . A number placed to the left of a group of symbols not separated by a point or comma, multiplies the entire group; thus 30H 2 denotes 3 molecules of water ; but to denote the multiplication of a molecule compounded of two other molecules, the whole formula must be enclosed in brackets, and the numeral placed to the left on the line, or to the right a little below it ; thus 2 molecules of sal-ammoniac are denoted by 2(NH 3 .HC1), or (NH 3 HC1) 2 . If the brackets were omitted in the first of these formulae, the 2 would multiply only the part of the formula to the left of the point; e. g. 30H 2 .S0 8 226 ATOMIC WEIGHTS.' TABLE OF ELEMENTARY BODIES WITH THEIR SYMBOLS AND ATOMIC WEIGHTS. Name. Symbol. Atomic Weight. Name. Symbol. Atomic Weight. Aluminium Al 27-4 Molybdenum Mo 96 Antimony (Sti- bium) Sb 122 Nickel Niobium Ni Nb 58-8 94 Arsenic As 75 Nitrogen N 14 Barium Ba 137 Osmium Os 199-2 Beryllium Bismuth Be Bi 94 210 Oxygen Palladium Pd 16 106-6 Boron B 11 Phosphorus P 31 Bromine Br 80 Platinum Pt 1974 Cadmium Cd 112 Potassium Caesium Cs 133 (Kalium) K 39-1 Calcium Ca 40 Rhodium Rh 104-4 Carbon C 12 Rubidium Rb 854 Cerium Ce 92 Ruthenium Ru 104-4 Chlorine Cl 35-5 Selenium Se 794 Chromium Cr 52-2 Silicium Si 28 Cobalt Co 58-8 Silver (Argen- Copper (Cu- tum) Ag 108 prum) Cu 634 Sodium (Na- Didymium D 95 trium) Na 23 Erbium E 112-6 Strontium Sr 87-6 Fluorine F 19 Sulphur S 32 Gold (Aurum) Au 197 Tantalum Ta 182 Hydrogen H 1 Tellurium Te 128 Indium In 74 Terbium (?) Iodine I 127 Thallium Tl 204 Iridium Ir 198 Thorinum Th 115-7 Iron (Ferrum) Fe 56 Tin (Stannum) Sn 118 Lanthanum La 93-6 Titanium Ti 50 Lead (Plum- Tungsten, or bum) Pb 207 Wolfram W 184 Lithium Li 7 Uranium U 120 Magnesium Mg 24 Vanadium V 51-2 Manganese Mn 55 Yttrium Y 61-7 Mercury (Hy- Zinc Zn 65-2 drargyrum) Hg 200 Zirconium Zr 89-6 denotes a compound of 3 molecules of water with 1 molecule of sulphur trioxide. Chemical reactions are represented by equations, in which the symbols of the acting bodies are placed on the left-hand side, and those of the bodies formed by the reaction, on the right hand, the molecules on either side being connected by the sign -(-. For example, the action of zinc on hy- drochloric acid, by which zinc chloride and free hydrogen are formed, is represented by the equation : Zn -f 2HC1 = ZnCl 2 + H 2 ; that of phosphorus pentachloride on water, which yields hydrochloric and phosphoric acids, by the equation: PC1 6 -f 40H 2 = 5HC1 P0 4 H 3 . ATOMIC WEIGHTS. 227 Numerous other examples will be found in the foot-notes to the preceding pages. Physical and Chemical Relations of Atomic Weights. We have hitherto regarded the atomic weights of the elements as mere numerical expressions, or as quantities adopted to represent the compo- sition of compounds without introducing fractions of equivalents. If this were all that could be said about them, they would not be of much impor- tance,. We shall see, however, that these same quantities exhibit some re- markable relations to the physical properties of the elements, and to the proportions in which they combine together by volume. 1. To the Specific Heat of the Elementary Bodies. The atomic weights of the elements, determined according to their modes of combination, are, for the most part, inversely proportional to their specific heats; so that the product of the specific heat into the atomic weight is a constant quantity. The same quantity of heat is required to produce a given change of tem- perature in 7 grams of lithium, 56 of iron, 207 of lead, 108 of silver, 196-7 of gold, 210 of bismuth, &c. This relation, already pointed out in the chapter on Heat (p. 73), holds good with respect to the greater number of the elements ; but it cannot be regarded as a universal law, inasmuch as three elements, carbon, silicium, and boron, whose atomic weights are well established on chemical grounds, exhibit unmistakable exceptions to it. Nevertheless, in case of doubt as to the correct determination of the atomic weight of an element according 'to its mode of combination, the agreement of the value thus obtained with the value determined according to the specific heat, is generally regarded as affording strong evidence in favor of the result. 2. To the Crystalline Forms of Compounds. It is found that, in many cases, two or more compounds which, from chemical considerations, are supposed to contain equal numbers of atoms of their respective elements, crystallize in the same or in very similar forms. Such compounds are said to be isomorphous.* Thus the sulphates represented by the general formula S0 4 M 2 (M denoting a monogenic metal) are isomorphous with the corre- sponding selenates Se0 4 M 2 ; the phosphates P0 4 M 3 are isomorphous with the corresponding arsenates As0 4 M 3 , &c. Accordingly, these isomorphous relations are often appealed to for the purpose of fixing the constitution of compounds, and thence deducing the atomic weights of their elements, in cases which would otherwise be doubt- ful. Thus aluminium forms only one oxide, viz., alumina, which is com- posed of 18-2 parts by weight of aluminium and 16 parts of oxygen. What, then, is the atomic weight of aluminium? The answer to this question will depend upon the constitution assigned to alumina, whether it is a mon- oxide, sesquioxide, dioxide, &c. Thus: 0. Al. Monoxide . A10 = 16 + 18-25 Sesquioxide A1 2 8 = 48 -f Dioxide . A10 2 = 32 -f 36-5 Trioxide . A10 3 = 48 -f 54-8 The numbers in the last column of this table ore the weights which must be assigned to the atom of aluminium, according to the several modes of constitution indicated in the first column ; but there is nothing in the con- * "looj, equal ; /*op^, form, 228 ATOMIC WEIGHTS. Btitution of the oxide itself that can enable us to decide between them. Now, iron forms two oxides, in which the quantities of oxygen united with the same quantity of iron are to one another as 1 : 1J, or as 2 : 3. These are therefore regarded as monoxide, FeO, and sesquioxide, Fe 2 3 , and this last oxide is known to be isomorphous with alumina. Consequently alumina is also regarded as a sesquioxide, A1 2 3 , and the atomic weight of aluminium is inferred to be 27-4. .. 3. To the Volume-Relations of Elements and Compounds. The atomic weights of those elements which are known to exist in the state of gas or vapor are, with one or two exceptions, proportional to their specific gravities in the same state. Taking the specific gravity of hydrogen as unity, those of the following gases and vapors are expressed by numbers identical with their atomic weights: Oxygen . Sulphur Selenium Tellurium . Hydrogen Chlorine Bromine Iodine 1 35.5 127 16 32 79 128 The exceptions to this rule are exhibited by phosphorus and arsenic, whose vapor-densities are twice as great as their atomic weights, that of phos- phorus being 62, and that of arsenic 150; and by mercury and cadmium, whose vapor-densities are the halves of their atomic weights, that of mer- cury being 100, and that of cadmium 56. LAWS OF COMBINATION BY VOLUME. From the preceding relations, it follows that the volumes of any two elementary gases which make up a compound molecule, are to one another in the same ratio as the numbers of atoms of the same elements which enter into the compound, excepting in the case of phosphorus and arsenic, for which the number of volumes thus determined has to be halved, and of mercury and cadmium, for which it must be doubled ; thus : The molecule HC1 contains 1 vol. H and 1 vol. Cl. H 2 " H 3 N H 3 P " Cl 3 As " Cl 2 Hg" If the smallest volume of a gaseous element that can enter into combi- nation be called the combining volume of that element, the law of combi- nation may be expressed as follows : The combining volumes of all elementary gases are equal, excepting those of phosphorus and arsenic, which are only half those of the other elements in the gaseous state, a?id those of mercury and cadmium, which are double those of the other elements. It appears, then, that in all cases the volumes in which gaseous elements combine together may be expressed by very simple numbers. This is the "Law of Volumes," first observed by Humboldt and Gay-Lussac in 1805, with regard to the combination of oxygen and hydrogen, and afterwards established in other cases by Gay-Lussac, whose observations, published in his "Theory of Volumes," afforded new and independent evidence of the combination of bodies in definite and multiple proportions, in corroboration of that derived from the previously observed proportions of combination by weight. Gay-Lussac likewise observed that the product of the union of two gases, 2 H 1 0. 3 H 1 N. { 3 tor6 H H 1 P. P. / 3 tor 6 Cl Cl I As. As. 2 ' Cl 2 ' Hg. ATOMIC THEORY. 229 when itself a gas, sometimes retains the original volume of its constituents, no contraction or change of volume resulting from the combination, but that when contraction takes place, which is the most common case, the volume of the compound gas always bears a simple ratio to the volumes of its elements; and subsequent observation, extended over a very large num- ber of compounds, organic as well as inorganic, has shown that, with a few exceptions, probably only apparent, the molecules of compound bodies in the gaseous state occupy twice the volume of an atom of hydrogen gas. No matter what may be the number of atoms or volumes that enter into the compound, they all become condensed into two volumes, thus: 1 vol. H and 1 vol. Cl form 2 vol. HC1. hydrochloric acid. 1 " N " 1 " " 2 " NO, nitrogen dioxide. 2 << H " 1 " " 2 " H 2 0, water. 3 " H " 1 " N " 2 " H 3 N, ammonia. 3 H i < p 2 " H 3 P, hydrogen phosphide. Similarly in the union of compound gases, e. g. 1 vol. ethyl, C 2 H 6 , and 1 vol. Cl, form 2 vol. C|H 6 C1, ethyl chloride. 2 ethyl, C 2 H 5 , 1 "2 (C 2 H 6 ) 2 0, ethyl oxide. 2 " ethene, C 2 H 4 , " 2 " Cl " 2 " C 2 H 4 C1 2 , ethene chloride. 2 " ethene, C 2 H 4 , " 1 '< "2 " C 2 H 4 0, ethene oxide. Hence it follows that the specific gravity of any compound gas or vapor, re- ferred to hydrogen as unity, is equal to half its atomic or molecular weight. The quotient obtained by dividing the molecular weight of a body by its specific gravity is called its Specific or Atomic volume; hence the law just stated may also be thus expressed: The specific volumes of compound gases or vapors referred to that of hydrogen as unity are, with a few exceptions, equal to 2. We shall presently show that the same law applies to the specific volumes of the elementary gases themselves. For many years past, attemj the results of Gay-Lussac's discovery of the law of gaseous combination by volume, the specific volumes of the bodies in question being determined by tlie method pursued in the case of gases namely, by dividing the mole- cular weight by the specific gravity. The numbers obtained in this manner, representing the specific volumes of the various solid and liquid elementary substances, present far more cases of discrepancy than of agreement. The latter are, however, sufficiently numerous to excite great interest in the in- vestigation. Some of the results pointed out are exceedingly curious as far as they go, but are not as yet sufficient to justify any general conclusion. The inquiry is beset with many great difficulties, chiefly arising from the unequal expansion of solids and liquids by heat, and the great differences of physical state, and, consequently, of specific gravity, often presented by the former. THE ATOMIC THEORY. The laws of chemical combination, and the relations between atomic and equivalent weights above explained, are the result of pure experimental in- quiry, and independent of all hypothesis. In this, however, as in other branches of science, the comprehension of experimental results may be greatly facilitated by endeavoring to refer them to a general law or mode of action. That no attempt should be made to explain the manner iu which 20 230 ATOMIC THEORY. chemical compounds are formed, and to point out the nature of the relations between the different modifications of matter which determine chemical changes, would, indeed, be contrary to the speculative tendency of the human mind. Such an attempt and a very ingenious and successful one it i 8 has, in fact, been made, namely, the atomic hypothesis of Dr. Dalton. From very ancient times, the question of the constitution of matter with respect to divisibility has been debated, some adopting the opinion that this divisibility is infinite, and others, that when the particles become reduced to a certain degree of tenuity, far, indeed, beyond any state that can be reached by mechanical means, they cease to be further diminished in magni- tude; they become, in short, atoms* Now, however the imagination may succeed in figuring to itself the condition of matter on either view, it is hardly necessary to mention that we have absolutely no means at our dis- posal for deciding such a question, which remains at the present day in the same state as when it first engaged the attention of the Greek philosophers, or perhaps that of the sages of Egypt and Hindostan long before them. Dalton's hypothesis sets out by assuming the existence of such atoms or indivisible particles, and states, that compounds are formed by the union of atoms of different bodies, one to one, one to two, &c. The compound atom, or molecule, joins itself in the same manner to a compound atom of another kind, and a combination of the second order results. Let it be granted, further, that the atoms of different elements have different weights, fixed and invariable for each, and the hypothesis becomes capable of rendering consistent and satisfactory reasons for all the observed numerical laws of chemical combination. Chemical compounds must always be definite: they must always contain the same number of atoms of the same kind arranged in a similar manner. The same kind and number of atoms need not, however, of necessity pro- duce the same substance, for they may be differently arranged; and much depends upon this circumstance. Again, the law of multiple proportions is perfectly well explained. One atom of carbon unites with one atom of oxygen to form carbon monoxide, and with two atoms to form carbon dioxide ; one atom of sulphur with two and three atoms of oxygen to form the dioxide and trioxide of sulphur; one atom of phosphorus with three and five atoms of chlorine to form the trichloride and pentachloride of phosphorus; two atoms of nitrogen with one, two, three, four and five atoms of oxygen to form the five oxides already mentioned (pp. 157, 220). The atomic hypothesis likewise affords an easy explanation of the manner in which bodies replace or may be substituted one for the other. Here, however, we come upon an extension of the original Daltonian hypothesis. It was formerly supposed that when one element replaced another in com- bination, the substitution always took place atom for atom ; and accordingly the terms "atoms" and "equivalent" were regarded as synonymous, at least so far as numerical value was concerned. But, according to the atomic weights now adopted, and determined by the considerations above explained, we must suppose that one atom of an element may take the place of two, three, four atoms, &c., of another. It is only, in fact, the atoms of monogenic elements that can replace each other one by one: an atom of a polygenic element, on the other hand, always takes the place of, or is equivalent to, two or more atoms of a monogenic element. This difference of equivalent or saturating power is often denoted by placing dashes or Roman numerals to the right of the symbol of an ele- ment, and at the top, as 0", B /// , C iT , &c. ; and the several elements are designated aa 'A.TOJIOJ, that which cannot be cut. ATOMIC THEORY. 231 Univalent elements, or Monads, as H Bivalent Trivalent Quadrivalent Quinquivalent Sexvalent Dyads Triads Tetrads Pentads Hexads 0" B/// C lT P W" Elements of even equivalency, viz., the dyads, tetrads, and hexads, are also included under the general term artiads,* and those of uneven equiva- lency, viz., the monads, triads, and pentads, are designated generally as perissads. -f Another method of indicating the equivalent values of the elementary atoms, and the manner in which they are satisfied by combination, is to arrange the symbols in diagrams in which each element is connected with others by a number of lines, or connecting bonds, corresponding to its degree of equivalence ; J a monad being connected with other elements by only one such bond, a triad by three, a hexad by six, &c., as in the follow- ing examples: Water, OH 2 Carbon dioxide, C0 2 Ammonium chloride, NH^Cl Sulphuric oxide, S0 3 . Sulphuric acid, S0 4 H 2 Nitric acid, N0 3 H Zinc nitrate, N 2 6 Zn S=0 II II H S H II o II N H II II II N Zn N ii It must be distinctly understood that these formulae which may be called constitutional formulx are not intended to represent the actual arrangement * "Apriof, even. t ntpiwAf, uneven. 1 The symbols of the elements in these diagrams are often enclosed in circles to represent the atoms, with rays diverpn- from them to indicate the number of connecting bonds; such tor- mula- are called graphic formula' ; but the circles do not add anything to the clearness ..1 t representation, and may as well be omitted. For lecture and class illustration, solid diagram* are constructed, with wooden halls of various colors, to represent the atoms, having hole* ft* the insertion of connecting rods; these representations are called glyptic formula. 232 ATOMIC THEORY. of the atoms in a compound ; indeed, even if we had a distinct notion of the manner in which the atoms of any compound are arranged, it could not be adequately represented on a plane surface. The lines connecting the different atoms indicate nothing more than the number of units of equiva- lency belonging to the several atoms, and the manner in which they are disposed of by combination with those of other atoms. Thus the formula for nitric acid indicates that two of the three constituent oxygen-atoms are combined with the nitrogen alone, and are consequently attached to that element by both their units of equivalency, whereas the third oxygen-atom is combined both with nitrogen and with hydrogen. By inspection of the preceding diagrams, it will be observed that every atom of a compound has each of its units of equivalency satisfied by com- bination with a unit belonging to some other atom. Such, indeed, is the case in every saturated or normal compound. Accordingly, it is found that in all such compounds the sum of the perissad elements is always an even num- ber. Thus a compound may contain two, four, six, &c., monad atoms, as HC1, OH 2 , CH 4 , C 2 H 6 , C 3 H 8 , SiH 3 Cl ; or one monad and one triad atom, as BC1 3 ; or one pentad and tive monads, as NH 4 C1; but never an uneven num- ber of perissad atoms. This is the "law of even numbers" announced some years ago by Gerhardt and Laurent as a result of observation. It was long received with doubt, but has now been confirmed by the analysis of so many well-defined compounds, that a departure from it is looked upon as a sure indication of incorrect analysis. For a similar reason, the atoms of elementary bodies rarely exist in the free state, but, when separated from any compound, tend to combine with other atoms, either of the same or of some other element. Perissad ele- ments, like hydrogen, chlorine, nitrogen, &c., separate from their compounds in pairs; their molecule contains two atoms, e.g. H H. Artiad elements may unite in groups of two, three, or more ; thus the molecule of oxygen, in its ordinary state, probably, contains two atoms, that of ozone three atoms; thus: Oxygen ........ 0=0 Ozone ........ The tendency of elementary atoms to separate in groups is shown in various ways. Thus when copper hydride, Cu 2 H 2 (to be hereafter de- scribed), is decomposed by hydrochloric acid, a quantity of hydrogen is given off equal to twice that which is contained in the hydride itself; thus: Cu 2 H 2 -f 2HC1 = Cu 2 Cl 2 + 2HH. This action is precisely analogous to that of hydrochloric acid on cuprous oxide : Cu 2 -f 2HC1 = Cu 2 Cl 2 + OH 2 . In the latter case, the hydrogen separated from the hydrochloric acid unites with oxygen, in the former with hydrogen. Again, when solutions of sulphurous acid and sulph-hydric acid are mixed, the whole of the sul- phur is precipitated: S0 3 H 2 -f 2SH 2 = 30H 2 -f S.S 2 the action being similar to that of sulphurous acid on selenhydric acid: S0 3 H 2 -f 2SeH 2 == 30H 2 -f S.Se 2 . In the one case, a sulphide of selenium is precipitated; in the other, a sulphide of sulphur. The precipitation of iodine, which takes place on ATOMIC THEORY. 233 mixing hydriodic acid with iodic acid, affords a similar instance of the combination of homogeneous atoms: 5IH + I0 3 H = 30H 2 = 311 Hydriodic acid. Iodic acid. Water. Free iodine. Another striking illustration of this mode of action is afforded by the re- duction of certain metallic oxides by hydrogen dioxide. When silver oxide is thrown into this liquid, water is formed; the silver is reduced to the metallic state, and a quantity of oxygen is evolved equal to twice that which is contained in the silver oxide: OAg 2 + 2 H 2 = OH 2 + Ag 2 4- 00 Silver Hydrogen Water. Silver. Oxygea. oxide. dioxide. Further, elementary bodies frequently act upon others as if their atoms were associated in binary groups. Thus, chlorine acting upon potash forms two compounds, the chloride and hypochlorite of potassium (p. 185) : C1C1 4- OKK = C1K 4. OC1K. Again, in the action of chlorine upon many organic compounds, one atom of chlorine removes one atom of hydrogen as hydrochloric acid, while an- other atom of chlorine takes the place of the hydrogen thus removed. For example, in the formation of chloracetic acid by the action of chorine on acetic acid: C 2 H 4 2 4- C1C1 = HC1 4- C 2 H,C10, Acetic acid. Chloracetic acid. Similarly, when metallic sulphides oxidize in the air, both the metal and the sulphur combine with oxygen; and sulphur acting upon potash forms both a sulphide and a hyposulphite. In all these cases the atoms of the elementary bodies act in pairs. On the supposition that the molecules of elementary bodies in the gaseous state are made up of two atoms, the specific volumes of these gases will come under the same law as that which applies to compounds (p. 229) ; and it may then be stated generally, that, with the few exceptions already no- ticed, the specific gravities of all bodies, simple and compound, in the gaseous state, are equal to half their molecular weights ; or the specific volume (the quo- tients of the molecular weight by the specific gravities) are equal to 2. Variation of Equivalency. Multivalent or polygenic elements often ex- hibit varying degrees of equivalency. Thus carbon, which is quadrivalent in marsh gas, CH 4 , and in carbon dioxide, C0 2 , is only bivalent in carbon monoxide, CO ; nitrogen, which is quinquivalent in sal-ammoniac, NH 4 C1, and the other ammonium salts, and in nitrogen pentoxide, N 2 6 , is trivalent in ammonia, NH 3 , and in nitrogen trioxide, N 2 3 , and univalent in nitrogen monoxide, N 2 ; sulphur, also, which is sexvalent in sulphur trioxide, S0 3 , is quadrivalent in sulphur dioxide, S0 2 , and bivalent in hydrogen sulphide, SH <2 , and in many metallic sulphides. In these cases, and in all others of varying equivalency, the variation always takes place by two units of equivalency. It is not very easy to account for these variations ; but it is observed in all cases that the compounds in which the equivalency of a po- lygenic element is most completely satisfied are more stable than the others, and that the latter tend to pass into the former by taking up the required number of univalent or bivalent atoms; thus, carbon monoxide, CO, o;isily takes up another atom of oxygen to form the dioxide, C0 2 : nitrogen tri- oxide, N 2 O 3 , is readily converted into the pentoxide, N 2 6 ; ammonia, NIT 3 , unites readily with hydrochloric acid to form sal-ammoniac, NH 4 C1, c. 20* 234 ATOMIC THEORY. Similar phenomena are exhibited by many organo-metallic bodies, as will be explained further on. From this it seems most probable that the true equivalency or atomicity of a polygeriic element is that which corresponds with the maximum num- ber of monad atoms with which it can combine, but that one or two pairs of its units of equivalency may, under certain circumstances, remain un- saturated. Whether a saturated or an unsaturated element is formed, will depend on a variety of conditions, often in great measure on the relative quantities of the acting substances. Thus, phosphorus, which is a pentad element, forms with chlorine, either a trichloride, PC1 3 , or a pentachloride, PC1 6 , according as the phosphorus or the chlorine is in excess (p. 217).* In compounds containing two or more atoms of the same polygenic element, one or more units of equivalence belonging to each of these atoms may be neutralized by combination with those of another atom of the same kind, so that the element in question will appear to enter into the compound with less than its normal degree of equivalence. Thus, in ethane, or di- methyl, C 2 H 6 , which is a perfectly stable compound, having no tendency to take up an additional number of atoms of hydrogen or any other element, the carbon appears to be trivalent instead of quadrivalent ; similarly in propane, C 3 H 8 , its equivalence appears to be reduced to f ; and in quartane or diethyl, C 4 H, , to f. In all these cases, however, the diminution of equivalent value in the carbon atoms is only apparent, as may be seen from the following formulae : Ethane. H HCH H C H i or, more shortly, omitting the equivalent marks of the monad atoms : Ethane. Propane. Quartane. CH 3 CH 3 CH 3 CH 3 CH 2 CH 2 CH 3 OH 2 CH 3 . In each of these compounds, every carbon atom, except the two outside ones, has two of its units of equivalence satisfied by combination with those of the neighboring carbon atoms, while each of the two exterior ones has only one unit thus satisfied. Hence in any similarly constituted compound containing n carbon atoms, the number of units of equivalence remaining to be satisfied by the hydrogen atoms is 4n 2(n 2) 2 = 2n -}- 2. The general formula of this series of hydrocarbons is, therefore, C n H 2n+2 , and the equivalent value of the carbon is ^ n ~\~^. n * See also Erlemneyer, " Lehrbuch der organischen Chemie." Leipzig und Heidelberg, ATOMIC THEORY. 235 In other cases, multivalent atoms may be united by two or more of their units of equivalence, so that their combining power may appear to be still further reduced, as in the hydrocarbon, C 2 H 4 , in which the carbon may be apparently bivalent, and in C 2 H 2 , in which it may appear to be univaleut ; thus: H C II C H H C H (j H. In all cases, the equivalent value or atomicity of an element must be de- termined by the number of monad atoms with which it can combine. Of dyad atoms, indeed, any element or compound may take up an indefinite number, without alteration of its equivalence or combining powers ; for each dyad atom, possessing two units of equivalency, neutralizes one unit in the compound which it enters, and introduces another, leaving, therefore, the equivalence or combining power of the compound just what it was be- fore. Thus potassium forms only one chloride, KC1, and is, therefore, uni- valent or monadic; but in addition to the oxide, K 2 0, corresponding to this chloride, it likewise forms two others, viz., K 2 3 and K 2 4 , in the former of which it might be regarded as dyadic, and in the latter as tetradic ; but the manner in which dyad oxygen enters these compounds is easily seen by inspection of the following diagrams: Monoxide Dioxide Tetroxide K K O-K A J O- It is evident that any number of oxygen-atoms might, in like manner, be inserted without disturbing the balance of equivalency. If, indeed, we turn to the sulphides of potassium, in which the sulphur is dyadic, like oxygen, we find the series, K 2 Sj, K 2 S 2 , K 2 S 3 , K 2 S 4 , K 2 S 5 , the constitution of which may be represented in a precisely similar manner. Hence the equi- valence of any element must be determined by the composition of its chlo- rides, bromides, iodides, or fluorides, not by that of its oxides or sulphides. Assuming then that the maximum equivalence of a polygenic element is that which represents its normal mode of combination, the element ary bodies may be classified as in the following table, in which the names of the metalloids are printed in italics, those of the metals in Roman type, and the elements are further divided by horizontal lines into groups consisting of elements closely related in their chemical characters: in each of these groups the elements are arranged in the order of their atomic weights, be- ginning with the lowest. (See Table, p. 226.) The position of several of the elements in this arrangement must be re- garded as still somewhat doubtful. Nitrogen, phosphorus, arsenic, antnnn>/, and bismuth, though quinquivalent in a considerable number of compounds, as ammonium-chloride, NH 4 C1, phosphorus pentachloride, PC1 6 , etc., never- theless form very stable compounds, as NH 3 . AsCl 3 , As 2 3 , etc., in which they are trivalent. It is true that these compounds pass with tolerable facility into others in which the nitrogen, phosphorus, etc., are quinqui- valent, and these latter show no disposition to attach to themselves .-my additional number of monad atoms; but, on the other hand, these 236 ATOMIC THEORY. compounds do not appear to be very stable, inasmuch as they easily split up, when volatilized, in such a manner as to yield compounds of the triadic Monads. Dyads. Triads. Tetrads. Pentads. Hexads. Hydrogen Oxygen Boron Carbon Silicon Titanium Tin Nitrogen Phosphorus Vanadium Arsenic Antimony Bismuth Sulphur Selenium Tellurium Fluorine Chlorine Bromine Iodine Calcium Strontium Barium Gold Thallium Chromium Molyb- denum Tungsten Aluminium Zirconium Berylium Yttrium Lanthanum Didymium Erbium Thorinum Lithium Sodium Potassium Rubidium Caesium Niobium Tantalum Rhodium Ruthenium Palladium Platinum Iridium Osmium Silver Magnesium Zinc Cadmium Lead Copper Mercurv Manganese Iron Cobalt Nickel Cerium Indium Uranium class; sal-ammoniac, for example, into hydrochloric acid and ammonia, phosphorus pentachloride into free chlorine and the trichloride : NH 4 C1 PC1 5 HC1 CL NH 3 PCI,. Iron, and the metals which follow it in the table, are sometimes classed as hexads, on account of their analogy with chromium, which is, undoubtedly, hexadic, inasmuch as it forms a hexnuoride, CrF 6 . Neither of these metals, however, is known to form any well-defined compounds in which it is more than quadrivalent, Iron, for example, is bivalent in the ferrous salts, as Fe^do, arid quadrivalent in the ferric compounds, ferric chloride, Fe 2 Cl 6 , FeCl 3 being constituted in the manner shown by the formula I . Manganese FeCl 3 is inferred to be a hexad, on account of the isomorphism and similarity of composition between the magnates and the chromates : but the isomorphism of two elements, or their corresponding compounds, does not afford decided proof of equal equivalency, for the fluoniobates are known to be isomor- phous with the fluosilicates and fluotitanates ; and yet niobium is a pentad element, whereas silicium and titanium are tetrads. Sulphur, selenium, and tellurium, are usually regarded as dyads, on account of the close analogy of their compounds to those of oxygen, and especially of their hydrogen compounds, SH 2 , &c., to water. But selenium and tel- lurium form well-defined tetrachlorides ; and even sulphur tetrachloride, ATOMIC THEORY. 237 SCI/,, though it has not been obtained in the free state, is known in combi- nation with metallic chlorides. Sulphur has also lately been shown to form certain organic compounds in which it is tetradic, and others in which it appears to be hexadic.* Moreover, the chemical relations of the sulphates are much more clearly represented by formulae, in which sulphur is sup- posed to be hexadic (like that given for sulphuric acid on page 231), than by formulae into which it enters as a dyad; and similar remarks apply to the selenates and tellurates; for these reasons, sulphur, selenium, and tellurium, are most conveniently regarded as hexads, though they sometimes enter into combination as tetrads, and very frequently as dyads. Compound Radicals. Suppose one or more of the component atoms of a fully saturated molecule to be removed: it is clear that the remaining atom or group of atoms will no longer be saturated, but will have a combining power corresponding to the number of units of equivalency removed. Such unsaturated groups are called residues or radicals. Methane, CH 4 , is a fully saturated compound; but if one of its hydrogen atoms be removed, the residue CH 3 (called methyl}, will be ready to combine with one atom of a univalent element, such as chlorine, bromine, &c., forming the compounds CH 3 C1, CH 3 Br, &c. ; two atoms of it unite in like manner with one atom of oxygen, sulphur, and other bivalent elements, forming the compounds // (CH 3 ) 2 , S"(CH ) 2 , &c. ; three atoms with nitrogen yielding N // (CH 3 ) 3 , &c. The removal of two hydrogen-atoms from CH 4 leaves the bivalent radical CH 2 , called methene. which yields the compounds CH 2 C1 2 , CH 2 0, CH 2 S, &c. The removal of three hydrogen atoms from CH 4 leaves the trivalent rsuil-al CH, which, in combination with three chlorine-atoms, constitutes chloro- form, CHC1 3 . And, finally, the removal of all four hydrogen-atoms from CH 4 leaves the quadrivalent radical carbon C iT , capable of forming the com- pounds CC1 4 , CS 2 , &c. In like manner, ammonia, NH 3 , in which the nitrogen is trivalent, yields, by removal of one hydrogen-atom, the univalent radical amidogen NH 2 , which with one atom of potassium forms potassamine, NH 2 K, and when combined with one atom of the univalent radical methyl, CH 3 , forms methy- lamine, NH 2 (CH 3 ), &c. The abstraction of two hydrogen-atoms from the molecule NH 3 , leaves the bivalent radical imidogen, NH, which with two methyl-atoms forms dimethylamine, NH(CH 3 ) 2 , &c. ; and the removal of all three hydrogen-atoms from NH 3 , leaves nitrogen itself, which frequently acts as a trivalent element or radical, forming tripotassamine NK 3 , trime- thylamine N(CII 3 ) 3 , &c. Finally, the molecule of water, OH 2 , by losing an atom of hydrogen, is converted into the univalent radical hydroxyl, OH, which, in its relations to other bodies, is analogous to chlorine, bromine, and iodine, and may be substituted in combination for one atom of hydrogen or other monads. Thus, water itself may be regarded as H.HO, analogous to hydrochloric acid HC1; potassium hydrate as K.HO, analogous to potassium chloride; barium hydrate, as Ba // .(OH) 2 , analogous to barium chloride Ba"Cl 2 . In a similar manner, the univalent radical, potassoxyl, KO, may be derived from potassium hydrate ; the bivalent radical, zincoxyl, Zn0 2 , by abstraction of H 2 from zinc hydrate, Zn^HjO^ The essential character of .these oxy- genated radicals is that each of the oxygen atoms contained in them is united to the other atoms by one unit of equivalency only, so that the radical has necessarily one or two units unconnected ; thus : Hydroxyl H ~~~~ PotassoxyF Zincoxyl Zn * Sulphur triethiodide, S* (Coir f ,) 3 I Sulphur diethene-dibromide, S* 238 ATOMIC THEORY. From the preceding explanations of the mode of derivation of compound radicals, it is clear that there is no limit to the number of them which may be supposed to exist ; in fact, it is only necessary to suppose a number of units of equivalency abstracted from any saturated molecule, in order to obtain a radical of corresponding combining power or equivalent value. But unless a radical can be supposed to enter into a considerable number of compounds, thus forming them into a group like the salts of the same metal, there is nothing gained in point of simplicity or comprehensiveness by assuming its existence. It must, also, be distinctly understood that these compound radicals do not necessarily exist in the separate state, and that those of uneven equi- valency, like methyl, cannot exist in that state, their molecules, if liberated from combination with others, always doubling themselves, as we have seen to be the case with most of the elementary bodies. Thus hydroxyl H is not known in the free state, the actually existing compound containing the same proportions of hydrogen and oxygen, being 2 H 2 or H H. In like manner, methyl, CH 3 , has no separate existence, but dimethyl C 2 H 6 is a known compound : Methyl. Dimethyl. H H H C H H C H -H H C 1 A CHEMICAL AFFINITY. rTlHE term chemical affinity, or chemical attraction, has been invented to .[_ describe that particular power or force, in virtue of which, union, often of a very intimate and permanent nature, takes place between two or more bodies, in such a way as to give rise to a new substance, having, for the most part, properties completely in discordance with those of its components. The attraction thus exerted between different kinds of matter is to be distinguished from other modifications of attractive force which are exerted indiscriminately between all descriptions of substances, sometimes at enor- mous distances, sometimes at intervals quite inappreciable. Examples of the latter are to be seen in cases of what is called cohesion, when the par- ticles of solid bodies are immovably bound together into a mass. Then, there are other effects of, if possible, a still more obscure kind ; such as the various actions of surface, the adhesion of certain liquids to glass, the repulsion of others, the ascent of water in narrow tubes, and a multitude of curious phenomena which are described in works on Natural Philosophy, under the head of molecular actions. From all these, true chemical attraction may be at once distinguished by the deep and complete change of characters which follows its exertion: we might define affinity to be a force by which new substances are generated. It seems to be a general law that bodies most opposed to each other in chemical properties evince the greatest tendency to enter into combination ; and, conversely, bodies between which strong analogies and resemblances can be traced manifest a much smaller amount of mutual attraction. For example, hydrogen and the metals tend very strongly indeed to combine with oxygen, chlorine, and iodine, but the attraction between the different members of these two groups is incomparably more feeble. Sulphur and phosphorus stand, as it were, midway : they combine with substances of one and the other class, their properties separating them sufficiently from both. Acids are drawn towards alkalies, and alkalies towards acids, while union among themselves rarely if ever takes place. Nevertheless, chemical combination graduates so imperceptibly into mere mechanical mixture, that it is often impossible to mark the limit. Solution is the result of a weak kind of affinity existing between the substance dis- solved and the solvent an affinity so feeble as completely to lose one of its most prominent features when in a more exalted condition namely, power of causing elevation of temperature ; for in the act of mere solution, the temperature falls, the heat of combination being lost and overpowered by the effects of change of state. The force of chemical attraction thus varies greatly with the nature of the substances between which it is exerted ; it is influenced, moreover, to a very large extent, by external or adventitious circumstances. An idea formerly prevailed that the relations of affinity were fixed and constant between the same substances, and great pains were taken in the prepara- tion of tables exhibiting what was called the precedence of affinities, order pointed out in these lists is now acknowledged to represent the order of precedence for the circumstances under which the experiments were made, but nothing more; so soon as these circumstances become changed, the order is disturbed. The ultimate effect, indeed, is not the result of the ex- ercise of one single force, but rather the joint effect of a number, so com- plicated and so variable in intensity, that it is but seldom possible to pre- dict the consequences of any yet untried experiment. It will be proper to examine shortly some of these extraneous causes to 239 240 CHEMICAL AFFINITY. which allusion has been made, which modify to so great an extent the direct and original effects of the specific attractive force. Alteration of temperature may be reckoned among these. When metallic mercury is heated nearly to its boiling-point, and in that state exposed for a lengthened period to the air, it absorbs oxygen, and becomes converted into a dark-red crystalline powder. This very same substance, when raised to a still higher temperature, separates spontaneously into metallic mercury and oxygen gas. It may be said, and probably with truth, that the latter change is greatly aided by the tendency of the metal to assume the vaporous state ; but precisely the same fact is observed with another metal, palladium, which is not volatile, excepting at extremely high temperatures, but which oxidizes superficially at a red heat, and again becomes reduced when the temperature rises to whiteness. Insolubility and the power of vaporization are perhaps, beyond all other disturbing causes, the most potent; they interfere in almost every reaction which takes place, and very frequently turn the scale when the opposed forces do not greatly differ in energy. It is easy to give examples. When a solu- tion of calcium chloride is mixed with a solution of ammonium carbonate, double interchange ensues, calcium carbonate and ammonium chloride being generated: CaCl 2 -\- C0 3 (NH 4 ) 2 = C0 3 Ca -|- 2NH 4 C1. Here the action can be shown to be in a great measure determined by the insolubility of the calcium carbonate. Again, when dry calcium carbonate is powdered and mixed with ammonium chloride, and the whole heated in a retort, a subli- mate of ammonium carbonate is formed, while calcium chloride remains behind. In this instance, it is no doubt the great volatility of the new am- moniacal salt which chiefly determines the kind of decomposition. When iron filings are heated to redness in a porcelain tube, and vapor of water passed over them, the water undergoes decomposition with the utmost facility, hydrogen being rapidly disengaged, and the iron converted into oxide. On the other hand, oxide of iron, heated in a tube through which a stream of dry hydrogen is passed, suffers almost instantaneous reduction to the metallic state, while the vapor of water, carried forward by the current of gas, escapes as a jet of steam from the extremity of the tube. In these experiments the affinities between the iron and oxygen and the hydrogen and oxygen are so nearly balanced, that the difference of atmos- phere is sufficient to settle the point. An atmosphere of steam offers little resistance to the escape of hydrogen; an atmosphere of hydrogen bears the same relation to steam ; and this apparently trifling difference of circum- stances is quite enough for the purpose. The decomposition of vapor of water by white-hot platinum, pointed out by Mr. Grove, will probably be referred in great part, to this influence of atmosphere, the steam offering great facilities for the assumption of the elastic condition by the oxygen and hydrogen. The decomposition ceases as soon as these gases amount to about J-^-Q-Q of the bulk of the mixture, and can only be renewed by their withdrawal. The attraction of oxygen for hydrogen is probably much weakened by the very high temperature. The recombination of the gases by the heated metal is rendered impossible by their state of dilution. What is called the nascent state is one very favorable to chemical com- bination. Thus, nitrogen refuses to combine with gaseous hydrogen ; yet when these substances are simultaneously liberated from some previous combination, they unite with great ease, as when organic matters are de- stroyed by heat, or by spontaneous putrefactive change. There is a remarkable, and, at the same time, very extensive class of actions, grouped together under the general title of cases of disposing af- finity. Metallic silver does not oxidize at any temperature: nay, more, its oxide is easily decomposed by simple heat; yet if the finely divided metal be mixed with siliceous matter and alkali, and ignited, the whole. CHEMICAL AFFINITY. 241 fuses to a yellow transparent glass of silver silicate. Platinum is attacked by fused potassium hydrate, hydrogen being probably disengaged while the metal is oxidized: this is an effect which never happens to silver under the same circumstances, although silver is a much more oxidable substance than platinum. The fact is, that potash forms with the oxide of the last- named metal a kind of saline compound, in which the platinum oxide acts as an acid ; and hence its formation under the disposing influence of the powerful base. , In the remarkable decompositions suffered by various organic bodies when heated in contact with caustic alkali or lime, we have other examples of the same fact. Products are generated which are never formed in the absence of the base ; the reaction is invariably less complicated, and its results few in number and more definite, than in the event of simple de- struction by a graduated heat. , There is yet a still more obscure class of phenomena, called catalj/sis, in which effects are brought about by the mere presence of a substance which itself undergoes no perceptible change: the experiment mentioned in the chapter on oxygen, in which that gas is obtained, with the greatest facility, by heating a mixture of potassium chlorate and manganese dioxide, is an excellent case in point. The salt is decomposed at a very far lower tem- perature than would otherwise be required, and yet the manganese oxide does not appear to undergo any alteration, being found after the experi- ment in the same state as before. It may, however, undergo a temporary alteration. We know, indeed, that this oxide is capable of taking up an additional proportion of oxygen and forming manganic acid; and it is quite possible that in the reaction just considered it may actually take oxygen from the potassium chlorate, and pass to the state of a higher oxide, which, however, is immediately decomposed, the additional oxygen being evolved, and the manganese-oxide returning to its original state. The same effect in facilitating the decomposition of the chlorate is produced by cupric oxide, ferric oxide, and lead oxide, all of which are known to be susceptible of higher oxidation. The oxides of zinc and magnesium, on the contrary, which do not form higher oxides, are not found to facili- tate the decomposition of the chlorate ; neither is any such effect produced by mixing the salt with other pulverulent substances, such as pounded glass or pure silica. The so-called catalytic actions are often mixed up with other effects which are much more intelligible, as the action of finely divided platinum on certain gaseous mixtures, in which the solid appears to condense the gas upon its greatly extended surface, and thereby to induce combination by bringing the particles within the sphere of their mutual attractions. Relations of Heal to Chemical Affinity. Whatever may be the real nature of chemical affinity, one most important fact is clearly established with regard to it; namely, that its manifestations are always accompanied by the production or annihilation of heat. Change of composition, or chem- ical action, and heat are mutually convertible: a given amount of chemical action will give rise to a certain definite amount of heat, which quantity of heat must be directly or indirectly expended, in order to reverse or undo the chemical action that has produced it. The production of heat by chemical action, and the definite quantitative relation between the amount of heat evolved and the quantity of chemical action which takes place, are roughly indicated by the facts of our most familiar experience ; thus, for instance, the only practically important method of producing heat arti- ficially consists in changing the elements of wood and coal, together with atmospheric oxygen, into carbon dioxide and water; and every one knows that the heat which can be thus obtained from a given quantity of coal is limited, and is, at least approximately, always the same. 242 CHEMICAL AFFINITY. The accurate measurement of the quantity of heat produced by a given amount of chemical action is a problem of very great difficulty; chiefly because chemical changes very seldom take place alone, but are almost always accompanied by physical changes involving further calorimetric eifects, each of which requires to be accurately measured and allowed for, before the effect due to the chemical action can be rightly estimated. Thus the ultimate result has, in most cases, to be deduced from a great number of independent measurements, each of which is liable to a certain amount of error. It is therefore not surprising that the results of various experi- ments should differ to a comparatively great extent, and that some uncer- tainty should still exist as to the exact quantity of heat corresponding to even the simplest cases of chemical action. The experiments are made by enclosing the acting substances in a vessel called a calorimeter, surrounded by water or mercury, the rise of tempera- ture in which indicates the quantity of heat evolved by the chemical action, after the necessary corrections have been made for the heat absorbed by the containing vessel and the other parts of the apparatus, and for the amount lost by radiation, &c. Combustions in oxygen and chlorine are made in a copper vessel surrounded by water ; the heat evolved by the mutual action of liquids or dissolved substances is estimated by means of a smaller calorimeter containing mercury. The construction of these instruments and the methods of observation involve details which are beyond the limits of this work.* The following table gives the quantities of heat, expressed in heat-units,-}- evolved in the combustion of various elements, and a few compounds, in oxygen, referred: (1) to 1 gram of each substance burned; (2) to 1 gram of oxygen consumed ; (3) to one atom or molecule (expressed in grams) of the various substances : Heat of Combustion of Elementary Substances in Oxygen. Substance. Product. Units of heat evolved Observer. by 1 grm. of substance. by 1 gram of oxygen. by 1 at. of substance. Hydrogen . . . OH 2 / 33881 \ 34462 4235 4308 53881 64462 Andrews. Favre & Silbermann. Carbon : Wood-charcoal C0 2 /7900 \8080 2962 3030 94800 96960 Andrews. Favre & Silbermann. Gas retort carbon it 8047 3018 96564 Native graphite 7797 2924 93564 Artificial graphite t 7762 2911 93144 Diamond . . . . 7770 2914 93940 Sulphur: Native .... S0 2 2220 2220 71040 Recently melted . 2260 2260 72320 (i Flowers . . . 2307 2307 73821 Andrews. Phosphorus : (Yellow) . . . PA 5747 4454 178157 Zinc .... ZnO 1330 5390 86450 Iron Fe,0, 1582 4153 88592 Tin 34 Sn0. 2 1147 4230 135360 Copper .... CuO 603 2394 38304 * See filler's Chemical Physics, pp. 338, ft sea., and Watts's Dictionary of Chemistry, iii. 28, 103. f The unit of heat here adopted, is the quantity of heat required to raise 1 gram, of water from to 1 C. CHEMICAL AFFINITY. 243 The following results have been obtained by the complete combustion of partially oxidized substances : Substance. Product. Units of heat evolved Observer. by 1 grm. of sub- stance. in formation of 1 molecule of the ultimate product. Carbon monoxide, CO Stannous oxide, SnO Cuprous oxide, Cu 2 C0 2 Sn0 2 CuO /2403 \2431 519 256, 67284 68054 69584 18304 Favre & Silbermann. Andrews. n The last three substances in this table contain exactly half as much oxygen as the completely oxidized products ; and on comparing the amount of heat evolved in the formation of one molecule of stannic or cupric oxide from the corresponding lower oxide, with the quantity produced when a molecule of the same product is formed by the complete oxidation of the metal in one operation, we find that the combination of the second half of the oxygen contained in these bodies evolves sensibly half as much as the combination of the whole quantity. In the formation of carbon dioxide, however, the second half of the oxygen appears to develop more than two thirds of the total amount of heat; but this result is probably due, in part at least, to the fact that when carbon is burned into carbon dioxide, a con- siderable but unknown quantity of heat is expended in converting the solid carbon into gas, and thus escape measurement ; while, in carbon monoxide, the carbon already exists in the gaseous form, and therefore no portion of the heat evolved in the combustion of this substance is similarly expended in producing a change of state. It seems probable, also, that a similar explanation may be given of the inequalities in the quantities of heat produced by the combustion of differ- ent varieties of pure carbon and of sulphur that is to say, that a portion of the heat generated by the combustion of diamond and graphite goes to assimilate their molecular condition to that of wood-charcoal, and that there is an analogous expenditure of heat in the combustion of native sulphur. Combustions in Chlorine, and Direct Combination of Chlorine, Bromine, and 'Iodine ivith other Elements. The folio wing table gives the quantities of heat evolved by the direct union of various elements with gaseous chlorine : Units of heat evolved Substance. Product. by 1 gram by 1 grm. by 1 at. (- 35-5 Observer. of sub- of grams) of stance. chlorine. chlorine. c 24087 678 24087 Abria. Hydrogen . HC1 1 23783 670 23783 ( Favre & \ Silbermann. Phosphorus Potassium . PC1 6 (?) KC1 3422 (?) 2655 607 2943 21548 104476 Andrews. Iron . . . Zinc . . . Fe 2 Cl 6 ZnCl 2 1745 1529 921 1427 82696 50058 Tin ... SnCl 4 1079 897 31722 Arsenic . AsCl s 994 704 24992 Copper . . Antimony Mercury CuCl 2 SbCl 3 9(51 707 9 859 860 822 30494 30491 29181 CHEMICAL AFFINITY. The heat evolved by the direct union of bromine and iodine with zinc and iron has also been determined by Andrews : the results obtained are given in the next table : Metal. Product. Units of heat evolved by 1 gram of metal. by 1 gram of bromine or iodine. by 1 atom of bromine or iodine. Bromine. Zinc Iron ZnBr 2 Fe. 2 Br 6 1269 1277 508 298 40640 23833 Iodine. Zinc Iron . . ZnI 2 FeJ 6 819 463 209 63 26617 8046 Reactions in Presence of Water. The thermal effects which may result from the reaction of different substances on one another in presence of water, are more complicated than those resulting from direct combination. In addition to the different specific heats of the reagents and products, and to the different quantities of heat absorbed by them in dissolving, or given out by them in combining with water, the conversion of soluble substances into insoluble ones, as a consequence of the cluemical action, or the inverse change of insoluble into soluble bodies, are among the secondary causes to which part of tho calorimetric effect may be due in these cases. When a gas dissolves in water, the heat due to the chemical action is augmented by that due to the liquefaction of the gas ; so also when a solid body is dissolved in water, the total thermal effect is due in part to the chemical action taking place between the water and the solid, and in part to the liquefaction of the substance dissolved. In the former cases the chemical and physical parts of the phenomenon both cause evolution of heat ; in the latter case the physical change occasions disappearance of heat, arid if this effect is greater than that due to the chemical action, the ultimate effect is the production of cold, and it is this which is generally observed. Cold produced by Chemical Decomposition. It is highly probable that the thermal effect of the reversal of a given chemical action is in all cases equal and opposite to the thermal effect of that action itself. A direct conse- quence of this proposition is that the separation of any two bodies is attended with the absorption of a quantity of heat equal to that which is evolved in their combination. The truth of this deduction has been experimentally estab- lished in various cases, by Wood,* Joule,f and Favre and Silbermann, by com- paring the heat evolved in the electrolysis of dilute sulphuric acid, or solu- tions of metallic salts, with that which is developed in a thin metallic wire by a current of the same strength ; also by comparison of the heat evolved in processes of combination accompanied by simultaneous decomposition, with that evolved when the same combination occurs between free elements. By determining the heat evolved when different metals were dissolved in water or dilute acid, Wood found that it was less than that which would be produced by the direct oxidation of the same metals, by a quantity equal to that which would be obtained by burning the hydrogen set free, or which was expended in decomposing the water or acid: and, therefore, that when this latter quantity was added to the results, they agreed with the numbers given by experiments of direct oxidation. * Phil. Mag. [4] ii. 368 ; iv. 370. * Ibid. iii. 481. CHEMISTBY OF THE VOLTAIC PILE. 245 ELECTRO-CHEMICAL DECOMPOSITION; CHEMISTRY OF THE VOLTAIC PILE. WHEN a voltaic current of considerable power is made to traverse various compound liquids, a separation of the elements of these liquids ensues ; provided that the liquid be capable of conducting the current, its decom- position almost always follows. The elements are disengaged solely at the limiting surfaces of the liquid, where, according to the common mode of speech, the current enters and leaves the latter, all the intermediate portions appearing perfectly quies- cent. In addition, the elements are not separated indifferently and at random at these two surfaces; but, on the contrary, make their appear- ance with perfect uniformity and constancy at one or the other, according to their chemical character namely, oxygen, chlorine, iodine, acids, &c., at the surface connected with the copper, or positive end of the battery ; hydrogen, the metals, &c., at the surface in connection with the zinc or negative extremity of the arrangement. The terminations of the battery itself usually, but by no means neces- sarily, of metal are designated poles or electrodes,* as by their interven- tion the liquid to be experimented on is made a part of the circuit. The process of decomposition by the current is called cle.ctrolysis.-\ and the liquids, which, when thus treated, yield up their elements, are denomi- nated electrolytes. When a pair of platinum plates are plunged into a glass of water to which a few drops of oil of vitriol have been added, and the plates con- nected by wires with the extremities of an active battery, oxygen is disen- gaged at the positive electrode, and hydrogen at the negative, in the pro- portion of one measure of the former to two of the latter nearly. This experiment has before been described. J A solution of hydrochloric acid mixed with a little Saxon blue (indigo), and treated in the same manner, yields hydrogen on the negative side and chlorine on the positive, the indigo there becoming bleached. Potassium iodide dissolved in water is decomposed in a similar manner: the free iodine at the positive side can be recognized by its brown color, or by the addition of a little gelatinous starch. All liquids are not electrolytes; many refuse to conduct, and no decom- position can then occur ; alcohol, ether, numerous essential oils, and other products of organic chemistry, besides a few saline inorganic compounds, act in this manner, and completely arrest the current of a powerful battery. One of the most important and indispensable conditions of electrolysis is fluidity : bodies which, when reduced to the liquid state, conduct freely, and as freely suffer decomposition, become absolute insulators to the elec- tricity of the battery when they become solid. Lead chloride offers a good illustration of this fact: when fused in a porcelain crucible, it gives up its elements with the utmost ease, and a galvanometer, interposed somewhere in the circuit, is strongly affected. But when the source of heat is withdrawn, and the salt suffered to solidify, signs of decomposition cease, and at the same moment the magnetic needle reassumes its natural position. In the same manner, the thinnest film of ice arrests the current * From ,\tKT 9 ov, and Md(, a way. t From frttrpov, and Mtiv, to loose. % Pago 143. 21 * 246 ELECTRO-CHEMICAL of a powerful voltaic apparatus ; but the instant the ice is liquefied at any one point, so that water communication is restored between the electrodes, the current again passes, and decomposition occurs. Fusion by heat, and solution in aqueous liquids, answer the purpose equally well. Generally speaking, compound liquids cannot conduct the electric cur- rent without being decomposed; but still there are a few exceptions to this statement, which perhaps are more apparent than real. Thus Hittorf has shown, that fused silver sulphide, which was formerly regarded as one of the exceptions, cannot be considered to be so, and Bectz has since proved the same to be the case as regards mercuric iodide and lead fluoride. The quantity of any given compound liquid which can be decomposed by any given electric battery depends on the resistance of the liquid: the more resistance the less decomposition. Distilled water has only a small power of conduction, and is therefore only slightly decomposed by a bat- tery of 30 to 40 pairs ; whilst diluted sulphuric acid is one of the best of fluid conductors, and undergoes rapid decomposition by a small battery. When a liquid which can be decomposed, and a galvanometer, are in- cluded in the circuit of an electric current, if the needle of the galvano- meter be deflected, it may be always assumed as certain that a portion of liquid, bearing a proportion to the strength of the current, is decomposed, although it may be impossible in many cases, without special contrivances, to detect the products of the decomposition, on account of their minute- ness. The metallic terminations of the battery, the poles or electrodes, have, in themselves, nothing in the shape of attractive or repulsive power for the elements separated at their surfaces. Finely divided metal suspended in water, or chlorine held in solution in that liquid, shows not the least symptom of a tendency to accumulate around them ; a single element is altogether unaifected directly, at least; separation from previous combi- nation is required, in order that this appearance should be exhibited. It is necessary to examine the process of electrolysis a little more closely. When a portion of hydrochloric acid, for example, is subjected to decomposition in a glass vessel with parallel sides, chlorine is disen- gaged at the positive electrode, and hydrogen at the negative : the gases are perfectly pure and unmixed. If, while the decomposition is rapidly proceeding, the intervening liquid be examined by a beam of light, or by other means, not the slightest disturbance or movement of any kind will be perceived ; nothing like currents in the liquid or bodily transfer of gas from one part to another can be detected ; and yet two portions of hydro- chloric acid, separated perhaps by an interval of four or five inches, may be respectively evolving pure chlorine and pure hydrogen. There is, it would seem, but one mode of explaining this and all similar cases of regular electrolitic decomposition: this is by assuming that all the particles of hydrochloric acid between the electrodes, and by which the current is conveyed, simultaneously suffer decomposition, the hydrogen travelling in one direction, and the chlorine in the other. The neighboring elements, thus brought into close proximity, unite and reproduce hydro- chloric acid, again destined to be decomposed by a repetition of the same change. In this manner, each particle of hydrogen may be made to travel in one direction, by becoming successively united to each particle of chlo- rine between itself and the negative electrode ; when it reaches the latter, finding no disengaged particle of chlorine for its reception, it is rejected, as it were, from the series, and thrown off in a separate state. The same thing happens to each particle of chlorine, which at the same time passes continually in the opposite direction, by combining successively with each particle of hydrogen that moment separated, with which it meets, until at length it arrives at the positive plate or wire, and is disengaged. A sue- CHEMISTRY OF THE VOLTAIC PILE. 247 cession of particles of hydrogen are thus continually thrown off from the decomposing mass at one extremity, and a corresponding succession of particles of chlorine at the other. The power of the current is exerted with equal energy in every part of the liquid conductor, though its effect* become manifest only at the very extremities. The action is one of a purely molecular or internal nature, and the metallic terminations of the battery merely serve the purpose of completing the connection between the latter and the liquid to be decomposed. The figures 141 and 142 are M *)! Hydrochloric acid in its usual state. intended to assist the imagination of the reader, who must at the same time avoid regarding them in any other light than that of a somewhat figurative mode of representing the curious phenomena described. The circles are intended to indicate the elements, and are distinguished by their respective symbols. Like hydrochloric acid, all electrolytes, when acted on by electricity, are split into two constituents, which pass in opposite directions. The one Fig. 142. Hydrochloric acid undergoing electrolysis. class of substances, like oxygen, chlorine, &c., are evolved at the positive electrode ; the other class, like hydrogen and the metals, at the negative electrode. ' It is of importance to remark that oxygen salts, such as sulphates and nitrates, when acted on by the current, do not divide into acid and basic oxide, but, as Daniell and Miller proved, into metal and a compound sub- stance, or group of elements, which is transferred in such a state of asso- ciation that, as regards its electrical behavior, it represents an element. Thus, cupric sulphate, S0 4 Cu, splits, not into S0 3 and CuO, but into me- tallic copper and sulphiom S0 4 . Hydrogen sulphate, or sulphuric acid, S0 4 H 2 , divides into the same compound group and hydrogen. In a similar way, also, the part of the electrolyte which passes to the negative pole may consist of a group of element^. A solution of sal-ammoniac, NH 4 C1, fur- nishes a beautiful instance of this fact, since it is decomposed by the cur- rent in such a manner that the ammonium NH 4 goes to the negative, and the chlorine to the positive pole. A distinction must be carefully drawn between true and regular e trolysis, and what is called secondary decomposition, brought about by tl reaction of the bodies so eliminated upon the surrounding liquid, or upor the substance of the electrodes: honce the advantage of platinum to latter purpose, when electrolytic actions arc to be studied in their pn-ati-! , simplicity, that metal being scarcely attacked by any ordinary ajrc-nts. When, for example, a solution of lead nitrate or acetate is decomposed by 24:8 ELECTRO-CHEMICAL DECOMPOSITION; the current between platinum plates, metallic lead is deposited at the ne- gative side, and a brown powder, lead dioxide, at the positive: the latter substance is the result of a secondary action; it proceeds, in fact, from the nascent oxygen at the moment of its liberation reacting upon the monoxide of lead present in the salt, and converting it into dioxide, which is insoluble in the dilute acid. When nitric acid is decomposed, no hydrogen appears at the negative electrode, because it is oxidized at the expense of the acid, which is reduced to nitrous acid gas. When potassium sulphate, S0 4 K 2 , is electrolyzed, hydrogen appears at the negative electrode, together with an equivalent quantity of potassium hydrate OKH, because the potassium which is evolved at the electrode immediately decomposes the water there present. At the same time, the sulphione, S0 4 , which is transferred to the positive electrode, takes hydrogen from the water there present, forming sulphuric acid, S0 4 H 2 , and liberating oxygen. In like manner hydrogen sulphate, or sulphuric acid itself, is resolved by the current into hydrogen and sulphione, which latter decomposes the water at the positive electrode, reproducing hydrogen sulphate, and liberating oxygen, just as if the water itself were directly decomposed by the current into hydrogen and oxygen. A similar action takes place in the electrolytic decomposition of any other oxygen-salt of an alkali-metal, or alkaline earth-metal, alkali and hydrogen gas making their appearance at the negative electrode, acid and oxygen gas at the positive electrode. This observation explains a circumstance which much perplexed the earlier experimenters upon the chemical action of the voltaic battery. In all experiments in which water was decomposed, both acid and alkali were liberated at the electrodes, even though distilled water was employed ; and hence it was believed for some time that the voltaic current had some mysterious power of generating acid and alkaline matter. The true source of these compounds was, however, traced by Davy,* who showed that they proceeded from impurities either in the water itself, or in the vessels which contained it, or in the surrounding atmos- phere. Having proved that ordinary distilled water always contains traces of saline matter, he redistilled it at a temperature below the boiling-point, in order to avoid all risk of carrying over salts by splashing. He then found that when marble cups were used to contain the water used for de- composition, hydrochloric acid appeared at the positive electrode, soda at the negative, both being derived from sodium-chloride present in the mar- ble; when agate cups were used, he obtained silica; and when he used gold vessels, he obtained nitric acid and ammonia, which he traced to at- mospheric air. By operating in a vacuum, indeed, the quantity of acid and alkali was reduced to a minimum, but the decomposition was almost arrested, although he operated with a battery of fifty pairs of 4-inch plates. Hence it is manifest that ivater itself is not an electrolyte, but that it is enabled to convey the current if it contains only traces of saline matter.f If a number of different electrolytes, such as dilute sulphuric acid, cupric sulphate, potassium iodide, fused lead chloride, &c., be arranged in a series, and the same current be made to traverse the whole, all will suffer decom- position at the same time, but by no means to the same amount. If arrange- ments be made by which the quantities of the eliminated elements can be accurately ascertained, it will be found, when the decomposition has pro- ceeded to some extent, that these latter have been disengaged exactly in the ratio of their chemical equivalents. The same current which decomposes 9 parts of water will separate into their elements 106 parts of potassium iodide, 139 parts of lead chloride, &c. Hence the very important conclusion : The action of the current is perfectly definite in its nature, producing a fixed and constant amount of decomposition, expressed in each electrolyte by the value of its chemical equivalent. * Philosophical Transactions, 1807. f Miller's Chemical Physics, p. 484. CHEMISTRY OF THE VOLTAIC PILE. 249 Fig. 143. From a very extended series of experiments, based on this and other methods of research, Faraday was enabled to draw the general inference that effects of chemical decomposition are always proportionate to the quantity of circulating electricity, and may be taken as an accurate and trustworthy measure of the latter. Guided by this highly important prin- ciple, he constructed his voltameter, an instrument which has rendered the greatest service to electrical science. This is merely an arrangement by which dilute sulphuric acid is decomposed by the current, the gas evolved being collected and measured. By placing such an instrument in any part of the circuit, the quantity of electric force necessary to pro- duce any given effect can be at once estimated; or, on the other hand, any required amount of the latter can be, as it were, measured out and adjusted to the object in view. The voltameter has received many different forms: one of the most extensively useful is that shown in fig. 143, in which the platinum plates are separated by a very small interval, and the gas is collected in a graduated jar standing on the shelf of the pneu- matic trough, the tube of the instrument, which is filled to the neck with dilute sulphuric acid, being passed beneath the jar. The decompositions produced by the voltaic battery can be effected by the electricity of the common machine, by that developed by magnetic action, and by that of animal origin, but to an extent incomparably more minute. This arises from the very small quantity of electricity set in motion by the machine, although its tension that is, power of overcoming obsta- cles, and passing through imperfect conductors is exceedingly great. A pair of small wires of zinc and platinum, dipping into a single drop of dilute acid, develop far more electricity, to judge from the chemical effects of such an arrangement, than very many turns of a large plate electrical machine in powerful action. Nevertheless, polar or electrolytic decompo- sition can be distinctly and satisfactorily effected by the latter, although on a minute scale. With a knowledge of the principles laid down, the study of the voltaic battery may be resumed and completed. In the first place, two very different views have been held concerning the source of the electrical dis- turbance in that apparatus. Volta himself ascribed it to mere contact of dissimilar metals or other substances conducting electricity, to what was denominated an electro-motive force, called into being by such contact. Proof was supposed to be given of this fundamental proposition by an ex- periment in which discs of zinc and copper attached to insulating handles, after being brought into close contact, were found, by the aid of a very delicate gold-leaf electroscope, to be in opposite electrical states. It appears, however, that the more carefully this experiment is made, the smaller is the effect observed; and hence it is judged highly probable that the whole may be due to accidental causes, against which it is almost impossible to guard. On the other hand, the observation was soon made that the power of the battery always bears some kind of proportion to the chemical action upon the zinc ; that, for instance, when pure water is used, the effect is extremely feeble; with a solution of salt, it becomes much greater; and, lastly, with dilute acid, greatest of all; so that some relation evidently exists between the chemical effect upon the metal and the evolution of electrical force. The experiments of Faraday and Daniell have given very great support to the chemical theory, by showing that the contact of dissimilar metals is not necessary in order to call into being powerful electrical currents, and 250 ELECTRO-CHEMICAL DECOMPOSITION; that the development of electrical force is not only in some way connected with the chemical action of the liquid of the battery, but that it is always in direct proportion to the latter. One very beautiful experiment, in which electrolytic decomposition of potassium iodide is performed by a current, generated without any contact of dissimilar metals, can be thus made : A plate of zinc is bent at a right angle, and cleaned by rubbing with sand- paper. A plate of platinum has a wire of the same metal attached to it by careful riveting, and the latter bent into an arch. A piece of folded filter- paper is wetted with solution of potassium iodide, and placed upon thn zinc ; the platinum plate is arranged opposite to the latter, with the end of its wire resting upon the paper; and then the pair is plunged into a glass of dilute sulphuric, mixed with a few drops of nitric acid. A brown spot of iodine becomes in a moment evident beneath the ex- Fig. 144. tremity of the platinum wire that is, at the positive side of the arrangement. A strong argument in favor of the chemical view is founded on the easily proved fact, that the direction of the current is determined by the kind of action upon the metals, the one least attacked being always positive. Let two polished pL-ites, the one iron and the other copper, be con- nected by wires with a galvanometer, and then immersed in a solution of an alkaline sulphide. The needle in a moment indicates a powerful current, passing from the copper through the liquid to the iron, and back again through the wire. Let the plates be now removed, cleaned, and plunged into dilute acid; the needle is again driven round, but in the opposite direction, the current now passing from the iron through the liquid to the copper. In the first instance, the copper is acted upon" and not the iron; in (he second, these conditions are reversed, and with them the direction of the current. The metals employed in the practical construction of voltaic batteries are zinc for the active metal, and copper, silver, or, still better, platinum, for the inactive one: the greater the difference of oxidability, the better the arrangement. The liquid is either dilute sulphuric acid, sometimes mixed with a little nitric, or occasionally, where very slow and long-con- tinued action is wanted, salt and water. To obtain the maximum effect of the apparatus with the least expenditure of zinc, that metal must be em- ployed in a pure state, or its surface must be covered by an amalgam, which in its electrical relations closely resembles the pure metal. The zinc is easily brought into this condition by wetting it with dilute sulphuric acid, and then rubbing a little mercury over it, by means of a piece of rag tied to a stick. The principle of the compound battery is, perhaps, best seen in the crown of cups: by each alternation of zinc, fluid, and copper, the current is urged forward with increased energy; its intensity is augmented, but the actual amount of electrical force thrown into the current form is not increased. The quantity, estimated by its decomposing power, is, in fact, determined by that of the smallest and least active pair of plates, the quantity of electricity in every part or section of the circuit being exactly equal. Hence large and small plates, batteries strongly and weakly charged, can never be connected without great loss of power. When a battery, either simple or compound, constructed with pure or with amalgamated zinc, is charged with dilute sulphuric acid, a number of highly interesting phenomena may be observed. While the circuit remains broken, the zinc is perfectly inactive, no acid is decomposed, no hydrogen liberated ; but the moment the connection is completed, torrents of hydrogen arise, not from the zinc, but from the copper or platinum surfaces alone, CHEMISTRY OF THE VOLTAIC PILE. 251 while the zinc undergoes tranquil and imperceptible oxidation and solution. Thus, exactly the same effects are seen to occur in every active cell of ;i closed circuit, that are witnessed in a portion of sulphuric acid undergoing electrolysis: oxygen appears at the positive side, with respect to the cun-n.t, and hydrogen at the negative; but with this difference : that the oxygen, instead of being set free, combines with the zinc. It is, in fact, a real case of electrolysis, and electrolytes alone are available as exciting liquids. Common zinc is very readily attacked and dissolved by dilute sulphuric acid ; and this is usually supposed to arise from the formation of a multitude of little voltaic circles, by the aid of particles of foreign metals or graphite, partially imbedded in the zinc. This gives rise in the battery to what is called local action, by which, in the common forms of apparatus, three fourths or more of the metal are often consumed, without contributing in the least to the general effect, but, on the contrary, injuring it to some ex- tent. This evil is got rid of by amalgamating the surface. From experiments very carefully made with a "dissected" battery of peculiar construction, in which local action was completely avoided, it has been distinctly proved that the quantity of electricity set in motion by the battery varies exactly with the zinc dissolved. Coupling this fact with that of the definite action of the current, it will be seen that when a perfect battery of this kind is employed to decompose hydrochloric acid, in order to evolve 1 grain of hydrogen from the latter, 32-5 grains of zinc must be dissolved as chloride, and its equivalent quantity of hydrogen disengaged in each active cell of the battery that is to say, that the electrical force generated by the solution of an equivalent of zinc in the battery is capable of effecting the decomposition of an equivalent of hydrochloric acid or any other electrolyte out of it. This is an exceedingly important discovery: it serves to show, in the most striking manner, the intimate nature of the connection between chem- ical and electrical forces, and their remarkable quantitative or equivalent relations. It almost seems, to use an expression of Faraday, as if a trans- fer of chemical force took place through the substance of solid metallic conduct- ors; that chemical actions, called into play in one portion of the circuit, could be made at pleasure to exhibit their eifects without loss or diminution in any other. There is an hypothesis, not of recent date, long countenanced and sup- ported by the illustrious Berzelius, which refers all chemical phenomena to electrical forces which supposes that bodies combine because they are in opposite electrical states; even the heat and light accompanying chemical union may be, to a certain extent, accounted for in this manner. In short, we are in such a position, that either may be assumed as cause or effect: it may be that electricity is merely a form or modification of ordinary chem- ical affinity ; or, on the other hand, that all chemical action is a manifesta- tion of electrical force. , . This electro-chemical theory is no longer received as a true explanation of chemical phenomena to the full extent intended by its author. Berzelius, indeed, supposed that the combining tendencies of elements, and their func- tions in compounds, depend altogether on their electric polarity ; and ac- cordingly he divided the elements into two classes, the electro-positive, which, like hydrogen and the metals, move towards the negative pole of the bat- tery, as if they were attracted by it, and the electro-negative, which, like oxygen, chlorine, and bromine, move towards the positive pole. We are, however, acquainted with a host of phenomena which show that the chem- ical functions of an element depend upon its position with regard to other elements in a compound, quite as much as upon its individual character. Thus chlorine, the very type of an electro-negative element, can be substi tuted for hydrogen, one of the most positive of the elements, in a large 252 ELECTKO-CHEMICAL DECOMPOSITION number of compounds, yielding new products, which exhibit the closest analogy in composition and properties to the compounds from which they are derived. It is impossible, therefore, to admit that the chemical func- tions of bodies are determined exclusively by their electrical relations. Still it is true in a general way that those elements which differ most strongly in their electrical characters, chlorine and potassium, for example, are likewise those which combine together with the greatest energy ; and the division of bodies into electro-positive and electro-negative is therefore retained ; the former are also called acid or chlorous, and the latter basylous or zincous. One of the most useful forms of the common voltaic battery is that con- trived by Dr. Wollaston (fig. 145). The copper is made completely to en- circle the zinc plate, except at the edges, the two metals being kept apart by pieces of cork or wood. Each zinc is soldered to the preceding copper, and the whole screwed to a bar of dry mahogany, so that the plates can be lifted into or out of the acid, which is contained in an earthenware trough, divided into separate cells. The liquid consists of a mixture of 100 parts water, 2 parts oil of vitriol, and 2 parts commercial nitric acid, all by meas- ure. A number of such batteries are easily connected together by straps of sheet copper, and admit of being put into action with great ease. Fig. 145. The great objection to this and to all the older forms of the voltaic bat- tery is, that the power rapidly decreases, so that, after a short time, scarcely the tenth part of the original action remains. This loss of power depends, partly on the gradual change of the sulphuric acid into zinc sulphate, but still more on the coating of hydrogen, and, at a later stage, on the precipi- tation of metallic zinc on the copper plates. It is self-evident that if the copper plate in the liquid became covered with zinc, it would act electrically like a zinc plate. This is precisely the action of the hydrogen, whereby a decrease of electrical power is produced. This effect, produced by the sub- stances separated from the liquid, is commonly called polarization. An apparatus of immense value for purposes of electro-chemical research, in which it is desired to maintain powerful and equable currents for many successive hours, has been contrived by Professor Daniell (fig. 146). Each cell of this "constant" battery consists of a copper cylinder 3 inches in diameter, and of a height varying from 6 to 18 inches. The zinc is em- ployed in the form of a rod f of an inch in diameter, carefully amalga- mated, and suspended in the centre of the cylinder. A second cell of porous CHEMISTRY .OF THE VOLTAIC PILE. 253 of vitriol and Fig. 146. earthenware or animal membrane intervenes between the zinc and the cop- per : this is filled with a mixture of 1 part by measure of oil of vitriol and 8 of water, and the exterior space with the same liquid, saturated with copper sulphate. A sort of little colan- der is fitted to the top of the cell, in which crystals of the copper sulphate are placed, so that the strength of the solution may remain unimpaired. When communi- cation is made by a wire between the rod and the cylin- der, a powerful current is produced, the power of which may be increased to any extent by connecting a sufficient number of such cells into a series, on the principle of the crown of cups, the copper of the first being attached to the zinc of the second. Ten such alternations constitute a very powerful apparatus, which has the great advan- tage of retaining its energy undiminished for a long time. By this arrangement of the voltaic battery, the polar- ization of the copper plate is altogether avoided ; the zinc in the porous cell, whilst it dissolves in the sulphuric acid, decomposes it, but does not liberate any hydrogen; for by the progress of the decomposition (see p. 246) up to the boundary of the copper solution, the hydrogen takes the place of the copper, and thus ultimately the copper is precipitated on the copper plate. The copper plate therefore remains in its original state, so long as a sufficient quantity of copper sulphate is present in the solution. By increasing the generative and reducing the antagonizing chemical affinities, Mr. Grove succeeded in forming the constant nitric acid battery which bears his name. This instrument is capable of producing a fur greater degree of power than the battery previously mentioned, and hence it has become one of the most important means of promoting electrical science in the present day. The zinc dips into dilute sulphuric acid; and instead of a solution of copper, concentrated nitric acid is used, which surrounds a platinum plate. It is evident that the electrolytic action which begins at. the zinc passes through the sulphuric acid, and in a precisely similar way through the contiguous nitric acid. Hydrogen would thus be liberated on the platinum plate. This action is not rendered visible by the evolution of gas, but only gradually by the change of color in the nitric acid : for the hydrogen liberated Fi 9- 147 - by the electrical action forms water at the expense of the oxygen yielded by the nitric acid ; and by this means, so long as sufficient nitric acid is present, the purity of the surface of the platinum plate is maintained. One of the cells in this battery is represented in sec- tion in fig. 147. The zinc plate is bent wmnd, so as to present a double surface, and well amalgamated : within it stands a thin flat cell of porous earthenware, filled with strong nitric acid, and the whole is immersed in a mixture of 1 part by measure of oil of vitriol and 6 of water, contained either in one of the cells of W'ollaston's trough, or in a separate cell of glazed porcelain, made for the purpose. The apparatus is completed by a plate of platinum foil, which dips into the nitric acid, and forms the positive side of the arrangement, With ten such pairs, experi- ments of decomposition, ignition of wires, the light between charcoal points, c., can be exhibited with great brilliancy, while the battery itself is very compact and portable, and, to a great extent, constant in its net ion. The zinc, as in the case of Daniell's battery, is consumed only while the 22 A 254 ELECTRO-CHEMICAL DECOMPOSITION ; Fig. 148. current passes, so that the apparatus may be arranged an hour or two before it is required for use, which is often a matter of great convenience; and local action from the precipitation of copper on the zinc is avoided. Professor Bunsen has modified the Grove battery by substituting for the platinum dense charcoal or coke, which is an excellent conductor of elec- tricity. By this alteration, at a very small expense, a battery may be made nearly as powerful and useful as that of Grove. On account of its cheapness, any one may put together one hundred or more of Bunsen's cells, by which the most magnificent phenomena of heat and light may be obtained. The accompanying figure shows the form of the round carbon cylinder, which is used in these cells. It is hol- lowed so as to receive a porous earthenware cell, in which a round plate of zinc is placed. The upper edge of the cylinder of carbon is well saturated with wax, and is surrounded by a copper ring, by means of which it may be put in connection with the zinc of the adjoin- ing pair. Bunsen's carbon cylinder is likewise well adapted for the use of dilute sulphuric acid alone, without the addi- tion of nitric acid. It is, however, better to saturate the dilute sulphuric acid with potassium bichromate. When this mixture contains at. least double the amount of sul- phuric acid which is necessary to decompose the chromate, a battery thus formed surpasses in power the nitric acid battery, but does not furnish currents of the same constancy. Mr. Smee has contrived an ingenious battery, in which silver, covered with a thin coating of finely divided metallic platinum, is employed in as- sociation with amalgamated zinc and dilute sulphuric acid. The rough sur- face appears to permit the ready disengagement of the bubbles of hydrogen. Within the last twenty-five years, several very beautiful and successful applications of voltaic electricity have been made, which may be slightly mentioned. Mr. Spencer and Professor Jacobi have employed it in copy- ing, or rather in multiplying, engraved plates and medals, by depositing upon their surfaces a thin coating of metallic copper, which, when sepa- rated from the original, exhibits, in reverse, a most faithful representation of the latter. By using this in its turn as a mould or matrix, an absolutely perfect fac-simile of the plate or medal is obtained. In the former case, the impressions taken on paper are quite undistinguishable from those directly derived from the work of the artist; and as there is no limit to the number of electrotype plates which can be thus produced, engravings of the most beautiful description may be multiplied indefi- Fig. 149. nitely. The copper is very tough, and bears the action of the pre^s perfectly well. The apparatus used in this and many similar processes is of the simplest possible kind. A trough or cell of wood is divided by a porous diaphragm, made of a very thin piece of sycamore, into two parts; dilute sulphuric acid is put on one side, and a saturated solution of copper sulphate, some- times mixed with a little acid, on the other. A plate of zinc is soldered to a wire or strip of copper, the other end of which is secured by similar means to the engraved copper plate. The latter is then immersed in the solution of sulphate, and the zinc in the acid. To prevent deposition of copper on the back of the copper plate, that portion is covered with varnish. For medals and small works, a porous earthenware cell, placed in a jelly-jar, may be used, CHEMISTRY OF THE VOLTAIC PILE. 255 Other metals may be precipitated in the same manner, in a smooth and compact form, by the use of certain precautions which have been gath- ered by experience. Electro-gilding and plating are now carried on very largely and in great perfection by Messrs. Elkington and others. F.vi-ii non-conducting bodies, as sealing-wax and plaster of Paris, may be coated with metal; it is only necessary, as Mr. Robert Murray has shown, to rub over them the thinnest possible film of plumbago. Seals may thus be copied in a very few hours with unerring truth. Becquerel, several years ago, published an exceedingly interesting ac- count of certain experiments in which crystallized metals, oxides, and other insoluble substances had been produced by the slow and continuous action of feeble electrical currents, kept up for months, or even years. These products exactly resemble natural minerals; and, indeed, the ex- periments throw great light on the formation of the latter within the earth.* The common but very pleasing experiment of the lead-tree is greatly dependent on electro-chemical action. When a piece of zinc is suspended in a solution of lead acetate, the first effect is the decomposition of a por- tion of the latter, and the deposition of metallic lead upon the surface of the zinc; it is simply a displacement of a metal by a more oxidable one. The change does not, however, stop here: metallic lead is still deposited in large and beautiful plates upon that first thrown down, until the solution becomes exhausted, or the zinc entirely disappears. The first portions of lead form with the zinc a voltaic arrangement of sufficient power to decompose the salt: under the peculiar circum- JV^.150. stances in which the latter is placed, the metal is precipi- tated upon the negative portion that is, the lead while the oxygen and acid are taken up by the zinc. Mr. Grove has contrived a battery in which an electrical current, of sufficient intensity to decompose dilute sulphuric acid, is produced by the reaction of oxygen upon hydrogen. Each element of this interesting apparatus consists of a pair of glass tubes to contain the gases dipping into a vessel of acidulated water. Both tubes contain platinum plates, covered with a rough deposit of finely divided platinum, and furnished with conducting wires, which pass through the tops or sides of the tubes, and are hermetically sealed into the latter. When the tubes are charged with oxygen on the one side and hydrogen on the other, and the wires connected with a galvanoscope, the needle of the instrument becomes instantly affected ; and when ten or more are combined in a series, the oxygen-tube of the one with the hydrogen-tube of the next, &c., while the terminal wires dip into acidulated water, a rapid stream of minute bubbles from either wire in- dicates the decomposition of the liquid; and when the experiment is made with a small voltameter, it is found that the oxygen and hydrogen disen- gaged exactly equal in amount the quantities absorbed by the act of com- bination in each tube of the battery. Heat developed by the Electric Current. All parts of the electric circuit, the plates, the liquid in the cells of the battery, the conducting wires. and any electrolytes undergoing decomposition, all become heated during the passage of the current. The rise of temperature in any part of the circuit depends partly on the strength of the current, partly on its resistance, those bodies which offer the greatest resistance, or are the worst conduct- ors, being most strongly heated by a current of given strength. Thus, * Traite do I'Electricitfi et du MagnStisme, iii. 239. 256 ELECTRO-CHEMICAL when a thick and a thin wire of the same metal are included in the same circuit, the latter becomes most strongly heated, and a platinum wire is much more strongly heated than a silver or copper wire of the same thickness. By exact experiments it has been found that both in metallic wires and in liquids traversed by an electric current, the evolution of heat is directly proportional: 1st, to the resistance ; 2d, to the strength of the current. Joule has* also shown that the evolution of heat in each couple of the voltaic battery is subject to the same law, which, therefore, holds good in every part of the circuit, including the battery. The strength of an electric current is measured by the quantity of de- tonating gas (2 vol. H. to 1 vol. 0.) which it can evolve from acidulated water in a given time, and the unit of current strength is the current which eliminates one cubic centimetre of detonating gas at C. and 760mm. barometric pressure in a minute. Now Lenz has shown that when a current of the unit of strength passes through a wire whose resistance is equal to that of a copper wire 1 metre long and 1 millimetre in diameter, it develops a quantity of heat sufficient to raise the temperature of 1 gram of water from to 1 C. in 5| minutes; and assuming as the unit of heat the quantity required to raise the temperature of 1 gram of water from to 1 C., the law may be thus expressed: A current of the unit of strength passing through a conductor ivhich exerts the unit of resistance, develops therein 1-057 heat-units in an hour, or 0.076 heat- unit in a minute. With a current of a given strength, the sum of the quantities of heat evolved in the battery and in the metallic conductor joining its poles, is constant, the heat actually developed in the one part or the other varying according to the thickness of the metallic conductor. This was first shown by De la Rive, and has been confirmed by Favre.f De la Rive made use of a couple consisting of platinum and distilled zinc or cadmium, excited by pure and very strong nitric acid, the two metals being united by a platinum wire, more or less thick, which was plunged into the same quantity of strong nitric acid contained in a capsule similar to that which held the voltaic couple. By observing the temperatures in the two vessels with delicate thermometers, the sum of these temperatures was found to be constant, the one or the other being greater according to the thickness of the connecting wire. Favre,J by means of a calorimeter, similar to that which he used in his experiments on the development of heat by chemical action, has shown that in a pair of zinc and platinum plates, excited by dilute sulphuric acid and connected by platinum wires of various length and thickness, for every 32-5 grams of zinc dissolved, a quantity of heat is developed in the entire circuit equal to 18,137 'heat-units, but variously distributed between the battery-cell and the wire, according to the thickness of the latter. Now this quantity of heat is nearly the same as that which is evolved in the simple solution of 32 -5 grams of zinc in dilute sulphuric acid, without the formation of a voltaic circuit, viz. 18,444 units. Hence Favre concludes that the heat developed by the resistance of a metallic or other conductor connecting the poles of the battery is simply borrowed from the total quantity of heat evolved by the chemical action taking place in the battery, and is rigorously complementary to that which remains in the cells of the battery, the heat evolved in the entire circuit being the exact equivalent of the chemical action which takes place. If any external work is performed by the cur- * Phil. Mag. [3] xix. 210. f Ann. Ch. Phys. [3J xl. 393. % Comptes Reridus, xlv. 56. CRYSTALLIZATION; CRYSTALLINE FORM. 257 rent, such as electrolysis, or mechanical work, or by MM electro magnetic engine, the heat evolved in the circuit is diminished by the heat-eqaivalent of the decomposition or mechanical work done. CRYSTALLIZATION ; CRYSTALLINE FORM. Almost every substance, simple or compound, capable of existing in the solid state, assumes, under favorable circumstances, a distinct geometrical form or figure, usually bounded by plane surfaces, and having angles of fixed and constant value. The faculty of crystallization seems to be denied only to a few bodies, chiefly highly complex organic principles, which stand, as it were, upon the very verge of organization, and which, when in the solid state, are frequently characterized by a kind of beady or globular appearance, well known to microscopical observers. The most beautiful examples of crystallization are to be found among natural minerals, the results of exceedingly slow changes constantly occur- ring within the earth. It is invariably found that artificial crystals of salts, and other soluble substances which have been slowly and quietly deposited, surpass in size and regularity those of more rapid formation. Solution in water or some other liquid is a very frequent method of effecting crystallization. If the substance be more soluble at a high than at a low temperature, then a hot and saturated solution left to cool slowly will generally be found to furnish crystals; this is a very common case with salts and various organic principles. If it be equally soluble, or nearly so, at all temperatures, then slow spontaneous evaporation in the air, or over a surface of oil of vitriol, often proves very effective. Fusion and slow cooling may be employed in many cases : that of sulphur is a good example : the metals, when thus treated, usually afford traces of crystalline figures, which sometimes become very beautiful and distinct, as with bismuth. A third condition under which crystals very often form is in passing from the gaseous to the solid state, of which iodine affords a good instance. When by any of these means time is allowed for the sym- metrical arrangement of the particles of matter at the moment of solidifi- cation, crystals are produced. That crystals owe their figure to a certain regularity of internal structure is shown both by their mode of formation and also by the peculiarities at- tending their fracture. A crystal placed in a slowly evaporating saturated solution of the same substance grows or increases by a continued deposition of fresh matter upon its sides, in such a manner that the angles formed by the meeting of the latter remain unaltered. The tendency of most crystals to split in particular directions, called by mineralogists cleavage, is a certain indication of regular structure, while the curious optical properties of many among them, and their remarkable mode of expansion by heat, point to the same conclusion. It may be laid down as a general rule that every substance has its own crystalline form, by which it may very frequently be recognized at once not that each substance has a different figure, although very great diversity in this respect is to be found. Some forms are much more common than others, as the cube and six-sided prism, which are very frequently assumed by a number of bodies riot in any way related. The same substance may have, under different sets of circumstances, as high and low temperatures, two different crystalline forms, in which case it is said to be dimorphous. Sulphur and carbon furnish, as already .noticed, examples of this curious fact; another case is presented by calcium car- bonate in the two modifications of calc spar and arragonite, both chemically the same, but physically different. A fourth example might be given in mercuric iodide, which also has two distinct forms, and oven two distinct colors, offering as great a contrast as those of diamond and graphic. 22 * 258 CRYSTALLINE FORM. The angles of crystals are measured by means of instruments called gonio- meters, of which there are two kinds in use, namely, the old or common goniometer, and the reflecting goniometer of Dr. Wollaston. The common goniometer consists of a pair of steel blades moving with friction upon a centre, as shown in fig. 151. The edges a a are carefully Fig. 151. adjusted to the faces of the crystal whose inclination to each other it is required to ascertain, and then the instrument being applied to the* divided semicircle, the contained angle is at once read off. An approximative measurement, within one or two degrees, can be easily obtained by this instrument, provided the planes of the crystal are tolerably perfect, and large enough for the purpose. Some practice is of course required before even this amount of accuracy can be attained. The reflecting goniometer is a very superior instrument, its indications being correct within a fraction of a degree : it is applicable also to the measurement of the angles of crystals of very small size, the only condition required being that their planes be smooth and brilliant. The subjoined sketch (fig. 152) will convey, an idea of its nature and mode of use. Fig. 152. a is a divided circle or disc of brass, the axis of which passes stiffly and without shake through the support b. This axis is itself pierced to admit the passage of a round rod or wire, terminated by the milled-edged head c, and destined to carry the crystal to be measured, by means of the jointed arm d. The crystal at / can thus be turned round, or adjusted in any CRYSTALLINE FORM. 259 desired position, without the necessity of moving the disc. A vernier, e, immovably fixed to the upright support, serves to measure with great ac- curacy the angular motion of the divided circle. The principle upon which the measurement of the angle rests is very simple. If the two adjacent planes of a crystal be successively brought into the same position, the angle through which the crystal will have moved will be the supplement to that contained between the two planes If, for example, in a small crystal, cab (fig. 153) be the angle which is to be determined) Fig. 153. and the reflecting surface a b be placed in such a position that the reflection of the image of a distant point S seen from exactly covers a point E lying in the line of the reflected ray, then the other side a c of the angle cab must be turned through the angle c af, in order to assume the same po- sition, and to give the same phenomena as the plane a b previously did. The angle c a f is the supplement of the angle cab. All that is required to be done, therefore, is to measure the angle c a /with accuracy, and sub- tract its value from 180 ; and this the goniometer effects. One method of using the instrument is the following : The goniometer is placed at a convenient height upon a steady table in front of a well illuminated window. Horizontally across the latter, at the height of eight or nine feet from the ground, is stretched a narrow black ribbon, while a second similar ribbon, adjusted parallel to the first, is fixed beneath the window, a foot or eighteen inches above the floor. The object is to obtain two easily v'sible black lines, perfectly parallel. The crystal to be examined is attached to the arm of the goniometer at / by a little wax, and adjusted in such a manner that the edge joining the two planes whose inclination is to be measured shall nearly coincide with, or be parallel to. the axis of the instrument. This being done, the adjustment is completed in the following manner: The divided circle is turned until the zero of the vernier comes to 180 ; the crystal is then moved round by means of the inner axis c (fig. 152) until the eye placed near it perceives the image of the upper black line reflected from the surface of one of the planes in question. Fol- lowing this image, the crystal is still cautiously turned until the upper black line seen by reflection approaches and overlaps the lower black line seen directly by another portion of the pupil. It is obvious, that if the plane of the crystal be quite parallel to the axis of the instrument (the latter being horizontal), the two lines will coincide completely. If, however, this should not be the case, the crystal must be moved upon the wax until the two lines fall in one when superposed. The second face of the crystal must then be adjusted in the same manner, care being taken not to derange the position of the first. When by repeated observation it is found that both have lieen correctly placed, so as to bring the edge into the required condition <>f parallelism with the axis of motion, the measurement of the angle may be made. 260 CRYSTALLINE FORM. For this purpose the crystal is moved as before by the inner axis until the image of the upper line, reflected from the first face of the crystal, covers the lower line seen directly. The great circle, carrying the whole with it, is then cautiously turned until the same coincidence of the upper with the lower line is seen by means of the second face of the crystal ; that is, the second face is brought into exactly the same position as that previously occupied by the first. Nothing then remains but to read off by the vernier the angle through which the circle has been moved in this operation. The division upon the circle itself is very often made bac^vard, so that the angle of motion is not obtained, but its supplement, or the angle of the crystal required. It may be necessary to remark, that, although the principle of the operation described is in the highest degree simple, its successful practice requires considerable skill and experience. If a crystal of tolerably simple form be attentively considered, it will be- come evident that certain directions can be pointed out in which straight lines may be imagined to be drawn, passing through the central point of the crystal from side to side, from end to end, or from one angle to that opposed to it, &c., about which lines the particles of matter composing the crystal may be conceived to be symmetrically built up. Such lines, or axes, are not always purely imaginary, however, as may be inferred from the re- markable optical properties of many crystals: upon their number, relative lengths, position, and inclination to each other, depends the outward figure of the crystal itself. All crystalline forms may upon this plan be arranged in six classes or systems; these are the following: 1. The monometric, regular, or cubic system. The crystals of this division have three equal axes, all placed at right angles to each other. The most important forms are the cube (1), the regular octahedron (2), and the rhombic dodecahedron (3). The letters a a (fig. 154) show the termination of the three axes, placed as stated. Very many substances, both simple and compound, assume these forms, as most of the metals, carbon in the state of diamond, common salt, po- tassium iodide, the alums, fluor-spar, iron bisulphide, garnet, spinelle, &c. 2. The dimetric, quadratic, square prismatic, or pyramidal system. Three axes are here also observed, at right angles to each other. Of these, how- ever, two only are of equal length, the third being longer or shorter. The most important forms are, a right square prism, in which the lateral axes terminate in the central point of each side (1) ; a second right square prism, in which the axes terminate in the edges (2) ; a corresponding pair of right, square-based ocfohedrons (3 and 4). Examples of these forms are to be found in zircon, native stannic oxide, apophyllite, yellow potassium ferrocyanide, &c. CRYSTALLINE FORM. Fig. 155. 261 I... a a. Principal or vertical axes. 6 b. Secondary or lateral axes. 3. The rhombohedral system. This is very important and extensive ; it is characterized by four axes, three of which are equal, in the same plane, and inclined to each other at angles of 60, while the fourth or principal axis is perpendicular to all. The regular six-sided prism (1), the quartz-dode- cahedron (2), the rhombohedron (3), and a second dodecahedron, called a scalenohedron, whose faces are scalene triangles (4), belong to the system in question. Fig. 156. 12 34 a a. Principal axis. b b. Secondary axes. . Examples are readily found ; as in ice, calc spar, sodium nitrate, beryl, quartz or rock-crystal, and the semi-metals, arsenic, antimony, and tel- lurium. 4. The trimetric, rhombic, or right prismatic system. This is characterized by three axes of unequal lengths, placed at right angles to each other, as Fig. 157 Principal axis, b 6, C c. Secondary axes. in the right rectangular prism (1), the right rhombic prism ("2}, tho right rec- tangular-based octohedron (3), and the right rhombic-based octahedron (4). 262 CRYSTALLINE FORM. The system is exemplified in sulphur crystallized at a low temperature, arsenical iron pyrites, potassium nitrate and sulphate, barium sulphate, &c. 5. The monodinic or oblique prismatic system. Crystals belonging to this group have also three axes, which may be all unequal; two of these (the secondary) are placed at right angles, the third being so inclined as to be oblique to one and perpendicular to the other. To this system may be re- a a. Principal axis. 6 b, c c. Secondary axes. ferredthe four following forms: The oblique rectangular prism (1), the oblique rhombic prism (2), the oblique rectangular-based oclohedron (3), the oblique rhombic-based octohedron (4). Such forms are taken by sulphur crystallized by fusion and cooling, real- gar, sulphate, carbonate and phosphate of sodium, borax, green vitriol, and many other salts. 6. The triclinic, anorthic, or doubly oblique prismatic system. The crys- talline forms comprehended in this division are, from their great apparent irregularity, exceedingly difficult to study and understand. In them are a a. Principal axis, as before. 6 b, c c. Secondary axes. traced three axes, which may be all unequal in length, and are all oblique to each other, as in the two doubly oblique prisms (1 and 2), and in the cor- responding doubly oblique octohedrons (3 and 4). Copper sulphate, bismuth nitrate, and potassium quadroxalate afford illustrations of these forms. If a crystal increase in magnitude by equal additions on every part, it is quite clear that its figure must remain unaltered ; but if, from some cause, this increase should be partial, the newly deposited matter being distributed unequally, but still in obedience to certain definite laws, then alterations of form are produced, giving rise to figures which have a direct geometri- CRYSTALLINE FORM. 263 cal connection with that from which they are derived. If, for example, in the cube, a regular omission of successive rows of particles of mutter in a certain order be made at each solid angle, while the crystal continues to increase elsewhere, the result will be the production of small triangular planes, which, as the process advances, gradually usurp the whole of the surface of the crystal, and convert the cube into an octohedron. The new Fig. 160. Passage of cube to octohedron. planes are called secondary, and their production is said to take place by regular decrements upon the solid angles. The same thing may happen on the edges of the cube ; a new figure, the rhombic dodecahedron, is then generated. The modifications which can thus be produced of the original or primary figure (all of which are subject to exact geometrical laws) are very numerous. Several distinct modifications may be present at the same time, and thus render the form exceedingly complex. Crystals often cleave parallel to all the planes of the primary figure, as in calc spar, which offers a good illustration of this perfect cleavage. Some- times one or two of these planes have a kind of preference over the rest in this respect, the crystal splitting readily in these directions only. A very curious modification of the figure sometimes occurs by the exces- sive growth of each alternate plane of the crystal; the rest become at length obliterated, and the crystal assumes the character called hemihedral or half-sided. This is well seen in the production of the tetrahedron from the regular octohedron, and of the rhombohedric form by a similar change from the quartz-dodecahedron already figured. Fig. 161. Passage of octohedron to tetrahedron. Forms belonging to the same crystallographic system are related to each other by several natural affinities. 1. It is only the simple forms of the same system that can combine into a com- plex form. For in all fully developed (holohedral) natural crystals it is found that all the similar parts, if modified at all, are modified in an ex- actly similar manner (in hemihedral forms, half the^ similar edges and angles alternately situated are similarly modified). Now this can be the case only when the dominant form and the modifying form are developed according to the same law of symmetry. Thus, if a cube and a regular octohedron are developed round the same system of axes, each summit of the cube is cut off to the same extent by a face of the octohedron, or vice versd. But a cube could never combine in this planner with a rhombic octo- 264 CRYSTALLINE FORM; ISOMORPHISM. hedron, because it would be impossible to place the two forms in such a manner that similar parts of the one should throughout replace similar parts of the other. The crystals of each system are thus subject to a peculiar and distinct set of modifications, the observation of which very frequently constitutes an excellent guide to the discovery of the primary form itself. 2. Crystals belonging to the same system are intimately related in their optical properties. Crystals belonging to the regular system (as the diamond, alum, rock-salt, &c.) refract light in the same manner as uncrystallized bodies; that is to say, they have but one refractive index, and a ray of light passing through them in any direction is refracted singly. But all other crystals refract doubly, that is to say, a ray of light passing through them (except in certain directions) is split into two rays, the one, called the ordinary ray, being refracted as it would be by an amorphous body, the other, called the extraordinary ray, being refracted according to peculiar and more complex laws (see LIGHT). Now the crystals of the dimetric and hexagonal systems resemble each other in this respect, that in all of them there is one direc- tion, called the optic axis, or axis of double refraction (coinciding with the principal crystallographic axis), along which a ray of light is refracted singly, while in all other directions it is refracted doubly; whereas in crys- tals belonging to the other systems, viz., the trimetric and the two oblique systems, there are always two directions or axes, along which a ray is singly refracted. 3. Crystals belonging to the same system resemble each other in their mode of con- ducting heat. Amorphous bodies and crystals of the regular system con- duct heat equally in all directions, so that, supposing a centre of heat to exist within such a body, the isothermal surfaces will be spheres. But crystals of the dimetric and hexagonal systems conduct equally only in directions perpendicular to the principal axis, so that in such crystals the isothermal surfaces are ellipsoids of revolution around that axis ; and crystals belonging to either of the three other systems conduct unequally in all directions, so that in them the isothermal surfaces are ellipsoids with three unequal axes. Relations of Form and Constitution ; Isomorphism. Certain substances, to which a similar chemical constitution is ascribed, possess the remarkable property of exactly replacing each other in crys- tallized compounds without alteration of the characteristic geometrical figure. Such bodies are said to be isomorphous.* For example, magnesia, zinc oxide, cupric oxide, ferrous oxide, and nickel oxide are allied by isomorphic relations of the most intimate nature. The salts formed by these substances with the same acid and similar pro- portions of water of crystallization, are identical in their form, and, when of the same color, cannot be distinguished by the eye: the sulphates of magnesium and zinc may be thus confounded. These sulphates, too, all combine with potassium sulphate and ammonium sulphate, giving rise to double salts, whose figure is the same, but quite different from that of the simple sulphates. Indeed this connection between identity of form and parallelism of constitution runs through all their combinations. In the same manner alumina and iron sesquioxide replace each other continually without change of crystalline figure: the same remark may be made of the oxides of potassium, sodium, and ammonium, these bodies being strictly isomorphous. The alumina in common alum may be replaced by iron sesquioxide, the potash by ammonia or by soda, and still the figure of the crystal remains unchanged. These replacements may be partial Jvom fffoj. equal, and n6pi], shape or form. CRYSTALLINE FORM ISOMORPHISM. 265 only: we may have an alum containing both potash and ammonia, or alumina and chromium sesquioxide. By artificial management namely, by transferring the crystal successively to different solutions we may have these isomorphous and mutually replacing compounds distributed in different layers upon the same crystal. For these reasons, mixtures of isomorphous salts can never be separated by crystallization, unless their difference of solubility is very great. A mixed solution of ferrous sulphate and nickel sulphate, isomorphous salts, yields on evaporation crystals containing both iron and nickel. But if before evaporation the ferrous salt be converted into ferric salt, by chlorine or other means, then the crystals obtained are free from iron, except that of the mother-liquor which wets them. The ferric salt is no longer iso- morphous with the nickel salt, and easily separates from the latter. When compounds are thus found to correspond, it is inferred that the elements composing them are also sometimes isomorphous. Thus, the metals magnesium, zinc, iron, and copper are presumed to be isomorphous: arsenic and phosphorus have not the same crystalline form; nevertheless, they are said to be isomorphous, because arsenic and phosphoric acids give rise to combinations which agree most completely in figure and constitution. The chlorides, iodides, bromides, and fluorides agree, whenever they can be observed, in the most perfect manner : hence the elements themselves are believed to be also isomorphous. Unfortunately, for obvious reasons, it is very difficult to observe the crystalline figure of most of the elemen- tary bodies, and this difficulty is increased by the frequent dimorphism they exhibit. Absolute identity of value in the angles of crystals is not always ex- hibited by isomorphous substances. In other words, small variations often occur in the magnitude of the angles of crystals of compounds which in all other respects show the closest isomorphic relations. This should occa- sion no surprise, as there are reasons why such variations might be ex- pected, the chief perhaps being the unequal effects of expansion by heat, by which the angles of the same crystal are changed by alteration of tem- perature. A good example is found in the case of the carbonates of cal- cium, magnesium, manganese, iron, and zinc, which are found native crys- tallized in the form of obtuse rhombohedrons (fig. 156), not distinguishable from each other by the eye, or even by the common goniometer, but show- ing small differences when examined by the more accurate instrument of Dr. Wollaston. These compounds are isomorphous, and the measurements of the obtuse angles of their rhombohedrons are as follows: Calcium carbonate . . . 105 5' Magnesium " ... 107 25' Manganous " ... 107 20' Ferrous " ... 107 Zinc " ... 107 40' Anomalies in the composition of various earthy minerals, which formerly threw much obscurity upon their chemical nature, have been in great measure explained by these discoveries. Specimens of the same mineral from different localities were found to afford very discordant results on analysis. But the proof once given of the extent to which substitution of isomorphous bodies may go, without destruction of what may be called the primitive type of the compound, these difficulties vanish. Decision of a doubtful point concerning the constitution of a compound may now and then be very satisfactorily made by a reference to this same law of isomorphism. Thus, alumina, the only known oxide of aluminium, is judged to be a sesquioxide, from its relation to sccquioxide of iron, 23 266 CRYSTALLINE FORM ISOMORPHISM. which is certainly so ; the black oxide of copper is inferred to be really the monoxide, although it contains twice as much oxygen as the red oxide, because it is isomorphous with magnesia and zinc oxide, both undoubted monoxides. The subjoined table will serve to convey some idea of the most important families of isomorphous elements ; it is taken, with slight modification, from Professor Graham's Elements of Chemistry,* to which the pupil is referred for fuller details on this interesting subject: (I-) Sulphur Selenium Tellurium. . Magnesium Calcium Manganese Iron Cobalt Nickel Zinc Cadmium Copper Chromium Aluminium Glucinum. Isomorphous Groups. (3.) Barium Strontium Lead. (4.) Platinum Iridium Osmium. Titanium Zirconium Tungsten Molybdenum Tantalum Niobium. (6.) liun Sodium Silver Thallium Gold Potassium Ammonium. (70 Chlorine Iodine Bromine Fluorine Cyanogen. (8.) Phosphorus Arsenic Antimony Bismuth Vanadium. A comparison of this table with that on page 236 will show that, in many instances, isomorphous elements exhibit equal equivalence or combining power, and more generally that the isomorphous groups consist either wholly of perissad or wholly of artiad elements. The only apparent ex- ception to this rule is aiforded by tantalum and niobium, which, although pentads, are isomorphous with tin, tungsten, and other tetrad and hexad elements. * Second Am. edition, p. 149. CHEMISTRY OF THE METALS, rpHE metals constitute the second and larger group of elementary bodies. JL A great number of them are of very rare occurrence, being found only in a few scarce minerals ; others are more abundant, and some few almost universally diffused throughout the globe. Some of these bodies are of most importance when in the metallic state ; others, when in combination, chiefly as oxides, the metals themselves being almost unknown. Many are used in medicine and in the arts, and are essentially connected with the progress of civilization. If arsenic be included, the metals amount to fifty in number. Physical Properties. One of the most remarkable and striking charac- ters possessed by the metals is their peculiar lustre : this is so character- istic, that the expression metallic lustre has passed into common speech. This property is no doubt connected with the extraordinary degree of opa- city which the metals present in every instance. The thinnest leaves or plates, and the edges of crystalline laminae, arrest the passage of light in the most complete manner. An exception to the rule is usually made in favor of gold-leaf, which, when held up to the daylight, exhibits a greenish, and in some cases a purple color, as if it were really endued with a certain degree of translucency : the metallic film is, however, generally so imper- fect that it is somewhat difficult to say whether the observed effect may not be in some measure due to multitudes of little holes, many of which are visible to the naked eye; but Faraday's experiments have established the translucency of gold beyond all doubt. In point of color, the metals present a certain degree of uniformity : with two exceptions viz., copper, which is red, and gold, which is yellow all these bodies are included between the pure white of silver and the bluish-gray tint of lead : bismuth, it is true, has a pinkish color, and cal- cium and strontium a yellowish tint, but these tints are very feeble. The differences of specific gravity are very wide, passing from lithium, potassium, and sodium, which are lighter than water, to platinum, which is nearly twenty-one times heavier than an equal bulk of that liquid. Table of the Specific Gravities of Metals at 15-5 C. (60 F.) Platinum . . . .21-50 Gold .... 19-50 Uranium .... 18-4 Tungsten . . . 17-00 Mercury .... 13-59 Palladium . . . 11-30 to 11-8 Lead H'45 Silver .... 10-50 Bismuth . . . .9-90 Copper .... 8-96 Nickel .... 8-80 Cadmium . . . 8-70 Molybdenum . . .8-63 268 CHEMISTRY OF THE METALS. Cobalt . Manganese Iron Tin Zinc Antimony Tellurium . Arsenic Aluminium Magnesium . Sodium . Potassium . Lithium . 8-54 8-00 7-79 7-29 6-86 to 7-1 6-80 6-11 5-88 2-56 to 2-67 1-75 0-972 0-865 0-593 The property of malleability, or power of extension under the hammer, or between the rollers of the flatting-mill, is possessed by certain of the metals to a very great extent. Gold-leaf is a remarkable example of the tenuity to which a malleable metal may be brought by suitable means. ' The gilding on silver wire used in the manufacture of gold lace is even thinner, and yet presents an unbroken surface. Silver may be beaten out very thin copper also, but to an inferior extent ; tin and platinum are easily rolled out into foil ; iron, palladium, lead, nickel, cadmium, the metals of the alkalies, and mercury when solidified, are also malleable. Zinc may be placed midway between the malleable and brittle division ; then perhaps bismuth ; and, lastly, such metals as antimony and arsenic, which are al- together destitute of malleability. The specific gravity of malleable metals is usually very sensibly increased by pressure or blows, and the metals themselves are rendered much harder, with a tendency to brittleness. This condition is destroyed and the former soft state restored by the operation of annealing, which consists in heating the metal to redness out of contact with air (if it will bear that temperature without fusion), and cooling it quickly or slowly according to the circum- stances of the case. After this operation, it is found to possess its original specific gravity. Ductility is a property distinct from the last, inasmuch as it involves the principle of tenacity, or power of resisting tension. The Fig. 162. art of wire-drawing is one of great antiquity : it consists in drawing rods of metal through a succession of trumpet- shaped holes in a steel plate, each being a little smaller than its predecessor, until the requisite degree of fineness is at- tained. The metal often becomes very hard and rigid in this process, and is then liable to break : this is remedied by annealing. The order of tenacity among the metals suscep- tible of being easily drawn into wire is the following: it is determined by observing the weights required to break asunder wires drawn through the same orifice of the plate : \J Iron Copper Platinum Silver Gold Zinc Tin Lead. Metals differ as much in fusibility as in density. The following table will give an idea of their relations to heat. The melting-points of the metals which fuse only at a temperature above ignition, and that of zinc, are on the authority of the late Professor Daniell, having been observed by the help of his pyrometer before described: CHEMISTRY OF THE METALS. 269 " Mercury Melting points. F. C. Rubidium Potassium Sodium Lithium Tin , 101-3 38-5 144-5 62-5 207-7 97-6 356 180 442 27-8 Fusible below a red heat. Cadmium Bismuth . Thallium Lead (about) 442 228 497 258 561 294 617 325 Tellurium rather less fusible than lead. Arsenic unknown. Zinc 773 Antimony just below redness. 412 Melting points. F. C. f Silver 1873 1023 1996 1091 Gold 2016 1102 2786 1530 v Pure iron Nickel Cobalt Highest heat of forge . Manganese Palladium Infusible below Molybdenum a red heat. Uranium Agglomerate, but do not melt in the Tungsten forge. Chromium Titanium Cerium Osmium Iridium Rhodium Infusible in ordinary blast-furnaces ; fusible by oxy-hydrogen blowpipe. Platinum Tantalum Some metals acquire a pasty or adhesive state before becoming fluid: this is the case with iron and platinum, and also with the metals of the alkalies. It is this peculiarity which confers the very valuable property of welding, by which pieces of iron and steel are united without solder, and the finely divided metallic sponge of platinum is converted into a solid and compact bar. Volatility is possessed by certain members of this class, and perhaps by all, could temperatures sufficiently elevated be obtained. Mercury boils and distils below a red heat; potassium, sodium, zinc, magnesium, and cadmium rise in vapor when heated to bright redness ; arsenic and tellu- rium are volatile. 23* 270 CHEMISTRY OF THE METALS. CHEMICAL RELATIONS OF THE METALS. Metallic combinations are of two kinds namely, those formed by the union of metals among themselves, which are called alloys, or, where mer- cury is concerned, amalgams; and those generated by combination with the non-metallic elements, as oxides, chlorides, sulphides, &c. In this latter case, the metallic characters are almost invariably lost. Alloys. Most metals are probably, to some extent, capable of existing in a state of combination with each other in definite proportions; but it is difficult to obtain these compounds in a separate condition, since they dissolve in all proportions in the melted metals, and do not generally differ so widely in their melting points from the metals they may be mixed with, as to be separated by crystallization in a definite condition. Exceptions to this rule are met with in the cooling of argentiferous lead, the crystal- lization of brass, and of gun-metal. The chemical force capable of being exerted between different metals is for the most part very feeble, and the consequent state of combination is therefore very easily disturbed by the influence of other forces. The stability of such metallic compounds is, however, greater in proportion to the general chemical dissimilarity of the metals they contain. But in all cases of combination between metals, the alteration of physical characters, which is the distinctive feature of chemical combination, does not take place to any great extent. The most unquestionable compounds of metals with metals are still metallic in their general physical characters, and there is no such transmutation of the individuality of their constituents as takes place in the combination of a metal with oxygen, or sulphur, chlorine, &c. The alteration of characters in alloys is generally limited to the color, de- gree of hardness, tenacity, &c., and it is only when the constituent metals are capable of assuming opposite chemical relations that these compounds are distinguished by great brittleness. The formation of actual chemical compounds, in some cases, when two metals are melted together, is indicated by several phenomena, viz., the evolution of heat, as in the case of platinum and tin, copper and zinc, &c. The density of alloys differs from that of mere mixtures of the metals. In the solidification of alloys, the temperature does not always fall uni- formly, but often remains stationary at particular degrees, which may be regarded as the solidifying points of the compounds then crystallizing. Tin and lead melted together in any proportions always form a compound which solidifies at 187 C. The melting-point of an alloy is often very different from the point of solidification, and it is generally lower than the mean melting point of the constituent metals. But though metals may combine when melted together, it is doubtful whether they remain combined after the solidification of the mass, and the wide differences between the melting and solidifying points of certain alloys appear to indicate that the existence of these compounds is limited to a certain range of temperature. Matthiessen* regards it as probable that the condition of an alloy of two metals in the liquid state may be either that of 1. A solution of one metal in another; 2. Chemical combination ; 3. Mechanical mixture ; or, 4. A solution or mixture of two or all of the above; and that similar differences may obtain as to its condition in the solid state. The chemical action of reagents upon alloys is sometimes very different from their action upon metals in the separate state : thus, platinum alloyed * British Association Reports, 1863, p. 97. CLASSIFICATION OF METALS. 271 with silver is readily dissolved by nitric acid, but is not affected by that acid when unalloyed. On the contrary, silver, which in the separate sun- is readily dissolved by nitric acid, is not dissolved by it when alloyed with gold in proportions much less than one fourth of the alloy by weight. COMPOUNDS OF METALS WITH METALLOIDS. CLASSIFICATION OF METALS. A classification of the metals according to their equivalence or atomicity is given in the table on p. 236, each of the classes thus formed being divided into groups, the individual members of which possess certain physical or chemical characters in common. CLASS I. Monad Metals. 1. Among these metals potassium, sodium, csesium, rubidium, and lithium are called alkali-metals. They are soft, easily fusible, volatile at higher temperatures; combine very energetically with oxygen; decompose water at all temperatures; and form strongly basic oxides, which are very soluble in water, yielding powerfully caustic and alkaline hydrates, from which the water cannot be expelled by heat. Their carbonates are soluble in water, arid each metal forms only one chloride. The hypothetical metal ammonium, NH 4 (p. 348), is usually added to the list of alkali-metals, on account of the general similarity of its compounds to those of potassium and sodium. 2. Silver differs greatly from the alkali-metals in its physical and most of its chemical properties, but it is related to them by the isomorphism of some of its compounds with the corresponding compounds of those metuls; thus it forms an alum, similar in form and composition to ordinary potash alum. CLASS II. Dyad Metals. 1. The three metals, barium, strontium, and calcium, form oxides called alkaline earths, less soluble in water than the true alkalies, but exhibiting similar taste, causticity, and action on vegetable colors. The metals of this group form but one chloride, e.g. BaCl 2 ; their carbonates are insoluble in water, and barium sulphate is also insoluble ; strontium and calcium sulphates slightly soluble. 2. The metals of the next group, viz. glucinum, thorinum, yttrium, erbium, lanthanum, and didymium, form oxides called earths, which are insoluble in water, and cannot be reduced to the metallic state by hydrogen or carbon ; their carbonates are insoluble in water, their sulphates soluble. These metals also form but one chloride, viz. a dichloride. They are all very rare. 3. Magnesium, zinc, and cadmium resemble one another in being volatile at high temperatures, and burning when heated in the air ; they decompose water at high temperatures, eliminate hydrogen from dilute acids, and form only one oxide and one chloride, e.g. ZnO and ZnCl 2 . Magnesium was for- merly classed as an earth-metal, but it bears a much closer analogy to zinc. 4. Mercury and copper each form two chlorides and two oxides : mercury, for example, forms the two chlorides, HgCl 2 and II0. The copper com- Hg-Cl Hg pounds are similarly constituted. These metals do not decompose water at any temperature ; they are oxidized by nitric and by strong sulphuric acid. The oxides of mercury are reduced to the metallic state by heat alone ; those of copper, by ignition with hydrogen or charcoal. CLASS III. Triad Metals. The only two metals belonging to this class are thallium and gold. Each of them forms a monochloridc and a trichlo- ride, also corresponding oxides, e.g. gold chlorides, AuCl and AuCl 3 ; oxides, 272 CLASSIFICATION OF METALS. Au 2 and Au 2 3 . The mono-compounds of thallium are much more stable than the tri-compounds, and in respect of these compounds thallium exhibits very close analogies with the alkali-metals, forming, for example, an alum isomorphous with common potash alum, and phosphates analogous in com- position to the phosphates of sodium. CLASS IV. Tetrad Metals. 1. Platinum, palladium, iridium, rhodium, ruthenium, and osmium form a natural group of metals, occurring together in the metallic state, and resembling each other in many of their proper- ties. Platinum and palladium form dichlorides and tetrachlorides, with corresponding oxides, as, e.g., PtCl 2 , PtCl 4 , PtO, Pt0 2 . Iridium forms a dichloride, a tetrachloride, and an intermediate chloride, lr 2 C! 6 , which may be regarded as a compound of the other two, or as constituted according to IrCl 3 the formula | . Ruthenium and osmium form chlorides similar in con- IrCl 3 stitution to those of iridium ; rhodium only a dichloride, RhCl 2 , and a tri- chloride, Rli 2 Cl 6 . All these metals form oxides analogous in composition to their chlorides, e. g. IrO, Ir 2 3 , Ir0 2 and likeAvise higher oxides, iridium and rhodium forming trioxides, Ir0 3 and Rh0 3 , and osmium and ruthenium forming tetroxides, Os0 4 and Ru0 4 : whence it might be inferred that iridium and rhodium are hexad, osmium and ruthenium octads ; but there are no Chlorides corresponding to these oxides, and, as already observed (p. 355), the atomicity of an element cannot be inferred from the composi- tion of its oxides. The metals of the platinum group are not acted upon by nitric acid, but only by chlorine or nitromuriatic acid. With the exception of osmium, they do not oxidize in the air at any temperature, and their oxides are all reducible by heat alone. These metals, together with gold, silver, and mercury, which likewise exhibit the last-mentioned character, are sometimes called noble metals. 2. Tin and titanium are closely related to silicium, each forming a volatile tetrachloride ; namely, stannic chloride, SnCl 4 , and titanic chloride, TiCl 4 , together with the corresponding oxides. Tin likewise forms the stannous compounds, in which it is bivalent, e.g., SnCl 2 , SnO; and titanium forms the titanous compounds, in which it is apparently trivalent, but really quadrivalent, like aluminium. 3. Lead stands by itself. Its quadrivalence is inferred from the compo- sition of plumbo-tetrethide, Pb(C 2 H 5 ) 4 ; but in most of its compounds it is bivalent, forming only one chloride, PbCl 2 , with corresponding iodide, bromide, and fluoride. It forms also the corresponding oxide, PbO, together with a lower oxide, Pb 2 0, and three higher oxides, Pb 3 4 . Pb 4 5 , and Pb0 2 . Lead is allied to barium and strontium by isomorphism of its sulphate with the sulphates of barium and strontium, and to silver, thallium, and mercury by the sparing solubility of its chloride, which is precipitated by hydro- chloric acid from solutions of lead salts. 4. Zirconium forms a tetrachloride, ZrCl 4 , and a dioxide, Zr0 2 . Aluminium is inferred to be tetradic from its analogy to iron in the ferric compounds, but it forms only one class of salts in which it is apparently trivalent, the A1C1 3 0=A1 chloride being A1 2 C1 6 I , and the oxide I >0. Aluminium and A1C1 3 =A1 zirconium belong to the class of earth-metals, and will be described in con- nection with them. 5. The Iron group comprises iron, manganese, cobalt, nickel, uranium, cerium, and indium. The atomicity of these metals has already been discussed. Manganese forms a chloride of somewhat doubtful composition, in which it is apparently septivalent ; but the rest do not form any compounds with CLASSIFICATION OF METALS. 273 monad elements in which they exhibit an equivalent value greater than 4. All these metals decompose water at high temperatures. N\ckel and cobalt are magnetic, like iron, and their salts are isomorphous with the cor- responding iron compounds. Indium is a-very rare metal, which has been but imperfectly examined, but it probably belongs to the same group. CLASS V. Pentad Metals. 1. Arsenic and antimony form trichlorides and pentachlorides analogous to those of phosphorus, also the corresponding oxides. Bismuth forms a volatile trichloride, and a dichloride, BLCL. BiCl 2 or | . Vanadium was formerly supposed to belong to the tungsten BiCl 2 group, but it has lately been shown to be a pentad. Its chlorides are not known, but it forms an oxychloride, VOC1 3 , analogous to phosphorus oxy- chloride ; also the oxides, V 2 3 and V./) 5 , analogous to those of phosphorus and arsenic, the latter yielding a series of salts, the vanadates, isomorphous with the phosphates and arsenates of corresponding composition. 2. Tantalum and niobium, formerly regarded as tetrads, have lately been shown by Marignac to form pentachlorides and pentoxides. The oxides of the pentad metals are, for the most part, of acid character. CLASS VI. Hexad Metals. 1. Chromium forms a hexfluoride, CrF 6 , and a corresponding oxide, Cr0 3 . It likewise forms two series of compounds, in which it exhibits lower degrees of equivalence, viz., the chromic com- pounds analogous to the ferric compounds, in which it is apparently tri- Offff C1 8 valent, but really quadrivalent: e.g., chromic chloride, Cr.,Cl 6 or I Cr"' n 3 and the chromous compounds, analogous to the ferrous compounds, in which it is bivalent, e.g., Cr"Cl 2 , Cr"0. 2. Tungsten forms a hexchloride, WC1 6 , and the corresponding oxide, W0 3 . Molybdenum is not known to form a chloride higher than MoCl 4 , but its trioxide, Mo0 3 , is known; and from the general similarity of the tung- sten and molybdenum compounds, the latter metal is inferred to the hexadic. The metals of the alkalies and alkaline earths, on account of their inferior specific gravity, are often called light metals ; the others, heavy metals. Metallic Chlorides. All metals combine with chlorine, and most of them in several proportions, as above indicated, forming compounds which niuy be regarded as derived from one or more molecules of hydrochloric acid, by substitution of a metal for an equivalent quantity of hydrogen ; thus : From HC1 are derived monochlorides like KC1 H.C1 2 " dichlorides " Ba"Cl a " H,CL " trichlorides " AuC1 3 " H^Cl^ " tetrachlorides " Sn if Cl 4 , &c. &c. Hydrochloric acid may, in fact, be regarded as the type of chlorides in general. Several chlorides occur as natural products. Sodium chloride, or com- mon salt, occurs in enormous quantities, both in the solid state as rock-salt, and dissolved in sea-water, and in the water of rivers and springs. Po- tassium chloride occurs in the same forms, but in smaller quantity ; Uie chlorides of lithium, csesium, rubidium, and thallium also occur in small 274 CHEMISTRY OF THE METALS. quantities in certain spring waters. Mercurous chloride, Hg 2 Cl 2 , and silver chloride, AgCl, occur as natural minerals. 1. Chlorides are generally prepared by one or other of the following processes: 1. By acting upon the metal with chlorine gas. Antimony pen- tachloride and copper dichloride are examples of chlorides sometimes pro- duced in this manner. The chlorides of gold and platinum are usually pre- pared by acting upon the metals with nascent chlorine, developed by hydro- chloric and nitric acids. Sometimes, on the other hand, the metal is in a nascent state, as when titanic chloride is formed by passing a current of chlorine over a heated mixture of charcoal and titanic oxide. The chlo- rides of aluminium and chromium may be obtained by similar processes. 2. Chlorine gas, by its action upon metallic oxides, drives out the oxygen, and unites with the respective metals to form chlorides. This reaction sometimes takes place at ordinary temperatures, as is the case with silver oxide ; sometimes only at a red heat, as is the case with the oxides of the alkalies and alkaline earth-metals. The hydrates and carbonates of these last metals, when dissolved or suspended in hot water and treated with ex- cess of chlorine, are converted, chiefly into chlorides, partly into chlorates. 3. Many metallic chlorides are prepared by acting upon the metals with hydrochloric acid. Zinc, cadmium, iron, nickel, cobalt, and tin dissolve readily in hydrochloric acid, with liberation of hydrogen ; copper only in the strong boiling acid; silver, mercury, palladium, platinum, and gold, not at all. Sometimes the metal is substituted, not for hydrogen, but for some other metal. Stannous chloride, for instance, is frequently made by distilling metallic tin with mercuric chloride; thus: 2HgCl -f- Sn 2 = 2Snd, 4. By dissolving a metallic oxide, hydrate, or carbonate in hydrochloric acid. All monochlorides and dichlorides are soluble in water, excepting silver chloride, AgCl, and mercurous chloride, Hg 2 Cl 2 ; lead chloride, PbCl 2 , is sparingly soluble ; these three chlorides are easily formed by precipitation. Many metallic chlorides dissolve also in alcohol and in ether. Most monochlorides, dichlorides, and trichlorides volatilize at high tem- peratures without decomposition : the higher chlorides, when heated, give off part of their chlorine. Some chlorides which resist the action of heat alone are decomposed by ignition in the air, yielding metallic oxides and free chlorine : this is the case with the dichlorides of iron and manganese ; but most dichlorides remain undecomposed, even in this case. All metallic chlorides, excepting those of the alkali-metals and earth-metals, are de- composed at a red heat by hydrogen gas, with formation of hydrochloric acid : in this way, metallic iron may be obtained in fine cubical crystals. Silver chloride placed in contact with metallic zinc or iron, under dilute sul- phuric or hydrochloric acid, is reduced to the metallic state by the nascent hydrogen. Sulphuric, phosphoric, boric, and arsenic acids decompose most metallic chlorides, sometimes at ordinary, sometimes at higher temperatures. All metallic chlorides, heated with lead dioxide or manganese dioxide and sul- phuric acid, give off chlorine, e. g, : 2NaCl -f Mn0 2 -f 2S0 4 H 2 = S0 4 Na 2 -f S0 4 Mn -j- 20H 2 -f C1 2 . Sodium Manganese Sulphuric Sodium Mauganous chloride. dioxide. acid. sulphate. sulphate. Chlorides distilled with sulphuric acid and potassium chromate, yield a dark bluish-red distillate of chromic oxychloride. Some metallic chlorides are decomposed by water, forming hydrochloric acid and an oxychloride, e. g. : BiCL, -f OH 2 = 2HC1 -f- BiClO. The chlorides of antimony and CHLORIDES; BROMIDES. 275 stannous chloride are decomposed in a similar manner. All soluble chlo- rides give with solution of silver nitrate, a white precipitate of silver chlo- ride, easily soluble in ammonia, insoluble in nitric acid. With nt> mtrons nitrate, they yield a white curdy precipitate of mercurous chloride, black- ened by ammonia; and with lead-salts, not too dilute, a white crystalline precipitate of lead chloride, soluble in excess of water. Metallic chlorides unite with each other and with the chlorides of the non-metallic elements, forming such compounds as potassium chloromcrcu- rate, 2KCl.HgCl 2 , sodium chloroplatinate, 2NaCl.PtCl 4 , r>otassium chlorio- date, KC1,IC1 3 , &c Metallic chlorides combine in definite proportions with ammonia and organic bases; the chlorides of platinum form with ammonia the compounds 2NH 3 .PtCl 2 , 4NH 3 .PtCl 2 , 2NH s .PtCl 4 , and 4NH 3 .PtCl 4 ; mer- curic chloride forms with aniline the compound 2C 6 H 7 N.HgCl 2 , &c. Chlorides also unite with oxides and sulphides, forming oxy chlorides and oxy sulphides, which may be regarded as chlorides having part of their chlo- rine replaced by an equivalent quantity of oxygen or sulphur (C1 2 by or S). Bismuth, for example, forms an oxychloride having the composition Bi /x/ C10 or BiCl s .Bi 2 8 . Bromides. Bromine unites directly with most metals, forming com- pounds analogous in composition to the chlorides, and resembling them in most of their properties. The bromides of the alkali-metals occur in sea- water and in many saline springs ; silver bromide occurs as a natural mineral. Nearly all bromides are soluble in water, and may be formed by treating an oxide, hydrate, or carbonate, with hydrobromic acid, the solu- tions when evaporated giving oif water for the most part, and leaving a solid metallic bromide ; some of them, however, namely, the bromides of magnesium, aluminium, and the other earth-metals, are more or less decomposed by evaporation, giving off hydrobromic acid, and leaving a mixture of metallic bromide and oxide. Silver bromide and mercurous bromide are insoluble in water, and lead bromide is very sparingly soluble ; these are obtained by precipitation. Metallic bromides are solid at ordinary temperatures ; most of them fuse at a moderate heat, and volatilize at higher temperatures. The bromides of gold and platinum are decomposed by mere exposure to heat; many others give up their bromine when heated in contact with the air. Chlo- rine, with the aid of heat, drives out the bromine and converts them into chlorides. Hydrochloric acid also decomposes them at a red heat, giving off hydrobromic acid. Strong sulphuric or nitric acid decomposes them, with evolution of hydrobromic acid, which, if the sulphuric or nitric acid is con- centrated and in excess, is partly decomposed, with separation of bromine and formation of sulphurous oxide or nitrogen dioxide. Bromides heated with sulphuric acid and manganese dioxide or potassium chromate, give off free bromine. Bromides in solution are easily decomposed by chlorine, either in the form of gas or dissolved in water, the liquid acquiring a red or reddish- yellow color, according to the quantity of bromine present; and on agitat- ing the liquid with ether, that liquid dissolves the bromine, forming a red solution, which rises to the surface. Soluble bromides give with silver nitrate a white precipitate of silver bromide, greatly resembling the chloride, but much less soluble in am- monia, insoluble in hot nitric acid. Mercurous nitrate produces a yellowisl white precipitate ; and lead acetate, a white precipitate much less soluble in water than the chloride. Palladium nitrate produces in solutions of bromides not containing* chlorine, a black precipitate of bromide. Pal- ladium chloride produces no precipitate; neither does the nitrate, il soluble chlorides are present. 276 CHEMISTRY OF THE METALS. Bromides unite with each other in the same manner as chlorides; also with oxides, sulphides, and ammonia. Iodides. These compounds are obtained by processes similar to those which vield the chlorides and bromides. Many metals unite directly with iodine. Potassium and sodium iodides exist in sea-water and in many salt springs; silver iodide occurs as a natural mineral. Metallic iodides are analogous to the bromides and chlorides in compo- sition and properties. But few of them are decomposed by heat alone ; the iodides of gold, silver, platinum, and palladium, however, give up their iodine when heated. Most metallic iodides are perfectly soluble in water; but lead iodide is very slightly soluble, and the iodides of mercury and silver are quite in- soluble. Solutions of iodides evaporated out of contact of air, generally leave anhydrous metallic iodides, which partly separate in the crystalline form before the water is wholly driven off. The iodides of the earth-metals, however, are resolved, on evaporation, into the earthy oxides and hydri- odic acid, which escapes. A very small quantity of chlorine colors the solution yellow or brown, by partial decomposition; and a somewhat larger quantity takes up the whole of the metal, forming a chloride, and separates the iodine, which then gives a blue color with starch ; a still larger quantity of chlorine gives the liquid a paler color, and converts the separated iodine into trichloride of iodine, which does not give a blue color with starch, and frequently enters into combination with the metallic chloride produced. Strong sulphuric acid and somewhat concentrated nitric acid color the solution yellow or brown ; and if the quantity of the iodide is large, and the solution much concentrated or heated, they liberate iodine, which partly escapes in violet vapors. Starch mixed with the solution, even if it be very dilute, is turned blue permanently, when the decom- position is effected by sulphuric acid ; for a time only when it is effected by nitric acid, especially if that acid be added in large quantity. The aqueous solution of an iodide gives a brown precipitate with salts of bismuth; orange-yellow with lead-salts; dirty-white with cuprous salts, and also with cupric salts, especially on the addition of sulphurous acid ; greenish-yellow with mercurous salts ; scarlet with mercuric salts ; yellowish- white with silver salts; lemon-yellow with gold salts; brown with platinic salts first, however, turning the liquid dark brown-red; and black with salts of palladium, even when extremely dilute. All these precipitates consist of metallic iodides, many of them soluble in excess of the soluble iodide : the silver precipitate is insoluble in nitric acid and very little sol- uble in ammonia. Metallic iodides unite with one another, forming double iodides, analogous to the double chlorides; they also absorb ammonia gas in definite propor- tions. Some of them, as those of antimony and tellurium, unite with the oxides of the corresponding metals, forming oxyiodides. Fluorides. These compounds are formed: 1. By heating hydrofluoric acid with certain metals. 2. By the action of that acid on metallic ox- ides. 3. By heating electro-negative metals antimony, for example with fluoride of lead or fluoride of mercury. 4. Volatile metallic fluorides may be prepared by heating fluor-spar with sulphuric acid and the oxide of the metal. Fluorides have no metallic lustre ; most of them are easily fusible, and for the most part resemble the chlorides. They are not decomposed by ignition, either alone or when mixed with charcoal. When ignited in contact with the air, in a flame which contains aqueous vapor, many of them are converted into oxides, while the flugrine is criven off as hydrofluoric acid. FLUORIDES ; CYANIDES. 277 All fluorides are decomposed by chlorine and converted into chlorides. They are not decomposed by phosphoric oxide, unless silica is present. They are decomposed at a gentle heat by strong sulphuric acid, with formation of a metallic sulphate and evolution of hydrofluoric acid. The fluorides of tin and silver are easily soluble in water; those of po- tassium, sodium, and iron are sparingly soluble; those of strontium and cadmium very slightly soluble, and the rest insoluble. The solutions of ammonium, potassium, and sodium fluoride have an alkaline reaction. The aqueous solutions of fluorides corrode glass vessels in which they are kept or evaporated. They form with soluble calcium-salts a precipitate of cal- cium fluoride, in the form of a transparent jelly, which is scarcely visible, because its refractive power is nearly the same as that of the liquid ; the addition of ammonia makes it plainer. This precipitate, if it does not contain silica, dissolves with difficulty in hydrochloric or nitric acid, and is re-precipitated by ammonia. The aqueous fluorides give a pulverulent precipitate with lead acetate. The fluorides of antimony, arsenic, chromium, mercury, niobium, os- mium, tantalum, tin, titanium, tungsten, and zinc, are volatile without decomposition. Fluorine has a great tendency to form double salts, consisting of a fluo- ride of a basic or positive metal united with the fluoride of hydrogen, boron, silicon, tin, titanium, zirconium, &c., e.g.: Potassium hydrofluoride . . . KHF 2 = KF.HF. Potassium borofluoride . . . KBF 4 = KF.BF 3 . Potassium silicofluoride . . . K 2 SiF 6 = 2KF.SiF 4 . Potassium titanofluoride . . . K. 2 TiF 6 = 2KF.TiF 4 . Potassium stannofluoride . . . K 2 SnF a = 2KF.SnF 4 . Potassium zircofluoride . . . K 2 ZrF, = 2KF.ZrF 4 . The four classes of compounds just described, the chlorides, bromides, iodides, and fluorides, form a group often designated as haloid compounds or haloid* salts, from their analogy to sodium chloride or sea-salt, which may be regarded as a type of them all. The elements, chlorine, bromine, iodine, and fluorine, are called halogens. Cyanides. Closely related to these haloi'd compounds are the cyanides, formed by the union of metals with the group CN, cyanogen, which is a monatomic radical derived from the saturated molecule, C iv N x// H (hydrocy- anic acid), by abstraction of H. ; in short, the cyanides may be regarded as chlorides having the element Cl replaced by the compound radical CN. Some metals potassium among the number are converted into cyanides by heating them in cyanogen gas or vapor of hydrocyanic acid. The cya- nides of the alkali-metals are also formed (together with cyanates) by pass- ing cyanogen gas over the heated hydrates or carbonates of the same metals; potassium cyanide also, by passing nitrogen gas over a mixture of charcoal and hydrate or carbonate of potassium at a bright-red heat. Cyanides are formed abundantly when nitrogenous organic compounds are heated with fixed alkali. Other modes of formation will be mentioned hereafter. The cyanides of the alkali-metals and of barium, strontium, calcium, mag- nesium, and mercury, are soluble in water, and may be produced by t not- ing the corresponding oxides or hydrates with hydrocyanic acid. Nearly all other metallic cyanides are insoluble, and are obtained by precipitation from the soluble cyanides. The cyanides of the alkali-metals sustain a red heat without decomposi- tion, provided air and moisture be excluded. The cyanides of many of the * From uA>, the sea. 24 278 CHEMISTRY OF THE METALS. heavy metals, as lead, iron, cobalt, nickel, and copper, under these circum- stances, give off all their nitrogen as gas, and leave a metallic carbonate; mercuric cyanide is resolved into mercury and cyanogen gtis; silver cyanide gives off half its cyanogen as gas. Most cyanides, when heated with dilute acids, give off their cyanogen as hydrocyanic acid. Cyanides have a strong tendency to unite with one another, forming double cyanides. The most important of these are the double cyanides of iron and potassium, namely, potassio-ferrous cyanide Fe /x K 4 (CN) 6 , commonly called yellow prussiate of potash; and potassio-ferric cyanide, Fe /x/ K 3 (CN } 6 , commonly called red prussiate of potash. Both these are splendidly crys- talline salts, which dissolve easily in water, and form highly characteristic precipitates with many metallic salts. These salts, with the other cyanides, will be more fully described under "Organic Chemistry;" but they are mentioned here, on account of their frequent use in the qualitative analysis of metallic solutions. Oxides. All metals combine with oxygen, and most of them in several proportions. In almost all cases oxides are formed corresponding in com- position to the chlorides, one atom of oxygen taking the place of two atoms of chlorine. Many metals also form oxides to which no chlorine analogues are known ; thus, lead, which forms only one chloride, PbCl 2 , forms, in addition to the monoxide, PbO, a dioxide, Pb0 2 , besides oxides of interme- diate composition ; osmium also, the highest chloride of which is OsCl 4 , forms, in addition to the dioxide, a trioxide and a tetroxide. This arises from the fact that any number of atoms of oxygen or other dyad element may enter into a compound without disturbing the balance of equivalency (p. 235). Just as chlorides are derived by substitution from hydrochloric acid, HC1 (p. 304), so likewise may oxides be derived from one or more molecules of water, H 2 ; but as the molecule of water contains two hydrogen-atoms, the replacement of the hydrogen may, as already explained (p. 223), be either total or partial, the product in the first case being an anhydrous metallic oxide, and in the second a hydrated oxide or hydrate, in which the oxygen is associated both with hydrogen and with metal ; in this manner the fol- lowing hydrates and anhydrous oxides may be constituted : Type. Hydrates. Oxides. H 2 . . . KHO . K 2 Ba"0 H 4 0. . . Ba"H 2 2 . . . SnK> 2 Bi'"H0 2 H 6 3 . . . As v H0 3 . . . Sb'" 2 Sn*vH 2 3 . . . W0 3 H 8 4 . . Zr iv H 4 4 . . . Os viii 4 H 10 5 Sbv 2 6 . It may be observed that the hydrates of artiad metals contain the ele- ments of a molecule of the corresponding anhydrous oxide, and of one or more molecules of water; thus; Barium hydrate , Ba // H 2 2 ~ Ba"O.H 2 Stannic hydrate ..... Sn iv H 2 3 = Sn lv 2 .H 2 O Zirconium hydrate , Zr iv H 4 4 Zr iv 2 .2H 2 O. But the hydrate of a perissad metal contains in its molecule only half the number of atoms required to make up a molecule of oxide together with a molecule of water ; thus ; Potassium hydrate . . . KHO = (K 2 O.H 2 Oj Bismuth hydrate , . . Bi /// H0 2 = J (Bi"' 2 O 3 .H 2 0) Arsenic hydrate .... As^H0 3 == | (As v 2 6 .H 2 0). OXIDES. 279 These perissad hydrates cannot, therefore, be correctly regarded as com- pounds of anhydrous oxide and water. Many metallic oxides occur as natural minerals, and some, especially those of iron, tin, and copper, in large quantities, forming ores from which the metals are extracted. All metals, except gold, platinum, iridium, rhodium, and ruthenium, are capable of uniting directly with oxygen. Some, as potassium, sodium, and barium, oxidize rapidly on exposure to the air at ordinary temperatures, and decompose water with energy. Most metals, however, when in the massive state, remain perfectly bright and unacted on in dry air or oxygen gas, but oxidize slowly when moisture is present; such is the case with iron, zinc, and lead. Some of the ordinarily permanent metals, when in a very finely divided state, as lead when obtained by ignition of its tartrate, and iron reduced from its oxide by ignition iu hydrogen gas, take fire and oxidize spontaneously as soon as they come in contact with the air. Lead, iron, copper, and the volatile metals, arsenic, antimony, zinc, cadmium, and mercury, are converted into oxides when heated in air or oxygen. Many metals, especially at a red heat, are readily oxidized by water or steam. A very general method of preparing metallic oxides is to subject the corresponding hydrates, carbonates, nitrates, sulphates, or any oxygen- salts containing volatile acids, to the action of heat. Oxides are for the most part opaque earthy bodies, destitute of metallic lustre. The majority of them are fusible; those of lead and bismuth at a low red heat; those of copper and iron at a white heat; those of barium and aluminium before the oxy-hydrogen blowpipe ; while calcium oxide (lime) does not fuse at any temperature to which it has yet been subjected. Oxides are, for the most part, much less fusible than the uncombined metals. Osmium tetroxide, and the trioxides of arsenic and antimony, are readily volatile. A greater or less degree of heat effects the decomposition of many me- tallic oxides. Those of gold, platinum, silver, and mercury are reduced to the metallic or reguline state by an incipient red heat. At a somewhat higher temperature, the higher oxides of barium, cobalt, nickel, and lead are reduced to the state of monoxides ; while the tri-metallic tetroxides of manganese and iron, Mn 9 4 and Fe 3 4 , are produced by exposing manga- nese dioxide, Mn0 2 , and iron sesquioxide, Fe 2 3 , respectively to a still Stronger heat. By gentle ignition, arsenic pentoxide is reduced to the state of trioxide, and chromium trioxide to sesquioxide. The superior oxides of the metals are easily reduced to a lower state of oxidation by treatment with a current of hydrogen gas at a more or less elevated temperature. At a higher degree of heat, hydrogen gas will trans- form to the reguline state all metallic oxides except the sesquioxides of aluminium and chromium, and the monoxides of manganese, magnesium, barium, strontium, calcium, lithium, sodium, and potassium. The temper- ature necessary to enable hydrogen to effect the decomposition of some oxides is comparatively low. Thus even metallic iron may be reduced from its oxides by hydrogen gas at a heat considerably below redness, so as to form an iron pyrophorus. Carbon, at a red or white heat, is a still more powerful deoxidating agent than hydrogen, and seems to be capable of completely reducing all metallic oxides whatsoever. The oxidizable metals in general act as reducing agents. Chlorine decomposes all metallic oxides, except those of the earth-metals, converting them into chlorides, and expelling the oxygen. With silver oxide this reaction takes place at ordinary temperatures; with the alkalies and alkaline earths, at a full red heat, Sulphur, at high temperatures, can decompose most metallic oxides. With many oxides, those of silver, mer- cury, lead, and copper, for instance, metallic sulphides and sulphur diox- 280 CHEMISTRY OF THE METALS. ide are produced. With the highly basylous oxides, the products are me- tallic sulphate and sulphide. There are some oxides upon which sulphur exerts no action. Of these the principal are magnesia, alumina, chromic, stannic, and titanic oxides. By boiling sulphur with soluble hydrates, mixtures of polysulphide and hyposulphite are produced. "With the ex- ception of magnesia, alumina, and chromic oxide, most metallic oxides can absorb sulphuretted hydrogen, to form metallic sulphide or sulph-hydrate, and water. Oxygen-salts, or Oxysalts. It has been already explained in the .chapter on Oxygen (p. 133), that oxides may be divided into three classes, acid, neu- tral, and basic; the first and third being capable of uniting with one another in definite proportions, and forming compounds called salts. The most characteristic of the acid oxides are those of certain metalloids, as nitrogen, sulphur, and phosphorus, which unite readily with water or the elements of water, forming compounds called oxygen-acids, distinguished by sour taste, solubility in water, and the power of reddening certain vegetable blue colors. The most characteristic of the basic oxides, on the other hand, are those of the alkali-metals and alkaline earth-metals (p. 271), which likewise dissolve in water, but form alkaline solutions, possessing in an eminent degree the power of neutralizing acids and forming salts with them. The same power is exhibited more or less by the monoxides of most other metals, as zinc, iron, copper, manganese, &c., and by the sesquioxides of aluminium, iron, chromium, and others. The higher oxides of several of these metals the trioxide of chromium, for example exhibit acid characters, being capable of forming salts with the more basic oxides ; and some metals, as arsenic, antimony, niobium, and tantalum, form only acid oxides. In some cases salts are formed by the direct combination of an acid and a basic oxide. Thus, when vapor of sulphuric oxide, S0 3 , is passed over red-hot barium oxide, BaO, the two combine together and form barium- sulphate, S0 3 .BaO or S0 4 Ba. Silicic oxide, Si0 2 , phosphoric oxide, P 2 5 , arsenic oxide, As 2 5 , boric oxide, B 2 3 , and other acid oxides capable of withstanding a high temperature without decomposing or volatilizing, like- wise unite with basic oxides when heated with them, and form salts. But in the majority of cases metallic salts are formed by substitution or interchange of a metal for hydrogen, or of one metal for another. It is clear, indeed, that any metallic salt (zinc-sulphate, S0 3 .ZnO, for example) may be derived from the corresponding acid or hydrogen-salt (S0 3 .H.,0) by substitution of a metal for an equivalent quantity of hydrogen. Ac- cordingly, metallic salts are frequently produced by the action of an acid on a metal, or a metallic oxide or hydrate, thus : (1) S0 4 H 2 + Zn" = S0 4 Zn" + H 2 . Hydrogen sulphate. Zinc sulphate. (2) 2N0 3 H -f OAg 2 = 2N0 3 Ag + OH 2 Hydrogen nitrate. Silver oxide. Silver nitrate. Water. (3) N0 3 H 4- OKH = N0 3 K -f OH 2 Hydrogen nitrate. Potassium hydrate. Potassium nitrate. Water. In the instances represented by these equations, the metallic salts formed are soluble in water. Insoluble salts are frequently prepared by inter- change of the metals between two soluble salts ; thus : (4) (N0 8 ) 8 Ba" -f S0 4 Na 2 = S0 4 Ba" + 2N0 3 N& Barium nitrate. Sodium sulphate. Barium sulphate. Sodium nitrate. In this case the barium sulphate, being insoluble, is precipiated, while the sodium nitrate remains in solution. OXYGEN-SALTS. 281 In all these reactions, hydrochloric acid, or a metallic chloride, might be substituted for the oxygen-acid or oxygen-salt without the slightest altera- tion in the mode of action, the product formed in each case being a chloride instead of a nitrate or sulpate ; thus : (1)' 2HC1 -f Zn" = ZnCL 4- H 2)' 2HCI + OAg, , 2A R ('l + oil, 3)' HC1 -f OKH == KH 4- OH 4)' N0 3 Ag -f NaCl = AgCl N0 3 Na. From all these considerations it appears that oxygen-salts may be re- garded, either as compounds of acid oxides with basic oxides, or as ana- logous in composition to chlorides, that is to say, as compounds of a motal with a radical or group of elements, such as N0 3 (nitrionc) in the ni- trates, S0 4 (sulphione] in the sulphates, discharging functions similar to those of chlorine, and capable, like that element, of passing unchanged from one compound to another. For many years, indeed, it was a subject of discussion among chemists whether the former or the latter of these views should be regarded as re- presenting the actual constitution of oxygen-salts. Bcrzelius divided salts into two classes: (1). Haloid salts, comprising, as already mentioned, the chlorides, bromides, iodides, and fluorides, which are compounds of a metal with a monad metallic element. (2). Amp hid salts, consisting of an acid or electro-negative oxide, sulphide, selenide, or tclluride, with a basic or electro-positive compound of the same kind; such as potassium arscnate, P 5 .30K 2 ; potassium sulpharsenate, P 2 S 5 .3SK 2 ; potassium seleniophosphatc P 2 Se 5 .2SeK 2 , &c. Davy, on the other hand, observing the close analogy between the reac- tions of chlorides, on the one hand, and of oxygen-salts, such as sulphates, nitrates, &c., on the other, suggested that the latter might be regarded, like the former, as compounds of metals with acid or electro-negative radi- cals, the only difference being, that in the former the acid-radical is an elementary body, Cl, Br, &c., whereas in the former it is a compound, as S0 4 , N0 3 . P0 4 , &c. This was called the binary theory of salts ; it was sup- ported by many ingenious arguments by its proposer and several contem- porary chemists ; in later years also by Liebig, and by Daniell and Miller, who observed that the mode of decomposition of salts by the electric current is more easily represented by this theory than by the older one (p. 247). At the present day, the relative merits of these two theories are not re- garded as a point of very great Importance. Chemists, in fact, no longer attempt to construct formula which shall represent the actual arrangements of atoms in a compound, the formuloa now in use being rather intended to exhibit, first, the balance or neutralization of the units of equivalency or atomicity of the several elements contained in a compound (p. 231); and, secondly, the manner in which any compound or group of atoms splits up into subordinate groups under the influence of different reagents. Accord- ing to the latter view, a compound containing three or more elementary atoms may be represented by different formulae corresponding to the several ways in which it decomposes. Thus hydrogen sulphate or sul- phuric acid, S0 4 H 2 , may be represented by either of the following formu- la: (1.) S0 4 .H 2 , which represents the separation of hydrogen and formation of a metallic sulphate by the action of zinc, &c. : this is the formula cor- responding to the binary theory of salts. (2.) SO S .OH 2 . This formula represents the formation of the acid by direct hydration of sulphuric oxide ; the separation of water and formation 24* 282 CHEMISTRY OF THE METALS. of a metallic sulphate by the action of magnesia and other anhydrous oxides ; and the separation of sulphuric oxide and formation of phosphoric acid by the action of phosphoric oxide : S0 3 .OH 2 -|- MgO = S0 3 .MgO -f OH 2 S0 8 OH 2 -f P 25 = P 25- OH 2 + S 3- (3.) S0 2 .0 2 H 2 , or S0 2 (OH) 2 . This formula represents such reactions as the elimination of hydrogen dioxide by the action of barium dioxide, Ba0 2 . (4.) SH 2 4 . This formula represents the formation of sulphuric acid by direct oxidation of hydrogen sulphide SH 2 , and the elimination of the latter by the action of ferrous sulphide : SH 2 .0 4 -f- FeS = S0 4 Fe -f SH 2 . Formulae of the third of these types, like S0 2 (OH) 2 , which represent oxygen-acids as compounds of hydroxyl with certain acid radicals, as SO./ 7 (sulphuryl), CO" (carbonyl), PO X// (phosphoryl), &c., correspond to a great variety of reactions, and are of very frequent use. They exhibit in particular the relation of the oxygen-acids (hydroxylates) to the corres- ponding chlorides, e. a. : (S0 2 )"(OH) 2 (S0 2 )"C1 2 Sulphuric acid. Sulphuric chloride. (PO)'"(OH) 8 (PO)'"C1 8 Phosphoric acid. Phosphoric chloride. Basicity of Acids. Normal, Acid and Double Salts. Acids are monobasic, bibasic, tribasic, &c., according as they contain one or more atoms of hydro- gen replaceable by metals ; thus nitric acid, N0 3 H, and hydrochloric acid, C1H, are monobasic ; sulphuric acid, S0 4 H 2 , is bibasic ; phosphoric acid, P0 4 H 3 , is tribasic. Monobasic acids form but one class of salts by substitution, the metal taking the place of the hydrogen in one, two, or three molecules of the acid, according to its equivalent value or atomicity; thus the action of hydrochloric acid on sodium, zinc, and aluminum is represented by the equa- tions : C1H -f Na = CINa -f H, 2C1H -f- Zn" = Cl 2 Zn" 4- H 2 3C1H 4- Al'" = C1 8 A1'" 4- H 3 , and that of nitric acid on the hydrates of the same metals by the equations : N0 3 H -f Na (HO) = N0 3 Na 4- H(HO) 2N0 3 r! + Ba"(HO) 2 = (N0 3 ) 2 Ba" 4- 2H(HO) 3i\0 3 H -f A1'"(HO) 8 = (N0 3 ) 8 A1'" 4- 3H(HO). Bibasic acids, on the other hand, form two classes of salts, viz. mono- metallic or acid salts, in which half the hydrogen is replaced by a metal; and bimetallic salts, in which the whole of the hydrogen is thus replaced, the salt being called normal or neutral if it contains one metal, and double if it contains two metals ; thus: From S0 4 H 2 is derived S0 4 KH { ^ * acid P otassium Jbipotassic or normal potassium 42 \ sulphate. " " S0 4 Ba x/ barium sulphate. 2S0 4 H 2 " (S0 4 ) 2 K 3 Na sodio-tripotassic sulphate. " " (S0 4 ) 2 A1 /// K potassio-aluminic sulphate. 3S0 4 H 2 " (S0 4 ) 3 Al /// 2 normal aluminium sulphate. BASICITY OP ACIDS. 283 Tribasic acids in like manner form two classes of acid salts, mono-metallic or bimetallic, according as one third or two thirds of the hydrogen is replaced by a metal; also normal and double or triple sails, in which the hydrogen is wholly replaced by one or more metals ; in quadribasic acids the variety ia of course still greater. The use of the terminations ous and ic, as applied to salts, has already been explained. We have only further to observe in this place that when a metal forms but one class of salts, it is for the most part better to desig- nate those salts by the name of the metal itself than by an adjective ending in ic ; thus potassium nitrate, and lead sulphate are mostly to be preferred to potassic nitrate and plumbic sulphate But in naming double salts, and in many cases where a numeral prefix is required, the names ending in ic are more euphonious ; thus triplumbic phosphate sounds better than trilead phos- phate, and hydrodisodic phosphate is certainly better than hydrogen and diso- dium phosphate; but there is no occasion for a rigid adherence to either system. All oxygen-salts may also be represented as compounds of an acid oxide with one or more molecules of the same or different basic oxides, including water, e. g. : Hydro-potassic sulphate 2S0 4 KH = 2S0 3 .K 2 O.H 2 Sodio-tripotassic sulphate 2(S0 4 ) 2 KH = 4S0 3 3K 2 O.Nn 2 Potassio-aluminic sulphate 2(S0 4 ) 2 Al / "K = 4S0 3 .A1 / " 2 3 .K 2 Hydrodisodic phosphate 2PO 4 Na 2 H == P 2 5 . 2 Na 2 O.H 2 0. When a normal oxygen-salt is thus formulated, it is easy to see that the number of molecules of acid oxide contained in its molecule is equal to the number of oxygen-atoms in the base; thus: Normal potassium sulphate S0 4 K 2 = S0 3 K 2 " barium sulphate S0 4 Ba S0 3 .BaO " stannic sulphate (S0 4 ) 2 Sn" = 2S0 3 .Sn0 2 " aluminium sulphate (S0 4 ) 3 Al'" a = 3S0 3 A1 2 O 3 . When the proportion of acid oxide is less than this, the salt, is called basic; such salts may be regarded as compounds of a normal salt with one or more molecules of basic oxide, or as derived from normal salts by sub- stitution of oxygen for an equivalent quantity of the acid radical; thus: Tribasic lead nitrate . N 2 s - 3pb " = (N0 3 ) 2 Pb".2Pb"0 = Pb" 3 (N0 3 ) 2 0" 2 = (S0 4 ),Al"' r 8Al'"A = A1"' 8 (S0 4 )",0",. The last mode of formulation exhibits the analogy of these basic oxysalts to the oxychlorides, oxyodides, &.c. ; thus the basic lead nitrate, Pb,(NO $ )2O r just mentioned, is analogous to the oxychloride of that metal, Pl> 3 'l,<> r which occurs native as mendipite. The term basic and acid are sometimes applied to salts with reference to their action on vegetable colors. The normal salts formed by the union of the stronger acids with the alkalies and alkaline earths, such as potassium sul- phate, S0 4 K 2 , barium nitrate, (N0 5 ) 2 Ba", &c., are perfectly neutral to vege- table colors, but most other normal salts exhibit either an acid or an alka- line reaction ; thus ferrous sulphate, cupric sulphate, silver nitrate, and many others redden litmus, while the normal carbonates and phosphates of the alkali-metals exhibit a decided alkaline reaction. It is clear then that the action of a salt on vegetable colors bears no definite relation to its composi- tion: hence the term normal, as applied to salts in which the basic hydro- 284 CHEMISTRY OF METALS. gen of the acid is wholly replaced, is preferable to neutral, and the terms basic and acid, as applied to salts, are best used iii the manner above explained with reference to their composition. When a normal salt containing a monoxide passes by oxidation to a salt containing a sesquioxide, dioxide, or trioxide, the quantity of acid present is no longer sufficient to saturate the base. Thus when a solution of fer- rous sulphate, S0 4 Fe, or S0 3 .FeO (common green vitriol), is exposed to the air, it absorbs oxygen, and an insoluble ferric salt is produced contain- ing an excess of base, while normal ferric sulphate remains in solution : 4(S0 3 .FeO) -f- 2 = 3S0 3 .Fe 2 3 -f S0 3 .Fe 2 3 Ferrous sulphate. Jformal ferric sulphate. Basic ferric sulphate. These basic salts are very often insoluble in water. Salts containing a proportion of acid oxide larger than is sufficient to form a neutral compound, are called anhydro-salts (sometimes, though im- properly, acid salts) ; they may evidently be regarded as compounds of a normal salt with excess of acid oxide ; e. g. : The following is a list of the most important inorganic acids arranged according to their basicity : Monobasic Acids. . Sb0 3 H C10H . C10 2 H CIO.H . C10 4 H Br0 3 H . I0 3 H I0 4 H Hydochloric Hydrobromic . Hydriodic . Hydrofluoric . Nitrous Nitric Hypophosphorous Metaphosphoric Boric . . C1H BrH m FH . N0 2 H N0 3 rl (PH 2 2 )H PO,H . BOJI Antimonic . Hypochlorous Chlorous . Chloric . Perchloric Bromic . lodic . Periodic Bibasic Acids. Hydric (water) . Sulph-hydric Selenhydric Tellurhydric . Sulphurous Sulphuric Hyposulphurous Dithionic Trithionic . Tetrathionic . Pentathionic Orthophosphoric Pyrophosphoric OH 2 Selenious SH 2 Selenic SeH 2 Tellurous TeH 2 Telluric S0 3 H 2 Manganic S0 4 H 2 Permanganic S 2 3 H 2 Chromic . S 2 6 H 2 Stannic S 3 6 H 2 Metasilicic S 4 6 H 2 Carbonic S 5 6 H 2 Phosphorous Tribasic Acids. P0 4 H 3 | Arsenic . Tetrabasic Acids. P 2 7 H 4 | Orthosilicic Se0 3 H 2 Se0 4 H 2 Mn 2 8 H 2 . Cr0 4 H 2 Sn0 3 H 2 . Si0 3 H 2 C0 3 H 2 (PH0 3 )H 2 . As0 4 H s Si0 4 H 4 'HOSPHAT] The general characters of most of the non-metallic acids and their salts have been already considered; but the phosphates require further notice. PHOSPHATES. There are three modifications of phosphoric acid: one >eirig monobasic, the second tribasic, and the third tetrabasic, as indicated in the preceding table. Hydrogen phosphide, PII 3 , burnt in air or oxygen gas, takes up four atoms of oxygen, and forms trihydric phosphate or tribasic phosphoric acii!' P0 4 H 3 . The same acid is produced by the oxidation of hypophosphorous or phosphorous acid; by oxidizing phosphorus with nitric acid (p. 214); by the decomposition of native calcium phosphate (apatite) and other na- tive phosphates; and by the action of boiling water on phosphorus pent- oxide, P 2 5 . This acid forms three distinct classes of metallic salts. With sodium, for example, it forms the three salts, P0 4 NaH 2 , P0 4 Na 2 H, and PO 4 Na 3 , the first two of which, still containing replaceable hydrogen, are acid salts, while the third is the normal or neutral salt. If now the monosodic phosphate, P0 4 NaH 2 , be heated to redness, it gives off one molecule of water, arid leaves an anhydrous monosodic phosphate, P0 3 Na, the aqueous solution of which, when treated with lead nitrate, yields a lead-salt of corresponding composition; thus: 2P0 3 Na -f (N0 3 ) 2 Pb" = (P(V 2 Pb" + 2N0 3 Na; and this lead-salt decomposed by sulph-hydric acid, yields a monohydric acid having the composition P0 3 H, possessing properties quite distinct from those of the trihydric acid above mentioned: (P0 3 ) 2 Pb" + SH 2 = 2P0 3 H -f Pb"S. The trihydric acid which is produced by the oxidation of phosphorus, and by the decomposition of the ordinary native phosphates, is called orthophosphoric acid or ordinary phosphoric acid; the monohydric acid is called metaphosphoric acid. The former may be regarded as a trihydrate, the latter as a monohydrate of phosphoric oxide : 2P0 4 IT 3 = P 2 3 .30H 2 , orthophosphoric acid, 2P0 8 H = P 2 6 .OH 2 , metaphosphoric acid. Both are soluble in water, and the former may be produced by the action of boiling water, the latter by that of cold water on phosphoric oxide. They are easily distinguished from one another by their reactions with al- bumin and with silver nitrate. Metaphosphoric acid coagulates albumin, and gives a white precipitate with silver nitrate; whereas orthophosphoric acid does not coagulate albumin, and gives no precipitate, or a very slight one, with silver nitrate, till it is neutralized with an alkali, in which case a yellow precipitate is formed. Metaphosphoric acid and its salts differ from orthophosphoric acid and the orthophosphates by the want of one or two atoms of water or base ; thus: Metaphosphates. Orthophosphates. P0 8 H = P0 4 1I 3 OH 2 PO.Na == P0 4 N.-iTI, OH 2 (P0 8 ) 2 Ba" = (P0 4 ) 2 Ba"H 4 - (PO S 8 ) 2 Pb" ~= (P0 4 j 2 P 8 b" 8 20Pb". Accordingly, we find that metaphosphates and orthophosphates are con- vertible one into the other by the loss or gain of one or two atoms of water or metallic base ; thus : 286 CHEMISTRY OF THE METALS. a. A solution of metaphosplioric acid is converted, slowly at ordinary temperatures, quickly at the boiling heat, into orthophosphoric acid, and the metaphosphates of sodium and barium are converted by boiling with water into the corresponding monometallic orthophosphates (see the first three equations above). /?. The metaphosphate of a heavy metal, silver or lead, for example, is converted by boiling with water into a trimetallic phosphate and orthophosphoric acid: 3P0 3 Ag + 30H 2 = P0 4 Ag 3 -f 2P0 4 H 3 . y. When any metaphosphate is fused with an oxide, hydrate or carbonate, it becomes a trimetallic orthophosphate, e. g. P0 3 Na + C0 3 Na 2 = P0 4 Na 3 -f C0 2 . On the other hand (6), when orthophosphoric acid is heated to redness, it loses water and becomes metaphosplioric acid ; and when a monometallic orthophosphate is heated to redness, it also loses water and is transformed into a metaphosphate. Intermediate between orthopTiosphates and metaphosphates, there are at least three distinct classes of salts, the most important of which are the pyrophosphates or paraphosphates, which may be derived from the tetrahydric or quadribasic acid, P 2 7 H 4 , the normal sodium salt, for example, being P 2 7 Na 4 , the normal lead salt, P^Pb''^, &c. These salts may be viewed as compounds of orthophosphate and metaphosphate, e. g. : P 2 7 Na 4 = P0 4 Na 3 -f P0 3 Na. Sodium pyrophosphate is produced by heating disodic orthophosphate to redness, a molecule of water being then given off: 2P0 4 Na 2 H =, OH 2 -f P 2 7 Na 4 . The aqueous solution of this salt yields insoluble pyrophosphates with lead and silver salts; thus with lead nitrate: and lead pyrophosphate decomposed by hydrogen sulphide yields hydrogen pyrophosphate or pyrophosphoric acid : P 2 7 Pb" 2 -f 2SH 2 = 2Pb"S -f- P 2 7 H 4 . Pyrophosphoric acid is distinguished from metaphosphoric acid by not coagulating albumin and not precipitating neutral solutions of barium or silver salts, and from orthophosphoric acid by producing a white instead of a yellow precipitate with silver nitrate. Pyrophosphates are easily converted into metaphosphates and ortho- phosphates, and vice versQ,, by addition or subtraction of water or a metallic base. a. The production of a pyrophosphate from an orthophosphate by loss of water has been already mentioned. /?. Conversely, when a pyrophos- phate is heated with water or a base, it becomes an orthophosphate, e. g. : P 2 7 Na 4 -f- H 2 =2P0 4 Nn 2 H P 2 7 Na 4 -|- 20NaH = 2P0 4 Na 3 -f OH 2 . In like manner orthophosphoric acid heated to 215 is almost entirely con- verted into pyrophosphoric acid : 2P0 4 H 3 OH 2 =. P 2 7 H 4 ; and conversely, when pyrophosphoric acid is boiled with water, it is transformed into orthophosphoric acid. y. Pyrophosphoric acid heated to dull redness is converted into meta- phosphoric acid: P 2 7 H 4 OH 2 =2P0 3 H. The converse reaction is not PHOSPHATES. 287 sily effected, inasmuch as motaphosphoric acid by absorbing water gener- ally passes directly to the state of orthophosphoric acid. Peligot, h<>. \r\rv. observed the formation of pyrophosphoric from metaphosphoric acid by very slow absorption of water. f>. When a metallic rnctaphosph:it< is treated with a proper proportion of a hydrate, oxide, or carbonate, it is converted into a pyrophosphate ; thus : 2P0 3 Na -f C0 3 Na 2 = P 2 0-Na 4 4. C0 2 Metaphosphate. Carbonate. Pyrophosphate. Carbon dioxide. Fleitmann and Henneberg,* by fusing together a molecule of sodium py- rophosphate, P0 4 Na 3 .P0 3 Na, with two molecules of metaphosphate, P() 3 Na, obtained a salt having the composition P0 4 Na 3 .3P0 3 Na = lY), 3 N.-) 6 , which is soluble without decomposition in a small quantity of hot water, and crystallizes from its solution by evaporation over oil of vitriol. An excess of hot water decomposes it, but its cold aqueous solution is moderately per- manent. Insoluble phosphates of similar composition may be obtained from the sodium-salt by double decomposition. Fleitmann and Henneberg obtained another crystallizable but very insoluble salt, having the compo- sition P0 4 Na 3 .9P0 3 Na = Pj 3 ,Na 12 , by fusing together one molecule of sodium-pyrophosphate with eight molecules of the metaphosphate ; and in- soluble phosphates of similar constitution were obtained from it by double decomposition. The comparative composition of these different phosphates is best shown by representing them as compounds of phosphoric oxide with metallic oxide, and assigning to them all, the quantity of base contained in the most com- plex member of the series ; thus (for the sodium salts) : Orthophosphate 2P 2 5 . 6Na 2 = 4P0 4 Na Pyrophosphate 3P 2 5 . 6Na 2 == 3P 2 7 Na 4 Fleitmann and Henneberg's phosphate (a) 4P 2 O 5 . 6Na 2 O = 2P 4 0, 3 Na 6 (b) 6P 2 5 .6Na,0 = r io 31 Xa l8 Metaphosphate 6P 2 6 . 6Na 2 = lliPO 3 Xa. Metallic Sulphides. These compounds correspond, for the most part, to the oxides in composition: thus there are two sulphides of arsenic, As.,S 3 and As 2 S 5 , corresponding to the oxides, As 2 3 and As 2 5 ; also two sulphides of mercury, Hg 2 S and HgS, analogous to the oxides, Hg 2 and HgO. Oc- casionally, however, we meet with oxides to which there are no correspond- ing sulphides (manganese dioxide, for example), and more frequently sul- phides to which there are no corresponding oxides, the most remarkable of which are perhaps the alkaline polysulphides. Potassium, for example, forms the series of sulphides K 2 S, K 2 S 2 , K 2 S 3 , K 2 S 4 , and K 2 S 5 , the third and fifth of which have no analogues in the oxygen series. There are also sulph-hydrates analogous to the hydrates, and containing the elements of a metallic sulphide and hydrogen sulphide, or sulph-hydric acid; e. g. potassium sulph-hydrate K 2 S.H 2 S = 2KHS ; lead sulph-hydrate Pb /x S.H 2 S = Pb x/ H 2 S 2 . Sulph-hydrates and sulphides may be derived from sulph-hydric acid by partial or total replacement of the hydrogen by metals, just as metallic hydrates and oxides are derived from water : SHH SKH SKK Sulph-hydric Sulph-hydrate Sulphide, acid OHH OKH OKK Water Hydrate Oxide, * Ann. Ch. Pharm. Ixv. 304. 288 CHEMISTRY OF THE METALS. Many metallic sulphides occur as natural minerals, especially the sulphides of lead, copper, and mercury, which afford valuable ores for the extraction of the metals, and iron bisulphide or iron pyrites, FeS 2 , which is largely used as a source of sulphur, and for the preparation of ferrous sulphate. Sulphides are formed artificially by heating metals with sulphur ; by the action of metals on gaseous hydrogen sulphide ; by the reduction of sul- phates with hydrogen or charcoal ; by heating metallic oxides in contact with gaseous hydrogen sulphide, or vapor of carbon bisulphide ; and by precipitation of metallic solutions with hydrogen- sulphide or a sulphide of alkali-metal. Some metals, as copper, lead, silver, bismuth, mercury, and cadmium, are precipitated from their acid solutions by hydrogen sulphide, passed into them as gas or added in aqueous solution, the sulphides of these metals being insoluble in dilute acids ; others, as iron, cobalt, nickel, man- ganese, zinc, and uranium, form sulphides which are soluble in acids, and these are precipitated by hydrogen sulphide only from alkaline solutions, or by ammonium or potassium sulphide from neutral solutions. Many of these sulphides exhibit very characteristic colors, which serve as indications of the presence of the respective metals in solution (p. 201). Metallic sulphides are al^o formed by the reduction of sulphates with organic substances ; many native sulphides have doubtless been formed in this way. The physical characters of some metallic sulphides closely resemble those of the metals in certain particulars, such as the peculiar opacity, lustre, and density, especially when they are in a crystalline condition. They are generally crystallizable, brittle, and of a gray, pale yellow, or dark brown color. The sulphides of the alkali-metals are soluble in water, most of the others are insoluble. They are frequently more fusible than the cor- responding oxides, and some are volatilizable, as mercury sulphide and ar- senic sulphide. Many sulphides, when heated out of contact with atmospheric air, do not undergo any decomposition; this is the case chiefly with those containing the smallest proportions of sulphur, such as the monosulphides of iron and zinc. Sulphides containing larger proportions of sulphur are partially de- composed by heat, losing part of their sulphur, and being converted into lower sulphides ; as in the case of iron bisulphide. The sulphides of gold and platinum are completely reduced by heat. By the simultaneous action of heat and of substances capable of combin- ing with sulphur, some sulphides may be decomposed. Thus, for instance, silver, copper, bismuth, tin, and antimony sulphides are reduced by hydro- gen ; copper, lead, mercury, and antimony sulphides are reduced by heat- ing with iron. Sulphides which are not reduced by heat alone, are always decomposed when heated in contact with oxygen or atmospheric air. Those of the alkali-metals and earth-metals are converted into sulphates by this means. Zinc, iron, manganese, copper, lead, and bismuth sulphides are converted into oxides, and sulphurous oxide is produced ; but when the temperature is not above dull redness, some sulphate is formed by direct oxidation. Mercury and silver sulphides are completely reduced to the metallic state. Some native sulphides gradually undergo alteration by mere exposure to the atmosphere; but it is then generally limited to the production of sul- phates, unless the oxidation takes place so rapidly that the heat generated is sufficient to decompose the sulphate first produced. In the production of some metals for use in the arts, the separation of sulphur from the na- tive minerals is effected chiefly by means of this action in the operation of roasting. Metallic sulphides are decomposed in like manner when heated with metallic oxides in suitable proportions, yielding sulphurous oxide and the SELENIDES AND TELLURIDES. 289 metal of both the sulphide and oxide. Lead is reduced from the native sulphide in this manner. Many metallic sulphides are decomposed by acids in the presence of water, sulphuretted hydrogen being evolved while the metal enters into combination with the acid or chlorous radical of the acid. Nitric acid when concentrated decomposes most sulphides, with formation of metallic oxide, sulphuric acid, sulphur, and a lower oxide of nitrogen. Nitromuriatic acid acts in a similar manner, but still more energetically. SULPHUR-SALTS. The sulphides of the more basylous metals unite with those of the more chlorous or electro-negative metals, and of the metalloids, forming sulphur-salts, analogous in composition to the oxygen-salts, e.g.: Carbonate C0 3 K 2 C0 2 .K 2 Sulphocarbonate CS 3 K 2 = CS 2 .K 2 S Arsenate 2As0 4 K 3 = As 2 5 .3K 2 Sulpharsenate 2AsS 4 K 3 = As 2 S 5 .3K 2 S Selenides and Tellurides. These compounds are analogous in composi- tion, and in many of their properties, to the sulphides, and likewise unite one with the other, forming selenium-salts and tellurium salts analogous to the oxygen and sulphur salts. Metals also form definite compounds with nitrogen, phosphorus, silicon, boron, and carbon ; but these compounds are comparatively unimportant, excepting the carbonides of iron, which form cast iron and steel. 25 CLASS L MONAD METALS. GROUP L METALS OF THE ALKALIES. POTASSIUM. Atomic weight, 39-1. Symbol, K (Kalium). T)OTASSIUM was discovered in 1807 by Sir H. Davy, who obtained it in very small quantity by exposing a piece of moistened potassium hydrate to the action of a powerful voltaic battery, the alkali being placed between a pair of platinum plates connected with the apparatus. Processes have since been devised for obtaining this metal in almost any quantity that can be desired. An intimate mixture of potassium carbonate and charcoal is prepared by calcining, in a covered iron pot, the crude tartar of commerce ; when cold it is rubbed to powder, mixed with one tenth part of charcoal in small lumps, and quickly transferred to a retort of stout hammered iron : the lat- ter may be one of the iron bottles in which mercury is imported. The retort is introduced into a furnace a (fig. 162), and placed horizontally on supports of fire-brick, /", /*. A wrought-iron tube d, four inches long, serves to con- vey the vapors of potassium into a receiver e, formed of two pieces of wrought-iron, a, b (fig. 163), which are fitted closely to each other so as to form a shallow box only a quarter of an inch deep, and are kept together by clamp-screws. The iron plate should be one sixth of an inch thick, twelve inches long, and five inches wide. The receiver is open at both ends, the socket fitting upon the neck of the iron bottle. The object of giving the receiver this flattened form is to ensure the rapid cooling of the potassium, and thus to withdraw it from the action of the carbon monoxide, which is disengaged during the entire process, and has a strong tendency to unite with the potassium, forming a dangerously explosive compound. Before connecting the receiver with the tube d, the fire is slowly raised till the iron bottle attains a dull red heat. Powdered vitrefied borax is then sprin- kled upon it, which melts and forms a coating, serving to protect the iron from oxidation. The heat is then to be urged until it is very intense, care being taken to raise it as equally as possible throughout every part of the furnace. When a full reddish-white heat is attained, vapors of potassium begin to appear and burn with a bright flame. The receiver is then adjusted to the end of the tube, which must not project more than a quarter of an inch through the iron plate forming the front wall of the furnace; other- wise the tube is liable to be obstructed by the accumulation of solid potas- sium, or of the explosive compound above mentioned. Should any obstruc- tion occur, it must be removed by thrusting in an iron bar, and if this fail, the fire must be immediately withdrawn by removing the bars from the fur- nace, with the exception of two which support, the iron bottle. The receiver is kept cool by the application of a wet cloth to its outside. When the oper- ation is complete, the receiver with the potassium is removed and immedi- 290 POTASSIUM. 291 ately plunged into a vessel of rectified Persian naphtha provided with a cover, and kept cool by immersion in water. When the apparatus is suffi- ciently cooled, the potassium is detached and preserved under naphtha. If the potassium be wanted absolutely pure, it must be afterwards re- distilled in an iron retort, into which some naphtha has been put, that its vapor may expel the air, and prevent oxidation of the metal. Potassium is a brilliant white metal, with a high degree of lustre ; at the common temperature of the air it is soft, and may be easily cut with a knife, but at it is brittle and crystalline. It melts completely at (5li-o, and distils at a low red heat. It floats on water, its specific gravity being only 0-865. Exposed to the air, potassium oxidizes instantly, a tarnish covering the surface of the metal, which quickly thickens to a crust of caustic potash. Thrown upon water, it takes fire spontaneously, and burns with a beautiful purple flame, yielding an alkaline solution. When it is brought into con- tact with a little water in a jar standing over mercury, the liquid is decom- posed with great energy, and hydrogen liberated. Potassium is always preserved under the surface of naphtha. POTASSIUM CHLORIDE, KC1. This salt is obtained in large quantity in the manufacture of the chlorate : it is easily purified from any portions of the latter by exposure to a dull red heat. Within the last few years large quantities of this salt have been obtained from sea-water, by a peculiar process suggested by M. Balard.* It is also contained in kelp, and is sep- arated for the use of the alum-maker. Considerable quantities of it are now obtained from the salt-beds of Strassfurt, near Magdeburg, in Prussia. Potassium chloride closely resembles common salt in appearance, assum- ing, like that substance, the cubic form of crystallization. The crys- tals dissolve in three parts of cold, and in a much smaller quantity of boil- ing water: they are anhydrous, have a simple saline taste, with slight bit- terness, and fuse when exposed to a red heat. Potassium chloride is volatilized by a very high temperature. POTASSIUM IODIDE, KI. There are three different methods of preparing this important medicinal compound. (1.) When iodine is added to a strong solution of caustic potash free from carbonate, it is dissolved in large quantity, forming a colorless solution containing potassium iodide and iodate ; the reaction is the same as in the * Reports by the Juries of the International Exhibition of 1862, Claas n. 292 MONAD METALS. analogous case with chlorine. When the solution begins to be permanently colored by the iodine, it is evaporated to dryness, and cautiously heated to redness, by which the iodate is entirely converted into potassium iodide. The mass is then dissolved in water, and, after nitration, made to crys- tallize. (2.) Iodine, water, and iron filings or scraps of zinc, are placed in a warm situation until the combination is complete, and the solution colorless. The resulting iodide of iron or zinc is then filtered, and exactly decomposed with solution of pure potassium carbonate, great care being taken to avoid excess of the latter. Potassium iodide and ferrous carbonate, or zinc car- bonate, are thus obtained: the former is separated by filtration, and evap- orated until the solution is sufficiently concentrated to crystallize on cooling, the washings of the filter being added to avoid loss: FeI 2 -f C0 3 K 2 = 2KI +' C0 3 Fe". (3.) A very simple method for the preparation of potassium iodide has recently been proposed by Liebig. One part of amorphous phosphorus is added to 40 parts of warm water ; 20 parts of dry iodine are then gradu- ally added and intimately mixed with the phosphorus by trituration. The dark-brown liquid thus obtained is now heated on the water-bath until it becomes colorless; it is then poured off from the undissolved phosphorus and neutralized, first with barium carbonate and then with baryta water, until it becomes slightly alkaline. The insoluble barium phosphate is fil- tered off and washed ; the filtrate now contains nothing but barium iodide, which, when treated with potassium sulphate, yields insoluble barium sul- phate and potassium iodide in solution. Lime answers nearly as well as baryta. Potassium iodide crystallizes in cubes, which are often, from some unex- plained cause, milk-white and opaque : they are anhydrous, and fuse rea- dily when heated. The salt is very soluble in water, but not deliquescent, when pure, in a moderately dry atmosphere: it is dissolved by alcohol. Solution of potassium iodide, like those of all the soluble iodides, dis- solves a large quantity of free iodine, forming a deep-brown liquid, not decomposed by water. POTASSIUM BROMIDE, KBr. This compound maybe obtained by pro- cesses exactly similar to those just described, substituting bromine for the iodine. It is a colorless and very soluble salt, quite undistinguishable in appearance and general characters from the iodide. POTASSIUM OXIDES. Potassium combines with oxygen in three propor- tions, forming a monoxide, OK 2 , a dioxide, 2 K 2 , and a tetroxide, 4 K 2 , besides a hydrate, OKH, corresponding to the monoxide. Potassium monoxide, OK 2 , also called anhydrous potash, or potassa, is formed when potassium in thin slices is exposed at ordinary temperatures to dry air free from carbon dioxide ; also when the hydrate is heated with an equivalent quantity of metallic potassium: 20KH -f K 2 = 20K 2 + H 2 . It is white, very deliquescent and caustic, combines energetically with water, forming potassium hydrate, and becoming incandescent when moist- ened with it ; melts at a red heat, and volatilizes at very high temperatures. OK The dioxide 2 K 2 or I is formed at a certain stage in the preparation OK of the tetroxide, but has not been obtained quite pure. By carefully reg- ulating the heat and supply of air, nearly the whole of* the potassium POTASSIUM. 293 may be converted into a white oxide, having nearly the composition of tin- dioxide. An aqueous solution of this oxide is formed by the action of K water on the tetroxide. The tetroxide, 4 K 2 , or I , is produced when K potassium is burnt in excess of dry air or oxygen gas. It is a chrome- yellow powder, which cakes together at about 280. It absorbs moisture rapidly, and is decomposed by water, giving off oxygen and forming a solution of the dioxide. When gently heated in a stream of carbon mon- oxide, it yields potassium carbonate and two atoms of oxygen : 4 K 2 + CO == C0 3 K 2 + 2 : with carbon dioxide it acts in a similar manner, giving off three atoms of oxygen.* POTASSIUM HYDRATE, OKH, commonly called caustic potash, or potassa, is a very important substance, and one of great practical utility. It is al- ways prepared for use by decomposing the carbonate with calcium hydrate (slaked lime), as in the following process, which is very convenient: 10 parts of potassium carbonate are dissolved in 100 parts of water, and heated to ebullition in a clean untinned iron, or, still better, silver vessel; 8 parts of good quicklime are meanwhile slaked in a covered basin, and the resulting calcium hydrate added, little by little, to the boiling solution of carbonate, with frequent stirring. When all the lime has been intro- duced, the mixture is suffered to boil for a few minutes, and then removed from the fire and covered up. In the course of a very short time, the so- lution will have become quite clear, and fit for decantation, the calcium carbonate, with the excess of hydrate, settling down as a heavy, sandy precipitate. The solution should not effervesce with acids. It is essential in this process that the solution of potassium carbonate be dilute, otherwise the decomposition becomes imperfect. The proportion of lime recommended is much greater than that required by theory, but it is always proper to have an excess. The solution of potassium hydrate may be concentrated by quick evap- oration in the iron or silver vessel to any desired extent; when heated until vapor of water ceases to be disengaged, and then suffered to cool, it furnishes the solid hydrate, OKH, or OK. 2 .OH r Pure potassium hydrate is also easily obtained by heating to redness for half an hour in a covered copper vessel, one part of pure powdered nitre with two or three parts of finely divided copper foil. The mass, when cold, is treated with water. Potassium hydrate is a white solid substance, very deliquescent and sol- uble in water ; alcohol also dissolves it freely, which is the case with com- paratively few potassium compounds : the solid hydrate of commerce, which is very impure, may thus be purified. The solution of this substance pos- sesses, in the very highest degree, the properties termed alkaline : it re- stores the blue color to litmus which has been reddened by an acid; neu- tralizes completely the most powerful acids; has a nauseous and peculiar taste; and dissolves the skin, and many other organic matters, when the latter are subjected to its action. It is frequently used by surgeons as a cautery, being moulded into little sticks for that purpose. Potassium hydrate, both in the solid state and in solution, rapidly absorbs carbonic acid from the air ; hence it must be kept in closely stopped bot- tles. When imperfectly prepared, or partially altered by exposure, it effervesces with an acid. * Ilarcourt, Clicni Soc. Journ. xiv. 267. 294 MONAD METALS. This compound is not decomposed by heat, but volatilizes undecomposed at a very high temperature. The following table of the densities and value in anhydrous potassium oxide, OK 2 , of different solutions of potassium hydrate, is given on the authority of Dalton: Density. 1-68 1-60 1-52 1-47 1-44 1-42 1-39 1-36 Percentage of OK 2 . . 51-2 46-7 . 42-9 39-6 . 36-8 34-4 . 32-4 29-4 Density. 33 28 23 19 15 11 1-06 Percentage of OK 2 . . 2G-3 23-4 . 19-5 16-2 . 13-0 9-5 . 4-7 POTASSIUM NITRATE; NITRE; SALTPETRE, N0 3 K N0 2 (OK). This im- portant compound is a natural product, being disengaged by a kind of efflorescence from the surface of the soil in certain dry and hot countries. It may also be produced by artificial means namely, by the oxidation of ammonia in presence of a powerful base. In France, large quantities of artificial nitre are prepared by mixing animal refuse of all kinds with old mortar or calcium hydrate and earth. and placing the mixture in heaps, protected from the rain by a roof, but freely exposed to the air. From time to time the heaps are watered with putrid urine, and the mass turned over, to expose fresh surfaces to the air. "When much salt has been formed, the mixture is lixiviated, and the solution, which contains calcium nitrate, is mixed with potassium carbonate ; calcium carbonate is formed, and the nitric acid transferred to the alkali. The fil- tered solution is then made to crystallize, and the crystals are purified by re-solution and crystallization, the liquid being stirred to prevent the for- mation of large crystals. The greater part of the nitre used in this country comes from the East Indies: it is dissolved in water, a little potassium carbonate added to pre- cipitate lime, and then the salt purified as above. Considerable quantities of nitre are now manufactured by decomposing native sodium nitrate (Chile saltpetre), with carbonate or chloride of po- tassium. In Belgium the potassium carbonate obtained from the ashes of the beetroot sugar manufactories is largely used for this purpose; the po- tassium nitrate thus prepared is very pure, and is produced at a low price. Potassium nitrate crystallizes in anhydrous six-sided prisms, with di- hedral summits, belonging to the rhombic or trimetric system: it is soluble in 7 parts of water at 15-5, and in its own weight of boiling water. Its taste is saline and cooling, and it is without action on vegetable colors. At a temperature below redness it melts, and by a strong heat is completely decomposed. When it is thrown on the surface of many metals in a state of fusion, or when mixed with combustible matter and heated, rapid oxidation ensues, at the expense of the oxygen of the nitric acid. Examples of such mixtures are found in common gunpowder, and in nearly all pyrotechnic compositions, which burn in this manner independently of the oxygen of the air, and even under water. Gunpowder is made by very intimately mixing together potassium nitrate, charcoal, and sulphur, in proportions which approach 2 molecules of nitre, 3 atoms of carbon, and 1 atom of sulphur. These quantities give, reckoned to 100 parts, and compared with the proportions used in the manufacture of the English Government powder,* the following results : * Dr. M'Culloch, Encyclopedia Britaunica. POTASSIUM. 295 Theory. Proportions in practice. Potassium nitrate . 74-8 . 75 Charcoal . . . 13 3 . .15 Sulphur . . . 11-9 . 10 100-0 100 The nitre is rendered very pure by the means already mentioned, freed from water by fusion, and ground to fine powder; the sulphur and char- coal, the latter being made from light wood, as dogwood or alder, are also finely ground, after which the materials are weighed out, moistened with water, and thoroughly mixed by grinding under an edge-mill. The mass is then subjected to great pressure, and the rnillcake thus produced broken in pieces, and placed in sieves made of perforated vellum, moved by machinery, each containing, in addition, a round piece of heavy wood. The grains of powder broken off by attrition fall through the holes in the skin, and are easily separated from the dust by sifting. The powder is, lastly, dried by exposure to steam-heat, and sometimes glazed or polished by agitation in a kind of cask mounted on an axis. It was formerly supposed that when gunpowder is fired, the whole of the oxygen of the potassium nitrate was transferred to the carbon, forming carbon dioxide, the sulphur combining with the potassium, and the nitrogen being set free. There is no doubt that this reaction docs take place to a considerable extent, and that the large volume of gas thus produced, and still further expanded by the very exalted temperature, sufficiently accounts for the explosive effects. But recent investigations by Bunsen, Karolyi, and others, have shown that the actual products of the combustion of gun- powder are much more complicated than this theory would indicate, a very large number of products being formed, and a considerable portion of the oxygen being transferred to the potassium sulphide, converting it into sul- phate, which, in fact, constitutes the chief portion of the solid residue and of the smoke formed by the explosion.* POTASSIUM CHLORATE, C10 3 K = C10 2 (OK). The theory of the produc- tion of chloric acid, by the action of chlorine gas on a solution of caustic potassa, has been already explained (p. 187). Chlorine gas is conducted by a wide tube into a strong and warm solu- tion of potassium carbonate, until absorption of the gas ceases; and the liquid is, if necessary, evaporated, and then allowed to cool, in order that the slightly soluble chlorate may crystallize out. The mother-liquor affords a second crop of crystals, but they are much more contaminated by potas- sium chlorido. It may be purified by one or two re-crystalli/ations. Potassium chlorate is soluble in about. 20 parts of cold and 2 of boiling water: the crystals are anhydrous, flat, and tabular; in taste it somewhat resembles nitre. When heated, it gives off the whole of its oxygen jras and leaves potassium chloride. By arresting the decomposition when the evolution of gas begins to slacken, and redissolving the salt, potassium per- chlorate and chloride may be obtained. This salt deflagrates violently with combustible matter, explosion often occurring by friction or blows. When about, one grain-weight of chlorate and an equal quantity of sulphur are rubbed in a mortar, the mixture ex- plodes with a loud report: hence it cannot be used in the preparation of gunpowder instead of the nitrate. Potassium chlorate is now a large article of commerce, being employed, together with phosphorus, in making instan- taneous-light matches. POTASSIUM PERCHLOBATB, C10 4 K = C10 3 (OK). This salt has been already * See Watts's Dictionary of Chemistry, vol. ii. p. 958. 296 MONAD METALS. policed under the head of perchloric acid. It is best prepared by project- ing powdered potassium chlorate into warm nitric acid, when the chlo- ric acid is resolved into perchloric acid, chlorine and oxygen gases. The salt is separated by crystallization from the nitrate. Potassium perchlorate is a very slightly soluble salt : it requires 55 parts of cold water, but is more freely taken up at a boiling heat. The crystals are small, and have the figure of an octohedron with square base. It is decomposed by heat, in the same manner as the chlorate. POTASSIUM CARBONATES. Potassium forms two well-defined carbonates, namely, a normal or neutral carbonate, C0 3 K 2 , and an acid salt containing C0 3 KH. Normal potassium carbonate, or dipotassic carbonate = CO(OK) 2 = C0 2 .OK 2 . Potassium-salts of vegetable acids are of constant occurrence in plants, where they perform important, but not yet perfectly iinderstood functions in the economy of those beings. The potassium is derived from the soil, which, when capable of supporting vegetable life, always contains that sub- stance. When plants are burned, the organic acids are destroyed, and the potassium is left in the state of carbonate. It is by these indirect means that the carbonate, and, in fact, nearly all the salts of potassium, are obtained. The great natural depository of the alkali is the felspar of granitic and other unstratified rocks, where it is combined with silica, and in an insoluble state. The extraction thence is attended with great difficulties, and many attempts at manufacturing it on a large scale from this source have failed ; but experiments quite recently made by Mr. T. 0. Ward appear to indicate that the object may be accom- plished by fusing potassic rocks with a mixture of calcium carbonate and fluoride. There are, however, natural processes at work, by which the potash is constantly being eliminated from these rocks. Under the influ- ence of atmospheric agencies, these rocks disintegrate into soils, and as the alkali acquires solubility, it is gradually taken up by plants, and accumu- lates in their substance in a condition highly favorable to its subsequent applications. Potassium-salts are always most abundant in the green and tender parts of plants, as may be expected, since from these, evaporation of nearly pure water takes place to a large extent : the solid timber of forest-trees contains comparatively little. In preparing the salt on an extensive scale, the ashes are subjected to a process called lixiviation: they are put into a large cask or tun, having an aperture near the bottom, stopped by a plug, and a quantity of water is added. After some hours the liquor is drawn off", and more water added, that the whole of the soluble matter may be removed. The weakest solu- tions are poured upon fresh quantities of ash, in place of water. The solu- tions are then evaporated to dryness, and the residue calcined, to remove a little brown organic matter : the product is the crude potash or pearlash of commerce, of which very large quantities are obtained from Russia and America. This salt is very impure : it contains potassium silicate, sulphate, chloride, &c. The purified potassium carbonate of pharmacy is prepared from the crude article by adding an equal weight of cold water, agitating and filtering : most of the foreign salts are, from their inferior degree of solubility, left behind. The solution is then boiled down to a very small bulk, and suffered to cool, when the carbonate separates in small crystals contniinnc: 2 mole- cules of water, C0 3 K 2 .20H 2 ; these are drained from the mother-liquor, and then dried in a stove. A still purer salt may be obtained by exposing to a red-heat purified cream of tartar (acid potassium tartrate), and separating the carbonate by solu- tion in water and crystallization, or evaporation to dryness. POTASSIUM. Potassium carbonate is extremely deliquescent, and soluble in less than its own weight of water: the solution is highly alkaline to test-j>aj.i-r. It is insoluble in alcohol. By heat the water of crystallization is driven ,n; and by a temperature of full ignition the salt is fused, but not otherwise changed. This substance is largely used in the arts, and is a compound of great importance. Acid potassium carbonate, Hydrogen potassium carbonate, or Mono-polassic carbonate, CO 3 KH = C0 2 (KHO) ; commonly called bicarbonate of potash. When a stream of carbonic acid gas is passed through a cold solution of potassium carbonate, the gas is rapidly absorbed, and a white, crystalline, and less soluble substance separated, which is the acid salt. It is collected, pressed, re-dissolved in warm water, and the solution left to crystallize. Acid potassium carbonate is much less soluble than the normal carbon- ate : it requires for that purpose 4 parts of cold water. The solution is nearly neutral to test-paper, and has a much milder taste than the normal salt. When boiled it gives off carbon dioxide. The crystals, which are large and beautiful, derive their form from a monoclinic prism: they are decomposed by heat, water and carbon dioxide being evolved, and normal carbonate left behind : 2C0 3 KH = C0 3 K 2 -f OH 2 -f C0 2 . POTASSIUM SULPHATES. Potassium forms a normal or neutral sulphate, two acid sulphates, and an anhydrouulphate. Normal potassium sulphate, or JJipo/assic sulphate, S0 4 K 2 = S0 2 (OK) 2 -- S0 3 .OK 2 , is obtained by neutralizing the acid residue left in the retort when nitric acid is prepared, with crude potassium carbonate. The solution yields, on cooling, hard transparent crystals of the neutral sulphate, which may be re-dissolved in boiling water, and re-crystallized. Potassium sulphate is soluble in about 10 parts of cold, and in a much smaller quantity of boiling water: it has a bitter taste, and is neutral to test-paper. The crystals are combinations of rhombic pyramids and prisms, much resembling those of quartz in figure and appearance: they arc anhy- drous, and decrepitate when suddenly heated, which is often the case with salts containing no water of crystallization. They are quite insoluble in alcohol. Acid potassium sulphate, Hydrogen and potassium, sulphate, or Monopotassic sulphate, S0 4 KH = S0 2 (OK)(OH) = S0 3 .OKH, commonly called bmilphate of potash. To obtain this salt, the neutral sulphate in powder is mixed with half its weight of oil of vitriol, and the whole evaporated quite to dryness in a platinum vessel, placed under a chimney: the fused salt is dissolved in hot water, and left to crystallize. The crystals have the figure of flattened rhombic prisms, and are much more soluble than the neutral salt, requiring only twice their weight of water at 15-5, and less than half that quantity at 100. The solution has a sour taste and strongly acid reaction. Another acid sulphate, containing (S0 4 ) 3 K 4 H 2 or 2S0 4 K 2 .S0 4 H 2 , crystal- lizing in fine needles resembling asbestos, was obtained by Phillips from the nitric acid residue. Jacquelain was unsuccessful in his attempts to repro- duce this compound. The anhydrosulphate, S0 4 K 2 .S0 3 = 2S0 3 .OK 2 , commonly called MAgfdhMM l>ixnlphate of potash, is obtained by dissolving equal weights of the normal sulphate and oil of vitriol in a small quantity of warm distilled water, and hviving the solution to cool. The anhydrous sulphate crystalli/.es out in long delicate needles, which if left for several days in the mother-liquor, disappear, and give place to crystals of the ordinary acid sulphate above described. This salt is decomposed by a large quantity of water.* * Jacquelain, Ann. Chim. Phys. [3], vol. vii. p. 311. 298 MONAD METALS. POTASSIUM SULPHIDES. Potassium heated in sulphur vapor burns with great brilliancy. It unites with sulphur in five diU'ercnt proportions, forming the compounds SK 2 , S,K 2 , S 3 K 2 , S 4 K 2 , S 5 K 2 ; also a sulph-hydrate, SKII. Monosulphide, SK 2 . It is doubtful whether this compound has been ob- tained in the pure state. It is commonly said to be produced by heating potassium sulphate in a current of dry hydrogen, or by igniting the same salt in a covered vessel with finely divided charcoal; but, according to Bauer, one of the higher sulphides is always formed at the same time, to- gether with oxide of potassium. The product has a reddish-yellow color, is deliquescent, and acts as a caustic on the skin. When potassium sulphate is heated in a covered crucible with excess of lamp-black, a mixture of potas- sium sulphide and finely divided carbon is obtained, which takes fire spontane- ously on coming in contact with the air. The monosulphide might perhaps be obtained pure by heating 1 molecule of potassium sulph-hydrate, KHS, with 1 atom of the metal. When sulph-hydric acid gas is passed to saturation into a solution of caustic potash, a solution of the sulph-hydrate is obtained, which is color- less at first, but if exposed to the air, quickly absorbs oxygen, and turns yellow, in consequence of the formation of bisulphide : 2SKH -f = S 2 K 2 -f OH 2 . If a solution of potash be divided into two equal parts, and one half saturated with hydrogen sulphide, and then mixed with the other, a solu- tion is formed which may contain potassium monosulphide : SKH 4- OKH = SK 2 4- OH 2 . But it is also possible that the hydrate and the sulph-hydrate may mix without mutual decomposition. The solution, when mixed with one of the stronger acids, gives oft' hydrogen sulphide without deposition of sulphur, a reaction which is consistent with either view of its constitution. The bisulphide, S 2 K 2 , is formed, as already observed, on exposing a solu- tion of the sulph-hydrate to the air till it begins to show turbidity. By evaporation in a vacuum, it is obtained as an orange-colored, easily fusible substance. The trisulphide, S 3 K 2 , is obtained by passing the vapor of carbon bisul- phide over ignited potassium carbonate, as long as gas continues to escape : 2C0 3 K 2 + 3CS 2 =r 2S 3 K 2 -f 4CO + C0 2 . Also, together with potassium sulphate, forming one of the mixtures called liver of sulphur, by melting 552 parts (4 molecules) of potassium carbonate with 320 parts (10 atoms) of sulphur: 4C0 3 K 2 -f S 10 == S0 4 K 2 + 3S 3 K 2 + 4C0 2 . The tetrasulphide, S 4 K 2 , is formed by reducing potassium sulphate with the vapor of carbon bisulphide. The pentasulphide, S 5 K 2 , is formed by boiling a solution of any of the preceding sulphides with excess of sulphur till it is saturated, or by fusing either of them in the dry state with sulphur. The excess of sulphur then separates and floats above the dark-brown pentasulphide. Liver of sulphur, or hepar sulphuris, is a name given to a brownish sub- stance, sometimes used in medicine, made by fusing together different proportions of potassium carbonate and sulphur. It is a variable mix- ture of the two higher sulphides with hyposulphite and sulphate of po- tassium. When equal parts of sulphur and dry potassium carbonate are melted together at a temperature not exceeding 250 C. (482 F.), the decomposi- SODIUM. 299 lion of the salt is quite complete, and all the carbon dioxide is expelled. The fused mass dissolves in water, with the exception of a little mei-han- ically mixed sulphur, with dark-brown color, and the solution is foun{ sulphide and hyposulphite al- ways results. Potassium-salts are colorless, when not associated with a colored metallic oxide or acid. They are all more or less soluble in water, and may be distinguished by the following characters : (1.) Solution of tartaric acid, added in excess to a moderately strong solu- tion of potassium-salt, gives, after some time, a white crystalline precipi- tate of cream of tartar ; the effect is greatly promoted by strong agitation. (2.) Solution of platinic chloride with a little hydrochloric acid, if neces- sary, gives, under similar circumstances, a crystalline yellow precipitate, which is a double salt of platinum tetrachloride and potassium chloride. Both this compound and cream of tartar are, however, soluble in about 60 parts of cold water. An addition of alcohol increases the delicacy of both tests. (3.) Perchloric acid, and silicojluoric acid, give rise to slightly soluble white prcipitates when added to a potassium-salt. (4.) Potassium-salts usually color the outer blowpipe-flame purple or violet : this reaction is clearly perceptible only when the potassium-salts are pure. (5.) The spectral phenomena exhibited by potassium compounds are men- tioned at p. 88. SODIUM. Atomic weight, 23. Symbol, Na. (Natrium). SODIUM is a very abundant element, and very widely diffused. It occurs in large quantities as chloride, in rock-salt, sea-water, salt-springs, and many other mineral waters ; more rarely as carbonate, borate, and sul- phate, in solution or in the solid state, and as silicate in many minerals. Metallic sodium was obtained by Davy soon after the discovery of po- tassium, and by similar means. Gay-Lussac and Thenanl afterwards pre- pared it by decomposing sodium hydrate with metallic iron at a white heat; and Brunner showed that it may be prepared with much greater facility by distilling a mixture of sodium carbonate and charcoal. The preparation of sodium by this last-mentioned process is much easier than that of potassium, not being complicated, or only to a slight extent, 300 MONAD METALS. by the formation of secondary products. Within the last few years it has been considerably improved by Deville and others, and carried out on the manufacturing scale, sodium being now employed in considerable quantity as a reducing agent, especially in the manufacture of aluminium and mag- nesium, and in the silver amalgamation process. The sodium carbonate used for the preparation is prepared by calcining the crystallized neutral carbonate. It must be thoroughly dried, then pounded and mixed with a slight excess of pounded charcoal or coal. An inactive substance, viz. pounded chalk, is also added to keep the mixture pasty condition during the operation, and prevent the fused sodium carbonate from separating from the charcoal, portions recommended by Deville : The following are the pro- For Laboratory Operations. Dry sodium carbonate, 717 parts Charcoal 175 " Chalk 108 " For Manufacturing Operations. Dry sodium carbonate, 30 kilogr. Coal 13 Chalk . . 3 " These materials must be very intimately mixed by pounding and sifting, and it is advantageous to calcine the mixture before introducing it into the distilling apparatus, provided the calcination can be effected by the waste heat of a furnace ; the mixture is thereby rendered more compact, so that a much larger quantity can be introduced into a vessel of given size. The distillation is performed, on the laboratory scale, in a mercury bottle heated exactly in the manner described for the preparation of potassium. For manufacturing operations, the mixture is introduced into iron cylin- ders, which are heated in a reverberatory furnace, and so arranged that, at the end of the distillation, the exhausted charge may be withdrawn and a fresh charge introduced, without displacing the cylinders or putting out the fire. The receivers used in either case are the same in form and di- mensions as those employed in the preparation of potassium (p. 291). When the process goes on well, the sodium collected in the receivers is nearly pure; it may be completely purified by melting it under a thin layer of naphtha. This liquid is decanted as soon as the sodium becomes per- fectly fluid, and the metal is run into moulds like those used for casting lead or zinc. SODIUM CHLORIDE ; COMMON SALT, NaCl. This very important substance is found in many parts of the world in solid beds or irregular strata of im- mense thickness, as in Cheshire, Spain, Galicia, and many other localities. An inexhaustible supply exists also in the waters of the ocean, and large quantities are obtained from saline springs. Hock-salt is almost always too impure for use. If no natural brine-spring exists, an artificial one is formed by sinking a shaft into the rock-salt, and, if necessary, introducing water. This when saturated is pumped up, and evaporated more or less rapidly in large iron pans. As the salt separates, it is removed from the bottom of the vessel by means of a scoop, pressed while still moist into moulds, arid then transferred to the drying-stove. When large crystals are required, as for the coarse-grained bay-saH used in curing provisions, the evaporation is slowly conducted. Common salt is apt to be contaminated with magnesium chloride. Sodium chloride, when pure, is not deliquescent in moderately dry air. It crystallizes in anhydrous cubes, which are often -grouped together into pyramids, or steps. It requires about 1\ parts of water at 1-5-5 C. (60 F.) for solution, and its solubility is not sensibly increased by heat; it dis- solves to some extent in spirit of wine, but is nearly insoluble in absolute alcohol. It melts at a red heat, and is volatile at a still higher temperature. The economical uses of common salt are well known. SODIUM. 301 The iodide and bromide of sodium much resemble the corresponding potas- um-compoumls: they crystallize in cubes which are anhydrous, and very sium soluble in water. SODIUM OXIDES. Sodium forms a monoxide and a dioxide ; also drate corresponding to the former. hy- Sodium Monoxide, or Anhydrous Soda, ONa 2 , is produced, together with the dioxide, when sodium burns in the air, and may be obtained pure by exposing the dioxide to a very high temperature; or by heating sodium hydrate with an equivalent quantity of sodium : 20NaH -(- Na 2 = 20Na -f- H 2 . It is a gray mass, which melts at a red heat, and volatilizes with difficulty. Sodium Hydrate, or Caustic Soda, ONaH or ONa 2 , OH 2 . This substance is prepared by decomposing a somewhat dilute solution of sodium carbonate with calcium hydrate: the description of the process employed in the case of potassium hydrate, and the precautions necessary, apply word for word to that of sodium hydrate. The solid hydrate is a white, fusible substance, very similar in properties to potassium hydrate. It is deliquescent, but dries up again after a time in consequence of the absorption of carbonic acid. The solution is highly alkaline, and a powerful solvent for animal matter: it is used in large quantity for making soap. The strength of a solution of caustic soda may be roughly determined from a knowledge of its density, by the aid of the following table drawn up by Dalton: TABLE OF PERCENTAGE OP ANHYDROUS SODA, ONa 2 , IN SOLUTIONS OF DIFFERENT DENSITY. Density. 2-00 1-85 1-72 1-63 1-55 1-50 1-47 1-44 Percentage of anhydrous soda. Density. . 77-8 40 63-6 36 . 53-8 32 46-6 29 . 41-2 23 36-8 18 . 34-0 12 31-0 06 Percentage of anhydrous soda. . 29-0 26-0 . 23-0 19-0 . 16-0 13-0 . 9-0 4-7 Sodium Dioxide, 2 Na 2 . Sodium, when heated to about 200 in a current of dry air, absorbs oxygen, and is converted into dioxide : this substance is white, but becomes yellow when heated, which tint it again loses on cool- ing. It is soluble in water without decomposition: the solution maybe evaporated under the receiver of the air-pump, and, when sufficiently con- centrated, deposits crystalline plates having the composition 2 Na 2 .80H a . These crystals left to effloresce over oil of vitriol for nine days lose three fourths of their water, and yield another hydrate containing 2 Na 2 .20H 3 (Ilarcourt). The aqueous solution of sodium dioxide when heated on the water-bath, is decomposed into oxygen and the monoxide. SODIUM CARBONATES. The Neutral or Disodic Carbonate, C0 3 Na 2 .100H r was once exclusively obtained from the ashes of sea-weeds, and of plants, such as the Salsola soda, which grow by the sea-side, or, being cultivated in suitable localities for the purpose, are afterwards subjected to incinera- tion. The barilla, still employed to a small extent in soap-making, is thus produced in several places on the coast of Spain, as Alicante, Carthagena, . That made in Brittany is called varec. 26 302 MONAD METALS. Sodium carbonate is now manufactured on a stupendous scale from com- mon salt by a series of processes which may be divided into two stages : (1.) Manufacture of sodium sulphate, or salt-cake, from sodium chloride (common salt); this is called the salt-cake process. (2.) Manufacture of sodium carbonate, or soda-ash; called the soda-ash process. (1.) Salt-cake process. This process consists in the decomposition of common salt by sulphuric acid, and is effected in a furnace called the Salt- cake furnace, of which fig. 164 represents a section. It consists of a large Fig. 164. covered iron pan, placed in the centre, and heated by a fire underneath ; and two roasters, or reverberatory furnaces, placed one at each end, and on the hearths of which the salt is completely decomposed. The charge of half a ton of salt is first placed in the iron pan, and then the requisite quantity of sulphuric acid is allowed to pass in upon it. Hydrochloric acid is evolved, and escapes through a flue, with the products of combustion, into towers or scrubbers, filled with coke and bricks moistened with a stream of water; the whole of the acid vapors are thus condensed, and the smoke and heated air pass up the chimney. After the mixture of salt and acid has been heated in the iron pan, it becomes converted into a solid mass of acid sodium sulphate and undecomposed sodium chloride : 2NaCl -f S0 4 H 2 = NaCl -f S0 4 NaH + HC1. It is then raked on to the hearths of the furnaces at each side of the decom- posing pan, where the flame and heated air of the fire complete the decom- position into neutral sodium sulphate and muriatic acid : NaCl + S0 4 NaH = S0 4 Na 2 -f HC1. (2.) Soda-ash process. The sulphate is next reduced to powder, and mixed with an equal weight of chalk or limestone, and half as much small coal, both ground or crushed. The mixture is thrown into a reverberatory furnace, and heated to fusion, with constant stirring, 2 cwts. are about the quantity operated on at once. When the decomposition is judged complete, the melted matter is raked from the furnace into an iron trough, where it is allowed to cool. This crude product, called black ash or ball-soda, is broken up into little pieces, when cold, and lixiviated with cold or tepid water. The solution is evaporated to dryness, and the salt calcined with a little sawdust in a suitable furnace. The product is the soda-ash, or British alkali of commerce, which, when of good quality, contains from 48 to 52 per cent, of anhydrous soda, ONn 2 , partly in the state of carbonate, and partly as hydrate, the remainder being chiefly sodium sulphate and common salt, with occasional traces of sulphite or hyposulphite, and also cyanide of sodium. By dissolving soda-ash in hot water, filtering the solution, and then allowing it to cool slowly, the carbonate is deposited in large trans- parent crystals. The reaction which takes place in the calcination of the sulphate with chalk and coal-dust seems to consist, first, in the conversion of the sodium sulphate into sulphide by the aid of the combustible matter, and, secondly, SODIUM. in the interchange of elements between that substance and the calcium car- bonate : SNa 2 -f C0 3 Ca = SCa + C0 3 Na 2 Sodium Calcium Calcium Sodium sulphide. carbonate. sulphide. carbonate. Other processes have been proposed, and even carried into execution; but the above, which was originally proposed by Leblanc, is found most advantageous. The ordinary crystals of sodium carbonate contain ten molecules of water ; but by particular management the same salt may be obtained with fifteen, nine, seven, molecules, or sometimes with only one. The common form of the crystals is derived from an oblique rhombic prism; they effloresce in dry air. and crumble to a white powder. Heated, they fuse in their water of crystallization; when the latter has been expelled, and the dry salt exposed to a full red heat, it melts without undergoing change. The common crystals dissolve in two parts of cold, and in less than their own weight of boiling water : the solution has a strong, disagreeable, alkaline taste, and a powerfully alkaline reaction. Hydrogen and Sodium Carbonate, Hydrosodic Carbonate, Monosodic Car- bonate, Acid Sodium Carbonate, C0 3 NaH, or C0 5 Na 2 .C0 3 H 2 , commonly called Bicarbonate of soda. This salt is prepared by passing carbonic acid gas into a cold solution of the neutral carbonate, or by placing the crystals in an atmosphere of the gas, which is rapidly absorbed, while the crystals lose the greater part of their water, and pass into the new compound. Monosodic carbonate, prepared by either process, is a crystalline wl;ite powder, which cannot be re-dissolved in warm water without partial de- composition. It requires 10 parts of water at 15-5 for solution : the liquid is feebly alkaline to test-paper, and has a much milder taste than that of the simple carbonate. It does not precipitate a solution of magnesia. By exposure to heat, the salt is converted into neutral carbonate. Dihydro-tetrasodic Carbonate, (C0 3 ) 3 Na 4 H 2 . 20H 2 . This salt, commonly called sesquicarbonate of soda, may be regarded as a compound of the neutral and acid salts just described (C0 3 Na 2 .2C0 3 NaH). It occurs native on the banks of the soda lakes of Sokenna, near Fezzan, in Africa, where it is called trona; also as urao, at the bottom of a lake in Maracaibo, South America. It is produced artificially, though with some difficulty, by mixing the mo- nosodic and disodic carbonates in the proportions above indicated, melting them together, drying and exposing the dried mass in a cellar for some weeks; it then absorbs water, becomes crystalline, and contains spaces filled with the tetrasodic carbonate. Sodium and Potassium Carbonate, C0 3 NaK . 60H 2 , separates in monoclinic crystals from a solution containing the two carbonates in equivalent pro- portions. A mixture of these two carbonates in equivalent proportions melts at a much lower heat than either of the salts separately; such a mixture is very useful in the fusion of silicates, &c- Alkalimetry. Analysis of Alkaline Hydrates and Carbonates. The amount of alkali or alkaline carbonate in commercial potash, flpda, or ammonia, is estimated by determining the quantity of an acid of gm-n strength required to neutralize a given weight of the sample. The estim.-i- tion depends upon the facts that the alkaline salts of strong acids (sul- phuric, oxalic, &c.) are neutral to litmus; and that the violet solution of litmus is colored blue by caustic alkalies or alkaline carbonates, wine-red by carbonic acid, and light red by strong acids. 304 MONAD METALS. The first step is the preparation of the standard acid. It is best to make this liquid of such strength that 1000 cubic centimetres (1 litre) shall contain exactly one J gram-molecule (i. e., 1 molecule expressed in J grams) of the acid. About 70 grams of concentrated sulphuric acid are diluted with about 600 grams of water ; when the mixture is cool, the volume of it necessary to saturate 5-3 grams (one J-decigram-moleculc) of pure anhydrous sodium carbonate, C0 3 Na 2 , is determined.* For this purpose 5-3 grams of freshly ignited sodium carbonate are dissolved in hot water, the solution colored blue with a few drops of litmus, and the acid added from a burette or al- kalimeter (p. 305), at last drop by drop, till the color just passes from wine-red to light red, and till strips of litmus-paper, moistened with the solution begin to retain the color when dry. The volume of acid employed is then noted, and the whole diluted so as to approximate to the required strength. Suppose, for instance, 37 cubic centimetres of acid have been used ; water is then added till every 100 volumes is diluted to 250 volumes, and another determination is made. If 90 cubic centimetres are now re- quired to saturate the J-decigram alkaline solution, every 90 volumes of the acid must be diluted to 100, and the result controlled by a fresh determina- tion; 100 cubic centimetres of this acid should exactly saturate 5-3 grams of sodium carbonate, and will contain 1 half-dccigram-rnolecule of acid; 2 cubic centimetres will therefore contain 1 milligram-molecule (0-098 gram)f and will saturate 2 milligram-molecules of an alkali (OKH or ONaH), or 1 milligram-molecule of an alkaline carbonate (C0 3 K 2 or C0 3 Na 2 ). To estimate the proportion of alkali in a commercial sample, a weighed portion of the substance is dissolved in water (if a solid), a few drops of litmus added, and the standard acid added from a burette, until the first permanent appearance of a light red color ; and the volume of acid em- ployed is read off. Each cubic centimetre of acid corresponds to 1 milli- gram-molecule of alkali, or 1 half milligram-molecule of alkaline carbonate ; i. e., to - 053 gram sodium carbonate, C0 3 Na 2 , 0-069 gram potassium carbo- nate, C0 3 K 2 , 0.040 gram caustic soda ONaH, 0-056 gram caustic potash OKH, and 0-017 gram ammonia NH 3 ; and a simple proportion gives the amount of alkali or alkaline carbonate present (e. g. 100 : 6-9 : : number of cubic centimetres employed: potassium carbonate present). By operating on 100 times the ^-milligram-molecule (e. g. 6-9 grams in the case of potassium carbonate, 5-3 grams in the case of sodium carbonate), all calculation is saved : for as this amount, if present, would require 100 cubic centimetres of acid for its saturation, the number of cubic centimetres actually required at once indicates the percentage of alkaline carbonate. The burettes commonly used contain 50 cubic centimetres, and are graduated into half cubic centimeters; so that by operating on 50 times the ^-milligram-mole- cule, the number of divisions employed indicates the percentage. Sometimes, instead of exactly neutralizing the alkali with the standard acid, it is better to add the acid till the litmus assumes a distinct light-red color, then heat the solution to boiling, and add a small excess (5 to 10 cubic centimetres) of acid. The hot solution is freed from carbonic acid by agitation and by drawing air through it with a glass tube ; and then neu- tralized with a standard solution of caustic soda (100 cubic centimetres of which exactly saturate 100 cubic centimetres of the standard acid) till the color just changes from red to blue. Since the acid and alkaline solutions neutralize each other volume for volume, it is only necessary to deduct the number of cubic centimetres employed of the latter from that of the former, and calculate the amount of alkali from the residue. This method, called the indirect or residual method, is preferable to the direct method previously * The molecule of sodium carbonate CO ? Na 2 weighs 12 -f 48 -f 46 :r 106. f The molecular weight of sulphuric acid S0 4 IL. is 98 = 32 + 64 -f- 2. SODIUM. 305 described, for the analysis of carbonates, since the change from blue to red is more distinctly marked than that from one shade of red to another. The standard solution of caustic soda must be kept in a flask, into the cork of which is inserted a calcium chloride tube tilled with a mixture of sodium sulphate and quicklime, which eifectually prevents the absorption of carbonic acid. If the burette be closed with a similar tube, the soda so- lution may remain in it for days. The " alkalimeter " or "burette" is a glass tube (fig. 165) Fig- 165. closed at one end, and moulded into a spout or lip at the other, and marked with any convenient scale of equal parts, generally, as above mentioned, into 100 half cubic centimetres.* A strip of paper is pasted on the tube and suifered to dry, after which the instrument is graduated by counterpoising it in a nearly upright position in the pan of a balance of moderate delicacy and weigh- ing into it, in succession, 5, 10, 15, 20, &c., grams of distilled water at 4 C. (39-2 F.) until the whole quantity, amounting to 50 grams (50 cubic centimetres), has been introduced, the level of the water in the tube being, after each addition, carefully marked with a pen upon the strip of paper, while the tube is held quite upright, and the mark made between the top and bottom of the curve formed by the surface of the water. The smaller divisions of the scale, of a half cubic centimetre each, may then be made by dividing with compasses each of the spaces into 10 equal parts. When the graduation is complete, and the operator is satisfied with its accuracy, the marks may be transferred to the tube itself by a sharp file, and the paper removed by a little warm water. The numbers are scratched on the glass with the hard end of the same file, or with a diamond. Or the glass is covered with etching wax, the scale traced upon it with a fine needle point, and the marks etched by exposing the tube to the vapor of hydrofluoric acid. fig. 166. Fig. 167. Fig- 168. n > 1 3 * 1 10 20 T E 4 -| 20 30 | 30 430 -5 40 50 Ir i BO In 5O 70 ->sc ^ CO 80 f 1 ^ TO 80 \ 90 no gf* c 3 _=- 1 90 QP " Ni> J 100 * It mav also be divided into 1000 grain-mcasim-H. th grain-measure being the capacity of a ain of distilled water at 60 *V, 70,000 siu-h measure* go to an imperial gallon, and 8,7^0 to a pint. 26* 306 MONAD METALS. The alkalimeter, represented in fig. 165, is the simplest form of this in- strument. The pouring out of minute quantities is, however, greatly facil- itated by providing the measure with a narrow dropping tube, fig, 166, the lower extremity of which is soldered into the measure, while the upper one is bent outward and sharply cut off. This kind of burette, which is known as Gay-Lussac's, is chiefly used in France. The liquid may be very conveniently poured from it ; but it is rather easily broken, so that its manipulation requires a good deal of care. This defect is greatly obviated in the burette, fig. 167, in which the graduated tube is provided with a spout at the top, there being at the same time an orifice for pouring in the liquid. A very elegant instrument has been contrived by Dr. Mohr of Coblentz. It is a graduated tube, drawn out at one end to a paint, to which is at- tached, by means of a narrow vulcanized caoutchouc tube, a short glass tube, likewise drawn out to a point (fig. 108). There is a small space (about inch) between the two tubes, upon which is fixed a metallic clamp, a, represented in its actual dimensions in fig. 169. This clamp shuts off the connection between the graduated cylinder and the small glass tube. But by pressing with the fingers upon the ends, b 6, of this clamp, it opens, and allows the liquid to flow out of the lower tube. It is evident that by this arrangement the amount of liquid may be regulated with the greatest nicety. It is often desirable, in the analysis of carbonates, to determine directly the proportion of carbonic acid: the following methods leave nothing to be desired in point of precision: A small light glass flask of three or four ounces capacity, with lipped edge, is chosen, and a cork fitted to it. A piece of tube about three inches long is drawn out at one extremity, and fitted, by means of a small cork and a bit of bent tube, to the cork of the flask. This tube is filled with fragments of calcium chloride, prevented from escaping by a little cotton at either end: the joints are secured by sealing-wax. A short tube, closed at one extremity, and small enough to go into the flask, is also provided, and the apparatus is complete. Fifty grains of the carbonate to be exam- Fig. 169. Fig. 170. Fig. 171. t> ined are carefully weighed out and introduced into the flask, together with a little water; the small tube is then filled with oil of vitriol, and placed in the flask in a nearly upright position, and leaning against its side in such a manner that the acid does not escape. The cork and calcium chlor- ide tube are then adjusted, and the whole apparatus accurately counter- poised on the balance This done, the flask is slightly inclined, so that th*e oil of vitriol may slowly mix with the other substances and decompose the carbonate, the gas from which escapes in a dry state from the extremity SODIUM. 307 of the tube. When the action has entirely ceased, the liquid is until it boils, and the steam begins to condense in the drying-tube; it is then left to cool, and weighed, when the loss indicates the quantity of carbon dioxide. The acid must be in excess after the experiment. When calcium carbonate is thus analyzed, hydrochloric acid must be substituted for the sulphuric acid. Instead of the above apparatus, a neat arrangement may be used, which was first suggested by Will and Fresenius. It consists of -two small plass flasks, A and B, the latter being somewhat smaller than the former. Kadi of the flasks is provided with a doubly perforated cork. A tube, open at both ends, but closed at the upper extremity by means of a small quantity of wax, passes through the cork of A to the very bottom of the Husk, whilst a second tube, reaching to the bottom of B, establishes a communi- cation between the two flasks. The cork of B is provided, moreover, with a short tube d. In order to analyze a carbonate, a suitable quantity (fifty grains) is put into A, together with some water. B is half filled with con- centrated sulphuric acid, the apparatus tightly fitted and weighed. A small quantity of air is now sucked out of flask B by means of the tube rf, whereby the air in A is likewise rarefied. On allowing the air to return, a quantity of the sulphuric acid ascends to the tube c, and flows over into flask A, causing a disengagement of carbon dioxide, which escapes at d, after having been perfectly dried by passing through the bottle B. This opera- tion is repeated until the whole of the carbonate is decomposed, and the process terminated by opening the wax stopper, and drawing a quantity of air through the apparatus. The apparatus is now re-weighed. The dif- ference of the two weighings expresses the quantity of carbon dioxide in the compound analyzed. SODIUM SULPHATE, S0 4 Na 2 .100H 2 , commonly called Glauber 1 s salt, is a by-product in several chemical operations and an intermediate product in the manufacture of the carbonate as above described : it may of course be prepared directly, if wanted pure, by adding dilute sulphuric acid, to sat- uration, to a solution of sodium carbonate. It crystallizes in forms de- rived from an oblique rhombic prism: the crystals contain 10 molecules of water, are efflorescent, and undergo watery fusion when heated, like those of the carbonate: they are soluble in twice their weight of cold water, and rapidly increase in solubility as the temperature of the liquid rises to- 33 C. (91-5 F ), when a maximum is reached, 100 parts of water dis- solving 117-9 parts of the salt, corresponding to 52 parts anhydrous sodium sulphate. When the salt is heated beyond this point, the solubility dimin- ishes, and a portion of sulphate is deposited. A warm saturated solution, evaporated at a high temperature, deposits opaque prismatic crystals, which are anhydrous. The salt has a slightly bitter taste, and is purga- tive. Mineral springs sometimes contain it, as that at Cheltenham. Sodium and Hi/droycn Sulphate, or Acid Sodium Sulphate, 2S0 4 NaH 30H 2 , or S0 4 Na 2 S0 4 H 2 .30H 2 , commonly called bisulphate of soda, is prepared by adding to 10 parts of the anhydrous neutral sulphate, 7 of oil of vitriol, evaporating the whole to dryness, and gently igniting. The acid sulphate is very soluble in water, and has an acid reaction. It is not deliquescent. When very strongly heated, the fused salt gives up anhydrous sulphuric acid, and becomes neutral sulphate; a change which necessarily supposes the previous formation of an anhydro-bisulphate, S0 4 Na.,.SO 3 . SODIUM HYPOSULPHITE, R.,0 3 Xa 2 . There are several modes of procur- ing-this salt, which is now used in considerable quantity for photographic purposes and as antichlore. One of the best is to form nputr.-il -v, ,/;,///, sul- phite, by passing a stream of well- washed sulphurous oxide gas inm a 308 MONAD METALS. strong solution of sodium carbonate, and then digest the solution with sulphur at a gentle heat during several days. By careful evaporation at a moderate temperature, the salt is obtained in large and regular crystals, which are very soluble in water. SODIUM NITRATE, N0 3 Na. This salt, sometimes called Cubic Nitre, or Chile Saltpetre, occurs native, and in enormous quantity, at Tarapaca in Northern Peru, where it forms a regular bed, of great extent, along with gypsum, common salt, and remains of recent shells. The pure salt com- monly crystallizes in rhombohedrons, resembling those of calcareous spar. It is deliquescent, and very soluble in water. Sodium nitrate is employed for making nitric acid, but cannot be used for gunpowder, as the mixture burns too slowly, and becomes damp in the air. It has been lately used with some success in agriculture as a superficial manure or top-dressing ; also for preparing potassium nitrate (p. 294). SODIUM PHOSPHATES. The composition and chemical relations of these salts have already been explained in speaking of the basicity of acids (p. 285). Disodiohydric Phosphate, or Disodic Orthophosphate ; Common Tribasic Phos- phate, P0 4 Na 2 H.120H 2 . This salt is prepared by precipitating the acid calcium phosphate obtained in decomposing bone-ash by sulphuric acid, with a slight excess of sodium carbonate, and evaporating the clear liquid. It crystallizes in oblique rhombic prisms, which are efflorescent. The crystals dissolve in 4 parts of cold water, and undergo the aqueous fusion when heated. The salt is bitter and purgative; its solution is alkaline to test-paper. Crystals containing 7 molecules of water, and having a form different from that above mentioned, have been obtained. A trisodic, orthophosphate, sometimes called subphosphate, P0 4 Na 3 120H 2 , is obtained by adding a solution of caustic soda to the preceding salt. The crystals are slender six-sided prisms, soluble in 5 parts of cold water. It is decomposed by acids, even carbonic, but suffers no change by heat, ex- cept the loss of its water of crystallization. Its solution is strongly alka- line. A third tribasic phosphate, often called superphosphate or biphos- phate, P0 4 NaH 2 .OH 2 , may be obtained by adding phosphoric acid to the ordinary phosphate, until it ceases to precipitate barium chloride, and exposing the concentrated solution to cold. The crystals are prismatic, very soluble, and have an acid reaction. When strongly heated, the salt becomes changed into monobasic sodium phosphate, or metaphosphate. Sodium, Ammonium, and Hydrogen Phosphate; Phosphorous Salt; Micro- cosmic Salt, P0 4 Na(NH 4 )H.40H 2 . Six parts of common sodium phosphate are heated with two of water, until the whole is liquefied, and 1 part of powdered sal-ammoniac is added; common salt then separates, and may be removed by a filter, and from the solution, duly concentrated, the micro- cosmic salt is deposited in prismatic crystals, which may be purified by one or two re-crystallizations. Microcosmic salt is very soluble. When gently heated, it parts with its 4 molecules of crystallization water, and, at a higher temperature, the basic hydrogen is likewise expelled as water, together with ammonia, and a very fusible compound, sodium metaphos- phate, remains, which is valuable as a flux in blow-pipe experiments. Microcosmic salt occurs in decomposed urine. Tetrasodic Phosphate or Sodium Pyrophosphate, P 2 7 Na 4 100H 2 , is prepared by strongly heating common disodic 01 thophosphate, dissolving the residue in water, and re-crystallizing. The crystals are very brilliant, permanent in the air, and less soluble than the original phosphate : their solution is alkaline. A sodiohydric pyrophosphate has been obtained ; but it does not crystallize. SODIUM. 309 Monosodic Phosphate, or Sodium Mctaphosphate, P0 3 Na, is obtained by heat- ing either the acid tribasic phosphate, or microcosmic salt. It is a trans- parent glassy substance, fusible at a dull red heat, deliquescent, and very soluble in water. It refuses to crystallize, but dries up into a gum-like mass. If this glassy phosphate be cooled very slowly, it separates as a beauti- fully crystalline mass. It may be purified by means of boiling water from the vitreous metaphosphate, which will not crystallize. Another metaphos- phate has been obtained by adding sodium sulphate to an excess of phos- phoric acid, evaporating and heating to upwards of 315 (600 F.). Possibly these several metaphosphates may be represented by the formulae P0 3 Na, P 2 6 Na 2 , and P 3 9 Na 3 . (Graham.) The tribasic phosphates or orthophosphates give a bright-yellow precipi- tate with solution of silver nitrate ; the bibasic and monobasic phosphates aft'ord white precipitates with the same substance. The salts of the two latter classes, fused with excess of sodium carbonate, yield orthophosphoric acid. Respecting the phosphates intermediate in composition between the meta- phosphate and pyrophosphate of sodium, discovered by Fleitmann and Henneberg, see page 287. SODIUM EQUATES. The neutral borate or metaborate, B0 2 Na, or B 2 3 .ONa 2 , is formed by fusing common borax and sodium carbonate in equivalent proportions, and dissolving the mass in water. It forms large crystals containing B0 2 Na.30H 2 . The Anhydroborate, Biborate, or Borax, 2B0 2 Na.B 2 3 .100H 2 = 2B 2 3 .ONa 2 . 100 H 2 , occurs in the waters of certain lakes in Thibet and Persia: it is im- ported in a crude state from the East Indies under the name of tim-al. When purified it constitutes the borax of commerce. Much borax is now, however, manufactured from the native boric acid of Tuscany, and also from a native calcium borate called hayesine, which occurs in southern Peru. Borax crystallizes in six-sided prisms, which effloresce in dry air, and require 20 parts of cold, and 6 of boiling water for solution. Exposed to heat, the 10 molecules of water of crystallization are expelled, and at a higher tempera- ture the salt fuses, and assumes a glassy appearance on cooling : in this state it is much used for blowpipe experiments, the metallic oxides dissolv- ing in it to transparent beads, many of which are distinguished by charac- teristic colors. By particular management, crystals of borax can be ob- tained with 5 molecules of water: they are very hard, and permanent in the air. Although by constitution an acid salt, borax has an alkaline reaction to test-paper, it is used in the arts for soldering metals, its action consisting in rendering the surfaces to be joined metallic, by dis- solving the oxides, and it sometimes enters into the composition of the glaze with which stoneware is covered. SODIUM SULPHIDE, SNa 2 . Prepared in the same manner as potassium monosiilphide : it separates from a concentrated solution in octohedral crystals, which are rapidly decomposed by contact with the air into a mix- ture of sodium hydrate and hyposulphite. It forms double sulphur-salts with hydrogen sulphide, carbon bisulphide, and other sulphur-acids. Sodium sulphide is supposed to enter into the composition of the beauti- ful pigment ultramarine, which is prepared from the lapis lazuli, and is now imitated by artificial means. An intimate mixture of 37 kaolin, 15 sodium sulphate, 22 sodium carbonate, 18 sulphur, and 8 charcoal, is heated from twenty-four to thirty hours in large crucibles. The product thus obtained is again heated in cast-iron boxes at a moderate temperature till the re- quired tint is obtained. After being finely pulverized, washed and dried, 310 MONAD METALS. it constitutes commercial ultramarine. The composition of this color varies, and its true constitution is not known. There is no good precipitant for sodium, all its salts being very soluble, with the exception of the metantimonate, which is precipitated on mixing a solution of a sodium salt with a solution of potassium metantimonate; the use of this reagent is, however, attended with some difficulties. The pres- ence of sodium is often determined by negative evidence. The yellow color imparted by sodium salts to the outer flame of the blowpipe, and to combustible matter, is a character of considerable importance. The spec- tral phenomena exhibited by sodium compounds are mentioned on page 88. AMMONIUM. The ammonia salts are most conveniently studied in this place, on account of their close analogy to those of potassium and sodium. These salts are formed by the direct union of ammonia NH 3 with acids, and as already pointed out (p. 163), they may be regarded as compounds of acid radicals, Cl, N0 3 , S0 4 , &c., with a basylous radical NH 4 , called ammonium, which plays in these salts the same part as potassium and sodium in their respec- tive compounds ; thus: NH 3 Ammonia. NH 3 NH 3 2NH, -f HC1 Hydrochloric acid. -f HN0 3 Nitric acid. + H 2 S0 4 Sulphuric acid. NH 4 .C1 Ammonium chloride. NH 4 .N0 3 Ammonium nitrate. NH 4 .H.S0 4 Acid ammoniuD onium sulphate. H 2 S0 4 (NH 4 ) 2 .S0 4 Neutral ammonii .en \- an ammonium-salt, e.g., NH 4 C1 or (NH 4 ) 2 S0 4 , similar reactions take place, and the tube becomes filled with a blue liquid mixed with excess of am- monia. This blue liquid, which is also formed by the action of potassium hydrate on potassammonium, appears to consist of ammonium itself. N ? IU It is even more unstable than the metallammoniums, being resolved into ammonia and hydrogen, partly even before the reaction between the am- monium-salt and the sodammonium is completed. But whether ammonium has any separate existence or not, it is quite certain that many ammoniacal salts are isornorphous with those of potas- sium; and if from any two of the corresponding salts, as the nitrates, * Pogg. Ann. cxxi. 697. 312 MONAD METALS. KN0 3 and NH 4 N0 3 , we subtract the radical N0 3 common to the two, there remain the metal K and the group NH 4 , which are, therefore, supposed to be isomorphous. AMMONIUM CHLORIDE, SAL-AMMONIAC, NH 4 C1. Sal-ammoniac was for- merly obtained from Egypt, being extracted by sublimation from the soot of camels' dung: it is now largely manufactured from the ammoniacal liquid of the gas-works, and from the condensed products of the distillation of bones, and other animal refuse, in the preparation of animal charcoal. These impure and highly offensive solutions are treated with a slight ex- cess of hydrochloric acid, by which the free alkali is neutralized, and the carbonate and sulphide are decomposed, with evolution of carbonic acid and sulphuretted hydrogen gases. The liquid is evaporated to dryness, and the salt carefully heated, to expel or decompose the tarry matter; it is then purified by sublimation in large iron vessels lined with clay, sur- mounted with domes of lead. Sublimed sal-ammoniac has a fibrous texture ; it is tough, and difficult to powder. When crystallized from water it separates, under favorable circumstances, in distinct cubes or octohedrons ; but the crystals are usually small, and ag- gregated together in rays. It has a sharp saline taste, and is soluble in 2| parts of cold, and in a much smaller quantity of hot water. By heat, it is sublimed without decomposition. The crystals are anhydrous. Ammonium chloride forms double salts with the chlorides of magnesium, nickel, cobalt, iron, manganese, zinc, and copper. AMMONIUM NITRATE, N0 3 (NH 4 ), is easily prepared by adding ammonium carbonate to slightly diluted nitric acid until neutralization has been reached. By slow evaporation at a moderate temperature it crystallizes in six-sided prisms, like those of potassium nitrate ; but, as usually prepared for making nitrogen monoxide, by quick boiling until a portion solidifies completely on cooling, it forms a fibrous and indistinct crystalline mass. Ammonium nitrate dissolves in two parts of cold water, producing con- siderable depression of temperature ; it is but feebly deliquescent, and deflagrates like nitre on contact with heated combustible matter. Its decom- position by heat has been already explained (p. 159). AMMONIUM SULPHATE, S0 4 (NH 4 ) 2 . Prepared by neutralizing ammonium carbonate with sulphuric acid, or on a large scale, by adding sulphuric acid in excess to the coal-gas liquor just mentioned, and purifying the product by suitable means. It is soluble in 2 parts of cold water, and crystallizes in long, flattened, six-sided prisms. It is entirely decomposed, and driven off by ignition, and, even to a certain extent, by long boiling with water, ammonia being expelled and the liquid rendered acid. AMMONIUM CARBONATES. H. Rose admits the existence of a considerable number of these salts, to which he assigns very complicated formulas; but, according to H. Sainte Claire-Deville,* there exist only two ammonium carbonates of definite composition, namely : (a ) Ammonium and Hydrogen Carbonate, or Mono-ammonic Carbonate, C0 3 (NH 4 )H, commonly called Bicarbonate, or Acid carbonate of ammonia. This salt is obtained by saturating an aqueous solution of ammonia, or of the sesquicarbonate, with carbonic acid gas ; or by treating the finely pounded sesquicarbonate with strong alcohol, which dissolves out normal or diam- monic carbonate, leaving a residue of the mono-amtnonic salt. Cold water may be used instead of alcohol for this purpose ; but it dissolves a larger * Ann. Chim. Phys. [3] xl. 87. AMMONIUM. quantity of the mono-ammonic carbonate. All ammonium-carbonates when left to themselves are gradually converted into mono-amrnonic csirbnnnti-. This salt forms large crystals belonging to the trimetric system. According to Deville it is dimorphous, but never isomorphous with monopotassic car- bonate ; when exposed to the air, it volatilizes slowly, ami gives off a faint ammoniacal odor. It dissolves in 8 parts of cold water, the solution decom- posing gradually at ordinary temperatures, quickly when heated above 30 C. (86 F.) with evolution of ammonia. It is insoluble in alcohol, but when exposed to the air, under alcohol, it dissolves as normal carbonate, evolving carbon dioxide. It has been found native in considerable quantity in the deposits of guano, on the western coast of Patagonia, in white crystalline masses, having a strong ammoniacal odor. (6.) Tetrammonio-dihydric Carbonate, C 3 9 N 4 H, 8 = (C0 3 ) 3 (NH 4 ) 4 H 2 . This salt, commonly called sesqui-carbonate of ammonia, contains the elements of 1 molecule of diammonic and 2 molecules of mono-ammonic carbonate, into which it is, in fact, resolved by treatment with water or alcohol : (C0 3 ) 3 (NH 4 ) 4 H 2 = C0 3 (NH 4 ) 2 + 2[(CO,(NH 4 )H]. It, is obtained by dissolving the commercial carbonate in strong aqueous ammonia, at about 30 C. (86 F.) and crystallizing the solution. It forms large transparent rectangular prisms, having their summits truncated by octohedral faces. These crystals decompose very rapidly in the air, giving off water and ammonia, and being converted into mono-ammonic carbonate. The normal or diammonic carbonate, C0 3 (NH 4 ) 2 , has not been obtained in the solid state. Commercial carbonate of ammonia (sal volatile, salt of harts- horn) consists of sesqui-carbonate more or less pure. It is prepared on the large scale by the dry distillation of bones, hartshorn, and other animal mat- ter, and is purified from adhering empyreumatic oil by subliming it once or twice with animal charcoal in cast-iron vessels, over which glass receivers are inverted. Another method consists in heating to redness a mixture of 1 part ammonium chloride or sulphate, and 2 parts calcium carbonate (chalk), or potassium carbonate, in a retort, to which a receiver is luted.* AMMONIUM SULPHIDES. Several of these compounds exist, and may be formed by distilling with sal-ammoniac the corresponding sulphides of potassium or sodium. Ammonium and Hydrogen Sulphide, or Ammonium Sulph-hydrate, S(NH 4 )H, is a compound of great practical utility ; it is obtained by saturating a solu- tion of ammonia with well-washed sulphuretted hydrogen gas, until no more of the latter is absorbed. The solution is nearly colorless at first, but becomes yellow after a time, without, however, suffering material injury, unless it has been exposed to the air. It gives precipitates with most metal lie solutions, which are very often characteristic, and is of great service in analytical chemistry. Ammoniacal salts are easily recognized ; they are all decomposed or vola- tilized at a high temperature; and when heated with calcium hydrate or solution of alkaline carbonate, they give off ammonia, which may be recog- [* Diammnnio-hydric Phosphate; Ommon Tribasic Phosphate, P0 4 , 2(NH 4 )II.OII 2 . This salt is prepared by precipitating the acid calcium phosphate, with an excess of the COmBCVOlal am- monium carbonate and evaporating at a moderate temperature. It crystalli/es in rix-OdM tables derived from oblique quadrangular prisms The crystals dissolve in 4 parts of water and in alcohol. They are efflorescent, have a saline, alkaline last- and alkaline reaction. The acid tribasin phosphate P0 4 .NH 4 .Ho.40H is forme.] when a solution of the common is boiled as long as ammonia is given off. It crystallizes in 4-sided prisms, which are permanent s,,l,,M.- in five parts of water and have an acid' taste and reaction. When ammonia in excess is added (,, either of these salts, the triammouic phosphate P0 4 3(NH 4 ) is deposited as a granular precipitate U. B.J 21 314 MONAD METALS. nized by its odor and alkaline reaction. The salts are all more or less soluble ; the acid tartrate and the platinochloride being, however, among the least soluble ; hence ammonium salts cannot be distinguished from potassium salts by the tests of tartaric acid and platinum solution. When a solution containing an ammoniacal salt, or free ammonia, is mixed with patash, and a solution of mercuric iodide in potassium iodide is added, a brown precipitate or coloration is immediately produced, consisting of dimercur- ammonium iodide, NHg 2 /x I : NH 3 -\- 2Hg"I 2 = NHg" 2 I + SHI. This is called Nessler's test ; it is by far the most delicate test for ammonia that is known. Amic Acids and Amides. SULPHAMIC ACID. When dry ammonia gas is passed over a thin layer of sulphuric oxide S0 3 , the gas is absorbed, and a white crystalline powder is formed, having the composition N 2 H 6 S0 3 , that is, of ammonium sulphate minus one molecule of water : N 2 H 6 S0 3 == S0 4 (NH 4 ) 2 OH 2 . It is not, however, a salt of sulphuric acid : for its aqueous solution does not give any precipitate Avith baryta-water or soluble barium salts. It is, in fact, the ammonium salt of sulphamic acid, an acid derived from sulphuric acid, S0 4 H 2 or S0 2 (HO) 2 , by substitution of the univalent radical NH 2 * for one atom of hydroxyl, HO. The formula of this acid is S0 3 (NH 2 )H, and that of its ammonium salt, S0 3 (NH 2 )NH 4 , or S0 3 N 2 H 6 . Ammonium sul- phamate is permanent in the air, and dissolves without decomposition in water. Its solution, evaporated in a vacuum, over oil of vitriol, yields the salt in transparent colorless crystals. The solution of the ammonium salt, mixed with baryta-water, gives off ammonia, and yields a solution of barium sulphamate, (S0 3 NH 2 ) 2 Ba // , which may be obtained by evaporation in well defined crystals ; and the solution of this salt, decomposed with potassium sulphate, yields pataseium sul- phamate, S0 3 NH 2 K. CARBAMIC ACID. When dry ammonia gas is mixed with carbon dioxide, the mixture being kept cool, the gases combine in the proportion of 2 volumes of the former to 1 volume of the latter, forming a pungent, very volatile substance, which condenses in white flocks. This substance has the composition C0 2 N 2 H 6 , that is, of normal ammonium carbonate, C0 3 (NH 4 ) 2 , minus one molecule of water. It was formerly called anhydrous car- bonate of ammonia; but, like the preceding salt, is not really a carbonate, but the ammonium salt of carbamic acid, C0 2 (NH 2 )H, derived from carbonic ncid, C0 3 H 2 or CO(OH) 2 , by substitution of amidogen NH 2 for 1 atom of hydroxyl. Ammonium carbamate dissolves readily in water, and quickly takes up one molecule of that compound, whereby it is converted into am- monium carbonate, When treated with sulphuric oxide, it is converted into ammonium sulphamate. CARBAMIDE, CON 2 H 4 . When ammonia gas is mixed with carbon oxy- chloride or phosgene gas, COC1 2 , a white crystalline powder is formed, having th.is, composition : COC1 2 -f 2NH a = 2HC1 -f CON 2 H 4 . This compound, which is likewise formed in other reactions to be after- wards considered, is 4eriyed from carbonic acid, CO(OH) 2 , by substitution * See page 237. AMMONIUM. 315 of 2 atoms of amidogen for 2 atoms of hydroxyl. It differs from carbamic acid in being a neutral substance, not containing any hydrogen easily re- placeable by metals. Other bibasic acids likewise yield an amic acid and a neutral amide by substitution of 1 or 2 atoms of amidogen for hydroxyl. Tribasic acids yield in like manner two amic acids and one neutral amide, and tetrabasic acids may yield three arnic acids and a neutral amide ; thus, from pyro- fhosphoric acid, P. 2 7 H 4 = P.O.(HO 4 ), are obtained the three amic acids ' 2 6 (NH 2 )H 3 , P 2 5 (NH 2 ) 2 H 2 , and P 2 4 (NH 2 )H. Monobasic acids, which contain but one atom of hydroxyl, yield by this mode of substitution only neutral amides, no amic acids: thus, from acetic acid, C 2 H 4 2 = C 2 H 3 2 .HO, is obtained acetamide, C ? H 3 0(NH 2 ). The neutral amides may also be regarded as derived from one or more molecules of ammonia, by substitution of univalent or multivalent acid radicals, for hydrogen; thus, acetamide = N /// H.(C.H 3 0) ; carbamide N X// H (CO)", &c. By similar substitution of metals, or basylous compound radicals for the hydrogen of ammonia, basic compounds, called amines, are formed. Thus, when potassium is gently heated in ammonia gas, monopotassamine, NH 2 K, is formed. It is an olive-green substance, which is decomposed by water into ammonia and potassium hydrate: NH 2 K 4- OH 2 = NH 3 + OKH. It melts at a little below 100, and when heated in a close vessel, is resolved into ammonia and tripotassamine : 3NH 2 K = 2NH 3 -f NK 3 . The latter effervesces violently with water, yielding ammonia and potas- sium hydrate : NK 3 + 30H 2 = NH 3 4- 30KH. The formation and properties of amides and amines will be further con- sidered under Organic Chemistry. METALLAMMONIUMS. We have already spoken of the formation of com- pounds which may be regarded as derived from ammonium, N 2 H 8 , by sub- stitution of metals for hydrogen: e.g. sodammonium, N 2 H 6 Na 2 . Salts of such radicals are also formed in several ways. Ammonia gas is absorbed by various metallic salts in different proportions, forming compounds, some of which may be formulated as salts of inetallammoniums. Thus, platinum dichloride, Ptd 2 , absorbs two molecules of ammonia, forming platosammo- nium chloride, N 2 H 6 Pt/ / .Cl 2 ; and platinum tetrachloride, Pt lT Cl 4 , absorbs four molecules of ammonia, forming platinammonium chloride, N 4 H| 2 Pt iT .Cl 4 In like manner, cupric chloride and sulphate form the chloride and sulphate of cuprammonium, ILl^Ca''.^ and N^Cu^-SO,,. Similar compounds are formed in many cases by precipitating metallic salts with ammonia or ammoniacal salts: thus, ammonia added to a solution of mercuric chloride, HgCl 2 , forms a white precipitate, consisting of diinrr- curammonium chloride, N 2 H 4 Hg // 2 .Cl 2 ; and by dropping a solution of mer- curic chloride into a boiling solution of sal-ammoniac mixed with free am- monia, crystals are obtained, consisting of mer -cur -ammonium chloride, N 2 H 4 Hg // .Cl 2 . Some of these compounds will be further considered in con- nection with the several metals. 316 MONAD METALS. LITHIUM. Atomic weight, 7. Symbol, Li. Lithium is found in petalite, spocUimene, lepidolite, triphylline, and a few other minerals, and sometimes occurs in minute quantities in mineral springs. The metal is obtained by fusing pure lithium chloride in a small thick porcelain crucible, and decomposing the fused chloride by electricity. It is a white metal like sodium, and very oxidizable. Lithium fuses at 180 C. (356 F.); its specific gravity is 0-59: it is, therefore, the lightest solid known. A lithium salt may be obtained from petalite on the small scale, by the following process: The mineral is reduced to an exceedingly fine powder, mixed with five or six times its weight of pure calcium carbonate, and the mixture heated to whiteness, in a platinum crucible placed within a well covered earthen one, for twenty minutes or half an hour. The shrunken coherent mass is digested in dilute hydrochloric acid, the whole evaporated to dryness, acidulated water added, and the silica separated by a filter. The solution is then mixed with ammonium carbonate in excess, boiled, and filtered; the clear liquid is evaporated to dryness, and gently heated in a platinum crucible, to expel the sal-ammoniac ; and the residue is wetted with oil of vitriol, gently evaporated once more to dryness, and ignited : pure fused lithium sulphate then remains. This process will serve to give a good idea of the general nature of the operation by which alkalies are extracted in mineral analysis, and their quantities determined. Lithium hydrate, LiHO, is much less soluble in water than the hydrates of potassium and sodium ; the carbonate and phosphate are also sparingly soluble salts. The chloride crystallizes in anhydrous cubes which are deli- quescent. Lithium sulphate is a very beautiful salt ; it crystallizes in length- ened prisms containing one molecule of water. It gives no double salt with aluminium sulphate. The salts of lithium color the outer flame of the blowpipe carmine-red. The spectral phenomena exhibited by lithium compounds are mentioned on page 89. CESIUM AND RUBIDIUM. Cs = 133. Rb = 85-4. The two metals designated by these names were discovered by Bunsen and Kirchhoff by means of their spectrum apparatus mentioned on page 88: the former in 1860 and the latter in 1861. These metals, it appears, are widely diffused in nature, but always occur in very small quantities ; they have been detected in many mineral waters, as well as in some min- erals, namely, lithia-mica or lepidolite, and petalite; lately also in fel- spar; they have also been found in the alkaline ashes of the beet-root. The brine of Diirkheim has up to the present moment been the richest source of caesium. The best material for the preparation of rubidium, is lepidolite, which has been found to contain as much as 0-2 per cent, of that metal. Both metals are closely analogous to potassium" in their de- portment, and cannot be distinguished from that metal or from one another, either by reagents or before the blowpipe. SILVER. 317 Rubidium and cesium, like potassium, form double salts with tetra- chloride of platinum, which arc, however, much more insoluble than tho corresponding potassium salts: it is on this property that the separation of these metals from potassium is based. The mixture of platinochlorides is repeatedly extracted with boiling water, when a difficultly soluble re- sidue, consisting chiefly of the platinochlorides of caesium and rubidium, remains. The hydrates of these new metals are powerful bases, which attract car- bonic acid from the air, passing, first into normal carbonate and then into acid carbonate. Caesium carbonate is soluble in absolute alcohol; rubi- dium carbonate is nearly insoluble in that liquid: this property is made use of for the -separation of these two metals. The chloride crystallizes in cubes, and is somewhat more soluble in water than chloride of potas- sium. Rubidium chloride, when in a state of fusion, is easily decomposed by the electric current ; the metal produced rises to the surface and burns with a reddish light. If this experiment be performed in an atmosphere of hydrogen, to prevent oxidation, the separated metal is nevertheless lost, dissolving as it does in the fused chloride, which is transformed into a subchloride having the blue color of smalt. Rubidium, when separated under mercury by the electric current, forms a crystalline amalgam of sil- very lustre, which is rapidly oxidized by the air, and decomposes water in the cold. Caesium chloride, under the influence of the electric current, exhibits exactly the same deportment as rubidium choride. Rubidium is electro-positive towards potassium, caesium is electro-positive towards ru- bidium and potassium, and thus constitutes the most electro-positive member of the elements. SILVER. Atomic weight, 108. Symbol, Ag (Argentum). Silver is found in the metallic state, as sulphide, in union with sulphide of antimony and sulphide of arsenic, also as chloride, iodide, and bromide. Among the principal silver mines may be mentioned those of the Hartz mpuntains in Germany, of Kongsberg in Norway, and, more particularly, of the Andes, in both North and South America. The greater part of the silver of commerce is extracted from ores so poor as to render any process of smelting or fusion inapplicable, even where fuel could be obtained, and this is often difficult to be procured. Recourse, therefore, is had to another method that of amalgamation founded on the easy solubility of silver and many other metals in metallic mercury. The amalgamation process adopted in Germany which differs somewhat from that in use in America is as follows: The ore is crushed to powder, mixed with a quantity of common salt, and roasted at a low red heat in a suitable furnace, by which treatment any sulphide of silver it may contain is converted into chloride. The mixture of earthy matter, oxides of iron, copper, soluble salts, silver chloride, and metallic silver, is sifted and put into large barrels made to revolve on axes, with a quantity of water and scraps of iron, and the whole is agitated together for some time, during which the iron reduces the silver chloride to the state of metal. A certain proportion of mercury is then introduced, and the agitation repeated: the mercury dissolves out the silver, together with gold, if there be any. metnl- lic copper, and other substances, forming a fluid anial-rain easily separable! from the thin mud of earthy matter by subsidence and washing. This amalgam is strained through a strong linen cloth, and the solid portion 27* 318 MONAD METALS. exposed to heat in a kind of retort, by which the remaining mercury is distilled off and the silver left behind in an impure state. Considerable loss often occurs in the amalgamation process from the com- bination of a portion of the mercury with sulphur, oxygen, &c., whereby it is brought into a pulverulent condition, known as "flouring," and is then liable to be washed away, together with the silver it has taken up. This inconvenience may be prevented, as suggested by Mr. Crookes, by amalga- mating the mercury with 1 or 2 per cent, of sodium, which by its superior affinity for sulphur and oxygen, prevents the mercury from becoming floured. A considerable quantity of silver is obtained from argentiferous galena : in fact, almost every specimen of native lead sulphide is found to contain traces of this metal. When the proportion rises to a certain amount, it becomes worth extracting. The ore is reduced in the usual manner, the whole of the silver remaining with the lead ; the latter is then re-melted in a large vessel, and allowed to cool slowly until solidification commences. The portion which first crystallizes is nearly pure lead, the alloy with silver being more fusible than lead itself: by particular management this is drained away, and is found to contain nearly the whole of the silver [Pattinson's process]. This rich mass is next exposed to a red heat on the shallow hearth of a furnace, while a stream of air is allowed to impinge upon its surface ; oxidation takes place with great rapidity, the fused oxide or lith- arge being constantly swept from the metal by the blast. When the greater part of the lead has been thus removed, the residue is transferred to a cupel or shallow dish made of bone-ashes, and again heated: the last portion of the lead is now oxidized, and the oxide sinks in a melted state into the porous vessel, while the silver, almost chemically pure, and exhibiting a brilliant surface, remains behind. Pure silver may be easily obtained. The metal is dissolved in nitric acid : if it contains copper, the solution will have a blue tint; gold will remain undissolved as a black powder. The solution is mixed with hydrochloric acid or with common salt, and the white, insoluble, curdy precipitate of sil- ver chloride is washed and dried. This is then mixed with about twice its weight of anhydrous sodium carbonate, and the mixture, placed in an earthen crucible, is gradually raised to a temperature approaching white- nes, during which the sodium carbonate and the silver chloride react upon each other ; carbon dioxide and oxygen escape, while metallic silver and soda chloride result: the former melts into a button at the bottom of the crucible, and is easily detached. The following is perhaps the most simple method for the reduction of silver chloride. The silver-salt is covered with water, to which a few drops of sulphuric acid are added ; a plate of zinc is then introduced. The silver chloride soon begins to decompose, and is, after a short time, entirely converted into metallic silver ; the silver thus obtained is gray and spongy; it is ultimately purified by washing with slightly acidulated water. Pure silver has a most perfect white color and a high degree of lustre : it is exceedingly malleable and ductile, and is probably the best conductor both of heat and electricity known. Its specific gravity is 10-5. In 'hard- ness it lies between gold and copper. It melts at a bright red heat, about 1023 C, (1873 F.), according to the observation of Mr. Daniell. Silver is unalterable by air and moisture : it refuses to oxidize at any temperature, but possesses the extraordinary faculty already noticed of absorbing many times its volume of oxygen when strongly heated in an atmosphere of that gas, or in common air. The oxygen is again disengaged at the moment of solidification, and gives rise to the peculiar arborescent appearance often remarked on the surface of masses or buttons of pure silver. The addition of 2 per cent, of copper is sufficient to prevent the absorption of oxygen. SILVER. 319 Silver oxidizes when heated with fusible siliceous matter, as glass, which it stains yellow or orange, from the formation of a silicate. It is little attacked by hydrochloric acid; boiling oil of vitriol converts it into sulphate, with evolution of sulphurous oxide; nitric acid, even dilute and in the cold, dis- solves it readily. The tarnishing of surfaces of silver exposed to the air is due to hydrogen sulphide, the metal having a strong attraction for sulphur. SILVER CHLORIDES. Two of these compounds are known containing re- spectively 1 and 2 atoms of silver to 1 atom of chlorine; the second, how- ever, is a very unstable compound.* The Monochloride or Argentic Chloride, Ag Cl, is almost invariably pro- duced when a soluble silver salt and a soluble chloride are mixed. It falls as a white curdy precipitate, quite insoluble in water and nitric acid; but one part of silver chloride is soluble in 200 parts of hydrochloric acid when concentrated, and in about 600 parts when diluted with double its weight of water. When heated it melts, and on cooling becomes a grayish crys- talline mass, which cuts like horn : it is found native in this condition, constituting the horn-silver of the mineralogist. Silver chloride is decom- posed by light, both in the dry ;ind in the wet state, very slowly if pure, and quickly if organic matter b"e"~]5resent. : it is reduced also when put into water with metallic zinc or iron. It dissolves with great ease in ammonia and in a solution of potassium cyanide. In practical analysis the propor- tion of chlorine or hydrochloric acid in a compound is always estimated by precipitation with silver solution. The liquid is acidulated with nitric acid, and an excess of silver nitrate added; the chloride is collected on a filter, or better by subsidence, washed, dried, and fused ; 100 parts corre- spond to 24-7 of chlorine, or 25-43 of hydrochloric acid. Argentous Chloride, Ag 4 Cl 2 , is obtained by treating the corresponding oxide with hydrochloric acid or by precipitating an argentous salt, the citrate, for example, with common salt. It is easily resolved by heat or by am- monia into argentic chloride and metallic silver. SILVER FLUORIDE, AgF, is produced by dissolving argentic oxide or car- bonate in aqueous hydrofluoric acid, and separates on evaporation in trans- parent quadratic octohedrons, which contain AgF.OH 2 , and give off their water when fused. Their solution gives, with hydrochloric acid, a precip- itate of argentic chloride. When chlorine gas is passed over fused silver fluoride, silver chloride is formed and fluorine is set free (p. 192). SILVER IODIDE, Agl, is a pale-yellow insoluble precipitate, produced by adding silver nitrate to potassium iodide ; it is insoluble, or nearly so, in ammonia, and in this respect forms an exception to the silver-salts in gen- eral. Deville has obtained a crystalline silver iodide by the action of con- centrated hydriodic acid upon metallic silver, which it dissolves with dis- engagement of hydrogen. Hydriodic acid converts silver chloride into iodide. The bromide of silver very closely resembles the chloride. SILVER OXIDES. There are three oxides of silver, only one of which can, however, be regarded as a well-defined compound, namely : The Monoxide or Argentic Oxide, OAg 2 . This oxide is a powerful base, * The existence of two silver chlorides is utterly incoinpatihle with the hyp<>the-i- t! silver iiml chlorine are monad ele.nents. The composition of the uranttptU Compound* perhaps very well established; but supposing the chloride to contain CI 2 Ag 4 , H8 u-ually st: NO, its constitution maybe represented by the formula T "", in which the chlorine play, the ClAg a part of a triad. 320 MONAD METALS. yielding salts isomorphous with those of the alkali-metals. It is obtained as a pale-brown precipitate on adding caustic potash to a solution of silver nitrate : 2N0 3 Ag + OKH = OAg 2 + N0 3 K -f N0 3 H Silver Potassium Silver Potassium Hydrogen nitrate. hydrate. oxide. nitrate. nitrate. It is very soluble in ammonia, and is dissolved also to a small extent by pure water; the solution is alkaline. Recently precipitated silver chloride, boiled with a solution of caustic potash of specific gravity 1-25, is con- verted, according to Gregory, although with difficulty, into argentic oxide, which in this case is black and very dense. Argentic oxide neutralizes acids completely, and forms, for the most part, colorless salts. It is decomposed by a red-heat, with evolution of oxygen, spongy metallic silver being left ; the sun's rays also effect its decomposition to a small extent. Argentous Oxide, OAg 4 .* When dry argentic citrate is heated to 100 in a stream of hydrogen gas, it loses oxygen and becomes dark-brown. The product, dissolved in water, gives a dark-colored solution containing free citric acid and argentous citrate, which .udien mixed with potash yields a precipitate of argentous oxide. This oxide is a black powder, very easily decomposed, and soluble in ammonia. The solution of argentous citrate is rendered colorless by heat, being resolved into argentic citrate and metallic silver. According to Wohler, argentous oxide is also formed by boiling ar- gentic arsenite with caustic alkalies. In this case it is mixed with metallic silver. OAg Silver Dioxide, 2 Ag 2 or I . This is a black crystalline substance OAg which forms upon the positive electrode of a voltaic arrangement employed to decompose a solution of silver nitrate. It is reduced by heat, evolves chlorine when acted upon by hydrochloric acid, explodes when mixed with phosphorus and struck, and decomposes solution of ammonia, with great energy and rapid disengagement of nitrogen gas. SILVER NITRATE or ARGENTIC NITRATE, N0 3 Ag. This salt is prepared by dissolving silver in nitric acid, and evaporating the solution to dryness, or until it is strong enough to crystallize on cooling. The crystals are colorless, transparent, anhydrous tables, soluble in an equal weight of cold, and in half that quantity of boiling water; they also dissolve in alcohol. They fuse when heated, like those of nitre, and at a high temperature suffer decomposition: the lunar caustic of the surgeon is silver nitrate which has been melted and poured into a cylindrical mould. The salt blackens when exposed to light, more particularly if organic matters of any kind are present, and is frequently employed to communicate a dark stain to the hair; it enters into the composition of the "indelible" ink used for mark- ing linen. The black stain has been thought to be metallic silver; it may possibly be argentous oxide. Pure silver nitrate may be prepared from the metal alloyed with copper: the alloy is dissolved in nitric acid, the solution evaporated to dryness, and the mixed nitrates cautiously heated to fusion. A small portion of the melted mass is removed from time to time for exami- nation ; it is dissolved in water, filtered, and ammonia added to it in excess. While any copper-salt remains undecomposed, the liquid will be blue, but when that no longer happens, the nitrate maybe suffered to cool, dissolved in water, and filtered from the insoluble black oxide of copper. * If this formula be correct, oxygen must be a tretrad. SILVER. 321 SILVER SULPHATE, S0 4 Ag 2 . The sulphate may be prepared by boiling together oil of vitriol and metallic silver, or by precipitating a concentrated solution of silver nitrate with an alkaline sulphate. It dissolves in 88 parts of boiling water, and separates in great measure in the crystalline form on cooling, having but a feeble degree of solubility at a low temper- ature. It forms with ammonia a crystallizable compound which is freely soluble in water, contains S0 4 Ag 2 . 2NH 3 , and may therefore be regarded as argentammonium sulphate, S0 4 (NH 3 Ag) 2 . Silver hyposulphate, S 2 6 Ag 2 .OH 2 , is a soluble crystallizable salt, perma- nent in the air. The hyposulphite is insoluble, white, and very prone to decomposition: it combines with the alkaline hyposulphites, forming sol- uble compounds distinguished by an intensely sweet taste. The alkaline hyposulphites dissolve both oxide and chloride of silver, and give rise to similar salts, an oxide or chloride of the alkaline metal being at the same time formed: hence the use of alkaline hyposulphites in fixing photographic pictures (p. 97). Silver carbonate is a white insoluble substance .obtained by mixing solutions of silver nitrate and sodium carbonate. It is black- ened and decomposed by boiling. SILVER SULPHIDE, SAg 2 . This is a soft, gray, and somewhat malleable substance, found native in the crystallized state, and easily produced by melting together its constituents, or by precipitating a solution of silver with hydrogen sulphide. It is a strong sulphur-base, and combines with the sulphides of antimony and arsenic : examples of such compounds are found in the beautiful minerals, dark and light-red silver ore. AMMONIA-COMPOUND OF SILVER ; BERTHOLLET'S FULMINATING SILVER. When precipitated, argentic oxide is digested in ammonia, a black substance is produced, possessing extremely dangerous explosive properties. While moist, it explodes when rubbed with a hard body, but when dry the touch of a feather is sufficient. The ammonia retains some of this substance in solution, and deposits it in small crystals by spontaneous evaporation. A similar compound exists containing oxide of gold. It is easy to understand the reason why these bodies are subject to such violent and sudden decom- position by the slightest cause, on the supposition that they contain an oxide of an easily reducible metal and ammonia: the attraction between the two constituents of the substance is very feeble, while that between the oxygen of the one and the hydrogen of the other is very powerful. The explosion is caused by the sudden evolution of nitrogen gas and aqueous vapor, the metal being set free. Soluble silver salts are perfectly characterized by the white curdy pre- cipitate of silver chloride, darkening by exposure to light, and insoluble in hot nitric acid, which is produced by the addition of any soluble chlor- ide. Lead and mercury are the only metals which can be confounded with silver in this respect; but lead chloride is soluble to a great extent in boiling water, and is deposited in brilliant acicular crystals when the solu- tion cools ; and mercurous chloride is instantly blackened by ammonia, whereas silver chloride is dissolved thereby. Solutions of silver are reduced to the metallic state by iron, c/>/>rr, mrr- cury, and other metals. They give with hydrogen sulphide a black precipi- tate of argentic sulphide insoluble in ammonium sulphide: with nmstir. alkalies, a brown precipitate of argentic oxide; and with n/fcalinr carbonate*, a white precipitate of argentic carbonate, both precipitates being easily soluble in ammonia. Ordinary sodium phosphate forms a yellow precipitate 322 MONAD METALS. of argentic orthophosphate ; potassium chromate or bichromate, a red-brown precipitate of argentic chromate. The economical uses of silver are many: it is admirably adapted for culinary and other similar purposes, not being attacked in the slightest degree by any of the substances used for food. It is necessary, however, in these cases, to diminish the softness of the metal by a small addition of copper. The standard silver of England contains 222 parts of silver and 18 parts of copper. CLASS II. DYAD METALS. GROUP I. METALS OF THE ALKALINE EARTHS. BARIUM.* Atomic weight, 137. Symbol, Ba. nnHIS metal occurs abundantly as sulphate and carbonate, forming the u veinstone in many lead mines. Davy obtained it in the metallic state by means similar to those described in the case of lithium. Bunsen sub- jects barium chloride mixed up to a paste with water and a little hydro- chloric acid, at a temperature of 100, to the action of the electric current, using an amalgamated platinum wire as the negative pole. In this manner the metal is obtained as a solid, highly crystalline amalgam, which, when heated in a stream of hydrogen, yields barium in the form of a tumefied mass, tarnished on the surface, but often exhibiting a silver-white lustre in the cavities. Barium may also be obtained, though impure, by passing vapor of potassium over the red-hot chloride or oxide of barium. It is malleable, melts below a red heat, decomposes water, and gradually oxi- dizes in the air. BARIUM CHLORIDE, BaCl 2 . OH 2 . This valuable salt is prepared by dis- solving the native carbonate in hydrochloric acid, filtering the solution, and evaporating until a pellicle begins to form at the surface: the solution on cooling deposits crystals. When native carbonate cannot be procured, the native sulphate may be employed in the following manner: The sul- phate is reduced to fine powder, and intimately mixed with one third of its' weight of powdered coal ; the mixture is pressed into an earthen cru- cible to which a cover is fitted, and exposed for an hour or more to a high red heat, by which the sulphate is converted into sulphide at the expense of the combustible matter of the coal; the black mass thus obtained is powdered and boiled in water, by which the sulphide is dissolved; and the solution, filtered hot, is mixed with a slight excess of hydrochloric acid. Barium chloride and hydrogen sulphide are then produced, the latter es- caping with effervescence. Lastly, the solution is filtered to separate any little insoluble matter, and evaporated to the crystallizing point. The crystals of barium chloride are flat four-sided tables, colorless and transparent. They contain two molecules of water, easily driven off by heat. 100 parts of water dissolve 43-5 parts at 15-5, and 78 parts at 104 5, which is the boiling-point of the saturated solution. BARIUM MONOXIDE, BARYTA, BaO. The best method of preparing this jompound is to decompose the crystallized nitrate by heat in a capacious porcelain crucible until red vapors are no longer disengaged: the nitric * From /JaptJf, heavy, in allusion to the great specific gravity of the native carbonate and sulphate. 323 324 DYAD METALS. acid is resolved into nitrous acid and oxygen, and the baryta remains be- hind in the form of a grayish spongy mass, fusible at a high degree of heat. When moistened with water, it combines into a hydrate, with great elevation of temperature. BARIUM HYDRATE, BaH 2 2 = BaO . H 2 0. This compound is prepared on a large scale by decomposing a hot concentrated solution of barium chlor- ide with a solution of caustic soda; on cooling, crystals of barium hydrate are deposited, which may be purified by re-crystallization. In the labora- tory the barium hydrate is often prepared by decomposing the sulphide with black oxide of copper. (See barium sulphide.) The crystals of barium hydrate contain BaH 2 2 . 8 aq. ; * they fuse easily, and lose their water of crystallization when strongly heated. The hydrate is a white, soft powder, having a great attraction for car- bonic acid, and soluble in 20 parts of cold and 2 parts of boiling water. Solution of barium hydrate is a valuable reagent: it is highly alkaline to test-paper, and instantly rendered turbid by the smallest trace of car- bonic acid. BARIUM DIOXIDE, Ba0 2 . This oxide maybe formed, as already men- tioned, by exposing baryta, heated to full redness in a porcelain tube, to a current of pure oxygen gas. The dioxide is gray, and forms with water a white hydrate, which is not decomposed by that liquid in the cold, but dissolves in small quantity. Barium hydrate, when heated to redness in a current of dry atmospheric air, loses its water, and is converted, by ab- sorption of oxygen, into barium dioxide, from which the second atom of oxygen may be expelled at a higher temperature. Boussingault has pro- posed to utilize these reactions for the preparation of oxygen upon a large scale. The dioxide may also be made by heating pure baryta to redness in a platinum crucible, and then gradually adding an equal weight of po- tassium chlorate, whereby barium dioxide and potassium chloride are pro- duced. The latter may be extracted by cold water, and the dioxide left in the state of hydrate. It is interesting chiefly in its relation to hydrogen dioxide. When dissolved in dilute acid, it is decomposed by potassium bichromate, and by the oxide, chloride, sulphate, and carbonate of silver. BARIUM NITRATE, (N0 3 ) 2 Ba. The nitrate is prepared by methods ex- actly similar to those adopted for preparing the chloride, nitric acid being substituted for hydrochloric. It crystallizes in transparent colorless octo- hedrons, which are anhydrous. They require for solution 8 parts of cold, and 3 parts of boiling water. This salt is much less soluble in dilute nitric acid than in pure water: errors sometimes arise from such a preci- pitate of crystalline barium nitrate being mistaken for sulphate. It dis- appears on heating, or by large affusion of water. BARIUM SULPHATE, S0 4 Ba. Found native as heavy spar or barytes, often beautifully crystallized: its specific gravity is as high as 4-4 to 4-8. This compound is always produced when sulphuric acid or a soluble sulphate is mixed with a solution of a barium salt. It is not sensibly soluble in water or in dilute acids: even in nitric it is almost insoluble: hot oil of vitriol dissolves a little, but the greater part separates again on cooling. Barium sulphate is now produced artificially on a large scale ; it is used as a sub- stitute for white lead in the manufacture of oil-paints. The sulphate to be used for this purpose is precipitated from very dilute solutions : it is known in commerce as blancfixe. Powdered native barium sulphate, being * The symbol aq. (abbreviation of aqua) is often used to denote water of crystallization. STRONTIUM. 325 rather crystalline, has not sufficient body. For the production of sulphate, the chloride of barium is first prepared, which is dissolved in a large quantity of water, and then precipitated by dilute sulphuric acid. BARIUM CARBONATE, C0 3 Ba. The natural carbonate is called wiiherite: the artificial is formed by precipitating the chloride or nitrate with an al- kaline carbonate, or carbonate of ammonia. It is a heavy, white powder, very sparingly soluble in water, and chiefly useful in the preparation of the rarer barium salts. BARIUM SULPHIDES. The monosulphide, BaS, is obtained in the manner already described; the higher sulphides may be formed by boiling it with sulphur. Barium monosulphide crystallizes from a hot solution in thin, nearly colorless plates, which contain water, and are not very soluble : they are rapidly altered by the air. A strong solution of this sulphide may be employed in the preparation of barium hydrate, by boiling it with small successive portions of black oxide of copper, until a drop of the liquid ceases to form a black precipitate with lead salts ; the filtered liquid on cooling yields crystals of the hydrate. In this reaction, besides hydrate of barium, the hyposulphate of that base, and sulphide of copper, are pro- duced ; the latter is insoluble, and is removed by the filter, while most of the hyposulphate remains in the mother-liquor. Solutions of barium hydrate, nitrate, and chloride, are constantly kept in the laboratory as chemical tests, the first being employed to effect the separation of carbonic acid from certain gaseous mixtures, and the two latter to precipitate sulphuric acid from solution. Soluble barium salts are poisonous, which is not the case with those of the base next to be described. For their reactions, see p. 332. STRONTIUM. Atomic weight, 87-5. Symbol, Sr. The metal strontium may be obtained from its oxide by means similar to those described in the case of barium: it is usually described as a white metal, heavy, oxidizable in the air, and capable of decomposing water at common temperatures. Matthiessen states, however, that it has a dark- yellow color, and specific gravity 2-54. He prepares it by filling a small crucible having a porous cell with anhydrous strontium chloride mixed with some ammonium chloride, so that the level of the fused chloride in the cell is much higher than in the crucible. The negative pole placed in the cell consists of a very fine iron wire. The positive pole is an iron cylinder placed in the crucible round the cell. The heat is regulated so that a crust forms in the cell, and the metal collects under this crust. STRONTIUM MONOXIDE; STRONTIA; SrO. This compound is best pre- pared by decomposing the nitrate with aid of heat: it resembles in almost every particular the earth baryta, forming, like that substance, a white hydrate, soluble in water. A hot saturated solution deposits crystals on cooling, which contain SrH 2 2 . 8 aq. : heated to dull redness they lose the whole of their water, anhydrous strontia being left. The hydrate has a great attraction for carbonic acid. STRONTIUM DIOXIDE, Sr0 2 Prepared in the same manner as barium dioxide : it may be substituted for the latter in making hydrogen dioxide. 28 326 DYAD METALS. The native carbonate and sulphate of strontium serve for the prepara- tion of the various salts by means exactly similar to those already described in the case of barium salts : they have a very feeble degree of solubility in water. STRONTIUM CHLORIDE, SrCl 2 . The chloride crystallizes in colorless needles or prisms, which are slightly deliquescent, and soluble in 2 parts of cold and a still smaller quantity of boiling water: they are also soluble in alcohol, and the solution, when kindled, burns with a crimson flame. The crystals contain 6 molecules of water, which they lose by heat: at a higher temperature the chloride fuses. STRONTIUM NITRATE, (N0 3 ) 2 Sr. This salt crystallizes in anhydrous octo- hedrons, which require for solution 5 parts of cold, and about half their weight of boiling water. It is principally of value to the pyrotechnist, who employs it in the composition of the well-known "red-fire."* The spectral phenomena exhibited by strontium compounds are mentioned on page 89. CALCIUM. Atomic weight, 40. Symbol, Ca. Calcium is one of the most abundant and widely diffused of the metals, though it is never found in the free state. As carbonate, it occurs in a great variety of forms, constituting, as limestone, entire mountain-ranges. Cal- cium was obtained in an impure state by Davy, by means similar to those adopted for the preparation of barium. Matthiessen prepares the pure metal by fusing a mixture of two molecules of calcium chloride and one of strontium chloride with some chloride of ammonium in a small porcelain crucible, in which an iron cylinder is placed as positive pole, and a pointed iron wire or a little rod of carbon connected with the zinc of the battery is made to touch the surface of the liquid. The reduced metal fuses and drops off from the point of the iron wire, and the bead is removed from the liquid by a small iron spatula. Lies-Bodart and Gobin-f- prepare calcium by ig- niting the iodide with an equivalent quantity of sodium in an iron crucible having its lid screwed down. Calcium is a light yellow metal of sp. gr. 1-5778. It is about as hard as gold, very ductile, and may be cut, filed, or hammered out into plates as thin as the finest paper. It tarnishes slowly in dry, more quickly in damp air, decomposes water quickly, and is still more rapidly acted upon by dilute acids. Heated on platinum foil over a spirit-lamp, it burns with a bright flash ; with a brilliant light also when heated in oxygen or chlorine gas, or in vapor of bromine, iodine, or sulphur. CALCIUM CHLORIDE, CaCl 2 , is usually prepared by dissolving marble in hydrochloric acid ; also a by-product in several chemical manufactures. * RED FIRE: Grains. Dry strontium nitrate . 800 Sulphur ... 225 Potassium chlorate . 200 Lampblack ... 50 GREEX FIRE : Grains. Dry barium nitrate . . 450 Sulphur . . . .150 Potassium chlorate . . 100 Lampblack .... 25 The strontium or barium-salt, the sulphur and the lampblack, must be finely powdered and intimately mixed, after which the potassium chlorate should be added in rather coarse powder, and mixed, without much rubbing, with the other ingredients. The red fire compo- sition has been known to ignite spontaneously. t Comptes Rendus, xlvii. 23. CALCIUM. 327 The salt separates from a strong solution in colorless, prismatic, and exceed- ingly deliquescent crystals, which contain 6 molecules of \v:itrr. I'.v ln-at this water is expelled, and by a temperature of strong ignition the Mil is fused. The crystals reduced to powder are employed in the production of artificial cold by being mixed with snow or powdered ice ; and the chloride, strongly dried or in the fused state, is of great practical use in desiccating rases, for which purpose the latter are slowly transmitted through tubes tilled with fragments of the salt. Calcium chloride is also freely soluble in alcohol, which, when anhydrous, forms with it a definite crystallizable com- pound. CALCIUM FLUORIDE; FLUOR-SPAR; CaF 2 . This substance is important as the most abundant natural source of hydrofluoric acid and the other fluorides. It occurs beautifully crystallized, of various colors, in lead-veins, the crystals having commonly the cubic, but sometimes the octohedral form, parallel to the faces of which latter figure they always cleave. Some varie- ties, when heated, emit a greenish, and some a purple phosphorescent light. The fluoride is quite insoluble in water, and is decomposed by oil of vitriol in the manner already mentioned (p. 192). CALCIUM MONOXIDE ; LIME; CaO. This extremely important compound may be obtained in a state of considerable purity by heating to full redness for some time fragments of the black bituminous marble of Derbyshire or Kilkenny. If required absolutely pure, it must be made by igniting to whiteness, in a platinum crucible, an artificial calcium carbonate, prepared by precipitating the nitrate with ammonia carbonate. Lime in an impure state is prepared for building and agricultural purposes by calcining, in a kiln of suitable construction, the ordinary limestones which abound in many districts ; a red heat, continued for some hours, is sufficient to disengage the whole of the carbonic acid. In the best contrived lime-kilns the process is carried on continuously, broken limestone and fuel being constantly thrown in at the top, and the burned lime raked out at intervals from beneath. Sometimes, when the limestone contains silica, and the heat has been very high, the lime refuses to slake, and is said to be over-burned; in this case a portion of silicate has been formed. Pure lime is white, and often of considerable hardness ; it is quite infus- ible, and phosphoresces, or emits a pale light at a high temperature. When moistened with water, it slakes with great violence, evolving heat, and crumbling to a soft, white, bulky powder, which is a hydrate containing a single molecule of water: the latter can be again expelled by red-heat. This hydrate, CaH 2 2 or CaO . OH 2 , is soluble in water, but far less so than either the hydrate of barium or of strontium, and, what is very remark- able, the colder the water, the larger is the quantity of the compound that is taken up. A pint of water at 15-5 C. (60 F.) dissolves about 11 grains, while at 100 C. ((212 F.) only 7 grains are retained in solution. The hy- drate has been obtained in thin delicate crystals by slow evaporation under the air-pump. Lime-water is always prepared for chemical and pharma- ceutical purposes by agitating cold water with excess of calcium hydrate in a closely stopped vessel, and then, after subsidence, pouring off the clear liquid, and adding a fresh quantity of water, for another operation: there is not the least occasion for filtering the solution. Lime-water has a strong alkaline reaction, a nauseous taste, and when exposed to the air becomes almost instantly covered with a pellicle of carbonate, by absorption of car- bonic acid. It is used, like baryta-water, as a test for carbonic acid, and also in medicine. Lime-water prepared from some varieties of limestone may contain potash. The hardening of mortars and cements is in a great measure due to the 328 DYAD METALS. gradual absorption of carbonic acid ; but even after a very great length of time, this conversion into carbonate is not complete. Mortar is known, under favorable circumstances, to acquire extreme hardness with age. Lime-cements which resist the action of water contain iron oxides, silica, arid alumina : they require to be carefully prepared, and the stone not over- heated. When they are ground to powder and mixed with water, solidifi- cation speedily ensues, from causes not yet thoroughly understood, and the cement, once in this condition, is unaffected by wet. Parker's or Roman cement is made in this manner from the nodular masses of calcareo-argil- laceous ironstone found in the London clay. Lime is of great importance in agriculture : it is found more or less in every fertile soil, and is often very advantageously added by the cultivator. The decay of vegetable fibre in the soil is thereby promoted, and other important objects, as the destruc- tion of certain hurtful compounds of iron in marsh and peat-land, are often attained. The addition of lime probably serves likewise to liberate potas- sium from the insoluble silicate of that base contained in the soil. CALCIUM DIOXIDE, Ca0 2 . This compound is stated to resemble barium dioxide, and to be obtainable by treating lime with hydrogen dioxide. CALCIUM SULPHATE ; S0 4 Ca. Crystalline native calcium sulphate, con- taining two molecules of water, is found in considerable abundance in some localities as gypsum : it is often associated with rock-salt. When regularly crystallized, it is termed selenite. Anhydrous calcium sulphate is also occa- sionally met with. The salt is formed by precipitation, when a moderately concentrated solution of calcium chloride is mixed with sulphuric acid. Calcium sulphate is soluble in about 500 parts of cold water, and its solu- bility is a little increased by heat. It is more soluble in water containing ammonium chloride or potassium nitrate. The solution is precipitated by alcohol. Gypsum, or native hydrated calcium sulphate, is largely employed for the purpose of making casts of statues and medals, and also for moulds in the porcelain and earthenware manufactures, and for other applications. It is exposed to heat in an oven where the temperature does not exceed 127 C. (260 F.), by which the water of crystallization is expelled, and it is afterwards reduced to a fine powder. When mixed with water, it solidi- fies after a short time, from the re-formation of the same hydrate ; but this effect does not happen if the gypsum has been over-heated. It is often called Plaster of Paris. Artificial colored marbles, or scagliola, are frequently prepared by inserting pieces of natural stone in a soft stucco containing this substance, and polishing the surface when cement has become hard. Calcium sulphate is one of the most common impurities of spring water. The peculiar property water acquires by the presence of calcium salts is termed hardness. It manifests itself by the effect such waters have upon the palate, and particularly by its peculiar behavior with soap. Hard water yields a lather with soap only after the whole of the calcium salts have been thrown down from the water in the form of an insoluble lime- soap. Upon this principle Prof. Clark's soap-test for the hardness of water is based.* The hardness produced by calcium sulphate is called permanent hardness, since it cannot be remedied. CALCIUM CARBONATE ; CHALK; LIMESTONE; MARBLE; C0 3 Ca. Calcium carbonate, often more or less contaminated with iron oxide, clay, and or- ganic matter, forms rocky beds, of immense extent and thickness, in almost every part of the world. These present the greatest diversities of texture and appearance, arising, in a great measure, from changes to which they have been subjected since their deposition. The most ancient and highly * Journal of the Pharmaceutical Society, vol. vi. p. 526. CALCIUM. 329 crystalline limestones are destitute of visible organic remains, while those of more recent origin are often entirely made up of the shelly exuviae of once-living beings. Sometimes these latter are of such a nature as to show that the animals inhabited fresh water; marine species and corals are, however, most abundant. Cavities in limestone and other rocks are very often lined with magnificent crystals of calcium carbonate or calcareous spar, which have evidently been slowly deposited from a watery solution. Calcium carbonate is always precipitated when an alkaline carbonate is mixed with a solution of that base. Although this substance is not sensibly soluble in pure water, it is freely taken up when carbonic acid happens at the same time to be present. If a little lime-water be poured into a vessel of that gas, the turbidity first produced disappears on agitation, and a transparent solution of calcium carbonate in excess of carbonic acid is obtained. This solution is decom- posed completely by boiling, the carbonic acid being expelled, and the car- bonate precipitated. Since all natural waters contain dissolved carbonic acid, it is to be expected that calcium in this state should be of very com- mon occurrence ; and such is really found to be the fact, river, and more especially spring water, almost invariably containing calcium carbonate thus dissolved. In limestone districts, this is often the case to a great ex- tent. The hardness of water, which is owing to the presence of calcium carbonate, is called temporary, since it is diminished to a very considerable extent by boiling, and may be nearly removed by mixing the hard water with lime-water, when both the dissolved carbonate and the dissolved lime, which thus becomes carbonated, are precipitated. Upon this principle Prof. Clark's process of softening water is based. This process is of con- siderable importance, since a supply of hard water to towns is in many re- spects a source of great inconvenience. As already mentioned, the use of such water, for the purposes of washing, is attended with a great loss of soap. Boilers, in which such water is heated, speedily become lined with a thick stony incrustation.* The beautiful stalactitic incrustations of lime- stone caverns, and the deposit of calc-sinter or travertin upon various ob- jects, and upon the ground, in many places, are thus explained by the solubility of calcium carbonate in water containing carbonic acid. Crystallized calcium carbonate is dimorphous ; calc-spar and ar-ragonite, although possessing exactly the same chemical composition, have different crystalline forms, different densities, and different optical properties. Rose has observed that calcium carbonate appears in the form of calc-spar when deposited from its solution in water containing carbonic acid at the ordi- nary temperature. At 90 C. (194 F.), and on ebullition, however, it is chiefly deposited in the form of arragonite ; at lower temperatures the formation of arragonite decreases, whilst that of calc-spar increases, the limit for the formation of the former variety being between 30 and 50 C. (86 122 F.). Calc-spar occurs very abundantly in crystals derived from an obtuse rhombohedron, whose angles measure 105 5' and 7455 / : its density varies from 2-5 to 28. The rarer variety, or arragonite, is found in crys- tals whose primary form is a right rhombic prism, a figure having no geo- metrical relation to the preceding: it is, besides, heavier and harder. CALCIUM PHOSPHATES. A number of distinct calcium salts of phos- phoric acid are known. The tribasic phosphates, or orlhophosphates, (P0 4 ) 2 * Many proposals have boon made to prevent the formation of boiler deposits. The m0 = Ce ferrosoferric or magnetic iron oxide, is produced when cerous hydrate, carbonate, or nitrate is ignited in an open vessel. It is yellowish-white, acquires a deep orange-red color when heated, but recovers its original tint on cooling. It is not converted into a higher order by ignition in hydrogen. Ceroso-ceric hydrate, Ce 3 4 . 30H 2 , obtained by passing chlorine into aqueous potash in which cerous hydrate is suspended, is a bright- yellow precipitate, which dissolves readily in sulphuric and nitric acids, forming yellow solutions of ceroso-ceric salts; and in hydrochloric acid, with evolution of chlorine, forming colorless cerous chloride. The solution of the sulphate yields by spontaneous evaporation, first, brown-red crystals of the salt, (S0 4 ) 6 Ce 5 . 18 aq., or SSC^Ce". (S0 4 ) 3 Ce /// 2 . 18 aq., and afterwards a yellow indistinctly crystalline salt, containing S0 4 Ce". (S0 4 ) s Ce'" 2 . 18 aq.f All ceroso-ceric compounds, when heated with hydrochloric acid, give off chlorine, and are reduced to the corresponding cerous compounds; thus: Ce 3 4 + 8HC1 = 3CeCl 2 + 4 H 2 + Cl r Ceroso-ceric oxide. Cerous chloride. * A sesquioxide, C^Og, is commonly said to exist, and is designated as eerie oxide, but there is no proof of its existence; neither are any salts of analogous composition known with cer- tainty. t The symbol aq. (abbreviation of aqua) is often used to denote water of crystallization. 29* 342 EARTH-METALS. Lanthanum is bivalent, forming only one set of compounds, viz. g, LaO, LaS0 4 . There is, however, a higher oxide, the composition of which is not exactly known. Lanthanum salts are colorless ; their solutions yield, with alkalies, a precipitate of lanthanum hydrate, LaH 2 2 , or LaO . OH 2 , which, when ignited, leaves the white anhydrous monoxide. Both the hy- drate and the anhydrous oxide dissolve easily in acids. Lanthanum sulphate forms small prismatic crystals, containing S0 4 La . 30H 2 . Lanthanum and potassium sulphate, (S0 4 ) 2 LaK 2 , is formed, on mixing the solution of a lan- thanum salt with potassium sulphate, as a white crystalline precipitate, resembling the corresponding cerium salt. Didymium is also bivalent ; its salts are rose-colored, and their solutions give, with alkalies, a pale rose-colored precipitate of the hydrate, DiH 2 2 , which, when ignited in a covered crucible, leaves the anhydrous monoxide, DiO, in white, hard lumps. When, however, the hydrate, nitrate, carbon- ate, or oxalate of didymium is heated in contact with the air, and not very strongly, a dark-brown peroxide is left, containing from 0-8 to 0-9 per cent, oxygen more than the monoxide. This, when treated with acids, dissolves readily, giving off oxygen and yielding a salt of the monoxide. Didymium sulphate separates from an acid solution, by spontaneous evaporation, in well-defined rhombohedral crystals, exhibiting numerous secondary faces, and containing 3S0 4 Di . 8 aq. : they are isomorphous with the similarly constituted sulphates of yttrium, erbium, and cadmium. The sulphate is more soluble in cold than in hot water, and a solution saturated in the cold deposits, when heated to the boiling-point, a crystalline powder containing S0 4 Di 2 aq. Didymium and potassium sulphate, (S0 4 ) 2 DiK 2 , resembles the lanthanum salt. Solutions of didymium salts exhibit a well-marked absorption spectrum,* containing two black lines inclosing a very bright space. One of these black lines is in the yellow, immediately following Fraunhofer's line D; the other is situated between E and b. These characters can be distinctly recognized in a solution half an inch deep, containing only O'Ol per cent, of didymium salt. Lanthanum salts do not exhibit an absorption spectrum (Gladstone). YTTRIUM AND ERBIUM. Y = 61-7. Eb = 112-6. These metals exist as silicates in the gadolinite or ytterbite of Ytterby in Sweden, and in a few other rare minerals. A third metal, called terbium, has also been supposed to be associated with them ; but recent experiments, especially those of Bahr and Bunsen,f have thrown very great doubt upon its existence. To obtain the earths, yttria and erbia, in the separate state, gadolinite is digested with hydrochloric acid, and the solution separated from the silica is treated with oxalic acid, which throws down the oxalates of erbium and yttrium, together with those of calcium, cerium, lanthanum, and didy- mium. These oxalates are converted into nitrates; the solution is treated with excess of solid potassium sulphate, to separate the cerium metals; the erbium and yttrium, which still remain in solution, are again precipi- tated by oxalic acid; and the same treatment is repeated, till the solution of t,he mixed earths, when examined by the spectral apparatus, no longer exhibits the absorption bands characteristic of didymium. To separate * See LIGHT, p. 90. f Ann. Ch. Pharm. cxxxvii. 1. EARTH-METALS. 343 the erbia and yttria, they are again precipitated by oxalic acid. The oxa- lates are converted into nitrates, and the nitrates of erbium and yttrium are separated by a series of fractional crystallizations, the erbium salt being the less soluble of the two, and crystallizing out first; but the pro- cess requires attention to a number of details, which cannot be here de- scribed.* Metallic erbium has not been isolated. Yttrium (containing erbium) was obtained by Berzelius, as a blackish-gray powder, by igniting yttrium chloride with potassium. Erbia, Eb /X 0, obtained by ignition of erbium nitrate or oxalate, has a faint rose color. It does not melt at the strongest white heat, but aggre- gates to a spongy mass, glowing with an intense green light, which, when examined by the spectroscope, exhibits a continuous spectrum intersected by a number of bright bands. Solutions of erbium-salts, on the other hand, give an absorption-spectrum exhibiting dark bands, and the points of maximum intensity of the light bands in the emission- spectrum of glowing erbia coincide exactly in position with the points of greatest darkness in the absorption- spectrum. The position of these bands is totally different from those in the emission and absorption-spectra of didymium. ) Erbium salts have a rose-red color, deeper in the hydrated than in the anhydrous state ; they have an acid reaction and sweet astringent taste. The sulphate, 3S0 4 Eb /x . 8aq., forms light rose-colored crystals, isomorphous with the sulphates of yttrium and didymium. Yttria, Y x/ 0, is a soft, nearly white powder, which when ignited glows with a pure white light, and yields a spectrum not containing any bright bands, like that of erbia. It does not unite directly with water, but is precipitated as a hydrate by alkalies, from solutions of yttrium-salts. It dissolves slowly but completely in hydrochloric, nitric, and sulphuric acids, forming colorless solutions, which do not exhibit an absorption-spectrum. Yttrium sulphate, 3S0 4 Y /X . 8aq., forms small colorless crystals. Reactions of the Earth-Metals. 1. All these metals are precipitated from their solutions by ammonium sulphide, as hydrates, not as sulphides. They are not precipitated by hydrogen sulphide. 2. The hydrates of aluminium and beryllium are soluble in caustic pot- ash; those of the other earth-metals are insoluble. 3. Beryllium hydrate dissolves in a cold saturated solution of ammonium carbonate, and is precipitated, as carbonate, on boiling. Aluminium hydrate is insoluble in ammonium carbonate (see further, p. 337). 4. Of the earth-metals whose hydrates are insoluble in potash, namely, zirconium, thorinum, cerium, lanthanum, didymium, erbium, and yttrium, zirconium and thorinum may be precipitated as hyposulphites by boiling the solution with sodium hi/posulphite, the other metals remaining in solution. The precipitate when ignited leaves pure z-irconia or thorina, or a mixture of the two. 5. Zirconium and thorinum may be separated one from the other by means of ammonium oxalate, which, when added in excess, precipitates the thorinum as oxalate, and leaves the zirconium in solution. 6. Cerium, lanthanum, and didymium are separated from yttrium and erbium by adding an excess of potassium sulphate, which throws down the * See Watts'* Dictionary of Chemistry, vol v. p. 721. f The paper by Tiahr and Bnusen. above referred to, is accompanied by exact diagrams of the erbium and didymitun sport ra. 344: EARTH-METALS. cerium metals, leaving yttrium and erbium in solution ; to insure complete precipitation, the solution must be left in contact for some time with a piece of solid potassium sulphate Cerium may be separated from lanthanum and didymium, as already observed, by treating the mixed oxides several times with nitric acid (p. 340). Another method is to boil the mixed oxides (the cerium being in the state of ceroso-ceric oxide) with solution of sal-ammoniac. The lantha- num and didymium then gradually dissolve, as chlorides, while the cerium remains as ceroso-ceric oxide. A third method is to precipitate the solu- tion of the three metals with excess of potash, and pass chlorine in excess through the solution and precipitate ; the cerium is then separated as bright-yellow ceroso-ceric hydrate, while the lanthanum and didymium redissolve as chlorides. This reaction serves to detect very small quanti- ties of cerium mixed with the other two metals. Cerium is further distin- guished by the light-yellow color of anhydrous ceroso-ceric oxide, and by the reaction of its compounds when fused before the blow-pipe with borax or phosphorus salt, the glass thus formed being deep-red while hot, and becoming colorless on cooling. Didymium is distinguished by the dark- brown color of its higher oxide; by the pale rose-color which its salts impart to a bead of borax or phosphorus salt; and by the peculiar character of its absorption spectrum (p. 342). The methods of separating lanthanum from didymium, and yttrium from erbium imperfect at the best have been already noticed. MANUFACTURE OF GLASS, PORCELAIN, AND EARTHENWARE. Glass. Glass is a mixture of various insoluble silicates with excess of silica, altogether destitute of crystalline structure ; the simple silicates, formed by fusing the bases with silicic acid in equivalent proportions, very often crystallize, which happens also with the greater number of the natural silicates included among the earthy minerals. Compounds identical with some of these are also occasionally formed in artificial processes, where large masses of melted glassy matter are suffered to cool slowly. The alkaline silicates, when in a state of fusion, have the power of dissolving a large quantity of silica. Two principal varieties of glass are met with in commerce namely, glass composed of silica, alkali, and lime, and glass containing a large proportion of lead silicate ; crown and plate glass belong to the former di- vision ; flint glass, and the material of artificial gems, to the latter. The lead promotes fusibility, and confers also density and lustre. Common green bottle-glass contains no lead, but much silicate of iron, derived from the impure materials. The principle of the glass manufacture is very sim- ple. Silica, in the shape of sand, is heated with potassium or sodium car- bonate, and slaked lime or lead oxide ; at a high temperature, fusion and combination occur, and the carbonic acid is expelled. Glauber's salt mixed with charcoal is sometimes substituted for soda. When the melted mass has become perfectly clear and free from air-bubbles, it is left to cool until it assumes the peculiar tenacious condition proper for working. The operation of fusion is conducted in large crucibles of refractory fire-clay, which in the case of lead-glass are covered by a dome at the top, and have an opening at the side, by which the materials are introduced, and the melted glass withdrawn. Great care is exercised in the choice of the sand, which must be quite white and free from iron oxide. Red lead, one of the higher oxides, is preferred to litharge, although immediately reduced to monoxide by the heat, the liberated oxygen serving to destroy any combustible matter that might accidentally find its way into the crucible, and stain the glass by reducing a portion of the lead. Potash gives a better MANUFACTURE OF GLASS. 345 glass than soda, although the latter is very generally employed, from its lower price. A certain proportion of broken and waste glass of the same kind is always added to the other materials. Articles of blown glass are thus made : The workman begins by collecting a proper quantity of soft pasty glass at the end of his blowpipe, an iron tube five or six feet in length, terminated by a mouthpiece of wood ; he then begins blowing, by which the lump is expanded into a kind of flask, susceptible of having its form modified by the position in which it is held, and the velocity of rotation continually given to the iron tube. If an open- mouthed vessel is to be made, an iron rod, called a pontil or puntil, is dipped into the glass pot and applied to the bottom of the flask, to which it thus serves as a handle, the blowpipe being removed by the application of a cold iron to the neck. The vessel is then re-heated at a hole left for the purpose in the wall of the furnace, and the aperture enlarged, and the vessel otherwise altered in figure by the aid of a few simple tools, until completed. It is then detached, and carried to the annealing oven, where it undergoes slow and gradual cooling during many hours, the object of which is to obviate the excessive brittleness always exhibited by glass which has been quickly cooled. The large circular tables of crown glass are made by a very curious process of this kind : the globular flask at first produced, transferred from the blowpipe to the pontil, is suddenly made to assume the form of a flat disc by the centrifugal force of the rapid rotatory move- ment given to the rod. Plate glass is cast upon a flat metal table, and, after very careful annealing, ground true and polished by suitable machinery. Tubes are made by rapidly drawing out a hollow cylinder ; and from these a great variety of useful small apparatus may be constructed with the help of a lamp and blowpipe, or, still better, the bellows-table of the barometer- maker. Small tubes may be bent in the flame of a spirit-lamp or gas jet, and cut with great ease by a file, a scratch being made, and the two por- tions pulled or broken asunder in a way easily learned by a few trials. Specimens of the two chief varieties of glass gave the following results on analysis : English flint glass.f Silica . . . 51-93 Potassium oxide . 13-77 Lead oxide 33-28 Bohemian plate glass (excellent).* Silica . . . 60-0 Potassium oxide . 25-0 Lime . . . 12-5 97-5 The difficultly fusible white Bohemian tube, so valuable in organic analysis, has been found to contain, in 100 parts : Silica 72-80 Lime, with trace of alumina . . . 9-68 Magnesia ....... -40 Potassium oxide 16-80 Traces of manganese, &c., and loss . . *32 Different colors are often communicated to glass by metallic oxides. Thus, oxide of cobalt gives deep blue; oxide of manganese, amethyst; cuprous oxide, ruby-red ; cupric oxide, green ; the oxides of iron, dull green or brown, &c. These are either added to the melted contents of the glass- pot, in which they dissolve, or applied in a particular manner to the surface of the plate or other object, which is then reheated, until fusion of the coloring matter occurs : such is the practice of enamelling and glass-paint- * Mitscherlich, Lehrbuch, ii. 187. t Faraday. 346 DYAD METALS. ing. An opaque white appearance is given by oxide of tin; the enamel of watch-faces is thus prepared. When silica is melted with twice its weight of potassium or sodium car- bonate, and the product treated with water, the greater part dissolves, yield- ing a solution from which acids precipitate gelatinous silica. This is the soluble glass of Professor Fuchs : its solution has been used for rendering muslin and other fabrics of cotton or linen less combustible, for making artificial stone, and preserving natural stone from decay, and for a peculiar style of mural painting called stereochromy.* Porcelain and Earthenware. The plasticity of natural clays, and their hardening when exposed to heat, are properties which suggested in very early times their application to the making of vessels for the various pur^ poses of daily life : there are few branches of industry of higher antiquity than that exercised by the potter. True porcelain is distinguished from earthenware by very obvious char- acters. In porcelain the body of the ware is very compact and translucent, and breaks with a conchoi'dal fracture, symptomatic of a commencement of fusion. The glaze, too, applied for giving a perfectly smooth surface, is closely adherent, and, in fact, graduates by insensible degrees into the sub- stance of the body. In earthenware, on the contrary, the fracture is open and earthy, and the glaze detachable with greater or less facility. The compact and partly glassy character of porcelain is the result of the admix- ture with the clay of a small portion of some substance which is fusible at the temperature to which the ware is exposed when baked or fired, and being absorbed by the more infusible portion, binds the whole into a solid mass on cooling: such substances are found in felspar, and in a small admixture of calcic or alkaline silicate. The clay employed in porcelain- making is always directly derived from decomposed felspar, none of the clays of the secondary strata being pure enough for the purpose: it must be white, and free from iron oxide. To diminish the contraction which this substance undergoes in the fire, a quantity of finely divided silica, carefully prepared by crushing and grinding calcined flints or chert, is added, together with a proper proportion of felspar or other fusible material, also reduced to impalpable powder. The utmost pains are taken to effect per- fect uniformity of mixture, and to avoid the introduction of particles of grit, or other foreign bodies. The ware itself is fashioned either on the potter's wheel a kind of vertical lathe or in moulds of plaster of Paris, and dried first in the air, afterwards by artificial heat, and at length com- pletely hardened by exposure to the temperature of ignition. The porous biscuit is now fit to receive its*glaze, which may be either ground felspar, or a mixture of gypsum, silica, and a little porcelain clay, diffused through water. The piece is dipped for a moment into this mixture, and withdrawn ; the water sinks into its substance, and the powder remains evenly spread upon its surface ; it is once more dried, and, lastly, fired at an exceedingly high temperature. The porcelain-furnace is a circular structure of masonry, having several fireplaces, and surmounted by a lofty dome. Dry wood or coal is con- sumed as fuel, and its flame directed into the interior, and made to circu- late around and among the earthen cases, or scggars, in which the articles to be fired are packed. Many hours are required for this operation, which must be very carefully managed. After the lapse of several days, when the furnace has completely cooled, the contents are removed in a finished state, so far as regards the ware. The ornamental part, consisting of gilding and painting in enamel, has yet to be executed ; after which the pieces are again heated, in order to flux the colors. The operation has sometimes to be repeated more than once. * See Richardson and Watts's Chemical Technology, vol. i. part iv. pp. 69-104. MAGNESIUM. 347 The manufacture of porcelain in Em-ope is of modern origin : the Chi- nese have possessed the art from the commencement of the seventh century, and their ware is, in some respects, altogether unequalled. The materials employed by them are known to be kaolin, or decomposed felspar ; petuntze, or quai'tz reduced to fine powder ; and the ashes of fern, which contain po'tassium carbonate. Stoneware. This is a coarse kind of porcelain, made from clay contain- ing oxide of iron and a little lime, to which it owes its partial fusibility. The glazing is performed by throwing common salt into the heated furnace: this is volatilized, and decomposed by the joint agency of the silica of the ware and of the vapor of water always present ; hydrochloric acid and soda are produced, the latter forming a silicate, which fuses over the surface of the ware, and gives a thin, but excellent glaze. Earthenware. The finest kind of earthenware is made from a white sec- ondary clay, mixed with a considerable quantity of silica. The articles are thoroughly dried and fired ; after which they are dipped into a readily fusible glaze mixture, of which lead oxide is usually an important ingre- dient, and, when dry, re-heated to the point of fusion of the latter. The whole process is much easier of execution than the making of porcelain, and demands less care. The ornamental designs in blue and other colors, so common upon plates and household articles, are printed upon paper in enamel pigment mixed with oil, and transferred, while still wet, to the unglazed Avare. When the ink becomes dry, the paper is washed off, and the glazing completed. The coarser kinds of earthenware are sometimes covered with a whitish opaque glaze, which contains the oxides of lead and tin ; such glaze is very liable to be attacked by acids, and is dangerous for culinary vessels. Crucibles, when of good quality, are very valuable to the practical chemist. They are made of clay free from lime, mixed with sand or ground ware of the same description. The Hessian and Cornish crucibles are among the best. Sometimes a mixture of plumbago and clay is em- ployed for the same purpose ; and powdered coke has been also used with the earth : such crucibles bear rapid changes of temperature with impunity. GROUP III. MAGNESIUM. Atomic weight, 24. Symbol, Mg. This metal was formerly classed with the metals of the alkaline earths, but it is much more nearly related to zinc by its properties in the free state, as well as by the volatility of its chloride, the solubility of its sul- phate, and the isomorphism of several of its compounds with the analo- gously constituted compounds of zinc. Magnesium occurs in the mineral kingdom as hydrate, carbonate, borate, phosphate, sulphate, and nitrate, sometimes in the solid state, sometimes dissolved in mineral waters : magnesian limestone, or dolomite, which forms entire mountain masses, is a carbonate of magnesium and calcium. Magne- sium also occurs as silicate, combined with other silicates, in a variety of minerals, as steatite, hornblende, augite, talc, &c. : also as aluminate in spinelle and zeilanite. It likewise occurs in the bodies of plants and ani- mals, chiefly as carbonate and phosphate, and in combination with organic acids. Metallic magnesium is prepared: 1. By the electrolysis of fused magnesium chloride, or, better, of a mix- 348 DYAD METALS. ture of 4 molecules of magnesium chloride and 3 molecules of potassium chloride with a small quantity of sal-ammoniac. A convenient way of effecting the reduction is to fuse the mixture in a common clay tobacco-pipe over an Argand spirit-lamp or gas-burner, the negative pole'being an iron wire passed up the pipe-stem, and the positive pole a piece of gas-coke, just touching the surface of the fused chlorides. On passing the current of a battery of ten Bunsen's cells through the arrangement, the magnesium collects round the extremity of the iron wire (Matthiessen). 2. Magnesium may be prepared in much larger quantity by reducing magnesium chloride, or the double chloride of magnesium and sodium or potassium, with metallic sodium. The double chloride is prepared by dis- solving magnesium carbonate in hydrochloric acid, adding an equivalent quantity of sodium or potassium chloride, evaporating to dryness, and fusing the residue. This product, heated with sodium in a wrought-iron crucible, yields metallic .magnesium, containing certain impurities, from which it may be freed by distillation. This process is now carried out on the manufacturing scale, and the magnesium is drawn out into wire or formed into riband for burning.* Magnesium is a brilliant metal, almost as white as silver, somewhat more brittle at common temperatures, but malleable at a heat a little below red- ness. Its specific gravity is 1-74. It melts at a red heat, and volatilizes at nearly the same temperature as zinc. It retains its lustre in dry air, but in moist air it becomes covered with a crust of magnesia. Magnesium in the form of wire or riband takes fire at a red heat, burning with a dazzling bluish-white light. The flame of a candle or spirit-lamp is sufficient to inflame it, but to insure continuous combustion the metal must be kept in contact with the flame. For this purpose lamps are con- structed, provided with a mechanism which continually pushes three or more magnesium wires into a small spirit-flame. The magnesium flame produces a continuous spectrum, containing a very large proportion of the more refrangible rays: hence it is well adapted for photography, and has, indeed, been used for taking photographs, in the absence of the sun, or in places where sunlight cannot penetrate, as in caves or subterranean apartments. MAGNESIUM CHLORIDE, MgCl 2 . When magnesia, or its carbonate, is dissolved in hydrochloric acid, magnesium chloride and water are produced ; but when this solution is evaporated to dryness, the last portions of water are retained with such obstinacy, that decomposition of the water is brought about by the concurring attractions of magnesium for oxygen, and of chlor- ine for hydrogen; hydrochloric acid is expelled, and magnesia remains. If, however, sal-ammoniac, potassium chloride, or sodium chloride is present, a double salt is produced, which is easily rendered anhydrous. The best mode of preparing the chloride is to divide a quantity of hydrochloric acid into two equal portions, to neutralize one with magnesia, and the other with ammonia, or carbonate of ammonia: to mix these solutions, evaporate them to dryness, and then expose the salt to a red heat in a loosely covered porcelain crucible. Sal-ammoniac sublimes, and magnesium chloride in a fused state remains; the latter is poured out upon a clean stone, and when cold transferred to a well stopped bottle. The chloride so obtained is white and crystalline. It is very deliquescent and highly soluble in water, from which it cannot again be recovered by evaporation, for the reasons just mentioned. When long exposed to the air in a melted state, it is converted into magnesia. It is soluble in alcohol. * For details of the manufacturing process, see Richardson and Watts' s Chemical Technology, vol. i. pt. v. pp. 336-339. MAGNESIUM. 349 MAGNESIUM OXIDE, or MAGNESIA, MgO. This oxide is easily prepared by exposing the magnesia alba of pharmacy, which is a hydro-carbonate, to a full red heat in an earthen or platinum crucible. It forms a soft, white powder, which slowly attracts moisture and carbonic acid from the air, and unites quietly with water to a hydrate which possesses a feeble degree of solubility, requiring about 5000 parts of water at 15.5 and 36,000 parts at 100. The alkalinity of magnesia can only be observed by placing a small portion in a moistened state upon test-paper; it neutralizes acids, however, in the most complete manner. It is infusible. Magnesium sulphide is formed by passing vapor of carbon sulphide over magnesia, in capsules of coke, at a strong red heat. MAGNESIUM SULPHATE; EPSOM SALT; S0 4 Mg.70H 2 . This salt occurs in sea-water, and in that of many mineral springs, and is now manufac- tured in large quantities by acting on magnesian limestone with dilute sul- phuric acid, and separating the magnesium sulphate from the greater part of the slightly soluble calcium sulphate by filtration. The crystals are de- rived from a right rhombic prism ; they are soluble in an equal weight of water at 15-5, and in a still smaller quantity at 100. The salt has a nauseous bitter taste, and, like many other neutral salts, possesses pur- gative properties. When it is exposed to heat, 6 molecules of water readily pass off, the seventh being energetically retained. Magnesium sul- phate forms beautiful double salts with the sulphates of potassium and ammonium, which contain 6 molecules of crystallization-water, their for- mula) being (S0 4 ) 2 Mg"K 2 . 60 H 2 , and (S0 4 ) 2 Mg"(NH 4 ) a . 60H 2 . These salts are isomorphous, and form monoclinic crystals. MAGNESIUM CARBONATE. The neutral carbonate, C0 3 Mg or C0 2 .MgO, oc- curs native in rhombohedral crystals, resembling those of calc-spar, im- bedded in talc slate : a soft earthy variety is sometimes met with. When magnesia alba is dissolved in aqueous carbonic acid, and the solu- tion left to evaporate spontaneously, small prismatic crystals are deposited, consisting of trihydrated magnesium carbonate, C0 5 Mg. 30H 2 . The magnesia alba itself, although often called carbonate of magnesium, is not so iu reality ; it is a compound of carbonate with hydrate. It is prepared by mixing hot solutions of potassium or sodium carbonate and magnesium sulphate, the latter being kept in slight excess, boiling the whole a few minutes, during which time much carbonic acid is disengaged, and well washing the precipitate so produced. If the solution be very dilute, the magnesia alba is exceedingly light and bulky ; if otherwise, it is denser. The composition of this precipitate is not perfectly constant. In most cases it contains 4C0 3 Mg.MgH 2 2 . 60H 2 . Magnesia alba is slightly soluble in water, especially when cold. MAGNESIUM PHOSPHATE, P0 4 Mg /x H . 70H 2 . This salt separates in small colorless prismatic crystals when solutions of sodium phosphate and mag- nesium sulphate are mixed and suffered to stand for some time. According to Graham, it is soluble in about 1000 parts of cold water. Magnesium phosphate exists in the grain of the cereals, and can be detected in con- siderable quantity in beer. MAGNESIUM AND AMMONIUM PHOSPHATE, P0 4 Mg /x (NH 4 ) . 60H 2 . When ammonia or its carbonate is mixed with a magnesium salt, and a soluble phosphate is added, a crystalline precipitate having the above composition, subsides, immediately if the solutions are concentrated, and after some time if very dilute : in the latter case, the precipitation is promoted by stirring. This salt is slightly soluble in pure water, but nearly insoluble 30 350 DYAD METALS. in saline and ammoniacal liquids. When heated, it gives off water and ammonia, and is converted into magnesium pyrophosphate, P 2 7 Mg 2 : 2P0 4 Mg(NH 4 ) = P 2 7 M S 2 + OH 2 + 2XH 3 . At a strong red-heat it fuses to a white enamel-like mass. Magnesium and ammonium phosphate sometimes form a urinary calculus, and occur also in guano. In practical analysis, magnesium is often separated from solutions by bringing it into this state. The liquid, free from alumina, lime, &c., is mixed with sodium phosphate and excess of ammonia, and gently heated for a short time. The precipitate is collected upon a filter and thoroughly washed with water containing a little ammonia, after which it is dried, ig- nited to redness, and weighed. The proportion of magnesia is then easily calculated. SILICATES. The following natural compounds belong to this lUe, Si0 4 Mg 2 = Si0 2 .2MgO, a crystallized mineral, sometimes MAGNESIUM class : Chrysoli employed for ornamental purposes: a portion of the magnesia iscommonlv replaced by ferrous oxide, which communicates a green color. Meerschaum. liSiO 3 Mg.SiO a = 3Si0 2 .2MgO, a soft, sectile mineral, from which pipe-bowls are made. Talc. 4Si0 3 Mg.Si() 2 . | aq. (called steatite when massive), is a toft, white sectile, transparent or translucent mineral, used as fire-stones for furnaces and stoves, and in thin plates for glazing lanterns, &c. ; also in the state of powder for diminishing friction. Soapstone, also called steatite, is a silicate of magnesium and aluminium of somewhat variable composition. Serpentine is a combination of silicate and hydrate of magnesium. Jade, an exceedingly hard stone, brought from New Zealand, is a silicate of magne- sium and aluminium: its green color is due to chromium. Augite and horn- blende are essentially double salts of silicic acid, magnesia, and lime, in which the magnesia is more or less replaced by its isomorphous substitute, ferrous oxide. Magnesium salts are isomorphous with zinc salts, ferrous salts, cupric salts, cobalt salts, and nickel salts, &c. ; they are usually colorless, and are easily recognized by the following characters: A gelatinous white preci- pitate with caustic alkalies, including ammonia, insoluble in excess, but soluble in solution of sal-ammoniac. A white precipitate with potassium and sodium carbonates, but none with ammonium carbonate in the cold. A white crystalline precipitate with soluble phosphates, on the addition of a little ammonia. ZINC. Atomic weight, 65. Symbol, Zn. Zinc is a somewhat abundant metal: it is found in the state of carbonate, silicate, and sulphide, associated with lead ores in many districts, both in Britain and on the Continent; large supplies are obtained from Silesia, and from the neighborhood of Aachen. The native carbonate, or calamine, is the most valuable of the zinc ores, and is preferred for the extraction of the metal: it is first roasted to expel water and carbonic acid, then mixed with fragments of coke or charcoal, and distilled at a full red heat in a large earthen retort; carbon monoxide escapes, while the reduced metal volatilizes and is condensed by suitable means, generally with minute quan- tities of arsenic. ZINC. 351 Zinc is a bluish-white metal, which slowly tarnishes in the air; it has a lamellar, crystalline structure, a density varying from 6-8 to 7-2, and is, under ordinary circumstances, brittle. Between 120 and 150 C. (248 300 F.) it is, on the contrary, malleable, arid may be rolled or hammered without danger of fracture ; and, what is very remarkable, after such treatment, it retains its malleability when cold; the sheet-zinc of commerce is thus made. At 210 C. (410 F.) it is so brittle that it may be reduced to powder. At 412 C. (773 F.) it melts: at a bright red heat it boils and volatilizes, and, if air be admitted, burns with a splendid greenish light, generating the oxide. Dilute acids dissolve zinc very readily : it is constantly employed in this manner for preparing hydrogen gas. Zinc is a dyad metal, forming* only one class of compounds. ZINC CHLORIDE, ZnCl 2 , may be prepared by heating metallic zinc in chlorine: by distilling a mixture of zinc filings and corrosive sublimate; or, more easily, by dissolving zinc in hydrochloric acid. It is a nearly white, translucent, fusible substance, very soluble in water and alcohol, and very deliquescent. A strong solution of zinc chloride is sometimes used as a bath for obtaining a graduated heat above 100. Zinc chloride unites with sal-ammoniac and potassium chloride to double salts: the former of these, made by dissolving zinc in hydrochloric acid, and then adding an equivalent quantity of sal-ammoniac, is very useful in tinning and soft-soldering copper and iron. ZINC OXIDE, ZnO, is a strong base, forming salts isomorphous with the magnesium salts. It is prepared either by burning zinc in atmospheric air, or by heating the carbonate to redness. Zinc oxide is a white, taste- less powder, insoluble in water, but freely dissolved by acids. When heated it is yellow, but turns white again on cooling. It is getting into use as a substitute for white lead. To prepare zinc-white on a large scale, metallic zinc is volatilized in large earthen muffles, whence the zinc vapor passes into a small receiver (guerite}, where it comes in contact with a current of air and is oxidized. The zinc oxide thus formed passes immediately into a condensing chamber divided into several compartments by cloths sus- pended within it. ZINC SULPHATE, S0 4 Zn.70H 2 , commonly called white vitriol. This salt is hardly to be distinguished by the eye from magnesium sulphate: it is prepared either by dissolving the metal in dilute sulphuric acid, or, more economically, by roasting the native sulphide, or blende, which, by absorp- tion of oxygen, becomes in great part converted into sulphate. The altered mineral is thrown hot into water, and the salt obtained by evaporating the clear solution. Zinc sulphate has an astringent metallic taste, and is used in medicine as an emetic. The crystals dissolve in 2 parts of cold, and in a much smaller quantity of hot water. Crystals containing 6 molecules of water have been observed. Zinc sulphate forms double salts with the sul- phates of potassium and ammonium, namely, (S0 4 ) 2 ZnK 2 . 60H 2 , and (S0 4 ) 2 Zn(NH 4 ) 2 . OOH 2 , isomorphous with the corresponding magnesiujn salts. ZINC CARBONATE, C0 3 Zn, is found native; the white precipitate obtained by mixing solutions of zinc and of alkaline carbonates, is a combination of carbonate and hydrate. When heated to redness, it yields pure zinc oxide. ZINC SULPHIDE, ZnS, occurs native as blende, in regular tetrahedrons, dodecahedrons, and other monometric forms, and of various colors, from white or yellow to brown or black, according to its degree of purity : it is a valuable ore of zinc. A variety called black jack occurs somewhat abun- dantly in Derbyshire, Cumberland, and Cornwall. A hydrated sulphide, ZnS. 352 DYAD METALS. OH 2 , is obtained as a white precipitate on adding an alkaline sulphide to the solution of a zinc salt. Zinc salts are distinguished by the following characters: Caustic potash and soda give a white precipitate of hydrate, freely soluble in excess of alkali. Ammonia behaves in the same manner ; an excess redissolves the precipitate instantly. Potassium and sodium carbonates give white precipi- tates, insoluble in excess. Ammonium carbonate gives also a white precipi- tate, which is redissolved by an excess. Potassium f err ocyanide gives a white precipitate. Hydrogen sulphide causes no change in zinc solutions containing free mineral acids: but in neutral solutions, or with zinc salts of organic acids, such as the acetate, a white precipitate is formed. Ammonium sul- phide throws down white sulphide of zinc, insoluble in caustic alkalies. The formation of this precipitate in a solution containing excess of caustic alkali, serves to distinguish zinc from all other metals. All zinc compounds, heated on charcoal with sodium carbonate in the inner blowpipe flame, give an incrustation of zinc oxide, which is yellow while hot, but becomes white in cooling. If this incrustation be moistened with a dilute solution of cobalt nitrate, and strongly heated in the outer flame, a fine green color is produced. The applications of metallic zinc to the purposes of roofing, the con- struction of water-channels, &c., are well known; it is sufficiently durable, but inferior in this respect to copper. It is much used also for protecting iron and copper from oxidation when immersed in saline solutions, such as sea-water, or exposed to damp air. This it does by forming an electric circuit, in which it acts as the positive or more oxidable metal (p. 249). Galvanized iron consists of iron having its surface coated with zinc. CADMIUM. Atomic weight, 112. Symbol, Cd. This metal was discovered in 1817 by Stromeyer, and by Hermann : it accompanies the ores of zinc, especially those occurring in Silesia, and, being more volatile than that substance, rises first in vapor when the cala- mine is subjected to distillation with charcoal. Cadmium resembles tin in color, but is somewhat harder : it is very malleable, has a density of 8-7, melts below 260 C. (500 F.), and is nearly as volatile as mercury. It tarnishes but little in the air, but, when strongly heated, burns. Dilute sulphuric and hydrochloric acids act but little on this metal in the cold ; nitric acid is its best solvent. The observed vapor-density of cadmium is 3-94 compared with air as unity, or 56-3 compared with hydrogen, which latter number does not differ greatly from the half of 112, the atomic weight of the metal: hence it ap- pears that the atom of cadmium in the state of vapor occupies twice the space of an atom of hydrogen (see p. 229). Cadmium, like zinc, is dyadic, and forms but one series of compounds. CADMIUM OXIDE, CdO. This oxide may be prepared by igniting either the carbonate or the nitrate : in the former case it has a pale-brown color, and in the latter a much darker tint, and forms octohedral microscopic crystals. Cadmium oxide is infusible : it dissolves in acids, producing a COPPER. 353 series of colorless salts : it attracts carbonic acid from the air, and turns white. CADMIUM SULPHATE, S0 4 Cd . 40H 2 , is easily obtained by dissolving the oxide or carbonate in dilute sulphuric acid: it is very soluble in water, and forms double salts with the sulphates of potassium and ammonium, which contain respectively (S0 4 ) 2 CdK 2 . 60H 2 and (S0 4 ) 2 Cd(NH 4 ) . 60H 2 . CADMIUM CHLORIDE, CdCl 2 , is a very soluble salt, crystallizing in small four-sided prisms. CADMIUM SULPHIDE is a very characteristic compound, of a bright-yellow color, forming microscopic crystals, fusible at a high temperature. It is obtained by passing sulphuretted hydrogen gas through a solution of the sulphate, nitrate, or chloride. This compound is used as a yellow coloring matter, of great beauty and permanence. It occurs native as greenockite. The salts of cadmium are thus distinguished : Fixed caustic alkalies give a white precipitate of hydrated oxide, insoluble in excess. Am- monia gives a similar white precipitate, readily soluble in excess. The fixed alkaline carbonates, and ammonia carbonate, throw down white cadmium carbonate, insoluble in excess of either precipitant. Hydrogen sulphide and ammonium sulphide precipitate the yellow sulphide of cadmium. GROUP IV. COPPEE. Atomic weight, 63-5. Symbol, Cu (Cuprum). Copper is a metal of great value in the arts; it sometimes occurs in the metallic state, crystallized in octohedrons, or more frequently in dodeca- hedrons, but is more abundant in the form of red oxide, and in that of sulphide combined with sulphide of iron, as yelloiv copper ore, or copper jn/rilfs. Large quantities of the latter substance are annually obtained from the Cornish mines, and taken to South Wales for reduction, which is effected by a somewhat complex process. The principle of this may, how- ever, be easily made intelligible. The ore is roasted in a reverberatory furnace, by which much of the iron sulphide is converted into oxide, while the copper sulphide remains unaltered. The product of this operation is then strongly heated with siliceous sand; the latter combines with the iron oxide to a fusible slag, and separates from the heavier copper-compound. When the iron has, by a repetition of these processes, been got rid of, the copper sulphide begins to decompose in the flame-furnace, losing its sulphur and absorbing oxygen: the temperature is then raised sufficiently to reduce the oxide thus produced, by the aid of carbonaceous matter. The last part of the operation consists in thrusting into the melted metal a pole of birch-wood, the object of which is probably to reduce a little re- maining oxide by the combustible gases thus generated. Large quantities of extremely valuable ore, chiefly carbonate and red oxide, have lately been obtained from South Australia and Chile. Copper has a well-known yellowish-red color, a specific gravity of 8-96, and is very malleable and ductile : it is an excellent conductor of heat and electricity ; it melts at a bright rod heat, and seems to be slightly volatile at a very high temperature Copper undergoes no change in dry air; ex- !> a, moist jitmosphi-re, it becomes covered with a strongly adherent 30* 354 DYAD METALS. green crust, consisting in a great measure of carbonate. Heated to redness in the air, it is quickly oxidized, becoming covered with a black scale Dilute sulphuric and hydrochloric acids scarcely act upon copper; boiling oil of vitriol attacks it, with evolution of sulphurous oxide ; nitric acid, even dilute, dissolves it readily, with evolution of nitrogen dioxide. Copper is a dyad metal, its most stable compounds, the cupric compounds, containing 1 atom of the metal combined with 2 atoms of a univalent, or 1 atom of a bivalent negative radical, e.g., Cu // Cl 2 , Cu 7/ 0, Cu // (N0 3 ). 2 , Cu /x S0 4 , &c. Some of these, however, are capable of taking up another atom of copper, and forming compounds, called cuprous compounds, in which CuCl the copper is apparently univalent ; thus cuprous chloride, Cu 2 Cl 2 = | ; Cu^ CuCl cuprous oxide, Cu 2 = | J^>^- These compounds are very unstable, be- ing easily converted into cupric compounds by the action of oxidizing agents. COPPER CHLORIDES. Cupric chloride, CuCl 2 , is most easily prepared by dissolving cupric oxide in hydrochloric acid, and concentrating the green solution thence resulting. It forms green crystals, CuCl 2 . 20H 2 , very soluble in water and in alcohol: it colors the flame of the latter green. When gently heated, it parts with its water of crystallization and becomes yellowish-brown ; at a high temperature it loses half its chlorine and be- comes converted into cuprous chloride. The latter is a white fusible sub- stance, but little soluble in water, and prone to oxidation : it is formed when copper-filings or copper-leaf are put into chlorine gas ; also by pre- cipitating a solution of cupric chloride or other cupric salt with stannous chloride : 2CuCl 2 -f SnCl 2 = Cu 2 Cl 2 + SnC| 4 Cupric Stannous Cuprous Stannic chloride. chloride. chloride. chloride. A plate of copper immersed in hydrochloric acid in a vessel containing air, becomes covered with white tetrahedrons of cuprous chloride. This com- pound dissolves in hydrochloric acid, forming a colorless solution, which gradually turns blue on exposure to the air. A hydrated cupric oxychloride, CuCl 2 . 3CuH 2 2 , occurs native as atacamite. Both the chlorides of copper form double salts with the chlorides of the alkali-metals. CUPROUS HYDRIDE, Cu 2 EI 2 . When a solution of cupric sulphate is heated to about 70, with hypophosphorous acid, this compound is deposited as a yellow precipitate which soon turns red-brown. It gives off hydrogen when heated, takes fire in chlorine gas, and is converted by hydrochloric acid into cuprous chloride, with evolution of a double quantity of hydrogen, the acid giving up its hydrogen as well as the copper hydride : Cu 2 H 2 -f 2HC1 = Cu 2 Cl 2 -f 2H 2 . This reaction affords a remarkable instance of the union of two atoms of the same element to form a molecule (see page 232). COPPER OXIDES. Two oxides of copper are known, corresponding to the chlorides ; and a very unstable dioxide or peroxide, Cu0 2 , is said to be formed, as a yellowish-brown powder, by the action of hydrogen dioxide on cupric hydrate. Copper Monoxide, Cupric oxide, or Black oxide of copper, CuO, is prepared by calcining metallic copper at a red-heat, with full exposure to air, or more conveniently, by heating the nitrate to redness, which suffers com- COPPER. 355 plcte decomposition. Cupric salts mixed with caustic alkali in excess, yield a bulky pale-blue precipitate of hydrated cupric oxide, or cupric hydrate, CtlHjO, or CuO.OH 2 , which, when the whole is raised to the boiling-point, becomes converted into a heavy dark-brown powder: this also is anhydrous oxide of copper, the hydrate suffering decomposition, even in contact with water. The oxide prepared at a high temperature is perfectly black and very dense. Cupric oxide is soluble in acids, and forms a series of very important salts, isomorphous with magnesium salts. Cuprous oxide, Cu 2 0, also called Red oxide and Suboxide of copper. This oxide may be obtained by heating in a covered crucible a mixture of 5 parts of black oxide and 4 parts of fine copper-filings; or by adding grape-sugar to a solution of cupric sulphate, and then putting in an excess of caustic potash ; the blue solution, heated to ebullition, is reduced by the sugar, and deposits cuprous oxide. This oxide often occurs in beautiful transparent ruby-red crystals, associated with other ores of copper, and can be obtained in the same state by artificial means. It communicates to glass a magnifi- cent red tint, while that given by the cupric oxide is green. Cuprous oxide dissolves in excess of hydrochloric acid, forming a solu- tion of cuprous chloride, from which that compound is precipitated on dilu- tion with water. Most oxygen-acids, namely, sulphuric, phosphoric, acetic, oxalic, tartaric, and citric acids, decompose cuprous oxide, forming cupric salts, and separating metallic copper; nitric acid converts it into cupric nitrate. Hence there are but few cuprous oxygen-salts, none indeed except- ing the sulphites and certain double sulphites formed by mixing a cupric solution with the sulphite of an alkali-metal, e.g., ammonio-cuprous sul- phite, SO,Cu'(NH 4 ). CUPRIC SULPHATE, S0 4 Cu . 50H 2 . This beautiful salt, commonly called blue vitriol, is prepared by dissolving cupric oxide in sulphuric acid, or, at less expense, by oxidizing the sulphide. It forms large blue crystals, soluble in four parts of cold and two parts of boiling water; when heated to 100 C. (212 F.) it readily loses four molecules of crystallization-water; but the fifth is retained with great pertinacity, and is expelled only at alow red heat. At a very high temperature, cupric sulphate is entirely converted into cupric oxide, with evolution of sulphurous oxide and oxygen. Cupric sulphate combines with the sulphates of potassium and of ammonium, form- ing pale-blue salts, (S0 4 ) 2 CuK 2 . OOH ? and (S0 4 ) 2 Cu(NH 4 ) 2 . 60H 2 , isomor- phous with the corresponding magnesium salts. CUPRIC NITRATE, (N0 3 ) 2 Cu. 30 H 2 , is easily made by dissolving the metal in nitric acid ; it forms deep-blue crystals, very soluble and deliquescent. It is highly corrosive. An insoluble basic nitrate is known ; it is green. CUPRIC CARBONATES. When sodium carbonate is added in excess to a solution of cupric sulphate, the precipitate is at first pale-blue and floc- culent, but by warming it becomes sandy, and assumes a green tint; in this state it contains C0 3 Cu.CuH 2 2 -f-a,q. This substance is prepared as a pigment. The beautiful mineral malachite has a similar composition, but contains no water of crystallization, its composition being CO 3 Cu.CuH 2 2 . Another natural compound, called azurite, not yet artificially imitated, occurs in large transparent crystals of the most intense blue: it contains 2C0 3 Cu.CuH 2 O 2 . Verditer, made by decomposing cupric nitrate with chalk, is said, however, to have a somewhat similar composition. CUPRIC ARSENITE is a bright-green insoluble powder, prepared by mix- ing the solutions of a cupric salt with an alkaline arsenite. COPPER SULPHIDES. There are two well-defined copper sulphides, anal- 356 DYAD METALS. ogous in composition to the oxides, and four others, containing larger proportions of sulphur, but of less denned constitution; these latter are precipitated from solutions of cupric salts by potassium pentasulphide. Cupric Sulphide, CuS, occurs native as indiyo copper or covellin, in soft bluish-black hexagonal plates and spheroidal masses, and is produced arti- ficially by precipitating cupric salts with hydrogen sulphide. Cuprous Sulphide, Cu 2 S, occurs native as copper-glance or redruthite, in lead-gray hexagonal prisms, belonging to the rhombic system ; it is pro- duced artificially by the combustion of copper-foil in sulphur vapor, by igniting cupric oxide with sulphur, and by other methods. It is a power- ful sulphur-base, uniting with the sulphides of antimony, arsenic, and bis- muth, to form several natural minerals. The several varieties of fahl-ore, or tetrahedrite, consist of cuprous sulphantimonite or sulpharsenite, in which the copper is more or less replaced by equivalent quantities of iron, zinc, silver, and mercury. The important ore, called copper-pyrites, is a cuproso-ferric sulphide, Cu / Fe /// S 2 , or Cu 2 S.Fe 2 S 3 , occurring in tetrahedral crystals of the quadratic system, or in irregular masses. Another species of copper and iron sulphide, containing various proportions of the two metals, occurs native, as purple copper or erubescite, in cubes, octohedrons, and other monometric forms. AMMONIACAL COPPER COMPOUNDS. The chlorides, sulphate, nitrate, and other salts of copper, unite with one or more molecules of ammonia, form- ing, for the most part, crystalline compounds of blue or green color, some of which may be regarded as salts of metallammoniums (p. 315). Thus, cupric chloride forms with ammonia, the compounds, 2NH 3 .CuCl 2 , 4NH 3 . CuCl 2 , and 6NH 3 .CuCl 2 , the first of which may be formulated as cupro- diammonium chloride, (N 2 H 6 Cu // )Cl 2 . Cupric sulphate forms, in like manner, cupro-diammonium sulphate, (N 2 H 6 Cu // )S0 4 , which is a deep-blue crystalline salt. Cuprous iodide forms with ammonia the compound, 4NH 3 .Cu 2 l 2 . The characters of the cupric salts are well marked. Caustic potash gives a pale-blue precipitate of cupric hydrate, becoming blackish-brown anhydrous oxide on boiling. Ammonia also throws down the hydrate; but, when in excess, redissolves it, yielding an intense pur- plish-blue solution. Potassium and sodium carbonates give pale-blue preci- pitates of cupric carbonate, insoluble in excess. Ammonium carbonate, the same, but soluble with deep-blue color. Potassium fe.rro cyanide gives a fine red-brown precipitate of cupric ferrocyanide Hydrogen sulphide and ammonium sulphide afford black cupric sulphide, insoluble in ammonium sulphide. The alloys of copper are of great importance. Brass consists of copper alloyed with from 28 to 84 per cent, of zinc ; the latter may be added directly to the melted copper, or granulated copper may be heated with calamine and charcoal-powder, as in the old process. Gun-metal, a most valuable alloy, consists of 90 parts copper and 10 tin. Bell and speculum metal contain a still larger proportion of tin ; these are brittle, especially the last named. A good bronze for statues is made of 91 parts copper, 2 Earts tin, 6 parts zinc, and 1 part lead. The brass or bronze of the ancients 5 an alloy of copper with tin, often also containing lead, and sometimes zinc. MERCURY. 357 MERCURY. Atomic weight, 200. Symbol, Hg. (Hydrargyrum). This very remarkable metal, sometimes called quicksilver, has been known from early times, and perhaps more than all others has excited the atten- tion and curiosity of experimenters, by reason of its peculiar physical properties. Mercury is of great importance in several of the arts, and enters into the composition of many valuable medicaments. Metallic mercury is occasionally met with in globules disseminated through the native sulphide, which is the ordinary ore. This latter substance, sometimes called cinnabar, is found in considerable quantity in several localities, of which the most celebrated are Almaden in Spain, and Idria in Austria. Only recently it has been discovered in great abundance, and of remarkable purity, in California and Australia. The metal is obtained by heating the sulphide in an iron retort with lime or scraps of iron, or by roasting it in a furnace, and conducting the vapors into a large chamber, where the mercury is condensed, while the sulphurous acid is allowed to escape. Mercury is imported into this country in bottles of hammered iron, containing seventy-five pounds each, and in a state of considerable purity. When purchased in smaller quantities, it is sometimes found adulterated with tin and lead, which metals it dissolves to some extent without much loss of fluidity. Such admixture may be known by the foul surface the mercury exhibits when shaken in a bottle containing air, and by the globules, when made to roll upon the table, leaving a train or tail. Mercury has a nearly silver-white color, and a very high degree of lustre : it is liquid at all ordinary temperatures, and solidifies only when cooled to 40. In this state it is soft and malleable. At 350 C. (662 F.) it boils, and yields a transparent, colorless vapor, of great density. The metal volatilizes, however, to a sensible extent at all temperatures above 19 or 21 C. (66 or 68 F.) ; below this point its volatility is imperceptible. The volatility of mercury at the boiling heat is singularly retarded by the presence of minute quantities of lead or zinc. The specific gravity of mercury at 15-5 is 13-59; that of frozen mercury about 14, great contrac- tion taking place in the act of solidification. Pure mercury is quite unalterable in the air at common temperatures, but when heated to near its boiling-point, it slowly absorbs oxygen, and becomes converted into a crystalline dark-red powder, which is the highest oxide. At a dull red heat this oxide is again decomposed into its constit- uents. Hydrochloric acid has little or no action on mercury, and the same may be said of sulphuric acid in a diluted state : when the latter is con- centrated and boiling-hot, it oxidizes the metal, converting it into mercuric sulphate, with evolution of sulphurous oxide. Nitric acid, even dilute and in the cold, dissolves mercury freely, with evolution of nitrogen dioxide. The observed vapor-density of mercury referred to air as unity is 6-7;* this referred to hydrogen is nearly 100 ;f that is to say, half the atomic weight of the metal: consequently the atom of mercury, like that of cad- mium, occupies in the gaseous state twice the volume of an atom of hydro- gen (see page 229). Mercury forms two series of compounds ; namely, the mercuric compounds, which it is bivalent, as Hg // Cl 2 , Hg /r O, Hg /x S0 4 , &c., and the mercurous * Bineau, Comptes Rendus, xlix. 799. t ~~0'6926 = 98 ' 3 ' 358 DYAD METALS. compounds, in which it is apparently univalent, as Hg 2 Cl 2 , Hg 2 0, &c. These compounds are analogous in constitution to the cupric and cuprous com- pounds ; and the rnercurous compounds, like the latter, are easily converted into mercuric compounds by the action of oxidizing agents, which remove one atom of mercury; but they are, on the whole, much more stable than the cuprous compounds. MERCURY CHLORIDES. Mercuric Chloride, Hg // Cl 2 , commonly called cor- rosive sublimate. This compound may be obtained by several different pro- cesses: (1) When metallic mercury is heated in chlorine gas, it takes fire and burns, producing this substance. (2) It may be made by dissolving mercuric oxide in hot hydrochloric acid, crystals of corrosive sublimate then separating on cooling. (3) Or, more economically, by subliming a mixture of equal parts of mercuric sulphate and dry common salt; and this is the plan generally followed. The decomposition is represented by the equation : SQ 4 Hg -f 2NaCl = HgCl 2 -f S0 4 Na 2 . Mercuric Sodium Mercuric Sodium sulphate. chloride. chloride. sulphate. Sublimed mercuric chloride forms a white transparent crystalline mass of specific gravity 543; it melts at 265 C, (509 F.); boils at 295 C. (563 F.), and volatilizes somewhat more easily than calomel, even at ordinary temperatures. Its observed vapor-density, referred to hydrogen as unity, is 140 : and the density calculated from the formula HgCl 2 , sup- posing that the molecule occupies the same space as a molecule or two atoms 200 -f 2 X 35-5 of hydrogen (p. 229) is - = 135-5 ; the near agreement of this number with the observed result shows that the vapor is in the normal state of condensation. Mercuric chloride dissolves in 16 parts of cold and 3 parts of boiling water, and crystallizes from a hot solution in long white prisms. Alcohol and ether also dissolve it with facility ; the latter even withdraws it from a watery solution. Mercuric chloride combines with a great number of other metallic chlor- ides, forming a series of beautiful double salts, of which the ancient sal alembroth may be taken as a good example : it contains HgCl 2 . 2NH 4 C1 . OH 2 . Corrosive sublimate absorbs ammoniacal gas with great avidity, generating the compound HgCl 2 . NII 3 . Mercuric chloride forms several compounds with mercuric oxide. These are produced by several processes, as when an alkaline carbonate is added in varying proportions to a solution of mercuric chloride. They differ greatly in color and physical character, and are mostly decomposed by water. Mercuric chloride forms insoluble compounds with many of the azotized organic principles, as albumin, &c. It is perhaps to this property that its strong antiseptic properties are due. Animal and vegetable substances are preserved by it from decay, as in Ryan's method of preserving timber and cordage. Albumin is on this account an excellent antidote to corrosive subli- mate in cases of poisoning. Mcrcurous Chloride, Hg 2 Cl 2 , commonly called Calomel. This very im- portant substance may be easily and well prepared by pouring a solution of rnercurous nitrate into a large excess of dilute solution of common salt. It falls as a dense white precipitate, quite insoluble in water ; it must be thoroughly washed with boiling distilled water, and dried. Calomel is, however, generally procured by another and more complex process. Dry MERCURY. 359 mercuric sulphate is rubbed in a mortar with as much metallic mercury as it already contains, and a quantity of common salt, until the globules dis- appear, and a uniform mixture has been produced. This is subjected to sublimation, the vapor of the calomel being carried into an atmosphere of steam, or into a chamber containing air; it is thus condensed into a mi- nutely divided state, and the laborious process of pulverization of the sub- limed mass is avoided. The reaction is thus explained : S0 4 Hg -f Hg + 2NaCl = Hg 2 Cl 2 -f S0 4 Na 2 Mercuric Sodium Mercurous Sodium sulphate. chloride. chloride. sulphate. Pure calomel is a heavy, white, insoluble, tasteless powder : it rises in vapor at a temperature below redness, and is obtained by ordinary sub- limation as a yellowish-white crystalline mass. It is as insoluble in cold diluted nitric acid as silver chloride ; boiling-hot strong nitric acid oxidizes and dissolves it. Calomel is instantly decomposed by an alkali, or by lime- water, with production of mercurous oxide. It is sometimes apt to con- tain a little mercuric chloride, which would be a very dangerous contami- nation in calomel employed for medical purposes. This is easily discovered by boiling with water, filtering the liquid, and adding caustic potash. Any corrosive sublimate is indicated by a yellow precipitate. The observed vapor-density of calomel, referred to hydrogen as unity, is 119-2. Now the formula Hg 2 Cl 2 , if it represents a molecule occupy- ing in the gaseous state two volumes (i. e., twice the volume of an atom of hydrogen, p. 229), would give a density nearly double of this : for 400 -f- 2 x 35-5 2 ~ 235 '5. Hence it might be inferred that the composition of calomel should rather be represented by the simpler formula HgCl, which would give for the vapor-density the number 117-75. But this formula (the adoption of which would, of course, involve that of similar formulae for the other mercurous salts, e, g., N0 3 Hg for the nitrate) is objectionable on account of its inconsistency with the law of even numbers, according to which a dyad element like mercury can never unite with an uneven num- ber of monad atoms (p. 232). Moreover, the frequent decomposition of mercurous salts into mercuric salts and free mercury is in favor of the sup- position that their molecules contain two atoms of mercury; and the anom- aly in the vapor-volume of calomel may be explained by supposing that the vapor of this compound, like that of many others, undergoes at high temperatures the change known as dissociation (p. 531), the two volumes of mercurous chloride, Hg 2 Cl, being resolved into two volumes of mercuric chloride, HgCl 2 , and two volumes of mercury, Hg. This supposition is, to some extent, warranted by the observation that calomel vapor amalgamates gold-leaf, and that corrosive sublimate may be detected in resublimed cal- omel. IODIDES. Mercuric Iodide, Hg 77 !^ is formed, when solution of potassium iodide is mixed with mercuric chloride, as a precipitate which is at first yellow, but in a few moments changes to a most brilliant scarlet, this color being retained on drying. This is the neutral iodide : it may be made, although of rather duller tint, by triturating equivalent quantities of iodine and mercury with a little alcohol. In preparing it by precipitation, it is better to weigh out the proper proportions of the two salts, as the iodide is soluble in an excess of either, more especially in excess of potassium iodide. Mercuric iodide exhibits a very remarkable case of dimorphism, attended with difference of color, which is red or yellow, according to the figure assumed. Thus, when the iodide is suddenly exposed to a high tempera- ture, it becomes bright-yellow throughout, and yields ft copious sublimate 360 DYAD METALS. of minute but brilliant yellow crystals. If in this state it be touched by a hard body, it instantly becomes red, and the same change happens spon- taneously after a certain lapse of time. On the other hand, by a very slow and careful heating, a sublimate of red crystals, having a totally different form, may be obtained, which are permanent. The same kind of change happens with the freshly precipitated iodide, as Mr. Warington has shown, the yellow crystals first formed breaking up in the course of a few seconds from the passage of the salt to the red modification.* Mercuric iodide forms double salts with the more basic or positive me- tallic iodides, as those of the alkali-metals and alkaline earth-metals ; thus it dissolves in aqueous potassium iodide, and the hot solution deposits on cooling, crystals of potassio-mercuric iodide, 2(KI.HgI 2 ).30H 2 . Mercurous Iodide, Hg 2 I 2 , is formed when a solution of potassium iodide is added to mercurous nitrate : it then separates as a dirty yellow, insoluble precipitate, with a tinge of green. It may also be prepared by rubbing mercury and iodine together in a mortar in the proportion of 1 atom of the former to 1 atom of the latter, the mixture being moistened from time to time with a little alcohol. OXIDES. Monoxide, or Mercurous Oxide, HgO, commonly called Red Oxide of Mercury, or Red Precipitate. There are numerous methods by which this compound may be obtained. The following may be cited as the most im- portant: (1) By exposing mercury in a glass flask with a long narrow neck, for several weeks, to a temperature approaching 315 C. (599 F.). The product has a dark red color, and is highly crystalline; it is the red precipi- tate of the old writers. (2) By cautiously heating any of the mercuric or mercurous nitrates to complete decomposition, whereby the acid is decom- posed and expelled, oxidizing the metal to a maximum, if it happen to be in the state of mercurous salt. The product thus obtained is also crystal- line and very dense, but has a much paler color than the preceding ; while hot, it is nearly black. It is by this method that the oxide is generally pre- pared: it is apt to contain undecomposed nitrate, which may be discovered by strongly heating a portion in a test-tube : if red fumes are produced, or the odor of nitrous acid exhaled, the oxide has been insufficiently heated in the process of manufacture. (3) By adding caustic potash in excess to a solution of corrosive sublimate, by which a bright yellow precipitate of mercuric oxide is thrown down, which differs from the foregoing prepara- tions merely in being destitute of crystalline texture and much more mi- nutely divided. It must be well washed and dried. Mercuric oxide is slightly soluble in water, communicating to the latter an alkaline reaction and metallic taste: it is highly poisonous. When strongly heated, it is decomposed, as before observed, into metallic mercury and oxygen gas. Mercurous Oxide, Hg 2 ; Suboxide, or Gray Oxide of Mercury. This oxide is easily prepared by adding caustic potash to mercurous nitrate, or by di- gesting calomel in solution of caustic alkali. It is a dark gray, nearly black, heavy powder, insoluble in water, slowly decomposed by the action of light into metallic mercury and red oxide. The preparations known in pharmacy by the names blue pill, gray ointment, mercury with chalk, &c., often supposed to owe their efficacy to this substance, merely contain the finely divided metal. MERCURY NITRATES. Nitric acid varies in its action upon mercury, according to the temperature. When cold and somewhat diluted, it forms only mercurous salts, and these are neutral or basic i. e., oxynitrates * Memoirs of the Chemical Society of London, i. 85. MEKCUliY. 361 (p. 283) as the acid or the metal happens to be in excess. When, on the contrary, the nitric acid is concentrated and hot, the mercury is raised to its highest state of oxidation, and a mercuric salt is produced. Both classes of salts are apt to be decomposed by a large quantity of water, giving rise to insoluble, or sparingly soluble basic compounds. Mercuric Nitrates. By dissolving mercuric oxide in excess of nitric acid, and evaporating gently, a syrupy liquid is obtained, which, enclosed in a bell-jar over lime or sulphuric acid, deposits bulky crystals and crystalline crusts, both having the composition 2(N0 3 ) 2 Hg // .OH 2 . The same substance is deposited from the syrupy liquid as a crystalline powder by dropping it into concentrated nitric acid. The syrupy liquid itself appears to be a de- finite compound containing (N0 3 ) 2 Hg // .OH 2 . By saturating hot dilute nitric 'acid with mercuric oxide, a salt is obtained on cooling, which crystallizes in needles, permanent in the air, containing (N0 3 ) 2 Hg // . Hg // O.OH 2 . The preceding crystallized salts are decomposed by water, with production of compounds more and more basic as the washing is prolonged or the tempe- rature of the water raised. Mercurous Nitrate, (N0 3 ) 2 Hg 2 .20H 2 , forms large colorless crystals soluble in a small quantity of water without decomposition ; it is made by dissolving mercury in an excess of cold dilute nitric acid. When excess of mercury has been employed, a finely crystallized basic salt is deposited after some time, containing 2(N0 8 ) 2 Hg 2 *Hg 2 0.30H r or 2N 2 5 .3Hg 2 0.30H 2 ; this is also decomposed by water. The two salts are easily distinguished when rubbed in a mortar with a little sodium chloride; the neutral compound gives sodium nitrate and calomel; the basic salt, sodium nitrate and a black compound of calomel with niercurous oxide. A black substance, called Hahnemann 's soluble mercury, is produced when am- monia in small quantity is dropped into a solution of mercurous nitrate: it contains N 2 5 .3Hg 2 0.2NH 3 , or, according to Kane, N 2 05.2Hg 2 0.2NH 3 ; the composition of this preparation evidently varies according to the tem- perature and the concentration of the solutions. MERCURY SULPHATES. Mercuric Sulphate, S0 4 Hg // , is readily prepared by boiling together oil of vitriol and metallic mercury until the latter is wholly converted into a heavy white crystalline powder, which is the salt in question; the excess of acid is then removed by evaporation carried to perfect dryness. Equal weights of acid and metal may be conveniently em- ployed. Water decomposes the sulphate, dissolving out an acid salt, and leaving an insoluble, yellow, basic compound, formerly called turpith or tur- beth mineral, containing, according to Kane's analysis, S0 4 Hg // .2Hg // > or S0 3 .3Hg /x O. Long-continued washing with hot water entirely removes the remaining acid, and leaves pure mercuric oxide. Mercurous Sulphate, S0 4 Hg 2 , falls as a white crystalline powder when sul- phuric acid is added to a solution of mercurous nitrate : it is but slightly soluble in water. MERCURY SULPHIDES. Mercuric Sulphide, HgS, occurs native as cinnabar, a dull red mineral, which is the most important ore of mercury. Hydrogen sulphide passed in small quantity into a solution of mercuric nitrate, or chloride, forms a white precipitate, which is a compound of mercuric sul- phide with the salt itself. An excess of the gas converts the whole into sulphide, the color at the same time changing to black. When this black sulphide is sublimed, it becomes dark-red and crystalline, but undergoes no change of composition: it is then cinnabar or vermilion. Mercuric sul- phide is most easily prepared by subliming an intimate mixture of 6 parts of mercury and 1 part of sulphur, and reducing the resulting cinnabar to very fine powder, the beauty of the tint depending much upon the extent 31 362 DYAD METALS. to which division is carried. The red or crystalline sulphide may also be formed directly, without sublimation, by heating the black precipitated substance in a solution of potassium pentasulphide ; the mercuric sulphide is, in fact, soluble, to a certain extent, in the alkaline sulphides, and forms with them crystallizable compounds. When vermilion is heated in the air, it yields metallic mercury and sul- phurous oxide : it resists the action both of caustic alkali in solution, and of strong mineral acids, even nitric, and is attacked only by nitromuriatic acid. Mercurous sulphide, Hg 2 S, is obtained by passing hydrogen sulphide into a solution of mercurous nitrate, as a black precipitate, which is resolved at a gentle heat into mercuric sulphide and metallic mercury. AMMONIACAL MERCURY COMPOUNDS. MERCURAMMONIUM SALTS. By the action of ammonia and its salts on mercury compounds, a variety of sub- stances are formed which may be regarded as salts of mercurammoniums that is, of ammonium-molecules in which the hydrogen is more or less replaced by mercury, in the proportion of 100 or 200 parts of mercury to 1 part of hydrogen, according as the compound is formed from a mercurous or a mercuric salt. The following are the most important of these com- pounds: Mercuric Compounds. Mercuro-diammonium chloride, (N 2 H 6 Hg // )Cl 2 , known in pharmacy as fusible white precipitate, is produced by adding potash to a solution of ammonio-mercuric chloride, (2NH 4 Cl.HgCl 2 ), or by dropping a solution of mercuric chloride into a boiling solution of sal-ammoniac con- taining free ammonia, as long as the resulting precipitate redissolves : it then separates on cooling in regular dodecahedrons. At a gentle heat it gives off ammonia, leaving a chloride of dimercur-ammonium and hydrogen, (NH 2 Hg")Cl.HCl: N 2 H c Hg"Cl 2 = N H 3 Hg"Cl 2 -f NH S . Mercurammonium chloride, (NH 2 Hg // )Cl. This salt, known in pharmacy as infusible white precipitate, is formed by adding ammonia to a solution of mercuric chloride. When first produced, it is bulky and white, but by contact with hot water, or by much washing with cold water, it is converted into hydrated dimercurammonium chloride, NHg // 2 C1.0H 2 . Trimercuro-diammonium nitrate, (N 2 H 2 Hg // 3 )(NO 3 ) 2 . 20H 2 , is formed as a white precipitate, on mixing a dilute and very acid solution of mercuric nitrate with very dilute ammonia. Trimercuro-diamine, N 2 Hg // 3 , a compound derived from a double molecule of ammonia, N 2 H 6 , by substitution of 3 atoms of bivalent mercury for 6 atoms of hydrogen, is formed by passing dry ammonia gas over dry pre- cipitated mercuric oxide : 3Hg"0 -f- 2NH S = N 2 Hg" 3 -f 30H 2 . The excess of oxide being removed by nitric acid, the trimercuro-diamine is obtained as a dark-brown powder, which explodes by heat, friction, percussion, or contact with oil of vitriol, almost as violently as nitrogen chloride. Dimercurammonium chloride, NHg // 2 C1.0H 2 , is obtained, as already ob- served, by boiling mercurodiammonium chloride (infusible white precipi- tate) with water. It is a heavy, granular, yellow powder, which turns white again when treated with sal-ammoniac. Dimercurammonium iodide, NHg // 2 I . OH 2 . This compound may be formed by digesting the corresponding chloride in a solution of potassium iodide; or by heating mercuric iodide with excess of aqueous ammonia: MERCURY. 363 2HgI 2 + 4NH 3 + OH 2 = NHg" 2 I.OH 2 + 3NH 4 I; also by passing ammonia gas over mercuric oxy-iodide : Hg // 4 I 2 3 -f 2NH 3 = 2(NHg" 2 I.OH 2 ) -f OH 2 ; and, lastly, by adding ammonia to a solution of potassio-mercuric iodide mixed with caustic potash: 2(2KI. HgI 2 ) + NH 3 + 3KHO = NHg" 2 I. OH 2 + 7KI -f 20H 2 . This last reaction affords an extremely delicate test for ammonia. A solu- tion of potassio-mercuric iodide is prepared by adding potassium iodide to a solution of corrosive sublimate, till a portion only of the resulting red precipitate is redissolved, then filtering, and mixing the filtrate with caustic potash. The liquid thus obtained forms, with a very small quantity of ammonia, either free or in the form of an ammoniacal salt, a brown pre- cipitate soluble in excess of potassium iodide. This is called Nessler's test for ammonia.* Dimercurammonium hydrate, NHg /x 2 HO. This compound is formed by treating precipitated mercuric oxide with aqueous ammonia, or by treating either of the dimercurammonium salts with a caustic alkali. It is a brown powder, which dissolves in acids, yielding salts of dimercurammonium. Dimercurammonium sulphate, (NHg // 2 ) 2 S0 4 . 20H 2 , formerly called ammoni- acal turpethum, is prepared by dissolving mercuric sulphate in ammonia, and precipitating the solution with water. It is a heavy white powder, yellowish when dry, resolved by heat into water, nitrogen, ammonia, and mercurous sulphate. Mercurous Compounds. Mercurosammonium chloride, NH 3 Hg / Cl, is the black precipitate formed when dry calomel is exposed to the action of am- monia gas. When exposed to the air, it gives off ammonia and leaves white mercurous chloride. Dimer cur osamm.onium chloride, NH 2 Hg / 2 Cl, is formed, together with sal-ammoniac, by digesting calomel in aqueous ammonia: Hg 2 Cl 2 + 2NH 3 = NH 2 Hg 2 Cl + NH 4 C1. It is gray when dry, and is not altered by boiling water. Dimercurosam- monium nitrate, 2(NH 2 Hg 2 )N0 3 .OII 2 . This, according to Kane, is the com- position of the velvet-black precipitate known as Hahnemann's soluble . mercurj', which is produced on adding ammonia to a solution of mercurous nitrate. According to C. G. Mitscherlich, on the other hand, the precipi- tate thus formed has the composition 2NH 3 .N 2 O 5 .3Hg 2 0, which is that of a hydrated trimercurosammonium nitrate, 2(NHHg 3 )N0 3 .20H 2 . Reactions of Mercury Salts. All mercury compounds are volatilized or decomposed by a temperature of ignition : those which fail to yield the metal by simple heating may in all cases be made to do so by heating in a test-tube with a little dry sodium carbonate. The metal is precipitated from its soluble combinations by a plate of copper, and also by a solution of stannous chloride used in excess. Hydrogen sulphide, and ammonium sulphide, produce in solutions, both of mercuric and of mercurous salts, black precipitates insoluble in ammonium sulphide. In mercuric salts, however, if the quantity of the reagent added is not sufficient for complete decomposition, a white precipitate is formed, consisting of a compound of mercuric sulphide with the original salt, and often colored yellow or brown by excess of mercuric sulphide. An excess * Chemical Gazette, 1856, pp. 445, 463. 364 DYAD METALS. of hydrogen sulphide, or ammonium sulphide, instantly turns the precipi- tate black. This reaction is quite characteristic of mercuric salts Mercuric salts are further distinguished by forming a yellow precipitate with caustic potash or soda ; white with ammonia or ammonium carbonate, in- soluble in excess: red-brown with potassium or sodium carbonate. With potassium iodide they yield a bright scarlet precipitate, soluble in excess, either of the mercuric salt or of the alkaline iodide. Mercurous salts are especially characterized by forming with hydrochloric acid or soluble chlorides, a white precipitate which is turned black by am- monia. They also yield black precipitates with caustic alkalies, white with alkaline carbonates, soon turning black ; greenish-yellow with potassium iodide. Alloys of mercury with other metals are termed amalgams: mercury dis- solves in this manner many of the metals, as gold, silver, tin, lead, &c. These combinations sometimes take place with considerable violence, as in the case of potassium, in which light and heat are produced ; besides this, many of the amalgams crystallize after a while, becoming solid. The amalgam of tin used in silvering looking-glasses, and that of silver and of copper, sometimes employed for stopping hollow teeth, are examples. CLASS III TRIAD METALS. THALLIUM. Atomic weight, 204. Symbol, Tl. rpHIS element was discovered by Crookes, in 1861, in the seleniferous JL deposit of a lead-chamber of a sulphuric acid factory in the Hartz mountains, where iron pyrites is used for the manufacture of sulphuric acid. The name is derived from 0aAAd,-, "green," because its existence was first recognized by an intense green line, appearing in the spectrum of a flame in which thallium is volatilized. It was at first suspected to be a metalloid, but further examination proved it to be a true metal. It was first, obtained in a distinct metallic form by Crookes towards the end of the year 1861, and soon afterwards by Lamy, who prepared it from the deposit in the lead-chamber of M. Kuhlmann, of Lille, where Belgian pyrites is employed for the manufacture of sulphuric acid. Thallium appears to be very widely diffused as a constituent of iron and copper pyrites, though it never constitutes more than the 4000th part of the bulk of the ores. It has also been found in lepidolite from Moravia, in mica from Zinnwald in Bohemia, and in the mother-liquors of the salt works at Nauheim. Thallium is most economically prepared from the flue-dust of pyrites burners. This substance is stirred up in wooden tubs with boiling water, and the clear liquor siphoned off from the deposit is mixed with excess of strong hydrochloric acid, which precipitates impure thallium monochloride. To obtain a pure salt, this crude chloride is added by small portions at a ^ime to half its weight of hot oil of vitriol in a porcelain or platinum dish, the mixture being constantly stirred, and the heat continued till the whole of the hydrochloric acid and the greater portion of the excess of sulphuric acid are driven off. The fused acid sulphate is now to be dissolved in an excess of water, and an abundant stream of hydrogen sulphide passed through the solution. The precipitate, which may contain arsenic, anti- mony, bismuth, lead, mercury, and silver, is separated by filtration, and the filtrate is boiled till all free hydrogen sulphide is removed. The liquid is now to be rendered alkaline with ammonia, and boiled; the precipitate of iron oxide and alumina, which generally appears in this place, is filtered off: and the clear solution evaporated to a small bulk. Thallium sulphate then separates on cooling, in long, clear prismatic crystals. Metallic thallium may be reduced from the solution of the sulphate, either by electrolysis, or by the action of zinc. Thallium is a heavy metal, resembling lead in its physical properties. When freshly cut, it exhibits a brilliant metallic lustre and grayish color, somewhat between those of silver and lead, assuming a slight yellowish tint by friction with harder bodies. It is very soft, being readily cut with a knife, and making a streak on paper like plumbago. It is very malleable, is not easily drawn into wire, but may be readily squeezed into that form 31* 365 366 TRIAD METALS. by the process technically called "squirting." It has a highly crystalline structure, and crackles like tin when bent. It melts at 294. In contact with the air, thallium tarnishes more, rapidly than lead, becoming coated with a thin layer of oxide, which preserves the rest of the metal. The most characteristic property of thallium is the intense green color which the metal or any of its compounds impart to a colorless flame ; and this color, when viewed by the spectroscope, is seen to be absolutely mono- chromatic, appearing as one intensely brilliant and sharp green line. Thallium dissolves in hydrochloric, sulphuric, and nitric acids, the latter attacking it very energetically, with copious evolution of red vapors. Thallium forms two classes of compounds namely, the thallious com- pounds, in which it is univalent ; and the thallic compounds, in which it is trivalent. Thus it forms two oxides, T1 2 and T1 2 3 , with corresponding chlorides, bromides, iodides, and oxygen-salts. In some of its chemical relations it resembles the alkali-metals, forming a readily soluble and highly alkaline monoxide, a soluble and alkaline carbonate, an insoluble platino- chloride, a thallio-aluminic sulphate, similar in form and -composition to common potash-alum, arid several phosphates exactly analogous in compo- sition to the phosphates of sodium. In most respects, however, it is more nearly allied to the heavy metals, especially to lead, which it resembles closely in appearance, density, melting point, specific heat, and electric conductivity. THALLIUM CHLORIDES. Thallium forms four chlorides, represented by the formulae T1C1, T1 4 C1 6 , T1 2 C1 4 , and T1C1 3 ; the second and third of which may be regarded as compounds of the monochloride and trichloride. The monochloride or Thallious chloride, T1C1, is formed by direct combina- tion, the metal burning when heated in chlorine gas ; or as a white curdy precipitate, resembling silver chloride, by treating the solution of any thallious salt with a soluble chloride. When boiled with water it dissolves like lead chloride, and separates in white crystals on cooling. It forms double salts with trichloride of gold and tetrachloride of platinum. The platinum-salt, 2T1C1. PtCl 4 . separates as a pale yellow very slightly soluble crystalline powder, on adding platinic chloride to thallious chloride. The trichloride or Thallic chloride, T1C1 3 , is obtained by dissolving the tri- oxide in hydrochloric acid, or by acting upon thallium, or one of the lower chlorides, with a large excess of chlorine at a gentle heat. It is soluble in water, and separates by evaporation in a vacuum in hydrated crystals; melts easily, and decomposes at a high temperature. It forms crystalline double salts with the chlorides of the alkali-metals. The sesquichloride, T1 4 C1 6 = T1C1 3 .3T1C1, is produced by dissolving thal- lium or the monochloride in nitromuriatic acid, and separates on cooling in yellow crystalline scales. By aqueous ammonia, potash, or even by thallious oxide, it is instantly decomposed into sesquioxide and mono- chloride, according to the equation: 2T1 4 C1 6 -f 3KHO = T1 2 3 -f 6T1C1 -f 3KC1 + 3HC1. The dichloride, T1 2 C1 4 = T1C1 3 .T1C1, is formed by carefully heating thal- lium, or the monochloride, in a slow current of chlorine. It is a pale-yel- low substance reduced to sesquichloride by further heating. The BROMIDES of thallium resemble the chlorides. IODIDES. Thallious iodide, Til, is formed by direct combination of its elements, or by double decomposition. It forms a beautiful yellow powder, rather daj-ker than sulphur, and melting, below redness, to a scarlet liquid, THALLIUM. 367 which, as the mass cools, remains scarlet for some time after solidification, then changes to bright-yellow. The dried precipitate, when spread on paper with a little gum-water, undergoes a similar but opposite change to that experienced by mercuric iodide when heated, the yellow surface when held over a flame suddenly becoming scarlet, and frequently remaining so after cooling for several days ; hard friction with a glass rod, however, changes the scarlet color back to yellow. It is very slightly soluble in water, requiring, according to Crookes, 4453 parts of water at 17-2, and 842-4 parts at 100, to dissolve it. Thallic iodide, T1C1 3 , is formed by the action of thallium on iodine dis- solved in ether, as a brown solution which gradually deposits rhombic prisms. It forms crystalline compounds with the iodides of the alkali- metals. THALLIUM OXIDES. Thallium forms a monoxide and a trioxide. The monoxide, or Thallious oxide, T1 2 0, constitutes the chief part of the crust which forms on the surface of the metal when exposed to the air. It may be prepared by allowing granulated thallium to oxidize in warm moist air, and then boiling with water. The filtered solution first deposits white needles of thallium carbonate, and, on further cooling, yellow needles of the hydrate, T1HO or T1 2 O.H 2 0, which, when left over oil of vitriol in a vacuum, yields the anhydrous monoxide as a reddish-black mass retaining the shape of the crystals. It is partially reduced to metal by hydrogen at a red heat. When fused with sulphur it yields thallious sulphide. It dis- solves readily in water, forming a colorless strongly alkaline solution, which re-acts with metallic salts very much like caustic potash. This solution treated with zinc, or subjected to electrolysis, yields metallic thallium. The trioxide, or Thallic oxide, is the chief product obtained by burning thallium in oxygen gas. It is best prepared by adding potash to the solu- tion of a thallic salt, and drying the precipitate at 260 C. (500 F.). It is also formed by electrolysis of thallious sulphate. It is a dark-red pow- der reduced to thallious oxide at a red heat; neutral, insoluble in water and in alkalies. Thallic hydrate, T1 //X H0 2 , is obtained by drying the above-mentioned precipitate at 100. OXYGEN SALTS. Both the oxides of thallium dissolve readily in acids, forming crystalline salts, soluble in water; there are also a few insoluble thallium salts formed by double decomposition. Thallious Carbonate, C0 3 T1 2 , is deposited in crystals, apparently trimetric, when a solution of thallious oxide is exposed to the air. It is soluble in water, and the solution has a slightly caustic taste and alkaline reaction. Sulphates. Thallious sulphate, S0 4 T1 2 , obtained by evaporating the chloride or nitrate with sulphuric acid, or by heating metallic thallium with that acid, crystallizes in anhydrous rhombic prisms, isomorphous with potassium sulphate. It forms, with aluminium sulphate, the salt (SO 4 ) 2 A1 X// T1. 120H 2 , isomorphous with common alum; and with the sulphates of magnesium, nickel, &c., double salts containing 6 molecules of water, and isomorphous with magnesium and potassium sulphate, &c. (p. 349). Thallic sulphate, (S0 4 ) 3 T1 2 /// .70H 2 , separates by evaporation from a solution of thallic oxide in dilute sulphuric acid, in thin colorless lamina^ which are decomposed by water, even in the cold, with separation of brown thallic oxide. Phosphates. The thallious phosphates form a series nearly as complete as those of the alkali-metals, which they also resemble in their behavior when heated. There are three orlhophosphates containing respectively P(> 4 H 2 T1, P0 4 HT1 2 , and P0 4 T1 3 . The first two are soluble in water; the sc-coii.t is obtained by neutralizing dilute phosphoric acid at boiling heat with thai- 368 TRIAD METALS. lious carbonate; and the first by mixing the dithallious salt with excess of phosphoric acid. The trithallious salt, P0 4 Tl g , is very sparingly soluble, and is formed as a crystalline precipitate on mixing the saturated solutions of ordinary disodic phosphate and thallious sulphate; also, together with ammonio-thallious phosphate, by treating the monothallious or dithallious salt with excess of ammonia. There are two thallious pyrophosphates, P 2 7 H 2 T1 2 and P 2 7 T1 4 , both very soluble in water : the first produced by care- fully heating monothallious orthophosphate, the second by strongly heating dithallious orthophosphate. Of thallious metaphosphate, P0 3 T1, there are two modifications : the first remaining as a slightly soluble vitreous mass when monothallious orthophosphate is strongly ignited, the second obtained as an easily soluble glass by igniting ammonio-thallious 01 thophosphate. Thallic orthophosphate, P0 4 T1 /X/ . 20H 2 , separates as an insoluble gelatinous precipitate on diluting a solution of thallic nitrate mixed with phosphoric acid. THALLIUM SULPHIDE, T1 2 S. This compound is precipitated from all thal- lious salts by ammonium sulphide, and from the acetate, carbonate, or oxalate, by hydrogen sulphide (incompletely also from the nitrate, sulphate or chloride), in dense flocks of a grayish or brownish-black color. Thallic salts appear to be reduced to thallious salts by boiling with ammonium sulphide. Thallium sulphate projected into fused potassium cyanide is re- duced to sulphide, which then forms a brittle metallic-looking mass, having the lustre of plumbago, and fusing more readily than metallic thallium. Reactions of Thallium salts. The reactions of thallious salts with hydrogen sulphide and ammonium sulphide have just been mentioned. From their aqueous solutions thallium is rapidly precipitated in metallic crystals by zinc, slowly by iron. Soluble chlorides precipitate difficultly soluble white thallious chloride ; soluble bromides throw down white, nearly insoluble bromide ; soluble iodides precipitate insoluble yellow thallious iodide. Caustic alkalies and alkaline carbonates form no precipitate; sodium phos- phate forms a white precipitate, insoluble in ammonia, easily soluble in acids. Potassium chromate gives a yellow precipitate of thallious chromate, in- soluble in cold nitric or sulphuric acid, but turning orange-red on boiling in the acid solution. Platinic chloride precipitates a very pale-yellow in- soluble double salt. Thallic sails are easily distinguished from thallious salts by their be- haviour with alkalies, and with soluble chlorides or bromides. Their solu- tions give with ammonia, and with fixed alkalies and their carbonates, a brown gelatinous precipitate of thallic oxide, containing the whole of the thallium. Soluble chlorides or bromides produce no precipitate in solutions of pure thallic salts ; but if a thallious salt is likewise present, a precipitate of scsquichloride or sesquibromide is formed. Oxalic acid forms in solutions of thallic salts a white pulverulent precipitate ; phosphoric acid a white gelatinous precipitate; and arsenic acid a yellow gelatinous precipitate. Thallic nitrate gives with potassium ferrocyanide a green, and with the ferri- cyanide a -yellow precipitate. In examining a mixed metallic solution, thallium will be found in the precipitate thrown down by ammonium sulphide, together with iron, nickel, manganese, &c. From these metals it may be easily separated by precipi- tation with potassium iodide or platinic chloride, or by reduction to the metallic state with zinc. Thallium salts are reduced before the blowpipe with charcoal and sodium carbonate or potassium cyanide. The green color imparted to flame by thallium, and the peculiar character of its spectrum, have already been mentioned. GOLD. 369 GOLD, Atomic weight, 196-7. Symbol, Au (Aurum). Gold, in small quantities, is a very widely diffused metal ; traces of it are constantly found in the iron pyrites of the more ancient rocks. It is always met with in the metallic state, sometimes beautifully crystallized in the cubic form, associated with quartz, iron oxide, and other substances, in regular mineral veins. The sands of various rivers have long furnished gold derived from this source, and separable by a simple process of washing ; such is the gold-dust of commerce. When a veinstone is wrought for gold, it is stamped to powder, and shaken in a suitable apparatus with water and mercury ; an amalgam is thus formed, which is afterwards separated from the mixture and decomposed by distillation. Formerly, the chief supply of gold was obtained from the mines of Brazil, Hungary, and the Ural mountains; but California and Australia now yield by far the largest quantity. The new gold-field of British Columbia is also very productive. Native gold is almost always alloyed with silver. The purest specimens have been obtained from Schabrowski, near Katharinenburg, in the Ural. A specimen analyzed by Gustav Rose was found to contain 98-96 per cent, of gold. The Californian gold averages from 87-5 to 88-5 per cent., and the Australian from 96 to 96-6 per cent. In some specimens of native gold, as in that from Linarowski, in the Altai mountains, the percentage of gold is as low as 60 per cent., the remainder being silver. There is also an auri- ferous silver found at Konigsberg, in Hungary, containing 28 per cent, of gold and 72 of silver. Pure gold is obtained from its alloys by solution in nitro-muriatic acid and precipitation with a ferrous salt, which reduces the gold, and is itself converted into a ferric salt, thus : 6S0 4 Fe + 2AuCl 3 = 2(S0 4 ) 3 Fe'" 2 -f Fe /// 2 Cl 6 + Au 2 . Ferrous Auric Ferric Ferric Gold, sulphate. hloride. sulphate. chloride. The gold falls as a brown powder which acquires the metallic lustre by friction. .Gold is a soft metal, having a beautiful yellow color. It surpasses all other metals in malleability, the thinnest gold leaf not exceeding, it is said, Tfftfhnnr ^ an i ncn m thickness, while the gilding on the silver wire used in the manufacture of g old-lace is still thinner. It may also be drawn into very fine wire. Gold has a density of 19-5: it melts at a temperature a little above the fusing point of silver. Neither air nor water affects it in the least at any temperature ; the ordinary acids fail to attack it singly. A mixture of nitric and hydrochloric acids dissolves gold, however, with ease, the active agent being the liberated chlorine. Gold forms two series of compounds : the aurous compounds, in which it is univalent, as AuCl, Au 2 0, &c., and the auric compound, in which it is triva- lent, as Au'"Cl 3 , Au'" 2 a , &c. CHLORIDES. The mono chloride or Aurous chloride, AuCl, is produced when ic trichloride is evaporated to dryness, and exposed to a heat of 227 C. (440 F.), until chlorine ceases to be exhaled. It forms a yellowish-white lass, insoluble in water. In contact with that liquid it is decomposed lowly in the cold, and rapidly by the aid of heat, into metallic gold and trichloride. The trichloride, or Auric chloride, AuCl 3 , is the most important compound ' gold : it is always produced when gold is dissolved in nitro-muriatic acid. 370 TRIAD METALS. The deep-yellow solution thus obtained yields, by evaporation, yellow crys- tals of the double chloride of gold and hydrogen : when this is cautiously heated, hydrochloric acid is expelled, and the residue, on cooling, solidifies to a red crystalline mass of auric chloride, very deliquescent, and soluble in water, alcohol, and ether. Auric chloride combines with a number of me- tallic chlorides, forming a series of double salts, called chloro-aurates, of which the general formula in the anhydrous state is MCl.AuCl 3 , M repre- senting an atom of a monad metal. These compounds are mostly yellow when in crystals, and red when deprived of water. The ammonium salt, NH 4 Cl.AuCl 3 . OH 2 , crystallizes in transparent needles; the sodium salt, NaCl. AuCl 3 . 20H 2 , in long four-sided prisms. Auric chloride likewise forms crystalline double salts with the hydrochlorides of many organic bases. A mixture of auric chloride with excess of acid potassium or sodium car- bonate is used for gilding small ornamental articles of copper: these are cleaned by dilute nitric acid, and then boiled in the mixture for some time, by which means they acquire a thin but perfect coating of reduced gold. OXIDES. The monoxide, or Aurous oxide, is produced when caustic potash in solution is poured upon the monochloride. It is a green powder, partly soluble in the alkaline liquid ; the solution rapidly decomposes into metallic gold, which subsides, and auric oxide, which remains dissolved. Trioxide, or Auric oxide, Au0 3 . When magnesia is added to auric chlor- ide, and the sparingly soluble aurate of magnesium well washed and digested with nitric acid, auric oxide is left as an insoluble reddish-yellow powder, which when dry becomes chestnut-brown. It is easily reduced by heat, and also by mere exposure to light; it is insoluble in oxygen-acids, with the exception of strong nitric acid, insoluble in hydrofluoric acid, easily dissolved by hydrochloric and hydrobromic acids. Alkalies dissolve it freely: indeed, the acid properties of this substance are very strongly marked ; it partially decomposes a solution of potassium chloride when boiled with that liquid, potassium hydrate being produced. When digested with ammonia, it yields fulminating gold consisting, according to Berzelius, of Au 2 3 .4NH 3 OH 2 . The compounds of auric oxide with alkalies are called auratcs. The potassium salt, Au 2 3 .OK 2 . 60H 2 , or Au0 2 K.30H 2 , is a crystalline salt, the solution of which is sometimes used as a bath for electro-gilding. A com- pound of aurate and acid sulphite of potassium, or potassium aurosulphite, 2(Au0 2 K.4S0 3 HK) . OII 2 . is deposited in yellow needles when potassium sulphite is added, drop by drop, to an alkaline solution of potassium aurate. - Gold shows but little tendency to form oxygen-salts. Auric oxide dis- solves in strong nitric acid, but the solution is decomposed by evaporation or dilution. A sodio-aurous hyposulphite, (S 2 3 ) 2 AuNa 3 .20H 2 , is prepared by mixing the concentrated solutions of auric chloride and sodium hyposul- phite, and precipitating with alcohol. It is very soluble in water and crystallizes in colorless needles. Its solution is used for fixing daguerreo- type pictures. With barium chloride, it yields a gelatinous precipitate of bario-aurous hyposulphite, (S 2 3 ) 4 Au 2 Ba / ' / 3 . SULPHIDES. Aurous sulphide, Au 2 S, is formed as a dark-brown, almost black precipitate when hydrogen sulphide is passed into a boiling solution of auric chloride. It forms sulphur-salts with the monosulphidcs of potas- sium and sodium. Auric sulphide, Au 2 S 3 , is precipitated in yellow flocks when hydrogen sulphide is passed into a cold dilute solution of auric chloride. Both these sulphides dissolve in ammonium sulphide. The presence of gold in solution may be detected by the brown precipi- tate with ferrous sulphate, fusible before the blowpipe to a bead of metallic GOLD. 371 gold; also by the brownish-purple precipitate, called "Purple of Cassius," formed when stannous chloride is added to dilute gold solutions. The com- position of this precipitate is not exactly known, but after ignition it doubtless consists of a mixture of stannic oxide and metallic gold.* It is used in enamel painting. Oxalic acid slowly reduces gold to the metallic state: to insure complete precipitation, the gold-solution must be digested with it for 24 hours. For the quantitative analysis of a solution containing gold and other metals, oxalic acid is in most cases a more convenient precipitant than ferrous sul- phate; inasmuch as, if the quantities of the other metals are also to be determined, the presence of a large quantity of iron salt may complicate the analysis considerably. Gold intended for coin, and most other purposes, is always alloyed with a certain proportion of silver or copper, to increase its hardness and durability: the first-named metal confers a pale greenish color. English standard gold contains ^ of alloy, now always copper. Gold when alloyed with copper may be estimated by fusion in a cupel with lead, in the same way as in the alloy with silver. If the alloy be free from silver, the weight of the globule of gold left in the cupel will, after repeated fusions, accu- rately represent the quantity of gold which is present in the alloy. But if the alloy contains silver, that metal remains with the gold after cupella- tion. In this case the original alloy, consisting of gold, silver, and copper, is fused in the mutfle together with lead and silver; the alloy of gold and silver remaining after cupellation is then boiled with nitric acid, which dissolves the silver, the gold being left behind. By treatment of the alloy of gold and silver with nitric acid, an accurate separation is obtained only when the two metals are present in certain proportions. If the alloy con- tains but little silver, that metal is protected from the action of the nitric acid by the gold ; again, if it contains too much silver, the gold is left as a powder when the silver is dissolved out. Experience has shown that the most favorable proportions are J gold to f silver ; the gold is then left pure, retaining the original shape of the alloy, and can be easily dried and weighed. The quantity of silver which is added to the alloy must there- fore vary with the amount of gold which it contains. Gold-leaf is made by rolling out plates of pure gold as thin as possible, and then beating them between folds of membrane with a heavy hammer, until the requisite degree or tenuity has been reached. The leaf is made to adhere to wood, &c., by size or varnish. Gilding on copper has very generally been performed by dipping the articles into a solution of mercury nitrate, and then shaking them with a small lump of a soft amalgam of gold with that metal, which thus be- comes spread over their surfaces: the articles are subsequently heated to expel the mercury, and then burnished. Gilding on steel is done either by applying a solution of auric chloride in ether, or by roughening the sur- face of the metal, heating it, and applying gold-leaf with a burnisher. Gilding by electrolysis an elegant, and simple method, now rapidly super- ceding many of the others has already been noticed. The solution usu- ally employed is obtained by dissolving oxide or cyanide of gold in a solu- tion of potassium cyanide. * Graham's Elements of Chemistry, Am. edit. p. 466, CLASS IV. TETRAD METALS. GROUP L PLATINUM METALS. PLATINUM. Atomic weight, 197-4. Symbol, Pt. "QLATINUM, palladium, rhodium, iridium, ruthenium, and osmium, form a group of metals, allied in some cases by properties in common, and still more closely by their natural association. Crude platinum, a native alloy of platinum, palladium, rhodium, iridium, and a little iron, occurs in grains and rolled masses, sometimes of tolerably large dimensions, mixed with gravel and transported materials, on the slope of the Ural mountains, in Russia, in Brazil, and Ceylon, and in a few other places. It has never been seen in the rock, which, however, is judged from the accompanying materials to have been serpentine. It is stated to be always present in small quantities with native silver. From this substance platinum is prepared by the following process : The crude metal is acted upon as far as possible by nitro-muriatic acid, contain- ing an excess of hydrochloric acid and slightly diluted with water, in order to dissolve as small a quantity of iridium as possible: to the deep yellow- ish-red and highly acid solution thus produced, sal-ammoniac is added, by which nearly the whole of the platinum is thrown down in the state of am- monium platinochloride. This substance, washed with a little cold water, dried, and heated to redness, leaves metallic platinum in the spongy state. This metal cannot be fused into a compact mass by ordinary furnace-heat, but the same object may be accomplished by taking advantage of its prop- erty of welding, like iron, at a high temperature. The spongy platinum is made into a thin uniform paste with water, introduced into a slightly conical mould of brass, and subjected to a graduated pressure, by which the water is squeezed out, and the mass rendered at length sufficiently solid to bear handling. It is then dried, very carefully heated to whiteness, and hammered, or subjected to powerful pressure. If this operation is properly conducted, the platinum will then be in a state to bear forging into a bar, which can afterwards be rolled into plates, or drawn into wire, at pleasure. A method for refining platinum has lately been proposed by MM. Deville and Debray.* It consists in submitting the crude metal to the action of an intensely high temperature in a crucible of lime. The apparatus they em- ploy is as follows: The lower part of the furnace consists of a piece of lime, hollowed out in the centre to the depth of about a quarter of an inch ; a small notch is filed at one side of this basin, through which the metal is introduced and poured out. A cover made of another piece of lime fits on the top of this basin: it is also hollowed to a small extent, and has a conical perforation at the top, into which is inserted the nozzle of an oxy- hydrogen blowpipe. The whole arrangement is firmly bound with iron wire. To use the apparatus, the stopcock supplying the hydrogen (or coal gas) is opened and the gas lighted at the notch in the crucible: the oxygen * Ann. Chim. Phys. [3] Ivi. 385. 372 PLATINUM. 373 is then gradually supplied ; and when the furnace is sufficiently hot, the metal is introduced in small pieces through the orifice. By this arrange- ment as much as 50 pounds of platinum and more may be fused at once. All the impurities in the platinum, except the iridium and rhodium, are separated in this manner : the gold and palladium are volatilized ; the sulphur, phosphorus, arsenic, and osmium, oxidized and volatilized ; and the iron and copper oxidized and absorbed by the lime of the crucible. Platinum is a little whiter than iron : it is exceedingly malleable and ductile, both hot and cold, and is very infusible, melting only before the oxy-hydrogen blowpipe, or in the powerful blast-furnace just described. It is the heaviest substance known, its specific gravity being 21-5. Neither air, moisture, nor the ordinary acids attack platinum in the slightest degree at any temperature : hence its great value in the construction of chemical vessels. It is dissolved by nitro-muriatic acid, and superficially oxidized by fused potassium hydrate, which enters into combination with the oxide. The remarkable property of the spongy metal to determine the union of oxygen and hydrogen has been already noticed. There is a still more curious state in which platinum can be obtained that of platinum-black, in which the division is carried much further. It is easily prepared by boiling a solution of platinic chloride, to which an excess of sodium car- bonate and a quantity of sugar have been added, until the precipitate formed after a little time becomes perfectly black, and the supernatant liquid colorless. The black powder is collected on a filter, washed and dried by gentle heat. This substance appears to possess the property of con- densing gases, more especially oxygen, into its pores to a very great extent ; when placed in contact with a solution of formic acid, it converts the latter, with copious effervescence, into carbonic acid ; alcohol, dropped upon the platinum-black, becomes changed by oxidation to acetic acid, the rise of temperature being often sufficiently great to cause inflammation. When exposed to a red-heat, the black substance shrinks in volume, assumes the appearance of common spongy platinum, and loses these peculiarities, which are no doubt the result of its excessively comminuted state. Platinum forms two series of compounds: the platinous compounds, in which it is bivalent, e.g. Pt x/ Cl 2 , Pt /X 0, and the platinic compounds, in which it is quadrivalent, e.g., Pt iv Cl 4 , Pt"0 2 , &c. CHLORIDES. The dichloride, or Platinous chloride, Pt // Cl 2 , is produced when platinic chloride, dried and powdered, is exposed for some time to heat of about 200, whereby half the chlorine is expelled ; also, when sul- phurous acid gas is passed into a solution of the tetrachloride until the latter ceases to give a precipitate with sal-ammoniac. It is a-greenish-gray powder, insoluble in water, but dissolved by hydrochloric acid. The latter solution, mixed with sal-ammoniac or potassium chloride, deposits a double salt in fine red prismatic crystals, containing, in the last case, 2KCl.PtCl 2 . The corresponding sodium-compound is very soluble and difficult to crys- tallize. These double salts are called platinoso-chlorides or chloroplalinites. Platinous chloride is decomposed by heat into chlorine and metallic platinum. The tetrachloride, or Platinic chloride, Pt"Cl 4 , is always formed when platinum is dissolved in nitro-muriatic acid. The acid solution yields, on evaporation to dryness, a red or brown residue, deliquescent, and very soluble both in water and in alcohol; the aqueous solution has a pure orange-yellow tint. Platinic chloride unites with a great variety of metal- lic chlorides, forming double salts called piatwo-chloridet or chloro-platinates ; the most important of these compounds are those containing the metals of the alkalies and ammonium. Potassium platinochloride, 2KCl.PtCl 4 , forms a bright yellow crystalline precipitate, being produced whenever solutions of the chlorides of platinum and of potassium are mixed, or a potassium 32 374 TETRAD METALS. salt mixed with a little hydrochloric acid is added to platinum tetrachloride. It is feebly soluble in water, still less soluble in dilute alcohol, and is de- composed with some difficulty by heat. It is easily reduced by hydrogen at a high temperature, yielding a mixture of potassium chloride and plati- num-black: the latter substance may thus, indeed, be very easily prepared. The sodium-salt, 2NaCl.PtCl 4 .60H 2 , is very soluble, crystallizing in large, transparent, yellow-red prisms of great beauty. The ammonium-salt, 2NH 4 Cl.PtCl 4 . is undistinguishable, in physical characters, from the potassium- salt; it is thrown down as a precipitate of small, transparent, yellow, octo- hedral crystals when sal-ammoniac is mixed with platinic chloride ; it is but feebly soluble in water, still less so in dilute alcohol, and is decomposed by heat, yielding spongy platinum, while sal-ammoniac, hydrochloric acid, and nitrogen are driven off. Platinic chloride also forms crystallizable double salts with the hydrochlorides of many organic bases; with ethy la- mine, for example, the compound, 2[NH 2 (C 2 H 5 )HCl].PtCl 4 . The bromides and iodides of platinum are analogous in composition to the chlorides, and likewise form double salts with alkaline bromides and iodides. OXIDES. The monoxide, or Platinous oxide, Pt /X 0, is obtained by digesting the dichloride with caustic potash, as a black powder, soluble in excess of alkali. It dissolves also in acids with brown color, and the solutions are not precipitated by sal-ammoniac. When platinum dioxide is heated with solution of oxalic acid, it is reduced to monoxide, which remains dissolved. The liquid has a dark-blue color, and deposits fine copper-red needles of platinous oxalate. The dioxide, or Platinic oxide, Pt"0 2 , is best prepared by adding barium nitrate to a solution of platinic sulphate ; barium sulphate and platinic nitrate are then produced, and from the latter caustic soda precipitates one half of the platinum as platinic hydrate. The sulphate is itself obtained by acting with strong nitric acid upon platinum bisulphide, which falls as a black powder when a solution of the tetrachloride is dropped into potas- sium sulphide. Platinic hydrate is a bulky brown powder, which, when gently heated, becomes black and anhydrous. It may also be formed by boiling platinic chloride with a great excess of caustic soda, and then adding acetic acid. It dissolves in acids, and also combines with bases : the salts have a yellow or red tint, and a great disposition to unite with salts of the alkalies and alkaline earths, giving rise to a series of double compounds, which are not precipitated by excess of alkali. A combination of platinic oxide with ammonia exists, which is explosive. Both oxides of platinum are reduced to the metallic state by ignition. SULPHIDES. The compounds Pt r/ S and Pt iv S 2 are produced by the action of hydrogen sulphide, or the sulph-hydrate of an alkali-metal, on the di- chloride and tetrachloride of platinum respectively ; they are both black substances, insoluble in water. Platinic sulphide heated in a close vessel gives off half its sulphur and is reduced to platinous sulphide. It dissolves in alkaline hydrates, carbonates, and sulphides, forming salts called sulpho- platinates, which are decomposed by acids. A.mmoniacal Platinum Compounds. The chlorides, oxides, sulphates, &c., of platinum are capable of taking up two or more molecules of ammonia, and forming compounds analogous in many respects to the ammoniacal mercury compounds already described. There are five series of these compounds, which may be formulated as in the following table, the symbol K- denoting a univalent chlorous radical such as Cl, Br, N0 3 , &c. PLATINUM. 375 I. Diammonio-platinous compounds . 2NH 3 .Pt/ / R 2 . II. Tetrammonio-platinous compounds . 4NH 3 .Pt // R 2 . III. Diarnmonio-platinic compounds . 2NH 3 . Pt iT R 4 . IV. Tetrammonio-platinic compounds . 4NH 3 . Pt iT R 4 . V. Octarnnionio-diplatinic compounds . 8NH 3 . Pt' T 2 R 6 // . Any number of atoms of the univalent radical R may be replaced in these compounds by an equivalent quantity of another radical, univalent or multi- valent, thus giving rise to oxychlorides, nitrato-chlorides, oxynitrates, &c. The diammonio-platinous and tetrammonio-platinic compounds (I. and IV.) may evidently be derived from double and quadruple molecules of am- monium salts, by the substitution of Pt x/ or Pt iv for an equivalent quantity of hydrogen: e.g., 2NH 3 .Pt"Cl 2 =(N 2 H 6 Pt").Cl 2 ; and 4NH 3 .Pt iT Cl 4 =(N 4 H 12 Pt iv ).Cl 4 . The composition of the tetrammonio-platinous compounds (II.) will be understood when it is remembered that, nitrogen being a pentad element, NH 3 , is a bivalent radical, and that any number of such radicals may be added to a compound without disturbing the balance of equivalency (pp. 234, 235). Further, since the addition of NH 3 to any compound con- taining hydrogen comes to the same thing as replacing an atom of hydrogen in that compound by ammonium, NH 4 , these tetrammonio-platinous com- pounds may also be regarded as salts of diammoplatoso-diammonium, that is, of a double ammonium molecule, N 2 E 8 , in which two atoms of hydrogen are replaced by Pt /x , and two more by (NH 4 ) 2 . In the diammonio-platinic compounds (III.), the bivalent radical (Pt^CLj)' 7 plays the same part as Pt x/ in the diammonio-platinous compounds. The following table exhibits the constitution of the several groups of compounds according to these views, taking the chlorides as examples: NH 3 C1 I. 2NH 3 .PtCl 2 = (N 2 H 6 Pt")Cl a = Pt NH 3 C1 NH 3 C1 NH 3 II. 4NH 3 .Pt"Cl 2 = [N 2 H 4 (NH 4 ) 2 Pt"]Cl 2 = Pt NH 3 NH 3 C1 NH 3 C1 III. 2NH 3 .Pt*Cl 4 = [N 2 H 6 (Pt"Cl 2 )"]Cl 2 = PtCl 2 NH 3 C1 N 2 II 6 C1 2 I! IV. 4NH 8 .Pt iT Cl 4 = (N 4 H 12 Pt lT )Cl 4 N 2 H 6 C1 2 . V. The octammonio-diplatinic compounds consist of double molecules of tetrammonio-platinic compounds having two or more molecules of the uni- 376 TETRAD METALS. valent radical R, replaced by an equivalent quantity of a bivalent radical : e. ff ., the oxynitrate = 8NH 3 .Pt* 2 (N0 3 ) 6 O" = (N 8 H M Pt* 2 ) j (^s). I. Diammonio-platinous Compounds. These compounds are formed by the action of heat on those of the following series, half the ammonia of the latter being then given off. They are for the most part insoluble in water, but dissolve in ammonia, reproducing the tetrammonio-platinous com- pounds: they detonate when heated. Chloride, NgHgPf'Cl.j. Of this compound there are three isomeric mod- ifications: a. Fellow, obtained by adding hydrochloric acid, or a soluble chloride, to a solution of diamrnonio-platinous nitrate or sulphate, or by boiling the green modification, y, with ammonium nitrate or sulphate; or, by neutralizing a solution of platinous chloride in hydrochloric acid with ammonium carbonate, heating the mixture to the boiling point, and adding a quantity of ammonia equal to that already contained in the liquid, filter- ing from a dingy green substance, which deposits after a while, then leav- ing the solution to cool, and decanting the supernatant liquid as soon as the yellow salt is deposited. (3. Red. If, in the last mode of preparation, the ammonium carbonate, instead of being added at once in excess, be added drop by drop to the hydrochloric acid solution of platinous chloride, the liquid on cooling deposits small garnet- colored crystals having the form of six-sided tables. This red modification may also be obtained in other ways. y. Green. This modification, usually denominated the green salt of Magnus, was the first discovered of the ammoniacal platinum compounds. It is obtained by gradually adding an acid solution of platinous chloride to caustic ammonia; or by passing sulphurous acid gas into a boiling solution of platinic chloride, till it is completely converted into platinous chloride (and therefore no longer gives a precipitate with sal-ammoniac), and neu- tralizing the solution with ammonia; the compound is then deposited in green needles. The same modification of the salt may also be obtained by adding an acid solution of platinous chloride to a solution of tetrammonio- platinous chloride, N 4 H 12 Pt // Cl 2 . The corresponding iodide, N 2 H 6 Pt x/ I 2 , is a yellow powder, obtained by heating the aqueous solution of the compound, N 4 H l2 Pt // I 2 . It dissolves in ammonia, reproducing the latter compound. The oxide, N 2 H 6 Pt // 0, obtained by heating tetrammonio-platinous hydrate to 110, is a grayish mass, which, when heated to 100 in a close vessel, gives off water, ammonia, and nitrogen, and leaves metallic platinum. The sulphate, N 2 H 6 Pt // S0 4 .OH 2 , and the nitrate, N 2 H 6 Pt // (N0 3 ) 2 , are obtained by boiling the iodide with sulphate and nitrate of silver: they are crystalline and have a strong acid reaction. The sulphate retains a molecule of crys- tallization-water, which cannot be removed without decomposing the salt. II Tetrammonio-platinous Compounds. The chloride, N 4 H l2 Pt // Cl 2 , is pre- pared by boiling platinous chloride, or the green salt of Magnus, with aqueous ammonia till the whole is dissolved, and evaporating the liquid to the crystallizing point. The bromide and iodide of this series are obtained by treating the solution of the sulphate with bromide or iodide of barium : they crystallize in cubes. The oxide, N 4 H 12 Pt // 0, is obtained as a crystal- line mass by decomposing the solution of the sulphate with an equivalent quantity of baryta-water, and evaporating the filtrate in a vacmim. It is strongly alkaline and caustic, like potash, absorbs carbonic acid rapidly from the air, and precipitates silver oxide from the solution of the nitrate. It is a strong base, neutralizing acids completely, and expelling ammonia from its salts. It melts at 110, giving off water and ammonia, and leav- ing diammonio-platinous oxide. Its aqueous solution does not give off ammonia, even when boiled. Carbonates. The oxide absorbs carbon dioxide rapidly from the air, forming first a neutral carbonate, N 4 H, 2 Pt // C0 3 .OH 2 , and afterwards an. PLATINUM. 377 acid salt, N 4 H, 2 Pt"CO s .C0 3 H 2 . The sulphate, N 4 H 12 Pt"S0 4 , and the nitrate, N 4 H, 2 Pt // (N0 3 ) 2 , are obtained by decomposing the chloride with silver sul- phate or nitrate ; they are neutral, and crystallize easily. III. Diammonio-platinic Compounds. The chloride, N 2 H 6 Pt' T Cl 4 , is obtained by passing chlorine gas into boiling water in which diammoriio-platinous chloride (the yellow modification) is suspended. This compound is insolu- ble in cold water, and very slightly soluble in boiling water, or in water containing hydrochloric acid. It dissolves in ammonia at a boiling heat, and the solution, on cooling, deposits a yellow precipitate, consisting of tetnimmoriiacal platinic chloride. It dissolves in boiling potash without evolving ammonia. Nitrates. An oxynitrate, N 2 H 6 Pt lT (NO s ) 2 0", is obtained by boiling the chloride, N 2 H 6 PtCl 4 , for several hours with a dilute solution of silver nitrate. It is a yellow crystalline powder, sparingly soluble in cold, more soluble in boiling water. The normal nitrate, N 2 II 6 Pt iT (N0 3 ) 4 , is obtained by dissolving the oxynitrate in nitric acid: it is yellowish, insoluble in cold water, solu- ble in hot nitric acid. The oxide, N 2 H 6 Pt iv 2 , is obtained by adding ammonia to a boiling solu- tion of diammonio-platinic nitrate ; it is then precipitated in the form of a heavy yellowish, crystalline powder, composed of small shining rhomboi'dal prisms; it is nearly insoluble in boiling water, and resists the action of boiling potash. Heated in a close vessel, it gives off water and ammonia, and leaves metallic platinum. It dissolves readily in dilute acids, even in acetic acid, and forms a large number of crystallizable salts, both neutral and acid, having a yellow color, and sparingly soluble in water.* Another compound of platinic oxide with ammonia, called fulminating platinum, whose composition has not been exactly ascertained, is produced by decomposing ammonium platino-chloride with aqueous potash. It is a straw-colored powder, which detonates slightly when suddenly heated, but strongly when exposed to a gradually increasing heat. IV. Tetrammonio-platinic Compounds. The oxide of this series has not yet been isolated. The chloride, N 4 H l2 Pt iv Cl 4 , is obtained by passing chlorine gas into a solution of tetrarnmonio-platinous chloride ; by dissolving diam- monio-platinic chloride in ammonia, and expelling the excess of ammonia by evaporation ; or by precipitating a solution of tetrammonio-platinic .oxynitrate or nitrato-chloride with hydrochloric acid. It is white, and dis- solves in small quantity in boiling water, from which solution it is deposited in the form of transparent regular octohedrons, having a faint yellow tint. When a solution of this salt is treated with silver nitrate, one-half of the chlorine is very easily precipitated, but to remove even a small portion of the remainder requires a long-continued action of the silver-salt. The cklorobromide, N 4 H l2 Pt lT Br 2 Cl 2 , is prepared by treating tetrammonio-platinous chloride with bromine. An oxynitrate, N 4 H, 2 Pt iT (N0 3 ) 2 ; a nitrato-chloride, NjHpPWNO^Cl,; a MtlphQto-chloride, N 2 H l2 Pt lT (S0 4 )"Cl a ; and an oxalo- chlvrtde, ^ 4 H 12 i't i (C 2 4 )"Cl a , have likewise been obtained. V. Octammonio-diplatinic Compounds. An oxynitrate or basic nitrate, NgH.^ Pt iv 2 (NO 3 ) 6 O // , is produced by boiling tetrammonio-platinous nitrate with nitric acid. It is a colorless, crystalline, detonating salt, slightly soluble in cold water, more soluble in boiling water, insoluble in nitric acid. (Gerhardt.) A nitrat-oxychloride, N g H 24 Pt lT 2 (N0 8 ) 4 p"Cl 2 , discovered by Kaewsky, is formed when Magnus's green salt is boiled with a large excess of nitric acid, lied fumes are then evolved, and the resulting solution de- * Gerhardt, Comtes n-nclus des travaux en Chimie, 1849, p. 273. 32 * 378 TETRAD METALS. posits the nitrat-oxychloride in small brilliant needles, which deflagrate when heated, giving oft' water and sal-aminoniac, and leaving metallic platinum. The nitric acid in this salt may be replaced by an equivalent quantity of carbonic or oxalic acid, yielding the compounds, N 8 H 24 P ir 2 (C0 3 ) // 2 0"C1 2 , and N 8 H 24 Pt iT 2 (C 2 4 )" 2 0" G1 2> both of which are crystallizable and sparingly soluble. A basic oxalo-nitrate, N 8 H 24 Pt iv 2 (C 2 4 ) // 2 (K0 3 ) 2 // , insolu- ble in water, is obtained by adding ammonium oxalate to the oxynitratet (Gerhardt.) Reactions of Platinum Salts. Platinic chloride or a platinic oxygen-salt may be recognized in solution by the yellow precipitate with sal-ammoniac, decomposable by heat, with production of spongy metal. Hydrogen sulphide and ammonium sulphide gradually form a brown precipi- tate of platinic sulphide, soluble in excess of ammonium sulphide. Zinc precipitates metallic platinum. Platinic chloride and sodium platinochloride are employed in analytical investigations to detect the presence of potassium, and separate it from sodium. For the latter purpose, the alkaline salts are converted into chlorides, and in this state mixed with four times their weight of sodium platinochloride in crystals, the whole being dissolved in a little water. When the formation of the yellow salt appears complete, alcohol is added, and the precipitate collected on a weighed filter, washed with weak spirit, carefully dried, and weighed. The potassium chloride is then easily reck- oned from the weight of the double salt ; and this, subtracted from the weight of the mixed chlorides employed, gives that of the sodium chloride by difference ; 100 parts of potassium platinochloride correspond to 30-51 parts of potassium chloride. Capsules and crucibles of platinum are of great value to the chemist: the latter are constantly used in mineral analysis for fusing siliceous matter with alkaline carbonates. -They suffer no injury in this operation, although caustic alkali roughens and corrodes the metal. The experimenter must be particularly careful to avoid introducing any oxide of an easily fusible metal, as that of lead or tin, into a platinum crucible. If reduction should by any means occur, these metals will at once alloy themselves with the platinum, and the vessel will be destroyed. A platinum crucible must never be put naked into a coke or charcoal fire, but always placed within a covered earthen crucible. PALLADIUM. Atomic weight, 106-5. Symbol, Pd. When the solution of crude platinum, from which the greater part of that metal has been precipitated by sal-ammoniac, is neutralized by sodium car- bonate, and mixed with a solution of mercuric cyanide, palladium cyanide separates as a whitish insoluble substance, which, on being washed, dried, and heated to redness, yields metallic palladium in a spongy state. The palladium may then be welded into a mass, in the same manner as platinum. Palladium closely corresponds with platinum in color and appearance ; it is also very malleable and ductile. Its density differs very much from that of platinum, being only 11-8. Palladium is more oxidable than plati- num. When heated to redness in the air, especially in the state of sponge, it acquires a blue or purple superficial film of oxide, which is again reduced at a white heat. This metal is slowly attacked by nitric acid; its best solvent is nitro-muriatic acid. PALLADIUM. 379 Palladium, like platinum, forms two classes of compounds ; namely, the palladious compounds, in which it is bivalent, and the palladic compounds, in which it is quadrivalent. CHLORIDES. The dichloride, or Palladious chloride, Pd x/ Cl 2 , is obtained by dissolving the metal in nitro-muriatic acid, and evaporating the solution to dryness. It is a dark-brown mass, which dissolves in water if the heat has not been too great, arid forms double salts with many metallic chlorides. The palladio-chlorides of ammonium and potassium are much more soluble than the corresponding platino-chlorides : they have a brownish-yellow tint. The tetrachloride, or Palladic chloride, Pd iv Cl 4 , exists only in solution and in combination with the alkaline chlorides. It is formed when the dichlor- ide is digested in nitro-muriatic acid. The solution has an intense brown color, and is decomposed by evaporation. Mixed with potassium chloride, or sal-ammoniac, it gives rise to a red crystalline precipitate, which is but little soluble in water. PALLADIOUS IODIDE, Pd x/ I 2 , is precipitated from the chloride or nitrate by soluble iodides, as a black mass, which gives off its iodine between 300 and 360 C. (572 and 680 F.) Palladium-salts are employed for the quan- titative estimation of iodine, chlorine and bromine not being precipitated by them. OXIDES. The monoxide, or Palladious oxide, Pd x/ 0, is obtained by evapo- rating to dryness, and cautiously heating, the solution of palladium, in nitric acid. It is black, and but little soluble in acids. The hydrate falls as a dark-brown precipitate when sodium carbonate is added to the above solu- tion. It is decomposed by a strong heat. The dioxide, or Palladic oxide, Pd iv 2 , is not known in the separate state. From a solution of palladic chloride, alkalies and alkaline carbonates throw down a brown precipitate consisting of hydrated palladic oxide combined with the alkali. This compound gives off half its oxygen at a moderate heat, and the whole at a higher temperature. From hot solutions, a black precipitate is obtained containing the anhydrous dioxide. The hydrate dis- solves slowly in acids, forming yellow solutions. In strong hydrochloric acid it dissolves without decomposition, forming potansio-palladic chloride, aris- ing from admixed potash ; with dilute hydrochloric acid, on the contrary, it gives off chloride. PALLADIOUS SULPHIDE, Pd /x S, is formed by fusing the metal with sulphur, or by precipitating a solution of a palladious salt with hydrogen sulphide. It is insoluble in ammonium sulphide. AMMONIAC AL PALLADIUM COMPOUNDS. A moderately concentrated solu- tion of palladium dichloride treated with a slight excess of ammonia, yields a beautiful flesh-colored or rose-colored precipitate, consisting of N 2 H 6 Pd // Cl 2 . This precipitate dissolves in a larger excess of ammonia ; and the ammonia- cal solution, when treated with acids, yields a yellow precipitate having the same composition. This yellow modification is likewise obtained by heating the red compound in the moist state to 100, or in the dry state to 200 C. (392 F.) The yellow compound dissolves abundantly in aqueous potash, forming a yellow solution, but without giving off ammonia, even when the liquid is heated to the boiling-point; the red compound behaves in a simi- lar manner, but, before dissolving, is converted into the yellow modification. For this reason, Hugo Miiller regards the red compound as palladium innnio- nio-chloride, 2NH 3 .Pd // CI 2 , and the yellow as palladammomum chloride, N 2 H 6 IM"C1 2 . The yellow compound, digested with water and silver oxide, yields palladammonium oxide, N 2 H 6 Pd // 0, which is a strong base, soluble in 380 TETRAD METALS. water, having an alkaline taste and reaction, and absorbing carbonic acid from the air. Palladammonium sulphite, N 2 H 6 Pd // .S0 3 , is formed by the action of sulphurous acid on the oxide or chloride ; it crystallizes in orange- yellow octohedrons. The sulphite, chloride, iodide, and bromide, have likewise been formed. The compound, 4NH 3 .Pd // Cl 2 , or ammopalladammonium chloride, [N 2 H 4 Pd x/ (NH 4 ) 2 ] // C1 2 , separates from an ammoiiiacal solution of palladammonium chloride in oblique rhombic prisms. The oxide, N 4 H, 2 Pd // 0, obtained by decomposing the solution of this chlor- ide with silver oxide, is also a strong base yielding crystallizable salts.* Palladious salts are well marked by the pale yellowish- white precipitate with solution of mercuric cyanide. It consists of palladious cyanide, Pd x/ Cy 2 , and is converted by heat into the spongy metal. Hydriodic acid and potassium iodide throw down a black precipitate of palladium iodide, visible even to the 500,000th degree of dilution. Palladium is readily alloyed with other metals, as copper ; one of these compounds namely, the alloy with silver has been applied to useful purposes. An amalgam of palladium is now extensively used by dentists for stopping teeth. A native alloy of gold with palladium is found in Brazil. RHODIUM. Atomic weight, 104. Symbol, Rh. The solution from which platinum and palladium have been separated, in the manner already described, is mixed with hydrochloric acid, and evap- orated to dryness. The residue is treated with alcohol of specific gravity 0-8?7, which dissolves everything except the double chloride of rhodium and sodium. This is well washed with spirit, dried, heated to whiteness, and then boiled with water, whereby sodium chloride is dissolved out, and metallic rhodium remains. Thus obtained, rhodium is a white, coherent, spongy mass, more infusible and less capable of being welded than plati- num. Its specific gravity varies from 10-6 to 11. Rhodium is very brittle : reduced to powder and heated in the air, it be- comes oxidized, and the same alteration happens to a greater extent when it is fused with nitrate or bisulphate of potassium. None of the acids, singly or conjoined, dissolve this metal, unless it be in the state of alloy, as with platinum, in which state it is attacked by nitro-muriatic acid. Rhodium forms but one chloride, containing RhCl 3 : hence it might be supposed to be a triad; but, from its analogy to the other platinum metals, it is generally regarded as a tetrad, the chloride just mentioned being RhCl 3 represented by the formula Rh 2 Cl 6 , or I RhCl 3 This chloride is prepared by adding silicofluoric acid to the double chloride of rhodium and potassium, evaporating the filtered solution to dryness, and dissolving the residue in water. It forms a brownish-red deli- quescent mass, soluble in water, with a fine red color. It is decomposed by heat into chlorine and metallic rhodium. Rhodium and Potassium chlorides. The salt, Rh 2 Cl 6 .6KC1.60H 2 , formed by * Hugo Milller, Ann. Ch. Pharm. Ixxxvi. 341. RHODIUM. 381 mixing a solution of rhodic oxide in hydrochloric acid with a strong solu- tion of potassium chloride, crystallizes in sparingly soluble efflorescent prisms. Another double salt containing Rh a Cl 6 .4KCl.'JOH 8 , is prepared by heating in a stream of chlorine a mixture of equal parts ot finely powdered metallic rhodium and potassium chloride. The salt has a fine red color, is soluble in water, and crystallizes in four-sided prisms Rhodium and sodium chloride, Rh 2 Cl 6 .6NaC1.240H 2 , is also a very beautiful red salt, prepared like the last. The ammonium salt, Bh 2 01 6 . 6NH 4 C1. 30H 2 , obtained by de- composing the sodium salt with sal-ammoniac, crystallizes in fine rhombo- hedral prisms. RHODIUM OXIDES. Rhodium forms four oxides, containing RhO, Rh 2 3 , Rh0 2 , and Rh0 3 . The monoxide, RhO, is formed, with incandescence, when the hydrated sesquioxide, Rh 2 3 .30H 2 , is heated in a platinum crucible. It is a dark- gray substance, perfectly indifferent to acids. The sesquioxide or rhodic oxide, Rh 2 3 , obtained by heating the nitrate, is a gray porous mass, with metallic iridescence ; insoluble in acids, easily reduced by hydrogen. It forms two hydrates : Rh 2 3 .30H 2 , or RhH 3 O 3 , obtained by precipitating a solution of rhodium and sodium chloride with potash in presence of alcohol, and Rh 2 3 .50H 2 or RhH 3 3 .OH 2 , formed by precipitating the same salt with aqueous potash. The dioxide, Rh0 2 , obtained by fusing pulverized rhodium or the sesqui- oxide with nitre and potash, and digesting the fused mass with nitric acid, to dissolve off the potash, is a dark-brown substance, insoluble in acids. When chlorine is passed into a solution of rhodic pentahydrate, Rh 2 3 .50H 2 , a black-brown gelatinous precipitate of the trihydrate, Rh 2 8 .30H 2 , is formed at first; but this compound gradually loses its gelatinous consistence, becomes lighter in color, and is finally converted into a green hydrate of the dioxide, Rh0 2 .20H 2 . The alkaline solution at the same time acquires a deep violet-blue color. Trioxide, Rh0 3 . The blue alkaline solution above mentioned, deposits, after a while, a blue powder, becoming green when dry, and yielding, when treated with nitric acid, a blue flocculent substance, consisting of the tri- oxide, easily reduced to the dioxide. RHODIC SULPHATE, (S0 4 ) 3 Rh 2 .120H 2 , formed by oxidizing the sulphide with nitric acid, is a yellowish-white crystalline mass. Potassio-rhodic sul- phate, (S0 4 ) 3 RhK 3 , is a reddish-yellow crystalline powder formed by adding sulphuric acid to a solution of rhodium and potassium chloride. AMMONIACAL RHODIUM COMPOUNDS. An ammonio-chloride, 10NH 3 .Rh 2 Cl 6 , or [N 6 H, 4 Rh /// 2 (NH 4 ) 4 ] vi Cl 6 , is obtained as a yellow crystalline powder on mixing a dilute solution of rhodium and ammonium chloride with excess of ammonia, and leaving the filtered solution to evaporate. The corresponding oxide, 10NH 3 .Rh 2 3 , obtained by heating the chloride with silver oxide, is a strong base, from which the sulphate and oxalate may be obtained in crystalline form. Rhodic salts are, for the most part, rose-colored, and exhibit, in solution, the following reactions: with hi/dror/en sulphide, and ammonium sulphide, a brown precipitate of rhodic sulphide, insoluble in excess of ammonium sulphide: with soluble sulphites, a pale-yellow precipitate, affording a char- acteristic reaction; with potash, a yellow precipitate of rhodic oxide, solu- ble in excess; with ammonia and with alkaline carbonates, a yellow precipitate after a while. No precipitate with alkaline chlorides or mercuric cyanide. Zinc precipitates metallic rhodium. 382 TETKAD METALS. An alloy of steel with a small quantity of rhodium is said to possess ex- tremely valuable properties. IRIDITJM. Atomic weight, 198. Symbol, Ir. When crude platinum is dissolved in nitromuriatic acid, a small quantity of a gray scaly metallic substance usually remains behind, having altogether resisted the action of the acid : this is a native alloy of iridium and osmium, called osmiridium or iridosmine; it is reduced to powder, mixed with an equal weight of dry sodium chloride, and heated to redness in a glass tube, through which a stream of moist chlorine gas is transmitted. The farther extremity of the tube is connected with a receiver containing solution of ammonia. The gas, under these circumstances, is rapidly absorbed, iridium chloride and osmium chloride being produced: the former remains in com- bination with the sodium chloride ; the latter, being a volatile substance, is carried forward into the receiver, where it is decomposed by the water into osmic and hydrochloric acids, which combine with the alkali. The contents of the tube when cold are treated with water, by which the iridium and sodium chloride is dissolved out: this is mixed with an excess of sodium carbonate and evaporated to dryness. The residue is ignited in a crucible, boiled with water, and dried ; it then consists of a mixture of ferric oxide and a combination of iridium oxide with soda : it is reduced by hydrogen at a high temperature, and treated successively with water and strong hy- drochloric acid, by which the alkali and the iron are removed, while me- tallic iridium is left in a finely divided state. By strong pressure and ex- posure to a white heat, a certain degree of compactness may be communi- cated to the metal.* Iridium is a white brittle metal, fusible with great difficulty before the oxy-hydrogen blowpipe. Deville and Debray, by means of their powerful oxy-hydrogen blast furnace, have fused it completely into a pure white mass, resembling polished steel, brittle in the cold, somewhat malleable at a red heat, and having a density equal to that of platinum, viz. 21-15, (21 '8 Hare.) By moistening the pulverulent metal with a small quantity of water, pressing it tightly, first between filtering paper, then very forci- bly in a press, and calcining it at a white heat in a forge-fire, it may be obtained in the form of a compact, very hard mass, capable of taking a good polish, but still very porous, and of a density not exceeding 16-0. After strong ignition it is insoluble in all acids, but when reduced by hy- drogen at low temperatures, it oxidizes slowly at a red heat, and dissolves in nitro-muriatic acid. It is usually rendered soluble by fusing it with nitre and caustic potash, or by mixing it with common salt, or better, with a mixture of the chlorides of potassium and sodium, and igniting it in a current of chlorine, as above described. Iridium forms three series of compounds, namely, the hypoiridious com- pounds, in which it is bivalent, as Ir // Cl 2 , IrO ; the iridious compounds, in IrCl 3 which it is quadrivalent, but apparently trivalent, e. g., Ir 2 Cl 6 = I , IrCl 3 and the iridic compounds, in which it is also quadrivalent, as in IrCl 4 , Ir0 2 , * Osmiridium, however, generally contains platinum, ruthenium, and other metals of the same group, which are not effectually separated by the method above described. The complete separation of the several metals of the platinum group has of late years formed the subject of several elaborate investigations, into which the limits of this work will not permit us to enter. (See Watts's Dictionary of Chemistry, iii. 35 ; iv. 241, 680; v. 101, 124.) IRIDIUM. 383 &c. It appears to be incapable of uniting with more than four atoms of a monad element, and is therefore regarded as a tetrad.* It forms also a trioxide, Ir0 3 , in which it is apparently sexvalent, but the oxide may be represented by the formula Ir , in which the metal appears also to be quadrivalent. CHLORIDES. Iridium appears to form three chlorides, but only two of them namely, the trichloride and tetrachloride have been obtained in definite form. The dichloride, Ir // Cl 2 , is not known in the separate state, but appears to exist in certain double salts, called hypochloriridites. The trichloride or Iridious chloride, Ir 2 Cl 6 , is prepared by strongly heating iridium with nitre, adding water and enough nitric acid to saturate the alkali, warming the mixture, and then dissolving the precipitated hydrate of the sesquioxide in hydrochloric acid ; it forms a dark yellowish-brown solution. This substance combines with other metallic chlorides, forming compounds called irido so- chlorides or chloriridites, which may be prepared by reducing the corresponding chloriridiates with sulphurous acid, hydrogen sulphide, or potassium ferrocyanide. Glaus has obtained the compounds Ir 2 Cl 6 .6NH 4 Cl 60H 2 , Ir 2 Cl 6 .6KC1.60H 2 , and Ir 2 Cl 6 .6NaC1.240H 6 . They are olive-green pulverulent salts, soluble in water. The tetrachloride, or Iridic chloride, IrCl 4 , is obtained in solution by dis- solving very finely divided iridium, or one of its oxides, or the trichloride, in nitromuriatic acid, and heating the liquid to the boiling point. On evaporating the solution, it remains in the form of a black, deliquescent, amorphous mass, translucent with dark-red color at the edges; soluble, with reddish-yellow color, in water. It unites with alkaline chlorides, forming compounds called iridio chlorides or chloriridiates, analogous in com- position to the chloroplatinates. The ammonium salt, IrCl 4 .2NH 4 C1.0H 2 , and the potassium salt, IrCl 4 .2KCl, are formed, as dark-brown crystalline precip- itates, on mixing the solutions of the component chlorides. The potassium salt may also be prepared by passing chlorine over a gently ignited and finely divided mixture of iridium with potassium chloride. It is soluble in boiling water, and crystallizes in black octohedrons, yielding a red powder. The sodium salt, IrCl 4 .2NaC1.60H 2 , prepared like the potassium salt, forms easily soluble black tables and prisms, isomorphous with the corresponding platinum salt. IODIDES. Iridium forms three iodides, IrI 2 , Ir 2 I$, and IrI 4 , analogous to the chlorides, and yielding similar double salts with the iodides of the alkali-metals, f OXIDES. Iridium forms four oxides, IrO, Ir 2 3 , Ir0 2 , and Ir0 3 . The monoxide, or hypoiridious oxide, IrO, is but little known. It is obtained by precipitating an alkaline hypochloriridite with caustic alkali in an atmo- sphere of carbon dioxide (p. 166) ; but on exposure to the air it is quickly converted into a higher oxide. The sesquioxide, or Iridious oxide, Ir 2 3 , was formerly regarded as the most easily formed and most stable of the oxides of iridium ; but, according * A hexchloride, IrC1 6 , was said by Berzelins to be obtained in combination with potassium chloride by fusing iridosmine with nitre; but according to Glaus, the suit thus formed was really a ruthenium compound, having been prepared by Bcrzelius from iridosmiuo containing ruthenium. t Offler, Ueber die lodwrUndungen des Iridiums. Qottingen, 1857, 384: TETRAD METALS. to Glaus, it has a great tendency to take up oxygen and pass to the state of dioxide. It may be prepared by gently igniting a mixture of potassium chloriridite (Ir 2 Cl 6 .6KCl) with sodium carbonate in an atmosphere of car- bon dioxide; on treating the product with water, the sesquioxide remains in the form of a black powder insoluble in acids. It forms two hydrates, Ir 2 3 .30H 2 , and Ir 2 3 .50H 2 . It unites with bases, forming salts which may be called iridites. A solution of a chloriridite in excess of lime-water de- posits, after standing for some time out of contact of air, a dirty yellow precipitate containing Ir 2 3 .3CaO. The dioxide, or Iridic oxide, Ir0 2 , is, according to Glaus, the most easily prepared and most stable of all the oxides of iridium, and is always de- posited in the form of a bulky, indigo-colored hydrate, Ir0 2 .20H 2 , when a solution of either of the chlorides of iridium or their double salts is boiled with an alkali ; but it always retains 3 or 4 per cent, of the alkali. The hydrate may also be obtained by dissolving the hydrated sesquioxide in potash and treating the solution with an acid. It dissolves in acids, form- ing solutions which are dark-brown when concentrated, reddish-yellow when dilute. The trioxide. or Periridic oxide, Ir0 3 , is not known in the free state, but is formed in combination with potash, when iridium is fused for some time with nitre. The resulting blackish-green mass dissolves in water, forming a deep indigo-colored solution of basic potassium periridiate, leaving a black crystalline powder consisting of acid periridiate.* Iridium, like the other platinum metals, shows but little tendency to form oxygen-salts. The oxides dissolve in acids, but no definite salts are obtained in this way. The solution of iridic oxide in sulphuric acid has a dark-brown color, which is not modified by potash in the same manner as that of the dichloride, neither does it yield any blue precipitate on boiling. The only definite oxygen-salts of iridium that have been obtained are double salts containing sulphurous and dithionic acids. Hypo-iridoso-potassic sulphite, S0 3 Ir // .3S0 3 K 2 , is obtained as a white crys- talline powder, when the mother-liquor obtained in preparing potassium chloriridite by passing sulphurous oxide through a solution of the chlor- iridiate, is evaporated to a small bulk. SULPHIDES. Three sulphides of iridium are known, analogous to the first three oxides above described. The sesqvisulphide and disulphide are obtained as brown-black precipitates by treating the solutions of the tri- chloride and tetrachloride respectively with hydrogen sulphide. The mono- sulphide is a grayish-black substance obtained by decomposing either of the higher sulphides in a close vessel. AMMONIACAL COMPOUNDS OF IRIDIUM. The ammonio-chlorides, N 2 H 6 Ir" C1 2 and N 4 H, 2 IrCl 2 , or [N 2 H 4 Ir"(NH 4 ) 2 ]Cl 2 , together with the corresponding sulphates, are prepared like the platinous compounds of analogous compo- sition, which they also resemble in their properties. The nitratochloride, [N 2 H 4 Ir // (NH 4 ) 2 ](N0 3 )Cl, analogous to Gros' platinum nitrate, is formed by heating the chloride, N 2 H 6 IrCl 2 , with strong nitric acid. Tetrammonio-iridic chloride, (N 4 H 12 Ir lv )Cl 2 , is obtained as a violet precipitate by treating the nitrate just mentioned with hydrochloric acid.f The compound, 10NH 3 .Ir 2 Cl 6 , or [rf 8 H 7 Ir'"(NH 4 ) 2 ]'" 2 CV to which there is no analogue in the platinum series, is obtained as a flesh-colored crys- talline powder by prolonged digestion of ammonium chloriridite with warm aqueous ammonia. The corresponding carbonate, nitrate, and sulphate have also been prepared. J * Clans, Ann. Ch. Pharm. lix. 249. f Skoblikoff. Ann. Ch. Pharm. Ixxxiv. 275. j Claus, Beitrafie zur C/iemie der Platinmetalle. Dorpat, 1854. RUTHENIUM. 385 Iridic solutions (containing the dioxide or tetrachloride) are of a dark brown-red color; iridious solutions (containing the sesquioxide or tri- chloride) have an olive-green color. The characters of an iridic solution are best observed with sodium chloriridiate, all the other iridic compounds being but slightly soluble. Iridic solutions give with ammonium or potassium chloride a crystalline precipitate of ammonium or potassium chloriridiate, which is distinguished from the corresponding platinum precipitate by its dark brown-red color, and further by its reduction to soluble chloriridite when treated with solu- tion of hydrogen sulphide. This reaction serves for the separation of iridium from platinum. RUTHENIUM. Atomic weight, 104. Symbol, Ru. This metal, discovered by Glaus, in 1846, occurs in platinum ore, and chiefly in osmiridium, of which there are two varieties one scaly, consist- ing almost wholly of osmium, iridium, and ruthenium, while the other, which is granular, contains but mere traces of osmium and ruthenium, but is very rich in iridium and rhodium. To obtain ruthenium, scaly osmiri- dium is heated to bright redness in a porcelain tube, through which a cur- rent of air (freed from carbonic acid by passing through potash, and from organic matter by passing through oil of vitriol) is drawn by means of an aspirator. The osmium and ruthenium are thereby oxidized, the former being carried forward as tetroxide and condensed in caustic potash solution, while the ruthenium oxide remains behind, together with iridium ; and by fusing this residue with potassium hydrate, treating the mass with water, and leaving the liquid in a corked bottle for about two hours to clarify, an orange-colored solution of potassium rutheniate is obtained, which, when neutralized with nitric acid, deposits velvet-black ruthenium sesquioxide, and this when washed, dried, and ignited in hydrogen, yields the metal. Ruthenium thus prepared, forms porous lumps very much like iridium, and is moderately easy to pulverize. It is the most refractory of all metals except osmium. Deville and Debray have, however, fused it by placing it in the hottest part of the oxy-hydrogen flame. After fusion it has a density of 11-4; that of the porous metal is 8-6. Ruthenium is scarcely attacked by nitromuriatic acid. It is, however, more easily oxidized than platinum, or even than silver. When pure it is easily oxidized by fusion with potassium hydrate, still more easily on addi- tion of a small quantity of nitrate or chlorate, producing potassium ruthe- niate, which dissolves in water with orange -yellow color. CHLORIDES. Ruthenium is a tetrad, like the other platinum metals, and forms three chlorides, RuCl 2 , Ru 2 Cl 6 , and RuCl 4 . The dichloride, RuCl 2 , is produced, together with the trichloride, by igniting pulverized ruthenium in a stream of chlorine, the trichloride then volatilizing, while the dichloride remains in the form of a black crystalline powder, insoluble in water and in all acids, even nitro-muriatic acid, and only partially decomposed by alkalies. A soluble dichloride is formed by passing sulpliydric acid gas into a solution of the trichloride, a brown sul- phide being then precipitated, and the solution acquiring a lino blue color. The trichloride or Ruthcnious chloride, Ru. 2 Cl 6 . prepared by precipitating a solution of potassic rutheniate with an acid, dissolving the precipitated black oxide in hydrochloric acid, and evaporating, is a yellow-brown, crys- talline, very deliquescent mass, becoming dark-green and blue at certain 33 386 TETRAD METALS. points when strongly heated. It dissolves easily in water and in alcohol, leaving a small quantity of a yellow insoluble salt. The concentrated solution of ruthenious chloride, mixed with concen- trated solutions of the chlorides of potassium and ammonium, yields the double salts, Ru 2 Cl 6 .4KCl, and Ru 2 C1 6 .4NH 4 Cl, in the form of crystalline precipitates, with violet iridescence, very slightly soluble in water, insoluble in alcohol. The tetrachloride or Ruthenic chloride, RuCl 4 , is known only in its double salts. The potassium-salt, RuCl 4 .2KCl, is prepared by mixing a solution of ruthenic hydrate in hydrochloric acid with potassium chloride, and evapo- rating to the crystallizing point. It is brown, with rose-colored iridescence, very soluble in water, but insoluble in alcohol. The ammonium salt, RuCl 4 .2NH 4 Cl, is prepared like the potassium salt, which it resembles closely. OXIDES. Ruthenium forms five oxides, viz., RuO, Ru 2 3 , Ru0 2 , Ru0 3 , and Ru0 4 , the fourth, however, being known only in combination. The monoxide, RuO, obtained by calcining the dichloride with sodium carbonate in a current of carbon dioxide, and washing the residue with water, has a dark-gray color and metallic lustre ; is not acted upon by acids ; but is reduced by hydrogen at ordinary temperatures. The sesquioxide, or Ruthenious oxide, Ru 2 3 , is a bluish-black powder, formed by heating the metal in the air. The corresponding hydrate, Ru 2 3 . 30H, or RuH g 3 , is obtained by precipitating ruthenious chloride with an alkaline carbonate, as a blackish-brown substance which dissolves with yellow color in acids. The dioxide, or Ruthenic oxide, Ru0 2 , is a black-blue powder, obtained by roasting the disulphide. Ruthenic hydrate, Ru0 2 .20H 2 , or Ru iv H 4 4 , is ob- tained as a gelatinous precipitate by decomposing potassium chlororutheniate with sodium carbonate. The trioxide, Ru0 3 , commonly called ruthenic acid, is known only as a potassium-salt, wjiich is obtained by igniting ruthenium with caustic potash and nitre: it forms an orange-yellow solution. The tetroxide, Ru0 4 , is a volatile compound, analogous to osmic tetroxide, ob- tained by heating ruthenium with potash and nitre, in a silver crucible, dis- solving the fused mass in water, and passing chlorine through the solution in a tubulated retort, connected by a condensing-tube with a receiver con- taining potash. The tetroxide then passes over and condenses in the neck of the retort, and in the tube, as a golden-yellow crystalline crust, which melts between 50 and 60. It is heavier than oil of vitriol, dissolves slightly in water, readily in hydrochloric acid, forming a solution easily decomposed by alcohol, sulphurous acid, and other reducing agents. SULPHIDES. Hydrogen sulphide, passed into a solution of either of the chlorides of ruthenium, usually forms a precipitate consisting of ruthenium sulphide and oxysulphide mixed with free sulphur. The blue solution of the dichloride yields a dark-brown sesquisulphide, Ru 2 S 3 . When hydrogen sulphide is passed for a long time into a solution of the trichloride, ruthe- nium disulphide, RuS 2 , is formed, as a brown-yellow precipitate, becoming dark-brown by calcination. AMMONIACAL RUTHENIUM COMPOUNDS. Tetrammonio-hyporuthcnious chlor- ide, 4NH 3 .RuCl 2 .30H 2 , or [N 2 H 4 Ru // (NH 4 ) 2 ]Cl 2 30H 2 , is formed by boiling the solution of ammonium chlororutheniate (RuCl 4 .2NH 4 Cl), with ammonia. It forms golden-yellow oblique rhombic crystals, very soluble in water, in- soluble in alcohol. Treated with silver oxide, it yields the corresponding oxide, 4NH 3 RuO, which, however, is decomposed by evaporation of its solution, giving oft 7 half its ammonia, and leaving the compound 2NH 3 .RuO, or (N 2 H 6 Ru // )0. The carbonate, nitrate, and sulphate, obtained by treat- ing this last-mentioned oxide with the corresponding silver salts, form yellow crystals. OSMIUM. 387 The compounds of ruthenium may readily be distinguished from those of the other platinum-metals, by fusing a few milligrammes of the sub- stance in a platinum-spoon, with a large excess of nitre, leaving it to cool when it ceases to froth, and dissolving the cooled mass in a little distilled water. An orange-yellow solution of potassium rutheniate is thus formed, which on addition of a drop or two of nitric acid, yields a bulky, black precipitate ; and on adding hydrochloric acid to the liquid, with the pre- cipitate still in it, and heating it in a porcelain crucible, the oxide dissolves, forming a solution which has a fine orange-yellow when concentrated, and when treated with hydrogen-sulphide, till it becomes nearly black, yields a nitrate of a splendid sky-blue color. Characteristic reactions are also ob- tained with potassium sulphocyanate, which colors the liquid deep red, chang- ing to violet on heating, and with lead acetate, which forms a purple-red precipitate. OSMIUM. Atomic weight, 199. Symbol, Os. The separation of this metal from iridium, ruthenium, and the other metals with which it is associated in native osmiridium, and in platinum residues, depends chiefly on its ready oxidation with nitric or nitromuratic acid, or by ignition in air or oxygen, and the volatility of the oxide thus produced. To prepare metallic osmium, the solution obtained by condensing the vapor of osmium tetroxide in potash (p. 385) is mixed with excess of hy- drochloric acid, and digested with mercury in a well-closed bottle at 40 C. (104 F.) The osmium is then reduced by the mercury, and an amalgam is formed, which, when distilled in a stream of hydrogen till all the mer- cury and calomel are expelled, leaves metallic osmium in the form of a black powder (Berzelius). The metal may also be obtained by igniting ammonium chloro-osmite with sal-ammoniac. The properties of osmium vary according to its mode of preparation. In the pulverulent state it is black, destitute of metallic lustre, which, how- ever, it acquires by burnishing; in the compact state, as obtained by Ber- zelius's method above described, it exhibits metallic lustre, and has a den- sity of 10. Deville and Debray, by igniting precipitated osmium sulphide in a crucible of gas-coke, at the melting heat of nickel, obtained it in bluish-black, easily divisible lumps. When heated to the melting point of rhodium, it becomes more compact, and acquires a density of 21-3 to 21-4. At a still higher temperature, capable of melting ruthenium and iridium, and volatilizing platinum, osmium likewise volatilizes, but still does not melt; in fact, it is the most refractory of all metals. Osmium in the finely divided state is highly combustible, continuing to burn when set on fire, till it is all volatilized as tetroxide. In this state also it is easily oxidized by nitric or nitromuriatic acid, being converted into tetroxide. But after exposure to a red heat, it becomes less combus- tible, and is not oxidized by nitric or nitromiiriatic acid. Osmium which has been heated to the melting-point of rhodium, does not give off any vapor of tetroxide -when heated in the air to the melting-point of zinc, but takes fire at higher temperatures. OSMIUM CHLORIDES. Osmium forms three chlorides, analogous to those of iridium and ruthenium. When it is heated in dry chlorine g: s, there is formed, first a blue-black sublimate of the dichloride, then a red subli- mate of the tetrachloride. The dichloride, or hypo-osmious chloride, dissolves 388 TETRAD METALS. in water with dark violet-blue color. It is likewise formed by the action of reducing agents on either of the higher chlorides, into which, on the other hand, it is easily converted by oxidation. The addition of potassium chloride renders it more stable, by forming a double salt. The trichloride, Os 2 C1 6 , has not been isolated, but is contained in the solution obtained by treating the sesquioxide with hydrochloric acid. It forms double salts with alkaline chlorides. The potassium-salt, Os 2 Cl 6 .6KC1.60H 2 , is produced together with potassium chlorosmate, when a mixture of pulverized osmium and potassium chloride is ignited in chlorine gas; it forms dark red-brown crystals. The tetrachloride, or Osmic chloride, OsCl 4 , is the red compound which con- stitutes the principal part of the product obtained by igniting osmium in chlorine gas. It dissolves with yellow color in water and alcohol, and is decomposed quickly in dilute solution, more slowly in presence of hydro- chloric acid or metallic chlorides, yielding a black precipitate of osmic oxide, and a solution of osmium tetroxide in hydrochloric acid. Osmic chloride unites with the chlorides of the alkali-metals, forming salts sometimes called osmio chlorides, or chlorosmates. From the solutions of these salts, hydrogen sulphide, and ammonium sulphide, slowly precipitate a yellow-brown sulphide insoluble in alkaline sulphides ; silver nitrate forms an olive-green, stannous chloride a brown precipitate. Tannic acid, on heat- ing, produces a blue color, but no precipitate; potassium ferrocyanide, first a green, then a blue color; potassium iodide, a deep purple-red color. Potash gives a black, ammonia a brown precipitate, slowly in the cold, immediately on boiling. Metallic zinc and sodium formate throw down metallic osmium. Sodium osmiochloride, OsCl 4 .2NaCl, prepared by heating a mixture of osmium sulphide and sodium chloride in a current of chlorine, crystallizes in orange-colored rhombic prisms, an inch long, easily soluble in water, and in alcohol. The potassium and ammonium salts, of analogous composi- tion, are obtained as red-brown crystalline precipitates on adding sal-am- moniac or potassium chloride to the solution of the sodium salt. OXIDES. Osmium forms five oxides analogous to those of ruthenium. The monoxide or hypo-osmious oxide, OsO, is obtained by igniting hypo-osmi- ous sulphite in a stream of carbonic acid gas ; also as blue-black hydrate, by heating the same salt with strong potash solution in a closed vessel. Hypo-osmious sulphite, S0 3 0s // or S0 2 ,OsO, is a black-blue salt, produced by mixing the aqueous solution of osmium tetroxide with sulphurous acid. The sesquioxide or osmious oxide, Os 2 3 , is obtained by heating either of the double salts of the trichloride with sodium carbonate in a stream of car- bonic acid gas. It is a black powder insoluble in acids. The hydrate, ob- tained by precipitation, has a dirty brown-red color, is soluble in acids, but does not yield pure salts. The dioxide, or Osmic oxide, OsO ? , is obtained as a black insoluble powder, by heating potassium osmiochloride with sodium carbonate in a stream of carbonic acid gas, or in copper-red metallic-shining lumps, by heating the corresponding hydrate. Osmic hydrate, OsO r 20H 2 , is obtained by precipi- tating a solution of potassium osrnio-chloride with potash, at the boiling heat, or in greater purity by mixing a solution of potassic osmite, Os0 3 .K 2 0, with dilute nitric acid. The trioxide, Os0 3 , is not known in the free state, but combines with alkalies, forming salts called osmitcs, which are produced by the action of reducing agents on the tetroxide in presence of alkalies. The potassium salt, Os0 3 .K 2 0.20H 2 , is a rose-colored crystalline powder. The tetroxide, Os0 4 , commonly called osmic acid, is the volatile, strong- smelling compound, formed when osmium or either of its lower oxides is heated in the air, or treated with nitric or nitromuriatic acid. It may be TIN. 389 prepared by heating osmium in a current of oxygen gas, and condenses in the cool part of the apparatus in colorless, transparent crystals. It melts below 100, and boils at a temperature a little above its melting point. Its vapor has an intolerably pungent odor ; attacks the eyes strongly and pain- fully, and is excessively poisonous. Osmium tetroxide is dissolved slowly, but in considerable quantity, by water, forming an acid solution. It is a powerful oxidizing agent, decolorizing indigo solution, separating iodine from potassium iodide, converting alcohol into aldehyde and acetic acid, &c. It dissolves in alkalies, forming yellow-red solutions, which are inodorous when cold, but when heated, give off the tetroxide and free oxygen, leaving a residue of alkaline osmite. SULPHIDES. Osmium burns in sulphur-vapor. Five sulphides of osmium are said to exist, analogous to the oxides, the first four being produced by decomposing the corresponding chlorides with hydrogen sulphide, and the tetrasulphide by passing that gas into a solution of the tetroxide. The last is a sulphur-acid, perfectly soluble in water, whereas the others are sul- phur-bases, slightly soluble in water, and forming deep yellow solutions. AMMONIACAL OSMIUM COMPOUNDS. A cold solution of potassium osmite, mixed with sal-ammoniac, yields a yellow crystalline precipitate, consisting, according to Glaus, of hydra-ted osmammonium chloride, (N 2 H 6 Os // )Cl 2 . An aqueous solution of the tetroxide treated with ammonia, yields a brown- black powder, consisting of N 2 H 8 Os0 3 , or [N 2 H 6 (OsO)"]O.OH 2 . OSMIAMIG ACID, Os 2 N 2 5 H 2 . The potassium-salt, of this bibasic acid, Os 2 N 2 5 K 2 , is produced by the action of ammonia on a hot solution of osmium tetroxide in excess of potash : 60s0 4 -f 8NH 3 -f 60KH == 30s 2 N 2 5 K 2 -f 150H 2 -f N 2 . It separates as a yellow crystalline powder, and its solution, treated with sil- ver nitrate, yields a precipitate of silver osmiamate, Os 2 N 2 5 Ag 2 , from which the aqueous acid may be prepared by decomposition with hydrochloric acid. It is a strong acid, decomposing, not only the carbonates, but also the chlor- ides, of potassium and sodium. The osmiamates of the alkali-metals and alkaline earth-metals are soluble in water ; the lead, mercury, and silver salts are insoluble. All osmium compounds, when heated with excess of nitric acid, give off the unpleasant odor of osmium-tetroxide. By ignition in hydrogen gas, they are reduced to metallic osmium, which, as well as the lower oxides, emits the same odor when heated in contact with the air. The reactions of osmium salts in solution have already been described. GROUP II. TIN. Atomic weight, 118. Symbol, Sn. (Stannum.) This valuable metal occurs in the state of oxide, and more rarely as sul- phide : the principal tin mines are those of Saxony and Bohemia, Malacca, and more especially Cornwall. In Cornwall the tin-stone is found as a con- stituent of metal-bearing veins, associated with copper ore, in granite and slate-rocks; and as an alluvial deposit, mixed with rounded pebbles, in the beds of several small rivers. The first variety is called mine- and the 33* 390 TETRAD METALS. second stream-tin. Tin oxide is also found disseminated through the rock itself in small crystals. To prepare the ore for reduction, it is stamped to powder, washed, to separate as much as possible of the earthy matter, and roasted, to expel sulphur and arsenic: it is then strongly heated with coal, and the metal thus obtained is cast into large blocks. Two varieties of commercial tin are known, called grain- and bar-tin; the first is the best; it is prepared from the stream ore. Pure tin has a white color, approaching that of silver; it is soft and malleable, and when bent or twisted emits a peculiar crackling sound; it has a density of 7-3 and melts at 237 C. (457 F.) Tin is but little acted upon by air and water, even conjointly; when heated above its melting point, it oxidizes rapidly, becoming converted into a whitish powder, used in the arts for polishing under the name of putty-powder. The metal is attacked and dissolved by hydrochloric acid, with evolution of hydrogen ; nitric acid acts with great energy, converting it into a white hydrate of the dioxide. Tin is a tetrad metal, and forms two well-defined classes of compounds, namely, the stannous compounds, in which it is bivalent, as Sn /x Cl 2 , Sn x/ I 2 , Sn x/ 0, &c., and the stannic compounds, in which it is quadrivalent, as Sn' T Cl 4 , Sn iv O., &c. ; also a few compounds called stannoso-stannic compounds, of inter- mediate composition, and probably formed by combination of stannous and stannic compounds, e.g., Sn 2 Cl 6 =rSnCl 2 .Snd 4 ; Sn 2 3 SnO.Sn0 2 . CHLORIDES. The dichloride, or Stannous chloride, SnCl 2 , is obtained in the anhydrous state by distilling a mixture of calomel and powdered tin, pre- pared by agitating the melted metal in a wooden box until it solidifies. It is a gray, resinous-looking substance, fusible below redness, and volatile at a high temperature. The hydrated, chloride, commonly called tin-salt, is easily prepared by dis- solving metallic tin in hot hydrochloric acid. It crystallizes in needles con- taining SnCl 2 .20H 2 , which are freely soluble in a small quantity of water, but are apt to be decomposed in part when put into a large mass, unless hydrochloric acid in excess be present. Solution of stannous chloride is employed as a deoxidizing agent ; it reduces the salts of mercury and other metals of the same class. It is also extensively employed as a mordant in dyeing and calico-printing; sometimes also as an antichlore. Stannous chloride unites with the chlorides of the alkali-metals, forming crystallizable double salts, SnCl 2 .2KCl, &c., called Stannoso-chlorides or Chloroslannitcs. The tetrachloridj, or Stannic chloride, SnCl 4 , is an old and very curious compound, formerly called fuming liquor of Libavius. It is made by ex- posing metallic tin to the action of chlorine, or, more conveniently, by dis- tilling a mixture of 1 part of powdered tin with 5 parts of corrosive subli- mate It is a thin, colorless, mobile liquid, boiling at 120 C. (248 F.), and yielding a colorless invisible vapor. It fumes in the air, and when mixed with a third part of water, solidifies to a soft fusible mass called butter of tin. The solution of stannic chloride is much employed by the dyer for the brightening and fixing of red colors, and is sometimes designated by the old names, "composition, physic, or tin solution;" it is commonly prepared by dissolving metallic tin in a mixture of hydrochloric and nitric acids, care being taken to avoid too great elevation ot temperature. The solution when evaporated yields a deliquescent crystalline hydrate, SnCl 4 ,50H 2 . Stannic chloride forms, with the chlorides of the alkali -meta.ls and alkaline earth-metals, crystalline double salts, called Slannochloridcs or Chloroslannates, e.g., SnCl 4 .2NH 4 Cl; SnCl 4 .BaCl 2 , &c. It also forms crystalline compounds with the pentachloride and oxychloride of phosphorus, viz., SnCl 4 .PCl 5 . ;ind SnCl 4 .POCl 3 , and a solid compound with phosphine, containing 3SnCl 4 2PH 3 . TIN. 391 The trichloride, or Stannoso- stannic chloride, known only in solution, is produced by dissolving the sesquioxide in hydrochloric acid. The solu- tion acts like a mixture of the dichloride and tetrachloride. FLUORIDES. Stannous fluoride, SnF 2 , obtained by evaporating the solution of stannous oxide in hydrofluoric acid, crystallizes in small shining opaque prisms. Stannic fluoride, SnF 4 , is not known in the free state, but unites with other metallic fluorides, forming crystalline compounds called stanno- ftuorides or jluostannatcs, isomorphous with the corresponding silicofluor- ides, titariofluorides, and zircofluorides. The potassium salt contains SnF 4 .2KC1.0H 2 , the barium salt, SnF 4 .BaF 2 , &c. OXIDES. The monoxide, or Stannous oxide, SnO, is produced by heating stannous oxalate out of contact with the air; also by igniting starmous hy- drate. This hydrate, 2SnO.OH 2 , or Sn 2 H 2 3 , is obtained as a white precipi- tate by decomposing stannous chloride with an alkaline carbonate, carbon dioxide gas being at the same time evolved. This hydrate, carefully washed, dried, and heated in an atmosphere of carbon dioxide, leaves anhydrous stannous oxide as a dense black powder, which is permanent in the air, but when touched with a red-hot body, takes fire and burns like tinder, pro- ducing the dioxide. The hydrate is freely soluble in caustic potash; the solution decomposes by keeping into metallic tin and dioxide. It dissolves also in sulphuric acid, forming stannous sulphate, S0 4 Sn x/ , which crystallizes in needles. The sesquioxide, Sn 2 3 , is produced by the action of hydrated ferric oxide upon stannous chloride: it is a grayish, slimy substance, soluble in hydro- chloric acid, and in ammonia. This oxide has been but little examined. The dioxide, or Stannic oxide, Sn0 2 , occurs native as tin-stone or cassi- terite, the common ore of tin, and is easily formed by heating tin, stan- nous oxide, or stannous hydrate in contact with the air. As thus pre- pared, it is a white or yellowish amorphous powder ; but by passing the vapor of stannic chloride mixed with aqueous vapor through a red-hot porcelain tube, it may be obtained in crystals. It is not attacked by acids, even in the concentrated state. Stannic oxide forms two hydrates, differing from one another in compo- sition and properties ; both, however, being acids, and capable of forming salts by exchanging their hydrogen for metals. These hydrates or acids are stannic acid, Sn0 2 .OH 2 , or Sn() 3 IT 2 , and metastannicacid, Sn 6 I0 .50H 2 , orSn g 15 H 10 , the former being capable of exchanging the whole of its hydrogen for metal, and forming the stannates, containing Sn0 3 M 2 ; while the latter ex- changes only one fifth of its hydrogen, forming the metastannates, SnjO^IIgM^. Stannic acid is precipitated by acids from solutions of alkaline stanuates, also from solution of stannic chloride, by calcium or barium carbonate not in excess ; alkaline carbonates throw down an acid stannate. When dried in the air at ordinary temperatures, it has, according to Weber, the com- position, Sn0 2 .20H 2 ; in a vacuum half the water is given off, leaving Sn0 2 .OH 2 . Stannic hydrate dissolves in the stronger acids, forming the stannic salts; thus with sulphuric acid it forms stannic sulphate (S0 4 ) 2 Sn iT , or 2SO s .Sn0 2 . Hydrochloric acid converts it into the tetrachloride. The stannic salts of oxygen acids are very unstable. Stannates. Stannic hydrate exhibits acid much more decidedly than basic properties. It forms easily soluble salts with the alkalies, and from these the insoluble stannates of the earth-metals and heavy metals may be obtained by precipitation. Sodium stannate, SnO 3 N,%. which is much used in calico-printing as a ''preparing salt" or mordant, is produced on the large scale by fusing tin-stone with hydrate, nitrate, chloride, or sulphide 392 TETRAD METALS. of Bodium ; by boiling the tin ore with caustic soda solution ; by fusing metallic tin with a mixture of sodium nitrate and carbonate ; or heating it with soda solution mixed with sodium nitrate and chloride.* Metastannic acid is produced hy the action of nitric acid upon tin. When dried in the air at ordinary temperatures, it contains 5Sn0 2 . 100H 2 , or Sn 6 10 H 15 .50H 2 , but at 100 it gives off 5 molecules of water, and is reduced to Sn 5 15 H, . It is a white crystalline powder, insoluble in water and in acids. It dissolves slowly in alkalies forming metastannates, but is grad- ually deposited in its original state as the solution absorbs carbonic acid from the air. The potassium salt, Sn 5 15 H 8 K 2 , or (Sn0 2 ) 6 1 Q K 2 , may be precipitated in the solid state by adding pieces of solid potash to a solution of metastannic acid in cold potash. It is gummy, uncrystallizable, and strongly alkaline. The sodium salt, Sn 5 15 H g Na 2 , prepared in like manner, is crystallo-granular, and dissolves slowly, but completely, in water. The metastannates exist only in the hydrated state, being decomposed when deprived of their basic water. TIN SULPHIDES. The monomlphide, SnS, is prepared by fusing tin with excess of sulphur, and strongly heating the product. It is a lead-gray, brittle substance, fusible at a red heat, and soluble, with evolution of sul- phuretted hydrogen, in hot hydrochloric acid. A sesquisulphide may be formed by gently heating the above compound with a third of its weight of sulphur : it is yellowish-gray, and easily decomposed by heat. The bisul- phide, SnS 2 , or Mosaic gold, is prepared by exposing to a low red heat, in a glass flask, a mixture of 12 parts of tin, 6 of mercury, 6 of sal-ammoniac, and 7 of flowers of sulphur. Sal-ammoniac, cinnabar, and stannous chlor- ide sublime, while the bisulphide remains at the bottom of the vessel in the form of brilliant gold-colored scales: it is used as a substitute for gold pow- der. The same compound is obtained as an amorphous light-yellow pow- der by passing hydrogen sulphide into a solution of stannic chloride. Stannous salts give with : Fixed caustic alkalies : white hydrate, soluble in excess. Ammonia : carbonates "| of potassium, sodium, V white hydrate, nearly insoluble in excess, and ammonium . . ) ( black-brown precipitate of monosulphide,- sol- Hydrogen sulphide . . J uble in ammonium sulphide containing excess Ammonium sulphide . 1 of sulphur, and reprecipitated by acids as yellow bisulphide. Stannic salts give with : Fixed caustic alkalies: white hydrate, soluble in excess. Ammonia: white hydrate, slightly soluble in excess. Alkaline carbonates: white hydrate, slightly soluble in excess. Ammonium carbonate: white hydrate, insoluble. Hydrogen sulphide : yellow precipitate of bisulphide. Ammonium sulphide: the same, soluble in excess. Trichloride of gold, added to a dilute solution of stannous chloride, gives rise to a brownish-purple precipitate, called purple of Cassius (p. 371). The useful applications of tin are very numerous. Tinned plate consists of iron superficially alloyed with this metal ; pewter, of the best kind, is chiefly tin, hardened by the admixture of a little antimony, &c. Cooking- * Richardson and Watts's Chemical Technology, vol. i. pt. iv. p. 35, and pt. v. p. 342. TITANIUM. 393 vessels of copper are visually tinned in the interior. The use of tin solu- tions in dyeing and calico-printing has been already mentioned. TITANIUM. Atomic weight, 50. Symbol, Ti. This is one of the rarer metals, and is never found in the metallic state. The most important titanium minerals are rutile, brookite, and anatase, which are different forms of titanic oxide, and the several varieties of titaniferous iron, consisting of ferrous titanate, sometimes alone, but more generally mixed with ferric or ferroso-ferric oxide. Occasionally in the slag adhering to the bottom of blast-furnaces in which iron ore is reduced, small brilliant copper-colored cubes, hard enough to scratch glass, and in the highest degree infusible, are found. This substance, of which a single smelting furnace in the Hartz produced as much as 80 pounds, was formerly believed to be metallic titanium. Recent researches of Wohler, however, have shown it to be a combination of titanium cyanide with titanium nitride. When these crystals are powdered, mixed with potassium hydrate, and fused, ammonia is evolved, and potassium titanate is formed. Metallic titanium in a finely divided state may be obtained by heating titanium and potassium fluoride with potassium. This element is remarkable for its affinity for nitrogen : when heated in the air, it simultaneously absorbs oxygen and nitrogen. Titanium is tetradic, like tin, and forms two classes of compounds : the titanic compounds, in which it is quadrivalent, e.g. Ti iv Cl 4 , Ti iv 2 , and the titanous compounds, in which it is apparently trivalent but really also quadrivalent, e. g. : TiCL Ti a Cl 6 , or | TiClg. CHLORIDES. Titanous chloride, T5 2 C1 6 , is produced by passing the vapor of titanic chloride mixed with hydrogen through a red-hot tube; it forms dark violet scales having a strong lustre. Titanic chloride, TiCl 4 , is prepared by passing chlorine over an ignited mixture of titanic oxide and charcoal. It is a colorless volatile fuming liquid, having a specific gravity of 1-7609 at 0, vapor density = 6-658, and boiling at 135. It unites very violently with water, and forms definite compounds with ammonia, ammonium chlor- ide, hydrogen cyanide, cyanogen chloride, phosphine, and sulphur tetra- chloride. FLUORIDES. Titanous fluoride, Ti. 2 F 6 , is obtained as a violet powder by igniting potassio-titanic fluoride in hydrogen gas, and treating the resulting mass with hot water. Titanic fluoride, TiF 4 , passes over as a fuming color- less liquid, when titanic oxide is distilled with fluor-spar and fuming sul- phuric acid in a platinum apparatus. It unites with hydrofluoric acid and metallic fluorides, forming double salts called titano-fluorides or fluotitanmiti'*, isomorphous with the silicofluorides, zircofluorides, &c., e. g., TiF 4 .lMvF ; TiF 4 .CaF 2 . OXIDES. The scsquioxide, or Titanous oxide, Ti 2 3 , is obtained by igniting the dioxide in hydrogen, as a black powder, which, when heated in the air to a very high temperature, oxidizes to titanic oxide. The dioxide or Titanic oxide occurs native in three different forms, viz., as rutile and anatase, which are dimetric, and brookite, which is trimetric; of these, anatase is the purest, and rutile the most abundant. To obtain 394 TETRAD METALS. pure titanic oxide, rutile or titaniferous iron ore, reduced to fine powder, is fused with twice its weight of potassium carbonate, and the fused mass is dissolved in dilute hydrofluoric acid, whereupon titano-fluoride of potas- sium soon begins to separate. From the hot aqueous solution of this salt, ammonia throws down snow-white ammonium titanate, which is easily soluble in hydrochloric acid, and when ignited gives reddish-brown lumps of titanic oxide. This oxide is insoluble in water, and in all acids except strong sulphuric acid. By fusing it with six times its weight of acid potas- sium sulphate, a clear yellow mass is obtained, which dissolves perfectly in warm water. Titanic oxide appears to form two hydrates or acids, analogous to stannic and metastannic acids. One of these, called titanic acid, is precipitated by ammonia from a solution of titanic chloride, as a white powder which dis- solves easily in sulphuric, nitric, and hydrochloric acids, even when these acids are rather dilute ; but these dilute solutions, when boiled, deposit metatitanic hydrate, as a soft white powder, which, like the anhydrous oxide, is insoluble in all acids except strong sulphuric acid. The tilanates have not been much studied ; most of them may be repre- sented by the formulae, Ti0 4 M 2 = Ti0 2 .2M 2 0, and Ti0 3 M 2 = Ti0 2 .M 2 (the symbol M denoting a univalent metal). The titanates of calcium and iron occur as natural minerals. The titanates of the alkali-metals are formed by fusing titanic oxide with alkaline hydrates, carbonates, or acid sulphates some of them also in the wet way. When finely pulverized and levigated, they dissolve in moderately warm, concentrated hydrochloric acid ; but the greater part of the dissolved titanic acid is precipitated on boiling the solution with dilute acids. The neutral titanates of the alkali-metals, Ti0 3 M 2 , are insoluble in water, but soluble in acids. The titanates of the earth-metals and heavy metals are insoluble, and may be obtained by pre- cipitation. In a solution of titanic acid in hydrochloric acid, containing as little free acid as possible, tincture of galls produces an orange-colored precipitate ; potassium f err o cyanide, a dark-brown precipitate. Titanic oxide fused with borax, or better, with microcosmic-salt, in the inner blowpipe flame, forms a glass which is yellow while hot, but becomes violet on cooling. The deli- cacy of the reaction is much increased by melting a little metallic zinc in the lead. GROUP III. LEAD. Atomic weight, 207. Symbol, Pb (Plumbum). This abundant and useful metal is altogether obtained from the native eulphide, or galena, no other lead-ore being found in large quantity. The reduction is effected in a reverberatory furnace, into which the crushed lead-ore is introduced and roasted for some time at a dull red heat, by which much of the sulphide becomes changed by oxidation to sulphate. The contents of the furnace are then thoroughly mixed, and the tempera- ture raised, when the sulphate and sulphide react upon each other, pro- ducing sulphurous oxide and metallic lead : S0 4 Pb + PbS =r Pb 2 + 2S0 2 . Lead melts at 315-5 C. (000 F.), or a little above, and boils and volatilizes at a white heat. By slow cooling it may be obtained in octohedral crystals. In moist air this metal becomes coated with a film of gray matter, thought LEAD. 395 to be suboxide, and when exposed to the atmosphere in the melted state it rapidly absorbs oxygen. Dilute acids, with the exception of nitric acid, act but slowly upon lead. Lead is a tetrad, as shown by the constitution of plumbic ethide, Pb iT (C 2 H s ) 4 ; but in its inorganic combinations it appears dyadic, forming but one chloride, Pb // Cl ;2 , with corresponding bromide and iodide. The oxide cor- responding to these is Pb /X 0, and there are also higher oxides in which the metal may be regarded either as a dyad or as a tetrad: thus the dioxide Pb0 2 may be formulated either as = Pb = 0, or as LEAD CHLORIDE, PbCl 2 , is prepared by precipitating a solution of lead nitrate or acetate with hydrochloric acid or common salt. It separates as a heavy white crystalline precipitate, which dissolves in about 33 parts of boiling water, and separates again, on cooling, in needle-shaped crystals. There are several oxychlorides of lead, one of which, Pb 3 Cl 2 2 , or PbCl 2 . 2PbO, occurs crystallized in right rhombic prisms on the Mendip Hills, thence called mendipite. Another, constituting Pattinson's white oxychlor- ide, Pb 2 Cl 2 or PbCl 2 .PbO, is prepared for use as a pigment by grinding galena with strong hydrochloric acid, dissolving the resulting chloride in hot water, and precipitating with lime-water. A third oxychloride, PbCl 2 . 7PbO, called patent yellow or Turner's yellow, is prepared by heating 1 part of sal-ammoniac with 10 parts of litharge. LEAD IODIDE, PbI 2 , is precipitated, on mixing lead nitrate or acetate with potassium iodide, as a bright yellow powder, which dissolves in boiling water, and crystallizes therefrom in beautiful yellow iridescent spangles. OXIDES. The monoxide, PbO, called litharge or massicot, is the product of the direct oxidation of the metal. It is most conveniently prepared by heating the carbonate to dull redness; common litharge is impure monoxide which has undergone fusion. Lead oxide has a delicate straw-yellow color, is very heavy, and slightly soluble in water, giving an alkaline liquid. It is soluble in potash, and crystallizes from the solution in rhombic prisms. At a red heat it melts, and tends to crystallize on cooling. In the melted state it attacks and dissolves siliceous matter with astonishing facility, often penetrating an earthen crucible in a few minutes. It is easily reduced when heated with organic substances of any kind containing carbon or hydrogen. It forms a large class of salts, often called plumbic salts, which are colorless if the acid itself is not colored. Triplumbic tetroxide, or Red lead, is not of very constant composition, but generally contains Pb 3 2 or 2PbO.Pb0 2 . It is prepared by exposing the monoxide, which has not been fused, for a long time to the air, at a very faint red heat; it is .a brilliant red and extremely heavy powder, decom- posed, with evolution of oxygen, by a strong heat, and converted into a mixture of monoxide and dioxide by acids. It is used as a cheap substitute for vermilion. The dioxide, Pb0 2 , often called puce or brown lead-oxide, is obtained without difficulty by digesting red lead in dilute nitric acid, whereby lead nitrate is dissolved out, and insoluble dioxide left behind in the form of a deep-brown powder. The dioxide is decomposed by a red heat, yielding up one half of its oxygen. Hydrochloric acid converts it into lead chloride, with dis- engagement of chlorine ; hot oil of vitriol forms with it lead sulphate, and liberates oxygen. The dioxide is very useful in separating sulphurous acid from certain gaseous mixtures, lead sulphate being then produced : PbO ? + S0 3 = PbS0 4 . 396 TETRAD METALS. Diplumbic oxide, or Lead sub oxide, Pb 2 or Pb Pb, is formed when the monoxide is heated to dull redness in a retort; a gray pulverulent sub- stance is then left, which is resolved by acids into monoxide and metal. It absorbs oxygen with great rapidity when heated, and even when simply moistened with water and exposed to the air. LEAD NITRATE, (N0 3 ) 2 Pb or N 2 5 PbO, may be obtained by dissolving lead carbonate in nitric acid, or by acting directly upon the metal by the same agent with the aid of heat: it is, as already noticed, a by-product in the preparation of the dioxide. It crystallizes in anhydrous octohedrons, which are usually milk-white and opaque. It dissolves in 7J parts of cold water, and is decomposed by heat, yielding nitrogen tetroxide, oxygen, and lead monoxide, which obstinately retains traces of nitrogen. When a solution of this salt is boiled with an additional quantity of lead oxide, a portion of the latter is dissolved, and a basic nitrate is generated, which may be obtained in crystals. Carbonic acid separates this excess of oxide in the form of a white compound of lead carbonate and lead hydrate. Neutral and basic compounds of lead oxide with the trioxide and tetroxide of nitrogen, have been described. These last are probably formed by the combination of a nitrite with a nitrate. LEAD CARBONATE ; WHITE LEAD ; C0 3 Pb x/ or C0 2 PbO. This salt is some- times found beautifully crystallized in long white needles, accompanying other metallic ores. It may be prepared artificially by precipitating in the cold a solution of the nitrate or acetate with an alkaline carbonate : when the lead solution is boiling, the precipitate is a basic salt containing 2C0 3 Pb. PbH 2 2 ; it is also manufactured to an immense extent by other means for the use of the painter. Pure lead carbonate is a soft, white powder, of great specific gravity, insoluble in water, but easily dissolved by dilute nitric or acetic acid. Of the many methods put in practice, or proposed, for making white lead, the two following are the most important and interesting : One of these consists in forming a basic nitrate or acetate of lead by boiling finely powdered litharge with the neutral salt. This solution is then brought into contact with carbonic acid gas, whereby all the excess of oxide previously taken up by the neutral salt is at once precipitated as white lead. The solution strained or pressed from the latter is again boiled with litharge, and treated with carbonic acid: these processes are susceptible of indefinite repetition, whereby the little loss of neutral salt left in the precipitates is compensated. The second, and by far the more ancient method, is rather more complex, and at first sight not very intelligible. A great number of earthen jars are prepared, into each of which is poured a few ounces of crude vinegar ; a roll of sheet-lead is then introduced in such a manner that it shall neither touch the vinegar nor project above the top of the jar. The vessels are next arranged in a large building, side by side, upon a layer of stable manure, or, still better, spent tan, and closely covered with boards. A second layer of tan is spread upon the top of the latter, and then a second series of pots ; these are in turn covered with boards and decom- posing bark, and in this manner a pile of many alternations is constructed. After the lapse of a considerable time, the pile is taken down and the sheets of lead are removed and carefully unrolled ; they are then found to be in great part converted into carbonate, which merely requires washing and grinding to be fit for use. The nature of this curious process is generally explained by supposing the vapor of vinegar raised by the high tempera- ture of the fermenting matter, merely to act as a carrier between the car- bonic acid evolved from the tan, and the lead oxide formed under the in- fluence of the acid vapor, a neutral acetate, a basic acetate, and a carbonate IROX. 397 "being produced in succession, and the action gradually travelling from the surface inwards. The quantity of acetic acid used is, in relation to the lead, quite trilling, and cannot directly contribute to the production of the carbonate. A preference is still given to the product of this old mode of manufacture, on account of its superiority of opacity, or body, over that obtained by precipitation. Commercial white lead, however prepared, always contains a certain proportion of hydrate. It is sometimes adul- terated with barium sulphate. When clean metallic lead is put into pure water and exposed to the air, a white, crystalline, scaly powder begins to show itself in a few hours, and very rapidly increases in quantity. This substance may consist of lead hydrate, formed by the action of the oxygen dissolved in the water upon the lead. It is slightly soluble, and may be readily detected in the water. In most cases, however, the formation of this deposit is due to the action of the carbonic acid dissolved in the water: it consists of carbonate in combination with hydrate, and is nearly insoluble in water. When common river or spring water is substituted for the pure liquid, this eifect is less observable, the little sulphate, almost invariably present, causing the depo- sition of a very thin but closely adherent film of lead sulphate upon the surface of the metal, which protects it from further action. It is on this account that leaden cisterns are used with impunity, at least in most cases, for holding water: if the latter were quite pure, it would be speedily con- taminated with lead, and the cistern would be soon destroyed. Natural water highly charged with carbonic acid cannot, under any circumstances, be kept in lead or passed through leaden pipes with safety, the carbonate, though very insoluble in pure water, being slightly soluble in water con- taining carbonic acid. The soluble salts of lead behave with reagents as follows : Caustic potash and soda precipitate a white hydrate freely soluble in ex- cess. Ammonia gives a similar white precipitate, not soluble in excess. The carbonates of potassium, sodium, and ammonium, precipitate lead car- bonate, insoluble in excess. Sulphuric acid or a sulphate causes a white pre- cipitate of lead sulphate insohible in nitric acid. Hydrogen sulphide and ammonium sulphide throw down black lead sulphide. Lead is readily de- tected before the blowpipe by fusing the compound under examination on charcoal with sodium carbonate, when a bead of metal is easily obtained, which is recognized by its chemical as well as physical properties. An alloy of 2 parts of lead and 1 of tin constitutes plumbers' solder; these proportions reversed give a more fusible compound, called fine solder. The lead employed in the manufacture of shot is combined with a little arsenic. GROUP IV. IRON METALS. IKON. Atomic weight, 56. Symbol, Fe (Ferrum). This is the most important of all metals: there are few substances to which it yields in interest, when it is considered how very intimately the knowledge of its properties and uses is connected with human civilisation. Metallic iron is of exceedingly rare occurrence : it has been found at Canaan, in Connecticut,* forming a vein about two inches thick in mica-slate ; but it * Phillips' Mineralogy, 4th edit. p. 208. 84 398 TETRAD METALS. invariably enters into the composition of those extraordinary stones known to fall from the air, called meteorites. Isolated masses of soft malleable iron also, of large dimensions, lie loose upon the surface of the earth in South America and elsewhere, and are presumed to have had a similar origin: these latter, in common with the iron of the undoubted meteorites, contain nickel. In an oxidized condition, the presence of iron may be said to be universal: it constitutes a great part of the common coloring matter of rocks and soils; it is contained in plants, and forms an essential component of the blood of the animal body. It is also very common in the state of bisulphide. Pure iron may be prepared, according to Mitscherlich, by introducing into a Hessian crucible 4 parts of fine iron wire cut small, and 1 part of black iron oxide. This is covered with a mixture of white sand, lime, and potassium carbonate, in the proportions used for glass-making, and a cover being closely applied, the crucible is exposed to a very high degree of heat. A button of pure metal is thus obtained, the traces of car- bon and silicium present in the wire having been removed by the oxygen of the oxide. Pure iron has a white color and perfect lustre : it is extremely soft and tough, and has a specific gravity of 7-8. Its crystalline form is probably the cube, to judge from appearances now and then exhibited. In good bar- iron or wire, a distinct fibrous texture may always be observed when the metal has been attacked by rusting or by the application of an acid, and upon the perfection of this fibre much of its strength and value depends. Iron is the most tenacious of all the metals, a wire ^ of an inch in diame- ter bearing a weight of GO Ibs. It is very difficult of fusion, and before becoming liquid passes through a soft or pasty condition. Pieces of iron pressed or hammered together in this state cohere into a single mass : the operation is termed welding, and is usually performed by sprinkling a little sand over the heated metal, which combines with the superficial film of oxide, forming a fusible silicate, which is subsequently forced out from between the pieces of iron by the pressure applied : clean surfaces of metal are thus presented to each other, and union takes place without difficulty. Iron does not oxidize in dry air at common temperatures: heated to red- ness, it becomes covered with a scaly coating of black oxide, and at a high white heat burns brilliantly, producing the same substance. In oxygen gas the combustion occurs with still greater ease. The finely divided spongy metal prepared by reducing the red oxide with hydrogen gas takes fire spontaneously in the air. Pure water, free from air and carbonic acid, does not tarnish a surface of polished iron, but the combined agency of free oxygen and moisture speedily leads to the production of rust, which is a hydrate of the sesquioxide. The rusting of iron is wonderfully promoted by the presence of a little acid vapor. At a red heat, iron decomposes water, evolving hydrogen, and passing into the black oxide. Dilute sul- phuric and hydrochloric acids dissolve it freely, with separation of hydro- gen. Iron is strongly magnetic up to a red heat, when it loses all traces of that remarkable property. Iron is a tetrad, forming two classes of compounds; namely, ike ferrous compounds, in which it is bivalent, e.g., Fe^CLj, Fe x/ 0, Fe /x S0 4 , c., and the ferric compounds, in which it is really quadrivalent, though apparently Fe'"Cl, r I ; Fe"' 2 3 ; Fe'^JSOA, &c. Fe'"Cl 3 CHLORIDES. The dicMoride, or Ferrous chloride, FeCl 3 , is formed by trans- mitting dry hydrochloric acid gas over red-hot metallic iron, or by dissolv- ing iron in hydrochloric acid. The latter solution yields, when duly con- centrated, green crystals of the hydrated dichloride FeC 1 2 .40H 2 ; they are very soluble and deliquescent, and rapidly oxidize in the air. IRON. 399 The trichloride, or Ferric chloride, Fe 2 Cl 6 , is usually prepared by dissolving ferric oxide in hydrochloric acid. The solution, evaporated to a syrupy consistence, deposits red hydrated crystals, which are very soluble in water and alcohol. It forms double salts with potassium chloride and sal-ammo- niac. When evaporated to dry ness and strongly heated, much of the chlor- ide is decomposed, yielding sesquioxide and hydrochloric acid : the remain- der sublimes, and afterwards condenses in the form of small brilliant red crystals, which deliquesce rapidly. Anhydrous ferric chloride is also pro- duced by the action of chlorine upon the heated metal. The solution of ferric chloride is capable of dissolving a large excess of recently precipi- tated ferric hydrate, by which it acquires a much darker color. IODIDES. Ferrous iodide, FeI 2 , is an important medicinal preparation: it is easily made by digesting iodine with water and metallic iron. The solution is pale-green, and yields, on evaporation, crystals resembling those of the chloride, which rapidly oxidize on exposure to air. It is best preserved in solution in contact with excess of iron. Ferric iodide, Fe 2 I 6 , is yellowish- red and soluble. IRON OXIDES. Three oxides of iron are known, namely, ferrous oxide, FeO, and ferric oxide, Fe 2 3 , analogous to the chlorides, and an intermi- diate oxide, usually called magnetic iron oxide, containing Fe 3 4 , or FeO. Fe 2 3 . A trioxide, Fe0 3 , is supposed to exist in a class of salts called fer- rates, but it has not been isolated. Monoxide or Ferrous oxide, FeO. This is a very powerful base, neutraliz- ing acids, and isomorphous with magnesia, zinc oxide, &c. It is almost unknown in the separate state, from its extreme proneness to absorb oxy- gen and pass into the sesquioxide. When a ferrous salt is mixed with caustic alkali or ammonia, a bulky whitish precipitate of ferrous hydrate falls, which becomes nearly black when boiled, the water being separated. This hydrate changes very rapidly when exposed to the air, becoming green and ultimately red-brown. The soluble ferrous salts have commonly a delicate pale-green color and a nauseous metallic taste. Sesquioxide or Ferric oxide, Fe 2 3 . A feeble base, isomorphous with alu- mina. It occurs native, most beautifully crystallized, as specular iron ore, in the Island of Elba, and elsewhere ; also as red and brown hsematite, the latter being a hydrate. It is artificially prepared by precipitating a solution of ferric sulphate or chloride with excess of ammonia, and washing, dry- ing, and igniting the yellowish-brown hydrate thus produced ; fixed alkali must not be used in this operation, as a portion is retained by the oxide. In fine powder, this oxide has a full red color, and is used as a pigment, being prepared for the purpose by calcination of ferrous sulphate; the tint varies somewhat with the temperature to which it has been exposed. The oxide is unaltered in the fire, although easily reduced at a high temperature by carbon or hydrogen. It dissolves in acids, with difficulty after strong ignition, forming a series of reddish salts, which have an acid reaction and an astringent taste. Ferric oxide is not acted upon by the magnet. Triferro-tetroxide, Ferrosoferric oxide, Fe 3 4 = FeO.Fe 2 O 3 , also called black iron oxide, magnetic oxide, and loadstone. A natural product, one of the most valuable of the iron ores, often found in regular octohedral crystals, which are magnetic. It may be prepared by mixing due proportions of ferrous and ferric salts, precipitating them with excess of alkali, and then boiling the mixed hydrates ; the latter then unite to a black sandy sub- stance, consisting of minute crystals of the magnetic oxide. This oxide is the chief product of the oxidation of iron at a high temperature in the air and in aqueous vapor. It is incapable of forming definite salts. FERRATES. When a mixture of one part of pure ferric oxide and four 400 TETKAD METALS. parts of dry nitre is heated to full redness for an hour in a covered cruci- ble, and the resulting brown, porous, deliquescent mass is treated when cold with ice-cold water, a deep amethystine-red solution of potassium fer- rate is obtained. The same salt may be more easily prepared by passing chlorine gas through a strong solution of potash in which recently precipi- tated ferric hydrate is suspended ; it is then deposited as a black powder, which may be drained upon a tile. It consists of Fe0 4 K 2 or Fe0 3 .OK 2 . The solution of the salt gradually decomposes, even in the cold, and rapidly when heated, giving off oxygen and depositing sesquioxide. The solution of potassium ferrate gives no precipitate with salts of calcium, magnesium, or strontium, but when mixed with a barium salt, it yields a deep crimson, insoluble, barium ferrate, Fe0 4 Ba, or Fe0 3 .BaO, which is very permanent. Neither the hydrogen salt nor ferric acid, Fe0 4 H 2 , nor the corresponding anhydrous oxide, Fe0 3 , is known in the separate state. FERROUS SULPHATE, S0 4 Fe // .70H 2 , S0 3 .Fe0.70H 2 . This beautiful and important salt, commonly called green vitriol, iron vitriol, or copperas, may be obtained by dissolving iron in dilute sulphuric acid : it is generally prepared, however, and on a very large scale, by contact of air and moisture with common iron pyrites, which, by absorption of oxygen, readily fur- nishes the substance in question. Heaps of this material are exposed to the air until the decomposition is sufficiently advanced : the salt produced is then dissolved out by water, and the solution made to crystallize. It forms large green crystals, of the composition above stated, which slowly effloresce and oxidize in the air: it is soluble in about twice its weight of cold water. Crystals containing 4 and also 2 molecules of water have been obtained. Ferrous sulphate forms double salts with the sulphates of potas- sium and ammonium, containing (S0 4 ) 2 Fe x/ K 2 .60H 2 , and (S0 4 ) 2 Fe"(NH 4 ) a . 60H 2 , isomorphous with the corresponding magnesium salts. FERRIC SULPHATE, (S0 4 ) 3 Fe /// 2 , or 3S0 3 .Fe 2 3 , is prepared by adding to a solution of the ferrous salt exactly one half as much sulphuric acid as it already contains, raising the liquid to the boiling-point, and then dropping in nitric acid until the solution ceases to blacken by such addition. The red liquid thus obtained furnishes, on evaporation to dryness, a buff-colored amorphous mass, which dissolves very slowly when put into water. With the sulphates of potassium and ammonium, this salt yields compounds hav- ing the form and constitution of alums ; the potassium salt, for example, has the composition (S0 4 ) 2 Fe /x/ K. 120H 2 . The crystals are nearly destitute of color ; they are decomposed by water, and sometimes by long keeping in the dry state. These salts are best prepared by exposing to spontaneous evaporation a solution of ferric sulphate to which potassium or ammonium sulphate has been added. FERROUS NITRATE (N0 3 ) 2 Fe // . When dilute cold nitric acid is made to act to saturation upon iron monosulphide, and the solution is evaporated in a vacuum, pale-green and very soluble crystals of ferrous nitrate are obtained, which are very subject to alteration. Ferric nitrate is readily formed by pouring nitric acid, slightly diluted, upon iron : it is a deep-red liquid, apt to deposit an insoluble basic salt, and is used in dyeing. FERROUS CARBONATE, CO^Fe" or C0 2 .Fe // 0. The whitish precipitate obtained by mixing solutions of ferrous salt and alkaline carbonate : it cannot be washed and dried without losing carbonic acid and absorbing oxygen. This substance occurs in nature as spathose iron ore, or iron spar, associated with variable quantities of calcium and magnesium carbonates ; also in the common clay iron-stone, from which nearly all the British iron is made. It is often found in mineral waters, being soluble in excess of IRON. 401 carbonic acid : such waters are known by the rusty matter they deposit on exposure to the air. No ferric carbonate is known. The phosphates of iron are all insoluble. IRON SULPHIDES. Several compounds of iron and sulphur are described: of these the two most important are the following. The monosulphide, or ferrous sulphide, FeS, is a blackish brittle substance, attracted by the mag- net, formed by heating together iron and sulphur. It is dissolved by dilute acids, with evolution of sulphuretted hydrogen gas, arid is constantly em- ployed for that purpose in the laboratory, being made by projecting into a red-hot crucible a mixture of 2 parts of sulphur and 4 parts of iron fil- ings or borings of cast-iron, and excluding the air as much as possible. The same substance is formed when a bar of white-hot iron is brought in contact with sulphur. The bisulphide, FeS 2 , or iron pyrites, is a natural product, occurring in rocks of all ages, and evidently formed in many cases by the gradual deoxidation of ferrous sulphate by organic matter. It has a brass-yellow color, is very hard, not attracted by the magnet, and not acted upon by dilute acids. When it is exposed to heat, sulphur is ex- pelled, and an intermediate sulphide, Fe s S 4 , analogous to the black oxide, is produced. This substance also occurs native, under the name of magnetic pyrites. Iron pyrites is the material now chiefly employed for the manu- facture of sulphuric acid; for this purpose the mineral is roasted in a cur- rent of air, and the sulphurous acid formed is passed into the lead cham- bers ; the residue consists of iron oxide, frequently containing a quantity of copper large enough to render the extraction of that metal remunerative. Compounds of iron with phosphorus, carbon, and silicium exist, but little is known respecting them in a definite state. The carbonide is contained in cast-iron and in steel, to which it communicates ready fusibility ; the silicium compound is also found in cast-iron. Phosphorus is a very hurt- ful substance in bar iron, as it renders it brittle or cold-short. REACTIONS OF IRON SALTS. Ferrous salts are thus distinguished: Caustic alkalies, and ammonia, give nearly white precipitates, insoluble in excess of the reagent, rapidly becoming green, and ultimately brown, by exposure to air. The carbonates of potassium, sodium, and ammonium throw down whitish ferrous carbonate, also very subject to change. Hydrogen sulphide gives no precipitate, but ammonium sulphide throws down black fer- rous sulphide, soluble in dilute acids. Potassium ferrocyanide gives a nearly white precipitate, becoming deep-blue on exposure to air. Ferric salts are thus characterized : Caustic fixed alkalies and ammonia, give foxy-red precipitates of ferric hydrate, insoluble in excess. The carbonates behave in a similar manner, the carbonic acid escaping. Hydrogen sulphide gives a nearly white precipitate of sulphur, and re- duces the sesquioxide to monoxide. Ammonium sulphide gives a black pre- cipitate, slightly soluble in excess. Potassium ferrocyanide yields Prussian blue. Tincture or infusion of gall-nuts strikes intense bluish-black with the most dilute solutions of ferric salts. Iron Manufacture. This most important branch of industry consists, as now conducted, of two distinct parts viz., the production from the ore of a fusible carbonide of iron, and the subsequent decomposition of the car- bonide, and its conversion into pure or malleable iron. The clay-iron ore is found in association with coal, forming thin beds or nodules : it consists, as already mentioned, of ferrous carbonate mixed with 402 TETRAD METALS. clay ; sometimes lime and magnesia are also present. It is broken in pieces, and exposed to heat in a furnace resembling a lime-kiln, by which the water and carbonic acid are expelled, and the ore rendered dark- colored, denser, and also magnetic : it is then ready for reduction. The furnace in which this operation is performed is usually of very large di- mensions, 50 feet or more in height, and constructed of brickwork with great solidity, the interior being lined with excellent fire-bricks : the shape will be understood from the section shown in fig. 173. The furnace is close Fig. 173. at the bottom, the fire being maintained by a powerful artificial blast in- troduced by two or tree twyere-pipes, as shown in the section. The mate- rials, consisting of due proportions of coke or carbonized coal, roasted ore, and limestone, are constantly supplied from the top, the operation proceed- ing continuously night and day, often for years, or until the furnace is judged to require repair. In the upper part of the furnace, where the temperature is still very high, and where combustible gases abound, the iron of the ore is probably reduced to the metallic state, being disseminated through the earthy matter of the ore. As the whole sinks down and attains a still higher degree of heat, the iron becomes converted into carbonide by cementation, while the silica and alumina unite with the lime, purposely added, to a kind of glass or slag, nearly free from iron oxide. The carbon- ide and slag, both in a melted state, reach at last the bottom of the furnace, where they arrange themselves in the order of their densities : the slag flows out at certain apertures contrived for the purpose, and the iron is discharged from time to time, and sutfered to run into rude moulds of sand by opening an orifice at the bottom of the recipient, previously stopped IRON. 403 with clay. Such is the origin of crude or cast-iron, of which there are several varieties, distinguished by differences of color, hardness, and com- position, and known by the names of gray, black, and white iron. The first is for most purposes the best, as it admits of being filed and cut with perfect ease. The black and gray kinds probably contain a mechanical admixture of graphite, which separates during solidification. A great improvement has been made in the above-described process, by substituting raw coal for coke, and blowing hot air instead of cold into the furnace. This is effected by causing the air, on leaving the blowing-machine, to circulate through a system of red-hot iron pipes, until its temperature becomes high enough to melt lead. This alteration has already effected a prodigious saving in fuel, without, it appears, any injury to the quality of the product. The conversion of cast into bar iron is effected chiefly by an operation called puddling ; previous to which, however, it commonly undergoes a pro- cess called refining. It is remelted, in contact with the fuel, in small low furnaces called refineries, while air is blown over its surface by means of twyeres. The effect of this operation is to deprive the iron of a great part of the carbon and silicium associated with it. The metal thus purified is run out into a trench, and suddenly cooled, by which it becomes white, crystalline, and exceedingly hard : in this state it is called fine metal. The puddling process is conducted in an ordinary reverberatory furnace, into which the charge of fine metal is introduced by a side aperture. This is speedily melted by the flame, and its surface covered with a crust or oxide. The workman then, by the aid of an iron tool, diligently stirs the melted mass, so as intimately to mix the oxide with the metal: he now and then also throws in a little water, with the view of promoting more rapid oxida- tion. Small jets of blue flame soon appear upon the surface of the iron, and the latter, after a time, begins to lose its fluidity, and acquires, in succession, a pasty and a granular condition. At this point the fire is strongly urged, the sandy particles once more cohere, and the contents of the furnace now admit of being formed into several large balls or masses, which are then withdrawn, and placed under an immense hammer, moved by machinery, by which each becomes quickly fashioned into a rude bar. This is reheated, and passed between grooved cast-iron rollers, and drawn out into a long bar or rod. To make the best iron, the bar is cut into a number of pieces, which are afterwards piled or bound together, again raised to a welding heat, and hammered or rolled into a single bar; and this pro- cess of piling or fagoting is sometimes twice or thrice repeated, the iron becoming greatly improved thereby. The general nature of the change in the puddling furnace is not difficult to explain. Cast iron consists essentially of iron in combination with car- bon and silicium. When strongly heated with iron oxide, those compounds undergo decomposition, the carbon and silicium becoming oxidized at the expense of the oxygen of the oxide. As this change takes place, the metal gradually loses its fusibility, but retains a certain degree of adhesiveness, so that when at last it comes under the tilt-hammer, or between the rollers, the particles of iron become agglutinated into a solid mass, while the readily fusible silicate of the oxide is squeezed out and separated. All these processes are, in Great Britain, performed with coal or coke ; but the iron obtained is, in many respects, inferior to that made in Sweden and Russia from the magnetic oxide, by the use of wood charcoal, a fuel too dear to be extensively employed in England. Plate iron is, however, sometimes made with charcoal. Steel. A very remarkable and most useful substance, prepared by heating iron in contact with charcoal. Bars of Swedish iron are imbedded in charcoal powder, contained in a large rectangular crucible or chest of 404 TETRAD METALS. some substance capable of resisting the fire, and exposed for many hours to a full red heat. The iron takes up, under these circumstances, from 1-3 to 1-7 per cent, of carbon, becoming harder, and at the same time fusible, with a certain diminution, however, of malleability. The active agent in this cementation process is probably carbonic monoxide : the oxygen of the air in the crucible combines with the carbon to form that substance, which is afterwards decomposed by the heated iron, one half of its carbon being abstracted by the latter. The carbon dioxide thus formed takes up an additional dose of carbon from the charcoal, and again becomes monoxide, the oxygen, or rather the carbon dioxide, acting as a carrier between the charcoal and the metal. The product of this opei-ation is called blistered steel, from the blistered and rough appearance of the bars: the texture is afterwards improved and equalized by welding a number of these bars together, and drawing the whole out under a light tilt-hammer. Some chemists have recently asserted that nitrogen is necessary for the production of steel, and have, in fact, attributed to its presence the peculiar properties of this material ; others, again, have disputed this assertion, and believe that the transformation of iron into steel depends upon the assimilation of carbon only ; experimentally, the question remains un- decided. Excellent steel is obtained by fusing gray cast-iron with tungstic oxide ; the carbon of the iron reduces the tungstic oxide to tungsten (p. 424), which forms with the iron an alloy possessing the properties of steel. The quantity of tungsten thus absorbed by the iron is very small, and some chemists attribute the properties of the so-called tungsten steel to the gen- eral treatment rather than to the presence of tungsten. The most perfect kind of steel is that which has undergone fusion, hav- ing been cast into ingot-moulds, and afterwards hammered: of this all fine cutting instruments are made. It is difficult to forge, requiring great skill and care on the part of the operator. Steel may also be made directly from some particular varieties of cast- iron, as that from spathose iron ore containing a little manganese. The metal is retained, in a melted state, on the hearth of a furnace, while a stream of air plays upon it, and causes partial oxidation : the oxide pro- duced reacts, as before stated, on the carbon of the iron, and withdraws a portion of that element. When a proper degree of stiifness or pastiness is observed in the residual metal, it is withdrawn, and hammered or rolled into bars. The ivootz, or native steel of India, is probably made in this manner. Annealed cast iron, sometimes called run-steel, is now much em- ployed as a substitute for the more costly products of the forge : the arti- cles, when cast, are imbedded in powdered iron ore, or some earthy ma- terial, and, after being exposed to a moderate red heat for some time, are allowed to cool slowly, by which a very cxtraordinay degree of softness and malleability is attained. It is very possible that some little decarbonization may take place during this process. Bessemer steel is produced by forcing atmospheric air into melted cast-iron. The carbon being oxidized more readily than the iron, it is converted into carbon monoxide, which escapes in a sufficiently heated state to take fire on coming in contact with atmospheric air. Considerable heat is generated by the oxidation of the carbon and iron, so that the temperature is kept above the melting point of steel during the whole of the operation. When the decarburation has been carried far enough, the current of air is stopped, and a small quantity of white pig-iron, containing a large amount of man- ganese, is dropped into the liquid metal. This serves to facilitate the sep- aration of any gas retained with the melted metal, which, after a few minutes' rest, is run into ingot-moulds. The most remarkable property of steel is that of becoming exceedingly NICKEL. 405 hard when quickly cooled. When heated to redness, and suddenly quenched in cold water, steel, in fact, becomes capable of scratching glass with facility: if reheated to redness, and once more left to cool slowly, it again becomes nearly as soft as ordinary iron; and between these two con- ditions, any required degree of hardness may be attained. The articles, forged into shape, are first hardened in the manner described ; they are then tempered, or let down by exposure to a proper degree of annealing heat, which is often judged of by the color of the thin film of oxide which ap- pears on the polished surface. Thus, a temperature of about 221 C. (430 F.), indicated by a faint straw color, gives the proper temper for razors: that for scissors, penknives, &c., is comprised between 243 C. (470 F.) and 254 C. (490 F.), and is indicated by a full-yellow or brown tint. Swords and watch-springs require to be softer and more elastic, and must be heated to 288 C. (550 F.) or 293 C. (560 F.), or until the surface becomes deep blue. Attention to these colors has now become of less im- portance, as metal baths are often substituted for the open fire in this operation. NICKEL. Atomic weight, 58-8. Symbol, Ni. Nickel is found in tolerable abundance in some of the metal-bearing veins of the Saxon mountains, in Westphalia, Hessia, Hungary, and Sweden, chiefly as arsenide, the kupfernickel of mineralogists, so called from its yellowish-red color. The word nickel is a term of detraction, having been applied by the old German miners to what was looked upon as a kind of false copper ore. The artificial, or perhaps rather merely fused, product, called speiss, is nearly the same substance, and may be employed as a source of the nickel- salts. This metal is found in meteoric iron, as already mentioned. Nickel is easily prepared by exposing the oxalate to a high white heat, in a crucible lined with charcoal, or by reducing one of the oxides by means of hydrogen at a high temperature. It is a white, malleable metal, having a density of 8-8, a high melting-point, and a less degree of oxida- bility than iron, since it is but little attacked by dilute acids. Nickel is strongly magnetic, but loses this property when heated to 350. Nickel, from its resemblance to iron and cobalt, is regarded as a tetrad, although it forms only one chloride, in which it is bivalent, and no oxygen- salts analogous to the ferric salts. NICKEL CHLORIDE, Ni^Cl^ This compound is easily prepared by dis- solving oxide or carbonate of nickel in hydrochloric acid. A green solu- tion is obtained which furnishes crystals of the same color, containing water. When rendered anhydrous by heat, the chloride is yellow, unless it contains cobalt, in which case it has a tint of green. NICKEL OXIDES. Nickel forms two oxides analogous to the two principal oxides of iron. The monoxide, Ni // 0< is prepared by heating the nitrate to redness, or by precipitating a soluble nickel salt with caustic potash, and washing, drying, and igniting the apple-green hydrated oxide thrown down. It is an ashy- gray powder, freely soluble in acids, which it completely neutralizes, form- ing salts isomorphous with those of magnesium and the other members of the same group. Nickel salts, when hydrated, have usually a beautiful emerald-green color ; in the anhydrous state they are yellow. 406 TETRAD METALS. The sesquioxide, Ni 2 3 , is a black insoluble substance, prepared by pass- ing chlorine through the hydrated monoxide suspended in water ; nickel chloride is then formed, and the oxygen of the oxide decomposed is trans- ferred to a second portion. It is also produced when a salt of nickel is mixed with a solution of bleaching-powder. The sesquioxide is decomposed by heat, and evolves chlorine when treated with hot hydrochloric acid. NICKEL SULPHATE, S0 4 Ni.70H 2 . This is the most important of the nickel- salts. It forms green prismatic crystals, which require 3 parts of cold water for solution. Crystals with 6 molecules of water have also been obtained. It forms with the sulphates of potassium and ammonium beautiful double salts, (S0 4 ).,Ni // K.60PI 2 , and (SOJ.jNi^NHJ.GOH^ isomorphous with the corresponding magnesium salts. When a strong solution of oxalic acid is mixed with sulphate of nickel, a pale bluish-green precipitate of oxalate falls after some time, very little nickel remaining in solution. The oxalate can thus be obtained for pre- paring the metal. NICKEL CARBONATE, C0 3 Ni. When solutions of nickel sulphate or chlor- ide and of sodium carbonate are mixed, a pale-green precipitate falls, which is a combination of nickel carbonate and hydrate. It is readily decomposed by heat. Pure nickel-salts are conveniently prepared on the small scale from crude speiss or kupfernickel by the following process : The mineral is broken into small fragments, mixed with from one fourth to half its weight of iron filings, and the whole dissolved in nitromuriatic acid. The solution is gently evaporated to dryness, the residue treated with boiling water, and the insoluble iron arsenate removed by a filter. The liquid is then acidu- lated with hydrochloric* acid, treated with hydrogen sulphide in excess, which precipitates the copper, and, after filtration, boiled with a little nitric acid to bring back the iron to the state of sesquioxide. To the cold and largely diluted liquid solution, acid sodium carbonate is gradually added, by which the ferric oxide may be completely separated without loss of nickel-salt. Lastly, the filtered solution, boiled with sodium carbonate in excess, yields an abundant pale-green precipitate of nickel carbonate, from which all the other compounds may be prepared. The precipitate thus obtained may still, however, contain cobalt, the separation of which is not very easy. Several methods of separating these metals have been proposed, the best of which is, perhaps, that of H. Rose. The mixed oxides or carbonates being dissolved in excess of hydrochloric acid, the solution, largely diluted with water, is super-saturated with chlor- ine gas, whereby the cobalt monoxide is converted into sesquioxide, while the nickel monoxide remains unaltered. The liquid is next mixed with excess of recently precipitated barium carbonate, left to stand for twelve to eighteen hours, and shaken up from time to time. The whole of the cobalt is thereby thrown down as sesquioxide, while the nickel remains in solu- tion, and may be precipitated as hydrate by potash, after the barium also contained in the solution has been removed by precipitation with sulphuric acid.* Nickel-salts are well characterized by their behavior with reagents. Caustic alkalies give a pale apple-green precipitate of hydrate, insoluble in excess. Ammonia affords a similar precipitate, which is soluble in excess, with deep purplish-blue color. Potassium and sodium carbonates give pale- green precipitates. Ammonium carbonate, a similar precipitate, soluble in excess, with blue color. Potassium ferrocyanide gives a greenish-white pre- * For other modes of separating nickel and cobalt, see Gmelin's Handbook, vol. v. pp. 355-360; and Watts's Dictionary of Chemistry, vol. i. p. 1046. COBALT. 407 cipitate. Potassium cyanide produces a green precipitate, which dissolves in an excess of the precipitant to an amber-colored liquid, and is reprecipitated by an addition of hydrochloric acid. Hydrogen sulphide occasions no change, if the nickel be in combination with a strong acid. Ammonium sulphide pro- duces a black precipitate of nickel sulphide, which dissolves slightly in excess of the precipitant with dark-brown color. Nickel sulphide when once precipitated is insoluble in dilute hydrochloric acid ; it is soluble in nitromuriatic and in hot nitric acid. The chief use of nickel in the arts is in the preparation of a white alloy, sometimes called German silver, made by melting together 100 parts of cop- per, 60 of zinc, and 40 of nickel. This alloy is very malleable, and takes a high polish. COBALT. Atomic weight, 58-8. Symbol, Co. This substance bears, in many respects, a close resemblance to nickel: it is often associated with the latter in nature, and may be obtained from its compounds by similar means. A cobalt-salt free from nickel may be prepared by Rose's process just described. The precipitate, consisting of cobalt sesquioxide mixed with barium carbonate, is boiled with hydrochloric acid to reduce the cobult sesquioxide to monoxide, and dissolve it as a chloride together with the barium. The latter metal is then precipitated by sulphuric acid, and from the filtered liquid the cobalt may be precipitated as hydrate by potash. A solution of cobalt free from nickel may also be obtained by precipitating the mixed solution with oxalic acid ; the whole of the nickel is thereby precipitated, together with a small portion of the cobalt, leaving pure cobalt in solution. Cobalt is a white, brittle, very tenacious metal, having a specific gravity of 8-5, and a very high melting-point. It is unchanged in the air, and but feebly attacked by dilute hydrochloric and sulphuric acids. It is strongly magnetic. Cobalt forms two classes of salts, analogous in composition to the ferrous and ferric salts ; but the cobaltic salts, in which the metal is apparently trivalent, are very unstable. CHLORIDES. The dichloride or Cobaltous chloride, Co // Cl 2 , is easily pre- pared by dissolving the oxide in hydrochloric acid; or it may be prepared directly from cobalt-glance, the native arsenide, by a process exactly similar to that described in the case of nickel. It forms a deep rose-red solution, which, when sufficiently strong, deposits hydrated crystals of the same color : when the liquid is evaporated by heat to a very small bulk, it de- posits anhydrous crystals, which are blue: these latter by contact with water again dissolve to a red liquid. A dilute solution of cobalt chloride constitutes the well-known blue sympathetic ink: characters written on paper with this liquid are invisible, from their paleness of color, until the salt has been rendered anhydrous by exposure to heat, when the letters appear blue. On laying it aside, moisture is absorbed, and the writing once more disappears. Green sympathetic ink is a mixture of the chlorides of cobalt and nickel. The trichloride, or Cobaltic chloride, Co 2 Cl 6 , is obtained in solution by dis- solving the sesquioxide in hydrochloric acid, and in small quantity by saturating a solution of the dichloride with chlorine gas. The liquid has 408 TETRAD METALS. a dark -brown color, but easily decomposes, giving off chlorine and leaving the rose-colored dichloride. OXIDES. Cobalt forms two oxides analogous to those of nickel, also two or three of intermediate composition but not very well denned. The mon- oxide, or Cobaltous oxide, Co x/ 0, is a gray powder, very soluble in acids, and is a strong base, isomorphous with magnesia, affording salts of a fine red tint. It is prepared by precipitating cobaltous sulphate or chloride with sodium carbonate, and washing, drying, and igniting the precipitate. When the cobalt-solution is mixed with caustic potash, a beautiful blue precipitate falls, which, when heated, becomes violet, and at length dirty red, from ab- sorption of oxygen and a change in the state of hydration. The sesquioxide, or Cobaltic oxide, Co 2 3 , is a black, insoluble, neutral powder, obtained by mixing solutions of cobalt and chloride of lime. It dissolves in acids, yielding the cobaltic salts. Cobaltoso-cobaltic oxide, Co 3 4 , analogous to the magnetic oxide of iron, is formed when cobaltous nitrate .or oxalate, or hydrated cobaltic oxide, is heated in contact with the air. According to Fre"my, it is a salifiable base. Another oxide, of acid character, is said to be obtained in the form of a potassium salt by fusing the monoxide or sesquioxide with potassium hy- drate. A crystalline salt is thus formed consisting, according to Schwarzen- berg, of 3Co 3 5 .K 2 0. 3Aq. COBALTOUS SULPHATE, S0 4 Co // .70H 2 . This salt forms red crystals, re- quiring for solution 24 parts of cold water: they are identical in form with those of magnesium sulphate. It combines with the sulphates of potassium and ammonium, forming double salts, which contain, as usual, 6 molecules of water. A solution of oxalic acid added to cobaltous sulphate occasions, after some time, the separation of nearly the whole of the base in the state of oxalate. COBALTOUS CARBONATE. The alkaline carbonates produce in solutions of cobalt a pale peach-blossom-colored precipitate of combined carbonate and hydrate, containing 3 CoH 3 2 .2C0 3 Co. AMMONIACAL COBALT COMPOUNDS. Cobaltous salts treated with ammonia in a vessel protected from the air, unites with the ammonia, forming com- pounds which may be called ammonio-coballous salts. Most of them contain 6 molecules of ammonia to 1 molecule of the cobalt salt ; thus the chloride contains CoCl 2 .6NH 3 . Aq. ; the nitrate, Co(N0 3 ) 2 .6NH 3 . 2 Aq. They are generally crystallizable and of a rose-color, soluble without decomposition in ammonia, but decomposed by water, with formation of a basic salt. H. Rose, by treating dry cobalt chloride with ammonia-gas, obtained the com- pound CoCl 2 .4NH 3 ; and in like manner an ammonio-sulphate has been formed containing S0 4 Co.6NH ? . When an ammoniacal solution of cobalt is exposed to the air, oxygen is absorbed, the liquid turns brown, and new salts are formed containing a higher oxide of cobalt (either Co 2 3 or CoOA and therefore designated generally as peroxidized ammonio-cobalt salts. Several of them, containing different bases, are often formed at the same time. Most of the peroxidized ammonio-cobalt salts are composed of cobaltic salts united with two or more molecules of ammonia. The composition of the normal salts may be illustrated by the chlorides, as in the following table : Tetrammonio-cobaltic chloride , . Co 2 Cl 6 . 4NH 3 Hexammouio-cobaltic chloride , . Co 2 Cl 6 . 6NH 3 COBALT. 409 Octammonio-cobaltic (or fusco-cobaltic) chloride Co 2 Cl 6 . 8NH 3 Decammonio-cobaltic (roseo- and pur- pureo-cobaltic) chloride . . . Co 2 Cl 6 . 10NH 3 Dodecammonio-cobaltic (or luteo-cobal- tic) chloride Co 2 Cl 6 . 12NH 3 . The formulae of the corresponding normal nitrates are deduced from the preceding by substituting N(3 3 for Cl ; those of the sulphates, oxalates, and other bibasic salts, by substituting SO 4 . C 2 4 , &c., for C1 2 . Thus decammonio- cobaltic sulphate = Co 2 (S0 4 ) 3 .10NH 3 . There are also several acid and basic sats of the same ammonia-molecules. Further, there is a class of salts con- taining the elements of nitrogen dioxide or nitrosyl, NO, in addition to nm- monia, e. g., decammonio-nilroso-obaltic or xantho- cobaltic oxy chloride, Co 2 Cl 4 0. 10NH 3 .N 2 O 2 . Lastly, Fre"my has obtained ammoniacal compounds (oxy- cobaltic salts) containing salts of cobalt corresponding to the dioxide.* Cobaltous salts have the following characters: Solution of potash gives a blue precipitate, changing by heat to violet and red. Ammonia gives a blue precipitate, soluble with difficulty in excess, with brownish-red color. Sodium carbonate affords a pink precipitate. Am- monium carbonate a similar compound, soluble in excess. Potassium ferro- cyanide gives a grayish-green precipitate. Potassium cyanide affords a yel- lowish-brown precipitate, which dissolves in an excess of the precipitant. The clear solutions, after boiling, may be mixed with hydrochloric acid without giving a precipitate. Hydrogen sulphide produces no change, if the cobalt be in combination with a strong acid. Ammonium sulphide throws down black sulphide of cobalt, insoluble in dilute hydrochloric acid. Cobaltic salts, formed by dissolving cobaltic oxide in acids, give with potash a dark-brown precipitate of hydrated cobaltic oxide ; with ammonia a brownish-red solution ; with the fixed alkaline carbonates a green solution, which deposits a small quantity of cobaltic oxide; with ammonium sulphide (after saturation of the free acid by ammonia) a black precipitate. Oxide of cobalt is remarkable for the magnificent blue color it communi- cates to glass : indeed, this is a character by which its presence may be most easily detected, a very small portion of the substance to be examined being fused with borax on a loop of platinum wire before the blowpipe ; the pro- duction of this color both in the inner and in the outer flame distinguishes cobalt from all other metals. The substance called smalt, used as a pigment, consists of glass colored by cobalt: it is thus made: The cobalt ore is roasted until nearly free from arsenic, and then fused with a mixture of potassium carbonate and quartz-sand, free from oxide of iron. Any nickel that may happen to be contained in the ore then subsides to the bottom of the crucible as arsen- ide : this is the speiss of which mention has already been made. The glass, when complete, is removed and poured into cold water: it is afterwards ground to powder and elutriated. Cobalt-ultramarine is a fine blue color prepared by mixing 16 parts of freshly-precipitated alumina with 2 parts of cobalt phosphate or arsenate : this mixture is dried and slowly heated to red- ness. By daylight the color is pure blue, but by artificial light it is violet. A similar compound, of a fine green color, is formed by igniting zinc oxide with cobalt-salts. Za/er is the roasted cobalt ore mixed with siliceous sand, * For the preparation and properties of all these salts, see Wa^ts's Dictionary of Chemistry, vol. i. p. 1051. Their rational formula are similar to those of the ainmoniacal platiuum Baits (p. 375). 85 410 TETRAD METALS. and reduced to fine powder ; it is used in enamel painting. A mixture in due proportions of the oxides of cobalt, manganese, and iron is used for giving a fine black color to glass. MANGANESE. Atomic weight, 55. Symbol, Mn. MANGANESE is tolerably abundant in nature in an oxidized state, forming, or entering into the composition of, several interesting minerals. Traces of this substance are very frequently found in the ashes of plants. Metallic manganese, or perhaps, strictly, manganese carbonide, may be prepared by the following process: The carbonate is calcined in an open vessel, by which it becomes converted into a dense brown powder : this is intimately mixed with a little charcoal, and about one-tenth of its weight of anhydrous borax. A charcoal crucible is next prepared by filling a Hessian or Cornish crucible with moist charcoal powder, introduced a little at a time, and rammed as hard as possible. A smooth cavity is then scooped in the centre, into which the above-mentioned mixture is compressed, and covered with charcoal powder. The lid of the crucible is then fixed, and the whole arranged in a very powerful wind-furnace. The heat is slowly raised until the crucible becomes red-hot, after which it is urged to its maximum for an hour or more. When cold, the crucible is broken up, and the metallic button of manganese extracted. Deville has lately prepared pure manganese by reducing pure manganese oxide with an insufficient quantity of sugar charcoal in a crucible made of caustic lime. Thus prepared, metallic manganese possesses a reddish lustre like bismuth ; it is very hard and brittle, and, when powdered, decomposes water, even at the lowest temperature. Dilute sulphuric acid dissolves it with great energy, evolving hydrogen. Brunner produced metallic man- ganese from manganese and sodium fluoride by means of sodium. The metal obtained by this process scratches glass and hardened steel, and has a specific gravity of 7-13. Manganese, from its general relations to the metals of the iron group, is usually regarded as a tetrad, forming a dichloride and trichloride analogous to the iron chlorides, together with oxides and other compounds of corre- sponding constitution. It is also said to form a heptachloride, Mn a d l4 , or MnCl 7 | , according to which it should be regarded as an octad ; but the com- MnCl 7 position of this compound is not very well established. MANGANESE CHLORIDES. The dichloride or Manganous chloride maybe prepared in a state of purity from the dark-brown liquid residue of the preparation of chlorine from manganese dioxide and hydrochloric acid, which often accumulates in the laboratory to a considerable extent in the course of investigation : from the pure chloride, the carbonate and all other salts can be conveniently obtained. The liquid referred to consists chiefly of the mixed chlorides of manganese and iron ; it is filtered, evapo- rated to perfect dryness, and the residue is slowly heated to dull ignition in an earthen vessel, with constant stirring. The iron chloride is thus either volatilized, or converted by the remaining water into insoluble sesquioxide, while the manganese salt is unaffected. On treating the grayish-looking powder thus obtained with water, the manganese chloride is dissolved out, and may be separated by filtration from the iron oxide. Should a trace of the latter yet remain, it may be got rid of by boiling the liquid for a few ] MANGANESE. 411 minutes with a little manganese carbonate. The solution of the chloride has usually a delicate pink color, which becomes very manifest when the salt is evaporated to dryness. A strong solution deposits rose-colored ta- bular crystals, which contain 4 molecules of water ; they are very soluble and deliquescent. The chloride is fusible at a red-heat, is decomposed slightly at that temperature by contact with air, and is dissolved by alco- hol, with which it forms a crystallizable compound. The trichloride, or Manganic chloride, Mn 2 Cl 6 , is formed when precipitated manganese oxide is immersed in cold dilute hydrochloric acid, the oxide then dissolving quietly without evolution of gas. Heat decomposes the trichloride into the monochloride and free chlorine. Heptachloride, Mn 2 Cl l4 (?). When potassium permanganate is dissolved in strong sulphuric acid, and fused sodium chloride is added by small portions at a time, a greenish-yellow gas is given off, which condenses at to a greenish-brown liquid. This compound, when exposed to moist air, gives off fumes colored purple by permanganic acid, and is instantly de- composed by water into permanganic and hydrochloric acids. It is regarded by Dumas, who discovered it, as the heptachloride of manganese ; but H. Rose regards it as an oxychloride, MnCl 2 2 , analogous to chromic oxy- chloride, a view which is corroborated by its mode of formation. Fluorides of manganese have been formed analogous to each of these chlor- ides. MANGANESE OXIDES. Manganese forms four well-defined oxides, con- stituted as follows : Monoxide, or Manganous oxide .... MnO Trimangano-tetroxide, or Manganoso-manganic oxide Mn 3 4 Sesquioxide, or Manganic oxide .... Mn 2 3 Dioxide or Peroxide ...... Mn0 2 . The first is a strong base, the third a weak base ; the second and fourth are neutral ; the second may be regarded as a compound of the first and third, MnO.Mn 2 3 . There are also several oxides intermediate between the monoxide and dioxide, occurring as natural minerals or ores of manga- nese. Manganese likewise forms two series of oxygen salts, called manga- nates and permanganates, the composition of which may be illustrated by the potassium salts, viz. : Potassium manganate . . Mn0 4 K 2 = Mn0 3 ,OK 2 Potassium permanganate . Mn 2 8 K 2 . Mn 2 7 .OK 2 . The oxides, Mn0 3 and Mn 2 7 , corresponding to these salts, are not known. Monoxide or Manganous oxide, MnO. When manganese carbonate is heated in a stream of hydrogen gas, or vapor of water, carbon dioxide is disen- gaged, and a greenish powder left behind, which is the monoxide. Pre- pared at a dull red heat only, the monoxide is so prone to absorb oxygen from the air, that it cannot be removed from the tube without change; but when prepared at a higher temperature, it appears more stable. This oxide is a very powerful base, being isomorphous with magnesia and zinc oxide ; it dissolves quietly in dilute acids, neutralizing them completely and form- ing salts, which have often a beautiful pink color. When alkalies are added to solutions of these compounds, the white hydrated oxide first precipitated speedily becomes brown by passing into a higher state of oxidation. Sesquioxide or Manganic oxide, Mn 2 3 . This compound occurs in nature as braunite, and in the state of hydrate as rnanganite : a very beautiful crystallized variety is found at Refold, in the Hartz. It is produced artificially, by exposing the hydrated monoxide to the air, and forms the principal part of the residue left in the iron retort when oxygen gas is prepared by exposing the native dioxide to a moderate red-heat. The 412 TETRAD METALS. color of the sesquioxide is brown or black, according to its origin or mode of preparation. It is a feeble base, isomorphous with alumina : for, when gently heated with diluted sulphuric acid, it dissolves to a red liquid, which, on the addition of potassium or ammonium sulphate, deposits octohedral crystals having a constitution similar to that of common alum : these are, however, decomposed by water. Strong nitric acid resolves this oxide into a mixture of monoxide and dioxide, the former dissolving, and the latter remaining unaltered; while hot oil of vitriol destroys it by forming man- ganous sulphate and liberating oxygen gas. On heating it with hydro- chloric acid, chlorine is evolved, as with the dioxide, but in smaller amount. Dioxide, Mn0 2 . Peroxide of manganese. Pyrolusite. The most common ore of manganese ; it is found both massive and crystallized. It may be obtained artificially in the anhydrous state by gently calcining the nitrate, or in combination with water, by adding solution of bleaching-powder to a salt of the monoxide. Manganese dioxide has a black color, is insoluble in water, and refuses to unite with acids. It is decomposed by hot hydro- chloric acid and by oil of vitriol in the same manner as the sesquioxide. As this substance is an article of commerce of considerable importance, being used in very large quantity for making chlorine, and as it is subject to great alteration of value from admixture of the sesquioxide and several impurities, it becomes desirable to possess means of assaying different sam- ples that may be presented, with a view of testing their fitness for the pur- poses of the manufacturer. One of the best and most convenient methods is the following: 50 grains of the mineral, reduced to very fine powder, are put into the little vessel employed in the analysis of carbonates (p. 306), together with about half an ounce of cold water, and 100 grains of strong hydrochloric acid ; 50 grains of crystallized oxalic acid are then added, the cork carrying the drying tube is fitted, and the whole quickly weighed or counterpoised. The application of a gentle heat suffices to determine the action ; the oxalic acid is oxidized into water and carbon dioxide, which escapes as gas while the manganese remains in solution as manganous chloride : Mn0 2 + C 2 4 H 2 -f 2HC1 = MnCl 2 -f 20H 2 -f- 2C0 2 Manganese Oxalic Manganese Carbon dioxide. acid. chloride. dioxide. This equation shows that every two molecules of carbon dioxide evolved correspond to one molecule of manganese dioxide decomposed. Now the molecular weight of this oxide, 87, is so nearly equal to twice that of car- bon dioxide, 44, that the loss of weight suffered by the apparatus when the reaction has become complete, and the residual gas has been driven off by momentary ebullition, may be taken to represent the quantity of real dioxide in the 50 grains of the sample. It is obvious that the apparatus of "Will and Fresenius, described at page 307, may also be used with advantage in this process. Trimango-tetr oxide, or Red manganese oxide, Mn 3 4 , or probably MnO.Mn 2 3 . This oxide is also found native, as hausmannite, and is produced artifi- cially by heating the dioxide or sesquioxide to whiteness, or by exposing the monoxide or carbonate to a red heat in an open vessel. It is a reddish- brown substance, incapable of forming salts, and acted upon by acids in the same manner as the two other oxides already described. Borax arid glass in the fused state dissolve this substance, and acquire the color of the amethyst. Varvicite, Mn 4 7 .OH 2 or Mn0.3Mn0 2 .OH 2 , is a natural mineral, discovered by Mr. Phillips among certain specimens of manganese ore from Warwick- shire : it has also been found at Ilefeld. It much resembles the dioxide, but is harder and 'more brilliant. By a strong heat, varvicite is converted into red oxide, with disengagement of aqueous vapor and oxygen gas. MANGANESE. 413 Several other oxides, intermediate in composition between the monoxide and dioxide, also occur native; they are probably mere mixtures, and in many cases the monoxide is more or less replaced by the corresponding oxides of iron, cobalt, and copper. MANGANOUS SULPHATE, S0 4 Mn.70H 2 =S0 3 .Mn0.70H 2 . A beautiful rose- colored and very soluble salt, isomorphous with magnesium sulphate. It is prepared on the large scale for the use of the dyer, by heating in a close vessel manganese dioxide and coal, and dissolving the impure monoxide thus obtained in sulphuric acid, with addition of a little hydrochloric acid towards the end of the process. The solution is evaporated to dryness, and again exposed to a red heat, by which ferric sulphate is decomposed. Water then dissolves out the pure manganese sulphate, leaving ferric oxide behind. The salt is used to produce a permanent brown dye, the cloth steeped in the solution being afterwards passed through a solution of bleaching-powder, by which the monoxide is changed to insoluble hydrate of the dioxide. Manganese sulphate sometimes crystallizes with 5 mole- cules of water. It forms a double salt with potassium sulphate, containing (S0 4 ) 2 Mn"K 2 .60H 2 . MANGANESE CARBONATE, C0 3 Mn x/ = C0 2 Mn // 0. Prepared by precipi- tating the dichloride with an alkaline carbonate. It is an insoluble white powder, sometimes with a buff-colored tint. Exposed to heat, it loses carbon dioxide and absorbs oxygen. MANGANATES. When an oxide of manganese is fused with potash, oxygen is taken up from the air, and a deep green saline mass results, which con- tains potassium manganate, Mri0 4 K 2 or Mn0 3 .OK 2 . The addition of potas- sium nitrate, or chlorate, facilitates the reaction. Water dissolves this compound very readily, and the solution, concentrated by evaporation in a vacuum, yields green crystals. Barium manganate, Mn0 4 Ba x/ , is formed in a similar manner. PERMANGANATES. When potassium manganate, free from any great ex- cess of alkali, is put into a large quantity of water, it is resolved into hy- drated manganese dioxide which subsides, and potassium permanganate, Mn 2 8 K 2 , or Mn 2 7 .OK 2 , which remains in solution, forming a deep-purple liquid: 3Mn0 4 K 2 -|--20H 2 = Mn0 2 + 40KH -f Mn 2 8 K 2 . This effect is accelerated by heat. The changes of color accompanying this decomposition are very remarkable, and have procured for the manga- nate the name mineral chameleon; excess of alkali hinders the reaction in some measure, by conferring greater stability on the manganate. Potas- sium permanganate is easily prepared on a considerable scale. Equal parts of very finely powdered manganese dioxide and potassium chlorate are mixed with rather more than one part of potassium hydrate dissolved in a little water, and the whole is exposed, after evaporation to dryness, to a temperature just short of ignition. The mass is treated with hot water, the insoluble oxide separated by decantation, and the deep-purple liquid concentrated by heat, until crystals form upon its surface: it is then left to cool. The crystals have a dark-purple color, and are not very soluble in cold water. The manganates and permanganates are decomposed by con- tact with organic matter: the former are said to be isomorphous with the sulphates, and the latter with the perchlorates. The green and red disin- fecting agents, known as Condy's fluids, are alkaline manganates and per- manganates. Hydrogen permanganate, or Permanganic acid, Mn./) 8 H 2 , is obtained by dis- 35* 414 TETRAD METALS. solving potassium permanganate in hydrogen sulphate (S0 4 H 2 ) diluted with one molecule of water, and distilling the solution at 60-70. Permanganic acid then passes over in violet vapors, and condenses to a greenish-black liquid, which has a metallic lustre, absorbs moisture greedily from the air, and acts as a most powerful oxidizing agent, instantly setting fire to paper and to alcohol.* Manganous salts are very easily distinguished by reagents. The fixed caustic alkalies and ammonia give white precipitates, insoluble in excess, quickly becoming brown. The carbonates of the fixed alkalies, and carbonate of ammonia, give white precipitates, but little subject to change, and insolu- ble in excess of carbonate of ammonia. Hydrogen sulphide gives no preci- pitate, but ammonium sulphide throws down insoluble flesh-colored sulphide of manganese, which is very characteristic. Potassium f err ocyanide gives a white precipitate. Manganese is also easily detected by the blowpipe: it gives with borax an amethyst-colored bead in the outer or oxidizing flame, and a colorless one in the inner flame. Heated upon platinum foil with sodium carbonate, it yields a green mass of sodium manganate. URANIUM. Atomic weight, 120. Symbol, U. This metal is found in a few minerals, as pitchblende, which is an oxide? and uranite, which is a phosphate; the former is its principal ore. The metal itself is isolated by decomposing the chloride with potassium or sodium, and is obtained as a black coherent powder, or in fused white malleable globules, according to the manner in which the process is con- ducted. It is permanent in the air at ordinary temperatures, and dots not decompose water ; but in the pulverulent state it takes fire at 207, burning with great splendor and forming a dark-green oxide. It unites, also, very violently with chlorine and with sulphur. Uranium forms two classes of compounds: viz., the uranous compounds, in which it is bivalent, e.g., U // C1 2 , U"0, U"S0 4I , &c., and the uranic com- pounds, in which it is apparently trivalent, like iron in the ferric com- pounds, e. g. : U'" a O" 8 , TI'" a O" 2 Cl 2f .U"' a O" 2 (N0 8 ) 2 , U'" 2 0" 2 (S0 4 )". There are also two oxides intermediate between uranous and uranic oxide- There is no chloride, bromide, iodide, or fluoride corresponding to uranic oxide, such as U 2 C1 6 ; neither are there any normal uranic oxysalts analo- gous to the normal ferric salts, such as U'" 2 (N0 3 ) 6 , U'" 2 (S0 4 )" 8 , &c. ; but all the uranic salts contain the group U 2 2 , which may be regarded as a bivalent radical (uranyl), uniting with acids in the usual proportions and forming normal salts ; thus : Uranic oxide or Uranyl oxide . . . (U Uranic oxychloride or Uranyl chloride . (U 2 2 X / C1 2 Uranic nitrate or Uranyl nitrate . . . (U 2 O 2 ) // (N0 3 ) 2 Uranic sulphate or Uranyl sulphate . . (U 2 2 ) // (S0 4 )^. This view of the composition of the uranic salts is not, however, essential, * Terrell, Bulletin de la Societe Chimique de Paris, 1862, p. 40. URANIUM. 415 since they may also be formulated as basic salts in the manner above illustrated. CHLORIDES. Uranous chloride, U // C1 2 , is formed, with vivid incandescence, by burning metallic uranium in chlorine gas, also by igniting uranous oxide in hydrochloric acid gas. It crystallizes in dark-green regular octohedrons, and dissolves easily in water, forming an emerald-green solution, which is decomposed when dropped into boiling water, giving off hydrochloric acid and yielding brown precipitate of hydrated uranous oxide. It is a power- ful deoxidizing agent, reducing gold and silver, converting ferric salts into ferrous salts, &c. Uranic oxychloride or Uranyl chloride, U 2 2 C1 2 , is formed when dry chlorine gas is passed over red-hot uranous oxide, as an orange-yellow vapor, which solidifies to a yellow crystalline fusible mass, easily soluble in water. It forms double salts with the chlorides of the alkali-metals, the potassium salt, for example, having the composition U 2 2 C1 2 .2KC1.20H 2 . OXIDES. Uranous oxide, U /X 0, formerly mistaken for metallic uranium, is obtained by heating the oxide, U 3 4 , or uranic oxalate, in a current of hydrogen. It is a brown powder, sometimes highly crystalline. In the finely divided state it is pyrophoric. It dissolves in acids, forming green salts. Uranoso-uranic oxide, U 3 4 = UO.U 2 3 . This oxide, analogous to the magnetic oxide of iron, forms the chief constituent of pitchblende. It is obtained artificially by igniting the metal or uranous oxide in contact with the air, or by gentle ignition of uranic oxide or uranic nitrate. It forms a dark-green velvety powder, of specific gravity 7-1 to 7-3. When ignited in hydrogen, or with sodium, charcoal, or sulphur, it is reduced to uranous oxide. When ignited alone, it yields a black oxide, U 4 5 , which is most probably a mixture of uranoso-uranic and uranous oxide. Uranoso-uranic oxide dissolves in strong sulphuric or hydrochloric acid, yielding a mixture of uranous and uranic salt; by nitric acid it is oxidized to uranic nitrate. Uranic oxide, or Uranyl oxide, U 2 3 = (U 2 2 ) // 0. Uranium and its lower oxides dissolve in nitric acid, forming uranic nitrate ; and when this salt is heated in a glass tube till it begins to decompose, at 250, pure uranic oxide remains in the form of a chamois-yellow powder. Uranic hydrate, U a 3 .20H 2 , cannot be prepared by precipitating a uranic salt with alkalies, inasmuch as the precipitate always carries down alkali with it; but it may be obtained by evaporating a solution of uranic nitrate in absolute alcohol at a moderate heat, till, at a certain degree of concentration, nitrous ether, aldehyde, and other vapors are given off, and a spongy yellow mass remains, which is the hydrate. In a vacuum at ordinary temperatures, or at 100 in the air, it gives off half its water, leaving the monohydrate, U 2 3 .OH 2 . This hydrate cannot be deprived of all its water without exposing it to a heat sufficient to drive off part of the oxygen, and reduce it to uranoso- uranic oxide. Uranic oxide and its hydrates dissolve in acids, forming the uranic sails. Tho nitrate, (U 2 2 ) // (N0 3 ) 2 .GOH 2 , may be prepared from pitchblende by dis- solving the pulverized mineral in nitric acid, evaporating to dryness, adding water, and filtering ; the liquid yields, by due evaporation, crystals of uranic nitrate, which are purified by a repetition of the process, and, lastly, dissolved in ether. This latter solution yields the pure nitrate. Uranates. Uranic oxide unites with the more basic metallic oxides. The uranates of the alkali-metals are obtained by precipitating a uranir salt. with a caustic alkali; those of the earth-metals and heavy metals, by pre- cipitating a mixture of a uranic salt and a salt of the other metal with am- monia, or by igniting a double carbonate or acetate of uranium and the 416 TETRAD METALS. other metal (calcio-uranic acetate, for example) in contact with the air. The uranates have, for the most part, the composition 2U 2 3 .M 2 0. They are yellow, insoluble in water, soluble in acids. Those which contain fixed bases are not decomposed at a red heat ; but at a white heat, the uranic oxide is reduced to uranoso-uranic oxide, or by ignition in hydrogen to uranous oxide; the mass obtained by this last method easily takes fire in contact with the air. Sodium uranate, 2U 2 3 .Na 2 0, is much used for im- parting a yellowish or greenish color to glass, and as a yellow pigment on the glazing of porcelain. The "uranium-yellow" for these purposes is prepared on the large scale by roasting pitchblende with lime in a rever- beratory furnace; treating the resulting calcium uranate with dilute sul- phuric acid; mixing the solution of uranic sulphate thus obtained with sodium carbonate, by which the uranium is first precipitated together with other metals, but then redissolved, tolerably free from impurity, by excess of the alkali; and treating the liquid with dilute sulphuric acid which throws down hydrated sodium uranate, 2U 2 3 .Na 2 GAq. Ammonium uranate is but slightly soluble in pure water, and quite insoluble in water containing sal-ammoniac; it may, therefore, be prepared by precipitat- ing a solution of sodium-uranate with that salt. It occurs in commerce as a fine deep-yellow pigment, also called "uranium yellow." This salt when heated to redness leaves pure uranoso-uranic oxide, and may, there- fore, serve as the raw material for the preparation of other uranium com- pounds. Uranous salts form green solutions, from which caustic alkalies throw down a red-brown gelatinous precipitate of uranous hydrate ; alkaline carbonates, green precipitates, which dissolve in excess, especially of ammonium car- bonate, forming green solutions. Ammonium sulphide forms a black preci- pitate of uranous sulphide ; hydrogen sulphide, no precipitate. Uranic salts are yellow, and yield with caustic alkalies a yellow precipitate of alkaline uranate, insoluble in excess of the reagent. Alkaline carbonates form a yellow precipitate consisting of a carbonate of uranium and the alkali-metal, soluble in excess, especially of acid ammonium or potassium carbonate. Ammonium sulphide forms a black precipitate of uranic sul- phide. Hydrogen sulphide forms no precipitate, but reduces the uranic to a green uranous salt. Potassium fcrrocyanide forms a red-brown precipitate. All uranium compounds, fused with phosphorus salt or borax in the outer blowpipe flame, produce a clear yellow glass, which becomes greenish on cooling. In the inner flame the glass assumes a green color, becoming still greener on cooling. The oxides of uranium are not reduced to the metallic state by fusion with sodium carbonate on charcoal. Uranium compounds are used, as already observed, in enamel painting, and for the staining of glass, uranous oxide giving a fine black color, and uranic oxide a delicate greenish-yellow, highly fluorescent glass. Uranium salts are also used in photography. INDIUM. Atomic weight, 74. Symbol, In. This metal has been recently discovered by Reich and Richter,* in the zinc-blende of Freiberg. Its spectrum is characterized by two indigo- colored lines, one very bright and more refrangible than the blue line of strontium, the other fainter but still more refrangible, approaching the blue line of potassium. It was the production of this peculiar spectrum that * Journal fur praktische Chemie, Ixxxix. 441. INDIUM. 417 led to the discovery of the metal. The ore, consisting chiefly of blende, galena, and arsenical pyrites, was roasted to expel sulphur and arsenic, then treated with hydrochloric acid, and the solution was evaporated to dryness. The impure zinc chloride thus obtained exhibited, when ex- amined by the spectroscope, the first of the indigo lines above mentioned. The chloride was afterwards obtained in a state of greater purity, and from this the hydrate and the metal itself were prepared. The first line then came out with much greater brilliancy, and the second was likewise observed Indium has hitherto been obtained in very small quantity only, so that its properties have been but imperfectly studied. It appears, however, to belong to the iron group. The metal itself is of a lead-gray color, soft, very malleable, and marks paper like lead. It dissolves easily in hydro- chloric acid, forming a deliquescent chloride. From the solution of this salt, it is precipitated by ammonia and potash as a hydrate, insoluble in excess of either reagent. Hydrogen sulphide does not precipitate it from an acid solution. The oxide heated on charcoal with soda, yields a metallic globule, which when reheated oxidizes to a yellowish powder. The compounds of indium impart a violet tint to the flame of a Bunsen's burner. CLASS V. PENTAD METALS. ANTIMONY. Atomic weight, 122. Symbol, Sb (Stibium). rpHIS important metal is found chiefly in the state of sulphide. The ore X is freed by fusion from earthy impurities, and is afterwards decomposed by heating with metallic iron or potassium carbonate, which retains the sul- phur. Antimony has a bluish-white color and strong lustre ; it is extremely brittle, being reduced to powder with the utmost ease. Its specific gravity is 6-8; it melts at a temperature just short of redness, and boils and vola- tilizes at a white heat. This metal has always a distinct crystalline, platy structure, but by particular management it may be obtained in crystals, which arc rhombohedral.* Antimony is not oxidized by the air at common temperatures ; when strongly heated, it burns with a white flame, producing oxide, which is often deposited in beautiful crystals. It is dissolved by hot hydrochloric acid, with evolution of hydrogen and production of chloride. Nitric acid oxidizes it to antimonic acid, which is insoluble in that liquid. Antimony forms two classes of compounds, the antimonious compounds in which it is trivalent, as Sb'^Clg, Sb"'^, Sb /// 2 S 3 , &c., and the antimonic compounds in which it is quinquivalent, as Sb v Cl 5 , Sb T g 6 , Sb T 2 S 6 , &c. CHLORIDES. The trichloride or Antimonious chloride, SbCl 3 , formerly called butter of antimony, is produced when hydrogen sulphide is prepared by the action of strong hydrochloric acid on antimonious sulphide. The impure and highly acid solution thus obtained is put into a retort, and distilled, until each drop of the condensed product, on falling into the aqueous liquid of the receiver, produces a copious white precipitate. The receiver is then changed and the distillation continued. Pure antimonious chloride then passes over, and solidifies on cooling to a white, highly crystalline mass, from which the air must be carefully excluded. The same compound is formed by distilling metallic antimony in powder with 2| times its weight of corrosive sublimate. Antimonious chloride is very deliquescent : it dis- solves in strong hydrochloric acid without decomposition, and the solution poured into water gives rise to a white bulky precipitate, which, after a short time, becomes highly crystalline, and assumes a pale fawn- color. This is the old powder of Algarotli; it is a compound of trichloride and tri- oxide of antimony. Alkaline solutions extract the chloride and leave the oxide. Finely powdered antimony thrown into chlorine gas takes fire. The pentachloride, or Antimonic chloride, SbCl 5 . is formed by passing a stream of chlorine gas over gently heated metallic antimony : a mixture of the two chlorides results, which may be separated by distillation. The pentachloride is a colorless volatile liquid, which forms a crystalline com- pound with a small portion of water, but is decomposed by a larger quantity into antimonic and hydrochloric acids. * On olectrolyzin.e; a solution of 1 part of tartar-emetic in 4 parts of antimonions chlorido by a small battery of two elements, antimony forming the positive, and metallic cupper tlie nega- tive pole, crusts of antimony are obtained which possess the remarkable property of exploding aud catching fire when cracked or broken (Gore, Proceedings of the Royal Society, ix. 70). 418 ANTIMONY. 419 ANTIMONIOUS HYDRIDE. ANTIMOXETTED HYDROGEN. STIBINE, SbH 3 A compound of antimony and hydrogen exists, but has not been isolated: when zinc is put into a solution of antimonious oxide, and sulphuric acid added, part of the hydrogen combines with the antimony, and the resulting gas burns with a greenish flame, giving rise to white fumes of antimonious oxide. When the gas is conducted through a red-hot glass tube of narrow dimensions, or burned with a limited supply of air, as when a cold porcelain surface is pressed into the flame, metallic antimony is deposited. On pass- ing a current of antimonetted hydrogen through a solution of silver nitrate, a black precipitate is obtained, containing SbAg 3 : from the formation of this compound it is inferred that the gas has the composition SbII 3 , analo- gous to ammonia, phosphine, and arsine. There are also several analogous compounds of antimony with alcohol-radicals, such as trimethylstibine, Sb(CH 3 ) 3 , triethylstibine, Sb(C 2 H 5 ) 3 , &c. OXIDES. Antimony forms two oxides, Sb 2 3 and Sb 2 5 , analogous to the chlorides, the first being a basic and the second an acid oxide, also an inter- mediate neutral oxide, Sb 2 4 . The trioxide, or Antimonious oxide, Sb 2 8 , occurs native, though rarely, as valentinite or white antimony, in shining white trimetric crystals ; also as scnarmontite in regular octohedrons : it is therefore dimorphous. It may be prepared by several methods : as by burning metallic antimony at the bot- tom of a large red-hot crucible, in which case it is obtained in brilliant crys- tals; or by pouring solution of antimonious chloride into water, and digest- ing the resulting precipitate with a solution of sodium carbonate. The oxide thus produced is anhydrous ; it is a pale buflf-colored powder, fusible at a red heat, and volatile in a closed vessel, but in contact with air at a high temperature, it absorbs oxygen and becomes changed into the tetroxide. When boiled with cream of tartar (acid potassium tartrate), it is dissolved, and the solution yields on evaporation crystals of tartar-emetic, which is almost the only antimonious salt that can bear admixture with water with- out decomposition. An impure oxide for this purpose is sometimes pre- pared by carefully roasting the powdered sulphide in a reverberatory furnace, nace, and raising the heat at the end of the process, so as to fuse the product : it has long been known under the name of glass of antimony, or vitrum anti- monii. Antimonious oxide likewise acts as a feeble acid, forming salts called an- timonites, which however are very unstable. The tetroxide, or Antimonoso-antimonic oxide, Sb 2 3 .Sb 2 6 , occurs native as cervanlite or antimony ochre, in acicular crystals, or as a crust or powder. It is the ultimate product of the oxidation of the metal by heat and air: it is a grayish-white powder, infusible, and non-volatile, in- soluble in water and acids, except when recently precipitated. On treat- ing it with tartaric acid (acid potassium tartrate), antimonious oxide is dis- solved, antimonic acid remaining behind; and when a solution of the tetroxide in hydrochloric acid is gradually dropped into a large quantity of water, antimonious oxide is precipitated, while antimonic acid remains dissolved. From these and similar reactions it has been inferred that the tetroxide is a compound of the trioxide and pentoxide. On the other hand, it is sometimes regarded as a distinct oxide, because it dissolves without decomposition in alkalies, forming salts (often called antimonitcs}, which may be obtained in the solid state. Two potassium salts, for example, have been formed, containing Sb 2 4 . K 2 and 2Sb 2 4 . K 2 ; and a calcium salt 2Sb./) 4 . 3CaO, occurs as a natural mineral called roiaeine. These salts may, how- ever, be regarded as compounds of antimonates and antimonites (contain- ing Sb 2 3 ) : thus, 2(Sb 2 4 . K 2 0) = (Sb 2 5 . K 2 0) -f (Sb 2 3 . K 2 0). The pentoxide, or Antimonic oxide, Sb 2 6 , is formed as an insoluble hydrate 420 PENTAD METALS. when strong nitric acid is made to act upon metallic antimony ; and, on ex- posing this hydrate to a heat short of redness, it yields the anhydrous pen- toxide as a pale straw-colored powder, insoluble in water and acid. It is decomposed by a red-heat, yielding the tetroxide. Hydrated antimonic oxide is likewise obtained by decomposing antimony pentachloride with an excess of water, hydrochloric acid being formed at the same time. The hydrated oxides, or acids, produced by the two pro- cesses mentioned, dift'er in many of their properties, and especially in their deportment with bases. The acid produced by nitric acid, called antimonic acid, is monobasic, producing normal salts of the form Sb 2 O s .M 2 0, or Sb0 3 M, and acid salts containing 2Sb 2 5 .M 2 0, or Sb 2 B .2SbO a M. The other, called melantimonic acid, is bibasic, forming normal salts containing Sb 2 5 . 2M 2 0, or Sb 2 7 M 4 , and acid salts, containing 2Sb 2 5 . 2M 2 0, or Sb,0 . M 2 0, so that the acid metantimonates are isomeric or polymeric, with the normal antimonates. Among the metantimonates an acid potassium salt, Sb 2 6 . K 2 . 70H, is to be particularly noticed as yielding a precipitate with sodium salts: it is, indeed, the only reagent which precipitates sodium. It is obtained by fusing antimonic oxide with an excess of potash in a silver crucible, dissolving the fused mass in a small quantity of cold water, and allowing it to crystallize in a vacuum. The crystals consist of normal potassium metantimonate, Sb 2 5 . 2KO, and, when dissolved in pure water, are decomposed into free potash and acid metantimonate. SULPHIDES. The trisulphide or Anlimonious sulphide, Sb 2 S 3 , occurs native as a lead-gray, brittle substance, having a radiated crystalline texture, and is easily fusible. It may be prepared artificially by melting together anti- mony and sulphur. When a solution of tartar-emetic is precipitated by hydrogen sulphide, a brick-red precipitate falls, which is the same sub- stance combined with a little water. If the precipitate be dried and gently heated, the water may be expelled without other change of color than a little darkening, but at a higher temperature it assumes the color and aspect of the native sulphide. This remarkable change probably indicates a passage from the amorphous to the crystalline condition. When powdered antimonious sulphide is boiled in a solution of caustic potash, it is dissolved antimonious oxide, and potassium sulphide being produced, the latter unites with an additional quantity of antimonious sul- phide to form a soluble sulphur-salt, in which the potassium sulphide is the sulphur base, and the antimonious sulphide is the sulphur acid: 3K 2 + 2Sb 2 S 3 = Sb 2 3 + Sb 2 S 8 . 3K 2 S. The antimonious oxide separates in small crystals from the boiling solu- tion when the latter is concentrated, and the sulphur-salt dissolves an extra portion of antimonious sulphide, which it again deposits on cooling as a red amorphous powder, containing a small admixture of antimonious oxide and potassium sulphide. This is the kcrmes mineral of the old chemists. The filtered solution mixed with an acid gives a potassium salt, hydrogen sulphide, and precipitated antimonious sulphide. Kermes may also be made by fusing a mixture of 5 parts antimonious sulphide and 3 of dry sodium carbonate, boiling the mass in 80 parte of water, and filtering while hot: the compound separates on cooling. The compounds of antimonious sulphide with basic sulphides are called sulph-antimonites ; many of them occur as natural minerals. For example : zinkenite, Sb 2 S 3 .PbS ; feather ore, Sb 2 S 8 .2PbS ; boulangerite, Sb 2 S s .3PbS ; fahlore, or tetrahedrite, Sb 2 S 3 .4Cu 2 S. the antimony being more or less replaced by arsenic, and the copper by silver, iron, zinc, and mercury. The pentasulphide or Antimonic sulphide, Sb 2 S 3 , formerly called sulphur au- ratum, is also a sulphur acid, forming salts called sulphantimonates, most of ANTIMONY. 421 which have the composition Sb 2 S 5 . 3M 2 S, or SbS 4 M 3 , analogous to the normal orthophosphates and arsenates. When 18 parts finely powdered antimoni- ous sulphide, 17 parts dry sodium carbonate, 13 parts slaked lime, and 3^ parts sulphur, are boiled for some hours in a quantity of water, calcium carbonate, sodium antimonate, antimony pentasulphide, and sodium sulphide are produced. The first is insoluble, and the second partially so: the two last-named bodies, on the contrary, unite to form soluble sodium sulph- antirnonate, SbS 4 Na 3 , which may be obtained by evaporation in beautiful crystalc. A solution of this substance, mixed with dilute sulphuric acid, furnishes sodium sulphate, hydrogen sulphide, and antimony pentasulphide, which falls as a golden-yellow flocculent precipitate. The sulphantimonates of the alkali-metals and alkaline earth-metals are very soluble in water, and crystallize for the most part with several mole- cules of water. Those of the heavy metals are insoluble, and are obtained by precipitation. The few salts of antimony soluble in water are distinctly characterized by the orange or brick-red precipitate with hydrogen sulphide, which is solu- ble in a solution of ammonium sulphide, and again precipitated by an acid. Antimoriious chloride, as already observed, is decomposed by water, yielding a precipitate of oxychloride. The precipitate dissolves in hy- drochloric acid, and the resulting solution gives, with potash, a white pre- cipitate of trioxide, soluble in a large excess of the reagent ; with ammonia the same, insoluble in excess ; with potassium or sodium carbonate, also a pre- cipitate of trioxide, which dissolves in excess, especially of the potassium salt, but reappears after a while. If, however, the solution contains tartaric acid, the precipitate formed by potash dissolves easily in excess of the alkali ; ammonia forms but a slight precipitate, and the precipitates formed by al- kaline carbonates are insoluble in excess. The last-mentioned characters are likewise exhibited by a solution of tartar-emetic (potassio-antimonious tartrate). Zinc and iron precipitate antimony from its solutions as a black powder. Copper precipitates it as a shining metallic film, which may be dissolved off by potassium permanganate, yielding a solution which will give the characteristic red precipitate with hydrogen sulphide. Solid antimony compounds fused upon charcoal with sodium carbonate or potassium cyanide, yield a brittle globule of antimony, a thick white fume being at the same time given off, and the charcoal covered to some distance around with a white deposit of oxide. Besides its application to medicine, antimony is of great importance in the arts, inasmuch as, in combination with lead, it forms type-metal. This alloy expands at the moment of solidifying, and takes an exceedingly sharp impression of the mould. It is remarkable that both its constituents shrink under similar circumstances, and make very bad castings. Britannia metal is an alloy of 9 parts tin and 1 part antimony, frequently also containing small quantities of copper, zinc, or bismuth. An alloy of 2 parts tin, 1 part antimony, and a small quantity of copper, forms a superior kind of pewter. Alloys of antimony with tin, or tin and lead, are now much used for machinery-bearings in place of gun-metal. Alloys of antimony with nickel and with silver occur as natural minerals. Antimony trisulphide enters into the composition of the blue signal-lights used at sea.* Blue or Bengal light : Dry potassium nitrate ... 6 parts Sulphur 2 " Antimony trisulphide 1 part. All in fine powder, and intimately mixed. 36 422 PENTAD METALS. ARSENIC. Atomic weight, 75. Symbol, As. ARSENIC is sometimes found native: it occurs in considerable quantity as a constituent of many minerals, combined with metals, sulphur and oxygen. In the oxidized state it has been found in very minute quantity in a great many mineral waters. The largest proportion is derived from the roasting of natural arsenides of iron, nickel, and cobalt. The operation is con- ducted in a reverberatory furnace, and the volatile products are condensed in a long and nearly horizontal chimney, or in a kind of tower of brick- work, divided into numerous chambers. The crude arsenious oxide thus produced is purified by sublimation, and then heated with charcoal in a retort; the metal is reduced, and readily sublimes. Arsenic has a steel-gray color, and high metallic lustre: it is crystalline and very brittle; it tarnishes in the air, but may be preserved unchanged in pure water. Its density, in the solid state, is 5-7 to 59. When heated, it volatilizes without fusion, and if air be present, oxidizes to arsenious oxide. Its vapor density, compared with that of hydrogen, is 150, which is twice its atomic weight, so that its molecule in the gaseous state, like that of phosphorus, occupies only half the volume of a molecule of hy- drogen (p. 228). The vapor has the odor of garlic. Arsenic combines with metals in the same manner as sulphur and phos- phorus, which it resembles, especially the latter, in many respects: indeed, it is often regarded as a metalloid. Arsenic, like nitrogen, behaves in most respects as a triad element, not being capable of uniting with more than three atoms of any one monad element. Thus, it forms the compounds AsH 3 , AsCl 3 , AsBr 3 , &c., but no compound analogous to the pentachloride of phosphorus or antimony. But just as ammonia, NH g , can take up the elements of hydrochloric acid to form sal-ammoniac, NH 4 C1, in which nitrogen appears quinquivalent, so likewise can arsenetted hydrogen or arsine, As //x H 3 , unite with the chlorides, bromides, &c. of the radicals, methyl, ethyl, &c., to form salts in which the arsenic appears to be quinquivalent, e. y. : Arsenethylium bromide . . . As v II 3 (C 2 H 5 )Br., &c. Arsenmethylium chloride . . . As v H 3 (CH 3 )Cl. In like manner, arsentrim ethyl, As /// (CH 3 ) 3 , unites w r ith the chlorides of methyl and ethyl, forming the compounds As v (CH 3 ) 4 Cl and As T (CH 3 ) 3 (C 2 H 6 )C1. Arsenic likewise forms two oxides, viz., arsenious oxide, As x// 2 3 , and arsenic oxide, As T2 5 , with corresponding acids and salts, analogous to phos- phorous and phosphoric compounds; the arsenates, in particular, are iso- morphous with the other phosphates, and resemble them closely in many other respects. ARSENIOUS CHLORIDE, AsCl 3 . This, the only known chloride of arsenic, is produced, with emission of heat and light, when powdered arsenic is thrown into chlorine gas. It is prepared by distilling a mixture of 1 part of metallic arsenic and 6 parts of corrosive sublimate, and by distil- ling arsenious oxide with strong hydrochloric acid, or with a mixture of common salt and sulphuric acid. It is a colorless, volatile, highly poisonous liquid, decomposed by water into arsenious and hydrochloric acids. Arse- nious iodtde, AsI 3 , is formed by heating metallic arsenic with iodine : it is a deep-red crystalline substance, capable of sublimation. The corresponding bromide arid fluoride are both liquid, ARSENIC. 423 HYDRIDES. Arsenic forms two hydrides, containing 2 and 3 atoms of hydrogen combined with 1 atom of arsenic. The trihydride, Arsenious hydride, Arsenetted hydrogen or Arsine, AsH~, analogous in composition to ammonia, phosphine, and stibine, is obtained pure by the action of strong hydrochloric acid on an alloy of equal parts of zinc and arsenic, and is produced in greater or less proportion whenever hydrogen is set free in contact with arsenious acid. Arsenetted hydrogen is a colorless gas, of specific gravity 2-G95, slightly soluble in water, and having the smell of garlic. It burns, when kindled, with a blue flame, generating arsenious .acid. It is also decomposed by transmission through a red-hot tube. Many metallic solutions are precipitated by this substance. When inhaled, it is exceedingly poisonous, even in very minute quantity. AsH 2 The dihydride, AsH 2 , or rather As 2 H 4 | , is produced by passing an AsH 2 electric current through water, the negative pole being formed of metallic arsenic : also when potassium or sodium arsenide is dissolved in water. It is a brown powder, which gives oft' hydrogen when heated in a close vessel, and burns when heated in the air. It is analogous in composition to arsendimethyl or cacodyl, As 2 (CH 3 ) 4 . ARSENIOUS OXIDE, ACID, AND SALTS. Arsenious oxide, As 2 3 , also called white oxide of arsenic, is produced in the manner already mentioned. It is commonly met with in the form of a heavy, white, glassy-looking substance, with smooth conchoi'dal fracture, which has evidently undergone fusion. When freshly prepared it is often transparent, but by keeping becomes opaque, at the same time slightly diminishing in density, and acquiring a greater degree of solubility in water. 100 parts of that liquid dissolve at 100 about 11-5 parts of the opaque variety: the largest portion separates, however, on cooling, leaving about 3 parts dissolved: the solution, which contains arsenious acid, feebly reddens litmus. Cold water, agitated with powdered arsenious oxide, takes up a still smaller quantity. Alkalies dis- solve this substance freely, forming arsenites; compounds with ammonia, baryta, strontia, lime, magnesia, and manganous oxide also have been formed: the silver salt is a beautiful lemon-yellow precipitate. The ar- senites are, however, very unstable, and have been but little examined. Those which have the composition As0 2 M, or As 2 3 . M 2 0, are generally re- garded as normal salts; there are also arsenites containing As 2 5 M 4 . or As 2 3 . 2M 2 0, and As0 3 M 3 , or As 2 3 3M 2 0, besides acid salts. Arsenious oxide is easily soluble in hot hydrochloric acid. Its vapor is colorless and inodorous, and it crystallizes on solidifying in brilliant transparent octo- hedrons. The oxide or acid itself has a feeble sweetish and astringent taste, and is a most fearful poison. ARSENIC OXIDE, ACID, AND SALTS. When powdered arsenious oxide is dissolved in hot hydrochloric acid, and oxidized by the addition of nitric acid, the latter being added as long as red vapors are produced, the whole then cautiously evaporated to complete dryncss, and the residue heated to low redness, arsenic oxide, As 2 5 , remains in the form of a white anhydrous mass which has no action upon litmus. When strongly heated, it is resolved into arsenious oxide and free oxygen. In water it dissolves slowly but com- pletely, giving a highly acid solution, which, on being evaporated to a syrupy consistence, deposits, after a time, hydrated crystals of arsenic acid, containing 2AsO 4 IT 3 . 6lI 2 , or As 2 6 .30H 2 -f Aq. These crystals, wlu-n heated to 100, give off their water of crystallization and leave trikydrated arsenic acid, As0 4 H 3 , or As 2 g . 3OII 2 ; at 140 100 the dihydrale, As,(> 7 II 4 , or As 2 6 . 20H 2 , is left ; and at 260 the monohydrate, AsO s II, or As 2 6 . OII a . 424 PENTAD METALS. The aqueous solutions of the three hydrates and of the anhydrous oxide exhibit exactly the same characters, and all contain the trihydrate, the other hydrates being immediately converted into that compound when dis- solved in water ; in this respect the hydrates of arsenic acid differ essen- tially from those of -phosphoric acid (p. 285). Arsenic acid is a very powerful acid, forming salts isomorphous with the corresponding phosphates : it is also tribasic. A sodium arsenate, As0 4 HNa, 2 . 120H 2 , undistinguishable in appearance from common sodium phosphate, may be prepared by adding the carbonate to a solution of arsenic acid, until an alkaline reaction is apparent, and then evaporating. This salt also crystallizes with 7 molecules of water. Another arsenate, As0 4 Na 3 . 120H 2 , is produced when sodium carbonate in excess is fused with arsenic acid, or when the preceding salt is mixed with caustic soda. A third, As0 4 H 2 Na. OH 2 , is made by substituting an excess of arsenic acid for the solution of alkali. The alkaline arsenates which contain basic water lose the latter at a red heat, but, unlike the phosphates, recover it when again dissolved. The arsenates of the alkalies are soluble in water: those of the earths and other metallic oxides are insoluble, but are dissolved by acid. The precip- itate with silver nitrate is highly characteristic of arsenic acid: it is red- dish-brown. SULPHIDES. Two sulphides of arsenic are known. The disulphide, As 2 S 2 , occurs native as Realgar. It is formed artificially by heating arsenic acid with the proper proportion of sulphur. It is an orange-red, fusible, and volatile substance, employed in painting, and by the pyrotechnist in making white fire. The trisulphide or arsenious sulphide, AsS 3 , also occurs native as Orpiment, and is prepared artificially by fusing arsenic with the appropriate quantity of sulphur, or by precipitating a solution of arsenious acid with hydrogen sulphide. It is a golden-yellow, crystalline substance, fusible, and volatile by heat. A cold solution of arsenic acid is not immediately precipitated by hydrogen sulphide, but after some hours the solution, satu- rated with hydrogen sulphide, yields a light-yellow deposit of sulphur, the arsenic acid being reduced to arsenious acid, which is then gradually con- verted into lemon-yellow arsenious sulphide. In boiling solutions the pre- cipitation takes place immediately. The mixture of sulphur and trisulphide, thus produced, was formerly regarded as a pentasulphide, corresponding to arsenic acid. The disulphide and trisulphide of arsenic are sulphur-acids, uniting with other metallic sulphides to form sulphur-salts. Those of the disulphide are called hyposulpharsemtes ; they are but little known. The salts of arsenious sulphide are called sulpharsenites. Their composition may be represented by that of the potassium salts, viz., As 2 S 2 K, or AsS 3 .K 2 S; As 2 S 5 K 4 , or As 2 S 3 . 2K 2 S, and AsS 3 K 3 , or As 2 S 3 . 3K 2 S. Of these the bibasic salts are the most common. The sulpharsenites of the alkali-metals and alkaline earth- metals are soluble in water, and may be prepared by digesting arsenious sulphide in the solutions of the corresponding hydrates or sulph-hydrates ; the rest are insoluble and are obtained by precipitation. Sulphur-salts, called sulpharsenates, corresponding in composition to the arsenates, are pro- duced, in like manner, by digesting the mixture of sulphur and arsenious sulphide, precipitated, as above mentioned, from arsenic acid, in solutions of alkaline hydrates or sulph-hydrates ; also by passing gaseous hydrogen sulphide through solutions of arsenates. There are three sulph-arsenates of potassium, containing AsS 3 K, or As 2 S 5 .K 2 S; As 2 S 7 K 4 , or As 2 S 5 .2K 2 S; and AsS 4 K ? , or As 2 S 5 . 3K 2 S. The sulph-arsenates of the alkali-metals and alkaline earth-metals are soluble in water ; the rest are insoluble and are obtained by precipitation. ARSENIC. 425 Fig. 174. Arsenious acid is distinguished by characters which cannot be misun- derstood. Silver nitrate, mixed with a solution of arsenious acid in water, occasions no precipitate, or merely a faint cloud : but if a little alkali, or a drop of ammonia, be added, a yellow precipitate of silver arscnite immediately falls. The precipitate is exceedingly soluble in excess of ammonia ; that sub- stance must, therefore, be added with great caution ; it is likewise very soluble in nitric acid. Cupric sulphate gives no precipitate with solution of arsenious acid, until the addition has been made of a little alkali, when a brilliant yellow-green precipitate (Scheele's green) falls, which also is very soluble in excess of ammonia. llijdrogcn sulphide passed into a solution of arsenious acid, to which a few drops of hydrochloric or sulphuric acid have been added, occasions the pro- duction of a copious bright-yellow precipitate of orpimcnt, which is dis- solved with facility by ammonia, and reprecipitated by acids. Solid arsenious oxide, heated by the blowpipe in a narrow glass tube with small fragments of dry charcoal, affords a sublimate of metallic arsenic in the shape of a brilliant steel-gray metallic ring. A portion of this, detached by the point of a knife, and heated in a second glass tube, with access of air, yields, in its turn, a sublimate of colorless, transparent, octohedral crystals of arsenious oxide. All these experiments, which jointly give demonstrative proof of the presence of the substance in question, may be performed with perfect pre- cision and certainty upon exceedingly small quantities of material. The detection of arsenious acid in complex mixtures, con- taining organic matter and common salt, as beer, gruel, soup, &c., or the fluid contents of the stomach in cases of poison ing, is a very far more difficult problem, but one which is, unfortunately, often required to be solved. These organic matters interfere completely with the liquid tests, and render their indications worthless. Sometimes the difficulty may be eluded by a diligent search in the suspected liquid, and in the vessel containing it, for fragments or powder of solid arseni- ous oxide, which, from its small degree of solubility, often escape solution, and from the high density of the substance, may be found at the bottom of the vessels in which the fluids are contained. If anything of the kind be found, it may be washed by decantation with a little cold water, dried, and then reduced with charcoal. For the latter purpose, a small glass tube is taken, having the figure represented in the margin ; white German glass, free from lead, is to be preferred. The arsenious oxide, or what is suspected to be such, is dropped to the bottom, and covered with splinters or little fragments of charcoal, the tube being filled to the shoulder. The whole is gently heated, to expel any moisture that may be present in the charcoal, and the deposited water wiped from the interior of the tube with bibulous paper. The narrow part of the tube containing the charcoal, from a to b, is now heated by the blowpipe flame ; when red-hot, the tube is inclined, so that the bottom also may become heated. The arsenious oxide, if present, is vaporized, and reduced by the charcoal, and a ring of metallic arsenic deposited on the cool part of the tube. To complete the experiment, the tube may be melted at a by the point of the flame, drawn off, and closed, and the arsenic oxidized to arsenious oxide, by chasing it up and down by the boat of a small spirit-lamp. A little water may after- wards be introduced, and boiled in the tube, by which the arsenious oxide will be dissolved, and to this solution the tests of silver nitrate 30* 426 PENTAD METALS. and ammonia, copper sulphate and ammonia, and hydrogen sulphide, may be applied. When the search for solid arsenious oxide fails, the liquid itself must be examined; a tolerably limpid solution must be obtained, from which the arsenic may be precipitated by hydrogen sulphide, and the orpiment col- lected, and reduced to the metallic state. It is in the first part of this operation that the chief difficulty is found: such organic mixtures refuse to filter, or filter so slowly as to render some method of acceleration indispen- sable.* Boiling with a little caustic potash or acetic acid will sometimes effect this object. The following is an outline of a plan which has been found successful in a variety of cases in which a very small quantity of arsenious acid had been purposely added to an organic mixture: Oil of vitriol, itself perfectly free from arsenic, is mixed with the suspected liquid, in the proportion of about a measured ounce to a pint, having been previously diluted with a. little water, and the whole is boiled in a flask for half an hour, or until a complete separation of solid and liquid matter becomes manifest. The acid converts any starch that may be present into dextrin and sugar: it completely coagulates albuminous substances, and casein, in the case of milk, and brings the whole in a very short time into a state in which filtration is both easy and rapid. Through the filtered solution, when cold, a current of hydrogen sulphide is transmitted, and the liquid is warmed, to facilitate the deposition of the arsenious sulphide, which falls in combination with a large quantity of organic matter, which often communicates to it a dirty color. This is collected upon a small filter, and washed. It is next transferred to a capsule, and heated with a mix- ture of nitric and hydrochloric acids, by which the organic impurities are in great measure destroyed, and the arsenic oxidized to arsenic acid. The solution is evaporated to dryness, the soluble part taken up by dilute hy- drochloric acid, and then the solution saturated with sulphurous acid, whereby the arsenic acid is reduced to the state of arsenious acid, the sul- phurous being oxidized to sulphuric acid. The solution of arsenious acid may now be precipitated by hydrogen sulphide without any difficulty. The liquid is warmed, and the precipitate washed by decantation, and dried. It is then mixed with black flux, and heated in a small glass tube, similar to that already described, with similar precautions; a ring of reduced arsenic is obtained, which may be oxidized to arsenious oxide, and further ex- amined. The black flux is a mixture of potassium carbonate and charcoal, obtained by calcining cream of tartar in a close crucible ; the alkali trans- forms the sulphide into arsenious acid, the charcoal subsequently effecting the deoxidation. A mixture of anhydrous sodium carbonate and charcoal may be substituted with advantage for the common black flux, as it is less hygroscopic. Other methods of proceeding, different in principle from the foregoing, have been proposed, as that of the late Mr. Marsh, which is exceedingly delicate. The suspected liquid is acidulated with sulphuric acid, and placed in contact with metallic zinc; the hydrogen reduces the arsenious acid and combines with the arsenic, if any be present. The gas is burned at a jet, and a piece of glass or porcelain held in the flame, when any ad- mixture of arsenetted hydrogen is at once known by the production of a brilliant black metallic spot of reduced arsenic on the porcelain; or the gas is passed through a glass tube heated at one or two places to redness, whereby the arsenetted hydrogen is decomposed, a ring of metallic arsenic appearing behind the heated portion of the tube. It has been observed (page 419) that antimonetted hydrogen gives a similar result. In order to distinguish the two substances, the gas may be passed into a solution of silver nitrate. Both gases give rise to a black * Respecting the separation of the arsenious acid by dialysis, see pago 149. BISMUTH. 427 precipitate, which, in the case of antimonetted hydrogen, consists of silver antimonide, Ag 3 Sb, whilst in the case of arsenettcd hydrogen, it is pure silver, the arsenic being then converted into arsenious acid, which com- bines with a portion of silver oxide. The silver arsenite remains dissolved in the nitric acid which is liberated by the precipitation of the silver, and Fig. 175. may be thrown down with its characteristic yellow color by adding ammonia to the liquid filtered off from the black precipitate. The black silver antimonide, when carefully washed, and subsequently boiled with a solution of tartaric acid, yields a solution containing antimony only, from which hydrogen sulphide sepa- rates the characteristic orange-yellow precipitate of an- timonious sulphide. A convenient form of Marsh's instrument is that shown in fig. 175: it consists of a bent tube, having two bulbs blown upon it, fitted with a stop-cock and nar- row jet. Slips of zinc are put into the lower bulb, which is afterwards filled with the liquid to be ex- amined. On replacing the stop-cock, closed, the gas collects and forces tfre liquid into the upper bulb, which then acts by its hydrostatic pressure, and ex- pels the gas through the jet so soon as the stop-cock is opened. It must be borne in mind that both common zinc and sulphuric acid often contain traces of arsenic. Mr. Bloxam* has proposed an important modification of Marsh's process for the detection of arsenic and antimony in organic substances, which is based on the behavior of solutions of these metals under the influence of the electric current. Antimony is deposited in the metallic state, without any disengagement of antimonetted hydrogen, while arsenic is evolved as arsenetted hydrogen, which may be recognized by the characters already indicated. A slip of copper-foil boiled in the poisoned liquid, previously acidulated with hydrochloric acid, withdraws the arsenic, and becomes covered with a white alloy. By heating the metal in a glass tube, the arsenic is expelled, and oxidized to arsenious acid. This is called Reinsch's test. BISMUTH. Atomic weight, 210. Symbol, Bi. BISMUTH is found chiefly in the metallic state, disseminated through various rocks, from which it is separated by simple exposure to heat. The metal is highly crystalline and very brittle : it has a reddish-white color, and a density of 9-9. Crystals of great beauty may be obtained by slowly cooling a considerable mass of this substance until solidification has com- menced, then piercing the crust, and pouring out the fluid resi ''.'.::. J>i.s- muth melts at about 2t)0 C. (500 F.), and volatilizes at a high temperature. It is remarkable as being the most diamagnetic of all known bodies. It is little oxidized by the air, but burns when strongly heated with a bluish flame. Nitric acid, somewhat diluted, dissolves it freely. Bismuth forms three classes of compounds, in which it is bi-, tri-, and quinquivalent respectively. The tri-compounds are the most stable and the most numerous. The only known compounds in which bismuth is quin- quivalent are indeed the pentoxide, l>i.,(),, together with the corresponding acid and metallic salts. Nevertheless, bismuth is regarded as a pentad, ou * Journal Cbcin. Soc., xiii. 338. 428 PENTAD METALS. account of the analogy of its compound with those of antimony. Several bismuth compounds are known in which the metal is apparently bivalent, but really trivalent, as : Bi"Cl a Bi"0 Bi 2 Cl 4 , or I ; Bi 2 2 , or I , &c. Bi"Cl 2 Bi"0 CHLORIDES. The trichloride or Bismuthous chloride is formed when bis- muth is heated in a current of chlorine gas, and passes over as a white, easily fusible substance, which readily attracts moisture from the air, and is converted into a crystallized hydrate. The same substance is produced when bismuth is dissolved in nitromuriatic acid, and the solution evapo- rated. Bismuthous chloride dissolves in water containing hydrochloric acid, but is decomposed by pure water, yielding a white precipitate of oxy- chloride : BiCl 3 + OH 2 = BiCIO + 2HC1. The dichloride, Bi 2 Cl 4 , produced by heating the trichloride with metallic bismuth, is a brown, crystalline, easily fusible mass, readily decomposed by water. At a high temperature it is resolved into the trichloride and metallic bismuth. OXIDES. The trioxide, or Bismuthous oxide, is a straw-yellow powder, ob- tained by gently igniting the neutral or basic nitrate. It is fusible at a high temperature, and in that state acts towards siliceous matter as a powerful flux. The hydrate, Bi /// H0 2 , or Bi 2 3 . OH 2 , is obtained as a white precipitate when a solution of the nitrate is decomposed by an alkali. Both the hy- drate and the anhydrous oxide dissolve in the stronger acids, forming the bismuthous salts, which have the composition Bi x// R 3 , where R denotes an acid radical, e. .9., Bi"'Cl 8 , Bi /// (N0 3 ) 3 , Bi'" 2 (S0 4 ) 8 . Many of these salts crystallize well, but cannot exist in solution unless an excess of acid is present. On diluting the solutions with water, a basic salt is precipitated, and an acid salt remains in solution. The normal nitrate, Bi'"(N0 3 ) 3 . 50H 2 , or Bi 2 3 . 3N 2 5 . 100H 2 , forme large transparent colorless crystals, which are decomposed by water in the man- ner just mentioned, yielding an acid solution containing a little bismuth, and a brilliant white crystalline powder, which varies to a certain extent in composition according to the temperature and the quantity of water em- ployed, but frequently consists of a basic nitrate, Bi 2 3 . N 2 5 . 20H 2 , or Bi /// (N0 3 ) 3 . Bi./) 3 . 30H 2 . A solution of bismuth nitrate, free from any great excess of acid, poured into a large quantity of cold water, yields an insoluble basic nitrate, very similar in appearance to the above, but con- taining rather a large proportion of bismuth oxide. This basic nitrate was once extensively employed as a cosmetic, but it is said to injure the skin, rendering it yellow and leather-like. It is used in medicine. Bismuth pentoxide, or Bismuthic oxide. When bismuth trioxide is sus- pended in a strong solution of potash, and chlorine passed through the liquid, decomposition of water ensues, hydrochloric acid being formed, and the trioxide being converted into the pentoxide. To separate any trioxide that may have escaped oxidation, the powder is treated with dilute nitric acid, when the bismuthic oxide is left as a reddish powder, which is insoluble in water. This substance combines with bases, but the compounds are not very well known. According to Arppe, there is an acid potassium bismuthate containing Bi 2 KH0 6 , or 2Bi 2 5 . j ^ 2 Q. The pentoxide when heated loses oxygen, an intermediate oxide, Bi 2 4 , being formed, which may be considered as bismuthous bismuthate, 2Bi 2 4 = Bi 2 3 . Bi 2 5 . VANADIUM. 429 Bismuth is sufficiently characterized by the decomposition of the nitrate and chloride and by water, and by the black precipitate of bismuth sulphide, insoluble in ammonium-sulphide, which its solutions yield when exposed to the action of hydrogen sulphide. A mixture of 8 parts of bismuth, 5 parts of lead, and 3 of tin, is known under the name of fusible metal, and is employed in taking impressions from dies and for other purposes : it melts below 100C. Bismuth is used, in conjunction with antimony, in the construction of thermo-electric piles, these two metals forming the opposite extremes of the thermo-electric series. VANADIUM. Atomic weight, 51-2. Symbol, V. VANADIUM is found, in small quantity, in some iron ores, and also as vana- date of lead. It has also been discovered in the iron slag of Statfordshire, {tnd recently, by Roscoe,* in larger quantity in the copper-bearing beds at Alderley Edge and Mottram St. Andrews, in Cheshire. Metallic vanadium remains when vanadium nitride is heated to whiteness in ammonia gas, but it does not appear to have been obtained pure. It is described as a white, brittle substance, having a strong lustre, and very refractory in the fire. Vanadium was, till lately, regarded as a hexad metal, analogous to tang- sten and molybdenum; but Roscoe has shown that it is a pentad, belonging to the phosphorus and arsenic group. This conclusion is based upon the composition of the oxides and oxychlorides; and on the isomorphism of the vanadates with the phosphates. The chlorides, and other compounds of vanadium with monad chlorous elements, have not yet been obtained. VANADIUM OXIDES. Vanadium forms four oxides, represented by the formulae, V 2 2 , V 2 3 , V 2 4 , V 2 5 , analogous therefore to the oxides of nitro- gen, excepting that the vanadium oxide analogous to nitrogen monoxide is not yet known. The dioxide, V 2 2 , which was regarded by Berzelius as metallic vanadium, is obtained by reducing either of the higher oxides with potassium, or by passing the vapor of vanadium-oxytrichloride, (VOC1 3 ), mixed with excess 6f hydrogen, through a combustion-tube containing red-hot charcoal. As obtained by the second process, it forms a light-gray glittering powder, or a metallically lustrous crystalline crust, having a specific gravity of 3-64, brittle, very difficult to fuse, and a conductor of electricity. When heated to redness in the air, it takes fire and burns to black oxide.. It is insoluble in sulphuric, hydrochloric, and hydrofluoric acid, but dissolves easily in nitromuriatic acid, forming a dark-blue liquid. The dioxide may be prepared in solution by the action of nascent hydro- gen (evolved by metallic zinc, cadmium, or sodium-amalgam), on a solution of vanadic acid in sulphuric acid. After passing through all shades of blue and green, the liquid acquires a permanent lavender tint, and then contains the vanadium in solution as dioxide, or as hi/po-vanadious salt. This com- pound absorbs oxygen more rapidly than any other known agent, and bleaches indigo and other vegetable colors as quickly as chlorine. Vanadium dioxide may be regarded as entering into many vanadium compounds, as a bivalent radical (just like uranyl in the uranic compounds), and may therefore be called nimnl/il. Vanadium trioxide, V 2 3 , or Vanadyl monoxide, (V 2 2 ) // 0, is obtained by * Proceedings of the Royal Society, xvi. 223. 430 PENTAD METALS. igniting the pentoxide in hydrogen gas, or in a crucible lined with char- coal. It is a black powder, with an almost metallic lustre, and infusible; by pressure it may be united into a coherent mass which conducts elec- tricity. When exposed warm to the air, it glows, absorbs oxygen, and is converted into pentoxide. At ordinary temperatures, it slowly absorbs oxygen, and is converted into tetroxide. By ignition in chlorine gas it is converted into vanadyl-trichloride and vanadium-pentoxide. It is insoluble in acids, but may be obtained in solution by the reducing action of nascent hydrogen (evolved from metallic magnesium) on a solution of vanadic acid in sulphuric acid. Vanadious oxide, Vanadium tetroxide, or Vanadyl dioxide, ~V 2 4 = (V 2 ? )0 ? . This oxide is produced, either by the oxidation of the dioxide or trioxide, or by the partial reduction of the pentoxide. By allowing the trioxide to absorb oxygen at ordinary temperatures, the tetroxide is obtained in blue shining crystals. It dissolves in acids, the more easily in proportion as it has been less strongly ignited, forming solutions of vanadious salts, which have a bright blue color. The same solutions are produced by the action of moderate reducing agents, such as sulphurous, sulph-hydric, or oxalic acid, upon vanadic acid in solution ; also by passing air through acid solu- tions of the dioxide till a permanent blue color is attained. With the hydrates and normal carbonates of the fixed alkalies, they form a grayish-white precipi- tate of hydrated vanadious oxide, which dissolves in a moderate excess of the reagent, but is reprecipitated by a large excess in the form of a vanadite of the alkali-metal. Ammonia in excess produces a brown precipitate, soluble in pure water, but insoluble in water containing ammonia. Ammonium sulphide forms & black-brown precipitate, soluble in excess. Tincture of galls forms a finely divided black precipitate, which gives to the liquid the appearance of ink. Vanadium-tetroxide also unites with the more basic metallic oxides, form- ing salts called vanadites, all of which are insoluble, except those of the alkali-metals. The solutions of the alkaline vanadites are brown, but when treated with hydrogen sulphide, they acquire a splendid red-purple color, arising from the formation of a sulphur-salt. Acids color them blue, by forming a double vanadious salt ; tincture of galls colors them blackish-blue. The insoluble vanadites, when moistened or covered with water, become green, and are converted into vanadates. Vanadium pentoxide, Vanadic oxide, or Vanadyl trioxide, V 2 ^5 (^2^2)^3- This is the highest oxide of vanadium. It may be prepared from native lead vanadate. This mineral is dissolved in nitric acid, and the lead and arsenic are precipitated by hydrogen sulphide, which at the same time re- duces the vanadium pentoxide to tetroxide. The blue filtered solution is then evaporated to dryness, and the residue digested in ammonia, which dissolves out the vanadic oxide reproduced during evaporation. In this solution a lump of sal-ammoniac is put; as that salt dissolves, ammonium vanadate subsides as a white powder, being scarcely soluble in a saturated solution of ammonium chloride. By exposure to a temperature below red- ness in an open crucible, the ammonia is expelled, and vanadic oxide left. By a similar process, Rosco has prepared vanadic oxide from a lime precip- itate containing 2 per cent, of vanadium, obtained in working up a poor cobalt ore from Mottram in Cheshire. Vanadium pentoxide has a reddish-yellow color, and dissolves in 1000 parts of water, forming a light yellow solution. It dissolves also in the stronger acids, forming red or yellow solutions, some of which yield crys- talline compounds (vanadic salts) by spontaneous evaporation. It unites, however, with bases more readily than with acids, forming salts called vana- dates. When fused with alkaline carbonates, it eliminates 3 molecules of car- bon dioxide, forming orthovanadates analogous to the orthop'tosphates ; thus : VANADIUM. 431 3(C0 2 . Na 2 0) -f V 2 5 = V 2 5 . 3Na 2 -f 3C0 2 . Sodium car- Vanadic Sodium ortho- Carbon bonate. oxide. vanadate. dioxide. It also forms mefavanadates analogous to the metaphosphates, and two series of acid vanadates or anhydrovanadates, viz. : Lead orthovanadate . (V0 4 ) 2 Pb x/ 3 or V 2 5 . 3Pb /x O Strontium metavanadate (V0 3 ) 2 Sr // or V 2 5 . Sr // Strontium divanadate (V0 3 ) 2 Sr // . V 2 5 or 2V 2 5 . Sr 7/ Strontium trivanadate (V0 8 ) a SrV,. 2V 2 6 or 3V 2 5 . Sr"0. Lead metavanadate occurs native as dechcnite; the orthovanadate also, combined with lead chloride, as vanadinite or vanadite, PbCl 2 . 3(V0 4 ) 2 Pb 3 , the mineral in which vanadium was first discovered. Descloizite is a di- plumbic vanadate, V 2 7 Pb x/ 2 or V 2 5 . 2PbO, analogous in composition to a pyrophosphate. The metavanadates are mostly yellow ; some of them, however, especially those of the alkaline earth-metals, and of zinc, cadmium, and lead, are con- verted by warming either in the solid state, or under water, or in aque- ous solution, especially in presence of a free alkali or alkaline carbonate into isomeric colorless salts. The same transformation takes place also, though more slowly, at ordinary temperatures. The metavanadates of al- kali-metal are colorless. The acid vanadates are yellow, or yellowish-red, both in the solid state and in solution: hence the solution of a neutral vana- date becomes yellowish-red on addition of an acid. The metavanadates of ammonium, the alkali-metals, barium, and lead, are but sparingly soluble in water; the other metavanadates are more soluble. The alkaline vana- dates are more soluble in pure water than in water containing free alkali or salt: hence they are precipitated from their solutions by addition of alkali in excess, or of salts. The vanadates are insoluble in alcohol. The aqueous solutions of vanadates form yellow precipitates with antimony, cop- per, lead, and mercury salts: with tincture of galls, they form a deep black liquid, which has been proposed for use as vanadium ink. Hydrogen sulphide reduces them to vanadites, changing the color from red or yellow to blue, and forming a precipitate of sulphur. Ammonium sulphide colors the solutions brown-red, and, on adding an acid, a light-brown pre- cipitate is formed consisting of vanadic sulphide mixed with sulphur, the . liquid at the same time turning blue. Hydrochloric acid decomposes the vanadates, with evolution of chlorine and formation of vanadium tetroxide. VANADIUM OXYCHLORIDES, or VANADYL CHLORIDES. Four of these com- pounds are known, viz., VOC1 8 , VOC1 2 , VOC1, and V 2 2 C1. The oxy trichloride, VO // C1 3 (formerly regarded as vanadium trichloride), is prepared : (1) By the action of chlorine on the trioxide: 3V 2 3 + C1 12 = V 2 6 -f 4VOC1 3 . (2) By burning the dioxide in chlorine gas, or by passing that gas over an ignited mixture of the trioxide, tetroxide, or pentoxide, and condensing the vapors in a cooled U-tube. Vanadium oxy trichloride, or vanadyl trichloride, is a golden-yellow liquid, of specific gravity 1-841 at, 14-5 C. (58 F.). Boiling point, 127 C. (260 F.). Vapor-density, by experiment, G-108; by calculation, 6-1 10. AVhen exposed to the air, it emits cinnabar-colored vapors, being resolved by the moisture of the air into hydrochloric and vanadic acids. It oxidizes mag- nesium and sodium. Its vapor, passed over perfectly pure carbon at a red heat, yields carbon dioxide; and when passed, together with hydrogen, 432 PENTAD METALS. through a red-hot tube, yields vanadium trioxide. These reactions show that the compound contains oxygen. The other oxychlorides of vanadium are solid bodies obtained by partial reduction of the oxytrichloride with zinc or hydrogen. VANADIUM SULPHIDES. Two of these compounds are known, analogous to the tetroxide and pentoxide ; both are sulphur acids. The telrasulphide, or Vanadious sulphide, V 2 S 4 , is a black substance formed by heating the tetroxide to redness in a stream of hydrogen sulphide ; also as a hydrate by dissolving a vanadious salt in excess of an alkaline monosulphide, and precipitating with hydrochloric acid. The penta sulphide, or Vanadic sul- phide, V 2 S 5 , is formed in like manner by precipitation from an alkaline vanadate. VANADIUM NITRIDES. The mononitride, VN, is formed by heating the compound of vanadium oxytrichloride with ammonium chloride to white- ness in a current of ammonia gas. It is a greenish-white powder unalter- able in the air. The dinitride, VN 2 , or V 2 N 4 , is obtained by exposing the same double salt in ammonia gas to a moderate heat. It is a black powder strongly acted upon by nitric acid. These compounds are of importance, as they promise to yield metallic vanadium, and thence also the chlorides, bromides, &c., of that metal. All vanadium compounds heated with borax or phosphorus-salt in the outer blow-pipe flame produce a clear bead, which is colorless if the quantity of vanadium is small, yellow when it is large ; in the inner flame the bead acquires a beautiful green color. Vanadic and chromic acids are the only acids whose solutions are red: they are distinguished from one another by the vanadic acid becoming blue, and the chromic acid green, by deoxidation. When a solution of vanadic acid, or an acidulated solution of an alkaline vanadate, is shaken up with ether containing hydrogen dioxide, the aqueous solution acquires a red color, like that of ferric acetate, while the ether remains colorless. This reaction will serve to detect the presence of 1 part of vanadic acid in 40,000 parts of liquid. The other reactions of vanadium in solution have already been described. TANTALUM. Atomic weight. 182. Symbol, Ta. THIS metal was discovered, in 1803, by Ekeberg, in two Swedish minerals, tantalite and yttrotantalite. A very similar metal, columbium, had been discovered in the preceding year by Hatchett, in columbite from Massachu- setts; and Wollaston, in 1807, on comparing the compounds of these metals, concluded that they were identical, an opinion which was for many years received as correct; but their separate identity has been completely estab- lished by the researches of H. Rose (commenced in 1846), who gave to the metal from the American and Bavarian columbites, the name Niobium, by which it is now universally known. More recently, Marignac has shown that nearly all tantalites and columbites contain both tantalum and niobium (or columbium), some tantalates, from Kimito, in Finland, being, how- ever, free from niobium, and some of the Greenland columbites containing only the latter metal unmixed with tantalum. In all these minerals tan- talum exists as a tantalate of iron and manganese ; yttrotantalite is essen- TANTALUM. 433 tially a tantalate of yttrium, containing also uranium, calcium, iron, and other metals. Tantalum is also contained in some varieties of wolfram. Metallic tantalum is obtained by heating the fluotantalate of potassium or sodium with metallic sodium in a well-covered iron crucible, and washing out the soluble salts with water. It is a black powder, which, when heated in the air, burns with a bright light, and is converted, though with difficulty, into tantalic oxide. It is not attacked by sulphuric, hydro- chloric, nitric, or even nitromuriatic acid. It dissolves slowly in warm aqueous hydrofluoric acid, with evolution of hydrogen, and very rapidly iu a mixture of hydrofluoric and nitric acids. Tantalum, in its principal compounds, is quinquivalent, the formula of tantalic chloride being TaCl 5 , that of tantalic fluoride, TaF 5 , and that of tantalic oxide (which, in combination with bases, forms the tantalates), Ta./) 5 . There is also a tantalous oxide, said to have the composition Ta0 2 ' and a corresponding sulphide, TaS 2 . TANTALIC CHLORIDE. TaCI 5 is obtained, as a yellow sublimate, by ignit- ing an intimate mixture of tantalic oxide and charcoal in a stream of chlorine gas. It begins to volatilize at 144 C. (291 F.) and melts to a yellow liquid at 221 C. (430 F.) The vapor-density between 350 and 440 (662 and 824 F.) has been found by Deville and Troost to be 12-42 referred to air, or 178-9 referred to hydrogen: by calculation, for the normal condensation to two volumes, it is 179-75. Tantalic chloride is de- composed by water, yielding hydrochloric and tantalic acids; but the de- composition is not complete even at the boiling-heat. TANTALIC FLUORIDE, TaF 5 , is obtained in solution by treating tantalic hy- drate with aqueous hydrofluoric acid. The solution, mixed with alkaline fluorides, forms soluble crystallizable salts, called tantalofluorides or fluotan- talates. The potassium salt, TaK 2 F 7 or TaF 5 .2KF, crystallizes in monoclinic prisms, isomorphous with the corresponding fluoniobate. TANTALIC OXIDE, Ta 2 5 , is produced when tantalum burns in the air, also by the action of water on tantalic chloride, and may be separated as a hydrate from the tantalates by the action of acids. It may be prepared from tan- talite, which is a tantalate of iron and manganese, by fusing the finely pul- verized mineral with twice its weight of potassium hydrate, digesting the fused mass in hot water, and supersaturating the filtered solution with hy- drochloric or nitric acid : hydrated tantalic oxide is then precipitated in white flocks, which may be purified by washing with water.* Anhydrous tantalic oxide, obtained by igniting the hydrate or sulphate, is a white powder, varying in density from 7-022 to 8-264, according to the temperature to which it has been exposed. Heated in ammonia gas it yields tantalum nitride: heated with carbon bisulphide, it is converted into tantalum bisulphide. It is insoluble in all acids, and can be rendered solu- ble only by fusion with potassium hydrate or carbonate. Hydrated Tantalic Oxide, or Tantalic acid, obtained by precipitating an aqueous solution of potassium tantalate with hydrochloric acid, is a snow- white bulky powder, which dissolves in hydrochloric and hydrofluoric acids; when strongly heated, it glows and gives off water. Tantalic oxide unites with basic metallic oxides, forming the tantalates, which are represented by the formulae, Ta 2 O 6 . M 2 and 3Ta,0 5 . 4M 2 0, the first including the native tantalates, such as ferrous tantalate, and the second certain easily crystallizable tantalates of the alkali-metals. The tantalates of the alkali-metals are soluble in water, and are formed by fusing tantalic oxide with caustic alkalies: those of the earth-metals and heavy metals are insoluble, and are formed by precipitation. * For more complete methods of preparation, see Wntts's Dictionary of Chemistry, v< 1. v. p. C68. 37 434 PENTAD METALS. Tantalum dioxide, or Tantalous oxide, Ta0 2 , may be represented by the TaivQ 2 formula | , in which the metal is still quinquivalent. It is produced Ta"0 2 by exposing tantalic oxide to an intense heat in a crucible lined with char- coal. It is a hard dark-gray substance, which, when heated in the air, is converted into tantalic oxide. Hydrochloric, or sulphuric add, added in excess to a solution of alkaline tantalate, forms a precipitate of tantalic acid, which redissolves in excess of the hydrochloric, but not of the sulphuric acid. Potassium ferrocyanide, added to a very slightly acidulated solution of an alkaline tantalate, forms a yellow precipitate; the ferricyanide, a white precipitate. Infusion of galls forms a light-yellow precipitate, soluble in alkalies. When tantalic chloride is dissolved in strong sulphuric acid, and then water and metallic zinc are added, a fine blue color is produced, which does not turn brown, but soon disappears. Tantalic oxide fused with microcosmic salt in either blowpipe flame forms a clear, colorless glass, which does not turn red on addition of a ferrous salt. With borax it also forms a transparent glass, which may be rendered opaque by interrupted blowing, or flaming. NIOBIUM, or COLUMBIUM. Atomic weight, 94. Symbol, Nb. This metal, discovered in 1801 by Hatchett, in American columbite, exists likewise, associated with tantalum, in columbites from other sources, and in most tantalites ; also, associated with yttrium, uranium, iron, and small quantities of other metals, in Siberian Samarskite, urano-tantalite, or yttroilmenite ; also in pyrochlore, euxenite, and a variety of pitchblende from Satersdalen in Norway. The metal, obtained in the same manner as tantalum, is a black powder, which oxidizes with incandescence when heated in the air. It dissolves in hot hydrofluoric acid, with evolution of hydrogen, and, at ordinary tem- peratures, in a mixture of hydrofluoric and nitric acid ; slowly, also, when heated with strong sulphuric acid. It is oxidized by fusion with acid potas- sium sulphate, and gradually converted into potassium niobate by fusion with potassium hydrate or carbonate. Niobium is quinquivalent, and forms only one class of compounds, namely, a chloride, NbCl 6 ; oxide, Nb 2 6 ; oxychloride, NbOCl 3 , &c. NIOBIC OXIDE, Nb 2 6 , is formed when the metal burns in the air. It is prepared from columbite, &c., by fusing the levigated mineral in a platinum crucible with 6 or 8 parts of acid potassium sulphate, removing soluble salts by boiling the fused mass with water, digesting the residue with ammonium sulphide to dissolve tin and tungsten, boiling with strong hydrochloric acid to remove iron, uranium, and other metals, and finally washing with water. Niobic oxide is thus obtained generally mixed with tantalic oxide, from which it is separated by means of hydrogen and potassium fluoride, HF . KF, which converts the tantalum into sparingly soluble potassium tantofluoride, 2KF . TaF 2 , and the niobium into easily soluble potassium nioboxyfluoride, 2KF. NbOF 3 . Aq. Niobic oxide is also produced by decomposing niobic chloride, or oxy- chloride, with water : when pure it has a specific gravity of 4-4 to 4-5. It 485 is an acid oxide, uniting with basic oxides, and forming salts called niobates, some of which occur as natural minerals : columbite, for example, being a ferro-manganous niobate. The potassium niobates crystallize readily, and 3Nb 2 5 . 5aq. as a pulverulent precipitate, by boiling a solution of potassium nioboxy-fluoride with potassium carbonate. The sodium niobates are crys- talline powders which decompose during washing. There is also a sodium and potassium niobate, containing Na 2 . 3K 2 . 3Nb 2 5 . 9aq. NIOBIC CHLORIDE, NbCl 5 , is obtained, together with the oxychloride, by heating an intimate mixture of niobic oxide and charcoal in a stream of chlorine gas. It is yellow, volatile, and easily fusible. Its observed vapor- density, according to Deville and Troost, is 9-6 referred to air, or 138-6 referred to hydrogen as unity : by calculation for a two-volume condensa- Q4- I r -\ 3'V^ tion, it is _== 135-75. The oxychloride, NbOCl 3 , is white, vola- tile, but not fusible : its specific gravity, referred to hydrogen, is, by obser- vation, 114-06; by calculation, 94 + ^ + 3. 35-5^ m . 2 ^ Both thege compounds are converted by water into niobic oxide. NIOBIC OXYFLUORIDE, NbOF 3 , is formed by dissolving niobic oxide in hydrofluoric acid. It unites with the fluorides of the more basic metals, forming salts isomorphous with the titanofluorides, stannofluorides, and tungstofluorides, 1 atom of oxygen in these salts taking the place of 2 atoms of fluorine. Marignac has obtained five potassium nioboxyfluorides, all perfectly crystallized, namely: 2KF.NbOF 3 . aq., crystallizing in monoclinic plates; " cuboid forms (systems undetermined), monoclinic needles, 5KF.3NbOF 3 .aq. " hexagonal prisms, 4KF.3NbOF 3 .2aq. triclinic prisms. Potassium niobofluoride, 3KF.NbF 5 , separates in shining monoclinic nee- dles from a solution of the first of the nioboxyfluorides above mentioned in hydrofluoric acid. Nioboxyfluorides of ammonium, sodium, zinc, and copper have also been obtained. The isomorphism of these salts with the stannofluorides, titanofluorides, and tungstofluorides, shows clearly that the existence of isomorphism be- tween the corresponding compounds of any two elements, must not be taken as a decided proof that those elements are of equal atomicity : for in the case now under consideration, we have isomorphous salts formed by tin and titanium, which are tetrads, niobium, which is a pentad, and tung- sten, which is a hexad. The compounds of niobium cannot easily be mistaken for those of any other metal except tantalum. The most characteristic reactions of niobates and tantalates with liquid reagents are the following : 436 PENTAD METALS. Hydrochloric acid Ammonium chloride . Potassium ferrocyanide " ferricyanide Infusion of galls . . Niobates. White precipitate, insol- uble in excess. Precipitation slow and incomplete. Red precipitate. Bright yellow precipi- tate. Orange-red precipitate. Tantalates. White precipitate, solu- ble in excess. Complete precipitation as acid ammonium tantalate. Yellow precipitate. White precipitate. Light yellow precipi- tate. Niobic oxide, heated with borax in the outer blow-pipe flame, forms a colorless bead, which, if the oxide is in sufficient quantity, becomes opaque by interrupted blowing or naming. In microcosmic salt it dissolves abundantly, forming a colorless bead in the outer flame, and in the inner a violet-colored, or if the bead is saturated with the oxide, a beautiful blue bead, the color disappearing in the outer flame CLASS VI. HEX AD METALS. CHROMIUM. Atomic weight, 52-5. Symbol, Cr. /CHROMIUM is found in the state of oxide, in combination with iron \J oxide, in some abundance in the Shetland Islands, and elsewhere: as lead chromatc it constitutes a very beautiful mineral, from which it was first obtained. The metal itself is prepared in a half-fused condition by mixing the oxide with half its weight of charcoal-powder, enclosing the mixture in a crucible lined with charcoal, and then subjecting it to the very highest heat of a powerful furnace. Deville has prepared metallic chromium by reducing pure chromium sesquioxide, by means of an insufficient quantity of charcoal, in a lime crucible. Thus prepared, metallic chromium is less fusible than platinum, and as hard as corundum. It is readily acted upon by dilute hydrochloric acid, less so by dilute sulphuric acid, and not at all by concentrated nitric acid. Fre'my obtained chromium in small cubic crystals, by the action of sodium vapor on chromium trichloride at a red heat. The crys- talline chromium resists the action of concentrated acids, even of nitromu- riatic acid. Chromium forms a hexfluoride, Cr^Fg, and a corresponding oxide, Cr^Oj, analogous to sulphuric oxide ; also, an acid, Cr0 4 H 2 , analogous to sul- phuric acid, with corresponding salts, the chromates, which are isomorphous with the sulphates. In its other compounds, chromium resembles iron, form- ing the chromic compounds Cr 2 Cl 6 , Cr 2 3 , c., in which it is apparently triva- lent but really quadrivalent, and the chromous compounds, CrCl 2 , CrO, &c., in which it is bivalent. CHLORIDES. The dichloride or Chromous chloride, CrCl 2 , is prepared by heating the violet-colored trichloride, contained in a porcelain or glass tube, to redness in a current of perfectly dry and pure hydrogen gas : hy- drochloric acid is then disengaged, and a white foliated mass is obtained, which dissolves in water with great elevation of temperature, yielding a blue solution, which, on exposure to the air, absorbs oxygen with extraor- dinary energy, acquiring a deep green color, and passing into the state of chromic oxychloride, Cr 2 Cl 6 .Cr 2 3 . Chromous chloride is one of the most powerful reducing or deoxidizing agents known, precipitating calo- mel from a solution of mercuric chloride, instantly converting tungstic acid into blue tungsten oxide, and precipitating gold from a solution of auric chloride. It forms, with ammonia, a sky-blue precipitate which turns green on exposure to the air; with ammonia and sal-ammoniac, a blue solution turning red on exposure to the air ; and with ammonium sulphide, a black precipitate of chromous sulphide. The trichloride or Chromic chloride, Cr 2 Cl 6 . is obtained in the anhydrous state by heating to redness in a porcelain tube a mixture of chromium M-S- quioxide and charcoal, and passing dry chlorine gas ovor it. The tri- chloride sublimes, and is deposited in the cool part uf the tube, in the form 37 * 437 438 HEXAD METALS. of beautiful crystalline plates of a pale violet color. It is totally insoluble in water under ordinary circumstances, even at the boiling-heat. It dis- solves, however, and assumes the deep-green hydrated state in water con- taining an exceedingly minute quantity of the dichloride in solution. The hydration is marked by the evolution of much heat. This remarkable effect must probably be referred to the class of actions known at present under the name of catalysis. The green hydrated chromic chloride is easily formed by dissolving chromic hydrate in hydrochloric acid, or by boiling lead chromate, or silver chromate, or a solution of chromic acid, with hydrochloric acid and a re- ducing agent, such as alcohol, or sulphurous acid, or even with hydro- chloric acid: 2Cr0 3 -f 12HC1 = Cr 2 Cl 6 -f 60H 2 + C1 6 . The solution thus obtained exhibits the same characters as the chromic oxygen-salts. When evaporated it leaves a dark-green syrup, which, when heated to 100 in a stream of dry air, yields a green mass containing Cr 2 Cl 6 . 90H 2 . The same solution evaporated in a vacuum yields green granular crystals containing O 2 C1 6 .OH 2 . FLUORIDES. The trifluoride, or Chromic fluoride, Cr 2 F 6 , is obtained by treating the dried sesquioxide with hydrofluoric acid, and strongly heating the dried mass, as a dark-green substance, which melts at a high tempera- ture, and sublimes when still more strongly heated, in shining regular oc- tohedrons. The hexfluoride, CrF 6 , is formed by distilling lead chromate with fluorspar and fuming oil cf vitriol in a leaden retort, and condensing the vapors in a cooled and dry leaden receiver. It then condenses to a blood-red fuming liquid, which volatilizes when its temperature rises a few degrees higher. The vapor is red, and, when inhaled, produces violent coughing and severe oppression of the lungs. The hexfluoride is decomposed by water, yield- ing hydrofluoric and chromic acids. A fluoride, intermediate in composi- tion between the two just described, is obtained in solution by decomposing the brown dioxide by hydrofluoric acid. The solution is red, and yields by evaporation a rose-colored salt, which is redissolved without alteration by water, and precipitated brown by ammonia. OXIDES. Chromium forms five oxides, containing CrO, Cr 3 4 , Cr 2 3 , Cr0 2 , and Cr0 3 , the first three being analogous in composition to the three oxides of iron. The monoxide, or Chromous oxide, Cr // 0, is formed on adding potash to a solution of chromous chloride, as a brown precipitate, which speedily passes to deep foxy-red, with disengagement of hydrogen, being converted into a higher oxide. Chromous oxide is a powerful base, forming pale-blue salts, which absorb oxygen with extreme avidity. Potassio-chromous sulphate contains (S0 4 ) 2 > Cr // K 2 , like the other members of the same group. Trichromic tetroxide, Cr 3 4 = CrO.Cr 2 3 , is the above mentioned brownish- red precipitate produced by the action of water upon the monoxide. The decomposition is not complete without boiling. This oxide corresponds with the magnetic oxide of iron, and is not salifiable. Sesquioxide, or Chromic oxide, Cr 2 3 . When mercurous chromate, pre- pared by mixing solutions of mercurous nitrate and potassium chromate, or bichromate, is exposed to a red heat, it is decomposed, pure chromium ses- quioxide, having a fine green color, remaining. In this state the oxide is, like alumina after ignition, insoluble in acids. The anhydrous sesquioxide may be prepared in a beautifully crystalline form by heating potassium bi- chromate, K 2 0.2Cr0 3 , to full redness in an earthen crucible. One-half of CHROMIUM. 439 the chromium trioxide contained in that salt then suffers decomposition, oxygen being disengaged and sesquioxide left. The melted mass is then treated with water, which dissolves out neutral potassium chromate, and the oxide is, lastly, washed and dried. Chromium sesquioxide communicates a fine green tint to glass, and is used in enamel painting. The crystalline sesquioxide is employed in the manufacture of razor-strops. From a solu- tion of chromium sesquioxide in potash, or soda, green gelatinous hydrated sesquioxide of chromium is separated on standing. When finely powdered arid dried over sulphuric acid, it consists of Cr. 2 3 .60H 2 . A hydrate may also be prepared by boiling a somewhat dilute solution of potassium bichro- mate strongly acidulated with hydrochloric acid, with small successive por- tions of sugar or alcohol. In the former case carbon dioxide escapes: in the latter, aldehyde and also acetic acid are formed, substances with which we shall become acquainted in organic chemistry ; and the chromic acid of the salt becomes converted into chromium trichloride, the color of the liquid changing from red to deep green. The reduction may also be effected, as already observed, by hydrochloric acid alone. A slight excess of ammonia precipitates the hydrate from this solution. It has a pale purplish-green color, which becomes full green on ignition ; an extraordinary shrinking of volume and sudden incandescence are observed when the hydrate is decom- posed by heat. Chromium sesquioxide is a feeble base, resembling, and isomorphous with, iron sesquioxide and alumina; its salts (chromic salts) have a green or purple color, and are said to be poisonous. Chromic sulphate, (S0 4 ) 3 Cr 2 , is prepared by dissolving the hydrated oxide in dilute sulphuric acid. It unites with the sulphates of potassium and ammonium, giving rise to magnificient double salts, which crystallize in regular octohedrons of a deep claret-color, and possess a constitution re- sembling that of common alum, the aluminium being replaced by chromium. The ammonium-salt, for example, has the composition (S0 4 ) 2 Cr /// (NH 4 ).12 aq. The finest crystals are obtained by spontaneous evaporation, the solu- tion being apt to be decomposed by heat. The dioxide, Cr0 2 , which is, perhaps, a chromic chromate, Cr0 3 . Cr 2 3 , is a brown substance obtained by digesting chromic oxide with excess of chromic acid, or by partial reduction of chromic acid with alcohol, sulphur- ous acid, &c. CHROMIUM TRIOXIDE, Cr0 3 ; in combination with water, forming Chromic atid, Cr0 3 . OH 2 = Cr0 4 H 2 = (Cr0 2 ) // (OH) 2 . Whenever chromium sesqui- oxide is strongly heated with an alkali, in contact, with air, oxygen is ab- sorbed and the trioxide generated. Chromium trioxide may be obtained nearly pure, and in a state of great beauty, by mixing 100 measures of a cold saturated solution of potassium bichromate with 150 measures of oil of vitriol, and leaving the whole to cool. It crystallizes in brilliant crimson- red prisms: the mother-liquor is poured off, and the crystals are placed upon a tile to drain, being closely covered by a glass or bell-jar.* It is also formed by decomposing the hexfluoride with a small quantity of water. Chromium trioxide is very deliquescent and soluble in water : the solution is instantly reduced by contact with organic matter. Chromic acid is bibasic and analogous in composition to sulphuric acid ; its salts are isomorphous with the corresponding sulphates. Potassium chromate, Cr0 4 K 2 , or (Cr0 2 ) // (OK) 2 . This salt is made directly from the native chrome-iron-ore, which is a compound of chromium sesqui- oxide and ferrous oxide, analogous to magnetic iron ore, by calcination with nitre or with potassium carbonate, or with caustic lime, the ore being re- duced to powder and heated for a long time with the alkali in a reverbera- * * Warington, Memoirs of the Chemical Society, i. 18. 440 HEXAD METALS. tory furnace. The product, when treated with water, yields a yellow solu- tion, which, by evaporation, deposits anhydrous crystals of the same color, isomorphous with potassium sulphate. Potassium chromate has a cool, bitter, and disagreeable taste, and dissolves in 2 parts of water at 15-5. Potassium bichromate, or anhydrochr ornate, 2Cr0 3 . K. 2 0, or Cr0 4 K 2 . Cr0 3 . When sulphuric acid is added to the preceding salt in moderate quantity, one half of the base is removed, and the neutral chromate converted into bichromate. The new salt, of which immense quantities are manufactured for use in the arts, crystallizes by slow evaporation in beautiful red tabular crystals, derived from a prism. It melts when heated, and is soluble in 10 parts of water; the solution has an acid reaction. Potassium trichromate,3Cr0 3 .~K.< i O, or Cr0 4 K 2 . 2Cr0 3 , maybe obtained in crystals by dissolving the bichromate in an aqueous solution of chromic acid, and allowing it to evaporate over sulphuric acid. Lead chromate, Cr0 4 Pb // . On mixing solutions of potassium chromate or bichromate with lead nitrate or acetate, a brilliant yellow precipitate falls, which is the compound in question ; it is the chrome-yelloiv of the painter. Then this compound is boiled with lime-water, one half of the acid is with- drawn, and a basic lead chromate of an orange-red color left. The basic chromate is also formed by adding lead chromate to fused nitre, and after- wards dissolving out the soluble salts by water: the product is crystalline, and rivals vermilion in beauty of tint. The yellow and orange chrome- colors are fixed upon cloth by the alternate application of the two solutions, and in the latter case by passing the dyed stuff through a bath of boiling lime-water. Silver chromate, Cr0 4 Ag 2 . This salt precipitates as a reddish-brown pow- der when solutions of potassium chromate and silver nitrate are mixed. It dissolves in hot dilute nitric acid, and separates, on cooling, in small ruby-red platy crystals. The chrornates of barium, zinc, and mercury are insoluble ; the first two are yellow, the last is brick-red. CHROMIUM DIOXYDICHLORIDE, Cr0 2 Cl 2 , commonly called Chlorochromic acid. When 3 parts of potassium bichromate and 3 parts of common salt are intimately mixed and introduced into a small glass retort, 9 parts of oil of vitriol then added, and heat applied as long as dense red vapors arise, this compound passes over as a heavy deep-red liquid resembling bromine: it is decomposed by water, with production of chromic and hydrochloric acids It is analogous to the so-called chloromolybdic, chlorotungstic, and chlorosulphuric acids in composition, and in the products which it yields when decomposed. It may be regarded as formed from the trioxide by substitution of C1 2 for 0, or from chromic acid, (Cr0 2 ) // (OH) 2 , by substitu- tion of C1 2 for (OH) 2 ; also as a compound of chromium hexchloride (not known in the separate state), with chromium trioxide: CrC] 6 .2Cr0 3 300 2 C1 2 . PERCHROMIC ACID is obtained, according to Barreswil, by mixing chromic acid with dilute hydrogen oxide, or potassium bichromate with a dilute but very acid solution of barium dioxide in hydrochloric acid; a liquid is then formed of a blue color, which is removed from the aqueous solution by ether. This very unstable compound has perhaps the composition Cr 2 8 H 2 or Cr 2 7 . OH 2 , analogous to that of permanganic acid. Reactions of Chromium compounds. A solution of chromic chloride or a chromic oxygen salt is not precipitated or changed in any way by hydrogen sulphide. Ammonium sulphide throws down a grayish-green precipitate of chromic hydrate. Caustic fixed alkalies also precipitate the hydrated oxide, and dissolve it easily when added in excess. Ammonia, the same, but nearly TUNGSTEN", OR WOLFRAM. insoluble. The carbonates' of potassium, sodium, and ammonium also throw down a green precipitate of hydrate, slightly soluble in a large excess. Chromous salts are but rarely meth with ; for their reactions, see Chro- mium dichloride, p. 437. Chromic acid and its salts are easily recognized in solution by forming a pale yellow precipitate with barium salts, bright yellow with lead salts, brick- red with mcrcurous salts, and crimson with silver salts ; also by their capa- bility of yielding the green sesquioxide by reduction. All chromium compounds, ignited with a mixture of nitre and an alka- line carbonate, yield an alkaline chromate, which may be dissolved out by water, and on being neutralized with acetic acid, will give the reactions just mentioned. The oxides of chromium and their salts, fused with borax in either blow- pipe flame, yield an emerald-green glass. The same character is exhibited by those salts of chromic acid whose bases do not of themselves impart a decided color to the bead. The production of the green color in both flames distinguishes chromium from uranium and vanadium, which give green beads in the inner flame only. TUNGSTEN, or WOLFRAM. Atomic weight, 184. Symbol, W. TUNGSTEX is found, as ferrous tungstate, in the mineral wolfram, tolerably abundant in Cornwall ; occasionally also as calcium tungstate (scheelite or tungsten), and as lead tungstate (scheeletine). Metallic tungsten is obtained in the state of a dark-gray powder, by strongly heating tungstic oxide in a stream of hydrogen, but requires for fusion an exceedingly high tem- perature. It is a white metal, very hard and brittle : it has a density of 17-4. Heated to redness in the air, it takes fire and reproduces tung- stic oxide. Tungsten forms two classes of compourids, in which it is quadrivalent and sexvalent respectively, and a third class, of intermediate composition, in which it is apparently quinquivalent. CHLORIDES. These compounds are formed by heating metallic tungsten in. chlorine gas. The he.cchloride or tungstic chloride, WC1 6 , is also produced, together with oxy chloride, by the action of chlorine on an ignited mixture of tungstic oxide and charcoal. The oxychlorides, being more volatile than the hexchloride, may be separated from it by sublimation. The hex- chloride forms dark violet scales or fused crusts having a bluish-black me- tallic iridescence. By contact with water or moist air, it is converted into hydrochloric and tungstic acids. The tetrachloride, WC1 4 , is formed, accord- ing to some authorities, as a dark -red compound, when tungsten is heated in chlorine gas ; but according to others, this red compound is a pcnta- chloride, W 2 C1 JO , or WC1 4 .WC1 6 , the tetrachloride not being known in the separate state. The bromides of tungsten are analogous to the chlorides. The hcxfl>t<>ri<1r, WF 6 , is obtained by evaporating a solution of tungstic acid in hydrofluoric acid. OXIDES. Tungsten forms three oxides, W0 2 , W0 3 , and W 2 5 , neither of which exhibits basic properties, so that there are no tungsten salts in which the metal replaces the hydrogen of an acid, or takes the electro-positive part. The trioxide exhibits decided acid tendencies, uniting with basic metallic oxides, and forming crystallizable salts called tungstates. The pentoxide may be regarded as a compound of the other two. , cipitate of tungstic, monohydrate or tungstic acid, W0 4 H 2 , 3 . 2 . dilute solutions, on the other hand, yield with acids a 442 HEXAD METALS. The dioxide, or Tungstous oxide, W0 3 , is most easily prepared by exposing tungstic oxide to hydrogen, at a temperature not exceeding dull redness. It is a brown powder, sometimes assuming a crystalline appearance and an imperfect metallic lustre. It takes fire when heated in the air, and burns, like the metal itself, to tungstic oxide. It forms a definite compound with soda. The trioxide, or Tungstic oxide, WO 3 , is most easily prepared from native calcium tungstate by digestion in nitric or hydrochloric acid, the soluble calcium-salt thereby produced being washed out with water, and the re- maining tungstic acid ignited. From wolfram it may be prepared by repeatedly digesting the mineral in strong hydrochloric acid, ultimately with addition of a little nitric acid, to dissolve out the iron and manga- nese ; dissolving the remaining tungstic acid in aqueous ammonia ; evapo- rating to dryness ; and heating the residual ammonium tungstate in con- tact with the air. Tungstic oxide is a yellow powder insoluble in water, and in most acids, but soluble in alkalies. The hot solutions of the result- ing alkaline tungstate, when neutralized with an acid, yield a yellow pre- ungstic acid, W0 4 H 2 , or W0 3 . OH 2 . Cold yield with acids a white precipitate, hydrated tungstic acid, W0 3 . 20H 2 , or W0 4 H 2 . OH 2 . Tungstic acid reddens litmus and dissolves easily in alkalis. Tungstates. Tungstic acid unites with bases in various, and often in very unusual proportions. It is capable of existing also in two isomeric modifications, viz : 1. Ordinary tungstic acid, which is insoluble in water, and forms insoluble salts with all metals, except the alkali-metals and mag- nesium ; 2. Metatungstic acid, which is soluble in water, and forms soluble salts with nearly all metals. Ordinary tungstic acid forms normal salts containing W0 4 M 2 orW0 3 .M 2 0, and acid salts containing 7WO 3 .3M 2 0, which may perhaps be regarded as double salts composed of diacid and triacid tungstates, that is, as 2(2W0 3 . M 2 0) -f- 3W0 3 . M 2 0. The tung- stat.es of potassium and sodium, especially the latter, are sometimes used as mordants in dyeing, in place of stannates ; also for rendering muslin and other light fabrics uninflammable. Tungstous tungstate, WO 3 . WO 2 , which has the composition of tungsten pentoxide, W 2 5 , is a blue sub- stance produced by reducing tungstic oxide or tungstic acid with zinc and hydrochloric acid ; also by heating ammonium tungstate to redness in a retort. Metatung 'states. These salts, which have the composition of quadacid tungstates, 4W0 3 . M 2 0, are formed from ordinary tungstates by addition of tungstic acid, or by removing part of the base by means of an acid. They are for the most part soluble and crystallizable. By decomposing barium metatungstate with dilute sulphuric acid, and evaporating the filtrate in a vacuum, hydrated metatungstic acid is obtained in quadratic octohedrons apparently containing 4W0 3 . OH 2 -f- 31 aq. ; it is very soluble in water. Silicotung states.* By boiling gelatinous silica with acid potassium tungs- tate, a crystalline salt is obtained, having the composition of a diacid potas- sium tungstate, 6(2W0 3 . K ? 0), or 12W0 3 .K 2 6 , in which one third of the potassium is replaced by silicium, viz., 12W0 3 . K 8 Si iv 6 , so that the silicium here enters as a basylous element. The resulting solution yields with mer- curous nitrate a precipitate of mercurous silicotung state ; this, when decom- posed by an equivalent quantity of hydrochloric acid, yields a solution of hydrogen silicotung state or silicotung stic acid; and the other silicotungstates, which are all soluble, are obtained by treating the acid with carbonates. Silicodecitungstic acid, 10W0 3 . H 8 Si iv 6 , is obtained as an ammonium-salt * Marignac, Ann. Chim. Phys. [4] iii. 5 ; Watts's Dictionary of Chemistry, v. 913. TUNGSTEN, OR WOLFRAM. 443 by boiling gelatinous silica with solution of acid ammonium tungstate ; and from this, the acid and its other salts may be obtained in the same manner as the preceding. The silicodecitungstates are very unstable, and the acid is decomposed by mere evaporation, depositing silica, and being converted into tungsto- silicic acid, which is isomeric with silicotungstic acid, and like- wise decomposes carbonates. All three of these acids are capable of ex- changing either one-half or the whole of their basic hydrogen for metals, thereby forming acid and neutral salts; silicotungstic acid also forms an acid sodium-salt in which only one-fourth of the hydrogen is replaced by sodium. TUNGSTEN SULPHIDES. The disulphide, or Tungstous sulphide, WS 2 , is ob- tained in soft black needle-shaped crystals by igniting tungsten, or one of its oxides, with sulphur. The trisulphide, or Tungstic sulphide, WS 3 , is formed by dissolving tungstic acid in ammonium sulphide, and precipitating with an acid, or by adding hydrochloric acid to the solution of an alkaline tungstate saturated with hydrogen sulphide. It is a light-brown precipitate, turning black when dry. It unites easily with basic metallic sulphides, forming the sulphotung states, WS 4 M 2 , analogous to the normal tungstates. Reactions of Tungsten compounds. Soluble tungstates, or metatungstates, supersaturated with sulphuric, hydrochloric, phosphoric, oxalic, or acetic acid, yield, on the introduction of a piece of zinc, a beautiful blue color, arising from the formation of blue tungsten oxide. A soluble tungstate, mixed with ammonium sulphide, and then with excess of acid, yields a light- brown precipitate of tungstic sulphide, soluble in ammonium sulphide. Hydrogen sulphide does not precipitate the acidulated solution of a tungstate, but turns it blue, owing to the formation of the blue oxide. Ordinary tung- states give with potassium ferrocyanide, after addition of hydrochloric acid, a brown flocculent precipitate, soluble in pure water free from acid ; meta- tungstates give no precipitate. Acids added to solutions of ordinary tung- states, throw down a white or yellow precipitate of tungstic acid ; with metatungstates no precipitate is obtained. All tungsten compounds form colorless beads with borax and phos- phorus salt, in the outer blowpipe flame. With borax, in the inner flame, tliey fofm a yellow glass, if the quantity of tungsten is somewhat consider- able, but colorless with a smaller quantity. With phosphorus salt in the inner flame they forma glass of a pure blue color, unless metallic oxides are present, which modify it ; in presence of iron the glass is blood-red, but the addition of metallic tin renders it blue. Steel, alloyed with a small quantity of tungsten, acquires extraordinary hardness. Wootz, or Indian steel, contains tungsten. Tungsten has also a remarkable effect on steel in increasing its power of retaining magnetism when hardened. A horse-shoe magnet of ordinary steel weighing two pounds is considered of good quality when it, bears seven times its own weight; but, according to Siemens, a similar magnet made with steel con- taining tungsten may be made to carry twenty times its weight suspended from the armature.* * Journal of the Chemical Society, July, 1868. 2d Series, vol. vi. p. 284. 444 HEXAD METALS. MOLYBDENUM. Atomic weight, 92. Symbol, Mo. This metal occurs in small quantity as sulphide and as lead molybdate. Metallic molybdenum is obtained by exposing molybdic oxide in a charcoal- lined crucible to the most intense heat that can be obtained. It is a white, brittle, and exceedingly infusible metal, having a density of 8-6, and oxid- izing, when heated in the air, to molybdic oxide. CHLORIDES. Molybdenum forms three chlorides, containing MoCl 2 , Mo 2 C1 6 , and MoCl 4 . The tetrachloride, or molybdic chloride, is obtained in dark metallically lustrous crystals by passing chlorine in excess over gently heated molybdenum ; when heated in a stream of hydrogen, it is reduced to the MoCl 3 dark copper-colored trichloride, I . The dichloride, or molybdous chloride, MoCl 3 is obtained, though not in the pure state, by exposing the trichloride to a moderate heat in an atmosphere of carbon dioxide, or by heating metallic molybdenum with calomel. In solution it is obtained by saturating hydro- chloric acid with molybdous hydrate. The bromides of molybdenum correspond in composition to the chlorides ; there is also an oxybromide containing Mo T 'Br 2 2 . FLUORIDES. Molybdenum forms three fluorides, MoF 2 , MoF 4 , MoF 6 , which are obtained by dissolving the corresponding oxides in hydrofluoric acid. The hexfluoride is not known in the free state, but only in combina- tion with basic metallic fluorides and molybdates; thus there is a po- tassium salt containing Mo0 4 K 2 . MoF 8 K 2 . OXIDES. Molybdenum forms the three oxides, Mo /X 0, Mo iT 2 , and Mo vi 3 , besides several oxides intermediate between the last two, which may be regarded as molybdic molybdates. The monoxide, or Molybdous oxide, MoO, is produced by bringing the di- oxide or trioxide, in presence of one of the stronger acids, in contact with any of the metals which decompose water. Thus, when zinc is immersed in a concentrated solution of an alkaline molybdate mixed with a quantity of hydrochloric acid sufficient to redissolve the precipitate first thrown down, zinc chloride and molybdous chloride are formed. The dark-colored solu- tion thus obtained is mixed with a large quantity of caustic potash, which precipitates a black hydrated molybdous oxide, and retains the zinc oxide in solution. The freshly precipitated hydrate is soluble in acids and am- monium carbonate; when heated in the air it burns to dioxide, but when dried in a vacuum it leaves the black anhydrous monoxide. The dioxide, or Molybdic oxide, Mo0 2 , is obtained in the anhydrous state by heating sodium molybdate with sal-ammoniac, the molybdic trioxide being reduced to dioxide by the hydrogen of the ammoniacal salt ; or, in the hy- drated state, by digesting metallic copper in a solution of molybdic acid in hydrochloric acid, until the liquid assumes a red color, and then adding a large excess of ammonia. The anhydrous dioxide is deep brown, and in- soluble in acids ; the hydrate resembles ferric hydrate, and dissolves in acids, yielding red solutions. It is converted into molybdic acid by strong nitric acid. Trioxide, Mo0 3 . To obtain this oxide (commonly called Molybdic acid), native molybdenum sulphide is roasted, at a red heat, in an open vessel, and the impure molybdic trioxide thence resulting is dissolved in ammonia. The filtered solution is evaporated to dryness, and the salt is taken up by MOLYBDENUM. 445 water, and purified by crystallization. It is, lastly, decomposed by heat, and the ammonia expelled. The trioxide may also be prepared by decom- posing native lead molybdate with sulphuric acid. It is a white crystalline powder, fusible at a red heat, and slightly soluble in water. The solution contains molybdic acid; but this acid, or hydrate, is not known in the solid state. The trioxide is easily dissolved by alkalies, and forms two series of salts, viz., normal or neutral molybdates, Mo0 4 R 2 , or Mo0 3 . R 2 0, and anltydro- molybdates or bimolybdates, Mo0 4 R 2 . Mo0 3 , or 2Mo0 3 . R 2 O, the symbol R de- noting a univalent metal. The neutral molybdates of the alkali-metals are easily soluble in water, and their solutions yield, with the stronger acids, a precipitate either of a less soluble bimolybdate, or of the anhydrous tri- oxide. The other molybdates are insoluble, and are obtained by precipita- tion. Lead molybdate, Mo 4 Pb, occurs native in yellow quadratic plates and octohedrons. SULPHIDES. Molybdenum forms three sulphides, MoS 2 , MoS 3 , and MoS 4 , the last two of which are acid sulphides, forming sulphur-salts. The di- sulphide, or Molybdic sulphide, MoS 2 , occurs native, as molybdenite, in crystallo- laminar masses, or tabular crystals, having a strong metallic lustre and lead-gray color, and forming a gray streak on paper like plumbago. The same compound is produced artificially by heating either of the higher sulphides, or by igniting the trioxide with sulphur. When roasted in con- tact with the air, it is converted into trioxide. The trisulphide, MoS 3 , commonly called sulphomolybdic add, is obtained by passing hydrogen sulphide into a concentrated solution of an alkaline mo- lybdate, and precipitating with an acid. It is a black-brown powder, which is dissolved slowly by alkalies, more easily by alkaline sulphides and sulph-hydrates, forming sulphur-salts called sulphomolybdates. Most of these salts have the composition MoS 4 R 2 , or MoS 3 .R 2 S, analogous to that of the molybdates. The sulpho-molybdates of the alkali-metals, alkaline earth-metals, and magnesium, are soluble in water, forming solutions of a fine red color ; the rest are insoluble. Tetrasidphide, MoS 4 . This is also an acid sulphide, forming salts called persulphomolybdates, the general formula of which is MoS.R r or MoS 4 . R 2 S. The potassium-salt is obtained by boiling the sulpho-molybdate with molyb- denum trisulphide, washing the resulting precipitate till the wash-water gives a red fiocculent precipitate with hydrochloric acid, and then digest- ing the residue with cold ivater, which dissolves out potassium persulpho- molybdate, and leaves the disulphide. The solution of this potassium salt, treated with hydrochloric acid, yields a dark-red precipitate of molybdenum tetrasulphide, which dissolves in alkalies. Molybdenum in solution is characterized as follows: Molybdous salts, obtained by dissolving molybdous oxide in acids, are opaque and almost black. They yield, with hydrogen sulphide, a brown- black precipitate soluble in ammonium sulphide ; with alkalies and alkaCne. carbonates, a brownish-black precipitate of molybdous hydrate, easily soluble in acid potassium carbonate, or in ammonium carbonate ; with potassium ferrocyanide, a dark-brown precipitate; with sodium phosphate, a white pre- cipitate. Solutions of molybdic salts have a reddish-brown color. When heated in the air, they have a tendency to become blue by oxidation. In contact with metallic zinc, they first blacken and then yield a black precipitate of molybdous hydrate. Their reactions with ). Fire is first applied to the anterior part of the tube containing the metal and unmixed oxide, and, when this is red-hot, to the extreme end. Combustion of the first portion of the mixture takes place, the gaseous products sweeping before them nearly the 454: THE ELEMENTARY OR ULTIMATE whole of the air of the apparatus. When no more gas issues, the tube is slowly heated by half an inch at a time, in the usual manner, and all the gas very carefully collected in a graduated jar, until the operation is at an end. The volume is then read off, and some strong solution of caustic potash thrown up into the jar by & pipette with a curved extremity. When the absorption is complete, the residual volume of nitrogen is ob- served, and compared with that of the mixed gases, proper correction being made for differences of level in the mercury ; and from these data the exact proportion borne by the nitrogen to the carbon can be at once determined.* If the proportion of nitrogen be but small, the error from the nitrogen of the residual atmospheric air becomes so great as to destroy all confidence in the result of the experiment; and the same thing happens when the sub- stance is incompletely burned by copper oxide: other means must then be employed. The absolute method of determination, also known by the name of Dumas' method, may be had recourse to when the foregoing, or comparative method, fails from the first cause mentioned : it gives excellent results, and is ap- plicable to all azotized substances. A tube of good Bohemian glass, 28 inches long, is securely sealed at one end ; into this enough dry acid sodium carbonate is put to occupy 6 inches. A little pure copper oxide is next introduced, and afterwards the mixture of oxide and organic substance, the weight of the latter, between 4-5 and 9 grains, in a dry state, having been correctly determined. The remainder of the tube, amounting to nearly one-half of its length, is then filled up with pure copper oxide and spongy metal, and a round cork, perforated by Fig. 188. a piece of narrow tube, is securely adapted to its mouth. This tube is connected by means of a caoutchouc joint with a bent delivery-tube, a, and the combustion-tube is arranged in the furnace. A few coals are now ap- * A molecule of carbon dioxide (C0 2 ) containing 1 atom of carbon [= 12], occupies the same space as a molecule (or double atom) of nitrogen (NN) [2 . 14 =: 28]. If, therefore, the volumes of carbon dioxide and nitrogen in the gaseous mixture are as m : 1, it follows that the number of carbon-atoms in the compound is to the number of nitrogen-atoms as m : 2 ; and consequently that the weight of the carbon in the compound is to that of the nitrogen as m X 12 : 2 X 14, or 3 m : 7, so that if the percentage of carbon (c) has been previously found, the percentage of nitrogen (n) will be given by the equation : 7 n ~ c. 3m For example, caffeine, which contains 47-48 per cent, of carbon, is found, by the process just described, to yield carbon dioxide and nitrogen in the proportion by volume of 4 : 1 ; the per- centage of nitrogen in caffeine is therefore X 49-48 = 28-89. ANALYSIS OF ORGANIC COMPOUNDS. 455 plied to the farther end of the tube, so as to decompose a portion of the acid sodium carbonate, the remainder of the carbonate, as well as of the other part of the tube, being protected from the beat by a screen n. The current of carbon dioxide thus produced is intended to expel all the air from the apparatus. In -order to ascertain that this object, on which the success of the whole operation depends, is accomplished, the delivery-tube is depressed under the level of a mercurial trough, and the gas, which is evolved, col- lected in a test-tube filled with concentrated potash-solution. If the gas be perfectly absorbed, or if, after the introduction of a considerable quantity, only a minute bubble be left, the air may be considered as ex- pelled. The next step is to fill a graduated glass jar two-thirds with mer- cury and one-third with a strong solution of potash, and to invert it over the delivery-tube, as represented in fig. 188. This done, fire is applied to the tube, commencing at the front end, and gradually proceeding to the closed extremity, which still contains some un- decomposed acid sodium carbonate. This, when the fire at length reaches it, yields up carbon dioxide, which chases forward the nitrogen lingering in the tube. The carbon dioxide generated during the combustion is wholly absorbed by the potash in the jar, and nothing is left but the nitrogen. When the operation is at an end, the jar, with its contents, is transferred to a vessel of water, and the volume of the nitrogen read off. This is pro- perly corrected for temperature, pressure, and aqueous vapor, and its weight determined by calculation. When the operation has been very suc- cessful, and all precautions minutely observed, the result still leaves an error in excess, amounting to 0-3 or 05 per cent., due to the residual air of the apparatus, or that condensed in the pores of the copper oxide. A most elegant process for estimating nitrogen in all organic compounds, except those containing the nitrogen in the form of nitrous acid or nitrogen tetroxide, and in some organic bases, has been put in practice by Will and Varrentrapp. When a non-azotized organic substance is heated to redness with a large excess of potassium or sodium hydrate, it suffers complete and speedy combustion at the expense of the water of the hydrate, the oxygen combining with the carbon of the organic matter to form carbon dioxide, which is retained by the alkali, while its hydrogen, together with that of the substance, is disengaged, sometimes in union with a little carbon. The same change happens when nitrogen is present, but with this addition : the whole of the nitrogen thus abandoned combines with a portion of the liberated hydrogen to form ammonia. It is evident, therefore, that if this experiment be made on a weighed quantity of matter, and circumstances allow the collection of the whole of the ammonia thus produced, the pro- portion of nitrogen can be easily calculated. An intimate mixture is made of 1 part caustic soda and 2 or 3 parts quicklime, by slaking lime of good quality with the proper proportion of strong caustic soda, drying the mixture in an iron vessel, and then heating it to redness in an earthen crucible. The ignited mass is rubbed to powder in a warm mortar, and carefully preserved from the air. The lime is useful in many ways: it diminishes the tendency of the alkali to deliquesce, facilitates mixture with the organic substance, and prevents fusion and liquefaction. A proper quantity of the substance to be analyzed, namely, from 5 to 10 grains, is dried and accurately weighed out: this is mixed in a warm porcelain mortar with enough of the soda-lime to fill two-thirds of an ordinary combustion-tube, the mortar being rinsed with a little more of the alkaline mixture, and, lastly, with a small quantity of powdered glass, which completely removes everything adherent to its surface; the tube is then filled to within an inch of the open end with the lime-mixture, and arranged in the chauffer in the usual manner. The ammonia is col- lected in a little apparatus of three bulbs (fig. 189), containing moderately strong hydrochloric acid, attached by a cork to the combustion-tube. 456 THE ELEMENTARY OB ULTIMATE Matters being thus adjusted, fire is applied to the tube, commencing with the anterior extremity. When it is ignited throughout its whole length, and when no gas issues from the ap- 9 ' paratus, the point of the tube is bro- ken, and a little air. drawn through the whole. The acid liquid is then emptied into a capsule, the bulbs rinsed into the same, first with a little alcohol, and then repeatedly with distilled water ; an excess of pure platinic chloride is added, and the whole evaporated to dryness in a water-bath. The dry mass, when cold, is treated with a mixture of alcohol and ether, which dissolves out the superfluous platinum chloride, but leaves untouched the yellow crystalline ammonium platinochloride. The latter is collected upon a small weighed filter, washed with the same mixture of alcohol and ether, dried at 100 C. (212 F.), and weighed; 100 parts correspond to 6-272 parts of nitrogen. Or, the salt with its filter may be very carefully ignited, the filter burned in a platinum crucible, and the nitrogen reckoned from the weight of the spongy metal, 100 parts of that substance corresponding to 14-18 parts of nitrogen. The former plan is to be preferred in most cases. Bodies very rich in nitrogen, as urea, must be mixed with about an equal quantity of pure sugar, to furnish incondensable gas, and thus diminish the violence of the absorption which otherwise occurs ; and the same pre- caution must be taken, for a different reason, with those which contain little or no hydrogen. A modification of this process has been suggested by Peligot, which is very convenient if a large number of nitrogen-determinations is to be made. By this plan, the ammonia, instead of being received in hydro- chloric acid, is conducted into a known volume (10 to 20 cubic centimetres) of a standard solution of sulphuric acid, contained in the ordinary nitro- gen-bulbs. After the combustion is finished, the acid containing the am- monia is poured out into a beaker, colored with a drop of tincture of litmus, and then neutralized with a standard solution of soda in water or of lime in sugar-water, the point of neutralization becoming perceptible by the sudden appearance of a blue tint. The lime-solution is conveniently poured out from the graduated glass tube, described under the head of Alkalimetry. The volume of lime-solution necessary to neutralize the same amount of acid that is used for condensing the ammonia, having been ascertained by a preliminary experiment, it is evident that the difference of the quantities used in the two experiments gives the ammonia collected in the acid during the combustion. The amount of nitrogen may thus be calculated. If, for instance, an acid be prepared, containing 20 grains of pure hydrogen sulphate (S0 4 H 2 ) in 1000 grain-measures 200 grain-meas- ures of this acid the quantity introduced into the bulbs correspond to 1-38 grains of ammonia, or 1-14 grains of nitrogen. The alkaline solu- tion is so graduated that 1000 grain-measures will exactly neutralize the 200 grain-measures of the standard acid. If we now find that the acid, partly saturated with the ammonia disengaged during the combustion of a nitrogenous substance, requires only 700 grain-measures of the alkaline 200 X 300 solution, it is evident that TnnT) == ^ grain-measures were satu- rated by the ammonia, and the quantity of nitrogen is obtained by the pro- 1-14 X GO portion 200 : 1-14 ;== 60 ; x, wherefore x = r>oO = ' 342 S rains of nitrogen. ANALYSIS OF ORGANIC COMPOUNDS. 457 Estimation of Sulphur in Organic Compounds. When bodies of this class containing sulphur are burned with copper oxide, a small tube containing lead dioxide may be interposed between the calcium-chloride tube and the potash apparatus, to retain any sulphurous acid that may be formed. It is better, however, to use lead chromate in such cases. The proportion of sulphur is determined by oxidizing a known weight of the substance with strong nitric acid, or by fusion in a silver vessel with ten or twelve times its weight of pure potassium hydrate and half as much nitre. The sul- phur is thus converted into sulphuric acid, the quantity of which can be determined by dissolving the fused mass in water, acidulating with nitric acid, and adding a barium salt. Phosphorus is ? in like manner, oxidized to phosphoric acid, the quantity of which is determined by precipitation as ammonio-magnesian phosphate, or otherwise. Estimation of Chlorine. The case of a volatile liquid containing chlor- ine is of very frequent occurrence, and may be taken as an illustration of the general plan of proceeding. The combustion with copper oxide must be very carefully conducted, and two or three inches of the anterior portion of the tube kept cool enough to prevent volatilization of the copper chloride into the calcium-chloride tube. Lead chromate is much better for the purpose. The chlorine is correctly determined by placing a small weighed bulb of liquid in a combustion-tube, which is afterwards filled with fragments of pure quicklime. The lime is brought to a red heat, and the vapor of the liquid driven over it, when the chlorine displaces oxygen from the lime, and gives rise to calcium chloride. When cold, the contents of the tube are dissolved in dilute nitric acid, filtered, and the chlorine pre- cipitated by silver nitrate. Bromine and iodine are estimated in a similar manner. EMPIRICAL AND MOLECULAR FORMULAE. A chemical formula is termed empirical when it merely gives the simplest possible expression of the composition of the substance to which it refers. A molecular formula, on the contrary, expresses the absolute number of i atoms of each of its elements supposed to be contained in the molecule, as well as the mere relations existing between them. The empirical formula is at once deduced from the analysis of the substance, reckoned to 100 parts; but to determine the molecular formula, other considerations must be taken into account: namely, the combining or saturating power of the compound, if it is acid or basic; the number of atoms of any one of its elements (generally hydrogen) which may be replaced by other elements; the law of even numbers, which requires that the sum of the numbers of atoms of all the perissad elements (hydrogen, nitrogen, chlorine, &c.) con- tained in the compound shall be divisible by 2; and the vapor-density of the compound (if it be volatile without decomposition) which, in normally constituted compounds, is always half the molecular weight (p. 229). The molecular formula may either coincide with the empirical formula, or it may be a multiple of the latter. Thus, the composition of acetic acid is expressed by the formula CH 2 0, which exhibits the simplest relations of the three elements; but if we want to express the quantities of these, in atoms, required to make up a molecule of acetic acid, we have to adopt the formula C 2 H 4 2 : for only one-fourth of the hydrogen in this acid is re- placeable by metals to form salts, C 2 H 3 K0 2 , for example; and its vapor- density, compared with hydrogen, is nearly 30, which is half the weight of the molecule, C 2 H 4 2 = 2.12-j-4.1-f-2.16. Again, the empirical formula of benzene is CH; but this contains an uneven number of hydrogen atoms; 39 458 EMPIRICAL AND MOLECULAR FORMULAE. and, moreover, if it expressed the weight of the molecule of benzene, the 12-1-1 vapor-density of that compound should be - = 6-5, whereas experi- ment shows that it is six times as great, or equal to 39: hence the molecular formula of benzene is C 6 H 6 . The deduction of an empirical formula from the ultimate analysis is very easy ; the case of sugar, already cited, may be taken as an example. This substance contains, according to the analysis, in 100 parts Carbon 41-98 Hydrogen ...... 6-43 Oxygen 51-59 100-00 If each of these quantities be divided by the atomic weight of the corre- sponding element, the quotients will express the relations existing between the numbers of atoms of the three elements: these are afterwards reduced to their simplest expression. This is the only part of the calculation attended with any difficulty. If the numbers were rigidly correct, it would only be necessary to divide each by the greatest divisor common to the whole; as they are, however, only approximative, something is of necessity left to the judgment of the experimenter. In the case of sugar, we have 41-98 6-43 51-59 = 3-50 ; - = 6-43 ; - = 3-22, 12 1 16 or 350 atoms carbon, 643 atoms hydrogen, and 322 atoms oxygen. Now it is evident, in the first place, that the hydrogen and oxygen are present in the proportions to form water, or twice as many atoms of the former as of the latter. Again, the atoms of carbon and hydrogen are nearly in the proportion of 12 : 22, so that the formula C, 2 H 22 O n appears likely to be correct. It is now easy to see how far this is admissible, by reckoning it back to 100 parts, comparing the result w'th the numbers given by the actual analysis, and observing whether the difference falls fairly, in direction and amount, within the limits of error of what may be termed a good ex- periment, viz., two or three-tenths per cent, deficiency in the carbon, and not more than one-tenth or two-tenths per cent, excess in the hydrogen : Carbon . . . . 12 X 12 = 144 Hydrogen . . . . 1 x 22 = 22 Oxygen . . . . 16 x H = 176 342 342 : 144 = 100 : 42-11 342 : 222 = 100 : 6-43 342 : 176 = 100 : 51 46 Organic acids and salt-radicals have their molecular weights most fre- quently determined by an analysis of their lead and silver salts, by burning these latter with suitable precautions in a thin porcelain capsule, and noting the weight of the lead oxide or metallic silver left behind. If the lead oxide be mixed with globules of reduced metal, the quantity of the latter must be ascertained by dissolving away the oxide with acetic acid. Or the lead salt may be converted into sulphate, and the silver compound into chloride, and both metals thus estimated. An organic base, pn the contrary, has its DETERMINATION OF THE DENSITY OF VAPORS. 459 molecular weight fixed by the observation of the quantity of a mineral acid, or an inorganic salt-radical, required to form with it a combination having the characters of neutrality. The rational and constitutional formulae of organic compounds will be considered further on. Fig. 190. DETERMINATION OF THE DENSITY OF VAPORS. The determination of the specific gravity of the vapor of a volatile sub- stance is frequently a point of great importance, inasmuch as it gives the means, in conjunctioii with the analysis, of representing the constitution of the substance by measure in a gaseous state. The following is a sketch of the plan of operation usually followed : Alight glass globe about three inches in diameter is taken, and its neck softened and drawn out in the blowpipe-flame, as represented in fig. 190: this is accurately weighed. About one hundred grains of the volatile liquid are then introduced, by gently warming the globe and dipping the point into the liquid, which is then forced upwards by the pressure of the air as the vessel cools. The globe is next firmly attached by wire to a han- dle, in such a manner that it may be plunged into a bath of boiling water or heated oil, and steadily held with the point projecting upwards. The bath must have a temper- ature considerably above that of the boiling point of the liquid. The latter becomes rapidly converted into vapor, which escapes by the narrow orifice, chasing before it the air of the globe. When the issue of vapor has wholly ceased, and the temperature of the bath, carefully observed, appears pretty uniform, the open extremity of the point is hermetically sealed by a small blowpipe-flame. The globe is removed from the bath, suffered to cool, cleansed if necessary, and weighed, after which the neck is broken off be- neath the surface of water which has been boiled and cooled out of contact of air, or (better) of mercury. The liquid enters the globe, and, if the expulsion of the air by the vapor has been complete, fills it; if otherwise, an air-bubble is left whose volume can be easily ascertained by pouring the liquid from the globe into a graduated jar, and then refilling the globe, and repeating the same observation. The capacity of the vessel is thus at the same time known : and these ar all the data required.* An example will render the whole intelligible. Determination of the Vapor- Density of Acetone. Capacity of globe ....... Weight of globe filled with dry air at 52 F. and 30-24 inches barometer . Weight of globe filled with vapor at 212 F. temp, of the bath at the moment of sealing the point, and 30*24 inches barometer ..... Residual air, at 45 F., and 30-24 inches barometer 31-61 cubic inches. 2070-88 grains. 2070-81 grains. 0-60 cubic inches. * Messrs. Playfair and "\Vanklyn have lately described an important modification of this process, whereby (he densities of a vapor at temperatures below the boiling point of the liquid may be. determined. This object is attained by mixing the vapor of the body with a meas- ured volume of a permanent gas hydrogen, for instance. Journ. of the C/iein. Sue., vol. xv. p. 143. 460 DETERMINATION OF THE DENSITY OF VAPORS. 31-61 cubic inches of air at 52 and 30-24 in. bar. 32 -36 cubic inches at 60 F., and 30 inch bar., weighing- . . . . 10-035 grains. Hence, weight of empty globe, 2070-88 10-035 = 2060-845 grains. 0-6 cubic inch of air at 45 0-8 cubic inch at 212 ; weight of do. by cal- culation 0-1 91 grain. 31-61 0-8 = 30-81 cubic inches of vapor at 212 and 30-24 in. bar., which, on the supposition that it would bear cooling to 60 without liquefaction, would, at that temperature, and under a pressure of 30 inch, bar., become re- duced to 24-18 cubic inches. Hence, Weight, of globe and vapor 2076-810 grains. " residual air 0-191 2076-619 Weight of globe 2060-845 Weight of the 24-18 cubic inches of vapor . . . 15-774 Consequently, 100 cubic inches of such vapor must weigh 65-23 100 cubic inches of air, under similar circumstances, weigh 31 -01 65-23 = 2-103, the specific gravity of the vapor in question, air being unity. 31-01 Or, the weight of 100 cubic inches of hydrogen being 2-14 grains, 65-23 = 30-44 is the specific gravity of acetone vapor referred to hydrogen 2-14 as unity. In the foregoing statement, we have, for the sake of simplicity, omitted a correction, which, in very exact experiments, must not be lost sight of, viz., the expansion and change of capacity of the glass globe by the ele- vated temperature of the bath. The density so obtained will be always on this account a little too high. The error of the mercurial thermometer at high temperatures is in the opposite direction. The preceding method, which is that of Dumas, is applicable to the de- termination of the vapor-densities of all substances whose boiling points are within the range of the mercurial thermometer, that is to say, not exceed- ing 300 C. (572 F.), and therefore to nearly all volatile organic compounds: indeed, there are but few such compounds which can bear higher tempera- tures without decomposition. But for mineral substances, such as sulphur, iodine, volatile metallic chlorides, &c., it is often necessary to employ much higher temperatures; and for such cases a modification of the process has been devised by Deville and Troost. It consists in using a globe of porce- lain instead of glass, heating it in the vapor of a substance whose boiling point is known and constant, and sealing the globe by the flame of the oxy- hydrogen blowpipe. The vapors employed for this purpose are those of mercury, which boils at 350 C. (662 F.) ; of sulphur, which boils at 440 C. (824 F. ) ; of cadmium, boiling at 860 C. (1580 F. ) ; of zinc, boiling at 1040 C. (1900 F.). The use of these liquids of constant boiling point obviates the necessity of determining the temperature in each experiment, which at such degrees of heat would be very difficult. In the processes above described, the density of a vapor is determined "by weighing the quantity of the vapor contained in a vessel of known ca- DETERMINATION OF THE DENSITY OF VAPORS. 461 pacity. Another method, devised by Gay-Lussac, consists in ascertaining the volume occupied by a given weight of substance when heated up to a temperature considerably above its boiling point. The density of a vapor referred to air as unity may be converted into that which it has compared with hydrogen, by dividing by 0*06926, the specific gravity of hydrogen referred to air as unity. The vapor-density of a compound thus determined, that is to say, the weight of a unit-volume of its vapor compared with that of hydrogen, is found to be in nearly all cases half its molecular weight; for example, the molecular weight of acetone, C 3 H 6 0, is 36 -f- 6 -f 16 = 58, the half of which is 29, or nearly equal to the vapor-density of acetone determined by experiment. Hence the law already stated (p. 229), that the molecules of all normally constituted compounds in the state of vapor occupy twice the volume of an atom of hydrogen. Some compounds, however, exhibit a departure from this rule, their ob- sei'ved specific gravities being equal to only one-fourth their molecular weights, or their molecules occupying four times the volume of an atom of hydrogen. Such is the case with sal-ammoniac, NH 4 C1, phosphorus penta- chloride, PC1 5 , sulphuric acid, S0 4 H 2 , ammonium-sulph-hydrate, SH(NH 4 ), and a few others. This anomaly is probably due, in some cases at least, to a decomposition or "dissociation" of the compound at the high tempera- ture to which it is subjected for the determination of its vapor-density ; KH 4 C1, for example, splitting up into NH 3 and HC1, each of which occupies two volumes, and the whole therefore four volumes ; and in like manner S0 4 H 2 may be supposed to separate into S0 3 and OH 2 ; PC1 5 into PC1 3 and C1 2 ; SH(NH 4 ) into SH 2 and NH 3 , &c. On the other hand, some substances, both simple and compound, exhibit, at temperatures not far above their boiling points, vapor-densities consider- ably greater than they should have according to the general law, whereas when raised to higher tempei'atures they exhibit, normal vapor-densities. Thus sulphur, which boils at 440 C. (824 F.), exhibits at 1000 C. (1832 F.), like elementary gases in general, a vapor-density equal to its atomic weight, viz., 32 (see p. 229) ; but at 500 C. (932 F.) its vapor-density is nearly three times as great. Again, acetic acid, C 2 H 4 2 , whose molecular weight is 24 -j- 4 -f- 16 = 60, has, at temperatures considernbly above its boiling point, a vapor-density nearly equal to 30; but at 125 C. (257 F.), 8 C. (14 F.) above its boiling point, its vapor-density is rather more than 45, or 1 j times as great. This anomalous increase of vapor-density appears t'o take place when the substance approaches its liquefying point, at which also it exhibits irregularities in its rate of expansion and contraction by varia- tions of pressure and temperature at which, in short, it begins to behave itself like a liquid ; but at higher temperatures it exhibits the physical characters of a perfect gas, and then also its specific gravity becomes normal. There are two elements, however, namely, phosphorus and arsenic, which, at all temperatures hitherto attained, exhibit a vapor-density twice as great as they should have according to the general law, that of phosphorus being always 62, and that of arsenic 150. This has been explained by supposing that^the molecule of each of these elements in the free state contains 4 atoms instead of two, as is the case with most elementary bodies ; thus the mole- cule of phosphorus is supposed to be represented by the formula LJ. 39* 462 DECOMPOSITIONS AND TRANSFORMATIONS DECOMPOSITIONS AND TRANSFORMATIONS OF ORGANIC COMPOUNDS. Organic bodies are, generally speaking, distinguished by the facility with which they decompose under the influence of heat or of chemical reagents : the more complex the body, the more easily does it undergo decomposition or transformation. 1. Action of Heat. Organic bodies of simple constitution and of some permanence, but not capable of subliming unchanged, like many of the organic acids, yield, when exposed to a high, but regulated temperature, in a retort, new compounds, perfectly definite and often crystallizable, which partake, to a certain extent, of the properties of the original substance : the numer- ous pyro-adds, of which many examples will occur in the succeeding pages, are thus produced. Carbon dioxide and water are often eliminated under these circumstances. If the heat be suddenly raised to redness, the regu- larity of the decomposition vanishes, while the products become more un- certain and more numerous; carbon dioxide and watery vapor are suc- ceeded by inflammable gases, as carbon monoxide and hydrocarbons; oily matter and tar distil over, and increase in quantity until the close of the operation, when the retort is found to contain, in most cases, a residue of charcoal. Such is dry or destructive distillation. If the organic substance contains nitrogen, and is not of a kind capable of taking a new and permanent form, at a moderate degree of heat, then that nitrogen is in most instances partly disengaged in the shape of ammo- nia, or substances analogous to it, partly left in combination with the car- bonaceous matter in the distillatory vessel. The products of dry distillation thus become still more complicated. A much greater degree of regularity is observed in the effects of heat on fixed organic matters, when these are previously mixed with an excess of strong alkaline base, as potash or lime. In such cases an acid, the nature of which is chiefly dependent upon the temperature applied, is produced, and remains in union with the base, the residual element or elements escap- ing in some volatile form. Thus benzoic acid distilled with calcium hy- drate, at a dull red heat, yields calcium carbonate and benzene ; woody fibre and caustic potash, heated to a very moderate temperature, yield free hydrogen, and a brown, somewhat indefinite substance called ulmic acid; with a higher degree of heat, oxalic acid appears in the place of the ulmic ; and, at the temperature of ignition, carbon dioxide, hydrogen being the other product. 2. Action of Oxygen. Oxygen, either free or in the nascent state, in which latter condition it is most active, may act on organic compounds in four different ways: a. By simple addition, as C 2 H 4 + = C 2 H 4 2 Aldehyde. Acetic acid. * /?. By simply removing hydrogen: C 2 H 6 -f = OH 2 -f C 2 H 4 Alcohol. Aldehyde. y. By removing hydrogen and taking its place, 2 atoms of hydrogen being replaced by one of oxygen ; e. g. : C 2 H 6 + 0, = OH 2 + CJT 4 2 Alcohol. Acetic acid. OF ORGANIC COMPOUNDS. 463 t. By removing both carbon and hydrogen. In this manner complex organic bodies containing large numbers of carbon and hydrogen atoms are reduced to others of simpler constitution, and ultimately the carbon and hydrogen are wholly converted into carbon dioxide and water. Nitrogen, chlorine, bromine, and iodine, if present, are at the same time disengaged, for the most part in the free state, and sulphur is oxidized. Moist organic substances, especially those containing nitrogen, undergo, when exposed to the air, a slow process of oxidation, by which the organic matter is gradually burned and destroyed without sensible elevation of temperature; this process is called Decay, or Eremacausis. Closely con- nected with this change are those called Fermentation and Putrefaction, con- sisting in a new arrangement of the elements of the compound (often with assimilation of the elements of water), and the consequent formation of new products. The change is called putrefaction, when it is accompanied by an offensive odor; fermentation, when no such odor is evolved, and especially if the change results in the formation of useful products : thus, the decom- position of a dead body, or of blood or urine, is putrefaction ; that of grape- juice or malt-wort, which yields alcohol, is fermentation. Putrefaction and fermentation are not processes of oxidation ; nevertheless, the presence of oxygen appears to be indispensable to their commencement; but the change, when once begun, proceeds without the aid of any other substance external to the decomposing body, unless it be water or its elements. Every case of putrefaction thus begins with decay ; and if the decay, or its cause, namely, the absorption of oxygen, be prevented, no putrefaction occurs. The most putrescible substances, as animal flesh intended for food, milk, and highly azotized vegetables, are preserved indefinitely, by enclosure in metallic cases from which the air has been completely removed and excluded. Fermentation and putrefaction are always accompanied by the develop- ment of certain living organisms of the fungous class; but whether the growth of these is a cause or a consequence of the chemical change is a point not yet decided. We shall return to this subject in speaking of the fermentation of sugar. 3. ^Action of Chlorine, Bromine, and Iodine. Chlorine and bromine exert precisely similar actions on organic bodies ; that of chlorine is the more energetic of the two. The reactions consist: a. In simple addition of chlorine or bromine to the organic molecule ; e. g. : C 4 H 4 4 + Br 2 = C 4 H 4 Br 2 4 Fumaric Dibromosuccinic acid. acid. /?. In removal of hydrogen without substitution : C 2 H 6 -f C1 2 = 2HC1 + C 2 H 4 Alcohol. Aldehyde. y. In substitution of chlorine or bromine for hydrogen : C 2 H 4 2 -f C1 2 = HC1 + C 2 H 3 C10 2 Acetic Chloracetic acid. acid. C 2 H 4 2 -f 3C1 2 = 3HC1 + C 2 HC1 3 2 Acetic Trichloracetic acid. acid The substitution-products thus formed undergo transformations closely analogous to those of the original compounds, under the influence of simi- lar reagents ; but they are always more acid, or less basylous, in propor- 464: DECOMPOSITIONS AND TRANSFORMATIONS tion to the quantity of chlorine or bromine substituted for hydrogen. Thus aniline, C 6 H 7 N, which is a strong base, may be converted, by processes to be hereafter described, into the chlorinated compounds, C 6 H 6 C1N, C 6 H 5 C1 2 N, and C 6 H 4 C1 3 N, the first and second of which are less basic than aniline itself, while the third does not show any tendency to form salts with acids. 6. In presence of water they remove the hydrogen of that liquid, arid set free the oxygen: hence, chlorine-water and bromine-water act as powerful oxidizing agents. Iodine may also act in this manner as an oxidizing agent; and it some- times attaches itself directly to organic molecules ; but it never acts directly by substitution. Iodine substitution-products may, however, be obtained in some cases by treating organic bodies with chloride of iodine, the chlor- ine then removing hydrogen, and the iodine taking its place. 4. Action of Nitric Acid. This acid acts very powerfully on organic sub- stances. The action may be of three kinds: a. Direct combination, as with organic bases ; e. g. : C 2 H 7 N -f N0 3 H = C 2 H 7 N.N0 3 H Ethylamine. Nitric Ethylamine acid. nitrate. /?. Oxidation. This mode of action is most frequently observed with the somewhat diluted acid. y. Substitution of nitryl (N0 2 ) for hydrogen ; e. g. : C 6 H 6 + N0 2 (OH) = OH 2 -f- C 6 H 5 (N0 2 ) Benzene. Nitric acid. Nitrobenzene. C 6 H 10 5 + 3N0 2 (OH) = 30H 2 -f C 6 H 7 (N0 2 ) 3 5 Cellulose. Nitric acid. Tritrocellulose (gun-cotton). This action takes place most readily with the strongest nitric acid (pure hydrogen nitrate). The products (called nitro-compounds} are always easily combustible, and in many cases highly explosive. 5. Action of Alkalies. The hydrates of potassium and sodium act on organic bodies in a great variety of ways, the most important and general of which are the following: a. By direct combination: CO -f OKH = CHK0 2 Carbon Potassium Potassium monoxide. hydrate. formate. C, H 16 + OKH = C 10 H 17 K0 2 Camphor. Potassium Potassium hydrate. campholate. /?. By double decomposition with acids, water being eliminated, and a salt produced : C 2 H ? 2 .H -f OKH = OH, + C 2 H 3 2 .K Acetic acid. Potassium acetate. y. Oxidation, with elimination of hydrogen: C 2 H 6 -f OKH = C 2 H 3 K0 2 -f 2H 2 Alcohol. Potassium acetate. i. From chlorinated compounds they remove a part or the whole of the chlorine : OF ORGANIC COMPOUNDS. 465 C 2 H 4 C1 2 Ethene chloride. C 6 H U C1 Amyl chloride. OKH = -f OKH = C 2 H 3 C1 Chlor- ethene. Amylene. KC1 OH 2 e. Amides (pp. 315, 471) are decomposed by them in such a manner that the whole of the nitrogen is given off as ammonia, and a potassium or sodium salt of the corresponding acid is produced : NH 2 .C 2 H 5 -f OKH = NH 3 + C 2 H 3 O.OK Acetamide. Potassium acetate. Many other azotized organic compounds, when heated with alkaline hydrates, likewise give up the whole of their hydrogen in the form of ammonia. 6. Action of Reducing Agents. This name is given to bodies whose action is the inverse of that of oxygen, chlorine, bromine, and iodine ; such are nascent hydrogen, obtained by the action of sodium-amalgam on water, or by that of zinc on aqueous acids or alkalies ; also hydrogen sulphide, am- monium sulphide, sulphurous acid, and metals, especially potassium and sodium, all of which either give up hydrogen, or abstract oxygen, chlor- ine, &c. Reducing agents may act in the following ways:- a. By adding hydrogen to an organic body : Ethene oxide. HH C 2 H 6 Alcohol. 0. By removing oxygen, chlorine, bromine, or iodine, without introducing anything in its place ; thus : C 7 H 6 2 Benzoic acid. HH = OH Benzoic aldehyde. Y. By substituting hydrogen for oxygen, chlorine, &c. This process is called inverse substitution. It may take place either in equivalent quanti- ties; e.g.: C 7 H 5 . OH -f 2HH = OH 2 -f- C 7 H 7 . OH Benzoic Benzylic acid alcohol or it may happen that the quantity of hydrogen introduced is only half that which is equivalent to the oxygen removed. This mode of substitu- tion takes place with nitro-compounds, which are thereby reduced to others containing amidogen, (NH 2 ), in place of nitryl, (N0 2 ) ; thus : 3IL Nitrobenzene. 20H 2 C 6 H 5 (NH 2 ) Amidobenzene (aniline). A large number of organic bases are formed in this manner from nitro- compounds. 7. Action of Dehydrating Agents. Strong sulphuric acid, sulphuric oxide, phosphoric oxide, and zinc chloride remove oxygen and hydrogen from organic bodies in the form of water, the elements of which are derived, 466 CLASSIFICATION OF ORGANIC COMPOUNDS. sometimes from a single molecule of the organic body, sometimes from two molecules : C 2 H 6 OH 2 = C 2 H 4 Alcohol. Ethene. 2C 2 H 6 OH 2 = C 4 H 10 Alcohol. Ether. Compounds which, like sugar, starch, and woody fibre, consist of carbon united with hydrogen and oxygen in the proportions to form water, are often reduced by these dehydrating agents to black substances consisting mainly of carbon. Other reactions of less generality than those above described will be suffi- ciently illustrated by special cases in the sequel. CLASSIFICATION OF ORGANIC COMPOUNDS. ORGANIC SERIES. The classification of organic compounds is based upon the equivalence or atomicity of carbon. This element is a tetrad, being capable of uniting with at most four atoms of hydrogen or other monatomic elements. Me- thane or marsh gas, CH 4 , is therefore a saturated hydro-carbon, not capa- ble of uniting directly with chlorine, bromine, or other monad elements, but only of exchanging a part or the whole of its hydrogen for an equiv- alent quantity of another monad element. It may, however, as already explained (p. 235), take up any number of dyad elements or radicals, be- cause such a radical introduced into any group of atoms whatever, neutral- izes one unit of equivalency, and adds another, leaving therefore the com- bining power or equivalence of the group just the same as before. Ac- cordingly, the hydro-carbon, CH 4 , may take up any number of molecules of the bivalent, radical, CH 2 , thereby giving rise to the series of saturated hydro-carbons, CH 4 , C 2 H 6 , C 3 H 8 , C 4 H 10 . . . . A series of compounds, the terms of which differ from one another by CH 2 , is called an homologous series. There are many such series besides that of the hydro-carbons just mentioned ; thus methyl-chloride, CH 3 C1, gives by continued addition of CH 2 , the series of chlorides, CH 3 C1, C 2 H 5 C1, C 3 H 7 C1, C 4 H 9 C1 . . . C 11^+ Cl; and from methyl-alcohol, CH 4 0, is derived in like manner the series of homologous alcohols, CH 4 0, C 2 H 6 0, C 3 H 8 0, C 4 H 10 . . . C.H to+ 0. The terms of the same homologous series resemble one another in many respects, exhibiting similar transformations under the action of given re- agents, and a regular gradation of properties from the lowest to the high- est ; thus, of the hydro-carbons, C n H 2 n+2, the lowest terms CH 4 , C 2 H 6 , and C 3 H 8 , are gaseous at ordinary temperatures, the highest containing 20 or more carbon-atoms, are solid, while the intermediate compounds are liquids, becoming more and more viscid and less volatile, as they contain a greater number of carbon-atoms, and exhibiting a constant rise of about 20 C. (36 F.) in their boiling points for each addition of CH 2 to the molecule. The saturated hydro-carbons, C n H 2n -j- 2> may, under various circumstances, * See page 234. ORGANIC SERIES. 467 be deprived of two atoms, or one molecule, of hydrogen, thereby producing a new homologous series, CH 2 , C 2 H 4 , C 3 H 6 , C 4 H 8 . . . CjjHj,, These are unsaturated molecules, having two units of equivalency uncom- bined, and therefore acting as bivalent radicals, capable of taking up 2 atoms of chlorine, bromine, or other univalent radicals, and 1 atom of oxy- gen or other bivalent radical. The first term of this last series cannot give up 2 atoms of hydrogen without being reduced to the atom of carbon ; but the remaining terms may each give up 2 atoms of hydrogen, and thus give rise to the series, C 2 H 2 , C 3 H 4 , C 4 H 6 .... C n H 2n _ 2 . each term of which is a quadrivalent radical. And, in like manner, by successive abstractions of H 2 , a number of ho- mologous series may be formed whose general terms are C n H 2n+2> (^H 2 ". CaH^. C u H 2n _ 4 . . . . &c. The individual series, as far as C 6 , are given in the following table, to- gether with the names proposed for them by Dr. Hofmann : * CH 4 CH 2 Methane Methene C 2 H 6 C 2 H 4 C 2 H 2 Ethane Ethene Ethine CgHg CgHg CgF^ Cgllj Propane Propene Propine Propone C 4 H 10 C 4 H 8 C 4 H 6 C 4 H 4 C 4 H 2 Quartane Quartene Quartine Quart one Quartune C 5 H 12 C 5 H 10 C 5 H 8 C 5 H 6 C 5 H 4 C 6 H, Quintane Quintene Quintine Qumtone Quintune C 6 H, 4 C 6 H, 2 C 6 H 10 C 6 H 8 C 6 H 6 C 6 H 4 C 6 H 2 . Sextane Sextene Sextine Sextone Sextune Each vertical column of this table forms a homologous series, in which the terms differ by CH 2 , and each horizontal line an isologous series, in which the successive terms differ by H 2 . The bodies of these last series are designated as the monocarbon, dicarbon group, &c. The formulae in the preceding table represent hydrocarbons all of which are capable of existing in the separate state, and many of which have been actually obtained. They are all derived from saturated mole- cules, C n Hon+2, by abstraction of one or more pairs of hydrogen-atoms. But a saturated hydrocarbon, CH 4 , for example, may give up 1, 2, 3, or any number of hydrogen-atoms in exchange for other elements; thus marsh gas, CH 4 , subjected to the action of chlorine under various circumstances, yields the substitution- products, CH 3 C1, CH 2 C1 2 , CHC1 3 , CC1 4 , which may be regarded as compounds of chlorine with the radicals, (CH 3 )', (CH 2 )", (CH 3 )'", C"; and in like manner each hydrocarbon of the series, C n H^-f^, may yield a series of radicals of the forms, &c. each of which has an equivalent value, or combining power, corresponding * Proceedings of the Royal Society, xv. 57. 468 CLASSIFICATION OF ORGANIC COMPOUNDS. with the number of hydrogen-atoms abstracted from the original hydro- carbon. Those of even equivalence contain even numbers of hydrogen- atoms, and are identical in composition with those in the table above given; but those of uneven equivalence contain odd numbers of hydrogen-atoms, and are incapable of existing in the separate state, except, perhaps, as double molecules (p. 238). These hydrocarbon radicals of uneven equivalence are designated by names ending in yl, those of the univalent radicals being formed from me- thane, ethene, &c., by changing the termination ane into yl; those of the trivalent radicals by changing the final e in the names of the bivalent radicals, methene, &c., into yl ; and similarly for the rest. The names of the whole series will therefore be as follows: CH 4 (CH 3 )' (CH 2 )"' (CH)'" Methane Methyl Methene Methenyl C 2 H 6 (C 8 H 6 )' (C 8 H 4 )" (C,H,)"/ (C 2 H 2 )" (C 2 H)* Ethane Ethyl Ethene Ethenyl Ethine Ethinyl C 3 H 8 (C,H T )' (C,Hj)" (C,H 6 )'" (C 8 H 4 )* (C,H,)* (C 3 H 2 )* (C.H)* Propane Propyl Propene Propenyl Propine Propinyl Propone Proponyl. &c. &c. &c. From these hydrocarbon radicals, others of the same degree of equiva- lence may be derived by partial or total replacement of the hydrogen by other elements, or compound radicals. Thus from propyl, C 3 H 7 , may be derived the following univalent radicals : C 3 H 6 C1 C 3 H 3 C1 4 C 3 H 5 C 3 H 2 C1 3 C 3 H 6 (CN)' Chloropropyl Tetrachloro- Oxypropyl Trichlor- Cyanopropyl. propyl oxy propyl C 3 H 6 (N0 2 ) C 3 H 4 (NH 2 )0 C 3 H 6 (CH 3 ) C 3 H 5 (C 2 H 5 ) 2 Nitropropyl Amidoxypropyl Methylpropyl Diethylpropyl. From the radicals above mentioned, all well-defined organic compounds may be supposed to be formed by combination and substitution, each radical entering into combination, just like an elementary body of the same degree of equivalence. Organic compounds may thus be arranged in the following classes : I. Hydrocarbons containing even numbers of hydrogen atoms. These are the compounds tabulated on page 467 ; they are sometimes regarded as hy- drides of radicals containing uneven numbers of hydrogen atoms; e. g+: Methane, CH 4 = CH 3 . H, Methyl hydride. II. Halo'id Ethers. Compounds of hydrocarbons with halogens ; e. g. : CH S C1 C 2 H 4 Br 2 C 3 H 6 I 3 Methyl chloride. Ethene bromide. Propenyl iodide. These compounds are often formed by direct substitution of chlorine, bro- mine, &c., for hydrogen in hydrocarbons containing even numbers of hydro- gen atoms. III. Alcohols. Compounds of hydrocarbon radicals (hence called alcohol radicals), with hydroxyl ; e. g. : C,H 6 (HO) (CAX'CHO), (C,H 6 )"/(HO) S Ethyl alcohol. Ethene alcohol Propenyl alcohol (Glycol). (Glycerin). These compounds may be formed from the corresponding haloid ethers, by the action of water or alkalies, just as metallic hydrates are formed from the corresponding chlorides, &c. CLASSIFICATION OF ORGANIC COMPOUNDS. 469 IV. Oxygen Ethers, or Alcoholic Oxides. Compounds of hydrocarbon radicals with oxygen ; e. g. : (C 2 H 5 ) 2 (C,H 4 )"0 (C 3 H 6 )'" 2 3 Ethyl Ethene Propenyl oxide. oxide. oxide. These ethers are related to the alcohols in the same manner as anhydrous metallic oxides to the corresponding hydrates or hydrylates, and may be formed, in many instances, by direct dehydration of the alcohols, as by the action of sulphuric acid, zinc chloride, &c. V. Sulphur and Selenium Alcohols and Ethers. Compounds analogous in composition to the oxygen alcohols and ethers, the oxygen being replaced by sulphur or selenium. The sulphur and selenium alcohols are also called mercaptans. VI. Acid Halides. Compounds of oxygenated radicals (acid radicals) with chlorine, bromine, &c. ; e. g. : C 2 H 3 O.C1 (C 4 H 4 ? )"Cl a (CsHsOV'Cls Acetyl Succinyl Citryl chloride. chloride. chloride. These compounds are formed by the action of the chlorides, bromides, &c., of phosphorus on the compounds of the next class. VII. Organic Acids. Compounds of oxygenated radicals with hydroxyl; C 2 H 3 . HO (C 4 H 4 0,)" . (HO), (C.H 8 4 )'" . (HO), Acetic acid. Succinic acid. Citric acid. These compounds are formed in a variety of ways; among others, by oxi- dation of alcohols, and by the action of water on the corresponding acid halides, just as alcohols are formed from alcoholic chlorides. A very large number of them exist also ready-formed in the bodies of plants and ani- mals. The hydrogen in the radicals of these acids may be more or less replaced by chlorine, bromine, nitryl, (N0 2 ), and other chlorous radicals; thus, from benzoic acid, C 7 H 5 . HO, are derived: C 7 H 4 C10 . HO C 7 H 5 (N0 2 )0 . HO C 7 H 5 (NH 2 )0 . HO Chlorobenzoic Nitrobenzoic Amidobenzoic acid. acid. acid. VIII. Acid Oxides, sometimes called Anhydrous acids, or Anhydrides; (C 2 H 3 0) 2 (C,H 4 0,)"0 (C 2 H 3 0)(C ? H 5 0)0 Acetic oxide. Succinic oxide. Acetobenzoic oxide. These are related to the acids in the same manner as the oxygen-ethers to the alcohols, and are formed from them in some instances by direct dehy- dration. IX. Ethereal Salts, also called Compound Ethers. Compounds formed from acids by substitution of alcohol radicals for hydrogen, just as metallic salts are produced by substitution of metals for the hydrogen in acids ; e.g.: C 2 H 3 2 . H S0 4 . HII P0 4 .HHH Acetic Sulphuric Phosphoric acid. acid. acid. 40 470 CLASSIFICATION OF ORGANIC COMPOUNDS. C 2 H 3 2 . C 2 H 5 S0 4 . (C 2 H 5 )H P0 4 . (C 2 H 5 )HH Ethylic Monet hylic Monethylic acetate. sulphate. phosphate. o/~v /p TJ \ T>A I '{*i VJ \ IT i^vJ 4 . (^O^lfi/Q \J*. IV^nllcJrttl Diethylic Diethylic sulphate. phosphate. P0 4 .(C 2 H 5 ) 3 Triethylic phosphate. They are produced in many cases by heating an acid or the corresponding chloride with an alcohol. X. Aldehydes. These are compounds intermediate between alcohols and acids. Thus: C 2 H 6 C 2 H 4 C 2 H 4 2 Ethyl Acetic Acetic alcohol. aldehyde. acid. They are produced by oxidation of alcohols, and are reconverted into the latter by the action of nascent hydrogen. By further oxidation they are converted into acids. XI. Ketones. These are bodies derived from aldehydes by the replace- ment of 1 atom of hydrogen by an alcohol radical; e.g. : Acetic ketone or Acetone, C 3 H 6 = C 2 H 3 (CH 3 )0. They are produced by the dry distillation of the calcium or barium salts of monobasic acids, and by other processes which will be mentioned fur- ther on. XII. Amines, also called Alcohol-bases, or Compound ammonias. Com- pounds of alcohol radicals with amidogen, (Nt^)', imidogen, (NH)'', and trivalent nitrogen ; e. g. : C 2 H 5 . H 2 N (C 2 H 5 ) 2 . HN (C 2 H 5 ) 3 N Ethylamine. Diethylamine. Triethylamine. (C 2 H 4 )" . (H 2 N) 2 (C 2 H 4 )" 2 . (HN) 2 {C.H 4 )" tv N r Ethene-diamine. Diethene-diamine. Triethene-diamine. The modes of formation of these bodies will be explained hereafter. They are mostly of basic character, and capable of forming salts with acids, like ammonia, H 3 N, from which they may, in fact, be derived by substitution of alcohol radicals for part or the whole of the hydrogen. Those in which the hydrogen is wholly thus replaced are called nitriles; and among these special mention must be made of a group consisting of nitrogen combined with a trivalent hydrocarbon radical, such as (CH)'"N (C 2 H 3 )'"N (C S H 6 )'"N Methenyl Ethenyl Propenyl nitrile. nitrile. nitrile. These nitriles have no basic properties, but are all neutral, except the first, which is a monobasic acid, capable of exchanging its hydrogen for metals, and in this character may be regarded as a compound of hydrogen with the univalent radical cyanogen C N; it is accordingly named hy- drogen cyanide, or hydrocyanic acid, and the other nitriles homologous with it are the ethers of this acid ; thus : CLASSIFICATION OP ORGANIC COMPOUNDS. 471 Methenyl nitrile, (CH) 777 N = CN. H, Hydrogen cyanide, Ethenyl nitrile, (C 1 H f ( / ' y H = CN. CH 3 , Methyl cyanide, Propenyl nitrile, (C 3 H 5 ) 777 N = CN. C 2 H 6 , Ethyl cyanide. The metallic cyanides have been already noticed (p. 277). XIII. Alcoholic Ammonium-compounds. Compounds containing pentad nitrogen, and having the composition of ammonium salts in which the hy- drogen is more or less replaced by alcohol radicals ; e.g. : N T (C 2 H 5 )H 3 Cl Ethylammonium chloride, N T (C a H 8 ) 2 H 2 Cl Diethylammonium chloride, N v (C 2 H 5 ) 3 HCl Triethylammonium chloride, N>(C 8 H ft i 4 Cl Tetrethylammonium chloride, NT(C 2 H 5 ) 4 (HO) Tetrethylammonium hydrylate. This last compound and its analogues, containing methyl, amyl, &c., are powerful alkalies, obtainable in the solid state, by evaporation of their aqueous solutions, as white deliquescent crystalline masses resembling caustic potash. XIV. Phosphorus, Arsenic, and Antimony Compounds, analogous to the nitrogen compounds XII. and XIII. ; e. g. : P'"(CH 8 ) S As"/(C 2 H 5 ) 3 Sb'"(C,H B ), Triethyl phos- Tricthyl Triethyl phine. arsine. stibine. P'(CH 3 ) 4 C1 As*(CH,)(C,H 5 ) s Cl SV(C,H 6 ) 4 (HO) Tetramethyl- Methyl-triethyl-ar- , Tetrethyl-sti- phosphonium sonium chloride. bonium hydrate. chloride. XV. Organo-metallic bodies, not analogous to ammonia or ammonium salts. Compounds of hydrocarbon radicals with monad, dyad, and tetrad metals; e.g.: NaC 2 H 6 Zn"(CH 8 ) 2 Sn*(C 2 H 6 ) lr Sodium ethide. Zinc ethide. Stannic ethide. Hg"(CH,)Cl Sn"(C 2 H 5 )Cl 3 Sn*(CH 3 ) 2 I 2 Mercuric chloro- Stannic chloro- Stannic dimethyl methide. triethide. di-iodide. XVI. Amides. Compounds exactly analogous to the amines, but with aciu radicals instead of alcohol radicals ; those which contain bivalent acid radicals combined with imidogen, (NH) 77 , are called imides; e.g.: Acetamide C 2 H 3 O.H 2 N Succinamide (C 4 H 4 2 ) 77 . (H 2 N) 2 Diacetamide (C 2 H 3 0) 2 .HN Succinimide (C 4 H 4 O 2 ) 77 . HN Citramide (C 6 H 6 4 )'" . N 777 . XVII. Amic acids Acids consisting of a bivalent or trivalent acid rad- ical combined with hydroxyl and with amidogen ; e. g. : Succinamic acid (C 4 H 4 2 )". HO. H 2 N Citramic acid* (C 6 H 5 O 4 ) 777 . HO. (HN) 77 . Each of the classes of carbon compounds above enumerated may be di- vided into homologous and isologous groups, though in most cases the series are far from being complete. * This compound is not actually known; but its derivative, phenyl-citramic acid, (C 6 U & O t )'". C 6 II 5 . UN, has been obtained. 472 CLASSIFICATION OF ORGANIC COMPOUNDS. The preceding classes, most of which have their analogues amongst in- organic compounds, include nearly all artificially prepared organic bodies, and the majority of those produced in the living organism. There are still, however, many compounds formed in the bodies of plants and animals, the chemical relations of which are not yet sufficiently well made out to enable us to classify them with certainty. Such is the case with many vegetable oils and resins, with most of the alkaloids or basic nitrogenized compounds found in plants, such as morphine, quinine, strychnine, &c., and several definite compounds formed in the animal organism, as albumin, fibrin, casein, and gelatin. Rational Formulae of Organic Compounds It must be distinctly under- stood that the formulae above given are not the only ones by which the constitution of the several classes of organic compounds may be repre- sented. Rational formulae are intended to represent the mode of formation and decomposition of compounds, and the relation which allied compounds bear to one another: hence, if a compound can, under varying circum- stances, split up into different atomic groups or radicals, or if it can be formed in various ways by the combination of such radicals, different ra- tional formulae must be assigned to it. This point has been already noticed in connection with the constitution of metallic salts, and illustrated espe- cially in the case of the sulphates (p. 281) ; but organic compounds, which for the most part contain larger numbers of atoms, and are therefore capable of division into a greater number of groups, afford much more abundant illustration of the same principle. Take, for example, acetic acid, the molecular formula of which is C 2 H 4 2 . This may be resolved into the following rational formulae : 1. C 2 H 3 2 .H. This formula, analogous to that of hydrochloric acid, Cl. H, indicates that a molecule of acetic acid can give up one atom of hy- drogen in exchange for a univalent metal or alcohol-radical, forming, for example, sodium acetate, C 2 H 3 2 . Na, ethyl acetate, C 2 H 3 0. C 2 H 5 , &c. ; that two molecules of the acid may give up two hydrogen atoms in exchange for a bivalent metal or alcohol-radical, forming barium acetate, (C 2 H 3 2 ) 2 Ba // , ethene acetate, (C 2 H 3 O 2 ) 2 . (C 3 H 4 y / J &c. ; in other words, that acetic acid is a monobasic acid (p. 282). 2. C 2 H 3 . HO. This formula, analogous to that of water, H . HO, cor- responds to such reactions as the formation of acetic acid from acetic chloride by the action of water : C 2 H 3 O.C1 -f H.HO == HC1 -f C 2 H 3 O.HO. 3. C 2 HgO . H . 0. This formula, also comparable to that of water, HH . 0, corresponds to the conversion of acetic acid into acetic chloride, hydro- chloric acid, and phosphorus oxychloride, by the action of phosphorus pentachloride : C 2 H 3 . H . + PC1 3 . C1 2 = C 2 H 3 . Cl + HC1 -f- PC1 3 ; also to the formation of thiacetic acid, C 2 H 3 . H . S, by the action of phos- phorus pentasulphide on acetic acid : 5(C 2 H 3 . H . 0) + P 2 S 5 == 5(C 2 H 3 . H . S) + P 2 5 . 4. (C 2 H 8 ) /X/ . HO . 0. This represents the formation of acetic acid from ethenyl nitrile, (C 2 H 3 ) /// N, by heating with caustic alkalies: H = NH + CH,>". 0. HO. Ethenyl Water. nitrile. CLASSIFICATION OF ORGANIC COMPOUNDS. 473 5. (CH 3 . CO) . HO. This formula, in which the radical acetyl, C 2 H 3 0, is resolved into carbonyl, (CO)", and methyl, corresponds: a. To the de- composition of acetic acid by electrolysis, in which hydrogen is evolved at the positive pole, while carbon dioxide and ethane, C 2 H 6 , appear at the negative : 2(CO . CH 3 . HO) = H 2 -f C 2 H 6 -f- 2C0 2 . /?. To the production of methane (marsh gas) by heating potassium ace- tate with excess of potassium hydrate (p. 169) : CO . CH 3 . KO -f HKO = CH 4 + (CO)" . (K0) 2 . Potassium acetate. Potassium Methane. Potassium hydrate. carbonate. y. To the production of acetone and barium carbonate by the dry distil- lation of barium acetate : (CO . CH 3 ) 2 . Ba0 2 = (CO)"(CH 3 ) 2 -f (CO)".Ba0 2 . Barium acetate. Acetone. Barium carbonate. Now, on comparing those several rational formulae, it will be seen that they are all included under the constitutional formula, H H C C H, A in which the molecule is resolved into its component atoms, and these atoms are grouped, as far as possible, according to their different equivalences, or combining powers. These constitutional formulae are the nearest approach to the representation of the true constitution of a compound that our knowl- edge of its reactions enables us to give; but the student cannot too care- fully bear in mind that they are not intended to represent the actual ar- rangement of the atoms in space, but only, as it were, their relative mode of combination, showing which atoms are combined together directly, and which only indirectly, that is, through the medium of others. Thus, in the formula of acetic acid, it is seen that three of the hydrogen atoms are united directly with the carbon, while the fourth is united to it only through the medium of oxygen ; that one of the two oxygen atoms is combined with carbon alone, the other both with carbon and with hydrogen ; and that one of the carbon atoms is combined with the other carbon atom and with hy- drogen ; the second with carbon and with oxygen. Abundant illustration of these principles will be afforded by the special descriptions of organic compounds in the following pages. ISOMERISM. Two compounds are said to be isomeric when they have the same empirical formula or percentage composition, but exhibit different properties. A few examples of isomerism are met with amongst inorganic compounds ; but they are much more numerous amongst organic or carbon compounds. Isomeric bodies may be divided into two principal groups, namely : A. Those which have the same molecular weight; and these are sub- divided into: a. Isomeric bodies, strictly so called ; namely, those which exhibit analogous decompositions and transformations when heated or subjected to the action of the same reagents, and differ only in physical properties. Such is the case with the volatile oils of turpentine, lemons, juniper, &c., all of which have the composition C 10 H 16 , resemble each other closely in their chemical reactions, and are distinguished chiefly by their odor and their action on polarized light. 40* 474: HYDROCARBONS. /?. Metameric bodies, which, with the same percentage composition and molecular weight, exhibit dissimilar transformations under similar circum- stances. Thus the molecular formula, C 3 H 6 2 , represents three different bodies, all exhibiting different modes of decomposition under the influence of caustic alkalies, viz., (1) Propionic acid, C 3 H 5 .OH, which is converted by caustic potash, at ordinary temperatures, into potassium propionate, C 3 H 6 . OK. (2) Methyl acetate, C 2 H 3 . OCH 3 , a neutral liquid not acted upon by potash at common temperatures, but yielding, when heated with it, potassium acetate and methyl alcohol : C 2 H 3 . OCH 3 -f OKH = C 2 H 3 . OK -f CH 3 . OH. (3) Ethyl formate, CHO . OC 2 H 5 , converted in like manner, by heating with potash, into potassium formate, CHO . OK, and ethyl alcohol, C 2 H 5 .OH. These three compounds may be represented by the following constitu- tional formulae, the dotted lines indicating the division into radicals indi- cated by the rational formulae above given : H 3 C H 3 C H H H 2 C- 0=C CH 3 , 0=C C CH 3 . 0=C H, H Propionic acid. Methyl acetate. Ethyl formate. B. Compounds which have the same percentage composition, but differ in molecular weight; such bodies are called polymeric. The most striking example of polymerism is exhibited by the hydro-carbons CJi^, all of which are multiples of the lowest, namely, methene, CH 2 . Another exam- ple is afforded by certain natural volatile oils, which are polymeric with oil of turpentine, and have the formulae, C 20 H 32 , C 30 H 48 , &c. All polymeric compounds exhibit regular gradations of boiling point, vapor-density, and other physical characters from the lowest to the highest. Some are chemi- cally isomeric, exhibiting analogous transformations under similar circum- stances, while others are metameric, exhibiting dissimilar reactions under given circumstances. HYDROCARBONS. FIRST SERIES, C n II 2n -(- 2 . PARAFFINS.* This series, as already observed, consists of saturated hydrocarbons, not capable of uniting with any other bodies, simple or compound. The names and formulae of the first six are given in the table on page 467 ; the follow- ing terms may be called, septane, octane, nonane, decane, undecane, dodecane, &c. All the members of the series above the first, CH 4 , may be regarded as derived from that compound by replacement of one of the hydrogen-atoms, by a univalent hydrocarbon radical of the series CnH^-f! (p. 466) ; thus . (H I TT Methane C< H t-H * From parum affmis. indicating their chemical indifference. The name paraffin has long been applied to the solid compounds of the series, on account of this character; and many of the liquid compounds of the same series are known commercially as paraffin nils. It is con- venient, therefore, to employ the term paraffin as a generic name for the whole series. PARAFFINS. 475 Ethane C 2 H 6 = C { C J[ Propane C 3 H 8 = C { C ^L C j C % CH * Quartane C 4 H 10 = C { C ^ == C { c g c i H s = C { CH,CH,CH 8 &c., &c. Occurrence and Formation. Many of the paraffins occur ready-formed in American petroleum and other mineral oils of similar origin. They are formed artificially by the following processes: 1. By the simultaneous action of zinc and water on the alcoholic iodides (p. 468), compounds derived from these same hydrocarbons by the substi- tution of one atom of iodine for hydrogen. This reaction, which appears to be applicable to the formation of the whole series of paraffins, is represented by the general equation : 2C n H 2n + t I -f Zn 2 + 20H 2 = ZnH 2 2 -f ZnI 2 + 2C n H 2n - f 2 Alcoholic Zinc. Water. Zinc Zinc Paraffin. iodide. hydrate. iodide. As an example, we may take the formation of ethane from ethyl iodide : 2C 2 H 5 I -f Zn 2 -j- OH 2 = ZnH 2 2 + ZnI 2 -f 2C 2 H 6 Ethyl Ethane. iodide. 2. All the paraffins may be produced by heating the alcoholic iodides with zinc alone. Generally speaking, however, two of these hydrocarbons are obtained together, the first product of the reaction being a paraffin containing twice as many carbon-atoms as the alcoholic iodide employed; and this compound being then partly resolved into the paraffin containing half this number of carbon-atoms and the corresponding define, (CnlLjn); thus: 2C 2 H 5 I -f Zn = ZnI 2 -f- C 4 H 10 Ethyl Quartane. iodide. and, C 4 H IO = C 2 H 4 + C 2 H 6 Quartane. Etheire. Ethane. Generally : 2C n H 2n+1 I -f Zn == ZnI 2 -f- C to H to+i and, C 2B H 8n+2 = C.H* -f C*K*+ r 3. By the electrolysis of the fatty acids (C n H 2n 2 ). For example, a solu- tion of potassium acetate, divided into two parts by a porous diaphragm, yields pure hydrogen, together with potash, at the negative electrode, and at the positive electrode (if of platinum) a mixture of carbon dioxide and ethane gases: F2C 2 H 4 2 = 2C0 2 -f C 2 H 6 + H r We may suppose that the two molecules of acetic acid are resolved by the rrent into H 2 and C 4 H 6 4 , and that the latter then splits up into 2C0 2 and H 6 . The general reaction is: SC.Hj.O, = 2C0 2 + C^H^ + H 2 . 4. Some of the paraffins are obtained from acids of the series C n H 2n O 2 476 HYDROCARBONS. and C n H 2n _ 2 4 , by the action of alkalies, which abstract carbon dioxide from those acids, the hydrocarbon thus eliminated containing one atom of carbon less than the acid from which it is produced : C n+1 H 2n+2 2 * = C0 2 +C n H 2n+2 , C n+2 H 2n+2 4 == 2C0 2 +C a H 2n+2 . In this maner methane (marsh gas) is obtained by heating potassium acetate with excess of potassium hydrate (p. 169) : C 2 H 3 2 K + OHK = C0 3 K 2 -f CH 3 Potassium Potassium Potassium Methane, acetate. hydrate. carbonate. Also, sextane and octane, by similar treatment of the potassium salts of suberic acid, C 8 Hj 4 4 , and sebacic acid, C 10 H J8 O 4 : C 8 H 12 4 K 2 + 20HK = 2C0 3 K 2 + C 6 H, 4 Potassium Sextane. suberate. C 10 H 16 4 K 2 + 20HK = 2C0 3 K 2 + C 8 H ]8 Potassium Octane. sebate. Generally speaking, however, a further decomposition takes place, result- ing in the formation of hydrocarbons containing a smaller proportion of hydrogen than the paraffins. 5. The paraffins may also be produced from the olefines, C n H 2ll) by combining the latter with bromine, and heating the resulting compound, C n H 2n Br 2 , with a mixture of potassium iodide, water, and metallic copper. The bromine-compound is then decomposed, and the hydrocarbon, CnHo,,, is partly reproduced in the free state, partly converted, by the addition of hydrogen, into a paraffin, C n H 2n -}- 2 . 6. Several of the paraffins are produced by the dry or destructive dis- tillation of butyrates and acetates. 7. They are also found amongst the products of the dry distillation of coal, especially Boghead and Cannel coal, and, as already observed, they consti- tute the principal portion of many mineral oils, formed by the gradual decay or decomposition of vegetable matter beneath the earth's surface. 8. Quintyl alcohol, or amyl alcohol, C 5 H ]2 0, distilled with zinc chloride, yields quintane, C 5 H 12 , and several of its homologues, together with olefines and other hydrocarbons containing still smaller proportions of hy- drogen. 9. Methane, or marsh gas, CH 4 , the first term of the series, is produced synthetically by passing a mixture of hydrogen sulphide and vapor of carbon bisulphide over red-hot copper. The copper abstracts the sulphur from both compounds, and the carbon and hydrogen thus liberated unite to form marsh gas : CS 2 -f 2H 2 S + Cu 4 = 4CuS + CH 4 . Properties and Reactions of the Paraffins. The properties of methane have been already described (p. 169). Of the other paraffins, ethane, propane, and quartane are gaseous at ordinary temperatures ; most of the others are liquids regularly increasing in specific gravity, viscidity, boiling point, and vapor density, as their molecular weight becomes greater : those con- taining 20 carbon atoms or more are crystalline solids. The following table exhibits the specific gravities and boiling points of the paraffins ob- tained from American petroleum : j- * By substitution of n+ 1 for n, the formula Cn H n O 2 becomes C + 1 IT2n+ 2 2 ; and by sub- stitution of n+2 for n, the formula C n H2n-->0 4 is converted into C +oll2n-fo04. f Pelouze and Cahonrs, Ann. Ch. Pharm.'cxxiv. 289; cxxvii. 196; cxxix. 87. PARAFFINS. 477 Specific gravity Name. Formula. Boiling point. of liquid. of vapor drogon : liv- r 1. Ethane C 2 II 6 Gascons at ordinary _ 15 tempe atures. Propane 0~ HQ _ 22 Qiiiirtane CiHin a little above 0-60 at 0C. 32 F. 29 Quintane C 5 H 12 30 C. 86 F. 0-628 17" 63" 36 Sextane CfiHii 68 " 154 " 0-6G9 16" 61" 43 Septane C 7 H 16 9294 " 198201 " 0-699 15" 69" 50 . Octane 116118 " 241245 " 0-726 15" 59" 57 Nonane Gallon 136138 277280 " 0-741 15" 59" 64 Decane Cellos 160162 " 320324 " 0-757 , 15 o 59" 71 TJndecane C n II 2 < 180184 " 356363 " 0-765 " 16 " 61" 78 Duodecane 196200 " 384-392 " 0-776 20 " 68" 85 Tridecane cJjiiS 216218" 421424 " 0792 , 20 o < 68 92 Quatuordecane 236240 " 456464 " 99 Quindecane cfiaS 255260 " 491500 " 106 American petroleum likewise yields a quantity of liquid boiling above 300 C. (572 F.), and doubtless containing paraffins of still higher order. Some specimens of the crude oil, as it issues from the ground, contain ethane, C 2 H 6 , and propane, C 3 H 8 , which are given off from it as gas at or- dinary temperatures. In boring for the oil also, large quantities of gas escape, exhibiting the characters of methane; hence it is probable that in the great geological changes which have given rise to the separation of the petroleum, the whole series of paraffins have been formed from marsh gas upwards. Solid paraffin is a colorless crystalline fatty substance, probably consist- ing of a mixture of several of the higher members of the series C n H 2n -|- 2 . It is found native in the coal-measures, and other bituminous strata, con- stituting the minerals known as fossil wax, ozocerite, hatchettin, &c. It exists also in the state of solution in many kinds of petroleum, and may be sepa- rated by distilling off the more volatile portions, and exposing the remain- der to a low temperature. In a similar manner also may solid paraffin be obtained from the tar of wood, coal, and bituminous shale. It was first prepared by Reichenbach from wood-tar. It is tasteless and inodorous, insoluble in water, slightly soluble in alcohol, freely in ether, and miscible in all proportions, when melted, with fixed or volatile oils. It burns with a very bright flame, and those varieties of it which melt at temperatures above 45 C. (113 F. ) are very hard, and well adapted for making candles. Paraffin is largely used also as a substitute for sulphur for dipping matches; and Dr. Stenhouse has patented its application to woollen cloths, to increase their strength and make them waterproof. More extensive, however, are the uses of the liquid compounds of the paraffin series, known in commerce as paraffin oil, photogcne, solar oil, eupione, &c. These oils are largely used for burning in lamps; and, when mixed with fatty oils, such as rape and cotton-seed oils, form excellent materials for lubricating machinery. For the former purpose they are exceedingly well adapted, as, with a proper supply of air, they give a much brighter light than that obtained from fatty oils containing oxygen, and are much cleaner in use. It is necessary to observe, however, that natural petroleum and the oils obtained by the dry distillation of coal, &c., at low temperatures, are mix- tures of a great number of paraffins differing greatly in volatility, und that to render them safe for burning in lamps of ordinary construction, they must be freed by distillation from the more volatile members of the series; otherwise they will take fire too easily, and, when they become heated, will 478 HYDROCARBONS. give off highly inflammable vapors, which, mixing with the air in the body of the lamp, may easily produce dangerously explosive mixtures ; serious accidents have indeed arisen from this cause. It has been found by expe- rience that it is not safe to use a paraffin oil which will take fire on the application of a match and burn continuously, at a temperature below 38 C. (100 F.). Substitution-products of the Paraffins, Paraffins subjected to the action of bromine or chlorine, give up a part, or in some cases the whole of their hy- drogen in exchange for the halogen element. Thus equal volumes of chlorine and methane, CH 4 , exposed to diifused daylight, yield the com- pound CH 3 C1, called chlorornethane or methyl chloride: and. by further subjecting this product to the action of an excess of chlorine in direct sun- shine, it may be successively converted into the more highly chlorinated compounds CH 2 C1 2 , CHC1 3 , and CC1 4 . Ethane, C 2 H 6 , also yields, by a series of processes to be hereafter described, the substitution-products C 2 H 5 C1, C 2 H 4 C1 2 , C 2 H 3 C1 3 , C 2 H 2 C1 4 , C 2 HC1 5 , and C 2 C1 6 ; and similarly for the other compounds of the series. These bodies, which may be regarded as com- pounds of chlorine and other halogen elements with the radicals (CHg)', ^CH 2 )", (CH) /// , &c., are called halo'id ethers; the more important of them will be specially described in connection with the corresponding alcohols. When treated with water or aqueous alkalies, they exchange the haloid element for an equivalent quantity of hydroxyl, (HO), thereby producing alcohols (p. 468) ; and, on the other hand, they may be formed from the alcohols by the action of the chlorides, bromides, and iodides of hydrogen or phosphorus. Nitric acid attacks the higher members of the paraffin series, forming nitro-compounds ; octane, C 8 H, 8 , thus treated, yields the compound, C 8 H 1T (N0 2 ). The lower paraffins, on the other hand, are not aft'ected in the slightest degree by nitric acid; but by indirect means compounds may be formed, having the composition of paraffins, in which the hydrogen is more or less replaced by nitryl ; for example, trinitromethane or nilroform, CH(N0 2 ) 3 . Isomerism in the Paraffin series. It has already been mentioned that these hydrocarbons are sometimes regarded as hydrates of the univalent alcohol radicals C n H 2n +,, methane, for example, as methylhydride, H . CH 3 , ethane as ethyl hydride, H . C 2 H 5 . This view of their constitution is sug- gested by their formation by the action of water on the zinc compounds of the same radicals ; e. g. : Zn(CH 3 ) 2 -f 20H 2 = ZnH 2 2 -f 2(H.CH 3 ); Zinc methyl. Water. Zinc hydrate. Methyl hydride. and by the facility with which they give up one atom of hydrogen in ex- change for chlorine and bromine, whereas the replacement of the remain- ing hydrogen-atoms is much more difficult. On the other hand, all these hydrocarbons, except methane, may be regarded as compounds of two equivalents or half-molecules of alcohol radicals C^H^-f-j, thus : C 2 H 6 = H.C 2 H 6 or CH 3 . CH 3 , Ethane. Ethyl hydride. Dimethyl. C 3 H 8 = H.C 3 H r or CH 3 . C 2 H 5 , Propane. Propyl hydride. Methyl-ethyl. C 4 H, = H . C 4 H 9 or C 2 H 6 . C 2 H 6 or CH 3 . C 3 H 7 , Quartane. Quartyl Diethyl. Methyl- hydride propyl. This latter view appears to accord with their formation by the action of PARAFFINS. 479 zinc on the iodides of the alcohol radicals, which is similar to that of hydro- gen by the action of zinc on hydriodic acid ; thus : Zn + 2HI ZnI 2 -f HH, Hydrogen Zinc iodide. Hydrogen. iodide. Zn -f- 2C 2 H 6 I = ZnI 2 + C 2 H 5 . C 2 H 5 Ethyl iodide. Diethyl. Zn -f- CH 3 I -f C 2 H 5 I = ZnI 2 -f CH 3 .C 2 H 5 , Methyl Ethyl Methyl- iodide. iodide. ethyl. The first three hydrocarbons of the series, however, viz., CH 4 , C 2 H 6 , C 3 H g , exhibit exactly the same physical and chemical properties in whatever way they may be prepared; and indeed the constitutional formulae of these bodies, viz. CH 3 CH 4 CH CH 2 show that they are not susceptible of isomeric modification, inasmuch as there is but one way in which the carbon-atoms in either of them can be grouped : in ethane each carbon-atom is directly combined with three hy- drogen-atoms and the other carbon-atom ; and whether we regard it as CH 3 ethyl hydride, H CH 2 , or as dimethyl, H 3 C CH 3 , this arrangement re- mains the same. In propane, C 3 H 8 , each carbon-atom is directly combined with at most two other carbon-atoms, and there is no other way in which the atoms can be arranged. But if we look at the formula of the 4-carbon paraffin, C 4 H 10 , we see that it may be written in either of the following forms : CH 3 " n nTT CH CH 2 f I CH 5 CH 3 in the first of which, neither of the carbon-atoms is directly united with more than two others, whereas in the third, one of the carbon-atoms is directly combined with three others. The first may be represented, either as propyl-methane, C j H 2 CH 2 CH 3 = c f GH 2 C a H 6 = c f C 8 H 7 Qr ftg ^_ I -"3 I "3 t H 3 thyl, H 5 C 2 . C 2 H 6 , according to the manner in which we may suppose it to be divided; the second as trimethyl methane, C I "v^ n 8/a produced by the action of zinc on isopropyl iodide ; this compound may be represented by the constitutional formula : H H - C 4. Those in which one carbon-atom is associated with four others, as in f /T'H ^ dimethyl-diethyl-methane, or carbdimethyl-diethyl, C j > c J'? , a compound produced by the action of zinc-ethyl, Zn(C 2 H 5 ) 2 , on dimethyl-dichlorome- thane, C (CH 3 ) 2 the transformation being effected by the substitution of 2 atoms of ethyl for 2 atoms of chlorine : Dimethyl-dichloro-methane. Dimethyl-diethyl-methane. CH Cl H 3 C C CH 3 i | H H 3 C C CH S C H fl The paraffins of each of these groups exhibit a regular increase in boil- ing point as they ascend in the series by successive addition of CH 2 , and the boiling point of a paraffin containing a given number of carbon-atoms, is found to be lower in proportion as its structure is more complex. In the first and second groups the difference of boiling point, for each incre- ment of CH 2 , is about 31 C. (56 F.), whereas in the third it is only 25 C. (45 F.). SECOND SERIES, CnHjn- OLEFINES. The hydrocarbons of this series are polymeric, as well as homologous with one another, inasmuch as their formulae are all exact multiples of that of the lowest CH 2 . The lower members of the series are gaseous at ordinary temperatures, the higher members are solid, and the intermediate compounds liquid. The names and formulae of the known members of the olefine series are given in the following table, together with their melting and boiling points: Name. Formula. Melting point. Boiling point. Ethene or Ethylene C 2 H 4 _ _ Propene Quartene " Propylene Butylene ~ 17-8 C. 14 F. +3 " 37-4 Quintene Arnylene C^HIO 35 " 95 Sextene llexylene C 6 II 12 68-70 " 154-158 Septene Octene Ilcptylene Octylene C 7 Ul4 P 8 Hl6 95 " 203 115-117 " 239-242 Noneno Nonylene ._. 140 " 284 Decene Paramylene Plo"i20 __ 1CO " 320 jSexdecene Cetene CjiHoo 275 $' 527 Beptivigintine " Trigintene " Cerotene Melene C 27 !! 5 * 57 C. 135 F. 62 " 144 " (?) (?) 375 (?) i 707 (?) " OLEFINES. 481 Methene, CII 2 , the lowest term of the series, does not appear to be ca- pable of existing in the separate state ; but its oxygen analogue, carbon monoxide or carbonyl, CO, is a well-known compound, which has been al- reudy described (p. 168). Formation of the Olefines. 1. By abstraction of the elements of water from the alcohols of the series C n H 2n -}_ 2 O, homologous with common alcohol, under the influence of powerful dehydrating agents, such as oil of vitriol, phosphoric oxide, or zinc chloride; thus: C 2 H 6 OH 2 = C 2 H 4 Ethyl alcohol. Water. Ethene. The preparation of ethene, or olefiant gas, by heating common alcohol with oil of vitriol, has been already described (p. 1G9). Quintyl, or amyl alcohol, C 5 H 12 0, distilled with zinc chloride, yields besides the corre- sponding oletiiie, quintene or amylene, C 6 H, a number of others poly- meric with it; besides quintane, C 5 H, 2 , and its homologues, and hydrocar- bons containing a smaller proportion of hydrogens than the olefines. 2. By passing the vapors of the haloid compounds of the monad radicals, C n H 2n -j-i, over lime at a dull red heat; e.g. : 2C 6 H U C1 -f CaO = CaCl 2 -f OH 2 + 2C 5 H JO Quintyl Lime. Calcium Water. Quintene. chloride. chloride. 3. By the decomposition of the paraffins at the moment of their forma- tion by the action of zinc or sodium on the alcoholic iodides of the monad alcohol-radicals C n H.^ +j (see p. 475). 4. By the action of these same iodides on the sodium compounds of the same radicals ; for example : C 2 H 5 I + C 2 H 5 Na = Nal + C 2 H 4 + C 2 H 6 Ethyl Sodium Sodium Ethene. Ethane, iodide. ethyl. iodide. 5. By decomposition of the hydrates of ammonium bases containing four atoms of a monad alcohol-radical (p. 471), these compounds when heated splitting up into a tertiary monamine (p. 470) and an olefine; thus: N(C 2 H 5 ) 4 (HO) = N(C 2 H 5 ) 3 + OH 2 + C 2 H 4 Tetrethylammo- Triethyl- Water. Ethene. nium hydrate. ammine. 6. Olefines are formed by the decomposition of acetates and butyrates at a red heat, distilling over together with several other products, from which they are separated by combining them with bromine, and heating the resulting bromine-compounds, C n H 2 nBr 2 , to 275 C. (527 F.), with cop- per, water, and potassium iodide. In this manner Berthelot has obtained ethene, propene, quartene, and quintene. 7. Several of the olefines may be produced by direct synthesis from other hydrocarbons of simpler constitution. a. Ethene is formed by the action of nascent hydrogen upon ethine or acetylene (p. 484) : C 2 H 2 + H 2 = C 2 H 4 Ethine. Ethene. /?. Propene, C 3 H 6 , is formed by passing a mixture of methane and carbon monoxide (oxymethene) through a red-hot tube : 2CH 4 + CO = OII 2 + C 3 II fl . Also by the action of methenyl chloride (chloroform) on zinc ethide : 41 482 HYDROCARBONS. 2CHC1 3 + 3Zn(C 2 H 6 ) 2 = 3ZnCl 2 + 4C 3 H 6 -f 2CH 4 . y. Quintene, or amylene, C 5 H, , or a compound isomeric with it, is formed by the action of zinc ethide on propenyl (allyl) iodide : 2C 3 H 5 I + Zn(C 2 H 5 ) 2 = Znl + 2C 5 H 10 . 6. Sextene, or hexylene, C 6 H 12 , is obtained in combination with hydriodic acid by the action of that acid on mannite, which is a sugar having the composition of a hexatomic alcohol: C 6 H 8 (HO) 6 + 11HI = 60H 2 + 5I 2 + C 6 H 12 . HI; Mannite. Sextene hydriodide. and this hydriodide, heated with potassium hydrate, yields the hydro- carbon : C 6 H, 2 . HI + OKH = KI -f OH 2 + C 6 H, 2 . e. Quartene, or butylene, C 4 H 8 , is obtained by precisely similar reactions from erythrite, which is also a saccharine substance having the composition of a tetratomic alcohol, C 4 H 6 (HC) 4 . Reactions. 1. The olefines are dyad radicals, uniting with 2 atoms of chlorine, bromine, &c., and with one atom of oxygen. 2. The chlorides, bromides, and other haloid compounds of the olefines, treated with an alcoholic solution of potash, give up one atom of hydrogen and one atom of the haloid element, yielding an olefine in which one atom of hydrogen is replaced by chlorine, bromine, &c., together with water and a haloid salt of potassium ; thus : C 2 H 4 Br 2 -j- OKH = KBr -f OH 2 -f C 2 H 3 Br. Ethene bromide. Bromethene. The resulting chlorinated, brominated, or iodated compound can, in its turn, take up 2 atoms of chlorine, bromine, or iodine, forming a body which can likewise give up hydrochloric, hydrobromic, or hydriodic acid, under the influence of alcoholic potash ; the body thus formed can again take up 2 atoms of chlorine, bromine, or iodine ; then give up HC1, HBr, or HI ; and thus, by a series of perfectly similar reactions, we at length arrive at bodies consisting of the primitive olefine with all its hydrogen replaced by chlorine, bromine, or iodine, and the dichlorides, dibromides, and di-iodides of these last-mentioned bodies : thus, from ethene may be derived the two following series of brominated compounds : Ethene .... C 2 H 4 Bromethene . . C 2 H 3 1 Dibromethene . C H Br, Ethene bromide .... C 2 H 4 Br 2 Bromethene bromide Dibromethene bromide . . C 2 H 2 Br 2 . Br 2 Tribromethene . C 2 HBr 3 I Tribromethene bromide . C 2 HBr 3 . Br 2 Tetrabromethene C 2 Br 4 | Tetrabromethene bromide . C 2 Br 4 . Br 2 These compounds will be more particularly described in connection with the corresponding alcohols. 3. A monochlorinated or monobrominated olefine may give up the atom of chlorine or bromine which it contains, in the form of hydrochloric or hydrobromic acid, whereby it is reduced to a hydrocarbon of the following series, C n H 2n _ 2 . This reaction may take place at 130 150 C. (266 302 F.), under the influence of alcoholic potash, or, better, of sodium ethyl- ate (obtained by dissolving sodium in anhydrous alcohol); thus: C 2 H 3 Br -f C 2 H 5 NaO =r NaBr + C 2 H 5 (HO) -f C 2 H 2 . Bromethene. Sodium Sodium Ethyl Ethine. thylate. bromide, alcohol. OLEFINES. 483 4. Ethene bromide and its homologues, treated with silver acetate or potassium acetate, exchange their bromine for an equivalent quantity of the halogenic residue of the acetate, C 2 H 3 2 (p. 472), giving rise to di- atomic acetic ethers; thus: (C,H 4 )"Br s + 2C 2 H 3 2 K == 2KBr + (C 2 H 4 )"(C 2 H 3 2 ) 2 ; Ethene Potassium Potassium Ethene bromide.' acetate. bromide. diacetate. and these ethers, distilled with a caustic alkali, yield diatomic alcohols or glycols; for example: (C 2 H 4 )")C 2 H 3 2 ) 2 + 20HK = 2C 2 H 3 2 K + (C 2 H 4 )^(OH) 2 . Ethene Potassium Ethene diacetate. acetate. alcohol. 5. The bromides, C n H 2n Br 2 , heated to 275 C. (527 F.) with a mixture of potassium iodide, copper, and water, give up their bromine and reproduce the original olefine, together with other hydrocarbons (p. 476). 6. Some olefines, when briskly shaken up with strong snlphuric acid, unite with it, forming acid ethers of sulphuric acid, which contain the monatomic alcoholic radicals corresponding to the olefines; thus: C 2 H 4 -f S0 4 H 2 = S0 4 .C 2 H 5 .H; Ethene. Sulphuric acid. Ethyl-sulphuric acid. and these acid ethers distilled with water reproduce sulphuric acid, and the monatomic alcohol corresponding to the olefine : S0 4 .C 2 H5H -f H(OH) = S0 4 H 2 + C 2 H 5 (OH). Ethyl-sulphuric acid. Water. Ethyl alcohol. With fuming sulphuric acid (which contains sulphuric oxide in solution) the olefines yield sulpho-acids which are isomeric with the preceding, but are not decomposed by water, with formation of an alcohol. 7. Olefines unite with hydrochloric, hydrobromic, and hydriodic acids; and the resulting compounds treated with silver oxide in presence of water, give rise to two different reactions which go on simultaneously, one part of the compound exchanging its halogen element for hydroxyl, and thereby producing an alcohol, while another portion gives up hydrochloric, hy- drobromic, or hydriodic acid, reproducing the original olefine: 2(C 6 H 12 .HI) + OAg 2 -f OH 2 = 2AgI + 2C 6 H I4 Hexylene Hexyl hydriodide. alcohol. 2(C 6 H 6 .HI) -f OAg 2 = 2AgI + OH,, + 2C 6 H 6 . Hexyleue hydriodide. Hexylene. The greater number of the olefines are not of sufficient importance to require special description in this work. Ethene has been already de- scribed (p. 170). Quintene, or amylene, and a few others will be noticed in connection with the corresponding alcohols. Isomerism in the Olefine series. From theoretical considerations, it might be expected that each member of the olefine series would exist in two isomeric modifications, the one being a dyad radical, and the other a satu- rated hydrocarbon; the compound C 2 H 4 , for example, might exhibit the two modifications represented below: CH 2 CH 2 CH 2 CH 2 Dyadic. Saturated. 484 HYDROCARBONS. But the dyadic members of the series are the only ones actually known. These, however, exhibit in some of their compounds a different kind of isomerism, which does not affect their equivalent value. a. The dichlorides of the defines are isomeric with the monochlorinated chlorides of the monad alcohol radicals, CnH-ja+j; for example: CH 2 CH f CH 3 I is isomeric with J | CH 2 C1 J ( CHC1 2 Ethene Monochlorinated dichloride. ethyl chloride. Both these compounds 2 when treated with alcoholic potash, yield the same product, namely, vinyl chloride, C 2 H 3 C1 ; but they differ in boiling point, the first boiling at 85 C. (185 F.), the second at 64 C. (147 F.) /?. The oxides of the olefines are isomeric with the corresponding alde- hydes, and with the alcohols of the series CnH^n^OH CH, CH S OH, ^ CH 2 COH CHOH Ethene oxide. Acetic aldehyde. Vinyl alcohol. The dyad radical, called ethidene, or ethylidene, which may be supposed to exist in aldehyde and in monochlorinated ethyl chloride, has not been iso- lated : it probably differs from ethene in the manner shown by the follow- ing formulae : CH 2 CH 2 CH Ethene. Ethidene. Similar instances of isomerism are observed in the compounds of tho other members of the olefine series. THIRD SERIES, C a U 2a _ y Of these hydrocarbons five only have as yet been prepared, viz. : Ethine or Acetylene, C 2 H 2 Propine " Allylene, C 3 H 4 Quartine " Crotonylene, C 4 H 6 Quintine " Valerylene, C 5 H 8 Sextine " Diallyl, C 6 H, . The only general method of preparing these bodies consists in heating _ie monobrominated derivatives of the ethylate to 130-150 C. (266-302 F.): CnH^Br -f C 2 H 5 NaO = NaBr -f C 2 H 5 (HO) + C^H^. Sodium Ethyl alcohol, ethylate. Ethine and propine, which are gaseous at ordinary temperatures, are sepa- rated from the alcohol vapor with which they are mixed, by passing the gas into an ammoniacal solution of cuprous chloride, whereby an explosive compound is precipitated, containing copper, carbon, hydrogen, and ETHINE, OR ACETYLENE. 485 oxygen ; and this precipitate, treated with hydrochloric acid, yields the hydrocarbon in the pure state. The other hydrocarbons of the series, which are liquid, do not form any precipitate with ammoniacal cuprous chloride; but they may be separated from excess of alcohol by addition of water, and further purified by dis- tillation. The hydrocarbons of this series should exhibit three isomeric modifica- tions : saturated, dyadic, and tetradic, according to the manner in which the carbon atoms are united; thus, for the compound C 2 H 2 : C H C H C H C_H C H C H Saturated. Dyadic. Tetradic. The actually known compounds are, however, all tetradic, being capable of uniting with four atoms of chlorine, bromine, and other monad elements, though they can also form half-saturated compounds containing only 2 atoms of a monad element. When agitated with hydrobromic or hydriodic acid, they take up one or two molecules of these acids. The dihydrobromides and dihydriodides thus produced have the same composition as the dibrominated derivatives of the olefine series; thus: C n Ha,., . 2HBr = C n H^Br^ The two classes of bodies are, however, isomeric, not identical. Ethine, or Acetylene, C 2 H 2 . This hydrocarbon is one of the constituents of coal gas. It is produced: 1. By synthesis from its elements. When an electric arc from a powerful voltaic battery passes between carbon poles in an atmosphere of hydrogen, the carbon and hydrogen unite in the pro- portion to form ethine. 2. By the action of heat upon ethene, or the vapor of alcohol, ether, or wood-spirit, or by passing induction-sparks through marsh-gas. 3. By passing the vapor of chloroform over ignited copper: 2CHC1 3 -f Cu 6 = 3Cu 2 Cl 2 -f C 2 H 2 . 4. By the incomplete combustion of bodies containing carbon and hy- drogen : for example : 4CH 4 -f 6 = 60H 2 -f 2C 2 H 2 Methane. Ethine. 2C 2 H 4 -f 0, = 20 H 2 -1- 2C 2 H 2 Ethene. Ethine. 5. By passing a mixture of marsh-gas and carbon monoxide through a red-hot tube: CH 4 + CO = OH 2 + C 2 H 2 . 6. By the action of alcohol potash on monobromethene : C 2 H 3 Br -f OHK = KBr -f OH 2 -f C 2 H 2 . The crude ethine obtained by either of these processes is purified in the manner above mentioned. Ethine is a colorless gas of specific gravity 0-92, having a peculiar and un- pleasant odor, moderately soluble in water, not condensed by cold or pres- sure. It burns with a very bright and smoky flame, one volume of the gas 41* 486 HYDROCARBONS. consuming 2 volumes of oxygen and producing 2 volumes of carbon dioxide. When mixed with chlorine, it detonates almost instantly, even in diffused daylight, with separation of carbon. Ethine passed into an ammoniacal solution of cuprous chloride forms a red precipitate consisting of cuproso-vinyl oxide, C 4 Cu x 4 H 2 0, or (C 2 Cu / 2 H) 2 0, that is to say, vinyl-oxide (C 2 H 3 ) 2 0, having four of its hydrogen-atoms re- placed by four atoms of apparently univalent copper.* The constitution of this compound may be understood from the following formulae : H H H H H H c=c o c=c | U ^>c=c o c=c ) H ( OH ( OH Each of these fulfils the essential condition of a primary alcohol ; but the first contains normal propyl, CH 2 (C 2 H 5 ), whereas the second contains isopropyl, CII(Cir 3 ). 2 ; and in the higher alcohols it is easy to see that a still larger number of modifications may exist ; but only a very few of them have hitherto" been actually obtained. The methods of producing secondary and tertiary alcohols, and the differences of character exhibited by the several modifications, will be explained further on. 512 ALCOHOLS AND ETHERS. A very convenient nomenclature for these isomeric alcohols has been proposed by Kolbe. Methyl alcohol, CH 3 (OH), is called carbinol ; and the primary alcohols formed from it by successive substitution of methyl, ethyl, &c., for an atom of hydrogen, are named according to the radicals which they contain ; thus, Carbinol, or Methyl alcohol .... C(OH)H 3 Methyl carbinol, or Ethyl alcohol . . C(OH)H 2 CH 3 Ethyl carbinol, or Propyl alcohol . . C(OH)H 2 C 2 H 5 Dimethyl carbinol, or Isopropyl alcohol . C(OH)H(CH 3 ) 2 Propyl carbinol, or Quartyl alcohol . . C(OH)H 2 (C 3 H 7 ) Isopropyl carbinol, or Isoquartyl alcohol . C(OH)H 2 CH(CH 3 ) 2 Methyl-ethyl carbinol, or Secondary Quartyl alcohol C(OH)HCH 3 C 2 H 6 Trimethyl carbinol, or Tertiary Quartyl al- cohol C(OH)(CH 3 ) 3 . METHYL ALCOHOL AND ETHERS. Methyl Alcohol, Hydroxymethane, or Carbinol, CH 4 or CH 3 (OH). Thia is the simplest member of the series. It is produced: 1. From marsh-gas, by subjecting that compound to the action of chlorine in sunshine, whereby chloromethane, or methyl chloride, CH 3 C1, is produced, and distilling this chloride with potash. 2. From wintergreen oil, which consists chiefly of acid methyl salicy- late, C 7 H 4 . H . CH 3 , by distillation with potash, whereby potassium salicy- late is formed, and methyl alcohol distils over : C 7 H 4 3 . H . CH 3 -f KOH == C 7 H 4 3 . H . K + CH 8 (OH) Acid methyl Potassium Acid potassium salicylate. hydrate. salicylate. This reaction, which consists in the interchange of methyl and potassium, yields very pure methyl alcohol. 3. From crude wood-vinegar, the watery liquid obtained by the destruc- tive distillation of wood : it was in this liquid that methyl alcohol was first discovered by P.Taylor, in 1812: hence it is often called wood-spirit. Crude wood-vinegar probably contains about T i^ part of methyl alcohol, which is separated from the great bulk of the liquid by subjecting the whole to distillation, and collecting apart the first portions which pass over. The acid solution thus obtained is neutralized with slaked lime, and the clear liquid, separated from the oil which floats on the surface, and from the sediment at the bottom of the vessel, is again distilled. A vola- tile liquid is thus obtained, which burns like weak spirit ; this may be strengthened by rectification, and ultimately rendered pure and anhydrous by careful distillation from quicklime at the heat of a water-bath. Pure methyl alcohol is a colorless, thin liquid, very similar in smell and taste to ethyl alcohol; crude wood-spirit, on the other hand, which contains many impurities, has an offensive odor and a nauseous, burning taste. Methyl alcohol boils at 66-6 C. (152 F.), and has a density of 0-798 at 20 C. (68 F.). Vapor-density (referred to hydrogen) = 16. Methyl alcohol when pure mixes in all proportions with water : it dissolves resins and volatile oils as freely as ethyl alcohol, and is often substituted for ethyl alcohol in various proce'sses in the arts, for which purpose it is prepared on a large scale. It may be burnt instead of ordinary spirit in lamps : the flame is pale-colored, like that of ethyl alcohol, and deposits no soot. METHYL ALCOHOL AND ETHERS. 513 Methyl alcohol dissolves caustic baryta: the solution deposits, by evapora- tion in a vacuum, acicular crystals, containing Ba0.2CH 4 0. It dissolves calcium chloride in large quantity, and gives rise to a crystalline compound containing, according to Kane, CaCl 2 .2CH 4 0. Potassium and sodium dissolve in it, with evolution of hydrogen yielding potassium and sodium methylates or methyl ethers, CH 3 OK, and CH 3 ONa. By oxidation, as by exposure to the air in contact with platinum black, it is converted into formic acid, CH 2 2 , or CHO . OH, which is derived from it by substitution of 1 atom of oxygen for 2 atoms of hydrogen : CH 4 -f 2 = OH 2 + CH 2 2 . Methyl Chloride, or Chloromethane, CH 3 C1, is formed, according to Ber- thelot, when a mixture of equal volumes of methane (marsh-gas) and chlorine is exposed to reflected sunlight. It is more easily prepared, how- ever, by heating a mixture of 2 parts of common salt, 1 part of wood- spirit, and 3 parts of concentrated sulphuric acid. It is a gaseous body, which may be conveniently collected over water, as it is but slightly soluble in that liquid. It is colorless ; has a peculiar odor and sweetish taste, and burns, when kindled, with a pale flame, greenish towards the edges, like most combustible chlorine-compounds. Its density, referred to hydrogen as unity, is 25-25; it is not liquefied at 18 C. (0 F.). The gas is decom- posed by transmission through a red-hot tube, with slight deposition of cai-bon, into hydrochloric acid gas and a hydrocarbon which has been but little examined. By the action of chlorine in sunshine it is successively converted into methene chloride, or dichloromethane, CH 2 C1 2 , a liquid boiling at 30-5 C. (87 F.) ; methenyl chloride, trichloromethane, or chloroform, CHC1 3 ; and carbon tetrachloride, CC1 4 . Methyl Iodide, or lodome thane, CH 3 I, is a colorless and feebly combustible liquid, obtained by distilling together 1 part of phosphorus, 8 of iodine, and 12 or 15 of wood-spirit. It is insoluble in water, has a density of 2-237, and boils at 40 C. (111 F.). The density of its vapor, referred to hydrogen as unity, is 71. When digested in sealed tubes with zinc, it yields a colorless gaseous mixture containing ethane, or dimethyl, C 2 H 6 , and the residue contains zinc iodide, together with zinc methide, Zn(CH 3 ) 2 , a very volatile liquid, which takes fire spontaneously in contact with the air: 2CH 3 I -f Zn = ZnI 2 -f C 2 H 6 2CH 3 l Zn 2 = ZnI 2 -f Zn(CH 3 ) 2 . Methyl Ether, Methyl Oxide, or Methoxyl-methane, C 2 H 6 = (CH 3 ) 2 TT = C -I TT- This compound, which bears the same relation to methyl alco- [OCH 3 hoi that anhydrous potassium oxide bears to potassium hydrate, is produced by abstraction of the elements of water from methyl alcohol: 2CH 4 OH 2 =C 2 H 6 0. To prepare it, 1 part of wood-spirit and 4 parts of concentrated sul- phuric acid are mixed and exposed to heat in a flask fitted with a perfo- rated cork and bent tube : the liquid slowly blackens, and emits large quan- tities of gas, which may be passed through a little strong solution of caustic potash, and collected over mercury. This is methyl ether, a permanently gaseous substance, which does not liquefy at 16 C. (3 F.). It is color- less, has an ethereal odor, and burns with a pale and feebly luminous flame. Its specific gravity is 1-617 referred to air, or 23 referred to hydrogen as unity. Cold water dissolves about 33 times its volume of this gas, acquiring thereby its characteristic taste and odor : on boiling the solution, the gas 514 ALCOHOLS AND ETHERS. is again liberated. Alcohol, wood-spirit, and concentrated sulphuric acid dissolve it in still larger quantity. Methyl Nitrate, CH 3 .N0 3 , or CH 3 .ON0 2 , or H 3 C N. This ether is obtained by distilling 50 grams of pounded nitre with 50 grams of wood- spirit and ] 00 grams of sulphuric acid, in a retort without external heat- ing. It is a colorless liquid of sp. gr. 1-182 at 20 C. (68 F.) ; boils at 66 C. (151 F.) : has a faint, ethereal odor. Its vapor detonates violently when heated to 150 C. (302 F.). Heated with alcoholic ammonia, it yields me- thylamine nitrate, CH 5 N.N0 3 H. Distilled with aqueous potash, it yields methyl ether. Methyl Sulphates, Sulphuric acid being a bibasic acid, yields two methyl ethers one acid, the other neutral. Acid methylsulphate, Methyl and Hydrogen sulphate, Methylsulphuric acid, or Sulphomethylic acid, CH 3 .H.S0 4 , or CH 3 . OSO a H=H 3 C S OH. To ft prepare this acid ether, 1 part of wood-spirit is slowly mixed with 2 parts of concentrated sulphuric acid, and the whole is heated to ebullition, and left to cool, after which it is diluted with water, and neutralized with barium carbonate. The solution is filtered from the insoluble sulphate, and evaporated, first in a water-bath, and afterwards in a vacuum to the proper degree of concentration. The salt crystallizes in beautiful, square, colorless tables, containing (CH 3 ) 2 Ba // S0 4 . 20H 2 , which effloresce in dry air, and are very soluble in water. By exactly precipitating the base from this substance with dilute sulphuric acid, and leaving the filtered liquid to evaporate in the air, methylsulphuric acid may be procured in the form of a sour, syrupy liquid, or in minute acicular crystals, very soluble in water and alcohol. It is very instable, being easily decomposed by heat. Potas- sium methylsulphate, CH 3 KS0 4 , crystallizes in small, nacreous, deliquescent rhombic tables. The lead-salt is also very soluble. " Neutral Methyl sulphate, or Dimethylic sulphate, (CH 3 ) 3 S0 4 , or CH 3 . OS0 3 CH 3 , or H 3 C S CH 3 . This ether is prepared by distilling 1 part of wood-spirit with 8 or 10 parts of strong oil of vitriol; the dis- tillation may be carried nearly to dryness. The oleaginous liquid found in the receiver is agitated with water, and purified by rectification from powdered caustic baryta. The product is a colorless, oily liquid, of alli- aceous odor, having a density of 1-324, and boiling at 188 C. (370 F.). It is neutral to test paper, and insoluble in water, but decomposed by that liquid, slowly in the cold, rapidly and with violence at a boiling tempera- ture, into methylsulphuric acid and wood-spirit. Anhydrous lime and baryta have no action on this ether : their hydrates, however, and those of potassium and sodium, decompose it instantly, with production of a methylsulphate of the base, and methyl alcohol. When neutral methyl- sulphate is heated with common salt, it yields sodium sulphate and methyl chloride ; with mercuric cyanide, or potassium cyanide, it gives a sulphate ETHYL ALCOHOL. 515 of the base, and methyl cyanide ; with dry sodium formate, it yields sodium sulphate and methyl formate Methyl Borate, (CH 3 ) 3 B0 3 = B /// (OCH 3 ) 3 , is formed by the action of gaseous boron chloride on anhydrous methyl alcohol. It is a limpid liquid, of specific gravity 0-9551 at 0, boiling at 72 C. (162 F.). Water decom- poses it into boric acid and methyl alcohol. Methyl Phosphates. Two methyl phosphates have been obtained, viz., methylphosphoric acid, (PO) /// (OH).,(OCH 3 ), and dimethylphosphoric acid, (PO) /// (OH)(OCH 3 ) 2 . They are formed by the action of phosphorus oxy- chloride on methyl alcohol under different circumstances. Methyl Silicate, Si iT (OCH 3 ) 4 , is obtained by acting upon perfectly pure and dry methyl alcohol with silicium tetrachloride, and distilling the pro- duct. It is a colorless liquid, of pleasant, ethereal odor, specific gravity 1-0539 at 0, distilling between 121 and 126 C. (250-258 F.). It dis- solves with moderate facility in water, and the solution does not become turbid from separation of silica for some weeks. Its observed vapor-den- sity is 5 38 referred to air, or 312 referred to hydrogen, the calculated number being 304. Hexmethijl-disilidc ether, (CH 3 ) 6 Si 2 T , or Si iT 2 0(OCH 3 ) 6 , is produced, to- gether with the compound last described, when the methyl alcohol used is not quite dry. It boils at 201 to 202-5 C. (294-295 F.), and has a density of 1-1441 at 0. In other respects it resembles the preceding. Methyl Sulph-hydrate, CH 3 SH, also called Methyl Mercaptan. This com- pound, which has the composition of methyl alcohol with the oxygen re- placed by sulphur, is formed by distilling in a water-bath, with efficient condensation, a mixture of calcium methylsulphate and potassium sulph- hydrate: (S0 4 ) 2 (CH 3 ) 2 Ca // -f 2KSH = S0 4 K 2 + S0 4 Ca + 2CH 3 SH. It is a liquid lighter than water, and having an extremely offensive odor. It forms wic.h lead-acetate a yellow precipitate, and with mercuric oxide a white compound, (CH 3 ) 2 S 2 Hg // , which crystallizes from alcohol in shining laminae. Methyl Sulphide, S(CH 3 ) 2 , or H 3 CSCH 3 , is obtained by passing gaseous methyl chloride into a solution of potassium monosulphide in wood-spirit. It is a colorless, mobile, fetid liquid, of specific gravity 0-845 at 21 C. (7(5 F.), boiling at 41 C. (106 F.). It forms several substitution-pro- ducts with chlorine. Methyl Bisulphide, (CH 3 ) 2 S 2 , is prepared by passing gaseous methyl chlor- ide through an alcoholic solution of potassium bisulphide. It is a limpid, strongly refracting liquid, having a specific gravity of 1-046 at 18, and an intolerable odor of onions; boils between 116 and 118. It forms substi- tution-products with bromine and chlorine. By substituting pentasulphide for bisulphide of potassium in the preced- ing preparation, a trisulphide of methyl, (CH 3 ) 2 S 3 , is obtained, boiling at about 200, ETHYL ALCOHOL AND ETHERS. Ethyl Alcohol, Hydroxyl-ethane, or Methyl Carbinol, CH 3 C 2 TT 6 = C 2 H 5 (OH) = | CH 2 (OH) 516 ALCOHOLS AND ETHERS. This important compound, the oldest and best known of the whole group of alcohols, and generally designated by the simple name "alcohol," is produced : 1. From ethene, C 2 H 4 , by addition of the elements of water. When ethene gas and strong sulphuric acid are violently agitated together for a long time, the gas is absorbed, and ethylsulphuric acid, C 2 H 6 S0 4 , is pro- duced ; and this compound, distilled with water, yields sulphuric acid and ethyl alcohol: C 2 H 6 S0 4 + OH 2 = S0 4 H 2 + C 2 H 6 0. Now we have seen that ethene can be formed by addition of hydrogen to ethine, C 2 H 2 , which is itself formed by direct combination of carbon and hydrogen. It follows, therefore, that alcohol can be produced syntheti- cally from its elements. 2. By the fermentation of certain kinds of sugar. When a moderately warm solution of cane-sugar or grape-sugar (glucose) is mixed with cer- tain albuminous matters, as blood, white of egg, flour-paste, and especially beer-yeast, in a state of decomposition, a peculiar process, called fermenta- tion, is set up, by which the sugar is resolved into ethyl alcohol and carbon dioxide. In the case of glucose, these products result from a simple split- ting up of the molecule : C 6 H W 0, = 2C0 2 + 2C 2 H 6 0. Glucose. Carbon Alcohol dioxide. Cane sugar, C, 2 H 12 Oj,, is first converted into glucose by assumption of water (Ci 2 H 22 O u -j- OH 2 = 2C 6 H 12 6 ), and the latter is then decomposed as above.* If ordinary cane-sugar be dissolved in a large quantity of water, a due proportion of active yeast added, and the whole maintained at a tempera- ture of 21-26 C. (70-80 F.), the change will go on with great rapidity. The gas disengaged is nearly pure carbon dioxide : it is easily collected and Examined, as the fermentation, once commenced, proceeds perfectly well in a close vessel, such as a large bottle or flask fitted with a cork and a conducting-tube. When the effervescence is at an end, and the liquid has become clear, it will yield alcohol by distillation. The spirit first obtained by distilling a fermented saccharine liquid is very weak, being diluted with a large quantity of water. By a second dis- tillation, in which the first portions of the distilled liquid are collected apart, it may be greatly strengthened : the whole of the water cannot, however, be thus removed. The strongest rectified spirit of wine of com- merce has a density of about 0-835, and yet contains 13 or 14 per cent, of water. Pure or absolute alcohol may be obtained from it by redistilling it with half its weight of fresh quicklime. The lime is reduced to coarse powder, and put into a retort ; the alcohol is added, and the whole mixed by agitation. The neck of the retort is securely stopped with a cork and the mixture left for several days. The alcohol is distilled off by the heat of a water-bath. Pure alcohol is a colorless, limpid liquid, of pungent and agreeable taste and odor; its specific gravity, at 15-5 C. (60 F.), is 0-7938, and that of its vapor referred to air, 1-613. It is very inflammable, burning with a pale- bluish flame, free from smoke ; it has never been frozen. Alcohol boils at 78-4 C. (173 F.) when in the anhydrous state ; in a diluted state the boil- * Side by side with this principal decomposition, a variety of other changes are simultane- ously accomplished. According to Pasteur, glycerine, succinic acid, cellulose, fats, and occa- sionally lactic acid, are observed among the products of alcoholic fermentation. Some of the homologues of ethyl alcohol are also found amoqg the products. ETHYL ALCOHOL. 517 ing point is higher, being progressively raised by each addition of water. In the act of dilution a contraction of volume occurs, and the temperature of the mixture rises many degrees : this takes place not only with pure alcohol, but also with rectified spirit. Alcohol is iniscible with water in all proportions, and, indeed, has a great attraction for the latter, absorb- ing its vapor from the air, and abstracting the moisture from membranes and other similar substances immersed in it. The solvent powers of alco- hol are very extensive : it dissolves a great number of saline compounds, and likewise a considerable proportion of potash. With some salts it forms definite crystalline compounds, called alcoholates : with zinc chloride, ZnCl 2 . 2C 2 H 6 ; with calcium chloride, CaCl 2 . 4C 2 II 6 O ; with magnesium ni- trate, (N0 8 ) 3 Mg . 6C 2 H 6 0. Alcohol dissolves, moreover, many organic sub- stances, as the vegeto-alkalies, resins, essential oils, and various other bodies : hence its great use in chemical investigations and in several of the arts. Potassium and sodium dissolve in ethyl alcohol in the same manner as in methyl alcohol, forming the compounds C 2 H 5 KO and C 2 H 5 NaO. Alcohol, passed through a red-hot tube, is resolved into marsh-gas, hy- drogen, and carbon monoxide : C 2 H 6 = H CO. Small quantities of ethene, benzene, and naphthalene are, however, formed at the same time by the mutual action of these primary products, and car- bon is deposited. By oxidation, alcohol is converted, first, into aldehyde, then into acetic acid: H 6 johol Alcohol. + OH, C 2 H 4 0, Aldehyde. C 2 H 4 -f == C 2 H 4 2 Aldehyde. Acetic acid. Chlorine gas is rapidly absorbed by anhydrous alcohol, imparting to it a yellow color, and causing considerable rise of temperature. At the' same time it rapidly abstracts hydrogen, which is partly replaced by the chlo- rine, producing hydrochloric acid, aldehyde, acetic acid, ethyl acetate, ethyl chloride, and finally chloral. The mixture of these substances, freed by water from the soluble constituents, was formerly called heavy muriatic 'ether. The formation of the several products is represented by the follow- ing equations : C 2 H 6 Alcohol. Alcohol. C 2 H 6 Alcohol. C 2 H 6 Alcohol. Alcohol. -f- C1 2 = 2HC1 -f 4C1 2 = 5HC1 C 2 H 4 0, Aldehyde. C 2 HC1 3 0, Chloral. HC1 = OH 2 -f C 2 H 5 C1, Ethyl chloride. Acetic acid. = 4IIC1 = OH, Acetic acid. C 2 H 3 2 .C 2 H 6 . Ethyl acetate. When the action of the chlorine is continued for a long time, chloral is always the principal product. This compound is a heavy oily liquid, having the composition of aldehyde with 3 atoms of hydrogen replaced by chlorine ; 44 518 ALCOHOLS AND ETHERS. but it cannot be formed by the direct action of chlorine upon aldehyde. When alcohol containing water is used, scarcely any chloral is obtained, the chief product being aldehyde. Chlorine, in presence of alkalies, converts alcohol into chloroform and carbon dioxide: C 2 H 6 -f 4C1 2 + OH 2 = C0 2 + 5HC1 -f- CHC1 3 . Alcohol. Chloro- form. The same products are formed by distilling dilute alcohol with bleaching powder. Aqueous alcohol heated with strong sulphuric acid is converted into ethyl- sulphuric acid, C 2 H 6 SO.,, or C 2 H 5 (OS0 3 H), (p. 526) ; but when anhydrous alcohol is exposed to the vapor of sulphuric oxide, S0 3 , a white crystalline substance is formed, called ethionic oxide, formerly sulphate of carbyl, C 2 H 4 S 2 6 . This, when dissolved in water or in aqueous alcohol, is converted into ethionic acid, C 2 H 6 S 2 7 , a bibasic acid, which forms a soluble barium salt. Lastly, a solution *of ethionic acid, when boiled, is resolved into sul- phuric acid and isethionic acid, an acid isomeric with ethylsulphuric acid (p. 527). Commercial Spirit, Wine, Beer, $c. Vinous Fermentation. The strength of commercial spirit, when free from sugar and other substances added sub- sequent to distillation, is inferred from its density: a table exhibiting the proportions of real alcohol and water in spirits of different densities will be found at the end of the volume. The excise proof spirit has a sp. gr. of 0-9198 at 60 F., and contains 49J per cent, by weight of real alcohol. The high duty on spirits of wine in this country has hitherto interfered with the development of many branches of industry, which are dependent on the free use of this important liquid. The labors of the scientific chemist have been likewise often checked by this inconvenience. A remedy for the evil has been supplied in Great Britain by a very important measure, proposed and carried out by the late Mr. John Wood, Chairman of the Board of Inland Revenue. This measure consists in issuing for manufacturing and scientific purposes, duty free, a mixture of 90 per cent, of spirits of wine of not less strength than corresponds to a density of 0-830, with 10 per cent, of partially purified wood-spirit, which is now sold by licensed dealers under the name of Methylated Spirit. It appears that a mixture of this kind is rendered per- manently unfit for human consumption, the separation of the two substances, in consequence of their close analogy, being not only difficult, but to all appearance impossible: at the same time, and for the same reasons, this mixture is not materially impaired for the greater number of the more valuable purposes in the arts to which spirits are usually employed. Methyl- ated spirit may be used, instead of pure spirit, as a solvent of resinous substances, and of many chemical preparations, especially of the alkaloids and other organic products. It may be used for the production of fulmi- nating mercury, ether, chloroform, iodoform, olefiant gas, and all its de- rivatives in fact, for an endless number of laboratory purposes. Mythyl- ated spirit may also be substituted for pure spirit of wine in the preser- vation of anatomical preparations. The introduction of this spirit has already exerted a very beneficial effect upon the development of organic chemistry in that country.* * See Report on the Supply of Spirits of Wine, free from duty, for use in the Arts and Manu- factures, addressed to the Chairman of Inland Revenue, by Professors Graham, Hofinann, and Kedwood. (Quarterly Journal of Chemical Society, vol. via", p. 120. WINE BEER. 519 Wine, beer, &c., owe their intoxicating properties to the alcohol they con- tain, the quantity of which varies very much. Port and sherry, and some other strong wines, contain, according to Mr. Brande, from 19 to 25 per cent, of alcohol, while in the lighter Avines of France and Germany it some- times falls as low as 12 per cent. Strong ale contains about 10 per cent. ; ordinary spirits, as brandy, gin, whiskey, 40 to 50 per cent., or occasionally more. These latter owe their characteristic flavors to certain essential oils, present in very small quantity, either generated in the act of fermentation or purposely added. In making wine, the expressed juice of the grape is simply set aside in large vats, where it undergoes spontaneously the necessary change. The vegetable albumin of the juice absorbs oxygen from the air, runs into de- composition, and in that state becomes a ferment to the sugar, which is gradually converted into alcohol. If the sugar be in excess, and the azotized matter deficient, the resulting wine remains sweet; but if, on the other hand, the proportion of sugar be small and that of albumen large, a dry wine is produced. When the fermentation stops, and the liquor becomes clear, it is drawn off from the lees, and transferred to casks, to ripen and improve. The color of red wine is derived from the skins of the grapes, which in such cases are left in the fermenting liquid. Effervescent wines, as cham- pagne, are bottled before the fermentation is complete ; the carbonic acid is disengaged under pressure, and retained in solution in the liquid. A certain quantity of sugar is frequently added. The process requires much delicate management. During the fermentation of the grape-juice, or must, a crystalline, stony matter, called argol, is deposited. This consists chiefly of acid potassium tartrate with a little coloring matter, and is the source of all the tartaric acid met with in commerce. The salt in question exists in the juice in con- siderable quantity ; it is but sparingly soluble in water, but still less so in dilute alcohol : hence, as the fermentation proceeds, and the quantity of spirit increases, it is slowly deposited. The acid of the juice is thus re- moved as the sugar disappears. It is this circumstance which renders grape-juice alone fit for making good wine ; when that of gooseberries or currants is employed as a substitute, the malic and citric acids which these fruits contain cannot be thus withdrawn. There is then no other resource but to add sugar in sufficient quantity to mask and conceal the natural acidity of the liquor. Such wines are necessarily acescent, prone to a second fermentation, and, to many persons, at least, very unwholesome. Beer is a well-known liquor, of great antiquity, prepared from germi- nated grain, generally barley, and is used in countries where the wine does not flourish. The operation of malting is performed by steeping the barley in water until the grains become swollen and soft, then piling it in a heap or couch, to favor the elevation of temperature caused by the absorption of oxygen from the air, and afterwards spreading it upon a floor, and turning it over from time to time to prevent unequal heating. When germination has proceeded far enough, the vitality of the seed is destroyed by kiln- drying. During this process, a peculiar nitrogenous substance called diastase is produced, which acts as a ferment on the starch of the grain, converting a portion of it into sugar and rendering it soluble. In brewing, the crushed malt is infused in water at about 77 C. (170 F.), and the mixture is left to stand during the space of two hours or more. The easily soluble diastase has thus an opportunity of acting upon the un- altered starch of the grain, and changing it into dextrin and sugar. The clear liquor, or wort, strained from the exhausted malt, is next pumped up into a copper boiler, and boiled with the requisite quantity of hops, to com- municate a pleasant bitter flavor, and confer on the beer the property of 520 ALCOHOLS AND ETHERS. keeping without injury. The flowers of the hop contain a bitter, resinous principle, called lupulin, and an essential oil. When the wort has been sufficiently boiled, it is drawn from the copper, and cooled as rapidly as possible, to near the ordinary temperature of the air, in order to avoid an irregular acid fermentation, to which it would otherwise be liable. It is then transferred to the fermenting vessels, which in large breweries are of great capacity, and mixed with a quantity of yeast, the product of a preceding operation, by which the change is speedily induced. This is the most critical part of the whole operation, and one in which the skill and judgment of the brewer are most called into play. The process is in some measure under control by attention to the temperature of the liquid ; and the extent to which the change has been carried is easily known by the diminished density, or attenuation of the wort. The fermenta- tion is never suffered to run its full course, but is always stopped at a par- ticular point, by separating the yeast, and drawing off the beer into casks. A slow and almost insensible fermentation succeeds, which in time renders the beer stronger and less sweet than when new, and charges it with car- bonic acid. Highly colored beer is made by adding to the malt a small quantity of strongly dried or charred malt, the sugar of which has been changed to caramel ; porter and stout are so prepared. The yeast of beer is a very remarkable substance, and has excited much attention. To the naked eye it is a greenish-yellow soft solid, nearly in- soluble in water, and dries up to a pale-brownish mass, which readily putrefies when moistened, and becomes offensive. Under the microscope it exhibits a kind of organized appearance, being made up of little trans- parent globules, which sometimes cohere in clusters or strings, like some of the lowest members of the vegetable kingdom. Whatever may be the real nature of the substance, no doubt can exist that it is formed from the soluble azotized portion of the grain during the fermentative process. No yeast is ever produced in liquids free from azotized matter ; that added for the purpose of exciting fermentation in pure sugar is destroyed, and ren- dered inert thereby. When yeast is deprived, by straining and strong pressure, of as much water as possible, it may be kept in a cool place, with unaltered properties, for a long time ; otherwise it speedily spoils. The distiller, who prepares spirits from grain, makes his wort, or wash, much in the same manner as the brewer ; he uses, however, with the malt a large quantity of raw grain, the starch of which suffers conversion into sugar by the diastase of the malt, which is sufficient for his purpose. He does not boil his infusion with hops, but proceeds at once to the fermentation, which he pushes as far as possible by large and repeated doses of yeast. Alcohol is manufactured in many cases from potatoes. The potatoes are ground to pulp, mixed with hot water and a little malt, to furnish diastase, made to ferment, and then the fluid portion is distilled. The potato-spirit is contaminated by a very offensive volatile oil, again to be mentioned : the crude product from corn contains a substance of a similar kind. The busi- ness of the rectifier consists in removing or modifying these volatile oils, and in replacing them by others of a more agreeable character. In making bread, the vinous fermentation plays an important part : the yeast added to the dough converts the small portion of sugar the meal nat- urally contains into alcohol and carbonic acid. The gas thus disengaged forces the tough and adhesive materials into bubbles, which are still further expanded by the heat of the oven, which at the same time dissipates the alcohol: hence the light and spongy texture of all good bread. The use of leaven is of great antiquity : this is merely dough in a state of incipient putrefaction. When mixed with a large quantity of fresh dough, it excites in the latter the alcoholic fermentation, in the same manner as yeast, but VINOUS FERMENTATION. 521 less perfectly ; it is apt to communicate a disagreeable sour taste and odor. Sometimes carbonate of ammonia is employed to lighten the dough, being completely volatilized by the high temperature of the oven. Bread is now sometimes made by mixing a little hydrochloric acid and sodium carbonate in the dough ; if proper proportions be taken and the whole thoroughly mixed, the operation appears to be very successful. Another mode of bread-making, now practised on a large scale with great success, is that invented by the late Dr. Dauglish, which consists in agitat- ing the dough in a strong vessel with water saturated under pressure with carbonic acid gas. When the dough thus treated is subsequently released from this pressure and exposed to the air, the gas escapes in bubbles, and lightens the mass as effectually as that evolved within its substance by fer- mentation. The bread thus made, called "aerated bread," is of excellent quality, not being subject to the deterioration which so frequently takes place in ordinary bread, when the fermentation is allowed to go too far. Vinous fermentation, that is to say the conversion of sugar into alcohol and carbon dioxide, never takes place except in presence of some nitrogenous body of the albuminoid class in a state of decomposition (p. 463). The manner in which these bodies act in inducing fermentation is very obscure : they neither add anything to the sugar nor take anything from it ; but the motion or disturbance of their particles, while undergoing putrefaction, is supposed to be communicated to the particles of the sugar with which they are in contact, and thus to induce the decomposition above mentioned; hence such bodies are called ferments. There are other modes of fermen- tation, which sugar and substances allied to it are capable of undergoing, and the particular change induced varies with the kind of ferment present: thus vinous fermentation is induced with peculiar facility by yeast; lactous fermentation, or the conversion of sugar into lactic .acid, by putrefying cheese. Another very remarkable circumstance connected with fermenta- tion is that it is always accompanied by the development of certain minute living organisms fungi and infusoria like those already mentioned as existing in yeast. So constantly indeed is this the case, that many chem- ists and physiologists regard these organisms as the exciting cause of fer- mentation and putrefaction ; and this view appears to be corroborated by the fact that each particular kind of fermentation takes place most readily in contact with a certain living organism, or at least with nitrogenous mat- ter containing it; thus beer-yeast contains two species of fungus, called .Torvula cerevisix and Penicillium glaucum, the cells of which are of very dif- ferent sizes, so that they may be separated by filtering an infusion of the yeast, the larger cells of the Torvula remaining on the filter, while those of the Penicillium, which are much smaller, pass through with the liquid. Now, it is found that the residue on the filter brings a solution of sugar into the state of vinous fermentation, whereas the filtered liquid induces lactous fermentation. But whether this effect is due to the fungi them- selves, or to the peculiar state of the albuminous matter in which they oc- cur, is a question not yet decided. The investigation is attended with peculiar difficulties, arising chiefly from the universal diffusion of the germs of these minute organisms, which are present not only in all decaying albu- minous matter, and on the skins of fruits, leaves, and other parts of plants, but are likewise diffused through the air ; so that in experiments made for the purpose of ascertaining whether fermentation can take place without them, it is extremely difficult to insure their complete exclusion from the substances under examination.* See the article " Fermentation," in Watts's Dictionary of Chemistry, vol. ii. p. 6'23. 522 ALCOHOLS AND ETHERS. ET HYLIC ETHERS. fCH 3 Ethyl Chloride, or Chlorethane, C 2 H 5 C1, or C 4 H 2 , often called Hy- (ci drochloric ether. To prepare this compound, rectified spirit of wine is saturated with dry hydrochloric acid gas, and the product distilled with very gentle heat; or a mixture of 3 parts oil of vitriol and 2 parts of alco- hol is poured upon 4 parts of dry common salt in a retort, and heat applied ; in either case the vapor of the hydrochloric ether should be conducted through a little tepid water in a wash-bottle, and then conveyed into a small receiver surrounded by ice and salt. It is purified from adhering water by contact with a few fragments of fused calcium chloride. Hydro- chloric ether is a thin, colorless, and excessively volatile liquid, of a pene- trating, aromatic, and somewhat alliaceous odor. At the freezing point of water, its sp. gr. is 0-921, and it boils at 12-5 C. (55 F.); it is soluble in 10 parts of water, is but incompletely decomposed by solution of silver nitrate when the two are heated together in a sealed tube, but is quickly resolved into potassium chloride and ethyl alcohol by a hot aqueous solu- tion of caustic potash : C 2 H 5 C1 + KOH = KC1 + C 2 H 5 OH. With alcoholic potash, on the other hand, or potassium ethylate, it yields ethyl-oxide, or common ether: C 2 H 5 C1 + C 2 H 5 OK = KC1 + (C 2 H 6 ) 2 0. Heated with soda-lime, it yields ethene or olefiant gas : 2C 2 H 5 C1 + ONa 2 = 2NaCl + OH 2 -f C 2 H 4 . When vapor of ethyl chloride is mixed with chlorine gas in a vessel ex- posed first to diffused daylight, and afterwards to direct sunshine, hydro- chloric acid is formed, and the chlorine displaces one atom of hydrogen in the ethyl chloride, producing monochlorinated ethyl chloride, or dichlor- ethane, C 2 H 4 C1 2 , a colorless, oily liquid, isomeric with ethene chloride or Dutch liquid. By the prolonged action of chlorine in excess, the com- pounds C 2 H ? C1 3 , C 2 H 2 C1 4 , C 2 HC1 5 , and C 2 C1 6 are produced, the last of which is a crystalline body, identical with the carbon trichloride produced by the action of chlorine on Dutch liquid. Ethyl Bromide, or Bromethane, C 2 H 5 Br, also called Hydrobromic ether, is prepared by distilling a mixture of 8 parts bromine, 1 part phosphorus, and 39 parts alcohol. It is a very volatile liquid, heavier than water, hav- ing a penetrating taste, and odor, boiling at 41 C. (106 F.). Ethyl Iodide, or lodethane, C 2 H fi I, also called Hydriodic ether, may be con- veniently prepared with 5 parts of phosphorus, 70 parts of alcohol (of 0-84 sp. gr.) and 100 parts of iodine. The phosphorus is introduced into a tu- bulated retort, covered with part of the alcohol, and heated to fusion. The rest of the alcohol is poured upon the iodine, and the solution thus obtained is allowed to flow gradually through a tap-funnel into the retort. The brown liquid is at once decolorized, and ethyl iodide distils over, which is condensed by a good cooling apparatus. The distillate, consisting of al- cohol and ethyl iodide, is again poured on the residuary iodine, which is thus rapidly dissolved, introduced into the retort, and ultimately entirely converted into ethyl iodide. The latter is washed with water to remove adhering alcohol, separated from this water by a tap-funnel, digested with calcium chloride, and rectified in the water-bath. Ethyl iodide may also be formed by heating in a sealed glass vessel a mixture of hydriodic acid and olefiant gas. Hydriodic ether is a colorless liquid, of penetrating ethe- ETHYLIC ETHERS. 523 real odor, having a density of 1-92, and boiling at 72 C. (162 F.). It be- comes red by exposure to light, from a commencement of decomposition. This substance has become highly important as a source of ethyl, and from its remarkable deportment with ammonia, which will be discussed in the Section on Organic Bases. Ethyl Oxide, or Ethylic ether, C 4 H iq O=C 2 H 6 (OC 2 H 6 )=(C 2 H 6 ) 2 0. This compound, also called common ether, or simply ether, contains the elements of 2 molecules of alcohol minus 1 molecule of water : 2C 2 H 6 OH 2 = C 4 H 10 0; and it is in fact produced by the action of various dehydrating agents, such as zinc chloride, phosphoric oxide, and strong sulphuric acid, upon alcohol. The process does not appear, however, to be one of direct dehy- dration, at least in the case of sulphuric acid ; for when that acid is heated with alcohol to a certain temperature, it does not become weaker by taking water from the alcohol, but ether and water distil over together, and the sulphuric acid remains in its original state, ready to act in the same man- ner on a fresh portion of alcohol. The reaction is in fact one of sub- stitution, the ultimate result being the conversion of alcohol, C 2 H 5 (OH), into ether, C 2 H 5 (OC 2 H 6 ), by the substitution of ethyl for hydrogen. The manner in which this takes place will be better understood when another mode of the formation of ether has been explained. When a solution of sodium ethylate, C 2 H 5 ONa, in anhydrous alcohol, ob- tained by dissolving sodium to saturation in that liquid, is mixed with ethyl iodide, double decomposition takes place, resulting in the formation of so- dium iodide and ethyl oxide : C 2 H 5 ONa -f C 2 H 5 I = Nal -f C 2 H 6 (OC 2 H 5 0). The result would be the same if chloride or bromide of ethyl were substi- tuted for the iodide : moreover, when methyl iodide is added, instead of the ethyl iodide, an oxygen ether is formed containing both ethyl and methyl: C 2 H 6 ONa -f CH 3 I = Nal + C 2 H 6 QCH S . Sodium ethylate. Methyl Methyl-ethyl iodide. ether. In each case the reaction consists in an interchange between the sodium and the alcohol-radical. Now, when alcohol is heated with strong sulphuric acid, the first result is the formation of ethylsulphuric acid, S0 2 (OC 2 H 6 )OH, by substitution of ethyl for hydrogen in the acid : S0 2 (OH)(OH) + C 2 H 5 (OH) = H(OH) -f S0 2 (OC 2 H 6 )(OH); Sulphuric Alcohol. Water. Ethylsulphuric acid. acid. and when the ethylsulphuric acid thus formed is brought in contact, at a certain temperature, with a fresh portion of alcohol, the reverse sub- stitution takes place, resulting in the formation of ethyl oxide and sulphu- ric acid: SO,(OC 2 H 5 )(OH) + C 2 H 6 (OH) = C 2 H 5 (OC 2 H 6 ) + S0 4 (OH) 2 Ethylsulphuric Alcohol. Ether. Sulphuric acid. acid. The sulphuric acid is thus reproduced in its original state, and if the sup- ply of alcohol be kept up, and the temperature maintained within certain limits, the same series of actions is continually repeated, and ether and water distil over together. 524: ALCOHOLS AND ETHERS. The most favorable temperature for etherification is between 127 and 154 C. (200 and 310 F.); below 127 very little ether is produced, and above 154 a different reaction takes place, resulting in the formation of olefiant gas. The maintenance of the temperature within the ether-pro- ducing limits is best effected by boiling the mixture of sulphuric acid and alcohol in a flask into which a further quantity of alcohol is supplied in a continuous and regulated stream. This is called the continuous ether process, A wide-necked flask is fitted with a sound cork, perforated by three apertures, one of which is destined to receive a thermometer with the grad- uation on the stem; a second, a vertical portion of a long, narrow tube, terminating in an orifice of about J^ O f an inch in diameter ; and the third, fig. 191.* a wide bent tube, connected with the condenser, to carry off the volatilized products. A mixture is made of 8 parts by weight of concentrated sul- phuric acid, and 5 parts of rectified spirit of wine, of about 0-834 sp. gr. This is introduced into the flask, and heated by a lamp. The liquid soon boils, and the thermometer very shortly indicates a temperature of 140 C. (284 F.). When this happens, alcohol of the above density is suffered slowly to enter by the narrow tube, which is put into communication with a reservoir of that liquid, consisting of a large bottle perforated by a hole * Fig. 191. Apparatus for the preparation of ether, a. Flask for containing the mixture of oil of vitriol and alcohol, b. Reservoir with stopcock, for supplying a constant stream of alcohol, c. Wide bent tube connected with the condenser for conveying away tho vapors, d. The thermometer for regulating the temperature of the boiling liquid. ETHYLIC ETHERS. 525 near the bottom, and furnished with a small brass stopcock fitted by a cork. The stopcock is secured to the end of the long tube by a caoutchouc connector. As the tube passes nearly to the bottom of the flask, the al- cohol gets thoroughly mixed with the acid liquid, the hydrostatic pressure of the fluid column being sufficient to insure the regulai-ity of the flow ; the quantity is easily adjusted by the aid of the stopcock. For condensation a Liebig's condenser may be used, supplied with ice-water. The arrange- ment is shown in figure 191. The intensity of the heat, atid the supply of alcohol, must be so adjusted that the thermometer may remain at 140 C. (284 F.), or as near that tem- perature as possible, while the contents of the flasMkre maintained in a state of rapid and violent ebullition a point of essential importance. Ether and water distil over together, and collect in the receiver, forming two distinct strata : the mixture slowly blackens, from some slight secondary action of the acid upon the spirit, or upon the impurities in the latter, but retains, after many hours' ebullition, its etherifying powers unimpaired. The acid, however, slowly volatilizes, partly in the state of oil of wine, and the quantity of liquid in the flask is found, after the lapse of a considerable interval, sensibly diminished. The loss of acid constitutes the only limit to the duration of the process, which might otherwise be continued indefinitely. On the large scale, the flask may be replaced by a vessel of lead, the tubes being also of the same metal: the stem of the thermometer may be made to pass air-tight through the cover, and heat may perhaps be advan- tageously applied by high-pressure steam, or hot oil, circulating in a spiral tube of metal immersed in the mixture of acid and spirit. The crude ether is to be separated from the water on which it floats, agitated with a little solution of caustic potash, and re-distilled by the heat of warm water. The aqueous portion, treated with an alkaline solution, and distilled, yields alcohol containing a little ether. Sometimes the spon- taneous separation before mentioned does not occur, from the accidental presence of a larger quantity than usual of undecomposed alcohol; the addition of a little water, however, always suffices to determine it. Pure ethylic ether is a colorless, transparent, fragrant liquid, very thin and mobile. Its sp. gr. at 15-5 is about 0-720 ; it boils at 35-6 C. (96 F.) under the pressure of the atmosphere, and bears without freezing the severest cold. When dropped on the hand it occasions a sharp sensation of cold, from its rapid volatilization. Ether is very combustible, and burns with a white flame, generating water and carbon dioxide. Although the substance itself is one of the lightest of liquids, its vapor is very heavy, having a density of 2-586 (referred to air). Mixed with oxygen gas, and fired by the electric spark, or otherwise, it explodes with the utmost vio- lence. Preserved in an imperfectly stopped vessel, ether absorbs oxygen, and becomes acid from the production of acetic acid: this attraction for oxygen is increased by elevation of temperature. It is decomposed by transmission through a red-hot tube into ethene, methane, aldehyde, and ethine, and two substances yet to be described. Ether is miscible with alcohol in all proportions, but not with water; it dissolves to a small extent in that liquid, 10 parts of water taking up about 1 part of ether. It may be separated from alcohol, provided the quantity of the latter is not excessive, by addition of water, and in this manner samples of commercial ether may be conveniently examined. Ether dis- solves oily and fatty substances generally, and phosphorus to a small extent, also a few saline compounds and some organic principles; but its powers in this respect are much more limited than those of alcohol or water. Anhydrous ether, subjected to the action of chlorine, yields the three sub- stitution-products C 4 H 8 01 2 0, C 4 H 6 C1 4 0, and C 4 C1 10 0, the first two of which are liquids, while the third, produced by the prolonged action of chlorine on ether in sunshine, is a crystalline solid. The second chlorine compound 526 ALCOHOLS AND ETHERS. is converted by hydrogen sulphide into the two crystalline compounds C 4 H 6 C1 2 SO and C 4 H 6 S 2 0. Ethyl-methyl oxide, Ethyl-methyl ether, Ethyl melhylate, or Methyl ethylate, C 3 H 8 = C 2 H 5 OCH 3 , is produced, as already mentioned, by the action of methyl iodide on potassium ethylate, or of ethyl iodide on potassium me- thylate. It is a very inflammable liquid, boiling at 11 C. (52 F.). Ethyl Nitrate, C 2 H 6 N0 3 , or C 2 H 5 ON0 2 . Nitric ether. When nitric acid is heated with alcohol alone, part of the alcohol is oxidized, and the nitric acid is reduced to nitrous acid, which, with the remainder of the alcohol, forms ethyl nitrite, C 2 H-N0 2 , together with other products; but by adding urea to the liquid, whicMfrdecomposes the nitrous acid as fast as it is formed, this action may be prevented, and the alcohol and nitric acid then form ethyl nitrate. The experiment is most safely conducted on a small scale, and the distillation must be stopped when seven-eighths of the whole have passed over; a little water added to the distilled product separates the nitric ether. Nitric ether has a density of 1-112; it is insoluble in water, has an agreeable sweet taste and odor, and is not decomposed by an aqueous solution of caustic potash, although that substance dissolved in alcohol attacks it even in the cold, with production of potassium nitrate. Its vapor is apt to explode when strongly heated. ETHYL NITRITE, C 2 H 5 ONO. Nitrous ether. Pure nitrous ether can only be obtained by the direct action of the acid itself upon alcohol. 1 part of starch and 10 parts of nitric acid are gently heated in a capacious retort or flask, and the vapor of nitric acid thereby evolved is conducted into alcohol mixed with half its weight of water, contained in a two-necked bottle, which is to be plunged into cold water and connected with a good condensing arrangement. All elevation of temperature must be carefully avoided. The product of this operation is a pale-yellow volatile liquid, having an exceedingly agreeable odor of apples: it boils at 16-4 C. (61 F.), and has a density of 0-947. It is decomposed by potash, without darkening, into potassium nitrite and alcohol. Nitrous ether, but contaminated with aldehyde, may be prepared by the following simple method. Into a tall cylindrical bottle or jar are to be in- troduced successively 9 parts of alcohol of sp. gr. 0-830, 4 parts of water, and 8 parts of strong fuming nitric acid; the two latter are added by means of a long funnel with a very narrow orifice, reaching to the bottom of the bottle, so that the contents may form three distinct strata, which slowly mix from the solution of the liquids in each other. The bottle is then loosely stopped, and left two or three days in a cool place, after which it is found to contain two layers of liquid, of which the uppermost is nitrous ether. It is purified by rectification. A somewhat similar product may be obtained by carefully distilling a mixture of 3 parts rectified spirit and 2 of nitric acid of 1-28 sp. gr. : the fire must be withdrawn as soon as the liquid boils. The sweet spirits of nitre of pharmacy, prepared by distilling three pounds of alcohol with four ounces of nitric acid, is a solution of nitrous ether, aldehyde, and perhaps other substances, in spirits of wine. Ethyl Sulphates. There are two of these ethers, corresponding to the methyl sulphates. Acid Ethyl sulphate, Ethylsulphuric acid or Sulphovinic acid, C 2 H 6 S0 4 =: C 2 H 5 OS0 3 H=S0 2 (OC 2 H 5 )(OH)=S0 4 (C 2 H 6 )H, which has the composition of sulphuric acid, S0 4 H 2 , with half the hydrogen replaced by ethyl, is formed by the action of sulphuric acid upon alcohol. To prepare it, strong rectified spirit of wine is mixed with twice its weight of concentrated sul- phuric acid ; the mixture is heated to its boiling point, and then left to cool. When cold, it is diluted with a large quantity of water, and neutralized ETHYLIC ETHERS. 527 with chalk, whereby much calcium sulphate is produced. The mass is placed upon a cloth filter, drained, and pressed; and the clear solution is evaporated to a small bulk by the heat of a water-bath, filtered from a little sulphate, and left to crystallize: the product is calcium ethylsulphate, in beautiful, colorless, transparent crystals, containing (S0 4 ) 2 (C 2 H 5 ) 2 Ca // . 20H 2 . They dissolve in an equal weight of cold water, and effloresce in a dry atmosphere. Barium ethylsulphate, (S0 4 ) 2 (C 2 H 5 )Ba // . 20H 2 , equally soluble, and still more beautiful, may be produced by substituting, in the above process, barium carbonate for chalk : from this substance the acid may be procured by exactly precipitating the base with dilute sulphuric acid, and evaporat- ing the filtered solution in a vacuum at the temperature of the air. It forms a sour, syrupy liquid, in which sulphuric acid cannot be recognized by the ordinary reagents, and is very easily decomposed by heat, and even by long exposure in the vacuum of the air-pump. All the ethylsulphates are soluble ; the solutions are decomposed by ebullition. The lead-salt re- sembles the barium-compound. The potassium salt, S0 4 (C 2 H 6 )K easily made by decomposing calcium ethylsulphate with potassium carbonate is anhydrous, permanent in the air, very soluble, and crystallizes well. Potassium ethylsulphate distilled with concentrated sulphuric acid, gives ether; with dilute sulphuric acid, alcohol; and with strong acetic acid, acetic ether. The ethylsulphates heated with calcium or barium hydrate, yield a sulphate of the base and alcohol. Isethionic acid, C 2 H 6 S0 4 , an acid isomeric with ethylsulphuric acid, is ob- tained, as already observed, by boiling ethionic acid (p. 518) with water; also by the prolonged action of strong sulphuric acid or sulphuric oxide on alcohol or ether, and is found among the residues of the preparation of ether. It is a viscid, strongly acid liquid, which decomposes acetates and common salt, bears without decomposition a heat of 150 C. (302 F.), but blackens at a higher temperature. The metallic isethionates are soluble and crystallizable, and are distin- guished from the ethylsulphates, with which they are isomeric, by their much greater stability, most of them sustaining, without alteration, a tem- perature of 200 C. (392 F.I. Potassium isethionate, C 2 H 5 KS0 4 , distilled with phosphorus pentachlo- ride, yields isethionic chloride, C 2 H 4 S0 2 C1 2 ; and this compound, heated in sealed tubes with ammonia, is converted into taurin, a neutral crystallizable Bubstance likewise obtained from bile: C 2 H 4 S0 2 C! 2 -f NH 3 + OH 2 = 2HC1 -f C 2 H 7 NS0 3 . Isethionic Taurin. chloride. Taurin, treated with nitrous acid, is reconverted into isethionic acid. Neutral Ethyl sulphate, S0 4 (C 2 H 5 ) 2 , or S0 2 (OC 2 H 5 ) 2 , is formed by passing the vapor of sulphuric oxide into perfectly anhydrous ether. A syrupy liquid is produced, which, when shaken with 4 vols. of water and 1 vol. of ether, separates into two layers, the lower containing ethylsulphuric acid and various other compounds, while the upper layer consists of an ethereal solution of neutral ethyl sulphate. At a gentle heat the ether is volatilized, and the ethyl sulphate remains as a colorless liquid. It cannot be distilled without decomposition. Ethyl Sulphites. The acid sulphite, or Ethylsulphurous acid, S0 3 (C 2 H 5 )H, is produced by the action of nitric acid on ethyl sulphhydrate or sulpho- cyanate. When concentrated by evaporation it is a heavy oil of specific gravity 1-30. It is a monobasic acid, forming crystallizable salts, which decompose when heated, giving off sulphurous oxide. Neutral Ethyl sul- phite, S0 3 (C 2 H 6 ) 2 , is obtained by adding absolute alcohol in excess to chlorine. 528 ALCOHOLS AND ETHERS. bisulphide (p. 203). Hydrochloric acid is evolved, and sulphur deposited, while the ethyl sulphite distils as a limpid strongly-smelling liquid, of sp. gr. 1-085, boiling at 170; it is slowly decomposed by water. Ethyl Phosphates. Three ethyl orthophosphates have been obtained, two acid and one neutral, analogous in composition to the sodium phos- phates ; also a neutral pyrophosphate. Monethylic phosphate, or Ethylphosphoric acid, P0 4 (C 2 H 5 )H 2 , or (P0) /r/ (OC 2 H 6 )(OH) 2 , also called Phosphovinic acid. This acid is bibasic. Its barium salt is prepared by heating to 82 C. (180 F.) a mixture of equal weights of strong alcohol and syrupy phosphoric acid, diluting this mixture, after the lapse of 24 hours, with water, and neutralizing with barium carbonate. The solution of ethylphosphate, separated by filtration from the insoluble phosphate, is evaporated at a moderate temperature. The salt crystallizes in brilliant hexagonal plates, which have a pearly lustre, and are more soluble in cold than in hot water; it dissolves in 15 parts of water at 20 C. (68 F.). The crystals contain P() 4 (C 2 H 6 )Ba" . 60H 2 . From this salt the acid may be obtained by precipitating the barium with dilute sulphuric acid, and evaporating the filtered liquid in the vacuum of the air-pump : it forms a colorless, syrupy liquid, of intensely sour taste, sometimes exhibit- ing appearances of crystallization. It is very soluble in water, alcohol, and ether, and easily decomposed by heat when in a concentrated state. The ethylphosphates of calcium, silver, and lead possess but little solubil- ity; those of the alkali-metals, magnesium, and strontium, arc freely soluble. JJiethylie phosphate, or Diethylphosphoric acid, P0 4 (C 2 H 5 ) 2 H, or (P0) //x (0 2 C 2 H 5 ) 2 (OH), is a monobasic acid, obtained, together with the preceding, by the action of syrupy phosphoric acid upon alcohol. Its barium, silver, and lead-salts are more soluble than the methylphosphates. The calcium salt, (P0 4 ) 2 (C 2 H 5 ) 4 Ca // , and the lead-salt, (P0 4 ) 2 (C 2 H 6 ) 2 Pb", are anhydrous. Triethylic phosphate, P0 4 (C 2 H 5 ) 3 , or (PO)"'(OC 2 H 6 ) 8 , is obtained in small quantity by heating the lead-salt of diethylphosphoric acid to 100, more easily by the action of ethyl-iodide on triargentic phosphate, or of phos- phorus oxychloride on sodium ethylate: 3C 2 H 5 ONa -f (PO)"'C1 S = 3NaCl + (PO)'"(OC 2 H 6 ) 8 . It. is a limpid liquid of sp. gr. 1-072 at 12 C. (54 F.), boiling at 215 C. (129 F.), soluble in alcohol and ether, and also 'in water, by which how. ever it is slowly decomposed. Tetrethylic Pyrophosphate, P 2 ^7(C 2 H 5 ) 4 , produced by the action of ethyl iodide on argentic pyrophosphate, is a viscid liquid of sp. gr. 1-172 at 17 C. (63 F.), decomposed by potash, with formation of potassium diethyl- phosphate. Ethyl Berates. Three of these ethers are known, viz. : Triethylic borate . (C 2 H 5 ) 3 B0 3 , Monethylic borate . C 2 H 5 B0 2 , Ethylic anhydroborate, \on H BO BO orbiborate . . / ^VV^ . J5 2 U 3 . Triethylic borate is formed by the action of boron trichloride on alcohol : 3C 2 H 6 (OH) -j- BC1 3 = 3HC1 + (C 2 H 6 ) 3 B0 3 . It is a thin limpid liquid, of agreeable odor, sp. gr. 0-885, boiling at 119 C. (246 F,), decomposed by water. Its alcoholic solution burns with a fine green flame, throwing off a thick smoke of boric acid. Monethylic borate, C 2 H 5 B0 2 , is formed, with separation of boric acid, by the action of alcohol on the anhydroborate : 2C 2 HB0 2 .B 2 3 + C 2 H 5 (OH) = HB0 2 + 3C 2 H 6 B0 2 . ETHYLIC ETHERS. 529 It is a colorless, mobile liquid, resembling triethylic borate. The anhy- droborate, 2C 2 H 6 B0 2 . B 2 3 , is formed by the action of boric oxide on an equal weight of anhydrous alcohol, and may be obtained by concentration, in the form of a viscid liquid, which solidifies at 300 C. (572 F.), giving off alcohol vapor and etheue gas, and leaving boric oxide. Ethyl Silicates. Tetrethylic silicate, (C 2 H 5 ) 4 Si0 4 , or Si iT (OC 2 H 6 ) 4 , is pro- duced by treating silicic chloride with a small quantity of anhydrous al- cohol: 4C 2 H 5 OH + SiCl 4 = 4HC1 + Si(OC 2 H 5 ) 4 . It is a colorless liquid, having a rather pleasant ethereal odor, and strong peppery taste ; sp. gr. 0-993 at 20. It boils without decomposition be- tween 166 and 160 C. (329-330 F.), and when set on fire burns with a dazzling flame, diffusing a white smoke of finely divided silica. It is de- composed slowly by water, quickly by ammonia and the fixed alkalies. Diethylic silicate, (C 2 H5) 2 Si0 3 , or (SiO) // (OC 2 H 6 ) 2 , is produced, according to Ebelmen,* by the action of silicic chloride on aqueous alcohol: 2C 2 H 5 OH -f OH 2 -f SiCl 4 = 4HC1 -f (SiO)(OC 2 H 6 ) 2 . It is a colorless liquid, of sp. gr. 1 -079, boiling at 350 C. (662 F. ), decomposed by water, with separation of silica. On distilling it with a small quantity of aqueous alcohol, a liquid remains in the retort consisting of diethylic di- silicate, (C 2 H 5 ) 2 Si.,0 5 , or (C 2 H 5 ) 2 Si0 3 . Si0 2 . Hezethylic disilicate, (C 2 H 5 )gSi 2 7 , or 6(C 2 H 6 ) 4 Si0 4 . 2Si0 2 . Friedel and Crafts* were not able to obtain the two ethylic silicates last mentioned; but having prepared a considerable quantity of tetrethylic silicate with al- cohol that was not quite anhydrous, they found that the greater part of the product distilled over toward 240, and that it was not possible, by distil- lation under the ordinary atmospheric pressure, to obtain a product of definite boiling point. By distillation in a vacuum, however (under a pres- sure of 3 to 5 millimetres), they obtained, after eight fractionations, a pro- duct boiling between 125 and 130 C. (257-266 F.), and having the com- position of hezethylic disilicate. This ether is a slightly oily liquid, having a rather fragrant odor, like that of tetrethylic silicate, and a specific grav- ity of 1-0 196 at 0. Silicic ethers containing ethyl and methyl, and ethyl and amyl, have likewise been obtained. The ethylic ethers of organic acids (carbon acids) will be described in connection with those acids. Ethyl Sulph-hydrate, or Mercaptan, C 2 H 5 SH. This compound, the sul- phur analogue of ethyl alcohol, is produced analogously to methyl sulph-hydrate (p. 515), by the action of potassium sulph-hydrate on cal- cium ethylsulphate. A solution of caustic potash of sp. gr. 1-28 or 1-3, is saturated with sulphuretted hydrogen, and mixed in a retort with an equal volume of solution of calcium ethylsulphate of the same density. The re- tort is connected with a good condenser, and heat is applied by means of a bath of salt and water. Mercaptan and water distil over together, and are easily separated by a tap-funnel. The product thus obtained is a colorless, limpid liquid, of sp. gr. 0-842, but slightly soluble in water, easily miscible, on the contrary, with alcohol. It boils at 36 C. (96 F.). The vapor of mercaptan has a most intolerable odor of onions, which adheres to the clothes and person with great obstinacy: it is very inflammable, and burns with a blue flame. When mercaptan is brought into contact with mercuric oxide, even in * Ann. Chim. Phys. [3] xvi. 144. f Ann. Chim. Phys. [4] ix. 5. 45 530 ALCOHOLS AND ETHERS. the cold, violent reaction ensues, water is formed, and a white substance is produced, soluble in alcohol, and separating from that liquid in distinct crystals which contain (C 2 H 5 ) 2 S 2 Hg // . This compound is decomposed by sulphuretted hydrogen, mercuric sulphide being thrown down, and mer- captan reproduced. By adding solutions of lead, copper, silver, and gold to an alcoholic solution of mercaptan, corresponding compounds containing those metals are formed. Caustic potash produces no eifect upon mercap- tan, but potassium displaces hydrogen, and gives rise to a crystallizable compound, C 2 H 5 SK, soluble in water. Sodium acts in a similar manner. Ethyl Sulphides. Three of these compounds have been obtained, analo- gous in composition to the methyl sulphides, and produced by similar re- actions. The monosulphide, (C 2 H 5 )S, or C 2 H 5 SC 2 H 5 , is a colorless oily liquid, having a very pungent alliaceous odor, a specific gravity of 0-825 at 20 C. (68 F.), and boiling at 72 C. (162 P.). It is very inflammable, and burns with a blue flame. When poured into chlorine gas, it takes fire ; but when dry chlorine is passed into a flask containing it, not at first into the liquid, the vessel being kept cool and in the shade, substitution-products are formed and hydrochloric acid is copiously evolved. The product consists chiefly of dichlorethylic sulphide, (C 2 H 4 C1) 2 S. If the action takes place in diifused daylight, and without external cooling, the compounds (C 2 H 2 C1 3 ) 2 S and (C 2 HC1 4 ) 2 S are obtained, which may be separated by fractional distil- lation, the first boiling between 189 and 192 C. (372-378F.), the second between 217 and 222 C. (423-432 F.). The action of chlorine on ethyl sulphide in sunshine yields a more highly chlorinated compound, probably (C 2 C1 6 ) 2 S. Ethyl bisulphide, (C 2 H 5 ) 2 S 2 , obtained by distilling potassium bisulphide with potassium ethylsulphate or with ethyl oxalate, is a colorless oily liquid, very inflammable, boiling at 151 C. (302 F.). The trisulphide, (C 2 H 5 ) 2 S 3 , is a heavy oily liquid, obtained by acting in like manner on potassium pentasulphide. Triethylsulphurous Compounds.* When ethyl monosulphide and ethyl iodide are heated together, they unite and form sulphurous iodotriethide, (C 2 H 5 ) 2 S . C 2 H 5 I, or S iv (C 2 H 6 ) 3 I, which crystallizes in needles. The same compound is formed by the action of ethyl iodide on ethyl sulph-hydrate : 2C 2 H 5 I + C 2 H 5 SH = HI + S(C 2 H 6 ) 3 I, or of hydrogen iodide on ethyl monosulphide : HI + 2(C 2 H 5 ) 2 S = C 2 H 5 SH + S(C 2 H 5 ) 3 I. Sulphurous iodotriethide is insoluble in ether, slightly soluble in alcohol, and crystallizes from the solution in white deliquescent needles belonging to the monoclinic system. It unites with metallic chlorides. Ethyl chloride and ethyl bromide unite in like manner, but less readily, with ethyl sulphide, forming the compounds S(C 2 H 5 ) 3 C1 and S(C 2 H 5 ) 3 Br, both of which crystallize in needles. By treating the iodine compound with recently-precipitated silver oxide, a strongly alkaline solution is obtained, which dries up over oil of vitriol to a crystalline deliquescent mass, consisting of sulphurous triethyl-hydroxy- late, (C 2 H 5 ) 3 S(OH). The solution of this substance dissolves the skin like caustic potash, and forms similar precipitates with various metallic salts. It neutralizes acids, forming definite crystallizable salts, e.g., the nitrate, (C 2 H 5 ) 3 SON0 2 , the acetate (C 2 H 6 ) 8 S(OC 2 H,0), &c. The formulae of these compounds show that sulphur is at least quadri- valent (p. 237). * A. vnn OeffeJc, Chem. Soc. Journal, xvii. 108. Cahours, Ann. Ch. Pharm. cxxxv. 352; cxxxvi. 151. ftehn, Aim. Cl*. Pharm. Suppl. iv. 83. PROPYL ALCOHOL. 531 PROPYL ALCOHOLS AND ETHERS. It has already been observed that the three-carbon alcohol, C 3 H 8 0, is susceptible of two isomeric modifications, namely : CH 3 (CH 2 CH 3 7 Normal Propyl alcohol C -j H 2 or CH 2 thus CH 2 ( 2 (OH OH H 3 C CH 3 Isopropyl alcohol C 1 ^" 8 or \/ HCOH {I each of which may give rise to a corresponding set of ethers and other derivatives. The normal propyl compounds, however, are but little known, none of them having yet been prepared synthetically, except propylamine and propyl cyanide, to be afterwards considered. Chancel, in 1853, by subjecting the fusel-oil of marc brandy, prepared in the south of France, to fractional distillation, obtained a number of alcohols, among which was one to which he assigned the composition C 3 II 8 0; this has usually been regarded as normal propyl alcohol, but it was not obtained pure, and is altogether very little known. Isopropyl Alcohol, CII(CH 3 ) 2 OH. This alcohol is prepared: 1. From acetone, (CO) // (CH 3 ) 2 , by direct addition of hydrogen, evolved by the action of water on sodium amalgam: H 3 C CH 3 H 3 C CH, V + H 2 = v CO HCOH Acetone. Isopropyl alcohol. This mode of synthesis affords direct proof of the constitution of iso- 'propylic alcohol, the addition of the two hydrogen-atoms being tantamount to the replacement of the bivalent radical oxygen by the two monad radi- cals, hydrogen and hydroxyl. 2. Isopropyl iodide is prepared by the action of iodine and phosphorus on glycerin ; this iodide is easily converted into the oxalate or acetate by treatment with silver oxalate or acetate ; and from either of these ethers the alcohol may be obtained by distillation with potash or soda. Isopropyl alcohol is a colorless, not very mobile liquid, having a peculiar odor, a specific gravity of 791 at 15 C. (60 F.), boiling at 83 to 84 C. (181-183F.), under a barometric pressure of 739 millimetres, not freezing at 20. It does not act on polarized light. It is very difficult to dry, as it mixes with water in all proportions, and forms with it three definite and very stable hydrates, viz., 3C 3 H 8 0.20H 2 , boiling at 78-80 C. (172-176 F.); 2C,H 8 O.OII 2 , boiling at 80; and 3C 3 H 8 . OH 2 , boiling at 81. The second of these hydrates exhibits a very close resemblance to ethyl alcohol, and has the same percentage composition, boils at nearly the same tem- perature, and likewise yields acetic acid by oxidation (see p. 532) ; more- over it retains its water of hydration so obstinately, that it does not even change the white color of anhydrous cupric sulphate to blue. The readiest mode of distinguishing between this hydrate and ethyl alcohol is to submit 532 ALCOHOLS AND ETHERS. them to the action of iodine and phosphorus, whereby the former is con- verted into isopropyl iodide, the latter into ethyl iodide. The characteristic property of isopropyl alcohol is that it yields acetone by oxidation with dilute chromic acid, this transformation being the reverse of that by which it is produced : H 3 C CH, H 3 C CH 3 V + = V + OH 2 HCOH CO On pushing the oxidation further, the acetone breaks up into acetic acid, carbon dioxide and water : CO(CH 3 ) 2 -f 4 = CO(CH 3 )OH -f C0 2 -f OH 2 Acetone. Acetic acid. The evolution of carbon dioxide in this reaction affords a further distinc- tion between hydrated isopropyl alcohol and ethyl alcohol. The formation of a ketone by oxidation is the essential characteristic of a secondary alcohol, and is an immediate consequence of its structure. The primary alcohols, C n H 2n + 2 O, are directly converted by oxidation into aldehydes, C n H^O, and acids, C n H 2a 2 , not into ketones; thus: CH 3 CH 3 I ' + = OH 2 + | * CH 2 OH H C=0 Ethyl alcohol. Aldehyde. C 2 H 4 + = C 2 H 4 2 Aldehyde. Acetic acid. Isopropyl alcohol, heated with acetic acid, or with potassium acetate and sulphuric acid, is converted into isopropyl acetate, CH(CH 3 ) 2 OC 2 H 3 0. ISOPROPYL IODIDE, CH(CH 3 ) 2 I, is most conveniently prepared by the ac- tion of hydriodic acid, concentrated and in larger excess, on glycerin (propenyl alcohol) C 3 H g 3 : C 3 H 8 3 + 5HI = C 3 H 7 I -f 30H 2 -f- 2I 2 . The iodine, as fast as it is set free by the reaction, may be reconverted into hydriodic acid by means of phosphorus, and will then be ready to act upon another portion of glycerin. It may also be produced by the ac- tion of hydriodic acid on isopropyl alcohol, allyl iodide, C 3 H 5 I, propene, or propene alcohol. Isopropyl iodide is an oil boiling at 89-90 C. (192-194 F.), and having a specific gravity of 1-70. With sodium in presence of ether it yields pro- pene, propane, and di-isopropyl, C 6 H 14 . Bromine expels the iodine and forms isopropyl bromide. QUARTYL OR BUTYL ALCOHOLS AND ETHERS. Theory indicates the existence of four alcohols included in the formula C 4 H 10 0, two primary, one secondary, and one tertiary ; thus, QUABTYL OR BUTYL ALCOHOLS. 533 Primary. CH, C V H Secondary. Tertiary. CH 3 H 8 C1 CH S CH 2 COH CH 3 GH t H 2 COH H 2 COH H 2 COH CH 3 Propyl carbinol Isopropyl Methyl-ethyl Trimethyl carbinol carbinol carbiuol. Propyl Carbinol, C rCH 2 CH 2 CH 3 loft . This alcohol is obtained from quartyl chloride, C 4 II 9 C1 (produced by the action of chlorine or quartane or diethyl, C 14 H 10 ), by heating that chloride with potassium acetate arid strong acetic acid, whereby it is converted into quartyl acetate, and treating that com- pound with barium hydrate. The alcohol thus prepared yields butyric acid by oxidation.* Isopropyl Carbinol, C rCH(CH 3 ) 2 1 H (o OH . This variety of primary butyl-alcohol was found by Wurtz in the fusel-oil obtained by fermenting the molasses of beet-root sugar. To separate it, this oil is submitted to fractional distil- lation, and the liquid boiling between 108 and 118 is repeatedly rectified over potassium hydrate, till it boils constantly at 110 C. (230 F.). Pure isopropyl carbinol is a colorless liquid, having an odor somewhat like that of amyl al<:ohol, but less pungent, and more vinous: sp. gr. = "0-8032 at 18-5 C. (05 F.). It dissolves in 10 times its weight of water, and is separated therefrom, as an oil, by calcium chloride, sodium chloride, and other soluble salts. By oxidation it is converted into butyric acid, C 4 II 8 2 , whence it appears to be a primary alcohol. Formerly also this alco- hol was assumed to have the constitution represented by the first of the for- jnuhe above given ; in other words, to consist of propyl-carbinol,Cl{ 2 (C 3 tt^OR ; and all the other alcohols of the series produced by fermentation were sup- posed to be similarly constituted. This assumption, however, did not rest on very exact experimental data ; and from recent experiments by Erlenmeyer,j" it appears that butyl alcohol produced by fermentation con- sists of isopropyl-carbinol, CH 2 [CH(CH 3 ) 2 ]OH, or is represented by the second of the formulae above given for the primary four-carbon alcohol. Isopropyl-carbinol is acted upon by acids and other chemical reagents much in the same manner as common alcohol (methyl-carbinol). With strong sulphuric acid it yields quartyl- sulphuric acid, S0 4 H(C 4 H 9 ), if the mix- ture is kept cool; but on heating the liquid quartern, or butylene, C 4 H 8 is given off mixed with sulphurous oxide and carbon dioxide. Heated with hydrochloric acid in a sealed tube, or treated with phosphorus pentachloride or oxychloridc, it is converted into quartyl chloride, C 4 H 9 C1, or chloroquartane, an ethereal liquid, having a pungent odor, and boiling at 70 C. (158 F.); quartyl bromide, C 4 H 9 Br, obtained in like manner, boils at 89, the iodide C 4 II 9 i, at 121 C. (250 F.). The iodide is decomposed by potassium or sodium, yielding diquartijl or dibutyl, C 8 H 18 , probably : * Ftr.Ju'h/en, Ann. Oh. Pharm. cxxx., 233. f Zcitsrlirift fur Cheinie, Ncue Koilio, iii. 117. The details of the investigation arc not yet published. 45* 534 ALCOHOLS AND ETHERS. H 3 C... H H H H ...-CH S H.C H H CH, a limpid liquid, lighter than water, and boiling at 105 C. (221 F.). The same hydrocarbon is obtained by the electrolysis of valeric acid, C 5 H 10 2 . Methyl-ethyl Carbinol, or Secondary Butylic Alcohol, C This alcohol is obtained from erythrite (erythromannite), a saccharine substance having the composition of a tetratomic alcohol, C 4 H, 4 , or C 4 H 6 (OH) 4 . The erythrite, distilled with fuming hydriodic acid, yields methyl-ethyl- iodomethane, or secondary butyl iodide, C(CH 3 )(C 2 H 6 )HI, and this liquid, treated with moist silver oxide, is converted into methyl-ethyl carbinol: C(CH 3 )(C 2 H 5 )HI Methyl-ethyl iodo- methane. AgOH = Agl -f- Silver Silver hydrate. iodide. C(CH 3 )(C 2 H 5 )HOH. Methyl-ethyl- carbinol. Methyl-ethyl carbinol is a colorless oily liquid, having a strong odor and burning taste, a specific gravity of 0-85 at 0, and boiling at 95-98 C. (208-208 F.) (about 10 C. (18 F.) lower than the primary alcohol). When heated to 250 C. (482 F.), it is for the most part resolved into water and quartene or butylene: C 4 H 10 = OH 2 -}- C 4 H 8 . Methyl-ethyl lodomethane, or Secondary Butyl iodide, prepared as above, or by the action of strong hydriodic acid on the alcohol, is a liquid having a pleasant ethereal odor, a specific gravity of ] -632 at 0, 1-600 at 20 C. (68 F.) and 1-584 at 30 C. (86 F.). It boils at 118 C. (244 F.). Bromine decomposes it, expelling the iodine and forming quartene dibromide C 4 H 8 C1 2 . When distilled with alcoholic potash it gives off quartene. This tendency to give off the corresponding olefine is characteristic of all the secondary alcohols and ethers, as will be further noticed in connection with the five-carbon compounds. Trimethyl Carbinol or Tertiary Butyl Alcohol, C | \y^*\ is produced by treating zinc methide with carbonyl chloride (phosgene gas) or acetyl chloride, and submitting the product to the action of water.* = ZnCl 2 + 2COCH 3 C1 Carbonyl Zinc"" Zinc. Acetyl chloride. methide. chloride. chloride. + C^ COCHgCl -f Zn(CH 3 ) 2 = ZnO Acetyl chloride. Zinc methide. HOH Water. Zinc, oxide. Trimethyl chloromethane. = HC1 -f Trimethyl- Water. Trimethyl chloromethane. carbinol. When acetyl chloride is used, the formation of trimethyl-chloromethane takes place by a very simple reaction. In the case of carbonyl chloride it * Buitlerow, Zeitschrift fUr Chem. und Pharm. 1864, pp. 385, 702. QUINTYL OR AMYL ALCOHOLS. 535 takes place by two stages, the first of which is the production of acetyl chloride. The other tertiary alcohols, to be noticed hereafter, are obtained by similar series of reactions. The properties of this, and of the other tertiary alcohols, have not been much studied. They are distinguished from the primary and secondary alcohols by the products which they yield with oxidizing agents. Primary alcohols of the series C n H^-f 2 0, oxidizing with chromic acid, yield, as already observed, the corresponding acids, C n H 2n O 2 ; secondary alcohols, the corre- sponding ketones. Tertiary alcohols, on the other hand, are split up by oxidation, yielding bodies containing a smaller number of carbon-atoms: thus, trimethyl carbinol is converted by oxidizing agents into formic and propionic acids : C 4 H 10 + 4 = CH 2 2 + C 3 H 6 2 + OH 2 Trimethyl Formic Propionic carbinol. acid. acid. QUINTYL OR AMYL ALCOHOLS AND ETHERS. The formula C 5 H I0 may include six different alcohols: two primary, three secondary, and one tertiary, viz. : rCH 2 CH 2 CH 2 CH 3 fCH 2 CH(CH 3 ) 2 Primary C \ ^ and C j ** [OH [OH Butyl carbinol. Isobutyl carbinol.* fCH 2 CH 2 CH 3 rCH(CH 3 ) 2 fCH 2 CH 8 Secondary CJ H ' ^H 1 ^ and C j H ' CH * [OH [OH [OH Methyl-propyl Methyl-isopropyl Diethyl carbinol. carbinol. carbinol. rCH 2 CH 3 Tertiary Cj ^ 3 Dimethyl-ethyl carbinol. [OH 3 Of these, however, only two have been distinguished with certainty, viz., a primary alcohol, produced by fermentation, and a secondary alcohol ob- tained from the corresponding olefine, namely, quintene or amylene. Isobutyl Carbinol, CH 2 (C 4 H 9 )OH. This, according to Erlenmeyer, is the ordinary amyl alcohol produced by fermentation. In the manufacture of brandy from corn, potatoes, or the must of grapes, the ethyl alcohol is found to be accompanied by an acrid oily liquid called fusel-oil, which is very difficult to separate completely from the ethyl alcohol. It passes over, however, in considerable quantity towards the end of the distillation, and may be collected apart, washed by agitation with several successive por- tions of water to free it from ethyl alcohol, and re-distilled. The liquid thus obtained consists chiefly of amyl alcohol, sometimes mixed with pro- pylic, butylic, and other alcohols. The amyl alcohol maybe obtained pure by fractional distillation, the portion which passes over between 128 and 132 C. (2(')2-270 F. ) being collected apart. Potato fusel-oil consists almost wholly of ethyl and amyl alcohols, the latter constituting the greater quantity. * Tho four-carbon radical derived from methyl by substitution of isopropyl for one atom of hydrogen may be called isoquartyl or isobutyl. 536 ALCOHOLS AND ETHERS. Amyl alcohol is an oily, colorless, mobile liquid, having an odor peculiar to itself, and a burning acrid taste. Its vapor when inhaled produces coughing and oppression of the chest. Its specific gravity is 0-8111. When dropped on paper it forms a greasy stain, which, however, disappears after a while. It is not perceptibly soluble in water, but floats on the surface of that liquid like an oil; common alcohol, ether, and various essential oils dissolve it readily. Amyl alcohol usually exerts a rotatory action on polarized light, but the rotatory power varies considerably in different samples. Pasteur, indeed, has shown that ordinary amyl alcohol is a mixture of two isomeric alcohols, having the same vapor-density, but differing in their optical properties, one of them turning the plane of polarization to the right, whereas the other is optically inactive. They are separated by converting the crude amyl alcohol into amylsulphuric acid, saturating with barium carbonate, and crystallizing the barium amyl sulphate thus formed. The salt obtained from the active amyl alcohol is 2J more soluble than that obtained from the inactive alcohol, and consequently the latter crystallizes out first; and by precipitating the barium from the solution of either salt with sulphuric acid, and distilling the amylsulphuric acid thus separated with water, the corresponding amyl alcohol is obtained. The difference of optical character between the two alcohols which is traceable through many of their de- rivatives has not been satisfactorily explained; but it probably depends upon the arrangement of the molecules, rather than upon that of the atoms within the molecule. Vapor of amyl alcohol passed through a red-hot tube, yields a mixture of ethene, propene, quartene, and quintene or amylene. Amyl alcohol takes fire easily and burns with a blue flame. When ex- posed to the air in contact with platinum black, it is oxidized to valeric acid, C 5 H 10 2 . The same acid is obtained by heating amyl alcohol with a mixture of potassium bichromate and sulphuric acid. CH 2 (C 4 H 9 )OH -f 3 = OH 2 + CO(C 4 H 9 )OH. Amyl alcohol. Valeric acid. Amyl alcohol, heated to 220 C. (423 F.) with a mixture of potassium hydrate and lime, is converted into valeric acid, with evolution of hydrogen: C 5 H 12 -f KHO = C 5 H 9 K0 2 -f H 2 . Amyl al- Potassium cohol. valerate. Potassium and sodium dissolve in amyl alcohol as in ethyl alcohol, yield- ing the compound, C 6 H U KO, and C 5 H n NaO, which, when treated with amyl iodide, yield amyl oxide or amyl ether, (C 5 H n ) 2 ; and with ethyl iodide, ethyl-amyl oxide, (C 2 H 5 )(C 5 H U )6. Chlorine acts upon amyl alcohol as upon ethyl alcohol, excepting that it finally removes only four atoms of hydrogen, instead of five : C 5 H J2 -f 3C1 2 = 4HC1 + C 5 H 8 C1 2 0. Amyl alcohol. Chloramylal. Amyl alcohol is acted upon by acids, like common alcohol, yielding ethers. When mixed with strong sulphuric acid, it is converted into amyl- sulphuric acid, (C 5 H 11 )HS0 4 ; and, on distilling the mixture, amyl oxide, (C 6 H n ) 2 0, passes over, together with amylene, and several other hydrocar- bons. AMYLENE, on QUINTENE, C 5 H, . is likewise obtained, together with quin- tane, C 5 H 12 , and higher homologues of both these bodies, by distilling amyl alcohol with zinc chloride. It is a colorless liquid, having a peculiar and somewhat unpleasant odor; boils at 35 C. (95 F.), and when set on fire, AMYL ALCOHOLS AND ETHERS. 537 burns with a bright, very smoky flame. Vapor of amylene is completely absorbed by antimony pentachloride and sulphuric oxide. Strong sul- phuric acid dissolves amylene, when the two are shaken up together, but the hydrocarbon soon separates as an oily layer, which however consists, not of amylene, but of diamylem (par amylene}, C^H^. Amylene unites with hydrochloric, hydrobromic, and hydriodic acid, forming compounds isomeric with amyl chloride, &c. AMYL CHLORIDE, C 6 H,,C1, is prepared by distilling equal weights of amyl alcohol and phosphorus pentachloride, washing the product repeatedly with alkaline water, and rectifying it from calcium chloride. Less pure it may be obtained by saturating amyl alcohol with hydrochloric acid. It is a colorless liquid, of agreeable aromatic odor, insoluble in water, and neu- tral to test-paper: it boils at 102 C. (216 F.), and ignites readily, burn- ing with a flame green at the edges. By the long-continued action of chlo- rine, aided by powerful sunshine, it is converted into octochlorinated amyl chloride, or nonochloroquintane, C 5 H 3 C1 9 , a volatile, colorless liquid, smelling like camphor : the whole of the hydrogen has not yet, however, been re- moved. AMYL BROMIDE, C 5 TI,,Br, is a volatile, colorless liquid, heavier than water. It is obtained by distilling amyl alcohol, bromine, and phosphorus together. (See ethyl bromide, p. 522.) Its odor is penetrating and allia- ceous. The bromide is decomposed by an alcoholic solution of potash, with reproduction of the alcohol and formation of potassium bromide. AMYL IODIDE, C 5 H,,I, is procured by distilling a mixture of 15 parts of amyl alcohol, 8 of iodine, and 1 of phosphorus. It is colorless when pure, heavier than water, volatile without decomposition at 146 C. (295 F.), and in other respects resembles the bromide : it is partly decomposed by ex- posure to light. Heated to 290 C. (554 F.) in sealed tubes, with zinc, it yields diamyl, C 10 H 22 , or C 5 H n . C 5 H n , a colorless ethereal liquid, boiling at 155 C. (311 F.), and isomeric, or identical with decane (p. 474). At the same time there is formed a compound of zinc iodide with zinc amylide, Zn(C 5 H u ) 2 , which is decomposed by contact with water, yielding zinc oxide and quintane or amyl hydride (p. 478) : Zn(C 6 H n ) 2 + OH 2 = ZnO + 2C 5 H 12 . ^ AMYL OXIDE, (C 5 H n ) 2 0, obtained by the processes already mentioned, is a colorless oily liquid, of specific gravity of 0-779, and boiling at 176. AMYL SULPHURIC, or SULPHAMYLIC ACID, (Cr 5 H n )HS0 4 , or C 5 H n OS0 3 H. The barium salt of this acid, (C 5 H 11 ) 2 Ba // (SO 4 t 2 . 2 aq., prepared like the ethylsulphate (p. 527). crystallizes on evaporating the solution in small bril- liant pearly plates ; the difference of solubility of the salts prepared from op- tically active and optically inactive amyl alcohol has already been mentioned. The barium may be precipitated from the salt by dilute sulphuric acid, and the sulphamylic acid concentrated by spontaneous evaporation to a syrupy, or even crystalline state: it has an acid and bitter taste, strongly reddens litmus-paper, and is decomposed by ebullition into amyl alcohol and sul- phuric acid. The potassium salt forms groups of small radiated needles, very soluble in water. The sulphamylates of calcium and lead are also sol- uble and crystallizable. Amyl sulph-hydrate, C 5 Hj,SH, and Amyl sulphide, (C 5 H n ) 2 S, have likewise been obtained : they resemble the ethyl compounds in their properties and reactions. Fusel-oil or Grain-spirit. The fusel oil, separated in large quantities from grain-spirit by the London rectifiers, consists chiefly of amyl alcohol 538 ALCOHOLS AND ETHERS. mixed with ethyl alcohol and water. Sometimes it contains in addition more or less of the ethyl- or amyl-compounds of certain fatty acids thought to have been identified with cenanthylic and palmitic acids. These last- named substances form the principal part of the nearly solid fat produced in this manner in whiskey distilleries conducted on the old plan. Mulder has described, under the name of corn-oil, another constituent of the crude fusel-oil of Holland: it has a very powerful odor, resembling that of some of the umbelliferous plants, and is unaffected by solution of caustic potash. According to Mr. Rowney, the fusel-oil of the Scotch distilleries contains in addition a certain quantity of capric acid, C 10 H 20 2 . Amyl alcohol, in addition to butyl alcohol, has been separated from the spirit distilled from beet-molasses, and from artificial grape-sugar made by the aid of sulphu- ric acid. Although much obscurity yet hangs over the history of these substances, it is generally supposed that they are products of the fermen- tation of sugar, and have an origin contemporaneous with that of common alcohol. H 3 C CH 3 V CH Methyl-isopropyl carbinol, CH(CH 3 )[CH(CH 3 ) 2 ]'OH = | or Amyl- HCOH CH 3 ene hydrate, (C 6 H 10 )"JQ H ' This is a secondary alcohol produced from amylene, C 5 H 10 , by combining that substance with hydriodic acid, and de- composing the resulting hydriodide, C 5 H, .HI, with moist silver oxide, whereby silver iodide and amylene hydrate are obtained : 2(C 6 H 10 .HI) + Ag 2 + H 2 = 2AgI + 2[C 5 H 10 .H(OH)]. A portion of the hydriodide is at the same time resolved, by the heat evolved in the reaction, into hydriodic acid and amylene ; and, on submit- ting the resulting liquid to fractional distillation, the amylene passes over first, and then, between 105 and 108 C. (221 and 226 F.), the amylene hydrate or methyl-isopropyl carbinol. This alcohol is a liquid having a specific gravity of 0-829 at 0, and a pungent ethereal odor, quite distinct from that of ordinary amyl alcohol. Heated with strong sulphuric acid, it is converted, not into amylsulphuric acid, but into hydrocarbons polymeric with amylene, viz., diamylene, or decene, C^H^, and triamylene, or quindecene, G l5 H- go . Hydriodic acid con- verts it, at ordinary temperatures, into amylene hydriodide, C 5 H, .HI, boiling at 130 C. (266 F.), (amyl iodide at 146 C. [295 F.]). Hydrochloric acid converts it (even at 0) into amylene hydrochloride, C 5 H 10 .HC1, having a boiling point 10 C. (18 F.) below that of amyl chloride. On mixing it with two atoms of bromine at a very low temperature, a red liquid is formed, which, as soon as it attains the ordinary temperature of the air, is resolved into water and amylene bromide. Heated for some time to 100 C. with strong acetic acid, it yields amylene, together with a small quantity of amylene acetate. Sodium dissolves in amylene hydrate with evolution of hydrogen, forming a colorless translucent mass, which has the composition C 5 H, NaOH, and is decomposed by amylene hydriodide in the manner shown by the equation: C 6 H 10 NaOH -f C 5 H 10 HI = C 5 H 10 + C 5 H 10 H(OH) + Nal. Sodium com- Amylene Amylene. Amylene pound. hydriodide. hydrate. From these reactions it is apparent that amylene hydrate or methyl- HEXYL ALCOHOLS AND ETHERS. 539 isopropyl carbinol is especially distinguished from amyl alcohol or butyl carbinol, by the facility with which it gives up the corresponding olefiue. This peculiarity is exhibited also by all the secondary alcohols of the series. These alcohols indeed may be regarded as connecting links between the primary monatomic alcohols and the secondary alcohols, or glycols; e. g. : C 5 H n (OH) C 5 Amyl alcohol. Amylene Amylene glycoL hydrate. SEXTYL, OR HEXYL, ALCOHOLS AND ETHERS. The number of possible modifications of an alcohol increases with the number of carbon-atoms in its molecular formula. Thus we have seen that there may be two propyl alcohols, C 3 H 8 0, four butyl alcohols, C 4 H 10 0, and six amyl alcohols, C 5 H, 2 0. The six-carbon formula, C 6 H 14 0, will in like manner be found to include ten isomeric alcohols three primary, four secondary, and three tertiary ; but as the manner in which these modifica- tions arise has been sufficiently explained in the preceding pages, the further development of the theoretical formulae may be left as an exercise for the student. The number of modifications of the six-carbon alcohol actually known, is five ; of which two are primary, one is secondary, and the remaining two are tertiary. Primary Hexyl Alcohols. The normal alcohol, or Amyl-carbinol, G 6 H I3 (OH), or C \ H 2 , is prepared by treating sextane, or hexyl hydride, (OH C 6 H, 4 , obtained from American petroleum, with chlorine, converting the resulting hexyl chloride, C 6 H 13 C1, into hexyl acetate, C 6 H 13 (OC 2 II 3 0), by treatment with silver acetate, and distilling the hexyl acetate with potash. The hexyl alcohol thus prepared boils at about 150 C. (302 F.), and smells like arnyl alcohol. Another primary hexyl alcohol was found by Faget in fusel-oil. The statements respecting it are not very exact, but as it is produced by fermentation, it is probably constituted like ordinary amyl alcohol, and C CH 2 CH 2 CH(CH 3 ) 2 therefore in the manner represented by the formula, C \ H (OH Both these alcohols, when oxidized by chromic acid, yield caproic acid, ( CH 2 CH(CH 3 ) 2 1 /~^1T Secondary HexylAlcohol,probablyMethyl-isobutylcarbinol,C -I g * ( OH or Hexylene hydrate, C 6 H 12 j ^ This alcohol, discovered by Wanklyn and Erlenmeyer,* is produced from mannite, a saccharine body having the composition of a hexatomic alcohol, C 6 H 8 (OH) 6 , by treating that substance with a large excess of very strong hydriodic acid, whereby it is converted into secondary hexyl iodide, or hexylene hydriodide, C 6 H, 2 .HI: C 6 H 8 (OH) 6 + 11 III = C 6 H 12 HI -f- 60H 2 -f- 5I 2 ; and digesting this hydriodide with silver oxide and water: C 12 H 12 HI + H 2 + Ag 2 = 2AgI + C 6 H 12 H(OH). * Journal of the Chemical Society [2], i. 221. 540 ALCOHOLS AND ETHERS. It is a viscid liquid, having a pleasant, refreshing odor; boils at 137; has a sp. gr. of 0-8327 at 0, 0-8209 at 16, and 0-7482 at 99, so that it ex- pands somewhat rapidly by heat. Strong hydrochloric acid converts it into the corresponding hydrochloride, C 6 H 12 HC1, which boils at 120 C. (248 F.), and yields hexylene when digested at 100 C., with alcoholic potash. Hexylene hydrate, or methyl-isobutyl carbinol, is converted by oxidation with potassium bichromate and sulphuric acid, into a ketone, C 6 H 12 = CH 2 CH further treated with the oxidizing mixture just mentioned, yields butyric, acetic, and carbonic acids, and water. These reactions show that the al- cohol in question is a secondary alcohol. Tertiary Hexyl Alcohols. Three of these alcohols are possible, namely : Methyl-diethyl carbinol rCH 2 (C 2 H 6 ) Propyl-dimethyl carbinol C \ (CH 3 ) 2 (OH (CH(CH 3 ) 2 Isopropyl-dimethyl carbinol C -1 (CH 8 ) 3 (OH. The third has not yet been obtained. The first is prepared by treating zinc ethyl with acetyl chloride, and decomposing the resulting methyl- f CH 3 diethyl-chlorethane, C 4 (C 2 H 6 ) 2 , with water ; the second by proceeding in ( Cl like manner with zinc methyl and butyryl chloride, CO(C S H ? )C1. SEPTYL, OR HBPTYL, ALCOHOLS AND ETHERS. Of these compounds only the normal primary alcohol, C 7 Hi 6 (OH), or Hexyl carbinol, C -| H 2 , is known with certainty. It is prepared, either by the action of nascent hydrogen (evolved by the action of sodium amal- gam on water) on oenanthylic aldehyde (oenanthol) : CH 14 + Hj = C 7 H 16 0; Aldehyde. Alcohol. or from septane or heptyl hydride, C 7 H, 6 , in the same manner as hexyl alcohol from hexyl hydride (p. 539). It is a colorless, oily liquid, insoluble in water ; but its properties are not much known. Another heptyl alcohol was separated by Faget from fusel-oil ; and a third has been said by several chemists to be obtained, together with octyl alcohol, by distilling castor-oil with excess of potash ; but, according to the most trustworthy experiments, there is but one alcohol obtained by this process, viz., an 8-carbon alcohol. OCTYL ALCOHOLS AND ETHERS. 541 OCTYL ALCOHOLS AND ETHERS. Alcohols having the composition C 8 H, 8 are obtained: 1. From the octane or octyl hydride of American petroleum, by the series of processes already indicated in the case of hexyl alcohol. 2. By distilling castor-oil with potash. The first is an oily liquid, having a specific gravity of 0-82G at 16, and boiling at 180-184 C. (356-363 F.). Its structure is not exactly known, but it closely resembles the alcohol obtained from castor-oil, both in its physical properties and in its reactions. The chloride, C 8 fl, 7 Cl, obtained by the action of chlorine on octane, is also very similar in its properties to that obtained from the alcohol of castor-oil by the action of phosphorus pentachloride. Secondary Octyl Alcohol, or Methyl-hexyl Carbinol, C 6 H, 3 H H H H H X CH 3 CH 3 or H 3 C C C C C C <' OH OHH H H ''' CH 3 This alcohol is produced by heating castor-oil with excess of solid potas- sium hydrate. Castor-oil contains ricinoleic acid, CjgH^Og; and this acid, when heated with potash, yields free hydrogen, a distillate containing methyl-hexyl carbinol, together with products of its decomposition, and a residue of potassium sebate : C 18 H 34 3 + 2KOH = C 8 H 18 + C 10 H 16 K 2 4 + H r , Ricinoleic Octyl Potassium acid. alcohol. sebate. To separate the alcohol, the distillate is repeatedly rectified over fused potash, the portion boiling below 200 C. (392 F.) only being collected: this liquid, subjected to fractional distillation, yields a portion boiling at 181, which is the pure secondary octyl alcohol. The portions of the orig- inal distillate having a lower boiling point, consist of olefines, amongst which octylene, C 8 H I6 , boiling at 125 C. (257 F.), preponderates.* Methyl-hexyl carbinol is a limpid oily liquid, having a strong aromatic edor, and making grease spots on paper. It has no action on polarized light. It has a specific gravity of 0-823 at 17, and boils at 181 C. (358 F.). It is insoluble in water, but dissolves in alcohol, ether, wood-spirit, and acetic acid. It mixes with sulphuric acid, forming octyl-sulphuric acid, C 8 H, 7 HS0 4 , generally also octylene and neutral octyl-sulphate. Fused zinc chloride converts it into octylene. With potassium and sodium it yields substitution-products. Methyl-hexyl carbinol, oxidized with potassium bichromate and sulphu- ric acid, yields the corresponding ketone, viz., methyl-oenanthol, !C* H" CH 3 13 ; thus, 0" -f = OH 2 + OH Methyl-hexyl Methyl carbinol. oenanthol. * ,SbA0rkmier, Proceedings of tho Royal Society, xvi. 376. 46 542 ALCOHOLS AND ETHERS. By the prolonged action of the oxidizing mixture, this ketone is further oxidized to caproic and acetic acids : C 8 H 18 + 4 = C 6 H 12 8 + C 2 H 4 2 + OH r Methyl Caproic Acetic renantliol. acid. acid. These reactions show that the alcohol produced from castor-oil is a sec- ondary alcohol ; and from further considerations, for which we must refer to Schorlemmer's paper above cited, it is inferred to contain the radical isopropyl, that is, to have one of its carbon-atoms directly combined with three others. Octyl chloride, C 8 H 17 C1, produced by the action of phosphorus pentachlo- ride on the alcohol, has a specific gravity of 0-892 at 18 C. (64 F.), and boils at 175 C. (347 F.). Heated with alcoholic potash, it yields octene, C 8 H 16 ; by alcohol and potassium acetate, it is converted into octene and octyl acetate. Nonyl Alcohol, C 9 H 20 0, or Octyl Carbinol, C | H a , is obtained by the Oil series of reactions above described from nonane or nonyl-hydride, which is one of the constituents of American petroleum, and likewise occurs, to- gether with nonene, C 9 H 18 , in that portion of the liquid obtained by dis- tilling amyl alcohol with zinc chloride, which boils between 134 and 150 C. (273 and 302 F.). Nonyl alcohol boils at about 200. Nonyl chloride, C 9 H, 9 C1, has a specific gravity of 0-899 at 16 C. (60 F.), and boils at 196. The alcohols of the series, C n H 2n -f 2 0, containing from 10 to 15 carbon- atoms, are not known, but compound ethers containing 12 and 14 carbon- atoms appear to occur in spermaceti. Sexdecyl, or Cetyl Alcohol, C 16 H 34 0=:C 16 H 33 (OH), also called Ethal, is ob- tained from spermaceti, a crystalline fatty substance found in peculiar cav- ities in the head of the sperm whale (Physeter macroccphalus}. This sub- stance consists of cetyl palmitate, C 32 H 64 2 , or C, 6 H 31 2 CjgHgg, and when heated for some time with solid potash, is resolved into potassium palmitate and cetyl alcohol : CwHsA.CrtHa + KOH = C 16 H 31 2 K + C 16 H 33 fOH). The cetyl alcohol is dissolved out from the fused mass by alcohol and ether, and purified by several crystallizations from ether. Cetyl alcohol, or ethal, is a white crystalline mass, which melts at about 50, and crystallizes by slow cooling in shining laminae. It has neither taste nor smell, is insoluble in water, but dissolves in all proportions in alcohol and ether. When heated it distils without decomposition. With sodium it gives off hydrogen and yields sodium cetylate, O^H^RO. It is not dissolved by aqueous alkalies ; but when heated with a mixture of pot- ash and lime, it gives off hydrogen, and is converted into palmitic acid: C^O + KOH = C, 6 H 31 2 K -f 2H 2 . Distilled with phosphorus pentachloride it yields cetyl chloride, C, 6 H 33 01, a limpid oily liquid, having a specific gravity of 0-8412 at 12, and distilling with partial decomposition at a temperature above 200. Cetyl iodide, CjeHggl, obtained by treating the alcohol with iodine and phosphorus, is a solid substance which melts at 22, dissolves in alcohol and ether, and crystallizes from alcohol in interlaced laminse. According to Heintz, cetyl alcohol, or ethal, prepared as above, is not a definite compound, but a mixture of sexdecyl alcohol, C 16 H !4 2 , with small quantities of three other alcohols of the same series, containing re- ALCOHOLS AND ETHERS. 543 spectively 12, 14, and 18 atoms of carbon, inasmuch as, when fused with potash-lime, it yields the corresponding fatty acids C n H 2n 2 . Ceryl Alcohol, C^H^O = C 27 H 65 (OH) ; also called Cerolic alcohol and Cerotin. This alcohol is obtained from Chinese wax or Pela, a secretion enveloping the branches of certain trees in China, and supposed to be pro- duced by the puncture of an insect. This wax consists mainly of ceryl cerotate, C 27 H 53 2 . C 27 H 55 , and is decomposed by fused potash in the same manner as spermaceti, yielding potassium cerotate and ceryl alcohol: C^O.K + C 27 H 56 (OH). On digesting the fused mass with boiling water, a solution of potassium cerotate is obtained, holding ceryl alcohol in suspension ; and by precipi- tating the cerotic acid with barium chloride and treating the resulting pre- cipitate with alcohol, the ceryl alcohol dissolves, and may be purified by repeated crystallization from alcohol or ether. It then forms a waxy sub- stance, melting at 97 C. (206 F.). Heated with potash-lime, it gives off hydrogen, and is converted into potassium cerotate. At very high temper- atures it distils, partly undecomposed, partly resolved into water and cero- tene, C 27 H 54 ; by this character it would appear to be related to the secon- dary alcohols. With sulphuric acid in excess, it forms hydrated neutral ceryl sulphate, (C 27 H 55 ) 2 S0 4 . OH 2 . Myricyl Alcohol, C 30 H 62 = C^, (OH). This alcohol, the highest known member of the series, C n H 2n + 2 O, is obtained from myricin, the por- tion of common bees'-wax which is insoluble in boiling alcohol. Myricin consists of myricyl palmitate, C 16 H 31 2 . C^II^, and when heated with potash is decomposed in the same manner as spermaceti and Chinese wax, yielding potassium palmitate and myricyl alcohol. On dissolving the pro- duct in water, precipitating with barium chloride, exhausting the precipi- tate with boiling alcohol, and dissolving the substance deposited from the alcohol in mineral naphtha, pure myricyl alcohol separates as a crystalline substance, having a silky lustre. When heated, it partly sublimes unal- tered, and is partly resolved (like ceryl alcohol) into water and melene, C 30 H 60 . With strong sulphuric acid it yields myricyl sulphate. Heated with potash lime, it gives off hydrogen, and is converted into potassium melissate : C 30 H 62 + KOH = C 30 H 59 2 K + 2H 2 . The mother-liquor from which the myricyl alcohol has crystallized out, as above mentioned, retains a small quantity of an isomeric alcohol, which melts at 72 C. (162 F.), and when treated with potash-lime yields an acid containing a smaller proportion of carbon. /?. Monatomic Alcohols, C n H 2n O, or C n II 2Il _ 1 OH. Two alcohols of this series are known, viz. : Vinyl alcohol, C 2 H 4 = C 2 IT 3 (OII). Allyl alcohol, C 3 H 4 == C 3 II 5 (OH). The first, discovered by Berthelot* in I860, is produced by combining ethine or acetylene with sulphuric acid, and distilling the product with water, just as in the preparation of ethyl alcohol from ethene : SOJIII -f C 2 H 2 = S0 4 H(C 2 H 3 ). Sulphuric acid. Ethine. Vinyl-sulphuric acid. * Comptes Rendus, i. 805. 544 ALCOHOLS AND ETHERS. S0 4 H(C 2 H 3 ) + HOH = S0 4 HH -f C 2 H 3 (OH) Viriyl-sul- Water. Sulphuric Vinyl pliuric acid. acid. alcohol. It is an easily decomposable liquid, having a highly pungent odor, some- what more volatile than water, soluble in 10 to 15 parts of that liquid, and precipitated from the solution by potassium carbonate. Its chemical reac- tions have not been much examined, but it is probably a secondary alcohol, CH 2 represented by the formula || . It is isomeric with acetic aldehyde CHOH and ethylene oxide (p. 484). The univalent radical vinyl, C 2 H 3 , which may be supposed to exist in it, is related to the trivalent radical ethenyl (p. 468), in the same manner as allyl to propenyl (see below). CH 2 Allyl Alcohol, C 3 H 6 , = C 3 H 6 (OH) = CH . This alcohol, discovered CH 2 OH by Cahours and Hofmann * in 1856, may be supposed to contain the univalent radical allyl, C 3 H 5 , derived from a saturated hydrocarbon, CH 2 CH, by abstraction of one atom of hydrogen, and isomeric with the triva- CH 3 lent radical propenyl, (C 3 H 2 ) /// , derived in like manner from the bivalent CH 2 radical propene, CH , or from the saturated hydrocarbon propane, CH 3 CH 2 , by abstraction of three atoms of hydrogen. Allyl and propenyl com- 1 CH 3 pounds, indeed, are easily converted one into the other by addition or sub- traction of two atoms of a monad element or radical. To obtain the alcohol, allyl iodide is first prepared by the action of phos- phorus tetriodide on propenyl alcohol (glycerin) : 2(C 8 H B )'"(OH) 8 + P 2 I 4 = 2C 3 H 5 I -f 2P(OH) 3 + I 2 . Propenyl Allyl Phosphorous alcohol. iodide. acid. The allyl iodide is next decomposed by silver oxalate, yielding allyl oxalate : 2C 3 H 6 I + C 2 4 Ag 2 = 2AgI + C 2 4 (C a H 5 ) 2 ; Allyl Silver Silver Allyl iodide. oxalate. iodide. oxalate. and the allyl oxalate is decomposed by ammonia, yielding oxamide and allyl alcohol: CAfCA), + 2NH 3 = (C 2 2 )"(NH 2 ) 2 + 2C 3 H 5 (OH) Allyl Ammonia. Oxamide. Allyl oxalate. alcohol. * Phil. Trans., 1837, p. 1. ALLYL ALCOHOLS AND ETHERS. 545 Ally! alcohol is a colorless liquid, having a pungent odor and a spirituous burning taste. It mixes in all proportions with water, common alcohol, and ether; boils at 103 C. (217 F.) ; burns with a brighter flame than common alcohol. Allyl alcohol is a primary alcohol, similar in all its ordinary reactions to ethyl alcohol. By oxidation in contact with platinum-black, or more quickly by treatment with potassium bichromate and sulphuric acid, it is converted into acrylic aldehyde (acrolein), C 3 H 5 0, and acrylic acid, C 3 H 4 2 , compounds related to it in the same manner as common aldehyde and acetic acid to ethyl alcohol. Heated with phosphoric oxide, it yields allylene, C 3 II 4 . With potassium and sodium it yields substitution-products. Strong sulphuric acid converts it into allyl-sulphuric acid. With the bromides and chlorides of phosphorus it yields allyl bromide, C 3 H 5 Br, and allyl chloride, CjjIIeCl. ALLYL BROMIDES. The monobromide, C 3 H 5 Br, prepared as just men- tioned, or by distilling propene bromide, C 3 H 6 Br 2 , with alcoholic potash, is a liquid of sp. gr. 1-47, and boiling at 62 C. (144 F.). A tribromide of allyl, C 3 H 5 Br 3 , is obtained by adding bromine to the mono-iodide in a vessel surrounded by a freezing mixture. It is a liquid of sp. gr. 1-436 at 23 C. (73 F.), boiling at 217 C. (422 F.), and solidifying when cooled below 10 C. (50 F.). It is isomeric with propenyl bromide or tribromhydrin, obtained by the action of phosphorus pentabromide on glycerin. A diallyl tetrabromide, C 6 H, Br 4 , is formed by the direct combination of diallyl (p. 487) with bromine ; it is a crystalline body, melting at 37. ALLYL IODIDES. The mono-iodide, C 3 H 5 I, obtained, as above described, by distilling glycerin with phosphorus tetriodide, is a liquid of sp. gr. 1-780 at 16 C. (60 F.), and boiling at 100 C. (320 F.), It is decom- posed by sodium, with formation of diallyl, C 6 H 10 . By the action of zinc or mercury and hydrochloric or dilute sulphuric acid, it is converted into propene (or allyl hydride) : 2C 3 H 5 I -f Zn 2 -f 2HC1 = ZnCl 2 -f ZnI 2 -f 2C 3 H 6 . Diallyl tetriodide, C 6 H, I 4 , is a crystalline body obtained by dissolving iodine in diallyl at a gentle heat. ALLYL-SULPHURIC ACID, S0 4 H(C 3 H 5 ), is produced by adding allyl alcohol to strong sulphuric acid. The solution, diluted with water and neutralized with barium carbonate, yields barium allylsulphate, (S0 4 ) 2 Ba // (C 3 H 5 ) 2 . ALLYL OXIDE, (C 3 H 5 ) 2 0, is produced by the action of allyl iodide on potassium allylate (the gelatinous mass obtained by dissolving potassium in allyl alcohol) : C 3 H 5 OK -f C,H 5 I == KI + (C 3 H 5 ) 2 0. It is a colorless liquid, boiling at 82. ALLYL SULPHIDE, (C 3 H 5 ) 2 S. This compound exists, together with a small quantity of allyl oxide, in volatile oil of garlic, and is formed arti- ficially by distilling allyl iodide with potassium monosulphide : 2C 3 H 5 I + K 2 S = 2KI + (C,II 6 ) 2 S. To prepare it from garlic, the sliced bulbs are distilled with water, and the crude oil thus obtained which is a mixture of the sulphide and oxide of allyl is subjected to the action of metallic potassium, renewed until it is no longer tarnished, whereby tho allyl oxide is decomposed, after which the sulphide may he obtained pure by redistillation. In this state it forms 46 * 546 ALCOHOLS AND ETHERS. a colorless liquid, lighter than water, of high refractive power, possessing in a high degree the peculiar odor of the plant, and capable of being dis- tilled without decomposition. Allyl sulphide, dissolved with alcohol and mixed with solutions of platinum, silver, and mercury, gives rise to crys- talline compounds, consisting of a double sulphide of allyl and the metal, either alone or mixed with a double chloride. Volatile oil of mustard consists of allyl sulphocyanate, C 3 H 6 . CNS, and will be described in connection with the sulphocyanic ethers. ALLYL SULPH-HYDRATE, or ALLYL MERCAPTAN, C 3 H 6 (SH), obtained by distilling allyl iodide with potassium sulph-hydrate, is a volatile oily liquid, having an odor like that of garlic oil, but more ethereal ; boiling at 90 C. (194 F.). It attacks mercuric oxide, like ethyl mercaptan, forming the compound (C 3 H 5 ) 2 S 2 Hg". y. Monatomic Alcohols, Cn.Hg^O, or C n H 2n _ 3 OH. Only one alcohol of this series is at present known, viz. : Camphol, C 10 H 18 = C 10 H 17 (OH). Of this compound there are several physical modifications, distinguished from one another by their action on polarized light. One variety, called JBorneol or JSorneo camphor, is obtained from Drya- balanops camphora, being found in cavities of the trunks of old trees of that species. It has a dextro-rotatory power = 34-4. A second, having a dextro-rotatory power of 44-9, is produced, together with camphic acid, by the action of alcoholic potash on common camphor, to which indeed camphol bears the same relation that ethyl alcohol bears to aldehyde : 2C 10 H 16 + OH 2 == C 10 H 18 + C }0 H 16 2 Camphor. Camphol. Camphic acid. A third variety, possessing a dextro-rotatory power of 4-5, is obtained by distilling amber with potash ; and a fourth, called lievo-camphol, which has a laevo-rotatory power of 33-4 (equal and opposite to that of borneol), is found in the alcohol produced in the fermentation of sugar from mad- der-root. Dextro-rotatory camphol, both natural and artificial, forms small trans- parent, colorless crystal.s, apparently having the form of regular hexago- nal prisms, insoluble in water, very soluble in alcohol and ether. It melts at 198 C. (388 F.), and boils at 212 C. (414 F.), distilling without altera- tion. Laevo-rotatory camphol forms crystalline laminae, or a white powder, sparingly soluble in water, easily in acetic acid, alcohol, and ether. Both varieties smell like pepper and common camphor. Camphol, distilled with phosphoric oxide, gives up water, and yields a hydrocarbon, C 10 H 16 , isomeric with turpentine oil. When boiled with nitric acid, it gives off two atoms of hydrogen, and is reduced to the correspond- ing aldehyde, viz., common or laurel camphor, C 10 H 16 0, which is dextro- or laevo-rotatory, according to the variety of camphol used. With other acids, camphol behaves like alcohols in general, forming ethers: thus, when heated in a sealed tube with strong hydrochloric acid, it forms camphor chloride, C 10 H 17 C1, a crystalline laevo-rotatory substance isomeric with hy- drochloride of turpentine oil, C 10 H 16 .HC1 (p. 489). With benzoic acid camphol forms camphyl benzoate, C 7 II 5 2 . C 10 H W . AROMATIC ALCOHOLS AND ETHERS. 547 408 F.), with weak soda-lye to separate hydrocarbons, supersaturating the alka- line liquid with sulphuric acid, and repeating the treatment with soda-lye and sulphuric acid, till the oil becomes perfectly soluble in the alkaline liquid. The oil thus obtained is a mixture of phenol and cresol, which are separated by fractional distillation. Cresol is a colorless, strongly refracting liquid, which boils at 203 C. (397 F.). It is slightly soluble in water, and mixes in all proportions with alcohol and ether. It reacts with potassium, phosphorus pentachloride, sulphuric acid, and nitric acid, in the same manner as phenol, forming analogously constituted compounds. Trinitrocresol, or Trinitrocresylic acid, C 7 H-(N0 2 ) 3 0, crystallizes in yellow needles like picric acid: its potassium- salt, C 7 H 4 K(N0 2 ) 3 0, in orange-red needles, moderately soluble in water. Crysol is isomeric with benzyl alcohol and with anisol : the difference of constitution of these three compounds is exhibited in the following dia- grams : H C C H H C C OH H-C C OCH S H J U nJ, U H Jj LH H C=rC CH 2 OH H C=C CH 3 H C=C H Benzyl alcohol. Cresol. Anisol. Eight-carbon Xylylic Phenols, C 8 TI 10 0. This formula may include two secondary alcohols, isomeric with xylyl alcohol, viz., Dimethyl-phenol C 6 H 3 (CH 3 ) 2 OH Ethyl-phenol C 6 H 4 (C 2 H 5 )OH. 47 554 ALCOHOLS AND ETHERS. A xylylic phenol is mentioned by Hugo Muller* as occurring in coal-tar. This is probably dimethyl phenol, inasmuch as products obtained by de- structive distillation have hitherto been found to contain only methyl deriva- tives of benzene. The portion of aloi'sol (a product obtained by distilling aloes with lime), which is soluble in potash, has, according to Rembold,f the composition of a xylylic phenol, and is, perhaps, identical with that occurring in coal-tar. Phlorol, an oily liquid obtained by the dry distillation of the barium salt of phloretic acid, C 9 H 10 3 , has also the composition C 8 H 10 0, and probably consists of ethyl-phenol. Its formation is represented by the equation, C 9 H 10 3 = C0 2 + C 8 H 10 0. Phlorol is a colorless, strongly refracting oil, having a specific gravity of 1-0374 at 12 C. (54 P.), and boiling between 190 and 200. It dis- solves in strong sulphuric acid, forming a sulpho-acid which yields a soluble barium salt. With chlorine it forms a substitution-product. It reacts vio- lently with strong nitric acid, forming the compound, C 8 H 7 (N0 2 ) 3 0. Ten-carbon Phenols. The formula, C 10 H 14 0, may evidently include a considerable number of phenols isomeric with cymyl alcohol (p. 549); only one of these, however, is known, viz., thymol, and even of this the exact constitution has not been ascertained. Thymol, C 10 H U 0, is a crystalline body, occurring (together with thymene, C 10 H 16 , and cymene, C, H 14 ) in the volatile oil of thyme (Thymus vulgaris), It sometimes crystallizes out spontaneously, and may in all cases be sepa- rated by agitating the oil with soda-solution, and supersaturating the alka- line liquid with hydrochloric acid. It is also obtained from the volatile oil of horse-mint (Monarda punctata), and from that of an East Indian umbelli- ferous plant called Ptychotis Ajowan. Thymol crystallizes in transparent rhomboi'dal plates, melting at 44. It has^a mild odor, peppery taste, and boils without decomposition at 220 C. (428 F.). It is distinguished from cymyl alcohol by yielding with oxidiz- ing agents, not cuminic acid, but thymoi'l, C, 2 H, 6 2 . With sodium it forms the compound, C, H J3 NaO, which absorbs carbon dioxide, forming the so- dium salt of thyinotic acid, C, H, 4 3 , or C, H, 4 O.C0 2 . Strong sulphuric acid converts thymol into thymylsulphuric acid, C, H 14 S0 4 . With bromine in sun- shine it yields pentabromothymol, C 10 H 9 Br 6 0; and with chlorine, Ci H,,Cl 3 0, or C, H 9 C1 5 0, according as the reaction takes place in the shade or in sun- shine ; both these, as well as the bromine-compound, are crystalline. There are two nitro-thymols, C, H, 2 (NO 2 ) 2 and C 10 H n (N0 2 ) 3 0, obtained by the action of nitric acid on thymyl-sulphuric acid. Both form potassium- salts, which crystallize in yellow or orange-yellow needles. e. Monatomic Alcohols, C n H 2n _ 8 0, or C n H 2n _ 7 (OH). Two only of these bodies are known, viz., cinnyl alcohol and cholesterin. Cinnyl Alcohol, Styryl Alcohol, or Styrone, C 9 H 10 0, or C 9 H 9 OH, is obtained by heating styracin or cinnyl ci-nnamate, C 9 H 9 (OC 9 H 7 0), (a compound con- tained in liquid storax and in balsam of Peru,) with caustic alkalies. It crystallizes in soft silky needles, having a sweet taste and an odor of hya- cinths, melting at 33, and volatilizing, without decomposition, at a higher * Zeitschrift fur Chemie, 1865, p. 271. f Ann, Ch. Pharm. cxxxviii. 186. DIATOMIC ALCOHOLS AND ETHERS. 555 temperature. It is moderately soluble in water, freely in alcohol and ether. By oxidizing agents it is converted into cinnamic aldehyde, C 9 H 8 0, and cin- namic acid, C 9 H 8 2 , being related to those compounds in the same manner as ethyl alcohol to acetic aldehyde and acetic acid. With fuming sulphuric acid it forms a sulpho-acid, C 9 H, S0 3 , the barium-salt of which is soluble in water. Cholesterin, C^H^O CggH^OH). This substance is found in small quantity in various parts of the animal system, as in the bile, the brain and nerves, and the blood: it forms the chief ingredient of biliary calculi, from which it is easily extracted by boiling the powdered gall-stones in strong alcohol, and filtering the solution while hot; on cooling, the choles- terin crystallizes in brilliant colorless plates. It is a fatty substance, in- soluble in water, tasteless and inodorous; it is freely soluble in boiling spirit and in ether, and crystallizes from the alcoholic solution in beautiful white laminae having a mother-of-pearl lustre. It melts at 137 0. (279 F.), and sublimes at 200 C. (392 F.). Heated with strong sulphuric acid, it gives up water, and yields a res- inous hydrocarbon, C 26 H 42 . With nitric acid it yields cholesteric acid, C 8 H 10 6 , together with other products. With chlorine and bromine it forms substitution-products. Heated to 200 with acetic, butyric, benzoic, and stearic acids, it forms compound ethers, thus: C 26 H 43 (OH) + C^OCOH) = C^OC^O) -f OH 3 Cholesterin. Stearic Cholesteryl acid. stearate. DIATOMIC ALCOHOLS AND ETHERS. The diatomic alcohols are derived from saturated hydrocarbons by sub- stitution of two equivalents of hydroxyl for two atoms of hydrogen, and may, therefore, be regarded as compounds of bivalent alcohol radicals with two equivalents of hydroxyl. Thus ethene alcohol, C 2 H 6 2 , may be formu- lated in either of the three following ways: CH 2 OH (C 2 H 4 )"(OH) 2 ; the first of which represents it as a derivative of methane, CH 4 ; the second CH 3 as a derivative of ethane | ; the third as a compound of ethene, C 2 H 4 , CH 3 with hydroxyl ; or as derived from a double molecule of water, H 2 (OH) 2 , by substitution of ethene for two atoms of hydrogen. Two series of these alcohols are known; the first derived from the par- affins, the second from the aromatic hydrocarbons. 1. Diatomic Alcohols, CJI^+.jO.,, or (C n H 2n )^(OH) 2 . The alcohols of this series are designated by the generic name of gly- cols.* They may be regarded as compounds of olefines with two equivalents of hydroxyl. The following are known : * This term, formed from the first syllable of flljicerin and the last of alcohol, indicates that tho compounds to which it is applied nrc internu'diato between the alcohols, commonly so called, and the glycerins or triatomic alcohols. 556 DIATOMIC ALCOHOLS AND ETHERS. Name. Formula. Boiling point. Ethene alcohol . . . C 2 H 6 2 = C 2 H 4 (OH) 2 197-5 C. (388 F.). Propene alcohol . . C 3 H 8 2 = C S H 6 (OH) 2 188-189 C. (370-372 F ) e 2 = C ACOH), 183-184 C. (361-365 *)! 5 H 12 2 = C 5 H 10 (OH) 2 177 C. (351 F.). Octene alcohol . . ". C 8 H 18 2 =: C 8 H 16 (OH) 2 235-240C. (455-464F.). Methene alcohol, CH 2 (OH) 2 , has not been obtained. The glycols are formed by the following processes : 1. By combining an olefine with bromine ; treating the resulting dibro- mide with an alcoholic solution of potassium acetate or with silver acetate, whereby it is converted into a diacetate of the olefine ; and decomposing this compound with solid potassium hydrate, whereby potassium acetate and a diatomic alcohol are formed, the latter of which may be distilled off. CH 2 Br CH 2 OC 2 H 3 -f 2AgOC 2 H 3 = 2AgBr + | CH 2 Br CH 2 OC 2 H 3 Ethene bromide. Silver acetate. Ethene diacetate. CH 2 OC 2 H 3 CH 2 OH 4- 2KOH = 2KOCJLO + I ' CH 2 OC 2 H 3 CH 2 OH Ethene di- Potassium Potassium Ethene acetate. hydrate. acetate. alcohol. 2. By treating a monochlorohydrate corresponding to a triatomic alcohol (a glycerin) with nascent hydrogen (evolved from water by sodium amal- gam) ; the chlorine is then replaced by hydrogen, and a diatomic alcohol results; thus, (C,H B )'"(OH) 2 C1 + HH = HC1 + (C,H e )'(OH) s Propenyl monochloro- Propene hydrate. alcohol. Properties. The glycols are colorless, inodorous, more or less viscid liquids, freely soluble in water and alcohol; ethene alcohol is but sparingly soluble in ether ; the rest dissolves easily in that liquid. The boiling points of ethene, propene, quartene, and quintene glycols, exhibit the singular anomaly of becoming lower as the molecular weight of the compound in- creases (see table, above) : octene glycol, however, exhibits a higher boil- ing point. This anomaly probably arises from difference of constitution in the successive terms of the series at present known, ethene glycol being a primary alcohol, whereas the higher numbers may be secondary or tertiary alcohols. Thus the ethene and propene glycols probably differ in consti- tution in the manner shown by the following formulae : CH 2 OH H 3 C CH 3 CH 2 OH HOCOH Ethene Propene alcohol. alcohol. The reactions of the higher glycols are not sufficiently known to decide this question : it is known, however, that propene alcohol heated with hy- driodic acid, yields isopropyl iodide. The chemical reactions of the glycols have been studied chiefly in the case of ethene alcohol. They are, for the most part, similar to those of the DIATOMIC ALCOHOLS AND ETHERS. 557 monatomic alcohols ; but inasmuch as the glycols contain two atoms of re- placeable hydrogen, or of hydroxyl, the reactions generally take place by two stages, yielding two series of products. 1. Ethene alcohol treated with nitric acid gives up 2 or 4 atoms of hydro- gen in exchange for oxygen, and is converted into glycollic, or oxalic acid, according as the action takes plaice at ordinary or at higher temperatures, CH 2 OH Glycol. CH 2 OH CO(OH) Glycollic acid. CO(OH) + 4 = 20H 2 + | 2 OH CO(OH) Ethene Oxalic acid, alcohol. CH 2 ( Under certain circumstances the corresponding aldehydes are also pro- COH duced, as glyoxal, \ , from ethene alcohol, by removal of four hydrogen- COH atoms without substitution. Ethene alcohol is also converted into oxalic acid by fusion with potash: C 2 H 6 2 Ethene alcohol. 2KOH = 4H, Potassium oxalate. Propene glycol, C 3 H 6 2 , is converted into lactic acid, C 3 H 6 3 , by slow oxida- tion in contact with platinum black. When heated with dilute nitric acid it yields glycollic acid, losing carbon as well as hydrogen; and concentrated nitric acid oxidizes it still further to oxalic acid. Quartene glycol, C 4 H 10 2 , is converted by slow oxidation with nitric acid into oxy butyric acid, C 4 H 8 3 , and when the action is accelerated by heat, into oxalic acid. Quintene glycol, CgH 12 2 , likewise yields oxybutyric acid by slow oxidation with dilute nitric acid. 2. Potassium and sodium eliminate one or two atoms of hydrogen from the glycols, and form substitution-products. Ethene alcohol is strongly attacked by sodium, yielding sodium ethcnate, C 2 H 6 Na0 2 ; and this compound, fused with excess of sodium, is converted into disodium ethcnate, C 2 H 4 Na 2 2 . These compounds, treated with monatomic alcoholic iodides, yield the alcoholic ethers of the glycols; thus, C 2 H 6 I = CH 2 ONa CH 2 OH Sodium Ethyl ethenate. iodide. Nal 2C 2 H 2 I = 2NaI -f CH 2 OC 2 H 6 CH 2 OH Sodium Ethyl iodide. ethenate. CH 2 OC 2 H 5 Disodium ethenate. Ethyl iodide. Sodium iodide. CH 2 OC 2 H, Diethyl ethenate. 3. Oxygen acids, heated with glycols in closed vessels, act upon them in the same manner as upon the monatomic alcohols, converting them into ethereal salts or compound ethers, mono-acid or di-acid, according to the pro- 47* 558 DIATOMIC ALCOHOLS AND ETHERS. HOC 2 H 3 Acetic acid. portions used. In the di-acid glycol-ethers, the two radicals by which the hydrogen is replaced may belong either to the same or to different acids ; e.g., CH 2 OH CH 2 OH ' ' " ' ' Ethene glycol. CH 2 OH CH 2 OH Ethene glycol. + 2HOC 2 H 3 = Acetic acid. CH 2 OC 2 H 3 Ethene mono- acetate. CH 2 OC 2 H 3 i CH 2 OCH0 Eth 23 ene. di-acetate. CH 2 OH -f HOC 4 H 7 = Ethene mono-acetate. Butyric acid. CH 2 OC 4 H 7 CH 2 OC 2 H 3 Ethene butyracetate. The halo'id acids act in the same manner as oxygen-acids, excepting that the reaction never goes beyond the first stage; e. g., CH 2 OH CHjOH Ethene alcohol. HC1 = OH 2 CH 2 C1 CH 2 OH Ethene chloro-hydrate. The bichlorinated, bibrominated ethers, &c., resulting from the substitu- tion of the remaining equivalent of hydroxyl by the haloid element, may, however, be obtained from the glycols by the action of the chlorides, bro- mides, and iodides of phosphorus; e. g., C 2 H 4 (OH) 2 + Ethene alcohol. 2PC1 6 = 2PC1 3 Phosphorus penta- chloride. Phosphorus oxy- chloride. -f 2HC1 -f C 2 H 4 C1 2 Hydrogen Ethene chloride. chloride. The same compounds are produced, as already observed, by direct combi- nation of chlorine, bromine, and iodine with the olefines. ETHENE CHLORIDE, C 2 H 4 C1 2 , has long been known by the name of Dutch liquid, having been discovered by four Dutch chemists in 1795. When equal measures of ethene gas and chlorine are mixed over water, absorption of the mixture takes place, and a yellowish oily liquid is produced, which collects upon the surface of the water, and ultimately sinks to the bottom in drops. It may be easily prepared, in quantity, by causing the two gases to combine in a glass globe, having a narrow neck at the lower part, dip- ping into a small bottle, destined to receive the product. The two gases are conveyed by separate tubes, and allowed to mix in the globe, the ethene gas being kept a little in excess. The chlorine should be washed with water, and the ethene passed through strong oil of vitriol, to remove vapor of ether: the presence of sulphurous and carbonic acids is not injurious. Combination takes place very rapidly, and the liquid product trickles down the sides of the globe into the receiver. When a considerable quantity has been collected, it is agitated, first with water, and afterward with concen- trated sulphuric acid, and, lastly, purified by distillation. DIATOMIC ALCOHOLS AND ETHERS. 559 Pure ethene chloride is a thin, colorless liquid, of agreeably fragrant odor, and sweet taste : it is slightly soluble in water, and readily so in alco- hol and ether. It is heavier than water, and boils when heated to 82-3 C. (180 F.): it is unaffected by oil of vitriol, or solid potassium hydrate. When inflamed, it burns with a Fig- 192. greenish, smoky light. When treated with an alco- holic solution of potash, it is slowly resolved into potassium chloride, which separates, and an exceed- ingly volatile substance, containing C 2 H 3 C1, whose vapor requires to be cooled down to 18 C. (0 F.) before it condenses. At this temperature it forms a limpid, colorless liquid. Chlorine is absorbed by this latter substance, and a compound is produced, which contains C 2 H 3 C1 3 : this is in turn decomposed by an alcoholic solution of potash into potassium chloride and another volatile liquid, C 2 H 2 C1 2 . This series of reactions is analogous to that already noticed in the case of the bromine compounds (p. 465). PRODUCTS OP THE ACTION OF CHLORINE ON ETHENE CHLORIDE ; CHLORIDES OF CARBON. Ethene chloride readily absorbs chlorine gas, and yields four new compounds, produced by the abstraction of successive portions of hydrogen, and its replacement by equiv- alent quantities of chlorine. Three out of the four are volatile liquids, containing respectively, C 2 H 3 C1 3 , C 2 H 2 C1 4 , and C 2 HC1 5 ; the fourth, C 2 C1 6 , in which the substitution of chlorine for hydrogen is complete, is the chloride of carbon long ago obtained by Faraday by putting Dutch liquid into a vessel of chlorine gas, and exposing it to sunshine. CC1 3 Carbon trichloride, C 3 CL, or I , the chlorine analogue of ethane, C 2 H 6 , CC1 3 is a white, crystalline substance, of aromatic odor, insoluble in water, but easily dissolved by alcohol and ether: it melts at 160 C. (320 F.), and boils at a temperature a little above. It burns with difficulty, and is not altered by distillation with aqueous or alcoholic potash. Its vapor, passed through a red-hot porcelain tube filled with fragments of glass or rock-crystal, is decomposed into free chlorine, and the dichlo- ride, C 2 C1 4 , analogous to ethene. This substance condenses in the form of a volatile, colorless liquid, which has a density of 1*55, and boils at 120 C. (248 F.). The density of its vapor is 5-82 (referred to air). When heated to 200 C. (392 F.) with potassium hydrate, it is completely con- verted into potassium chloride and oxalate, with evolution of hydrogen: C 2 C1 4 -f- GKOH = 4KC1 + -f- 20H, + H s It absorbs chlorine and bromine in sunshine, forming in the one case the trichloride, C 2 C1 6 , and on the other the chlorobromide, C 2 Cl 4 Br 2 , a white crystalline body resembling the trichloride. Carbon monochloride, C 2 C1 2 , analogous to ethine or acetylene, is obtained by passing the vapor of chloroform or of carbon-dichloride through a red- hot tube. It forms white needles subliming between 175 and 200 C. (347 and 392 F.). Carbon tetrachloride, CC1 4 , may also be described in this place, though it belongs to another series, being the chlorine analogue to marsh-uus. It is formed by passing the vapor of carbon bisulphide, together witli chlorine, through a red-hot porcelain tube. A mixture of sulphur chloride 560 DIATOMIC ALCOHOLS AND ETHERS. and carbon tetrachloride is formed, which is distilled with potash, where'by the chloride of sulphur is decomposed, and pure tetrachloride passes over. It is a colorless liquid of 1-56 sp. gr., and boils at 77? C (170 F.). The same compound is formed by exhausting the action of chlorine upon marsh- gas or methyl chloride in sunshine. An alcoholic solution of potash con- verts this compound into a mixture of potassium chloride and carbonate. ETHENE BROMIDE AND IODIDE, C 2 H 4 Br 2 and C 2 H 4 I 2 , are produced by bringing olefiant gas in contact with bromine and iodine. The bromide is a colorless liquid, of agreeable ethereal odor, and has a density of 2-16: it boils at 129-5 C. (265 F.), and solidifies when cooled to near 18. The iodide is a colorless, crystalline, volatile substance, of penetrating odor: it melts at 79 C. (174 F.), resists the action of sulphuric acid, but is decomposed by caustic potash. The action of bromine upon ethene bromide gives rise to the compound C 2 H 3 Br 3 , from which the other bromine-compounds corresponding to the chlorine bodies above mentioned may be obtained by treatment with bromine. Ethene bromide acts strongly upon an alcoholic solution of potassium sulph- hydrate, forming ethene sulph-hydrate or ethene mercaptan, C 2 H 4 (SH) 2 , a colorless oil, which is partially decomposed by distillation, and yields, with lead acetate, a yellow precipitate consisting of C 2 H 4 S 2 Pb. With potassium monosulphide, in like manner, ethene bromide forms ethene sulphide, C 2 H 4 S, which crystallizes in white prisms. The haloid ethers corresponding to the higher glycols are similar in their reactions to those of ethene alcohol. OXYGEN ETHERS OF THE GLYCOLS. The ethereal salts of the glycols (acetates, butyrates, &c.) are decomposed by alkalies in the same manner as those of the monatomic alcohols, reproducing the alcohols themselves: this is, in fact, the general mode of preparing the glycols (p. 556). But the mono-acid haloi'd ethers of the glycols are decomposed by alkalies in a different manner, giving up the elements of hydrochloric, hydriodic, or hydrobromic acids, and leaving an oxide of the diatomic alcohol-radical; thus, (C 2 H 4 )"C1(OH) + KOH = KC1 -f OH 2 -f (C 2 H 4 )"0 Ethene Ethene chloro-hydrate. oxide. Ethene oxide is isomeric with aldehyde and with vinyl alcohol (p. 484). It is a transparent colorless liquid, boiling at 13-5 C. (56 F.,) (aldehyde boils at 21 C. [70 F.]), and miscible in all proportions with water and with alcohol. When the aqueous solution is treated with sodium amalgam, in a vessel surrounded with a freezing mixture, the ethene oxide takes up hydrogen, and is converted into ethyl alcohol: C 2 H 4 + H 2 = C 2 H 6 0. Ethene oxide unites with ammonia in several proportions, forming the following basic compounds, all of which are syrupy liquids: Monoxethylenamine ..... C 2 H 4 O.NH 3 Dioxethylenamine (C 2 H 4 0) 2 .NH 3 Trioxethylenamine (C 2 H 4 0) 3 .NH 3 Tetroxethylenamine (C 2 H 4 0) 4 .NH 3 . This character distinguishes ethene oxide from aldehyde, which forms with ammonia a crystalline compound not possessing basic properties. A further distinction between these two isomeric bodies is, that aldehyde forms crystalline compounds with the acid sulphites of the alkali-metals, a property not possessed by ethene oxide. DIATOMIC ALCOHOLS AND ETHERS. 561 Ethene oxide is a powerful base, uniting directly with acids, precipitating magnesia from a solution of magnesium chloride at ordinary temperatures, and ferric oxide and alumina from their saline solutions, at 100 C. With and with hydrochloric acid, it forms ethene chlorohydrate, (C 2 H 4 ) // \ ,-., acetic acid, ethene acetohydrate, or monoacetate, (C 2 H 4 ) // | 0i j2 3 m it also unites with water in several proportions, forming glycol and other compounds to be noticed immediately. The oxygen-ethers 'of the higher glycols are not much known ; but they appear to be less disposed to combine with water and acids in proportion as their molecules become heavier; thus amylene oxide does not appear to reproduce amylene alcohol by combination with water. Polyethenic Alcohols. These are bodies which contain the elements of two or more molecules of ethene oxide combined with one molecule of water, and may be regarded as formed by the union of two or more mole- cules of glycol (mono-ethenic alcohol), with elimination of a number of water-molecules less by one than the number of glycol molecules which enter into combination; or as derived from three or more molecules of water, by substitution of ethene for the whole of the hydrogen except two atoms; thus, C 2 H 6 2 or (C 2 H 4 )"H 2 2 Monethenic alcohol (glycol). C 4 H lq 3 or (C 2 H 4 )'/ 2 H 2 ; Diethenic alcohol. C 2 H 4 O.OH 2 Ethene oxide. 2C 2 H 4 O.OH 2 Ethene oxide. 2C 2 H 6 OH 2 Glycol. C 6 H 14 4 or (C 2 H 4 )" 3 H 2 4 Triethenic alcohol. = 3C 2 H 4 O.OH 2 = 3C 2 H 6 20H 2 Ethene Glycol. oxide. Ethene oxide. Glycol. C 8 H 18 6 or(C 2 H 4 )" 4 H 2 5 Tetrethenic alcohol. Generally C 2n H 4n+2 O n+I or (C 2 H 4 )" n H a O n +, == nC 2 H 4 O.OH 2 = wC 2 H 6 (n 1)OH 2 n-ethenic alcohol. Ethene Glycol. oxide. The polyethenic alcohols are formed: 1. By heating ethene oxide with water in sealed tubes. In this manner Wurtz obtained diethenic alcohol together with monethenic, and a small quantity of tri-ethenic alcohol. 2. By heating ethene oxide with glycol in sealed tubes: this process yields the di- and tri-ethenic alcohols. 3. By heating glycol with ethene bro- mide in sealed tubes to 100-120 C. (212-248 F.). The first products of this reaction are diethenic alcohol, ethene bromo-hydrate and water : 8(C,H 4 )"H,O a Monethenic alcohol. bromide. alcohol. C 2 H 4 Br 2 = (C 2 H 4 )" 2 H 2 3 Ethene Diethenic 2(C 2 H 4 )"Br(OH) Ethene bromo- hydrate. OH and the other polyethenic alcohols are formed, each from the one next be- low it in the series, by the action of ethene bromo-hydrate, according to the general equation: (C 2 H 4 )" n H 2 O n+I + (n+ 2 . should ac- cordingly yield a series of triatomic alcohols of the form (C n H 2n _,) /// (OH) 3 , yiz. : Methenyl alcohol CH(OH) 3 Ethenyl alcohol C 2 H 3 (OH) S Propenyl alcohol C 3 H 5 (OH) 3 Quartenyl alcohol C 4 H 7 (OH) 3 Quintenyl alcohol C 6 H 9 (OH) 3 &c. &c. Of these, however, only two are known, viz., propenyl alcohol, or glycerin, and quintenyl alcohol, or amyl glycerin. There are also two or three bodies which may be regarded as triatomic phenols, represented by the general formula C n H, n _0 8 , or C n H 2n _ 9 (OH 3 ). Each triatomic alcohol, subjected to the action of acids, or of the chlo- rides, bromides, or iodides of phosphorus, may yield three classes of ethers, derived from it by substitution of a halogen element, or acid radical, for part or the whole of the hydroxyl; thus, from glycerin may be obtained the three hydrochloric ethers, C 3 H 5 C1(OH) 2 , C 3 H 6 C1 2 OH, C 3 H 5 C1 3 , and the three acetic ethers, C 3 H 5 (OC 2 H 3 0)(OH) 2 , C 3 H 5 (OC 2 H 3 0) 2 OH, and C 3 H 5 (OC 2 H 3 0) 3 . Methenyl Ethers. Methenyl alcohol, CH(OH) 3 , has not been obtained; but ethers are known which may be derived from it, by substitution of halogen elements for the three equivalents of hydroxyl, CHC1 3 for example. These compounds, which may also be directly derived from methane, are usually distinguished bynames ending in "form," to denote their relation to formic acid, (CH) /// 0(OH). METHENYL CHLORIDE OR CHLOROFORM, CHC1 3 . This compound is pro- duced: 1. Together with methene chloride, CH 2 C1 2 , when a mixture of chlorine and gaseous methyl chloride is exposed to the sun's rays. 2. By the action of alkalies on chloral (p. 517): C 2 HC1 3 -f KOH = CHC1 3 + CH0 2 K Chloral. Cnloro- Potassium form. formate. 3. By boiling trichloracetic acid with aqueous alkalies: C 2 HC1 3 2 -f 2KOH = CHC1 3 -f C0 3 K 2 -f OH 2 Trichlor- Chloro- Potassium acetic acid. form. carbonate. 4. By the action of nascent hydrogen on carbon tetrachloride : CC1 4 + H 2 = HC1 -f CHCL,. 48 566 TRIATOMIC ALCOHOLS AND ETHERS. 5. By the action of hypochlorites, or of chlorine in presence of alkalies, on various organic substances, as methyl, ethyl, and amyl alcohols, acetic acid, acetone, &c. The reaction is complicated, giving rise to several other products ; with common alcohol and calcium hypochlorite the principal reaction appears to be 2C 2 H 6 + 5Cl 2 2 Ca = 2CHCL, + 2C0 3 Ca -f 2CaCl 2 -f CaH 2 2 -f 40 H 2 . Chloroform is prepared on the large scale by cautiously distilling together good commercial chloride of lime, water, and alcohol. The whole product distils over with the first portions of water, so that the operation may be soon interrupted with advantage. The chloroform, which constitutes the oily portion of the distillate, is purified by agitation with water, desicca- tion with calcium chloride, and distillation in a water-bath. Chloroform is a thin, colorless liquid of agreeable ethereal odor, much resembling that of Dutch liquid, and of a sweetish taste. Its density is 1-48, and it boils at 61 C. (142 F.): the density of its vapor (compared with air) is 4-20. Chloroform is difficult to kindle, and burns with a green- ish flame. It is nearly insoluble in water, and is not affected by concen- trated sulphuric acid. When boiled with aqueous potash in a closed tube, it is converted into potassium chloride and formate : CHC1 3 + 4HOK = 3KC1 + CHO(OK) + 20H 2 Chloroform. Potassium Potassium hydrate. formate. Chloroform is well known for its remarkable effects upon the animal system, in producing temporary insensibility to pain when its vapor is inhaled. BROMOFORM, CHBr 3 , is a heavy, volatile liquid, prepared by the simul- taneous action of bromine and aqueous alkalies on alcohol, wood-spirit, and acetone. It is converted by caustic potash into potassium bromide and formate. IODOFORM, CHI 3 , is a solid, yellow, crystallizable substance, easily ob- tained by adding alcoholic solution of potash to tincture of iodine, avoiding excess, evaporating the whole to dryness, and treating the residue with water. It is nearly insoluble in water, but dissolves in alcohol, and is de- composed by alkalies in the same manner as the preceding compounds. Bromine converts it into bromiodoform, CHBr 2 I, a colorless liquid which solidifies at 0. lodoform distilled with phosphorus pentachloride or mer- curic chloride, is converted into chloriodoform, CHC1 2 I, a colorless liquid of sp. gr. 1-96, which does not solidify at any temperature. Nitroform, CH(N0 2 ) 3 , a body analogous in composition to the methenyl ethers, will be considered in connection with the cyanogen compounds. Propenyl Alcohol, or Glycerin, CH 2 OH (OH | C 3 H 8 3 = (C 3 H 5 )'"JOH or CHOH (OH CH 2 OH This compound is obtained by the action of alkalies on natural fats, which are, in fact, the propenylic ethers of certain fatty acids; thus stearin, one of the constituents of mutton suet, consists of propenyl tri- stearate, (C 3 H 5 ) /// (OC 18 H 35 0) 3 , a compound derivable from glycerin itself, by substitution of stearyl, C ]8 H 35 0, for hydrogen. Now, when stearin is boiled with a caustic alkali, it is converted into a stearate of the alkali- metal and glycerin, thus ; GLYCEKIlSr. 567 C 3 H 6 (OC 1? H 35 0) 3 + 3KOH = 3KOC 18 H 35 -f C,H 6 (OH) 8 Stearin. Potassium Glycerin. stearate. A similar reaction takes place when any other similarly constituted fat is treated with a caustic alkali. The metallic salts of the fatty acids thus obtained are the well-known bodies called soaps, and the process is called saponification ; this term, originally restricted to actual soap-making, has been extended to all cases of the resolution of a compound ether into an acid and an alcohol, such, for example, as the conversion of ethyl acetate into acetic acid and ethyl alcohol by the action of alcoholic potash. Glycerin was originally obtained by heating together olive or other suit- able oil, lead oxide, and water, as in the manufacture of common lead-plaster ; an insoluble soap of lead is thereby formed, while the glycerin remains in the aqueous liquid. The latter is treated with sulphuretted hydrogen, digested with animal charcoal, filtered and evaporated in a vacuum at the temperature of the air. Glycerin is now produced in very large quantity and perfect purity in the decomposition of fatty substances by means of overheated steam, a process which Mr. George Wilson has lately introduced into the manufacture of candles.* In this reaction a fatty acid and glycerin are produced by assimilation of the elements of water ; they are carried over by the excess of steam in a state of mechanical mixture, which rapidly separates into two layers in the receiver. The reaction is exactly similar to that which takes place when a caustic alkali is used to effect the saponification, e. g. : C 3 H 5 (OC 1? H 35 0) 3 + 30H 2 = SHOCjgH^O + C 3 H 5 (OH) 3 Stearin. Stearic acid. Glycerin. Glycerin may also be produced from propenyl bromide, (C < H i ) /// Bjv a compound formed, as already observed, by the action of bromine on allyl iodide, C 3 H 5 I. The process consists in converting the propenyl-bromide into propenyl triacetate, (C 3 H 6 ) /// (OC 2 H 3 0) 3 , by the action of silver acetate, and decomposing this compound ether with potash. This mode of formation must not, however, be regarded as an actual synthesis of glycerin from compounds of simpler constitution ; for the allyl-compounds are themselves prepared from glycerin (p. 544), and have never yet been obtained from any other source. . Glycerin is a nearly colorless and very viscid liquid, of sp. gr. 1-27, which cannot be made to crystallize. It has an intensely sweet taste, and mixes with water in all proportions : its solution does not undergo the alcoholic fermentation, but when mixed with yeast and kept in a warm place, it is gradually converted into propionic acid. Glycerin has no action on vege- table colors. Exposed to heat, it volatilizes in part, darkens, and decom- poses, giving off', amongst other products, a substance called acrolein, C 3 H 4 0, having an intensely pungent odor. Concentrated nitric acid converts glycerin into glyccric acid, C 3 H 6 4 . an acid related to glycerin in the same manner as glycollic acid to glycol, and acetic acid to ethyl alcohol ; being formed from it by substitution of oxygen for two atoms of hydrogen in immediate relation to hydroxyl; thus: CH 2 OH CH.OH CHOH -f O a = OH 2 + CHOH CH 2 OH COOH Glycerin. Glyceric acid. * By Tilghman's process, an emulsion of water and fat is passed under pressure through a highly heated tul>e, and alter delivery at tho extreme end separates into a solution of glycerin and the fatty acid. 11. B. 568 TKIATOMIC ALCOHOLS AND ETHERS. The formula of glycerin indicates the possibility of effecting a second sub- stitution of the same kind, which would yield diglyceric acid, C 3 H 4 6 , but this acid has not been actually obtained. Glycerin, treated with a mixture of strong nitric and sulphuric acids, forms nitroglycerin, C 3 H 5 (N0 2 ) 3 3 , a heavy oily liquid which explodes power- fully by percussion. It is much used for blasting in mines and quarries, but is very dangerous to handle, and has given rise to several fatal ac- cidents. Glycerin combines with the elements of sulphuric acid, forming a sul- phogly eerie acid, C 3 H 8 3 S0 3 , w r hich gives soluble salts with lime, baryta, and lead oxide. Monatomic oxygen acids (acetic, benzoic, stearic, &c.), heated in sealed tubes with glycerin, yield compound ethers, in which 1, 2, or 3 hydrogen- atoms of the glycerin are replaced by an equivalent quantity of the acid radical, according to the proportions employed. The resulting compound ethers are denoted by names ending in in ; thus : C 3 H 5 (OH) 3 + HOC 2 H 3 = C 3 H 5 (OH) 2 OC 2 H 3 + OH 2 Glycerin. Acetic acid. Mono-acetin. C 3 H 5 (OH) 3 -j- 2HOC 2 H 3 = C 3 H 5 (OH)(OC 2 H 3 0) 2 + 20H 2 Glycerin. Acetic acid. Diacetin. C 3 H 5 (OH) 3 + 8HOC,H,0 = C 3 H 5 (OC 2 H 3 0) 3 -f 30H 2 Glycerin. Acetic acid. Triacetin. The glyceric ethers or glycerides thus produced are, for the most part, oily liquids increasing in viscidity as the acid from which they are formed has a higher molecular weight; those formed from the higher members of the fatty acid series, C n H 2n 2 (such as palmitic and stearic acids), are solid fats. Some of the triacid glycerides, produced artificially in the way just mentioned, are identical with natural fats occurring in the bodies of plants and animals ; thus tristearin is identical with the stearin of beef and mutton suet; triolein with the olein of olive oil, &c. Hydrochloric and hydrobromic acids act upon glycerin in the same manner as oxygen acids, excepting that the reaction always stops at the second stage (just as in the action of these acids on the glycols it stops at the first stage). The ethers thus formed are called chlorhydrins and bromhydrins, &c., e. nir. acid, and its origin ascribed to the reaction of the alkali on the ulmin or humus of the soil. It is known that, these bodies differ exceedingly in composition: they arc too indefinite to admit of ready investigation. 586 HEXATOMIC ALCOHOLS AND ETHERS. C 12 H 22 O n + 6 = 2C 6 H 10 8 OH 2 Sugar. Saccharic acid. At the boiling heat, the product consists chiefly of oxalic acid. Very strong nitric acid, or a mixture of strong nitric and sulphuric acids, con- verts sugar into nitrosacc/tarose, probably C 12 H 18 (N0 2 ) 4 O ir Sugar is like- wise oxidized by chloride of lime, but the products have not been examined. 4. Cane-sugar does not turn brown when triturated with alkalies, a character by which it is distinguished from glucose : it combines with them, however, forming compounds called sucrates. By boiling with potash- lye it is decomposed, but much more slowly than the glucoses. Potassium- and Sodium-compounds of cane-sugar, C 12 H 21 KO n and C ]2 TI 21 NaO u , are formed, as gelatinous precipitates, on mixing an alcoholic solu- tion of cane-sugar with potash- or soda-lye. A barium-compound, C 12 H 20 Ba // O n . H 2 0, or C 12 H 22 U . Ba // 0, is obtained, as a crystalline precipitate, on adding hydrate or sulphide of barium to an aqueous solution of sugar. It may be crystallized from boiling water, but is insoluble in alcohol. Calcium-compounds. Lime dissolves in sugar-water much more readily than in pure water. The solution has a bitter taste, and is completely but slowly precipitated by carbonic acid. There are three or four of these compounds, which may be approximately represented by the following for- mulae : 1. C 12 H 22 O n . Ca"0. 3. 2. 2C u H a O u .3Ca"0(?) Magnesia and lead oxide are also dissolved by sugar-water. A crystalline lead-compound, C 12 H 18 Pb // 2 11 , is precipitated on mixing sugar-water with neutral lead-acetate and ammonia. Sugar also forms, with sodium chloride, a crystalline compound contain- ing C, 2 H 22 O n . NaCl. Cane-sugar is not directly fermentable, but when its dilute aqueous solu- tion is mixed with yeast, and exposed to a warm atmosphere, it is first resolved into a mixture of dextrose and levulose (p. 577), which then enter into fermentation, yielding alcohol and carbon dioxide. Paras accharose, Ci 2 H 22 O n . This is an isomer of cane-sugar, produced, according to Jodin,* by spontaneous fermentation. An aqueous solution of cane-sugar containing ammonium phosphate left to itself for three months in summer, yielded, under circumstances not further specified, a crystallizable sugar, isomeric with saccharose, together with an amorphous sugar having the composition of a glucose, both dextro-rotatory. Para- saccharose is very soluble in water, nearly insoluble in alcohol of 90 per cent. Its specific rotatory power at 10 = -f- 108, appearing to increase a little with rise of temperature. It does not melt at 100, but becomes colored, and appears to decompose. It reduces an alkaline cupric .solution, but only half as strongly as dextro-glucose. It is not perceptibly altered by dilute sulphuric acid, even at 100 ; hydrochloric acid weakens its rota- tory power, turns the solution brown, and heightens its reducing power for cupric oxide. Melitose, C, 2 IT 22 0,,. A kind of sugar obtained from the manna which falls in opaque drops from various species of Eucalyptus growing in Tas- mania. It is extracted by water, and crystallizes in extremely thin inter- laced needles, having a slightly saccharine taste. The crystals of melitose are hydrated, containing C, 2 II 22 O n . 30II 2 . They give off 2 atoms water at 100, and become anhydrous at 130 C. (266 F.). * Comptes Rendus, torn. liii. p. 1252 ; liv. 720. MELEZITOSE TREHALOSE MYCOSE MILK-SUGAK. 587 They dissolve in 9 parts of cold water, very easily in boiling water, and dissolve also in boiling alcohol more freely than mannite. The alcoholic solution yields small but well-developed crystals. The aqueous solution turns the plane of polarization to the right : for the transition tint [a] = + 102. Melitose, heated with dilute sulphuric acid, is resolved into a fermentable sugar (probably dextroglucose), and non-fermentable eucalyn (p. 578). Melitose ferments in contact with yeast, but is resolved, in the first in- stance, into glucose and eucalyn. It does not reduce an alkaline cupric solution, and is not altered by boiling with dilute alkalies or with baryta- water. It is oxidized by nitric acid, yielding a certain quantity of mucic acid, together with a large quantity of oxalic acid. Melezitose, C 12 H 22 O n . This variety of sugar is found in the so-called manna of Briangon, which exudes from the young shoots of the larch (Larix Europsea). The manna is exhausted with alcohol, which, when evap- orated, yields melezitose in very small, hard, shining efflorescent crystals, which give off 4 per cent, of water when heated, melt below 140 without further alteration, forming a liquid which solidifies to a glass on cooling. Melezitose is dextro-rotatory; [a] = -(- 94-1. It dissolves easily in water, is nearly insoluble in cold, slightly soluble in boiling alcohol. Melezitose decomposes at about 200 C. (392 F.). It is carbonized by cold strong sulphuric acid, quickly turns brown with boiling hydrochloric acid, and forms oxalic acid with nitric acid. By an hour's boiling with dilute sulphuric acid, it is converted into glucose. In contact with yeast it passes slowly, or sometimes not at all, into vinous fermentation. It is not altered at 100 by aqueous alkalies, and scarcely by potassio-cupric tar- trate. Trehalose, C 12 H 22 0,, . 20H 2 * is obtained from Trehala manna, the produce of a species of Echinops growing in the East, by extraction with boiling alcohol. It forms shining rhombic crystals, containing C, 2 H 22 O n . 20H 2 , which melt when quickly heated to 109 C. (228 F.) ; but if slowly heated give off their water even below 100. It has a strongly saccharine taste, dissolves easily in water and in boiling alcohol, but is insoluble in ether. The aqueous solution is dextro-rotatory ; [] -}- 199. By several hours' boiling with dilute sulphuric acid, it is converted into dextroglucose. With strong nitric acid it forms a detonating nitro-com- pound ; heated with dilute nitric acid it yields oxalic acid. In contact with yeast it passes slowly and imperfectly into alcoholic fermentation. It is not altered by boiling with alkalies, and does not reduce cuprous oxide from alkaline cupric solutions. Heated with acetic or butyric acid, it yields compounds not distinguishable from those which are formed in like man- ner from dextroglucose (p. 577). Mycose, C 12 H 22 O n . 20H 2 , is a kind of sugar very much like trehalose, obtained from ergot of rye by precipitating the aqueous extract of the fungus with basic lead acetate, removing the lead from the filtrate by sulph-hydric acid, evaporating to a syrup, and leaving the liquid to crys- tallize. It differs from trehalose only in possessing a somewhat feebler rotatory power; [a] = -4- 192-5, and in not being completely dehydrated at 100. Milk-sugar, Lactin, or Lactose, C^Tl^O^ . OH 2 . This kind of sugar is an important constituent of milk; it is obtained in large quantities by evap- orating whey to a syrupy state, and purifying the lactose, which slowly crystallizes out, with animal charcoal. It forms white, translucent, four- sided, trimetric prisms, of great hardness. It is slow and difficult of solu- tion in cold water, requiring for that purpose 5 or 6 times its weight : it 588 HEXATOMIC ALCOHOLS AND ETHERS. lias a faint, sweet taste, and in the solid state feels gritty between the teeth. When heated, it loses water, and at a high temperature blackens and de- composes. Milk-sugar combines with bases,,forming compounds which have an alkaline reaction, and are easily decomposed. Dilute acids con- vert it into galactose -{p. 578). Milk-sugar, when distilled with oxidizing mixtures, such as sulphuric acid arid manganese dioxide, yields formic acid. With nitric acid, it forms mucic, saccharic, tartaric, and a small quantity of racemic acid, and finally oxalic acid. Very strong nitric acid, or a mixture of nitric and sulphuric acids, converts milk-sugar into a crystalline substitution-product called nitro-lactin. Milk-sugar is not brought immediately by yeast into the state of alco- holic fermentation; but when it is left for some time in contact with yeast, fermentation gradually sets in. When cheese or gluten is used as the fer- ment, the milk-sugar is converted into lactic acid. Alcohol is, however, always formed at the same time, especially if no chalk is added to neutral- ize the acid as it forms ; the quantity of alcohol formed is greater also as the solution is more dilute. Gum. Gum-arabic, which is the produce of several species of acacia, may be taken as the most perfect type of this class of bodies. In its purest and finest condition, it forms white or slightly yellowish irregular masses, which are destitute of crystalline structure, and break with a smooth cou- choi'dal fracture. It is soluble in cold water, forming a viscid, adhesive, tasteless solution, from which the pure soluble gummy principle, or arabin, is precipitated by alcohol, and by basic lead acetate, but not by the neutral acetate. Arabin is composed of C 12 H 22 O n , and is consequently isomeric with cane-sugar. Mucilage, so abundant in linseed, in the roots of the mallow, in salep, the fleshy root of Orchis mascula, and in other plants, diifers in some respects from gum-arabic, although it agrees in the property of dissolving in cold water. The solution is less transparent than that of gum, and is precipi- tated by neutral lead acetate. Gum-tragacanth is chiefly composed of a kind of mucilage to which the name bassorin has been given ; it refuses to dissolve in water, merely softening and assuming a gelatinous aspect. It is dissoved by caustic alcali. Cerasin is the insoluble portion of the gum of the cherry-tree ; it resembles bassorin. The composition of these vari- ous substances has been carefully examined by Schmidt, who finds that it closely agrees with that of starch. Mucilage invariably contains hydrogen and oxygen in the proportion in which they form water, and when treated with acid, yields glucose. Pectin, or the jelly of fruits, is, in its physical properties, closely allied to the foregoing bodies. It may be extracted from various vegetable juices by precipitation with alcohol. It forms when moist a transparent jelly, which is soluble in water, tasteless, and dries up to a translucent mass. It is to this substance that the firm consistence of currant and other fruit- jellies is ascribed. According to Fre"my, the composition of pectin is C 32 H 48 32 . By ebullition with water and with dilute acids it is changed into two isomeric modifications, called paropectin and metopectin. In contact with bases, these three substances are converted intopectic acid, C 16 H 22 C 15 (?), which closely resembles pectin, except that it possesses feeble acid proper- ties, and is insoluble in water. By long boiling with caustic alkali, a fur- ther change is produced, and metopectic acid, C 24 H 32 27 (?), is formed, which does not gelatinize. The metallic pectates and metapectates are uncrystal- lizable. Much doubt still exists respecting the composition of the various bodies of the pectin group ; but from the analyses hitherto made, they do not appear to contain hydrogen and oxygen in the proportion to form water and therefore scarcely belong to the sugar and starch group. uu OXYGEN-ETHERS STAKCH. 589 OXYGEN-ETHERS, OR ANHYDRIDES, OF THE POLYGLUCOSIC ALCOHOLS. These compounds, which are important constituents of the vegetable or- ganism, may be derived from glucose and the polyglucosic alcohols by abstraction of a molecule of water: C 6 H Ia 6 - H 2 Glucose. CwH-jAj H 2 = CuH^Ojo, or 2C 6 H 10 5 , Diglucosic alcohol. CwH^O,, H 2 = C^Otf, or 3C 6 H 10 5 , Triglucosio alcohol. C 6 JI 10 n+ 2 b 5 n+i H 2 = C 6n H 10n 5 All these bodies are therefore isomeric or polymeric one with the other. Their compounds with metallic oxides, &c., have not been sufficiently in- vestigated to fix their exact molecular weight, or to determine in each case the value of n; but from the mode of conversion of starch into glu- cose, and the constitution of certain substitution-products obtained by the action of nitric acid on cellulose, it appears most probable that in these bodies n=3. Starch, nC 6 H 10 6 , probably C 18 H 30 ]5 , also called Fecultt and Amidine. This is one of the most important and widely diffused of the vegetable prox- imate principles, being found to a greater or less extent in every plant. Tt is most abundant in certain roots and tubers, and in soft stems : seeds often contain it in large quantity. From these sources the starch can be obtained by rasping or grinding the vegetable structure to pulp, and washing the mass upon a sieve, by which the torn cellular tissue is retained, while the starch passes through with the liquid, and eventually settles down from the latter as a soft, white, insoluble powder, which may be washed with cold water, and dried at a very gentle heat. Potatoes treated in this manner yield a large -fig- 193. proportion of starch. Starch from grain may be prepared in the same manner, by mixing the meal with water to a paste, and washing the mass upon a sieve : a nearly white, insoluble substance called gluten is then left, containing a large proportion of nitrogen. The gluten of wheat-flour is extremely tenacious and elastic. The value of meal as an article of food greatly depends upon this substance. Starch from grain is commonly manufactured on the large scale by steeping the material in water for a consider- able time, when the lactic acid, always devel- oped under such circumstances from the sugar of the seed, disintegrates, and in part dissolves the azotized matter, thereby greatly facilitating the mechanical separation of that which re- mains. A still more easy and successful process has lately been introduced, in which a very dilute solution of caustic soda, containing about 200 grains of alkali to a gallon of liquid, is employed with the same view. Excellent starch is thus prepared from rice. Starch is insoluble in cold water, as 50 590 HEXATOMIC ALCOHOLS AND ETHERS. indeed its mode of preparation sufficiently shows : it is equally insoluble in alcohol and other liquids, which do not effect its decomposition. To the naked eye it presents the appearance of a soft, white, and often glis- tening powder : under the microscope it is seen to be altogether destitute of crystalline structure, but to possess, on the contrary, a kind of organi- zation, being made up of multitudes of little rounded transparent bodies, upon each of which a series of depressed parallel rings, surrounding a central spot or hilum, may often be traced. The starch-granules from dif- ferent plants vary both in magnitude and form: those from the Canna coc- cinea, or tons les mois, and potato being lai-gest ; and those from wheat, and the cereals in general, very much smaller. Figure 193 will serve to con- vey an idea of the appearance of the granules of potato-starch, highly mag- nified. When a mixture of starch and water is heated to near the boiling-point of the latter, the granules burst and disappear, producing, if the propor- tion of starch be considerable, a thick gelatinous mass, very slightly opal- escent, from the shreds of fine membrane, the envelope of each separate granule. By the addition of a large quantity of water, this gelatinous starch, or amidin, may be so far diluted as to pass in great measure through filter-paper. It is very doubtful, however, how far the substance itself is really soluble in water, at least when cold; it is more likely to be merely suspended in the liquid in the form of a swollen, transparent, and insoluble jelly, of extreme tenuity. Gelatinous starch, exposed in a thin layer to a dry atmosphere, becomes converted into a yellowish, horny substance, like gum, which, when put into water, again softens and swells. Thin gelatinous starch is precipitated by many of the metallic oxides, as lime, baryta, and lead oxide ; also by a large addition of alcohol. In- fusion of galls throws down a copious yellowish precipitate containing tan- nic acid, which re-dissolves when the solution is heated. By far the most characteristic reaction, however, is that with free iodine, which forms with starch a deep indigo-blue compound, which appears to dissolve in pure water, although it is insoluble in solutions containing free acid or saline matter. The blue liquid has its color destroyed by heat, temporarily if the heat be quickly withdrawn, and permanently if the boiling be long con- tinued, in which case the compound is decomposed and the iodine volatil- ized. Dry starch, put into iodine-water, acquires a purplish-black color. The unaltered and the gelatinous starch, in a dried state, have the same empirical formula, C 6 H 10 5 . A compound of starch and lead oxide was found to contain, when dried at 100, C 6 H 10 5 . PbO, or C^H^O^ . 3PbO. DEXTRIN. When gelatinous starch is boiled with a small quantity of di- lute sulphuric, hydrochloric, or indeed, almost any acid, it speedily loses its consistency, and becomes thin and limpid, from having suffered conver- sion into a soluble gum-like substance, called dextrin, on account of its dextro-rotatory action on polarized light. The experiment is most con- veniently made with sulphuric acid, which may be afterward withdrawn by saturation with chalk. The liquid filtered from the nearly insoluble gypsum, may then be evaporated to dryness in a water-bath. The result is a gum-like mass, destitute of crystalline structure, soluble in cold water, precipitable from its solution by alcohol, and capable of combining with lead oxide. When the ebullition with the dilute acid is continued for a considerable time, the dextrin first formed undergoes a further change, and becomes converted into dextro-glucose, which can be thus artificially produced with the greatest facility. The length of time required for this remarkable change depends upon the quantity of acid present ; if the latter be very small, it is necessary to continue the boiling many successive hours, re- STARCH. 591 placing the water which evaporates. With a larger proportion of acid, the conversion is much more speedy. A mixture of 15 parts of potato-starch, 60 parts water, and parts sulphuric acid, may be kept boiling for about four hours ; the liquid neutralized with chalk, filtered, and rapidly evapo- rated to a small bulk. By digestion with animal charcoal and a second filtration, much of the color will be removed, after which the solution may be boiled down to a thin syrup and left to crystallize : in the course of a few days it solidifies to a mass of glucose. There is another method of preparing this substance from starch which deserves particular notice. Germinating seeds, and buds in the act of development, are found to con- tain a small quantity of a peculiar azotized substance, called diastase ; formed at this particular period from the gluten of vegetable albuminous matter. This substance possesses the same curious property of effecting the conver- sion of starch into dextrin and glucose, and at a much lower temperature than that of ebullition. When a little infusion of malt, or germinated bar- ley, in tepid water, is mixed with a large quantity of thick gelatinous starch, and the whole maintained at about 71, complete liquefaction takes place in the space of a few minutes from the production of dextrin and glucose. If a greater degree of heat be employed, the diastase is coagulated and rendered insoluble and inactive. Very little is known respecting diastase itself; it seems very much to resemble vegetable albumin, but has never been obtained in a state of purity. The change of starch or dextrin into sugar, whether produced by the action of dilute acid or by diastase, takes place quite independently of the oxygen of the air, and is unaccompanied by any secondary product. The acid takes no direct part in the reaction; it may, if not volatile, be all withdrawn without loss after the experiment. The whole reaction lies between the starch and the elements of water, a fixation of the latter oc- curring in the new product, as will be seen on comparing the composition of starch and glucose. Dextrin itself has exactly the same composition as the original starch. It was formerly supposed that, in the action of acids or of disastase upon starch, the starch is first converted into dextrin by a mere alteration of physical structure, and that the dextrin then takes up the elements of water, and is converted into glucose, this second stage of the process oc- cupying a much longer time than the first; but from recent experiments by Musculus* it appears that both dextrin and glucose are produced at the very commencement of the reaction, and always in the proportion of 1 molecule of glucose to 2 molecules of dextrin, whence it may be inferred that the molecule of starch contains C 18 H 30 15 , and that it is resolved into glucose and dextrin by taking up a molecule of water: C 18 H 30 15 + OH 2 = C.H W 6 + 2C a H 10 6 Starch. Glucose. Dextrin. When the conversion is effected by a dilute acid, the dextrin is, after sev- eral hours' boiling, completely converted into glucose, which is therefore the sole ultimate product of the reaction. But when diastase is used as the converting agent, the production of glucose goes on only so long as there is any unaltered starch still present, the dextrin undergoing no fur- ther alteration. Dextrin is used in the arts as a substitute for gum ; it is sometimes made in the manner above described, but more frequently by heating dry potato- starch to 400 C. (752 F.), by which it acquires a yellowish tint and be- comes soluble in cold water. It is sold in this state under the name of Britith dun. Starch is an important article of food, especially when associated, as in * Comptes Rendus, 1. 785; liv. 191; Ann. Ch. Phys. [3], Ix. 208; [4], vi. 177. 592 HEXATOMTC ALCOHOLS AND ETHERS, ordinary meal, with albuminous substances. Arrowroot, and the fecula of the Canna coccinea, are very pure varieties, employed as articles of diet; arrowroot is obtained from the Maranta arundinacea, cultivated in the West Indies; it is with difficulty distinguished from potato-starch. Tapioca is prepared from the root of the Jalropha manihot, being thoroughly purified from its poisonous juice. Cassava is the same substance modified while moist by heat. Sago is made from the soft central portion of the stem of a palm ; and salep from the fleshy root of the Orchis mascula. STARCH FROM ICELAND Moss. The lichen called Cetraria Islandica, puri- fied by a little cold solution of potash from a bitter principle, yields, when ^ boiled in water, a slimy and nearly colorless liquid, which gelatinizes on ' cooling, and dries up to a yellowish amorphous mass, which does not dis- solve in cold water, but merely softens and swells. A solution of this sub- stance in warm water is not affected by iodine, although the jelly is ren- dered blue. It is precipitated by alcohol, lead acetate, and infusion of galls, and is converted into glucose by boiling with dilute sulphuric acid. Ac- cording to Mulder, it contains C 6 H 10 5 . The jelly from certain algse, as that of Ceylon, and the so-called Carragheen moss, closely resembles the above. INULIN. This substance, which differs from common starch in some important particulars, is found in the root of Inula hclenium, Helianthus tu- berosus, dahlia, and several other plants : it may be easily obtained by wash- ing the rasped root on a sieve, and allowing the inulin to settle down from the liquid; or by cutting the root into thin slices, boiling these in water, and filtering while hot; the inulin separates as the solution cools. It is a white, amorphous, tasteless substance, nearly insoluble in cold water, but freely dissolves by the aid of heat; the solution is precipitated by alcohol, but not by acetate of lead or infusion of galls. Iodine colors it brown. Inulin has the same percentage composition as common starch. By boiling with dilute acids, it is completely converted into levulose (p. 577) Cellulose, wC 6 H| 6 , probably C 18 H 30 13 ; also called Lignin. This sub- stance constitutes the fundamental material of the structure of plants ; it is employed in the organization of cells and vessels of all kinds, and forms a large proportion of the solid parts of every vegetable. It must not be confounded with ligneous or ivoody tissue, which is in reality cellulose with other substances superadded, incrusting the walls of the original mem- branous cells, and conferring stiffness and inflexibility. Thus woody tissue, even when freed as much as possible from coloring matter and resin by repeated boiling with water and alcohol, yields, on analysis, a result indi- cating an excess of hydrogen above that required to form water with the oxygen, besides traces of nitrogen. Pure cellulose, on the other hand, has the same percentage composition as starch.* The properties of cellulose may be conveniently studied in fine linen and cotton, which are almost entirely composed of the body in question, the associated vegetable principles having been removed or destroyed by the variety of treatment to which the fibre has been subjected. Pure cel- lulose is tasteless, insoluble in water and alcohol, and absolutely innutri- tions: it is not sensibly affected by boiling water, unless it happens to have been derived from a soft or imperfectly developed portion of the plant, in which case it is disintegrated and rendered pulpy. Dilute acids and alkalies exert but little action on lignin, even at a boiling tempera- ture ; strong oil of vitriol converts it, in the cold, into a nearly colorless, adhesive substance, which dissolves in water, and presents the characters * Dumas, Chimie appliqu6e aux Arts, vi. 5. CELLULOSE. 593 of dextrin. This curious and interesting experiment may be conveniently made by very slowly adding concentrated sulphuric acid to half its weight of lint, or linen cut into small shreds, taking care to avoid any rise of tem- perature which would be attended with charring or blackening. The mix- ing is completed by trituration in a mortar, and the whole left to stand a few hours ; after which it is rubbed up with water, warmed, and filtered from a little insoluble matter. The solution may then be neutralized with chalk, and again filtered. The gummy liquid retains lime, partly in the state of sulphate, and partly in combination with sulpholignic acid, an acid composed of the elements of sulphuric acid, in union with those of cellulose. If the liquid, previous to neutralization, be boiled during three or four hours, and the water replaced as it evaporates, the dextrin becomes entirely changed to glucose. Linen rags may, by these means, be made to furnish more than their own weight of that substance. If a piece of un- sized paper be dipped for a few seconds into a mixture of 2 volumes of con- centrated sulphuric acid and 1 volume of water, and then thoroughly washed with water and dilute ammonia, a substance is obtained which resembles parchment, and has the same composition as cellulose; it occurs in commerce under the name of parchment paper (papyrin). An excel- lent application of this substance in diffusion experiments is mentioned on page 149. Cellulose dissolves in an ammoniacal solution of cupric oxide (prepared by dissolving basic cupric carbonate in strong ammonia), from which it is precipitated by acids in colorless flakes. Cellulose is not colored by iodine. XYLOIDIN AND PYROXYLIN. When starch is mixed with nitric acid of spe- cific gravity 1-5, it is converted, without disengagement of gas, into a transparent, colorless jelly, which, when put into water, yields a white, curdy, insoluble substance: this is xylo'idin. When dry, it is white and tasteless, insoluble even in boiling water, but freely dissolved by dilute nitric acid, and the solution yields oxalic acid when boiled. Other sub- stances belonging to the same class also yield xylo'idin ; paper dipped into the strongest nitric acid, quickly plunged into water, and afterward dried, becomes in great part so changed : it assumes the appearance of parch- ment, and acquires an extraordinary degree of combustibility. If pure, finely divided ligneous matter, as cotton-wool, be steeped for a few minutes in a mixture of nitric acid of sp. gr. 1-5 and concentrated sulphuric acid, then squeezed, thoroughly washed, and dried by very gentle heat, it will be found to have increased in weight about 70 per cent., and to have become highly explosive, taking fire at a temperature not much above 149 C. (300 F.), and burning without smoke or residue. This is pyroxylin, the gun-cotton of Professor Schonbein. Xylo'idin and pyroxylin are substitution-products consisting of starch and cellulose, in which the hydrogen is more or less replaced by nitryl, N0 2 . Xylo'idin consists of C 6 H 9 (N0 2 )0 5 , or C,gH 27 (N0 2 ) 3 J5 . Of pyroxylin several varieties are known, distinguished by their different degrees of stability and solubility in alcohol, ether, and other liquids. According to Hadow,* the three principal varieties are : a. C 18 1[ 21 (N0 2 ) 9 0, 5 , or C 6 H 7 (N0 2 ) 3 5 , insoluble in a mixture of ether and alcohol, but soluble in ethylic acetate. It is produced by repeated immer- sion of cotton-wool in a mixture of 2 molecules of nitric acid, N0 3 H, 2 molecules of oil of vitriol, S0 4 H 2 , and three molecules of water. 0. C 18 H 22 (N0 2 ) 8 0, 5 , soluble in ether-alcohol, insoluble in glacial acetic * Chom. Soc. Journal, vii. 201. A series of elaborate and valuable researches on gmi- coltnu IM-, n-<-.-iitlv buun published by Abd (Proceed. ttuyal Soc.) xv. 182; Chetu. Soc. J. [15], XT. 310. 50* 594 HEXATOMIC ALCOHOLS AND ETHERS. acid. Produced when the acid mixture contains half a molecule more water than in a. y . 18 H 23 (N0 2 ) 7 0, 5 (Gladstone's cotton-xyloidin}, soluble in ether and in glacial acetic acid. Produced when the acid mixture contains one mole- cule more water than in o. The first of these, which consists of trinitrocellulose, is the most explo- sive of the three, and the least liable to spontaneous decomposition. It is the only one adapted for use in gunnery, and is especially distinguished as "gun-cotton." From the experiments of General von Lenk, of the Aus- trian service,it appears that to insure the uniform production of this par- ticular compound the following precautions are necessary: 1. The cleansing and perfect desiccation of the cotton, previously to its immersion in the mixed acids. 2. The employment of the strongest acids procurable in commerce. 3. The steeping of the cotton in a fresh strong mixture of acids after the first immersion and partial conversion into gun- cotton. 4. The continuance of the steeping for forty-eight hours. 5. The thorough purification of the gun-cotton thus produced from every trace of free acid, by washing the product in a stream of water for several weeks ; subsequently a weak solution of potash may be used, but this is not essen- tial. The solution of the less highly nitrated compounds in alcohol and ether is called collodion. This solution, when left to evaporate, dries up quickly to a thin, transparent, adhesive membrane : it is employed with great ad- vantage in surgery as an air-tight covering for wounds and burns. It is also largely used in photography (p. 98). Glycogen, wC 6 H 10 5 , was obtained by Bernard from the liver of several animals (calf or pig) by exhaustion with water and precipitating with boiling alcohol. The precipitate is purified by boiling with dilute pot- ash, repeatedly dissolving in strong acetic acid, and precipitating by alcohol. Glycogen also enters largely into the composition of most of the tissues of the embryo. The muscles of foetal calves of three to seven months have been found to yield from 20 to 50 per cent, of it. Glycogen is a white, amorphous, starch-like substance, without odor or taste, yielding an opalescent solution with water, but insoluble in alcohol. It does not reduce an alkaline solution of copper. This substance does not ferment with yeast, but is converted into glucose by boiling with dilute acids, or by contact with diastase, pancreatic juice, saliva, or blood. ORGANIC ACIDS. ORGANIC ACIDS, or carbon acids, are derived, as we have several times had occasion to observe, from alcohols, by the substitution of oxygen for an equivalent quantity of hydrogen (0 for H 2 ) ; in fact they are often produced directly from alcohols by the action of oxidizing agents. Now the formula of an alcohol is derived from that of a hydrocarbon by substitution of one or more equivalents of hydroxyl (OH) for an equal number of hydrogen-atoms, the number of such substitutions determining the atomicity of the alcohol (p. 508), that is to say, the number of its hy- drogen-atoms that can be replaced by a monatomic alcohol radical or acid radical, and in some cases by an alkali-metal; in other words, the number of ethers that an alcohol can form with a monatomic alcohol radical is equal to the number of equivalents of hydroxyl contained in its molecules; thus glycerin, which is a triatomic molecule, yields three ethylic ethers : CH 2 OH CH 2 OC 2 H 6 CH 2 OC 2 H 5 CH 2 OC 2 H 5 CHOH CHOH CHOH CHOC 2 H 6 CH 2 OH OH 2 OH CH 2 OC 2 H 5 CH 2 OC 2 H 5 Glycerin. Mono ethylin. Diethylin. Triethylin. The hydrogen thus replaceable, called typic hydrogen, is that which is combined with the carbon, not directly, but only through the medium of oxygen. The number of acids which any alcohol can yield is equal to the number of times that the group or radical, CH 2 OH, enters into its molecule ; and the passage from the alcohol to the acid consists in the substitution of for H 2 in this group, or in the conversion of CH 2 OH into the acid radical CH 3 t!OOH, called oxatyl. Thus ethyl alcohol, I ' , which is monatomic, CELOH CH 3 can yield but one acid, namely, acetic acid, | ; but ethene alcohol or COOH glycol, which is diatomic, yields two, viz., glycollic and oxalic acids: CH 2 OH CH 2 OH COOH CH 2 OH COOH COOH Ethene Glycollic Oxalic alcohol. acid. acid. Further observation shows that the basicity of an organic acid, that is to say the number of its hydrogen-atoms that can be replaced by metals to form salts, is equal to the number of equivalents of oxatyl contained in it, or, in other words, to the number of hydrogen-molecules (H 2 ) that have been replaced by oxygen (0), in the immediate neighborhood of hydroxyl (Oil), to convert the alcohol into an acid. Thus from propene-glycol, C 3 I1 8 0. 2 , are derived the two diatomic acids, lactic acid, C 3 !J 6 ().,, which is monobasic, and malouic acid, C 3 H 4 O 4 , which is bibasic : 595 596 ORGANIC ACIDS. CH 2 OH CH 2 OH COOH CH 2 CH 2 CH 2 CH 2 OH COOH COOH Propene Lactic Malonic glycol. acid. acid. The atomicity of an acid is the same as that of the alcohol from which it is derived ; thus lactic acid, though it contains only one atom of basic hy- drogen, and therefore forms only one class of metallic salts, represented by the formula C 3 H 5 3 M, can form two ethylic ethers, viz., ethyl-lactic acid and diethyl-lactate or ethyl-lactate ; thus : CH a OH CH 2 OC 2 H 5 CH 2 OC 2 H 6 CH 2 CH 2 CH 2 COOH COOH COOC 2 H 6 Lactic acid Ethyl-lactic Diethylic (monobasic). acid (mono- lactate basic). (neutral). From these considerations it appears, that monatomic acids must neces- sarily be monobasic ; but diatomic acids may be either monobasic or bibasic ; triatomic acids, either monobasic, bibasic, or tribasic ; and so on. Many of the most important acids are derived, in the manner above ex- plained, from actually known alcohols ; others, though they have no alco- hols actually corresponding to them, are homologous with other acids de- rived from known alcohols; but there is also a considerable number of acids, especially those formed in the vegetable or animal organism, which cannot be regarded as derivatives of alcohols of any known series; but the number of these unclassified acids will doubtless diminish as their com- position and reactions become more thoroughly known. These acids may also be regarded as compounds of hydroxyl with oxygen- ated radicals (acid radicals) formed from the corresponding alcohol-radi- cals by substitution of for H 2 , or as derived from one or more molecules of water (according to their atomicity), by substitution of such radicals for half the hydrogen in the water ; e. g., Type. Slo C ^\o c ^\o a. j a. j Jti j Water. Ethyl alcohol. Acetic acid. H \0 H Water (2 mol.) Propene Lactic acid. Malonic acid, glycol. In these typical formulae of polyatomic acids, the typic or alcoholic hy- drogen (replaceable only by alcoholic or acid radicals), is placed, for dis- tinction, above the acid radical ; and the basic hydrogen, replaceable either by metals or alcohol radicals, below. The acid radicals are denoted by names ending in yl, formed from those of the acids themselves ; thus, C 2 H 3 0, the radical of acetic acid, is called acetyl ; C 3 H 4 0, is lactyl; C 3 H.,O.,, is malonyl, &c. The replacement of the hydroxyl in an acid by chlorine, bromine, or MONATOMIC ACIDS. 597 iodine, gives rise to acid chlorides, &c. ; thus from acetic acid, C 2 H 3 0(OH), is derived acetic chloride, C 2 H 3 OC1, &c. The replacement of the hydrogen within the radical (radical hydrogen) by the same elements, or by the rad- icals, CN, N0 2 , NH 2 , &c., gives rise to chlorinated, brominated, cyanated, nitrated, and amidated acids (see p. 469). Lastly, the replacement, of the typic hydrogen by alcohol-radicals gives rise to ethereal salts or compound ethers ; and its replacement by acid radicals yields acid oxides or anhy- drides (p. 409). The derivatives of each acid will be described in connec- tion with the acid itself. MONATOMIC ACIDS. These acids, being derived from monatomic alcohols by substitution of for H 2 , necessarily contain two atoms of oxygen. Each series of hydro- carbons yields a series of monatomic alcohols and a series of monatomic acids ; thus : Alcohols. Acids. CaH 2n+2 C n H 2n 2 Hydrocarbons. C n H 2n+2 C n H 2n Cn H 2n _ 2 C n H 2n _ 4 &C. C a H 2n _ 2 C n H 2n _ 4 &c. C n H 2n - 4 2 H 2n &c. C n H 2n _ 6 2 The best known monatomic acids are those belonging to the series C n H 2n 2 , C n H 2n _ 2 2 , C n H 2u _ 8 2 , and C n H 2n _ J0 2 . Of the other series only a few terms have hitherto been obtained. 1. Acids belonging to the series C n H 2n 2 , or C n H 2n _ 1 0(OH). These acids are called fatty or adipic acids, most of them being of an oily consistence, and the higher members of the series solid fats. The follow- ing is a list of the known acids of the series, together with their melting and boiling points. Name. Formula. Melting point. Boiling point. Formic acid . CII 2 2 +1C. (34 F.) 100 C. (212 F.) Acetic acid C 2 II 4 2 +17 (62 ) 117 " (242 " ) Propionic acid C 3 H 6 2 141 (280 " ) Butyric acid . C 4 II 8 2 below 20 C. (-4 F.) 161 " (322 ) Valeric acid . C 5 H 10 2 , 175 " (347 " ) Caproic acid . . . C 6 n 12 o 2 +5C. (41 F.) 198 " (389 " ) (Enaiithylic acid . C 7 u 14 oj 212 >41 4 o ) Caprylic acid . C 8 Hio0 2 +14 C. (57 F.) 23(5 " 457 ) Pdargonic acid . . llutic or Capric acid cyi 18 o 2 Cio'laA +18 " ? -(-30 (64 " ) (86 " 260 " (500 ) Laurie acid . C,Ho 4 2 +43-6 1 10 " Mvristic acid . c u rr:^o, 53-8 " 129' Palmitic acid CIGI&; 62" 144' Margaric acid . Cn3A 59-9 " ? 140 ' Stearic acid . OwHaSS 69-2 " q. r >7 ' Ararhidic acid C^H^O, 75 " (167 ' Beheiiic acid C.olI 44 Oo 76" 169' Cerotic acid <3HS3 78 o. 172' Melissic acid ciujjo! 88 " (190 " These acids may be represented on the marsh-gas type and on the water- type by the following formulae : 598 MONATOMIC ACIDS. Acid. (C.-iH^i' or | )H f(C^.iH^4' yn-ii Marsh-gas.. oj or^ Water . . } or HOH (C^-iO)' 1 or ((^H^O/OH. If in either of these formulae we make n successively equal to 1, 2, 3, &c., we get the formulas of formic, acetic, propionic, &c. acid ; thus : fH fCH, rC 2 H 5 fC 3 H 7 (C 4 H 9 ClO" CIO" CIO" CIO" C]0" (OH (OH (OH (OH (OH Formic. Acetic. Propionic. Butyric. Valeric. The acid radicals C n H 2n _iO, in the water-type formulae, may be regarded as compounds of carbonyl with alcohol radicals, C n II 2n _ 1 = CO(C n _iH 2n _i), and accordingly the several acids may be represented as follows : COH| Q CO(CH 3 )| Formic. Acetic. Propionic. All the acids of the series containing more than three carbon-atoms admit of isomeric modifications, according to the constitution of the alcohol-radi- cal which they contain: butyric acid, C 6 H 8 2 , for example, may exhibit the following modifications : Normal butyric acid. Isobutyric acid. v^rio I H 3 C CH 3 CH 2 CH 2 CH S CH 2 CH(CH S ) 2 V or or CH >=C OH CH 2 0=C OH 0=C OH =C OH But none of these acids can exhibit modifications analogous to the second- ary and tertiary alcohols : because in them the carbon-atom which is asso- ciated with hydroxyl has two of its other units of equivalence satisfied by an atom of bivalent oxygen, and therefore cannot unite directly with more than one other atom of carbon. Accordingly, it is found that the second- ary and tertiary alcohols are not converted by oxidation into acids contain- ing the same number of carbon-atoms as themselves. Occurrence. Most of the fatty acids are found in the bodies of plants or animals, some in the free state: formic acid in ants and nettles: valeric acid in valerian root ; pelargonic acid in the essential oil of Pelargonium roseum; and cerotic acid in bees'-wax. Others occur as ethereal salts of monatomic or polyatomic alcohols : as cetyl palmitate in spermaceti ; ceryl cerotate in Chinese wax; glyceric butyrate, palmitate, stearate, &c., in natural fats. Formation. 1. By oxidation of the primary alcohols of the methyl series, as by exposure to the air in contact with platinum black, or by heating with aqueous chromic acid. 2. By the oxidation of aldehydes. In this case an atom of oxygen is simply added; e. ff., C 2 H 4 (aldehyde) -f- = C 2 H 4 2 (acetic acid). 3. By the action of carbon dioxide on the potassium or sodium compound of an alcohol-radical of the methyl series ; thus, FATTY ACIDS. 599 CH 3 C0 2 4- CH 3 Na = | COONa Carbon Sodium Sodium dioxide. methide. acetate. 4. By the action of alkalies or acids on the cyanides of the alcohol- radicals; CnH.jQ.f-!: thus, C n H 2n+1 C n H 2n+1 4- KOH 4- OH 2 = | 4- NH 3 CN COOK Alcoholic Potassium Water. Potassium-salt Ammo- cyanide. hydrate. of fatty acid. nia. and: 4- HC1 4- 20H 3 = | 4- NH 4 C1 CN COOH Alcoholic Hydrochloric Water. Potassium Ammonium cyanide. acid. salt. chloride. In this manner the cyanide of each alcohol-radical yields the potassium salt of the acid next higher in the series, that is, containing one atom of carbon more; methyl cyanide, for example, yielding acetic acid, ethyl cyanide, yielding propionic acid, &c. ; thus, CH 3 CH, 4- KOH 4- OH 3 = 4- NH, CN COOK Methyl Potassium cyanide. acetate. 5. By the action of water on the corresponding acid chlorides; e. g. t C 2 H 3 OC1 4- HOH = HC1 4- C 2 H 3 0(OH) Acetyl Acetic acid. chloride. Now, these acid chlorides can be produced, in some instances at least, by the action of carbonyl chloride (phosgene gas) on thecorresponding par- affins ; * thus, CH 4 -|- COC1 2 = HC1 -}- C 2 H 3 OC1 Methane. Carbonyl Acetyl chloride. chloride. C 4 H, 4- COC1 2 = HC1 4- C 5 H 9 OC1 Quartane. Carbonyl Valeryl chloride. chloride. By these combined reactions, therefore, the paraffins may be converted into the corresponding fatty acids. 6. By the following reaction, the fatty acids may be built up one from the other, starting from acetic acid.f Ethyl acetate, treated with sodium, gives up one atom of radical hydrogen in exchange for that metal: CH 3 CH 2 Na 2l 4- Na 2 = 2 | 4- H a COOC 2 H 6 COOC 2 H 5 Ethyl Monosodic acetate. ethyl acetate. * Harnitz-Harnitzky, Ann. Ch. Pharm. cxxxvi. 121. f Franltland aud Duppa, Proceed. Roy. Soc. xiv. 198, 458; xv. 37. 600 MONATOMIC ACIDS. By acting on this body with the iodide of a radical, CnHjn-j-j, ethylic ethers of the higher acids may be produced; thus, CH 2 Na CH 2 CH 3 I ' + CH 3 I = Nal + | COOC S H. COOC 2 H 5 Monosodic Methyl Ethyl ethyl acetate. iodide. propionate. If ethyl iodide were used instead of methyl iodide, the product would be ethyl butyrate, C 4 H 7 2 C 2 H 5 . It has not been found possible to produce, by this reaction, the higher acids of the series from formic acid. The six modes of formation above given are general, or capable of being made so. There are also special methods of producing particular acids of the series, but in most of these cases the reactions cannot be distinctly traced ; thus formic, acetic, propionic, butyric, and valeric acids are pro- duced by the oxidation of albumin, fibrin, casein, gelatin, and other similar substances: propionic and butyric acids in certain kinds of fermentation; acetic acid by the destructive distillation of wood and other vegetable substances. Properties. Most of the fatty acids are, at ordinary temperatures, trans- parent and colorless liquids ; formic and acetic acids are watery ; propionic acid and the higher acids, up to pelargonic acid, are oily ; rutic acid and those above it are solid at ordinary temperatures, most of them being crys- talline fats ; cerotic and melissic acids are of waxy consistence. By in- specting the table on page 597, it will be seen that the boiling points of these acids dift'er, for the most part, by 24 C. (43 F.) for each addition of CH 2 . There are, however, a few exceptions to this rule, some of which may arise from the existence of isomeric modifications. The boiling points of formic and acetic acids, however, which cannot exhibit any such modifi- cations, differ by only 17 C. (30 F.). Reactions. 1. When the fatty acids are submitted to the action of nas- cent oxygen evolved by electrolysis, the oxatyl (COOH) contained in them, is resolved into water and carbon dioxide, and the alcohol radical is set free ; thus, C 4 H 9 C 4 H 9 21 + = OH 2 + 2C0 2 + | COOH C 4 H 9 Valeric acid. Diquartyl. 2. When the ammonium salt of either of these acids is heated with phos- phoric oxide, it gives up water and is converted into the cyanide of the alcohol-radical next below it, e. g., CH 3 CH. | ' 20H 2 = | ' COONH 4 CN Ammonium Methyl acetate. cyanide. This reaction is the converse of the fourth mode of formation above given. 3. By distilling the potassium salt of a fatty acid with an equivalent quantity of potassium formate, the corresponding aldehyde is obtained: = CO(CH 3 )H + C0 3 K 2 ; Potassium Potassium Aldehyde. Potassium acetate. formate. carbonate. FATTY ACIDS. 601 and the aldehyde, treated with nascent hydrogen, is converted into a pri- mary alcohol: CH 3 CH 3 | + H 2 = COH CH 2 OH Aldehyde. Alcohol. 4. By subjecting the barium or calcium salt of a fatty acid to dry distil- lation, a similar decomposition takes place, resulting in the formation of a ketone : + C 3 Ca"; Calcium Acetone. Calcium acetate. carbonate. and the ketone, treated with nascent hydrogen, yields a secondary alcohol : CH 3 H 3 C CH 3 I ' + H 2 V COCH S CHOH Acetone. Secondary propyl alcohol. By these reactions, the fatty acids may be converted into alcohols. 5. The fatty acids, heated with alcohols in sealed tubes, yield compound ethers, or ethereal salts, water being eliminated : C 4 H 7 0(OH) -f HOC 2 H 6 = OH 2 -f C 4 H 7 0(OC 2 H 6 ) Butyric Ethyl Ethyl acid. alcohol. butyrate. The conversion, however, is never complete, a portion, both of the acid and of the alcohol, remaining unaltered in whatever proportion they may be mixed. The ethereal salts of the fatty acids are, for the most part, more easily obtained by acting upon the alcohol with an acid chloride, or by passing hydrochloric acid gas into a solution of the fatty acid in the alcohol : C 4 H 7 OC1 -f HOC 2 H 6 == HC1 + C 4 H 7 0(OC 2 H 6 ) Butyric Ethyl Ethyl chloride. alcohol. butyrate. Another method very commonly adopted is, to distil a potassium salt of the fatty acid with a mixture of the alcohol and strong sulphuric acid. In this case an acid sulphuric ether is first formed (as ethyl-sulphuric acid from ethyl alcohol, p. 527), and this acts upon the salt of the fatty acid in the manner illustrated by the equation : S0 2 (OH)(OC 2 H 5 ) -f C 4 H 7 0(OK) = C 4 H 7 0(OC 2 H 6 ) + S0 2 (OH)(OK) Ethyl-sulphuric Potassium Ethyl Acid potassium acid. butyrate. butyrate. sulphate. The ethereal salts of the fatty acids are either volatile, oily, or syrupy liquids, or crystalline solids, for the most part insoluble in water, but sol- uble in alcohol and in ether. When distilled with potash or soda, they take up water and are saponified, that is to say resolved into the alcohol and acid; e. g., C 4 H 7 0(OC 2 H 6 ) -f HOH = C 4 H 7 0(OH) -f- C 2 H 5 (OH) Ethyl Water. Butyric Ethyl butyrate. acid. alcohol. 51 602 MONATOMIC ACIDS. 6. The fatty acids are strongly acted upon by the chlorides, bromides, oxychlorides, and oxybromides of phosphorus, yielding acid chlorides and bro- mides, the phosphorus being at the same time converted into phosphorous or phosphoric acid ; thus, 3C 2 H 3 0(OH) + PC1 3 = P0 3 H 3 + 3C 2 H 3 OC1 Acetic acid. Phosphorus Phosphorus Acetic trichloride. acid. chloride. 3C 2 H 3 0(OH) + PC1 3 = P0 4 H 3 + 3C 2 H 3 OC1 Acetic acid. Phosphorus Phosphoric Acetic oxybromide. acid. chloride. C 2 H 3 0(OH) + PC1 6 = PC1 3 4- HC1 4- C 2 H 6 OC1 Acetic acid. Phosphorus Phosphoric Hydro- Acetic pentachloride. oxychloride. chloric acid, chloride. These acid chlorides, are, for the most part, oily liquids, having a pun- gent acid odor ; they are easily decomposed by water, yielding the fatty acid and hydrochloric" acid. This decomposition takes place also when they are exposed to the air : hence they emit dense acid fumes. They react in an exactly similar manner with alcohols, as above mentioned, yielding hydrochloric acid and a compound ether. 7. The chlorides of the acid radicals, C n H 2n _,0, act violently on ammonia, forming ammonium chloride, and the amide corresponding to the acid from which they are derived ; e. a., C 2 H 3 OC1 4- 2NH 3 = NH 4 C1 + NH 2 (C 2 H 3 0) Acetic Ammonia. Ammonium Acetamide. chloride. chloride. 8. The acid chlorides, distilled with a metallic salt of the corresponding acid, yield a metallic chloride and the oxide or anhydride corresponding to the acid : thus, C 2 H 3 OC1 4- C 2 H 3 0(OK) = KC1 + (C 2 H 3 0) 2 Acetic Potassium Acetic chloride. acetate. oxide. In like manner, when distilled with the potassium salt of another mon- atomic acid, they yield oxides or anhydrides containing two monatomic acid radicals ; e. g., C 2 H 3 OC1 4- C 7 H 6 0(OK) = KC1 + C$ Acetic Potassium Aceto-ben- ehloride. benzoate. zoic oxide. The oxides of the fatty acid radicals may also be prepared by heating a dry lead-salt of the acid, in a sealed tube, with carbon bisulphide ; e. g., 2Pb {oC 2 H 3 + CS 2 = 2PbS + C 2 + 2(C 2 H 3 0) 2 Lead acetate. Acetic oxide. The oxides of the fatty acid radicals are gradually decomposed by water, quickly when heated, yielding two molecules of the corresponding acid : (C 2 H 3 0) 2 4- OH 2 = 2C 2 H 3 0(OH) Those containing two acid radicals yield one molecule of each of the Corresponding acids. FATTY ACIDS. 603 In contact with alcoholic oxides (oxygen ethers], the acid oxides are con- verted into ethereal salts : (C 2 H 3 0) 2 + (C 2 H 5 ) ? = 2C 2 H 3 0(OC 2 H 6 ) Acetic oxide. Ethyl oxide. Ethyl acetate. With alcohols, in like manner, they yield a mixture of a compound ether with the acid : (C 2 H 3 0) 2 + C 2 H 5 (OH) = C 2 H 3 0(OC 2 H 6 ) + C.H 3 0(OH) Acetic oxide. Ethyl alcohol. Ethyl acetate. Acetic acid. The acid oxides are decomposed by ammonia gas, yielding a mixture of an ammonium-salt with an amide : (C 2 H 3 0) 2 + 2NH 3 = C 2 H 8 0(ONH 4 ) + NH 2 C 2 H 3 Acetic Ammonia. Ammonium Acetamide. oxide. acetate. 9. The fatty acids, subjected to the action of chlorine or bromine, give off hydrochloric or hydrobromic acid, and are converted into substitution-com- pounds containing one or more atoms of chlorine or bromine in place of hydrogen; but it is only the hydrogen within the radical that can be thus exchanged, the typic hydrogen remaining unaltered, so that the number of chlorine or bromine-atoms introduced in place of hydrogen is always less by at least one than the number of hydrogen-atoms in the acid : C 2 H 3 0(OH) -f C1 2 = HC1 + C 2 H 2 C10(OH) Acetic acid. Chloracetic acid. C 2 H 3 0(OH) -f 3C1 2 = 3HC1 -f C 2 C1 3 0(OH) Acetic acid. Trichloracetic acid. The iodated acids of the same series (or rather their ethereal salts) are obtained by heating the corresponding bromine-compounds with potassium iodide : C 2 H 2 BrO(OC 2 H 6 ) + KI = KBr -f- C 2 H 2 IO(OC 2 H 5 ) ; Ethyl-brom- Ethyl-iodacetate. acetate. land the ethers treated with potash yield potassium salts of the iodated acids, from which the acids may be obtained by decomposition with sulphu- ric acid. The chlorinated and brominated fatty acids, boiled with water and silver oxide, exchange the whole of their chlorine or bromine for an equivalent quantity of hydroxyl, producing new acids, which differ from the primi- tive acids by a number of atoms of oxygen equal to the number of atoms of chlorine or bromine present ; e. g., 2C 2 H 3 Br0 2 -f Ag 2 -f H 2 = 2AgBr + 2C 2 H 4 3 Bromacetic Glycollic acid. acid. CJT 6 Br 2 2 -f Ag 2 + H 2 -f- 2AgBr + C 4 H 8 O 4 , Dibromo- Dioxy-bu- butyric acid. tyric acid. Dichloracetic and trichloracetic acid are not sufficiently stable to exhibit this transformation, their molecules splitting up altogether when boiled with silver oxide. The monochlorinated and monobrormnated acids, subjected to the action of an alcoholic solution of ammonia gas, yield ammonium chloride and a new 604 MONATOMIC ACIDS. acid, in which the chlorine or bromine is replaced by amidogen. Thus monochloracetic acid yields amidacetic acid, or glycocine : C 2 H 3 C10 2 + 2NH 3 = NH 4 C1 + C 2 H3(NH 2 )0 2 Chloracetic Amidacetic acid. acid. There is another way of viewing these amidated acids which will be con- sidered hereafter. (H H Formic Acid, CH 2 2 =CHO(OH)=C^ 0" = \ .This acid occurs in (OH COOH the concentrated state in the bodies of ants, in the hairs and other parts of certain caterpillars, and in stinging nettles. It may be produced by the first, second, and fourth of the above-mentioned general methods of form- ing the fatty acids viz., by the slow oxidation of methyl alcohol, or of formic aldehyde, in contact with platinum black, and as a potassium salt by heating hydrocyanic acid (hydrogen cyanide) with an alcoholic solution of potash : HCN -f KOH + OH 2 = NH 3 -f CHO(OK) Hydrogen Potassium cyanide. formate. It is also produced by certain special reactions viz : a. By passing car- bon monoxide over moist potassium hydrate, the gas being thereby ab- sorbed, and producing potassium formate : CO + HOK = COH(OK) The absorption of the gas is accelerated by the presence of a considerable quantity of water, and still more by alcohol or ether. /?. By distilling dry oxalic acid mixed with sand or pumice-stone, or better with glycerin: C 2 H 2 4 = C0 2 + CH 2 2 Oxalic Carbon Formic acid. dioxide. acid. The distillation of oxalic acid with glycerine is a very advantageous mode of preparing formic acid. The glycerine takes no part in the decom- position, but appears to act by preventing the temperature from rising too high : when oxalic acid is distilled alone or with sand, the greater part of the formic acid produced is resolved into water and carbon monoxide. y. By passing carbon dioxide and water-vapor over potassium at a mod- erate heat, acid potassium carbonate being formed at the same time : K 2 4- 2C0 2 -f OH 2 = C0 3 KH + CH0 2 K Acid car- Formate, bonate. i. By the oxidation of sugar, starch, gum, and organic substances in general. A convenient mode of preparation is the following : 1 part of sugar, 3 parts of manganese dioxide, and 2 parts of water, are mixed in a very capacious retort, or large metal still ; 3 parts of oil of vitriol, diluted with an equal weight of water, are then added, and when the first violent effervescence from the disengagement of carbon dioxide has subsided, heat is cautiously applied, and a considerable quantity of liquid distilled over. This is very impure : it contains a volatile oily matter, and some substance which communicates a pungency not proper to formic acid in that dilute state. The acid liquid is neutralized with sodium carbonate, and the re- FORMIC ACID. 605 suiting formate purified by crystallization, and, if needful, by animal char- coal. From this, or any other of its salts, solution of formic acid may be readily obtained by distillation with dilute sulphuric acid. To obtain the acid in its most concentrated state, the dilute acid is satu- rated with lead oxide, the liquid is evaporated to complete dryness, and the dried lead formate, reduced to fine powdei*, is very gently heated in a glass tube connected with a condensing apparatus, through which a cur- rent of dry sulphuretted hydrogen gas is transmitted. It forms a clear, colorless liquid, which fumes slightly in the air, has an exceedingly pene- trating odor, boils at 983 C. (210 F.), and crystallizes in large brilliant plates when cooled below 0. The specific gravity of the acid is 1 235 ; it mixes with water in all proportions: the vapor is inflammable, and burns with a blue flame. Concentrated formic acid is extremely corrosive, at- tacking the skin, and forming a blister or an ulcer, painful and difficult to heal. Formic acid mixes with water in all proportions. The aqueous acid has an odor and taste much resembling those of acetic acid : it reddens litmus strongly, and decomposes alkaline carbonates with effervescence. Formic acid likewise dissolves readily in alcohol, being partly converted into ethyl formate. Formic acid is a powerful reducing agent. It may be readily distin- guished from acetic acid by heating it with solution of silver nitrate; the metal is thus reduced, sometimes in the pulverulent state, sometimes as a specular coating on the glass tube, and carbon dioxide is evolved. Mer- curic chloride is reduced by formic acid to calomel. Formic acid heated with oil of vitriol splits up into water and carbon monoxide, CH 2 2= OH 2 +CO. Chlorine converts it into hydrochloric acid and carbon dioxide: CH 2 2 -f C1 2 = 2HC1 -f C0 2 Formic acid heated with strong bases is converted into oxalic acid, with disengagement of hydrogen: 2CH 2 2 -f BaO = C 2 Ba0 4 -f H 2 + OII r Formic Baryta. Barium acid. oxalate. Formates. The composition of these salts is expressed by the formulas, Cll(> a M, (CHO a ),M // , (CH0 2 ) 3 M"', &c., according to the equivalent value of the metal or other positive radical contained in them. They are all soluble in water: their solutions form dark-red mixtures with ferric salts. When distilled with strong sulphuric acid they give off acid carbon monox- ide, arid leave a residue of sulphate. The formates of the alkali-metals heated with the corresponding salts of other fatty acids, yield a carbonate and an aldehyde (p. GOO). Sodium formate crystallizes in rhombic prisms containing CH0 2 Na. Aq. It reduces many metallic oxides when fused with them. Potassium formate, CH0 2 K, is difficult to crystallize, on account of its great solubility. Ammo- nium formate crystallizes in square prisms: it is very soluble, and is decom- posed at high temperatures into hydrocyanic acid ami water, the elements of which it contains: CII0 2 NH 4 =20II 2 +CNH. The formates of barium, strontium, calcium, and magnesium form small prismatic, easily soluble crystals. Lead formate crystallizes in small, diverging, colorless needles, which require for solution 40 parts of cold water. The manganous, ferrous, zinc, nickel, and cobalt formates are also crystallizable. Cupric formate is very beautiful, constituting bright-blue rhombic prisms of considerable magni- tude. Si/r,'/- format*' is white, but slightly soluble, and decomposed by the least elevation of temperature. 606 MONATOMIC ACIDS. Methyl formate, CH0 2 CH 3 , isomeric with acetic acid, is prepared by heat- ing in a retort equal weights of neutral methyl sulphate and sodium for- mate. It is a very volatile liquid, lighter than water, boiling between 36 and 38. Ethyl formate, CH0 2 C 2 H 5 , isomeric with methyl acetate and propionic acid (p. 475), is prepared by distilling a mixture of 7 parts of dry sodium for- mate, 10 of oil of vitriol, and 6 of strong alcohol. The formic ether, separated by the addition of water to the distilled product, is agitated with a little magnesia, and left for several days in contact with calcium chloride. Ethyl formate is colorless, has an aromatic odor, a density of 0-915, and boils at 56 C. (133 F.). Water dissolves it to a small extent. ( CH 3 CH 3 Acetic Acid, C 2 H 4 2 = C 2 H 3 0(OH), or COCH 3 (OH) = C I O" = I ._ I OH COOH This acid is found in small quantities in the juices of plants and in animal fluids. It may be produced by either of the first five general methods of formation given on pages 598, 599, and in particular by the slow oxidation of alcohol. When spirit of wine is dropped upon platinum black, the oxygen condensed in the pores of the latter reacts so powerfully upon the alcohol as to cause its instant inflammation. When the spirit is mixed with a little water, and slowly dropped upon the finely divided metal, oxidation still takes place, but with less energy, and vapor of acetic acid is abun- dantly evolved. In all these modes of formation, the acetic acid is ultimately producible from inorganic materials. It is also formed by the action of nascent hydrogen on trichloracetic acid, which may itself be produced from inorganic materials. Lastly, acetic acid is obtained, together with many other products, in the destructive distillation of wood and other vegetable substances. Preparation. 1. Dilute alcohol, mixed with a little yeast, or almost any azotized organic matter susceptible of putrefaction, and exposed to the air, speedily becomes oxidized to acetic acid. Acetic acid is thus manufactured in Germany, by suffering such a mixture to flow over wood-shavings steeped in a little vinegar, contained in a large cylindrical vessel through which a current of air is made to pass. The greatly extended surface of the liquid expedites the change, which is completed in a few hours. No carbonic acid is produced in this reaction. The best vinegar is made from wine by spontaneous acidification in a partially filled cask to which the air has access. Vinegar is first introduced into the empty vessel, and a quantity of wine added ; after some days, a second portion of wine is poured in, and after similar intervals, a third and a fourth. When the whole has become vinegar, a quantity is drawn off equal to that of the wine employed, and the process is recommenced. The temperature of the building is kept up to 30 C. (86 F.). Such is the plan adopted at Orleans.* In England, vinegar is prepared from a kind of beer made for the purpose. The liquor is exposed to the air in half empty casks, loosely stopped, until acidification is complete. Frequently a little sulphuric acid is afterwards added, with the view of checking further decomposition, or mothering, by which the product would be spoiled. When dry, hard wood, as oak and beech, is subjected to destructive dis- tillation at a red heat, acetic acid is found among the liquid condensable products of the operation. The distillation is conducted in an iron cylinder of large dimensions, to which a worm or condenser is attached; a sour watery liquid, a quantity of tar, and much inflammable gas pass over, while charcoal of excellent quality remains in the retort. The acid liquid is subjected to distillation, the first portion being collected apart for the * Dumas, Chiinie applique aux Arts, vi. 5o7. ACETIC ACID. 607 preparation of wood-spirit. The remainder is saturated with lime, concen- trated by evaporation, and mixed with the solution of sodium sulphate; calcium sulphate is thereby precipitated, while the acetic acid is transferred to the soda. The filtered solution is evaporated to its crystallizing point; and the crystals are drained as much as possible from the dark, tarry mother-liquor, and deprived by heat of their combined water. The dry salt is then cautiously fused, by which the last portions of tar are decomposed or expelled : it is then re-dissolved in water, and re-crystallized. Pure sodium acetate, thus obtained, readily yields acetic acid by distillation with sulphuric acid. The strongest acetic acid is prepared by distilling finely powdered anhy- drous sodium acetate with three times its weight of concentrated oil of vitriol. The liquid is purified by rectification from sodium sulphate acci- dentally thrown up, and exposed to a low temperature. Crystals of pure acetic acid, C 2 H 4 2 , then form in large quantity : they may be drained from the weaker fluid portion, and suffered to melt. Below 15-5 C. (GO F.) this substance, often called glacial acetic acid, forms large, colorless, trans- parent crystals, which above that temperature fuse to a thin, colorless liquid, of exceedingly pungent and well-known odor: it raises blisters on the skin. It is miscible in all proportions with water, alcohol, and ether, and dissolves camphor and several resins. When diluted it has a pleasant acid taste. Glacial acetic acid in the liquid state has a density of 1-063, and boils at 120 C. (248 P.). Its vapor is inflammable, and exhibits the variations of density noticed at page 461. At 300 C. (572 F.), or above, it is 2-08 compared with air, er 30 compared with hydrogen, agreeing ex- actly with the theoretical density, which is half the molecular weight ; but at temperatures near the boiling point it is considerably greater, being 2-90 at 140 C. (284 F.), and 3-20 at 125 C. (257 F.) (referred to air). Dilute acetic acid, or distilled vinegar, used in pharmacy, should always be carefully examined for copper and lead ; these impurities are contracted from the metallic vessel or condenser sometimes employed in the process. The strength of any sample of acetic acid cannot be safely inferred from its density, but it is easily determined by observing the quantity of dry sodium carbonate necessary to saturate a known weight of the liquid. Acetic acid exhibits all the reactions of the fatty acids in general (pp. 601-604). The acid itself does not readily conduct the electric current, but a solution of potassium acetate is decomposed by electrolysis, with for- mation of dimethyl or ethane: CII 8 2 | + OH 2 = C 2 H 6 + II 2 + C0 2 + CO(OK) 2 COOK Potassium Ethane. Potassium acetate. carbonate. Acetic acid is not attacked by nitric acid, but periodic acid converts it by oxidation into formic acid and carbon dioxide, being itself reduced to iodic acid or even to free iodine: C 2 H 4 2 + 3 = CII 2 2 + C0 2 + OH 2 . Potassium acetate distilled with arscnious oxide gives off a highly inflam- mable and characteristically fetid oil, consisting chiefly of arsendimethyl or cacodyl, As 2 (CH 3 ) 4 . Acetates. Acetic acid forms a large number of highly important salts, rc]>n-sciiu-(l by the formula}, (yi s (),M, (C 2 H S O 2 ) 2 M // , or ( is prepared by digesting a mixture of ethene dibromide, silver acetate, and glacial acetic acid in the water-bath, and exhausting the digested mass with ether. On distilling the ethereal solution, the ether first passes over, then the acetic acid, and lastly, when the temperature has reached 187 C. (368 F.), ethene diacetate. It is a colorless, neutral liquid, of sp. gr. 1-128, at 0; soluble in 7 parts of water and in every proportion in alcohol and ether. PROPENYL OR GLYCERYL ACETATES ; OR ACETINS. These ethers are de- rived from propenyl alcohol (glycerin) by substitution of 1, 2, or 3 equiva- lents of acetyl for hydrogen. The formula of glycerin being (C 3 H 6 ) /// OH 3 , those of the three acetins are : Monoacetin . . . (C 3 H 6 )'"(OH) 2 (OC 2 H 8 0) Diacetin . . . (C 3 H 5 )'"(OH)(OC 2 H 3 0) 2 Triacetin .... (C 8 H 6 )'"(OC 2 H S 0) 8 They are oily liquids, produced by heating glycerin and acetic acid to- gether, in various proportions, in sealed tubes. ACETIC CHLORIDE OR ACETYL CHLORIDE, C 2 H 3 OC1. This compound, which has the constitution of acetic acid with chlorine substituted for hydroxyl, is produced, as already observed (p. 602), by the action of phosphorus tri- chloride, pentachloride, or oxychloride on glacial acetic acid. The pro- duct heated with water and dilute soda-solution, to remove phosphorus oxychloride and hydrochloric acid, and then rectified, yields acetic chlo- ride as a colorless liquid, having a suffocating odor and emitting dense fumes of hydrochloric acid in contact with the air. It is heavier than water, boils at 55 C. (131 F.), and is decomposed by water and alkaline solutions, yielding hydrochloric and acetic acids. ACETIC OXIDE OR ANHYDRIDE, C 4 H 6 3 = (C 2 H 3 0) 2 0, sometimes called Anhydrous acetic acid. This compound is obtained: 1. By the action of acetyl chloride on potassium or sodium acetate: C 2 H 3 0(ONa) -f C 2 H 3 OC1 = NaCl -f (C 2 H 3 0) 2 0. 2. By heating sodium acetate with benzoyl chloride, C 7 H 5 OC1, whereby benzo-acetic oxide is formed in the first instance, and subsequently resolved into acetic and benzoic oxides, the former distilling over, while the latter remains : C 2 H 3 0(ONa) + C 7 H 5 OC1 = NaCl + ^n Sodium acetate. Benzoyl Benzo-acetic chloride. oxide. and: (C 2 H 3 0) 2 + (C 7 H 6 0) 2 Benzo-acetic Acetic Benz.oic oxide. oxide. oxide. Acetic oxide is a heavy oil which dissolves slowly in water, being gradu- ally converted into acetic acid : (C 2 H 3 0) 2 -|- OH 2 == 2C 2 H 3 C(OH). 612 MONATOMIC ACIDS. Acids derived from Acetic Acid by Substitution. CHLORACETIC ACIDS. The three acids, C 2 H 3 C10 2 , C 2 H 2 C1 2 2 , and C 2 HC1 3 2 , are produced by the action of chlorine on acetic acid in sunshine ; the second, however, is formed in small quantity only, the first or the third be- ing produced in greatest abundance according as the acetic acid or the chlorine is in excess. Monochloracetic acid, C 2 H 2 C10(OH), is produced, according to R. Hoff- mann, by the action of chlorine on boiling glacial acetic acid in sunlight. Dr. H. Miiller finds that the formation of monochloracetic acid is facilitated by dissolving a little iodine in the hydrated acetic acid, and passing a stream of chlorine through the boiling solution. On submitting the products of this reaction to repeated distillation, a substance is obtained boiling at 186 C. (367 F.), and solidifying to a crystalline mass which melts at 64 C. (147 F.) and dissolves with facility in water. This acid, when heated with potash, is converted into potassium glycollate (p. 604): C 2 H 3 C10 2 + 2KHO = KC1 -f C 2 H 3 3 K -f OH 2 Chloracetic Potassium acid. glycollate. Dichloracetic acid, C 2 HC1 2 0(OH), is produced, together with the preceding compound, by the action of chlorine and iodine on boiling acetic acid, and is found in that portion of the product which boils above 188 C. (370 F.). According to Maumene*,* it may be obtained by exposing monochlor- acetic acid in large flasks to the action of dry chlorine (5 atoms of chlorine to 3 molecules of chloracetic acid) for twenty-four hours, warming the product to expel hydrochloric acid, and then distilling. At ordinary temperatures it is a liquid having a specific gravity of 1-5216 at 15 C. (59 F.), and boiling at 105 C. (221 F.). According to Miiller, it remains liquid when cooled ; but according to Maumene, it crystallizes in rhombohedral plates. It forms a soluble silver salt, C 2 HCl 2 2 Ag, which is decomposed when its solution is heated with silver oxide to 75 or 80, giving off a mixture of carbon mon- oxide and dioxide : 2C 2 HCl 2 2 Ag -f 3Ag 2 = 2CO + 2C0 2 -f 4AgCl + 2Ag 2 -f OH 2 . Trichlor acetic acid, C 2 C1 3 0(OH). Discovered by Dumas. When a small quantity of crystallizable acetic acid is introduced into a bottle of dry chlorine gas, and the whole exposed to the direct solar rays for several hours, the interior of the vessel is found coated with a white crystalline substance, which is a mixture of trichloracetic acid with a small quantity of oxalic acid. The liquid at the bottom contains the same substances, to- gether with the unaltered acetic acid. Hydrochloric and carbonic acid gases are at the same time produced, together with a suffocating vapor, re- sembling carbonyl chloride. The crystalline matter is dissolved out by a small quantity of water added to the liquid contained in the bottle, and the whole is placed in the vacuum of the air-pump, with capsules containing fragments of caustic potash and concentrated sulphuric acid. The oxalic acid is first deposited, and afterward the trichloracetic acid, in beautiful rhombic crystals. If the liquid refuses to crystallize, it may be distilled with a little anhydrous phosphoric acid, and then evaporated. The crys- tals are spread upon bibulous paper to drain, and dried in a vacuum. The reaction probably takes place according to the equation : 4C 2 H 4 2 -f 11C1 2 = 2C 2 HC1 3 2 -f C 2 H 2 4 + 10HC1 Acetic acid. ' Trichloracetic Oxalic acid. acid. + 2CHC1 3 Chloroform. * Bull. S0c. Chim. de Paris, [2], i. 417. ACETIC ACID. 613 The chloroform is converted, by the further action of the chlorine, into carbon tetrachloride, CC1 4 (Maumene"). Trichloracetic acid may also be produced synthetically, viz., by the ac- tion of chlorine and water on carbon tetrachloride, this compound first taking up 2 atoms of chlorine and ftmning carbon trichloride, C 2 C1 6 , and the latter being converted by the water into hydrochloric and trichloracetic acids : C 2 C1 6 + 20H 2 = 3HC1 -f C 2 HC1 3 2 Trichloracetic acid is a colorless and extremely deliquescent substance : it has a faint odor, and sharp caustic taste, bleaching the tongue and de- stroying the ski-n ; the solution is powerfully acid. At 46 C. (115 F.) it melts to a clear liquid, and at 199 C. (390 F.) boils and distils unchanged. The density of the fused acid is 1-617; that of the vapor, which is very ir- ritating, is probably 5-0. The trichloracetates are analogous to the acetates. The potassium-salt, 2C 2 C1 3 2 K. aq., crystallizes in fibrous silky needles, permanent in the air. The ammonium-salt, 2C 2 C1 3 2 NH 4 . 5 Aq., is also crystallizable and neutral. The silver-salt, C 2 Cl 3 2 Ag, is soluble, and crystallizes in small, grayish scales, easily altered by light. Trichloracetic acid boiled with excess of ammonia yields ammonium car- bonate and chloroform : C 2 HC1 3 2 + 2NH 3 -f OH 2 = C0 3 (NH 4 ) 2 -f CHCL, With caustic potash, it yields a smaller quantity of chloroform, together with potassium chloride, carbonate, and formate. The chloride and for- mate are secondary products of the reaction of the alkali upon the chloro- form. Nascent hydrogen reduces trichloracetic to acetic acid. When potassium or sodium amalgam is put into a strong aqueous solution of trichloracetic acid, the temperature of the liquid rises, without disengagement of gas, and the solution is found to contain acetate and chloride of potassium, to- gether with caustic potash. BROMACETIC ACIDS. Monobromacetic acid, C 2 H 2 BrO(OH), discovered by Perkin and Duppa, is analogous in every respect to monochloracetic acid. It. is formed by acting with bromine on glacial acetic acid in sealed tubes at a temperature above that of boiling water. Ammonia converts it into glycocine, C 2 H 5 N0 2 (p. 614). Dibromacetic acid, C 2 HBr 2 0(OH), is obtained by the further action of bro- mine upon bromacetic acid. It is a liquid boiling at 240 C. (464 F.); heated with silver oxide and water, it is decomposed into silver bromide and bromoglycollic acid: 2C 2 H 2 Br 2 2 + Ag 2 + H 2 = 2AgBr + 2C 2 H 3 Br0 3 Dibromacetic Bromogly- acid. collie acid. Ethyl-dibromacctate, C 2 HBr 2 2 . C 2 H 5 , produced by heating an alcoholic solution of the acid in a sealed tube, is an oily liquid which is decomposed by ammonia, yielding alcohol and dibromacetamide : C 2 HBr 2 2 . C 2 H 5 -f NH 3 = C 2 H 5 OH -f NH 2 C 2 HBr 2 IODACETIC ACID, C 9 H 3 I0 2 , and DI-IODACETIC ACID, C 2 H 2 I 2 2 , have like- wise been obtained. CH 3 TIIIACETIC ACID, C 2 H 4 OS, or C 2 H 3 0(SH), or | .This acid, dis- O^rC SH 52 614 MONATOMIC ACIDS, C n H 2I1 O 2 . covered by Kekule", is formed by the action of phosphorus pentasulphide on glacial acetic acid : 5C 2 H 3 0(OH) + P 2 S 6 = P 2 5 + 5C 2 H 3 0(SH) Thiacetic acid is a colorless liquid, boiling at 93 C. (199 F.) ; it smells like acetic acid and hydrogen sulphide. With solution of lead acetate, it forms a crystalline precipitate containing (C 2 H 3 0) 2 Pb // S 2 , or Pb " \ Qp 2 JJ 3 2 ) ov/a"^ AMIDACETIC ACID, or GLYCOCINE, C 2 H 3 N0 2 , or C 2 H 3 (NH 2 )0 2 . This com- pound is formed by the action of ammonia on bromacetic or chloracetic acid: C 2 H 3 C10 2 -f 2NH 3 = NH 4 C1 -f- C 2 H 3 (NH 2 )0 2 Chloracetic Amidacetic acid. acid. It is also produced by the action of acids or alkalies upon animal sub- stances, such as glue, hippuric acid, glycollic acid, etc. From hippuric acid it is formed according to the equation : C 9 H 9 N0 3 + OH 2 = C 2 H 5 N0 2 + C 7 H 6 2 Hippuric acid. Glycocine. Benzoic acid. To prepare it, hippuric acid is boiled for several hours with concentrated hydrochloric acid ; the liquid is evaporated nearly to dryness ; the residue exhausted with cold water; the solution treated with lead oxide, to sepa- rate the hydrochloric acid, and filtered : the filtrate, after precipitation of the lead by sulphuretted hydrogen, yields on evaporation hard transparent crystals of glycocine. Glycocine is easily soluble in water, nearly insol- uble in alcohol and ether. ' It combines with acids in different proportions. With sulphuric acid it forms the compound (C 2 H 5 N0 2 ) 2 S0 4 H 2 ; and on addi- tion of alcohol to a solution of this sulphate, a salt crystallizing in rectan- gular prisms is deposited, containing 3C 2 H 5 N0 2 . S0 4 H 2 . Glycocine also forms saline compounds by substitution of metal for hydrogen ; for example, C^HgCu^N^ . OH 2 , and C 2 H 4 AgN0 2 : it also combines with metallic salts, forming crystalline compounds, such as C 2 H 5 N0 2 . N0 8 K, and C 2 H 5 N0 2 . Nitrous acid converts glycocine into glycollic or oxyacetic acid : C 2 H 3 (NH 2 )0 2 + 2NO(OH) = C 2 H 3 (OH)0 2 -f OH 2 + N 2 Amidacetic Oxyacetic acid. acid. MetTiyl-glycocine, or Sarcosine, C 3 H 7 N0 2 , or C 2 H 4 (CH 3 )N0 2 , isomeric with alanine (p. 619), is produced by digesting ethyl-chloracetate with an excess of a concentrated aqueous solution of methylamine : C 2 H 2 C10 2 .C 2 H 6 + 2NH 2 CH 3 + OH 2 = C 2 H 2 (CH 3 )(NH 2 )0 2 Sarcosine. -f NH 2 CH 3 .HC1 + C,H 6 (OH) Methylamine Alcohol, hydrochloride. The same compound is formed by boiling creatine * with baryta-water ; ammonia is then eliminated, a precipitate of barium carbonate separates, and the solution, after the removal of the barium by carbonic acid, yields on evaporation colorless rhombic prisms of Sarcosine. The creatine splits into sarcosine and urea, the latter being further decomposed into ammonia * See the chapter on Organic Bases. PROPIONIC ACID. 615 and carbonic acid. Sarcosine dissolves with facility in water ; it is diffi- cultly soluble in alcohol, insoluble in ether, and has no action upon vege- table colors. It combines with acids to soluble salts, which have an acid reaction. The double salt of sarcosine with platinum tetrachloride crys- tallizes in large yellow octohedrons having the composition 2C 3 H 7 N0 2 . 2HCl.PtCl 4 .2 Aq. C H Propionic Acid, C 3 H 6 2 = C 3 H 5 0(OH) == | 2 5 . This acid is pro- COOH' duced : 1. As a potassium-salt by the combination of carbon-dioxide with potassium-ethyl, C0 2 -+- C 2 H 5 K CO(C 2 H 5 )OK. 2. By the action of acids or alkalies on ethyl cyanide (p. 599). 3. By the simultaneous action of water and carbonyl chloride on ethane (p. 599)- 4. By the oxidation of propionic aldehyde, C 3 H 6 0. It should also be formed by oxidation of nor- mal propylic alcohol : but that compound is not known with certainty (p. 531). 5. Together with acetic acid, by oxidizing propione, or meta- cetone, C 5 Hi 0, with aqueous chromic acid. This is the process by which it was first obtained. 6. From lactic acid from which it differs only by containing one atom of oxygen less by the action of hydriodic acid: C 3 H 6 3 + 2HI = C 3 II 6 2 + OH 2 -f I 2 Lactic Propionio acid. acid. 7. Together with several other products, in the fermentation of glycerin, and likewise of sugar, by the action of putrid cheese in presence of cal- cium carbonate. Propionic acid is usually prepared by the second of the above-mentioned processes. Ethyl cyanide is added by drops to a moderately strong solution of potash heated in a tubulated retort, the distillate being repeatedly poured back as long as it smells of ethyl cyanide. The residue in the retort, con- sisting of potassium propionate, is then evaporated down to dryness, and distilled with syrupy phosphoric acid. Propionic acid, when perfectly dry, crystallizes in laminae, and boils at 140 C. (284 F.). It is soluble in water, and when the water is quite saturated with it, the excess of acid floats on the surface in the form of an oil. It has a very sour taste, and a somewhat pungent odor. The propionates are soluble in water. The barium-salt, (CgHjO.^.jBa", 'yields propione by dry distillation. Propionic acid forms substitution-products with chlorine, bromine, and iodine. Chloropropionic acid, CgHgClO^ does not appear to be formed by the action of chlorine on propionic acid; but it is obtained by treating the calcium salt of lactic acid with phosphorus pentachloride, whereby lactyl chloride or chloropropionyl chloride is formed, and decomposing this chloride with water : C 3 H 4 0(OH) 2 -f PC1 5 = C 3 H 4 C10.C1 -f- PC1 3 -f OH 3 Lactic acid. Chloropropionyl chloride. C 3 H 4 C10.C1 -f OH 2 = HC1 + C 3 H 4 C10(OH) Chloropropionyl Chloropropionio chloride. acid. Chloropropionic acid is a liquid less volatile than propionic acid, and hav- ing the odor of trichloracetic acid. Nascent hydrogen converts it into propionic acid. liromopropionic acid, C 3 II 5 Br0 2 , produced by the action of bromine on propionic acid, is converted by alcoholic ammonia into alanine, or amido- propianic acid: C 3 II 5 Br0 2 + 2NH, = C 3 H 6 (NH 2 )0 2 + NH 4 Br. 616 MONATOMIC ACIDS, C n H 2n O 2 . Alanine, homologous with glycocine and isomeric with sarcosine (p. 614), is also produced by boiling a mixture of aldehyde-ammonia and hydro- cyanic acid with dilute hydrochloric acid: C 2 H 4 O.NH 3 + CNH + HC1 + OH 2 = NH 4 C1 + C 3 H 7 N0 2 . Aldehyde- Alanine. ammonia. On evaporating the solution, extracting the hydrochloride of alanine with alcohol, and separating the hydrochloric acid by hydrated lead oxide, a solution is obtained containing alanine in combination with lead oxide, from which the alanine may be separated by saturating the solution with sulphuretted hydrogen, filtering, and evaporating. It forms rhombic prisms of a pearly lustre, easily soluble in alcohol, sparingly soluble in ether. Alanine, like glycocine, combines with acids, bases, and salts. Nitrous acid converts alanine into lactic or oxypropionic acid, C 4 H 6 3 , the reaction being exactly similar to that by which glycocine is converted into glycollic acid. Butyric Acid, C 4 H 8 2 =C 4 H 7 0(OH). Acids having this composition, are obtained by the following synthetical processes: a. By the action of ethyl-iodide on monosodic ethyl acetate (p. 600), and decomposition of the resulting ethylic ethyl-acetate with potash: the pro- duct thus obtained is ethyl-acetic or normal butyric acid : CH 2 Na CH 2 C 2 H 6 | + C 2 H 6 I = Nal + I COOC 2 H 5 COOC 2 H 6 Monosodic Ethyl Ethylic ethyl-acetate. iodide. ethyl-acetate. CH 2 C 2 H 5 CH 2 C 2 H 5 I + HOH = C 2 H 5 (OH) + | COOC 2 H 6 COOH Ethylic Water. Ethyl Ethylacetic ethyl-acetate. alcohol. acid. fi. Disodic ethyl-acetate, treated in like manner with methyl-iodide, yields dimethylic ethyl-acetate : CHNa 2 JCH(CH 3 ) 2 + 2CH,I = 2NaI + I COOC 2 H 6 COOC 2 H 5 ; and this compound, treated with potash, is converted into dimethyl-acetic CH(CH 3 ) 2 or isobutync acid, COOH. Ethylacetic acid boils at 161 C. (322 F.), dimethylacetic acid at 152 C. (305 F.) (Frankland and Duppa). Butyric acid, identical with the first of these synthetical products, occurs ready-formed in tamarinds and a few other plants, and in certain beetles, and is obtained artificially by several processes. 1. By oxidation of primary butyl alcohol.* 2. By saponification of ordi- nary butter, which contains tributyrin : (C 8 H 5 )'"(OC 4 H 7 0) 3 + 3KOH = 3C 4 TI 7 OH + C 3 H 5 (OH 3 ) Tributyrin. Potassium Glycerin. butyrate. * If Erlenmeyer's view of the constitution of the fermentation alcohols be correct, the acid produced by oxidation of butyl alcohol obtained from fusel oil, should be isobutyric acid: the point requires further investigation. BUTYRIC AND VALERIC ACIDS. 617 Other acids of the series are, however, formed at the same time, which are difficult to separate. 3. By the fermentation of sugar in contact with putrid cheese and chalk, calcium lactate being first formed in large quantity, and afterward dis- solved and converted into butyrate, which may be decomposed by sulphuric acid, and distilled. The conversion of lactic into butyric acid probably takes place as shown by the equation : 2C 3 H 6 3 = C 4 H 8 2 + 2C0 2 -f- 2H 2 Lactic acid. Butyric acid. Butyric acid thus obtained is a colorless, very mobile liquid, having an odor of acetic acid and also of rancid butter. Its specific gravity is 0-9886 at 0, and 0-9739 at 15. At the temperature of a mixture of solid car- bonic acid and ether it crystallizes in large laminae. It boils at 164 C. (327 F.), giving off a vapor which burns with a blue flame. It dissolves in all proportions in water, alcohol, and wood-spirit. Boiling nitric acid converts it into succinic acid : 2C 4 H 8 2 + 6 = 20II 2 -f 2C 4 H 6 3 Butyric Succinic acid. acid. The metallic butyrates are, for the most part, soluble in water, and crys- tallizable. The calcium salt C 4 H 7 O a Ca", yields butyrone, C 4 H 7 . C 3 H 7 , by dry distillation. Ethyl Butyrate, C 4 H 7 2 . C 2 H 5 , is a liquid having a pleasant fruity odor: it is sometimes used for flavoring confectionery. Butyric acid, subjected to the action of dry chlorine, is converted first into dlchlorobutyric acid, C 4 H 6 C1 2 2 , and afterward into tetrachlorobutyric acid, C 4 H 4 C1 4 2 . Heated with bromine in sealed tubes to 150-200 C. (302- 392 F.), it forms mono- or dibromobutyric acid, according to the propor- tions used. Dibromobutyric acid is crystallizable. Amidobutyric acid, C 4 H 9 N0 2 , or C 4 H 7 (NH 2 )0 2 , is said to exist, together with its homologue, leucine or amidocaproic acid, in the pancreas of the ox. Valeric, or Valerianic Acid, C 5 TI 10 2 = C 5 H 9 0(OH). This acid occurs in valerian root, in angelica root, in the berries of the guelder rose ( Vibur- num opulus], and probably in many other plants. It is produced by the oxidation of amyl alcohol, either by absorption of atmospheric oxygen under the influence of platinum black, or by treatment with aqueous chromic acid, or by heating it with a mixture of caustic potash and quick- lime, the reaction, in this last case, being attended with evolution of hy- drogen : C 5 H i 2 O + KOH = C 5 H 9 2 K -f OH 2 -f H 2 Amyl Potassium alcohol. valerate. The potassium salt, distilled with sulphuric acid, yields valeric acid. The most advantageous mode of preparing valeric acid, is to oxidize amyl alcohol with a mixture of sulphuric and potassium bichromate. 4 parts of the bichromate in powder, 6 parts of oil of vitriol, and 8 parts of water are mixed in a capacious retort, and 1 part of amyl alcohol is added by small portions, with strong agitation, the retort being plunged into cold water to moderate the violence of the reaction. When the change appears complete, the deep-green liquid is distilled nearly to dryness, the product mixed with excess of caustic potash, and the aqueous solution separated mechanically from a pungent, colorless, oily liquid which floats upon it, consisting of amyl valerate. The alkaline solution is then evaporated to a 52* 618 MONATOMIC ACIDS, C n H 2n O 2 . small bulk, and decomposed by dilute sulphuric acid in excess. The greater part of the valeric acid then separates as an oily liquid lighter than water: this is a hydrate consisting of C 5 H 10 2 . OH 2 . When distilled alone, it undergoes decomposition : water, with a little of the acid, first appears, and eventually the pure acid, C 5 H 10 2 , in the form of a thin, mo- bile, colorless oil, having the persistent and characteristic odor of valerian root. It has a sharp and acid taste, reddens litmus strongly, bleaches the tongue, and burns when inflamed with a bright, yet smoky light. Valeric acid has a density of 0-937: it boils at 175 C. (347 F.). Placed in con- tact with water, it absorbs a certain quantity, and is itself to a certain ex- tent soluble. Valeric acid is active or inactive to polarized light, accordingly as it has been prepared from active or inactive amyl alcohol. That which has been prepared from the active alcohol produces a right-handed rotation of 43 in a tube 50 centimetres long.* The metallic valerates are not of much importance; several of them are crystallizable. The silver-salt contains C 5 H 9 2 Ag. A solution of potassium valerate, subjected to electrolysis, yields dibutyl,C 8 H ]8 (p. 475). Ethyl valerate, C 6 H 9 2 . C 2 H 5 , is obtained by passing hydrochloric acid gas into an alcoholic solution of valeric acid. Ammonia converts it into vale- ramide, C 5 H 9 ONH 2 . CHLOROVALERIC ACIDS. Trichlorovaleric acid, C 5 H 7 C1 3 2 , obtained by the prolonged action of chlorine on valeric acid in the dark, aided toward the end of the process by a gentle heat, is an oily liquid, becoming very viscid at 18 C. (64 F.), perfectly mobile at 30 C. (86 F.). In contact with water it forms a very viscid hydrate, which sinks to the bottom. It dis- solves in aqueous alkalies, and is precipitated by acids in its original state. Tetrachlorovaleric acid, C 5 H 6 C1 4 2 , is the ultimate product of the action of chlorine on the preceding substance, aided by exposure to the sun. It is a semifluid, colorless oil, destitute of odor, of powerful pungent taste, and heavier than water. It can neither be solidified by cold nor distilled with- out decomposition. In contact with water, it forms a hydrate containing C 6 H 6 C1 4 2 . OH 2 , which is slightly soluble in water, easily soluble in alcohol and ether. Isomeric forms of Valeric acid. The formula C 5 H 10 2 may include the four following compounds: CII 2 CH 2 CII 2 CH 3 CH 2 CH(CH 3 ) 2 CHCH 3 [CH 2 CH 3 ] C(CH 3 ) 3 COOH COOH COOH COOH Propyl- Isopropyl- Methyl-ethyl- Triinethyl acetic acid. acetic acid. acetic acid. acetic acid. The second and fourth of these acids have been prepared by Frankland and Duppa.j- CH 2 CH(CH 3 ) Ethyl isopropylacetate, \ , is obtained by the action of isopro- COOC 2 H 5 pyliodide, CH(CH 3 ) 2 I, on monos is obtained by decomposing the normal salt with 1000 parts or more of water, and separates in silvery scales from solution in boiling alcohol. Normal sodium stearate, C, 8 H 35 2 Na, is very much like the potassium-salt, but harder. The acid salt, C 1 8ll 35 2 Na . C 18 H 36 2 , obtained by decomposing the normal salt with 2000 parts or more of water, sepa- rates from the hot solution in nacreous laminae. The stearates of the earth-metals and heavy metals are insoluble in water, and are obtained by precipitation. * Journal fur praktiscbe Chemie, Ixxxix. 215, AKACHIDIC BENIC CEKOTIC ACID. 625 Soaps consist of mixtures of the sodium or potassium-salts of stearic, palmitic, oleic, and other fatty or oily acids, and are produced by saponifying tallow, olive oil, and other fats with caustic alkalies. The soda-soaps are called hard soaps : they separate from the alkaline liquor, on addition of common salt, in hard, unctuous masses, which are the soaps in common use : this mode of separation is called salting out. The potash soaps, on the other hand, cannot be thus separated ; for on adding salt to their solu- tion, they are decomposed and converted into soda-soaps; but they are ob- tained in a semi-solid state by evaporating the solution. The products, called soft soap, always contain a considerable excess of alkali, and are used for cleansing and scouring when a powerful detergent is required. Stearic ethers are formed by heating stearic acid with alcohols, mon- atomic or polyatomic. Ethyl stearate, C, 8 H 35 2 ..C 2 H 5 , is most easily obtained by passing hydrochloric acid gas into an alcoholic solution of stearic acid. It resembles white wax, is inodorous and tasteless, melts at 80 C. (86 F.), and cannot be distilled Avithout decomposition. It is readily decomposed by boiling with caustic alkalies. There are three glyceryl stearates or stearins, analogous in composition to the palmitins: Monostearin, (C 3 H 5 ) /// (OH) (CjgHggOjj), prepared by heating a mixture of equal parts of stearic acid and glycerin to 200 C. (392 F.), in a sealed tube for 36 hours, forms very small white needles, melting at 61 C. (142 F.), and solidifying again at 60 C. (140 F.). Distearin, (C 3 H 5 ) /// OH(C 18 H 35 2 ) 2 , obtained by heating monostearin with 3 parts of stearic acid to 260 C. (500 F. ), for three hours, forms white microscopic laminoe, melts at 58 C. (136 F.), and solidifies at 55 C. (131 F.). Trislearin is prepared by heating monostearin with 15 to 20 times its weight of stearic acid to 270 C. (518 F.), for three hours in a sealed tube ; also from various solid natural fats by solution in ether and repeated crystallization from the hot solution. It crystallizes in masses of white pearly laminae or needles, inodorous, tasteless, neutral, and vola- tilizing without decomposition under reduced pressure. Both natural and artificial tristearin exhibit three isomeric or allotropic modifications. Stearin, separated from ether, melts at 69-7 C. (157 F.) ; but if heated to 73-7 C. (164 F.), or higher, and then cooled, it does not solidify till cooled to 51-7 C. (124 F.). It is solid below 52 C. (125 F.), but melts at that temperature, and if heated a few degrees higher, passes into a third modi- fication, which does not melt below 64-2 C. (148 F.).* Arachidic Acid, C 20 H 40 2 , is a fatty acid obtained by saponification of oil of earth-nut (Arachis hypoysea}. It crystallizes in very small, shining scales, melts at 75 C. (167 F.), and solidifies again at 73-5 C. (164 F.), to a ra- diated crystalline mass. It is but slightly soluble in cold alcohol of ordi- nary strength, but dissolves easily in boiling absolute alcohol and in ether. The silver-salt, C 20 H 39 2 Ag, is a white precipitate, which separates from boiling alcohol in slightly lustrous prisms, not altered by exposure to light. Ethyl arachidate, C 20 H 39 2 . C 2 H 6 , is a crystalline mass, melting at 52-5 C. (120 F.). Berthelot has obtained three glyceryl arachidates or arachins, analogous to the stearins, by heating the acid with glycerin in sealed tubes. by saponification of oil of ben, the oil expressed from the fruits of Moringa Nux Behen. It is a white crystalline fat, melting at 76, and solidifying at 70 C. (158 F.). Cerotic Acid, C^II^Oj. This acid is the essential constituent of cerin, the portion of bees'-wax which is soluble in boiling alcohol. It is prepared by heating the wax several times in succession with boiling alcohol, till the * Duffy, Chem. Soc. Journal, vol. v., pp. 197, 303. 63 626 MONATOMIC ACIDS, C n H 2n _ 2 O 2 . deposit, which forms on cooling, melts at 70 or 72 C. (158-162 F.), and may be further purified by precipitating it from the boiling alcoholic solu- tion with lead acetate, decomposing the precipitate with strong acetic acid, and crystallizing the separated acid from boiling alcohol. Cerotic acid is also produced by the dry distillation of Chinese wax, which consists of ceryl cerotate, C^H^C^ . C^H 55 , or by melting that substance with potash, and decomposing the resulting potassium-salt with an acid (p. 543). Pure cerotic acid crystallizes in small grains, melting at 78 C. (172 F.), and distilling without alteration. Chlorine converts it into chlorocerotic acid, C 27 H 42 C1 12 2 , a thick transparent gum of a pale-yellow color. Ceryl cerotate, or Chinese wax, is produced on certain trees in China by the puncture of a species of coccus. It is crystalline, of a dazzling whiteness, like spermaceti, melts at 82 C. (180 F.) ; dissolves in alcohol ; yields cerotic acid and cerylene, C^H^, by dry distillation. It is used in China for making candles. Melissic Acid, CgoH^Og, the highest known member of the fatty series, is obtained by heating myricyl alcohol (p. 543) with potash lime : Myricyl alcohol. KOH = C 30 H 59 2 K Potassium, melissate. 2H, It bears considerable resemblance to cerotic acid, but melts at a higher temperature, viz., at 88 or 89 C. (190-192 F.). The silver-salt, C^ is a white precipitate. Monatomic Acids of the Series C n H 2n _ 2 2 . Acrylic Series. This series comprises two isomeric groups of acids : the one consisting of acids occurring in the vegetable or animal organism, or obtained from natural products by special processes ; the other of acids formed by a gen- eral synthetical process: we shall designate the acids of the first group as normal acrylic acids, those of the second as isoacrylic acids. Normal Acrylic Acids. The following are the known acids of this group : Acrylic acid . Crotonic acid Angelic acid . Pyroterebic acid . ? Damaluric acid ? Damolic acid . . C 13 H 24 2 Doeglic acid . . . C 19 H 36 2 Moringic acid "I Cimicic acid / Most of these acids are oily liquids. When fused with potassium hydrate, they yield the potassium-salt of acetic and of another acid of the fatty series, with elimination of hydrogen, thus : C 3 H 4 2 Physetoleic acid C 4 H 6 2 C 6 H 8 2 Hypogseic acid Gai'dic acid C 6 H 10 2 Oleic acid ) C H Elai'dic acid / CXX Doeglic acid C 15 H 28 2 Brassic acid ~) Erucic acid J 2KOH Acrylio acid. Angelic acid, == C 2 H 3 K0 2 Acetate. 2KOH = Acetate. CHK0 2 Formate. C 3 H 5 K0 2 Propionate, ACRYLIC CROTONIC ANGELIC ACID. 627 C^HsA + 2KOH = C 2 H 3 K0 2 + C 16 H 31 K0 2 -f H, Oleic acid. Acetate. Palmitate. Generally : C a H 2n _ 2 2 + 2KOH = C 2 H 3 K0 2 + C n _ 2 H 2n _ 6 K0 2 + H 2 They are also converted into fatty acids by the action of nascent hydrogen ; C 4 H 6 2 + H 2 = C 4 H 8 2 Crotonic Butyric acid. acid. Acrylic Acid, C 3 H 4 2 , is produced by the oxidation of its aldehyde, acro- lein, C 3 H 4 0, with moist silver oxide. It is a colorless liquid, having a slightly empyreumatic odor, and miscible in all proportions with water. Its salts resemble the formates and acetates, and are for the most part very soluble in water. Acrylic acid is converted by nascent hydrogen into propionic acid, C 3 H 6 2 , and by bromine into dibromopropionic acid, C 3 H 4 Br 2 2 . Crotonic Acid, C 4 H 6 2 , is produced by saponification of the oil of Croton Tiglium. It is an oily liquid, having a somewhat pungent odor and an acrid taste, moderately soluble in pure water, insoluble in saline water. Heated with potassium hydrate it gives off hydrogen and forms two molecules of potassium acetate : C 4 H 6 2 + 2KOH = 2C 2 H 3 K0 2 + H 2 . Angelic Acid, C 5 H 8 2 , exists in the root of the archangel (Angelica arch- angelica], and in sumbul or moschus root, a drug imported from Asia Minor, and probably also belonging to an umbelliferous" plant. It is obtained from archangel-root, by boiling the root with lime and water, and distilling the strained and concentrated liquid with dilute sulphuric acid. It is also pro- duced by heating the essential oil of chamomile, which consists of angelic aldehyde together with a hydrocarbon, with potassium hydrate: C 5 H 8 + KOH = C 7 H 7 K0 2 -f H 2 . Also, together with oreoselin, by treating peucedanin or imperatorin (a neutral substance contained in the root of Imperaloria Ostruthium, and some other umbelliferous plants), with alcoholic potash : C,,H I2 0, -f KOH = C 5 H 7 K0 2 -f C 7 H 6 2 Peucedanin. Potassium Oreoselin. angelate. Angelic acid crystallizes in long prisms and needles, melts at 45 C. (113 F.), boils at 190 C. (374 F.), and distils without decomposition. It has an aromatic taste and odor, dissolves sparingly in cold, abundantly in hot water, also in alcohol and ether. The angelates of the alkali-metals are soluble in water and in alcohol. Calcium angclate, (C 5 H 7 2 ) 2 Ca x/ . Aq., forms shining, very soluble laminae. The lead-salt, (C 5 H 7 O 2 ) 2 Pb // , is a white precipitate. Potassium angclate treated with phosphorus oxychloride yields angelic oxide, or anhydride, (C 5 II 7 0) 2 0, which is a viscid uncrystallizable oil, boil- ing at 240 C. (464 F.). Pyroterebic acid, C 6 H 10 2 , is produced by dry distillation of terebic acid, C 7 II ]0 O 4 (one of the products of the action of nitric acid on turpentine oil). It is a liquid, boiling at 210 C. (410 F.).J)amaluric acid, C 7 H 12 C 2 , and Damolic acid, C, 3 H 24 2 , are volatile acids, said to exist in the urine of cows 628 MONATOMIC ACIDS, C n H 2n _ a O 2 . and horses. Moringic acid, C, 5 H 28 2 , is an oily acid obtained, together with palmitic, stearic, and benic acids, by the saponification of oil of ben (p. 625). Cimicic acid is a yellow crvstallizable acid, having a rancid odor, extracted by alcohol and ether from a kind of bug (Raphigaster puncti- pennis). Hypogseic Acid, C, 6 H 30 2 , is contained, as a glyceride, together with pal- mitin and arachin, in oil of earth-nut (Arachis hypogiea}. To obtain it, the mixture of fatty acids obtained by saponifying the oil, is dissolved in alco- hol; the palmitic and arachidic acids are precipitated by ammonia and magnesium acetate; the filtrate is mixed with ammonia and lead acetate; the lead precipitate is decomposed by hydrochloric acid ; and the separated hypogseic acid is dissolved out by ether. It is also produced by oxidation of axinic acid (C^H^O^), an acid obtained by saponification of age or axin, a fatty substance contained in the Mexican plant Coccus Axin. Hypogasic acid crystallizes from ether in stellate groups of needles, melting at 34 or 35 C. (93-95 F.), easily soluble in alcohol and ether. Its potassium and sodium salts are soluble in water, the barium salt is soluble in hot, insoluble in cold water; the copper and silver salts are obtained by precipitation. The ethylic ether, C 16 H 29 2 . C 2 H 5 , is a yellow oil, not volatile without decom- position. Nitrous acid converts hypogaoic acid into the isomeric or allotropic com- pound, Ga'idic acid, related to it in the same manner as elai'dic acid to oleic acid. It forms a colorless crystalline mass which melts at 38 C. (100 F.). Physetolcic acid, a crystalline acid obtained from sperm-oil, is isomeric, if not identical, with hypogeeic acid ; it melts at 30, and solidifies at 28 C. (82 F.). Oleic Acid, C ]8 H 34 2 . This acid, the most important of the series, is ob- tained by saponification of olein, the fluid constituent of most natural fats and fixed oils. To obtain pure oleic acid, olive or almond oil is saponified with potash; the soap is decomposed by tartaric acid ; and the separated fatty acid, after being washed, is heated for some hours in the water-bath, with half its weight of lead oxide previously reduced to fine powder. The mixture is then well shaken up with about twice its bulk of ether, which dissolves the oleate of lead and leaves the stearate ; the liquid after standing for some time is decanted and mixed with hydrochloric acid ; the oleic acid thereby eliminated dissolves in the ether, and the ethereal solution, which rises to the surface of the water, is decanted, mixed with water, and freed from ether by distillation. Large quantities of crude oleic acid are now obtained in the manufacture of stearin-candles, by treating with dilute sulphuric acid the lime-soap resulting from the action of lime upon tallow. The fatty acids resulting from the decomposition are washed with hot water, and solidify in a mass on cooling; and this mass, when subjected to pressure, yields a liquid rich in oleic acid, but still retaining a considerable quantity of stearic acid. After remaining for some time in a cold place, it deposits a quantity of solid matter, and the liquid decanted from this is sent into the market as oleic acid or red oil. It may be purified by the process just described. Oleic acid crystallizes from alcoholic solution in dazzling white needles, melting at 14 C. (57 F.) to a colorless oil, which solidifies at 4 C. (39 F.) to a hard, white crystalline mass, expanding considerably at the same time. Specific gravity = 0-808 at 19 C. (66 F.). The acid volatilizes in a va- cuum without decomposition. It is tasteless and inodorous, and reacts neu- tral when unaltered (not oxidized), also in alcoholic solution. It is insoluble in water, very soluble in alcohol, and dissolves in all proportions in ether. Cold strong sulphuric acid dissolves it without decomposition. It dissolves OLEIC AND ISO-ACRYLIC ACIDS. 629 solid fats, stearic acid, palmitic acid, &c., and is dissolved by bile, with formation of a soap and strong acid reaction. Oleic acid, in the solid state, oxidizes but slowly in the air; but when melted, it rapidly absorbs oxygen, acquiring a rancid taste and smell and a decided acid reaction. Its decomposition by fusion with potash has been already mentioned. Chlorine and bromine, in presence of water, convert it into dichloroleic and dibromoleic acid. Bromine, added by drops to fused oleic acid, forms tribromoleic acid, C J8 H 31 Br 3 2 . Strong nitric acid attacks oleic acid with violence, giving off red nitrous vapors, and producing volatile acids of the series C n H 2n 2 , viz., acetic, pro- pionic, butyric, valeric, caproic, cenanthylic, caprylic, pelargonic, and rutic acids; also fixed acids of the series C n H 2n -40 2 , viz., suberic, pimelic, adipic, lipic, and azelaic acids, the number and proportion of these products vary- ing with the duration of the action. Nitrous add converts oleic acid into a solid isomeric or allotropic modifi- cation, called ela'idic acid. Oleates. ThQ formula of the neutral oleates isC l8 H 33 2 M, or (C 18 H 33 2 ) 2 M // , according to the equivalence of the metal; there are likewise acid oleates. The neutral oleates of the alkali-metals are soluble in water, and not so com- pletely precipitated from their solutions by the addition of another soluble salt, as the stearates and palmitates. The acid oleates are liquid and in- soluble in water. The oleates dissolve in cold absolute alcohol and in ether, a property by which they may be distinguished and separated from the stearates and palmitates. Oleins. Oleic acid forms three glycerides, viz., monolein, (C 3 H 5 ) /// (OH) (C, 8 H 33 ? ); diolein, (C 3 H 5 )^(OH)(C I8 H 33 2 ) 2 ; and triolein, (C 8 H B )'"(C 18 H B 2 ) 3 , which are produced by heating oleic acid and glycerin together in sealed tubes in various proportions. The first two solidify at about 15. The olein of animal fats, and of olive oil and several other oils, both ani- mal and vegetable, which do not dry up in the air by slow oxidation, but are converted into viscid masses having a rancid odor and acid reaction (non-drying oils), appears to be identical with triolein, but there is great difficulty in obtaining it pure. Olive oil, cooled to 4 C. (39 F.) or a lower temperature, deposits a large quantity of solid fat, consisting mainly of palmitin (originally called margarin, from its pearly lustre), and the oil filtered therefrom consists mainly of olein. A purer olein is obtained by treating olive oil with a cold strong solution of caustic soda, which saponi- fies the solid fats, and leaves the olein unaltered. Olein, subjected to dry distillation, yields gaseous products, liquid hydrocarbons, acrolein, and sebic acid. Some non-drying oils contain the glycerides of acids homologous with oleic acid ; such is the case, as already observed, with croton-oil, earth-nut oil, and sperm-oil. Doegling train-oil, obtained from the doegling or bottle- nosed whale (Balama rostrata), yields doealic acid, C^H^O^ Colza-oil, ob- tained from the seeds of certain species of Brassica, especially the summer rape or colza, Brassica campestris, var. oleifera, yields brassic acid, C 2 .,H 42 2 ; and the oil of black mustard-seed yields a similar and probably identical acid, called erucic acid. Drying oils, such as linseed and poppy oils, and castor-oil which is a non-drying oil, contain the glycerides of acids belonging to other series, which will be noticed hereafter. Iso-acrylic Acids. Acids isomeric with the natural acrylic acids are produced by abstraction of the elements of water from certain acid ethers, having the composition 630 MONATOMIC ACIDS, C u H 2n _ 2 O 2 . of oxalic acid in which one atom of oxygen is replaced by two equivalents of an alcohol-radical of the series, C n H 2 n4- 1 : CH CH 2 CH 3 HO C CH 3 HO C:=0 Ethometh- oxalic acid. CH 2 CH 3 HO C CH 2 CH 3 HO C=0 Dieth oxalic acid. HO C=0 HO C CH HO C=0 HO 0=0 Oxalic acid. Dimethoxalic acid. Now, when the ethylic ethers of these acids are treated with phosphoric oxide or phosphorus trichloride, they give up a molecule of water (OH 2 ), at the expense of one of the molecules of hydroxyl (OH) and an atom of hydrogen abstracted from one of the monad alcohol-radicals, which is thereby converted into a dyad radical (an olefine) capable of saturating the unit of equivalence of the carbon-atom set free by abstraction of the hy- droxyl. The product is the ethylic ether of an iso-acrylic acid ; thus, CH HO C CH, I H 6 C 2 C=0 Ethylic dimeth- oxalate. - OH 2 = H 2 C=C CH 3 | H 6 C 2 C=0 Ethylic methyl- acrylate. The ethylic ether thus formed is converted into methacrylic acid by saponi- fication with potash in the usual way. In this manner the following iso- acrylic acids have been obtained : C(CH 3 )(CH 2 )" Methacrylic acid . . . | isomeric with Crotonic acid COOH C(CH 3 )(C 2 H 4 )" Methylcrotonic acid . | COOH C(C 2 H 5 )(C 2 H 4 )" Ethylcrotonic acid . . | COOH Angelic acid Pyroterebic acid The actual formation of the ethers of these acids, by the action of phos- phoric oxide and phosphorous chloride on the oxalic compounds above mentioned, takes place in the manner shown by the following equations: C(OH)(CH 3 )(C 2 H 6 ) C Ethylic ethometh- oxalate. C(OH)(C 2 H 6 ) 2 Phosphoric oxide. C(CH 3 )(C 2 H 4 ) Ethylic methyl- Metaphos- crotonate. phoric acid. C(C 2 H,)(C 2 HJ" ' Ethylic dieth- Phosphor- Ethylic* Phosphor- oxalate. ous chloride, ethyl-crotonate. ous acid. The iso-acrylic acids, when fused with potassium hydrate, are converted, like the normal acrylic acids, into two acids of the acetic series. The dyad radical of the iso-acrylic acid is displaced by two atoms of hydrogen de- rived from two molecules of potassium hydrate (2KOH), and enters into ISO-ACRYLIC ACIDS. 631 combination with two atoms of oxygen; and at the same time the two atoms of potassium displace the basic hydrogen-atoms of the two acids thus produced, converting them into potassium-salts, and expelling the hydro- gen as gas; thus: C(CH 2 )"CH 3 CH 2 CH 3 H COOH 2KOH = 1 COOK COOK Methacrylic Propionate. Formate. acid. C(C,H 4 )"CH CH 2 CH 3 CH 3 I -f COOH 2KOH = 1 COOK COOK Methyl-cro- Propionate. Acetate. tonic acid. C(C 2 H 4 )"C 2 H 6 CH 2 C 2 H 6 CH 3 COOH 2KOH = | COOK + 1 COOK Ethyl-cro- Butyrate. Acetate. tonic acid. + The normal acrylic acids are decomposed by potash in a similar manner, yielding two acids of the series, C n H 2n 2 ; but one of these is always acetic acid. Hence it is inferred that they have a constitution represented by C(C Q H 2n )"H the formula I , and that their decomposition by potash is rep- COOH resented by the equation : C(CnH 2n )"H CH, Cn-.EU..! | + 20H 2 =1 +| + H 2 COOH COOH COOH Iso-acrylic Acetic Homologue of acid. acid. acetic acid. The formulae of the individual acids are as follows : CH(CH,)" CH(C a H 4 )" CH(C 8 H 6 )" CH(C 4 H 8 )" CH(C 16 H 32 ) COOH COOH COOH COOH ' ' COOH Acrylic. Crotonic. Angelic. Pyroterebic. Oleic. It is easily seen from these formulae that crotonic acid, when decomposed by an alkali, must yield two molecules of acetic acid; and that the other acids above formulated must yield acetic acid together with formic, pro- pionic, butyric, and palmitic acids respectively. An acid isomeric with crotonic acid, and differing from methacrylic acid, has been obtained by boiling allyl cyanide with caustic potash: C 3 H 5 CN + KOH -}- OH 2 = NH 3 + C 4 H 5 K0 2 CH(CH 2 )" Frankland assigns to this acid the composition CH 2 COOH There is also an acid called campholic acid, C ]0 H, 6 2 , produced by heating common camphor, C^H^O, with potassium hydrate. It cannot be included in either of the series of acrylic acids, inasmuch as it does not exhibit the 632 MONATOMIC ACID, C u H 2n _ 6 O 2 . reactions of either. It is a white crystalline body, insoluble in water, soluble in alcohol and ether, decomposed by distillation with phosphoric oxide, into carbon monoxide, water, and campholene, C 9 H J6 . Monatomic Acids belonging to the series CnH 2n _ 4 2 , or C n H 2n _ 5 0(OH). Only three acids of this series are known, viz. : sorbic and parasorbic acids, both having the composition C 6 H 8 2 , and camphic acid, C^H^O.^. Parasorbic acid is a volatile oily acid obtained from mountain-ash berries; sorbic acid is a crystallizable acid produced from it by gentle heating with solid potash, or boiling with strong hydrochloric acid; it melts at 134-5 C. (274 F.), volatilizes without decomposition, and decomposes carbonates. Camphic acid, C 10 H 16 2 , is obtained, together with the corresponding alco- hol, camphol (p. 546), by heating common camphor with alcoholic soda- solution in sealed tubes to 170-190 C. (338-374 F.). 2C 10 H W + OH 2 = C 10 H 18 + C 10 H 16 2 Camphor. Camphol. Camphic acid. By neutralizing the resulting alkaline solution with sulphuric acid, dis- solving out the sodium camphate with alcohol, evaporating, and again adding sulphuric acid, the camphic acid is obtained as a solid mass heavier than water, insoluble therein, easily soluble in alcohol. The potassium and sodium salts are insoluble in strong alkaline lyes. They precipitate the salts of copper, iron, silver, and zinc, not those of the alkali-metals ; all the precipitates are soluble in a large quantity of water. Monatomic Acid belonging to the series CnH^^C-.,. Ilydrobenzoic acid, C 7 H 10 2 , or C 7 H 9 0(OH).* This acid, corresponding to the unknown alcohol, C 7 H 12 0, is formed, together with other products, by the action of sodium amalgam on benzoic acid: C 7 H 6 2 + 2H 2 = C 7 H 10 2 Benzoic Hydroben- acid. zoic acid. It is more easily obtained, however, by boiling hydrobenzyluric acid (a product of the decomposition of hippuric acid by sodium amalgam) with alkalies in a close vessel: C 16 H 21 N0 4 + OH 2 = C 2 H 5 N0 2 + C 7 H 8 + C 7 H 10 2 Hydrobenzyl- Glycocine. Benzyl Hydroben- uric acid. alcohol. zoic acid. It is a crystalline acid, forming a crystalline calcium salt, (C 7 H 9 2 ) 2 Ca, and, when recrystallized either in the free state or in the form of calcium salt, is ultimately converted by oxidation into benzoic acid. Its ethylic ether, C 7 H 9 2 . C 2 H 5 , has the odor of ethyl valerate. * M. Hermann, Ann. Ch. Pharm. cxxxii. 75. R. Otto, ibid, cxxxiv. 303. BENZOIC ACID. 633 Monatomic Acids belonging to the series OH 2n _ 8 2 . Aromatic Acids. These acids are produced by some of the processes which yield the fatty acids, viz. 1. By the oxidation of the corresponding aldehydes and primary alcohols: thus benzoic acid, C 7 H 8 2 , is formed by oxidation of benzole aldehyde, C 7 H 6 0, and of benzylic alcohol, C 7 H 8 0. 2. By the action of water on the corresponding acid chlorides. 3. By the action of alkalies on the cyanides of aromatic alcohol-radicals. They are likewise obtained : 4. By the simultaneous action of sodium and carbon dioxide on the monobrominated derivatives of the aromatic hydro- carbons: thus, C 6 H 5 Br + Na -f C0 2 = NaBr -f- C 7 H 5 Na0 2 Bromo- Sodium benzene. benzoate. 5. Certain aromatic acids are produced by the oxidation of hydrocar- bons homologous with benzene. The known acids of this series are : Benzoic acid, C 7 H 6 2 . Toluic and Alpha-toluic acids, C 8 H 8 2 . Xylic and Alpha-xylic acids, C 9 H 10 2 . Cumic acid, C 10 H 12 2 , homologous with toluic acid. Alpha-cymic acid, C 11 H U 2 , homologous with alpha-toluic acid. Benzoic Acid, C 7 H 6 2 = C 7 H 5 0(OH). This acid is the analogue of ben- zylic alcohol, and is produced from it by oxidation with aqueous chromic acid: C 6 H 5 .CH 2 OH + 2 = OII 2 -f C 6 H 5 .COOH Benzyl al- Benzoic cohol. acid. It is also formed by oxidation of benzoic aldehyde, C 7 H 6 (bitter-almond oil), in presence of platinum black, or with nitric acid. It may be produced directly from benzene, by acting upon that com- pound in the state of vapor with carbonyl chloride (phosgene gas) whereby .it is converted into benzoyl chloride, and decomposing this chloride with water : C 6 H 6 + COC1 2 = HC1 -f C 7 H 5 OC1 Benzene. Carbonyl Benzoyl chloride. chloride. C 7 H 6 OC1 + OH 2 = HC1 -f C 7 H 6 0(OH) Benzoyl Benzoic chloride. acid. Fourthly, it is obtained by boiling hippuric acid (or the urine of cows or horses which contains that acid) with hydrochloric acid. The hippuric acid, C ( jH 9 NO 3 , which has the composition of benzoyl-glycocine, then takes up a molecule of water, and is resolved into glycocine (p. G14) and benzoic acid: C 2 H 4 (C 7 H 6 0)N0 2 + OH 2 = C 2 H 6 N0 2 -f- C 7 H 6 2 Hippuric acid. Glycocine. Benzoic acid. This process is applied to the preparation of benzoic acid on the large scale. Benzoic acid is also produced by the oxidation of a great variety of or- 634 MONATOMIC ACIDS, C n H 2n _ 8 O 2 , ganic bodies, as cumene, cinnamic aldehyde, cinnamic acid, cinnamene, casein, gelatin, &c. Benzoic acid exists ready formed in large quantity in several balsams and gum-resins, especially in gum-benzoin, a resin which exudes from the bark of Styrax benzoin, a tree growing in Sumatra, Java, Borneo, and Siam. When this substance is exposed to a gentle heat in a subliming ves- sel, the benzoic acid is volatilized, and may be condensed. The simplest and most efficient apparatus for this and all similar operations is the con- trivance of Dr. Mohr: it consists of a shallow iron pan, over the bottom of which the substance to be sublimed is thinly Fig. 194. spread ; a sheet of bibulous paper, pierced with a number of pin-holes, is then stretched over the ves- sel, and a cap made of thick, strong drawing or car- tridge-paper, is secured by a string or hoop over the whole. The pan is placed upon a sand-bath, and slowly heated to the requisite temperature ; the va- por of the acid condenses in the cap, and the crystals are kept by the thin paper diaphragm from falling back again into the pan. Benzoic acid thus obtained assumes the form of light, feathery, coloi^less crys- tals, which exhale a fragrant odor, not belonging to the acid itself, but due to a small quantity of volatile oil. A more productive method of preparing the acid is to mix the pow- dered gum-benzoin very intimately with an equal weight of slaked lime, boil this mixture with water, and decompose the filtered solution, concen- trated by evaporation to a small bulk, with excess of hydrochloric acid ; the benzoic acid crystallizes out on cooling in thin plates, which may be drained upon a cloth filter, pressed, and dried in the air. By sublimation, which is then effected with trifling loss, the acid is obtained perfectly white. Benzoic acid is inodorous when cold, but acquires a faint smell when gently warmed: it melts just below 121 C. (250 F.), and sublimes at a temperature a little above ; it boils at 249 C. (480 F.), and emits a vapor of the density of 4-27. It dissolves in about 200 parts of cold and 25 parts of boiling water, and with great facility in alcohol. Benzoic acid is not affected by ordinary nitric acid, even at boiling heat; but with fuming nitric acid it forms a substitution-product. Chlorine also acts on benzoic acid, forming substitution-products. Phosphorus pentachloride converts it into benzoyl chloride, C 7 H 5 OC1. Benzoic acid dissolves in ordinary strong sul- phuric acid, but is precipitated unaltered on addition of water. By fuming sulphuric acid, however, and still more readily by sulphuric oxide, it is converted into sulphobenzoic acid, C 7 H 6 S0 5 , a bibasic acid to be described hereafter. By nascent hydrogen (evolved by sodium-amalgam) it is partly reduced to benzoic aldehyde and benzylic alcohol, and is partly converted, by addition of hydrogen, into hydrobenzoic acid, C 7 H 10 2 (p. 632). All the benzoates are more or less soluble : they are easily formed, either directly or by double decomposition. The benzoates of the alkalies and of am- monia are very soluble, and somewhat difficult to crystallize. Calcium ben- zoate forms groups of small colprless needles, which require 20 parts of cold water for solution. The barium salts are soluble with difficulty in the cold. Neutral ferric benzoate is a soluble compound; but the basic salt ob- tained by neutralizing as nearly as possible with ammonia a solution of ferric oxide, and then adding ammonium benzoate, is quite insoluble. Iron is sometimes thus separated from other metals in quantitative analysis. Neutral and basic lead benzoate are freely soluble in the cold. Silver ben- zoate crystallizes in thin transparent plates, which blacken on exposure to light. BENZOIC ACID. 635 Calcium benzoate is resolved by dry distillation into calcium carbonate and benzone, or benzophenone, C 13 H 10 0, the ketone of benzoic acid: (C 7 HA) 2 Ca" = C0 3 Ca + CO(C 6 H 6 ) 2 Calcium. l}en- Benzone. zoate. On the other hand, benzoic acid, distilled with excess of lime, is resolved into carbon dioxide and benzene: C 7 H 6 2 = C0 2 + C 6 H 6 . BENZOIC CHLORIDE, OR BENZOYL CHLORIDE, C 7 H 5 OC1. This compound, derived from benzoic acid by substitution of chlorine for hydroxyl, is pre- pared by the action of phosphorus pentachloride on benzoic acid: C 7 H 5 0(OH) + PC1 3 C1 2 = POC1 3 + HC1 -f C 7 H 6 OC1. The two substances are mixed in equivalent quantities, and gently heated. A brisk reaction ensues, hydrochloric acid is evolved, while oxychloride of phosphorus distils over; and when the temperature rises to 196 C. (884 F.), the receiver is to be changed, and the benzoyl chloride, which passes over at that temperature, collected separately. It may also be prepared by sub- jecting bitter-almond oil (C 7 H 6 0) to the action of dry chlorine gas. It is a colorless liquid of peculiar, disagreeable, and pungent odor; its density is 1'106. The vapor is inflammable, and burns with a greenish flame; its density (referred to air) is 4-987. Benzoyl chloride is decomposed slowly by cold and quickly by boiling water into benzoic and hydrochloric acids : with an alkaline hydrate, a benzoate, and chloride of the alkalic metal, are generated. BENZOYL IODIDE, C 7 H 5 OI, is prepared by distilling the chloride with po- tassium iodide: it forms a colorless, crystalline, fusible mass, decomposed by water and alkalies in the same manner as the chloride. The bromide, C 7 H 5 OBr, has very similar properties. Benzoyl cyanide, C 7 H 5 . CN, ob- tained by heating the chloride with mercuric cyanide, forms a crystalline mass, fusing at 31 C. (87 F.), boiling at 207 C. (404 F.), and having a pungent odor, somewhat resembling that of cinnamon. All these com- pounds yield benzamide with dry ammonia. BENZOYL OXIDE, OR ANHYDRIDE, C, 4 H 10 3 , or (C 7 H 5 0) 2 0, is obtained by the action of benzoyl chloride on potassium benzoate : C 7 H 5 0(ONa) -f C 7 H 6 OC1 = NaCl + (C 7 H 5 0) 2 0. Benzoyl chloride acts in like manner on acetate or valerate of sodium, form- ing aceto-benzoic or valero-benzoic oxide, either of which splits up on dis- tillation into acetic or valeric oxide and benzoic oxide : C 7 H 5 OC1 Benzyl chloride. C 6 H fl O(ONa) = Sodium valerate. NaCl 59 Valero-ben- zoic oxide. and f C 7 H 5 \ Valero-ben- zoic oxide. (C 7 H 5 0) 2 Benzoic oxide. () 2 Valeric oxide. Benzo-oenanthylic, benzostearic, ben/o-angelic, benzo-cuminic oxide, and several others, have been obtained by similar processes. Benzoic oxide crystallizes in oblique rhombic prisms, melting at 42 C. 636 MONATOMIC ACIDS, C n H 2n _ 8 O 2 . (107 F.), and distilling undecomposed at 310 C. (590 F.). It melts in boiling water, remaining fluid for a long time, but is ultimately converted into benzoic acid, and dissolves : caustic alkalies etfect the conversion much more rapidly. With ammonia it forms ammonium benzoate and benzamide : (C 7 H.O) 2 + 2NH 3 = C 7 H 6 0(NH 4 )0 -f NH 2 C 7 H 5 Benzoic Ammonium Benzamide. oxide. benzoate. BENZOYL DIOXIDE, OR PEROXIDE, C 14 H 10 4 , or (C 7 H 5 2 ) 2 . Brodie ob- tained this compound by bringing benzoyl chloride in contact with bari- um dioxide under water; the product, when re-crystallized from ether, yields large shining crystals of benzoyl dioxide, which explode when heated. When submitted to the action of a boiling solution of potash, this substance evolves oxygen, and forms potassium benzoate. BENZOYL SULPHIDE, (C 7 H 5 0) 2 S, obtained by distilling the chloride with finely powdered lead sulphide, is a yellow fetid oil, solidifying at a low temperature to a soft crystalline mass. DIBENZOYL, C 14 H 10 4 . Cupric benzoate subjected to gradual dry distil- lation, gives a residue containing salicylic and benzoic acids, and an oily distillate which crystallizes on cooling, and consists of dibenzoyl. This substance possesses the odor of the geranium, melts at 70 C. (158 F.). It was discovered by Ettling, and subsequently studied by Stenhouse. By heating with potassium hydrate, it is instantly converted into benzoic acid, with evolution of hydrogen. Acids derived from Benzoic Acid by substitution. CHLOROBENZOIC ACID, C 7 H 5 C10 2 , is obtained by treating benzoic acid with potassium chlorate and hydrochloric acid. Acids having the same com- position are produced by the action of chlorine upon benzoic acid in sun- light, and also by distilling sulphobenzoic acid, salicylic acid, or hippuric acid, with phosphorus pentachloride, and boiling the distillate with water. The acids obtained by these several methods, however, diifer in their prop- erties. Chlorobenzoic acid treated with sodium amalgam and water is con- verted into benzoic acid. BROMOBENZOIC ACID, C 7 H 6 Br0 2 , is formed by the action of bromine on silver benzoate : C 7 H 5 2 Ag -f Br 2 = AgBr + C 7 H 5 Br0 2 . Bromine docs not act on benzoic acid at ordinary temperatures. NITROBENZOIC ACID, CjH^NOgjOj, is obtained by boiling benzoic acid for several hours with fuming nitric acid; and by prolonged action of the fum- ing nitric acid, or more readily by the action of a mixture of nitric and sulphuric acids, dinitrobenzoic acid, C 7 H 4 (N0 2 ) 2 2 , is produced. Both these are crystalline bodies, analogous in most of their reactions to benzoic acid. AMIDOBENZOIC ACIDS. Nitrobenzoic and dinitrobenzoic acids are re- duced, by treatment with certain reducing agents, as hydrogen sulphide or ammonium sulphide, to amido-benzoic and diamido -benzoic acids : C 7 1T 5 (N0 2 )0 2 -f 3SH 2 = 20H 2 + S 3 + C 7 H 5 (NH 2 )0 2 Nitrobenzoic Amidobenzoic acid. acid. C 7 H 4 (N0 2 ) 2 2 -f 6SH 2 = 40H 2 + S 6 -f- C 7 H 4 (NH 2 ) 2 2 Dinitrobenzoic Diamido- acid. benzoic acid. ACETAMIDOBENZOIC HIPPURIC ACIDS. 637 Both these are crystalline compounds. Amidobenzoic acid is a monobasic acid, forming metallic salts and ethers ; diamidobenzoic acid, on the con- trary, possesses no acid properties, but is rather a base, combining readily with hydrochloric and other acids, and forming crystallizable salts. When amidobenzoic acid, C 7 H 7 N0 2 , is subjected to the action of nitrous acid, two molecules of it give up three atoms of hydrogen in exchange for one atom of nitrogen, and are converted into a compound containing C M H lt N/>, 2C 7 H 7 N0 2 + N0 2 H = 20 H 2 -j- C 14 H U N 3 4 . This substitution of hydrogen for nitrogen was first observed by Griess, Avho has since shown that it is susceptible of very general application. By the prolonged action of nitrous acid, the compound C 14 H U N 3 4 is partially converted into oxybenzoic acid, C 7 H 6 2 . ACETAMTDOBENZOIC ACID,* CgHgNO,, = C 7 H 5 [NH(C 2 H 3 0)]0 2 , or C 7 H 4 NH(CH 3 0) . This acid is produced by digesting amidobenzoic acid COOH with acetic acid at 130-140 C. (266-284 F.) in a sealed tube: C 7 H 5 (NH 2 )0 2 + C 2 H 3 0(OH) = OH 2 + C 7 H 5 [NH(C 2 H 3 0)]0 2 , Amidobenzoic Acetic Acetamidobenzoic acid. acid. acid. or by the action of acetyl chloride or acetic acid on zinc amidobenzoate : (C 7 H 6 N0 2 ) 2 Zn" -f 2C 2 H 8 OC1 == ZnCl 2 -f 2C 7 H 6 (C 2 H 3 0)N0 2 Zinc oxybenzoate. Acetyl Acetamidobenzoic chloride. acid. Acetamidobenzoic acid is a white powder, consisting of microscopic crys- tals, insoluble in cold water and ether, slightly soluble in boiling water, easily in boiling alcohol. It is a monobasic acid, forming easily soluble salts with the metals of the alkalies and alkaline earths ; sparingly soluble salts with lead, silver, and zinc. By boiling with hydrochloric or dilute sulphuric acid, it is resolved into acetic and amidobenzoic acids : C 9 H 9 N0 3 + OH 2 = C 2 H 4 2 + C 7 H 7 N0 2 . HIPPURIC ACID, OR BENZAMIDACETIC ACID, C fi rLNO. = C,H.(C 7 H-0)N0 2 C 2 H 2 NH(C 6 H 6 0) = C 2 H 3 [NH(C 7 H 5 0)]0 2 or | . This acid, isomeric with COOH acetamidobenzoic acid, is produced by the action of benzoyl chloride on the zinc salt of amidacetic acid (glycocine) : (C 2 H 4 N0 2 ) 2 Zn" + 2C 7 H 5 OC1 = ZnCl 2 + 2C 2 H 3 [NH(C 7 H 5 0)]0 2 ; the reaction being analogous to the second of those above given for the formation of acetamidobenzoic acid. Hippuric acid occurs, often in large quantity, as a potassium or sodium- salt, in the urine of horses, cows, and other graminivorous animals ; in smaller quantity also in human urine. It is prepared by evaporating in a Iivater-bath perfectly fresh cows' urine to about a tenth of its volume, filter- .ng from the deposit, and then mixing the liquid with excess of hydro- chloric acid. Cows' urine frequently deposits hippuric acid without con- centration, when mixed with a considerable quantity of hydrochloric acid, in which the acid is less soluble than in water. The brown crystalline * G. C. Foster, Chem. Soc. Journal, xili. 235. " 638 MONATOMIC ACIDS, C n H 2n _8O 2 . mass, which separates on cooling, is dissolved in boiling water, and treated with a stream of chlorine gas, until the liquid assumes a light amber color, and begins to smell of chlorine : it is then filtered and left to cool. The still impure acid is re-dissolved in water, neutralized with sodium carbonate, and boiled for a short time with animal charcoal: the hot filtered solution is, lastly, decomposed by hydrochloric acid. Hippuric acid crystallizes in long, slender, milk-white, and exceedingly delicate square prisms, which have a slightly bitter taste, melt on the ap- plication of heat, and require for solution about -400 parts of cold water: it also dissolves- in hot alcohol. It has an acid reaction, and forms salts with bases, many of which are crystallizable. Exposed to a. high temper- ature, hippuric acid undergoes decomposition, yielding benzoic acid, am- monium benzoate. and benzonitrile, with a coaly residue. With hot oil of vitriol, it gives off benzoic acid ; boiling hydrochloric acid converts it into benzoic acid and amidacetic acid or glycocine : C 2 H 4 (C 7 H 5 0)N0 2 + H(OH) = C 7 H 5 0(OH) + C 2 H 6 N0 2 , Hippuric acid. Water. Benzoic Amidacetic acid. acid. just as acetamidobenzoic acid is resolved into acetic and amidobenzoic acids. Hippuric acid, treated with nitrous acid, gives off nitrogen, and is con- verted into benzoglycollic acid, an acid containing the elements of benzoic and glycollic (oxyacetic) acids, minus one molecule of water : C 9 H 9 N0 3 -f N0 2 H = C 9 H 8 4 + OH 2 -f N 2 Hippuric Nitrous Benzogly- acid. acid. collie acid. Benzoglycollic acid, when boiled with water, splits up into benzoic and gly- collic acids : C 9 H 8 4 + OH 2 = C T H 6 2 + C 2 H 4 3 . If, in the preparation of hippuric acid, the urine be in the slightest de- gree putrid, the hippuric acid is all destroyed during the evaporation, am- monia is disengaged in large quantity, and the liquid is then found to yield nothing but benzoic acid, not a trace of which can be discovered in the unaltered secretion. Complete putrefaction effects the same change : benzoic acid might thus be procured to almost any extent. When benzoic acid is taken internally, it is rejected from the system in the state of hip- puric acid, which is then found in the urine. Hippuric acid is monobasic, the formula of the hippurates of monatomic metals being C 9 H 8 MN0 3 . Most metallic oxides dissolve readily in hippuric acid. The hippurates of potassium, sodium, and ammonium, are very soluble, and difficult to crystallize ; their solutions form a cream-colored precipitate with ferric salts, and white curdy precipitates with silver ni- trate and mercurous nitrate. A characteristic reaction of the hippurates is, that, when fused with excess of potash or lime, they give off ammonia and yield benzene by distillation. Mineral acids decompose them, separat- ing the hippuric acid. Hippuric acid dissolves so abundantly in an aqueous solution of sodium phosphate, that this solution loses its alkaline reaction and becomes acid. This reaction may explain the acid character of the recent urine of man and animals. Toluic Acid, C 8 H 8 2 = C 8 H t O(OH). This formula includes two isomeric acids, viz. : Normal toluic acid, C 6 H 4 (CH 3 ) . COOH, corresponding to xylylic alcohol, C 6 H 4 (CH 3 ) . CH 2 OH, derived from dimethyl-benzene (p. 497). XYLIC CUMIC ACIDS. 639 Alpha-toluic acid, 6 H 5 . CII 2 COOH, corresponding to the unknown alco- hol, C 6 H 5 .CH 2 CH 2 OH, derived from ethyl-benzene. Normal toluic add is produced 1. By oxidation of xylene with dilute nitric acid: C 8 H W + 3 = OH 2 + C 8 H 8 2 Also by the prolonged action of dilute nitric acid on cymene (p. 500), oxalic acid being formed at the same time : C 10 H 14 + 8 = C 8 H 8 2 + C 2 H 2 4 + 20H 2 Cymene. Toluic Oxalic acid. acid. 2. Synthetically, by the action of sodium and carbon dioxide on bromo- toluene : C 7 H 7 Br -f Na 2 -f- C0 2 = NaBr -f- C 7 H 7 .C0 2 Na Bromo- Sodium toluene. toluate. Toluic acid is precipitated by acids from the solution of its salts as a white crystalline mass, which melts at about 175 C. (347 F.), and sub- limes without decomposition in fine needles. Its chemical reactions are analogous to those of benzoic acid. By distillation with lime or baryta it is resolved into carbon dioxide and toluene, C 7 H 8 . Distilled with phos- phorus pentachloride, it yields toluic chloride, C 8 H 7 OC1, or C 6 H 4 CH 3 . COC1. Strong nitric acid, at the boiling heat, converts it into nitrotoluic acid, C 8 H 7 (N0 2 )0 2 . When introduced into the animal organism, it is excreted as toluric acid, C, H n N0 3 , a homologue of hippuric acid. Alpha-toluic acid, C 6 H 6 . CH 2 C0 2 H, is produced by boiling benzyl cyanide with strong potash solution as long as ammonia is given oif : C 6 H 6 .CH 2 CN + 20H 2 = NH 3 + C 6 H 5 CH 2 COOH Benzyl- Alpha-toluic cyanide. acid. The reaction amounts to an interchange between an atom of trivalent nitrogen and the group // (OH) : hence the constitution of the acid is apparent. Alpha-toluic acid crystallizes from boiling water in broad, thin laminae, very much like benzoic acid : it has an odor like that of the perspiration of horses. It melts at 76-5 C. (169 F.), gives oif, even below 100, vapors which excite coughing, and boils at 265-5 C. (510 F.). It forms a sub- stitution-product with nitric acid, and when distilled with phosphorus pentachloride, yields alpha-toluic chloride, C 8 H 7 OC1, or C 6 H 6 . CH 2 COC1, which passes over as a colorless heavy liquid. Xylic Acid, C 9 H 10 2 = C 6 H 3 (CH 3 ) 2 . C0 2 H, homologous with benzoic and with normal toluic acid, is produced by the action of sodium and carbon dioxide on bromo-xylene, C 8 H 9 Br; also, by oxidizing cumene, C 9 H 12 , with nitric acid. Insolinic acid, C 9 H 8 4 , is formed at the same time, but the two acids are easily separated by distillation, the xylic acid passing over, while the insolinic acid remains behind. Xylic acid crystallizes from boiling water in needles, melts at 103 C. (217 F.), boils at 273 C. (523 F.), and sublimes easily in needles. Alpha-xylic acid, C 6 H 4 (CH 3 ) . CH 2 C0 2 H, is obtained by boiling xylyl chlo- ride with potassium cyanide (whereby xylyl cyanide, C 8 H 9 C1, is produced), and then with potash. It crystallizes in broad needles, having a satiny lustre, easily soluble in water, and boiling at 42 C. (108 F.). Cumic Acid, C 10 H 12 2 , probably C 6 H 4 (C 3 H 7 ) . C0 2 H, homologous with ben- 640 MONATOMIC ACIDS, C H 2n _ 10 O 2 . zoic and normal toluic acids, is produced by oxidation of cuminol or cumic aldehyde, C 10 H 12 0, one of the constituents of oil of cumin. It is very much like benzoic acid, is converted by fuming nitric acid into nitrocumic acid, Ci H u (NO) 2 4 , and resolved, by distillation with lime, into carbon dioxide and cumene, C 9 H, 2 . Cymic Acid, C U H U 2 . Normal cymic acid is not known, but alphacymic acid, probably C 6 H 3 (C 2 H 6 ) 2 COOH, is produced by the action of caustic alkalies on cymyl cyanide, C JO H 13 CN. Monatomic Acids, C n H 2n _ 10 2 . The acids of this series are related to the aromatic acids, in the same manner as those of the acrylic series to the fatty acids. Only two of them, however, are at present known, viz. : cinnamic and atropic acids, both containing C q HoO,. CH(C 7 H 6 )" CINNAMIC ACID, C 9 H 8 2 = C 9 H 7 0(OH) | . This acid is C0 2 H produced synthetically: 1. By heating benzoic aldehyde in close vessels with acetyl chloride: C 7 H 6 + C 2 H 3 OC1 = HC1 + C 9 H 8 2 . 2. By treating potassium benzoate with chlorethylidene (produced by the action of carbonyl chloride on acetic aldehyde) : C 2 H 4 -f COC1 2 == HC1 + C0 2 + C 2 H 3 C1 Aldehyde. Carbonyl Chlorethyl- chloride. idene. C 2 H 3 C1 + C 7 H 5 2 K = KC1 -f C 9 H 8 2 Chlorethyl- Potassium Cinnamic idene. benzoate. acid. Cinnamic acid is also produced by oxidation of cinnamon-oil (cinnamic aldehyde, C 9 H 8 0) in air or oxygen, and exists ready formed, together with benzoic acid, and certain oily and resinous substances, in Peru and Tolu balsams, being doubtless produced by oxidation of cinnyl alcohol or styrone, C 9 H, (p. 554), likewise contained therein. It ma'y be procured by the following process in great abundance, and in a state of perfect purity. Old, hard Tolu balsam is reduced to powder and intimately mixed with an equal weight of slaked lime : this mixture is boiled for some time in a large quan- tity of water, and filtered hot. On cooling, calcium cinnamate crystallizes out, while calcium benzoate remains in solution. The impure salt is redis- solved in boiling water, digested with animal charcoal, and, after filtration, suffered to crystallize. The crystals are drained and pressed, once more dissolved in hot. water, and an excess of hydrochloric acid being added, the whole is allowed to cool. The pure cinnamic acid separates in small plates or needle-formed crystals of perfect whiteness. From the original mother-liquor much benzoic acid may be procured. The crystals of cinnamic acid are smaller and less distinct than those of benzoic acid, which in most respects it very closely resembles. It melts at 120 C. (248 F.), and enters into ebullition at 293 C. (560 F.) ; the vapor is pungent and irritating. Cinnamic acid is much less soluble, both in hot and cold water, than benzoic acid ; a hot saturated solution becomes on. DIATOMIC ACIDS. 641 cooling a soft solid mass of small nacreous crystals. It dissolves with perfect ease in alcohol. Boiling nitric acid decomposes cinnamic acid with great energy, and with production of copious red fumes: bitter almond-oil distils over, and benzoic acid remains in the retort. When oinnamic acid is heated in a retort with a mixture of strong solution of potassium bichromate and sulphuric acid, it is almost instantly converted into benzoic acid, which afterwards distils over with the vapor of water; the odor of bitter-almond oil is at the same time very perceptible. Cinnamic acid fused with excess of potassium hydrate, is decomposed into benzoic and acetic acids: C 9 H 8 2 + 20H 2 = C 7 H 6 2 -f C 2 H 4 2 + H 2 . This decomposition is precisely analogous to that of an acid of the acrylic series into two acids of the fatty series (p. 626). Cinnamic acid is resolved by distillation with lime or baryta, and par- tially also, when distilled alone, into carbon dioxide and cinnamene, C 8 H 8 (p. 501). The cinnamates, C 9 H ? 2 M (for monatomic metals), are very much like the benzoates. Cinnyl cinnamalc, Cmnamcin, or Styracin, C 9 H 7 2 . C 9 H 9 , is con- tained, together with cinnamene and styrol, in liquid storax (which exudes from Styrax calamita, a shrub growing in Greece and Syria) ; also, together with styrol and other substances, in Peru and Tolu balsams, the produce of certain species of Myroxylum growing in South America. It is obtained from storax by distilling the balsam to expel the styrol, then boiling it with aqueous sodium carbonate to remove free cinnamic acid, and kneading the spongy residue between the fingers. Styracin then runs out as an oily liquid, and may be obtained in tufts of beautiful prisms by crystallization from alcohol. When distilled with potash, it is resolved into cinnyl alcohol and cinnamic acid. ATROPIC ACID, C 9 II 8 2 , is a crystalline acid, isomeric with cinnamic acid, obtained, together witli a basic compound, tropme, by the action of alkalies on atropine, an alkaloid existing in Atropa Belladonna and Datura Stram- monium : C 17 H 23 N0 3 == C 9 H 8 2 + C 8 H 15 NO Atropine. Atropic acid. Tropine. DIATOMIC ACIDS. These acids are derived from diatomic alcohols by substitution either of for H 2 , in which case they contain three atoms of oxygen and are mono- basic, or by substitution of 2 for H 4 , in which case they contain four atoms of oxygen and are bibasic. The relation between the saturated hydrocarbons, the glycols, and the diatomic acids, is shown in the following table: Diatomic Acids. Hydrocarbons. Glycols. Monobasic. Bibasic. C n H2n-f2 C n ll2n+ 2 2 C n H 2n 3 C n II 2n _ 2 4 CTT r 1 TT n PTTA r< w n n n 2n '-'n* : *2n'-'2 ^- / n**2n 2*-'3 '-''n"2n 4^4 CnH 2n _ 2 C n II 2n _ 2 2 C n II 2a _ 4 8 C n H 2n _4 C n H 2n _40 2 C B n ta ^O, &c. &c. 54* 642 DIATOMIC AND MONOBASIC ACIDS ; C u H 2n O 3 . Diatomic and Monobasic Acids. 1. Lactic Series, C n H 2n 3 . The acids of this series may be divided into two groups, distinguished as normal lactic acids and isolactic acids. The known members of the series Glycollic or Oxyacetic acid, C 2 H 4 3 . Lactic or Oxypropionic acid, C 3 H 6 O 3 . Oxybutyric acid, C 4 H 8 3 , and its isomer, Dimethoxalic acid. Oxyvaleric acid, C 5 H 10 3 , and its isomer, Ethomethoxalic acid. Leucic or Oxycaproic acid, C 6 H 12 3 , and isomer, Diethoxalic acid. Acids homologous with dimethoxalic acid, and containing 7, 9, and 12 atoms of carbon, have also been obtained. The normal lactic acids correspond to the diatomic alcohols homologous with ethenic alcohol (glycol) ; thus : C n _i H 2n _ 2 OH C^H^OH CH 2 OH COOH Diatomic Normal acid of alcohol. lactic series. If in the second formula we make n successively equal to 1, 2, 3, &c., we get the series : OH CH 2 OH C 2 H 4 OH C 3 H G OH COOH COOH COOH COOH Carbonic Glycollic Lactic Oxybutyric acid. acid. acid. acid. Carbonic acid is, however, a bibasic acid, for reasons which will be ex- plained further on, and will be considered by itself. The normal lactic acids are produced : 1. From the glycols by slow oxidation in contact with platinum black, or by the action of dilute nitric acid. The higher glycols, however, are partly split up by oxidation, part of their carbon as well as hydrogen being oxi- dized, and a lower acid of the series produced; thus amylene glycol yields Oxybutyric instead of oxyvaleric acid. 2. By the action of moist silver oxide on the monochlorinated or mono- brominated fatty acids (p. 708), e. g.: C 3 H 5 C10 2 + AgHO = AgCl + C 3 H 6 3 Chloropro- Lactic pionic acid. acid. By the action of nitrous acid on the amidated derivatives of the fatty acids : C 2 H 5 N0 2 -j- N0 2 H = C 2 H 4 3 + OH 2 + N 2 Amidacetic acid Glycollic (glycocine). acid. C(C n H 2n+1 ) 2 OH The Isolactic acids are represented by the general formula, I COOH They are obtained in the form of ethers by the action of the zinc-com- pound of an alcohol-radical, CnH^+j, on a neutral ether of oxalic acid con- taining a radical of the same series, such as diethylic oxalate. The reac- DIATOMIC AND MONOBASIC ACIDS, C H 2D O 3 . 643 tion consists in the replacement of an atom of oxygen in the oxalic ether by two equivalents of alcohol-radical, and the simultaneous replacement of an equivalent of ethyl, methyl, &c., in the oxalic ether by an equivalent* of zinc, whereby an ether of zinc-diethyloxalic acid, &c., is produced, which by certain obvious transformations may be converted into the required acid ; thus : COOCH 3 C(C 2 H 5 ) 2 OZn' 4- SZn'CJL = Zn'(CH 3 )0 -f | COOCH 3 COOCH, Dimethylic Zinc Zinc Methylic zinco- oxalate. methide. methylate. diethoxalate. C(C 2 H 5 ) 2 OZn' C(C 2 H 5 ) 2 OH + HOH = Zn'HO + COOCH 3 COOCH 3 Methylic zinco- Water. Zinc Methylic diethoxalate. hydrate. diethoxalate. The methylic diethoxalate is easily decomposed by baryta-water, yield- ing methyl alcohol and barium diethoxalate : C(C 2 H 5 ) 2 OH C(C 2 H 5 ) 2 OH + Ba'HO = CH 8 (OH) + | COOCH, COOBa' Methylic Barium diethoxalate. diethoxalate. And this salt decomposed by sulphuric acid yields diethoxalic acid, C(C 2 H 5 ) 2 OH , isomeric with leucic acid. COOH In the first stage of the process it is found best to use a mixture of ethyl iodide with metallic zinc, which produces zinc-ethide, instead of the latter compound previously prepared. The other isolactic ethers are prepared in a similar manner. The acids of either group are reduced by hydjiodic acid to the corre- sponding acids of the acetic series ; e. g. : C 3 H tf 3 + 2HI = C 3 H 6 2 -f- OH 2 -f I 2 Lactic Propionic acid. acid. The ethereal salts of the isolactic acids are converted by phosphorus tri- chloride or pentoxide, into ethers of the iso-acrylic acids (p. 625) ; the ethereal salts of the normal lactic acids do not exhibit this reaction. The normal lactic acids, when heated, give up a molecule of water, and are converted into oxygen ethers or anhydrides ; e . g. : C 3 H 6 3 OH 2 = C 3 H 4 2 Lactic Lactide. acid. Two molecules of a normal lactic acid may also be deprived of a molecule of water, thereby producing a condensed acid, analogous to the polyethenic alcohols ; e. g. : 2C 3 H 6 3 OH 2 CH 610 5 Lactic Dilactic acid. acid. * To simplify the equations, we have made use of tho equivalent (32-5) instead of the atom (65) of zinc, denoting it by the symbol Zu'. 644: DIATOMIC AND MONOBASIC ACIDS, C n H 2U O 3 . Glycollic Acid, C 2 H 4 3 = \ . This acid is produced in a variety COOH of reactions, several of which have been already mentioned, viz., the oxi- dation of glycol by contact with platinum black or by treatment with dilute nitric acid; the decomposition of benzoglycollic acid by boiling with water ; the decomposition of glycocine by nitrous acid ; the action of water or alkalies on bromacetic and chloracetic acid, or their salts (pp. 603, 614, 638), e.g., by boiling silver bromacetate with water: C 2 H 2 BrAg0 2 4- OH 2 = AgBr 4- C 2 H 4 3 It is also produced : a. By the action of alkalies on glyoxal and glyoxylic acid : C 2 H 2 2 4- OH 2 = C 2 H 4 3 Glyoxal. Glycollic acid. 2C 2 H 4 4 = C 2 H 2 4 4- C 2 H 4 3 4- OH 2 . Glyoxylic Oxalic Glycollic acid. acid. acid. /?. Together with glyoxal, glyoxylic acid, and other products by the ac- tion of nitric acid upon alcohol. y. By the action of nascent hydrogen (evolved by zinc and sulphuric acid) upon oxalic acid: C 2 H 2 4 4- 2H 2 = OH 2 4- C 2 H 4 3 Oxalic Glycollic acid. acid. Glycollic acid differs somewhat in its properties, according to the man- ner in which it is prepared, being sometimes syrupy and uncrystallizable, sometimes separating from its solution in ether in large regular crystals. It has a very sour taste, dissolves easily in water, alcohol, and ether ; melts at 78 or 79 C. (172-174 F.) ; begins to boil at 100 ; decomposes when heated to above 150 C. (302 F.). All the glycollates are more or less solu- ble and crystallizable. Diglycollic acid, C 4 H 6 5 2C 2 H 4 3 OH 2 , also called Paramalic acid. This acid, isomeric with malic acid, and related to glycollic acid in the same manner as diethenic alcohol to glycol, is produced by the dehydra- tion of glycollic acid, and by the oxidation of diethenic or triethenic alco- hol. It is also formed in the preparation of glycollic acid by heating sodium chloracetate with caustic soda, which in fact is the process by which it was first obtained : C 2 H 3 C10 2 4- 2NaHO == NaCl 4- OH 2 + C 2 H 3 Na0 3 Chloracetic Sodium gly- acid. collate. C 2 H 3 C10 2 4- C 2 H 3 Na0 3 = NaCl 4- C 4 H 6 6 Chloracetic Sodium Diglycollic acid. glycollate. acid. Diglycollic acid is a crystalline bibasic acid, forming with univalent metals, normal salts containing C 4 H 5 M X 5 , and acid salts, C 4 H 4 M 2 5 ; with bivalent metals it forms only normal salts, C 4 H 4 M // 5 . C 2 H 4 OH (HC 2 H,OH Lactic Acid, C 3 H 6 3 I or C \ 0" .Of this acid there are COOH ( OH two modifications : one called ordinary lactic acid, produced by a peculiar fermentation of sugar ; the second, called paralactic or sarcolactic acid, * ' LACTIC ACID. 645 existing in muscular flesh. The difference of constitution between these two acids is represented by the following formulae : CH 3 CH 2 OH CHOH CH 2 COOH COOH Ordinary lactic acid. Paralactic acid. Ordinary lactic acid is also produced by the first three general methods given on page 642, viz., by the slow oxidation of propene glycol; by the action of moist silver oxide on chloro-propionic or bromo-propionic acid ; and by the action of nitrous acid on alanine ; further, by the following special processes: a. By the action of nascent hydrogen on pyruvic acid : C 3 H 4 3 -4- H 2 = C 3 H 6 3 . 0. By the action of hydrocyanic acid and water on acetic aldehyde: CH 2 CH 3 | 4- CNH = CHOH CO"H I CN Aldehyde. Hydrocyanic Unknown inter- acid, mediate compound. CH 3 CH 3 CHOH + 20H 2 = NH S 4- CHOH CN COOH Intermediate Lactic acid, compound. Paralactic acid is produced: 1. By heating ethene chlorohydrate with an alcoholic solution of potassium cyanide, and boiling the resulting ethene cyano-hydrate with caustic potash, whereupon ammonia is given off, and potassium paralactate is produced : CH 2 OH CH 2 OH 4- CNK = KC1 4- | ' CH 2 C1 CH 2 CN Ethene chlor- Ethene cyano- hydrate. hydrate. CH 2 OH CH 2 OH 4- 20H 2 = NH 3 4- CH 2 CH 2 CN | Ethene cyano- COOH hydrate. Paralactic acid. 2. By combining ethene with carbonyl chloride, whereby paralactyl chloride is produced, and decomposing this chloride with an alkali: CH 2 C1 CH, I 4- COCL CH, CH, I COC1 Ethene. Paralactyl chloride. DIATOMIC AND MONOBASIC ACIDS, C n H 2I1 O 3 . CH 2 C1 CH 2 OH CH 2 -f 2HOH 2HC1 + CH 2 COC1 COOH Paralactyl chloride. Paralactic acid. Paralactic acid is extracted from muscular flesh by cold water or dilute alcohol. Preparation of ordinary lactic acid by Fermentation. Various kinds of sugar, and dextrin, when subjected to the action of particular ferments, are con- verted into lactic acid, the change consisting in a resolution of the molecule, preceded in some cases by the assumption of the elements of water: C 6 H 12 6 = 2C3H 6 03 Glucose. Lactic acid. C 12 H 22 O n -f OH 2 + 4C 3 H 6 3 Milk sugar. Lactic acid. This lactous fermentation requires a temperature between 20 and 40 C. (58 and 104 F.), and the presence of water and certain ferments viz., albuminous substances in a peculiar state of decomposition, such as casein, glutin, or animal membranes, especially the coating of the stomach of the calf (rennet), or of the dog, or bladder. According to Pasteur and others, it depends upon the presence of a peculiar fungus, Pcmcillium glaucum (p. 521). The following is a good method for preparing the acid in consider- able quantity: 2 gallons of rnilk are mixed with 6 pounds of raw sugar, 12 pints of water, 8 ounces of putrid cheese, and 4 pounds of chalk, which should be mixed up to a creamy consistence with some of the liquid. This mixture is exposed in a loosely covered jar to a temperature of about 80 C. (86 F.), with occasional stirring. The use of the chalk is to neutralize the lactic acid, which would otherwise coagulate the casein, render it insol- uble, and thereby put a stop to the process. At the end of two or three weeks it will be found converted into a semi-solid mass of calcium lactate, which may be drained, pressed, and purified by re-crystallization from water. The lactate may be decomposed by the necessary quantity of pure oxalic acid, the filtered liquor neutralized with zinc carbonate, and, after a second filtration, evaporated until the zinc-salt crystallizes out on cooling. An important modification of this process consists in employing commercial zinc-white instead of powdered chalk, which yields at once difficultly soluble zinc lactate, easily purified by re-crystallization. The zinc lactate may, lastly, be re-dissolved in water, and decomposed by sulphuretted hydrogen, in order to obtain the free acid. Together with the lactic acid a certain quantity of mannite is invariably formed. This is separated by agitating the concentrated aqueous solution with ether, in which lactic acid alone is soluble. If, in the first part of the process, the solid calcium lactate be not re- moved at the proper time from the fermenting liquid, it will gradually re-dissolve and disappear, being converted into soluble butyrate (p. 617). Lactic acid may be extracted from a great variety of liquids containing decomposing organic matter, as sauerkraut, a preparation of white cabbage, the sour liquor of the starch-maker, &c. Solution of lactic acid may be concentrated in the vacuum of the air- pump, over a surface of oil of vitriol, until it appears as a colorless, syrupy liquid, of sp. gr. 1-215. It has an intensely sour taste and acid reaction: it is hygroscopic, and very soluble in water, alcohol, and ether. All its salts are soluble. When syrupy lactic acid is heated in a retort to 130 C. (266 F.), water LACTIC ACID. 617 containing a little lactic acid distils over, and the residue on cooling forms a yellowish, solid, fusible mass, very bitter, and nearly insoluble in water. This is dilactic acid, C 6 H, 3 2C 3 H 6 3 OH 2 . Long-continued boiling with water re-converts it into lactic acid. When this substance is further heated, it decomposes, yielding numerous products. One of these is lacride, or lactic anhydride, C 3 H 4 O 2 , a volatile substance, crystallizing in brilliant, colorless, rhombic plates, which, when put into water, slowly dissolve, with production of lactic acid. Lactide combines with ammonia, forming lactamide, a soluble crystallizable substance isomeric with alanine or amidopropionic acid (p. G15). The dif- ference between these two bodies and their relation to lactic acid is ex- hibited by the following formulae : C 2 H 4 NH 2 C 2 H 4 OH C 2 H 4 OH COOH COOH CONH 2 Alanine. Lactic acid. Lactamide. Alanine may be derived from lactic acid by substitution of amidogen for the alcoholic hydroxyl of the acid (which comes to exactly the same thing as replacing an atom of hydrogen in propionic acid, C 3 H 6 2 , by amidogen) ; accordingly it retains an atom of basic hydrogen, and therefore reacts as an acid (lactamic or amidopropionic acid) ; but in lactamide the basic hy- droxyl is replaced by amidogen, and therefore the compound is neutral. Another product of the action of heat on lactic acid is lactone, a colorless volatile liquid, boiling at 92-2 C. (198 F.). Acetone is also formed, and carbon monoxide and dioxide are given off. Lactic acid, boiled with dilute nitric acid, or with dioxide of lead or barium, is converted into oxalic acid. Distilled with dilute sulphuric acid and dioxide of lead or manganese, it yields a large quantity of aldehyde, together with carbon dioxide. Hy- driodic acid, or a mixture of phosphorus tetroxide and water, reduces it to propionic acid, with liberation of iodine : C 3 H 6 3 + 2HI = C 3 H 6 2 + OH 2 + I 2 . Paralactic acid in solution or in the syrupy state is undistinguishable from ordinary lactic acid. When heated it is converted into lactide, which, when boiled with water, yields ordinary lactic acid. . Lactates. The best denned of these salts are represented by the formulae, C-jIIjOgM', and (C 3 H 5 3 ) 2 M // . Barium and calcium also form acid lactates, e. g., (C 3 H 5 3 ) 2 Ca // . 2C 3 lf 6 3 . The lactates are, for the most part, sparingly soluble in cold water, and effloresce rapidly from their solutions: they are all insoluble in ether. When heated with excess of strong sulphuric acid, they give off a large quantity of pure carbon monoxide, The paralactates have, for the most part, the same composition as the lactates ; but some of them differ in form, solubility, and other characters. Calcium lactate, (C 3 H 5 8 ) 8 Ca" . 5 Aq., is obtained in the fermentation pro- cess above described, or by boiling aqueous lactic acid with calcium car- bonate. It dissolves in 9-5 parts of water at ordinary temperatures. The paralactate contains only 4 molecules of water, which however it retains longer than the lactate, and requires 12 parts of water to dissolve it. Zinc lactate, (C 3 H 6 3 ) 2 Zn // . 3 Aq., gives off its water quickly at 100, dis- solves in 6 parts of boiling water, in 5-8 parts of cold water, and is nearly insoluble in alcohol. The paralactate contains only 2 molecules of crystal- lization-water, which it retains with considerable force. It dissolves in 2-88 parts of boiling, 5-7 parts of cold water, and in 2-23 parts of alcohol, either cold or boiling. Ferrous lactate is precipitated in small yellowish needles on mixing ammonium lactate with ferrous chloride or sulphate. Ferric lactate is a brown deliquescent mass. 64:8 CARBONIC ACID. Lactic Ethers. Lactic acid, like the other members of the group, can form three different ethers containing the same univalent alcohol-radical, according as the alcoholic or the basic hydrogen-atom, or both, are re- placed ; thus : C 2 H 4 OH C 2 H 4 OC 2 H 5 C 2 H 4 OH C 2 H 4 OC 2 H 5 COOH COOH COOC.Hg COOC 2 H 5 Lactic Ethyl-lactic Monethylic Diethylic lactate, acid. acid. lactate. or ethylic ethyl lactate. Monethylic lactate, C 3 H 5 4 . C 2 H 5 , is produced by distilling potassium or sodium lactate with potassium ethylsulphate. It is a syrupy liquid, boiling at 176 C. (348 F.). Potassium dissolves in it, with evolution of hydrogen, C 2 H 4 OK forming ethylic potassio-lactate, I . Ethyl-lactic acid, C 3 H 4 (C 2 H 5 )0 3 .H, COC 2 H 5 is obtained as a potassium or calcium-salt by decomposing diethylic lactate with potash or milk of lime. When separated from these salts by sulphuric acid, it forms a viscid liquid, boiling with partial decomposition between 195 and 198 C. (383-388 F.). Diethylic lactate, C 3 H 4 (C 2 H 5 )0 3 . C 2 H 5 , is produced by the action of ethyl-iodide on ethylic potassio-lactate, or on sodium ethylate, and by that of sodium ethylate on ethyl-chloropropionate : C 3 H 4 C10.C 2 H 5 -f C 2 H 5 ONa == NaCl + C 3 H 4 3 . (C 2 H 5 ) 2 Ethyl-chloro- Sodium Diethylic propionate. ethylate. lactate. Methyllactic acid, C 3 H 4 (CH 3 )0 3 (OH), and its zinc and silver salts have also been obtained. The alcoholic hydrogen of lactic acid may also be replaced by ncid radi- cals, forming such compounds as acetolactic acid, C 3 H 4 (C 2 H 3 0)0 2 . OH. LACTYL CHLOIMDE, C 3 H 4 OC1 2 , OR CHLOROPROPIONYL CHLORIDE, C 3 H 4 C10 . Cl, is obtained, together with phosphorus oxychloride, by gently heating a mixture of calcium lactate with phosphorus pentachloride ; also by the direct combination of ethene with carbonyl chloride. It is a colorless liquid, boiling above 100, and decomposed with water, forming hydro- chloric and chloropropionic acids. C 6 H 10 OH Leucic Acid, C 6 H 12 3 = | . This acid, isomeric with diethoxalic COOH acid, is produced by the action of nitrous acid on leucine or amidocaproic acid (p. 619). It forms needles or monoclinic prisms, soluble in water, al- cohol, and ether, melting at about 73 C. (163 F.), and volatilizing at 100. When heated for some time at that temperature, it gives off water, and leaves a syrupy oxide or anhydride. It forms crystallizable salts analogous to the lactates. (OH Carbonic Acid, CH 2 3 = C \ 0". This acid belongs to the lactic series, (OH so far as its constitution is concerned, being derived from the unknown roil methane glycol, C -I H 2 , by substitution of for H, ; but it differs from all (OH CARBONIC ETHERS. 649 the other acids of the series in being bibasic, both the hydroxyl groups contained in it being immediately connected with an atom of oxygen, so that either of the hydrogen-atoms may be regarded as belonging to the group C0 2 H. Carbonic acid itself, or hydrogen carbonate, is not known, inasmuch as when a metallic carbonate is decomposed by a stronger acid, the hydrogen carbonate, CH,,0 3 , always splits up into water and carbon dioxide, which escapes as gas. The corresponding sulphur-compound, CII 2 S 3 , is, how- ever, obtained as an oily liquid when a metallic sulpho-carbonate is decom- posed by an acid (p. 203). With the alkali-metals carbonic acid forms acid and normal or neutral salts, according as one or both of the hydrogen-atoms are replaced ; e. g. : ( OH Acid sodium carbonate, Normal sodium carbonate, CNa 2 3 , or CO(ONa) 2 . With the earth-metals and other dyad metals, carbonic acid forms only normal salts, CM /X 3 , and basic salts ; the so-called acid carbonates of barium, calcium, &c., are known only in solution, and are, in fact, merely solutions of neutral carbonates in aqueous carbonic acid, which give off carbon dioxide on boiling. The basic carbonates of dyad metals may be viewed as compounds of normal carbonates with metallic oxides or hydrates; for example, slaked lime, produced by exposing quicklin.e to moist air, has the composition of a dicalcic carbonate, Ca"0 . C0 3 Ca // . Aq. ; and native green copper carbonate, or malachite, consists of Cu /X . CO-jCu" . Aq. These basic carbonates may, however, be viewed in another way, namely, as derived from a tetratomic carbonic acid, or orthocarbonic add, CH 4 ,0 4 , or C(OH) 4 , analogous to methane and carbon tetrachloride ; thus, dicalcic car- bonate = CCa" ? 4 . Aq. ; malachite = CCu" 2 4 . Aq. With metals of higher atomicity, carbonic acid does not form definite salts. CARBONIC ETHERS. The only carbonic ethers known are those in which the two hydrogen-atoms of carbonic acid are replaced either by two equiv- alents of a monad alcohol-radical, or by one equivalent of a monad alco- hol-radical and one equivalent of a metal. Ethyl carbonate, C0 3 (C 2 H 5 ) 2 , is formed by the action of ethyl iodide on silver carbonate : C0 3 Ag 2 + 2C,H 6 I = 2AgI + C0 3 (C 2 H 5 ) 2 ; also by the action of potassium or sodium on ethyl oxalate, C 2 4 (C 2 H 6 ) 2 : this reaction is not quite understood ; but it amounts to the removal of car- bon monoxide, or carbonyl, CO, from the oxalic ether. Fragments of po- tassium or sodium are dropped into oxalic ether as long as gas is disen- gaged: the brown pasty product is then mixed with water and distilled. The carbonic ether is found floating upon the surface of the water of the receiver as a colorless, limpid liquid of aromatic odor and burning taste. It boils at 125 C. (1^57 F.), and is decomposed by an alcoholic solution of potash into potassium carbonate and alcohol. By chlorine in diffused day- light it is converted into tetrachlorethyl carbonate, C0 3 . (C 2 H 3 C1 2 ) 9 , and in sunshine into pentachlorethyl carbonate, C0 3 (C 2 Cl 5 ) a . Ethyl-potassium carbonate, C0 3 (C 2 H 6 )K, is produced by passing carbonic acid gas into a cooled solution of potassium hydrate in absolute alcohol : C 2 H 6 -f KHO -f C0 2 =r OH a -f C0 3 .(C 2 H 6 )K. It is a white nacreous salt, decomposed by water into potassium carbonate and alcohol. 55 650 SULPHO-CAEBONIC ETHERS. Ethyl-methyl carbonate, C0 3 (C 2 H 5 )(CH 3 ), is obtained by distilling a mixture of ethyl-potassium sulphate and methyl-potassium carbonate : S0 4 .(C 2 H 5 )K + C0 3 .(CH 3 )K == S0 4 K 2 + C0 3 (C 2 H 5 )(CH 3 ). Methyl-barium carbonate, (C0 3 ) 2 (CH 3 ) 2 Ba // , is obtained as a white pre- cipitate by passing carbonic acid gas into a solution of baryta in methyl alcohol. Carbonates of butyl, amyl, and allyl, analogous in composition to ethyl carbonate, have also been obtained. Phenyl hydrogen carbonate, or acid phenyl carbonate, C0 3 (C 6 H 5 )H, is identical with salicylic acid, which will be described further on. Ethyl orthocarbonate,* C(OC 2 H 5 ) 4 , is produced by heating a mixture of chloropicrin (trichloro-nitromethane) with absolute alcohol and sodium : C(N0 2 )C1 3 -f 4C 2 H5NaO = SNaCl -f N0 2 Na + C(OC 2 H 5 ) 4 Chloropicrin. Sodium Sodium Sodium Ethyl ortho- ethylate. chloride. nitrile. carbonate. It is a colorless oil, boiling at 158-159 C. (313-318F.). Heated with boric oxide to 100, it is resolved into ethyl anhydroborate (p. 528), and ordinary ethyl carbonate : C(OC 2 H 5 ) 4 + 2B 2 3 = 2B0 2 C 2 H 5 .B 2 3 + C0 3 (C 2 H 5 ) 2 . SULPHOCARBONIC ETHERS. These are bodies having the composition of carbonic ethers in which the oxygen is replaced, wholly or partly, by sul- phur. The following table exhibits their names and formulae, the ethyl and ethene compounds being taken as examples : Ethyl-monosulphocarbonic acid . . C0 2 S . (C 2 H 5 )H. Diet-hylic monosulphocarbonate . Ethyl-disulphocarbonic or Xanthic acid Diethylic disulphocarbonate Ethyl-trisulphocarbonic acid Diethylic trisulphocarbonate Ethene disulphocarbonate Ethene trisulphocarbonate . C0 2 S . (C 2 H 5 ) 2 . COS 2 . (C 2 H 6 )H. COS 2 . (C 2 Hg) 2 . CS 3 . (C 2 H 5 )H. CS 3 . (C 2 H 5 ) 2 . COS 2 . (C 2 H 4 )". CS 3 . (C,H 4 )". The metallic salts of the acid sulphocarbonic ethers are produced in the same manner as those of the carbonic ethers : thus carbonic dioxide unites with potassium sulphethylate (mercaptide), to form potassium ethyl-mono- sulphocarbonate, just as it unites with potassiiim ethylate to form the ethyl- carbonate ; and, in like manner, carbon disulphide acts on potassium ethylate or alcoholic potash, so as to form potassium ethyldisulphocarbon- ate ; and on potassium mercaptide, or an alcoholic solution of the sulph- hydrate, so as to form the ethyltrisulphocarbonate, thus: C0 2 -f (C 2 H 5 )KO = C0 3 (C 2 H 5 )K Ethylcarbonate. C0 2 -(- (C 2 H 5 )KS = C0 2 S(C 2 H 5 )K Ethylmonosulphocarbonate. CS 2 + (C 2 H 5 ) 6 KO = COS 2 (C 2 H 6 )K Ethyldisulphocarbonate. CS 2 + (C 2 H 5 )KS == CS 3 (C 2 H 5 )K Ethyltrisulphocarbonate. The neutral sulphocarbonic ethers (containing monatomic alcohol-radicals) are produced by the action of the chlorides, bromides, &c. of alcohol-radi- cals on the metallic salts of the corresponding acid ethers, e. g. : (C 2 H 8 )KCS, + C 2 H 6 C1 = KC1 -f (C,H 5 ),CS, Potassic ethyl- Ethylic trisul- trisulphocarbonate. phocarbonate. * H. J3assett, Chem. Soc. Journal [2], i. 198. DIATOMIC AND MONOBASIC ACIDS. 651 The sulphocarbonic ethers of diatomic alcohol-radicals are formed by the action of diatomic alcoholic bromides, iodides, &c., on sodium sulphocar- bonate, e. C 2 H 4 Br 2 + CS 3 Na 2 = 2NaBr + CS 3 (C 2 H 4 )" Ethene Ethene tri- bromide. sulphocarbonate. The neutral sulphocarbonic ethers are oily liquids ; so likewise are the acid ethers, such at least as are known in the free state, or as hydrogen- salts; their metallic salts are mostly crystalline. The best known of these compounds are the ethyldisulphocarbonales or xanthates. To prepare xanthic acid, alcohol of 0-800 sp. gr. is saturated, whilst boil- ing, with potash, and into this solution carbon bisulphide is dropped till it ceases to be dissolved, or until the liquid loses its alkalinity. On cooling the whole to 18 C. (0 F.), the potassium-salt separates in the form of brilliant, slender, colorless prisms, which must be quickly pressed between folds of bibulous paper, and dried in a vacuum. It is freely soluble in water and alcohol, but insoluble in ether, and is gradually destroyed by exposure to air, by oxidation of part of the sulphur. Xanthic acid may be prepared by decomposing this salt with dilute sulphuric or hydrochloric acid. It is a colorless, oily liquid, heavier than water, of powerful and peculiar odor, and very combustible : it reddens litmus-paper, and ulti- mately bleaches it. Exposed to gentle heat (about 24 C. [75 F.]), it is decomposed into alcohol and carbon bisulphide. Exposed to the air, or kept beneath the surface of water open to the air, it becomes covered with a whitish crust, and is gradually destroyed. The xanthates of the alkali- metals and of barium are colorless and crystallizable ; the calcium-salt dries up to a gummy mass ; the xanthates of zinc, lead, and mercury are white, and but slightly soluble ; that of copper is a flocculent, insoluble substance, of beautiful yellow color. Ethylic duulphocarbonate or Xanthic ether, COS 2 . (C 2 H 5 ) 2 , obtained by the action of ethyl chloride on potassium xanthate, is a pale-yellow oil, boiling at 200 C. (392 F.), insoluble in water, soluble in all proportions of alcohol or ether. Ammonia- gas passed into its alcoholic solution forms mercaptan and a crystalline substance called xanthamide : COS 2 (C 2 H 5 ) 2 + NH, = C S H 5 (SH) + COS(C 2 H 5 )NH 2 Xanthic ether. Mercaptan. Xanthamide. Amyl-disulphocarbonate, COS(C 5 H U ) 2 , treated in like manner, yields xan- thamylamide, COS(C 6 H 11 )NH 2 . 2. Pyruvic Series, C n H 2n -20 3 . This is a small group of acids, including Pyruvic acid, C 3 H 4 3 I Jalapinoleic acid, C^H^Og? Convolvulinoleic acid, C 13 H 24 3 ? | Ricinoleic acid, C 18 H 34 O 3 . Glyoxylic acid, a product of the oxidation of alcohol, glycol, and glyoxal, is sometimes said to have the composition C 2 H 2 O 3 ; but it is more probably C 2 H 4 4 , arid belongs to another series, as will be explained hereafter. Pyruvic Acid, C 3 H 4 3 , also called Pyroracemic acid, is produced by dry distillation of racemic or tartaric acid : C 4 II 6 6 = C 3 H 4 3 + C0 2 -f OH 2 . 652 DIATOMIC AND MONOBASIC ACIDS, C n H 2n _gO 4 . It is a liquid, boiling, with partial decomposition, at about 165 C. (329 F.). Treated with sodium amalgam, or hydriodic acid, it takes up two atoms of hydrogen, and is converted into lactic acid, C 3 H 6 3 , or if the reagent is used in large excess, into propionic acid, C 3 H 6 O 2 . It also unites directly with bromine, forming the acid, C 3 H 4 Br 2 3 , probably dibromolactic acid. Its salts crystallize readily. Convolvulinoleic cid and Jalapinoleic Acid, are produced by the action of acids or alkalies from certain resinous glucosides contained in the root of tuberose or officinal jalap (Convolvulus Schiedanus], and of Convolvulus (or Ipomsea) orizabensis, the jalap-stalks or jalap-wood of commerce; but their formulae have not been exactly determined. Eicinoleic Acid, C 18 H 34 3 , is a yellow oily acid, produced by the saponifi- cation of castor-oil. At temperatures between 6 and 7 C (19-21 F.), it solidifies to a granular mass. The neutral ricinoleates of the alkali-metals when distilled alone yield a distillate of osrianthol; but when distilled with excess of caustic alkali, they give off hydrogen, and yield a distillate of octyl alcohol, C 8 H 18 0, and a residue of alkaline sebate, C 10 H, 6 K 2 4 (? 541). 3. Series C n H 2n _40 3 . The only known acid of this series is guaiacic acid, C 6 H 8 3 , which is a crystallizable substance contained in guaiacum, a resin obtained from Guai- acum offitinale, a tree growing in Jamaica. It sublimes in needles resem- bling benzoic acid, and is resolved by dry distillation into carbon dioxide and guaiacene, C 6 H 8 0. 4. Series C n H 2 n_80 3 . This series includes the following acids, related to the aromatic acids in the same manner as the lactic acids are related to the fatty acids : Oxybenzoic, Para-oxybenzoic, and Salicylic acids . . C 7 H 6 3 Formobenzoic, Creosotic, Carbocresylic, and Anisic acids C 8 H 8 3 Phloretic acid C 9 H 10 3 Thymotic and Thymyl-carbonic acids .... C n H u O 3 Oxybenzoic Acid, C 7 H 6 3 , or C 6 H 4 (OH). C0 2 H, is produced by the action of nitrous acid on amidobenzoic acid : C 6 H 4 (NH 2 ) . C0 2 H -f NO(OH) = C 6 H 4 (OH) . C0 2 H + OH 2 + X 2 . Amidobenzoic acid. Oxy-benzoic acid. Oxybenzoic acid is only slightly soluble in cold water or alcohol, but dis- solves easily in either of these liquids at the boiling heat, and separates as a crystalline powder on cooling. At higher temperatures it melts and sublimes without decomposition, a character by which it is distinguished from its two isomers. With strong nitric acid it forms nitro-oxybenzoic acid, C 7 H 5 (N0 2 )0 3 , which is converted by ammonium sulphide into amid- oxybenzoic acid, C 7 H 6 (NH 2 )0 3 . Para-oxybenzoic Acid is produced by heating anisic acid to 125-130 with strong hydriodic acid: C 8 H 83 + HI = CH 3 I + C 7 H 6 3 . SALICYLIC ACID. 653 It is more soluble in cold water than oxybenzoic acid, dissolving in 126 parts of water at 15: from a hot solution it crystallizes in small distinct monoclinic prisms. It melts with partial decomposition at 210 C. (410 F.), and is easily resolved at higher temperatures into carbon di- oxide and phenol: C 7 H 6 S = C0 2 -f C 6 H 6 0. Its solution forms, with ferric chloride, a yellow precipitate insoluble in excess, without violent coloration. These characters distinguish it from oxybenzoic acid. With most metals it reacts like a monobasic acid, its potassium-salt containing C 7 H 5 3 K, and its cadmium-salt (C 7 H 6 3 ) 2 Cd / ' / ; but it appears also, like salicylic acid, to form a barium-salt containing C 7 H 4 Ba"0 3 . Salicylic Acid is produced: 1. By passing carbon dioxide into phenol containing small pieces of sodium : NaOC 6 H 5 -f C0 2 = Sodium phenate. Sodium salicylate. 2. From salicylol, C 7 H 6 2 , by oxidation with, aqueous chromic acid, or by melting salicylol or salicin with potassium hydrate, in which case hydro- gen is evolved : C 7 H 6 2 -f KOH = C 7 H 5 3 K -f H 2 . Salicylol. Potassium salicylate. 3. Coumaric acid, heated with potassium hydrate, yields potassium sali- cylate and acetate : C 9 H 8 3 + 2KOH == C 7 H 5 3 K + C 2 H 3 2 K + H 2 . 4. Oil of wintergreen (Gaultheria procumbens], which consists of methyl- salicylic acid, is resolved, by distillation with potash, into methyl alcohol and salicylic acid : C 7 H 5 (CH 3 )0 3 + KOH = CH 3 (OH) -f C 7 H 6 K0 3 . Salicylic acid crystallizes from its alcoholic solution by spontaneous eva- . poration in large monoclinic prisms. It requires about 1000 parts of cold water to dissolve it, but is much more soluble in hot water and in alcohol. Its aqueous solution imparts a deep violet color to ferric salts. It melts at 130 C. ('206 F.j, gives off phenol at a higher temperature, and when heated with pounded glass or quicklime, is completely resolved into carbon dioxide and phenol. It is distinguished from both its isomers by its beha- vior with ferric salts, its very slight solubility in water, and its lower melting point : it differs from oxybenzoic acid by its behavior when heated. In its relations to metals, salicylic acid appears to be intermediate be- tween monobasic and bibasic acids. With the alkali-metals and silver, it forms only acid salts like C 7 H 6 K0 3 ; but with dyad metals it forms both acid and neutral salts ; with calcium, for example, the two salts, C 7 H 4 Ca"0 3 and Ci 4 H, Ca"0 6 , or (C 7 H 5 3 ) 2 Ca". The neutral salts are, however, much less easily formed than the acid salts, being produced only in presence of a large excess of base. Its formation from carbon dioxide and phenol seems to show that it may be regarded as acid phenyl carbonate, (C0) 7/ (00 6 ir 5 )(OH) ; and in the neutral salicylates of bivalent metals, such as C 7 H 4 Ca // 3 , the metal appears to replace one atom of hydrogen from the group OH, and another from the group OC 6 H 6 .* * Piria, Ann. Ch. Pharm. xciii. 262. 65* 654 DIATOMIC AND MONOBASIC ACIDS, C n H 2n _gO 3 . Salicylic acid forms both acid and neutral ethers. Oil of wintergreen, as already observed, consists of methyl-salicylic acid, C 7 H 6 (CH 3 )O 3 . A similar compound, containing ethyl, is obtained by distilling crystallized salicylic acid with alcohol and sulphuric acid These compounds are mono- basic acids, the basic hydrogen of which may be replaced by metals or by alcoholic-radicals, forming neutral salicylic ethers, such as C 7 H 4 (CH 3 ) 2 3 , C 7 H 4 (CH 3 )(C 2 H 6 )0 3 , &c. There is also an ethene-salicylic acid, C 14 H, (C 2 H 4 ) X/ 6 , consisting of a double molecule of salicylic acid with two hy- drogen-atoms replaced by ethene ; it is produced by heating ethene-bromide with silver salicylate. Carbocresylic and Cresotic Acids,* C 8 H 8 3 . The sodium-salts of these acids are formed simultaneously by the action of carbon dioxide and sodi- um on cresol, C 7 H 6 0. On treating the product with hydrochloric acid, the carbocresylic acid is resolved into carbonic dioxide and cresol, while the cre- sotic acid remains undecomposed, and may be washed out with ammonium carbonate ; the solution, on evaporation, yielding the cresotic acid in fine large prisms which melt at 153 C. (307 F.), are slightly soluble in water, easily in alcohol and ether. It forms a deep violet color with ferric chlo- ride. When heated with causic baryta, it is resolved into carbon dioxide and cresol. With regard to their comparative facility of decomposition, carbocresylic and cresotic acids appear to be related to one another, in the same manner as salicylic and oxybenzoic acids. Formobenzoic Acid, C 8 H 8 3 , is produced by evaporating crude bitter- almond oil to dryness with hydrochloric acid, and exhausting the residue with ether, which leaves sal-ammoniac undissolved. It contains the ele- ments of benzoic acid, C 7 H 6 2 , and formic acid, CH 2 2 , minus an atom of oxygen; and its formation appears to be due to the action of the hydro- chloric acid on the hydrocyanic acid of the crude bitter-almond oil, where- by that acid is resolved into ammonia and formic acid. Formobenzoic acid forms white crystals soluble in water. It is resolved by oxidizing agents into bitter-almond oil (C 7 H n O), and carbon dioxide. Anisic Acid, C 8 H 8 3 , or Methyl-paraoxybenzoic acid. C 7 H 6 (CH 3 )0 3 . This acid is produced by oxidation of anisic aldehyde, C 8 H 8 O 2 , in contact with platinum black, or by treatment with dilute nitric acid (strong nitric acid would convert it into nitranisic acid) ; also by dropping anisic aldehyde into fused potash : C 8 H 8 2 -f KOH = C 8 H 7 K0 3 -f H 2 . It is usually prepared by oxidizing anise-camphor, C, H 12 0, or the crude oils of anise, fennel, and tarragon, which contain that compound in solu- tion, with nitric acid. Anisic aldehyde is first produced, according to the equation : C 10 H 12 + 6 = C 8 H 8 2 + C 2 H 2 4 + OH 2 , Anise- Anisic Oxalic camphor. aldehyde. acid. and subsequently oxidized to anisic acid. It may also be produced syn- thetically by treating potassium para-oxybenzoate with methyl iodide, whereby the methylic ether of methyl-paraoxybenzoic acid is produced : C 7 H 4 K 2 3 -f 2CH 3 I =r 2KI -f C 7 H 4 (CH 3 )0 3 . CH 3 Potassium Methylic para-oxybenzoate. methyl-paraoxybenzoate. * Kolbe and Lautemann, Ann. Ch. Pharm. cxv. 203. PHLORETIC THYMOTIC COUMARIC ACIDS. 655 And boiling this compound with potash : C 7 H 4 (CH 3 )0 3 .CH 3 -f OH 2 = CH 3 (OH) + C 7 H 5 (CH 3 )0 3 Methylic methyl- Methyl Met-hyl-para- paraoxybenzoate. alcohol. benzoic acid. Ethyl-parabenzoic acid, C T H 6 (C 2 H 6 )0 3 , may be produced in a precisely similar manner. Anisic acid crystallizes in brilliant colorless prisms melting at 175 C. (347 F.), moderately soluble in hot water, easily in alcohol and ether. It yields substitution-products with chlorine, bromine, and nitric acid. By distillation with lime or baryta it is resolved in carbon dioxide and ani- sol or methyl-phenol (p. 551) : C 8 H 8 3 C0 2 + C 7 H 8 2 . Anisic acid is monobasic, and most of its salts are crystallizable. Phloretic Acid, C 9 H 10 3 , is produced, together with phloroglucin, by the action of potash on phloretin, a substance resulting from the action of di- lute acids on phlorizin (p. 581) : CH I4 6 + V OH 2 = C 9 H 10 3 + C 6 H 6 3 Phloretin. Phloretic Phloro- acid. glucin. It forms prismatic crystals melting at about 129 C. (264 F.), somewhat less soluble in water than in alcohol; produces a green color with ferric chloride. When heated with lime or baryta, it is resolved into carbon di- oxide and phlorol, C 9 H J0 0, which passes over as a brown oily distillate : C 9 H 10 3 + BaO = C0 3 Ba + C 8 H 10 0. Phloretic acid is bibasic, forming acid and neutral salts. Another acid containing C 9 H, ? 3 is formed by the action of potash on the cyauo-hydrate or cyanhydrin of anisic alcohol, C 8 H 10 2 : C 8 H 8 (CN)(OH) + 20H 2 = NH 3 -f C 9 H 10 3 Anisic Acid, cyanhydrin. Thymotic and Thymyl-carbonic Acids, C n H 14 3 . These isomeric acids are produced simultaneously by the action of sodium and carbon dioxide on thymol,C, H u O (p. 554) ; and are separated in the same manner as the homologous compounds, cresyl-cai'bonic and cresotic acids. Thymotic acid is a crystalline body, melting at 120, nearly insoluble in cold, slightly soluble in boiling water ; it produces a fine blue color with ferric chloride. Heated with baryta, it is resolved into carbon dioxide and thymol. 5.- Series C n H 2n _ 10 3 . Coumaric Acid, C 9 H 8 3 , the only known acid of this series, is produced by the action of boiling potash solution on coumarin, C 9 H 6 2 , the odorifer- ous principle of the Tonka bean. It crystallizes in laminae, having a bitter taste, soluble in water, alcohol, and ether, melting at 190 C. (374 F.). Fused with potash, it gives off hydrogen, and yields potassium salicylate and apparently also acetate : C 9 H 8 3 -f- 2KOH = C 7 H 6 K0 3 + C 2 H 3 K0 2 -f H 2 . It is monobasic, and decomposes carbonates. There are no known acids belonging to the series C n II 2n _ 12 3 and C n H 2n _, 4 3 . 656 DIATOMIC AND BIBASIC ACIDS. 6. Series C n H 2n _ 16 3 . Benzilic Acid, C 14 H 12 3 . This acid is produced by the action of alcoholic potash on benzoin, C 14 H, 2 2 , a polymeric modification of benzoic aldehyde, C 7 H 6 2 , which remains in the retort when the crude oil is distilled with lime or iron-oxide to free it from hydrocyanic acid ; or on benzile, C U H, 2 , a crystalline substance formed from benzoin by the action of chlorine. On saturating the alkaline solution with hydrochloric acid, and leaving the filtered liquid to cool, benzilic acid separates in small colorless transparent crystals, slightly soluble in cold, more soluble in boiling water; it melts at 120 C. (248 F.), and cannot be volatilized without decomposition. It dissolves in cold strong sulphuric acid with fine carmine color. DIATOMIC AND BIBASIC ACIDS. These acids contain the group oxatyl, C0 2 H, twice, and must therefore contain four atoms of oxygen. They may all be included in the general formula, R // (C0 2 H) 2 , B denoting a diatomic hydrocarbon-radical, or they may be regarded as compounds of oxygenated radicals with two equi- valents of hydroxyl, e. g., succinic acid = (C 4 H 4 2 )" (OH) 2 . They are produced: 1. By oxidation of the corresponding glycols, B/ / (CH 2 OH) 2 , the change consisting in the substitution of O 2 for H 4 (p. 557). In this manner oxalic acid, C 2 H 2 4 , is formed from ethene alcohol, C 2 II 6 2 , and malonic acid, C 3 H 4 4 , from propene alcohol, C 3 H 8 2 ; but the higher glycols split up under the influence of oxidizing agents, and do not yield bibasic acids containing the same number of carbon-atoms as themselves. 2. By boiling the cyanides of diatomic alcohol-radicals with alcoholic potash ; e. g. : (C.H t )"{CN) a + 2KOH + 20H 2 = 2NH 3 + (C 8 H 6 )"(C0 2 K) Propene Potassium cyanide. pyrotartrate. This reaction is analogous to that by which the fatty acids are formed from the cyanides of the monatomic alcohol-radicals, C n H 2n -f j (p. 599). 3. By the addition of hydrogen to other acids containing a smaller pro- portion of that element ; in this manner succinic acid, C 4 H 6 4 , is formed from fumaric acid, C 4 H 4 4 . 4. By the action of heat on acids of more complicated structure ; e. g. : 2C 4 H 6 6 = 3C0 2 + 20H 2 -f C 6 H 8 4 Tartaric Pyrotar- acid. taric acid. 5. Many of these acids are produced by the action of powerful oxidizers on a variety of organic bodies: thus, succinic acid, C 4 H 6 4 , and its homo- logues, are produced by treating various fatty and resinous bodies with nitric acid. The known acids of this group belong to the series C n H 2n _ 2 4 , C n H 2n _40 4 , C n H 2D _ 8 4 , and C n H 2n _io0 4 . The acids of the first series, and probably also those of the third and fourth, are saturated compounds ; but those of the second are imsaturated, being capable of taking up two atoms of hydrogen, bromine, and other monad elements, whereby they are converted into acids of the first series. OXALIC ACID. 657 1. Oxalic or Succinic Series, C n H 2n _ 2 4 . The known acids of this series are: Oxalic acid Malonic acid . Succinic acid . Pyrotartaric acid Adipic acid C 2 H 2 4 C,H 4 4 . C 4 H 6 4 C 5 H 8 4 C 6 H 10 4 Pimelic acid . Suberic acid . Anchoic acid . Sebic acid Roccellic acid COOH Oxalic C 7 H 12 4 C 8 H 14 4 CH0 = ( C 2 2 ) // ( H )r This important acid lie Acid, C 2 H 2 4 = \ COOH exists ready formed in many plants as a potassium or calcium-salt, and is produced by the oxidation of a great variety of organic compounds. In some cases the reaction consists in a definite substitution of oxygen for hy- drogen ; thus oxalic acid is formed from ethene alcohol, C 2 H 6 2 , by sub- stitution of 2 for H 4 , and from ethyl alcohol, C 2 H 6 0, by the same substitu- tion and further addition of one atom of oxygen. But in most cases the reaction is more complex, consisting in a complete breaking up of the mole- cule. In this manner oxalic acid is produced in great abundance from more highly carbonized organic substances, such as sugar, starch, cellulose, &c., by the action of nitric acid, or by fusion with caustic alkalies. Oxalic acid is also produced: a. As a sodium or potassium-salt by direct combination of the alkali-metal with carbon dioxide : 2C0 2 -f Na 2 = C 2 4 Na 2 . The sodium-salt is obtained by passing the carbon dioxide over a heated mixture 'of sodium and sand ; the potassium-salt, by heating potassium amalgam in the gas.* 0. As an ammonium-salt, together with other products, in the decompo- sition of cyanogen by water: C 2 N 2 40H C 2 (NH 4 ) 2 0< y. As a potassium-salt by heating potassium formate with excess of pot- ash: 2CHK0 2 = C 2 K 2 4 -f- H 2 . Preparation. 1. By the oxidation of sugar with nitric acid : CH0 U + I8 = 6C 2 H 2 4 + 50H 2 . One part of sugar is gently heated in a retort with 5 parts of nitric acid of sp. gr. 142, diluted with twice its weight of water; copious red fumes are then disengaged, and the oxidation of the sugar proceeds with violence and rapidity. When the action slackens, heat may be again applied to the vessel, and the liquid concentrated, by distilling off the superfluous nitric acid, until it deposits crystals on cooling. These are drained, redissolved in a small quantity of hot water, and the solution is set aside to cool. 2. By heating sawdust with caustic alkali. Many years ago, Gay-Lussac observed that wood and several other or- ganic substances were converted into oxalic acid by fusion with caustic potash. Messrs. Roberts, Dale & Co. have lately founded upon this obser- vation a new method for the preparation of oxalic acid, which furnishes this acid much cheaper than any other process. A mixed solution of the hydrates of sodium and potassium in the proportion of two equivalents of the former to one of the latter, is evaporated to about 1 -35 sp. gr. and then mixed with sawdust, so as to form a thick paste, which is placed in thia * Kolbe and Drechsel, Chem. Soc. Journal [2], vi. 121. 658 DIATOMIC AND BIBASIC ACIDS, C n H 2n _ 2 O 4 . layers on iron plates. The mixture is now gradually heated, care being taken to keep it constantly stirred. The action of heat expels a quantity of water, and the mass intumesces strongly, with disengagement of much inflammable gas, consisting of hydrogen and carbonetted hydrogen. The mixture is now kept for some hours at a temperature of 204 C. (400 F.), care being taken to avoid charring, which would cause a loss of oxalic acid. The product thus obtained is a gray powder ; it is now treated with water at about 15-5 C. (60 F.), which leaves the sodium oxalate undis- solved. The supernatant liquid is drawn off, evaporated to dryness, and heated in furnaces to recover the alkalies, which are caustified and used for a new operation. The sodium oxalate is washed and decomposed by boiling with slaked lime, and the resulting calcium oxalate is again decom- posed by means of sulphuric acid. The liquid decanted from the calcium sulphate is evaporated to crystallization in leaden vessels, and the crystals are purified by re-crystallization. Oxalic acid separates from a hot solution in colorless, transparent crys- tals derived from an oblique rhombic prism, and consisting of C 2 H 2 4 . 20H 2 . The two molecules of crystallization- water may be expelled by a very gentle heat, the crystals crumbling down to a soft white powder, con- sisting of anhydrous oxalic acid, C 2 H 2 4 , which may be sublimed in great measure without decomposition. The crystallized acid, on the contrary, is decomposed by a high temperature into formic acid, carbon monoxide and carbon dioxide, without leaving any solid residue : 2C 2 H 2 4 = CH 2 2 -f CO + 2C0 2 + OH 2 . The crystals of oxalic acid dissolve in 8 parts of water at 15-5, and in their own weight, or less, of hot water: they are also soluble in spirit. The aqueous solution has an intensely sour taste and most powerful acid reaction, and is highly poisonous. The proper antidote is chalk or mngne- sia. Oxalic acid is decomposed by hot oil of vitriol into a mixture of car- bon monoxide and carbon dioxide : it is slowly converted into carbonic acid by nitric acid, whence arises a considerable loss in the process of manufacture from sugar. The dioxides of lead and manganese eifect the same change, becoming reduced to monoxides, which form salts with the unaltered acid. Oxalates. Oxalic acid, like other bibasic acids, forms with mon-atomic metals, neutral or normal salts containing C 2 M 2 4 , and acid salts, C 2 HM0 4 . "With potassium and ammonium it likewise forms hyper-acid salts, e. g., C 2 HK0 4 . C 2 H 2 4 , or C 4 H 3 K0 8 . With most diatomic metals it forms only neutral salts, C 2 M // 4 ; with barium and strontium, however, it forms acid salts analogous to the hyper-acid oxalates of the alkali-metals. It also forms numerous well-crystallized double salts. It is one of the strongest acids, decomposing dry sodium chloride when heated, with evolution of hydrochloric acid, and converting sodium chloride or nitrate in aqueous solution into acid oxalate. The oxalates of the alkali-metals are soluble in water : the rest are for the most part insoluble in water, but soluble in dilute acids. All oxalates are decomposed by heat. The oxalates of the alkali-metals, and also of the alkaline earth-metals, if not too strongly heated, give off carbon monoxide and leave carbonates, while the oxalates of those metals whose carbonates are decomposed by heat (zinc and magnesium, for ex- ample) give off carbon monoxide and carbon dioxide, and leave metallic oxides. The oxalates of the more easily reducible metals (silver, copper, &c.) give off carbon dioxide and leave the metal; the lead-salt leaves sub- oxide of lead, and gives off 3 volumes of carbon dioxide to 1 volume of car- bon monoxide : 2C 2 Pb 4 4 = Pb 2 + 3C0 2 + CO. OXALIC ACID. 659 Oxalates heated with sulphuric acid give off carbon monoxide and dioxide, and leave a residue of sulphate. In this case, as well as in the decompo- sition by heat alone, no separation of carbon takes place, and consequently the residue does not blacken : this character distinguishes the oxalates from the salts of all other carbon acids. Oxalic acid and the soluble oxalates give with calcium chloride a precipi- tate of calcium oxalate, insoluble in water and in acetic acid, but soluble in hydrochloric and nitric acid. This reaction affords a very delicate test for the presence of oxalic acid: the insolubility of the precipitated oxalate in acetic acid distinguishes it at once from the phosphate. POTASSIUM OXALATES. The neutral salt, C 2 K 2 4 . 2 Aq., prepared by neu- tralizing oxalic acid with potassium carbonate, crystallizes in transparent rJhombic prisms, which become opaque and anhydrous by heat, and dissolve in 3 parts of water. The acid oxalate or binoxalate, C 2 HK0 4 . 2 Aq., some- times called salt of sorrel, from its occurrence in that plant, is found also in other species of Rumex, in Oxalis acetosella, and in garden rhubarb, as- sociated with malic acid. It is easily prepared by dividing a solution of oxalic acid in hot water into two equal portions, neutralizing one with po- tassium carbonate, and adding the other: the salt crystallizes, on cooling, in colorless rhombic prisms. The crystals have a sour taste, and require 40 parts of cold, and 6 of boiling water for solution. A solution of this salt is often used for removing ink from paper. The hyper-acid oxalate or quad- roxalate, C 2 HK0 4 . C 2 H 2 4 . 2 Aq., is prepared by a process similar in prin- ciple to that last described. The crystals are modified octohedrons, and are less- soluble than those of the binoxalate, which the salt in other re- spects resembles. Sodium oxalate, C 2 Na 2 4 , has but little solubility ; a binoxalate exists. AMMONIUM OXALATES. The neutral salt, C 2 (NH 4 ) 2 4 . 2 Aq., is prepared by neutralizing a hot solution of oxalic acid with ammonium carbonate. It crystallizes in long, colorless, rhombic prisms, which effloresce in dry air from loss of water of crystallization. They are not very soluble in cold water, but dissolve freely by the aid of heat. The dry salt when heated in a retort gives off water, and yields a subli- mate of oxamide : * (C 2 2 ) // (ONH 4 ) 2 = 20H 2 + (C 2 2 )"(NH 2 ) 2 . Ammonium oxalate. Oxamide. When distilled with phosphoric oxide, it gives up four molecules of water and yields a considerable quantity of cyanogen, C 2 (NH 4 ) 2 4 40H 2 = 2CN. Other products are, however, formed at the same time. Acid ammonium oxalate, or binoxalate, C 2 H(NH 4 )0 4 . Aq., is still less soluble than the neutral salt. When heated in an oil-bath to 232 C. (450 F.), it loses one molecule of water, and yields oxamic acid, C 2 H 3 N0 3 , or (C 2 2 ) x/ (OH)(NH 2 ); other producis are, however, formed at the same time. CALCIUM OXALATE, C 2 Ca // 4 . 4 Aq., is formed whenever oxalic acid or an oxalate is added to a soluble calcium-salt ; it falls as a white powder, which acquires density by boiling, and is but little soluble in dilute hydrochloric, and quite insoluble in acetic acid. Nitric acid dissolves it easily. When dried at 100, it retains a molecule of water, which may be driven off by a rather higher temperature. Exposed to a red heat in a close vessel, it is converted into calcium carbonate, with escape of carbon monoxide. The oxalates of barium,, zinc, manganese, copper, nickel, cobalt, and ferrous oxalaU, are nearly insoluble in water: magnesium oxalate is sparingly solu- ble; ferric oxalate is freely soluble. Pot assio- chromic oxalate, (C 2 4 ) 3 Cr /// * See the chapter ou Amides. 660 DIATOMIC AND BIBASIC ACIDS, C n H 2IJ _ a O 4 . K 3 . 3 Aq., prepared by dissolving in hot water 1 part of potassium bichro- mate, 2 parts of potassium binoxalate, and 2 parts of crystallized oxalic acid, is one of the most beautiful salts known. The crystals appear black by reflected light from the intensity of their color, which is pure deep blue : they are very soluble. A corresponding potassio-fcrric oxalate has been formed: it crystallizes freely, and has a beautiful green color. ETHYL OXALATES. The neutral oxalate, or Oxalic ether, C 2 4 (C 2 H 5 ) 2 , is most easily obtained by distilling together 4 parts of potassium binoxalate, 5 parts of oil of vitriol, and 4 parts of strong alcohol. The distillation may be pushed nearly to dryness, and the receiver kept warm to dissipate any ordinary ether that may be formed. The product is mixed with water, by which the oxalic ether is separated from the undecomposed spirit: it is repeatedly washed to remove adhering acid, and re-distilled in a small re- tort, the first portion being received apart and rejected. Another very simple process consists in digesting equal parts of alcohol and dehydrated oxalic acid in a flask furnished with a long glass tube in which the volatil- ized spirit may condense. After six or eight hours' digestion, the mixture generally contains only traces of unetherified oxalic acid. Pure oxalic ether is a colorless, oily liquid, of pleasant aromatic odor, and 1-09 sp. gr. It boils at 183-8 C. (362 F.), is but little soluble in water, and is readily decomposed by caustic alkalies into a metallic oxalate and alcohol. With solution of ammonia in excess, it yields oxamide and alco- hol; thus: (C 2 2 )"(OC 2 H 5 ) 2 + 2NH 3 = 2HOC 2 H 5 + (C 2 2 )"(NH 2 ) 2 Ethyl oxalate. Ethyl Oxamide. alcohol. This is the best process for preparing oxamide. When dry gaseous ammonia is conducted into a vessel containing oxalic ether, the gas is rapidly absorbed, and a white solid substance produced, which is soluble in hot alcohol, and separates on cooling in colorless, trans- parent, scaly crystals. They dissolve in water, and are both fusible and volatile. This substance is oxamethane, the ethylic ether of oxamic acid (p. 659): (C 2 2 )"(OC 2 H 5 ) 2 + NH 3 = HOC 2 H 5 + C 2 2 (NH 2 )(OC 2 H 6 ) Ethyl oxalate. Alcohol. Ethyl oxamate. The same substance is formed when ammonia in small quantity is added to a solution of oxalic ether in alcohol. When oxalic ether is treated with dry chlorine in excess in sunshine, a white, colorless, crystalline, fusible body is produced, insoluble in water, and instantly decomposed by alcohol. It consists of pcrctdor ethylic oxalate, C 6 C1 10 4 , or C 2 4 (C 2 C1 6 ) 2 , or oxalic ether in which the whole of the hydro- gen is replaced by chlorine. Ethyl oxalate is converted by potassium or sodium into ethyl carbonate, with evolution of carbon monoxide: C 2 (C 2 H 5 ) 2 4 = C(C 2 H 5 ) 2 S -f CO; but the reaction is complicated by the formation of several other products. When ethyl oxalate is agitated with sodium amalgam in a vessel exter- nally cooled, a product is obtained which is separated by ether into a soluble and an insoluble portion, the latter consisting of fermentable sugar, to- gether with sodium oxalate and at least one other sodium-salt, while the ethereal solution yields, by spontaneous evaporation, crystals having the composition C n H ]8 8 , and consisting of the ethylic ether of a tribasic acid, C 5 H 6 8 , called desoxalic acid, because it is produced by deoxidation of oxalic acid: 5C 2 H 2 4 -f 5H 2 = 2C 6 H 6 8 -f 40H 2 ; and racemo-carbonic acid, be- cause it, contains the elements of racemic acid, C 4 H 6 6 , and carbon dioxide, COg, and is resolved into those two compounds when its aqueous solution is MALONIC ACID. 661 heated in a sealed tube with a small quantity of sulphuric acid. The de- composition of ethylic oxalate by sodium amalgam has not been completely investigated, but the formation of desoxalic acid and glucose may be re- presented by the equation : 8C 2 H 2 4 + 14H 2 = 2C 5 H 6 8 -f C 6 H 12 6 + 10H 2 0. Oxalic acid. Desoxalic acid. Glucose. Ethyl oxalate treated with zinc-ethyl, and afterward with water, yields the ethylic ether of diethoxalic acid, C 2 H 2 (C 2 H 5 ) 2 O e , and similar products with zinc-methyl and zinc-amyl (p. G30). Acid ethyl oxalate, or Ethyloxalic acid, C 2 H(C 2 H 5 )0 4 , or (C 2 2 )"(OH)(OC 2 H 5 ), is obtained as a potassium-salt by adding to a solution of neutral ethyl oxalate in absolute alcohol, a quantity of alcoholic potash less than suffi- cient to convert the whole into potassium oxalate and alcohol; on dissolv- ing this salt in hydrated alcohol, carefully saturating with sulphuric acid, and neutralizing with carbonate of lead or barium, the ethyloxalate of lead or barium is obtained. The acid itself is prepared by decomposing either of these salts with sulphuric acid ; but it is very unstable, and is de- composed by concentration into alcohol and oxalic acid. The potassium- salt, C 2 (C 2 H 5 )K0 4 , forms crystalline scales which begin to decompose to- ward 100. METHYL OXALATE, C 2 (CH 8 ) 2 4 , or (C 2 2 )"(OCH 3 ) 2 , is easily prepared by distilling a mixture of equal weights of oxalic acid, wood-spirit, and oil of vitriol. A spirituous liquid collects in the receiver, which, when exposed to the air, quickly evaporates, leaving the methyl oxalate in the form of rhombic, transparent, crystalline plates, which may be purified by pressure between folds of bibulous paper, and redistilled from a little oxide of lead. The product is colorless, and has the odor of ethyloxalate ; it melts at 51 C. (123 F.), and boils at 161C. (321 F.), dissolves freely in alcohol and wood-spirit, and also in water, which, however, rapidly decomposes it, es- pecially when hot, into oxalic acid and wood-spirit. The alkaline hydrates effect the same change even more easily. Solution of ammonia converts it into oxamide and methyl alcohol. With dry ammoniacal gas it yields methyl oxamate, or oxamethylane, (C 2 2 ) // (NH 2 )(OCH 3 ), a white, solid sub- stance, which crystallizes from alcohol in pearly cubes. ' ETHENE OXALATE, C 2 (C 2 H 4 )"0 4 , or (C 2 2 )"(C 2 H 4 2 )", appears to be formed by the action of ethene bromide on silver oxalate. Malonic Acid, C 3 H 4 4 = (CH 2 ) // . (C0 2 H) 2 == (C 3 H 2 2 ) // (OH) 2 . This acid is formed by the slow oxidation of propene glycol (p. 595) : C 3 H 6 2 + 4 = 20H 2 + C 3 H 4 4 ; also by oxidizing malic acid with a cold solution of potassium chromate : C 4 H 6 5 + 2 = C0 2 + OH 2 + C 3 H 4 4 ; Malic Malonic acid. acid. and by the action of alkalies on cyanacetic acid, or, better, on ethyl cyan- acetate : C 2 H 2 fCN)0 2 . C 2 H 6 + 30H 2 = NH S -f C 2 H 6 + C 3 H 4 4 Ethyl cyanacetate. Alcohol. Malonic acid. Malonic acid forms large rhombohedral crystals, soluble in water and alcohol, melting at 140 C. (284 F.), and resolved at 150 C. (302 F.) into carbon dioxide and acetic acid. Its relations to bodies of the uric acid group will be noticed hereafter. 50 662 DIATOMIC AND BIBASIC ACIDS, CuH^O,. Succinic Acid, C 4 H 6 4 = (C 2 H 4 )"(C0 2 H) 2 = (C 4 H 4 2 )"(OH) 2 . This acid is produced: 1. By heating ethene cyanide* with alcoholic potash: C 2 H 4 (CN) 2 + 40H 2 : : 2NH 3 + C 4 H 6 4 . 2. By the action of nascent hydrogen (evolved by sodium-amalgam) on maleic acid, or its isomer, fumaric acid, C 4 H 4 4 -\- H 2 = C 4 H 6 4 . 3. By the action of hydriodic acid (or water and phosphorus iodide) on malic acid, C 4 H b 5 , or tartaric acid, C 2 H 6 6 , the reaction consisting in the abstrac- tion of 1 or 2 atoms of oxygen, with formation of water and separation of iodine. 4. By the fermentation of malic or fumaric acid, and of many other organic substances, especially under the influence of putrefying casein; in small quantity also during the alcoholic fermentation of sugar (p. 516, foot-note). 5. By the oxidation of many organic substances, especially of the fatty acids, l a H 2n 2 , and their glycerides, under the in- fluence of nitric acid. Its formation from butyric acid is represented by the equation C 4 H 8 2 -f- 3 = OH 2 -f C 4 H 6 O 4 . Succinic acid occurs ready formed in amber and in certain lignites, and occasionally in the animal organism. By heating amber in iron retorts, it may be obtained in colored crystals, which may be purified by treatment with nitric acid and re-crystallization from boiling water. The acid is, however, more advantageously prepared by the fermentation of malic acid, the crude calcium malate obtained by neutralizing the juice of mountain- ash berries with chalk or slaked lime being used for the purpose. This salt is mixed in an earthen jar with water and yeast, or decaying cheese, and left for a few days at 30 or 40; the calcium succinate thus obtained is decomposed by dilute sulphuric acid ; and the succinic acid is purified by crystallization from water and by sublimation. Succinic acid crystallizes in colorless, oblique rhombic prisms, which dissolve in 5 parts of cold and in 3 parts of boiling water: it melts at 180 C. (356 F.) and boils at 235 C. (455 F.), at the same time under- going decomposition into water and succinic oxide, or anhydride, C 4 H 4 3 , or (C 4 H 4 2 ) // 0. The same compound is formed by the action of phosphorus pentachloride on succinic acid: C 4 H 6 4 + PC1 5 = 2HC1 -f POC1 3 + C 4 H 4 3 . It is a white mass, less soluble in water, but more soluble in alco- hol, than succinic acid. Succinic acid, being bibasic, forms, with monad metals, acid and neutral salts, C 4 H 5 M0 4 and C 4 H 4 M 2 4 , and with dyad metals, neutral salts, con- taining C 4 H 4 M // 4 , and acid salts, C 4 H 4 M0 4 . C 4 H 6 4 . There are also a few double succinates, several basic lead-salts, and a hyperacid potassium- salt. Succinic acid is distinguished from benzoic acid by not being precipi- tated from its soluble salts by mineral acids, and by forming a white pre- cipitate with barium chloride, on addition of ammonia and alcohol. Pyrotartaric Acid, C^H 8 4 = (C 3 H 6 )"(C0 2 H) 2 = (C 6 H 6 2 )"(OH) 2 , is pro- duced by the dry distillation of tartaric acid, and by the action of alco- holic potash on propene cyanide, C 3 H 6 (CN) 2 . It forms rhombic prisms, very soluble in water, alcohol, and ether; melts at 112 C. (233 F.), vola- tilizes at about 200 C. (392 F.), being partly resolved into water and pyrotartaric oxide, C 6 H 6 3 . It forms acid and neutral salts analogous to the succinates. Adipic Acid, C 6 H, 4 , and Pimelic Acid, -C 7 H 12 4 , are produced by the oxi- dation of fats with nitric acid. Suberic Acid, C 8 H U 4 , has long been known as a product of the oxida- * Ethene cyanide is obtained by heating othene bromide, C 2 H 4 lir 2 , with an alcoholic solu- tion of potassium cyanide. FUMARIC AND MALEIC ACIDS. 663 tion of cork by nitric acid. Recently it has been produced, together with other acids of the series, by the long-continued action of nitric acid upon stearic and oleic acids and other fatty bodies. Suberic acid is a white crystalline powder, sparingly soluble in cold water, fusible and volatile by heat. Anchoic Acid, or Lepargylic Acid, C 9 H 16 4 , is formed, together with other products, by the action of nitric acid on Chinese wax and on the fatty acids of cocoa-nut oil. Azelaic acid, obtained by oxidizing castor-oil with nitric acid, has the same composition as anchoic acid, but differs so much from it in physical properties, that it must be regarded as an isonieric or allo- tropic modification. Sebic or Sebacic Acid, C, H, 8 4 , is a constant product of the destructive distillation of oleic acid, oiein, and all fatty substances containing those bodies; it is extracted by boiling the distilled matter with water: it is also formed by the action of potash on castor-oil (see p. 652.) It forms small pearly crystals resembling those of benzoic acid. It has a faintly acid taste, is but little soluble in cold water, melts when heated, and sub- limes unchanged. Roccellic Acid, C 17 H 32 4 , exists in Roccella tinctoria, and other lichens of the same genus, also in Lecanora tartarea, and is obtained by exhausting the first-mentioned plant with aqueous ammonia, precipitating the filtered liquor with calcium chloride, and decomposing the resulting calcium-salt with hydrochloric acid. When purified by solution in ether, it forms white, rectangular, four-sided tabular crystals, melting at 132 C. (270 F.), and subliming at 200 C. (392 F.), being partially converted at the same time into an oxide, C 17 H 30 3 . This acid decomposes carbonates. 2. Fumaric Series C n H 2n _ 4 4 . This series includes the two following groups of isomeric acids: Fumaric and Maleic acids ..... C 4 H 4 4 Itaconic, Citraconic, and Mesaconic acids . C 5 H 6 4 . They are unsaturated compounds, capable of taking up two atoms of hy- drogen, bromine, and other monad elements, and passing into acids of the preceding series. Fumaric and Maleic Acids, C 4 H 4 4 = (C 2 H 2 )"(C0 2 H) 2 = (CJI 2 2 )"(OH) 2 . When malic acid is heated in a small retort, nearly filled, it melts, emits water, and enters into ebullition, and a volatile acid passes over, which dissolves in the water of the receiver. After a time, small solid, crystal- line scales make their appearance in the boiling liquid, and increase in quantity until the whole becomes solid. The process may now be inter- rupted, and the contents of the retort, after cooling, treated with cold water: unaltered malic acid is thereby dissolved out, and a less soluble acid is left behind, called fumaric acid, from its identity with an acid extracted from the common fumitory (Fumaria officinalis}. Fumaric acid forms small, white crystalline laminoo, which dissolve freely in hot water and alcohol, but require for solution about 200 parts of cold water: it is unchanged by hot nitric acid. When heated in a current of air it sublimes, but in a retort undergoes decomposition ; this is a phenom- enon often observed in organic bodies of small volatility. Fumaric acid forms acid and neutral metallic salts, and an ether, which, by the action of 664 DIATOMIC AND BIBASIC ACIDS, C n H 2n _ 4 O 4 . ammonia, yields fumaramide, (C 4 H 2 2 ) // (NH 2 ) 2 , in the form of a white, amorphous, insoluble powder. The volatile acid produced simultaneously with fumaric acid is called maleic acid; it may be obtained in crystals by evaporation in a warm place. It is very soluble in water, alcohol, and ether, has a strongly acid taste and reaction, and is convertible by heat into fumaric acid. Maleic and fumaric acids are formed from malic acid by separation of a molecule of water. Fumaric acid, when heated with bromine, combines with 2 atoms of that element, forming dibromo succinic acid, C 4 H 4 Br 2 4 , which resembles in all its properties the dibrominated acid prepared from succinic acid by direct substitution. On heating fumaric acid with hydriodic acid, it passes into succinic acid. The same reaction takes place on treating fumaric acid with water and sodium-amalgam, C 3 H 4 4 -j- H 2 = C 4 H 6 4 . The deportment of maleic acid with bromine and nascent hydrogen, is perfectly analogous to that of fumaric acid: when treated with hydriodic acid, it passes first into fumaric acid, and then into succinic acid (Kekule). Itaconic, Citraconic, and Mesaconic Acids, C 5 E 6 4 . The first two of these acids are produced by the action of heat on citric acid. When crystallized citric acid is heated in a retort it first melts in its water of crystallization, and then boils, giving oif water. Afterwards, at about 175 C. (347 F.), vapors of acetone distil over, and a copious disengagement of carbon mon- noxide takes place. At this time the residue in the retort consists of aco- itic acid. If the distillation be still continued, carbon dioxide is given oif, and itaconic acid crystallizes in the neck of the retort. If these crys- tals be repeatedly distilled, an oily mass of citraconic oxide or anhydride is obtained, which no longer solidifies. These compositions are represented by the following equations : C 6 H 8 7 OH 2 = C 6 H 6 Oe; C 6 H 6 06 C0 2 = C 5 H 6 4 ; Citric Aconitic Aconitic Itaconic acid. acid. acid. acid. C 5 H 6 4 - OH 2 = C 5 H 4 3 Itaconic Citraconic acid. oxide. The citraconic oxide when exposed to the air absorbs moisture, and is con- verted into crystallized citraconic acid, C 5 H 6 4 . Mesaconic acid is produced by boiling itaconic acid with weak nitric acid. These three isomeric acids are all converted by nascent hydrogen into pyrotartaric acid, C 5 H 8 4 . They also take up a molecule of hydrobromic acid, HBr, forming monobromopyrotartaric acid, C 5 H 7 Br0 4 , or of bromine, Br 2 , forming dibromopyrotartaric acid. Itaconic and citraconic acids are, however, more inclined to these transformations than mesaconic acid, which is altogether a more stable compound.* Camphoric Acid, C 10 H 16 4 , produced by heating camphor (C, H 16 0) with nitric acid, is likewise included in the general formula, CnH 2n _ 4 4 ; but it appears to be a saturated compound, inasmuch as its ethylic ether shows no tendency to take up chlorine or other elements. The acid forms small colorless needles or plates, of acid and bitter taste, sparingly soluble in cold water. It melts when heated, and yields by distillation a colorless, crystalline, neutral substance, consisting of camphoric oxide, or anhydride, C io H H3- Calcium camphorate when distilled yields a volatile oil consisting of phorone, C 9 H J4 0, the ketone of camphoric acid: C, H )4 Ca0 4 --= C0 3 Ca -f C 9 H, 4 0. * "For an explanation of the isomerism between these three acids, see KekuU (Bulletin de la Societe Royale de Belgique [2], xxxiv. 8; also Laboratory, p. 369). DIATOMIC AND BIBASIC ACIDS, C n H 2n _^O 4 . 665 3. Series C n H 2n _ 6 4 . The only known acid belonging to this series is : Mellitic Acid, C 4 H 2 4 , which occurs as an aluminium-salt in a very rare mineral called mellite or honeystone, found in deposits of lignite. It is soluble in water and alcohol, and is crystallizable, forming colorless needles. It is a bibasic acid, forming acid and neutral salts: the mellitates of the alkali-metals are soluble and crystallizable ; those of the earths and heavy metals are mostly insoluble. Ammonium mellitate yields by distillation paramide and euchroic acid. The former is a white, amorphous, insoluble substance, containing C 4 HN0 2 (i. e., acid ammonium mellitate, C 4 H(NH 4 )0 4 minus 20H 2 ), and convertible by boiling with water into acid ammonium mellitate. Euchroic acid forms colorless, sparingly soluble crystals, containing in the anhydrous state C 6 H 4 N 2 4 . In contact with metallic zinc and deoxidizing agents in general, it yields a deep blue insoluble substance called euchrone. 4. Series CnH 2n _ 8 O 4 . Quinonic or Quinoylic acid, C 6 H 4 4 , is not actually known, but its dichlori- nated derivative, C 6 H 2 C1 2 4 , is produced by the action of potash on tetra- chloroquinone, C 6 C1 4 2 . It is a crystalline substance, which gives off water when heated. It is bibasic, forming acid and neutral salts. Orsellinic acid, C 8 H 8 4 , and Evernic acid, C 9 H, 4 , perhaps belong to the ne series. They will be further noticed in the chapter on Coloring same Matters. 6. Series C n H 2n _ 10 4 . This series includes the isomeric acids, phthalic and terephthalic, C 8 H 6 4 ; also insolinic acid, C 9 H 8 4 . Phthalic Acid, C 8 H 6 4 , also called Alizaric and Naphthalic acid, is pro- duced by the action of nitric acid on naphthalene, dichloride of naphtha- lene, alizarin, and purpurin (the coloring matters of madder* ) : C IO H 8 + 8 = C 8 H 6 4 + C 2 H 2 4 Naphthalene. Phthalic acid. Oxalic acid. C, H 6 3 + OH 2 +0 4 = C 8 H 6 4 -f C 2 H 2 4 . Alizarin. 2C 9 H.O, + OH 2 +0 6 = 2C 8 H 6 0, + C 2 H 2 4 . Purpurin. It is usually prepared by treating naphthalene dichloride with boiling ni- tric acid. Phthalic acid crystallizes in colorless plates : it is but slightly soluble in cold water, but dissolves freely in alcohol and ether. It is bibasic, form- ing acid and neutral salts. When heated, it loses a molecule of water, and leaves phthalic oxide, C 8 TI 4 3 . Treated with fuming nitric acid, it yields nitro-phthalic acid, C 8 H 5 (N0 2 )0 4 . When distilled with baryta, it gives off benzene: C 8 H 6 4 + 2BaO = 2C0 3 Ba + C 6 H 6 . 56* 666 TEIATOMIC AND MONOBASIC ACIDS. Terephthalic Acid, C 8 H 6 4 , is produced by the oxidizing action of nitric acid on turpentine oil, lemon-oil, and other terpenes, also on cymene. It is a white, tasteless, crystalline powder, not perceptibly soluble in water, alcohol, or ether. It is distinguished from phthalic acid by subliming without alteration when heated, and not being resolved into water and an anhydride. Although bibasic, it forms no double salts, and shows but little tendency to form acid salts. Nearly all the terephthalates are soluble arid crystallizable, and so inflammable that they may be set on fire by a spark from a flint and steel, and burn away slowly like tinder, emitting the odor of benzene. Insolinic Acid, C 9 H 8 4 , is produced by the action of potassium bichro- mate and sulphuric acid on cumic acid,* and by that of nitric acid on coal- tar cumene (trimethyl-benzene, p. 498), zylic acid being first produced, and afterward further oxidized to insolinic acid: f C 10 H,,0 2 + 6 = C0 2 + 20H 2 + C 9 H 8 4 Cumic Isolinic acid. acid. C 9 H 12 + 3 = C ? H 10 2 + OH 2 Cumene. Zylic acid. CgHjoO, + 3 = C 9 H 8 4 -f OH 2 . Zylic acid. Insolinic acid. Insolinic acid is a white crystalline powder, and resembles terephthalic acid in being nearly insoluble in cold and sparingly soluble in hot water ; from hot alcohol it separates in crystalline crusts. When heated it sub- limes without previous fusion, and in part without decomposition. It is bibasic, forming neutral acid and double salts, also a neutral and acid ethylic ether (Hofmann). TRIATOMIC AND MONOBASIC ACIDS. These acids are derived from triatomic alcohols by substitution of for H 2 , as glyceric acid, C 3 H 6 4 , from glycerin, C 3 H 8 3 : CH 2 OH CH 2 OH CHOH CHOH CH 2 OH COOH Glycerin. Glyceric acid. The known acids of the group are : Glyoxylic acid . C 2 H 4 4 Glyceric acid . . C 3 H 6 4 Eugetic acid . C n H 12 D 4 Piperic acid . . C 12 Hi 4 Oxysalicylic acid . C 7 H 6 4 OH Glyoxylic Acid, C 2 H 4 4 = CHOH. This acid is produced: 1. By the COOH action of nascent hydrogen (evolved by zinc and sulphuric acid) on oxalic acid: C 2 H 2 4 + H 2 = C 2 H 4 4 . * Hofmann, Ann. Ch. Pharm. xcvii. 197. t Hired and Heilstein, Bull. Soc. Chim. de Paris [2J, vii. 345. GLYCERIC OXYSALICYLIC ACIDS. 667 2. By boiling silver bromogly collate with water: C 2 H 2 AgBrO s + OH 2 = AgBr + C 2 H 4 4 . 3. By the oxidation of glycol, alcohol, or glyoxal with nitric acid : C 2 H 6 2 + 3 = C 2 H 4 4 + OH 2 Glycol. C 2 H 6 + 4 = C 2 H 4 4 + OH 2 Alcohol. C 2 H 2 2 -f- -f OH 2 = C 2 H 4 4 . Glyoxal. Glyoxylic acid may be obtained by evaporation in the form of a viscid transparent syrup, which dissolves readily in water, and distils without alteration at 100. It dissolves zinc without evolution of hydrogen, and is converted into glycolic acid : C 2 H 4 4 -f- H 8 = C 2 H 4 3 + OH 2 . Glyoxylic acid forms salts most of which are represented by the formulae C 2 H 3 4 M, and (C 2 H S 4 ) 2 M", e. g., the silver-salt is C 2 H 3 4 Ag, and the calcium-salt, (C 2 H 3 4 ) 2 Ca // . The ammonium- salt, however, has the composition C 2 H0 2 (NH 4 ), apparently derived from an acid containing C 2 H 2 3 . This is indeed the formula originally assigned to glyoxylic acid by Debus,* who discovered it. This formula is perfectly consistent with the formation of the acid by oxidation of glyoxal, glycol, and alcohol ; but, on the other hand, its forma- tion from oxalic and from bromoglycolic acid seems rather to show that it consists of C 2 H 4 4 .f Moreover, if the acid were really C 2 H 2 3 , it would be necessary to suppose that all the glyoxylates, except the ammonium salt, contain water of crystallization, the silver-salt, for example, being C 2 H0 3 Ag.OH 2 ; now, there is no other known instance of a silver-salt containing water. The ammonium-salt above mentioned is probably an amide, (C 2 H 3 3 )NH 2 , formed from the true ammonium glyoxylate, C 2 H 3 4 (NH 4 ), by ab- straction of water. Glyceric Acid, C 3 H 6 4 . This acid, isomeric with pyruvic acid, is pro- duced by the action of nitric acid on glycerin: also by the spontaneous decomposition of nitroglycerin, and by heating glycerin with bromine and a large quantity of water to 100 in a sealed tube : C 3 H 8 3 + 2Br 2 -f OH 2 = 4HBr + C 3 H 6 4 . Glyceric acid, when concentrated, is a colorless non-crystallizing syrup 'which, when heated for some time to 105 C. (221 F .), gives off water and is converted into glyceric oxide or anhydride, C 3 H 4 3 . This acid, treated with phosphorus iodide, is converted into iodopropionic acid, C 3 H 5 I0 2 . The gly cerates, C 3 H 5 4 M' and (C S H 5 4 ) 2 M // , are soluble in water and crystallize well. They are not reddened by ferrous sulphate, and are thereby distinguished from the pyruvates, with which they are isomeric. Oxysalicylic Acid, C 7 I1 6 4 , is produced by boiling a solution of iodosali- cylic acid, C 7 H 5 I0 3 , with potash. It forms highly lustrous needles, soluble in water, alcohol, and ether. The aqueous solution is colored deep blue by ferric chloride. The crystallized acid melts at 193 C. (379 F.), and is resolved between 210 and 212 C. (410-414 F.) into carbonic dioxide and oxyphenol or pyrocatechin, C 6 H 6 2 (p. 562), and its isomer, hydro-quinone. The oxysalicylates are very unstable. There are three acids isomeric with oxysalicylic acid, viz., hypogallic acid, produced by the action of boiling hydriodic acid on hemipinic acid, C 10^ 10^6 : C 10 H 10 6 -f 2HI = C 7 H 6 4 -f 2CH 3 I + C0 2 ; * Phil. Mag. [4], xii. 36. t 1'erkin and Duppa, Obem. Soc. J. [2], vi. 197. 668 TBIATOMIC AND BIBASIC ACIDS. protocatechuic acid, produced, together with oxalic and acetic acids, by the action of melted potash on piperic acid, C 12 H, 4 : C 12 H 10 4 + 80H 2 = C 7 H 6 4 + C 2 H 2 4 + C 2 H 4 2 + C0 2 + 7H 2 , and carbohydroquinonic acid, produced by a peculiar transformation of quinic acid. Eugetic Acid, C U H 12 4 , is produced by the action of carbon dioxide and sodium on eugenol or eugenic acid (oxidized essence of cloves) : C 10 H u Na0 2 + C0 2 C 11 H 11 NaO, Sodium Sodium eugenate. eugetate. It crystallizes from hot aqueous solution in long colorless prisms, melting at 124 C. (255 F.), slightly soluble in cold water, very soluble in alcohol and ether. The aqueous solution is colored blue by ferric chloride. The acid is resolved by heat into carbon dioxide and eugenic acid. Piperic Acid, C 12 H 10 4 , is produced, together with piperidine, by boiling piperine (an alkaloid from pepper) with potash : C 17 H 19 N0 3 + OH 2 = C I2 H 10 4 + C 5 H U N Piperine. Piperic Piperidine. acid. It forms yellowish capillary needles, melting at 150 C. (302 F.), and sub- liming at about 200 C. (392 F.) ; nearly insoluble in water, easily soluble in boiling alcohol. When fused with potassium hydrate it yields protoca- techuic acid, together -with other products. The piperates even of the alkali-metals are sparingly soluble in water, the rest insoluble. TRIATOMIC AND BIBASIC ACIDS. The only known acids of this group are malic acid, C 4 H 6 5 , and tartronic acid, C 3 H 4 5 , obtained by the spontaneous decomposition of nitrotartaric acid, and perhaps also croconic acid, C 5 H 2 5 (p. 678). H -| Malic Acid, C 4 H 6 5 = (C 4 H S 2 )'"(OH) 8 , or (C 4 H 8 O a )'" VX .This acid is formed synthetically by the action of moist silver oxide on monobromo- succinic acid: 2C 4 H 5 Br0 4 + OAg 2 -f OH 2 = 2AgBr + 2C 4 H 6 5 . It is also produced by the action of nitrous acid on asparagin, a sub- stance existing in asparagus, marsh-mallow, and other plants, or on aspar- tic acid, an acid formed by the decomposition of asparagin under the influ- ence of acids or alkalies: C 4 H 8 N 2 3 -f 2N0 2 H = C 4 H 6 5 -f 20H 2 -f 2N 2 . Asparagin. Malic acid. C 4 H 7 N0 4 -f N0 2 H == C 4 H 6 6 -f OH 2 -f N 2 . Aspartic acid. Malic acid. Malic acid is the acid of apples, pears, and various other fruits : it often associated with citric acid. An excellent process for preparing it is TRIATOMIC AND TRIBASIC ACIDS. 669 that of Everitt, who has demonstrated its existence, in great quantity, in the juice of the common garden rhubarb : it is there accompanied by acid potassium oxalate. The rhubarb stalks are peeled, and ground or grated to pulp, which is subjected to pressure. The juice is heated to the boiling point, neutralized with potassium carbonate, and mixed with calcium ace- tate: insoluble calcium oxalate then falls, and may be removed by filtra- tion. To the clear and nearly colorless liquid, solution of lead acetate is added as long as a precipitate continues to be produced; and the lead ma- late is collected on a filter, washed, diffused through water, and decom- posed by sulphuretted hydrogen.* The filtered liquid is carefully evap- orated to the consistence of a syrup, and left in a dry atmosphere until it becomes converted into a solid and somewhat crystalline nruass of malic acid: regular crystals have not been obtained. From the berries of the mountain-ash (Sorbus aucuparia), in which malic acid is likewise present in, considerable quantity, especially at the time they begin to ripen, the acid may be prepared by the same process. Malic acid is colorless, slightly deliquescent, and very soluble in water: alcohol also dissolves it. The aqueous solution has an agreeable acid taste : it becomes mouldy and spoils by keeping. In contact with ferments, es- pecially of putrefying cheese, it is decomposed, yielding succinic and acetic acids and carbon dioxide : 3C 4 H 6 5 = 2C 4 H 6 4 -f C 2 H 4 2 + 2C0 2 -f- OH 2 . Sometimes also butyric acid and hydrogen are found among the products of the fermentation. Malic acid is converted into succinic acid by digest- ing it in sealed tubes with hydriodic acid: C 4 H 6 5 + 2HI = C 4 IJ 6 4 + OH 2 + I 2 . The reconversion of succinic into malic acid has been already mentioned. The sodium-salt of bromomalic acid, C 4 H 5 Br0 5 , obtained by boiling an aqueous solution of sodium dibromosuccinate (C 4 II 3 NaBr 2 4 ), is converted by boiling with lime-water into the calcium-salt of tartaric acid, C 4 H 6 6 : C 4 H 5 Br0 5 + OH 2 = HBr + C 4 H 6 6 . Malic acid forms both acid and neutral salts. The most characteristic of the malates are acid ammonium malate, C 4 H 5 5 (NH 4 ), which crystallizes remarkably well, and lead malate, C 4 H 4 5 Pb // . 3 Aq., which is insoluble in pure water, but dissolves to a considerable extent in warm dilute acids, and separates on cooling in brilliant silvery crystals, containing water. By this character the acid may be distinguished. Acid calcium malate, C 4 H 4 5 Ca . C 4 H 6 5 . 8 Aq., is also a very beautiful salt, freely soluble in warm water. It is prepared by dissolving the sparingly soluble neutral malate in hot dilute nitric acid, and leaving the solution to cool. Malic acid, as it exists in plants, and as obtained from asparagin, or from aspartic acid produced from the latter, exerts a rotatory action on polarized light ; [<*]= 5 ; but by the action of nitrous acid on inactive aspartic acid (resulting from the decomposition of fumarimide), Pasteur has obtained a modification of malic acid which is also optically inactive. TRIATOMIC AND TRIBASIC ACIDS. But few of these acids have yet been obtained ; the most important are aconitic acid and carballylic acid. * If the acid bo required pure, crystallized lead malate must be used, the freshly precipi- t;xt'-"-< L, tjiree hydrogen-atoms in the molecule C 6 H 8 7 , are replaced by metals; \vn,-' .ir;///'// >:. for example, it forms the salts U 6 lI 6 C\i // 0,, . Aq., and (C 6 H 5 0.) 2 Ca // 3 . A 4. A\ .,',7 !;>/ it. formw two salts similar in constitution to the calcium-salts, and likewise a tetra- plumbic salt containing (C 6 H 6 7 ) 2 Pb" s . Pb"H 2 O a . The citrates of the alkali-metals are soluble and crystallize with greater or less facility ; those of barium, strontium, calcium, lead, and silver are in- soluble. Citric acid resembles tartaric acid in its relations to ferric oxide, pre- venting the precipitation of that substance by excess of ammonia. The citrate obtained by dissolving hydratcd ferric oxide in solution of citric acid, dries up to a pale-brown, transparent, amorphous mass, which is not very soluble in water ; an addition of ammonia increases the solubility. Citrate and ammonia-citrate of iron are elegant medicinal preparations. Very little is known respecting the composition of these curious com- pounds : the absence of crystallization is a great bar to exact inquiry. Citric acid is sometimes adulterated with tartaric acid: the fraud is easily detected by dissolving the acid in a little cold water, and adding to the solution a small quantity of potassium acetate. If tartaric acid be present, a white crystalline precipitate of cream of tartar will be produced on agitation. Citric acid forms ethers in which 1, 2, or 3 hydrogen-atoms are replaced by methyl and other monad alcohol-radicals. Meconic Acid, C 7 H 4 7 , a tribasic acid existing in opium, may also be de- scribed here. To prepare it, the liquid obtained by exhausting opium with water, is neutralized with powdered marble and precipitated by calcium chloride ; and the calcium meconate thus precipitated is sus- pended in warm water and treated with hydrochloric acid ; on cooling, im- pure meconic acid crystallizes, which may be purified by repeated trer.t- ment with hydrochloric acid. The pure acid crystallizes in mica-like plates, easily soluble in boiling, difficultly soluble in cold water, soluble likewise in alcohol. The crystals contain C 7 H 4 7 . 3 Aq. and give off their water at 100. The meconates are, for the most part, mono- and bi-metal- lic. There are two silver mcconates, one yellow, containing C 7 HAg 3 7 ; the other white, consisting of C 7 H 2 Ag 2 7 . Meconic acid produces a deep red color with ferric salts. COMENIC ACID, C 6 H 4 5 , is a product of decomposition of meconic acid. When an aqueous, or, better, a hydrochloric solution of meconic acid is boiled, carbon dioxide is evolved, and the solution now contains cotnenic acid, which crystallizes on cooling, being very difficultly soluble in cold water. The same acid may be obtained by heating meconic acid to 200 C. (892 F.). It is bibasic : its formation is represented by the equation C 7 H 4 7 ^ C 6 H 4 5 + C0 2 . PYROMECONIC or PYROCOMENIC ACID, C 6 H 4 3 , is a monobasic acid, formed by submitting either comenic or meconic acid to dry distillation, one mole- cule of carbon dioxide being evolved in the former case and two in the latter. Pyrocomenic acid is a weak acid: it is soluble in water and alcohol: from these solutions it crystallizes in long colorless needles, which melt at 120 C. (248 F.), and begin to sublime at the boiling point of water. Both comenic and pyrocomenic acids exhibit the red coloration with ferric salts. The salts of meconic acid and comenic acid, together with several deriva- 680 PENTATOMIC ACIDS. tives of these substances, have been studied by Mr. How,* but our space will not permit us to describe these compounds. An acid much resembling U^^'^% acid has been extracted from the Che- lidonium majus : .JJ^ ;.s PC^ffmea with lime, and associated with malic and - funiaric aci' 1 . . '''' Cbfendonic acid is tribasic, forming three classes of salts. 1 When exposed to a high temperature, it yields a pyro-acid, with evolution of water and carbon dioxide. It crystallizes in slender colorless easily sol- uble needles, containing C ? H 4 5 . Aq. PENTATOMIC ACIDS. There is but one known acid that can be referred to this group, namely : Quinic or Kinic Acid, C 7 H 12 6 , which is monobasic, and may perhaps be represented by the formula (C 6 H 7 ) T -| \Q A 4 . The calcium-salt of this acid is found in the solution from which the alkalies of cinchona bark have been separated by lime, and is easily obtained by evaporation, and purified by animal charcoal. From the calcium-salt the acid may be extracted by de- composing it with dilute sulphuric acid. The clear solution evaporated to a syrupy consistence deposits large, distinct crystals, resembling those of tartaric acid, and soluble in 2 parts of water. Quinic acid has also been found in coffee-berries and in the leaves of the bilberry-bush. When quinic acid is heated with a mixture of sulphuric acid and manga- nese dioxide, it yields a very volatile substance termed quinone, the vapor of which is exceedingly irritating to the eyes. This body forms crystals, both by sublimation and by solution in boiling water: it melts at a gentle heat, crystallizes on cooling, colors the skin permanently brown. It con- tains C 6 H 4 2 , and its formation is represented by the equation: C 7 H 12 6 + 2 : : C 6 II 4 2 4- C0 2 + 4II 2 0. By destructive distillation, quinic acid yields numerous arid interesting products, which have been studied by Wohler, as benzoic acid, phenol, sa- licylol, benzene, a tarry substance not examined, and colorless hydroquinone, C 6 II 6 2 , containing 2 atoms of hydrogen more than quinone. This sub- stance forms colorless six-sided prismatic crystals ; it is neutral, destitute of taste and odor, fusible, and easily soluble both in water and in alcohol. Colorless hydroquinone can be easily and directly produced from qui- none by assimilation of hydrogen, as by addition of hydriodic acid to a so- lution of the latter, iodine being then set free, or by sulphurous acid. An intermediate product of reduction is green hydroquinone, or quinhy- drone, C I2 H 10 4 . This is obtained by the incomplete action of sulphurous acid upon quinone, or by the action of ferric chloride, chlorine, silver ni- trate, or chromic acid, upon colorless hydroquinone ; or by mixing together solutions of quinone and colorless hydroquinone. It forms slender green crystals, having the color of the wing-case of the rose-beetle, and of the greatest brilliancy and beauty. It is fusible, has but little odor, and dis- solves freely in boiling water, crystallizing out on cooling. If quinic acid be submitted to distillation with an ordinary chlorine-mix- ture, an acid liquid and a crystalline sublimate are formed. The former is a solution of formic acid, and the latter a mixture of four chlorinetted compounds, which are chloroquinone, C 6 H 3 C10 2 , dichloroquinone, C 6 II 2 C1 2 2 , trichloroquinone, C 6 IIC1 3 2 , and tetrachloroquinone, C 6 C1 4 2 . They are all * Chem. Soc. Quar. Journal, iv. 363. HEXATOMIC ACIDS. 681 yellow crystalline substances, which can be separated only with great diffi- culty. Like quinone itself, they possv e e '^g faculty of combining with 1 or 2 atoms of hydrogen, producing two series & M/ .fyces analogous to green and colorless hydroquinone. Telrachloroquinone, ''ueTM5F known by the name chloranil, likewise occurs among the products of de^*oi>' A 2o s iii'^Q ~&, indigo. Other products are obtained by the action of sulphuretted hydrogen and strong hydrochloric acid upon quinone. HEXATOMIC ACIDS. Three acids of this class are known ; namely, mannitic, saccharic, and mucic acids,, all of which appear to be bibasic. Mannitic Acid, C 6 H, 2 7 , is produced by oxidation of mannite, C 6 H, 4 6 , under the influence of platinum black. It is a gummy mass, soluble in water and in alcohol, insoluble in ether. According to its constitution (p. 573) it might be expected to be monobasic, but from the observations of Gorup-Besanez, who discovered it,* it appears to be bibasic, its potas- sium-salt containing C 6 H 10 K 2 7 , and the calcium-salt, C 6 H 10 Ca // O r Saccharic Acid, C 6 H 10 8 = ( C 4 H 4) vi { [co H) This acid is produced by the action of dilute nitric acid on cane-sugar, glucose, milk-sugar, and mannite, and is often formed in the preparation of oxalic acid, being, from its superior solubility, found in the mother-liquor from which the oxalic acid has crystallized. It may be made by heating together 1 part of sugar, 2 parts of nitric acid, and 10 parts of water. When the reaction seems terminated, the acid liquid is diluted, neutralized with chalk, and the fil- tered liquid is mixed with lead acetate. The insoluble lead saccharate is washed, and decomposed by sulphuretted hydrogen. The acid slowly crys- tallizes from a solution of syrupy consistence in long coloi'less needles ; it has a sour taste, and forms soluble salts with lime and baryta. When mixed with silver nitrate it gives no precipitate, but, on the addition of ammonia, a white insoluble substance separates, which is reduced by gently warming the whole to metallic silver, the vessel being lined with a smooth and brilliant coating of the metal. Nitric acid converts saccharic into oxalic acid. There are two potassium saccharates, containing C 6 H 9 K0 8 and C 6 H 8 K 2 8 ; the silver-salt contains C 6 M 8 Ag 2 8 ; the barium, magnesium,, zinc, and cadmium salts have the composition C 6 H 8 \I X/ ; and there are two ethylic ethers, contain- ing C 6 H 9 (C 2 H 5 )0 8 and C 6 H 8 (C 2 H 6 ) 2 8 . In these compounds saccharic acid appears to be bibasic, as might be expected from its mode of formation (p 573) ; the composition of the lead-salts, however, seems to show that it is saxbasic as well as hexatomic, for Heintz has obtained a lead-salt con- taining C 6 II 4 Pb // 3 8 ; but the composition of the lead saccharates varies con- siderably according to the manner in which they are prepared. Mucic Acid, C 6 H, 8 . This acid, isomeric with saccharic acid, is produced, together with a small quantity of oxalic acid, by the action of rather dilute nitric acid on sugar and gum. It may be easily prepared by heating to- gether in a flask or retort, 1 part of milk-sugar or gum, 4 parts of nitric acid, and 1 part of water; the mucic acid is afterwards collected upon a filter, washed and dried. It has a slightly sour taste, and reddens vegetable * Aim. Ch. Pharra. cxviii. 257. 682 SULPHO-ACIDS. colors. It requires for solution 66 parts of boiling water. Oil of vitriol dissolves it, with production of^escl color. Mucic acid is decomposed by heat, yielding, among r^tj^wpfoducts, pyromucic acid, C 5 H 4 6 , which is vola- tile, soluble in vzSfr^and crystallizes in a form resembling that of benzoic 4d^____^' Mucic acid is bibasic, yielding for the most part neutral salts containing C 6 H 8 M 2 8 and C 6 H 8 M // 8 ; with the alkali-metals it also forms acid salts, such as C 6 H 9 K0 8 . There are also mucic ethers, containing one and two equivalents of monad alcohol-radical. SULPHO-ACIDS. This name is applied to a group of acids formed from hydrocarbons, al- cohols, acids, and amides, by the action of fuming sulphuric acid or sul- phuric oxide. They contain the elements of a hydrocarbon, an alcohol, or an acid, combined with one or two molecules of sulphuric oxide, and may be regarded as derived from hydrocarbons, alcohols, and acids by substitu- tion of the univalent radical, S0 3 H, for hydrogen ; thus, sulphacetic acid, C 2 H 4 S0 5 , has the composition : H 2 C S OH C 2 H 4 2 . S0 3 , or CH 2 (S0 3 H) . C0 2 H, or I = C OH. The sulphur in these acids is in immediate combination with the carbon; in this respect they differ from sulphuric ethers (p. 509), in which the sulphur is united with carbon only through the medium of oxygen. SULPHACETIC ACID is produced by digesting glacial acetic acid with sul- phuric oxide at 60-75 C. (140-167 F.) for several days. The aqueous solution of the mass saturated with barium or lead carbonate deposits a crystalline barium or lead-salt, containing respectively C 2 H 2 Ba /x SO K . 1 \ Aq. and C 2 H 2 Pb x/ S0 5 . From these salts the acid may be obtained by means of sulphuric or sulph-hydric acid. It is bibasic, since it contains two equiv- alents of hydroxyl in immediate association with oxygen, one belonging to the group C0 2 H, the other to the group S0 3 H. When sulphacetic acid is subjected to the prolonged action of fuming sulphuric acid, carbon dioxide is evolved, and disu/p hornet holic or mcthionic acid, CH 4 (S0 3 ) 2 , or CH 2 (S0 3 H) 2 , is formed, which is also bibasic, and may be derived from methane, CH 4 , by substitution of 2S0 3 H for H 2 . The product diluted with water and saturated with barium carbonate, yields a beauti- fully crystallized, and rather sparingly soluble barium-salt, containing CH^OgBa"; from this salt the acid may be separated by sulphuric acid. . Both sulphacetic and disulphometholic acids may be produced by the action of fuming sulphuric acid on acetamide or on acetonitrile, the former when the mixture is kept cool, the latter when the temperature is allowed to rise, carbon dioxide being then given off; thus: C 2 H 3 N -f OH 2 -f 2S0 4 H 2 = S0 4 H(NH 4 ) -f C 2 H 4 S0 5 Acetonitrile. Sulphuric Acid am- Sulphacetic acid. monium acid, sulphate. C 2 II 3 N -f 3S0 4 H 2 = S0 4 H(NH 4 ) -f CH 4 S 2 O 6 -f- C0 2 Acetonitrile. Disulpho- metholic acid. ALDEHYDES. 683 With acetaraide, C 2 H 3 ONH 2 , which differs from acetonitrile only by the elements of water, the two reactions are exactly similar. STJLPHOPROPIONIC ACID, C 2 H 4 (S0 3 H) . C0 2 H, and DISULPHETHOLIC Acir>, C 2 H 4 (S0 3 H) 2 . are prepared in the same way from propionic acid, propiona- mide, or propionitrile. SULPHOBENZOIC ACID, C 6 H 4 (S0 3 H) . C0 2 H, is produced by the action of sulphuric oxide on benzoic acid ; also, together with disulphobenzolic acid, C 6 H 4 (S0 3 H) 2 , by that of fuming sulphuric acid on benzonitrile or phenyl cyanide, C 7 H 5 N. Both are bibasic. Sulphobenzolic acid, C 6 H 5 (S0 3 H), is pro- duced, together with sulphobenzide, C 12 H 10 S0 2 , by the action of sulphuric oxide on benzene. On mixing the resulting viscid liquid with a large quan- tity of water, the sulphobenzide is precipitated as a crystalline powder, while sulphobenzolic acid remains in solution, and may be obtained in the crystalline form by converting it into a copper-salt, decomposing the latter with sulphuretted hydrogen, and evaporating. It is monobasic, and forms soluble salts with the alkali-metals, barium, iron, copper, and silver. By the prolonged action of fuming sulphuric acid, it is converted into disulpho- benzolic acid, C 6 H 4 (S0 3 H) 2 . SULPHONAPHTHALIC ACID, C, H 7 (S0 3 H), and DlSTJLPHONAPHTHALIC AdD, C ]0 H 6 (S0 3 H) 2 , are produced by melting naphthalene with strong sulphuric acid or sulphuric oxide. By neutralizing the aqueous solution of the pro- duct with barium carbonate, concentrating, and adding alcohol, the disul- phonaphthalate of barium is precipitated, while the sulphonaphthalate re- mains dissolved. By using a large excess of sulphuric acid, and applying a strong heat, nearly the whole of the naphthalene is converted into disul- phonaphthalic acid. Both these acids are crystalline, and form soluble and crystallizable salts; sulphonaphthalic acid is monobasic; disulphonaph- thalic acid bibasic. Isethionic acid, C 2 H 6 S0 4 , ethionic acid, C 2 H 6 S 2 7 , and eihionic oxide, or anhy- dride, C 2 H 4 S 2 6 , produced, as already mentioned (pp. 518, 527), by the ac- tion of sulphuric oxide, or fuming sulphuric acid, on alcohol and ether, likewise belong to this class of bodies, and may be represented by the fol- lowing formulae, which show that isethionic acid is monobasic, ethionic acid bibasic, and ethionic oxide neutral: H 2 CH H 2 C S0 3 H H 2 C S O H 2 C-S0 3 H H 2 C-S0 3 H H 2 C S O Isethionic acid. Ethionic acid. Ethionic oxide. ALDEHYDES. These are bodies derived from alcohols by elimination of one or more molecules of hydrogen (H 2 ), without introduction of an equivalent quan- tity of oxygen, so that they hold a position intermediate between the alco- hols and the acids ; thus : CH 3 CJHjj dij CH 2 OH COH COOH Ethyl Acetic Acetic alcohol. aldehyde. acid. 684: ALDEHYDES FROM MONATOMIC ALCOHOLS. The hydrogen eliminated in the conversion of an alcohol into an acid is that which is in immediate connection with the hydroxyl, or which belongs to the group CH 2 OH; consequently a monatomic alcohol can yield but one aldehyde ; but a diatomic alcohol can yield two, by substitution of for H 2 , and of 2 for 2H 2 ; a triatomic alcohol three, and so on. At present, however, we are acquainted only with aldehydes derived from monatomic and diatomic alcohols. Aldehydes derived from Monatomic Alcohols. Of these aldehydes four series are known, viz. : 1. Aldehydes, C n H 2tl O, corresponding to the Fatty adds. Formic aldehyde Acetic aldehyde . . Propionic aldehyde Butyric aldehyde Valeric aldehyde . C 2 H 4 Oaproic aldehyde (Enanthylic aldehyde Caprylic aldehyde . Euodic aldehyde . C 8 H, n, 6 C n H 22 0. 2. Aldehydes, C n H 2n _ 2 0, corresponding to the Acrylic acids. Acrylic aldehyde, or Acrolein . . . C 3 H 4 3. Aldehydes, C n H 2n _ 8 0, corresponding to the Aromatic acids. Benzoic aldehyde, or Bitter-almond oil . . C T H 6 Toluic aldehyde C 8 H 8 Cumic aldehyde C 10 H 15! C Sycocerylic aldehyde .... 4. Aldehydes, C n H 2n _ 10 0. Cinnamic aldehyde .... C Q H 0, All these aldehydes contain two atoms of hydrogen less than the corre- sponding alcohols, and one atom of oxygen less than the corresponding acids. They are produced : 1. By oxidation of alcohols, either by the action of atmospheric oxygen, or by that of a mixture of dilute sulphuric acid and potassium bichromate or manganese dioxide, or by the action of chlorine on the alcohol diluted with water, the chlorine in this case decomposing the water, and thus acting as an oxidizing agent. 2. By distilling an intimate mixture of the potassium-salt of the corre- sponding acid with potassium formate ; e. g. : COCH 3 (OK) Potassium acetate. COC 6 H 6 (OK) Potassium benzoate. -f COH(OK) = CO(OK) 2 -f Potassium Potassium formate. carbonate. + COH(OK) = CO(OK) 2 -f Acetic aldehyde. C 6 H 5 .COH Benzoic aldehyde. 3. By the action of nascent hydrogen (evolved by the action of dry hy- drochloric acid gas on sodium amalgam) on the cyanides of acid radicals : C 7 H 5 OCN Benzoyl cyanide. H, CNH Hydrocyanic acid. Benzoic aldehyde. ALDEHYDES FKOM MONATOMIC ALCOHOLS. 685 Properties. The following properties are common to all the monatomic aldehydes : 1. They easily take up oxygen, and are converted into the corresponding acids. 2. When fused with potash, they are converted into the corresponding acids, with evolution of hydrogen : e. g. : C 7 H 6 4- KOH = C 7 H 5 K0 2 + H 2 . Benzoic Potassium aldehyde. benzoate. 3. Nascent hydrogen, evolved by the action of water on sodium amalgam, converts them into the corresponding alcohols; e. g., C 2 H 4 -f- H 2 = C 2 H 6 0. If, however, the aldehyde belongs to a non-saturated series, the action goes further, an additional quantity of hydrogen being then taken up, whereby the alcohol first formed is converted into a saturated alcohol be- longing to another series; thus: C 3 H 4 + H a = C 3 H 6 0; and C 3 H 6 -f H 2 = C 3 H 8 Acrylic Allyl Allyl Propyl aldehyde. alcohol. alcohol. alcohol. Nascent hydrogen evolved by the action of zinc on sulphuric acid does not appear to unite with aldehydes. 4. Phosphorus pentachloride converts aldehydes into chloraldehydes, com- pounds derived from aldehydes by substitution of C1 2 for ; thus : CH 3 CH 3 I + PC1 6 = PC1 3 4- I COH CHC1 2 Aldehyde. Chloraldehyde. .The compounds thus produced are isomeric with the chlorides of the ole- fines; e.g., acetic chloraldehyde, CH 3 .CHCL, or ethidene chloride, with ethene chloride, C 2 H 4 . C1 2 (p. 484). 5. Chlorine and bromine convert aldehydes into chlorides of acid radicals : C 2 H 4 -f- C1 2 = HC1 4- C 2 H 3 O.C1 Aldehyde. Acetyl chloride. C 2 H 4 + 2C1 3 = 2HC1 + C 2 H 2 C10.C1 Aldehyde. Chloracetyl chloride. 6. The alkali-metals dissolve in aldehydes, eliminating an equivalent quantity of hydrogen : 2CH 4 + K 3 = H 2 -f 2C 2 H 3 KO Aldehyde. Potassium aldehyde. 7. Aldehydes treated with hydrocyanic acid, hydrochloric acid, and water, are converted into an ammonium-salt, or an amidated acid, containing an ad- ditional atom of carbon, the former reaction taking place chiefly in th Cyanogen, in its capacity of a quasi-element, is often represented by the symbol Cy. C=N Cyanogen in the free state, C 2 N 2 , or | , may be obtained by decom- C=N posing certain metallic cyanides. Pulverized and well-dried mercuric cy- anide, (CN) 2 Hg", heated in a small retort of hard glass, undergoes decom- position, like the oxide under similar circumstances, yielding metallic mer- cury, a small quantity of a brown substance, of which mention will again be made, and cyanogen itself, a colorless, permanent gas, which must be collected over mercury. It has a pungent and very peculiar odor, remotely resembling that of peach-kernels, or hydrocyanic acid ; exposed while at the temperature of 7-2 C. (45F.)to a pressure of 3-6 atmospheres, it condenses to a thin, colorless, transparent liquid. Cyanogen is inflam- mable : it burns with a beautiful purple or peach-blossom-colored flame, generating carbon dioxide, and liberating nitrogen. The specific gravity of this gas is 1-806. Its composition may be demonstrated by mixing it with twice its measure of pure oxygen, and firing the mixture in the eudi- ometer ; carbon dioxide is formed equal in volume to the oxygen employed, and a volume of nitrogen equal to that of the cyanogen is set free. Water dissolves 4 or 5 times its volume of cyanogen gas, and alcohol a much larger quantity : the solution rapidly decomposes, yielding ammonium-ox- alate, (C 2 N 2 -f 40H 2 = C 2 (NH 4 ) 2 4 ), a brown insoluble matter, and other products. PARACYANOGEN. This is the brown or blackish substance above re- ferred to, which is always formed in small quantity when cyanogen is prepared by heating mercuric cyanide, and probably, also, by the decom- position of solutions of cyanogen and of hydrocyanic acid. It is insoluble in water and alcohol, is dissipated by a very high temperature, and con- tains, according to Johnston, carbon and nitrogen in the same proportion as cyanogen. 700 HYDROCYANIC ACID. 701 Hydrogen Cyanide; Hydrocyanic or Prussic Acid, HCy. This very im- portant compound, so very remarkable for its poisonous properties, was discovered as early as 1782 by Scheele. It may be formulated as azomelhane, ^ i H ' ^ ia ^ * s to Sa ^' metnane or marsh-gas having three of its hydro- gen-atoms replaced by nitrogen, or as methenyl nitrile, (CH) /// N, that is, ammonia in which the three atoms of hydrogen are replaced by the triva- lent radical methenyl. Hydrocyanic acid may be prepared in a state of purity, and anhydrous, by the following process: A long glass tube, filled with dry mercuric cyan- ide, is connected by one extremity with an arrangement for furnishing dry sulphuretted hydrogen gas, while a narrow tube attached to the other end is made to pass into a narrow-necked phial plunged into a freezing mix- ture. Gentle heat is applied to the tube, the contents of which suifer de- composition in contact with the gas, mercuric sulphide and hydrogen cyan- ide being produced : the latter is condensed in the receiver to the liquid form. A little of the mercuric cyanide should be left undecomposed, to avoid contamination of the product with sulphuretted hydrogen. The pure acid is a thin, colorless, and exceedingly volatile liquid, which has a den- sity of 0-7058 at 7-2 C. (45 F.), boils at 26-1 C. (79 F.), and solidities, when cooled, to 18 C. ( 0-4 F.) ; its o lor is very powerful and most characteristic, much resembling that of peach-blossoms or bitter-almond oil ; it has a very feeble acid reaction, and mixes with water and alcohol in all proportions. In the anhydrous state this substance constitutes one of the most formidable poisons known, and even when largely diluted with water, its effects upon the animal system are exceedingly energetic: it is employed, however, in medicine, in very small doses. The inhalation of the vapor should be carefully avoided in all experiments in which hydro- cyanic acid is concerned, as it produces headache, giddiness, and other disagreeable symptoms: ammonia and chlorine are the best antidotes. The acid in its pure form can scarcely be preserved : even when enclosed in a carefully stopped bottle, it is observed after a very short time to darken, and eventually to deposit a black substance containing carbon, nitrogen, and perhaps hydrogen : ammonia is formed at the same time, and many other products. Light favors this decomposition. Even in a dilute condition it is apt to decompose, becoming brown and turbid, but not al- 'ways with the same facility, some samples resisting change for a great length of time, and then suddenly solidifying to a brown, pasty mass in a few weeks. When hydrocyanic acid is mixed with concentrated mineral acids, hydro- chloric acid, for example, the whole solidifies to a crystalline paste of sal- ammoniac and formic acid : CNH + 2H 2 = NH 3 + CH,0 2 . On the other hand, when dry ammonium formate is heated to 200, it is almost entirely converted into hydrocyanic acid and water. Aqueous solution of hydrocyanic acid may be prepared by various means. The most economical, and by far the best, where considerable quantities are wanted, is to decompose yellow potassium ferrocyanide at boiling heat with dilute sulphuric acid. For example, 500 grains of the powdered fer- rocyanide may be dissolved in four or five ounces of warm water, and in- troduced into a capacious flask or globe, connected by a perforated cork and wide bent tube with a Liebig's condenser well supplied with cold wa- ter ; 300 grains of oil of vitriol are diluted with three or four times as much water and added to the contents of the flask; and the distillation is carried on till about half the liquid has distilled over, after which the pro- cess may be interrupted. The residue in the retort is a white or yellow 59* 702 CYANOGEN COMPOUNDS. mass, consisting of potassio-ferrous ferrocyanide (see p. 707), mixed with potassium sulphate : 2K 4 Fe"Cy e -)- SS0 4 H 2 = GHCy + K 2 Fe" 2 Cy 6 + 3S0 4 K 2 Potassium Hydrogen Hydrogen Potassio- Potassium ferrocyanide. sulphate. cyanide. ferrous sulphate. ferrocyanide. When hydrocyanic acid is wanted for the purposes of pharmacy, it is best to prepare a strong solution in the manner above described, and then, having ascertained its exact strength, to dilute it with pure water to the standard of the Pharmacopoeia, viz., 2 per cent, of real acid. This exami- nation is best made by precipitating with excess of silver nitrate a known weight of the acid to be tried, collecting the insoluble silver cyanide upon a small filter previously weighed, washing, drying, and lastly reweighing the Avhole. From the weight of the cyanide that of the hydrocyanic acid can be easily calculated, a molecule of the one (CNAg=134) corresponding to a molecule of the other (CNH=27) ; or the weight of the silver cyanide may be divided by 5, which will give a close approximation to the truth. Another very good method for determining the amount of hydrocyanic acid in a liquid has been suggested by Liebig. It is based upon the pro- perty possessed by potassium cyanide of dissolving a quantity of silver cyanide sufficient to produce with it a double cyanide containing equivalent quantities of silver cyanide and potassium cyanide (KCy . AgCy). Hence a solution of hydrocyanic acid, which is supersaturated with potash, and mixed with a few drops of solution of common salt, will not yield a perma- nent precipitate with silver nitrate before the whole of the hydrocyanic acid is converted into the above double salt. If we know the amount of silver in a given volume of the nitrate solution, it is easy to calculate the quantity of hydrocyanic acid : for this quantity will stand to the amount of silver in the nitrate consumed, as 2 molecules of hydrocyanic acid to 1 atom of silver, i. e. : 108 : 54 =r silver consumed : x. It is a common remark, that the hydrocyanic acid made from potassium ferrocyanide keeps better than that made by other means. The cause of this is ascribed to the presence of a trace of mineral acid. Everitt found that a few drops of hydrochloric acid, added to a large bulk of the pure dilute acid, preserved it from decomposition, while another portion, not so treated, became completely spoiled. A very convenient process for the extemporaneous preparation of an acid of definite strength, is to decompose a known quantity of potassium cyanide with solution of tartaric acid : 100 grains of crystallized tartaric acid in powder, 44 grains of potassium cyanide, and 2 measured ounces of distilled water, shaken up in a phial for a few seconds, and then left at rest, in order that the precipitate may subside, will yield an acid of very nearly the required strength. A little alcohol may be added to complete the separation of the cream of tartar: no nitration or other treatment need be employed. The production of hydrocyanic acid from bitter almonds has been already mentioned in connection with the history of this volatile oil. Bitter al- monds, the kernels of plums and peaches, the seeds of the apple, the leaves of the cherry-laurel, atid various other parts of plants belonging to the great natural order Rosacece, yield on distillation with water a sweet-smell- ing liquid containing hydrocyanic acid. This is probably clue in all cases to the decomposition of amygdalin under the influence of emulsin or synap- tase present in the organic structure (p. 579). Hydrocyanic acid exists ready formed to a considerable extent in the juice of the bitter cassava. METALLIC CYANIDES. 703 The presence of hydrocyanic acid is detected with the utmost, ease: its remarkable odor and high degree of volatility almost sufficiently charac- terize it. With solution of silver v nitrate it gives a dense curdy white pre- cipitate, much resembling the chloride, but differing from that substance in not blackening so readily by light, in being soluble in boiling nitric acid, and in suffering complete decomposition when, heated in the dry state, me- tallic silver being left: the chloride under the same circumstances merely fuses, but undergoes no chemical change. The production of Prussian blue by " Scheele's test" is an excellent and most decisive experiment, which may be made with a very small quantity of the acid. The liquid to be ex- amined is mixed with a few drops of solution of ferrous sulphate and an excess of caustic potash, and the whole exposed to the air for 10 or 15min- utes, with agitation, whereby the ferrous salt is partly converted into ferric salt: hydrochloric acid is then added in excess, which dissolves the iron oxide, and, if hydrocyanic acid be present, leaves Prussian blue as an insoluble powder. The reaction will be explained in connection with the ferrocyanides (p. 707). Another very delicate test for hydrocyanic acid will be mentioned in con- nection with sulphocyanic acid. Metallic Cyanides. The most important of the metallic cyanides arc the following : they bear the most perfect analogy to the haloid salts. POTASSIUM CYANIDE, CNK or KCy. Potassium heated in cyanogen gas, takes fire and burns in a very beautiful manner, yielding potassium cy- anide : the same substance is produced when potassium is heated in the va- por of hydrocyanic acid, hydrogen being liberated. When pure nitrogen gas is transmitted through a white-hot tube containing a mixture of potas- sium carbonate and charcoal, a small quantity of potassium cyanide is formed, which settles on the cooler portions of the tube as a white amor- phous powder: carbon monoxide is at the same time evolved.* If azotized organic matter of any kind, capable of furnishing ammonia by destructive distillation, as horn-shavings, parings of hides, &c., be heated to redness with potassium carbonate in a close vessel, a very abundant production of potassium cyanide results, which cannot, however, be advantageously ex- tracted by direct means, but in practice is always converted into ferrocy- anide, which is a much more stable substance, and crystallizes better. There are several methods by which potassium cyanide may be prepared for use. It may be made by passing the vapor of hydrocyanic acid into a cold alcoholic solution of potash : the salt is then deposited in the crystal- line form, and may be separated from the liquid, pressed, and dried. Po- tassium ferrocyanide, heated to whiteness in a nearly close vessel, evolves nitrogen and other gases, .and leaves a mixture of carbon, iron carbide, and potassium cyanide, which latter salt is not decomposed unless the temper- ature is excessively high. Mr. Donovan recommends the use in this pro- cess of a wrought-iron mercury-bottle, which is to be half filled with the ferrocyanide, and arranged in a good air-furnace capable of giving the requisite degree of heat; a bent iron tube is fitted to the mouth of the bottle and made to dip half an inch into a vessel of water: this serves to give exit to the gas. The bottle is gently heated at first, but the tem- perature is ultimately raised to whiteness. When no more gas issues, the tube is stopped with a cork, and, when the whole is quite cold, the bottle is cut asunder in the middle by means of a chisel and sledge-hammer, and the pure white fused salt carefully separated from the black spongy mass * According to recent experiments by MM. Marirwritte and d" Sourdeval. the formation of cyanide appears to be more abundant if the ]>ot;ish lie replaced l>y baryta. If the barium cyanide thus formed he exposed to a stream of superheated steam at :;ove given is more convenient. f The ferrocyanides and ferricyanides are sometimes regarded as salts of peculiar com- pound radicals containing iron, vi/., .furrocyanngen, Fe"Cy c , and t\'rri<-iii. Fe'"Cy 6 , the first being quadrivalent, the second trivalent; but there is nothing gained' by this assump- tion. For a discussion of the formulae of these salts, and of the double cyanides iu general see Watts's Dictionary of Chemistry, vol. ii. p. 201. 706 CYANOGEN COMPOUNDS. Ferrocyanides. POTASSIUM FERROCYANIDE, K 4 Fe"Cy 6 , or 4KCy . Fe // Cy a , commonly called yellow prussiate of potash. This important salt is formed: 1. By digesting precipitated ferrous cyanide in aqueous solution of potassium cyanide. 2. By digesting ferrous hydrate with potassium cyanide, potash being formed at the same time : 6KCy + Fe"H 2 2 == 2KHO -f- K 4 Fe"Cy 6 . 3. Ferrous cyanide with aqueous potash : 3F"Cy 2 4. 4KHO = 2Fe"H 2 2 + K 4 Fe"Cy 6 . 4. Aqueous potassium cyanide with metallic iron : if the air be excluded, hydrogen is evolved : GKCy + Fe + 20H 2 = K 4 Fe"Cy e -f 2KHO + H 2 ; but if the air has access to the liquid, oxygen is absorbed, and no hydrogen is evolved : 6KCy + Fe + OH 2 + = K 4 Fe"Cy 6 + 2KHO. 5. Ferrous sulphide with aqueous potassium cyanide : GKCy + Fe"S = K 2 S -f K 4 Fe"Cy 6 . 6. Any soluble ferrous salt with potassium cyanide ; e. g. : GKCy -f S0 4 Fe" = S0 4 K 2 -f K 4 Fe"Cy 6 . Potassium ferrocyanide is manufactured on the large scale by the follow- ing process: Dry refuse animal matter of any kind is fused at a red heat with impure potassium carbonate and iron filings, in a large iron vessel, from which the air should be excluded as much as possible; potassium cyanide is generated in large quantity. The melted mass is afterwards treated with hot water, which dissolves out the cyanide and other salts, the cyanide being quickly converted by the oxide or sulphide* of iron into ferrocyanide. The filtered solution is evaporated, and the first-formed crystals are purified by re-solution. If a sufficient quantity of iron be not present, great loss is incurred by the decomposition of the cyanide into po- tassium carbonate and ammonia. A new process for the preparation of potassium ferrocyanide has lately been proposed by M. Gelis. It consists in converting carbon bisulphide into ammonium sulphocarbonate by agitating it with ammonium sulphide: CS 2 -^ (NH 4 ) 2 S =i (NH 4 ) 2 CS 3 , and heating the product thus obtained with potassium sulphide, whereby potassium sulphocyanate (p 717) is formed, with evolution of ammonium sulphide and hydrogen sulphide : 2(NH 4 ) 2 CS 3 -f RjS = 2CNSK -f 2(NH 4 )HS -f 3H 2 S. The potassium sulphocyanate is dried, mixed with finely divided metallic iron, and heated for a short time in a closed iron vessel to dull redness, whereby the mixture is converted into potassium ferrocyanide, potassium sulphide, and iron sulphide : 6CNSK -f Fe 6 = K 4 Fe"Cy 6 -f 5Fe"S -f K 2 S. By treatment with water, the sulphide and ferrocyanide of potassium are dissolved, and on evaporation the ferrocyanide is obtained in crystals. It remains to be seen whether this ingenious process is capable of being carried out upon a large scale. * The sulphur is derived from the reduced sulphate of the crude pearl-ashes and the animal substances used in the manufacture. FERROCYANIDES. 707 Potassium ferrocyanide forms large, transparent, yellow crystals, K 4 Fe 7/ Cy 6 . 3 Aq., derived from an octahedron with a square base: they cleave with facility in a direction parallel to the base of the octohedron, and are tough and difficult to powder. They dissolve in 4 parts of cold and 2 parts of boiling water, and are insoluble in alcohol. They are permanent in the air, and have a mild saline taste. The salt has no poisonous -properties, and, in small doses at least, is merely purgative. Exposed to a gentle heat, it loses 8 molecules of -water, and becomes anhydrous : at a high tempera- ture it yields potassium cyanide, iron carbide, arid various gaseous pro- ducts; if air be admitted, the cyanide becomes cyanate. Potassium ferrocyanide is a chemical reagent of great value; when mixed in solution with neutral or slightly acid salts of the heavy metals, it gives rise to precipitates which very frequently present highly characteristic colors. In most of these compounds the potassium is simply displaced by the new metal : the beautiful brown ferrocyanide of copper contains, for example, Cu // 2 Fe // Cy 6 , or 2Cu"Cy 2 . Fe"Cy 2 , and that of lead, Pb'^ Fe"Cy 6 . With ferrous salts, potassium ferrocyanide gives a precipitate which is perfectly white, if the air be excluded and the solution is quite free from ferric salt, but quickly turns blue on exposure to the air. It consists of potassio-ferrous ferrocyanide, K 2 Fe // 2 Cy 6 , or potassium ferrocyanide having half the potassium replaced by iron. The same salt is produced in the preparation of hydrocyanic acid by distilling potassium ferrocyanide with dilute sulphuric acid (p. 701). When a soluble ferrocyanide is added to the solution of & ferric salt, a deep blue precipitate is formed, consisting of ferric ferrocyanide, Fe 7 Cy 18 , or Fe'^Fe'^Cjis' or 4Fe /// Cy 3 . 3Fe // Cy 2 , which in combination with 18 mole- cules of water constitutes ordinary Prussian blue. This beautiful pigment is best prepared by adding potassium ferrocyanide to ferric nitrate or chloride : 3K 4 Fe"Cy 6 -f 2Fe'" 2 Cl e = 12KC1 + Fe 7 Cy 18 . It is also formed by precipitating a mixture of ferrous and ferric salts with potassium cyanide : 18KCy + 3Fe"Cl a + 2Fe'" 2 Cl 6 = 18KC1 + Fe 7 Cy 18 . This reaction explains Scheele's test for prussic acid (p. 703). Prussian blue is also formed by the action of air, chlorine-water, and other oxidizing agents, on potassio-ferrous ferrocyanide ; probably thus : 6K,Fe" s Cy. + 3 = Fe 7 Cy 18 + 8K 4 Fe"Cy e + Fe 2 3 . It is chiefly by this last reaction that Prussian blue is prepared on the large scale, potassium ferrocyanide being first precipitated by ferrous sul- phate, and the resulting white or light blue precipitate either left to oxidize by contact with the air, or subjected to the action of nitric acid, chlorine, hypochlorites, chromic acid, &c. The product, however, is not pure ferric ferrocyanide: for it is certain that another and simpler reaction takes place at the same time, by which the potassio-ferrous ferrocyanide, (I^Fe") Fe /x Cy 6 , is converted, by abstraction of an atom of potassium, into potas- sio-ferrous ferricyanidc, (KFe // )Fe /// Cy 6 , which also possesses a fine deep- blue color. Commercial Prussian blue is, therefore, generally a mixture of this compound with ferric ferrocyanide, Fe /// 4 Fe // 3 Cy ]8 , the one or the other predominating according to the manner in which the process is con- ducted. Prussian blue in the moist state forms a bulky precipitate, which shrinks to a comparatively small compass when well washed and dried by a gentle heat. In the dry state it is hard and brittle, much resembling in appear- 708 CYANOGEN COMPOUNDS. ance the best indigo : the freshly fractured surfaces have a beautiful cop- per-red lustre, similar to that produced by rubbing indigo with a hard body. Prussian blue is quite insoluble in water and dilute acids, with the exception of oxalic acid, in a solution of which it dissolves, forming a deep- blue liquid, which is sometimes used as ink : concentrated oil of vitriol converts it into a white, pasty mass, which again becomes blue on addition of water. Alkalies destroy the color instantly: they dissolve out a ferro- cyanide, and leave ferric oxide. Boiled with water and mercuric oxide, it yields a cyanide of the metal, and ferric oxide. Heated in the air, Prus- sian blue burns like tinder, leaving a residue of ferric oxide. Exposed to a high temperature in a close vessel, it gives off water, ammonium cyanide, and ammonium carbonate, and leaves carbide of iron. It forms a very beautiful pigment, both as oil and water color, but has little permanency. Common or basic Prussian blue is an inferior article prepared by pre- cipitating a mixture of ferrous sulphate and alum with potassium ferrocy- anide, and exposing the precipitate to the air. It contains alumina, which impairs the color, but adds to the weight. Soluble Prussian blue is obtained by adding ferric chloride to an excess of potassium ferrocyanide ; it is insoluble in the saline liquor, but soluble in pure water. It has a deep blue color, and probably consists of potassio- ferrous ferricyanide. HYDROGEN FERROCYANIDE OR, HYDROFERROCYANIC ACID, H 4 Fe /x Cy 6 , dis- covered by Mr. Porrett, is prepared by decomposing ferrocyanide of lead or copper suspended in water by a stream of sulphuretted hydrogen gas. The filtered solution evaporated in a vacuum over oil of vitriol, yields the acid in the solid form. If the aqueous solution be agitated with ether, nearly the whole of the acid separates in colorless, crystalline laminge ; it may even be made in large quantity by adding hydrochloric acid to a strong solution of potassium ferrocyanide in water free from air, and shaking the whole with ether. The crystals may be dissolved in alcohol, and the acid again thrown down by ether. Hydroferrocyanic acid differs completely from hydrocyanic acid : its solution in water has a powerfully acid taste and reaction, and decomposes alkaline carbonates with effervescence : it does not dissolve mercuric oxide in the cold, but when heat is applied, un- dergoes decomposition, forming mercuric cyanide and ferrous cyanide : H 4 Fe"Cy 6 + 2Hg"0 = 2Hg"Cy a + Fe"Cy s + 20H 2 ; but the ferrous cy- anide is immediately oxidized by the excess of mercuric oxide, with sepa- ration of metallic mercury. In the dry state the acid is very permanent, but when long exposed to the air in contact with water, it is entirely con- verted into Prussian blue. Sodium ferrocyanide, Na // Fe // Cy 6 . 12 Aq., crystallizes in yellow four- sided prisms, which are efflorescent in the air and very soluble. Ammonium ferrocyanide, (NH 4 ) // Fe // Cy 6 . 3 Aq., is isomorphous with po- tassium ferrocyanide : it is easy soluble, and is decomposed by ebullition. Barium ferrocyanide, Ba // 2 Fe // Cy 6 , prepared by boiling potassium ferrocy- anide with a large excess of barium chloride, or Prussian blue with baryta- water, forms minute yellow, anhydrous crystals, which have but a small de- gree of solubility even in boiling water. The corresponding compounds of strontium, calcium, and magnesium are more freely soluble. The ferro- cyanides of silver, lead, zinc, manganese, and bismuth are white and insoluble ; those of nickel and cobalt are pale-green and insoluble ; and, lastly, that of copper has a beautiful reddish-brown tint. There are also several double ferrocyanides. When, for example, con- centrated solutions of calcium chloride and potassium ferrocyanide are mixed, a sparingly soluble crystalline precipitate falls, containing K 2 Ca x/ FERRICYANIDES. 709 Ferricyanides. These salts are formed, as already observed, by abstraction of metal from the ferrocyanides ; in other words, by the action of oxidizing agents. POTASSIUM FERRICYANIDE, K 3 Fe //v Cy 6 , often called red prussiate of potash, is prepared by slowly passing chlorine, with agitation, into a somewhat dilute and cold solution of potassium ferrocyanide, until the liquid acquires a deep reddish-green color, and ceases to precipitate a ferric salt. The solution is evaporated until a skin begins to form upon the surface, then filtered, and left to cool ; and the salt is purified by re-crystallization. It forms regular, prismatic, or sometimes tabular crystals, of a beautiful ruby- red tint, permanent in the air, and soluble in 4 parts of cold water: the solution has a dark-greenish color. The crystals burn when introduced into the flame of a candle, and emit sparks. The salt is decomposed by ex- cess of chlorine, and by deoxidizing agents, as sulphuretted hydrogen. Hydrogen ferricyanide is obtained in the form of a reddish-brown acid liquid, by decomposing lead ferricyanide with sulphuric acid : it is very unstable, and is resolved, by boiling, into hydrated ferric cyanide, an in- soluble dark-green powder containing Fe 2 Cy 6 . 3 Aq., and hydrocyanic acid. The ferricyanides of sodium, ammonium, and of the alkaline earths, are sol- uble ; those of most of the other metals are insoluble. Potassium ferri- cyanide, added to a ferric salt, occasions no precipitate, but merely a dark- ening of the reddish-brown color of the solution ; with ferrous salts, on the other hand, it gives a deep blue precipitate, consisting of ferrous ferricyanide, Fe 6 Cy, 2 . x Aq., or Fe // 3 Fe /// 2 Cy, 2 . x Aq., which, when dry, has a brighter tint than Prussian blue : it is known under the name of TurnbulVs blue. Hence, potassium ferricyanide is as delicate a test for ferrous salts as the yellow ferrocyanide is for ferric salts. COBALTICYANIDES. This name is applied to a series of compounds analo- gous to the preceding, containing cobalt in place of iron ; a hydrogen-acid has been obtained, and a number of salts, which much resemble the ferri- cyanides. Several other metals of the same isomorphous family are found capable of replacing iron in these compounds. NITROPRUSSIDES. The action of nitric acid upon ferrocyanides and fer- ricyanides gives rise to the formation of a very interesting series of new salts, which were discovered by Dr. Playfair. The general formula of these salts appears to be M 2 (NO)Fe // Cy 5 , which exhibits a close relation with those of the ferro- and ferricyanides. The formation of the nitroprussides appears to consist in the reduction of the nitric acid to the state of nitrogen dioxide or nitrosyl, NO, which replaces 1 molecule of metallic cyanide, MCy, in a molecule of ferricyanide, M 3 Fe /// Cy 6 . The formation of these salts is attended by the production of a variety of secondary products, such as cyanogen, oxamide, hydrocyanic acid, nitrogen, carbonic acid, &c. One of the finest compounds of this series is the nitroprusside of sodium, Na 2 (NO)Fe // Cy 6 . 2 Aq., which is readily obtained by treating 2 parts of the powdered ferrocyanide with 5 parts of common -nitric acid previously diluted with its own volume of water. The solution, after the evolution of gas has ceased, is digested on the water-bath, until ferrous salts no longer yield a blue, but a slate-colored precipitate. The liquid is now allowed to cool, when much potassium nitrate, and occa- sionally oxamide, is deposited : it is filtered and neutralized with sodium carbonate, which yields a green or brown precipitate, and a ruby-colored filtrate. This, on evaporation, gives a crystallization of the nitrates of po- tassium and sodium, together with the nitroprusside. The crystals of the 60 710 CYANOGEN COMPOUNDS. latter are selected and purified by crystallization ; they are rhombic and of a splendid ruby color. The soluble nitroprussides strike a most beau- tiful violet tint with soluble sulphides. This reaction is recommended by Playfair as the most delicate test for alkaline sulphides. ALCOHOLIC CYANIDES OR HYDROCYANIC ETHERS. These compounds play an important part in organic chemistry : we have already had occasion to notice them several times in speaking of the con- version of alcohols into acids containing a greater number of carbon-atoms. The cyanides of univalent alcohol-radicals may also be regarded as com- pounds of nitrogen with trivalent radicals : hence they are often called nilriles ; thus : Hydrogen cyanide II . CN = (C H )'"N Methenyl nitrile. Methyl cyanide C H 3 . CN == (CgH,)'"!* Ethenyl nitrile. Ethyl cyanide C 2 H 6 . CN = (CgH^^'N Propenyl nitrile. Propyl cyanide C 3 H 7 . CN = (C 4 H 7 ) //X N Quartenyl nitrile. Phenyl cyanide C 6 H 6 . CN = (C T H 6 )"'N Benzonitrile. These alcoholic cyanides are produced: 1. By distilling a mixture of potassium cyanide and the potassium-salt of ethylsulphuric or a similar acid: CNK -f S0 4 (C 2 H 5 )K = S0 4 K 2 -f CN . C 2 H 5 Potassium Potassium Potassium Ethyl cyanide. ethyl-sulphate. sulphate. cyanide. 2. By the dehydrating action of phosphoric oxide on the ammonium- salts of the corresponding acids containing the radicals C n H 2n iO and C n H 2n _ 7 0; thus: C 2 H 3 2 .NH 4 20H 2 -= C 2 H 8 N Ammonium Ethenyl acetate. nitrile. C 7 H 5 2 .NH 4 20H 2 == C 7 H 5 N Ammonium Benzonitrile. benzoate. The bodies obtained by these two processes are oily liquids, exhibiting the same properties whether prepared by the first or the second method, excepting that those obtained by the latter have an aromatic fragrant odor, whereas those prepared by the former have a pungent and repulsive odor, due to the presence of certain isomeric compounds, to be noticed farther on. Methyl cyanide, Ethenyl-nitrile, or Acetonitrile, boils at 77 C. (170 F.) ; Ethyl cyanide, or Propenyl-nitrile, at 82 C. (180 F.); Butyl cyanide, or Valeronitrile, at 125-128 C. (257-262 F.) ; Amyl cyanide, or Capronitrile, at 146 C. (295 F.); Phenyl cyanide, or Benzonitrile, at 190-6 C. (375 F.). All these cyanides, when heated with fuming sulphuric acid or sulphu- ric oxide, imdergo the decomposition already mentioned (p. 682), yielding sulpho-acids. By heating with caustic potash or soda, they are resolved into ammonia and the corresponding fatty or aromatic acid, just as hydro- cyanic acid similarly treated is resolved into ammonia and formic acid ; thus: CNH -f 2II 2 = NIT 3 -f CH 2 2 Hydrogen Formic cyanide. acid. ALCOHOLIC CYANIDES. 711 CN.C 2 H 5 + 2H 2 NH 3 + C 3 H 6 2 Ethyl Propionic cyanide. acid. CN.C 6 H 5 + 2H 2 NH 3 + C 7 H 6 2 Phenyl Benzoic acid, cyanide. Ethene cyanide, (C 2 H 4 ) // (CN) 2 , is obtained by distilling potassium cyanide with ethene bromide : C 2 H 4 Br 2 + 2CNK = 2KBr + C 2 H 4 (CN) 2 . It is a crystalline body, melting at 50, and converted by alcoholic potash into ammonia and succinic acid: C 2 H 4 (CN) 2 -f 4H 2 = 2NH 3 -f C 4 H 6 4 . ISOCYANIUES. On examining the equations just given for the decompo- sition of the alcoholic cyanides under the influence of alkalies, it is easy to see that the reaction might be supposed to take place in a different way, each cyanide or nitrile yielding, not ammonia and an acid containing the same number of carbon-atoms as itself, but an alcoholic ammonia, or amine, and formic acid ; thus : CN . C 2 H 5 -f 2H 2 = NH 2 C 2 H 5 + CH 2 2 Ethyl Ethyl- Formic cyanide. amine. acid. In the one case the alcohol-radical remains united with the carbon, pro- ducing a homologue of formic acid, together with ammonia; in the other it remains united with the nitrogen, producing a homologue of ammonia, together with formic acid. A class of cyanides exhibiting the second of these reactions has lately been discovered by Dr. Hofmann.* They are obtained by distilling a mixture of an alcoholic ammonia-base and chloroform with alcoholic potash ; for example : C 6 H 7 N -f CHC1 3 =: 3HC1 -f C 7 H 6 N Aniline. Chloro- Phenyl- form. isocyanide. The potash serves to neutralize the hydrochloric acid produced, which would otherwise quickly decompose the isocyanide. Phenyl isocyanide, when freed from excess of aniline by oxalic acid, then dried with oaustic potash and rectified, is an oily liquid, green by transmitted, blue by re- flected light, and having an intolerably pungent and suffocating odor. It is i^omeric with benzonitrile, and is resolved by boiling with dilute acids into formic acid and aniline : C 7 H 6 N -f 2H 2 = CH 2 2 -f C 6 H 7 N. It is a remarkable fact that, whereas the normal alcoholic cyanides are easily decomposed by boiling alkaline solutions, the isocyanides are scarcely altered by alkalies, but are easily hydrated under the influence of acids. The isocyanides of ethyl and amyl have been obtained by similar pro- cesses; also by the action of ethylic and amylic iodides on silver cyanide. They resemble the phenyl compound in their reactions, and are also char- acterized by extremely powerful odors. The repulsive odor possessed by the normal alcoholic cyanides when prepared by distilling potassium cya- * Proceedings of the Royal Society, xvi. 144, 148, 150. 712 CYANOGEN" COMPOUNDS. nide with the ethyl-sulphate, appears to be due to the presence of small quantities of these isocyanides. The difference of constitution between the normal cyanides and the iso- cyanides may be represented by the following formulae,* taking the methyl compounds for example: . Cyanide. Isocyanide. In the isocyanide the carbon belonging to the alcohol-radical is united di- rectly with the nitrogen; in the isocyanide, only through the medium of the carbon belonging to the cyanogen. This difference of structure may perhaps account for the difference in the reactions of the cyanides and isocyanides under the influence of hydrating agents ; thus : CH Methyl cyanide. 2H 2 = NH 3 CH 3 " Ammonia. 2H 2 = Methyl isocyanide. Methylamine. rci \ 0' (01 ;tic a fH 1 1 01 OH Acetic acid. OH Formic acid. Cyanic and Cyanuric Acids. These are two remarkable polymeric bodies, related in a very close and intimate manner, and presenting phenomena of great interest. Cyanic acid is formed as a potassium-salt, in conjunction with potassium cyanide, when cyanogen gas is transmitted over heated hydrate or carbonate of po- tassium, or passed into a solution of the alkaline base, the reaction resem- bling that by which potassium chlorate and potassium chloride are generated when chlorine is passed into a solution of potash, (p. 186.) Potassium cyanate is, moreover, formed when the cyanide is exposed to a high tem- perature with access of air : unlike the chlorate, it bears a full red heat without decomposition. CYANIC ACID, CNHO, is procured by heating to dull redness in a hard glass retort connected with a receiver cooled by ice, cyanuric acid deprived of its water of crystallization. The cyanuric acid is resolved, without any other product, into cyanic acid, which condenses in the receiver to a limpid, colorless liquid, of exceedingly pungent and penetrating odor, like that of the strongest acetic acid: it even blisters the skin. When mixed with water, it decomposes almost immediately, giving rise to ammonium bicar- bonate : CNHO OH = C0 NH This is the reason why the acid cannot be separated from a cyanate by a stronger acid. A trace of cyanic acid, however, always escapes decom- position, and communicates to the carbon dioxide evolved a pungent smell similar to that of sulphurous acid. The cyanates may be easily distin- guished by this smell, and by the simultaneous formation of an ammonia- salt, which remains behind. Pure cyanic acid cannot be preserved : shortly after its preparation it changes spontaneously, with sudden elevation of temperature, into a solid, white, opaque, amorphous substance, called cyamelide. This curious body * Naqud, Laboratory, p. 411. CYANATES. 713 has the same composition as cyanic acid : it is insoluble in water, alcohol, ether, and dilute acids: it dissolves in strong oil of vitriol by the aid of heat, with evolution of carbon dioxide and production of ammonia; boiled with solution of caustic alkali, it dissolves, ammonia being disengaged, and a mixture of cyanate and cyanurate of the base generated. By dry distil- lation it is again converted into cyanic acid. Potassium Cyanate, CNKO. The best method of preparing this salt is, according to Liebig, to oxidize potassium cyanide with litharge. The cyanide, already containing a portion of cyanate, described at page 704, is re-melted in an earthen crucible, and finely powdered lead oxide added by small portions : the oxide is instantaneously reduced, and the metal, at first in a state of minute division, ultimately collects to a fused globule at the bottom of the crucible. The salt is poured out, and, when cold, pow- dered and boiled with alcohol; the hot filtered solution deposits crystals of potassium cyanate on cooling. The great deoxidizing power exerted by potassium cyanide at a high temperature promises to render it a valuable agent in many of the finer metallurgic operations. Another method of preparing the cyanate is to mix dried and finely-pow- dered potassium ferrocyanide with half its weight of equally dry manganese dioxide ; heat this mixture in a shallow iron ladle, with free exposure to air and frequent stirring, until the tinder-like combustion is at an end ; and boil the residue in alcohol, which extracts the potassium cyanate. This salt crystallizes from alcohol in thin, colorless, transparent plates, which suffer no change in dry air, but on exposure to moisture are gradu- ally converted, without much alteration of appearance, into potassium bi- carbonate, ammonia being at the same time given off. Water dissolves po- tassium cyanate in large quantity : the solution is slowly decomposed in the cold, and rapidly at a boiling heat, into potassium bicarbonate and am- monia. When a concentrated solution is mixed with a small quantity of dilute mineral acid, a precipitate falls, consisting of acid potassium cyanu- rate. Potassium cyanate is reduced to cyanide by ignition with charcoal in a covered crucible. Mixed with solutions of lead and silver, it gives rise to white insoluble cyanates of those metals. Ammonium cyanate ; Urea. When the vapor of cyanic acid is mixed with excess of ammoniacal gas, a white, crystalline, solid substance is produced, which has all the characters of a true, although not neutral ammonium cyanate. It dissolves in water, and if mixed with an acid, evolves carbon dioxide : with an alkali, it yields ammonia. If the solution be heated, or if the crystals be merely exposed for a certain time to the air, a portion of ammonia is dissipated, and the properties of the compound are completely changed. It may now be mixed with acids without the least sign of de- composition, and does not evolve the smallest trace of ammonia when treated with cold caustic alkali. The result of this curious metamorphosis of the cyanate is urea, a product of the animal body, the chief and charac- teristic constituent of urine. This transformation, the discovery of which is due to Wohler, is especially interesting as the first instance of the arti- ficial formation of a product of the living organism. The properties of urea, and the most advantageous methods of preparing it, will be found described a few pages hence. CYANURIC Acin, C 3 N 3 H 3 3 . The substance called melam, of which fur- ther mention will be made, is dissolved by gentle heat in concentrated sul- phuric acid, the solution mixed \\-itli '20 or 30 parts of water, and the whole maintained at a temperature approaching the boiling point, until a speci- men of the liquid, on being tried by ammonia, no longer gives a white pre- cipitate : several days are required to effect this change. The liquid, con- [ 714 CYANOGEN COMPOUNDS. centrated by evaporation, deposits on cooling cyanuric acid, which is purified by re-crystallization. Another, and perhaps simpler method, is to heat dry and pure urea in a flask or retort : the substance melts, boils, gives off ammonia in large quantity, and at length becomes converted into a dirty-white, solid, amorphous mass, which is impure cyanuric acid. This is dissolved by the aid of heat in strong oil of vitriol, and nitric acid added by small portions till the liquid becomes nearly colorless : it is then mixed with water, and left to cool, whereupon the cyanuric acid separates. The urea may likewise be decomposed very conveniently by gently heating it in a tube, while dry chlorine or hydrochloric acid gas passes over it. A mixture of cyanuric acid and sal-ammoniac results, which is separated by dissolving the latter in water. Cyanuric acid forms colorless efflorescent crystals, seldom of large size, derived from an oblique rhombic prism. It is very little soluble in cold water, and requires 24 parts for solution at a boiling heat : it reddens lit- mus feebly, has no odor, and but little taste. The acid is tribasic: the crystals contain C 3 N 3 H S 3 . 2 Aq., and are easily deprived of their water of crystallization. In point of stability, cyanuric acid offers a most remark- able contrast to its isomer, cyanic acid ; it dissolves, as above indicated, in hot oil of vitriol, and even in strong nitric acid, without decomposition, and, in fact, crystallizes from the latter in the anhydrous state. Long- continued boiling with these powerful agents resolves it into ammonia and carbonic acid. The connection between cyanic acid, urea, and cyanuric acid, may be thus recapitulated : Ammonium cyanate is converted by heat into urea. Urea is decomposed by the same means into cyanuric acid and ammonia. Cyanuric acid is changed by a very high temperature into cyanic acid, one molecule of cyanuric acid splitting into 3 molecules of cyanic acic. ETHYL CYANATE AND CYANURATE. When a dry mixture of potassium cyanate and ethylsulphate is distilled, a product is obtained which consists of a mixture of the above ethers. They are separated without difficulty, the cyanate boiling at 60 C. (140 F.), while the boiling point of the cyan- urate is much higher namely, 276 C. (528 F.). Ethyl cyanate, CNO . C 2 H 5 , is a mobile liquid, the vapor of which excites a flow of tears. Its formation is represented by the equation, CNOK + S0 4 (C 2 H 5 )K = S0 4 K 2 + CNO . C 2 H 5 . Ethyl cyanurate contains C 3 N 3 3 . (C 2 H 5 ) 3 : it arises in this reaction from the coalescence of 3 molecules of ethyl cyanate. It may be likewise ob- tained by distilling a mixture of potassium ethylsulphate and cyanurate. Ethyl cyanurate is a crystalline mass, slightly soluble in water, readily soluble in alcohol and ether, melting at 85 C. (185 F.). By substituting for potassium ethylsulphate, salts of methyl- and amyl-sulphuric acid, the corresponding methyl- and amyl-compounds may be obtained. The study of the cyanic and cyanuric ethers, which were discovered by Wurtz, has led to very important results, which will be fully described in the section on the Organic Bases. FULMINIC ACID. This remarkable compound, which is polymeric both with cyanic and cyanuric acids, originates in the peculiar action exercised by nitrous acid upon alcohol in presence of a salt of silver or mercury. The acid itself, or hydrogen fulminate, has not been obtained. Silver fulminate is prepared by dissolving 40 or 50 grains of silver, which FULMINTC ACID. 715 need not be pure, in about f oz. by measure of nitric acid of sp. gr. 1-37, by the aid of a little heat. To the highly acid solution, while still hot, 2 measured ounces of alcohol are added, and heat is applied until reaction commences. The nitric acid oxidizes part of the alcohol to aldehyde and oxalic acid, becoming itself reduced to nitrous acid, which, in turn, acts upon the alcohol in such a manner as to form nitrous ether, fulminic acid, and water, 1 molecule of nitrous ether and 1 molecule of nitrous acid containing the elements of 1 molecule of fulminic acid and 2 molecules of water : N0 2 G 2 II 5 + N0 2 H = C 2 N 2 H 2 2 + 20H 2 . Ethyl nitrite. Nitrous Fulminic acid. acid. The silver fulminate slowly separates from the hot liquid in the form of small, brilliant, white, crystalline plates, which may be washed with a little cold water, distributed upon separate pieces of filter-paper in portions not exceeding a grain or two each, and left to dry in a warm place. When dry, the papers are folded up and preserved in a box. The only perfectly safe method of keeping the salt is by immersing it in water. Silver fulmi- nate is soluble in 36 parts of boiling water, but the greater part crystallizes out on cooling: it is one of the most dangerous substances known, ex- ploding with fearful violence when strongly heated, or when rubbed or struck with a hard body, or when touched with concentrated sulphuric acid: the metal is reduced, and a large volume of gaseous matter suddenly liberated. Strange to say, it may, when very cautiously mixed with cop- per oxide, be burned in a tube with as much facility as any other organic substance. Its composition thus determined is expressed by the formula C 2 N 2 2 Ag 2 . Fulminic acid is bibasic : when silver fulminate is digested with caustic potash, one-half of the silver is precipitated as oxide, and a silver potassium fulminate, C 2 N 2 2 AgK, is produced, which resembles the neutral silver-salt, and detonates by a blow. Corresponding compounds containing sodium or ammonium exist ; but a pure fulminate of an alkali-metal has never been formed. If silver fulminate be digested with water and copper, or zinc, the silver is entirely displaced, and a fulminate of the other metal produced. The zinc-salt mixed with baryta-water gives rise to a precipitate of zinc oxide, while zinco-baric fulminate, (C 2 N 2 2 ).;Zn // Ba // , remains in solution. Mercuric fulminate, C 2 N 2 2 Hg // , is prepared by a process very similar to that by which the silver-salt is obtained : one part of mercury is dissolved in 12 parts of nitric acid, and the solution mixed with an equal quantity of alcohol; gentle heat is applied, and if the reaction becomes too violent, it may be moderated by the addition from time to time of more spirit: much carbonic acid, nitrogen, and red vapors are disengaged, together with a large quantity of nitrous ether and aldehyde : these are sometimes con- densed and collected for sale, but are said to contain hydrocyanic acid. The mercuric fulminate separates from hot liquid, and after cooling may be purified from an admixture of reduced metal by solution in boiling wa- ter and re-crystallization. It much resembles the silver salt in appear- ance, properties, and degree of solubility. It explodes violently by friction or percussion, but, unlike the silver compound, merely burns with a sud- den and almost noiseless flash when kindled in the open air. It is manu- factured on a large scale for the purpose of charging percussion-caps ; sul- phur and potassium chlorate, or more frequently nitre, are added, and the powder, pressed into the cap, is secured by a drop of varnish. The relation of composition between the three isomeric acids are beauti- fully seen by comparing their silver salts: the first acid is monobasic, the second bibasic, and the third tribasic : 716 CYANOGEN COMPOUNDS. Silver cyanate CNOAg. Silver fulminate C 2 N 2 2 Ag 2 . Silver cyanurate .... C 3 N 3 3 Ag 3 . Until lately, beyond that of identity of composition, no relation was known to exist between fulminic acid and its isomers. Dr. Gladstone has, however, shown that, when a solution of copper fulminate is mixed with excess of ammonia, filtered, treated with sulphuretted hydrogen in excess, and again filtered from the insoluble copper sulphide, the liquid obtained is a mixed solution of urea and ammonium sulphocyanate. Another view regarding the constitution of fulminic acid was proposed by Gerhardt. The fulminates may be considered as methyl cyanide (aceto- nitrile), in which one atom of hydrogen is replaced by N0 2 and 2 atoms of hydrogen by mercury or silver : CNCHHH Methyl cyanide. CNC(N0 2 )Ag 2 . . . Silver fulminate. CNC(N0 2 )Hg // . . . Mercuric fulminate. This view has received some support by the interesting observation, lately made by Kekule', that the action of chlorine upon mercuric fulminate gives rise to the formation of chloropicrin, CC1 3 N0 2 (p. 588), a substance originally obtained by Stenhouse, which may be viewed as chloroform, tl'e hydrogen of which is replaced by N0 2 . The connection of fulminic acid with the methyl series is thus established. FULMINURIC ACID, C 3 N 3 H 3 3 . This acid, isomeric with cyanuric acid, was discovered simultaneously by Liebig and by Schischkoff. It is ob- tained by the action of a soluble chloride upon mercuric fulminate. On boiling mercuric fulminate with an aqueous solution of potassium chloride, the mercury-salt gradually dissolves, and the clear solution, after some time, becomes turbid, in consequence of a separation of mercuric oxide ; it then contains potassium fulminurate : 3C 2 N 2 2 Hg" -f 8KC1 + OH 2 == 4KC1 -f 2HgCl 2 + Hg"0 + 2C 3 N 3 3 HK 2 Mercuric Potassium fulminate. fulminurate. If, instead of potassium chloride, sodium or ammonium chloride be em- ployed, the corresponding sodium and ammonium-compounds are obtained. The fulminurates crystallize with great facility ; they are not explosive. Fulminuric acid has the same composition as cyanuric acid, but it is monobasic, whereas cyanuric acid is tribasic. CYANOGEN CHLORIDES. Chlorine forms with cyanogen, or its elements, two compounds, which are polymeric, and correspond to cyanic and cyan- uric acids. Gaseous cyanogen chloride, CyCl, is formed by passing chlorine gas into anhydrous hydrocyanic acid, or by passing chlorine over moist mercuric cyanide contained in a tube sheltered from the light. It is a per- manent and colorless gas at the temperature of the air, of insupportable pungency, and soluble to a very considerable extent in water, alcohol, and ether. At 18 C. (0 F.) it congeals to a mass of colorless crystals, which at 15 C. (5 F.) melt to a liquid whose boiling point is 11 6 C. (18 F.). At the temperature of the air it is condensed to the liquid form under a pressure of four atmospheres, and when long preserved in this condition in hermetically sealed tubes gradually passes into the solid modification. On passing gaseous cyanogen chloride into a solution of ammonia in anhydrous ether, ammonium chloride is deposited, and the ether contains cyanamide, CN 2 H 2 , in solution, from which it separates on evaporation in the crystalline form. Cyanamide is easily soluble in water, alcohol, and ether ; it melts at 40 C. (104 F.}. SULPHOCYANATES. 717 Solid cyanogen chloride, C 3 N 3 C1 3 , or Cy 3 Cl 3 , is generated when anhydrous hydrocyanic acid is put into a vessel of chlorine gas, and the whole exposed to the sun : hydrochloric acid is formed at the same time. It forms long colorless needles, which exhale a powerful and offensive odor, compared by some to that of the excrement of mice ; it melts at 140 C. (284 F.), and sublimes unchanged at a higher temperature. When heated in contact with water, it is decomposed into cyanuric and hydrochloric acids. It dis- solves in alcohol and ether without decomposition. CYANOGEN BROMIDE AND IODIDE correspond to the first of the preceding compounds, and are prepared by distilling bromine or iodine with mercuric cyanide. They are colorless, volatile, solid substances, of powerful odor. CYANOGEN SULPHIDE, C 2 N 2 S, or Cy 2 S, recently obtained by Linnemann by the action of cyanogen iodide upon silver sulphocyanate, crystallizes in transparent, volatile, rhombic plates, having an odor similar to that of cyanogen iodide. It melts at 60, but decomposes rapidly at a higher tem- perature ; dissolves in ether, alcohol, and water, and separates from hot concentrated solutions, on cooling, in the crystalline form. Sulphocyanic Acid, CNHS. This acid is the sulphur analogue of cyanic acid, and, like the latter, is monobasic, the sulphocyanates of monad metals being represented by the formula CNSM. Potassium sulphocyanate, CNSK. To prepare this salt, yellow potassium ferrocyanide, deprived of its water of crystallization, is intimately mixed with half its weight of sulphur, and the whole heated to tranquil fusion in an iron pot, and kept for some time in that condition. When cold, the melted mass is boiled with water, which dissolves out a mixture of potas- sium sulphocyanate and iron sulphocyanate, leaving little behind but the excess of sulphur. This solution, which becomes red on exposure to the air, from oxidation of the iron, is mixed with potassium carbonate, by which the iron is precipitated, and potassium substituted: an excess of the carbonate must be, as far as possible, avoided. The filtered liquid is concentrated, by evaporation over an open fire, to a small bulk, and left to cool and crystallize. The crystals are drained, purified by re-solution, if necessary, or dried by enclosing them, spread on filter-paper, over a sur- face of oil of vitriol covered with a bell-jar. The reaction between the sulphur and the potassium ferrocyanide is represented by the equation: K 4 Fe"C 6 N 6 + S 6 = 4CNSK + (CNS) 2 Fe" Another, and even better process, consists in gradually heating to low redness in a covered vessel a mixture of 46 parts of dried potassium fer- rocyanide, 32 of sulphur, and 17 of pure potassium carbonate. The mass is exhausted with water, the aqueous solution is evaporated to dryness, and the residue is exhausted with alcohol. The alcoholic liquid deposits splendid crystals on cooling or evaporation. Potassium sulphocyanate crystallizes in long, slender, colorless prisms, or plates, which are anhydrous: it has a bitter saline taste, and is desti- tute of poisonous properties: it is very soluble in water and alcohol, and deliquesces when exposed to a moist atmosphere. When heated, it melts to a colorless liquid, at a temperature far below that of ignition. When chlorine is passed into a strong solution of potassium sulphocya- nate, a large quantity of a bulky, deep yellow, insoluble substance, re- sembling some varieties of lead chromate, is produced, together with potas- sium chloride; the liquid sometimes assumes a deep-red tint, and emits a pungent vapor, probably cyanogen chloride. The yellow matter may be collected on a filter, well washed with boiling water, and dried: it retains L 718 CYANOGEN COMPOUNDS. its brilliancy of tint. It was formerly called sulphocyanogen, from its sup- posed identity with the radical of the sulphocyanates ; it is, however, inva- riably found to contain hydrogen, and is represented by the formula C 3 N 3 HS 3 . The yellow substance, now generally called per sulphocyanogen, is quite insoluble in water, alcohol, and ether: it dissolves in concentrated sulphuric acid, from which it is precipitated by dilution. Caustic potash also dissolves it, with decomposition ; acids throw down from this solution a pale-yellow, insoluble body, having acid properties. When heated in the dry state, it evolves sulphur and carbon bisulphide, and leaves a pale, straw-yellow substance, called hy drome Hone, C 6 N 9 rl 3 , the decomposition being represented by the equation : 3C 3 N 3 HS 3 = 3CS 2 + S 3 + C 6 N 9 H 3 . Hydrogen Sulphocyanate, or Hydrosulphocj/anic Acid, CNSH, is obtained by decomposing lead sulphocyanate, suspended in water, with sulphuretted hydrogen. The filtered solution is colorless, very acid, and not poisonous ; it is easily decomposed, in a very complex manner, by ebullition, and by exposure to the air. By neutralizing the liquid with ammonia, and evapo- rating very gently to dryness, ammonium sulphocyanate, CNSNH 4 , is obtained as a deliquescent, saline mass. The salt may be conveniently prepared by digesting hydrocyanic acid with yellow ammonium sulphide (containing excess of sulphur), and boiling off the excess of the latter: 2CNH -j- (NH 4 ) 2 S + S 2 = H 2 S -j- 2CNS(NH 4 ). The sulphocyanates of sodium, barium, strontium, calcium, manganese, and iron, are colorless and very soluble: those of lead and silver are white and insoluble. A soluble sulphocyanate mixed with a ferric salt gives no precipitate, but causes the liquid to assume a deep blood-red tint: hence the use of potassium sulphocyanate as a test for iron in the state of ferric salt. The red color produced by sulphocya- nates in ferric solutions is exactly like that caused under similar circum- stances by meconic acid. The two substances may, however, be readily distinguished by the addition of a solution of gold chloride, which de- stroys the color produced by sulphocyanates. The ferric meconate may also be distinguished from the sulphocyanide, as Everitt has shown, by an addition of corrosive sublimate, which bleaches the sulphocyanate, but has little effect upon the meconate. This is a point of considerable prac- tical importance, as in medico-legal inquiries, in which evidence of the presence of opium is sought for in complex organic mixtures, the detec- tion of meconic acid is usually the object of the chemist: and since traces of alkaline sulphocyanide are to be found in the saliva, it becomes very desirable to remove that source of error and ambiguity. The great facility with which hydrocyanic acid may be converted into ammonium sulphocyanate enables us to ascertain its presence by the iron test just described. The cyanide to be examined is mixed in a watch-glass with some hydrochloric acid, and covered with another watch-glass, to which a few drops of yellow ammonium sulphide adhere. On heating the mixture, hydrocyanic acid is disengaged, which combines with the am- monium sulphide, and produces ammonium sulphocyanate : this, after ex- pulsion of the excess of sulphide, yields the red color with solution of ferric chloride. SULPHOCYANIC ETHERS. These ethers exhibit isomeric modifications, probably analogous to those of the alcoholic cyanides and isocyanides (p. 711). The normal sulphocyanates of methyl and its homologues were dis- covered by Cahours;* and quite recently Hofmann has obtained the corre- sponding isosulphocyanates.f The same chemist some years ago obtained * Ann. Chim. Phys. [3], viii. 2f>4. f Proceedings of the Royal Society, xvi. 254. SULPHOCYANIC ETHERS. 719 phcnyl isosulphocyanate.* Allyl isosulphocyanate has long been known as a natural product. Normal Ethyl Sulphocyanate, C { QP , is obtained by saturating a con- centrated solution of potassium sulphocyanate with ethyl chloride : PTTPl T?T1 -I- P/ N u a H 5 w U \SC 2 H 6 ; also by distilling a mixture of calcium ethylsulphate and potassium sulpho- cyanate. It is a mobile, colorless, strongly refracting liquid, having a some- what pungent odor, like that of mercaptan. It boils at 146 C. (295 F.) With ammonia it does not combine directly, but yields products of decomposition. The methyl and amyl sulphocyanic ethers resemble the ethyl compound, and are obtained by similar processes. The methyl ether boils at about 132 C. (270 F.); the amyl ether at 197 C. (387 F.). f (CS)" \C 2 H 5 phocarbamide with phosphoric oxide, which abstracts ethylamine: Ethyl Isosulphocyanate, N [ L ' , is produced by distilling diethyl-sul- (. ^25 Diethyl-sulpho- Ethylamine. Ethyl isosul- carbamide. phocyanate. This ether differs essentially in all its properties from ethyl sulphocyan- ate. It boils at 134 C. (273 F.), and has a powerfully irritating odor, like that of mustard-oil, and quite different from that of normal ethyl-sul- phocyanate. It unites directly with ammonia in alcoholic solution, forming ethylsulphocarbamide, N 2 (CS) // (C 2 H 5 )H 3 , and forms similar compounds with methylamine and ethylamine. The pungent odor and the direct combina- tion with ammonia and amines, are characteristic of all the ethers of this group. Phenyl Isosulphocyanate, N(CS)"(C 6 H 5 ), is obtained by distilling phenyl- sulphocarbamide, N 2 (CS)"(C 6 H 6 )H 8 , with phosphoric oxide: naphthyl iso- sulphocyanate, N(CS) // (C 10 H 7 ), in like manner from dinaphthylsulpho- cavbamide. The former boils at 220 C. (428 F.). Allyl Isosulphocyanate, N j '^ . This is the intensely pungent yolatile oil obtained by distilling the seeds of black mustard with water. It does not exist ready formed in the seeds, but is produced by the decomposition of myronic acid under the influence of myrosin, an albuminous substance analogous to the synaptase of bitter almonds (see p. 579). The same compound, or perhaps its isomer, normal ethylsulphocyanate, is produced by the action of potassium sulphocyanate or silver sulphocyanate. on allyl iodide or allyl oxide. Oil of mustard is a transparent, colorless, strongly refracting oil, possessing in the highest degree the sharp penetrating odor of black mustard. The smallest quantity of the vapor excites tears, and is apt to produce inflammation of the eyes. It has a burning taste, and rapidly blisters the skin. Its specific gravity is 1-009 at 15. It boils at 148 C. (298 F. ). It is sparingly soluble in water, easily soluble in alcohol and ether; dissolves sulphur and phosphorus when heated, and deposits them in the crystalline state, on cooling. It is violently oxidized by nitric and by nitromuriatic acids. Heated in a sealed tube with potassium monosul- phide, it yields potassium sulphocyanate and allyl sulphide (volatile oil of garlic, p. 545) : 2NCS(C 3 H 6 ) -f- K 2 S = 2CNSK + (C S H 6 ), * Proceedings of the Royal Society, jx. 27,4, 487, 720 CYANOGEN COMPOUNDS. It likewise yields garlic oil when decomposed by potassium. Heated to ]20 in a sealed tube with pulverized soda-lime, it yields sodium sulpho- cyanate and allyl oxide, the oxidized constituent of garlic oil : 2NCS(C 3 H 5 ) + Na 2 = 2CNSNa + (C 3 H 5 ) 2 0. Aqueous potash, soda, baryta, and the oxides of lead, silver, and mercury, in presence of water, convert oil of mustard into sinapoline, C 7 H 12 N 2 0, with formation of metallic sulphide and carbonate ; thus : 2NCS(C 3 H 6 ) + 3PbO -f- OH 2 = 2PbS -f C0 3 Pb -f C 7 H, 2 N 2 0. Sinapoline is a basic substance, which crystallizes in colorless plates, soluble in water and alcohol, and having a distinct alkaline reaction. Oil of mustard unites readily with ammonia, forming thiosinamine, C 4 H 5 f(CS) NS . NH 3 , or allyl-sulphocarbamide, N 2 -j C 3 H 5 , which is also a basic com- pound, forming colorless prismatic crystals, having a bitter taste and solu- ble in water. The solution does not affect test-paper. Thiosinamine melts when heated, but cannot be sublimed. Acids combine with it, but do not form crystallizable salts: the double salts of the hydrochloride with pla- tinic and mercuric chloride are the most definite. Thiosinamine is decomposed by metallic oxides, as lead oxide or mercuric oxide, with production of a metallic sulphide and sinamine, C 4 H 6 N 2 , a basic compound which crystallizes very slowly from a concentrated aqueous so- lution in brilliant, colorless crystals containing water. It has a powerfully bitter taste, is strongly alkaline to test-paper, and decomposes ammonium salts at the boiling heat. Its oxalate is crystallizable. The formation of sinamine from thiosinamine by the action of mercuric oxide is represented by the equation C 4 H 8 N 2 S + HgO = HgS -f OH 2 -f C 4 H 6 N 2 . Seleniocyanates. A series of salts containing selenium, and correspond- ing in composition and properties with the sulphocyanates, have been dis- covered and examined by Mr. Crookes.* Melam. This name is given by Liebig to a buff-colored, insoluble, amorphous substance, obtained by the distillation of ammonium sulphocy- anate at a high temperature. It may be prepared in large quantity by in- timately mixing 1 part of perfectly dry potassium sulphocyanate with 2 parts of powdered sal-ammoniac, and heating the mixture for some time in a retort or flask: carbon bisulphide, ammonium sulphide, and sulphuretted hydrogen, are disengaged and volatilized, while a mixture of melam, potas- sium chloride, and sal-ammoniac remains: the two latter substances are removed by washing with hot water. Melam contains C 6 H 9 N n : it dissolves in concentrated sulphuric acid, and gives, by dilution with water and long boiling, cyanuric acid. The same substance is produced, with disengage- ment of ammonia, when melam is fused with potassium hydrate. When strongly heated, melam is resolved into mellone and ammonia. If melam be boiled for a long time in a moderately strong solution of caustic potash, until the whole has dissolved, and the liquid be then con- centrated, a crystalline substance separates on cooling, which is called mclamine. By re-crystallization it is obtained in colorless crystals, having the figure of an octohedron with rhombic base : it is but slightly soluble in cold water, fusible by heat. Melamine is also formed on heating cyana- mide to 150 C. (302 F.), and even on evaporating an aqueous solution of that substance. It contains C 3 H 6 N 6 , and acts as a base, combining with acids to form crystallizable compounds. A second basic substance, called * Journal of the Chemical Society, iv. 12, UREA. 721 ammeline, very similar in properties to melamine, is found in the alkaline mother-liquor from which the melamine has separated : it is thrown down on neutralizing the liquid with acetic acid. The precipitate, dissolved in di- lute nitric acid, yields crystals of ammeline nitrate, from which the pure ammeline may be separated by ammonia. It forms a brilliant white pow- der composed of minute needles, insoluble in water and alcohol, and con- tains C 3 H 5 N 5 0. When ammeline is dissolved in concentrated sulphuric acid, and the solution mixed with a large quantity of water, or, better, spirit of wine, a white, insoluble powder falls, which is called ammelide, and is found to contain C 6 H 9 N 9 3 . By the action of acids or alkalies, melamine maybe converted into amme- line, ammelide, and, lastly, into cyanuric acid, water being assimilated and ammonia evolved : C 3 H 6 N 6 + H 2 = C 3 H 5 N ? + NH S Melamine. Ammeline. 2C 3 H 5 N 5 -f H 2 = C 6 H 9 N 9 3 -f NH 3 Amjneline. Ammelide. C 6 H 9 N 9 3 + 8H 2 = 2C 3 H 3 N 3 3 -f 3NH 3 . Ammelide. Cyanuric acid. Mellone and its Compounds. The formation of mellone as a residuary product of the action of heat on persulphocyanogen, and upon melam, has been already mentioned. This substance, which does not appear to have been obtained in a state of purity, possesses the properties of an organic radical. At a high temperature it combines directly with potassium, pro- ducing a well-defined saline compound, tripotassic mellonide, C 9 H, 3 K 3 , and the same salt is produced in the action of mellone upon potassium bromide and iodide, bromine and iodine being liberated. A better method of pre- paring it consists in fusing crude mellone with potassium sulphocyanate. It may also be produced by fusing the ferrocyanide with half its weight of sulphur. The fused mass obtained by either process is dissolved in boiling water, from which the tri-potassic mellonide crystallizes on cooling, and may be purified by repeated crystallization. Acetic acid converts this salt into dipotassic mellonide, C 9 H 13 K 2 H, which is also soluble. Hydrochloric acid produces the monopotassic salt, C 9 N 13 KH 2 , which is insoluble. These three salts stand to each other in the same relation as the several salts of phosphoric and cyanuric acids. Tripotassic mellonide produces with solu- ble silver-salts a white precipitate, C 9 N l3 Ag 3 ; with lead-salts and mercury- salts, precipitates containing respectively C^N^Pbg, and CjgN^Hgj. The latter dissolved in hydrocyanic acid, and treated with sulphuretted hydro- gen, yields hydromellonic acid, C 9 N 13 H 3 . It is known only in solution, which has an acid taste : on evaporation it is decomposed. UREA. URIC ACID AND ITS PRODUCTS. These bodies are closely connected with the cyanogen-compounds, and may be most conveniently discussed in the present place. Urea, CN 2 H 4 0. Urea maybe extracted from its natural source, the urine, or it may be prepared by artificial means. Fresh urine is concen- trated in a water-bath, until reduced to an eighth or a tenth of its original volume, and filtered through cloth from the insoluble deposits of urates and phosphates. The liquid is mixed with about an equal quantity of a strong solution of oxalic acid in hot water, and the whole vigorously agi- 61 722 UKEA. tated and left to cool. A very copious fawn-colored crystalline precipitate of urea oxalate is obtained, which may be placed upon a doth filter, slightly washed with cold water, and pressed. This is to be dissolved in boiling water, and powdered chalk added until effervescence ceases, and the liquid becomes neutral. The solution of urea is filtered from the insoluble cal- cium oxalate, warmed with a little animal charcoal, again filtered, and con- centrated by evaporation, avoiding ebullition, until crystals form on cool- ing: these are purified by a repetition of the last part of the process. Urea may be extracted in great abundance from the urine of horses and cattle duly concentrated, and from which the hippuric acid has been sepa- rated by addition of hydrochloric acid ; oxalic acid then throws down the oxalate in such quantity as to render the whole semi-solid. Another pro- cess consists in precipitating the evaporated urine with concentrated nitric acid, when urea nitrate is precipitated, which is purified by re-crystalliza- tion with animal charcoal, and, lastly, decomposed by barium carbonate, whereby a mixture of barium nitrate and urea is formed, which is to be evaporated to dryness on the water-bath, and exhausted with hot alcohol ; the urea then crystallizes on cooling. Urea is produced artificially by heating a solution of ammonium cya- nate. The following method of proceeding yields it in any quantity that can be desired. Potassium cyanate, prepared by Liebig's process (p. 713), is dissolved in a small quantity of water, and a quantity of dry neutral ammonium sulphate, equal in weight to the cyanate, is added. The whole is evaporated to dryness in a water-bath, and the dry residue boiled with strong alcohol, which dissolves out the urea, leaving the potassium sul- phate and the excess of ammonium sulphate untouched. The filtered solu- tion, concentrated by distilling off a portion of the spirit, deposits the urea in beautiful crystals of considerable size. Urea forms transparent, colorless, four-sided prisms, which are anhy- drous, soluble in an equal weight of cold water, and in a much smaller ?uantity at a high temperature. It is also readily dissolved by alcohol, t is inodorous, has a cooling saline taste, and is permanent in the air, unless the latter be very damp. When heated it melts, and at a higher temperature decomposes, with evolution of ammonia and ammonium cya- nate ; cyanuric acid remains, which bears a much greater heat without change. The solution of urea is neutral to test-paper : it is not decom- posed in the cold by alkalies or by calcium hydrate, but at a boiling heat emits ammonia, and forms a metallic carbonate. The same change hap- pens by fusion with the alkaline hydrates, and when urea is heated with water, in a sealed tube, to a temperature above 100: COH 4 N 2 + H 2 = C0 2 -f 2NH 3 . Urea contains, in fact, the elements of ammonium carbonate minus the ele- ments of water: C0 3 (NH 4 ) 2 2H 2 0, and has accordingly been supposed to be identical with carbamide. Recent experiments have shown, however, that it is isomeric, not identical with that compound, inasmuch as, when heated with a large excess of potassium permanganate in presence of much free alkali, it gives off all its nitrogen in the free state as gas, whereas when amides and ammonium-salts are thus treated, the whole of the nitro- gen is oxidized to nitric acid.* The difference of constitution between the three isomeric compounds ammonium cyanate, urea, and carbamide may perhaps be represented by the following formulae : (NH)" (NH 2 NH 2 C 1 NH 2 .OH {&' Ammonium cyanate. Urea. Carbamide. * Wanllyn and Gpmgee, Chera. Soc. Journal [2], yi. 25. URIC ACID. 723 A solution of pure urea shows no tendency to change by keeping, and is not decomposed by boiling ; in the urine, on the other hand, where it is associated with putrefiable organic matter, as mucus, the case is different. In putrid urine no urea can be found, but enough ammonium carbonate to cause brisk effervescence with an acid; and if urine, in a recent state, be long boiled, it gives off ammonia and carbonic acid from the same source. Urea is instantly decomposed by nitroiis acid into carbon dioxide, nitro- gen, and water : COH 4 N 2 -f 2N0 2 H = C0 2 -f 2N 2 -f 3H 2 ; this decompo- sition explains the use of urea in preparing nitric ether (p. 526). When chlorine gas is passed over melted urea, hydrochloric acid and nitrogen are evolved, and there remains a mixture of sal-ammoniac and cyanuric acid : 6COH 4 N 2 -f 3C1 2 = 2C 3 H 3 N 3 3 + 4NH 4 C1 -f 2HC1 + N 2 ; but by chlorine in presence of water, or by hypochlorous acid, it is resolved into hydrochloric acid, carbon dioxide, water, and nitrogen : COH 4 N 2 -f 3C1HO = 3HC1 -f C0 2 -f 2H 2 + N 2 . Urea acts as a base : with nitric acid it forms a sparingly soluble com- pound, which crystallizes, when pure, in small, indistinct, colorless plates, containing COH 4 N 2 . N0 3 H. When colorless nitric acid is added to urine concentrated to a fourth or a sixth of its volume, and cold, the nitrate crystallizes out in large, brilliant, yellow laminae, which are very insoluble in the acid liquid. The production of this nitrate is highly characteristic of urea* The ozalate, (COH 4 N 2 ) 2 . C 2 H 2 4 , when pure, crystallizes in large, transparent, colorless plates, which have an acid reaction, and are spar- ingly soluble. Urea forms several compounds with metallic salts, e. g., with those of mercury. On mixing a liquid containing urea with a solution of mercuric nitrate, a white precipitate is formed, consisting of COH 4 N 2 . 2HgO. If the nitric acid which is thus set free be neutralized by the addition of an alkali or baryta-water, the whole of the urea is removed from the liquid in the form of the above compound. Liebig has based upon this reaction a process of determining the amount of urea in urine : 2 volumes of urine are mixed with 1 volume of a baryta-solution prepared with 2 volumes , baryta-water saturated in the cold, and 1 volume of a solution of barium- nitrate also saturated in the cold ; the liquid is filtered from the precipi- tated sulphate and phosphate of barium; and a graduated solution of mer- curic nitrate is added to a measured quantity of this filtered liquid (about 15 c.c.) till a sample taken out gives a yellow precipitate with sodium car- bonate. It is convenient to dilute the mercuric solution to such a degree that 1 cubic centimetre of it shall correspond to 0-01 grm. of urea.* A series of substances analogous to urea, which are known under the names of methyl-urea, ethyl-urea, biethyl-urea, &c., will be noticed in the section on Organic Bases. Uric Acid, C 5 N 4 H 4 3 ; formerly called Lithic acid. This acid is a product of the animal organism, and has never been formed by artificial means. It may be prepared from human urine by concentration and addition of hy- drochloric acid, and crystallizes out after some time in the form of small, reddish, translucent grains, very difficult to purify. A much preferable method is, to employ the solid white excrement of serpents, which can be easily procured: this consists almost, entirely of uric acid and ammo- nium urate. It is reduced to powder, and boiled in dilute solution of caus- tic potash: the liquid, filtered from the insignificant residue of feculent * Respecting certain precautions to he observed in performing this process, see the article " Urine," by Dr. Michael Foster, in Watts's Dictionary of Chemistry. 724: URIC ACID. matter and earthy phosphates, is mixed with excess of hydrochloric acid, boiled for a few minutes, and left to cool. The product is collected on a filter, washed until free from potassium chloride, and dried by gentle heat. Uric acid, thus obtained, forms a glistening, snow-white powder, taste- less, inodorous, and very sparingly soluble. It is seen under the micro- scope to consist of minute, but regular crystals. It dissolves in concen- trated sulphuric acid without apparent decomposition, and is precipitated by dilution with water. By destructive distillation, uric acid yields cyanic acid, hydrocyanic acid, carbon dioxide, ammonium carbonate, and a black coaly residue, rich in nitrogen. By fusion with potassium hydrate, it yields potassium carbonate, cyanate, and cyanide. When treated with nitric acid and with lead dioxide, it undergoes decomposition in a manner to be pres- ently described. Uric acid is bibasic : its most important salts are those of the alkali- metals. Acid potassium urate, C 5 N 4 H 3 K0 3 , is deposited from a hot saturated solution of uric acid in the dilute alkali, as a white, sparingly soluble, con- crete mass, composed of minute needles: it requires about 500 parts of cold water for solution, is rather more soluble at a high temperature, and much more soluble in excess of alkali. Sodium urate resembles the potas- sium-salt : it forms the chief constituent of the gouty concretions in the joints called chalk-stones. Ammonium urate is also a sparingly soluble com- pound, requiring for solution about 1000 parts of cold water : the solubility is very much increased by the presence of a small quantity of certain salts, as sodium chloride. The most common of the urinary deposits, forming a buff-colored or pinkish cloud or muddiness, which disappears by re-solution when the urine is warmed, consists of a mixture of different urates. Uric acid is perfectly well characterized, even when in very small quan- tity, by its behavior with nitric acid. A small portion mixed with a drop or two of nitric acid in a small porcelain capsule dissolves with copious effervescence. When this solution is cautiously evaporated nearly to dry- ness, and, after the addition of a little water, mixed with a slight excess of ammonia, a deep-red tint of murexide is immediately produced. Impure uric acid, in a remarkable state of decomposition, is now im- ported into this country, in large quantities, for use as a manure, under the name of guano or huano. It comes chiefly from the barren and unin- habited islets of the western coast of South America, and is the production of the countless birds that dwell undisturbed in those regions. The people of Peru have used it for ages. Guano usually appears as a pale-brown powder, sometimes with whitish specks : it has an extremely offensive odor, the strength of which, however, varies very much. It is soluble in great part in water, and the solution is found to be extremely rich in oxalate of ammonia, the acid having been generated by a process of oxidation. Guano also contains a peculiar substance called guanine, which will be described further on. Products formed from Uric Acid by Oxidation, $c. Uric acid is remarkable for the facility with which it is altered by oxi- dizing agents, and the great number of definite and crystallizable compounds obtained in this manner, or by treating the immediate products of oxida- tion with acids, alkalies, reducing agents, &c. The following is a list of most of the compounds thus produced : DERIVATIVES OF URIC ACID. 725 Uric acid C 5 N 4 H 2 3 . II * Thionuric acid C 4 NJI,0 6 S . H Pseudo-uric acid . C.NJWH Hydurilic acid C 4 N 4 II 4 6 .H 2 Uroxanic acid C 5 N 4 II 8 O e .H a Allantoin C 4 N 4 II 6 3 Alloxan C 4 N 2 II 2 4 Glycoluvil C 4 N 4 II 6 2 Alloxanic acid C 4 N 2 H 2 5 .H 2 . Mycomelic acid C 4 N 4 H 3 2 .H Alloxantin . C 8 N 4 H 4 7 . 3 Aq. Oxaluric acid C 3 N 2 H 3 4 . H Barbituric acid . C 4 N 2 H 2 3 . H 2 Allanturic acid C 3 N 2 H 3 3 . H Bromobarbi- \ turic acid J C 4 N 2 H 2 Br0 3 . H Hydantoin Hydantoic acid C 3 N 2 M 4 2 C 3 N 2 H 5 3 .H Dibromobar- \ Allituric acid C 6 N 4 H 5 4 . H bituric acid / C 4 N 2 H 2 Br 2 3 Leucoturic acid C 6 N 4 H 3 5 .H Violuric acid C 4 N 3 II 2 4 . H Parabanic acid cXA Dilituric acid C 4 N 3 H 2 5 . H Dibarbituric acid . C 8 N 4 H 4 5 .H 2 Violantin C 4 N 6 H 6 9 Murcxide C 8 N 6 H 8 6 Dialuric acid C 4 N 2 H 3 4 .H Mesoxalic acid C 3 5 .H 2 Urarnil C 4 N 3 H 5 3 When uric acid is subjected to the action of an oxidizing agent in pres- ence of water, it gives up two of its hydrogen-atoms to the oxidizing agent, while the dehydrogenized residue (which may be called dehyduric acid) re- acts with water to form mesoxalic acid and urea: C 5 N 4 H 2 3 Dehyduric acid. Mesoxalic acid. 2CN 2 H 4 Urea. The separation of the urea generally takes place, however, by two stages, the first portion being removed more easily than the second ; thus, when dilute nitric acid acts upon uric acid, alloxan is produced; and this, when heated with baryta-water, is further resolved into mesoxalic acid and urea: Dehyduric acid. C 4 N 2 H 2 4 Alloxan. 2H 2 = C 4 N 2 H 2 4 Alloxan. 2H 2 = C 3 H 2 5 Mesoxalic acid. CN 2 H 4 Urea. CN 2 H 4 Urea. . Moreover, the urea is frequently resolved into carbonic acid and am- monia by the action of the acids or alkalies present. Alloxan is a monu- reide of mesoxalic acid that is to say, it is a compound of that acid with one molecule of urea minus 2H 2 O; and the hypothetical dehyduric acid is the diureide of the same acid, derived from it by addition of 1 molecule of urea and subtraction of 4 molecules of water. Now, by hydrogenizing mesoxalic acid, we obtain tartronic acid, C 3 H 4 5 (p. 668) ; and by hydrogenizing al- loxan, we obtain dialuric acid, which two bodies, accordingly, bear to uric acid the same relation that mesoxalic acid and urea bear to dehyduric acid ; thus: C.HA Mesoxalic acid. C 4 N 2 H 2 4 Alloxan. C 4 N 2 H 4 4 Dialuric acid. Dehyduric acid. - x C 2 H 2 4 , Oxalic..-"' C 3 N 2 H 2 3 , Parabanic. C 5 N 4 H 4 0, Hy poxanthine. C 5 N 4 H 4 2 , Xanthine. C 6 N 4 H 4 3 , Uric acid. -C 5 N 4 H B O ll , Pseudo-uric. C 4 N 2 H 4 S , Barbituric. C 4 N 2 H 4 4 , Dialuric.^ xC 4 N 2 H 4 5 ,Alloxanic. C 3 H 2 6 , Mesoxalic./ C 4 N 2 H 2 4 , Alloxan. Between some of the consecutive monureides shown in this table, there exist bodies formed by the union of the two consecutive monureides, with elimination of water. Such is the mode of formation of allituric, lantan- uric, and hydurilic acids, and of alloxantin ; thus : C 6 N 4 H 6 4 = C 3 N 2 H 4 2 -f C 3 N 2 H 4 3 H 2 Allituric Hydantoin. Lantanuric acid. acid. C 6 N 4 H 4 5 Leucoturic acid. C 8 N 4 H ? 6 Hydurilic acid. C 8 N 4 H 4 7 Alloxantin. = C. AHA Lantanuric acid. C 4 N 2 H 4 3 Barbituric acid. C 4 N 2 H 4 4 Dialuric acid. C 3 N 2 H 2 3 Parabanic acid. C 4 N 2 H 4 4 Dialuric acid. C 4 N 2 H 2 4 Alloxan. H 2 H 2 * This table, together with the preceding view of the relations between the several deriva- tives of uric acid, is taken from (Ming's " Lectures on Animal Chemistry." London, 1866, pp. 129-135. 728 DERIVATIVES OF URIC ACID. The following is a description of some of the more important compounds above enumerated : ALLANTOIN, C 4 N 4 H 6 Og. This substance, which contains the elements of 2 molecules of ammonium oxalate minus 5 molecules of water [2C 2 (NH 4 ) 2 4 5H 2 0], is contained in the allantoi'c liquid of the foetal calf and in the urine of the sucking calf. It is produced artificially, together with oxalic acid and urea, by boiling uric acid with lead dioxide and water : 2CsN 4 H/) 3 + 30 2 + 5H 2 = C 4 N 4 H 6 3 + 2C 2 H 2 4 + 2CN 2 H 4 3 Uric acid. Allantoin. Oxalic acid. Urea. The liquid filtered from lead oxalate, and duly concentrated by evapora- tion, deposits on cooling crystals of allantoin, which are purified by re- solution and the use of animal charcoal. The mother-liquor, when further concentrated, yields crystals of pure urea. Allantoin forms small but most brilliant prismatic crystals, which are transparent and colorless, des- titute of taste, and without action on vegetable colors. It dissolves in 160 parts of cold water, and in a smaller quantity at the boiling heat. It is decomposed by boiling with nitric acid, and by oil of vitriol when concen- trated and hot, being in this case resolved into ammonia, carbon dioxide, and carbon monoxide. Heated with concentrated solutions of caustic alka- lies, it is decomposed into ammonia and oxalic acid. ALLOXAN, C 4 N 2 H 2 4 . This is the characteristic product of the action of concentrated nitric acid on uric acid in the cold. An acid is prepared of sp. gr. about 1-45, and placed in a shallow open basin: into this a third of its weight of dry uric acid is thrown, by small portions, with constant agitation, care being taken that the temperature never rises to any con- siderable extent. The uric acid at first dissolves, with copious efferves- cence of carbon dioxide and nitrogen, and eventually the whole becomes a mass of white, crystalline, pasty matter. This is left to stand some hours, drained from the acid liquid in a funnel having its neck stopped with pow- der and fragments of glass, and afterward more effectually dried upon a porous tile. This is alloxan in a crude state: it is purified by solution in a small quantity of water, and crystallization. Alloxan crystallizes with facility from a hot and concentrated solution, slowly suffered to cool, in solid, hard, anhydrous crystals of great regular- ity, which are transparent, nearly colorless, have a high degree of lustre, and the figure of a modified rhombic octohedron. These crystals are monohydrated, consisting of C 4 N 2 H 2 4 . Aq. A cold solution, on the other hand, left to evaporate spontaneously, deposits large foliated crystals con- taining 4 molecules of water: they effloresce rapidly in the air. The monohydrate heated to 150-160 C. (302-320 F.) in a stream of dry hy- drogen gives off its water, and leaves anhydrous alloxan, C 4 N 2 H 2 4 . Al- loxan is very soluble in water: the solution has an acid reaction, a dis- agreeably astringent taste, and stains the skin, after a time, red or purple. It is decomposed by alkalies, and both by oxidizing and deoxidizing agents: its most characteristic property is that of forming a deep-blue compound with a ferrous salt and an alkali. ALLOXANIC ACID, C 4 N 2 H 4 5 . The barium-salt of this acid is deposited in small colorless, pearly crystals, when baryta-water is added to a solu- tion of alloxan, heated to 60 C. (140 F.), as long as the precipitate first produced redissolves, and the filtered solution is then left to cool. The barium may be separated by the cautious addition of dilute sulphuric acid, and the filtered liquid by gentle evaporation yields alloxanic acid in small radiated needles. It has an acid taste and reaction, decomposes carbon- ates., and dissolves zinc with disengagement of hydrogen. It is a bibasic THIONURIC ACID. 729 acid. The alloxanates of the alkali-metals are freely soluble: those of the earth-metals dissolve in a large quantity of tepid water; that of silver is quite insoluble and anhydrous. MESOXALIC ACID, C 3 H 2 5 . When a warm saturated solution of barium alloxanate is heated to ebullition, a precipitate falls, which is a mixture of barium carbonate, alloxanate, and mesoxalate : the solution is found to contain unaltered barium alloxanate and urea. Mesoxalic acid is best prepared by slowly adding solution of alloxan to a boiling-hot solution of lead acetate : the heavy granular precipitate of lead mesoxalate thus pro- duced is washed and decomposed by sulphuretted hydrogen : urea is also formed in this reaction (p. 725). Mesoxalic acid is crystallizable : it has a sour taste and powerfully acid reaction, and resists a boiling heat: it forms sparingly soluble salts with barium and calcium, and a yellowish in- soluble compound with silver, which is reduced with effervescence when gently heated. MYCOMELIC ACID, C 4 N 4 H 4 2 . This acid is formed when ammonia in excess is added to a solution of alloxan, the whole heated to ebullition, and afterward supersaturated with dilute sulphuric acid : it then separates as a yellow, light precipitate, which increases in quantity as the liquid cools. It is but feebly soluble in water, easily dissolved by alkalies, and forms a yellow silver-salt. Its formation from alloxan and ammonia is represented by the equation : C 4 N 2 H 2 4 + 2NH 3 = C 4 N 4 H 4 2 -f 2H 2 0. PARABANIC ACID, or PARABAN, C 3 N 2 H 2 3 . This is the characteristic product of the action of moderately strong nitric acid on uric acid or al- loxan, by the aid of heat : Cy^HA + 2 + 2H 2 = C 3 N 2 H 2 3 -f 2C0 2 + 2NH 3 . It is conveniently prepared by heating together 1 part of uric acid and 8 parts of nitric acid until the reaction has nearly ceased ; the liquid is eva- porated to a. syrupy state and left to cool; and the acid drained from the mother-liquor is purified by re-crystallization. Parabanic acid forms colorless, transparent, thin, prismatic crystals, which are permanent in the a'ir: it is easily soluble in water, has a pure and powerfully acid taste, and reddens litmus strongly. Neutralized with ammonia, and mixed with sil- ver nitrate, it gives a white precipitate. OXALURIC ACID, C 3 H 2 N 4 4 . The ammonium-salt of this acid separates in colorless needles, when a solution of parabanic acid saturated with am- monia is boiled for a moment, and then left to cool. The acid is obtained by adding an excess of dilute sulphuric acid to a hot and strong solution of the ammonium-salt, and cooling the whole rapidly. It forms a white, crystalline powder, of acid taste and reaction, capable of combining with bases: the barium- and calcium-salts are sparingly soluble; the silver-salt crystallizes from the mixed hot solution of silver nitrate and ammonium oxalurate in long, silky needles. Oxaluric acid contains the elements of 1 molecule of parabanic acid and 1 molecule of water. Its solution is resolved by ebullition into free oxalic acid and oxalate of urea. THIONURIC ACID, C 4 N 3 H 6 SO tf . This acid, which contains the elements of alloxan, ammonia, and sulphurous oxide (C 4 N 2 H 2 4 -(- NH 3 -f- S0 2 ), is formed, as an ammonium-salt, when a cold solution of alloxan is mixed with a saturated aqueous solution of sulphurous acid, in such quantity that the odor of the gas remains quite distinct ; an excess of ammonium car- bonate mixed with a little caustic ammonia is then added, and the whole 730 DERIVATIVES OF URIC ACID. boiled for a few minutes. On cooling, ammonium thionurate is deposited in great abundance, forming beautiful, colorless, crystalline plates, which by solution in water and re-crystallization acquire a fine pink tint. A solu- tion of this salt gives with lead-acetate a precipitate of insoluble lead thio- nurate, which is at first white and gelatinous, but shortly becomes dense and crystalline : from this compound the acid may be obtained by the aid of sulphuretted hydrogen. It forms a white crystalline mass, permanent in the air, very soluble in water, of acid taste and reaction, and capable of combining directly with bases. When its solution is heated to the boil- ing point, it undergoes decomposition, yielding sulphuric acid and uramile, or dialuramide, C 4 N 3 H 5 3 : URAMILE. To prepare this substance, ammonium thionurate is dissolved in hot water, mixed with a small excess of hydrochloric acid, and the whole boiled in a flask: the uramile then separates as a white, crystalline sub- stance, increasing in quantity till the contents of the vessel often become semi-solid. After cooling, it is collected on a filter, washed with cold water to remove the sulphuric acid, and dried by gentle heat, during which it frequently becomes pinkish. It is tasteless and nearly insoluble in water, but dissolves in ammonia and the fixed alkalies. The ammoniacal solution becomes purple in the air. It is decomposed by strong nitric acid, with formation of alloxan and ammonium nitrate : C 4 N 3 H 5 3 + = C 4 N 2 H 2 4 + NH 3 . Uramile, heated with aqueous solution of potassium cyanate, is converted into pseudo-uric acid, C 5 N 4 H 6 4 = C 4 N 8 H 5 3 + CNIIO. Uramile, added to argentic or mercuric oxide suspended in boiling water, is converted into murexide (p. 732). ALLOXANTIN, C 8 N 4 H 4 7 . 3 Aq. This substance is the chief product of the action of hot dilute nitric acid upon uric acid, and is likewise produced by the action of deoxidizing agents upon alloxan, anhydrous aljoxantin, in fact, containing 1 atom of oxygen less than 2 molecules of alloxan. It is best prepared by passing sulphuretted hydrogen gas through a moderately strong and cold solution of alloxan. The mother-liquor from which the crystals of alloxan have separated answers the purpose perfectly well : it is diluted with a little water, and a copious stream of gas transmitted through it. Sulphur is then deposited in large quantity, mixed with a white, crystalline substance, which is the alloxantin. The product is drained upon a filter, slightly washed, and then boiled in water : the fil- tered solution deposits the alloxantin on cooling. Alloxantin forms small, four-sided, oblique rhombic prisms, colorless and transparent; it is soluble with difficulty in cold water, but more freely at a boiling temperature. The solution reddens litmus, gives with baryta-water a violet-colored pre- cipitate, which disappears on heating, and when mixed with silver nitrate produces a black precipitate of metallic silver. Heated with chlorine or nitric acid, it is changed by oxidation to alloxan. The crystals become red when exposed to ammoniacal vapors. They contain 3 molecules of water, which they do not give off till heated above 150 C. (302 F.). Alloxantin is readily decomposed : when a stream of sulphuretted hydro- gen is passed through its boiling solution, sulphur is deposited and dialuric acid is produced. A hot saturated solution of alloxantin mixed with a neu- tral salt of ammonia instantly assumes a purple color, which, however, quickly vanishes, the liquid becoming turbid from the formation of ura- mile : the solution is then found to contain alloxan and free acid. With silver oxide, alloxantin gives off carbon dioxide, reduces a portion of the BARBITURIC ACID. 731 metal, and converts the remainder of the oxide into oxalurate. Boiled with water and lead dioxide, alloxantin gives urea and lead carbonate. DIALTJRIC ACID, C 4 N.;H 4 4 . This acid is the final product of the action of reducing agents on alloxan, and is formed when sulphuretted hydrogen is passed through a boiling solution of alloxan till no further action takes place : C 4 N 2 H 2 4 -+- H 2 S = C 4 N 2 H 4 4 -|- S. It forms colorless needles, re- sembling those of alloxantin, has a strong acid reaction, and neutralizes acids completely, forming salts which are sparingly soluble in water. HYDURILIC ACID, C 8 N 4 H 6 6 . Dialuric acid, heated to about 160 C. (320 F.), with glycerin (which acts merely as a solvent), splits up into formic acid, carbon dioxide, and the ammonium-salt of hydurilic acid: 5C 4 N 2 H 4 4 = CH 2 2 -f 3C0 2 + 2C 8 N 4 H 5 (NH 4 )0 6 . By converting this ammonium-salt into a copper-salt, and decomposing the latter with hydrochloric acid, hydurilic acid is obtained in crystals. Hydurilic acid is converted by fuming nitric acid into alloxan, without any other product ; but with nitric acid of ordinary strength it yields al- loxan, together with violuric acid, violantin, and dilituric acid:* C 8 N 4 H 6 6 + N0 3 H = C 4 N 3 H 3 4 + C 4 N 2 H 2 4 + H 2 Hydurilic Violuric Alloxan. acid. acid. C 8 N 4 Hg0 6 + 2N0 3 H = C 4 N 3 H 3 5 -f C 4 N 2 H 2 4 + N0 2 H + H 2 0. Hydurilic Dilituric Alloxan. acid. acid. If the action be carried on to the end, dilituric acid is the only product. This acid may indeed be regarded as a product of the oxidation of violuric acid two. DiBROMOBARBiTURic ACID, or BROMALLOXAN, C 4 N 2 H 2 Br 2 3 , is produced, together with alloxan, by the action of bromine on hydurilic acid: C 4 N 4 H 6 6 + Br 6 + H 2 = C 4 N 2 H 2 Br 2 3 + C 4 N 2 H 2 4 + 4HBr. It crystallizes in colorless, shining plates, or prisms, belonging to the tri- metric system, soluble in water, very soluble in alcohol and ether. By hy- drogen sulphide, in presence of water, it is reduced to dialuric acid : C 4 N 2 H 2 Br 2 3 + H 2 S -f H 2 = C 4 N 2 H 4 4 + 2HBr + S. With a small quantity of hydriodic acid it yields hydurilic acid : 2C 4 N 2 H 2 Br 2 3 + 6HI = C 8 N 4 H 6 6 -f 4HBr -f 3I 2 ; but when it is heated with excess of hydriodic acid, the reduction goes a step 'farther, and barbituric acid, C 4 N 2 H 4 3 , is produced : C 4 N 2 H 2 Br 2 3 -f 4HI = C 4 N 2 H 4 3 -f 2HBr -f 2I 2 . Barbituric acid crystallizes in beautiful prisms, containing two molecules of water. It is bibasic, and yields chiefly acid salts, which are obtained by treating the corresponding acetates with barbituric acid. Barbituric acid is converted by fuming nitric acid into dilituric acid, by potassium nitrate into potassium violurate. When boiled with potash it gives off ammonia, and yields the potassium-salt of malonic acid, C 3 H 4 4 * For descriptions of these several products, see Watts's Dictionary of Chemistry. 732 COMPOUND AMMONIAS OR AMINES. (D 661) whence it appears to have the constitution of malonyl urea, CN 2 H 2 (CX*)" = C 2 H A + CN 2 H 4 2H 2' MUREXIDE, C 8 N 6 H 8 6 . Aq. ; Prout's Purpurate of Ammonia. There are several methods of preparing this magnificent compound. It may be made directly from uric acid, by dissolving that substance in dilute nitric acid, evaporating to a certain point, and then adding to the warm but not boil- ing liquid a very slight excess of ammonia. In this process alloxantin is first produced, and is afterward partially converted into alloxan: the pres- ence of both is requisite for the production of murexide. This process is, however, very precarious, and often fails altogether. An excellent method is to boil for a few minutes in a flask a mixture of 1 part of dry uramile, 1 part of red oxide of mercury, and 40 parts of water, to which two or three drops of ammonia have been added : the whole assumes in a short space of time an intensely deep purple tint, and when filtered boil- ing hot, deposits, on cooling, splendid crystals of murexide, unmixed with any impurity. The reaction in this case is : 2C 4 N 3 H 5 0, + = C 8 N 6 H 8 6 + H 2 0. Uramile. Murexide. A third, and perhaps even still better process, is that of Dr. Gregory : 7 parts of alloxan and 4 parts of alloxantin are dissolved in 240 parts of boil- ing water, and the solution is added to about 80 parts of cold, strong solu- tion of ammonium carbonate : the liquid instantly acquires such a depth of color as to become opaque, and gives on cooling a large quantity of murexide: the operation succeeds best on a small scale. Murexide* crystallizes in small square prisms, which by reflected light exhibit a splendid green metallic lustre, like that of the wing-cases of the rose-beetle and other insects: by transmitted light they are deep purple- red. It is soluble with difficulty in cold water, much more easily at the boiling heat, insoluble in alcohol and ether. Mineral acids decompose it, with separation of a white or yellowish substance called murexan, probably identical with uramile, and caustic potash dissolves it, with production of a most magnificent purple color, which disappears when the solution is boiled. A few years ago, murexide was extensively used in dyeing ; it is now rapidly being superseded by rosaniline, the crimson derived from aniline. A series of substances closely related to the derivatives of uric acid will be noticed under the head of Caffeine. COMPOUND AMMONIAS or AMINES. These names are given to a class of compounds derived from ammonia, NH 3 , by substitution of alcohol-radicals for hydrogen, these radicals being either monatomic or polyatomic ; the substitution may take place in one, two, or a greater number of ammonia molecules, thus giving rise to mona- mines, diamines, triamines, &c. Moreover, the nitrogen in these bases may be replaced by phosphorus, arsenic, or antimony, giving rise to phos- phines, arsines, and stibines, bases analogous in composition and properties to the amines. Connected with these last-mentioned bases are certain com- pounds of alcohol-radicals with metals not belonging to the nitrogen class. The natural organic bases, or alkalo'ids, found in plants, and certain artifi- cial bases whose constitution has not been very exactly made out, will be treated in an appendix to the alcoholic ammonias. * Po called from the Tyrian dye, said to have been prepared from a species of murese, or eliell-fish. AMINES. 733 AMINES DERIVED FROM MONATOMIC ALCOHOLS. Ammonia, NH 3 , may give up one, two, or three of its hydrogen-atoms in exchange for univalent alcohol-radicals (methyl and its hoinologues, for example), producing primary, secondary, and tertiary amines. If A, B, C, denote three such alcohol-radicals, the amines formed by substituting them for hydrogen in ammonia will be represented by the general formulae : A f A ( A B C Primary. Secondary. Tertiary. In the secondary and tertiary amines the alcohol-radicals denoted by A, B, C may be either the same or different ; for example : Secondary. Tertiary. NJH N|B H-J U U 1 fCH 3 JH CH 3 IH CH 8 C..H, Diamethyl- Methyl- amine. ethylamine. I CH CH ( CH, JCH, , 3 (C 2 H 5 5U Trimethyl- Dimethyl- Methyl-ethyl- amine. ethylamine. amylamine. f CH, NJC 2 H 5 (C 5 H U It is clear that amines containing only univalent alcohol-radicals must be derived from only one molecule of ammonia : for to bind together two or more such molecules would require the introduction of a polyatomic radi- cal: thus, is a stable compound, but such a compound as N ! (C 2 H 5 ) 2 would split up into two molecules, each consisting of N H In other words, amines derived from monatomic alcohols must be mona- mines. These amines are basic compounds more or less resembling ammonia in odor, having an alkaline reaction on vegetable colors, and uniting with acids to form salts which are analogous in composition to the ammonium- salts, and, like the latter, may be regarded either as compounds of ammo- nia-molecules with acids, or of ammonium molecules with halogen elements and acid radicals analogous thereto (see p. 310) ; thus: NH 3 -f HC1 Ammonia. NH 2 (C 2 H 5 ) + HC1 Ethyl- ammonia. NH(C 2 H 5 ) 2 4- HC1 Diethyl- ammonia. = NH 4 . Cl Ammonium chloride. = NH 3 (C 2 H 6 ) . Cl Ethylammonium chloride. = NH 2 (C 2 H 6 ) 2 . Cl Diethylammonium chloride. N(C,H 8 ) 8 Triethyl- -f HC1 = NH(C 2 H 5 ) 3 . Cl Triethylammonium chloride. 2N(C 2 H 5 ) 3 Triethyl- H 2 S0 4 = [NH(C 2 H 6 ) 3 ] 2 S0 4 Triethylammonium sulphate. 62 734 AMINES. All the salts of these amines, when heated with potash, give off the amine, just as ammonia-salts give off ammonia. The tertiary amines can unite with the chlorides, &c., of alcohol-radi- cals in the same manner as with acids : thus triethylamine, N(C 2 H 5 ) 3 . unites directly with ethyl iodide, C 2 H 5 I, forming a compound which may be re- garded either as triethylamine ethyliodide, N(C 2 H 5 ) 3 . C 2 H 5 I, or as tetrethyl- ammonium iodide, N(C 2 H 5 ) 4 .I. Now this iodide, when heated with potash, does not give off ammonia or a volatile ammonia-base ; but when heated with silver oxide and water, it is converted, by exchange of iodine for hy- droxyl, into a strongly alkaline base, called tetrethylammonium hydrate, which may be obtained in the solid state, and exhibits reactions closely analogous to those of the fixed caustic alkalies. Its formation is represented by the equation : N(C 2 H 5 ) 4 I + KOH = KI -f N(C 2 H 5 ) 4 (OH). Moreover, this base can exchange its hydroxyl for chlorine, bromine, and other acid radicals, just like potash or soda, forming solid crystallizable salts like the iodide above mentioned. These compounds, containing four equivalents of alcohol-radicals, are, in fact, analogous in every respect to ammonium-salts, excepting that the corresponding hydrates are capable of existing in the solid state, whereas ammonium hydrate, NH 4 (OH), splits up, as soon as formed, into ammonia and water. The radicals N(C 2 H 6 ) 4 , &c., corresponding to ammonium, are not known in the free state. The monamines containing more than one carbon-atom are susceptible of isomeric modifications similar to those of the alcohols ; thus ethylamine, NH 2 (C 2 H 6 ), is isomeric with dimethylamine, NH(C 2 H 3 ) 2 ; propylamine, NH 2 (C 3 H 7 ), is isomeric with methyl-ethylamine, NH(CH 3 )(C 2 H 6 ), and with trimethylamine, N(CH 3 ) 3 , &c., &c., the number of possible' modifications of course increasing with the complexity of the molecules. Moreover, a monamine, either primary, secondary, or tertiary, may admit of modifica- tion in the alcohol-radical itself; thus the primary monamine, NH 2 (G 3 H 7 ), may exhibit the two following modifications : rCH 2 CH 2 CH 3 rCH(CH 3 ) 2 N < H N -I H IH (H Propylamine. Isopropylamine. An instance of isomerism of this latter kind has lately been observed by Wurtz in amylamine, NH 2 (C 5 H n ). Amines may of course be formulated on the methane or marsh-gas type instead of the ammonia type, the radical amidogen, NH 2 , and others de- rived from it, being substituted for an atom of hydrogen ; thus : H [NH 2 lNH 2 [NH(CH 3 ) LN(CH 3 ) 2 Methane. Methyl- Ethyl- Dimethyl- Trimethyl- amine. amine. amine. amine. This mode of representation is convenient in some cases, but the amines and their salts are so closely related to the ammonia-compounds in their modes of formation and transformation, that they are for the most part more appropriately represented by formulas derived from ammonia, NH 3 , and sal-ammoniac, NH 4 C1. A great number of amines and their salts have been obtained, but the limits of this work will not allow us to describe more than the most impor- ETHYLAMINES. 735 tant of those containing the radicals, methyl, ethyl, amyl, and phenyl. In describing them it will be convenient to make a slight departure from the natural order, and commence with the ethyl bases, which have been more completely studied than their homologues. BASES OF THE ETHYL SERIES. Ethylamine, or Ethyl-ammonia, C 2 H 7 N = NH 2 (C 2 H 6 ). On digesting ethyl bromide or iodide with an alcoholic solution of ammonia, the alka- line reaction of the ammonia gradually disappears ; and on evaporating the solution on the water-bath, a white crystalline mass is obtained, which consists chiefly of ethyl-ammonium bromide or iodide: NH 3 -f- C 2 H 6 I = NH 3 (C 2 H 5 )I. On distilling this salt in a retort provided with a good con- denser, with caustic lime, the ethylamine is liberated and distils over: 2NH 3 (C 2 H 6 )I -f CaO = 2NH 2 (C 2 H 5 ) + H 2 Cal r Another method of preparing this compound, and, indeed, the method by which it was first obtained by Wurtz, consists in submitting ethyl cyanate to the action of potassium hydrate. Cyanic acid (p. 710), when treated with boiling solution of potash, splits into carbon dioxide and ammonia; and ethyl cyanate (p. 714) suffers- a perfectly analogous decomposition, yielding carbon dioxide and ethylamine : CNHO -f 2KHO == K 2 C0 3 + NH 3 Cyanic acid. Ammonia. CN(C 2 H 5 )0 + 2KHO = K 2 C0 3 -f NH 2 (C 2 H 5 ) Ethyl cyanate. Ethylamine. Ethyl cyanurate, polymeric with the cyanate, likewise gives off ethyl- amine when boiled with potash. Ethylamine is a very mobile liquid, of sp. gr. 0-6964, at 8 C. (46 F.), boiling at 19 C. (66 F.). The specific gravity of its vapor is 1-57. It has a most powerful ammoniacal odor, and restores the blue color to red- dened litmus-paper. It produces white clouds with hydrochloric acid, and is absorbed by water with great avidity. With acids it forms a series of neutral crystallizable salts perfectly analogous to those of ammonium. Ethylamine imitates, moreover, in a remarkable manner, the deportment of ammonia with metallic salts. It precipitates the salts of magnesium, aluminium, iron, manganese, bismuth, chromium, uranium, tin, lead, and mercury; zinc-salts yield a white precipitate, which is soluble in excess. Like ammonia, ethylamine dissolves silver chloride, and yields with cop- per-salts a blue precipitate, which is soluble in an excess of ethylamine. On adding ethylamine to oxalic ether, a white precipitate of biethyl-oxamide, N 2( C 2^2) // H 2 (C 2 H 5 ) 2 , is produced: a compound analogous to oxamic acid (p. 659) has also been obtained. Ethylamine may, however, be readily distinguished from ammonia: its vapor is inflammable, and it produces with platinic chloride, a salt, [NH 3 (C 2 H 5 )Cl] 2 PtCl 4 , crystallizing in golden scales, which are rather soluble in 'water. Treated with chlorine, it yields ethyl-ammonium chloride and bichlor ethylamine, NC1 2 C 2 II 5 , a yellow liquid having a penetrating, tear-exciting odor. When treated with potash, it is converted into ammonia, potassium acetate, and potassium chloride: NCL (C 2 H 5 ) + 3KHO = C 2 H 3 K0 2 + 2KC1 -f Nil, + H 2 0. Ethyl-urea. On passing the vapor of cyanic acid into a solution of ethylamine, the liquid becomes hot, and deposits, after evaporation, fine 736 ETHYLAMINES. crystals of ethyl-urea: C 2 H 7 N + CNHO = C 3 H 8 N 2 = CH 3 (C 2 H 5 )N,0. This substance, which may be viewed as ordinary urea (p. 721 ), having 1 atom of hydrogen replaced by ethyl, may also be prepared by treating cyanic ether with ammonia: CN(C 2 H 5 )0 -f- NH 3 = C 3 H 8 N 2 0. Ethyl-urea is very soluble in w r ater and alcohol : the concentrated aqueous solution, unlike that of ordinary urea, yields no precipitate with nitric acid ; but on gently evaporating the mixture, a very soluble crystalline nitrate of ethyl- urea is obtained. Boiled with potash, this substance yields a mixture of equivalent quantities of ammonia and ethylamine : C 3 H 8 N 2 -f 2KHO = K 2 C0 3 + NH 3 + C 2 H 7 N. Biethylamine, C 4 H n N = NH(C 2 H 5 ) ? . A mixture of the solutions of ethylamine and ethyl bromide, heated in a sealed tube for several hours, solidifies to a crystalline mass of biethyl-ammonium bromide: NH 2 C 2 H 6 -(- C 2 H 6 Br = NH 2 (C 2 H 5 ) 2 Br. This bromide, distilled with potash, yields biethylamine as a colorless liquid, still very alkaline, and soluble in water, but less so than ethylamine. This compound boils at 57-5 C. (135 F.). It forms beautifully crystallizable salts with acids. A solution of biethyl- ammonium chloride forms with platinic chloride a very soluble double salt, 2NH 2 (C 2 H 5 ) 2 C1 . PtCl 4 , crystallizing in orange-red grains, very different from the orange-yellow leaves of the corresponding ethyl-ammonium salt. Biethyl-urea. Biethylamine behaves with cyanic acid like ammonia and ethylamine, giving rise to biethyl-urea. A substance similar to, but not identical with, the former, has been produced by the action of cyanic ether upon ethylamine : CN(C 2 H 5 )0 + C 2 H 7 N = C 6 H 12 N 2 = C[H 2 (C 2 H 6 ) 2 ]N 2 0. The biethyl-ureas are very crystallizable, and readily form crystalline ni- trates. Boiled with potash, the biethyl-ureas yield, the former 1 molecule of biethylamine and 1 molecule of ammonia, C[H 2 (C 2 H 5 ) 2 ]N 2 -f- 2KHO = K 2 C0 3 + NH(C 2 H 6 ) 2 4- NH 3 ; the latter, pure ethylamine, C[H 2 (C 2 H 5 ) 2 ] N 2 + 2KHO = K 2 C0 3 + 2NH 2 (C 2 H 5 ), Triethylamine, C 6 H 15 N = N(C 2 H 6 ) S . The formation of this body is per- fectly analogous to that of ethylamine and of biethylamine. On heating for a short time a mixture of biethylamine with ethyl bromide in a sealed glass tube, a beautiful fibrous mass of triethyl-ammonium bromide is ob- tained, from which the triethylamine may be separated by potash. Tri- ethylamine is a colorless, powerfully alkaline liquid, boiling at 91 C. (196 F.). The salts of this base crystallize remarkably well. "With platinic chloride it forms a very soluble double salt, 2NH(C 2 H 6 ) 3 C1 . PtCl 4 , which crystallizes in magnificent, large, orange-red rhombs. The action of ethyl iodide or bromide on ammonia gives rise to the si- multaneous formation of the three ethylated bases, which, though differing considerably in their boiling points, can scarcely be separated by fractional distillation. The separation succeeds, however, by digesting the mixture of these three bases with anhydrous ethyl oxalate. Ethylamine is thus converted into diethyloxamine : C 2 4 (C 2 H 5 ) 2 -f 2NH 2 (C 2 H 6 ) = 20 2 H 6 (OH) -f N 2 (C 2 2 )"H 2 (C 2 H 5 ) 2 Ethyl oxalate. Ethyl- Alcohol. Diethyl-oxamide. amine. and diethylamine forms diethyloxamate: C 2 4 (C 2 H 5 ) 2 + NH(C 2 H 5 ) 2 = C 2 H 5 (OH) + C 2 2 [N(C 2 H 5 ) 2 ](OC 2 H 5 ) Ethyl oxalate. Diethyl- Alcohol. Ethylic diethyloxamate ; amine. whereas triethylamine does not combine with oxalic ether. The separation is carried out in the following manner : On distilling the product of the reaction of ethyl oxalate upon the mix- METHYLAMINE. 737 ture of ethyl bases in the water-bath, pure triethylamine passes over; and on treating the residue with boiling water, diethyloxamide is dissolved, while ethyl diethyloxamate remains as an insoluble layer floating upon the hot solution : it may be separated by a tap-funnel. Diethyloxamide treated with potash yields pure ethylamine, while pure diethylamine is obtained by treating ethylic diethyloxamate with the same reagent. Tetrethyl-ammonium Hydrate, C 8 H 2I NO N(C 2 H 5 ) 4 (OH). When anhy- drous triethylamine is mixed with dry ethyl iodide, a powerful reaction ensues, the mixture enters into ebullition, and solidifies on cooling to a white crystalline mass of tetrethyl-ammonium iodide: N(C 2 H 5 ) 3 -(- C 2 H 5 I =i N(G 2 H 5 ) 4 I. This iodide is readily soluble in hot water, from which It crystallizes on cooling in beautiful crystals of considerable size. This sub- stance is not decomposed by potash : it may be boiled with the alkali for hours without yielding a trace of volatile base. The iodine may, however, be readily removed by treating the solution with silver-salts. If in this case silver sulphate or nitrate be used, we obtain, together with silver iodide, the sulphate or nitrate of tetrethyl-ammonium, which crystallizes on evaporation: on the other hand, if the iodide be treated with freshly pre- cipitated silver oxide, the hydrate of tetrethyl-ammonium itself is sepa- rated. On filtering off the silver precipitate, a clear colorless liquid is ob- tained, which contains the isolated base in solution. It has a strongly alka- line reaction, and intensely bitter taste. The solution of tetrethyl-ammo- nium hydrate has a remarkable analogy to potash and soda. Like these substances, it destroys the epidermis and saponifies fatty substances, with formation of true soaps. With metallic salts it exhibits exactly the same reactions as potash. On evaporating a solution of the base in a vacuum, long slender needles are deposited, which are evidently the hydrate with an additional amount of crystallization water. After some time these nee- dles disappear again, and a semi-solid mass is left, which is the hydrate of tetrethyl-ammonium. A concentrated solution of this substance in water may be boiled without decomposition, but on heating the dry sub- stance, it is decomposed into pure triethylamine, water, and olefiant gas : N(C 2 H 5 ) 4 (OH) == H 2 + N(C 2 H 5 ) 3 + C 2 H 4 . Tetrethyl-ammonium hydrate forms neutral salts with acids. These salts are mostly very soluble ; several yield beautiful crystals. The platinum- salt, 2N(C 2 H 5 ) 4 C1 . PtCl 4 , forms orange-yellow octohedrons, which are about as soluble as the corresponding potassio-platinic salt. BASES OF THE METHYL SERIES. Methylamine, CH 5 N=rNH 2 (CH 3 ). The formation and the method of pre- paring this compound from methyl cyanate are perfectly analogous to those of ethylamine (p. 735) : however, methylamine being a gas at the common temperature, it is necessary to cool the receiver by a freezing mixture. The distillate, which is an aqueous solution of methylamine, is saturated with hydrochloric acid, and evaporated to dryness. A crystalline residue is thus obtained, consisting of methylammonium chloride, and this, when distilled with dry lime, yields methylamine gas, which, like ammonia gas, must be collected over mercury. It is distinguished from ammonia by a slightly fishy odor, and by the facility with which it burns. Methylamine is liquefied at about 18: its sp. gr. is 1-08. This substance is the most soluble of all gases; at 12 C. (54 F.), one volume of water absorbs 1040 62* 738 AMYLAMINES. volumes of the gas. It is likewise very readily absorbed by charcoal. In its chemical deportment with acids and other substances, methylamine resembles in every respect ammonia and ethylamine. Methylamine ap- pears to be produced in a great number of processes of destructive distilla- tion : it has been formed by distilling several of the natural organic bases, such as codeine, morphine, caffeine, and several others, with caustic potash ; frequently a mixture of several bases is produced in this manner. Among the numerous derivatives already obtained with this substance, methyl-urea, CH 3 (CH 3 )N 2 0, bimethyl-urea, CH 2 (CH 3 ) 2 N 2 0, and methyl- ethyl- urea] CH 2 (CH 3 )(C 2 H 5 ]N 2 0, may be mentioned. The latter substance has been produced by the action of ethyl cyanate upon methylamine. A series of platinum-bases, analogous to those produced by the action of ammonia upon platinous chloride (p. 426), have likewise been obtained with methyl- amine. Bimethylamine, C 2 H 7 N NH(CH 3 ) 2 . This compound, isomeric with ethyl- amine, is prepared by the action of ammonia on methyl iodide. Its sepa- ration from the methylamine and trimethylamine simultaneously formed, is accomplished by means of oxalic ether (p. 735). Trimethylamine, C 3 H 9 N N(CH 3 ) 3 . This substance is readily obtained in a state of perfect purity, by submitting tetramethyl-ammonium hydrate to the action of heat. It is gaseous at the common temperature, but lique- fies at about 90 C. (194 F.), to a mobile liquid of very powerfully alkaline reaction. Trimethylamine produces very soluble salts with acids. The platinum-salt, 2NH(CH 3 ) 3 C1 . PtCl 4 , is likewise very soluble, and crystallizes in splendid orange-red octohedrons. According to Mr. Winkles, large quan- tities of trimethylamine are found in the liquor in which salt herrings are preserved. Tetramethyl-ammonium Hydrate, C 4 H 13 NO N(CH 3 ) 4 (OH). The corre- sponding iodide may be obtained by adding methyl iodide to trimethylamine. The two substances unite with a sort of explosion. The same iodide is prepared, however, with less difficulty, simply by digesting methyl iodide with an alcoholic solution of ammonia. In this reaction a mixture of the iodides of ammonium, methyl-ammonium, bimethyl-ammonium, trimethyl- ammonium, and tetramethyl-ammonium is produced. The first and last compounds are formed in largest quantity, and may be separated by crys- tallization, the iodide of tetramethyl-ammonium being but sparingly soluble in water. From the iodide the base itself is separated by means of silver oxide. Its properties are similar to those of the corresponding ethyl-com- pound. It differs, however, from tetrethyl-ammonium hydrate in its be- havior when heated (p. 737), yielding trimethylamine and pure methyl alcohol, N(CH 3 ) 4 OH=N(CH 3 ) 3 +CH 3 (OH). BASES OF THE AMYL SERIES. The formation of these bodies being perfectly analogous to that of the corresponding terms in the ethyl series, we refer to the fuller statement given on page 735, and confine ourselves to a brief description of their principal properties. Amylamine, CJI^N = NH 2 (C 5 H n ), is a colorless liquid of peculiar, pene- trating, aromatic odor, slightly soluble in water, to which it imparts a strong alkaline reaction. With the acids it forms crystalline salts, which have a fatty lustre. Amylamine boils at 93 C. (199 F.). An amylamine-urea has beeu prepared. AROMATIC AMINES. 739 Biamylamine, C^H^N = NH(C 5 H n ) 2 . An aromatic liquid, less soluble in water, and less alkaline than amylamine. It boils at about 170 C. (338 P.). Triamylamine, C^H^N = N(C 5 H n ) 3 . A colorless liquid, of properties similar to those of the two preceding bases, but boiling at 257 C. (495 F.). The salts of triamylamine are very sparingly soluble in water, and fuse,, when heated, to colorless liquids, floating upon water. Tetramyl-ammonium Hydrate, C 20 H 45 NO = N(C 6 H n ) 4 OH. This sub- stance is far less soluble than the corresponding bases of the methyl and ethyl series, and separates as an oily layer on adding potash to the aque- ous solution. On evaporating the solution in an atmosphere free from car- bonic acid, the alkali may be obtained in splendid crystals of considerable size. When submitted to distillation, it splits into water, triamylamine, and amylene : N(C B H 11 ) 4 OH = H 2 + N(C 5 H n ) 3 + C 5 H 10 . In addition to the bases already enumerated, the following have been ob- tained by analogous processes, viz., treatment of the iodides of the corre- sponding alcohol-radicals with ammonia : propylamine, C 3 H 9 N, hexal- amine, C 6 H 15 N, heptylamine, C 7 H 17 N, octylamine, C 8 H 19 N, and nonylamine, BASES OF THE AROMATIC SERIES. In speaking of the aromatic hydrocarbons, we have explained that each of the hydrocarbons homologous with benzene may be regarded as a com- pound of phenyl with one or more alcohol-radicals of the methyl series, and may give rise to two series of derivatives, accordingly as the hydro- gen in the phenyl or in the alcohol-radical is replaced: thus from toluene or methyl-phenyl, C 6 H 5 .CH 3 , are derived chlorotoluene, C 6 H 4 C1.CH 3 , iso- meric with benzyl chloride, CgH 5 . CH 2 C1, and cresol, C 6 H 4 OH . CH 3 , iso- meric with benzyl alcohol, C 6 H 6 ,CH 2 OH. Each of these hydrocarbons can in like manner yield two isomeric bases, accordingly as an atom of hy- drogen in one part or the other of its molecule is replaced by amidogen, $H 2 : thus from toluene are derived two bases containing C 7 H 9 N, viz. : C 6 H 4 (NH 2 ) . CH 3 C 6 H 5 . CH 2 NH 2 Toluidine. Benzylamine. The second of these, benzylamine, is analogous in its mode of formation, and all its principal characters, to the bases of the methyl series, and may be represented by the formula NH 2 (C 7 H 7 ), derived from ammonia by sub- stitution of the univalent radical, benzyl, C 7 H 7 , for hydrogen. But tolu- idine is formed in a different manner, viz., by the action of reducing agents on nitrotoluene, and differs in its chemical relations from benzylamine, much in the same manner as cresol from benzyl alcohol, being altogether a less active substance. Xylidine, C 8 H U N = C 6 H 8 (NH 2 ) . (CH 3 ) 2 ; cumidine, C 9 H, 3 N = C 6 H 4 (NH 2 ) . C 3 H 7 , and cymidine, C 10 H 15 N, bases homologous with toluidine, are obtained in like manner from the nitro-derivatives of the corresponding hydrocarbons. The corresponding bases homologous with benzylamine have not yet been obtained. Aniline, C 6 H 7 N. There is but one aromatic monamine containing six atoms of carbon, viz., aniline, C 6 H 7 N ; and this may be regarded indiffer- ently, either as amidobenzene, C 6 H 6 (NH 2 ), or as phenylamine, N < Vr , that 740 ANILINE. is to say, as a lower homologue either of. toluidine or benzylamine. The two formulae just given are in fact identical; and moreover aniline, both in its modes of formation and in its properties, exhibits resemblances, on the one hand to toluidine and its homologues, and on the other to benzyl- amine and the monamines of the methylic series. Aniline is produced: 1. By heating phenol with ammonia in sealed tubes: C 6 H 6 (OH) + NH 3 = H 2 + NH 2 (C 6 H 5 ). 2. By the action of hydrogen sulphide and other reducing agents on nitro- benzene: C 6 H 5 (N0 2 ) + 3H 2 S = 2H 2 + S 3 + C 6 H 5 (NH 2 ). The first of these reactions exhibits the relation of aniline to benzylamine: the second, its relation to toluidine. 3. By the action of caustic potash upon indigo : C 8 H 5 NO + 4KHO -f- H 2 = C 6 H 7 N = 2C0 3 K 2 + 2H 2 . Indigo. Aniline. The name aniline indicates the relation of this compound to the indigo group, the botanical name of the indigo-plant being Indiyofera anil. Preparation, 1. From indigo. Powdered indigo boiled with a highly concentrated solution of potassium hydrate dissolves, with evolution of hy- drogen, to a brownish-red liquid containing anthranilic acid. If this mat- ter be transferred to a retort and still further heated, it swells up and gives off aniline, which condenses in the form of oily drops in the neck of the retort and in the receiver. Separated from the ammoniacal water by which it is accompanied, and redistilled, it is obtained nearly colorless. 2. In order to prepare aniline from nitrobenzene (see p. 495), this sub- stance is submitted to a process discovered by Zinin, which has proved a very abundant source of artificial organic bases. An alcoholic solution of nitrobenzene is treated with ammonia and sulphuretted hydrogen, until after some hours a precipitation of sulphur takes place. The brown liquid is now again saturated with sulphuretted hydrogen, and the process repeated until sulphur is no longer separated. The reaction may be remarkably accelerated by occasionally heating or distilling the mixture. The liquid is then mixed with excess of acid, filtered, boiled to expel alcohol and un- altered nitrobenzene, and then distilled with excess of caustic potash. If the aniline be required quite pure, it must be converted into oxalate, the salt several times crystallized from alcohol, and again decomposed by potash. Be"champ has shown that the reduction of nitrobenzene may be effected even more conveniently by the action of ferrous acetate. The distillation of one part of nitrobenzene, one part of acetic acid, and one and a half part of iron filings, seems, in fact, to be the best process for preparing aniline.* The mass swells violently, and very capacious, retorts are required. Aniline exists among the products of the distillation of coal, and probably of other organic matters: it is formed in the distillation of anthranilic acid, and occasionally in other reactions. Aniline, when pure, forms a thin, oily, colorless liquid, of faint vinous odor, and aromatic, burning taste. It is very volatile, but has, neverthe- less^ high boiling point (182C. [260 F.]). In the air it gradually becomes yellow or brown, and acquires a resinous consistence. Its density is 1-028. Water dissolves aniline to a certain extent, and also forms with it a kind of hydrate: alcohol and ether are miscible with it in all proportions. It is * According to Schoiiror-Kostncr, the treatment of nitrobenzene with a very large quantity of iron filings ami acetic arid reproduces benzene and ammonia. IULJ ANILINE. 741 destitute of alkaline reaction to test-paper, but is quite remarkable for the number and beauty of the crystallizable compounds which it forms with acids. Two extraordinai-y reactions characterize this body and distinguish it from all others viz., that with chromic acid, and that with solution of calcium hypochlorite. The former gives with aniline a deep-greenish or bluish-black precipitate, and the latter an extremely beautiful violet-colored compound, the fine tint of which is, however, very soon destroyed. When nitrous acid is passed into aniline, or when aniline hydrochloride is treated with silver nitrate, water and phenol are produced, and nitrogen is evolved: C 6 H 7 N + N0 2 H = C 6 H 6 + H 2 -f N 2 . On the other hand, when nitrous acid is passed through an alcoholic solu- tion of aniline, 2 molecules of aniline are linked together, 3 atoms of the hydrogen being replaced by 1 atom of nitrogen. Azodiphenyldiamine, the substance thus produced, contains C 12 H U N 3 . The following equation re- presents its formation : 2C 6 H 7 N + N0 2 H = C 12 H U N 3 + 2H 2 0. By treatment of azodiphenyldiamine with nitrous acid, the same change is repeated once more, three additional atoms of hydrogen being again re- placed by one of nitrogen, whereby a new substance, C 12 H 8 N 4 , is formed according to the equation : C 12 H U N 3 + N0 2 H = C 12 H 8 N 4 + 2H 2 0. Th'is body is remarkable for the violence with which, like fulminate of silver, it explodes. Griess, who discovered these substances, has succeeded in obtaining similar compounds from several others of the basic derivatives of aniline. Paraniline. In the manufacture of aniline upon a large scale, several bases, having much higher boiling points than aniline, are formed; among them there is a beautifully crystalline compound called paraniline, poly- meric with aniline and represented by the formula C 12 H, 4 N 2 = 2C 6 H 7 N. It forms two series of salts, of which the hydrochlorides, Ci 2 H u N 2 . HC1 and C 12 H 14 N 2 . 2HC1, may be quoted as examples. Substitution-products of Aniline. Under the head of indigo, a product of oxidation of this substance will be noticed, to which the name isatin has been given. When isatin is dis- tilled with an exceedingly concentrated solution of caustic potash, it is, like indigo, resolved into aniline, carbon dioxide, and free hydrogen. In like manner, chlorisatin and dichlorisatin, similarly treated, yield products anal- ogous to aniline, but containing one or two atoms of chlorine respectively in the place of hydrogen. The chloraniline, C 6 H 6 C1N, and dichloraniline, C 6 H 5 C1 2 N, thus produced, cannot, however, be obtained by the direct action of chlorine upon aniline, thus differing from ordinary substitution-com- pounds; but aniline may be reproduced from them by the same reagent that is capable of reconverting chloracetic acid into ordinary acetic acid namely, an amalgam of potassium or sodium (see p. 613). They are the first cases on record of organic bases containing chlorine. Chloraniline forms large, colorless octohedrons, having exactly the odor and taste of aniline, very volatile, and easily fusible : it distils without de- composition at a high temperature, and burns, when strongly heated, with a red smoky flame with greenish border. It is heavier than water, in- different to vegetable colors, and, except in being solid at common tempera- tures, resembles aniline in the closest manner. It forms numerous and 742 TOLUIDINE. beautiful crystallizable salts. If aniline be treated with chlorine gas, the action goes further, trichloraniline, C 6 H 4 C1 3 N, being produced, a volatile crystalline body which has no longer any basic properties. The corre- sponding bromine compounds have also been formed and described. Nitraniline, C 6 H 6 (N0 2 )N. This compound is formed by the action of ammonium sulphide on dinitrobenzene, C 6 H 4 (N0 2 ) 2 (p. 495). The attempts to prepare it directly from aniline by means of nitric acid were unsuccess- ful, the principal product being usually picric acid. It forms yellow, acicular crystals, but little soluble in cold water, although easily dissolved by alcohol and ether. When warmed it exhales an aromatic odor, and melts. At a higher temperature it distils unchanged. By very gentle heat it may be sublimed without fusion. It is heavier than water, does not affect test-paper, and like chlor- and brom-aniline fails to give with cal- cium hypochlorite the characteristic reaction of the normal compound. Nitraniline forms crystallizable salts, of which the hydrochloride is the best known. Diphenylamine, NH(C 6 H 6 ) 2 , is produced by the distillation of triphenyl- rosaniline (aniline blue). It is a crystalline body, melting at 45 C. (113 F.) to a yellow oil, which boils constantly at 810 C. (590 F.). A substance possessing the composition of triphenylamine, C 18 H 15 N, but probably not con- nected with the phenyl series, is formed by submitting the compound pro- duced by the action of cinnamic aldehyde upon ammonium sulphite to de- structive distillation, together with an excess of lime. Cyananiline is formed by the action of cyanogen upon aniline : it is a crystalline substance capable of combining with acids like aniline, but very prone to decomposition. It contains C 14 H, 4 N 2 (C 6 H 7 N) 2 . Cy 2 , and is therefore a compound of cyanogen with aniline, not a substitution-deri- vative. Derivatives of Aniline containing Alcohol-radicals. By treating aniline with iodide or bromide of methyl, ethyl, &c., in different proportions, bases are pbtained in which the hydrogen of the aniline is more or less replaced by those radicals. Ethylaniline, C 6 H 6 (C 2 H 5 )N, or NH(C 2 H 5 )(C 6 H 5 ), and Methyl- aniline, N(C 2 H 6 ) 2 (C 6 H 5 ), are liquids greatly resembling aniline ; the former boils at 204 C. (399 F.) ; the latter at 213-5 C. (416 F.). Ethylaniline treated with amyl iodide yields the hydriodide of ethyl-amyl-aniline, N(C 2 H 5 ) (C 5 H n )(C 6 H 5 ) . HI, or iodide of ethyl-amyl-phenylammonium, NH(C 2 H 6 )(C 5 H n ) (C 6 H 5 )I, from which the ethyl-amyl-aniline may be separated by distilla- tion with potash. It is an aromatic oil boiling at 262 C. (504 F.). "When treated with methyl iodide, it is converted into iodide of methyl- ethyl- amyl- phenylammonium, N(CH 3 )(C 2 H 5 )(C 5 H n )(C 6 H 5 )I, from which the correspond- ing hydrate, N(CH 3 )(C 2 H 5 )(C 5 H, 1 )(C 6 H 5 ) . OH, may be obtained by treat- ment with silver oxide and water. This hydrate is very soluble in water, powerfully alkaline, and has an extremely bitter taste. Many other substitution-derivatives of aniline maybe obtained in a simi- lar manner. Toluidine, C 7 H 9 N, or Amido toluene, C 7 H 7 (NH 2 ) = C 6 H 4 (NH 2 ) . CH 3 . This base is homologous with aniline, and is obtained, similarly to the latter, by the action of hydrogen sulphide or ferrous acetate on nitrotoluene, C 7 H 7 (N0 2 ). It forms colorless platy crystals, very sparingly soluble in water, easily in alcohol, ether, and oils : it is heavier than water, has an aromatic taste and odor, and a very feeble alkaline reaction. At 40 C. (104 F.) it melts, and at 205-206 C. (402 F.), boils and distils unchanged. It forms well- crystallized salts, but is nevertheless a weak base, and, according to Wanklyn, is absolutely incapable of neutralizing dilute sulphuric acid. It forms sub- stitution-derivatives similar to those of aniline ; those containing methyl and its homologues are more basic than toluidine itself. DIAMINES AND TRIAMINES. 743 Benzylamine, C 6 H 5 . CH 2 (NH 2 ) or NH 2 (C 7 H 7 ). This compound, isomeric with toluidine, is obtained, together with dibenzylamine, NH(C 7 H 7 ) 2 , and tribenzylamine, N(C 7 H 7 ) 3 , by the action of alcoholic ammonia on benzyl chloride, C 6 H 5 . CH 2 C1 (p. 496), the mode of formation of these bases being exactly analogous to that of methylamine and its homologues, and alto- gether different from that of toluidine. Benzylamine is a colorless liquid, boiling at 182-183 C. (360 F.) (23 C. (73 F.) lower than toluidine). It mixes in all proportions with water, and is separated therefrom by potash. It is a much stronger base than toluidine ; absorbs carbon dioxide rapidly, forming a crystalline carbonate ; unites readily with other acids, producing rise of temperature ; and fumes with hydrochloric acid. The hydrochloride crystallizes in striated tables ; the platinochloride, 2NH 3 (C 7 H 7 )C1 . PtCl 4 , in orange-colored laminae. Xylidine, C 8 H U N = C 6 H 3 (NH 2 ) . (CH 8 ) 2 , Cumidine, C 9 H 13 N, or probably C 6 H 4 (NH 2 ) . C 3 H 7 , and Cymidine, C 10 H, 5 N, or C, H, 3 (NH 2 ), homologous with toluidine, are obtained in like manner by reduction of the corresponding nitro-derivatives. Xylidine boils at 214-216 C. (417-420F.) ; cumidine at 225 C. (437 F. ) ; cymidine at 250 C. (482 F.). Xylidine and cumidine form well-crystallized salts. The isomers of these three bases, homologous with benzylamine, have not yet been obtained. Naphthalidine, C lp H 9 N=C, H 7 (NH 2 ), is interesting, as being one of the first compounds of its kind produced by Zinin's process. It is obtained by the action of ammonium sulphide upon an alcoholic solution of nitro-naph- thalene, one of the numerous products of the action of nitric acid upon naphthalene, C 10 H 8 . When pure it forms colorless silky needles, fusible, and volatile without decomposition. It has a powerful, not disagreeable odor, and burning taste, is nearly insoluble in water, but dissolves readily in alcohol and ether; the solution has an alkaline reaction. Naphthalidine forms numerous crystalline salts. DIAMINES and TRIAMINES. These are bases derived from two or three molecules of ammonia, N 2 H 6 and N 3 H 9 , by substitution of bivalent and trivalent alcohol-radicals for a part or the whole of the hydrogen. A portion of the hydrogen may at the same time be replaced by univalent alcohol-radicals. Diamines are formed by the action of the chlorides, bromides, and iodides of the diatomic alco- hol-radicals on ammonia. The examination of these compounds is far from being complete. ETHENE-DIAMINE AND DIETHENE-DIAMINE. The action of ammonia upon ethene dibromide is very complex ; but among the products of the reaction there are invariably present the hydrobromides of two bases which are derived from two molecules of ammonia, viz., ethene-diamine, C 2 H 8 N 2 = N ? (C 2 H 4 )"H 4 , an oily liquid boiling at 117 C. (242 F.), and diethene-dia- mine, C 4 H IO N 2 = N 2 (C 2 H 4 ) // 2 H 2 , a crystalline solid, boiling at a high tem- perature. The formation of these bodies, which saturate two equivalents of acid, may be represented by the following equations : 2NH 3 + (C 2 H 4 )"Br 2 = [N 2 (C 2 H 4 )"H 6 ]"Br 2 , and 4NH 3 + 2(C 2 H 4 )"Br 2 = [N,(C,H 4 )",H 4 ]"Br a + 2NH 4 Br. Distillation with potash separates the bases from these salts, potassium bromide being formed at the same time. 744 DIAMINES AND TEIAMINES. By the action of ethyl iodide upon ethene-diamine and diethene-diamine, two series of ethylated derivatives have been obtained. We can here give only the names and formulae of the iodides : Bases derived from Ethene-diamine. Iodide of Ethene-diammonium . . . Iodide of Diethyl-ethene-diammonium. Iodide of Tetrethyl-ethene-diammonium Iodide of Pentethyl-ethene-diammonium Iodide of Hexethyl-ethene-diammonium N a H 6 (C 2 H 4 )"]"I r N 2 H 4 (C 2 H 4 )"(C 2 H 5 ) 2 ]"I 2 . N 2 H 2 (C 2 H 4 )"(C 2 H 5 ) 4 ]"I 2 . N 2 H(C 2 H 4 )"(C 2 H 5 ) 5 ]"I 2 . [N 2 (C 2 H 4 )"(C 2 H 5 ) 6 ]"I 2 . 'Bases derived from Diethene-diamine. Iodide of Diethene-diammonium . . . [N 2 H 4 (C 2 H 4 )" 2 ]"I 2 . Iodide of Diethyl-diethene-diammonium [N 2 H 2 (C 2 H 4 ) // 2 (C 2 H 5 ) 2 ] // I 2 . Iodide of Triethyl-diethene-diammonium [N 2 H(C 2 H 4 )" 2 (C 2 H 6 ) 8 ]"I 2 . Iodide of Tetrethyl-diethene-diammonium [N 2 (CN 2 H 4 )" 2 (C 2 H 5 ) 4 ]"I 2 . DlETHENE-TRIAMINE AND TRIETIIENE-TRIAMINE. More recently two other bases have been separated from the product of the action of ethene dibromide upon ammonia, viz., diethene triamine, (C 2 H 4 ) 2 H 5 N 3< and tri- ethene-triamine, (C 2 H 4 ) 3 H 3 N 3 . The formation of these bodies, which satu- rate 3 equivalents of acid, may be represented by the following equations : 4NH. + 2(C 2 H 4 )"Br 2 = [N 3 (C 2 H 4 )" 2 H 8 ]'"Br 3 -f NH 4 Br 6NH 3 + 3(C 2 HJ"Br 2 = [N s (C,H 4 )" B H 6 ]'"Br 8 + 3NH 4 Br. DlPHENYL-ETHENE-DIAMINE, N 2 H 2 (C 2 H 4 ) " (C 6 H 5 ) 2 , and DlPHENTL-DI- ETHENE-DIAMINE, N 2 (C 2 H 4 ) // 2 (C 6 H 5 ) 2> Aniline, when submitted to the ac- tion of ethene bromide, C 2 H 4 Br 2 , solidifies to a crystalline mass, from which potash separates two crystalline bases, which are soluble in alcohol and in ether, but insoluble in water. If a large quantity of ethene bromide be made to act upon a comparatively small quantity of aniline, the new salt contains the hydrobromide of diphenyl-ethene-diamine, or ethene-dianaline, C 14 Hi 6 N 2 . 2HBr = 2C 6 H 7 N -f- C 2 H 4 Br 2 . On the other hand, if the aniline be employed in excess, hydrobromide of diethene-dianiline, or diphenyl- diethene-diamine, C ]6 H 18 N 2 . 2HBr, is formed, together with hydrobromide of aniline : 4C 6 H 7 N + 2C 2 H 4 Br 2 == C 16 H 18 N 2 . 2HBr + 2(C 6 H 7 N . HBr). METHENYL-DIPHENYL-DIAMINE, C 13 H 12 N 2 = N 2 H(CH) /// (C 6 H 5 ) 2 , also called Formyl-aniline. A mixture of aniline and chloroform exposed in sealed tubes to a temperature of 180 solidifies to a crystalline mass, consisting of aniline hydrochloride and the hydrochloride of methenyl-diphenyl-dia- mine: 4C 6 H 7 N + CHC1 3 = 2(C 6 H 7 N . HC1) + C 13 H 12 N 2 . HC1. By washing with cold water, the aniline hydrochloride is removed, and the residue, treated with potash, yields the diatomic base in a state of purity. It is crystalline, insoluble in water, soluble in alcohol and in ether. phenylene-diamine presents itself as a slightly-colored, heavy oil, which, like phenylamine, has a tendency to assume a brown color on exposure to the air. The base gradually solidifies into a mass of crystals, which be- come hard and white by washing with ether. The melting point of pheny- lene-diainine is 63 C. (145 F.), the boiling point near 280 C. (536 F.) ; it distils without alteration. This substance is very soluble in water and ANILINE COLORS. 745 alcohol, less soluble in ether. It combines with 2 molecules of acid, form- ing well crystallized, rather soluble salts. The distillation of dinitrotoluene and dinitrocumene with acetic acid and iron filings produces the corresponding bases, toluylene-diamine, C 7 H, N 2 , and cumylene-diamine, C 8 H, 2 N 2 , which in their properties and chemical deportment bear a great resemblance to phenylene-diamine. I (C 6 H 5 ) 2 CARBODIPHENYL-TRIAMINE, OR MELANILINE, C, 3 H, 3 N 3 :=:N 3 ^ C iv . The (. H s action of dry cyanogen chloride upon anhydrous aniline gives rise to the formation of a resinous substance, which is the hydrochloride of melani- line. Dissolved in water and mixed with potash, the above salt yields me- laniline in the form of an oil, which rapidly solidifies to a beautiful crys- talline mass. The following equation represents its formation : 2C 6 H 7 N -f- CNC1 = C 13 H 14 N 3 C1. Melaniline treated with chlorine, bromine, iodine, or nitric acid, yields basic substitution-products, in which invariably two atoms of hydrogen are replaced. It combines with two equivalents of cyanogen, and forms salts with acids, most of which are crystallizable. CARBOTRIPHENYL-TRIAMINE, OR PHENYL-MELANILINE, C, 9 H 17 N 3 = N 3 H 2 C iv (C 6 H 6 ) 3 . Aniline, when exposed to the action of carbon tetrachloride at a temperature of 150 C. (302 F.), solidifies into a resinous mass, consisting of a mixture of the hydrochlorides of rosaniline (p. 746), and of several other bases, from which, by appropriate treatment, a beautiful basic com- pound may be extracted, constituted as above. The formation of this body, which in its properties closely resembles melaniline, may be represented by the equation : 6C 6 H 7 N + CC1 4 = 3(C 6 H 7 N.HC1) + C 19 H 17 N 3 . HC1. Melaniline is sometimes represented as cyano-diphenyl-diamine, N 2 H 3 (CN)(C 6 H 5 ) 2 , and phenyl-melaniline as cyano-triphenyl-diamine, N 2 H 2 (CN) (C 6 H 5 ) 3 ; but these can scarcely be regarded as true formulae of diamines, inasmuch as they contain only monatomic radicals, and may therefore be resolved into formulae of monamines. Aniline Colors. Aniline has during the last few years found an extensive application in the arts, a long series of coloring matters unequalled in brilliancy and beauty having, by the action of different oxidizing agents, been produced from it. It was Mr. W. H. Perkin who had first the happy idea of apply- ing practically the well-known property possessed by aniline, of forming violet and blue solutions when treated with a solution of chloride of lime or chromic acid. He succeeded in fixing these colors, and bringing them into a form adapted for the dyer. We will here notice some of the most important of these coloring matters. ANILINE-PURPLE, MAUVE. According to Mr. Perkin, mauve is prepared by mixing solutions of aniline sulphate and potassium bichromate in equi- valent proportions, and allowing the mixture to stand for several hours; the black precipitate formed is filtered off and purified from admixed po- tassium sulphate by washing with water; it is then dried and freed from resinous matter by repeated digestion with coal-tar naphtha, and finally dissolved in boiling alcohol. For its further purification, the alcoholic solution is evaporated to dryness, the substance is dissolved in a large 63 746 ANILINE COLORS. quantity of boiling water, reprecipitated with caustic soda, washed with water, and dissolved in alcohol; and the filtered solution is evaporated to dryness. Mauve thus prepared forms a brittle substance, having a beau- tiful bronze-colored surface : it is difficultly soluble in cold water, although it imparts a deep purple color to that liquid: it is more soluble in hot water, very soluble in alcohol, nearly insoluble in ether and hydrocar- bons : it dissolves in concentrated acetic acid, from which it crystallizes. Mauve is the sulphate of a base called mauveine, having the composition C 27 H 24 N 4 , and capable of forming numerous crystalline salts with acids. ANILINE-RED, ROSANILINE, C^HjgNg. This substance occurs more or less pure in commerce under the names roseine, fuchsine, magenta, azaleine, &c. A red color had been observed at different times in experimenting with aniline, more especially when that substance was digested with Dutch liquid. The red coloring matter, though still impure, was first obtained in a separate state from the product formed by digesting aniline with carbon tetrachloride at 150, in which reaction it is formed, together with carbo- triphenyltriamine. It was M. Verguin who first prepared it upon a large scale by the action of stannic chloride upon aniline. Since that time it has been produced by the action of mercuric salts, arsenic acid, and many other oxidizing agents, upon aniline. The most advantageous mode of pre- paration is the following: A mixture of 12 parts of the dry arsenic acid which occurs in commerce, and 10 parts of aniline, is heated to 120 or 140 C. (250-280 F.), for about six hours: a little water may be added with advantage. The product, which is a hard mass possessing the lustre of bronze, is dissolved in hot water and precipitated by a slight excess of soda: the precipitate when washed with water, and dissolved in acetic acid, forms the roseine of commerce. In order to purify this still crude substance, it is boiled with an excess of soda, to separate any aniline that it may contain ; and the washed precipitate is dissolved in very dilute mineral acid, filtered from undissolved tarry matter, and re-precipitated with alkali. The compounds of rosaniline with one molecule of acid are beau- tifully crystallized substances, which in the dry state possess a green color with golden lustre; with water they furnish a very intensely colored red solution. The free base, first obtained by Mr. Nicholson, presents itself in colorless crystalline plates, insoluble in water, soluble in alcohol and ether, with a red color, which it also acquires on exposure to the air. Ros- aniline in the anhydrous state is represented by the formula C^H^Ng, and in the hydrated state, such as it assumes when isolated from its com- pounds, by the formula C 20 H, 9 N 3 . H 2 0. It is a triamine capable of com- bining with one, two, or three equivalents of acid. The aniline reds of commerce are saline compounds, more or less pure, of rosaniline with one equivalent of acid. The acetate, which is chiefly found in commerce in England, has been prepared by Mr. Nicholson in splendid crystals of very considerable dimensions, having the composition C^H^Ng . C 2 H 4 2 . In France, the chloride is chiefly employed ; its formula is C^H^Ng . HC1. The action of ammonium sulphide upon rosaniline gives rise to leucaniline, C.^ H 2 ,N 3 , a base containing two additional atoms of hydrogen. This base is itself colorless, and forms colorless salts containing 3 equivalents of acid, such as Cj0H 8 |Ng . HC1. Oxidizing agents reproduce rosaniline. The molecular constitution of rosaniline has not been distinctly made out. Neither is its mode of formation thoroughly understood ; but one very important fact has been brought to light by the researches of Hof- mann, and confirmed by the experience of manufacturers namely, that pure aniline, from whatever source it may be obtained, is incapable of fur- nishing aniline-red. Commercial aniline prepared from coal-tar always in fact contains toluidine as well as aniline ; and Hofmann has shown that the APPENDIX TO THE ALCOHOLIC AMMONIAS. 747 presence of this base, together with aniline, is essential to the formation of the red dye. Toluidine by itself is just as incapable of yielding the red as pure aniline, but when a mixture of pure aniline and pure toluidine is treated with stannic or mercuric chloride, or with arsenic acid, the red coloring matter is immediately produced. Its formation may perhaps be represented by the equation: C 6 H 7 N -f 2C 7 H,N = C^H,^ + 3H 2 Aniline. Toluidine. Rosaniline. Rosaniline is doubtless a triamine, and the formula N 3 (C 7 H 6 ) // 2 . (C 6 H 4 )"H 8 has been suggested as the rational expression of its constitution. This, however, is not the formula of a true triamine, since it contains only biva- lent radicals, and may be resolved into NH 3 -f N 2 (C 7 H 6 ) // 2 (C 6 H 4 ) // , or N(C 6 H 4 )"H + N 2 (C 7 H 6 )" 2 H 2 . ANILINE-BLUE and ANILINE-VIOLET. MM. Girard and De Laire obtained aniline-blue by digesting rosaniline with an excess of aniline at 150 160 C. (300-320 F.). Together with aniline-blue, which is the principal pro- duct of the reaction, several other coloring matters (violet and green) and indifferent substances are formed, considerable quantities of ammonia being invariably evolved. The crude blue is purified by treating it successively with boiling water acidified with hydrochloric acid, and with pure water. The blue coloring matter is said to be obtained from its boiling alcoholic solution in brilliant needles. It consists of the hydrochloride of triphenyl- rosaniline, C 20 H, 6 (C 6 H 5 ) 3 N 3 . By heating rosaniline with ethyl-iodide, Dr. Hofmann* has obtained an aniline-violet, having the composition of hydri- odide of triethyl-rosaniline, C 20 H, 6 (C 2 H 5 ) 3 N 3 . Another aniline-violet is pro- duced by heating rosaniline with a quantity of aniline less than sufficient to form aniline-blue. ANILINE-YELLOW, CHRYSANILINE. In the preparation of aniline-red, a considerable quantity of secondary products is produced, from which Mr. Nicholson has succeeded in extracting a yellow coloring matter. This sub- stance, which has been called chrt/saniline, contains C 20 H 17 N 3 : it is also a well-defined base, forming two series of salts, the majority of them being very well crystallized. The two hydrochlorides of chrysaniline are C^H^ N 3 .HC1, and C.^H^N,, . 2HC1. The nitrate of chrysaniline is so insoluble in water, that nitric acid may be precipitated even from a dilute solution of nitrates by means of the more soluble hydrochlorate or acetate of chrysaniline. Chrysaniline is intimately related to rosaniline and leucani- line, differing from the former by 2 and from the latter by 4 atoms of hy- drogen: Chrysaniline . . . C^H^N,, Rosaniline . . . C 20 H, 9 N 3 Leucaniline . . . CHN. APPENDIX TO THE ALCOHOLIC AMMONIAS. Under this head we shall include certain artificial organic bases, the molecular constitution of which has not been very distinctly made out; also the natural bases or alkaloids found in living organisms; the phos- phorus, arsenic, and antimony bases, analogous in composition to the amines ; and certain other compounds of organic radicals with metals. * Proceedings of the Royal Society, xiii. 13. 748 ARTIFICIAL ORGANIC BASES. I. Artificial Organic Bases obtained from various Sources. BASES OBTAINED BY DESTRUCTIVE DISTILLATION. The destructive distillation of organic substances has furnished a rich harvest of basic compounds. A few of the more interesting may here be noticed. CHINOLINE (LEUCOLINE), C 9 H 7 N. Quinine, cinchonine, strychnine, and probably other bodies of this class, when distilled with a very concentrated solution of potash, yield an oily product resembling aniline in many re- spects, and possessing strong basic powers : it is, however, less volatile than that substance, and boils at 235 C. (455 F.). When pure, it is color- less, and has a faint odor of bitter almonds. Its density is 1-081. It is slightly soluble in water, and miscible in all proportions with alcohol, ether, and essential oils. Chinoline forms salts with acids, which, generally speaking, do not crystallize very freely. Chinoline is a tertiary monamine. When digested with ethyl iodide, it yields iodide of ethylchinoline, C n H, 2 NI = C H (C 2 H 5 )NI. Treatment of this iodide with silver oxide liberates the base 9 C n H, 2 N(HO), which exhibits all the characters of the .ammonium bases, being powerfully alkaline, easily soluble in water, and not volatile. Mr. C. Greville Williams has shown that the basic oil obtained by distilling cin- chonine contains, in addition to chinoline, two other bases of very similar properties, to which the names of lepidine and cryptidine have been given. Lepidine contains C 10 H 9 N, cryptidine C U H U N. CHINOLINE-BLUE, CYANINE. The action of amyl iodide upon chinoline gives rise to iodide of amylchinoline, C J4 H 18 NI. Addition of an excess of soda to an aqueous solution of this iodide produces a black resinous pre- cipitate, which dissolves in alcohol with a magnificent blue color. This precipitate is the iodide of a new base, discovered by Mr. C. G. Williams, which has been called cyanine. The color of this body is unfortunately very fugitive. According to recent researches,* the formation of the new iodide is represented by the following equation : 2Ci 4 H 18 NI = C 28 H 35 N 2 I + HI. PICOLINE, C 6 H 7 N. Dr. Anderson has described under this name a vol- atile, oily base, which is present in certain varieties of coal-tar naphtha, being there associated with aniline, chinoline, and several other volatile substances but imperfectly understood. It is separated without difficulty from the two bases just mentioned, by distillation, in virtue of its superior volatility. Picoline, when pure, is a colorless, transparent, limpid liquid, of powerful and persistent odor, and acrid, bitter taste. It is unaffected by a cold of 18. It is extremely volatile, evaporates rapidly in the air, and does not become brown like aniline when kept in an ill-stopped bottle. Picoline has a sp. gr. of 0-955, and boils at 133 C. (271 F.). It mixes in all proportions with pure water, but is insoluble in caustic potash and most saline solutions. The alkalinity of this substance is exceedingly well marked: it restores the blue color of reddened litmus, and forms a series of crystallizable salts. It is isomeric with aniline, but completely dis- tinguished from that body by numerous characteristic reactions. BASES FROM ANIMAL OIL. The oily liquid obtained by the distillation of bones and animal matter generally, frequently designated by the term Dippel's Oil, contains several * Hofmann, Compt. Rend. Iv. 849. BASES FROM ANIMAL OIL. 749 volatile organic bases. Together with some of the substances already de- scribed, such as methylamine, ethylamine, picoline, aud aniline, Dr. Ander- son has found in it several peculiar bases. PETININK, C 4 H U N. The properties of this substance are very analogous to those of biethylamine and triethylamine. It has the same composition as biethylamine, but differs from it by its higher boiling-point, which is 79-5 C. (175 F.), that of biethylamine being 57-5 C. (135 P.) (p. 736). Some chemists are inclined to explain this difference by assuming that petinine is identical with butylamine, NH 2 (C 4 H 9 ). This assumption may be correct, but is not as yet supported by any experimental evidence. The true butylamine has been obtained by M. Wurtz from butyl-alcohol in the same manner as ethylamine is obtained from common alcohol. PYRIDINE, C 5 H 5 N, much resembles picoline, and is obtained by repeatedly rectifying the bases of Dippel's oil, which distil at 115 C. (239 F.). LUTIDINE, C 7 H 9 N. Oily base contained in the portion which distils at 154 C. (309 F.). COLLIDINE, C 8 H U N. Oily base very similar to the preceding ones. Boil- ing point 179 C. (354 F.). To the same series also belongs an oily base, lately isolated by Mr. C. Greville Williams from the basic products of the distillation of Dorsetshire shale, and described by him under the name of parvoline. Parvoline is said to contain C 9 H 13 N. It will be observed that these bases, the constituent radicals of which are not yet clearly made out, are isomeric with the homologues of aniline : ? . C 5 H 5 N . Pyridine. Aniline . C 6 H 7 N . Picoline. Toluidine . C 7 H 9 N . Lutidine. Xylidine . C 8 H,,N . Colliding Cumidine . C 9 H, 3 N . Parvoline. Cymidine . 10 H 15 N. The first term of the aniline series, and the last of the pyridine series, are unknown. The bases of the aniline series are primary, those of the pyridine series tertiary monamines. PYRROL, C 4 H 5 N. This substance was first observed by Runge in coal- tar; Anderson afterward obtained it from animal oil. It has the proper- ties of a very weak base, the compounds of which with acids are destroyed by boiling with water. To prepare pyrrol, the bases of animal oil are dis- solved in sulphuric acid; the solution, when submitted to protracted ebulli- tion, retains the stronger bases, allowing the pyrrol to pass over. The distillate is heated with solid potassium hydrate, when the pyrrol combines slowly with the alkali, admixed impurities being volatilized. By dissolving the potassium-compound in water, the pyrrol separates as an oily liquid, floating on the surface of the solution. Pyrrol is colorless, insoluble in water and alkalies, slowly soluble in acids : it has an ethereal odor resem- bling that of chloroform, a specific gravity = 1-077, and boils at 133 C. (271 F.). Pyrrol is easily recognized by the purple color which it imparts to fir-wood moistened with hydrochloric acid. By heating an acid solution of pyrrol, a red, flaky substance, pyrrol-red, is produced, containing Ci 2 H u N 2 2 , the formation of which is represented by the following equation: 3C 4 H 6 N + H 2 = C 12 H U N 2 + NII 3 . 63* 750 ARTIFICIAL ORGANIC BASES. BASES OBTAINED BY THE ACTION OF AMMONIA UPON ALDEHYDES. The bodies called hydramides, produced by the action of ammonia on fur- furol (p. 695), and on the aldehydes of the aromatic series, are neutral substances, not capable of uniting with acids ; but, when boiled with aque- ous potash, they are converted, without addition or abstraction of any ele- ments whatever, into isomeric compounds, which are strong bases, com- bining readily with acids and forming definite salts. FURFURINE, C 15 H, 2 N 2 3 ,* is formed in the manner just described from furfuramide, a hydramide obtained by the action of ammonia on furfurol (p. 695). It is a powerful organic base, forming with acids a series of beautiful crystallizable salts, decomposing at a boiling heat the saline compounds of ammonia. Furfurine is very sparingly soluble in cold water, but dissolves in about 135 parts at about 100. Alcohol and ether dissolve it freely: the solutions have a strong alkaline reaction. It melts below the boiling point of water, and, when strongly heated, inflames and burns with a red and smoky light, leaving but little charcoal. Its salts are in- tensely bitter. AMARINE (BENZOLINE), C 21 H 18 N 2 . Hydrobenzamide, produced by the action of ammonia on pure bitter-almond oil (p. 690), when long boiled with a solution of caustic potash, suffers the same kind of change as fur- furamide, becoming entirely converted into the isomeric base called ama- rine. Precipitated by ammonia from a cold solution of the hydrochloride or sulphate, amarine separates in white curdy masses, which when washed and dried become greatly reduced in volume. In this state it becomes strongly electric by friction with a spatula. It is insoluble in water, but dissolves abundantly in alcohol : the solution is highly alkaline to test- paper, and if sufficiently concentrated, deposits the amarine on standing in small, colorless, prismatic crystals. Below 100 it melts, and on cooling assumes a glassy or resinous condition. Strongly heated in a retort, it de- composes, with production of ammonia, a volatile oil not yet examined, and a new body, pyrobenzoline or lophine, C 2 ,H 16 N 2 (?), which appears to be a feebly basic substance, insoluble in water, soluble in boiling alcohol. It is fusible by moderate heat, and on cooling becomes a mass of colorless radiating needles or plates. The salts of amarine are mostly sparingly soluble ; the sulphate, nitrate, and hydrochloride are crystallizable and very definite. THIALDINE, C 6 H, 3 NS 2 . This base is obtained by dissolving the crystal- line compound of aldehyde with ammonia (p. 687) in from 12 to 16 parts of water, mixing the solution with a few drops of caustic ammonia, and then subjecting the whole to a feeble stream of sulphuretted hydrogen. After a time the liquid becomes turbid, and deposits thialdine as a white crystalline substance. It is separated, washed, dissolved in ether, and the solution mixed with alcohol and left to evaporate spontaneously, by which means the base is obtained in large, regular, rhombic crystals, having the form of gypsum. The crystals are heavier than water, transparent and colorless. They refract light strongly. Thialdine has a somewhat aro- matic odor, melts at 43-3, and volatilizes slowly at common temperatures. It distils unchanged with the vapor of water, but decomposes when heated alone. It is very sparingly soluble in water, easily in alcohol and ether. It has no action on vegetable colors, but dissolves freely in acids, forming crystallizable salts. Heated with slaked lime, it is said'to yield chinoline. A very similar compound containing selenium has been prepared. * This remarkable substance, the nearest approach to the native alkaloids yet made, was discovered by the author of this manual. EDS. NATURAL ORGANIC BASES, 751 ALALINE, C 3 H 7 N0 2 , produced by treating acetic aldehyde with hydro- cyanic and hydrochloric acids, and leucme, C 6 H 13 N0 2 , obtained, in like manner, from valeric aldehyde, are likewise bases, forming definite salts with acids; but they are also acids, capable of forming salts by exchanging their hydrogen for metals ; they have indeed the composition of amido- propionic and amidocaproic acids, and as such have been already de- scribed (pp. 615, 619). Glycocine., C 2 H 5 N0 2 (p. 614), is another body of the same series, and possessing similar properties. II. Natural Organic Bases, or Alkaloids. The organic alkaloids constitute a remarkable and most interesting group of bodies: they are met with in various plants, some of them also in the animal organism. They are, for the most part, sparingly soluble in water, but dissolve in hot alcohol, from which they often crystallize in a very beautiful manner on cooling. Several of them, however, are oily, volatile liquids. The taste of the vegeto-alkalies, when in solution, is usually in- tensely bitter, and their action upon the animal economy exceedingly ener- getic. They all contain a considerable quantity of nitrogen, and are very complicated in constitution, having high combining numbers. This class of bodies is very numerous ; but the limits of this elementary work permit us to study only the more important members included in it. None of the organic bases occurring in plants have yet been formed by artificial means ; and their constitution is far from being completely under- stood. There can be no doubt, however, that the natural alkaloids, like the artificial bases, are substitution-products of ammonia. Many of them, when submitted to the action of methyl or ethyl iodide, are capable of ab- sorbing a smaller or greater number of equivalents of methyl and ethyl, and their deportment with these alcohol-iodides permits us to ascertain with great precision their degree of substitution. If a natural alkaloid, when submitted to the action of ethyl iodide, be found to require for con- version into a base of the formula, ( A ) Me [ OH ' U-l either 1, or 2, or 3 equivalents of ethyl, we may infer that the alkaloid in question belongs to the class of bases represented by the formulae : fA fA fA N \ B or N 1 B or N \ H lc U U . i. e., that it is a tertiary, a secondary, or a primary monamine. All natu- ral alkaloids which have been examined, with the exception of conine, are tertiary bases. Morphine, or Morphia, C 17 H, 9 N0 3 . This is the chief active principle of opium : it is the most characteristic body of the group, and the earliest known, dating back to the year 1804, when it was discovered by Sertiirner. Opium, the inspissated juice of the poppy-capsule, is a very complicated substance, containing, besides morphine, a host of other alkaloids in very variable quantities, combined with sulphuric acid and meconic acid (p. 670). In addition to these, there are gummy, resinous, and coloring matters, caoutchouc, &c., besides mechanical impurities, as chopped leaves. The 752 NATURAL ORGANIC BASES. opium of Turkey is the most valuable, and contains the largest quantity of morphine : the opiums of Egypt and of India are considerably inferior. Opium has been produced in England of the finest quality, but at great cost. If ammonia be added to a clear, aqueous infusion of opium, a very abun- dant buff-colored or brownish-white precipitate falls, which consists prin- cipally of morphine and narcotine, rendered insoluble by the withdrawal of the acid, The product is too impure, however, for use. The chief dif- ficulty in the preparation of these substances is to get rid of the coloring matter, which adheres with great obstinacy, redissolving with the precipi- tates, and being again in part thrown down when the solutions are satu- rated with an alkali. The following method, which succeeds well upon a small scale, will serve to give the student some idea of a process very com- monly pursued when it is desired to isolate at once an insoluble organic base, and the acid with which it is in combination: A filtered solution of opium in tepid water is mixed with lead acetate in excess; the precipitated lead meconate is separated by a filter, and through the solution containing morphine acetate, now freed to a considerable extent from color, a stream of sulphuretted hydrogen is passed. The filtered and nearly colorless liquid, from which the lead has been thus removed, may be warmed to ex- pel the excess of gas, once more filtered, and then mixed with a slight excess of caustic ammonia, which throws down the morphine and narco- tine : these may be separated by boiling ether, in which the latter is solu- ble. The lead meconate, well washed, suspended in water, and decomposed by sulphuretted hydrogen, yields a solution of meconic acid. Morphine and its salts are advantageously prepared, on the large scale, by the process of Dr. Gregory. A strong infusion of opium is mixed with a solution of calcium chloride, free from iron; calcium meconate, which is nearly insoluble, then separates, while the hydrochloric acid is transferred to the alkaloids. By duly concentrating the filtered solution, the hydro- chloride of morphine may be made to crystallize, while the narcotine and other bodies are left behind. Repeated recrystallization, and the use of animal charcoal, then suffice to whiten and purify the salt, from which the base may be precipitated in the pure state by ammonia. Other processes have been proposed, as that of M. Thiboumery, which consists in adding slaked lime in excess to an infusion of opium, by which the meconic acid is rendered insoluble, while the morphine is taken up with ease by the alka- line earth. By exactly neutralizing the filtered solution with hydrochloric acid, the morphine is precipitated, but in a somewhat colored state. Morphine, when crystallized from alcohol, forms small but very brilliant prismatic crystals, which are transparent and colorless, It requires at least 1QOO parts of water for solution, tastes slightly bitter, and has an alkaline reaction. These effects are much more evident in the alcoholic solution. It dissolves in about 30 parts of boiling alcohol, and with great facility in dilute acids ; it is also dissolved by excess of caustic potash or soda, but scarcely by excess of ammonia. When heated in the air, mor- phine melts, inflames like a resin, and leaves a small quantity of charcoal, which easily burns away. Morphine in powder strikes a deep-bluish color with neutral ferric salts, decomposes iodic acid with liberation of iodine, and forms a deep-yellow or red compound with nitric acid : these reactions are by some considered characteristic. Crystallized morphine contains C 17 H, 9 N0 3 . H 2 0. The most characteristic and best-defined salt salt of this base is the hydro- chloride. It crystallizes in slender, colorless needles, arranged in tufts or stellated groups, soluble in about 20 parts of cold water, and in its own weight at the boiling heat. The crystals contain 3 molecules of water. The sulphate, nitrate, and phosphate are crystallizable salts: the acetate crys- NARCOTINE CODEINE. 753 tallizes with great difficulty, and is usually sold in the state of a dry pow- der. The artificial meconate is sometimes prepared for medicinal use. An alcoholic solution of morphine, heated in sealed tubes with methyl iodide, forms a crystalline compound, C, 8 H 22 N0 3 l = C, 7 (H, 9 CH 3 )N0 3 T; this substance yields, with silver oxide, a very alkaline solution, obviously con- taining an ammonium base. Morphine is therefore a tertiary amine, the group C 17 H 19 3 representing one or several radicals, which are together capable of replacing 3 atoms of hydrogen. Narcotine. The marc, or insoluble portion of opium, contains much narcotine, which maybe extracted by boiling with dilute acetic acid. From the filtered solution the narcotine is precipitated by ammonia, and after- wards purified by solution in boiling alcohol, and filtration through animal charcoal. Narcotine crystallizes in small, colorless, brilliant prisms, which are nearly insoluble in water. The basic powers of narcotine are very feeble : it is destitute of alkaline reaction, and although freely soluble in acids, refuses, for the most part, to form with them crystallizable com- pounds. According to Matthiessen and Foster, narcotine contains C^H^NOj. Narcotine yields some curious products by the action of oxidizing agents, as a mixture of dilute sulphuric acid and manganese dioxide, or a hot solu- tion of platinic chloride. They have been chiefly studied by Wohler, Blyth, Anderson, and lately also by Matthiessen and Foster. The most important of these is opianic acid, a substance forming colorless, prismatic, reticulated crystals, sparingly soluble in cold, easily in hot water. It melts when heated, but does not sublime. After fusion it becomes quite insoluble in dilute alkalies, but without change of composition. This acid forms crys- tallizable salts and an ether: it contains C, H ]0 6 . The ammonia-salt, by evaporation to dryness, yields a nearly white insoluble powder, called opiammone, containing C^H^NOg, convertible by strong acids into opianic acid and ammonia. Sulphurous acid yields with opianic acid two products containing sulphur. A basic substance, cotarnine, C^II^NOg, is contained in the mother-liquor from which opianic acid has crystallized : it forms a yellow crystalline mass, very soluble, of bitter taste, and feebly alkaline reaction. Its hydrochloride is a well-defined salt. The transformation of narcotine into opianic acid and cotarnine is represented by the equation: C n H B N0 7 + = C 10 H 10 5 + C 12 H 13 N0 3 . Another basic substance, narcogenine, was accidentally produced in an at- tempt to prepare cotarnine with platinic chloride. It formed long orange- colored needles, and contained C 18 H, 9 N0 5 . By heating opianic acid with a strong solution of potash, it is converted into a crystallizable neutral and volatile substance called meconin, C, H 10 4 , and a bibasic crystallizable acid, termed hemipinic acid, C, H 10 6 : 2C 10 H 10 6 = C 10 H 10 4 + C 10 H 10 6 . Hemipinic acid, treated with hydriodic acid, splits up into methyl iodide, carbonic acid, and hypogallic, C 7 H 6 4 , the relation of which to gallic acid has already been mentioned (p. 607). When cotarnine is gently heated with very dilute nitric acid, it is converted into methylamine nitrate and co- tarnic acid, a bibasic acid containing C U H, 2 6 : C 12 H 13 N0 3 + 2H 2 + N0 3 H = CH 6 N.N0 3 + C U II H 8 . Codeine, C, 8 H 21 N0 3 . Hydrochloride of morphine, prepared directly from opium, as in Gregory's process, contains codeine-salt. On dissolving it in water, and adding a slight excess of ammonia, the morphine is preci- pitated, and the codeine left in solution. Pure codeine crystallizes, by 754 NATURAL ORGANIC BASES. spontaneous evaporation, in colorless transparent octohedrons: it is soluble in 80 parts of cold, and 17 of boiling water, has a strong alkaline reac- tion, and forms crystallizable salts. With ethyl iodide codeine forms a crystalline iodide, C^H^NOgl = C 18 H 21 (C 2 H 5 )N0 3 I, furnishing with silver oxide a soluble base. Codeine being considered as a tertiary monamine, the group C 18 H 21 3 represents 3 atoms of hydrogen. Codeine is homologous with morphine, C, 8 H 2 ,N0 3 . It has been the sub- ject of a careful investigation by Dr. Anderson, who has prepared a great number of its derivatives, all of which establish the formula above given. Thebaine or Paramorphine. This substance is contained in the precipi- tate formed by calcium hydrate in a strong infusion of opium, in Thibou- mery's process for preparing morphine. The precipitate is well washed, dissolved in dilute acid, and mixed with ammonia in excess, and the the- baine is thrown down crystallized from alcohol. When pure, it forms colorless needles like those of narcotine, but sparingly soluble in water, readily soluble in the cold in alcohol and ether. It melts when heated, and decomposes at a high temperature. With dilute acids it forms crystalliz- able compounds, and when isolated and in solution has a powerfully alka- line reaction. A series of other bases, papaverine, C 20 H 2 ,N0 4 , pseudo-morphine, narceine, C^H^NOg, opianine, and porphyroxine, are also at least occasionally contained in opium: they are of small importance, and comparatively little is known respecting them. A considerable number of derivatives of papa- verine have been prepared, which confirm the formula above given for it. Cinchonine and Quinine. It is to these vegeto-alkalies that the valuable medicinal properties of the Peruvian barks are due. They are associated in the barks with sulphuric acid, and with a special acid, called the quinic or kinic. Cinchonine is contained in largest quantity in the pale bark, or Cinchona condaminea ; quinine in the yellow bark, or Cinchona cordifolia ; the Cinchona oblongifolia contains both. The simplest, but not the most economical, method of preparing these substances is to add a slight excess of calcium hydrate to a strong decoc- tion of the ground bark in acidulated water, wash the precipitate which ensues, and boil it in alcohol. The solution, filtered while hot, deposits the vegeto-alkali on cooling. When both bases are present, they may be separated by converting them into sulphates : the quinine-salt is the less soluble of the two, and crystallizes first. Pure cinchonine, or cinchonia, crystallizes in small, but beautifully bril- liant, transparent, four-sided prisms. It is but very feebly soluble in water, dissolves readily in boiling alcohol, and has but little taste, although its salts are excessively bitter. It is a powerful base, neutralizing acids completely, and forming a series of crystallizable salts. Cinchonine turns the plane of polarization to the right. Quinine or quina, much resembles cinchonine: it does not crystallize so well, however, and is much more soluble in water : its taste is intensely bitter. Quinine turns the plane of polarization toward the left. Cinchonine is composed of . . . C.^H^N/), and Quinine Q f C^H^N.O.,. Quinine sulphate is manufactured on a very large scale for medicinal use : it crystallizes in small white needles, which give a neutral solution. This substance contains ^C^H^N./^ . S0 4 H 2 . 7 Aq. Its solubility is much in- creased by the addition of a little sulphuric acid, whereby the acid salt, C M H 24 N 22- S0 4 H 2 . 7 Aq., is formed. A very interesting compound lias been produced by Dr. Herapath, by the action of iodine upon quinine sul- QUINIDINE. 755 phate. It is a crystalline substance of a brilliant emerald color, which appears to consist of equal equivalents of the sulphate of quinine and of iodine. This remarkable compound possesses the optical properties of the tourmaline (p. 92). Cinchonine and quinine yield with methyl iodide, compounds represented respectively by the formulae C^H^CHg^OI and C 20 H 24 (CH 3 )N 2 O 2 I, which are converted by silver oxide into soluble bases analogous to tetrethyl- ammonium hydrate. Quinidine. In manufacturing quinine sulphate, a new base has been ob- tained, which differs from quinine in some of its physical properties, but is said to have the same composition. It has been described under the name of quinidine, and appears to have the same medicinal properties as quinine. The substance has been carefully examined by Pasteur, whose researches have led to the following interesting results: The substance which is found in commerce under the name of quinidine is generally a mixture of two alkaloids, of which the one is isomeric with quinine, and the other with cinchonine. Pasteur designates these two sub- stances respectively as quinidine and cinchonidine. They differ from quinine and cinchonine in several properties, but particularly in their deportment with polarized light : for while quinine turns the plane of polarization con- siderably towards the left, quinidine exerts a powerful action towards the right. Again, while cinchonine deflects considerably towards the right, the action of the isomeric cinchonidine is in the opposite direction namely, towards the left. It is evident that quinine and quinidine on the one hand, and cinchonidine and cinchonine on the other, stand to each other in about the same relation as levo- and dextro-tartaric acids (p. 677). Nor are the terms wanting which correspond to racemic acid. Pasteur has, in fact, proved that both quinine and quinidine, and likewise cinchonine and cin- chonidine, are peculiarly modified by the action of heat: exposed for sev- eral hours to a temperature varying between 120 and 130 C. (248-256F.), quinine and quinidine are converted into a third isomeric alkaloid, which Pasteur terms quinicine, while cinchonine and cinchonidine furnish an iso- meric cinchonicine under the same circumstances. In racemic acid the right- handed action of dextro-tartaric, and the left-handed action of levo-tar- taric acid, are exactly balanced, racemic acid possessing no longer any ac- tion upon polarized light : in quinicine and cinchonicine, such a perfect balance is not observed ; both still exert a feeble right-handed action, which is, however, very slight when compared with the rotatory powers of the alkaloids which give rise to them. The following table exhibits the relations of the six alkaloids, and their analogy with the racemic group, in a more conspicuous manner: Quinine Quinicine Quinidine Left-handed, Right-handed, Right-handed, powerfully. feebly. very powerfully, Cinchonine Cinchonicine Cinchonidine Right-handed, Right-handed, Left-handed, very powerfully. feebly. powerfully. Dextro-tartaric acid Racemic acid Levo-tartaric acid. Right-handed. neutral. Left-handed. Chino'idine, Quino'idine, or Amorphous quinine, is contained in the refuse, or mother-liquors, of the quinine manufacture. In its purest state it forms a yellow or brown resin like mass, insoluble in water, freely soluble in alco- hol and ether. It is easily soluble also in dilute acids, and is thence pre- cipitated by ammonia. Quinoidine possesses powerful febrifuge properties, and is identical in composition with quinine. It evidently bears to quinine 756 NATURAL ORGANIC BASES. the same relation that uncrystallizable syrup bears to ordinary sugar, being produced from quinine by the heat employed in the preparation. From Cusco- or Arica-bark, and likewise from the Cinchona ovata, or white quinquina of Condamine, a substance denominated Aricine or Cinchovatine has been extracted : it closely resembles cinchonine, and is said to contain C 2 o H 26 N 24- This fo rmula exhibits a close analogy with the formulae of cinchonine and quinine. Aricine is useless in medicine. Strychnine and Brucine, also called Strychnia and Brucia, are contained, together with several still imperfectly known bases, in Nux vomica, in St. Ignatius' bean, and in false Angustura bark. Strychnine and brucine are generally associated with a peculiar acid, called igasuric acid. Nux vomica seeds are boiled in dilute sulphuric acid until they become soft: they are then crushed, and the expressed liquid is mixed with excess of calcium hydrate, which throws down the alkaloids. The precipitate is boiled in spirits of wine of sp. gr. 0-850, and filtered hot. Strychnine and brucine are then deposited together in a colored and impure state, and may be sep- arated by cold alcohol, in which the latter dissolves readily. Pure strychnine crystallizes under favorable circumstances in small but exceedingly brilliant octohedral crystals, which are transparent and color- less. It has a very bitter, somewhat metallic taste (1 part in 1,000,000 parts of water is still perceptible), is slightly soluble in water, and fear- fully poisonous. It dissolves in hot, and somewhat dilute spirit, but not in absolute alcohol, ether, or solution of caustic alkali. This alkaloid may be readily identified by moistening a crystal with concentrated sulphuric acid, and adding to the liquid a crystal of potassium bichromate, when a deep violet tint is produced, which disappears after some time. Strychnine forms with acids a series of well-defined salts, which were examined by Messrs. Nicholson and Abel, who established for strychnine the formula C 21 H 22 N 2 2 . Strychnine forms with ethyl iodide a crystalline compound, C 21 H 22 (C 2 H 5 ) N 2 4 I, converted by silver oxide into a soluble base. Brucine, C^H^N^, is easily distinguished from the preceding substance, which it much resembles in many respects, by its ready solubility in alco- hol, both hydrated and absolute. It dissolves also in about 500 parts of hot water. The salts of brucine are, for the most part, crystallizable. Veratrine, or Veratria, C 32 H 52 N 2 8 , is obtained from the seeds of Veratrum sabadilla. In the pure state it is a white or yellowish-white powder, which has a sharp burning taste, and is very poisonous. It is remarkable for occasioning violent sneezing. It is insoluble in water, but dissolves in hot alcohol, in ether, and in acids : the solution has an alkaline reaction. A substance called colchicine, extracted from the Colchicum autumnale, and formerly confounded with veratrine, is now considered distinct : its history is still imperfect. Harmaline, C 13 H, 4 N 2 0. This compound is extracted by dilute acetic acid from the seeds of the Peganum harmala, a plant which grows abun- dantly on the Steppes of Southern Russia, and the seeds of which are used in dyeing. When pure, it forms yellowish prismatic crystals, soluble in alcohol and dilute acids, but scarcely forming crystallizable salts. By oxi- dation it gives rise to another compound, harmine, C, 3 H, 2 N 2 0, which also possesses basic properties. Caffeine, or Theine, C 8 H, N 4 2 . This remarkable substance occurs in four articles of domestic life, infusions of which are used as beverages over the greater part of the known world namely, in tea and coffee, in the leaves of Guarana ojficinalis, or Paullinia sorbilis, and in those of Ilex Paraguay ensts ; THEOBROMINE XANTHINE. 757 it will probably be found in other plants. A decoction of common tea, or of raw coffee-berries, previously crushed, is mixed with excess of solution of basic lead acetate. The solution, filtered from the copious yellow or greenish precipitate, is treated with sulphuretted hydrogen to remove the lead, then filtered, evaporated to a small bulk, and neutralized by ammo- nia. The caffeine crystallizes out on cooling, and is easily purified by animal charcoal. It forms tufts of delicate, white, silky needles, which have a bitter taste, melt when heated with loss of water, and sublime with- out decomposition. It is soluble in about 100 parts of cold water, and much more easily at the boiling heat, or if an acid be present. Alcohol also dissolves it, but not easily. The basic properties of caffeine are fee- ble. The salts which it forms with hydrochloric and sulphuric acids are obtained only with difficulty. It forms, however, splendid double salts with platinum tetrachloride and gold trichloride. The products of oxida- tion of caffeine, which have been studied by Rochleder, are of considerable interest, inasmuch as both their composition and their properties establish a close connection between these products and the derivatives of uric acid. Under the influence of chlorine, caffeine yields amalic acid, a substance of feebly acid properties, having the composition of hydrated tetramethyl- alloxantin, C 8 (CH 3 ) 4 N 4 7 . Aq. When treated with oxidizing agents, it yields cholestrophane, C 6 H 6 N 2 3 , corresponding to parabanic acid of the uric acid series. Cholestrophane may be viewed as dimethyl-parabanic acid; it has, in fact, been obtained by digesting silver parabanate with methyl iodide : C 3 Ag 2 N 2 3 + 2CH 3 I == 2AgI + C 5 H 6 N 2 3 . Lastly, the murexide of the caffeine series is formed by the treatment of amalic acid with ammonia, exactly as the true murexide from uric acid is formed by the action of ammonia upon alloxantin. The new murexide imitates its prototype, not only in composition, but likewise in the green metallic lustre of its crystals, and the deep crimson color of its solutions. Theobromine. The seeds of the Theobroma Cacao, or cacao-nuts, from which chocolate is prepared, contain a crystallizable principle, to which this name is given. It is extracted in the same manner as caffeine, and forms a white, crystalline powder, which is much less soluble than the last- named substance. It contains, according to Glasson, C 7 H 8 N 4 2 . Theobro- mine is easily soluble in aqueous ammonia ; by adding silver nitrate to this solution, and boiling, a crystalline precipitate of silver-theobromine, C 7 H t AgN 4 2 , is obtained. By treating this silver compound with methyl iodide, Strecker obtained silver iodide and caffeine : C 7 H 7 AgN 4 2 -f CH 3 I = Agl ~h C 8 H 10 N 4 2 , which may be extracted with alcohol. Caffeine must there- fore be regarded as methyl-theobromine. The products obtained from theobromine by oxidation appear to be homologous with several terms of the uric acid series. Xanthine, C 5 H 4 N 4 2 . Xanthine was first described by Dr. Marcet under the name of xanthic oxide, which he discovered as a constituent of urinary calculi; recently it has been found among the products of the decomposi- tion of guanine. It is present in nearly every part of the animal organism, and, although in very minute quantities, in urine. Xanthine, according to Strecker, may be prepared with the greatest facility from guanine (p. 758). Potassium nitrite is added to a solution of guanine in concentrated nitric acid until a powerful evolution of red fumes takes place: the solution is then mixed with a large quantity of water, whereby a yellow substance is precipitated, which, after washing with wa- ter, is issolved m ammonia. A solution of ferrous sulphate is now added 758 NATURAL ORGANIC BASES. until a black precipitate of iron oxide begins to appear.* The still power- fully ammoniacal solution is filtered and evaporated to dryness ; and the residue is extracted with water in order to separate the ammonium sulphate; then dissolved in ammonia, and evaporated. Xanthine is a white, amor- phous powder, difficultly soluble in water, soluble in acids, with which it forms crystalline compounds. The sulphate has the composition 2C 5 H 4 N 4 . S0 4 H 2 . Xanthine dissolves with facility in ammonia and potash. Its characteristic property is to dissolve without evolution of gas in nitric acid, and to give on evaporation a deep-yellow residue, which, on addition of ammonia or solution of potash, assumes a yellow-red color. By treatment of silver-xanthine, C 5 H 2 Ag 2 N 4 H 2 , with methyl iodide, Strecker obtained a body isomeric with theobromine, differing, however, in its properties from that substance : C 5 H 2 Ag 2 N 4 2 + 2CH 3 I = 2AgI -f C 7 H 8 N 4 2 . Sarcine (Hypoxanthine), C 5 H 4 N 4 0. This base is a constituent of the flesh of vertebrata. It is best prepared from the mother-liquor of creatin (p. 902), by diluting with water and boiling with cupric acetate, whereby the sarcine is precipitated in combination with cupric oxide. This preci- pitate is dissolved in nitric acid and mixed with silver nitrate; the crys- tals, a compound of sarcine nitrate with silver nitrate, are purified by re-crystallization from nitric acid, and are then, by ebullition with an am- moniacal solution of silver nitrate, converted into the compound of sarcine with silver oxide, C 5 H 4 N 4 . Ag 2 0, which is decomposed by sulphuretted hydrogen. Sarcine forms delicate white microscopic needles, difficultly soluble in cold water, easily soluble in boiling water, in dilute acids, ammonia, pot- ash, and baryta-water. Sarcine forms crystallizable salts, containing 1 equivalent of acid. It unites with bases, like guanine, forming crystalline compounds containing 2 equivalents of metallic oxide. Guanine, C 5 H 5 N 5 0. This base was first obtained from guano; it has also been proved to exist in the pancreatic juice of mammalia, and in the excrement of the spider. To prepare it, guano is boiled with water and calcium hydrate until a portion of the liquid, when filtered, appears but slightly colored: the whole is then filtered, and the filtrate saturated with acetic acid, whereby the guanine is precipitated, mixed with uric acid. It is purified by solution in hydrochloric acid and precipitation by ammonia. Guanine is a colorless, crystalline powder, insoluble in water, alcohol, ether, and ammonia, soluble in acids and solution of potash. With acids it forms crystallizable salts containing 1 and 2 equivalents of acid : it com- bines with bases to crystalline compounds containing 2 equivalents of metal- lic oxide. Guanine, sarcine, and xanthine bear a great resemblance to each other, and are all found in the animal organism. Guanine, on account of its in- solubility in water and ammonia, may easily be separated from the two other substances. To separate xanthine and sarcine, they are converted into the hydrochlorides, which are treated with warm water : xanthine hy- drochloride is so little soluble in that liquid, that it may easily be separated from the admixed sarcine hydrochloride. Guanidine, CH 5 N 3 This substance is prepared from guanine. Guanine is treated with hydrochloric acid and potassium chlorate, whereby it is con- verted into a mixture of guanidine and parabanic acid. As soon as the guanine is completely dissolved, the liquid is evaporated till the parabanic * The treatment of gnanine with nitric acid gives rise to xanthine and nitroxanthine, which by the action of reducing agents is converted into xanthine. Strecker recommends a ferrous salt for this purpose. CREATIN CREATININE SARCOSINE. 759 acid has crystallized out. The mother-liquor is treated with a mixture of alcohol and ether, which, separated from the residue and evaporated, yields on evaporation the crude guanidine hydrochloride. The hydro- chloride may, by digestion with silver sulphate, be converted into the sulphate, and the latter finally into the free base by addition of baryta- water. Guanidine thus prepared forms colorless crystals, readily soluble in water and alcohol; the solution has a powerfully alkaline reaction. It absorbs carbonic acid from the air, forming a carbonate 2CH 5 N 3 . H 2 COj, which has an alkaline reaction, and crystallizes in square prisms. The transforma- tion of guanine into parabanic acid and guanidine is represented by the following equation: C 5 H 5 N 5 + 0. + H 2 = C 3 H 2 N 2 8 + CH 5 N 3 + C0 2 . Triethylguamdine. The action of sodium alcohol upon ethyl cyanate or cyanurate gives rise to a base having the composition C 7 H 17 N 3 , which is that of triethylguanidine (carbotriethyltriamine). It is formed according to the following equation : 3CN(C 2 H 6 )0 + 2C 2 II 5 NaO = C 7 H 17 N 3 + 2C 2 H 4 + C0 2 + Na 2 C0 3 . Creatin, C 4 H 9 N 3 2 . 2 Aq. Creatin was first observed by Chevreul, and has been studied very carefully by Liebig, who obtained it from the soup of boiled meat. It is prepared from the juice of raw flesh by the follow- ing process : A large quantity of lean flesh is cut up into shreds, exhausted by successive portions of cold water, strained and pressed. The liquid, which has an acid reaction, is heated to coagulate albumin and coloring matter of blood, and passed through a cloth. It is then mixed with pure baryta-water as long as a precipitate appears, filtered from the deposit of phosphates, and evaporated in a water-bath to a syrupy state. After standing some days in a warm situation, the creatin is gradually deposited in crystals, which are easily purified by re-solution in water and digestion with a little animal charcoal. * When pure, creatin forms colorless, brilliant, prismatic crystals, which become dull by loss of water at 100. They dissolve readily in boiling water, sparingly in cold water, and are but little soluble in alcohol. The aqueous solution has a weak bitter taste, followed by a somewhat acrid sensation. In an impure state the solution readily putrefies. Creatin is a neutral body, not combining either with acids or with alkalies. In the crystallized state it contains C 4 H 9 N 3 2 . 2H 2 0. Creatinine, C 4 H 7 N 3 0. By the action of strong acids, creatin is converted into creatinine, a powerful organic base, with separation of the elements of water. The new substance forms colorless prismatic crystals, and is much more soluble in water than creatin: it has a strong alkaline reaction, and forms crystallizable salts with acids Creatinine pre-exists to a small extent in the juice of flesh, together with lactic acid and other bodies not yet perfectly examined. It is also found in conjunction with creatin in urine. Sarcosine, C 3 H 7 N0 2 , formed by boiling creatin with baryta-water, has the composition of methyl-glycocine or methyl-amidacetic acid, C 2 H 4 (CII 3 ) N0 2 , and has been already described among the derivatives of acetic acid (p. 614). * The mother-liquid from flesh from which the creatin has been deposited contains, among other things, a new acid, the inosinic. the aqueous solution of which refuses to crystallize. It has a strong acid reaction, and is precipitated in a white amorphous condition by alcohol. It probably cont 760 PHOSPHORUS, ANTIMONY, AND ARSENIC BASES. Berberine, C 21 H, 9 N0 6 , is a substance crystallizing in fine yellow needles, slightly soluble in water, extracted from the root of the Berberis vulgaris. It has feeble basic properties. This must not be confounded with bcbeerine, an uncrystallizable basic substance, from the bark of the green-heart tree of Guiana, which has the composition C, 9 H 21 N0 3 . Piperine, C 34 H 38 N 2 6 . A colorless, or slightly yellow crystallizable prin- ciple, extracted from pepper by the aid of alcohol. It is insoluble in water. Piperine readily dissolves in acids ; definite compounds are, however, dif- ficult to obtain. Conine (Conitine, or Conia), Nicotine, and Sparteine differ from the other vegetable bases in physical characters ; they are volatile oily liquids. The first is extracted from hemlock, the second from tobacco, and the third from broom (Spartium Scoparium). They agree in most of their characters, having high boiling points, very poisonous properties, strong alkaline reac- tion, and the power of forming crystallizable salts with acids. The for- mula of nicotine is C 10 H 14 N 2 ; that of conine, C 8 H, 5 N ; and that of sparteine, 10 2fi 2* Clos'ely allied to conine is conhydrine, C g H, 7 NO, a crystalline base, ex- tracted by Wertheim from hemlock. When distilled with anhydrous phos- phoric acid, it splits into conine and one molecule of water. A mixture of nicotine with methyl or ethyl iodide solidifies after a short time to crystalline masses, containing C 10 H 14 (CH 3 ) 2 N 2 I 2 , andC JO H u (C 2 H 6 ) 2 N 2 I 2 , convertible by silver oxide into soluble bases. Conine is a secondary monamine. Treated with ethyl iodide, it yields successively two iodine-compounds namely, C 8 H 15 (C 2 H 5 )NI and C 8 H U (C 2 H 5 ) 2 NI. The latter is converted by silver oxide into a soluble base. There are very many other bodies, more or less perfectly known, having to a certain extent the properties of alkaloids : the following statement of the names and mode of occurrence of a few of them must suffice. Hyoscyamine (Dc/turinc). A white, crystallizable substance, from Hyos- cyamus niger ; it occurs likewise in Datura Stramonium. Atropine. Colorless needles, from Atr op a Belladonna ; formula ^H^NO.,. Solanine. A pearly, crystalline substance, from various solanaceous plants; formula C 43 H n NO l6 (?) (p. 582). Aconitine. A glassy, transparent mass, from Aconitum Napellus : formula Delphmine. A yellowish, fusible substance, from the seeds of Delphinium Staphisagria. Emetine. A white and nearly tasteless powder from ipecacuanha root. Curarine. The arrow-poison of Central America. HI. Phosphorus, Antimony, and Arsenic Bases. Phosphorus, antimony, and arsenic being, like nitrogen, either trivalent or quinquivalent, are capable of forming compounds analogous to the amines and the compound ammonium salts. A few of these remarkable compounds will be briefly described in the following paragraphs. PHOSPIIINES. Paul Th^nard, by passing the vapor of methyl chloride over calcium phosphide heated to about 180 C. (356 F.), obtained a mixture of phos- ANTIMONY BASES. 761 phoretted bodies, from which he separated three compounds believed to correspond in composition with the three hydrides of phosphorus (p. 215), viz., P 2 (CH 3 ), P(CH 3 ) 2 , and P(CH 3 ) 3 ; these bodies were, however, but very imperfectly investigated. More recently Cahours and Hofmann, by sub- jecting zinc-methyl and zinc-ethyl to the action of phosphorus trichloride, have obtained saline compounds, from which, by distillation with potash, the bases P(CH 3 ) 3 and P(C 2 H 5 ) 3 , analogous to the tertiary monamines, may be liberated ; thus : 3Zn(C 2 H 5 ) 2 + 2PC1 3 = 3ZnCl 2 + 2P(C 2 H 5 ) 3 . Zinc-ethyl. Triethyl-phosphine. Thriethylphosphine, C 6 H 15 P P(C 2 H 5 ) 3 . This substance is a colorless oil having a very penetrating phosphorus odor, and boiling at 133. It is slowly oxidized in atmospheric air. The vapor, heated with air or oxygen, explodes. In chlorine gas it burns with separation of carbon, hydro- chloric acid and phosphorus pentachloride being produced. With acids it forms crystalline compounds, which are very deliquescent. With iodide of methyl, ethyl, and amyl, it solidifies after a few moments to crys- talline compounds, containing respectively P(C 2 H 6 ) 3 (CH 3 )I, P(C 2 H 5 ) 4 I, and P(C 2 H 5 ) 3 (C 5 H 11 )I, which are decomposed by silver oxide, yielding power- fully alkaline liquids, containing the hydrates P(C 2 H 5 ) 3 (CH 3 )(OH), P(C 2 H 5 ) 4 (OH), and P(C 2 H 5 ) 3 (C 5 H 11 )OH, which in every respect resemble hydrate of tetrethyl ammonium and its homologues. Trimethylphosphine, C 3 H 9 P = P(CH 3 ) 3 . This substance is very similar to the corresponding ethyl-base, but more volatile. When left in contact with atmospheric air, it forms an oxide which crystallizes in beautiful white needles. With iodide of methyl, ethyl, and amyl, it yields the iodides P(CH 3 ) 4 I, P(CH 3 ) 3 (C 2 H 5 )I, and P(CH 3 ) 3 (C5H n ) I, from which three analogous hydrates may be produced by means of silver oxide. ANTIMONY BASES or STIBINES. Triethylstibine, or Stibethyl, Sb(C 2 H 5 ) 3 , is obtained by distilling ethyl iodide with an alloy of antimony and potassium. It is a transparent, very mobile liquid, having a penetrating odor of onions. It boils at 158 C. (316 F.). In contact with atmospheric air, it emits a dense white fume, and frequently even takes fire, burning with a white brilliant flame. It is analogous in many of its reactions to triethylamine, but has much more powerful combining tendencies, uniting readily with two atoms of chlorine, bromine, or iodine, and 1 atom of oxygen or sulphur, thereby forming compounds in which the antimony is quinquivalent, such as Sb v (C 2 H 6 ) 3 Cl 2 , Sb v (C 2 H 5 ) 3 // , &c. The same tendency to act as a bivalent-radical is, how- ever, exhibited by triethylamine, which, though it does not unite directly with elementary bodies, can nevertheless take up a molecule of hydrogen chloride, ethyl iodide, &c., likewise producing compounds in which the nitrogen is quinquivalent, e.g., N V (C 2 H 5 ) ? HC1, N V (C 2 H 5 ) 3 (C 2 H 6 )I, &c. Stibethyl oxide, Sb(C 2 H 5 ) 3 0, forms a viscid transparent mass, soluble in water and alcohol. It is extremely bitter and not poisonous. It cannot be volatilized without decomposition. It combines with acids, giving rise to crystallizable salts containing two equivalents of acid. Stibethyl sulphide, Sb(C 2 H 5 ) 3 S. Beautiful crystals of silvery lustre, solu- ble in water and alcohol. Their taste is bitter, and their odor similar to that of mercaptan. The solution of this compound exhibits the deport- ment of an alkaline sulphide : it precipitates metals from their solutions 64* 762 ARSENIC BASES. as sulphides, a soluble salt of stibetbyl being formed at the same time. This deportment, indeed, affords the simplest means of preparing the salts of stibethyl. Stibethyl chloride, Sb(C 2 H 6 ) 3 Cl 2 . Colorless liquid having the odor of tur- pentine oil. Stibethyl iodide, Sb(C 2 H 5 ) 3 T 2 . Colorless needles of intensely bitter taste. The analogy of triethylstibine with triethylamine is best exhibited in its deportment with ethyl iodide. The two substances combine, forming a new iodide, containing Sb(C 2 H 5 ) 4 I, from which silver oxide separates a powerful alkaline base analogous to tetrethyl-ammonium hydrate : N(C 2 H 6 ) 4 (OH) Sb(C 2 H 5 ) 4 OH. A series of analogous substances exist in the methyl series. They have been examined by Landolt, who has described several of their compounds, and separated the methyl-antimony-base corresponding to tetramethyl- ammonium hydrate. The iodide, Sb(CH 3 ) 4 I, produced by the action of methyl iodide upon tri- methylstibine, Sb(CH 3 ) 3 , crystallizes in white six-sided tables, which are easily soluble in water and alcohol, and slightly soluble in ether. It has a very bitter taste, and is decomposed by the action of heat. When treated with silver oxide, it yields a powerfully alkaline solution, exhibiting all the properties of potash, from which, on evaporation, a white crystalline mass, the hydrate of tetramethylstibonium, Sb(CH 3 ) 4 (OH), crystallizes. This com- pound forms an acid salt with sulphuric acid, which crystallizes in tables. It contains Sb(CH 3 ) 4 HS0 4 . ARSENIC BASES. Triethylarsine, As(C 2 H 5 ) 3 , is produced by distilling an alloy of arsenic and sodium with ethyl iodide. At the same time, also, there is formed an- other body, containing As 2 (C 2 H 5 ) 4 , analogous to arsendimethyl or cacodyl. Both compounds are liquids of powerful odor; they may be separated by distillation in an atmosphere of carbon-dioxide, the triethylarsine passing over last. Triethylarsine may be obtained pure by a process analogous to that em- ployed for the preparation of triethylphosphine, namely, by distilling arse- nious chloride, AsCl 3 , with zinc-ethyl. It is a colorless liquid of most dis- agreeable odor, similar to that of arsenetted hydrogen, soluble in water, alcohol, and ether, and boiling at 140. Triethyiarsine combines directly with oxygen, sulphur, bromine, and iodine, giving rise to a series of com- pounds containing 2 atoms of bromine or iodine, 1 atom of sulphur or oxy- gen, and analogous to the corresponding compounds of triethylstibine. Triethylarsine submitted to the action of ethyl iodide yields a crystalline compound, As(C 2 H 5 )^I, from which freshly precipitated silver oxide sepa- rates the corresponding hydrate, As(C 2 H 5 ) 4 OH, a powerfully alkaline sub- stance, similar to the corresponding nitrogen-, phosphorus-, and antimony- compounds. Analogous substances exist in the methyl series. Trimethylarsine, As ( CH 3)a' is formed, together with arsendimethyl or cacodyl, As 2 (CH 3 ) 4 , when an alloy of arsenic and sodium is submitted to the action of methyl iodide. It unites with methyl iodide, producing tetramethylarsonium iodide, As(CH 3 ) 4 I, from which silver oxide separates the hydrate, As(CH 3 ) 4 )H. The iodide just mentioned is formed, together with iodide of cacodyl, when cacodyl is acted upon by methyl iodide: As 2 (CH 3 ) 4 + 2CH 3 I = As(CH 3 ) 4 I -f As(CH 3 ) 2 I. AESENIC BASES. 763 By substituting ethyl iodide for methyl iodide in this reaction, the com- pound As(CH 3 ) 2 (C 2 H 5 ) 2 I is formed. All these iodides, treated with moist silver oxide, yield the corresponding hydrates. Arsendimethyl and arsenmonomethyl will be most conveniently described in this place, though they do not strictly belong to the ammonia type, at least when in the free state. As'"(CH 3 ) 2 Arsendimethyl or Cacodyl, As 2 (CH 3 ) 4 , or j . The arsenic in this compound is still trivalent, one unit of equivalence of each of the arsenic-atoms being satisfied by combination with the other, just as in the solid hydrogen arsenide, As 2 H 4 (p. 423). When, however, the arsendi- methyl combines with chlorine or other monatomic radicals, the molecule splits into two ; thus : As(CH 3 ) 4 + C1 2 = 2AS'"(CH 8 ) a Cl. Cacodyl, so called from its repulsive odor, constitutes, together with its products of oxidation, the spontaneously inflammable liquid known as Ca- det's fuming liquid, or Alkarsin. This liquid is prepared by distilling potas- sium acetate with arsenious oxide. Equal weights of these two substances, both well dried, are intimately mixed and introduced into a glass retort connected with a condenser and tubulated receiver cooled by ice, a tube being attached to the receiver to carry away the permanently gaseous pro- ducts to some distance from the experimenter. Heat is then applied to the retort, which is gradually increased to redness. At the close of the opera- tion, the receiver is found to contain two liquids, besides a quantity of re- duced arsenic : the heavier of these is the crude cacodyl; the other consists chiefly of water, acetic acid, and acetone. The gas given off during the distillation is principally carbon dioxide. The crude cacodyl is repeatedly washed by agitation with water previously freed from air by boiling, and afterwards redistilled from potassium hydrate in a vessel filled with pure hydrogen gas. All these operations must be conducted in the open air. Pure cacodyl is obtained by 'decomposing the chloride with metallic zinc, dissolving out the zinc chloride with water, and dehydrating the oily liquid with calcium chloride. The strong tendency of cacodyl to take fire in the air, and the extremely poisonous character of its vapors, render it neces- 'sary to perform all the distillations in sealed vessels filled with dry carbon dioxide. Bunsen, to whose skill and perseverance we are indebted for the discovery of this remarkable compound, proceeds as follows : 1. A dilute alcoholic solution of alkarsin is cautiously mixed with an equally dilute solution of mercuric chloride, avoiding an excess of the lat- ter; a white crystalline, inodorous precipitate then falls, containing As 3 (CH 3 ) 4 . HgCl 2 : when this is distilled with concentrated hydrochloric acid, it yields mercuric chloride, water, and cacodyl chloride, which distils over. The product is left for some time in contact with calcium chloride and a little quicklime, and then distilled alone in an atmosphere of carbon dioxide. 2. To obtain free cacodyl, the pure anhydrous chloride is digested for three hours at a temperature of 100 with slips of clean metallic zinc con- tained in a bulb blown upon a glass tube previously filled with carbonic acid gas, and hermetically sealed. The metal dissolves quietly without evolution of gas. When the action is complete, and the whole cool, the vessel is observed to contain a white saline mass, which, on the admission of a little water, dissolves, and liberates a heavy oily liquid, the cncod \1 itself. This is rendered quite pure by distillation from a fresh quantity of zinc, the process being conducted in the little apparatus shown in 764 ARSENIC BASES. fig. 196, which is made from a piece of glass tube, and is intended to serve the purpose both of retort and receiver. The zinc is introduced into the upper bulb, and the tube drawn out in the manner represented. The whole is then filled with carbon dioxide, and the lower Fig. 196. extremity put into communication with a little hand- syringe. On dipping the point a into the crude cacodyl, and making a slight movement of exhaustion, the liquid is drawn up into the bulb. Both extremities are then sealed in the blowpipe flame, and after a short digestion at 100, or a little above, the pure cacodyl is distilled off into the lower bulb, which is kept cool. It forms a color- less, transparent, thin liquid, much resembling alkarsin in odor, and surpassing that substance in inflammability. When poured into the air, or into oxygen gas, it ignites instantly: the same thing happens with chlorine. With very limited access of air it throws off white fumes, pass- ing into oxide, and eventually into cacodylic acid. Caco- dyl boils at 170 C. (338 F.), and when cooled to 6 C. (21 F.), crystallizes in large, transparent, square prisms. It combines directly also with sulphur. Cacodyl is decomposed at a temperature, below redness into metallic arse- nic, and a mixture of 2 measures of marsh-gas and 1 measure of ethene gas. The powerful combining tendencies of cacodyl indicate that it is an un- saturated compound : it can, in fact, take up 2 atoms of a monad or 1 atom of a dyad element, forming compounds like the chloride, As 2 (CH 3 ) 4 Cl 2 = 2As(CH 3 ) 2 Cl, and the oxide, As 2 (CH 3 ) 4 0, in which the arsenic is trivalent; or again, 6 atoms of a monad or 3 atoms of a dyad element, forming com- pounds like the trichloride, As 2 (CH 3 ) 4 Cl 6 2As(CH 3 ) 2 Cl 3 , in which arsenic is quinquivalent. These last-mentioned bodies are the most stable of all the cacodyl compounds. CACODYL CHLORIDE, or ARSEN-CHLORODIMETHIDE, As'"(CH s ) 2 Cl, prepared as above described, is a colorless liquid, which does not fume in the air, but emits an intensely poisonous vapor. It is heavier than water, and in- soluble in that liquid, as also in ether; alcohol, on the other hand, dis- solves it with facility. The boiling point of this compound is a little above 100 ; its vapor is colorless, spontaneously inflammable in the air, and has a density of 4-56. Dilute nitric acid dissolves the chloride without change ; with the concentrated acid, ignition and explosion occur. Cacodyl chloride combines with cuprous chloride, forming a white, insoluble, crystalline double salt, containing As 2 (CH 3 ) 4 Cl 2 . Cu'yCljj also with cacodyl oxide. Cacodyl chloride forms a hydrate which is thick, viscid, and readily de- hydrated by calcium chloride. CACODYLTRICHLORIDE, As v (CH 3 ) 2 Cl 3 , is produced by the action of phos- phorus pentachloride on cacodylic acid : As*(CH s ) 2 0"(OH) + 2PC1 5 = As(CH 3 ) 2 Cl 3 + 2POC1 3 + HC1. Also by the action of chlorine gas on the monochloride. Prepared by the first method, it forms splendid large prismatic crystals, which however are very unstable, being instantly decomposed, at temperatures between 40 and 50 C. (104-122 F.), into methyl chloride and arsen-monomethyl chlo- ride: As^(CH 3 ) 2 Cl 3 = CH 3 C1 + As"'(CH 3 )Cl 2 . CACODYL IODIDE, As(CH 3 ) 2 T, is a thin, yellowish liquid, of offensive odor, and considerable specific gravity, prepared by distilling alkarsin with CACODYL. 765 strong solution of hydriodic acid. A yellow crystalline substance is formed at the same time, which is an oxyiodide. Cacodyl bromide and fluoride have also been obtained. CACODYL CYANIDE, As(CH 3 ) 2 CN, is easily formed by distilling alkarsin with strong hydrocyanic acid, or mercuric cyanide. Above 32-7 C. (90 F.), it is a colorless, ethereal liquid, but below that temperature it crys- tallizes in colorless four-sided prisms, of beautiful diamond lustre. It boils at about 140 C. (284 F.), and is but slightly soluble in water. It requires to be heated before inflammation occurs. The vapor of this substance is most fearfully poisonous: the atmosphere of a room is said to be so far contaminated by the evaporation of a few grains of it as to cause instan- taneous numbness of the hands and feet, vertigo, and even unconscious- ness. CACODYL OXIDE, As /// 2 (CH 3 ) 4 // . This compound is formed by the slow oxidation of cacodyl. When air is allowed access to an aqueous solution of alkarsin, so slowly that no sensible rise of temperature follows, that body is gradually converted into a thick, syrupy liquid, full of crystals of cacodylic acid. On dissolving this mass in water, and distilling, water hav- ing the odor of alkarsin passes over, and afterward an oily liquid, which is the cacodyl oxide. Impure cacodylic acid remains in the retort. Cacodyl oxide, purified by rectification from caustic baryta, is a color- less, oily liquid, having a pungent odor, sparingly soluble in water, and boiling at 120 C. (248 F.), strongly resembling alkarsin in odor, in its relations to solvents, and in the greater number of its reactions; but it neither fumes in the air, nor takes fire at common temperatures : its vapor mixed with air, and heated to about 88 C. (190 F.), explodes with vio- lence. It dissolves in hydrochloric, hydrobromic, and hydriodic acids, forming chloride, bromide, and iodide of cacodyl. Cacodyl dioxide, As 2 (CH 3 ) 4 2 , is the thick syrupy liquid produced by the slow oxidation of cacodyl or of alkarsin. It is decomposed by water, and then yields a distillate of cacodyl monoxide, with a residue of cacodylic acid: 2As 2 (CH 3 ) 4 2 -f H 2 = As 2 (CH 3 ) 4 -f- 2As(CH 3 ) 2 0(OH.) CACODYLIC ACID, As T (CH ? ) 2 0"(OH), also called Alkargcn. This is the ultimate product of the action of oxygen at a low temperature upon caco- dyl or alkarsin in presence of water: it is best prepared by adding mer- curic oxide to alkarsin, covered with a layer of water and artificially cooled, until the mixture loses all odor, and afterward decomposing any mercuric cacodylate that may have been formed, by the cautious addition of more alkarsin. The liquid yields, by evaporation to dryness and solu- tion in alcohol, crystals of cacodylic acid. The sulphide and other com- pounds of cacodyl yield the same substance on exposure to air. Cacodylic acid forms brilliant, colorless, brittle crystals, which have the form of a modified square prism : it is permanent in dry air, but deliquescent in a moist atmosphere. It is not at all poisonous, though it contains more than 50 per cent, of arsenic. It is very soluble in water and in alcohol, but not in ether: the solution has an acid reaction. When mixed with alkalies and evapo^ rated, it leaves a gummy, amorphous mass. With the oxides of silver and mercury, on the other hand, it yields crystallizable compounds. It unites with cacodyl oxide, and forms a variety of combinations with metallic salts. Cacodylic acid is exceedingly stable: it is not affected by red fuming nitric acid, nitromuriatic acid, or even chromic acid in solution: it may be boiled with these substances without the least change. It is deoxidized, however, by phosphorous acid and stannous chloride, yielding cacodyl oxide. Dry hydriodic acid gas decomposes it, with production of water, cacodyl iodide, 766 ARSENIC BASES. and free iodine. With dry hydrochloric acid gas, or with the concen- trated aqueous acid, cacodylic acid unites directly, forming the compound As (CH 3 ) 2 2 H . HC1. But by exposing cacodylic acid for a long time to a stream of hydrochloric acid gas, arsen-monomethyl dichloride is obtained, to- gether with water and methyl chloride : As(CH 3 ) 2 2 H -f 3HC1 = As(CH 3 )Cl 2 + 2H 2 -f CH 3 C1. Phosphorus pentachloride converts cacodylic acid into cacodyl trichloride (p. 764). CACODYL SULPHIDE, As 2 (CH 3 ) 4 S, is formed by adding barium sulphide to crude cacodyl, or by distilling barium sulph-hydrate with cacodyl chloride. It is a transparent liquid which re-tains its fluidity at 40, and boils at a temperature considerably above 100. Cacodyl disulphide, As 2 (CH 3 ) 4 S 2 , is formed by the action of sulphur on ca- codyl or the monosulphide, or by treating cacodylic acid with sulphuretted hydrogen in a vessel externally cooled. It separates from the solution in large rhombic crystals. The alcoholic solution of this compound yields with various metallic solutions, precipitates consisting of salts of sulphoca- codylic acid, As(CH 3 ) 2 S 2 H, analogous to cacodylic acid. The lead-salt, As 2 (CH 3 ) 4 S 4 Pb // , forms small white crystals. Arsenmonomethyl, As(CH 3 ). This radical, which is not known in the separate state, is either bivalent or quadrivalent. Its dichloride, As x// (CH 3 )C1 2 , is produced either by the decomposition of cacodyl trichloride by heat: As(CH 3 ) 2 Cl 3 ^As(CH 3 )Cl 2 -f CH 3 C1; or by the prolonged action of hydrochloric acid on cacodylic acid (p. 765). It is a colorless, heavy, mo- bile liquid, having a strong reducing power ; boils at 133 C. (271 F.). Its vapor exerts a most violent action on the mucous membranes ; on smelling it, the eyes, nose, and whole face swell up, and a peculiar lancinating pain is felt, extending down to the throat. The tetrachloride, As v (CH 3 )Cl 4 , is ob- tained in large crystals by passing chlorine over a mixture of the dichlo- ride and carbon bisulphide cooled to 10. It is very unstable, decom- posing even near into methyl chloride and arsenious chloride, AsCl 3 . There is also a chlorobromide, As(CH 3 )ClBr, and a di-iodide, As(CH 3 )I 2 . The oxide, As(CH 3 )0, obtained by decomposing the dichloride with potas- sium carbonate, forms large cubical crystals, soluble in water, alcohol, and ether, and resolved by distillation with potash into arsenious oxide and cacodyl oxide : 4As(CH 3 )0=:As 2 3 + As 2 (CH 3 ) 4 0. Arsenmethylic Acid, As*(CH s )0"(OH) a , is obtained as a barium-salt by decomposing arsenmethyl dichloride with a slight excess of silver-oxide ; and this salt, decomposed by sulphuric acid, yields the acid which remains on evaporation in the form of a laminated mass. It is bibasic. Arsenmethyl sulphide, As(CH 3 )S, is obtained as a white mass by passing hydrogen sulphide over the dichloride. On comparing the combining or equivalent values of the several arse- nides of methyl, it will be seen that they all unite with elementary bodies and compound radicals, in such proportion as to form compounds in which the arsenic is either trivalent or quinquivalent, the last-mentioned com- pounds being by far the most stable. Thus : Arsenmonomethyl, As(CH 3 ), is bi- and quadri-valent, forming the chlo- rides As'"(CH 8 )Cl 2 and Asv(CH 3 )Cl 4 . Arsendimethyl, As(CH 3 ^ 2 , is mono- and tri-valent, forming the chlorides As'"(CH,) 2 Cl and As*(CH 3 ) 2 Cl s . Arsentrimethyl, As(CIL),, is bivalent only, and forms the chloride As v (CH 3 ) 3 C1 2 . Arsenmethylium, or Tetramethylarsonium, As(CH),, is univalent, form- ing the chloride Asv(CH 3 ) 4 Cl. DIATOMIC PHOSPHORUS AND ARSENIC BASES. 767 Bismethyl or Triethylbismuthine, Bi(C 2 H 5 ) 3 , analogous in composition to triethj&lstibine and triethylarsiae, is formed by the action of ethyl iodide on an alloy of bismuth and potassium, and is extracted from the residue by ether. It is a yellow liquid of specific gravity 1-82, has a most nau- seous odor, and emits vapors which take fire in contact with the air. It unites with oxygen, chlorine, bromine, iodine, and nitric acid. Borethyl, B(C 2 H 5 ) 3 . Dr. Frankland has obtained this compound by treating boric ether with zinc-ethyl: it is a colorless mobile liquid having a pungent odor, irritating the eyes, of sp. gr. 0-696, and boiling at 95 C. (203 F.). Borethyl is insoluble in water, but very slowly decomposed when left in prolonged contact with it. When exposed to the air it is spon- taneously inflamed, burning with a beautiful green and somewhat smoky flame. It combines with ammonia, forming the compound NH 3 .B(C 2 H 5 ) 3 . By the gradual action of dry air, and, ultimately, of dry oxygen, borethyl is converted into an oxygen-compound of the formula B(C 2 H 5 ) 3 2 . DIATOMIC BASES OF THE PHOSPHORUS AND ARSENIC SERIES. The action of ethene bromide on triethylphosphine gives rise to the for- mation of two crystalline bromides, according to the proportions in which the substances are brought in contact. These bromides are C 8 H 19 PBr 2 =r C 6 H, 5 P+C 2 H 4 Br 2 and C, 4 H 34 P 2 Br 2 r= 2C 6 H 15 P-f C 2 H 4 Br 2 . The first of these compounds is the bromide of a phosphonium in which 3 atoms of hydro- gen are replaced by ethyl and one atom by the univalent radical bromethyl, C 2 H 4 Br, thus [(C 2 H 4 Br)(C 2 H 5 ) 3 P]Br. Half the bromine in this salt is un- affected by the action of silver-salts; it may accordingly be designated as bromide of bromethyl-tricthyl-phosphonium. Numerous salts of this compound are known, but the free base cannot be obtained, since silver oxide elimi- nates the latent bromine, giving rise to the formation of a base containing [(C 2 H 5 0)(C 2 H 5 ) 3 P]OH. The second compound is the dibromide of ethene- hexethyl-diphosphonium, [(C 2 H 4 )"(C 2 H ? ) 6 P 2 ]"Br 2 . This radical, which cor- responds to 2 equivalents of ammonium, 2NH 4 = N 2 H g , forms a series of very stable and beautiful salts, especially an iodide which is difficultly soluble in water. In all these salts the base, which is composed of 1 mole- cule of ethene, 6 molecules of ethyl, and 2 atoms of phosphorus, is united with 2 molecules of univalent-acid radical; the platinum-salt contains (C 2 H 4 ) // (C 2 H 5 ) 6 P 2 Br 2 . Pt iv Cl 4 . The free, very caustic, and stable base has the composition [(C 2 H 4 )"(C 2 EI 5 ) 6 P 2 ]"(OH) 2 . The dibromide of ethene-hexethyl-diphosphonium may be formed by the action of triethylphosphine upon the brominated bromide which has been mentioned as the first product of the action of ethene dibromide upon tri- ethylphosphine : C 3 H 19 PBr 2 +C 6 H 15 P=C, 4 H 34 P 2 Br 2 . If the triethylphosphine be replaced in this process by ammonia or by monamines in general, or by monarsines, an almost unlimited series of diatomic salts may be formed, in which phosphorus and nitrogen or phosphorus and arsenic are associated. Thus the action of ammonia, of ethylamine, and of triethylarsine, gives rise respectively to the fpllowing compounds ; Dibromide of Ethene-triethyl- 1 ,, y , (r H >, H PN y/Br phosphammonium . . / A^J (b^gj^^ 15r 2 . Dibromide of Ethene-tetrethyl) rfr w v/ , p . w pxn//iu. phosphammonium . . [( C 2 H 4)"(C 2 H 6 ) 4 H 2 PN]"Br 2 . Dibromide of Ethene-hexethyl- phospharsonium . . 768 ZINC-ETHYL. Treated with silver oxide, these bromides yield the very caustic diatomic bases [(C ! H 4 )"(C 2 H 6 ) 3 H 3 PN]-(OH), The arsenic bases, when submitted to the action of ethene dibromide, give rise to perfectly analogous results. The limits of this Manual will not permit us to examine these remarkable compounds in detail. IV. Compounds of Alcohol- radicals with Bivalent and Quadrivalent Metals and Metalloids. The bodies of this group which contain bivalent elements, such as zinc, are saturated compounds, not capable of uniting directly with chlorine, oxy- gen, &c. ; those which contain quadrivalent metals, like tin, are saturated or unsaturated accordingly as they contain four or only two equivalents of alcohol-radicals. All these compounds are frequently designated as organo-metallic bodies, a term likewise including the compounds of alcohol-radicals with arsenic, antimony, and bismuth. We shall describe chiefly the ethyl compounds, to which the methyl and amyl compounds are strictly analogous. Zinc-ethyl or Zinc ethide, Zn /x (C 2 H 6 ) 2 . This compound, discovered by Frankland, is formed, together with zinc-iodide, when ethyl iodide is heated with metallic zinc in a sealed glass tube, or, for larger quantities, in a strong and well-closed copper cylinder : 2C 2 H 5 I -(- Zn 2 = ZnI 2 -j- Zn(C 2 H 5 ) 2 . The two products remain combined together in the form of a white crystal- line mass, from which the zinc-ethyl may be separated by distillation in an atmosphere of hydrogen. It is a mobile and very volatile liquid, having a disagreeable odor, taking fire instantly on coming in contact with the air, and diffusing white fumes of zinc oxide. Water decomposes it violently, with formation of zinc hydrate, and evolution of ethane or ethyl-hydride : Zn(C 2 Hg) 2 4- 2H 2 = ZnH 2 2 -f C 2 H 6 . When gradually mixed with dry oxygen, it passes through two stages of oxidation, yielding first zinc ethyl- ethylate, Zn"/S?k, and finally zinc ethylate, Zn"(OC 2 H 6 ) 2 . With I UL-jjllg iodine and other halogens, the reaction also takes place by two stages, but consists in the successive substitution of the halogen for the ethyl ; thus : Z n (C 2 H 5 ) 2 + I 2 = C 2 H 5 I + Zn(C 2 H 5 )I, and Zn(C 2 H 6 )I -f I 2 = C 2 H 6 I + ZnI 2 . Zinc ethide has become a very important reagent in organic chemistry, serving to effect the substitution of the positive radical ethyl for chlorine, iodine, and other negative elements, and thus enabling us to build up carbon-compounds from others lower in the scale. Many examples of these reactions have already been given in the chapters on alcohols and acids. In like manner it serves for the preparation of many other or- gano-metallic bodies. The following equations exhibit the mode of forma- tion of mercuric methide, stannic ethide, and triethylarsine by means of zinc ethide : ALUMINIUM METHIDE. 769 Zn"(C 2 H 5 ) 2 + Hg"Cl 2 = ZnCl 2 + Hg"(C 2 H 5 ) 2 2Zn"(C 2 H 5 ) 3 -f- Sn*Cl 4 = 2ZnCl 2 + Sn*(C 2 H 5 ) 4 3Zn"(C 2 H 5 ) 2 -f- 2As"'Cl 3 = 3ZnCl 2 + 2As'"(C 2 H 6 ) 3 . Zinc Methide, Zn'^CH^), is analogous in its reactions to zinc ethide, but is still more volatile and inflammable. Potassium Ethide, C 2 H 6 K, and Sodium Ethide, C 2 H 5 Na, are not known in the separate state, but only in combination with zinc-ethyl. These mixed compounds are produced by the action of potassium on sodium zinc-ethyl; thus: 3Zn(C 2 H 5 ) 2 + Na 2 = Zn -f 2(C 2 H 5 ) 3 These compounds and their homologues, discovered by Wanklyn, have also played an important part in chemical synthesis. The production of the fatty acids by the combination of carbon dioxide with sodium ethide, &c. has been frequently mentioned. Mercuric Ethide, Hg // (C 2 H 5 ) 2 . This compound is formed, as already ob- served, by the action of mercuric chloride on zinc ethide, but it is more easily prepared by the action of sodium-amalgam on ethyl iodide in presence of acetic ether : 2C 2 H 5 I + Na 2 + Hg = 2NaI + Hg(C 2 H 5 ) 2 . The acetic ether takes no part in the reaction ; nevertheless its presence appears to be essential. Mercuric ethide is a transparent, colorless liquid, boiling at 159. It burns with a smoky flame, giving off a large quantity of mercurial vapor. Chlorine, bromine, and iodine remove one equivalent of ethyl from this com- pound, and take its place, forming mercuric chlorethide, &c. ; thus : Hg(C 2 H 6 ) 2 + C1 2 = C 2 H 5 C1 + Hg(C 2 H 5 )Cl. A similar action is exerted by acids, e. g., by hydrobromic acid, the pro- ducts being, ethane and mercuric bromethide: C 2 H 6 + Hg(C 2 H 5 )Br. The chlorethide or bromethide is converted by water into mercuric ethyl- "hydrate, Hg x/ (C 2 H 6 )(OH). Mercuric ethide serves for the preparation of several other organo-metallic bodies. Aluminium Methide, A1 /// (CH 3 ) 3 , or A1 2 (CH 3 ) 6 . This compound, dis- covered by Buckton and Odling,* is formed by heating mercuric ethide with aluminium. It is a mobile liquid, which crystallizes at a little above 0, and boils at 130 C. (266 F.). At and above 220 C. (428 F.) the den- sity of its vapor, compared with that of air, is 2-8, which is near to the theoretical density calculated for the formula A1(C 2 H 5 ) 3 , namely, 2*5. This seems to show that the true formula of the compound is A1(C 2 H 6 ) 3 , and not A1 2 (C 2 H 5 ) 6 , and, consequently, that aluminium is a triad, not a tetrad (p. 333). At temperatures near the boiling point, however, the vapor-density becomes 4-4, approximating to the theoretical density calculated for the formula A1 2 (C 2 H 6 ) 6 . Aluminium ethide resembles the methyl compound. It boils at 194 C. (381 F.), and its vapor likewise exhibits, at temperatures considerably above its boiling point, a density nearly equal to that required by the for- mula A1(C 3 H 5 ) 3 , for a two-volume condensation. -J- * Proceedings of the Royal Society, xiv. 19. f The vapor-density of aluminium chloride, as determined by Deville, agrees with that re- quired by the formula A1 2 C1 C ; but as this compound has a very high boiling point, it was per- haps not heated sufficiently to convert it into a perfect gas (see page 461). 65 770 PLUMBIC ETHIDE. Ethyl Compounds of Tin. Tin forms two ethyl compounds, Sn // (C 2 H 5 ) 2 and Sn iv (C 2 H 5 ) 4 , analogous to stannous and stannic chloride ; also a stan- noso-stannous ethide, Sn 2 (C 2 H 5 ) 6 , analogous in constitution to ethane, C 2 H 6 . Stannic ethide is a saturated compound, but the other two are unsaturated bodies, capable of uniting with chlorine, bromine, oxygen, and acid radi- cals, and being thereby converted into compounds of the stannic type. STANNOUS ETHIDE, Sn // (C 2 H 5 ) 2 . When ethyl iodide and tinfoil are heated together in a sealed glass tube to about 150 or 180 C. (302-356 F.), stannous iodethide, Sn iT (C 2 H 5 ) 2 I 2 , is produced, crystallizing in colorless needles. The same compound is obtained when tin and ethyl iodide are exposed to the rays of the sun concentrated by a parabolic reflector. The reaction is considerably facilitated if the tin be alloyed by one-tenth of its weight of sodium. This iodide is decomposed by sodium or zinc, which abstracts the iodine and leaves stannous ethide in the form of a thick, oily liquid, insoluble in water, and having the sp. gr. 1-55. Stannous ethide combines directly with 2 atoms of chlorine, iodine, and bromine, forming stannic chlorethide, Sn' T (C 2 H 5 ) 2 Cl 2 , &c, Exposed to the air, it absorbs oxy- gen and is converted into stannous oxethide, Sn iT (C 2 H 6 ) 2 0, a whitish, taste- less, inodorous powder, which, when treated with oxygen-acids, yields well crystallized stannous salts, such as Sn iv (C 2 H 6 ) 2 (N0 3 ) 2 , Sn iv (C 2 H 5 ) 2 S0 4 , &c. STANNOSO-STANNIC ETHIDE, Sn 2 (C 2 H 5 ) 6 , is always produced in small quan- tity when stannous ethide is prepared by the methods above mentioned. It is really obtained in the free state by digesting an alloy of 1 part of sodium and 5 parts of tin with ethyl iodide, exhausting the mass with ether, evaporating the ethereal solution, and exhausting the residue with alcohol. The stannoso-stannic ethide, being insoluble in that liquid, then remains behind. It is a yellow oil, boiling at 380 C. (356 F.), combining directly with chlorine, bromine, and iodine to form two molecules of a stannic com- pound ; e. ff. : Sn 2 (C 2 H 5 )6 + C1 2 = 2Sn*(C 2 H 5 ) 3 Cl; Stannic chloro-triethide. also with oxygen, forming distannic oxy-hexethide, Sn iv 2 (C 2 H 5 ) 6 0. This oxide is, however, best obtained by distilling stannous oxy-diethide, Sn iT ( C 2 H s)2 (above described), with potash. It is an oily liquid, soluble in alcohol, ether, and water ; the aqueous solution has a strong alkaline reac- tion. It is easily acted upon by oxygen-acids, yielding the corresponding sulphate, Sn 2 (C 2 H 5 ) 6 S0 4 , &o. STANNIC ETHIDE, Sn*(C 2 H 5 ) 4 , is produced by the action of zinc ethide on stannic chloride ; also by the distillation of stannous ethide, 2Sn(C 2 H 5 ) 2 = Sn -(- Sn(C 2 H 5 ) 4 . It is a colorless, nearly odorless liquid, of sp. gr. 1-19, boiling at 181 C. (358 F.), and very inflammable, burning with a highly luminous flame. When treated with chlorine, bromine, &c., or with acids, it forms substitution-products : thus, with iodine, it splits up into ethyl iodide and stannic iodotriethide : Sn(C 2 H 5 ) 4 + I 2 = C 2 H 5 I + Sn(C 2 H 5 ) 3 I. With strong hydrochloric acid, it yields ethane and stannic chlorotriethide, Sn (C 2 H 5 ) 4 + HC1 = C 2 H 6 + Sn(C 2 H 5 ) 3 Cl. Plumbic Ethide, Pb(C 2 H 5 ) 4 , is produced by the action of plumbic chloride on zinc ethide : 2Zn(C 2 H 5 ) 2 + 2PbCl 2 = 2ZnCl 2 + Pb -f Pb(C 2 H 6 ) 4 . It is a colorless limpid liquid, soluble in ether but not in water. It is not acted upon by oxygen at ordinary temperatures ; but chlorine, bromine, TELLURETHYL. 771 and iodine act violently upon it, in the same manner as on stannic ethide, forming plumbic chloro-triethide, Pb(C 2 H 6 ) 3 Cl, &c. Plumbic ethide is interesting, as affording a proof that lead is really a tetrad (p. 398.) Tellurethyl, Te"(C 2 H 5 ) 2 , is obtained by distilling potassium telluride with potassium ethylsulphate. It is a heavy, oily liquid of yellowish-red color, very inflammable, and having a most insufferable odor. It acts as a bivalent radical, uniting directly with chlorine, bromine, oxygen, &c., to form compounds in which the tellurium enters as a tetrad, e. g., Te iv (C 2 H 6 ) 2 C1 2 , Te T (C 2 H 5 ) 3 0", &c. The nitrate Te(C 2 H 5 ) 2 (N0 3 ) 2 , is obtained by treat- ing tellethuryl with nitric acid ; the other salts by double decomposition ; the chloride, for example, settles down, as a heavy oil, on adding hydro- chloric acid to a solution of the nitrate. The oxide is best prepared by treating the chloride with water and silver oxide. It dissolves in water, forming a slightly alkaline liquid. Telluro-methyl, Te(CH 3 ) 2 , and tdluramyl, Te(C 6 H u ) 2 , are similar in their properties to tellurethyl. The corresponding selenium compounds have like- wise been obtained. There are also compounds of sulphur with alcohol-radicals in which the sulphur plays the part of a quadrivalent element, viz., the triethylsulphurous compounds, already described (p. 530). Sulphurous iodo-1riethide, Si v (C 2 H 6 > 3 I, for example, is produced by combination of ethyl monosulphide, S(C 2 H 5 ) 2 , with ethyl iodide, C 2 H 5 I. Other compounds, in which the sulphur may be regarded as a hexad, are obtained by combining ethyl sulphide and ethene sulphide with ethene dibromide: thus sulphuric diethene-dibromide, S iv (C 2 H 4 ) // 2 Br. J , is formed by combination of S(C 2 H 4 ) with C 2 H 4 Br 2 , and sulphuric diethyl-ethene-dibromide, S vi (C 2 H 5 ) 2 (C 2 H 4 )''Br 2 , in like manner by combination of S(C 2 H 6 ) 2 with C 2 H 4 Br a . AMIDES. WE have had frequent occasion to speak of these compounds, as derived from ammonium-salts by abstraction of water, or from acids by substitu- tion of amidogen, NH 2 , for hydroxyl, OH, or from one or more molecules of ammonia by substitution of acid-radicals for hydrogen. They are divided (like amines) into monamides, diamides, and triamides, each of which groups is further subdivided into primary, secondary, and tertiary amides, accordingly as one-third, two-thirds, or the whole of the hydrogen is replaced by acid-radicals. If the hydrogen is replaced partly by acid- radicals, and partly by alcohol-radicals, the compound is called an alkala- mide\ for example, ethylacetamide, NH(C 2 H 5 )(C 2 H 3 0) ; ethyldiacetamide N(C 2 H 5 )(C 2 H 3 0) 2 . AMIDES DERIVED FROM MONATOMIC ACIDS. A monatomic acid yields but one primary amide, which may be formed : 1. From its ammonium-salt by abstraction of a molecule of water, under the influence of heat ; thus : C 2 H 3 (NH 4 )0 2 - H 2 = C 2 H 5 NO = | ' = Ammonium Acetamide. CONH 2 acetate. These amides are also produced: 2. By the action of ammonia on acid chlorides ; e. g. : C 2 H 3 OC1 4- NH 3 = HC1 -f NH 2 (C 2 H 3 0). This method is especially adapted to the preparation of those amides which are insoluble in water. 3. By the action of ammonia on compound ethers : C 2 H 3 O.OC 2 H 5 4- NH 3 = HOC 2 H 5 + NH 2 (C 2 H 3 0). Ethyl acetate. Ethyl alcohol. Acetamide. Acetamide, which may be regarded as a type of primary monamides, is a white crystalline solid melting at 78 C. (172 P.), and boiling at 221 or 222 C. (480 F.). When heated with acids or with alkalies, it takes up water and is converted into acetic acid and ammonia. Distilled with phos- phoric oxide, it gives up water and is converted into acetonitrile or methyl cyanide, C 2 H 5 N0 2 H 2 C 2 H 3 N. Heated in a stream of dry hydrochlo- ric acid, it yields diacetamide, together with other products : 2NH 2 (C 2 H 3 0) + HC1 = NH 4 C1 -f NH(C 2 H 3 0) 2 . Acetamide acts both as a base and as an acid, combining with hydrochloric and with nitric acid, and likewise forming salts in which one atom of its hydrogen is replaced by a metal : silver-acetamide, C 2 H 4 NAgO, for example, is obtained in crystalline scales by saturating an aqueous solution of ace- tamide with silver oxide. 772 AMIDES. 773 Benzamide, C 7 H 7 NO = NH 2 (C r H 6 0), is produced by methods similar to those above given for the formation of acetamide ; also by oxidizing hip- puric acid with lead dioxide : C 9 H 9 N0 8 + 2 = C 7 H 7 NC1 -f 2C0 2 + H 2 Benzamide is a crystalline substance nearly insoluble in cold water, easily soluble in boiling water, also in alcohol and ether; it melts at 1 15 C. (239 F. ), and volatilizes undecomposed between 286 and 290 C. (547-554 F.). Its reactions are for the most part similar to those of acetamide. Heated with benzoic oxide or chloride, it yields benzonitrile and benzoic acid : C 7 H 7 NO + (C 7 H 5 0),0 = C 7 H ? N + 2C 7 H 6 2 Benzamide. Benzoic oxide. Benzonitrile. Benzoic acid. C 7 H 7 NO -f C ? H 5 OC1 = C 7 HgN -f C 7 H 6 2 4-HC1 Benzamide. Benzoic chloride. Benzonitrile. Benzoic acid. Heated with fuming hydrochloric acid, it forms hydrochloride of benz- amide, C 7 H 7 NO . HC1, which separates on cooling in long aggregated prisms. Its aqueous solution dissolves mercuric oxide, forming benzomercuramide, N 2 H 2 (C 7 H 5 0) 2 Hg". Secondary monamides are those in which two atoms of hydrogen in a mole- cule of ammonia are replaced by two univalent or one bivalent acid-radi- cal, or by one acid-radical and one alcohol-radical. Those containing only univalent radicals are formed by the action of dry hydrochloric acid gaa on primary monamides at a high temperature ; e. g. : 2NH 2 (C 2 H 3 0) -f HC1 = NH 4 C1 + NH(C 2 H 3 0) 2 Acetamide. Diacetamide. Those containing bivalent acid-radicals are called imides ; e. g , succinimides, NH(C 4 H 4 2 )". They are derived from bibasic acids, and will be noticed farther on. Secondary monamides (alkalamides} containing an acid-radical and an alcohol-radical, are formed by processes similar to those .above given for .the formation of the primary monamides, substituting amines for ammo- nia; thus: NH 2 (C 2 H 6 ) -f C 2 H 3 OC1 = HC1 + NH(C 2 H 5 )(C 2 H 3 0) Ethylamine. Acetic Ethyl-acetamide. chloride. NH 2 (C 2 H 5 ) -f- C 2 H S 0(OC 2 H 6 ) = HOC 2 H 5 -f NH(C 2 H 6 )(C 2 H 3 0) Ethylamine. Ethyl acetate. Alcohol. Ethyl-acetamide. They are crystalline, and for the most part do not combine with acids. When boiled with acids or alkalies, they take up water and regenerate their acid and primary amine ; thus : NH(C 6 H 5 )(C 2 H 3 0) + HOH = C 2 H 3 0(OH) + NH 2 (C 6 H 6 ) Phenyl-acetamide. Acetic acid. Aniline. Tertiary monamides are those in which the whole of the hydrogen in one molecule of ammonia is replaced by acid-radicals or by acid- and alcohol- radicals. Those of the latter kind, called tertiary alkalamides, are produced by the action of acid chlorides on secondary alkalamides : NH(C 6 H 5 )(C 7 H 6 0) + C 7 H 5 OC1 = HC1 -f N(C 6 H 5 )(C 7 H 5 0) 2 Phenyl-benzamide. Bonzoyl Phenyl-dibenzamide. chloride. 65* 774: AMIDES. Or by the action of monatomic acid oxides on cyanic ethers ; e. g. : (C 2 H 3 0) 2 + N(CO)"(C 2 H 6 ) = C0 2 + N(C 2 H 5 )(C 2 H 3 0) 2 Acetic oxide. Ethyl cyanate. Ethyl-diacetamide. AMIDES DERIVED FROM DIATOMIC AND MONOBASIC ACIDS. Acids of this group may give rise to two monamides, both formed by substitution of one equivalent of NH 2 for OH, and therefore having the same composition. They are however isomeric, not identical, the one formed by replacement of the alcoholic hydroxyl being acid, while the other, formed by replacement of the basic hydroxyl, is neutral. The acid amides thus formed are called amic acids. Glycollic acid, for example, yields glycollamic acid and glycollamide, both containing C 2 H 6 N0 2 : CH 2 OH CH 2 NH 2 CH 2 OH COOH COOH CONH 2 Glycollic Glycollamic Glycollamide. acid. acid. These amic acids and amides are sometimes represented as derived from a molecule of ammonia and a molecule of water, bound together by the sub- stitution of a diatomic acid-radical for two atoms of hydrogen; thus: Type. Glycollamic acid. The amic acids of this group are identical with the amidated acids de- rived from the corresponding monatomic acids, C n H 2n 2 , by substitution of amidogen for hydrogen ; thus glycollamic acid is identical with amidacetic acid ; lactamic with amidopropionic ; leucamic with amidocaproic acid; for example : CH 3 CH 2 (NH 2 ) CH 2 (OH) COOH COOH COOH Acetic acid. Amidacetic or Glycollic acid. Glycollamic acid. These amic acids are formed, as already observed, by the action of am- monia on the monochlorinated or monobrominated derivatives of the fatty acids; the corresponding neutral amides are produced by the action of ammonia, in the gaseous state or in alcoholic solution, on the corresponding oxides or anhydrides, or on the ethylic ethers of glycollic and lactic acids ; thus: C 3 H,0 2 + NH S = C 3 H 7 N0 2 Lactide. Lactamide. C 2 H 4 (OH) C 2 H 4 OH 4- NH 2 H = HOC 2 H 6 + I CO(OC 2 H 5 ) CONH 2 Ethyl lactate. Alcohol. Lactamide. Leucamide, the neutral ether of leucic acid, is not known. The amic acids of this series possess basic as well as acid properties, and are therefore often designated by names ending in ine, the ordinary ter- AMIDES. 775 ruination for organic bases, glygollamic acid being designated as glycocine, lactamic acid as alanine, leucamic acid as leucine (pp. 614, 615, 620). Amidobenzoic acid, C 7 H 6 (NH 2 )0 2 , or C 6 H 4 (NH ? ) . C0 2 H, produced from nitro-benzoic acid, C 7 H 4 (N0 2 )0 2 , by the action of hydrogen sulphide, may also be regarded as oxy-benzamic acid, derived from oxy-benzoic acid, C 6 H 4 (OH) . C0 2 H, by substitution of NH 2 for OH. Diamidobenzoic acid, C 7 H 4 (NH 2 ) 2 2 , formed in like manner from dinitro- benzoic acid, may also be viewed as dioxybenzamic acid, derived from a hy- pothetical dioxybenzoic acid, C 6 H 3 (OH) 2 . C0 2 H ; but according to the mode of formation of these acids, they are more conveniently regarded as deriva- tives of benzoic acid. Similar remarks apply to the amidated acids derived from the homologues of benzoic acid. AMIDES DERIVED FROM DIATOMIC AND BIBASIC ACIDS. Each acid of this group may give rise to three amides: viz., 1. An odd, amide, or amic acid, formed from the acid ammonium-salt by abstraction of one molecule of water. 2. A neutral monamide or imide, formed from the acid ammonium-salt by abstraction of two molecules of water. 3. A neu- tral diainide, derived from the neutral ammonium-salt by abstraction of two molecules of water. Thus from succinic acid, (C 4 H 4 2 ) X/ (OH) 2 are derived : H 2 C 4 H 5 (NH 4 )0 4 H 2 = C 4 H 7 N0 3 = (C 4 H 4 2 )"(NH a )(OH) = (C 4 H 4 O a )" Acid ammonium Succinamic H succinate. acid. CA(NH 4 )0 4 -2H 2 0=C 4 H 5 N0 2 =(C 4 H 4 2 )"(NH)" = (C 4 H 4 O f )" \ N Acid salt. Succinimide. H / C 4 H 4 (NH 4 ) 2 4 - 2H 1 0=C 4 H 8 N 1 0,=(C ,H 4 2 )^(NH 2 ) 2 = (C 4 H 4 0,)" Neutral salt. Succinamide. H 4 The amic acids of this group are produced: 1. By the action of heat on the acid ammonium-salts of the correspond- ing acids. 2. By the action of aqueous ammonia on the neutral ethers of bibasic acids ; e. g. : (C 2 2 )"(OC 2 H 5 ) 2 + NH 3 -f H(OH) = 2H(OC 2 H 6 ) -f (C 2 2 )"(NH 2 )(OH) Ethyl oxalate. Alcohol. Oxamic acid. 3. By boiling imides with ammonia, under which circumstances they take up a molecule of water and are converted into amic acids ; thus suc- cinimide, C 4 H 5 N0 2 , with H 2 forms succinamic acid, C 4 H 7 N0 3 . The typic or extra-radical hydrogen in these amides may also be replaced by alcoholic or by acid radicals, thereby producing alkalamides, secondary and tertiary diamides, &c. The mode of producing such compounds may be understood from the following equations : (C 2 O a )"(ONH 8 CH,)OH H 2 = (C a O a )"NH(CH s ) . (OH) Acid methylamino- Methyloxamic acid, nium oxalate. (C 4 H 4 S )"0 + NH 2 (C 6 H 5 ) = 2H 2 .+ N(C 8 H 6 )(C 4 H 4 8 )" Succinic Aniline. Phenylsuccin- oxide. imide. (CA)"(OC,H 6 ) S + 2NII 2 (CH 3 ) = 2H(OC 2 H 5 ) + N,H,(C a 2 )"(CIT 3 ) a Ethyl oxalate. Methylamine. Ethyl alcohol. Dimethyl-oxamidc. 776 AMIDES. (CO)C1 2 + 2NH 2 (C 6 H 5 ) = 2HC1 + N 2 H 2 (CO)"(C 6 H 6 ), Carbonyl Aniline. Diphenyl-carbonide. chloride. 2N(C 4 H 4 2 )"Ag + (C 4 H 4 2 )"C1 2 = 2AgCl + N 2 (C 4 H 4 2 )" 3 Argent osuccin- Succinyl Tnsuccmamide. imide. chloride. Amides of Carbamic Acid. Carbonic acid, (CO)"(NH 2 )(OH), is not known in the free state, that is, as a hydrogen-salt, but its ammonium-salt, (CO)" (NH 2 )(ONH 4 ), is produced, as already noticed (p. 314), by the direct com- bination of carbon dioxide and ammonia-gas. This salt is easily obtained pure and in large quantity by passing the two gases, both perfectly dry, into cold absolute alcohol, separating the copious crystalline precipitate by filtration from the greater part of the liquid, and heating it with absolute alcohol in a sealed tube to 100, or above.* The liquid, on cooling, de- posits ammonium carbamate in large crystalline laminae. This salt, if per- fectly dried over oil of vitriol, and then heated in a sealed tube to 130-140 C. (266-284 F.), splits up into ammonium carbonate and urea, one mole- cule of it giving up a molecule of water to another: 2CN 2 Hg0 2 = CN 2 H 4 -f CN 2 H 8 3 Ammonium Urea. Ammonium carbamate. carbonate. Hence Kolbe concludes that urea is the amide of carbamic acid, not the amide of carbonic acid ; but it is not easy to see in what the supposed dif- ference consists; for carbonic acid being (CO)"(OH)(OH), and carbamic acid, (CO) // (NH 2 )(OH), the amide of the latter must be identical with the diamide of the former. It appears, also, from the observations of Basa- roff, that ordinary commercial ammonium carbonate, when treated in the manner just described, likewise yields urea. On the other hand, the ex- periments of Wanklyn and Gamgee, already quoted (p. 722), seem to show that urea is essentially different from carbamide, f CARBAMIC ETHERS. Carbamic acid forms acid and neutral ethers, ac- cordingly as an atom of hydrogen in the group NH 2 or OH is replaced by an alcohol-radical. Ethylcarbamic acid, (CO)" . NH(C 2 H 6 ) . OH, is not known in the free state, but its ethylammonium-salt, (CO)" . NH(C 2 H 5 ) . ONH 3 (C 2 H 6 ), is pro- duced, as a snow-white powder, by passing carbon dioxide into anhydrous ethylamine cooled by a freezing mixture. Its aqueous solution, like that of ammonium carbamate, does not precipitate barium chloride unless aided by heat. The methylammonium-salt of methylcarbamic acid is obtained in a similar manner. Phenylcarbamic acid, (CO)" . NH(C 6 H 5 ) . OH, also called carbanilic and anthranilic acid, isomeric with amidobenzoic acid, is obtained by boiling indigo with potash and manganese dioxide. It is a crystalline body, soluble in water, and converted by nitrous acid into salicylic (phenyl-carbonic) acid, with evolution of nitrogen : (CO)". NH(C 6 H 5 ) . OH + N0 2 H = (CO)". OC 6 H 6 . OH + H 2 + N 2 . Phenyl-carbamic acid. Phenyl-carbonic acid. The neutral carbamic ethers are called urethanes. Ethyl carbamate, (CO)". NH 2 . OC 2 H 5 , called simply urethane, is formed by leaving ethyl car- * KoTbe and Basarnff, Chem. Soc. Journal [2], vi 194 f Basaroff's experiments have not yet been published in detail, and there is no proof given in the paper above referred to, that the compound obtained by the dehydration of ammonium carbamate was really urea and not carbamide. AMIDES. 777 bonate in contact with aqueous ammonia ; and by the action of ammonia on ethyl chlorocarbonate (alcohol saturated with carbonyl chloride) : (CO)"(OC 2 H 5 )C1 + NH 3 = HC1 + (CO)"(NH 2 )(OC 2 H.) It forms colorless crystals easily soluble in water. Methyl carbamate, methy- lie urethane or urethylane, and amyl carbamate or amylic urethane, are obtained in like manner. Carbamic acid in which the whole of the oxygen is replaced by sulphur, constitutes sulpho-carbamic acid, (CS) // (NH 2 )(SH). There is also an oxy- sulpho-carbamic acid, (CS) // (NH 2 )(OH), the ethylic ether of which is xan- thamide, (CS)"(NH 2 )(OC 2 H 6 ) (p. 651). CARBIMIDE, (CO) // (NH) // or N< ^JT ' , is the same as cyanic acid; and many of the reactions of cyanic acid are most naturally represented by the formula just given, especially its conversion into carbon dioxide and ammonia under the influence of acids or alkalies : NH(CO)" + H 2 = NH 3 + (C0)"0, and the corresponding formation of ethylamine and its homologues by dis- tilling cyanic ethers with potash. CARBAMIDE, CN 2 H 4 or N 2 (CO)"H 4 . This compound is produced by the action of ammonia-gas on carbonyl chloride: COC1 2 + 2NH 3 = 2HC1 + N 2 COH 4 ; also by the action of ammonia on ethyl carbonate, and by the decomposi- tion of oxamide at a red heat : C 2 2 N 2 H 4 = CON 2 H 4 -f- CO. It bears a very close resemblance to urea ; the only difference indeed yet observed between the two compounds, is in the products which they yield when oxidized by potassium permanganate in presence of free alkali (p. 722). Amides of Oxalic Acid. Oxamic add, C 2 NH 3 3 = (C 2 2 )"(NH 2 )(OH), is produced by heating acid ammonium oxalate to about 230 ; also as an ammonium-salt by boiling oxamide with aqueous ammonia : C 2 H 4 N 2 2 -f- H 2 = C 2 H 2 (NH 4 )N0 3 . Oxamic acid is a white crystalline powder, spar- ingly soluble in cold water, still less soluble in alcohol and ether. It is monobasic, and forms numerous crystalline metallic salts. Oxamic ethers may be formed by substitution of ethyl-radicals for hydro- gen, either in the group NH 2 or in the group OH of oxamic acid, the re- sulting ethers being acid in the former case, neutral in the latter. The neutral ethers, also called oxamethanes (p. 660), are formed by the action of ammonia, in the gaseous state or in alcoholic solution, on neutral oxalic ethers; thus: (C 2 2 )"(OC 2 H 5 ) 2 + NH 3 = HOC 2 H 5 + (C 2 2 )"(NH 2 )(OC 2 H 5 ) Ethyl oxalate. Alcohol. Ethyl oxamate. They are crystalline bodies soluble in alcohol, decomposed by boiling water, yielding ammonium oxalate and the corresponding alcohol. The acid ethers of oxamic acid, containing one equivalent of alcohol- radical, are produced by dehydration of the acid oxalates of the corre- sponding amines ; thus : (C 2 2 )"(ONH 3 C 2 H 5 )(OH) - OH, = (C 2 2 )"rNH(C 2 H 5 )](OH) Acid ethylammonium Ethyloxamic acid, oxalate. 778 AMIDES. Methyloxamic and phenyloxamic acids are also known. These acid ethers are metameric with the neutral oxamic ethers containing the same alcohol- radicals. The replacement of both the hydrogen-atoms in the group NH 2 in oxamic acid, would also yield monobasic acid ethers ; none of these are, however, known in the free state, but the ethylic ethers of dimethyl- and diethyl- oxamic acids have been obtained; e.g., ethylic dimethyl-oxamate, (C 2 0,) // N (CH 3 ) 2 (OC 2 H 5 ). The imide of oxalic acid is not known. OXAMIDE, N 2 (C 2 2 ) // H 4 . This compound is produced by the action of heat on neutral ammonium oxalate (p. 659), but is more advantageously prepared by the action of ammonia on neutral ethyl oxalate. It is also formed in several reactions from cyanogen and cyanides: an aqueous solu- tion of hydrocyanic acid, mixed with hydrogen dioxide, yields a crystal- line deposit of oxamide : 2CNH -f H 2 2 = C 2 N 2 H 4 2 . Oxamide is a white, light, tasteless powder, insoluble in cold water, slightly soluble in boiling water, insoluble in alcohol. Heated in an open tube, it volatilizes and forms a crystalline sublimate ; but its vapor, passed through a red-hot tube, is completely resolved into carbon monoxide, am- monium carbonate, hydrocyanic acid, and urea (or carbamide) : 2C 2 N 2 H 4 2 = CO + C0 2 -f NH 3 + CNH + CN 2 H 4 0. Dilute mineral acids decompose it, yielding an ammonium-salt and free oxalic acid ; e. g. : C 2 N 2 H 4 2 + S0 4 H 2 + 2H 2 = S0 4 (NH 4 ) 2 + C 2 H 2 4 . Dimethyloxamide, N 2 (C 2 2 ) // H 2 (CH 3 ) 2 , is produced by the dry distillation of methylammonium oxalate: C 2 (CH 6 N) 2 4 2H 2 = C 2 N 2 H 2 (CH 3 ) 2 2 . Diethyloxamide, diamyloxamide, diphenyloxamide, and dinaphthyloxamide, are obtained in a similar manner. AMIDES DERIVED FROM ACIDS OF HIGHER ATOMICITY. Our knowledge of these amides is somewhat limited : we shall notice only those derived from malic and from citric acid. Malic acid, (C 4 H 3 2 ) /// (OH) 3 , which is triatomic and bibasic, forms an acid amide and a neutral amide : fOH fOH fOH (C 4 H 8 2 ) //X I OH (C 4 H,0 S )'" I NH 2 (C 4 H 8 S )'" j NH, Malic acid. Malamic acid. Malamide. Malamide is deposited in small crystals, when ammonia-gas is passed into an alcoholic solution of ethyl malate : R q-r 7 on bonates, phosphates, and sulphates . / Calcium and magnesium carbonates ; \ phosphates of calcium, magnesium, I 2-10 1-42 and iron ; ferric oxide . . . J Loss 2-40 2-59 1000-00 1000-00 * Ann. Chim. Phys. xlviii. 320. URINE. 807 In healthy individuals of different sexes these proportions are found to vary: the fibrin and coloring matter are usually more abundant in the male than in the female : in disease, variations of a far wider extent are often apparent. It appears singular that the red corpuscles, which are so easily dissolved by water, should remain uninjured in the fluid portion of the blood. This seems partly due to the presence of saline matter, and partly to that of al- bumin, the corpuscles being alike insoluble in a strong solution of salt and in a highly albuminous liquid. In the blood the limit of dilution within which the corpuscles retain their integrity appears to be nearly reached, for when water is added they immediately become attacked. URINE. The urine is the great channel by which the azotized matter of those portions of the body which have been taken up by the absorbents, and by which the excess of nitrogenous food is conveyed away and rejected from the system in the form of urea. It serves also to remove superfluous water and foreign soluble matters which get introduced into the blood. The two most remarkable and characteristic constituents of urine, urea, and uric acid, have already been fully described ; in addition to these, it- contains lactic and hippuric acids, creatin, creatinine, and traces of glucose and indican, calcium and magnesium sulphates, chlorides, and phosphates, alkaline salts, and certain yet imperfectly known principles, including an odoriferous and a coloring substance. Healthy human urine is a transparent, light amber-colored liquid, which, while warm, emits a peculiar, aromatic, and not disagreeable odor. This is lost on cooling, while the urine at the same time occasionally becomes turbid, from a deposition of urates, which redissolve with slight elevation of temperature. It is very decidedly acid to test-paper; this acidity, which continually varies in amount, has been ascribed to acid sodium phos- phate, to free uric acid, and to free lactic acid ; lactic acid can, however, hardly co-exist with alkaline urates, and the amorphous buff-colored de- posit obtained from fresh urine by spontaneous evaporation in a vacuum, is not uric acid, but mixed acid urates, modified as to crystalline form by the presence of minute quantities of sodium chloride. That a free acid is sometimes present in the urine is certain : in this case the reaction to test- paper is far stronger, and the liquid deposits on standing, little, red, hard crystals of uric acid ; but this is no longer a normal secretion. An alkaline condition of the urine from fixed alkali is sometimes met with. Such alkalinity can always be induced by the administration of neu- tral potassium or sodium-salts of a vegetable acid, as tartaric or acetic acid : the acid of the salt is burned in the blood in the process of respira- tion, and a portion of the base appears in the urine in the state of car- bonate. The urine is often alkaline in cases of retention, from ammonium carbonate produced by putrefaction in the bladder itself; but this is easily distinguished from alkalinity from fixed alkali, in which it is secreted in that condition. The density of the urine varies from 1 005 to 1-030: about 1-020 to 1-025 may be taken as the average specific gravity. A high degree of density in urine may arise from an unusually large proportion of urea : in such a case, the addition of nitric acid will occasion an almost immediate produc- tion of crystals of urea nitrate ; whereas with urine of the usual degree of concentration, very many hours will elapse before the nitrate begins to separate. The quantity of urine passed depends much upon circumstances, as upon the activity of the skin. It is usually more deficient in quantity and of higher density in summer than in winter. Perhaps about 32 ounces in the 24 hours may be assumed as a mean. When kept at a moderate temperature, urine after some days begins to 808 ANIMAL FLUIDS. decompose : it exhales an offensive odor, becomes alkaline from the pro- duction of ammonium carbonate, and turbid from the deposition of earthy phosphates. The ammonium carbonate is due to the putrefactive decom- position of the urea, which gradually disappears, the ferment, or active agent of the change, being a peculiar nitrogenous substance which is always voided with the urine. It has been found also that the yellow ad- hesive deposit containing infusoria from stale urine is a most powerful fer- ment to the fresh secretion. In this putrefied state urine is used in several of the arts, as in dyeing, and forms perhaps the most valuable manure for land known to exist. Putrid urine always contains a considerable quantity of ammonium sul- phide: this is formed by the deoxidation of sulphates by the organic mat- ter. The highly offensive odor and extreme pungency of the decomposing liquid may be prevented by previously mixing the urine, as Liebig sug- gests, with sulphuric or hydrochloric acid, in sufficient quantity to saturate all the ammonia that can be formed. The following is an analysis of human urine by Berzelius. 1000 parts contained Water 933-02 Urea 30-10 Lactates and extractive matter . . 17-14 Uric acid 1-00 Potassium and sodium sulphates . 6-87 Sodium phosphate . . . . .2-92 Ammonium phosphate . . . 1-65 Calcium and magnesium phosphates . 1-00 Sodium chloride 4-45 Sal-ammoniac 1-50 Silica 0-03 Mucus of bladder . . . . .0-32 1000-00 In certain states of disorder and disease, substances appear in the urine which are never present in the normal secretion : of these the most com- mon is albumin. This is easily detected by the addition of nitric acid in excess, which then causes a white cloud or turbidity, which is permanent when boiled, or by corrosive sublimate, the urine being previously acidi- fied with a little acetic acid ; boiling usually causes a precipitate which is not dissolved by a drop or two of acid. Mere turbidity by boiling is no proof of albumin, the earthy phosphates being often thrown down from nearly neutral urine under such circumstances ; the phosphatic precipitate is, however, instantly dissolved by a drop of any acid. In diabetes the urine contains grape-sugar, the quantity of which varies with the intensity of the disease ; sometimes it is enormous, the urine ac- quiring a density of 1-040 and beyond. It does not appear that the urea is deficient absolutely, although more difficult to discover from being mixed with such a mass of syrup. Very small traces of sugar may be discovered in urine by Trommer's test, formerly mentioned (p. 576) : a few drops of solution of cupric sulphate are added to the urine, and afterwards an ex- cess of caustic potash: if sugar be present, a deep blue liquid results, which, on boiling, deposits red cuprous oxide. With proper management this test is very valuable. Urine containing sugar, when mixed with a little yeast, and put in a warm place, readily undergoes vinous fermenta- tion, and afterwards yields, on distillation, weak alcohol contaminated with ammonia. The urine of children is said sometimes to contain benzoic acid : this is URINARY CALCULI. 809 produced by the decomposition of hippuric acid, which constantly occurs in the urine of healthy persons. When benzoic acid is taken, the urine after a few hours yields on concentration, and the addition of hydrochloric acid, needles of hippuric acid, soiled by adhering uric acid. The deposit of buff-colored or pinkish amorphous sediment, which so frequently occurs in urine upon cooling, after unusual exercise or slight derangements of health, consists of a variable mixture of colored acid urates uncrystallized: it may be at once distinguished from a deposit of ammonio-magnesian phosphate by its instant disappearance on the appli- cation of heat. The earthy phosphates, besides, are hardly ever deposited from urine which has an acid reaction. The coloring matters of the urine have been carefully examined by Dr. Schunck. He finds that most of the substances hitherto described as col- oring healthy urine are products of the change of one, or at most two, coloring matters, which are always present. The first and most important of these, Dr. Schunck has obtained as a dark-yellow extract, amorphous and deliquescent, with a peculiar odor. It is soluble in alcohol and ether, as well as in water, and has the composition C^H^NO^. It is decomposed at a boiling temperature, yielding a large quantity of a brown resin and volatile organic acid. A second extractive matter, soluble in water and al- cohol, but not in ether, he found had the formula C, 9 H 27 NO, 4 . This is cer- tainly produced in the process of preparing the first extractive matter, and, perhaps, does not pre-exist in healthy urine. Heat and all strong alkalies and acids decompose these extractive matters, and give rise to most of the coloring matters which have hitherto been described as exist- ing in healthy urine. The reddish-pink coloring matter, called purpurin or uro-erythrin, which adheres so tenaciously to the urates, is not an ordi- nary constituent of healthy urine, but is formed more especially when the secretion of bile is diminished. With regard to the presence of indican in healthy urine, see p. 583. The yellow principle of bile may be observed in urine in cases of jaun- dice. The urine of the carnivorous mammifera is small in quantity and highly acid. It has a very offensive odor, and quickly putrefies. In composition it resembles that of man, and is rich in urea. In birds and serpents, the urine is a white pasty substance, consisting almost entirely of urate of am- monia. In herbivorous animals it is alkaline and often turbid from earthy carbonates and phosphates : urea is still the characteristic ingredient, while of uric acid there is scarcely a trace: hippuric acid is usually, if not always, present, sometimes to a very large extent. When the urine putre- fies, this hippuric acid, as already noticed, becomes changed to benzoic acid. URINARY CALCULI. Stony concretions, differing much in physical char- acters and in chemical composition, are unhappily but too frequently formed in the bladder itself, and give rise to one of the most distressing complaints to which humanity is subject. Although many endeavors have been made to find some solvent or solvents for these calculi, and thus su- persede the necessity of a formidable surgical operation for their removal, success has been but very partial and limited. Urinary calculi are generally composed of concentric layers of crystal- line or amorphous matter, of various degrees of hardness. Very frequent- ly the central point or nucleus is a small foreign body: curious illustrations of this will be seen in any large collection. Calculi are not confined to man: the lower animals are subject to the same affliction ; they have been found in horses, oxen, sheep, pigs, and almost constantly in rats. The foil owing is a sketch of the principal characters of the different varieties of calculi: 68* 810 ANIMAL FLUIDS. 1. Uric Acid. These are among the most common : externally they are smooth or warty, of yellowish or brownish tint: they have an imperfectly crystalline, distinctly concentric structure, and are tolerably hard. Be- fore the blowpipe the uric acid calculus burns away, leaving no ash. It is insoluble in water, but dissolves with facility in caustic potash, with but little ammoniacal odor : the solution mixed with acid gives a copious white curdy precipitate of uric acid, which speedily becomes dense and crystal- line. Cautiously heated with nitric acid, and then mixed with a little am- monia, it gives the characteristic reaction of uric acid, viz., deep purple- red murexide. 2. Ammonium Urate. Calculi of ammonium urate much resemble the preceding; they are easily distinguished, however. The powder boiled in water dissolves, and the solution gives a precipitate of uric acid when mixed with hydrochloric acid. It dissolves also in hot potassium carbo- nate with copious evolution of ammonia. 3. Fusible Calculus; Calcium Phosphate icith Ammonio-Magnesian Phos- phate. This is one of the most common kinds. The stones are usually white or pale-colored, smooth, earthy, and soft; they often attain a large size. Before the blowpipe this substance blackens from animal matter, which calculi always contain ; then becomes white, and melts to a bead with comparative facility. It is insoluble in caustic alkali, but readily sol- uble in dilute acids, and the solution is precipitated by ammonia. Calculi of unmixed calcium phosphate are rare, as also those of magnesium and ammonium phosphate; the latter salt is sometimes seen, forming small bril- liant crystals, in cavities in the fusible calculus. 4. Calcium Oxalate Calculus; Mulberry Calculus. The latter name is de- rived from the rough, warty character, and dark blood-stained aspect of this variety: it is perhaps the worst form of calculus. It is exceedingly hard: the layers are thick and imperfectly crystalline. Before the blow- pipe the calcium oxalate burns to a carbonate by a moderate red heat, and, when the flame is strongly urged, to quicklime. It is soluble in moderately strong hydrochloric acid by heat, and very easily in nitric acid. When finely powdered and long boiled in a solution of potassium carbonate, potassium oxalate may be discovered in the filtered liquor when carefully neutralized by nitric acid, by white precipitates with solutions of lime, lead, and silver. A sediment of calcium oxalate in very minute, transpar- ent, octohedral crystals, only to be seen by the microscope, is of common occurrence in urine, in which a tendency to deposits of urates exists. 5. Cystine and Xanthine. These calculi are very rare, especially the latter. Calculi of cystine or cystic oxide are very crystalline, and often present a waxy appearance externally : sediments of cystic oxide are some- times met with. This substance is a definite crystallizable organic prin- ciple, containing sulphur to a large amount, its formula being C 3 H 7 NS0 2 . The powdered calculus dissolves in great part, without effervescence, in dilute acids and alkalies, including ammonia : the ammoniacal solution de- posits, by spontaneous evaporation, small but beautiful colorless crystals, which have the form of six-sided prisms and tables. It forms a saline compound with hydrochloric acid. Caustic alkalies disengage ammonia from this substance by continued ebullition. When the solution in nitric acid is evaporated to dryness, it blackens : when it is dissolved in large quantity of caustic potash, a drop of solution of lead acetate added, and the whole boiled, a black precipitate containing lead sulphide makes its appear- ance. By these characters cystine is easily recognized. Xanthine or xanthic oxide, also a definite organic principle, C 5 H 4 N 4 2 , is distinguished by the peculiar deep-yellow color produced when its solution in nitric acid is evaporated to dryness: it is soluble in alkalies and in boil- ing, strong hydrochloric acid. SWEAT BILE. 811 Very many calculi are of a composite nature, the composition of the dif- ferent layers being occasionally changed, or alternating: thus, mixed urates aud calcium oxalate are not unfrequently associated in the same stone. SWEAT. The watery fluid poured out by the skin contains from to 2 per cent, of solid matter : the acidity of the secretion depends on organic acids, chiefly formic : acetic and butyric acids also exist in it. Lactic acid has been stated to be absent, even in rheumatism : a new acid named sudoric acid, and somewhat resembling uric acid in composition, is said to be al- ways present. In disease, and in health, small quantities of urea also exist in sweat. The salts in the sweat are chlorides of sodium and potassium. Phosphoric acid, lime, magnesia, and iron oxide have been found. SALIVA is a mixture of several fluids secreted by different glands of the mouth. Its specific gravity is from 1 *002 to 1 -009. It is usually alkaline : dur- ing and after eating, the alkaline reaction increases, while it decreases by fasting. It contains an albuminous substance, ptyalin, which acts on starch, rapidly changing it into sugar. The secretion of the submaxillary gland, with the mucus of the mouth, chiefly produces this effect. On the passage of the food into the acid gastric juice, this conversion of starch into sugar ceases. The second remarkable substance in saliva is potassium sulpho- cyanate, which exists in very small quantities, but is very easily detected. The solid constituents of the saliva are about 1 per cent., and in 100 parts of solid constituents from 7 to 21 parts are fixed salts, chiefly chlorides, with calcium carbonate and phosphate. GASTRIC JUICE is a clear, colorless, transparent fluid, of sp. gr. 1-002, containing 1 to 2 per cent, of solid constituents, chiefly sodium chloride and lactate. It has an acid reaction, and contains hydrochloric, lactic, butyric, propionic, and acetic acids. It is slightly, or not. at all, coagulable by boiling, though it contains two albuminous substances, one insoluble in wa- ter and absolute alcohol, the osmazome of older authors ; the other soluble in water, but precipitated by alcohol, tannin, mercuric chloride, and lead- salts. This is pepsin. In the gastric juice of man it exists to the amount .of 0-319 per cent. When the gastric juice has the greatest solvent power, 100 parts of fluid are saturated by 1-25 parts of potash. The gastric juice dissolves the albuminous substances taken as food, and slightly changes their reactions. Thus albumin, fibrin, casein, legumin, gluten, and chon- drin give rise to as many different peptones. (See pepsin, p. 801.) BILE. This is a secretion of a very different character from the pre- ceding : the largest internal organ of the body, the liver, is devoted to its preparation, which takes place from venous, instead of arterial blood. Ac- cording to Gorup-Besanez, human bile contains in 1000 parts Water 823908 Solid matter 177 92 Bile acids with alkali . . 108 56 Fat and cholesterin . . 47 40 Mucus and coloring matter 24 15 Ash 11 6 In its ordinary state, bile is a very deep-yellow, or greenish, viscid, trans- parent liquid, which darkens by exposure to the air, and undergoes changes which have been yet imperfectly studied. It has a disagreeable odor, a most nauseous, bitter taste, a distinctly alkaline reaction, and is miscililc with ^ter in all proportions. When evaporated to dryness at 100, and treateu with alcohol, the greater part dissolves, leaving behind an in- 312 ANIMAL FLUIDS. soluble jelly of mucus of the gall-bladder. This alcoholic solution contains coloring matter and cholesterin : from the former it may be freed by di- gestion with animal charcoal, and from the latter by a large admixture of ether, in which the bile is insoluble, and separates as a thick, syrupy, and nearly colorless liquid. The coloring matter may also be precipitated by baryta-water. Pure bile thus obtained, when evaporated to dryness by a gentle heat, forms a slightly yellowish brittle mass, resembling gum-arabic. It is com- pletely soluble in water and absolute alcohol. The solution is not affected by the vegetable acids ; hydrochloric and sulphuric acids, on the contrary, give rise to turbidity, either immediately or after a short interval. Lead acetate partly precipitates it ; tribasic acetate precipitates it completely : the precipitate is readily soluble in acetic acid, in alcohol, and to a cer- tain extent in excess of lead acetate. When carbonized by heat, and in- cinerated, bile leaves between 11 and 12 per cent, of ash, consisting chiefly of sodium carbonate, with a little common salt and alkaline phosphate. The beautiful researches of Strecker show that bile is essentially a mix- ture of the sodium-salts of two peculiar acids, resembling the resinous and fatty acids. One of these contains nitrogen, but no sulphur, and is termed glycocholic acid, being a conjugated compound* of a non-nitrogenous acid, cholic acid, with the azotized substance glycocine (p. 614); the other, containing nitrogen and sulphur, is called taurocholic acid, being a conjugated compound of the same cholic acid with a body to be presently described under the name of taurin, containing both nitrogen and sulphur. The rela- tive proportion in which these acids occur in bile, remains pretty constant with the same animal, but varies considerably with different classes of animals. GLYCOCHOLIC ACID may be thus obtained: When ox-bile is perfectly dried and extracted with cold absolute alcohol, and after nitration is mixed with ether, it first deposits a brownish tough resinous mass, and after some time, stellate crystals, consisting of the glycocholates of sodium and potas- sium. These mixed crystals were first obtained by Plattner, and they com- pose his so-called crystallized bile. Glycocholic acid may be obtained by decomposing sodium glycocholate with sulphuric acid: it crystallizes in fine white needles of a bitterish- sweet taste, is soluble in water and alcohol, but only slightly in ether, and has a strong acid reaction. It is represented by the formula C 26 H 43 N0 6 . When boiled with a solution of potash, the acid divides into cholic acid and glycocine : C 26 H 43 NOe + H 2 = C^H^ + C 2 H 5 N0 2 Glycocholic Cholic acid. Glycocine. acid. Boiled with concentrated sulphuric or hydrochloric acid, it likewise yields glycocine, but instead of cholic acid, another white amorphous acid, cholo- 'idic acid (C 24 H 3 g0 4 cholic acid minus 1 molecule of water), or, if the ebul- lition has continued for some time, a resinous substance, from its insolu- bility in water called dy sly sin (C^HggOg = cholic acid minus 2 molecules of water). TAUROCHOLIC ACID is thus procured : Ox-bile is freed as far as possible from glycocholic acid by means of neutral lead acetate, and is then pre- cipitated by basic lead acetate, to which a little ammonia is added. The precipitate is decomposed by sodium carbonate, whereby tolerably pure sodium taurocholate is obtained. By decomposing the taurocholate of lead with sulphuretted hydrogen, taurocholic acid is liberated. This sub- * A compound is sometimes said to bo " conjugated" O f two others, when it co^ins the elements ot those two bodies, minus the elements of water. BILE. 813 stance, however, which was previously called cholic acid and bilin, has never been obtained in the pure state; its formula, as inferred from the study of its products of decomposition, appears to be C 26 H 46 NS0 7 . When boiled with alkalies, it divides into cholic acid and taurin : C^H^NSO, + H 2 = C 24 H 40 ? + C 2 H 7 NS0 3 Taurocholic acid. Cholic acid. Glycocine. With boiling acids it likewise gives taurin, but instead of cholic acid either choloi'dic acid or dyslysin, according to the duration of the ebullition. TAURIN, C 2 H 7 NS0 3 , crystallizes in colorless regular hexagonal prisms, which have no odor and very little taste. It is neutral to test-paper, and permanent in the air. When burnt, it gives rise to much sulphurous acid. It contains upwards of 25 per cent, of sulphur. It is easily prepared by boiling purified bile for some hours with hydrochloric acid. After nitra- tion and evaporation, the acid residue is treated with five or six times its bulk of boiling alcohol, from which the taurin separates on cooling. Strecker made many attempts to prepare taurin artificially. Ultimately he found that when ammonium isethionate (p. 527), which melts at 180, is heated to 210 or 220 C. (410-428 F.), it loses 1 molecule of water, and becomes taurin. The substance is dissolved in water, and on the addition of alco- hol, gives crystals having all the properties of taurin. Kolbe has recently observed the formation of taurin under very interesting circumstances. The treatment of potassium isethionate with phosphorus pentachloride gives rise to a heavy oily liquid, with simultaneous formation of hydro- chloric acid and phosphorus oxychloride. This oily liquid, the so-called chloride of chlorethylsulphuric acid, C 4 H 4 C1S0 2 C1, when mixed with water, yields the corresponding acid, chlorethylsulphuric acid, C 2 H 6 C1S0 3 , which on digestion with an excess of ammonia at 100, produces taurin: C,H 5 C1S0 3 + 2NH 3 = NH 4 C1 -f C 2 H 7 NS0 3 . CHOLIC ACID, C 24 H 40 5 , crystallizes in tetrahedrons. It is soluble in sul- phuric acid, and on the addition of a drop of this acid and a solution of sugar (1 part of sugar to 4 parts of water), a purple-violet color is pro- duced, which constitutes Pettenkofer's test for bile. At 195 C. (383 F.), .it loses a molecule of water, and is converted into choloidic acid, which change, as already pointed out, is also produced by ebullition with acids. Cholic acid is best obtained by boiling the resinous mass precipitated by ether from the alcoholic solution of the bile, with a dilute solution of -potash for 24 or 36 hours, till the amorphous potassium-salt that has separated begins to crystallize. When the dark-colored soft mass is removed from the alkaline liquid, dissolved in water, and hydrochloric acid added, a little ether causes the deposition of the cholic acid in crystals. The principal coloring matter of the bile has been called cholepj/rrhin. When dry it is reddish-brown and uncrystallizable, insoluble in water, more soluble in alcohol, which become? yellow, and most soluble in caustic alkali. On the addition of nitric acid to the yellow alkaline solution, a change ensues. It passes through green, blue, violet, and red: after some time, it again turns yellow, probably in consequence of a gradual process of oxidation. Another coloring matter has been called biliverdin. It is dark-green, amorphous without taste or smell, insoluble in water, slightly soluble in alcohol, but soluble in ether. Berzelius considers it to be identical with chlorophyl, the green coloring matter of leaves. According to the researches of Strecker and Gundelach, pigs' bile differs from the bile of other animals. This bile contains an acid, to which the name of glyco-hyocholic acid has been given. It may be prepared in the following manner: fresh pigs' bile is mixed with a solution of sodium sul- 314 ANIMAL FLUIDS. phate, and the precipitate obtained is dissolved in absolute alcohol, and decolorized by animal charcoal. From this solution ether throws down a sodium-salt, which on addition of sulphuric acid yields glyco-hyocholic acid as a resinous mass, which is dissolved in alcohol and re-precipitated ^Glyco-hyocholic acid contains C^H^NOg. When heated with solutions of the alkalies, it undergoes a decomposition perfectly analogous to that of glycocholic acid, splitting up into glycocine and a crystalline acid, very soluble in alcohol, less so in ether, which has been termed hyocholic acid. This substance contains 025114004 ; and the change is represented by the following equation: C 27 H 43 N0 5 + H 2 = C 25 H 40 4 + C 2 H 5 N0 2 Glyco-hyocholic Hyocholic Glycocine. acid. acid. When boiled with acids, glyco-hyocholic acid yields likewise glycocine, but instead of hyocholic acid, a substance representing the dyslysin of the ordinary bile, which might be termed hyodyslysin. The composition of hyodyslysin is C 25 H 38 3 = hyocholic acid minus H 2 0. Pigs' bile contains a very trifling quantity of sulphur, probably in the form of a sulphuretted acid corresponding to taurocholic acid of ox-bile. Strecker believes this acid to contain C 27 H 45 NS0 6 : it might be called tauro- hyocholic acid; when boiled with an alkali, it should yield taurin and hyo- cholic acid. The sulphuretted acid must be present in pigs' bile in very minute quantity; it is even less known than taurocholic acid. The once celebrated oriental bazoar stones are biliary calculi, said to be procured from a species of antelope: they have a brown tint, a concentric structure, and a waxy appearance, and consist essentially of a peculiar and definite crystallizable principle called Ulhofellic acid. To procure this substance, the calculi are reduced to powder and exhausted with boiling alcohol; the dark solution is decolorized by animal charcoal, and left to evaporate by gentle heat, whereupon the lithofellic acid is deposited in small, colorless, transparent six-sided prisms. It is insoluble in water, and sparingly soluble in ether, but dissolves with ease in alcohol: it melts at 94-5 C. (202 F.), and at a higher temperature burns with a smoky flame, leaving but little charcoal. Lithofellic acid dissolves without decom- position in concentrated acetic acid and in oil of vitriol: it forms a soluble salt with potash, and dissolves also in ammonia, but crystallizes out un- changed on evaporation. By analysis, lithofellic acid is found to consist of C^Hg/V The liver not only forms bile which is excreted, but it also effects a re- markable change in the blood that passes through it. M. Bernard dis- covered that after death, sugar could be detected in the blood from the hepatic vein, whilst no sugar was found in blood from the portal vein. In the progress of his researches into the origin of this sugar, he found that a glycogenic substance was formed in the substance of the liver itself, and this he succeeded in extracting and isolating (p. 594). PANCREATIC FLUID is strongly alkaline, and has a specific gravity of about 1-008 to 1-009, containing from 9 to 11 per cent, of solid constitu- ents; among these are an albuminous substance resembling ptyalin, to- gether withleucine, guanine, xanthine, and inosite, and about 1 per cent, of ash, chiefly chlorides and phosphates. It has three distinct actions first on starch, secondly on fat, and thirdly on albuminous matter. Starch is converted into sugar more energetically by the pancreatic fluid than by the saliva. Fat is changed into fatty acid and glycerin at a temperature of 35 ; and boiled albumin and fibrin are CHYLE MUCUS AND PUS. 815 quickly dissolved at the same temperature, whilst the alkalescence dis- tinctly remains. INTESTINAL JUICE is a colorless, alkaline fluid, containing from 3 to 4 per cent, of solid constituents. It is thought to be capable of dissolving fibrinous substances only. CHYLE. The fluid of the lacteal vessels. This is a very variable fluid, milky, and feebly alkaline. Its fibrin begins to coagulate when taken from the vessels, in five to twelve minutes, and is perfectly coagulated in two to four hours. The coagulum is much smaller and weaker than that of the blood. That of the horse, from a yellowish color changes in the air to light red. The albuminous saline serum cpntains very finely divided molecules, con- sisting of the minutest particles of fatty matter, which give rise to the milkiness ; also larger chyle globules, and colorless blood globules. Thus the chyle approximates in composition and properties to the blood. In the chyle of the horse there was found: Water 91-00 to 96-00 per cent. Fixed constituents . . . 9-00 4 00 " Nuclei and cells . . . Variable. Fibrin 0-19 0-7 Albumin 1-93 4-34 Fat 1-89 0-53 Extractive matter free from salts 7-27 834 Soluble salts . . . .7-49 6-78 Insoluble . . . about 2-00 LYMPH is the name given to the fluid in the lymphatic vessels. It is colorless, has an alkaline reaction, and coagulates in from four to twenty minutes. It closely resembles the blood without the blood globules. It contains colorless globules, resembling the white globules of the blood. It contains much less albumin and fat than the serum of the blood, but more water, and proportionately more extractive matter. Closely resembling this fluid is that poured out by serous membranes and the cellular tissue. It has been called exsudation fluid, and may be divided into fibrinous and non-fibrinous. It may be considered as the serum of the blood with or without fibrin, which is far more commonly present than has been supposed. Mucus AND Pus. The slimy matter effused upon the surface of various mucous membranes, as the lining of the alimentary canal, that of the blad- der, of the nose, lungs, &c., to which the general name mucus is given, is so small in quantity, and so variable in consequence of any irritation of the membranes, that it is difficult to characterize. It always contains more or less epithelium and mucous cells. It contains a peculiar nitrogenous principle to which the name of mucin has been given (p. 800). Pus, the natural secretion of a wounded or otherwise injured surface, is commonly a creamy, white, or yellowish liquid, which, under the micro- scope, appears to consist of multitudes of minute globules floating in a serum. It is neither acid nor alkaline. The pus globules are distended by very dilute mineral and organic acids : imperfectly dissolved by alkalies, leaving the membrane of the cells ad- hering in a gelatinous mass. This cell membrane is an albuminous sub- stance, soluble in very dilute acids. The pus serum contains more or less albumin, in all respects identical with that of the blood and a peculiar sub- stance, pyin (p. 800). The quantity of fatty substance is remarkable in pus, varying from 2 to 816 ANIMAL FLUIDS. 6 per cent. As much as 1 per cent, of cholesterin has been found to be present; but neither by this nor by any other character can the passage of mucus into pus be determined. MILK. The peculiar special secretion destined for the nourishment of the young is, so far as is known, very much the same in flesh-eating ani- mals and in those which live exclusively on vegetable food. The propor- tions of the constituents may, however, sometimes differ to a considerable extent. The specific gravity varies from 1 018 to 1-045. It will be seen hereafter that the substances present in milk are wonderfully adapted to the office of providing materials for the rapid growth and development of the animal frame. It contains an azotized matter, casein or potassium al- buminate, fatty principles, and a peculiar sugar, and lastly, various salts, among which may be mentioned calcium phosphate, held in complete solu- tion in a slightly alkaline liquid. This last is especially important to a process then in activity, the formation of bone. The white, and almost opaque, appearance of milk is an optical illusion : examined by a microscope of even moderate power, it is seen to consist of a perfectly transparent fluid, in which float about numbers of transparent globules : these consist of fat, surrounded by an albuminous envelope, which can be broken mechanically, as in the churning, or dissolved by the chemi- cal action of caustic potash, after which, on agitating the milk with ether, the fat can be dissolved. When milk is suffered to remain at rest some hours at the ordinary tem- perature of the air, a large proportion of the fat-globules collect at the surface into a layer of cream; if this be now removed and exposed for some time to strong agitation, the fat-globules coalesce into a mass, and the re- maining watery liquid is expelled from between them and separated. The butter so produced must be thoroughly washed with cold water, to remove, as far as possible, the last traces of casein, which readily putrefies, and would in that case spoil the whole. A little salt is usually added. Ordinary butter still, however, contains some butter-milk, and when in- tended for keeping should be clarified, as it is termed, by fusion. The watery part then subsides, and carries with it the residue of the azotized matter. The flavor is unfortunately somewhat impaired by this process. The consistence of butter, in other words, the proportions of solid fat and olein, is dependent upon the season, or more probably upon the kind of food ; in summer the oily portion is always more considerable than in win- ter. The volatile odoriferous principle of butter, butyrin, has been already referred to. The casein of milk, in the state of cheese, is in many countries an im- portant article of food. The milk is usually heated to about49C. (120 F.), and coagulated by rennet, or an infusion of the stomach of the calf in water: the curd is carefully separated by a sieve from the whey, mixed with a due proportion of salt, and sometimes some coloring matter, and then subjected to strong and increasing pressure. The fresh cheese so prepared, being constantly kept cool and dry, undergoes a particular kind of putrefactive fermentation, very little understood, by which principles are generated which communicate a particular taste and odor. The good- ness of cheese, as well as much of the difference of flavor perceptible in different samples, depends in great measure upon the manipulation: the best kinds contain a considerable quantity of fat, and are made with new milk : the inferior descriptions are made with skimmed milk. Some of the Tartar tribes prepare a kind of spirit from milk by suffering it to ferment, with frequent agitation. The casein converts a part of the milk-sugar into lactic acid, and another part into grape-sugar, which in turn becomes converted into alcohol. Mare's milk is said to answer better for this purpose than that of the cow. MILK. 817 In a fresh state, and taken from a healthy animal, milk is always feebly alkaline. When left to itself, it very soon becomes acid, and is then found to contain lactic acid, which cannot be discovered in the fresh milk. The alkalinity is due to the soda which holds the casein in solution. In this soluble form casein possesses the power of taking up and retaining a very considerable quantity of calcium phosphate. The density of milk varies exceedingly: its quality usually bears an inverse ratio to its quantity. From an analysis of cow-milk in the fresh state by Haidlen,* the following statement of its composition in 1000 parts has been deduced: Water Butter Casein . . ... Milk-sugar .... Calcium phosphate Magnesium " Iron "... Potassium chloride . Sodium " . Soda in combination with casein 873-00 30-00 48-20 43-90 2-31 0-42 0-07 1-44 0-24 0-42 1000-00 Human milk is remarkable for the difficulty with which it coagulates: it generally contains a larger proportion of sugar than cow-milk, but scarcely differs in other respects. * Annalen der Cheraio und Pharmacie, xiv. 263. 69 ON THE ANIMAL TEXTURES. NERVOUS SUBSTANCE; CONTRACTILE SUBSTANCE; ELASTIC TISSUE; SKIN. NERVOUS SUBSTANCE. The brain and nerves contain protagon (p. cholesterin, and albuminous matter. In the watery extract are found cre- atin, uric acid, xanthine, sarcine, inosite, lactic acid ; in the ash, sulphuric and phosphoric salts, especially potassium salts, a little sodium chloride, calcium and magnesium. The substance yields from 75 to 80 per cent, of water, and 3 to 4 of ash. CONTRACTILE SUBSTANCE. This, like nerve substance, consists of many different compounds. It contains 74 to 80 per cent, water, and 26 to 20 solid constituents. The most remarkable of these is syntonin, Liebig's fibrin of flesh (see p. 795). Casein, albumin, creatin, hypoxanthine, uric acid, and fat are also present. The solid constituents contain 4 to 5 per cent, of ash. Potash, soda, lime, magnesia, sulphuric, phosphoric, and hydrochloric acids are present. ELASTIC TISSUE; SKIN. The tendons and skin consist also of many dif- ferent substances. Of these elastin (see p. 802) is one of the most remark- able. A cellular tissue, which yields gelatin when long boiled, is another constituent. These two principles combine with tannic acid, forming leather. The principle of tanning, of such great practical value, is easily ex- plained. When the skin of an animal, carefully deprived of hair, fat, and other impurities, is immersed in a dilute solution of tannic acid, the cellu- lar and elastic tissues gradually combine with that substance as it pene- trates inwards, forming a perfectly insoluble compound, which resists pu- trefaction completely : this is leather. In practice, lime-water is used for cleansing and preparing the skin, and an infusion of oak-bark, or some- times catechu, or other astringent matter, as the source of tannic acid. The process itself is necessarily a slow one, as dilute solutions only can be safely used. Of late years, however, various contrivances, some of which show great ingenuity, have been adopted, with more or less success, for quickening the operation. All leather is not tanned: glove leather is dressed with alum and common salt, and afterwards treated with a prepa- ration of the yolks of eggs, which contain an albuminous matter and a yellow oil. Leather of this kind still yields a size by the action of boiling water. BONES. At the age of 21 years the weight of the skeleton is to that of the whole body as 10-5 to 100 in man, and as 8-5 to 100 in woman, the weight of the body being about 125 or 130 Ibs. Bones are constructed of organic matter called osse'in, which yields gelatin on boiling, and is made stiff by insoluble earthy salts, of which calcium phosphate, (P0 4 ) 2 Ca // 3 , is the most abundant. The proportions of earthy and animal matter vary very much with the kind of bone and with the age of the individual, as 818 BONES. 819 will be seen in the following table, in which the corresponding bones of an adult and of a still-born child are compared : ADULT. CHILD. Inorganic Organic Inorganic Organic matter. matter. matter. matter. Femur . . 62-49 37-51 57-51 4249 Humerus . . 63.02 36-98 58-08 41-92 Radius . . 60-51 39-49 56-50 43-50 Os temporum . 63-50 36 50 55-90 44-10 Costa. . . 57-49 42-51 53-75 46-25 The bones of the adult are constantly richer in earthy salts than those of the infant. The following complete comparative analysis of human and ox bones is due to Berzelius: Human bones. Ox bones. Animal matter soluble by boiling . . 32-17 \ Vascular substance .... 1-13 / Calcium phosphate, with a little ) K0 A , e _ OK calcium fluoride . . }' ' 53 ' 04 Calcium carbonate .... 11-30 3-85 Magnesium phosphate .... 1-16 2-05 Soda, and a little common salt . . 1-20 3-45 100-00 100-00 The teeth have a very similar composition, but contain less organic mat- ter : their texture is much more solid and compact. The enamel does not contain more than 2 or 3 per cent, of animal matter, whilst 81 to 88 per cent, of calcium phosphate with 7 or 8 per cent, of carbonate are present ; and more calcium fluoride than in the bones. ON CHEMICAL FUNCTIONS IN ANIMALS. RESPIRATION, DIGESTION, NUTRITION. RESPIRATION. The simplest view that can be taken of a respiratory organ in an air-breathing animal, is that of a little membranous bag, satu- rated with moisture, and containing air, over the surface of which mean- der minute blood-vessels, whose contents, during the passage, are thus subjected to the chemical action of the air, through the substance of the membranes, and in virtue of the solubility of the gaseous matter itself in the water with which the membranes are imbued. In some of the lower classes of animals, where respiration is sluggish and inactive, these air- cells are few and larger ; but in the higher kinds they are minute, and greatly multiplied in number, in order to gain extent of surface, each com- municating with the external air by the windpipe and its ramifications. Respiration is performed by the agency of the muscles which lie between and about the ribs, and by the diaphragm. In an ordinary respiration, from 22 to 43 cubic inches of air are thrown out. It has been said that as little as 3 and as much as 100 cubic inches have been expired. By a forced eifort, ordinarily from 50 to 60 cubic inches are expelled, and after a full inspiration possibly from 100 to 300 cubic inches may be expired. Even then the lungs are not emptied of air. The residual quantity may be esti- mated at from 40 to 260 cubic inches. After an ordinary expiration a fur- ther quantity of air, amounting to from 77 to 170 cubic inches, may be expired, and after an ordinary inspiration, by the deepest sigh, from 119 to 200 more cubic inches may be drawn into the lungs. Usually about 15 respirations are made in a minute : the number, however, even in health, varies from 9 to 20. The expired air is found to have undergone a remarkable change: it is loaded with aqueous vapor, while a very large proportion of oxygen has disappeared, and its place been supplied by carbon dioxide, air once breathed containing enough of that gas to extinguish a taper. The quan- tity of this gas is very liable to variation; usually from 8-3 to 6-2 per cent, of carbon dioxide is found to be present; when the respirations are few, the carbon dioxide is greatest, when many, least: thus with 6 respi- rations per minute, 55 per cent, has been found: with 48 respirations, 2-9 per cent. A full meal, cold weather, and increased barometric pres- sure, increase the carbon dioxide. Heat, alcohol, tea, and diminished pres- sure, lessen the carbon dioxide ; age and sex produce definite effects. It appears most probable that nitrogen in small quantities is exhaled. Whatever may be the difficulties attending the investigation of these sub- jects, and difficulties there are, as the discrepant results of the experi- ments prove, one thing is clear: namely, that quantities of hydrogen and carbon are daily oxidized in the body by the free oxygen of the atmos- phere, and their products expelled from the system in the shape of water and carbon dioxide. Now, if it be true that the heat developed in the act of combination is a constant quantity, and no proposition appears more reasonable, part or all of the high temperature of the body must be the result of this exertion of chemical force. 820 BESPIRATION. 821 The oxidation of combustible matter in the blood is effected in the capil- laries of the whole body, not in the lungs, the temperature of which scarcely exceeds that of the other parts. The oxygen of the air is taken up in the lungs, and carried by the blood to the distant capillary vessels ; by the aid of which, secretions, and all the mysterious functions of animal life, are undoubtedly performed: here the combustion takes place, although how this happens, and what the exact nature of the combustible may be, beyond the simple fact of its containing carbon and hydrogen, yet remains a matter of conjecture. The carbon dioxide produced is held in solution by the now venous blood, and probably confers, in great measure, upon the latter its dark color and deleterious action upon the nervous system. Once more poured into the heart, and by that organ driven into the second set of capil- laries bathed with atmospheric air, this carbon dioxide is conveyed out- wards, through the wet membrane, by a kind of false diffusion, constantly observed under such circumstances ; while at the same time oxygen is, by similar means, carried inwards, and the blood resumes its bright-red color, and its capability of supporting life Much of this oxygen is, no doubt, simply dissolved in the serum. The haemoglobin of the corpuscles, becom- ing oxyhaemoglobin in the arteries, acts as a carrier of another portion (p. 798). Mulder considers the fibrin to act in the same manner, being true fibrin in the veins, and, in part at least, oxidized in the arteries. It would be very desirable to show, if possible, that the quantity of com- bustible matter daily burned in the body is adequate to the production of the heating eifects observed. Something has been done with respect to the carbon. Comparison of the quantities and composition of the food con- sumed by an individual in a given time, and of the excretions, shows an excess of carbon in the former over the latter, amounting, in some cases, according to Liebig's high estimate,* to 14 ounces: the whole of which is thrown off in the state of carbon dioxide, from the lungs and skin, in the space of twenty-four hours. This statement applies to the case of healthy, vigorous men, much employed in the open air, and supplied with abundance of nutritious food. Females, and persons of weaker habits, who follow in- door pursuits in warm rooms, consume a much smaller quantity : their res- piration is less energetic, and the heat generated less in amount. Those who inhabit very cold countries are well known to consume enormous quan- tities of food of a fatty nature, the carbon and hydrogen of which are, without doubt, chiefly employed in the production of animal heat. These people live by hunting: the muscular exertion required quickens and deepens the breathing ; while, from the increased density of the air, a greater weight of oxygen is taken into the lungs, and absorbed into the blood at each inspiration. In this manner the temperature of the body is kept up, notwithstanding the piercing external cold : a most marvellous adjustment of the nature of the food, and even of the inclinations and ap- petite of the man, to the circumstances of his existence, enable him to bear with impunity an atmospheric temperature which would otherwise injure him. The carbon consumed in respiration in one day, by a horse moderately fed, amounted, in a valuable experiment of M. Boussingault,f to 79 ounces; that consumed by a cow to 71 ounces. The determination was made in the manner just mentioned, viz., by comparing the quantity and composition of the food. New and very important experiments on respiration have been made in Munich by Drs. Pettenkofer and Voit. The apparatus was large enough to allow a man to breathe and move as in an ordinary dwelling-room for twenty-four hours at least. The air * Animal Chemistry, p. 14. f Annales de Chimie, vol. Ixxi. pp. 136 and 137. 69* 822 DIGESTION AND NUTRITION. could be changed to the extent of from fifteen to seventy-five cubic meters an hour : the chemical difference between the air that went in and that which came out was determined. The King of Bavaria gave about $3000 for the construction of the appa- ratus, and it acted so well that the quantity of carbon and of hydrogen in a stearin candle burnt in the apparatus could be determined as accurately by the quantity of carbon dioxide and water produced as by an organic analysis. A dog and a man were experimented on. In the dog the amount of car- bon dioxide expired was least after ten days of hunger; when a full diet of flesh and fat was taken, three times as much carbon dioxide was pro- duced. The urea was increased twenty-two times as much as during star- vation. In man not quite one-third more carbon dioxide was produced when full diet was taken than was found during starvation. From the amount of carbon dioxide and urea formed when animal food alone was taken, it appears that soni'i fatty matter must be produced and retained in the system. Starch and sugar diet do not appear to cause a deposit of fat directly, though they may do so indirectly. Careful determination of the amount and composition of the food and oxygen consumed led to the belief that hydrogen and light carburetted hydrogen (CH 4 ) were given off in respiration. This is fully confirmed by these experiments. It follows from this important fact, first, that the car- bon dioxide produced cannot be looked on as the measure of the amount of oxygen taken from the air, and secondly, that hydrogen cannot be as- sumed to be oxidized in the body in preference to carbon. In a paper read to the Academy of Sciences at Munich, November, 1866, the authors give their latest results. They find that the proportion of car- bon dioxide exhaled to oxygen inhaled is much greater in the day than in the night ; with perfect rest day and night, nearly twice as much ; with active motion during the day, nearly three times as much. The amount of oxygen taken in during rest by day is only half as much as is taken in at night, and after active motion the amount of oxygen taken in at night is still more. In diabetes the proportion of carbon dioxide exhaled by day to the oxygen inhaled is less than in health ; at night the amount of oxygen inhaled may be less than half the amount that would be inhaled in health. When one-third of the blood consisted of white globules, the proportion of carbon dioxide exhaled to oxygen inhaled by day was much less than in health, and the amount of oxygen taken in at night was even less than is taken in during the day. DIGESTION AND NUTRITION. The various substances of which the food of man is composed must become finely divided in order to admit of their passage into the blood. In the process of fine division or solution different substances undergo different changes in the alimentary canal. We learn nothing by saying that the food is converted into chyme, and the chyme is changed into chyle ; but each animal and vegetable substance must be con- sidered separately, as regards the changes it undergoes when exposed to the action of the different fluids which constitute the saliva, gastric juice, bile, pancreatic juice, and intestinal fluid. Shortly, it may be stated that mineral substances, when exposed to these reagents, are but little changed. Hydrates of carbon, as cellulose, gum, starch, sugar, are each acted on differently by different secretions ; thus cellulose and gum are probably not changed. Starch, by the action of the saliva and pancreatic fluid, be- comes dextrin and glucose. Cane-sugar is changed by gastric juice and DIGESTION AND NUTRITION. 823 heat into glucose, and all sugars are ultimately changed by the intestinal fluid and heat into acids. Fat is unchanged by the saliva and gastric juice ; but the bile, the pan- creatic and intestinal fluid, change the fat into a finely divided emulsion, but effect no perfect solution. Albuminous substances, as albumin, fibrin, casein, globulin, undergo subdivision and solution chiefly in the stomach. Each of these substances is chemically changed in the process of solution by the gastric juice (p. 797) into corresponding peptones. The rate of change and of solution depends on the mechanical subdivision as well as on the chemical properties of the different substances acted on. Gelatinous substances are changed chemically by the gastric juice, and thereby lose the property of gelatinizing when cold. But this change is not requisite to their solution, which occurs so readily that these sub- stances can often be taken as food when albuminous substances would re- main in the stomach undissolved. The constant and unceasing waste of the animal body in the process of respiration, and in the various secondary changes therewith connected, necessitates an equally constant repair and renewal of the whole frame by the deposition or organization of matter from the blood, which is thus gradually impoverished. To supply this deficiency of solid material in the circulating fluid is the office of the food. The striking contrast which at first appears in the nature of the food of the two great classes of animals, the vegetable feeders and the carnivorous races, diminishes greatly on close examination : it will be seen that, so far as the materials of blood, or, in other words, those devoted to the repair and sustenance of the body it- self, are concerned, the process is the same. In a flesh-eating animal great simplicity is observed in the construction of the digestive organs ; the stomach is a mere enlargement of the short and simple alimentary canal; and the reason is plain : the food of the creature, flesh, is absolutely iden- tical in composition with its own blood, and with the body that blood is destined to nourish. In the stomach it undergoes mere solution, being brought into a state fitted for absorption by the lacteal vessels, by which it is nearly' all taken up, and at once conveyed into the blood : the excre- ments of such animals are little more than the comminuted bones, feathers, hair, and other matters which refuse to dissolve in the stomach. The same condition, that the food employed for nourishment of the body must have the same, or nearly the same, chemical composition as the body itself, is really fulfilled in the case of animals that live exclusively on vegetable substances. It has been shown* that certain of the azotized principles of plants, which often abound, and are never altogether absent, have a chem- ical composition and assemblage of properties which assimilate them in the closest manner, and it is believed even identify them, with the azotized principles of the animal body : vegetable albumin, fibrin, and casein are scarcely to be distinguished from the bodies of the same name extracted from blood and milk. If a portion of wheaten flour be made into a paste with water, and cau- tiously washed on a fine metallic sieve, or in a cloth, a grayish, adhesive, elastic, insoluble substance will be left, called gluten or glutin, and a milky liquid will pass through, which by a few hours' rest becomes clear by de- positing a quantity of starch. If now this liquid be boiled, it becomes again turbid from the production of a flocculent precipitate, which, when collected, washed, dried, and purified from fat by boiling with ether, is found to have the same composition as animal albumin. The glutin itself is a mixture of true vegetable fibrin, and a small quantity of a peculiar azotized matter called gliadin, to which its adhesive properties are due. * Liebig, Ann. Ch. Pharm. xxxix. 129. 324 DIGESTION AND NUTRITION. The gliadin may be extracted by boiling alcohol, together with a thick, fluid oil, which is separable by ether: it is gluey and adhesive, quite in- soluble in water, and when dry, hard and translucent like horn ; it dis- solves readily in dilute caustic alkali, and also in acetic acid. The fibrin of other grain is unaccompanied by gliadin : barley and oatmeal yield no glutin, but inadherent filaments of nearly pure fibrin. Vegetable albumin in a soluble state abounds in the juice of many soft succulent plants used for food: it may be extracted from potatoes by ma- cerating the sliced tubers in cold water containing a little sulphuric acid. It coagulates when heated to a temperature dependent upon the degree of concentration, and cannot be distinguished when in this state from boiled white of egg in a divided condition. Almonds, peas, beans, and many of the oily seeds, contain a principle which bears the most striking resemblance to the casein of milk. When a solution of this substance is heated, no coagulation occurs, but a skin forms on the surface, just as with boiled milk. It is coagulable by alcohol, and by acetic acid, the last being a character of importance. Such a solution, mixed with a little sugar an emulsion of sweet almonds, for instance and left to itself, soon becomes sour and curdy, and exhales an offensive smell: it is then found to contain lactic acid. All these substances dissolve in caustic potash, with production of a small quantity of alkaline sulphide : the filtered solution mixed with ex- cess of acid gives precipitates of protein. The following is the composition in 100 parts of vegetable albumin and fibrin : it will be seen that they agree very closely with the results before given : Albumin. Fibrin. Carbon 65 01 54-60 Hydrogen 7-23 7-30 Nitrogen 15-92 1581 Oxygen, sulphur, and phosphorus . 21-84 22-29 100-00 10.0-00 The composition of vegetable casein, or legumin, has not been so well made out : so much discrepancy appears in the analyses as to lead to the supposition that different substances have been operated upon. The great bulk, however, of the solid portion of the food of the herbi- vora consists of bodies which do not contain nitrogen, and therefore can- not yield sustenance in the manner described: some of these, as vegetable fibre or ligniri, and waxy matter, pass unaltered through the alimentary canal; others, as starch, sugar, gum, and perhaps vegetable fat, are ab- sorbed into the system, and afterwards disappear entirely : they are sup- posed to contribute very largely to the production of animal heat. On these principles, Liebig* made the now doubtful distinction between what he terms plastic elements of nutrition and elements of respiration. In the former class he placed Vegetable fibrin, Vegetable albumin, Vegetable casein, Animal flesh, Blood. To the latter : Fat, Starch, Gum, Cane-sugar, Grape-sugar, Milk-sugar, Pectin, Alcohol ? * Auimal Chemistry, p. 96. DIGESTION AND NUTRITION. 825 When the muscular movements of a healthy animal are restrained, a genial temperature kept up, and an ample supply of food containing much amylaceous or oily matter given, an accumulation of fat in the system rap- idly takes place : this is well seen in the case of stall-fed cattle. On the other hand, when food is deficient, and much exercise is taken, emaciation results. These effects are ascribed to differences in the activity of the respiratory function : in the first instance, the heat-food is supplied faster than it is consumed, and hence accumulates in the form of fat; in the second, the conditions are reversed, and the creature is kept in a state of leanness by its rapid consumption. The fat of an animal appears to be a provision of Nature for the maintenance of life during a certain period under circumstances of privation. The origin of fat in the animal body was at one time the subject of much discussion. On the one hand it was contended that satisfactory evidence exists of the conversion of starch and saccharine substances into fat, by separation of carbon and oxygen, the change somewhat resembling that of vinous fermentation ; it was argued on the other side, that oily or fatty matter is invariably present in the food supplied to the domestic animals, and that this fat is merely absorbed and deposited in the body in a slightly modified state. The question has been decided in favor of the first of these views, which was enunciated by Liebig, by the very chemist who formerly advocated the second opinion. By a series of very beautiful experiments, MM. Dumas and Milne Edwards proved that bees exclusively feeding upon sugar were still capable of producing wax, which is known to be a veri- table fat. The food of animals, or rather that portion of the food which is destined to the repair and renewal of the frame itself, is thus seen to consist of sub- stances identical in composition with the body it is to nourish, or requir- ing but little chemical change to become so. The chemical phenomena observed in the animal system resemble so far those produced out of the body by artificial means, that they are all, or nearly all, so far as is known, changes in a descending series. Albumin and fibrin are probably more complex compounds than gelatin or the mem- brane which furnishes it: this, in turn, has a far greater complexity of constitution than urea, which contains most of the azotized matter that is rejected from the body. The animal lives by the assimilation into its own substance of the most complex and elaborate products of the organic king- dom ; products which are, and, apparently, can only be, formed under the influence of vegetable life. The existence of the plant is maintained in a manner strikingly dissimi- lar: the food supplied to vegetables is wholly inorganic ; the carbon di- oxide and nitrogen of the atmosphere ; the water which falls as rain, or is deposited as dew; the minute traces of ammoniacal vapor present in the air ; the alkali and saline matter extracted from the soil ; such are the substances which yield to plants the elements of their growth. That green healthy vegetables do possess, under circumstances to be mentioned imme- diately, the property of decomposing carbon dioxide absorbed by their leaves from the air, or conveyed thither in solution through the medium of their roots, is a fact positively proved by direct experiment, and ren- dered certain by considerations of a very stringent kind. To effect this very remarkable decomposition, the influence of light is indispensable; the diffused light of day suffices in some degree, but the direct rays of the sun greatly exalt the activity of the process. The carbon separated in this manner is retained in the plant in union with the elements of water, with which nitrogen is also sometimes associated, while the oxygen is thrown off into the air from the leaves in a pure and gaseous condition. The effect of ammoniacal salts upon the growth of plants is so remark- 826 DIGESTION AND NUTRITION. able as to leave little room for doubt concerning the peculiar functions of the ammonia discovered in the air. Plants which in their cultivated state contain, and consequently require, a larger supply of nitrogen, as wheat, and the cereals in general, are found to be greatly benefited by the appli- cation to the land of such substances as putrefied urine, which may be looked upon as a solution of ammonium carbonate, or of guano, which is the partially decomposed dung of birds, found in immense quantities on some of the barren islets of the western coast of South America, as that of Peru. More recently, similar deposits have been found on the coast of Southern Africa. The guano now imported into England from these locali- ties is usually a soft, brown powder, of various shades of color. White specks of bone-earth, and sometimes masses of saline matter, may be found in it. That which is most recent, and probably most valuable as manure, often contains undecomposed uric acid, besides much ammonium oxalate or chloride, alkaline phosphates, and other salts : it has a most offensive odor. The specimens taken from older deposits have but little smell, are darker in color, contain no uric acid, and much less ammoniacal salt; the chief components are bone-earth, a peculiar dark-colored organic matter, and soluble inorganic salts. (See also p. 724). Upon the members of the vegetable kingdom thus devolves the duty of building up, as it were, out of the inorganic constituents of the atmos- phere, the carbon dioxide, the water, and the ammonia, the numerous complicated organic principles of the perfect plant, many of which are afterwards destined to become the food of animals, and of man. The chem- istry of vegetable life is essentially a process of reduction caused by the action of light, but the mode in which this is effected is at present by no means made out. One thing, however, is manifest, namely, the wonderful relations between the two orders of organized beings, in virtue of which the rejected and refuse matter of the one is made to constitute the essen- tial and indispensable food of the other. While the animal lives, it exhales incessantly from its lungs, and often from its skin, carbon dioxide ; when it dies, the soft parts of the body undergo a series of chemical changes of degradation, which terminate in the production of carbon dioxide, water, ammonium carbonate, and, perhaps, other products in small quantity. These are taken up by a fresh generation of plants, which may in their turn serve for food to another race of animals. APPENDIX. HYDROMETER TABLES. COMPARISON OF THE DEGREES OP BAUME's HYDROMETER WITH THE REAL SPECIFIC GRAVITIES. 1. For Liquids heavier than Water. Degrees. Specific Gravity. Degrees. Specific Gravity. Degrees. Specific Gravity. 1-000 26 1-206 52 1-520 1 1-007 27 1-216 53 1-535 2 1-013 28 1-225 54 1-551 3 1-020 29 1-235 55 1-567 4 1-027 30 1-245 56 1-583 5 1-034 31 1-256 57 1-600 6 1-041 32 1-267 58 1-617 7 1-048 33 1-277 59 1-634 8 1-056 34 1-288 60 1-652 9 1.063 35 1-299 61 1-670 10 1-070 36 1-310 62 1-689 11 1-078 37 1-321 63 1-708 12 1-085 38 1-333 64 1-727 13 i-094 39 1-345 65 1-747 14 1-101 40 1-357 66 1-767 15 1-109 41 1-369 67 788 16 1-118 42 1-381 68 809 17 1-126 43 1-395 69 831 18 1-134 44 407 70 854 19 1-143 45 420 71 877 20 1-152 46 434 72 900 21 1-160 47 448 73 944 22 1-169 48 462 74 04 ( . 23 1-178 49 476 75 974 24 1-188 50 1-490 76 2-000 26 1-197 51 1-495 827 828 APPENDIX. 2. BaumPs Hydrometer for Liquids lighter than Water. Degrees. Specific Gravity. Degrees. Specific Gravity. Degrees. Specific Gravity. 10 1-000 27 0-896 44 0-811 11 0-993 28 0-890 45 0-807 12 0-986 29 0-885 46 0-802 13 0-980 30 0-880 47 0-798 14 0-973 31 0-874 48 0-794 15 0-967 32 0-869 49 0-789 16 0-960 33 0-864 50 0-785 17 0-954 34 0-859 51 0-781 18 0-948 35 0-854 52 0-777 19 0-942 36 0-849 53 0-773 20 0-936 37 0-844 54 0-768 21 0-930 38 0-839 55 0-764 22 0-924 39 0-834 56 0-760 23 0-918 40 0-830 57 0-757 24 0-913 41 0-825 58 0-753 25 0-907 42 0-820 59 0-749 26 0-901 43 0-816 60 0-745 These two tables are on the authority of Francoeur ; they are taken from the Handworterbuch der Chemie of Liebig, Poggendorif, and Wohler. Baum^'s hydrometer is very commonly used on the Continent, especially for liquids heavier than water. For lighter liquids the hydrometer of Cartier is often employed in France. Cartier's degrees differ but little from those of Bailing. In the United Kingdom, Twaddell's hydrometer is a good deal used for dense liquids. This instrument is so graduated that the real specific grav- ity can be deduced by an extremely simple method from the degree of the hydrometer; namely, by multiplying the latter by 5, and adding 1000; the sum is the specific gravity, water being 1000. Thus 10 Twaddle indicates a specific gravity of 1050, or 1-05; 90 Twaddell, 1450, or 1-45. In the Customs and Excise, Sikes's hydrometer is used. APPENDIX. 829 ABSTRACT OP DR. DALTON'S TABLE OP THE ELASTIC FORCE OF TAPOUR OF WATER DIFFERENT TEMPERATURES, EXPRESSED IN INCHES OF MERCURY. Temperature. Force. Temperature. Force. Temperature. Force. Fah. Cent. Fah. Cent. Fah. Cent. 32 o-o 0-200 57 13o-88 0-474 90 32-2 1-36 33 C-55 0-207 58 140.4 0-490 95 35 1-58 34 1-1 0-214 59 15 0-507 100 8.70.77 1-86 35 l-66 0-221 60 15-5 0-524 105 40 -5 2-18 36 2-2 0-229 61 16-1 0-542 110 43-3 2-53 37 2-77 0-237 62 i6-66 0-560 115 46-l 2-92 38 3-3 0-245 63 17-2 0-578 120 48-88 3-33 39 3-88 0-254 64 170.77 0^597 125 51-66 3-75 40 40.4 0-263 65 18-3 0-616 130 54-4 4-34 41 5 0-273 66 18-88 0-635 135 57-2 5-00 42 5 -55 0-283 67 19-4 0-665 140 60 6-74 43 6-l 0-294 68 20 0-676 145 620.77 6-53 44 6-66 0-305 69 20 -55 0-698 150 65-5 7-42 45 70.2 0-316 70 21-1 0-721 160 71-1 9-46 46 70.77 0-328 71 21-66 0-745 170 76-66 12-13 47 8 -3 0-339 72 22 -2 0-770 180 82-2 15-15 48 8-88 0-351 73 22-77 0-796 190 87-77 1900 19 90.4 0-363 74 23-3 0-823 200 93o-3 23-64 50 10 0-375 75 230-88 0-851 210 98 -88 28-84 51 10-55 0-388 76 24-4 0-880 212 100 30-00 52 11-1 0401 77 25o 0-910 220 1040.4 34-99 53 llo-66 0-415 78 25-5 0-940 230 110 41-75 54 12-2 0-429 79 26-l 0-971 240 115-5 49-67 65 12-77 0443 80 26-66 1-000 250 121-1 68-21 56 13-3 0-458 85 29-44 1-170 300 148-88 111-81 70 830 APPENDIX. TABLE OF THE PBOPORTION BY WEIGHT OF ABSOLUTE OR REAL ALCOHOL IN 100 PARTS OF SPIRITS OF DIFFERENT SPECIFIC GRAVITIES. (FOWNES.) Sp. Or. at 60 (15-5C). Per cent, of real Alcohol. Sp. Or. at 60 (15-5C.) Per cent, of real Alcohol. Sp. Or. at 60 (15-5C). Per cent, of real Alcohol. 0-9991 0-5 0-9511 34 0-8769 68 0-9981 1 0-9490 35 0-8745 69 0-9965 2 0-9470 36 0-8721 70 0-9947 3 0-9452 37 0-8696 71 0-9930 4 0-9434 38 0-8672 72 0-9914 5 0-9416 39 0-8649 73 0-9898 6 0-9396 40 0-8625 74 0-9884 7 0-9376 41 0-8603 75 0-9869 8 0-9356 42 0-8581 76 0-9855 9 0-9335 48 0-8557 77 0-9841 10 0-9314 44 0-8533 78 0-9828 11 0-9292 45 0-8508 79 0-9815 12 0-9270 46 0-8483 80 0-9802 13 0-9249 47 0-8459 81 0-9789 14 0-9228 48 0-8434 82 0-9778 15 0-9206 49 0-8408 83 0-9766 16 0-9184 50 0-8382 84 0-9753 17 0-9160 51 0-8357 85 0-9741 18 0-9135 52 0-8331 86 0-9728 19 0-9113 53 0-8305 87 0-9716 20 0-9090 54 0-8279 88 0-9704 21 0-9069 55 0-8254 89 0-9691 22 09047 56 0-8228 90 0-9678 23 0-9025 57 0-8199 91 0-9665 24 0-9001 58 0-8172 92 0-9652 25 0-8979 59 0-8145 93 0-9638 26 0-8956 60 0-8118 94 0-9623 27 0-8932 61 0-8089 95 0-9609 28 0-8908 62 0-8061 96 0-9593 29 0-8886 63 0-8031 97 0-9578 30 0-8863 64 0-8001 98 0-9560 31 0-8840 65 0-7969 99 0-9544 32 0-8816 66 0-7938 100 0-9528 33 0-8793 67 APPENDIX. 831 TABLE OF THE PROPORTION BY VOLUME OF ABSOLUTE OR REAL ALCOHOL IN 100 VOL- UMES OF SPIRITS OF DIFFERENT SPECIFIC GRAVITIES (GAY-LUSSAC) AT 59 F. (15 C.) 100 vol. Spirits. 100 vol. Spirits. 100 vol. Spirits. Spec. Grav. Contain vol. of real Alcohol. Spec. Grav. Contain vol. of real Alcohol Spec. Grav. Contain vol. of real Alcohol. 1 0000 0-9608 34 0-8956 68 0-9985 1 0-9594 35 0-8932 69 0-9970 2 0-9581 36 0-8907 70 0-9956 3 0-9567 37 0-8882 71 09942 4 0-9553 38 0-8857 72 0-9929 5 0-9538 39 0-8831 73 0-9916 6 0-9523 40 0-8805 74 0-9903 7 0-9507 41 0-8779 75 0-9891 8 0-9191 42 0-8753 76 0-9878 9 0-9474 43 0-8726 77 0-9867 10 0-9457 44 0-8699 78 0-9855 11 0-9440 45 0-8672 79 0-9844 12 0-9422 46 0-8645 80 0-9833 13 0-9404 47 0-8617 81 0-9822 14 0-9386 48 0-8589 82 0-9812 15 0-9367 49 0-8560 83 09802 16 0-0348 50 0-8531 84 9792 17 0-9329 51 0-8502 85 0-9782 18 0-9309 52 0-8472 86 0-9773 19 0-9289 53 0-8442 87 09763 20 0-9269 54 0-8411 88 0-9753 21 0-9248 55 0-8379 89 0-9742 22 0-9227 56 0-8346 90 0-9732 23 0-9206 57 0-8312 91 0-9721 24 0-9185 58 08278 92 0-9711 25 0-9163 59 08242 93 0-9700 26 0-9141 60 0-8206 94 0-9690 27 0-9119 61 0-8168 95 0-9679 28 0-9096 62 0-8128 96 0-9668 29 09073 63 0-8086 97 0-9657 30 0-9050 64 0-8042 98 0-9645 31 0-9027 65 0-8006 99 0-9633 32 0-9004 66 0-7947 100 0-9621 33 0-8980 67 ANALYSES OF Source, . . Name of Spring, . Vichy, France. Puits Carre. Ems, Nassau. Keasel- brunnen. Sellers, Nassau. Karla- brunnen, Silesia, Karlsbad, Bohemia. Sprudel. Calcium .... Barium .... Strontium .... Magnesium Sodium .... Potassium 117-1 "i-7 64-2 1814-0 162-7 594 0-3 0-6 29-3 1122-9 34-7 113-9 0-1 1-4 51-2 1232-9 47-8 trace 241-8 '7-4 125-0 "6-5 50-3 1793-0 Aluminium Iron Manganese . . . Chlorine .... Bromine .... "2 -a trace 324-8 trace 1-6 0-2 487-0 trace trace trace 1388-5 31-9 14-1 trace 1-7 0-4 630-2 Iodine Fluorine .... Carbonic acid (C0 3 ) Sulphuric acid (SO 4 ) Nitric acid (NO,) 2415-0 196-8 "6-1 952-0 38-7 "i-5 7538 28-4 378-8 39-6 'l-5 1028-5 1749-1 0-4 Phosphoric acid (P0 4 ) Arsenic acid (As0 4 ) Silicic acid (SiO,) Sulphur .... 16-7 1-0 68-0 539 0-4 39-2 72-1 0-4 75-1 Organic Matter Total solid constituents in 1 1,000,000 parts . . / Gaseous Constituents in "1 cubic centimetres per 1 litre at C. and 760 [ mm. bar. : Carbon dioxide Nitrogen Ether .... 5184-0 445 2780-7 93 0-4 3659-1 1087 785-7 406 5456-1 1100 Hydrogen sulphide . Temperature (Cent.) . Specific gravity Analysts ... J 43-75 Bou- quet 46 1-0034 15 8 Meiss- ner 74 1-00497 Berze- lius 832 MINERAL WATERS. Piillna, Bohemia. Seidschlitz Bohemia. Seidlitz, Bohemia. Bath. Chelten- ham. Harrow- gate- Wheat Clifford, Cornwall. Saratoga. Chief Spring. Chief Spring. King's Bath. Royal WeU. Old Sul- phur Well. Congress. 139-6 385-8 722-9 386-7 179-5 493-6 1163-6 405-5 *" * *** ... *"* * "*6-6 3319-0 2813-7 2918-5 "53-9 " 8-1 198-7 "31-9 209-3 5222-0 1974-0 ... 160-0 2701-4 4940-4 20422 2134-4 344-0 239-6 ... 29-8 ... 479-7 111.2 1607 ... ... ... ... ... ... 61-3 ... ... ... ... ... ) 6 ... )andC0 3 r ... 7-4 4-1 f traces 1-4 ... C 24-9J ... ... ... ... j 1-7 1913-3 211-1 292-0 265-3 2066-7 9187-4 5632-5 1505-6 ... trace ... ... 23-2 ... ... 6-3 ... 4-3 ... ... ... ... 2 ... 463-7 904-0 "86-9 639-5 104-8 ... '... 656-2 14273-4 11568-6 1029-5 2259-1 18-2 i'23-8 13132 21154-0 2746-0 ... ... ... ... ... 12-2 ... ... ... ... 2-6 ... ... ... 0-3 ... ... ... ... ... ... 22-9 4-7 ... 42-6 14-6 *3-4 66-0 19-2 ... ... ... ... 87-7 ... ... ... ... ... ... 240-7 ... ... ... 32771-3 23141-2 16406-0 2062-1 8139-4 15513-9 9232-5 5777-9 69 200 91-6 125 80-3 69-5 ... ... ... ... 10-6 ... ... ... 21-3 ... ... ... ... 19-6 ... ... 14 9 52 10- 1-0064 1-01113 1-007 ... Struve Berze- lius Nau- mann Merck and Gal- loway Abel and Rowney Hof- mann Miller Schwei- tzer 833 ANALYSES FRESH SPRING AND Source, . . . Spring at Whitley, Surrey. Spring at Watford, Herts. Artesian Well, Trafalgar Square. Artesian Well, Guy's Hospital. Artesian Well, Crenelle, Paris. Calcium 8-1 110-1 18-8 15-0 27-2 Magnesium 1-8 ... 9-1 9-8 4-0 Sodium 6-4 11-0 265-3 237-3 ... Potassium 2-3 ... 99-0 7-8 23-8 Iron .... ... ... Alumina and Ferric " oxide . . j ... ... ... ... Chlorine 12-8 12-1 174-2 139-3 5-2 Carbonic acid (C0 3 ) trace. 156-0 197-1 134-4 60-5 Sulphuric acid (SOJ . 13-3 6-8 1805 158-4 6-6 Nitric acid (N0 3 ) ... 19-0 ... ... Phosphoric acid (P0 4 ) ... ... ... 07 ... Silicic acid (Si0 3 ) 12-3 ii'-6 13-1 11 3 6-0 Organic matter 16-0 11-6 13-0 13-4 20 Total solid constitu- ") ent in 1,000,000 I 73-0 338-2 970-1 727-4 135-3 parts. . . J Gaseous constituents, cub. cent, per litre: Carbon dioxide . trace. 304 0-7 15 Oxygen ... 3-4 3-6 Nitrogen ... ... 20-5 13-0 Temperature 14-5 15-5 28 Specific gravity . 1-00095 1-00077 Hardness . 2-8 ... 8 ... r Graham, Analysis . . J Miller, and Hof- Camp- bell Abel and Rowney Odling Payen I mann 834 OF RIVER WATER, St. Wini- fred's Holy Well, North Thames, at Twicken- ham. Thames, at Lambeth Rhone, near Geneva. Rhine, at Basle. Ulls- Wiiter Lake. Loch Katrine. Walt*. 115-9 83-8 69-4 45-3 65-5 8-3 1-9 11-0 4-7 6-0 2-7 4-8 1-8 0-8 13-6 9-2 11-1 3-1 06 5-4 ... trace 4-2 6-1 ... ... ... ... trace ... 3-9 ... ... ... trace 12-1 ... ... 1 4 35-7 14-2 16-8 1-0 1 5 99 4-7 156-3 119-9 91-7 50-8 86-2 20-4 1-7 52-5 31-4 37-6 429 15-4 6-4 5-6 ... ... ... 8-5 ... ... ... ... ... ... ... trace 39-1 "3-9 149 23-8 2-1 3-0 01 ... 49-7 37-0 ... 3-3 5-0 11-4 4L<-1 321-0 302-7 1820 169-4 60-2 27-6 V . 81-8 5-1 63-2 8-4 1-8 0-3 ... ... ... 8-0 7-5 9-3 ... ... ... 18-4 .... 15-5 18-4 11 9-5 1-001 1-0003 ... ... ... ... ... 5 ... 20-2 ... ... 1-9 ... Graham, Barrat Clark Miller, and Deville Pagen- stecher Way Wallace Hofmann 835 836 APPENDIX. WEIGHTS AND MEASURES. 480-0 grains Troy = 1 oz. Troy. 437-5 " = 1 oz. Avoirdupoids. 7000-0 " = 1 Ib. Avoirdupoids. 5760-0 =1 Ib. Troy. Ibe imperial gallon contains of water at 60 (15 -50) 70,000- grains. The pint ( of gallon) 8,750- The fluid-ounce (^ of pint) 437-5 " The pint equals 34-66 cubic inches. The Fren:h kilogramme = 15,433-6 grains, or 2-679 Ib. Troy, or 2-205 Ib. avoirdupoids. The grammme = 15-4336 grains. " decigramme = 1-5434 " " centigramme = 0-1543 " " milligramme = 0-0154 " The metre of France = 39-37 inches. " decimetre = 3-937 " " centimetre = 0-394 < " millimetre = 00394 " APPENDIX. 837 h Miles yards. I" CO 7"! CD t> *O O O O CO CO ^H CD O O O O kO -O *O O -tf CO CO ^H CO O O O Tf CO CO ^H CO ooooo^cbcb iO 3* I" w CO CO CO CO CO O CO CO -H O5 CO CO CO CO ^- O r-i O C5 CO CD CO CO i > OOr- lOOSCpCpCO OOOrHOCTlCOCO i-. O 05 CO 1-1 ^i o H II w a co c-i co o co O5 p cp till 11 g 838 APPENDIX. n Bushels ons = 221 Cubic In In Gallons = Pints = 277-27 Cubic Inches. o i^ b- oo b- t o o r-t ai CD co i- co i^ >o O t-i t- co o r- i co r* O ^-i l^ CO O l^ t^ CO O i-l CO LC 00 O 1^ COr-iCOtOOOO o cc i < CD tra co CO O CO i i CO lO O CO tO CO r-f CO O O CO lO CO T-H (M l^ O tO i i iO 1-1 CS O 1 1^ O O Z, +-> -M S S O o -j D o> H S o o -e ii 1 1 ' n Cwts. = 112 LbB. = 784,000 Grains. 1 EH ^ Is (MOtOCOfNr-icOCO (M 03fi nsa f.SS f,82 6S.T r.77 109 f>29 67.. f',70 r.29 7S5 r.s:j S62 f.lti 770 fi.'50 r,C)l fi2S Wfi (170 6C.5 60S 7 Si) 787 804 ,199 004 Of,4 714 71ti 603 OL'S 070 072 (U',7 SI -2 si:5 774 f,44 COO 073 (-,.",7 5S5 7 ^ IS'.t 032 bromo-phenisic bromo-propionic 552 615 Acetal 687 Acctamide 772 616 diamido-benzoic 636, dibromacetic Acetates metallic 607 765 Acetic acid, manufacture of 607 632 campholic 631 dichloracetic diethylacetic diethjlphosphoric diglycollic ethers 610 664 620 Acetone 698 caproic 619 determination of vapor- density of. 4-59 620 di-iodacetic carballylic 670 dilactic Acetonitrile 710 carbamic ..314, 776 552 654 dilituric Acetosalipyl 694 Acetyl chloride 611 carbazotic carbocresylic dimethylacetic Acetylene 485 carbolic 550 disulphetholic disulphobenzolic disulphometholic 597, disnlphoiiaphtholic ditartaric Acid acetic 606 carbonic liquefaction of..... .166, 648 ...66, 167 AfiK acetamidobenzoic 637 acetonic 699 aconitic 670 carbohydroquinonic 668 carminic 787 cerotic 625 acrylic 627 adipic 662 dithionic cla'idic alizaric 665 all'inturic 75 chelidonic . . 690 612 allituric . ... 727 chlorhydric 181 alloxanic 728 alpha-orsellic 7S6 chloric chlorobenzoic 186 626 erythric...... 670, ethionic 518, ethene-diglycollic ... etliylacetic alpha-toluic . .. . 639 440 alphaxylic 639 184 chloronitrous 184 amidacetic 614 amido-benzoic 636, 775 . amido-butyric 617 chlorophenesic 552 552 chloropropionic .... 615 ethylpliosphoric ethylsulphnric 804 amido-propionic 615 amylacetic ... b'20 chlorous 185 618 anchoic 663 cholic 812, 813 812 anilic . ... 784 439 evernic . . . 665 anisic 654 789 anthranilic 776,784 antimonic 419 chrysanilic 784 . 789 ferric arachidic 625 chrysophanic 787 628 fill niin ic 440 fulniiimric 664 atropic 641 auric 370 citric 678 408 pudic liarbitviric . 7-51 . .. 679 frallotannic ... . 580 benic or bohonic 625 bcnz'imidacetic 638 convolvulinoleic .... 652 655 I) ( >ii7ilic 050 654 |lC||/uic Ifc'.o 678 ben/oglycollic 638 827 #1 vcollir 614 bfta-orscllii- 786 440 lijmniithic 428 712 boric "OS 7i;j brassic 629 440 hiimic bromaretic 613 (;27 IiVg pyrophosphoric .. pyrotartaric 286 661 trichlorovaleric 618 trithi6nic 199 mucic 681 muriatic Jiiycoinolic 181 729 pyroterobic pyruvic 6-J7 ... 651 tungstic 442 ulmic ... 585 INDEX. 845 Arid : PAGE lira tni lie 730 Alcohol: PACE i|iiarlvlic 532 Aluminium: PAGE fluoride 334 uric 7'>3 MO hydrates 334 quintylic 53(3 methide 76 ( > IIMIIV 7V[ sexdecylic 542 oxide 334 silicates. 337 vanadic 430 xvlylic 549 sulphate 335 violuric 731 Alcohol bases 470 Aluminium salts reac- xanthic *. 651 Alcuholic ammonias 470 tions of 337 xylic * <'>:;<) Alcoholic oxides 469 Alum .stone 336 \ri.ls 133 Alcohol radicals 4(W ju-rvlic 626 Alcohols, generally 4tJ8 Amalgams . . 1563 iinic 314 471 aromatic 548 A marine. . . 690 750 ironi'itic 633 primary secondary, and Amber ' 790 tertiary 511 Amic acids 314 47'' 775 basicity of. 282, 595 fitly 597 and ethers, diatomic 5.^5 Amides 314, 472, 772 Amidin 590 iso-icrylic . . . 6'29 monatomic 510 Amidogen 314 diatomic and mono- basic 642 tetratoinic 571 Amines 470, 732 Aldebvde, acetic 681 natiiinic alcohols 733 nionatomic . . 640 Anunelide. . . . 721 pentatomic (iso tions of . 6S7 acrylic 689 triatoinic and bibasic 60S anisic 695 hen/oic C90 basic 666 cinnamic 691 copper-compounds ... . 356 triatoniic and tribasic 669 cumic 691 Aconitates 670 formic ('88 Acrolcin 6S) salicylic 692 turpethum 363 Aconitiiie . . 7*>0 Actinism 96 toluic . 6 ( .;0 FM-uietin 579 Aldehyde-ammonia (87 phosphate 349 810 Aesculiu . 579 Affinity chemical 239 \ldehvdes 470 63 acetate 608 relations of heat to 241 from monatomic alco- alum 336 disposilV *?40 hols . 684 carbonates 312 Air-pump 37 aromatic 690 chloride 312 Alembroth sal- 359 cyanate . 713 Alanine 615 751 Albite 337 Ali/arin 788 Allminin 70.3 Alkalies 271 2tJO nitrate 312 test for 80"' oxalate 659 vegetable S"l ganic bodies 464 phosphates . . 313 'All'iiminatc 794 Alkalimeter M';"i AllniiiiiiniUR principles.... 793 Alkaliuietrv 303 sulphate 312 All 'i! mini ins .substances Alkaline earths . . 323 sulphide. 313 coagulated 797 Alkaloids 751 absolute 516 Alkargen . . 70)5 urate 724 810 allylic . 544 Alkarsin 763 amvlcnic 556 \llantoin 728 Amphid salts 281 amylic 535 Allox-in 728 Anivdalin 579 anisic . . 564 Alloxantin 730 Amvl acetate 610 Alloys ''70 Amyl alcohols and ethers 535 butylic 532 \llvl alcohol 543 Amvl bases .. 738 cervlic. 543 cyanide 710 cetylic 54'' iodides 5-15 Amvl oxide 537 cinnylic 554 sulph-hvdrate 537 cresvlic. 553 oxide 545 Atnvhiiuino 738 evmvlic ... 549 siil])h-hv.',' isnprnpvlic 531 Aloes 789 jn vricy'lic. 543 A Inn is ',\'.Vi Amvl-Hvceriii 669 iionvlir 5-lt> Alumina . 334 (n-tsiii- nii phenvlic Aluminium 333 Analcime 337 clitnride :;.".:; prop v lie 531 ethide 769 ..aiiic bodies 448 71 * 846 INDEX. PAGE PAGE PAGE Assafoetida 789 Battery, constant 252 diatts and cai >on5 Cadet's fuming liquid 763 Cadmium and its com- pounds . . . 352 Catechin ( 73 salts reactions of 353 Cavendish's eudiometer... 144 Cellulose 592 Blue ink CfO-amu 316 Caesium alum . 336 Cements 3 -/ 7 Blue li"-ht C'iffeine 756 CeraMii 588 Cerite 340 708 345 229 58 819 309 767 208 546 546 208 209 209 209 39 356 411 784 526 519 421 591 742 C95 767 568 188 275 188 783 494 5re 694 4! 7 35li 393 505 750 254 177 305 507 816 418 532 710 74'.) 480 finfi Calamine 350 Calcium and its com- Cerium 340 Ccrotates G'^6 Bohemian tdass Boilers, deposits in Cerotene .. . 480 carbonate 3''8 chloride 3' 7 6 Cctene 480 fluoride 327 oxalate 659 810 Cet U alcohol ;.42 Chalk 328 ]>' >ivthvl Boric oxide and acid oxide 327 stones 7''4 phosphate . 328 810 Chameleon, mineral 413 Change of stat produced by heat 55 phosphide 332 Boron salts reactions of 332 chloride sulphate . 328 Charcoal, animal and vege- table 165 fluoride sulphides 331 Calculi biliary 814 urinary 809 Chemical philosophy 219 rays of the eolar spec- trum 95 fusible 810 Braiinite mulberry . 810 Calomel 358 Chimneys, action of f.3 ChincM' wax 543 Bread . Calotype process 97 Camphenu . 489 Chinoline 748 Camphol 546 Chinoline-blue 74S r *'t'O Camphor 691 Chinoidine 7;"> of liorneo 546 Cliitin 880 8( 3 Chloral 817 688 Bromethyl triethyl-phos- insoluble 1 88 Chloranil . . .. 681 Candle, flame of 175 Caoutchin . ... 491 Chloraniline 741 Chlorates 180 Bromide-*, metallic Caoutchouc 401 Chlorl.vdrins 568 mineral 506 Caoutrhoucin 491 Chlorides, metallic :27:i C'ir-miel 5S5 Chlurimetrv 331 ,, . Chlorine . . . 189 Carbamic ethers 776 Carbamide 314, 777 Carbides of hydrogen..lG9, 474 of iron 401 402 action of, on organic bo- dies 463 JSron/e compounds of, with hy- dio'en 181 Carbimide 777 with nitrogen IsT Bnicine Carbinol 512 wit li carbon 1ST Bunsrifs battery Carbon 103 chlorides 187 5.',9 estimation in organic bodies 457 Burette bisulphide 'J02 con)])ounds with oxvgen 165 with hydrogen ' 10 y 8e !* e '"*." OOQ acetates 609 sion of 'aqueous vapor... 829 alloys 356 Dammar-resin . . 790 Chyle 815 arsenite 355 Daniell's battery 253 pyrometer 47 Cinchonidine 755 chlorides 354 Daturine 760 cal 356 Decane 477 Decay . 463 Decene 480 une i m '" 50^ oxides 354 p' nn '1 f 610 pyrites .. 353 356 Cinnyl alcohol 554 salts, reactions of 356 coal 165 cinnamate 641 sulphate 355 sulphides 355 li"ht 93 Cork-borer 137 Dehydratin"" agents ac- Circulation of the blood 805 Corn-oil 538 Citramide 780 Corundum 334 De la Rive's floating bat- Citrates * . 678 Corrosive sublimate 358 ter v 123 Delphinine 760 Classification of metals... 271 Cotton-xylo'idin 593 Density 27 Coumaric acid 695 Clay 336 Coumarin . 694 ironstone 400 Cream 694 tion of 459 Cleavage . . 257 of tartar. .. . 674 Dew 101 Coal 505 Creatin 759 gas 170 Creatinine .' 759 Dextrin . 590 Coal-tar creosote . 550 Creosol 5^3 Coal-tar, volatile princi- Creosote 550 563 ples of. 493 Cresol 553 Cobalt 407 Crown-glass 345 Diabetes 575 808 amiuoniacal compounds Crucibles 347 Diacetamide 773 of 408 Cryolite . .. 334 Diacetin fill Cobalt-glance 407 Cryophorus 68 liiallyl . 487 Cobalticvanides 709 Cryptidine 748 Dialysis 148 Cobalt-salts, reactions of.. 40 ( J Crystalline forms 257 Diamagnetic bodies 110 Cobalt-ultramarine 409 Crystallization . . 257 Coccus cacti 787 Cochineal 787 Crystallization, water of... 147 Crystalloids 149 Diammonio-platinic com- Cocoa oil 620 Cubebs oil of 491 pounds .......... J7o Codeine 753 Cudbear 785 Cohesion 239 Coke 165 Cumin oil ' 691 Diastase 519 577 591 Colchicine 756 Cuminol 691 Diathermancy 102 Cold produced by evapora- Cumene 499 Dibenzoyl .. .. 636 tion 68 Diben/yl 503 Collidine 749 Didymium 340 Collodion 594 Diethenic alcohol 562 Colloids 149 Curarine 760 Colophone 489 Curd 795 Colophony 790 Cyamelide 712 Coloring principles, or- Cvananiline . . 742 ganic 781 Cyanates 713 Columbium or Niobium... 634 Combination by volume... 228 Cyandiphenyldiamine 745 Cyanides, alcoholic 710 mide, sulphuric 771 Diethyl-ethene-diammoni- Combustion 172 furnan- 449 Cyanine 748 Cvaiiitt- 337 Diffnsion of gases 137 Diffusion of liquids 148 heat of 241 Cyanogen .... ,... 700 Digestion..., .... 822 INDEX. 849 PAGE Elements : PAGE Ethyl : PAOB -LM^IUCOS . ... ^ genie 22 %? Emery 334 telluride 791 Emetine . 760 I)ij)lii'iiyl 503 Emodin 787 Ethylacetamide 773 Kmiilsin 579 Ethylaniino 735 Diphenyl-ethene-diamine.. 74-4 Epichlorhidriu 569 -urea 735 Epidermis 803 I)ijl)c]"s oil 748 Disacryl 815 Epithelium 803 Epsoinsalt 349 Ethyl-ainyl-phenyl-animo- nium iodide. .". . 742 Disinfection 331 Equivalency, variation of.. 233 Ethylsaniline 742 Oisposin"- influence 240 Equivalents, law of. 221 Ethyl-benzene 498 Dissiici'ition . .. 461 Erbium 242 Ethyl-codeine . 754 Distillation 61 Ethyl-conine 760 Erythrite 573 Ethyl-methyl oxide 526 Diterebene 489 Essence of turpentine 488 Ethyl-oxamide 778 Double refraction 91 Essential oils 492 Ethvl-phenylainine 742 Double salts 282 Ethalic alcohol 542 Ethyl-toluidine 742 Dragon's blood 790 Ethane . ... 467 475 Ethvl-salicylol 694 Ductility of metals 269 Ethene 170, 481 Ethyl-strychnine 756 Dulcite .. 573 Ethene alcohol or glycol . 556 Eucalyn .. 578 Ethene bromide 5tO Euchlorine. 186 chloride 558 Dvads 331 cyanide 711 Dyes yellow 7^9 iodide 560 Enclase 33Z Dyeing 781 oxalate '660 Eirxanthone ~ 789 oxide ... . . 560 Dyslysin 812 sulphide 560 Ethene-diamine 743 Eventia prur.astri 786 Excretin . . 804 E dide 744 Ethene-hexethyl diphos- Expansion by heat 42 phonium. 767 of liquids . 48 50 Farth-metals 333 Ethene - hexethyl - phos - of gases 51 pharsonium . 767 of solids 45 Ebonite 491 Ethene - tetrethyl - phos- of water . . . 50 Ebullition 57 phammonium 767 Effervescing draughts 675 Ethene - triethyl - phos - F E (r(r albumin 791 Ethereal salts 409 Egg white of . . 791 Etherincation 524 Fat origin of in the ani- Ela'idin 629 mal body 825 Eluldehyde 687 diatomic 555 Fats . .. . 566 623 625 Elastic tissue .. .. 818 Fatty acids. . 597 Electric battery 119 monatomic 510 Feathers 803 current 119 pentatomic 572 Fecula 589 tetratomic . 571 Felspar . 336 Electric discharge 116 triatomic 565 Fermentation 463 Electric eel 122 Ethides metallic... 768 butyric 617 Ethyl acetate 610 lactic 646 Electricity positive and borates 528 bromide .. 522 Ferments . . 463 646 Ferrate 4 * . 399 Electro-chemical decom- carbonates 649 Ferric and ferrous com- chloride 522 pounds 398 Electrodes 45 cyanite 714 Electrolysis . .. 245 cyanide 710 Ferrieyanides 709 Electrolytic decomposi- cyanurato 714 Ferrocyanides 706 Fibroin 03 Electmlytos 24 f) Ficus rubriginosa, resin of 549 nitrate 526 Fire blue 421 nitrite 526 -damp 178 Electro-negative and elec- oxalates 660 red and green 326 Flame structure of.. .172, 175 Eleetrophorus 119 oxide f)''. ) Klccho-plating 2f>n palmitatc . . . 622 berg's phosphates 287 Kli-ctruscope 10(5 Flint-glass 44 Electrotype 'T)4 Elementary bodies fable. Fluorescence 91 stearate C'^o Fluorides metallic 276 symbols of "'li Fluorin" 192 Klenii'iltS 127 svilph-hvdrate - 529 Fluor-spar 327 sulphides 530 Food ... 822 sulphites 527 Formates . C05 lent value. .... .... 2C6 sulnhocarbonates ... 650 Formula}..... ... 226 850 INDEX. Formulae : PAGE PAGE Glass 344 empirical and molecular 457 graphic and glyptic 231 i" tiotial 981 472 346 307 823 143 337 574 578 802 823 823 566 569 644 594 813 801 801 774 555 725 692 580 692 692 231 369 705 371 370 371 258 609 336 575 231 164 35 132 27 459 326 353 376 266 253 255 563 758 758 826 588 588 634 591 588 588 593 356 294 491 328 799 399 798 789 800 798 363 Gliadin Franguliu 571 French weights and meas- ures 837, 838 Frigorific mixtures 56 Fruit sugar 837 838 Glue Gluten Fuchsine 746 Glutin Glycerin Glycide Fucusoi 696 Fulminates 714 Glycogen Glyco-hyocholic acid Glycocine 614, Fulminurates 716 Glvcocol Fuming liquor of Libavius 390 Furfur'imide 696 Glycollamide Glycols Furfurine 696 Glycoluril Furfurol 695 Gly cosine Furnace, reverberatory.... 173 Furnace for combustion... 451 Fusel-oil 535 Glycyrrhizin Glyoxal of grain spirit 537 Fusibility of metals 268 Fusible calculus . . 810 Glyptic formulas Gold and its compounds... cyanide of. Fusible metal 429 Fustic wood 789 Gold-leaf -salts, reactions of -standard of England... G. Gadolinite 337 342 Galactose 578 Graphic formulae Graphite Galena 394 Gallates 671 Galls, nut- 672 Gravitation Gravity, specific Galvanism ... . 119 of metals Galvanometer 103 122 Garancin 788 Garlic, oil of. 545 Greenockite Garnets .... 337 Green salt of Magnus Groups, isomorphous Grove's battei'y Gas, coal and oil 170 defiant 170, 557 battery 255 burners . 177 Gas furnace for organic analysis 451 Gases, absorption of.. ..139, 150 capillary transpiration of. 140 Guanidine Guano 724, Gum arabic .. collection and preserva- tion of 199 British diffusion of. 137 effusion of 140 eudiometric analysis of 156 expansion of. 51 Gun-cotton Gun-metal liquefaction of 66 occlusion of 140 osmose of. 138 Gypsum physical constitution of 35 specific gravity of 132 specific heat of 71 Gas-holder 130 H. Haematin Gastric juice 811 Gaultheria procumbens, oil of. 654 Haematite Haamatocrystallin Gelatin 801 Gelatin-sugar 801 German silver 407 Ilaunin crystals Haemoglobin Hahnemann's soluble mer- cury Geyser springs of Iceland 153 Gilding 371 PAGE Hair 803 Halitus 806 Halides, acid 469 Haloid ethers 4t;8 Haloid salts 281 Hardness of water 328 permanent 328 temporary 329 Harmaline 756 Harmine 756 Hatchetin . 507 Hausmannite 412 Heat, absorption of. ...101, 106 animal 821 capacity for 69 conduction of 54 developed by the elec- tric current 255 dynamical theory of. 77 expansion produced by. 42 latent, of fusion 55 latent, of vaporization.. 57 mechanical equivalentof 75 radiation of 99 reflection of. 99 relations of, to chemi- cal affinity 241 sources of 74 specific 69 transmission of 102 Heavy spar 324 Helicin 582 Helvite 337 Hcmihedral crystals 2C3 Hemming's safety-jet.. 141, 179 Hepar sulphuds 298 Heptyl alcohols and ethers 539 Ileptylene 480 Heiilandite 337 Heveene 491 Hexads 231 llexethyl-ethene-diammo- niuni iodide 744 Hexyl alcohols and ethers 539 Hexyl-carbinol 541 Hexylene 480 hydrate 480 Hofmann's gas-furnace for organic analysis 451 Homologous series 466 Honeystone 665 Hops, oil of 520 Hornblende 350 Horn silver 319 Horny substance 802 Huan'o 724 Humus 585 Hydantoin 725 Hydrates 147 of turpentine oil 489 Hydrides of alcohol-radi- cals 478 Hydriodic acid 189 Hydrobenzamide 690 Hydrobromic acid 188 Hydrocarbons, table of.... 467 Hydrochloric acid 181 Hydrocyanic acid 701 Hydroferricyanic acid 709 Hydroferrocyanic acid 708 Hydrofluoric acid 192 Hydrofluosilicic acid 210 Hydrogen- 136 antimonide 419 arsenides ... 423 INDEX. 851 Hydrogen : . PAGE Iridinm : PAGE aiiimonjacal compounds of 384 PAGE Lac tin .. 587 carbides 169 Lactone 647 chloride 181 Lactose 587 combination of, with oxygen 140 Iron . 397 Lake . 781 acetates 609 dioxide 153 estimation of, in organic bodied 448 ben/i-'s bulbs 451 Kir , .. .. 507 Liebig's condenser 62 Light, 83 Indium 416 Kre.atin, seeCreatin 759 Kreatinine, seeCreatinine 759 Kreosote, see Creosote 550, 563 Kupfernickel 405 Kyan's method of preserv- ing timber 358 Induction coil 126 blue or Bengal .... 421 chemical rays of 95 dispersion of 85 reflection and refraction of 83 !<({ n (magnetic 124 magnetic 108 Ink, label 7'.K blue, sympathetic 407 Inosite 578 L. Labarraque's disinfecting fluid 330 Iniilin 592 Inverted sugar 585 Li< r nin 592 lodicacid 190 Lignite . 504 Iodides, metallic 276 Lime 327 Iodine 188 Label ink 7 ( action of, on organic bodies '. 4tU Lac 790 Lac dye 7 ( .l ( i Limestone. 228 Liqnelaetion of gases 66 of carbonic acid 66, 167 Liquids, boiling points of. 57 and nitrogen 191 and o\v 47 chloride 1 ( )1 lodoform ;";><> Iridiuui 3S2 Lactic ethers 4 silicates 515 INDEX. 853 PAGE Naphthalidine 743 PAGE Octane 467 477 PAGE Oxalates 659 Naiveine 754 Octene or octylene 467 glycol 556 Oxalic acid 657 ethers 660 Narcotine 753 Octyl alcohols and ethers. 541 chloride 542 \efte-de'>-il 507 \ephelin 337 carbinol 543 Oxamic acid 659 777 Nervous substance 818 Neurine 803 (Enanthol or oenanthylic ether 6(il 777 Oxamide 659 778 Neutrality of salts 283 Nii-kel 405 Oil gas 172 Oil of aniseed 695 Oxatyl 595 -salts reactions of . 406 Oxides 132 Nicotine 760 of bitter almonds 690 of cicuta 691 alcoholic 469, 509 metallic 278 Niobium ... 634 N i tramline 742 Oxygen 128 Nitraniside 695 of cloves ;. 491 its action on organic compounds 462 Nitranisidine . . 551 of copaiba . 491 \itranisol 551 of cubebs 491 of cumin . . 691 Nitrates 159 of the glycols 560 of the polyglucosic alco- hols. 589 Nitre 294 cubic 308 of garlic 545 of gaultheria procum- bens 654 sweet spirits of 526 Nitric acid 158 Oxygen-salts 133, 280 Oxy-hydrogen flame and blowpipe 142 action of, upon amyla- ceous and saccharine substances 593 of juniper 491 of laurel 491 safety-jet 141 of lavender 491 Oxvphenol 562 acid, fuming 161 of lemon ... . 491 Ozocerite 507 Nitrides metallic ... 162 Ozone 135 Nitrile-bases 470, 732 of mustard 711 P. Palladium 278 Nitro-benzene? 495 Nitro-cumene 499 Nitro-cymene 500 Nitroform 566 of ptychotis 554 Nitroglycerin 568 ammoniacal compounds of 479 Nitrogen 153 of rue . 689 chloride . . . ... 189 of spiraea ulmaria 693 of thyme 554 Palmitins 62 9 compounds with oxygen 157 with hydrogen 162 Palm-oil 622 of turpentine 488 Pancreatic fluid 814 with boron . . 208 of vitriol 196 dioxide 160 of wintergreen 654 Oils, drying and non-dry- ing 630 Papyrin 593 estimation in organic Paraban 729 iodide 191 volatile 491 492 Paraffin 477 monoxide 160 Oleflant gas 170 Paraffins 474 pentoxide 158 Olefines 459 substitution-products of 478 Paraglobin 796 tetroxide 161 compounds of, with hal- oo'ens 482 trioxide Til Paraglobulin 796 Nitrolactin 588 Oleins 629 Paralactates .... .. 647 Nitro-naphthalenes 503 Olive oil 629 Paralbnmin 795 Paramagnetic bodies 110 Paramide 665 Nitro-phenols . . 552 Nitro-prussides 704 Opianine 754 Nitre-thymols 554 Nitro-toluenes . 497 Orange-flowers, oil of. 691 -peel oil of 691 Paramylene 537 ether 526 Orcein 691 Paraniline 741 oxide 161 Orcin . 691 Parapectin 588 Nitro-xylenes 498 Organic bases 732 chemistry, the chemis- try of carbon corn- Nomenclature .. 132 of alcohols 512 l>. '.'!] i '' ' 'l ir , C , (Jjo of hydrocarbons 469 Parmelia parietina 787 of salts 2*2 substances, action of heat on 462 substances, classification of 464 Paviin 579 Nonane .467, 477 Pe'irl-'ish 296 Nonene 480 Pectin 588 Nonvl alcohol 542 Pendulum, compensating. 46 Pentads . 231 Nordhausen sulphuric acid T.Mi Notation, chemical 225 Nut-galls .. 672 substances, decomposi- tion of 462 Pentetlivl-ethene-diammo- nium iodide 744 Pepsin . . .. SOO substances, elementary analysis of. 4-18 substances, synthesis of 447 Orgnno-metalHc bodies 471, 768 Orpimont 4 -> 4 Nutrition, animal S-_>2 plastic elements of S - _>4 vegetable 825 Peptone 797 Perchl, .rates - 1^6 Percussion-caps. 715 peris-ads "31 0. Occlusion of gases 139 Octammonio-platinic com- pounds 377 Orthophosphatcs 2S5 Osmium 3S7 Osmose of gases .... 138 Permanganates 413 Peroxide of chlorine 1Sf> Persulphide of hydrogen.. 202 Peru balsam. ... ... 7'J1 of liquids 149 Osseiu .... ... 818 72 854 INDEX. PAGE PAGE PAGE Proportions multiple 220 diamaguetic 112 Propyl 478 531 Pt-tlitf> 316 337 electric 115 Propyl alcohol 531 IVtinine 749 magnetic 107 Propylamiue 734 IVttunkofer's bile-test 813 Polarization of light 91 circular 93 Propylene, see Propene.... 480 Propyl-phycite 571 ' .',", ln " 01- Poles electric ..115, 245 Prota^ou 803 1 ( tunty.t Polybasic acids 282 Protein . 794 pf w V' g-g Polyethenic alcohols 561 Prussian blue 707 Phenamylol 551 Polygenic elements 222 Prussiate of potash, red... 709 Polyglucosic alcohols 583 yellow 706 Phenetol 551 oxygen ethers of 589 Prussic acid 701 Phenol 550 Polylycerins 569 Pseudo-erythrin 786 Phenols 550 Polymeric bodies 475 Pseudo-morphine 754 diatomic 562 xylylic 553 Populin 582 Ptvalin 810 Puddling . 403 Phenyl ... 494 Purple of Cassius 371 Porphyry 336 Potash 293 Purpurin 7 88 chloride 551 crude 296 Potash-bulbs 450 liydrate 550 Potassammonium 311 Pus , 800 815 Plu-nvlainine 739 Potassio-ferrous fcrricyan- Putrefaction 463 Phenyl-dibenz'imide 773 ide 707 Pyin 800 815 Phenylene 500 Potassium . 290 acetates 608 Pyrites 401 Philosophy chemical 219 al um 335 Phloretin 581 Phlorizin 581 bicarbonate 297 Phloroglucin 570 bisulphate 297 Pliorone 6fl4 bromide 292 carbonate 296 Pyrolusite . 412 Phosphates 285 chlorate . . ... 295 Phosphide of calcium 332 chloride 291 Phosphine 285 Phosphines 471 760 cyanide 703 Pyroxylin 593 Phosphoretted hydrogen.. 215 ferricyanide 709 Pyrrol 749 Phosphoric acid 214 Phosphorus .. 212 hydrate 293 Q -bases 604 iodide 291 bromides 217 chlorides 216 estimation of in organic nitrate 294 Qu'irtene 4(j7 480 oxalate 659 hydride 215 oxides 292 Chrirtine 4G7 487 iodides 217 Qu'irtyl 467 sulphides 217 ethers 532 Photography 96 sulphates 297 Phycite 571 sulphides 298 Picoline 748 (hercetin ' 4 ammoniacal compounds white 362 of 374 Prehnite 337 Quinoidine . 755 chlorides 373 Quinone 680 oxides 374 salts reactions of . . 378 Prism Nichol's 93 Quintane 467 477 sulphides 374 Proof spirit 518 Quintene 467 480 482 surface action of 142 Platinum-black 373 Propane 467, 475 Propene 480 Quintene glycol 556 Quintenyl alcohol 569 Plumbago 104 Quintine . . 487 Plumbethvl 770 Plumbic compounds 395 Propine 686 Pneumatic trough 129 Propione ... 697 ethers.... ... 535 INDEX. 855 R. I AGE 677 99 237 507 424 32(3 395 412 465 403 99 83 91 84 427 816 237 790 549 820 505 508 173 sso Salt: PAGE definition of 133 280 Salts acid 281 Radicals . basic 283 binary theory of 281 Realgar double . 281 Red lead Red oxide of manganese... Reducing agents, action of, Saltpetre 294 Sai>(nification 567 Refining of pig-Iron Reflection of heat Sipphire 334 Sarcolactates 647 of light Refraction, double of light S'ircosine . 614 759 Sca"-liola 328 Reinsch's test for arsenic- Rennet Sea-water, composition of. 146 Secondary butyl alcohol. .. 534 Residues Resins Resin of Ficus rubiginosa octyl alcohol 541 propyl alcohol 531 electrolytic decomposi- tion 247 Retene . Reverberator y furnace Rhodium ... Seggars 347 Sei ir nettc salt 675 River - water, analyses of 834, 835 Roccella tinctoria 786 Selenetted hydrogen 205 Selenic acid . 205 Selenides metallic 289 Rocoellinin 786 675 W6 Ruck-oil Selenite 328 Rock-salt 300 Selenium 204 336 740 746 679 787 788 788 788 316 336 334 398 385 387 393 93 584 178 788 789 592 358 312 592 581 693 653 692 654 693 692 692 581 682 811 801 800 Septivigintene 480 Series, homologous and Rue, oil of Serpentine .. . . 350 Serum of blood 8u6 Rubiadn Rubiacic acid Nubian Scxdeccne 480 Sexdecyl alcohol . 542 Sextino 487 Rubidium Sexvalent elements 331 Sbale .. . 337 Ruby Shellac 790 Rust Sikes's hydrometer 828 Silica .... 210 -salts, reactions of Rutile Silicated hydrogen 211 Silicates of aluminium.... 336 S. Silicic acid 210 Silicic ethers 515, 529 Silicotungstates 443 Silicium or Silicon 209 chloride 211 fluoride 210 hydride . . 211 oxide 210 Sa (r o Silver 317 acetate 610 Sal-ammoniac Salep ben/oate .. . 634 carbonate 321 Salicin chloride 319 Salicylamido cyanate 713 aldehyde S'llicylites fluoride 319 Salicylol fulminate 714 Salieylous acid liyposulphate 321 hyposulphite 321 Iodide 319 Baliva oxides . . 319 Milplrite 320 Salt. common.... Silver-alum.... .... ."2S PAGE Silver-salts, reactions of... 321 Silver-standard of England 322 Sinamine 720 Sinapuline 720 Size 802 Skin 818 Slate 337 Smalt 409 Smee's battery 254 Soap 625 Soup-stone 350 Soda 301 Soda-ash process 302 Soda-ash, testing its value 303 Sodammonium 310 Sodium ,..., 299 acetate 608 bicarbonate 303 bisulphate 307 borates 309 bromide 301 carbonate 301 chloride 300 cyanide 704 ferrocyanide 708 hydrate 301 hyposulphite 307 iodide 301 nitrate 308 oxalate 659 oxides 301 phosphates 308 sulphates 307 sulphides 309 tartrates 675 unite 724 Solaniue, 769 Solar spectrum 86 Solder 397 Soleil's saccharimeter 93 Solids, expansion of 45 specific gravity of 29 Solubility of salts 147 Soranjee , 789 Sorbin 578 Sorrel, salt of ;,y Spar, calcareous 229 Sparteine 760 Spathose iron ore 400 Specific gravities of metals 267 gravity of solids and liquids 27 heat 69 Speculum metal 356 Spectroscope 88 Spectrum 86 Spectrum-analysis 87 Spoiss 405 Spermaceti 543 Spirit, methylated 518 Spirit of Mindererus 608 Spirit-lamp 176 Spirits, table of spec. gr. of 830, 831 Spodumene 316, 337 Spongin 803 Springs 147 Spring-water, fresh, analy- ses of 834, 835 Staimites, metallic .".'.H Stamicthyls 770 Stannic and stannous com- pounds :;.io Stannic rtliide 770 Stanuoso-stannic ethide... 770 856 INDEX. PAGE Sulphur: PAGE and carbon * 202 bromides 204 PAGE Tetrethyl-ethcne-diamino- nium iodide 744 Thallium and its com- pounds 305 State, change of, by heat.. 55 Steam, clastic force of 59 chlorides 203 estimation of, in organic bodies 457 Thallium salts, reactions Steam engine CO specific gravity of 145 iodides 204 oxides and oxygen acids 194 Sulphur-acids and bases... 289 Sulphuretted hydrogen.... 200 Sulphuric acid 196 ethers 514, 526 of 368 Thebaine 754 Theine 756 Theobromine 757 Stearin 625 Thermo - electrical phe- nomena 103 Stearoptene 492 Sulphurous acid 195 Thermometer 42 differential 45 gteel 403 Sulphur-salts 289 Surface action of platinum, charcoal, &c 142, 165 g wea t 811 Thermomultiplier 104 Thialdiue 750 Stickhic 790 Thiosinamine 720 Thorina 339 Stilbite 337 Sycocerylic alcohol 549 gylvic acid 790 Thorinum 339 Thorite 339 Symbols, chemical 129, 330 Tbujin 582 Strontium and its corn- Thymol 554 Synthesis of organic bodies 447 Tin 389 Strontium salts, reactions of 326, 332 alloys 392 Synthetical method of chlorides 390 fluorides ... 391 oxides 391 Styracin 641 Systems of crystals 200 T. T'tlc 350 sulphides 392 Tin-salts, reactions of 392 Tincal 309 Tinned plate 392 Sublimate, corrosive 358 Sublimation 61 634 Tissue, membranous 818 lifueoxis 592 Tannates 672 Substitution 225 330 T-uining . . .. 818 Titanium 393 Tolene . . . 790 Sugar 584 action of dilute acids Tantalite 432 Tantalum 432 Tolu balsam 790 Toluene 495 T'ipioca 592 Toluidine 496 action of alkalies upon. 586 candy 589 Tartar 674 Toluylic alcohol 549 Tonka bean .-.. 94 Sugar, copper test for the emetic 675 Tartaric acid 673 Trachyte 336 Trade winds 52 from diabetes 575 Sugar from starch or dex- trin 575 Tartaric ethers 676 Transmission of heat 302 Transpiration of gases 139 Travertin 229 Tartrates, metallic 674 T-mrin 5 9 7 Teeth 819 Triacetin 611 from ergot of rye 587 of lead 609 Tellurethyl 771 Tellurhydric acid 207 Telluric acid .. 207 Triads 231 Triamines 743 of milk 587 Triatomic alcohols and ethers .. 565 Tellui'ides 289 Sugar-forming ferments in saliva 801 Sugars, action of, on polar- ized lifht 575 Telluromethyl 771 Tellurous acid 206 Triamylamine 739 Ten-carbon phenols 565 Tension of vapors 63 Terbium . 242 Tribasic acids 284, 669, 678 Sulphamic acid 314 Trichloroquinone 680 Trichlorophenol 552 Tridecane 477 Sulphanisolic acid 551 Sulphantimonates .. 4 9 Terebene 489 Terpenes 488 Terpentin-hydrate 490 Sulphantimonites 420 Sulpharsenates 424 Sulpharsenites 424 Sulphione 24" Sulphisathyde 784 Triethene alcohol 561 Terpin 4QO Triethene-triamine 744 Triethylamino 736 Triethylarsine 762 Triethylbismuthine 767 Triethyl - diethene - diam- monium iodide 744 Terpin-hydrate 490 Terpinol 490 Tertiary butyl alcohol 534 hexyl alcohol 540 Tetrachloroquinone 680 Tetrads . . 231 Sulphites 196 Sulpho-acids 682 Sulphobenzide 483 Sulphocarbonic ethers 650 Sulphocyanates, metallic.. 717 Sulphocyanic ethers 718 Sulphomolybdates 445 Sulphophosphatefl 218 Tetramethyl - ammonium hydrate 738 Tetrammonio - platinic compounds 377 Triethylrosaniline 747 Triethylstibine 761 Triethyl sulphurous com- pounds . . 530 Tetrammonio - platinous compounds 376 Tetramylammonium hy- drate 739 Sulphotungstates 443 Bnlphovinatea 526 Tri0 Uramilicacid .. .. .. 7-'!0 Uranates 415 Yellow dyes 789 Uranium 414 Yttria 343 Uranium-salts, reaction of 416 Uranite 414 Water 143 Yttrium . 242 Yttro-tantalite 432 Untes 724 distilled 146 Z. 7'\ffre 409 Urea 713 721 expansion of, by heat... 48 of crystallization 147 maximum density of.... 50 not an electrolyte 248 oxygenated 153 solvent properties of..... 147 Uric acid 723 Zeolites 337 7inc . . 350 Urinary calculi 809 Urine 807 alloys 352 analysis of 808 in disease 808 tension of vapor of 63 tvpe 278 596 coloring matter of 809 chloride . 351 sea-, analysis of 146 spring and river-, analy- ses of 834 835 j'irtate 648 V. Valerian oil of . .. 492 oxide ... 351 Waters, mineral, analyses of s:;2. s:;:; Water-vapor, composition of, by volume 146 sulplnte 351 sulphide 351 -ethyl or/inoethide 768 -methyl or /inc-methide 769 -oxyl 337 -salts, reactions of 352 Zircon 338 Zirconia 338 Valeric or valerianic acid. 617 Valeric ethers tiitf W-i\ 542 65 fossil 507 Weights and measures 836 comparison of French and English 837, 838 Weights atomic 2"2 Yaleronitrile 710 V'llervlene 487 V'llylene 4ss Zirconium 338 -salts, reactions of. 343 Vanor of water, tension of 63 table of.... ... 226 BRANDE AND TAYLOR'S CHEMISTRY, NEW EDITION, JUST ISSUED. CHEMISTRY WILLIAM THOMAS BRANDE, D. C. L., &c., AND ALFRED SWAINE TAYLOR, M. D., F. R. S., Professor of Chemistry and Medical Jurisprudence in Guy's Hospital, London. Second American Edition, thoroughly revised by Dr. Taylor. In one large octavo volume of 764 closely printed pages ; extra cloth, $5 ; leather, $6. We do not hesitate to pronounce this the ablest work on chemistry in the English language. Iowa Med. Journal, April, 1868. The recognized value of this treatise, and its reputation both here and abroad, render it unnecessary for us to more than call attention to this new edition, which the American pub- lisher has brought out with great care and accuracy, the supervision of the work, as it passed through the press, being intrusted to a competent chemist. New York Medical Journal, March, 1868. An eminently practical and truly admirable work. Leavenworth Med. Herald, Nov. 5867. One of the most useful and complete in the language. It has been already announced offi- cially as the text-book in one of our medical colleges, and we expect other schools to follow. St. Louis Med. and Surg. Journal, Dec. 1867. This is an elegant volume of nearly eight hundred pages, and as a manual for students seems all that could be desired. It is full without being lengthy, minute without being wearisome, and written in a manner calculated to attract. It is a first-class book for students, and as such we confidently recommend it to them. Those who may desire to purchase it may be sure of having in it all the latest chemical knowledge. Canada Med. Journal, Nov. 1867. The one before us, which is the joint labor of two of the greatest minds in Great Britain, can most certainly demand for itself the highest rank in the special department of which it treats. Although a work of large size, being an octavo of over seven hundred pages, it is filled with such subjects as arc useful to the student of every-day chemistry, or to the practical man who measures the utility of every scientific fact in proportion to its capability of being demon- strated. In other words, it is calculated in our opinion to give to the medical man the broadest possible groundwork for the study of chemisty, and the application of its great truths to the every-day necessities of practical life. Nothing more is attempted, and nothing more is needed, in a work specially designed for medical practitioners and students. N. Y. Medical Record, ' Nov. 15, 1867. One of the standard works on chemistry; alike valuable for the student and for reference by the practitioner ; well up to the times, containing the latest discoveries. Detroit Review of Medicine and Pharmacy, Dec. 1867. Any full or critical notice of such a work, in this place, would seem to be uncalled for. To the careful student, who desires a full and complete text-book in this department of study, we commend the volume before us. Cincinnati Lancet and Observer, Nov. 1867. A work of real merit, such as every student and practitioner will find useful, both for study and reference. Chicago Medical Examiner, Oct. 1867. The pervading idea is to afford such information on chemistry as will be of most advantage to the student who cannot devote his whole time to the study. The foundation is laid in this work for a deeper research, if time and inclination permit. Altogether it is a very valuable text-book for the student of medicine, and may well be adopted by every medical college; the constant reference which the physician must make to this science will render the work abso- lutely necessary on his shelves. St. Louis Medical Reporter, Nov. 1, 1867. The author appears to have extended his care to all portions of the work, organic and inor- ganic. Among the former, additions will be found at chloroform, nitro-glycerine, anilin colors, valerianates, spectrum analysis, and other subjects have also been enlarged, so that the claims of the book presented to the student are strong and decided, as being up to the present time, and meriting his confidence. Am. Journal of Pharmacy, Nov. 1867. (lives, in the clearest and most summary method possible, all the facts and doctrines of chem- istry, with more especial reference to the wants of the medical student. London Medical Times. HENRY C. LEA, Philadelphia GRAHAM'S CHEMISTRY. THE ELEMENTS OP CHEMISTRY, INCLUDING THE APPLICATIONS OF THE SCIENCE TO THE ARTS. BY THOMAS GRAHAM, F. K. S. Second American, from the Second Revised and Enlarged English Edition. EDITED BY HENRY WATTS, F. C. S., AND ROBERT BRIDGES, M. D. With Two Hundred and Thirty-three Illustrations on Wood. Complete in one volume, large octavo, of 850 closely printed pages, extra cloth, $5.50. Containing the whole of the two -volumes of the London edition. The publishers have gotten up the work in their usually excellent style; the wood en grav- ing are bountifully executed, and altogether the chemical student or physician will find nothing better or so good, as a standard and complete text-book, as this new edition of Graham. Cincinnati Lancet. We have always regarded Graham's Chemistry as one of the best standard works upon the important department of science to which it is directed, and its merits we believe are so gen- erally admitted that any lengthened commendation from us becomes unnecessary. Suffice it, then, to observe that we know of no more reliable authority to which reference can be made than' the text of this valuable work, nor of any better adapted to the general purposes of the student in search of sound and profitable intelligence. Of the totality it may be curtly ob- served it is everywhere good, and the descriptions are as intelligible as they are comprehen- sive. Montreal Med. Chronicle. The very best work on Inorganic Chemistry extant, and published in the best style. N. 0. Med. News and Hosp. Gazette. BOWMAN'S PRACTICAL CHEMISTRY. INTRODUCTION TO PRACTICAL CHEMISTRY Including Analysis. BY JOHN E. BOWMAN, M. D. EDITED BY C. L. BLOXAM, Professor of Practical Chemistry in King's College, London. Fourth American, from the Fifth and Revised English Edition. In one handsome royal I2mo. volume, with numerous illustrations ; extra cloth, $2.25. The works of the late Professor Bowman, on Chemistry, have long and deservedly held a prominent place in our scientific literature, and, if there be any one reason for this more marked than another, we should say it is because of their combined conciseness with correct- ness. Not a superfluous word is employed, and much space is thus saved that in many authors is wasted in vague generalities and confusing theoretical discussions, that bewilder rather than enlighten the student. This edition, which is prepared by Professor Bowman's successor at King's College, is quite up to the advances that are constantly making in this progressive science. N. Y. Medical Journal. It will be found one of the best guides for the student of practical chemistry, and a very convenient manual for reference by the profession generally. Chicago Med. Examiner. BOWMAN'S MEDICAL CHEMISTRY. PRACTICAL HANDBOOK OF MEDICAL CHEMISTRY. BY JOHN E. BOWMAN, F. C. S., Formerly Professor of Practical Chemistry in King's College, London. EDITED BY CHARLES L. BLOXAM, Professor of Practical Chemistry in King's College, London. Fourth American, from the Fourth and Revised London Edition; with numerous illustrations. In one neat royal I2mo. volume of 351 pages; extra cloth, $2.25. Bowman's Handbook of Medical Chemistry has been so well appreciated by the medical public, that any extended notice of a new edition would be unnecessary were it not for the appearance of another name on the title-page, and the extensive alterations and additions which have been made. The student and practitioner have here offered to them a book which will be found very useful, as a guide and aid in the application of modern chemistry and microscopic analysis to medical science, the importance of which will be more and more appreciated, as phy- sicians avail themselves of the means which are thus offered. Am. Journal of Med. Sciences. Few students of medicine, we suppose, are without a copy of one or other editions of this valuable and handy work, and possibly there are but few of our younger fellow-practitioners who do not find it still a useful book for reference. On this supposition it can hardly be neces- sary for us to offer any criticism on its merits. British and Foreign Medico- Chirurgical Review, HENEY 0. LEA, Philadelphia, CATALOGUE OF BOOKS PUBLISHED BY o. (LATE LEA & BLANCHARD.) The books in the annexed list will be sent by mail, post-paid, to any Post Office in the United States, on receipt of the printed prices. No risks of the mail, however, are assumed, either on money or books. Gen- tlemen will therefore, in most cases, find it more convenient to deal with the nearest bookseller. Detailed catalogues furnished or sent free by mail on application. An illustrated catalogue of 64 octavo pages, handsomely printed, mailed on receipt of 10 cents. Address, HENRY C. LEA, Nos. 706 and 708 Sansom Street, Philadelphia. A MERICAN JOURNAL OF THE MEDICAL SCIENCES. ") p fi -" Edited by Isaac Hays, M.D., published quarterly, about j ^ 1100 large 8vo. pages per annum, MEDICAL NEWS AND LIBRARY, monthly, 384 large . nr 8vo. pages per annum, j 1D OR, A MERICAN JOURNAL OF THE MEDICAL SCIENCES, 1 " Quarterly, For six Dollars per MEDICAL NEWS AND LIBRARY, monthly, RANKING' S HALF-YEARLY ABSTRACT OF THE MEDICAL SCIENCES. 2 vols. a year, of about 300 pages each. In all, over 2000 large 8vo. pages per annum, ABSTRACT, RANKING'S HALF-YEARLY, per volume, $150; per " annum, $2 50. ALLEN (J.M.) THE PRACTICAL ANATOMIST; or, THE STUDENT'S -** GUIDE IN THE DISSECTING ROOM. With 266 illustrations. 1 vol. royal 12mo., over 600 pages, cloth, $2. ASHTON (T. J.) ON THE DISEASES, INJURIES, AND MALFOR- MATIONS OF THE RECTUM AND ANUS. With remarks on Habitual Constipation. Second American from the fourth London edition, with illustrations. 1 vol. 8vo. of about 300 pp., cloth, $3 25. ABEL AND BLOXAM'S HANDBOOK OF CHEMISTRY, THEORE- TICAL, PRACTICAL, AND TECHNICAL. With illustrations. 1 vol. 8vo. of 662 pages, cloth, $4 50. ARNOTT (NEIL). ELEMENTS OF PHYSICS ; or, NATURAL PHILO- SOPHY, GENERAL AND MEDICAL. 1 vol. 8vo., with illustrations, cloth, $2 25. ASHWELL (SAMUEL). A PRACTICAL TREATISE ON THE DIS- -tl EASES OF WOMEN. Third American from the third London edi- tion. In one 8vo. vol. of 528 pages, cloth, $3 50. BRINTON (WILLIAM). LECTURES ON THE DISEASES OF THE STOMACH ; with an introduction on its Anatomy and Physiology. From the second London edition, with illustrations. 1 vol. 8vo. of about 300 pages, cloth, $3 25. -DRANDE (WM. T.), AND ALFRED S. TAYLOR. CHEMISTRY. D Second American edition, thoroughly revised by Dr. Taylor. In one large and handsome octavo volume, extra cloth, $5 ; leather, $6. HENRY C. LEA'S PUBLICATIONS. BTJMSTEAD (F. J.) THE PATHOLOGY AND TREATMENT OF VENEREAL DISEASES. Including the results of recent investi- gations upon the subject. A new and revised edition, with illustra- tions. 1 vol. 8vo., of 640 pages, cloth, $5. AND CULLERIER'S ATLAS OF VENEREAL. See 'CTJLLERIER.' -DUCKNILL (J. C.) AND DANIEL M. TUKE. A MANUAL OF -D PSYCHOLOGICAL MEDICINE. Containing the History, Nos- ology, Description, Statistics, Diagnosis, Pathology, and Treatment of Insanity. With a Plate. 1 vol. 8vo., of 536 pages, cloth, $4 25. QARCLAY (A.. W.) A MANUAL OF MEDICAL DIAGNOSIS; being D an Analysis of the Signs and Symptoms of Disease. Third American from the second revised London edition. 1 vol. 8vo., of 451 pages, cloth, $3 50. BENNET (HENRY). A PRACTICAL TREATISE ON INFLAMMA- TION OF THE UTERUS, ITS CERVIX AND APPENDAGES, AND ON ITS CONNECTION WITH UTERINE DISEASE. Sixth American, from the fourth and revised English edition. 1 vol. 8vo., of about 500 pages, cloth, $3 75. . A REVIEW OF THE PRESENT STATE OF UTERINE PA- THOLOGY. 1 small vol. 8vo., cloth, 50 cents. "DABLOW (GEORGE H.) A MANUAL OF THE PRACTICE OF -D MEDICINE. With additions by D. F. Condie, M.D. 1 vol. 8vo., of over 600 pages, cloth, $2 50. BUOWN (ISAAC BAKER). ON SOME DISEASES OF WOMEN ADMITTING OF SURGICAL TREATMENT. With illustrations. 1 vol. 8vo., of 276 pages, cloth, $1 60. BROWNE (R. W.) A HISTORY OF GREEK CLASSICAL LITERA- TURE. Second American, from a revised English edition. 1 vol. crown 8vo., of about 500 pages, cloth, $1 90. A HISTORY OF ROMAN CLASSICAL LITERATURE. Second American, from a revised English edition. 1 vol. crown 8vo., of about 500 pages, cloth, $1 90. BAIRD (ROBERT). IMPRESSIONS AND EXPERIENCES OF THE WEST INDIES AND UNITED STATES. 1 vol. royal 12mo., cloth, 75 cents. TDUDD (GEORGE). ON DISEASES OF THE LIVER. Third American, D from the third and enlarged London edition. With four colored plates and numerous wood-cuts. 1 vol. 8vo., of 500 pages, cloth, $4. BUCKLER (THOMAS H.) ON FIBRO-BRONCHITIS AND RHEU- MATIC PNEUMONIA. 1 vol. 8vo., of 150 pages, cloth, $1 25. BOWMAN (JOHN E.) A PRACTICAL HAND-BOOK OF MEDICAL CHEMISTRY. Edited by C. L. Bloxam. Fourth American, from the fourth and revised London edition. With numerous illustra- tions. 1 vol. royal 12mo. of 350 pages, cloth, $2 25. INTRODUCTION TO PRACTICAL CHEMISTRY, INCLUDING ANALYSIS. Edited by C. L. Bloxam. Fourth American, from the fifth and revised London edition, with numerous illustrations. 1 vol. royal 12mo. of 350 pages, cloth, $2 25. -RRODIE (SIR BENJAMIN) . CLINICAL LECTURES ON SURGERY. -D l vol. 8vo., of 350 pages, cloth, $1 25. flHAMBERS (T. K.) THE INDIGESTIONS ; OR, DISEASES OF THE V DIGESTIVE ORGANS FUNCTIONALLY TREATED. Second American, from the second and enlarged London edition. 1 vol. 8vo., of over 300 pages, cloth, $3 00. paiOMBAT DE L'ISERE. THE DISEASES OF FEMALES. Trans- ^ lated by Charles D. Meigs, M.D. Second edition, with numerous illustrations. 1 vol. 8vo., of 720 pages, cloth, $3 75. HENRY C. LEA'S PUBLICATIONS. pARPENTER (WM. B.) PRINCIPLES OF HUMAN PHYSIOLOGY, U WITH THEIR CHIEF APPLICATIONS TO PSYCHOLOGY, PA- THOLOGY, THERAPEUTICS, HYGIENE, AND FORENSIC MEDICINE. A new American edition edited by Francis G. Smith, M.D. With nearly 300 illustrations. In one large vol. 8vo., of nearly 900 closely printed pages, cloth, $5 50 ; leather, raised bands, $6 50. PRINCIPLES OF COMPARATIVE PHYSIOLOGY. New Ameri- can, from the fourth and revised London edition. With over 300 beautiful illustrations. 1 vol. 8vo., of 752 pages, cloth, $5 00. THE MICROSCOPE AND ITS REVELATIONS. With an Appen- dix containing the applications of the Microscope to Clinical Medi- cine, by Francis G. Smith, M.D. With 434 handsome illustrations. 1 vol. 8vo., of 724 pages, cloth, $5 25. PRIZE ESSAY ON THE USE OF ALCOHOLIC LIQUORS IN HEALTH AND DISEASE. New edition, with a Preface by D. F. Condie, M.D. 1 vol. I2mo. of 178 pages, cloth, 60 cents. PARSON (JOSEPH) . A SYNOPSIS OF THE COURSE OF LECTURES v ON MATERIA MEDICA AND PHARMACY, delivered in the Uni- versity of Pennsylvania. Fourth and revised edition. 1 vol. 8vo. , extra cloth, $3 00. (Just issiied.) PHRISTISON (ROBERT.) DISPENSATORY OR COMMENTARY ON V THE PHARMACOPOEIAS OF GREAT BRITAIN AND THE UNITED STATES. With a Supplement by R. E. Griffith. In one 8vo. vol. of over 1000 pages, containing 213 illustrations, extra cloth, $4 00. pHURCHILL (FLEETWOOD). ON THE THEORY AND PRACTICE U OF MIDWIFERY. A new American from the fourth revised Lon- don edition. With notes and additions by D. Francis Condie, M.D. With about 200 illustrations. In one handsome 8vo. vol. of nearly 700 pages, extra cloth, $4 00 ; leather, $5 00. ON THE DISEASES OF WOMEN : INCLUDING THOSE OF PREGNANCY AND CHILDBED. A new American edition re- vised by the author. With notes and additions by D. Francis Condie, M.D. In one large and handsome 8vo. vol. of 768 pages, with numerous illustrations, extra cloth, $4 00 ; leather, $5 00. ESSAYS ON THE PUERPERAL FEVER, AND OTHER DIS- EASES PECULIAR TO WOMEN. In one neat octavo vol. of about 450 pages, extra cloth, $2 50. HLYMER ON FEVERS. In one 8vo. vol. of 600 pages, leather, $1 75. CONDIE (D. FRANCIS). A PRACTICAL TREATISE ON THE DIS- EASES OF CHILDREN. Sixth edition, revised and enlarged. In one large octavo volume of nearly 800 pages, extra cloth, $5 25 ; leather, $6 25. (Just issued ) PROPER (B. B.) LECTURES ON THE PRINCIPLES AND PRAC- v* TICE OF SURGERY. In one large 8vo. vol. of 750 pages, extra cloth, $2 00. PURLING (T. B.) A PRACTICAL TREATISE ON DISEASES OF V THE TESTIS, SPERMATIC CORD, AND SCROTUM. 1 vol. 8vo. of 420 pages, extra cloth, $2 00. pULLERIER (A.) AN ATLAS OF VENEREAL DISEASES. Trans- V-J lated and edited by FREEMAN J. BUMSTEAD, M.D. A large imperial quarto volume, with 26 plates containing about 150 figures, beauti- fully colored, many of them the size of life. In five parts, price per part, $3 00. Same Work, complete in one volume 4to., extra cloth, $17 00. (Now ready.) HENRY C. LEA'S PUBLICATIONS. CYCLOPEDIA OF PEACTICAL MEDICINE. By Dunglison, Forbes, \J Tweedie, and Conolly. In four large super royal octavo volumes, of 3254 double-columned pages, leather, raised bands, $15 ; extra cloth, $11. CAMPBELL'S LIVES OF LORDS KENYON, ELLENBOROUGH, AND U TENTERDEN. Being the third volume of " Campbell's Lives of the Chief Justices of England." In one crown octavo vol., cloth, $2. D ALTON (J. C.) 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TJUNGLISON (ROBLEY). MEDICAL LEXICON; a Dictionary of -L' Medical Science. Containing a concise explanation of the various subjects and terms of Anatomy, Physiology, Pathology, Hygiene, Therapeutics, Pharmacology, Pharmacy, Surgery, Obstetrics, Medical Jurisprudence, and Dentistry. Notices of Climate and of Mineral Waters ; Formulae for Officinal, Empirical, and Dietetic Preparations, with the accentuation and Etymology of the Terms, and the French and other Synonymes ; so as to constitute a French as well as English Medical Lexicon. In one very large royal 8vo. vol. of 1048 double columned pages, in small type ; strongly bound in cloth, $6 ; leather, raised bands, $6 75. - HUMAN PHYSIOLOGY. Eighth edition, thoroughly revised. In two large 8vo. vols. of about 1500 pages, with 532 illustrations, extra cloth, $7. - NEW REMEDIES, WITH FORMULA FOR THEIR PREPARA- TION AND ADMINISTRATION. Seventh edition. In one very large 8vo. vol. of 770 pages, extra cloth, $4. 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A PRACTICAL TREATISE ON THE DIAGNOSIS AND TREAT- MENT OF DISEASES OF THE HEART. In one neat 8vo. vol. of nearly 500 pages, extra cloth, $3 50. FOWNE (GEORGE) . A MANUAL OF ELEMENTARY CHEMISTRY. With 197 illustrations. In one royal 12mo. vol. of 600 pages, extra cloth, $2 ; leather, $2 50. PULLER (HENRY). ON DISEASES OF THE LUNGS AND AIR L PASSAGES. Their Pathology, Physical Diagnosis, Symptoms and Treatment. From the second English edition. In one 8vo. vol. of about 500 pages, extra cloth, $3 50. (Just issued.) FLETCHER'S NOTES FROM NINEVEH, AND TRAVELS IN MESO- POTAMIA, ASSYRIA, AND SYRIA. In one 12mo. vol., cloth, 75cts. GARDNER'S MEDICAL CHEMISTRY. In one 12mo. vol. of 396 pages, cloth, $1. GLUGE (GOTTLIEB). ATLAS OF PATHOLOGICAL HISTOLOGY. Translated by Joseph Leidy, M.D., Professor of Anatomy in the University of Pennsylvania,